Piezo Motor Foil Mounting at Vibration Nodes for Minimal Backlash
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Solution Overview
Problem
Existing ultrasonic piezo motors face challenges in compact design, ease of installation, and minimizing mechanical backlash, while maintaining high positioning accuracy and efficiency.
Innovation Solution
A mounting system using flexure hinges and foil elements that allow the piezo motor to move in the normal direction, with fixation points positioned at node positions of bending modes to prevent interference with eigenmodes, ensuring minimal backlash and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the piezo motor element is rigidly fixed to prevent all movement, then positioning accuracy is improved, but mechanical backlash increases and resonance modes are interfered with
Solution Approach 1:
The patent employs thin foil elements (connection foils) that are flexible enough to allow the piezo motor element to move in the normal direction while maintaining a stiff connection in the tangential direction. This flexible film approach enables the motor to achieve positioning accuracy without introducing mechanical backlash, as the foil maintains a consistent connection without rigid mechanical joints.
Solution Approach 2:
The patent changes the mechanical parameters of the connection system by using flexure hinges with specific geometric designs that provide different stiffness characteristics in different directions. The flexure hinges are designed to be compliant in the normal direction (allowing movement) while maintaining stiffness in the tangential direction (preventing backlash), thus optimizing both positioning accuracy and eliminating harmful backlash effects.
2Volume of moving object
If the motor size is reduced for compactness, then device miniaturization is achieved, but the displacement capability is reduced
Solution Approach 1:
The patent enables unlimited travel range in a compact motor by allowing the piezo motor element to move dynamically in the normal direction through the flexible foil connection. The motor can achieve large displacements by accumulating small steps over time, while the flexible connection allows the element to return to its starting position, enabling continuous operation without mechanical limits.
3Stability of the object's composition
If fixation points are positioned to prevent interference with eigenmodes, then resonance mode symmetry is improved, but the number of available fixation positions is limited
Solution Approach 1:
The flexible foil connection allows the piezo motor element to be fixed at node positions of bending modes while still maintaining the ability to move in the normal direction. The foil's flexibility compensates for the limited fixation positions, allowing the system to achieve resonance mode symmetry without sacrificing adaptability.
4Ease of manufacture
If a simple mounting system is used for easy installation, then ease of manufacture is improved, but positioning accuracy and backlash control are compromised
Solution Approach 1:
The flexible foil connection can be easily attached to the piezo motor element and the stator component using simple bonding methods, making the mounting process easy and quick. Despite the simplicity of the connection method, the foil's specific geometric design ensures it maintains stiff tangential connection for positioning accuracy while allowing normal direction movement for unlimited travel.
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 solution enables a compact, backlash-free, and thermally stable ultrasonic piezo motor system with improved resonance mode symmetry, facilitating easy manufacturing and assembly, while maintaining high force and travel speed capabilities.
Implementation Method 1
ultrasonic piezo motors... the piezo element(s) of resonant motors are excited with driving signals at a frequency which is close to two eigenfrequencies of the motor
Implementation Method 2
a connection element comprising arms with flexure hinges for fixating the piezo motor element... the flexure hinges being such that the piezo motor element is allowed to move in the normal direction and the flexure hinges being stiff in the tangential direction
Implementation Method 3
resonant motors, which are often called 'ultrasonic' because of the high operating frequencies... the piezo element(s) of resonant motors are excited with driving signals at a frequency which is close to two eigenfrequencies of the motor
Data Source
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AI summary
A piezo actuator, particularly a resonant vibration actuator for an ultrasonic motor, comprises a piezo element having a top surface and a bottom surface, and a connection element (foil) comprising arms with flexure hinges for contacting the piezo element at different fixation positions located at node positions of a bending mode of the piezo element. The flexure hinges are such that the piezo element is allowed to move only in a normal direction (radial direction of an expansion mode) while being stiff in an orthogonal tangential direction.