GB1590160A - Electrical cables - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRICAL CABLES (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company of 190 Strand, London W.C.2, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to retractable cables for interconnecting two electrical devices, and especially (but not exclusively) to a retractable cable for connecting a telephone handset to the instrument body.

According to the present invention there is provided a retractable electrical cable arrangement, which includes a cable wound round a cylindrical rotatable member, and a spiral spring coupling the rotatable member to a stationary shaft, the spring being a strip of an electrically insulating material pre-tensioned to render it springy, wherein movement of the cable as it is extended rotates the rotatable member so as to tension the spring, wherein when the cable is released the tensioning of the spring rotates the rotatable member in such direction as to retract the cable, and wherein the strip of electrically insulating material which forms the spring bears printed circuit tracks the outer ends of which are electrically connected to the conductors of the cable.

An embodiment of the invention will now be described with reference to the accompanying drawing, which is an exploded view of a retractable telephone cable arrangement embodying the present invention.

The mechanism described herein includes a drum which carries a retractable telephone cable or cord and a spring which keeps the cable wound up on the drum, the whole being mounted on a stationary shaft. To convey current between the cable and the telephone set, the spring is formed of a specially pre-tensioned strip of an electrically insulating material which has printed circuit tracks on it. Commercially available flexible printed circuit ribbon is used in the arrangement described herein.

This ribbon provides the spring tension needed to keep the cable wound up when the handset is on-hook.

In the exploded diagram is shown a drum formed by two circular plates 1, 2, and an inner wall 3 which is mounted on a hollow shaft 4. This shaft extends through the middle of the drum. Into the top of the hollow shaft fits a cylindrical moulding 5, being the inner end of the printed circuit spring. The spring passes through a slot 6 in the shaft. The spring is pre-tensioned to act as a "pull-in" spring, and its outer end is terminated in a terminal block 8. This block has contact pins which are connected to the wires of the inner end of the telephone cable 9, and fits into a gap 10 in the inner wall 3.

The electrical connecaons from the telephone set pass up the hollow shaft to the moulding 5 and are there connected to elec trically conductive tracks on the printed circuit spring, and therefrom to the inner end of the flexible telephone cable. The outer portion of the cable 9 passes to the outside world, and hence to the handset, via a stationary guide 11 which is mounted on the telephone set's casing.

When the handset is lifted, the cable 9 is pulled out of the drum formed by the plates 1 and 2, which rotates the lower plate 1 with the wall 3. Hence the spring formed by the printed circuit 7 and the tracks thereupon is unwound. On movement of the handset towards the instrument body, either during the call or when the subscriber hangs up, the tension produced in the spring rotates the plate 1 of the drum to pull the cable 9 back into the drum.

Thus it will be seen that the flexible printed circuit acts as the retracting spring for the cable and also provides the electrical connetcion from the cable to the telephone set.

The arrangement described above has a number of advantages as compared with known arrangements. Thus since the spring and the electrical connections are the same item, manufacturing is simplified and is cheaper. As the use of such a springlcon- ductor combination avoids the use of slip rings, there is no chance of electrical noise due to slipring or contact bounce, which is a disadvantage of known devices using slip rings. Finally the arrangement is compact.

WHAT WE CLAIM IS: 1. A retractable electrical cable arrangement, which includes a cable wound round a cylindrical rotatable member, and a spiral spring coupling the rotatable member to a stationary shaft, the spring being a strip of an electrically insulating material pre-tensioned to render it springy, wherein movement of the cable as it is extended rotates the rotatable member so as to tension the spring, wherein when the cable is released the tensioning of the spring rotates the rotatable member in such direction as to retract the cable, and wherein the strip of electrically insulating material which forms the spring bears printed circuit tracks the outer ends of which are electrically connected to the conductors of the cable.

2. A retractable cable arrangement as claimed in claim 1, wherein the shaft about which said rotatable member rotates is a hollow shaft, wherein said shaft has a cylindrical member on it to which the inner end of the flexible printed circuit is anchored, and wherein electrical connections reach said inner end via the hollow shaft.

3. A retractable cable arrangement as claimed in claim 2, wherein said flexible printed circuit has a terminal block on its outer end the terminals of which are connected to the wires of the cable, and wherein the cylindrical member has a gap in its circumference in which said terminal block fits.

4. A retractable cable arrangement for the cable between a telephone instrument's handset and its base unit, substantially as described with reference to the drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. due to slipring or contact bounce, which is a disadvantage of known devices using slip rings. Finally the arrangement is compact. WHAT WE CLAIM IS:

1. A retractable electrical cable arrangement, which includes a cable wound round a cylindrical rotatable member, and a spiral spring coupling the rotatable member to a stationary shaft, the spring being a strip of an electrically insulating material pre-tensioned to render it springy, wherein movement of the cable as it is extended rotates the rotatable member so as to tension the spring, wherein when the cable is released the tensioning of the spring rotates the rotatable member in such direction as to retract the cable, and wherein the strip of electrically insulating material which forms the spring bears printed circuit tracks the outer ends of which are electrically connected to the conductors of the cable.

2. A retractable cable arrangement as claimed in claim 1, wherein the shaft about which said rotatable member rotates is a hollow shaft, wherein said shaft has a cylindrical member on it to which the inner end of the flexible printed circuit is anchored, and wherein electrical connections reach said inner end via the hollow shaft.

3. A retractable cable arrangement as claimed in claim 2, wherein said flexible printed circuit has a terminal block on its outer end the terminals of which are connected to the wires of the cable, and wherein the cylindrical member has a gap in its circumference in which said terminal block fits.

4. A retractable cable arrangement for the cable between a telephone instrument's handset and its base unit, substantially as described with reference to the drawing.