eliminate most errors in bearings, supports, and guides used in high precision measuring devices. This is due to active bearings and supports possessing several degrees of freedom, in which one or both contacting elements are made from piezoactive material with predetermined excitation zones. Radial or axial play, backlash and dead zones—traditional errors—are minimized in these devices. The schematic of active bearing is shown in Fig. 20.85(a) where number of axial n and radial m electrode sectors is n = m = 3. Active bearings are used in precision component surface and profile measuring systems to scan the surface. The example is outer ring errors evaluation in high precision ball bearings. Here rotating the component simultaneous measurements of profile and surface are obtained. This is possible due to piezoelectric transducers (Fig. 20.85(b)) contacting with the component in two areas with the same pattern of oscil- lation distribution and phase shift between normal and tangential components of oscillations. There being no external forces, it is evident that errors caused by torque, generated in the contact zone, are negligible. References 1. Cady, W. G., Piezoelectricity, Dover Publications, New York, 1964. 2. Volkov, V., Some Theoretical Problems in Modern Techniques of Diagnostics in Mechanical Systems, in Proc. Int. AMSE Conf. Systems Analysis, Control and Design, Lyon, France, 205. 3. Uchino, K., Piezoelectric Actuators and Ultrasonic Motors, Kluwer Academic Publishers, MA, 1997, 349. 4. Ragulskis, K., Bansevicius, R., Barauskas, R., Kulvietis, G., Vibromotors for Precision Microrobots, Hemisphere Publishing Corporation, 1988, 310. 5. Suzuki, Y., Tani, K., Sakuhara, T., Development of new type piezoelectric micromotor, J. Sensors & Actuators, 83, 244, 2000. 6. Catalog Ceramic Multilayer Actuator CMA d 33 & d 31 , July 2000. 7. Sashida, T., Kenjo T., An Introduction to Ultrasonic Motors, Oxford Science Publications, 1993, Oxford University Press, New York, 242. 8. Ueha S., Tomikawa Y., Ultrasonic Motors, Theory and Application, Oxford Science Publications, Oxford Press, Oxford, 1993, 298. 20.4 Hydraulic and Pneumatic Actuation Systems Massimo Sorli and Stefano Pastorelli Introduction The primary function of an actuation system is to influence the controlled system so as to obtain the desired movement or action. This objective is made possible by the actuation system, which converts the primary energy with which the actuator operates into the final mechanical energy. There are three main types of power with which actuation systems work: electric power, hydraulic power, and pneumatic power. The first envisages the use of electric actuators such as motors, solenoids, and electromagnets. The remaining two envisage the use of cylinders (linear motors) and rotary motors, substantially similar in form and dimensions, the motion of which is respectively governed by a fluid considered uncompressible in an initial approximation (a hydraulic liquid, mineral oil generally, or a liquid with lower viscosity) and by a compressible fluid (compressed air or a generic gas). Other types of energy are available but are fairly unusual in automatic systems. Chemical energy and thermal energy, which cause a change of phase in a material or the thermodynamic expansion of the systems into a mechanical movement, can be considered in this category. The characteristics of fluid servosystems are examined below, with particular reference to systems which permit continuous control of one of the two physical magnitudes which express the fluid power: pressure and flow rate. In general, pressure control is carried out in cases in which it is necessary to create a determined force or torque law, while flow rate control is used to carry out controls on kinematic magnitudes such as position, speed, and acceleration. 0066_Frame_C20 Page 62 Wednesday, January 9, 2002 5:49 PM ©2002 CRC Press LLC eliminate most errors in bearings, supports, and guides used in high precision measuring devices. This is due to active bearings and supports possessing several degrees of freedom, in which one or both contacting elements are made from piezoactive material with predetermined excitation zones. Radial or axial play, backlash and dead zones—traditional errors—are minimized in these devices. The schematic of active bearing is shown in Fig. 20.85(a) where number of axial n and radial m electrode sectors is n = m = 3. Active bearings are used in precision component surface and profile measuring systems to scan the surface. The example is outer ring errors evaluation in high precision ball bearings. Here rotating the component simultaneous measurements of profile and surface are obtained. This is possible due to piezoelectric transducers (Fig. 20.85(b)) contacting with the component in two areas with the same pattern of oscil- lation distribution and phase shift between normal and tangential components of oscillations. There being no external forces, it is evident that errors caused by torque, generated in the contact zone, are negligible. References 1. Cady, W. G., Piezoelectricity, Dover Publications, New York, 1964. 2. Volkov, V., Some Theoretical Problems in Modern Techniques of Diagnostics in Mechanical Systems, in Proc. Int. AMSE Conf. Systems Analysis, Control and Design, Lyon, France, 205. 3. Uchino, K., Piezoelectric Actuators and Ultrasonic Motors, Kluwer Academic Publishers, MA, 1997, 349. 4. Ragulskis, K., Bansevicius, R., Barauskas, R., Kulvietis, G., Vibromotors for Precision Microrobots, Hemisphere Publishing Corporation, 1988, 310. 5. Suzuki, Y., Tani, K., Sakuhara, T., Development of new type piezoelectric micromotor, J. Sensors & Actuators, 83, 244, 2000. 6. Catalog Ceramic Multilayer Actuator CMA d 33 & d 31 , July 2000. 7. Sashida, T., Kenjo T., An Introduction to Ultrasonic Motors, Oxford Science Publications, 1993, Oxford University Press, New York, 242. 8. Ueha S., Tomikawa Y., Ultrasonic Motors, Theory and Application, Oxford Science Publications, Oxford Press, Oxford, 1993, 298. 20.4 Hydraulic and Pneumatic Actuation Systems Massimo Sorli and Stefano Pastorelli Introduction The primary function of an actuation system is to influence the controlled system so as to obtain the desired movement or action. This objective is made possible by the actuation system, which converts the primary energy with which the actuator operates into the final mechanical energy. There are three main types of power with which actuation systems work: electric power, hydraulic power, and pneumatic power. The first envisages the use of electric actuators such as motors, solenoids, and electromagnets. The remaining two envisage the use of cylinders (linear motors) and rotary motors, substantially similar in form and dimensions, the motion of which is respectively governed by a fluid considered uncompressible in an initial approximation (a hydraulic liquid, mineral oil generally, or a liquid with lower viscosity) and by a compressible fluid (compressed air or a generic gas). Other types of energy are available but are fairly unusual in automatic systems. Chemical energy and thermal energy, which cause a change of phase in a material or the thermodynamic expansion of the systems into a mechanical movement, can be considered in this category. The characteristics of fluid servosystems are examined below, with particular reference to systems which permit continuous control of one of the two physical magnitudes which express the fluid power: pressure and flow rate. In general, pressure control is carried out in cases in which it is necessary to create a determined force or torque law, while flow rate control is used to carry out controls on kinematic magnitudes such as position, speed, and acceleration. 0066_Frame_C20 Page 62 Wednesday, January 9, 2002 5:49 PM ©2002 CRC Press LLC . kinematic magnitudes such as position, speed, and acceleration. 0066_Frame_C20 Page 62 Wednesday, January 9, 20 02 5:49 PM 20 02 CRC Press LLC eliminate most errors in bearings, supports, and guides used. kinematic magnitudes such as position, speed, and acceleration. 0066_Frame_C20 Page 62 Wednesday, January 9, 20 02 5:49 PM 20 02 CRC Press LLC . governed by a fluid considered uncompressible in an initial approximation (a hydraulic liquid, mineral oil generally, or a liquid with lower viscosity) and by a compressible fluid (compressed air