Tachless-motor-speed-controller

Description: This circuit is particularly applicable to digitally controlled systems in robotic and X-Y positioning applications. By operating from a 5-V logic supply, it eliminates the need for additional motor drive supplies. The tachless feedback mechanism saves both space and cost. The circuit senses the motor's back EMF to determine its speed. The difference between the actual speed and a set point is utilized to close a sampled loop around the motor, with an operational amplifier (A1) generating a pulse train. When A1's output is high, transistor Q1 is biased, allowing transistor Q3 to drive the motor's ungrounded terminal. As A1's output decreases, Q3 turns off, and the motor's back EMF becomes available after the inductive flyback ceases. During this period, the input of switch S1 is activated, and the 0.047-µF capacitor captures the value of the back EMF. Operational amplifier A2 compares this captured value with the set point, and the amplified difference adjusts A1's duty cycle, thereby controlling the motor speed.

The circuit operates on a closed-loop feedback mechanism that enhances the precision of motor control in robotic applications. The use of a 5-V logic supply simplifies the design by eliminating the need for additional power sources, which can lead to reduced complexity and cost. The tachless feedback approach is particularly advantageous as it utilizes the back EMF generated by the motor, allowing for real-time speed measurement without the need for external sensors, which can further minimize the physical footprint of the system.

In operation, when the output from operational amplifier A1 is high, it activates transistor Q1, which in turn biases transistor Q3. This action allows current to flow to the motor's ungrounded terminal, enabling motor operation. As the motor accelerates, it generates back EMF proportional to its speed. When A1's output decreases, indicating a reduction in the desired speed, transistor Q3 turns off, ceasing the power to the motor. The back EMF is then available for measurement after the inductive flyback period, which is when the motor's internal inductance generates a brief voltage spike as the current flow is interrupted.

At this point, switch S1 is engaged, and the 0.047-µF capacitor charges to the voltage level of the back EMF. This stored voltage is then compared to the predetermined set point by operational amplifier A2. The output from A2 represents the difference between the measured back EMF and the set point, which is amplified to provide a control signal back to A1. This feedback loop adjusts A1's duty cycle, effectively modulating the power delivered to the motor, thereby achieving precise control over its speed.

This circuit design exemplifies efficient motor control for applications requiring high accuracy and responsiveness, particularly in environments where space and cost are critical considerations. The integration of feedback mechanisms and the elimination of additional power supplies contribute to a streamlined and effective solution for modern robotic systems.This circuit is particularly applicable to digitally-controlled systems in robotic and X-Y positioning applications. By functioning from the 5-V logic supply, it eliminates additional motor-drive supplies. The tachless feedback saves additional space and cost. The circuit senses the motor"s back EMF to determine its speed. The difference between the speed and a set point is used to close a sampled loop around the motor. Al generates a pulse train. When Al"s output is high, Ql is biased, and Q3 drives the motor"s ungrounded terminal. When Al decreases, Q3 turns off and the motor"s back EMF appears after the inductive flyback ceases. During this period, Sl"s input is turned on, and the 0.047-I"F capacitor acquires the back EMF"s value.

A2 compares this value with the set point and the amplified difference (trace D) changes Al "s duty cycle, controlling the motor speed.