DATA-DRIVEN AUTOMATION 4 ENABLING HARDWARE

aterials-handling systems Automating of materials handling can integrate otherwise isolated islands of automated machine tools

To function at their full potential, ex­pensive and highly automated pro­duction machines have to be inte­grated into systems. Work in process has tO be t r a n s p o r t e d q u i c k l y ΰΠϋ

reliably from one work station to the next, and stored workpieces must be easily accessible. Without this fast and orderly flow of parts and prod­ucts, automated machines become

islands of automation, operating at much lower efficiency and "up time" than when integrated into flexible manufacturing systems [see "Production: a dynamic challenge," p. 36].

Flexible manufacturing systems (FMSs) can be set up for both large-batch and small-batch production in which manual, semi-automated, and fully automated work stations are served by an automated materials-handling system, all under computer con­trol. Computer direction is the heart of the FMS concept, con-^ Λ Ι Ι Ι ' Μ Λ f k a ~-± 1- _ _ _ *1 -C — C

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work through the stations and storage areas. With constantly available parts, the machines in an FMS can be productive 80 to 90 percent of the time. Without FMS, they may be productive only 20 to 30 percent of the time. Production 'just in t ime'

A flexible manufacturing system is designed to manufacture products only as they are required to fill customer orders. This "just in time" method reduces inventories (and therefore carry­ing costs) to a minimum. Moreover, less floor space is needed.

FMS uses fewer machines, albeit more versatile ones. Indeed, many FMS numerical-control machines can do multiple machin­ing operations simultaneously. And robotic, automated, and manual work stations can be integrated so the special virtues of each can be maximized.

Through FMS technology, and automated materials-handling systems in particular, many companies tell of major im­provements in productivity and quality and of reductions in in­ventory. Toshiba Ltd. reports these findings after applying the FMS concept to its Japanese production operations: © Number of machine tools reduced by 88 percent. • Production personnel reduced by 77 percent. • Machine efficiency improved 3 ,5 times. • Production time reduced by 77 percent. • Floor space reduced by 76 percent. • Product cost reduced by 50 percent.

Handling materials at different speeds The FMS concept poses major demands on the materials-

handling system: high speed, precision, accumulation, and non-

L. Jack Bradf and James K. Allied SI Handling Systems inc.

synchronous operation (the capability to perform several dif­ferent kinds of operations simultaneously within the system). But in transit, materials should move rapidly to minimize cycle time at machinery and to reduce inventory. As it approaches a work station, the workpiece carrier decelerates so that components are not damaged and so that it can be engaged by equipment inter­faces or transported through a specialized production area at dif­ferent speeds. Workpiece carriers can be held temporarily at queuing stations to provide "banks of work" between work stations.

Robots and other automated machinery can maintain con­sistently high quality only if the workpieces are positioned within the allowable limits. It is not unusual to require the transport system to position the workpiece within ±0.005 inch. In addi­tion, the materials-handling system must be capable of sending any workpiece to any location at any time in the production cy­cle. This reduces the floor space and the number of production work stations needed while maximizing the use of manufacturing equipment..

Many types of materials-handling systems approach these ideal characteristics. In tow-line systems, for example, carts are affixed to a chain in the floor, and the chain is driven by an elec­tric motor. The carts may be switched on and off the chain and may be accumulated at storage and work positions. This system can be computer-directed to mesh with manufacturing equip­ment and other transport and storage systems. Although the tow-line system is an older technology, it is still used extensively where precise handling of materials is not required.

Car-on-track systems employ a computer-directed workpiece carrier that is propelled along a section of track. One, called Car-trac, from SI Handling Systems Inc. in Easton, Pa. , incorporates a rotating drive tube, mounted in a track, to power the workpiece carriers. The angular relationship between the drive wheel (mounted on the underside of the carrier) and the drive tube determines the speed of the carrier. Car-on-track systems offer nonsynchronous, variable-speed transportation, accumulation, and precise positioning features.

Vehicles are automatically guided Vehicles that are computer-controlled and guided by signals in

a wire embedded in the production floor may also be used [Fig. I] . Although wire-guided vehicles are not in themselves new, the application of computer-control technology has caused a surge in their popularity. Several systems operate by following a visible or chemical guide path in the form of a painted line, but these have not gained anywhere near the popularity of the wire path systems because of the need to keep the painted lines clean and clear of debris.

Automatic guided vehicles have either a small microcomputer or a control panel. "Smart" vehicles of this type permit the main control computer to download a substantial amount of routing information to the on-board computer so that the vehicle can perform a number of operations before requesting additional in-

74 0O18-9235/83/05GO-O074$l.O0©1983 I E E E IEEE Spectrum MAY 1983

formation from the central computer. One central computer can thus control a great number of vehicles as they move about the factory. A central control box prevents them from colliding with eech other.

The on-board microcomputer determines the fastest or most direct route for a vehicle to follow to its destination. Com­munication between the vehicles and the central computer can be furnished by optical or magnetic devices on each vehicle and transmitters on the factory floor. Or an in-floor communication loop can transmit RF signals to the vehicles and also receive similar signals from the vehicles.

Overhead monorail systems that convey workpiece carriers

through a manufacturing area by various means are another ap­proach to materials handling. Again, recent control advances, such as the placing of microprocessor chips on carriers, have in­creased iiic capabilities of this older technology. For example, the carriers can now be diverted from their original paths and rerouted in transit to accommodate quickly the needs of the various machines they are serving.

Communication with the microcomputer aboard a monorail carrier is via either a separate set of conductor bars or a high-frequency signal imposed on the conductor rails that carry the power for operating the carrier motors.

Other types of overhead systems, such as chain conveyors,

Ail photographs in this article by SI Handling Systems Inc.

[I] Automatically guided vehicles deliver and pick up automobile compo­nents at the Fiat assembly plant in Turin, Italy

[2] An automated storage and retrieval system de­signed by Ishikawa Jima-Harima Heavy Industry Ltd, in Japan.

Bradt, Ailred—Materials-handling systems 75

continue to be used in flexible manufacturing systems. Roller and belt conveyors are similarly employed, although these conven­tional methods are limited to applications that do not require ac-cuddle pQS!tiC*iut£.

Automated storage and retrieval systems also permit rapid recovery of both work in process and finished product [Fig. 2J. The systems are basically high-density storage-rack machines with rail vehicles that automatically load and unload the rack structure. They have been used primarily in large warehousing operations where many loads of 4000 to 6000 pounds each have been stored. Now, smaller versions of these systems are finding their way onto the factory floor, where parts and work in process

are being stored alongside the production machinery so that the manufacturing process can approach the just-in-time ideal. These "miniload stacker" systems are handling loads of up to 500 pounds pel locaiiun. Musi of liie loads are in Une buxes or captive bins instead of the open pallets normally found in warehouses.

Carousels are primarily used for storing small workpieces and tools. Combined with robotlike loaders and unloaders, they also allow immediate access to parts on the factory floor [Fig. 3].

It is not at all inconceivable that the automatic factory might employ a large automatic storage and retrieval system in the receiving area, where large volumes of goods are received from

[3] Carousel handles materials in a system developed by Fanuc Ltd. and installed in its plant near Tokyo.

76 IEEE spectrum MAY 1983

[4] A major U.S. auto¬ mobile producer uses a car-on-track system to deliver work to manual stations, robots, and automatic machines

[5] Pallets on a tow line carry work to machining stations at the John Deere Waterloo plant.

[6] A flexible manufacturing system (right) joins group technology at the Harris Corp. 's plant in Texas. The production line turns out rollers for printing presses, machined to a tolerance of tens of thousandths of an inch.

vendors and large bulky items are staged for shipping. In such cases a miniload stacker system is used for handling bins of work in process and a carousel is used for handling parts and tools.

F M S s at work

Fanuc Ltd., in its electric-motor factory near Tokyo, has established a grouping of simple but ingenious flexible manufac­turing systems. Each has a materials-handling robot that loads and unloads workpieces from a carousel onto a numerical-control machine. Workers load parts manually onto the carousels from the main aisle of the factory floor. Only one materials handler is required to keep 10 of these FMS units func­tioning. This concept has been implemented by Fanuc in a much larger installation, also in Japan.

In the United States, General Electric has installed an FMS in an appliance assembly plant in Louisville, Ky. The system uses a small-scale car-on-track transport loop to deliver workpieces to manual assembly stations. Components, stored at each of the work stations, are installed on a workpiece at each station.

The controls for the assembly loop permit the system to be operated either manually or automatically. In the automatic mode, the control systems log any downtime. This light-assembly FMS is just one of many similar ones being installed in American factories.

An American car manufacturer's assembly plant employs a monorail system to deliver bodies to a car-on-track assembly system [Fig. 4J. The automated transport system interfaces with manual work stations, assembly and welding robots, and hard-automation machines, all on the same line. The car-on-track car­riers can be positioned so accurately that interfacing with automated assembly equipment is not a problem. At the end of the assembly line, inspection robots, making use of computerized vision, ensure product quality before the workpieces leave.

Another U .S . manufacturer, John Deere, uses flexible manufacturing systems to machine heavy castings in Waterloo, Iowa. Forklift trucks take the castings to accumulation con­veyors, which are at stations where workers mount the parts manually on fixtured machining pallets. The workers then load the pallets, which carry individual identification codes onto carts

of a computer-controlled tow-line conveyor [Fig. 5]. The pallet identification codes control the routing of parts to the proper machine tools. Electromechanical limit-switches read the iden­tification codes at various verification points on the machining centers.

Two interconnected tow-line loops serve two rows of com­puter-numerical control machines in this installation. Pallets are automatically transferred from the carts to the machine tools. After the castings have been machined, the pallets pass through to the opposite side of the machine, where they are automatically picked up by the tow line. The computer routes a part from any one machine to the next machine that is available to machine the part.

At the Harris Corp.'s printing-press-equipment manufactur­ing plant in Fort Worth, Texas, one of the most advanced flexible manufacturing systems in existence uses a car-on-track system to supply machine-feeding robots [Fig. 6]. These robots then posi­tion the workpieces accurately in various numerical-control machine tools for welding, cutting, and grinding. The car-on-track system incorporates in-process storage cells for rapid recovery of parts.

Harris has grouped together in one area those machines that perform most of the manufacturing operations for similar families of parts. This application of group technology has im­proved the efficiency and cost-effectiveness of the manufactur­ing processes substantially. And the combination of group tech­nology and flexible manufacturing system has enabled the manufacturer to consolidate the operations of a number of plants into one [see "Streamlining process routes with group technology,'* p. 46].

About the authors

L. Jack Bradt is chairman and chief executive officer of SI Handling Systems Inc. in Hasten, Pa., a company he started in 1958. It designs, manufactures, and installs computer-controlled order-selection systems and automated transportation systems for distribution and manufacturing. Mr. Bradt holds a degree in mechanical and industrial engineering from Cornell University.

James K. Allred is vice president for factory automation systems at SI Handling Systems Inc. He is a specialist in automated warehousing and the application of materials handl­ing to FMSs. He was previously general manager of Eaton-Ken way, a Subsidiary cf the Eaton Corp. and producer of automated materials-transport and -storage systems. He received the B.S. degree in industrial engineering from the University of Utah. φ

Bradt, Allred—Materials-handling systems 77