Robot Encoder Fault Detection Using Corrected Commanded Position
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Solution Overview
Problem
General-purpose operating devices with single encoders face challenges in fault detection, as existing methods require additional sensors and complex modifications, leading to increased costs and man-hours, and can result in faulty encoder misdetection when the servo driver controls the motor independently.
Innovation Solution
The method involves the servo driver transmitting control information to the controller, which generates new commanded-position information based on this information and sends it to the fault detection unit, allowing for accurate fault detection in the encoder without additional hardware or functions in the servo driver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the technique of Patent Literature 1 (using multiple encoders) is applied to general-purpose motors, then fault detection capability is improved, but the cost increases due to requiring multiple sensors
Solution Approach 1:
The encoder is made to serve multiple functions: it not only detects the rotational position for motor control but also provides fault detection capability. The control unit utilizes the existing encoder signals to generate both control commands and fault detection comparisons, eliminating the need for additional sensors while maintaining reliability.
Solution Approach 2:
The system uses its own existing components (the single encoder and control unit) to perform fault detection without requiring external or additional components. The control unit compares the encoder's detected position with the commanded position to self-diagnose encoder faults, making the system self-monitoring.
2Reliability
If the technique of Patent Literature 2 (adding fault detection function to servo driver) is applied to general-purpose systems, then fault detection capability is improved, but the complexity of development increases due to requiring new functions in servo driver and safety unit
Solution Approach 1:
The control unit is designed to perform multiple functions simultaneously: it generates control commands for motor operation and performs fault detection by comparing commanded position with detected position. This multi-functionality eliminates the need for separate fault detection modules, reducing development complexity while maintaining reliability.
Solution Approach 2:
The fault detection function is merged with the existing control unit and encoder system rather than being implemented as a separate safety unit or servo driver function. The comparison between commanded and detected positions is performed within the existing control architecture, consolidating functions and reducing overall system complexity.
3Speed
If the servo driver controls the motor independently without transmitting control information to the controller, then response speed is improved, but fault detection accuracy deteriorates due to mismatch between commanded and detected position
Solution Approach 1:
The system implements feedback by continuously comparing the commanded position (from servo driver's independent control) with the detected position (from encoder). This feedback mechanism allows the control unit to accurately detect faults even when the servo driver operates independently, maintaining both fast response and high detection accuracy.
Solution Approach 2:
The control unit acts as an intermediary that receives both the commanded position information from the servo driver and the detected position information from the encoder. It performs the comparison function that bridges the independent control path and the detection path, enabling accurate fault detection without interfering with the fast response of independent control.
Data Source
AI summary
A robot including a motor is used to machine a workpiece. The robot further includes the following components: a controller configured to output a speed command and commanded-position information; an encoder; a position sensor configured to output, as a differential signal, the amount of displacement of the position of the workpiece W from a predetermined position; a servo driver configured to control the motor upon receiving the speed command, the output signal of the encoder, and the differential signal; and a safety unit configured to detect a fault in the encoder. When controlling the motor based on the speed command, the output signal, and the differential signal, the servo driver sends the differential signal to the controller. The controller sends the safety unit new commanded-position information, which is generated by adding a correction value based on the differential signal to the commanded-position information.