How automatic guided vehicles link shop operation: applications in manufacturing.
Part 2--Applications in manufacturing
The 1980s could be the decade in which the automatic guided vehicle system --the "AGVS'--comes into its own in US manufacturing.
The technology isn't new, but thus far it has been underutilized and not well known by this country's production people. Conceived in the early 1950s, the AGVS saw its first applications in warehouses and distribution centers. Controls, layouts, and fixturing for the early systems were fairly simple, as were their assigned tasks.
When on-board microprocessor and centralized minicomputer controls emerged in the early 1970s, though, they enabled the complex interfaces and realtime control needed in manufacturing. The AGVS then rapidly matured into a viable, powerful tool for the mechanical, material-handling aspects of factory integration.
Within the past year or so, signs have indicated that American manufacturers are at last becoming aware of the potential benefits of AGVS. General Motors, for instance, is installing three AGV systems in two plants at Lansing, MI (see Part 1 of this series, January 1984). And the Vought Aerospace subsidiary of LTV Corp, Dallas, TX, has specified wireguided vehicles for a $10-million flexible manufacturing system (Figure 5).
Moreover, US suppliers report that orders and inquiries are running higher than ever before. "Growth in usage of AGVSs in US industry from the 1950s through the 1970s held at a comfortable rate of 5 to 6 percent a year,' says Walter Adams, AGVS account manager with the Materials Handling Group of Portec, Oak Brook, IL.
"Growth in the 1980s will be much more dramatic, though,' he continues. "We see sales and unit rates climbing to five or six times the previous rates during the next few years. Of all the new systems that will be installed, a much greater percentage will be going into US factories than during the previous decades.'
FMSs (flexible manufacturing systems) have been getting a lot of publicity in recent months; for that reason, the use of an AGVS in FMS is now probably the best-known type of manufacturing application, Fact is, though, the potential for use of AGVS is far greater in assembly and plant integration applications than in FMS.
While an FMS may typically employ anywhere from two to ten vehicles, plant integration systems--such as the one at Deere's Hydraulics Div, Waterloo, IA-- may use up to 2 or 3 doz vehicles. Suppliers estimate that in US industry today, there are far more potential applications for plant integration systems than there are for FMSs with AGVSs.
Notable, too, is the fact that where wire-guided vehicles are employed as roving assembly platforms, the total number of vehicles in the system may run up in the hundreds.
Equipped with customized fixturing, the unit-load AGV is ideal for use as a movable assembly platform. AGV systems employing unit-load, wire-guided vehicles ae now serving in flexible assembly lines for automobiles, trucks, tractors, engines, and transmissions in plants throughout the industrialized world.
The facility with the largest number of wire-guided vehicles operating today is the Volvo auto assembly plant at Kalmar, Sweden (Figure I). Brought on-line in 1975, two AGV systems in the plant employ a total of over 400 vehicles. These were built by Volvo's AutoCarrier Div.
The photo shows a completed auto chassis on a high-level AutoCarrier that has just collected an auto body from the second-floor assembly line. After certain assembly operations have been completed on the high-level carrier, the body will be lowered onto and married with the chassis.
Then workers will transfer the body/ chassis assembly to another type of AGV, a low-level carrier. This type of vehicle can tilt the car at a 90-degree angle, allowing easy access to areas that were previously difficult to reach.
Volvo says that by making the job easier for its assembly workers, the two types of AGV are contributing notably to productivity and product quality.
For information on AutoCarrier vehicles, and on other vehicle designs provided in the US by Volvo Automated Systems, Sterling Heights, MI, circle E91.
Wire-guided vehicles are also finding application as assembly platforms for tractors and other off-highway mobile equipment. For instance, at International Harvester's Farmall Div plant in Rock Island, IL, five linked AGV systems aid in the assembly of four-wheel-drive articulated farm tractors (Figure 2).
The five systems include assembly, control and buffer stations for front and rear sections and for completed tractors. At a mating station, workers connect the front and rear sections on a special aircushion frame. One man, unaided, can maneuver the tractor halves into position for articulation.
The wire-guided vehicles and controls for these linked AGV systems were provided by Conco-Tellus, Mendota, IL. For information, circle E92.
Integrating the plant
The second major type of AGVS application that holds strong promise in the years ahead is plant integration. In many cases, the vehicles are used to mechanically link an automated storage/retrieval system (AS/RS) or manned storage system with the production areas in the plant.
An example of a relatively small AGVS that is serving its users well is the two-vehicle system at Keystone Carbon Co, St Marys, PA. Three years ago, the company expanded its production capabilities, and in the process lost some storage area.
To solve the problem, Keystone built a 40,000-sq-ft warehouse addition to its plant. The addition includes 9200 sq ft of 11-level, steel rack storage with 2100 openings for work in process and finished parts.
To provide automated transport between the production aceas and the new warehouse, Keystone installed an AGVS having two unit-load vehicles and four load-transfer stations (Figure 3). The vehicles travel back and forth between warehouse and plant through a narrow tunnel.
Workers dispatch the vehicles by means of remote-dispatch terminals near the load-transfer stations. The system can handle 32 trips a shift during the three-shift workday. A battery-charge provides 16 hr of operation.
The vehicles, stations, and controls were built by The Raymond Corp, Greene, NY. For details, circle E93.
A more elaborate use of AGVS in plant integration may be found at the new facilities of Wang Laboratories Inc, Lowell, MA. Here the company assembles, tests, and packages Wang word processors, printers, and CRT terminals.
Because of limitations in available real estate, the company decided to build the plant three stories high (Figure 4). On each floor, an AGVS transports parts through various kit-makeup assembly, test, packaging, and storage areas.
Connecting the three floors are two vertical lifts (see drawing). For automatic transfer of materials from one floor to another, a vehicle stops at a load-transfer station next to a lift and discharges a load to the station. This in turn moves the load into the lift, which raises or lowers the load to the destination floor. There another transfer station moves the load onto a waiting vehicle.
In all, the plant uses 13 wire-guided vehicles on three guidepaths totaling 6000 ft in longth. Each vehicle can carry up to 2000 lb. Operators control the vehicles manually by means of on-board push buttons, and also remotely by means of remote-dispatch terminals.
The vehicles and controls for these integrated, three-floor systems were supplied by Control Engineering Co, an affiliate of Jervis B Webb Co, Farmington Hills, MI. For information, circle E94.
Third among the major kinds of applications for AGVS is the flexible manufacturing system (FMS).
In general, AGV systems may be selected for use in FMSs when the following conditions exist:
1) Maximum load weight does not exceed 8000 lb.
2) The distances to be traveled are relatively long.
3) The flow is random and relatively complex, perhaps including a number of sidings, crossings, and spurs.
4) Quiet operation is essential, or at least desirable.
Latest of the flexible manufacturing systems in the US to use AGVS is the system now being installed by Cincinnati Milacron at the Vought Aerospace plant in Dallas, TX. A subsidiary of LTV Corp, Vought will use the FMS to produce machined aluminum parts for fuselage sections of the US Air Force's B-1 bomber. The company i a major subcontractor to Rockwell International, prime contractor for the B-1.
In this FMS (Figure 5), four wirefguided unit-load transporters will shuttle palletized parts and racks of tooling under control of the FMS minicomputer. Capable of carrying loads up to 5000 lb, the vehicles and their guidewire control system are being supplied by Eaton-Kenway, Salt Lake City, UT.
The manufacturing process will begin with manual loading of aluminum workpieces on pallets at two carousels, shown at left in the drawing. From that point on, no manual intervention will be required. A three-shift workday is planned for the FMS.
Thanks to computer control and the use of AGVS, the FMS--due to start up in July this year--will be able to take parts in random sequence, handle similar or dissimilar parts, and accommodate a broad family of shapes and sizes. The system will even be able to process single, one-of-a-kind parts without disrupting the flow of production.
For more information on FMS from Cincinnati Milacron, circle E95. For details on wire-guided vehicles and controls from Eaton-Kenway, circle E96.
Another notable example of the use of AGVS in FMS may be found at the Renault Vehicules Industriels plant at Boutheon, France. Here an eight-vehicle system (Figure 6) carries cast-iron and aluminum parts for gearbox casings. The vehicles travel between four CNC machining centers, two CNC fine-boring and facing machines with horizontal spindles, a rinsing tunnel, and the stations where parts are palletized and depalletized.
Controlled by the FMS minicomputer, routing is different for each of four different parts being produced. The system includes a battery-changing station (bottom of drawing) in which a special wire-guided vehicle transfers spent batteries from parts-transport carts into the chargers, and loads charged batteries into the carts--all automatically.
The vehicles and their controls were provided by Seiv Automation, a subsidiary of Renault. For information on Renault Seiv AGVS, available in the US through IDPI, Southfield, MI, circle E97.
Why use AGVS?
Considering recent advances in the technology, growth in the industry, and the ever-widening scope of applications, AGVS as a material-handling genre obviously has a few things going for it. Following are some of the major advantages and benefits of AGVS:
Automatic interface with other systems. AGV systems can interface automatically and continuously with production machines, conveyors, robots, and other equipment.
Automatic control of load tracking and inventory. Controlled by computers, and aided by sensors and manual input on the factory floor, AGV controls assist in real-time load tracking and continuous updating of inventory files.
Reduced labor. The use of wireguided vehicles eliminates or reduces the need for vehicle drivers, and also for the clerical support--clerks, expediters, and dispatchers--typically requdired for manned systems.
Easy modification. As requirements change for material movement in the plant, the AGV system can also be changed quickly and inexpensively. The guidepath can be modified, expanded, or contracted, and vehicles can be added or withdrawn from the system.
Reliable system capacity. It one vehicle goes down and requires maintenance, the productivity of the other vehicles in the system is not lessened. This contrasts favorably with the characteristics of conveyor systems.
Other potential advantages and benefits of AGVS are unobstructed aisles, improved housekeeping, reduced damage to materials and structures, low energy consumption, no air pollution, low noise level, ease of installation, and relatively fast payback.
Clearly the AGVS, with all its capabilities and potential merits, deserves your consideration as you plan your Factory of the Future.
Photo: 1. Workers complete the marriage of an auto body and chassis on a high-level carrier in Volvo's assembly plant at Kalmar, Sweden. This and another AGV system in the plant employ a total of over 400 wireguided vehicles. (Volvo Automated Systems)
Photo: 2. Five linked AGV systems are used in assembly of four-wheel-drive farm tractors at International Harvester's Farmall Div plant, Rock Island, IL. (Conco-Tellus)
Photo: 3. At Keystone Carbon Co, one of the two wire-guided vehicles automatically acquires a tub of parts from rack storage. Once the tub is on board, the vehicle will travel down into a tunnel, at right in the photo, and then up into the main plant. The load-transfer stations and vehicles are equipped with powered roller conveyors. (The Raymond Corp)
Photo: 4. A 13-vehicle AGVS on three floors, along with two vertical lifts, link the kit-makeup, assembly, test, packaging, and storage areas in the Wang Laboratories plant, Lowell, MA. Operators control the vehicles manually and by means of remote-dispatch terminals. (Jervis B Webb Co)
Photo: 5. Early proposal drawing for the $10-million flexible manufacturing system (FMS) being installed by Cincinnati Malacron at the Vought Aerospace plant in Dallas, TX. Utilizing eight Milacron 20HC CNC machining centers and a four-vehicle AGVS from Eaton-Kenway, the FMS will produce machined aluminum parts for fuselage sections of the US Air Force's B-1 bomber. (Cincinnati Milacron)
Photo: 6. At a Renault transmission plant in Boutheon, France, an eight-vehicle AGVS carries cast-iron and aluminum gearbox parts through an FMS with four CNC machining centers and two CNC fine-boring and facing machines. The station represented at the bottom of the drawing automatically transfers racks of batteries between chargers and wire-guided vehicles. (Renault Industries)
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|Title Annotation:||part 2 of 2|
|Author:||Quinlan, Joseph C.|
|Publication:||Tooling & Production|
|Date:||Feb 1, 1984|
|Previous Article:||Multistage cold forming: less stock, more product.|
|Next Article:||FLEXIBLE manufacturing system solutions.|