Lead Screw Actuator with Piezoelectric Stacks for High Stiffness
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Solution Overview
Problem
Actuator devices, particularly in applications like internal combustion engine valve trains, face challenges in providing precise movements with high holding force and stiffness over a wide range of forces while operating in environments like oil mist, where existing solutions fail to meet performance requirements effectively.
Innovation Solution
A lead screw actuator device is designed with a base supporting multiple piezoelectric stacks that drive bridges and a nut with sliding contact friction, enabling high force density, torque, and stiffness, along with precise movements through relative rotation between the screw and nut, and incorporating a drive and control circuit for dynamic adjustments and energy harvesting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional actuator devices are used, then they can operate in oil mist environment, but they fail to provide precise movements with high holding force and stiffness
Solution Approach 1:
The actuator is divided into multiple independent piezoelectric stacks (first stack, second stack, third stack) that can be individually controlled. This segmentation allows precise independent actuation of each stack, enabling fine movement control while maintaining high holding force through the combined effect of all stacks on the common nut.
Solution Approach 2:
The patent replaces conventional mechanical actuators (motors, gears) with piezoelectric stacks that convert electrical energy directly to mechanical displacement. This substitution eliminates backslash and mechanical play, providing both precise movement control and high holding force without requiring complex mechanical retention mechanisms.
2Measurement precision
If high holding force and stiffness are provided, then precise movements are achieved, but the device volume increases
Solution Approach 1:
The nut is positioned to surround the screw, with piezoelectric stacks arranged radially around the screw axis. The bridges connect the stacks to the nut, creating a nested configuration where the actuator components are compactly arranged in concentric layers, minimizing the overall volume while maintaining high force and precision.
Solution Approach 2:
The patent transitions from linear actuation to radial actuation by arranging piezoelectric stacks in a circular pattern around the screw. This dimensional change allows multiple actuators to work in parallel within a compact footprint, achieving high holding force and precision without increasing the axial length or radial footprint significantly.
3Force
If high force density and torque are achieved, then precise movements are produced, but the device complexity increases
Solution Approach 1:
The bridges serve multiple functions: they mechanically connect the piezoelectric stacks to the nut, transmit axial and radial forces, and provide structural support for the nut. The nut simultaneously receives axial loads from all stacks, converts radial displacement to axial motion, and provides a rotating interface with the screw. This multi-functionality reduces the number of separate components needed.
Solution Approach 2:
The patent combines the functions of multiple actuators into a single integrated system where three piezoelectric stacks work together on a common nut and screw mechanism. The bridges merge the independent stack outputs into a unified mechanical action on the nut, achieving high force density and torque through combined action while maintaining a relatively simple overall structure.
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 lead screw actuator device achieves high holding force and stiffness, allowing for small and fast adjustments with low dynamic force, and operates effectively in confined spaces, suitable for applications requiring precise movement over a wide force range, including internal combustion engine valve trains.
Implementation Method 1
A first bridge (18) supported by a first piezoelectric stack (16(1), 16(2)) and a second bridge (20) supported by a second piezoelectric stack (16(3), 16(4)) are provided
Implementation Method 2
A nut (22) supported by the first bridge (18) and the second bridge (20) is rotatably coupled to a screw (12) with a sliding contact friction between the screw (12) and the nut (22)
Data Source
AI summary
A lead screw actuator device includes a base configured to support a plurality of actuators. A first bridge is supported by one of the plurality of actuators and a second bridge is supported by another one of the plurality of actuators. A nut is supported by the first bridge and the second bridge and is rotatably coupled to a screw with a sliding contact friction between the screw and the nut. The plurality of actuators generate small movements of the first bridge, the second bridge, and the nut that produce relative rotation between the nut and the screw. A method of making a lead screw actuator device is also disclosed.