MBEYA UNIVERSITY OF SCIENCE AND TECHNOLOGY Lecture Summary on BASIC MECHATRONICS ENGINEERING NTA - 4 Mechatronics Engineering 2016 Page 1
INTRODUCTION TO MECHATRONICS Mechatronics is the field of study concerned with the design, selection, analysis, and control of systems that combine mechanical elements with electronic components, including computers and/or microcontrollers. Mechatronics topics involve elements from mechanical engineering, electrical engineering, and computer science, and the subject matter is directly related to advancements in computer technology. The term mechatronics was coined by Yasakawa Electric Company to refer to the use of electronics in mechanical control (i.e., mecha from mechanical engineering and tronics from electrical or electronic engineering). Auslander, et al. have defined mechatronics as the application of complex decision-making to the operation of physical systems. Figure 1. Typical components of a mechatronics system A mechatronic system has at its core a mechanical system which needs to be commanded or controlled. Such a system could be a vehicle braking system, a positioning table, an oven, or an assembly machine. The controller needs information about the state of the system. This information is obtained from variety of sensors, such as those that give proximity, velocity, temperature, or displacement information. In many cases, the signals produced by the sensors are not in a form ready to be read by the controller and need some signal conditioning operations performed on them. The conditioned, sensed signals are then converted to a digital form (if not already in that form) and presented to the controller. The controller is the mind of the mechatronic system, which processes user commands and sensed signals to generate command signals to be sent to the actuators in the system. The user commands are obtained from a variety of NTA - 4 Mechatronics Engineering 2016 Page 2
devices, including command buttons; graphical user interfaces (GUIs), touch screens, or pads. In some cases, the command signals are sent to the actuators without utilizing any feedback information from the sensors. This is called open-loop operation, and for it to work, this requires a good calibration between the input and output of the system with minimal disturbances. The more common mode of operation is the closed loop mode in which the command signals sent to the actuators utilize the feedback information from the sensors. This mode of operation does not require calibration information, and it is much better suited for handling disturbances and noise. In many cases, the command signals to the actuators are first converted from a digital to analog form. Amplifiers implemented in the form of drive circuits also can be used to amplify the command signals sent to the actuators. The actuator is the mechanism that converts signals into useful mechanical motion or action. The choice of the controller for the mechatronic system depends on many factors, including cost, size, ease of development, and transportability. Many mechatronic systems use personal computers (PCs) with data acquisition capabilities for implementation. Examples include control of manufacturing processes such as welding, cutting, and assembly. A significant number of controllers for a mechatronic system are implemented using a microcontroller unit (MCU), which is a single-chip device that includes a processor, memory, and input-output devices on the same chip. Microcontrollers often are used for control of many consumer devices, including toys, hand-held electronic devices, and vehicle safety systems. Control systems that use MCUs often are referred to as embedded control systems. The control system for a mechatronic system can be classified as either a discrete event control system or a feedback control system. In a discrete-event system, the controller controls the execution of a sequence of events, while in a feedback control system, the controller controls one or more variables using feedback sensors and feedback control laws. Almost all realistic systems involve a combination of the two. A mechatronic system integrates mechanical components, electronic components, and software implemented either on a PC or MCU to produce a flexible and intelligent system that performs the complex processing of signals and data. In many cases, a mechatronic system can be used to improve the performance of a system beyond what can be achieved using manual means. In some cases, a mechatronic system is the only means by which that system can operate. Modern society depends on mechatronic-based systems for its conveniences and luxurious standard of living. From intelligent appliances to safety features in cars (such as air bags and anti-lock brakes), mechatronic systems are widely used in NTA - 4 Mechatronics Engineering 2016 Page 3
everyday life. The availability of low-cost, compact, and powerful processors in the form of MCUs accelerated the widespread use of mechatronic systems. An example is the use of embedded controllers to control many of the devices in a vehicle. A list of such applications is shown in Table below. Examples of Mechatronic Systems Industrial Robots Robots, whether of the fixed type (such as industrial robots) or of the mobile type, are good examples of mechatronic systems. A robot is a mechanical device that can be programmed to perform a wide variety of applications. The main components of a robot system are the controller and the mechanical arm. The controller handles several operations, including the user interface, programming, and control of the arm. Figure 2. Industrial robot The mechanical arm consists of several mechanical links that are connected at joints. An actuator is used to drive each link, and each actuator has a feedback sensor to indicate the location of the link. A multi-link robot is a complicated device that requires coordination of the motion of the links. This job is done by the control software, which processes information from the desired motion of the arm, and the feedback sensors, which send commands to the actuators or the servomotors to perform the desired task. To enable a robot to handle variation in the environment NTA - 4 Mechatronics Engineering 2016 Page 4
in which it operates, additional sensors are normally used (such as vision and proximity). Scanner A scanner is a device that captures an image of a document and converts it into a format suitable for electronic storage. The main components of a scanner include the scanning head, the transport device, the controller, and the control software. Figure 3. Scanner The controller commands the transport device which carries the scanner head. The transport device uses a stepper motor and a system of gears and belts to move the scanning head in precise steps. After each step, the transport device stops, and a scan is sampled. The scanning head involves some form of a line camera that measures the reflectivity of a scanned line. The scanned line is brought to the scan sensor through a system of mirrors and lenses. The output of the scanning head is processed by the control software to create a map of the scanned document. This map is further analyzed to reveal all of the features in the document and to filter any noise signals from the captured data. The control software sequences the operation of the scanner and communicates with the PC. When the scanning job is completed, the scanned image is then transferred to a PC using a USB or a parallel-port connection. This mechatronic system involves all of the elements of a typical control system: sensor, actuator, and controller. It is also an example of a discrete-event system. Parking Gate A parking garage gate is another example of a mechatronic system that involves a number of elements. The system has an electric motor to raise and lower the gate arm. It also has a proximity sensor to prevent the gate from striking people and vehicles. In addition, it has a microcontroller in which software is used to run the gate in different operating modes. NTA - 4 Mechatronics Engineering 2016 Page 5
Figure 3. Parking gate Typically, a parking-garage gate operates as follows: The user presses a button to get a ticket or swipes a card in a card scanner. Once the ticket is picked up by the user or the card is validated, the gate arm rotates upward. The gate arm remains in a raised position until the vehicle has completely cleared the gate, at which point the gate drops down. The operation of each stage of this system is dependent on sensor feedback and timing information. The controller for this system cycles between the different operating stages each time a vehicle needs to enter the parking garage. Reference Fundamentals of Mechatronics, SI, Musa Jouaneh CHAPTER OBJECTIVES: When you have finished this chapter, you should be able to: Define/Explain what is a mechatronic system Explain the history of mechatronics List and describe components of a mechatronic system Give examples of real-world mechatronic systems Identify the role of mechatronics in technology advancement Explain the advantages and disadvantages of mechatronics Key terminologies: Computer, microcontroller, Signal, digital signal, analog signal, sensor, actuator, signal conditioning, user interface, processor, command, open loop, closed loop, memory, embedded control, software, robot, feedback, stepper motor, gear, belt drive, proximity sensor, input output device, amplifier, noise, disturbance, user interface, calibration, discrete event, sequential event. NTA - 4 Mechatronics Engineering 2016 Page 6