Patent Publication Number: US-2002012192-A1

Title: System for recording and/or reproducing information medium for use in thesystem, and magnetic emboss head and arrangement for formatting medium

Description:
[0001] System for recording and/or reproducing information, medium for use in the system, and magnetic emboss head and arrangement for formatting the medium.  
       [0002] The invention relates to a system for recording and/or reproducing information, comprising  
       [0003] a) a magnetizable medium provided with a track pattern comprising  
       [0004] buried servotracks of a first type containing a first signal, and  
       [0005] buried servotracks of a second type containing a second signal, which servotracks extend substantially in a longitudinal direction and which track pattern, in a transverse direction perpendicular to the longitudinal direction, alternately comprises a servotrack of the first type followed by a servotrack of the second type, and b) an apparatus comprising  
       [0006] a magnetic data head comprising a plurality of data channels positioned at different positions in the transverse direction at a center-to-center distance p 1 ,  
       [0007] means for moving the medium relative to the magnetic data head in the longitudinal direction,  
       [0008] an actuator for moving the magnetic data head relative to the medium in the transverse direction, and  
       [0009] a control unit for controlling the actuator, which control unit is adapted to generate a position signal based on the signals read by the data channels.  
       [0010] The invention also relates to a medium for such a system.  
       [0011] The invention further relates to a magnetic emboss head comprising a head face with a longitudinal direction in which a magnetizable medium is movable relative to the magnetic emboss head, and a transverse direction oriented transversely to the longitudinal direction, and further comprising a structure of integrated emboss channels, which structure terminates in the head face, which emboss channels are disposed adjacent one another in the transverse direction and extend substantially in the transverse direction.  
       [0012] The invention also relates to an arrangement comprising such a magnetic emboss head and means for scanning a magnetizable medium with the magnetic emboss head.  
       [0013] Such a medium, such a system and such a magnetic emboss head are known from WO 96/30897-A2. The known medium is a magnetic tape on which seven servotracks have been written by means of the known magnetic emboss head, the signal in the first servotrack being in phase with the signal in the third, the fifth and the seventh servotrack and the signals in the second, the fourth and the sixth servotrack being in phase opposition to the signals in the first, the third and the fifth servotrack. By means of an apparatus forming part of the known system it is possible to write information signals over the servotracks on the magnetic tape thus formatted. For this purpose, the apparatus comprises a magnetic data head having four data channels and means for moving the magnetic tape past the magnetic data head in a longitudinal direction. The known apparatus further comprises an actuator for positioning the magnetic data head in a transverse direction and a control unit for controlling the actuator. The control circuit comprises a comparator for generating a position signal based on the difference between the signal supplied by a first data channel and the signal supplied by a second data channel. The magnetic data head follows the servotracks on the magnetic tape on the basis of the position signal. A disadvantage of the known system, the known medium and the known magnetic emboss head is that after the whole magnetic tape has been written or read the magnetic tape is to be rewound in order to return it into its initial position. Another disadvantage of the known system is that the servotrack pattern is not suited for future generations with a double data track density.  
       [0014] It is an object of the invention to provide a system of the type defined in the opening paragraph, in which the medium is prepared for a future generation with a double track density. To this end, the system in accordance with the invention is characterized in that the track pattern comprises a group of at least two bands of a first type separated by a band of a second type, which bands of the first type adjoin a servotrack at their sides remote from the band of the second type,  
       [0015] the bands of the first type comprising at least one servotrack having a typical width W 1 , and  
       [0016] the band of the second type having a typical width D, which complies with  
       D=(k+½)W 1   
       [0017] where k=0, 1, 2 etc. and the center-to-center distance p between the data channels complies with the relationship p=n.W 1 , where n=2, 4, 6, . . . etc.  
       [0018] By means of the measures in accordance with the invention it is achieved that the information can be read from and/or written on the servo track pattern in data tracks with a typical data track pitch T 1 =W 1  and in data tracks with a typical data track pitch T 2 =½W 1 . This means that the data track density can be approximately equal and can be approximately twice as high as the servo track density. This means that the investments made for media can be used for two generations of data apparatuses. This makes the system very attractive for data back-up purposes in which a relatively large amount of money is invested in media.  
       [0019] The embodiment according to dependent claim  2  has the advantage that in each pass at least four data channels are positioned on a boundary of servotracks so that four data channels supply information about the position of the magnetic data head relative to the medium. Another four data channels will be positioned entirely on a servotrack so that these data channels can supply information on the speed of the medium relative to the magnetic data head. In this way a very robust system is obtained which is insensitive to local dropouts on the medium.  
       [0020] It is to be noted that the track pattern can be repeated several times in the transverse direction of the medium, as a result of which the magnetic data head can inscribe additional track patterns with information after a displacement in the transverse direction.  
       [0021] An embodiment of the system in accordance with the invention is characterized in that the medium has at least one servotrack having a width of at least n.W 1 . Owing to these measures one data channel can be disposed wholly on the n.W 1  wide servotrack during all passes, thereby enabling this data channel to be used for reading the servo signal without the need to position the magnetic data head accurately in the transverse direction. This simplifies starting of the system in accordance with the invention.  
       [0022] The medium in accordance with the invention is characterized in that the track pattern comprises a group of at least two bands of a first type separated by a band of a second type, which bands of the first type adjoin a servotrack at their sides remote from the band of the second type,  
       [0023] the bands of the first type comprising at least one servotrack having a typical width W 1 , and  
       [0024] the band of the second type having a typical width D, which complies with  
       D=(k+{fraction (1/2)})W 1   
       [0025] where k=0, 1, 2 etc.  
       [0026] The medium in accordance with the invention can be used in the system in accordance with the invention with the advantages outlined above.  
       [0027] Due to the measures of dependent claim  5 , the magnetic emboss head for writing the servo pattern can be manufactured easily because the emboss channels do not have to be made smaller than W 1 . This is advantageous because smaller emboss channels are more difficult to produce. The dimensions of the emboss channels are also limited by the magnetic domain configuration of the material used for making flux guides in the emboss channel.  
       [0028] The embodiment according to dependent claim  6  has the advantage that the signals read from the servotracks in the band of the second type provide additional information about the position of the magnetic data head relative to the medium. This additional information makes it possible to determine quickly which data tracks are being accessed.  
       [0029] In a preferred embodiment the magnetic data head has eight data channels disposed at a center-to-center distance of 4 W 1  and a recording width of approximately {fraction (1/2)}W 1  or less. By means of such a magnetic data head it is possible to write 64 information tracks over this track pattern in eight passes. The choice for eight data channels results in a good balance between data rate (eight channels in parallel) and yield of the magnetic data head (more channels results in a lower yield).  
       [0030] In another embodiment the magnetic data head has at least sixteen data channels disposed at a center-to-center distance of 2W 1  and a recording width of approximately {fraction (1/2)}W 1  or less. By means of such a magnetic data head it is possible to write 64 information tracks in four passes. Since in this embodiment a large number of data channels are positioned on a boundary of servotracks a high degree of robustness is achieved. This enables a satisfactory tracking to be obtained even if a part of the servotracks is unreadable. Some of the data channels are always situated wholly on one servotrack, as a result of which these data channels can supply information about the phase of the servosignal and the speed of the medium relative to the magnetic data head. Another advantage of this embodiment is that each pass can be identified on the basis of the servosignals read by the data channels. This makes it possible to preclude that the servosystem, for example after having been subjected to an external mechanical shock, locks to another pass, where the apparatus continues writing.  
       [0031] An embodiment of the medium in accordance with the invention is characterized in that the first signal and the second signal each contain a fundamental and the first signal and the second signal are in phase opposition to one another. By means of the same frequency these measures it is achieved that the signal read by a data channel is zero if it is centered with respect to a boundary line between two servotracks. This is advantageous because, as a result of this, differences in sensitivity between the data channels have substantially no influence on the generation of the position signal and because a measurement signal which varies about zero makes it possible to implement a servosystem which is accurate and highly insensitive to offsets in the control unit.  
       [0032] The invention is particularly advantageous if the medium is a tape-like medium wound on a reel hub and accommodated in a housing of a cassette. With such a cassette the position of the medium relative to an apparatus with which the cassette cooperates is generally inaccurate because a tape-like medium is slack and this position is also determined by the housing of the cassette. In addition, the dimensions of a tape-like medium in the transverse direction can vary owing to expansion or contraction as a result of the absorption of moisture or release of moisture by the medium. The measures in accordance with the invention yet ensure an accurate position of the magnetic data head with respect to the medium, as a result of which high-density information storage is possible on the medium. Moreover, the medium in such a cassette is not fully protected against the ingress of dust and dirt from the environment and there is mechanical contact between the medium and the magnetic data head, which may give rise to scratches. As a result of dust, dirt or scratches some of the servosignals may be disturbed or completely unreadable at some locations. The measures in accordance with the invention mitigate the effect of dust, dirt and scratches on the tracking.  
       [0033] The magnetic emboss head and the arrangement in accordance with the invention are characterized in that  
       [0034] the structure comprises a group of at least two bands of a first type, which are separated by a band of a second type,  
       [0035] the bands of the first type adjoin an emboss channel at their sides remote from the band of the second type,  
       [0036] the bands of the first type have emboss channel having a typical width W 1 , and  
       [0037] the band of the second type has a typical width D, which complies with  
       D=(k+{fraction (1/2)})W 1   
       [0038] where k=0, 1, 2 etc.. 
     
    
    
     [0039] The invention will be now be described in more detail, by way of example, with reference to the drawings, in which  
     [0040]FIG. 1 shows diagrammatically the system in accordance with the invention,  
     [0041]FIG. 2 shows a magnetic emboss head, a magnetic data head, an actuator and a first embodiment of the medium in accordance with the invention,  
     [0042]FIG. 3 shows two servosignals and their phase relationship to one another,  
     [0043]FIG. 4 shows diagrammatically a second embodiment of the medium in accordance with the invention,  
     [0044]FIG. 5 shows diagrammatically a third embodiment of the medium in accordance with the invention,  
     [0045]FIG. 6 shows diagrammatically a fourth embodiment of the medium in accordance with the invention,  
     [0046]FIG. 7 shows diagrammatically a fifth embodiment of the medium in accordance with the invention, and  
     [0047]FIG. 8 shows diagrammatically an arrangement according to the invention. 
    
    
     [0048]FIG. 1 shows diagrammatically the system in accordance with the invention. The system includes an apparatus  100  and a magnetizable medium, in the present case a magnetic tape  10  accommodated in the housing of a cassette  11 . The magnetic tape  10  has been provided with a pattern of servotracks in which servosignals are stored in the form of a magnetisation pattern recorded at a deep level (see FIG. 2). These deep servotracks are referred to as buried servotracks. The apparatus  100  comprises a magnetic data head  20  and means, in the present case a motor  30 , for the relative movement of the magnetic tape  10  with respect to the magnetic data head  20  in a longitudinal direction x along the servotracks (see FIG. 2). The apparatus  100  further comprises an actuator  40 , for moving the magnetic data head  20  transversely to the servotracks, and a servocircuit  50 , arranged between the magnetic data head  20  and the actuator  40 . The apparatus  100  comprises control means, in the present case a microcomputer  70 , for controlling the actuator  40  and the magnetic data head  20 .  
     [0049]FIG. 2 shows diagrammatically a magnetizable medium in the form of the magnetic tape  10 , a magnetic emboss head  60 , the magnetic data head  20  and the actuator  40 . The magnetic tape  10  has been provided with a pattern of servotracks ST 1 -ST 17  which extend in a longitudinal direction x and which adjoin one another in a transverse direction y which is perpendicular to the longitudinal x. The servotracks ST 1 , ST 3 , ST 5  etc. are of a first type containing a servosignal Sa and the servotracks ST 2  and ST 4  are of a second type containing a servosignal Sb. The servosignals Sa and Sb each contain a fundamental of the same frequency but are in phase opposition to one another (see FIG. 3). The servosignals have been recorded by means of a magnetic emboss head  60  having a comparatively large gap length s. As a result of this, the servosignals are stored deep into the magnetic tape  10 . The magnetic emboss head  60  has a head face  61  and a structure of integrated emboss channels S 1 -S 17 , which structure terminates in the head face  61 , which emboss channels are disposed adjacent one another and extend substantially in the transverse direction. The structure comprises a group of two bands of a first type A with emboss channels S 2 -S 8  and S 10 -S 16 , which are separated by a band of a second type B, in this case consisting of an emboss channel S 9 . The emboss channels S 2 -S 8  and S 10 -S 16  have a first typical width W 1  and the emboss channel S 9  has a second typical width D=1.5W 1 . By means of this magnetic emboss head  60  the track pattern ST 1 -ST 17  is written onto the magnetic tape  10  in a single pass. This writing is preferably effected in an arrangement (see FIG. 8) specially designed for this purpose, when the magnetic tape is manufactured or when the magnetic tape  10  is loaded into the cassette  11 .  
     [0050] The magnetic data head  20  forms part of the apparatus  100  as shown in FIG. 1 and comprises four data channels H 1 , H 2 , H 3  and H 4  capable of reading and writing simultaneously. The apparatus  100  as shown in FIG. 1 is adapted to write information signals in information tracks D 1 -D 16 . To this end, the magnetic data channels have a width of approximately W 1 . For positioning the magnetic data head  20  during writing and/or reading of the information tracks D 1 -D 16  the apparatus  100  comprises an actuator  40  and a servocircuit  50 . The servocircuit  50  is arranged between the magnetic data head  20  and the actuator  40  and is adapted to position the magnetic data head  20  with respect to the track pattern ST 1 -ST 17  in response to the servosignals V 1 , V 2 , V 3  and V 4  read from the servotracks by the data channels H 1 , H 2 , H 3  and H 4 , respectively. The servocircuit  50  comprises a selector  51  for selecting the signals received from data channels which are disposed on a boundary line between two servotracks and a first adder  52  for generating a signal Vdif from the selected signals. The selector  51  is controlled by the microcomputer  70  shown in FIG. 1. The servocircuit  50  further comprises a second adder  54  for generating a reference signal Vref obtained from the data channels which are disposed entirely on one of the servotracks. A multiplier  53  is employed to generate a position signal Vp by multiplying the signal Vdif and the reference signal Vref. The actuator  40  is driven until the position signal Vp is substantially equal to zero. For each pass of the magnetic data head  20 , the reference signal Vref=V 1 +V 2  and the signal Vdif=V 3 +V 4  so that the selector is not operative in this embodiment.  
     [0051] The magnetic data head  120  shown in FIG. 2 is an example of a second generation embodiment in which the number of data tracks is doubled by halving the width of the magnetic data channels and adapting the generation of the position signal Vp. The magnetic data head  120  also forms part of an apparatus  100  as shown in FIG. 1 and also comprises four data channels H 1 , H 2 , H 3  and H 4  capable of reading and writing simultaneously. For positioning the magnetic data head  120  during writing and/or reading of information tracks the apparatus comprises an actuator  140  and the same servocircuit  50 . In this second generation the servocircuit  50  is arranged between the magnetic data head  120  and the actuator  140  and is adapted to position the magnetic data head  120  with respect to the track pattern ST 1 -ST 17  in response to the servosignals V 1 , V 2 , V 3  and V 4  in this second generation read from the servotracks by the data channels H 101 , H 102 , H 103  and H 104 , respectively. In the second generation again the actuator  140  is driven until the position signal Vp is substantially equal to zero. For the subsequent passes of the magnetic data head  120 , the reference signal Vref and the signal Vdif are generated as indicated below by appropriate control of the selector  51  by the microprocessor  70  (see FIG. 1).  
                                       pass   Vref   Vdif                  1   V3 + V4   V1 + V2       2   −(V1 + V2)     V3 + V4       3   V3 + V4   V1 + V2       4   V1 + V2   −(V3 + V4)         5   V3 + V4   V1 + V2       6   −(V1 + V2)     V3 + V4       7   V3 + V4   V1 + V2       8   V1 + V2   −(V3 + V4)                    
 
     [0052] The center-to-center distance p 1  between the magnetic data channels H 101 -H 104  is also equal to four times the typical width W 1  of the servotracks ST 2 -ST 8  and the width of the data channels is approximately ½W 1 . As a result, eighth passes are needed to provide the magnetic tape  10  wholly with 32 information tracks. After these passes the magnetic tape  10  has resumed its initial position.  
     [0053]FIG. 4 shows diagrammatically a second embodiment of the medium in accordance with the invention. The magnetic tape  210  has been provided with a pattern of servotracks which extend in a longitudinal direction. The non-shaded servotracks contain a servosignal Sa and the shaded servotracks contain a servosignal Sb. The servosignals Sa and Sb each contain a fundamental of the same frequency but are in phase opposition to one another (see FIG. 3). The servosignals have been recorded by means of a magnetic emboss head, not shown, as described with reference to FIG. 2. The magnetic tape  210  is adapted to co-operate with an apparatus comprising a magnetic data head  220  having eight data channels H 201 -H 208 . The center-to-center distance p 2  between the magnetic data channels H 201 -H 208  is equal to four times the typical width W 1 . As a result four passes are needed to provide the whole magnetic tape  210  with  32  information tracks in a manner comparable to that described with reference to FIG. 2. After these four passes the magnetic tape  210  has again reached its initial position.  
     [0054] The magnetic tape  210  is also suited to cooperate with a second generation apparatus comprising a magnetic data head having eight data channels H 301 -H 308  with a center-to-center distance p 2  and a width of approximately ½W 1 . Eight passes are needed to provide the whole magnetic tape  210  with 64 information tracks in a manner comparable to that described with reference to FIG. 2. After these eight passes the magnetic tape  210  has again reached its initial position.  
     [0055] The magnetic tape  210  is also suited to cooperate with a second generation apparatus comprising a magnetic data head having sixteen data channels H 401 -H 416  with a center-to-center distance p 4 =2.W 1  and a width of approximately ½W 1 . Four passes are needed to provide the whole magnetic tape  210  with 64 information tracks in a manner comparable to that described with reference to FIG. 2.  
     [0056]FIG. 5 shows diagrammatically a part of third embodiment of the medium in accordance with the invention. The medium comprises a group of servotracks ST 501 -ST 505  which extend in a longitudinal direction. The odd-numbered servotracks contain a servosignal Sa and the even-numbered servotracks contain a servosignal Sb. The servosignals Sa and Sb each contain a fundamental of the same frequency but are in phase opposition to one another (see FIG. 3). The servosignals have been recorded by means of a magnetic emboss head, not shown, as described with reference to FIG. 2. The servotracks ST 502  and ST 504  have a typical width W 1  and are separated by the servotracks ST 503  having a typical width of D=1.5W 1 . The magnetic tape is adapted to cooperate with an apparatus comprising magnetic data channels H 501  and H 502 . As a result, two passes are needed to provide the shown pattern with four information tracks in a manner comparable to that described with reference to FIG. 2.  
     [0057] The magnetic tape is also suited to cooperate with an apparatus comprising magnetic data channels H 601  and H 602 . With such an apparatus, four passes are needed to provide the shown pattern with eighth information tracks in a manner comparable to that described with reference to FIG. 2. This group of servotracks can be repeated many times on a magnetic tape so that a large number of parallel servotracks is obtained over which data tracks it is possible to write with single and double track density.  
     [0058]FIG. 6 shows diagrammatically a part of a fourth embodiment of the medium in accordance with the invention and magnetic data channels H 201 -H 208  and H 301 -H 308 . This embodiment differs from that shown in FIG. 4 in that the bands of the first type I are separated by a band of second type II which consists of a single servotracks with a width D=9.5 W 1  and which comprises a periodic servosignal Sb (see FIG. 3). As this servotrack is wider than twice the center-to-center distance between the magnetic data channels, there are in each pass at least two data channels, i.e. H 204  and H 205  or H 304  and H 305 , which read the signal from this servotrack without interference of neighbouring tracks. As this signal is periodic it can be used, for example, as a speed signal representative of the speed of the magnetic data head relative to the medium.  
     [0059]FIG. 7 shows diagrammatically a part of a fifth embodiment of the medium in accordance with the invention and magnetic data channels H 201 -H 208  and H 301 -H 308 . This embodiment differs from that shown in FIG. 4 in that the bands of the first type I are separated by a band of second type II which consists of five servotracks with a width W 2 =1.5 W 1 . With this fifth embodiment each of the four passes of the data channels H 201 -H 208  can be identified on basis of the signals read by the data channels because the relation between the signals differs per pass.  
     [0060]FIG. 8 shows an embodiment of the arrangement according to the invention. The arrangement  400  comprises a space for accommodating a cassette  11 . The cassette  11  has two reel hubs  12  and  13  on which a magnetic tape ( 10 ) is wound. The arrangement  400  further comprises a magnetic emboss head  60  and a motor  430  for moving the magnetic tape  10  past the magnetic emboss head  60  so that the tape  10  can be scanned. The arrangement  100  further comprises control electronics  440  for driving the magnetic emboss head  60  and the motor  430 . With this arrangement a magnetic tape  10  can be provided with servotracks as explained with reference to FIG. 2.  
     [0061] It is to be noted that the invention is not limited to the embodiments disclosed herein. Various other embodiments are possible within the scope of the invention. It is possible, for example, to use a magnetic disc instead of a magnetic tape. Besides, the servosignals Sa and Sb can be signals of different frequency, the servo circuit generating a position signal for controlling the actuator in dependence on the amplitude of the servosignals Sa and Sb as read by a number of data channels.