The Sunram 7 is a robotic system for MR-safe breast biopsy, driven by pneumatic stepper motors controlled by pneumatic valves. Pneumatic stepper motors typically operate in discrete steps, but depending on the control method and output characteristics (load, stiffness, valve control method, step size, speed, etc), it may be possible to generate smooth motions at some (approximately) constant speed. This has several obvious advantages in related applications. However, the exact conditions for smooth vs. stepwise motion have not been thoroughly investigated. This BSc assignment aims to examine the range of parameters that enable smooth control of selected stepper motors (i.e. velocity and acceleration control) and also includes the development of efficient and re-usable controller hardware to operate the pneumatic valves accordingly.
For acceleration control, the extent to which these motors can be accelerated will be investigated to see which parameters, like motor step size, speed, mass and load stiffness, result in a stepwise movement and a fluent speed. This will be tested with different masses, pulleys, and stiffnesses of ropes and motors.
Right now, when developing new versions of this robot, the new electronics are currently built on prototype boards, which takes a lot of time and effort. The software also needs to be adjusted for this, and a more modular option is needed. The second part of this assignment is, therefore, the designing, building and testing of reusable and modular pneumatic stepper motor driver hardware (e.g. stackable Arduino shields with a sufficient number of outputs) and extending the current software for easy control of this hardware and implementing the acceleration control on that hardware as well.
Research questions:
- To what extent influence parameters like motor step size, speed, mass, load stiffness and pneumatic tube length the ability of pneumatic stepper motors to operate at (near-)constant speed instead of step-wise motion, and thus enable dynamic control of velocity and acceleration?
- What is the best way to develop controller hardware for biopsy robots, including (but not limited to) the Sunram 7, taking into account valve count, range of motor specifications, modularity, cost efficiency and ease of use configuration?