Can't get backlash compensation to work

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2 years 7 months ago #296583 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:
Code:
# 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:
Code:
# 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 #******************************************

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2 years 7 months ago #296588 by PCW
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?

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2 years 7 months ago #296593 by ltcnc
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!

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2 years 7 months ago #296602 by tommylight
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.

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