JP2899047B2 - Eccentric bearings for internal planetary gear units - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eccentric bearing which is used in an internal planetary gear reducer.

[Conventional technology]

For example, there is an inscribed planetary gear reducer having a small backlash and high positioning accuracy, and is used for various industrial robots.

As shown in FIG. 15, the inscribed planetary gear reducer has an input shaft 2 and an output shaft 3 that are directly driven by a motor 1 arranged coaxially, and is rotated around the input shaft 2 via an eccentric bearing 4. A plurality of through holes 6 are provided on a curved plate 5 movably mounted, and an inner pin 8 is provided on an output flange 7 provided at the inner end of the output shaft 3 to loosely fit into each through hole 6. 7 are connected in the rotation direction, and a plurality of curved concave portions formed at regular intervals on the outer periphery of the curved plate 5 are engaged with outer pins 10 arranged at regular intervals on the inner periphery of the casing 9. .

This reduction gear gives eccentric motion to the curved plate 5 via the eccentric bearing 4 by the rotation of the input shaft 2, and causes the curved plate 5 to rotate by the difference in the number of curved concave portions of the outer pin 10, thereby causing the inner pin 8 to rotate. The decelerated rotation is taken out to the output shaft 3 via the.

By the way, in the above-described speed reducer, since an impact load acts on the eccentric eccentric bearing 4, a large load capacity is required. Therefore, the life of the speed reducer largely depends on the eccentric bearing.

[Problems to be solved by the invention]

However, due to the structure of the internal planetary gear reducer, the eccentric bearing is used in a lubricated state at a high temperature and in a dilute state.

Conventionally, carbonitriding of rolling elements has been carried out as a measure to prolong the life of eccentric bearings.However, long life can be obtained, but special heat treatment furnaces are required for these treatments, which greatly reduces the processing cost. There is a problem of being expensive.

Therefore, an object of the present invention is to evaluate the surface roughness of the rolling surface of the rolling element of the eccentric bearing not only in the axial direction but also in the rolling direction, and to suppress the surface roughness in the axial direction and the circumferential direction to a certain range. For an internal planetary gear reducer that can form an oil film advantageously, has excellent lubricating oil holding capacity even under severe lubrication conditions, can prolong the life of the bearing, and can reduce the processing cost of rolling elements An eccentric bearing is provided.

[Means for solving the problem]

In order to solve the above-described problems, the present invention forms countless small concave recesses at random on the surface of a rolling element of an eccentric bearing to reduce the surface roughness of the rolling element surface in the axial direction and the circumferential direction. When each of the directions is obtained and displayed as a parameter RMS, the axial surface roughness RMS (L) and the circumferential surface roughness RMS (C)
RMS (L) / RMS (C) is 1.0 or less, and the parameter SK value of surface roughness is -1.6 or less.
The configuration in which the value of S (C) is 0.10 μm or more is adopted.

[Action]

The surface of the rolling element is formed into a random micro-rough surface, and the finished surface roughness parameter RMS of the micro-rough surface is set in the axial direction (L),
In the circumferential direction (C), calculate the ratio RMS (L) / RMS (C)
The value of RMS (L) and RMS (C) is 1.0 or less, and the parameter SK value is -1.6 or less in both the axial and circumferential directions.
0.10μm or more, improves the oil film formation rate on the rolling contact surface, prevents peeling damage and wear on the mating surface regardless of the surface roughness of the mating surface, prevents temperature rise and prevents seizure Prevention and long life can be obtained.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

The eccentric bearing 4 of the present invention has an inner race 21 as shown in FIG.
And a number of cylindrical roller pairs held at regular intervals by the cage 22
An eccentric bearing 4 is used by being attached to the input shaft 2 inside the inscribed planetary gear reducer shown in FIG.

Accordingly, the outer race is the curved plate 5, and the inner diameter surface of the curved plate 5 supported by the rolling elements 23 has a finished surface with a surface roughness of 3 to 5 s by grinding.

The rolling element 23 has a fine rough surface 23 whose surface is in a random direction.
This micro-rough surface 23a is formed on the surface roughness RMS (L) and the circumferential surface roughness RMS (L) when the surface roughness is obtained in each of the axial direction and the circumferential direction of the rolling element 23 and displayed by a parameter RMS. The ratio RMS (L) / RMS (C) of the direction surface roughness RMS (C) is set to 1.0 or less, for example, 0.7 to 1.0, and the parameter SK value of the surface roughness is -1.6 or less in both the axial direction and the circumferential direction. It has become.

In the surface processing for obtaining the rough surface condition of the rolling surface as described above, a desired finished surface can be obtained by special barrel polishing.

FIG. 2C shows a sectional roughness shape of the micro-rough surface 23a. As shown in FIG. 2, a special surface is formed such that a concave portion is formed on a flat surface and a convex portion does not occur from the flat surface.

The parameter SK value is the skewness of the surface roughness distribution curve (SKEWNESS), that is, the quantification of the asymmetry of the unevenness distribution with respect to the center line of the surface roughness. If the SK value is negative, There are many concave portions (valleys) with respect to the center line of the roughness, and in the case of a positive value, there are many convex portions (projections) with respect to the center line of the roughness. The parameter SK value of the surface roughness is represented by the following definition formula.

SK = ∫ (X−X ₀ ) ³ P (X) dX / σ ³ X: Roughness height X ₀ : Average height of roughness P (X): Probability density function of roughness amplitude σ: Square Average roughness The average height of the roughness in the definition formula for obtaining the SK value means an absolute value taken from a reference which is a center line in each case.

By setting the parameter SK value to be less than or equal to -1.6 in both the circumferential direction and the axial direction, there are many minute concave portions with respect to the center line, and the surface having RMS (L) / RMS (C) of less than or equal to 1.0. By limiting the numerical value of the directionality of the roughness, the shape and distribution of the surface concave portions are in a range advantageous for forming an oil film.

Since the above parameter SK value is a guideline for knowing the asymmetry of the unevenness distribution, taking a roughness curve on a general polished surface as an example, in a distribution where the concave and convex portions are symmetrical,
The SK value is close to 0, and takes a negative value when the unevenness distribution of the surface unevenness is an asymmetric distribution that is biased toward the concave side, and takes a positive value when the unevenness distribution is opposite.

The outer surface of the rolling element 23 is excellent in the ability to form an oil film, secures a sufficient oil film thickness, and suppresses metal contact of the rolling contact portion as much as possible, even under conditions where the finished surface roughness of the mating surface is poor.

By reducing the metal contact ratio of the rolling contact portion, surface damage of the outer diameter of the rolling element, peeling, abnormal friction from peeling and peeling are prevented, and durability is improved.

Next, a description will be given of the results of producing a plurality of types of needle bearings in which the surface of a rolling element is subjected to a surface treatment having a different finished surface, and performing a life test while changing the surface roughness of a mating shaft.

As shown in FIG. 3, the needle bearing used in the life test has an outer diameter Dr = 38 mm, an inner diameter dr = 28 mm, and a diameter D of the rolling element 23 =
5 mm, length L = 13 mm, cage 14 using 14 rolling elements
It is a bearing with.

As the test bearings, five types of rolling elements having different surface roughness finishes were manufactured. Surface roughness parameter RM for each test bearing
The characteristic values in S are shown in Table 1, the machining types of each test bearing are shown in Table 2, and the finished surface condition of the rolling element of each test bearing is shown in comparison with FIGS. 2A, 2B, and 2C.

The test apparatus used was a radial load tester 11 as schematically shown in FIG. 4 and test bearings X were mounted on both sides of a rotating shaft 12 to apply rotation and load to perform a position test. It is what you do.

The finish of the inner race (partner shaft) used in the test is Rmax 0.4 to 4 μm in the grinding finish. The outer race (outer ring) is Rmax 1.6 μm and is common to both cases.

The test conditions are as follows.

Bearing radial load 1465kg f Number of revolutions 3050rpm Lubricant Turbine oil (10cst under test conditions) The results of each rolling element life test performed on each test bearing under the above conditions are shown in Figs. 5 to 9 Show.

FIGS. 5 to 7 show test results obtained mainly with the test bearing C of the present invention, and FIGS. 8 and 9 show test results of the test bearings D and E of the present invention.

As is clear from the above test results, all of the test bearings C, D, and E of the present invention exhibited a long service life regardless of the mating shaft surface roughness.

In addition, peeling damage was often observed on the finished surface side when rolling the finished surface and the rough surface, but was not observed in the test bearings C, D, and E of the present invention.

FIG. 10 and FIG. 11 show the SK values, RMS of the test bearings A to E, respectively.
2 shows the results obtained by determining the L / C and the life (L ₁₀ ).

As shown in Fig. 10, test bearings C, D, E with SK value -1.6 or less
Shows a long life.

It was also found that the axial roughness RMS (L / C) was long even with a special barrel polishing of 1.0 as shown in FIG.

It was also found that the RMS (L / C) value alone was not sufficient to evaluate the rolling elements of a long-life bearing.

Next, Table 3 shows the calculated values of the oil film parameters A based on Grubin's equation based on the combination of the test bearings A to C with the mating shaft under the above test conditions.

As a result of the calculation, the oil film parameter A largely depends on the roughness of the mating shaft surface, and is in the range of 0.91 to 1.30 at 2 μm.

Generally, there is a relationship between the oil film parameter and the oil film formation rate as shown in FIG. 12, and it is said that a larger oil film parameter is better from the viewpoint of life. However, as is clear from the life test results, only A is generally used. Can not explain.

Regarding the confirmation of the oil film formation state on the finished surface of the rolling element and the peeling resistance, a test piece having the same surface condition as the test bearings C and A of the present invention was used under free rolling conditions using a two-cylinder testing machine. Accelerated peeling test. The state of formation of the oil film was confirmed by a direct current method.

Test conditions Maximum contact surface pressure 227 kg f / mm ² peripheral speed 4.2 m / sec (2000 rpm) Lubricant Turbine oil (10 cst under test conditions) Repeated load frequency 4.8 × 10 ⁵ (4 hr) As shown in FIG. 13 and FIG. 14, the oil film formation rate on the finished surface of the test bearing C of the present invention was improved by about 20% at the start of operation as compared with the test bearing A.

In addition, it was confirmed that an oil film was formed almost completely when the number of repetitive loads was 1.2 × 10 ⁵ .

Further, on the finished surface of the test bearing A, many occurrences and developments of peeling having a length of about 0.1 mm were observed, whereas no damage was found on the finished surface of the test bearing C of the present invention.

〔effect〕

As described above, according to the present invention, the surface of the rolling element is formed into a random micro-rough surface, and the axial and circumferential roughness of the micro-rough surface is suppressed to a certain range. It is advantageous for forming an oil film on the surface, and the minute dents become oil pools, so long life can be obtained even for mating surfaces with rough surfaces and good finishing surfaces, and wear of the inner and outer rings of eccentric bearings. Or peeling damage.

In addition, the durability of the internal planetary gear reducer can be greatly improved by extending the life of the eccentric bearing,
Since the rolling element can be processed by special barrel polishing, the processing cost can be reduced as compared with the heat treatment.

[Brief description of the drawings]

FIG. 1 is a sectional view of an eccentric bearing using a cylindrical roller bearing showing a first example of a roller bearing, FIG. 2 is a schematic view showing a finished surface condition of a rolling element in a test bearing, and FIG. FIG. 4 is a cross-sectional view of the used needle bearing, FIG.
5 to 9 are graphs showing the results of the rolling element life test, FIG. 10 is a graph showing the relationship between the SK value and the life, and FIG.
Fig. 12 is a graph showing the relationship between the RMS / (L / C) value and the service life. Fig. 12 is a graph showing the relationship between the oil film parameters and the oil film formation rate. Figs. 13 and 14 are graphs showing the oil film formation rate. The figure is a partially cutaway front view of the internal planetary gear reducer. 2 ... input shaft, 3 ... output shaft, 4 ... eccentric bearing, 5 ... curved plate, 21 ... inner ring, 22 ... cage, 23 ... rolling element, 23a ... fine rough surface.

Claims (1)

(57) [Claims] An input shaft and an output shaft are coaxially arranged, and a curved plate rotatably mounted on the input shaft via an eccentric bearing and an output flange provided on the output shaft are connected by pins. In the inscribed planetary gear reducer that takes out the differential rotation generated on the curved plate by the rotation of the curved plate to the output shaft, countless random concaves are formed randomly on the surface of the rolling element of the eccentric bearing, When the surface roughness of the rolling element surface is determined in each of the axial direction and the circumferential direction and is represented by a parameter RMS, a ratio of the axial surface roughness RMS (L) to the circumferential surface roughness RMS (C) is obtained. RMS
(L) / RMS (C) is 1.0 or less and the surface roughness parameter SK value is -1.6 or less, and the RMS (L) and RMS (C)
The eccentric bearing for an inscribed planetary gear reducer characterized by having a value of 0.10 μm or more.