GB1603029A - Recording and/or playback apparatus - Google Patents

Description

(54) RECORDING AND/OR PLAYBACK APPARATUS (71) We, N. V. PHILIPS' GLOEILAMPEN FABRIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands, 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:- The invention relates to a recording and/or playback apparatus having at least one rotatable device for carrying a record carrier and a braking device which serves to brake the carrying device and which comprises a braking disc which is coaxial with and is rigidly connected to the carrying device, and a brake band which can be brought into operative contact with the circumferential surface of the braking disc. Such apparatus is known from, for example, German patent specification no. 1090444.

A requirement imposed on such apparatus is that when the carrying device is braked the braking device ensures that the record carrier comes to an immediate halt, so that, for example, in the case of a record carrier in the form of a tape, no undesired loops can be formed in the record carrier. It is well known that during subsequent transport of the record carrier or a subsequent recording and/or playback operation, such loops may result in faulty operation and may even lead to the record carrier being damaged. Therefore, it must be ensured that during a braking operation there is no slip between the braking disc and the brake band which acts on the circumferential surface of said disc. One way of achieving this is to apply the brake band to the circumferential surface of the braking disc with greater force; but this leads to undesirably high mechanical loads. Slip can also be prevented by the use of special materials with high coefficients of friction for the braking disc and the brake band respectively. However, such materials are expensive, which may also be a disadvantage.

According to the present invention there is provided a recording and/or playback apparatus having at least one rotatable device for carrying a record carrier and a braking device which serves to brake the carrying device and which comprises a braking disc which is coaxial with and is rigidly connected to the carrying device, and a brake band which can be brought into operative contact with the circumferential surface of the braking disc, wherein the braking disc has the form of a right prismatic body whose ends are each defined by a polygon and whose edges which extend between the ends are disposed on an imaginary right circular cylindrical surface which is coaxial with the braking disc.

Surprisingly, it has been found that a braking disc of this form, even when the brake band exerts only a small force on the circumferential surface of the braking disc and without special friction conditions being created between the brake band and the circumferential surface of the braking disc, the braking disc and thus the device for carrying the record carrier are always braked reliably and immediately, without the occurrence of slip between the brake band and the braking disc. This is specifically based on the fact that the brake band directly engages around at least one of the axially extending edges of the right prismatic body and thus holds the braking disc immediately. In this way it is ensured that a braking operation is effected quickly and reliably with particularly simple and cheap means.

With the construction in accordance with the invention the travel of the brake band from the lifted, disengaged position to the braking position in which it engages with the braking disc is essentially determined by the difference between the circumference of the imaginary circular cylindrical surface on which the axially extending edges of the right prismatic body are disposed and the circumference of the prismatic body constituting the braking disc. Therefore, in order to obtain a rapid actuation of the brake, it is particularly advantageous if the number of edges of the right prismatic body which are disposed on the imaginary circular cylindrical surface is at least five. In this respect it is furthermore advantageous for larger braking discs if the circumference of the imaginary circular symmetrical surface is greater than five centimetres and the quotient of this circumference expressed in centimetres and the number of said edges of the right prismatic body is approximately unity. Thus it is ensured that the difference between the said two circumferences is optimal for a minimal travel of the brake band, so that large movements and expensive constructions necessary for these movements are avoided.

Preferably. the edges of the right prismatic body are rounded, as this results in minimal mechanical loading of the brake band, which is favourable for a long life of the band.

Hereinafter an embodiment of the invention is described in more detail with reference to the accompanying drawings, in which Fig. 1 is a sectional elevation of the part of a recording and/or playback apparatus for use with a tape-like record carrier which is relevant to the invention, the section being taken on the line I-I in Fig. 2, which is is a sectional plan view taken on the line Il-Il in Fig. 1.

Fig. 1 shows a deck plate 1 of a recording and/or playback apparatus for use with a record carrier in the form of a tape. Two spindles 4 and 5 of two winding devices 6 and 7, which serve as devices for carrying the record carrier, are rotatably journalled in the deck plate I by means of two bearing bushes 2 and 3. The two winding devices 6 and 7 each serve for driving a reel of the tape-like record carrier.

The winding device 6 comprises a first disc 8 which is rigidly connected to the spindle 4, and a second disc 11 which is freely rotatable around the spindle 4 and which has a friction lining 9 which is urged against the first disc 8 under the influence of a helical coil spring 10 which is compressed between the disc 11 and the bearing bush 2. The two discs 8 and 11 and the friction lining 9 constitute a slip coupling, of which the disc 11 can be driven by a drive wheel 12 which is itself driven in a known manner not shown. The disc 8 can also be driven directly by a further drive wheel 13 with the slip coupling disengaged.

A braking disc 14 is rigidly mounted on the spindle 4, to which disc the driving force acting on the disc 8 is transmitted. The braking disc 14 is provided on its upper side with a cylindrical reduced portion 15, which in its upper face 16 has a central axial bore 17 into which open three radially extending slots 18 spaced at regular angular distances around the wall of the bore. A winding hub 19 which is slid onto the spindle 4 comprises three projections 20 which correspond to the slots 18 and which engage in the slots 18 to establish a driving connection between the braking disc 14 and the winding hub 19. The winding hub 19 is held against a retaining ring 23 on the free end 22 of the spindle 4 by a compression spring 21 which is lodged in the bore 17.

Similarly, the winding device 7 comprises a disc 24 which is rigidly connected to the spindle and which can be driven directly by a drive wheel 25 which is driven in a known manner not shown. Furthermore, the spindle 5 carries a braking disc 26 with a cylindrical reduced portion 27 which in its upper side 28 has a central axial bore 29 into which open three radially extending slots 30 which are disposed at regular angular distances around the wall of the bore. The slots 30 also are adapted to be engaged by projections 32 formed on a winding hub 31 whih is slid onto the spindle 5. The winding hub 31 also is held against a retaining ring 35 on the free end 34 of the spindle 5 by a compression spring 33.

Fig. 1 shows a recording tape 38 wound in two reels 36 and 37 on flanged tape spools 39 and 40 respectively which can be fitted on the winding hubs 19 and 31 respectively in known manner to be driven thereby for transporting the recording tape from one spool to the other. For the sake of simplicity the spools 39 and 40 are shown removed from the winding hubs 19 and 31 respectively. Obviously, the reels of tape may also be accommodated in a cassette. To bring the tape spools into operative engagement with the winding hubs 19 and 31 the spools 39 and 40 are slid onto the winding hubs until the spools rest with their flanges on the upper sides 16 and 28 of the cylindrical portions 15 and 27 respectively of the braking discs 14 and 26 respectively.

During transport of the recording tape 38 at normal speed the tape is driven in known manner by drive elements not shown, the tape being transferred from the spool 40 to the spool 39, and a recording and/or playback operation can be performed with scanning elements, not shown, which co-operate with the tape. In this case the winding hub 19 which drives the spool 39 is driven by the drive wheel 12 via the slip coupling 11, 9, 8. If the recording tape 38 is to be transported between the two spools 39 and 40 at a speed which is higher than the normal speed, the tape is driven via the winding hub 6 or 7 respectively, the respective winding hub then being driven by the associated drive wheel 13 or 25, depending on the desired direction of transport of the recording tape.

When the tape transport is stopped after a recording and/or playback operation or after a rewinding operation, the winding hubs 19 and 31 must be braked. For this purpose each winding device 6 and 7 is provided with a braking device 41 and 42 respectively. The braking devices 41 and 42 each comprise the previously mentioned braking disc 14 and 26 respectively and a common brake band 45 which can be brought into operative contact with the circumferential surfaces 43 and 44 of the braking discs 14 and 26 respectively.

At its ends, which are each formed with a loop 46 and 47 respectively, the brake band is connected to pins 48 and 49 respectively, which are stationarily mounted in the apparatus, as is shown in Fig. 2. In the middle the brake band 45 passes around a pin 50 on a slide 51 which is guided in its longitudinal direction by means of two pin-and-slot combinations 54 and 53 and which is subjected to the action of a tension spring 54. The slide 51 carries a fork 55, with which a pivotable armature 56 of an electromagnet 57 engages, which armature acts as an actuating lever.

Fig. 2 shows the situation in which the braking devices are operative, in which situation the brake band 45 is held against the circumferential surfaces 43 and 44 of the braking discs 14 and 26 by the spring 54. The electromagnet 57 is then not energized, so that the armature 56 is released and under the influence of the tension spring 54 the slide 51 has moved as far as the brake band 45 allows. Thus, the braking force which the brake band exerts on the braking discs is determined by the tension spring 54. To allow transport of the recording tape 38, i.e.

to enable the winding hubs 19 and 31 to be rotated, the brake band 45 must be lifted off the braking discs 14 and 26. For this purpose, in a manner not shown, for example upon actuation of a switching device for switchingon a specific mode of operation of the apparatus, the electromagnet 57 is energized, so that its armature 56, through the fork 55, moves the slide 51 against the action of the spring 54 sufficiently for the brake band 45, which passes around the pin 50 on the slide, to release the braking discs 14 and 26 so that these discs are free to rotate. For subsequent braking of the winding hubs again the electromagnet 57 is de-energized, whereupon the brake band 45 is again applied to the braking discs 14 and 26 by the tension spring 54.

When the winding hubs are braked it is important, as is known, that they are stopped immediately so that no undesired loops can be formed in the recording tape. Therefore, care must be taken that no slip can occur between the brake band and the braking discs. In order to ensure this, each braking disc 14 and 26 in the present apparatus has the form of a right prismatic body whose ends (the lower ends are designated 58 and 59 respectively in Fig. 1) are each defined by a polygon and those edges 60 and 61 respectively which extend between the ends are disposed on an imaginary right circular cylindrical surface which is coaxial with the axis 4 and 5 of the braking disc 14 and 26 respectively. In the present example a regular pentagon has been chosen as the polygon.

Obviously, it is also possible to select a polygon with a different number of vertices, for example, a hexagon or an octagon. The number of vertices chosen will depend inter alia on the size of the braking disc. At any rate the number of vertices must be selected to ensure that in any position of the braking disc the brake band can directly engage around at least one of the axially extending edges 60 or 61 of the prismatic body.

Surprisingly, it has been found that when braking discs of such a form are used, no slip occurs between the brake band and the braking discs when the braking operation is performed. Thus, it is achieved that without a high actuating force for the brake band, which would result in unfavourably high mechanical loads, and without the use of special materials with high coefficients of friction for the brake band and the braking discs, which would lead to a substantial increase in costs, the winding devices ae always braked reliably and faultlessly, so that these devices come to an immediate halt.

Thus, no loops are formed in the recording tape, so that faulty operation during subsequent transport of the tape and damage to the tape are avoided.

As can be seen in Fig. 2, the travel to be obtained by the movement of the armature 56 of the electromagnet 57 for releasing the brakes, i.e., the travel of the brake band from the position in which it is applied to the braking discs and holds these discs stationary to the position in which it is lifted clear of the braking discs so that they are free to rotate, depends on the difference between the circumference of the imaginary circular cylindrical surface which circumscribes the edges 60 and 61 respectively of each braking disc 14 and 26, and the circumference of each prismatic body constituting the braking disc 14 and 26 respectively. Experiments have shown that in this respect it is advantageous if the number of edges 60 or 61 of each prismatic body which are disposed on the respective imaginary circular cylindrical surface is at least five. Furthermore, it has been found to be advantageous in this respect if for a circumference of the imaginary circular cylindrical surface of more than five centimetres, the quotient of this circumference expressed in centimetres and the number of axially extending edges 60 or 61 of the right prismatic body is substantially unity. From the drawings, which are drawn to a scale of approx. 2:1, it can be seen that this requirement is met in the present example, because the relevant circumference at full size is approx. 5 cm and the number of axially extending edges of each braking disc is also five. When the afore-mentioned dimensional limits for the braking discs are adhered to, rapid and reliable braking is guaranteed at minimum travel of the brake band. The lastmentioned point is of advantage in the present apparatus, in which the travel of the brake band is obtained by an electromagnet, because this travel obviously determines the dimensions of this magnet and the dimensions of this magnet can be reduced as the travel of the brake band decreases.

In order to ensure minimum mechanical wear of the brake band, the axially extending edges 60 and 61 respectively of the right prismatic body constituting each braking disc 14 and 26 are rounded, as can be seen in Fig. 2. As a result of this, excessive mechanical loading of the braking band by the edges of the braking discs is avoided, which is favourable for a long life of the band.

As is apparent from the foregoing, the construction of the braking discs in accordance with the invention always ensures reliable and immmediate braking of the winding devices of a recording and/or playback apparatus in a particularly simple and cheap manner and in such a way that the formation of loops in the record carrier and consequent faulty operation of the apparatus are avoided. Obviously, such braking devices may also be employed in recording and/or playback apparatus having other types of devices for carrying a record carrier, such as, for example, a turntable for carrying a discshaped record carrier.

WHAT WE CLAIM IS: 1. A recording and/or playback apparatus having at least one rotatable device for carrying a record carrier and a braking device which serves to brake the carrying device and which comprises a braking disc which is coaxial with and is rigidly connected to the carrying device, and a brake band which can be brought into operative contact with the circumferential surface of the braking disc, wherein the braking disc has the form of a right prismatic body whose ends are each defined by a polygon and whose edges which extend between the ends are disposed on an imaginary right circular cylindrical surface which is coaxial with the braking disc.

2. An apparatus as claimed in Claim 1, wherein the number of edges of the right prismatic body which are disposed on the imaginary circular cylindrical surface is at least five.

3. An apparatus as claimed in Claim 2, wherein the circumference of the imaginary circular cylindrical surface is greater than five centimetres and the quotient of this circumference expressed in centimetres and the number of said edges of the right prismatic body is approximately unity.

4. An apparatus as claimed in any of the preceding Claims, wherein said edges of the right prismatic body are rounded.

5. A recording and/or playback apparatus substantially as herein described with reference to the accompanying drawings.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. present apparatus, in which the travel of the brake band is obtained by an electromagnet, because this travel obviously determines the dimensions of this magnet and the dimensions of this magnet can be reduced as the travel of the brake band decreases. In order to ensure minimum mechanical wear of the brake band, the axially extending edges 60 and 61 respectively of the right prismatic body constituting each braking disc 14 and 26 are rounded, as can be seen in Fig. 2. As a result of this, excessive mechanical loading of the braking band by the edges of the braking discs is avoided, which is favourable for a long life of the band. As is apparent from the foregoing, the construction of the braking discs in accordance with the invention always ensures reliable and immmediate braking of the winding devices of a recording and/or playback apparatus in a particularly simple and cheap manner and in such a way that the formation of loops in the record carrier and consequent faulty operation of the apparatus are avoided. Obviously, such braking devices may also be employed in recording and/or playback apparatus having other types of devices for carrying a record carrier, such as, for example, a turntable for carrying a discshaped record carrier. WHAT WE CLAIM IS:

1. A recording and/or playback apparatus having at least one rotatable device for carrying a record carrier and a braking device which serves to brake the carrying device and which comprises a braking disc which is coaxial with and is rigidly connected to the carrying device, and a brake band which can be brought into operative contact with the circumferential surface of the braking disc, wherein the braking disc has the form of a right prismatic body whose ends are each defined by a polygon and whose edges which extend between the ends are disposed on an imaginary right circular cylindrical surface which is coaxial with the braking disc.

2. An apparatus as claimed in Claim 1, wherein the number of edges of the right prismatic body which are disposed on the imaginary circular cylindrical surface is at least five.

3. An apparatus as claimed in Claim 2, wherein the circumference of the imaginary circular cylindrical surface is greater than five centimetres and the quotient of this circumference expressed in centimetres and the number of said edges of the right prismatic body is approximately unity.

4. An apparatus as claimed in any of the preceding Claims, wherein said edges of the right prismatic body are rounded.

5. A recording and/or playback apparatus substantially as herein described with reference to the accompanying drawings.