US3890702A - Method of making thermal recording print head - Google Patents

Abstract

A thermal print head and a method of manufacturing it using a thermally stable support mandrel and a plurality of spaced turns of copper-coated resistance wire wrapped on the mandrel. The turns are held on the mandrel by slabs of potting compound retained in under-cut grooves on the mandrel while the connections to the print elements are made by slitting the turns along a longitudinal groove in the mandrel. The copper coating is removed to expose the resistance wire at the desired printing element locations.

Description

United States Patent 1 1 Lane, III

[ June 24, 1975 METHOD OF MAKING THERMAL RECORDING PRINT HEAD [75] lnventor: Charles E. Lane, III, Meadowbrook,

[73] Assignee: Honeywell, Inc., Minneapolis, Minn.

[22] Filed: July 22, 1974 [21] Appl. No.: 490,230

Related US. Application Data [62] Division of Ser. No. 457,622, April 3, 1974.

[52] US. Cl. 29/611 [51] Int. Cl. H05b 3/00 [58] Field of Search 29/611, 629, 597, 610;

[56] References Cited UNITED STATES PATENTS 2,703,917 3/1955 Pankove 29/253 3,578,946 5/1971 Colello 3,781,983 l/1974 Hiruma et a1 29/611 3,795,884 3/1974 Kotaka 29/629 X FOREIGN PATENTS OR APPLICATIONS 525,991 2/1954 Belgium 29/611 Primary ExaminerC. W. Lanham Assistant ExaminerVictor A. Di Palma' Attorney, Agent, or FirmArthur H. Swanson; Lockwood D. Burton; Mitchell .1. Halista [5 7 ABSTRACT A thermal print head and a method of manufacturing it using a thermally stable support mandrel and a plurality of spaced turns of copper-coated resistance wire wrapped on the mandrel. The turns are held on the mandrel by slabs of potting compound retained in under-cut grooves on the mandrel while the connections to the print elements are made by slitting the turns along a longitudinal groove in the mandrel. The copper coating is removed to expose the resistance wire at the desired printing element locations.

3 Claims, 5 Drawing Figures 1 METHOD OF MAKING THERMAL RECORDING PRINT HEAD This is a division of app'lication'S er. No. 457,622 filed on Apr. 3, 1974. t

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is dir ected to a thermalprinter' print head and to a method for manufacturing such a head. More specifically, the present invention is directed to a thermal printer print head, for thermal recording on a heat sensitive recording medium and for mounting on a printed circuit board. Thermal print heads may be found in Class 219 Electric Heating, Subclass 216 of the United States Patent Off ce classification system. I

2. Description of the Prior Art In order to obviate theproblem associated with conventional recording techniques in recording information, particularly from data processing systems, thermal recorders have been developed forrecording on a thermally responsive recording medium. Forexample, such thermal recorders obviate the use. of an inking pen which type of pen is undesirable for many recorder applications because of problems associated with clogging of the pen as well as the need to replenish the ink supply. Similary, the thermal recorder is free of the problems associated with a high voltage type of recording wherein recording electrodes using an electric arc to mark a recording medium are exposed to arc erosionwhile the arc imposes limitations on the environmental exposure of the recording apparatus, e.g., an explosive atmosphere. Further, the thermal recorder can be used for recording analog and digital information on the same recording medium. Conventional thermal recording devices are shown ,in U.S. Pat. Nos. 3,145,071; 3,312,979; 3,334,352; 3,354,817; 3,453,647; and 3,718,564. While these prior art thermal recorders are capable of recording on a thermally responsive medium, none of the aforesaid recorders employs a recording head which is capable of being assembled by an automatic manufacturing technique. Further, a practical thermal print head must lend itself for use with printed circuits to minimize the manufacturing costs thereof and to produce a miniaturized print head capable of operating as a high speed printing element, i.e., a light weight printing head having minimal thermal inertia, or heating and cooling time.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved thermal print head adapatable for automatic manufacturing techniques while exhibiting high speed recording capabilities in a miniaturized assembly.

Another object of the present invention is to provide a novel method of manufacturing a thermal print head.

In accomplishing these and other objects, there has been provided, in accordance with the present invention, a thermal print head having a plurality of spaced resistance heating elements supported on a first longitudinal edge of a thermally stable triangular crosssection support mandrel. A longitudinal undercut groove is located in each face of the support mandrel adjacent to this first longitudinal edge with a first free end of each of the heating elements passing across a first one of the longitudinal grooves and a second free end of each of the heating elements passing across a second one of the longitudinal grooves. A retainer means is located within each of the grooves and is arranged to encompass the portion of the heating elements passing acrossa corresponding groove to retain the heating elements on the first longitudinal edge and to fill the corresponding longitudinal groove. The print head is manufactured by a method including the steps of winding a resistance heating wire having an electrically conductive coating with spaced turns on the mandrel with each turn of the wire passing across the first longitudinal support edge of the mandrel to form a thermal printing element at the apex of the first longitudinal support edge, and moulding a slab of retaining material around the portions of the wires passing over the undercut grooves while filling the undercut groove by the retaining material to be retained therein. The wire turns are cut along a third longitudinal groove located in a third face of the mandrel to form free wire ends for each printing element suitable for providing a connection to energizing circuits for the print head.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the present invention may be had when the following detailed description is read in connection with the accompanying drawings in which:'

FIGS. 1 through 4 are step-by-step illustrations ofa sequential manufacturing techniques embodying the present invention for producing a novel thermal recording head, and

FIG. 5 is a cross-section of an assembled and mounted novel thermal recording head formed by the method shownin FIGS. 1 to 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT DETAILED DESCRIPTION Referring to FIGS. 1 to 4 in more detail, there is shown a sequential manufacturing operation embodying the present invention for producing a thermal recording head having a plurality of thermal recording elements in an integral arrangement. Starting with FIG. 1, there is shown a thermally stable support mandrel 2 having a triangular cross-section. A pair of longitudinal undercut grooves, or dovetails, 4 and 6 are provided in adjacent faces 2A and 28, respectively, of the support mandrel 2 which faces 2A and 2B join along one edge to define a longitudinal support edge 8. A third face 2C of the mandrel 8 is also provided with a longitudinal groove 10 suitable for attaching the thermal print head to a support member, as discussed hereinafter. The support mandrel 8 may be an aluminum bar which is hard-anodized and coated with a suitable material, e. g., tetrafluorethylene, to provide electrical insulation for the aluminum base member. The mandrel 8 is wound with a single layer of spaced turns of an electrically insulated and copper plated resistance wire 12 with the spaced turns of the winding passing across the first longitudinal support edge 8. This wire consists of a core of resistance wire which is copper plated and coated with solder-through, i.e., heat-meltable, electrical insulation to enable the resistance wire to be connected to a support member, as discussed hereinafter.

As shown in FIG. 3, a wire retaining member in the form ofa slab ofa potting compound 14, I6 is moulded in place on the outside surface of each of the faces 2A and 2B having the aforesaid undercut longitudinal grooves 4 and 6, respectively. therein. This potting compound 14, 16 is arranged to have the turns of the resistance wire 12 embedded therein whereby to retain the wires on the mandrel 2 in a fixed spaced relationship while the portion of the potting compound extending into the undercut grooves 4 and 6 provides a means for locking the potting compound 14, 16 to the mandrel 2. Subsequently, each of the turns of the resistance wire 12 is cut by passing a cutter (not shown) along the groove located in the third face 2C of the mandrel 2. This cutting operation is effective to provide a pair of free ends for each of the segments of the resistance wire passing across the aforesaid first longitudinal support edge 8, as shown in FIG. 4.

The completed thermal print head is attached to a support member, such as a printed circuit board 18, by self-tapping attaching screws 20 passing through the circuit board 18 into the longitudinal groove 10 in the third face 2C of the mandrel 2. The width and depth of the groove 10 is selected to provide suitable space for the self-tapping attaching screw 20. The free ends of the resistance wire heating elements are attached to platedthrough holes 22 in the printed circuit board 18 by any suitable soldering technique which removes the solder-through insulation from the wires and connects the copper-plating to the plated-through holes 22. Each of the plated through holes 22 is, in turn, connected to printed wiring 24 located on the printed circuit board 18 for conducting an energizing signal to a corresponding one of the thermal printing elements and may, further, be connected to other associated equipment located on the printed circuit board 18 to minimize extraneous electrical connections.

The exposure of the core of the resistance wires forming each of the printing areas at the apex of the first longitudinal support edge 8 may be achieved either before or after attaching the thermal print head to the printed circuit board 18 by etching the wires to a predetermined distance on either side of the first support edge 8. This etching process using, for example, a solution of ferric chloride, is arranged to remove the solderthrough coating and the copper plating on the resistance wires while not affecting the electrical insulation of the surface of the mandrel 2. Thus, the resistance wires will heat up only in the area where the copper plating has been removed since the copper plating will serve as a conductor along other portions of the resistance wires to bypass the internal core of resistive material. Thus, the amount of material to be heated to form a thermal print character is limited to the etched area on the first longitudinal support edge 8.

Accordingly, it may be seen that there has been provided, in accordance with the present invention, a novel thermal print head and a novel method for producing the thermal print head in an automatic manufacturing operation to produce a plurality of thermal printing elements in a integral constuction.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A method of manufacturing a print head comprising the steps of winding a single layer of spaced turns of a wire on an electrically resistive support mandrel having a longitudinal wire support edge and an undercut groove in each face of said mandrel adjacent to said support edge, filling said grooves in said mandrel and encompassing adjacent ones of said wires with a wire retaining compound and cutting said winding of wire along a predetermined longitudinal line on said mandrel.

2. A method as set forth in claim 1 wherein said wire is a resistance wire having an electrically conductive coating thereon and including the further step of removing said conductive coating at said support edge to leave said resistance wire passing across said support edge.

3. A method as set forth in claim 1 and including the further step of attaching the free ends of said wire turns adjacent to said longitudinal line to respective printed wires on a printed circuit board.

Claims (3)

1. A method of manufacturing a print head comprising the steps of winding a single layer of spaced turns of a wire on an electrically resistive support mandrel having a longitudinal wire support edge and an undercut groove in each face of said mandrel adjacent to said support edge, filling said grooves in said mandrel and encompassing adjacent ones of said wires with a wire retaining compound and cutting said winding of wire along a predetermined longitudinal line on said mandrel.

2. A method as set forth in claim 1 wherein said wire is a resistance wire having an electrically conductive coating thereon and including the further step of removing said conductive coating at said support edge to leave said resistance wire passing across said support edge.

3. A method as set forth in claim 1 and including the further step of attaching the free ends of said wire turns adjacent to said longitudinal line to respective printed wires on a printed circuit board.

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