菠萝采摘机械手的设计与试验.pdf

第 28 卷增刊 2农 业 工 程 学 报Vol.28Supp.2422012 年10 月Transactions of the Chinese Society of Agricultural EngineeringOct.2012Design and test of pineapple harvesting manipulatorWang Haifeng1,Li Bin2,Liu Guangyu1,Xu Liming3(1.Chinese Academy of Modern Agricultural Mechanization Sciences,Beijing 100083,China;2.National Engineering Research Center of Intelligent Equipment for Agriculture,Beijing 100089,China;3.College of Engineering of China Agricultural University,Beijing 100083,China)Abstract:Pineapple harvest is a pretty heavy job and it is in great need to automate the harvesting process.This paperpresented a kind of manipulator designed for pineapple harvest and the test was conducted to validate its feasibility.Basedon the growth characteristics of the fruit,two steps were determined for the harvest operation,catching the fruit andholding it steadily in horizontal direction first,and then harvesting it by rotating in vertical direction.The manipulator wasdesigned by using professional mechanical design software Pro/E,which consists of three parts,the grabbing mechanism,the hand driving mechanism and the rotating mechanism.A control system based on AT89C51 microcontroller wasdesigned to control two stepping motors,which can finish the whole harvest process.The experimental results showedthat,the designed manipulator can realize the harvest operation with the control system.The max rotation angle is180 and the harvest duration is 21-24 s.The research can provide a reference for the development of pineapple harvestingrobots.Key words:design,experiments,robots,manipulator,pineapple harvesting,AT89C51 microcontrollerdoi：10.3969/j.issn.1002-6819.2012.z2.008CLC number:TP 241.3,S 225.93Document code:AArticle ID:1002-6819(2012)-Supp.2-0042-05Wang Haifeng,Li Bin,Liu Guangyu,et al.Design and test of pineapple harvesting manipulatorJ.Transactions of theChinese Society of Agricultural Engineering(Transactions of the CSAE),2012,28(Supp.2):4246.(in English withChinese abstract)王海峰,李斌,刘广玉，等.菠萝采摘机械手的设计与试验J.农业工程学报，2012，28(增刊2)：4246.0IntroductionPineapple is an important tropical fruit in theworld.The fruit grows on the top of the tree and it iseasy to harvest because the junction area is very brittle.The pineapple trees usually grow intensively andwhen the harvesting season comes,the farmers haveto challenge the hot weather,high labor intensity andsharpthornsfromtheleaves.Theautomaticharvesting machine is in great need.Agricultural harvesting robots can solve theproblemandresearchershaveconductedmanyexperiments to design all kinds of robots to realize theautomatic harvest for fruits and vegetables.The fruitsare usually easy bruised and the harvest skills andtime should be carefully considered.The design ofmanipulator and its control system is very important.Kondo,et al1developed a kind of manipulatorReceived date：2012-06-21Revised date：2012-09-03Biography：Wang Haifeng(1985),male,Shangdong,Master,Major inAgriculturalMechanizationdesign,ChineseAcademyofModernAgricultural Mechanization Sciences,Beijing,100083.Email:wanghaifeng-Corresponding author：Liu Guangyu(1969),Male,senior engineer,Jilin,Major in Mechanism design,Chinese Academy of Modern AgriculturalMechanization Sciences,Beijing 100083.Email:for apple harvesting robots.The manipulator grabs thefruit with three fingers and an pressure sensor islocated in the finger to avoid the bruise1;Reed2,etal in Silsoe Institute in England developed kind ofMushroom picking robots,and the manipulator isdesigned as an attractor with soft liner2.Van,et al3in the Netherlands developed kind of cucumberpicking robot.A flexible manipulator and electrodecutter was designed to protect the cucumber and froman enclosed cutting scar.The fruit cutting scar can behealed quickly to reduce the water loss.Liu,et al4inJiangsuUniversitydevelopedkindoftomatoharvesting robot.The manipulator consists of a pair ofscissors and vacuum tube,and the scissor is driven bytwo mechanical springs and a solenoid.As part of a pineapple harvesting robot,a typicalmanipulator and its control system were designed andtestedinthisstudy.Basedonthegrowthcharacteristics of the fruit,two steps were determinedfor the harvest operation.Catch the fruit and hold itsteadily in horizontal direction first and then,harvestit by rotating in vertical direction.The designedmanipulator consists of three parts,the grabbingmechanism,the manipulator driving mechanism andthe rotating mechanism using professional mechanical增刊 2王海峰等：菠萝采摘机械手的设计与试验43design software.A control system based on AT89C51Microcontroller was designed to control two steppingmotors.The experiment was conducted and the resultsand discussion were given below.1Model development1.1Mechanical DesignThe pineapple species Queenwas selected fordesigning and testing physical parameters of themanipulator in this study.For the pineapple samples,the width range is from 92.4 to 134 mm,the heightfrom 118 to 187 mm,and the weight from 0.85 to1.915 kg.According to the harvesting process,themanipulator consists of three parts,one part is forgrabbing motion,another is for driving motion,andthe third part is for rotary motion.The professionalmechanical design software Pro/E was used to designthe manipulator.The designed manipulator model isshowed in Fig.1.Fig.1Designed manipulator model using Pro/E1.1.1Grabbing mechanism designDouble pivots rotating gripper was designed forgrabbing and holding pineapples steadily.It consistsof two fingers,two handles,two L bars,base plate,pin and driving bar.Fingers are fixed on the handlesseparately;the handles are hinged on the handles bybolts,so they can rotate around the pivots.Handles areconnected by the pin.The handles rotate around thepivots when the pin slides in the grooves of handles.Pineapples are grabbed and put off with the fingersclosing and opening.For the gripper,the distance of the two rotatingpivots and the length of the handle are the significantfactors.So they were placed on a higher agenda in thepaper.Fig.2 is the sketch of the double pivots rotatinggripper.Based on the triangle relationship,formulascan be inferred as follows.Fig.2Sketch of the double pivots rotating gripper2222cosACABBCABBClllll（1）Where lABis the length of the handle,mm;isthe deflection angle of the finger,();X is the distancefrom the central point of the two pivots to the central pinof pineapple,mm.In ACD,222AClXa（2）Where 2is defined as the distance of the tworotating pivots,mm./sinBClR（3）Where2is the angle of V type of finger,().22221sin cossinsinABABXRlla（4）It can be founded that the X,which affected thegripper s capability,varied with different size ofpineapples.The deflection is determined by the biggerone calculated by formula(5)and(6).22maxmax12222cossinsinsinABABABRRllala（5）22minmin22222cossinsinsinABABABRRllala（6）and 11cossinABRal（7）Generally,the average radius and =90wereselected to calculate the deflection angle.Obviously,the deflection and deflection angledepend on and lAB.Therefore,the optimizedcombination of and lABshould be chosen for a goodcapacity of gripper.Withaand lABincreased,the deflection and thedeflection angle got larger.Combining 12 points of lAB(from 80 mm to 220 with an interval of 10 mm)with农业工程学报2012 年4412 points of(ranging from 50 to 160 mm with aninterval of 10 mm),the proper group of and lABisdecided as 60 and 90 mm.In this way,not only abetter size of the whole mechanism can be acquired,but also the deflection is limited to a certain range.The deflection is 15.4 mm,and the deflection angle is84.08 degree,which could be acceptable comparedwith the pineapple size.1.1.2Driving mechanism designThe mechanism of sliding leadscrew nut isdesigned for driving the grabbing mechanism.Itconsisted of stepping motor 1,the mechanism ofsliding leadscrew nut and the driving shaft.One endof the driving shaft is connected with the pin ofgrabbing mechanism,the other end is fixed on theslider,and the driving shaft could rotate in the hole ofslider.The leadscrew would be propelled to rotate andinverse by the stepping motor 1.1.1.3Rotating mechanismA couple of spur gears were used to rotategrabbing mechanism.It consisted of stepping motor 2,a couple of spur gears with transmission ratio of 1to 1,power input shaft,output shaft and a stopper.Thedriving shaft went through the hole of power inputshaft so that it could rotate following with thegrabbing mechanism.The grabbing mechanism is onone end of the output shaft and stopped by the stopper.So the grabbing mechanism would be able to rotatewith the output shaft s rotation.Power input shaft isconnected with the stepping motor2 with a coupler.The three parts were fixed to the body consistingof side plate,up plate,down plate and bracing bars.1.2Control system designThe main job of the control system is to controlstepping motors 1 and 2 according to the harvestingprocess.AT89C51 microcontroller is the core of thecontrol system in this study.The impulse signalgenerated by AT89C51 is divided by motor driversinto a proper ratio,and the divided signal drives thestepping motors to work.SH-20806C is the type ofmotor driver.The control flow is shown in Fig.3.Fig.3Control flow graphAt the beginning,the fingers are at the longestdistance.Stepping motor 1 starts to work,themechanism of sliding lead screw nut drives the fingersto close,when the fingers grabs pineapple steadily,stepping motor 1 stops,at the point,the cycles ofstepping motor 1 is marked as“n”,stepping motor 2starts to drive the gears,the grabbing part turns andpineapple is broken down from the stem,the cycles ofstepping motor 2 is marked as“m”,stepping motor 2reverses m cycles and the grabbing part returns to theinitial place,stepping motor 1 reverses n cycles andthe fingers open to put pineapple down into thecollecting box,fingers are at the longest distanceagain.Then next cycle begins.The force sensor is implemented in the way ofWheatstone Bridge-full bridge.Without any non-linear error,the voltage sensitivity of full bridge is asfour times well as the one bridge,at the same time thetemperature error can be compensated.In fig.4,theweak voltage signals would be exemplified by theLM368,which is the operational amplifier circuit.Theanalog signals were converted into digital signals byA/D converter.After being divided by motor drivers,the impulse signals were sent to operate steppingmotor1 and 2.Fig.4Amplifier circuit of force sensorThe control system is shown in Fig.5.Fig.5Real controller2Results and discussionThe designed manipulator and control system areshown in Fig.6.In order to see whether this devicecouldworkwelltoharvestdifferentsizesof增刊 2王海峰等：菠萝采摘机械手的设计与试验45pineapples in different rotation angles.The experimentwas carried out in the lab.The manipulator andcontrolsystemwereplacedonatable.Themanipulator could not find pineapples without visionsystem.A pineapple is put between the two fingersbefore the manipulator works.The fingers are set atthe longest distance;it is 200 mm between the frontsof the fingers.Two different rotation angles,180and90 areselectedtovalidatethemanipulator sfeasibility.Three different sizes of pineapples areselected randomly and marked as number 1,2 and 3.They are separately grabbed at the two differentangles.Each pineapple is grabbed five times,thesuccessful times and average times are counted,theresults are shown in Table 1 and Table 2.Fig.6Real manipulator and control systemTable 1Successful times and average time at rotationangle 180NumberSuccessful timesAverage time/s152125233524Table 2Successful times and average time at rotationangle 90NumberSuccessful timesAverage time/s141525173518The results indicate that,pineapples can begrabbed steadily and harvested when the grabbingmechanism rotates at 180,the average time is 23seconds;one time failed for number 1 pineapple whenthe grabbing part rotated at 90,and the average timeis 17 seconds.It can be seen that the harvesting job forpineapples can be done at both rotation angles.Thereason for the failure is that the interval of thestepping motor 2 between turning and inversion isquite short;the rotational inertia is so large that thetorque of stepping motor 2 is not enough to balance it.Grabbing mechanism rotating at 180 can ensure theharvest work well.The actual condition in the field is much morecomplex than in the lab.And the harvesting work ismuch harder.The manipulator had to challenge theshields of the leaves and the stem lodging.There isstill a lot of work to do for the further study.3ConclusionsAiming at the great need of automatic harvest forpineapple,a typical manipulator and its control systemwas designed and tested in this study,which willprovideareferencefordevelopingpineappleharvesting robots.The main conclusions were drawnas follows:1)A harvesting manipulator was designed.Itconsists of three parts,the grabbing mechanism,themanipulator driving mechanism and the rotatingmechanism using professional mechanical designsoftware.The mechanism can realize the harvestoperation automatically.2)AcontrolsystembasedonAT89C51AT89C51 microcontroller was designed.The systemcan drive two stepping motors according to the controlflow and realize the control to the manipulator.3)It proved that,the manipulator can harvest thefruits successfully by rotating separately at 90and180after grabbing,and the duration is 1524 s.Thefinal rotation angle is selected as 180 for thefollowing fruit-collecting step.The designed manipulator will work together withthe vision system of the pineapple harvesting robot toconduct the whole harvesting process in the field andmuch more work willbe carried out in the future.References1Kondo N S,Ting K C.Robotics for bio-productionsystems M.New York:ASAE Publisher,1998.2Reed J N.Miles S J,Butler J,et al.Automatic mushroomharvesterdevelopmentJ.JournalofAgriculturalEngineering Research,2001,78(1):1523.3Van Henten E J,Van Tuijl B A J,Hemming J,et al.Fieldtestof anautonomous cucumberpicking robotJ.Biosystems 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