Echoraiser the ultrasonic power assisted lifting cart Group 11: David L. Chen, William Cheung, Neil Nguyen ME102 Mechatronics Design Professor H. Kazerooni May 7th, 2007
INTRODUCTION Purpose It is hard to lift and carry heavy objects at home improvement stores, especially when you have sustained an injury or have limited mobility. Current shopping carts are great, and assist greatly, but it is often difficult to maneuver objects into the cart bed. Furthermore, though stores will assist patrons in loading their cars, there is no aid during the shopping experience: patrons are left moving around heavy objects themselves. Though key stake holders include partially injured and older workers, pregnant women and young families, and people with limited mobility, we aimed to make a product that would benefit all patrons of home improvement stores, regardless of their strength and ability. We believe Echoraiser achieves this goal, improving the shopping experience greatly, allowing patrons to automatically lift and lower their cart payloads to facilitate easier movement of heavy and unwieldy goods in home improvement stores.
What It Does Since most energy is wasted lifting and lowering heavy objects due to the change in potential energy, Echoraiser assists by lifting and lowering the payload bay, moving with your hand to your desired height to make it easier for users to load and unload the carts. It has three modes: 6-12cm range Echoraiser modes of operation: Hold: At 8 centimeters, Echoraiser holds the position of the platform steady. 12-40cm range Lift: From 12-40 centimeters, Echoraiser lifts the platform 3-6cm range Lower: From 3-6 centimeters, Echoraiser lowers the platform.
Key Stakeholders Older workers women injuries Young families Women and young families are increasingly driving sales at home improvement stores. According to the San Jose Business Journal, Women initiate 80 percent of all home improvement projects and represent half of Lowe's customer base, according to the company. Compared to a year earlier, women characterized themselves as intermediate or advanced as opposed to beginners, says Lowe's. Ninety-four percent of all female homeowners have completed a home improvement project on their own at least once... Furthermore, construction workers are high-risk individuals who put their bodies at risk every day. These users demand products that help them in their work and help to prevent injuries over time. Echoraiser is a reliable and intuitive product that can give accessibility to users that may find it difficult to get help otherwise, and facilitates a more positive shopping experience.
HOW IT WORKS Overview The ultrasonic sensor detects how far away your hand is, which activates the motor on a high PWM duty cycle, upwards direction if it is to be raised, and a lower PWM duty cycle, downwards if the platform is to be lowered, since lowering requires less effort. The motor turns the miter bevel gears and aluminum collar, which makes the ball screw spin and ball nut rise and fall. Echoraiser was engineered for high performance, reliability, and ease of use. We achieved these elements by using steel support rods, a high grade ball screw, and an aluminum plate, mounted to a wood frame and secure motor housing and hardened steel bevel gears. The schematic below shows the basic setup: Echoraiser schematic
Original Design and Changes As with most engineering projects, the design of the product evolved through many iterations. Before beginning the building process, we sketched out our ideas. Key elements of the original UPcart stayed the same: a payload bay would rise and fall according to user input driven by a motor housed on the bottom of the four-wheeled cart. However, other elements, such as the hydraulically actuated scissor lifting system and range sensors were deemed too complicated for our proof of concept, and the control panel was removed, replaced with a more intuitive hand waving solution, explained in the next section. Most importantly, the ball screw dictated that we needed to mount this screw through the center of the top plate, to minimize the torque moment and ensure that the plate lifted smoothly for the proof of concept usability study. This will be replaced by hydraulic actuated scissor lifting mechanism in future iterations, for a more useful cart. Original Design After sourcing parts and beginning the build, part and cost constraints dictated the final design for our prototype Echoraiser. Working with a limited budget, we contacted San Jose Ball Screw and Actuator Company, Metal Super Markets, and Bearing Engineering Company to source scrap parts that they were willing to give to our project. Although the parts were generously donated or discounted, they were often parts that did not exactly fit our original design spec. Thus, we often had to change our design to best utilize our resources. The following section details key parts and the challenges we faced.
Key Parts and Challenges ultrasonic sensor We originally wanted to go with a piezoelectric sensor that would sense small changes in the force on the top aluminum plate and automatically assist the user, augmenting the upward or downward force expended on the plate. However, we found this approach non-transparent, and decided to use an ultrasonic distance sensor instead, so users would be able to decide cart height without doing any lifting themselves. Furthermore, users would no longer need to bend all the way down to adjust the height. We needed a coupler to join the keyed motor shaft to the miter bevel gears. This coupler was fairly difficult to machine. Initially, we machined a slot in the coupling that fit the motor s keyed shaft exactly. However, we were unable to mill a precise enough coupler, and ended up with two wobbling couplers. We overcame this challenge by boring the coupling to force fit the shaft and tapping two set screws across the protruding key. This process took 20 minutes, versus the 2-3 hour machining time for the original part. Although we initially designed the gears to mesh at 90 degrees, the gears given to us by Bearing Engineering were 15 degrees off, and we had to mount the motor at a 15 degree angle in order to have the gears mesh correctly. Furthermore, we did not want to machine the thin, load-bearing collar piece down further from 1/2 inch, and had to bore out the gears to this diameter. Luckily, only the gear teeth were hardened steel, and the gears machined without a problem. motor coupling and gears Though ball screw we used was rated for almost 500 pounds, motors capable of transmitting such high torque were ridiculously large. We came up with a compromise of a motor that could lift 100 pounds for our proof of concept, something that will change in the next iteration of Echoraiser, when we utilize hydraulic actuators and decrease the size significantly. motor
ball screw and bearing collar The ball screw donated by San Jose Ball Screw and Actuator company was the first part we obtained and gave us a strong foundation around which to build the rest of the cart. We had to find a way to attach the ballscrew to the bottom plate and mesh with the gears and motor, ensuring an efficient transfer of energy from the spinning motor to the rising top plate. We machined a ball screw and bearing collar on the lathe and tapped set screws to ensure a secure fit, attaching it on the bottom to a bearing secured by another set screw. Although the bearing we found was not a thrust bearing, Ralph Baca at Bearing Engineering company assured us that this bearing would support at least 40% of rated axial weight, and rated at 500 pounds, we figured that a 200 pound rating would be more than sufficient for our load bearing needs. This ended up being easy and cheap to implement, and smoother than comparably priced thrust bearing installations. ball nut and aluminum plate coupling Ballscrew/ball nut combinations generally are able to transfer almost 95% of rotating energy into lifting energy. During transport, however, the ball nut slipped off the ball screw and we lost several bearings. Although we continued testing with some missing bearings, the motor was still able to transfer energy, although with decreased efficiency, and we sourced a few bearings from Gordon in the machine shop to get the ball nut back to its highest efficiency. We needed the ball nut to couple with the aluminum plate, and machined a collar on the Monarch lathe with custom tap threads to mesh with the ball nut. DSP and breadboard The DSP and breadboard mounting posed a few challenges for our group. We mounted the DSP on the base plate of our cart to ensure that wiring would be short and efficient. However, we worried that objects slipping off the and around the lifting cart may pull off wires or damage the DSP and breadboard. Originally, we had a wooden cover, but were not able to see the signals from the DSP. Thus, we constructed a clear box out of acrylic to make a strong cover that would allow us to continue monitoring the DSP. A second challenge that we encountered was that the DSP power input protruded past the acrylic base plate and we needed to notch the base plate. Instead, we simply flipped the DSP over so that the power plug was on the inside and we did not need to widen or modify base plate, and kept all wires neatly exiting only one side of the breadboard/dsp.
Bill Of Materials!!!!! Notes!! Price 12 x 18 1/4 aluminum plate $50.12 Ultrasonic Sensor $29.95 Ball Screw and Nut Donated $140.00 Gears Discounted $15,00 Axial Bearing Discounted $10.00 Motor Provided ($50?) 6 of 3 diameter aluminum stock rod Provided ($5?) 2 of 1 diameter aluminum stock rod Provided ($5?) 4 x cart wheels and casters 4 x 5.89 each = $23.56 Wood Provided ($10?) Fasteners Provided ($10?) Total Spent (Including Donations)!!!! 128.63 (348.63)
Why Echoraiser Competitive Advantage The Echoraiser is an intuitive and reliable product that can make it easier for people to shop and move around at home improvement stores. Its simple and robust design would be easy to scale and support, and would be a very useful aid to all shoppers. During our inventor s open house, reaction to the product was very positive, and people ranging in age from 10 to 70 years old were immediately familiar with the controls and able to control cart height adeptly. Many responded that it was an interesting product and that it would be a useful aid if it were available. Our Magic! Echoraiser cart was a product that people wanted to try and enjoyed using. We feel that our project not only achieved success as a product to improve the livelihood of reduced mobility individuals, but would also be useful to the general public. Furthermore, these carts would enable home improvement stores to differentiate themselves in terms of a shopping experience, and would add value to any goods sold within these stores. As such, the Echoraiser is a low-cost, pragmatic, and marketable product that can immediately add value to any home improvement store. The Team David Chen is a ME Junior at UC Berkeley. Working with RSSP Marketing, David has experience in web and graphic design and provides web support for numerous UC Berkeley Housing Department websites. In addition to his interest in web development, David is also interested in aeronautic and aerospace design and plans to pursue a career in these fields. William Cheung is a ME Senior at UC Berkeley, and directs Berkeley Innovation, the campus product design group, in addition to the Undergraduate Finance Association and the Berkeley Venture Group. He is deeply interested in Product Design and is working at Pay By Touch as a Enrollment Product Design Intern this summer. Neil (Nghia) Nguyen is a ME Junior at UC Berkeley. Neil is currently working as an Academic Services Asistant at Unit 3 dormitory and also as a Academic Coach at Berkeley High School. Neil has a special interests in robotics and mechatronics design and plans to have a special study/ research section in Japan during Spring 2008. For summer 2007, Neil will be working for the Good Samaritan Medical Ministry, a non-profit medical organiztion that provides free medical care for the poor of selected remote villages.