chapt8 - ME 4204 Mechatronic Systems Lesson Objectives...

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1 Interfacing 1 2008/09 Semester 1 Lecture 7 ME 4204 Mechatronic Systems 2 Lesson Objectives ± Interfacing Introduction ± Signal Conditioning ± A/D and D/A Signal Conversion 3 Introduction ± Interface refers to any device connecting between the peripherals (sensors, actuators, keyboard, etc.) and controller in a mechatronic system. ± There could be inputs from sensors, switches and keyboards, outputs to display and actuators. The simplest interface is a wire for signal transmission . However, the interface used in mechatronic systems often contains signal conditioning , signal conversion , device protection circuitry , etc. ± Interface is used because it is not normally possible to connect all system devices directly due to a lack of compatibility in signal forms and levels. Controller Peripherals Interfaces 4 Example: Computer-based Numerical Control (CNC) milling machine ± A schematic block diagram for the closed-loop control system: Sensors (Tooling Head Position, Speed, Torque) Analog Signal Conditioning (Noise filtering, amplification , etc.) Physical Environment (Cutter tools) Actuators (XYZ-Axis Motors, Spindle Motors, etc.) CNC Controller (or Computer) Analog Signal Conditioning ( amplification , etc.) Analog/ Digital Converter Digital/ Analog Converter Interface Interface
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5 Signal Classification ± An analog or analogue signal is a continuous signal for which the time varying variable is a representation of some time varying quantity. ± A digital signal is a series of discrete number of levels with respect to time and are represented as binary digits or bits . Signals Analog Digital Non-periodic Periodic Time Domain Frequency Domain t t t f 6 Interfacing Processes ± Circuit Protection ± To prevent damage to next element, e.g. microprocessor ± Signal Conversion ± Getting the signal into right type , e.g. resistance change of a strain gauge converted into voltage change, or making the signal digital or analog. ± Signal Amplification ± Getting the level of the signal right, e.g. the signal from a sensor may be just a few millivolts. If the signal is to be fed into a microprocessor then it needs to be made larger volts. ± Noise Suppression ± Eliminating or reducing noise , e.g. filters may be used to eliminate mains noise from a signal. ± Signal Manipulation ± e.g. making the signals from some non-linear sensors a linear function. 7 Protection Circuits ± There are many situations where the connection of a sensor to the next unit, e.g. a microprocessor, can lead to the possibility of damage due to high current or voltage. ± A high current can be protected by incorporating a series resistor in the input line to limit the current to an acceptable level and a fuse to break if the current exceed a safe level. ± High voltage and wrong polarity may be protected by the use of a Zener diode
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chapt8 - ME 4204 Mechatronic Systems Lesson Objectives...

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