Speaker
Description
Forestry operations are under growing pressure to supply sawlogs as quickly, cost-effectively and customer-specifically as possible. In fully and highly mechanised timber harvesting systems, harvesters and processors take on a key role at the front end of the wood supply chain, as they determine the assortment lengths directly in the machine. The commonly used length measurement systems rely on a tactile measuring wheel that is pressed against the trunk during feed. However, under the extreme operating conditions, these systems are increasingly reaching their technical and methodological limits.
The current measuring principle records the distance travelled along the log surface, which corresponds to the shortest end-to-end connection only in the ideal case. In addition, variable contact conditions affect the measurement: contact pressure, wood and bark properties as well as weather conditions (wetness, ice, temperature) change the effective rolling circumference. Furthermore, slippage, missing bark, branches and branch stubs can interrupt continuous contact with the log surface and lead to measurement errors.
In practice, machine manufacturers therefore prescribe regular manual calibrations, often several times per day, to detect and reduce systematic deviations. This additional step, however, reduces productivity, is itself prone to errors and has little effect on the variation of the measured data. To reliably meet the required minimum length and avoid the risk of quality downgrades due to undersized lengths, additional overlength is therefore often applied. This results in an economic loss of value for forest owners, as sawmills usually only pay for the required nominal length.
Within this context, a systematic literature review is being conducted to examine the current state of research on non-contact alternatives for length measurement in harvester and processor heads. The aim is to identify existing approaches, compile and compare them and thereby develop a clear insight into the challenges and potential of individual measurement methods in view of the extreme operating conditions in timber harvesting.
Alternative contactless measurement methods have been investigated since the early 2000s. Optical approaches are considered promising, as are methods using microwave or laser technology. Key limitations are interference from contamination, vibration and occlusion. At the same time, advances in sensing technologies and analysis algorithms are expected to further increase measurement accuracy and robustness. In light of these findings, subsequent research will focus on developing and evaluating a novel, non-contact, multi-sensor system to achieve more precise, calibration-independent length measurements.
| Keywords | Harvester; Length-measurement; Calibration; Non-contact-measurement |
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