A good working knowledge of electronics has four distinct elements:
• knowledge of the basic physical laws that apply to the operation of electronic devices, including basic device laws
• knowledge of circuit analysis techniques, i.e., the mathematical techniques used to understand the operation of circuits (Kirchhoff’s Voltage and Current Law)
• knowledge of the state of the art in electronic components in order to decide how to proceed with a particular design and what parts to use
• mastery of the vocabulary of electronics which is essential for reading the electronics literature
Digital Logic Electronics
The goal is to investigate the application of digital logic components to safety applications and glue logic.
Modern industry and the military are reluctant to use microcomputers to perform the safety functions for their products. Anyone who has had a program hang up and have to reboot a computer can understand the concern. Also, safety regulatory agencies such as Underwriters Laboratories (UL), a private company and the American National Standards Institute (ANSI) a non-profit organization in the United States and safety agencies in Canada (CSA - Canadian Standards Association) and Europe insist that safety functions be performed by “hard” logic. Only then will they certify that the product meets the required safety operation. In Europe, products need to show the CE mark for safety. CE has no meaning as an abbreviation but may have originally stood for Conformité Européenne (French for European Conformity). In the United States, many customers want to buy products that have a UL symbol.
Occasionally, a simple logic circuit can replace a large amount of code in the microcomputer. In these cases, it is cost effective to build the circuit and perhaps use a lower cost microcomputer with a smaller memory size. Another possible application of glue logic is to increase the number of outputs available from the microcomputer. For example, the product may require the microcomputer to control the function four digital outputs. Thus the user would need to use four output pins on the microcomputer. An alternative would be to use one or two output pins on the microcomputer to control the four functions by designing a digital logic circuit to produce the four required functions using the one or two signals from the microcomputer. In these instances, the logic circuit is essentially the glue which attaches the microcomputer to the application.
The goal is to provide an understanding of these elements of analog electronics as they relate to mechatronic system design.
Passive components: Resistors, Capacitors, Inductors, DC / AC Circuits, RC (Filter) Circuits, Impedance, Loading Effects
• Understand the three most fundamental passive electronic components, the resistor, capacitor and inductor which together comprise the essential building blocks of both analog and digital circuits. Kirchhoff’s laws provide the means of analyzing and constructing analog circuits using these components.
• Examine some basic circuits: voltage dividers, RC filters and RLC filters (2nd order filters) and learn about input / output impedance and loading effects.
Active Analog Electronics. Operational Amplifiers (OpAmps), Active Lead and Lag Circuits, Analog Filters and Buffers
• Understand the most versatile analog integrated circuit (IC), the operational amplifier (OpAmp). OpAmps are used as a basic building block for a wide variety of analog signal processing applications. In control applications, OpAmps are used as compensators for the feedback loop.
• Become familiar with active electronic circuits used for controllers and active filters. Construct active lead and lag controllers and compare the performance to the passive lead and lag controllers. Construct active high-pass and low-pass filters and compare their performance to the passive versions.
Use of analog electronics to control a fundamentally unstable system: Electromagnetic Levitation (Mag Lev)
• Use two of the OpAmp circuits from the previous part to form the control compensator for an electromagnetic levitation (Mag Lev) system. OpAmps are an effective means of providing continuous feedback control for mechatronic systems. While most mechatronic systems would use a microcomputer for digital control of systems, continuous (or analog) control often has many advantages. Modern OpAmps are low cost and have many control system performance advantages which cannot be achieved with microcomputers.
• Control of electromagnetic levitation is not simple and the system requires several adjustments before levitation is achieved. The system dynamics are both nonlinear and unstable. Levitation cannot be achieved with only permanent magnets; it requires active feedback control. The compensator circuit provides both phase lead and feedback gain to make the active feedback control stable. While both phase lead and gain can be provided with one OpAmp, two OpAmps are used to allow for independent adjustment of the gain.
Digital Input/Output System (Solenoid)
Feedback control involves the measuring of a sensor signal and deriving an input to the system to produce a required response in real time. While feedback control often involves the measurement and use of continuous (analog) signals, a very large number of embedded control applications require simply measuring a discrete (digital) source such as a switch and turning a device on or off.
The microcomputer is a very effective device for sophisticated on/off control applications. While some microcomputers have A/D converter inputs to read analog signals and pulse width modulated (PWM) outputs to produce analog signals, all have digital (on/off) input and output ports for interfacing to the system. Programming the microcomputer involves setting the properties on the port for the desired operation (reading or writing) and setting internal registers for the desired control. Considerations for turning power devices on or off can involve simple timing (open loop) or the state of digital sensors (closed loop feedback).
The goal is to provide an understanding of the issues and techniques for on/off control using an embedded microcontroller.
Stepper motors are often used for controlling the angular displacement of a load, or the linear displacement via a mechanism. They are the preferred technology for position control systems such as those in machine tools.
The goal is to provide an understanding of the issues and techniques for stepper motor control using an embedded microcomputer.
DC Motor Control
DC (Direct Current) motors are used for precision velocity control.
A DC motor converts direct-current (DC) electrical energy into rotational mechanical energy. A major fraction of the torque generated by the rotor (armature) of the motor is available to drive an external load. DC motors are widely used in numerous control applications because of features such as high torque, speed controllability over a wide range, portability, well-behaved speed-torque characteristics, and adaptability to various types of control methods. DC motors are typically classified as either integral-horsepower motors (> 1 hp) or fractional-horsepower motors (< 1 hp). Within the class of fractional-horsepower motors, a distinction can be made between those that generate the magnetic field with field windings (an electromagnet) and those that use permanent magnets. In heavy industrial DC motor products, the magnetic field is usually generated by field windings, while DC motors used in instruments, business machines or consumer products normally have a permanent magnet field.