Piezoelectric Motor Control via Phase-Shifted Periodic Voltages
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Solution Overview
Problem
Piezoelectric ultrasonic motors face challenges in controlling position at slow drive speeds due to high energy consumption and non-linear transfer characteristics, leading to vibrations and positional errors.
Innovation Solution
Applying periodic control voltages with a phase shift and varying amplitude ratios to the driving electrodes of piezoelectric motors, which reduces static friction and hysteresis, allowing for precise control and minimal energy usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high voltage amplitude is applied to overcome static friction and engagement states, then the output element can be released from static friction, but this leads to high energy consumption and high acceleration that is difficult to control at low speeds
Solution Approach 1:
The patent applies periodic control voltages with a phase shift between driving electrodes to generate oscillating motion of the friction element. This periodic action gradually overcomes static friction through repeated small impulses rather than a single high-voltage冲击, enabling reliable release from engagement states while maintaining low energy consumption and controllable acceleration at low speeds.
2Reliability
If a high voltage amplitude is applied to overcome static friction, then the output element can be released from engagement state, but this results in high acceleration that is difficult to control in terms of control technology
Solution Approach 1:
By using periodic control voltages with phase shift, the system generates controlled oscillations that progressively build up motion. The phase-shifted periodic excitation creates a smooth, controllable acceleration profile rather than abrupt high-g acceleration, making the system easy to operate and control even at very low speeds and short displacements.
3Speed
If periodic control voltages are applied to generate elliptical motion path of friction element, then propulsion of output element is achieved, but non-linearity or hysteresis in transfer characteristic causes dead regions and makes position control difficult at low speeds
Solution Approach 1:
The patent introduces asymmetry by applying phase-shifted control voltages with different amplitude ratios to the driving electrodes. This asymmetric excitation modifies the elliptical motion path of the friction element to optimize the propulsion characteristics. The asymmetric control compensates for the non-linearities and hysteresis in the friction interface, eliminating dead regions and enabling precise position control even at very low speeds.
Solution Approach 2:
The system dynamically adjusts control parameters including phase shift angle and amplitude ratio of the periodic voltages applied to different driving electrodes. By changing these parameters, the friction element's motion path and velocity distribution are optimized to linearize the transfer characteristic, removing dead zones and improving measurement precision for position control at low speeds.
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 method enables simplified position control at low speeds with reduced energy consumption and minimized positional errors, improving control accuracy and reducing unwanted vibrations.
Implementation Method 1
a specific periodic deformation of a piezoceramic element (actuator) is generated by applying periodic control voltages to its driving electrodes
Implementation Method 2
This deformation is transmitted via a so-called friction element (friction lug) to an output element being in frictional contact therewith in order to generate a propulsion of this output element
Data Source
AI summary
A method and device are disclosed for actuating a piezoelectric motor by two driving electrodes by applying periodic control voltages to the driving electrodes. A simplified closed-loop control of the piezoelectric motor is realized by reducing the static friction of a friction contact between a friction element of the piezo-electric motor and an output element to be driven by the friction element without a propulsion of the output element at the same time. In exemplary embodiments, the periodic control voltages are applied with a phase shift to the driving electrodes in a first step of the method, and in a second step of the method, the amplitude ratio of the periodic control voltages is changed with respect to the first step.