Abstract:
A magnetic-tape-cassette apparatus includes a tape-loading device having supports (17, 18) which are longitudinally movable on guide members (19, 20) and are caused to perform oppositely directed synchronous movements by means of two traction-means drives (29 to 34) for the purpose of threading a magnetic tape (4). The two traction-means drives (29 to 34) are mechanically coupled by a third traction-means drive (35). Toothed belts (31, 34, 35) used as traction means are driven by a torque generated by an electric motor (36).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a tape-guide device for a magnetic-tape-cassette apparatus having a drum-shaped scanning device comprising a rotary magnetic head, first and second elongate guide members, and a tape-loading device comprising two supports having tape-guide elements engageable behind a magnetic tape accommodated in a magnetic-tape cassette, said supports being longitudinally moveable on said guide members to extract the tape from the magnetic-tape cassette and wrap it at least partly around the drum-shaped scanning device. 
     Such a tape-guide device is known from DE 37 29 661 A1. Supports carrying tape-guide elements are guided by two guide members arranged to the left and the right of a scanning device, two flexible metal bands of rectangular cross-section being in sliding engagement at the inner and the outer radius of each guide member. Supports secured to ends of the metal bands can be moved along the guide path of the guide member by winding or unwinding the metal bands. 
     Moreover, EP 0.024,361 B1 discloses a tape-guide device comprising a wire-drive device for moving two tape-guide supports, which wire-drive device comprises a rotatable wire drum and two wires which each act on one of the two tape-guide supports substantially in the direction of movement of the support from a rest position to an operating position. The wires are guided by a plurality of wire drums and are passed through two trough-shaped guide members. 
     In addition, DE 30 25 465 C2 discloses a magnetic-tape extraction device for a cassette recorder, in which the guides comprise at least one guide slot having an arcuate shape and extending from one side of the drum-shaped scanning device to the opposite side of the drum-shaped scanning device via the cassette holder section. The tape draw-in device is connected to a strip-shaped guide member, the strip-shaped guide member having an elongate continuously arcuate shape corresponding to the arcuate shape of the guide slot and engages the guide slot so as to be longitudinally movable therein. The strip-shaped guide member is deformable to adapt to the shape of the guide slot. The strip-shaped guide member is driven by a driving device. 
     The known devices have the drawback that the relevant loading mechanisms require the use of a large number of complicated parts, some of which can be manufactured only by intricate production methods. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a tape-guide device of the type mentioned in the opening sentence, whose loading mechanism is of simple construction and which guides the magnetic tape exactly. 
     This object is achieved in that a magnetic tape apparatus of the type described in the opening paragraph is characterized by a first traction drive means with positive transmission, said first drive means comprising a first driving wheel and a first driven wheel arranged at ends of the first guide member and a first traction means which extends between the first driving wheel and the first driven wheel and is positively coupled to one of the longitudinally movable supports, a second traction drive means with positive transmission, said second drive means comprising a second driving wheel and a second driven wheel arranged at ends of the second guide member and a second traction means which extends between the second driving wheel and the second driven wheel and is positively coupled to the other one of the two longitudinally movable supports, and a third traction drive means with positive transmission, in which a third traction means drives a driving wheel one of the first and second traction drive means, and a motor for transmitting a torque to one of the driving wheels. 
     The tape-guide device in accordance with the invention has the advantage that the supports which are longitudinally movable on two guide members perform oppositely directed synchronous movement during threading of the magnetic tape owing to the use of three mechanically coupled traction-means drives with positive transmission, for example three toothed-chain drives, driven by a single motor. A further advantage is that this type of threading mechanism does not require much space. 
     Advantageous modifications and improvements of the tape-guide device claimed in Claim 1 can be realised by means of the steps defined in the subsidiary Claims. A particularly advantageous feature is that the position of the longitudinally movable support on the relevant guide member can be determined by a potentiometer driven by the threading mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     An embodiment of the invention will now be described in more detail, by way of example, with reference to the accompanying drawing. The drawing shows a diagrammatic plan view of a magnetic-tape threading mechanism with the parts which are relevant to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the drawing the reference numeral 1 denotes a drum-shaped scanning device comprising a rotary head disc carrying magnetic heads 2&#39;, 2&#34; at its periphery. The head disc rotates in the direction indicated by an arrow 3. A magnetic tape 4 is partly wrapped around the drum-shaped scanning device 1. The magnetic tape 4 is accommodated in a magnetic-tape cassette 5 comprising a supply reel 6 and a take-up reel 7. Tape-guide elements 9, 10, 11 or 12, 13, 14 engage behind the magnetic tape 4 at the location of the cassette mouth 8. The tape-guide elements 9, 10, 11, which are constituted by rollers and/or pins, are arranged on a pivotable roller plate 15. The tape-guide elements 12, 13, 14, which are also constituted by rollers and/or pins, are arranged on a pivotable roller plate 16. Each of the roller plates 15, 16 is carried by a slide-type support 17 or 18 which is slidable on a rail-like guide member 19 or 20. 
     During threading-in the magnetic tape 4, behind which the tape-guide elements 9 to 14 engage, is extracted from the magnetic-tape cassette 5 and is led in the directions indicated by the arrows 21 and 22. Concurrently with this operation tape-traction levers 23 and 24 pass the magnetic tape 4 around stationary rollers 25, 26 and 27 arranged in the tape-guide path. The transport speed of the tape is determined in a manner known per se by a capstan 28 which is in contact with the magnetic tape 4. 
     At each of its ends the rail-like guide member 19 carries a chain wheel 30 or 29 to function as a driving wheel and a driven wheel respectively, between which wheels a first drive chain 31 extends. The drive chain 31 can be, for example, a toothed belt. The driven wheel guiding the drive chain 31 can be formed by a guide roller or guide wheel instead of by the chain wheel 29. The guide member 19 is positively coupled to the left-hand part of the first drive chain 31. 
     A second toothed-chain drive similar to the first toothed-chain drive is arranged to the right of the drum-shaped scanning device 1 and comprises two chain wheels 33 and 32 arranged at the ends of the guide member 20 as a driving wheel and a driven wheel respectively. A second drive chain 34 extends between the two chain wheels 32 and 33 and at its left it is also positively coupled to the slide-type support 18. Again the drive chain 34 can be a toothed belt and the driven wheel can be formed by a guide roller or guide wheel instead of by the chain wheel 32. 
     The two toothed-chain drives 29 to 34 are driven by a third toothed-chain drive coupled to the chain wheels 30 and 33 by a third drive chain. Obviously, it is possible to provide third chain wheels for the third drive chain, which wheels are locked in rotation to the chain wheels 30 and 33. The drive chains 31, 34 and 35 can be made of a plastic material, for example rubber. 
     The three toothed-chain drives are driven by an electric motor 36 whose drive shaft is locked in rotation to a worm 37. The worm 37 meshes with a worm wheel 38 which, together with the chain wheel 30, is locked in rotation to a spindle 39. The wiper of a potentiometer 40 is coupled to the spindle 39, enabling the instantaneous positions of the supports 17 and 18 on the rail-like guide members 19 and 20 to be derived from the wiper position of the potentiometer 40. 
     During threading-in, as already stated, the tape-guide elements 9 to 14 engage behind the magnetic tape 4 and the supports 17 and 18 are moved into an end position 41 in the directions indicated by the arrows 21 and 22. The magnetic tape 4 is then wrapped around the drum-shaped scanning device 1 along a helical path. During the threading movement of the tape the roller plates 15 and 16 are pivoted by cam-surface control. In the end position 41 the roller plates 15 and 16 abut against a stop (not shown). 
     The present arrangement of interlocked toothed-chain drives enables an oppositely directed synchronous movement of the first toothed-chain drive relative to the second toothed-chain drive to be obtained by means of a small number of cheap standard elements. The precisely operating tape-loading device can be arranged around the scanning device 1 in a space-saving manner. Since the positions of the movable tape-guide elements 9 to 14 at any point along the tape-threading path can be derived from the wiper position of the potentiometer 40 the electric motor 36 can be controlled exactly by means of a control device during threading-in and threading-out. This also applied in the case of initialisation of such a control device after a fault condition, for example a power failure.