Sensors for Mechatronics

Paul P.L. Regtien, Edwin Dertien

• Publisher: Elsevier
• Year: 2018
• ISBN:
  9780128138113
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Sensors for Mechatronics, Second Edition, offers an overview of the sensors and sensor systems required and applied in mechatronics. Emphasis lies on the physical background of the operating principles that is illustrated with examples of commercially available sensors and recent developments. Chapters discuss the general aspects of sensors, with a special section on quantities, notations and relations. In addition, the book includes a section devoted to sensor errors and error minimization that apply to most of the sensors discussed. Each subsequent chapter deals with one class of sensors, pursuing a classification according to physical principles rather than measurands.

Categories discussed include resistive, capacitive, inductive and magnetic, optical, piezoelectric and acoustic sensors. For each category of sensors, a number of applications is given. Where appropriate, a section is added on the interfacing of the sensor.

• Presents a fully revised, updated edition that focuses on industrial applications
• Provides comprehensive coverage of a wide variety of sensor concepts and basic measurement configurations
• Written by a recognized expert in the field with extensive experience in industry and teaching
• Suitable for practicing engineers and those wanting to learn more about sensors in mechatronics

1

Introduction

Abstract

This introductory chapter gives a general view on sensors. In the first section, the sensor’s functionality, sensor nomenclature, and global properties are presented, as a prelude to a more in-depth discussion about sensor performance and operation principles in subsequent chapters. According to the amount of information the output signal may contain, three categories of sensor are distinguished and each briefly discussed: binary, analogue, and image sensors. The latter category comprises optical, acoustic, and tactile image sensors. The second section presents a general approach to the selection process of sensors for a specified application. The last section introduces a platform for sensor architectures in an embedded environment and serves as the basis for the specific embedded sensing solutions discussed in the ensuing chapters.

Keywords

Transducer; sensor; actuator; proximity sensor; reed switch; imaging; sensor nomenclature; embedded sensing

Worldwide, sensor development is a fast growing discipline. Today’s sensor market offers thousands of sensor types, for almost every measurable quantity, for a broad area of applications, and with a wide diversity in quality. Many research groups are active in the sensor field, exploring new technologies, investigating new principles and structures, aiming at reduced size and price, at the same or even better performance.

System engineers have to select the proper sensors for their design, from an overwhelming volume of sensor devices and associated equipment. A well-motivated choice requires thorough knowledge of what is available on the market, and a good insight in current sensor research to be able to anticipate forthcoming sensor solutions.

This introductory chapter gives a general view on sensors—their functionality, the nomenclature, and global properties—as a prelude to a more in-depth discussion about sensor performance and operation principles.

1.1 Sensors in mechatronics

1.1.1 Definitions

A transducer is an essential part of any information processing system that operates in more than one physical domain. These domains are characterized by the type of quantity that provides the carrier of the relevant information. Examples are the optical, electrical, magnetic, thermal, and mechanical domains. A transducer is that part of a measurement system that converts information about a measurand from one domain to another, ideally without information loss.

A transducer has at least one input and one output. In measuring instruments, where information processing is performed by electrical signals, either the output or the input is of electrical nature (voltage, current, resistance, capacitance, and so on), whereas the other is a nonelectrical signal (displacement, temperature, elasticity, and so on). A transducer with a nonelectrical input is an input transducer, intended to convert a nonelectrical quantity into an electrical signal in order to measure that quantity. A transducer with a nonelectrical output is called an output transducer, intended to convert an electrical signal into a nonelectrical quantity in order to control that quantity. So, a more explicit definition of a transducer is an electrical device that converts one form of energy into another, with the intention of preserving information.

According to common terminology, these transducers are also called sensor and actuator, respectively (Fig. 1.1). So, a sensor is an input transducer and an actuator is an output transducer. It should be noted, however, that this terminology is not standardized. In literature other definitions are found. Some authors make an explicit difference between a sensor and a (input) transducer, stressing a distinction between the element that performs the physical conversion and the complete device—for instance, a strain gauge (the transducer) and a load cell (the sensor) with one or more strain gauges and an elastic element.

Figure 1.1 Sensors and actuators.

Attempts to standardize terminology in the field of metrology have resulted in the Vocabulaire International de Métrologie (VIM) [1]. According to this document a transducer is a device, used in measurement, that provides an output quantity having a specified relation to the input quantity. The same document defines a sensor as the element of a measuring system that is directly affected by a phenomenon, body, or substance carrying a quantity to be measured.

Modern sensors not only contain the converting element but also part of the signal processing (analogue processing such as amplification and filtering, AD conversion, and digital processing). Many of such sensors have the electronics integrated with the transducer part onto a single chip. Present-day sensors may have a bus-compatible output, implying full signal conditioning on board, or include transmission electronics within the device, for instance, for biomedical applications.

Signal conditioning may be included:

• • to protect the sensor from being loaded or to reduce loading errors;
• • to match the sensor output range to the input range of the analog to digital converter (ADC);
• • to enhance the S/N (signal-to-noise ratio) prior to further signal processing;
• • to generate a digital, bus-compatible electrical output; or
• • to transmit measurement data for wireless applications.

In conclusion, the boundaries between sensor and transducer as proclaimed in many sensor textbooks are disappearing or losing their usefulness: the user buys and applies the sensor system as a single device, with a nonelectrical input and an electrical output (e.g., an analogue signal, a microprocessor compatible digital signal, or a radio signal).

1.1.2 Sensor development

Sensors provide the essential information about the state of a (mechatronic) system and its environment. This information is used to execute prescribed tasks, to adapt the system properties or operation to the (changing) environment or to increase the accuracy of the actions to be performed.

Sensors play an important role not only in mechatronics but also in many other areas. They are widely applied nowadays in all kind of industrial products and systems. A few examples are as follows:

• • Consumer electronics
• • Household products
• • Public transport, automotive
• • Process industry
• • Manufacturing, production
• • Agriculture and breeding industry
• • Medical instruments

and many other areas where the introduction of sensors has increased dramatically the performance of instruments, machines, and products.

The world sensor market is still growing substantially. The worldwide sensor market offers over 100,000 different types of sensors. This figure not only illustrates the wide range of sensor use but also the fact that selecting the right sensor for a particular application is not a trivial task. Reasons for the increasing interest in sensors are as follows:

• • Reduced prices: the price of sensors not only depends on the technology but also on production volume. Today, the price of a sensor runs from several ten thousands of euros for single pieces down to a few eurocents for a 100 million volume.
• • Miniaturization: the IC-compatible technology and progress in micromachining technology are responsible for this trend [2–4]. Pressure sensors belong to the first candidates for realization in silicon (early 1960s). Micro-ElectroMechanical Systems (MEMS) are gradually taking over many traditionally designed mechanical sensors [5–7]. Nowadays, solid-state sensors (in silicon or compatible technology) for almost every quantity are available, and there is still room for innovation in this area [8,9].
• • Smart sensing: the same technology allows the integration of signal processing and sensing functions on a single chip. Special technology permits the processing of both analogue and digital signals (“mixed signals”), resulting in sensor modules with (microprocessor compatible) digital output.

Popular MEMS sensors are accelerometers and gyroscopes. A MEMS accelerometer can be made completely out of silicon, using micromachining technology. The seismic mass is connected to the substrate by thin, flexible beams, acting as a spring. The movement of the mass can be measured by, for instance, integrated piezoresistors positioned on the beam at a location with maximum deformation (Chapter 4) or by a capacitive method (Chapter 5).

In mechatronics, mainly sensors for the measurement of mechanical quantities are encountered. The most frequent sensors are for displacement (position) and force (pressure), but many other sensor types can be found in a mechatronic system.

Many sensors are commercially available and can be added to or integrated into a mechatronic system. This approach is preferred for systems with relatively simple tasks and operating in a well-defined environment, as commonly encountered in industrial applications. However, for more versatile tasks and specific applicatio...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface for the second edition
• Preface for the first edition
• 1. Introduction
• 2. Sensor fundamentals
• 3. Uncertainty aspects
• 4. Resistive sensors
• 5. Capacitive sensors
• 6. Inductive and magnetic sensors
• 7. Optical sensors
• 8. Piezoelectric sensors
• 9. Acoustic sensors
• Appendix A. Symbols and notations
• Appendix B. Relations between quantities
• Appendix C. Basic interface circuits
• Appendix D. Practical guideline and code examples
• Index