Linear Actuator End Stop Switch Noise Reduction
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Solution Overview
Problem
Linear actuators using pulse width modulation (PWM) experience electric noise issues when the spindle nut is driven out of an end position due to the reverse recovery time of the short circuit diode, causing current spikes and electromagnetic compatibility (EMC) problems.
Innovation Solution
Incorporating an additional component in series with the short circuit diode, such as a diode, Zener diode, bipolar transistor, or field effect transistor, and an inductor, to reduce or eliminate the circulating current during pulse pauses, thereby minimizing the effect of reverse recovery time and associated noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a short circuit diode is connected across the DC motor to short circuit back EMF current, then the motor stops faster when current is interrupted, but current spikes and electric noise are generated during pulse width modulation due to reverse recovery time
Solution Approach 1:
An additional diode is introduced as an intermediary component connected in series with the short circuit diode. This additional diode acts as a mediator that prevents the circulating motor current from flowing through the short circuit diode during pulse pauses, thereby eliminating the reverse recovery effect and associated electric noise while maintaining the motor stopping performance.
Solution Approach 2:
The current path is segmented by introducing an additional diode in series with the short circuit diode. This segmentation creates a controlled current flow path that directs the circulating current through the additional diode during PWM operation, preventing it from flowing through the short circuit diode and causing reverse recovery noise.
2Use of energy by moving object
If pulse width modulation is used to control motor speed, then energy efficiency is improved, but electric noise and electromagnetic compatibility problems occur when the spindle nut is driven out of end position
Solution Approach 1:
The additional diode serves as an intermediary that resolves the conflict between PWM energy efficiency and electric noise generation. It allows PWM operation to continue for energy efficiency while preventing the specific noise-generating current path that occurs during reverse direction operation from the end position.
3Reliability
If the end stop switch is arranged to connect a short circuit diode across the motor, then the motor stops as fast as possible when current is interrupted, but resonance oscillations occur in the cable
Solution Approach 1:
The additional diode acts as an intermediary that prevents the circulating current from creating voltage spikes across the cable inductance. By directing the current through itself during PWM operation, it eliminates the conditions that cause resonance oscillations in the cable while maintaining reliable motor stopping when the end stop switch activates.
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
The solution significantly reduces or eliminates current spikes and related electric noise, improving the electromagnetic compatibility of the system and preventing resonance oscillations in the actuator's cable.
Implementation Method 1
connect a first diode across the DC motor for short circuiting a current resulting from a back electromotive force produced by the DC motor, when the motor current is interrupted
Implementation Method 2
at least one additional component connected in series with said first diode so that the additional component can conduct a current in the same direction as the first diode while providing a voltage drop over itself
Implementation Method 3
Incorporating an additional component in series with the short circuit diode, such as a diode, Zener diode, bipolar transistor, or field effect transistor, and an inductor, to reduce or eliminate the circulating current during pulse pauses
Data Source
AI summary
A linear actuator (1) comprises a spindle nut arranged to be moved between two end positions on a spindle driven by a DC motor (2). An end stop switch (31) is arranged to be activated when the spindle nut is in an end position. In its activated state, the end stop switch disconnects the motor current and connects a first diode (33) across the DC motor for short circuiting the motor when the current is interrupted. A second diode (32) is connected over the end stop switch for enabling the DC motor to drive the spindle nut out of said end position. An additional component (43) in series with the first diode reduces noise problems caused by motor current circulating through this diode during pulse pauses while the spindle nut is driven out of an end position by a pulse width modulated voltage via a cable from a control box.