Sensors and Actuators A 149 (2009) 113–119 Contents lists available at ScienceDirect Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna A multilayer TWILA ultrasonic motor Lionel Petit ∗ , Paul Gonnard INSA Lyon-LGEF, 8 rue de la physique, 69621 Villeurbanne Cedex, France article info Article history: Received 14 May 2008 Received in revised form 30 September 2008 Accepted 30 September 2008 Available online 17 October 2008 Keywords: Ultrasonic motor Piezoelectric multilayers Finite Element Model Longitudinal actuators abstract A fully operational ultrasonic motor using bulk piezoelectric longitudinal actuators has been already introduced in our previous works. But despite of its interesting characteristics and its easily implementa- tion, its high supply voltage (from 200 V rms ) could be a technological lock-in by imposing supplementary constraints in order to satisfy the electrical safety standards. To overcome this drawback, we have developed a new stator version which integrated multilayer longitudinal actuators, based on the bulk TWILA ultrasonic motor. If the global motor structure stays relatively closed to the bulk one, the new longitudinal actuator topology has been optimised with the help of a Finite Element Modeling. The higher capacitance value of the multilayer actuators requires the use of inductance compensation to optimise the motor drive. Finally, The mechanical performances are not only preserved but are now obtained under a main supply voltage (12 V rms ) 17 times lower than the previous bulk version. Moreover, the global efficiency is largely improved by reaching 20%. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Our previous works [1–3] on ultrasonic motors led to a func- tional traveling wave induced by longitudinal actuators (TWILAs) motor which combines good mechanical performances and low production cost. This motor belongs to the traveling wave ultra- sonic motor (TWUM) family because it uses the propagation of a flexional traveling wave inside a ring-shaped stator. Each point of the surface then describes an elliptical movement by rotation of the ring cross-section. This traveling wave results from the super- position of two stationary waves spatially dephased of a quarter of wavelength in space and of a pi/2 factor in time. The flexional vibrations of the stator are generated by longitudinal vibrations of composite piezoelectric actuators (Langevin type) perpendicularly disposed to the stator and distributed along the circumference. The rods are divided into two electrical channels, each one creating a flexion stationary wave (Fig. 1a). The key point of the TWILA design relies on a particular rods arrangement “in three quarter of wavelength” that not only allows a reduction of the rods number but also an increase of their diame- ter. This last point, associated with the use of the conical couplers, inhibits the parasitic flexion of the longitudinal actuators, so harm- ful for the motor efficiency. ∗ Corresponding author. E-mail address: lionel.petit@insa-lyon.fr (L. Petit). A maximal mechanical output power of 1.3 W is then obtained in a 63 cm 3 (20 mm × 52 mm) and 40 g weight tubular motor (Fig. 1b). The longitudinal actuators integrate bulk hard PZT material which needs a high supply voltage (200 V rms for the standard ver- sion). This point could be industrially penalizing by imposing some supplementary constraints in order to satisfy the electrical safety standards (shielding, twin wiring...). Moreover, the power sup- ply design has to take into account the inter-phases mechanical coupling [4] because the motor is obligatory driven near of its oper- ational resonance frequency. To overcome theses limitations, a new version of the TWILA integrated MultiLayer actuators (so-called ML TWILA) has been designed with two purposes: • to decrease the supply voltage • to open new perspectives of easy-strategy command, such as developed in [5]. Multilayer piezoelectric actuators are now commonly used in some industrial applications. The more significative is certainly the Piezoelectric Common Rail Injectors for diesel engine such as the Siemens AG [6] or Bosch [7] solutions. But it should be noted that these applications use a static or quasistatic working of the multilayer elements whereas ultra- sonic motors need a resonant state condition in order to increase the mechanical output. For that reason integration of mutlilayer elements in ultrasonic motors is now a technological key to over- 0924-4247/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2008.09.020