位置环增益调整.doc

1：准备 在调节位置环之前，一定首先调节伺服驱动器上速度环PID参数。本篇文章是在以下假设条件下完成的：速度环响应特性良好，电机双向都有一段安全运动距离。在调节位置环时，为了使增益参数准确，需要在带实际负载的情况下进行调节。下面是用来调节参数的程序，在控制器内执行。这段程序让电机在正负八分之一圈内来回旋转。 Intialise the axis for P Loop tuningBASE(0)UNITS=1DEFPOS(0)WAIT UNTIL OFFPOS=0counts_per_rev=4000 set speed to 3000 rpmSPEED=counts_per_rev*3000/60ACCEL=SPEED*1000DECEL=ACCELFE_LIMIT=counts_per_rev/2SERVO=ONWDOG=ONstepsize=INT(counts_per_rev/8)WHILE TRUETRIGGERWA(20)MOVE(stepsize)WA(500)MOVE(-stepsize)WA(480)WEND如果机械结果决定只能向一个方向运动。程序修改如下：stepsize=INT(counts_per_rev/8)WHILE TRUETRIGGERWA(20)MOVE(stepsize)WA(480)DEFPOS(0)WEND在运行程序之前，确定该轴当前运动状态为IDLE。打开轴参数和示波器。设置示波器观测参数为该轴的MPOS和DPOS，横轴时间参数为20msec。点击option，设置每格采样点数为10或20.设置示波器为程序触发。2： 调节P参数安全起见，P参数先给一个比较小的值，编码器如果是1000到1024线，最好从0.5调起，其他增益参数都设置为0运行程序，并触发示波器，响应曲线应该如下图所示：接下来一点一点的，小心的增加P参数，直到曲线显示如下图：如果曲线如下图所示，证明P参数过大了，此是应该适当减小。一般系统只用P参数就可以了，如果需要进一步减小跟随误差，可以用以下两种方法： 1），用P参数和VFF参数 2），用P,I,D,三个参数3，设置VFF参数设置VFF方法比较简单，有计算法和尝试法两种。在用前面讲过的方法设好P参数后，让电机在额定速度的30%到60%之间常速运动，逐渐加VFF参数，直到跟差减小到最小范围。设定好后，这个参数在其他速度下也是正确的。如果计算，按一下公式，12位DC（dac_scale=16):VFF_GAIN = (60 / motor_rpm_10V) * (1000 / encoder_pulses_per_rev) * 204816位DC：VFF_GAIN = (60 / motor_rpm_10V) * (1000 / encoder_pulses_per_rev) * 327684：设置I和D参数： 在设置I参数是，应加倍小心，以为I值一般很小就够了，一般可以从0.001开始调起。调到如下图所显示的状态： 超调相对只有P参数的时候要大，而且有多次震荡后才平稳。D参数可以削减震荡，D参数范围一般在8到20之间。下图显示的是PID参数调好后的运动状态：超调明显减小，运动很快进入稳定状态。OV参数和D参数起的作用大致相同，一般可以不设，如果要设的话，应为负值。附录：下面是手册上给出的各个参数的含义：Proportional GainDescription The proportional gain creates an output voltage, Op that is proportional to thefollowing error E.Op = Kp x EAxis parameter is called P_GAINSyntax: P_GAIN=0.8Note: All practical systems use proportional gain, many use this gain parameteralone.Integral gainDescription The Integral gain creates an output Oi that is proportional to the sum of theerrors that have occurred during the system operation.Oi=Ki x SEIntegral gain can cause overshoot and so is usually used only on systems workingat constant speed or with a slow acceleration.Axis parameter is called I_GAINSyntax: I_GAIN=0.0125Derivative gainDescription This produces an output Od that is proportional to the change in the followingerror and speeds up the response to changes in error whilst maintaining thesame relative stability.Od = Kd x DEThis gain may create a smoother response. High values may lead to oscillation.Axis parameter is called D_GAINSyntax: D_GAIN=5Output Velocity GainDescription This increases the system damping, creating an output that is proportional to thechange in measured position.Oov = Kov x DPm.This parameter can be useful for smoothing motions but will generate high followingerrors. Note that a NEGATIVE OV_GAIN is required for damping.Axis parameter is called OV_GAINSyntax: OV_GAIN=-5Velocity Feed Forward GainDescription As movement is created by following errors at high speed the following error canbe quite appreciable. To overcome this the Velocity Feed Forward creates an outputproportional to the change in demand position so creating movement withoutthe need for a following error.Ov = Kvff x DPdAxis parameter is calle