A GUIDE DEVICE FOR THE NEEDLES OF A PRINT HEAD OF A DOT MATRIX PRINTER AND PROCESS FOR ITS PRODUCTION

Abstract: A guide device for the needles of a print head of a dot matrix printer is described, of the type in which the needles are supported by a matrix and by at least one other guide element, as well as the process for its production; the principle character­ istic of this device lies in the fact that at least the matrix (4) is formed by one or more thin superimposed plates (11) provided with guide holes (12) for the needles formed by photo-etching; if more than one, such plates are glued together with their holes offset.

Description: The present invention relates to a guide device for the needles of a print head of a dot matrix printer of the type comprising at least one matrix and one other element supported in a position parallel to one another by a support rigidly connected to the print head or to a part integral therewith, as well as to a process for the production of such device. The invention moreover relates to the print head including such device. Here, and in the following description, by "matrix" must be understood the guide element closest to the paper to be printed and positioned at the end of the support; by "focus" of a print head must be understood the plane perpendicular to the axis of symmetry of the head on which the ends of the needles converge in the same vertical line. In known print heads the matrix, which is the element on which the print quality depends, is usually made of precious materials and above all involves the use of sophisticated production technology. The object of the invention is that of providing a guide system for the needles of a dot matrix print head and a process for its production, which will have low cost and which will allow the use of sophisticated production technology to be avoided whilst guaranteeing a print quality equivalent to that of known heads. The said objects are achieved by the invention in that it relates to a process for the production of a guide system for the needles of a dot matrix print head comprising a matrix and at least one other guide element for the said needles disposed parallel to the said matrix and mounted with it on a support rigidly connected to the said head, characterised by the fact that at least the said matrix is made by means of the following stages: - preparation of at least one flat plate of small thickness with respect to the transverse dimensions thereof utilising a chemically corrodable material; - production of a plurality of through holes in the said plate by means of photo-etching; and - assembly of the said photo-etched plate on the said support. The invention moreoever relates to a guide device for the needles of a dot matrix print head comprising a matrix and at least one other guide element for the said needles disposed parallel to the said matrix and mounted with it on a support for the said head, characterised by the fact that at least the said matrix comprises a flat plate of reduced thickness with respect to its transverse dimensions and provided with a plurality of through holes for guiding the said needles, which holes have been formed by photo-etching of the said plate. For a better understanding of the invention a non-limitative description of an embodiment thereof is now given with reference to the attached drawings, in which: Figure 1 schematically illustrates in elevation a longitudinal view of the front or support part of a dot matrix print head of a type the remainder of which is known but which is formed according to the principles of the invention; Figure 2 schematically illustrates on an enlarged scale a detail of a part of the print head shown in Figure 1; and Figure 3 illustrates a plan view on an enlarged scale of an element of the print head of Figure 1 of which the detail of Figure 2 forms part. With reference to Figures from 1 to 3 there is generally indicated with the reference numeral 1 a dot matrix print head the structure and operation of which are known overall, comprising a plurality of needles 2, housed within a support 3 and slidably supported by a guide device or system comprising a matrix 4, a possible intermediate guide element 5 and a guide and shoulder element 6 of known type with which respective heads 8 of the needles 2 cooperate through respective biasing springs 7, which needles 2 are able to translate by suitable pneumatic devices of known type and therefore not illustrated for simplicity, by a controlling magnetic field generated by appropriate electro magnets also known and not illustrated for simplicity. Upon overcoming the reaction of the springs 7 the needles 2 are thrust against an abutment surface 9 schematically indicated in broken outline. Printing takes place, by the interposition of an ink ribbon, onto a paper substrate lying on the abutment surface. The needles 2, which are disposed inclinedly in such a way as to converge towards the focus of the head 1, are guided in their movement by the elements 4 and 5. To this end the matrix 4 (Figures 2 and 3) comprises, according to the invention, one or more thin flat plates 11 of a thickness appropriate for the process of photo-etching, superimposed over one another and fixed rigidly together, each of which is provided with an identical number of through holes 12 disposed in corresponding positions and able to define respective seats for guiding the needles 2. According to the invention the plate or plates 11 composing the matrix 4 are made of a chemically corrodable material in which the holes 12 are obtained not by mechanical working but by photo-­ etching; photo-etching is a well known method particularly applied to the production of printing blocks. In the non-limitative example illustrated the matrix 4 is composed of three plates 11 of a thickness equal to about 0.1 mm, which are superimposed and fixed together by gluing or welding with corresponding holes disposed in corresponding positions. According to the invention, for the purpose of forming inclined seats 13 in the matrix 4, in such a way as to be able to guide the inclined needles 2 with precision, the holes 12, which because of the production system adopted (photo-etching) can only be formed with their axes parallel to the axis of the head 1, are disposed offset from one another in a radial sense. In particular, the corresponding holes 12 of the different plates 11 have axes passing through the points of intersection of the axes of the needles 2 of the head 1 with the respective ideal section planes parallel to the plates 11 and disposed at progressively greater distances from the focus of the print head 1. It is also possible to utilise different materials for the construction of the plate 11 as long as these are capable of being worked, according to the invention, by photo-etching for the purpose of obtaining the guide holes 12; in this case the expert in the art would chose the most appropriate technology to ensure the joining of several superimposed plates 11 in the case in which the matrix 4 is composed of more than one individual plate; this is appropriate in cases where it is desired to significantly increase the resistance to wear of the interior of the holes by the sliding of the needles. Experimental tests performed by the applicant have in fact shown that in print heads provided with matrices formed like the matrix 4 described the wear in the holes is a function of the thickness of the matrix 4 and lower values are achieved the greater is the number of plates comprising the matrix. Moreover, the print quality is equivalent to that of print heads equipped with matrices of known type. Finally, to obtain the best results it is necessary that the thickness of each plate 11 be small with respect to the transverse dimensions thereof, and in particular, lie between 0.05 and 0.5 mm, otherwise the process for obtaining the holes 12 by photo-etching gives unsatisfactory results. For the production of the print head 1 described one procedes in the following manner. First of all a single sheet of dimensions such as to contain a plurality of flat plates 11 is prepared by rolling a chemically corrodable material, preferably metal, to a thickness such as to be small with respect to the transverse dimensions of the plates 11. Then, after having sub-divided it into sectors, each corresponding to the dimensions of the plate 11, there is formed in this plate a plurality of closely spaced through holes 12 equal in number, in each sector of the sheet, to the needles 2 which the head 1 must have, the holes are obtained according to the invention by photo-etching, operating in a known way which will therefore not be described in detail for simplicity. Finally, the plates 11 intended to constitute the matrix 4 are cut from the sheet just worked; if the matrices 4 are composed of more than one plate 11 these are superimposed in a stack and glued together taking care to arrange the described offset between the corresponding holes of the different plates, and are mounted fixedly on the support 3 with a single operation; to this end, preferably, the plates 11 are provided, for example again by photo-etching, with respective reference holes 20 able to allow the mutual positioning of these and of the matrices 4 on the support 3 with adhesives or by clinching, welding or other appropriate connection system. It is desired to emphasise the fact that the description of the matrix 4 given here includes, by its natural and logical extension, also the following cases: (a) matrices with a plurality of plates 11 in which the offset of corresponding holes is nil; there is therefore produced a matrix having any desired thickness resulting from the sum of the thicknesses of the individual plates 11 (not necessarily all of the same thickness), and with a plurality of through holes parallel to one another and to the axis of the print head. Such a matrix can in this way be utilised for the guidance of needles the axis of which assume a partial curvilinear configuration maintained in this way by the other guide elements present in the support, whether or not these are formed according to the principles of the invention. In proximity to the matrix, the curvature of the axes of the needles assumes practically nil values in such a way that the said needles project from the support towards the print zone all parallel to one another and to the axis of the print head in a configuration defined by the position of the holes in the matrix. (b) matrices formed according to what has been described but utilising a single plate 11 with the holes formed by photo-etching. Such a configuration of the matrix will evidently be able to provide an adequate guide both in the case in which the needles have rectilinear axes and in the case in which the needles have partially curvilinear axes. From what has been described the advantages connected with the guidance system adopted for the print head described and formed according to the present invention will be evident; it is clear that the adoption of matrices such as the matrix 4 produced with single thin plates of metal material not only drastically reduces the material costs of the head but makes it possible to use simple and low cost, as well as reliable production technology such as photo-etching, at the same time making it possible to maintain the print quality almost unchanged, although at the cost of a shorter life of the head, a life which, however, can be increased by means of the further technique of gluing several photo-etched plates into a stack with offset holes. Finally, it is evident that variations and modifications can be introduced into what has been described without by this departing from the ambit of the invention as already evidenced above.

Claims: 1. A process for the production of a guide system for the needles of a dot matrix print head comprising a matrix (4) and at least one other guide elemnent (6) for the said needles disposed parallel to the said matrix and mounted with it on a support fixed to the said head, characterised by the fact that at least the said matrix is formed by means of the following steps: - preparation of at least one flat plate (11) of small thickness with respect to the transverse dimensions thereof utilising a chemically corrodable material; - production of a plurality of closely spaced through holes (12) in the said plate (11) by photo-etching; and - assembly of the said photo-etched plate (11) on the said support. 2. A process according to Claim 1, characterised by the fact that for each matrix (4) there are prepared a plurality of the said plates (11) of small thickness made of a chemically corrodable material, the said plates (11) being photo-etched in such a way as to form on each of these an equal number of through holes (12) and the said plates (11) are finally joined together, superimposed with their corresponding holes (12) disposed in corresponding positions and mounted with a single operation on the said support (3). 3. A process according to Claim 2, characterised by the fact that during the photo-etching step the corresponding holes (12) of each said plate (11) are formed in radially offset positions with respect to those of the corresponding holes of the other plates of the same matrix (4) in such a way that when the plates are superimposed the said corresponding holes (12) define respective inclined seats (13) for the said needles (2). 4. A device for guiding the needles of a dot matrix print head comprising a matrix (4) and at least one other guide element (6) for the said needles (2) disposed parallel to the said matrix (4) and mounted with it on a support (3), characterised by the fact that at least the said matrix (4) comprises at least one flat plate (11) of small thickness with respect to its transverse dimensions and provided with a plurality of through holes (12) for guiding the said needles (2) which holes (12) have been formed by photo-etching of the said plate (11). 5. A device according to Claim 4, characterised by the fact that the said matrix (4) includes a plurality of the said photo-etched plates (11) glued fixedly together in superimposed positions, the guide holes (12) of these latter being formed with their axes parallel to the axes of the head, but offset from one another in such a way as to define inclined seats (13) for the said needles (2). 6. A device according to Claim 5, characterised by the fact that the holes (12) of the said superimposed photo-etched plates (11) have axes passing through the points of intersection of the axes of the said needles (2) of the head with respective section planes parallel to the said plates (12) and disposed at progressively greater distances from the focus of the said print head. 7. A dot matrix print head characterised by the fact that it includes a guide device for the needles (2) according to any of Claims from 4 to 6.

Inventors: GAIARDO, MARIO
Applicants: MICROLYS S.P.A.
Application year: 1987
Main classification: B41J2
IPC codes: B41J2