Basic advantages of laser systems for thickness measurements:* Non contact measurement
* No radioactive source
* Not sensitive to material’s electromagnetic behaviour as with capacitive and inductive
sensors (changing amount of graphite)
* High precise
* Small spot
Special conditions in the rubber industry:
Small amount of light reflecting from the product surface (black)
Surface reflectance is changing (fresh calendered or extruded caoutchouc)
Laser sensor with high sensitive CCD light detection chip and appropriate intensity control device.
Most laser sensors have accuracy problems and/or function problems if the special conditions (see above) happens.Only a few laser sensors combine the features necessary for a well working laser thickness measurement system. The company Dr. Noll selected these sensor out of the amount of offered laser sensor and adjusted them together with the laser producer, to have an improved functionality, specially for the tire industry.
Non scanning thickness measurement devices can have different outlines:
- Absolute measurement against a measuring roll
- Measurement in difference
- Measurement against calender roll
For each sensor outline different positioning outlines are possible:
- Fixed sensors
- Fixed with lift up
Absolute Measurement against a measuring roll
This measurement is performed by measuring against a roll with specific condition. The roll has to be tempered ( not always required), sandblasted, must have a minimum diameter of 150mm and the run-out should be small.
The surface of the measuring roll is the zero position. The system is calibrated without a product in front.
If an absolute measurement is not possible an measurement in difference can be performed. Two sensors are needed for each measurement position. No additional roll is necessary.
Measurement against calender roll
In some cases the measurement has to be performed directly at the calender roll. During production the shape of the calender roll can change due to temperature effects and due to caoutchouc pressure. Two reference sensors recognises the changes of the roller’s position. The reference sensors are placed beneath the product edges and looking onto the roll