JP3897924B2 - Inner meshing planetary gear unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internally meshed planetary gear device, and more particularly to an internally meshed planetary gear device in a field that requires all speed reduction and speed increase from a high load reducer for construction machinery to a precision reducer for industrial robots . Is.
[0002]
[Prior art]
As an intermeshing type planetary gear device, for example, the one described in Japanese Patent Publication No. 31-3801 has been known, but particularly in a high load reduction gear or a precision reduction gear, the inner gear is arranged inward. A trochoidal external gear having a different number of teeth is provided, which is often used so as to be eccentrically rotatable by a plurality of crankshafts so as to be internally meshed with the internal gear.
In this type of device, the rotation of the external gear that rotates while meshing with the internal gear is extracted from the carrier (output shaft) as the revolution of the crankshaft relative to the internal gear.
[0003]
In addition, since a large Hertzian stress is generated on the tooth surface of the external gear and the contact surface with the bearing needle on the inner wall surface of the crankshaft hole, carburizing quenching and high frequency are performed after gear cutting to provide sufficient strength to the tooth surface. The tooth surface is hardened by heat treatment such as quenching. Further, since the accuracy of the gear is deteriorated due to the deformation caused by the heat treatment, when a relatively high-precision gear is manufactured, tooth surface grinding is performed after the heat treatment to perform final tooth surface finishing.
[0004]
[Problems to be solved by the invention]
However, in such a conventional internally meshing planetary gear device, the lead time for manufacturing the external gear is long, resulting in high cost of the device.
[0005]
That is, in a gear that transmits a large amount of power, as described above, it is necessary to perform a surface hardening heat treatment so that the teeth have sufficient strength, which leads to a long lead time.
[0006]
On the other hand, if the heat treatment for surface hardening can be omitted, in some cases, tooth surface grinding becomes unnecessary, which can greatly contribute to the improvement of productivity. Therefore, if the heat treatment of the power transmission gear can be omitted, the manufacturing cost of the intermeshing planetary gear device can be greatly reduced.
[0007]
Therefore, the present invention realizes a tooth profile that generates a Hertz stress that is much smaller than the conventional one even when a normal torque is applied. It is an object of the present invention to provide a planetary gear device that can have equivalent performance and durability.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is capable of rotating eccentrically with a plurality of crankshafts via a plurality of bearings arranged at equal pitches in the circumferential direction with an external gear that is eccentric with respect to the internal gear and internally meshed with the internal gear. And an internal meshing planetary gear device in which the revolution movement of the crankshaft accompanying the rotation of the external gear in the internal gear is transmitted to the carrier that holds the crankshaft. teeth, has an arc tooth profile, the external teeth of the external gear, and a contact portion which contacts against the internal teeth of the internal gear, a tooth tip having a tooth surface inward from the tooth profile of the contact portion A modified trochoidal tooth profile that transmits torque with only 2 to 8% of external teeth out of the total number of teeth, and is located on the eccentric meshing side with respect to the internal gear, and the tooth surface of the external gear is The entire surface part including the same as the inside surrounded by the surface part A cylindrical body that is harder than the external gear and fitted in the external gear, and between the cylindrical body and the crankshaft, between the external gear and the plurality of crankshafts. A bearing having a plurality of rolling members interposed so as to be capable of rolling is interposed .
[0009]
In the present invention, substantial torque transmission at the tooth tip side where the total curvature at the meshing point of the theoretical trochoidal tooth profile and the arc tooth profile is increased is eliminated, and meshing occurs at the contact portion from the center portion of the tooth to the root portion where the total curvature decreases. Therefore, the Hertz stress can be effectively suppressed, and the outer gear can be manufactured from graphite cast iron or the like without subjecting the surface hardening to heat treatment, and a highly accurate gear can be obtained without grinding. Therefore, the cost can be greatly reduced.
[0011]
Further, since the surface portion and the inside of the external gear have the same hardness, there is no need to perform heat treatment for surface hardening and subsequent finishing by tooth surface polishing as in the prior art. A cylindrical body that is harder than the gear is fitted into the external gear, and the external gear is rotatably supported by the crankshaft via this and a plurality of rolling members, so that the external gear can be stably rotated eccentrically. The required meshing state of the internal gear and the external gear can be maintained.
[0012]
Furthermore, by setting the number of meshing teeth between the contact portion and the internal gear based on the total curvature of each internal tooth and the external tooth at the meshing position with each internal tooth on the tooth profile of the external tooth, Stress can be suppressed more effectively. Further, when the curvature of the arc tooth profile of the inner tooth is −1 / r and the curvature of the tooth profile curve of the trochoidal tooth profile of the outer tooth is 1 / ρ, the total curvature 1 / of the contact surface of the inner tooth and the outer tooth is 1 / r. R is represented by the following formula:
1 / R = -1 / r + 1 / ρ = (-Ρ + r) / (r · ρ)
The predetermined tooth profile curve is set so that the absolute value of the total curvature 1 / R is large on the tooth tip side of the external tooth and small on the tooth root side of the external tooth, and the total curvature 1 The contact portion may be formed within a range where the absolute value of / R is a predetermined value or less.
[0013]
In addition, high rigidity is an important performance index for a reduction gear for robot joints. A full roller needle bearing is easy to assemble by controlling the axial movement of the needle roller with the shell of the shell type needle and holding the needle roller with grease. In addition, the rigidity can be increased.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
[0015]
FIGS. 1-10 is a figure which shows one Embodiment of the internal meshing type planetary gear apparatus which concerns on this invention.
[0016]
First, the configuration will be described. In FIGS. 1 and 2, reference numeral 10 denotes an annular internal gear, which has a plurality of circular teeth 11 on the inner periphery of the annular body 11. The internal teeth 12 are formed by, for example, rotating a round pin made of stainless steel or the like in an arc groove of the annular body 11 so as to be rotatable. Reference numeral 20 denotes a pair of external gears which are arranged eccentrically in opposite directions with respect to the internal gear 10 and mesh with the internal teeth 12 of the internal gear 10 respectively. These external gears 20 have external teeth 21 that have a different number of teeth from the internal gear 10, for example, slightly fewer (for example, one or two) than the internal teeth 12. Further, the external gear 20 is supported by the crankshaft 25 via bearings 30 in a plurality of crank hole portions 22 provided at a predetermined radial position and at a constant circumferential pitch.
[0017]
As shown in FIG. 1, the crankshaft 25 eccentrically rotates the external gear 20 within the internal gear 10 while maintaining a predetermined eccentricity e that is the distance between the center O10 of the internal gear 10 and the center O20 of the external gear. It is like that. Further, when rotation is input from the input shaft 15 to the crankshaft 25 via the gears 16 and 17 constituting the preceding speed reduction unit, the external gear 20 is eccentrically rotated while maintaining the predetermined eccentricity e while meshing with the internal gear 10. (Eccentric circular motion, revolution), the difference in the number of teeth of both gears 10 and 20 (for example, the number of teeth of the external teeth 21 of the external gear 20 is one or two less than the number of teeth of the internal teeth 12 of the internal gear 10) Accordingly, it rotates (rotates) around the center O20 relative to the internal gear 10. Then, the revolution movement around the center O10 of the crankshaft 25 accompanying the rotation movement of the external gear 20 is taken out from the carrier 27 as the output shaft, and the movable carrier 27 rotates at a low speed with respect to the fixed internal gear 10. Alternatively, the movable-side internal gear 10 rotates at a low speed with respect to the fixed carrier 27 (fixed side). Reference numerals 18 and 19 denote a pair of bearings that rotatably support the crankshaft on the carrier 27, and also have an axial positioning function of the crankshaft 25.
[0018]
As shown in FIGS. 3A and 3B, the bearing 30 is interposed between the crank hole portion 22 of the external gear 20 and the plurality of crankshafts 25. A cylindrical body 31 as an outer shell that is hard and fitted in the crank hole portion 22 of the external gear 20, and is interposed between the cylindrical body 31 and the crank pin portions 25 a and 25 b of the crankshaft 25 so as to be able to roll. A plurality of rolling members 32.
[0019]
As will be described in detail later, the external teeth 21 of the external gear 20 are in contact with the internal teeth 12 of the internal gear 10 so as to be substantially pressurized, and are inward of the tooth profile curve of the contact portions 21a. A tooth tip portion 21b having a tooth surface on the gear center O20 side, and the tooth shape of the external tooth 21 is an external tooth 21 (this is all teeth) located on the eccentric meshing side with respect to the internal gear 10. It is a modified trochoidal tooth profile that transmits torque with only 2 to 8% of the external teeth).
[0020]
Further, the outer gear 20 has the same hardness (hardness) as the inner surface surrounded by the entire surface portion including the tooth surface. That is, the external gear 20 is made of an inexpensive material such as a steel material FCD450 or SCM420 normalizing material, graphite casting, powder metallurgy, or the like, and is not subjected to heat treatment for surface hardening. Therefore, the hardness is almost the hardness of the material, and no post-treatment finish polishing or the like for the heat treatment deformation is performed.
[0021]
Next, the tooth profile of the external gear 20 and its manufacture will be described.
[0022]
Conventionally, an external gear manufactured from carburized and hardened alloy steel has a tooth surface allowable Hertz stress of about 1400 MPa. However, annealing alone gives about 400 to 600 MPa, which is reduced to 1 / 3.5. This Hertzian stress is proportional to the square root of the load acting on the tooth surface. Therefore, if the surface hardening heat treatment is not performed with the shape of the conventional external gear, the transmission capacity of the gear device is greatly reduced to 1/10 or less. It will drop to.
[0023]
Therefore, in the present invention, a tooth profile that generates only a Hertz stress much smaller than the conventional one is realized, and the heat treatment for surface hardening is omitted.
[0024]
Specifically, in the prior art, the teeth on the eccentric side of the external gear 20 (internal tooth pins No. 1 to No. 1 in FIG. About half of the external teeth adjacent to 21) are close to each other when engaged with the internal teeth 12 in the range from the root to the tip. Therefore, the trochoidal tooth profile of the external tooth 21 has a curvature (1 / curvature radius) of the tooth surface continuously changed on the tooth surface. The tooth surface position where the internal teeth 12 of the pins No. 1 to 21 shown in FIG. 2 mesh with the external teeth 21 of the external gear 20 is represented on the tooth profile curve of the external teeth 21 as shown in FIG.
[0025]
The change in the curvature of the tooth surface is shown in FIG. As shown in the figure, the vicinity of the tooth bottom is concave (the sign is positive), and the curvature is relatively large. On the other hand, the curvature is small at the center of the tooth. At the inflection point where the curvature is 0, the tooth profile is linear and the curvature radius is infinite. When this inflection point is exceeded, the tooth surface becomes convex and the curvature becomes negative. When the curvature of the arc tooth profile (radius r) of the inner tooth 12 that is the meshing partner is −1 / r and the curvature of the outer tooth is 1 / ρ, the total curvature 1 / R of the contact surface is expressed by the following equation.
[0026]
1 / R = −1 / r + 1 / ρ = (− ρ + r) / (r · ρ) (1)
[0027]
The total curvature of the meshing points on the tooth surface is shown in FIG. As can be seen from FIG. 6, the total curvature at the position on the tooth bottom side corresponding to the pins No. 1 and 2 is close to 0 (zero), and the central portion where the difference in tooth surface curvature between the two gears 10 and 20 is large and On the tooth tip side, the absolute value of the total curvature increases.
[0028]
FIG. 7 shows the load applied to the tooth surface when torque is applied, and FIG. 8 shows the Hertz stress on the tooth surface. Since the Hertzian stress σ is proportional to the square root of | 1 / R |, as shown in FIG. 7, the maximum tooth surface load is generated at the corresponding position of the pin No. 6, but as shown in FIG. In addition, the maximum Hertz stress due to the influence of the overall curvature is pin No. It occurs at the position (No. 9, 10). Here, if a tooth profile satisfying −r + ρ≈0 can be designed, the Hertz stress is theoretically minimized.
[0029]
Therefore, when an appropriate tooth profile parameter is selected, it is possible to obtain a tooth profile whose curvature (concave surface) is close to the curvature of the arc tooth profile of the inner tooth 12 with which the tooth is engaged, in a slight range close to the root of the trochoidal tooth profile.
[0030]
As shown in FIG. 9, the tooth profile is corrected so that a portion having a large difference from the curvature of the arc of the mating counterpart is released, so that substantial load transmission at this portion is eliminated, and the absolute value of the total curvature is less than a predetermined value. If the load torque is transmitted only in the portion, the Hertz stress on the tooth surface can be suppressed to a small value even though the number of simultaneously meshing teeth is small.
[0031]
The analysis result is shown in FIG .
[0032]
As shown in the figure, the pin No. corresponding to the contact portion 21a of the external tooth 21 is shown. Between No.1 and No.3, pin surface No. in which substantial torque transmission is not made while tooth surface hertz stress of 600 MPa is generated. On the tooth tip side from 4 to 20, the Hertz stress is 0 (zero). Therefore, although the number of simultaneously meshing teeth is small, the Hertz stress generated on the tooth surface can be reduced.
[0033]
Further, since the bearing between the external gear 20 and the crankshaft 25 is a needle bearing with an outer shell, the needle roller as a rolling member does not directly contact the crank hole inner wall portion of the external gear 20. Since the problem of strength of the inner wall of the hole is eliminated, the heat treatment for hardening the surface is unnecessary, and the hole processing is simplified.
[0034]
As described above, in the present embodiment, substantial torque transmission at the tooth tip side where the total curvature at the meshing point of the theoretical trochoidal tooth profile and the arc tooth profile becomes large is eliminated, and the total curvature 1 / R becomes a predetermined value or less. Since the meshing is performed only at the portion 21a, the Hertzian stress can be effectively suppressed, and the outer gear can be manufactured with graphite cast iron or the like without subjecting the surface hardening to heat treatment. Without it, a highly accurate gear can be obtained. Therefore, the manufacturing cost of this type of planetary gear device having a plurality of external gears 20 can be greatly reduced.
[0035]
In addition, since the cylindrical body 31 that is harder than this is fitted into the external gear 20 and a plurality of rolling members 32 that are movably interposed between the cylindrical body 31 and the crankshaft 25 are provided, Despite the fact that the gear 20 is not surface hardened, it is possible to ensure the required strength on the rolling surface of the rolling member and ensure the durability of the support portion by the crankshaft. Can be stably rotated eccentrically. In particular, the robot joint speed reducer needs to have high rigidity, but the cylindrical body 31 of the needle bearing 30 with an outer shell restricts the axial movement of the rolling elements (needle rollers) 32, and is not shown. By holding these needle rollers with grease, a full roller needle bearing with good assemblability can be obtained. Therefore, the rigidity can be increased.
[0036]
Furthermore, at the meshing position (tooth surface position in FIG. 8) with each internal tooth 12 on the tooth profile of the external tooth 21, the external gear 20 is based on the total curvature 1 / R of each internal tooth 12 and the external tooth 21. Since the number of meshing teeth between the contact portion 21a of the external tooth 21 and the internal gear 10 is set, the Hertz stress can be more effectively suppressed.
[0037]
【The invention's effect】
According to the present invention, the internal teeth of the internal gear have an arc tooth shape, and the external teeth of the external gear come into contact with the internal teeth of the internal gear so as to be substantially pressurized, and the contact portions And a tooth tip portion having a tooth surface inward from the tooth profile curve, and is located on the eccentric meshing side with respect to the internal gear, and torque is generated only with 2 to 8% of external teeth out of the total number of teeth. Because it is a modified trochoidal tooth profile that transmits torque, it eliminates substantial torque transmission on the tip side where the total curvature at the meshing point of the theoretical trochoidal tooth profile and the arc tooth profile increases, and from the center of the tooth where the total curvature decreases to the root part It is possible to effectively suppress the Hertz stress by meshing at the contact portion. As a result, it is possible to manufacture the outer gear with graphite cast iron or the like without subjecting it to a surface hardening heat treatment, and it is possible to manufacture a highly accurate gear without performing tooth surface grinding. Therefore, the manufacturing cost of the intermeshing planetary gear device can be greatly reduced.
[0038]
In addition, a bearing having a cylindrical body as an outer shell is interposed between the outer gear and the crankshaft, while the entire surface portion including the tooth surface of the outer gear and the inner portion surrounded by the entire surface are made to have the same hardness. Therefore, it is possible to stably rotate the external gear eccentrically without performing heat treatment for surface hardening and subsequent finishing by tooth surface polishing as in the prior art. The meshing state can be maintained.
[0039]
Furthermore, at the meshing position with each internal tooth on the tooth profile of the external tooth, the number of meshing teeth between the contact portion and the internal gear is set based on the total curvature of each internal tooth and the external tooth. Hertz stress can be suppressed more effectively.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of an intermeshing planetary gear device according to the present invention.
FIG. 2 is a cross-sectional view showing the positional relationship between the internal gear and the external gear of the embodiment of FIG.
FIG. 3 is a longitudinal sectional view and a transverse sectional view showing a configuration of a bearing provided between an external gear and a crankshaft according to an embodiment.
FIG. 4 is a normal basic tooth profile curve showing a number of meshing positions of an internal gear and an external tooth having a trochoidal tooth profile.
5 is a graph showing a change in tooth surface curvature at each meshing position of the external teeth in FIG. 4; FIG.
6 is a graph showing a change in total curvature obtained from the tooth surface curvature of the external tooth and the tooth surface curvature of the internal tooth shown in FIG. 5 at each meshing position of the external tooth.
7 is a graph showing a difference in tooth surface load at each meshing position of the external teeth in FIG. 4; FIG.
8 is a graph showing transition of Hertz stress actually generated at each meshing position with respect to the tooth surface load shown in FIG.
FIG. 9 is a tooth profile curve diagram showing the shape of a modified trochoidal tooth profile of an external tooth according to an embodiment;
FIG. 10 is a graph showing tooth surface Hertz stress at each meshing position in one embodiment employing the tooth profile shown in FIG. 9;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Internal gear 12 Internal tooth 20 External gear 21 External tooth 21a Contact part 21b Tooth part 21c Tooth surface 25 Crankshaft 30 Bearing 31 Cylindrical body (outer shell)
32 Rolling elements (needle rollers)

Claims (1)

An external gear that is eccentric with respect to the internal gear and is in mesh with the internal gear is supported by a plurality of crankshafts via a plurality of bearings arranged at equal circumferential circumferential pitches so as to be eccentrically rotatable. In the intermeshing planetary gear device configured to transmit the revolution movement of the crankshaft accompanying the rotation of the external gear to the carrier that holds the crankshaft,
The internal teeth of the internal gear have an arc tooth profile,
The external teeth of the external gear include a contact portion that is formed along a predetermined tooth profile curve and contacts the internal teeth of the internal gear, and a tooth tip portion having a tooth surface inward of the tooth profile curve. And it is a modified trochoidal tooth profile that is located on the eccentric meshing side with respect to the internal gear and transmits torque with only external teeth of 2 to 8% of the total number of teeth,
All surface portion including a tooth surface of the outer gear, have a enclosed internal identical hardness by said surface surface,
Between said external gear of the plurality of crankshaft, a plurality interposed rollably between the and outer gear harder in fitted by a cylindrical body on the outer gear, cylindrical body and said crankshaft A rolling member is interposed ,
When the curvature of the arc tooth profile of the inner tooth is −1 / r and the curvature of the tooth profile curve of the trochoidal tooth profile of the outer tooth is 1 / ρ, the total curvature 1 / R of the contact surface of the inner tooth and the outer tooth is Is represented by the following equation:
1 / R = -1 / r + 1 / ρ = (-Ρ + r) / (r · ρ)
And the predetermined tooth profile curve is set so that the absolute value of the total curvature 1 / R is large on the tooth tip side of the external tooth and small on the tooth root part side of the external tooth,
An intermeshing planetary gear device , wherein the contact portion is formed within a range where the absolute value of the total curvature 1 / R is equal to or less than a predetermined value .

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