Has anyone experienced the issues which we are experiencing on a
robustly-designed gantry comprising the Y-axis of a large-bed CNC router
(size 2.75 x 1.83m bed)?
The system runs LinuxCNC 2.5 on Core 2 Duo platform equipped with Mesa 5i23
(firmware SVST4_8) controlling the four stepper motors (via Gecko 203V's).
Jitter is a max of ~43us, but that should not be an issue using the 5i23
controller.
If we exercise only a single joint (Y or gantrykins slave A) with other
joint drive mechanically isolated, entirely smooth movement of the gantry is
observed (as also independent X and Z axes).
However, changing to teleop (world) mode always give rise to Y and/or A
joint drive racking, and after much experimentation with .ini and .hal
parameter adjustment, we have observed what appears to be the cause of this
racking. Although it occurs more frequently at higher Y-axis velocities, it
cannot be avoided even at low speeds, particularly during acceleration /
deceleration trajectories.
The issue is that the gantry slave A-joint commences motion after that of
the Y-joint primary drive; this is particularly noticeable at very small
acceleration settings (such as in attached .ini file), even a half-second
lag being observable - and (entirely smoothly) repeatable. The lag is not
noticeable at normal operational parameter settings, except that we can
attribute the racking only to Y / A instantaneous position discrepancies.
Observing joint motion with very small acceleration parms, it is as if the
slave joint motion is triggered by a position delta versus the primary
joint, rather than actual (what should be expected to be concurrent)
position target command under teleop mode.
I can even demonstrate a degree of damped instability between primary and
slave Y-axis gantry joints with 'appropriate' acceleration parm values.
However, this may be attributable only to the deceleration / overshoot lag
between joints, and stiffness of the gantry giving rise to racking by the
(identical spring -loaded) stepper drives. I have observed A-Y-A racking
under certain acceleration / lag conditions. There is of course no position
feedback from the machine, the control loop being entirely within LinuxCNC.
Needless to say, FERROR parms need to be large (as in the attached file) to
avoid continuous software error reporting, and the larger-than-default (for
Gecko 203V) stepper controller parms are insignificant, we believe.
You will infer from the above that some tuning will be required to
critically damp the joint controllers (to balance overshoot and trajectory
time), but we need first to get to the root cause of the lag between primary
and slave joints. It's almost as if the platform is ticking over at a slow
cycle rate, but we rule out hardware performance issues. Indeed, no
difference in behaviour is observed when halving servo thread period to
0.5ms.
The .hal file is consistent I believe with LinuxCNC sample gantry .hal
configuration, so I trust someone will be able to explain the source and
remedy for the control lag observed.
Incidentally, the machine is executing small jobs (0.5m square or less)
without problem under Mach-3 control (same, or Celeron platform), but we
wish to use LinuxCNC and prefer not to bridge stepper drives to allow
independent joint homing.
Thank you
Hugh Wylie
# Generated by PNCconf at Tue Jul 10 12:01:08 2012
# If you make changes to this file, they will be
# overwritten when you run PNCconf again
[EMC]
MACHINE = ParacreoSP
DEBUG = 4
[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/paracreo/linuxcnc/nc_files
INCREMENTS = 5mm 1mm .5mm .1mm .05mm .01mm .005mm
POSITION_OFFSET = RELATIVE
POSITION_FEEDBACK = ACTUAL
DEFAULT_LINEAR_VELOCITY = 33.333333
MAX_LINEAR_VELOCITY = 133.333333
MIN_LINEAR_VELOCITY = 0.166667
DEFAULT_ANGULAR_VELOCITY = 6.0
MAX_ANGULAR_VELOCITY = 12.0
MIN_ANGULAR_VELOCITY = 0.016667
EDITOR = gedit
GEOMETRY = xyz
[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
[EMCMOT]
EMCMOT = motmod
COMM_TIMEOUT = 1.0
COMM_WAIT = 0.010
BASE_PERIOD = 60000
SERVO_PERIOD = 1000000
[HOSTMOT2]
# **** This is for info only ****
# DRIVER0=hm2_pci
# BOARD0=5i23
[HAL]
HALUI = halui
HALFILE = ParacreoSP.hal
HALFILE = custom.hal
POSTGUI_HALFILE = postgui_call_list.hal
SHUTDOWN = shutdown.hal
[HALUI]
[TRAJ]
AXES = 4
COORDINATES = X Y Z A
MAX_ANGULAR_VELOCITY = 133.33
DEFAULT_ANGULAR_VELOCITY = 13.33
LINEAR_UNITS = mm
ANGULAR_UNITS = degree
CYCLE_TIME = 0.010
DEFAULT_VELOCITY = 13.33
MAX_LINEAR_VELOCITY = 133.33
NO_FORCE_HOMING = 1
[EMCIO]
EMCIO = io
CYCLE_TIME = 0.100
TOOL_TABLE = tool.tbl
#********************
# Axis X
#********************
[AXIS_0]
TYPE = LINEAR
HOME = 0.0
FERROR = 75
MIN_FERROR = 15
MAX_VELOCITY = 133.3333333
MAX_ACCELERATION = 25.0
# these are in nanoseconds
DIRSETUP = 500
DIRHOLD = 500
STEPLEN = 2000
STEPSPACE = 2000
STEP_SCALE = 115.7491
MIN_LIMIT = -5.0
MAX_LIMIT = 1830.0
HOME_OFFSET = 0.0
#********************
# Axis Y
#********************
[AXIS_1]
TYPE = LINEAR
HOME = 0.0
FERROR = 50
MIN_FERROR = 20
MAX_VELOCITY = 133.33333333
MAX_ACCELERATION = 1
# these are in nanoseconds
DIRSETUP = 5000
DIRHOLD = 5000
STEPLEN = 5000
STEPSPACE = 5000
STEP_SCALE = -115.7491
MIN_LIMIT = -5
MAX_LIMIT = 2750
HOME_OFFSET = 0.0
#********************
# Axis Z
#********************
[AXIS_2]
TYPE = LINEAR
HOME = 0.0
FERROR = 50
MIN_FERROR = 10
MAX_VELOCITY = 200.0
MAX_ACCELERATION = 25.0
# these are in nanoseconds
DIRSETUP = 500
DIRHOLD = 500
STEPLEN = 2000
STEPSPACE = 2000
STEP_SCALE = 115.7491
MIN_LIMIT = -5.0
MAX_LIMIT = 350.0
HOME_OFFSET = 0.0
#********************
# Axis A
#********************
[AXIS_3]
TYPE = ANGULAR
HOME = 0.0
FERROR = 50
MIN_FERROR = 20
MAX_VELOCITY = 133.333333333
MAX_ACCELERATION = 1
# these are in nanoseconds
DIRSETUP = 5000
DIRHOLD = 5000
STEPLEN = 5000
STEPSPACE = 5000
STEP_SCALE = 115.7491
MIN_LIMIT = -5
MAX_LIMIT = 2750
HOME_OFFSET = 0.0
#********************
# Spindle
#********************
[SPINDLE_9]
# Generated by PNCconf at Tue Jul 10 12:01:07 2012
# If you make changes to this file, they will be
# overwritten when you run PNCconf again
loadrt gantrykins
# Settings for gantrykins
setp gantrykins.joint-0 0
setp gantrykins.joint-1 1
setp gantrykins.joint-2 2
setp gantrykins.joint-3 1
loadrt [EMCMOT]EMCMOT base_period_nsec=[EMCMOT]BASE_PERIOD
servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[TRAJ]AXES
loadrt probe_parport
loadrt hostmot2
loadrt hm2_pci config="firmware=hm2/5i23/SVST4_8.BIT num_encoders=0
num_pwmgens=1 num_3pwmgens=0 num_stepgens=4 "
setp hm2_5i23.0.pwmgen.pwm_frequency 100000
setp hm2_5i23.0.pwmgen.pdm_frequency 1000000
setp hm2_5i23.0.watchdog.timeout_ns 2000000
loadrt hal_parport cfg="0x0378 in"
loadrt charge_pump
addf parport.0.read servo-thread
addf charge-pump servo-thread
addf parport.0.write servo-thread
addf hm2_5i23.0.read servo-thread
addf motion-command-handler servo-thread
addf motion-controller servo-thread
addf hm2_5i23.0.write servo-thread
addf hm2_5i23.0.pet_watchdog servo-thread
# external output signals
# --- CHARGE-PUMP ---
setp hm2_5i23.0.gpio.045.is_output true
net charge-pump hm2_5i23.0.gpio.045.out
# --- SPINDLE-CW ---
setp hm2_5i23.0.gpio.046.is_output true
net spindle-cw hm2_5i23.0.gpio.046.out
# --- COOLANT-MIST ---
setp hm2_5i23.0.gpio.047.is_output true
net coolant-mist hm2_5i23.0.gpio.047.out
# external input signals
# --- ESTOP-EXT ---
net estop-ext <= hm2_5i23.0.gpio.026.in_not
# --- ALL-LIMIT ---
net all-limit <= hm2_5i23.0.gpio.027.in
#*******************
# AXIS X
#*******************
# Step Gen signals/setup
setp hm2_5i23.0.stepgen.00.dirsetup [AXIS_0]DIRSETUP
setp hm2_5i23.0.stepgen.00.dirhold [AXIS_0]DIRHOLD
setp hm2_5i23.0.stepgen.00.steplen [AXIS_0]STEPLEN
setp hm2_5i23.0.stepgen.00.stepspace [AXIS_0]STEPSPACE
setp hm2_5i23.0.stepgen.00.position-scale [AXIS_0]STEP_SCALE
setp hm2_5i23.0.stepgen.00.step_type 0
setp hm2_5i23.0.stepgen.00.control-type 0
setp hm2_5i23.0.stepgen.00.maxaccel [AXIS_0]MAX_ACCELERATION
setp hm2_5i23.0.stepgen.00.maxvel [AXIS_0]MAX_VELOCITY
net x-pos-fb axis.0.motor-pos-fb <= hm2_5i23.0.stepgen.00.position-fb
net x-pos-cmd axis.0.motor-pos-cmd => hm2_5i23.0.stepgen.00.position-cmd
net x-enable axis.0.amp-enable-out => hm2_5i23.0.stepgen.00.enable
# ---setup home / limit switch signals---
net x-home-sw => axis.0.home-sw-in
net all-limit => axis.0.neg-lim-sw-in
net all-limit => axis.0.pos-lim-sw-in
#*******************
# AXIS Y
#*******************
# Step Gen signals/setup
setp hm2_5i23.0.stepgen.01.dirsetup [AXIS_1]DIRSETUP
setp hm2_5i23.0.stepgen.01.dirhold [AXIS_1]DIRHOLD
setp hm2_5i23.0.stepgen.01.steplen [AXIS_1]STEPLEN
setp hm2_5i23.0.stepgen.01.stepspace [AXIS_1]STEPSPACE
setp hm2_5i23.0.stepgen.01.position-scale [AXIS_1]STEP_SCALE
setp hm2_5i23.0.stepgen.01.step_type 0
setp hm2_5i23.0.stepgen.01.control-type 0
setp hm2_5i23.0.stepgen.01.maxaccel [AXIS_1]MAX_ACCELERATION
setp hm2_5i23.0.stepgen.01.maxvel [AXIS_1]MAX_VELOCITY
net y-pos-fb axis.1.motor-pos-fb <= hm2_5i23.0.stepgen.01.position-fb
net y-pos-cmd axis.1.motor-pos-cmd => hm2_5i23.0.stepgen.01.position-cmd
net y-enable axis.1.amp-enable-out => hm2_5i23.0.stepgen.01.enable
# ---setup home / limit switch signals---
net y-home-sw => axis.1.home-sw-in
net all-limit => axis.1.neg-lim-sw-in
net all-limit => axis.1.pos-lim-sw-in
#*******************
# AXIS Z
#*******************
# Step Gen signals/setup
setp hm2_5i23.0.stepgen.02.dirsetup [AXIS_2]DIRSETUP
setp hm2_5i23.0.stepgen.02.dirhold [AXIS_2]DIRHOLD
setp hm2_5i23.0.stepgen.02.steplen [AXIS_2]STEPLEN
setp hm2_5i23.0.stepgen.02.stepspace [AXIS_2]STEPSPACE
setp hm2_5i23.0.stepgen.02.position-scale [AXIS_2]STEP_SCALE
setp hm2_5i23.0.stepgen.02.step_type 0
setp hm2_5i23.0.stepgen.02.control-type 0
setp hm2_5i23.0.stepgen.02.maxaccel [AXIS_2]MAX_ACCELERATION
setp hm2_5i23.0.stepgen.02.maxvel [AXIS_2]MAX_VELOCITY
net z-pos-fb axis.2.motor-pos-fb <= hm2_5i23.0.stepgen.02.position-fb
net z-pos-cmd axis.2.motor-pos-cmd => hm2_5i23.0.stepgen.02.position-cmd
net z-enable axis.2.amp-enable-out => hm2_5i23.0.stepgen.02.enable
# ---setup home / limit switch signals---
net z-home-sw => axis.2.home-sw-in
net all-limit => axis.2.neg-lim-sw-in
net all-limit => axis.2.pos-lim-sw-in
#*******************
# AXIS A
#*******************
# Step Gen signals/setup
setp hm2_5i23.0.stepgen.03.dirsetup [AXIS_3]DIRSETUP
setp hm2_5i23.0.stepgen.03.dirhold [AXIS_3]DIRHOLD
setp hm2_5i23.0.stepgen.03.steplen [AXIS_3]STEPLEN
setp hm2_5i23.0.stepgen.03.stepspace [AXIS_3]STEPSPACE
setp hm2_5i23.0.stepgen.03.position-scale [AXIS_3]STEP_SCALE
setp hm2_5i23.0.stepgen.03.step_type 0
setp hm2_5i23.0.stepgen.03.control-type 0
setp hm2_5i23.0.stepgen.03.maxaccel [AXIS_3]MAX_ACCELERATION
setp hm2_5i23.0.stepgen.03.maxvel [AXIS_3]MAX_VELOCITY
net a-pos-fb axis.3.motor-pos-fb <= hm2_5i23.0.stepgen.03.position-fb
net a-pos-cmd axis.3.motor-pos-cmd => hm2_5i23.0.stepgen.03.position-cmd
net a-enable axis.3.amp-enable-out => hm2_5i23.0.stepgen.03.enable
# ---setup home / limit switch signals---
net a-home-sw => axis.3.home-sw-in
net all-limit => axis.3.neg-lim-sw-in
net all-limit => axis.3.pos-lim-sw-in
#*******************
# SPINDLE S
#*******************
# ---setup spindle control signals---
net spindle-vel-cmd-rps <= motion.spindle-speed-out-rps
net spindle-vel-cmd <= motion.spindle-speed-out
net spindle-enable <= motion.spindle-on
net spindle-cw <= motion.spindle-forward
net spindle-ccw <= motion.spindle-reverse
net spindle-brake <= motion.spindle-brake
net spindle-revs => motion.spindle-revs
net spindle-at-speed => motion.spindle-at-speed
net spindle-vel-fb => motion.spindle-speed-in
net spindle-index-enable <=> motion.spindle-index-enable
# ---Setup spindle at speed signals---
sets spindle-at-speed true
#******************************
# connect miscellaneous signals
#******************************
# ---HALUI signals---
net joint-select-a halui.joint.0.select
net x-is-homed halui.joint.0.is-homed
net jog-x-pos halui.jog.0.plus
net jog-x-neg halui.jog.0.minus
net jog-x-analog halui.jog.0.analog
net joint-select-b halui.joint.1.select
net y-is-homed halui.joint.1.is-homed
net jog-y-pos halui.jog.1.plus
net jog-y-neg halui.jog.1.minus
net jog-y-analog halui.jog.1.analog
net joint-select-c halui.joint.2.select
net z-is-homed halui.joint.2.is-homed
net jog-z-pos halui.jog.2.plus
net jog-z-neg halui.jog.2.minus
net jog-z-analog halui.jog.2.analog
net joint-select-d halui.joint.3.select
net a-is-homed halui.joint.3.is-homed
net jog-a-pos halui.jog.3.plus
net jog-a-neg halui.jog.3.minus
net jog-a-analog halui.jog.3.analog
net jog-selected-pos halui.jog.selected.plus
net jog-selected-neg halui.jog.selected.minus
net spindle-manual-cw halui.spindle.forward
net spindle-manual-ccw halui.spindle.reverse
net spindle-manual-stop halui.spindle.stop
net machine-is-on halui.machine.is-on
net jog-speed halui.jog-speed
net MDI-mode halui.mode.is-mdi
# ---charge pump signals---
net estop-out => charge-pump.enable
net charge-pump <= charge-pump.out
# ---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-ext => iocontrol.0.emc-enable-in
# ---toolchange signals for custom tool changer---
net tool-number <= iocontrol.0.tool-prep-number
net tool-change-request <= iocontrol.0.tool-change
net tool-change-confirmed => iocontrol.0.tool-changed
net tool-prepare-request <= iocontrol.0.tool-prepare
net tool-prepare-confirmed => iocontrol.0.tool-prepared
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