WO1997015516A1

WO1997015516A1 - Dynamic tracking and focus for optical tape systems

Info

Publication number: WO1997015516A1
Application number: PCT/US1995/013733
Authority: WO
Inventors: William S. Oakley
Original assignee: Lots Technology
Priority date: 1995-10-23
Filing date: 1995-10-23
Publication date: 1997-05-01
Also published as: AU4009695A

Abstract

A memory tape drive system is described. The tape drive system transports memory tape (202) by releasing (301) the memory tape (202), positioning the memory tape (202) in a predetermined position by applying a force (201) to the surface of the memory tape, and receiving (305) the memory tape (202).

Description

DYNAMIC TRACKING AND FOCUS FOR OPTICAL TAPE SYSTEMS

FIELD OF THE INVENTION

The present invention relates to the field of memory tape drive and transport systems. More particularly, the present invention relates to the design of tape positioning mechanisms and tension measuring devices.

BACKGROUND OF THE INVENTION

Data can be stored in a variety of different mediums. One popular medium entails storing data onto a tape of a tape drive system. Referring to Figure 1 a typical prior art tape drive system is shown. The memory tape drive system transports memory tape 101 across a head 102 (also known as a transducer) for reading or recording. In addition, many memory tape drive systems incorporate positioning mechanisms to position the memory tape in the proper location for reading or recording. The positioning mechanism acts as an alternative to moving the head to track transverse tape motion. One prior positioning mechanism utilized a tape edge guide to position the memory tape as shown in Figure 1. The tape edge guide operates by spring fingers 103 applying a force on one edge of the memory tape against a ceramic base. Thus, its operation is dependent on the dimensional characteristics of the memory tape and more specifically, the dimensional characteristics of the edges of the memory tape. However, memory tape edges inherently exhibit variations and are not perfectly straight due to imperfections in the memory tape manufacturing process. The variations in turn cause small but significant transverse motions of the memory tape when transported through the tape edge guide. The transverse motions result in tape spool wrap winding lateral position and tension variations which further aggravate the transverse tape motion.

In optical memory tape systems, the recorded bit size is in the sub¬ micron range and the transverse tape motion caused by tape edge imperfections will cause recording of information in an unpredictable location on the memory tape. One prior technique to compensate for transverse tape motion involves the use of a tracking actuator servo system where the optical recording lens follows the transverse tape motion. However, the transverse tape motions contain high frequency components making it difficult for a tracking actuator servo system to follow the transverse tape motions. Thus, in prior memory tape drive systems, the tracking actuator servo mechanism could not fully compensate for high frequency transverse tape movement. The inability to compensate for transverse tape motion results in read out bit and tracking errors when using small bit sizes. This leads to the necessity of having to use larger bit sizes. The disadvantage to using larger bit sizes is that the memory capacity diminishes.

Thus, what is needed is a memory tape drive system incorporating a positioning mechanism which reduces high frequency components of transverse tape movement so that smaller bit sizes can be utilized to increase memory capacity of the memory tape.

SUMMARY OF THE INVENTION

A novel memory tape drive system is described. The tape drive system transports memory tape by releasing the memory tape, positioning the memory tape in a predetermined position by applying differential stresses to the memory tape, and receiving the memory tape. In addition, the tape drive system can include a device for adjusting the position of the memory tape. The device adjusts the position of the memory tape by tilting a roller about an axis perpendicular to the surface of the memory tape or by tilting a roller about an axis along the length of the memory tape. Moreover, the tape drive system can include a device to measure the tension of the memory tape and a device to cause a motor to change torque in response to the tension level. Finally, the tape drive system can include a device to measure tension comprising a flexible mount which responds to tension levels by bending and a strain gage coupled to the flexible mount for measuring strain caused by the bending.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

Figure 1 illustrates a prior art tape positioning mechanism.

Figure 2 illustrates the tape positioning mechanism of one embodiment of the present invention.

Figure 3 illustrates the crowned roller of the tape positioning mechanism of Figure 2.

Figure 4 illustrates the tilt adjustment device of an alternative embodiment of the present invention.

Figure 5 illustrates the memory tape drive system of an alternative embodiment of the present invention.

Figure 6 illustrates a device for measuring tension of a tape drive system.

DETAILED DESCRIPTION

A memory tape drive system is described. In the following description, the invention is described with reference to specific exemplary embodiment thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Figure 2 illustrates a positioning mechanism of one embodiment of the present invention. The positioning mechanism comprises of crowned roller 201. Memory tape 202 travels over crowned roller 201 and contacts crowned roller 201 causing crowned roller 201 to spin in the direction of travel of memory tape 202. After contacting crowned roller 201 , memory tape 202 travels underneath recording lens 203 and recording lens 203 then records information on memory tape 202. While memory tape 202 travels over crowned roller 201 , it may move slightly up or down in the transverse direction along the crowned roller. When the movement occurs, crowned roller 201 applies differential stresses to memory tape 202. The portion of memory tape 202 in contact with the center of crowned roller 201 experiences the most stress because it has the greatest contact with crowned roller 201. The portions of memory tape 202 away from the center of crowned roller 201 experiences progressively less stress because it has progressively less contact with crowned roller 201. The difference in stress translates to differences in stretching across the width of memory tape 202. Greater stress causes greater amounts of stretching. This difference in stretching causes memory tape 202 to bow away from the center of crowned roller 201. The bowing in turn causes memory tape 202 traveling towards crowned roller 201 to be slanted towards the center. The slanting causes memory tape 202 to reposition itself on crowned roller 201. Thus, the differential stresses causes memory tape 202 to move back to its original proper position. In this manner, crowned roller 201 keeps memory tape 202 in the correct position for recording of information by recording lens 203. Because crowned roller 201 relies on differential stresses to position memory tape 202 instead of the edges of memory tape 202, the transverse motion of memory tape 202 has lower frequency components. The lower frequency components makes it easier for a tracking actuator servo system to follow the transverse motions of memory tape 202. As a result, the tracking actuator servo system can more fully compensate for transverse motions in memory tape 202. The compensation in turn provides improved data tracking and allows for optical recording with smaller bit sizes leading to increased memory tape capacity.

Figure 3 illustrates in further detail crowned roller 201. Crowned roller 201 has a crown height of 0.076mm (0.003") and a length of 13.00± 0.02mm. The radius of curvature is 280.00mm (1 1.024"). Under a second embodiment of the present invention, crowned roller 201 has slots along the surface to bleed out air. When memory tape speeds reach 2 m/s, air can be trapped between the memory tape and crowned roller 201. The trapped air can cause the memory tape to lose contact with the surface of crowned roller 201. To remove the trapped air, crowned roller 201 includes slots along the surface as illustrated in Figure 3.

Moving memory tape 202 positions itself in a location depending on the tilt orientation of crowned roller 201. Under a third embodiment of the present invention, the tilt orientation of crowned roller 201 can be adjusted. Crowned roller 201 can be tilted about an axis perpendicular to the surface of memory tape 202 as shown in Figure 4 and crowned roller

201 can also be tilted about an axis along the length of memory tape 202. Either tilt adjustment will cause moving memory tape 202 to occupy a different position on crowned roller 201. However, the tilt adjustment has different effects on the position of moving memory tape 202 depending on the wrap angle of moving memory tape 202. When moving memory tape

202 has a high wrap angle, tape 202 is more sensitive to changes in the tilt orientation about an axis perpendicular to the surface of memory tape 202 than changes in the tilt orientation about an axis along the length of memory tape 202. On the other hand, when moving memory tape 202 has a shallow wrap angle (less than ten degrees), tape 202 is more sensitive to changes in the tilt orientation about an axis along the length of memory tape 202 than changes in the tilt orientation about an axis perpendicular to the surface of memory tape 202. A one degree tilt about an axis along the length of memory tape 202 produces a 0.001 inch transverse change in the position of memory tape 202. In contrast, a ten degree tilt about an axis perpendicular to the surface of memory tape 202 is required to produce the same 0.001 inch transverse change in tape position.

Figure 4 also illustrates in detail tilt adjustment device 501. The tilt adjustment device comprises of T-plate 502, screw adjustments 503, screw adjustment 504, and complaint mount 505. Screw adjustment 503 has a spring around it and is located at the end of one leg of T-plate 502. Screw adjustment 504 also has a spring around it and is located on the other leg of T-plate 502, 90 degrees away from screw adjustment 503. Complaint mount 505 is located at the intersection of the three legs of T- plate 502 and is made complaint by the use of Bellville washers.

Figure 5 illustrates a memory tape drive system under an alternative embodiment of the present invention. The memory tape drive system comprises of reel 301 which releases memory tape 202. Memory tape 202 travels to crowned roller 302 causing crowned roller 302 to rotate in the direction of travel of memory tape 202. Crowned roller 302 causes memory tape 202 to position itself at a predetermined location on crowned roller 302. Memory tape 202 then travels to cylindrical roller 303 causing cylindrical roller 303 to rotate. The optical writing zone is located slightly beyond the point where memory tape 202 contacts cylindrical roller 303 as shown in Figure 4. After writing of data, memory tape 202 travels to cylinder roller 306 and then to crowned roller 304 causing crowned roller 304 to rotate in the direction of travel of memory tape 202. Crowned roller 304, like crowned roller 302, causes moving memory tape 202 to occupy a predetermined position on crowned roller 304. Finally, memory tape 202 travels to reel 305 which receives memory tape 202. A motor is coupled to reel 305 providing torque to reel 305. The torque causes reel 305 to rotate and causes memory tape 202 to travel from reel 301 to reel 305. A second motor is coupled to reel 301 providing torque to reel 301 in the opposite direction. In this manner, the torque applied to reel 305 and the opposite torque applied to reel 301 results in tension in memory tape 202. The torque applied to reel 305 is greater than that applied to reel 301 causing memory tape 202 to travels towards reel 305.

In order to operate the memory tape drive system at higher tape speeds, tape tension control is required to minimize tape dynamic motion and tape velocity variations. Prior memory tape drive systems controlled tape tension by first measuring tape tension utilizing air bearings and air pressure sensors. Then the control system adjusts accordingly. Under the present invention, the use of crowned rollers does not facilitate the use of air pressure sensors and air bearings because the crowned rollers require frictional forces to properly position the memory tape, and thus, require contact between it and the memory tape. Thus, under an alternative embodiment of the present invention, the memory tape drive system utilizes an alternative mechanism for measuring tape tension. As shown in Figure 6, the crowned roller is mounted on flexible mount 401. Tension on memory tape 202 causes a force to be generated on the crowned roller. The force causes flexible mount 401 to bend in response to this force. However, the bending of flexible mount 401 must not change the tilt orientation of the crowned roller. Any change in tilt orientation will cause a corresponding undesirable change in the position of memory tape 202. Thus, to maintain the proper tilt orientation under varying tension levels, flexible mount 401 has parallel legs as shown in Figure 6. The parallel legs allow flexible mount 401 to bend in response to the force generated by tape tension but at the same time maintains the same tilt orientation under varying tension levels. The bending of flexible mount 401 in turn causes strain in flexible mount 401. Strain gauge 402 is coupled to flexible mount 401 at the point of bending and measures the amount of the strain as shown in Figure 6. In this manner, tension on memory tape 202 is translated into strain appearing on strain gauge 402. Strain gauge 402 is coupled to a control device which monitors strain gauge 402. The control device is coupled to the motor driving reel 305 and causes the motor to change the torque applied to reel 305 in response to strain levels appearing on strain gauge 402. When strain gauge 402 indicates greater strain, thus greater tension, the control device causes the motor to apply less torque to reel 305. Likewise, when strain gauge 402 senses less strain, thus less tension, the control device causes the motor to apply greater torque to reel 305. In a similar manner, the control device is also coupled to the second motor driving reel 301 and causes the second motor to change the torque applied to reel 301 in response to strain levels appearing on strain gauge 402. When strain gauge 402 indicates greater strain, thus greater tension, the control device causes the motor to apply less torque to reel 301. In this manner, tape tension is kept to a predetermined level.

Thus, a novel memory tape drive system for transporting memory tape has been described.

Claims

What is claimed is:

1 A memory tape drive system for transporting a memory tape comprising: a first reel for releasing said memory tape, a second reel for receiving said memory tape, a crowned roller for positioning said memory tape, said crowned roller located between said first reel and said second reel; and a motor coupled to said second reel for rotating said second reel

2. The memory tape drive system of Claim 1 further comprising a tilt adjustment device for tilting said crowned roller about an axis perpendicular to the surface of said memory tape.

3 The tilt adjustment device of Claim 2 comprising. a screw for adjusting tilt orientation of said crowned roller, a Bellville washer for providing a complaint mount

4. The memory tape drive system of Claim 1 further comprising a tilt adjustment device for tilting said crowned roller about an axis along the length of said memory tape

5. The memory tape drive system of Claim 1 further comprising a second crowned roller for positioning said memory tape, said second crowned roller located between said first reel and said second reel.

6 The memory tape drive system of Claim 1 further comprising- a device for measuring tension, and a control device coupled to said device for measuring tension, said control device causing said motor to change torque in response to a tension level.

7. The device for measuring tension of Claim 6 comprising: a first flexible mount for responding to said tension level by bending; and a strain gage coupled to said flexible mount for measuring strain in said flexible mount caused by bending of said flexible mount.

8. The device for measuring tension of Claim 7 further comprising: a second flexible mount parallel to said first flexible mount for maintaining tilt orientation of said crowned roller under a plurality of tension levels.

9. The crowned roller of Claim 1 comprising: a slot in the surface of said crowned roller for removing air.

10. A method for transporting a memory tape comprising: releasing said memory tape; receiving said memory tape; positioning said memory tape in a first position by applying differential stresses to said memory tape; and rotating said second reel.

1 1. The method of Claim 10 further comprising: tilting a roller about an axis perpendicular to the surface of said memory tape.

12. The method of Claim 10 further comprising: tilting a roller about an axis along the length of said memory tape.

13. The method of Claim 10 further comprising: measuring tension of said memory tape; and changing torque of a motor coupled to said second reel in response to a tension level.

14. The method of Claim 13 wherein measuring tension further comprises: bending of a flexible mount in response to said tension level; and measuring strain in said flexible mount caused by bending of said flexible mount.

15. The method of Claim 13 further comprising: maintaining tilt orientation of a roller under a plurality of tension levels.

16. The method of Claim 10 further comprising: removing air from the surface of a roller.

17. A memory tape drive system for transporting a memory tape comprising: a means for releasing said memory tape; a means for receiving said memory tape; a means for positioning said memory tape in a first position by applying differential stresses to said memory tape; and a means for rotating said second reel.

18. The memory tape drive system of Claim 17 further comprising : a means for tilting a roller about an axis perpendicular to the surface of said memory tape.

19. The means for tilting a roller of Claim 18 further comprising: a means for adjusting tilt orientation of said roller; and a means for providing a complaint mount.

20. The memory tape drive system of Claim 17 further comprising: a means for tilting a roller about an axis along the length of said memory tape.

21. The memory tape drive system of Claim 17 further comprising: a means for measuring tension of said memory tape; and a means for changing torque of a motor coupled to said second reel in response to a tension level.

22. The means for measuring tension of Claim 21 comprising: a means for maintaining tilt orientation of a roller under a plurality of tension levels.

23. The memory tape drive system of Claim 21 wherein the means for measuring tension comprises: a means for bending in response to said tension level; and a means for measuring strain caused by bending of said bending means.

24. The means for positioning in Claim 17 comprising: a means for removing air from a surface of said means for positioning.