Valve Actuator Duty Cycle Correction for Stick-Slip
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Solution Overview
Problem
The stick-slip effect occurs in electrically controlled valves due to pronounced static friction, which existing methods fail to adequately address, especially when the superimposition component's amplitude is insufficient to prevent this effect.
Innovation Solution
The method involves correcting the duty cycle signal and superimposition component to ensure sufficient movement of the closing element by shifting the superimposition switchover time to align with the PWM period raster points, maintaining mean-value neutrality and allowing for easy adaptation to changing specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a superimposition component is added to the PWM signal to prevent the stick-slip effect, then the closing element moves cyclically around the basic position, but operating states arise where the superimposition component cannot be provided with the required amplitude
Solution Approach 1:
The patent applies asymmetry by allowing the superimposition component to have different amplitudes in different operational phases. Instead of a fixed symmetric superimposition signal, the system dynamically adjusts the amplitude based on the current duty cycle position, enabling sufficient movement amplitude even when operating near the limits of the PWM range.
Solution Approach 2:
The superimposition component's amplitude is made dynamic rather than static. The system continuously adapts the superimposition amplitude based on the current operating state, allowing the closing element to receive sufficient excitation to overcome static friction throughout the entire operational range, not just at a fixed operating point.
2Ease of manufacture
If the superimposition switchover time is shifted from the middle of the superimposition period to another point in time, then mean-value neutrality is maintained while aligning with PWM period raster points, but exact mean value neutrality may deviate due to rounding or calculation precision
Solution Approach 1:
The patent changes the timing parameter of the superimposition switchover from a fixed midpoint to a dynamically adjusted time point that aligns with PWM period raster points. This parameter adaptation allows the system to maintain compatibility with the PWM generation architecture while preserving mean-value neutrality within acceptable precision limits.
3Manufacturing precision
If the duty cycle signal is corrected to keep values within permissible limits, then the closing element movement is maintained, but the superimposition component must be adjusted
Solution Approach 1:
The patent applies preliminary action by pre-calculating and correcting the duty cycle signal before it is used to generate the PWM output. The correction is performed in advance to ensure that the duty cycle values remain within permissible limits while maintaining the intended closing element movement, avoiding the need for complex real-time adjustments.
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 approach effectively prevents the stick-slip effect by ensuring sufficient mechanical movement of the closing element, maintaining mean-value neutrality, and allowing for easy adaptation to changing conditions without altering other parameters like PWM period duration.
Implementation Method 1
the closing element is moved by means of an electric current flowing in a coil
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The method and device serve to electrically actuate a valve (2) with a mechanical closing element (4) by means of an electric current (I). The latter is generated by means of a pulse width-modulated PWM signal (Sp) that has a PWM period (TPWM) and a pulse duty factor. A pulse duty factor signal (TV) is composed of a base portion (SQ) and of a superimposed portion (SU) with a superimposition period (TU), during which the pulse duty factor signal (TV) is switched between a high and a low pulse duty factor value. It is verified whether the addition of the base portion (SG) and of the original superimposed portion (SU) furnishes a fictitious pulse duty factor value of less than zero or greater than one. If yes, a correction is carried out by increasing the low pulse duty factor to at least zero and increasing the high pulse duty factor is increased to a corrected high pulse duty factor or the high pulse duty factor is lowered to no greater than one, and the low pulse duty factor is lowered to a corrected low pulse duty factor, and in that a pulse duty factor period is set from the start of the superimposition period (TU) up to the switching between both pulse duty factor values as an integral multiple of the PWM period (TPWM). During the correction, the mean value of the pulse duty factor signal (TV) is not changed.