The present invention relates to a method for the production of a device for transmitting a signal between two end points at least one of which is movable relative to the other and between which a wound line which forms a coil and is contained in a substantially circular cassette is arranged. Further extending lines being connected to the line at the two end points, the cassette consisting of two parts, namely a stator and a rotor which rotates around its axis and around the stator (European patent EP-OS 0 417 350).
Such a device is required, for instance, for the transmitting of a signal in order to release the "airbag" of an anti-impact system for motor vehicles. It is arranged in the steering wheel of a vehicle for the transmission of an electrical or optical signal. A "line" within the meaning of the invention can therefore be an electrical line or an optical line. One basic problem with this device is the transmitting of signals between fixed and moving parts of the vehicle. The wiper contacts or wiper rings serving for the transmission of current which have been used for a long time in such cases are subject to wear and are disadvantageous, particularly in the case of low current intensities, due to varying contact resistance.
In the known device in accordance with the aforementioned EP-OS 0 417 350, electric current is used for the transmission of the signal. The current is transmitted over a ribbon cable which is wound into a coil, in the manner, for instance of a spring housing. Upon relative rotation of the two end points which are connected by the ribbon cable, the coiled ribbon cable "breathes" like the spring of a watch. The turns of the wound ribbon cable are contracted in the one direction of rotation to a smaller diameter. In the other direction of rotation, they return to a larger diameter. The ribbon cable can in this way participate in the turning movements of the steering wheel without the signal path being interrupted. For the production of the cassette, the individual parts, particularly its stator and rotor, are placed together. In this connection spring parts and other detent elements engage in recesses in the other part. They assure the holding together of all the parts of the cassette. The spring parts and detent elements are bent upon assembling of the individual parts of the cassette. They slide with a relatively high force of application along surfaces of the other parts. Damage to these surfaces can therefore not be avoided, particularly when tools are used for the assembling. In the case of this cassette, the rotor and stator are furthermore assembled with a relatively large amount of play. Upon the turning of the rotor, therefore, disturbing noises are produced because of the damaged, non-circular surfaces and the play between stator and rotor.