Measuring of thickness...


Thread Starter

Jury Efremov

May be abyone can help me?
The thickness of wood-shaving plate (particle board) must be continuously measured on the seven points on the width.
The wood-shaving plate (the particle board) moves under (above) the sensors as a continuous production line.

A few suggestions. Solution probably depends on the environment, cost/benefit and performance requirements.

1. Laser distance measurement. Banner and Sick make reasonably economical models. There are others. You could arrange one unit on a transverse tack and continually traverse a path to get comprehensive data.

2. Riders (cams, rollers) in conjunction with displacement sensors. Contacting, yes, but probably simple and potentially good precision if implemented corectly.

3. Image processing. Imagine a collimated light source projecting a beam at 45 degrees to the surface. The position of the spot on an image taken at 90 degrees is dependent on the thickness. A line laser could be used to get a complete profile. Diode lasers are inexpensive thanks to the huge number of applications in
commercial equipment. A laser and rotating mirror could also be used. (try a search for active stereoptics)

Why do you need to measure it? I would have thought that the thickness would depend on the settings of the production equipment and that sampling would be adequate.


Chris Jennings

Other alternatives are for example, a radiation source to determine the thickness. This method is less popular than using LASER now mainly because the cost of a LASER is significantly lower now.

I work on a papermachine and we measure the thickness of paper using a contacting sensor. It consists of a ferrite button with a sapphire
coating on top which is pushed up onto the sheet using air (the button is mounted on a rubber diaphragm). The top section of the sensor is located such that is pushes down on the paper. The top sensor contains a microcoil that produces an electro-magnetic field that is used to
determine the thickness of the paper using the relationship between distance and magnetic reluctance.

I doubt if either of these methods would be suitable for you but they may give you an idea of the available techniques for measuring thickness.

Chris Jennings Ph +61(0)351360417
Elect/Control Engineer Fax +61(0)351360540
Australian Paper Maryvale Mob +61(0)407320113
In lieu of thickness, consider a non-contacting weight scale that will give weight/area information before the particleboard is pressed.
Ohmart-Vega (Cincinnati, OH) manufactures a scale that will provide multiple zone measurements across the width of the production line.

Michael R. Batchelor

I did some work several years ago with an MDF plant which used Trienco laser gages. The system took the data stream from the gages and drew a realtime profile of the board as it passed the
measuring station, and flagged anything which was out of tolerance. Seemd to work fine at about 2 meters/sec. Don't know how well it would have worked with a faster conveyor speed. Each
sample was approximatly 60-90 cm apart, so they weren't super high speed.

Overall the Trienco gages worked pretty well, but the manufacturer was a real PITA to work with. Wouldn't disclose any information whatsoever. Seemed pretty odd to me since we were using their product. Most companies *WANT* you to use their

Michael R. Batchelor - Industrial Informatics & Instrumentation, Inc.
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Enrico Guasco

Wenglor Sensoric has a number of analog output laser that can be used even one opposite to the other with minimum interference, of course this
has to be tested on your machine. I've used two laser analog sensors to continuously measure thickness of tapes in a bitumen production plant with good results, +/- 0,1mm. As you know bitumen is black and light absorbent so it is more difficult to measure in that way. And of course, precision depends on thickness and distance range.

Enrico Guasco

Tex.El. di Guasco Enrico
Borgata Ricca, 6
13822 - Mosso (Bi)

Tel. +39015702972
Fax. +390152548911
email. [email protected]

Curt Wuollet

Radiation will probably be out due to the density differences in the OSB with wood type and glue percentage at a given point. I think the line laser and camera approach would be good as it
could provide average and profile information and gives you the most information to work with.