Motor Runaway Detection via Torque Jerk Sign Mismatch
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Solution Overview
Problem
Existing motor control systems face challenges in detecting motor runaway states quickly and accurately, particularly under conditions of miswiring or biased loads, leading to erroneous detections and delayed recognition of runaway situations.
Innovation Solution
A motor control device that compares the signs of the torque command differential value and motor jerk, determining a runaway state when a mismatch continues for a predetermined time, and includes a low-pass filter to reduce noise-induced errors, allowing for rapid detection and emergency stops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the runaway detection method compares torque command and acceleration direction, then runaway can be detected, but erroneous detection occurs in the case of biased load
Solution Approach 1:
The patent changes the detection parameters from comparing torque command and acceleration direction to comparing torque command differential value and jerk (acceleration change rate). This parameter transformation allows the system to distinguish between normal biased load operations and actual runaway states, as the differential comparison reveals inconsistencies only present during runaway conditions
Solution Approach 2:
The system continuously monitors the relationship between torque command differential value and jerk, using this feedback to detect runaway states. By maintaining continuous comparison and updating detection status based on sustained mismatch conditions, the system achieves reliable runaway detection without false positives from biased loads
2Reliability
If the method monitors speed until it exceeds peak speed, then runaway detection is more accurate, but detection time is delayed particularly with large inertial load
Solution Approach 1:
The patent performs preliminary detection by comparing torque command differential value and jerk from the moment acceleration begins, rather than waiting for speed to exceed peak speed. This early detection approach using differential parameters allows runaway identification during the acceleration phase itself, significantly reducing detection time while maintaining accuracy
Solution Approach 2:
The patent replaces the mechanical speed-threshold-based detection method with a mathematical differential comparison method. By substituting the physical speed monitoring approach with a computational analysis of torque and acceleration relationships, the system achieves faster detection without being constrained by mechanical response times or inertial delays
3Reliability
If the detection method uses speed comparison with displacement speed, then runaway can be detected, but erroneous detection may occur due to control instability oscillation
Solution Approach 1:
The patent transforms the detection parameters from speed-based comparison to differential-based comparison (torque command differential value and jerk). This parameter change makes the detection immune to oscillations caused by control instability, as the differential relationship between torque and acceleration remains consistent during normal oscillation but breaks down during actual runaway
Solution Approach 2:
The patent introduces jerk (acceleration change rate) as an intermediary parameter that mediates between torque command and acceleration. This intermediary provides a more stable detection basis that filters out the effects of control oscillations, allowing accurate distinction between normal operational variations and genuine runaway conditions
Data Source
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AI summary
Provided is a motor control device that controls a motor by generating a torque command such that the detected speed of the motor matches the command speed. The motor control device is provided with the following: a torque command differential means that attains a torque command differential value by taking a differential of the torque command; an actual motor speed second order differential means that attains the motor jerk by taking a second order differential of the detected speed of the motor; and a runaway detection means that determines that the motor is in a runaway state if an anomalous state, in which the sign of the motor jerk and the sign of the torque command differential value do not match, continues for a prescribed amount of time or longer. Due to this configuration, it is possible to detect a runaway state in a motor in a short period of time while mitigating false detection.