Forest machine automation and ergonomics

. Harvesters and forwarders are the main part of cut-to-length logging system equipment. The perfection of the hydraulic cranes has a very large impact on the overall operating efficiency of these forest machines. The impact of the crane partial automation on the operator’s work cycle and workload is described in this article. Two machines were studied in field conditions. Differences in the frequency and duration of telescopic extension boom control activations were identified. It was determined that, as a result of automation, one of the degrees of freedom of the crane controls is almost completely excluded from use in the case of the forwarder. A significant reduction in the duration of its use is observed in the case of the harvester. As a result, this saves the psycho-physiological resources of the operator for more efficient use of the remaining degrees of freedom, which, coupled with a simpler and more intuitive logic of the controls operation, improves the productivity, accuracy and safety of cut-to-length logging. In addition, a simpler work algorithm reduces the level of stereotyping of the operator’s actions, fatigue and loss of attention, which usually emerge at the end of the shift. This work was supported by the Russian Federation Ministry of Science and Higher Education (state research target, theme no. 075-03-2023-128).


Introduction
The main technology currently used in wood harvesting is the Nordic cut-to-length logging system based on the use of harvesters and forwarders (Piskunov, 2020(Piskunov, , 2021. The harvester is a multi-operational machine that performs felling of a tree, dragging it to the forwarding trail, limbing, measuring the length and crosscutting into separate log assortments. The forwarder is a terrain transport machine with the main task of collecting the harvested assortments and transporting them to the loading area located near the forest road. A big advantage of modern multi-operational machines is the revolutionary improvement of the operator's working place comfort. Before the introduction of modern multi-operational machines, the working conditions of logging workers were unsafe and uncomfortable (Attebrant et al., 1997;Gerasimov and Sokolov, 2014;Østensvik et al., 2008). The work was often carried out outdoors, exposed to a full range of weather factors that varied greatly from season to season. Now the comfort of harvesters and forwarders is at the same level as the latest passenger cars. On the other hand, the algorithmic complexity of the operators' work cycle, as well as the monotony of work, has increased significantly (Gellerstedt, 2002). This often leads to a fast fatigue increment and, as a result, to a decrease in the working capacity and labour productivity. In addition, operators often experience some psychological impact associated with being alone in the forest for long periods of time, especially during the night shift (Gellerstedt, 2003;Häggström and Lindroos, 2016). Thus, any actions aimed at the reduction of forest machine operators' work severity are important not only in terms of productivity, but also in terms of the worker's safety and health. In addition, it can increase the attractiveness of the forest machine operator profession. Important aspect is the predictable reduction of the operator's workload by automating some functions. This effect is important and certainly should be analysed from the ergonomic point of view.
An analysis of the impact of the John Deere crane partial automation option "Intelligent Boom Control" (IBC) on the work cycle and workload of forest machines operators will be described in this article.

Material and methods
The approach to the partial automation currently implemented by leading forest machine manufacturers such as John Deere and Ponsse is called "Boom-tip control" (BTC) (Löfgren and Wikander, 2009;Manner et al. 2017Manner et al. , 2019. When using the conventional control system without automation (Conventional Boom Control (CBC)) the operator controls each movement of the crane separately. Most often, the cranes of both harvesters and forwarders consist of a slewing pillar, first boom, second boom and telescopic extension boom (Fig. 1). The pillar can be rotated around a vertical axis, the first boom is connected through a hinge with the pillar, and the second boom has a hinge with the first boom. The first and second booms rotate around horizontal axes. The extension boom can extend and retract, changing the overall outreach. The main controls of the forest crane are two joysticks. Each of the joysticks has an additional two-position rocker switch (Fig. 2). This article describes the results of a study of the BTC operation on the example of John Deere machines equipped with Intelligent Boom Control (IBC) (John Deere, 2022). This system changes the control logic. As a result, control becomes simpler and more intuitive. In addition, there is theoretically no need to use the left rocker switch that controls the extension boom.
The case study was carried out in the field. Two machines equipped with IBC systems were studied: John Deere 1270G harvester (operating weight 20,650 kg; engine power 190 kW; wheel arrangement 6x6; crane CH 710; harvester head H480C) (Fig. 3); and John Deere 1510G forwarder (operating weight 18,230 kg; engine power 164 kW; wheel arrangement 8x8; crane CF 710; grapple FX-26 (LogLift)) ( Fig. 1). Field studies were carried out in August 2021 in the Muezersky district of the Republic of Karelia of the Russian Federation (Fig. 4). Clear-cutting was carried out in a cutting area with a typical Karelian mixed pinespruce stand. Relatively new logging machines with an operating time of about 5.4 thousand motor-hours were studied.
Professional operators constantly working on these machines were involved in the research. The harvester operator had 10 years' experience and the forwarder operator had worked on similar machines for 18 years. To exclude the influence of the technical condition of the equipment, before starting the research the cranes of both machines were checked and adjusted in accordance with the manufacturer's specifications with the participation of an independent John Deere dealer technical support and training instructor.
Video recording in the cab of the machines was chosen as a method of collecting information about the operator's work cycle. After that, a laboratory chronometric analysis of the received video recordings was performed. As noted above, the use of IBC has the greatest impact on the function of extending and retracting the extension boom up to the full automation of these movements. This should probably significantly reduce the frequency or completely eliminate the use of the corresponding control-rocker switch on the left joystick. The remaining controls continue to be used with almost unaltered intensity. For this reason, this study was entirely devoted to comparing the parameters of using the extension boom rocker switch with and without the IBC system.
Observation and video recording of the operators' work were carried out in constant natural and production conditions at the same harvesting site. At first, the operators worked without the IBC system. The recording time was under 1 hour for the harvester. For the forwarder the recording was carried out during one cycle, including loading, moving with a load and unloading. The recording was repeated after the IBC was activated for the same time (cycle) for each machine.

Harvester
Video recordings lasting 37 minutes 36 sec. for the harvester with the deactivated IBC system and 60 min. 9 sec. for the harvester with the activated IBC system were accepted for analysis after removing the fragments related to the initial and final operations, as well as the time of short-term operational stops.
200 activations of the extension boom rocker switch were recorded throughout the entire video recording (37 min. 36 sec.) for the harvester without the IBC system. The number of activations was 246 in 60 min. 9 sec. in the case of the harvester with IBC.
The overall results of analysis are contained in Table 1. In general, it shows that the use of the IBC system significantly reduces the required frequency and duration of use of the extension boom control. The average frequency of use of the rocker switch on the left joystick decreased by 24.4% from 5.41 to 4.09 clicks per minute, the average duration of a single press was reduced by almost a third (31.4%), and the total duration of all presses that occurred within an hour almost halved (by 47.8%) from 6.38 min. to 3.33 min. On the other hand, the

Forwarder
Video recording of the forwarder work was carried out during the cycle, which included three phases: a) collection and loading of assortments at the harvesting site; b) moving with a load; c) unloading. The time of moving with a load was excluded from consideration. Thus, for the forwarder without IBC, fragments with a duration of 26 min. 27 sec. on loading and 11 min. 47 sec. on unloading were accepted for analysis. For the forwarder with the IBC system, the duration of these fragments was 29 min. 12 sec. on loading and 14 min. 01 sec. on unloading. Note that loading and unloading in each case belong to the same run.
224 activations of the extension boom control switch were recorded in the case of the forwarder without IBC during loading. During unloading the number of activations was 83. In the case of the forwarder with IBC, the number of activations was 32 during loading, and only 13 during unloading.
The overall results of analysis are given in Table 3. In general, it shows that the use of the IBC system in the case of the forwarder reduces the required frequency and duration of use of the extension boom control by about 10 times. The average frequency of using the rocker switch on the left joystick during loading decreased by 87.6% from 8.85 to 1.10 clicks per minute, and during unloading there was a similar decrease: by 86.8% from 7.04 to 0.93 clicks per minute. The average duration of a single press during loading decreased by almost 2 times (47.1%), while during unloading it decreased by more than two times (63.3%). The total duration of all presses occurring within an hour decreased by more than 15 times: by 93.5% from 15.22 min. to 0.99 min. on loading and by 95.2% from 11.88 min. to 0.57 min. on unloading. On the other hand, the average period between switch presses increased by almost 8 times during loading, from 6.78 sec. up to 53.09 sec. At unloading, an increase of this value was by about 7 times from 8.52 sec. up to 60.07 sec.

Discussion and conclusions
The results of this study clearly show that the use of Intelligent Boom Control (IBC) has a significant impact on the operator work cycle parameters on John Deere harvesters and forwarders. Moreover, the effect is quite different in the cases of the harvester and the forwarder. Partial automation of the crane control does not completely eliminate the need to use the extension boom rocker switch, but it reduces the time of its use to an insignificant value in the case of a forwarder and reduces it by about 2 times in the case of a harvester. The average frequency of rocker switch use is reduced in the case of a forwarder by about 8 times (Fig. 11 a), and the total duration of this control actuation is reduced by 15~20 times. a b Fig. 2. Overall results. The results are not so remarkable in the case of the harvester. The average frequency of the boom extension control use is reduced by about a quarter (Fig. 2 a) and the total duration of all presses within an hour is reduced by about 2 times. The average duration of a single switch press is reduced by about a third for the harvester, by half for the forwarder on loading, and by two thirds for the forwarder on unloading (Fig. 2 b).
It should be noted that, without the IBC system, the intensity of use of the extension boom in the case of the harvester is generally lower than in the case of the forwarder.
Thus, one of the degrees of freedom of the crane controls is almost completely excluded from use in the case of the forwarder. A significant reduction in the duration of its use is observed in the case of the harvester. As a result, this saves the psycho-physiological resources of the operator for more efficient use of the remaining degrees of freedom, which, coupled with a simpler and more intuitive logic of the controls operation, improves the productivity, accuracy and safety of cut-to-length harvesting. In addition, a simpler work algorithm reduces the level of stereotyping of the operator's actions, fatigue and loss of attention, which usually emerge at the end of the shift.
The results of this study once again confirm the importance of the use of automation and the correctness of the decision made by the leading forestry equipment manufacturers, who have chosen the principle of "Boom-tip control" (BTC) as the main one for the development of automation systems for forest machinery cranes at the current stage of technology development.