Abstract:
Multiple (e.g. 500) ultra-thin flexible storage disks are stacked in a closely spaced configuration between circular end plates and arranged for rotation together with the plates about a common axis. Recording surfaces of the rotating disks are deflected to successively expand (open) and contract (close) a selected interface and thereby provide recording access at the expanded interface. Separation of the selected interfacing surfaces for access is facilitated by maintaining a predetermined air pressure between the contracted disks which conditions the rotation of the disks to bistability in the contracted position. Thus only a small initiating force is required to expand any selected interface with the disks initially contracted. This reduces disk wear. Expansion of a selected interface is accelerated (for shortening access time) by applying vacuum to the disks in synchronism with the initiating force. Advantageously recording surfaces on both sides of the expanded interface rotate in generally flat planar paths, simplifying track location when both surfaces are subject to recording usage.

Description:
CROSS REFERENCES TO RELATED PATENT APPLICATIONS 
     1. U.S. patent application Ser. No. 414,614, by R. J. Penfold et al, filed Nov. 7, 1973, entitled &#34;Multiple Flexible Disk File&#34;, assigned to the assignee of the present application, now U.S. Pat. No. 3,867,723 issued Feb. 18, 1975.  2. U.S. Pat. No. 3,810,243, issued May 7, 1974, by B. W. McGinnis et al, entitled &#34;Selectively Tensioned Transducer Assembly for Operation in Compliant Relation to Individual Memory Discs of a Partitionalbe Aggregrate of Rotating Flexible Discs&#34;, assigned to the assignee of the present application. 
     3. U.S. patent application Ser. No. 375,988, by R. A. Barbeau et al, filed July 2, 1973, entitled &#34;Stabilization of Partitionable Memory With Flexible Rotating Discs&#34;, assigned to the assignee of the present application, now U.S. Pat. 3,852,820 issued Dec. 3, 1974. 
     4. U.S. patent application Ser. No. 375,989, by R. A. Barbeau et al, filed July 2, 1973, entitled &#34;Partitionable Disc Memory With Flexible Discs and Conformally Suspended Head&#34;, assigned to the assignee of the present application, now U.S. Pat. No. 3,838,462 issued Sept. 24, 1974. 
     5. U.S. patent application Ser. No. 484,482, filed July 1, 1974 by E. D. Barkhuff et al, entitled &#34;Random Access Disk File With Axial Translation of Disks and End Plate&#34;, commonly assigned herewith. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to random access storage devices in which selected interfaces between recording surfaces, in a stack of multiple flexible memory disks rotating about a common axis, are alternately expanded and contracted while the disks rotate in order to provide access clearance for insertion of a transportable transducing head. 
     DESCRIPTION OF THE PRIOR ART 
     The above cross-referenced co-pending patent applications and references cited therein concern stacked configurations of multiple flexible disks which are subject to being deflected apart while rotating in order to form space for insertion of a transducing head relative to a selected disk surface. A problem in the known prior configurations is to avoid or reduce abrasional contact between the disks and the deflection apparatus and thereby lengthen useful recording life of the disks. Another problem is to position the separated recording surfaces on both sides of the opened interface in predetermined orbits which do not vary from interface to interface so that both sides of the disks are useful without special apparatus to relate recording track locations to interface positions. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a method of flexing rotating flexible disk multiples for transducing access with reduced abrasive and/or deformational contact between the disks and the selecting apparatus. 
     Another object is to provide a method of bistably expanding any selected interface in a rotating flexible disk multiple whereby the force required for expansion is lessened due to bistability of the disk rotation and whereby the shape of the expanded interface is uniform over the range of all useful disks so that tracks on both sides of the useful disks are conveniently locatable. A related object is to have flat recording surface paths on both sides of the expanded interface. 
     Another object is to provide a method and associated apparatus for bistably conditioning the rotation of multiple flexible disks to facilitate triggered expansion of any selected interface and thereby reduce abrasional contact with disk surfaces, in which expansion of the interface is stable in the absence of contact with or deformational stress on the disks. 
     An advantage of having flat recording surface paths on both sides of the expanded interface is that locating recording tracks on the disks is thereby simplified in comparison to track location when the recording surface paths vary from interface to interface. 
     Another object is to provide for reduction of disk contact hitherto required to separate packs of co-rotating flexible disks for access. 
     Yet another object is to provide a reliable and simple method for displacing multiple flexible disks to afford random selective access to recording surfaces within the multiple. 
     A feature of the invention is the provision of controlled air pressure between multiple flexible disks in a stacked rotating configuration to facilitate stable expansion of any selected interface with negligible abrasive contact and/or deformational stress, and to stabilize the steady state rotation of the disks with said interface expanded. 
     Another feature is the provision of a predetermined steady state air flow making the rotation of the contracted disks bistable to facilitate interface expansion for recording access -- thereby reducing the abrasive and/or distortional contact between the recording surfaces and the apparatus used to cause said expansion -- and providing stable maintenance of the expanded configuration without physical contact or bearing support. 
     A related feature is the discovery that interface openings produced by such bistable expansion can be made to have uniform symmetrical shape at all interfaces whereby opposite sides of disks are useful for recording without special adaptation to relate track location to interface position in the stack. 
     Another feature is the use of momentary applied vacuum to accelerate the expansion displacement without loss of stability. 
     The foregoing and other objects and features hereof will be more fully appreciated and understood from the following detailed description of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 provides an elevational view partly sectioned and partly schematic of a centrally pressurized rotating flexible disk file with pressure controlled to bistabilize disk rotation and thereby to facilitate interface expansion; 
     FIG. 2 shows the contracted interface rotational configuration of the centrally pressurized disks; 
     FIG. 3 shows an expanded interface; 
     FIG. 4 shows an expanded interface receiving a transducing head; 
     FIG. 5 is a sectional view of the hollow spindle assembly and a spacer disk; 
     FIG. 6 is an elevational view partly sectioned and partly schematic of a second embodiment of flexible disk file with spaced interfaces ventilated through off-axis holes in the disks; 
     FIG. 7 shows a disk employed in FIG. 6; 
     FIG. 8 is a sectional view of a detail of the air supply coupling in the apparatus of FIG. 6; and 
     FIGS. 9 and 10 are respective views of a contracted and expanded interface in the apparatus of FIG. 6. 
    
    
     DEFINITIONS 
     Terms such as &#34;expand&#34; and &#34;contract&#34; are used herein to respectively characterize widening and narrowing of a selected space between facing recording surfaces; whereby the affected surfaces are respectively rendered accessible and inaccessible for transducing access. In this context it will be understood that the narrowed interface need not be completely closed (i.e. the affected surfaces need not be touching) and indeed may have variable spacing as nearby interfaces are selectively expanded and contracted. 
     The term &#34;bistable&#34; is used herein to characterize a condition of the disk aggregate in which the disks, while rotating in one stable configuration -- e.g. with all interfaces contracted --, are actuatable to another stable configuration (e.g. with a selected interface expanded and other interfaces contracted) by a transient actuating force. This does not mean to imply that the aggregate is necessarily bistable or reversely actuable in the other configuration. 
     DETAILED DESCRIPTION 
     Two embodiments are disclosed. In one of these (FIGS. 1-5) air flows centrally through a radially vented spindle and radially porous spacers into spaces between consecutive disk recording surfaces. In the other embodiment (FIGS. 6-10) air flows through aligned off-axis apertures in the storage disks into spaces between consecutive recording surfaces. 
     The central air flow arrangement of FIGS. 1-5 resembles the apparatus disclosed in the above-referenced Penfold et al application; except that the steady state air supply is critically adjusted in the present disclosure, for providing bistable expansion operation of the contracted pack, and due to this feature the means presently used for selecting the disks need only act transiently upon the edges of the selected disks and need not be maintained adjacent the disks or otherwise deployed in the expanded interface. 
     The present off-axis ventilation configuration resembles the above-referenced Krijnen patent U.S. Pat. No. (3,509,553) apparatus, except that present disk apertures and the steady state air supply thereto are respectively designed and adjusted to provide rotational bistability. The present apparatus for selecting the disks, aided by said bistability, is used only to expand a selected interface to a stable configuration suitable for head clearance; whereas the Krijnen selector is integral with the head and operates in a totally different manner. 
     Referring to FIGS. 1-5, in the centrally ventilated embodiment floppy-type disks 1 are arranged, together with stabilizing end plates 2, 3, for rotation about common axis 4 (FIG. 2). Typically the disks are ultra-thin mylar disks coated with magnetic oxide -- ranging in thickness sizes from 1-3 mils and in outer diameter sizes from 8-15 inches -- and are rotated at angular velocities ranging from 1100-2400 rpm. It is understood however that these are exemplary values not limiting the range of useful operation. 
     FIG. 1 is schematic in respect to the number of disks illustrated. The disks are drawn over-sized for clarity. It should be understood however that several hundred recording disks would be provided in the space between end plates indicated in FIG. 1, and 1000 or more storage disks could be aggregated in the indicated configuration for bistable random access selection according to our invention. 
     The end plates and disks have central holes for mounting upon spindle 5 between clamping end members 6, 7. Disk separations in the contracted configuration (FIG. 2) are determined by thin spacer disks 8 which are mounted between successive memory disks. The assembly of parts 1-8 is rotated by motor 9. In the above-referenced embodiments the spacers typically are approximately 2 mils thick and have outer diameters of approximately 2 inches. In the centrally vented embodiment spindle 5 is hollow and contains longitudinal openings 5a; spacers 8 are radially porous. 
     In the contracted configuration (FIG. 2) spaces 10 between successive recording surfaces are insufficient for unobstructed insertion of transducing head 12 (FIG. 4). Upon selection the selectively interface space is widened sufficiently (10a, FIG. 3) to receive the head 12 without interference (FIG. 4) for compliant positioning (not shown) relative to the rotation path of one of the two recording surfaces 16, 18 at said interface. 
     A problem in regard to displacing recording surfaces of flexible disks is to reduce or minimize abrasive or distortional contact between the displacing apparatus and the selected recording surfaces. We have found that with a particular adjustment of steady state air pressure in the interface spaces between the disks the contracted disks become bistable, as defined above, whereby a selected interface can be expanded by a transient actuating force with negligible or no abrasive contact between the actuating apparatus and the disks. Our invention stems from this discovery. 
     Rotating hollow member 7 (FIG. 1) is coupled via sealed bearings 7a to a stationary duct-work 13. A steady state supply of air received at intake passage 13a for conveyance to the hollow interior of spindle 5 is manually adjusted at valve 13b to a constant critical pressure level in a range associated with conditioning the contracted pack for bistable rotation as defined above. In this condition the unclamped recording portions of all disks 1 are stable while rotating initially in the contracted configuration (FIG. 2) and are transiently actuable to a stable expanded position (FIG. 3) in which a selected interface is expanded. The actuating displacement force 20 (FIGS. 2, 3) at edges of the affected interfacing disks is sufficient to trigger expansional displacement of the disks to the stable expanded position (FIG. 3). 
     The steady state pressure adjustment for rotational bistability is determined empirically and is just above the range providing little or no air flow in the interfaces of the contracted pack. In the latter condition the interfaces are subject to uncontrollable spontaneous expansion without external actuation, due to development of vacuum in the interfaces by centrifugal pumping action. In the bistable range the pressure in the unexpanded interfaces is kept below atmosphere to a lesser degree but the interface spacing remains uniform in stable pressure equilibrium until disturbed by positive external actuation. Any initial widening of a selected interface, as by a probe, air, jet, etc., admits an increased supply of air to that interface. This upsets the pressure equilibrium and forces the adjacent disks apart until a new stable equilibrium is reached between the pressure in the expanded space and the pressures in the other interfaces. Surprisingly this new equilibrium is reached quite rapidly with oscillational overshoot and undershoot if any being quickly damped. Also surprising, the width of the expanded interface is ample for transducing access. 
     Experimental observations indicate that the bistable adjustment range is variable in relation to such determining factors as disk geometry, number of disks in the pack, rotational speed and ventilation configuration for distributing air to the disks. For the centrally ventilated configuration of FIGS. 1-5, with geometry and rotation in ranges as specified above, the steady state supply pressure associated with rotational bistability is found typically to lie in the range 2-5 inches of water. 
     The displacement action of the selected disks in response to selecting force 20, under bistable air flow conditions may be likened conveniently to the switching action of electronic flip-flop circuits. Naturally it is understood that the head 12 and the selecting apparatus exerting force 20 are transportable relative to the disk assembly, and operable to actuate the selected interface, by means not relevant to the present invention and described elsewhere in the above cross-references. Furthermore, force 20 may be exerted by a contacting probe or a directed air jet. 
     Interestingly and advantageously the displaced recording surfaces at the selected interface (16, 18 FIG. 3) stabilize uniformly in flat rotational paths over a broad range of interfaces, simplifying track location. In earlier arrangements of the type disclosed in the above-referenced Ser. No. 375,989 by Barbeau et al the facing disks at the selected interface rotate in unsymmetrical paths, one flat and the other curved, and the curved paths vary from interface to interface depending upon the number of disks contained in the pack segment displaced into the curved path. Thus, track positions in the curved path and signal packing in the curved path would vary; such variation complicating reproduction access. 
     A word of explanation is in order, concerning the reference in the preceding paragraph to a range of interfaces. As noted in the previously cross-referenced U.S. Pat. No. 3,810,243 to McGinnis et al the compliant action between the head and selected surface can be held to uniformly tight tolerances only when a predetermined minimum number of &#34;cushioning&#34; disks (e.g. 25) are backing the selected surface. In said patent the disks shown are &#34;unspaced&#34; when not positively deflected apart, but the same principles apply to the present spaced bistable configuration. 
     Upon entering the expanded space 10a head 12 is guided laterally into &#34;dimpling&#34; compliant relation to the rotation path of one of the interfacing surfaces 16, 18, essentially in the manner disclosed in the above-referenced commonly assigned U.S. Pat. No. 3,810,243 by McGinnis et al; this intimately couples the head with the selected surfaces for high density. At completion of such operation the head may be withdrawn from the selected interface and the disks then restored to the contracted rotation position in preparation for the next selection operation. In the illustration contraction is caused by momentarily energizing solenoid valve 13c. This admits air, at a non-critically pre-adjusted elevated pressure, to contraction supply duct 13d. This restores the disks to contracted position and when the air supply returns to steady state level the disks are once again bistable. The action is non-critical and other methods of restoring the disks to contracted bistable operation will readily occur to those skilled in the art. 
     The time required to expand the selected interface can be reduced, thereby reducing storage access time, by applying vacuum to the disks during their transitional displacement to the expanded position. For this purpose vacuum is applied to duct passage 13e by operation of solenoid valve 13f in synchronism with said transitional displacement. 
     Hollow spindle 5 contains reduced diameter hollow end portion 5b supporting end plate 3 (said plate having a corresponding reduced diameter central opening for mounting on the spindle) which is threaded externally to couple threadably with an internal thread on hollow member 7; whereby member 7 seats retainingly adjacent plate 3. 
     In operation the adjusted steady state air supply to passage 13a is distributed to the spaces between disks 1 via passage 13, hollow interiors of member 7 and spindle 5, apertures 5a in spindle 5 and pores in spacers 8. This steady state supply of air is pumped radially out of the spaces between the contracted disks by centrifugal action. The resulting continuous negative pressure between the disks conditions the rotation of the unclamped portions of disks 1 to bistability exclusively in the contracted position. 
     Meanwhile the mechanism supplying selection force 20 is positioned adjacent the desired contracted interface to which access is required and operated to exert force 20 upon the facing disks. This initiates expansional deflection of the facing disks to the stable expanded position (FIG. 3); said expansional displacement being accelerated by synchronous application of vacuum to passage 13e through operation of solenoid 13f. Meanwhile the head which has been concurrently positioned opposite the selected interface is inserted centrally into the stabilized expansion opening and guided smoothly into hydrodynamically lubricated relation to one of the facing recording surfaces. When the head operation is completed, and assuming the next operation to be scheduled relative to a different interface, the head is retracted. The disks are then contracted by operation of solenoid valve 13c, and the operations for selecting the next interface are started. 
     In the second embodiment of FIGS. 5-10 flexible storage disks 1a, separated by spacer disks 8a, are mounted upon spindle 35 and retained axially by end plates 2a and 37. Spacers 8a and spindle 35 need not conduct air. Spindle 35 is connected to shaft 39 which is rotated continuously by a not-shown motor. The disks, end plates and spindle thereby rotate as a unit. The end plates are axially clamped by shoulder extensions 41 of shaft 39 and 43 of the spindle. 
     Disks 1a have aligned off-axis ventilation openings 44 which are further aligned with holes 45 in end plate 37. Housing 47 attached to end plate 37 forms part of a ventilation sub-chamber 49 which communicates via end plate holes 45 with disk ventilation holes 44. Spindle extension 51 is rotatably linked to spindle 35 and adapted for axial displacement relative to the spindle. Throttle plate 53 attached to extension 51 completes the closure of ventilation sub-chamber 49 relative to atmosphere when extension 51 is in its most extended position relative to the spindle. Non-rotating air supply coupling 55, supported on the rotating extension 51 via bearings 57 receives filtered air through elements 59, 61 and 63. Adjustable valve 61 provides an adjusted opening 63 between atmosphere and an internal chamber connecting to flexible tubing 59. This supplies steady state air pressure, through passage 65 in non-rotating coupling 55 and passages 67 and 69 in rotating coupling 51, to sub-chamber 49. In turn this transfers steady state air pressure, via end plate openings 45 and aligned disk openings 44, to the interfaces. 
     Normally, spring 71 biases extension 51 to the most extended position in which sub-chamber 49 is sealed off from atmospheric air by abutment of plate 53 against housing 47. In this condition only the above-mentioned steady state air supply reaches the sub-chamber 49 and the disk openings 44. Said supply is adjusted to cause rotational bistability in the unclamped portions of the disks 1a when the disks are initially in contracted mode (FIG. 9), as explained above for the centrally pressured embodiment. Therefore the disks can be stably triggered apart at any selected interface for transducing access in this mode. Expansional deflections can be accelerated by actuating valve 61 to close opening 63 in synchronism with the initial deflection movement, thereby effectually applying vacuum to space 49. 
     To contract the expanded disks, after completion of transducing operation, as explained above for the centrally pressured embodiment, solenoid 75 is excited momentarily displacing armature 77 against bearing surface 79 of extension 55 moving said extension toward the spindle and thereby displacing plate 53 away from sub-chamber housing 47. This opens the sub-chamber to atmosphere momentarily, and thereby momentarily increases air flow through the disks to a level cancelling their rotational stability and restoring them to contracted configuration in readiness for bistable operation. 
     In the illustrated embodiment the disks have eight holes 44, each 1 1/2 inch diameter, centered at radial distances of 2 1/4 inches from the axis of rotation and uniformly located in a circle around said axis. Again, these dimensions are given as exemplary and not limiting. 
     The use of atmospheric air as the source of steady state air pressure need not be uniquely restricted to this second embodiment. In the centrally pressured embodiment of FIG. 1 a similar atmospheric coupling could be used if the shape of spacer disks is selected to have suitable lower resistance to air flow than the mesh spacers disclosed by Penfold et al; e.g. by using spacers having open radial channels for air conduction. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.