×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Error compensation in Machine tools, Software

Error compensation in Machine tools, Software

Error compensation in Machine tools, Software

(OP)

I am planning to implement a dynamic error compensation system for a CNC Milling Machine to improve its accuracy. Machine is controlled by Sinumeric 840 controller. The Real 3D-trajectory of the tool will be measures on line.


Tasks may include:
   Conversion of NC-code (currently only G01) into a 3D   
   trajectory (reference tool trajectory)
   Comparing the reference tool trajectory with online   
   measured trajectory
   Calculating the path deviations (predicted errors)
   Recursive software compensation of predicted errors
   while generating a modified NC Code

These tasks would be performed in a software way on a separate real time computing unit (Matlab based), and modified path will be fed to the machine controller through an effective interface.

Any hint's/guideline concerning software aspects of the tasks would be really appreciable. Any contacts related to existing software packages or fictional libraries would also be welcome.

Thanks in advance
simasa
 

RE: Error compensation in Machine tools, Software

Much of what you are trying to compensate out is from machine deflection created by load. These loads include positioning of the machines mass, cutting tool length and diameter, and spindle torque.

Some of these deflections are non-linear and some become vibrations. When we looked at doing this in the late 1990's we thought the best method was to treat it as an axis feedback error rather than modifying the commanded position. Our approach was going to use lasers measuring through mirrors as the encoder to the control. The machine was to be a traveling column design with the lasers originating from the work piece table to account for yaw in any direction. The yaw control would require at least a 5 axis control, precise rigid high speed positioning and may have required additional PID loop work.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: Error compensation in Machine tools, Software

1) Put the machine in a 69 degree F temperature controlled room.

2) Use temperature controlled Ball Screws (coolant through the ball screw center).  Better to use linear motors.  Water cool the forcers.

3) Use high resolution, high accuracy linear scales for position feedback (Think Heidenhain zerodur Glass Scales).  Use the "Flash" Interpolator Boards.  Still use rotary encoders on the drive motors for velocity feedback.

4) "Survey" all axes for pitch, roll, yaw and translation slide errors (or use really high accuracy slides).  Still survey and compensate for secondary errors.  (see Renishaw or Heidenhain for Laser Machine Survey Tools).

5) Use PID control with 100% velocity and acceleration Feed Forward.  Use digital Bi-Quad Filters to get you through the first resonant mechanical frequency.

6) Flood cool the cutting work piece using temperature controlled cutting fluid.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources