Engineering recommendation report : Prosthesis electric power pack control system Sanchez, Edson; Anzovino, Francesco; Watanabe, Thomas
Prosthesis is a two story tall, 3000 kg, four legged wearable walking machine intended to be human controlled. Its movements will be controlled by a pilot standing inside of the machine. The pilot‟s movements will be mapped to the legs of Prosthesis via an exoskeletal interface. The final machine will require approximately 60 kW of hydraulic power to reach top speed and will be 100% electric. The current prototype leg, also known as the Alpha leg, requires a 12 kW continuous power supply, which will come from a pump and electric motor combination. Our team developed the control system for the electric power pack of Prosthesis. The work involved computer programming, mostly in C, as well as the processing of sensor data. In terms of the physical components of the pack, we helped our project sponsor by providing him with a set of calculations and performance curves detailing the possible states of the electric motors that will be used on Prosthesis. To perform tests on the controller that we developed, we chose a gear pump proportional to the electric power pack available to us at the time of testing. In other words, we determined the capacity of the pump we needed to be able to move the Alpha leg with a different power pack. The control is done via an Arduino microcontroller that is programmed in C. It is in charge of keeping the pressure as close as possible to a user-specified pressure, known as the setpoint. This was done by implementing a software PID controller on the Arduino. The controller has two operating modes, one of which follows a simplified PID control scheme, using a constant pressure as the “target” or setpoint. The other controller setting, referred to as Load Sense, keeps the pressure at the pump outlet some constant amount higher than the pressure at a predetermined spot in the hydraulic line. Simply put, the pump outlet pressure adapts to the load in the hydraulic line. The setpoint based PID control was tested and found to be within acceptable operating parameters. An initial version of the Load Sense control was created, but it was neither completed nor tested by the submission of this report.
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