Conveyors for simple to complex transport

Conveyors move bulk material or discrete productsfrom one area to another and serve as main material-handlingarteries to improve efficiency and throughput. Advances in materials,controls and modular subcomponents have spurred new largeconveyors for bulk material transport, miniature conveyors fordiscrete sorting, and everything in between.

During manufacture, myriad products move on conveyors. So conveyors come in an array of shapes and widths of less than 2 in. (for moving extremely small parts) to several feet wide. Once viewed as an afterthought, conveyors have become an integral component in nearly all automated facilities and applications.

Select a conveyor by first asking: What types of product is the application moving? Conveyors for material handling of bulk product are more rugged than those for moving discrete product. In contrast, the latter often requires conveyors that can advance product with more precision.

How does surrounding equipment interact with the product riding on the conveyor? Conveyor Class 1 includes material-handling uses in which the conveyor serves as an artery to transport bulk or discrete product in a steady stream (with little interaction along the way). Class 2 includes conveyors that act as bridges to take product from one location or machine to another. Class 3 includes conveyors that take materials into or out of machines or stations. Class 4 includes conveyors that run right through machinery without break. The first two classes generally prioritize ruggedness or throughput. The last two classes need positioning and (in many cases) custom workpiece pucks to steady product while machines perform work on the product pieces.

What is the maximum weight of the product being moved? Does the conveyor need to operate at a certain speed? Does the application require the conveyor system to have inclines, declines or curves? Look for conveyor features that secure or enclose material or product onto the conveyor. Will moisture be present in the application? Does the application need to be sanitary? Look for rugged or washdown-rated conveyors with open frames.

Most conveyors in light to medium-duty discrete-transport applications use belt that’s wrapped around two or more pulleys. A motor powers the pulleys that in turn engage the conveyor belt. Styles and materials abound to meet specific applications. Some belts are low friction, so product can slide a bit for accumulation. In contrast, high-friction belts have more grip to better hold products to the belt. Engineers can design such conveyors to meet exact application specifications.

Magnetic conveyors are built with ceramic magnets for applications that need parts to adhere to the belt during processing, or for jobs that require elevation changes. The designer can specify higher magnet strength for use in inverted applications. In contrast, metal-free conveyors have Delrin bedplates (instead of the traditional steel bedplate) under sections where metal-scanning equipment checks product—usually food—for metal shavings. (Delrin is an inflexible polymer that works as a tough, heat-resistant metal substitute.) This lets a device check passing product without getting false readings.

Pivot conveyors mount to a pivot base to swing out of the way when workers need to walk through the line. Interlock switches and a timer let the conveyor clear before the gate opens. Some controls can automatically resume product flow after the conveyor returns to the inline position.

Servo drives accurately start and stop belt conveyors to provide precise part location. They also let engineers control acceleration and deceleration, so are most suitable for conveyors used in assembly operations. Manufacturers mount encoders to a conveyor’s drive shaft to sense shaft rotation or count pulley revolutions for accurate control of the belt in feeding or indexing applications.

Single-drive, multi-belt conveyors serve two or more lanes of product for the sake of efficiency. Here, two or more conveyors run off a single gearmotor on a common drive shaft or coupled shafts. In some arrangements, the belts even mount to a single conveyor frame.

Timing-belt conveyors use toothed belts that engage synchronous drive pulleys while serving as the conveyor surface as well. These provide excellent belt-movement control for accurate part or fixture positioning.

Vacuum conveyors work with a perforated belt that draws air through grooves in the conveyor bedplate to hold light or flimsy parts on inclines or during especially fast transport.

This is a stainless-steel micro-pitch plastic modular belt conveyor from mk North America with a diverter for bottles.

POWER AND FREE CONVEYORS: WHERE DO THEY EXCEL?

Power and free conveyors are designed for manufacturing environments where products need to be transported in a non-linear fashion — that is, where materials aren’t necessarily delivered in the order they were loaded or at the same pace. Traditional linear conveyors on the other hand lack the flexibility to handle manufacturing environments where different production processes run at different cadences or where various materials have different flow paths.

Note that because of their flexibility in handling and delivering products, power and free conveyors are also referred to as asynchronous or non-linear conveyors.

The defining feature of a power and free conveyor is that it consists of two tracks — an upper track and a lower track. The upper track is powered by a chain, and the lower track is unpowered. Trolleys, which carry the load, run on the lower track, supported by rolling wheels. Mechanical devices — often referred to as pusher dogs — on the powered track engage with the trolleys to move them and disengage with the trolleys to stop them. The pusher dogs are engaged and disengaged by cam action caused by a trolley in front or by a stop blade positioned along the powered chain. Air-activated stops, triggered by switches, can also be used to control the movement of trolleys.

Much like cars on a road, conveyor traffic can also be merged or diverted among multiple conveyor lines, and both sharp turns and elevation changes can be executed. And unlike traditional linear conveyors, power and free versions can allow products to accumulate, or “stack up” by holding trolleys stationary while other trolleys “catch up” and join them. The trolleys can then be released in the required sequence. All of this is accomplished through mechanical linkages via the pusher dogs and trolleys, without requiring complex automation.

To maximize space, especially during accumulation, trolleys can be connected via rigid load bars that set the spacing between trolleys at as little as 6 inches (depending on the size and shape of the load). And storage density can be maximized with trolleys that hold the load diagonally relative to the conveyor path.

Circuits of conveyors up to 300 feet can be controlled with just one motor, and complex “traffic” patterns and timing sequences can be controlled via sensors triggered by a PLC or PC-based controller. In addition, bar codes or RFID tags on the trolleys can be used to identify individual loads and carry instructions for sequencing.

While most power and free conveyors are mounted overhead, above the working area, and carry products below the tracks, floormounted designs are available that carry the product above the tracks. This is especially useful when overhead space is a concern, or when potential contamination from the conveyor or product is an issue, as is often the case in cleanroom environments. And when overhead space is limited but floor-mounting is not an option, some manufacturers offer overhead versions with powered and nonpowered tracks positioned side-by-side, rather than in a top-and-bottom configuration.

Power and free conveyors are customdesigned for each application and can carry loads from just a few pounds to several hundred pounds. They’re used extensively in the automotive industry, where robot cells are sometimes used to load/unload products from the trolleys or to perform work on the parts being conveyed as they’re held stationary. Power and free designs are available in heat and corrosion-resistant versions, so they can transport loads through processes such as washing and painting or through ovens.