Encoder Fault Detection via Commanded Position Translation
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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 increased costs, and modifying point-of-origin information can lead to fault misdetection in safety units.
Innovation Solution
A method that involves sending commanded-position information based on the original point-of-origin information to the safety unit when the controller holds modified information, allowing for fault detection in encoders without additional structure or function in the servo driver, and compensating for time delays in motor drive control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the technique of Patent Literature 1 is applied to general-purpose motors with single encoders, then encoder fault detection capability is improved, but additional sensors are required which increases system cost and complexity
Solution Approach 1:
The existing encoder serves dual purposes: both for normal motor control and for fault detection. The controller utilizes the encoder's output signals to generate commanded-position information and compare it with detected-position information, enabling the encoder to detect its own faults without requiring additional sensors.
Solution Approach 2:
The encoder is made multi-functional by using it for both motor control feedback and fault detection. The same encoder hardware provides position information for both the servo driver's control operations and the safety unit's fault monitoring, eliminating the need for separate detection sensors.
2Reliability
If the technique of Patent Literature 2 is applied to general-purpose systems without fault detection function, then encoder fault detection is improved, but the servo driver requires new functions which increases development time and man-hours
Solution Approach 1:
The fault detection function is extracted from the servo driver and implemented separately in the safety unit. The servo driver maintains its original control functions while the safety unit independently performs fault detection by receiving encoder signals and comparing commanded-position information with detected-position information.
Solution Approach 2:
The system is segmented into distinct functional modules: the servo driver handles motor control while the safety unit handles fault detection. This separation allows the servo driver to remain unchanged in general-purpose applications while the safety unit provides optional fault detection capability.
3Adaptability or versatility
If the controller holds modified point-of-origin information, then adaptability to different operating conditions is improved, but fault detection accuracy deteriorates due to mismatch with safety unit's original information
Solution Approach 1:
The controller acts as an intermediary that translates commanded-position information based on modified point-of-origin data into a format compatible with the safety unit's original point-of-origin information. This translation enables accurate fault detection despite the controller using different reference information.
Solution Approach 2:
The system handles parameter changes in point-of-origin information by allowing the controller to use modified values for control operations while the safety unit retains original values for fault detection. The commanded-position information serves as a bridge that accommodates both parameter sets.
Data Source
AI summary
In a robot including a motor and an encoder for detecting the rotational position of the motor, the controller outputs a speed command indicating the rotational position of the motor and sends commanded-position information indicating the rotational position of the motor according to the speed command to a safety unit for detecting a fault in the encoder. When the controller is holding modified point-of-origin information of the motor and the safety unit is holding the original point-of-origin information, the controller sends commanded-position information generated based on the original point-of-origin information to the safety unit.