The predominate approach today to introduce factory automated technology into manufacturing is to selectively apply automation and to create islands of automation. The phrase "islands of automation" has been used to describe the transition from conventional or mechanical manufacturing to the automated factory. Interestingly, some appear to use the phrase as though it were a worthy end object. On the contrary, the creation of such islands can be a major impediment to achieving an integrated factory.
Manufacturing examples of islands of automation often include numerically controlled machine tools; robots for assembly, inspection, painting, and welding; lasers for cutting, welding and finishing; sensors for test and inspection; automated storage/retrieval systems (AS/RS) for storing work-in-process, tooling and supplies; smart carts, monorails, and conveyors for moving material from work station to work station; automated assembly equipment and flexible machining systems. Such islands are often purchased one at a time and justified economically by cost reductions. An example of an AS/RS system is disclosed in the U.S. Pat. No. 4,328,422 to Loomer. A different type of AS/RS system and control system therefor is disclosed in the U.S. Pat. No. 4,232,370 to Tapley.
To integrate the islands of automation it is necessary to link several machines together as a unit. For example, a machine center with robots for parts loading and unloading can best be tied to visual inspection systems for quality control Computer numerical control machine tools can all be controlled by a computer that also schedules, dispatches, and collects data. Selecting which islands to link can be most efficiently pursued on the basis of cost, quality and cycle time benefits.
In some cases the islands of automation will be very small (e.g. an individual machine or work station). In other cases the islands might be department-sized. The U.S. Pat. No. 4,611,749 to Kawano discloses the use of robots to transfer parts between such islands which are relatively close to each other.
From a systems viewpoint, islands of automation are not necessarily bad, so long as they are considered to be interim objectives in a phased implementation of an automated system. However, to obtain an integrated factory system, the islands of automation must be tied together or synchronized. Systems synchronization frequently occurs by way of a material-handling system; it physically builds bridges that join together the islands of automation. Early examples of such islands of automation linked together by a material-handling system are disclosed in the U.S. Pat. Nos. 4,369,563 to Williamson and 3,854,889 to Lemelson.
The '563 patent discloses a system including machine tools which perform machining operations on workpieces loaded on pallets. The pallets are delivered to the machine tools from a storage rack by transporters. The workpieces are manually loaded onto the pallets.
The '889 patent discloses a system including work-holding carriers which are selectively controlled in their movement to permit work to be transferred to selected machine tools while bypassing other machine tools.
Automated material handling has been called the backbone of the automated factory. Other than the computer itself, this function is considered by many automation specialists as the most important element in the entire scenario of automated manufacturing. It is the common link that binds together machines, workcells, and departments into a cohesive whole in the transformation of materials and components into finished products. For example, the U.S. Pat. No. 4,332,012 to Sekine et al discloses a control system for assembly lines for the manufacture of different models of automotive vehicles. Temporary storage is provided between assembly steps by a storage section.
To date, the major application for industrial robots has been material handling. Included here are such tasks as machine loading and unloading; palletizing/depalletizing; stacking/unstacking; and general transfer of parts and materials--for example, between machines or between machines and conveyors. An example of one such application is disclosed in the U.S. Pat. No. 4,519,761 to Kenmochi. The '761 Patent discloses a combined molding and assembling apparatus wherein a pallet is conveyed by a conveyor. Resin components are carried by the pallet for use in the molding and assembling operation.
Robots are often an essential ingredient in the implementation of Flexible Manufacturing Systems (FMS) and the automated factory. Early examples of the use of robots for assembling small parts is disclosed in the U.S. Pat. Nos. 4,163,183 and 4,275,986 wherein robots are utilized to assemble parts from pallets onto a centrally located worktable.
The automated factory may include a variety of material transportation devices, ranging from driver-operated forklifts to sophisticated, computer-operated, real-time reporting with car-on-track track systems and color graphics tracking. These material transport systems serve to integrate workcells into FMS installations and to tie such installations and other workcells together for total factory material transport control.
With all of their versatility, robots suffer from a limitation imposed by the relatively small size of their work envelope, requiring that part work fixtures and work-in-process be brought to the robot for processing. Complete integration of the robot into the flexible manufacturing system requires that many parts and subassembIies be presented to the robot on an automated transport and interface system. For example, installation of an assembly robot without an automated transport system will result in an inefficient island of automation needing large stores of work-in-process inventory for support, which are necessary to compensate for the inefficiencies of manual and fork truck delivery.
A recent example of the use of robots in a manufacturing assembly line is disclosed in the U.S. Pat. No. 4,611,380 to Abe et al. The '380 Patent also discloses the use of a bar code to identify the components to be assembled to a base component to control the assembly operations.
The U.S. Pat. No. 4,616,411 to Suzuki et al discloses a fastening apparatus including a bolt receiving and supply device for use in the automated assembly of a door to a vehicle.
The handling, orienting and feeding of parts as they arrive from vendors are formidable jobs which must be done prior to robotic assembly since, in general, all such parts require reorienting for the assembly robot. The U.S. Pat. No. 4,527,326, to Kohno et al., for example, discloses a vibratory bowl which feeds parts to an assembly robot. A vision system enables the robot to properly pick up the parts from the bowl.
Part feeding is a technology that generally has lagged behind the advanced automation systems it supports. However, in general, part feeding curtails flexibility, increases costs, increases floor space requirements and lengthens concept-to-delivery time. For maximum flexibility, a minimum amount of tooling should be considered. On the other hand, additional tooling can be used effectively to "buy time" by assisting the robot. Typically, dedicated hardware--bowl feeders, magazines, pallets--is required to feed parts to the robot. Unlike the robot, dedicated hardware is not easily reusable and therefore is less economical for medium-volume applications.
The U.S. Pat. No. 4,383,359 discloses a part feeding and assembly system, including multiple stage vibration and magazine feeders. A robot is utilized to change the position of the fed parts for assembly on a chassis supported on a line conveyor. The robot operates in combination with a vision system to reorient the parts.
Neither flexible nor sophisticated, part feeding equipment is usually constructed by highly skilled artisians working with welding torch and hammer in small specialized shops. The most common and most inexpensive feeding method--vibratory bowl feeding--provides the builder with a versatile base easily modified to handle many different parts which are not delicate and which are substantially identical. Delicate parts or parts that tangle, such as motors, are better fed by magazines or trays for exact orientation.
Also, not all parts, for example, can be bowl fed. For most parts, the overriding concern is geometry and, in particular, symmetry. If a part is either symmetric or grossly asymmetric, then vibratory bowl feeding will be easier and more efficient.
Robots may load and unload workpieces, assemble them on the transport, inspect them in place or simply identify them. The kind of activity at the robot or machine and material transport system interface dictates the transport system design requirements. One of the design variables relating to the interface includes accuracy and repeatability of load positioning (in three planes). Also, care in orienting the workpiece when it is initially loaded onto the transport carrier will save time when the work is presented to the robot or the tool for processing. Proper orientation of the part permits automatic devices to find the part quickly without "looking" for it and wasting time each time it appears at the workstation.
Fixtures may be capable of holding different workpieces, reducing the investment required in tooling when processing more than one product or product style on the same system.
The transport system must be capable of working within the space limitations imposed by building and machinery configurations, yet must be capable of continuous operation with the loads applied by a combination of workpiece weight, fixture weight, and additional forces imposed by other equipment used in the process.
The system must also have the ability to provide queuing of parts at the workstation so that a continuous flow of work is maintained through the process. Automatic queuing of transport carriers should provide gentle accumulation without part or carrier damage.
The primary impediment to robotic assembly is economic justification. When the cost of robotic assembly is compared against traditional manual methods or high volume dedicated machinery, robots oftentimes lose out. On one side of the spectrum are the high-volume, high-speed applications where hard automation is used. It's difficult for robots to compete in that environment. On the other side are the low-volume, high variety products that are assembled manually. Robots may lack the dexterity to perform these jobs, and they may cost more than relatively low-paid manual assemblers. There is a middle ground between these two extremes for flexible assembly. Many believe that the best approach is a combination of robots, dedicated equipment and manual assembly.
There are other barriers to the use of robots in mechanical assembly. They include the following: (1) the high cost of engineering a new system, which may run three to five times the cost of the robot itself; (2) the amount of time it takes to engineer the system; (3) the difficulty of coordinating multiple arms; (4) the difficulty of integrating an assembly system; (5) the high cost of tooling, software sensors, part presentation equipment, and other peripherals; (6) the difficulty of finding knowledgeable personnel; (7) insufficient speed, lift capacity, and positioning accuracy and repeatability on the part of the robots; and (8) a lack of supporting technology in such areas as high-level programming languages, end-of-arm tooling, and sensors.
Additional impediments to the successful implementation of robots in assembly are insufficient communication among departments, a general slowdown in capital equipment acquisition, a disinclination to plan ahead, fear of change, and the infamous NIH (Not Invented Here) Syndrome that keeps companies from accepting ideas originating outside their walls.
Still, while assembly is probably the most difficult area of robotic application, many say it also holds the most promise. Assembly robots offer an array of benefits that cannot be ignored. They can produce products of high and consistent quality, in part because they demand top-quality components. Their reprogrammability allows them to adapt easily to design changes and to different product styles. Work-in-process inventories and scrap can be reduced. Therefore, it is important that the materials transport system serving the robots be capable of quickly moving into position with parts, then quickly moving out of the workstation and on to downstream stations. Prompt transporter movements between stations allow work-in-process inventory to be minimized. Batch sizes are smaller and work faster with only a minimum of queuing at each workstation.
The U.S. Pat. No. 4,594,764 to Yamamoto discloses an automatic apparatus and method for assembling parts in a structure member such as an instrument panel of an automobile. A conveyor conveys a jig which supports the panel to and from assembly stations. Robots mount the parts on the instrument panel at the assembly stations. Robots are provided with arm-mounted, nut-driving mechanisms supplied from vibratory parts bowls.
A link for tying together some of the independently automated manufacturing operations is the automatic guided vehicle system (AGVS). The AGVS is a relatively fast and reliable method for transporting materials, parts or equipment, especially when material must be moved from the same point of origin to other common points of destination. Guide path flexibility and independent, distributed control make an AGVS an efficient means of horizontal transportation. As long as there is idle space and a relatively smooth floor to stick guide wires or transmitters into, the AGVS can be made to go there.
As an alternative to traditional conveying methods, the AGVS provides manufacturing management with a centralized control capability over material movement. Also, the AGVS occupies little space compared with a conveyor line. Information available from the AGVS also provides management with a production monitoring data base. The U.S. Pat. No. 4,530,056 to Mackinnon et al. discloses an AGVS system including a control system for controlling the individual vehicles.
A relatively new type of link for tying together independently automated manufacturing operations is the mechanical guided vehicle (MGV) commercially available from the Roberts Corporation of the Cross and Trecker Corporation of Bloomfield Hills, Mich. The MGV is a self-contained, self-propelled, battery-operated vehicle which travels on a track system. The vehicle is utilized to carry a load much like an automated guided vehicle.
Robot installations for transporter interface can be grouped into three principal categories: (1) stationary robots, (2) moving (i.e. mobile) robots (on the floor or overhead), and (3) robots integral with a machine. The moving robots subdivide into two types. First are stationary robots, mounted on a transporter to move between work positions to perform welding, inspection, and other tasks. The second type of moving robot is the gantry unit that can position workpieces weighing more than one ton above the workcells and transport system. The system only has to deliver and pick up somewhere under the span of gantry movement.
End effectors used in material handling include all of the conventional styles--standard grippers, vacuum cups, electromagnets--and many special designs to accommodate unusual application requirements. Dual-purpose tooling is often used to pick up separators or trays, as well as the parts being moved through the system.
Vacuum-type grippers and electromagnetic grippers are advantageous because they permit part acquisition from above rather than from the side. This avoids the clearance and spacing considerations that are often involved when using mechanical grippers.
However, the use of vacuum and electromagnetic grippers is not without its problems since cycle time is not just a function of robot speed and its accelerating/decelerating characteristics. Cycle time is dependent on how fast the robot can move without losing control of the load. Horizontal shear forces must be considered in the application of these grippers. This often means that the robot is run at something less than its top speed.