Merge Considerations in an Automatic Environment

20180803 - merges considerations

When designing an automated system, it is important to protect production rates. Small oversights in a fast-paced environment can quickly multiply and create unintended consequences, weakening the impact of invested capital. This leads to heavy penalties to fix situations that could have been avoided outright.

In automation, one of the most significant influencers of your overall output rate is merge junctures. These junctures govern your throughput and – if implemented without proper forethought – can easily deteriorate into choke points. Poor design decisions result in capital loss and missed opportunities.

While there are many variables, two seemingly innocuous but critical factors to consider are:

  1. Sensor placement
  2. Conveyor type

Take the following 2:1 merge. Sensors are placed at each merge inlet (1, 2) with a single sensor at the merge outlet (3). These sensors can read either the leading edge or the trailing edge of each case. The conveyors are sized at two case lengths and are rated at 100 cases per minute.

20180803 - merges considerations diagram

Say you have cases passing through the 1st inlet and cases waiting at the 2nd. To release the load from belt 2, two checks are needed. Sensor 1 will have to have a “no case” read and sensor 3 will have to have read the leading edge of the last box in the batch. This logic, combined with the sensor placement, creates a problem.

When belt 2 releases its load, a one case gap already exists between the two batches. At first glance, this may not seem like a lot. But, if each merge batch has 10 cases, you would’ve just lost 10% of your potential output rate! Your 100 cases/min has shrunk down to 90 cases per min.

Consider conveyor belts 1 and 2. If cases are passing through inlet 1 and a case appears at sensor 2, conveyor 2 will halt, waiting for inlet 1 to complete before activating. What happens if another case approaches inlet 2 during this wait time?

If you’ve selected a simple belt instead of an accumulation belt in your design phase, the 2nd case will be stuck at the entrance of the belt, waiting for it to become active again. This adds another case length of space. Let’s say that this happens once every 10 cases again – once per batch. The merge has just suffered another 10% loss, bringing the output rate further down to only 80 cases per minute.

To protect capital in an increasingly automated environment, it is critical to keep production rates at the forefront of design. As shown, even a deceptively simple 2:1 merge can quickly create large productivity losses. Had the sensors been better placed and the right conveyor types selected, a 20% productivity loss could have been avoided. For example, if sensor 3 lacks the necessary range, purchasing a 4th sensor would be more prudent than accepting a 10% output loss over the warehouse lifespan. As such, careful consideration must be applied at all junctures to guard against decisions that may undercut your warehouse’s success.

Automation, warehouse automation

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