High speed and quick response precise linear stage system using V-shape transducer ultrasonic motors K. Asumi, T. Fujimura and M. K. Kurosawa Taiheiyo-cement Corporation, Japan Tokyo Institute of Technology, Japan mkur@ip.titech.ac.jp Abstract Maximum speed of 1.5m/s and 1nm positioning accuracy ultrasonic motors have been developed. By using a V-shape transducer ultrasonic motor (VSM), a 15kg weight lower layer stack stage was driven. The stage speed reached at 0.2m/s with controlled maximum acceleration of 3m/s 2 for thrust of 45N. For the high speed and precise positioning, the driving mode of the transducers changed from a resonance frequency drive, an impact inertia drive and a DC drive depending on the required speed, acceleration, positioning stroke and resolution. The stage was driven 20mm distance from an initial position in static condition with 1 nm resolution within 350ms. A small VSM was fabricated and installed in a 10kg weight stage. 1 Introduction A high speed and large thrust ultrasonic motor using two sandwich-type transducers has been proposed[1]. The ultrasonic motor driving method has been improved[2] to obtain superior performances in control systems. In this paper, several massive ceramics linear stage systems driven by the ultrasonic motors were fabricated, and then, motion control performances have been investigated. 2 Transducer and stage Two types of V-shape transducer ultrasonic linear motor (VSM) have been fabricated to drive heavy ceramic linear stages. 2.1 Transducer for actuator As shown in Fig. 1, each transducer has one head duralumin block, two multi layered PZT stacks, one duralumin angled block, and two column blocks for the end 406
Figure 1: V-shape transducers for ultrasonic motor and cofired PZT stack. nut. The head block and the column blocks were bolt combined sandwiching PZT stacks and the angled block. The PZT stacks were thin layer cofired elements to reduce the driving voltage. The angled block was placed around the mid position for fixing the transducer without influence on vibration mode. At the tip of the head block, friction material of an alumina ceramics were glued. The diameter of the PZT stack and the column end nut were 20 mm. The dimensions of the transducers were 122x67x20 mm 3 and 92x52x20 mm 3. The driving frequencies were 31 khz and 39 khz. 2.2 Set up for linear motor An example of a ceramics linear motor is shown in Fig. 2; the stage had a small VSM unit and moving mass was 1 kg. The detail of the driving unit is shown in Fig. 2. The transducer was fixed at the angled block. Coil springs were place behind the angled block to supply the preload. An alumina ceramics plate was attached to the ceramics linear slider; the ceramics plate was driven by the VSM unite. 2.3 Driving mode of motor The VSM has three operation mode; single phase resonance frequency driving mode for fast motion, inertia driving mode using low frequency saw wave voltage for low speed motion and DC voltage drive for nanometer motion. Speed and thrust of Figure 2: Set up for linear motor and VSM housing unit. 407
the motor was estimated from the measurement of transient response. From the transient response, the acceleration was calculated, then, the thrust was obtained using the moving mass of 1 kg weight linear slider. No-load speed of the motor was 1.6 m/s and 0 speed thrust was about 40 N using a small VSM unit as shown in Fig. 3. At the low speed motion by the resonance driving when the motor speed was 1mm/s, the position deviation from the target position was within 100 nm. Much lower speed range from 0.1 m/s to 0.3 mm/s was obtained by the inertia driving. For the precise positioning, the DC drive was used; resolution of a linear scale was obtained. Figure 4 shows an experimental result of stepping positioning in 10 nm steps every 1 second within 1 nm deviation. 3 Motion control of ceramics stages For massive stage linear motion driving system, quick and precise operation is required. Thus, three operation modes, namely, the resonance drive, the inertia drive, and the DC drive of the VSM were used depending on the required speed and/or preciseness at an instance. 3.1 Motion control design The resonance drive was used for long distance traveling in quick motion. The resonance driving mode had higher speed than 1 m/s and large thrust such as several tens newton. However, from viewpoint of wear, the acceleration should be controlled for moderate frictional condition between the VSM tip and the aluminum plate. Therefore, the acceleration and the derivation of the acceleration were controlled during the starting up, stable high-speed motion, and slowing down approaching to a target position. Figure 3: Thrust-speed of small VMS. Figure 4: Step position of 10 nm. 408
Figure 5: X-Y stage and 10 kg stage with 10 kg additional mass. In the vicinity of a stopping position, the motor speed should be slow down. However, the low speed operation by the resonance drive becomes unstable. Thus the inertia drive was used to approach close to the target position. For precise positioning in nanometer range, the DC driving mode was used. The sensitivity of the actuator was 2 nm/v; the driving voltage resolution was about 10 mv. Hence, sub nanometer positioning control was available; the positioning resolution depends on the linear scale resolution. 3.2 Ceramics Stage motion A 15 kg ceramics stage was driven using the VSM shown in Fig. 1 left hand. The stage was X-Y construction as shown in Fig. 5. The bottom and the upper stages were 8 kg and 7 kg. The motion of the bottom stage is shown in Fig. 6. For traveling distance of 20 mm, stage motion was controlled at the conditions of 0.2m/s speed position Figure 6: 15 kg stage (XY stage, bottom), 20mm, 200mm/s, 3m/s 2, 90m/s 3. 409
speed, 3m/s 2 acceleration, and 90m/s 3 acceleration differential. Precise positioning of 1 nm was carried out within 350 ms. A 10 kg ceramics stage was driven using the smaller VSM shown in Fig. 1 right hand. The stage was single axis as shown in Fig. 5. The traveling distance of 20 mm, stage motion was controlled at the conditions of 0.2m/s speed, 3m/s 2 acceleration, and 90m/s 3 acceleration differential. Precise positioning of 1 nm was carried out within 350 ms as shown in Fig. 7. 4. Conclusions High speed and precise positioning massive ceramics linear stages were produced using V-shaped transducer ultrasonic linear motors. For stable operation, speed, acceleration and acceleration differential were controlled. The demonstrated maximum speed was 0.2m/s and the position resolution was 1nm. The maximum speed of 0.5m/s and the position resolution of 0.1 nm or less will be available. References: [1] M. K. Kurosawa, O. Kodaira, Y. Tsuchitoi, and T. Higuchi, Transducer for high speed and large thrust ultrasonic linear motor using two sandwich-type vibrators, IEEE Trans. on Ultrason. Ferroelectrics, and Freq. Cont., vol.45, no. 5, pp. 1188-1195, 1998. [2] K. Asumi, T. Fujiwara, R. Time (s) Fukunaga and M. K. Kurosawa: "Improvement of the low speed position controllability of a V-shaped, two bolt-clamped Langevintype transducer, ultrasonic linear motor", Proc. of Symp. speed Time (s) on Micro-Nano Mechatronics and Human Science, MHS2007, pp. 377-382, Nagoya, 2007.11 Figure 7: 10 kg stage motion to travel 20 mm driven by a small VMS. Position error (nm) Position error (nm) Position (mm) 410