Is the V-Curve the best option for setting accumulation line speed?

Author LineView Admin, February 14, 2020

As we celebrate the start of 2020, it’s interesting to reflect on how technology and innovation have changed the shop floor.

We generally have more technology innovation than ever, but new challenges are evolving at an equivalent pace:

  • Changing consumer taste means more packaging sizes and variations, resulting in more frequent changeovers
  • Modern lines mean faster processing speeds
  • New technology and integrations add complexity

We’re not telling you anything new of course. For Operations, dealing with these challenges is daily life. Still, it’s relevant because within this new reality, line philosophy needs to be perfect and most often, it can be overlooked.

In a typical accumulation packaging line, a so-called V-Curve is most often used to set the line speed.

 

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What is a V-Curve? Is there a ‘better way’ to set line speed?

Today we’ll dive into the V-Curve theory, the pros and cons of this set-up and ,most importantly, a dynamic alternative to line speed control.

 

Are you using the V-Curve theory to set line speed?

Accumulation lines rely on this structure to optimise running states. The V-Curve set-up is relatively straightforward:

1. Start by identifying the slowest machine on your line. This will be the critical machine.

2.Then, set the standard running speed for all machines according to the critical machine speed (in normal conditions).

3.Next up: Set the two machines immediately before and after the critical machine to 10% faster in recovery speed (this is after a buildback scenario downstream, and after a lack scenario upstream of the critical machine).

4. After these two are configured, adjust each machine after/before them to run faster by 10% increments in recovery speed.

5. On top of all of this, machines will use sensors on the infeed and outfeed to intelligently identify lack or buildback.

 

Picture this setup as a 'V'. The critical machine may be a filler. The one after it, a labeller. The piece of equipment before the filler might be a depalletiser.

Here's a shot of what a V-Curve might look like in a typical production line.

 

Advantages of the V-Curve theory:

  • Setting up the line balance is easier and a comparatively quick process.
  • Dynamic accumulation triggers allow the line to manage flow intelligently.

Disadvantages of the V-Curve theory:

  • The only machine that will run at a consistent speed is your bottleneck or critical machine. All other machine will be stopping frequently in either lack or buildback
  • With equipment constantly changing speed, inertia changes increase. Inertia changes can cause an increase in minor stops, a reduced operating window of machines, more wear and tear, more breakdowns and a higher potential for quality issues.
  • Lastly, conveyor space may not be optimally utilised.

 

While the traditional V-Curve method is a proven approach, communication between PLCs and other technology advances allow for more precise and dynamic line control.

 

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Improving upon the V-Curve theory

Dynamic accumulation allows for additional empty conveyor space, lending operations a bigger buffer zone in the case of stoppages or breakdowns.

While in these instances the critical machine is the only one that will be running at a consistent speed, all other equipment can handle lack and buildback.

 

Getting the V-Curve right:

  • There are some tweaks that can be made to optimise your V-Curve.
    • First, your critical machine has to be running at its rated speed. This is a big warming if it isn't.
    • Is recovery speed at its peak? Take the 'ramp-up' time frame into consideration, too, as this affects working conditions dramatically.

Identify the real critical machine:

  • What we're suggesting here is that there are potentially more ways to determine the critical machine.
  • It doesn't have to be the slowest machine, as the standard V-Curve dictates. Maybe, it's actually the one that has the greatest impact on your product and operations?

Your line can be optimally balanced

  • When a line is running a traditional V-Curve, has conveyors full of product, sees regular start-up delays and receives frequent human intervention, then it can certainly be improved.
  • Recovery speeds need to be set, machines should run at their designed speed and your critical machine should be dependent on your own situation.
  • All of this and more makes up a strategy to attain the most balanced line possible.

 

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Want to learn more? Sign up for our Line Balance Optimisation (LBO) Crash Course.
Designed for operation management teams, this 7-week crash course will introduce proven methodologies to optimise line balance and minimise performance loss.

 

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