Conveyor Systems

The meaning of the term "materials handling" has expanded tremen~ dously in tho last few years. It includes such diverse equipment as lift trucks, skid platforms, hand-pushed monorail, gravity roller conveyors, and many types of powered product movers. This chapter will discuss only a few types adaptable to automatic control for integration into more or less complex systems and commonly called conveyors.

Applications. Conveyors are used for movement and/or storage of parts or products between manufacturing operations, through processing, assembly, testing, and packaging and to warehouse or shipping point. Conveyors can control production rate by simply varying speed of system to compensate for manpower available, etc. They provide the tie between automatic machines to make an automated system. Conveyor applications can be broken down into four rough classifications:

1. Bulk handling. Materials such as coal, sand, ores, chemicals, and grains. Using troughed belts, buckets, pneumatic, and similar types of conveyors.

2. Package handling. Cartons, boxes, tote pans, and similar packages for products. Using gravity roller and wheel conveyors, flat belt, live roller, pusher bar, slat, chutes, and similar types of conveyors.

3. Trolley and chain conveyors based largely on rivetless type chains. Includes trolley, floor pusher, power and free, and similar types.

4. Special designs for handling products between machining operations including reciprocating transfers, turnovers, rollovers, and lifts operated by air or hydraulic cylinders.

Design of Automatic Controls for Conveyors. In general, there is no such thing as a "standard" conveyor. There are standard components, but every conveyor is tailor-made to perform a certain function in a specific place. System design requires:

1. A thorough knowledge and analysis of devices controlled. This includes their limitations as well as potentialities. Equipment that is suitable for precision machine tools may be totally inadequate for less precise conveyors without expensive added operating means.

2. Close cooperation is required between mechanical parts designer and control designer to assure that control elements can be incorporated in correct positions in basic design. The control requirements frequently dictate elements in the mechanical design. Too frequently, the control design is left until too late, the designed mechanism is inflexible, and expensive rework is required to make the machine operate.

3. Design of controls is a logical step from a complete description of mechanical sequence of functions required. Simple sequence functions using limit switches, wipers, pushbuttons, relays, solenoid valves, and motor starters are used to control most conveyors.

4. 'Vhen more units are coordinated together, centralized panels with provisions for starting, stopping, speed changing, and condition signaling for each unit may be required. The special requirements for multiple drivers, synchronization for automatic transfer between several conveyors, and selective dispatching require more challenging consideration.