Modular Cabling System

Abstract

A flexible flat cable having a plurality of parallel conductors arranged on an insulating support and covered by an insulating layer is provided with openings formed in the insulating layer located at regular intervals along the cable length. The portions of the cable having the openings are formed into connectors at the user's site, or connectors are provided, one at each of the openings, to produce a modular cable which may be separated into usable lengths.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a modular connection system for electronic devices. More particularly, the present invention relates to a modular connection system for data processing electronic systems, which employs flexible flat cables for the connection of distinct units in the system.

It is known that in modern data processing systems several electronic signals may be transferred simultaneously from one unit to the other and that a plurality of wires are needed for this purpose. In addition to this, the signals to be transmitted are often pulses having a rectangular shape, i.e. with leading and trailing edges which are extremely steep, the pulses being sent with extremely high repetition rates, of the order of megacycles. In order to avoid attenuations, distortions and mutual couplings between adjacent wires it is therefore often necessary to use coaxial shielded wires which are cumbersome and, when collected in a single cable, become mechanically rigid and difficult to arrange in conduits.

The systems installation at the customer site therefore becomes costly, requiring a large amount of time and making use of cables previously prepared in convenient lengths provided with factory prepared terminal connectors. A quality connection between the cables and connectors is in fact essential whether it is accomplished by soldering or by crimping operations, to insure the correct performance of the system, and to prevent introducing malfunctions which are generally intermittent and whose origins are extremely difficult to identify. The cables are therefore prepared at the factory in required lengths and undergo suitable tests before being sent to their respective users.

Inconvenience is caused by the foregoing in that for every installed system it is necessary to define the configuration and the length and arrangement of connection cables, in order to thus provide for their preparation, or it is necessary to plan for storing a large number of previously prepared cables of different lengths and types, to be chosen according to the needs imposed by any circumstance. Besides the inconvenience and the handling costs deriving from it, if the electronic system configuration is to be modified to add, replace, or remove some electronic units, it will generally be necessary to replace the connection cables which requires that the system be out-of-service for long periods of time, due to the period required for the changes.

In order to avoid at least in part the inconveniences mentioned the use of flat cables in which the conductor wires are arranged one parallel to the other on an insulating flexible support shaped as a tape has been proposed and is now being implemented. These cables present a section with a very low moment of inertia to flexure in the direction normal to the plane of the cable, and are therefore capable of assuming bends with very short curve radii. The installation of these cables is much easier than the cylindric cables. The inconveniences, already mentioned, however, related to the need of laboratory preparation and testing and subsequent installation, handling spare parts, possible need for replacement cables, are still present.

A further aspect to be put in evidence, and one which forms a serious inconvenience for the connection cables used up to now, whether they are flat or not, concerns the so called "bus" connections which are largely used in the connection into a system of several units, generally of the same type. The "bus" connection, compared to the "star" connection, is characterized in that a certain group of wires interconnect several distinct units in sequence; for example, a controller device may be connected to several magnetic tape handlers. A group of wires is connected at one end, by means of a connector to the controller device and at the other end by means of a connector, to the first tape handler. The cable end connector enters on an input connector set on the first tape handler; suitable jumpers connect the input connector to an output connector. A second group of wires, forming a second cable is connected by means of a connector to the output connector of the first tape handler and at the other end, always by means of a connector, to a second tape handler. The second tape handler, also has an output connector, connected, by means of jumpers, to the input connector, and therefore it is possible to accomplish a cascade connection with a third tape handler and subsequently to a fourth and so on, up to a maximum number limited in general by the signal transfer time along the cable. For the correct performance of the devices, the signal transfer time cannot exceed a certain value and therefore imposes a limit to the total length of the bus connected cables. In a connection of this type it is evident that the probability of a bad contact between connectors, with subsequent introduction of malfunctions doubles with each added unit, and in correlation, the reliability of the connection decreases.

An object of the present invention is to eliminate the inconveniences mentioned by providing the flat cable modular connection system, which is characterized in that for the connections a flat, flexible and continuous cable is used, on which connecting elements not interrupting the cable continuity are set during a continuous manufacturing process. A cable of this type may therefore be installed to the desired length and cut during installation without being subjected to preparations in the factory and to subsequent tests, the normal continuous manufacturing tests being sufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further advantages will be explained by the following description which is given by way of example and not limitations when taken with reference to the enclosed drawings in which:

FIG. 1 shows a flexible flat cable structure known in the state of the art;

FIG. 2 shows a terminal connection method, known in the state of the art, employed for a flexible flat cable of the type shown in FIG. 1;

FIG. 3 represents the structure of a second type of flexible flat cable known in the state of the art;

FIG. 4 represents a terminal connector, known in the state of the art, employed for a flexible flat cable of the type as per FIG. 3;

FIG. 5 represents schematically a preferred form of embodiment of a flexible flat cable according to the invention;

FIG. 6 represents another type of embodiment of a flexible flat cable according to the invention;

FIG. 7 represents schematically a way to use a flexible flat cable according to the invention;

FIG. 8 represents in detail a connection mode for a flat flexible cable according to the invention;

FIG. 9 represents a first variant of the embodiment of connectors for a flat flexible cable according to the invention; and

FIG. 10 represents a second form of connection for a flat flexible cable according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before describing the invention it is suitable to refer to the flexible flat cables existing on the market.

FIG. 1 represents a very common type of flexible flat cable A. On a flexible support 1 of insulating material shaped like a tape, parallel conductors 2, having a pre-established width, are obtained through photo-etching of a metallic film deposited on the flexible support.

In order to avoid oxidizing and degrading of the conductors 2, a protective insulating film is laid by painting the film on the conductors, or as an alternative a continuous covering tape 3 is applied using suitable adhesives. In addition, in order to improve the cable electric characteristics, a continuous screening metallic film 4 may be applied on one or both sides of the flat cable A which in turn may be protected by a possible insulating sheet 5. The terminal connections are formed for this type of cable by stripping the end of the conductors 2, that is freeing them from the protective sheath, strengthening and passivating the uncovered terminals of the conductors by means of electrolytic plating methods and the subsequent depositing of noble metals, and bending the so prepared terminal of the cable on a conveniently rigid support, as shown in FIG. 2. The flat cable A is then blocked on a rigid support 6 by means of suitable clamping devices 7. A terminal connector which can be inserted in a female connector of the type used for printed circuit boards, is thus formed by use of the same flat cable.

Evidently other solutions may also be adopted. For example, the terminals may be soldered to connection pins of connectors of the common type, having clamping devices for the flexible cable so to avoid the mechanical stresses of the soldering points. In all the cases, the concept followed is always that of a flexible electric connection element, obtained from a continuous element with a defined length and provided, at the terminals only, with convenient devices for electric contacts. The cable must be prepared and tested in the factory and therefore the possibility of preparation at the user's site is excluded.

FIG. 3 represents another type of flat cable B in which several conductors 8 with a circular cross section, parallel one to the other, are set on an insulating and flexible support 9. The conductors 8 are clad and maintained in place by an insulating sheet 10 which is made to adhere to support 9 with suitable glues, or with other means or methods. In this case a suitable screening for the cable may be provided for, consisting in general of a metallic grid 11 set on a sheet 10 and in turn covered with an insulating film 12. For this type of flat cable, terminal connectors are used substantially similar to those already described. In addition to these, connectors may be used whose connection between the wires and the connector contact elements is accomplished by means of an operation, known as crimping.

FIG. 4 illustrates an exploded view of a typical connector for the described flat cable B formed by wires with circular cross section. The terminal connector consists of an insulating body 13 in which contact pins 14 are inserted terminating at one end with the same number of pointed forks 15. In the fork's teeth there is an indent which defines a round opening having a diameter slightly smaller than the one of the wires to be connected, and the pointed end of the teeth is shaped so to form a "guide" for receiving the conductors. The connector is completed by a rigid counterboard 16 having suitable cavities, in each one of which the end of a fork 15 is located after the assembly is completed. With suitable control means or "jigs" the connector body 13 is pressed on the terminals of the flat cable, from which eventually the terminal portion of the screening grid 11 has been removed. Due to this operation the connector forks 15 punch the insulating sheets 9 and 10 each one closes on a conductor insuring the electrical contact. The counterboard 16 is clamped on the body of the connector completing it.

The operations to prepare a cable with these types of connectors are very delicate and require the use of auxiliary devices (the aforesaid "jigs") for the correct reciprocal positioning of the parts, and the use of suitable tools for the normal check and tests of the connections.

According to the present invention all of these limitation and these requirements are overcome with the use of the flat cables of the described preformed types, i.e. prepared with connection means obtained or applied during the same process of continuous production at a modular distance one from the other so that cables of the desired length may be obtained on the installation site simply by cutting a continuous cable having an undefined length.

FIG. 5 shows in its most simple form a flexible flat cable C according to the invention. The physical structure of the cable C is identical to the one previously described and represented in FIG. 1 but at regular intervals I the covering protective tape presents some openings which leave the conductors 2C underneath uncovered. In these areas the conductors 2C are plated with noble metals to prevent degrading due to the atmospheric agents while also obtaining a local strengthening of the conductors themselves. Such a plating operation may be done by a continuous process during the cable production.

As shown in FIG. 6, when the flat cable also includes a screening or ground metallic plane 11D, this also will be provided with openings at regular intervals and of a size slightly exceeding that of the opening in the covering tape for the conductors 8D. In order to allow for possible connections to the ground plane 11D, the edges of the ground plane near the opening can be plated and left uncovered as shown in FIG. 6.

FIGS. 7 and 8 represent a possible method of use for a type of cable as described above.

FIG. 7 represents in its structural assembly an electronic hypothetical system consisting of several distinct units. The different units are distributed on a hollow false floor 17, in which the connection cables among the various units are laid down and fastened. At regular intervals, the false floor presents suitable openings 18 through which it is possible to have access to the cables C located internally so that the connection areas pre-arranged on the cables correspond with these openings. Through these openings it is possible to make the connections between the cables and the electronic system units. In all those modular positions in which no insertion of a unit is planned, the openings are closed with protective covers.

FIG. 8 represents in detail a particularly suitable method of connection within the false floor. The false floor provides internally on the lower plane, and in correspondence with every opening, two parallel raised portions 19 and 20 which define a groove 21 having a suitable width and depth. The portion of the flat cable in which the conductors are uncovered is inserted and folded in this groove 21. The sides, the bottom and the upper edges of the groove 21 present a slight depression having a width equal to that of the tape, which is used for the correct transverse positioning of the flat cable. A clamping bracket 22 maintains the flat cable in the correct position. The assembly of the folded flat cable and of the portion of false floor described thus forms a female connector in which it is possible to insert either the terminal rack of a printed circuit board or a connector of equivalent type, as for example a connector formed with a flexible flat cable as described in FIG. 2.

The use of a printed circuit board directly for the connection with the flat cable is particularly advantageous where it is necessary to have connection circuits of high performance; in fact it is possible to assemble circuits on the board having suitable impedance and circuits for line terminations, of suitable impedance, such as to avoid misadjustments of the line and subsequent reflexions on the transmitted circuits. FIG. 8 represents a particularly simple connection system however, other solutions may be adopted in accordance with the spirit of the present invention.

FIG. 9 shows a second form of the invention which is preferred for the formation of connectors prepared on flat cable. The cable is provided with openings in the protective film covering the conductors, at regular intervals uncovering suitable portions. On the uncovered part of the conductors two flexible tabs 22 and 23 are applied, consisting of small portions of a flexible flat cable with conductors at a distance equal to the distance between the conductors on the cable. The conductors on the tabs 22 and 23 are suitably processed, for example by plating with noble metals to avoid oxidizing and degrading due to atmospheric agents. The portions of conductors on the flexible tabs 22 and 23 are each soldered to the corresponding conductor on the cable and form a flexible socket in which a male connector of the type already described may be inserted. On the sides, rigid, suitably shaped 24 and 25 elements (here shown at a mutual distance greater than the distance normally used) and cooperating with the male connector are provided to insure the necessary contact pressure.

FIG. 10 shows how the same inventive concept may be used with a flat cable D of the type described in FIG. 3. The flat cable D is provided at regular intervals with openings on the screening grid 110 and in the upper protective film. Systematically, in correspondence to such openings, connectors are applied, of the type already described in FIG. 4. Male or female connectors are applied at random so as to obtain a continuous flat cable provided with a plurality of connectors at modular distance which may be cut in the required lengths on the installation site. In the examples previously described, it is evident that the cable preparation may be accomplished by means of continuous production with the aid of all the tools and simplified procedures which are allowed by mass production, with a continuous check on the product insuring its quality and reliability.

In the examples previously described it is also evident that for star connections the cable continuity is not interrupted in any way, and the connection reliability therefore remains high independent of the number of connected peripheral units or their connection sequence. It should further be clear from the foregoing that other changes may be made to the described invention without departing from the spirit of the invention itself. For example, in the case of a flat cable with a screening layer it is not necessary that the openings planned for in the protection insulating layers be made on the side in which the screening layer is located with respect to the assembly of the conductors. These openings may be made on the opposite side, without requiring openings in the screening conductive layer. Similarly, openings may be made on two opposite sides to allow access, respectively, to the conductor assembly and to the screening layer, without departing from the spirit of the invention.

Claims

What is claimed is:

1. A female connector intermediate the ends of a flat cable having a plurality of spaced parallel conductors, which comprises a portion of said cable having said insulating material removed to expose said plurality of conductors and means adjacent said cable portion forming a groove for receiving a male connector in conducting relation with said cable, said groove forming means having a pair of parallel spaced elements disposed adjacent the exposed conductors on said cable portion and a pair of flexible tabs having insulating material removed from one side to expose an equal number of conductors with the same spacing as said cable conductors, said tabs being positioned with the exposed conductors facing the exposed cable conductors and extending between said spaced elements to provide a conductor between said cable and a male connector when received therebetween, each of said flexible tabs comprise a relatively short length of flexible flat cable.

2. The connector of claim 1 wherein said exposed conductors on each of said flexible tabs is provided with a surface plated with a noble metal to prevent oxidation of said exposed conductors.