Line Balance Optimisation
Line Balance Optimisation is ‘the process of optimising line performance through the effective use of automation and control philosophies.
The main aim is:
- To maintain the critical machine (slowest machine on the line) in a running state at its rated speed.
- When upstream or downstream equipment fails, maintain the critical machine is a running state for as long as possible.
- When the critical machine stops, restart it as quickly as possible.
This can be applied to production lines:
- That are automated
- That consist of multiple machines that are linked by conveyors and set up in the traditional ‘V-curve’ with the equipment having variable speeds
- Which have conveyors / transport systems that can be used as a buffer
- Machines stop / start automatically in build back (when downstream conveyors are full) or lack (when there is no product at in feed of machine) conditions
The main reason for optimising the set-up of a production line is to maximise the throughput of the line to ensure that conditions pre and post the critical machine do not restrict output. Extra efficiencies of up to 10% can be found on lines that have not been previously optimised since initial set up.
A well balanced line will:
- Run at its rated speed
- Be more resilient when equipment breaks down
- Restart faster (potentially instantly)
- Recover to nominal running quickly
Vision of Perfect Flow
In order to understand how the production line should operate, we created a model of ‘Perfect Flow’ and the aim should be to get your production line to operate in this way.
Explanation of the model:
To understand the concept of perfect flow through a bottle neck it is worth considering a principle that can be imagined. The example utilised here provides a reference that can be easily imagined and is very close to achieving perfect flow.
- Imagine stacking hour glasses on top of each other, with the hole in the 2nd one down being smallest (Critical Machine) and the holes (machines) increasing in size (speed) as you move away from this one.
- There would also be an infinite amount of sand at the top and an infinite amount of space at the bottom (a bit like Fork Lift Trucks supplying and removing containers).
- Each hole represents a machine – the hole size represents how fast that machine runs.
- The glass balls between each pair of holes represent the conveyors.
- The sand represents the containers, whether they be cans, bottles, cartons, packs.
- The throughput of the this line is determined by the critical machine (size of hole number 2)
- If hole three is blocked (machine stopped) the glass ball above will fill, and so long as it is unblocked (machine started) prior to the ball above it filling, the overall throughput of sand (containers) will not be affected.
There are three scenarios considered below; normal steady state, during a stoppage condition and in a recovery condition:
In normal steady state conditions
- The glass balls (conveyors) before the critical machine are full before and empty after.
- The flow through each hole (machine) is exactly the same.
- The flow through the whole system is determined by the smallest hole (critical machine).
- The single stream of sand (containers) through the holes (machines) after the smallest hole (critical machine) leaves lots of space in the event of a stoppage lower down.
- Minor stops of flow can occur on holes (machines) other than the smallest hole (critical machine) without affecting the overall throughput.
In a stoppage condition
- The glass balls (conveyors) fill all the way up
- The flow through the smallest hole (critical machine) keeps consistent (design speed) until there is no more space below
In a recovery condition (after stoppage clears)
- The restart of flow through all holes (machines) is almost instantaneous
- For holes (machines) below the smallest hole (critical machine) flow through is maximised until the ball above (feed conveyor) is back to its normal condition (empty)
- For holes (machines) above the smallest hole (critical machine) flow through is maximised until the ball below (discharge conveyor) is back to its normal condition (full)
Imagine your lines run like this…
- All equipment on the line runs in automatic with no manual intervention required.
- In normal conditions the line speed is matched to the speed of the critical machine.
- Minor stops on machines upstream or downstream do not affect the critical machine.
- Extended stops affect the critical machine for a minimum period.
- Critical machine starts almost instantaneously with the machines downstream after a buildback situation.
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Line Balance Optimisation is:Correct
In nominal state all variable speed machines should:Correct
Fill the gap:
- A structured methodology to achieve perfect flow is called (5 Levels of Control, Five levels of control)