Elevator Drive Encoder Fault Detection and Brake Control
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Solution Overview
Problem
Elevator systems with synchronous motor elevator machines face challenges in detecting absolute angular rotor position when encoder feedback is lost, leading to uncontrolled motion due to delayed detection of encoder failure, which can result in up to two meters of unintended movement before the brake is engaged.
Innovation Solution
Implementing a velocity threshold comparison and an encoder fault timer to incrementally disable the elevator drive system when the velocity falls below a minimum threshold, ensuring the brake is engaged within a set fault threshold time to prevent uncontrolled motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the encoder feedback signal is lost, then the position of the rotor is no longer known to the elevator drive system, but the time between loss of feedback signal and detection of this condition can be substantial, resulting in uncontrolled motion
Solution Approach 1:
The system performs preliminary monitoring of encoder signal characteristics by comparing velocity from encoder feedback with velocity from drive current. This continuous comparison detects anomalies before they result in complete encoder failure, enabling early intervention and preventing the substantial detection delay that causes uncontrolled motion.
Solution Approach 2:
The system uses dual feedback paths: primary feedback from the encoder and secondary feedback from drive current measurement. When encoder feedback is lost or becomes unreliable, the system detects this through the velocity comparison and switches to alternative detection methods, ensuring continuous monitoring without delay.
2Object-affected harmful factors
If the brake is engaged immediately upon encoder signal loss, then uncontrolled motion is prevented, but the time delay in detecting the condition results in up to two meters of uncontrolled motion
Solution Approach 1:
The system continuously compares velocity from encoder feedback with velocity calculated from drive current before complete encoder failure occurs. This preliminary detection mechanism identifies encoder problems early, allowing the brake to be engaged promptly rather than waiting for complete signal loss, thereby preventing substantial uncontrolled motion.
Solution Approach 2:
The drive current measurement serves as an intermediary indicator of actual velocity. When encoder feedback becomes unreliable, this intermediary measurement provides continuous velocity information, enabling the system to detect anomalies and engage the brake before significant uncontrolled motion occurs.
3Reliability
If a velocity threshold comparison and encoder fault timer are implemented, then the brake is engaged within a set fault threshold time, but the system complexity increases
Solution Approach 1:
The velocity comparison mechanism serves multiple functions: it monitors encoder health, detects velocity anomalies, and provides alternative velocity measurement when encoder fails. The fault timer similarly provides both detection and control functions. This multi-functionality reduces the need for separate dedicated components, managing system complexity while improving reliability.
Solution Approach 2:
The system uses existing components (encoder, drive current measurement, controller) to perform the velocity comparison and fault detection. Rather than adding entirely new hardware, the system repurposes existing elements to provide fault detection capabilities, minimizing the increase in device complexity while enhancing reliability.
Data Source
AI summary
An encoder failure in an elevator drive system is detected and managed. A velocity of the elevator drive system is provided by an encoder signal (60) and compared with a minimum velocity threshold (62). An encoder fault timer is incremented when the velocity is less than the minimum velocity threshold (64). The elevator drive system is disabled when the encoder fault timer reaches a fault threshold time (66).