UBC Undergraduate Research

Noise and PID control for low consistency pulp refiner Reynolds, Byron; Pang, Haotian; Zhang, Lionel


The main objective of this project was to remove the noise on various measurement signals for the low consistency pulp refiner, and implement a controller for the gap distance in two different modes of operation. The project is sponsored by Dr. Jens Heymer and Dr. James Olson from UBC Mechanical Engineering. A design of the noise reduction algorithm and gap size control algorithm was implemented and tested by Byron Reynolds, Haotian Pang and Lionel Zhang. Spectrum analysis showed that the majority of the noise on the gap signal is above 20Hz. As a result, a 12Hz Butterworth low pass filter of order 10 was chosen to reduce the noise on raw gap signal in volts. As the filtered signal is converted to size in mm, noise is also amplified. Therefore, an averaging of every 15 samples was employed to keep the signal clean enough so that it does not compromise the performance of the gap size controller. It was found after filtering and averaging of every 15 samples; the gap size uncertainty can be kept under 0.02mm, which meets the specification. Before the gap size controller was implemented, a safety algorithm was developed and fully tested to ensure that no plate clashing or equipment damage occurs as it constantly checks the current gap size and keeps the gap size in a safe range. Based on the results from the actual effects of the P, D and I term. It was determined that a traditional PID controller is not suitable for the system due to the fact that the system is never stable with any value of P, D and I gain. The instability of the system is likely caused by the non-linearity and slow response of the actuator. Consequently, a combination of proportional control, pre-control and lock algorithm was used as the final gap size controller. The testing results showed that it is capable of moving the plate to any targeted position with a precision and maximum overshoot of ±0.05mm. Also, the gap size can be changed by 1mm within 10 seconds. The energy based mode of the position controller cannot be fully implemented and tested prior to the completion of this report due to some issue with the refiner that needs to be fixed before it can be run properly with load. All software codes including the filters and the gap size based position controller have been provided to our sponsor Dr. Jens Heymer. A list of recommendations is also included in this report, aiming to further reduce noise, help compensate for signal delay caused by averaging, and some suggestions on safety.

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