Flex Bar Magnetostrictive Actuator Preload Design
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Solution Overview
Problem
Existing systems for inducing vibration in large masses, such as tree trunks, using magnetostrictive actuators like Terfenol-D face challenges with mechanical preloading, maintaining linear motion, and preventing non-compressive loading, which can lead to actuator failure due to friction, damping losses, and torque transmission, especially when using Belleville springs or other traditional spring designs.
Innovation Solution
The use of flex bars with spherical endcaps and shims to provide axial alignment and preload to the magnetostrictive actuator, eliminating the need for traditional springs and threaded assemblies, and ensuring collinear motion with the actuator axis to prevent torque and coupled moment transmission, while maintaining infinite life and minimizing mechanical losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If traditional spring-based solutions (Belleville springs) are used for preloading the magnetostrictive actuator, then preload is provided, but friction and damping losses increase significantly
Solution Approach 1:
The patent removes traditional spring-based preloading mechanisms (Belleville springs, threaded assemblies) from the system and replaces them with a gravity-based counterweight system. This extraction eliminates the friction and damping losses inherent in spring mechanisms while maintaining the necessary preload force on the magnetostrictive actuator through the flex bar and spherical contact surface design.
Solution Approach 2:
The patent substitutes mechanical spring-based preloading with a gravity-based mechanical system using counterweights and flex bars. The flex bar with spherical contact surfaces provides preload through gravitational force on the counterweights, replacing the energy-lossy spring mechanism with a passive gravity-based system that maintains constant preload without friction or damping losses.
2Strength
If threaded assemblies are used for mounting the magnetostrictive actuator, then secure mounting is achieved, but torque transmission can cause actuator failure
Solution Approach 1:
The patent completely removes threaded assemblies from the mounting system. Instead of using threaded connections that can transmit torque to the actuator rod, the design uses flex bars with spherical contact surfaces that mount the magnetostrictive actuator through pure compression loading, eliminating the torque transmission pathway that leads to actuator failure.
Solution Approach 2:
The flex bar acts as an intermediary element between the mounting structure and the magnetostrictive actuator. The spherical contact surfaces on the flex bar provide a mechanical interface that transmits only compressive forces to the actuator rod, isolating it from torque and coupled moments while maintaining secure mounting.
3Productivity
If the magnetostrictive actuator is used at high frequency with large reaction mass, then vibration output is increased, but mechanical preloading and suspending systems require significant advancement
Solution Approach 1:
The system uses the reaction mass itself to provide the necessary preload through gravity. The counterweights are positioned such that their gravitational force automatically maintains compressive loading on the magnetostrictive actuator during operation, eliminating the need for separate active preloading mechanisms and simplifying the overall system design for high-frequency operation.
Solution Approach 2:
The use of spherical contact surfaces on the flex bars provides a simple, elegant solution for maintaining linear motion and preload. The spherical geometry naturally guides the actuator rod along its axis without requiring complex linear guides or bearings, reducing device complexity while enabling high-frequency operation with large reaction masses.
4Force
If Belleville springs are used in stacks for preload, then high force is achieved, but friction levels (mechanical loss) are higher than equivalent coil springs
Solution Approach 1:
The patent removes Belleville springs entirely from the system, replacing them with a gravity-based counterweight system using flex bars. This extraction eliminates the high friction mechanical losses associated with stacked Belleville springs while maintaining the necessary preload force through gravitational loading on the counterweights.
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 solution effectively doubles the force output of magnetostrictive actuators, achieves infinite life, and minimizes mechanical losses, providing predictable and reliable vibration for efficient tree harvesting with minimal damage to the trees, and is applicable to various high-performance vibration systems.
Implementation Method 1
Terfenol-D is a giant magnetostrictive material (GMM) which transforms magnetic field waveforms in the physical strain
Implementation Method 2
The use of a Terfenol-D magnetostrictive actuator with hardened endcaps and flex bars that provide axial alignment and preload through spherical contact surfaces
Data Source
AI summary
The present invention provides methods and apparatus for inducing (harmonic) vibration of objects having a large mass(es), such as the trunk of a fruit or nut tree, the crop of which may be harvested by shaking the tree through the induced vibration. Linear and radial embodiments utilize and include an actuator using Terfenol-D, a magnetostrictive actuator. Different versions utilize a piston rod actuator.