Design of a Seeder to achieve Highly Uniform Sowing Patterns. H.W. Griepentrog 1, P.T. Skou 1 J.F. Soriano 2, B.S. Blackmore 1

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1 Peer Reviewed Conference Paper Design of a Seeder to achieve Highly Uniform Sowing Patterns H.W. Griepentrog 1, P.T. Skou 1 J.F. Soriano 2, B.S. Blackmore 1 1 The Royal Veterinary and Agricultural University (KVL), Frederiksberg / Copenhagen, Denmark hwg@kvl.dk 2 Polytechnic University of Madrid, Madrid, Spain In Proceedings: 5 th European Conference on Precision Agriculture, Uppsala, Sweden, 9 th 12 th June 2005, pp

2 Design of a seeder to achieve highly uniform sowing patterns H.W. Griepentrog 1, P.T. Skou 1, J.F. Soriano 2, B.S. Blackmore 1 1 The Royal Veterinary and Agricultural University, Copenhagen, DK 2 Polytechnic University of Madrid, SP hwg@kvl.dk Abstract Conventional sowing patterns have some drawbacks for crop plants. Mainly due to uneven spatial distribution they suboptimal utilize space, nutrients and water, have a low ability to suppress weeds and are in general difficult to treat individually. Electric stepper motors have been retrofitted to a precision seeder for sugar beet to achieve very accurate control of the seeding mechanisms and therefore being able to create precise regular seeding patterns. Lab testing has been conducted to check the accuracy of seed spacing as well as the evenness of row synchronization. The defined and required accuracy for grid seeding of sugar beet has been achieved. Keywords: grid seeding, seed spacing, row synchronization, weed control Introduction Today crop plants are spatially not evenly distributed across a field. This has some drawbacks since crop plants i) sub-optimally utilize space, nutrients and water, ii) have a low ability to suppress weeds and iii) are difficult to physically treat because of the uneven spatial patterns. The main reason that crop plants are established in uneven spatial patterns is the insufficient performance of seeding machinery, especially the metering and seed conveying systems (Griepentrog, 1999). Uneven spatial distribution of seeds creates heterogeneous growth conditions for the crop plants and is the reason for a suboptimal utilization of available growth resources. A regular spatial distribution of seeds creates the best crop growth condition because it minimizes the intra-specific competition effects by giving all crop plants the same space to utilize water and nutrients. This will affect the whole plant development both the above- and below-ground parts. Furthermore, an even spatial distribution increases the ability to suppress weeds by better and earlier coverage of the soil surface (Weiner et al., 2001). Ideal distributions of crop plants have triangular arrangements which give individual hexagonal plant areas (Griepentrog, 1999; Heege & Billot, 1999; Fisher & Miles, 1973). Much research has been conducted to improve the performance of seeders focusing on metering systems as well as seed tubes and seed coulters. Leading manufacturers of agricultural machinery developed sowing machines that carry out the drilling in different ways, such as in rows, bands and broadcast (Heege & Billot, 1999). Currently available seeding machinery does not achieve highly even plant distributions because of (i) insufficient evenness of seed spacing within the rows, (ii) non-synchronization within the working width, and (iii) between operation passes. However, no acceptable seeder has been developed yet to establish crops in ideal spatial patterns. A precision seeder for sugar beet with electric drive has been developed by the research group Environment, Resources and Technology at KVL, Denmark. Electric stepper

3 motors drive and control the seeder s metering discs with high accuracy. Due to the electronic control, the position of the discs is always known and can therefore be used to determine the points of seed drop and hence the seed placement. Synchronization between the rows within the working width of the machine is achievable. Furthermore, in combination with an ultra high accuracy GPS (RTK), synchronization between all passes in a field can be achieved to get an even overall crop plant distribution across a whole field. In general, due to the advanced seeder control, almost any desired or varying pattern of crop plants is achievable. Triangular (hexagonal) and rectangular patterns are possible to establish. Furthermore, the possibility of leaving gaps with no seeds at defined locations in the direction of driving will e.g. allow accurate cross or transversal hoeing. The gaps may be adapted to track width and tire size of a tractor. For grid seeding the evenness of seed placement and spacing is essential. Table 1 shows how longitudinal seed spacing in lab testing is evaluated. This assessment scheme is common and recognized for European machinery testing stations (Anon., 1998). To achieve an equidistant pattern across a whole field e.g. for cross hoeing, we assume that an excellent or at least a good performance of the seeder should be achieved. The standard deviations of the measured spacing data should therefore not exceed 10 mm. Table 1: Evaluation scheme for evenness of seed spacing for lab testing of sugar beet precision seeders (Anon., 1998) Seed Spacing Evaluation Standard Deviation mm < 5 Excellent < 10 Good < 15 Acceptable < 20 Sufficient > 20 Not sufficient Seed synchronization and transversal overlap can be done by a GPS controlled sideshift system which was also developed by our group. Figure 1 shows the proposed principle of grid seeding attached to an autonomous tractor. Both the tractor and the implement are controlled by an RTK GPS and guided by virtual predefined passes across the field. The patterns can be varied but are kept the same across the field and are synchronized between the operation passes of sowing. Seed mapping of a previous pass will be used as a reference for seed placements of the current operation for synchronization between passes. Seed mapping has been successfully conducted by using high accurate RTK GPS systems (Griepentrog et al., 2005). The objective of the project was to test the machine in the lab for its general performance (e.g. acceleration of discs and evenness of seed spacing) and the synchronization between the units within the working width. 2

4 Figure 1: System principle of a grid seeder mounted on an autonomous tractor Materials and Methods The seeder The machine used for the laboratory test was a precision seeder for sugar beet (Kverneland Accord / Kleine Unicorn 3). Four seeder units were attached to a toolbar. The seeder was factory-fitted with housings for conventional electric motors to drive the seeding discs. Optical sensors, which were also preinstalled, detected the seeds as they dropped into the furrow. These sensors are normally used to check the general performance of each unit. For the final version of the seeder, the sensors were used to allow a geo-referencing of the dropped seeds (Griepentrog et al., 2003). Four seeder units were modified and prepared for the lab tests. These units can be attached to an autonomous tractor and also be used for future field experiments (Blackmore et al., 2004). Table 2 details the properties and settings of the seeder. Table 2: Main characteristics and settings of the mechanical precision seeder for sugar beet (KVERNELAND ACCORD, Germany, Kleine Unicorn 3) Metering mechanism Drive Disc diameter Cells per disc Target seed spacing Fully mechanical with vertical discs and tangential inside feeding Independent electric stepper motors 228 mm mm (zero ground speed) Zero ground speed The position where seeds drop into the furrow and where they remain after seed coverage are likely to be different. Although the vertical drop height is low (5 cm), bouncing and rolling can occur when the seed reaches the bottom of the furrow. To minimize seed displacement, seeds should be dropped into the furrow with a horizontal velocity equal and opposite to the forward velocity (Heege & Billot, 1999). This machine setting is called the zero ground speed effect. To benefit from the effect, the goal of the controller is therefore to set the disc speeds at seed drop time equal to the forward speed. 3

5 Stepper motors The most important change made to the standard seeder was that the conventional electric motors that powered the seeding discs were substituted with stepper motors (PHYTRON ZSS42). In full step mode, the motors had a resolution of 200 steps per revolution. Due to this high resolution an accurate control of the disc speeds and hence the seed drop times should be sufficient. Stepper motors can be viewed as electric motors without commutators, meaning that all of the commutation must be handled externally by the motor controller (Hughes, 1993). Perhaps the most valuable and interesting feature of a stepper is the ability to position the shaft in fine predictable increments, without the need to query the motor as to its position. The motor shaft led to a gearbox which had a transmission ratio of 36:1, meaning that the rotation speed decreases 36 times but the torque increases 36 times. Motor Controllers (Power stages) Each of the four stepper motors is controlled by a power stage (PHYTRON GLD) to which different running programs are downloaded by particular software from a connected computer (PHYTRON IPCOMM). For the lab tests, the running programs were started and stopped for all four stages by an externally-switched strobe signal (digital IO input). A control bus connected the four power stages in series. Batch commands were saved in the power stages, one for each frequency (4 000 and Hz) and an additional one for the initialization process. Initialization process To ensure that the units drop the seeds at the same time, the controllers need to recognize the position of each seeder disc. An optical disc position detector was used to find an attached mark inside each seeder disc. The mark was carefully placed at the same location on each disc. The initialization sensors are directly connected to the power stages. Predefined controller software was used before each start of a test run to position all discs in the same way. This process is called initialization or referencing. Data logging The aim of the measuring system was to obtain data about the seed drop times and the speed of the discs. Seed spacing times were recorded from the seed detection sensors and the disc speed was measured using an extra encoder attached to one seeder disc. In order to record data, an acquisition system (DAQBOOK) was connected to a PC via a parallel port. A computer application (DAISYLAB) was used for programming the logging setup. A schematic of the lab testing system is shown in Figure 2. Lab experiment The seeder was tested with standard coated beet seeds of the variety Manhattan (DANISCO). The average diameter of the seeds was 4 mm. The experiment was divided into two parts to evaluate i) seeder disc acceleration and ii) seeder general performance. 4

6 - The acceleration was evaluated by measuring the time needed to accelerate the stepper motor from 0 to Hz, which accelerates the seeder disc to 50 min -1 or a forward speed of 2.1 km h -1. In order to control the disc speeds for dropping seeds at predefined times or locations, the speed responses to new target settings should be as short as possible. The acceleration ramps were predefined in the controller software as 5 000, , , and Hz s Two different motor control frequencies (4 000 and Hz) were adjusted to check the seed spacing, cell filling and row synchronization. Cell filling data show the share of missing seeds in disc cells. In general, cell filling should be as high as possible in order to avoid gaps in the crop stand. Table 3 shows the setting of the machine for evaluating the seeder performance. The speeds were relatively low but required to gain high seed spacing accuracies. The seeder is planned to be attached to an autonomous tractor, therefore higher speeds shouldn t be necessary or are even not aimed at (Blackmore et al., 2004). Before every test run the hoppers were discharged and the metering mechanisms were cleaned to ensure consistent operation conditions. The lab test has been carried out by the research group Environment, Resources and Technology at The Royal Veterinary and Agricultural University (KVL, Denmark). Figure 2: Measuring system setup for lab testing (only one seeder unit out of four is displayed) Data processing The recorded data were analyzed according to standard analysis for evaluating precision seeder performance e.g. by machinery testing stations (Griepentrog, 1992; Burema et al., 1980; Anon., 1998). The mean spacing and standard deviation was determined by using only single spacing data. This ensured that the cell filling had no influence on the values of mean spacing and standard deviation. The standard deviation is a measure to express the accuracy of seed spacing for lab testing as well as for field tests with plant spacing data. To show the accuracy of row synchronization, more than 300 spacing sequences per seeder for one test run were analyzed. The standard deviation of the accumulated time per seed detection for the same spacing sequence was calculated from the four seeders. 5

7 If one motor or more would become unsynchronized a graph of the standard deviations would show higher values and a general trend. Table 3: The two speed variants of the lab test experiment to determine the accuracy of seed spacing and row synchronization (motors 200 full steps). Results and Discussion Tractor speed Seeder disc Motor speed Fullsteps m s -1 km h -1 min -1 min -1 Hz Motor torque and inertial and friction forces have an influence on the acceleration performance of the seeder mechanisms. Table 4 shows the durations to accelerate to Hz motor speed depending on the definable ramp by the controller software. The motors show a satisfactory ability to change the speed in even very short periods. Therefore the adaptation to varying forward speeds and even advanced control to drop seeds at particular times seems possible and promising. Table 4: Acceleration time from stop to target speed for one seeder equipped with a stepper motor Acceleration (ramp) Time to reach Hz motor speed Hz s -1 theoretical measured s s To arrange plants in regular grids, very accurate seed spacing is required. The values for mean spacing, as shown in Table 5, are very low and independent from the seeder unit and from the motor speed. The motors are therefore able to drive the discs at a constant and very accurate speed. As shown in Table 1 the required values of the standard deviations are low. Measured standard deviations less than 5 mm are rated as excellent whereas values with higher than 5 mm but less than 10 mm as good (Anon., 1998). The standard deviation is influenced only by the forward speed and not by seeder units. The fact that forward speed or speed of the discs has an influence on the accuracy of spacing is well known in machinery testing. The cell filling was normal except for seeder unit 4 which could not reach 90 % cell filling for unknown reasons. The standard deviation of the accumulated time per seed detection for the same spacing sequence between the four seeders is shown in Figure 3. This parameter allows 6

8 evaluating the synchronization between the four rows. The figure shows a constant range of the values during the test run. If only one of the motors had become unsynchronized the graph would have shown much higher values and a trend in the plotted data of the graph. The mean of these 309 standard deviations is 4.23 ms. The test run was done with a motor speed of Hz or m s -1 forward speed. The mean absolute standard deviation was calculated to 2.53 mm. Assuming a normal distribution, 95 % of the data were in a range of ± 5.1 mm. Grid seeding with such a spacing accuracy has to be regarded as sufficient and very accurate. However, field experiments have to be conducted to investigate the effects under dynamic operation and field conditions. Table 5. Seed spacing analysis for two forward speeds and four seeder units Seeder Forward Motor n Seed Spacing Cell Unit Speed m/s Speed Hz Mean mm Standard Deviation mm Filling % Standard deviation [ms] Spacing sequence Figure 3. Synchronization of the four seeder units for Hz motor speed expressed in standard deviation versus time or spacing sequence Conclusions The first step of the design of a precision seeder for accurate grid seeding has been achieved by i) obtaining good to excellent seed spacing accuracy and ii) a sufficient synchronization between the four seeder rows. The next step will be to develop a 7

9 controller to manage the transversal overlap (side-shift) and the transversal synchronization between the operation passes of a field. Planned field experiments will show the accuracy of crop plant patterns sown by the grid seeder. Acknowledgements This project was funded by the Danish Agricultural and Veterinary Research Council (SJVF), Copenhagen, Denmark. We thank O. Plet, C. Beier and T. Meinel from the company Kverneland Accord, Soest, Germany for their advice and support. Thanks also to J. Resting-Jeppesen, M. Nørremark and J. Nielsen from KVL for setting up the lab testing equipment and A.M. Thonning Skou for improving the manuscript. References Anonymous, DLG-Prüfrahmen für Einzelkornsämaschinen. (DLG-Test rules and evaluation for precision seeders) Frankfurt a.m., Germany, Deutsche Landwirtschaftsgesellschaft (DLG). Blackmore, B.S., Griepentrog, H.W., Nielsen, H., Nørremark, M., and Resting- Jeppesen, J Development of a deterministic autonomous tractor. In: Proceedings CIGR, Bejing, China Burema, H.J., Meijer, E.N.C. and Telle, M.G Development and study of a selfrecording sticky belt. Wageningen, IMAG. Research Report 80-3 Demmel, M.; Hahnenkamm, O.; Peterreins, M Höhere Erträge durch bessere Standraumverteilung - Versuchsergebnisse zur Gleichstandsaat von Mais (Improved spatial crop distribution gives higher yields - results from trials with equidistant seeding of maize). mais (1) 4-7 Fisher, R.A. and Miles, R.E The role of spatial patterns in the competition between crop plants and weeds - a theoretical analysis. Mathematical Biosciences 18, Griepentrog, H.W Zur Bewertung der Flächenverteilung von Saatgut. (Assessment of spatial distribution of seeds). Agrartechnische Forschung 5(2) Griepentrog, H.W Bewertung von Längsverteilungen bei Einzelkornsämaschinen. (Assessment of longitudinal distribution of precision seeders) Landtechnik 47(3) Griepentrog, H.W., Nørremark, M., Nielsen, H., and Blackmore, B.S Individual plant care in cropping systems. In: Proceedings of the 4th European Conference on Precision Agriculture ed Stafford, J. V. & Werner, A., Wageningen Academic Press, Wageningen, The Netherlands, Griepentrog, H.W., Nørremark, M., Nielsen, H.; Blackmore, B.S Seed mapping of sugar beet. Precision Agriculture (6) 1-9, in press Heege, H.J. and Billot, J.F Seeders and Planters. In: CIGR Handbook of Agricultural Engineering, p ASAE, St. Joseph, MI, USA Hughes, A Electric motors and drives - fundamentals, types and applications, 2nd edn. Newnes, Oxford, UK Weiner, J., Griepentrog, H.W. and Kristensen, L Increasing the suppression of weeds by a cereal crop. Journal of Applied Ecology 38,