GB1597096A

GB1597096A - Needle guide for the head of a rapid printer and a grooved element for such a needle guide

Info

Publication number: GB1597096A
Application number: GB15320/78A
Authority: GB
Original assignee: Seitz AG
Current assignee: Seitz AG
Priority date: 1977-04-20
Filing date: 1978-04-18
Publication date: 1981-09-03
Also published as: DE2816096B2; IT7822428A0; IT1094432B; DE2816096A1; JPS5910312B2; FR2387779B1; DE2816096C3; FR2387779A1; CH609916A5; JPS53140122A

Description

(54) A NEEDLE GUIDE FOR THE HEAD OF A RAPID PRINTER AND A GROOVED ELEMENT FOR SUCH A NEEDLE GUIDE (71) We, SEITZ S.A., a Swiss body corporate, of 2416 Les Brenets, canton of Neuchatel, Switzerland, 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 present invention relates to a needle guide for the head of a rapid printer, and a grooved element for such a needle guide.

The impression of characters on paper by a rapid printer, such as a peripheral device for a computer, takes place by successive impacts of needle points. According to a first type of needle gtlide, a printer head generally comprises seven needles (sometimes more) disposed perpendicularly to the impression surface and in a vertical alignment, according to the height of the characters to be impressed. When the printer head is displaced laterally, one or a group of needles is activated at a very high frequency. A character is generally completed after five successive steps. The impression on the paper may be made by an interposed inked ribbon.

According to a second type of needle guide, the needles are no longer disposed in a vertical alignment, but are shifted in relation to each other. Seen from the front, the needles are disposed in zig-zag arrangement.

This disposition permits different kinds of characters to be produced more easily.

One of the most appropriate materials for supporting the needles, or providing the needle guide, is corundum. In fact, its hardness of nine on the Mohs scale is only surpassed by diamond; it has a very low friction coefficient with metallic needles; and it przveç to have excellent resistance to thermal slick (about 1000"C/several min uses?. Wearing out of the components of the printer head (needle guide plus needles) is thus minimal.

Other wear-resistant materials can be used. In particular hard sintered alloys, ceramics or others are a case in point.

Known needle guides are generally composed of two parallelepipeds the extremities of which are adhered to metallic strips. Each parallelepiped has practically identical transverse millings or grooves on one of its two narrow elongate faces. The parallelepipeds are adhered so that these ground, polished faces are opposite to each other. The cylindrical needles of the printer head are therefore housed in and slide on the openings formed by the said grooves.

In a needle guide according to the first type, the grooves have a semicircular profile and are positioned in such a way that they are facing one another. The openings for the needles are therefore aligned and circular.

In a needle guide according to the second type, the grooves have a U-shaped profile and they are deeper and more widely spaced and are positioned in such a way that they are shifted (i.e. that a groove of one of the parallelepipeds faces a top of the other parallelepiped).

According to one aspect of the invention there is provided a needle guide for the head of a rapid printer, comprising two elements of wear-resistant material at least one of which elements comprises grooves thereby to define by said grooves spaces between said two elements for guiding respective needles, wherein the at least one element comprising grooves is provided by a cylinder in which these grooves are formed and which comprises a flat support surface defined between two lines, at the circumference of said cylinder, which extend substantially parallel to the axis of the cylinder.

The needle guide generally may have seven grooves or more.

The two elements may be supported either in a housing provided on the front of a printer head or in a housing of a module of a printer head.

The guiding surface for a needle at the bottom of each groove can be slightly convex along the length of the groove. This favours minimum friction by a minimal contact surface.

According to another aspect of the invention there is provided a grooved element for a needle guide according to the one aspect of the invention, the grooved element being substantially as hereinafter described with reference to Figures 1 and 2 of the accompanying drawing.

For a better understanding of the invention and to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawing which relates to a needle guide according to the invention and according to the first type discussed hereinbefore, and to a grooved element according to the invention in which: Figure 1 is a longitudinal section of a cylindrical element of a needle guide for the head of a rapid printer; Figure 2 is a transverse section of the element of Figure 1; and Figure 3 is a perspective view of one possible mounting of a needle guide in a module.

Figure 1 shows a corundum element 1. A needle guide for the head of a rapid printer comprises two similar elements 1 positioned in an appropriate housing. Seven identical grooves 2 with a substantially semicircular profile can be seen positioned next to one another, the grooves 2 extending parallel to one another and in a direction perpendicular to the axis 3 of the element 1.

The transverse section of Figure 2 illustrates the fact that the element 1 is obtained from a cylindrical section of which the axis 3 can be seen. On one side of the element 1 the grooves 2 can be seen, and on the other side a flat surface 4 which is defined by two generators 5 and 6 of the cylinder. This surface 4 is usually parallel to the direction of the needles.

It can be seen from Figure 2 that the bottoms of the grooves are slightly convex along the lengths of the grooves to favour minimum friction of the needles on the material of the element 1. Alternatively, these bottoms could be straight.

Two elements 1 will be supported by means of their surfaces 4 on the faces of a housing assigned to them.

This is illustrated in the exploded view in Figure 3. The two elements 1 to be mounted facing each other in a module 7 of a printer head 8 can be seen. The surfaces 4 will, in this example. be adhered to two opposite faces 9 and 10 of a housing 11 of the module 7, or fixed by a mechanical means. It is to be appreciated that it is no longer adhesion onto a metallic strip that determines the gap between the two elements 1 made of corundum, but that this gap is determined by the distance between the two faces 9 and 10 of the housing 11. The importance of the role of the adhesive is henceforth greatly diminished and is reduced to keeping the surfaces 4 in contact with the faces 9 and 10 of the housing 11.The mechanical and thermal constraints which the adhesive undergoes at these points are likewise greatly reduced.

Figure 3 illustrates a case where the housing Il is part of a module 7 which will be fixed to the printer head 8. The housing 11 can alternatively be directly provided on the printer head 8.

Figures 1 to 3 relates to a needle guide of the first type discussed earlier. It will be appreciated, however, that the invention is equally applicable to a needle guide of the second type discussed earlier.

The described and illustrated needle guide overcomes or goes some way to overcoming several disadvantages of a needle guide known in the prior art and comprising parallelepiped needle guide elements.

A first disadvantage of the known needle guide is the number of machining operations required in the manufacture of its parallelepiped elements. The relative complexity of their geometrical shape requires a considerable number of operations for cutting and polishing each face. Given the hardness of corundum in particular and any other wearresistant material, these operations all take place by means of abrasive stones or by paste based on diamond powder. Each machining operation is long and onerous.

A second disadvantage is that the two parallelepipeds are held together by adhesion to two metallic strips. Setting the gap between the two parallelepipeds has to be correct to within +50 microns in order to avoid any dangerous vibration of the needles in the grooves. The adhesive represents a weak element for holding the installation.

The adhesive is in fact subject to fatigue as a result of mechanical and thermal shocks, and could be held responsible for a failure of the printer head.

A third disadvantage of the known needle guide arises from the rectangular shape of its needle guide elements, which presents edges and angles for the inked ribbon to catch on.

The described and illustrated needle guide is economical to produce and overcomes or goes some way to overcoming the aforesaid disadvantages.

The advantages of the described and illustrated needle guide are numerous. The manufacture of cylindrical sections make use of proved techniques similar to those used in the manufacture of jewels in watchmaking.

Making a cylindrical element can take place in particular by rotating the element freely between two stones. The number of opera tions and the machining time are considerably reduced compared with the manufacture of a parallelepiped. There is even a gain in the operation of milling the grooves, since the quantity of material which must be removed from a cylindrical section is less than that from a rectangular section. The two elements of our needle guide may be firmly supported against two opposite faces in a housing which is either provided directly on the front of a rapid printer head or in a module of a rapid printer head. They can be held in position by adhesive and/or another mechanical means, but the adhesive is no longer responsible for setting the gap between the two elements or for holding the installation.At the same time, a preassembling step of the needle guide is avoided.

The diameter of the cylindrical elements of the needle guide can be slightly larger than the depth of the housing where they are fixed. The inked ribbon may then be guided by the projecting part of the cylindrical elements. Therefore it will not rub against the adjacent parts of the printer head which are less wear-resistant. The rounded shape of the elements ensures guiding without the ribbon catching.

WHAT WE CLAIM IS: 1. A needle guide for the head of a rapid printer, comprising two elements of wearresistant material at least one of which elements comprises grooves thereby to define by said grooves spaces between said two elements for guiding respective needles, wherein the at least one element comprising grooves is provided by a cylinder in which these grooves are formed and which comprises a flat support surface defined between two lines, at the circumference of said cylinder, which extend substantially parallel to the axis of the cylinder.

2. A needle guide according to claim 1, wherein each of said two elements comprises grooves as aforesaid and is provided by a cylinder in which these grooves are formed and which comprises a flat support surface defined between two lines, at the circumference of said cylinder, which extend substantially parallel to the axis of the cylinder.

3. A needle guide according to claim I or 2, wherein in the or each said cylinder element comprising grooves as aforesaid these grooves are substantially identical.

4. A needle guide according to any one of the preceding claims, wherein each of said grooves in the or each said cylinder element has a substantially semicircular profile.

5. A needle guide according to any one of claims I to 3, wherein each of said grooves in the or each said cylinder element has a substantially U-shaped profile.

6. A needle guide according to claim 4, wherein in the or each element comprising grooves as aforesaid the number of grooves is seven.

7. A needle guide according to claim 4, wherein in the or each element comprising grooves as aforesaid the number of grooves is greater than seven.

8. A needle guide according to any one of the preceding claims, further comprising a housing, said two elements being directly mounted in said housing.

9. A needle guide according to any one of claims 1 to 7, further comprising a housing, said housing forming part of a module of a rapid printer's head, said elements being mounted in said housing.

10. A needle guide according to claim 8 or 9, wherein the housing comprises two support surfaces which face one another and which support respective ones of the two elements to define the relative positions of the two elements with respect to one another.

11. A needle guide according to claim 10, wherein the elements are secured to said support surfaces by adhesive.

12. A needle guide according to claim 10 or 11 wherein said support surfaces are so positioned that a gap is defined between the elements.

13. A needle guide according to any one of the claims 8 to 12, wherein the elements have a diameter which is slightly larger than the depth of that part of the housing wherein they are mounted, whereby an inked ribbon may be guided on portions of the elements which project from the housing.

14. A needle guide according to claim 13, wherein said portions of the elements provide smooth rounded surfaces which can guide an inked ribbon without it catching thereon.

15. A needle guide according to any one of the preceding claims, wherein the bottom of each of said grooves in the or each said cylinder element is substantially straight along the length of the groove when viewed in a direction parallel to the axis of the element.

16. A needle guide according to any one of claims 1 to 14, wherein the bottom of each of said grooves in the or each said cylinder element is slightly convex along the length of the said groove when viewed in a direction parallel to the axis of the element.

17. A needle guide according to any one of the preceding claims, wherein said elements are corundum elements.

18. A needle guide according to any one of the preceding claims, comprising at least one grooved element which is substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawing.

19. A needle guide according to claim 2 or any one of claims 3 to 18 when appended to claim 2, and comprising two grooved

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tions and the machining time are considerably reduced compared with the manufacture of a parallelepiped. There is even a gain in the operation of milling the grooves, since the quantity of material which must be removed from a cylindrical section is less than that from a rectangular section. The two elements of our needle guide may be firmly supported against two opposite faces in a housing which is either provided directly on the front of a rapid printer head or in a module of a rapid printer head. They can be held in position by adhesive and/or another mechanical means, but the adhesive is no longer responsible for setting the gap between the two elements or for holding the installation. At the same time, a preassembling step of the needle guide is avoided. The diameter of the cylindrical elements of the needle guide can be slightly larger than the depth of the housing where they are fixed. The inked ribbon may then be guided by the projecting part of the cylindrical elements. Therefore it will not rub against the adjacent parts of the printer head which are less wear-resistant. The rounded shape of the elements ensures guiding without the ribbon catching. WHAT WE CLAIM IS:

1. A needle guide for the head of a rapid printer, comprising two elements of wearresistant material at least one of which elements comprises grooves thereby to define by said grooves spaces between said two elements for guiding respective needles, wherein the at least one element comprising grooves is provided by a cylinder in which these grooves are formed and which comprises a flat support surface defined between two lines, at the circumference of said cylinder, which extend substantially parallel to the axis of the cylinder.

elements each of which is substantially as herein before described with reference to Figures 1 and 2 of the accompanying drawing.

20. A needle guide according to claim 19, when mounted substantially as hereinbefore described with reference to Figure 3 of the accompanying drawing.

21. A grooved element for a needle guide according to claim 1 or 2, the grooved element being substantially as hereinbefore described with reference to Figures l and 2 of the accompanying drawing.