In factories and large scale industries, it is required that the speed of the motor in operation, remains constant. It should not fall below or beyond the specified limit. Speed of a motor is given in rotations per minute or RPM. The RPM for industrial standard needs to be acute and precise. Hence a motion is required to maintain the precision. This project from Multyremotes.com is a closed loop control system which maintains a constant speed for a stepper motor. The speed of the motor is sensed and feedback to the controller. The controller then compares it with the set value and if deviation is found then it will either increase or decrease the speed of the motor.
The mechanical arrangement for the control consists of two wooden housings facing each other. The first wooden housing bears a laser source while the other is fitted with a LDR followed by a pulse generator (555 timer IC). Above the first housing is a stepper motor. A slotted wheel is fixed along the shaft of the motor which directly inhibits the laser light from falling on the light dependent resistor except at the slot. The stepper motor is driven by a motor driver which in turn is controlled by microcontroller89C51 (Main controller).
When the motor shaft rotates, the slotted wheel also rotates along with. During every rotation light from the laser source falls on LDR once which trigger the multivibrator to generate rectangular pulses. These pulses are fed to 89C2051 (auxiliary controller) that counts these pulses for calculated time and after counting final RPM it will send this final count serially to main controller. The main controller then compares the current rpm value to the set value. Both of these values are displayed on the LCD for user feedback. Finally, user gives instructions about increasing or decreasing the motor speed using push buttons. Hence a closed-loop control is obtained.