Motor Runaway Detection via Adaptive Speed Deviation Thresholds
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Solution Overview
Problem
Conventional methods fail to detect abnormal motor rotation during acceleration or deceleration states, leading to delayed detection of motor runaway and inadequate protection, especially in software servo-controlled motors without position feedback.
Innovation Solution
A motor control apparatus that integrates speed deviation and includes an abnormal-rotation detector, overspeed detector, and magnetic-pole position checker, allowing for immediate detection of abnormal states by adjusting threshold values and using incremental sensors to monitor magnetic-pole positions, and a short-circuiting device to safely stop the motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional speed deviation threshold detection is used, then the detection method is simple, but abnormal rotation cannot be detected during acceleration or deceleration states
Solution Approach 1:
The patent applies dynamics by making the threshold value adaptive rather than fixed. The threshold dynamically changes based on the motor's operational state (acceleration, deceleration, constant speed), allowing accurate detection during all phases including transient states where conventional fixed thresholds fail.
Solution Approach 2:
The patent changes the parameter of threshold value based on operating conditions. By adjusting the threshold according to whether the motor is accelerating, decelerating, or running at constant speed, the system achieves reliable detection across all states without requiring complex additional hardware.
2Speed
If stepwise speed command changes are used, then the control response is fast, but speed deviation becomes large causing delayed abnormal rotation detection
Solution Approach 1:
The patent makes the detection threshold dynamic by adjusting it according to the motor's acceleration state. During stepwise speed changes, the threshold adapts to the expected speed deviation, preventing false negatives while maintaining fast control response. This resolves the conflict between rapid response and timely detection.
3Measurement precision
If position feedback is used for runaway detection, then detection accuracy is high, but the method cannot be used for motors without position feedback
Solution Approach 1:
The patent creates a universal detection method that works for both motors with and without position feedback. By using speed deviation and acceleration information that are available in all motor control systems, the invention achieves runaway detection capability across different motor types, including software-servo controlled motors.
Solution Approach 2:
The patent substitutes position feedback (mechanical measurement) with acceleration-based detection (dynamic parameter analysis). By monitoring the relationship between speed command, actual speed, and acceleration, the system achieves detection functionality equivalent to position feedback without requiring additional position sensors.
4Reliability
If high overspeed threshold is set for protection, then false detection is reduced, but detection of abnormal rotation becomes slow
Solution Approach 1:
The patent applies dynamics by making the threshold adaptive to operational context. During acceleration, higher thresholds prevent false detection while still enabling timely abnormal rotation detection. During constant speed operation, lower thresholds enable rapid detection. This dynamic adjustment resolves the trade-off between accuracy and speed.
Data Source
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AI summary
A motor control apparatus 1 that controls a rotation speed of a motor driven according to a speed command includes an abnormal-rotation detector 21 which determines that the motor is in an abnormal-rotation state, such as a runaway, when a speed deviation Ver obtained by subtracting a detection speed TSA of a motor rotation from a speed command VCMD is equal to or larger than a threshold value, when a sign of a product of acceleration ΔTSA obtained by subtracting a last detection speed from a detection speed this time that is detected in a predetermined cycle and a torque command Tc obtained by proportionally integrating the speed deviation is negative, and when an integration value VerSUM of the speed deviation Ver exceeds a predetermined value ALMlevel. With this arrangement, an abnormal rotation of the motor can be instantly detected even during acceleration or deceleration of the motor, thereby increasing the performance of protecting the motor.