Electricity: motive power systems – With particular motor-driven load device – Tension-maintaining type of motor-control system
Patent
1995-10-27
1997-11-25
Ip, Paul
Electricity: motive power systems
With particular motor-driven load device
Tension-maintaining type of motor-control system
318 7, 360 69, 360 70, 360 7305, G11B 1564, G11B 1518, G11B 15473
Patent
active
056916108
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
For shortening the access time of information stored on recording media in tape form, recording and/or playback devices operating by the helical-scan process, such as for example commercially available video recorders, are known, in which the recording medium stored in a cassette on drivable winding elements remains threaded even during winding operation and thereby wraps around the head drum as in the recorder operating modes of "play" and "search". Such recorders are also referred to as full-loading recorders, as distinct from so-called half-loading and non-loading recorders, in which the recording medium is not in engagement with the head drum during winding operation. In the case of a half-loading recorder, the recording medium is partly unthreaded from the cassette and in the case of a non-loading recorder it is drawn fully into the cassette during winding operation. The head drum comprises a stationary lower part, also referred to as the lower head drum, and a rotatable upper part, which is arranged coaxially with respect to the said lower part, has recording and/or playback heads and is also referred to as the upper head drum.
Because the tape remains threaded during winding operation and because of the resulting sliding friction between the recording medium and the head drum, full-loading recorders suffer, however, from a problem of increased wearing of the head drum and the recording medium. The "backward" winding operation, also referred to as rewind, is the critical case here, since the recording medium and the head drum have opposed driving directions, which can result in a disturbance of the air cushion essentially determining the sliding friction between the recording medium and the head drum, and consequently in an increase in the sliding friction, in particular towards the end of the winding time. Particularly susceptible to this are relatively smooth head drum outer surfaces and cassettes with a recording medium of relatively thin material, such as for example a VHS tape cassette of the E 300 type with an average thickness of the recording medium of 12.5 .mu.m.
To prevent the increase in sliding friction, the solutions listed below are known: half-loading recorders, driving speed of the recording medium as a function of an increase in current of the head-drum drive motor, spirals and/or additional grooves and/or a circumferential bevel at the end neighbouring the lower head drum, head drum by the recording medium.
However, these solutions have the following disadvantages: at lower winding speed according to a), the winding time is greater. The closed-loop control of the winding speed as a function of the head-drum motor current according to b) requires more complex software for the drive mechanism, usually controlled by means of a microprocessor. In a case of machining the head-drum outer surface according to solution c), the production of the head drum becomes more expensive. The idling operation of the head drum according to d) makes it more difficult for the head drum or the head drum drive to run up to speed when switching over, since the upper head drum, because it is turning in the wrong direction of rotation, first has to be stopped and then accelerated to nominal speed against the recording medium held taut by the unwinding hub.
In order not to increase the wearing of the recording medium and the head drum in comparison with non-loading and half-loading recorders, but on the other hand to cater for the requirement for relatively short winding times, present-day full-loading recorders preferably have a specific machining profile of the upper head drum and a powerful head-drum drive and a powerful hub drive. In addition, closed-loop control of the rewinding speed of the recording carrier as a function of the head-drum motor current is provided.
SUMMARY OF THE INVENTION
It is the object of the invention to reduce the complexity caused by the winding operation in a full-loading recorder.
The invention is based on the idea of increasing the speed of rotation of the head d
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Davenport Francis A.
Deutsche Thomson-Brandt GmbH
Ip Paul
Tripoli Joseph S.
Wein Frederick A.
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