Multi-purpose laser/optical sensor in a storage library subsystem

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FIELD OF THE INVENTION

The present invention relates to storage library subsystems as commonly used in the computer data storage arts, and in particular, to a single laser device in combination with a single optical sensor for multiple sensing purposes within a storage library subsystem.

PROBLEM

Storage library subsystems provide large capacity secondary storage to modern computing environments. Such storage library subsystems typically employ robotic control mechanisms to physically manage media cartridges used by host computer system. A plurality of media cartridges are stored within the storage library subsystem. Each media cartridge is in a particular slot in the library subsystem. Each slot is identifiable by its physical position in the library subsystem. Each cartridge is typically uniquely identified by a machine readable label. The subsystem maintains inventory information to associate a particular media cartridge with a particular slot in the subsystem. Responsive to a host computer system request, an appropriate media cartridge is physically retrieved from its associated slot in the library, moved to an appropriate read/write device for processing, and inserted into that device. Conversely, when the use of the media cartridge is complete, the media cartridge is retrieved by the robotic mechanisms from the read/write device, moved adjacent its associated slot according the inventory maintained by the subsystem, and inserted into the storage slot of the library ready for future use in response to another host computer system request.

Prior storage library subsystems were often complex and therefore costly, potentially appropriate for centralized large data processing environments, but inappropriate in the more modern decentralized workgroup environments. Computing environments have tended to become smaller ("downsized") and less centralized. In these decentralized computing environments, reduced complexity and associated reduction in costs are essential elements.

One problem with prior designs which contributed to their relatively higher complexity and resultant higher costs relates to the multiplicity and/or complexity of various sensing mechanisms used to sense several parameters of the operating library subsystem. A first sensing mechanism may be used to calibrate the positioning of the robotic servo control mechanisms relative to the locations of the stored media cartridges (stored in associated slots within the library). In more complex robotic mechanisms, a plurality of sensing devices may be required to calibrate the robotic mechanisms in each of several directions. A second sensing mechanism, independent of the first, may be used to sense the presence or absence of a cartridge in a slot. When the slots are grouped into removable magazines additional sensing mechanisms may be required to sense the presence or absence of a removable magazine. Additionally, a third sensing mechanism is commonly used to read machine readable labels on a media cartridge (barcode labels or other optically or magnetically encoded labels).

From the above discussion, it is evident that there is a need for a simpler, lower cost apparatus to calibrate the robotic mechanism positioning, to sense the presence or absence of a removable magazine or of a single media cartridge, and to read optically encoded labels on media cartridges.

Solution

The present invention solves the above problems and thereby advances the art by providing a simpler apparatus for calibrating robotic mechanism positioning, for sensing presence or absence of a magazine or single media cartridge, and for reading optically encoded labels on media cartridges stored within the library. The present invention comprises a laser light source and associated semiconductor reflectivity semiconductor sensor attached to the moveable robotic gripper hand of the library subsystem. The reflection of the laser light source from various surfaces is sensed by the reflectivity semiconductor sensor. Sensing the reflectivity from target lines within the library subsystem is used to calibrate the absolute position of the robotic gripper hand relative to the target marks. All other components within the storage library subsystem are positioned at fixed offsets from the target lines. Once calibrated, reflectivity sensor can be positioned to measure the reflection off the front face of a desired magazine to detect the presence or absence of a magazine in the library. Similarly, the reflectivity sensor can be positioned to measure the reflection off the front face of a desired media cartridge to detect the presence or absence of a cartridge in a particular slot. Finally, the reflectivity sensor can be positioned to sense the optical (barcode) label on the front face of a media cartridge. The barcode sense signal from the reflectivity sensor can be digitally processed to decode the textual equivalent of the optically (barcode) encoded label.

Specifically, the robotic manipulator of the storage library of the present invention is a gripper hand which is moveable vertically (Y-axis) to align with any one of a plurality of slots for holding media cartridges or any one of a plurality of read/write electronic devices which are vertically aligned in a column. The gripper hand is moved vertically in the Y-axis, along a vertically oriented Y-axis support, by a digitally controlled DC servo motor. When vertically positioned in vertical alignment with the desired slot or electronic read/write device, the gripper hand is extended forward (away from, and perpendicular to the Y-axis support) or retracted backward (toward the Y-axis support) by a second digitally controlled DC servo motor. A plurality of magazines having slots adapted to hold media cartridges are positioned around the outer circumference of a rotatable carousel. The carousel is driven to rotate about an axis parallel to the Y-axis support by a third digitally controlled DC servo motor. Solenoid actuators are used to control gripper jaws of the gripper hand. The jaws are spring biased in a closed position in which the jaws are forced toward one another to grip a cartridge between the jaws. The jaws are forced to an open position (with the jaws spread to an wider separation apart from one another) by actuation of the solenoids. The control apparatus of the library subsystem controls the DC servo motors to move the gripper hand or the rotatable carousel to permit the gripper hand to be aligned with any slot in the library subsystem. By extending and retracting the gripper hand in combination with actuation of the solenoids, the control apparatus of the present invention can controllably grip and release a media cartridge for purposes of moving the cartridge within the library subsystem.

A laser light source and reflectivity sensor are mounted on the gripper hand. The rotatable carousel has a white target patch to calibrate the maximum gain of the reflectivity sensor when measuring the reflection of the laser light source. Near the white patch on the carousel is a void patch on the edge of the carousel (a cutout void area in the edge of the material forming the carousel). The void area provides no reflection of the laser light (for all practical purposes). These two patches provide a high and low level of reflectivity to calibrate the roughly linear response of the reflectivity sensor. Once calibrated at power on reset of the library subsystem, the reflectivity sensor may be used to calibrate the positioning of the robotic mechanisms.

An "L-shaped" white target is positioned at two joining edges of the void patch on the edge of the carousel. The white L-shaped target provides a sharp dividing line between high reflectivity at each leg of the L-shaped target and the void patch to which it adjoins. The position of the L-shaped target on the carousel and the vertical position of other fixed components relative to the L-shaped target are fixed with tight tolerances at time of manufacture. The position of the removable magazines relative to the L-shaped target is known to the limits of human intervention in seating the magazines in their support guides. The position of the laser light source and the reflectivity sensor relative to the gripper hand vertical servo position are known with precision from tight manufacturing tolerances. The position of the robotic gripper hand relative to the target is determined by use of the laser light and reflectivity sensor.

The approximate position of the white patch relative to both the carousel rotational servo position and the gripper hand vertical motion servo motor is known from manufacturing specifications. Once positioned at the white patch and after calibrating the gain of the sensor, the control electronic of the library rotate the carousel while sensing the reflectivity to approximately locate the vertical member of the L-shaped target. The control electronics next moves the gripper hand vertically up or down to locate the horizontal member of the L-shaped target. With each member of the L-shaped target located, the more precise position of each edge of the target may be located by finding the vertical or rotational position at which the reflectivity of the laser light is exactly half of the full gain of the reflectivity sensor. That point is the position at which the sensor is most precisely positioned half on vertical or horizontal the edge of the L-shaped target, and half on the corresponding edge of the void patch.

Once the reflectivity gain and servo positioning parameters are calibrated, the laser source and reflectivity sensor are used to detect the presence or absence of a magazine on the carousel, to sense the presence or absence of a cartridge in a particular slot of a magazine, and to read barcoded labels on the face of a media cartridge. This single, simple, inexpensive sensor mechanism replaces various sensors typically used for these multiple purposes in prior designs. The present invention thereby reduces complexity and associated costs as compared to prior approaches in storage library subsystems. Numerous other advantages and features of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective cut away view of a storage library subsystem which employs the methods and associated apparatus of the present invention;

FIG. 2 shows a perspective view of the details of the gripper hand and its relationship to media cartridges in a magazine within the storage library subsystem shown in FIG. 1;

FIG. 3 shows a side cut view of the storage library subsystem show in FIG. 1 with its outer covers removed;

FIG. 4 shows additional detail of the mounting of laser light source and reflectivity sensor on the robotic gripper hand of FIG. 2;

FIG. 5 shows additional detal of the L-shaped target and calibration patches on the carousel of FIG. 2;

FIG. 6 is a flowchart of the process of calibrating the gain on the reflectivity sensor of FIG. 4;

FIG. 7 is a flowchart of the process of calibrating the robotic positions using the sensor of FIG. 4;

FIG. 8 is a flowchart of the process of sensing the presence or absence of a magazine or carriage in the library of FIG. 1; and

FIG. 9 is a diagram of control apparatus which operates the methods of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

OVERVIEW

FIG. 1 depicts a storage library subsystem 100 which embodies the methods and apparatus of the present invention. Storage library subsystem 100 is enclosed by covers 102. Access port 104 permits operator access to the media cartridges in subsystem 100 through covers 102. Within covers 102, structural members 118 form a frame to which components of subsystem 100 are attached. Operator panel 122 provides operator interaction for user manual control of subsystem 100. Rotatable carousel 106 within subsystem 100, holds a plurality of removable magazines 108. Magazines 108 are positioned and supported on carousel 106 by magazine supports 116. Each magazine 108 is adapted to hold a plurality of media cartridges 114. Each cartridge is placed within a slot of the magazine 108. A magazine 108 positioned under access port 104 may be removed by an operator by opening a sliding door (not shown) covering access port 104, and lifting magazine 108 vertically upward and out of library 100. Conversely, an operator may insert a new magazine 108 into library 100 through access port 104. The inserted magazine 108 is mated with, and positioned by, magazine supports 116 on carousel 106. When the sliding door (not shown) covering access port 104 is again closed, library subsystem 100 may manipulate cartridges 114 held in any slot of any magazine 108 on carousel 106. Schneider et al., in U.S. Pat. No. 5,231,552 issued Jul. 27, 1993, discloses a magazine for holding media cartridges useful in storage library subsystem 100. The magazine disclosed by Schneider et al. includes means associated with each slot in the magazine for retaining a media cartridge within the slot. The retention means are actuated to retain or release the associated cartridge by a spring loaded mechanism when the cartridges is pushed deeper into the slot.

Electronic read/write devices 124 are capable of storing and retrieving information on media cartridges 114. Robotic mechanisms within storage library subsystem 100 move media cartridges 114 from slots in a magazine 108 to and from read/write electronic devices 124. Control electronics 110 control and sense the movement of the robotic mechanisms within storage library subsystem 100. Control electronics 110 further provide interface electronics for exchanging command and data with attached host computer systems (not shown). In response to a host computer system request, control electronics 110 actuates the robotic mechanisms to retrieve a requested media cartridge 114 from the magazine 108 in which it is held, move the media cartridge 114 to electronic read/write device 124, and insert the media cartridge 114 into the read/write device 124 for further processing. When the requested processing has completed, control electronics 110 actuates the robotic mechanisms to retrieve the media cartridge 114 from electronic read/write device 124 in which it was previously inserted, and returns the media cartridge 114 to the slot in magazine 108 where it was previously held. Control electronics 110 maintains in an associated memory device an inventory of the location by slot and magazine of each media cartridge 114 within storage library subsystem 100.

Robotic mechanisms of library 100 comprise gripper hand 112 and rotatable carousel 106. Gripper hand 112 is controllably movable by control electronics 110 vertically up and down on Y axis support 120. Rotatable carousel 106 is controllably rotated by control electronics 110 to position one of the plurality of magazines 108 to be aligned with Y-axis support 120. Gripper hand 112 may also be extended forward (toward magazine 108) or retracted backward (away from magazine 108) by control electronics 110. The extension and retraction motion of gripper hand 112 is referred to as "Z-axis" motion. Solenoids 208 (of FIG. 2) are used by control electronics 110 to actuate the grip and release of a media cartridge 114 between gripper jaws 208 of FIG. 2. By combining gripper hand Z-axis motion, vertical motion of the gripper hand on Y-axis support 120, solenoid grip and release, and rotation of carousel 106, control electronics 110 may move any requested cartridge 114 from a slot in a magazine 108 to a read/write device 124 or from a read/write device 124 back to a slot in a magazine 108.

FIG. 3 shows storage library subsystem 100 from a side view with covers 102 removed to reveal additional detail of the robotic mechanisms within. Rotatable carousel 106 is controllably rotated by control electronics 110 by use of digitally controlled DC servo motor 302 and transmission assembly 304. By actuating DC servo motor 302 in a first direction, control electronics 110 controllably rotates carousel 106 in a clockwise direction. By actuation of DC servo motor 302 in the opposite direction, carousel 106 is rotated counterclockwise. Gripper hand 112 is controllably moved vertically up and down on Y-axis support 120 by control electronics 110 use of digitally controlled DC servo motor 306, transmission assembly 308, and driving belt 310. Gripper hand 112 is attached to belt 310 at joint 312. By activating DC servo motor 306 in a first direction, gripper hand 112 can be moved vertically upward on Y-axis support 120. By controllably rotating DC servo motor 306 in an opposite direction, gripper hand 112 can be moved vertically downward on Y-axis support 120. Rollers 300 attached to gripper hand 112 secure the gripper hand to Y-axis support 120 and permit the gripper hand 112 to slide vertically up and down on the support. DC servo motor 204 is controllably activated by control electronics 110, to extend gripper hand 112 forward on its Z-axis (leftward in FIG. 3) toward magazine 108, and controllably activated to retract gripper hand 112 rearward on its Z-axis (rightward in FIG. 3) away from magazine 108. Gripper hand 112 slides on Z-axis rail 202 as it is extended forward and retracted rearward by activation of DC servo motor 204. Gripper jaws 208 are opened by activation of solenoids 206 and closed by deactivation of solenoids 206 to grip or release a media cartridge 114.

As shown in FIG. 3, gripper hand 112 is gripping a cartridge 114 between gripper jaws 208. The media cartridge 114 has been partially retracted rearward to remove the media cartridge 114 from magazine 108. Laser/optical sensor unit 314, is positioned toward the front of gripper hand 112, and is used to calibrate the positioning of gripper hand 112 relative to carousel 106 and slots in magazines 108.

FIG. 2 shows a perspective view with additional detail of gripper hand 112 as it relates to magazine 108 inserted and supported within guides 116 on carousel 106. Gripper hand 112 is adapted to slide forward and backward on Z-axis rail 202. Rollers 216 secure gripper hand 112 to Z-axis rail 202 and permit gripper hand 112 to slide on rail 202. DC servo motor 204 turns pulley 210, which in turn drives belt 212. Gripper hand 112 is affixed to a position on belt 212 (not shown) such that when servo motor 204 is actuated to turn in one direction will move gripper hand 112 forward, and when turned in the opposite direction will move gripper hand 112 rearward. Gripper jaws 208 are spring biased to maintain a closed position, squeezed toward one another when solenoids 206 are inactive. When solenoids 206 are activated by control electronics 110, gripper jaws 208 are driven apart from one another to an open position. In the open position, a media cartridge 114 may be inserted between gripper jaws 208. In the closed position, gripper jaws 208 hold a media cartridge 114 between the jaws.

When retrieving or inserting a media cartridge 114 into a particular slot of a magazine 108, gripper hand 112 is moved vertically up or down on the Y-axis support, such that the top edge of Z-axis rail 202 is aligned just below the bottom edge of the cartridge 114 to be manipulated (either retracted or inserted). When control electronics 110 inserts a cartridge 114 into magazine 108, gripper hand 112 is moved forward by activation of DC servo motor 204. When retracting a media cartridge 114, control electronics 110 moves gripper hand 112 rearward by activation of DC servo motor 204 in the opposite direction. Furthermore, control electronics 110 activates and deactivates solenoids 206 to open or close jaws 208 to thereby release or grip a cartridge 114.

In response to a request received from an attached host computer system, control electronics 110 of library subsystem 100 moves robotic gripper hand 112 vertically up or down on Y-axis support 120 to align gripper hand 112 with an appropriate slot in a magazine 108 containing a requested cartridge 114. In addition, control electronics 110 rotates rotatable carousel 106 to align the desired magazine 108 with the gripper hand 112. The gripper hand 112 is controlled to retrieve a cartridge 114 from a desired slot in magazine 108, or to return a cartridge 114 into a desired slot.

FIG. 9 shows additional detail of control electronics 110 which performs the methods of the present invention to control the robotic gripper hand 112 and carousel 108 of the storage library 100. Control electronics 110 comprises a CPU 1200 which executes programmed instructions for the methods of the present invention fetched from ROM 1202 over memory bus 1252. CPU 1200 exchanges data with RAM 1204 also over memory bus 1252. Data stored in RAM 1204 includes control variables relating to control of the robotic mechanisms of the library 100 as well as host computer 1210 related communication variables and buffers. CPU 1200 exchanges, information (including commands, status and data) with one or more host computer systems 1210 via bus 1254 and host I/F controller 1208. Host I/F controller 1208 converts information exchanged with CPU 1200 over bus 1254 into signals and protocols applicable to host communications bus 1250. Host communications bus 1250 may be any of several well known peripheral interface standards including local area network (LAN) connections, or, in the preferred embodiment of the present invention, SCSI.

CPU 1200 exchanges command and status information with each of three precision motion controllers 1206 over bus 1256. Precision motion controllers (PMC) 1206 are any of several standard motion controller integrated circuits used for the control of servo motors. In the preferred embodiment of the present invention, a National Semiconductor LM628 or LM629 is used for each of three PMCs 1206. One of ordinary skill in the art will recognize many equivalent controller circuits which are capable of controlling servo motors on behalf of CPU 1200 and providing status information back to the CPU 1200. A first PMC 1206 controls DC servo motor 204 over bus 1258 to extend and retract the gripper hand 112. A second PMC 1206 controls Y-axis DC servo motor 306 over bus 1260 to move the gripper hand 112 up and down on Y-axis support 120. The third PMC 1206 rotates carousel 106 by applying signals over bus 1262 to servo motor 302. CPU 1200 applies signals over bus 1266 to solenoid controller 1212 which, in turn, activates and deactivates solenoids 206 to open and close gripper jaws 208. Reflectivity sensor 314 applies its analog output signal to A/D converter 1214 over path 1268. CPU 1200 samples the output of reflectivity sensor 314 converted to digital values via bus 1270 through A/D converter 1214. Laser light source 316 is controlled by CPU 1200 via path 1272.

CPU 1200 combines motions of the robotic mechanisms, exchanging information with PMCs 1206 to control DC servo motors 204, 302, and 306, and activation and deactivation of solenoids 206 through solenoid controller 1212, to grip, release, and move media cartridges 114 within library 100.

FIG. 4 depicts additional detail of the laser light source 316 mounted in mounting block 400 adjacent reflectivity sensor 314 (also mounted in mounting block 400). Conductor path 1272 from control electronic 110 turns the laser light source 316 on and off. Reflectivity sensor 314 applies it analog output signal to conductive path 1268. Laser light source 316 may be any of several standard light sources and is preferably a Toshiba TOLD-9211 or Hitachi HL-6712-G1 generating a collimated beam at a wavelength of approximately 670 nm. with a power of approximately 5 mW. Reflectivity sensor 314 may be any of several standard optoelectronic sensing devices and is preferably an Optek QP560A, OP560B, or QP560C NPN Silicon Photodarlington. Reflectivity sensor 314 is unfocused and achieves a high depth of field (up to approximately 5 inches) with a 10 degree view angle. The laser light source 316 produces a spot size of approximately 0.008". Laser light source 316 emits its light through hole 402 in mounting block 400. Reflectivity sensor 314 receives unfocused reflections of light through hole 404 of mounting block 400. As shown in FIG. 2, mounting block 400 with mounted holes 402 and 404 positioned at the forward edge of the Z-axis rail 202 of gripper hand 112.

FIG. 2 shows a highly reflective white patch 506 on the edge of rotatable carousel 106. Adjacent the white patch 506 is a void patch 500 where the material forming the carousel 106 is removed to provide (essentially) no reflectivity. FIG. 5 shows the white patch 506 and the void patch 500 in a straight edge on view. White patch 605 and void patch 500 are used as described below in calibrating the gain of the reflectivity sensor and associated A/D converter 1214 of FIG. 2. In FIG. 5, it can be seem that the void patch 500 is bordered on two of its three edges with white stripes, namely a horizontal stripe 502 abutting a vertical stripe 504. The abutting white stripes together are also referred to herein as L-shaped target 508. The reflectivity sensor 314 is used to locate the L-shaped target 508 in initial position calibration of the moveable, servo controlled, robotic mechanisms.

SENSOR GAIN CALIBRATION

FIG. 6 is a flowchart of the steps used when calibrating the gain of reflectivity sensor 314 and the associated A/D converter 1214 of FIG. 2. Element 600 is operable to move the laser light source 316 and the reflectivity sensor on gripper hand 112 vertically on Y-axis support 120 by activation of DC servo motor 304 to the nominal vertical position of the center of the white patch 506. Element 602 is then operable to rotate the carousel 106 to the nominal rotational axis position to align the center of white patch 506 with the reflectivity sensor 314 and laser light source 316. Manufacturing tolerances and the size of white patch 506 are sufficient to assure that positioning the carousel 106 and the gripper hand 112 at nominal positions to align at the center point of the patch will assure that the light from laser light source 316 will strike the patch and will further assure that the entire angle of view of reflectivity sensor 314 will be covered by the white patch 506.

Element 604 is next operable to turn on laser light source 316 by applying a signal to path 1272. Element 604 is further operable to measure the reflectivity as signified by the signal output from reflectivity sensor 314 on conductive path 1268. The output signal on path 1268 is applied as input to A/D converter 1214 and converted to a digital value applied to bus 1270 for use by CPU 1200. The digital value represents the highest level of output of the sensor 314 for application in the storage library subsystem 100.

Element 606 rotates carousel 106 by activation of DC servo motor 304 to align void patch 500 on the edge of the carousel 106 with the position of laser light source 316 and reflectivity sensor 314 on gripper hand 112. As in element 602 above, the size of void patch 500 and manufacturing tolerances are sufficient to assure that the light from laser light source 316 and the entire angle of view of reflectivity sensor 314 fall completely within the bounds of void patch 500.

Element 608 next measures the reflectivity output signal from sensor 314. This signal output represents the lowest level of output of sensor 314 for application in the storage library subsystem 100. Element 610 then turns off laser light source 316. This low value measured by element 608 and the high value measure by element 604 are used by element 612 to compute coefficients of the linear response curve of reflectivity sensor 314. These coefficients are then applied to all further measurements of reflectivity to normalize all reflectivity measurements made by reflectivity sensor 314.

THETA AND VERTICAL POSITION CALIBRATION

FIG. 7 is a flowchart describing the operation of the present invention applied to the calibration of the theta position (rotat