Optimising Line Control

December 2, 2008 by  

We believe that ineffective line control is THE HIDDEN OEE Waste! By optimising your line control you will be able to increase your performance (OEE) by up to 7%! 

  • Do you operate in an industry that requires filling of some sort of containers like bottles, cans, bags, etc?
  • Do you have continuous flow production lines with conveyor systems between the machines?
  • Do you feel that there is something not quite right with the configuration of the lines and there is scope of making the lines run a lot smoother? 

If you answer yes to the questions above…..then read on 

What do we mean by line control?

On continuous flow production lines, typical found in FMCG environments, there are broadly 2 types of production line configuration; block and accumulation.

Block production lines operate with most machines running at the same speed. Typically block lines run with very little conveyor space between the machines (often single track). Therefore a stop on any of the blocked machines quickly or instantly causes a direct loss of performance (OEE) for the line.

Machines are typically controlled through linking the PLC controls to change speeds/stop automatically for the entire line.

Accumulation production lines, typically food related such as Coca-Cola bottlingCrisp packaging and food packaging operate with individual machines linked with large amounts of conveyor space and generally take up a lot of factory space. Typically the machines in an accumulation line have the capability of running at variable speeds, and will normally have one machine (or one block of machines) which runs the slowest; we call this the bottleneck or ‘critical’ machine. The Performance (OEE) of this line is determined by the amount of time that we’re able to keep the critical machine running at its rated speed.

Assuming good line balance and control, the accumulation minimises the impact of minor stops on all machines other than the critical machine

Machines are typically controlled by conveyor-based sensors with little direct interaction between the machines.

Line control or line philosophy is the way in which machines are stopped / started in response to changing conditions on the line. E.g. Stopping in build back when a machine downstream stops, stopping in lack when a machine upstream stops.

Have you ever wondered WHY on your production line…..

  • the conveyors are running almost full all the time
  • the machines on the line stop and start from no apparent reason i.e. there has been no fault or blockage upstream or downstream of the machine
  • when there is a fault downstream, it almost immediately stops the critical or constraint machine although there is plenty of accumulation conveyors in between
  • when there has been a stop downstream, it takes a long time for the critical machine to start up again
  • the machines downstream of the critical machine are always ‘hunting for product’ i.e. either running flat out or not at all
  • when the machine stops due to a build back situation, the operator has to start the machine up again and this always causes a delay on starting up again

Would you like to see more of the following happen…..

  • All equipment on the line runs in automatic with no manual intervention required
  • In normal condition 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 as the machines downstream after a build back situation

…..this is our vision of perfect flow and it is possible to get as close to this philosophy as you want

At OptimumFX, we have perfected a way of optimising the Line Control philosophy of an automated production line by using what we call the ‘5 Levels of control for automated flow lines’.  This includes looking at (not limited to) the following concepts:

  • Look at automating all machines on the line, so that machines automatically stop and start during lack or build back situations requiring no manual intervention and the machine speeds are automatically set requiring no manual adjustment
  • The conveyor speeds are adjusted so that in normal conditions they are running mostly empty maximising the dynamic accumulation space
  • By adjusting lack and build back sensors the conveyor space is maximised
  • Link the machines together so that speeds of all the machines on the line are matched to the critical machine during normal conditions preventing wear on machines due to sudden stop / starts
  • On restart after stoppages ensure that the machines downstream have sufficient over speed capability, this enables clearing of the accumulation conveyors quicker and starts the critical machine as quickly as possible
  • Look at maximising the time before the critical machine stops when there is a fault downstream and minimising the time before the critical machine starts up again when the fault is repaired

We have developed a comprehensive method of auditing the production line that will identify what needs to be changed to achieve the vision of perfect flow.  This is based on prioritising the actions that will give you the greatest benefit.  Give us a call and we will be more than happy to help you achieve this!