ARCUATE SCANNING HEAD ASSEMBLY AND TAPE CARTRIDGE THEREFOR

Abstract: An improved arcuate scanning head assembly (ASHA) is angled relative to the line of travel of the tape. The relative sizes of the angle, the diameter of the ASHA and the amount by which the heads protrude from the cylinder end face of the ASHA are such that the magnetic heads make firm contact with the tape when above one side of the ASHA's rotating cylinder face, but at most grazing contact with the tape when above the other side of the cylinder face. Preferably, they make firm contact on the one side and do not make contact at all when on the other side. Preferably, the angle also is such that on the side making contact, the head makes and loses contact with the tape a small distance in from the edge of the tape, reducing or eliminating problems due to the head striking the edge of the tape. Alternatively, the ASHA is left straight, but the tape cartridge for use with the ASHA is modified so that the tape is presented at an angle across the media access opening.

Description: ARCUATE SCANNING HEAD ASSEMBLY AND TAPE CARTRIDGE THEREFOR Field of the Invention The present invention relates to arcuate scanning head assemblies, and in particular to mechanisms for improving the tape- head interface. Description of the Related Art Tape drives conventionally have used either a fixed head (often used on audio and computer data tapes) or a Vertical Helical Scan ( VHS) head (often used on video tapes and sometimes on computer data tapes). With a fixed head, the head stays still, and the tape moves linearly past it. With a VHS head, one or more heads are located on the outside of a rotating cylinder or drum. The tape moves past the side of the cylinder, wrapping slightly around the cylinder as it does. The cylinder is angled, so that the path of each head along the tape is a helix. In both of these conventional designs, contact between the head(s) and the tape can be maintained simply by having the tape wrap part way around the head or drum. Another type of drive recently has been developed using an Arcuate Scanning Head Assembly (ASHA). Such a drive is fully described in PCT published application WO 93/26005 (James U. Lemke), and therefore will not be described in detail here. Like a VHS drive, an ASHA 20 has magnetic heads 21 mounted to a cylinder 22 (see Figs. 1A, 1 B), which rotates in the direction of arrow 23. However, with an ASHA 20 the heads 21 are mounted to the end 24 of the cylinder 22 rather than the side 26, and the end 24 is in a_plane parallel to the plane of the tape 28. The heads 21 protrude slightly from the end 24 of the cylinder 22, so they come into contact with the tape 28 as it moves past the ASHA in the direction of the arrow 29. The cylinder 22 rotates at very high speeds, e.g., 15,000 RPM, so the path of each head 21 across the tape 28 is essentially an arc. While just one head could be used, typically a plurality of heads would be preferable to increase the density of the tracks on the tape, e.g., eight heads as shown in the drawings. Upon studying Figs. 1A, 1 B, it will be appreciated that one problem with this design is that contact between the tape 28 and the ASHA 20 cannot be maintained simply by wrapping the tape 28 part way around the ASHA. The heads 21 on both the front side 30 and back side 32 of the ASHA 20 are in contact with the tape 28, but moving in opposite directions. If the tape 28 were wrapped tightly around the heads 21 , it would be twisted around by the motion of the heads. Since wrapping the tape is not practical with the prior art design, the ASHA 20 includes a vacuum tube, shown schematically at 34, to pull the tape 28 down onto the heads 21. With this structure, the ASHA makes contact with the tape 28 as shown schematically in Fig. 1 C. Specifically, the vacuum tube 34 pulls the tape down most strongly at 36, corresponding to the center of the ASHA 20, while the heads 21 push the tape up at 38, 40, corresponding to the paths of the heads 21 on the front side 30 and back side 32 of the ASHA, respectively. In this configuration, the heads 21 strike the edge of the tape 28 at locations 44 and 46 each time they rotate. Thus, another problem with this design is that this striking of the tape edge could result in high wear on the tape 28. Summary of the Invention The present invention tilts the ASHA by a slight angle β relative to the plane of the tape along the center axis of the tape. Depending on the angle of the head and how much the heads protrude from the cylinder end face, the heads are either completely out of contact with the tape on the back side of the cylinder, or make only slight contact. The problems of contact between the back side heads and the tape are eliminated or substantially reduced by doing this. In addition, since the tape is no longer subjected to significant twisting forces due to heads moving past it in both directions, it can be wrapped slightly around the front side heads to improve head to tape contact. Of course, the greater the degree of wrapping, the larger the angle β must be to avoid problems. In addition to eliminating or reducing the twisting problems, angling the ASHA also eliminates or reduces problems with the heads striking the edge of the tape. With the ASHA at an angle, the heads move up into and then down out of the plane of the tape as the ASHA cylinder rotates. With a large enough angle β, the heads simply are not in the plane of the tape when they are positioned below the tape edge, so they do not make contact with it. They then make initial contact some distance δ in from the edge of the tape as they move up into the plane of the tape, completely eliminating the problem of striking the edge. As can also be seen, the distance δ increases as the angle β is increased. In contrast, with a small angle β, the heads will just graze the edge, but the problem will be significantly diminished. It will be appreciated that how large an angle β is needed to eliminate the problem completely will depend on the width of the tape, the diameter of the cylinder and how much the heads protrude above the cylinder edge face. An alternative embodiment of the present invention is to leave the ASHA straight, but change the angle of presentation of the tape by the tape cartridge so that instead of running straight across the media access opening of the tape cartridge, the tape is presented at an angle β. The net effects of changing the tape presentation angle within the cartridge are substantially the same as those from changing the ASHA angle, since the relative geometry of the tape and ASHA are the same in either embodiment. However, angling the tape instead of the ASHA may allow a simpler design for the tape drive, since the ASHA can be positioned perpendicular to the face of the cartridge. Brief Description of the Drawings The invention will be further described with reference to the drawings, in which: Fig. 1 A is a schematic front view of a prior art ASHA with a tape moving past it. Fig. 1B is a schematic bottom view of the device of Fig. 1 A. Fig. 1 C is a schematic representation of the deformation effects on the tape of the prior art ASHA of Fig. 1 A. Fig. 2A is a schematic front view of an angled ASHA according to the present invention with a tape moving past it. Fig. 2B is a schematic top view of the device of Fig. 2A. Fig. 2C is a schematic representation of the deformation effects on the tape of the ASHA of Fig. 2A according to the present invention. Fig. 2D is a schematic view of a tape cartridge with a conventional straight tape presentation used with the angled ASHA of Fig. 2A. Fig. 3 is a schematic representation of an alternative embodiment of the invention in which the ASHA is left perpendicular to the front face of the cartridge, but the tape cartridge presents the tape at an angle. Detailed Description of the Preferred Embodiments Referring to Figs. 2A, 2B, the structure and function of the cylinder 122, heads 121 and the like are substantially the same as the prior art ASHA 20 described above. Features substantially the same as in ASHA 20 therefore have been labeled in the figures with the same reference numerals with the addition of 100, and will not be described further here. It also should be noted that the absolute sizes of the head protrusion, the angle β, and the resultant tape deformation have been grossly exaggerated in all of the drawings for clarity of explanation. According to the present invention, the ASHA 120 differs from the prior art ASHA 20 in that it is angled relative to the plane of the tape 128 by an angle β between the center line of the ASHA 120 and a line perpendicular to the tape 128. As will be apparent, relative sizes of the angle β, the diameter of the cylinder 122 and how much the heads 121 protrude from the end face 124 of the cylinder 122 will control the degree to which the heads 121 contact the tape 128 on the back side 132 of the ASHA 120. Preferably, the relative sizes are such that the heads 121 do not make contact with the tape 128 on their return path along the back side 132 of the ASHA 120. Alternatively, the relative sizes can allow minimal contact. Largely due to the angling, the tape 128 itself wraps slightly around the heads 121 on the front side 130 of the ASHA 120 . Fig. 2C illustrates the effects of the ASHA 120 on the tape 128. Specifically, the heads 121 push the tape up along the path 150 corresponding to the path of the head when it is on the front side 130 of the ASHA 120. In the preferred embodiment, the path 150 differs from path 38 because it does not extend all the way to the edges of the tape 128. As the cylinder 122 rotates, each head 121 moves up into, then down out of the plane of the tape 128. As it does this, it first makes contact with the tape 128 some distance δ-| in from the edge of the tape 128 and then loses contact some distance 62 from the other edge of the tape 128. As will be apparent, the exact size of the distances δ* * and δ will depend upon the relative sizes of the angle β, the width of the tape 128, the diameter of the cylinder 122 and the degree to which the heads 121 protrude from the cylinder end face 124. It also will be apparent that the relative sizes of distances δ-j and δ will depend upon whether the tape is centered about the center line of the cylinder 122. Under most circumstances, the tape preferably will be centered, so that the distances δ* * and 82 will be substantially equal. Fig. 2C assumes that sizes of the heads 121 , angle β and the diameter of cylinder 122 are such that there is no contact between the heads 121 and the tape 128 on the back side 132 of the ASHA 120. As a result, there is no deformation of the tape along the back side 132 of the ASHA 120 to correspond to the path 40 with the prior art ASHA 20. If the dimensions were such that there was some minimal contact between the heads 121 and the tape 128, there would be a path analogous to path 40. However, this path also would contact only part of the tape 128, near the edges, as the heads 121 moved into and out of the plane of the tape 128. Note also that due to the angling, Fig. 2C shows no dimpling around the vacuum tube 134. Such dimpling is substantially eliminated since the end of the vacuum tube 134 is not in contact with the tape 128. Indeed, while a vacuum tube 134 is shown in Figs. 2A, 2B, it may well be possible to eliminate it entirely with the present ASHA 120. As a specific example of the present invention, the ASHA cylinder 120 might be 1.77 ± .05 cm in diameter and the heads 121 might protrude.02 ± .005 mm above the cylinder end face 124. With such a structure, and assuming the cylinder end face at the center line of the ASHA is position in the plane of the tape 128, an angle of just 2/3 degrees would be sufficient to prevent the heads 121 from contacting the tape 128 on the back side 132 of the cylinder 122, though an angle of about 2 degrees might be preferable to ensure there is no contact. Fig. 2D illustrates a tape cartridge 160 with a conventional straight line presentation of the tape 128, shown positioned for use with the angled ASHA 120 just described. In such a tape cartridge 160, guide rollers or pins 162, 164 typically are positioned to present the tape 128 in a straight line across the media access opening 168 of the tape cartridge 160. The small angling of the ASHA 120 in the first embodiment generally may be expected to have little effect on other elements, e.g., the positioning mechanism, of the drive (shown schematically in Fig. 2B as 155) in which the ASHA 120 is mounted, while having a large impact on the tape to head interface. The present invention therefore can very easily be adapted for use with prior ASHA drive designs. The alternative embodiment shown in Fig. 3 may be useful in those situations where even limited angling of the ASHA 120 is difficult, e.g., due to space considerations in the drive. In Fig. 3, an ASHA 20 is shown conventionally positioned with its axis perpendicular to the tape cartridge 170. The cartridge 170 includes the usual baseplate 172 and front face 174, with a reference plane defined proximate the front face 174 and perpendicular to the baseplate 172 (i.e., proximate the front face 174 and perpendicular to the plane of the drawing) for accurate positioning of the cartridge with respect to the reference plane of the drive. However, the guide pin or roller 175 has been shifted relative to the guide pin or roller 176 so that the tape 178 is presented at an angle β across the media access opening 179. The net effect is the same as in the first embodiment -- the ASHA 20 makes contact with the tape 178 at an angle β. It will be noted that with the geometry shown in Fig. 3, the right side of the ASHA 20 as seen in the drawing comes into contact with the tape 176, in contrast to the embodiment of Figs. 2A - 2D, in which the left side of the ASHA 120 as seen in the drawing came into contact with the tape 128. It will be appreciated that either embodiment can be modified to have the other side of the ASHA come into contact with the tape by changing which direction the ASHA 120 or the tape 176 is angled. Various changes and modifications to the embodiments of the invention as described will be readily apparent to one of ordinary skill in the art. For example, the alternative embodiment shows the presentation angle of the tape being changed by modifying the position of the guide pins. Other methods of accomplishing the same change in presentation position will be readily apparent to one of ordinary skill in the art, such as including guide plates or modifying other aspects of the tape support. The present invention therefore is intended to be limited only by the following claims.

Claims: claim: 1. An improved arcuate scanning head assembly for use with a magnetic tape movable along a line of travel, the assembly having a cylindrical body rotatable about a central axis, with a cylinder end face and at least one head protruding slightly from the cylinder end face near an outer circumference thereof, characterized in that the central axis about which the cylinder rotates is at an angle β relative to a line normal to the line of travel of the tape, the angle β being less than 90°. 2. The improved arcuate scanning head assembly of claim 1 , wherein the relative sizes of the angle β, the diameter of the cylinder and the amount by which the at least one head protrudes from the cylinder end face are such that the least one head contacts the tape when it is positioned on a first side of the cylinder and makes at most grazing contact with the tape when it is on a second side of the cylinder opposite from the first side. 3. The improved arcuate scanning head assembly of claims 1 or 2, wherein the relative sizes of the angle β, the width of the tape, the diameter of the cylinder and the amount by which the at least one head protrudes from the cylinder end face are such that the least one head makes contact with the tape when it is positioned on the first side of the cylinder a distance δ* * in from an edge of the tape and loses contact with the tape a distance 82 in from an opposite edge of the tape. 4. The improved arcuate scanning head assembly of claim 3, wherein the distances δ-j and δ are substantially equal. 5. A tape cartridge for use with the tape head assembly of any of claims 1-4, comprising: a. a housing having a front face, a head/media access opening formed in the front face, a baseplate, and a reference plane proximate and substantially parallel to the front face and substantially perpendicular to the base plate; b. tape contained in the housing, a portion of the tape being accessible by the tape head assembly from the outside of the housing through the head/media access opening; and c. presentation means for presenting the portion of the tape accessible through the head/media access opening substantially in a plane at a predetermined, stable, defined angle β relative to the reference plane and substantially perpendicular to the baseplate. 6. The tape cartridge of claim 5, wherein the presentation means comprises a first guide mechanism on one side of the media access opening and a second guide mechanism on the other side of the media access opening, one of the guide mechanisms being further from the front face than the other. 7. The tape cartridge of claim 6, wherein the housing has a corner proximate the media access opening, the guide mechanisms are at different distances from the corner and the guide mechanism closest to the corner is further from the front face than the guide mechanism farthest from the corner. 8. The tape cartridge and tape head assembly of any of claims 1-7, wherein the tape head assembly and tape cartridge are positioned with respect to a common reference plane, and further characterized in that the plane of the tape where the head assembly makes contact with the tape through the media access opening is not parallel to the reference plane. 9. The tape cartridge of any of claims 1-8, wherein the angle β is less than about 2 degrees. 10. The tape cartridge of any of claims 1-9, wherein the angle β is about 2/3 degrees.

Inventors: ARGENTO DAN J, NOTHAFT EUGENE M, SAGA HIDEAKI, ARGENTO, DAN, J., NOTHAFT, EUGENE, M., SAGA, HIDEAKI
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1995
Main classification: G11B5
IPC codes: G11B5, G11B15, G11B23