Construction and Control of a 3-axisAutomated Liquid Sampling UnitUtilizing Hybrid Stepper Motors

Abstract: High accuracy autonomous positioning systems are becoming increasingly important in today’s chemical industry because they can obtain precise experiment results automatically and hence allow lab technicians to focus on other tasks concurrently. One time consuming process is the process of sampling chemical test results into the correct container, especially when the tests are many and infrequent. This is where an automated sampling machine, or an autosampler, comes into play. If this sampling process is automated, the accurate sampling is achievable without the full time attendance of a lab technician. This thesis explores how to construct a small footprint autosampler in the form of a gantry, complete with electronics, actuation of all axes and relevant embedded software needed for implementation in a lab setting. This thesis also explores how to optimally control the stepper motors in charge of axis actuation, by comparing classic open loop control, PD control and an adaptive LQI controller. This is done by developing a mathematical model of the system using MATLAB Simulink, followed by developing and optimizing the controllers on the model and then implementing and verifying the controllers on the physical system. The conclusion of this thesis is that the PD controller performs best for controlling a stepper motor. It performs slightly better than open loop control and has the additional advantage of reference following. The adaptive LQI performed the worst on the model and additionally, it could not be implemented on the physical system due to how the system was constructed in hardware.