Best practice for using measuring wheels in Repeat Length Measurement applications

Our customers often use our Repeat Length Measurement System to measure and record repeat lengths on film in a printing press or die cutting machine.  Film will often stretch as it moves through the press making it difficult to get precise registration control.  Our system can be used to take accurate measurements that can assist in better process control of these stretchable materials.  It uses a print mark scanner and precision encoder to measure the actual repeat length of the material during the operation of the press.

We recommend you mount the encoder on a driven shaft that the web material passes over.  This has proven to give better accuracy of web movement.  In some cases it is just not possible to attach the encoder to the end of a shaft.  As an alternative, we provide a 12” measuring wheel which is attached to the encoder’s shaft and then placed on the face of the material as the web passes through the press. With the known circumference of the measuring wheel you can get accurate measurements of web movement.

One might assume that because the manufacturer specifies the encoder wheel as 12” circumference that this measurement can be relied upon.  In reality, there are tolerances in the manufacturing of the measurement wheel and its outer rubber tire that can make the circumference a bit longer or shorter.  If you are using a measuring wheel, it is best practice to determine the actual circumference of the wheel you are using.

Circumference is easily calculated by measuring the diameter of the measuring wheel with a micrometer and multiplying by Pi (3.141592).

Once you know the actual circumference of the measuring wheel and have installed the system we recommend a manual check.  Run some of the material you are measuring through the press, take a manual measurement, and compare it to the measurement from the system’s console.  This should validate that you have set up the system correctly and are ready to go.  

If you need advice on measuring repeat lengths, need a Repeat Length Measurement System, Scanners, Encoders or Measuring Wheel, please give us a call (800-323-3347).