Can't get backlash compensation to work
23 Mar 2024 16:10 #296583
by ltcnc
Can't get backlash compensation to work was created by ltcnc
I have a new build using the 7i96s + 7i85s and closed loop stepper motors. I've worked through pncconf and am able to drive my motors and am getting encoder feedback. I'm trying to take a few thou (0.025-0.075mm) of backlash out of various axes by testing in Axis, but no matter what I set the backlash setting to on each axis, I still get the same backlash reading from my dial indicator. (Even when I set 1mm+ of backlash.) I've ensured STEPGEN_MAXACCEL is 2x MAX_ACCELERATION for each axis. Anyone know what I'm doing wrong?
One more note: pncconf did automatically assign the stepgen position-fb signals to the pos-fb net of each axis, which I had to comment out just to get Axis to open the configuration without throwing an error.
HAL file:
INI file:
One more note: pncconf did automatically assign the stepgen position-fb signals to the pos-fb net of each axis, which I had to comment out just to get Axis to open the configuration without throwing an error.
HAL file:
# Generated by PNCconf at Thu Mar 21 17:28:52 2024
# Using LinuxCNC version: Master (2.9)
# If you make changes to this file, they will be
# overwritten when you run PNCconf again
loadrt [KINS]KINEMATICS
loadrt [EMCMOT]EMCMOT servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[KINS]JOINTS
loadrt hostmot2
loadrt hm2_eth board_ip="10.10.10.10" config="num_encoders=5 num_pwmgens=1 num_stepgens=9 sserial_port_0=0xxxxxxx"
setp hm2_7i96s.0.pwmgen.pwm_frequency 20000
setp hm2_7i96s.0.pwmgen.pdm_frequency 6000000
setp hm2_7i96s.0.watchdog.timeout_ns 5000000
loadrt pid names=pid.x,pid.y,pid.z,pid.s
addf hm2_7i96s.0.read servo-thread
addf motion-command-handler servo-thread
addf motion-controller servo-thread
addf pid.x.do-pid-calcs servo-thread
addf pid.y.do-pid-calcs servo-thread
addf pid.z.do-pid-calcs servo-thread
addf pid.s.do-pid-calcs servo-thread
addf hm2_7i96s.0.write servo-thread
setp hm2_7i96s.0.dpll.01.timer-us -50
setp hm2_7i96s.0.stepgen.timer-number 1
# external output signals
# external input signals
# --- MIN-X ---
net min-x <= hm2_7i96s.0.inm.00.input-00
# --- MAX-X ---
net max-x <= hm2_7i96s.0.inm.00.input-01
# --- MIN-Y ---
net min-y <= hm2_7i96s.0.inm.00.input-02
# --- MAX-Y ---
net max-y <= hm2_7i96s.0.inm.00.input-03
# --- MIN-Z ---
net min-z <= hm2_7i96s.0.inm.00.input-04
# --- MAX-Z ---
net max-z <= hm2_7i96s.0.inm.00.input-05
#*******************
# 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
# This setting is to limit bogus stepgen
# velocity corrections caused by position
# feedback sample time jitter.
setp pid.x.maxerror 0.012700
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_7i96s.0.stepgen.00.dirsetup [JOINT_0]DIRSETUP
setp hm2_7i96s.0.stepgen.00.dirhold [JOINT_0]DIRHOLD
setp hm2_7i96s.0.stepgen.00.steplen [JOINT_0]STEPLEN
setp hm2_7i96s.0.stepgen.00.stepspace [JOINT_0]STEPSPACE
setp hm2_7i96s.0.stepgen.00.position-scale [JOINT_0]STEP_SCALE
setp hm2_7i96s.0.stepgen.00.step_type 0
setp hm2_7i96s.0.stepgen.00.control-type 1
setp hm2_7i96s.0.stepgen.00.maxaccel [JOINT_0]STEPGEN_MAXACCEL
setp hm2_7i96s.0.stepgen.00.maxvel [JOINT_0]STEPGEN_MAXVEL
# ---closedloop stepper signals---
net x-pos-cmd <= joint.0.motor-pos-cmd
net x-vel-cmd <= joint.0.vel-cmd
net x-output => hm2_7i96s.0.stepgen.00.velocity-cmd
# net x-pos-fb <= hm2_7i96s.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_7i96s.0.stepgen.00.enable
# ---Encoder feedback signals/setup---
setp hm2_7i96s.0.encoder.00.counter-mode 0
setp hm2_7i96s.0.encoder.00.filter 1
setp hm2_7i96s.0.encoder.00.index-invert 0
setp hm2_7i96s.0.encoder.00.index-mask 0
setp hm2_7i96s.0.encoder.00.index-mask-invert 0
setp hm2_7i96s.0.encoder.00.scale [JOINT_0]ENCODER_SCALE
net x-pos-fb <= hm2_7i96s.0.encoder.00.position
net x-vel-fb <= hm2_7i96s.0.encoder.00.velocity
net x-pos-fb => joint.0.motor-pos-fb
net x-index-enable joint.0.index-enable <=> hm2_7i96s.0.encoder.00.index-enable
net x-pos-rawcounts <= hm2_7i96s.0.encoder.00.rawcounts
# ---setup home / limit switch signals---
net x-home-sw => joint.0.home-sw-in
net min-x => joint.0.neg-lim-sw-in
net max-x => joint.0.pos-lim-sw-in
#*******************
# AXIS Y JOINT 1
#*******************
setp pid.y.Pgain [JOINT_1]P
setp pid.y.Igain [JOINT_1]I
setp pid.y.Dgain [JOINT_1]D
setp pid.y.bias [JOINT_1]BIAS
setp pid.y.FF0 [JOINT_1]FF0
setp pid.y.FF1 [JOINT_1]FF1
setp pid.y.FF2 [JOINT_1]FF2
setp pid.y.deadband [JOINT_1]DEADBAND
setp pid.y.maxoutput [JOINT_1]MAX_OUTPUT
setp pid.y.error-previous-target true
# This setting is to limit bogus stepgen
# velocity corrections caused by position
# feedback sample time jitter.
setp pid.y.maxerror 0.012700
net y-index-enable => pid.y.index-enable
net y-enable => pid.y.enable
net y-pos-cmd => pid.y.command
net y-pos-fb => pid.y.feedback
net y-output <= pid.y.output
# Step Gen signals/setup
setp hm2_7i96s.0.stepgen.01.dirsetup [JOINT_1]DIRSETUP
setp hm2_7i96s.0.stepgen.01.dirhold [JOINT_1]DIRHOLD
setp hm2_7i96s.0.stepgen.01.steplen [JOINT_1]STEPLEN
setp hm2_7i96s.0.stepgen.01.stepspace [JOINT_1]STEPSPACE
setp hm2_7i96s.0.stepgen.01.position-scale [JOINT_1]STEP_SCALE
setp hm2_7i96s.0.stepgen.01.step_type 0
setp hm2_7i96s.0.stepgen.01.control-type 1
setp hm2_7i96s.0.stepgen.01.maxaccel [JOINT_1]STEPGEN_MAXACCEL
setp hm2_7i96s.0.stepgen.01.maxvel [JOINT_1]STEPGEN_MAXVEL
# ---closedloop stepper signals---
net y-pos-cmd <= joint.1.motor-pos-cmd
net y-vel-cmd <= joint.1.vel-cmd
net y-output => hm2_7i96s.0.stepgen.01.velocity-cmd
# net y-pos-fb <= hm2_7i96s.0.stepgen.01.position-fb
net y-pos-fb => joint.1.motor-pos-fb
net y-enable <= joint.1.amp-enable-out
net y-enable => hm2_7i96s.0.stepgen.01.enable
# ---Encoder feedback signals/setup---
setp hm2_7i96s.0.encoder.01.counter-mode 0
setp hm2_7i96s.0.encoder.01.filter 1
setp hm2_7i96s.0.encoder.01.index-invert 0
setp hm2_7i96s.0.encoder.01.index-mask 0
setp hm2_7i96s.0.encoder.01.index-mask-invert 0
setp hm2_7i96s.0.encoder.01.scale [JOINT_1]ENCODER_SCALE
net y-pos-fb <= hm2_7i96s.0.encoder.01.position
net y-vel-fb <= hm2_7i96s.0.encoder.01.velocity
net y-pos-fb => joint.1.motor-pos-fb
net y-index-enable joint.1.index-enable <=> hm2_7i96s.0.encoder.01.index-enable
net y-pos-rawcounts <= hm2_7i96s.0.encoder.01.rawcounts
# ---setup home / limit switch signals---
net y-home-sw => joint.1.home-sw-in
net min-y => joint.1.neg-lim-sw-in
net max-y => joint.1.pos-lim-sw-in
#*******************
# AXIS Z JOINT 2
#*******************
setp pid.z.Pgain [JOINT_2]P
setp pid.z.Igain [JOINT_2]I
setp pid.z.Dgain [JOINT_2]D
setp pid.z.bias [JOINT_2]BIAS
setp pid.z.FF0 [JOINT_2]FF0
setp pid.z.FF1 [JOINT_2]FF1
setp pid.z.FF2 [JOINT_2]FF2
setp pid.z.deadband [JOINT_2]DEADBAND
setp pid.z.maxoutput [JOINT_2]MAX_OUTPUT
setp pid.z.error-previous-target true
# This setting is to limit bogus stepgen
# velocity corrections caused by position
# feedback sample time jitter.
setp pid.z.maxerror 0.012700
net z-index-enable => pid.z.index-enable
net z-enable => pid.z.enable
net z-pos-cmd => pid.z.command
net z-pos-fb => pid.z.feedback
net z-output <= pid.z.output
# Step Gen signals/setup
setp hm2_7i96s.0.stepgen.02.dirsetup [JOINT_2]DIRSETUP
setp hm2_7i96s.0.stepgen.02.dirhold [JOINT_2]DIRHOLD
setp hm2_7i96s.0.stepgen.02.steplen [JOINT_2]STEPLEN
setp hm2_7i96s.0.stepgen.02.stepspace [JOINT_2]STEPSPACE
setp hm2_7i96s.0.stepgen.02.position-scale [JOINT_2]STEP_SCALE
setp hm2_7i96s.0.stepgen.02.step_type 0
setp hm2_7i96s.0.stepgen.02.control-type 1
setp hm2_7i96s.0.stepgen.02.maxaccel [JOINT_2]STEPGEN_MAXACCEL
setp hm2_7i96s.0.stepgen.02.maxvel [JOINT_2]STEPGEN_MAXVEL
# ---closedloop stepper signals---
net z-pos-cmd <= joint.2.motor-pos-cmd
net z-vel-cmd <= joint.2.vel-cmd
net z-output => hm2_7i96s.0.stepgen.02.velocity-cmd
# net z-pos-fb <= hm2_7i96s.0.stepgen.02.position-fb
net z-pos-fb => joint.2.motor-pos-fb
net z-enable <= joint.2.amp-enable-out
net z-enable => hm2_7i96s.0.stepgen.02.enable
# ---Encoder feedback signals/setup---
setp hm2_7i96s.0.encoder.02.counter-mode 0
setp hm2_7i96s.0.encoder.02.filter 1
setp hm2_7i96s.0.encoder.02.index-invert 0
setp hm2_7i96s.0.encoder.02.index-mask 0
setp hm2_7i96s.0.encoder.02.index-mask-invert 0
setp hm2_7i96s.0.encoder.02.scale [JOINT_2]ENCODER_SCALE
net z-pos-fb <= hm2_7i96s.0.encoder.02.position
net z-vel-fb <= hm2_7i96s.0.encoder.02.velocity
net z-pos-fb => joint.2.motor-pos-fb
net z-index-enable joint.2.index-enable <=> hm2_7i96s.0.encoder.02.index-enable
net z-pos-rawcounts <= hm2_7i96s.0.encoder.02.rawcounts
# ---setup home / limit switch signals---
net z-home-sw => joint.2.home-sw-in
net min-z => joint.2.neg-lim-sw-in
net max-z => joint.2.pos-lim-sw-in
#******************************
# connect miscellaneous signals
#******************************
# ---HALUI signals---
net axis-select-x halui.axis.x.select
net jog-x-pos halui.axis.x.plus
net jog-x-neg halui.axis.x.minus
net jog-x-analog halui.axis.x.analog
net x-is-homed halui.joint.0.is-homed
net axis-select-y halui.axis.y.select
net jog-y-pos halui.axis.y.plus
net jog-y-neg halui.axis.y.minus
net jog-y-analog halui.axis.y.analog
net y-is-homed halui.joint.1.is-homed
net axis-select-z halui.axis.z.select
net jog-z-pos halui.axis.z.plus
net jog-z-neg halui.axis.z.minus
net jog-z-analog halui.axis.z.analog
net z-is-homed halui.joint.2.is-homed
net jog-selected-pos halui.axis.selected.plus
net jog-selected-neg halui.axis.selected.minus
net spindle-manual-cw halui.spindle.0.forward
net spindle-manual-ccw halui.spindle.0.reverse
net spindle-manual-stop halui.spindle.0.stop
net machine-is-on halui.machine.is-on
net jog-speed halui.axis.jog-speed
net MDI-mode halui.mode.is-mdi
# ---coolant signals---
net coolant-mist <= iocontrol.0.coolant-mist
net coolant-flood <= iocontrol.0.coolant-flood
# ---probe signal---
net probe-in => motion.probe-input
# ---motion control signals---
net in-position <= motion.in-position
net machine-is-enabled <= motion.motion-enabled
# ---digital in / out signals---
# ---estop signals---
net estop-out <= iocontrol.0.user-enable-out
net estop-out => iocontrol.0.emc-enable-in
# ---manual tool change signals---
net tool-change-request <= iocontrol.0.tool-change
net tool-change-confirmed => iocontrol.0.tool-changed
net tool-number <= iocontrol.0.tool-prep-number
# ---Use external manual tool change dialog---
loadusr -W hal_manualtoolchange
net tool-change-request => hal_manualtoolchange.change
net tool-change-confirmed <= hal_manualtoolchange.changed
net tool-number => hal_manualtoolchange.number
# ---ignore tool prepare requests---
net tool-prepare-loopback iocontrol.0.tool-prepare => iocontrol.0.tool-prepared
INI file:
# Generated by PNCconf at Thu Mar 21 17:28:52 2024
# Using LinuxCNC version: Master (2.9)
# If you make changes to this file, they will be
# overwritten when you run PNCconf again
[EMC]
MACHINE = my_LinuxCNC_test4
DEBUG = 0
VERSION = 1.1
[DISPLAY]
DISPLAY = axis
POSITION_OFFSET = RELATIVE
POSITION_FEEDBACK = ACTUAL
MAX_FEED_OVERRIDE = 2.000000
MAX_SPINDLE_OVERRIDE = 1.000000
MIN_SPINDLE_OVERRIDE = 0.500000
INTRO_GRAPHIC = linuxcnc.gif
INTRO_TIME = 5
PROGRAM_PREFIX = /home/lukecnc/linuxcnc/nc_files
INCREMENTS = 50mm 10mm 5mm 1mm .5mm .1mm .05mm .01mm .005mm
POSITION_FEEDBACK = ACTUAL
DEFAULT_LINEAR_VELOCITY = 6.000000
MAX_LINEAR_VELOCITY = 25.000000
MIN_LINEAR_VELOCITY = 0.500000
DEFAULT_ANGULAR_VELOCITY = 12.000000
MAX_ANGULAR_VELOCITY = 180.000000
MIN_ANGULAR_VELOCITY = 1.666667
EDITOR = gedit
GEOMETRY = xyz
CYCLE_TIME = 100
[FILTER]
PROGRAM_EXTENSION = .png,.gif,.jpg Greyscale Depth Image
PROGRAM_EXTENSION = .py Python Script
png = image-to-gcode
gif = image-to-gcode
jpg = image-to-gcode
py = python
[TASK]
TASK = milltask
CYCLE_TIME = 0.010
[RS274NGC]
PARAMETER_FILE = linuxcnc.var
RS274NGC_STARTUP_CODE = G21 G40 G90 G94 G97 G64 P0.025
[EMCMOT]
EMCMOT = motmod
COMM_TIMEOUT = 1.0
SERVO_PERIOD = 1000000
[HMOT]
# **** This is for info only ****
CARD0=hm2_7i96s.0
[HAL]
HALUI = halui
HALFILE = my_LinuxCNC_test4.hal
HALFILE = custom.hal
POSTGUI_HALFILE = custom_postgui.hal
SHUTDOWN = shutdown.hal
[HALUI]
[KINS]
JOINTS = 3
KINEMATICS = trivkins coordinates=XYZ
[TRAJ]
COORDINATES = XYZ
LINEAR_UNITS = mm
ANGULAR_UNITS = degree
DEFAULT_LINEAR_VELOCITY = 3.75
MAX_LINEAR_VELOCITY = 37.50
[EMCIO]
EMCIO = io
CYCLE_TIME = 0.100
TOOL_TABLE = tool.tbl
TOOL_CHANGE_QUILL_UP = 1
#******************************************
[AXIS_X]
MAX_VELOCITY = 25.0
MAX_ACCELERATION = 100.0
MIN_LIMIT = -160.0
MAX_LIMIT = 240.0
[JOINT_0]
TYPE = LINEAR
HOME = 0.0
FERROR = 10.0
MIN_FERROR = 0.025
MAX_VELOCITY = 25.0
MAX_ACCELERATION = 100.0
# 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 = 31.25
STEPGEN_MAXACCEL = 200.0
P = 250.0
I = 1.0
D = 0.0
FF0 = 0.0
FF1 = 1.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.025
MAX_OUTPUT = 0.0
ENCODER_SCALE = -800.0
# these are in nanoseconds
DIRSETUP = 5000
DIRHOLD = 5000
STEPLEN = 2000
STEPSPACE = 2000
STEP_SCALE = -160.0
MIN_LIMIT = -160.0
MAX_LIMIT = 240.0
HOME_OFFSET = 0.0
HOME_SEQUENCE = 1
#******************************************
#******************************************
[AXIS_Y]
MAX_VELOCITY = 25.0
MAX_ACCELERATION = 250.0
MIN_LIMIT = -50.0
MAX_LIMIT = 50.0
[JOINT_1]
TYPE = LINEAR
HOME = 0.0
FERROR = 10.0
MIN_FERROR = 1.0
MAX_VELOCITY = 25.0
MAX_ACCELERATION = 250.0
# 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 = 31.25
STEPGEN_MAXACCEL = 312.50
P = 250.0
I = 0.1
D = 0.0
FF0 = 0.0
FF1 = 1.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.05
MAX_OUTPUT = 0.0
ENCODER_SCALE = 800.0
# these are in nanoseconds
DIRSETUP = 5000
DIRHOLD = 5000
STEPLEN = 2000
STEPSPACE = 2000
STEP_SCALE = 160.0
MIN_LIMIT = -50.0
MAX_LIMIT = 50.0
HOME_OFFSET = 0.0
HOME_SEQUENCE = 2
#******************************************
#******************************************
[AXIS_Z]
MAX_VELOCITY = 25.0
MAX_ACCELERATION = 150.0
MIN_LIMIT = -250.0
MAX_LIMIT = 0.00
[JOINT_2]
TYPE = LINEAR
HOME = 0.0
FERROR = 10.0
MIN_FERROR = 0.025
MAX_VELOCITY = 25.0
MAX_ACCELERATION = 150.0
# 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 = 46.88
STEPGEN_MAXACCEL = 300.0
P = 250.0
I = 0.5
D = 0.0
FF0 = 0.0
FF1 = 1.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.05
MAX_OUTPUT = 0.0
ENCODER_SCALE = -800.0
# these are in nanoseconds
DIRSETUP = 5000
DIRHOLD = 5000
STEPLEN = 2000
STEPSPACE = 2000
STEP_SCALE = -160.0
MIN_LIMIT = -250.0
MAX_LIMIT = 0.00
HOME_OFFSET = 0.0
HOME_SEQUENCE = 0
#******************************************Please Log in or Create an account to join the conversation.
23 Mar 2024 18:26 - 23 Mar 2024 18:35 #296588
by PCW
Replied by PCW on topic Can't get backlash compensation to work
1. I don't see any backlash settings in the ini file.
2. Your PID deadzone is about as big as your backlash, can you reduce this?
2. Your PID deadzone is about as big as your backlash, can you reduce this?
Last edit: 23 Mar 2024 18:35 by PCW.
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23 Mar 2024 20:17 #296593
by ltcnc
Replied by ltcnc on topic Can't get backlash compensation to work
Derp. Even after reading a bunch of forum posts, I was still (mistakenly) thinking that DEADBAND was the setting for backlash compensation. Now I see that it's BACKLASH, and after another test it looks to be working!
Thanks again for the help!
Thanks again for the help!
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- tommylight
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23 Mar 2024 23:25 #296602
by tommylight
Replied by tommylight on topic Can't get backlash compensation to work
Each joint that requires backlash compensation must have
BACKLASH = 0.2 #this is an example value
and can also have
BACKLASH_VELOCITY = 10 # the speed to move during compensation, if this is not present the joint/axis will try to move with the max velocity it can do. Value for metric machine, 600mm/m.
-
Should double check this, it is from memory and was way to long ago.
BACKLASH = 0.2 #this is an example value
and can also have
BACKLASH_VELOCITY = 10 # the speed to move during compensation, if this is not present the joint/axis will try to move with the max velocity it can do. Value for metric machine, 600mm/m.
-
Should double check this, it is from memory and was way to long ago.
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