On Wed, 26 Feb 2020, Ed W wrote:
Date: Wed, 26 Feb 2020 17:58:09 +0000
From: Ed W <li...@wildgooses.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: [Emc-users] Making progress
Hi, I've made good progress converting my little OmioCNC X6 from Mach3
to LinuxCNC. I think I owe a writeup at some point, but I still have a
few glitches before I'm ready to do that.
First thing which I'm worrying about is that having run pncconf, it
generates an output for my open loop steppers which involves a PID type
setup, eg here is my X axis from the ini
[AXIS_X]
MAX_VELOCITY = 100.0
MAX_ACCELERATION = 750.0
MIN_LIMIT = -0.01
MAX_LIMIT = 355.0
[JOINT_0]
TYPE = LINEAR
HOME = 0.0
FERROR = 1.0
MIN_FERROR = 0.01
MAX_VELOCITY = 100.0
MAX_ACCELERATION = 750.0
# The values below should be 25% larger than MAX_VELOCITY and
MAX_ACCELERATION
# If using BACKLASH compensation STEPGEN_MAXACCEL should be 100% larger.
STEPGEN_MAXVEL = 125.00
STEPGEN_MAXACCEL = 937.50
P = 1000.0
I = 0.0
D = 0.0
FF0 = 0.0
FF1 = 1.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.0
MAX_OUTPUT = 0.0
# these are in nanoseconds
DIRSETUP = 10000
DIRHOLD = 10000
STEPLEN = 5000
STEPSPACE = 5000
STEP_SCALE = 320.0
MIN_LIMIT = -0.01
MAX_LIMIT = 355.0
HOME_OFFSET = -5.000000
HOME_SEARCH_VEL = -33.333333
HOME_LATCH_VEL = 0.500000
HOME_FINAL_VEL = 33.333333
HOME_USE_INDEX = NO
HOME_IGNORE_LIMITS = YES
HOME_SEQUENCE = 1
The corresponding .hal (again by pncconf) is as follows:
#*******************
# AXIS X JOINT 0
#*******************
setp pid.x.Pgain [JOINT_0]P
setp pid.x.Igain [JOINT_0]I
setp pid.x.Dgain [JOINT_0]D
setp pid.x.bias [JOINT_0]BIAS
setp pid.x.FF0 [JOINT_0]FF0
setp pid.x.FF1 [JOINT_0]FF1
setp pid.x.FF2 [JOINT_0]FF2
setp pid.x.deadband [JOINT_0]DEADBAND
setp pid.x.maxoutput [JOINT_0]MAX_OUTPUT
setp pid.x.error-previous-target true
setp pid.x.maxerror .0005
net x-index-enable <=> pid.x.index-enable
net x-enable => pid.x.enable
net x-pos-cmd => pid.x.command
net x-pos-fb => pid.x.feedback
net x-output <= pid.x.output
# Step Gen signals/setup
setp hm2_5i25.0.stepgen.00.dirsetup [JOINT_0]DIRSETUP
setp hm2_5i25.0.stepgen.00.dirhold [JOINT_0]DIRHOLD
setp hm2_5i25.0.stepgen.00.steplen [JOINT_0]STEPLEN
setp hm2_5i25.0.stepgen.00.stepspace [JOINT_0]STEPSPACE
setp hm2_5i25.0.stepgen.00.position-scale [JOINT_0]STEP_SCALE
setp hm2_5i25.0.stepgen.00.step_type 0
setp hm2_5i25.0.stepgen.00.control-type 1
setp hm2_5i25.0.stepgen.00.maxaccel [JOINT_0]STEPGEN_MAXACCEL
setp hm2_5i25.0.stepgen.00.maxvel [JOINT_0]STEPGEN_MAXVEL
setp hm2_5i25.0.stepgen.00.step.invert_output true
setp hm2_5i25.0.stepgen.00.direction.invert_output true
# ---closedloop stepper signals---
net x-pos-cmd <= joint.0.motor-pos-cmd
net x-vel-cmd <= joint.0.vel-cmd
net x-output <= hm2_5i25.0.stepgen.00.velocity-cmd
net x-pos-fb <= hm2_5i25.0.stepgen.00.position-fb
net x-pos-fb => joint.0.motor-pos-fb
net x-enable <= joint.0.amp-enable-out
net x-enable => hm2_5i25.0.stepgen.00.enable
# ---setup home / limit switch signals---
net min-home-x => joint.0.home-sw-in
net min-home-x => joint.0.neg-lim-sw-in
net x-pos-limit => joint.0.pos-lim-sw-in
What would someone experienced recommend I do here? This is a simple
openloop stepper machine, no feedback or position sensors. Just a 6i25
to a basic breakout board, going to a chinese 556 stepper driver clone
and onto some small steppers on a 6040 type of machine?
Is there any disadvantage (or advantage) to leaving all the PID and
closed loop stuff in here?
Thanks
Ed W
You can use the built in position mode control loop in the driver (without PID)
but you can get better performance by using PID and velocity mode, especially
with regard to host servo thread jitter. This is why PNCCONF uses thsi control
mode even for open loop step motor systems.
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