- Testing & Validation
- In order to test the gripper force output against the design requirement of 6N, I borrowed a spring scale and grabbed the scale with the gripper. The gripper is able to output 8.5N, exceeding the design requirement.
- In order to investigate the latency of the system, I came up with the idea to record the camera output along with the user moving their hand. From this, we were able to determine that most of the latency came from the depth camera. This led to us deciding to switch to a regular webcam, which does not need to process the frames to get depth, reducing latency. Depth can instead be obtained from the ARUCO tag detection algorithm.
- I worked with the team to also test quantiative metrics including precision, payload and speed.
- For precision, we fixed a pen to the robot and drew lines on a piece of paper. The dimension of the lines were compared against commanded movements. We were able to reach +-1mm precision, exceeding our original requirement of 2mm.
- For speed, we commanded a fixed distance and recoreded the robot’s moves with a stopwatch in the frame. Speed could then be found from dividing the distance travelled with the time taken. While we were able to reach the design requirement of 100mm/s by tuning the software parameters, we found this speed to be too fast for the use case: jittery inputs are amplified due to the high speed.
- Some pictures from testing:
- I designed the new Z-axis mechanism, and printed the parts for them. I plan on adding these parts and finishing up the Z-axis mechanism next week.
- I also came up with a new way to control the force output of the gripper beyond binary open/close. This involves adding a foam pad to the grippers and measuring the relationship between compression of the foam and the force at the gripper. This relationship is most likely a linear function, if we model foam as an ideal spring. A limit switch will be used to detect an object making contact with the gripper. This way, when contact is made initially, the postion of the gripper is recorded. Force can then be controlled by advancing the gripper position past the initial contact point. How much to advance the gripper position is known from the force-position relationship measured.
Leland Mersky, Jack He, Zhenghao Jin