Piezoelectric Ultrasonic Motor Open-Loop Control with Dynamic Velocity
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Solution Overview
Problem
Positioning actuators, such as piezoelectric ultrasonic motors, face challenges in achieving fast operation with low acoustic noise and high precision due to variability in control factors, making them unsuitable for closed-loop control using traditional PID controllers.
Innovation Solution
A method involving open-loop control steps where a control device generates driving signals for positioning actuators based on a target travel distance and calibration values, recalibrating these values when the post-movement position is outside a tolerance range, using a calibration look-up table to adjust pulse coefficients and velocity control factors continuously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If positioning actuators are driven at higher velocity to achieve fast settling times, then the settling time is reduced, but acoustic audible emissions increase
Solution Approach 1:
The system dynamically adjusts the velocity profile during movement, using higher velocities for most of the travel distance and reducing velocity only near the target position. This dynamic velocity adjustment allows fast settling times while minimizing acoustic emissions during the critical final positioning phase.
Solution Approach 2:
The movement profile is segmented into different phases: a high-velocity cruise phase for most of the travel distance, and a low-velocity approach phase near the target position. This segmentation allows the system to optimize for speed during the majority of travel while controlling noise during the final positioning.
2Measurement precision
If traditional PID controllers are used for positioning actuators, then closed-loop control is achieved, but high variability in control factors makes precise control difficult
Solution Approach 1:
The system performs preliminary calibration to determine actuator-specific control factors before operation. These pre-determined factors (pulses per unit distance, velocity control factors) are stored and used during normal operation, eliminating the need for complex real-time adaptation while achieving precise control.
Solution Approach 2:
The system changes control parameters based on operating conditions, using different velocity control factors for different ranges of motion and positions. This allows the controller to adapt to the non-linear behavior of the actuator without requiring complex feedback algorithms.
3Device complexity
If open-loop control is used to reduce system cost, then controller cost is reduced, but positioning precision deteriorates
Solution Approach 1:
The system performs preliminary calibration to determine accurate control factors for each actuator, storing these in lookup tables. During normal operation, the controller uses these pre-determined factors to achieve precise positioning without requiring expensive feedback sensors or complex closed-loop control algorithms.
Solution Approach 2:
The patent introduces calibration lookup tables as an intermediary between the simple open-loop controller and the actuator. These tables contain pre-computed control parameters that compensate for actuator variability, allowing the simple controller to achieve precision normally requiring complex feedback systems.
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 enables precise movement of a moveable element in less total time with reduced acoustic noise generation, effectively addressing the variability issues in positioning actuator systems.
Implementation Method 1
A piezoelectric material changes shape when subjected to an electric field. With the appropriate structure design, this change of shape can be translated into a displacement.
Implementation Method 2
In the case of an ultrasonic motor, the motor vibrates mechanically at a frequency dictated by the drive circuitry and, if the amplitude of displacement is sufficient, the motor will generate external motion.
Implementation Method 3
Piezoelectric ultrasonic motors are frequently driven at resonance or semi resonance to take advantage of the amplification of the displacement due to the resonance itself.
Data Source
AI summary
A method, computer readable medium, and apparatus for controlling a moveable element includes generating and providing with a control device one or more driving signals to one or more positioning actuators to move the moveable element towards a target position based on a target travel distance and a calibration value. The control device determines when a post-movement position of the moveable element is outside of a tolerance range of the target position. The control device recalibrates the calibration value when the post-movement position is determined to be outside of the tolerance range. The control device repeats the generating, the determining, and the recalibrating as open loop steps until the post-movement position is within the tolerance range or until a limit, if any, on attempts is reached.