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

Optimal greenhouse cultivation control: survey and perspectives

Abstract: A survey is presented of the literature on greenhouse climate control, positioning the various solutions and paradigms in the framework of optimal control. A separation of timescales allows the separation of the economic optimal control problem of greenhouse cultivation into an off-line problem at the tactical level, and an on-line problem at the operational level. This paradigm is used to classify the literature into three categories: focus on operational control, focus on the tactical level, and truly integrated control. Integrated optimal control warrants the best economical result, and provides a systematic way to design control systems for the innovative greenhouses of the future. Research issues and perspectives are listed as well

Proceedings of the 4th field robot event 2006, Stuttgart/Hohenheim, Germany, 23-24th June 2006

Zeer uitgebreid verslag van het 4e Fieldrobotevent, dat gehouden werd op 23 en 24 juni 2006 in Stuttgart/Hohenhei

Collision-free inverse kinematics of the redundant seven-link manipulator used in a cucumber picking robot

The paper presents results of research on an inverse kinematics algorithm that has been used in a functional model of a cucumber-harvesting robot consisting of a redundant P6R manipulator. Within a first generic approach, the inverse kinematics problem was reformulated as a non-linear programming problem and solved with a Genetic Algorithm (GA). Although solutions were easily obtained, the considerable calculation time needed to solve the problem prevented on-line implementation. To circumvent this problem, a second, less generic, approach was developed which consisted of a mixed numerical-analytic solution of the inverse kinematics problem exploiting the particular structure of the P6R manipulator. Using the latter approach, calculation time was considerably reduced. During the early stages of the cucumber-harvesting project, this inverse kinematics algorithm was used off-line to evaluate the ability of the robot to harvest cucumbers using 3D-information obtained from a cucumber crop in a real greenhouse. Thereafter, the algorithm was employed successfully in a functional model of the cucumber harvester to determine if cucumbers were hanging within the reachable workspace of the robot and to determine a collision-free harvest posture to be used for motion control of the manipulator during harvesting. The inverse kinematics algorithm is presented and demonstrated with some illustrative examples of cucumber harvesting, both off-line during the design phase as well as on-line during a field test

Adaptive detection of volunteer potato plants in sugar beet fields

Volunteer potato is an increasing problem in crop rotations where winter temperatures are often not cold enough to kill tubers leftover from harvest. Poor control, as a result of high labor demands, causes diseases like Phytophthora infestans to spread to neighboring fields. Therefore, automatic detection and removal of volunteer plants is required. In this research, an adaptive Bayesian classification method has been developed for classification of volunteer potato plants within a sugar beet crop. With use of ground truth images, the classification accuracy of the plants was determined. In the non-adaptive scheme, the classification accuracy was 84.6 and 34.9% for the constant and changing natural light conditions, respectively. In the adaptive scheme, the classification accuracy increased to 89.8 and 67.7% for the constant and changing natural light conditions, respectively. Crop row information was successfully used to train the adaptive classifier, without having to choose training data in advanc

Precisie in de kas

De glastuinbouw heeft te maken met grote veranderingen die het noodzakelijk maken om na te denken over aanpassingen aan de gebruikte strategieën voor beheersing van fysiologische afwijkingen en ziekten en plagen. Het overschakelen op marktgedreven grootschalige productie vergt een strakke sturing, gebaseerd op een continu inzicht in de gewasontwikkeling, afgezet tegen een strak teeltplan. Het terugdringen van het gebruik van fossiele brandstoffen en het zoveel mogelijk binnen de kas houden van gedoseerde CO2 dwingen tot een beter inzicht in fysiologische (deel)processen onder invloed van het microklimaat rondom de plantenonderdele

Use of supplementary lighting top screens and effects on greenhouse climate and return on investment

Discomfort caused by light pollution from greenhouses that apply supplementary lighting is an issue in Dutch society nowadays. At this moment Dutch legislation requires an opaque screen that reduces light transmission of the greenhouse wall by 95%. In 2008 also the light transmission of the greenhouse roof must be reduced equally and supplementary light will be limited to 15,000lx(180¿mol/m2/s), unless light emission is totally prevented. The objective of this research was to calculate the economic consequences of installing reflecting, light emission reducing or blocking screens by considering crop yield and costs. A mathematical correction equation was developed to approach the light gain for the crop as a result of internal reflection. Greenhouse climate and tomato crop growth were simulated for a reference greenhouse with supplementary lighting and without an emission blocking screen and for a low-light-emission greenhouse with a blocking screen. The supplementary lighting level was set at 180¿mol/m2/s. Results show that the greenhouse climate below the screen remained manageable, but that the desired DIF of 2°C was affected. The light gain was on average about 3% and resulted in production increase. A small net yearly profit resulted based on direct and indirect effects of the screen. In conclusion, the simulation suggested that stopping light emission at the source with help of reflective opaque screens is economically feasible if screen operation is included in planning the lighting scheme

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

Greenhouse engineering: New technologies and approaches

Firstly, this article discusses the greenhouse engineering situation in three geographic areas which are relevant in the field of protected cultivation: Northern Asia, The Netherlands and the Mediterranean. For each area, the prevailing greenhouse type and equipment is briefly described. Secondly, the main technological constraints are pointed out and finally the research directions are discussed. For all areas under consideration, attempts to design more efficient greenhouse systems are under way. In Northern Asia progress is being made towards the optimisation of greenhouses as a solar collector and to the development of new heating strategies. Important subjects addressed in The Netherlands are energy conservation and the replacement or alleviation of human labour by increasing mechanisation. In the Mediterranean there is growing interest in semi-closed greenhouses with CO2 enrichment and control of excessive humidity. All geographic areas share the need of having an optimised climate control based on the crop response to the greenhouse environment. All areas also share the requirement of being respectful to the environment, therefore future greenhouses are expected to use engineering to produce with minimal or zero emissions

Technical solutions to prevent heat stress induced crop growth reduction for three climatic regions in Mexico

In the last 15 years a significant increase in greenhouse area has occurred in Mexico, from a modest 50 hectares in 1990 to over 2,000 hectares in 2004. The rapid increase in greenhouse area is a result of an attractive export market, USA. Mexican summer midday temperatures are well above crop optimum and cooling is needed if heat stress induced crop growth reduction is to be prevented. The objective of this study was to determine the effectiveness and feasibility of greenhouse cooling systems for tomato culture under desert, humid tropic and temperate Mexican weather conditions. These climate regions are represented by Mexicali, Merida and Huejutla respectively. The cooling systems included a variety of passive and active systems, which through an engineering design methodology were combined to suit the climate conditions of the 3 regions. The evaluation was conducted via simulation, taking into account the most important temperature effects on crop growth and yield. The results showed that the cooling systems were effective in decreasing heat stress to plants. Investment costs of greenhouse with cooling equipment were under USD 50 m-2 and operational costs were under USD 10 m-2 for all equipment combinations and treatments except for the humid tropic climate of Merida. Solutions for Merida were both economically and physically not feasible due to too high humidity levels. This model study clearly indicates that cooling is feasible in desert and moderate climate regions of Mexico but in humid tropic climate regions feasibility is a problem. Application of design methodology and design evaluation with help of simulation greatly contributed to pointing out effective and non-effective solutions to reduce heat stress in hot climates