The Analysis of the New Conception Transportation Cableway System Based on the Tractor Equipment

The proportion of cableway skidding is still increasing compared to other technological and transportation ground-based ways of wood skidding which can dramatically change the quality of the environment. Wood skidding can be performed by an unconventional double-drum tractor winch powered by the wheels of the tractor rear axle. The principle of this unique tree transportation cable system with working attachment is protected by the patent. The article is focused on the description of working functions of this transportation system and the analysis of the dynamic strain of the forestry cableway system at different stages of its operating cycle. During the experiment the forces in the towing rope at different weights of tree logs and different speeds of their towing were measured and evaluated.


INTRODUCTION
Cableway skidding is one of the main ways of transporting trees in the forest during their logging [1].This system has gone through its development since its beginning enthusiastic acceptance in the 1950's, stagnation or decline in the middle of the 1960´s and the 1970´s when special forest tractors capable of operating in safe also on the slopes over 40% were wide-spread [2].A rebirth of the forest cableways was seen in the mid-1980´s when a negative impact of building the heavy road system on the forest environment began to become evident.In mountainous regions, using of air haulage by cableways and helicopters is a condition of the ecological stability of most forest ecosystem types [3].Other technological and transportation groundbased ways of skidding can dramatically change the quality of the environment.Recently, the proportion of cableway skidding has been increasing again.Perspectives of forest cableway skidding are also confirmed by establishing the specialized branch of forestry machinery.Substantial part of production costs of the tractor cableway system for skidding are costs of transmission apparatus between the output shaft of the tractor and the cable wheel or reel drums which provide the cable carriage with drive by means of the moving line [4][5][6][7][8].
In an effort to better understand the dynamic strain of the cableway system, we focused on the tractor cableway system where the forces in the towing rope at different weights of tree stems and different speeds of towing were measured and analysed during the experiment.

MATERIALS AND METHODS
The mentioned analysis has resulted in the design of a new conceptual solution of the forest cableway.The system uses wheels of the tractor driving axle with the direct drive of the main reels of the cableway.The concept of this system and the final 3D design has been created in the CAD system Creo Parametric from the PTC (Parametric Technology Corporation).
The first concept of this cableway system is shown in Figure 1.The FEM (Finite Element Method) calculations and optimization of the main frame of tree transportation cableway system have been carried out by the method of finite elements and by means of the ANSYS software (Figure 2) [9][10][11][12].
The analysis of the dynamic forces has been carried out by using multibody dynamics and motion analysis ADAMS CAE software which has shown how loads and forces are distributed throughout our mecha-nical systems (Figure 3).Using the results of this complex analysis, the unconventional cableway system has been redesigned and manufactured, as shown in Figure 3 [13][14][15].
The unconventional tree transportation cableway system cooperates with the working attachment driven by the rope of this system.The equipment allows turning on fast and turning off the towed tree log automatically.
The designed solution of the tree transportation cableway system in Figure 4 cooperating with the working attachment shown in Figure 5 is protected by the patents No. 280 350 and 285 564 at the Industrial Property Office of the Slovak Republic.
The unconventional winch system consists of two single-drum winches attached functionally to two wheels of the rear driving axle.Each winch is made up of the telescopic shaft fixed to the tractor wheel hub.The telescopic shaft is placed in the bearing house which is fixed to the pivoted arm.The rope of the winch is guided from the winch drum through the guide pulley.The wheels of the rear axle are lifted by the straight hydraulic engine over the terrain up to such a height that they can freely rotate.In this position, the tractor stands on two front wheels and on the rear shield.The rope is reeled to the drum with the locked claw clutch and shifted differential lock.After having skidded logs to the shield the claw clutch is turned off and at the same time the rope is closed by the lock.Thus, the rope is ensured against pulling out during dragging the logs by the tractor travel.The main advantage of the solution compared to those existing ones is the fact that transmissions of the base machine are used between the tractor engine and reel drums and thus corresponding to the results of the carried out value analysis the production costs of the most expensive constructional node of the given equipment will be significantly reduced.
The theoretical and practical bases for the results were the experimental tests carried out on a prototype of the unconventional tree transportation cableway system.The tests were performed in the Educational, training and research centre of the Technical University in Zvolen, which covers all forestry activities, assessing wood and the environment, processing wood in the enterprise's own facilities and others.During the tests the main loads of the equipment were measured.The main load force was measured by means of the tensometric dynamometer.
The operation principle of the cableway system during of the measurement is shown in Figure 6 and the scheme of all measured load forces is illustrated in Figure 7. Details are available in [16][17][18][19][20].
The aim of the paper was to experimentally test the functionality of the designed cableway system.The tests focused on experimental establishing the size of pulling forces in the pull and haul-back ropes using different weights of logs and different speed of their skidding in particular phases of the cableway operating cycle.The experimental measurements were carried out on the logs towed on the slope inclined at ~ 30˚.We measured pulling force in the rope while skidding the logs up and down the slope and at the same time using different weights of logs and different skidding speed.The testing material for measuring the pulling forces was beech and completely parameters of the all three logs values used for experiment and calculations are presented in Table 1.The density of the used logs was found out by the indirect method on the basis of weighing the given stem volume where average density is 1180 kg.m -3 .

RESULTS
The aim of the work was observing and evaluating pulling force while skidding logs up and down the slope at a different speed and a different number of logs.The measured values were evaluated by means of the program STATISTICA.
The observed factors and resultant values are presented in Table 2 at the end of the paper.The factors observed include the woody species (beech), a number of logs (2 and 3 pieces) and skidding speed (speed gear: 2 nd , 3 rd , 4 th , and 5 th ).Skidding was going on at the rated speed of engine n=1800 min -1 .
Table 2 shows the results of the multi-factor analysis of dispersion for all numbers of logs, direction of skidding, and speed gear (speed of skidding).All of the given factors affecting the pulling force were statistically highly significant.Significance level p has to be lower than 0.05 in order that the results were statistically significant and thus, from the standpoint of evaluation, it would be possible to evaluate and take them into consideration.
The first line of Table 2 shows the likelihood that the total average value of pulling force is zero, i. e. it equals zero.The total average value of the pulling force for all skiddings and speed gear is zero H 1 : y ≠ 0 is in force.
The total average value of pulling force for a number of logs is not-zero, i. e. the hypothesis has not been confirmed.However, we can claim with 87% credibility that there are differences between numbers of skidded logs.Similarly, it can be stated with 100% credibility that a ѕіgnіfіcant difference is also between the way of skidding and speed gear.Likewise, all two-factor as well as three-factor іnterаctions are statistically significant.
From among three observed factors, the way of skidding has statistically the most significant effect and it is followed by speed gear and a number of logs.
The influence of a number of logs is included in random factors and therefore confidence intervals overlap (Figure 8), though it results from the table of the dispersion analysis (Table 2) that the influence of a number of logs is not statistically significant.However, we can claim with 87% confidence that there is a difference between numbers of skidded logs.From the graph of skidding -pulling force shown in Figure 9 it results that the pulling force in skidding upwards is stаtіѕtісally significantly higher than it is with two logs.That means that the total of all averages of pulling forces from measurements is higher when towing three logs as compared with towing two logs.In the graph of the single-factor analysis of speed gear -pulling force (Figure 10) it can be seen that at the highest speeds there was statistically significantly lower pulling force.We can claim that the effect of dynamic impacts was not reflected on an amount of pulling force when skidding logs as it was at lower speed gears.In the last graph (Figure 12) there is illustrated the influence of the interaction of all observed factors on pulling force.From the graph it is evident that the dispersion of measured data is even, except for the fifth gear where the dispersion is considerably higher.
From the observed interactions, the given interaction of a number of logs skidding has the greatest effect on the pulling force from the two-factor analysis.In the given graph (Figure 11) it can be seen that the load of skidded logs has markedly influenced the amount of pulling force when skidding downwards, where the pulling force decreased at a higher number of logs.
On this basis, the average value of pulling force was lower than at lower speed gears, which is confirmed also by the graph of pulling force and speed gear.This fact is caused by dynamic impacts of logs at a higher speed of skidding load which are transmitted onto the steel rope.
When skidding upwards there is a noticeable difference of pulling forces depending on a number of skidded loads.When skidding three logs downwards there is a linearly decreasing course of pulling force with increasing speed gear, where load weight was reflected positively in relation to the observed quantity.On the basis of the analysis we can claim that when skidding downwards a smaller number (weight) of logs there is greater pulling force in comparison with a greater number of skidded logs.

CONCLUSION
The designed equipment can be used as the tractor winch or the driving unit of the forest cableway which can be arranged in many constructional configurations.This is its biggest advantage over other types of cable systems usually designed as one-purpose cableway systems.
The pneumatic control of the cableway system significantly reduces the environmental impact on forest working environment.Many other types of cable systems are usually designed with hydraulics control system.
The designed tractor cableway system has a transport time to the workplace as compared with onepurpose cableway systems.Better mobility of the system can use the system more economically because downtime is minimized.
When skidding a smaller number (weight) of logs downwards, pulling force is greater compared to a gre-ater number of skidded logs.At a higher speed of skid-ding a load, an average pulling force is smaller than at a lower speed when the effect of dynamic impacts of skidded logs at a higher speed does not influence the amount of pulling force as it is at a lower speed of skidding.

Figure 1 .
Figure 1.Concept of the transportation cableway system.

Figure 2 .
Figure 2. FEM calculations and optimisation of the main frame in ANSYS CAE system.

Figure. 3
Figure. 3 Multibody dynamics and motion analysis in ADAMS CAE system.

Figure. 4
Figure. 4 Final design of the tractor unconventional cableway system powered by the wheels of driving axle.

Figure. 5
Figure. 5 Working attachment of the transportation cableway system.

Figure. 6
Figure.6 Operation principle of the cableway system.

Figure. 7
Figure.7 The scheme of measuring the loading forces in the cableway system.

Figure. 8
Figure. 8 Grаph of 95% confidence іnter аls for average values of pulling force depending on a number of logs.

Figure. 9
Figure. 9 Grаph of 95% confidence іnter аls for average values of pulling force depending on skidding.

Figure. 10
Figure. 10 Grаph of 95% confidence іnter аls for average values of pulling force depending on speed gear.

Figure. 11 Figure. 12
Figure.11 Grаph of 95% confidence іnter аls for average values of pulling force depending number of logs and skidding.