Multi-stack Piezo Actuator Amplitude Uniformity
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Solution Overview
Problem
Existing ultrasonic piezoelectric actuators face limitations in achieving higher vibration power due to electrical and mechanical constraints, leading to poor amplitude uniformity and potential bolt failure, especially when trying to increase the lateral dimension beyond a quarter wavelength, which affects their suitability for percussive and rotary drill applications.
Innovation Solution
A multi-stack piezoelectric actuator design with a larger radiating surface, achieved by compressing multiple piezoelectric stacks with bolts against a common backing structure, and incorporating tuning grooves and slots to enhance amplitude uniformity, allowing for a lateral dimension up to half the wavelength without compromising prestress integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the lateral dimension of the actuator surface is increased beyond a quarter wavelength to provide higher vibration power, then the radiated power increases, but radial displacement becomes dominant over axial displacement and amplitude uniformity deteriorates
Solution Approach 1:
The actuator surface is segmented into multiple independent piezoelectric stacks arranged in a circular pattern, each stack being a separate functional unit. This segmentation allows the large lateral dimension to be achieved while maintaining controlled displacement characteristics through the modular arrangement of stacks, preventing the radial displacement dominance that occurs in monolithic designs.
Solution Approach 2:
The design transitions from a single large lateral dimension approach to a multi-dimensional arrangement where multiple stacks are distributed circumferentially around a central axis. This dimensional reorganization allows the radiating surface area to be increased through circumferential distribution rather than simple lateral expansion, maintaining amplitude uniformity by spacing stacks at intervals greater than a quarter wavelength apart.
2Power
If the lateral dimension is increased to increase radiated power, then more power is radiated, but parasitic bending modes of the prestressed bolt increase leading to prestress loss and bolt failure
Solution Approach 1:
The prestress system is segmented into multiple independent bolts, each serving a specific piezoelectric stack rather than a single bolt supporting the entire structure. This segmentation distributes the mechanical load and isolates bending stresses to individual bolt-stack assemblies, preventing the propagation of parasitic bending modes across the entire structure that would lead to cumulative prestress loss.
Solution Approach 2:
A prestress distribution layer is introduced as an intermediary between the bolts and piezoelectric stacks. This layer acts as a stress-distributing interface that prevents direct transmission of bending moments from the horn to the bolts, thereby reducing parasitic bending modes and protecting bolt prestress integrity while still allowing effective force transmission.
3Power
If the amplitude of vibration is increased to provide higher power, then radiated power increases, but electrical and mechanical limits of piezoelectric materials are exceeded
Solution Approach 1:
The total power requirement is segmented across multiple piezoelectric stacks rather than requiring a single stack to operate at excessive amplitude levels. Each individual stack operates within safe electrical and mechanical limits, while the cumulative effect of multiple stacks produces the desired high total power output, avoiding material failure.
Solution Approach 2:
Multiple piezoelectric stacks operating at moderate, safe amplitude levels are merged in their mechanical output through the common horn structure. The individual contributions of each stack combine to produce high total radiated power, achieving the power goal through parallel operation rather than excessive single-element amplitude that would exceed material limits.
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 design significantly increases vibration power while maintaining uniform displacement amplitudes and reducing parasitic bending modes, enabling more efficient percussive and rotary drill actions with increased percussive power.
Implementation Method 1
ultrasonic piezoelectric actuator that can generate amplified ultrasonic (e.g., in a range of 20 kHz to 40 kHz) stress (e.g., displacement, vibration) at a tip (110b) of a horn (110) based on ultrasonic stress generated by a combination of piezoelectric elements (120)
Implementation Method 2
The ultrasonic stress is (rigidly) coupled/connected to a (radiating) surface S at a base (110a) of the horn (110) and amplified by the geometry of the horn (110) to provide the amplified ultrasonic stress at the tip (110b) of the horn (110)
Data Source
AI summary
An ultrasonic actuator with increased radiating surface is presented. The increased radiating surface is provided by a plurality of piezoelectric stacks that are each compressed by action of a respective bolt against a common backing structure of the actuator. According to one aspect, each of the stacks includes a plurality of stacked piezoelectric rings with the respective bolt arranged through the central opening of the rings. According to another aspect, one or both of the backing structure and the horn of the actuator include tuning grooves and/or tuning slots to produce amplitude uniformity of displacement through the actuator. According to another aspect, the radiating surface has a symmetrical shape about an axial direction of the actuator with a lateral dimension that is in a range between one quarter and one half of the wavelength of operation of the actuator.