Piezoelectric Actuator Hysteresis Reduction via Feedback and Feed-Forward Control
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Solution Overview
Problem
Piezoelectric actuators exhibit hysteresis, leading to non-linear behavior that reduces accuracy and precision in movements and placements, particularly in applications like microlithography systems where linear control is essential.
Innovation Solution
A control system with feedback of transducer displacements and feed-forward of electrical currents is used to reduce hysteresis, incorporating a feedback controller and current-feed-forward amplifier to provide more precise control of piezoelectric actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If piezoelectric actuators are used for high-precision positioning, then responsiveness and conversion efficiency are improved, but hysteresis causes non-linear behavior that reduces accuracy and precision
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the actual position of the piezoelectric actuator and compares it with the commanded position. The controller adjusts the driving voltage based on the position error to compensate for hysteresis effects, thereby maintaining high positioning accuracy despite the non-linear behavior of the piezoelectric material.
Solution Approach 2:
The patent employs hysteresis compensation algorithms that dynamically adjust control parameters based on the operating state of the actuator. By changing control parameters such as voltage offset and gain according to the current position and direction of motion, the system linearizes the overall transfer function and reduces hysteresis-induced positioning errors.
2Length of moving object
If piezoelectric actuators operate over large displacement ranges, then stroke length is improved, but hysteresis effects become more significant and harder to control
Solution Approach 1:
The patent divides the large displacement range into multiple smaller segments or regions. For each segment, a specific hysteresis compensation model is applied. This segmentation approach allows the control system to manage hysteresis effects more effectively in each local region while achieving overall large-stroke capability, reducing the complexity compared to attempting to control the entire large range with a single model.
Solution Approach 2:
The patent pre-characterizes the hysteresis behavior of the piezoelectric actuator across its full stroke range during calibration. These pre-determined compensation parameters are stored and automatically applied during operation, eliminating the need for real-time complex calculations and reducing control system complexity while maintaining accuracy over large displacement ranges.
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 control system significantly reduces hysteresis, resulting in more accurate and precise movements and positionings of piezoelectric actuators, enhancing their linear actuation and extending the range of applications, especially in long-stroke scenarios.
Implementation Method 1
A piezoelectric actuator is a type of transducer that converts applied electrical voltage into a corresponding mechanical displacement or stress by exploiting the piezoelectric effect
Implementation Method 2
These actuators also do the reverse, i.e., convert mechanical stress into corresponding voltage
Data Source
AI summary
An exemplary piezoelectric actuator includes a piezoelectric transducer that exhibits displacements when energized with corresponding voltages. A control system is electrically connected to the piezoelectric transducer so as to provide the transducer with the voltages. The control system includes feedback of displacements of the transducer as functions of respective voltage commands and feed-forward of electrical currents passing through the transducer as functions of the respective voltages applied to the transducer. The control system further has a feedback controller connected to receive transducer-displacement data corresponding to the voltages applied to the transducer. The control system further can include a current-feed-forward amplifier connected to receive transducer-current data corresponding to the voltages applied to the transducer. Such a control system facilitates reduction of hysteresis in controlled actuation of the actuator.