Geometrical instruments – Gauge – Coordinate movable probe or machine
Reexamination Certificate
2000-11-16
2002-10-08
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Gauge
Coordinate movable probe or machine
C033S19900R
Reexamination Certificate
active
06460261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a V-groove shape measuring method and apparatus, and more particularly to a V-groove shape measuring method and apparatus preferably used for measuring characteristic values such as pitch deviation or axial runout of side face of V-grooves of the work to be measured spirally forming V-grooves for worm gear, male threads, screw holes, and the like, by using a three-dimensional coordinate measuring machine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
As an instrument for measuring a solid figure of a work or other object to be measured at high precision, a three-dimensional coordinate measuring machine (or three-dimensional measuring machine)
10
as shown in
FIG. 1
has been known. It comprises a platen
12
with a smooth and flat polished surface made of, for example, granite, a portal frame
14
installed to be movable in the longitudinal direction (for example, Y-axis direction) of the platen
12
, a slider
16
installed to be movable in the lateral direction (for example, X-axis. direction) along a horizontal beam
15
of the portal frame
14
, an elevating shaft
18
installed on this slider
16
to be movable in the vertical direction (for example, z-axis direction), and a probe
22
for measuring coordinates, being provided at the lower end of this elevating shaft
18
through a probe holder
20
, and having a measuring element
24
formed at the leading end thereof.
Therefore, after putting a work W to be measured on the platen
12
, the probe
22
is moved in three directions (X-, Y-, Z-axis directions) to cause the measuring element
24
to contact with measuring positions of the work W, and at each contact point, sequentially, the coordinate values in each axial direction of the probe
22
are read from a scale not shown, and these coordinate values are calculated, so that the dimensions and angle of the work W can be measured at high precision.
As a method of measuring
1
the screw shape by using such three-dimensional measuring machine, the present applicant proposed a method of determining the center coordinates of screw hole in, for example, Japanese Laid-open Patent No.Hei 6(1994)-341826.
When measuring the work shape by using such three-dimensional measuring machine, it is required to scan and measure the work coordinates sequentially while moving the probe
22
for measuring the coordinates. As an automatic method for this scanning control by using a computer, without using a rotary table, a control method of scanning along the contour of the work while keeping constant the height from a reference plane by using an arbitrary plane as a reference plane (hereinafter called height constant scanning control), and a control method, shown in
FIG. 3
in case of using a rotary table
30
, of scanning along the contour of the work W within a cylindrical plane determined by specification of an arbitrary straight line and the distance (that is, the radius) from the straight line (hereinafter called radius constant scanning control).
Further, as shown in
FIG. 2
, with using the rotary table
30
, the applicant proposed U.S. Pat. No. 5,204,824 (corresponding to UK 2237661, DE4027339A1), in which one axis by rotary table is added to a three-axis scanning control without using a rotary table, scanning by a four-axis simultaneous control is realized while keeping constant the direction of the probe with respect to the measurement reference line of the work (called measuring element direction constant scanning control).
According to this method, when not using the rotary table, as in the case of the cylindrical cam shown in
FIG. 3
, if it is impossible to measure by one operation due to interference of the work and the probe, it is possible to measure the whole circumference by one operation without changing the position (direction) of the probe. Besides, even in the case of impeller or propeller blades that cannot be measured by one operation, the number of times of changing the position of the probe can be decreased.
Recently, on the other hand, as the objects of measurement are diversified, there are increasing demands for measuring a deviation (for example, maximum deviation) of thread pitch P of worm gear forming spiral V-grooves, general male threads, or screw holes formed in works as shown in
FIG. 5
, or the deviation (for example, maximum deviation &Dgr;R) in the radius R direction of the plane locus of threads superposed in the axial direction as shown in
FIG. 6
, but they could not be measured accurately in the conventional methods.
BRIEF SUMMARY OF THE INVENTION
The invention is devised to solve the problems of the prior arts, and it is hence an object thereof to measure the characteristic values of V-groove shape accurately, such as worm gears, general male threads, and screw holes.
The invention is for scanning and measuring a V-groove by using a scanning probe for measuring the position, while rotating a work by a rotary table, with the work having a spiral V-groove fixed on the rotary table, by combining:
a measuring element direction constant control aiming at keeping constant a vector projected on the table plane of the rotary table of a direction vector from the origin of the work to a measuring element of the scanning probe as seen from a machine coordinate system,
a rotary table radius constant scanning control of which confinement plane is a cylindrical plane, and
a two-flank contact scanning control for causing the measuring element to contact with two flanks for composing the V-groove,
wherein a V-groove rotary table scanning control and a measurement are performed while keeping the measuring element always in contact with the two flanks for composing the V-groove, thereby solving the problems.
The V-groove rotary table scanning control may be realized by:
sampling a position vector X of the scanning probe (hereinafter all vector symbols are omitted to avoid complication of description of the specification), its displacement amount &Dgr;X, and rotational angle &thgr; of the rotary table,
calculating an approach reverse direction vector Qu in a direction vertical to the axial center V of the object from the rotational angle &thgr; of the rotary table,
calculating the speed vector V of the probe while the rotary table is stopped at the rotational angle &thgr;,
calculating the angular velocity &ohgr;W of the rotary table by speed vector V of the probe as seen from the axial center of the work,
adjusting the advance or retardation from a target value of the rotational angle &thgr; of the table due to control error from the configuration of the table rotational angle &thgr; and the probe position X, determining a correction angular velocity &Dgr;&ohgr;, and correcting the angular velocity cow from this &Dgr;&ohgr;,
calculating a speed vector Vt following up the movement of the correction angular velocity &Dgr;&ohgr; at the probe position X and the table rotational angle &thgr;, and
calculating a vector sum Vf(=V+Vt) of the follow-up speed vector Vt and probe speed vector V to obtain a probe speed command, and correcting the angular velocity &ohgr;w by the correction angular velocity &Dgr;&ohgr; to obtain a value &ohgr;t(=&ohgr;w+&Dgr;&ohgr;) as a speed command of the rotary table.
The speed vector V of the probe may be the sum of the basic speed vector Vo showing the basic running direction of the scanning probe, a displacement correction vector Ve for keeping constant the displacement of the scanning probe, and a two-flank contact vector Vh for causing the measuring element to contact with two flanks of the V-groove.
Further, the radius correction vector Vr for keeping the radius constant may be added to the sum to obtain the speed vector V of the probe.
It may be regarded as an error when two-flank contact is not maintained during two-flank contact scanning control, so that a wrong measurement may not persist.
It may be judged that the two-flank contact is not maintained when an angle &agr;
Deguchi Hiromi
Noda Takashi
Ogura Katsuyuki
Jagan Mirellys
Mitutoyo Corporation
Oliff & Berridg,e PLC
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