Sensors and Actuators in Mechatronics

Design and Applications

Andrzej M Pawlak

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351837521
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

From large-scale industrial systems to components in consumer applications, mechatronics has woven itself into the very fabric of modern technology. Among the most important elements of mechatronic systems are electromagnetic sensors and electromechanical actuators. Cultivated over years of industrial and research experience, Sensors and Actuators in Mechatronics: Design and Applications builds a practical understanding of the features and functions of various electromagnetic and electromechanical devices necessary to meet specific industrial requirements.This work focuses on various components that receive less attention in the available literature, such as magnetic sensors, linear and latching solenoid actuators, stepper motors, rotary actuators, and other special magnetic devices including magnetic valves and heart pumps. Each chapter follows a consistent format, working from theory to design, applications, and numerical problems and solutions. Although the crux of the coverage is design and application, the author also discusses optimization and testing, introduces magnetic materials, and shares his enlightened perspective on the social and business aspects of developing world-class technologies. Examples from mainly the automotive industry illustrate the wide variety of mechatronic devices presented.Providing a complete picture from conception to completion, Sensors and Actuators in Mechatronics: Design and Applications places critical tools in the hands of any researcher or engineer seeking to develop innovative mechatronic systems.

1
Introduction

Mechatronics is the synthesis of mechanical engineering and electronics, two distinct technology areas that overlap in the design of complex systems. It is a synergetic combination of precision mechanical engineering, electronic control, and system thinking in the design of product and process (Alciatore and Histand 2003, Baumann et al. 2000, Bishop 2002, Triantafyllou et al. 1999). Sensors and actuators convert energy in mechatronics systems and the magnetic circuit seems to be the best medium for such a conversion (White and Woodson 1959). Therefore, the magnetic sensors and electromechanical actuators, with electromagnetic circuits that are electronically controllable, such as stepper motors, magnetic sensors, rotary actuators, linear solenoids, and other special devices with smart materials chosen for and described in this book, are critical components of mechatronic systems (Delphi 2002). This book discusses several families of modern electromagnetic and electromechanical devices in industrial applications and is devised to guide the reader in analysis and design optimization (Baumann et al. 2000, Bishop 2002, Box et al. 1969, Dąabrowski 1977, Fletcher 1987, Gieras and Wing 1994, Kuester et al. 1973, Navarra 1990, Pawlak 1989, Piron et al. 1999, Yoon et al. 1999). The presentation of prototypes and test results along with their analyses should allow for a better understanding of the progression from concept to mass production.

The first part of this chapter categorizes and describes several key families of electromechanical and electromagnetic devices utilized in mechatronic applications. With a focus on variable reluctance (VR) sensors, it describes and categorizes different types of magnetic sensors, linear and latching solenoids, stepper motors, and different types of rotary actuators (Pawlak et al. 1997, Pawlak 1996). Special magnetic devices also are introduced, including devices with smart materials with an emphasis on biomedical applications.

Because of their simplicity, low cost, controllability, and high performance, modern electromechanical and electromagnetic sensors and actuators are finding increasing use in industrial applications (Aftonin et al. 1999, Ellis and Collins 1980, Hanitsch 1994). Proper selection of magnetic materials is a key element in electromagnetic-circuit design. Because of this, both soft and hard magnetic materials are described in the second part of this chapter (Carpenter 1989, Daido 2003, Furlani 2001, Hitachi 1999, Kasai 1992). A review of soft and hard magnetic materials includes a recommendation for different applications (Dąabrowski 1980, Gieras and Wing 2002, Glinka 1995, Macoit 1999, Pawlak et al. 1999, Pawlak 2000a, Pawlak 1996, Rashidi 1982). New advancements in high-energy magnets are indicated; however, all of the applications discussed are based on commercially available magnetic materials. Furthermore, the magnetic material manufacturing technologies that should help the reader understand both the advantages and the magnetic material limitations are also discussed in this chapter.

1.1 Classification of Sensors and Actuators

The electromechanical and electromagnetic sensors and actuators such as stepper motors, sensors, rotary actuators, linear solenoids, which are electronically controllable in mechatronic systems, and other special devices with smart materials, are described and categorized in this chapter.

1.1.1 Magnetic Sensors

The magnetic sensors that are most commonly used in mechatronics systems today are VR and solid-state sensors [Hall-effect devices and magnetoresistive (MR)]. They are quickly making their way to the world market (Foster 1988, Ohshima and Akiyama 1989a, Ohshima and Akiyama 1989b, Podeswa and Lachman 1989). Over the last 10 years, the number of sensors installed in the average automobile has risen from several up to the current 20. It is expected to exceed 50 units in the near future. Worldwide, the automotive sensor market is valued at $5 billion and is expected to continue growing at an annual average rate of about 7%. Common applications for magnetic sensors include ignition timing, power sensing, valve position, current sensing, linear or rotary motion detection, speed sensing, length measurement, flow sensing, revolutions per minute (rpm) sensing, security systems, and more. Magnetic sensors are generally used to provide speed, timing, or synchronization data to a display (or control circuitry) in the form of a pulse train. Therefore, sensors for rpm and speed measurement, the two most popular applications, can be found in almost any market:

1. rpm measurement on engines for aircraft, automobiles, boats, buses, agricultural equipment, trucks, rail vehicles, as well as on motors for precision camera, tape recording and motion picture equipment, drills, grinders, lathes, automatic screw machines, etc.
2. speed measurement on processes for food, textile, woodworking, paper, printing, tobacco, and pharmaceutical industry machinery, for pumps, blowers, mixers, exhaust and ventilating fans, electric motors, and generators

Completely self-powered, VR magnetic sensors are simple, robust devices that do not require an external voltage source for operation (Pawlak et al. 1991d). They feature non-contact, error-free conversion of actuator speed to output frequency, as well as simple installation, with no moving parts. They are also usable over a wide speed range and adaptable to a wide variety of configurations. These properties have led to widespread utilization in a number of industries. As a result, VR sensors have become known by many use-related names such as magnetic pickups, speed sensors, motion sensors, pulse generators, variable reluctance sensors, frequency generators, transducers, magnetic probes, timing probes, monopoles, and pickoffs.

The drawback of VR sensors is that they generate a signal proportional to the magnetic field’s rate of change. Therefore, the signal strength decreases with decreasing speed and, below a certain flux change rate, the signal disappears into the noise. At high-frequency magnetic fields, the excess output voltage of the coil also causes problems for circuit designers. The generated voltage for VR sensors is up to 4000 V, for air gaps from 0.25 × 10^–3 to 3.0 × 10^–3 m with coils of resistance ranging from 200 to 4000 Ω over the wide range of temperatures from –40 to +165°C.

Analog VR sensors are passive sensors and do not require any external power source. Such a sensor generates a typically sinusoidal-like output voltage proportional to the speed of the exciter wheel. A signal level is a function of the air gap between the sensor and a toothed exciter wheel. Digital output VR speed sensors produce a digital (square wave) pulse that is directly proportional to exciter-wheel speed. The active solid-state signal conditioning integral with the sensor converts the analog VR output to digital pulses. The exciter-wheel speed sensing range is from 0.5 m/s to 40 m/s at frequencies up to 50,000 Hz.

In most applications, it is sufficient to have one voltage output; however, when speed sensor redundancy is required, multiple coil configurations are recommended. Instead of using two separate single coil sensors, multiple coil sensors accommodate redundancy needs while minimizing system costs and weight. Sensor coil options include single, dual, triple, or quad coil configurations for both redundancy and multiple readout needs, i.e., two coils for redundant speed detection and a third independent coil for ground trim, cockpit readout, etc. For multiple coil applications, output voltages for redundant applications are maintained in the event of a sensor or system fault, such as a short in the sensor harness or associated electronics, while maintaining speed detection integrity.

Neither the Hall-effect nor the magnetoresistive (MR) sensors can generate a signal voltage on their own and must have an external power source. Therefore, they are called active sensors. Solid-state sensors produce either a digital or an analog output. Digital output sensors are in one of two states — OFF or ON. Analog sensors provide a continuous voltage output, which increases with the strength of the magnetic field. There are three types of digital sensors: bipolar, unipolar, and omnipolar. Bipolar sensors require a positive magnetic field strength (south pole) to operate and a negative one (north pole) to release. Omnipolar sensors operate with either north or south poles. Unipolar sensors require a single magnetic pole (south pole) to operate; the sensor is released when the pole is removed. Analog sensors operate in proximity of either magnetic pole (Rowley and Stolfus 1990).

Hall-effect sensors are zero speed, noncontact sensors that can provide constant amplitude output over typical target speed ranges from 0 Hz to 50 kHz and even up to 100 kHz with air gaps up to 3.0 × 10^–3 m. Hall-effect circuitry measures speed accurately to true zero, direction of rotation or travel, and true angular position of gear. Hall-effect devices generate a very small raw signal because of low field sensitivities (0.5 to 5.0 mV/100 Oe applied field) and the device performance is strongly temperature dependent. Hall-effect sensors feature true zero speed sensing, a wide operating voltage range from 5.0 to 24.0 V, an open collector output with sinking currents to 35 mA, and an operating temperature range up to 150°C.

Giant magnetoresistive (GMR) metal multilayer sensors, which have recently been introduced, offer improvements over galvanometric MR sensors. A new passive solid-state magnetic (PSSM) sensor technology is based on a combination of two phenomena: the magnetostrictive effect and the piezoelectric effect. In response to a magnetic field, the magnetostrictive component imparts a strain on the piezoelectric element that in turn produces an electrical output signal of the PSSM sensor. It has the potential to replace existing sensors, provided that the technology is cost-effective in mass production and would work in the harsh environment of the final product. These sensors combine the advantages of the miniature size of Hall sensors and the passive nature of VR coil devices because the PSSM sensors consume no electrical power. Both solid-state and VR sensors are described in Chapter 2.

1.1.2 Linear and Latching Solenoid Actuators

Solenoid actuators are common industrial components used in almost every industrial motion control (Boldea and Nasar 2001). Solenoids can be found in applications that require a pinch, lock, divert, move, latch, or kicking type of functionality in a variety of industries, such as factory automation, material handling, transportation, automotive, food processing, medical equipment, agricultural equipment, vending machines, laundry equipment, construction equipment, marine, space, and aircraft. In addition, solenoid actuators are widely used in consumer markets.

A solenoid consists of a coil with magnetic wire wound on a bobbin with a moving armature and a return spring encapsulated within the housing. Depending on an armature’s shape, solenoids can be categorized as plunger, disk, ball, or conical types. When electricity is applied to the coil, the resulting magnetic field attracts the armature and pulls it into the solenoid body against an armature stop, contracting a return spring. When electricity is removed, the solenoid plunger is allowed to return to its original position due to a return spring or gravity. Solenoids are typically classified as alternating current (AC) or direct current (DC), linear or rotary, or on-off vs. variable positioning. A linear solenoid can be found in either an open frame solenoid configuration, which is used for lower-cost, less-efficient applications, or a tubular solenoid, which is most often used for longer-life, higher-force applications.

Linear solenoids convert electrical energy into mechanical work via a plunger with an axial stroke in either a push or pull action. The electromotive force (EMF) is supplied by the current applied to the coil and is limited by the heat dissipation capacity of the coil. The duty cycle, or the percentage of time that the solenoid is powered, is therefore a crucial factor in solenoid selection; the less time a solenoid needs to be powered, the more time it has to cool, and thus it can be used with a higher rated current, providing more force. The same solenoid design can have widely varying force ratings associated with different duty cycles. Continuous duty solenoids are rated for a 100% duty cycle. In general, this duty cycle will have the lowest force ratings.

Industrial work solenoids can be designed to accept the attachment of the load to the pulling or pushing end of the plunger. For some applications, the plunger assembly is designed to accept load attachments at both ends. The method of connecting the load to the industrial work solenoid must be developed with the consideration that side loads will be detrimental to solenoid life if not properly accounted for. Furthermore, if the installation causes a binding condition anywhere within th...