Analysis of Tiny Piezoelectric Ultrasonic Linear Motor

Abstract

A modified structure for tiny ultrasonic linear motors has been developed, and various shaft materials have been tested in order to improve dynamic properties. The shaft material has a direct influence on efficiency, reliability, and quality of the motors and their dynamic properties. The shaft material is crucial to achieve high performance. Shafts of with various materials, such as a stainless steel, stainless steel coated with diamond like carbon (DLC), a Pyrex, and a graphite, can make it possible to improve dynamic properties of the motors over a wide range of tribological conditions. For the motor with a stainless steel shaft coated with DLC at 47 kHz, its velocity is 6.5 mm/s and its force is 110 mN. When the motor has a Pyrex shaft, a force of 140 mN is reached at 52 kHz. Accordingly, the maximum force produced by a motor with a graphite shaft is estimated as 97 mN. The velocity of this motor was 15 mm/s. We found that graphite has a fine surface and a directional texture which can help a moving element achieve linear motion. Finally, the use of a cap resulted in significantly improving stable operation. A motor with a graphite or a Pyrex shaft showed very stable operation and improved dynamic characteristics.

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

“…Generally, the normal force F z (t) produced by these mechanisms is constant over one actuation cycle. It is produced by permanent magnets (Figure 2d, [30,50]; [89] (p. 15f); [93,[139][140][141]) or by elastic deformation, for example, of metal springs (Figure 2a,c,e, [26,31,44,75,76,142]) or rubber rings (Figure 2b, [27,77,138]). The normal force generated by all these mechanisms can change over time due to wear, ageing, or creep.…”

“…Different actuator designs can be used: axial actuators in monolithic (Figure 2e, [68,191]), stack ( Figure 2a, [26,28]) or multilayer design [26,149,192], axial actuators with transmission mechanism [192,193], shear actuators (Figure 2d, [30,90,153,155,157]), bending actuators of different types (Figure 2b,c, [24,27,28,105,194]), and other designs developed especially for use in inertia motors [195]. There is no general rule as to which type of piezoelectric actuator is most beneficial for inertia motors, as this depends on the particular application.…”

“…This contribution does not aim to provide a general review or classification of piezoelectric motors, as many authors have done so before, e.g., [8]; [9] (pp. [27][28][29][30][31][32][33]; [10]; [11] (p. 32); [12] (p. 414); [13] (p. 5); [14]; [15] (p. 9); [16][17][18]. The proposed classification schemas differ, and none of them comprises all motor variants described in literature.…”

“…Some inertia motors from the literature, using different piezoelectric actuators and different mechanisms to generate normal force. (a) Fixed actuator motor with one linear axis using a piezoelectric stack actuator and a metal spring to generate normal force (Reprinted from [26] with permission from Wiley); (b) Fixed actuator motor with one linear axis using a piezoelectric bending actuator (two piezoelectric discs glued to a passive central disc) and a rubber spring to generate normal force (Reprinted from [27], Copyright 2006 The Japan Society of Applied Physics); (c) Moving actuator motor for linear movement inside pipes (cross-section), using three piezeoeletric bending actuators and flat metal springs to generate normal force (as described in [28,29]); (d) Fixed actuator spherical motor with three rotational axes using piezoelectric shear actuators and a magnet (M) to generate normal force (Reprinted from [30] with the permission of AIP Publishing); (e) Schematic (left) and prototype (right) of a fixed actuator motor for resonant operation with one rotational axis, using a monolithic piezoelectric actuator and a helical spring to generate normal force (Reprinted with permission from [31]). …”

Piezoelectric Motor Using In-Plane Orthogonal Resonance Modes of an Octagonal Plate

“…In literature, we can see piezoelectric motors operated at resonance [56][57][58][59][60], where the generated modes are not in orthogonal directions. Because the generated movement at the contact point is in the tangential direction, these motors should be considered as inertia-drive types.…”