JP2009063109A - Shaft support structure for rotary encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shaft support structure for a rotary encoder, of which mechanically tolerable rotational frequency can be improved. <P>SOLUTION: In the shaft support structure for a rotary encoder, a hollow encoder shaft 2 is rotatably supported by a rolling bearing 3 to a housing 4 of a rotary encoder 1. Grease filled in the rolling bearing 3 has base oil viscosity of 50 mm<SP>2</SP>/s or less at 40°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a shaft support structure for a rotary encoder that detects the rotation of a rotary shaft in machine tools, various industrial equipment, electrical equipment, and the like.

As a rotary encoder used for detecting the rotation of the rotating shaft, a through-shaft type is known in which a hollow encoder shaft fitted to the rotating shaft is rotatably supported on an encoder housing via a rolling bearing. As a detection format, an optical type is common.
In the case of an optical rotary encoder, the allowable rotational speed is determined by an electrical limit related to the response frequency. If it is used at a higher rotational speed, the original functions such as control and measurement of the amount of rotation cannot be performed. However, often it may be necessary to rotate at a speed higher than its permissible rotational speed.

  The mechanically permissible rotational speed of the rotary encoder is determined by the heat generated by the built-in rolling bearing. If the rolling bearing generates too much heat, the rotation of the rotating slit plate may increase due to thermal expansion, and the optical system may be damaged. If it is a small rotary encoder, the built-in rolling bearing is small, and even if it rotates at high speed, heat generation is not a problem. However, for example, some shaft direct attachment type rotary encoders have a built-in rolling bearing having an inner ring inner diameter of 30 mm or more. In the case of such a large rotary encoder, the mechanical allowable rotational speed is low.

As a rolling bearing used for such a through-shaft type rotary encoder, the following measures have been taken in order to prevent the grease sealed in the bearing from scattering and adhering to the optical system of the rotary encoder. Each example is proposed.
-The seal provided on at least one side of the rolling bearing is composed of a plurality of sealing plates arranged in the axial direction (Patent Document 1).
• A cage that holds rolling elements of a rolling bearing is provided with a plurality of blades that generate an air flow inside the bearing by rotation of the cage (Patent Document 2).
・ Devise the composition of grease sealed in the bearing (Patent Document 3).
JP 2006-300161 A JP 2006-322594 A JP 2004-26941 A

  However, in each of the proposed examples described above, there is no room for improvement because a measure for improving the mechanical permissible rotational speed in the through shaft type rotary encoder is not disclosed.

  An object of the present invention is to provide a shaft support structure of a rotary encoder capable of improving a mechanical allowable rotational speed. In particular, a shaft structure of a rotary encoder that can be used under high-speed rotation is provided by improving the mechanical permissible rotational speed even in a large rotary encoder such as a direct-shaft type.

According to the shaft support structure of the rotary encoder of the present invention, in the shaft support structure in which a hollow encoder shaft is rotatably supported by a rolling bearing on the housing of the rotary encoder, the base oil viscosity at 40 ° C. is 50 mm ² / s or less. It is characterized in that grease is enclosed.
Thus, the friction torque of the rolling bearing can be reduced by making the grease sealed in the rolling bearing as low as 50 mm ² / s or less at a base oil viscosity at 40 ° C. As a result, heat generation during high-speed rotation can be suppressed, and the mechanical allowable rotational speed of the rotary encoder can be improved.

In this invention, the amount of grease filled may be 20% or less in space volume ratio. The space volume ratio refers to the ratio of the amount of grease enclosed to the volume of the space in which grease can be enclosed between the inner and outer rings. The space in which the grease can be sealed is generally a portion of the space between the seals on both sides between the inner and outer rings, excluding the rolling elements and the cage.
If the amount of grease enclosed is reduced to 20% or less, heat generation due to stirring resistance is suppressed, the heat generation suppression effect at high speed rotation is further increased, and the mechanical allowable rotational speed of the rotary encoder can be further improved.

  In this invention, the rolling element of the rolling bearing may be made of ceramics. If the rolling element is made of ceramics, it can be made lighter than that made of steel. If the rolling element is reduced in weight, the inertial force acting on the rolling element is reduced and the load applied to the outer ring by the rolling element is reduced, so that the friction torque can be reduced. Thereby, the heat generation suppressing effect is further enhanced, and the mechanical allowable rotational speed of the rotary encoder can be further improved.

  When the rolling elements are made of ceramics, for example, silicon nitride may be used. Silicon nitride has excellent characteristics in various aspects as a material for a ceramic rolling element.

  In the present invention, the rolling bearing may have a seal, and the structure of the seal may be in non-contact with either the inner ring or the outer ring. If the seal of the rolling bearing is a contact type, it becomes a heat generation source. However, by using the non-contact type, the heat generation is suppressed and the mechanical allowable rotational speed of the rotary encoder can be further improved.

  There are two types of non-contact seals, rubber and iron plate, but rubber is more effective in terms of better sealing and suppressing grease scattering.

According to the present invention, in a rotary encoder shaft support structure in which a hollow encoder shaft is rotatably supported by a rolling bearing in a rotary encoder housing, the grease sealed in the rolling bearing has a base oil viscosity of 50 mm ² / s or less at 40 ° C. Since it is low, the friction torque of the built-in rolling bearing can be reduced, and the mechanical allowable rotational speed of the rotary encoder can be improved.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a rotary encoder to which the shaft support structure of this embodiment is applied. The rotary encoder 1 is a through shaft type optical encoder having a hollow encoder shaft 2, and the encoder shaft 2 is rotatably supported by an encoder housing 4 via a rolling bearing 3. The encoder shaft 2 is hollow so as to fit a rotating shaft or the like in a machine tool, various industrial equipment, electrical equipment, or the like that is a rotation detection target.

The encoder housing 4 includes a housing frame 5 that is an L-shaped ring body having a bottom plate portion and an inner cylinder portion, and a cover 6 that is an L-shaped cylinder body having a top plate portion and an outer cylinder portion. It becomes. One end of the cylindrical portion 6a of the cover 6 is fitted to the outer periphery of the housing frame 5, and the flange portion 6b extends from the other end of the cylindrical portion 6a toward the inner diameter side to the vicinity of the outer periphery of the encoder shaft 2. Between the inner peripheral surface of the housing frame 5 and the outer peripheral surface of the encoder shaft 2, two rows of rolling bearings 3 arranged in the axial direction are interposed.
An annular slit plate mounting base 7 is fitted to a portion of the outer periphery of the encoder shaft 2 covered by the cover 6, and a disc-shaped rotating slit plate 9 is formed on the outer periphery of the slit plate mounting base 7. 2 and concentric. The rotating slit plate 9 is provided with slits 9a so that a plurality of the rotating slit plates 9 are arranged on a part of the circumferential direction or on the entire circumference.

  In the space covered with the cover 6, the circuit board 10 on which the light receiving elements 11 and the like are mounted is arranged so as to be arranged in parallel with the rotary slit plate 9. The circuit board 10 is fixed to the housing frame 5 via a plurality of support columns 12 extending in the axial direction. The light receiving element 11 is attached to one surface of the circuit board 10 facing the rotating slit plate 9, and an electronic component 13 constituting a waveform shaping circuit or the like is mounted on the surface opposite to the mounting surface of the light receiving element 11. Yes. The housing frame 5 is provided with a light emitting element 14 at a position facing the light receiving element 11 in the axial direction through the rotary slit plate 9 so that the light receiving element 11 and the optical axis are aligned. The light emitting element 14, the rotary slit plate 9, and the light receiving element 11 constitute an optical sensor unit 8 of the rotary encoder 1. The rotating slit plate 9, the circuit board 10, the light receiving element 11, and the light emitting element 14 are covered by the cover 6 so as to be blocked from the outside.

  In the rotary encoder 1, the rotation slit plate 9 rotates integrally with the encoder shaft 2 along with the rotation of a rotation shaft such as a motor fitted to the encoder shaft 2, and the rotation is detected by the optical sensor unit 8. That is, in the optical sensor unit 8, the light receiving element 11 receives radiated light from the light emitting element 14 every time each slit 9 a of the rotating rotary slit plate 9 passes on the optical axis of the light emitting element 14 and the light receiving element 11. To do. The detection signal is processed by a waveform shaping circuit or the like mounted on the circuit board 10 to detect the rotation of the rotary slit plate 9, that is, the rotation of the encoder shaft 2.

  FIG. 2 shows a partially enlarged cross-sectional view of the rolling bearing 3 incorporated in the rotary encoder 1. The rolling bearing 3 in this case is a deep groove ball bearing, and includes an inner ring 21, an outer ring 22, and a plurality of rolling elements 23 interposed between the inner and outer rings 21 and 22, and the outer surface of the inner ring 21 and the inner surface of the outer ring 22. The raceway surfaces 21a and 22a of the rolling elements 23 are formed respectively. The rolling element 23 is held by a cage 29. The rolling element 23 is made of ceramics, and silicon nitride is used as a specific material. The inner and outer rings 21 and 22 are made of steel.

  Both ends of the annular space between the inner ring 21 and the outer ring 22 are sealed with a non-contact seal 24, and grease (not shown) is sealed in the annular space between the non-contact seals 24 on both sides. The non-contact seal 24 is made of rubber, and includes a ring-shaped cored bar 25 and a rubber member 26 fixed to the cored bar 25. These non-contact seals 24 are attached to the outer ring 22 by fitting their outer diameter side ends into seal mounting grooves 27 formed on the inner diameter surface of the outer ring 22. The inner diameter side end of the non-contact seal 24 is close to the groove inner surface of the seal groove 28 formed on the outer diameter surface of the inner ring 21 and forms a seal gap with the groove inner surface.

As the grease sealed in the rolling bearing 3, a grease having a low base oil viscosity is used in order to reduce the friction torque. Specifically, a grease having a base oil viscosity at 40 ° C. of 50 mm ² / s or less is used. The base oil viscosity at 40 ° C. of the encapsulated grease is preferably 20 mm ² / s or more.
In addition, the amount of grease charged is 20% or less in terms of the space volume ratio in the bearing. This space volume ratio is the ratio of the enclosed grease volume to the volume of the space excluding the rolling elements 23 and the cage 29 in the portion between the non-contact seals 24, 24 on both sides in the annular space between the inner and outer rings 21, 22. It is.

According to the shaft support structure of the rotary encoder having this configuration, the grease encapsulated in the rolling bearing 3 has a low base oil viscosity of 50 mm ² / s or less at 40 ° C. Therefore, the friction torque of the rolling bearing 3 can be reduced. Thereby, the heat_generation | fever at the time of high speed rotation can be suppressed, and the mechanical permissible rotation speed of the rotary encoder 1 can be improved. Since the amount of grease enclosed is reduced to 20% or less, heat generation due to stirring resistance is suppressed, and the heat generation suppression effect at high speed rotation is further enhanced.
Further, since the rolling element 23 is made of ceramics, the weight of the rolling element 23 reduces the inertial force acting on the rolling element 23 and the load applied to the outer ring 22 by the rolling element 23 decreases. As a result, the friction torque can be reduced, thereby further increasing the heat generation suppressing effect. Also by this, the mechanical permissible rotational speed of the rotary encoder 1 can be further improved. Since the rolling element 23 uses silicon nitride among ceramics, the rolling element 23 has excellent characteristics in various aspects.

  If the seal of the rolling bearing 3 is a contact type, it becomes a heat source, but since it is a non-contact type, heat generation is suppressed and the mechanical allowable rotational speed of the rotary encoder can be further improved. When the non-contact type seal 24 is made of rubber as in this embodiment, the sealing performance is better than that of an iron plate, and it is effective in suppressing the scattering of grease.

  FIG. 3 shows another example of the rolling bearing 3 used in the rotary encoder 1 of FIG. The rolling bearing 3A of this example uses a non-contact seal made of iron plate as the non-contact seal 24A for sealing both ends in the rolling bearing 3 of FIG. 2, and the other configuration is the same as the example of FIG.

The analysis results and test results will be described. First, an example of analysis by calculating the friction torque of a rolling bearing is shown. The rolling bearing to be analyzed is JIS standard 6814ZZ (inner ring 21 has an inner diameter of 70 mm, non-contact seal made of iron plate), and has the above dimensions in the rolling bearing 3A shown in FIG.
Assuming a situation where an axial load of 100 to 500 N is applied to the rolling bearing 3A and the rolling bearing 3A is rotated at 2000 rpm, the relationship between the axial load and the friction torque is calculated. In addition, the effects of grease viscosity and rolling element specific gravity on the friction torque were calculated. In this calculation, it was assumed that the lubrication temperature was 40 ° C. and the contact angle was 20 °. Further, the friction between the rolling element 23 and the cage 29 was ignored, and it was assumed that the lubrication was performed normally.

FIG. 4 is a graph showing the calculation result of the relationship between the axial load and the friction torque. In the figure, (1) shows a graph of the calculation results when the viscosity of the grease base oil is 130 mm ² / s and the specific gravity of the rolling element 23 is 7800 kg / m ³ (equivalent to a steel rolling element). (2) is the case where the viscosity of the grease base oil is 22.5 mm ² / s and the specific gravity of the rolling element 23 is 7800 kg / m ³ (equivalent to a steel rolling element), and (3) is the viscosity of the grease base oil. When the specific gravity of the rolling element 23 is 3200 kg / m ³ (equivalent to a rolling element made of silicon nitride) at 130 mm ² / s, (4) shows that the viscosity of the grease base oil is 22.5 mm ² / s and the rolling element 23 The graph of the calculation result when the specific gravity of 3200 kg / m ³ (equivalent to a rolling element made of silicon nitride) is shown.

The greases having the above-mentioned viscosities used in the analysis and the greases used in the test described below are as follows in terms of trade names.
Grease with a viscosity of 130 mm ² / s: Showa Shell Sekiyu Albania Grease S2
Grease with a viscosity of 22.5 mm ² / s: Showa Shell Sekiyu Albania Grease HVQ
Grease having a viscosity of 46.0 mm ² / s: Joint fat and oil Multemp SB-M

The graph in FIG. 4 shows that the grease base oil viscosity is 22.5 mm ² / s ((2) compared to the case where the grease base oil viscosity at 40 ° C. is 130 mm ² / s ((1), (3)). (4)) shows that the friction torque is much smaller.
Furthermore, when the specific gravity of the rolling element is 7800 kg / m ³ (equivalent to a steel rolling element), when it is 3200 kg / m ³ (equivalent to a silicon nitride rolling element), the friction torque is somewhat reduced. ing.

Next, actual test examples will be described. The rolling bearing to be tested is JIS standard 6814LLB (the inner diameter of the inner ring 21 is 70 mm, a rubber non-contact seal), and the rolling bearing 3 shown in FIG.
This test object bearing was rotated and the temperature rise accompanying rotation was investigated. In this case, there are two types of bearings to be tested as examples: greases with a base oil viscosity of 46 mm ² / s at 40 ° C. sealed in 31% by space volume ratio and those in which 16% are sealed. As an example of a conventional product, there was prepared one type in which grease having a base oil viscosity at 40 ° C. of 130 mm ² / s was enclosed by 31% in space volume ratio. In all cases, the preload was adjusted and evaluated so that the starting torque was 0.05 Nm.

  As a result, when the conventional product was rotated at 2000 rpm, the steady state outer ring temperature exceeded 80 ° C., whereas in the case of the two examples that are the above examples, the steady state was maintained even when rotated at 3000 rpm. The outer ring temperature was not so high, about 48 ° C. when the amount of grease was 31%, and about 43 ° C. when the amount of grease was 16%.

As shown in the above test results and analysis results, according to the rolling bearings 3 and 3A with the base oil viscosity at 40 ° C. of 50 mm ² / s or less as the encapsulated grease, the friction torque can be reduced and the heat generation at high speed rotation can be achieved. Can be suppressed. Therefore, the mechanically permissible rotational speed of the rotary encoder 1 using the rolling bearings 3 and 3A can be improved.

The grease sealed in the rolling bearings 3 and 3A is not limited to that used in the test example, and any type of grease may be used as long as the base oil viscosity is as low as 50 mm ² / s or less. When the base oil viscosity is 20 mm ² / s or less, the oil is likely to be separated and scattered, and an oil film is hardly formed, so that metal contact may occur. Therefore, a material having a base oil viscosity of 20 mm ² / s or more is preferably used. Preferably, grease containing a thickening agent having oil retaining property that does not scatter even when rotated at a high speed is preferable. This is because grease having a low viscosity is used and is more easily scattered.

It is sectional drawing of the rotary encoder to which the shaft support structure concerning one Embodiment of this invention is applied. It is a partial expanded sectional view of the rolling bearing integrated in the rotary encoder. It is a partial expanded sectional view which shows the example of the other rolling bearing integrated in the rotary encoder. It is a graph which shows the result of having calculated the relationship between an axial load and a friction torque based on the rolling bearing of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rotary encoder 2 ... Encoder shaft 3 ... Rolling bearing 4 ... Encoder housing 8 ... Optical sensor part 21 ... Inner ring 22 ... Outer ring 23 ... Rolling element 24 ... Non-contact seal

Claims (6)

In a rotary encoder shaft support structure in which a hollow encoder shaft is rotationally supported by a rotary bearing in a rotary encoder housing, the rolling bearing is filled with grease having a base oil viscosity at 40 ° C. of 50 mm ² / s or less. A shaft support structure for a rotary encoder.   2. The shaft support structure for a rotary encoder according to claim 1, wherein an amount of the grease enclosed is 20% or less in space volume ratio.   The shaft support structure for a rotary encoder according to claim 1 or 2, wherein a rolling element of the rolling bearing is made of ceramics.   4. The shaft support structure for a rotary encoder according to claim 3, wherein the rolling element is made of silicon nitride.   5. The shaft support structure for a rotary encoder according to claim 1, wherein the rolling bearing has a seal, and the seal is not in contact with either the inner ring or the outer ring. 6.   6. The shaft support structure for a rotary encoder according to claim 5, wherein the non-contact seal is made of rubber.

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