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图中所示的测速电路仅需一片IC(除计数器外),其精度可达到以前介绍的三片IC的电路精度并且消除了游移现象。标准的轴旋转码盘A和B通道产生与轴旋转同频的方波信号。A的相位超前或滞后于B90°,其取决于旋转方向。为了获得最大分辨率,测速电路必须计数A和B信号每一次状态变化,输入的每一次变化在IC_(1A)输出端产生一次状态变化,并在IC_(1c)的输出端产生1μs的负跳变,时钟脉冲的正跳变沿使计数器加或减计数。加或减由轴旋转方向确定。一般选择R_1C_1时间常数大约是R_2C_2乘积的二倍,以保证与时钟脉冲正沿有关的加/减计数信号有一适当的建立时间和保持时间。IC_(1c)产生与IC_(1A)正或负变化相同周期的时钟脉冲,满足了定时要求。
The speed circuit shown in the figure requires only one IC, with the exception of the counter, which is accurate to the circuit accuracy of the three ICs described earlier and eliminates wandering. Standard axis rotary encoder A and B channels produce a square wave signal of the same frequency as the axis rotates. The phase of A leads or lags B90 °, depending on the direction of rotation. In order to get the maximum resolution, the speed-measuring circuit must count each state change of the A and B signals. Each change in input produces a state change at the IC_ (1A) output and a 1-μs negative transition at the output of IC_ (1c) The positive edge of the clock pulse increments or decrements the counter. Plus or minus is determined by the direction of shaft rotation. The general choice of R_1C_1 is about twice the time constant of the R_2C_2 product to ensure that the up / down count signal associated with the positive edge of the clock pulse has an appropriate settling time and hold time. IC_ (1c) generates a clock of the same period as the positive or negative change in IC_ (1A), meeting the timing requirements.