Positioning Control Of A Ball Screw Mechanism Using Disturbance Observer

Foo, Jia En (2015) Positioning Control Of A Ball Screw Mechanism Using Disturbance Observer. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

A ball screw mechanism is a mechanical actuator that is widely used in various high precision automated industries. Though it is highly efficient, the ball screw mechanism often exhibits non-linear behaviours due to various forms of external noises, frictions, unforeseen disturbances and parameters uncertainties. Such behaviours often cause instability, large steady-state error and poor transient performance in the mechanism. To overcome these problems, a Disturbance Observer with PD Controller (PDDO) is proposed. A PDDO is made up of nominal plant, low pass filter and a PD controller. Compare to classical controllers, the proposed controller has low sensitivity towards non-linearity of the mechanism. In this project, the plant model was modelled using non-linear least square method (NLLS). The nominal plant was designed based on the Ackermann’s formula. The cutoff frequency was taken as half of the cut-off frequency of the plant model. The PD controller was constructed through manual tuning method. The performance of PDDO was examined experimentally in tracking motion with sinusoidal inputs of different frequencies and amplitudes. A manually tuned PID controller was designed in order to compare with the proposed controller. The robustness towards mass variation of the controllers were examined. Overall, the experimental result has proved that PDDO has demonstrated better tracking performance and higher adaptability to the change of input’s amplitudes and frequencies. It was also found that PDDO is robust towards mass variation as compared to the PID controller.

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