滚筒集排式油菜精量排种器排种过程分析.pdf

第 30 卷 第 23 期 农 业 工 程 学 报 Vol.30 No.23 2014 年 12 月 Transactions of the Chinese Society of Agricultural Engineering Dec. 2014 17 Analysis on seeding process of pneumatic cylinder-type centralized rapeseed precision metering device Li Ming, Liao Qingxi , Liao Yitao, Shu Caixia, Li Lei (College of Engineering, Huazhong Agricultural University, Wuhan 430070, China) Abstract: In order to obtain the relationship model between required negative and positive pressures values and the structural and operating parameters in the main metering processes at the absorbing, retaining and dropping stages，the seeding process of pneumatic cylinder-type centralized rapeseed precision metering device were analyzed. Through analyzing the influence of operational and structural parameters on the performance of pneumatic cylinder-type centralized rapeseed precision metering device, the working principle of the pneumatic cylinder-type centralized precision metering device was summarized, and its basic configuration was designed. Dynamic and kinematics models were established in the main metering processes at the absorbing, retaining and dropping stages, and Extended Discrete Element Method software was used for the simulation and calculation of absorbing process, based on which the relationship model between required negative and positive pressures values and the structural and operating parameters were established in seeding process. The results of extended discrete element method simulation analysis indicated that in order to ensure the reliable work of the metering device, the height of seeds should be limited within the 0.65Dg, which was verified by the results obtained from our preliminary tests. Then the JPS-12 test-rig for the performance of the rapeseed metering device was adopted to conduct the single factor experiments, which showed that the quality index reached above 89.1% and the coefficient variation was 3.76% when the rotational speed was 20 r/min and the positive pressure value was 2 200 Pa and the vacuum was -2 200 Pa. The experimental results were in accordance with the analytical result of dynamic model. The analysis provided theoretical foundation for optimizing the operational and structural parameters of the centralized metering device. Key words: agricultural machinery; seed; models; rapeseed; pneumatic cylinder-type; metering device; dynamic analysis; kinematics simulation doi：10.3969/j.issn.1002-6819.2014.23.003 CLC number: S223.2 Document code: A Article ID: 1002-6819(2014)-23-0017-11 Li Ming, Liao Qingxi, Liao Yitao, et al. Analysis on seeding process of pneumatic cylinder-type centralized rapeseed precision metering deviceJ. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2014, 30(23): 1727. (in English with Chinese abstract) 李 明，廖庆喜，廖宜涛，等. 滚筒集排式油菜精量排种器排种过程分析J. 农业工程学报，2014，30(23)： 1727. 0 Introduction Rape is an important oil crop and the major source of edible oil as it has the quality of high oil yield and nutrition value. At present, China is the first largest producer of rape in the world with an estimated Received date：2014-05-22 Revised date：2014-11-05 Foundation item： National Natural Science Foundation of China(51275197); Earmarked Fund for Modern Agro-Industry Technology Research System (CARS-13); National Science and Technology Support Program (013BAD08B02) Biography：Li Ming, male, Hubei Xiaogan, Ph.D candidate, design and measurement for modern agricultural equipment. Wuhan College of Engineering, Huazhong Agricultural University, 430070, China. Email: llmmmingle Corresponding author ： Liao Qingxi, male, Hubei Jingzhou, Ph.D, Professor. Research field is rape planting machinery and rape harvest machinery. Wuhan. College of Engineering, Huazhong Agricultural University, 430070, China. Email: liaoqx production area of 74.32 million hm2 in 2012, which accounts for about 1/3 of the total world rape production1. However, the mechanical seeding level for rape is much lower and the main ways of sowing are, to a large extent, at the semi-mechanized stage and with manual seeding, which are time-consuming and with low efficiency, and eventually limit the scale of rape sowing2-3. Currently, using semi-mechanization devices and manual seeding are the main methods in rapeseed planting because of the mechanical damage to rapeseeds during planting. However, rapeseed planting is labor intensive and time consuming work, which brings a great demand to alternative planters. In recent years, many seeding metering devices, the essential components of seed planters, are designed or optimized to improve their performances4-9. Karalyel et al10 identified an optimal vacuum pressure to achieve a better performance of a metering 农业工程学报 2014 年 18 device by developing mathematical models of physical parameters for different seeds. Arzu et al11 optimized the speed of seed plate, the diameter of holes and the vacuum pressure of a pneumatic precision metering device for cotton. R.C. Singh et al12 obtained the optimal operational parameters for a pneumatic metering device of cotton using mathematical iterative method. The results were verified through experimental method which showed that the quality of feed index, the variation coefficient of spacing and effective spacing in the row were up to 94.7%, 8.6% and 251 mm, respectively. These methods and principles could be the reference for studying the metering device for planting other seeds13-14. However, the literatures that mention relationship between operational parameters and performance indexes are limited to the theoretical research. The objective of this study was to optimize the operational and structural parameters of the centralized metering device. A six-row pneumatic cylinder-type centralized metering device was designed with the guidance of absorbing under negative pressure and blowing under positive pressure, and this device was able to plant rapeseeds within six rows in one operation. Dynamic and kinematics models were established in the main metering processes in the absorbing, retaining and dropping stages, and the Extended Discrete Element Method software was used for simulating the absorbing process and calculating the quantity of seeds, based on which the relationship model between required negative and positive pressures values and the structural and operating parameters were also established in seeding process. These theoretical results are then verified by results of simulation and experiment. 1 Structure and working principle of centralized precision metering device A pneumatic cylinder-type centralized precision metering device was designed, and it was a positive and negative pressure precision metering device for rapeseed. The seeding system of the device comprehensively consisted of a pneumatic system, a transmission system, a bracket and pneumatic cylinder-type centralized precision metering device mainly composing of a seed box, a seeding cylinder and a seed outlet. The system diagram of pneumatic cylinder type precision seeding is shown in Figure 1. The air chamber was split into two parts by internal cylinder, one working as a negative chamber, the other as a positive chamber. At the end of the negative pressure outlet hole, there was a vacuum; and at the end of the positive pressure inlet hole, there was a positive pressure. The seeding cylinder was mounted to the air chamber. With the rotation of the seeding cylinder in the anticlockwise direction, seeds were absorbed by holes of the seed box when seeding cylinder passed through negative pressures chamber and fell into the seed outlet under the gravity forces and the positive differential pressure. 1. Pneumatic system 2. Transmission system 3. Bracket 4. Seeder 5. Seed tube system 6. Metering device Fig.1 System diagram of pneumatic cylinder type precision seeding 2 Dynamic analysis of seeding process The metering processes mainly include three stages; absorbing, retaining, and dropping. According to the structure of cylinder centralized metering device, the dropping regional angle 3 was 60. From Preliminary test results15, the height of seed box (h) was less than 0.65Dg, then the absorbing angle 1 was 0-103.1, and the retaining regional angle 2 was 196.9-300as shown in Figure 2. Note: 1 is absorbing angle, (); 2 is the retaining regional angle, (); 3 is dropping regional angle, (). Fig.2 Model diagram of seeding process To find out the optimum combination of the structural and performance parameters, the dynamic and kinematics models were established through 第 23 期 李 明等：滚筒集排式油菜精量排种器排种过程分析 19 simulation and theoretic analysis in the seeding process, which provided theoretical evidence for optimizing and improving pneumatic cylinder-type centralized precision metering device. 2.1 Assumptions of dynamic modeling The seeds in the centralized metering device were acted respectively upon by gravity, the absorption force, the support force from the cylinder and friction force, seeds pressure, centrifugal force, and the air resistance during the metering process. Therefore, the following assumptions were made for dynamic analysis. 1) Both the shape and size of seeds were not strictly required for pneumatic metering, the external force was on the center of mass16, and the seeds were of the uniform size. Each hole was only allowed to carry one seed, and the seeds in the box were distributed uniformly17. 2) The air flow was distributed uniformly in the cylinder pneumatic18 and was never changed with the change rotational speed of seeding cylinder. 3) The air resistance was so small that it was ignored during the metering process. 2.2 Analysis of absorbing process 2.2.1 Kinematics analysis on absorbing process During the absorbing process, the seeds at the bottom of the seed box were absorbed by the holes and scrapped under the effect of the interaction force among the seeds. The upper seeds were absorbed successfully after the repetitive absorption performance. This process was covering two stages. At the first stage, the seeds were absorbed from the seed box into the holes, and at the second stage, the seeds were rotated with seeding cylinder until they were departed from seed box. The dynamic and kinematics analysis of rapeseed for absorbing process was shown in Figure 3. Note: FQ is negative pressure on the absorption for rapeseeds, N; fg is seed friction on seeding cylinder, N; N2 is seed supported by flock of seeds ,N; fz is seed friction on seeds ,N; Ng is seed absorption from seeding cylinder, N; G is gravity of seed, N; is angle between horizontal direction and N2,(); is adsorption angle between FQ and horizontal direction, (); is speed of seeding cylinder, rad/s; h is surface height of seed box, mm. Fig.3 Force analysis of absorbing stage The coordinate system was established with the center of rapeseed as the coordinate origin, the normal direction of cylinder as y direction and the tangential direction of cylinder as x direction. Because the seeds were not in contact with cylinder, both the centrifugal inertia force and the support force of cylinder equaled 0. Then the seeds were with variable accelerated motions under the effect of negative pressure in the first stage. The time difference was ignored from the beginning to the end of the absorbing process and the balance equations of dynamic analysis of rapeseed are shown as follows: 2 2 cos() sin()sin coscos()sin()0 XQ zZ YZ FFN fmgma FmgfN =+ += =+= （1） Where: FQ is negative pressure on the absorption for rapeseeds, N; fz is Seed friction on seeds, N; is angle between horizontal direction and N2, (); N2 is seed supported by flock of seeds, N； is adsorption angle between FQ and horizontal direction, (); az is acceleration of rapeseeds, m/s2; m is quality of seed, kg; g is acceleration of gravity, m/s2; Fx is the sum of force in x axis, N; Fy is the sum of force in y axis, N. The centrifugal inertial force existed when the seeds rotated with the seeding cylinder in the second stage. The balance equations of dynamic analysis are as follows: 2 2 2 0,sin()cos() sin0 0,coscos() sin()0 XQZ Zgg YZ g FFfN GNmR FGf fN =+ = =+ += （2） 2 tan tan ggg ZZ fN fN = = （3） Where: z is natural rest angle for rapeseeds in 19.8, (); g is sliding friction angle between cylinder and rapeseeds in 25, (); fg is seed friction on seeding cylinder, N; Ng is seed absorption from seeding cylinder, G is gravity of seed, kg. From Eq. (1) to (3): () 1 cos sin() z QNz z Fmamg = + （4） From Eq. (2) to (3): ()() 2 2 2cos cossin coscos QNg zgzg zg FmR Nmg = + （5） 农业工程学报 2014 年 20 Where: FQN1 is FQ in the first stage, N; FQN2 is FQ in the second stage, N. The absorption force produced by pressure difference between the interior and exterior of the hole was calculated with the following equation: 2 QNk Fk PR= （6） Where: k is proportional coefficient of the flow field effects in 0.65; PN is pressure value of negative pressure range, Pa; Rk is radius of absorbing hole, m. The analytical results indicated that in order to absorb seeds successfully, FQ should be larger than that in the first stage because FQ needed to overcome the weight and the force among seeds in the second stage, which indicated that FQFQN2 should be met in selecting the fan. The minimum negative pressure was calculated through the following equation: ()() 2 min 2 2cos cossin coscos QNNk g zgzg zg Fk P R mR Nmg = = + + （7） Where: equals 205, PNmax is 113.6 Pa; when equals 90, PNmin is 45.6Pa; PNmax is maximal pressure value of negative pressure range, Pa; PNmin is minimum pressure value of negative pressure range, Pa; FQNmin in the minimum FQ, N. Where 3 60arcsin/ 2 gg hRR 270 Note: K is seed particle; Dg is the exterior cylinder diameter, mm; i is ratio between h and Dg.; h is height of seed surface, mm; Dg is the diameter of seeding cylinder, mm; is adsorption angle between FQ and horizontal direction, (). Table 2 Seeds quantity in simulation region at different rotational speed of seeding cylinder Seeding cylinder rotational speed/(rmin-1) Coordinate r/mm 15 20 25 30 40 50 82-85 1 1431 1251 241 1 198 1 1821 143 85-87 1 0691 0671 099 1 115 1 1111 089 87-89 1 1411 1531 130 1 162 1 1681 186 89-91 1 1821 1821 176 1 178 1 1781 214 91-93 1 0911 1271 090 1 124 1 1281 147 93-95 1 03610791 053 1 085 1 0661 067 Note: r is variable and uniform stratification, mm.The quantity of seed in box wasnt too much with the rotational speed of seeding cylinder increased, because seeding cylinder take away seed when the seeding cylinder rotated. The analysis of the variance indicated that the rotational speed did not significantly influence the spatial distribution of seeds, in other words, the size of absorption region was not significantly affected by the rotational speed. The influence of rotational speed on seeding performance was that the relative absorption time decreased and the miss index increased with the increase of the rotational speed. This result was in accordance with the actual experimental phenomena. 2.3 Dynamic analysis of retaining process In the retaining process, the absorbed seeds were acted by the adsorption force FQ, gravity Gz, normal support force of cylinder wall Ng and tangential friction force fg. The regional angle of retaining process changed with the change of the height of seed box when the range of variation of angle between the absorbing hole and the horizontal were 3 arcsin/240 2 gg hRR . The direction of tangential friction force was changed by the gravity when the adsorbed seeds passed through the different quadrants of seeding cylinder. The regional angle was divided into two adsorption angle ranges, such as 3 arcsin/240 2 gg hRR and 90240, therefore the force models were established respectively. In the retaining process, the adsorbed seeds moved with uniform circular motion because of the imposed centrifugal inertia force. The force models in normal direction and tangent direction were showed as follows: 2 0 xg y FmR F = = （9） First range: 3 arcsin/90 2 gg hRR The balance equations in normal direction and tangent direction along the cylinder were shown as follows: 农业工程学报 2014 年 22 2 sin cos0 tan xQgg yg ggg FFNmgmR Ffmg fN =+= =+= = （10） Solver results of the equations were shown as follows: 2 mgcos() m sin g Qg g FR + =+ 2 Nk k PR= （11） Where g=25, FQ firstly increased and then decreased in adsorption angle range. The required minimum and maximum pressures were obtained through the Equation (6) and (11). The results were shown as follows: max min 25 ,113.6 Pa 90 ,45.6 Pa N N P P = = = = （12） Second range: 90240, Establishing the balance equations: 22 sin 0,cos0 tan , xgQgg yg ggg FmRFNmgmR Fmgf fN =+= = + = = （13） Solver results of the Equation (13) were shown as follows: 2 cos() sin g Qg g mg FmR = （14） FQ firstly increased and then decreased on the range of adsorption angle 90240 in the process. The required minimum and maximum pressure values were obtained through the Eq. (6), (14) and the values (Table 1) shown as followed: max min 205 ,113.6Pa 90 ,45.6Pa N N P P = = = = （15） The analysis of retaining process showed that the required absorption pressure changed with the adjustment of adsorption angle. The absorption pressure changed with the increase of adsorption angle . When was 25 or 205, the maximum adsorption pressure maxN Pwas 113.6 Pa, which was the most difficult adsorption position whose adjacent area was called the retention unstable area. According to the required adsorption force, the required maxim