Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2000-02-08
2002-02-26
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S486000
Reexamination Certificate
active
06351312
ABSTRACT:
TECHNICAL FIELD
This invention relates to a length measuring device for generating a detection interference wave according to the distance between a light emitting portion, which is operative to emit laser light, and a moving detection portion, for A/D-converting the aforesaid detection interference wave and a reference interference wave to thereby obtain the phase difference between both of the interference waves, and for determining the position of the aforementioned moving detection portion from this phase difference and the detected wavelength of the aforesaid laser light.
BACKGROUND ART
A conventional length measuring device will be described hereinbelow with reference to
FIG. 4
,
FIG. 5
, FIG.
6
. FIG.
7
and FIG.
8
.
FIG. 4
is a block diagram schematically showing the configuration of a conventional length measuring device. Further,
FIG. 5
is a diagram showing a concrete length measuring mechanism of the conventional length measuring device. Moreover,
FIG. 6
is a diagram showing a part of a signal processing portion (namely, a phase difference processing portion), an operation portion and a storage portion of the conventional length measuring device. Moreover,
FIG. 7
is a diagram illustrating the relation between the wavelength of laser light thereof and the ratio of the intensity of transmitted light to that of reflected light thereof. Moreover,
FIG. 8
is a diagram showing the configurations of another part of the signal processing portion, the operation portion and the storage portion of the conventional length device.
In
FIG. 4
, reference numeral
100
designates a light emitting portion for emitting laser light having a frequency f;
200
an interference system;
300
a moving detection portion;
400
a light receive portion;
500
a signal processing portion;
600
an operation portion; and
700
a storage portion.
In
FIG. 5
, reference numeral
100
denotes a laser diode (LD) composing the light emitting portion; and
201
an acousto-optic modulator (AOM) adapted to generate light, whose frequency is (f+f
1
), when receiving laser light, whose frequency is f, from the laser diode
100
. Similarly, reference numeral
202
represents an acousto-optic modulator (AOM) which is driven at a frequency f
2
and generates light, whose frequency is (f+f
2
), when receiving laser light, whose frequency is f, from the laser diode
100
. The frequency difference between the frequency f
1
and the frequency f
2
is set at a very small value.
Light
801
outputted from the acousto-optic modulator
201
is reflected by a mirror
301
of the moving detection portion
200
and is then incident on the light receiving portion
400
through the interference system
200
. Further, light outputted from the acousto-optic modulator
202
is deflected by a prism
203
by a very small angle and thus becomes light
802
which is then reflected by the mirror
301
of the moving detection portion
300
and is further incident on the light receiving portion
400
through the interference system
200
. Incidentally, reference numeral
204
designates a beam splitter of the wavelength-dependent type;
805
reflected light; and
806
transmitted light.
Further, in
FIG. 5
, reference numeral
401
denotes an optical element (namely, PD: photo diode), which is provided in the light receiving portion
400
as shown in this figure. This optical element
401
is operative to detect an interference wave
803
formed from the interference between light coming from the acousto-optic modulator
201
and light coming from the acousto-optic modulator
202
. Similarly, reference numeral
402
designates an optical element (namely, PD: photo diode). This photo diode
402
is operative to detect an interference wave
804
produced from the interference between the light
801
and the light
802
which are incident on the light receiving portion
400
.
The interference wave
803
inputted to the light receiving element
401
is employed as a reference interference wave. The position of the moving detection portion
300
is determined on the basis of the phase difference between this reference interference wave and the detected interference wave
804
which is inputted to the light receiving element
402
.
As illustrated in
FIG. 6
, an output of the light receiving element
401
is inputted to a current-to-voltage conversion circuit
501
and is then converted into a voltage therein. Similarly, an output of the light receiving element
402
is inputted to a current-to-voltage conversion circuit
502
and is then converted into a voltage therein. A phase-difference count circuit
504
is operative to count clocks outputted from a phase-difference count clock generating circuit
503
in a time period between a zero-cross point of an output waveform of the current-to-voltage conversion circuit
501
and a zero-cross point of an output waveform of the current-to-voltage conversion circuit
502
. A result of the counting performed by this phase-difference count circuit
504
is inputted to the microcomputer
600
composing the operation portion. This microcomputer
600
is operative to obtain a phase difference, which is represented by using an electrical angle, according to the result of the counting.
When the difference in optical path length between the two interference waves changes by a wavelength of the laser light, the phase difference therebetween varies by 360. Therefore, a quantity acquired by adding 2&pgr; n (incidentally, “n” is an integer) to the phase difference obtained in the aforementioned manner is a total phase difference. The position of the moving detection portion
300
is determined from this total phase difference. The integer “n” is determined by counting cycles, which correspond to the time duration of the interference wave outputted from the light receiving element
402
while the moving detection portion
300
from an origin to a current position thereof, by means of the phase-difference count circuit
504
.
Generally, the wavelength of laser light is liable to vary. Moreover, the phase-difference between the interference waves is dependent on the wavelength of laser light outputted from the light emitting portion (namely, the laser diode)
100
. Thus, the aforementioned distance cannot be known only by obtaining the total phase difference between the interference waves. It is, therefore, necessary to know the exact wavelength of the laser light. In the case of the conventional length measuring device, the wavelength of laser light is detected from transmitted light and reflected light, into which the laser light is split by the beam splitter
204
of the wavelength-dependent type, in the following manner.
As shown in
FIG. 5
, the light, which has a wavelength &lgr; and is incident on the beam splitter
204
of the wavelength-dependent type, is split into the transmitted light
806
and the reflected light
805
. Furthermore, as illustrated in
FIG. 7
, there is established a predetermined relation between the wavelength &lgr; and (the ratio of the intensity of the transmitted light to the intensity of the reflected light). Therefore, the wavelength &lgr; of the incident light (namely, the laser light) can be found if the ratio of the intensity of the transmitted light to the intensity of the reflected light is known.
As illustrated in
FIG. 8
, the reflected light
805
coming from the beam splitter
204
of the wavelength-dependent type is incident on a light receiving element
403
and is then converted into a voltage by the current-to-voltage conversion circuit
505
. This voltage is converted by an A/D converter
511
through a sample-and-hold circuit
507
and a multiplexer
508
into digital data which is subsequently supplied to the microcomputer
600
.
Similarly, the transmitted light
806
of the wavelength-dependent type beam splitter
204
is incident on the light receiving element
404
and is then converted into a voltage by a current-to-voltage conversion circuit
506
. This voltage is converted by the A/D converter
511
through the sample-and
Nakajima Hajime
Nakashima Toshiro
Okamuro Takashi
Sakuma Hirokazu
Sato Yoshimitsu
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
Turner Samuel A.
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