WO1993016369A1

WO1993016369A1 - Improved sensor design

Info

Publication number: WO1993016369A1
Application number: PCT/US1992/010851
Authority: WO
Inventors: James R. Cox
Original assignee: Graphics Microsystems, Inc.
Priority date: 1992-02-11
Filing date: 1992-12-14
Publication date: 1993-08-19

Abstract

An improved light sensing apparatus (28) is disclosed. A cylindrical housing (30) has a first opening (32) in one end thereof and a second opening (33) in the other end thereof. A glass window (34) is affixed to the housing to cover the first opening. At least one filter (36) is mounted within the housing interiorly of the window. A glass sphere (38) is mounted within the housing interiorly of the filter. A header (44) having a light sensor mounted thereon is affixed to the housing to cover the second opening. A lip (30b) on the housing proximate to the second opening is crimped inwardly to help secure the header into the housing.

Description

IMPROVED SENSOR DESIGN

BACKGROUND Field of the Invention;

The present invention relates to light sensing 5 devices, and more particularly, to an improved sensor design for making color measurements.

Discussion of the Prior Art;

Light sensing devices are generally well known and have application in many fields. In a typical

10 design, a housing has a window which allows light to enter the device, a lens for focusing the incoming light, and a photodiode mounted within the housing for receiving the focused light and transforming it into an electrical signal. Frequently, the window is

15 also the lens.

It is often desirable to place filters inside the housing in order to make color measurements. For example, a reflectometer is a device that incorporates filters to measure the reflectance of

20 light, thereby obtaining a measure of the color quality of either the reflected light or the reflective surface. A common sensor design, the so- called lens-end can, is illustrated in Figure l. A cylindrical housing 10 has a glass lens 12 covering

25 an opening in one end of the housing. The lens 12 is affixed to the housing 10 by a conventional glass- to-metal seal. One or more filters 14 are mounted in the housing 10 behind the lens 12 and secured in place by using an adhesive such as epoxy or an O-

30 ring 16. A photodiode 18 is mounted on a header 20, and a pair of wire leads 22 are integrally attached f to the anode and cathode of the photodiode. The header 20 is either welded or epoxied to the housing One problem with the so-called lens-end can design is that interference filters do not work well when positioned behind lens 12 because of the converging cone of light which is produced by lens 12. One solution to this problem is to position the interference filters in front of the lens 12, i.e., in another device.

Another problem with the lens-end can design is the header-to-housing seal. Welding is not practical when a small number of sensors are constructed.

Epoxy is practical, but does not provide as good a seal as welding.

Glass spheres have been used in fiber optics communication links for coupling optic fibers to sensors and to each other. See, for example, the

Hewlett Packard HBFR-2204 40MBd Miniature Fiber Optic Receiver. Glass spheres are desirable in such applications because of their short focal length, and due to the ease with which a sphere can be positioned and held within a device housing. The short focal length couples more light than other known designs. However, fiber optic sensors are concerned with the measurement of modulated light, and not in the measurement of accurate spectral response. Thus, the use of glass spheres in combination with filters has not heretofore been tried.

SUMMARY OF THE INVENTION An improved light sensing apparatus is disclosed. In the preferred embodiment, a cylindrical housing has a first opening in one end thereof and a second opening in the other end thereof. A glass window is affixed to the housing to cover the first opening. At least one filter is mounted within the housing behind the window. A glass sphere is mounted within the housing adjacent to the filter. A header having a light sensor mounted thereon is affixed to the housing to cover the second opening. A lip on the housing proximate to the second opening is crimped inwardly to help secure the header into the housing. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description of the invention and accompanying drawings which set forth an illustrative embodiment in which the principles of the invention are utilized.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a cylindrical light sensor housing constructed in accordance with the prior art. Figure 2 is a cross-sectional view of a cylindrical light sensor housing constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to Figure 2, a cross-section of a light sensing device 28 in accordance with the present invention is illustrated. A cylindrical housing 30 has a first opening 32 in one end thereof to allow light to enter the housing 30, and a second opening 33 in the other end into which a header 44 fits, as will be hereinafter described. In the preferred embodiment, the housing 30 has an outside diameter of 3/16 inch, an inside diameter of 5/32 inch (first diameter) , and a length of approximately 1/3 inch. However, near the second opening 33, the housing has a neck 30a which corresponds to a slightly increased interior diameter (second diameter) of the housing 30. Further, a lip 30b extends from the neck 30a and further defines yet another increased interior diameter (third diameter) of the housing 30. A glass window 34 (or a filter with a glass surface) covers the opening 32 and is sealed to the housing 30 by epoxy. The housing 30 could also be manufactured with a planar window (not shown) affixed to the housing 30 with a conventional glass-to-metal seal. One or more filters 36 are fitted in the housing 30 directly behind the window 34. The filter(s) 36 may be of any of a variety of conventional optical filters. The filter(s) 36 may be fixed in place with epoxy. It should be noted that a separate window 34 would not be required if the filter(s) 36 is glass and can serve as the window. A glass sphere 38 is fitted behind the filter(s) 36 and is held in place by an O-ring 40. The glass sphere 38 is approximately 4 millimeters in diameter and may be of the type sold by Edmund Scientific. The O-ring 40 may be secured to the housing 30 with epoxy. Thus, the window 34, filter(s) 36, and sphere 38 are positioned immediately adjacent each other such that they are all pressed together toward the window end of the housing 30.

A light sensor 42 is mounted on a header 44. The light sensor 42 is a conventional PIN photodiode, and includes well known circuitry to amplify, buffer, and convert incoming light signals to electrical signals. The header 44 has a flange 44a which is wider than the first diameter of the housing 30, but less than the third diameter. A small amount of epoxy is applied to the face 30c of neck 30a such that the flange 44a of header 44 will be sealed against the neck 30a when the header 44 with the sensor 42 mounted thereon is inserted into the housing 30. The lip 30b is rolled inward (approximately 20°) with a crimping tool (not shown) to further secure the header 44 within the housing 30. In operation, a light beam is directed against the surface of an object, and the light sensing device 28 is positioned to receive the light which is rf» reflected off the surface. Preferably, the light 5 sensing device is oriented so that the reflected light is substantially perpendicular to the plane of window 32. The reflected light impinges on the light sensing device 28 through window 32 and filter(s) 36. The beam is then focused by the sphere 38 to a small

10 area near the opposite surface of the sphere (back focus) . The focused beam impinges on the photodiode 42, which generates an analog signal which is proportional to the reflectance of the surface. This signal may easily be converted to a density value.

15 It can be recognized that the present invention has the following advantages. The glass sphere 38 has a very short focal length, thus permitting it to be placed as close to the sensor as the physical layout of the device will permit, for example, 0.040

20 inches or less from the active surface of the sensor 42. As previously noted, the use of a glass sphere permits more efficient light collection, thus improving the resultant signal. Also, a glass sphere is relatively inexpensive to manufacture. Further,

25 the filter(s) can be placed immediately adjacent to the sphere in a position where the incoming light beam is more nearly collimated. Additionally, the use of epoxy and crimping to seal the housing allows a sensor to be easily constructed.

30 It should be understood that the invention is not intended to be limited by the specifics of the above-described embodiment, but rather defined by the accompanying claims.

Claims

Claims :

1. A light sensing apparatus, comprising: a. a housing; b. filter means coupled to the housing and adjacent to the window means for allowing a light beam to enter the housing and for filtering one or more preselected frequencies of the light beam; c. sphere means coupled to the housing adjacent to the filter means for focusing the light beam; and d. sensor means coupled to the housing adjacent to the glass sphere for receiving the focused light beam and transforming it into an electrical signal.

2. A light sensing apparatus according to claim 1, wherein the filter means comprises an optical filter and a glass window, said optical filter being mounted inside the housing interiorly of the window.

3. A light sensing apparatus according to claim l, wherein the filter means is at least one interference filter.

4. A light sensing apparatus according to claim 1, wherein the sphere means is a glass sphere.

5. A light sensing apparatus according to claim 1, wherein the sensor means is a photodiode.

6. A light sensing apparatus according to claim 4, wherein the photodiode is mounted on a header.

7. A light sensing apparatus according to claim 1, wherein the housing comprises a cylinder having a first opening at one end thereof and a second opening at the other end thereof, and wherein the filter means covers the first opening and the sensor means covers the second opening.

8. A light sensing apparatus, comprising: a. a cylindrical housing having a first opening in one end thereof and a second opening in the other end thereof; b. a glass window affixed to the housing and covering the first opening; c. at least one filter mounted inside the housing interiorly of the window; d. a glass sphere mounted inside the housing interiorly of the filter; e. a header affixed to the housing and covering the second opening; and f. a photodiode mounted on the header inside of the housing.

9. A light sensing apparatus according to claim 8, wherein the housing further comprises a first portion having a first interior diameter, a second portion having a second interior diameter, and a lip extending from the second portion and defining a third interior diameter, wherein the first opening is in the first portion and the second opening is in the second portion, and wherein the header is affixed to the housing at the second opening, and wherein the lip is crimped inwardly to secure the header in place.