GB2272781A - Holder for photosensitive material - Google Patents

Description

q I- 2272781 A HOUSING FOR A PHOTO-SETTING APPARATUS This invention

relates to a film or photo type setting apparatus.

It is known to form a housing for such an apparatus as a holder for transversely transportable web material, which is in the shape of a segment of a circular cylinder. Light pulses from a laser beam which rotates about the longitudinally extending holder central axis are reflected from the central axis onto the photosensitive inner surface of the web material. The outer surface of the web material lies in a lighttight air-gap free manner on the accurate inner surface of the holder.

Such housings have hitherto been made from largediameter metal tubes, which are first slit, undergo stressfree annealing, re-soldered, machined to the final dimension, and then cut open again. With this method, an accuracy of about 0.01 mm in the radius has been achieved hitherto which is classified as adequate. This accuracy relative to a drum housing of 1100 mm in length and a drum diameter of 500 mm is not however economically achieved owing to the high production costs. Furthermore, such drum housings are relatively heavy.

It is amongst the objects of this invention to provide a geometrically true housing for a film or photo-setting apparatus which is at least just as accurate or even more accurate than those known hitherto but the production costs of which are lower and which is lighter than the known housings.

A housing for a photo-setting apparatus in accordance with the invention comprises a holder for web material, the holder being in the shape of a segment of a circular cylinder, from the central axis of which light pulses are reflected onto the photosensitive inner surface of the web material, wherein the holder comprises a plurality of arcuate ribs spaced along the central axis and extending at right-angles thereto, the ribs having uniform arcuate inner surfaces against which the outer surface of the web material is transported in a light-tight, air-gap free manner.

hip 2 The advantages of this include, in particular, a considerable saving in material, considerably simpler production and the possibility of a geometrical and dimensional accuracy which is equal to or greater than that achieved hitherto. The housing can also be produced in a shorter time. In view of its lower weight, it also results in reduced transportation costs. The drum design ensures that any desired drum length can be produced without extra tooling and apparatus costs and without higher machining costs.

Very preferably, an insert of the same curvature as the inner arcuate surfaces of the ribs is attached thereto.

Air drainage channels may run along the inner surface of the insert. This makes it possible to ensure that the web material lies closely against the inside of the drum.

For assembly-related reasons, it is furthermore particularly advantageous for the ribs to be braced together to form a stack by means of a plurality of tierods running in the direction of the central axis which extends longitudinally. Spacer tube pieces may be attached to a tie-rod between two ribs.

This connection can be statically defined by locating a tie-rod at the apex of the arcuate ribs and in the region of the ends of the arcs.

The production of the ribs is facilitated, and can take place, e.g. by laser machining, if the ribs are cut out of flat material.

Alleviation of any non-uniform stresses which may occur can be produced as a precaution by making the distances between the ribs in the direction of the longitudinal central axis equal or increase step wise from the longitudinal centre of the stack.

In this case, it is likewise advantageous that the tensile forces applied in the tie-rods are set to be of equal size.

The desired accuracy of the radius from the longitudinal central axis is promoted by machining the 1 1 r, W 3 inner surfaces of the arcuate ribs after assembly together thereof by means of the tie-rods.

In addition to composite materials, such as glassfibre-reinforced plastics, it is in principle possible for all the components, with the exception of the tie-rods and threaded nuts used therewith, to be made from plastics material.

In a further development a support is attached to the outside of the ribs as a cover.

The invention will now be further described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a view of a housing from below; Figure 2 is a section taken along line A-A of Figure 1 of the housing in the operating position; Figure 3 is an enlarged view of the encircled portion "B" of Figure 2; and Figure 4 is an oblique perspective view taken from below.

The housing for a film-setting apparatus is in the form of a holder 1, in the shape of a segment of a circular cylinder, for web material 2. The web material 2 consists of photosensitive paper or of film and has variable dimensions. The inner surface 2a of the web material 2 bears the photosensitive layer, the outer surface 2b of the web material 2 lies on a guide surface of the housing.

In the longitudinal central axis 3 of the housing there is a rotating mirror which transmits laser light pulses. The exposue pulses are transmitted onto the photosensitive inner surface 2a of the web material 2, and form an image once the film has been developed. The web material 2 is guided with maximum accuracy around the longitudinal central axis 3 in a light-tight manner and without an air gap behind its outer surface 2b, i.e. the inside of the drum must lie with maximum accuracy on the 4 web back.

To this end, the holder 1 is formed of a plurality of ribs 5 spaced apart successively along the longitudinal central axis 3. On the uniform arcuate inner surface Sa of the ribs an identically curved thickness- tolerated insert 6 of metal or plastic is securely attached. Air drainage ducts 7 in the surface 6a of the insert 6 in the form of flutes, furrows or grooves enable the web material 2 to lie closely and without an air gap. The ribs 5, which are arranged, for instance, over a length of 1,100 mm, are screwed together and braced to form a stack 11 by means of tie- rods 8 and spacer tube pieces 9 which determine the distances between two ribs 5. The ends of the tie-rods 8 are closed by threaded nuts 10 screwed onto threaded sections Sa of the tie-rods 8 with washers 10a.

As illustrated herein, a tie-rod 8 is located in an apex 12 of the arcuate ribs 5 and in each case a tie-rod 8 is located in the regions of the ends of the arcs 13 and 14. This produces a statically defined system.

An alternative arrangement is yielded by the fact that the distances between the ribs 5 in the direction of the longitudinal central axis 3 are of equal size or become greater in steps starting from a longitudinal centre 15 of the stack 11.

The ribs 5 are cut out of flat material, such as sheet metal, in a stack by means of laser beams, and hence are completely identical; the cuttingout cannot take place until the tie-rods 8 have been introduced and braced. The tensile forces applied in the tie-rods 8 are of identical size.

With the exception of the tie-rods 8, the threaded nuts 10 and the washers 10a, all the other parts may be made of plastics material or of glass fibre-reinforced plastics material.

on the outer surface 5b of the ribs 5 there is attached a support 16 as a cover 17 for the ribs 5. Should the accuracy of the housing described hitherto not be 1 P, W suf f icient, a corresponding metal layer 18 may also be applied to the inner surface 6a of the insert 6, which is optionally finished, in order to ensure the required radial accuracy of a few micrometres.

6

Claims (14)

1. A housing for a photo-setting apparatus comprises a holder for web material, the holder being in the shape of a segment of a circular cylinder, from the central axis of which light pulses are reflected onto the photosensitive inner surface of the web material, wherein the holder comprises a plurality of arcuate ribs spaced along the central axis and extending at right-angles thereto, the ribs having uniform arcuate inner surfaces against which the outer surface of the web 'material is transported in a light-tight, air-gap free manner.

2. A housing as claimed in Claim 1, wherein the ribs are braced together to form a stack by means of a plurality of tie-rods extending parallel to the central axis.

3. A housing as claimed in Claim 2, wherein a tie rod is located at the apex of the arcuate ribs and a tie rod is located in the region of the ends of the arcs.

4. A housing as claimed in either Claim 2 or Claim 3, wherein the tensile forces applied in the tie-rods are equal.

5. A housing as claimed in any one of Claims 2 to 4, wherein the inner surfaces of the arcuate ribs are machined after assembly together of the ribs by means of the tie rods.

6. A housing as claimed in any one of claims 2 to 5, wherein the components, with the exception of tie-rods, are made from a plastics material.

7. A housing as claimed in any preceding Claim, wherein an insert of metal or plastic of the same curvature as the inner surfaces of the ribs is attached thereto.

1 7

8. A housing as claimed in Claim 7, wherein air channels run along the inner surface of the insert.

9. A housing as claimed in either Claim 7 or Claim 8,, wherein the inner surface of the insert is provided with a lining comprising at least one metallic layer.

10. A housing as claimed in any preceding Claim, wherein the ribs are cut out of flat material.

11. A housing as claimed in any preceding Claim, wherein the spacings between the ribs along the central axis are either of equal size or increase step-wise from the longitudinal centre of the stack formed by the ribs.

12. A housing as claimed in any preceding Claim, wherein a support is attached to the outer surfaces of the ribs as a cover.

13. A housing as claimed in any preceding Claim, wherein the web material is transversely transported around the central axis which extends longitudinally of the holder.

14. A housing substantially as hereinbefore described and illustrated in the accompanying drawings.