RS

Com~t. & I ~ .

Faqlr4 Vol. 4, pp. 269-279

03t0,43JZ/80/04020J-IIS02.a0q0

PerpmomP ~ . Ltd., IN0. Printed ia Grezt Briton

MICROCOMPUTER

MODEL AS/RS

PHILIP M. WOLFE School of Industrial Engineering and Management, Oklahoma State University, Stillwater, OK 74074, U.S.A.

(Received for publication 3 June 1980) M~raet---Automated storage/tetrieval systems (ASIRS) are being installed at an increasing rate as comlmnies ate striving to reduce material handling and inventory costs, in addition, microcomputers are being imaalled into mote and more devices. This paper describes a model AS/RS controlled by a roller that was built by an industrial engineering student: it is used to illustrate the concepts of applying AS/RS and microcomputertechnology. INTRODUCTION

Industry will undergo a profound change in the 1980s as automation is applied at an increasing pace. Materials handling equipment and methodology will be in the forefront of this change. Two recent developments, having been refined and judged as practical, are pointing the way: the automated storage/retrieval (AS/RS) and the microcomputer. Recognizing the impact of these two subjects, it was decided that some method was needed to teach these concepts at a university, however, because of limited funds, the approach used could not be a full size working system. Even so, a "hands on" teaching approach had the most potential as a learning aid. It was decided that an ideal approach would be a model AS/RS controlled by a microcomputer. Pursuing this idea led to the discovery that a model AS/RS had been built at Arizona State University[I]; however, it was controlled by an obsolete process control computer built in the mid.1960s. After some consideration, it was decided that a model AS/RS design could be modified so that it could be controlled by a microcomputer. At Oklahoma State University, in the School of Industrial Engineering and Management, a model AS/RS controlled by a microcomputer has been built and is now used extensively in teaching and for demonstrations[2]. Figure i is a picture of the resulting system. The system dramatically demonstrates the impact these new developments will have on

i

Fig. 1. Microcomputer controlled model ASIRS. 269

270

PHILIP M. WOLFE

materials handling. The following are some of the concepts demonstrated: • Use of high rise stacker cranes to minimize space requirements. • Ease of use of random storage in a computer controlled facility. • Ease of keeping the inventory records, including location, FIFO, etc. up-to-date in a computer controlled facility. • Possibility of labor reduction that can be obtained by an AS/RS. • Concepts and potential of microcomputers. • Ease of utilizing microcomputers. • Low cost of microcomputer systems. • Flexibility of microcomputers. Students have found this system exciting and enjoyable to work with, in addRion to being a good educational device. At demonstrations, non-students have been fascinated by what is being done with the new technology and are eager to talk about new applications. The remainder of this paper will describe in some detail the model warehouse system developed, which is the application of AS/RS concepts and microcomputer technology. AS/RS PHYSICAL DESCRIPTION

The model warehouse consists of a steel frame that resembles a cube; however, the top front of the steel frame extends beyond the body of the warehouse (refer to Figs. i-3). A moving beam extending across the warehouse, resembling an over head crane, rides on the top left and right sides of the warehouse frame. This beam provides the fore and aft motion. Riding this moving beam is a trolley from which the loader mechanism is hung (Figs. 3-7). The trolley provides the side to side motion. The loader provides vertical motion on a worm screw and rotational motion around this worm screw. This model consists of two aisles; each aisle having storage bays on each side with five levels of storage (Figs. l and 8). The storage bays are actually 3~ in. finishing nails on wood strips attached to the steel frame. These storage bays hold the inventory, consisting of dit~rent colored carboard tube sections 4 in. in diameter and 3 in long. Although cardboard tube sections may not appear to be realistic storage units, they are operationally handled like a pallet ( ~ l e being quite simple), allowing for good visibility of operations and wide tolerances for the loader and shelf systems. All actions of the system are initiated by three stepping motors (see Fig. 2 for locations of the stepping motors) which are controlled in both direction and speed by the microcomputer. Also, on the loader, one solenoid is used to change from vertical to rotational motion, which permits using the same motor for both types of motion. Figure 9 shows the loader mechanism where the so:enoid is located. Limit switches are used to initialize the loader to an exact ,-Stepper motor for vertical and rotational motion Ste;

sm

fore (Simpio

axle 'hill on ~e)

lied to

Fig. 2. Warehouse frame side view.

Microcomputer controlled model AS/RS

271

Fig. 3. Top view warehouse showing front extension of frame and movable beam with trolley.

Fig, 4. Trolley sitting on movable beam.

location during the startup. This initialization sets the origin for the system from which all locations in the warehouse are referenced. The origin location is also the location of the loading/unloading station. The motion of the beam in the fore and aft directions is produced by a stepping motor connected by a continuous loop of "tiger tail" wire to a wheel and axle assembly on the opposite end of the warehouse (Fig. 2). A bolt from the moving beam is attached to this to provide movement. On the other side of the wheel and axle assembly, a similar wire loop through a simple pulley is used to provide parallel motion to the moving beam. The left/fight motion of the trolley is provided by a stepping motor mounted on the back of the warehouse. This motor turns a rectangular rod that extends the length of the warehouse (on the fight fide) that slides through a bearing assembly on the moving beam (Figs. 3, 5 and 10). The turning of this rod by a stepping motor rotates a spool containiag the "tiler tail" wire which is attached to the trolley and then passes through a series of pulleys resulting in trolley movement.

272

PHILIP M. WOLFE

Trdley (ix~/s and col~eson unde~id, of m)lkly)

Shaft from stepper motor

Fig. 5. Top view of movable beam, trolley, and side to side rigging.

• Tro lily

~id c o n t r o l ~ ~

r t k ~ ~

Of

roIGtkm

Guide roils

Loader

Fig. 6. The worm screw and loader mechanism.

A stepping motor also provides the vertical movement of the loader mechanism by rotating a worm screw crated by soldering a 1/4 in. copper tubing onto a ?18 in. copper pipe. The loader travels on two vertical guide rails which are held fixed by a solenoid while the worm screw is rotating to provide vertical movement. To create the rotational movement, the guide rails are fixed to the worm screw by activating the solenoid (Fig. 6 and 9): In this case, the loader and worm screw rotate as a unit when the stepping motor is turning: therefore, no vertical

Microcomputercontrolled model AS/RS

273

Fig. 7. Lower end of loader containing a cylinder ready to be stored,

Fig. 8. Front corner view of warehouse showing aisles, loader and cylinders in storage.

movement occurs during this time. The speed of the loader, stepping motor is reduced by the computer to 1/16 of the full speed to prevent the item on the loader from being tossed off during loader rotational movgment. PROGRAM OPERATION

When the computer program is executed, it first initializes the loader and then prints the listing of the present warehouse inventory. After the initialization of the system, the operator can enter any one of the several commands which are given in Table I. These commands are

274

PHILIPM. WOLFE

Fig.9. Movable beam, trolleyand solenoidmechanism.

Fig. 10. Top side ~

of warehouse showing steg~ing motor, rod, bearing and slm~l that provides trolley side to side movement.

described bridy in the Table, but the operation of two of the major commmds, Store and Retrieve, will In discussed. When the Store command is given, the computer looks for empty storage beys. At present, the computer program is written such that the closest empty bay is chosen. In this location the item is stored under a three character serial number. When a Retrieve command is given for a certain unit (a three character serial number), the computer searches the inventory for all of the units with the desired serial number and retrieves the unit which can be retrieved the quickest. It then takes this unit to the original position for unloading. An example of the system and user interaction is given in Fig. 11. MICROCOMPUTERSYSTEM A Southwest Technical Products 6800 microcomputer system, based on a Motorola 6800 microcomprocessor, is used to control the model AS/RS (Figs. 12 and 13). The system has 40K

275

Microcomputer controlledmodel ASIRS -~,.;TableI. System of com~ndr~ ~:2,i:.~-~ ......

-, ~ :

(1)NVENTORY LISTING--Lists all occupied bay locations with theirserialand orientation

(S)TORF.,--S~oresand inventory item in a warehouse bay. (I[)EI?JEVE,--Picks up an inventory item and returnsitto the IoadingJunloadingstation. (P)UI~GF./--F.au~Illinventorydata from the inventorytable. (Z)ERO--Moves the load~r to itszero p~..itionat the front rightsideof the warehouse. (N)UMBER.-Pfiats the number of unitscurrentlystored in the warehouse." (E)XIT--Transfers program controlto SWTBIG. (Monitor Program). Pl(A)--Initializesthe PIA. (C)OMMANDS--Pfints listof commands. Note: Eote~ through the terminal only the letter in parenthesis for a certain command.

** ALrI'OMATEDWPJ~tOI~ESYSI'I~** TI-EREARE 00 ~ OJ~I~TLY IN SIORAGE.

~

LmlT sNn~

B~a~wr~

II~TI~LIZ~TI~ OF ~ ~j

~

~I~T~

~

TO BE USI~ IOZ TIE S]~.IAL NLI~E~-R]~

~ WILL BE s'mm~ IN BAY Ol YGI HRCE TB~ ~ TO ~ 11-~ LO~D~ aS u m ~ ot~tac'r~s TO BE US~B FOR ~ S~RI~ ~ - ~ ¢ r TIE ~ WILL BE ~ IN BAY 02 YOUmv~ TEN ~ , TO LOADBE LOADER. *I

**INVI~TORY LISTING** BAY NU~I~

STOCK IDOkTION NI.I~ER AISLE ROW LEVEL

BAY 01

RED

1 1 1

BAY 02

WHT

11 2

*R I~RJT THE SERIAL M.II~ER OF THE ITEMTO BE RETRIEVED-RED THE ITl~i RED WILL BE RETRIEVEDFROHBAY 01 *N THERE ARE Ol I T I ~ *C CI~MedkND SUMMARY

CURRENTLY IN STORAGE.

(1)NVI~rI'ORY LISTING-LISTS ALL OCOJPIES LOCATIONS WITH SERIAL

NLII~ERS FOR F.AO-IITEM (S)TORE-SOTI~ AN l ~ Y

ITI~

(R)ETRIEVE-PICKS UP AN INVF2ClDRY ITI~ FROM STORAGE (P)URGE-ERASES ALL INVENTORY DATA FROM MI~ORY (Z)I~D-MDVES THE LOADERTO THE ZERO POSITIOI~

('N)LI, BER-GIVES TI~ I~I,~ER OF UNITS CURRI~TLY IN STORAGE (E)XIT-TRANSFERS CONTROL TO SWTIR]G PI {A)-INITIALIZES THE PIA Fig. II. Sample output,interactionof user and model warehouse {underlinedcharaclersinputby operalor).

PHILIPM.

276

WOLFE

Fig. 12. Microcomputer system.

Fig. 13. Top view of microcomputerandtapeunit,

Bufflr

PIA ~

~ 1

t

I

3.5k,~ +5v

Swilch

Fig. 14. Limit switchinterface.

,,,]

Microcomputercontrolled

model

ASIRS

277

bytes of random access memory,, and several inputlo~tt~t inte~aces, all,of which are not needed in this application. The model warehouse control program requires 7K bytes of memory, so a computer with only 8 bytes of random access memory could be used. A peripheral interface adapter (PIA) is used to connect the warehouse to the computer, as well as an audio cassette tape recorder or disk to allow for storage of the program. The interface between the computer and the warehouse is the SWTP MP-L parallel interface card which uses the MC6820 PIA as its main component. The PIA typifies interface devices that have been developed to simplify interfacing. This card has 16 fully buffered lines, 8

m

CW

PIA Buffer device

Buffer CCW

PIA

Tmnalotor modu~ Fig. 15. Steppingmotor interface.

I

246 VAmp d.c, power s.i~ly

!

I

I

.2, v ~.o.

I

,vo.

*10 MFI), 150 V

1

External r

E

vJ..

~,L.

~

y

.I '.~ ~l

•

+~

"--i "OW ~

:

24V d.c.

I vo Fig. 16. Steppingmotor/translator/powersupplylpiainterface.

278

PHILIPM. WOLFE

for input and 8 for output. Currently, four input lines are tied to four pairs of limit switches. Seven output lines are used (see Fig. 14) for the limit switch interface); six lines carry pulses to the translators associated with the stepping motors (see Figs. 15 and 16),and the remaining line goes to a transistor that switches on the solenoid located on loader (see Fig. 17). Limit switches provide information about the location of the moving parts of the system: beam, trolley and loader. As noted above, one function of some of the limit switches is to initialize the location of these moving parts. Other limit switches are used to notify the computer of error conditions; such as, one of the moving parts has reached an end of travel (end of the warehouse). When this occurs, the computer stops turning the stepping motor responsible for travel in that direction and notifies the user that a limit switch has been encountered. Each pair of output lines is connected to a circuit card called a translator module. This module amplifies the pulse signals (TTL levels) from the PIA card into signals that the stepping motor recognizes. Each translator and stepping motor is powered by a 24 V power supply mounted in bottom of the AS/RS chassis. A 5 V supply for the limit switches is also housed there. Figure 18 shows the warehouse removed from the portable base of the warehouse, and Fig. 19 shows the power supplies and electronics in the base used to power and index the stepping motors.

CONCLUSION The benefits derived from developing this model warehouse system have been nuch greater than anticipated when the project was proposed. Students have been excited by the "hands on" environment this system provides. People viewing this system in action appear impressed with

Solenoid PIA

P318 Mot~ola tron=i=or

Fig. 17. Solenoidinterface.

Fig. 18. Warehouse frame removed from warehouse base.

.t +24V

Microcomputer controlled model AS/RS

~.79

Fig. 19. Top view of warehouse base showing power supplies and stepping motor indexing c~rcuitry.

the impact this new technology will have on our lives. Also, this type working system stimulated ideas and new applications. One result is a future objective to develop an automatic product recognition system in front of the warehouse input loading station. This system would use a television camera, video digitizer and microcomputer to identify the type of product to be stored in the model AS/RS. Consequently, as an educational aid systems such as the one described in this paper are very beneficial for all involved. REFERENCES I. D. D. Bedworth & J. E. Sobozek, Students learn on AS~S model. Indus. Engng(Dec. 1976). 2. C. M. Dalton. Computer controlled warehouse model. Unpublished MS Rep. School of Industrial Engineering and Management, Oklahoma State University, Stillwater, Oklahoma (July 197g).