MESA USA and LIMBS International Prosthetic Arm Project

Transcription

1 MESA USA and LIMBS International Prosthetic Arm Project On behalf of LIMBS International, Lucas Galey designed and assembled a prototype prosthetic arm following a $20 budget, and integrating a SparkFun Redboard Arduino. Other than the SparkFun kit used, the materials came from Wal-Mart, Home Depot, and Amazon. Additionally, the materials are those that a student might think of and use. This was done to make the prototype a realistic model of the possibilities available to a high school student.

2 In this folder, there is a subfolder for pictures of the design, a bill of materials, an annotated copy of the programming, a direct version of the programming, and a document highlighting alternative problems and solutions. The following will be a brief description of the prosthetic arm and how it works. The problem statement for this arm was to allow users to pick up everyday items. It was meant to be a continuation of the previous competition s work, but with a robotic aspect. The prosthesis is made of two components: the arm sleeve and the arm band. The arm band is the user s input button. Everything else is housed on the sleeve. The arm is used by holding down the band s button. If the button is held for more than 0.5 seconds, then the motor activates and the arm clamps. If the button is pushed or held less than 0.5 seconds, then the motor releases and the clamp returns to its neutral open position. The clamping mechanism works by having a motor pull on a pulley, which is attached to the clamp. The clamp is a pair of kitchen tongs, with the tips bent and filed to make a shape more suited to picking up items. The curvature allows for rounded items to be picked up easier. Additionally, hot glue is used to provide rubber grip to all the vital areas of the clamp. The leftover edge catches ridges on items that are being picked up. On the final version, a rubber band is included to help the clamp come forward and release. The picture below demonstrates the clamping mechanism.

3 The motor that pulls the string, and H-Bridge that controls the motor were provided by SparkFun. The labeled picture below shows the control aspect of the prototype. On prototyping boards such as this, the entire + columns are connected to themselves, and the same goes for the - columns. In the middle sections, each line is connected up until the middle separation. Therefore, the button wire that connects to line 26 and column a is connected to both the wires to the right of it. Basically, the arm band has a small push-button that connects the two wires when activated. One of the wires is connected to the HIGH terminal, which just means it s connected to positive 5 volts. Thus, when the button is pushed, HIGH is sent via the red input wire to the Arduino. When the button is not being pushed, the row is grounded via the resistor so that the red input wire sees LOW. The Arduino inputs must be given some form of input or they will assign their own input, which will confuse programming and function. When the Arduino activates the motors, it sends the information via the two blue wires to the H-Bridge. For better understanding of the H-Bridge, use the following link:

4 The bridge ensures that enough power is delivered to the motors and allows them to run forwards and backwards. When the Arduino sends the proper signal, the motor then begins to turn. Holding the button down causes the clamp to actuate until the user sees fit. For the clamp to be released, the button is pushed briefly, less than 0.5 seconds. This causes the clamp to release and move forwards. As the clamp moves forwards, the clamp itself comes in contact with a pin that is in place to keep it from moving too far outward. This pin is wired with the Turn-Off Pin Wire. The brown Turn-Off Pin Positive connects the clamp to HIGH. This means that once the clamp is fully extended, it gives a HIGH signal through the orange wire to the Arduino. This allows the Arduino to understand when to stop reversing the motor. The picture below the diagram shows the pin and clamp. Using this device, the user is able to pick up, hold, carry, and place items of all shapes and sizes.

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