Harvesters and processors commonly use diameter and length measurements to optimise trees into logs. However, in the future, harvesting and processor heads will be able to do much more than this.
The future will have these machines looking at many more properties to ensure that we can deliver the exact product that our customers want. Dzhamal Amishev and Professor Glen Murphy of Oregon State University have published an article in the International Journal of Forest Engineering (IJFE 2008: 19(2): 48-56) titled “Implementing Resonance-Based Acoustic Technology on Mechanical Harvesters/Processors for Real-Time Wood Stiffness Assessment: Opportunities and Considerations”. The research was carried out on Douglas-fir.
External measurements and defects can easily be taken or seen. However, trying to determine the internal properties of the stem using a forest machine is much more difficult. This study looked at the factors that might influence the quality of the results should acoustic technology be used in a harvester head, as well as possible work strategies for harvester productivity impacts and processing decisions. Acoustic technology uses sound waves transmitted through the tree to determine the internal properties. In this study, resonance based acoustics was used, which means that the sound must be transmitted along the entire length of the stem.
To get the most accurate result, the tree length and taper should be known and delimbing should have taken place. However, this would mean multiple passes of the tree through the head, with resulting low productivity. The research team decided to investigate three processing scenarios:
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Complete delimbing and scanning of the tree before cross-cutting (bucking)
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Delimbing and measuring a portion of them stem, and predicting length and taper beyond that point.
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The acoustic measurement is done straight after felling (no delimbing and no information on taper or length).
Some of the key findings are as follows:
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The metal grapples of harvesting machines do not influence the accuracy of acoustic readings.
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Removing bark or branches with the head can affect acoustic measurements and need to be considered.
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It is possible for forecasting models to make provision for a lack of information on stem length and taper, which means harvester cycle times can be kept low as no prior measurements would need to be taken.
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Acoustic measurement was not accurate if the entire top of the tree remained intact after felling.
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Logs produced from the lower portion of the stem were stiffer than those from the top.
Please access the International Journal of Forest Engineering for a detailed and more complete account of the research. Source: www.lib.unb.ca/Texts/IFE/July08