Motor Encoder Fault Diagnosis Using Disturbance Current

Solution Overview

Problem

Existing motor encoder diagnostic systems cannot distinguish between a motor that is not rotating and an encoder malfunction when the feedback position indicates a fixed motor position, leading to uncontrollable and potentially dangerous situations.

Innovation Solution

A failure diagnostic system and method that includes a safety module connected to the motor encoder and servo driver, which determines the motor's state by sending an additional current command to disturb the motor and analyzing the feedback position change, and outputs an alarming signal if the encoder is malfunctioning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the servo driver reads the encoder to obtain feedback position, then the motor position control is achieved, but the system cannot distinguish between motor non-rotation and encoder failure

Engineering Contradiction:

Improvemotor position control reliabilityVSAvoidencoder failure detection capability

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The system performs preliminary diagnostic actions by sending test current commands to the motor before normal operation to verify encoder functionality. When the feedback position indicates motor non-rotation, the safety module first sends a first current command to generate a first feedback position, then sends a second current command to generate a second feedback position, comparing the two to determine if the encoder is malfunctioning before allowing normal operation to proceed

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The safety module acts as an intermediary between the servo driver and the motor-encoder system. It intercepts the control flow by introducing diagnostic current commands and analyzing the resulting feedback positions, mediating between the servo driver's position control requests and the actual motor-encoder system state to detect encoder failures

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If the system operates without encoder failure detection, then the control system is simple, but the motor becomes uncontrollable and dangerous when encoder fails

Engineering Contradiction:

Improvecontrol system complexityVSAvoidmotor uncontrollability and safety hazards

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary diagnostic actions by sending test current commands to the motor before normal operation to verify encoder functionality. When the feedback position indicates motor non-rotation, the safety module first sends a first current command to generate a first feedback position, then sends a second current command to generate a second feedback position, comparing the two to determine if the encoder is malfunctioning before allowing normal operation to proceed

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The safety module provides beforehand protection by continuously monitoring feedback position and implementing diagnostic current commands to detect encoder failures before they lead to dangerous uncontrollable motor operation. The system cushions against potential hazards by having the safety module ready to intervene and alert when encoder malfunction is detected

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS11988503B2Failure diagnostic system and failure diagnostic method of motor encoder

Publication Date: 2024.05.21 DELTA ELECTRONICS INC(CN)

AI summary

A failure diagnostic system of a motor encoder is disclosed and includes a motor, an encoder, a servo driver, and a safety module. The servo driver controls the motor through a current command. The safety module continuously obtains a feedback position of the motor through the encoder. When the safety module determines based on the feedback position that the current state of the motor is consistent with a pre-determined disturbance condition, the safety module requests the servo driver to output an additional current command to disturb the motor. Next, the safety module determines whether the encoder is failure based on a variation of following feedback position.