Log Rotation Effect of Log Shape 2018 11

Log Rotation Effect of Log Shape 2018 11 07 Bruce Lehmann FPInnovations

Log Turning Errors

Rotation Theory

Distribution of Error • The distribution of the error is independent of the turn angle • Leads to the conclusion that the action of turning is not the source of the error.

Slippage & Bias

Apparent Slippage • A circle has the minimum circumference. • Rotating a nonround shape requires more movement of the rolls.

Slippage • Simulations of rotation shows that “slippage” is due to the log not being perfectly round • On average the effect is to under-rotate the log • There is a distribution of “slippage” and it is not constant even within a log. • For short sections, the slippage can be much larger than the average. • Since the “slippage” is not the same for both rolls, forces will be generated

Lever Arm – Unbalanced Torque • The lever arm can be surprisingly large. • On average, the maximum lever arm for a log is 20% of the log diameter • Large lever arms will create extra forces on the shifting cylinders, that they may not be able to provide, • However, lever arm does not predict rotation error.

Speed Bump Effect •

Loss of Roll Contact

Motion of the Rolls Areas of Loss of Contact Rolls Open Rolls Close on Log End of Log

Distribution of Bumpiness Mill A Mill B

Effect of Bumpiness on Rotation Error Mill A Mill B

Distribution of Errors by Range of Bumpiness Mean value is close to zero Rotation Error (deg)

Effect of Log ‘Bumpiness’ • Similar results from a third mill

Effect of Log “Bumpiness” • • • Created a variable that describes log ‘bumpiness’ The distributions of bumpiness from different mills are almost identical (characteristic of the species) The effect of bumpiness on rotation error is also very similar for different mills Bumpiness explains about 50% of the variation in log rotation error. However, even a log with high bumpiness can have a zero rotation error. The process seems to be the accumulation of many random events.

Tentative Conclusions • The process of turning (other than slippage) is not likely the cause of the errors – The variation in the error is independent of the rotation angle. • The process seems to be the accumulation of many random events. – Rolls bouncing off the log – Roll timing • log slipping on chain • Log gapping not maintained • Key factor to monitor seems to be the compression of the air cylinder. – If the cylinder is fully extended, then the roll is not in contact with the log

Mill Data • Can clearly see when rolls leave log • More mill data will create more ideas and hypotheses to investigate