The present invention relates to an eccentric rocking type reduction gear, and more specifically, to an improvement of a rotation balance of a crank shaft that performs eccentric rocking on an external gear of the eccentric rocking type reduction gear.
Eccentric rocking type reduction gears include a crank shaft. The crank shaft includes an eccentric cylindrical cam in order to perform eccentric rocking on an external gear. In general, the crank shaft is utilized as an input shaft, and rotates at a fast speed. Hence, fluctuating load acts on a bearing that supports the crank shaft due to centrifugal force produced inherently to the unbalanced shape of the eccentric cylindrical cam. For example, according to a reduction gear disclosed in Patent Document 1, in order to reduce such fluctuating load, the eccentric cylindrical cam is formed with a balancer weight. This suppresses the unbalance originating from the weight of the eccentric cylindrical cam.
Moreover, there are reduction gears that include two external gears. According to the reduction gears of this type, a crank shaft is provided with two eccentric cylindrical cams to support the two external gears, respectively. The respective eccentric cylindrical cams are disposed around the axial line of the crank shaft with respective phases shifted by 180 degrees from each other. This structure cancels translational force.
As explained above, according to the reduction gear of Patent Document 1, the balancer weight is formed inwardly of the eccentric cylindrical cam. This balancer weight eliminates the unbalance around the axial line of the crank shaft. However, the unbalance around the axial line orthogonal to the axial line of the crank shaft still remains unaddressed. Accordingly, couple is produced around the axial line orthogonal to the axial line of the crank shaft due to centrifugal force.
According to the reduction gears having the two external gears, the two eccentric cylindrical cams are disposed around the axial line of the crank shaft with respective phases being shifted by 180 degrees from each other. According to such a structure, the unbalance around the axial line of the crank shaft can be also addressed. However, the unbalance around the axial line orthogonal to the axial line of the crank shaft still remains unaddressed. Hence, couple is still produced around the axial line orthogonal to the axial line of the crank shaft.
The couple around the axial line orthogonal to the axial line of the crank shaft also applies fluctuating load to the bearing supporting the crank shaft. This often results in the shortage of the lifetime of the bearing. Moreover, the eccentric rocking type reduction gear is likely to generate vibration.
It is an object of the present invention to provide an eccentric rocking type reduction gear which reduces fluctuating load acting on a bearing due to a rotation of a crank shaft to extend the lifetime of the bearing, and which also suppresses a generation of vibration.
To accomplish the above object, a first aspect of the present invention provides an eccentric rocking type reduction gear comprising an internal gear, two external gears meshed with the internal gear, a crank shaft supporting both of the external gears, and a carrier rotating together with a rotation of both of the external gears, the crank shaft comprising first and second cylindrical cams disposed around an axial line of the crank shaft with respective phases being shifted by 180 degrees and in a manner offset from a rotation center of the crank shaft, both of the external gears being supported by the first and second cylindrical cams, respectively, in a freely rotatable manner and in a manner revolvable around an axial line of the internal gear, the carrier comprising a plurality of output pins fastened around an axial line of the carrier at an equal interval, each of the output pins being engaged with a plurality of through-holes provided in both of the external gears to be linked with a rotation movement of both of the external gears, the crank shaft being rotated as an input shaft and either one of the internal gear and the carrier being rotated as an output shaft, first and second eccentric holes which run in an axial direction of the crank shaft, and which are in communication with each other being formed in the crank shaft, the first eccentric hole running from a first end face of the crank shaft to a center position of the crank shaft in the axial direction, and being disposed in a manner offset in a same direction as that of the first cylindrical cam, and the second eccentric hole running from a second end face of the crank shaft to the center position of the crank shaft in the axial direction, and being disposed in a manner offset in a same direction as that of the second cylindrical cam.
According to such a structure, the first and second cylindrical cams are disposed around the crank shaft with respective phases being shifted from each other by 180 degrees. Hence, translational force due to centrifugal force acting on the crank shaft can be reduced. Moreover, the first and second eccentric holes reduce the moment of couple due to the centrifugal force acting on the crank shaft. Since both translational force and moment of couple are reduced as explained above, fluctuating load acting on the bearing supporting the crank shaft can be reduced. Accordingly, the lifetime of the bearing can be extended. Moreover, vibration caused by the reduction gear can be reduced.
In the above-explained eccentric rocking type reduction gear, it is preferable that axial-end balance adjusting portions which adjust a weight balance are provided at both ends of the crank shaft.
According to such a structure, the axial-end balance adjusting portions are provided at both ends of the crank shaft. Accordingly, the arm of couple can have the maximum length. Hence, when couple is produced around an axial line orthogonal to the axial line of the crank shaft, the adjustment for accomplishing the balancing can be reduced as much as possible.
In the above-explained eccentric rocking type reduction gear, it is preferable that the axial-end balance adjusting portions are provided at both end faces of the crank shaft, and are chamfers provided at respective circumference edges of openings of the first and second eccentric holes.
According to such a structure, by increasing the chamfering level in a chamfering process, the rotation balance of the crank shaft can be adjusted finely without any special process.
In the above-explained eccentric rocking type reduction gear, it is preferable that the axial-end balance adjusting portions are balancer weights provided at both ends of the crank shaft, respectively.
According to such a structure, by increasing or decreasing the weight of the balancer weight, the rotation balance of the crank shaft can be adjusted finely even after the assembling of the crank shaft is completed.
To accomplish the above object, a second of the present invention provides An eccentric rocking type reduction gear comprising an internal gear, two external gears meshed with the internal gear, a hollow crank shaft supporting both of the external gears, and a rotating carrier rotating together with a rotation of both of the external gears, the crank shaft comprising first and second cylindrical cams disposed around an axial line of the crank shaft with respective phases being shifted by 180 degrees and in a manner offset from a rotation center of the crank shaft, both of the external gears being supported by the first and second cylindrical cams, respectively, in a freely rotatable manner and in a manner revolvable around an axial line of the internal gear, the carrier comprising a plurality of output pins fastened around an axial line of the carrier at an equal interval, each of the output pins being engaged with a plurality of through-holes provided in both of the external gears to be linked with a rotation movement of both of the external gears, the crank shaft being rotated as an input shaft and either one of the internal gear and the carrier being rotated as an output shaft, two recesses being provided in an inner periphery of the crank shaft, and the respective recesses being disposed at opposite sides along offset directions of the first and second cylindrical cams, and being disposed at different positions along an axial direction of the crank shaft.
According to such a structure, the first and second cylindrical cams are disposed around the crank shaft with respective phases being shifted from each other by 180 degrees. Hence, translational force due to centrifugal force acting on the crank shaft can be reduced. Moreover, the two recesses are disposed in the inner periphery of the crank shaft at opposite sides to each other along respective offset directions of the first and second cylindrical cams. The respective recesses are disposed at different positions from each other along the axial direction of the crank shaft. In this case, both recesses cancel couple acting on the crank shaft when no such recesses are provided. Accordingly, moment of couple due to the centrifugal force acting on the crank shaft can be reduced. Since both translational force and moment of couple are reduced as explained above, fluctuating load acting on the bearing supporting the crank shaft can be reduced. Hence, the lifetime of the bearing can be extended.
a) is a vertical cross-sectional view illustrating the crank shaft in an axial condition, and
a) is a front view illustrating a solid member, and
a) is a vertical cross-sectional view of the crank shaft having a communication portion not chamfered, and
a) is a vertical cross-sectional view of the crank shaft having both ends thereof not chamfered, and FIG. 9(b) is a model diagram for explaining coupling by chamfered both ends of the crank shaft;
a) is a vertical cross-sectional view illustrating the left end of a crank shaft according to another embodiment, and
a) is a vertical cross-sectional view of a crank shaft according to the other embodiment,
An embodiment of the present invention in which an eccentric rocking type reduction gear thereof is applied to a joint of a robot arm will now be explained with reference to
<Structure of Reduction Gear>
As illustrated in
Two cylindrical cams 31 and 32 are formed integrally at the center of the crank shaft 3. As illustrated in
As illustrated in
As illustrated in
As illustrated in
d=2·e1+D (1)
where e1 is the offset level of the cams 31 and 32, and D is the external diameter of the output pin 7.
As illustrated in
<Crank Shaft>
Next, an explanation will be given of a shape of the crank shaft 3 in detail.
As illustrated in
As illustrated in the right part of
As illustrated in the left part of
The axial end f of the crank shaft 3 has a chamfer 34 formed around the entire circumference of the open end of the eccentric hole 36. Likewise, the axial end g of the crank shaft 3 has a chamfer 35 around the entire circumference of the open end of the eccentric hole 37. A communicated-part chamfer 33 is formed at a communicated part between the eccentric hole 36 and the eccentric hole 37. The communicated-part chamfer 33 is formed at, in the inner periphery of the crank shaft 3, a part near the cam 31 (the upper part in
The respective parts of the crank shaft 3 have dimensions that satisfy the following formula (2).
e1·D12·L1(L1+L2)=e2·d12·L32 (2)
where e1 is the offset level of the cams 31 and 32, D1 is the external diameter of the cams 31 and 32, L1 is the width of the cams 31 and 32, and L2 is an interval between the cams 31 and 32. e2 is an offset level of the eccentric holes 36 and 37, d1 is the internal diameter of the eccentric holes 36 and 37, and L3 is the length of the eccentric holes 36 and 37.
<Operation of External Gear>
Next, an explanation will be given of the two external gears 5 and 6.
As illustrated in
For example, the robot arm has a drive device attached to the joint. There is a demand for such a drive device that it should be lightweight and have a high torque output. In this case, the eccentric rocking type reduction gear 1 is effective which can allow a compact drive motor to rotate at a fast speed, and which can perform speed reduction on such a rotation at a large reduction ratio to output high torque. According to the reduction gear 1 of this type, the crank shaft 3 that is an input shaft rotates at a fast speed. Hence, when the crank shaft 3 has an unbalanced portion, a fluctuating load due to centrifugal force, acts on the bearings 11 and 15. In order to reduce such fluctuating load, it is necessary to let the crank shaft 3 to be balanced highly precisely.
<Balancing of Crank Shaft>
Next, an explanation will be given of the balancing of the crank shaft 3 in detail. First, a case in which the crank shaft 3 is a solid shaft will be examined.
As illustrated in
Fc=Mc·e1·ω2 (3)
where Mc is the mass of cam 31, 32, e1 is the offset level of the cam 31, 32, and ω is the rotation speed of the cam 31, 32. The two cams 31 and 32 have the same offset level e1, e1 and mass Mc, Mc.
Moreover, the mass Mc can be expressed by the following formula (4).
Mc=ρ·πD12·L1/4 (4)
where ρ is the density of the crank shaft 3 when it is a solid shaft, D1 is the external diameter of the cam 31, 32, and L1 is the width of the cam 31, 32.
Hence, when the formula (4) is applied to the formula (3), the centrifugal force Fc can be expressed as the following formula (5).
Fc=ρ·π·D12·L1·e1·ω2/4
(5) As explained above, the cams 31 and 32 are disposed around the rotation axis a1 of the crank shaft 3 in such a way that the cam 31 has the phase shifted by 180 degrees from the cam 32 as illustrated in
As illustrated in
Hence, the translational forces acting on the crank shaft 3 are canceled from each other. The translational force means force that causes the crank shaft 3 to move linearly in the direction orthogonal to the rotation axis a1. For example,
When, however, the crank shaft 3 is viewed from a direction orthogonal to the offset direction of the cams 31 and 32 (the vertical direction in
The effect of the eccentric holes 36 and 37 acting on the centrifugal force of the crank shaft 3 is equivalent to the subtraction of the effect of the centrifugal force acting on the solid member matching the shapes of the eccentric holes 36 and 37. The effect of the centrifugal force acting on a solid member 71 is as follow. The eccentric holes 36 and 37 are disposed in an offset manner by the same offset level e2 from the rotation axis a1. Hence, as illustrated in
Fh=Mh·e2·ω2 (6)
where Mh is the mass of the first and second portions 72, 73, e2 is the offset level of the first and second portions 72, 73 relative to the rotation axis a1, and ω is a rotation speed.
Moreover, the mass can be expressed by the following formula (7).
Mh=ρ·π·d12·L3/4 (7)
where ρ is the density of the solid member, d1 is the internal diameter of the eccentric hole 36 (in this example, the external diameter of the first and second portions 72, 73), and L3 is the length of the eccentric holes 36, 37 along the rotation axis a1 (in this example, the length of the first and second portions 72, 73).
Hence, when the formula (7) is applied to the formula (6), the centrifugal force Fh by the first and second portions 72, 73 can be expressed as the following formula (8).
Fh=ρ·π·d12·L3·e2·ω2/4 (8)
As explained above, the eccentric holes 36 and 37 are disposed in such a way that respective phases are shifted by 180 degrees from each other around the rotation axis a1. Accordingly, as illustrated in
As illustrated in
When, however, the solid member 71 is viewed from the direction orthogonal to the offset direction of the first and second portions 72 and 73, the centrifugal forces Fh, Fh acting on the first and second portions 72, 73, respectively act as couple to the solid member 71 as illustrated in
Accordingly, the effect of the centrifugal force acting on the crank shaft 3 with the two eccentric holes 36, 37 is as follow. First, when the crank shaft 3 is viewed from the axial direction, the centrifugal force acting in the upward direction in
Moment of couple=Fc·(L1+L2)−FhL3
(9) When the formula (5) and the formula (8) are applied to the formula (9), the moment of couple acting on the crank shaft 3 can be expressed as the following formula (10).
Moment of couple={D12·L1·(L1+L2)·e1−d12·L32·e2}·ρ·π·ω2/4 (10)
Respective dimension of the portions of the crank shaft 3 are designed so as to satisfy the relational expression of the above-explained formula (2). When the formula (2) is applied to the formula (10), it becomes clear that the moment of couple becomes zero.
In practice, it is necessary to consider centrifugal force F′ of the external gears 5 and 6 expressed by the following formula (11). When this centrifugal force F′ is taken into consideration, the formula (9) becomes the following formula (12).
F′=m′·e1ω2 (11)
where m′ is the mass of the external gear 5, 6.
(Fc+F′)·(L1+L2)−Fh·L3 (12)<
<Couple by Chamfering>
The couple in the left-turn direction in
First, the moment of couple by the communicated-part chamfer 33 will be explained.
As illustrated in
Conversely, a condition in which the communicated-part chamfer 33 is present as illustrated in
Next, a moment of couple by the chamfers 34, 35 at the axial ends will be explained.
As illustrated in
Conversely, a condition in which the chamfers 34, 35 are present as illustrated in
According to the present embodiment, the communicated-part chamfer 33 and the chamfers 34, 35 are provided in such a way that the couple in the left-turn direction by the communicated-part chamfer 33 is balanced with the couple in the right-turn direction by the chamfers 34, 35. Accordingly, the couple in the left-turn direction by the communicated-part chamfer 33 and the couple in the right-turn direction by the chamfers 34, 35 can be canceled from each other. Hence, the chamfers 34, 35 function as an axial-end balancing part for finely adjusting the weight balance of the crank shaft 3.
<Adjustment of Weight Balance of Crank Shaft>
Next, an explanation will be given of the adjustment of the weight balance of the crank shaft.
As explained above, the unbalancing of the crank shaft 3 can be eliminated in principle by forming the eccentric holes 36, 37, the communicated-part chamfer 33, and the chamfers 34, 35 at the axial ends in the predetermined shape. However, unbalancing inherent to an error in shape of respective portions of the crank shaft 3 often remains. Accordingly, after this unbalancing level is measured, the chamfers 34 and 35 are finish turned by a cutting tool like a turning tool based on the measured unbalancing level. By setting depths L4 and L5 of the chamfers 34 and 35 illustrated in
<Insertion of Wiring>
Hence, according to the present embodiment, the following advantages can be accomplished.
(1) The unbalancing of the crank shaft 3 when the crank shaft 3 rotates can be reduced by providing the two eccentric holes 36 and 37. This results in a reduction of the fluctuating load acting on the bearings 11 and 15 supporting the crank shaft 3. Accordingly, the lifetime of the bearing in the reduction gear 1 can be extended. Moreover, an occurrence of vibration of the reduction gear 1 originating from the unbalancing of the crank shaft 3 when it rotates can be also suppressed.
The value of the unbalancing level when the crank shaft 3 rotates, and thus the value of the fluctuating load acting on the bearings 11 and 15 supporting the crank shaft 3 can be easily suppressed to a value equal to or smaller than a desired value by simply providing the eccentric holes 36 and 37 in the crank shaft 3. Moreover, the lifetime of the bearing in the reduction gear 1 can be extended over a desired value, and the vibration of the reduction gear 1 originating from the unbalancing when the crank shaft 3 rotates can be suppressed to a value smaller than a desired value.
(2) The chamfers 34 and 35 as axial-end balance adjusting portions are provided at both ends of the crank shaft 3. In this case, the moment of couple acting on the crank shaft 3 can be adjusted by adjusting the chamfering depth, etc., of the chamfers 34 and 35. Moreover, the length of the arm of the couple can be maximized by providing the chamfers 34 and 35 at both ends of the crank shaft 3. Accordingly, when couple is produced around the axial line orthogonal to the axial line of the crank shaft 3, the adjusting level for obtaining the balancing in this case can be suppressed to a small level.
(3) The balancing of the couple acting on the crank shaft 3 is adjusted through the chamfers 34 and 35 at both ends of the crank shaft 3. Accordingly, the rotation balance of the crank shaft 3 can be adjusted finely by increasing or decreasing the chamfering level in a chamfering process without any additional special process.
(4) The lifetime of the bearings 11 and 15 of the reduction gear 1 can be extended. This also extends the lifetime of the robot, etc., using the reduction gear 1. Moreover, since vibration is little, the second arm 42 or the hand can be positioned precisely.
(5) The wiring or the pipe fitting can be caused to pass through the two eccentric holes 36 and 37 formed in the reduction gear 1. Accordingly, the wiring space for the reduction gear 1 or the robot arm can be reduced. Hence, the motion of the robot is not interfered from the exterior by the wiring, etc.
(6) The communicated-part chamfers 33, 33 are provided at the communicated part (uneven surface part) between the two eccentric holes 36 and 37. Accordingly, the insertion work of the wiring 50 is facilitated.
The present embodiment can be modified as follows.
In the present embodiment, the unbalance level of the crank shaft 3 is adjusted finely by increasing or decreasing the depths L4 and L5 of the chamfers 34 and 35, but the following modification can be applied. For example, as illustrated in
When the hole 87 is used to adjust the balancing of the couple acting on the crank shaft 3, the rotation balance of the crank shaft 3 can be adjusted finely by increasing or decreasing the number, depth, and diameter of the hole 87 even after the assembling of the crank shaft 3 completes. When the balancer weight 88 is used to adjust the balance of the couple of the crank shaft 3, the rotation balance of the crank shaft 3 can be adjusted finely by increasing or decreasing the number or weight of the balancer weight 88 even after the assembling of the crank shaft 3 completes.
The two eccentric holes 36 and 37 are provided in the present embodiment, but the following modification can be applied. That is, as illustrated in
In the present embodiment, it is not necessary to set the dimensions of respective portions of the crank shaft 3 so as to satisfy the formula (2). In this case, also, the reducing effect of the moment of couple by the eccentric holes 36 and 37 can be accomplished, and thus the moment of couple acting on the crank shaft 3 can be reduced.
In the present embodiment, the lengths L3 of the eccentric holes 36 and 37 are equal to each other, but may be different from each other. In this case, also, the couple reducing effect by the eccentric holes 36 and 37 can be accomplished.
The communicated-part chamfers 33, 33 can be omitted from the crank shaft 3. In this case, also, the couple reducing effect by the two eccentric holes 36 and 37 can be accomplished.
The chamfers 34 and 35 can be omitted from the crank shaft 3. In this case, also, the couple reducing effect by the two eccentric holes 36 and 37 can be accomplished.
In the present embodiment, the carrier including the two side plates 4 and 8 is utilized as an output shaft, but the internal gear 21 (housing 2) may be utilized as the output shaft. In this case, the joining between the housing 2 and the first arm 41 and the joining between the side plate 8 and the second arm 42 are released. The internal gear 21 (housing 2) is joined with the second arm 42.
In the present embodiment, the reduction gear 1 is applied to the joint of the robot arm, but the preset invention is not limited to this case.
Number | Date | Country | Kind |
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2010-269194 | Dec 2010 | JP | national |
2011-056538 | Mar 2011 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/077921 | 12/2/2011 | WO | 00 | 4/10/2013 |
Publishing Document | Publishing Date | Country | Kind |
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WO2012/074096 | 6/7/2012 | WO | A |
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Number | Date | Country | |
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