MECHANISM DESIGN OF COTTON PICKING GRIPPER Yagnesh G Limbasiya 1, Dr Jignash P.Maheta 2 PG Student (Mechanica CAD-CAM), V.V.P Engineering coege, yagnesh.imbasiya@gmai.com H.O.D -Mechanica Department in V.V.P Engineering coege, jignashapmaheta@yahoo.co.in Abstract Cotton is most important commodity in word and it cutivate by arge areas in India.cottons are pick from cotton ba by human hand which is costy and time consuming so automation of cotton picking is one way to increase profit. In this paper A mechanism of cotton picking gripper is designed for automatic picking robot. This gripper mechanism is design such that it can perform operation ike hoding cotton bos stem, grasping cotton and pucking that cotton. The various dimension of gripper are obtained from virtua mode. This designed gripper mechanism wi used in various gripper parts design and assemby aso it wi use in fabrication of gripper. Key word: four finger pivoted type grasping mechanism, sider-crank mechanism and power screw inear actuator. I. INTRODUCTION In this paper main goa is to design a mechanism for gripper which shoud be used for picking cotton from cotton bos. Cotton is a natura ceuose fiber, has a ot of characteristics such as comfortabe soft hand, good absorbency, coour retention, print we, machine-washabe, dryceanabe, good strength, drapes we, easy to hande and sew, ow easticity [1]. Sampe Coection of cotton bos. Anayse and define dimension of cotton bos and measure sampe dimensions. Define the parameter, opening and cosing and cacuation of gripper mechanism. 1. Studying process of cotton picking from cotton bos study was carried out of the picking motion of farmer at time of cotton picked from cotton bos. Among that motion best motion observing is to hod the cotton bos from stem after hoding use three fingers and thumb for grasping cotton bos and appying arm force cotton can be puck from cotton bos. Figure 1: front view and top view of cotton bo As shown in figure 1 white part which is cotton shoud be pick from cotton bos for that gripper and its mechanism shoud be design such that goa can be achieve. II. DESIGN METHODOLOGY Studying process of cotton picking from cotton bos Generate idea to manua hand picking into automated gripper picking. Seection of mechanisms for gripper. According idea creates and mechanisms seected make the virtua mode for hoding, grasping and pucking. Figure 2: method of cotton picking from cotton bos As shown in figure 2 first hoding the stem with two finger after hoding grasping cotton form cotton bos with hep of four finger after hoding puck the cotton bo and put it in cotton bag. 2. Studying process of cotton picking from cotton bos Gripper was generated to automate above cotton picking methods for that gripper shoud perform three operation hoding, grasping and pucking. To 1
perform above operation gripper require two fingers for hoding, four fingers for grasping and pucking mechanism for puck the cotton from cotton bos. 3. Seection of mechanisms for gripper There is various type of gripper mechanism avaiabe from that pivoted type four finger mechanisms seected for grasping operation. Fingers are open cosed with hep of power screw inear actuator. A sider crank type mechanism used for pucking operation and for hoding operation two finger pivoted type mechanism seected [2]. 4. Virtua mode of gripper According to idea generated and seection of mechanism a virtua mode was generated in creo parametric 2.0.this mode was generated on weak dimension after getting design parameter mode wi generate with strong dimension. It has four fingers pivoted type grasping mode with power screw inear actuator. It has sider crank mechanism for pucking operation and for hoding it has two finger in which one is fixed and second is movabe by pivot. samp e no Figure 4: cotton bo with dimension d= diameter of cotton bo h=height of cotton bo =ength of cotton bo stem b=ength of cotton buds a=ength of cotton buds sot a1=ength of cotton buds sot at stem t=thickness of steam A 20 sampe seected for measure the above dimension. A vernier caiper measurement instrument used to measure dimension of cotton bos. D h a a1 b t 1 55 58 25 36 12 27 2.5 2 61 56 20 31 10 25 2 3 70 56 24 36 9 26 3 4 71 56 26 36 10 26 3 Figure 3: gripper mode with weak dimension 5. SAMPLE COLLECTION OF COTTON BOLLS Sampes were coected from 20 farms where cotton was cutivated by farmer. 6. ANALYSE AND DEFINE DIMENSION OF COTTON BOLLS AND MEASURE SAMPLE DIMENSIONS After sampe coection sampe was anaysed and define some dimension which are as beow, 5 52 46 15 25 11 18 2 6 53 50 16 33 11 18 2.5 7 52 55 17 24 12 19 2 8 55 52 18 33 10 22 2.5 9 55 47 16 23 10 20 2.3 10 50 43 16 23 8 20 2.5 11 54 43 15 31 11 21 2.2 12 42 41 18 20 12 20 2.5 13 65 65 16 33 11 22 3 14 57 56 24 27 11 27 2.5 2
15 53 52 14 31 12 21 2.5 16 58 60 19 33 10 25 2.5 17 60 45 15 22 10 19 2.5 18 62 45 15 27 10 17 3 19 57 46 21 23 11 23 2.7 20 54 45 20 28 12 21 2.5 avera 56. 50. 18. 28. 10. 21. 2.5 ge 8 85 5 75 65 85 1 max 71 65 26 36 12 27 3 min 42 41 14 20 8 17 2 Tabe: 1 sampe dimension of cotton bos in mm Figure 6: one finger grasping mode 7. Define the parameter, opening and cosing and cacuation of gripper mechanism. (1) Parameter for grasping mechanism For grasping mode four finger are at 90 ange and symmetric with horizonta axes so a finger get same parameter. To find parameter of grasping mode considering one finger of grasping mode as shown in figure, Figure 5: four finger grasping mode Figure 7: ine diagram of one finger grasping mode Where, L 5 = 0.5 pate ength L 1 =0.5 nut width L 2 = ength of ink 2 L 3 = distance between pivot joint and ink 2-3 joint L 3 = distance between point 2-3 L 4 = distance between point 4-5 L 5 = distance between point 5-6 L 6 =0.5 pate ength dy = vertica distance between center ine and tips enddx= horizonta distance between center ine and tips end Θ1= ange between ink A and horizonta Θ2= ange between ink B and horizonta Θ3= ange between ink Band ink C Θ4= ange between ink C and ink D S1=distance between o-0 S2=screw ength In above parameter some them are got by appying opening and cosing condition of gripper and other parameter are got by tria and error method. During gripper move open to cose movement foowing parameter change, Θ 1 is 45< Θ 1 <90 Θ 2 is 0< Θ 2 <90 3
Θ 3 and Θ 4 wi remain constant throughout mechanism running and it is Θ 3 = 150 Θ 4 = 130 At cosing position dy=0.5 Db max=0.5 10=5 mm dx > hmax so dx =1.5 hmax=1.5 65=97.5 98 mm Link E shoud be vertica at cosing end. Figure 10: ine diagram with parameter vaue when gripper cose Figure 8: ine diagram when gripper cose At opening position d y > 0.5 D max =0.5 71=35.5 mms d y =1.5 35.5 =53.25 53 mm Figure 11: ine diagram with parameter vaue when gripper is open From above vaue Linear distance movement of nut Snut S1at open S1 at cose 54.27 32.43 21.81mm (2) Force cacuation The minimum grasping force is measure by experiment and it comes 6 N per finger. This force direction is vertica at the finger tips when it coses. The force requires at starting is more compare to end. In this gripper when finger going to cose vertica force exerted at finger is increase with finger gets coser. Figure 9: ine diagram when gripper open By taking above Θ 3, Θ 4, d x, d y vaue by using tria and error method with hep of graphica technique other parameter are got which are shown at beow figure. In grasping mode power screw type inear actuator was seected. We have to find minimum torque require to rotate screw for that screw oad must be require. In grasping mechanism design torque shoud appy such that more 6 N vertica force shoud be produce at the end for that consider 6 N vertica force appy at finger tips end as shown in figure 4
' F d =F COSθ (L SINθ )-F SINθ (L COSθ ) [3] g x 1 1 3 2 1 1 3 2 ' 6 116.36=F COS(47.93)(25 SIN(15.3))-F SIN(47.93)(25 COS(15.3)) 1 1 698.16=4.42F -17.9F 1 1 F =-50.22N 1 Figure 12: force acting on grasping mode Where, F g =grasping force per finger W=oad acting on screw Figure 13: force acting on joint 1 Force acting on joint 1 due to oad W is F1 = W W = =0.67W cos(θ ) cos(47.93) 1 (1) By putting F 1 vaue in equation (1) W 74.96 N As W getting negative the direction of oad is opposite side. (3) Torque require to rotate power screw A standard square singe threaded screw with made up by untreated stee materia seected which dry coefficient of friction is 0.18 [4]. screw thread size is seected according to IS-4694-1968 standard which specification as beow, nomina diameter : d 22 mm pitch : p 5 mm core diameter : d d - p 22-5 17mm 22 17 mean dia : dm 19.5mm 2 5 tan 0.0187 d 3.14 19.5 m coefficient of friction tan c w(tan tan ) w(0. 18 0.0817) power : P 0.096875w (1 tan tan ) (1 0.18 0.0817) dm tork require to over come the oad T P [5] 2 T 0.096875 4 74.96 29.047 N.mm Figure 14: force acting on pivoted ink From above figure 14 taking moment about pivoted joint 3, No of motor rotation require to cose the fingers S nu t 21.81 M n 4.362 rotation p 5 5
Condition for sider crank mechanism L s > L p and L p <L q Θ r is 0 to 180 Pucking stork ength is obtained by performing experiment and it wi get 40 mm. (4) Parameter for pucking mechanism Lp =1.125 0.5 40=20 mm Lq>20 so Lq=30 mm Ls>20 so Ls=30 mm Lr=70+10+30+20+30=160 mm Lv=2 L5=2 70=140 mm Figure 15: pucking mode As shown in figure 3 four rounds bar is connected with grasping mechanism mode. The ine diagram of grasping mode shown in beow figure, Figure 17: ine diagram with dimension of pucking mode (6) Pucking force cacuation Figure 16: ine diagram of pucking mode Where L r =ength of bar C p =cearance between pate and screw end of pucking stock end L s =distance between shaft and hoding pate L p =crank ink ength Θ r =ange between crank ink and horizonta axis L q =connecting ink ength L v =ength of mechanism hoding pate (5) Link ength soution L r =S +C p + L s + L p + L q As we know that ength of screw S =S 1max +nut width=54.27+15=69.27 S=70 mm taken C p =10 mm taken Figure 18: force acting on sider crank mechanism F r get maximum at θ r =90 Let θ is the ange between connecting ink and horizonta axis θ can be cacuated as beow, 1 p sin ( ) 20 30 1 sin ( ) 1 sin (0.666) 41.81 L L q 6
F When hoding gripper open distance between two p Fr finger tips J=10mm COS( ) 5 Fr COS(41.81) 5 Fr 6.71N 0.7454 Torque require to rotate crack ink T F L 6.71 20 134.16 N. mm c r p Aso θ fix =45 and θ mov wi change 45 to 90 but actuay it wi not change that much when gripper cosed θ mov =45. As hoding gripper connected at corner of hoding pate from thaty h =50 mm. By putting above vaue we wi get other dimension which shown in figure as beow, (7) Hoding mode Taking Y h1 = Y h2 =J t =8mm from that X h =48 mm, J h =17mm. By engineering graphics method other dimension can be obtain and that dimensions are show in beow figure. Figure 19: cotton bos stem hoding mode Figure 21: ine diagram with dimension vaue when hoding gripper is cose. Figure 20: ine diagram of hoding mode with parameter annotation. A various dimension are shown in figure 20 a fixed and a movabe ink have same dimensions. The finger tips dimension can be obtain from cotton bos stem dimension. As we know b minimum =17 mm and t minimum =2 mm From above dimension J J t c 0.5 17 8.5 8mm 0.5 2 1mm When hoding gripper cosed distance between two finger tips J=2mm Figure 22: ine diagram with dimension vaue when hoding gripper is open. From above figure 22 sider ink distance S sh =8 so sider ink have move 8 mm that inear stock ength for hoding gripper. 7
This hoding gripper is connected with mechanisms hoding pate which is shown in beow figure Figure 23: connection of cotton bos stem hoding mechanism with mechanism hoding pate X d L L L L b hod x r s q p minimum X hod 98 160 30 30 20 17 235mm. L (0.5 L ) (0.5 J ) L hod v t h o d (0.5 70) (0.5 8) 39 mm CONCLUSION By this mechanism design various parameter of gripper are achieved by which dimension of cotton picking gripper can be known and aso hepfu in assembing and fabrication of cotton picking gripper. REFERENCES [1]. http://www.swicofi.com/products/001cott on.htm [2]. Robotics technoogy and fexibe automation by S R DEB [3]. Industria Robotics technoogy, programming and appication by MIKELL P. GROOVER, MITCHELL WEISS, ROGER N. NAGEL and NICHOLAS G. ODREY. [4]. http://www.roymech.co.uk/usefu_tabes/ Triboogy/co_of_frict.htm [5]. Design of machine eements by V B BHANDARI 8