Carousel tape system

Apparatus for storing and transferring digital electromagnetic information. The apparatus makes use of a plurality of standard pipe cartridges each of which is independently capable of storing a quantity of electromagnetic information. The cartridges are removably stored in a carousel which is rotatably carried on a control housing. The carousel is removable from the control housing, permitting interchangeability of carousels and access to substantial quantitites of stored information. The control housing includes a plurality of independently operable read/write stations, each of which has a read/write head for transferring information. The read/write heads are selectively connected to output ports permitting access to computer equipment. The control housing also includes means for indexing a selected cartridge relative to a selected read/write station. Each of the stations includes means for effecting release of the indexed cartridge from the carousel and for transporting the cartridge to a read/write position within the station. After information is transferred between the cartridge tape and read/write head, the cartridge is returned to its stored position in the carousel. Each of the stations is provided with means for sensing improper orientation of the cartridge within the carousel and for preventing release of the cartridge from the carousel if improperly oriented.

The invention generally relates to peripheral equipment for digital 
computers, and is specifically directed to carousel apparatus which houses 
a plurality of identical electromagnetic tape cartridges in radial fashion 
and is operable to effect a transfer of electromagnetic information 
between a selected cartridge and an accessed digital computer. 
Various storage media and devices are available for the storage of data in 
electromagnetic form, and many types of peripheral equipment are capable 
of accessing a digital computer to a stored data base. 
One example of a data storage device is the tape cartridge or cassette, 
which offers certain advantages over other data storage devices. Among 
these is the feature of the cartridge being fully self-contained, with the 
supply and takeup reels as well as the tape housed in a single protective 
cartridge. Because the tape never needs to be threaded from one reel to 
the other, the tape cartridge is quite easy to use and is relatively 
foolproof. Further, although the usage of a plurality of cartridges for a 
data base may increase the access time of a computer to a given cassette 
due to the inherent time delays in mechanical functions, this is not an 
important consideration in many applications. In fact, the independent 
operability of each cartridge and the interchangeability of cartridges 
within a given data base provides such a system with a degree of 
versatility which far outweighs the slower access time in most cases. 
One particular tape cartridge, specifically developed by the Minnesota 
Mining and Manufacturing Company for computer applications and 
electromagnetic data storage, has been approved as an American National 
Standard by the American National Standards Institute. The cartridge uses 
a pulley and belt drive for simultaneous operation of both tape reels, and 
is operated by rotating a single, externally accessible capstan. With the 
exception of the capstan, the unit is entirely enclosed and includes a 
spring loaded access door that opens to permit contact of the tape with a 
read/write head. The standard cartridge is disclosed and claimed in U.S. 
Pat. No. 3,692,255. 
This invention is specifically directed to apparatus which makes use of a 
plurality of these standard cartridges to form a data base, and which 
provides efficient access of external digital computer equipment with the 
data base. More specifically, the apparatus includes a carousel in which 
the plurality of cartridges are releasably held in a radial arrangement. 
The carousel is used in conjunction with a control housing having a 
plurality of read/write stations, and which is capable of indexing any 
cartridge in the carousel for use by any of the plurality of read/write 
stations. Once indexed, a cartridge is released from the carousel by the 
station mechanism, which then automatically carries the cartridge to a 
read/write position. Electromagnetic information can then be transferred 
between the cartridge and accessed computer through a selected one of a 
plurality of input/output ports. 
As constructed, the apparatus is capable of automatically indexing, 
loading, processing and unloading a selected cartridge relative to a 
selected read/write station, and of independently operating all read/write 
stations simultaneously. 
The individual cartridges can be added or removed from the carousel while 
the system is in operation, and the carousel itself is removable, thus 
enabling the data base to extend to a plurality of carousels. Based on a 
recording density of 1600 bpi and the utilization of four tracks on the 
quarter inch computer grade magnetic tape, and with 300 feet of tape per 
cartridge, each cartridge has a storage capacity in excess of 2 million 
bytes, and a fully loaded carousel has a storage capacity in excess of 33 
million bytes. 
The various structural and functional features will become more fully 
apparent from the specification, claims and attendant drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIGS. 1 and 2, a standard magnetic tape cartridge for 
information interchange is represented generally by the numeral 11. 
Cartridge 11 may be generally described as a rectangular, shallow box 
defined by an opaque back plate 12 and a transparent cover 13 which 
constitutes an integrally formed front plate, sides, top and bottom. Each 
of the sides of cartridge 11 defines a longitudinal recess 20 which 
together serve as guides for its sliding movement toward and away from a 
read/write head. Back plate 12 includes two rectangular notches 12a along 
its lower side edges which enable the cartridge 11 to be engaged and moved 
by a loading/unloading mechanism relative to a read/write head. There are 
no corresponding notches in the transparent front plate of the cover 13. 
Thus, the cartridge 11 is asymmetrical in nature, which precludes loading 
and unloading while in an improperly oriented position. 
Cartridge 11 further comprises a tape supply hub 14 and tape takeup hub 15 
mounted in coplanar relation. Magnetic tape 16 is unwound from the supply 
hub 14, passing around a first tape guide 17, through an external access 
opening 18 (FIG. 1), around a second tape guide 19 and then on to takeup 
hub 15. 
A protective door 21 generally conforms in shape to the external access 
opening 18, and is pivotally mounted to the cartridge to provide access to 
tape 16 by a read/write head (not shown in FIGS. 1 and 2). Door 21 is 
normally biased to a closed position by a torsion spring 22 (FIG. 2), and 
is opened by engaging a rearwardly extending tab 21a. 
The supply hub 14 and takeup hub 15 are driven by a tensioned, flat drive 
belt 23 which is endlessly moved by a belt capstan 24. Capstan 24 is 
externally accessible through an opening 25 to be driven by a drive roller 
(not shown in FIGS. 1 and 2). 
Belt guide rollers 26 are rotatably mounted in each of the upper corners of 
cartridge 11. Drive belt 23 endlessly encircles the capstan 24 and each of 
the belt guide rollers 26, and by the disposition of supply hub 14 and 
takeup hub 15, necessarily engages the outer layer of magnetic tape of 
each in engaging relation. Thus, rotation of the belt capstan 24 by an 
external drive motor operating through a drive roller effects linear 
movement of the magnetic tape 16 relative to its access opening 18. 
Cartridge 11 further comprises a window 27 relative to which an internal 
angular mirror (not shown) is mounted to sense a beginning-of-tape marker, 
an end-of-tape marker, a load point marker and an early warning marker. 
Cartridge 11 also includes a rotatable plug 28 which cooperates with the 
read/write mechanism to enable or prevent the writing operation, depending 
on its position. 
Reference is made to U.S. Pat. No. 3,692,255 issued to Robert A. Von Behren 
on Sept. 19, 1972 and assigned to the Minnesota Mining and Manufacturing 
Company for further details on structure and operation of the cartridge 
11. 
FIG. 3 is a general perspective view of a carousel apparatus 31 capable of 
handling a plurality of the magnetic tape cartridges 11. Carousel 
apparatus 31 broadly comprises a carousel storage device 32 which receives 
and stores the individual cartridges 11, and a control housing 33 which 
receives and rotatably carries the carousel 32, and includes one or more 
read/write mechanisms with respect to which a selected cartridge 11 may be 
used, as described in further detail below. Housing 33 includes a control 
panel 34 which operates in conjunction with one or more microprocessors to 
control operation of the apparatus. Among other things, this operation 
includes the selection of a particular tape cartridge 11, positioning of 
the selected cartridge relative to a desired read/write mechanism, 
initiation of the cartridge load/unload cycle, as well as the read/write 
function itself. 
As indicated by the handle 35, housing 33 is entirely portable, with or 
without the carousel storage device 32. 
The carousel storage device 32 is shown in detail in FIGS. 5-11. The 
carousel 32 is removable from the housing 33, thus performing the function 
of an information storage device, any number of which may be used in 
connection with the system. 
Carousel 32 is of circular configuration and specifically designed to 
receive and carry sixteen of the magnetic tape cartridges 11. More 
specifically, carousel 32 is defined by a top circular plate 42 in which 
16 radially disposed recesses 43 are formed to receive the cartridges 11. 
The central region of the top circular plate 42 is recessed, as shown at 
44, and an irregularly shaped, central opening 45 is formed to fit over 
and cooperate with a supporting center post assembly, as discussed in 
detail below. 
Formed integrally with the top circular plate 42 is a downwardly projecting 
peripheral flange 46 of substantial cross section (FIG. 9). The top 
surface of the peripheral flange 46 is chamfered, as shown at 46a; and, as 
shown in FIGS. 3 and 5, the flange 46 is formed with sixteen semicircular 
notches 46b which are circumferentially spaced in staggered relation with 
respect to the radial cartridge recesses 43. 
As shown in FIG. 9, the carousel 32 further includes an integral 
cylindrical projection 47 that extends upwardly from the circular plate 42 
and acts as a supporting structure for a handle assembly 41. With 
additional reference to FIG. 3, it will be seen that handle assembly 41 is 
a composite structure, defining a handle 41a, a flat ring 41b from which 
the handle 41a projects, and a downwardly extending cylindrical 
projection 41c which fits snugly within the confines of the upwardly 
extending cylindrical projection 47. A pair of nut and bolt assemblies 48 
secure the handle structure 41 to the top circular plate 42. 
As also shown in FIG. 9, a gap is defined between the ring 41b and top edge 
of projection 47, and a cartridge retaining ring 51 is retainably disposed 
in this gap. With additional reference to FIGS. 3, 5 and 10, retaining 
ring 51 includes a plurality of radially projecting teeth 51a conforming 
in number to the number of cartridge recesses 43. The ring 51 further 
includes two diametrically opposed circumferential notches 51b which are 
sized and disposed to permit limited rotation of the ring 51 relative to 
the handle 41. As will be apparent from FIG. 5, the degree of rotation of 
the ring 51 is chosen so that the projecting teeth 51a are movable between 
a first position overlying the recesses 43 and precluding removal of the 
cartridges 11, and a second position permitting removal of the cartridges 
11. 
The ring 51 is normally biased to the recess blocking position by a pair of 
coil springs 52 (FIG. 10) which act between the ring 51 and the 
cylindrical projection 47. The ring 51 is manually rotated to the 
nonretaining position, and returns to the blocking position upon release. 
As viewed from the bottom of the carousel 32, the top circular plate 42 
with its central recess structure 44 and the outer peripheral flange 46 
together define an annular receptacle, the radial dimension of which 
generally corresponds to the longitudinal dimension of the cartridge 
recesses 43. To provide an understructure for the carousel 32 which is 
capable of holding each of the cartridges 11 in a position represented by 
the dotted line in FIG. 9, there is provided for each of the recesses 43 a 
ribbed divider represented generally by the numeral 53 (FIGS. 6, 9 and 
11). As best shown in the bottom plan of FIG. 6, each of the ribbed 
dividers 53 is generally wedge shaped and occupies the space between 
adjacent cartridge bases 43. As best shown in FIG. 11, each of the ribbed 
dividers 53 consists of a generally wedge-shaped top plate 54, an inner 
end plate 55, an outer end plate 56 of irregular shape, and vertical ribs 
57a, 57b. 
The ribbed divider 53 further comprises a cartridge retaining gate 58 which 
projects vertically downward from the wedge-shaped plate 54 in cantilever 
fashion. The retaining gate 58 is constructed and arranged so that it has 
an amount of lateral resilience at its lower end. With additional 
reference to FIG. 7, it may be seen that the retaining gate 58 is formed 
with a retaining foot 58a at its extreme lower end, which projects 
laterally outward to catch and retain the bottom of a cartridge 11. 
Projecting inwardly from the lower end of gate 58 is a member 58b, which 
can be engaged by a mechanism described in detail below to laterally flex 
the gate 58 and enable the release of a retained cartridge 11. The 
resilient nature of the gate 58 causes it to return to its normal 
retaining position upon release by the gate actuator mechanism. 
Each of the dividers 53 is secured to appropriately spaced studs 59 
projecting downwardly from the plate 42 with screws 60 (FIG. 9), and the 
dividers 53 together represent a composite understructure for the carousel 
32 that offers excellent strength while maintaining the overall carousel 
weight at a low level for portability. 
Preferably, each of the recesses 43 is identified by numerical indicia 
formed on the chamfered edge 46a. These numerical indicia give the 
cartridge spaces 43 visual uniqueness within the carousel 32, permitting 
an operator to place a selected cartridge 11 in a specific recess 43. The 
visual uniqueness of the carousel 32 has a mechanical counterpart which 
enables the control apparatus to determine and thereafter control the 
angular position of the carousel 32 within the control housing 33. 
This mechanical counterpart takes the form of a positioning ring 61 which 
forms part of the carousel 32, and which is specifically shown in FIGS. 6, 
8 and 9. Positioning ring 61 has an annular top surface 62, which, as best 
shown in FIG. 9, fits against the flat bottom surface opposite the 
recessed structure 44 of plate 42. The inside diameter of ring 61 
corresponds to the outside diameter of a downwardly extending axial 
projection 44a which defines the lowermost and largest region of the 
irregular central opening 45. The ring 61 has four circumferentially 
spaced screw holes 63, and it is secured to the underside of the recessed 
structure 44 with screws 64. 
The position uniqueness of ring 61 resides in a thin, axially extending 
peripheral flange 65. A pair of slots 65a is provided in the flange 65 for 
each of the cartridge slots 43 which bear the numerical indicia 1-16. As 
shown in FIG. 8, the slots 65a are of uniform width, and there is 
uniformity in their circumferential spacing. For the "home" position, 
which corresponds to numerical indicia 1, a pair of slots 65b is provided, 
each of which has a significantly greater width than that of the slot 65a. 
As will be discussed below, the wider slots 65b permit an optical sensor 
to determine the "home" position of the carousel 32 on the control housing 
33 by initially sensing the position of slots 65b. 
The position of ring 61 with respect to the carousel 32 must, of course, 
correspond to the reference indicia, and this is provided by a stud 66 
which is radially aligned with the slots 65b and projects upward from the 
planar surface 62. Stud 66 cooperates with an opening 44b (FIG. 9) formed 
in the recessed structure 44. 
The control housing 33 contains all apparatus necessary for the desired 
operation of the carousel 32 and the individual cartridges 11. FIG. 4 is a 
sectional view in top elevation of the control housing 33 with the 
carousel 32 removed, and specifically showing the layout and relative 
positions of the internal control apparatus. This control apparatus is 
mounted to a base plate 71 either directly or by appropriate brackets and 
other mounting structures (not shown) which are carried by the base plate 
71. 
A center post assembly represented generally by the numeral 72 is mounted 
to base plate 71 for receiving and rotatably carrying the carousel 32. The 
carousel 32 is rotated by a drive motor 73 having a drive wheel 73a formed 
from resilient, frictional material. Drive wheel 73a drivingly engages the 
bottom surface of the peripheral flange 46 of carousel 32. 
The carousel is held in a stable horizontal position during rotation by 
support wheel assemblies 74a-74c, which are mounted in a horizontal plane 
in opposed, circumferentially spaced relation. Support wheel 74c forms 
part of an indexing mechanism represented generally by the numeral 75, 
which cooperates with the drive motor 73 to position the carousel 32 in 
any of the sixteen positions. 
The control housing 33 further includes four station mechanisms 76, each of 
which is shown in phantom for purposes of clarity. The broad function of 
each station mechanism 76 is to release an indexed cartridge 11 from the 
carousel 32, to lower the cartridge to a read/write position relative to a 
magnetic tape head, to move the tape relative to a read/write head, and to 
return the cartridge to its proper position within the carousel 32. It 
will be appreciated that the apparatus 31 will operate with only a single 
station mechanism 76, but that the versatility of the apparatus 31 may be 
significantly expanded through additional station mechanisms numbering up 
to four, as shown. 
The center post assembly 72, which includes an optical sensor for the 
position ring 61, is shown in detail in FIG. 12. Assembly 72 consists of a 
base member 81 which is mounted directly to and projects axially upward 
from base plate 71. Base member 81 defines an axial socket in which a 
stepped bearing member 82 is received. An annular gap is defined between 
bearing member 82 and base member 81, which gap receives the lower end of 
a longitudinal tube 83. Tube 83 is also stepped, including an annular 
shoulder 83a which rests on the top edge of base member 81. Tube 83 has a 
pair of access openings 83b formed through its side, and an axially 
extending elongated opening 83c is formed generally opposite the springs 
83b, the purpose of which will be discussed below. 
A roller bearing assembly 84 rests on top of tube 83 and is held in place 
by a nose member 85, the lower end of which is frictionally inserted into 
the upper end of tube 83. The outer diameter of bearing assembly 84 is 
chosen to accommodate the central opening 45 of carousel 32, thus 
permitting the carousel 32 to freely rotate relative to the center post 
assembly 72, while at the same time being supported in a horizontal plane 
of rotation by drive wheel 73a and idler wheel assemblies 74a-74c. 
Nose member 85 is formed with a central axial opening, and, with bearing 
member 82, acts as an axial guide to a locking rod 86. Rod 86 is the 
longest member of the center post assembly 72, projecting slightly above 
nose member 85 in its lowest position. 
Nose member 85 is formed with an arcuate recess 85a in which a latch pawl 
87 is pivotally mounted. Latch pawl 87 is generally L-shaped, with one leg 
disposed generally vertically for swinging movement into and out of the 
recess 85a. The shorter leg end defines a circular bearing member that is 
received within a recess 86a formed at the top of locking rod 87. As such, 
the pawl 87 acts as a bell crank, and up and down movement of the rod 86 
causes its vertical leg to move in and out of the recess 85a. As best 
shown in FIG. 9, outward swinging movement of the latch pawl 87 causes it 
to retainably engage the upper edge of the central recessed structure 44, 
thus locking carousel 32 onto the center post assembly 72. 
Nose member 85 is formed with a tapered surface 85b above the bearing 
assembly 84 which assists in centering the carousel 32 onto the bearing 
assembly 84. 
Axial movement of the rod 86 to lock and unlock the pawl 87 is effected by 
a solenoid 88 having a plunger 88a that is pivotally connected to an 
L-shaped link 89. The laterally extending leg of the link 89 projects 
through the elongated opening, and the vertical leg is secured to locking 
rod 86 by a pair of screws which are accessible through the openings 83b. 
Solenoid 88 is normally biased to the lock position shown in FIG. 12, and 
energization of the solenoid 88 moves the rod 86 axially upward to retract 
the link 87, which unlocks the carousel 32 from center post assembly 72. 
A collar 90 is secured to the tube 83 at a position slightly below the 
bearing assembly 84. Collar 90 supports a laterally extending mounting 
plate 91 (FIGS. 4, 9 and 12), the outer end of which carries a sensor 92. 
With reference to FIG. 9, the sensor 92 defines a gap 92a which receives 
the peripheral flange 65 of position ring 61. Sensor 92 comprises a light 
source and a photosensor mounted in opposed relation, which permits it to 
sense the presence and character of slots 65a and 65b. The sensed 
information is passed onto the unit microprocessor through means not 
shown, where it is utilized for positioning the carousel 32 relative to 
the station mechanisms 76. 
As mentioned above, positioning of the carousel 32 relative to a station 
mechanism 76 is accomplished by cooperation of the drive motor 73 and 
indexing mechanism 75, the latter of which is shown in detail in FIG. 13. 
Index mechanism 75 comprises a base bracket 101 on which a solenoid 102 is 
mounted. Solenoid 102 includes a plunger 102a, the end of which is 
pivotally connected to one leg of a generally L-shaped bell crank 103. 
Bell crank 103 is pivotally connected at the juncture of its legs to base 
bracket 101 by a pivot pin 104. As such, the free end of bell crank 103 
may be moved toward and away from the peripheral flange 46 of carousel 32 
by energization of indexing solenoid 102. 
The free end of bell crank 103 carries a roller 105 which is sized to fit 
into the semicircular notches 46b in retaining engagement. Solenoid 102 is 
normally biased with the plunger 102a in an extended position so that the 
indexing wheel 105 is normally retracted from engagement with peripheral 
flange 46. This biasing function is provided by a spring 107 that is 
mounted in tension between the bell crank 103 and the side of solenoid 
102. Energization of solenoid 102 causes the indexing wheel 105 to engage 
the outer periphery of flange 46 until it falls into one of the notches 
46b, at which time the opposite end of the bell crank 103 engages a 
microswitch 106. The signal generated by actuation of the microswitch 106 
is utilized by the microprocessor to stop drive motor 73, as will be 
described in greater detail below. 
The notches 46b and indexing wheel 105 are relatively positioned so that 
each of the sixteen stopping positions of carousel 32 will place one of 
the cartridge recesses 43 (and the cartridge 11 which it carries) directly 
over one of the station mechanisms 76. 
Once a selected cartridge 11 has been indexed relative to a selected 
station mechanism 76, the station mechanism 76 can be operated to perform 
the desired function, whether it be cartridge loading or unloading, the 
reading of data from the cartridge tape for processing, or the writing or 
recording of data on the tape. In this regard, the station mechanism is 
not concerned with the actual use of data which its read/write head senses 
and communicates, or the character of data which it receives from an 
outside source for communication and storage on the cartridge tape. Thus, 
it serves the function of an input/output device, occupying an interfacing 
position between the data storage medium and the data processing 
equipment. 
The function of each station mechanism 76 consists of actuation of the 
retaining gate 58 of the selected cartridge 11, moving the cartridge 
downward into a read/write position or station entirely below the 
carousel, providing reference forces which align the cartridge tape 
relative to the read/write head to insure the accuracy of information 
transfer, the transfer of data to or from the cartridge, and elevation of 
the cartridge to its proper place within the carousel. Each station 
mechanism 76 is also capable of aborting the process if a cartridge has 
been improperly placed in the carousel or not properly received by the 
station mechanism itself. 
With reference to FIGS. 14 and 15, each of the station mechanisms 76 
comprises a frame having vertical side plates 111, 112 that are held in 
parallel spaced relation by four corner cross supports 113, the upper two 
of which can be seen in FIG. 14, with the lower two in FIG. 15. With 
additional reference to FIGS. 9 and 14-17, a pair of generally vertical 
transfer arm assemblies 114 are pivotally connected to the lower outer 
face of plate 111 by pins 115 in a manner which permits them to swing 
between cartridge "engage" and "release" positions. To this end, the 
transfer arm assemblies 114 are spaced apart so that, in vertically 
parallel relation (i.e., the cartridge "engage" position), the effective 
distance between them corresponds to the width of a tape cartridge 11. The 
degree of swing of the upper ends of the transfer arm assemblies 114 is 
sufficient to permit release of the tape cartridge 11, as well as to allow 
the carousel 32 to pass between the transfer arm assemblies 114 during its 
rotation. The transfer arm assemblies 114 are mirror images of each other 
(and are sometimes referred to as "righthand" or "lefthand"), each 
comprising first and second elongated extrusions 116, 117 bolted or 
otherwise secured together to define opposed, vertically elongated 
cartridge receiving slots 118. The juncture between extrusions 116, 117 
also defines a vertical recess 121 that extends around the entire 
periphery of the extrusions. An endless toothed belt 120 is disposed 
within the recess 121, movably carried at its upper end by an idler gear 
wheel 122 and at its lower end by a drive gear wheel 123. A pawl 124 
having a plurality of position retaining teeth is carried by the belt 121, 
the pawl 124 being vertically movable with travel of the belt 121 within a 
part of the cartridge receiving slot 118. A retaining clip 125 is mounted 
at the top of extrusion 117 to act as an upper limit to the pawl 124. 
Each of the transfer arm assemblies 114 also consists of an irregularly 
shaped block member 126 mounted at the bottom of the extrusions 116, 117. 
The blocks 126 provide a number of mounting functions for the transfer arm 
assemblies 114, among them the receipt of pivot pins 115. A small 
rotatable shaft 127 projects horizontally from the mounting block 126, 
extending into the lower part of the transfer arm assembly 114 where it 
receives the drive gear wheel 123. A gear pulley 128 is secured to the end 
of shaft 127 by set screws or the like to effect travel of the belt 121 
and pawl 124, as will be discussed in further detail below. 
The transfer arm assemblies 114 are normally biased together by a coil 
spring 129 disposed in tension between a pair of vertical spring holders 
130 mounted on opposed faces of the blocks 126 (FIGS. 15 and 16). 
The mechanisms disposed between the frame plates 111, 112 serve to actuate 
the cartridge gate 58 to permit cartridge entry into the station mechanism 
76, to move the transfer arm assemblies 114 between the cartridge release 
and engage positions, to move the pawls 124 up and down for movement of a 
selected cartridge 11 from the carousel 32 to the read/write head, to bias 
the cartridge 11 relative to the read/write head, and to abort the 
operation if the cartridge 11 is not properly oriented relative to the 
transfer arm assemblies 114. 
All of these operations are powered by a single 12 volt reversible D.C. 
motor 131 (FIG. 14) that is mounted on a horizontal position to the frame 
plate 112. The output shaft of motor 131 projects externally through plate 
112, and a gear drive pulley 132 is secured thereto. 
A drive shaft 133 is journaled between the frame plates 111, 112 by 
suitable bearings, and in parallel relation to the output shaft of motor 
131. Drive shaft 133 projects externally of the frame plate 112 in a 
position which is generally centered within the plate but below gear 
pulley 132. A driven slip clutch 134 is mounted on the outer end of shaft 
133 and secured in aligned relation with the gear pulley 132 by a pair of 
lock nuts 135. A drive belt 136 extends between the gear pulley 132 and 
slip clutch 134. Slip clutch 134 is of conventional design, transferring 
rotational energy to the shaft 133 except in the presence of an excessive 
load, in which case it simply rotates relative to the shaft 133 under the 
influence of motor 131. 
With additional reference to FIG. 19, a drive gear 141 is secured to the 
shaft 133 immediately inside the frame plate 112. Mounted adjacent the 
drive gear 141 is an interposer hub 142 carrying an L-shaped interposer 
143, the purpose of which will be described below. 
Adjacent the interposer hub 142 is a tensioner 144 which forms part of the 
drive train, as will be discussed below. On the opposite side of tensioner 
144 is a first synchronizing gear 145 and gear pulley 146, the latter of 
which is disposed in alignment with the gear drive pulley 128 of the 
righthand transfer arm assembly 114. A timing belt 147 operatively 
connects the gear pulleys 128, 146. 
A second synchronizing gear 148 and associated gear pulley 149 are mounted 
on a stub shaft 150 that projects from frame plate 111 parallel to drive 
shaft 133. The synchronizing gears 145, 148 are identical, and the former 
drives the latter to insure identical rotational velocities of the gear 
pulleys 146, 149. Gear pulley 149 is disposed in alignment to the gear 
pulley 128 of the lefthand transfer arm assembly 114, and a timing belt 
151 operatively interconnects the two. 
The synchronized rotational movement of the gear pulleys 146, 149 is 
carried through the timing belts 147, 151 to the gear pulleys 128 of the 
lefthand and righthand transfer arm assemblies 114, which in turn causes 
synchronized vertical movement of the pawls 124 to move the selected 
cartridge up and down in the proper reference position. As will become 
apparent below, downward movement of the pawls 124 follows actuation of 
the cartridge gate and inward movement of the transfer arm assemblies 114. 
Upward pawl movement begins the unload cycle. 
With reference to FIGS. 14 and 18, a cam shaft 155 is journaled between the 
frame plates 111, 112 by suitable bearings above and in parallel relation 
to the drive shaft 133. A cam drive gear 156 is mounted on the cam shaft 
155 immediately inside the frame plate 112. Cam drive gear 156 is 
constructed and positioned for gear engagement with drive gear 141, the 
gear ratio between the two being such that during each load or unload 
cycle, the drive shaft 133 rotates four revolutions for a cam shaft 
rotation of 345.degree.. A trigger member 157 is mounted on the face of 
cam drive gear 156 for rotation therewith by means of a nut 157a. An 
arcuate slot 157b permits the trigger member 157 to be adjusted relative 
to the drive gear 156. An axially projecting trigger 157c serves a 
cyclical function as will become apparent below. 
A spacer 158 is mounted on the cam shaft 155 by means of a set screw, and a 
latch cam 159 is affixed to the end of the spacer 158 by a plurality of 
mounting screws. 
Axially spaced from the latch cam 159 is an arm cam 160 mounted on a hub 
161, which is secured to cam shaft 155 by a set screw. 
Axially spaced from the arm cam 160 and hub 161 is a release cam 170, which 
is also secured to the cam shaft 155 by a set screw. 
With reference to FIGS. 15, 16 and 18, a third shaft 162 is mounted between 
the frame plates 111, 112 in parallel relation to the drive shaft 133 and 
cam shaft 155 somewhat below and to the side of the former. An arm cam 
follower assembly 163 is carried by the shaft 162 for swinging movement 
relative thereto. Arm cam follower assembly 163 includes a generally 
upwardly projecting follower 163a having a roller 163b connected to its 
upper end for low frictional engagement with the arm cam 160. Arm cam 
follower assembly 163 further comprises a laterally extending lever 163c 
which lies just adjacent to frame plate 111. The follower arm 163a is 
normally biased into engagement with arm cam 160 by a coil spring 164 
extending between the follower 163a and a stub shaft 165 projecting 
horizontally from the frame plate 111. 
With continued reference to FIG. 16, a pair of lever members 166, 167 are 
respectively secured to the mounting blocks 126 of the lefthand and 
righthand transfer arm assemblies 114, extending laterally toward each 
other with the ends in overlying relation. Lever 167 includes a lateral 
slot 167a at its extreme end, and the lever 166 includes a roller stud 
166a received by the slot 167a. 
The extreme end of lever 163c engages the bottom of roller stud 166a. It 
will thus be appreciated that swinging movement of the follower arm 163a, 
under the influence of arm cam 160, is transferred through the lever 163c 
to the levers 166, 167, and from thence to the transfer arm assemblies 
114, causing them to swing in and out relative to each other as indicated 
by the arrows in FIG. 16. 
The mechanism for actuating the retaining gate 58 of a selected cartridge 
11 is specifically shown in FIG. 20, and additional reference is made to 
FIGS. 7 and 14. A gate actuator 171 consists of a pair of opposed arms 
171a that are interconnected by a cross member 171b. An edge 171c of the 
cross member 171b is bent laterally outward for actuating engagement with 
a cartridge retaining gate. The arms 171a are pivotally mounted on a 
horizontal pin 172 which is secured at the upper edge of frame plate 111. 
A pin 173 is rotatably disposed between the arms 171a parallel to the pin 
172. An actuator link 174 projects downward from pin 173 into operative 
engagement with one end of a bell crank 175. Bell crank 175 is secured by 
a set screw to a transverse shaft 176 mounted between the upper cross 
supports 113. A torsion spring 177 encircling the shaft 176 acts between 
one of the cross supports 113 and the bell crank 175, normally biasing the 
outer end of the bell crank 175 downward, and at the same time forcing the 
gate actuator 171 into its lowest position. 
The opposite end of bell crank 175 pivotally carries an elongated, 
vertically disposed latch 178 by means of a pin 179. Latch 178 consists of 
two longitudinal rigid metal strips 178a, 178b which are disposed in 
overlapping relation and bolted together to permit longitudinal 
adjustment. A dog 178c projects laterally from an intermediate region on 
the latch strip 178b. Latch 178 is normally biased in the direction in 
which the dog 178c projects by a coil spring 180 extending between its 
lower end and the arm cam follower shaft 62. 
A guide plate 181 (FIGS. 15, 20) is mounted to the inner face of frame 
plate 112, projecting horizontally inward therefrom. Guide plate 181 
includes a slot 181a which serves to guide the latch 178 in its upward and 
downward movement. 
it will be appreciated that upward and downward movement of the latch 178, 
imparted by mechanisms described below, effects movement of the gate 
actuator 171 to open the gate 58 of a selected tape cartridge 11, thus 
releasing the cartridge for entry into the receiving area between transfer 
arm assemblies 114. Such upward and downward movement is accomplished by a 
follower for the latch cam 159, which is generally designated 182 and may 
be seen in FIGS. 15, 18, 19 and 20. Latch cam follower 182 is pivotally 
mounted on a fourth shaft 183, which is mounted between frame plates 111, 
112 in parallel relation to shafts 133, 155 and 162 generally above the 
latter. Latch cam follower 182 includes an arm 182a which projects toward 
latch 178 and is capable of upward and downward swinging movement. The 
extreme end of arm 182a is bent to the side 90.degree. and extends 
upwardly to form an engager 182b that cooperates with the latch dog 178c. 
The latch cam follower 182 moves up and down under the influence of the 
latch cam 159 (FIG. 18), which engages a roller 182c projecting from the 
side of the follower arm 182a. 
The torsion spring 177 of the bell crank 175 normally urges the latch 178 
upward. However, the latch cam 159 is disposed above the roller 182c so 
that the engager 182b through its engagement with the latch dog 178c 
permits the latch 178 to move upwardly only as the latch cam 159 moves 
away from its maximum dwell. So long as the latch dog 178c is engaged by 
the engager 182b, which is assisted in this function by the coil spring 
180, movement of the latch 178 and gate actuator 171 is controlled by 
rotation of the latch cam 159. 
Once the selected cartridge has been released from its recess 43 within the 
carousel 32 to the transfer arm assemblies 114, and then carried to the 
read/write position at the tape head, it is necessary to insure that the 
cartridge delivers and receives proper and accurate information to and 
from the read/write head. This is accomplished by inposing a lateral 
reference force on the side of the cartridge relative to a lateral stop, 
and imposing a downward force on the cartridge relative to a bottom stop. 
The lateral and bottom stops are best understood with initial reference to 
FIG. 14, in which a tape deck 191 is referred to generally by the numeral 
191. Tape deck 191 is a thick, rectangular plate which is vertically 
disposed and mounted in spaced relation to the side plate 111. The spaced 
mounting is accomplished with a generally rectangular spacer block 192 one 
side of which is secured to the side plate 111 along its bottom outer face 
(see also FIG. 9). The bottom face of the tape deck 191 is bolted to the 
opposite side of the spacer block 192, and it projects upwardly in the 
aforementioned spaced relation to the side plate 111 without additional 
structural support. As described, the side plate 111, tape deck 191 and 
the transfer arm assemblies 114 together define a pocket within which a 
cartridge 11 may be loaded for the read/write operation. 
With reference to FIGS. 14, 15 and 23, a cartridge guide, bearing the 
general reference numeral 193, is rigidly secured to each side of the tape 
deck for cooperation with one of the transfer arm assemblies 114. The 
function of the cartridge guides 193 is to firmly guide the cartridge 11 
as it is brought to the read/write position by the transfer arm assemblies 
114, and to provide the lateral and bottom stops mentioned above. 
The cartridge guide 193 consists of a vertically disposed, L-shaped support 
defined by legs 193a, 193b. A vertical tapered finger 193c is integrally 
formed with the leg 193b but projecting slightly thereabove as shown in 
FIG. 23. As particularly shown in FIG. 26, the tapered finger 193c has a 
cross sectional size which closely corresponds to the size of the 
longitudinal recesses 20 in the sides of cartridge 11; and it is this 
relationship which gives rise to accurate guiding of the cartridge 11 as 
it is brought to the read/write position. In this regard, the tapered or 
beveled effect at the top of the finger 193c insures its proper entry into 
the associated longitudinal recess 20. 
With reference to FIG. 2, the finger 193c also performs the function of 
engaging the rearwardly extending tab 21a of the cartridge door 21, which 
causes the door 21 to open as the cartridge 11 is lowered relative to the 
guides 193. This exposes the tape 16 to the read/write head via the access 
opening 18, thus permitting the interchange of information. 
With specific reference to FIG. 23, the vertical finger 193c is formed with 
two laterally extending bosses 193d which serve as stops against which the 
above-mentioned lateral reference forces can be imposed. The bottom stop 
is provided by a plate 193e which is secured to the bottom of the legs 
193a, 193b, and the vertical finger 193c. 
With reference to FIGS. 14, 22 and 23, the lateral reference force imposed 
on the cartridge 11 in the read/write position is provided by a pair of 
laterally spaced bias plates 201. Each of the plates 201 generally takes 
the form of and operates in a like manner to a bell crank, being pivotally 
connected by a pin 202 to a mounting block 203, which is in turn secured 
to the side plate 111 (FIG. 14). Each of the bias plates 201 defines a 
nose 201a which, upon pivotal rotation of the plate 201, directly engages 
the back plate 12 of cartridge 11 and thereby imposes the lateral 
reference force. 
Each of the plates 201 is normally biased into a cartridge engaging 
position by a coil spring 204 mounted between the rear corner of the plate 
201 and a stud shaft 205 disposed immediately below, and which is mounted 
to the side plate 111. 
Simultaneous movement of the bias plates 201 between cartridge engaging and 
nonengaging positions is effected by a bail 206, each end of which is also 
mounted by the pivot pins 202 to the mounting blocks 203. Each bias plate 
201 includes a rearwardly extending tab 201b which is positioned for 
engagement by the bail 206. It will be appreciated that upward pivotal 
movement of the bail 206 serves to retract the bias plates 201 from their 
cartridge engaging positions. 
With reference to FIGS. 18 and 22, the bail 206 includes a roller 206a 
mounted intermediate its ends and disposed for operative engagement by the 
release cam 170 is so constructed and disposed that the bail 206 is forced 
upwardly (retracting the bias plates 201) while the cartridge 11 is moving 
downward to the read/write position. As the cartridge reaches its bottom 
position (engaging the bottom reference plates 193e), the release cam 170 
rotates to a position permitting the bail 206 to swing downward. This 
enables the coil springs 204 to pull downward on the bias plates 201, 
forcing the engaging noses 201a outward into biasing engagement with the 
cartridge 11. As pointed out above, this lateral reference force is 
imposed through the cartridge 11 and resisted by the lateral reference 
stops 193d. 
The vertical reference force imposed on cartridge 11 is accomplished by the 
tensioner 144. With reference to FIGS. 15, 19, 24 and 25, the tensioner 
assembly 144 broadly comprises an input section and an output section 
which are relatively rotatable in a predetermined manner. The input 
section, which generally appears on the righthand side of FIG. 25, makes 
use of the drive shaft 133 for the input rotational force. A pin 211 
projects radially from and perpendicular to the shaft 133. A first spool 
half 212 is rotatably mounted on the shaft 133 by roller bearings 213, its 
axial position being immediately adjacent the pin 211. A retainer ring 214 
maintains the spool half 212 in this axial position. 
It will be noted that the spool 212 consists of a flange 212a secured to a 
hub 212b by a screw 212c, which passes through an arcuate slot in flange 
212a (not shown). This enables the flange 212a to be rotatably adjusted 
relative to the hub 212b for a reason described below. 
A pin 215 is carried by the spool half 212, projecting axially beyond the 
radial pin 211. As described, rotation of the shaft 133 in either 
direction will result in engagement of the axial pin 215 by the radial pin 
211, thus causing similar rotation of the spool half 212. 
The output section of tensioner 144 consists of a tubular output shaft 216 
which is mounted on the shaft 133 and rotatable relative thereto. One end 
of the tubular shaft 216 is disposed immediately adjacent the radial input 
pin 211, and it is held in this axial position by retainer ring 217. It 
will be observed in FIG. 25 that the first synchronizing gear 145 and the 
gear pulley 146 are both securely mounted on the tubular output shaft 216 
for rotation therewith. 
A flat ring 218 which defines a radial output pin 219 (FIG. 24) is staked 
to the end of tubular shaft 216 so that it lies adjacent the input radial 
pin 211. 
A second spool half 211 is mounted for independent rotation on the tubular 
shaft 216 by roller bearings 222. A second axial pin 233 is carried by the 
spool half 221, projecting from the spool half 221 a sufficient distance 
for engagement by each of the radial pins 211, 219 (FIG. 25). The axial 
pin 215 projects a corresponding distance from the spool half 212, so that 
it may also be engaged by both of the radial pins 211, 219. 
A torsion spring 224 circumferentially encloses the lesser diameter 
portions of spool halves 212, 221. Each end of the torsion spring 224 is 
secured to the associated flange portion of the spool halves 212, 221. 
The flange 212a is rotationally adjusted relative to the hub 212b to set 
the torque of spring 224 to a specific value. 
Assuming the radial and axial pins to be in the position shown in FIG. 24, 
counterclockwise rotation of the shaft 133 causes engagement of the radial 
input pin 211 with the axial output pin 223, which causes the second spool 
half 221 to rotate directly with the shaft 133. The first spool half 212 
is connected directly to the torsion spring 224. So long as the load 
torque on the tensioner 144 (i.e., the movement of cartridge 11 during the 
load/unload cycle) does not exceed the torque limit of the torsion spring 
224, the spring directly transfers rotation of the second spool half 221 
to the first spool half 212 and the axial input pin 215. Axial pin 215 in 
turn transfers the rotational motion by direct engagement with the radial 
output 219, which is rigidly secured to the output shaft 216, the first 
synchronizing gear 145 and the gear pulley 146. Stated otherwise, the 
gears 145, 146 rotate directly with the shaft 133. 
However, if the load torque exceeds the limit of the torsion spring 224, 
the rotational motion of the second spool half 221 cannot be transmitted 
directly to the first spool half 212. Rather, the torsion spring 224 
begins to wind up as a result of the differential motion between the spool 
halves, producing a torque buildup between the input section and output 
section of the tensioner 144. 
It will be appreciated that the same torque buildup may also result from 
clockwise rotation of the drive shaft 133 (as viewed in FIG. 24). With 
clockwise rotation of the shaft 133, the radial input pin 211 engages the 
axial input pin 215, and rotation to the output section of tensioner 144 
may be traced from the first spool section 212, torsion spring 224, second 
spool section 221, the axial output pin 223, radial output pin 219, output 
shaft 216 and gears 145, 146. If the load torque on the output section of 
tensioner 144 exceeds the limit of torsion spring 224, the first spool 
section 212 will continue to rotate relative to second spool section 221, 
and the differential motion causes the torque buildup of the torsion 
spring 224. 
The apparatus is designed so that the limit of torsion spring 224 is 
exceeded during the load cycle when the cartridge 11 reaches its 
read/write position and engages the bottom stop plate 193e. During the 
unload cycle, the limit of torsion spring 224 is exceeded at the time the 
cartridge carrying pawls 124 engage the retaining clips 125 of the 
transfer arm assemblies 114. 
The travel distance of the pawls 124 between the upper and lower stops 
represents approximately 21/2 revolutions of the drive shaft 133. However, 
as indicated above, the drive shaft 133 rotates approximately four 
revolutions during each complete load or unload cycle. Consequently, the 
drive shaft 133 rotates approximately 11/2 revolutions more than the 
synchronizing gear 145 and gear pulley 146 of the tensioner 144. The 
phasing of movement of the pawls 124 relative to the cam shaft 155 is such 
that the rotational difference in the input and output sections of 
tensioner 144 is evenly divided with respect to the upper and lower stops 
for the pawls 124. Stated otherwise, when the pawls 124 reach either the 
upper or lower pawl stops, the drive shaft 133 continues to rotate for 
approximately 3/4 of one revolution, which in turn causes the torque 
buildup within the tensioner assembly 144. 
During the load cycle, the torque buildup begins at the point that the 
cartridge 11 reaches the read/write position and engages the bottom 
reference plate 193e. It is this torque buildup, which is carried through 
the output section of the tensioner 144 to the pawls 124, which creates a 
downward biasing force on the cartridge 11. The combination of this 
downward reference force with the lateral reference force exerted by the 
bias plates 201, as described above, insures precise registration of the 
cartridge 11 in its read/write position (FIG. 23). 
During the torque buildup of tensioner 144, the continued 3/4 turn 
revolution of shaft 133 also causes continued rotation of the cam shaft 
155 and its components. The phasing is such that at the beginning of 
torque buildup, the arm cam 160, acting through the arm cam follower 163, 
causes the transfer arm assemblies 114 to swing outwardly. 
As the arm cam follower 163 is moved to its furthest position from cam 
shaft 155, it engages a microswitch 230 (FIGS. 15 and 27), which controls 
the supply of electricity to motor 131. Actuation of the switch 230 marks 
the end of the load cycle and prevents the motor 131 from continuously 
running against overload. However, at the time that motor 131 is shut off, 
the torque buildup of tension assembly 144 tends to urge the drive shaft 
133 in the opposite direction, which is undesired at this point. Reverse 
turning is avoided by a brake assembly 231, which is shown in detail in 
FIG. 21. 
Brake assembly 231 consists of a brake arm 232 which is rotatably mounted 
on a shaft 233. Shaft 233 is secured to and projects horizontally inward 
from the bottom of side plate 112. Brake arm 232 is held in a 
predetermined spaced relation to the side plate 112 by a spacer 233a which 
forms part of the shaft 233. Spacer 233a is formed with an axial threaded 
opening, which permits mounting of the assembly 231 to the side plate 112 
by a mounting screw (not shown). 
Brake arm 232 projects upwardly from the shaft 233, and its extreme upper 
end is bent 90.degree. to define an engaging foot 232a disposed in 
proximity to the drive gear 141. A rectangular recess is formed in the 
edge of guide plate 181 to accommodate the engaging foot 232a. 
Because of its construction, the engaging foot 232a is capable of moving 
into and out of brake engagement with the drive gear 141 by swinging 
movement of the arm 232. This movement is effected by a solenoid 234 which 
is mounted to the bottom of guide plate 181, and which includes a plunger 
234a pivotally connected to the brake arm 232. Energization of the 
solenoid 234 retracts the plunger 234a to disengage the foot 232a from the 
drive gear 141. 
Brake arm 232 is biased by a coil spring 235 so that the foot 232a normally 
engages the drive gear 141, preventing rotation of the shaft 133. The 
opposite end of spring 235 is connected to the shaft 162. 
Brake arm 232 further comprises a laterally extending tab 232b which 
projects through an access opening in the side plate 112 (FIGS. 14, 15) 
permitting manual override of the brake assembly 231. 
Actuation of the microswitch 230 by the arm cam follower 163 simultaneously 
turns the motor 131 off and deenergizes solenoid 234, thus permitting 
brake arm 232 to immediately engage drive gear 141 and preventing further 
rotation of either the drive shaft 133 or the cam shaft 155. This status 
is maintained until an unload cycle is initiated. 
Similarly, the brake assembly 231 is utilized at the end of the unload 
cycle, at which time the transfer arm assemblies 114 swing outwardly to 
release the cartridge 11 under the influence of arm cam 160. In this 
outward position, transfer arm assemblies 114 do not interfere with 
revolving movement of the carousel 32 (FIG. 9). The arm cam follower 163 
again engages microswitch 230 at this time, thus cutting electrical power 
to the motor 131 and de-energizing the brake solenoid 234. This status is 
also maintained until a new load cycle is initiated. 
Station mechanism 76 includes additional components which cooperate with 
the interposer hub 142 and interposer 143 to perform the cartridge 
aborting process mentioned above, where the cartridge is not properly 
received within the station mechanism 76 during the load cycle. 
With reference to FIGS. 19, 20 and 28, it will initially be noted that the 
interposer hub 142 is freely rotatable on the drive shaft 133, but is 
biased in the clockwise direction (FIG. 28) by a spring 142a one end of 
which is connected to a screw 142b on the hub 142. The other end looks 
onto the guide bracket 181 (FIGS. 15, 20). 
Interposer 143 is L-shaped as pointed out above, with one leg secured to a 
flattened section of the hub 142 by a pair of screws. Each of the legs of 
interposer 143 is formed with a stepped recess, as shown at 143a, 143b. 
With reference to FIGS. 15 and 19, the additional components used for the 
aborting process include a control arm 241 and a keeper 251. Control arm 
241 is immovably secured to one end of a shaft 242 that is mounted to and 
projects transversely from a lever arm 166 (see also FIG. 16). It will be 
recalled that the lever arm 166 is one of several components which effects 
the inward and outward swinging movement of the transfer arm assemblies 
114. As such, the movement of lever arm 166, and accordingly the shaft 
242, directly represent movement of the transfer arm assemblies 114. The 
arcuate arrows of FIG. 28 indicate the direction of lateral movement of 
the shaft 242, which of course dictates movement of the control arm 241. 
The outer end of control arm 241 forms a nose which is obtusely angled 
relative to the primary extension of the arm. A perpendicular control 
surface 241a is formed at the end of the nose and disposed for engagement 
with the stepped recess 143b of interposer 143. The nose also includes a 
beveled surface 241b. 
Keeper 251 comprises a U-shaped arm which is freely mounted on a stub shaft 
252 projecting inwardly from side panel 112. One leg of the keeper 251, 
which bears the reference numeral 251a, projects outwardly for engagement 
with the longest leg of interposer 143 under circumstances described 
below. The extreme end of the leg 251a is formed with a stepped recess 
which serves to lock the interposer 143 into a predetermined position. 
The other leg of the U-shaped keeper, which bears the reference numeral 
251b, projects in the same direction, and includes a lateral tab 251c that 
is disposed for engagement by the trigger 157c of the cam drive gear 156 
(FIG. 18). 
With reference to FIG. 28, keeper 251 is normally biased so that the leg 
251a engages interposer 143 by a spring 253, the remote end of which is 
connected to the shaft 162. 
Reference is made to the sequential operation (FIGS. 28-31), which show the 
interrelationship of the aborting process components when the cartridge 11 
has been properly received by the station mechanism 76. In these figures, 
the position of the pawls 124 (as determined by the position of transfer 
arm assemblies 114) is shown relative to the rectangular notch 12a of 
cartridge 11. Also included in each of these figures are the relative 
positions of the cartridge retaining gate 58 and the gate actuator 171. 
It will be understood that the relative positions of each of the three 
component groups of FIGS. 28-31 are shown at the same instant of time. 
Thus, FIG. 28 represents the start of a cartridge load cycle with the cam 
shaft 155 at the "home" or zero degree position. At this point, the 
transfer arm assemblies 114 are in their "out" position, and the pawl 124 
is retracted from the cartridge 11. Cartridge 11 is retained in its 
appropriate carousel recess by the retaining gate 58, and the gate 
actuator 171 is at its rest position. 
Similarly, the latch 178, which controls the position of the gate actuator 
171, is at its rest position, as is the latch cam follower 182. The 
interposer hub 142 is maintained in the rotational position shown by 
reason of engagement of the stepped recess 143b of interposer 143 with the 
control surface 241a of control arm 241. It will be recalled that the 
position of control arm 241 is directly related to the position of the 
control arm assemblies 114 (and hence the pawls 124). 
In FIG. 29, pawl 124 begins to make contact with the edge of cartridge 11, 
but has not yet entered the notch 12a. Latch cam follower 182 has at this 
point rotated downward so that its engager 182b engages the latch dog 
178c, thus moving the latch 178 downward. 
Interposer hub 142 is not rotated. However, the control arm 241 has swung 
arcuately downward in following the transfer arm assemblies 114, so that 
the corner edge between the surfaces 241a, 241b is in direct engagement 
with the edge of the stepped recess 143b. 
Gate actuator 171 has begun to swing upwardly toward engagement with gate 
58. 
In FIG. 30, the pawl 124 has entered the notch 12a of cartridge 11. This is 
a critical movement in the determination whether the cartridge 11 is in a 
proper position within the station mechanism 76 to permit its release from 
the carousel. This critical movement is sensed by the control arm 241, 
which continues to follow swinging of the transfer arm assemblies 114 to 
their "in" position. This in turn causes the corner edge between control 
surfaces 241a, 241b to fall below the edge of stepped recess 143b. This 
enables the interposer hub 142 to rotate in a clockwise direction until 
the interposer 143 comes to rest in engagement with the beveled surface 
241b. The opposite leg of the interposer 143 having been retracted from 
the line of movement of the latch dog 178c, downward movement of the latch 
178 under the influence of the latch cam follower 182 is permitted. 
It will be recalled that the gate actuator 171 is connected through linkage 
to the latch 178, and it thus approaches the gate 58 as shown. 
FIG. 31 shows the latch cam follower 182 and the latch 178 at the end of 
their down stroke, at which point the gate actuator 171 has engaged the 
gate 58, swinging it laterally to release cartridge 11. 
At this point, the pawl 124 continues its downward movement as heretofore 
described, pulling the cartridge 11 downwardly toward the read/write 
position. 
FIGS. 32-37 show the relative positions of the same components during the 
cartridge aborting process. In these figures, it will be noted that the 
cartridge 11 is shown in a reversed position, which obviously precludes 
entry of the pawl 124 into the nonexistent notch 12a. 
FIG. 32 is much the same as FIG. 28, showing relative component positions 
at the beginning of the load cycle. FIG. 33 is similar to FIG. 29, with 
the pawl 124 beginning to approach where the notch 12a should be. Control 
arm 241 is again positioned at the critical point where it will determine 
whether the cartridge can be released from the carousel, in which case it 
falls under the interposer 143; or whether the process should be aborted. 
As shown in FIG. 34, pawl 124 cannot enter the notch 12a, and the transfer 
arm assemblies 114 have reached their inwardmost position. This is 
reflected by the position of control arm 241, which has not varied its 
position from that shown in FIG. 33. Accordingly, control arm 241 
maintains the interposer 143 in a position of direct line engagement with 
the latch dog 178c. 
During this process, the latch cam follower 182 has continued its downward 
movement, carrying with it the latch 178 until engagement by the 
interposer 143 occurs. As shown in FIG. 35, the continued downward 
movement of the latch 178 causes the latch dog 178c to directly engage the 
interposer 143, effecting a lateral deflection of both components to the 
extent that the latch 178 moves out of the driving engagement of latch cam 
follower 182. Deflection of the interposer 143 takes the form of 
counterclockwise rotation of the interposer hub 142, to the extent that 
the opposite extreme end of interposer 143 slides up and enters the 
stepped recess at the end of keeper leg 251a. This of course precludes 
return of the interposer 143 to its nonobstructing position, even under 
the influence of the coil spring 142a. 
Although the gate actuator 171 has approached the gate 58 and effected 
minimal lateral deflection, it will be appreciated that further release is 
prevented since the latch 178 can no longer move downward. 
In FIG. 36, latch 178 has been deflected laterally a sufficient amount to 
fully avoid the engagement of latch dog 178c by the latch cam engager 
182b. It will be recalled that the torsion spring 177 operates against the 
bell crank 175 to normally urge the latch 178 vertically upward. 
Accordingly, when the latch dog 178c moves out of engagement with the 
latch cam engager 182b, latch 178 moves upward past the engager 182b. In 
FIG. 36, the latch cam follower 182 is shown at the end of its down 
stroke, and latch 178 has moved upward to its normal at rest position as 
dictated by torsion spring 177. 
At the same time, and also as shown in FIG. 36, gate actuator 171 is 
retracted to its normal at rest position, also under the influence of 
torsion spring 177. This of course precludes release of the cartridge 11 
from its carousel recess, since the corresponding gate 58 has not been 
deflected sufficiently. 
The position of the keeper arm 251a in FIGS. 35-37 acts as a memory to 
"store" the fact that there has been no cartridge release by the gate 
actuator 171 during the load cycle. With the interposer 143 maintained in 
this position by the keeper arm 251a, there can be no actuation of the 
gate 58 during the following unload cycle. As long as the interposer 143 
maintains this position, there can be no engagement by the latch cam 
follower 182 with the latch 178, as shown in FIG. 37. 
As the pawls 124 move up during the aborted unload cycle, they engage the 
lower edge of the cartridge 11 and attempt to raise the cartridge in its 
carousel recess. Since the cartridge 11 is retained in its recess by the 
retaining ring 51, the force exerted by the pawls 124 is resisted. As this 
force builds up, it creates a component force in the out position of the 
transfer arm assemblies 114 due to the chamfer on top of the pawls 124. 
This causes the pawls 124 to deflect around the lower edge of the 
cartridge and to reach the upper pawl stop (retaining clips 125), followed 
by swinging movement of the transfer arm assemblies 114 to their outermost 
position. 
At the end of the abort cycle, the trigger member 157 on the cam drive 156 
engages the tab 251c of keeper arm 251b. This causes a clockwise movement 
of the keeper arm 251a (as viewed in FIGS. 28-37), which releases the 
interposer 143 from the abort position. As a result, the coil spring 142a 
rotates the interposer hub 142 in a clockwise direction. At the end of the 
unload cycle, the control arm 241 has returned to the position shown in 
FIG. 28, and the mechanism is then ready for the next load cycle. 
With reference to FIG. 14, a recording head 261 is carried by a bracket 262 
in a position so that the portion of tape 16 passing through the external 
access opening 18 will engage the recording head 261 when the cartridge is 
in the load position. This relationship is best shown in FIG. 9, in which 
the mounting bracket 262 and tape deck 191 are not shown for purposes of 
clarity. 
As shown in FIG. 14, mounting bracket 262 is L-shaped, the vertical leg of 
which is mounted to the outer face of tape deck 191 by a plurality of 
screws 263. Recording head 261 is mounted to the horizontal leg of bracket 
262 in the aforesaid position. Head 261 is of the dual gap type, and is 
capable of reading and writing on up to four channels of the tape 16. 
With continued reference to FIG. 14, a twelve volt DC reversible motor 264 
is carried by the tape deck 191 for reversibly driving the tape 16 of a 
selected cartridge 11. Motor 264 has a drive shaft 265 projecting 
horizontally from each end. One end of the drive shaft 265 projects into 
the cartridge load area and carries a resilient drive wheel 266 which is 
sized and positioned for driving engagement with the belt capstan 24 when 
the cartridge 11 is in the load position. 
The opposite end of drive shaft 265 carries a timing disc 267 which rotates 
relative to a motor speed sensor 268 consisting of a photosensor disposed 
in alignment with light emitting diode. The speed sensor 268 is carried by 
an L-shaped bracket 269 mounted directly to the end of motor 264. The 
speed sensor 268 measures the rotational velocity of the timing disc 267, 
and this information is transmitted to the microprocessors, which make any 
necessary corrections to the speed of motor 264, thus insuring that it 
operates at a virtual constant speed. 
Motor 264 is resiliently mounted on the tape deck 191 in a manner which 
permits the belt capstan 24 to engage the resilient drive wheel 266 under 
the influence of a biasing force. With reference to FIGS. 14 and 14A, this 
is accomplished by a motor mounted on a parallelogram spring represented 
generally by the numeral 271. Parallelogram spring 271 is generally 
U-shaped, including symmetrical, horizontally disposed spring leaves 272 
(only the upper of which is visible in FIG. 14) interconnected by a 
vertical member 273. The end of motor 64 is secured to the member 273 by a 
plurality of screws (FIG. 14 only). 
Each of the spring leaves 272 includes outer planar legs 272a which are 
commonly connected at one end to a central planar leg 272b. The outer legs 
272a are connected directly to the vertical member 273. Each of the 
central legs 272b is mounted directly to the tape deck 191 by a mounting 
screw 274. 
As described, it will be appreciated that the outer legs 272a of both 
spring leaves 272 and the vertical member 273 are together vertically 
movable to a limited degree in spring fashion relative to the fixed 
central legs 272b. The construction is such that the four outer legs 272a 
together move as a parallelogram, thus insuring that the drive shaft 265 
of motor 264 is always perpendicular to the cartridge 11 and providing for 
proper driving engagement between the drive wheel 266 and the belt capstan 
24. Because of the spring relation between the sides 272a and the 
associated central leg 274b, the entire motor 264 and its assembly 
resiliently yield as the capstan 24 engages the drive wheel 266. The 
resulting biasing force also insures proper driving force between the two. 
With reference to FIGS. 9 and 14, a printed circuit board 275 is 
horizontally mounted to the spacer block 192 by a plurality of spacers 
276, so that its upper surface is at a predetermined level relative to the 
cartridge load position. In addition to its usual electrical connecting 
functions, printed circuit board 275 also serves to support a mounting 
block 277 and a pair of microswitches 278, 279. 
As best shown in FIG. 9, the vertical leg of mounting block 277 carries a 
light emitting diode 277a which projects light horizontally at a level 
causing it to strike the angular reflective mirror through the window 27 
of cartridge 11. The mirror is disposed above the cartridge tape and is 
positioned so that light is reflected downward onto the tape. The tape is 
provided with openings or transparent portions at the beginning and end 
which serve as beginning-of-tape and end-of-tape markers. These openings 
or transparent portions permit the reflected light to pass through the 
tape momentarily, where it is sensed by one of two photosensors 277b, 
277c, which are carried by the horizontal leg of mounting block 177 (FIG. 
14). 
Microswitches 278, 279 are also disposed immediately below and in line with 
cartridge 11. Microswitch 278 is specifically positioned relative to the 
rotatable plug 28 of cartridge 11, and thus serves as a write-inhibiting 
switch when the plug 28 is rotated to the read-only position. Microswitch 
279 is a cartridge-presence switch, and is disposed to be engaged by the 
cartridge 11 when it reaches the read/write position. 
The signals generated by photosensors 277b, 277c and microswitches 278, 279 
are transmitted to the microprocessors through means not shown. 
Reference is made to FIG. 38, which is a block schematic diagram depicting 
the functional relationship of the controlling and controlled components 
of the overall apparatus. The diagram of FIG. 38 discloses four read/write 
stations 76, although it will be appreciated that the apparatus 31 is 
entirely capable of operating with but a single read/write station 76, 
albeit with less versatility. 
The controlling components preferably include two microprocessors 301 when 
apparatus 31 includes four read/write stations 76. The microprocessors 301 
are synchronously controlled by, timing circuits 302. Buss controls 303 
are interposed between each of the microprocessors 301 and a master buss 
connector 304. The buss 304 establishes proper connection between the 
microprocessors 301 and the other control components. These include a 
read/write station select function component 305, first and second 
read/write and control function components 306, first and second 
input/output ports for interfacing with computer equipment, a port select 
function component 308, a carousel control function component 309, an 
operator panel 310 (which bears the reference numeral 34 in FIG. 3), an 
address switch 311, an address decoder 312, a random access memory 313 and 
a readout memory 314, as well as the read/write stations 76. 
The readout memory 314 may include a program which, in connection with the 
microprocessors 301, serves to control the apparatus in a desired manner. 
As such, the carousel apparatus 31 may simultaneously interface two 
external computers with the cartridge data base, with the cartridge 11 
selectively indexed, loaded, processed and unloaded automatically. The 
port select function component 308 selectively establishes communication 
between any read/write station 76 and either of the ports 307. 
The specific operation of carousel apparatus 31 begins with insertion of a 
plurality of cartridges 11 into the respective recesses 43 of the carousel 
32. This is accomplished by rotating the retaining ring 51 so that the 
retainers 51a do not block the recesses 43. Once the cartridges 11 are 
inserted into the recesses 43, the retaining ring 51 is released, and the 
biasing springs 52 return the ring to a point where the retainers 51a 
overlie the recesses 43 and prevent removal of the cartridges 11. 
The cartridges 11 are retained in the position shown in FIG. 3 by the gate 
58, the retainer 58a of which normally underlies the associated cartridge 
11. 
The carousel 32 may now be placed over the center post assembly (FIG. 9), 
where it will be locked in place by the latch pawl 87 (FIG. 12). The 
carousel 32 is randomly placed on the center post assembly 72 without 
regard to the position of cartridges 11 relative to station mechanisms 76. 
When the unit is switched on and readied for operation from the control 
panel 34, power is applied to the drive motor 73 in the form of stepped 
pulses at a predetermined frequency. This causes the drive motor 73 to 
operate at a first or high speed, causing the carousel 32 to revolve 
toward a "home" position. This position is determined by the sensor 92 
(FIG. 9), which "reads" the character of the slots 65a, 65b of the 
positioning ring 61 (FIG. 8). As pointed out above, the larger slots 65b 
are oriented relative to the stud 66, which is in turn oriented relative 
to the cartridge recess 43 bearing the numeral 1. Accordingly, when the 
slots 65b pass the sensor 92, this information passes to the 
microprocessors 301, and the speed of drive motor 73 is immediately 
reduced to a second or slow speed by pulses at a lesser frequency. 
At the same time, the solenoid 102 of indexing mechanism 75 is actuated, 
which causes the indexing wheel 105 to extend into engagement with 
peripheral flange 46 (FIG. 4). As the carousel 32 continues to revolve at 
the second or lower speed, the indexing wheel 105 falls into the next 
arcuate notch 46b, at which time opposite end of the bell crank 103 
engages the microswitch 106. As pointed out above, the signal generated by 
actuation of the microswitch 106 is utilized by microprocessors 301 to 
stop the drive motor 73, which places the carousel in a home or reference 
position. 
The controlling components of the apparatus 31 now have a reference 
position from which further movements of the carousel 32 may be made. This 
is accomplished by the signals generated by the sensor 92 as the slot 62a 
passes by, which signals are transmitted to the microprocessors 301. Thus, 
when the apparatus receives a command to index a specific cartridge 11 
relative to a particular station mechanism 76, the controlling components 
"know" where the selected cartridge 11 is by reason of the unique position 
of each of the recesses 43 relative to the "home" position, and the 
controlling components also "know" the intended position of the selected 
cartridge 11. The drive motor 73 can then be powered at its high speed, 
and the sensor 92 "counts" the passing of the required number of slots 
62a. After the proper number have been "counted" the indexing solenoid 102 
is actuated, the speed of drive motor 73 is reduced, and the carousel 32 
is stopped with the selected cartridge 11 in the indexed position relative 
to the proper station mechanism 76. Carousel control is also such that any 
of the cartridges 11, which are uniquely positioned relative to the "home" 
position or a derivative reference position, may be moved to the next 
closest available station mechanism 76 or to a particular station 
mechanism 76 of the operator's choosing. Under either circumstance, the 
control circuitry determines and takes the shortest possible route for the 
selected cartridge 11 to its destination. The carousel control also 
operates in conjunction with the random access memory 313 to remember 
where a selected cartridge has been loaded, and to reindex the carousel 32 
with the proper slot 43 adjacent the loaded station mechanism at a 
subsequent time, and even after a number of intervening operations. 
Because the read/write stations 76 are independently operable, the 
apparatus 31 is capable of loading selected cartridges in and 
simultaneously operating all four of the read/write stations. Accordingly, 
after one of the read/write stations 76 has been loaded, the carousel 32 
can be controlled to index other cartridges 11 relative to other 
read/write stations 76, while remembering the position of each cartridge 
11 and retaining the capability to retrieve it at a subsequent time. The 
control components also are capable of a prioritizing function so that one 
operation may take precedence over another depending on its relative 
importance. 
With the selected cartridge 11 properly indexed relative to the desired 
station mechanism 76, a load command signal is automatically given. 
Reference is made to the schematic representation of FIG. 27 for an 
overall view of operations of the station mechanism 76. 
With the load command, electrical power is applied to both the drive motor 
31 and the solenoid 234 of brake assembly 231. As pointed out above, 
energization of solenoid 234 causes its plunger 234a to retract and 
release engagement of the foot 232a with drive gear 141. It will be 
recalled that at each end of the load and unload cycles, the tensioner 144 
is operated to produce a torque buildup at the same time that the transfer 
arm assemblies 114 have swung outwardly. The torque buildup is maintained 
at that point by the foot 232a, which is normally biased into engagement 
with the drive gear 141 by the coil spring 235. Accordingly, when solenoid 
234 is energized, brake foot 232a releases the drive gear 141. 
Simultaneously, motor 131 is powered to rotate the drive shaft 133. This 
rotation is transferred through the cam drive gear 156 to cam shaft 155 
and arm cam 160 (FIG. 18). Arm cam follower 163 has been at the highest 
dwell on arm cam 160 at this point, and the rotation of shaft 155 causes 
it to move inward, thus permitting the spring 129 to urge the transfer arm 
assemblies 114 toward the cartridge engaging position (FIG. 15). Assuming 
that the cartridge 11 has been indexed properly relative to the station 
mechanism 76, the transfer arm assemblies 114 reach the cartridge engaging 
position with the pawls 124 (FIG. 17) positioned relative to the cartridge 
notches 12a. 
Due to manufacturing tolerances, the elevated position of the cartridge 11 
relative to the upper position of the pawls 124 may vary. To insure that 
the pawls 124 will engage notches 12a of the cartridge 11, contact of the 
pawls 124 actually occurs slightly above the notches 12a (see FIG. 29). 
The drive motor 131 is operating at this time, rotating the drive shaft 
133. As shown in FIG. 19, this causes simultaneous rotation of the 
synchronizing gears 145, 148 to move timing belts 147, 151. This in turn 
rotates each of the gear pulleys 128 of the transfer arm assemblies 114 
(FIG. 15), which rotates the shafts 127, drive gear wheels 123 and pawl 
belts 121 (FIG. 17) to synchronously move the pawls 124 downward. 
As the pawls 124 begin to move down, they slide along the edge of the 
cartridge 11 until they drop into the respective notches 12a under the 
force of the biasing spring 129 of the transfer arm assemblies 114. The 
position of pawls 124 relative to the notches 12a at this time is shown in 
FIG. 30. 
It will be observed that the top corner of each of the pawls 124 is formed 
with a chamfer. The chamfer allows the pawls 124 to begin to move into the 
notch 12a at an early stage, and to continue such movement at a controlled 
velocity. The same principle applies in reverse fashion during retraction 
of the pawls 124 from the notches 12a during the unload cycle. The chamfer 
also serves to cause deflection of the transfer arms during the abort 
function when the cartridge 11 is misaligned. 
At approximately the same time the pawls 124 initially contact the edge of 
the cartridge 11, gate actuator 171 begins its movement relative to the 
gate 58, which is holding the selected cartridge 11 within the carousel 
32. As explained above, such movement of the gate actuator 171 is brought 
above by rotation of the cam shaft 155 and latch cam 159. At this point, 
and as shown in FIG. 18, the roller 182c of latch cam follower 182 engages 
latch cam 159 at its lowest dwell. Consequently, rotation of latch cam 159 
urges the follower 182 downward. 
With reference to FIG. 20, and continuing the assumption that the cartridge 
11 is properly oriented so that the aborting function is not initiated, 
the latch cam engager 182b engages the dog 178c of latch 178, urging the 
latter downward. This in turn causes rotation of the bell crank 175 
against the bias of torsion spring 177, pushing actuator link 174 upward. 
As shown in FIG. 7, this results in rotation of the gate actuator 171 
about the pin 172, so that the edge 171c engages actuator member 58b to 
deflect gate 58 laterally to a cartridge release position. This sequential 
operation is shown in FIGS. 28-31. 
Once the pawls 124 are fully seated in the notches 12a and the gate 58 
deflected to a cartridge release position, the inner guiding surface of 
transfer arm assemblies 114 embrace the cartridge edges to guide it as it 
is pulled down toward the read/write position. With reference to FIGS. 1, 
2 and 26, the cartridge 11 slides downward into engagement with the 
cartridge guides 193 on each of the transfer arm assemblies 114. At this 
time, the tab 21a of the cartridge door 21 engages the guide finger 193c, 
which causes the door 21 to open (FIG. 1) and exposes the tape 16 to the 
read/write head 261 (see also FIG. 9). 
As the cartridge 11 reaches the bottom stop plate 193e (FIG. 23), the limit 
of torsion spring 224 is exceeded and tensioner 144 begins to wind up by 
reason of the continued rotation of drive shaft 133 for approximately 3/4 
of one revolution. As described above, this imposes a vertical reference 
force on the cartridge 11 which insures proper registration relative to 
the read/write head 261. It will also be recalled that the lateral 
reference force is imposed at this time by rotation of the release cam 170 
to its load dwell. This enables the bail 206 to swing downward, releasing 
the laterally spaced bias plates 201 for lateral engagement with the 
cartridge 11. 
At the same time that these vertical and lateral reference forces are being 
imposed, the continued travel of drive shaft 133 for 3/4 of one revolution 
also rotates the cam shaft 155 and arm cam 160, which moves to its highest 
dwell relative to the follower 163. This has the effect of moving the 
transfer arm assemblies to their outer position, which, as shown in FIG. 
9, is necessary to permit further rotation of the carousel 32 in indexing 
additional cartridges 11 to the outer station mechanisms 76. 
The pawls 124 swing outwardly with the transfer arm assemblies. However, 
the angular movement of the transfer arm assemblies 114 is relatively 
small (on the order of 5.degree.), and the arc subtended by the pawls 124 
while in their lowest position on the transfer arm assemblies 114 is 
therefore minimal. Consequently, the pawls 124 do not leave the notches 
12a, and they continue to bias the cartridge 11 downward. Coupled with the 
lateral reference force imposed by the bias plates 201, the cartridge 11 
remains rigidly fixed relative to the read/write head 261. 
At the end of the load cycle, the arm cam follower 163 engages microswitch 
230 (FIGS. 15 and 27), which interrupts the supply of electricity to motor 
131. Simultaneously, the solenoid 234 of brake assembly 231 is 
de-energized, causing the brake foot 232a to engage drive gear 141. This 
prevents further rotation of either the drive shaft 133 or the cam shaft 
155, so that all movements are terminated during the information 
interchange between tape 16 and read/write head 261. 
Also as described above, the arrival of cartridge 11 in the read/write 
position causes the cartridge presence microswitch 279 to be engaged. If 
microswitch 279 is not engaged, as would be the case during the abort 
function, the drive motor 264 for drive wheel 266 will not be actuated. 
Microswitch 278 senses the position of rotatable plug 28, and it 
accordingly permits or prevents information to be recorded on tape 16. 
Assuming the arrival of cartridge 11 into the read/write position, 
microswitch 279 is actuated and drive motor 264 immediately begins to run. 
This turns the capstan 24 of cartridge 11 at the proper speed, thus 
effecting information interchange between the read/write head 261 and tape 
16. This information is transferred through either of the ports 307 to the 
computer with which the apparatus 31 is interfaced. 
The controlling components shown in FIG. 38 cooperate with the selected 
cartridge 11 to perform a number of functions, including writing, erasing, 
reading both forward and backward, skipping a data block in both forward 
and reverse directions, skipping an entire data file in both forward and 
reverse directions and rewinding. 
After the information interchange has been completed, the carousel 32 is 
reindexed relative to the station mechanism 76, and the unload cycle, 
which simply is a reversal of the load cycle, as initiated. 
Operation of the station mechanism when a cartridge 11 is not properly 
oriented has been previously discussed in connection with FIGS. 32-37. 
However, it should be further noted that during an abort cycle, the 
station mechanism 76 goes through a complete load cycle even though the 
gate actuator 171 has not been permitted to move. Thus, the pawls 124 
begin to travel downward, and although they initially engage the sides of 
cartridge 11, they eventually drop below the cartridge for failure to 
engage the notches 12a. At this time, the transfer arm assemblies 114 are 
able to swing inward under the influence of spring 129. 
As shown in FIG. 36, control arm 241 swings in with the transfer arm 
assemblies 114 as if there were a cartridge 11 in the read-write station. 
This would allos operation of the gate actuator 171 were it not for the 
latching operation of the interposer 143 during the aborted load cycle. 
Thus, the interposer 143 serves to do what the control arm 241 is now 
unable to do. 
Further, the fact that no cartridge 11 has reached the read/write station 
during the aborted load is sensed by closure of the arm switch 230 and the 
unchanged state of the cartridge presence switch 279. These signals 
combine to tell the system to initiate an immediate unload cycle.