Position Control System using a Microprocessor-Based Controller

Consider the following figure illustrating a position control system employing a microprocessor-based controller with parallel ports:

The system above has one output port and three input ports (each port has its own address). The output port is partitioned: Six bits are converted in a Digital Analog Converter (DAC) to provide the analog motor-drive signal, the seventh bit specifies motor direction (1= clockwise, 0 = counter clockwise), and the eighth bit turns on an audio alarm if some emergency circumstance is detected. The first input port inputs the set-point data, the second inputs the ADC data from the sensor, and the third inputs various 1-bit logical variables. In this case, the system has three front-panel switches as well as two limit switches. The limit switches are used as a “back-up” to detect it if the load has gone out of its designated range.

Related: Microprocessors in Mechatronic Systems

Operation of the Microprocessor-based Position Control System

The controller inputs the data from port 03 to establish if the start (or stop) button has been pressed. If the start button has been pressed, then the set point is read in from port 01 and the digitized sensor data is read in from the port 02 and based on its control scheme, the controller outputs to port 00 a binary word representing the motor-control voltage. This digital data is converted to an analog voltage with the DAC. This entire sequence is repeated over and over until the stop button is pushed.

Advantages of Digital, Microprocessor Design in Control Systems

Some of the advantages of microprocessor-based control systems design include:

• Low-level signals from sensors, once converted to digital, can be transmitted long distances virtually error free.
• A microprocessor can easily handle complex calculations and control strategies.
• Long-term memory is available to keep track of parameters in slow moving systems.
• Changing the control strategy is easy by loading in a new program; no hardware changes are required.
• Microprocessor-based controllers are easily connected to the computer network within organization. This allows designers to enter program changes and read current systems status from their desk terminals.

Also Read: Microcontrollers