Automated storage library with horizontal array of storage cells

The invention is an automated storage library including one or more robotic accessors which move upon the surface of a horizontal plane including the openings to storage cells. The accessors are wireless, remotely controlled vehicles. The vehicles employ known tracking mechanism(s) to move between locations within the library. The storage cells are embedded beneath the horizontal surface. The horizontal plane is a floor which is formed by the surface of the storage cells. Openings in the floor are also the access openings to the storage cells. Storage media are raised and lowered into the storage cells by a picker mechanism on the vehicles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an improved automated storage library. More 
particularly, the invention is an automated storage library including one 
or more robotic accessors which move upon the surface of a horizontal 
plane including the openings to storage cells. 
2. Description of the Related Art 
Modern computers require a host processor including one or more central 
processing units and a memory facility. The processor manipulates data 
stored in the memory according to instructions provided to it. The memory 
must therefore be capable of storing data required by the processor and 
transferring that data to the processor at a rate capable of making the 
overall operation of the computer feasible. The cost and performance of 
computer memory is thus critical to the commercial success of a computer 
system. 
Because today's computers require large quantities of data storage 
capacity, computer memory is available in many forms. A fast but expensive 
form of memory is main memory, typically comprised of microchips. Other 
available forms of memory are known as peripheral storage devices and 
include magnetic direct access storage devices (DASD), magnetic tape 
storage devices, and optical recording devices. These memory devices store 
data on storage media, such as disks and tapes. Peripheral storage devices 
have a greater storage density and lower cost than main memory, but fail 
to provide the same performance. For example, the time required to 
properly position a tape or disk beneath a read/write mechanism of a drive 
cannot compare with the rapid, purely electronic data transfer rate of 
main memory. 
It is inefficient to store all of the data in a computer system on a single 
type of memory device. It is too costly to store all of the data in main 
memory and performance is reduced too much to store all of the data on 
peripheral storage devices. Thus, a typical computer system includes both 
main memory and one or more types of peripheral storage devices arranged 
in a data storage hierarchy. The data storage hierarchy arrangement is 
tailored to the performance and cost requirements of the user. In such a 
hierarchy, main memory is often referred to as primary data storage, the 
next level of the hierarchy is often to referred to as secondary data 
storage, and so on. Generally, the highest level of the hierarchy has the 
lowest storage density capability, highest performance and highest cost. 
As one proceeds down through the hierarchy, storage density generally 
increases, performance generally decreases, and cost generally decreases. 
By transferring data between different levels of the hierarchy as 
required, the cost of memory is minimized and performance is maximized. 
Data is thus stored in main memory only so long as it is expected to be 
required by the processor. The hierarchy may take many forms, include any 
number of data storage or memory levels, and may be able to transfer data 
directly between any two distinct memory levels. The transfer of data may 
employ I/O channels, controllers, or cache memories as is well known in 
the art. 
The need for memory is expanding. Data to be stored may include coded data 
and uncoded data, such as images. Images may be included in engineering 
drawings, financial and insurance documents, medical charts and records, 
etc. Images can take many forms, and therefore cannot be encoded into the 
binary 0's and 1's of computers as easily and compactly as text. Most of 
the world's data, particularly image data, is still stored on paper. The 
cost of filing, storing, and retrieving such paper documents including 
image data is escalating rapidly. It is no longer acceptable to maintain 
rooms or warehouses stocked full of documents which must be retrieved 
manually when access thereto is required. Optical scanners are now capable 
of converting images into machine readable form for storage on peripheral 
storage devices, but the storage space required for the image 
data--although significantly less than that required for paper 
documents--is still quite large. Numerous disks or tapes are required for 
most business applications. Automated storage libraries have thus been 
developed to manage the storage of such disks and tapes. 
Automated storage libraries include a plurality of storage cells for 
retaining removable data storage media, such as magnetic tapes, magnetic 
disks, or optical disks, a robotic accessor mechanism, and one or more 
internal peripheral storage devices. Each data storage medium may be 
contained in a cassette or cartridge housing for easier handling by the 
accessor. The accessor operates on command to transfer the data storage 
media between the storage cells and the internal peripheral storage 
devices without manual assistance. Once a data storage medium is mounted 
in an internal peripheral storage device, data may be written to or read 
out from that medium for as long as the system so requires. Data is stored 
on a medium in the form of one or more files, each file being a logical 
data set. The internal peripheral storage devices and storage cells may be 
considered distinct levels of a data storage hierarchy. In addition, data 
storage media in shelf storage (i.e. not in the storage cells, but instead 
outside the reach of the robotic accessor without manual intervention) may 
be considered yet another level of a data storage hierarchy. 
Several automated storage libraries are known. IBM Corporation introduced 
the 3850 Mass Storage Subsystem for the storage and retrieval of magnetic 
tape modules in the 1970's. This library stored tape modules in a 
stationary, honeycombed array of storage cells. The array was planar and 
oriented vertically. Tape modules were moved horizontally into and out of 
the storage cells and tape drives by the accessor. 
More recently, several firms have introduced automated storage libraries 
for magnetic tape cartridges and optical disks. These libraries include 
numerous variations in configuration, but always arrange the storage cells 
in a vertical array. For example, U.S. Pat. No. 4,654,727 discloses a 
magnetic tape cartridge library in which columns of stationary storage 
cells are arranged in a generally circular array. The openings of the 
storage cells face the center of the array, where the accessor is located. 
Although the storage cells tilt downward from their openings, the openings 
are arranged in one or more vertical planes. 
Another magnetic tape library is disclosed in U.S. Pat. Nos. 4,864,438, and 
4,864,511. The configuration of this library is similar to that disclosed 
in U.S. Pat. No. 4,654,727, except that an accessor may access two 
stationary arrays of storage cells. The arrays are generally circular and 
concentric. The accessor is located between the arrays. The openings of 
the inner array face outward and the openings of the outer array face 
inward. The openings of the storage cells are again arranged in one or 
more vertical planes. 
Yet another magnetic tape library is disclosed in U.S. Pat. No. 4,271,440. 
This library includes storage cells arranged in circular arrays which can 
be rotated to bring a particular cell to a position of close proximity to 
an accessor. Again, the openings of the storage cells are arranged 
vertically. Additional library configurations are known, but the openings 
of the storage cells are always arranged vertically. An example of a 
magnetic tape library with such an arrangement can be found in U.S. Pat. 
No. 5,015,139. Examples of optical disk libraries with such an arrangement 
can be found in U.S. Pat. Nos. 4,271,489, 4,527,262, 4,614,474, 4,608,679, 
4,766,581, and in the IBM 3995 Optical Library Dataserver. 
Several factors are known to affect library efficiency, including storage 
capacity, expandability, moving mass, connectivity, failure points, and 
flexibility. Storage capacity is the amount of data that may be contained 
within a library. Expandability is the ability to increase the storage 
capacity of a library. For example, the storage capacity can be increased 
by adding additional storage cells, if possible. Moving mass is the amount 
of mass which must be moved during the transfer of storage media. 
Generally, a reduction in moving mass increases the speed of movement and 
improves reliability. Connectivity is the freedom to transfer storage 
media between specific storage cells and peripheral storage devices. 
Ideally, a library can transfer any storage medium therein to any 
peripheral storage device therein. Failure points are the areas where the 
library is likely to fail. Ideally, a library will contain no single 
points of failure, thereby improving reliability. Flexibility is the 
ability to change certain library characteristics, such as the number of 
accessors or grippers per accessor. 
Existing libraries fail to achieve adequate efficiency because of one or 
more of the aforementioned factors. For example, the libraries disclosed 
in U.S. Pat. Nos. 4,654,727, 4,864,438 and 4,864,511 each have a robotic 
accessor mechanism which is a single point of failure relating to all or a 
portion of the storage media therein. In addition, expandability is 
inhibited because the vertically arranged storage cells completely 
surround the accessor. The library disclosed in the '438 and '511 patents 
can be expanded by interconnecting several silos (a silo is a single 
accessor and its surrounding storage cells) with mechanical passthru 
mechanisms. Unfortunately, the passthru mechanism is relatively slow and 
reduces reliability. Also, expansion can only occur in silo increments, 
thereby reducing floor space utilization in many installations. 
Other libraries may improve upon some of the aforementioned factors, but at 
the expense of other such factors. To the extent, if any, that machines 
used outside of the data processing industry (such as jukeboxes) are 
analogous, the same tradeoffs apply. A heretofore unrecognized and 
unresolved problem is thus the optimization of the aforementioned factors 
in automated storage libraries. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is the principal object of this invention to 
improve automated storage libraries. 
Another object of this invention is to improve the efficiency of automated 
storage libraries. 
Still another object of this invention is to improve the configuration of 
automated storage libraries. 
These and other objects of this invention are accomplished by an automated 
storage library including one or more robotic accessors which move upon 
the surface of a horizontal plane including a plurality of openings to 
associated storage cells. 
The accessors are wireless, remotely controlled vehicles. The vehicles 
employ known tracking mechanism(s) to move between locations within the 
library. The storage cells are embedded beneath the horizontal surface. 
The horizontal plane is a floor which is formed by the surface of the 
storage cells. Openings in the floor are also the access openings to the 
storage cells. Storage media are raised and lowered into the storage cells 
by a picker mechanism on the vehicles. 
The configuration of the aforementioned automated storage library improves 
efficiency. The library may be easily expanded by adding storage cells in 
either (or both) of two non-vertical directions. Storage cells can be 
added in any increments thereof. The moving mass is reduced because the 
vehicle is wireless. Because the direction of vehicle travel is not 
constrained by rails or other means, any storage media can be transferred 
to any peripheral storage device, even after the library is expanded. 
Single points of failure are eliminated by employing multiple vehicles. 
The library is flexible in that additional vehicles may be added without 
twisting or entanglement of control cables (because there are none). 
The foregoing and other objects, features, and advantages of the invention 
will be apparent from the following more particular description of the 
preferred embodiment of the invention, as illustrated in the accompanying 
drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now more particularly to the drawing, like numerals denote like 
features and structural elements in the various figures. The automated 
storage library of the invention will be described as embodied in a 
magnetic tape and optical disk library for a data processing environment. 
As used hereafter, "peripheral storage device" and "automated storage 
library" also refer to similar devices used outside of the data processing 
industry, such as jukeboxes. 
Referring to FIG. 1, the configuration of the automated storage library is 
shown attached to a host processor 1. Host processor 1 may be any known 
host computer system, such as an IBM 3090 mainframe computer running the 
MVS operating system. Host processor 1 communicates with the library via a 
library control unit 2. Library control unit 2 may be an IBM PS/2 personal 
computer running the OS/2 operating system and programmed to control the 
remainder of the library. Library control unit 2 stores the library 
configuration file, storage media inventory, error information, etc. and 
directs the automatic operation of the robotic accessors and peripheral 
storage devices of the library--such as creating and deleting files on the 
storage media, writing to and reading from the storage media, transferring 
the storage media between storage cells and peripheral storage devices, 
and providing statistics on usage and errors. 
The keyboard to library control unit 2 allows a storage administrator to 
manually enter library operation requests and other information. The 
coupling of library control unit 2 to other components is represented 
schematically by arrows. The bus, interface, and protocol for 
communicating with the other components may be any known in the industry. 
For example, host processor 1 may be coupled to library control unit 2 
using an IBM System/370 or System/390 channel attachment. The remaining 
features of library control unit 2 are not relevant to the subject 
invention. 
The library includes a floor formed by a plurality of panels 10. A 
horizontal array of storage cells is embedded beneath most panels 10 in a 
region 5. Panel 10a is exemplary of other such panels in the library and 
is magnified to reveal a series of horizontal openings 11a to the storage 
cells 15. Each storage cell 15 is capable of storing one peripheral data 
storage medium therein. In the embodiment shown, each storage medium is a 
magnetic tape cartridge 9 or an optical disk cartridge 8 capable of having 
data recorded on and read from a magnetic tape or optical disk therein. 
The library also includes one or more peripheral storage devices for 
writing data to and reading data from the storage media in the library. 
The embodiment shown includes a plurality of optical disk drives 7 and a 
magnetic tape drive 16. The optical disk drives 7 are set above the floor 
to expose a series of vertical openings 18 therein. The magnetic tape 
drive 16 is embedded beneath the floor. Panel 10b is magnified to reveal a 
horizontal opening 11b therein. 
Drives 7 and 16 and cartridges 8 and 9 need not be of any specific type as 
such details are not relevant to the subject invention. For example, the 
optical disks may include ablative, phase-change, magneto-optic, or any 
other active recording layers and may be read-only, write-once, or 
rewritable, as is known, so long as they are compatible with optical disk 
drives 7. The magnetic tapes may be metal particle, chromium dioxide, or 
any other active recording layer, as is known, so long as they are 
compatible with magnetic tape drive 16. The storage media and devices may 
be any size form factor, so long as the necessary compatibility is 
maintained. In addition, the recording formats are not part of the subject 
invention and may be any known in the art. 
The vertical opening 18 in each optical disk drive 7 permits a cartridge 8 
to be mounted therein in a horizontal position (i.e. such that the disk is 
set flat), as is known in the art. Such a position simplifies drives 7 by 
eliminating the need to compensate for certain gravitational effects 
during operation, but requires that the library include the capability to 
rotate a cartridge 8 between its vertical position in a storage cell 15 
and its horizontal position in a drive 7. The horizontal opening 11b in 
magnetic tape drive 16 permits magnetic tape cartridges to be mounted 
therein in a vertical position (i.e. such that the cartridge is set on its 
edge), as is known in the art. Such a position permits drive 16 to be 
embedded beneath the floor and eliminates the need for a cartridge 9 to be 
rotated between horizontal and vertical positions. 
In alternative embodiments, any combination of peripheral storage device 
numbers, types (magnetic tape drive, optical disk drive, etc.) and 
orientations (horizontal access opening, vertical access opening, etc.) 
may be used. For example, in one alternative embodiment, all peripheral 
storage devices in the library may be oriented to have a horizontal access 
opening. In another embodiment, all peripheral storage devices may be 
oriented to have a vertical access opening. In either of these 
embodiments, all of the devices could be the same type. 
Two robotic accessors 6 are four-wheeled vehicles which are capable of 
moving horizontally upon the surface of the floor. The horizontal movement 
permits the vehicles to be positioned in proximity above or beside any 
storage cell or peripheral storage device in the library. A picker 
mechanism 12 on each vehicle enables it to insert a storage medium in or 
retrieve a storage medium from a storage cell or peripheral storage device 
in proximity to a vehicle. The vehicles are wireless, battery or capacitor 
powered, and remotely controlled. Library control unit 2 includes control 
algorithms to prevent vehicles 6 from colliding into one another. 
Control commands are relayed to each vehicle by a vehicle controller 3. 
Controller 3 communicates with a vehicle via a controller antenna 13 and a 
vehicle antenna 30 over a communication channel represented by dotted line 
4. The communication channel may be infrared wave, radiowave, microwave, 
etc. In alternative embodiments, the library may include a different 
number of vehicles (i.e. one, three, or more), and each vehicle may 
include a plurality of picker mechanisms 12. 
Referring to FIG. 2, a vehicle 6 is magnified to reveal additional detail. 
Control commands received from vehicle controller 3 are distributed to the 
various vehicle components by vehicle electronics 39. The electrical 
couplings between electronics 39 and the other components of the vehicle 
are not shown for convenience. Such couplings may be accomplished using 
any known technique. 
Vehicle 6 includes a chassis and four wheels 32. Each of the two rear 
wheels are driven by a wheel motor 33. Steering is accomplished by a 
steering actuator 34 coupled to an axle 35 supporting the two front 
wheels. Vehicle positioning is accomplished by optically sensing the 
surfaces of floor panels 10 and drives 7, as is known. A printed pattern 
of lines 17 on floor panels 10 are sensed and counted to determine the 
precise position of a vehicle. For such sensing, a light source (i.e. 
laser, light emitting diode, etc.) 36 emits an optical beam which reflects 
off of the floor and is detected by photosensor 37. In alternative 
embodiments, other vehicle positioning techniques may be used, such as 
optically or mechanically sensing and counting the seams between floor 
panels 10 and openings 11a to determine the position of a vehicle. 
Vehicle 6 also includes a picker mechanism 12. Picker 12 includes a frame 
40 in which an axle 41 is slidably and rotatably mounted. Two gripping 
arms 42 are attached to axle 41 for gripping a cartridge 8 or 9 therein. 
Detents at the end of the arms opposite axle 41 are used to retain or 
release the cartridges. As shown in FIG. 2, a magnetic tape cartridge 9 is 
retained in picker 12 by the detents of arms 42. The cartridge 9 is 
positioned vertically to enable it to be moved through vehicle chassis 
opening 43. Actuator 44 drives axle 41 vertically within frame 40 to 
enable a cartridge to be retrieved from or delivered to a storage cell 15 
or a device 16 through opening 43. 
To interface with a device 7, picker 12 is capable of rotating arms 42 to a 
horizontal position. The solid lines in FIG. 2 show picker 12 retaining a 
cartridge 9 in a vertical position. The rotation of picker 12 is shown by 
dotted arrow 50 pointing to horizontal position 51. Actuator 52 rotates 
axle 41 to swing arms 42 and the optical disk cartridge 8 (if any) 
therein, in the direction of dotted arrow 50. Once arms 42 reach 
horizontal position 51, actuator 44 enables a cartridge 8 to be retrieved 
from or delivered to a device 7. Actuator 52 may be reversed to reorient 
arms 42 to a vertical position as required. 
Referring to FIG. 3, the electronics of controller 3 and vehicle 6 are 
shown schematically. Library control unit 2 is coupled between host 
processor 1 and controller 3. More specifically, control unit 2 is coupled 
to a control processor and a picker command generator. The control 
processor accepts vehicle positioning requests from control unit 2 and 
generates a target position signal. The target position signal is compared 
to an actual position signal. The actual position signal is received from 
vehicle 6 by antenna 13 and is amplified, demodulated, and deserialized 
before being compared to the target position signal. Depending upon the 
results of the comparison, a steering command generator and/or a motion 
command generator may output commands to reposition the vehicle. The 
picker command generator translates picker action requests from control 
unit 2 into a form which can be understood by the vehicle. The commands 
(picker, steering, and motion) are multiplexed, modulated, and amplified 
before transmission to the vehicle. 
The commands are received by antenna 30 of vehicle 6. The commands are 
amplified, demodulated, demultiplexed before being directed to the proper 
driver. Picker commands are directed to a picker actuators driver, which 
then drive the actual electromechanical actions of picker actuators 44 and 
52. Steering commands are directed to a steering actuator driver, which 
then drives the actual electromechanical action of steering actuator 34. 
Motion commands are directed to a wheel motors driver, which then drives 
the actual electromechanical actions of wheel motors 33. As the vehicle is 
positioned about the library, the signal from photosensor 37 is amplified, 
the lines (seams, openings, etc.) crossed are counted, and the signal is 
modulated and amplified. The position signal is then transmitted to 
control unit 3 for use as previously described. In this manner, a feedback 
loop is operated in which positioning of a vehicle is directed depending 
upon the desired library operation and the current sensed position of such 
vehicle. 
While the invention has been described with respect to a preferred 
embodiment thereof, it will be understood by those skilled in the art that 
various changes in detail may be made therein without departing from the 
spirit, scope, and teaching of the invention. For example, while the 
invention has been disclosed in the context of a magnetic tape and optical 
disk library, similar consideration may make it equally applicable to 
other types of libraries. In addition, numerous variations in the 
libraries may be made, such as the number of drives and storage cells. The 
size of the described library may be modularly altered by adding and 
deleting peripheral storage devices, or by adding and deleting floor 
panels in the horizontal plane with storage cells or devices embedded 
therebelow. Accordingly, the invention disclosed herein is to be limited 
only as specified in the following claims.