Application of DSP in Motor Speed ​​Measurement

In the precision control of the motor, the speed measuring unit is very important. The higher the resolution of the unit, the faster the reaction is, the better the control of the motor is. DSP chips have low power consumption and short instruction execution cycles, usually in the ns order, which greatly improves the controller's real-time control capability. TI's TMS320 series DSP architecture is designed for real-time signal processing and will be processed in real time. The capability and control peripheral functions are all suitable for use in a control system. The TVS320LF2407A of this series is used as an example to introduce its application in motor speed measurement.

2 Quadrature Encoded Pulse Electronics (QEP) Overview Each EV module has a quadrature encoded pulse circuit. Using this circuit, quadrature encoded pulses can be input on two corresponding pins. This circuit can be used to connect the optoelectronic encoder to obtain information such as position and speed of the rotary machine, but note that the capture function on the corresponding pin must be disabled at this time.

The time base of the quadrature coded pulse circuit can be provided by the general-purpose timer 2 (or the general-purpose timer 4, EVB module), the general-purpose timer must be set to the direction increase/decrease mode, and the quadrature coded pulse circuit is used as the clock source.

Orthogonal coded pulses are pulses that change in frequency and are orthogonal (90° out of phase). They are generated by an optical encoder on the motor shaft. The principle is 圄1. The code wheel is on the motor shaft and has many empty slots. It can transmit light. When the motor drives the encoder disk to rotate, if the light emitted by the LED is blocked by the photoelectric sensor behind the JP, it will not receive a signal. Then the photoelectric sensor will send out a low pulse, ie, 0” if the rotation position. Just so that the light source can pass through the slot, when the photoelectric sensor senses the signal, it sends out a high level pulse, that is "1". If there are two adjacent light emitting diodes, then there will be two pulses.

The direction detection logic of the quadrature code pulse circuit determines which of the two pulse trains is the leader sequence, and then it generates the direction signal as the count direction input of the general purpose timer. Both edges of the two orthogonal input pulses of the two columns are positive. The cross-numeral encoding circuit counts, so the generated clock frequency is 4 times each input sequence, and this clock is used as the input clock of the general-purpose timer 2 or 4.

圄 2 gives the CLRCINTM; open total interrupt 4 Conclusion Through the above analysis, we have obtained a method for measuring the motor speed and the mechanical angle position using a DSP, but this method is affected by the sampling time interval and the actual speed of the motor. Adjust these parameters in combination with these influencing factors in the measurement. For example, for the motor with too low speed, the sampling time should be increased. For the motor with too fast speed, the sampling time can be reduced, but the time should be