JP3765393B2 - Articulated robot speed reducer - Google Patents
Articulated robot speed reducer Download PDFInfo
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- JP3765393B2 JP3765393B2 JP2001068103A JP2001068103A JP3765393B2 JP 3765393 B2 JP3765393 B2 JP 3765393B2 JP 2001068103 A JP2001068103 A JP 2001068103A JP 2001068103 A JP2001068103 A JP 2001068103A JP 3765393 B2 JP3765393 B2 JP 3765393B2
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Description
【0001】
【発明の属する技術分野】
本発明は、アーム姿勢や搬送物の重量に依らず、ロボットが制御系にとって好ましい負荷となるように設計された二段以上の減速機構を備えた多関節ロボットの減速装置に関するものである。
【0002】
【従来の技術】
従来の電動ロボットの関節は、モータ+減速機+アームの組み合わせで構成されている。モータ軸の慣性モーメントとモータ軸に固定された減速機の入力側の慣性モーメントの合計値をJM、減速機の減速比をRG、関節軸回りのアームの慣性モーメントをJAとすると、JA/(JMRG 2)は慣性比と呼ばれている。
小型のモータであっても、減速比RGが大きな減速機を用いれば、原理的にはいくらでも大型のアームを駆動させることができる。しかし、制御性能の点からは、経験的に慣性比は3〜10、理論的には4が良いとされている。
【0003】
【発明が解決しようとする課題】
つまり、ロボットの設計においては、慣性比を3〜10に抑え、できるだけ4に近くすれば、制御効果を十分に引き上げることができる。しかし、ロボットアームは動作中姿勢を変化するため関節軸に作用する慣性(イナーシャ)が変化し、また、ペイロード等の搬送物の重量や慣性モーメントによっても関節軸に作用する慣性が変化する。近年では、産業用ロボットは、動作範囲の拡大傾向、可搬重量の増大傾向にあり、機械系の設計において慣性比を常に3〜10に抑えることは、実用上不可能であると言える。
【0004】
例えば、特開昭58−137577号公報には、産業用ロボットの慣性比をある範囲に抑える機構が開示されている。この技術では、慣性比を調整する手段として、リンクの取り付け位置が変更可能な機構を採用し、モータからアームまでの減速比を変化させている。しかし、このように、リンクの付加機構により慣性比を調節するとなると、ロボットが大型化し、コストが増大する。また、この方法では、負荷の重量に応じた慣性比の補償は可能となるが、動作中のアームの姿勢変化による慣性比の補償は、事実上不可能である。
【0005】
本発明は上記の諸点に鑑みなされたもので、本発明の目的は、アーム姿勢、ペイロード等の搬送物の重量に依らず、各関節の慣性比を望ましい範囲に抑えることができる減速機構を備えた多関節ロボットの減速装置を提供することにある。
【0006】
【課題を解決するための手段】
上記の目的を達成するために、本発明の多関節ロボットの減速装置は、多関節ロボットにおけるモータとアームの間に組み付ける減速機が、アームの姿勢及び搬送物の重量に依らず、各関節の慣性比を常に望ましい範囲に収めて、ロボットの制御系にとって好ましい負荷となるように設計された二段減速機構を備えた構成としている。
【0007】
すなわち、モータとアームの間に組み付ける減速機に、モータ側要素の慣性モーメントをJR1、中間部要素の慣性モーメントをJR2、一段目減速比をRG1、二段目減速比をRG2とする二段減速機構を採用する(図1参照)。ただし、JR1、JR2、RG1、RG2には、以下の数1に示す(1)式の関係がある。
【0008】
【数1】
【0009】
ここで、JAmin、JAmaxはアームイナーシャの最小値、最大値、JMはモータ回転軸の慣性モーメント、RGはモータからアームへの全体減速比、Nminは慣性比で4以下の3近傍の値、Nmaxは慣性比で4以上の10近傍の値である。一般には、アームイナーシャがJAminのとき、荷重(図1では、ペイロード)は取り付けられておらず、アームイナーシャがJAmaxのとき、許容最大重量の荷重(ペイロード)が取り付けられている。さらに、一段目の減速機よりも、二段目の減速機の剛性は高くなるようにする。
そのような二段減速機を用いた場合の慣性比は、以下の数2に示す式で求められる。
【0010】
【数2】
【0011】
よって、慣性比の変化範囲は、
JA=JAminのとき、N=Nmin
JA=JAmaxのとき、N=Nmax
となり、ペイロードを交換したり、アームが大きく姿勢を変えても、慣性比は望ましい値の範囲に収まることになる。
JAmax、JAmin、JM、RGは、上流工程の設計で決定されるため、それらの値によっては、RG1、RG2が1以下になることもある。その場合には、二段のうち一段は増速機構になる。
【0012】
また、モータとアームの間に組み付ける減速機に、上述した二段減速機構と同じ意図に基づく三段減速機構を採用することができ、この場合は、以下の数3に示す(2)式の条件を満たす必要がある。
【0013】
【数3】
【0014】
また、モータとアームの間に組み付ける減速機に、上述した二段減速機構と同じ意図に基づく四段以上の多段減速機構を採用することも可能である。
【0015】
【発明の実施の形態】
以下、本発明の実施の形態について説明するが、本発明は下記の実施の形態に何ら限定されるものではなく、適宜変更して実施することが可能なものである。
上述した設計法に基づき、図2に示すスカラーロボットのジョイント1の減速機を設計する。設計仕様は以下のように定められている。
ジョイント1回りの慣性モーメントの最大値(アーム最伸、最大負荷)
JAmax=26.99 [kg・m2]
ジョイント1回りの慣性モーメントの最小値(アーム最縮、無負荷)
JAmin=2.735 [kg・m2]
モータ軸の慣性モーメント
JM=3.20×10-6 [kg・m2]
全体減速比
RG=600 [-] 程度
【0016】
この仕様から、単に全体減速比だけを見て、減速機を設計してしまうと、慣性比JA/(JMRG 2)は最小で2.3、最大で23程度となり、非常に制御のしにくい機械系となる。そこで、本発明による設計法の流れで、減速機を設計する。
まず、上記の数1に示す(1)式を用いて、二段減速機の設計値の拘束条件を以下のように得る。
JR1=6.425×10-6,RG1 2=4.7000×104JR2,
RG1RG2=600
ここで、アーム全体のサイズを考慮して、JR2を以下の範囲で選択し、その際のRG1、RG2を得る。
JR2=1.0〜3.0×10-4,RG1=2.167〜3.755,
RG2=276.9〜159.8
【0017】
この場合、一段目減速比は小さく、二段目減速比が高いので、一例として、一段目の減速機構には歯車対、二段目の減速機構にはハーモニック減速機を採用する。これらの仕様に当てはまるよう、減速機構の部品として以下のものを選択した。
この結果、全体減速比はRG=(96/25)×160=614.4となる。
【0018】
RG=614.4、RG1=3.84として、もう一度上記の数1に示す(1)式に代入して以下を得る。
JR1=6.425×10-6,JR2=2.992×10-4
歯車とハーモニックギアの慣性モーメントを考えると、一段目減速機ではΔJR1=5.02×10-6、二段目減速機ではΔJR2=4.19×10-5分慣性モーメントが足りない。この不足分は、例えば、フライホイールを取り付けることで補えばよい。このようにして、減速機を設計した結果、アームの姿勢や負荷の重さがどのように変化しても、このロボットの慣性比は常に3〜10に収まることになる(図3参照)。よって、制御系の設計が非常に容易なロボットが実現できる。
【0019】
図4は、上記のようにして設計した二段減速装置10をモータ12とアーム14の間に組み付けた構成の一例を示している。一段目減速機16は平歯車18、20からなり、シャフト22を介して二段目減速機であるハーモニック減速機24が取り付けられている。平歯車18、シャフト22には、慣性モーメントの不足分を補うためのフライホイール26、28が取り付けられている。
【0020】
【発明の効果】
本発明は上記のように構成されているので、つぎのような効果を奏する。
(1) 多関節ロボットの減速機構を、本発明のように、二段、または、それ以上にし、そして、それぞれの減速機の設計値を本発明で示した拘束条件に従い決定すれば、アームの姿勢や負荷の重さがどのように変化しても、各関節の慣性比を常に望ましい範囲に抑えることができる。よって、制御系設計に負担の少ない、高性能なロボットを実現できる。
(2) 大型の付帯機構を必要とせず、ロボットの動作中も常に、制御系にとって好ましい負荷となるように慣性比が抑制される。
【図面の簡単な説明】
【図1】本発明の多関節ロボットの減速装置における二段減速機構の一例を示す模式図である。
【図2】本発明の実施の第1形態における多関節ロボットの一例(スカラーロボット)を示す概略構成図である。
【図3】本発明の実施の第1形態における二段減速機における慣性比Nを従来の減速機との比較で示したグラフである。
【図4】本発明の実施の第1形態における二段減速装置をモータとアームの間に組み付けた構成の一例を示す断面構成説明図である。
【符号の説明】
10 二段減速装置
12 モータ
14 アーム
16 一段目減速機
18、20 平歯車
22 シャフト
24 ハーモニック減速機(二段目減速機)
26、28 フライホイール[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reduction device for an articulated robot provided with a two-stage or more reduction mechanism designed so that the robot has a preferable load for the control system regardless of the arm posture and the weight of the conveyed product.
[0002]
[Prior art]
The joint of a conventional electric robot is composed of a combination of a motor, a speed reducer, and an arm. If the sum of the inertia moment of the motor shaft and the inertia moment on the input side of the reduction gear fixed to the motor shaft is J M , the reduction gear ratio of the reduction gear is R G , and the inertia moment of the arm around the joint shaft is J A , J A / (J M R G 2 ) is called the inertia ratio.
Even if it is a small motor, if a reduction gear with a large reduction ratio RG is used, in principle, any number of large arms can be driven. However, from the viewpoint of control performance, the inertia ratio is empirically 3 to 10 and theoretically 4 is good.
[0003]
[Problems to be solved by the invention]
That is, in designing the robot, the control effect can be sufficiently increased if the inertia ratio is suppressed to 3 to 10 and is as close to 4 as possible. However, since the robot arm changes its posture during operation, the inertia acting on the joint shaft changes, and the inertia acting on the joint shaft also changes depending on the weight and moment of inertia of the transported object such as the payload. In recent years, industrial robots have a tendency to expand their operating range and increase their load capacity, and it can be said that it is practically impossible to keep the inertia ratio at 3 to 10 constantly in the design of mechanical systems.
[0004]
For example, Japanese Patent Application Laid-Open No. 58-137577 discloses a mechanism for suppressing the inertia ratio of an industrial robot within a certain range. In this technique, a mechanism capable of changing the attachment position of the link is adopted as means for adjusting the inertia ratio, and the reduction ratio from the motor to the arm is changed. However, if the inertia ratio is adjusted by the link addition mechanism in this way, the robot becomes larger and the cost increases. Also, with this method, it is possible to compensate the inertia ratio according to the weight of the load, but it is practically impossible to compensate the inertia ratio by changing the posture of the arm during operation.
[0005]
The present invention has been made in view of the above-described points, and an object of the present invention is to provide a speed reduction mechanism that can suppress the inertia ratio of each joint to a desired range regardless of the arm posture, the weight of a transported object such as a payload. Another object of the present invention is to provide a speed reducer for an articulated robot.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the speed reducer for an articulated robot according to the present invention is such that the speed reducer assembled between the motor and the arm in the articulated robot is independent of the posture of the arm and the weight of the transported object. The structure is provided with a two-stage reduction mechanism designed so that the inertia ratio is always within a desirable range and is a preferable load for the control system of the robot.
[0007]
That is, for the reducer assembled between the motor and the arm, the moment of inertia of the motor side element is J R1 , the moment of inertia of the intermediate element is J R2 , the first stage reduction ratio is R G1 , and the second stage reduction ratio is R G2 . A two-stage reduction mechanism is employed (see FIG. 1). However, J R1 , J R2 , R G1 , R G2 have the relationship of the following formula (1) shown in the following formula 1.
[0008]
[Expression 1]
[0009]
Here, J Amin and J Amax are the minimum and maximum values of the arm inertia, J M is the inertia moment of the motor rotation shaft, R G is the overall reduction ratio from the motor to the arm, and N min is the inertia ratio of 4 or less. The neighborhood value, N max, is a neighborhood value of 10 with an inertia ratio of 4 or more. In general, when the arm inertia is J Amin, no load (payload in FIG. 1) is attached, and when the arm inertia is J Amax , a load (payload) with an allowable maximum weight is attached. Furthermore, the rigidity of the second stage reduction gear is made higher than that of the first stage reduction gear.
The inertia ratio when such a two-stage reduction gear is used can be obtained by the following equation (2).
[0010]
[Expression 2]
[0011]
Therefore, the change range of the inertia ratio is
When J A = J Amin , N = N min
When J A = J Amax , N = N max
Thus, even if the payload is changed or the posture of the arm changes greatly, the inertia ratio falls within the desired value range.
Since J Amax , J Amin , J M , and R G are determined by the design of the upstream process, R G1 and R G2 may be 1 or less depending on their values. In that case, one of the two stages becomes a speed increasing mechanism.
[0012]
In addition, a three-stage reduction mechanism based on the same intention as the above-described two-stage reduction mechanism can be adopted as a reduction gear assembled between the motor and the arm. In this case, the following equation (2) It is necessary to satisfy the conditions.
[0013]
[Equation 3]
[0014]
It is also possible to employ a four-stage or more multi-stage reduction mechanism based on the same intention as the above-described two-stage reduction mechanism for the reduction gear assembled between the motor and the arm.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications.
Based on the design method described above, the speed reducer for the joint 1 of the scalar robot shown in FIG. 2 is designed. Design specifications are defined as follows.
Maximum value of moment of inertia around joint (maximum arm extension, maximum load)
J Amax = 26.99 [kg · m 2 ]
Minimum value of moment of inertia around joint (arm contraction, no load)
J Amin = 2.735 [kg · m 2 ]
Motor shaft inertia moment J M = 3.20 × 10 -6 [kg · m 2 ]
Overall reduction ratio R G = 600 [-] or so [0016]
From this specification, if the speed reducer is designed by simply looking at the overall reduction ratio, the inertia ratio J A / (J M R G 2 ) will be 2.3 at the minimum and 23 at the maximum. It becomes a mechanical system that is difficult to rub. Therefore, the speed reducer is designed according to the design method according to the present invention.
First, the constraint condition of the design value of the two-stage speed reducer is obtained as follows using the equation (1) shown in the above equation 1.
J R1 = 6.425 × 10 −6 , R G1 2 = 4.7000 × 10 4 J R2 ,
R G1 R G2 = 600
Here, considering the size of the entire arm, J R2 is selected in the following range, and R G1 and R G2 at that time are obtained.
J R2 = 1.0 to 3.0 × 10 −4 , R G1 = 2.167 to 3.755
R G2 = 276.9-159.8
[0017]
In this case, since the first stage reduction ratio is small and the second stage reduction ratio is high, as an example, a gear pair is adopted as the first stage reduction mechanism, and a harmonic reduction gear is adopted as the second stage reduction mechanism. In order to meet these specifications, the following parts were selected as parts of the speed reduction mechanism.
As a result, the overall reduction ratio is R G = (96/25) × 160 = 614.4.
[0018]
Assuming that R G = 614.4 and R G1 = 3.84, the following is obtained by substituting again into the above equation (1).
J R1 = 6.425 × 10 −6 , J R2 = 2.992 × 10 −4
Considering the moment of inertia of the gear and the harmonic gear, ΔJ R1 = 5.02 × 10 −6 for the first reduction gear, and ΔJ R2 = 4.19 × 10 −5 minutes for the second reduction gear. This shortage may be compensated by attaching a flywheel, for example. As a result of designing the speed reducer in this way, the inertia ratio of the robot is always within 3 to 10 (see FIG. 3), regardless of how the arm posture and the load weight change. Therefore, a robot with a very easy control system design can be realized.
[0019]
FIG. 4 shows an example of a configuration in which the two-
[0020]
【The invention's effect】
Since this invention is comprised as mentioned above, there exist the following effects.
(1) If the speed reduction mechanism of the articulated robot is made to have two or more stages as in the present invention, and the design values of the respective speed reducers are determined according to the constraint conditions shown in the present invention, Regardless of how the posture or load weight changes, the inertia ratio of each joint can always be kept within the desired range. Therefore, it is possible to realize a high-performance robot with less burden on the control system design.
(2) A large-sized auxiliary mechanism is not required, and the inertia ratio is suppressed so that the load is always preferable for the control system even during operation of the robot.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a two-stage speed reduction mechanism in a speed reduction device for an articulated robot according to the present invention.
FIG. 2 is a schematic configuration diagram showing an example (scalar robot) of an articulated robot in the first embodiment of the present invention.
FIG. 3 is a graph showing an inertia ratio N in the two-stage reduction gear according to the first embodiment of the present invention in comparison with a conventional reduction gear.
FIG. 4 is a cross-sectional configuration explanatory view showing an example of a configuration in which the two-stage reduction gear device according to the first embodiment of the present invention is assembled between a motor and an arm.
[Explanation of symbols]
DESCRIPTION OF
26, 28 Flywheel
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