Operator s Manual. Accessible Laptop Desk for Julia. Team 5. Kayla Gosse. Jordan Smith. Leah McElhaney. Client Contact Information: Megan Baker

Transcription

1 University of Connecticut Senior Design BME 4910 Operator s Manual Accessible Laptop Desk for Julia Team 5 Kayla Gosse Jordan Smith Leah McElhaney Client Contact Information: Megan Baker Mansfield Middle School (Room 17) BakerME@mansfieldct.org

2 Important Safety Instructions The following list of safety instructions should be followed at all times when operating the Accessible Laptop Tray device to prevent injury to the user or damage to the tray system. Before operating tray, make sure there is at least 2 feet of space to the right of the wheelchair. Release the directional switch to halt tray movement if there is not enough room to complete the tray rotation due to close proximity to an object or person. When operating the tray from in the chair, make sure hands and arms are held close to the body to prevent interference with the tray movement. Before adjusting any of the wiring or electrical components, make sure that both the tray system and the wheelchair are turned off. In case of a medical emergency, the tray may be moved out of desk position into hanging position by turning the tray by hand. However, in day to day use, avoid turning the tray by hand because this can build up a charge on the electronic parts and burn them out when the power is turned on. If any wires become exposed during use (if the metal part inside the wires is showing), turn off the system power and cover the exposed part with electrical tape before resuming use of the tray. 2

3 Parts and Accessories The following parts of the laptop tray system are labeled in photographs on the following two pages: A Tray Edging B Polycarbonate Tray C Support Piece D Laptop Case E Strap System F Rectangular Arm Piece G PVC Tray Frame H Stepper Motor I Electrical Box J Motor Bracket K Gearbox L Arduino Board M Motor Driver Board N- Power Switch O Directional Switch P Push-button Switch Q Battery Leads R - Fuses 3

4 4

5 5

6 Features The laptop tray has many different features including the most important one, which is ability to provide an accessible method for the client to use her laptop. This device also has features including the protection of the laptop, easy-open case, a case that can be repositioned and easy detachment from wheelchair. This device functions to rotate a laptop tray from the side of the wheelchair, up into a position in front of the operator at the flick of a switch. The tray is made of polycarbonate and is strong enough to support the Julia s body weight should she lean on it. This device essentially allows an easier method for the client to use her laptop, without the hassle of having to attach and detach a separate tray. The laptop tray also features a laptop case that functions to protect the laptop while it is not in use. The laptop remains attached to the tray when it is not in use, which demonstrates a need for the laptop to be sufficiently protected. The tray rests on the right side of the wheelchair when it s not in use and the laptop rests inside a case that protects it from getting damaged. The way the tray rests on the side of the wheelchair allows for the laptop to be shielded on the inside, away from potential hazards such as getting bumped into on the outside. This laptop case also has two features that will make it easy form Julia to use. The case has a large ring attached to the zipper that allows the operator to open the case with ease. The large metal ring is easier for Julia to grip and provides a better solution to unzipping the laptop case. The laptop case also has the ability to be positioned on the tray in multiple locations to suit the Julia s needs. There are a set of straps that are attached to the laptop case. The laptop case assembly can be moved to the left or right depending on what the operator desires. Another feature of the accessible laptop tray is that it has the ability to be detached from the wheelchair. It is possible to unscrew the motor bracket and detach the wiring so that it can be separated from the wheelchair. However, it is not recommended to do this every time the operator desires to use the tray. This should only be done if Julia no longer decides to use the laptop tray. 6

7 Table of Contents Important Safety Instructions Page 2 Parts and Accessories Page 3 Features Page 6 Table of Contents Page 7 1. Introduction 1.1 Overview and Assembly Page Step By Step Instructions for Operation Page Maintenance Page Technical Description Page Troubleshooting Page 31 Appendix Page 39 7

8 1. Introduction 1.1 Overview and Assembly Overview The purpose of this project was to provide Julia with a new attachable tray for her wheelchair which will be electronically controlled so she can use it on her own. The tray will hang by the side of the wheelchair when not in use, and flip up in front of Julia when she needs to use her laptop. This tray will also assist Julia in the transportation of her laptop. The tray will have the option of holding the laptop safely and securely in place when the tray is in desk position up in front of Julia, and down by the side of her wheelchair as she navigates the school hallways. Figure 1 The tray itself (Figure 1) will have the ability to hold a laptop in a case with a system of straps. The tray has a ½ lip around the top edges to prevent objects from falling of the tray when it is in use as a desk. Additionally, a support piece made of PVC pipe will allow the tray to rest on the left arm rest of Julia s wheelchair and make the tray a more stable surface. The tray is hinged to a rectangular piece of polycarbonate which is to be clamped onto the right arm of 8

9 Julia s wheelchair. A stepper motor and gearbox serve to drive tray movement. The shaft of the gearbox connects into the hinge created by the tray frame with the rectangular arm piece. When the motor is spun, so is the tray. A bracket secured to the back right side of the wheelchair will hold the gearbox, stepper motor and a box containing the tray s electronics. The assembly of this motor bracket and the clamping system will be described in depth in the following section. The battery from Julia s electric wheelchair will provide power to both the motor and driver and Arduino board which control the tray system. Three leads have been run from the battery out the back of the wheelchair to power the system. These will be discussed further in the Technical Description section. The whole system will be operated by a button to turn the system on and off, and a switch to control whether the tray is moving up or down. The coding of the Arduino board (Figure 2) which controls the entire system will allow the tray to move in the following ways: if the tray position is less than 270 degrees (which represents the tray in desk position) and the up direction is pushed on the directional switch, the tray will begin to move up. If the switch is released, or if desk position has been reached, the tray will no longer move forward even if the switch continues to be pressed. If the tray is in a position of more than zero degrees (hanging position) and the switch is pressed down, the tray will move downward until the switch is release or until the tray returns to zero degree position. The code prevents the tray from moving past its desired start and end positions, even if the switch is being pressed, by keeping track of the motor position in relation to the 270 degree tray trajectory. The code also contains an input from the push button switch which is mounted to the rectangular arm piece of the tray. When the tray is moved into desk position, the button will be pressed down. In the coding, this will stop forward tray movement and act as a code reset if the tray is to lose power part way through its movement. Figure 2 The block diagram in Figure 3 will help outline the components involved in tray movement and how the components work together. A more in depth description of each of the subunits referenced in the overview can be found in the Technical Description section. 9

10 Figure 3 Assembly A. The Armrest Clamping System This section will give instructions on how to assemble and remove the tray itself from Julia s wheelchair by way of the clamping system on the right arm of the wheelchair. The clamp system consists of a thin aluminum beam which will run beneath the armrest parallel to it and will be screwed into two existing holes on the vertical armrest support beams. This piece is painted black to blend into the wheelchair frame. The second component of the clamping design consists of two L shaped brackets. These are attached to the underside of the rectangular polycarbonate arm piece which hinges to the tray. When the tray is placed in position for attachment to the chair, the one side of the L will hang over the armrest and hit the horizontal aluminum bar. These two pieces will be screwed together to complete the clamping system and attach the tray securely to the chair as shown in Figure 4. 10

11 Figure 4 To assemble the clamping system, complete the following steps: 1. First, attach the aluminum bar part to the two vertical beams of the wheelchair frame underneath the right armrest. 2. To do this, line the holes in the two L shaped pieces attached to the back of the aluminum beam with the two holes in the vertical wheelchair beams (as shown in the right side of Figure 4). 3. Then insert one quarter inch screw through each of the holes. Once in place, twist a nut onto the end of each screw. Tighten the nuts down as much as possible. 4. Next, take the tray and line up the rectangular arm piece with the chair s right arm rest. Line it up so that the inner edge of the rectangular arm piece is even with the inner edge of the chair. You may need two people for this assembly. Hold the tray as shown in Figure 5 when positioning it for clamping. 11

12 Figure 5 5. At this point slide the rectangular arm piece such that the L brackets hanging over the arm line up with the two holes in the aluminum beam piece. 6. Once the holes in these two components are aligned, use two more quarter inch screws and nuts to connect them together. 7. Once again, tighten the screws as much as possible so that the tray is held tightly on the arm of the wheelchair. 8. To remove the tray and unassembled the clamping system, reverse these directions. B. The Motor Bracket This section will give instructions on how to assemble and remove the motor bracket and the components that is holds from Julia s wheelchair. This part of the tray system should not be removed often if at all because it holds the motor and the wiring for the tray. 1. To attach the motor bracket to the chair, unscrew the bolts that hold the two sides of the circular clamps together. You should be left with two half clamps which are separate from the motor bracket. 2. Hold the motor bracket against the vertical rod at the back right hand corner of the wheelchair frame so that the side of the clamps attached to the bracket lines up with the rod. 3. One at a time, line up the second side of the clamp on the back of the rod. Push and turn the bolts through the holes in the two sides of the clamp to hold it together around the wheelchair frame. 4. Put the nuts on the end of the bolts and tighten down part way. Figure 6 shows attached motor bracket. 12

13 Figure 6 5. Set the motor/gearbox combination on the bracket so that the front of the gearbox lines up with the part of the bracket which resembles its faceplate. 6. Use four screws to connect this piece with the gearbox to hold it in place. 7. Move the bracket into position such that the gearbox shaft is vertically in line with the end of the hinge of the tray which should already be attached to the chair. At this point, tighten the bracket s circular clamps all the way. 8. Screw the gearbox shaft into the tray by lining up the holes on the shaft with the screw holes in the tray coupling (See Figure 7). Figure 7 13

14 To remove the tray and leave the motor bracket on the chair, unscrew the gearbox from the motor as described in the technical descriptions section and from the motor bracket. Unclamp the tray from the arm of the chair and then lift to remove the tray with the motor bracket attached. The motor should then be screwed into the faceplate on the bracket where the gearbox had been in order to keep it secured. C. The Laptop Securing System The following instructions list the steps for the attachment and removal of the laptop to Julia s tray as shown in Figure 8. Figure 8 Laptop attachment to underside and top of tray. 1. Take one of the blue straps and find the end without the clip. Start on the underside of the tray and feed this end of the strap between the tray frame and the polycarbonate. 2. Next, feed that strap through the slit in the top right hand corner of the laptop case, from outside the case to the inside. Then feed the strap through the top lefthand slit. (The laptop should be removed from the case during assembly. 3. Line this strap up with the openings in the tray edging (as shown below) and then feed the strap between the polycarbonate and tray frame back around to the bottom of the tray. 14

15 Figure 9 4. Repeat the same procedure with the second strap, positioning this one though the bottom slits in the laptop case. This strap should line up with where the tray edging ends. 5. Finally feed both straps through their clip and tighten the straps down as much as possible. This step would be most easily accomplished with the tray in hanging position. 6. When the tray is back in desk position, set the laptop in the case and zip it when not in use. 1.2 Step by Step Instructions for Operation When the device is correctly assembled on the chair as described in Section 1.1, and shown in Figure 10, it can be operated using the following step by step instructions. Figure 10 15

16 1.2.1 Moving the tray from Hanging Position 1. Start with the tray in hanging position at the side of the wheelchair, with the power switch set to off position represented by the circle O on the switch. 2. When the chair power is on, press the power switch to on, represented by the line on the switch. 3. Check to make sure there is room on the right side of the chair before operating the tray. Make sure to hold arms close to the body. 4. To bring the tray up into desk position, press and hold up on the directional switch. Release the switch when the desk is in position. If the switch remains pressed for too long the tray coding or the pressing of the push button switch should cut off the motor so the tray will not continue to move forward. If the switch is released before final position is reached, the tray should stop in its last position and remain there until up or down are pressed on the directional switch. 5. When the tray has been moved to desk position (Figure 11), the system can then be turned off with the power switch to conserve battery power and prevent the system from drawing unnecessary current. 16

17 Figure To access and use the laptop, simply unzip the laptop case Moving the tray from Desk Position 1. Before returning the tray from desk position to hanging position, make sure that the laptop is closed and the case is fully zipped around it. 2. Turn on the power to the system by pressing the power switch to on (illustrated by the line on the switch). 3. Check to make sure there is room on the right side of the chair before operating the tray. Make sure to hold arms close to the body. 4. To bring the tray down to hanging position, press and hold down on the directional switch. Release the switch when the tray is in position. If the switch remains pressed for too long the tray coding or should cut off the motor so the tray will not continue to move forward. If the switch is released before final position is reached, the tray should stop in its last position and remain there until up or down are pressed on the directional switch. 5. When the tray has been moved to hanging position, the system can then be turned off with the power switch to conserve battery power and prevent the system from drawing unnecessary current Lost Power 1. If power is lost part way though tray movement, allow the tray to remain in its last position and restore power to the tray. 2. When power is returned, press the switch forward until the tray is in desk position. Regardless of what direction the tray was travelling when power was 17

18 lost, the tray must go to desk position to reset the code for the tray and allow normal tray movement 3. At this point, Julia can return keep the tray in desk position, or return it to hanging position If the push button switch is hit accidentally 1. If the push button switch is press accidentally, the tray will no longer be able to move in the forward direction, regardless of tray position. 2. If this occurs, turn the tray s power off and back on. 3. Press the directional switch up until the tray is in desk position. This will reset the code. 2. Maintenance 2.1 Mechanical There are a couple things that can be done for preventative maintenance to ensure the laptop tray s lifespan is maximized. It is important to take into consideration these pieces of advice to ensure that the tray is less likely to break or wear out over time. Every few months, it is necessary to double check the bolts holding the tray to the wheelchair to make sure they are tightened securely. This is one of the most important parts of the wheelchair and is necessary for the system to function properly. Bolts and screws on the clamping system, tray frame and motor bracket should be check and tightened to keep the tray system safe and functioning correctly. The motor attachment piece should be checked periodically to ensure that the motor does not slip when attached to the hinge arm of the tray. There are two screws that securely hold the shaft of the gearbox from slipping when the shaft rotates. These screws may come loose over time and it s necessary to tighten them in order to make sure that the shaft of the motor does not slip when the tray rotates. The cleanliness of the wheelchair is another thing that is necessary to increasing the lifespan of the device. The wheelchair should be cleaned periodically to ensure that it does not collect dust, which can hinder movement of the mechanical components. Cleaning the wheelchair every couple months will ensure it is free of bacteria and will provide a healthier setting for those using the chair. 18

19 Additional tips for maintaining the mechanical system of the tray and fixing any problems can be found in the troubleshooting section. 2.2 Electrical Inspect electrical wiring to ensure that there are no loose wires. All wiring should be tucked away and not exposed. Wiring should be wrapped in the black plastic tubing so that it does not get torn or damaged. Electrical boards should remain enclosed in the gray plastic electronics box located on the motor bracket. Any wires that are torn or exposed could produce a risk of electrical shock. Exposed wires could also get caught on things as Julia uses her wheelchair in her classrooms. Overall, there should not be too much maintenance that needs to be performed on the tray or its components. The laptop tray has been design to be as easy to use and maintenance free as possible. 3. Technical Description This section will provide a detailed technical description of each of the essential tray components. Photographs, illustrations and diagrams will also be included to enhance the explanations. A. The Tray, Tray Frame and Hinge System The tray itself will be made of clear polycarbonate inches thick. This is the same material as Julia s current tray, so we know that it is strong enough for her needs, yet not too heavy. Since polycarbonate is transparent, it will also not impact her line of vision when maneuvering her wheelchair. We also cut the rectangular arm piece from the polycarbonate, with the dimensions of 4 inches wide and 14 inches long, matching the length of Julia s armrest. The dimensions of Julia s tray are shown in Figure 12 below. 19

20 Figure 12 The polycarbonate tray has a frame made out of 1 PVC pipe pieces. This frame not only acts as a hinge system and allows for direct connection to the gearbox shaft, but also takes all of the torque off of the thin polycarbonate and distributes it throughout the PVC. The design consists of a ½ metal pipe that attaches directly to the gearbox shaft and act as the base of the hinge. Around that, a frame made of 1 PVC pipe is attached to the underside of the polycarbonate tray. The PVC pieces that attach to the underside of the tray are also attached with screws to the metal pipe inside of them so that when the motor spins the pipe, it also spins the tray. Alternating PVC sections are attached to the polycarbonate piece on the armrest of the wheelchair. The metal pipe is not attached to these sections so that it can spin freely through them, thus creating a hinge system. The frame is attached to the polycarbonate tray with small screws that connect the polycarbonate and PVC and lie flush on the top side of the tray so that they don t interfere with the desk function. This system is diagramed in Figure 13 below. Figure 13 20

21 Two other important aspects to the tray which make it more suitable to Julia s needs include the tray edging and the support piece which sticks off of the left side of the tray. The edging is made of pieces of quarter round molding which we cut to size and glued to the perimeter of the tray with strong acrylic glue. The edging provides a ½ lip on the tray to prevent anything from falling off of it when in use as a desk. We also left cutouts in the molding on the tray where the laptop straps were secured to prevent them from slipping when the tray is in use. The support piece is made of PVC pipe which is connected to the tray frame and extends out about three inches from the bottom left corner of the tray. This piece will rest on the edge of the left arm rest of Julia s chair when the tray is in desk position and serve to support the tray on the left side. These two components can be seen on the tray in Figure 14. Figure 14 B. The Armrest Clamping System The clamping system allows the tray to hook into the metal support beams under the right armrest on her chair. This distributes the torque of tray movement into the frame of the wheelchair, instead of solely on the plastic top of the armrest. The system consists of a thin aluminum beam which runs beneath the armrest parallel to it and can be screwed into two existing holes on the vertical armrest support beams. This will be painted black to blend into the wheelchair frame. Although easily removable, this piece could be left on the wheelchair without interfering with its function or Julia s comfort. The second component of the clamping mechanism consists of two L shaped brackets. One side of each L is attached to the underside of the rectangular polycarbonate arm piece. When the tray is placed in position for attachment to the chair, the second side of the L will hang over the armrest and hit the horizontal aluminum bar. These two pieces can be screwed together to complete the clamping system and attach the tray securely to the chair as discussed in the 21

22 Assembly section. Figure 15 below shows this system on Julia s chair. The right hand image illustrates how the aluminum bar is screwed into the wheelchair frame. Figure 15 C. The Motor Bracket The motor has to sit outward from the chair frame in order to line up with the hinge of the tray to drive movement. The motor bracket attaches to the vertical beam in the right back corner of Julia s wheelchair and attaches with two circular clamps as described in the Assembly section. The entire bracket is made out of aluminum. The gearbox screws into the bracket via an aluminum piece which matches the motor s face plate dimensions and screw hole patterns. This piece is welded onto a thicker aluminum plate which the gear box and motor will sit on. The motor bracket will house three important components: gearbox, stepper motor and electronics box. The gearbox will be directly connected to the bracket as described above. The stepper motor will be bolted to the back of the gearbox so it will remain in place even though it is not directly connected to the motor bracket. Finally, the electronics box which holds the Arduino board and motor driver board, sit on the bracket in between the gearbox and the frame of the wheelchair. The motor bracket has been painted black to better blend into the wheelchair frame. All sharp edges have been sanded down to make the bracket safe to use in a school environment. 22

23 Figure 16 D. The Stepper Motor and Gearbox A bipolar stepper motor is used to power tray movement. A stepper motor is a brushless electric motor, the position of which can be accurately controlled since its rotation is divided into a large number of steps. For example our motor has 200 steps for a 360 degree rotation which means that each step provides a 1.8 degree rotation. This type of motor was chosen for our design for several reasons. First, stepper motors operate with high torque at low speeds. They can also be easily programmed to move in two directions, which is perfect for moving our tray up and down. Also, stepper motors also fail in a fixed position which means that if Julia lets go of the switch in the process of bringing the tray to desk position, it will stay in its last position instead of crashing back down to the side. An image of our stepper motor is shown below in Figure 17. Figure 17 23

24 The motor purchased a stepper motor KelingInc.com and has a torque rating of 1200 ozin. It runs on 24V and has 8 wires. We connected these wires such that the motor has a series connection. The type of connection was used because while the motor has 8 wires, the motor driver board that it connects to only has four spots for wire attachment. To accomplish series connection the red and yellow wires were twisted together and the orange and black wires were twisted together. This leaves four remaining wires to connect to the driver board. In this setup, the motor needs 3A of current to run at maximum torque. The specifications and dimensions of this motor can be found in the data sheet in the Appendix section. To increase the torque of the motor, the team also purchased a gearbox from the same vendor. The gearbox has a 5:1 gear ratio, which essentially means that the torque of 1200 oz-in is multiplied by five. The gearbox fits over the front of the motor and connects to its shaft. The two are bolted together so that the gearbox shaft becomes that part that attaches into the tray hinge. Figure 18 below shows the gearbox in gray, partially connected to the motor. Figure 18 To connect the motor to the gear box, insert the motor shaft into the back of the gearbox. Then use a small hex key Allen wrench to tighten down the screws which are accessed through the two holes shown in the base of the gearbox shown above. E. The Motor Driver Board To help control the movement of our stepper motor, a stepper motor driver board manufactured by Probotix.com (Figure 19) was used. This specific motor board has pins which connect to the motor wires and a pin for input voltage and ground. The current for the board can be adjusted up to 3A, which is the current needed to run our motor at maximum torque. The 24

25 input voltage for the board can range between 8 and 32V, which means that it is compatible with the wheelchair s 24V battery. The motor drive board connects to the Arduino board which allows it to translate the code to the motor. A heat sink was purchased and attached to the board to prevent the part from getting too hot as is runs the motor. A datasheet for the driver can be found in the Appendix. Figure 19 below shows how the wiring connects to the motor drive board, in case the part needs to be replaced for any reason. The electric circuit diagram in the Appendix also outlines the connections that are made to this board. To remove or replace wires, use a small screwdriver to unscrew or tighten the screw on the connection pins. When the screw is loose, the wire can be slid in or out from underneath it. The drive board is located inside of the gray plastic electronics box which is located on the motor bracket. Figure 19 F. The Switches Figure 20 25

26 Three different switches are used to control tray movement and are shown above in Figure 20. The first is a power switch (N). This switch is connected to the 12V and 24V battery leads and, when in the on position, provides power to both the Arduino board and motor driver board. This switch gives Julia the ability to turn the tray system off completely when not in use so that extra power will not be drawn from the wheelchair battery. The 12V and 24V leads run from the battery into the middle terminals on the back of this switch. Then two wires leave the switch, bringing 12V and 24V to the Arduino board and driver board respectively. These wires are all soldered to the switch which means that they should remain secure and shouldn t need replacing. However, the circuit diagram shows the switch connections, should there be a problem. Electrical troubleshooting will be described in the next section. The second switch gives Julia the ability to move the tray up and down at her disposal. For this switch we will use a momentary switch (O). This type of switch defaults to neutral position when let go of. We chose this type of switch in order for tray movement to occur safely. If the client accidentally lets go of the switch while the tray is in motion, tray movement will halt and the tray will be held by the motor in its last position. Out the back of this switch there are two wires which are inputs to the Arduino Board and one wire that is grounded. The wires that connect to the Arduino Board are blue and yellow. These should be attached to pins 11 and 10 respectively. The last switch is a simple push button switch (P). It is mounted to the rectangular arm piece of the tray so that when the tray is moved into desk position, the button will be pressed down. This button will act as another safety feature that prevents the tray from moving past its end position and act to reset the Arduino code. In the coding, pressing the push button switch will stop forward tray movement and set the step count to 150, meaning that it will tell the motor that the tray has reached desk position. This acts as a code reset if the tray were to lose power part way through its movement. Losing power would reset the code which keeps track of position so the push button switch would be a way to re-identify tray position. The push button switch has one pin connected to the Arduino board. This wire is white and attaches to pin 6. The black wire from the switch is grounded. Due to the positions of the motor (on the right) and the switches (on the left), many wires must be run around the backside of Julia s wheelchair. These wires run inside the chair frame as much as possible to prevent them from getting caught on anything when the chair is in use. The wires are covered in black plastic conduit (see Figure 21). This organizes the wires, protects them from exposure in a middle school environment and helps the system to blend in with the black chair frame. 26

27 Figure 21 G. Arduino UNO Board The Arduino board is located in the gray plastic box on the motor bracket. It is preloaded with the code that controls the laptop tray. This code is given in the Appendix, along with a link to the Arduino website where additional information about the board and the coding language can be found. Based on our code, the Arduino board will read the state of three switches (the power switch, the up/down switch and the push button switch) and based on their states, communicate with the motor drive on how the motor should perform. The Arduino Board can take up to 12V. It connected to the motor driver and two switches. It also has a reset button that can be pressed to restart the reading of the loaded code. Figure 22 below shows the features of the Arduino board and the connection that are made to it. The colors shown represent the actual color of the wire that goes to the indicated pin. 27

28 Figure 22 H. The Power Source As discussed previously, the batteries which power Julia s wheelchair were used to power the tray system. Figure 23 below shows the wheelchair batteries. Julia s wheelchair is powered by two 12V batteries connected in series which produces 24V to power the chair and our system. 28

29 Figure 23 The team used ring connectors to run leads from three of the battery terminals. The first lead goes to the positive terminal of the first 12V battery in the series. The wire connected to this terminal is white colored and provides 12V to power our Arduino Board, since it is not meant to take the full 24V. The second lead is connected to the positive terminal of the second 12V battery in the series. This red wire provides 24V to the motor by way of the motor driver board. Both of the positive leads first go to the power switch to allow the system to be turned on and off. The final connection we made goes to the negative terminal of the second battery. This wire (black) will provide ground connections for all of the switches and boards. The wires we attached to the battery were run out the back of the wheelchair where many other wires to the battery were already positioned. These wires can be seen below labeled in Figure 24. There are fuses in line with both positive wires to protect the wheelchair batteries from any malfunctions the tray system might have during testing. The fuses are shown in Figure

30 Figure 24 Figure 25 I. The Total Electrical System The electrical system in our prototype is shown in the circuit diagram in the Appendix. This diagram puts together all the separate electrical components which were discussed in the sections above. The diagram will allow for reassemble of the electrical system if a part or wire requires replacement. This will be discussed further in the Troubleshooting section below. 30

31 4. Troubleshooting The troubleshooting of the tray device will be discussed in this section. It will be broken into subunits similar to the technical description section. Being able to identify where on the tray device the problem is occurring will help simplify the repair process. Hopefully this section will provide solutions to all foreseeable issues that could occur with the tray. A. The Tray, Tray Frame and Hinge System Most issues with the tray itself should be pretty straightforward to fix. Cracks in any of the PVC pipe pieces that make up the hinge can be replaced by purchasing a new part for around $0.50 at any hardware store, unscrewing the only piece from the tray and reattaching the new piece. Cracks in the pieces that form the hinge system of the tray and are attached around the metal pipe will be much more difficult to replace because this would involve taking apart the whole hinge and removing the PVC pieces attached to it from the tray. A crack on PVC which is part of the hinge should therefore not be replaced. A solution for these types of cracks would include covering the crack with white duck tape. That being said, the PVC frame is unlikely to crack if the tray is being used properly and carefully. The screws holding the frame of the tray could loosen over time, however. Every so often, the tray should be checked for loose screws and any that are found should be tightened with a screwdriver. Detachment of the quarter round molding used as tray edging is another problem that might occur. Any loose pieces of edging can be reattached to the tray by applying a thin layer of acrylic glue along the bottom and pressing the piece onto the tray in its correct position. Allow the glue to dry for a few hours before exerting any pressure on the edging. The last topic to address in the section is problems with the laptop securing system. One common problem might be fraying of the straps that attach the laptop case. This can be easily fixed by applying a thin layer of glue to the fraying edges and allow it to dry. Additionally, if Julia gets a new laptop that will not fit in the case provided, adapting a new laptop case for the system should be an easy process. The new laptop case should have a hard shell to protect the laptop. To attach the new case to the tray using the original straps, simply use a box cutter to make 4 slits in the case, one near each corner. The slits should not be too large, so that straps fit through them snuggly. 31

32 B. The Armrest Clamping System The main problem anticipated with this system would be the loosening of screws overtime which could interfere with the ability of the system to hold the tray securely to the right armrest of Julia s wheelchair. Therefore the screws connecting the aluminum pieces and the screws holding the L shaped brackets to the bottom of the rectangular tray piece should be tightened periodically. Figure 26 C. The Motor Bracket One problem that may be experience with the motor bracket is the slipping of the circular clamps which attach it to the wheelchair frame. It is important to make sure that the motor bracket holds the gearbox shaft at the same level as the hinge of the tray. If the two parts are not lined up and they connect at an angle, the motor could have trouble spinning the tray. If the bracket looks like it is not level, it should be repositioned and the circular clamps should be tightened. D. The Stepper Motor and Gearbox These two tray components are very sturdy and in general should not have any trouble. However, if the tray will not move when the system is on and the directional switch is pressed, there are a few ways to determine of the problem is arising from the motor or gearbox. The following test should be performed after checking the electronics as described in a following section. If the problem is not resolved after checking the wiring and connections, the motor should be looked at to determine if it is functioning correctly. 32

33 To test the motor, detach it from both the gearbox and the tray. Leave it connected to the electronics and switches. First turn the motor shaft once by hand, just to make sure it still moves. Next, you can try pressing the directional switch up to see if the shaft is spinning. Make sure to hit reset on the Arduino board first. If it does not, a problem with the electronics may have been missed, or the motor has stopped working. If this is the case, a new motor can be ordered from the website provided in the Appendix. If the motor is spinning after the test, you will then need to look at the gearbox. Reattach the gearbox to the motor shaft, but not to the tray hinge. Make sure to tighten the screws in the back of the gearbox down all the way. At this point, hit reset on the Arduino Board and then press forward on the directional switch. If the shaft of the gearbox does not spin, then that is the source of the problem. At this point you should double check to make sure that the screws are completely tightened on the motor shaft and that the motor shaft is not slipping within the gearbox. Gearbox replacements can be found on the website provided in the Appendix. If the gearbox shaft does spin during the test, then the problem has been isolated to the attachment of the gearbox shaft to the end of the tray hinge where it is being inserted (Figure 27). Make sure that when the gearbox shaft is reinserted the screws that go into the coupling with the tray hinge are both correctly aligned and tightened all the way down. Figure 27 Many times if the gearbox to tray hinge connection is slipping you will be able to tell right away. In this scenario the tray will be able to move up slightly when the switch is pressed but will be unable to move past about 45 to 90 degrees. 33

34 E. The Motor Driver Board The motor driver board is a very sensitive part of the electronics system. It can only take up to about 3A of current before frying or overheating. There are several ways to prevent these things from occurring which will be described in this section. First, avoid turning the tray by hand. This could cause a charge to build up on the electrical components. Second, make sure there are no exposed or stripped wires which, if contacted together, could short out the system and overload the driver board. Finally, it is important not to overwork the system which could cause the driver to overheat. Turn off the system when the tray is not in use and don t use the tray unnecessarily. Moving the tray up and down repetitively just for fun could damage the driver board or system. The driver board offers a way to test and control the voltage that the board is sending out. The area labeled voltage adjustment in Figure 28 below can be turned with a small screwdriver to adjust the voltage and current going through the board. The voltage is currently set at 4.8V which corresponds to 3A of current. This is the maximum value that the board should be subjected to. Figure 28 To determine how much voltage the board is sending to the motor, a voltmeter or digital multimeter can be used. The two ends of the voltmeter should be pressed against the two metal rings labeled VREF Test Points in Figure 29 below. The value given by the meter will give the board s voltage. Perform this test with the power to the system turned on. Figure 29 comes from the datasheet for the driver board. The full datasheet can be found in the Appendix. 34

35 Figure 29 When troubleshooting for the electronics of the tray system make sure to check that all the wires connected to the driver board are secure and that they are positioned according to Figure 28. Finally, there are several ways to tell if the driver board is not functioning and needs to be replaced. First, if the voltmeter test shows no voltage through the board even after adjusting it with the VREF trimmer (shown above) then the board is not working. In addition if the board has overheated there will be visual clues. Some of the metal pins on the board may look brown or may have even separated from the board. There may also be singing on the bottom of the heat sink. If any of these signs are noted, the board will need to be replaced from the website given in the Appendix. Note, if the board is fried, the power light may still come on. This does not mean that the board is working correctly. F. The Switches If any of the switches are not working as they should, the first thing that should be checked is their wiring. Pull gently on the wires attached to the switch; they should not come 35

36 loose. If a wire is found to be loose, reconnect the wire and retest. The wires to the power switch are soldered on, so they are not expected to come loose. Next, follow the wires from the malfunctioning switch back to their origins at the Arduino board. Make sure that the ends are securely inserted in the correct position according to the pin numbers discussed earlier and found in the circuit diagram. If the switch is still not working and no other problems with the electronics have been found, a new switch will have to be purchased. Radio Shack is a good place to look if a switch needs replacement. G. Arduino Board When troubleshooting the Arduino Board, first make sure that the power light LED is on. Next, make sure all the wires are secured in the correct pin number as specified in Figure 30 below. Finally, press the reset button. Hopefully, this will reset the system and allow for tray movement when the switch is pressed. If the board has a singed look, or if the power to the board will not come on even after the power source connection has been checked (see the following section), a new Arduino UNO board will need to be purchased. The boards can be purchased from a number of online vendors. We got ours from Amazon. The new board will need to be reprogrammed. To do this, the Arduino software will need to be downloaded (link given in the Appendix) and the code will need to be loaded onto the board. After installing the software, attach the Arduino board to the computer using a standard USB printer cable. Copy the code provided in the Appendix and upload it to the board. Then reattach the wires according to the circuit diagram. 36

37 Figure 30 H. The Power Source Troubleshooting for the power source is very straightforward. If the batteries powering Julia s wheelchair die or are in need of charging, you will be able to tell based on the behavior of the chair. If the batteries are not powering the chair, then they will not power the tray system. If the batteries are working but the tray is not moving even though the power to the system is on, open the gray electronics box and make sure that the power lights for the Arduino and driver boards are on. If they are, the problem is not with the power source. If the lights are no on then the most likely explanation is that the fuses to the batteries may have blown and need replacing. Turn off the system and chair power and then unscrew the fuse covers shown below. Start with the 12V fuse (white). This takes a 1A fuse. Replace this fuse, turn on the system and see if the boards have power. If they do, the problem is solved. If not, repeat the process and 37

38 replace the 5A fuse that goes in the black fuse holder on the 24V red wire. Both fuse types can be purchased at Radio Shack. Figure 31 If Julia s wheelchair batteries ever need replacing, remove the battery leads on the ring connectors from the terminals of the old batteries and replace them on the respective terminals of the new batteries. Run the wires out the back of the wheelchair as before. I. The Total Electrical System If there is a problem with tray movement, the electronics should always be the first components to undergo troubleshooting. This is because this part of the system is the most complex and could therefore have the most problems. The following a short checklist you should perform if tray movement is not occurring when the directional switch is pressed. Hopefully performing these actions will restore tray movement. 1. Make sure the power switch is set to on position 2. Check to see if the Arduino board and Driver board are receiving power. If not, replace the fuses starting with the 1A one. 3. Press reset on the Arduino Board 4. Make sure all wires to the three switches and two boards are secure and in the correct position. 5. Check the voltage of the driver board 6. Look for any signs of a burnt out part (singeing, smoke, melting etc.) that requires replacing 38

39 Appendix A. Datasheet with Specifications for Motor: 39

40 B. Stepper Motor Driver Datasheet 40

41 41

42 C. Arduino Code int count = 0; void setup() { pinmode(2, OUTPUT); pinmode(4, OUTPUT); pinmode(10, INPUT); pinmode(11, INPUT); digitalwrite(10, HIGH); digitalwrite(11, HIGH); pinmode(6, INPUT); digitalwrite(6, HIGH); } void loop (){ if(digitalread(6)==high) { count = 150; } if(digitalread(10)== HIGH && digitalread(11)==low && count < 150 && digitalread(6)== LOW)//up! { digitalwrite(4, HIGH); digitalwrite(2, HIGH); delay(35); digitalwrite(2, LOW); delay(35); count++; } else if (digitalread(10)== LOW && digitalread(11)==high && count > 0) { digitalwrite(4, LOW); digitalwrite(2, HIGH); delay(35); digitalwrite(2, LOW); delay(35); count--; } } 42

43 D. Full Electrical Circuit Diagram 43

44 E. Websites for Parts Motor Driver Board: Stepper Motor: Model # KL34H A Gearbox: Model # KL-34GH51 44