A motor involves a simple design that can be embedded into a plate structure by incorporating ultrasonic horn actuators into the plate. The piezoelectric material that is integrated into the horns is pre-stressed with flexures. Piezoelectric actuators are attractive for their ability to generate precision high strokes, torques, and forces while operating under relatively harsh conditions (temperatures at single-digit K to as high as 1,273 K).
Electromagnetic motors (EM) typically have high rotational speed and low torque. In order to produce a useful torque, these motors are geared down to reduce the speed and increase the torque. This gearing adds mass and reduces the efficiency of the EM. Piezoelectric motors can be designed with high torques and lower speeds directly without the need for gears.
Designs were developed for producing rotary motion based on the Barth concept of an ultrasonic horn driving a rotor. This idea was extended to a linear motor design by having the horns drive a slider. The unique feature of these motors is that they can be designed in a monolithic planar structure. The design is a unidirectional motor, which is driven by eight horn actuators, that rotates in the clockwise direction. There are two sets of flexures. The flexures around the piezo-electric material are pre-stress flexures and they pre-load the piezoelectric disks to maintain their being operated under compression when electric field is applied. The other set of flexures is a mounting flexure that attaches to the horn at the nodal point and can be designed to generate a normal force between the horn tip and the rotor so that to first order it operates independently and compensates for the wear between the horn and the rotor.
This motor could be stacked to increase the torque on the rotor, or flipped and stacked to produce bidirectional rotation. The novel features of this motor are:
- A monolithic planar piezoelectric motor driven by high-power ultrasonic horns that can be manufactured from a single piece of metal using EDM (electric discharge machining), precision machining, or rapid prototyping.
- A plate structure that can rotate a rotor in a plane.
- A flexure system with low stiffness that accommodates mechanical wear at the rotor horn interface and maintains a constant normal force.
- The ability to embed many horns in a plate to increase the torque.
- A rotary actuator that can be designed to rotate clockwise or counterclockwise, depending on the direction of extension of the horn with respect to the center axis of the rotor.
- A linear actuation mechanism that operates bidirectionally in the plate.
- A mechanism that is operated with soft flexure springs that maintains constant normal and hence friction forces in a motor.
- A planar rotary piezoelectric motor that is driven by ultrasonic horns that can be stacked to produce higher torques.
- Actuator plates that can be flipped and stacked to produce bidirectional drive.
This work was done by Stewart Sherrit, Xiaoqi Bao, Mircea Badescu, and Yoseph Bar-Cohen of Caltech; Daniel Geiyer of Rochester Institute of Technology; and Patrick N. Ostlund and Phillip Allen of Cal Poly Pomona for NASA’s Jet Propulsion Laboratory. NPO-47813
This Brief includes a Technical Support Package (TSP).
Planar Rotary Piezoelectric Motor Using Ultrasonic Horns
(reference NPO-47813) is currently available for download from the TSP library.
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Overview
The document presents a Technical Support Package for a novel "Planar Rotary Piezoelectric Motor Using Ultrasonic Horns," developed by researchers at NASA's Jet Propulsion Laboratory (JPL) and associated institutions. This innovative motor design is based on the concept of utilizing ultrasonic horns to generate rotary motion, offering significant advantages over traditional electromagnetic motors.
Key features of the motor include its monolithic planar structure, which can be manufactured from a single piece of metal using techniques such as electrical discharge machining (EDM), precision machining, or rapid prototyping. This design not only simplifies manufacturing but also reduces costs. The motor operates by converting off-axis extension into rotation, allowing for high torque generation without the need for gears, which are typically required in electromagnetic motors to increase torque at the expense of efficiency and added mass.
The motor employs a flexure system with low stiffness that accommodates mechanical wear at the rotor-horn interface, maintaining a constant normal force. This feature is crucial for ensuring consistent performance and longevity of the motor. The design allows for the integration of multiple ultrasonic horns within the plate structure, enabling increased torque output. Additionally, the motor can be configured to rotate in either direction, depending on the arrangement of the actuators and the direction of extension.
The document also outlines the potential applications of this technology, particularly in aerospace and robotic systems, where high torque and low-speed operation are essential. The ability to produce rotary and linear motion in a compact form factor makes this motor suitable for various manipulator joints and robotic arms, enhancing dexterity and functionality in challenging environments, such as space missions.
Overall, the Technical Support Package emphasizes the innovative aspects of the planar rotary piezoelectric motor, highlighting its advantages in terms of efficiency, cost-effectiveness, and versatility. The research is acknowledged as part of a broader effort to advance technology for future planetary missions, showcasing the potential for this motor design to contribute significantly to the field of robotics and aerospace engineering.
