Software for improving the accuracy of machines

• US 6,980,881 B2
• Filed: 08/20/2003
• Issued: 12/27/2005
• Est. Priority Date: 06/06/1996
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Greenwood, Thomas A., Pastusak, Thomas W.
• Primary Examiner(s): PATEL, RAMESH B
• Application Number:
  US10/644,149
• Publication Number:
  US 20040260422A1
• Time in Patent Office: 860 Days
• Field of Search: 700/160, 700/163, 700/186, 700/195, 700/71, 700/193, 356/634, 318/569, 318/568.11, 318/560, 318/568.1, 318/568.21, 901/30
• US Class Current: 700/193
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/39033 Laser tracking of end effector, measure orientation of rotatable mirror
• CPC Class Codes: G05B 2219/49207 Compensate thermal displacement using measured distance
• CPC Class Codes: G05B 2219/50057 Compensation error by probing test, machined piece, post or pre process

Abstract

Large machines, especially those having working envelopes in excess of fifteen feet, exhibit unacceptable errors because of thermal expansion and mechanical misalignments between the axes. The errors have traditionally been minimized by enclosing the machine in a thermal enclosure, by careful calibration, or by mounting a laser interferometer on each axis. These solutions are costly, may require frequent recalibration, and do not correct for small rotations of one axis relative to another axis due to wear etc. The present invention uses an interferometric laser tracker or a comparable 3D position sensor to measure the position of a retroreflector attached to the end effector, e.g. a machine head when the machine comes to rest. A computer compares the measured position to the desired position according to the machine media, and adds the appropriate correction with trickle feed media statements to move the machine to the correct position prior to further machining.

Claims

1. Information storage media for improving the accuracy of a machine tool, comprising:

computer software storage media having computer-readable information recorded to provide trickle feed repositioning commands to a machine controller associated with the machine tool from an external software controller, wherein the repositioning commands correct for a position error of a machine tool end effector and are based upon a comparison of measured true position of the end effector measured by an independent laser tracker measurement system and a commanded rest position derived from a digital definition representing a part.

2. The information storage media of claim 1, further comprising a standard deviation control protocol for determining the rest position of the end effector.

3. The information storage media of claim 2 further comprising a first code portion that uses least squares fit algorithms for providing a first order, linear approximation of the position error.

4. The information storage media of claim 1 further comprising a first code portion that uses least squares fit algorithms for providing a first order, linear approximation of the position error.

5. A machine tool system for improving positioning accuracy of a machine tool, comprising;

(a) a machine having a machine tool and a machine controller; and

(b) a software controller connected to the machine controller for executing the information storage media of claim 1.

6. Information storage media, comprising:

computer software storage media having computer-readable information recorded to provide trickle feed, delta correction commands in machine media from an external software controller to a machine controller to correct for a position error determined by a comparison of the true position of a machine tool under the control of the machine controller measured by an independent laser tracker measurement system and the position that the machine controller locates the machine tool following machine media positioning commands derived from an engineering specification of a part, the delta correction commands moving the machine tool if the position error exceeds a predetermined offset threshold, wherein the software controller records the correction commands for later analysis of machine wear.

7. The information storage media of claim 6 further comprising a first code portion that uses least squares fit algorithms for providing a first order, linear approximation of the position error.

8. A machine tool system for improving positioning accuracy of a machine tool, comprising;

(a) a machine having a machine tool and a machine controller; and

(b) a software controller connected to the machine controller for executing the information storage media of claim 6.

9. A method for improving the accuracy of a machine having a machine controller for guiding movement of a machine tool, comprising the step of:

providing trickle feed delta correction commands in machine media to the machine controller from an external software controller that records the correction commands for later analysis of machine wear, wherein commands are provided when a comparison of the true position of a machine tool under the control of the machine controller measured by an independent laser traker measurement system and the position to which the machine controller locates the machine tool following machine media derived from an engineering specification of a part exceeds a predetermined offset threshold,

wherein the software controller uses a standard deviation protocol to determine the rest position when the machine tool stops following movement.