Robot Encoder Abnormality Detection Under Load-Induced Vibration
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Solution Overview
Problem
Existing methods for detecting abnormalities in encoders used in general-purpose motor systems are inefficient, requiring additional sensors and system configurations, leading to increased costs and complexity, and are prone to erroneous detection due to variations in attachment loads and operation frequencies.
Innovation Solution
An abnormality detection method that uses a controller to output speed commands and commanded position information, with a driver receiving and processing signals from an encoder, and an abnormality detection device that corrects for vibration components and time delays, allowing for accurate abnormality determination without additional configurations or functions in the existing system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional sensors and system configurations are used to detect encoder abnormalities, then detection accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The encoder abnormality detection function is implemented using the existing encoder and control system components that are already present in the drive system. The controller utilizes the encoder's output signals and existing processing capabilities to perform abnormality detection without requiring external sensors or additional hardware, thereby achieving self-service detection that avoids increasing device complexity
Solution Approach 2:
The existing encoder and controller are made to serve dual purposes: the encoder continues to provide positional feedback for normal motor control while simultaneously providing data for abnormality detection. The controller processes both motor control commands and abnormality detection algorithms using the same hardware resources, making the system multi-functional without adding dedicated components
2Stability of the object's composition
If filter constants are switched according to attachment load weight to remove vibration components, then operation stability is improved, but erroneous abnormality detection increases
Solution Approach 1:
The detection threshold is made dynamic by adapting it to the current operating conditions, specifically the attachment load weight. The controller switches between different detection thresholds corresponding to different load conditions, allowing the system to maintain high detection reliability across varying operational states. This dynamic adaptation prevents erroneous detection by matching the threshold to the expected vibration characteristics under each load condition
Solution Approach 2:
The detection algorithm incorporates parameter changes by adjusting the threshold values based on the attachment load weight. When the load weight changes, the system modifies the detection parameters (thresholds) to account for the resulting changes in vibration characteristics, thereby maintaining accurate abnormality detection across different operating conditions without false positives
3Productivity
If the robot operates at frequencies closer to natural frequency, then productivity is improved, but unintended vibrations increase
Solution Approach 1:
The system intentionally utilizes mechanical vibration by operating the robot at frequencies接近 to its natural frequency to improve productivity. The encoder abnormality detection function is designed to distinguish between normal vibration-induced position deviations and actual encoder failures by comparing the magnitude and pattern of deviations against dynamically adjusted thresholds, thereby enabling high-speed operation while maintaining reliable detection capability
Data Source
AI summary
An abnormality detection method for detecting an abnormality of an encoder provided for a robot includes: obtaining corrected position information according to commanded position information output from a controller that designates the rotational position of a motor and an output signal output from the encoder; and, determining, after comparing the corrected position information with the detected position information according to the output signal output from the encoder, the abnormality of the encoder, if there is a difference greater than or equal to a predetermined value between the corrected position information and the detected position information. The controller removes a vibration component of the robot corresponding to the weight of an attachment load from the commanded position information and compensates for a time delay to obtain the corrected position information.