Ola Lindroos

Productivity of harvesters and forwarders in CTL operations in northern Sweden based on large follow-up datasets

Modern computerization facilitates data-gathering from forest machines, and offers new opportunities to develop models for predicting productivity in forest harvest operations. In this study, we analyze the productivity of cut-to-length harvesting and forwarding in thinning and final felling using a routinely recorded follow-up dataset. The data originate from over 700 machines that, over a 3-year period, harvested and forwarded more than 20 million m3 of round-wood from upwards of 20 thousand stands, making the dataset larger than any that has previously been used for productivity modelling. Results comprise a range of stand-based productivity models of varying complexity for both harvesters and forwarders. Mean stem size was the most influential variable for harvesting productivity: modelling based on mean stem size explained 57.6% of the variance in thinnings and 55.3% in final fellings. However, accurate predictions of forwarding productivity required the simultaneous consideration of several variables. For instance, modelling of forwarder productivity based on the variables mean stem size, mean extraction distance and forwarder load capacity explained 26.4% of the variance in thinnings and 35.2% in final fellings. Results should be of interest to both practitioners and researchers interested in the study and modelling of forest operations.

Path tracking in forest terrain by an autonomous forwarder

Abstract Autonomous navigation in forest terrain, where operation paths are rarely straight or flat and obstacles are common, is challenging. This paper evaluates a system designed to autonomously follow previously demonstrated paths in a forest environment without loading/unloading timber, a pre-step in the development of fully autonomous forwarders. The system consisted of a forwarder equipped with a high-precision global positioning system to measure the vehicles heading and position. A gyro was used to compensate for the influence of the vehicles roll and pitch. On an ordinary clear-cut forest area with numerous stumps, the vehicle was able to follow two different tracks, three times each at a speed of 1 m s−1, with a mean path tracking error of 6 and 7 cm, respectively. The error never exceeded 35 cm, and in 90% of the observations it was less than 14 and 15 cm, respectively. This accuracy is well within the necessary tolerance for forestry operations. In fact, a human operator would probably have a hard time following the track more accurately. Hence, the developed systems function satisfactorily when using previously demonstrated paths. However, further research on planning new paths in unknown unstructured terrain and on loading/unloading is required before timber transports can be fully automated.

Potentials of possible machine systems for directly loading logs in cut-to-length harvesting

In conventional mechanized cut-to-length systems, a harvester fells and cuts trees into logs that are stored on the ground until a forwarder picks them up and carries them to landing sites. A propo ...In conventional mechanized cut-to-length systems, a harvester fells and cuts trees into logs that are stored on the ground until a forwarder picks them up and carries them to landing sites. A proposed improvement is to place logs directly into the load spaces of transporting machines as they are cut. Such integrated loading could result in cost reductions, shorter lead times from stump to landing, and lower fuel consumption. However, it might also create waiting times for the machines involved, whereas multifunctional machines are likely to be expensive. Thus, it is important to analyze whether or not the advantages of any changes outweigh the disadvantages. The conventional system was compared with four potential systems, including two with autonomous forwarders, using discrete-event simulation with stochastic elements in which harvests of more than 1000 final felling stands (containing in total 1.6 million m3) were simulated 35 times per system. The results indicate that harwarders have substantial pote...

Spatially explicit assessment of roundwood and logging residues availability and costs for the EU28

ABSTRACT Competition for woody biomass between material and energy uses is expected to further increase in the future, due to the limited availability of forest resources and increasing demand of wood for material and bioenergy. Currently, methodological approaches for modeling wood production and delivery costs from forest to industrial gates are missing. This study combines forest engineering, geographically explicit information, environmental constraints and economics in a bottom-up approach to assess cost–supply curves. The estimates are based on a multitude of wood supply systems that were assigned according to geographically explicit forestry characteristics. For each harvesting and transportation system, efficiencies were modeled according to harvesting sites and main delivery hubs. The cost–supply curves for roundwood and logging residues as estimates for current time and for the future (2030) show that there are large regional differences in the potential to increase extraction in the EU28. In most EU Member States, the costs of logging residues extraction increase exponentially already for low levels of mobilization, while extraction of roundwood can be increased to a larger extent within reasonable costs (30–40 

Human, technology, organization and environment – a human factors perspective on performance in forest harvesting

/m3). The large differences between countries in their harvest potential highlight the importance of spatially explicit analyses.

Cable yarding productivity models: a systematic review over the period 2000–2011

ABSTRACT In recent years, concern has been raised that the trend of continuous productivity improvements of forest harvesting has stagnated and even declined in the Nordics. This selective literature review therefore examines human factors research with regard to the performance of the harvesting system, and outlines how human factors research can stimulate continued performance improvements. The focus is on implications for mechanized cut-to-length (CTL) operations and, especially, research of importance to the operation of the single grip harvester and the harvester-forwarder system. Most literature for this review was found in the Web of Knowledge and Google Scholar databases or as a consequence of the snowballing approach also applied. A conceptual framework was used to facilitate the analysis of the interrelated elements – Human, Technology, Organization and Environment (HTO-E). The right abilities, skills, techniques and training alone are not sufficient for ensuring high performance of the logging system. To address this discrepancy, education, training, (semi-) automation, shift scheduling, harvester-forwarder cooperation, inter- and intra- organizational knowledge exchange were all recognized as important areas for improvement and development. Great difficulties exist in predicting outcomes when introducing change, for example automation, into a system. However, the consequences of not trying may be detrimental to productivity as well as safety in mechanized forestry. Thus, it is important to research into methods, interfaces, forms of interaction, risk analyses and automation technology. HTO-E and a systems perspective provide a good basis for understanding the work today and making educated predictions for the future.

Examining the gaze behaviors of harvester operators: an eye-tracking study

ABSTRACT The efficiency of cable-based yarding systems has been studied extensively, resulting in numerous work productivity models (i.e. models predicting the ratio between output and time). Productivity models are used in both research and operations management, but are laborious to develop. Efficient use of existing models is essential, but there is a lack of overviews of available models. Therefore, work productivity models developed in recent years were compiled, with the aim of increasing their visibility, accessibility and comparability to potential users and other interested parties. This compilation should facilitate comparisons and evaluations of the models and their influential parameters, and the synthesis of existing models. A systematic review of the international scientific literature on cable logging published between 2000 and 2011 was performed. Twenty-one publications describing productivity models were identified. These publications originated from four different continents, with most coming from Asia (specifically, Turkey). Many similarities were found between the models. For instance, more than half use yarding distance as an independent variable, whereas lateral yarding distance and load characteristics were used in only a third of the models. However, there were also many differences in terms of modeling praxis, model features, included parameters and the units used. Analysis of the compiled models suggests some potentially fruitful directions for future work in the field of cable logging productivity. More generally, model compilations such as that presented herein enable a range of analyses and harmonizations that benefit all kinds of forest operations.

Automatic load level follow-up of forwarders' fuel and time consumption

In forest harvesting, operators must visually monitor the terrain, machinery, the stand and the trees they are cutting in order to plan, evaluate and adjust their tasks. To exploit increasing opportunities to automate these tasks and create decision support systems it is essential to understand not only what forestry workers do, but also what they look at and why they focus on specific aspects during specific tasks. This knowledge may also aid operator training and knowledge transfer between age and experience groups. Eye-tracking (ET) is therefore a potentially valuable technique that may facilitate both extraction of implicit knowledge and elucidation of operators’ information acquisition strategies. However, real world ET-recordings are sensitive to environmental variations and analyzing them is time consuming. Thus, the aims of this study were to examine the utility of a head-mounted eye-tracking system in forest harvesting machines in a natural setting and obtain information on operators’ visual behavior (gaze patterns) during harvesting. The output from the eye-tracker was affected by large head movements, changes in illumination and (possibly) vibrations. The gaze pattern analysis revealed that the operators looked at the harvester head or forest most of the time, but their gaze behaviors varied during different harvesting operations. They looked at the monitor, canopy and falling trees less frequently during first thinning than during second thinning and final felling. The results suggest that some harvesting information is gathered in advance to get an overview and plan the work, but most eye movements closely follow actions.

Seated postural neck and trunk reactions to sideways perturbations with or without a cognitive task

ABSTRACT Automatic collection of forwarding follow-up data has recently become possible. The objective of this study was to obtain representative values of fuel consumption for large forwarders in final felling operations. Since fuel consumption is dependent on time consumption, speed, and total driven distance, these variables were also included in the study. The study explored data collected and presented by John Deere forwarders’ conventional on-board computers (TimberLink). Nine operators forwarded 15,329 loads, in total, at sites with representative terrain conditions for large parts of mid-Sweden. A limitation with the used dataset was that load-sizes (e.g. volume or mass) were not available. The median driven distance was 670 m/load, and median total fuel consumption was 8.5 l/load or 12.4 l/km. Typically, Driving only and Crane work only accounted for most of the fuel consumption (50 and 40%, respectively). Median forwarding time was 43.1 minutes/load at average speeds of 2.2–3.3 km/h. Fuel consumption, time consumption and total driven distance were clearly correlated. Standard TimberLink data were found to be intuitively logical and to provide results consistent with current literature. It enabled gathering of high resolution fuel consumption data during whole years of work. However, elucidating main and interactive effects of predictive variables and operator behavior on fuel and time consumptions is challenging, and requires more detailed information about loads (e.g. volumes and numbers of assortments) and stand conditions (e.g. log concentrations and terrain conditions) than provided in this study.

Adaptation of Postural Reactions in Seated Positions and Influence of Head Posture when Exposed to a Single Sideway Perturbation: Relevance for Driving on Irregular Terrain

Driving on irregular terrain will expose the driver to sideways mechanical shocks or perturbations that may cause musculoskeletal problems. How a cognitive task, imposed on the driver, affects seated postural reactions during perturbations is unknown. The aim of the present study was to investigate seated postural reactions in the neck and trunk among healthy adults exposed to sideways perturbations with or without a cognitive task. Twenty-three healthy male subjects aged 19-36 years, were seated on a chair mounted on a motion system and randomly exposed to 20 sideways perturbations (at two peak accelerations 5.1 or 13.2m/s(2)) in two conditions: counting backwards or not. Kinematics were recorded for upper body segments using inertial measurement units attached to the body and electromyography (EMG) was recorded for four muscles bilaterally in the neck and trunk. Angular displacements (head, neck, trunk and pelvis) in the frontal plane, and EMG amplitude (normalised to maximum voluntary contractions, MVC) were analysed. The cognitive task provoked significantly larger angular displacements of the head, neck and trunk and significantly increased EMG mean amplitudes in the upper neck during deceleration, although 10% of MVC was never exceeded. A cognitive task seems to affect musculoskeletal reactions when exposed to sideways perturbations in a seated position.