Research of Crop Production Positioner Theory Design

Based on existing crop production positioner analytical investigation and according to working principle of crop production positioner, this study did a research of crop production positioner transmission design. The paper mainly designed worm and worm gear retarding mechanism of working table rotary direction. Aiming at mechanical structure of crop production positioner, related parts were calculated and checked, including checking calculation keyed shaft, selection and calculation of sliding bearing. Calculated results are of certain theoretical significance for crop production positioner design study.


INTRODUCTION
Crop production positioner is auxiliary equipment, which is operation machine and it is called the three machines together with wheel frame and auxiliary equipment.Crop production positioner is to be mechanized and automated industry and development needs generated by rotating and tilting mechanism, workpiece placed in ideal position displacement machinery.Crop production positioner can be composed and operate machines and other supporting automatic machine; robot can be used as peripheral equipment supporting automation and robotics; it can also be used alone and independently.It is used as equipment, mainly used for lateral pipe butt welding, pipe and flange weld seam both inside and outside ring, all-position of pipes tubes.Crop production positioner horizontal flip angle, rotating and flipping through movement of workpiece table so that weld is in best position for welding, thus greatly improving weld quality, to reduce labor intensity welder, especially suitable for various shaft, disc type, such as rotating cylinder workpiece.And crop production positioner has a compact structure, small size, attractive appearance, light weight, etc., is a pressure vessel, metallurgy, electric power, chemical machinery, metal structures and other industries ideal equipment (Wang and Liu, 1995).

CROP PRODUCTION POSITIONER WORKING PRINCIPLE
Crop production positioner rotary This study did a research of crop production positioner transmission design.The paper mainly designed worm and worm gear retarding mechanism of working table rotary direction.Aiming at mechanical structure of crop production positioner, related parts were calculated and checked, including checking calculation keyed shaft, selection and calculation of sliding bearing.Calculated results are of certain theoretical significance for crop production positioner design study.

Crop production positioner drive deive:
• Direction of rotary o Determine the formula for calculating value of each calculation a. Selected test load factor K.
Because work load is stable, they chose uneven load distribution coefficient K β = 1; Select from Table 1 using coefficient K A = 1.15;As speed and impact is not high, desirable dynamic load factor can be K V = 1.05; then: Determine role of torque on worm T 2 .
As Z 1 = 1, then the efficiency is η = 0.7.First hypothesis and worm indexing circle diameter d 1 and ratio of transmission center distance a is: From where it can be gotten that.
d. Donfirmation of elastic modulus influence coefficient Z E .
For selecting cast tin phosphor bronze worm gear and worm matching of steel.Then: According to the worm gear material for casting tin phosphor bronze ZC u S n 10P1, metal film casting, worm helical gear tooth surface hardness >45HRC,  g.Coefficient of contact fatigue life K HN1 = 0.9; K HN2 = 0.95。 h.Calculation of contact fatigue allowable stress Failure probability is 1% and safety factor S = 1, then: Bending strength meets the requirements.

• Confirmation of precision grade tolerance and
surface roughness: Considering design of power transmission, worm drive type belongs to general machinery gear reducer, to choose 8th precision accuracy magnitude from cylindrical worm and worm gear of GB / T10089-1988 type of lateral clearance is f, which is labeled as 8 f of GB / T10089-1988.And then tolerance requires related manual check items and surface roughness and it is omitted here.
• Check and calculation of belt key shaft 2 : Axis is under both torque and bending moment.45 steel is selected as shaft material, quenched and tempered.

• Check and calculation of shaft hardness:
According to torsional strength check and calculation, shaft torsional strength conditions should be: Shaft is obtained by selected diameter, which meets strength requirements.
Because bearing pedestal only bears radial force with no impact and speed is small, through force analysis F = Mg(N) and there are two bearing and thus half of force in gravity, It can be gotten that: Choice and calculation of key: Choice of key: Due to displacement of machine, key is only under shear force to choose ordinary flat key (type A).Key of both sides is working by key and keyway profile extrusion to transfer torque.Bond between surface and wheel hub keyway is on the underside of gaps.Flat key connection has a simple structure, convenient installation and advantages of better to neutral and widely used.But unable to bear axial force, thus shaft parts effect was less than the axial fixation.[P] = Allowable pressure of weakest material among key, shaft and hub, MPa, as is shown in Table 6 Transfer torque is ; k = 0.5× 14 = 7; l = 75 -25 = 50; d = 90 mm º and thus , so it is up to standard.

CONCLUSION
Main design of transmission parts crop production positioner a detailed calculation and verification, although this is more complicated, it can be more precise and accurate calculation to select desired components to ensure machine running in good condition and avoid some problems that may be caused by wearing and tearing and can extend machine life.Part of calculation and verification includes checking calculation keyed shaft, selection and calculation of a plain bearing selection and calculation as well as the key.Design after crop production positioner movement than previous products with high accuracy, small inertia, good braking and stability, enabling variable speed, easy to realize advantages of reversing.The obtained results of calculation and design have some theoretical significance for crop production positioner design study.Feng, X.A., 2005. Mech. Ind. Press, Beijing, pp: 85. Pu, L.G. and M.G. Ji, 2005. Higher Edu. Press, Beijing, pp: 62. Wang, Z. and P. Liu, 1995. Mech. Ind. Press, Beijing, pp: 60. Yu, J.Y. and Q. Zou, 2004. Mech. Ind. Press, Beijing, pp: 85. Zeng, G.Q. and J. Hu, 2002.Huazhong U. Sci.Tech.
of contact coefficient Z ρ .

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Calculation of key: o Connection strength calculation of flat key: Assuming load distributed evenly on working plate of key and connection strength calculation of common flat key is: height between key and hub, k = 0.5h L = Working length of key, mm, ball peen flat key of key, mm, b b is width of key, mm d = Diameter of shaft, mm [σ p ] = Allowable bearing stress of weakest material among key, shaft and hub, MPa, as is shown in Table 6 table mechanism consists of work platform, slewing mechanism, tilt mechanism, base, electronic control devices, conductive devices and other components.It is driven by a DC motor, variable speed DC motor using SCR, to obtain a continuously adjustable rotary table speed.Its transmission routes are: DC motor-belt drive-first stage of worm rotation-second stage worm gear-gear, enabling rotary table.Table tilt mechanism AC brake motor, transmission line as: AC motor-belt drive-worm reducer-transition gear-worm reducer-gear, in order to achieve tilt table.Tilt shaft is equiped with limit switches, inclination angle strictly controlled between 0° and 90°, table and base unit to avoid collision.

Table 1 :
Tooth width coefficient of cylindrical gear KA

Table 4 :
Ordinary cylindrical worm transmission value of vs, fv and φv It is known that γ = 28.18 º ; φ v = arctan f v ; f v ; is related with v s .

Table 6 :
Key connection allowable compressive stress and allowable stress 5