Influence of forest machine operator work practices and operator assistance systems on the efficiency of fully mechanized timber harvesting systems
by Florian Hartsch
Date of Examination:2023-10-06
Date of issue:2023-12-01
Advisor:Prof. Dr. Dirk Jaeger
Referee:Prof. Dr. Dirk Jaeger
Referee:Prof. Dr. Carola Paul
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Abstract
English
Introduction: Fully mechanized harvesting systems consisting of harvesters and forwarders represent state-of-the-art technology within modern timber harvesting operations. The droughts of the past years, consecutive bark beetle infestations and associated large-scale dieback of forests, especially of pure Norway spruce (Picea abies) stands, have once again shown that fully mechanized timber harvesting is well suited in the forestry sector due to high productivity and high occupational safety. Harvesters fell trees, process them according to bucking instructions and place the logs along machine operating trails. Forwarders load the logs, separated by assortment, and transport them to the landing. Due to the complexity and heterogeneity of forest areas, various factors affect the productivity of these harvesting systems. In particular, stand and assortment parameters, terrain-related aspects, machine performance and -payload, and organizational aspects determine productivity, as well as environmental impacts, and the quality of timber harvesting. Research of recent years has shown that the forest machine operator in particular has considerable influence on these parameters. Experience and cognitive ability play an important role in terms of the "performance" of large machines. Forest machine operators work under high cognitive strain. Furthermore, work practices play a significant role in the economic performance as well as the ecological impact and the acceptance of fully mechanized timber harvesting within the population. Work practices characterize the individual execution of work methods, e.g., different crane operation mannerisms. These work practices can also have a negative impact on timber harvesting operations. To support the machine operator at work, guarantee productivity, and to ensure high work quality, assistance systems such as boom-tip controls and rotating cabins have become commonplace on the market in recent years. The analysis of the interactions between work practices and operator assistance represents the core part of the present work. Work practices seem to have a decisive influence on the economic and ecological performance within timber harvesting. These work practices remain largely undefined and unknown in terms of their characteristics and effects in the context of forest machine operations. The performance of the forwarder operator is especially critical to the overall productivity of fully mechanized timber harvesting systems. Taking a deeper look at forwarding activities, the loading element occupies nearly 50% of the total forwarding cycle time. However, it is unclear how forwarder operator work practices affect the time required per loading cycle. For example, depending on the precursory work of the harvester operator and the positioning of the forwarder thereafter, different loading distances, loading angles, and log orientation angles result. Furthermore, it remains unclear to what extent machine operator assistance can reduce the forwarder’s loading cycle time. Therefore, the present work pursued the following objectives: Firstly, to define and quantify positive and negative work practices in the context of fully mechanized timber harvesting. Secondly, to quantify the effects of different loading distances, loading angles, and log orientation angles, partly resulting from the harvester's precursory work, on the forwarder’s loading cycle time consumption. Thirdly, to investigate the effects of the use of forest machine operator assistance systems on the time consumption per loading cycle of forwarders. Methods Paper I: To achieve the research objectives, a multi-stage approach was chosen comprising three different studies reported in individual publications. Since work practices and their effects are largely unknown in the context of fully mechanized timber harvesting, a combination of literature analysis and expert interviews was performed within Paper I. The literature search followed the PRISMA approach and ultimately integrated 16 references into the analysis where evidence of positive and negative work practices was found. A semi-structured interview guide was developed as part of the expert interviews. After conducting the interviews with 15 forest machine operator instructors from Germany, Sweden and Norway, audio files were transcribed, anonymized, and analyzed using MAXQDA software. A coding system was used to assign statements relevant to the research objective. Results Paper I: The results of Paper I revealed that the work practices of forest machine operators might have a decisive influence on productivity as well as machine wear and fuel emissions within fully mechanized timber harvesting systems. The literature review showed that scientific literature only sparsely covers the analysis of forest machine operator work practices. The interviews, on the other hand, resulted in an extensive list of work practices within crane work, machine positioning, work organization, value creation, and teamwork. Therefore, work practices can be described as positive if they lead to increased productivity of both harvesters and forwarders, decreased fuel consumption and thus carbon footprint, optimized value creation through optimized harvesting, or simply improved cooperation between harvester and forwarder operators. Based on the results, “positive” work practices can be quantified as follows (excerpt): Positioning the machine within (“productive”) crane reach of as many trees to be felled (harvester) or logs to be loaded (forwarder) as possible, frequent repositioning of the machine, regular maintenance of the machine, crane speed adjustments related to personal preferences, separate positioning of logs by assortment after processing (harvester) or frequent use of the telescope during the entire crane operations. If a machine operator does not follow these and other aspects (Paper I), the work practices methods can be considered as “negative”. Methods Paper II: In Paper II, an experiment with standardized loading cycles was conducted to investigate the effects of loading distance, loading angle, and log orientation angle on time consumption of forwarder loading cycles. A professional forest machine operator was tasked with performing loading cycles on a realistic forwarder simulator at the Forest Education Center in Münchehof. To achieve a range of loading scenarios, five different loading distances (3 m, 4 m, 5 m, 6 m, 7 m) and three different loading angles (45°, 90° and 135° azimuthal to the machine axis) were tested. For each of these 15 loading positions, the log orientation angle was also varied (45°, 90° and 135° to the machine axis). These 45 test setups, with 10 repetitions each, resulted in a total of 450 loading cycles, recorded by stopwatch and video. Results Paper II: The results of the first field study, published in Paper II, showed that work practices of forest machine operators can have a significant impact on the time consumption per loading cycle of a forwarder. All tested variables (loading distance, loading angle, and log orientation angle) had a significant impact on the time required per loading cycle. Based on the results, optimal loading ranges could be identified. On the opposite, the highest time requirement for loading was observed for the distance range closest to the machine (3 m) and for the range furthest from the machine (7 m), where no significant difference between the two distance ranges could be observed. However, in medium loading distances (4-6 m), significant differences in loading time from the 3 m and 7 m loading distances were observed. The loading cycle time also increased with increasing loading angles. The lowest time requirement was observed for the 45° and 90° angles, respectively. The loading cycle duration also increased with increasing log orientation angle. Compared to the reference replicate, significant increases in loading cycle time of up to 75% were observed when the machine operator loaded logs from close to the machine (3 m), at a 135° loading angle and a log orientation angle of 90°. Methods Paper III: In Paper III, the methodology of Paper II was adapted and supplemented. The machine type and the machine operator were changed, the loading angles (55°, 90° and 125° to the machine axis) and loading distances (4 m, 5.5 m, 7 m, 8.5 m, 10 m) were adapted. Since the effect of machine operator assistance (boom-tip control, "IBC" and John Deere rotating cab) on time consumption per loading cycle was studied, the 15 loading positions were tested, but with four variants: 1. IBC and rotating cabin deactivated; 2. IBC deactivated and rotating cabin activated; 3. IBC activated and rotating cabin deactivated; 4. IBC and rotating cabin activated. A total of 60 sub-variants were tested in 10 repetitions each, which resulted in a total of 600 loading cycles. Results Paper III: The results of Paper III revealed that rotating cabins alone did not significantly reduce time consumption per loading cycle for a forwarder. Boom-tip controls, on the other hand, significantly reduced loading cycle time. When crane tip controls and rotating cabs were both activated, time consumption per loading cycle was significantly reduced by up to 14%. The effects of these assistance systems were mainly evident within medium loading distance (5.5-8.5 m) setups, while the effect was smaller at closer (4 m) and further loading distances (10 m). The shortest time consumption per loading cycle was achieved at 4 m loading distance, at a 55° loading angle, using boom-tip control and rotating cabin assistance. Compared to this variant, the time consumption per loading cycle increased significantly, by up to 66%, when working at a loading distance of 10 m, at a 55° loading angle, with boom-tip control and rotating cabin deactivated. General discussion: The results of Paper I showed that work practices of forest machine operators and also their productivity (measured via time consumption per loading cycle within the present studies) were closely linked. Due to the limited sample size, the insights provided into work practices of forest machine operators cannot represent the working behavior of the full population of forest machine operators in Germany and Scandinavia. However, expert interviews offered reasonable insight into the work practices of machine operators working in Germany and Scandinavia. Due to the competence of the interviewees to communicate interview responses proficiently, many years of experience and the high number of trained and educated operators, it can be assumed that the identified work practices also play a significant role in practice. Above all, the literature analysis showed that work practices in forest science have only been sparsely characterized. An investigation into work practices and their effects on different aspects within the cooperation between harvester and forwarder operator is strongly recommended. Related to this aspect, the results of Paper II showed a statistically significant effect of loading distance, loading angle, and log orientation angle on the forwarder´s time consumption per loading cycle. Preliminary studies and observations of other machine operators suggest that the observed patterns could hold true for the performance of other operators as well. Therefore, conclusions can be drawn from the results that can be used in the context of defining "best practices" within fully mechanized timber harvesting systems. Based on the results and therefore to optimize forwarder loading, a harvester operator should deposit the logs as close to the machine operating trail as possible (to reach optimal loading distances for the forwarder), at a 45° or 90° angle, and the forwarder operator should position his machine so that the loading distance is as short as possible, and the loading angle does not exceed 90°. The results can therefore also be used in forest machine operator education. In Paper III, it was observed that synergies occur when rotating cabins and boom-tip control are used simultaneously. This combination can significantly reduce the time consumption per loading cycle of a forwarder by up to 14%. Based on experience reports and observations, as well as the results of other scientific studies, it can be assumed that the results presented are in-line with practice. This shows that the use of operator assistance can have positive effects on the loading cycle duration, and thus also on productivity in fully mechanized timber harvesting. The effects of operator assistance on mental and physical strain could not be investigated. However, it seems likely that the use of boom-tip controls in particular, could reduce mental strain by eliminating the need to operate the telescope. Based on observations, a rotating cabin could lead to a reduced number of movements that are considered harmful to the upper body. Overall, it can be stated that in Central European forestry change is underway due to catastrophic events affecting the timber stock and technical innovations in the timber harvesting sphere. For reasons of productivity and occupational safety, fully mechanized timber harvesting systems have been commonplace in the timber harvesting sector for several decades now. Large-scale technical revolutions should not be expected in the coming years, which is why fully mechanized harvesting systems, which represent a significant part of the entire wood production process, will most likely to be rationalized through integrative data utilization and the use of operator assistance systems. In times of tense labor markets, it is even more important to attract and retain well-qualified and motivated specialists in forestry, including forest operations. This is not possible through attractive remuneration alone - a modern workplace that relieves the machine operator and increases job satisfaction should be part of the solution to the problem as well.
Keywords: harvester; forwarder; forest work science; forest engineering; time studies; efficiency; forestry 4.0