Within reach

The agricultural tractor was the machine that boosted the development process of Brazilian agriculture due to its versatility in carrying out numerous tasks in rural areas, serving as a source of power and traction for various agricultural equipment and implements. Many authors consider the agricultural tractor to be the basis of modern agricultural mechanization.

Operating agricultural tractors, like any other agricultural machine, is an arduous task, requiring physical and mental effort on the part of the operator, resulting in fatigue over the course of a working day. The intensity of this fatigue will depend on the quality of the machine's operating station. High levels of fatigue considerably increase the risk of accidents and economic losses in the production chain.

The operating station is the place of interaction between man and machine, composed of control bodies and equipment that assist in driving the machine in the work environment. A well-designed operating station must consist of a workplace organized according to the safety and nature of the operator.

The dimensions of the operating station of an agricultural machine must respect the human factor, following the standards established by standards such as: ISO (International Organization for Standardization), ABNT (Brazilian Association of Technical Standards) and Asae (American Society of Agricultural Engineers). These standards define parameters to be used in agricultural machinery projects, establishing maximum and minimum distances for access to controls and delimiting areas where operating controls must be positioned to provide comfort and safety to the operator.

To simulate the operator sitting at the operating station of an agricultural machine, a reference point is adopted on the operator's seat, the Seat Reference Point (SIP), which is defined by the ISO 5353 standard. The ISO 15077 standard delimits reach areas for the seated operator, in relation to the SIP, covering all controls present at the operating station of self-propelled agricultural machines. Also according to this standard, commands activated within an interval equal to or less than five minutes during operation are considered frequently used, otherwise, these commands are classified as rarely used.

There are areas or zones that delimit the positioning of controls in the operating station, which are classified as comfort zones, access zones and inaccessible zones, covering both manual and foot-operated controls. Thus, it becomes coherent to know the space that the hands and arms need for grasping and movement, which leads to better planning of the positioning of controls and operation commands.

The comfort zone allows easy access to the controls by the operator and the main controls must be located there, and is associated with controls frequently operated by hands and feet. The access area allows the driver of the agricultural tractor to reach from his sitting position, allowing movement and tilting sideways or forwards to activate the operation controls in that position. This zone is associated with rarely activated commands. A command located in an area inaccessible to the operator will occur when it is located outside the previously defined comfort or access zone.

In this sense, an evaluation was carried out by researchers from the Federal University of Santa Maria with the aim of identifying and comparing the location of controls frequently and rarely used by the operator, in relation to the range areas, in four different models of national agricultural tractors, with 75 hp of power, establishing the SIP as a reference, under the guidance of the NBR ISO 4253 and ISO 15077 standards.

To carry out this work, only tractors belonging to Class III (70 to 100 hp) were evaluated, according to the classification proposed by Farias 2014. The option for this class of tractors is justified by the fact that the market for these machines is booming due, in part, to incentives provided by the Federal Government, especially the Mais Alimentos program. Thus, four platform-type operating stations for Massey Ferguson tractors, model MF 4275, were evaluated; New Holland, model TL 75E; Valtra, model A750, and John Deere, model 5078E.

The measurements were carried out at dealerships representing each brand, as all the tractors studied were new. None of the machines had a reduced gauge configuration (less than 1.150mm), allowing the application of the NBR ISO 4253 and ISO 15077 standards as an evaluation reference.

To determine the SIP, a metallic device was used, following the guidelines of the ISO 5353 standard. Standardized metallic masses were added to this device until reaching 75kg, which is considered the average mass of Brazilian operators. Once this was done, with the help of a spirit level, square and measuring tapes, a first line was positioned horizontally between the SIP and the center of the steering wheel, followed by another two lines, passing through the center of the SIP, perpendicular to the first line. , were fixed horizontally to the inner sides of the tractor.

Each measured operation command was represented by a point identified by coordinates in three dimensions (x, y and z). Three mutually perpendicular reference planes were considered, passing through the SIP, shown in Figure 1. Thus, the longitudinal vertical plane divides the tractor into two parts: left and right, indicating the lateral positioning of the controls in relation to the SIP. The transverse vertical plane, in turn, divides the tractor into two portions: anterior and posterior, indicating the front and rear positioning of the operation controls in relation to the SIP. Likewise, the horizontal plane divides the agricultural tractor into two hemispheres: upper and lower, establishing the height of the controls in relation to the SIP. The SIP coordinates originated at point zero (0, 0, 0).

Figure 1 – Planes used as a reference to determine the coordinates of each operation command

All controls present at the tractors' operating station were measured, whether they are activated frequently or rarely. The controls classified as frequently used are: brake pedals (right and left); clutch pedal; accelerator pedal; manual accelerator; hydraulic system controls (position, depth, sensitivity and remote control); exchange controls (gear control, group selector and regime selector). Those classified as rare activation are: light switches; horn; power socket; front traction control and differential lock. The coordinates of the operation commands (x, y and z) were compared with the ISO 15077 standard, which determines the regions within reach of the seated operator and the positions of the controls in relation to the SIP.

Figures 2A and 2B represent the range areas in the vertical longitudinal plane (PVL) and in the superior horizontal plane (PSH), respectively.

Figure 2 – Reach areas of the operator seated in the vertical longitudinal plane (A) and in the upper horizontal plane (B). Source: ISO 15077

The results of the distribution of controls at the evaluated operating stations were compared with each other, with the aim of generating information for carrying out subsequent work, demonstrating the great importance of ergonomics and safety parameters for the preparation and execution of agricultural machinery projects.

MASSEY FERGUSON MF4275

25 operation commands were evaluated, 15 of which were classified as frequent activation commands and ten as rare activation commands. When analyzing the PVL, 33,3% of frequently activated commands are distributed in the comfort zone; 33,3% in the access zone and 33,3% in the inaccessible zone. When evaluating rare activation commands, no commands were found located in the comfort zone, with 70% in the access zone and 30% in the inaccessible zone. In the upper horizontal plane (PSH), frequent activation commands were distributed in the proportion of 60% in the comfort zone and 40% in the inaccessible zone.

VALTRA A750

In this model, 23 operating commands were evaluated, 13 of which were classified as frequent activation and ten as rare activation. When evaluating frequently activated commands in the PVL, 38,5%, 23% and 38,5% were located in the comfort, access and inaccessible zone, respectively. As for rare activation controls, 100% were positioned in the access zone. In the PSH assessment, the frequently activated controls were positioned 38,5% in the comfort zone, 38,5% in the access zone and 23% in the inaccessible zone.

NEW HOLLAND TL 75E

This model had the highest number of items evaluated, 27 in total, 16 of which were classified as frequently activated and 11 as rare. In the PVL assessment, 25% of frequently activated commands were located in the comfort zone, 43,8% in the access zone and 31,2% in the inaccessible zone. Those considered to be rare, 72,7% were positioned in the access zone and 27,3% in the inaccessible zone. Regarding the upper horizontal plane (PSH), 50% of frequently activated commands were located in the comfort zone, 12,5% ​​in the access zone and 37,5% in the inaccessible zone.

JOHN DEERE 5078E

This model was the one with the lowest number of operation commands, 22 in total, of which ten are frequently activated and 12 are rarely activated. When evaluating the PVL, it was found that 40% of frequently activated commands were located in the comfort zone and 60% in the access zone. As for rare activation commands, 8,33% were positioned in the comfort zone; 58,33% in the access zone and 33,33% in the inaccessible zone. When evaluating the frequently activated commands in the PSH, 70% were located in the comfort zone, 10% in the access zone and 20% in the inaccessible zone. All results found are presented in Figure 3.

Figure 3 – Distribution of frequent and rare activation commands in the PVL and PSH of the four agricultural tractors evaluated

In more modern agricultural machines, it is common for the majority of operating controls to be located in the comfort and access zones, expressing the evolution of the designs of these machines, with regard to ergonomics and safety.

Analyzing the PVL, the John Deere tractor had the highest number of frequently used controls present in the comfort and access zones, with no controls in the inaccessible zone. Regarding PSH, the JD 5078E tractor has the largest number of frequently used commands in the comfort zone and the Valtra A750 the largest number of frequently used commands in the access zone.

All machines present some non-conformity in the positioning of certain operating controls. Although there are some nonconformities, based on the profile of Brazilian operators, current agricultural machinery projects present satisfactory results in terms of ergonomics and safety of agricultural tractors manufactured in the country.

This article was published in issue 145 of Cultivar Máquinas magazine. Click here to read the edition.