Concept and design of the ROPS for a small articulated tractor for extreme sloped vineyards

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1 Ref: C0505 Concept and design of the ROPS for a small articulated tractor for extreme sloped vineyards Marco Bietresato, UNIBZ-Libera Università di Bolzano, FaST-Facoltà di Scienze e Tecnologie, Piazza Università 5, I Bolzano, Italia (corresponding author) Adriano Guarnieri and Valda Rondelli, UNIBO-Università degli Studi di Bologna, DISTAL- Dipartimento di Scienze e Tecnologie Agro-Alimentari, via Fanin 50, I Bologna, Italia Johannes Weger, FIR-Fraunhofer Italia Research s.c.a.r.l., via Macello 57, I Bolzano, Italia Fabrizio Mazzetto, UNIBZ-Libera Università di Bolzano, Facoltà di Scienze e Tecnologie, Piazza Università 5, I Bolzano, Italia Abstract A new reversible wheeled articulated tractor has been designed and realized by WM s.r.l. (Prato all Isarco, BZ, Italy) in collaboration with UNIBZ and FIR, to address the problem of working in terraced vineyards trained with the so-called pergola system, very common in mountain areas. The whole design process of this tractor was characterized by a constant dialogue between engineers and a selected pool of farmers, representative of final users, to have a product as much as possible answering to the users needs and, hence, free from future requests of design changes, according to the logic of Concurrent Engineering. In particular, conceiving and designing a Roll-Over Protective Structure (ROPS) suitable to equip this small tractor was a real engineering challenge: many design constraints, coming from the difficult environment in which this tractor will operate and resulting from the very particular design of the front part of the tractor, had to be matched with the (dimensional, structural) requests stated from the OECD code 7 used for ROPS strength tests. The operating environment for this tractor imposed reduced dimensions to the external outline of this vehicle: vineyards inter-rows are very narrow (often lower than 1.00 m), as well as spans under the arbours (commonly 1.80 m, often 1.60 m). A high compactness of the vehicle was obtained by adopting an unconventional architecture for this tractor, i.e. an articulated body with a Diesel engine placed in the front part, a reversible driving seat directly placed on the motor, and the rear part acting as implement-carrier. Also the ROPS has some peculiarities, studied to match safety-volume requirements with the possibility for farmers of further reducing the overall height, if needed in some very narrow passages. In fact, the tractor was equipped with a non-removable, tiltable and telescopic rear-mounted ROPS combined with a top horizontal element and a frontal protection for the driver s feet. The absence of a conventional steering wheel (the tractor is driven by a cloche) and of an engine-bonnet in front of the driver make this ROPS absolutely unique and not-provided for by the norm; this latter fact puts two important questions to the testers, respectively on: (1) how defining the front outline of the clearance zone (i.e. the point D of OECD code 7, fig. 7.1.a p. 23), usually defined in relation with the forward external edge steering wheel, and (2) how identifying the hard points of the tractor capable of supporting the whole mass of the overturned vehicle (i.e. the points defined on the basis of the imaginary ground plane). Thanks to a careful interpretation of the inspiring principles of the norm and to the great experience of the staff of the University of Bologna, these problems were successfully over- Proceedings International Conference of Agricultural Engineering, Zurich, /8

2 come respectively by (1) limiting the clearance zone to the vertical line passing through the point C (OECD code 7, fig. 7.1.a p. 23), thus operating even with a higher safety level, and (2) by using the external edge of the feet protective structure to define the clearance zone and the virtual ground plane in case of overturning. Keywords: articulated tractor; tractor safety; OECD code 7; ROPS; clearance zone for tractors 1 Introduction Most of the vineyards assigned to the production of high-quality grapes and wines are very problematic by the point of view of the mechanisation. In fact, these vineyards are often placed in steep hillsides and use traditional training systems (such as pergola ), considered by farmers essential for obtaining a better maturation of grapes and a full development of the aromas which characterize the wines obtained from those grapes. The only possible mechanization in these difficult environments makes use of small tracked or wheeled tractors capable of operating in: i) very narrow inter-rows, often lower than 1.00 m and with the risk of rollover, ii) reduced spans under the arbours (commonly 1.80 m, often 1.60 m); iii) steep and very tight curves in row heads, with great difficulties of manoeuvre. In particular, the tractor resulting from these design requirements and proposed in this work has small dimensions, necessary to operate in this environment, and presents 4-wheel drive together with a central articulation having two rotational degrees-of-freedom. Among all the functional subsystems of the tractor, the Rollover Protective Structure (ROPS) required a great attention and effort in the design phase. In fact, due to the difficult environment in which the tractor could operate (steep hillsides, very low arbours) and to the very particular shape of the front part of the tractor, one of the most interesting challenges for the engineers and for the manufacturer was warranting the safety for the driver in case of overturning but keeping compact the overall dimensions. This is also the key point to homologate the vehicle thus letting the manufacturer sell in the future a tractor that is in accordance with the current international safety standards (in particular the OECD testing procedure for the dimensions of the clearance zone and the strength of the ROPS). The whole design process of this tractor and of its ROPS in particular was inspired by the product development philosophy of Concurrent Engineering : all the technical requirements suggested by the possible future users (a selected pool of farmers), the production department and the international standards were made explicit, thus defining the boundaries of the ROPS project. By answering in the design phase to all these requirements and by using in the meantime a series of computer-aided tools (CAD and FEM) to verify periodically the project under development, the designer reduced at the minimum all possible later requests of design changes in the preproduction phase and all possible structural and dimensional problems in the ROPS certification test phase (several loading tests). The aim of this work is presenting and describing the design process which led to the development and testing of the ROPS for the narrow-track wheeled articulated farm tractor realized by the company WM s.r.l., in collaboration with FUB and FIR. Moreover, the principal features of the design of this ROPS will be described in detail, evidencing how they satisfy the many constraints coming from the production department, the users and the OECD codified testing procedure in particular (OECD, 2013). 2 Materials and methods 2.1 The small articulated tractor for extreme sloped vineyards The agricultural tractor presented in this work is a 4-wheel drive articulated tractor, extremely compact, i.e. with a narrow track (1240 mm) and a low centre of gravity (345 mm from the ground), and with the reversible driving seat (Figure 1). The steering is made by means of the central articulation of the chassis, it is hydraulically-operated and can reach a maximum angle of 110 in both directions. A joystick replaced the conventional steering wheel, to have Proceedings International Conference of Agricultural Engineering, Zurich, /8

a simplified man-machine interface. The engine is housed in the front part and the reversible driving seat is placed immediately above it.

It is conceived without any cabin but rather with a ROPS having a limited vertical dimension, detailed in the present article.

weights distribution and position of the centre of gravity. 2.

result of a series of decisions taken by the designer for each component.

possibility and type of reciprocal motion. The definition of most of the features listed above is carried out in the early stages of the development of an industrial product, i.e. in the phases prior to the industrial production (conceptual design, detailed design).

Indeed, through the study of a real, physical prototype the engineers can notice some shortcomings of the initial project which may relate to inherent difficulties of manufacture, assembly, operate

The more these changes are radical, with respect to the initial project, and distant in time from the design phase, the more they will be expensive in terms of involved economic, material and human

A high degree of virtualization of the verification process of the project s dimensions and mechanical resistance through engineering software (CAD, FEM) is particularly useful to anticipate problems

3 a simplified man-machine interface. The engine is housed in the front part and the reversible driving seat is placed immediately above it. The hydrostatic transmission simplifies the power connections between the front and rear halves. It is conceived without any cabin but rather with a ROPS having a limited vertical dimension, detailed in the present article. A C B D Figure 1 (A) scheme of the tractor; (B) overview of one of the first prototypes equipped with a frontcoupled mower and a rear dumper; (C) characteristic dimensions of the prototype (mm); (D) weights distribution and position of the centre of gravity. 2.2 A Concurrent Engineering approach to the development of the ROPS The final design characteristics of a complex system to be produced industrially (such as the small tractor presented here) is the result of a series of decisions taken by the designer for each component. In particular, the designer defines: morphology, dimensions, materials, interfaces with the other components and with the operator (linkage, articulation, operation systems of that component), possibility and type of reciprocal motion. The definition of most of the features listed above is carried out in the early stages of the development of an industrial product, i.e. in the phases prior to the industrial production (conceptual design, detailed design). Occasionally, some choices are reviewed also in the product development stages subsequent to the design, e.g. when the product is in the pre-production phase and a prototype has already been built. Indeed, through the study of a real, physical prototype the engineers can notice some shortcomings of the initial project which may relate to inherent difficulties of manufacture, assembly, operate the product or to possible problems to achieve the minimum dimensional and structural requirements to ensure the operator s safety, primarily, and the homologation of the product, secondarily. The more these changes are radical, with respect to the initial project, and distant in time from the design phase, the more they will be expensive in terms of involved economic, material and human resources. A high degree of virtualization of the verification process of the project s dimensions and mechanical resistance through engineering software (CAD, FEM) is particularly useful to anticipate problems which, otherwise, would arise in the stages following the design. The use of computer tools and the anticipation at the design stage of problems typical of the subsequent stages are typical of Concurrent Engineering (CE). The CE (also referred to as Simultaneous Engineering ) is an integrated process for designing, developing, manufacturing and marketing a new product / product line. It may be defined as a systematic approach to the integrated, concurrent design of products and their related processes, including: manufacture, support, maintenance and many other life-cycle considerations, including test, inspection, reliability, safety, human factors and disposability (Chang, Wysk, & Wang, 2005). The goal of CE is to design and manufacture a product in such a way it will meet the customer s requirement to the fullest extent; it can be seen as the implementation arm of the total quality management (TQM) and a modern treatment of systems engineering that combines quality Proceedings International Conference of Agricultural Engineering, Zurich, /8

4 engineering methods in a computer-integrated environment (Chang et al., 2005). The CE approach characterized the whole development of the tractor presented here and, in particular, it was used for defining the design of its ROPS. Thanks to the development of the whole project in a 3D parametric CAD, in this case Inventor Professional (Autodesk, Mill Valley, California, USA), it was possible to have a virtual prototype of the tractor at disposal of the designer, to early verify its dimensions and simulate different load scenarios (typically the ROPS test load conditions), but also to be shown to a selected pool of farmers (possible future purchaser of such a tractor), so having a constant feedback by them (Figure 2). Figure 2 Comparison between a traditional and a computer-aided product development process (regarding in particular ROPS); red/blue arrows indicate inter/intra-phase design changes; a dotted line in the computer-aided design process (in accordance with CE principles) indicates a scenario that rarely occurs. 3 Results and discussion 3.1 Definition of ROPS principal requirements A series of critical points and indications for the design of the ROPS were outlined by joining together all the requirements coming from (Figure 3): a pool of farmers, which potentially will purchase the tractor (potential users); the production department, which will product and assembly the vehicle; the international OECD code 7 standard, which will be used as a reference for the strength tests (OECD, 2013). The main requirements are the following: the ROPS has to be fitted on an unconventional articulated tractor, with a very particular design of the front part (seat placed directly over the engine, absence of an engine-bonnet, absence of a conventional steering wheel but rather presence of a cloche); the ROPS has to let an easy access to the driver s seat from the front of the tractor, as there is no possibility for a driver to access laterally to the seat (as usual for conventional tractors); the ROPS has to allow the driver s seat to rotate on its central vertical axis, to let the operator drive the tractor in the reverse mode (backward); the ROPS dimensions have to let the tractor operate under the reduced span of the typical training system for side-hill vineyards; the ROPS has to satisfy a series of dimensional requirements concerning the clearance zone, i.e. a safety volume around the driver, accounting also for the deflection Proceedings International Conference of Agricultural Engineering, Zurich, /8

of the protective structure occurring when tested with prescribed loads; the dimensional requirements of the clearance zone prescribed in the international norms (in this case, the OECD code 7) can

value of the forces that would be used during the strength tests (parameterized to the vehicle reference mass) the ROPS has to be simple and not expensive to manufacture and assembly (few pieces to

interpreting the requests of potential future users, production department and homologation tests. 3.

5 of the protective structure occurring when tested with prescribed loads; the dimensional requirements of the clearance zone prescribed in the international norms (in this case, the OECD code 7) can therefore be expressed also in term of strength requirements (elastic and plastic deflections of the ROPS) the ROPS (as well as the whole tractor) has to weight the less as possible, to limit the value of the forces that would be used during the strength tests (parameterized to the vehicle reference mass) the ROPS has to be simple and not expensive to manufacture and assembly (few pieces to be linked together, conventional manufacturing processes and materials) Figure 3 Definition of the design of a tractor (or of one of its subsystems) as a result of a series of constraints interpreting the requests of potential future users, production department and homologation tests. 3.2 Definition of OECD requirements for the present case The reference standard for the ROPS strength tests was the OECD Code 7, titled Standard Code for the Official Testing of Rear Mounted Roll-over Protective Structure on Narrow-track Wheeled Agricultural and Forestry Tractors (OECD, 2013). In fact, the present tractor seems to be accordance with the definitions of narrow-track wheeled agricultural and forestry tractors to which the standard is applicable (defined in the chapter 2 of the cited standard). However, the absence of a conventional steering wheel (the tractor is driven by a cloche) and of an engine-bonnet in front of the driver make this ROPS absolutely unique and notprovided for by the norm; the spatial definition of the clearance zone (in particular of point D ; Figure 4A) and the line of the imaginary ground plane with respect to the overturned vehicle are in fact referred respectively to the steering wheel (top edge; Figure 4A) and to the a front hard point, normally identified as the engine-bonnet. This fact puts two important questions to the testers, respectively on: how defining the front outline of the clearance zone (i.e. the point D of Figure 4A); how identifying the hard points in the front part of the tractor capable of supporting the whole mass of the overturned vehicle (i.e. the points defined by the imaginary ground plane). Thanks to a careful interpretation of the codified testing procedure and to the consolidated experience (many other cases examined) at the OECD Test Station of Bologna, Department of Agricultural and Food Sciences (DISTAL), University of Bologna, these problems were solved respectively by: limiting the clearance zone to the vertical line passing through the point C of Figure 4A (OECD code 7, fig. 7.1.a p. 23) and to the external edge of the feet protective structure, thus operating even with a higher safety level; in fact, the resulting clearance volume is narrower than a traditional clearance volume and the OECD standard prescribes absolutely not to have any intrusion of the deformed ROPS in it using the external edge of the feet protective structure, properly reinforced and tested, as hard fixture supporting the mass of the vehicle in case of overturning (Figure 4B). Proceedings International Conference of Agricultural Engineering, Zurich, /8

A B Figure 4 (A) side view of the clearance zone as defined in OECD code 7, fig. 7.1.a p.

picture); in the same picture the used clearance zone is visible (a vertical line has been drawn from point C ). 3.

retaining a minimum level of safety in case of lateral rollover even if completely retracted), the following solution has been shaped: the ROPS should have been tiltable and retractable in maximum

Then, the attention of the designer focused on how building the articulation between the top part and the vertical uprights (Figure 5).

adopted (only one hinge, kinematically acceptable back-reversal; Figure 5B).

manufactured simply by bending a metal sheet, without welding any other metal sheet component (compare the small boxes of Figure 5).

6 A B Figure 4 (A) side view of the clearance zone as defined in OECD code 7, fig. 7.1.a p. 23, (OECD, 2013); note that point D is defined in relation to the steering wheel s top edge; (B) position of the virtual plane in case of overturning of the tractor during frontward travelling (right picture); in the same picture the used clearance zone is visible (a vertical line has been drawn from point C ). 3.3 Evolution of the ROPS design Having deduced from the farmers advices that the ROPS should have been rear-mounted and somehow collapsible, to compact the tractor outline when not in use (however retaining a minimum level of safety in case of lateral rollover even if completely retracted), the following solution has been shaped: the ROPS should have been tiltable and retractable in maximum two movements (1, lifting of the top part; 2, retracting of the vertical uprights). Then, the attention of the designer focused on how building the articulation between the top part and the vertical uprights (Figure 5). After an initial proposal making use of two hinges, which would have let a complete and kinematically correct back-reversal of the top part of the ROPS (Figure 5A), a simpler solution have been adopted (only one hinge, kinematically acceptable back-reversal; Figure 5B). In the meantime, the support for the top part leaning on the vertical uprights (laterally shaped as a triangle in Figure 5) was simplified for an easy manufacturing: with only a wing it can be manufactured simply by bending a metal sheet, without welding any other metal sheet component (compare the small boxes of Figure 5). (1) (1) (2) (2) A B Figure 5 Side views of the articulated tractor (front part only) with two different versions (A, B) of the ROPS in working position; in the same pictures it is possible to see how the two ROPSs can be tilted and retracted (two movements: 1, lifting of the top part, 2, retracting of the vertical uprights). Finally, a total review of the seat placement and of the dimensions of the protective frame for the driver s feet let the designer remove the lateral protective structures (two bended tubular beams visible in Figure 5), initially provided for in the project to give a support to the imaginary ground plane in case of frontal overturning (together with the top part of the ROPS; Figure 6). Proceedings International Conference of Agricultural Engineering, Zurich, /8

Figure 6 Comparison between two different configurations of

superimposed in black and white; previous configuration: in

4 Final design of the ROPS The protective structure in its

welded and bended tubular beams, most of them made of Fe510

The ROPS is joined to the tractor chassis by means of a

structure; the platform is fixed to the tractor by means of

8. On the front part, two supports, with a different shape on

joined to the gear box cover by means of M10-8.8 and M10-10.

On the rear position there is a central support, made of

support. Figure 7 Final design of the ROPS. 3.

passes successfully by the ROPS (horizontal loadings:

7 Figure 6 Comparison between two different configurations of the front part of the tractor (last configuration: picture superimposed in black and white; previous configuration: in colours). 3.4 Final design of the ROPS The protective structure in its final design (Figure 7) is a metallic frame composed by welded and bended tubular beams, most of them made of Fe510 EN10025 (1990) - S355 EN10025 (2004) structural steel. The ROPS is joined to the tractor chassis by means of a platform, which represents the lower part of the protective structure; the platform is fixed to the tractor by means of supports with silent-blocks and bolts M On the front part, two supports, with a different shape on the two sides and made of 6 and 8 mm shaped sheets, are joined to the gear box cover by means of M and M bolts. On the rear position there is a central support, made of plates (thickness: 8 / 15 mm), joined to the lift system support. Figure 7 Final design of the ROPS. 3.5 ROPS strength tests Strength tests were carried out in the OECD Test Station of Bologna (Italy). Thanks to the previous virtual dimensioning, all tests were passes successfully by the ROPS (horizontal loadings: deformation energy > minimum; vertical crushes: applicable load > minimum; Figure 8) and therefore the ROPS fulfil the test requirements (DISTAL-UNIBO, 2014). Proceedings International Conference of Agricultural Engineering, Zurich, /8

16500 15000 13500 12000 10500 Force [N] 9000 7500 A 6000 4500 3000 1500 B 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 Deflection [mm] 17000 16000 15000 14000 13000 12000 11000 10000

rear, side) and vertical loadings (in the front / rear of the top part); examples of the obtained force-deflection and force-time diagrams (A, B: front, side horizontal loads; C, D: front, rear

4 Conclusions Thanks to the adopted integrated approach, inspired by Concurrent Engineering product design philosophy, an innovative ROPS (non-removable, tiltable and telescopic rear-mounted) was

The described tests on the ROPS certified the high levels of passive safety for the driver (the safety volume is warranted for the vehicle overturned both frontally and laterally); when the path

Computer-Aided Manufacturing (3rd ed., p. 684). Prentice Hall international. DISTAL-UNIBO. (2014). Test report n. 5391 - WMA-A-001 protective structure.

8 Force [N] A B Deflection [mm] Force [N] C D Time [s] Figure 8 (on the top, from left to right) test configurations for ROPS horizontal loads (front, rear, side) and vertical loadings (in the front / rear of the top part); examples of the obtained force-deflection and force-time diagrams (A, B: front, side horizontal loads; C, D: front, rear vertical crushes). 4 Conclusions Thanks to the adopted integrated approach, inspired by Concurrent Engineering product design philosophy, an innovative ROPS (non-removable, tiltable and telescopic rear-mounted) was developed and all the tests provided for by OECD code 7 (the standard that fitted best to the ROPS of the present unconventional agricultural tractor) were passed at the first attempt. The described tests on the ROPS certified the high levels of passive safety for the driver (the safety volume is warranted for the vehicle overturned both frontally and laterally); when the path leading to the homologation will be concluded for this prototype, the tractor will be industrially produced. 5 References Chang, T.-C., Wysk, R. A., & Wang, H.-P. (2005). Computer-Aided Manufacturing (3rd ed., p. 684). Prentice Hall international. DISTAL-UNIBO. (2014). Test report n WMA-A-001 protective structure. Cadriano, BO, Italy: University of Bologna - Dipartimento di Scienze e Tecnologie Agro-Alimentari. OECD. (2013). Code 7 - OECD Standard Code for the Official Testing of Rear Mounted Rollover Protective Structure on Narrow-track Wheeled Agricultural and Forestry Tractors. Paris, France: Organisation for the Economic Co-operation and Development. Retrieved from Final.pdf Proceedings International Conference of Agricultural Engineering, Zurich, /8

Dynamic and static ROPS tests on modern tractors

Ref: C0373 Dynamic and static ROPS tests on modern tractors Bruno Franceschetti, Valda Rondelli, Adriano Guarnieri and Enrico Capacci, Department of Agricultural Food and Sciences, University of Bologna,