DEVICE FOR GUIDING AN INFORMATION CARRIER IN TAPE FORM

Abstract: Device for guiding an information carrier (1,24) which is in tape form and moves between two reels (21,22). The device is situated in the path of transport between the two reels and embodied as a guide member (2,25) along which the tape is moved with a certain tape tension. The guide member is a non-rotatable sliding member adapted to oscillate in a direction at right angles to the local direction of movement of the tape, with a maximum acceleration which is at least a few times greater than the transverse component of the tape tension divided by the mass of that part of the tape which is affected by the sliding member.

Description: The invention relates to a device for guiding an information carrier which is in tape form and moves be­ tween two reels, this device being situated in the path of transport between the two reels and being in the form of a guide member along which the tape is moved with a certain tape tension. A device of this kind is described in Dutch Pat­ ent Application No. 7907293 as a component of a cassette for a recording carrier in tape form. In this known de­ vice the guide member consists of a cylindrical body which on the one hand is disposed in a fixed position in relation to the cassette, but in the other hand is ro­ tatable about a shaft fastened to the body of the cas­ sette. During the transport of the optical tape from one reel to the other the tape runs over this rotatable cylindrical body and is at the same time positioned in relation to an optical read/write head, so that by way of a window in the side wall of the cassette light can fall onto that part of the recording carrier tape which at that moment is supported by the cylindrical guide body. Although the use of a rotatable guide member has the effect that friction between that member is very slight or completely absent, the use of a rotatable mem­ ber mounted on a separate shaft, which in turn has to be fastened to the front or rear wall of the cassette, is a serious disadvantage in respect of cost. In devices of this kind it is generally attempted to use the smallest possible number of moving parts, and in particular as small as possible a number of moving parts which have to be accurately and effectively mounted if the rotation is to take place with the least possible hindrance. The invention now seeks to eliminste these disad­ vantages, or at least to reduce them considerably, and to simplify still further the construction of a device of this kind. In a device of the type first defined above this aim is achieved in that the guide member is a non-rotat­ able sliding member adapted to oscillate in a direction at right angles to the local direction of movement of the tape, with a maximum acceleration which is at least a few times greater than the transverse component of the tape tension divided by the mass of that part of the tape which is affected by the sliding member. A possible explanation is given below of the re­ duction of sliding resistance observed. Through the os­ cillatory movement of the sliding member in the afore­ said direction at right angles to the local direction of tape movement the tape is alternately pushed by the sliding mnember a short distance in one direction against the transverse component of the tape tension, and because of the rapid reverse oscillation of the guide member is then so-to-speak released, and during a certain period can in a manner of speaking be trans­ ported free from the slidingmember until the tape, pulled as the result of the transverse component of the tape tension in the direction of the sliding mem­ ber, is once again fully pressed against the sliding member. Thereupon the sliding member again pushes fully against the tape in the next part of the oscilla­ tion, and so on. On each occasion the sliding body therefore exerts its full force on the tape only brief­ ly, so that the friction between the tape and the slid­ ing member is substantially restricted to these short periods. Viewed in time, practically frictionless guidance of the tape is thus achieved. It is preferable for the abovementioned number of times by which the maximum acceleration is greater than the transverse component of the tape tension, divided by the aforesaid mass, to be greater than five, and in par­ ticular greater than ten. Because of this relatively great difference between the maximum acceleration and the transverse component of the tape tension, contact between the guide member and the tape, whereby some force is mutually exerted, is greatly reduced. It is preferable for the mass of the guide member and the maximum acceleration and frequency of the oscil­ latory movement to be so selected that the maximum de­ flection of the sliding member between the two end posi­ tions of the oscillatory movement will be smaller than 5 µm and preferably smaller than 1 µm. Therewith the defined speed at which the tape is usually trans­ ported along a predetermined position, for example the place where the information is written on or read from the tape, is not affected, or certainly not affected to any significant extent by the movement of the guide mem­ ber. In the abovementioned Dutch Patent Application No. 7907293 the guide member, as already stated, is situated directly in front of a window for the passage of light from the optical read/write head. If the guide device according to the invention is placed in a posi­ tion which corresponds approximately to that of the cyl­ indrical member in the known device, then during trans­ port from one reel via the guide member to the other reel the tape will nevertheless, despite the oscillatory movement of the guide member, come each time into con­ tact with the guide member, even if only very briefly, and thus be subjected to some friction and wear against the guide member. In order further to reduce any fric­ tion between the tape and the guide member, it is pre­ ferable for the position where the tape passes the guide body to lie, at least approximately, at the point of in­ tersection of the two imaginary lines which are tangent to the core of the one reel and to the outermost turn of the other reel, which is fully wound. Since this point of intersection of the two imaginary lines will change position only very slightly during the complete winding of the tape from one reel to the other, it is thus en­ sured that the tape will be pushed in the direction of the guide member only by a very slight, and usually neg­ ligible transverse tape tension component. The fric­ tion and hence the wear between the tape and the guide member is therefore greatly reduced. In view of the fact that for reasons of manufac­ ture the guide member must have certain minimum dimen­ sions, it is preferable for the shape of the guide mem­ ber to be so selected that that portion of the guide surface which can come into contact with the tape is re­ duced to a relatively shall area. It is therefore pre­ ferable for the sliding member to be provided with a relatively shall central area, viewed in the direction of movement of the tape, at right angles to the direc­ tion of the oscillatory movement, together with adjoin­ ing side surfaces which extend at right sngles to the tape movement plane and are at such an angle to said cen­ tral area that the information carrier tape does not make contact with these surfaces or extends approximately parallel thereto. In a particularly simple form of construction of the apparatus the sliding member consists of a piezo­ electric member of such shape and construction that when a predetermined voltage is applied the sliding member will make the desired oscillatory movement. Through precise selection of the shape, the frequency and the amplitude of this predetermined voltage, the movement of the sliding member can be controlled as desired. In another embodiment the sliding member is at least partly made of magnetizable material, and the de­ vice is provided with an electromagnetic or magnetic field generator by which the sliding member can be set in vibration. The embodiments discusssed so far are mainly in­ tended solely for achieving a smooth and uniform tape transport movement along the guide member. However, the device according to the invention may also be used for stopping the movement of the tape temporarily during a shorter or longer period, for example in order to read or write a determined piece of information on the tape. A device according to the invention which is provided with this facility is characterized in that on the other side of the tape stop means are provided, and that the aforesaid field generator or the piezoelectric member can be so controlled that the sliding member can be stopped in a position in which the sliding member is held against said stop means, with the tape clamped therebetween. Al­ though separate means, for example in the form of project­ ing wall parts or separate members can be used as stop means, it is preferable, particularly when an electromag­ netic or magnetic field generator is used, for the field generator to be provided with pole shoes which extend, on one side of the information carrier tape, in the direction of the sliding member which is situated on the other side of the information carrier tape, while between these pole shoes a window is provided through which the information carrier tape can be read or written, and which can serve as stop means. When a sliding member is used which has a rela­ tively small central area and adjoining side surfaces which form an angle with said central area, as already indicated above, it is preferable for the end surfaces of the pole shoes to lie at right angles to the band movement plane, opposite said adjoining side surfaces of the sliding member, in such a manner that the surfaces lying opposite one another enclose a predetermined small angle. With this form of construction of the pole shoes on the one hand, and of the sliding member on the other hand, a certain centering action is achieved for the sliding member in relation to the pole shoes of the field generator. In view of the fact that, depending on dimensions, the and surfaces of the pole shoes may make more or less extensive contact with the tape, it is pre­ fereable for the edges of the pole shoes to be rounded. However, the pole shoes come into contact with that side of the information carrier tape on which no information carrying structure is provided, so that contact between the pole shoes and the tape does not result in any wear of, in particular, the information carrying structure of the tape. The invention relates not only to a device of the abovedescribed type, but in addition also to a holder or cassette for an information carrier in tape form which is provided with two tape reels and also provided with a device of this kind. The invention further relates to a device in which a holder or cassette of this type can be placed for further use, which device is then pro­ vided with an optical read/write head and also with an electromagnetic or magnetic field generator. The invention will be explained more fully below with reference to the accompanying drawings. Figure 1 shows schematically one example of a slid­ ing member according to the invention. Figure 2 shows one form of construction of a slid­ ing member according to the invention, which is set in oscillatory motion with the aid of an electromagnetic field generator. Figure 3 shows an example of a cassette in which the device according to the invention is used. Figure 4 is a schematic diagram explaining the po­ sition of the sliding member in the cassette shown in Figure 3. Figure 5 is a detail view of the device used in the cassette shown in Figure 3. Figure 1 shows very schematically a section through an information carrier 1 in tape form which is trans­ ported along a guide member 2 in the direction of the arrow 3. During this transport of the tape the guide member 2 makes an oscillatory movement, which in Figure 1 is indicated by the double arrow 4. The oscillatory movement of the sliding member 2 can for example be achieved by making the sliding member entirely or partially of a piezoelectric material, on which are disposed contacts which can be connected to a suitable voltage source for producing the desired movement. Constructions of this kind are in particular suitable for use as guide members along which a tape can change direction. It is however also possible for the sliding mem­ ber 2 to be made at least partially of a magnetizable material and for the part so made to be coupled to the magnetic circuit of an electromagnetic or magnetic field generator in such a manner that the part in question of the sliding member, and thus the sliding member as a whole, can be caused to perform the desired oscillatory vibrations when the field generator is controlled ac­ cordingly. A possible form of construction of an ar­ rangement of this kind is shown in Figure 2. That part of the sliding member 11 which is shown in Figure 2 is made of a magnetizable material and is situated in the magnetic circuit of the yoke 12 of the field generator. The yoke 12 is in addition provided with an electric coil 13, which by means of the termin­ als 14 and 15 can be connected to a suitable voltage source. As can be seen in the figure, the two ends of the yoke 12 are positioned on one side of the tape 10, and the sliding member 11 is situated on the other side of the tape 10, but arrangements in which both the field generator and the sliding member are disposed on the same side of the tape 10 also come within the scope of the invention. Even without more detailed consideration of the voltage forms to be applied, it will be clear that by correct excitation of the field generator 12, 13, 14, 15 it will be possible for the sliding member to be alter­ nately attracted by the field generator in the upward direction in Figure 2, whereby the top part of the tape 10 will be displaced in the upward direction, and then, with no attractive force applied by the field generator, to move together with the band 10 through the action of the transverse component of the tension existing in the tape 10 and/or through the return action of the stop member (the pole shoes 12 in Figure 2). Although in this case a certain contact will be made with the slid­ ing member throughout the movement, the forces occurring are extremely slight. Only during the relatively brief upward displacement movement of the sliding member 11 could there be any question of any friction and there­ fore wear between the member 11 and the tape 10. Figure 3 shows very schematically a tape cassette of which only the side wall 20 is visible in section. The cassette contains two reels 21 and 22, which are mounted in known manner (not shown) for rotation in the cassette. The tape 24 is wound on the reels. The outer turns of the respective parts of the tape on the reels 21 and 22 are indicated schematically by a broken line. Figure 3 also shows the sliding member 25 along which the tape 24 is moved, together with a three-part member 26 forming part of the field generator. Figure 5 shows further details of the member 26 and the appertaining field generator. In Figure 3 it is only shown that the side wall of the cassette is provided at the top with an indentation in which the member 26 is fastened, for ex­ ample by adhesive bonding. The space in the side wall of the cassette is used to receive the end of the actual field generator in the way shown in Figure 5, in such a manner that this field generator can be coupled to the member 26. In Figure 3 the sliding member 25 is not posi­ tioned, as in known arrangements, near one of the longer sides of the cassette, but is moved inwards in relation thereto. The selection of this position will be ex­ plained with reference to Figure 4. Figure 4 shows schematically two reels 30 and 31 which are provided with respective cores 32 and 33. The reels are fastened rotatably in fixed positions relative to one another, as is the case in the tape cassette shown in Figure 3. When one of the reels, for example the reel 30, is fully wound and the other reel 31 is empty, the tape will run between the two reels as indicated by the line 34. If on the other hand the reel 30 is empty and the reel 31 fully wound, the path of the tape will be as indicated by the line 35. The point of intersection of the two lines 34 and 35 is designated 36. During the winding of the tape from one reel to the other this point 36 will scarcely change position. It is therefore preferable for the sliding member 25 to be positioned in the prox­ imity of this point 36, because in that case the trans­ verse tape tension component, which results in the tape and the sliding member being pressed one against the other, will be very slight and thus result in minimum wear of the tape against the sliding member. Figure 5 shows further details of the sliding member 25, the member 26 and the field generator coupled. to the latter. In Figure 5 the two parts of the cassette side wall which are visible are designated 40 and 41. Be­ tween the ends of these parts of the cassette wall is disposed an arrangement of yoke end sections 42 and 43 and a window 44 transparent to light. The yoke end sec­ tions 42 and 43 come into contact with the parts 44 and 45 respectively of the field generator yoke when the cassette is coupled to the electromagnetic or magnetic field generator, this yoke being inserted from outside into the recess in the side wall of the cassette until the coupled position shown in Figure 5 is reached. The sliding member 47 is positioned in accordance with the principle discussed in connection with Figure 4 and guides the tape between the reels, which are not visible in Figure 5. The cooperation between the yoke of the field generator and the sliding member 47 will require no further explanation in the light of the ex­ planations already given above. The parts 42, 43 and 44 are for example fixed with the aid of a suitable adhesive to the ends of the wall parts 40 and 41 of the cassette. By way of the window 44, which is transparent to light, light can pass from the top side in Figure 5 onto the tape 48, or at least onto that part thereof which is situated on the surface of the sliding member 47. As can be seen in Figure 5, this sliding member has next to its central surface two side surfaces adjoining the Iatter and ex­ tending at an angle. The angle of these side surfaces is so selected that the tape 48 never touches these sur­ faces and at most runs parallel to them, so that any wear on the lower face of the tape carrying the informa­ tion against these surfaces will be avoided. During fast forward winding and rewinding of the tape between the reels, which are not shown in the fig­ ure, it is preferable to avoid any contact with the sliding member. For this purpose the field generator is disconnected, so that through the action of the trans­ verse tape tension component and possibly through that of gravity the sliding member 47 will be moved in the direction of a member 49, which is provided with a re­ cess on the side facing the sliding member 47. This member 49 serves to limit the permissible movements of the sliding member 47. It may be advantageous for at least the central area of the sliding member to be made of, or to be coated with, a wear-resistant material having a low co­ efficient of friction. The end surfaces of the pole shoe sections 42 and 43, or at least their edges which can can come into contact with the tape 48, may also advan­ tageously be made of or coated with a wear-resistant ma­ terial having a low coefficient of friction. It will be clear that movements of the sliding member 47 in directions at right angles to the plane of the drawing are limited by the top and bottom surfaces of the cassette or by parts projecting therefrom. In view of the fact that it is possible for static charges to build up on the tape, and to have a detrimental effect on the uniform movement of the tape, it is preferable for at least a part of the sliding mem­ ber, which comes into contact with the tape and also regularly comes into contact with other sliding parts of the cassette, to be made of an electrically conduc­ tive material. It will thus be possible for any elec­ tric charges present in the tape 48 to be rapidly and effectively removed.

Claims: 1. Device for guiding an information carrier which is in tape form and moves between two reels, this device being situated in the path of transport between the two reels and being in the form of a guide member along which the tape is moved with a certain tape tension, characterized in that the guide member is a non-rotat­ able sliding member adapted to oscillate in a direction at right angles to the local direction of movement of the tape, with a maximum acceleration which is at least a few times greater than the transverse component of the tape tension divided by the mass of that part of the tape which is affected by the sliding member. 2. Device according to Claim 1, characterized in that said number of times is greater than five and in particular greater than ten. 3. Device according to Claim 1 or 2, characterized in that the mass of the guide member and the maximum acceleration and frequency of the oscillatory movement are so selected that the maximum deflection of the slid­ ing member between the end positions of the oscillatory movement will be smaller than 5 µm and preferably smaller than 1 µm. 4. Device according to one of the preceding claims, characterized in that the place where the tape moves past the sliding member is at least approximately situ­ ated at the point of intersection of the two imaginary lines which are tangent to the core of the one reel and to the outermost turn on the other reel, which is fully wound. 5. Device according to one of the preceding claims, characterized in that the sliding member is provided with a relatively small central area, viewed in the di­ rection of movement of the tape, at right angles to the direction of the oscillatory movement, together with adjoining side surfaces which extend at right angles to the tape movement plane and are at such an angle to said central area that the information carrier tape does not make contact with these surfaces or extends approximate­ ly parallel thereto. 6. Device according to one of the preceding claims 1 to 4, characterized in that the sliding member con­ sists of a piezoelectric member of such shape and con­ struction that when a predetermined voltage is applied the sliding member will make the desired oscillatory movement. 7. Device according to Claim 1 or 2, characterized in that the sliding member is at least partly made of magnetizable material, and that the device is provided with an electromagnetic or magnetic field generator by which the sliding member can be set in vibration. 8. Device according to Claim 6 or 7, characterized in that on the other side of the tape stop means are provided and that the aforesaid field generator or the piezoelectric member can be so controlled that the slid­ ing member can be stopped in a position in which the sliding member is held against said stop means, with the tape clamped therebetween. 9. Advice according to Claims 7 and 8, characterized in that said field generator is provided with pole shoes which extend, on one side of the information carrier tape, in the direction of the sliding member which is situated on the other side of the information carrier tape, while between these pole shoes a window is pro­ vided through which the information carrier tape can be read or written and which can serve as stop means. 10. Device according to Claims 5 and 9, characterized in that the end surfaces of the pole shoes lie opposite said adjoining side surfaces of the sliding member in such a manner that the surfaces lying opposite one an­ other enclose a predetermined small angle. 11. Device according to one of the preceding claims, characterized in that the sliding member is provided, at least in said central area, with a wear-resistant top layer. 12. Device according to one of the preceding claims, characterized in that the sliding member can be moved to a release position in which no further contact is made with the information carrier tape. 13. Device according to one of the preceding claims, characterized in that at least those parts of the slid­ ing member which can come into contact with the informa­ tion carrier tape are made of metal and that these parts of the sliding member are in electrical contact with an earthed part or the frame of the device. 14. Holder or cassette for an information carrier tape, which is provided with two tape reels and also with a device according to one of the preceding claims 15. Holder or cassette according to Claim 14, re­ ferring back to Claim 7, characterized in that the holder is provided with pole shoe parts which are mounted in the wall of the cassette and which after the cassette has been coupled to an external electromagnetic or magnetic field generator form part of the magnetic circuit of the generator. 16. Holder or cassette according to one of Claims 7 to 11 or 15, characterized in that one side wall of the cassette is provided with an indentation which is open towards the outside and in which the electromagnetic or magnetic field generator can be inserted from outside in such a manner that the magnetic circuit of the gener­ ator is functionally coupled to the guide member through the cassette wall or via the pole shoe parts disposed therein. 17. Device for reading and/or writing and/or erasing an information carrier tape disposed in a cassette or holder according to one of Claims 14 to 16, which device is provided with a head for reading and/or writing and/ or erasing an information carrier tape, and also with a space for positioning the holder or cassette in such a manner that after the positioning the head is located opposite that portion of the information carrier tape which is situated in front of the sliding member. 18. Holder or cassette according to Claim 14, re­ ferring back to Claim 6, characterized in that the holder is provided with hermetically sealed electrical lead-in members for the supply of an exciting signal to the piezoelectric member. 19. Device for reading and/or writing and/or erasing an information carrier tape contained in a cassette or holder according to Claim 18, which device is provided with a head for reading and/or writing and/or erasing an information carrier tape, and also with a space for po­ sitioning the holder or cassette in such a manner that after the positioning the head is situated opposite that portion of the information carrier tape which is situ­ ated in front of the sliding member, and is provided with electrical connection means which can be coupled to said lead-in members for the purpose of supplying an ex­ citing signal to the piezoelectric member from a voltage source in the device.

Inventors: BEAUJEAN, JOSEPH MARIE ELISE
Applicants: DOCDATA N.V.
Application year: 1986
Main classification: G11B15
IPC codes: G11B7, G11B15, G11B23