U.S. patent application number 09/766449 was filed with the patent office on 2001-06-28 for device for temperature measurement.
Invention is credited to Menchine, William, Rostalski, Hans-Jurgen, Schmidt, Volker, Wyrowski, Frank.
Application Number | 20010005393 09/766449 |
Document ID | / |
Family ID | 26017408 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005393 |
Kind Code |
A1 |
Schmidt, Volker ; et
al. |
June 28, 2001 |
Device for temperature measurement
Abstract
A device for temperature measurement uses an optical system to
image the heat radiation emanating from a measurement spot on an
object of measurement onto a detector. A sighting arrangement is
also provided which has a diffractive optical system by which a
light intensity distribution is produced which corresponds to the
position and size of the measurement spot on the object of
measurement.
Inventors: |
Schmidt, Volker; (Berlin,
DE) ; Menchine, William; (Santa Cruz, CA) ;
Rostalski, Hans-Jurgen; (Berlin, DE) ; Wyrowski,
Frank; (Jena, DE) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
26017408 |
Appl. No.: |
09/766449 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09766449 |
Jan 19, 2001 |
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08836369 |
Oct 20, 1997 |
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08836369 |
Oct 20, 1997 |
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PCT/EP96/03330 |
Jul 29, 1996 |
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Current U.S.
Class: |
374/130 ;
374/121 |
Current CPC
Class: |
G01J 5/0803 20130101;
G01J 5/0808 20220101; G01J 5/07 20220101; G01J 5/0896 20130101;
G01J 5/0806 20130101; Y10S 33/21 20130101; G01J 5/08 20130101 |
Class at
Publication: |
374/130 ;
374/121 |
International
Class: |
G01J 005/08; G01J
005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 1995 |
DE |
195 28 590.5 |
Claims
1. Device for temperature measurement comprising: a) a detector for
receiving heat radiation (3) emanating from a measurement spot on
an object of measurement; b) an optical system for imaging the heat
radiation emanating from the measurement spot onto the detector; c)
and a sighting arrangement comprising: a laser: a diffractive
optical system, aligned to be illuminated by said laser, to produce
a diffraction pattern in the form of light intensity distribution
which includes a 0.sup.th order point in the center and at least
one intensive circle displaced from the center; and an optical
element, aligned to be illuminated by said intensive circle to
position said intensive circle for identifying and outlining the
position and size of the measurement spot on the object of
measurement by means of visible light and for positioning the
0.sup.th order pattern near the center of the measurement spot to
facilitate sighting.
Description
BACKGROUND OF THE INVENTION
[0001] Device for temperature measurement
[0002] The invention relates to a device for temperature
measurement.
[0003] Such devices which are known in the art for contactless
temperature measurement comprise a detector for receiving heat
radiation emanating from a measurement spot on an object of
measurement, an optical system for imaging the heat radiation
emanating from the measurement spot onto the detector and a
sighting arrangement for identifying the position and size of the
measurement spot on the object of measurement by means of visible
light. A further processing arrangement which converts the detector
signal into a temperature indication is also connected to the
detector.
[0004] In this case the optical system is so designed that at a
certain measurement distance for the most part only heat radiation
from a certain area of the object of measurement, namely the
so-called measurement spot, is focussed onto the detector. In most
cases the size of the measurement spot is defined by the area from
which 90% of the heat rays focussed onto the detector strike.
However, applications are also known in which there are reference
to values between 50% and 100%.
[0005] The pattern of the dependence of the size of the measurement
spot upon the measurement distance depends upon the design of the
optical system. A fundamental distinction is made between distant
focussing and close focussing. In distant focussing the optical
system images the detector into infinity and in close focussing it
images it onto the focus plane. In the case of distant focussing it
is necessary to deal with a measurement spot which grows linearly
with the measurement distance, whereas in close focussing the
measurement spot will first of all become smaller with the
measurement distance and after the focus plane will enlarge again
if the free aperture of the optical system is greater than the
measurement spot in the focus plane. If the measurement spot in the
focus plane is greater than the free aperture of the optical
system, then the measurement spot is also enlarged with the
measurement distance even before the focus plane. Only the increase
in the size of the measurement spot is smaller before the focus
plane than after it.
[0006] In the past various attempts were made to render the
position and size of the measurement spot, which is invisible per
se, visible by illumination. According to JP-A-47-22521 a plurality
of rays which originate from several light sources or are obtained
by reflection from a light source are directed along the marginal
rays of a close-focussed optical system onto the object of
measurement. In this way the size and position of the measurement
spot for a close-focussed system can be rendered visible by an
annular arrangement of illuminated points around the measurement
spot. U.S. Pat. No. 5,368,392 describes various methods of
outlining measurement spots by laser beams. These include the
mechanical deflection of one or several laser beams as well as the
splitting of a laser beam by a beam divider or a fiber optic system
into several single beams which surround the measurement spot.
[0007] A sighting system is also known in the art which uses two
laser beams to describe the size of the measurement spot. This
system uses two divergent beams emanating from the edge of the
optical system to characterise a close-focussed system and two
laser beams which intersect in the focus point to characterise a
close-focussed optical system.
[0008] All known sighting arrangements are either only useful for a
certain measurement distance or require relatively complex
adjustment and are often quite expensive.
SUMMARY OF THE INVENTION
[0009] The object of the invention, therefore, is to make further
developments to the device for temperature measurement in such a
way as to facilitate simple identification of the position and size
of the measurement spot independently of the distance.
[0010] This object is achieved according to one aspect of the
invention, in that the sighting arrangement has a diffractive
optical system for producing a light intensity distribution with
which the position and size of the measurement spot on the object
of measurement can be rendered visible.
[0011] According to another aspect of the invention, a diffractive
optical system is an optical element, the function of which is
based principally upon the diffraction or light waves. In order to
produce the diffraction, transverse microstructures which can
consist, for example, of a surface profile or a refractive index
profile are provided in the optical element. Diffractive optical
elements with a surface profile are also known as so-called
holographic elements. The surface patterns are produced for example
by exposure of photoresist layers to light and subsequent etching.
Such a surface profile can also be converted by electroplating into
an embossing printing block with which the hologram profile can be
transferred into heated plastic films and reproduced. Thus many
holographic elements can be produced economically from one hologram
printing block.
[0012] The pattern of the diffractive optical system is produced by
interference of an object wave with a reference wave. If for
example a spherical wave is used as the object wave and a plane
wave as the reference wave then an intensity distribution is
produced in the image plane which is composed of a point in the
centre (0.sup.th order), a first intensive circle (first order) and
further less intensive circle of greater diameter (higher orders).
By screening out of the 0.sup.th and the higher orders an
individual circle can be filtered out. A plurality of other
intensity distributions which are explained in greater detail below
with reference to several embodiments can be produced by other
object waves.
[0013] According to another aspect of the invention, usually
approximately 80% of the energy emanating from the light source
lies in the patterns produced by the diffractive optical system.
The remaining energy is distributed inside and outside the
measurement spot.
[0014] According to a further aspect of the invention, the light
intensity distribution which is produced can be formed, for
example, by a circular marking surrounding the measurement spot or
a cross-shaped marking.
[0015] Such a device can also be produced economically and only
requires a little adjustment work.
[0016] Further constructions of the invention are the subject of
the subordinate claims and are explained in greater detail below
with reference to the description of several embodiments and to the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a schematic representation of a device
according to the invention for temperature measurement according to
a first embodiment;
[0018] FIGS. 2a to 2g show schematic representations of various
light intensity distributions for identifying the position and size
of the measurement spot;
[0019] FIG. 3 shows a schematic representation or a device
according to the invention for temperature measurement according to
a second embodiment;
[0020] FIG. 4 shows a schematic representation of a device
according to the invention for temperature measurement according to
a third embodiment;
[0021] FIG. 5 shows a schematic representation of a device
according to the invention for temperature measurement according to
a fourth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] FIG. 1 shows a first embodiment of a device according to the
invention for temperature measurement, comprising
[0023] (a) a detector 1 for receiving heat radiation 3 emanating
from a measurement spot 2a of an object of measurement 2,
[0024] (b) an optical system 4 for imaging the heat radiation
emanating from the measurement spot 2a onto the detector 1,
[0025] c) and a sighting arrangement 5 for identifying the position
and size of the measurement spot 2a on the object of measurement 2
by means of visible light 6.
[0026] The sighting arrangement 5 consists essentially of a light
source 5a, a diffractive optical system formed for example by a
holographic element 5b and an additional refracting and/or
reflecting optical element 5c. The light source 5a sends a
reference wave 6a onto the holographic element 5b, resulting in a
conically opening hologram 6b which is transformed by the optical
element 5c so that it forms an intensity distribution 6c which
describes the position and size of the measurement spot 2a over all
measurement distances.
[0027] A laser is advantageously used as the light source 5a for
generating the reference wave. However, it is also possible to use
a semiconductor light-emitting diode or a thermal light source.
When a thermal light source is used a filter is advantageously
provided in order to reduce the chromatic aberrations.
[0028] The optical system 4 is formed by a dichroic beam divider 4a
and an infrared lens 4b. The heat radiation 3 emanating from the
measurement spot 2a first of all reaches the beam divider 4a which
deflects the heat radiation, i.e., the infrared radiation, by
90.degree. and delivers it to the infrared lens 4b .
[0029] Since the beam divider 4a must of necessity lie in the beam
path of the sighting arrangement 5 it is constructed as a
dichromatic beam divider which is reflective for the heat radiation
emanating from the measurement spot 2a and transparent for the
visible light of the sighting arrangement 5.
[0030] The size of the marking to be produced depends essentially
upon two parameters, namely the measurement distance and the
desired accuracy of measurement. The accuracy of measurement
results from the percentage of the rays emanating from the
measurement spot and focussed onto the detector. The area of the
measurement spot can for example be defined by the fact that 90% of
the emanating radiation reaches the detector. However, depending
upon the application this percentage can also be changed.
[0031] The optical element 5c which is adapted to the optical
system 4 is provided in order to ensure that in each measurement
distance the marking produced for identifying the measurement spot
has the correct size for the desired accuracy or measurement.
[0032] FIGS. 2a to 2g show light intensity distributions such as
might be produced on the object of measurement 2 for identifying
the measurement spot 2a. FIGS. 2a to 2d show annular markings which
substantially outline the measurement spot 2a. In this case the
markings can be configured as in FIGS. 2a and 2c as a closed circle
3a of in FIGS. 2b and 2d as a broken circle 3b. It may also be
advantageous to represent the centre of the measurement spot by a
further marking 3c, for example in the form of a dot.
[0033] In FIGS. 2e and 2f the light intensity distributions are
represented as cross-shaped markings 3d and 3e respectively. In
this case the point of intersection represents the centre of the
measurement spot 2a and the four corner points represent the outer
limits thereof.
[0034] A very advantageous light intensity distribution is
represented in FIG. 2g in the form of a plurality of concentric
circles 3f, 3g, 3h. In this case each circle represents a region of
the measurement spot 2a from which a certain percentage of the
energy of the received heat radiation originates. Thus for example
the inner circle 3f could represent the region of the measurement
spot from which 90% of the energy striking the detector originates.
The second ring 3g represents an energy value of 95% and the third
ring 3h would correspond to an energy value of 99%. With the aid of
such a light intensity distribution the user can recognise the
level of accuracy with which he can measure objects of a certain
size.
[0035] A further device according to the invention for temperature
measurement is represented in FIG. 3. The same reference numerals
are used in this case for the same components. This second
embodiment differs from the first one essentially in the design of
the optical system 4 and the optical element 5'c of the sighting
arrangement 5. In FIG. 3 the optical element 5'c is constructed as
an annular lens and accordingly is designed to produce a light
intensity distribution according to FIGS. 2a to 2d. The infrared
lens 4'b is arranged so that it is surrounded by the annular lens
5'c. The detector 1 is then provided between the holographic
element 5b and the infrared lens 4'b.
[0036] Such an arrangement has the advantage that a beam divider
can be omitted. However, a somewhat more complicated fixing of the
detector must be accepted, since the conically opening hologram 6b
must not be restricted thereby.
[0037] In the third embodiment illustrated in FIG. 4 the problem of
mounting the detector I is circumvented by providing the beam
divider 4'a between the holographic element 5b and the arrangement
consisting of the annular lens 5c and the infrared lens 4'b. Thus
the heat radiation emanating from the measurement spot 2a is
focussed first of all by the infrared lens 4'b onto the beam
divider 4'a and is there deflected by 90.degree. onto the detector
1.
[0038] Whereas all the previously described embodiments related to
distant-focussed systems, an embodiment is shown in FIG. 5 in which
the shape of the measurement spot of a close-focussed system can be
rendered visible with the aid of a diffractive optical system. In
this case the measurement plane, i.e., the object of measurement 2,
lies directly in the focus plane of the optical system 4. In each
case two rays 3i, 3k delimiting the infrared beam are shown in the
drawing. The ray 3i extends from the upper edge of the infrared
lens 4'b to the upper edge of the measurement spot 2a or from the
lower edge of the infrared lens 4'b to the lower edge of the
measurement spot. By contrast, the ray 3k extends from the lower
edge of the infrared lens 4'b to the upper edge of the measurement
spot 2a or from the upper edge of the infrared lens 4'b to the
lower edge of the measurement spot.
[0039] The optical element 5'c of the sighting arrangement 5 is
designed so as to produce two intensity cones 6d and 6e which
substantially follow the course of the marginal rays 3k and 3i. In
this case the intensity cone 6e describes the size of the
measurement spot as far as the focus plane and the intensity cone
6d describes the divergent measurement spot after the focus
plane.
[0040] A disadvantage of this embodiment is that the intensity cone
6d extends inside the marginal ray 3k, whilst the intensity cone 6e
extends outside the marginal ray 3i. However, this disadvantage can
be overcome by another design of the refracting and/or reflecting
optical element 5'c.
[0041] In the embodiment according to FIG. 5 the light intensity
distribution could advantageously be formed by two circular
concentric markings, wherein one circular marking identifies the
measurement spot lying between the optical element 5'c and the
focus plane and the other marking identifies the measurement spot
lying behind the focus plane--when viewed from the optical
element.
* * * * *