Mechatronics involves systems

system - a black box with inputs and outputs
example: motor

measurement system - a system that measures something
example: thermometer

control system - a system that controls its output to a particular value or sequence of values
example: central heating system (input = required temperature, output = actual temperature)

Components of a measurement system

1. sensor (e.g., thermocouple)
2. signal conditioner (e.g., amplifier)
3. display (e.g., pointer on a scale, or digital readout)

Two kinds of control systems

1. open loop system (e.g., furnace that is just turned on or off, volume control on a radio)

2. closed loop system, also called a feedback control system (e.g., thermostat controlled furnace)

Components of a closed-loop system

1. comparison element
produces error signal (= ref val. sig. - measured val. sig.)

2. control element
hardwired or programmable

3. correction element
may be a switch or valve; may be operated by an actuator

4. process element
the process being controlled

5. measurement element
produces the feedback signal


Example: thermostaticly controlled central heating system

Example: water level in a tank

Example: shaft speed control

* Potentiometer sets reference value
* differential amplifier = comparison and control elements
* amplified error signal is fed to motor (correction element)
* motor turns shaft (process)
* shaft has bevel gear to drive a second shaft that is mechanical input to a tachogenerator (measuring element)
* signal from tachogenerator feeds back to differential amplifier

Complex controllers:

1. sequential controllers
example: washing machine
inputs are clock and program
correction elements are pump, valve, heater, motor
process is the washing machine drum
outputs are water level, water temperature, drum speed and door status (open or closed) -- all of these are measured and fed back to control unit

In old machines, the control unit was cam-operated switches. Modern machines use microprocessors.

Many microcontrollers are programmed with one specific program. Programmable logic controllers are more flexible. Some microcontrollers are also reprogrammable. (Java grew out of this.)

2. microprocessor-based controllers

example: automatic camera
inputs: on-off switch, shutter button, battery test, range sensor, light sensor, lens position sensor
effectors: motors to advance film, set lens position, set aperture; solenoid actuators to open shutter, to close shutter; display of data in viewfinder

example: automobile engine management system
inputs: engine speed, crankshaft position, spark timing feedback, engine temperature, throttle position, mass air flow
outputs: spark timing, air-fuel mixture solenoid, fuel injection valve