Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1988-03-01
1990-01-09
Evans, F. L.
Optics: measuring and testing
By polarized light examination
With light attenuation
33 1M, 33 50B, 356373, G01B 1100
Patent
active
048924075
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to optical measuring apparatus for checking the accuracy of a machine, for example, a co-ordinate measuring machine or a machine tool.
Co-ordinate measuring machines consist of a base on which a workpiece may be mounted, a mechanical structure carrying a measuring probe, and means for producing relative movement between the base and the measuring probe in three mutually orthogonal directions whereby the measuring probe can be accurately located in all three directions known as the x, y and z directions. Scales attached to the base and the mechanical structure, and which extend in the x, y and z directions, are read by opto-electronic read heads to provide information whereby a computer can calculate the x, y and z co-ordinates of points on a workpiece positioned on the base which are sequentially contacted by the measuring probe.
Similarly machine tools require to position a cutting tool along three co-ordinate axes to perform cutting operations on a workpiece, or to position a measuring probe for measuring the workpiece after a cutting operation as part of the production process. Movements of the relatively movable machine parts are read by scales and read heads in known manner.
The accuracy of the measurements of the workpiece obtained using a measuring machine depends on how closely the readings taken by the scale read head represent the position in space of the measuring probe. The scale readings, however, take no account of relative pitching, rolling, yawing and lateral movements of the parts of the mechanical structure during said relative movement which arise due to slackness in the machine slideways, or due to physical bending and twisting of the parts of the structure. In order to minimise these pitch, roll and yaw and other movements, the machine structure has to be made relatively massive and the slideway along which the relative movements of the structure take place have to be machined extremely accurately, use being made of air bearings on the slideway to provide ease of movement between the relatively massive structures and the base.
Similar inaccuracies occur during relative movements of parts of machine tools which affect the accuracy of the cutting operations and the measurements made by a measuring probe fitted in the tool for measuring workpieces after machining.
As an alternative to the expense of building greater accuracy into such machines, increasing use is being made of optical techniques for measuring the position of the probe independently of the scale readings. By this means the errors due to pitch, roll, yaw and lateral movements in the measurements of the machine framework can be identified and eliminated by making corrections to the measurement readings in the machine software.
One example of such independent measuring apparatus is described in U.S. Pat. No. 4,261,107 in which a plurality of laser systems is provided on a machine to measure the yaw, pitch and roll components of the machine movement in addition to the x, y and z movements. This system has the problem that it requires multiple lasers and beam benders on each of the three axes to measure all of the errors.
Other examples of optical techniques for checking errors in measuring machines and machine tools are shown in U.S. Pat. Nos. 3,661,463, and 4,276,698.
U.S. Pat. No. 3,661,463 describes a system in which a single laser beam is deflected sequentially along all three axes of a machine, thus reducing the number of lasers, but this system has no capability for measuring roll, pitch or yaw of the moving parts during their movement, and thus does not correct the machine reading for these errors.
U.S. Pat. No. 4,276,698 describes a system in which although pitch, yaw and roll of the parts of a machine are acknowledged, the errors due to many of these movements are discounted as insignificant. In large machines however, these errors may not be insignificant. Also, in the described method of making optical measurements, the laser is in some cases mounted on movable parts of the machine. The
REFERENCES:
patent: 3661463 (1972-05-01), Brainard et al.
patent: 3715599 (1973-02-01), Marcy
patent: 3765764 (1973-10-01), Niss
patent: 4261107 (1981-04-01), Coleman et al.
patent: 4276698 (1981-07-01), Dore et al.
Chaney Raymond J.
McMurtry David R.
Evans F. L.
Renishaw plc
LandOfFree
Optical measuring apparatus for use on machines does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical measuring apparatus for use on machines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical measuring apparatus for use on machines will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-142573