| 摘要 |
A 2 phase BLDC motor is driven by a trapezoidal waveform. For one half of the motor rotation period T, the phase is driven by the trapezoidal waveform and for the other half period, the coil remains undriven. Accordingly, if the optimum slope duration is around 10% of the duration of the driven portion, then it is of the order of T/20. All up-down counter is operable to increment at a first frequency f 1 and to decrement at a second frequency f 2 . Incrementing operation is initiated at the start of the driven period of the waveform and stopped at the start of the down slope of the wavefrom (or, if desired at the start of the up slope of another (the other for a two coil system) output's driving waveform). Decrementing operation is initiated at the start of the down slope of the waveform and stopped at the end of the down slope (also the end of the driven period of the waveform). The ratio of frequencies f 1 :f 2 is used to measure the relative duration of the slope to the driven period and is selected to mirror the desired ratio of slope duration:driven period duration. If the ratio of frequencies f 1 :f 2 is equal to the ratio slope duration:driven period duration then the counter should register zero when stopped. If however the counter output is less than zero, it indicates that the slope duration is greater than the desired duration. Conversely, if the counter output is greater than zero, it indicates that the slope duration is less than the desired duration. As such, the output of the counter can be used to increment/decrement the control register of the waveform generator for the motor to vary the slope duration as required. |
