JPH04131542A - Differential planetary gear device - Google Patents

Abstract

PURPOSE:To provide a differential planetary gear device having a speed reduction ratio of a specific value or less for the purpose of miniaturizing and high-speed driving of a robot by determining the number of teeth of a planetary gear and those of internal gears, and a diameter of a tip circle of the internal gear having the larger number of teeth by specific expression, respectively. CONSTITUTION:In a differential planetary gear device 10 provided with two internal gear 5, 9 having the different number of teeth in mesh with a single planetary gear 7, relationship between the number of teeth Zb of the planetary gear 7 and the number of teeth Zd of the internal gear 5, 9 is determined by Zb/Zd<1-tanalphakd/tanalphabd, wherein alphakd represents a pressure angle at a tip circle of the rotary internal gear 9 and alphabd, a mesh pressure angle between the rotary internal gear 9 and the planetary gear 7. Furthermore, a diameter Dkd of the tip circle of the internal gear having the larger number of teeth is determined by Dkd>{Zd-2+2(Xd+y)}m, wherein Xb represents an addendum modification coefficient of the planetary gear 7; (y), an increasing coefficient of a center distance; and (m), a module of the internal gear. Therefore, it is possible to provide the differential planetary gear device having a speed reduction ratio of 60:1 or less for the purpose of miniaturizing and high-speed driving of a robot.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a differential planetary gear device, which is a type of reduction gear that constitutes a power transmission mechanism.

(Prior Art) Generally, a motor as a drive source and a speed reducer for converting the rotation of the motor into large torque are used to drive the joints of a robot or the like. There are various types of speed reducers that convert the rotation of a motor into large torque, but a differential planetary gear system is known as one that can withstand relatively large loads.

FIG. 4 is a side sectional view showing such a conventional differential planetary gear device. 20 The differential planetary gear device 100 rotates the input shaft 101 to rotate the sun gear 103, and transmits the rotation of the sun gear 1030 to both the sun gear 103 and the fixed internal gear 105, for example, which are equally arranged so as to mesh with each other. The signal is transmitted to three planetary gears 107, and these planetary gears 107 revolve around the sun gear 103 while rotating on their own axis.

In addition to the fixed internal gear 105, each planetary gear 107 is
This fixed internal gear 105 meshes with a rotating internal gear 109 having a slight difference in the number of teeth, and the output shaft 111 is rotated by this rotating internal gear 109. therefore,
When each planetary gear 107 revolves around the sun gear 103 while rotating, the rotating internal gear 109 rotates according to the difference in the number of teeth with the fixed internal gear 105. As a result, the rotating internal gear 109
The output shaft 111 integrated with the input shaft 101 rotates at a reduced speed relative to the rotation speed of the input shaft 101.

By the way, in such a differential planetary gear device 100, generally one planetary gear 10 is used as shown separately in FIG.
7, the fixed internal gear 105 and the rotating internal gear 109, which have different numbers of teeth, must be concentrically meshed with each other with high precision.
The design is designed to increase the dislocation coefficient of 5. and,
The diameter of the tip circle 105a of the fixed internal gear 109 and the diameter of the tip circle 109a of the rotating internal gear 109 (both Dkd) are:
Each is calculated from the following formula.

D, d= (Zd-2+2 (Xb+y))m However,
Zb...Number of teeth of the internal gear The diameter of the addendum circle 109a of the rotating internal gear 109 is designed to be equal in size.

Furthermore, since the plurality of planetary gears 107 that mesh with both internal gears 105 and 109 are integrated with common gear specifications, the diameters of the addendum circles 107a of the portions that mesh with both internal gears 105 and 109 are all the same. are of equal size.

In such a differential planetary gear device 100, a large reduction ratio can be obtained by differential action according to the difference in the number of teeth between both internal gears 105 and 109. Since the planetary gears 107 are shared and integrated as described above, there is little deformation of the planetary gears 107, and the output is directly obtained from the rotating internal gears 109, resulting in high torsional rigidity. Due to the direct output from the common/integrated planetary gear 107 and rotating internal gear 109, the differential planetary gear device has a small number of parts and is characterized by being a small and lightweight speed reducer.

However, in recent years, the demand for smaller robots and faster drive speeds has increased, and even with the conventional differential planetary gear system configured as described above, a number of considerations have become necessary to meet these demands. It is expected. On the other hand, the conventional technology has the following problems.

That is, in order to drive a robot I at high speed, it has conventionally been conventional to attach a direct drive motor (hereinafter referred to as a DD motor) to the joint of the robot. However, when using a DD motor, the moment of inertia acting on the joints of the robot has a large effect on increasing the volume and weight of the DD motor, which has the drawback of hindering miniaturization of the robot.

On the other hand, if the joints of a robot are constructed by combining a normal motor and a differential planetary gear, the overall size will not increase so much even if there is an influence of the moment of inertia. Therefore, the demand for miniaturization of robots requires differential planetary gearing as a component.

The problem here is that the differential planetary gear system was originally intended to generate a large reduction ratio, but from the perspective of downsizing the robot, it was designed to generate a small reduction ratio, contrary to the conventional method. A differential planetary gear system will be required.

On the other hand, with conventionally used differential planetary gears, the reduction ratio obtained is approximately 60:1 to 10/0.1.
It is designed to be. (According to the literature of Masaso Senba et al.) In other words, conventionally, a design method has been established for a differential planetary gear device with a reduction ratio of 60:1 or more, but when the reduction ratio is less than 60=1, the design method has been established. There was no such method available for dynamic planetary gears. This is thought to be due to the fact that conventionally there was no need for a differential planetary gear device with a reduction ratio of 60:1 or less.

(Problems to be Solved by the Invention) As described above, when considering the miniaturization and high-speed drive of future robots, a differential planetary gear device with a reduction ratio of 60:1 or less will become necessary. However, in the past, there was no need for a differential planetary gear device with a reduction ratio of 60:1 or less, so no design method had been established at all.

The present invention has been made to solve the above problems, and aims to provide a differential planetary gear device with a reduction ratio of 60.1 or less in order to make robots smaller and faster to drive. It is.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention includes two internal gears having different numbers of teeth that can mesh with the same planetary gear. In the differential planetary gear device, (1)■ Number of teeth Zb of the planetary gear and number Z of teeth of the internal gear
b, Z /Z <1-1anα, d/lanαb.

d However, α5. ...Pressure angle α5 in the tip circle of the rotating internal gear. ...The meshing pressure angle between the rotating internal gear and the planetary gear, and the diameter Dkd of the tip circle of the internal gear with the larger number of teeth.
, D > (Z −2+2(Xb+7))mkd
d However, Xb: Shift coefficient of planetary gear y: Center distance increase coefficient m: A differential planetary gear device serving as a module of internal gears.

(2) In particular, the diameter Dk11 of the tip circle of the internal gear with the larger number of teeth is defined as D ≧2 ((a2+ (D /2) 2kd
gb+2 a (D/2
) eat abd)b However, a...Distance between the meshing center of the internal gear and the planetary gear Dgb...Base circle diameter of the planetary gear α5. ...A differential planetary gear device with a meshing pressure angle between the internal gear and the planetary gear.

(Operation) By satisfying the above (1) (2), a differential planetary gear device with a reduction ratio smaller than 60.1 can be realized in terms of calculation. However, if this continues, involute interference will inevitably occur between the internal gear and the planetary gear, which is not desirable in practice. Therefore, by further satisfying (2), the point of interference between the internal gear and the planetary gear can be moved in a direction where involute interference is reduced. (The diameter of the internal gear can be increased.) Therefore, a differential planetary gear device with a reduction ratio of 60:1 or less is provided.

Moreover, by satisfying the above (2), involute interference between the internal gear and the planetary gear can be completely eliminated.

(Example) The present invention will be described below with reference to the drawings.

Fig. 1 is a side sectional view showing an embodiment of the differential planetary gear device of the present invention, Fig. 2 is an enlarged side sectional view showing the meshing part between the planetary gear and the fixed gear, and Fig. 3 is the planetary gear and the fixed gear. FIG. 3 is a front cross-sectional view showing a part that meshes with a gear.

The differential planetary gear device 10 of this embodiment has a sun gear 3 at the center.
A fixed internal gear 5 and a rotatable rotating internal gear 9, which are two internal gears having different numbers of teeth, are provided concentrically with the sun gear 3. A planetary gear 7 is provided around the sun gear 3 so as to mesh with both the fixed internal gear 5 and the rotating internal gear 9. Three planetary gears 7 are used here. Further, in this embodiment, all rolling bearings are removed, and only sliding bearings are used.

Further, in this embodiment, in order to obtain a minute gear, the entire module is made small and an internal gear with as few teeth as possible is used. Each gear 35.7.9 is connected to a module 0.08. An involute spur gear with a pressure angle of 20°, and a sun gear3. The number of teeth of each of the fixed internal gear 599, the rotating internal gear, and the planetary gear 7 is 15. 36.39 and 11. Also, sun gear 3. The fixed internal gear 51, the rotating internal gear 9, and the planetary gear 7 each have a shift coefficient of 0.
4249.1. ．． 7697°0 and 0.32, each having the same center distance of 10913 m.

Here, a design method for a differential planetary gear device with a reduction ratio of 60.1 or less will be described. For comparison, Table 1 shows the specifications of a differential planetary gear device based on a conventional design method.

Below Margin First, we will discuss the fact that a differential planetary gear system with a reduction ratio of 60:1 or less cannot be designed using conventional methods. In the conventional differential planetary gear device design method, the following calculation formula is used to achieve a reduction ratio R:1.

R=ω /ω, = (1+Zc/Zb')/ (1-Z
/Zb) ... (2) However, ω...Rotational speed ω of the sun gear,...Rotational speed Z of the rotating internal gear...Number of teeth of the sun gear Z...Number of teeth of the fixed internal gear Zb: Number of teeth of the rotating internal gear Therefore, it can be seen that in order to obtain a small reduction ratio, it is necessary to reduce the number of teeth Zd of the rotating internal gear.

Table 1 also shows the results of examining whether the following formula holds true with regard to the meshing between the rotating internal gear and the planetary gear. It has been newly confirmed through experiments that if the following formula is not satisfied, involute interference occurs and the two do not mesh properly.

There is.

Z / Z ・< 1 tan αkd/ta
n a bdd ... (4) Z /Z ≧1 1an (E kd/ tan
(1bdd... (3) However, Zb...Number of teeth of the planetary gear α3...Pressure angle at the tip circle of the rotating internal gear α5...Meshing pressure angle between the rotating internal gear and the planetary gear According to the above formula (3), the number of teeth Z of the rotating internal gear.

is less than 48 (cases (C) to (f) in Table 1), it can be seen that involute interference occurs.

However, Zb=48 is the number of teeth at which the reduction ratio of the differential planetary gear device is approximately 60:1. Therefore, in order to achieve the object of the present invention, the following equation in which the direction of the equal sign is different from the above equation (3) must be established.Next, the occurrence of involute interference will be explained using FIG. 3.

In FIG. 3, the center of the rotating internal gear 9 is located at 02, the center of the planetary gear 7 is located at 01, and the common tangent of the respective base circles 9g and 7g is the meshing line of action. Then, both rotate so that the meshing contact point moves on this meshing action line. When the tip circle of the rotating internal gear 9 according to the conventional design method is shown by a broken line 9a', the meshing start point A' in this case is
(The intersection point between the tip circle 9g' of the rotating internal gear 9 and the line of meshing action) is on the left side of the interference point 1 in the figure.

This means that both gears 7.9 are involutely interfering with each other. In other words, the conventional design method cannot provide a differential planetary gear device with appropriate meshing.

In order to reduce this involute interference, in Fig. 3, the meshing start point should not be on the left side of the interference point 11.
That is, it is necessary to design it so that it moves to the right side of the interference point (1), for example, to point A.

In other words, by correcting the tip circle diameter of the rotating internal gear 9 to a larger value, in other words, by establishing the following equation that changes the sign of equality to the sign of inequality for the above equation (1), meshing starts. The point can be moved in the direction to the right of the interference point 11.

D > (Z −2+2 (Xb+y)) mk
+] d... (5) Therefore, if a design method is adopted that satisfies the above equations (4) and (5) at the same time, the influence of involute interference will be reduced, and the difference in reduction ratio will be less than 60 = 1. A dynamic planetary gear system becomes possible.

Furthermore, in order to completely eliminate the occurrence of involute interference, the following equation may be used instead of the above equation (5).

D ≧2/ (a2+ (D /2) 2ktl
gb+ 2 a (Dgb
/2) cot ffbd)... (6) However, a... Distance between the meshing centers of the internal gear and the planetary gear.As a result, the meshing start point coincides with point A in Figure 3.

By the method described above, it is possible to manufacture a differential planetary gear device with a reduction ratio of 60:1 or less for the purpose of downsizing and driving a robot at high speed.

Note that the present invention is not limited to the above embodiments. In the above embodiment, the number of planetary gears is three, but the effects of the present invention can be achieved as long as the number of planetary gears is one or more.

[Effects of the Invention] As explained above, according to the present invention, it is possible to provide a differential planetary gear device with a reduction ratio of 60=1 or less in order to make the robot smaller and drive it at higher speed.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing an embodiment of the differential planetary gear device of the present invention, Fig. 2 is an enlarged side sectional view showing the meshing part between the planetary gear and the fixed gear, and Fig. 3 is the planetary gear and the fixed gear. FIG. 4 is a side sectional view showing a conventional differential planetary gear device, and FIG. 5 is an enlarged side sectional view showing a conventional meshing portion between a planetary gear and a fixed gear. be. 3...Sun gear 5...Fixed internal gear 7...Planetary gear 9...Rotating internal gear 0...Differential planetary gear device

Claims (2)

[Claims] (1) In a differential planetary gear device comprising two internal gears with different numbers of teeth that can mesh with the same planetary gear, the number of teeth Z_b of the planetary gear and the number of teeth Z_d of the internal gear , Z_b/Z_d<1-tanα_k_d/tanα_b
_d However, α_k_d...The pressure angle in the tip circle of the rotating internal gear α_b_d...The meshing pressure angle between the rotating internal gear and the planetary gear, and the diameter of the tip circle of the internal gear with the larger number of teeth. D_k_
d is D_k_d>{Z_d-2+2(X_b+y)}m, where: Planetary gearbox. (2) Diameter D_k of the tip circle of the internal gear with the larger number of teeth
_d, D_k_d≧2√{a^2+(D_g_b/2)^2+
2a(D_g_b/2) cos α_b_d} However, a
...The meshing center distance between the internal gear and the planetary gear D_g_b...The basic circle diameter α_b_d of the planetary gear...The difference according to claim 1, characterized in that it is the meshing pressure angle between the internal gear and the planetary gear. Dynamic planetary gear system.