How to buffer: Zero Pressure Accumulation Conveyor Systems
In a perfect world, a conveyor will take a package from the induct, transport it along the length and then be removed without hinderance or stoppage. Life isn’t perfect, conveyors need to be designed with imperfections allowed, to give the calculated system efficiency required for a return on investment or ROI.
Most conveyor systems will require elements of accumulation or buffering to allow different elements within the line to stop and start; allow different operations along the line with asynchronized cycles; allow operator interaction with the packages without finger trap points or other operations to take place and allow queuing of packages without pressure, preventing damage or loss off the conveyor.
The method chosen will be driven by many input factors: package size and weight; speed of the line; length of time for accumulation required and numbers of product to accumulate.
What is accumulation on a conveyor system?
The simplest method to accumulate product on a conveyor system, whether driven roller conveyor or belt conveyor, is to drive the product or package to an end stop, such as blade or gate. The conveyor is continuously driven under the queueing package, causing friction, and wasted energy not to mention undue load on the motor and gearbox. The next package will be driven into the first and onwards until the stop is released or a queue-back sensor is made which will stop the feed to this section of the system.
In a simple low volume system, this may work, but anything more than 2-3 boxes and the back pressure will cause damage to the packaging and undue strain on the conveyor drive. If handling irregular boxes and sizes of products, these will not form an orderly queue. The products could ride over the top of the previous package in front or they will spill off the conveyor.
How to buffer
The ideal conveyor to provide accumulation or buffering in a material handling solution is a zero-pressure or zero-line pressure conveyor (ZLP) system. In effect a length of driven roller conveyor is constructed of individual driven sections, each containing its own drive and reflective product sensor. The length of each section is usually based on the longest product to be transported plus ~100mm.
The drive is generally 24VDC drum motors linked by v-belts for frequent high-torque stopping and starting. By utilising individual zone control, efficient queuing and release can be programmed for high-volume throughputs. Where operator interaction is required, the systems allow easy removal and placement of packages without finger trapping or undue effort caused by friction between the packages.
As each zone has individual control, some or all of the sections can be easily switched between continuous throughput of packages to buffering and accumulation and then back again, as demand requires. At all times, no reduction in capacity results. By varying the speeds of individual sections, Increases or decreases in gapping, the distance between packages, can be achieved for downstream operations, such as dynamic weighing or sortation modules.
Applications outside logistics
Whilst Axiom are primarily known to design, manufacture and install material handling systems for logistics and warehouse applications, the techniques and methodology can be applied in many industries where conveyor and control of the products is required.
For example for end of line packaging solutions, Axiom conveyor systems provide the ideal infeed solution. Zero-pressure systems allow buffering of the product on the infeed to a robotic palletising cell. Releasing boxes as required to allow the formation of a row or layer to be held by the robot end-of-arm-tooling (EOAT) or gripper. By controlling the feed to the picking zone, box turning can be accommodated for non-uniform queues of boxes. If gapped rows are required, careful sizing of ZLP zones will allow this without additional box stops or indexers. Less mechanical parts to operate and maintain.
Another application for zero-line pressure conveyor systems is the transportation of product on pallets, or carriers, along an assembly line. By utilising the control modes allowed by the individual section drives, pallets can be conveyor or stopped at will on any section. For example for loading of a machining cell; feed from a continuous process to a indexing system and back.
Why Axiom GB Ltd?
Axiom are a family business based in Tamworth, Staffordshire, UK. The company has 25-years of experience as a leading supplier of material handling automation solutions across a range of industries, but specialising in the supply of systems for logistics, warehousing and fulfilment applications. The combination of conveyors, sorting systems, control and data handling provides turnkey projects for many well-known companies.
By reviewing each project on its own merits, Axiom strives to provide the optimum solution to exceed the base requirements of the automation.
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