GB1558780A - Illiminator - Google Patents

Description

(54) ILLUMINATORS (71) We, XEROX CORPORATION, of Xerox Square, Rochester, New York, United States of America, a corporation organized under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to illuminators particularly for use in copying machines.

At the present time there are a great number of applications where an illuminator is required which is safe to operate and is capable of providing a high intensity of illumination per unit volume. Proposals and some current modern machines use quartz-halogen lamps or illuminators of the type illustrated for example, in USA patent 3,211,938 in which a coiled element extends the length of quartz envelope containing gaseous iodine. In copying machines, there is usually a requirement for an illuminator which is capable of providing illumination of substantially uniform intensity over a wide area. At the present time fluorescent lamps are commonly used in copying machines but difficulties arise in ensuring a level of uniform intensity is maintained at the extremes of the lamps. Thus, to achieve a uniform light distribution over a wide area, the lamp (and therefore the overall dimension of the copying machine) must be substantially longer than the width of the area to be illuminated.

Further, as is described in the above mentioned patent, the lamp generates a great amount of heat as well as light and causes, in its described configuration, difficulties of dissipating the heat and of the effect of heat on a mounted reflector, for example.

Generally whereas a quartz-halogen lamp of the type mentioned provides a high degree of illumination compared with a similar sized fluorescent lamp, it has certain drawbacks including difficulty of heat dissipation. Such quartz-halogen lamps are also less robust mechanically and in copying machines in particular, the lamp is often required to stand up to high levels of acceleration and deceleration of scanning mechanisms. A difficulty of satisfactorily mounting the filament is also experienced while retaining uniform illumination output along the length of the lamp throughout the required lifetime of the lamp.

It is an object of the present invention to provide an improved illuminator for a copying machine.

According to the invention, there is provided a copying machine having a platen for supporting documents to be copied and an illuminator for illuminating said platen, said illuminator comprising a diffusely reflective elongate tubular envelope and having a narrow window or opening extending at least the length of the envelope through which light can pass out of said illuminator and towards said platen, said illuminator also comprising at each end of said envelope a specular reflector surface having its periphery juxtaposed to a respective end of said envelope, and an illumination element mounted within said reflector, said reflector having a surface which is arranged to focus light into an annulus around the inside of said envelope and such that light reflected directly by said surface out of said window is directed obliquely so as not to strike said platen without reflection.

An illuminator for a copying machine according to the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 shows schematically in section the general form of the illuminator; Fig. 2 shows view A-A of Fig. 1; and Fig. 3 shows schematically the illuminator in more detail and a document to be copied.

Referring to the drawings, an elongated tubular envelope 10 is provided on its external surface with diffuse reflective material 11 extending over the internal surface.

The envelope 10 subtends an arc of 315" about its longitudinal axis (see Fig. 2 where angle B = 45 ) to provide a narrow window 12 extending along the length of the envelope 10 through which light can pass. At each end of the envelope 10, there is provided a quartz-halogen lamp 13 and 14, each with an integral reflector. These lamps are different from the commercially available integral reflector projector lamps (e.g.

"Atlas" type A1/231) in having a special shape of reflector surface instead of the elliptical reflector normally supplied with projector lamps. The lamps 13 and 14 are releasably attached by means not shown to the envelope 10. The lamps 13 and 14 have respective specular reflective surfaces 13b and 14b, which are generally ellipsoidal in shape (as will be described in more detail later) behind the filaments 13a and 14a, and peripheries of the reflective surfaces 13b and 1 4b are held against respective ends of the envelope 10, which direct light generally along the envelope 10.

In use, light also radiates through the window 12 from the filaments 13a and 14a either directly or after single or multiple reflection within the envelope 10 as is discussed in more detail later.

The lamps 13 and 14 are preferably matched where the illuminator is for use in electrostatographic copying machines especially those machines incorporating liquid development. This ensures a high intensity and substantially uniform intensity of illumination output along the length of the window 12. In practice, the lamps are tested as supplied and matched in pairs for equal or near equal output.

iaiIn the illuminator described. a substan amount of heat is liberated by the lamps and a convection cooling system is provided in a copying machine application to dissipate the heat generated. Compared to quartz-halogen lamps in which the active part, that is the filament, extends along the length of the illuminator, the cooling system is much simplified. This is because it is relatively easier to provide cooling air ducts for example, at either side of the illuminator than along the whole length.

In the embodiment, the lamps 13 and 14 are releasably attached to the envelope 10.

This facilitates the attachment and replacement of the lamps in the event of lamp fail- ure. It will be appreciated, however, that the illuminator can be formed as an- integral unit with the lamp 13 and 14 permanently or more permanently attached than described.

Preferably, the reflective material comprises a high diffuse reflectance material such as for example, available under the trade mark EASTMAN white reflective paint no 6080.

In other embodiments, the envelope 10 itself is formed of reflective material, or is transparent and has a reflective layer on its outer surface instead of its inner surface. The envelope may be formed such that the window is defined by the part of the envelope, its inner or outer surface, not coated with reflective material. Further, it is within the scope of this invention to provide further layers for absorbing unwanted visible and invisible light rays, such as in techniques commonly used in optical filter technology.

The window 12 may be formed by a slot removed from the surface of the envelope 10 or otherwise. Generally, as there is no requirement for a sealed atmosphere, manufacturing the envelope 10 is much easier than the manufacture of the comparable envelopes of fluorescent and enveloped quartzhalogen lamps. In one embodiment, for example comparatively cheap plastic materials have been used to form the envelope 10.

In matching illumination intensity output of lamps and illumination sensing properties of image forming surfaces, a technique of varying the optical path between them in some way is often used. It will be apparent that such can be readily and integrally incorporated in this invention. For example, window 12 can be shaped to provide such adjustment and compensation as might be required. However one aspect of the present invention is that it enables an illuminator having the possibility of maximum intensity of illumination at its ends, so less compen- sation is usually required in practice. Falloff of illumination at ends of extended filament quartz-halogen lamps and fluorescent lamps is one difficulty of using such lamps in copying machines.

We prefer to use as illumination sources the quartz-halogen lamps of the type shown because they provide a high output per unit volume. However, an illuminator according to the invention can be formed with other types of source, such as vacuum filament lamps or xenon discharge tubes. But in each case due regard is given to the spectral output of the chosen lamps in relation to the spectral response of the associated image receiving components.

For general purpose copying machines, a satisfactory illuminator can be provided in which the arc subtended by the window is in the range-of a few degees up to around 65". We - prefer an arc of about 45" for use with an.electrostatomaphic copying machine incorporating liquid development.

In an illuminator of the kind shown in Figures 1 and 2, the irradiance of a copving machine platen, and hence the radiation reaching a document on the platen to be copied, can be regarded as being made up of three components. The first component is direct light from the lamp filaments 13a and 14a, the second component is specular reflection from reflectors 13b and 14b, and the third component is diffuse light from the inner walls of the surface 11. The first and third components are generally smoothly varying and reasonably easy to adjust by some configuration changes in the illuminator design as have been mentioned above, for example shaping the window 12.

We have found that the second component tends to vary abruptly along the length of the platen making compensation particularly difficult. A smooth profile of radiation along the length of the illuminator could be provided if the reflectors 1 3b and 14b are not used. However, this reduces considerably the magnitude of the third component. It is also possible to overcome the problem by preventing the second component from falling directly onto the platen by making its path so oblique that the second component travels across the width of the illuminator but does not impinge directly on to the platen. End reflectors, one at each end of the illuminator positioned between the illuminator and the platen, which are specular or diffusely reflective can, if desired, be arranged to re-direct the second component on to the platen. However, this solution tends to cause a significant quantity of the second component to remain within the illuminator and strike the opposite end specular reflector (13b or 14b) rather than striking the surface 11. Thus, again the third component tends to be reduced so that the overall efficiency of the illuminator is impaired.

The illuminator provided by the present invention, as will now be described in more detail with reference to Figure 3, comprises an illuminator in which the specular reflectors 13b and 14b are of a special design. We have found that light from the filaments 13a and 14a must be concentrated within the tube 11 into annuli at positions 20 and 21 respectively. This is achieved by making half the reflector 1 3b between points 22 and 23 and by making half the reflector 14b between points 24 and 25 at least substantially elliptical with foci 13a and 20 and 14a and 21 respectively. In practice of course as the filaments 13a and 14b are not point sources the points 20 and 21 are blurred images.

The other halves of the reflectors 13b and 14b are surfaces of revolution about the illuminator axis of the parts 22 to 23 and 24 to 25. This provides in use annular concentrations of light inside the illuminator in the regions adjacent foci 20 and 21.

In practice the desired overall shape of the reflectors 13b and 14b has been found easier to Droduce by using polynomial leastsquares fitted curves techniques rather than relying on a complicated equation of an offaxis ellipsoid of revolution.

The various dimensions of the illuminator of the present invention will depend on the requirements of the illuminator. However, the separations between positions 20 and 26 and positions 21 and 27 must be such that the second component, described above, does not strike the platen directly.

(The separations will be generally greater than half the length of the illuminator).

We believe the invention relies to some extent on focussing the light onto the inner surface of the envelope and preventing specular light being directed at the reflector at the opposite end of the envelope. Generally, the annuli will be preferably positioned near the centre of the illuminator, where the irradiance directly from the filaments is least.

However, as the platen should be positioned close to the illuminator some compromise is required. The annuli are designed to form sufficiently far from the lamps or the platen moved away from the illuminator so that directly reflected light misses the platen. In practice we have found this compromise is not difficult to achieve while maintaining high and generally uniform intensity of illumination across the platen.

WHAT WE CLAIM IS:- 1. A copying machine having a platen for supporting documents to be copied and an illuminator for illuminating said platen, said illuminator comprising a diffusely reflective elongate tubular envelope and having a narrow window or opening extending at least the length of the envelope through which light can pass out of said illuminator and towards said platen, said illuminator also comprising at each end of said envelope a specular reflector surface having its periphery juxtaposed to a respective end of said envelope and an illumination element mounted within said reflector, said reflector having a surface which is arranged to focus light into an annulus around the inside of said envelope and such that light reflected directly by said surface out of said window is directed obliquely so as not to strike said platen without reflection.

2. A copying machine according to claim I, wherein each of said reflector surfaces is provided with a cut-out portion forming an extension into said surface of said window or opening.

3. A copying machine substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. and 14a, the second component is specular reflection from reflectors 13b and 14b, and the third component is diffuse light from the inner walls of the surface 11. The first and third components are generally smoothly varying and reasonably easy to adjust by some configuration changes in the illuminator design as have been mentioned above, for example shaping the window 12. We have found that the second component tends to vary abruptly along the length of the platen making compensation particularly difficult. A smooth profile of radiation along the length of the illuminator could be provided if the reflectors 1 3b and 14b are not used. However, this reduces considerably the magnitude of the third component. It is also possible to overcome the problem by preventing the second component from falling directly onto the platen by making its path so oblique that the second component travels across the width of the illuminator but does not impinge directly on to the platen. End reflectors, one at each end of the illuminator positioned between the illuminator and the platen, which are specular or diffusely reflective can, if desired, be arranged to re-direct the second component on to the platen. However, this solution tends to cause a significant quantity of the second component to remain within the illuminator and strike the opposite end specular reflector (13b or 14b) rather than striking the surface 11. Thus, again the third component tends to be reduced so that the overall efficiency of the illuminator is impaired. The illuminator provided by the present invention, as will now be described in more detail with reference to Figure 3, comprises an illuminator in which the specular reflectors 13b and 14b are of a special design. We have found that light from the filaments 13a and 14a must be concentrated within the tube 11 into annuli at positions 20 and 21 respectively. This is achieved by making half the reflector 1 3b between points 22 and 23 and by making half the reflector 14b between points 24 and 25 at least substantially elliptical with foci 13a and 20 and 14a and 21 respectively. In practice of course as the filaments 13a and 14b are not point sources the points 20 and 21 are blurred images. The other halves of the reflectors 13b and 14b are surfaces of revolution about the illuminator axis of the parts 22 to 23 and 24 to 25. This provides in use annular concentrations of light inside the illuminator in the regions adjacent foci 20 and 21. In practice the desired overall shape of the reflectors 13b and 14b has been found easier to Droduce by using polynomial leastsquares fitted curves techniques rather than relying on a complicated equation of an offaxis ellipsoid of revolution. The various dimensions of the illuminator of the present invention will depend on the requirements of the illuminator. However, the separations between positions 20 and 26 and positions 21 and 27 must be such that the second component, described above, does not strike the platen directly. (The separations will be generally greater than half the length of the illuminator). We believe the invention relies to some extent on focussing the light onto the inner surface of the envelope and preventing specular light being directed at the reflector at the opposite end of the envelope. Generally, the annuli will be preferably positioned near the centre of the illuminator, where the irradiance directly from the filaments is least. However, as the platen should be positioned close to the illuminator some compromise is required. The annuli are designed to form sufficiently far from the lamps or the platen moved away from the illuminator so that directly reflected light misses the platen. In practice we have found this compromise is not difficult to achieve while maintaining high and generally uniform intensity of illumination across the platen. WHAT WE CLAIM IS:-

1. A copying machine having a platen for supporting documents to be copied and an illuminator for illuminating said platen, said illuminator comprising a diffusely reflective elongate tubular envelope and having a narrow window or opening extending at least the length of the envelope through which light can pass out of said illuminator and towards said platen, said illuminator also comprising at each end of said envelope a specular reflector surface having its periphery juxtaposed to a respective end of said envelope and an illumination element mounted within said reflector, said reflector having a surface which is arranged to focus light into an annulus around the inside of said envelope and such that light reflected directly by said surface out of said window is directed obliquely so as not to strike said platen without reflection.

2. A copying machine according to claim I, wherein each of said reflector surfaces is provided with a cut-out portion forming an extension into said surface of said window or opening.

3. A copying machine substantially as herein described with reference to the accompanying drawings.