Design And Partial Development Of A Kiwfruit Harvester

The objective of this research was to design and develop an innovative,practical and energy efficient method to harvest kiwifruit on a trellised kiwifruit Farm.The growing environment of the kiwifruit farm when trellised provides an opportunity to design a machine that takes advantage of the tree architecture.The trellised kiwifruit farm allows fruits to be grown in the central region providing sufficient space for a mobile device to maneuver.There is also adequate spacing between ready to harvest Hayward variety kiwifruits such that an appropriately designed device can reach the fruits independently.This paper theoretically and graphically outlined this advantage and proposed a design to utilize it.In the course of this research many design ideas were initially explored before settling for the most advantageous designs of the group,mathematical relationships relevant to the research were developed and various part prototypes were constructed and analyzed.The research proposed a complete design of a semi-automated harvester but the discussion in this paper is confined to two main parts of the overall assembly: The picking section and the packaging section.In developing the mechanism,the following important results were yielded:1.Various designs were investigated before a final design was chosen.These designs were rejected due to too much complexity,being too heavy,requiring too much power or impracticality.Research on the physical characteristics of the kiwifruit was undertaken,some important parameters for the design were found outlined in previous research but other necessary parameters such as stem length and stem diameter were measured in this research.In the end a lightweight electromechanical end effector that provides sufficient cutting torque was developed.The design employs a novel approach to fruit stem cutting using a linear solenoid actuated scissor motion,this motion was triggered by a pressure sensor that literally ?feels? the fruit in the right location.To ensure the design could completely cut the stem of the kiwifruit;mathematical relationships were developed to determine the minimum length of cutting blade,the location for placing the actuating solenoid and the location to make the cut.This device is part of the overall assembly design.Using the knife concept actuated by a linear solenoid actuation for picking the fruit appears to be very feasible as it uses significantly less power allowing the device to be battery powered thereby increasing the mobility of the machine.A cutting torque of approximately 1.35 Nm is required to sever ready to harvest Hayward variety kiwifruits at the stem;the detachment force of the kiwifruit if pulled straight down is an average of 13.5N with a standard deviation of 2.5N.This research outlined that a suitable activation pressure to cut the fruit stem from the vine.This activation pressure should be less than 10 N otherwise the fruit will likely break from the tree before the machine has the opportunity to cut the stem.The design of the device was done using PTC? Creo? and simulation of the cutting motion was conducted within the software platform.For the cutting section a 3D models was printed and the prototype constructed from it.Further studies that can be undertaken include investigating the role of momentum in fruit cutting and the impact of the blade shape.2.An angled surface allowing the kiwifruit to roll using its momentum was constructed with an angle of ten(10)degrees.This angle appears sufficient to induce motion;however this motion is highly dependent on the friction coefficient between the kiwifruit and the surface.The friction coefficient used in simulations was 0.42(static friction between the fruit and an aluminum surface)which yielded speeds greater than 0.25m/s which is suitable for developing a machine that can place one kiwifruit per second.However,if a number of kiwifruits are cut from the vine in quick succession there will be a problem in placing the fruits because they will roll together in clusters.The prototype constructed also showed problems with the method chosen to open the holes the kiwifruit would fall into.3.MATLAB?,VREP? API Integration: Although this research is not focused on the software interface,the MATLAB? integration between a Virtual Robot Experimental Platform(VREP)provided the ability to view simulated sensor output information from the vision sensors and proximity sensors and be able demonstrate data manipulation possible.VREP provides the ability to create scene mimicking how fruits would be arranged and visually illustrating the vision sensor range and the proximity sensor range.This software provides an opportunity to refine sensor fusion which can be then developed in MATLAB.Overall,this results in providing a clearer picture of how the machine would operate in practice.This research is not concerned with analyzing the sensor information,but illustrates how the sensors will be integrated within the machine framework.4.Power Supply and Control: The power supplies used in the prototypes are two,2VDC,2A Lithium ion batteries;one for the base section and one for each end-effector.This power supply is sufficient to pick at least 3000 fruits before recharging is needed;this was calculated from the power consumption of the various parts in the prototype.From the prototype developed,the actual algorithm that would control the cutting of the fruit at the stem and guiding the placement of the kiwifruit was implemented and successfully tested using the ARDUINO? platform.The algorithm handles the cutting procedure and provides some amount of disturbance rejection from leaves and vines.This is because for the solenoid to be actuated in requires two inputs from two separate force sensors that are tuned to accepting the activation pressure input as target pressure.The physical location of the sensors also prevents leaves or vines from triggering the solenoid in error.A refining of the algorithm for smoother operation can be done,but overall the control strategy developed in this research is feasible.