Magnetostrictive transducer for cylinder and blade positions in sawmills

• Application: Accurate control of the cylinders and blade positioning in Sawmill
• Products: Magnetostrictive transducer WRA-S/WPA-S – stroke 400 mm
• Result: WRA-S controls the cylinder position and WPA-S the blade position with a resolution of 0.05 µm

The sawmill machine is the sawing or cutting system that turns round log into square timbers.

The two main types of sawmills are stationary mills and mobile or portable mills. They range in size from large-scale fixed structures mounted on foundations down to small productions either trailered or truck-mounted.

There is another angle to sawmill types, which involves the saw blade types that mills use. Modern sawmills utilize a combination of blade types. Circular blades are excellent for cross cutting or bucking logs into specific lengths. Bandsaws, on the other hand are far more efficient for cutting logs laterally.

All the machine movements described in the process diagram (fig.2) – chipping, trueing, sawing etc. should be accurately controlled in terms of positioning. All the phases are driven by the PLC that receives the exact position of the hydraulic actuators and sawing blade through the linear position sensors installed on the machine.

Particularly the hydraulic cylinders, installed with rod design sensors WRA-S (fig.1), carry out the trueing of the log – the number of cylinders and the number of rod sensors depends on the machine length – typically a machine 3 meters long, will have 3 cylinders that operate in the trueing function. The profile design sensor WPA-S vertically installed (fig.1) provides the exact position of the bandsaw.

Working process from the log to the boards:

• Scanner to control the shape of the log
• Chipping 1
• Trueing 1
• Sawing side boards 1
• Chipping 2
• Trueing 2

WRA-S and WPA-S transducers

• Absolute and accurate signal: linearity ≤±0.01%/FS
• High reliability
• IP67
• High vibration resistance: 15g / 10…2000Hz (DIN IEC68T2-6)

The position transducers HYPERWAVE WRA-S (fig.3) and WPA-S (fig.4) (Synchronous Serial Interface) Magnetostrictive technology with 0.5 µm resolution and high signal stability during all the phases (see vibrations), allow an accurate position measurement.

Moreover, the IP67 protection degree and the high reliability makes sure that the sensor is fully suited for such an application. The fine wood dust could affect the performance of the sensors if the housing is not duly sealed.

The model selected are the WRA-S/WPA-S, SSI output 400 mm synchronous stroke with 25 bits and Gray coding ensures high resolution and safety of the transmitted data.