Data processing: measuring – calibrating – or testing – Calibration or correction system – Position measurement
Reexamination Certificate
2002-10-04
2004-03-02
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Position measurement
C702S094000, C702S104000, C033S503000, C033S559000
Reexamination Certificate
active
06701268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for calibrating a scanning probe and a computer-readable medium therefore, and particularly to a method for calibrating error of a scanning probe measuring surface texture such as size, shape, undulation, roughness, etc. of a work and a computer-readable medium therefor.
2. Description of the Related Art
There are known surface texture measuring machine for measuring a contour, roughness, undulation, etc. of a surface of a work, such as a Coordinate Measuring Machine (hereinafter, referred to CMM) for measuring the three-dimensional shape of a work, a contour measuring machine or vision measuring machine for measuring a two-dimensional contour of a work, a roundness measuring machine for measuring a roundness of a work, a surface roughness tester for measuring waviness, roughness, etc. of a surface of a work, and so on. In most cases, each of these machines has a uniaxial or multiaxial guide mechanism for moving the work relatively to a contact type or non-contact type sensor.
The guide mechanism has a guide, a feed screw, and a nut thread-engaged with the feed screw. The guide mechanism moves a slider connected to the nut. In most cases, the movement of the slider is measured with a linear scale or the like.
The guide mechanism need not have a feed screw. That is, the guide mechanism may have a guide, and a slider, in which a displacement quantity of the slider moved manually is read by a linear scale or the like. Generally, at least one kind of sensor such as a probe or a CCD camera is attached to the slider. Probes used for these applications are classified into touch signal probes and scanning probes.
FIG. 6
shows an example of use of a scanning probe
118
attached to a forward end of a spindle
117
in a CMM
100
.
The CMM
100
is configured as follows. A measuring table
112
is placed on a vibration isolating stand
111
so that an upper surface of the measuring table
112
forms a base plane coincident with a horizontal plane. A beam
114
extended in an X-axis direction is supported at upper ends of beam supports
113
a
and
113
b
erected from opposite side ends of the measuring table
112
. A lower end of the beam support
113
a
is driven in a Y-axis direction by a Y-axis drive mechanism
115
. A lower end of the beam support
113
b
is supported by an air bearing so that the beam support
113
b
can move in the Y-axis direction relatively to the measuring table
112
. The current position of the moved beam supports
113
a
and
113
b
is detected by a Y-axis scale
245
.
The beam
114
supports a column
116
extended in a vertical direction (Z-axis direction). The column
116
is driven along the beam
114
in the X-axis direction. The current position of the moved column
116
is detected by an X-axis scale
244
. The column
116
is provided with the spindle
117
so that the spindle
117
is driven along the column
116
in the Z-axis direction. The current position of the moved spindle
117
is detected by a Z-axis scale
246
.
The scanning probe
118
having a stylus
119
and a contact ball
121
is attached to a lower end of the spindle
117
. The probe
118
measures a work placed on the measuring table
112
. For example, an optical linear scale or the like is used as each of the X-axis scale
244
, the Y-axis scale
245
and the Z-axis scale
246
.
As shown in
FIG. 7
which is a block diagram, an X-axis sensor
251
, a Y-axis sensor
252
and a Z-axis sensor
253
are built into the scanning probe
118
. The sensors
251
to
253
output the quantities of displacement of the scanning probe
118
in accordance with the displacement of the stylus
119
of the scanning probe
118
in the X-axis, Y-axis and Z-axis directions respectively.
A drive unit
260
has an x-axis drive circuit
261
for driving an X-axis drive mechanism
105
, a Y-axis drive circuit
262
for driving the Y-axis drive mechanism
115
, a Z-axis drive circuit
263
for driving a Z-axis drive mechanism
125
, an X-axis counter
264
for counting the output of the X-axis scale
244
, a Y-axis counter
265
for counting the output of the Y-axis scale
245
, a Z-axis counter
266
for counting the output of the Y-axis scale
246
, an X-axis P counter
267
for counting the output of the X-axis sensor
251
, a Y-axis P counter
268
for counting the output of the Y-axis sensor
252
, and a Z-axis P counter
269
for counting the output of the Z-axis sensor
253
. The respective members of the drive unit
260
are connected to a computer
270
.
Hence, each of the X, Y and Z axes in the CMM
100
can be positioned in any position at any speed on the basis of an instruction given from the computer
270
. Further, the computer
270
is formed so that the current position of the spindle
117
in the X, Y and Z axes and the current displacement of the measurer
119
of the scanning probe
118
can be found when the respective count values of the counters
264
to
269
are input into the computer
270
.
The computer
270
has a connection unit not shown but for exchanging information with the drive unit
260
. Other constituent requirements for the computer
270
are the same as those for a known computer. That is, the computer
270
has a central processing unit, a storage device, an input device, a display device, a printing device, and an output device. Further, constitutive processes for the CMM
100
may be automatically controlled by a program stored in the storage device, or each of functions of the constitutive processes may be semi-automatically or manually controlled as occasion demands.
The constitutive processes for the CMM
100
include error compensation of the CMM
100
, collection of scanning probe data, calculation of error, display of error, functionalization of error, output of correction data, and so on.
Generally, information exchange between the computer
270
and the drive unit
260
is performed by wire communication through a transmission control procedure such as IEEE488. Alternatively, wireless communication, optical communication or the like may be used as occasion demands.
The scanning probe
118
can measure the position of the work continuously, so that contour data can be obtained easily densely at a high speed when a plurality of points in the work are measured. Hence, the scanning probe
118
is hardly influenced by the environmental change, so that there is the possibility that high accuracy measurement is made as a whole.
Such a scanning probe has been described in JP-A-5-256640 (see FIG.
8
). In the probe, a stylus is supported through an X-axis slider, a Y-axis slider and a Z-axis slider which can move in respective directions perpendicular to a pedestal.
Slide portions between the pedestal and the three sliders are supplied with compressed air to form air bearings. Hence, a frictionless guide mechanism is formed.
The guide mechanism further includes three sensors, that is, a Z-axis sensor for detecting the displacement of the Z-axis slider relative to the pedestal, a Y-axis sensor for detecting the displacement of the Y-axis slider relative to the Z-axis slider, and an X-axis sensor for detecting the displacement of the X-axis slider relative to the Y-axis slider.
The three-dimensional displacement quantity of the stylus can be measured with the three sensors.
For example, an absolute optical linear scale is used as each of the sensors. When the scanning probe is moved relatively to a work in a direction of a surface of the work while the stylus (measurer) of the scanning probe is kept in contact with the surface of the work, the stylus is displaced along the contour of the surface of the work. Hence, contour data of the work can be collected continuously.
In this case, the values of the linear scales measuring displacement of the drive mechanisms of the CMM are synthesized with the three sensor outputs from the scanning probe to thereby obtain the contour data. Incidentally, when the stylus is not in contact with the work, the ordinary stop positions (rest
Deguchi Hiromi
Noda Takashi
Takesako Koji
Barlow John
Dougherty Anthony T
Mitutoyo Corporation
Rankin, Hill Porter & Clark LLP
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