Piezoelectric inertia motors—also known as stick-slip motors or (smooth) impact drives—use the inertia of a body to drive it in small steps by means of an uninterrupted friction contact. In addition to the typical advantages of piezoelectric motors, they are especially suited for miniaturisation due to their simple structure and inherent fine-positioning capability. Originally developed for positioning in microscopy in the 1980s, they have nowadays also found application in mass-produced consumer goods. Recent research results are likely to enable more applications of piezoelectric inertia motors in the future. This contribution gives a critical overview of their historical development, functional principles, and related terminology. The most relevant aspects regarding their design—i.e., friction contact, solid state actuator, and electrical excitation—are discussed, including aspects of control and simulation. The article closes with an outlook on possible future developments and research perspectives.

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Piezoelectric Inertia Motors—A Critical Review of History, Concepts, Design, Applications, and Perspectives.

By using only one pneumatic line, an inchworm like micro robot for pipe inspection is invented. This paper is based on drilling different-sized micro holes in two plates among three chambers. The rear clamp, the elongation module, and the front clamp work sequentially as the air flows to each chamber. It enables the robot not only to generate inchworm like locomotion, but also to allow significant reduction of the stiffness of pneumatic lines and the drag force due to one pneumatic line. In addition, a micro robot with diameter of 10 mm could be accomplished owing to its simple structure of chambers. In order to operate the robot efficiently, the stroke according to the supplied pneumatic pressure is investigated. Based on the result, maximum theoretical velocity is obtained by tuning the air insufflation time under in-pipe condition. Finally, the adoptability of the robot is tested under variation of pipe diameter.

Pneumatic robot based on inchworm motion for small diameter pipe inspection

With developments of micro-machining and advanced functional materials, smart actuators have been developed and applied in various micro underwater vehicles (MUVs) or micro underwater robots. Since there is a tradeoff between the miniature size and output performance for MUVs driven by traditional electromagnetic motors, piezoelectric motors with features of compact structure, large force or torque at small size and no electromagnetic interference provide another promising alternative for actuating MUVs. However, there is a few research to explore the possibility of utilizing piezoelectric motors to realize underwater actuations. In this paper, a novel piezoelectric inertial rotary motor is designed to power the underwater vehicle, which is capable of forward swimming, rotating, rising and diving. This motor consists of two rotors and one disk type stator. One piece of piezoelectric wafer adhered to the bottom face of the stator’s metal disk is used to excite the radial in-plane vibration mode of stator’s outer ring, which is converted into the revolved motion of the inner tube through the connection beams. To utilize the inertial driving mechanism, the motor works at a “slip-slip” mode by the saw-tooth type driving signal. One prototype motor with the appearance size of Φ 20 mm × 20 mm and weight of 3.6 g is designed, fabricated and characterized. Experimental results show that the prototype motor could rotate at a steady speed of 2200 r/min with 150 Vp-p driving voltage. In addition, the motor also performs well with a slightly decrease of operating speed in underwater environments when the silver electrode is coated by waterproof material. Consequently, sealing ring is not necessary for the proposed motor as immersed in water, which is different with conventional electromagnetic motors and enables the actuation unit to be smaller. And then, the prototype motor is coupled with a propeller to build a thruster, which could output the steady speed and maximum propulsion force of 1200 r/min and 4.6 mN, respectively. Finally, the thruster is installed in a spherical swimming robot, and the velocity of the robot could reach 80 mm/s. With merits of simple structure, compact size and great waterproof feasibility, the proposed piezoelectric inertial motor opens a new avenue for developing advanced and flexible MUVs.

A novel piezoelectric inertial rotary motor for actuating micro underwater vehicles

The piezoelectric properties of (1-x-y)PbZrO3-xPbTiO3-yPb(Ni1/3Nb2/3)O3 ceramics were investigated Specimens with a large Pb(Ni1/3Nb2/3)O3 content, which have compositions close to the triple point, show small g33 and d33 × g33 values because of their large eT33/e0 These values increased with a decrease in y (amount of Pb(Ni1/3Nb2/3)O3) and the specimen with x = 039 and y = 029 showed the largest g33 of 43 × 10−3 V·m/N and d33 × g33 of 252 × 10−12 m2/N Cantilever-type energy harvesters were fabricated using specimens with 038 ≤ x ≤ 041 and y = 029 The output power densities of the energy harvesters were related to the d31 × g31 × k312 value of the piezoelectric ceramics The energy harvester fabricated using a specimen with x = 039 and y = 029, which has a maximum d31 × g31 × k312 value, showed the maximum output power density of 101 mW/cm3

Piezoelectric properties of Pb(Zr,Ti)O3-Pb(Ni,Nb)O3 ceramics and their application in energy harvesters

We have developed an in-pipe micro locomotive system. This system is composed of an outside host and a microrobot. The outside host supplies energy and transmits commands to the robot by using microwaves. The microrobot is 9.5 mm in diameter and 60 mm in length. The microrobot moves in a pipe of 10 mm diameter without wire. The microrobot consists of a microwave (RF) module used for energy supply and communication, a control circuit and a locomotive mechanism using a piezoelectric bimorph actuator. The RF module consists of a compact antenna, power divider, rectifying circuits, filter and communication MMIC. The antenna receives two frequencies of microwaves: 22 GHz for energy supply and 24 GHz for communication. The rectifying circuits convert the microwave into DC. The demanded energy of 480 mW is supplied via microwave. The control circuit drives the locomotive device and other devices installed in the robot by outside commands. The direction and speed of the system are also controlled by commands. The condition of the system is communicated between the robot and the outside host. The locomotive mechanism using a piezoelectric bimorph actuator moves according to inertia drive method.

In-pipe wireless micro locomotive system

We have developed a multi-layered bimorph actuator whose power consumption is low and whose displacement is large. Each actuator layer comprises a piezoelectric element and elastic plate. Because volume of the piezoelectric element is constant, the actuator expands in the direction of applied voltage, but contracts in the perpendicular direction. This bends the elastic plate, amplifying displacement. Layer number determines actuator force. We also developed in-pipe locomotive mechanism utilizing the developed actuator and conventional stack type piezoelectric actuator. The power consumption and moving speed of two-actuator mechanism were investigated. The mechanism of the multi-layered actuator moves 2.5 times faster compared with that of the conventional one, and consumes only 1/80 of electric power of the conventional one.

S. Kawakita

Papers

Multi-layered piezoelectric bimorph actuator