Specially Calibrated Force Plate(Dedicated FP for Band Saw Cutting Force Measurement)
—Cutting Force Sensingin Wood Machining—

National Research and Development Agency Forest Research and Management OrganizationForestry and Forest Products Research Institute
Department of Wood Science and TechnologyWood Machining Laboratory

Research BackgroundTo produce lumber commonly used in construction, logs must be sawn into square timber using a sawmill machine.

Among various types of sawmill machines, band saw machines are widely used. The surface quality of processed wood can vary depending on multiple factors such as wood feed speed, blade geometry, sharpening condition, and rotational speed. In addition, different wood species exhibit different levels of growth stress (※1). This may cause stress release during cutting, resulting in deformation such as warping or bending, as well as variations in elastic recovery (※2).

Although high machining accuracy is required to produce uniform lumber, issues such as blade wandering or chipped teeth may lead to rough cutting surfaces. In such cases, additional planer finishing using a molder (to smooth the surface) becomes necessary, which reduces processing efficiency.

In this study, cutting forces generated during band saw machining are measured using a force plate.
The following three-axis force components are measured separately:

・Force in the traveling direction of the band saw (Fz)
・Force in the wood feed direction (Fy)
・Force in the direction of blade wandering (Fx)

By analyzing these cutting forces, it becomes possible to evaluate the characteristics of wood during machining as well as the condition of the cutting blade, enabling the determination of optimal machining conditions.

（※1）Growth Stress
Stress generated within a tree during its growth. It occurs as the tree resists environmental forces such as wind, slopes, and gravity while attempting to grow straight.

（※2）Elastic Recovery
A phenomenon in which deformation does not immediately return to its original state after the applied external force is removed, but gradually recovers over time. This is also known as the elastic after-effect.

• Band Saw Blade
• Band Saw Machine

Key Sensing Technology of the Force PlateThis force plate is calibrated using a special method rather than standard calibration.

In this measurement setup, the wood specimen is fixed onto the force plate while the cutting operation is performed. However, the cutting point of the wood is located outside the force plate. In other words, the point of force application exists outside the sensing area of the sensor.

Normally, force plates and force sensors are calibrated assuming that forces are applied directly to the sensing surface or sensing element. In this case, calibration is performed outside the sensor area so that the sensing condition matches the actual measurement environment.

This approach enables accurate measurement of forces that act remotely from the sensor area. Such special calibration techniques represent one of the key pieces of know-how developed through our extensive experience in force measurement technology.

• Wood is fixed on the force plate and the protruding part outside the FP
  is cut
• Output image of each sensor
  when load is applied inside the FP sensor
• Output image of each sensor
  when load is applied outside the FP sensor
  ※Illustration for explanatory purposes only. Actual outputs may become more complex depending on the load conditions.

• Forestry and Forest Products Research Institute：https://www.ffpri.affrc.go.jp/ffpri.html

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