INFLUENCE OF PUMP PRESSURE AND ENGINE SPEED ON ERGONOMIC PARAMETERS OF FORWARDER OPERATORS

Reducing engine speed and pressure of forest machine hydraulic pumps may be a strategy to achieve a reduction in fuel costs. However, this approach can positively or negatively aff ect the ergonomic parameters of the operators, in particular, the whole-body vibration and repetitive movements of the operators. The objective of this research was to evaluate the acceleration force resulting from normalized exposure (Aren) and the Real Occupancy Rate and Maximum Occupancy Rate considering Repetitive Activities (RORMORCRA) of forwarder operating at diff erent pump pressures, engine speed, and volume of trees. The research was carried out in forest stands with an individual average volume of 0.10, 0.14, and 0.29 m3 tree. For each volume, the machine was confi gured to operate at hydraulic pump pressures of 240, 235, and 230 bar and engine speed of 1550, 1475, and 1400 rpm, totaling 9 combinations. The values were measured in the 9 combinations and also in each phase of the machine operational cycle, using a triaxial accelerometer of the 01dB brand, model Vib 008. To determine ROR, percentage of rest due to regular breaks, percentage of time with low demand activities, percentage of usual irregular breaks, and percentage of very short breaks were calculated. To estimate MORCRA, the repetition, strength, and static eff ort factors were calculated. In volumes of 0.10, 0.14, and 0.29 m3 tree, the highest Aren values were 0.82, 0.88, and 0.99 m s, respectively, being obtained at the 1550 rpm engine speed. The forwarder logging operation is characterized as an ergonomic risk, which can cause discomfort, fatigue, and injuries to operators.


1.INTRODUCTION
The forwarder is a self-loading forestry tractor used in the extraction of wood from the felling site to the roadsides or intermediate yard. Among the wood extraction machines, the forwarder provides the best ergonomic conditions for operators (Gerasimov and Sokolov, 2014). Despite the advantages of the forwarder operation, it has a high operating cost, and fuel is the fourth greatest expense, representing about 14% of the total cost (Santos et al., 2016;Robert et al., 2018). Reducing engine speed and hydraulic pump pressure is an alternative that has been used to reduce the hourly fuel consumption of machines and consequently the overall cost (Prinz et al., 2018;Santos et al., 2018).
All functions of the forwarder, such as the driving the hydraulic crane, crane claw, and movement of the machine, are operated with electronic handles that require diff erent competencies and skills from the operators. Thus, changes in engine and hydraulic pump settings can aff ect operator ergonomic factors, as they already suff er from occupational diseases. The forwarder operation is known to cause Repetitive Strain Injury and can also cause nervousness and irritation (Silva et al., 2013). Also, forwarder operators are exposed to wholebody vibration values of 1.69 m s -2 , and preventive measures are required to reduce the vibration values (Rehn at al., 2005).
Occupational diseases in forest machine operators occur because, during operation, workers sit for long periods in ergonomically inadequate positions, are exposed to full-body vibration, and perform repetitive short cycle movements (Gerasimov and Sokolov, 2014). Exposure to whole-body vibration has been identifi ed as a cause of musculoskeletal disorders, such as low back pain and herniated discs (Osborne et al., 2012). Despite all the technology used in forest harvesting machines, the levels of exposure to vibrations are over the limits recommended by the relevant standards (Almeida et al., 2015).
Based on the above, the objective of this research was to evaluate the acceleration force value resulting from normalized exposure and the Index of Real Occupancy Rate and Maximum Occupancy Rate Considering Repetitive Activities of the forwarder operating at diff erent engine speeds, hydraulic pump pressure, and volume of trees.

2.1.Study area
The research was carried out in Brazil in the municipality of Nova Viçosa -BA. The region has an average annual temperature of 24.4° C and an average annual rainfall of 1350 mm. The area had a fl at relief, populated with hybrid clones of Eucalyptus grandis x Eucalyptus urophylla, planted at a distance of 4 meters between rows and 2.5 meters between plants. The evaluations were conducted during the day, starting at 06h00 and ending at 15h00.

2.2.Harvesting system
The research was carried out in a cut-to-length forest harvesting system composed of harvester and forwarder machines. The harvester carried out the cutting and processing trees, leaving 6.20 m long logs on the soil surface. The machine simultaneously felled four tree lines. The forwarder carried out the extraction of wood starting from the interior of the fi elds and worked towards to the roadsides.

2.3.Experimental units
The research was carried out at volumes of 0.10, 0.14, and 0.29 m³ tree -1 . In each volume, the forwarder was confi gured to operate with a hydraulic pump pressure of 240, 235, and 230 bar and at engine speeds of 1550, 1475, and 1400 rpm, totaling 9 treatments and with 4 repetitions each. One repetition was equivalent to a work shift, that is, 7.4 hours of eff ective work. The company where the research was carried out used the machine with a pump pressure of 240 bar and engine speed of 1400 rpm, which was the standard confi guration.

2.4.Machine used
The Komatsu model 895 forwarder was used. The machine was equipped with the 6-cylinder AGCO power 74CW3 engine with 193 kW of power at 1950 rpm. The hydraulic system consisted of a hydraulic piston pump with a maximum fl ow of 360 liters per minute at 2000 rpm and a maximum working pressure of 24.5 MPa.

2.5.Determination of individual tree volume
The individual average volume (IAV) was determined using the diameter and length sensors on the harvester head. Subsequently, the VMI was calculated by the MaxiXplorer machine operating system. The length sensor was positioned on the head feed rollers, and the diameter sensor was positioned on the delimbing knives of the head. The sensors were calibrated before the research was carried out.

2.6.Hydraulic pump pressure selection
The forwarder hydraulic pump was confi gured to pressures of 240, 235, and 230 bar. Values were obtained by manually adjusting the hydraulic pump. Hydraulic circuit pressure values were instantly displayed on the machine monitor through the MaxiXplorer operating system.

2.7.Engine speed selection
The forwarder was programmed to work at engine speeds of 1550, 1475, and 1400 rpm. The values were selected by the operator and controlled by the MaxiXplorer Control and Information System.

2.8.Assessment whole-body vibration
The whole-body vibration values were measured according to the technical recommendations established by the Occupational Hygiene Standard 09 (FUNDACENTRO, 2013). The measurements were taken with a triaxial accelerometer from the manufacturer 01dB, model Vib 008. The device was fi xed to the operator seat and positioned according to the three directions of the orthogonal coordinate system (x, y, and z). The acceleration force values resulting from normalized exposure (Aren) were measured for all the three volumes surveyed and in all combinations of pump pressure and engine speed. The Aren values were also measured at each stage that make up the forwarder operating cycle.
To account for the Aren values per operation, a video system was installed in the operator cabin. The timing of the video system was adjusted in relation to the time of the accelerometer. The forwarder operational cycle was divided into the following steps: empty travel, loading, loaded travel, and unloading. The data were processed using the dBMaestro 5.5 software.

2.9.Real Occupancy Rate (ROR) -Maximum Occupancy Rate Considering Repetitive Activities (MORCRA)
The potential of the forwarder operation to cause disorders such as fatigue, discomfort, diffi culties, and injuries was quantifi ed through the ROR (Real Occupancy Rate) -MORCRA (Maximum Occupancy Rate Considering Repetitive Activities) index (Couto, 2012). ROR was calculated using Equation 1. To determine the PRB, all short breaks times were quantifi ed (ret, bathroom breaks, smoking, stretching). Regarding the PTDA, the time spent on inspection of the machine at the beginning of the workday and cleaning and organization of the machine at the end of the workday was measured. To account for the time spent with very short breaks during the work, a video system was installed in the operator cabin. The video system consisted of four video cameras, a seven-inch monitor, and a Mobile Digital Video Recorder (MVDR). The fi rst camera was aimed at the left and right joystick, the second at the operator head, the third at the cargo box, and the fourth at the right side of the forwarder. Videos of 13 forwarder operating cycles were recorded in each combination with pump pressure and engine speed. Subsequently, the recorded content was analyzed to determine if there were very short pauses between cycles or within the cycle. Only short breaks with intervals of at least three seconds were considered.
The Maximum Occupancy Rate Considering Repetitive Activities was calculated according to Equation 2.
The repeatability, strength, and static eff ort factors were determined according to fl owcharts and tables (Couto, 2012). To facilitate the study of repetitiveness, the components and the respective functions, triggered by the forwarder operators (Table 1), were identifi ed.
At the beginning, middle, and end of the workday, operators answered a questionnaire in order to identify the occurrence or absence of fatigue caused by the operation (Couto, 2012).

2.10.Data analysis
The acceleration force value data resulting from normalized exposure with respect to combinations of pump pressure and engine speed within each volume were analyzed using a response surface methodology. The models were selected based on the determination coeffi cient, behavior of the phenomenon under study, and the signifi cance of the regression coeffi cients, using the Student's t-test and adopting the 5% probability level.
The acceleration force values resulting from normalized exposure per operation performed on the three volumes studied were analyzed using Analysis of Variance and compared by the Tukey test when signifi cant at the level of 5% probability. A completely randomized design (CRD) was adopted in a 3x4 factorial scheme, with three volumes of wood, and four phases of the machine's operational cycle, totaling 12 treatments with 4 repetitions each.

3.1.Full-body vibration
There was no signifi cant eff ect of the pump pressure on the Aren values in any of the studied wood volumes. The engine speed had a signifi cant, linear, and positive infl uence on the Aren values in all studied volumes (Figure 1). In volumes of 0.10, 0.14, and 0.29 m³ tree -1 , the highest Aren values were 0.82, 0.88, and 0.99 m s -2 , respectively, and there were obtained at the engine speed of 1550 rpm. At volumes of 0.10, 0.14, and 0.29 m³ tree -1 , the 10 rpm increase in engine speed caused an increase of 0.021, 0.008, and 0.008 m s -2 in the Aren values, respectively.
The acceleration force values resulting from the normalized exposure of the loading and loaded travel operations suff ered a signifi cant eff ect from the volume of trees, and in the other operations, there was no signifi cant eff ect ( Table 2). The Aren values also suff ered a signifi cant eff ect on the type of operation performed by the machine, observing the highest values for empty travel operation.

3.2.ROR-MORCRA index
There were no signifi cant diff erences between the values of the Real Occupancy Rate (ROR) and the Maximum Occupancy Rate considering repetitive activities (MORCRA) in the three volumes studied ( Table 3). The ROR-MORCRA values were the same in the 9 combinations of pump pressure and engine speed. During the execution of the research, there were no habitual irregular breaks, very short breaks, and force factors observed. MORCRA was 12.58, 10.96, 10.75% lower than ROR at volumes of 0.10, 0.14, and 0.29 m³ tree -1 , respectively. Thus, the forwarder wood extraction operation is characterized as an ergonomic risk, which can cause discomfort, fatigue, and injuries to operators. The reduction in pump pressure and engine speed did not intensify the occurrence of occupational diseases in operators. Table 4 presents the movements performed by the operator during the working day in the three volumes studied, as well as in the various combinations of pump pressure and engine speed. The forwarder operation is characterized as repetitive with simultaneous movements of the hands, wrists, and fi ngers; however, these are minmal.  Where: A = volume of 0.10 m³ tree -1 ; B = volume of 0.14 m³ tree -1 ; C = volume of 0.29 m³ tree -1 ; ** = signifi cant at the 1% probability level; ns = not signifi cant; and R² = coeffi cient of determination. Figura 1 -Superfície de resposta e Equação ajustada da Aceleração resultante de exposição normalizada (Aren) em função da pressão da bomba (PB) e rotação do motor (RM). Onde: A = volume de 0,10 m³ árvore-1; B = volume de 0,14 m³ árvore-1 C = volume de 0,29 m³ árvore -1 ; ** = signifi cativo ao nível de 1% de probabilidade; ns = não signifi cativo; e R² = coefi ciente de determinação.

4.1.Full-body vibration
The acceleration force values resulting from normalized exposure did not exceed the limit value for the 8-hour working day in all scenarios studied (FUNDACENTRO, 2013;ISO 2631ISO -1, 1997. However, at the low and medium tree volumes, the values are above the threshold, requiring the adoption of preventive measures. At the greatest volume studied, the Aren values are in a range of uncertainty, requiring the adoption of both preventive and corrective measures. Preventive measures that can be adopted include: reduction of engine speed, an increase of regular breaks during the working day, and change of the machine suspension from the bogie type to the pendulum type system. Bogie suspension systems are the most effi cient for forestry machines and can reduce vibration levels by up to 50% (Ismoilov et al., 2015).
In research carried out with diff erent types forwarders, an average Aren value of 0.70 m s -2 was observed. These values were lower than that observed in the current research, whtich resuled from diff erences in operating conditions and machines used in the research (Marzano et al., 2017). The forwarder vibration values are infl uenced by the diff erent models of the machines and operators (Rehn et al., 2005).
At the volume of 0.29 m³ tree -1 , the Aren value of the loading operation was statistically higher than the values of the other operations at the same volume. The result is justifi ed because during loading, some logs were released at a certain distance from the surface of the cargo box, causing a larger impact. Larger volume logs are heavier, and therefore, they caused greater impacts on the cargo box and, consequently, higher Aren values were transmitted to operators. At the volume of 0.29 m³ tree -1 , the Aren value of the loaded travel operation was statically lower than the others of the same volume. It is possible that the heavier wood acted as a ballast, thus providing more stability to the machine and reduced the Aren values.
The higher values for full-body vibration during empty travel operation are due to the machine travel speed, which was 1.59 m s -1 . Additionally, the machine carried out the displacement on uneven soil surface, given the presence of stumps and stones. The statistically lower aren values for the unloading operation, on the other hand, are attributed to performing the operation while the machine is parked and without sudden movements. In another research, the highest Aren values, in decreasing order, were obtained for operations, such as empty travel, loaded travel, loading, and unloading (Rehn et al., 2005). Similar results to the current research have been previously reported, despite the diff erences in the type and characteristics of the soil, machine, operator, travel speed, extraction distance, and tree volume.

4.2.ROR-MORCRA INDEX
From these results, it became evident that it is necessary to increase breaks during the work day in order to provide a reduction in ROR and an increase in Table 2 -Acceleration force values per operation resulting from normalized exposure (Aren) of the forwarder in the surveyed volumes. Tabela 2 -Valores, por operação, de aceleração resultante de exposição normalizada (Aren) do forwader nos volumes pesquisados.
Means followed by the same letter, uppercase in the columns and lowercase in the rows, do not diff er between each other by the Tukey test at the 99% probability level.
Médias seguidas pela mesma letra, maiúsculas nas colunas e minúsculas nas linhas, não diferem entre se pelo teste de Tukey ao nível de 99% de probabilidade.   MORCRA. Such measures can reduce the occurrence of occupational diseases in operators. Forest machine operators are susceptible to neck, arm, and cervical spine injuries, all caused by the excessive strain during work, staying in ergonomically incorrect fi xed positions for a long time, and due to repetitive short cycle movements (Gerasimov and Sokolov, 2014). Also, the prevalence of discomfort and pain in forest machine operators may be related to organizational factors (Østensvik et al., 2008).
The reduction of pump pressure and engine speed did not intensify the occurrence of occupational diseases. However, the hydraulic crane and gripper movements became more diffi cult to controll when the machine was confi gured to operate at the engine speed of 1550 rpm, regardless of the pump pressure, as it became more powerful and aggressive. During the execution of the research, it was evident that operators were not used to such rotation, and it can have either a negative or positive eff ect on the operator ergonomics and productivity in the long term.
At the smallest volume studied, these extraction processes were repeated more times to completely fi ll the machine cargo box, due to the greater number of wooden bundles necessary. The right joystick was the command most used by the operator in all scenarios studied. The result is justifi ed because this component had the function of activating the hydraulic cylinder that made it possible to raise and lower (vertical movement) the hydraulic crane and also to activate the hydraulic rotator that controlled the rotational movement of the gripper. The second most used component was the left joystick, which was used to drive the hydraulic cylinder that corresponded to the extension and contraction of the hydraulic crane, in addition to the mechanism that promoted the rotational movement of the hydraulic crane. Both joysticks were hand controlled by the Table 4 -Number of times, per shift, that the operator activated the machine commands in all the scenarios surveyed. Tabela 4 -Número de vezes, por turno, que o operador acionava os comandos da máquina em todos os cenários pesquisados.

Volume
Hydraulic pump Engine speed Command (m³ tree -1 ) pressure (bar) (rpm) A B C D E F 240 operators, requiring vertical and horizontal movements of the handles. From the results, it appears that the forwarder operation is characterized as repetitive, with simple simultaneous movements of hands, wrists, and fi ngers. These results corroborate those found in another study, in which 90% of workers considered the operation to be repetitive (Silva et al., 2013).

5.CONCLUSIONS
The Aren values of the forwarder operation do not exceed the limit for the eight-hour working day; however, it is necessary to adopt preventive measures. The increase in the volume of the wood and the engine speed causes a signifi cant increase in the Aren values. The empty travel operation exposes operators to the highest magnitudes of full-body vibration.
The forwarder operation was characterized as repetitive, requiring simple, simultaneous movements of the hands, wrists, and fi ngers. Besides, it is an ergonomic risk operation, which can cause occupational diseases, such as fatigue, physical, and mental tiredness, compromising operator productivity and also resulting in pain in the arm, wrist, and hands on both left and right side. However, the reduction in pump pressure and engine speed did not intensify the occurrence of occupational diseases in forwarder operators.

6.ACKNOWLEDGMENTS
This study was fi nanced in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES) -Finance Code 001 and Conselho Nacional de Desenvolvimento Científi co e Tecnológico (CNPq).