Design and full realization of physical weed control (PWC ... · Design and full realization of physical weed control (PWC) automated machine within ... weed management, ... the weed

Proceedings International Conference of Agricultural Engineering, Zurich, 06-10.07.2014 – www.eurageng.eu 1/7

Ref: C0705

Design and full realization of physical weed control (PWC) automated machine within the RHEA project

Christian Frasconi, Marco Fontanelli, Michele Raffaelli and Andrea Peruzzi, Department of Agriculture Food and Environment, University of Pisa, via del Borghetto 80, 56124, Pisa, Ita-ly.

Luisa Martelloni, Centro di Ricerche Agro-Ambientali “Enrico Avanzi”, University of Pisa, via vecchia di Marina 6, 56122, San Piero a Grado, Pisa, Italy.

Abstract

Currently precision agriculture can rely on modern technologies that allow to design and real-ize operative machines provided with perception systems, in order to perform precise and targeted treatments. The ultimate objective of this synergy consists in reducing the use of agrochemicals and energy, enhancing the sustainability of agricultural practices. In this re-gard, the RHEA project funded by EU, aims to develop a fleet of etherogenous autonomous robot units in order to perform precise treatments related to crop protection in different sce-narios. In this paper is reported the design and the development of an automatic machines able to perform, at the same time, mechanical and thermal weed control on maize is described and discussed. The equipment will be coupled to an autonomous ground mobile unit equipped with a row and a weed detection systems. The operative machines was designed to remove weeds mechanically from the inter-row spaces of the crop and perform selective and target-ed cross flaming, in the rows of the crop. The precision of the treatment is ensured by spe-cific vision based perception system for weed detection and crop row detection. Mechanical treatment (inter-row cultivation) will be performed in a continuous way, even without weed presence. The machine is provided with a guidance system managed by a crop row detec-tion system in order to avoid damaging the maize plants with the rigid tools used for mechan-ical weed removal. On the contrary cross flaming on the rows of the crop is actuated only if weed patches are detected. The thermal weed control is applied by mean of couples of rod burners LPG fed, able to treat a 25 cm wide strips with the crop row in the middle. The bio-logical selectivity is ensured by maize high tolerance and weeds sensitivity to flame exposure for few tenths of seconds. Moreover, the LPG working pressure can be adjusted according to the level of weed cover detected by the weed detection system: - no treatment, if weed cover is near to 0 %; - low LPG working pressure, if weed cover is lower than 25%; - high LPG working pressure, if weed cover is higher than 25%. Each unit for thermal weed control is provided with an ignition system able to properly swich on the burners at the selected LPG working pressure. This ignition system enables to avoid the use of pilot light, often adopted in the conventional “low-tech” flaming machines. This fact is very important for the overall safety of the system, since the implement is coupled with an unmanned ground mobile unit.

Keywords: non-chemical weed control, precision flaming, variable rate flaming


1 Introduction

The heterogeneous distribution of weeds in agricultural fields allows actuating site-specific weed management, resulting in significant herbicides save as well as economic and ecologi-cal benefits (Gutjahr & Gerhards, 2010). Weed seedlings distributions were found spatially and temporally heterogeneous within agricultural fields. They often occur in aggregated patches of varying size or in stripes along the direction of cultivation (Gerhards & Christen-sen, 2003). For this reason a uniform treatment of the entire fields can result in unsatisfactory weed control or unnecessary use of herbicides (Grisso et al., 2011). One of the aims of pre-cision agriculture is to minimize the amount of herbicides used to perform weed control (Gomes & Leta, 2012). The distribution of herbicides with fixed point and quantitative spray-ing is becoming one of the major research directions of precision weeding technology (Wu et al., 2011). Weed-specific chemical application can reduce the amount of chemicals by about 25-50%, thus reducing costs and protecting the environment (Perez-Ruiz & Upadhyaya, 2012). Both increasing cost of chemicals and soil pollution caused by herbicides residues ask for alternative methods of weed management. On the other hand, there is a strong political in-terest in the European Union to increase the amount of organically grown products as organ-ic farming is not only a political goal, but it also represent a need from the market. As more and more customers ask for organically grown products many companies need to increase this kind of supplies (Åstrand & Baerveldt, 2005). Autonomous mechanical or thermal weed control systems could contribute to increase the available of organic products allowing to replace hand weeding and reducing agriculture current dependency on herbicides and im-proving yields, product quality and economical incomes of the farmers (Bakker et al., 2010). In this regard, the RHEA (Robot fleet for Highly Effective Agriculture and forestry manage-ment) Project funded by EU, aims to develop a fleet of heterogeneous autonomous robot units in order to perform precise treatments related to crop protection in different scenarios. A new machine able to perform site-specific physical weed control in maize was design and fully realized at the University of Pisa, according to the activities planned in the RHEA Pro-ject. The aim was to develop an automatic operative machine able to perform mechanical non-selective weed control in the inter-row space and real-time site-specific flaming weed control on the rows of crops tolerant to thermal treatment.

2 Machine design and description

2.1 Machine structure

The machine structure is realized by integrating a inter-row cultivator to a flame weeding sys-tem. The inter-row cultivator was constituted by a 3.46 m wide steel frame, supporting 5 ar-ticulated parallelograms on which the mechanical weed removal tools were placed (Fig. 1). The LPG fed weed flaming system, consisting in a steel frame (0.76 m x 1.46 m) supporting four LPG tanks and the open flame burners installed on the articulated parallelograms (Fig. 2). According to the 0,75 m inter-row space of maize, the machine is adjusted in order to have a working width of 3 m and thus treat 4 crop rows and 5 inter-rows in a single pass. The three central articulated parallelograms are provided with a couple of burners and rigid ele-ments that till a 0.5 m space between the rows. Each couple of rod burners generates a flame able to control weeds on a strip 0.25 m wide with the maize plants placed in the middle (Fig. 2). The two external articulated parallelograms are provided with only one burner. The side rigid element for mechanical weed removal are removed to avoid overlapping in ma-chine pattern (Fig. 2). Each articulated parallelogram was designed in order to maintain the correct working depth of the tines and the proper distance of the burners from the soil sur-face during the treatment. This task is guarantee by a spring and two free pneumatic wheels (Fig. 3). The machine is coupled to an autonomous Ground Mobile Unit (GMU) equipped with a crop and a weed detection system.


Figure 1: Vertical and horizontal plane of the initial machine structure. A: steel frame; B: articulated parallelogram; C: tines.

Figure 2: Integration between steel frames and flaming system. A: steel frame supporting LPG tanks, B: LPG tanks, C: burner.

Figure 3: Scheme of the articulated parallelogram. A: spring, B: free pneumatic wheel.

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2.2 Mechanical tools

Mechanical tools for weeds removal are placed on the articulated parallelograms. The two external parallelograms are equipped with a goose-foot tine and only one “L” shaped sweep. On the other hand, the three central parallelograms are equipped with a goose-foot rigid el-ement and two sweeps. These rigid tools control weeds in the inter- row space, performing a shallow tillage (till a depth of 3-5 cm). Goose-foot elements are 0.24 m wide (Fig. 4), while, “L” shaped sweep elements are 0.15 m wide (Fig. 5).

Figure 4: Goose-foot rigid element (dimensions are expressed in mm).

Figure 5: “L” shaped sweeps (dimensions are expressed in mm).

2.3 LPG feeding system and burners

The flaming system is composed by a LPG feeding system, 8 burners and an ignition sys-tem. Flaming system is completely automatic and based on signals coming from a weed de-tection system. Four LPG tanks are supported by a steel frame placed in the middle of the main frame of the machine (Fig. 2). LPG tanks have to be manually inserted into proper heat


exchangers, that consists in cylindrical hoppers containing water heated by the exhausted gases of the endothermic engine of the GMU. The exhausted gases flow through a pipe placed in the inner basal part of the cylindrical hoppers (Fig. 6). The heat exchanger allows to perform continuously flaming treatment at high LPG working pressure avoiding the cooling of the tanks. As a matter of fact, if the temperature of LPG is lower than the vaporization one, the gas stops flowing and the flames of the burners are extinguished.

Figure 6: Heat exchanger. a) view of horizontal plane of the hopper with the internal holed support for tanks; b) pipe for the exhausted gases from the engine to the hoppers; c) hoppers half filled with wa-ter; d): junction for the proper connection of the pipe; e): chimney. Gas flow from the LPG tanks to the burners is controlled by normally closed solenoid valves managed by a PLC provided with inputs and outputs modules. Pressure sensors and ther-mocouples are connected to the inputs, while electro-valves and transformers are connected on the outputs. On the machine are placed four 15 kg LPG tanks. Each tank feeds a couple of burners. On each tank there is a manual pressure regulator with a gauge set at 0.5 MPa. A pressure sensor (Aplisen® PC29) supplied with a 12 V DC voltage, monitors the pressure status of the LPG tank and transmits an analog signal to the PLC. When the LPG in the tank is going to finish and the pressure falls below level of 0.4 MPa, the PLC closes the adjacent electro-valve. All the electro-valves are normally closed solenoid valves (Madas® EV6 DN15) enabling the gas flux when they are supplied with an electrical 24V DC input. In each working unit, after the pressure sensor the LPG feeding line is then split into two branches equipped with electrovalves, one for each working pressure adjusted by two manual pressure regula-tors provided with pressure gauge. The thermal treatment can be undertaken in real-time using two different LPG working pressures according to weed cover percentage detected by the weed detection system. The PLC sends the signal opening the proper electro-valve ac-cording to detected weed cover percentage. An external mixer provides to mix LPG with the primary air acting as a Venturi pipe. The external mixer is a hallow brass hexagonal prism mounted coaxially onto the LPG feeding pipeline upstream of the burner. The brass structure of the mixer has three circular inlets (ø 7 mm) on the lateral walls and a coaxial screwed nozzle (ø 1.1 mm) placed inside. The carter of the burners are provided with circular inlet (ø 9 mm) in order to enable the intake of the secondary air that increases the efficiency of the combustion. The LPG/air mixture then reaches the ignition electrode. Each burner is equipped with a K thermocouple, which monitors the presence of the flame sending a low


voltage output signal to the PLC. If the flame accidentally is extinguished, PLC activates the transformers in order to reignite the burners. If the ignition process fails after 10 s the PLC closes the electro-valve placed near the tank, avoiding LPG efflux. The wires of the thermo-couple are coated in fiberglass in the part close to the burner in order to prevent any damage caused by high temperatures. Burners are made in stainless steel and are composed by an external carter and an internal rod. The internal rod is 25 cm wide and 3 cm long and has circular inlets (ø 2.5 mm) placed 3.5 cm apart. The carter is reinforced with steel “wings” in order to avoid deformations due to the high temperatures. The ignition system is almost instantaneous. As a matter of fact the flame is active and able to control weeds 0.39 s after the activation of the relays by the PLC. The ignition system is composed by one transformer (Cofi® TRL 24-30C) for each burner, converting the voltage value of 24V-DC to 12kV-AC, and one bipolar electrode with a ceramic insulator body, placed on the burner. The transformer is wired to the electrode with special high voltage wires coated in silicone rubber in order to resist to high temperatures. The power of the transformer (80 W) allows to obtain a continuous electric arc between the two poles of the electrode, which ignites the LPG/air mixture even at the higher values of LPG working pres-sure avoiding the use of the pilot light. The use of the instantaneous ignition system, instead of a pilot light, is essential on an autonomous unmanned system in order to avoid during the turning phase of the work, risk of accidental fires due to the presence of flammable plant ma-terial on the headland.

2.4 Hydraulic system

The machine is equipped with a folding system in order to make easy the transfer and the transport. The main frame is divided into three parts: one central and two lateral foldable parts. Two cylinders powered by the hydraulic circuit of the GMU drive the folding system. The width of the implement when it is closed is 2.48 m. The folding system is equipped with two couples of inductive sensors in order to detect both the closed and the open configura-tion. In order to follow the direction given by guidance system of the GMU and avoid to damage the crop, the machine is equipped with an automatic steering system driven by a central double-rod hydraulic cylinder that enables little change in direction of two metal directional wheels that allow small lateral movement along the maize rows. Machine lateral displace-ment is measured by a linear sensory system (potentiometer and encoder). The positioning system measures the relative displacement of the implement with respect to the GMU in a direction perpendicular to its longitudinal axis. The system is based on a telescopic arm join-ing the GMU and the implement. An end of the arm is fixed to the GMU through a rotary pas-sive joint, with the rotation axis perpendicular to the sensor arm. The other was fixed to a carriage through a ball joint. The carriage can slide over a linear guide. A linear potentiome-ter measures the distance between the carriage and a fixed point.

3 Conclusions

The machine designed and fully realized at the University of Pisa within the RHEA project, in order to perform site-specific flame weeding in maize, actually needs only to be tested in or-der to optimize its functioning and the integration and synchronization with the positioning system and the WDS (Frasconi et al., 2014). Preliminary tests carried out in order to verify the management of actuation devices and sensors by the PLC, the coupling with the GMU and the integration with the perception system for weed and row detection (that make the machine autonomous) were promising but not completely satisfying. Therefore further re-search activities are needed in order to optimize all the sub-systems and verify their integra-tion. This autonomous system for site-specific thermal weed control designed and fully real-ized within the RHEA Project could be applied also to other tolerant crops (i.e. onion, garlic, sunflower, etc.).


4 Acknowledgements

RHEA Project was funded by the European Union’s Seventh Framework Programme [FP7/2007-2013] under Grant Agreement No. 245986 in the Theme NMP-2009-3.4-1 (Auto-mation and robotics for sustainable crop and forestry management).

5 References

Åstrand, B., & Baerveldt, A.J. (2005). A vision based row-following system for agricultural field machinery. Mechatronics, 15, 251-269. Bakker, T., van Asselt, K., Bontsema, J., Müller, J., & van Straten, G. (2010). Systematic design of an autonomous platform for robotic weeding. J. Terramechanics, 47, 63-73. Frasconi, C., Romeo, J., Martelloni, L., Fontanelli, M., Raffaelli, M., Pajares, G., Pirchio, M., & Peruzzi, A. (2014). Calibration and synchronization between WDS and flaming system within the RHEA Project. Accepted to be published in RHEA Conference Proceedings. Gerhards, R., & Christensen, S. (2003). Real-time weed detection, decision making and patch spraying in maize, sugar beet, winter wheat and winter barley. Weed Research, 43, 1-8. Gomes, J.F.S., & Leta, F.R. (2012). Applications of computer vision techniques in the agricul-ture and food industry: a review. Eur. Food Res. Technol., 235, 989-1000. Grisso, R., Alley, M., Thomason, W., Holshouser, D., & Roberson, G.T. (2011). Precision Farming Tools: Variable-Rate Application. In Virginia Cooperative Extension, 442-505, Ar-lington, US. Gutjahr, C., & Gerhards, R. (2010). Decision Rules for site-specific weed management. In Precision Crop Protection – the Challenge and Use of Heterogeneity, 223-239, Springer (Chapter 14). Perez-Ruiz, M., & Upadhyaya, S.K. (2012). GNSS in Precision Agricultural Operations. In New approaches of indoor and outdoor localization systems, 3-26, Intech, (Chapter 1). Wu, X., Xu, W., Song, Y., & Cai, M. (2011). A detection of weed in wheat field on machine vision. Procedia Engineering 15, 1998-2003.

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Design and full realization of physical weed control (PWC ... · Design and full realization of physical weed control (PWC) automated machine within ... weed management, ... the weed