Accumulation Conveyors

Accumulation conveyors are used to transport and accumulate cartons and unit loads. These conveyors are used to hold product for gradual release into a cell or work area. Such a conveyor might be used for instance to release one package at a time to a robotic pickup station, or to release a part to a dedicated machine in an industrial environment that performs some action on the part or it might be used in a distribution system to release a group of cases onto a spur for palletizing.

There are two major types of conveyors in this category; "Minimum Pressure Conveyors" and "Zero Pressure Conveyors". In this case the term pressure refers to the amount of force exerted from the conveyor onto a package or part. A Minimum Pressure Conveyor releases parts gradually into a work cell, but the parts are touching one another and exerting a slight force on one another. A Zero Pressure Conveyor also releases parts gradually into a work cell, with no part touching any other part. Pictured at the left is a Lineshaft Conveyor, which is an example of a Minimum Pressure Conveyor.

With conveyor minimum pressure accumulation, the product is accumulated and the driving force is not removed. It is called minimum pressure because the pressure of the driving force is kept to a minimum. Pressure will build up as more product accumulates, but can be overcome with controls designed specifically for the application. The advantage to a minimum pressure conveyor is a higher discharge or single load release rate than with zero pressure accumulation.

minimum pressure conveyor Zero pressure accumulation occurs when the driving force is completely removed form the load. This is usually accomplished by way of sensors in combination with various mechanical means such that when a load is stopped on a sensor, the driving force in the zone behind the stopped load is dropped away. When the next load is driven into the now dead zone, it too will stop, causing a like chain reaction upstream, or until such time that the first stopped load is released and moves on. Discharge from an accumulation point can be either one load at a time or a so-called slug discharge, where a pre-specified number of loads are released at one time. A slug is a very loose term and can be any number of units and is defined by the system designers.

So, in summary, a minimum pressure conveyor is a contiguous conveyor system. There are no zones and the amount of sensors and controls needed is at a minimum. One must be very careful when designing a minimum pressure system because proper operation is highly dependent upon the dimensions and weight of the specific packages involved. On the other hand, a zero pressure system can be comprised of almost any type of conveyor, roller, chain, belt etc. You need not be so careful with the design because the weight and dimensions are not so critical. A zero pressure system is by definition a zone type of system, where each conveyor section is a zone that will need to be controlled separately. So, more sensors and software are involved.