dc.description.abstract | The subject in this thesis is to design the circuit for detecting motor speed without velocity sensor in treadmill driver system. When a DC motor is functioning, the current ripples in the motor are generated while the carbon brush contacts with the commutator segments. Furthermore, the voltage signals of the ripples can be extracted straightforwardly from the counter-electromotive force in a DC motor. After signal processing and frequency computing, the signal frequency and the motor speed are obtained consequently. The next step is to implement the closed loop velocity control system. Because of the motor current is proportional to the load, the current signals provide information about the runner’s gait events just like a stride, step, foot-contact and foot-off events.
The system includes motor speed controller, detector and controller of the treadmill belt’s gradient, interface between LCD panel and microcontroller, protector for over current or abnormal voltage and function select keyboard. All these components are implemented using the PIC16F877 microcontroller.
The experimental results demonstrate that the rotation speed measurement of the system circuit is extremely close to that of the rotor encoder, and the closed loop control system is also well performed. Compared with the traditional devices, the system supplies a simpler method to analyze the variation of motor loading and the runner’s gait events.
The control system is directly connected to the power line of the DC motor to detect and control the motor speed without velocity sensor or extra mechanism. Therefore, the proposed system is absolutely practical for industrial and commercial applications. | en_US |