Piezoelectric Actuator Control for Hysteresis-Compensated Positioning
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Solution Overview
Problem
Piezoelectric actuators exhibit significant hysteresis, which poses a challenge in applications requiring high accuracy and minimal disturbance, such as semiconductor processing and electron microscopy, where precise positioning and movement of samples and tools are necessary.
Innovation Solution
A method and system for controlling piezoelectric actuators by selecting a path and applying a hysteresis-compensated drive signal, which includes identifying changes in direction based on the sign of the rate of change of the drive signal and using a hysteresis model to determine the inverse equation for compensation, thereby reducing hysteresis effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If piezoelectric actuators are used for high stiffness and fast response, then response time and stiffness are improved, but hysteresis causes positioning accuracy to deteriorate
Solution Approach 1:
The system performs preliminary characterization of the piezoelectric actuator's hysteresis behavior by applying a sequence of drive signals and measuring the resulting positions. This preliminary action creates a hysteresis model that is stored and used for compensation during subsequent positioning operations, allowing the system to pre-correct for hysteresis effects without affecting the fast response capability
Solution Approach 2:
The system implements feedback by continuously monitoring the actuator position using an encoder or other position sensing device. This position information is fed back to the control system, which uses it to determine the current state of the actuator and select appropriate hysteresis compensation parameters, thereby maintaining positioning accuracy despite the inherent hysteresis in the piezoelectric material
2Manufacturing precision
If hysteresis compensation is applied to improve positioning accuracy, then positioning precision is improved, but system complexity increases
Solution Approach 1:
The system changes the parameters of the drive signal based on the detected direction of motion and current position state. By switching between different hysteresis compensation models or parameters depending on whether the actuator is moving in the forward or reverse direction, the system achieves accurate compensation without requiring a completely complex control architecture
Solution Approach 2:
The control system segments the hysteresis compensation into discrete states based on direction of motion and position range. By dividing the compensation strategy into manageable segments (e.g., different polynomial orders for different quadrants of motion), the system reduces overall complexity while maintaining precision across the full operating range
3Measurement precision
If high-order polynomial fitting is used to model hysteresis, then compensation accuracy is improved, but computational requirements and processing time increase
Solution Approach 1:
The system applies partial action by using different polynomial orders for different segments of the actuator's travel range or different directions of motion. Instead of uniformly applying a high-order polynomial across all conditions, the system uses lower-order polynomials where sufficient and reserves higher-order models only where needed, thereby reducing average computational time while maintaining accuracy where critical
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 allows for precise positioning with reduced perturbations in position and velocity, enabling accurate and reliable operation of piezoelectric actuators in sensitive applications by compensating for hysteresis, thereby improving the accuracy and reliability of positioning systems.
Implementation Method 1
The actuator element comprises a piezoelectric material, and the drive signal comprises a voltage signal
Implementation Method 2
piezoelectric materials are known to exhibit a significant amount of hysteresis
Data Source
AI summary
A positioning system can include a drive unit having an actuator element and a control system. The actuator element can include a piezoelectric material. The control system can be configured to select a path between a first position and a second position, identify at least one change of direction of the actuator element along the selected path, generate a hysteresis-compensated drive signal based at least in part on the change in direction, and apply the hysteresis-compensated drive signal to the actuator element to move an object along the path.