Improving Efficiency by Managing Constraints
by Dale Whitfield, 30 November March 2011


The IPAV System of hardware devices, advanced algorithms and software tools facilitate managing the constraints inherent in a high-speed production-line. They constantly build an overall view of the line and analyse various aspects of it. This holistic view and the data it gathers allow improvements in Line Efficiency to be realised.

Managing the Constraint

Managing the Constraint happens in a number of significant ways.

  1. By tracking the location of the Constraint Machine at all times.
  2. By informing the operator of the status of their machine at all times.
  3. By informing each operator of the time available to them before they impact on the Constraint Machine and thereby affect Line Efficiency.

Where is the Efficiency measured?

The slowest machine on the line, whether designed or measured, is the one that relates directly to Line Efficiency. If it stops running, Line Efficiency is impacted and there is less product in the warehouse.

This means that we need to ensure that this machine runs as close to 100% of the available time as possible. In other words Machine Utilisation and Line Utilisation must be maximised. The aim is to keep it supplied with product and ensure that there is always space available for it to discharge completed product into its accumulator/buffer.

Tracking the Constraint?

Tracking the Constraint Machine is performed by evaluating what we call Productive Downtime. The machine with the lowest available Productive Downtime is the bottle-neck and becomes the constraint.

By virtue of Productive Downtime we know where the Constraint Machine is located at any time and are now able to manage it by ensuring that all operators are aware of how they impact on it.

There are two relevant definitions here:

  1. Current Bottleneck Machine (CBM) – the machine is the constraint but is producing.
  2. Current Constraint Machine (CCM) – the machine is the constraint but is stopped.

Informing the Operator

We are able to forewarn the operator and predict potential impacts on all machines but with special emphasis on the Constraint Machine.

The status of a machine is classified by means of 3 indicator lights:

  1. Green – machine has Productive Downtime available and may stop for that amount of time before there is any impact on line efficiency.
  2. Yellow – machine is the CBM and will become the CCM if it stops producing.
  3. Red – machine is the CCM and is costing line efficiency.

The status indicator light is the first and most visible predictor.

When the light is Red, the machine is stopped and is costing Line Efficiency. All efforts should be made to get it running again, as soon as possible.

If its stopped and the light is Green, there is no impact on Line Efficiency. Available time is being used productively. This is Productive Downtime.

The IPAV Systems Predictor's display shows the available Productive Downtime  in two forms:

  • Machine Time - the time available before efficiency of the neighbouring upstream or downstream machine is impacted.
  • Cumulative Time - the time before the machine impacts on the efficiency of the Constraint Machine.

These available times are predictions as to when the current machine will impact on the Constraint Machine and therefore impact on Line Efficiency

What to do with the information

This information allows operators to make decisions on when and for how long to stop their machine. This deceptively simple piece of information can be used in a number of ways which impact on the efficiency of both line and machine.

Impacts on Line Efficiency are straightforward. The aim is to ensure that the slowest machine on the line, at the bottom of the V-Profile, runs as close to 100% utilisation as possible. That translates directly into product in the warehouse. If a machine's status is yellow, it should not stop.

Impacts on Machine Efficiency relate to time available to perform preventative maintenance tasks during production. Tasks that fit into available Productive Downtime can be scheduled will help to eliminate downtime due to breakdowns.

The information also allows management to schedule maintenance tasks that will be performed during periods of Productive Downtime. By carrying out these tasks during production, maintenance days or maintenance periods are shortened. Less downtime means more uptime, Line Utilisation will be greater and with that efficiencies and most importantly, product in the warehouse, will increase.