How to correctly interpret and use data from the spectrum of a machine?

05 March 2018

MES systems provide enterprises with a range of various information on the condition of their manufacturing process. They enable persons responsible for this area of a company to make optimal decisions. One of more popular sets of information is the so called spectrum of a machine; however, it’s always properly used.

 

What is the spectrum of a machine?

The spectrum of a machine is a graphical or textual representation and visualization of each state of a given machine over a shift, a working day or a month. It usually has a form of a colourful diagram, on which the occurrences of individual events are marked: work, planned stoppage (for example, a changeover), failure, repair, planned break (for example, for a meal), etc. The illustration below shows an example of the spectrum of a machine from the Queris MES system.

 

 

How to use it?

Sometimes data recorded in this way is accumulated and only percent values for events, the most frequently in three categories, are presented:

  • work – X in the particular period of time,
  • planned stoppages – X in the particular period of time,
  • unplanned stoppages – X in the particular period of time.

Of course, a user obtains a certain picture of a situation, but it is insufficient to improve processes. The listing above does not provide enough information to make a decision which will significantly improve the production performance. Quantitative data is only the first level, which illustrates the scale of a problem (if any).

 

How to correctly use information from the spectrum of a machine?

The key to success is interpretation of qualitative data, which also should be gathered by the system. However, before it is done, it is recommended to break down the three-factor representation of the machine’s state by specifying it properly and assuming, for example, such a structure of information about the status of work:

  • work
  • planned stoppage (broken down into):
    • break/meal
    • maintenance/repair
    • changeover
  • unplanned stoppage (including):
    • stopping – waiting for a reaction
    • failure (type of failure)
    • a raw material missing
  • interference
    • removing a failure
    • feeding a raw material
  • inactivity (with a reason, for example “no order”)

Of course, every plant should define its range of states and their causes, which help in the qualitative interpretation of the course of events.

Then, when comparing proportions of events it is necessary to analyse causes and their duration. Only then we are able to answer the question where waste exists and look for ways of its elimination. Let’s look at the example below, which illustrates a situation in a certain plant.

 

The analysis of the spectrum of a machine in practice

 

 

The system recorded a range of events which occurred on a particular machine along with their causes. Thanks to this, three main states (work, stop, interference) can be additionally analysed from the point of view of causes (breaking off/raw material missing – waiting, breaking off/raw material missing – operator’s work). But it’s not all because the report also contains duration of every state, which in this case will be the key to making a decision. Let’s analyse the report step by step.

First of all, it is worth noting that it is not necessary to call maintenance technicians because the operator restores the machine to a working state, so the cause of the stoppage is not serious.

The time of restoring the machine to a working state is only 17-19 seconds, so we can suspect that the operator perfectly knows the technical aspect of the stoppage and is able to deal with it very quickly.

The time of waiting for a reaction and repairing are much higher values counted in minutes! This is the area we first need to improve according to the rule “first solve the problems the elimination of which will bring the greatest effect”.

First of all, the following conclusion emerges from the analysis: it is possible to obtain greater availability of the machine by eliminating the cause of the operator’s long reaction rather than the cause of the stoppage. Maybe there are too little operators or feeding a raw material involves going to a warehouse, which significantly influences the time of restoring the machine to a working state. This is the moment when an in-depth analysis and then a change of the current state should take place.

 

Summary

As you can see, the spectrum of a machine is not only the ratio of a machine’s uptime to downtime, but first of all the identification and control of causes of undesired events. When investing in a MES system which provides this kind of data it is necessary to know how to use the data.

In the case above, thanks to finding the cause of an operator’s long time of reaction it was possible to eliminate frequent, a few minutes long stoppages, which resulted in wasted hours (!) of the machine’s work over a day, not mentioning the scale of a month or a year. Therefore, apart from the correct implementation of a system it is important that a software vendor can also help to interpret information recorded. Then, using them will bring the company measurable benefits.

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