openmv中云台中pid函数有一点看不懂，请求指点
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openmv中云台中pid函数中，有一处“output += error * self._kp ”，self._kp的值一直为零，那么output的值也一直为零，此时pid函数的意义何在？我实在看不懂，请求指点
from pyb import millis from math import pi, isnan class PID: _kp = _ki = _kd = _integrator = _imax = 0 _last_error = _last_derivative = _last_t = 0 #定义私有属性 _RC = 1/(2 * pi * 20) def __init__(self, p=0, i=0, d=0, imax=0): #前后双下划线，魔法属性 self._kp = float(p) self._ki = float(i) self._kd = float(d) self._imax = abs(imax) self._last_derivative = float('nan') #最常见的计算有 无穷大 减 无穷大 结果为 nan def get_pid(self, error, scaler): tnow = millis() #插件重置后，返回毫秒数。 dt = tnow - self._last_t #这次时间与上次时间的差 output = 0 if self._last_t == 0 or dt > 1000: dt = 0 self.reset_I() self._last_t = tnow delta_time = float(dt) / float(1000) output += error * self._kp #self.kp=0,output=0？ if abs(self._kd) > 0 and dt > 0: if isnan(self._last_derivative): derivative = 0 self._last_derivative = 0 else: derivative = (error - self._last_error) / delta_time derivative = self._last_derivative + \ ((delta_time / (self._RC + delta_time)) * \ (derivative - self._last_derivative)) self._last_error = error self._last_derivative = derivative output += self._kd * derivative output *= scaler if abs(self._ki) > 0 and dt > 0: self._integrator += (error * self._ki) * scaler * delta_time if self._integrator < -self._imax: self._integrator = -self._imax elif self._integrator > self._imax: self._integrator = self._imax output += self._integrator return output def reset_I(self): self._integrator = 0 self._last_derivative = float('nan') 