Safety Drive Control Circuit Using Back-EMF for Return Speed Limiting
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Solution Overview
Problem
Safety drives with electric motors and return springs face significant strain and mechanical damage due to large forces and accelerations during reverse movements, particularly when transitioning to a fail-safe position without external energy supply.
Innovation Solution
A control circuit that determines the frequency of counter-electromotive force (back EMF) in the motor to regulate and limit the speed during reverse movements by converting excess kinetic energy into thermal energy, using electronic components like microcontrollers and ASICS, and employing pulse-width modulated short-circuiting of motor coils to actively brake the motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the return spring continuously applies a restoring force to move the fire damper to the safety position, then the fail-safe function is improved, but large forces and accelerations during reverse movement cause mechanical strain and damage
Solution Approach 1:
The control circuit detects the start of reverse movement and activates the motor to apply a braking torque that counteracts the return spring force before the damper reaches high speed, preventing excessive acceleration and mechanical stress throughout the return movement
Solution Approach 2:
The control circuit continuously monitors the movement state of the fire damper and adjusts the motor's braking torque in real-time based on the detected position and speed, optimizing the braking force to prevent mechanical damage while ensuring reliable return to safety position
2Speed
If the motor speed is not controlled during reverse movement, then the return to safety position is faster, but braking forces and accelerations lead to mechanical damage
Solution Approach 1:
The control circuit dynamically adjusts the motor's braking torque during reverse movement based on real-time detection of damper position and speed, transitioning from high braking force at the start of return to reduced braking force as the damper approaches the safety position, optimizing both speed and mechanical protection
3Strength
If pulse-width modulated short-circuiting is used to limit motor speed, then mechanical damage is prevented, but the control circuit complexity increases
Solution Approach 1:
The control circuit uses the motor's existing windings to generate counter electromotive force for speed detection and simultaneously uses pulse-width modulated short-circuiting of the same windings for speed limitation, making the motor components serve multiple functions and avoiding additional sensors or devices
Solution Approach 2:
The motor's own electromagnetic properties (counter EMF generation during rotation) are utilized for speed detection and control, allowing the motor to provide its own feedback signal and eliminating the need for external tachometers or encoders, thereby reducing 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
This solution allows for robust and safe control of motor speed during reverse movements, reducing mechanical stress and preventing damage by actively managing the motor's speed and energy conversion, ensuring reliable operation even without an external power supply.
Implementation Method 1
an electric motor (2) for moving the output member (3) against a force continuously exerted by the return spring (4) in the direction of the opposite end position
Implementation Method 2
a return spring (4) for driving the output member (3) during a return movement in the direction of the safety position (1)
Implementation Method 3
determine a frequency of a counter electromotive force (back EMF) induced in the motor and to determine a speed of the motor therefrom
Implementation Method 4
regulate or limit the speed of the motor during a return movement driven by the return spring by controlling the motor... converting excess kinetic energy into thermal energy
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
A control circuit (1) for a safety drive with an electric motor (2) and a return spring (4) is disclosed, the control circuit (1) being set up to set a frequency of an electromotive counterforce (counter-EMF) induced in the motor (2). to determine and therefrom to determine a speed of the engine (2); and wherein the control circuit (1) is set up to regulate or limit the speed of the motor (2) during a return motion driven by the return spring (4) by controlling the motor (2). A safety drive with a control circuit (1), a method for controlling a return movement of a safety drive and a computer program product are also disclosed.