Keeping a close eye on overhead conveyor systems

Overhead conveyor drive systems are perhaps the most critical of critical control points in a high throughput multi-shift poultry processing plant. Failure of any one overhead conveyor system will always result in lost production.
The ability to drive long air chill lines with 100% reliability was the main driver behind development of the Marel Active Tension Control (ATC) system some years ago. Today, this technology is more relevant than ever.

Measuring chain tension

The ATC system divides each processing line into smaller sections, each with its own frequency-controlled drive and device for measuring chain tension. A master drive unit determines line speed and a master tensioner the level of tension in the chain. The system’s software continuously monitors chain tension in each section, using feedback information from the measuring device to ensure uniform tension throughout the whole processing line. What if a measuring device detects that tension in a particular section deviates from the level set at the master tensioner? In that case, the software fine-tunes the speed of the section’s frequency-controlled drive to bring tension in the section back to the pre-set level.

Avoid damage

An important task of ATC is to stop an overhead conveyor immediately if it picks up any increased resistance caused, for example, by a shackle jam. Conventional conveyor lines without ATC will always try to keep running, no matter what error or defect has occurred. ATC’s auto-stop is therefore an invaluable feature, which prevents any further damage to shackles or, more importantly, to automatic equipment connected to the conveyor line. Thanks to ATC’s smart intervention, line stops will be shorter and any necessary repair work less and done more quickly.

Load cells and dancers

Marel offers two versions of its ATC system, Force and Displacement, the difference being the way in which each section measures chain tension. ATC Force, used mainly in defeathering and automatic evisceration lines, has load cells installed on a 90° or 180° corner wheel, whereas ATC Displacement, used mainly in long air chilling lines, has “dancers”. Put simply, a “dancer” is a 180° corner wheel, which can move backwards and forwards in its frame.

Synchronize shackle count

In today’s highest capacity processing systems, state-of-the-art LineLink re-hangers automatically transfer product from the defeathering to the evisceration line. The TR-DE rehanger, recommended for lower hourly throughputs, requires the evisceration line to run slightly faster than the de-feathering line. With LineLink, however, both lines must run at exactly the same speed expressed in shackles per minute. Differing chain stretch in the two conveyor systems presents a potential problem, as the linear speed of the two lines will then have to be different to achieve the same shackle count per minute.

This is only to be expected, as the lines have differing forces acting on them, which affect chain life. It is also unlikely that the two lines’ chains will have been replaced at the same time. ATC overcomes this problem electronically by fine-tuning the speed of drive units on the two lines to give the same shackle count per minute on both lines.

Several kilometers long

In the highest capacity processing plants, a combined air chill maturation line can be almost 7 km long, powered by a large number of drive units. ATC ties these units together into a single system, ensuring that the chain in each section is under exactly the same degree of tension. In a chilling maturation tunnel, this is particularly important, as product loading in different parts of the line can be radically different.

Another feature of ATC in a long chill maturation line is that should a drive fail, its nearest neighbor is able to take over the section’s workload. Replacement of the defective drive can be at a time to suit production needs.
Constantly uniform chain tension throughout a long chill line has yet more benefits. Chain life can be longer. When the time eventually comes to replace it, plant maintenance does not have to do the job in one go but can opt to do it in manageable sections.

Turkey and duck

ATC has applications in turkey and duck lines too. Many plants processing turkeys have combined plucking and evisceration lines. These lines can be quite long, needing multiple drive units to power them. As male turkeys can weigh in excess of 18kg, unequal line loading is a much bigger issue than with broilers.
In high throughput duck processing plants equipped with Marel automatic evisceration equipment, a single overhead conveyor system comprising multiple drive units transports product through both de-feathering and evisceration departments.
In both duck and turkey processing plants, ATC ensures uniform chain tension regardless of line length and loading.
When used in duck and turkey processing lines, ATC can compensate for the failure of a drive unit. The unit next to it automatically takes over with no loss in production.

By efficiently managing the operation of overhead conveyor systems equipped with it, ATC contributes very substantially to ensuring that up time in the highest throughput plants is as close to 100% as possible.