Abstract:
A two-color radiation thermometer includes an image pickup device having micro photo receiving units arranged two-dimensionally; a light diverging device for diverging incident light coming from a measuring object into two paths and irradiating the light on two different areas on a two-dimensional light receiving surface of the image pickup device; a wavelength limitation device for limiting wavelengths of the light irradiated on the two different areas to first and second wavelengths, respectively; and a temperature calculation device. The calculation device receives image signals corresponding to the first and second wavelengths respectively from the micro photo receiving units located at the two different areas, and calculates the temperature of the measuring object based on the two image signals.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
   The present invention relates to a two-color radiation thermometer for measuring a temperature of an object in a non-contact mode using thermal radiation from the object. 
   A two-color radiation thermometer (two-wavelength radiation thermometer) has been used for measuring a temperature of, for example, combustion or explosion inside a blast furnace in a non-contact mode (refer to Japanese Patent Publication (Kokai) No. 07-253361). Particularly, when a measuring object has a two-dimensional surface, a two-color radiation thermometer with a CCD camera is useful (refer to Japanese Patent Publication (Kokai) No. 2002-309307). In such a two-color radiation thermometer, the CCD camera captures an image of a measuring surface using two different wavelengths, so that it is possible to calculate a two-dimensional temperature distribution of the measuring surface based on a difference of two images in brightness information. 
   In such a tow-color radiation thermometer, as a method of obtaining images corresponding to two wavelengths, there has been a method in which two CCD cameras independently receive light separated by a wavelength selective prism (two-plate system). As disclosed in Japanese Patent Publication (Kokai) No. 2002-309307, there has been another method in which a RGB filter, ordinarily used as a CCD sensor for regular color photography, is provided for selecting a wavelength without an optical device such as a prism (single-plate system). 
   In the two-plate system, it is possible to freely select a measuring wavelength through changing the prism or the wavelength selective filter. However, it is necessary to provide two CCD cameras, thereby making the device complicated and increasing cost. On the other hand, in the single-plate system, it is possible to make the device simple and reduce cost. However, since the CCD sensor for regular color photography is used, it is difficult to select a measuring wavelength other than the three wavelengths, i.e. red, green, and blue (RGB). Accordingly, it is difficult to measure an accurate temperature depending on a color of light (wavelength) emitted from a measuring object. 
   In view of the problems described above, the present invention has been made, and an object of the present invention is to provide a two-color radiation thermometer capable of freely and easily selecting a measuring wavelength with a simple configuration such as the single-plate system. 
   Further objects and advantages of the invention will be apparent from the following description of the invention. 
   SUMMARY OF INVENTION 
   In order to attain the objects described above, according to the present invention, a two-color radiation thermometer includes an image pickup device having micro photo receiving units arranged two-dimensionally; a light diverging device for diverging incident light coming from a measuring object into two paths and irradiating the light on two different areas on a two-dimensional light receiving surface of the image pickup device; a wavelength limitation device for limiting wavelengths of the light irradiated on the two different areas to first and second wavelengths, respectively; and a temperature calculation device for receiving image signals corresponding to the first and second wavelengths respectively from the micro photo acceptance units located at the two different areas and for calculating the temperature of the measuring object based on the two image signals. 
   The image pickup device includes a CCD type or CMOS type image sensor. The light diverging device includes a prism, and may include a device such as a polarizing beam splitter in which the light is diverged according to a polarized component. The wavelength limitation device includes a filter with wavelength selectivity. Each of the constitution elements may be a device other than the above-described elements. 
   In the two-color radiation thermometer of the present invention, the light thermally radiated from the measuring object is diverged in two paths via the light diverging device. The light diverged via the wavelength limitation device in one of the two paths is limited to have the first wavelength component, and the light in the other of the two paths is limited to have only the second wavelength component. The light is irradiated to the two different areas not overlapping on the two-dimensional light receiving surface of the image pickup device as monochromatic light. Accordingly, the light forms identical images of the measuring object with different wavelengths on the two different areas. The temperature calculation device receives image signals of the images from the micro photo receiving units located at the two different areas, and the temperature of the measuring object is calculated, for example, from the difference in light brightness according to the two images, that is, the image corresponding to the first wavelength and the image corresponding to the second wavelength. 
   In the two-color radiation thermometer of the present invention, a single (only one) image pickup device is provided, thereby making the device simple, and reducing a size of the device and cost. Furthermore, it is possible to change the measuring wavelength only through changing the wavelength limitation device such as a wavelength selective filter. Accordingly, it is easy to select the measuring wavelength according to the measuring object. 
   In the present invention, the image pickup device includes an ordinary device for sequentially reading out a pixel signal obtained at each of the micro photo acceptance units. It is preferred that the image pickup device is arranged such that it is possible to read out the pixel signals from the micro photo acceptance units located at areas at both sides of a borderline between the two different areas in parallel (two systems). 
   With this arrangement, it is possible to perform data processing such as, for example,. differentiating the two images at a high speed, while reading out the pixel signals corresponding to the two images. Therefore, it is suitable for measuring a two-dimensional temperature distribution of a phenomenon such as, for example, an explosion or combustion at a high speed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing an overall structure of a two-color radiation thermometer according to an embodiment of the present invention; 
       FIG. 2  is a schematic view-showing a light path in an image pickup unit shown in  FIG. 1 ; 
       FIG. 3  is a front view of a light receiving surface of a CCD image sensor shown in  FIG. 2 ; 
       FIG. 4  is a schematic view showing a light path in an image pickup unit of a two-color radiation thermometer according to another embodiment of the present invention; and 
       FIG. 5  is a diagram showing an overall structure of the two-color radiation thermometer of a further embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Hereunder, embodiments of the invention will be explained with reference to  FIGS. 1–3 .  FIG. 1  is a diagram showing an overall structure of a two-color radiation thermometer according to an embodiment of the present invention.  FIG. 2  is a schematic view showing a light path in an image pickup unit shown in  FIG. 1 .  FIG. 3  is a front view of a light receiving surface of a CCD image sensor shown in  FIG. 2 . 
   According to the embodiment, the two-color radiation thermometer is provided with an image pickup unit  1  including a CCD image sensor  10  for receiving light radiated from a measuring object; a CCD driving unit  2  for sending various types of control signals to the CCD image sensor  10 ; an A/D conversion unit  3  for converting a pixel signal read out from the CCD image sensor  10  to a digital signal; an image signal processing unit  4  for dividing the digitized pixel signal into images corresponding to two wavelengths λ 1  and λ 2 , and for performing a predetermined signal processing as needed; and a temperature calculation unit  5  for calculating a two-dimensional temperature distribution information of the measuring object based on the two image signals. A temperature may be calculated from the image signals corresponding to the two wavelengths λ 1  and λ 2  with conventional algorithm. 
   One of features of the present embodiment is a light path structure in the image pickup unit  1 . More specifically, as shown in  FIG. 2 , a light blocking plate  13  and a prism  14  having a wavelength selective function are disposed between an incident lens system  12  for conversing incident light and the CCD image sensor  10 . The prism  14  is provided with a λ 1 -wavelength selective transmitting filter  15  for selectively transmitting light with the wavelength λ 1  on an incident surface with a 45° angle relative the incident light, and a λ 2 -wavelength selective reflective filter  16  for selectively reflecting light with the wavelength λ 2  (transmitting light with a wavelength other than the wavelength λ 2 ) on an exit surface 180° opposite to the incident surface. 
   A λ 1 -wavelength selective transmitting filter  17  for selectively transmitting light with the wavelength λ 1  is attached to the left half of the light receiving surface of the CCD image sensor  10 , and a λ 2 -wavelength selective transmitting filter  18  for selectively transmitting light with the wavelength λ 2  is attached to the right half of the light receiving surface of the CDD image sensor  10 . The set of selective transmitting filters  17  and  18  described in the present embodiment is an example of a wave limitation device as recited in the claims. 
   As shown in  FIG. 3 , the CCD image sensor  10  has a two-dimensional light receiving surface  10   a  imaginarily divided into right and left halves relative to a substantial center. A light receiving area  10 L for receiving light with the wavelength λ 1  is positioned on the left half surface, and a light receiving area  10 R for receiving light with the wavelength λ 2  is positioned on the right half surface. That is, in the two-color radiation thermometer, identical images corresponding to the two wavelengths of λ 1  and λ 2  are formed at positions not overlapped on the two-dimensional light receiving surface  10   a  of the exclusive CCD image sensor  10 . 
   An operation of measuring a radiation temperature using the two-color radiation thermometer will be explained next. The incident lens system  12  converses light L 1  with the wavelengths λ 1  and λ 2  radiated from the measuring object  11 . The light blocking plate  13  collimates the light L 1 , and the light L 1  enters the prism  14 . In the light L 1 , only light L 2  with the wavelength λ 1  transmits through the λ 1 -wavelength selective transmitting filter  15 . When the light L 2  transmits through the λ 1 -wavelength selective transmitting filter  17  attached to the front face of the CCD image sensor  10 , light with a wavelength other than the wavelength λ 1  is further attenuated, and the light L 2  reaches the λ 1 -light receiving area  10 L on the two-dimensional light receiving surface  10   a.    
   At the same time, in the light L 1  entering the prism  14 , light with a wavelength other than the wavelength λ 1  is reflected at the λ 1 -wavelength selective transmitting filter  15  at a roughly right angle, and incidents on the λ 2 -wavelength selective reflective filter  16 . At this point, light L 3  with the wavelength λ 2  is reflected at a roughly right angle and comes out from the prism  14 . When the light L 3  transmits through the λ 2 -wavelength selective transmitting filter  18  attached on the front face of the CCD image sensor  10 , light with a wavelength other than the wavelength λ 2  is further attenuated, and the light L 3  reaches the λ 2 -light receiving area  10 R on the two-dimensional light receiving surface  10   a . In an actual arrangement, the prism  14  and other components are arranged such that the light paths of the light L 2  and L 3  have a same length. 
   In the constitution described above, the prism  14  creates two images of the original image on the two-dimensional light receiving surface  10   a  of the CCD image sensor  10 . The filters  15  and  16  provided on the prism  14  select the wavelengths λ 1  and λ 2 . The wavelength selective transmitting filters  17  and  18  attached on the front face of the two-dimensional light receiving surface  10   a  enhance purity of the wavelength through providing additional wavelength selective function. In this constitution, the λ 1 -light receiving area  10 L is located close to the λ 2 -light receiving area  10 R, so that a cross talk due to stray light and the like at the prism  14  may be an issue. The wavelength selective transmitting filters  17  and  18  are disposed adjacent to the light receiving surface  10   a  to prevent the cross talk. It is not necessary to attach the wavelength selective transmitting filters  17  and  18  to the light receiving surface  10   a . It is. preferable to provide the wavelength selective transmitting filters  17  and  18  close to the light receiving surface  10   a  as possible. 
   As described above, the λ 1 -light receiving area  10 L of the CCD image sensor  10  accumulates charge signals corresponding to the image of the measuring object  11  with only the λ 1 -wavelength component, and the λ 2 -light receiving area  10 R of the CCD image sensor  10  accumulates charge signals corresponding to the image of the measuring object  11  with only the λ 2 -wavelength component. After the charge signals are accumulated for a predetermined period of time, the CCD driving unit  2  inputs a predetermined control signal into the CCD image sensor  10 , and the pixel signals are sequentially read out from a large number of pixels constituting the two-dimensional light receiving surface  10   a . The analogue pixel signals are converted to digital signals at the A/D conversion unit  3 . The digital signals are divided into pixel signals corresponding to the λ 1 -light receiving area  10 L and pixel signals corresponding to the λ 2 -light receiving area  10 R at the image signal processing unit  4 . The temperature calculation unit  5  calculates a temperature at every each small position of the measuring object  11  based on the λ 1 -corresponding image signal and the λ 2 -corresponding image signal, and creates a temperature distribution image as temperature distribution information. The image can be displayed, for example, on the screen. 
   In the constitution described above, when the measuring wavelengths λ 1  and λ 2  are changed, the prism  14  with the wavelength selective function and the wavelength selective transmitting filters  17  and  18  attached to the two-dimensional light receiving surface  10   a  of the CCD image sensor  10  are changed. 
   A two-color radiation thermometer according to another embodiment of the present invention will be explained next with reference to  FIG. 4 . In the embodiment described above, the prism is provided for forming the two images of the measuring object. In the present embodiment, a polarizing beam splitter is provided in place of the prism. As shown in  FIG. 4 , a polarizing beam splitter  24  is provided with a P-wave selective transmitting filter  25  on an incident surface thereof and a S-wave selective transmitting filter  26  on an exit surface thereof. Also, a P-wave selective transmitting filter  19  is provided on a front surface of the λ 1 -wavelength selective transmitting filter  17 , and a S-wave selective transmitting filter  20  is provided on a front surface of the λ 2 -wavelength selective transmitting filter  18 . 
   The light L 1  with the wavelengths λ 1  and λ 2  radiated from the measuring object  11  is conversed at the incident lens system  12 , collimated by the light blocking plate  13 , and enters the polarizing beam splitter  24 . In the light L 1 , light Lp with a P-wave component transmits through the P-wave selective transmitting filter  25 . When the light Lp transmits through the P-wave selective transmitting filter  19  attached on the front face of the CCD image sensor  10 , the light L 1  with the S-wave component is further attenuated. When the light Lp transmits through the λ 1 -wavelength selective transmitting filter  17 , light with a wavelength other than the wavelength λ 1  is further attenuated, and the light Lp reaches the λ 1 -light receiving area  10 L on the two-dimensional light receiving surface  10   a.    
   At the same time, in the light L 1  entering the polarizing beam splitter  24 , light with a component other than the P-wave component, i.e. light with the S-wave component, is reflected at the P-wave selective transmitting filter  25  at a roughly right angle, and enters the S-wave selective reflective filter  26 . At this point, light with the S-wave component is reflected at a roughly right angle and comes out from the polarizing beam splitter  24 . When light with the S-wave component transmits through the S-wave selective transmitting filter  20  attached on the front face of. the CCD image sensor  10 , light with a component other than the S-wave component is further attenuated. When light with the S-wave component transmits through the λ 2 -wavelength selective transmitting filter  18 , light with a wavelength other than the wavelength λ 2  is further attenuated, and light reaches the λ 2 -light receiving area  10 R on the two-dimensional light receiving surface  10   a.    
   Accordingly, in this embodiment, the polarizing beam splitter  24  corresponds to the light diverging means, and the wavelength selective transmitting filters  17  and  18  correspond to the wavelength limitation means. The P-wave selective transmitting filter  19  and the S-wave selective transmitting filter  20  support the polarizing beam splitter  24  to divert light. 
   In the constitution of the embodiment, the image of the λ 1 -wavelength light and the image of the λ 2 -wavelength light are formed at the λ 1 -light receiving area  10 L and the λ 2 -light receiving area  10 R on the two-dimensional light receiving surface  10   a  of the CCD image sensor  10 . In this embodiment, only the wavelength selective transmitting filters  17  and  18  may be replaced when the measuring wavelengths λ 1  and λ 2  are changed, thereby making the embodiment advantageous. 
   In the embodiments described above, the solid-state image sensing device (CCD image sensor or CMOS image sensor) sequentially reads out the pixel signals via a single system output signal line. When a solid-state image sensing device can read out the pixel signals in parallel via a double system output signal line, it is possible to provide a constitution shown in  FIG. 5 . 
   The pixel signals read out from the λ 1  light receiving area  10 L are digitized at the A/D conversion unit  3   a , and the pixel signals read out from the λ 2  light receiving area  10 R are digitized at the A/D conversion unit  3   b . The pixel signals corresponding to the two images are separated when the pixel signals are read out from the CCD image sensor  10 . Accordingly, it is not necessary to perform the process of separating the image signals. When the pixel signals are read out from the CCD image sensor  10 , the two pixel signals corresponding to identical positions of the original image are simultaneously read out in parallel. As a result, it is possible to perform the process of, for example, calculating a difference of the pixel signals at the temperature calculation unit  5  at a high speed. Therefore, as compared with the embodiments described above, it is possible to calculate the temperature distribution at a higher speed. 
   The above-mentioned embodiments are just examples, and can be modified within the scope of the present invention. 
   While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.