J. Bontsema

An Autonomous Robot for Harvesting Cucumbers in Greenhouses

This paper describes the concept of an autonomous robot for harvesting cucumbers in greenhouses. A description is given of the working environment of the robot and the logistics of harvesting. It is stated that for a 2 ha Dutch nursery, 4 harvesting robots and one docking station are needed during the peak season. Based on these preliminaries, the design specifications of the harvest robot are defined. The main requirement is that a single harvest operation may take at most 10 s. Then, the paper focuses on the individual hardware and software components of the robot. These include, the autonomous vehicle, the manipulator, the end-effector, the two computer vision systems for detection and 3D imaging of the fruit and the environment and, finally, a control scheme that generates collision-free motions for the manipulator during harvesting. The manipulator has seven degrees-of-freedom (DOF). This is sufficient for the harvesting task. The end-effector is designed such that it handles the soft fruit without loss of quality. The thermal cutting device included in the end-effector prevents the spreading of viruses through the greenhouse. The computer vision system is able to detect more than 95% of the cucumbers in a greenhouse. Using geometric models the ripeness of the cucumbers is determined. A motion planner based on the A*-search algorithm assures collision-free eye-hand co-ordination. In autumn 2001 system integration took place and the harvesting robot was tested in a greenhouse. With a success rate of 80%, field tests confirmed the ability of the robot to pick cucumbers without human interference. On average the robot needed 45 s to pick one cucumber. Future research focuses on hardware and software solutions to improve the picking speed and accuracy of the eye-hand co-ordination of the robot.

An autonomous weeding robot for organic farming

The objective of this research is the replacement of hand weeding in organic farming by a device working autonomously at field level. The autonomous weeding robot was designed using a structured design approach, giving a good overview of the total design. A vehicle was developed with a diesel engine, hydraulic transmission, four-wheel drive and four-wheel steering. The available power and the stability of the vehicle does not limit the freedom of research regarding solutions for intra-row weed detection and weeding actuators. To fulfill the function of navigation along the row a new machine vision algorithm was developed. A test in sugar beet in a greenhouse showed that the algorithm was able to find the crop row with an average error of less than 25 mm. The vehicle is a versatile design for an autonomous weeding robot in a research context. The result of the design has good potential for autonomous weeding in the near future.

Intra-Row Weed Control: A Mechatronics Approach

Abstract A fully automated system for mechanical weed control in a row of plants is described and discussed. The performance of the system is shown by laboratory experiments.

ON-LINE ESTIMATION OF THE VENTILATION RATE OF GREENHOUSES

Abstract, accepted for the 24th Benelux Meeting, March 22-24, 2005, Houffalize, Belgium On-line estimation of the ventilation rate of greenhouses using an unknown input observer Jan Bontsema, Eldert van Henten, Jan Kornet Jorrit Budding, Theo Rieswijk Agrotechnology and Food Innovations B.V. P.O. Box 17, 6700 AA Wageningen The Netherlands Email: Jan.Bontsema@wur.nl Priva B.V. P.O. Box 18, 2678 ZG De Lier The Netherlands Email: T.Rieswijk@priva.nl 1 Introduction In modern greenhouse horticulture, the climate in the greenhouse is controlled by a sophisticated greenhouse climate computer. The role of the grower is to define among others temperature trajectories, carbon dioxide setpoints and relative humidity bounds, in such a way that during the growing season the crop is maintained in an optimal condition and the crop production is maximised. The climate computer will then realise the by the grower desired climate. Beside the heat supply and the carbon dioxide supply, a main variable to control the inside climate in a greenhouse is the natural ventilation through the windows in the roof of the greenhouse. The ventilation is controlled by adjusting the window openings and is heavily depending on the outside wind conditions and the difference between inside and outside temperature. An easy method to estimate the ventilation on-line would give the grower valuable insight into the process of his greenhouse climate.

Monitoring and control of water and nutrients in closed growing systems.

In a review approach, this paper introduces some of the a priori knowledge of water and nutrient supply systems. Extra attention is paid to growing systems and their relation to pollution of the environment. In some European countries the year 2000 will be a target to enforce the use of closed growing systems in greenhouses. A project — started in this framework — aims at the design of a management and control system for processes in greenhouses.

Singular perturbation methods applied to a variational problem in greenhouse climate control

The application of singular perturbation methods to a variational problem in greenhouse climate control is demonstrated. An example of economically optimal carbon dioxide control is given. Some preliminary results are shown.<<ETX>>

Effect of inaccurate measurements on energy consumption in greenhouse horticulture

Abstract The influence of inaccurate sensors, used in practice in greenhouse climate control, on the energy consumption of greenhouse horticultural production is investigated. It is shown that the inaccuracy of sensors, caused for instance by improper maintenance, leads to a higher energy use.

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

Abstract 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 sowing.

On-line Monitoring of the Energy and Moisture Flows in Greenhouses

Abstract As the size of greenhouses in the Netherlands is increasing more and more, the on-line monitoring of certain, not directly measured, climate quantities and crop properties becomes important for good management of the greenhouse production system. For the ventilation rate, the crop evaporation and the air exchange through screens several monitors are developed, which calculates these quantities on-line from standard climate measurements. The design, implementation and performance in practice of the proposed methods will be shown.

Development of a Leaf Picking Device for Cucumber Greenhouse Production

Abstract The objectives of this study were to develop a leaf picking device for cucumber and to evaluate its performance. The picking device consisted of a picking rotor composed from knives and brushes, a motor and a vacuum cleaner. In laboratory experiments the performances of suction, cutting, torque and shredding were investigated to achieve the optimum mechanical setting. In a greenhouse experiment, the performance of suction, cutting and shredding were investigated.