Method of Producing a Multicontact Spring

1. Field of the Invention

The present invention relates to springs having contacts which are used as contacting parts of variable resistors, trimmers, motors, cameras, potentiometers, etc., and more particularly to a method of producing a spring having multicontacts (hereinafter referred to as "a multicontact spring").

2. Description of the Prior Art

For a contacting spring to have a high reliability, it is generally necessary that it have a plurality of contacts. Miniaturization of electrical apparatus using a contacting spring requires a corresponding decrease in the size of the contacting spring. Accordingly, for miniaturization of electrical apparatus it is necessary to increase the density of the number of contacts per unit width of a spring and to minimize the contact spacing (i.e. distance between adjacent edges of two adjacent contacts). For example, there is a demand to produce a multicontact spring which is 1 mm in width and has five contacts which are less than 0.2 mm in width, respectively. However, such a multicontact spring has not been successfully produced by conventional methods, i.e., a photo etching method and a blanking method.

In accordance with the conventional photo etching method, a multicontact spring is produced by the steps of:

coating both surfaces of a spring blank with a photo resist;

shining light on the photo resist through a negative pattern film;

removing parts of the resist;

etching the parts of the spring blank which are not coated with the resist, and;

removing the remaining resist. An illustration of the thus produced multicontact spring can be seen in FIGS. 1A and 1B. The contact spacing of the multicontact spring produced by the above mentioned photo etching method is usually limited by the thickness of the spring, in view of the so called side etching (i.e. etching of a part under the resist). Furthermore, it is difficult to make the contact spacing less than 0.1 mm. Finally, since each of the corner edges 1 of a contact is formed in an acute angle, as illustrated in FIG. 1B, the corner edges 1 may damage a contact surface of a member which comes in touch with the multicontact spring. In a case where a multicontact spring is produced by the photo etching method disclosed in the Japanese Patent Publication No. 52-46889, the spring material is a precious metal alloy (i.e. platinum and silver alloy), so that the etching rate is small. In this regard, it is possible, after photo etching a copper-base alloy blank, to plate a precious metal alloy for the contact material on the copper-base alloy spring, but the production process of such a multi-contact spring is rather complicated. Accordingly, such a photo etching method of producing a multicontact spring is not suitable for mass production.

An illustration of a multicontact spring produced by the conventional blanking method (i.e. a press working method) can be seen in FIGS. 2A and 2B. In the case of the conventional blanking method, the contact spacing of the produced multicontact spring is limited to approximately 0.2 mm by the conventional die producing technique. Furthermore the contact spacing increases as the thickness of the spring material increases. Finally, as the width of a contact decreases, an undesirable deformation (e.g. twisting or curling) may occur in the contact.

It is also known that the above mentioned multicontact spring having a plurality of contacts per unit width of the spring can be produced by a welding method. An illustration of the multicontact spring, which is a so called multi-wire spring brush, produced by this method can be seen in FIGS. 3A, 3B and 3C. In accordance with the welding method, the multicontact spring is produced by the steps of arranging a number of wires 2 contacting parts between a base plate 3 and an additional plate 4, welding the wires 2 and the plates 3 and 4 by spot welding or soldering, and then, cutting the wires 2. As the diameter of each of the wires used as contacts decreases, the density of the number of wires per one spring can be increased, but more uniform diameters and higher quality wires are required. Furthermore, as the number of the wires increases, it is possible to easily generate a small difference in the shapes of the welded wires, so that the quality of the multicontact springs produced by the welding method is not stable.

An object of the present invention is to provide a method of producing a multicontact spring having a high density of contacts.

Another object of the present invention is to provide a suitable method for mass production of the above mentioned multicontact springs.

A further object of the present invention is to produce multicontact springs having stable quality by using a press machine.

The above and other objects of the present invention are attained by a method of producing a multicontact spring which comprises the steps of: blanking a part of a metal tape for a spring to form a blank; pressing the blank to make linear dents therein which are parallel to each other and do not reach the ends of the blank; dividing the linear dents part of the blank by repeating a press working for cutting one of the linear dents, and; pressing the divided parts of the blank into suitable shapes for contacts.

FIG. 1A is a plan view of a multicontact spring of the prior art;

FIG. 1B is a sectional view taken along the line a--a' of FIG. 1A;

FIG. 2A is a plan view of a multicontact spring of the prior art;

FIG. 2B is a sectional view taken along the line b--b' of FIG. 2A;

FIG. 3A is a plan view of a multicontact spring of the prior art;

FIG. 3B is a side view of FIG. 3A;

FIG. 3C is a sectional view taken along the line c--c' of FIG. 3A;

FIGS. 4A through 4C are cross-sectional views of the multicontact spring of the present invention;

FIG. 5 is a plan view of the blank of the present invention;

FIG. 6 is a side elevational view of the present invention after an area is deformed for providing contact points;

FIG. 7A is a plan view of a modified embodiment of the present invention with end parts removed; and

FIG. 7B is a side elevational view of the embodiment of FIG. 7A.

Firstly, a blank for a multicontact spring is formed by blanking a metal sheet or a metal tape. The metal sheet or tape is made of contact materials or a copper-base alloy covered with a precious metal. The contact materials include copper, silver, and gold and their alloys, platinum and palladium alloys, and certain mixtures of metals.

In the case of FIG. 4A, a blank consists of a base plate 5 of phosphor bronze for a spring and a cladding layer 6 of gold. The blank is pressed with a die to make linear dents therein e.g., as illustrated in FIG. 4B. The dents are parallel to each other and are straight lines, circular arcs or curves. Furthermore, each of the dents has gently slope corners in its cross section. Since one of objects of making the dents is to prevent damage to a contact surface of an opposite member which is touched with a completed multicontact spring, no sharp corner edges should be produced by the press working for making the dents. Another object of making the dents is to prevent flash and burr from occurring, and to decrease the shearing force which is needed for cutting operations. None of the dents reach the ends of the blank. The dents may be made on one of the two surfaces of the blank, for example, on a clad surface of the blank. Also, the dents may be made in a deformation area for contact points.

Then, predetermined parts of the blank are divided by repeating a press working for cutting one of the linear dents or a predetermined linear part including one of the linear dents without scraps, as illustrated in FIG. 4C. According to the present invention, the contact spacing of the divided parts of the blank is from 0.01 to 0.05 mm. In the case of FIGS. 4B and 4C, the width W.sub.2 (FIG. 4C) is 0.04.about.0.2 mm longer than the width W.sub.1 (FIG. 4B) of the blank.

FIG. 5 is a schematic plan view of a blank having five divided parts. The lines a, b, c and d in FIG. 5 represent cut parts of the blank and the length l represents the cut distance of each of lines a, b, c and d. The cut parts correspond to the above-mentioned linear dents, respectively, the above-mentioned cutting operations are repeated in the alphabetical order (a, b, c and d) shown in FIG. 5. Furthermore, it is possible to make the width of each divided part (contact) 0.2 mm in the case of the thickness of the blank being 0.07.about.0.27 mm.

The blank having the divided parts is pressed to deform it into a suitable shape for contact points, as illustrated in FIG. 6. FIG. 6 is a schematic side view of a multicontact spring produced by the method of the present invention. in FIG. 6, the part e represents a deformed area for contact points and a cladding gold layer 6 serves as a contact material. Accordingly, both ends of each of the contacts are connected to each other through the end parts of the multicontact spring. It is convenient to cut an end part of the multicontact spring, represented by f in FIG. 6, so that each of the divided parts (contacts) has a free end. If such cutting operation is carried out prior to the deformation operation for forming the contact points, an undesirable deformation (e.g. twisting or curling) may occur in the contacts.

FIG. 7A is a schematic plan view of a multicontact spring with end parts removed by cutting. FIG. 7B is a schematic side view of FIG. 7A.

It is possible to easily carry out the production of multicontact springs in accordance with the proposed method by using a progressive die.

A metal tape 15 mm in width and 0.1 mm in thickness was used as a starting material. The metal tape was made of a spring material of phosphor bronze with a clad gold layer. The metal tape was blanked to form a blank 1 mm in width. The blank was pressed to make four linear dents 6.5 mm in length. The minimum thickness of the blank at each of the dents was 0.03 mm. A press working for cutting the blank at a predetermined part including one of the dents was repeated four times. The cutting length was 6.1 mm. Then, the blank having the cut parts was pressed into a suitable shape for contact points as illustrated in FIG. 6. Finally, an end part of the blank was cut to complete a multicontact spring. The multicontact spring had five contacts, each of which was 0.2 mm in width.

Although the present invention has been described with reference to the preferred embodiments and an example of the present invention, it will be understood by those skilled in the art that modification of the embodiments may be carried out without departing from the spirit and scope of the invention. For example, it is possible to form a multicontact spring in various desired shapes according to the method of the present invention.