# Design example and test of eccentric displacement gear

According to the method of generating tooth profile, the software of calculating the tooth profile of eccentric displacement gear is designed in MATLAB.

The program consists of interface display, undercut discrimination, gear parameter calculation, tooth profile envelope, intersection calculation, feature point sorting, data output and other modules. Taking the gears in the planetary system of eccentric displacement as an example to verify the correctness of the design of eccentric displacement gears. It is known that the number of teeth of eccentric gear z = 17, modulus M = 2.5mm, and eccentricity e = 3.5mm. The axial distance a between eccentric gear and conjugate gear is 42.8 mm. The resulting gear profile is shown in Figure 1.

1. Eccentric gear 2. Eccentric displacement gear

Fig. 2 is a comparative enlarged view of the engagement of the eccentric gear with the eccentric gear and the eccentric displacement gear respectively. It can be seen from the figure that there is side clearance when two eccentric gears 1 and 3 mesh, but there is no side clearance when eccentric gear 1 and eccentric displacement gear 2 mesh. In the initial position, the pitch curves of the two eccentric gears are separated, while the pitch curves of the eccentric gears and the eccentric modified gears are tangent. In the whole meshing process, the pitch curves of the two eccentric gears sometimes separate and sometimes intersect, only tangent at some specific points, which also proves that the assumption that the two pitch curves are always tangent and make pure rolling is not tenable, so there is backlash when the two gears mesh. The pitch curve of the eccentric gear and the eccentric modified gear is always tangent and pure rolling, meshing without backlash.

1.Profile of eccentric gear 2. Profile of conjugate eccentric displacement gear 3. Profile of conjugate eccentric gear 4. Pitch curve of conjugate eccentric gear 5. Pitch curve of conjugate eccentric displacement gear 6. Pitch curve of eccentric gear

In order to ensure the formation of lubricating oil film between the gear tooth surfaces and prevent the gear from being stuck due to thermal expansion deformation, the gear pair must have proper tooth side clearance when meshing. The tooth side clearance is guaranteed by the manufacturing tolerance. The design is still based on the meshing without tooth side clearance. In this example, the backlash of eccentric gear mechanism and eccentric displacement gear mechanism is shown in Figure 3. It can be seen that the backlash generated by the deflection method is zero, and the meshing without backlash is realized.

By improving the ratio of material, increasing the thickness of gear and increasing the modulus of gear, the strength problem of P / M gear is solved, and the accuracy is reliable, the cost is only 1% of that of the wire cut gear. Through the destructive test, the gearbox shell is damaged and the ϕ 19 mm transmission shaft is twisted, and there is no problem with the gear.

A rotating planetary system interpolating mechanism with eccentric displacement gear is adopted, as shown in Fig. 4. The mechanism is composed of 3 eccentric gears 1, 3, 5 and 2 eccentric displacement gears 2, 4, planet carrier (Gearbox) 10 and planting arms 7, 9. 1, 5 are planet wheels, 3 are sun wheels, 2, 4 are intermediate wheels. The eccentric gear and the eccentric gear are meshed to realize the non-uniform transmission. The proper eccentricity and the center distance are selected to form the required non-uniform transmission ratio and the angle relationship. The “waist shaped” static track 8, which meets the working requirements of the high-speed transplanter, is obtained.

1,5. Planetary gear (eccentric gear) 2, 4. Intermediate gear (eccentric displacement gear) 3. Sun gear (eccentric gear) 6. Yangmen 7, 9. Planting arm 8. “Waist shaped” static track 10. Planetary carrier

The eccentric displacement gear planetary system transplanting mechanism is applied to the 6-Row wide and narrow row riding transplanter, and the field test is carried out on the transplanter. The test prototype is shown in Figure 5.

Fig. 6 is a comparison diagram of the interpolating mechanism. Figure 6 shows the gear box of Japan’s eccentric gear transplanting mechanism, which has nine eccentric gears with the same radius and eccentricity. The planetary gear and the intermediate gear are superposed by two sheet gears and installed in a staggered manner. Two locating pins are respectively fixed on two superposed eccentric thin gears, and the worm coil spring makes the meshing gears close. Figure 11b shows the gear box of the eccentric displacement gear interpolating mechanism. The eccentric displacement gear interpolating mechanism used in this project only uses 5 gears, which simplifies the mechanism.

The experimental site is Qixing branch of Sanjiang farm built by Heilongjiang Provincial Bureau of agricultural reclamation. The area of the experimental plot is 0.7 Hm2, the mud is flat and the depth of the mud foot is 170 mm. The seedling is raised with a tray, the soil is not loose and the needles are coiled. The average height of the seedling is 150 mm, the age of the leaves is 3-4, the width of the tray is 300 mm, the thickness of the soil layer is 19-21 mm, and the moisture content of the soil is 48%.

(1) According to the law of tooth gap change, the method of non-zero unequal displacement of eccentric gear is feasible; the method of non-zero unequal displacement of eccentric gear generated by non-zero unequal displacement can eliminate the tooth side clearance and realize meshing without tooth side clearance.

(2) The displacement depends on the side clearance of meshing gear, the side clearance depends on the center distance variation coefficient, and the center distance variation coefficient depends on the position of gear pitch curve. Therefore, the amount of displacement depends on the position of the gear pitch curve.

(3) The test report of oblique wide narrow row rice transplanter with eccentric displacement gear transplanter shows that the operation quality is good and the test performance index reaches the national standard.

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