Patent Publication Number: US-2023142229-A1

Title: Magnetic tape device and method of operating magnetic tape device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application No. PCT/JP2021/015583 filed on Apr. 15, 2021, the disclosure of which is incorporated herein by reference in its entirety. Further, this application claims priority from Japanese Patent Application No. 2020-123831 filed on Jul. 20, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The technology of the present disclosure relates to a magnetic tape device and a method of operating a magnetic tape device. 
     2. Description of the Related Art 
     Various magnetic tape devices that cause a magnetic element of a magnetic head to act on a magnetic layer formed on a front surface of a magnetic tape to record data on the magnetic layer and/or read data recorded on the magnetic layer have been proposed. For example, JP1999-126318A (JP-H11-126318A) discloses a magnetic tape device that adjusts a position of a magnetic element in a width direction of a magnetic tape by using a piezoelectric element. 
     SUMMARY 
     Although the magnetic layer is flattened, the front surface of the magnetic tape has irregularities on the order of several nm to several tens of nm. In addition, the magnetic tape has positional variation on the order of several tens of nm to several µm in a normal direction of the front surface, due to, for example, adhesion of foreign matter to the magnetic head that has resulted from scrapes of the magnetic layer through a swell during running caused by eccentricity of a guide roller that guides the running thereof, through vibration caused by friction with the guide roller, or through contact with the magnetic element, and/or that has occurred for some other reason. Further, the magnetic element may be worn by an abrasive prescribed for the magnetic layer, and a positional relationship between the magnetic layer and the magnetic element in the normal direction may change with time. 
     Such a variation in the positional relationship between the magnetic layer and the magnetic element in the normal direction destabilizes recording and/or reading data. Therefore, it is necessary to adjust the position of the magnetic element in the normal direction. However, JP1999-126318A (JP-H11-126318A) discloses adjusting the position of the magnetic element in the width direction of the magnetic tape, but does not disclose adjusting the position of the magnetic element in the normal direction. 
     One embodiment according to the technology of the present disclosure provides a magnetic tape device and a method of operating a magnetic tape device capable of maintaining a positional relationship between a magnetic layer and a magnetic element in a normal direction of a front surface of a magnetic tape. 
     According to the present disclosure, there is provided a magnetic tape device comprising: a magnetic head having a magnetic element that acts on a magnetic layer formed on a front surface of a magnetic tape; and a position adjusting actuator that adjusts a position of the magnetic element in a normal direction of the front surface by moving the magnetic head; and a processor that controls an operation of the position adjusting actuator. 
     It is preferable that the magnetic head causes the magnetic element to act in proximity to the magnetic layer. 
     It is preferable that the magnetic head has a width smaller than a width of the magnetic tape. 
     It is preferable that the position adjusting actuator is a piezoelectric element. 
     It is preferable that the processor controls the operation of the position adjusting actuator on the basis of variation profile data representing a variation of the magnetic tape in the normal direction. 
     It is preferable that a pair of support members on which the front surface is slid is further provided, the pair of support members being disposed on both sides of the magnetic tape in a running direction with the magnetic head interposed therebetween. 
     It is preferable that a plurality of data bands on which data is recorded, and a plurality of servo bands on which a plurality of servo patterns used for servo control to move the magnetic head in a width direction of the magnetic tape are recorded are formed in the magnetic layer, and the magnetic head includes, as the magnetic element, a data element that acts on the data band and a servo pattern reading element that reads the servo patterns. 
     It is preferable that the data element includes a data recording element that records the data on the magnetic layer, and a data reading element that reads the data recorded on the magnetic layer. 
     According to the present disclosure, there is provided a method of operating a magnetic tape device, comprising: adjusting a position of a magnetic element of a magnetic head in a normal direction of a front surface of a magnetic tape by controlling an operation of a position adjusting actuator to move the magnetic head; and causing the magnetic element to act on a magnetic layer formed on the front surface. 
     According to the technology of the present disclosure, it is possible to provide a magnetic tape device and a method of operating the magnetic tape device capable of maintaining a positional relationship between a magnetic layer and a magnetic element in a normal direction of a front surface of a magnetic tape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments according to the technique of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG.  1    is a diagram showing an example of a magnetic tape device; 
         FIG.  2    is an enlarged view of a vicinity of a magnetic head; 
         FIG.  3    is a plan view of a magnetic tape as viewed from sides of the magnetic head and of a support member; 
         FIG.  4    is an exploded perspective view of a suspension and the magnetic head; 
         FIG.  5    is a perspective view of a piezoelectric bimorph element; 
         FIGS.  6 A to  6 C  are diagrams showing a situation in which a position of a magnetic element in a normal direction is adjusted by the piezoelectric bimorph element, in which  FIG.  6 A  shows a case where the magnetic tape is displaced in a direction of the magnetic head from a regular position and the piezoelectric bimorph element is bent in a direction away from the magnetic tape,  FIG.  6 B  shows a case where the magnetic tape is located at the regular position, and  FIG.  6 C  shows a case where the magnetic tape is displaced in a direction opposite to the magnetic head from the regular position and the piezoelectric bimorph element is bent in a direction of approaching the magnetic tape; 
         FIG.  7    is an enlarged view of the vicinity of the magnetic head; 
         FIG.  8    is a diagram showing a correspondence relationship between a data element and a data track; 
         FIG.  9    is an enlarged view of the data element; 
         FIG.  10    is a block diagram showing a computer constituting a control unit; 
         FIG.  11    is a block diagram of a CPU; 
         FIG.  12    is a diagram showing variation profile data; 
         FIG.  13    is a flowchart showing an operation procedure of the magnetic tape device; 
         FIG.  14    is a diagram showing an example in which a laminated piezoelectric element is used; and 
         FIGS.  15 A and  15 B  are diagrams showing a situation in which the position of the magnetic element in the normal direction is adjusted by the laminated piezoelectric element, in which  FIG.  15 A  shows a case where the magnetic tape is displaced in the direction of the magnetic head from the regular position and the laminated piezoelectric element contracts, and  FIG.  15 B  shows a case where the magnetic tape is displaced in the direction opposite to the magnetic head from the regular position and the laminated piezoelectric element expands. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG.  1   , a cartridge  11  is loaded into a magnetic tape device  10 . A cartridge reel  13  on which a magnetic tape  12  is wound is accommodated in the cartridge  11 . The magnetic tape device  10  records data on the magnetic tape  12  fed out from the cartridge reel  13 . Further, the magnetic tape device  10  reads data recorded on the magnetic tape  12 . 
     The magnetic tape  12  has, for example, a configuration in which a magnetic layer  16  and a back coating layer  17  are formed on a base film  15 . In the magnetic tape  12 , a surface on which the magnetic layer  16  is formed is a front surface  18  of the magnetic tape  12 . On the other hand, a surface on which the back coating layer  17  is formed is a back surface  19  of the magnetic tape  12 . Data is recorded on the magnetic layer  16 . The magnetic layer  16  contains ferromagnetic powder. As the ferromagnetic powder, ferromagnetic powder generally used in the magnetic layer of various magnetic recording media can be used. Preferable specific examples of the ferromagnetic powder can include hexagonal ferrite powder. As the hexagonal ferrite powder, for example, ferromagnetic powder, such as hexagonal strontium ferrite powder or hexagonal barium ferrite powder, can be used. The back coating layer  17  contains, for example, non-magnetic powder, such as carbon black. The base film  15  is also called a support and is formed of, for example, polyethylene terephthalate, polyethylene naphthalate, or polyamide. A non-magnetic layer may be formed between the base film  15  and the magnetic layer  16 . 
     The magnetic tape device  10  comprises a feeding motor  25 , a winding motor  26 , a winding reel  27 , a magnetic head  28 , support members  29 A and  29 B, a control unit  30 , and the like. The feeding motor  25  rotates the cartridge reel  13  provided in the cartridge  11  under the control of the control unit  30 . The magnetic tape  12  fed out from the cartridge reel  13  is wound on the winding reel  27 . Further, the magnetic tape  12  wound up on the winding reel  27  is rewound on the cartridge reel  13 . The winding motor  26  rotates the winding reel  27  under the control of the control unit  30 . 
     The magnetic tape  12  runs in a feed direction FWD or a rewind direction BWD while being guided by a plurality of guide rollers  31  with the drive of the feeding motor  25  and the winding motor  26 . The feed direction FWD is a direction from the cartridge reel  13  toward the winding reel  27 . The rewind direction BWD is, on the contrary, a direction from the winding reel  27  toward the cartridge reel  13 . The feed direction FWD and the rewind direction BWD are an example of the “running direction” according to the technology of the present disclosure. Further, in the magnetic tape  12 , the rotational speed and the rotational torque of the feeding motor  25  and the winding motor  26  are adjusted so that the tension during running and the running speed are adjusted to appropriate values. 
     The magnetic head  28  is disposed on the front surface  18  side of the magnetic tape  12  in order to access the magnetic layer  16 . The magnetic head  28  records data on the magnetic layer  16 . In addition, the magnetic head  28  reads data recorded on the magnetic layer  16 . 
     The magnetic head  28  operates in a case where the magnetic tape  12  is running in the feed direction FWD. In other words, the magnetic head  28  operates in a case where the magnetic tape  12  is fed out from the cartridge reel  13 . Further, the magnetic head  28  operates in a case where the magnetic tape  12  is running in the rewind direction BWD. In other words, the magnetic head  28  operates in a case where the magnetic tape  12  is rewound on the cartridge reel  13 . 
     The magnetic head  28  is a small magnetic head, such as a magnetic head used for a hard disk drive. The magnetic head  28  is provided at a distal end of a suspension  35  (see  FIG.  2    and the like). A proximal end of the suspension  35  is movably attached to, for example, the support member  29 B. The magnetic head  28  may be retracted to a standby position separated from the magnetic tape  12  during non-operation. 
     The support members  29 A and  29 B are disposed on the front surface  18  side of the magnetic tape  12  like the magnetic head  28 . The support members  29 A and  29 B have a substantially rectangular shape (see also  FIG.  2    and  FIG.  3   ) and are disposed on both sides in the feed direction FWD and the rewind direction BWD with the magnetic head  28  interposed therebetween. The support members  29 A and  29 B support the magnetic tape  12  from the front surface  18  side. 
     As shown in the enlarged view of  FIG.  2   , the support member  29 A has a sliding surface  38 A, and the support member  29 B has a sliding surface  38 B. Corners of the sliding surfaces  38 A and  38 B are subjected to R chamfering. The sliding surface  38 A has a first surface  38 A_ 1   and a second surface  38 A_ 2  that is inclined with respect to the first surface  38 A_ 1 . Similarly, the sliding surface  38 B has a first surface  38 B_ 1  and a second surface  38 B_ 2  that is inclined with respect to the first surface  38 B_ 1 . The front surface  18  of the magnetic tape  12  is slid on the sliding surfaces  38 A and  38 B. That is, the magnetic tape  12  runs while sliding the front surface  18  on the sliding surfaces  38 A and  38 B. The magnetic tape  12  runs such that the center in the width direction WD (see also  FIG.  3    and the like, a direction perpendicular to a paper surface in  FIG.  2   ) thereof coincides with the centers of the support members  29 A and  29 B. The term “coincide” as used herein indicates a coincidence in a sense including an error generally allowed in the technical field to which the technology of the present disclosure belongs, in addition to the complete coincidence. 
     The support members  29 A and  29 B are disposed at positions mirror-symmetrical to each other with respect to the magnetic head  28 , more specifically, with respect to a magnetic element ME of the magnetic head  28 . A disposition interval AI between the support members  29 A and  29 B is, for example, 2 mm to 20 mm. 
     A distance sensor  39  is attached to the support member  29 A. The distance sensor  39  is a sensor for acquiring variation profile data  80  (see  FIGS.  11  and  12   ), which will be described later, and measures a distance to the front surface  18  of the magnetic tape  12 . 
     Reference numeral ND indicates a normal direction of the front surface  18  of the magnetic tape  12 . In the vicinity of the magnetic head  28 , the normal direction ND is a direction orthogonal to the feed direction FWD and the rewind direction BWD, and to the width direction WD of the magnetic tape  12 . In addition, the normal direction ND is a direction parallel to a direction in which the magnetic tape  12  and the magnetic element ME face each other. Reference numeral SP indicates a spacing which is a gap between the magnetic layer  16  and the magnetic element ME. Here, “orthogonal” indicates orthogonality in the sense including an error generally allowed in the technical field to which the technology of the present disclosure belongs, and an error to the extent that does not violate the gist of the technology of the present disclosure, in addition to the complete orthogonality. 
     A moving mechanism  40  is connected to the suspension  35 . The moving mechanism  40  moves the suspension  35 , that is, the magnetic head  28 , in the width direction WD of the magnetic tape  12 . The moving mechanism  40  includes, for example, an actuator, such as a voice coil motor or a piezoelectric element. 
     In  FIG.  3    in which the magnetic tape  12  is viewed from the sides of the magnetic head  28  and of the support members  29 A and  29 B, a width W_H of the magnetic head  28  is smaller than a width W_T of the magnetic tape  12 . Specifically, the width W_H of the magnetic head  28  is about ½ of the width W_T of the magnetic tape  12 . The width W_T of the magnetic tape  12  is, for example, 12.65 mm, and the width W_H of the magnetic head  28  is, for example, 6.5 mm to 7.0 mm. Incidentally, other sizes such as the depth and the height of the magnetic head  28  are also smaller than the width W_T of the magnetic tape  12  and are, for example, about several mm. 
     The magnetic layer  16  has three servo bands SB 1 , SB 2 , and SB 3  and two data bands DB 1  and DB 2  on which data is recorded. The servo bands SB 1  to SB 3  and the data bands DB 1  and DB 2  are formed along the feed direction FWD and the rewind direction BWD (a length direction of the magnetic tape  12 ). The servo bands SB 1  to SB 3  are arranged at equal intervals along the width direction WD of the magnetic tape  12 . The data band DB 1  is disposed between the servo bands SB 1  and SB 2 , and the data band DB 2  is disposed between the servo bands SB 2  and SB 3 . That is, the servo bands SB 1  to SB 3  and the data bands DB 1  and DB 2  are alternately arranged along the width direction WD of the magnetic tape  12 . 
     A servo pattern  50  is recorded on the servo bands SB 1  to SB 3 . A plurality of the servo patterns  50  are provided at equal intervals along, for example, the feed direction FWD and the rewind direction BWD. The servo pattern  50  is composed of a pair of linearly symmetric magnetization regions  51 A and  51 B that are non-parallel to each other and that form a predetermined angle. The magnetization region  51 A is tilted toward the rewind direction BWD side, and the magnetization region  51 B is tilted toward the feed direction FWD side. The servo pattern  50  is used for servo control to move the magnetic head  28  in the width direction WD of the magnetic tape  12  through the moving mechanism  40 . 
     The magnetic head  28  records data on the data band DB 1  and reads data recorded on the data band DB 1 , in a case where the magnetic tape  12  is running in the feed direction FWD. In addition, the magnetic head  28  reads the servo patterns  50  recorded on the servo bands SB 1  and SB 2  in a case where the magnetic tape  12  is running in the feed direction FWD. 
     Further, the magnetic head  28  records data on the data band DB 2  and reads data recorded on the data band DB 2 , in a case where the magnetic tape  12  is running in the rewind direction BWD. Further, the magnetic head  28  reads the servo patterns  50  recorded on the servo bands SB 2  and SB 3  in a case where the magnetic tape  12  is running in the rewind direction BWD. 
     As shown in  FIG.  4    as an example, the suspension  35  has a load beam  55 , a piezoelectric bimorph element  56 , a flexure  57 , and the like. The load beam  55  is a thin flat plate made of metal having relatively high stiffness. The load beam  55  is attached to a base plate whose proximal end is not shown, and is connected to an actuator, such as a voice coil motor of the moving mechanism  40 , via the base plate. The load beam  55  is formed to have a length slightly shorter than that of the flexure  57 , and the piezoelectric bimorph element  56  is fixed to a distal end of the load beam  55 . 
     The piezoelectric bimorph element  56  has a configuration in which two flat plate-shaped piezoelectric bodies  60 A and  60 B are bonded to each other. One of the piezoelectric bodies  60 A and  60 B expands and the other contracts, in a case where a voltage is applied. The piezoelectric bimorph element  56  is an element that is bent by the expansion and contraction of the piezoelectric bodies  60 A and  60 B to move a target. The piezoelectric bodies  60 A and  60 B are, for example, lead zirconate titanate (PZT; Pb(Zr,Ti)O 3 ). The piezoelectric body  60 B side of the piezoelectric bimorph element  56  is attached to the flexure  57 . The piezoelectric bimorph element  56  is an example of the “position adjusting actuator” and the “piezoelectric element” according to the technology of the present disclosure. 
     The flexure  57  is a thin flat plate made of metal having relatively low stiffness. Therefore, the flexure  57  functions as a leaf spring. The magnetic head  28  is attached to a surface of the flexure  57  opposing a surface to which the piezoelectric bimorph element  56  is attached. 
     As shown in  FIG.  5    as an example, a length L_P and a width W_P of each of the piezoelectric bodies  60 A and  60 B are both several mm. A thickness T_P of each of the piezoelectric bodies  60 A and  60 B is several tens of µm. 
     As shown in  FIGS.  6 A to  6 C  as an example, the piezoelectric bimorph element  56  bends the distal end of the flexure  57  with the expansion and contraction of the piezoelectric bodies  60 A and  60 B to move the magnetic head  28 , thereby adjusting the position of the magnetic element ME in the normal direction ND. The piezoelectric bimorph element  56  operates so as to keep the spacing SP constant, under the control of the control unit  30 . Specifically, in a case where the position of the magnetic tape  12  is displaced in a direction of the magnetic head  28  from a regular position shown in  FIG.  6 B , the piezoelectric bimorph element  56  is bent in a direction away from the magnetic tape  12  as shown in  FIG.  6 A . On the other hand, in a case where the position of the magnetic tape  12  is displaced in a direction opposite to the magnetic head  28  from the regular position shown in  FIG.  6 B , the piezoelectric bimorph element  56  is bent in a direction of approaching the magnetic tape  12  as shown in  FIG.  6 C . 
     A bending amount ΔL of the piezoelectric bimorph element  56  in one direction is represented by Equation (1). Here, d denotes a piezoelectric strain constant, and V denotes an applied voltage.  
     
       
         
           
             Δ 
             L= 
             
               3 
               4 
             
             
               
                 
                   
                     
                       
                         L 
                         _ 
                         P 
                       
                       
                         T 
                         _ 
                         P 
                       
                     
                   
                 
               
               2 
             
             ⋅ 
             d 
             ⋅ 
             V 
           
         
       
     
     For example, a case where the length L_P and the width W_P of each of the piezoelectric bodies  60 A and  60 B are both 1 mm and the thickness T_P of each of the piezoelectric bodies  60 A and  60 B is 50 µm is considered. In a case where the piezoelectric strain constant d of each of the piezoelectric bodies  60 A and  60 B is, for example, 200 × 10 -12  m/V, and a voltage of, for example, 20 V is applied to the piezoelectric bodies  60 A and  60 B, the bending amount ΔL is 1.2 µm according to Equation (1). 
     In  FIG.  7   , which is an enlarged view of the vicinity of the magnetic head  28 , the magnetic head  28  has a plurality of magnetic elements ME that are provided on a surface facing the magnetic layer  16  and that act on the magnetic layer  16 . The magnetic head  28  causes the magnetic element ME to act on the magnetic layer  16  by bringing the magnetic element ME close to the magnetic layer  16  with the spacing SP on the order of several nm therebetween. 
     The magnetic element ME has two servo pattern reading elements SR 1  and SR 2 , and eight data elements DRW 1 , DRW 2 , DRW 3 , DRW 4 , DRW 5 , DRW 6 , DRW 7 , and DRW 8 . Hereinafter, in a case where there is no need to make a particular distinction, the servo pattern reading elements SR 1  and SR 2  are collectively denoted as a servo pattern reading element SR, and the data elements DRW 1  to DRW 8  are collectively denoted as a data element DRW. 
     The servo pattern reading element SR 1  is provided at a position corresponding to the servo band SB 1 , and the servo pattern reading element SR 2  is provided at a position corresponding to the servo band SB 2 . The data elements DRW 1  to DRW 8  are provided between the servo pattern reading elements SR 1  and SR 2 . The data elements DRW 1  to DRW 8  are arranged at equal intervals along the width direction WD of the magnetic tape  12 . The data elements DRW 1  to DRW 8  simultaneously record data and/or read data with respect to eight data tracks DT 1 , DT 2 , DT 3 , DT 4 , DT 5 , DT 6 , DT 7 , and DT 8 . 
     As shown in  FIG.  8    as an example, the data element DRW 1  is in charge of recording data on a data track group DTG 1  composed of a total of  12  data tracks DT, that is, data tracks DT 1 _ 1 , DT 1 _ 2 , DT 1 _ 3 , DT 1 _ 4 , ..., DT 1 _ 11 , and DT 1 _ 12 . In addition, the data element DRW 1  is in charge of reading data recorded on the data track group DTG 1 . Similarly, the data element DRW 2  is in charge of recording data on a data track group DTG 2 , which is composed of data tracks DT 2 _ 1  to DT 2 _ 12 , and of reading data recorded on the data track group DTG 2 . Hereinafter, similarly, the data element DRW 8  is in charge of recording data on a data track group DTG 8 , which is composed of data tracks DT 8 _ 1  to DT 8 _ 12 , and of reading data recorded on the data track group DTG 8 . Twelve data tracks DT constituting each of the data track groups DTG 1  to DTG 8  are arranged at equal intervals along the width direction WD of the magnetic tape  12 . The number of data tracks DT included in one data band DB is 8 × 12 = 96. In a case where there is no need to make a particular distinction, the data tracks DT 1  to DT 8  are collectively denoted as a data track DT. 
     The data element DRW is shifted to a position corresponding to one designated data track DT out of  12  data tracks with the movement of the magnetic head  28  in the width direction WD performed by the moving mechanism  40 . The data element DRW stays at a position corresponding to one designated data track DT through the servo control using the servo pattern  50 . 
     As shown in the enlarged view of  FIG.  9   , the data element DRW includes a data recording element DW and a data reading element DR. The data recording element DW records data on the data track DT. The data reading element DR reads the data recorded on the data track DT. 
     The data recording element DW is disposed on an upstream side of the feed direction FWD, and the data reading element DR is disposed on a downstream side of the feed direction FWD. The reason for such a disposition is that the data reading element DR immediately reads the data recorded by the data recording element DW to check errors in a case where the magnetic tape  12  is running in the feed direction FWD. 
     As shown in  FIG.  10    as an example, the control unit  30  is realized by, for example, a computer including a central processing unit (CPU)  65 , a memory  66 , and a storage  67 . The memory  66  is, for example, a random access memory (RAM) or the like and temporarily stores various types of information. The storage  67 , which is a non-transitory storage medium, is, for example, a hard disk drive or a solid state drive and stores various parameters and various programs. The CPU  65  loads the program stored in the storage  67  into the memory and executes processing in accordance with the program, thereby controlling the operation of each unit of the magnetic tape device  10  in an integrated manner. The CPU  65  is an example of the “processor” according to the technology of the present disclosure. 
     In  FIG.  11   , the CPU  65  executes an operation program  69  stored in the storage  67  to function as a running control unit  70 , a position detection unit  71 , a servo control unit  72 , a position adjustment control unit  73 , a data acquisition unit  74 , a recording control unit  75 , a read control unit  76 , and a data output unit  77 . 
     The running control unit  70  controls the drive of the feeding motor  25  and the winding motor  26  to cause the magnetic tape  12  to run in the feed direction FWD or the rewind direction BWD. Further, the running control unit  70  adjusts the rotational speed and the rotational torque of the feeding motor  25  and the winding motor  26  to adjust the tension during running and the running speed of the magnetic tape  12  to appropriate values. 
     A servo signal based on the servo pattern  50  read by the servo pattern reading element SR of the magnetic head  28  is input to the position detection unit  71 . The servo signal is intermittent pulses corresponding to the magnetization regions  51 A and  51 B. The position detection unit  71  detects the position of the servo pattern reading element SR in the servo band SB in the width direction WD, that is, the position of the magnetic head  28  in the width direction WD with respect to the magnetic tape  12 , on the basis of a pulse interval of the servo signal. The position detection unit  71  outputs the detection result of the position of the magnetic head  28  in the width direction WD to the servo control unit  72 . 
     Two types of servo signals based on the servo patterns  50  read by two servo pattern reading elements SR are input to the position detection unit  71 . The position detection unit  71  calculates the average value of the pulse intervals of two types of servo signals. Then, the position detection unit  71  detects the position of the magnetic head  28  in the width direction WD, on the basis of the calculated average value. 
     The servo control unit  72  compares the detection result of the position of the magnetic head  28  from the position detection unit  71  with a target position of the magnetic head  28 . In a case where the detection result is the same as the target position, the servo control unit  72  does nothing. In a case where the detection result is displaced from the target position, the servo control unit  72  outputs a servo control signal for making the position of the magnetic head  28  match the target position, to the moving mechanism  40 . The moving mechanism  40  operates so as to make the position of the magnetic head  28  match the target position according to the servo control signal. The target position is stored in the storage  67 , for example, in the form of a data table in which the values corresponding to the respective data tracks DT 1  to DT 8  are registered. 
     The position adjustment control unit  73  reads out the variation profile data  80  from the storage  67 . The variation profile data  80  is data representing variations of the magnetic tape  12  in the normal direction ND. The position adjustment control unit  73  controls the operation of the piezoelectric bimorph element  56  by outputting a position adjustment control signal based on the variation profile data  80  to the piezoelectric bimorph element  56 . Specifically, the position adjustment control signal is a signal for designating a voltage to be applied to the piezoelectric bimorph element  56 . 
     The data acquisition unit  74  reads out and acquires data to be recorded on the data band DB 1  or DB 2  by the magnetic head  28  from, for example, a host computer (not shown) connected to the magnetic tape device  10 . The data acquisition unit  74  outputs the data to the recording control unit  75 . 
     The recording control unit  75  encodes the data output from the data acquisition unit  74  into a digital signal for recording. Then, the recording control unit  75  causes a pulse current corresponding to the digital signal to flow into the data recording element DW of the magnetic head  28 , and causes the data recording element DW to record the data on the designated data track DT of the data band DB 1  or DB 2 . 
     The read control unit  76  controls the operation of the data reading element DR of the magnetic head  28  to cause the data reading element DR to read the data recorded on the designated data track DT of the data band DB 1  or DB 2 . The data read by the data reading element DR is a pulse-shaped digital signal. The read control unit  76  outputs this pulse-shaped digital signal to the data output unit  77 . 
     The data output unit  77  decodes the pulse-shaped digital signal output from the read control unit  76  to obtain data. The data output unit  77  outputs the data to, for example, the host computer. 
     As shown in  FIG.  12   , the variation profile data  80  is data in which an amount of displacement corresponding to a position of the magnetic tape  12  in the length direction (denoted as a magnetic tape position in  FIG.  12   ) is registered. The amount of displacement is an amount of displacement of the magnetic tape  12  from the regular position. The position of the magnetic tape  12  in the length direction is specified by, for example, the servo pattern  50 . The amount of displacement of the magnetic tape  12  from the regular position is set as a positive value in a case where the position of the magnetic tape  12  is displaced in the direction of the magnetic head  28  from the regular position, and is set as a negative value in a case where the position of the magnetic tape  12  is displaced in a direction opposite to the magnetic head  28  from the regular position. The position adjustment control unit  73  outputs, to the piezoelectric bimorph element  56 , the position adjustment control signal of a content that the amount of displacement of the magnetic tape  12  from the regular position is offset by adjusting the position of the magnetic element ME in the normal direction ND. 
     The variation profile data  80  is acquired by a test run of the magnetic tape  12  in the feed direction FWD prior to recording data on the magnetic layer  16  and/or reading data recorded on the magnetic layer  16 . The amount of displacement of the magnetic tape  12  from the regular position is converted from the measurement result of the distance sensor  39  attached to the support member  29 A on the distance to the front surface  18  of the magnetic tape  12 . The magnetic tape  12  is caused to test run by bringing the magnetic element ME into contact with the magnetic layer  16 , and a voltage generated in the piezoelectric bimorph element  56  according to the variation of the position of the magnetic tape  12  is measured, whereby the amount of displacement of the magnetic tape  12  from the regular position may be converted from the measurement result of the voltage. Alternatively, the amount of displacement of the magnetic tape  12  from the regular position may be converted from the strength of the magnetic field of the magnetic tape  12  sensed by the magnetic element ME. 
     In a case where the cartridge  11  is of an irreplaceable type installed in the magnetic tape device  10 , the variation profile data  80  is acquired at the factory at the time of shipment of the magnetic tape device  10 . In a case where the cartridge  11  is of a replaceable type, the variation profile data  80  is acquired when the cartridge  11  is first loaded. 
     The variation profile data  80  may be acquired in two types, one for the feed direction FWD and the other for the rewind direction BWD, by causing the magnetic tape  12  to test run not only in the feed direction FWD but also in the rewind direction BWD. In addition, the variation profile data  80  may be used without being updated once the variation profile data  80  has been acquired, or may be updated periodically. Further, the variation profile data  80  may be corrected in consideration of variation factors of the temporal spacing SP, such as aged deterioration of the magnetic tape  12  and/or the magnetic element ME. Further, the variation profile data  80  may be corrected in consideration of variation factors of the spacing SP of the ambient environment, such as thermal deformation of the magnetic tape  12  and/or the magnetic element ME. Furthermore, in a case where the cartridge  11  is replaceable, the variation profile data  80  may be stored in a radio frequency (RF) tag incorporated in the cartridge  11 , instead of the storage  67 . The variation profile data  80  may be predicted by simulation or derived using a machine learning model. 
     Hereinafter, the action of the above-described configuration will be described with reference to the flowchart of  FIG.  13   . First, under the control of the running control unit  70 , the feeding motor  25  and the winding motor  26  are operated, and the magnetic tape  12  runs in the feed direction FWD or the rewind direction BWD. With this, as shown in  FIG.  2   , the magnetic tape  12  runs while the front surface  18  of the magnetic tape  12  is slid on the sliding surfaces  38 A and  38 B of the support members  29 A and  29 B. 
     As shown in  FIGS.  6 A to  6 C  and the like, the position adjustment control unit  73  controls the operation of the piezoelectric bimorph element  56  on the basis of the variation profile data  80  to move the magnetic head  28 , thereby adjusting the position of the magnetic element ME in the normal direction ND (step ST 100 ). 
     Then, the magnetic element ME is caused to act on the magnetic layer  16  of the magnetic tape  12  (step ST 110 ). Specifically, the servo pattern  50  is read by the servo pattern reading element SR. Further, data is recorded on the data track DT by the data recording element DW under the control of the recording control unit  75 . Furthermore, the data recorded on the data track DT is read by the data reading element DR under the control of the read control unit  76 . 
     The position detection unit  71  detects the position of the magnetic head  28  in the width direction WD from the interval of the servo signals based on the servo patterns  50 . The servo control unit  72  compares the detection result of the position of the position detection unit  71  with the target position, and performs the servo control for making the position of the magnetic head  28  match the target position. 
     As described above, the magnetic tape device  10  comprises the magnetic head  28 , the piezoelectric bimorph element  56 , and the CPU  65 . The magnetic head  28  has the magnetic element ME that acts on the magnetic layer  16  formed on the front surface  18  of the magnetic tape  12 . The piezoelectric bimorph element  56  adjusts the position of the magnetic element ME in the normal direction ND of the front surface  18  of the magnetic tape  12  by moving the magnetic head  28 . The position adjustment control unit  73  of the CPU  65  controls the operation of the piezoelectric bimorph element  56 . Therefore, the position of the magnetic element ME in the normal direction ND can be adjusted. Accordingly, it is possible to maintain the positional relationship between the magnetic layer  16  and the magnetic element ME in the normal direction ND, that is, the spacing SP in this example. 
     As shown in  FIG.  2   , the magnetic head  28  causes the magnetic element ME to act in proximity to the magnetic layer  16 . In this case, maintaining the spacing SP is essential for stabilizing recording and/or reading data. For this reason, in a case where the magnetic element ME is caused to act in proximity to the magnetic layer  16 , the usefulness of the technology of the present disclosure is high as compared with a case where the magnetic element ME acts by coming into contact with the magnetic layer  16 . 
     As shown in  FIG.  3   , the width W_H of the magnetic head  28  is smaller than the width W_T of the magnetic tape  12 . Since the weight is lighter than that of a magnetic head having a width W_H equal to or more than the width W_T, the response speed of the movement in the width direction WD in the servo control and the response speed of the movement in the normal direction ND in the position adjustment control are high. Therefore, good followability can be obtained in the servo control and the position adjustment control. 
     Here, in the conventional magnetic head for a hard disk drive, a method (TFC; thermal flying-height control) of maintaining the spacing SP through thermal expansion or thermal contraction of the magnetic element ME has been employed. However, the amount of variation of the magnetic element ME using heat is at most several nm. Meanwhile, in this example, the piezoelectric element, particularly the piezoelectric bimorph element  56 , is used as the position adjusting actuator. In the piezoelectric bimorph element  56 , the bending amount ΔL is on the order of several µm, as obtained by Equation (1). Therefore, it is possible to sufficiently respond to the positional variation of the magnetic tape  12  in the normal direction ND on the order of several tens of nm to several µm. 
     As shown in  FIGS.  11  and  12   , the position adjustment control unit  73  controls the operation of the piezoelectric bimorph element  56  on the basis of the variation profile data  80  representing the variation of the magnetic tape  12  in the normal direction ND. Therefore, it is possible to easily and reliably maintain the positional relationship between the magnetic layer  16  and the magnetic element ME in the normal direction ND, as compared with a case where the variation of the magnetic tape  12  in the normal direction ND is measured in real time and the operation of the piezoelectric bimorph element  56  is controlled on the basis of the measurement result. The variation of the magnetic tape  12  in the normal direction ND may be measured in real time without referring to the variation profile data  80 , and the operation of the piezoelectric bimorph element  56  may be controlled on the basis of the measurement result. 
     As shown in  FIG.  2   , the magnetic tape device  10  comprises the pair of support members  29 A and  29 B disposed on both sides of the magnetic tape  12  in the running direction with the magnetic head  28  interposed therebetween. The front surface  18  of the magnetic tape  12  is slid on the support members  29 A and  29 B. Therefore, the variation of the magnetic tape  12  in the normal direction ND can be suppressed, and the adjustment of the position of the magnetic element ME in the normal direction ND performed by the piezoelectric bimorph element  56  can be minimized. Further, even in a case where foreign matter is generated because of, for example, scrapes of the magnetic layer  16  caused by contact between the magnetic element ME and the magnetic layer  16 , the foreign matter falls between the support members  29 A and  29 B while the magnetic tape  12  is running. Therefore, the effect of removing the foreign matter can also be expected. 
     As shown in  FIG.  7   , the magnetic head  28  has, as the magnetic element ME, the data element DRW that acts on the data band DB and the servo pattern reading element SR that reads the servo pattern  50 . As shown in  FIG.  9   , the data element DRW includes the data recording element DW that records data on the magnetic layer  16  and the data reading element DR that reads the data recorded on the magnetic layer  16 . Therefore, it is possible to smoothly perform the reading of the servo pattern  50 , and the data recording and the data reading. The data element DRW may be any one of the data recording element DW or the data reading element DR. 
     The position adjusting actuator and the piezoelectric element are not limited to the illustrated piezoelectric bimorph element  56 . A laminated piezoelectric element  92  shown in  FIGS.  14  and  15    may be used. 
     In  FIG.  14   , a suspension  90  has a load beam  91 , the laminated piezoelectric element  92 , a flexure  93 , and the like. A notch  94  is formed at a distal end of the load beam  91 , and the laminated piezoelectric element  92  is accommodated in the notch  94 . The laminated piezoelectric element  92  has a configuration in which a plurality of piezoelectric bodies  95  are laminated, and expands and contracts in a thickness direction by a voltage applied. One end of the laminated piezoelectric element  92  in the thickness direction is fixed to the distal end of the load beam  91 , and the other end thereof is fixed to a distal end of the flexure  93 . The magnetic head  28  is attached to a surface of the flexure  93  opposing a surface to which the laminated piezoelectric element  92  is attached. 
     As shown in  FIGS.  15 A and  15 B , the laminated piezoelectric element  92  bends the distal end of the flexure  93  with the expansion and contraction in the thickness direction to move the magnetic head  28 , thereby adjusting the position of the magnetic element ME in the normal direction ND. The laminated piezoelectric element  92  operates so as to keep the spacing SP constant under the control of the control unit  30 , as in the piezoelectric bimorph element  56 . Specifically, in a case where the position of the magnetic tape  12  is displaced in the direction of the magnetic head  28  from the regular position shown in  FIG.  14   , the laminated piezoelectric element  92  contracts in the thickness direction as shown in  FIG.  15 A . On the other hand, in a case where the position of the magnetic tape  12  is displaced in the direction opposite to the magnetic head  28  from the regular position shown in  FIG.  14   , the laminated piezoelectric element  92  expands in the thickness direction as shown in  FIG.  15 B . In this way, even with the laminated piezoelectric element  92 , it is possible to adjust the position of the magnetic element ME in the normal direction ND, and it is possible to maintain the positional relationship between the magnetic layer  16  and the magnetic element ME in the normal direction ND. 
     As the position adjusting actuator, in addition to the piezoelectric element, bimetal in which two metal plates having different thermal expansion factors are bonded to each other, a shape memory alloy, or the like may be used. 
     The aspect in which the magnetic element ME is caused to act in proximity to the magnetic layer  16  has been illustrated, but the technology of the present disclosure is not limited thereto. The magnetic element ME may act by coming into contact with the magnetic layer  16 . However, it is preferable to employ the aspect in which the magnetic element ME is caused to act in proximity to the magnetic layer  16  because the magnetic layer  16  is scraped off to generate foreign matter or the magnetic element ME is worn by an abrasive prescribed for the magnetic layer  16 , in a case where the magnetic element ME is brought into contact with the magnetic layer  16 . 
     The number of servo bands SB, the number of data bands DB, the number of data elements DRW, the number of data tracks DT that one data element DRW is in charge of, and the like shown above are merely an example, and the technology of the present disclosure is not particularly limited thereto. 
     For example, a magnetic tape in which five servo bands SB and four data bands DB are alternately arranged along the width direction WD may be used. Further, a magnetic tape in which nine servo bands SB and eight data bands DB are alternately arranged along the width direction WD may be used. Alternatively, a magnetic tape in which 13 servo bands SB and 12 data bands DB are alternately arranged along the width direction WD may be used. 
     One magnetic head  28  is shared between the feed direction FWD and the rewind direction BWD, but a magnetic head for the feed direction FWD (hereinafter, referred to as a feed head) and a magnetic head for the rewind direction BWD (hereinafter, referred to as a rewind head) may be provided. In this case, the magnetic element ME of the feed head performs, for example, the reading of the servo patterns  50  of the servo bands SB 1  and SB 2  and the recording of data on the data band DB 1  and/or the reading of data recorded on the data band DB 1 , and the magnetic element ME of the rewind head performs, for example, the reading of the servo patterns  50  of the servo bands SB 2  and SB 3  and the recording of data on the data band DB 2  and/or the reading of data recorded on the data band DB 2 . 
     The number of servo pattern reading elements SR disposed in one magnetic head may be one. Similarly, the number of data elements DRW disposed in one magnetic head may be one. 
     The number of data elements DRW disposed in one magnetic head may be, for example, 16, 32, or 64. Further, the number of data tracks DT that one data element DRW is in charge of for data recording and/or data reading is not limited to 12 illustrated above. The number of data tracks DT may be 1 or, for example, 4, 16, 32, or 64. 
     A pair of support rollers may be used instead of the pair of support members  29 A and  29 B. 
     The magnetic tape device  10  in which the cartridge  11  is loaded has been illustrated, but the technology of the present disclosure is not limited thereto. The magnetic tape  12  as it is in which the cartridge  11  is not accommodated may be a magnetic tape device wound on a feed reel, that is, a magnetic tape device in which the magnetic tape  12  is irreplaceably installed. 
     The magnetic tape  12  is not limited to the magnetic tape having the magnetic layer  16  containing ferromagnetic powder illustrated above. A magnetic tape in which a ferromagnetic thin film is formed by vacuum deposition, such as sputtering, may be used. 
     The computer constituting the control unit  30  may include, for example, a programmable logic device (PLD) which is a processor whose circuit configuration is changeable after manufacture, such as a field-programmable gate array (FPGA), and/or a dedicated electrical circuit which is a processor having a dedicated circuit configuration designed to execute specific processing, such as an application specific integrated circuit (ASIC), in place of or in addition to the CPU  65 . 
     The technology of the present disclosure can also appropriately combine the above-mentioned various embodiments and/or various modification examples. In addition, it goes without saying that the technology of the present disclosure is not limited to the above embodiments and various configurations may be employed without departing from the gist thereof. Furthermore, the technology of the present disclosure extends to a storage medium having the program non-transitorily stored thereon, in addition to the program. 
     The contents described and shown above are detailed descriptions of the parts related to the technology of the present disclosure, and are merely an example of the technology of the present disclosure. For example, the descriptions of the above configurations, functions, actions, and effects are the descriptions of an example of the configurations, functions, actions, and effects of the parts related to the technology of the present disclosure. Accordingly, it is needless to say that unnecessary parts may be deleted, new elements may be added, or replacements may be made with respect to the contents described and shown above, without departing from the gist of the technology of the present disclosure. Further, in order to avoid complications and facilitate understanding of the parts related to the technology of the present disclosure, descriptions of common general knowledge and the like that do not require special descriptions for enabling the implementation of the technology of the present disclosure are omitted, in the contents described and shown above. 
     In the present specification, “A and/or B” has the same meaning as “at least one of A or B”. That is, “A and/or B” means that only A may be used, only B may be used, or a combination of A and B may be used. In addition, in the present specification, the same concept as “A and/or B” is also applied to a case where three or more matters are expressed by “and/or”. 
     All documents, patent applications, and technical standards described in the present specification are incorporated in the present specification by reference to the same extent as in a case where the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference.