Abstract:
A rotary head apparatus includes a rotary drum having two magnetic heads mounted thereon. Each magnetic head has a recording-medium opposing surface curved in two convex shapes extending towards the outside of the drum, one along the longitudinal cross section of the magnetic head extending across the centerline laterally dividing the magnetic head into two parts so as to be orthogonal to the sliding direction of the recording medium, and the other along the lateral cross section orthogonal to the centerline. The apex of the lateral cross section is gradually displaced from the centerline as distancing itself from the center of the surface in the longitudinal direction and in the opposite direction to the above displacement as distancing itself from the center in the reverse longitudinal direction. Each displacement of the apex laterally away from the centerline in a sliding area of the recording medium is at most 2 μm.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a rotary head apparatus including at least one magnetic head and a magnetic playback apparatus using the same, and more particularly, the present invention relates to a rotary head which includes at least one magnetic head, with which a recording medium is unlikely scraped, and which prevents a decrease in output and deterioration in an error-detection characteristic due to a spacing loss caused by a deposition produced when the recording medium is scraped, and also relates to a magnetic playback apparatus using the same. 
   2. Description of the Related Art 
   In some of magnetic recording and playback apparatuses for use in video equipment or for saving computer data, a rotary head apparatus includes a rotary drum having at least one magnetic head mounted thereon, and when a magnetic tape runs while keeping in contact with the rotary drum along a helical trajectory, and the rotary drum rotates, data is recorded into and played back from the magnetic tape by the helical scanning method. 
     FIG. 8  is a plan view of a rotary head apparatus having magnetic heads mounted thereon and disposed in a magnetic recording and playback apparatus.  FIG. 9  is a perspective view of an example magnetic head mounted on the rotary head apparatus.  FIG. 10A  is a plan view of the magnetic head shown in  FIG. 9 , and viewed from the Z 1  direction indicated in FIG.  9  and rotated clockwise by 90 degrees, and  FIGS. 10B  to  10 D are illustrations respectively taken along the lines XB—XB, XC—XC, and XD—XD and viewed from the arrow X indicated in FIG.  10 A.  FIG. 11  is a partially magnified view illustrating a state in which a magnetic tape lies in contact with the rotary head apparatus shown in FIG.  8 .  FIG. 12  is a plan view of the magnetic head shown in FIG.  9  and viewed from the Y 2  direction indicated in FIG.  9 . 
   In a rotary head apparatus  1  shown in  FIG. 8 , a stationery drum (not shown) is fixed, and a rotary drum  1   a  is rotatably supported on the stationery drum so as to be coaxial therewith and is driven to rotate by a motor power in an upper-arrow direction indicated in the figure. A magnetic tape T serving as a recording medium is wound around the rotary head apparatus  1  by a predetermined angle along a helical trajectory and runs in a lower-arrow direction indicated in the figure. All the while, the rotary drum  1   a  rotates, and magnetic heads H 1   a  and H 1   b  mounted on the rotary drum  1   a  scan the magnetic tape T. In the rotary head apparatus  1 , a couple of the magnetic playback heads H 1   a  and H 1   b  are disposed so as to face each other. 
   The magnetic head H 1   a  shown in  FIG. 9  is formed by a base member  2  composed of an alumina titanium carbide; a playback-use, magnetic-resonance-type (MR-type) thin-film magnetic head  3 ; an insulating layer  4  serving as a protecting layer, both formed by a thin film forming process; and a protecting base member  5  composed of an alumina titanium carbide and bonded on the insulating layer  4  by adhering means (not shown) such as an epoxy adhesive. 
   A magnetic gap  6  of the MR-type thin-film magnetic head  3  is exposed to a magnetic-tape opposing surface (surface facing toward Y 2  in the figure) H 1   a A of the magnetic head H 1   a . The MR-type thin-film magnetic head  3  is supplied with current through electrodes  7 . 
   The magnetic head H 1   a  mounted on the rotary drum  1   a  abuts against the magnetic tape T in a state shown in FIG.  11 . Meanwhile, the X 1  and X 2  directions in  FIG. 11  indicate the rotating direction of the rotary drum  1   a  and the longitudinal direction serving as the sliding direction of the magnetic tape T, respectively. 
   As shown in  FIG. 10A , the magnetic head H 1   a  is shaped in a convex arc having a radius of curvature R, along the longitudinal direction serving as the sliding direction of the magnetic tape T. Also, as shown in  FIG. 10B , the magnetic head H 1   a  is shaped in a convex arc having a radius of curvature r, along the lateral direction (Z 1 -Z 2  direction indicated in  FIG. 9 ) perpendicular to the sliding direction of the magnetic tape T. 
   Since the recoding and playback apparatus is of a so-called helical scanning type, as shown in  FIG. 12 , the magnetic gap  6  of the MR-type thin-film magnetic head  3  disposed in the magnetic head H 1   a  is slanted at an azimuth having an angle θ corresponding to the helical trajectory. 
   Right and left edges  8  and  9  of the tape-opposing surface H 1   a A are also slanted at the same angle as that of the azimuth of the magnetic gap  6 . An acute angular corner  12  formed by the right edge  8  and an upper edge  10  lies further outwards in the longitudinal direction than a corner  13  formed by the right edge  8  and a lower edge  11 , and a corner  14  formed by the left edge  9  and the upper edge  10  lies further inwards in the longitudinal direction than an acute angular corner  15  formed by the left edge  9  and the lower edge  11 . Thus, the plane figure of the opposing surface H 1   a A viewed from the magnetic tape (from the Y 2  side in  FIG. 9 ) is a parallelogram as shown in FIG.  12 . 
   The magnetic head H 1   b  has the same structure as that of the magnetic head H 1   a . However, since the magnetic head H 1   b  is provided with an azimuth in the opposite direction to the magnetic head H 1   a , the plane figure of an opposing surface H 1   b A of the magnetic head H 1   b  viewed from the magnetic tape is a parallelogram slanted in the opposite direction to the magnetic head H 1   a.    
   A hatched area in  FIG. 12  indicates a magnetic-tape sliding area of the opposing surface H 1   a A in a state in which the magnetic head H 1   a  is mounted on the rotary drum  1   a  and the magnetic tape slides on the opposing surface H 1   a A. The X 1  direction in  FIG. 12  indicates the longitudinal direction serving as the sliding direction of the magnetic tape T. 
   Japanese Unexamined Utility Model Application Publication No. 62-018812 has disclosed a magnetic head shaped in two convex arcs, one having the curvature of radius R along the sliding direction of a magnetic, and the other having the curvature of radius r along a direction perpendicular to the sliding direction. 
   As mentioned previously, the magnetic head H 1   a  is formed such that the plane figure of the opposing surface H 1   a A viewed from the magnetic tape is a parallelogram. Accordingly, when the opposing surface H 1   a A is shaped in a convex arc having the curvature of radius r along the lateral direction, the apex of the convex arc having the curvature of radius r is likely formed toward the acute angular corners  12  and  15 ; as a result, a continuous line PL 1  formed by the apex becomes a curve extending towards the acute angular corners  12  and  15 , as shown by a dotted line in FIG.  12 . 
   That is, in an area from the magnetic gap  6  to the right edge  8 , as the apex of the convex arc having the curvature of radius r comes closer to the acute angular corner  12 , the apex is displaced further away from the center line O—O laterally dividing the opposing surface H 1   a A into two parts, towards the upper edge  10 , and, on the right edge  8 , the apex is formed at substantially the same position as the acute angular corner  12 . 
   For example, as shown in  FIG. 10B , in the illustration taken along the center line XB—XB longitudinally dividing the magnetic head H 1   a  into two parts and viewed from the X direction, the apex P 1  lies on substantially the same line as the center line XB—XB. Also, as shown in  FIG. 10C , in the illustration taken along the line XC—XC lying closer to the right edge  8  than the center line XB—XB and viewed from the X direction, the apex P 2  lies at a position displaced away from the center line O—O towards the upper edge  10 . 
   Meanwhile, in an area from the magnetic gap  6  to the left edge  9 , as the apex of the convex arc having the curvature of radius r comes closer to the acute angular corner  15 , the apex is displaced further away from the center line O—O towards the lower edge  11 , and, on the left edge  19 , the apex is formed at substantially the same position as the acute angular corner  15 . 
   For example, as shown in  FIG. 10D , in the illustration taken along the line XD—XD lying closer to the left edge  9  than the center line XB—XB and viewed from the X direction, the apex P 3  lies at a position displaced away from the center line O—O towards the lower edge  11 . 
   Meanwhile, since the magnetic head H 1   b  is provided with an azimuth in an opposite direction to the magnetic head H 1   a , the displacement of the continuous line PL 1  away from the center line O—O is symmetrical to the magnetic head H 1   a  with respect to the center line O—O. 
   Accordingly, when the magnetic tape T comes into contact with and slides on the magnetic-tape sliding area of the opposing surface H 1   a A, in two areas L 1  where the continuous line PL 1  is displaced away from the center line O—O, the continuous line PL 1  abuts against the magnetic tape T while having an angle generated in accordance with the displacement away from the center line O—O, thereby causing the continuous line PL 1  to generate a sliding resistance against the magnetic tape T and resultantly scraping magnetic powder applied on the magnetic tape T. The scraped magnetic powder is conveyed to the magnetic gap  6  associated with the running of the magnetic tape T and is deposited between the magnetic tape T and the MR-type thin-film magnetic head  3  disposed in the magnetic gap  6 . When the magnetic powder is deposited as mentioned above, a so-called spacing loss occurs, thereby leading to a reduced output. As a result, a servo characteristic deteriorates, for example, a servo mechanism becomes unstable, and an error is unlikely detected. This applies also to the magnetic head H 1   b.    
   Especially when the magnetic tape T is stopped and scanned, for example, for playing back a still picture, the magnetic powder of the magnetic tape T is likely scraped. 
   SUMMARY OF THE INVENTION 
   The present invention has been made so as to solve the above-mentioned problems. Accordingly, it is an object of the present invention to provide a recording and playback apparatus in which a recording medium such as a magnetic tape is unlikely scraped, a decrease in output and deterioration in a servo characteristic due to a spacing loss are unlikely to occur, and an error is easily detected. 
   A rotary head apparatus according to the present invention includes a rotary drum whose outer circumferential surface serves as a sliding surface relative to a recording medium; and at least one magnetic head lying on the sliding surface of the rotary drum. The magnetic head includes base members juxtaposed along a sliding direction relative to the recording medium; and a playback magnetic element disposed between the base members and slanted at a predetermined azimuth angle with respect to the sliding direction. A recording-medium opposing surface of the magnetic head is wider in a longitudinal direction serving as the sliding direction than in a lateral direction perpendicular to the longitudinal direction. The opposing surface is curved in two convex shapes extending towards the outside of the rotary drum, one along the longitudinal cross section of the magnetic head extending across the center line of the magnetic head laterally dividing the magnetic head into two parts, and the other along the lateral cross section of the magnetic head orthogonal to the center line. Also, the opposing surface is formed such that the apex of the lateral cross section is gradually displaced from the center line as distancing itself from the center of the opposing surface in the longitudinal direction and is gradually displaced from the center line in the opposite direction to the above displacement as distancing itself from the center in the reverse longitudinal direction. In addition, the opposing surface is formed such that the two displacements of the apex laterally away from the center line in the sliding area of the opposing surface with the recording medium are respectively at most 2 μm. 
   In the rotary head apparatus according to the present invention, the recording-medium opposing surface of the magnetic head is curved in two convex shapes extending towards the outside of the rotary drum, one along the longitudinal cross section extending across the center line laterally dividing the magnetic head into two parts so as to be orthogonal to the longitudinal direction in which the recording medium slides, the other along the lateral cross section orthogonal to the center line. Also, the apex of the lateral cross section is gradually displaced from the center line as distancing itself from the center of the opposing surface in the longitudinal direction and is gradually displaced from the center line in the opposite direction to the above displacement as distancing itself from the center in the reverse longitudinal direction. In addition, the opposing surface is formed such that the two displacements of the apex laterally away from the center line in the sliding area of the opposing surface with the recording medium are respectively at most 2 μm. With this structure, when the recording medium abuts against and slides on the opposing surface, since the displacements of the apex from the center line are very small in the sliding area, a sliding resistance of the apex exerted on the recording medium in the area where the displacement occurs can be reduced; as a result, the surface of the recording medium is unlikely scraped. Hence, the amount of a part of a scraped portion of the recording medium, deposited between the recording medium and the playback magnetic element, can be decreased, thereby preventing a so-called spacing loss and a decrease in output. Accordingly, deterioration in a servo characteristic is prevented, an error is easily detected, and deterioration in an error-detection characteristic is also prevented. 
   In this case, the rotary head apparatus may have a structure in which the opposing surface has a pair of long sides extending in the longitudinal direction and being parallel to each other; a pair of short sides slanted at the same angle as the azimuth angle and being parallel to each other; and a pair of acute angular corners formed by the long sides and the short sides, and also in which the apex is displaced from the center line and comes closer to either of the corners as distancing itself from the center of the opposing surface. 
   When the opposing surface has the pair of short sides slanted at the same angle as the azimuth angle and being parallel to each other, the apex is likely to come closer to either of the two corners and to be displaced away from the center line as distancing itself from the center of the opposing surface. Even in this case, the displacement of the apex away from the center line can be made very small, thereby preventing a decrease in output. 
   Also, a magnetic playback apparatus according to the present invention includes the rotary head apparatus according to the present invention. When the recording medium is wound around the circumferential surface of the rotary drum by a predetermined angle, and the rotary drum of the rotary head apparatus is driven to rotate, the magnetic head slides on the recording medium as the recording medium moves in the longitudinal direction, and the magnetic head thus reads magnetic information at least recorded in the recording medium. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of a rotary head apparatus an embodiment of the present invention; 
       FIG. 2  is a perspective view of an example magnetic head mounted on the rotary head apparatus shown in  FIG. 1 ; 
       FIG. 3A  is a plan view of the magnetic head shown in  FIG. 2 , viewed from the Z 1  direction indicated in FIG.  2  and rotated clockwise by 90 degrees, and  FIGS. 3B  to  3 D are illustrations respectively taken along the lines IIIB—IIIB, IIIC—IIIC, and IIID—IIID and viewed from the arrow X indicated in  FIG. 3A ; 
       FIG. 4  is a partially magnified view illustrating a state in which a magnetic tape lies in contact with the rotary head apparatus shown in  FIG. 1 ; 
       FIG. 5  is a plan view of the magnetic head shown in FIG.  2  and viewed from the Y 2  direction indicated in  FIG. 2 ; 
       FIG. 6  is a table illustrating the relationship between length of an opposing surface and displacement of an apex of each magnetic head; 
       FIG. 7  is a graph based on the data in  FIG. 6 ; 
       FIG. 8  is a plan view of a known rotary head apparatus; 
       FIG. 9  is a perspective view of an example magnetic head mounted on the rotary head apparatus shown in  FIG. 8 ; 
       FIG. 10A  is a plan view of the magnetic head shown in  FIG. 8 , viewed from the Z 1  direction indicated in FIG.  9  and rotated clockwise by 90 degrees, and  FIGS. 10B  to  10 D are illustrations respectively taken along the lines XB—XB, XC—XC, and XD—XD and viewed from the arrow X indicated in  FIG. 10A ; 
       FIG. 11  is a partially magnified view illustrating a state in which a magnetic tape lies in contact with the rotary head apparatus shown in  FIG. 8 ; and 
       FIG. 12  is a plan view of the magnetic head shown in FIG.  9  and viewed from the Y 2  direction indicated in FIG.  9 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a plan view of a rotary head apparatus having magnetic heads mounted thereon.  FIG. 2  is a perspective view of an example magnetic head mounted on the rotary head apparatus.  FIG. 3A  is a plan view of the magnetic head shown in  FIG. 2 , viewed from the Z 1  direction indicated in FIG.  2  and rotated clockwise by 90 degrees, and  FIGS. 3B  to  3 D are illustrations respectively taken along the lines IIIB—IIIB, IIIC—IIIC, and IIID—IIID and viewed from the arrow X indicated in FIG.  3 A.  FIG. 4  is a partially magnified view illustrating a state in which a magnetic tape lies in contact with the rotary head apparatus shown in FIG.  1 .  FIG. 5  is a plan view of the magnetic head shown in FIG.  2  and viewed from the Y 2  direction indicated in FIG.  2 . 
   A rotary head apparatus  100  shown in  FIG. 1  is mounted on a magnetic recording and playback apparatus for use in video equipment or on a magnetic playback apparatus such as a magnetic recording and playback apparatus for saving computer data. In the rotary head apparatus  100 , a stationery drum (not shown) is fixed, and a rotary drum  100   a  is rotatably supported on the stationery drum so as to be coaxial therewith and is driven to rotate by a motor power in an upper-arrow direction indicated in the figure. A magnetic tape T serving as a recording medium is wound around the rotary head apparatus  100  by a predetermined angle along a helical trajectory and runs in a lower-arrow direction indicated in the figure. All the while, the rotary drum  100   a  rotates and magnetic heads H 100   a  and H 100   b  mounted on the rotary drum  100   a  scan the magnetic tape T. In the rotary head apparatus  100 , a couple of the magnetic playback heads H 100   a  and H 100   b  are disposed so as to face each other. 
   The magnetic heads H 100   a  and H 100   b  are provided with azimuth angles in the opposite direction to each other. With this arrangement, of two recording tracks of the magnetic tape T having data recorded at the different azimuth angles, the magnetic head H 100   a  reads data in an R channel (Rch) recorded at one azimuth angle and the magnetic head H 100   b  reads data in an L channel (Lch) recorded at the other azimuth angle. 
   The magnetic head H 100   a  mounted on the rotary drum  100   a  abuts against the magnetic tape T in a state shown in FIG.  4 . Meanwhile, the X 1  and X 2  directions in  FIG. 4  indicate the rotating direction of the rotary drum  100   a  and the longitudinal direction serving as the sliding direction of the magnetic tape T, respectively. This applies also to the magnetic head H 100   b.    
   The magnetic head H 100   a  shown in  FIG. 2  is formed by a base member  112  composed of an alumina titanium carbide; a playback-use, MR-type thin-film magnetic head  113 ; an insulating layer  114  serving as a protecting layer, both formed by a thin film forming process; and a protecting base member  115  composed of an alumina titanium carbide and bonded on the insulating layer  114  by adhering means (not shown) such as an epoxy adhesive. 
   A magnetic gap  116  of the MR-type thin-film magnetic head  113  is exposed to a magnetic-tape opposing surface (surface facing toward Y 2  in the figure) H 100   a A of the magnetic head H 100   a . As shown in  FIG. 5 , the MR-type thin-film magnetic head  113  is disposed such that the center line laterally (i.e., towards the Z 1 -Z 2  direction in  FIG. 2 ) dividing the MR-type thin-film magnetic head  113  into two parts so as to be orthogonal to the longitudinal direction lies on the center line O—O laterally dividing the magnetic head H 100   a  into two parts. 
   The MR-type thin-film magnetic head  113  is supplied with current through electrodes  117 . 
   As shown in  FIG. 3A , the magnetic head H 100   a  is shaped in a convex arc having a radius of curvature R, along the longitudinal direction. Also, as shown in  FIG. 3B , the magnetic head H 100   a  is shaped in a convex arc having a radius of curvature r, along the lateral direction. 
   Since the rotary head apparatus is of a so-called helical scanning type, as shown in  FIG. 5 , the magnetic gap  116  of the MR-type thin-film magnetic head  113  disposed in the magnetic head H 100   a  is provided with an azimuth having an angle θ corresponding to the helical trajectory. 
   Right and left edges  118  and  119  of the tape-opposing surface H 100   a A are also slanted at the same angle as that of the azimuth of the magnetic gap  116 . An acute angular corner  122  formed by the right edge  118  and an upper edge  120  lies further outwards in the longitudinal direction than a corner  123  formed by the right edge  118  and a lower edge  121 , and a corner  124  formed by the left edge  119  and the upper edge  120  lies further inwards in the longitudinal direction than an acute angular corner  125  formed by the left edge  119  and the lower edge  121 . Thus, the plane figure of the opposing surface H 100   a A viewed from the magnetic tape (from the Y 2  side in  FIG. 2 ) is a parallelogram as shown in FIG.  5 . 
   A hatched area in  FIG. 5  indicates a first area  126  serving as a magnetic-tape sliding area of the opposing surface H 100   a A in a state in which the magnetic head H 100   a  is mounted on the rotary drum  100   a  and the magnetic tape slides on the opposing surface H 100   a A. Also, non-hatched area indicates second areas  127  where no magnetic tape slides. The X 1  direction in  FIG. 5  indicates the sliding direction of the magnetic tape T. 
   The magnetic head H 100   a  is formed such that the plane figure of the opposing surface H 100   a A viewed from the magnetic tape is a parallelogram. Accordingly, when the opposing surface H 100   a A is shaped in a convex arc having the curvature of radius r along the lateral direction, the apex of the convex arc having the curvature of radius r is likely formed towards the acute angular corners  122  and  125 ; as a result, a continuous line PL 2  formed by the apex becomes a curve extending towards the acute angular corners  122  and  125 , as shown by a dotted line in FIG.  5 . 
   That is, as shown in  FIG. 5 , in an area from the magnetic gap  116  to the right edge  118 , as the apex of the convex arc having the curvature of radius r comes closer to the acute angular corner  122 , the apex is displaced further away from the center line O—O laterally dividing the opposing surface H 100   a A into two parts, towards the upper edge  120 , and, on the right edge  118 , the apex is formed at substantially the same position as the acute angular corner  122 . 
   For example, as shown in  FIG. 3B , in the illustration taken along the center line IIIB—IIIB longitudinally dividing the magnetic head H 100   a  into two parts and viewed from the X direction, the apex denoted by P 10  lies on substantially the same line as the center line IIIB—IIIB. Also, as shown in  FIG. 3C , in the illustration taken along the line IIIC—IIIC lying closer to the right edge  118  than the center line IIIB—IIIB and viewed from the X direction, the apex denoted by P 20  lies at a position displaced away from the center line O—O towards the upper edge  120 . 
   Meanwhile, in an area of the opposing surface ranging from the magnetic gap  116  to the left edge  119 , as the apex of the convex arc having the curvature of radius r comes closer to the acute angular corner  125 , the apex is displaced further away from the center line O—O towards the lower edge  121 , and, on the left edge  119 , the apex is formed at substantially the same position as the acute angular corner  125 . 
   For example, as shown in  FIG. 3D , in the illustration taken along the line IIID—IIID lying closer to the left edge  119  than the center line IIIB—IIIB and viewed from the X direction, the apex denoted by P 30  lies at a position displaced away from the center line O—O towards the lower edge  121 . 
   As shown in  FIG. 5 , in the rotary head apparatus  100  including the rotary drum  110   a  having the magnetic head H 100   a  mounted thereon, the displacement m of the continuous line PL 2  relative to the center line O—O in the first area  126 , produced when the magnetic tape T slides on the opposing surface H 100   a A, is smaller than that in the second areas  127 . 
   Meanwhile, the magnetic head H 100   b  has the same structure as that of the magnetic head H 100   a . However, since the magnetic head H 100   b  is provided with an azimuth in the opposite direction to the magnetic head H 100   a , the plane figure of an opposing surface H 100   b A of the magnetic head H 100   b  viewed from the magnetic tape is a parallelogram slanted in the opposite direction to the magnetic head H 100   a . Also, the displacement of the continuous line PL 2  away from the center line O—O is symmetrical to the magnetic head H 100   a  with respect to the center line O—O. 
   When each of the lengths of the tape opposing surfaces H 100   a A and H 100   b A of the magnetic heads H 100   a  and H 100   b  in the tape sliding direction increase or each of the distances of the opposing surfaces H 100   a A and H 100   b A protruding from the rotary drum  100   a  towards the magnetic tape T decrease, the displacement m of the continuous line PL 2  relative to the center line O—O in the second areas  127  becomes smaller. 
   For example, as shown in  FIGS. 6 and 7 , areas of the opposing surface where the continuous line PL 2  is displaced away from the center line O—O are formed away from the magnetic gap  116  of the MR-type thin-film magnetic head  113 . 
     FIG. 6  is a table illustrating the relationship between the length (length L 3  in  FIG. 5 ) from one acute angular corner to the other angular corner of the opposing surface and the displacement of the apex of each magnetic head, and  FIG. 7  is a graph based on the data in FIG.  6 . In  FIGS. 6 and 7 , Rch and Lch respectively denote the magnetic heads H 110   a  and H 100   b  mounted on the rotary head apparatus  100 , and measured values were obtained by using the magnetic heads, each having a structure in which the curvatures of radius R and r of the two convex arcs are respectively 5 mm and 1.5 mm, and the azimuth angle is 25 degrees. 
   Each displacement m shown in  FIG. 6  was measured at a position lying away from the magnetic gap by a predetermined length with respect to the magnetic gap of each magnetic head. 
   As can be seen from  FIG. 6 , the displacement m at a position lying away from the magnetic gap by a predetermined length decreases as the length of the opposing surface increases. That is, as the length of the opposing surface increases, an area of the opposing surface where the displacement occurs tends to lie away from the magnetic gap. 
   As described above, in the magnetic heads H 100   a  and H 100   b , respective areas of the opposing surfaces where the corresponding displacements occur tend to lie further away from the corresponding magnetic gaps as the lengths of the opposing surfaces H 100   a A and H 100   b A become greater in the tape sliding direction. The recording and playback apparatus according to the present invention is constructed such that, for example, by adjusting the lengths of the opposing surfaces H 100   a A and H 100   b A, when the magnetic tape T is wound around the rotary head apparatus  100  including the rotary drum  100   a  having the magnetic head H 100   a  and H 100   b  mounted thereon and is driven to run, the magnetic tape T does not slide in the respective second areas where the displacements of the apexes away from the corresponding center lines O—O are great and it slides only in the respective first areas where the displacements are small. With this structure, when the magnetic head H 100   a  shown in  FIG. 5  is taken into account by way of example and when the magnetic tape T slides in the first area  126 , of two areas L 2  where the displacement occurs, only areas L 2   a  where the displacement is small abut against and slide on the magnetic tape, thereby reducing the sliding resistance of the apex exerted on the magnetic tape T. With this structure, since magnetic powder applied on the magnetic tape T is prevented from being scraped, the scraped magnetic powder is unlikely to be conveyed to the magnetic gaps  116  associated with the running of the magnetic tape T and to be deposited between the magnetic tape and the MR-type thin-film magnetic head  113  disposed in the magnetic gap  116 . Thus, a so-called spacing loss and a decrease in output can be prevented. 
   In addition, the rotary head apparatus  100  according to the present invention is constructed such that the displacement m is equal to 2 μm or less. When the displacement m is greater than 2 μm, an output decreases by that much; as a result, a servo characteristic deteriorates, for example, a servo mechanism becomes unstable, and an error is unlikely detected. However, in the rotary head apparatus according to the present invention, since the displacement m is equal to 2 μm or less, the servo characteristic is prevented from being deteriorated, for example, the servo mechanism is prevented from becoming unstable, and also an error is easily detected. 
   Although the above-described rotary head apparatus mounted on the magnetic playback apparatus includes the rotary drum  100   a  having the couple of magnetic playback heads H 100   a  and H 100   b  mounted thereon by way of example, the present invention is not limited to the above structure. The rotary drum  100   a  may have a single magnetic head or more than two magnetic heads mounted thereon. Also, the rotary drum  100   a  may have a magnetic writing head and/or a magnetic erasing head mounted thereon in place of the magnetic playback heads H 100   a  and H 100   b . In this case, it is preferable that each of magnetic-tape opposing surfaces of the magnetic writing head and the magnetic erasing head be shaped in convex arcs having the predetermined curvatures of radius R and r respectively along the longitudinal direction serving as the sliding direction of the magnetic tape and along the lateral direction perpendicular to the longitudinal direction, and also that the apex lying in the first area, of the convex arc having the curvature of radius r, be positioned in the lateral direction within 2 μm from the center line laterally dividing the magnetic head into two parts. With this structure, the magnetic tape is unlikely scraped by the magnetic writing or erasing head. 
   Also, although the magnetic head is formed only by the MR-type thin-film magnetic heads  113  by way of example, the present invention is not limited to the above structure. For example, the magnetic heads may be formed not only by an interactive head but also by the MR-type thin-film magnetic head  113 . In this case, the interactive head is disposed along the longitudinal direction with respect to the MR-type thin-film magnetic head  113 . With this structure, a single magnetic head can perform not only writing data but also playing it back. 
   In this case, a magnetic gap of the interactive head is also exposed to the opposing surface of the magnetic head, and the center line laterally dividing the interactive head into two parts lies on the center line O—O laterally dividing the magnetic head into two parts. 
   Also, the magnetic head mounted on the rotary head apparatus may be a so-called bulk-type, recording and playback magnetic head having a structure in which a pair of core half-bodies composed of high-permeability magnetic material such as ferrite are combined so as to face each other along their opposing surfaces opposed to the magnetic tape T, and the core half-bodies have a magnetic material layer serving as a magnetic gap, interposed between the opposing portions thereof. 
   In the rotary head apparatus  100  according to the present invention including the rotary drum  100   a  having the magnetic heads H 100   a  and H 100   b  mounted thereon, when the magnetic tape T is wound around the rotary head apparatus  100  and is driven to run, the magnetic tape T does not slide in the second areas where the displacement of the apex of the convex arc having the curvature of radius r away from the center line O—O is great and the magnetic tape slides only in the first area where the displacement is small. Also, the displacement of the apex in the first area is arranged within the 2 μm. With this structure, the sliding resistance of the apex exerted on the magnetic tape T can be reduced, whereby a so-called spacing loss can be reduced and a decrease in output can be prevented. Also, deterioration in the servo characteristic can be prevented, and an error-detection characteristic can be improved.