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.
Please Log in or Create an account to join the conversation.
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:
Please Log in or Create an account to join the conversation.
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
Please Log in or Create an account to join the conversation.
Time to create page: 0.133 seconds