GB2060164A

GB2060164A - Optical density measuring apparatus

Info

Publication number: GB2060164A
Application number: GB8016488A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-05-18
Filing date: 1980-05-19
Publication date: 1981-04-29
Also published as: DE2920120A1; DK215580A

Abstract

A measuring probe for optical density measurement on plan-view originals comprises light source 1 arranged over electrical measuring pick-up 2. For conducting the light to measuring opening 3 in measuring head 4, light-conducting system 5 containing the pick-up is provided. Light emerges from the light- conducting system rotationally symmetrically and illuminates all- round the measuring point of the original. <IMAGE>

Description

SPECIFICATION Optical density measuring apparatus This invention relates to apparatus for measuring the density of an original seen in plan view, comprising a measuring head having a measuring opening with which a light source and a photoelectric measuring pick-up are associated, so arranged that light radiated from the said source to the measuring opening and then reflected from the measuring point of the original enters the measuring pick-up.

Such apparatus for use in a continuous microfilm copying camera is known for example from German OLS 2,020,820.

The functional principle of such measuring apparatus consists in that the face whose optical density is to be measured is illuminated and the intensity of the light reflected from the measuring face is measured with a photoelectric measuring pick-up.

In order largely to exclude influence of the surface structure of the measuring face on the result, the measuring face is illuminated at an angle of about 450, for which purpose, as a rule, two or more light sources are arranged within the measuring apparatus. With the measuring apparatus according to German OLS 2,020,280, there are provided only one light source arranged in an inclined manner and a measuring pick-up arranged in a correspondingly oppositely inclined manner, both being directed towards a measuring opening. These known constructions are disadvantageous in many respects.

Thus, if only one light source is used, as in German OLS 2,020,280, this always leads to a one-sided illumination of the measuring field of the original. If several light sources are used it cannot be excluded, in practice, that the different light sources have unequal light intensities, apart from the fact that only a point-focal arrangement of the light source is ever possible, which can therefore never lead to an ideal continuous allround illumination of the measuring point.

Furthermore, the actual measuring heads must be made sufficiently wide on such measuring apparatus to enable the light source or sources to be installed inclined in such a way that the optimal irradiation angle of 450 is obtained. However the resulting overall width of the measuring head prejudices the precise positioning of the measuring head or of the measuring opening relative to the point of the original to be measured.

For this reason, if they are to be precisely applicable, known measuring apparatus are equipped with additional devices for a precise application.

The problem of the invention is therefore to provide a measuring apparatus by means of which said disadvantages are eliminated or at least reduced, that is a measuring apparatus which can use one light source whose light nevertheless provides continuous all-round illumination of the measuring point, with the provision of as small an overall width of the measuring head as is possible with regard to a simple and precise applicability of the measuring opening to the point of the original to be measured.

This problem is solved with a measuring apparatus of the above-mentioned type according to the invention by the light source being located beyond the measuring pick-up relative to the measuring opening and a light-conducting system which contains the measuring pick-up being arranged to conduct the light to the measuring opening in such manner that the light emerges from the light-conducting system rotationally symmetrically and illuminates all-round the measuring point of the original.

In this specification the term "light-conducting system" means all such systems with which the light radiated from the light source can be received all-round, and transmitted and radiated likewise all-round on the side of the original or of the measuring opening.

The light-conducting system may be composed of mirror-coated inner faces of the measuring head, or a glass body from whose side walls the light cannot emerge due to internal reflection, or glass bodies mirror-coated on the outside, or lightconducting strands, or combinations of such forms of construction or the like. Furthermore, "a lightconducting system containing the measuring pickup" means in this connection that the measuring pick-up (photocell) is arranged within the lightconducting system, that is e.g. in the glass body, or between the light-conducting strands or the like.

Since the light source is arranged above the photoelectric measuring pick-up and the light is transmitted through the light-conducting system to the measuring point, the measuring head also may be made correspondingly narrow, so that the provision of an additional aiming device for the precise application of the measuring opening becomes superfluous.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side view of a first embodiment, showing the entire measuring apparatus with the measuring head; Figure 2 is an enlarged section of a preferred embodiment of the measuring head; and Figures 3 to 7 are sections, likewise enlarged, of further embodiments of the measuring head.

According to Figure 1 the measuring head 4 of the apparatus is located at one end of a housing 18 which can be applied in the original plane 7' coinciding with the measuring opening plane 7 of the measuring head 4. 1 designates the light source, 2 the photoelectric measuring pick-up, 3 the measuring opening and 4 the actual measuring head, in all of Figures 1 to 7 irrespective of the particular arrangements and constructions.

In the preferred exemplary embodiment according to Figure 2 the light-conducting system comprises a light-conducting body 5 consisting of a frustum-shaped part 5' and a cylindrical part 5" in which the measuring pick-up 2 is arranged over a screen 8 with light entry opening 9. The lines leading away from the measuring pick-up 2 are not shown. Arranged above the measuring pick-up 2 which is naturaily not sensitive at the top is the light source 1 from which the light following the beam path suggested by broken lines passes through the light-conducting body 5 to the measuring opening or to the measuring opening plane 7 in which the measuring point of the original under examination is illuminated all-round by the light emerging from the light exit face 6.As may be seen, the light exit face 6 has a small distance from the measuring opening plane 7, the shaping and refractive index of the lightconducting body 5 being selected so that the light is incident at 450. To prevent the entry of stray light from the light-conducting body 5 into the light-conducting channel 10 and consequently to the photocell 2, the wall of this light-conducting channel 10 is screened with a thin-walled tube 11 which forms a structural part with the screen 8.

With the very simple embodiment according to Figure 3 the light-conducting body 5 is mirrorcoated on its outer faces and has at the bottom an annular collar appliance 17 which limits the measuring opening 3 and holds the light exit face 6 at a corresponding distance from the measuring opening plane 7 upon the application of the measuring head 4. Here, also, as with the embodiment according to Figure 1 , the light radiated from the light source 1 enters the lightconducting body 5 through the irradiation face 14 and passes, correspondingly refracted, through same to the measuring plane 7 from which it travels upwardly likewise through the lightconducting body 5 to the measuring pick-up 2.

With the exemplary embodiment according to Figure 4 the walls of the inner space 12 and of the measuring head 4 are mirror-coated, that is in this case the optical system is formed by the mirrorcoating of the walls.

A special insert body 1 9 underneath the measuring pick-up 2 contains the light-conducting channel 10.

Further simple variations are illustrated in Figures 5 and 6. With the embodiment according to Figure 5 the light-conducting body 5 is situated only in the actual measuring head 4 into which the light coming from the light source 1 passes after it has been guided past the measuring pick-up 2 from the reflecting face 13 to the irradiation face 14.

With the exemplary embodiment according to Figure 6 the light-conducting body 5 is drawn relatively high upwardly so that, in so doing, the light enters the light-conducting body with relatively strong refraction and arrives, as described, at the measuring point.

An especial form of realisation is illustrated in Figure 7. Here, the light-conducting system is represented by light-conducting strands 1 6 known per se which conduct the light directly to the measuring opening 3. In so doing, the ends 20 of the light-conducting strands 1 6 terminate at 450 and are associated with one another so tightly that the requirement of an ali-round illumination of the measuring point is satisfied.

The actual size of the measuring head 4 and of the probe housing 1 8 corresponds approximately to the size represented in Figure 1 and it may be perceived that owing to the narrow design of the measuring head 4 it is possible advantageously to apply the measuring head or the measuring opening 3 precisely on the desired measuring point without the assistance of additional aiming devices on the probe housing.

Naturally, nothing stands in the way of a use of the above-described measuring apparatus for density measurements on transparent originals, since, in this case, only the light source 1 is not to be included.

Claims

1. Apparatus for measuring the optical density of an original seen in plan view, comprising a measuring head having a measuring opening with which a light source and a photoelectric measuring pick-up are associated, so arranged that light radiated from the said source to the measuring opening and then reflected from the measuring point to the original enters the measuring pick-up, the light source being located beyond the measuring pick-up relative to the measuring opening and a light-conducting system which contains the measuring pick-up being arranged to conduct the light to the measuring opening in such manner that the light emerges from the light-conducting system rotationally symmetrically and illuminates all-round the measuring point of the original.

2. Apparatus according to claim 1, wherein the exit face of a frustum-shaped light-conducting body forming at least part of the said lightconducting system is arranged within the measuring head at a spacing from the plane of the measuring opening.

3. Apparatus according to claims 1 or 2, wherein a screen with a light entry opening and a light-conducting channel impervious to light and extending to the light exit face of the said lightconducting system are arranged between the said measuring pick-up and the measuring opening.

4. Apparatus according to claim 3, wherein the said light-conducting channel comprises a thinwalled tube forming a unit with the said screen.

5. Apparatus according to any of claims 1 to 4, wherein the space accommodating the light source is provided with a rotationally symmetrical face for reflecting the light.

6. Apparatus according to any of claims 1 to 5, wherein the light-conducting body is provided on the light source side with a plane irradiation face, and a cylindrical part between this and a frustumshaped part on the measuring side.

7. Appparatus according to any of claims 1 to 6, wherein half the aperture angle of a frustumshaped part of the light-conducting body is smaller than 450.

8. Apparatus according to claim 1, wherein the light-conducting system is composed of lightconducting strands.

9. Apparatus according to claim 1, wherein a light-conducting body forming the lightconducting system itself comprises a measuring head with mirror-coated outer faces.

10. Apparatus according to claim 9, wherein the light-conducting body is provided on the measuring side with an annular collar appliance.

11. Apparatus for measuring the light density of an original seen in plan view, substantially as hereinbefore described with reference to the accompanying drawings.