SPEED

Last month I started talking about packaging line speeds and found I had more words than space. This month I continue where I left off.

To recap: There are many speeds on a packaging line including linear speed, cycle speed and production rate (Generally expressed as packages per minute or ppm). I had concluded with “instantaneous speed”

The instantaneous speed is a fine starting place but doesn’t tell us too much about line throughput. That will depend on efficiency. Let us assume that a line has an instantaneous speed of 300 ppm based on timed observation. Over the course of a 400 minute shift, it should put out 120,000 products. (300 ppm X 400 min). In reality, this is unlikely to happen. There will be stoppages, jams, rejects, sampling and other issues that will reduce the overall output. The ratio of actual to theoretical output is a measure of efficiency. If the line output is 110,000 products over the shift, efficiency is 110,000/120,000 or 91%. Actual line speed has dropped from the observed instantaneous speed of 300 ppm to an actual throughput speed of 275 ppm.

If they rely only on instantaneous speed, at the end of the day the production manager is in for a shock when they find they are 10,000 products short.

Many machines will have displays continually indicating instantaneous speed. This is a good practice and I highly recommend it for every machine in every line, including conveyors. Just knowing what the speed is, though critical, is not enough. Standards must be established so that everyone knows what the speed should be. It is only by knowing the optimal and actual instantaneous speeds of all machines that the line can be kept in balance.

Every line must also have an averaging rate meter, generally at the discharge end. It should count each product and average its rate over a period of 5-20 minutes with the actual period determined based on the line characteristics. A longer period will give a more accurate throughput rate but will be slower to react to changes.

Another useful tool is a target counter. This should count bottles at the line discharge and display a running total. It should also display the target count as a running total. It will start at zero with a new job or shift then increment based on target production speed. On the 300 ppm line, it would update the count by 5 every second. It is also helpful to show the ratio of target to actual in real time. At the end of the first hour, in our example, it would show a target count of 18,000 as well as an actual count of 16,380 and an efficiency of 91%.

The presence of this display does two things to improve operations:

If the efficiency is low, say below 90%, it is immediately apparent and the production manager can address it right away rather than being surprised at the end of the day.

If the efficiency is high, say above 90%, that too is apparent and the manager does not need to worry about whether the line is running well. This frees them to perform more valuable work. Relieving worry also allows them to spend more time thinking about how to improve performance further.

The old accounting adage is: “If you don’t measure it, you won’t control it.” It is true of accounting. It is just as true about speed.