Project Overview

The Controls for Assistive and REhabilitation (CARE) Robotics Lab at SFSU focuses on wearable robotics that are designed to improve the lives of those who have lost some or all motor control of their upper or lower limbs. The powered prosthetic limbs being used today are designed to perform specific tasks that are programmed into them. There is limited research into how a powered prosthetic should respond to external stimuli that perturbs the prosthetic from its trajectory during a movement. For this reason, I am currently working with a Genmark Gencobot which was originally designed to use two parallel end-effectors for silicon wafer loading. The goal is to convert this robot into an upper limb physical therapy device in order to study the forces and torques at the joints in the human arm when an unexpected perturbation is introduced during an arm movement. This project will later involve clinical experiments in collaboration with SFSU's kinesiology department.

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Mechanical Design and Manufacturing

 Over summer 2020 I conducted research on the biomechanics of the lower arm and coordinated with vendors to select a 6 axis force sensor to mount at the end-effector of the robot. While we were waiting for the sensor to be delivered, I took precise measurements of a curved link at the end-effector and created a Solidworks model of it. Then, using the manufacturer's CAD model of the sensor, I designed an adapter plate that would allow us to mount the sensor at the end-effector. The goal was to utilize the holes in the curved link to mount the adapter plate. The curved shape presented a challenge so the holes had to line up just right. I also had to select the proper hardware to make sure there was enough clearance below the end-effector such that it did not collide with the surface below it (shown as a red plate in the photos below). To verify my design, I manufactured a prototype out of balsa wood using a laser-cutter. Once I confirmed that the holes lined up properly I machined the adapter plate out of 6061 Aluminum using manual milling and drilling methods. We also needed a joystick to attach on the tool side of the sensor. I designed this in Solidworks and manufactured it out of PLA using a 3D printer. 

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Coding

Once the sensor was delivered to the lab we had to develop the code to import and read the data in Matlab. The sensor sends force and torque measurements for all 6 axes in a single hexidecimal string. My task was to write a Matlab script to parse the hex data and extract the bits corresponding to each force/torque component. These were then converted into signed decimals that could be plotted within Matlab. I've also been collaborating with other students on the development of the control algorithms. 

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           Curved link and adapter plate

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        Joystick and full sensor assembly

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