Motor Driving System Encoder Error Compensation
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Solution Overview
Problem
In motor-driven systems, such as inkjet printers, control errors occur due to obstacles like dirt or grease adhering to encoder scales, leading to inaccuracies in motor control, which deteriorate processing accuracy and image quality.
Innovation Solution
A motor driving system that estimates obstructing areas on the encoder scale, calculates control errors, and compensates the motor control input to maintain accuracy by adjusting the control value based on pre-measured speed deviations after passing through the obstructing area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the control value is maintained in the abnormal area of the encoder scale, then the control stability is improved, but the control error increases due to load based on mechanical characteristics
Solution Approach 1:
The controller performs preliminary actions by estimating the obstructing area before the encoder sensor passes through it, calculating the control error that will occur, and determining the compensation amount in advance. This allows the system to pre-adjust the control input value to counteract the expected error when passing through the abnormal area, rather than simply maintaining the control value and accepting the error.
Solution Approach 2:
The system uses feedback by calculating the control error based on encoder signals output after passing through the obstructing area, then using this error information to determine compensation amounts for future passages through similar obstructing areas. This creates a learning mechanism that improves control accuracy over time.
2Measurement precision
If the abnormal area is longer, then the encoder sensor has more time to detect the obstacle, but the control error increases due to accumulated load effects
Solution Approach 1:
The controller estimates the obstructing area length and position in advance, allowing it to prepare the appropriate compensation amount before the encoder sensor actually passes through the abnormal area. This preliminary estimation and preparation prevents the accumulated load effects from causing excessive control error, regardless of the obstructing area length.
3Measurement precision
If feedback control is used, then the control accuracy is improved, but the system becomes unstable when the encoder outputs abnormal signals in the abnormal area
Solution Approach 1:
The system extracts or separates the handling of abnormal areas from the normal feedback control loop. When an obstructing area is detected, the controller switches to a different control mode that uses pre-calculated compensation values rather than relying on real-time feedback from abnormal encoder signals. This isolation prevents the unstable feedback from corrupting the overall control system.
Solution Approach 2:
The control system dynamically switches between different control strategies based on the operational context. During normal operation, feedback control is used for high accuracy. When passing through estimated obstructing areas, the system transitions to a compensation-based control mode that is stable even when encoder signals are abnormal. This dynamic adaptation allows the system to maintain both accuracy and stability under different conditions.
Data Source
AI summary
There is provided a motor driving system in which an encoder sensor is configured to move with a driven object with respect to an encoder scale and output an encoder signal. A controller is configured to control a motor based on the encoder signal, thereby controlling movement of the driven object. The controller estimates an obstructing area. In the obstructing area, the encoder sensor reads a part of the encoder scale where an obstacle is adhered. The controller calculates a control error of the motor in the obstructing area based on the encoder signal output after the encoder sensor passes through the obstructing area, and determines a compensation amount of a controlling input value input during a period while the encoder sensor passes through the obstructing area.