Head positioning mechanism for multitrack tape recorder

Abstract: A mechanism (10) for accurately positioning a recording/playback head (30) on the center of a track including a stepper motor (52) and coil assembly (60) in combination controlling coarse and fine transverse head position. The coil (62) is attached to a pivoting actuator arm (32) which provides a mounting member (30) for a recording/playback head. A torsion spring (46) is attached to the actuator arm (32) and to a stage (44) which is driven by a stepper motor lead screw (36) to incrementally position the actuator arm. The coil assembly (60) includes a coil bundle (62) juxtaposed between at least two sets of split magnets (40). The coil assembly operates to pivot the recording/playback head transversely, thereby providing fine position control.

Description: The present invention relates to magnetic tape recorders and to subassemblies utilized therein, particularly with respect to recorders adapted for multiple track recording using a multiple track head which is responsive to servo signals and transversely movable with respect to the recording tape, as basically known from EP-A-0 003 339. Data recording cartridges and recorders adapted for their use are disclosed in U.S. -A-3,692,225. The cartridge there disclosed includes an enclosure together with an endless flexible belt in frictional contact with the tape on both reel hubs for bidirectionally driving the tape. The cartridge can operate to drive the tape with rapid accelerations and decelerations, such as are encountered in digital data recording and playback. Recorders adapted to use such data cartridges originally employed fixed, multitrack heads which were complex, expensive and difficult to maintain in proper alignment. To eliminate the multitrack heads, U.S. -A-4,313,143 disclosed a head positioning mechanism by which a single track head could be transversely positioned with respect to the width of the recording tape to enable recording and playback of any of a plurality of parallel tracks. U.S. -A-4,750,067 discloses a head positioning mechanism for a multitrack data cartridge recorder including a stepper motor, a lead screw driven by the stepper motor and a head mounting slide engaged with the lead screw by a partial female thread. This known mechanism moves a recording/playback head transverse to the path of a magnetic recording tape. While the mechanism of US-A-4 750 067, works satisfactorily for some applications, a need has recently arisen to provide a mechanism which more accurately positions a magnetic recording head on the center of a selected track in response to servo signals derived from servo information carried on certain tracks on a multitrack tape. This accurate positioning is required to allow substantially higher track densities on recording tape. From EP-A-0 003 339 a mechanism for exactly positioning a recording/playback head assembly relative to a recording tape is disclosed. This known mechanism comprises a base and an actuating arm means for supporting the recording/playback head. Furthermore, the known mechanism comprises a means for pivotally mounting the actuating arm means allowing the actuating arm means to pivot around an axis parallel to the tape transport path. For positioning the recording/playback head in relation to a selected one of the plurality of data tracks of the tape, in the known mechanism a coarse linear positioning means is used which means is secured to the base for coarsely positioning the pivotal mounting means. Furthermore, means secured to the base, for fine positioning the actuating arm means is provided such that the recording/playback head is positioned in relation to the center of the selected data track. It is the object of the present invention to provide a recording/playback head positioning mechanism for use in a tape drive with enables head positioning with very close tolerances to finally position the head very accurately on the center of a track in response to servo signals carried by the tape. This object is solved by the recording/playback head positioning mechanim having the features of claim 1. The subclaims are directed to preferred embodiments of the invention. A preferred embodiment of the present invention provides a voice coil and stepper motor head positioning mechanism for a data cartridge recorder which variably positions a recording head transversely with respect to the width of the recording tape. The mechanism of the invention enables head positioning with very close tolerances due to the ability of the voice coil to finely position the head very accurately on the center of a track in response to servo signals carried by the tape. In this embodiment of the invention the voice coil is attached to the rotating actuator arm. The actuator arm provides a mounting member for a recording/playback head. The torsion spring is attached to the rotating actuator arm and the stage which is driven by the stepper motor lead screw to initially coarsely position the actuator arm. Following coarse positioning by the lead screw, the voice coil then finely positions the head on the center of a selected track. The voice coil includes a coil bundle which is juxtaposed between at least two sets of split magnets. The voice coil and magnets operate together to drive the recording/playback head transversely to the direction of movement of the tape by applying a positioning force. The present invention offers a magnetic recording head responsive to such servo signals having the advantage of offering an extremely compact head mechanism. A further advantage of the head mechanism provided by the instant invention is that it is nearly crashproof. The mechanism of the present invention also significantly reduces undesirable translational reactionary resonances which are typically present in prior art head mechanisms. The present invention will be more thoroughly described with reference to the accompanying drawings, wherein like numbers refer to like parts in the several views, and wherein: Figure 1 is an isometric view of one embodiment of the magnetic head assembly of the present invention; Figure 2A is a cut away side view of the embodiment of Figure 1 showing the magnetic head assembly in a fully extended position; and Figure 2B is a cut away side view of the embodiment of Figure 1 showing the magnetic head assembly in a bottom position. Now referring to Figure 1 which shows an isometric view of one embodiment of the magnetic head assembly of the present invention. As there is seen, the magnetic head assembly 10 includes a rotating actuator arm 32 including a magnetic recording head assembly 30 rigidly affixed thereto. A stepper motor 52, such as is shown in Figures 2A and 2B, drives a lead screw 36 which, in turn moves the stage 44 in a vertical direction perpendicular to the surface of a base 5. A coil assembly 60 is attached to one end of the rotating actuator arm 32. As best shown in the side cut-away view Figure 2A, the coil assembly 60 comprises a coil frame 61, a coil 62 and a mandrel 64. The coil 62 comprises an upper portion 62A and a lower portion 62B. A recording tape 50 having data contained on a multiplicity of parallel tracks moves along a transport path across the head assembly 30. The head mounting assembly 10 further includes a stage 44 having a bottom surface affixed to a torsion spring 46 which traverses the width of the rotating actuator arm 32. Torsion spring 46 is rigidly coupled at its ends 46A, 46B to opposing sides of the rotating actuator arm 32. The stage 44 includes apertures 44A and 44B which are sized to receive the lead screw 36 and an anti-rotation pin 34. Aperture 44A may advantageously be a half-nut aperture, slightly larger than necessary to accommodate the lead screw 36 so as to allow for movement of the actuating arm 32 in a direction normal to the plane of the tape to assure constant loading at the tape head interface. The aperture 44A is constructed to also allow pivotal movement of the magnetic head assembly. The pin 34 and the lead screw 36 are affixed in a well-known manner to a stepper motor 52. The pin 34 allows movement of the stage 44 in a direction perpendicular to the surface of the base 5 but minimizes rotation or movement in other directions. The stepper motor 52 turns the lead screw in response to control signals applied using well-known techniques. Referring to Figures 1 and 2A, a magnet housing 38, advantageously in the form of a metal U-shaped frame, is rigidly mounted to the fixed base 5. The magnet housing 38 is preferably substantially comprised of steel material. Magnets 40A and 40B are rigidly affixed to facing sides of the magnet housing using epoxy, for example. Magnets 40A and 40B may preferably be comprised of split magnets having, for example, a top portion being a north pole and a bottom portion being a south pole whose heights are equal or greater than the stepper motor translational distance plus the width of the coil bundle. The north and south poles of each magnet may be advantageously split at the approximate center of the vertical height of the magnets as indicated by broken line 70. The magnet housing 38 is mounted to the baseplate, as is the stepper motor 52. The U-shaped steel housing serves as a return path for the magnetic flux. The magnet housing is also used to stiffen the baseplate in the region wherein it is mounted. The base 5 is cut out in the region of the assembly to allow installation and movement of the assembly. Coil assembly 60 is movably juxtaposed between the magnets 40A and 40B so as to allow pivotal movement of the frame and, consequently, the entire magnetic head assembly transversely to the direction of motion of the magnetic tape as the tape moves across the head assembly 30. Now referring particularly to Figure 2A, a cut-away side view of the example of the invention illustrated in Figure 1 is shown wherein the magnetic head assembly 10 is in a raised position relative to a tape cartridge, a portion of the tape cartridge being represented here by a plate 16. A load spring 48 is retained between the plate 16 and the stage 44. The lead screw 36 may advantageously be positioned within the load spring 48 which may advantageously comprise a compliant coil spring having a sufficiently large opening in to accommodate the lead screw 36. In operation, the stepper motor 52 is used to coarsely position the head from track to track and the voice coil responds to a servo signal in a track following mode to make extremely small adjustments, as for example, within microinches or micrometers, to follow the center of the selected track. The torsion spring and voice coil design give the mechanism of the invention the ability to dynamically track the servo signal. Higher track density data cartridges are now made technically feasible as compared with conventional methods found in the prior art. The stepper motor 52 drives the stage 44 through the lead screw 36 which provides for substantially zero backlash with slight interference. The stage 44 is heavily loaded, the loading approaching the lifting capacity of the stepper motor 52 and lead screw 36. Loading is achieved by the compression spring 48 to prevent movement of the stage 44 or lead screw 36 after locking into position and to minimize resonance from this portion of the mechanism. The rotating actuator arm 32 is attached to the stage 44 by the torsion spring to eliminate any translational movement during rotation. In one embodiment of the invention, the torsion spring 46 holds the arm several mils above the stage. For some applications, a stop 66 is advantageously employed. The stop 66 may advantageously be, for example, an "L-shaped" member which extends from a portion of the stage 44 under and in proximity to the cross member of arm 32. Stop 66 serves as a crash stop and limits the motion of the arm to a few minutes of rotation in a direction substantially transverse to the direction of movement of the tape 50. An electrical current of sufficient magnitude, herein called a head location signal, may be applied in a well known manner to coil 62 in order to drive the cross member of arm 32 against the crash stop 66. The head location signal may be applied to the coil 62 in order to lock the head assembly 30 against the crash stop 66, thereby holding the head assembly 30 in a fixed position relative to the stage 44. In this way the position of the head assembly 30 may be located in the absence of a servo signal on the tape. Alternatively, if the magnetic head assembly 30 of the invention is used in a stepper mode only configuration, that is a configuration that does not use track following servo signals, the crash stop 66 provides protection against vibration and shock. Those skilled in the art will recognize that variations of the embodiment shown are readily ascertainable, such as employing multiple crash stops extending from the stage, and the invention is not to be considered as to be limited by the example discussed herein. The forward portion of the arm 32 is a simple rigid box terminated in a frame which secures the head. In the implementation shown, the arm height is less than its length to allow the moving mechanism to translate about 3,8 mm (150 mils) to access all tape tracks, yet allow the entire assembly to fit nominally within a 2.5 cm (1.0 inch) height profile. The rear portion of the arm 32 holds the coil. The minimum separation of the inner turn of the upper and lower portion of the coil 62 is about 250 mils to allow the coil 62 to be operated at full power whether the mechanism is at the bottom position or the fully extended position. The length of the coil 62 is determined by the force required to rotate or pivot the actuator properly at the desired frequency and acceleration. The coil 62 is wrapped around and bonded to the mandrel 64 which is epoxied into a frame at the rear of the arm, forming a rigid body. The mandrel 64 is weighted to balance the rotating arm 32 about its axis, reducing translational reactionary forces.

Claims: A recording/playback head positioning mechanism for use in a tape drive adapted for recording and playing back data from any one of a multiplicity of parallel tracks extending along a length of magnetic recording tape (50), in which the tape drive includes at least one recording/playback head (30) which is adapted to interface with the tape along a tape (50) transport path and to be variably positioned along the width of the tape, a recording/playback head positioning mechanism having: (a) a base (5); (b) actuacting arm means (32) for supporting the recording/playback head (30); (c) coarse linear positioning means (36,52,34) secured to the base (5) for coarsely positioning the actuating arm means (32) to coarsely position the at least one recording/playback head (30) in relation to a selected one of the plurality of data tracks; and (d) fine positioning means (60,62) for fine positioning the actuating arm means (32) such that the at least one recording/playback head (30) is positioned in relation to the center of the selected data track, characterized in that (i) the actuating arm means comprises a frame (32) including a head mounting member (30) for attaching the recording/playback head and first and second opposing arms, (ii) the coarse positioning means (36,52,34) comprises linear guiding means (34) secured to the base (5) generally parallel with the plane of the recording tape (50) along the transport path and perpendicular to the transport direction of the tape (iii) pivotal mounting means (44,46) is provided for pivotally mounting the actuating arm means (32) so that the actuating arm means (32) pivots around an axis parallel to the tape transport path, the pivotal mounting means (44,46) comprising: a) a stage (44) slideably engaged to the linear guiding means (34), and b) first and second torsion springs (46) having opposing ends, with one end of each of the first and second torsion springs (46) secured to one of the opposing arms of the frame (32) of the actuating arm means and the other end of each of the first and second torsion springs (46) attached to opposite sides of the stage (44), the torsion springs (46) applying a force substantially transversely to the direction of movement of the tape in its plane so as to bias the actuating arm means (32) towards the coarse position as set by the coarse positioning means (50), and (iiii) the fine positioning means (60,62) is secured to the base (5) to finely position the actuating arm means (32) by pivoting the actuating arm means (32) about the pivotal mounting means (44,46). A head positioning mechanism according to claim 1, characterized in that the fine positioning means (60,62) comprises a coil assembly (60), including a coil bundle (62) attached to the actuating arm means (32) , and means for applying a magnetic force to the coil bundle (62), the magnetic force means comprising at least two sets of split magnets (40A,40B) having the coil bundle (62) juxtaposed between the two sets, the coil bundle (62) and magnetic force means operating to drive the recording/playback head (30) transversely to the direction of movement of the tape (50) and in its plane, in response to a position signal applied to the coil bundle (62). A head positioning mechanism according to claim 1 or 2, characterized in that the stage (44) further comprises a stop member (66) which extends from a portion of the stage (44) under and in proximity to a portion of the actuating arm means (32), wherein the stop member (66) is positioned so as to lock said at least one head (30) in a fixed position relative to the stage (44) upon the application of a head location signal to the coil bundle (62). A head positioning mechanism according to any one of claims 1 to 3, characterized in that the coarse positioning means (36,52) further comprises means for incrementally driving the coarse positioning means including: a. a stepper motor (52) secured to the base (5) relative to the tape transport path and having a drive shaft (36) rotatably mounted therein; and b. wherein the drive shaft (36) of the stepper motor (52) engages the stage (44) to convert rotary motion of the drive shaft (36) into a corresponding linear movement of the stage (44). A head positioning mechanism according to any one of claims 2 to 4, characterized in that each of said sets of split magnets (40A,40B) comprises a pair of north-south split magnets, one pair on each side of the coil bundle (62), the height of each pair being equal to or greater than the maximum transverse movement of the actuating arm means (32) plus the height of the coil bundle (62), and that each set of magnets (40A,40B) is split into a top portion having a first polarity and a bottom portion having a second, opposite polarity. A head positioning mechanism according to claim 5, characterized in that the at least two split magnets (40A,40B) are enclosed in a substantially U-shaped housing serving as a return path for magnetic flux. A head positioning mechanism according to any one of claims 2 to 6, characterized in that the stage (44) is mounted to the linear support means (34) to allow the actuating arm means (32) to be transversely moved between a bottom-most and a top-most position and wherein the coil bundle (62) is positioned to have a top portion thereof located within the field of the top portion of the split magnets (40A,40B) and to have a bottom portion within the field of the bottom portion of the split magnets (40A,40B), regardless of whether the actuating arm means (32) is in the bottom-most or top-most position. A head positioning mechanism according to any one of claims 1 to 7, characterized by means for allowing movement of the actuating arm means relative to the base in a direction normal to the plane of the tape to assure constant loading at the tape head interface, wherein the movement allowing means comprises the pivotal mounting means (44,46) constructed to allow both the pivotal and normal directional movement. A head positioning mechanism according to any one of claims 1 to 8, characterized in that the actuating arm means (32) and all elements mounted thereto are constructed so as to be balanced about the pivot provided by the pivotal mounting means (44,46).

Inventors: SCHWARZ THEODORE A, SCHWARZ, THEODORE A., Schwarz, Theodore A., c/o Minnesota Min. and Man.
Applicants: IMATION CORP, IMATION CORP.
Application year: 1993
Main classification: G11B5
IPC codes: G11B5