US2802971A

US2802971A - Connecting strip

Info

Publication number: US2802971A
Application number: US396017A
Authority: US
Inventors: Pieter Van Leeuwen
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1952-12-05
Filing date: 1953-12-03
Publication date: 1957-08-13
Anticipated expiration: 1974-08-13

Description

Aug. 13, 1957 P. VAN LEEUWEN 2,802,971

CONNECTING STRIP Filed Dec. 3, 1953 INVENTOR United States Patent G CONNECTING STRIP Pieter van Leeuwen, Hilversum, Netherlands, assignor, by

mesne ass1gnments, to North American Philips Compauy, Inc., New York, N. Y., a corporation of Delaware Application December 3, 1953, Serial No. 396,017

Claims priority, application Netherlands December 5, 1952 8 Claims. (Cl. 317-112) This invention relates to a connecting strip comprising a plurality of relatively insulated connecting members or contact members and more particularly to a structural element of a contact bank for automatic telephone systems or similar apparatus.

It is known to build up contact banks by stacking a plurality of connecting strips, each comprising a series of contact members which in most cases project on each side from the edge of the strip. As a rule, the ends at one side of the strip are intended for securing the multiple cables and those at the other side for co-operation with a movable contact member. The known connecting strips for this purpose are, in most cases, formed by clampng a series of contact members between insulating strips or, as is more usual, surrounding the series of contact members in a templet by casting or moulding with an insulating plastic material, which is subsequently hardened. The connecting strips thus obtained have the disadvantage that there are comparatively large tolerances as a result of the limited accuracy in working and inner action of the insulating material, such as contraction in cooling. Not only comparatively large tolerances in the spacing between the contact members of a strip are present but also deviations in the mutual positions of the contact series of a plurality of connecting strips assembled into a contact bank are unavoidable. A consequence of all this is that a contact bank for a selector switch for automatic telephone systems which comprises a determined number of contacts per layer is limited to a determined minimum sze since it is necessary that the wipers shall co-operate in the correct manner with the contacts of the bank at each stop position of the wiper carrier of the selector. Therefore, as a result of the said tolerances, the spacing between the contact members cannot be so small as would be possible otherwise.

In the manufacture of known connecting strips comprsing fiat contact members use is commonly made of a series of contact members which are obtained in the correct mutual positions by punching a metal plate, and the extremities of which are connected to a remaining portion of the plate. After the said coherent series of contact members has been provided in the connecting strip,the positions of the plate connecting the extremities ofthe'contact member are cut away. This method has the disadvantage that an important loss of material is involved.

The object of the invention is to provide a connecting ing of a plurality of connecting strips according to the invention to form a contact bank, it is possible either to adinit more contact members per series with a given sze or to reduce the size of the strip when a determined number of contact members per series is retained. This atords the advantage that in a contact bank for a selector built up from such strips more contacts can be wiped per unit time without increasing the mass forces which occur when the wiper carrier is acceleratcd or stopped. This is very important, more particularly, in systems for direct telephony, that is to say, telephone systems without registers.

According to the invention, the connecting strip is constituted by a metal supporting strip having a plurality of transverse grooves in which pieces of metal wire projecting trom each side of the strip are centered in an insulatng manner by means of at least one wire or ribbon of flexible insulating material, for exarnple nylon cord, extending in the direction of the length of the supporting strip and under the successive pieces of wires, the pieces of wire and the insulating wire or rib bon, at their crossings, being inter-connected and connected to the supporting strip with the use of an insulating adhesive.

Since the supporting strip is of metal for which a light weight aluminium that may be anodized is preferred, it may be manufactured with very small tolerances. Furthermore, electric screening between the contact members of the various strips is ensured automatically in stacking a plurality of such connectng strips.

In order that the invention may be readily carried into effect, it will now be described in detail with reference to the accompanying drawing showing, by way of example, one embodiment thereof.

Fig. 1 is a plan view on a semi-circular connecting strip intended as a structural element for a contact bank of a rotary switch for automatic telephony.

Fig. 2 is a cross sectional view of this strip taken along the line IIII of Fig. 1.

Fig. 3 shows part of a longtudinal section taken along the line IIIIII of Fig. 1, and

Fig. 4 shows part of a longitudinal section taken along the line IVIV of Fig. 1.

The embodiment shown in the figures comprises a fiat aluminium supporting strip 1 which is semi-circular in shape. The strip 1 comprises, on its upper side, a plurality of transverse grooves -2, which are directed towards the center of the circle and in which contact members are provided in the form of pieces 3 of metal wire which project from each side of the strip.

For reasons which will be mentioned hereinafter, Fig. 1 shows three separate groups of pieces of wire, that is A, B and C, although the supporting strip 1 as shown actually comprises only pieces of wire such as those in group C.

The pieces of wire 3 are centered in an insulating mannr in the transverse grooves 2 by the aid of two nylon cords 4 which extend in the direction of the length of strip 1 at a small distance rom its edge. Said cords extend under the successive pieces of wire 3 in order 0 pass on the upper side of the strip 1 to the subsequent transverse groove. An insulating adhesive 5 is provided for the mutual attachment of the pieces of wire 3 and the nylon cords 4 to the supporting strip 1 at the crossing of a nylon cord and a piece of wire, that is to say in a groove 2 (see Fig. 4). Use is preferably made of an ethoxylehe resn. The resin, after being provided, is cured in known manner, so that the pieces of wire 3 and the portions of the nylon cords 4 surrounding them in part are extremely rigidly secured to the supporting strip 1. The nylon cords extend over the upper side of the supporting strip 1 in longitudinal grooves 6 in strip 1 having a depth smaller than that of the transverse. groo ves 2. Owirig to the provision in the grooves 6, of the cords 4, the cords 4 tlo not project above the profile of the supporting strip 1. -This is important,

sncc in stacking a plurality of such supportng strips the lower side of one supportng strip bears directly upon the upper side of the subsequent strip, so that the spacings between the series of pieces of wire in the connecting strips are determined only by the thickness of the metal supportng strips which can be obtained with very small tolerances.

The nylon cords 4, after having extended under all the wire pieces 3 in the supportng strip return through the said pieces of wire to their starting point, the returning part (4) also being sccured at a crossing with 2. piece of wire with the use of the insulating adhesive.

For the sake of clearness, Figs. 2 and 3 show .only a cross-section of the supportng strip 1, the pieces of wire 2 and the nylon cords 4 being omitted.

Not all of the contact members 3 provided in the supportng strip 1 are shown in Fig. 1. Those which are shown are divided into three groups A, B and C,

whch show the contact members 3 in different stages of working. As mentioned before, in the embodiment under consideration, all contact members provided in the supportng strip actually have the shape as shown for group C.

The contact members 3 of groups A are constituted by rectilinear pieces of metal wire having the same sectional area throughout their length.

The contact members of groups B are consttuted by pieces of wire similar to those of group A, but with both ends flattenecl. Flat terminal parts 7 and 8 located in the same plane are thus obtained. The parts 7 and 8 may be formed before the pieces of wire are provided in the supportng strip, but a simpler method is first to provide pieces of wire similar to those of group A and then to flatten all the ends of the pieces of wire simultaneously in one operation.

The contact members in group C have acquired their ultimate shape by punching the fiattened ends of pieces of wire (group B) secured in the supportng strip 1 to the desired size with the use of a cuttng tool specally made for this purpose. The correct mutual positiom'ng of the cutting tool and the connecting strip is obtained with the use of centering holes 11 provided in the extremitics of supportng strip 1. During the punching operation those extremities of the pieces of wire which are located on the inner side of the strip are formed into more or less rectangular flat contact surfaces 10 which are accurately spaced apart and which are intended to be engaged by a wiper in a selector, the contact bank of which is built up trom such connecting strips. The flattened ends 7 of the pieces of wire acquire by punching, as may be seen at 9, a profile whch facilitates the securing of connecting wires thereto, for example, by solder- 1ng.

To ensure satisfactory contact between the contacts 10 and the cooperating wiper in a selector constituted by a plurality of the connecting strips described, it may be desirable that the contact surfaces should be provided with rare metal, for example palladium or silver. This may be efrected by making those ends of the pieces of wire whch, after being flattened, are punched into the desired shape of the contact surfaces 10, wholly or in part from precious metal, for example either by welding or securing in another manner 2. piece of precious metal wire t pieces of wire of base metal, for example of brass which are to be arranged in the transverse grooves 2 or by providing the relative ends of the pieces of wire beforehand with a precious metal.

In the embodiment described, the supportng strip 1 is semi-circular in shape, so that the connecting strip may serve as a structural element of a semi-cylindrical contact bank. However, the supportng strip may alternatively have a different shape, for example, it may be rectilinear and thus constitute a structural element for a recti.liner contact bank.

strip being provided with a plurality of groves therein The connecting strip according to the nvention may also be used for purposes other than as a structural element for a contact bank. Thus, it may be used, for example, as a distributing strip in telephone exchanges, as an assembling support for electric component parts in apparatus and as a connecting strip for the windings for cnergizing an electrornagnetic relay. In relays the contact springs are in most cases clamped between insulating spacers mounted on a connecting strip secured to the yoke and comprise contact members for the energizing coils. Due to tolerances in the thickness of the connecting strip, the contact springs are not always correctly positioned relatively to the parts coupled to the armature and moving the contact springs, so that after adjustment of the contact springs is necessary. This disadvantage is obviated when using the connectingstrip according to the invention, the thickness of which is reproducible in manufacture with a high accuracy.

While I have shown and described the preferred em bodiment of my invention, it will be understood that the lattcr may be embodied otherwise than as herein specifi cally illustrated or described and that in the illustrated embodiment certan changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principle of the invention Within the scope of the appended claims.

What is clairned is:

1. A combination of an elongated metal connecting positioned transverse to the direction of length of said strip, a relatively insulated piece of bare metal wire having a circular cross-secton arranged in each of said grooves, at least one flexible, insulating member in each of said grooves, said member extending along a plane surface of said strip in the direction of length thereof and in said grooves and under said successive circular wires, and an insulating adhesive for connecting said circular wires and said insulating member at their points of engagement.

2. A combination as set forth in claim 1 further comprsing another groove extending in a direction parallel to the direction of length of said strip and having a depth smaller than that of said transverse grooves, and said insulating member bcing positioned in said other groove.

3. A combination as set forth in claim 1 wherein said insulating member addtionally engages a portion of the top surface of each of said wires and is secured at points of engagement therewith by said insulating adhesive.

4. A combination as set forth in claim 1 further comprising two insulating wires, each extending adjacent to an edge of said connecting strip, and said insulating wires being adapted to center said wire pieces in said transverse grooves.

5. A combination as set forth in claim 1 wherein said connecting strip is composecl of aluminum.

6. A combination as set forth in claim 1 wherein at least one end of each of said wires on the same side of said connecting strip is flattened.

7. A combination as set forth in claim 1 wherein said" insulating adhesive is an ethoxylene resin.

8. A combination of an elongated metal connecting strip being provided with a plurality of grooves therein positioned transverse to the direction of length of said strip, a relatively nsulated piece of bare metal wire having a circular cross-section arranged in each of said grooves, at least one flexible, insulating member in each of said grooves, said member extending along a plane surface of said strip in the direction of length thereof.

and in said grooves and under said successve circular wires, an nsulatng adhesive for connectng said circular wres and said insulatng member at tl1eir ponts of engagement, and one end of each of said wires ccnsisting of a base metal provded with a surface of precious metal.

References Cited in the file of ths patent UNITED STATES PATENTS Harvey Sept. 26, 1950 Fritts Dec. 19, 1950