Piezo-electric Motor Spring Strap Biasing Stick-Slip Motion
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Solution Overview
Problem
Existing piezo motors face challenges in efficiently utilizing the stick-slip principle for precise and controlled movement due to limitations in frictional engagement and biasing mechanisms, which affect their ability to achieve desired positional accuracy and range.
Innovation Solution
A piezo-electric motor design incorporating a piezo stack, a strip with actuation surfaces, and a spring strap that biases the movable pads into frictional engagement, allowing them to stick during one direction of movement and slip during the other, utilizing a cyclic voltage to amplify small piezo stack movements into controlled millimeter-scale displacements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a piezo stack is used to produce small movements, then the motor occupies a small space, but the movement range is limited
Solution Approach 1:
The patent employs periodic stick-slip motion through cyclic voltage application to the piezo stack. The motor operates in alternating stick phases (where pads remain stationary relative to actuation surfaces) and slip phases (where pads move relative to actuation surfaces), accumulating displacement over multiple cycles. This periodic action enables the motor to achieve millimeter-scale movements despite the piezo stack's inherently limited stroke, resolving the contradiction between compact size and extended movement range.
Solution Approach 2:
The patent introduces intermediate frictional engagement elements (pads and actuation surfaces) between the piezo stack and the output mechanism. These intermediaries amplify the piezo stack's small movements through controlled stick-slip friction, allowing the system to convert micrometer-scale piezo displacement into millimeter-scale output motion while maintaining a compact form factor.
2Measurement precision
If frictional engagement is used for stick-slip motion, then precise positional control is achieved, but frictional engagement reliability is insufficient
Solution Approach 1:
The patent systematically controls frictional engagement parameters including normal force (via spring biasing), surface material properties, and contact pressure. By optimizing these parameters, the design ensures consistent stick-slip behavior where pads reliably transition between sticking and slipping states. This parameter control enhances both positional precision during sticking phases and engagement reliability during transitions, addressing the contradiction between precision and reliability.
Solution Approach 2:
The patent incorporates spring elements that pre-bias the pads against the actuation surfaces, ensuring maintained contact and preventing loss of frictional engagement. This prior cushioning through elastic biasing forces ensures reliable stick-slip operation by preventing separation between contacting surfaces, thereby enhancing engagement reliability while preserving positional control during sticking phases.
3Force
If spring strap is used to bias the actuation surface, then the movable portion is biased toward retracted position, but the complexity of biasing mechanism increases
Solution Approach 1:
The patent employs a thin spring strap as the biasing mechanism instead of complex spring assemblies or actuators. This flexible strip provides the necessary restoring force to bias the actuation surface toward the retracted position while occupying minimal space and adding little structural complexity. The spring strap's simplicity directly addresses the contradiction by providing adequate biasing force with minimal increase in device complexity.
Solution Approach 2:
The spring strap functions as a self-contained biasing mechanism that automatically provides the restoring force without requiring external control systems or additional actuators. This self-service approach to biasing reduces overall system complexity while maintaining the necessary force characteristics for stick-slip operation, resolving the contradiction between force provision and mechanism simplicity.
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 motor achieves precise and controlled motion by leveraging the stick-slip principle, enabling movements of fractions of a millimeter to several millimeters with enhanced positional accuracy and reliability, while maintaining a compact form factor.
Implementation Method 1
a piezo stack that is operable in response to the application of a voltage to move the actuation surface along an actuation axis
Implementation Method 2
A spring strap partially surrounds the actuation portion and is operable to bias the actuation surface toward the retracted position
Implementation Method 3
The voltage is selected such that the movable portion sticks to the actuation surface as the actuation surface moves toward one of the retracted position and the extended position and slips on the actuation surface as the actuation surface moves toward the other
Data Source
AI summary
A piezo-electric motor 100 includes an actuation portion including an actuation surface 106 and a piezo stack 102 that is operable in response to the application of a voltage to move the actuation surface along an actuation axis 116 between a retracted position and an extended position. A spring strap 112 partially surrounds the actuation portion and is operable to bias the actuation surface toward the retracted position and a movable portion 108,110 is frictionally engaged with the actuation surface. The voltage is selected such that the movable portion sticks to the actuation surface as the actuation surface moves toward one of the retracted position and the extended position and slips on the actuation surface as the actuation surface moves toward the other of the retracted position and the extended position.