This invention relates to image projecting apparatus. More particularly, but not exclusively, this invention relates to image projecting apparatus for use in photocopiers.

Lenses are used in photocopiers to project an image from the object plane to the image plane either directly, for light sensitive copy media, or via optically sensitive charged drum to transfer to a non light-sensitive media (e.g. copy paper).

It is an disadvantage of such photocopiers that they are expensive to manufacture and bulky.

According to one aspect of the invention there is provided image projecting apparatus comprising a lens arrangement for projecting light rays for defining an image of an object, and inversion means provided in the path of said light rays for inverting said light rays and projecting said light rays onto a substrate for recording the image, the lens arrangement being in the form of an array of graded index lenses.

The array of graded index lenses may be substantially linear, and may be in the form of a narrow band, preferably comprising one or more lines of said lenses. The array may be substantially 15 to 30cm length, preferably, 17 to 25cm and more preferably 20 to 22cm length. The apparatus may have an image width or field of view of substantially 2 to 7mm preferably substantially 3 to 5mm, more preferably substantially 4 to 4.5mm. The array may be substantially 5 to 20mm wide, preferably substantially 7 to 17mm wide, more preferably substantially 10 to 15mm wide. Preferably, the apparatus is suitable for use in a photocopier.

Preferably, the lens arrangement is adapted to project said light rays to define a mirror image of said object, wherein said inversion means inverts said light rays to provide a true image for recordal on said substrate.

Preferably, each lens is substantially cylindrical in configuration and

may be substantially 1 to substantially 2 or 3mm in diameter, preferably substantially 1mm in diameter. Each lens may be substantially 5 to substantially 15 or 20mm in height, preferably substantially 16mm in height.

The inversion means may comprise means for reflecting the light rays from the lens arrangement. Preferably, the reflecting means is arranged to reflect said light rays in a direction transverse to their direction before reflection. Preferably, in a direction substantially perpendicular to their direction before reflection.

The reflecting means may be a mirror having a reflecting surface arranged, preferably, at an angle of substantially 45° to the direction of said light rays before reflection. The reflecting surface may be provided on the front or rear of the mirror. Preferably, the reflecting surface is silvered. In the case of a mirror having the rear face as the reflecting surface, the mirror may present a first face perpendicular to said light rays before reflection, and a second face perpendicular to said light rays after reflection. Preferably, the mirror has a cross sectional configuration which is substantially that of a right angled triangle.

Alternatively, the inversion means may comprise means for refracting said light rays. Preferably, the refracting means is arranged to refract said light rays in a direction substantially parallel to their directions before refraction.

The refraction means may be a prism which may have a longitudinal axis arranged substantially parallel to said array of lenses.

One face of said refracting means may be silvered to allow refraction of said light rays in said refracting means. Alternatively, said one face can be substantially unsilvered to allow reflection of said light rays to occur by total internal reflection.

According to another aspect of this invention there is provided a light transmission assembly comprising object support means; image projecting apparatus including an array of graded index lenses to project an image of an object carried by the object support means; and an illuminating assembly for illuminating the object, the illuminating assembly being adapted to produce a band of light incident on the object support means, the band of light so produced being such that, on passage of the light through the object carrying means, the light illuminating the object is of substantially the same width as, or of less width than, the width of the field of view of the array of graded index lenses. The band of light produced by the light source may be determined by taking into consideration such matters as, for example, the angle of incidence of the light striking the object support means, the thickness of the object support means and the refractive index of the object support means. The object support means may be a sheet of clear material e.g. glass.

The light transmission assembly may comprise a photocopier.

The illuminating assembly may comprise an arrangement of optical fibres, which can be illuminated by appropriate Light source, said arrangement may be a substantially linear arrangement of the optical fibres. Focusing means may be provided to focus diverging light from the optical fibres to form the band of light incident on the object carrying means. The focusing means may be in the form of a substantially cylindrical lens, preferably a substantially cylindrical rod lens.

Alternatively, the illuminating arrangement may comprise a reflector and lens assembly to produce said band of light incident on the object carrying means. The reflector may be adapted to provide a beam of parallel light and may be in the form of a parabolic reflector which may be elongate, and the lens may comprise a condenser lens which may be elongate. Preferably, the condenser lens is in the form of a hemi-cylindrical lens. The illuminating assembly may further include an elongate light source which may be in the form of an elongate bulb, or tube, for example a halogen tube.

Preferably, the image projecting apparatus is as described in paragraphs four to twelve above.

The image projecting apparatus may include path length compensating means to correct the path length of light passing through the array of graded index lenses. The path length compensating means may comprise a refracting member to refract light from the array of graded index lenses to the image plane.

The refracting member may comprise a sheet of glass or other suitable clear material to refract light onto the image plane. Thus, the refracting member acts to compensate for any deviations from the correct path length caused by the object support means.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:-

Fig. 1 is a schematic perspective view of image projecting apparatus in use;

Fig. 2 is a schematic side view of another embodiment of the image projecting apparatus shown in Fig. 1;

Fig. 3 is a schematic side view of alternative inversion means; and Fig. 4 is a schematic perspective view of image projecting apparatus using the inversion means shown in Fig. 1

Fig. 5 is a schematic view of a light transmission assembly; and

Figs. 6 to 8 are schematic views of alternative illuminating assemblies for a light transmission assembly.

Referring to Fig. 1, there is shown image projecting apparatus 10 in use in a photocopier. The image projecting apparatus 10 is arranged above an object sheet of paper 12 and to the left of a sheet of paper 14 onto which the image is to be projected. The photocopier further includes rollers 16 about which the image sheet of paper 14 can pass. The rollers 16 rotate in the direction of the arrows shown thereon. Similarly, the object and image

sheet 12,14 move in the direction of the arrows A,B thereon.

The image projecting apparatus 10 comprises a plurality of lenses 16 arranged in an array in a housing 18. The array comprises a large number of such lenses, closely spaced, extends across the width of the object. The array can be, for example substantially 20 to 22cm in length and have a field of view or image width of substantially 4 to 4.5mm, preferably 4.32mm. In the embodiment shown, the lenses are cylindrical in configuration arranged perpendicular to the object sheet paper 12. Each lens is approximately 1mm in diameter and approximately 10mm in length. The lenses 16 are arranged side by side in the housing 18. Such lenses are known as graded index lenses (GRIN lenses), and are sold, for example, by the company Nippon Sheet Glass NSA under the trade mark SELFOC, and have the property that the refractive index varies within a lens with the diameter of the lens.

Arranged above the housing 18, as shown in Fig. 1, is a mirror 20 having a silvered front face 22 to reflect light from the lenses onto the object sheet of paper 14. The purpose of the mirror 20 is to ensure that the image projected onto the image sheet of paper is a true image, and is required because light passing through the lenses 16 forms a mirror image, which must then be inverted in one plane only to form the true image.

Referring to Fig. 2, there is shown alternative apparatus 10 to that shown in Fig. 1. The apparatus 10 shown in Fig. 2 differs from that shown in Fig. 1 in that the mirror 20 is in the form of a triangular prism having a silvered reflecting surface 24 at the rear thereof. The prism presents a first face 26 to the light rays emerging from the lens 16, the first face 26 being substantially perpendicular to such light rays. The prism also presents a second face 28 perpendicular to light rays reflected from the rear face 24.

It will be appreciated that in the case of both types of mirrors the silvered surface is presented at substantially 45 ' to the rays emerging from the lenses 16.

The embodiment shown in Figs. 1 and 2 require that the image sheet of paper is substantially perpendicular to the object sheet of paper. Fig. 3 shows a modification which would enable the image sheet of paper to be parallel to the object sheet of paper. In this embodiment, the inversion means 20 comprises a prism 31, known as a dove prism, which, as can be seen from Fig. 3, inverts an object 32 to an inverted image 34 by refraction and reflection of rays of light 30.

Referring to Fig. 4, there is shown the projecting apparatus 10 incorporating the prism 31 in use. In Fig. 4, the object sheet of paper 12 moves in the direction of the arrow A at a predetermined speed V. The image sheet of paper which is arranged above, and parallel to, the object sheet of paper moves in the direction of the arrow B at a speed V, so that the relative velocity between the two sheets of paper is 2V. The image sheet of paper is coated with a photosensitive layer on its underside 36 and the image is recorded on the underside 36 of the paper 14.

Lenses of the type discussed above have the advantage that their cost is much lower than that of typical lenses, it is possible to use any number of lenses in an array thus enabling any length of array to be used merely by varying the number of lenses, the performance of the lens does not fall off at the edges and performance is constant at any length and, the lenses as ^' described have a short focal length (approx 8mm) which enables the size of the photocopying machine itself to be reduced.

Various modifications can be made without departing from the scope of the invention. For example, although the image projecting apparatus has beer iescribed with reference to the particular orientation shown in Figs. 1,2 and -i, it will be appreciated that the apparatus 10 can be arranged in any desired orientation within a photocopier. Also, the object sheet of paper could be kept still in the example shown in Fig. 4. Thus, the apparatus 10 moves at speed V and the image sheet of paper 14 moves at speed 2V, both moving in the same direction

Referring to Fig. 5, there is shown a light transmission assembly in the form of a photocopier assembly 110 which comprises image projecting apparatus 10 which is similar to the image projecting apparatus 10 shown in Fig.l in that it comprises an array of graded index lenses 16 (only one of which is shown in Fig. 5), and a mirror 20 having a silvered front face 22 to reflect light from the object 12 to the image 14. The photocopier assembly 110 comprises object support means in the form of top bed glass 112 on which the object 12 is arranged.

The assembly 110 further includes illuminating means 114 comprising an array of optical fibres 116 (only one of which is shown in Fig. 5 for clarity). The array of fibres 116 is held in a linear arrangement in appropriate holding means 118, and the fibres are illuminated by a suitable light source 120 to provide the appropriate amount of light.

The iUuminating assembly 114 further includes focusing means 122 in the form of a cylindrical rod lens to focus the light from the optical fibres 116 onto the top bed glass 112 in a narrow band such that the light incident on the object 12 is also in the form of a narrow band.

Examples of alternative illuminating means are shown in Figs. 6,7 and 8, and will be described below.

The photocopier assembly shown in Fig. 5 also includes path length compensation means in the form of a sheet of a glass 124. The path length of light passing through the top bed glass 122 will be distorted depending upon the refraction of the light through the top bed glass 112. The sheet of glass 124 acts to compensate for differences in path length by carrying out a further refraction on the light rays, to produce a sharp image 14.

Referring to Figs. 6,7 and 8, there is shown alternative illuminating assemblies for illuminating the objects on the top bed glass 112 of a photocopier assembly. Each of Figs. 6,7 and 8 comprises image projecting apparatus 10 and this is represented by showing one of the graded index

lenses 16. Referring to Fig. 6, the illuminating apparatus is designated 210 and comprises a parabolic reflector 212 adapted to reflect Ught from a light source 214 arranged at the focal point of the parabolic reflector 212. Thus, parallel light arrays are transmitted from the parabolic reflector 212. These are focused by a condenser lens 216 towards the top bed glass 112 of the photocopier assembly.

The parabolic reflector 212, and the Ught source 214, are elongate to provide a band of light at the top bed glass 212. This provides appropriate Ulumination of the object 12 in the same manner as described with reference to Fig. 5. The light source 214 can be any appropriate Ught source, for example a tungsten halogen bulb which can be approximately 20cm in length.

Referring to Fig. 7, there is again shown the paraboUc reflector 212, the elongate light source 214 and the condenser lens 216. In this case, the light from the condenser lens 216 is focused towards a rod lens 122 which can be the same as the rod lens 122 shown in Fig. 5. The rod lens 122 produces a narrow band of light to be reflected from a first planar mirror 218 and, thereafter, a second planar mirror 220 onto the top bed glass 112. The light so directed onto the top bed glass 112 iUuminates the object 12 in the same manner as shown in Fig. 5.

Referring to Fig. 8, there is also shown an elongate paraboUc reflector 212, and elongate light source 214, and an elongate condenser lens 216 to direct light onto a planar mirror 222 which is reflected onto the rod lens 122 focused towards the top bed glass 112. The object 12 is, thus, illuminated in the same way as shown in Fig. 5. In the embodiments shown in Fig. 8, the use of a curved mirror to replace the planar mirror 222 would produce an appropriate narrow band of light at the top bed glass 112 thereby obviating the need for the rod lens 122.

In each of the embodiments shown in Fig 5 to 8, there may be need for means to control colour balance and exposure. This could be

appropriate means arranged in the region designated X-X in Figs. 5 to 8, or Y-Y in Fig. 5.

The embodiments described above are particularly suitable for direct photocopying onto photo sensitive paper rather than via a charged drum as is usual in prior photocopiers.

In some cases it may be necessary to pre-expose the photo-sensitive paper prior to exposure with the image, in order to reduce the ij umination time to produce the image. Such pre-exposure may be accompUshed by reflecting Ught from the illumination assembly on the paper by the top bed glass. About 4% of the Ught from the illumination assembly is reflected by the top bed glass, which is sufficient for pre-exposure of the paper.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention beUeved to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.