Backpressure and Accumulation Conveyors
Accumulation conveyors provide buffer zones in material handling systems to manage product flow, which is especially important when there is an imbalance between upstream and downstream capacity. But accumulation often results in backpressure, which can damage products or cause downstream operational problems.
Common Drawbacks of Product Accumulation
Traditional conveying systems experience backpressure during product accumulation due to upstream pallets successively bumping into each other as they stack up behind the lead pallet. This backpressure can generate hundreds of pounds of force and, more importantly, compromise the integrity and quality of the products being accumulated.
In addition, a traditional conveyor system typically runs non-stop, regardless of the actual production requirements. This means the conveying media – belt or chain – also runs continuously beneath the product, even during accumulation, while the product is stationary. Not only does this cause unnecessary wear and tear on the conveyor and the motor, it also wastes energy.
The Traditional Solution
So, how do conveyor designers and manufacturers typically deal with the extra loads, friction, and wear and tear that occur during accumulation? Simple: up-size the conveyor system.
Of course, this means heavier-duty (and sometimes larger) components, which adds cost, both in terms of the conveyor itself and in higher energy usage. Plus, accumulation and backpressure still have to be managed with pneumatic stops and eyes, which require wiring, and code development, driving extra costs and effort into the project.
A Better Alternative - Zero Pressure Accumulation
Accumulation is a necessary part of many processes, but if it damages the product or jeopardizes previous assembly or other operations, it’s a detriment to the overall production and quality – not to mention the economic impact of scrap, rework and stopped production. Unfortunately, this is often the case with traditional accumulation, due to the impacts and shock loads the products experience as they “pile up” behind one another.
Indivually Managed Accumulation Zones
Referred to as “zero pressure accumulation,” a conveying system with individually managed accumulation zones ensures there’s always a gap between products, which provides gentle product handling by eliminating the hundreds of pounds of backpressure that can cause product damage. Each individual zone can handle up to 200 lb, so the ability to transport heavy loads is not compromised.
Zero pressure accumulation eliminates wear and tear due to friction by dividing the conveying system into multiple zones and operating each zone only as the process requires. This means that the conveyor media stops during accumulation rather than running continuously under the stopped product. Eliminating friction and running the motors and conveyor media only when needed drastically reduces energy consumption and wear and tear on the conveyor.
How Zero Pressure Accumulation Works
To manage each zone individually, the single ac motor used on a traditional conveyor is replaced by multiple, small brushless dc motors – one for each zone. Each motor incorporates a driver card with integrated “zero pressure” logic, and the motors are daisy-chained together to ensure that each zone operates only when needed. Pallet sensors are wired directly to the driver card for the motor, which means fewer motor starters or VFDs, less code development, simpler wiring and reduced overall effort. Not only does this simplify the control scheme and hardware costs, it significantly reduces wear and replacement parts.
Information courtesy of Design World Articles (November 2017)