Scanning Infrared Temperature Sensor With Sighting Apparatus

This invention relates generally to a scanning radiation sensor and method for remotely sensing radiation from a target and, more particularly, to such a radiation sensor with a sighting, or aiming, mechanism for marking the target with light at locations to be sensed.

Scanning radiation sensors are well known which have a scanning radiation sensing element assembly for scanning a target to concurrently sense radiation from a plurality of points on the target. In such sensors it is important to determine the precise location on the target from which radiation is being sensed. It is known in spot sensors to aim the sensor at the target by means of a sighting, or aiming, apparatus which projects a light, such as a laser light, to mark the spot on the target which will be sensed for radiation. Various means are used to ensure that the light mark on the target coincides with the precise locations which will be sensed.

An example of such a sighting apparatus is shown in U.S. Pat. No. 4,315,150 issued Feb. 9, 1982 to Darringer et al. In nonscanning, or spot, radiation sensors, a single spot on the target is marked with a light beam directed to the spot to be sensed. In scanning radiation sensors which scan radiation across a line on the target, a line of light across the target is used to mark the target.

Sensing the light mark on a target is a more difficult problem when the light is dispersed across the target and thus is reduced in intensity.

Another problem with such sighting apparatus is that because of poor imaging they are forced to use high intensity, nonsolid state lasers, such as HeNe lasers which are relatively fragile and require high voltage supplies.

Further, no apparatus are available for marking multiple spots on a target for individual concurrent measurement.

It is therefore a principal object of the present invention to provide a scanning radiation sensor with a sighting apparatus for locating a target whose radiation is to be sensed which marks the target with light in the visible spectrum to be both viewable by eye on the target and also easily viewable through means of a television camera and monitor. Both multiple spots and continuous lines can be marked.

Generally, this object is achieved by first selecting the light source in the visible spectrum which has a minimum wavelength significantly greater than the peak radiation response of human eye perception, of viewable light but still within the visible spectrum, so it is directly observable on the target. In addition, a camera is used having a relative response to light with wavelengths approximately equal to that of the minimum wavelength of the light source which is significantly greater than that of the relative response of human eye perception and which is significantly less responsive to wavelengths of light less than that of peak human eye response to enhance, or relatively brighten, the display of the marking line on said display. Viewability of the marking light on the display is also enhanced by viewing through a light filter which attenuates wavelengths of light significantly less than that of the minimum wavelength of the light source.

Specifically, it is an object of the present invention to provide a sighting apparatus for locating a target whose temperature is to be sensed in a scanning radiation sensor assembly having a scanning radiation sensing element comprising a source of visible light having a preselected minimum wavelength significantly greater than the wavelength of peak relative response of human eye perception of visible light, means for scanning a beam of light from said light source to produce a marking line of light on the target to be sensed by said sensing element assembly and means for enhancing viewability of the marking line including a sighting camera with a display screen for viewing the target and marking line thereon; the camera has a relative response to light with wavelengths approximately equal to the minimum wavelength of the light source which is significantly greater than that of the relative response of human eye perception to brighten display of the marking line on said screen.

A related objective is to provide a sighting apparatus for locating a target whose temperature is to be sensed in a scanning radiation sensor with a scanning radiation sensing element assembly comprising a source of light having a preselected minimum wavelength within the visible light spectrum, means for scanning a beam of light from said light source to mark said target and means for enhancing viewability of the marking line including a light filter; the light filter attenuates wavelengths of light significantly less than that of the minimum wavelength of the light source to enhance visibility of the light source reflected off the target relative to other visible light from the target.

A further object is to provide a scanning radiation sensor having a scanning sensing element assembly for detecting radiation along a line segment with a sighting apparatus for locating the line segment on a target to be sensed, comprising a solid state source of laser light in the visible spectrum, and means for scanning the laser light along a marking line segment on the target which coincides with a line segment along which temperatures will be sensed.

Still another objective of the invention is to provide in a scanning radiation sensor having a scanning sensing element assembly for detecting the individual temperatures of selected spot targets located along a scanning line with a method for locating the spot targets comprising the steps of directing a beam of light in the visible spectrum controlling the beam of light to produce light marking spots coinciding with the selected spot targets along said scan line to be sensed.

The foregoing objects and advantageous features of the invention will be explained in greater detail and others will be made apparent from the detailed description of the preferred embodiment of the present invention which is given with reference to the several figures of the drawing, in which:

FIG. 1 is a perspective view of the preferred embodiment of the radiation sensor of the present invention being used to mark a target with light markings;

FIG. 2 is a block diagram of the parts of the radiation sensor of FIG. 1 which relate to the present invention;

FIG. 3 is a block diagram of the control circuit block of FIG. 2; and

FIG. 4 is a graph of relative responsiveness of the camera and light filter of FIG. 2 to the responsiveness of the human eye to light of varying wavelengths.

Referring to FIG. 1, the preferred embodiment of the scanning radiation sensor 10 of the present invention is illustrated marking an exemplary target 12, such as a section of steel, plastic or glass or a substitute target, with a beam 14 of visible light along a line 16 on the target.

In the spot mode of operation, the marking line 16 comprises a series of spots, or relatively short line segments from which radiation and corresponding temperature will be individually determined. In a continuous mode of operation, the marking line 16 is substantially continuous over its length along which the temperature or radiation profile will be determined. The light from beam 14 which is reflected off of the target 12 at line 16 returns to the radiation sensor 10 along the optical path 15 and is detected by a camera (not shown) within a housing 18 of the sensor 10. The camera converts the light to an image viewable on a display, or television monitor (not shown).

During aiming of the sensor 10, the housing 18 is physically moved on a vertical swivel assembly connected to a base 21 and mounted on a horizontal swivel assembly 24 to move the marking line 16 until it is positioned on the target 12 at the precise location or, locations, on the target from which it is desired to sense the radiation. Sometimes, the target 12 is several feet from the sensor 10 which, in combination with problems due to ambient visible light and the scanning beam having reduced intensity radiation from the target 12, can cause the marking line to be difficult to view from the remote position of the sensor 10. This problem is solved in accordance with the present invention as explained in greater detail below.

Referring now to FIG. 2, contained within housing 18 is a scanner 22, including a scanning reflective member, such as a rotating, scanning mirror for obtaining radiation from selected locations on target 12 along the same sensing line 14 through which light from a light source 26 is directed to the target 12 by the scanner 22. The radiation from target 12 is passed to a detector 28 which converts the radiation to a representation of temperature. The scanner 22 and the light source 26 are operated by a control 30 which will be described in further detail below with reference to FIG. 3. However, the details of the structure and relative locations and general operation of the scanner 22, light source 26 and control 30 reference should be made to U.S. patent serial number 07/600638 of Sam Paris entitled "Scanning Radiation Sensor With Movable Baffle Assembly and Method of Sensing", filed on Oct. 19, 1990, contemporaneously herewith, and which has been assigned to the assignee of this application.

Still referring to FIG. 2, one aspect of the invention is achieved by virtue of light striking the target 12 along path 14 being reflected along a path 15, to a light filter 36. The light filter then passes, along a path 38, a preselected portion of the light at 32 to a television camera 40. The camera 40 then converts the light to electrical signals at an output 42 which are coupled to a display, or television monitor, 44. The camera 40 has a gain control circuit, preferably an automatic gain control circuit, 46.

Referring now to FIG. 3, the control circuit 30 includes a microprocessor 48 which responds to either manual or automatic control inputs 50 and inputs from a rotary encoder 52 to control an on/off driver circuit 54 and to provide control inputs for the scanning mirror 22 on scanner controller output 33. The rotary encoder provides an index pulse or pulses to synchronize the microprocessor 48 with the position of the scanning mirror 22 within the sensor housing 18 to provide an indication of the precise direction in which the sensor is "looking" for infrared radiation or directed for marking the target 12.

One objective of the invention is achieved by means of an on/off driver circuit 54 which selectively applies power to and removes power from the light source 26, so that a plurality of spots, or relatively short line segments, are marked on the target 12 at which individual temperatures are to be determined immediately after sighting has been accomplished. Because the measuring speed of the scanner is 80 KHz, the on/off cycles of the light source 26 must be at least half this fast. This is achieved in accordance with the present invention through use of a solid state laser.

Referring to FIG. 4, preferably, the solid state diode laser has a wavelength F in the range of approximately six hundred thirty to six hundred eighty nanometers which is significantly greater than the wavelength H of peak human eye response. The camera 40 is preferably a charge coupled device (CCD) and the response of the camera 40 has a relative response 58 to light with wavelengths F approximately equal to that of the light source 26 which is substantially greater than that of the relative response of human eye perception, as illustrated by the differential response 60.

In addition, it preferably, although not necessarily, has a response which is substantially less than that of human eye perception for a significant portion of the spectrum having wavelengths less than wavelength H of peak human response, as shown by the cross hatched area 62 under the response curve. Also, the camera 40 has a substantially uniform response to light for wavelengths from approximately four hundred nanometers to longer wavelengths beyond the wavelength F of the light source and the viewable light spectrum. Accordingly, a significant portion of light in the visual spectrum which has wavelengths significantly less than the minimum wavelength F are relatively attenuated on the display. Thus, the image of the reflected light from the light source 26 is relatively enhanced on the display.

Achieving another objective of the invention, the light filter 36 attenuates wavelengths of light significantly less from wavelength F of the light source 26 to enhance visibility of the reflected light from the light source 26 relative to other visible light from the target. Preferably, the light filter only passes light having a narrow band 64 of light on either side of wavelength F. This results in relative attenuation of light having wavelengths more as well as less than that of the wavelength F, as shown by diagonally lined area 66.

Preferably, in order to obtain optimum enhancement, the light filter 36 is used in combination with the camera 40 and is interposed between the target and the camera 26 to filter out the light to the camera 40 of wavelengths less than that of the wavelength F. As seen by dotted filter response 68, the wavelengths of light significantly greater than the wavelength F are also substantially attenuated, as shown by clear area 70 under curve 58.

Another advantageous feature of the invention is that the automatic gain control circuit 46 automatically responds to the reduction in light energy caused by light filter 36 by increasing gain, which further enhances viewability of the marking line 16. Alternatively, a manual gain control is employed.

While a detailed description of the preferred embodiment of the invention has been given, it should be appreciated that many variations can be made thereto without departing from the scope of the invention as set forth in the appended claims. For instance, while a CCD type camera display is recommended, other types of cameras with suitable responsiveness could also be used to advantage. Likewise, although a diode laser is recommended, other visible light sources could be employed. Also, the camera and display need not be mounted to the housing 18. In addition, the rotary encoder 52 could be substituted with an index position detector which detects the mirror position once for each rotation of the scanner 22 to send a pulse to the microprocessor 48 from which the position of the scanner 22 can be determined based on the speed of rotation. While in the preferred embodiment, infrared radiation is sensed to determine temperature, the advantages of the invention can be obtained with radiation sensors used for other purposes.