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Claims  |
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What we claim is:
1. An optical measuring instrument for contactless measurement of a
distance between the measuring instrument and a surface of an object which
is located in a predetermined measuring region of the measuring
instrument, said measuring instrument comprising:
a radiation source emitting a coherent beam of radiation which is directed
substantially normally to the surface of said object;
at least one radiation sensor means fixedly mounted in the measuring
instrument and receiving scattered radiation reflected from the surface of
said object when the object is located within the predetermined measuring
region of the measuring instrument;
an optical device arranged between said surface of said object and said at
least one radiation sensor means;
said at least one radiation sensor means comprising at least one
strip-shaped linear radiation sensor element scannable by the scattered
radiation reflected from the surface of said object when the object is
located within said predetermined measuring region of said measuring
instrument;
a hollow cylinder enclosing said at least one linear radiation sensor
element and having an axis;
means for rotating said hollow cylinder about said axis in an operative
position thereof;
said hollow cylinder containing at least one slot which is inclined
relative to said at least one linear radiation sensor element and which
traverses said at least one linear radiation sensor element at an acute
angle while said hollow cylinder rotates about its axis;
said at least one linear radiation sensor element receiving said scattered
radiation reflected from the surface of said object, when the object is
located within said measuring region of the measuring instrument at a
predetermined distance therefrom, through said optical device at a
location of the at least one linear radiation sensor element which is a
measure of the distance of the object from the measuring instrument;
said at least one linear radiation sensor element having output means;
an electronic evaluation circuit arrangement connected to said output means
of said at least one linear radiation sensor element;
said electronic evaluation circuit arrangement only generating measuring
signals during the traversal of said at least one slot in said hollow
cylinder over said location at said at least one linear radiation sensor
element, said location constituting the location where a maximum radiation
intensity is measured and which maximum radiation intensity exceeds a
predetermined threshold value; and
said electronic circuit arrangement suppressing said measuring signals
during the traversal of said at least one slot in said hollow cylinder
over remaining portions of said at least one linear radiation sensor
element.
2. The measuring instrument as defined in claim 1, wherein:
said at least one strip-shaped linear radiation sensor element is aligned
substantially parallel to said axis of said hollow cylinder.
3. The measuring instrument as defined in claim 1, wherein:
said at least one slot in said hollow cylinder traverses said at least one
linear radiation sensor element at an angle of about 45.degree..
4. The measuring instrument as defined in claim 1, wherein:
said at least one slot in said hollow cylinder includes three additional
such slots and thus constitute four slots.
5. The measuring instrument as defined in claim 1, wherein:
said hollow cylinder, in said operative position thereof, being rotatable
about its axis at a rotational speed in the range of about 5,000 to about
25,000 revolutions per minute.
6. The measuring instrument as defined in claim 1, wherein:
said at least one strip-shaped linear radiation sensor element defines a
predetermined width which is scannable by said scattered radiation
reflected from the surface of said object;
said at least one slot in said hollow cylinder defines a predetermined
width; and
the ratio of said scannable predetermined width of said at least one linear
radiation sensor element and of said predetermined width of said at least
one slot in said hollow cylinder having a value in the range of about 0.1
to about 4.
7. The measuring instrument as defined in claim 1, wherein:
said at least one linear radiation sensor element has two ends and
generates a respective current at each of said two ends; and
said electronic circuit arrangement connected to said output means at said
two ends of said at least one linear radiation sensor element comprising:
a subtracting and summing circuit arrangement connected at two related
inputs thereof to said two ends of said at least one linear radiation
sensor element and generating at two outputs thereof signals respectively
representing the difference and the sum of the two currents generated at
said two ends of said at least one linear radiation sensor element;
a divider unit connected on its input side to said two outputs of said
subtracting and summing circuit arrangement and generating at an output
thereof a signal representing the quotient of the difference of said two
currents divided by the sum of said two currents generated at the related
outputs of said subtracting and summing circuit arrangement;
a sample-and-hold unit generating said measuring signals and having a first
input connected to the output of said divider unit;
a squaring unit connected on its input side to one of the two outputs of
said subtracting and summing circuit arrangement at which a signal
representative of the sum of said two currents is generated;
said squaring unit generating at an output thereof a signal representing
the square of said sum signal received at the input side thereof;
a threshold value detector connected at a first input thereof to the output
of said squaring unit and defining a current threshold value corresponding
to said predetermined threshold value of the radiation intensity;
said sample-and-hold unit having a second input; and
said threshold value detector being connected on the output side thereof to
said second input of said sample-and-hold unit in order to activate the
same for generating said measuring signals for a time period during which
said current threshold value detector is exceeded.
8. The measuring instrument as defined in claim 7, further including:
a passage detector provided at said hollow cylinder;
said threshold value detector having a second input;
said passage detector being connected on the output side thereof to said
second input of said threshold value detector; and
said passage detector detecting at least the start of said traversal of
said at least one slot in said hollow cylinder over said at least one
linear radiation sensor element.
9. The measuring instrument as defined in claim 7, further including:
a controllable electronic switch having at least two modes of operation and
being connected to said electronic circuit arrangement;
said electronic switch being operatively connected to said radiation source
in order to turn off and turn on said radiation source;
said electronic switch defining a first operational state and a second
operational state of the measuring instrument;
said first operational state representing a scanning mode of operation
during which said radiation source and said at least one linear radiation
sensor element remain turned on at least for a time period required for
said traversal of said at least one slot in said hollow cylinder over said
at least one linear radiation sensor element;
said second operational state representing a measuring mode of operation
following said scanning mode of operation and during which said radiation
source and said at least one linear radiation sensor element are turned on
only for a time period required for the traversal of said at least one
slot in said hollow cylinder over said location at the at least one linear
radiation sensor element where said maximum radiation intensity has been
measured during the preceding scanning mode of operation; and
said radiation source being turned off during said measuring mode of
operation and during said traversal of said at least one slot in said
hollow cylinder over the remaining portions of said at least one linear
radiation sensor element.
10. The measuring instrument as defined in claim 7, further including:
a controllable electronic switch having at least two modes of operation and
being connected to said electronic circuit arrangement;
said electronic switch being operatively connected to said at least one
linear radiation sensor element in order to turn off and turn on said at
least one linear radiation sensor element;
said electronic switch defining a first operational state and a second
operational state of the measuring instrument;
said first operational state representing a scanning mode of operation
during which said radiation source and said at least one linear radiation
sensor element remain turned on at least for a time period required for
said traversal of said at least one slot in said hollow cylinder over said
at least one linear radiation sensor element;
said second operational state representing a measuring mode of operation
following said scanning mode of operation and during which said radiation
source and said at least one linear radiation sensor element are turned on
only for a time period required for the traversal of the at least one slot
in said hollow cylinder over said location at the at least one linear
radiation sensor element where said maximum radiation intensity has been
measured during the preceding scanning mode of operation; and
said linear radiation sensor element being turned off during said measuring
mode of operation and during said traversal of said at least one slot in
said hollow cylinder over the remaining portions of said at least one
linear radiation sensor element.
11. The measuring instrument as defined in claim 7, further including:
a controllable electronic switch having at least two modes of operation and
being connected to said electronic circuit arrangement;
said electronic switch being operatively connected to said radiation source
and to said at least one linear radiation sensor element in order to turn
off and turn on said radiation source and said at least one linear
radiation sensor element;
said electronic switch defining a first operational state and a second
operational state of the measuring instrument;
said first operational state representing a scanning mode of operation
during which said radiation source and said at least one linear radiation
sensor element remain turned on at least for a time period required for
said traversal of said at least one slot in said hollow cylinder over said
at least one linear radiation sensor element;
said second operational state representing a measuring mode of operation
following said scanning mode of operation and during which said radiation
source and said at least one linear radiation sensor element are turned on
only for a time period required for the traversal of said at least one
slot in said hollow cylinder over said location where said maximum
radiation intensity has been measured during the preceding scanning mode
of operation; and
said radiation source and said at least one linear radiation sensor element
being turned off during said measuring mode of operation and during said
traversal of said at least one slot in said hollow cylinder over the
remaining portions of said at least one linear radiation sensor element.
12. The measuring instrument as defined in claim 9, further including:
a passage detector provided at said hollow cylinder;
said threshold value detector having a second input;
said passage detector being connected on the output side thereof to said
second input of said threshold value detector;
said passage detector detecting at least the start of said traversal of
said at least one slot in said hollow cylinder over said at least one
linear radiation sensor element;
said passage detector being further connected on the output side thereof,
during said scanning mode of operation, to a control input of said
electronic switch in order to turn on and turn off said electronic switch;
and
a correlator circuit arrangement replacing said squaring unit in said
electronic circuit arrangement and connected, during said measuring mode
of operation, on its input side to the output of said subtracting and
scanning circuit arrangement and on its output side to the input of said
threshold value detector.
13. The measuring instrument as defined in claim 12, wherein:
said hollow cylinder comprises a multiple number of said slots;
said electronic switch being turned on during said scanning mode of
operation at least for a time period required for the traversal of at
least two of said multiple number of slots in said hollow cylinder over
said at least one linear radiation sensor element; and
said electronic switch being turned on during said measuring mode of
operation following said scanning mode of operation only at a traversal of
one of said multiple number of slots in said hollow cylinder over said at
least one linear radiation sensor element and at which traversal, during
the preceding scanning mode of operation, a maximum correlation has
occurred between the measured radiation intensities in excess of said
predetermined threshold value of the radiation intensity.
14. The measuring instrument as defined in claim 12, wherein:
said at least one linear radiation sensor element includes one additional
linear radiation sensor element and thus constitutes two linear radiation
sensor elements; and
said two linear radiation sensor elements are arranged in said hollow
cylinder at an angular offset of about 180.degree..
15. The measuring instrument as defined in claim 14, wherein:
said electronic switch is turned on during said measuring mode of operation
only at a traversal of said at least one slot in said hollow cylinder over
one of said two linear radiation sensor elements and at which traversal,
during the preceding scanning mode of operation, a maximum correlation has
occurred between the radiation intensities measured at said two linear
radiation sensor elements in excess of said predetermined threshold value.
16. The measuring instrument as defined in claim 10, further including:
a passage detector provided at said hollow cylinder;
said threshold value detector having a second input;
said passage detector being connected on the output side thereof to said
second input of said threshold value detector;
said passage detector detecting at least the start of said traversal of
said at least one slot in said hollow cylinder over said at least one
linear radiation sensor element;
said passage detector being further connected on the output side thereof,
during said scanning mode of operation, to a control input of said
electronic switch in order to turn on and turn off said electronic switch;
and
a correlator circuit arrangement replacing said squaring unit in said
electronic circuit arrangement and connected, during said measuring mode
of operation, on its input side to the output of said subtracting and
scanning circuit arrangement and on its output side to the input of said
threshold value detector.
17. The measuring instrument as defined in claim 16, wherein:
said hollow cylinder comprises a multiple number of said slots;
said electronic switch being turned on during said scanning mode of
operation at least for a time period required for the traversal of at
least two of said multiple number of slots in said hollow cylinder over
said at least one linear radiation sensor element; and
said electronic switch being turned on during said measuring mode of
operation following said scanning mode of operation only at a traversal of
one of said multiple number of slots in said hollow cylinder with said at
least one linear radiation sensor element and at which traversal, during
the preceding scanning mode of operation, a maximum correlation has
occurred between the measured radiation intensities in excess of said
predetermined threshold value of the radiation intensity.
18. The measuring instrument as defined in claim 16, wherein:
said at least one linear radiation sensor element includes one additional
linear radiation sensor element and thus constitutes two linear radiation
sensor elements; and
said two linear radiation sensor elements are arranged in said hollow
cylinder at an angular offset of about 180.degree..
19. The measuring instrument as defined in claim 18, wherein:
said electronic switch is turned on during said measuring mode of operation
only at a traversal of said at least one slot in said hollow cylinder over
said two linear radiation sensor elements and at which traversal, during
the preceding scanning mode of operation, a maximum correlation has
occurred between the radiation intensities measured at said two linear
radiation sensor elements in excess of said predetermined threshold value
of the radiation intensity.
20. The measuring instrument as defined in claim 11, further including:
a passage detector provided at said hollow cylinder;
said threshold value detector having a second input;
said passage detector being connected on the output side thereof to said
second input of said threshold value detector;
said passage detector detecting at least the start of said traversal of
said at least one slot in said hollow cylinder over said at least one
linear radiation sensor element;
said passage detector being further connected on the output side thereof
during said scanning mode of operation, to a control input of said
electronic switch in order to turn on and turn off said electronic switch;
and
a correlator circuit arrangement replacing said squaring unit in said
electronic circuit arrangement and connected, during said measuring mode
of operation, on its input side to the output of said subtracting and
scanning circuit arrangement and on its output side to the input of said
threshold value detector.
21. The measuring instrument as defined in claim 20, wherein:
said hollow cylinder comprises a multiple number of said slots;
said electronic switch being turned on during said scanning mode of
operation at least for a time period required for the traversal of at
least two of said multiple number of slots in said hollow cylinder over
said at least one linear radiation sensor element; and
said electronic switch being turned on during said measuring mode of
operation following said scanning mode of operation only at a traversal of
one of said multiple number of slots in said hollow cylinder over said at
least one linear radiation sensor element and at which traversal, during
the preceding scanning mode of operation, a maximum correlation has
occurred between the measured radiation intensities in excess of said
predetermined threshold value of the radiation intensity.
22. The measuring instrument as defined in claim 20, wherein:
said at least one linear radiation sensor element includes one additional
linear radiation sensor element and thus constitutes two linear radiation
sensor elements; and
said two linear radiation sensor elements are arranged in said hollow
cylinder at an angular offset of about 180.degree..
23. The measuring instrument as defined in claim 22, wherein:
said electronic switch is turned on during said measuring mode of operation
only at a traversal of said at least one slot in said hollow cylinder over
one of said two linear radiation sensor elements and at which traversal,
during the preceding scanning mode of operation, a maximum correlation has
occurred between the radiation intensities measured at said two linear
radiation sensor elements in excess of said predetermined threshold value
of the radiation intensity. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a new and improved optical measuring
instrument for contactless measurement of the distance between the
measuring instrument and an object.
In its more particular aspects, the present invention relates to a new and
improved optical measuring instrument for contactless measurement of the
distance between the measuring instrument and an object and comprising a
radiation source which emits a coherent beam of radiation normally to the
surface of the object. At least one radiation sensor element is mounted at
the measuring instrument and receives scattered radiation reflected from
the surface of the object which is located within a measuring range of the
measuring instrument. An electronic evaluation circuit arrangement is
connected to the output of the radiation sensor element. The position of
the scattered light on the radiation sensor element which is received
thereby through an optical device is a measure of the distance to be
measured.
In an optical measuring instrument as known, for example, from U.S. Pat.
No. 3,723,003, granted Mar. 27, 1973, the radiation sensor element
comprises a series arrangement of a multiple number of photodiodes. The
resolution of such optical measuring instrument is limited by the width of
the photodiodes. This measuring instrument is unsuited for precision
measurements with maximum precision.
A further optical measuring instrument as known, for example, from German
Patent Publication No. 3,009,534, comprises a light source, two light
sensor elements, each of which contains a multitude of individual sensors,
and two optical devices, each of which projects onto the light sensor
elements respective sections of two images which have been separately
obtained from the object to be measured. In this arrangement there also
exists the disadvantage that the resolution is restricted by the width of
the individual sensors.
In a laser dimensional comparator as known, for example, from German Pat.
No. 2,401,618, a laser light source directs coherent light normally to the
surface of a workpiece to be measured in order to generate thereat a laser
intensity gradient. An optical device is associated with a photo-detector
in such a manner that a pair of images of the laser light-intensity
gradient generated on the workpiece is imaged on the surface of the
photo-detector. The images of the pair are spaced from each other and are
reflected from the workpiece. The surface of the photo-detector is scanned
and during the scanning operation two output pulses are generated which
are separated in time by a time period which is proportional to the
spacing which exists between the two image points of the light spot. The
two output pulses switch scaling pulses which are generated by a scaling
oscillator to a forward/backward counter. The scale or scaling pulses
delivered to the counter are counted in a logic circuit and are compared
to a reference value. In this arrangement the scanning frequency limits
the resolution. This instrument furthermore has relatively large
dimensions and is also economically disadvantageous.
In a further distance measuring instrument as known, for example, from
German Pat. No. 2,650,422, a coherent light beam is directed to a
measuring surface at a predetermined angle of incidence. The rays
reflected from the measuring surface are guided to a receiver which
contains a light sensor and which evaluates the angle of reflection for
determining the distance. In front of the light sensor of the receiver
there is arranged an involute-shaped slot diaphragm or stop which is
located on a rotating disk, and thus, constitutes a movable measuring
slit. The slot diaphragm or stop runs past a stationarily arranged
apertured stop or diaphragm. The intersection point of the circulating
slot diaphragm or stop and the stationary apertured stop or diaphragm
defines the angular position of the circulating slot diaphragm or stop and
thereby the angle between a ray, which is diffusely reflected from the
measuring surface, picked up by a lens and passed through the slot
diaphragm or stop, and the axis of the optical system and thus the
distance under investigation.
In this arrangement the angular position of the circulating slot diaphragm
or stop must be determined by counting a graduation at the rim or marginal
portion of the disc, whereby the resolution of this instrument is also
limited. In order to prevent a distance-dependent optical distortion, the
rotating disc must be arranged parallel to the direction of the light ray
which impinges on the object to be measured. As a result, the angle of
incidence of the coherent light beam on the measuring surface is
relatively small. It has been found by experience that false reflections
of relatively high intensity occur in such an arrangement and result in a
false measurement. The arrangement of the receiver in this instrument is
such that all of the false reflections originating from the measuring
surface reach the light sensor and result in the generation of a measuring
signal. Therefore the uncertainty of the measurement is relatively great.
The interfering effects can be counter acted at the light sensor by
reducing the sensitivity thereof. Since, however, the intensity of the
reflected light ray depends on the material of the measuring surface, the
reduction in the sensitivity of the light sensor may have the result that
measuring surfaces of poorly reflecting materials either cannot be
utilized or require complicated adjusting operations.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is a primary object of the
present invention to provide a new and improved optical measuring
instrument for contactless, high resolution measurement of the distance
between the measuring instrument and an object.
A further significant object of the present invention is directed to a new
and improved optical measuring instrument for the contactless measurement
of the distance between the measuring instrument and an object and which
practically renders ineffective any interfering influences and which also
is economically advantageous.
Now in order to implement these and still further objects of the invention,
which will become more readily apparent as the description proceeds, the
measuring instrument of the present development is manifested by the
features that, the radiation sensor element comprises a strip-shaped
linear radiation sensor element scannable by the scattered radiation
reflected from within the measuring region. A hollow cylinder is rotatable
in an operative position thereof and encloses the linear radiation sensor
element. This hollow cylinder is provided with at least one slot
traversing the strip-shaped linear radiation sensor element at an acute
angle. There is also provided an electronic evaluation circuit arrangement
which generates measuring signals at the most during the traversal of one
slot over a location at the linear radiation sensor element where the
highest radiation intensity is measured and exceeds a predetermined
threshold value. The electronic evaluation circuit arrangement suppresses
the measuring signals during the traversal of the slot over the remaining
portions of the linear radiation sensor element.
Advantageously, the strip-shaped linear radiation sensor element is aligned
essentially parallel to the axis of the hollow cylinder.
Preferably, the slot traverses or crosses over the strip-shaped linear
radiation sensor element at an angle of about 45.degree..
Four slots can be provided at the hollow cylinder. In its operative
position this hollow cylinder may have a rotational speed in the range of
5,000 to 25,000 revolutions per minute.
The strip-shaped linear radiation sensor element has a width which is
scannable by the scattered light; the ratio of this scannable width and
the width of the slot in the hollow cylinder can have a value in the range
of about 0.1 to about 4.
The electronic evaluation circuit arrangement is connected to the two
opposite ends of the linear radiation sensor element and may contain a
subtracting and summing circuit arrangement for the currents issuing from
these two ends of the linear radiation sensor element, a dividing unit
series-connected thereto and dividing the difference of the currents by
the sum of the currents, and a sample-and-hold unit or circuit. A squaring
unit is provided for squaring the sum of the currents and controls a
series-connected threshold value detector which determines whether a
current limit corresponding to a predetermined limiting value of the
radiation intensity is exceeded and which activates the sample-and-hold
unit to generate the measuring signals for the time period during which
the current limit is exceeded.
A detector which detects at least the start of the passage or traversal of
the slot over the linear radiation sensor element can be provided at the
hollow cylinder.
The electronic evaluation circuit arrangement may contain a controllable
electronic switch having at least two operational modes and by means of
which the radiation source and/or the linear radiation sensor element can
be turned on and off in such a manner that, during a first scanning mode
of operation, the radiation source and the linear radiation sensor element
remain turned on at least for a time period required for at least one slot
to pass over the linear radiation sensor element and that, during a
successive measuring mode of operation, the radiation source and the
linear radiation sensor element are only turned on at a traversal location
at which a slot passes over such a location at the linear radiation sensor
element where the relatively largest radiation intensity has been measured
during the preceding scanning mode of operation. The radiation source
and/or the linear radiation sensor element are turned off during the slot
traversal over the remaining locations of the sensor element.
A connection to the detector may be present during the scanning mode of
operation for controlling the turn-on and the turn-off of the electronic
switch. In the measuring mode of operation a correlator circuit
arrangement and a threshold value detector can be series-connected to the
linear radiation sensor element.
In an optical measuring instrument comprising one linear radiation sensor
element the electronic switch may be turned on during the scanning mode of
operation for a time period required for the passage of at least two slots
over the linear radiation sensor element. In the subsequent measuring mode
of operation the electronic switch may be turned on only at such traversal
or cross over between a slot and the linear radiation sensor element at
which there has occurred, during the preceding scanning mode of operation,
a maximum correlation between the measured radiation intensities which
exceeded a predetermined limiting or threshold value.
In an optical measuring instrument comprising two linear radiation sensor
elements, the two linear radiation sensor elements may be offset by
180.degree. in the hollow cylinder. Preferably, the electronic switch is
turned on during the measuring mode of operation only at such traversal
location between a slot and one of the linear radiation sensor elements at
which traversal location, during the preceding scanning mode of operation,
a maximum correlation has occurred between the radiation intensities
measured at the two linear radiation sensor elements and a predetermined
limiting or threshold value has been exceeded.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects other than those set
forth above, will become apparent when consideration is given to the
following detailed description thereof, wherein throughout the various
figures of the drawings there have been generally used the same reference
characters to denote the same or analogous components and wherein:
FIG. 1 is a schematic illustration of a first embodiment of the optical
measuring instrument according to the invention;
FIG. 2 shows a development of a hollow cylinder provided with four slots
and forming a component of the optical measuring instrument shown in FIG.
1; also shown is the radiation intensity of the radiation source as well
as the measuring signals as a function of time;
FIG. 3 is a block diagram of an evaluation circuit arrangement in the
optical measuring instrument shown in FIG. 1;
FIG. 4 shows the development of a hollow cylinder provided with four slots
and forming a component of the optical measuring instrument shown in FIG.
1; also shown are the radiation intensity of the radiation source and the
measuring signals as a function of time in a modified electronic circuit
arrangement;
FIG. 5 is a block circuit diagram of the modified evaluation circuit
arrangement;
FIG. 6 is a schematic representation of a second embodiment of the optical
measuring instrument according to the invention containing two radiation
beams and two linear radiation sensor elements; and
FIG. 7 shows the development of a hollow cylinder provided with two slots
and forming a component in the optical measuring instrument shown in FIG.
6; also shown are the radiation intensity of the radiation source and the
measuring signals as a function of time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Describing now the drawings, it is to be understood that only enough of the
construction of the optical measuring instrument has been shown as needed
for those skilled in the art to readily understand the underlying
principles and concepts of the present development, while simplifying the
showing of the drawings. Turning attention now specifically to FIG. 1,
there has been schematically illustrated a first embodiment of the
inventive optical measuring instrument for contactless distance
measurements. The optical measuring instrument contains a radiation source
1 which emits radiation of an appropriate wavelength, for instance light
in the visible region of the spectrum and which may have the form of a
laser. The radiation source 1 emits a coherent radiation beam 2 in a
direction normally to a surface 3 of an object 3'. Stationary radiation
sensor means are fixedly mounted or arranged within a housing 4 and
comprise a strip-shaped linear radiation sensor element 5 which receives
scattered radiation 6 which is reflected from the object 3' through a
suitable optical device 7, such as a collecting lens. Such strip-shaped
linear radiation sensor elements are commercially available components
well known in the art, and one such suitable construction is marketed by
Sitek Laboratories AB, a Swedish firm located at Goteborg, Sweden, under
their commercial designation Type 1L10x1. This linear radiation sensor
element 5 is stationarily arranged within a hollow cylinder 8 which is
rotatable in its operative position by drive means 11 in a conventional
manner. The hollow cylinder 8 defines an axis 8' and the linear radiation
sensor element 5 is aligned parallel to this cylinder axis 8'. At least
one slot 9, and specifically in the illustrated exemplary embodiment, four
slots 9 are cut out in the hollow cylinder 8 and these slots 9 cross over
or traverse the linear radiation sensor element 5 at an acute angle 10.
For reasons of space the angle 10 is a small angle in the drawing of FIG.
2. Experiments have shown that optimum measuring results can be achieved
at an angle 10 of substantially 45.degree..
A development of this hollow cylinder 8 containing the four slots 9 is
illustrated in FIG. 2.
The hollow cylinder 8 is driven by the drive means or drive motor 11 at a
rotational speed in the range of 5,000 to 25,000 revolutions per minute,
preferably at a rotational speed of 20,000 revolutions per minute. At this
rotational speed the slot 9 requires only 0.75 milliseconds for passing
over or traversing the linear radiation sensor element 5.
In order to use the optical measuring instrument described hereinbefore the
surface 3 of the object 3' must be positioned within a predetermined
measuring region B. The distance to be measured is designated by reference
character A in FIG. 1 and the position of the received scattered radiation
6 at the linear radiation sensor element 5 is a measure of the distance A.
This position is indicated in FIG. 2 by the spacing a. It can be
mathematically deducted in known manner that the spacing a is proportional
to the quotient Ia-Ib/Ia+Ib. In this quotient Ia designates the current
tapped at the "a"-end and Ib represents the current tapped at the "b"-end
of the linear radiation sensor element 5.
During rotation of the hollow cylinder 8 the slots 9 pass over the linear
radiation sensor element 5 and ensure that only one single location at the
linear radiation sensor element 5 is accessible for scattered radiation 6
at each moment of time when an object 3' is present in the measuring
region B. The strip-shaped linear radiation sensor element 5 has a
predetermined width and is scannable or swept by the scattered radiation
6, and the slot 9 in the hollow cylinder 8 also has a predetermined width.
Advantageously, the ratio between the scannable width of the linear
radiation sensor element 5 and the width of the slot 9 in the hollow
cylinder 8 is in the range of about 0.1 to about 4. In the presently
described example the ratio has a value of about 1.5. Without using the
rotating hollow cylinder 8 which is provided with the slots 9 extending at
an inclination, the determination of the distance a on the basis of the
highest radiation intensity would not be possible, at least not with the
required precision, because interfering radiation which impinges on the
linear radiation sensor element 5 at locations which are outside the
spacing a, despite their lower intensity, would disproportionately
strongly affect the measuring operation. In other words, the hollow
cylinder 8 therefore shields the major portion of the linear radiation
sensor element 5 from such interfering radiation, exposing only a minor,
currently effective, measuring portion defined by the above-mentioned
ratio to incoming measurement radiation and possible but negligibly little
interference radiation.
The laser radiation source 1 continuously emits a pulse-modulated coherent
radiation beam 2 in a direction normally to the surface 3 of the object 3'
at an intensity L as indicated in FIG. 2 in which the time is designated
by t. The radiation beam 2 is merely schematically shown in FIG. 3
extending at an inclination with respect to the surface 3. The scattered
radiation 6, as shown in FIG. 3, is received at the linear radiation
sensor element 5 from the surface 3 through one of the slots 9 provided in
the hollow cylinder 8. Also in this case the hollow cylinder 8 and the
drive motor 11 are only schematically illustrated. The laser radiation
source 1 and output means 5' of the linear radiation sensor element 5 are
connected to an evaluation circuit arrangement 12 which is illustrated in
FIG. 3 in block circuit diagram. The currents Ia and Ib are conducted from
output means 5' at the "a"- and "b"-ends of the linear radiation sensor
element 5 through related preamplifiers 13 and 14 and are supplied to
related inputs 15a and 15b of a subtracting and summing circuit
arrangement 15. A divider unit 16 is connected on its input side to the
outputs 15c and 15d of the subtracting and summing circuit arrangement 15
and continuously derives from the quotient Ia-Ib divided by Ia+Ib a signal
which corresponds to the spacing a at the linear radiation sensor element
5. This signal is fed to a first input 17a of a sample-and-hold unit or
circuit 17.
A squaring unit 18 is connected on its input side to the output 15d of the
subtracting and summing circuit arrangement 15 and generates at an output
18a a signal which corresponds to the square of the sum of the two
currents, i.e. to (Ia+Ib).sup.2. The output 18a of the squaring unit 18 is
connected to a first input 19a of a threshold value detector 19. The
squared sum of the currents Ia and Ib renders discernible in the threshold
value detector 19 current magnitudes which exceed a current limiting or
threshold value which corresponds to a predetermined threshold value of
the radiation intensity and which is assumed to be about 80% in FIG. 2. In
this manner there can be detected the traversal which exists between one
of the slots 9 and that location at the linear radiation sensor element 5
at which there occurs the maximum radiation intensity in excess of the
predetermined threshold value. As soon as the current limiting value of
about 80% is reached in the threshold value detector 19, a signal is
generated on the output side thereof and conducted to a second input 17b
of the sample-and-hold unit 17 in order to activate the same for
generating measuring signals M as illustrated in FIG. 2.
These measuring signals M are generated only for a period of time during
which the current magnitudes in the threshold value detector 19 exceed the
current limiting threshold value set at about 80%. During the traversal of
the slots 9 over the remaining cross-over regions or locations of such
slots 9 with the linear radiation sensor element 5 the generation of the
measuring signals M is suppressed. Due to the fact that measuring signals
or measuring values M are generated only within a small region
encompassing the location at which the maximum radiation intensity exists
at the linear radiation sensor element 5, the exact position of the
maximum of the measuring value can be determined or recognized and the
intended high resolution of the measuring instrument can be achieved.
The current sum also affects a control unit 20 of the laser radiation
source 1 and thereby the correct radiation intensity is automatically
adjusted.
The threshold value detector 19 is controlled via a clock line 21 of the
system and via a passage detector 22 which scans the hollow cylinder 8 and
determines the start of each passage or traversal of a slot 9 over the
linear radiation sensor element 5. Such control enables synchronization of
the movement of the hollow cylinder 8 with further units such as, for
example, a microprocessor not particularly illustrated in the drawings.
Such further units may be connected to an analog output 23 or to an output
24 of an A/D-converter 25.
Instead of squaring the current sum values which are generated during the
passing-over or traversal of one of the slots 9 over the linear radiation
sensor element 5 in the squaring unit 18, there can also be multiplied
current values which were successively obtained in two successively
conducted measurements at the same location of the linear radiation sensor
element 5. Using such cross-correlation, interferences which do not occur
at the same time or not at the same position of the linear radiation
sensor element 5 can be eliminated in a simple manner. FIG. 4 shows the
course of events with respect to time and FIG. 5 shows the associated
block circuit diagram of a correspondingly modified electronic evaluation
circuit arrangement. Members or components shown in FIG. 5 and identical
with corresponding members or components shown in FIG. 3 are conveniently
provided with the same reference characters.
The passage detector 22 detects the start of the passing-over or traversal
of one slot 9 over the linear radiation sensor element 5 and turns on an
electronic switch 26 via a control input 26a thereof for the time period
required for the passage of two slots 9 over the linear radiation sensor
element 5. The controllable electronic switch 26 has at least two modes of
operation and is operatively connected to the radiation source 1 as shown
in the illustrated exemplary embodiment. Instead of this arrangement the
controllable electronic switch 26 may be operatively connected either to
the linear radiation sensor element 5 or to both the radiation source 1
and to the linear radiation sensor element 5. During this first scanning
mode of operation the electronic switch 26 activates the control unit 27
of the laser radiation source 1, and thus, causes coherent radiation beams
2 of the intensities L1 and L2 to be emitted during related times t1 and
t2 and during the aforementioned two passages or | | |
