Disc drive linear actuator and control system therefor

Abstract

A disc drive memory device is described utilizing a continuously rotating drive shaft and a roller which rides thereon to effect translational motion of a carriage to move a read/write head between address locations on a magnetic recording surface of a data storage disc.

We claim: 
     
       1. A random access memory apparatus comprising: A. a rotating magnetic recording disc for data storage;   B. a data transfer head for interaction with a record surface of said disc;   
     
     
       C. a linear actuator for moving said transfer head across the record surface of said disc between radially spaced address locations; said linear actuator comprising: 1. a carriage on which said transfer head is mounted;   2. a track on which said carriage is mounted for travel on a path providing movement of said transfer head between said radially spaced address locations;   3. a drive shaft having a cylindrical surface;   4. a support mounting said driveshaft for rotation thereof about the axis of said cylindrical surface and with said axis of said cylindrical surface generally parallel to said path;   
     
     
       5. power means connected to said driveshaft for rotating the same about said axis of said cylindrical surface; 6. coupling means for converting rotary motion of said driveshaft into translational motion of said carriage, said coupling means including: (a) a roller;   (b) means carried by said carriage for supporting said roller and maintaining the same in frictional engagement with said cylindrical surface of said driveshaft to be driven into rotation thereby; and   (c) roller control means for selectively changing the angular orientation of the axis of rotation of said roller between an orientation parallel to the axis of rotation of said cylindrical surface and one oblique with respect thereto in which rotation of said driveshaft causes motion of said roller and hence of said carriage along said path to provide said movement of said transfer head between said address locations on said record surface;     D. a position sensor for determining the position at any given time of said transfer head relative to a desired address location; and   E. a position servo control responsive to said position sensor indicating a difference between the position of said head and a desired address location by regulating said roller control means to change the angular orientation of said axis of rotation of said roller to one resulting in motion of said carriage in a direction moving said head to said desired address location.   
     
     
       2. The random access memory apparatus of claim 1 wherein said magnetic recording disc is axially mounted on a drive spindle for rotation and said drive shaft is connected to said spindle for rotating the same whereby said driveshaft transmits power for both movement of said carriage and rotation of said disc. 
     
     
       3. The random access memory apparatus of claim 1 further including means for taking up play between said drive shaft and the support therefor and between said roller and said carriage in the direction of said path to thereby prevent unintended motion of said carriage along to said path. 
     
     
       4. The random access memory apparatus of claim 3 wherein said means for taking up play includes resilient spring means urging said driveshaft and said roller in a direction along said path with a force greater than the component of the frictional force between said cylindrical surface and said roller extending along said path. 
     
     
       5. The random access memory apparatus of claim 4 wherein said driveshaft is journalled within bearings held by said support for said rotation about its axis of rotation, and said spring means for taking up play includes a compression spring which is compressed in the direction of said axis between the driveshaft and the support to resiliently urge said driveshaft in said direction with respect to said path. 
     
     
       6. The random access memory apparatus of claim 4 wherein said means carried by said carriage for maintaining said roller in frictional engagement with said cylindrical surface of said driveshaft includes a yoke having an axle extending between its legs upon which said roller is mounted for rotation, and a support rod for said yoke journalled for rotation with respect to said carriage about an axis passing through the center of rotation of said roller; and said means for taking up play includes a leaf spring mounted on said carriage bearing against said yoke to resiliently urge the same along said path with a force greater than the component of the frictional force between said roller and said cylindrical surface along said path. 
     
     
       7. The random access memory apparatus of claim 6 wherein means are provided for preventing axial movement of said roller with respect to said yoke along said path. 
     
     
       8. The random access memory apparatus of claim 7 wherein said means for preventing axial movement of said roller with respect to said yoke includes a duplexed pair of ballbearings which are clamped together to prevent axial motion between said roller and said axle therefor extending between said yoke legs. 
     
     
       9. The random access memory apparatus of claim 1 further including means for preventing travel of said carriage along said path beyond a predetermined limit. 
     
     
       10. The random access memory apparatus of claim 9 wherein said means for preventing travel of said carriage along said path beyond a predetermined limit includes a lever arm which travels with said roller and a stop in the path of said lever arm for engaging said lever arm upon said roller approaching a position representing said carriage limit to pivot said axis of rotation of said roller toward said orientation parallel to the axis of rotation of said cylindrical surface to thereby arrest said motion of said roller and hence of said carriage. 
     
     
       11. The random access memory apparatus of claim 1 wherein said apparatus includes a second magnetic recording disc for data storage, and said linear actuator further includes a second carriage on which a data transfer head is mounted for travel on a path providing movement of said transfer head between radially spaced address locations on a record surface of said second disc; said coupling means further including: A. a second roller, and   B. means carried by said second carriage for supporting said second roller and maintaining the same in frictional engagement with said cylindrical surface of said driveshaft to be driven into rotation thereby, whereby said driveshaft provides motive power for motion of both of said carriages.   
     
     
       12. The random access memory apparatus of claim 11 wherein said rollers engage said driveshaft on generally opposite sides of the axis of rotation of said cylindrical surface. 
     
     
       13. The random access memory apparatus of claim 11 further including means for taking up play between said drive shaft and the support therefor and between said rollers and their respective carriages in the direction of said paths therefor to thereby prevent unintended motion of said carriages along said paths. 
     
     
       14. The random access memory apparatus of claim 11 further including means for preventing travel of said carriages along their respective paths beyond predetermined limits, said means including for each of said carriages, a lever arm which travels with the roller associated therewith and a stop in the path of said lever arm for engaging the same upon said carriage approaching a position representing said carriage limit to pivot said axis of rotation of said roller toward said orientation parallel to the axis of rotation of said cylindrical surface to thereby arrest said motion of said roller and hence of the carriage with which it is associated. 
     
     
       15. The random access memory apparatus of claim 11 wherein said first and second roller control means each includes a lever arm secured to its associated roller having means spaced from said roller for generating a first magnetic field, means for generating a second magnetic field along the path traveled by said first magnetic means with said lever arm, the interaction of said magnetic fields applying sufficient force to said lever to pivot the same and thereby change the angle of orientation of the axis of rotation of its associated roller; and means are provided for changing the direction of one of said first and second magnetic fields of each of said roller control means relative to the other to correspondingly change the direction of the force applied to said lever of each by the interaction of said magnetic fields. 
     
     
       16. The random access memory apparatus of claim .[.11.]. .Iadd.1, .Iaddend.wherein .Iadd.said apparatus includes a second magnetic recording disk for data storage, and said linear actuator further includes a second carriage on which a data transfer head is mounted for travel on a path providing movement of said transfer head between radially spaced address locations on a record surface of said second disk; said coupling means further including: A. a second roller;   B. means carried by said second carriage for supporting said second roller and maintaining the same in frictional engagement with said cylindrical surface of said driveshaft to be driven into rotation thereby, whereby said driveshaft provides motive power for motion of both of said carriages; and   C. .Iaddend.second roller control means .[.are provided.]. for selectively changing the angular orientation of the axis of rotation of said second roller independently of changes in the angular orientation of the axis of rotation of said first roller.   
     
     
       17. The random access memory apparatus of claim 16 further including a position sensor for determining the position at any given time of said data transfer head of said second carriage relative to a desired address location; and a position servo control responsive to said position sensor for said data transfer head of said second carriage indicating a difference between the position of said head and the desired address location by regulating said roller control means for said roller associated with said second carriage to change the angular orientation of said axis of rotation of said roller to one resulting in motion of said second carriage in a direction moving said head to said desired address location. 
     
     
       18. The random access memory apparatus of claim 17 wherein said roller control means associated with each of said rollers for selectively changing the angular orientation of the axis of rotation of the respective rollers includes for each of said rollers an induction coil for generating a magnetic field to interact with another magnetic field for the development of a force to change said angular orientation of said axis of rotation; and said position servo control associated with each position sensor is first responsive to said position sensor indicating a position difference by first generating an information signal indicative of such position difference, and includes a power drive circuit for energizing said induction coil associated with its respective lever arm in response to receipt of said information signal, said power drive circuit including a power source connected to said induction coil through a first switching means responsive to receipt of a control signal by applying power from said power source to said coil, second switching means responsive to receipt of said information signal by generating a pulse control signal for application to said first switching means to alternately switch on and off the application of power from said source to said coil, the time delay between pulses of said pulse control signal being selected to be shorter than the decay time for current in said coil, and means for continuing current flow through said coil between said pulses whereby said coil remains energized during the duration of said information signal even though said first switching means is discontinuously operated during such duration. 
     
     
       19. The random access memory apparatus of claim 1 wherein said roller controller means for selectively changing the annular orientation of the axis of rotation of said roller includes an induction coil for generating a magnetic field to interact with another magnetic field for the development of a force to change said angular orientation of said axis of rotation; and said position servo control is first responsive to said position sensor indicating a position difference by first generating an information signal indicative of said position difference, and includes a power drive circuit for energizing said induction coil in response to receipt of said information signal, said power drive circuit including a power source connected to said induction coil through a first switching means responsive to receipt of a control signal by applying power from said power source to said coil, second switching means responsive to receipt of said information signal by generating a pulse control signal for application to said first switching means to alternately switch ON and OFF the application of power from said source to said coil, the time delay between pulses of said pulse control signal being selected to be shorter than the decay time for current in said coil, and means for continuing current flow through said coil between said pulses whereby said coil remains energized during the duration of said information signal even though said first switching means is discontinuously operated during such duration. 
     
     
       20. The random access memory apparatus of claim 19 wherein said first switching means is a transistor driver connected between said power source and said induction coil, and said control signal is received by the base of said driver. 
     
     
       21. The random access memory apparatus of claim 20 wherein said second switching means includes a high gain operational amplifier which receives said information signal on a primary input terminal thereof and the output of which is connected to said base of said transistor driver, and said induction coil is connected in series in a feedback connection of said amplifier for development of said pulse control signals and the discontinuous application by said transistor driver of said power to said coil during an information signal. 
     
     
       22. The random access memory apparatus of claim 21 wherein means are included in said feedback connection for setting the repetition rate at which said amplifier provides said pulses of said control signal. 
     
     
       23. The random access memory apparatus of claim 1 wherein said track includes a guiderail defining said translational path and said carriage is slidably mounted on said guiderail for said travel on said translational path. 
     
     
       24. The random access memory apparatus of claim 23 wherein said carriage is received on said guiderail for translational motion with respect thereto, at positions spaced a substantial distance from one another along the direction of said path to provide stability, and said roller is carried by said carriage at a location spaced transversely from said rail; said track further including a transverse restraint rail positioned on the side of said carriage opposite that on which said roller is provided; and said means for maintaining said roller in frictional engagement with said cylindrical surface of said driveshaft includes spring means resiliently urging said roller away from the remainder of said carriage into engagement with said cylindrical surface and also urge said carriage pivotally about said guiderail into engagement with said cylindrical surface and also urge said carriage pivotally about said guiderail into engagement with said transverse restraint rail. 
     
     
       25. The random access memory apparatus of claim 1 wherein said roller control means includes a lever arm secured to said roller having means spaced from said roller for generating a first magnetic field, means for generating a second magnetic field along the path traveled by said first magnetic means with said lever arm, the interaction of said magnetic fields applying sufficient force to said lever to pivot the same and thereby change the angle of orientation of the axis of rotation of said roller; and means are provided for changing the direction of one of said first and second magnetic fields relative to the other to correspondingly change the direction of the force applied to said lever by the interaction of said magnetic fields. 
     
     
       26. The random access memory apparatus of claim 25 wherein said means on said lever spaced from said roller for generating said first magnetic field includes an electrical coil, and said means for changing the direction of one of said first and second magnetic fields relative to the other includes a power drive circuit for selectively energizing said coil in opposite electrical directions. 
     
     
       27. The random access memory apparatus of claim 25 wherein said lever is secured to said roller for travel with said carriage and further including means for preventing travel of said carriage along said path beyond predetermined limits comprising a pair of opposed stops positioned in the path of said lever arm for engaging the same upon said carriage approaching spaced positions representing said predetermined limits for said carriage to pivot said axis of rotation of said roller toward said orientation parallel to the axis of rotation of said cylindrical surface to thereby arrest said translational motion of said roller and hence of said carriage. .Iadd. 28. A random access memory apparatus comprising: (a) a rotating magnetic recording disc for data storage;   (b) a data transfer head for interaction with a record surface of said disc;   (c) a linear actuator for moving said transfer head across the record surface of said disc between radially spaced address locations; said linear actuator comprising: (1) a carriage on which said transfer head is mounted;   (2) a track on which said carriage is mounted for travel on a path providing movement of said transfer head between said radially spaced address locations;   (3) a drive shaft having a cylindrical surface;   (4) a support mounting said drive shaft for rotation thereof about the axis of said cylindrical surface and with said axis of said cylindrical surface generally parallel to said path;   (5) power means connected to said drive shaft for rotating the same about said axis of said cylindrical surface;   (6) coupling means for converting rotary motion of said drive shaft into translational motion of said carriage, said coupling means including a roller, means carried by said carriage for supporting said roller and maintaining the same in frictional engagement with said cylindrical surface of said drive shaft to be driven into rotation thereby, and roller control means for selectively changing the angular orientation of the axis of rotation of said roller between an orientation parallel to the axis of rotation of said cylindrical surface and one oblique with respect thereto in which rotation of said drive shaft causes motion of said roller and hence of said carriage along said path to provide same movement of said transfer head between said address locations on said record surface; and     (d) means responsive to a difference between the actual position of said head and a desired address location for regulating said roller control means to change the angular orientation of said axis of rotation of said roller to one resulting in motion of said carriage in a direction moving said head to said desired address location. .Iaddend. .Iadd. 29. A disk drive comprising:   a support frame;   a magnetic recording disk mounted to said support frame for rotation about its axis;   at least one electromagnetic head mounted to a carriage and positionable relative to said magnetic recording disk by movement of said carriage along a predefined path; and   a linear actuator for selectively moving said carriage relative to said support frame along said predefined linear path, said linear actuator comprising a drive shaft having a cylindrical surface, means for rotatably mounting said drive shaft to said frame for rotation of said drive shaft about the axis of said cylindrical surface, means coupled to said drive shaft for rotating said drive shaft about said axis, a roller, means for mounting said roller to said carriage with said roller being rotatable about a first axis and pivotable about a second axis perpendicular to said first axis, means for mounting said carriage to said support frame with said carriage being movable relative to said support frame along said predefined linear path and with said roller being in frictional engagement with the cylindrical surface of said drive shaft whereby said roller is caused to rotate about said first axis by rotation of said drive shaft when said first axis is parallel to the axis of the drive shaft and is additionally caused to move along said predefined linear path during rotation of said drive shaft when said first axis is oblique to the axis of said drive shaft, and means for controllably pivoting said roller about said second axis to control movement of said roller and thus said carriage along said predefined linear path during rotation of said drive shaft. .Iaddend. .Iadd. 30. A disk drive comprising:   a support frame;   a magnetic recording disk mounted to said support frame for rotation about its axis;   at least one electromagnetic head mounted to a carriage and positionable relative to said magnetic recording disk by movement of said carriage along a predefined path; and   a linear actuator for selectively moving said carriage relative to said support frame along said predefined linear path, said linear actuator comprising a shaft having a cylindrical surface, means for rotatably mounting said shaft to a first predetermined one of said frame and said carriage for rotation of said shaft about a first axis, a roller, means for mounting said roller to a second predetermined one of said frame and said carriage with said roller being rotatable about a first axis and pivotable about a second axis perpendicular to said first axis, drive means coupled to a predetermined one of said shaft and said roller for rotating same about its first axis, means for mounting said carriage to said support frame with said carriage being movable relative to said support frame along said predefined linear path and with said roller being in frictional engagement with the cylindrical surface of said shaft, and means for controllably pivoting said roller about its second axis to control movement of said carriage along said predefined linear path during rotation of said shaft and said roller about their first axis. .Iaddend.