JP2010106299A - Bearing for robot arm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing for a robot arm which has excellent productivity, further, is lightweight and has long service life. <P>SOLUTION: The bearing for a robot arm comprises: an inner member having an orbital face at the outer circumferential face; an outer member having an orbital face confronted with the orbital face of the inner member and arranged at the outer part of the inner member; and a plurality of rolling elements arranged between the orbital face of the inner member and the orbital face of the outer member in a freely rollable manner, and at least either the inner member or the outer member is composed of an alloy steel having a specified composition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bearing used for a joint portion of a robot arm.

  Since the joint of the robot arm is required to have high rigidity and low torque, angular ball bearings are often used in general, and two angular ball bearings can be combined in the back or in front of each other. Used in parallel.

  In recent years, the inner and outer rings of bearings have been made thinner for the purpose of reducing the size and weight of the robot arm to save space and reducing the power required for operation. However, as the inner and outer rings are made thinner, the strength is insufficient and fatigue failure is likely to occur. In particular, when bending stress is applied while rotating, torsional stress is applied along with the rotation, and fatigue failure occurs when sufficient strength cannot be secured.

  In addition, the bearing is formed with a through hole for inserting a bolt for attaching the robot arm body. However, as the inner and outer rings become thinner, the mounting strength decreases, and the surrounding portion of the through hole easily deforms. It is also a concern. When the peripheral portion of the through hole is deformed, the perpendicularity with respect to the rotation center of the robot arm is deteriorated. As a result, both side surfaces of the robot arm are displaced in the axial direction along with the rotation, and a shake occurs. Even if the amplitude of the shake caused by such a cause is about several tens of μm, there is a possibility that the noise of the robot arm may be generated, and the durability of the braking performance of the robot arm is lowered. Accordingly, when the inner and outer rings are made thinner and lighter, sufficient fatigue strength, yield strength, etc. are indispensable.

  However, if the height of the material is simply increased to improve the strength of the inner and outer rings, the workability is remarkably lowered and the productivity is greatly deteriorated.

  From such a background, it has been practiced to improve steel materials for bearings. For example, Patent Document 1 discloses that 0.5 to 0.7 mass% of carbon and 0 to 0 of silicon are used as main alloy components. An alloy steel for rolling bearings containing 0.6% by mass, 0.4 to 1.2% by mass of manganese and 0.05 to 0.2% by mass of vanadium is disclosed. However, although the tensile strength and yield strength of the alloy steel for rolling bearings are disclosed, functions such as workability and rolling fatigue life, and various qualities are not considered.

  In Patent Document 2, as main alloy components, carbon is 0.5 to 0.7 mass%, silicon is 0.5 to 0.9 mass%, manganese is 0.5 to 1.0 mass%, 0.4% by mass or less of chromium, 0.01 to 0.15% by mass of vanadium, and C% + 1 / 7Si% + 1 / 5Mn% + 1 / 9Cr% -5 / 7S% + V% A high-strength induction hardening steel with excellent machinability having a carbon equivalent Ceq of 0.75 to 0.9 is disclosed. Since the yield strength does not depend only on hardness but also strongly depends on the microstructure and the like, it may not always meet the weight reduction by thinning.

  Furthermore, Patent Document 3 contains 0.5 to 0.7% by mass of carbon, 0.6 to 1.2% by mass of silicon, and 0.6 to 1.0% by mass of manganese as alloy elements. And L calculated by the formula 11271C% + 5796Si% + 2665Mn% -6955 is 5000 or more, and H calculated by the formula 48.0C% + 5.7Si% + 11.5Mn% -16.2 is 23-25. A certain rolling component having excellent workability, fatigue strength, and rolling fatigue life is disclosed. However, only the hardness and the surface hardness of the hardened layer are mentioned.

JP-A-10-324951 JP 2002-332535 A JP 2002-363700 A

  Thus, the thing of patent documents 1-3 does not fully satisfy both the intensity | strength and workability of steel materials. Accordingly, an object of the present invention is to solve the above-described problems of the prior art, and to provide a robot arm bearing that is lightweight and has a long life in addition to excellent productivity.

In order to achieve the above object, the present invention has an inner member having a raceway surface on an outer peripheral surface, and a raceway surface opposite to the raceway surface of the inner member, and is disposed outside the inner member. An outer member, and a plurality of rolling elements that are arranged to freely roll between the raceway surface of the inner member and the raceway surface of the outer member, and at least the inner member and the outer member Provided is a robot arm bearing, one of which is made of an alloy steel that satisfies the following three conditions.
(Condition 1) Carbon content C% is 0.45 mass% or more and 0.65 mass% or less, silicon content
Si% is 0.5 mass% or more and 1 mass% or less, and manganese content Mn% is 0.2 quality.
% To 0.6% by mass, chromium content Cr% to 0.4% to 1% by mass, vanadium content V% to 0% by mass or 0% by mass to 0.2% by mass or less It is.
(Condition 2) The ratio Cr% / Mn% of the chromium content Cr% and the manganese content Mn% is 0.00.
8 or more and 3 or less.
(Condition 3) Carbon content C%, silicon content Si%, manganese content Mn%, chromium
Content Cr% and vanadium content V% satisfy the following formula (I):
The
0.75 ≦ (C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 +
1.65 × V%) ≦ 0.95 (I)

  The robot arm bearing of the present invention is lightweight and has a long life in addition to excellent productivity.

  In the present invention, the type and structure of the robot arm bearing are not limited, and examples thereof include bearings as shown in FIGS.

  As shown in FIG. 1, the bearing device 10 includes a pair of single-row angular ball bearings 11 combined on the back surface. The single-row angular contact ball bearing 11 includes an outer ring 12 having an outer ring raceway surface 12a formed on an inner peripheral surface, an inner ring 13 having an outer ring raceway surface 13a formed on an outer peripheral surface, and an outer ring raceway surface 12a and an inner ring raceway surface 13a. Balls 14 which are a plurality of rolling elements arranged so as to be able to roll with a contact angle of 15 ° to 55 °, for example, 40 °, and a cage for holding the balls 14 at predetermined intervals in the circumferential direction. 15. A pair of single-row angular ball bearings 11 combined with the back surface is sealed with a seal member 16 disposed between the outer ring 12 and the inner ring 13 only on the outer side in the axial direction (counter bore side of the outer ring 12) with respect to the ball 14. Intrusion of foreign matter from the outside is prevented along with leakage of grease.

A pair of single-row angular contact ball bearings 11 whose both ends are sealed with a seal member 16 are filled with grease containing synthetic hydrocarbon oil and containing a urea-based thickener. Examples of urea-based thickeners include diurea, triurea, tetraurea, urea, and urethane compounds, but diurea is preferable in consideration of sound. The consistency of the grease is 240 to 250, preferably 243. The kinematic viscosity is 30 to 400 mm ² / s at 40 ° C., and 40 to 180 mm ² / s is preferable in consideration of sound and torque.

  The pair of single-row angular contact ball bearings 11 combined with the back surface has a seal member 16 disposed only on the outer side in the axial direction, so the internal space S of the pair of bearings 11 is large, and a large amount of grease can be enclosed. Further, the oxidation stability by the base oil, the thermal stability, the low temperature fluidity, the heat resistance by the urea-based thickener, and the water resistance effectively prevent wear and contribute to the extension of the angular ball bearing 11 life.

  A fastening outer member 20 is fitted on each outer ring 12 of the pair of single-row angular ball bearings 11, and a fastening inner member 30 is fitted on each inner ring 13. The fastening outer member 20 and the fastening inner member 30 are made of titanium, aluminum, or plastic and are reduced in weight. One member such as a robot arm that rotates relatively, and the other member. (Neither is shown).

  The fastening outer member 20 includes, as components, a cylindrical main body 21 that is externally fitted to each outer ring 12, and a pair of annular plate-like side plates 22 and 23 that are disposed on both sides in the axial direction of the cylindrical main body 21. It consists of and. The inner diameters of the pair of side plates 22 and 23 are smaller than the inner diameter of the cylindrical main body 21 and abut against the axial end face of each outer ring 12 to restrict each outer ring 12 in the axial direction. The cylindrical main body 21 may be loosely fitted to each outer ring 12 and fixed by adhesion, or may be fixed by press-fitting. Further, the cylindrical main body 21 and the pair of annular plate-like side plates 22 and 23 are fixed by screw fastening or adhesion. Thereby, the outer ring 12 is fixed to the outer member 20 for fastening.

  In addition, a plurality of through holes 24 for inserting fasteners (not shown) such as bolts are provided in one side plate 22 at a predetermined interval in the circumferential direction. In the cylindrical main body 21, a relief groove 25 is formed along the axial direction at a position corresponding to the plurality of through holes 24, and the other side plate 23 is smaller than the deepest portion of the relief groove 25. Has an outer diameter. The through hole 24 can be a screw hole or the like according to the shape of the counterpart part.

  The fastening inner member 30 includes, as components, a cylindrical main body portion 31 fitted in each inner ring 13 and a pair of annular plate-like side plates 32 disposed on both sides in the axial direction of the cylindrical main body portion 31. , 33. The cylindrical main body 31 includes a shaft hole 34 that passes through the shaft core, and a fastening through hole 35 that is provided radially outward of the shaft hole 34 and penetrates in the axial direction. The outer diameters of the pair of annular plate-like side plates 32 and 33 are larger than the outer diameter of the main body 31 and abut against the axial end face of each inner ring 13 to restrict each inner ring 13 in the axial direction. Further, the inner diameters of the pair of side plates 32 and 33 are set so as not to overlap with the through hole 35 when viewed from the axial direction. The cylindrical main body 31 may be loosely fitted to each inner ring 13 and fixed by adhesion, or may be fixed by press-fitting. The cylindrical main body 31 and the pair of annular side plates 32 and 33 are fixed by screw fastening or adhesion. Thereby, the inner ring 13 is fixed to the inner member 30 for fastening.

  When the bearing device 10 having such a configuration is used for inner ring rotation, a fastener such as a bolt is inserted into the through hole 24 of the outer member 20 for fastening, and a robot arm, A gear, a motor, a pulley, a speed reducer, and a toothed belt are fastened. The other member that rotates relative to the through hole 35 of the fastening inner member 30 is, for example, a gear, a motor, a pulley, a speed reducer, and a toothed A belt and a robot arm are fastened and used. When the outer ring is used for rotation, a fastener such as a bolt is inserted into the through hole 35 of the inner member 30 for fastening, and the robot arm is fastened as the other member that rotates relative to the outer member for fastening. For example, a gear, a motor, a pulley, a speed reducer, a toothed belt, and a robot arm are fastened and used as one of the relatively rotating members in the through hole 24 of 20.

  As described above, according to the bearing device 10 of the present invention, the outer member 20 for fastening and the inner member 30 for fastening are formed of titanium, aluminum, or plastic, so the weight of the bearing device 10 is reduced. As a result, the responsiveness is improved, the power is saved, and the contact of the bearing can be prevented. In addition, the angular ball bearing 11 has a rotational torque that is smaller than that of a roller bearing that is in line contact with the raceway surface because the balls 14 that are rolling elements make point contact with the raceway surfaces 12a and 13a. .

  Since the outer member 20 for fastening and the inner member 30 for fastening are provided with through holes 24 and 35 through which fasteners such as bolts and screws are inserted, other parts can be prepared without preparing dedicated parts. Can be easily fastened, the number of assembly steps can be reduced, and can be applied to both outer ring rotation and inner ring rotation, and has high versatility.

  Further, the pair of ball bearings 11 includes a pair of outer members 20 for fastening, a pair of cylindrical main bodies 31 and a pair of outer rings 12 and inner rings 13 each including a cylindrical main body 21 and a pair of annular plate-like side plates 22 and 23. Are fixed by the fastening inner member 30 composed of the annular plate-like side plates 32 and 33, so that when the pair of ball bearings 11 are assembled as the bearing device 10, dimensional management and preload adjustment can be performed. There is no need to perform complicated preload adjustment in a manufacturer that uses the bearing device 10 as a rotating portion.

  As shown in FIG. 2A, the fastening outer member 20 includes a main body 40 integrally formed with a cylindrical main body 21 and one annular plate-like side plate 22, and the other annular plate. It can also be composed of two parts with a side plate 23 having a shape. Further, as shown in FIG. 2 (b), the main body 41 is integrally formed of a cylindrical main body 21 and the other annular side plate 23, and one annular side plate 22 is constituted by two parts. May be. Each member is fixed by adhesion or screwing.

  Further, as shown in FIG. 3, the fastening inner member 30 includes a main body 50 integrally formed with a main body 31 and one of the annular plate-like side plates 32 and 33, and the other annular plate-like member. It can also be comprised from two parts with the side plates 32 and 33. FIG. Each member is fixed by bonding, screwing, press fitting, or the like.

  In addition, although not shown, a front combination or a parallel combination may be used. However, it is preferable to use a rear combination that can increase the radial load capacity because the apparatus can be downsized and power can be saved. Further, it can be similarly applied to deep groove ball bearings (3-point contact, 4-point contact).

In the present invention, each outer ring 12 and each inner ring 13 is made of alloy steel that satisfies the following conditions 1 to 3.
(Condition 1) Carbon content C% is 0.45 mass% or more and 0.65 mass% or less, silicon content
Si% is 0.5 mass% or more and 1 mass% or less, and manganese content Mn% is 0.2 quality.
% To 0.6% by mass, chromium content Cr% to 0.4% to 1% by mass, vanadium content V% to 0% by mass or 0% by mass to 0.2% by mass or less It is.
(Condition 2) The ratio Cr% / Mn% of the chromium content Cr% and the manganese content Mn% is 0.00.
8 or more and 3 or less.
(Condition 3) Carbon content C%, silicon content Si%, manganese content Mn%, chromium
Content Cr% and vanadium content V% satisfy the following formula (I):
The
0.75 ≦ (C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 +
1.65 × V%) ≦ 0.95 (I)

Below, critical significance, such as content of the alloy element in alloy steel, is demonstrated.
[Carbon content]
Carbon (C) is an element that is indispensable for ensuring the hardness of the non-tempered portion after hot forging and the hardness of the hardened layer after quenching and tempering. From the viewpoint of rolling fatigue life, 0.45% by mass or more is necessary. However, if the amount is too large, the hardness becomes too high, and proeutectoid ferrite that becomes a chip breaker is reduced, which may reduce the machinability. Therefore, the C content in the alloy steel needs to be 0.45 mass% or more and 0.65 mass% or less.

[About silicon content]
Silicon (Si) acts as a deoxidizer during steelmaking and has the effect of improving the hardness and hardenability after hot forging. In particular, after quenching and tempering, not only strengthens the martensite structure and improves the rolling fatigue life, but in the non-tempered part, it dissolves in the ferrite and improves the strength of the ferrite structure, yield strength and Has the effect of increasing fatigue strength. However, if there is too much Si, machinability may be reduced. Therefore, Si content in alloy steel needs to be 0.5 mass% or more and 1 mass% or less.

[About manganese content]
Manganese (Mn) acts as a deoxidizing agent as well as Si, and has an effect of improving hardenability. Therefore, it is necessary to add 0.2% by mass or more, and 0.3% by mass It is more preferable to add more. However, when there is too much Mn, there exists a possibility that machinability may fall. Therefore, the Mn content in the alloy steel needs to be 0.6% by mass or less, and more preferably 0.55% by mass or less.

[Chromium content]
Chromium (Cr) has the effect of improving the hardenability as well as Si and Mn, strengthening the martensite structure after quenching, and improving the rolling fatigue life. Further, by refining the prior austenite crystal grains, the ferrite is divided, and the balance between strength and workability is remarkably improved. Furthermore, even after induction hardening, since it has the effect of suppressing the growth of crystal grains, and has the effect of improving both the rolling fatigue life and fatigue strength, it is necessary to add 0.4% by mass or more, It is more preferable to add 0.45% by mass or more. However, if there is too much Cr, the machinability may decrease, and the Cr content in the alloy steel needs to be 1% by mass or less.

[Vanadium content]
Vanadium (V) has a function of forming a stable carbide or carbonitride in alloy steel and effectively suppressing the growth of prior austenite crystal grains during induction hardening in a very small amount. Further, by refining the prior austenite crystal grains, the ferrite is divided, and the balance between strength and workability is remarkably improved. For this reason, V may be added as necessary, but in order to sufficiently obtain the effect, it is preferable to add 0.03% by mass or more. However, if V is too much, the machinability may be reduced. Therefore, the V content in the alloy steel is preferably 0.2% by mass or less.

[About the balance of alloy steel]
The balance other than the alloy components described above is substantially iron (Fe), but may contain alloy components other than those described above. Inevitable impurities may include sulfur (S), phosphorus (P), aluminum (Al), titanium (Ti), oxygen (O), and the like. Since the cleanliness of the alloy steel greatly affects the rolling fatigue life particularly under clean lubrication conditions, the impurity content is preferably low. However, an extreme reduction in the amount of impurities may significantly increase the material cost. Therefore, the cleanliness level that can be used as a bearing material (as defined in JISG 4805) is not required, and there is no strict restriction on the amount of impurities that would cause an increase in cost. ) (Bearing quality) level is acceptable.

[Ratio Cr% / Mn% of Cr content Cr% and Manganese content Mn%]
If the ratio Cr% / Mn% is 0.8 or more, both the prior austenite crystal grains and pro-eutectoid ferrite are refined and the structure is densified. As a result, not only the yield strength and fatigue strength of the alloy steel but also the workability such as impact strength, machinability, and plastic workability are greatly improved. However, if the ratio Cr% / Mn% is too large, the amount of pro-eutectoid ferrite may increase and the effect of improving the strength may not be obtained.

[Formula (I)]
C, Si, Mn, Cr, and V are all elements that increase the hardness of the alloy steel after hot forging, and have the effect of improving fatigue strength. However, if the alloy steel is harder than necessary, there is an inconvenience that the machinability and plastic workability after hot forging are lowered and the cost is significantly increased. Therefore, the content of the alloy component needs to satisfy Formula (I).

[About hardness of alloy steel]
As described above in the section of “Formula (I)”, if the alloy steel is harder than necessary, there is a disadvantage in that the machinability and the plastic workability are lowered and the cost is significantly increased. Therefore, the Vickers hardness Hv is preferably 230 or more and 300 or less.

[Ferrite content and prior austenite grain size]
As described above in the section “Ratio Cr% / Mn% of chromium content Cr% and manganese content Mn%”, there is a possibility that problems may arise in strength if the ferrite content of the alloy steel is large. Therefore, the area ratio is preferably 8% or more and 20% or less. Further, if the prior austenite crystal grains are fine, the structure is densified, and not only yield strength and fatigue strength but also workability such as impact strength, machinability, and plastic workability are greatly improved. Therefore, it is preferable that the prior austenite grain size measured by the method prescribed in Japanese Industrial Standards JISG0551 is 6 or more in terms of grain size number.

[About the yield strength of alloy steel]
Yield strength of the alloy steel 500MPa or more, 10 preferably ⁷ cycle fatigue strength is at least 400 MPa, so as to have excellent processability and high durability than structural carbon steel such as S53C or SAE1055 the Japanese Industrial Standards Become.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited thereto.

(Preparation of test piece)
Test pieces made of alloy steel having the composition shown in Table 1 were prepared. In addition, the formula value (I) described in Table 1 means a value (C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 + 1.65 × V%) calculated from the above formula (I). .

[Measurement of hardness, ferrite content and prior austenite grain size]
The hardness of the test piece was measured with a Vickers hardness meter after embedding in a resin and finishing and polishing the cut surface with emery paper. Moreover, after etching the same surface as the surface where the hardness was measured with a picral corrosion solution, the content (area ratio) of pro-eutectoid ferrite and the prior austenite grain size were measured by performing microstructure observation and image processing.

[How to measure yield strength, fatigue strength and Charpy impact value]
The yield strength of the test piece was measured using a JIS No. 14A test piece (diameter 8.5 mm). Fatigue strength was measured using an Ono type rotating bending fatigue tester. The test conditions are a No. 1-8 test piece specified in JISZ2271, a rotation speed of 3700 min ⁻¹ , and a rotation speed of 10 ⁷ cycles. Furthermore, the Charpy impact value was measured using a U-notched test piece. The notch depth is 2 mm.

[Turnability evaluation method]
Grinding was performed under the following conditions in accordance with the bite test method defined in JIS B 4011. The time until the wear amount on the flank face of the cutting tool reached 0.2 mm was defined as the tool life, and the turning performance was evaluated by the length of the tool life.
Tool type: P10 defined in JIS B 4053
・ Cutting speed: 150 m / s
-Feed rate: 0.2mm / rev
・ Incision: 0.5mm

  The evaluation results of the above various physical properties and various performances are shown in Tables 2 and 3. The test pieces of each example are made of fine austenite crystal grains and proeutectoid ferrite by suitable alloy components. The balance between (turnability) and strength (yield strength, fatigue strength, Charpy impact value) is excellent.

[Life Evaluation]
Next, an outer ring and an inner ring are produced from the rods of Example 1 and Comparative Example 3, and the occurrence of flaking is detected by measuring the vibration of the outer ring by rotating under the following conditions, and flaking occurs. The life was evaluated by the total number of revolutions up to.
・ Radial load: 7000N
・ Axial load: 5000N
・ Rotation speed: 300 min ^-1

  As a result, the life of the bar of Example 1 was about 2.3 times longer than when the bar of Comparative Example 3 was used.

  FIG. 4 shows the correlation between the Vickers hardness Hv of the test piece and the ferrite content, and FIG. 5 shows the correlation between the Vickers hardness Hv and turning properties (tool life).

As can be seen from each graph, in the same hardness, both the yield strength and the ferrite content were superior to the comparative example. The processability without reducing significantly (turning resistance), since the yield strength 500 MPa, 10 ⁷ cycle fatigue strength 400MPa can be sufficiently achieved, which is advantageous in weight reduction of the bearing.

It is a longitudinal section of a bearing device concerning one embodiment of the present invention. It is the schematic which shows the other structural example of the outer member for fastening of the bearing apparatus shown in FIG. It is the schematic which shows the other structural example of the inner member for fastening of the bearing apparatus shown in FIG. It is a graph which shows the correlation with Vickers hardness Hv and yield strength. It is a graph which shows the correlation with Vickers hardness Hv and turning property.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Bearing apparatus 11 Single row angular contact ball bearing 12 Outer ring 12a Outer ring raceway surface 13 Inner ring 13a Inner ring raceway surface 14 Ball 20 Outer member 24 for fastening Through hole (fastening hole)
30 Inner member for fastening 35 Through hole (hole for fastening)

Claims (1)

An inner member having a raceway surface on an outer peripheral surface, an outer member having a raceway surface facing the raceway surface of the inner member, and disposed on the outer side of the inner member; and a raceway surface of the inner member And a plurality of rolling elements arranged to roll freely between the raceway surface of the outer member,
A robot arm bearing, wherein at least one of the inner member and the outer member is made of an alloy steel that satisfies the following three conditions.
(Condition 1) Carbon content C% is 0.45 mass% or more and 0.65 mass% or less, silicon content
Si% is 0.5 mass% or more and 1 mass% or less, and manganese content Mn% is 0.2 quality.
% To 0.6% by mass, chromium content Cr% to 0.4% to 1% by mass, vanadium content V% to 0% by mass or 0% by mass to 0.2% by mass or less It is.
(Condition 2) The ratio Cr% / Mn% of the chromium content Cr% and the manganese content Mn% is 0.00.
8 or more and 3 or less.
(Condition 3) Carbon content C%, silicon content Si%, manganese content Mn%, chromium
Content Cr% and vanadium content V% satisfy the following formula (I):
The
0.75 ≦ (C% + Si% / 10 + Mn% / 5 + 5 × Cr% / 22 +
1.65 × V%) ≦ 0.95 (I)

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