Geometrical instruments – Gauge – Coordinate movable probe or machine
Reexamination Certificate
2002-07-29
2004-02-24
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Gauge
Coordinate movable probe or machine
C033S533000, C033S505000
Reexamination Certificate
active
06694634
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of evaluating a position error of a movable body such as a gauge head or a tool, and to a method of improving position accuracy by use of the evaluation method, which are used in a three-dimensional coordinate measuring device for moving the gauge head in three axial directions orthogonal to each other or in a moving device such as a machine tool for moving the tool in biaxial or three axial directions orthogonal to each other.
BACKGROUND ART
With the advancement of automated and high-accuracy machinery processing, the three-dimensional coordinate measuring device is obliged to have a function of evaluating dimensional accuracy and form accuracy, which is indispensable in a production line and a production system. Meanwhile, increasing of measurement accuracy more than the present level by the three-dimensional coordinate measuring device as hardware incurs a result of raising manufacturing expenses besides the accompanying difficulty in a manufacturing technology. Thus, in recent years, improvement in the measurement accuracy which is a basic performance as a device has been attempted by grasping precision of the device in shipment thereof and by correcting movement of the gauge head.
However, the conventional correction of the movement of the gauge head is the one in which cumulative errors determined when the gauge head is sent for a certain interval are obtained, and then the errors are allocated in proportion to the interval. Thus, the conventional correction is not intended to perform the correction by grasping movement errors of the gauge head within the interval. The above-described is symbolized by the fact described as follows. That is, in the present situation, the evaluation method itself of the movement errors is in the stage of evaluating and comparing the errors of the measuring device in such a manner that a ball plate as shown in
FIG. 12
, which is an accuracy standard and is taken around by the world's leading organizations, is measured as shown in
FIG. 13
by three-dimensional coordinate measuring devices possessed by the world's leading organizations for searching for a standard method.
Incidentally, the ball plate is very expensive and has a considerable weight. Thus, handling thereof has not been easy. In addition, in tests by taking around the ball plate, the result thereof has not reached the point of obtaining a result as systematic as error characteristics of the three-dimensional coordinate measuring device can be stipulated. Note that FIGS.
14
(
a
) and
14
(
b
) are examples of displaying results of error measurement by the ball plate. FIG.
14
(
a
) shows directions and sizes of errors by use of bars; FIG.
14
(
b
) shows errors within a measured plane by deformation of meshes. In order to obtain position errors in three axial directions of the gauge head by locating the ball plate at a specified position in a space, it is necessary to repeat adjustment of highly accurate positioning of the ball plate of which handling is hardly easy. The above can be hardly achieved in reality, and it is extremely difficult to obtain an error space by the foregoing.
Although space errors are not obtained, as a standard error calibration method available for practical use, enumerated are: a method by use of a step gauge using standard blocks as shown in
FIG. 15
; a method by use of a normal block gauge; a method by use of a test bar as shown in
FIG. 16
; a method by use of an autocollimator as shown in
FIG. 17
; and a method by use of a laser measuring device as shown in FIG.
18
. However, in conventional methods such as the above-described method by use of the test bar, method by use of the autocollimator, laser measuring device, ball plate, and step gauge using the standard blocks, respectively, or a reverse method as shown in FIGS.
19
(
a
) and
19
(
b
), there are problems that adjustment thereof takes long time, automatic evaluation is hard to perform, and the accuracy of the measuring devices is hard to maintain.
Meanwhile, considering the case of machine tool, besides the autocollimator and a straight ruler, the laser measuring device is used for evaluating movement accuracy of a tip of a tool. However, in reality, it is hard to obtain the error space by using the above because of the following reasons and the like. Specifically, disposition and adjustment of the devices require time, the devices are not for use in evaluation of tool movement even though they are suitable for evaluating accuracy of work pieces, and the devices require too much work and time in identifying errors in three axial directions of a predetermined position in a space.
The various methods which have been heretofore used are the ones in which due consideration is given in terms of evaluating accuracy. However, from the view point of operability, productivity, price or the like concerning measurement, the above devices are not necessarily proper to be used for various purposes or to be standard devices. Therefore, it was actually hard to achieve improvement in accuracy of the device by correcting movement of the gauge head in such a manner that the error space is evaluated by the conventional method and set as a fundamental error characteristic to be an object of the correction, and a function of hardware is secured in a certain level.
Incidentally, the inventors of the present application have proposed a method of measuring a straightness error by use of a sequential two-point method in the article “Trend of Straightness Measuring Method and Development of Sequential Two-Point Method” which was previously presented in the pages 25 to 34 of “Production Research” Vol. 34, No. 6, published in June of 1982 by Institute of industrial Science, University of Tokyo. The sequential two-point method is the one for obtaining a straightness error of movement of a tool stage and a straightness error of a surface of an object to be measured simultaneously and independently of each other. Specifically, the sequential two-point method is carried out in the following manner: two displacement sensors disposed with a space therebetween on the tool stage are moved in a direction of the space at a pitch equal to the space, and simultaneously, a displaced quantity of each displacement sensor with respect to the surface of the object to be measured is measured, and thus the above straightness errors are obtained from data rows of the displaced quantities of the two displacement sensors. The inventors of the present application have achieved the points that, by application of the sequential two-point method to evaluation of errors as described above, the adjustment takes less time, the automatic evaluation can be performed easily, and the accuracy of the measuring device is easily maintained, compared to the conventional methods such as the method by use of the test bar, the methods by use of the autocollimator, laser measuring device, ball plate, and step gauge using the standard blocks or the reverse method as shown in FIGS.
19
(
a
) and
19
(
b
).
DISCLOSURE OF INVENTION
The present invention is intended to provide an error measuring method which has solved the problem of the conventional method advantageously in consideration for characteristics of the above-described sequential two-point method. A position error evaluating method of a moving device according to the present invention is characterized by including the following steps. Specifically, according to a method specified in claim
1
, in a moving device which moves a movable body in two axial directions or in three axial directions orthogonal to each other, obtaining by the sequential two-point method a straightness error curve indicating a state of change in a position error of the movable body along a uniaxial direction out of predetermined two axial directions is repeated for the other uniaxial direction out of the predetermined two axial directions, the position error being related to a direction orthogonal to the predetermined two axial directions out of the biaxi
Sato Hisayoshi
Umeda Kazunori
Educational Foundation Chuo University
Guadalupe Yaritza
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