Coordinate measuring machine

• US 4,333,238 A
• Filed: 03/31/1980
• Issued: 06/08/1982
• Est. Priority Date: 03/30/1979
• Status: Expired due to Term

• Current Assignee: David R. Mcmurtry
• Original Assignee: David R. Mcmurtry
• Inventors: McMurtry, David R.
• Primary Examiner(s): Little, Willis
• Application Number:
  US06/136,091
• Time in Patent Office: 799 Days
• Field of Search: 33/174 L, 33/172 E, 33/169 R, 33/169 C, 33/174 P, 33/179.5 D, 33/179.5 R, 33/1 M, 33/174 PC
• US Class Current: 33/504
• CPC Class Codes: G01B 11/005 coordinate measuring machines
• CPC Class Codes: G01B 21/045 Correction of measurements G01B9/02055 takes precedence
• CPC Class Codes: G01B 7/012 Contact-making feeler heads therefor
• CPC Class Codes: G01P 15/09 by piezoelectric pick-up

Abstract

A machine for measuring a workpiece is adapted to move a probe (10) relative to a workpiece to be measured, the measurement being determined by an electronic scale (25) when the probe contacts the workpiece (8). If the measurement is taken while the probe is in a state of acceleration, the deflection of those parts (e.g. 11) of the machine which extend between the probe and the scale falsifies the measurement. The invention provides an accelerometer (30) to determine the acceleration and thereby the deflection. A computer is arranged to determine the true measurement by taking account of the deflection.

Claims

1. A method of determining a measurement of a workpiece on a machine comprising a probe, structure supporting said probe for flexile and translational movement relative to a workpiece to be measured and relative to a means for continually measuring the position of the probe relative to a datum, the probe having means for generating a signal when having a predetermined relationship with a proximate surface of the workpiece;

said method comprising the steps of;

(a) moving said probe toward said surface;

(b) determining the output of said measuring means at the instant said signal is generated thereby defining the measured position of said probe;

(c) determining the deflection of said structure at said instant thereby defining the difference between the measured and the actual positions of said probe; and

(d) subtracting said difference to said output of the measuring means to establish a measure of the actual position of said probe.

2. A machine for determining a measurement of a workpiece comprising:

(a) a probe having means for generating a signal when having a predetermined relationship to a proximate surface of said workpiece;

(b) structure supporting said probe for flexile and translational movement relative to said workpiece;

(c) means for continually measuring the position of said probe, during said translational movement thereof, relative to a datum;

(d) means for determining the output of said measuring means at the instant said signal is generated thereby defining the measured position of said probe;

(e) means for determining the deflection of said structure during said flexile movement thereof, at the instant said signal is generated thereby defining the difference between said measured and actual positions of said probe; and

(f) means for subtracting said difference to said output of the measuring means to establish a measure of the actual position of said probe.

3. A machine for determining a measurement of a workpiece, comprising

(a) an elongate member;

(b) a guide supporting said member at one end thereof for motion in the direction perpendicular to the length of said member, the other end of said member being free;

(c) a stylus provided at the free end of said member for engagement with said workpiece;

(d) means provided at said one end of said member for continually measuring said motion and thereby continually determining a measurement of the position of said stylus relative to a datum, said member being subject to deflection from a rest position due to acceleration during said motion whereby an error may occur between the measurement as determined by the measuring means and the actual position of said stylus;

(e) means for measuring said acceleration;

(f) means for determining a measurement of said deflection responsive to a measurement of said acceleration; and

(g) means for subtracting said deflection measurement to said position measurement in the sense of compensating for said error.