Classic Rocker. Final Report

Transcription

1 Classic Rocker Final Report Team 7 NSF Legless Rocker Project Coordinator: Dr. Brooke Hallowell [hallowel@ohio.edu; ] Supervising Professor: Dr. John Enderle 04/14/06 Tom Dabrowski Sarah Philo Adam Rauwerdink

2 TABLE OF CONTENTS I. Abstract 2 II. Introduction 3-9 III. Design Constraints IV. Discussion A. Design One B. Design Two C. Design Three D. Optimal Design 1. Objective Subunits E. Prototype 1. Overview Subunits Safety Usability V. Engineering Solutions 92 VI. Life-Long Learning 93 VII. Budget 94 VIII. Team Member Contributions 95 IX. Conclusion 96 X. Appendix XI. References 100 XII. Acknowledgements 101 1

3 I. Abstract At the Passionworks Studio, in Athens, Ohio, where artists with disabilities are able to create new works, there is a need for a legless video rocker than rocks without user input. Some of the artists are not able to rock themselves in a rocking chair, and there is a need for assistance in the form of a mechanism that rocks the chair for them. Each user will have the ability to determine whether or not the chair will rock by using a simple switch. In addition to rocking without physical input from the user, this chair will be in the Multisensory Stimulation Room at Passionworks, and so there has been a request to incorporate a music output into the chair, which will be controlled by the user as well. A car audio CD player will be incorporated into the chair and output will come from two speakers that will be embedded in the headrest. The sound output from the speakers will also be controlled by the user through the activation of a simple switch. The caretakers at Passionworks will have the authority to turn off the entire power to the system, as well as the rocking motion and audio output separately. Also, the caretaker will have control over what music will be played and the volume of the music (but these can be requested by the user of the chair). 2

4 II. Introduction Background The Passionworks Studio provides a setting for artists with disabilities to pursue their interests. It is important for the Passionworks artists to have a setting that promotes the creative process. Passionworks has an entire room devoted to the process of aiding the artists in enhancing their creativity. The Classic Rocker will be housed in the studio s Multisensory Stimulation Room. The legless rocker provides the residents with an enjoyable experience while they develop new artistic ideas. Purpose The self-rocking Classic Rocker will provide the Passionworks Studio with an additional way to inspire its artists with disabilities. A self-rocking legless rocker will offer the artists a comfortable area where they can develop new ideas for their work. Having a legless rocker with integrated audio components can create an inspiring atmosphere for the artists, helping them to relax and enjoy themselves. Innovation is a key component to artistry, and being surrounded with innovative devices can further help the development of ideas. The Classic Rocker will also provide a new experience for those who cannot use a rocking chair on their own. Creating a self-propelled legless rocking chair for adults is a unique idea, not only because of the fact that it moves without any force from the user, but also because its rocking motion can be controlled by the user. Allowing the user to have control over whether or not he or she will rock allows a certain freedom of decision to those who often depend upon others for help in their daily routines. In a similar fashion, the user will have control of whether or not sound will be projected from the 3

5 speaker system within the chair, and this also presents another freedom of decision directly to the user. Scope Competing Products and Previous Projects The following list compiles marketed self-propelled rocking chairs available to the public, previously completed projects National Science Foundation funded projects, and current patents that have been issued for self-rocking devices. Electric and Mechanical Assistive Technologies (EMAT) Motorized Rocking Chair: To date, this product is the only self-propelled rocker available to the public. The chair is equipped with variable rocking speed and can be programmed to shut off automatically. This item was created for those who have special physical needs. This product is shown in Figure 1. The EMAT is located in Winnipeg, Manitoba, Canada, and this product costs $1500 Canadian, which equates to roughly $1300 American. This cost is far beyond the costs of what the new device will cost, which can only be built with the $750 available. Further, this product is only available to those who live in Manitoba. The Classic Rocker will ideally be available to anyone who needs it. Further, there is no integrated audio into the chair, and it is also not situated directly on the floor like the Classic Rocker will be. 4

6 Figure 1: EMAT Motorized Rocking Chair. National Science Foundation Project The Mechanical Rocking System : This project was completed at Rensselaer Polytechnic Institute for a child who has cerebral palsy. The mechanized rocking chair allows for the movement of the user without any physical exertion being required. A simple motor and cam system are used to induce a rocking motion, and the total cost of the project came to $455. This device relates more to how the Classic Rocker will move. A cam system is very advantageous to create a rocking motion. However, this chair is not legless and does not have integrated audio components. Further, if it was built for a child, there may not be enough force in the motor to move the chair for users with heavier weights. 5

7 Figure 2: NSF Project 1989, Rensselaer Polytechnic Institute. In addition to these self-rocking devices, there are numerous patents that have been granted for the use of self-rocking mechanisms or self-rocking chairs. The patents include: 6,899,393 Linkage mechanism for a motion chair 6,695,799 Relaxation apparatus (Oscillatory motion in a recliner) 6,412,867 Automatic two speed musical rocking chair (Infant rocker) 6,318,803 Chair executing oscillatory motion 6,152,529 Motor driven rocking chair These patented devices all relate to the classic rocker project because they involve the use of mechanisms to initiate a rocking motion, but none exactly cover the exact details and desires of what the Classic Rocker will do. Finally, there are several non-mechanized legless rocking chairs available for purchase by consumers from many different retailers dealing, at least in part, with home décor. Such retailers include Wal-Mart and Target (Please see Figure 3). The available chairs come in a range of qualities, from base qualities with cheaper fabrics and 6

8 frame constructions, to those of greater quality, perhaps spill-resistant fabrics, and also with better, sturdier frames. Many of these chairs do not provide high-quality frame materials, and also do not mechanically rock without user input. The few that do have hardwood frames will be the ones considered to be used as the chair component of the overall rocking device. Figure 3: Legless rocker example available at various retailers. Considerations When fabricating the classic rocker there are many factors to consider. Protecting and pleasing the target user are the main concerns, and so safety from electrical and or device malfunction is of the utmost importance. The safety goals of the project are to ensure that the electricity flowing to the device will stay isolated and the device will rock without tipping or without moving too quickly. The controls will be simple, and the overall design will be affordable, easy to move, and easy to use. 7

9 Specifications In addition to the above considerations, certain technical aspects are important to analyze before advancing further. The specifications are broken up based on mechanical concerns, maximum rocking angles, electrical concerns, device switches, environmental concerns, and power needs. Mechanical: Weight of Users: lbs. Frame Material: Aluminum square tubing, in x in x 48 ft Chair Dimensions: Height: 34 in Width: 21 in Length: 31 in Chair Weight: 30 lbs Rocking Speed: 20 Hz Rocking Displacement: ± 7 in (horizontal) at chair top Electrical: Power Supply: Audio input: Speakers: Rocking Mechanism: Switches: User Controlled: Caretaker Controlled: 12 VDC Output Boss Audio CD-3020 car CD player Two 3.5 diameter MA Audio HK35 speakers Dayton 1Z831 gearmotor Custom squish switch and touch switch Chair power, audio power, audio volume Environment: Operating temperature: 40 to 100 F Storage temperature: 0 to 120 F Power: AC 60 Hz 8

10 Report Map Discussion of the first three designs created for this project will be explained in the coming sections. After each description, the advantages, disadvantages, and final thoughts about each design will be provided. After this, the optimal design for the Classic Rocker design will be presented and explained. The final design and usability of the prototype is then described in detail. Concerns about design constraints will be explained, as will the timeline for the design of the project for the upcoming semester, as well as the total cost of the project. From this, conclusions will be made, references will be provided, and proper acknowledgements to those who helped with this project will be made. 9

11 III. Design Constraints When fabricating the classic rocker there are many factors to consider. Protecting and pleasing those who will use the rocker is the main concern, and so safety from electrical and or device malfunction is of the utmost importance. The safety goals of the project are to ensure that the electricity flowing to the device will stay isolated and the device will rock without tipping or without moving too quickly. The controls will be simple, and the overall design will be affordable, easy to move, and easy to use. In addition, economic, environmental, sustainability, social, and manufacturing constraints will need to be considered. Economic The chair must be able to be constructed within a budget of $750, and affordable to persons interested in the product. Because the chair will be marketed to persons with disabilities that regularly need to pay for medications, therapies, caretakers, and other daily expenses. Therefore the chair unit will need to be as inexpensive as possible. If the Classic Rocker were to be manufactured commercially, it would most likely cost less than the prototype, because purchasing components in bulk would be less expensive overall. Even at prototype cost, the Classic Rocker will be much less expensive than any available competing products. Environmental The Classic Rocker will consist of several components that will need to be separated for maximum environmental compatibility. The aluminum base and frame will be recyclable, while the various parts of the prefabricated chair will have to go to a 10

12 landfill and may or may not be biodegradable. The electrical components can be recycled; the copper wires, speakers, and CD player will also all be recyclable. Sustainability The chair will be placed in a recreation room where many persons will have access to it. The chair should therefore be easy to move, relatively easy to clean, and most importantly, durable. The Classic Rocker will need to withstand long periods of rocking persons of up to 190 pounds without malfunction. To ensure the longevity of the electrical components of the Classic Rocker it should be used between the temperatures of 40 and 100ºF, and stored between 0 and 120ºF. Manufacturability Manufacturing the Classic Rocker should be relatively easy once processes, molds and assembly methods have been developed and made efficient. Materials can be purchased in bulk and therefore lower the overall product cost. Lastly, manufacturing the Classic Rocker will likely improve the final appearance of the product and improve its marketability. Ethical and Political The Classic Rocker will need to be designed and marketed in accordance with the Americans with Disabilities Act (ADA). Safety precautions will be followed to ensure that use of the chair cannot harm the chair user, or those in close proximity to the chair while it is in use. Health and Safety All electrical components will be UL compliant, as well as made in accordance with FCC regulations. The electrical components will also be insulated from all other 11

13 materials and grounded to prevent excess charge buildup due to use or electronic malfunction from electrically shocking the chair user. The bottom of the chair will be reinforced with aluminum sheeting to prevent the rocking mechanism from penetrating the chair backing should the aluminum rocking bar fracture. The rocking mechanism consisting of gears and aluminum bars will be in an enclosed space that will impede access to components that could cause bodily harm. Both the rocking mechanism and the audio components will be controlled by switches that allow the caretaker to cut power to the entire chair, and control both the rocking and audio mechanisms individually. Additionally, the chair user will only be able to control the rocking and audio components when the caretaker has allowed him or her to do so by activating the power switches on the back of the chair. The chair has been designed to rock within a specified range of safe and comfortable angles at a comfortable speed, and blocks will be installed to ensure that the chair cannot physically tip over. Social Persons with disabilities can enjoy the rocking chair experience they would be otherwise unable to. There are currently no other affordable or easily accessible products that are similar on the market. 12

14 IV. DISCUSSION A. Design One Figure 4: Finished Chair Side View 13

15 Figure 5: Chair 3D View 14

16 SUBUNITS Frame As legless rockers typically do not have a frame capable of receiving large mechanical forces, an external frame in which the chair will fit is being built. The chair will rock on two maple rocking chair runner. The legless rocker will rest on these runners and be encased by plywood to keep it in place. Linear actuator rocking mechanism The rocking mechanism will consist of a linear actuator attached to the back of the runners. The actuator end will be in contact with the ground, and its movement in and out will rock the chair. Forces Analysis was performed using anthropometric data and scale drawings of the chair system. HIGH/FORWARD ANALYSIS M Fr = 0 = 22* Fc + 10* * 40 10*136 7 * 22 Fc = 56lb. 15

17 LOW/RECLINE ANALYSIS M Fr = 0 = 15* Fc * * 40 6*136 1* 22 Fc = 14lb. The data showed that the highest force on the actuator, 56 lbs., occurred at the top of the chair motion as it began to rock backwards. The actuators that were located online had numerous models with 25-30lb. capacities and several with lb. capacities but few were available in between. The combination of load capacity, stroke length, and speed were best met by an actuator built by Danaher Motion ( Their model D12-10A5-04D linear actuator has a maximum load of 280 pounds, a stroke length of 4, and a speed of inches per second. With the loads most likely to be present in our chair, the speed would be around 1.1 inches per second. As this model has a 4 stroke length, the frequency of rocking would be only 8 cycles per minute. If this model had the same specifications with a 2 stroke length model, the frequency would be 16 cycles per minute, which is a more desirable frequency. Power and Audio Power and audio components are identical to those of the optimal design. 16

18 ADVANTAGES -Natural rocking motion -Not dependent on legless rocker frame DISADVANTAGES -Linear actuator not ideal for fluid rocking motion -Unnatural look due to extensive wooden frame -Problems with balancing chair in order to keep actuator in contact with ground FINAL OPINION Though this design provides the most natural rocking motion of any of the considered designs, its rocking mechanism is not smooth and the problem of the actuator lifting off of the ground would be difficult to overcome. The large wooden frame also gives the chair an unnatural look. For these reasons this design was dropped. 17

19 B. Design Two Figure 6: Finished Chair Side View Linkage Bar Enclosed Motor and Cam CD Player and Chair On/Off Hinge Figure 7: Chair 3D View 18

20 SUBUNITS Frame The rocker frame will consist of two parts: the external frame on the ground and the internal frame reinforcing the legless rocker. The external frame will provide an attachment point for all parts of the rocking mechanism. The internal frame will provide the purchased legless rocker with additional rigidity and strength so that it can handle the forces placed on it by the rocking mechanism. On the front edge of the base, a plywood riser will be attached. The top of this riser will abut the bottom of the rocker at its most upright position. The purpose of this riser will be to prevent the application of a large force on the motor assembly when a user rests on the front edge of the rocker. Rocking Forces Analysis of the forces of rocking was done using a scaled drawing in Visio and a scale model in Working Model 2D. Analysis of this chair found that during comfortable rocking the back of the chair moved a horizontal distance of seven (7) inches from its normal position. 19

21 Fig. 8: Chair fully upright Fig. 9: Chair at midpoint of rocking motion 20

22 Fig. 10: Chair fully reclined UPRIGHT ANALYSIS M Fr = 0 = F * x 15( x 3.5) 136( x 10.5) + 40(20 x) + 15(16.5 x) + 24(40.5 x) M 3500 F M = 230 with leg outstretched x 21

23 2528 F M = 206 with leg assumed on ground x MIDDLE ANALYSIS M Fr = 0 = F * x 15( x 5) 136( x 11.5) + 40(23 x) + 15(19.5 x) + 24(43 x) M 3884 F M = 230 with leg outstretched x 2852 F M = 206 with leg assumed on ground x RECLINED ANALYSIS M Fa = 0 = F * x 15( x 6) 136( x 12) + 40(24.5 x) + 15(22 x) + 24(44 x) M 4088 F M = 230 with leg outstretched x 3032 F M = 206 with leg assumed on ground x 22

24 The above calculations show the relationship between the placement of the hinge and the force applied at the attachment point of the linkage bar on the back of the chair. Calculations were completed for two conditions: legs outstretched and legs resting on the ground. Further calculations were then done in Microsoft Excel to determine which hinge position resulted in the smallest maximum force at the linkage bar attachment point. x upright x reclined x middle Leg on ground Leg off ground Table 1: Excel Analysis of Optimal Hinge Position x upright x reclined x middle x upright x reclined x middle Leg on ground Leg on ground Leg off ground Leg off ground Table 2: Excel Analysis of Sub-Optimal Hinge Position The analysis found that the smallest maximum force occurred when the hinge was placed 13 inches from the back of the chair at its upright position. The greatest force exerted by the linkage bar at this hinge position was pounds when the chair was at its most reclined position and the user s legs were resting on the ground. Table 3 shows that the maximum force increases with movement of the hinge point. Cam and Linkage Bar The forces required for rocking will be transferred from the motor to the chair by a two part system consisting of a cam and linkage bar. The cam, with its diameter dependent on the placement of the motor, will be cylindrical in shape and be attached through its center to the shaft of the motor. A linkage bar, with its length dependent on 23

25 the placement of the motor, will connect the back of the chair to a point on the cam. This system will translate the rotational motion of the motor into linear motion of the chair. The exact size and position of this system will influence the torque requirements of the motor. The following analysis determines all of these unknown factors. The forces determined earlier in this report from the free body diagrams of the chair assumed that the linkage bar forces were in the vertical direction only. This is not the case, though, as at most positions the linkage bar supplies both vertical and horizontal forces. For this reason the moment required to balance the chair is what needs to be provided by the linkage bar. This moment, as well as the vertical and horizontal distances to the applied force, varies with the chair position. x upright x reclined x middle moment leg on ground in-lb moment leg off ground in-lb vertical in horizontal in Table 3: Moments and distances at different chair positions The position of the motor and therefore the position of the cam will determine what torque is required by the motor. Because the greatest forces are required at the upright and reclined positions, the linkage bar should be vertically in line with the motor shaft at these positions in order to minimize the torque. For this reason two positions for motor placement can be considered: just behind the chair so that at the upright position the linkage bar is vertical, or at the back of the frame so the linkage bar is vertical when the chair is in the reclined position. In either case the force would be acting at a minimal distance from the shaft, where the moment originates, and therefore result in very little demand on the motor. These two positions were analyzed to determine which resulted in the smallest demand for torque. 24

26 Cam located at back of frame, vertical linkage bar at full recline Distances determined from scale drawings in Visio Linkage bar length = 27.6 in X=horizontal Y=vertical Cam diamter = 4.5 in Reclined Position Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= 0 Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 0 in Leg On Ground Vertical 26.5 in Y= 2.25 in X= 0 Horizontal in Y= TORQUE Leg Off Ground Total Forces 0 in-lb leg on ground X= 0 Leg on ground lb 0 in-lb leg off ground Y= Leg off ground lb Upright Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 0.00 in Leg On Ground Vertical in Y= 2.25 in X= 1.79 Horizontal in Y= 7.40 TORQUE Leg Off Ground Total Forces 4.03 in-lb leg on ground X= 6.09 Leg on ground 7.62 lb in-lb leg off ground Y= Leg off ground lb Middle 1 Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= 0.19 Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 2.10 in Leg On Ground Vertical in Y= 0.50 in X= 4.34 Horizontal in Y= TORQUE Leg Off Ground Total Forces in-lb leg on ground X= 1.51 Leg on ground lb in-lb leg off ground Y= 7.61 Leg off ground 7.76 lb Middle 2 Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= 0.04 Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 2.25 in Leg On Ground Vertical in Y= 0.25 in X= 1.01 Horizontal in Y= TORQUE Leg Off Ground Total Forces in-lb leg on ground X= 0.35 Leg on ground lb in-lb leg off ground Y= 9.65 Leg off ground 9.65 lb 25

27 Cam located behind chair, vertical linkage bar at full upright Distances determined from scale drawings in Visio Linkage bar length = 27.9 in X=horizontal Y=vertical Cam diamter = 3.25 in Reclined Position Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 0.00 in Leg on ground Vertical in Y= 1.63 in X= Horizontal in Y= TORQUE Leg off ground Total Forces in-lb leg on ground X= No leg lb in-lb leg off ground Y= Leg lb Upright Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= 0.00 Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 0.00 in Leg on ground Vertical in Y= 1.63 in X= 0.00 Horizontal in Y= TORQUE Leg off ground Total Forces 0.00 in-lb leg on ground X= 0.00 No leg lb 0.00 in-lb leg off ground Y= Leg lb Middle 1 Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 1.63 in Leg on ground Vertical in Y= 0.00 in X= Horizontal in Y= TORQUE Leg off ground Total Forces in-lb leg on ground X= No leg lb in-lb leg off ground Y= Leg lb Middle 2 Moments Linkage bar angle from vertical = lb leg on ground Fraction of force in Y= lb leg off ground Fraction of force in X= Distance force is applied from motor shaft FORCES (lbs.) Chair force distances from hinge X= 1.50 in Leg on ground Vertical in Y= 0.50 in X= Horizontal in Y= TORQUE Leg off ground Total Forces in-lb leg on ground X= No leg lb in-lb leg off ground Y= Leg lb 26

28 This analysis found little difference between either position in terms of maximum torque on the motor. Positioning of the cam directly behind the chair does result in a much greater total force on the motor, though. For this reason the motor will be placed at the back of the base in a position that results in the linkage bar being vertical at the full recline position. Gearmotor The cam will be attached to a Dayton gearmotor which will provide the necessary torque for the project. Power and Audio Power and audio components are identical to those of the optimal design. 27

29 ADVANTAGES -Smooth motion throughout rock -Small forces and torques on motor DISADVANTAGES -Motion smooth but not a completely natural rocking motion -Dependent on legless rocker having stable frame -Long linkage bar is a potential danger if it breaks FINAL OPINION This design is the basis for the final optimal design. A chair with a strong internal chair was found so that disadvantage was overcome. The motion of the chair will be similar to that of an office chair which was found to provide an adequate rocking experience. For the optimal design the linkage bar was attached lower on the chair back to overcome the dangers inherent with the long bar. 28

30 C. Design Three SUBUNITS External Frame The external frame of the device will hold the entire chair and user off of the ground, as seen below. There will be two supports for the chair, one on either side. The supports will be constructed out of square metal tubing. Text Text Text Text Figure 11: Completed 3-D view of chair 29

31 Rocking Forces Analysis of the forces of rocking was done using a scaled drawing in Visio. During comfortable rocking the back of the chair moved a horizontal distance of seven (7) inches from its normal position. A gentler rocking distance of 6.6 inches is used for the following analysis Fig. 12: Chair at midpoint of rocking motion 30

32 Fig. 13: Chair fully forward 31

33 Fig. 14: Chair fully back MIDPOINT ANALYSIS = 7.5(3.5) - (79 + x) (10.5) - (79 + x)14 7.5(16.5) 23.5(20) +17.1(40.5) = 0 M@40.5 = -7.5(37) + (79 + x) (30) + (79 + x) (24) 23.5(20.5) = 0 X = 32 0, and ; 32

34 Therefore the pins must be able to support a minimum of = 111 lbs. FORWARD/BACK ANALYSIS Fig. 6: Geometry used to calculate horizontal rocking distance. Given a comfortable change in vertical height of about 2 when rocking, and after assigning a length of 12 for the four (4) supporting rods on either side of the chair, a rocking distance of 6.6 was determined using trigonometry. This value was close to the given comfortable value of 7 horizontal displacement, and was therefore an agreed upon geometry. Fig. 7: Forces on the chair imposed by the supporting rods in forward-most position When the chair is fully forward, the 111 lb force acting downward is supported at a angle. 33

35 x*cos(33.37) = 111; x = lb y = 111*tan(33.37); y = lb The free body diagram above demonstrates the forces on the chair when the chair is fully forward. When the chair is all the way back, the free body diagram is the same, except the horizontal forces are pointing in the opposite direction. Because of this, the calculations for the forward and back positions can be calculated simultaneously. Cam and Linkage Bar The forces required for rocking will be transferred from the motor to the chair by a two part system consisting of a cam and linkage bar. The cam, will have a diameter of 6.6, will be cylindrical in shape and be attached through its center to the shaft of the motor. A linkage bar, with its length about 32, will connect the back of the chair to a point on the cam. This system will translate the rotational motion of the motor into linear motion of the chair. The torque requirements on the motor were calculated to be 1693 inlb, or.54 hp. The following analysis shows how these numbers were obtained. 34

36 The free body diagram above shows the horizontal force of the motor needed to push and pull the chair is lb horizontally. Ideally the gearmotor and cam system could be placed such that the center of the cam would be in line with the pin connecting the linkage system to the chair so that the link would be perfectly horizontal at the forward and back positions. This would minimize the power and torque needed from the motor. However, because the cam will be pushing beneath the chair at the point of the heaviest load to eliminate the moment it creates, and not at the back of the chair, the cam must be positioned below its optimal height to avoid collision between the linkage bar and the back of the chair. It was decided to place the cam center 2 below its optimal position. Fig. 15: Linkage bar locations at forward, back, center, and optimal positions 35

37 The maximum torque should occur halfway in between the front/back and center lines through the origin of the cam. Because the front/back moment acts through the center of the cam, rotational force does not come into play, and the motor is only taking a linear load. As the chair moves toward center, the linear force on the motor decreases, but the distance from the center of the cam increases. The greatest load and distance from the cam center happen near half way in between the center line and front/back line. The calculations performed for these two positions yielded an estimated maximum torque of 1693 in-lb. Gearmotor The above analysis found the maximum torque on the motor to be 1693 in-lb. Gearmotors on the website of Bison Gear and Engineering Corp. [6] come in a variety of horsepowers and speeds. To accommodate for the large force created on the motor, a custom gearmotor would have to be manufactured. A similar product to the one needed is the AC Parallel Shaft Gearmotor 482 series. It can handle 1105 in-lb of torque, operates at.5 hp and 22 rpm. Our ideal motor would be able to handle 1700 in-lb, and operate at.55hp at 20 rpm, and run on DC. The Bison motor costs $388.96, with a less powerful DC equivalent in the $ range. Power and Audio Power and audio components are identical to those of the optimal design. 36

38 ADVANTAGES -Fully enclosed moving parts -Smooth swinging motion DISADVANTAGES -Required forces and torques are too great for the desired motor type FINAL OPINION This design showed promise but no system of automation could be found with acceptable forces and torques. 37

39 D. Optimal Design 1. Objective The goal of this project is to design and implement a mechanism to automate the rocking motion of a legless rocking chair. This will be achieved through the use of a motor and cam system to apply the necessary forces at the back of the chair. Initiation of the rocking motion will be through a simple user-operated switch. The user will also have the ability to control a built-in sound system. For safety, caretakers will have master control over the rocking motion as well as the audio system. The design being considered for the rocking mechanism will require that the legless rocker have a steel frame that will be able to withstand the forces created during rocking. As most legless rockers have cheap plastic frames, the number of rockers of acceptable structural strength will be limited. The rocker will be attached to a metal frame that will sit on the ground and extend from level with the front edge of the rocker to slightly past a vertical line from the top-back of the chair. The chair will be attached to this by a hinge system which the chair will rock on. To the back end of the frame a gearmotor will be attached. A cam system and linkage bar will be connected to this motor. These will provide the necessary forces for rocking. The interchangeable controls for the user will be a touch pad and a squish switch. These controls will give the user the ability to start and stop the rocking motion and to turn on and off the sound in a fashion similar to a mute button. The caretaker will have master control over all aspects of the chair. The master controls will be on the back of the chair, out of reach of the user. These controls will include a switch to control the rocking motion, and access to the CD player including controls for power, mute, volume, and 38

40 track. For safety reasons, there will be a master switch that will cut power to the entire chair, and may be a keyed switch or remote control. The audio component will be powered by a basic car CD player. This will provide amplification for the sound as well as anti-skip capabilities to limit CD skipping as the chair rocks. The CD player will be installed in a control tower behind the chair. Speakers will be built into the headrest. The chair will use power from a standard 120 volt wall socket via an electric cord. A battery system was considered, but the high amperage of the motor meant that the battery would either need to be charged frequently or be excessively large and therefore heavy. These factors would drastically lower ease of use of the chair. Because the CD player and motor both run off of 12VDC, a power supply of proper wattage like those in a computer will need to be installed. An automatic cord reel, like in a vacuum cleaner, is a consideration. This would allow the external cord length to be kept to a minimum, also it would protect against damage to the internal connections of the chair, as someone yanking on the cord would pull out more cord rather than breaking the internal electrical connections of the chair. The final unit will be a self-contained, easily moveable chair with all electrical and mechanical parts guarded as best as possible. 39

41 User Controls Motor Link Gearmotor and cam Hinge Figure 16: Finished Chair Side View Figure 17: Chair 3D View 40

42 2. SUBUNITS Frame The rocker frame will consist of two parts: the external frame on the ground and the internal frame reinforcing the legless rocker. The external frame will provide an attachment point for all parts of the rocking mechanism. The internal frame will provide the purchased legless rocker with additional rigidity and strength so that it can handle the forces placed on it by the rocking mechanism. The external frame will include a metal base that will lie on the ground, a metal hinge that will tie the frame and legless rocker together, and a riser on the front edge of the frame. The metal for the frame can be obtained from Yarde Metals in Southington, CT [1]. The base will be built from metal, and will be approximately 40 long and 22 wide. The exact dimensions will depend on the size of the legless rocker chosen. The width of the base will be approximately the width of the rocker, and the length is, at minimum the distance between the front edge of the rocker at its most upright position and the top-back of the chair at its most reclined position. The length may also need to be increased by a few inches if more room is needed for the motor attachment. The chair will be joined to the base by a large hinge that will ideally run the full width of the chair. The two attached faces of the hinge will be parallel to each other when the chair is upright and will rotate about a pivot in the middle. The hinge will need to be strong enough to hold the combined weight of both the chair and user, and will have to be constructed of a material strong enough to support said weight. A pre-built hinge of this kind has not yet been found, so a drawing of the basic design, which could be built in the machine shop, has been included. 41

43 Figure 18: Hinge Design On the front edge of the base, a metal riser will be attached. The top of this riser will abut the bottom of the rocker at its most upright position. The purpose of this riser will be to prevent the application of a large force on the motor assembly when a user rests on the front edge of the rocker. This will ensure that the overhung load rating of the motor is not surpassed. It will be important to keep the riser from infringing on the motion of the chair, so it will need to be positioned carefully. Another metal riser will be placed behind the chair so that if the cam link breaks, the chair will rest on the riser and not tip over. The design of the internal frame will be dependent on the existent frame in the purchased legless rocker. Framing will need to be placed at the location of both mechanical attachments: the hinge and linkage bar. Additional framing may also be necessary to ensure that the chair does not break at the junction of the back and seat. The forces applied by the rocking mechanism will create a moment about this point which could lead to the chair frame bending and ultimately failing. The back and bottom of the chair will likely need to be opened in order to accomplish the required strengthening of 42

44 the frame. The ease at which the required frame work could be accomplished will need to be considered when the pre-built legless rocker is chosen. Rocking Forces An analysis of the forces of rocking was performed using a scaled drawing in Visio and a scale model in Working Model 2D. The legless rocker dimensions were taken off of Linen n Things website [3]. The chair used, the Attitude Video Rocker, has a solid wooden frame, a key component for our design. The dimensions given for the chair were 31 inches high, 22 inches wide, and 34 inches deep. This chair was found at a local Linen n Things store and the structural integrity of the frame in the critical lower sections of the chair was confirmed. Figure 19: Attitude Video Rocker 43

45 Analysis of this chair found that during comfortable rocking the back of the chair moved a horizontal distance of seven (7) inches from its normal position. This value is used for the following analysis. With the chair dimensions and a value for the travel distance during rocking, a scaled drawing could be made in Visio. These drawings, along with anthropomorphic data from Dr. John Enderle s Introduction to Biomedical Engineering textbook [4], allowed for summation of the forces acting upon the chair to be calculated. The segment weight and center of mass were determined for the upper body, thigh, and lower leg. Dr. Hallowell provided information to us that patient weights would vary from pounds. To be safe, 300 pounds was used as the maximum weight in the performed calculations. Trunk, arm, head Thigh Foot and Leg Subject Weight (lbs) Center of mass Weight (lbs) Center of mass Weight Center of mass Weight Table 4: Anthropometric data 44

46 Figure 20: Chair fully upright Motor Link Figure 21: Chair at midpoint of rocking motion 45

47 Motor Link 15 Figure 22: Chair fully reclined UPRIGHT ANALYSIS M Fr = 0 = F ( x 2.5) 15( x 3.5) 204( x 10.5) + 60(20 x) + 15(16.5 x) M F M = 294x 3642 x

48 MIDDLE ANALYSIS M Fr = 0 = F ( x 6) 15( x 5) 204( x 11.5) + 60(23 x) + 15(19.5 x) M F M = 294x 4094 x 6 RECLINED ANALYSIS M Fa = 0 = F ( x 8.5) 15( x 6) 204( x 12) + 60(24.5 x) + 15(22 x) M F M = 294x 4338 x 8.5 The above calculations show the relationship between the placement of the hinge and the force applied at the attachment point of the linkage bar on the back of the chair. Calculations in the initial design II were completed for two conditions: legs outstretched 47

49 and legs resting on the ground. Upon analysis of a person using the rocker at the Linens n Things store is what found that it would be unlikely for one s legs to be off of the ground. Further calculations were then done in Microsoft Excel to determine which hinge position resulted in the smallest maximum force at the linkage bar attachment point. Position x upright x reclined x middle Fulcrum Distance in in in Force lb lb lb Table 5: Excel Analysis of Optimal Hinge Position The analysis found that the smallest maximum force occurred when the hinge was placed 11 inches from the back of the chair at its upright position. The greatest force exerted by the linkage bar at this hinge position was pounds when the chair was at its most reclined position. These forces will be important later in this report (Cam and Linkage Bar section), as they will be used to calculate the torque required by the gearmotor. The highest force is important, as gearmotors have an overhung load rating. This rating limits the amount of force that can be applied perpendicular to the motor shaft. The riser on the front edge of the entire system s base will act to prevent the chair from rocking too far forward so that the overhung load rating is not surpassed. Cam and Linkage Bar The forces required for rocking will be transferred from the motor to the chair by a two part system consisting of a cam and linkage bar. The cam, with its diameter dependent on the placement of the motor, will be cylindrical in shape and be attached through its center to the shaft of the motor. A linkage bar, with its length dependent on the placement of the motor, will connect the back of the chair to a point on the cam. This system will translate the rotational motion of the motor into linear motion of the chair. 48

50 The exact size and position of this system will influence the torque requirements of the motor. The following analysis determines all of these unknown factors. The forces determined earlier in this report from the free body diagrams of the chair assumed that the linkage bar forces were in the vertical direction only. This is not the case, though, as the linkage bar supplies both vertical and horizontal forces. For this reason the moment required to balance the chair is what needs to be provided by the linkage bar. This moment, as well as the vertical and horizontal distances to the applied force, varies with the chair position and is dependent on the linkage bars attachment point. For the sake of safety and to keep the linkage bar short it is being attached to the chair at a position 4 up from the bottom of the chair. x upright x reclined x middle moment leg in-lb vertical in horizontal in Table 6: Moments and distances at different chair positions The position of the motor and therefore the position of the cam will determine what torque is required by the motor. Because the greatest forces are required at the upright and reclined positions, the linkage bar should be in line with the motor shaft at these positions in order to minimize the torque. The shaft of the gear motor is 2.5 from the motor s base so the center of the cam will need to be at this position vertically. The horizontal position of the motor and the size of the cam are dependent on the desired range of motion of the chair. For the 7 of travel that is to be provided, analysis in Working Model and Visio found the ideal motor shaft position to be 4 from the back of the chair when it is fully upright. The cam size was also determined to be 0.8 in radius. If a circular cam is determined to be too difficult to machine a bar of equal length could be used in place of the cam. The length of the linkage bar was found to be 5. 49

51 Cam located 2.5" up from base and 4" behind chair at upright position Distances determined from scale drawings in Visio Linkage bar length = 5.0 in X=horizontal Y=vertical Cam diamter = 1.6 in Reclined Position Moments Linkage bar angle from vertical = in-lb Fraction of force in Y= 0.36 Fraction of force in X= 0.93 Distance force is applied from motor shaft FORCES Chair force distances from hinge X= 0.75 in X= Vertical 2 in Y= in Y= Horizontal 10 in TORQUE Total Forces 2.02 in-lb lb Upright Moments Linkage bar angle from vertical = in-lb Fraction of force in Y= 0.64 Fraction of force in X= 0.76 Distance force is applied from motor shaft FORCES Chair force distances from hinge X= in X= Vertical 4.00 in Y= 0.50 in Y= Horizontal 9.00 in TORQUE Total Forces in-lb lb Middle 2 Moments Linkage bar angle from vertical = in-lb Fraction of force in Y= 0.64 Fraction of force in X= 0.76 Distance force is applied from motor shaft FORCES Chair force distances from hinge X= 0.40 in X= Vertical 3.00 in Y= 0.70 in Y= 9.10 Horizontal 9.50 in TORQUE Total Forces in-lb lb Middle 1 Moments Linkage bar angle from vertical = in-lb Fraction of force in Y= 0.38 Fraction of force in X= 0.92 Distance force is applied from motor shaft FORCES Chair force distances from hinge X= 0.45 in X= Vertical 3.00 in Y= 0.65 in Y= 7.09 Horizontal 9.50 in TORQUE Total Forces in-lb lb Table 7: Torque requirements of the motor 50

52 The torques found through static analysis closely matched the values from the Working Model program. The maximum torque in the Working Model simulation was found to be 41.2 in-lb, which occurred as the chair was lowering towards it most reclined position. Gearmotor The above analysis found the maximum torque on the motor to be 41.2 in-lb. Gearmotors on the website of Grainger Inc. [2] come in a variety of horsepowers and speeds. A 1/15 HP gearmotor at a comfortable speed of 20 RPM has a full load torque of 150 in-lb and a overhung load rating of 250 pounds. A 1/30 HP gearmotor at 21 RPM has a full load torque of only 50 in-lb. Though the 1/15 HP gearmotor would have 3.6 times the calculated necessary torque, this motor is the ideal choice. The calculated values, though as accurate as possible at this point, will vary with the exact chair purchased and with the exact construction methods used. The high safety factor in for both full load torque and overhung load rating will provide the chair with greater reliability. The selected gearmotor, a Dayton model #1L474, is sold for $ on Grainger s website. This motor has full load current draw of 6.5 amps. A Dayton model #1L474 motor is provided for free from the Biomedical Engineering stock room. This motor has a speed of 6RPM so an external gear system will be needed to create the necessary speed of approximately 20RPM. 51

53 Figure 23: Dayton #1L474 gearmotor Figure 24: Dayton #1L474 Schematic Power Both the CD player and the motor providing the rocking motion require 12VDC power. There are two options to consider in choosing the power source: 120VAC power from the wall or a 12VDC battery. A battery would allow for more variability in location of the chair and would avoid the use of a cord. The problem with a battery is that with a high torque gearmotor, such as the one initially selected, requires 6.5 amperes of current. This amperage level would require a high amp-hour battery in order to avoid the need for constant recharging. As the amp-hour rating increases, both the price and weight of the battery also increase. The cost of a charger for a 40 amp-hour battery is over $

54 To lower costs and improve ease of use, a power cord that plugs directly into a wall socket will be used. This will require the use of a power supply to convert the 120VAC power from the wall into 12VDC power for the CD and motor. The power supply will need to be capable of handling up to 6.5A at the peak capacity of the motor and 15A at maximum for the CD player. Power supplies are rated first by wattage, so a calculation had to be completed in order to figure out the overall power required. The power was calculated by using the following equation. P = I * V Equation 1: Power equation (P=Power (Watts), I=Current (A), V=Voltage (V)) There are two separate sources to calculate the total power. The first is the gearmotor, which requires 78 Watts (6.5A * 12VDC = 78W) of total power for its maximum consumption. Also, the CD player requires the use of 180 Watts (15A Maximum * 12VDC = 180W). Thus, the total power needed is 258 W (180W+78W = 258W). In order to compensate for such a large value and also not cause a maximum stress on the power supply, a 600W power supply was chosen in order to allow the power to operate at a moderate loading. However, there is also a need for the Load (%) vs. Input Voltage (VAC) curve that is provided with the data sheet of the power supply to demonstrate that the power supply will operate at its full capability before it is put into use. Also, the amperage level needs to fall within a certain range without being at its absolute maximum rating so that it is not being overstressed. The power supply needs to be properly tested by the appropriate certification groups (especially by the UL). Finally, the noise rating should be as low of a value as possible. 53

55 The power supply that was chosen after many considerations were taken was the Mean Well SP Watt Enclosed Power Supply, supplied from Jameco Electronics, and can be seen below [14]. Figure 25: Mean Well SP Watt Enclosed Power Supply The Load (%) vs. Input Voltage (VAC) curve can be seen below, as well [14]. Note that its load reaches maximum level at about 100 VAC, so the supply will be able to operate at full capacity by 100 VAC. 54

56 Figure 26: Load (%) vs. Input Voltage (VAC) for the Mean Well SE Power Supply. The noise level of the device is only 150 mv, which is one of the lowest noise ratings available from any of the available devices, the device is UL approved, and also the unit operates from 0-50A in the 12VDC output range [14]. Finally, the unit is the best value within the range of operational requirements, and costs $ The rest of the information about this device can be seen in the Appendix. [14] To minimize the length of exposed cord and to prevent damage to the chair from someone pulling on the cord use an electric cord reel like those found in vacuum cleaners 55

57 will be used. Though an initial search was not successful, the assumption is that such a cord reel could be bought from a vacuum repair shop or other online merchant. Control Mechanisms The control system is to be comprised of two types of interchangeable switches that allow the user to turn on and off both the rocking mechanism and the audio output. The input from these switches will be overridden by a master control in the tower in the back of the chair that will control both the rocking motion and the volume, CD track, and on/off mechanism for the chair. The first type of interchangeable switch for the user will be a $49 squish switch, purchased from TFH USA Ltd [6]. The switch is used by squeezing, either with a hand or between elbows or knees, and will activate or deactivate the pre-set rocking motion. Because there is room in the budget for only one squish switch, this switch will only control the rocking motion. The user, if he or she prefers to use the squish switch, will have to notify his or her caretaker of his or her preference for music. Passionworks will have the option of purchasing an extra squish switch if they desire another, and it will be able to be fully implemented with the chair. 56

58 Figure 27: Squish Switch from TFH USA Ltd. The second kind of interchangeable user switch will be comprised of a singlepole, double-throw (SPDT) button switch (See Figure 12) enclosed in a box with a lid that rests on the button (See Figure 13). When the lid is pressed down it will depress the button in the button switch, and either activate or deactivate the rocking motion. This system, used in a second switch of the same type, will control the audio output on and off. The SPDT push button switches can be purchased from Electronix Express [7] for $1.70 each, and an inexpensive plastic box can be purchased to encase the switch. There are several different accommodatingly-sized boxes at OKW enclosures, which cost no more than $7.98 for the largest potter s box (Part Number A ), and $5.33 for its corresponding lid (Part Number A ) [5]. 57

59 Side View of Touch Switch Figure 28: Touch Switch Design. When the lid is depressed, the switch will depress, turning the rocking motion of the chair or the audio volume on or off. Power Input (From Wall Socket) A User Control Switch B Rocking Motor Figure 29: Schematic for a Single Pole Double Throw Switch. The red wire will alternate between contacts A and B when the button is depressed, allowing current to flow to the rocking motor. A similar mechanism will be wired directly into the CD player to alternate between the volume and mute functions. 58

60 The master power switch should allow caretakers to turn the chair off so that it can never be used without supervision. Additionally, the caretakers need to be able to activate or deactivate the rocking mechanism and the audio mechanism independently. Therefore, the master control switch system will need to be able to cut off power to both the rocking motor and the CD player individually, and it must also cut off power to the entire chair. There also needs to be mechanisms for adjusting CD volume and track, and each of these controls need to be out of reach of the user. The controls for adjusting CD volume and track will be on the interface of the CD player to be purchased. Two separate switches for the individual audio and rocking motion will be placed before the user controlled switches, and will be in series with the mechanisms to override control of both the rocking mechanism and the audio mechanism (See Figure 4). There will also be a master switch to control whether or not current flows through the chair at all. This switch will be placed before the individual caretaker controls in series, as shown in Figure 4. 59

61 Power Input (From Wall Socket) A Master Power Control Switch B Mute Function A Master Control I A Master Control II B B User Control Switch User Control Switch B A B A Mute Function Rocking Motor Audio Output Figure 30: Control Wiring Diagram. Includes caretaker control switches for both audio and rocking components individually, and a master control switch that controls all electrical mechanisms in the chair. Audio This section includes the audio components of the system. The artists at the Passionworks Studio are involved in various stimulatory activities that further increase 60

62 their creative process, and embedding an audio system into the chair will allow the artists to have an enjoyable experience of both rocking and listening to music at the same time. A flow chart can be seen for the basic wiring schematic that will be needed to connect the audio components. Power Supply (12 VDC) CD player 3.5" Speaker (full range) 3.5" Speaker (full range) Figure 31 : Basic Wiring Schematic of Audio Components To accommodate the request of the client, it was decided that a CD player would be the best system to use. After much debate about which type of CD player to use, it was determined that use of a CD player from a car stereo would be most appropriate to use. The use of an FM transmitter from a device somewhere else in the room would 61

63 require a very powerful broadcast signal that would have little interference. This would not be the case if the transmitter was placed far across the room from the location of the chair. The objective of the sound system is to provide comfortable, clear music at a reasonable level, not to have static come out through the speakers and interrupt the music. There was a need for a mute function to allow for control of the sound by the user and a need for a master power control for use by the caretaker. A car stereo CD player will be easier to control if mounted in the back of the chair and would be more easily accessible than if a portable CD player was used. In addition, the CD player will be wired into the master power switch so that all of it can be shut off at once. Finally, an anti-skipping mechanism will be needed so that the motion of the chair does not cause the CD to malfunction and/or skip. The required speakers cannot be too large to fit in the headrest of the chair, nor should they be so powerful as to injure the ears of the user. However, the speakers should not be too small to provide adequate sound for the user to hear, nor should they difficult to locate if alterations or repairs are needed. Also, too many speakers would become cumbersome to wire and work with, while too few would provide inadequate sound output. CD player The CD player chosen was a Boss Audio CD-3020, seen below [8]. 62

64 Figure 32: Boss Audio CD-3020 Face 6.2" Figure 33: Boss Audio CD-3020 Dimensions This CD player is 6.3 inches long by 6.2 inches wide by 2 inches high [9]. The Boss Audio CD-3020 is a single-disc unit that slides the CD in through an opening in the front face of the player. There are four (4) possible channels available from the player for speaker attachments. The following tables include the following specifications and features of the CD-3020 are listed in Tables 2 and 3, respectively, of the Appendix. [10] The CD player requires an input of 12 VDC like that typically provided by a battery/alternator power system of a car. In this design it will instead be powered from 63

65 the 12 VDC power supply that will plug directly into a wall outlet, which provides 120 VAC of power. Speakers The speakers chosen are two (2) MA Audio HK35 speakers, one of which is shown below [11]. Figure 34: MA Audio HK35 Speaker They are 3.5 inches in diameter and two (2) inches deep, so they will fit well into the chair at its headrest. The speakers are also considered to be full-range, because their frequency range is from 100 Hz to 22,000 Hz. The technical specifications and features are listed in Tables 4 and 5, respectively, of the Appendix. [11] Wiring The audio system must be wired from the CD player to each individual speaker. In order to properly connect the speakers and maximize their output quality, a lower gauge (thicker in size than a higher-gauged wire) will satisfy this requirement. The use of car audio cables is not necessary for use in a piece of furniture such as a rocking chair, 64

66 so wire that is capable of being used in walls of buildings and that has a large enough gauging will be acceptable. The chosen wire is 16-gauge speaker wire available at RadioShack and is pictured below [12]. Figure 35: 16-Gauge Speaker Wire from RadioShack Protection The entire audio system should be protected from any environmental and/or uncontrollable conditions (spills, leaks) and needs to be insulated from the rest of the chair so that it will not shock the user and/or short circuit this portion of the device. A box made of plywood will be built to house the CD player within the chair back so that it can slide into this component. An additional idea for protection is a stereo cover for marine applications. There is one such item available is the Aquatronics Marine Stereo Cover [13]. This cover is 9-5/8-inches wide by 4-3/8-inches high, which will adequately cover the face of our CD player. A picture of this is available below. Figure 36: Aquatronics Marine Stereo Cover Wiring 65

67 Wiring Electric Power from Outlet 600W 12VDC Power Supply Caretaker Control User Control Mute Function Boss Audio CD Two MA Audio HK35 Speakers Rocker Power Switch Interchangeable Rocking Motion Activation Switches Dayton #1L474 gearmotor 1/15 HP Geared to 20 RPM Figure 37: General Wiring Schematic 66

68 E. Prototype 1. Overview The optimal design from last semester was the inspiration for the design of the prototype. The framing was designed to be constructed using stock aluminum as described, but was actually built using 80/20 extrusions. This greatly increased the ease with which the frame was built. The hinge mechanism was constructed using an 80/20 hinge part with some modifications. The hinge attaches to another 80/20 frame which was screwed onto the chair. The CD player and caretaker controls were built onto an 80/20 tower at the back of the chair. The speakers were built into a plastic case within the chair. The user switches were designed to be moveable so that a chair user can place them in his or her lap. A 1/6 HP motor is used to rock the chair. The speed of the rocking is adjusted by a series of gears to be slower than the motors rotational speed. From these gears a cam drives the shaft that rocks the chair. All of the wiring is enclosed in the extrusion network. 2.Subunits Mechanical subsystem BASE FRAME Figure 38: Base frame design and completed assembly The base frame for the chair was built from 80/20 extrusions. The frame lengths were secured to each other with two-hole hinge brackets. The hinge was attached to a cross-brace. Five-hole mounting plates were used to ensure a secure connection between the hinge and the frame. Two cross-braces are used at the back of the frame in order to accommodate the motor and the caretaker tower. The overall length of the frame is 48 and the width is 28. The motor cross-braces are placed 6 3/8 on-center from each other. The hinge cross-brace is 17 from the closest edge of the motor cross-brace. 67

69 UPPER FRAME Figure 39: Upper frame design and completed assembly The upper frame was also built from 80/20 extrusions. The frame is L shaped to allow for seating of the legless rocker. Cross-braces and corner brackets are used throughout in order to secure the frame. An additional reinforcement made of 1 x4 aluminum was added to the back of the upright of the frame to keep it from twisting against the chair. This piece was prone to twisting because the motion of motor and cam system causes it to pull down on this frame piece. The addition of this extra support solved the problem. Two cross-braces were used to attach the hinge mechanism to this part of the frame. This allows for a strong and adjustable connection between the two frames. 68

70 HINGE Figure 40: Hinge CAD drawing The chair hinge was built from modified 80/20 parts. For the pivot point, a 90 active pivot hub was used. This attached to cross-brace on the base frame. Modified three-hole plates were attached to the cross-brace on the frame. The original pieces were too large and too thick at the pivot location, so 0.27 was milled from the radius and the thickness decreased to.22 in the machine shop. The milled pieces could then fit correctly onto the pivot hubs. The plates were attached to the cross-braces on the upper frame. The hinge can slide both back and forth and from side to side in order to optimize its position on the frame. Figure 41: Hinge assembly 69

71 MOUNTING OF CHAIR The chair was mounted the frame using a series of metal plates. Two plates were used on each side of the chair base to attach it to the frame. A third plate was used on each side to attach the chair to the upright part of the frame. This third plate also helped spread out some of the force of the rocking mechanism along frame. The plates were bolted to the frame and screwed to the chair. ANALYSIS OF ROCKING FORCES Before the motor and cam system could be attached to the chair and frame, its position and dimensions needed to be determined. This analysis was done primarily in Working Model 2D. A scaled model of the chair was made from measurements of the assembled frame. Figure 42: Force analysis drawing From the analysis, it was determined that the linkage bar should attach as far up on the frame as possible. The ideal position for the cam was also determined to be 14 behind the chair, as measured from the back of the chair frame. The resulting dimensions for the cam and linkage bar themselves will be discussed later. The maximum torque for a 190 pound person was calculated to be approximately 45in-lb for the ideal seating position. For safety and durability reasons, a motor with a much higher torque capability was be chosen. Initial testing of the chair with a 1/15 HP motor that had 75 in-lb of torque demonstrated a jerky motion for heavier occupants. This problem lead to the use of a larger motor as is discussed later. 70

72 MOTOR The motor used for the prototype is a Dayton 1Z831 1/6 HP DC gearmotor. It runs off of 12 VDC and produces 135 in-lb of torque at 80 RPM. The listed peak amperage was 18.5 amps. Because the motor speed was too high, a gear system was built to slow the rocking speed to 20 RPM. This mechanism is described later. During testing, this motor was shown to run at approximately 2.5 amps with no load and at 5.5 amps while rocking a 160 pound person. Figure 43: Dayton 1Z831 motor Figure 44: Motor schematic The motor was attached to a ¼ aluminum plate using screws threaded directly into the motor. This aluminum plate was then attached to the base frame on the two motor cross-braces. The positioning of the motor on this plate was determined by the gears and the ideal position of the cam center. 71

73 GEAR SYSTEM The natural speed of the motor was 80 RPM, which is not a safe or comfortable rocking speed. To lower the motor speed and increase torque, a system of gears was attached. A small 12 tooth gear was attached directly to the shaft of the motor. It was secured to the shaft by a 3/16 key and a set screw. A larger, 50 tooth gear is driven by this smaller gear. This results in a lower speed and higher torque according to the following calculations: 12Tooth 3" radius 80 RPM * = 19. 2RPM 135 in lb * = 405in lb 50Tooth 1" radius The largest gear is positioned so that its center is 14 from the back of the chair frame, which is the ideal position determined during analysis. It is attached to the same aluminum plate as the motor using four lag bolts. Figure 45: Gear assembly 72

74 CAM The rotational motion of the motor is converted into the rocking motion of the chair through the cam which is attached to a shaft running through the large gear. The cam was machined from a ¾ pieced of aluminum. The cam length is equal to half of the length between the back of the chair at its most forward and reclined positions and the center of the large gear. This distance was determined to be 1.4. A step down shaft was used to attach the cam to the large gear. The gear had a shaft opening of 7/8 and the cam had a 5/8 hole. This milling was done on the lathe in the machine shop. The shaft is attached to the gear with a tapered rod that passes through both. The shaft also has a slot for a key milled into it. The key secures the cam and keeps it from slipping around the shaft. A lock screw is also in place to keep the cam from sliding off of the shaft. A 3 length of 5/16 zinc rod was attached to the cam at through a hole 1.4 from the center of the shaft. This zinc rod joins the cam and the linkage bar as will be described later. The rod is secured with a lock screw. Figure 46: Machined Cam 73

75 LINKAGE PIVOT A pivot block was attached to the back of the chair frame to which the linkage bar would later attach. This block transfers the rocking force from the linkage bar to the chair itself. The piece was machined from a cube of aluminum. A 5/16 hole was drilled through the piece. A section of 5/16 zinc rod was secured through these holes by set screws. The linkage bar system would later attach to this rod. The entire pivot block was screwed onto an aluminum plate by two screws passing through the back of the block. This plate was then attached to the back of the chair frame. Figure 47: Linkage pivot design and assembly 74

76 LINKAGE BAR The motor and chair are tied together by a five part linkage bar. The main portion of the bar is a 3/8-32 threaded rod. Purchased bearing blocks were used to attach to the 5/16 rods on both the cam and pivot block. These blocks help lower friction in the drive system. Figure 48: Bearing block To these bearing blocks, adapter blocks were attached that allow for the linkage bar to thread in. The adapter blocks were milled to follow the profile of the bearing block bases and have threaded screw holes that match up with the holes in the bearing blocks. The threaded rod was screwed into these adapter blocks and secured with a nut locked tight to the adapter block. This linkage bar design allows for easy adjustment of the bar length by simply loosening a nut and then twisting one end of the bearing block assemblies. The ideal length is one that keeps the back of the chair frame just above the ground at the chair s most reclined position. Figure 49: Linkage bar assembly 75

77 COMPLETE DRIVE SYSTEM Figure 50: Motor and drive assembly 76

78 Electrical subsystem POWER SUPPLY The electronics of our chair are powered by a 12VDC power supply. A Meanwell S power supply was selected. This supply has an adequate current rating and is compact. A standard extension cord is used to attach this power supply to a wall outlet. Figure 51: Meanwell power supply Figure 52: Power supply specifications 77

79 MOTOR CONTROL An MC7 motor controller was originally used in our project to control the motor speed. Though this unit was far more important in our earlier designs, which relied on it entirely for control of the motor speed, it still serves two purposes. Firstly, a potentiometer is wired to the controller that allows the caretaker to slow the speed of the motor. When the potentiometer dial is turned to minimize the resistance in the circuit, the motor spins at the recommended speed of 20 RPM. As the potentiometer resistance is increased the motor slows. Slowing of the motor does have the negative side effect of lowering the voltage which limits the power of the motor. The second, and primary advantage of the motor controller is that it allows for the use of lower amperage switches. The current that passes through the switch while using the motor controller is less than one amp, where as it would be up to 12 amps without the motor controller. Figure 53: Motor controller schematic 78

80 Figure 54: Motor controller The motor controller is housed in an OKW enclosure with air holes drilled in the box top to allow for cooling of the board. This box also serves as the mount for the interchangeable switch sockets. One of these sockets is wired to the switch pins on the motor controller. Figure 55: Motor controller case 79

81 CD PLAYER AND SPEAKERS The sound input for our chair is from a Boss Audio CD The CD player is mounted within an OKW enclosure attached to the caretaker control tower. The player is wired to two MA Audio MK35 speakers. An antenna was also attached to the CD player in order to increase radio reception. This antenna was enclosed within the chair. The CD player has connections for 4 channels. To increase the signal strength to the two speakers, the negative of one right channel was wired with the positive of the other right channel. The same was done for the left channel. The speakers are installed within the chair inside a PVC box. The box provides a mounting place for the speakers and protects them. The box was installed behind the user s head. Figure 56: Audio system 80

82 Controls subsystem Two control systems are used in our chair: caretaker and user. The caretaker controls allow for master control of all aspects of the chair, and the user controls allow for initiation of rocking and music after they have been turned on by the caretaker. CARETAKER CONTROLS The caretaker is capable of cutting power to all parts of the chair. A master power switch cuts power to both the CD player and motor controller. With this switched turned on, the CD player can be used, but not the motor. With the master power on, turning on the motor power will allow the chair to rock. The caretaker also has control of the potentiometer which controls motor speed. The max speed of the motor is set to the ideal 20 RPM, but the caretaker can vary the speed between 20 and 0 RPM.. In the case that an audio or motor circuit breaker is blown the caretaker can reset them on this control panel. The switch box is mounted on top of the CD player case on the caretaker control tower. Figure 57: Caretaker controls 81

83 USER CONTROLS Two different interchangeable switches are used by the chair occupant. The first is a squish switch. This switch is flipped by simply squishing the foam filled fabric cylinder. The second switch is a touch switch. This switch requires the user to press down on the large spherical top of the switch. Both of these switches were designed with simplicity of operation in mind as they may be used by individuals with limited physical and/or mental capacity. Either switch can be used for the motor or audio. A switch is assigned to one of those two operations by switching two sockets on the caretaker control tower. Figure 58: Squish and touch switch 82

84 WIRING The numerous electrical systems of the chair are tied together by wiring hidden within the chair frame. Electrical power is supplied to the chair by a 15 extension cord attached to the power supply. At the power supply, the 120 VAC electricity is converted to the 12 VDC power needed by the chair components. The neutral wire from the power supply runs to the negative power in lead on the power supply and then braches off to the negative power lead of the CD player. The load wire runs first to the master power switch in the caretaker control box. After this switch the wire is branched through both of the circuit breakers. The CD load wire then runs directly to the CD player, while the motor load wire runs to the motor power switch and then to the motor controller positive lead. At the CD player wires run to the speakers and to the antenna. The antenna wire runs directly to the antenna with no interruption. The neutral wire of the audio output runs directly to the speakers. The positive wire runs to the user control switch sockets and then to the speakers. The control switch socket for the speakers is dual channel as it cuts off both audio channels. The audio will only play with the activation of the user switch. Turning off of the audio by the user will not shut off the CD player though, so sound can be activated again with a second pushing of the same switch. The motor controller has neutral and load outputs that are connected directly to the motor. Three wires from the motor controller also run to the potentiometer that allows for speed control. Another set of wires runs to the user control switch socket were they are connected through a user switch. Though only the audio socket is wired for dual channel, both of the switches are as they are meant to be interchangeable. A wiring diagram is included on the next page. 83

85 Figure 59: Wiring diagram 84

86 COMPLETE CONTROL TOWER Figure 60: Control tower 85

87 COMPLETE CHAIR Figure 61: Complete chair 86

88 3. Safety Numerous mechanical and electrical safety measures are in place in the chair. Safety is important because the chair will be used by individuals with limited mental and physical abilities. The large amount of electrical wiring running throughout the chair is a safety hazard. To protect against electrical shock, all of the wires are hidden behind 80/20 extrusion covers. These covers help to give the chair an organized and aesthetic look as well. They also prevent the user from pulling on wires which would damage the chair. Figure 62: Extrusion covers The most dangerous electrical hazard on the chair is the 120 VAC current that enters the power supply. For this reason the power supply is located behind the chair and is encased fully in a plexi-glass box. The taping over of all exposed wires within this box with electrical tape provides a secondary safety measure. Figure 63: Power supply cover 87

89 To prevent the extension cord from being pulled out of the power supply or the connections loosened, the extension cord is secured to the frame with zip ties. Figure 64: Extension cord stay The moving parts of the drive system pose a risk to user and caretaker alike. One could easily get a finger caught in between the gears or between the rotating cam and linkage bar. To prevent against this the moving parts are encased in plexi-glass boxes. Though these guards could be broker with heavy force, they provide protection against someone carelessly putting there fingers somewhere they should not be. Figure 65: Drive system guards 88

90 The chair itself is padded in all areas that will be open to the user. The user control switch holder is padded over as well, to prevent against someone from hitting their leg on it as they pass by. Figure 66: Padded user control holder 89

91 4. Usability with target clients CARETAKER The caretaker s controls are all located on the caretaker tower at the rear of the chair. This makes it possible for the caretaker to access all of the controls available to them from one location. All switches are clearly labeled and located within easy view. To power up the chair, the caretaker need only plug in a standard extension cord. No batteries are used within the chair so the caretaker is not required to access any battery ports. The main switches for the chair are simple to use and intuitively labeled. A master power switch is boldly labeled on the top of the control tower. With this switch turned to the on position the caretaker has control over the CD player. The CD player is a standard car model so the user will not be presented with an unknown control interface. Control of motor power is also through a clearly labeled, easy to use switch. With this switch turned on the chair will begin to rock when the user pushes their switch. The user controls were designed to be interchangeable. The responsibility of interchanging the switches lies with the caretaker. This process has been made very simple. Two sockets are located on the motor controller box. One is clearly labeled motor and the other audio. The caretaker need only pull out the plugs from these sockets and switch them. Figure 67: Caretaker switch controls 90

92 USER The intended users of this chair are individuals with limited mental and physical abilities. For this reason the user can not be expected to understand complex controls. The caretaker will present when the user wishes to use the chair. The chair is close to the ground so the user will be capable of easily entering and exiting the chair without the risk of falling a large distance to the ground. The caretakers at the Passion Works facility seat the user in the chair, as they have in the past with non-motorized legless rockers. Once the caretaker has turned on the desired systems the user is in control. The caretaker can take one of the controls and place it in the user s lap. The switches are large and easily switched so they will not require high dexterity. The user can push the switch with an elbow, a forearm, or with their hand. For users with greater physical abilities the switches can remain on their holder and can be pushed from there. Figure 68: User switching 91