This week, I conducted some research into how best to implement the gripping mechanism, as well as the robot arm upon which the gripper is mounted.
I spent a lot of time trying to design a simple enough mechanism that could control force at the grippers effectively. What I wanted to avoid was to simply attach a motor’s output shaft rigidly to the grippers. This is because it will be very difficult to control force precisely when the gripper makes contact with a solid object. This was solved by attaching a torsional spring mechanism to the output shaft, so that the force output is a linear function of the motor’s position.
I also spent time to size the motors needed to actuate various parts of the robot arm. I came to a decision by researching similar mechisms in 3D printers and laser cutters. For systems that are close in size, the most common option is a NEMA 23 stepper, so I decided to go with those.
Another challenge was to find a low-cost solution for precise linear movements. We needed linear movement over an area the size of a lab workbench, and many linear rails at that size were too pricey. I ended up finding a solution based on attaching wheelcarts to standard aluminimum extrusions, with an overall cost below $50.
After some discussion with my teammates, I drew up a preliminary mechanical design for the system based on the above considerations. Overall, I think I am on schedule, as I have another week to design the arm. I have a clear idea of what the robot arm hardware will look like, and have also started the detailed hardware design using OnShape, a CAD tool. It took some time to learn it, so I have not had the chance to complete the detailed design yet. While I have managed to identify the type and size of components needed, I will also need to shop for the best option on the market and submit them using the purchase form.
Sept 20 design notes – arm
