PID and Homing with index.
08 Dec 2017 22:36 - 08 Dec 2017 22:37 #102799
by UAVpilot
PID and Homing with index. was created by UAVpilot
Hello,
I have this configuration:
5i25 or 7i92 -> 7i77 -> servo (fast)
At the end of the process homing, the servo drive jerks sharply and sometimes shuts down due to overload. I found out why this happens:
At the signal index-enable (falling to low), the encoder counter pid.x.feedback do reset. However, pid.x.command will only be reset in the next servocycle. As a result, in the current servocycle, pid.x.error becomes
equal pid.x.command and a very large value appears briefly at the output of PID (pid.x.output). A fast servo manages to do it.
The PID component has a pin pid.x.error-previous-target, which is TRUE by default. If change it to FALSE, the result is slightly improved, but the problem does not resolve.
I have this configuration:
5i25 or 7i92 -> 7i77 -> servo (fast)
At the end of the process homing, the servo drive jerks sharply and sometimes shuts down due to overload. I found out why this happens:
At the signal index-enable (falling to low), the encoder counter pid.x.feedback do reset. However, pid.x.command will only be reset in the next servocycle. As a result, in the current servocycle, pid.x.error becomes
equal pid.x.command and a very large value appears briefly at the output of PID (pid.x.output). A fast servo manages to do it.
The PID component has a pin pid.x.error-previous-target, which is TRUE by default. If change it to FALSE, the result is slightly improved, but the problem does not resolve.
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08 Dec 2017 22:44 #102800
by UAVpilot
Replied by UAVpilot on topic PID and Homing with index.
I made a small patch for pid.c, which seems to completely solve this problem:
Results:
--- pid.c.orig 2017-11-25 04:26:15.000000000 +0300
+++ pid.c 2017-12-09 01:36:06.645777032 +0300
@@ -325,6 +325,8 @@
} else {
tmp1 = command - feedback;
}
+ if(pid->prev_ie && !*(pid->index_enable))
+ tmp1 = 0;
/* store error to error pin */
*(pid->error) = tmp1;
/* apply error limits */
Results:
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09 Dec 2017 21:59 - 09 Dec 2017 22:02 #102851
by UAVpilot
Replied by UAVpilot on topic PID and Homing with index.
So?
I tried it. As expected, the problem remained.
I noticed that on the given oscillograms I was mistaken in the designation of cycles: The inscription "Cycle N + 1" should be read as "Cycle N + 2". Below is the correct picture. Sorry.
My patch causes the PID to skip the cycle N+1
loadrt hostmot2
loadrt [HOSTMOT2]DRIVER0 board_ip=[HOSTMOT2]BOARD0IP config=" num_encoders=6 num_pwmgens=0 num_stepgens=0 sserial_port_0=000xxx"
addf hm2_7i92.0.read servo-thread
loadrt trivkins
loadrt [EMCMOT]EMCMOT servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[TRAJ]AXES
addf motion-command-handler servo-thread
addf motion-controller servo-thread
loadrt pid names=pid.x,pid.z,pid.s
addf pid.x.do-pid-calcs servo-thread
addf pid.z.do-pid-calcs servo-thread
addf pid.s.do-pid-calcs servo-thread
....
addf hm2_7i92.0.write servo-threadI tried it. As expected, the problem remained.
I noticed that on the given oscillograms I was mistaken in the designation of cycles: The inscription "Cycle N + 1" should be read as "Cycle N + 2". Below is the correct picture. Sorry.
My patch causes the PID to skip the cycle N+1
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