1. Field of the Invention
The present invention pertains to termination devices and a termination method. The invention more particularly concerns termination devices and a termination method which terminate flat conductors of a flat cable.
2. Discussion of the Background
Devices are well known in the art for terminating flat conductors of flat cables. A flat conductor is a conductor having a width dimension which is greater than its thickness dimension. The conductors are used to convey electricity. A flat cable is a cable which bundles together two or more conductors, where the conductors lie in the same plane. Known to the art are flat cables constructed from round conductors and flat cables constructed from flat conductors. Round conductors have a circular cross-section. However, this application concerns itself with flat cable constructed from flat conductors, where the cross-sectional shape of the conductor is generally rectangular. Flat conductors typically have a thickness of approximately 0.007 inches. Flat conductors having a thickness of 0.002 inches, or less, crosses over into the realm of flex circuitry and is not deemed pertinent to this discussion.
Typically, three different methods of constructing flat cable exist. The first method involves the steps of placing conductors between two insulator layers. The insulator layers bonded to each other and to the conductors by way of an adhesive; heat may also be used to help secure the bonding process. The second method involves the step of extruding the insulator material around the conductors. The third method of constructing flat cable includes the step of placing conductors between two insulator layers. The insulator layers being bonded to each other by way of sonic welding so as to trap the conductors between the insulator layers without the insulator layers being bonded to the conductors.
Often, flat cable is chosen for an application because of one of two advantages. One advantage of flat cable is that it provides a low profile. A low profile cable can be placed innocuously underneath floor carpeting, between a door frame and a door panel, or between a headliner and a roof of a vehicle. The second advantage of flat cable is that it is relatively flexible. A flexible cable can be placed inside a clockspring of a vehicle. A clockspring provides for the electrical connection between stationary crash sensors to a rotatably mounted airbag assembly on a vehicle. As such, the flat cable within the clockspring is repeatedly flexed or wound and unwound during the lifetime of the vehicle in which it is installed. Both applications require that the insulating layer not only have superb dielectric qualities, the insulating layers must be tough so as to withstand repeated flexure and industrial type environments.
Insulator layer material which satisfies such requirements includes polyester materials, namely MYLAR by E. I. Du Pont De Nemours and Company. MYLAR type polyester insulating layer film material is economical and has adequate dielectric properties while at the same time adequately whithstands industrial environmental hazards and endures large numbers of flexure before failure occurs.
Various methods of terminating or tapping into a flat cable exist such as crimping, welding, staking, and cutting insulation by way of an insulation displacement contact (IDC).
U.S. Pat. No. 5,389,741 discusses crimping. The crimping process involves the placement of a connection terminal in contact with the conductor by way of sliding the connection terminal in between the conductor and the insulation sheath. Crimping claws are then employed to surround the overlapping portion of the connection terminal and the conductor. The claws are bent so as to press the two pieces together. The crimping technique is time consuming and labor intensive.
U.S. Pat. No. 4,902,245 discusses staking. The staking process includes the steps of placing holes in the conductor and in the termination device. The holes of the two parts are then aligned so as to be coaxial. A copper insert is then placed in the coaxially aligned holes. The ends of the inserts are then upset so as to form heads being larger than the holes so as to secure the two parts together. This technique is also time consuming and labor intensive.
U.S. Pat. No. 4,705,481 discusses cutting by way of an insulation displacement contact. The patent discloses an IDC for connecting to a flat conductor of a flat cable, where the conductors are sheathed in a polymer film. The IDC includes a square piece of material having each of its four corners bent upwards so as to provide four sharp contact points. The four sharp contact points penetrate the polymer layer and make contact with the conductor. The construction and geometry of the IDC is complex and costly.
Furthermore, techniques of welding contacts or termination devices to conductors of cables are known in the art. Numerous steps are required to perform the welding process. To prepare the weld surface, the insulation must be removed from the conductor. The surface of the conductor must be cleaned and prepared for welding. The termination device is likewise cleaned and prepared for welding. Then the termination device is welded to the conductor of the cable. Such preparation and assembly of parts is time consuming and labor intensive and, hence, is costly. Additionally, when conductors of the cable are placed close together, the welding process becomes even more difficult.
FIGS. 1-5 disclose related art cables and termination devices. FIG. 1 is a perspective view showing a flat cable 10 having flat conductors 12, where the flat conductors 12 are covered with an insulating layer or sheath 14. FIG. 2 is an end view of the flat cable 10 showing ends of the flat conductors 12 covered by the insulating layer 14. FIG. 2 further shows the width X of one of the flat conductors 12. The width X is typical of all of the flat conductors 12 shown in FIG. 2.
FIG. 3 is a front view of a typical insulation displacement contact 16.
FIG. 4 is a front view of the IDC of FIG. 3 connected around the conductor 12 and insulation sheath 14. A problem develops in that the conductor does not make adequate electrical connection with the conductor, since the flat conductor 12 buckles, as shown in FIG. 4. The electrical connection between the IDC 16 and the flat conductor 12 would be enhanced if the flat conductor 12 were in a flat, i.e., non-buckled, orientation.
The IDC 16 of FIG. 3 fails for another reason, especially with use of insulation sheathing material 14 made of MYLAR type polyester film. FIG. 5 identifies that, even if the conductor 12 is flat, the insulating layer 14 is not cleanly removed from the side of the conductor 12. Through experimentation, Applicants have found that the insulating layer 14 rides up and is squeezed or wedged between the IDC 16 and the flat conductor 12. Thus, the electrical connection between the flat conductor 12 and the IDC 16 is impaired and is not adequate.
Thus, there is a need for an inexpensive, reliable, small, and easy to assemble termination device for flat conductors of a flat cable.
Furthermore, there is a need for an IDC that provides a clean, intimate contacting surface between the conductor and the IDC. Additionally, there is a need for an IDC which prevents the flat conductor from buckling and which prevents the insulating layer from being wedged between the IDC and the flat conductor of the flat cable.