U.S. patent number 3,612,243 [Application Number 05/021,801] was granted by the patent office on 1971-10-12 for material handing apparatus.
This patent grant is currently assigned to Collins Radio Company. Invention is credited to Lewis L. McAllister, Harry M. Passman, James P. Wiles.
United States Patent |
3,612,243 |
McAllister , et al. |
October 12, 1971 |
MATERIAL HANDING APPARATUS
Abstract
Material handling apparatus of the conveyor type especially
suited for computer controlled operation. Mechanical features and
electronic control features including safety precautions are
described in a printed circuit processing application.
Inventors: |
McAllister; Lewis L. (Marion,
IA), Passman; Harry M. (Cedar Rapids, IA), Wiles; James
P. (Richardson, TX) |
Assignee: |
Collins Radio Company (Dallas,
TX)
|
Family
ID: |
21806234 |
Appl.
No.: |
05/021,801 |
Filed: |
March 23, 1970 |
Current U.S.
Class: |
198/341.02;
198/346.3; 246/122R; 414/560 |
Current CPC
Class: |
B23Q
7/00 (20130101); B65G 49/0459 (20130101); B23Q
2707/00 (20130101) |
Current International
Class: |
B23Q
7/00 (20060101); B65G 49/04 (20060101); B65G
49/00 (20060101); B23q 005/22 () |
Field of
Search: |
;198/19 ;214/89,86,16B
;212/123,124,125,126 ;246/122R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Aegerter; Richard E.
Assistant Examiner: Lane; H. S.
Claims
We claim:
1. A conveyor system especially suited for computer controlled
operation comprising:
a. a plurality of work stations,
b. work receiving means associated with each work station,
c. a horizontal rail means spaced from and aligned with said
plurality of work stations,
d. at least one messenger means movable along said horizontal rail
means for transporting work means between work stations,
e. said messenger means including elevator means for depositing or
removing work means at said work stations and vertical rail means
along which said elevator means travels,
f. drive means for said messenger means and for said elevator
means, and
g. control means for selectively moving said messenger means to
work stations and removing or depositing work means at said work
stations including position register means and digital encoder
means associated with said drive means for cooperatively indicating
the position of said messenger means, and resync transducer means
associated with said horizontal rail means for correcting errors in
said position register means as said messenger means moves along
said horizontal track.
2. A conveyor system as defined by claim 1 wherein said plurality
of work stations are process tanks and said work means includes
printed circuits and a work support means.
3. A conveyor system as defined by claim 1 wherein said work
support means includes a vertical depending member which is
supportably received by said elevator means.
4. A conveyor system as defined by claim 1 and including two
messenger means movable along said horizontal rail means.
5. A conveyor system as defined by claim 4 wherein said control
means includes comparator means for comparing indicated positions
of said two messenger means and generating signal in response to
said indicated positions approaching each other below a minimum
limit, said drive means for said messenger means and for said
elevator means being responsive to said signal and stopping
movement of said messenger means and said elevator means.
6. A conveyor system as defined by claim 1 wherein said control
means includes switch means associated with each work station for
indicating the presence of a messenger and the completion of a
process operation, switch means associated with each work receiving
means for indicating the presence of a work support means, switch
means associated with said elevator means for indicating an upper
elevator position and a lower elevator position, and for indicating
the presence of work support means in said elevator means.
7. A conveyor system as defined by claim 6 wherein said control
means further includes means for permitting messenger movement
along said horizontal rail means only where said elevator means is
in said upper position and loaded or is in said lower position and
unloaded.
8. A conveyor system as defined by claim 7 and including two
messenger means movable along said horizontal rail means.
Description
This invention relates generally to material handling apparatus,
and more particularly to material handling apparatus of the
conveyor type which is especially suited for computer controlled
operation. One example use of such apparatus is in the processing
of printed electronic circuits, and the invention will be described
with respect to this application. However, it is to be appreciated
that other material handling applications are feasible and within
the scope of the invention.
In the processing of printed circuit boards, blanks or unprocessed
boards undergo a number of chemical processing steps including
cleaning, electrolysis copper deposition, photoresist masking,
copper, tin and tin-lead electroplating titnating, resist
stripping, and other chemical etching to define desired circuit
patterns. The process readily lends itself to a continuous process
flow with conveyor means for facilitating transfer of boards from
one process station to the next process station.
Several plating conveyors have been suggested and/or manufactured,
but all known systems have structural disadvantages and do not lend
themselves to automatic, computer control.
An object of the present invention is an improved material handling
apparatus of the conveyor type.
Another object of the invention is improved material handling
apparatus which is adaptable to the process of printed electronic
circuits.
Still another object of the invention is improved material handling
apparatus which is suited for computed controlled operation.
Yet another object of the invention is a printed circuit production
system including conveyor means which may be automatically,
computer controlled.
Another object of the invention is improved material handling
apparatus for printed electronic circuit fabrication which is
flexible in operation and which has no structural parts other than
board support means moving over process tanks.
Briefly, in a printed circuit processing application the present
invention includes a plurality of process tanks in a sequentially
spaced arrangement, board support means, each tank having an
opening for receiving said board support means, each board support
means including a lift member extending beyond the periphery of a
process tank when the support means is positioned within the tank.
A rail support and travel system is provided with each line of
tanks, and one or more lateral transfer means, or messengers,
including elevator means for removing or inserting board support
means into and out of each tank is provided which travels on the
rail support system. The drive means and control means for the
messengers is designed to allow either a manual test or computer
control mode of operation.
The invention and objects and features thereof will be more fully
understood from the following detailed description and appended
claims when taken with the drawings, in which:
FIG. 1 is a top view of a conveyor system in accordance with the
present invention;
FIG. 2 is a side view of the conveyor system of FIG. 1;
FIG. 3 is a side view of a messenger taken along the line of
lateral movement of a messenger;
FIG. 4 is a side view of the support means for the messenger cable
for power and logic circuits;
FIG. 5 is a section view of the support means in FIG. 4 including
moveable cable support members;
FIG. 6 is an isometric view of the messenger and elevator
means;
FIG. 7 is an isometric view of a messenger, work support means, and
load and unload stations;
FIG. 8 is an isometric view of a process tank, agitator and
messenger;
FIG. 9 is an isometric view of the messenger drive means and
encoder;
FIG. 10 is a functional block diagram of the messenger control
system;
FIG. 11 is a functional block diagram of the controller portion of
the messenger control system of FIG. 10;
FIG. 12 is a schematic of the messenger control relays;
FIG. 13 is a schematic of elevator control relays;
FIG. 14 is a schematic of controller address means of each
elevator; and
FIG. 15 is a schematic of work station clamp control relays.
Referring now to the drawings, FIG. 1 is a top view of a conveyor
system in accordance with the present invention adapted for the
production of printed circuit boards. A plurality of processing
tanks 10 are serially arranged for carrying out the rinsing,
plating and etching steps in printed circuit fabrication. A walkway
12 is provided along one side of the tanks for human operators, and
a horizontal rail assembly 14 comprising two parallel, vertically
spaced rails is provided along the other side of the tanks. Two
lateral transfer messengers 16 and 18 are provided which travel
along horizontal rail 14 for transferring workpieces between the
various process tanks. Only one such messenger is necessary in the
conveyor system, however, a preferred embodiment includes two such
messengers which may operate along the rail simultaneously. Various
safety features are incorporated to prevent collisions, as will be
described further below.
Referring again to the tanks 10, it will be noted that at either
end of the tank, support means 20 is provided for receiving a work
support member (not shown in this view). Reciprocating pneumatic
cylinders 22 are activated upon receipt of a work support assembly
to provide agitation of workpieces within each tank during a
processing operation. The agitator assembly will be further
described below with reference to FIG. 8. At one end of the line of
tanks a load station 24 and an unload station 26 are provided for
loading and unloading the work support assemblies.
The messengers 16 and 18 are provided with elevators 28 which lower
and raise workpieces into and out of the process tanks. The
elevators travel along a vertical rail assembly comprising a pair
of vertical rails 30 which are a part of the messenger. Arms 32
extend from either end of messenger 16 for initiating a safety
brake and absorbing impact should the messenger be involved in a
collision due to control means failure.
FIG. 2 is a side view of the conveyor system shown in FIG. 1 and
further illustrates the agitator support assembly 20 of the tanks
10, the load and unload stations 24 and 26, respectively, and the
messengers 16 and 18. It will further be noted that the horizontal
travel rail assembly includes an upper rail and a lower rail, both
designated 14, along which the messengers travel. As will be
described further below, the elevators 28 for each messenger may
assume one of three positions, namely a lower unloaded position as
assumed by the elevator of messenger 18, an upper loaded position
as assumed by the elevator of messenger 16, and an intermediate
position at which the workpieces are loaded and unloaded. Control
means to be described further below allows a messenger to move
along the horizontal travel rails 14 only when the messenger
elevator is unloaded and in the lower position or loaded and in the
upper position.
The two messengers are driven independently by cable drive means
including servo-controlled motors 34 and 36 located at one end of
the conveyor line. An encoder 37 is provided which senses the
movement of the drive cables and thereby indicates digitally the
movement and position of the messengers. The servo-controlled
motors and encoder will be further described below with reference
to FIG. 9 and the control system shown in FIG. 10.
FIG. 3 is a side section view taken along the axis of the lateral
rail assembly and further illustrates the relationship of the
messenger and a process tank. The walkway 12 is on one side of tank
10 and the messenger 16 and horizontal travel rails 14 are on the
opposite side of the tank. The agitator support 20 is pivotally
mounted to permit lateral movement when activated by reciprocating
pneumatic cylinder.
An upper messenger housing 38 includes bearings for riding an upper
rail 14 and further includes brake means for use in emergency
stops. The lower rail 14 is engaged by the messenger in a manner to
support the messenger assembly upright and counteract the movement
force when the elevator 28 is supporting a load. Movement of
elevator 28 along rail 30 is provided by means of cable 40 and
drive means 42, which are further described below.
Power to the elevator drive motor 42 is provided by means of cable
44. Cable 44 is accommodated by support 46 so that the cable may be
extended as the messenger moves along the rail assembly 14 thereby
maintaining power to the elevator drive 40. The support 46, as
further illustrated in FIG. 4, includes a channel 48 having a
bottom opening which is supported in spaced relationship with
respect to member 50 by means of a bracket 52. Member 50 is mounted
to support member 54 for upper rail 14 and bottom support member
56.
FIG. 5 is a section view of channel 48 and illustrates cable
support carriers 58 which include rollers 60 which provide movement
for the carriers 58 along the channel 48. Thus, as a messenger
moves along the rail assembly, cable 44 for the elevator drive is
extended by means of the cable carrier 58 movement along channel
48.
FIG. 6 is an isometric view which further illustrates details of
the messenger, elevator and rail assemblies. As the messenger 16
moves along upper rail 14, photoelectric detector means within
upper messenger housing 38 senses pins 60 which are provided along
the rail assembly, and the electrical pulse is transmitted to the
messenger control system to resync the indicated messenger
position. These resync signals are necessary to correct possible
errors from cable driven encoder 37. Cable 62 is associated with
tank position sensing means and transmits an in-position signal to
the controller when a messenger arrives at the tank position.
Cables 64 and 66 which provide movement of the messengers along
rail assembly 14 also drive the encoder 37 as described above with
reference to FIG. 2.
As described above, elevator 28 may assume one of three positions
as it moves along vertical rails 30, namely a lower unloaded
position (as shown in FIG. 6), an upper loaded position (not shown
in FIG. 6), and an intermediate position for receiving or
discharging a load. At each one of these positions a microswitch is
provided to generate a signal indicative of the elevator being at
the respective position. Microswitch 68 is shown for indicating the
intermediate position at which loads are received and discharged by
the elevator. Importance of these position indicating switches will
be appreciated from the description of the messenger control
system, below.
Elevator 28 is driven by means of cable 44 and a drive motor within
housing 42. As described above with reference to FIGS. 3-5, the
elevator drive motor receives its power through cable 44 which is
supported by channel 48.
The load receiving portion of elevator 28 is shown in a partially
cutaway view and includes an upper pair of rollers 70 and a lower
pair of rollers 72 which receive a pin member of the work support
means, described below with reference to FIG. 7. When the pin
member is in position within elevator 28, microswitch 74 is tripped
and a load-in-position message is transmitted to the messenger
control system.
FIG. 7 is an isometric view of a work holder 80 including a
plurality of printed circuit boards 82 arranged and supported
thereby to facilitate chemical processing. The work holder 80 is
shown in the unload position 26 with the load position 24 adjacent
thereto. Associated with load and unload positions 24 and 26 are
microswitches 84 and 86, respectively, which are actuated when a
work holder is in position in the load or unload stations.
Associated with each tank or work station is a microswitch similar
to switches 84 and 86 which indicates the presence of a work holder
in the tank. Extending downwardly from work holder 80 is a rod 88
which is received by elevator 28 when the work holder is to be
elevated, as described above with reference to FIG. 6. In this
figure the elevator 28 is shown in the down position ready to
receive pin 88 and work holder 80 upon raising of the elevator.
An isometric view of a tank 10 and associated agitator means is
shown in FIG. 8 along with a work holder 80 supported by elevator
28 and positioned for insertion into process tank 10. The agitator
support 20 includes members 100 and 102 at either end of the tank
for receiving the work holder 80 as the elevator is lowered. A
microswitch is associated with member 100 which is tripped upon the
positioning of work holder 80 in the agitator support and thereby
providing a work-in-place signal to the control means. Agitator
support 20 is pivotally mounted as shown at 104 and 106 thereby
permitting lateral movement of the agitator support when cylinder
22 is actuated. Tank 10 includes an opening 108 in its top surface
for receiving the protruding portion of work holder 80 as elevator
28 is lowered. Connected with elevator 28 is cable 40 which passes
over a pulley 110 mounted in the upper elevator structure and is
driven by the elevator drive means 42 (shown in FIG. 6).
The drive means and encoders for the two messengers are shown in
FIG. 9. Cables 64 and 66 which are connected to the two messengers
are driven respectively by servomotors 34 and 36. Power to the two
servomotors is provided by suitable SCR amplifiers such as General
Electric's VI SCR amplifier. Position indication for the two
messengers is provided by encoder means 37 which comprises two
incremental digital encoders 112 and 114 each of which is driven by
either cable 64 or cable 66. Commercially available encoders such
as the Model 834 optical encoder manufactured by Disc Instruments,
Inc. may be utilized for the encoders 112 and 114. By mounting a
6.6-inch diameter sheave on the encoder, 200 pulses per revolution
will result in a pulse for every 0.1056 inch of cable traveled.
Because of slippage and runout problems connected with driving the
encoder from a sheave driver by the drive cable, the index
transducers 60 (shown in FIG. 6) are provided to correct errors in
position by resyncing the position indicator in the control means,
as further described below.
The control means for the conveyor will now be described with
reference to FIGS. 10-15. Referring to FIG. 10, a functional block
diagram of the entire control means is illustrated. In computer
operations, program control is effected through the Time Division
Multiplexed (TDM) loop to the input device adapter 200. Device
adapter 200 stores incoming instructions and feeds command
information in compatible form to position controller 202 and feeds
back information to the computer. In response to command inputs,
position controller 202 through messenger command portions for a
messenger "A" and a messenger "B," controls the servoamplifiers 204
and 206 which in turn drive "A" messenger motor 208 and "B"
messenger motor 210, respectively. When driving the two messengers,
messenger motors 208 and 210 drive "A" encoder 212 and "B" encoder
214, as described above with reference to FIG. 9, which provide
messenger position information through encoder translators 216 and
218 back to the position controller 202.
Associated with the rail assembly are the "A" resync transducers
222 and "B" resync transducers 224 which provide corrections to the
"A" messenger and "B" messenger position registers which may be
required due to slippage and runout problems connected with driving
the encoders 212 and 214.
Associated with the position controller 202 is tank selection
decoding and comparison means 228 which controls the operations at
each work station tank through means of relay drivers 230 and tank
select relays 232. Auxiliary control relays 234 provide feedback to
the computer loop to indicate when a messenger and a tank
processing cycle is completed. The auxiliary relays 234, which
provides inputs to the "A" elevator motor control 236 and "B"
elevator motor control 238, incorporates safety features for safely
controlling "A" elevator motor 240 and "B" elevator motor 242, as
described further below with respect to FIGS. 12-15. Level sensors
244 including microswitches at the three stationary elevator
positions (lower unloaded position, intermediate load/unload
position, and upper loaded position) provide inputs to the elevator
controls 236 and 238 and auxiliary control 234.
Position controller 202 is programmed to provide emergency braking
should the indicated "A" messenger and "B" messenger positions
approach each other below a prescribed minimum. In such a
situation, the servoamplifiers 204 and 206 are deactuated, armature
excitation is removed from the drive motors, and the resulting
generator behavior of the motors provides dynamic braking.
Additionally, should the messenger approach each other and arms 32
engage, "A" rail clamp 252 and "B" rail clamp 254 are mechanically
actuated.
Test panel 256 is provided for a manual mode operation of the
conveyor system. Inputs to elevator controls 236 and 238, emergency
braking 248 and 250, position controller 202, and servoamplifiers
204 and 206 are provided from the test panel 256 to effect the
manual mode operation.
Power for the system is provided by a main power supply 258 which
may typically be 460 volts, 3 phase AC for compatibility with the
servoamplifiers. Logic power supply 260, typically +5 volts DC, and
relay power supply 262, typically 24 volts DC and encoder power
supply 263 are provided in cooperation with the main power supply
258.
The "A" messenger control portion of the position controller 202 is
illustrated within block 265 in FIG. 11. Command inputs from the
test mode or computer 264 are fed to a command register 266 in the
position controller. In response to the received command,
comparator 268 compares the command register position with the
indicated position "A" register 270 and in response thereto
provides an input to the servoamplifier 272 through
digital-to-analog converter 274. Amplifier 272 energizes "A"
messenger motor 276 which in turn drives the messenger to the
command position. Tachometer 278 provides feedback to the amplifier
272 and thereby governs the motor speed. Motor 276 also drives
encoder 282 which updates position "A" register 270. Also, as above
described, resync transducers 284 function to correct any errors in
the position "A" register caused by cable slippage, for example, as
the messenger is moved along the track.
As a safety feature proximity comparator 286 is provided to measure
the relative proximity of the two messengers and stop messenger
operation upon the distance between the two messengers dropping
below a prescribed minimum. Inputs are received by proximity
comparator 286 from the position "A" register 270 and from the "B"
position register, and control signals are provided to stop
operation of the elevators and the messengers upon the indication
of an imminent collision.
After a command is received by the position controller and a
messenger is moved to the command position, a comparator 268
provides a signal to the elevator control 288 which, together with
a signal from the messenger is position microswitch at the
prescribed tank station, commences elevator operation to load or
unload at the work station.
To prevent improper and possibly damaging operation of the conveyor
system, a number of safety features are incorporated in the
auxiliary control relays to insure safe operation of the messengers
and elevators.
FIG. 12 is the relay portion which controls the messenger
operation. A command to messenger "A" closes motor "A" relay
contacts 292 for initiating operation of servo "A" amplifier 204.
However, to complete the circuit to the servoamplifier the elevator
down position contacts 294 and the no load indication contacts 296
must be closed, or the elevator up contacts 298 and the load in
position contacts 300 must be closed as indicated by the parallel
network. That is to say, the messenger cannot be moved if the
elevator is in the load/unload position or is moving between the up
and down positions. Travel of the messenger is permitted only when
the elevator is down and unloaded or up and loaded. Further, relay
contacts 302 which are controlled by the proximity comparator 286
of FIG. 11 must be closed, brake contacts 304 which are controlled
by the messenger brake must be closed, overtravel contacts 306
which are located on microswitches at either end of the rail
assembly must be closed, and contacts 308 which are controlled by
the messenger arriving at the command destination must be closed.
Thus, for the messenger to operate in response to a command, the
elevator must be down and unloaded or up and loaded, proximity
comparator 286 must indicate a safe distance between messengers,
and the messenger brake must not be actuated. Further, should the
messenger travel exceed the limit of the rail assembly, overtravel
switch 306 is opened thus stopping the messenger, and once the
messenger arrives at the command position relay contacts 308 are
opened thus deenergizing the messenger drive.
The relays for raising and lowering the elevator on messenger "A"
are illustrated in FIG. 13. Power to actuate the raise elevator "A"
relay 310 includes the parallel network shown generally at 312, and
power to actuate the lower elevator "A" relay 314 includes a
parallel network shown generally at 316. Referring first to the
raise elevator circuitry, an elevator overtravel relay 318 is
normally closed but is opened upon the elevator overtravelling
either the upper position or the lower position. Power to the raise
relay 310 is provided through the overtravel switch 318 and through
one of the three legs of parallel network 310. The upper leg is for
test mode operation and includes a manually operated relay 320
which is serially connected with test mode relay 322. Automatic
mode operation of the elevator is provided by the middle and lower
legs of the parallel network 312. The middle leg includes relay 324
which is closed when the workpiece supported by the tank agitator
assembly is unclamped and thus ready to be raised. Serially
connected with relay 324 is relay 326 which is closed when no lower
command is present (thereby preventing conflicting command
signals), lower position relay 328 is closed when the elevator is
in the lower position, relay 330 is closed when the messenger is in
position at the proper work station, and relay 332 is closed when
automatic mode operation is desired.
Should the messenger be at the load station and a raise command is
received, a load station relay 334 is provided which shunts the
unclamped relay 324 since load stations do not have clamps. Once
the elevator begins moving upward it will be noted that the center
leg is opened by the lower position relay contact 328 opening. In
order to continue the raising of the messenger to the upper
position the bottom leg further includes a bar in place relay
contacts 336 which normally is closed but opens should the elevator
move past the intermediate pickup position and the load support
means fail to actuate switch 74 (see FIG. 6). Serially connected
with contacts 336 are bypass relay 338 which is opened upon
movement of the elevator and proximity switch 340 which is normally
closed but opens upon receiving a warning from the proximity
comparator 286, shown in FIG. 11.
In series with the parallel circuit 312 is a relay 342 which opens
upon the elevator assuming the upper position and a safety
interlock 344 which cooperatively functions with a safety interlock
relay 346 in the lower command circuit to prevent relays 210 and
214 from being simultaneously energized.
The lower elevator command relay circuit including parallel circuit
316 is very similar to the above-described circuit for the raise
command. The lower elevator relay 314 is energized through
overtravel contacts 318, through the parallel network 316, through
relay contacts 348 which opens upon the elevator assuming the lower
position, and interlock relay contacts 346. Again, the parallel
network 316 includes three legs including an upper leg having a
manually operated relay 350 which is serially connected with manual
mode operation relay contacts 352. The center leg includes relay
contacts 354 which indicate that the clamp solenoid is deenergized,
contacts 355 which indicate that no raise command has been
received, relay contacts 356 which are closed with the elevator in
the upper position, relay contacts 358 which are closed when the
messenger is in the proper work position, and the automatic mode
operation contacts 360. Shunting contacts 354 are unload position
contacts 361. The bottom leg comprises bypass relay contacts 362
which are closed upon the lowering of elevator "A" and provides a
bypass to the center leg which relay contacts 356 open. Serially
connected with bypass relay contacts 362 are proximity comparator
control relay contacts 364 which stop operation of the elevator
upon receipt of a command from proximity comparator 286, shown in
FIG. 11.
When the elevator assumes either the upper or lower positions, a
time delay relay 370 momentarily closes thereby initiating a "send
message" signal which is generated by the circuit shown in FIG. 14.
The time delay relay 370 is energized through upper position relay
contacts 372 or lower position relay contacts 374 which are closed
upon the elevator assuming the upper position or lower
position.
Referring to FIG. 14, the computer is advised that the previous
command has been completed by means of the time delay relays
actuated by the elevator assuming either the upper or lower
position, indicated at 370, or a similar time delay relay 376 upon
the messenger moving to a park position at either end of the
messenger travel tracks. Thus, when either the elevators move to
the upper or lower positions, or the messenger moves to a park
position, time delay relays are momentarily closed thereby sending
a next command signal back to the computer.
The relay controlling the clamp at each work station are
illustrated in FIG. 15. As above described with reference to FIG.
13, the elevator motor is disabled when the clamp at the work
station is activated and holding a work support means in position
within the tank. Thus, in order to allow the elevator to function
at a particular work station, the clamp solenoid relay 380 must be
deenergized. Clamp 380 is energized whenever a workpiece is in
place thereby closing relay contacts 382 and neither messenger "A"
nor messenger "B" are at the work station as indicated by the
position controller thereby opening relay contacts 384 or 386, or a
process at the particular work station is in progress thereby
closing relay contacts 388, or a messenger is not in position at
the particular work station as indicated by the messenger sensing
means at each work station thereby rendering relay contacts 390
closed. Thus, in order for a messenger to pick up a workpiece at
the particular work station, the process at the work station must
be completed, and a messenger must be at the selected tank location
as indicated by the position controller and by the messenger
sensing means at the work station.
An operation cycle for the messenger is as follows:
1. Receive command.
2. Move empty with elevator in lower position to the programmed
tank position.
3. Raise elevator, engage work support rack and elevate to upper
position.
4. Request next command.
5. Receive command.
6. Move loaded to programmed tank position.
7. Lower elevator, deposit work support rack in the tank.
8. Lower elevator to down position.
9. Request next command.
A specification summary of one embodiment of the conveyor system in
accordance with the above description is as follows:
Number of Tanks-- 30
Distance Between Tank Centerlines-- 30 .+-. 1/2 inches
(nonaccumulative)
Park Stations-- one/messenger; at opposite ends
Load/Unload Station-- One Each at Same End
Messenger Weight--300 pounds maximum including work load
Messenger Support-- Ball Bearing on 2-inch Diameter Rail
Drive-- Direct Cable Drive
Horizontal Positioning Accuracy--.+-. 0.250 inch
Horizontal Transfer Acceleration/Deceleration-- 5.33
feet/sec..sup.2 (constant)
Horizontal Transfer Velocity--10 feet/sec. maximum
Horizontal Drive Cable Size-- 1/8 -inch Diameter (7.times. 19)
s.s.
Horizontal Drive Sheave--9 -inch Diameter
Horizontal Drive Motor-- Servo-controlled
Horizontal Messenger Travel-- 1,052 inches, Park A to Park B
Horizontal Messenger Braking-- Dynamic plus Mechanical Braking
Horizontal Position Sensing-- Incremental Encoder
While the invention has been described with reference to a specific
embodiment and application, the description is illustrative and is
not to be construed as limiting the scope of the invention. Various
modifications and changes may occur to those skilled in the art
without departing from the spirit and scope of the invention.
* * * * *