Open-loop optimal temperature control in greenhouses

Earlier research has revealed that considerable energy savings can be achieved by maintaining an average temperature in the greenhouse in stead of maintaining rigid pre-defined temperature `blue-prints¿. A model based optimal control approach has proven to be a suitable framework to tackle these kind of control problems and it has been shown that these algorithms can be implemented on-line. But, when on-line optimal temperature control is considered, interesting questions arise, some of which are still unresolved. The issue tackled in this paper concerns the relation between the resolution of the control strategy (sample time) and energy savings of the control strategy. One would expect that an accurate and frequent anticipation to changing outdoor climate conditions might result in reduced energy consumption. It was indicated in the literature that a sample-time of 0.25 h or 1 hour should be sufficient, but these choices were hardly motivated. In this research, the relation between the control resolution and energy savings was quantitatively investigated using a dynamic greenhouse climate model and measurements of Dutch outdoor climate conditions containing high-frequency components. The results indicate that for an open-loop optimal control problem concerning the realization of an average temperature during a fixed period of one day using a minimum amount of energy with full a-priori knowledge of the outdoor weather, a resolution of the heating profile between half an hour and a hour suffices to produce accurate results in terms of energy conservation. These results were not much affected by parameter variations (heat capacity of the air, the solar heating efficiency) or opening and closing of thermal screens

Robotic weeding of a maize field based on navigation data of the tractor that performed the seeding (Preprint)

This research presents robotic weeding of a maize field based on navigation data of the tractor that performed the seeding. The availability of tractors equipped with RTK-DGPS based automatic guidance potentially enables robots to perform subsequent tasks in the same field. In an experiment a tractor guidance system generated a route for sowing based on an initial path consisting of two logged positions (A-B line) and then planned the subsequent paths parallel to the initial path one working width apart. After sowing the maize, the A-B line was transferred to the Intelligent Autonomous Weeder (IAW) of Wageningen University. The IAW generated a route plan based on this A-B line and eight coordinates defining the borders of the field and the two headlands. It then successfully performed autonomous weeding of the entire field except of the headlands. The row width was 75 cm and the width of the hoes mounted on the robot was 50 cm. The results show that it is possible to perform robot weeding at field level with high accuracy based on navigation data of the tractor that performed the sowin

A path following algorithm for mobile robots

This paper considers path following control for a robotic platform. The vehicle used for the experiments is a specially designed robotic platform for performing autonomous weed control. The platform is four-wheel steered and four-wheel driven. A diesel engine powers the wheels via a hydraulic transmission. The robot uses a Real Time Kinematic Differential Global Positioning System to determine both position and orientation relative to the path. The deviation of the robot to the desired path is supplied to two high level controllers minimizing the orthogonal distance and orientation to the path. Wheel angle setpoints are determined from inversion of the kinematic model. At low level each wheel angle is controlled by a proportional controller combined with a Smith predictor. Results show the controller performance following different paths shapes including a step, a ramp, and a typical headland path. A refined tuning method calculates controller settings that let the robot drive as much as possible along the same path to its setpoint, but also limit the gains at higher speeds to prevent the closed loop system to become unstable due to the time delay in the system. Mean, minimum and maximum orthogonal distance errors while following a straight path on a paving at a speed of 0.5 m/s are 0.0, -2.4 and 3.0 cm respectively and the standard deviation is 1.2 cm. The control method for four wheel steered vehicles presented in this paper has the unique feature that it enables control of a user definable position relative to the robot frame and can deal with limitations on the wheel angles. The method is very well practical applicable for a manufacturer: all parameters needed are known by the manufacturer or can be determined easily, user settings have an easy interpretation and the only complex part can be supplied as a generic software modul

CROPS : high tech agricultural robots

In the EU-funded CROPS (Clever Robots for Crops) project high tech robots are developed for site-specific spraying and selective harvesting of fruit and fruit vegetables. The harvesting robots are being designed to harvest high-value crops such as greenhouse vegetables, fruits in orchards and grapes for premium wines. The CROPS robots are also developed for canopy spraying in orchards and for precision target spraying in grape vines to reduce the use of pesticides. A CROPS robot will be able to detect the fruit, sense its ripeness, then move to grasp and gently detach only the ripe fruit. For crop protection the canopy sprayer can detect contours of trees in an orchard and consequently only spraying on the trees and the precision target sprayer can detect diseases on leaves of vine grapes and only spray pesticides on the affected spots of the leaves. In the CROPS project also attention is paid to reliable detection and classification of objects and obstacles for autonomous navigation in a safe way in plantations and forests. For the several applications within the CROPS project platforms were developed. Sensing systems and appropriate vision algorithms for the platforms have been developed. For the software platform the Robot Operating System (ROS) is used. A 9 degrees of freedom (DOF) manipulator was designed and built and tested for sweet-pepper harvesting, apple harvesting and in close range spraying. The 9-DOF manipulator is modular, since the joint configuration can be adapted to the applications, e.g. 6 DOF for the close range spraying. For the different applications different end-effectors were designed and tested. The main results of the CROPS project will be the applications, the so-called demonstrators For sweet pepper a platform that can move in between the crop rows on the common greenhouse rail system which also serves as heating pipes was built and equipped with a sensing and lightning system, the manipulator and end-effectors. The complete system was tested and showed to growers in a lab situation. The apple harvesting platform is based on a current mechanical grape harvester. In discussion with growers so-called 'walls of fruit trees' have been designed which bring robots closer to the practice. This system, equipped with a sensing system the CROPS manipulator and a special end-effector, has been successfully tested in an orchard. A canopy-optimised sprayer has been designed as a trailed sprayer with a centrifugal blower. The system has been successfully tested in an orchard with a significant reduction of pesticide use. For close range target spraying the spraying robot in a greenhouse experiment with grape vines reduced the pesticide consumption with 84%

On-line monitoring van transpiratie en fotosynthese: de praktijk

WUR Glastuinbouw heeft monitoren ontwikkeld voor de on-line bepaling van de verdamping en fotosynthese. Deze monitoren zijn uitgetest bij diverse vruchtgroentetelers en slatelers. In het onderzoek is ook een nieuwe transpiratiemonitor ontwikkeld, op basis van een statische energie- en vochtbalan

Analyse luchtsysteem Marjoland IV

Bij Marjoland in Waddinxveen is een installatie aangebracht waarmee via slurven een mengsel van opgewarmde buitenlucht en gecirculeerde kaslucht onder het gewas wordt geblazen. Daarmee hoopt men kleinere temperatuurverschillen in de kas te krijgen en vocht op een goedkopere wijze af te voeren dan met een minimum buis. Uit metingen bleek dat de horizontale temperatuurverschillen veroorzaakt werden door een koude luchtstroom boven het doek die niet met de luchtblaasinstallatie gecompenseerd konden worden, maar wel met verticale schotten boven het schermdoek. Na deze ingreep is geleidelijk de verhouding kaslucht en buitenlucht zodanig gewijzigd, dat er steeds meer buitenlucht werd toegevoerd. Daarmee kon nagenoeg altijd het vochtdeficit boven 2,0 g/kg worden gehouden. Afhankelijk van de buitencondities werd 60 g/m2kas/uur vocht afgevoerd. Er was weinig energie nodig voor de ventilatoren en voor het opwarmen van de buitenlucht. De minimum buis kon 8 graden lager en de rookgaskoeler van de WKK werd beter benut

An algorithm for optimal fertilization with pure carbon dioxide in greenhouses

Pure (bottled or piped) carbon dioxide is commonly supplied to increase productivity of greenhouse crops. As ventilation is necessary for controlling temperature, particularly under sunshine (when a high CO2 concentration would be most desired) there is a need for optimal management of supply, in order to ensure the maximum net return from cost of carbon dioxide supplied and increase in harvest. The optimal concentration depends on many factors: the expected increase of yield thanks to carbon dioxide supply under given climate conditions; the actual ventilation rate; the value of yield and the cost of carbon dioxide. We combined a calculation of the “value” of carbon dioxide supply with an algorithm to calculate the ventilation rate, into a calculation on-line of the optimal supply rate. The algorithm was implemented and tested into a commercial climate control computer