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TB048 Rev1 Laser Mapping Procedure Software Versions Prior to 2 61
Overview
This document describes how to use a laser for ball screw mapping with CNC7 version 7 17 to CNC10
version 2 61
It assumes that the laser measurement software is Optodyne 2 18
Laser set up
It is very important
to run Autotune and Drag mapping from the Centroid CNC7 control for checking the status
of the machine before proceeding with laser compensation Please refer to CNC Tech News TB044 TB045
and TB047 for more detailed information on Autotune and Drag mapping procedures Be certain drag and PID
values are within reasonable ranges before you continue with the laser mapping procedure
First install the laser measurement software on a PC or laptop these installation disks are provided by the
laser equipment supplier If the laser manufacturer is Optodyne a LDDM icon will be created after the
software setup is complete Make sure all laser cables are connected and the serial cable is connected to your
PC laptop serial port Turn on the power for the laser module and launch the laser measurement software If
Optodyne double click on the [LDDM] icon
Delete the CNC10? TAB File
Centroid recommends that you remove any existing correction CNC10? TAB file where ? is the axis on which
you are running the laser compensation
To delete the files
1 Goto the Laser Measument Menu by pressing F1 Setup
F3 Config
and enter password 137
press Enter
then press F4 PID
F7 Laser
2 Press F2 Delete
Comp
Setting up for the X axis
Move the X axis to the X travel limit If using version 7 17 move the X axis to Home position Double click
on the [Linear] icon and check on the [Intensity] to help align the laser beam Set up the laser with mirror
assembly on the table so the beam is aiming in the X+ direction Adjust the beam to run parallel to the X axis
Mount the mirror on the head in a drill chuck and set the window perpendicular to the beam Move the window
into the beam in the YZ plane until you see the beam reflecting back into the laser
1 At the X end of travel move in the Y and Z axes until intensity is 100 %
2 Begin to move in the X+ direction do not move in Y or Z and watch for the beam to move outside the
window
3 If and when the beam moves outside of the window use the alignment screws on the laser to bring it back
in and maximize the intensity reading When the intensity reading is at 100% repeat step 2 until you get
100% intensity at Max X+ travel
4 Repeat steps 1 to 3 until a 100% intensity reading is measured from both ends of the axis
Set Pitch and Lash
Be sure to set the pitch for the axis accurately on the Machine Configuration screen Once you have the laser
set up you can use it to measure the pitch over a large segment of the axis and update the pitch value
accordingly Move the axis to the zero position and press "Reset" on the laser software Command the axis to
move out to its travel limit Record the actual distance moved Move the axis back to the zero point Set the
pitch according to the equation below
Note Re home
the machine after setting the pitch
Set the lash to 0
Ready for data collection
On the PC
click Setup Fill in the identification information and choose the X axis Use the start position from
the Control screen If using version 7 17 set start to 0 For End use End position from the Control screen
Note if Number of points is End Position Start Position / Move Increment +1 or in our example 34 5 0
/ 5 + 1 = 70 The Optodyne software requires the exact measurement positions If Start Position End
Position is not an even multiple of the Move Increment subtract the fractional part of the Start Position from
the End Position on the Control and use the result for End For example 25 29 to 0 should be entered as
25 29 and 0 29 when using a 0 5 increment Click "Verify" to verify the number of points and measurement
positions Number of runs match with control Make sure the following check boxes are NOT checked
Forward only Positions Shown as below and both ATC boxes Click on the Auto button Set Target Window
to 0 1 inch Trigger Dwell to 0 9 second and Velocity Threshold to 0 1 Make sure Backlash is not checked
Click save then OK to get out of the setup and then Reset
At the CNC10 control's
main screen; press F1 Setup
press F3 Config
press F4 PID
and then press F7
to run the laser mapping The screen should look something like the picture below Note version 7 51
depicted here 7 17 does not have all the fields shown laser softwar e should be set as Optodyne v2 18 by
using Axis should be X Laser Units should be inches Start Position is for reference and cannot
be modified End position should be set as your X travel rounded down to the nearest half inch e g 34 87
inches travel would be 34 5 inches Move Increment should be 0 5 Working Area Start and Working Area End
should be the same as Start Position and End Position Number of runs use 1 Dwell Time should be 3 0
Feedrate should be 20 0 In version 7 17 you must specify the Laser File Name before the run and it should
be KssssXn LIN where ssss is the machine serial number and n is the trial # After pressing the the X axis will go to the X travel limit In version 7 17 it will go to the home position
At the PC
press [Reset] to reset the zero position for the laser Click [Start] The PC will capture the "zero"
position and then prepare to take the next measurement At the second beep/green light press Cycle Start
on the Control You should hear a beep from the PC every time the machine pauses Watch the PC to verify it
is collecting all points When it is finished click OK then save as A KssssXn lin where ssss is the machine
serial number and n is the trial You may want to also save it on the C drive with a filename like
C lddmKssssXn lin for later analysis After LDDM writes the file to disk take the disk out and put it into the
floppy drive of the Centroid control It will have a message asking for the file name Type in the file name
press Enter
and Enter
again when it asks for the disk After the file is read by the control run the procedure
again to verify the position accuracy of the X axis Successive trials on an axis will be added into the existing
corrections and should result in greater accuracy
Â
After completing the verification run be sure to manually set the first and last points in the compensation table
to 0 See "Verifying/Viewing Corrections" below for details
Repeat the same procedure for the other axes
Verifying/Viewing Corrections
In version 7 51 you can view the corrections in effect by going to the Machine Configuration Screen and
pressing F5 M Comp
See Tech Bulletin TB058 The automatic procedure performs a linear analysis on
the given work area and performs some smoothing to eliminate excessive correction values in the work area
Set the first forward and backward corrections to 0 Use the down arrow to scroll down to the very last entries
in the table and set the last forward and backward value to 0 Set the next to the last backward value to equal
the next to the last forward value For example if next to last forward value is 2 591 set the next to last
backward value to 2 591 Press F10 Save
Press Esc
and F5
select the axis and verify that the last
backward correction is set to zero
Version 7 51 uses independent forward and backward correction tables To verify forward corrections you
must have moved in the + direction To verify backward corrections you must have moved in the direction
See Tech Bulletin TB058 for details
To print the laser or drag output files perform the following steps
System requirements CPU7 & WIN95 & CNC7 software
1 Set screen to B/W by setting parameter #7 to 1
2 Press F2 Load
and F8 Graph
to view the files listed below from the C CNC7 directory
Drag Files Laser Files
drag_x out laser_x out
drag_y out laser_y out
drag_z out laser_z out
3 Press Print Screen putting the contents of the screen into the clipboard
4 Open Microsoft paint and paste contents of clipboard Invert the black background colors to white color
5 Print out a hard copy of drag plot
6 E mail all the drag and laser result files back to support@centroidcnc com for further analysis
Common Problems
All laser measurements are off by a fixed amount on both forward and backward runs
Probable causes
Stiction and/or slippage of the machine at some point after pressing "Reset" on the laser
Failure to set home on the axis after setting the pitch
The offset is well below the tolerance of the machine for example 0 00005 inches
Remedies
Set home on the axis and take another laser run
If the problem persists load the data from the second trial or delete the laser data and start over
Note
This does not necessarily indicate a problem with the laser compensation data Seeing approximately
the same error at all forward and backward points means that the relative positions of all those points to one
another are correct The problem may be a positioning error at the initial point If the initial point is at the end
of the axis this constant will not cause a problem under normal usage of the machine
There is a very slight but consistent slope on the corrected axis for example 0 0000 to 0 0003
Probable causes
Excessive pitch error on the initial run If it takes a large number of counts to correct the pitch the
corrections themselves can be off by very small amounts
Remedies
Load the data from the second trial
The laser readout shows larger or different errors when using the MDI to position the axis versus the
errors shown by the last automatic run
Probable causes
The feed rate is too high High feed rates can exacerbate positioning problems due to stiction and/or
slippage in the axis
Remedies
Use the same feed rate that was used in the laser menu to take the original data
When I load the data from the second run the results seem to get worse Loading data from
subsequent runs causes alternating "better" and "worse" results
Probable cause s
The errors shown are less than the positional repeatability of the axis Each subsequent run only
adds noise to the compensation data resulting in apparent worsening and improvement In this case
any apparent worsening and improvement is having no real effect
Remedies
Do not attempt to load correction data that is less than the positional repeatability of the axis To
gauge the repeatability of the axis take an automatic laser measurement containing at least three or
four runs the more the better and graph the results The resulting band shows the inherent
positional variability of the machine at any given point on the axis Laser compensation cannot reduce
errors below this inherent variability
Each time that I position the machine at for example 5 0000 inches the laser shows different errors
Probable causes
You are arriving at the position from different directions The error when traveling to the point from
plus or minus directions may be slightly different but within acceptable limits The error should be
consistent when arriving at the point from the same direction
The feed rate is too high High feed rates can exacerbate positioning problems due to stiction and/or
slippage in the axis
The axis has an inherent variability at this point or across its entire length
Any error shown is less than the repeatability of the axis
Remedies
Look at the "Abs Pos" readout for the axis on the PID screen When arriving at the point from the
same direction the "Abs Pos" should be identical The readout will be different but consistent when
arriving from the opposite direction If the readouts are identical when arriving at the same point from
the same direction yet the laser shows different readouts the difference is due to the inherent
variability of the axis
I cannot change the Move Increment in the laser menu
Probable causes
Compensation data has already been loaded and is in effect The move increment cannot be
changed once compensation data has been loaded
Remedies
Delete the compensation data and start over or use the same increment on confirming trials
Document History
Rev1 Created on 2002 01 22
by #000