Tensile force monitoring on large winch-assist forwarders operating in British Columbia

The forest industry around the world is facing common challenges in accessing wood fiber on steep terrain. Fully mechanized harvesting systems based on specialized machines, such as winch-assist forwarders, have been specifically developed for improving the harvesting perfor- mances in steep grounds. While the mechanization process is recognized as a safety benefit, the use of cables for supporting the machine traction needs a proper investigation. Only a few studies have analyzed the cable tensile forces of winch-assist forwarders during real operations, and none of them focused on large machines normally used in North America. Consequently, a preliminary study focused on tensile force analysis of large winch-assist forwarders was conducted in three sites in the interior of British Columbia during the fall of 2017. The results report that in 86% of the cycles, the maximum working load of the cable was less than one-third of the minimum breaking load. The tensile force analysis showed an expected pattern of minimum tensile forces while the forwarders were traveling or unloading on the road site and high tensile forces when operating on steep trails, loading or traveling. Further analysis found that the maximum cycle tensile forces occurred most frequently when the machines were moving uphill, independently of whether they were empty or loaded. While the forwarders were operating on the trails, slope, travel direction, and distance of the machines from the anchor resulted statistically significant and able to account for 49% of tensile force variability. However, in the same conditions, the operator settings accounted for 77% of the tensile force variability, suggesting the human factor as the main variable in cable tensile force behavior during winch-assist operations

Preharvest Veneer Quality Evaluation of Douglas-fir Stands Using Time-of-Flight Acoustic Technique

Acoustic technology has been successfully used as a nondestructive technique for assessing mechanical properties of various wood products and species as well as in tree selection and breeding based on stiffness. In an ongoing endeavor to optimize merchandizing and enhance timber value recovery, seven second-growth Douglas-fir stands of similar age classes in western Oregon were sampled, totaling 1400 trees and more than 3000 logs. The objectives of this research were to 1) investigate the spatial variability of time-of-flight (TOF) acoustic velocities in standing Douglas-fir trees; 2) develop relationships between average Director ST300® (ST300) TOF acoustic velocities of standing Douglas-fir trees and actual veneer produced; and 3) determine the influence of diameter at breast height (DBH) on TOF sound speeds. Spatial location of the stands in terms of their latitude, longitude, or altitude had no predictive capability regarding their veneer quality. Standing tree TOF acoustic velocity and the actual G1/G2 veneer produced using a stress-wave grade sorter had no significant correlation. Significant differences were found among the three different ST300 tools used along the duration of the study as well as between the two opposite side measurements within trees. DBH correlated poorly with both acoustic velocity and G1/G2 veneer recovery

In-forest log segregation based on acoustic measurement of wood stiffness

To remain competitive, the forest products industry needs to look for new and innovative processes and technologies to not only reduce costs but also to recover more value through the entire seedling-to-customer forest products supply chain. It is well recognized that measuring wood properties of logs in real time during harvesting would lead to improved log allocation decisions and increased value recovery. Wood stiffness is certainly one of the attributes defining the quality of forest products such as veneer and lumber. Accurately assessing stiffness in realtime can be a challenge for log supply managers requiring logs segregated into different product classes based on stiffness. Acoustic technology has proven to be a well established non-destructive technique for assessing potential product performance by identifying logs with high stiffness. Launched by the worldwide trend towards increased mechanization of forest harvesting operations, providing a platform for innovative measurement systems, the interest in incorporating technologies for measuring internal stem features into a harvester head is rapidly growing. Therefore, the purpose of this study was to provide forest products stakeholders with comprehensive scientific information on the potential capabilities, limitations, and applicability of acoustic technology to improve value recovery from Douglas-fir stands by means of in-forest sorting of veneer quality logs. This dissertation: • Demonstrated that recovery of high quality green veneer from Douglas-fir peeler logs could be accurately predicted using resonance-based acoustic velocity measurements, • modeled the predictive capabilities of spatial as well as internal and external log and tree characteristics in terms of veneer quality and analyzed their effects on acoustic velocity measurements of Douglas-fir wood stiffness, • determined whether time of flight acoustic technology could be used for pre-harvest veneer quality assessment of Douglas-fir stands in terms of stiffness requirements, • described influential factors arising from incorporating acoustic instruments on a mechanized harvester head and suggested optimal procedures for scanning in terms of feasibility and harvester productivity, • presented a general methodology to estimate breakeven prices of Douglasfir peeler logs based on the net return obtained when logs from stiffness graded stands using acoustic technology are processed and converted into end products

Tensile Force Monitoring on Large Winch-Assist Forwarders Operating in British Columbia

The forest industry around the world is facing common challenges in accessing wood fiber on steep terrain. Fully mechanized harvesting systems based on specialized machines, such as winch-assist forwarders, have been specifically developed for improving the harvesting performances in steep grounds. While the mechanization process is recognized as a safety benefit, the use of cables for supporting the machine traction needs a proper investigation. Only a few studies have analyzed the cable tensile forces of winch-assist forwarders during real operations, and none of them focused on large machines normally used in North America. Consequently, a preliminary study focused on tensile force analysis of large winch-assist forwarders was conducted in three sites in the interior of British Columbia during the fall of 2017. The results report that in 86% of the cycles, the maximum working load of the cable was less than one-third of the minimum breaking load. The tensile force analysis showed an expected pattern of minimum tensile forces while the forwarders were traveling or unloading on the road site and high tensile forces when operating on steep trails, loading or traveling. Further analysis found that the maximum cycle tensile forces occurred most frequently when the machines were moving uphill, independently of whether they were empty or loaded. While the forwarders were operating on the trails, slope, travel direction, and distance of the machines from the anchor resulted statistically significant and able to account for 49% of tensile force variability. However, in the same conditions, the operator settings accounted for 77% of the tensile force variability, suggesting the human factor as the main variable in cable tensile force behavior during winch-assist operations

Using Acoustic Sensors to Improve the Efficiency of the Forest Value Chain in Canada: A Case Study with Laminated Veneer Lumber

Engineered wood products for structural use must meet minimum strength and stiffness criteria. This represents a major challenge for the industry as the mechanical properties of the wood resource are inherently variable. We report on a case study that was conducted in a laminated veneer lumber (LVL) mill in order to test the potential of an acoustic sensor to predict structural properties of the wood resource prior to processing. A population of 266 recently harvested aspen logs were segregated into three sub-populations based on measurements of longitudinal acoustic speed in wood using a hand tool equipped with a resonance-based acoustic sensor. Each of the three sub-populations were peeled into veneer sheets and graded for stiffness with an ultrasonic device. The average ultrasonic propagation time (UPT) of each subpopulation was 418, 440 and 453 microseconds for the green, blue, and red populations, respectively. This resulted in contrasting proportions of structural veneer grades, indicating that the efficiency of the forest value chain could be improved using acoustic sensors. A linear regression analysis also showed that the dynamic modulus of elasticity (MOE) of LVL was strongly related to static MOE (R2 = 0.83), which suggests that acoustic tools may be used for quality control during the production process

Impact of Weed Control and Fertilization on Growth of Eastern White, Loblolly, Shortleaf, and Virginia Pine Plantations in the Virginia Piedmont

The relative growth response of planted loblolly (Pinus taeda L.), shortleaf (Pinus echinata Mill.), Virginia (Pinus virginiana Mill.), and Eastern white (Pinus strobus L.) pines to intensive silvicultural practices such as woody competition control and fertilization in the Piedmont Province of Virginia is unclear. To address this issue, during 1999, a mixed stand of Virginia pine and hardwoods was clearcut and site-prepared by herbicide application. Three replications containing strips of loblolly, shortleaf, Virginia, and white pines were planted at a 3 m x 1.5 m spacing during February-June, 2000. Four different sources of loblolly pine seedlings were used. The strips were subsequently split across to accommodate four different silvicultural treatments: (1) check (no treatment); (2) woody vegetation control; (3) fertilization; and (4) weed control plus fertilization. The weed control treatment used two directed spray herbicide applications in 2001 (triclopyr and glyphosate) and 2003 (glyphosate) and one mechanical cutting of the remaining hardwoods in 2004. Fertilizer containing N, P, K, and S was applied in 2001, only N in 2002, and N plus P in 2004. Crop tree survival was highest for loblolly pine, decreased in shortleaf and Virginia pines, and Eastern white pine had the poorest survival through age 5. Fertilization without controlling the competing hardwoods decreased survival in all planted pines due to the increased hardwood competition. Loblolly pine was tallest (4.7 m) through the five-year period, shortleaf and Virginia pines were shorter (2.95 m and 3.06 m, respectively), and white pine was shortest (1.7 m). When fertilized, hardwoods were taller than white pine seedlings, almost equal in height to shortleaf and Virginia pines, but shorter than loblolly pine seedlings. Silvicultural treatments had no significant impact on tree height. However, the weed control treatment increased fifth-year pine DBH and stem volume, while fertilization did not. When applied in combination with weed control, there was no additional increase in crop tree DBH and stem volume due to fertilization beyond that from weed control only. The increased availability of soil nutrients due to harvesting the previous stands and allocating them to the crop trees by controlling the competing woody vegetation was enough to meet the nutrient requirements of the young seedlings up to this age.Master of Scienc

Implementing Resonance-Based Acoustic Technology on Mechanical Harvesters/Processors for Real-Time Wood Stiffness Assessment: Opportunities and Considerations

Acoustic technology has been successfully used as a non-destructive technique for assessing the mechanical quality of various wood products and species based on stiffness. Many mechanical harvester/processor manufacturers have implemented mechanical sensors to measure tree diameter and length as well as optimal bucking algorithms on their equipment. There is a growing interest in incorporating technologies for measuring internal stem features into a harvester head. The objectives of this study, therefore, were to i) determine and investigate the factors arising from incorporating acoustic instruments on a mechanized harvester head that might influence resonance-based acoustic signal and velocity readings and quality in Douglas-fir, and ii) investigate the issues and considerations associated with suggested working strategies in regard to harvest productivity impacts and processing decisions. After taking into account some feasibility considerations, it was determined that the hold of the machine grapple would not compromise the accuracy of resonance-based acoustic velocity readings. There were three working procedures suggested for measuring resonance-based acoustic velocity: 1) after the stem is delimbed and run through the measuring equipment, 2) once a portion of the stem is measured and the length of its unmeasured portion is forecast, and 3) after the tree is felled by the harvester but before any further processing is done. Regardless of the working procedure, it was determined that logs produced from lower sections of the tree are stiffer than those from upper portions. If the processor head traverses the stem partially or completely, the removal of bark and branches and their effect on acoustic velocity readings should be taken into account. Forecasting routines could be developed to account for imperfect and even non-existing information about tree length with the second or third working procedure. Results yielded by the two methods used for stem height (and consequently acoustic velocity) prediction in this study (linear regression model and a k-nearest-neighbor) were considered rather promising. Testing feasibility concerns with the resonance-based acoustic technique were observed if the entire stem was intact to the very top offshoot bud

Steep terrain forest operations \u2013 challenges, technology development, current implementation, and future opportunities

While modern fully mechanized ground-based systems are a default option for safe and productive harvesting, they have always been limited by terrain factors such as slope, soil strength, and roughness. There is a limit with regard to the physical feasibility of operating machines on steep slopes because both the weight and also the force from the momentum created during traction loss can affect stability. A huge interest to improve traction of harvesting machines when operating on steep slopes is arising. One way to improve traction and stability on steep slopes is through assisting harvesting machines by winch and cable to anchor locations such as tree stumps or stationary equipment. This technology offers potential for improving the safety, productivity, and efficiency of a harvesting operation, as well as for improving machine mobility and reducing soil disturbance through the reduction of slip. With the exponential development of such technology, an integrated approach must be developed for conducting productive and injury-free mechanical harvesting operations on steep slopes that draws on the skills and accountabilities of the working team. Beyond a certain physical threshold, the only feasible and achievable solution providing some \u201cintelligent behavior\u201d to machines and systems would be the role of mechatronics application. One of the most relevant points could be the possibility to introduce the concept of \u201cteleoperation\u201d using unmanned ground vehicles. Combining teleoperation with winch-assist technology would provide a platform for extending the range of ground-based equipment to previously infeasible terrain condition