Elevator Holding Brake Drag Detection Using Motor Torque
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Solution Overview
Problem
Elevator holding brakes can go out of adjustment, leading to a dragging brake condition that causes friction, increased heating, excessive wear, and potential failure to hold the elevator cab when the motor is not providing a holding torque.
Innovation Solution
A system and method that uses a motor drive to detect a dragging brake by comparing torque values before and during constant speed operation, identifying a difference greater than a threshold as an indication of a dragging brake.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the holding brake is adjusted to apply sufficient braking force for safety, then the braking reliability is improved, but the brake may drag during normal operation causing friction and overheating
Solution Approach 1:
The system performs preliminary detection of brake dragging conditions by monitoring torque values during motor operation. Before significant damage occurs from friction and overheating, the system detects the abnormal torque pattern and can trigger maintenance alerts, preventing catastrophic failure while allowing the brake to maintain its safety-oriented adjustment settings
Solution Approach 2:
The motor drive provides continuous feedback on torque values during operation. By comparing actual torque values against expected values during constant speed operation, the system creates a feedback mechanism that monitors brake condition without requiring physical adjustment of the brake itself, thus maintaining the safe high-braking-force setting while detecting when the brake is dragging
2Measurement precision
If torque monitoring is continuously performed to detect dragging brakes, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The motor drive system that already exists for controlling the motor also performs the torque monitoring function. The existing current sensors and control electronics used for motor operation self-generate the torque data needed for brake detection, eliminating the need for separate dedicated sensors or monitoring hardware. The system essentially monitors itself using resources already allocated for motor control
Solution Approach 2:
The motor drive performs multiple functions: it controls motor operation, monitors torque values, detects brake dragging conditions, and can trigger maintenance alerts. By making the motor drive a multi-functional device that handles both motor control and brake monitoring, the system avoids adding separate dedicated monitoring equipment, thus improving detection capability without proportionally increasing overall system complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively detects dragging brakes, preventing excessive heating and wear by alerting technicians to maintenance needs, ensuring safe and efficient elevator operation.
Implementation Method 1
a spring configured to apply a force to the at least one braking surface, causing the at least one braking surface to engage the rotating member of the elevator drive
Implementation Method 2
an actuator selectively activated to apply a counter force to the spring. When the counter force is applied to the spring, the at least one braking surface disengages the rotating member of the elevator drive
Implementation Method 3
The motor is operably connected to cause rotation of the elevator drive
Implementation Method 4
The processor is configured to determine a first value of torque when the actuator of the elevator brake initially disengages the at least one braking surface from the rotating member of the elevator drive and prior to causing rotation of the elevator drive and to determine a second value of torque when the motor is rotating at a constant speed
Data Source
AI summary
A system and method for detecting a brake dragging during normal operation of a motor monitors torque at zero speed and at constant speed. For an inertial system acted upon by gravity, a value of torque required to maintain zero speed is approximately the same as a value of torque required to maintain operation at a constant speed. In an exemplary, elevator system, a motor drive determines the torque required to maintain zero speed operation of an elevator cab after a holding brake opens and before it begins controlling the motor to rotate. The motor drive again determines the torque required to maintain a constant speed and compares this value to the value of torque required to maintain zero speed. If the difference between the two values of torque is greater than a predefined threshold, then the motor drive determines that the brake is dragging and sets an error message.