Vranish, J.M., McConnel, R.L., Mahalingam, S., “Capaciflector collision avoidance sensors for robots,” Product Description, NASA Goddard Space Flight Center, Greenbelt, MD, Feb., 1991. Vuylsteke, P., Price, C.B., Oosterlinck, A., “Image sensors for real-time 3-D acquisition, part 1,” in Traditional and Non-Traditional Robotic Sensors, T.C. Henderson, ed., NATO ASI Series, Vol. F63, Springer-Verlag, pp. 187–210, 1990. Wavering, A.J., Fiala, J.C., Roberts, K.J., Lumia, R., “TRICLOPS: a high-powered trinocular active vision system,” IEEE International Conference on Robotics and Automation, pp. 410–417, 1993. White, D., “The hall effect sensor: basic principles of operation and application,” Sensors, pp. 5–11, May, 1988. Wildes, R.P., “Direct recovery of 3-D scene geometry from binocular stereo disparity,” IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 13, No. 8, pp. 761–774, Aug., 1991. Williams, H., “Proximity sensing with microwave technology,” Sensors, pp. 6–15, June, 1989. Wojcik, S., “Noncontact presence sensors for industrial environments,” Sensors, pp. 48–54, Feb., 1994. Wood, T., “The hall effect sensor,” Sensors, pp. 27–36, March, 1986. Woodbury, N., Brubacher, M., Woodbury, J.R., “Noninvasive tank gauging with frequency-modulated laser ranging,” Sensors, pp. 27–31, Sep., 1993. Young, M.S., Li, Y.C., “A high precision ultrasonic system for vibration measurements,” Rev. Sci. Instrum., Vol. 63, No.11, pp. 5435–5441, Nov., 1992. 19.8 Light Detection, Image, and Vision Systems Stanley S. Ipson Introduction Light detectors span a broad spectrum of complexity. The simplest are single sensors whose output signals are easy to interpret and to interface to other components like microprocessors. In contrast, the image sensors in video and digital cameras, incorporating arrays of up to several million detectors, produce output signals which are complicated to interface and require powerful processors to interpret. Regardless of complexity, the purpose of a light detector is to measure light, and the section ‘‘Basic Radiometry’’ introduces a number of radiometric terms that are employed in the characterization of light, light sources, and detectors. However, manufacturers often specify the performance of their devices using photometric units, which take into account the human visual response to light, and so it is necessary to understand both radiometric and photometric measures of light. Sources of light are briefly discussed in section ‘‘Light Sources.” There are several types of light detector in common use and the principles of operation and characteristics of the most widely used, including pyroelectric, photoresistive, photo- diode, and phototransistor are summarized in section ‘‘Light Detectors.” Vision systems have optical components to form an image and an image sensor to convert the light image into an electrical signal. Image formation is reviewed in section ‘‘Image Formation,” before introducing the most widely used detectors, based on charge-coupled device (CCD) technology and complementary metal oxide semicon- ductor (CMOS) technology, in section ‘‘Image Sensors.” The elements required to complete a vision system are discussed briefly in the final section. Basic Radiometry Visible light is electromagnetic energy radiated with very short wavelengths in the range between about 400 and 700 nm. At shorter wavelengths, to about 30 nm, is invisible ultraviolet light and at longer wave- lengths, up to about 0.3 mm, is invisible infrared radiation. Although electromagnetic radiation displays wave behavior including interference and diffraction, it can also behave like a stream of particles and is emitted and absorbed by matter in discrete amounts of energy called photons. The energy ε of a light 0066_frame_C19 Page 119 Wednesday, January 9, 2002 5:32 PM ©2002 CRC Press LLC Vranish, J.M., McConnel, R.L., Mahalingam, S., “Capaciflector collision avoidance sensors for robots,” Product Description, NASA Goddard Space Flight Center, Greenbelt, MD, Feb., 1991. Vuylsteke, P., Price, C.B., Oosterlinck, A., “Image sensors for real-time 3-D acquisition, part 1,” in Traditional and Non-Traditional Robotic Sensors, T.C. Henderson, ed., NATO ASI Series, Vol. F63, Springer-Verlag, pp. 187–210, 1990. Wavering, A.J., Fiala, J.C., Roberts, K.J., Lumia, R., “TRICLOPS: a high-powered trinocular active vision system,” IEEE International Conference on Robotics and Automation, pp. 410–417, 1993. White, D., “The hall effect sensor: basic principles of operation and application,” Sensors, pp. 5–11, May, 1988. Wildes, R.P., “Direct recovery of 3-D scene geometry from binocular stereo disparity,” IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 13, No. 8, pp. 761–774, Aug., 1991. Williams, H., “Proximity sensing with microwave technology,” Sensors, pp. 6–15, June, 1989. Wojcik, S., “Noncontact presence sensors for industrial environments,” Sensors, pp. 48–54, Feb., 1994. Wood, T., “The hall effect sensor,” Sensors, pp. 27–36, March, 1986. Woodbury, N., Brubacher, M., Woodbury, J.R., “Noninvasive tank gauging with frequency-modulated laser ranging,” Sensors, pp. 27–31, Sep., 1993. Young, M.S., Li, Y.C., “A high precision ultrasonic system for vibration measurements,” Rev. Sci. Instrum., Vol. 63, No.11, pp. 5435–5441, Nov., 1992. 19.8 Light Detection, Image, and Vision Systems Stanley S. Ipson Introduction Light detectors span a broad spectrum of complexity. The simplest are single sensors whose output signals are easy to interpret and to interface to other components like microprocessors. In contrast, the image sensors in video and digital cameras, incorporating arrays of up to several million detectors, produce output signals which are complicated to interface and require powerful processors to interpret. Regardless of complexity, the purpose of a light detector is to measure light, and the section ‘‘Basic Radiometry’’ introduces a number of radiometric terms that are employed in the characterization of light, light sources, and detectors. However, manufacturers often specify the performance of their devices using photometric units, which take into account the human visual response to light, and so it is necessary to understand both radiometric and photometric measures of light. Sources of light are briefly discussed in section ‘‘Light Sources.” There are several types of light detector in common use and the principles of operation and characteristics of the most widely used, including pyroelectric, photoresistive, photo- diode, and phototransistor are summarized in section ‘‘Light Detectors.” Vision systems have optical components to form an image and an image sensor to convert the light image into an electrical signal. Image formation is reviewed in section ‘‘Image Formation,” before introducing the most widely used detectors, based on charge-coupled device (CCD) technology and complementary metal oxide semicon- ductor (CMOS) technology, in section ‘‘Image Sensors.” The elements required to complete a vision system are discussed briefly in the final section. Basic Radiometry Visible light is electromagnetic energy radiated with very short wavelengths in the range between about 400 and 700 nm. At shorter wavelengths, to about 30 nm, is invisible ultraviolet light and at longer wave- lengths, up to about 0.3 mm, is invisible infrared radiation. Although electromagnetic radiation displays wave behavior including interference and diffraction, it can also behave like a stream of particles and is emitted and absorbed by matter in discrete amounts of energy called photons. The energy ε of a light 0066_frame_C19 Page 119 Wednesday, January 9, 2002 5:32 PM ©2002 CRC Press LLC 20 Actuators 20.1 Electromechanical Actuators Introduction • Type of Electromechanical Actuators—Operating Principles • Power Amplification and Modulation—Switching Power Electronics 20.2 Electrical Machines The dc Motor • Armature Electromotive Force (emf) • Armature Torque • Terminal Voltage • Methods of Connection • Starting dc Motors • Speed Control of dc Motors • Efficiency of dc Machines • AC Machines • Motor Selection 20.3 Piezoelectric Actuators Piezoeffect Phenomenon • Constitutive Equations • Piezomaterials • Piezoactuating Elements • Application Areas • Piezomotors (Ultrasonic Motors) • Piezoactuators with Several Degrees of Freedom 20.4 Hydraulic and Pneumatic Actuation Systems Introduction • Fluid Actuation Systems • Hydraulic Actuation Systems • Modeling of a Hydraulic Servosystem for Position Control • Pneumatic Actuation Systems • Modeling a Pneumatic Servosystem 20.5 MEMS: Microtransducers Analysis, Design, and Fabrication Introduction • Design and Fabrication • Analysis of Translational Microtransducers • Single-Phase Reluctance Micromotors: Microfabrication, Modeling, and Analysis • Three-Phase Synchronous Reluctance Micromotors: Modeling and Analysis • Microfabrication Aspects • Magnetization Dynamics of Thin Films • Microstructures and Microtransducers with Permanent Magnets: Micromirror Actuator • Micromachined Polycrystalline Silicon Carbide Micromotors • Axial Electromagnetic Micromotors • Conclusions 20.1 Electromechanical Actuators George T C. Chiu Introduction As summarized in the previous sections, a mechatronics system can be partitioned into function blocks illustrated in Fig. 20.1. In this chapter, we will focus on the actuator portion of the system. Specifically, we will present a general discussion of the types of electromechanical actuators and their interaction George T C. Chiu Purdue University C. J. Fraser University of Abertay Dundee Ramutis Bansevicius Kaunas University of Technology Rymantas Tadas Tolocka Kaunas University of Technology Massimo Sorli Politecnico di Torino Stefano Pastorelli Politecnico di Torino Sergey Edward Lyshevski Purdue University Indianapolis 0066_Frame_C20 Page 1 Wednesday, January 9, 2002 5:41 PM ©2002 CRC Press LLC energy side of the device. Typically, an LED source is combined with either a phototransistor or photo thyristor, see Fig. 20.35. In addition to signal isolation, optoisolators also help to reduce ground loop issues between the logic and power side of the circuit. Grounding It is important to provide common ground among the different devices. For electromechanical actuators, the high energy side is often switching at high frequency; if the ground point of the high energy side of the circuit is directly connected to the ground of the low energy side of the circuit, switching noise may propagate through the ground wire and negatively affect the operation of the low energy side of the system. It is recommended that separate common grounds are established for the high and low energy side and the two grounds are then connected at the power supply. In addition, an adequate-sized ground plane needs to be provided to minimize the possibility of differences among grounding points. 20.2 Electrical Machines C. J. Fraser The utilization of electric motors as the power source in a mechatronic application is substantial. Electric motors, therefore, often feature as the prime mover in a variety of driven systems. It is usually the mechanical features of the application that determines the type of electric motor to be employed. The torque–speed characteristics of the motor and the driven system are therefore very important. It is perhaps then a paradox that while the torque–speed characteristics of the motor are readily available from the supplier, the torque–speed characteristics of the driven system are often quite obscure. The dc Motor All conventional electric motors consist of a stationary element and a rotating element, which are separated by an air gap. In dc motors, the stationary element consists of salient “poles,” which are constructed of laminated assemblies with coils wound round them to produce a magnetic field. The function of the laminations is to reduce the losses incurred by eddy currents. The rotating element is traditionally called the “armature” and this consists of a series of coils located between slots around the periphery of the armature. The armature is also fabricated in laminations, which are usually keyed onto a location shaft. A very simple form of dc motor is illustrated in Fig. 20.56. The single coil is located between the opposite poles of a simple magnet. When the coil is aligned in the vertical plane, the conventional flow of electrons is from the positive terminal to the negative terminal. The supply is through the brushes, which make contact with the commutator segments. From Faraday’s laws of electromagnetic induction, the “left-hand rule,” the upper part of the coil will experience a force acting from right to left. The lower section will be subject to a force in the opposite direction. Since the FIGURE 20.56 Single-coil, 2-pole dc motor. Magnet N +ve -ve Brush Commutator S Coil 0066_Frame_C20 Page 33 Wednesday, January 9, 2002 5:49 PM ©2002 CRC Press LLC . employed. The torque–speed characteristics of the motor and the driven system are therefore very important. It is perhaps then a paradox that while the torque–speed characteristics of the motor. terminal. The supply is through the brushes, which make contact with the commutator segments. From Faraday’s laws of electromagnetic induction, the “left-hand rule,” the upper part of the coil will experience. common ground among the different devices. For electromechanical actuators, the high energy side is often switching at high frequency; if the ground point of the high energy side of the circuit is