Measurement of Linear Speed & Length

Over the years I have worked with companies producing or processing paper, foils, films or building materials such as plasterboard, chipboard, insulation, plastic extrusion, pipes etc.  In all of these applications, I have witnessed a need for accurate speed and length measurement solutions.

During the production of these materials, there is a requirement to synchronise the availability of raw materials with the production rate of the final product.  Failure to perform this accurately can lead to poor quality or the use of excessive raw materials.  Take the case of a plastic pipe extrusion process.  If extruded too slowly the pipe wall may end up thicker than specified.  As well as producing a product outside the specification, you may also be significantly increasing manufacturing costs by using more material than necessary.  If extruded too quickly, the wall thickness may end up too thin reducing the integrity of the final product.

Once manufactured there is often a need to synchronise the movement of the product with a secondary process for example lamination or printing.  Failure to synchronise properly can lead to illegible printing or poor lamination.  Materials are often then cut to length to satisfy the requirements of a customers order.

The choice of the correct Motion Control Sensor solution can help ensure high production quality together and optimum yield and productivity.

Rotary encoders

The industrial rotary encoder can be an accurate and reliable device for determining the speed and length of material when applied correctly.  The mechanical installation of the encoder will directly impact the performance of the final measurement.

Indirect measurement

If the material you want to measure passes over a roller or is transported by a conveyor then it may be possible to mount an encoder to the roller or the drive mechanics of the conveyor. 

A wide range of mechanical encoder designs are available to make the installation of the encoder to the conveyor as simple as possible.  SICK encoders are available in solid shaft or hollow shaft designs with different shaft diameters to make it easy to connect to an available drive element for the conveyor or roller.

Rotary encoders for indirect measurement

When considering indirect measurement, it is necessary to consider the impact of slippage.  Any slippage will be difficult to detect and will directly lead to measurement inaccuracies.  If slippage is likely, a direct form of measurement will be more beneficial.

Direct measurement

Measuring the material via a direct measurement method reduces the possibility of slippage.  A good solution for many applications is the use of a so-called "measuring wheel".  Fitting a wheel to the encoder can turn the encoder into a system that can be used to directly measure the movement of the material, although I have often seen this solution used to measure rollers and conveyors as well, as it is sometimes easier to retrofit a wheel encoder for indirect measurements.

When applying a measuring wheel solution it is important to find a way of ensuring the wheel remains in contact with the surface you want to measure (avoiding slippage) whilst at the same time not applying so much pressure that the material you are measuring becomes deformed or the bearings of the encoder become overloaded, leading to premature failure of the measuring system.

The SICK DBV50 measuring wheel encoder takes care of this for you.  Consisting of a rotary encoder, measuring wheel and spring assembly, the DBV50 is an out of the box measuring wheel encoder solution.  The spring is tensioned during mounting and ensures that a consistent 15N of force is applied to the wheel - more than enough to maintain contact with most materials, and a force that will not compromise the life of the encoder bearings.

The DBV50 is available in a range of linear resolutions, with 24V signal output or 5V signal output to suit the control system.  A right-angled bracket is available to simplify installation - see the accessory links for the following products.

DBV50 encoders for direct measurement

The Non-contact option.

In some cases, it isn't possible to use an indirect measurement method due to slippage and the product is too delicate, slippy or abrasive to use a measuring wheel in direct contact with the material.  For these instances, SICK introduced the Speetec Non-contact Speed & Length measurement sensor.

Speetec, uses eye-safe laser light incorporating the Doppler principle to measure on virtually any material.  

Summary

Investing in the best fit speed and length measurement system can quickly result in reduced costs, improved profitability and quality.  The material you want to measure and the design of your machines will determine which technology is the best for you.  Whether the best solution is indirect measurement using a rotary encoder, direct measurement using a measuring wheel encoder or non-contact measurement, the solution you need can be found in the SICK portfolio.