Autonomous Fruit Picking Machine:
A Robotic Apple Harvester
Johan Baeten1,Kevin Donn´e2,Sven Boedrij2,
山木培训课程Wim Beckers2,and Eric Claen1,2
1Fac.of Industrial Sciences and Technology,Katholieke Hogeschool Limburg, Belgium
Johan.Baeten@iwt.khlim.be
2ACRO:Automation Centre for Rearch and Education,
Katholieke Hogeschool Limburg,Belgium
Eric.Claen@iwt.khlim.be
Summary.This paper describes the construction and functionality of an Autonomous Fruit Picking Machine(AFPM)for robotic apple harvesting.The key element for the success of the AFPM is the integrated approach which combines state of the art in-dustrial components with the newly designedfle
xible gripper.The gripper consist of a silicone funnel with a camera mounted inside.The propod concepts guarantee ad-equate control of the autonomous fruit harvesting operation globally and of the fruit picking cycle particularly.Extensive experiments in thefield validate the functionality of the AFPM.
1Introduction
moonshellThe u of robots is no longer strictly limited to industrial environments.Also for outdoor activities,robotic systems are increasingly combined with new technolo-gies to automate labour intensive work,such apple harvesting[2,10].This paper describes the feasibility study for and the development of an Autonomous Fruit Picking Machine(AFPM)1.
There are two main approaches in robotic apple harvesting being bulk[9,10] or apple by apple harvesting[3,11].
Peterson et al.[9]developed a mechanical bulk robotic harvester for apples grown on narrow,inclined trellis.This type of bulk harvesting requires,in addition to the canopy-like growth habit,uniform fruit ripeness at harvest,firm fruit,resistant to damage,and short/stifflimbs[10].
The u of an apple by apple picking system,although inherently slower, does not suffer from any of the above restrictions.Moreover,only apples of satisfactory size and maturity are lected for harvesting and can be sorted out immediately.An apple by apple picking system does,however,require an adequate fruit gripper.The gripper is the key element in the success of automated apple by apple harvesting.A good gripper ought to prerve the quality of the 1Funded by IWT-Vlaanderen under TETRA40196.
C.Laugier and R.Siegwart(Eds.):Field and Service Robotics,STAR42,pp.531–539,2008. c Springer-Verlag Berlin Heidelberg2008
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apple and should not damage the tree(nor the apple)during the picking cycle. Setiawan et al.[11]propo a low cost gripper withflexible inflatable parts.Our gripper consists of aflexible silicone funnel and us suction to pick the apple.
An indispensable part of any autonomous apple harvesting machine is the vision system ud to locate the apple[5,10,11,12,13].Bulanon et al.[3] u a(RT)machine vision system to recognize the location of the fruit centre and the abscission layer of the peduncle.In contrast to most rearchers,in
our approach the camera is positioned in the centre of the gripper.This simplifies the calibration of the t-up and ensures adequate control.
According to the classification given by Hutchinson et al.[4],our image bad control is clor to a look and move strategy than to visual rvoing.There is, however,margin for improvement.
Despite previous developments towards a harvesting platform navigating au-tonomously between orchard rows[1],we cho not(yet)to implement an auto-mated navigation,such in[6]or[7],for reasons of both development time as well as safety approval.
The aim of this project was to prove the feasibility and demonstrate the func-tionality of an Autonomous Fruit Picking Machine(AFPM),by using existing state of the art(industrial)components.This resulted in the prototype AFPM, described in the following ctions.First,ction2describes the overall con-struction of the AFPM.Section3prents our new,patented gripper designed specifically for the apple harvesting task.Section4goes into the control details for one picking cycle.Finally,ctions5and6summarize the results of thefield experiments and conclude this paper.
2Overall Construction of AFPM
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The AFPM is built on a platform mounted behind an agriculture tractor. Figure1shows thefirst version of the AFPM.Figure2illustrates schematically the functional layout and dataflow.In order to reduce the development period of the AFPM,although overkill,an industrial robot(Panasonic VR006L)is cho-n as manipulator.The AFPM further consists of a tractor-driven generator for power supply,a(2D)horizontal stabilization unit,a7th external vertical axis to enlarge the operation range,a safety scanning device,a central control unit,a touch panel PC with Human Machine Interface,a canopy and all around curtain to even out light conditions and,finally,a fruit gripper designed specifically for this task,with a camera mounted in the centre of the gripper.Theflexible grip-per(described in ction3)guarantees afirm grip without damaging the fruit and rves in fact as the mouth of a vacuum cleaner.
The2D horizontal stabilization consists of two hydraulic feet and one turn over cylinder,configured as a3-point suspension.Controlled by two level nsors, the system ensures a stable positioning of the robot platform during the picking cycle.
Autonomous Fruit Picking Machine:A Robotic Apple Harvester 533
particularlyHigh frequency light source Soft gripper
with camera inside
6DOF industrial robot
Horizontal
stabilization
External vertical axis Power generation
and transfer
Fig.1.Construction of the AFPM
石家庄留学
Fig.2.Functional scheme of the AFPM
534J.Baeten et al.
3New Flexible Gripper
To pick the apple with as little energy as possible,a completely new fruit gripper had to be designed.Its patented design has two main functions:catching the apple and enclosing the camera.Figure3gives some examples.
The gripper assumes the shape of the apple and enclos itfirmly.After veral prototypes,the optimal funnel shape with respect to edge thickness,funnel angle and size with a trade offbetweenflexibility andfirmness was designed and tested. The current version has a maximum diameter of10.5cm.The gripping function is activated by vacuum suction.It possible the pick up an apple by just pushing the gripper onto the apple and closing the vacuum port with yourfinger. Experiments show that even an elongated exposure of the apple to the(rather small)vacuum levels2ud does not damage the apple in any way.
Fig.3.Left:two examples of silicone gripper;right:gripper mounted on robot with camera inside
Placing the camera in the centre of the gripper offers numerous advantages. First of all,the gripper is always in line with the camera and thus with the image,which simplifies the(necessary)coordinate transformation from image to robot.Furthermore,the position of the camera is fully controllable.The camera can always point its optical axis to the apple(e ction4and simulation figure7).This reduces image distortion and eliminates the necessity for thorough calibration.rain cats and dogs
2The magnitude of underpressure ranges from150mbar to230mbar with aflow rate of200m3/h.
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brisbane>comet
top-view
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Fig.4.3D,top and front view of the camera model defining the camera frame and illustrating the computation of the rotation anglesθx andθy,needed to centre the apple in the image来料加工英文
4Approach for Fruit Picking Cycle
The autonomous harvesting operation is hierarchically structured in three levels. Once the AFPM is stationed in front of the tree with active stabilization(first level),it scans the tree from40look-out positions or ctors(cond level).For each ctor,all ripe apples are listed and picked one by one in a looped task (third level).A picking operation consists of following steps:
1.The position of the apple in the image,possibly after declustering,is deter-
mined.Only ripe apples with qualified size are lected.
2.The camera rotates around x-and y-axes,byθx andθy respectively,in order
to point the optical axis straight to the apple.Positioning the camera by only rotating the wrist results in a small and therefore fast robot movement.
Figure4defines the ud t-up.The rotation angles yield:
θx=−arctan(y pμp/f)(1) for the rotation around the x-axis and
θy=arctan(x pμp/f)(2) for the(simultaneous)rotation around the y-axis,with f the focal length [mm],μp the pixel-size[mm/pix]and x p,y p the measured centre of the apple in the image plane[pix].As equations1and2show,the rotation angles do not depend on the distance to the apple z cam.Only the focal length f needs to be calibrated.
