Piezoelectric Inchworm Actuator Research Articles

The Development of Piezoelectric Inchworm Actuator Clamped With Magnetorheological Elastomer and Its Potential Application in Brain–Computer Interface Implantation

The piezoelectric inchworm actuator with high-positioning accuracy and large output force is a potential device to implant microelectrode in the invasive brain–computer interface (BCI). However, the traditional piezoelectric inchworm actuator adopts multichannel electrical control signals from external equipment and rigid-to-rigid friction contact to drive, resulting in complex control and uneven friction. To solve the above problems, in this article, magnetorheological elastomer (MRE) is first proposed as the clamping material of the piezoelectric inchworm actuator. An MRE–capillary–cover sandwich structure is adopted to achieve rigid-to-elastomeric clamping. The driving and clamping actions of the actuator are controlled by two cam mechanisms mounted on the same shaft, and a battery can feed the actuator. A kinetic model is established to analyze and predict the actuator motion. Several crucial clamping parameters are explored, and the performance experiments are conducted to evaluate actuator characteristics. A verification experiment is carried out to prove the feasibility of the microelectrode implantation in the pig brain (0.6% agarose gel). The actuator can reach the maximum velocity of 1250.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m/s and the maximum output force of 420 mN; in the forward/backward motion, the minimum step is 0.5837/0.5912 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m, and the repeatability is 0.0465/0.0469 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m; thus, the actuator has great application potential in BCI.

Modeling and Design Optimization of a New Piezoelectric Inchworm Actuator with Screw Clamping Mechanisms.

A new piezoelectric inchworm actuator with screw clamping mechanisms has been developed recently for the wing folding mechanism of a small unmanned aircraft where the actuator power density is a great concern. Considering that the prototype actuator was designed just with engineering intuition and the performance optimization through experimental developments would take a vast amount of cost and time, a mathematical model was developed to investigate the actuator's critical design parameters and optimize its presently undesirable performance. Based on the lumped parameter method reported previously, and taking full account of the detailed modeling of the complex actuator housing and the actual nonlinear behaviors from the high-force contact and friction occurring at the screw-nut interface, as well as the output performance of the main drive elements including the piezoelectric stack and hollow ultrasonic motors (HUSMs), this model was built and then was experimentally verified for its accuracy and availability. Finally, nine design parameters were studied for their individual effect on the actuator's output using the proposed model. The simulation results indicate that the performance can be considerably improved by performing a slight modification to the prototype, and the dynamic modeling and parameter optimization methods used in this study can also serve as a useful reference for the design of similar piezoelectric inchworm actuators with intermittent clamping behaviors.

Design and experimental performance of a novel piezoelectric inchworm actuator based on screw clamping principle.

The requirements of large thrust in bidirectional motion, high specific power (power/weight ratio), reliable self-locking at power off state, and compact size envelope for various applications of existing piezoelectric actuators are still urgent. To address these challenges, this study makes full use of the piezoelectric material's excellent dynamic performance, robust force output, and high energy density to propose a novel inchworm piezoelectric actuator, which relies on the alternate clamping of two nuts independently rotated by two ultrasonic motors on a feed-screw in accordance with a piezoelectric stack (piezo-stack) excitation to accumulate the piezo-stack's electric field-induced strain periodically and realize power output. The operation principle and design process of the presented actuator were elaborated, and a prototype was fabricated and experimented. Results indicate that the actuator has achieved an expected bidirectional motion for powering the tensile load and compressive load, attained a micrometer-sized step resolution, produced a 3.08 mm/s free speed, a 700 N stall load, and a 1.34 W/kg specific power, and shown a favorable prospect for further development.

A novel high-speed bi-directional piezoelectric inchworm actuator based on flexible supported baffles

Typical bionic piezoelectric inchworm actuators utilize at least two clamping piezo-stacks (PZTs) and one driving PZT to achieve bi-directional actuation, resulting in complex structures, complicated electronic systems, and high cost. Actuators with lesser PZTs (1 or 2) can effectively alleviate these problems; however, existing designs are limited to unidirectional or bidirectional low-speed motion. This study proposes a high-speed bi-directional inchworm actuator with two PZTs, where the clamping switching is achieved by only one PZT through innovative use of flexible supported baffles and enhanced clamping mechanisms. The design also reduces the six sub-steps of the driving principle (alternate elongation and shortening of three PZTs) required for each step of typical designs to four, thus effectively increasing the maximum speed of the actuation. Experimental results show that the proposed design facilitates bi-directional motions in a stable manner with a maximum speed of 5.1 mm s−1, which is approximately 23 times faster than the existing design with two PZTs. The proposed design can effectively expand the application range of dual-piezoelectric inchworm actuators and can find a promising application in the field of high-speed precision positioning.

Piezoelectric inchworm actuator using silicon as the mechanical material

Piezoelectric inchworm actuators allow for a large stroke and high precision. This paper aims to minimize the footprint of the actuator by using semiconductor and MEMS fabrication techniques to build the frame and channel out of silicon wafers. The high precision of the semiconductor processes allows for precise tolerances as well as the ability to use batch processing for a shorter fabrication time. Using silicon as the mechanical material can also allow for the incorporation of the electrical signals into the frame.

A Novel Piezoelectric Inchworm Actuator Driven by One Channel Direct Current Signal

A novel piezoelectric inchworm actuator driven by one channel dc signal is developed in this article to simplify excitation signal of the inchworm actuators, and the clamping force of the developed actuator is generated by a dc motor and two permanent magnets. The piezoelectric stack is excited by a sensing signal, which is generated by the separate photoelectric sensor to detect the position of the rotational permanent magnets. A mathematical model is established to predict the motion of the slider. The prototype of the proposed piezoelectric actuator is fabricated, and mechanical output performance is measured. At a voltage of 75 V and frequency of 3.2 Hz, the average output step is 0.241 μm under no-load conditions. The proposed inchworm actuator can be operated by just one channel dc signal and the output displacement is stable, which provides a new idea for the integration design of the piezoelectric actuators in the future.

A self-adapting linear inchworm piezoelectric actuator based on a permanent magnets clamping structure

Abstract A self-adapting structure is proposed in this study to match the driving and clamping signals of piezoelectric inchworm actuators. The excitation signal generated from a pair of opposite type laser photoelectric sensors which detect the positions of the permanent magnets. The proposed actuator can achieve stable motion by matching the clamping force controlled by rotating permanent magnets and the driving force generated by the piezoelectric stack. Simulation on magnetic flux density of the rotating permanent magnet and hysteresis characteristics of the flexible hinge with different thicknesses are conducted to optimize the structure parameters of the actuator. The dynamic model of the actuator is established and a series of experiments are carried out to evaluate the performance of the actuator in terms of resolution, maximum load, maximum output force and repeatability. The experimental results indicate that the actuator achieves maximum output force of 15 g, maximum load of 1100 g and resolution of 0.03 μm in the case of U = 150 V and f = 40 Hz respectively. Moreover, by comparing the theoretical and experimental results regarding the output displacement, it is found that they have the same movement trend. In conclusion, the self-adapting structure contributes to the easy integration of the piezoelectric inchworm actuator, which makes it rather promising considering the stable linear motion performance.

Mechanically reconfigurable reflector for future smart space antenna application

Smart space antennas with mechanically reconfigurable reflectors (MRRs) not only compensate for shape errors induced by distortions in the reflector but, depending on the purpose, also change the service coverage area on the ground with the reshaped reflector. Although several simulation studies regarding different types of MRRs have been performed in the past few years, MRR designs are few because of the difficulty in developing a reflector with the proper mechanical properties and actuators with sufficient drive capacity. Managing the array of actuators is also an issue, particularly in space applications. This paper presents a prototype of a MRR system that consists of a flexible reflector, an actuator array, and a servo controller. The reflector is a layered structure of simple construction with capability of flexible tailoring of its mechanical properties for reshaping. Piezoelectric inchworm actuators were developed, each with large driving stroke and load capacity. Thirteen actuators attached to the back of the reflector provide specified linear displacements that adjust the surface shape of the reflector. To reduce the overall size of the MRR prototype system and the operating power, a distributed time-sharing control strategy was designed to control the actuator array. For a given target shape, the actuation values of the array were optimized. The optimization algorithm and reconfiguration of the MRR prototype were validated in experiments where two different target shapes with extreme deformations and curvatures are specified.

Structure and control strategy for a piezoelectric inchworm actuator equipped with MEMS ridges

Compared with conventional piezoelectric inchworm actuators (PIAs), which rely on a frictional mechanism to produce large stroke and force outputs, PIAs equipped with MEMS ridges can achieve much higher power density in small geometries through the interlocking of micro-ridges. This is promising for future adaptive space structure applications. However, from a practical perspective, achieving stable interlocking MEMS ridges remains challenging, and so an accurate structural assembly and effective control strategy are required. This paper presents an actuator with a simple structure, thus simplifying the assembly process and reducing assembly errors, and then designs a reasonable control strategy that compensates for hysteresis and the uncertain compression of the structure induced by acting against external loads of different stiffness. Finally, the stable interlocking of MEMS ridges is experimentally validated by measuring the significant improvement in PIA load capacity.

Design and analysis of a piezoelectric inchworm actuator

Piezoelectric inchworm actuators are developed from the motion features of nature inchworm with the advantages of large stroke, high resolution and rigidity and flexible structure. They have a wide application in the fields of Nano positioning and ultra-precision detecting instruments. A new piezoelectric inchworm actuator based on the principle of flexible amplification is developed in this paper. In the moving mechanism of the actuator, its clamping mechanism adopts symmetrical lever amplification structure, and its middle drive mechanism uses compound bridge structure. Round and straight hinges are adopted to the design of the mechanism. Theoretical analyses, including stiffness, natural frequency, stress and deformation of the mechanism, are used to design the hinge structure which has influences on the properties of moving mechanism. Then finite element analysis is carried out to optimize the structure of the actuator. High precision cross roller guide ways are utilized to improve the positioning accuracy of the actuator. The laboratory platform of the piezoelectric inchworm actuator is built. The controlling program of the actuator is compiled by Lab-VIEW. The experimental results of the actuator are as follows. The working stroke of the actuator is 50 mm, the minimum step pitch is 60 nm, the maximum step pitch is 105 μm, the fast speed is 2.04 mm/s, the maximum clamping force is 21 N, the maximum stability load is 500 g, and the average speed of the actuator can still reach 1.47 mm/s when the driving frequency is 50 Hz and the load is 1 kg.

A piezoelectric inchworm actuator of linear type using symmetrical lever amplification

Piezoelectric inchworm actuators have a wide application in the field of nano-positioning and ultra-precision detecting instruments. Ultra-precision positioning equipments are urgently needed in the field of precision optics. A new piezoelectric linear actuator, based on inchworm motion principle, with a symmetry lever displacement amplification mechanism has been designed in this article. The whole structure adopts uniaxial-type double-notch right circular flexible hinge as its main hinges, which offers the driving part a larger displacement and makes clamping part have enough clamping force at the same time. High-precision cross roller guide ways are utilized to improve the positioning accuracy of the actuator. Both theoretical analysis and finite element analysis of clamping mechanism and driving mechanism have been carried out. An experimental test platform has been built, and a controlling program of the actuator is compiled by LabVIEW. The experimental results show that the working stroke of the actuator is ± 25 mm, resolution is 60 nm, the clamping force is 17 N, and the bearing capacity is 11 N; the actuator has a highest speed of 1.259 mm/s at the driving voltage 150 V.

Study of the Influence of Leakage Fields on the Inchworm Actuator

In this paper, we study the design parameters and especially the influence of leakage electric fields on the performance of a piezoelectric inchworm actuator. We consider the total deformation of the actuator and the first piezoelectric element capacitance as a good indication of the leakage fields produced in the insulators. Particularly, we study the effect of the thickness of insulating disks that separate the piezoelectric elements and the effect of the state of central element electrodes when unexcited. The result of a coupled electromechanical modeling is that the leakage field does not have an important effect for this device geometry.

Dynamic Modeling of an Innovative Piezoelectric Actuator for Minimally Invasive Surgery

Abstract A small piezoelectric inchworm actuator has been designed for use with a monolithic compliant end-effector in minimally invasive surgery procedures. A dynamic model of the inchworm actuator has been developed using SIMULINK. Utilizing the equations of motion for the inchworm actuator, the dynamic characteristics of the piezoelectric stack material, and the known compliance of the gripper, a force measurement model has been developed which extracts resisting force information from the piezoelectric signal. The focus of this paper is on the development of the dynamic model and the results of a simulation study that will be used to develop optimal driving signals for the inchworm actuator. Simulation results include the predicted displacement capabilities and settling time of the inchworm actuator over a range of driving frequencies.

Dynamic Modeling of an Innovative Piezoelectric Actuator for Minimally Invasive Surgery

A small piezoelectric inchworm actuator has been designed for use with a monolithic compliant end-effect or in minimally invasive surgery procedures. A dynamic model of the inchworm actuator has been developed using SIMULINK. Utilizing the equations of motion for the inchworm actuator, the dynamic characteristics of the piezoelectric stack material, and the known compliance of the gripper, a force measurement model has been developed which extracts resisting force information from the piezoelectric signal. The focus of this paper is on the development of the dynamic model and the results of a simulation study that will be used to develop optimal driving signals for the inchworm actuator. Simulation results include the predicted displacement capabilities and settling time of the inchworm actuator over a range of driving frequencies.