Operation: conveying

Jan. 1, 2006
How does a typical conveying application work in a packaging setting? Typically, conveyors fall into two main camps: synchronous and nonsynchronous. Synchronous

How does a typical conveying application work in a packaging setting?

Typically, conveyors fall into two main camps: synchronous and nonsynchronous. Synchronous conveyors provide indexed movement of parts or products from station to station along a fixed path and at a fixed rate. They are usually automated and run quick cycles. Cycle rate depends on the slowest process in the system.

Nonsynchronous conveyors provide independent movement of parts or products from station to station on an as-needed basis. In other words, a flexible path routes work pieces independently and delivers them to processing stations. This type of conveyor maximizes automated machinery throughput and manual workers' productive time.

One commonality between both types of conveyors is that they rely on a conveying medium, such as (plastic) belts, (stainless-steel) chains, and rollers, which mounts to a steel or aluminum chassis. A powered drive unit then pulls the chain or belt to deliver motion. While most chassis and drives mount to legs or posts, some are suspended from the ceiling. A moving belt in a mounted frame is the simplest example of a conveyor.

What are the primary types of motion in conveying applications?

The goal of motion in conveyors is to put products in the right place at the right time for maximum output. Components that contribute to smooth motion are critical, especially under load. A powered drive, for example, can pull the belt or chain at constant speed, or, in the case of a variable frequency drive, let users change conveyor speed at any time. This is important for in-process buffering systems because conveyor speed can then match variations in machine output to “balance” the entire operation's timing.

Conveyor layouts often make creative use of space for product transport or storage. For example, while many conveyors are deployed at a single level, others elevate items, snake around obstacles, and transport products between factory floors. Motion components involved in such routing utilize pneumatic and electrical actuators, ballscrew drives, linear guides, bushing and shaft assemblies, and sophisticated controllers. In conveyor systems that make tight curves, transport products vertically, or require precise positioning, the belt or chain's flexibility and friction can influence the conveyor's success. Complex packaging systems encompass any and all of these situations.

With many synchronous conveyors in packaging, boxes, bottles, or cans sit directly on the chain. External guides mounted on the conveyor's sides control chain motion. To move up or downhill, for example, conveyor chains are outfitted with (roller) cleats or friction pads to prevent products from sliding.

In nonsynchronous conveyors where products mount to a workpiece carrier or “pallet,” the pallet lifts, rotates, diverts, stops, and reroutes with conveyor modules and accessories. Such pallets frequently contain data “tags,” which sensors read at different processing stations. This intelligence, combined with modularity, routes products efficiently and even allows multiple products to be manufactured or packaged on a single conveyor system.

What are the main challenges when implementing motion in a conveying process?

Eliminating unproductive time: Transferring products must be bulletproof, and products should be delivered to stations at the pace necessary to meet customer or station demand. Neither manual assembly workers nor automatic processing stations should wait for products to arrive. This means that any motion systems involved in transferring, routing, or positioning should function predictably, quickly, and smoothly. For example, pneumatic cylinders that raise and lower conveyor segments to transfer parts from one level to another must provide reliable and repeatable cycles. In more sophisticated systems, careless programming can stop an entire automated assembly line.

Linear thinking: Commonly, people perceive conveyors as unsophisticated, nonvalue-adding movers. On the contrary, today's conveyors utilize state-of-the-art aluminum-bending technology to curve pathways, circumvent obstacles in a plant, provide steep up or downhill transport, and squeeze tight radius storage and buffering systems in small spaces.

Lack of upfront planning: Packages and products take many shapes and forms and moving them through space can prove complicated. Therefore, it's best to design the system upfront, accommodating known obstacles and atypical situations. For example, the biggest concern with packages riding directly on a chain is overhang. To solve this, conveyor planners can add guide rails to contain the package, while considering obstacles such as posts and pneumatic air supply units that may interfere. For products riding directly on a pallet, an additional planning concern is evenly distributed weight. When downward forces are applied to only one side of the conveyor, significant wear to belts and pulleys occurs on this heavier side. In addition, flexibility for future changes should be built into all systems.

Safety and ergonomics: Conveyors have many moving parts, and it's easy to accidentally catch clothing in belts or chains. This is especially dangerous as drives are powerful enough to pull several thousand pounds. Additionally, most conveyors use other positioning systems, such as pick-and-place gantry-style robots. Many of these systems also employ fast linear motors, which are dangerous if guarded improperly.

Ergonomic issues are equally important when designing conveyors. A case in point involves conveyor planners who must consider the height at which products are presented to lineside operators. To maximize productivity, they should eliminate or minimize the bending, reaching, and lifting required by operators.

Where can motion technology make the biggest difference in conveying?

Flexibility is arguably the most important characteristic of motion technology. In particular, linear motion components can help end users add functions to solve real, plant floor problems. A vertical transfer unit, for instance, can employ a rodless cylinder to raise and lower products from one conveyor, and, even one floor, to the next. Depending on the vertical travel distance, operators can affix linear guides to these “elevators” for greater smoothness.

Another helpful function based on motion is the ability to position products on nonsynchronous conveyors. This would require a locating plate that mounts to pneumatic cylinders and fastens in the conveyor's center. As pallets arrive at the lift-position unit, they are stopped and raised a few millimeters off the line so work can be performed to the product without damaging belts or chains.

Perhaps the most significant motion technology in conveyors is the belt or chain. Well-designed chains maximize load-carrying abilities and save money by eliminating additional drives (normally the most expensive part). Smart chain design also allows for transport around tight curves — critical to flexible layout. Curves allow “alpine”-style buffering systems to be built for balanced machine output. Additional chain enhancements, such as cleats or friction pads may be required to prevent backsliding.

Conveyors alone are usually not enough to transport products through a packaging or manufacturing system. Complete systems may include SCARA robots or Cartesian motion systems that pick up and move products to reorient them for other processes or place in a box. Motion systems can dispense products into containers on a conveyor, trace a small bead of glue onto passing products, solder, drive screws, or apply labels.

For additional information, please contact Bosch Rexroth Corp. at 800-322-6724, www.boschrexroth.com, or email the editor, Colleen Telling, at [email protected].

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