JPH0429985Y2 - - Google Patents

Description

[Detailed explanation of the invention] (Industrial application field) This invention uses a direct drive in the drive unit.
This invention relates to an inertial balance mechanism for parallel drive parallel links using motors.

(Prior art) Direct drive robots that use direct drive motors as joint drive units solve the problems of robots with reducers caused by resistance and rattling in the reducers. Since a motor is attached to each joint, there is a problem in that the weight of the motor itself greatly increases the weight of the arm, so it has been proposed to construct the arm with parallel drive parallel links (parallelogram links).

When parallel drive parallel links are used in a robot, as with general robots, a brake (safety brake) is provided on the drive section of each link to prevent the link from moving when an external force is applied when it is not in operation. It is something.

On the other hand, in order for the parallel drive parallel links to be balanced and for the force applied to one link not to cause interference forces such as reaction forces on other links, the following conditions need to be satisfied.

Figure 1 is a schematic diagram of the parallel drive parallel links used in the above-mentioned robot.The motor for rotating the first link 1 and the motor for rotating the second link 2 are connected to the shaft. Conventionally, a brake for stopping the rotation of the first link 1 and a brake for stopping the rotation of the second link are provided separately on the motor. Inter-axis distance l ₁ of the first link 1, inter-axis distance l ₂ of the fourth link 4, mass m ₃ of the third link 3, mass m ₄ of the fourth link 4, proximal axis to center of gravity of the third link 3 The following relationship between the distance g ₃ and the distance g ₄ between the tip axis and the center of gravity of the fourth link 4 is required.

m ₄ /m ₃・g ₄ /g ₃ =l ₂ /l _1The process of deriving the above equation will be explained below.

In general, the motion system of a direct drive robot is as follows: where the output torque of the i-th motor is τ _i and the rotation angle is θ _i , H _ii θ¨ _i + 〓 ^j≠i H _ij θ¨ _j + 〓 〓 〓 〓 ^{j k} (∂H _ik /∂θ _j −1/2 ∂H _jk /∂θ _i )θ・_j θ・
It is given by _k + τ _gi = τ _i .

H _ij : Telson's inertia of the arm about the motor axis
Component H _ii : Inertial load on motor i when all motor shafts other than the i-th motor shaft are fixed.The second term in the above equation is the interference torque received from other motor shafts, and the third term is called Coriolis force and centrifugal force. The fourth term represents the nonlinear torque and the gravitational torque.

In direct drive robots, these complex dynamic characteristics are directly reflected on the motor axis, complicating the control problem, so here we will find an arm structure and its mass distribution that will not generate interference or nonlinear forces. In other words, a mechanism is designed such that the diagonal component H _ii of the inertia tensor is constant regardless of the arm posture, and the off-diagonal component H _ij is also zero regardless of the arm posture.

An inertia tensor regarding the motor shaft is determined as the length l _i of each link, the mass m _i , the distance g _i between the shaft portion J _i and the link center of gravity, and the moment of inertia I _i around the link center of gravity.

(a) First, check the first diagonal component H _ii . This is the shaft
Motor when J ₂ or 2nd link is fixed
It represents the inertia of the other three links converted to the rotation axis (shaft portion J ₁ ) of M ₁ . Among these, the first link 1 is related to the rotation axis of the motor M ₁ (I ₁ + m _i g ₁
² ) It has an inertia that is constant regardless of the posture of the arm.

Since the third link 3 rotates in the same way as the first link, the inertia of the third link 3 on H ₁₁ is constant (I ₃ +m ₃ g ₃ ² ).

Further, since the fourth link 4 moves in parallel to the second link 2, it moves in a constant posture when the second link 2 is fixed. The movement of the center of gravity of the fourth link 4 with respect to the rotation of the motor _M1 coincides with the movement of the shaft portion _J5 . Therefore, the inertia exerted by the fourth link 4 is (m ₄ l ₁ ² ). The sum of these three inertias becomes H ₁₁ =I ₁ +m ₁ g ₁ ² +I ₃ +m ₃ g ₃ ² +m ₄ l ₁ ² , which remains constant regardless of the posture of the arm.

Similarly, if the shaft J ₁ is fixed and the inertia related to the motor M ₂ is investigated, the second diagonal component H ₂₂ is: H ₂₂ = I ₂ + m ₂ g ₂ ² + I ₄ + m ₄ g ₄ ² + m ₃ l ₂ ² , and is constant regardless of the arm posture.

(b) On the other hand, the off-diagonal components H ₁₂ and H ₂₁ of the inertia tensor are
Creates interference between the two motor axes. Generally, these change depending on the posture of the arm and are given by H ₁₂ = H ₂₁ = (l ₂ m ₃ g ₃ − _{l 1} m ₄ g ₄ ) ·cos(θ ₁ −θ ₂ ).

As is clear from this equation, the condition for making the off-diagonal component zero regardless of changes in the posture of the arm is to satisfy l ₂ m ₃ g ₃ −l ₁ m ₄ g ₄ =0. In other words, the ratio of the two sides of the parallel link l ₂ /l ₁ , the ratio of the masses of the third link 3 and the fourth link 4 m ₄ /m ₃ , and the ratio of the distance between the shaft end and the center of gravity position g ₄ /g ₃ , m ₄ /m ₃・g ₄ /g ₃ =l ₂ /l ₁ .

By the way, for robots using such parallel links, the relationship is usually set to (l ₁ >l ₂ ).
Therefore, it is necessary to set (m ₄ g ₄ < m ₃ g ₃ ) according to the ratio of l ₁ and l ₂ . To achieve this, it is necessary to take measures such as moving the center of gravity of mass m ₄ closer to the direction of shaft portion J ₄ to reduce distance g ₄ or increasing mass m ₃ . However, increasing the weight of each link itself goes against the weight reduction of the robot, and moving the center of gravity requires changing the link shape or adding a balance weight, which creates structural problems.

(Problems to be Solved) This invention provides a lightweight and well-balanced device using parallel drive parallel links, which is used, for example, in articulated robots.

(Means for Solving the Problems) In this invention, in the parallel drive parallel link as described above, instead of providing a brake to stop the rotation of the second link 2 in the drive part of the second link, the third link
It is provided at the shaft support between the link 3 and the fourth link 4.

(Function) Even if an external force is applied to the fourth link 4 when the parallel drive parallel link is not in operation, the shaft supports of the third link 3 and the fourth link 4 are braked, so they will not rotate. Because there is no, the second link 2
does not receive any reaction force and will not rotate. Note that the brake for stopping the movement of the second link 2 is usually
Although it is attached together with the motor that drives the second link 2, when an external force is applied to the fourth link 4, the interference force applied to this motor cannot be suppressed.

(Example) An example in which this invention is applied to an articulated industrial robot with three degrees of freedom will be described with reference to FIGS. 2 and 3.

An articulated industrial robot (hereinafter referred to as robot) R having three degrees of freedom has a frame F rotatably supported on a base B. The frame F has a first direct drive motor M1 disposed on one side, through which the base end of the first arm 1 is rotatably supported. The shaft support 6 is provided with a first brake 8 that operates in the event of an emergency of the parallel drive parallel links constituted by the first link 1 to the fourth link 4. Also, on the other side, a second direct
A drive motor M2 is arranged on the same axis 5 as the first direct drive motor M1,
This is rotatably supported by the base end of a second rotatable link 2. The second link 2 rotatably supports the base end of a third link 3 at its other end, and the third link 3 rotatably supports the base end of a fourth link 4 at its other end. are doing. The shaft support 7 is provided with a second brake 9 that operates when the parallel driving parallel links formed by the first link 1 to the fourth link 4 are not in operation. The brakes 8 and 9 can be not only electromagnetic brakes but also air brakes, hydraulic brakes, and other brakes. In this embodiment, taking the second brake 9 as an example, an electromagnetic brake is provided as shown in FIG. and electrical wiring is provided between it and a control device (not shown). In FIG. 3, a multi-stage cylindrical shaft 10 having a flange is fixed to the distal end of the third link 3 by a bolt 11, and the shaft 10 is attached to the proximal end of the fourth link 4. It is supported by bearings 12, 12 provided in cylindrical holes provided in the. An electromagnetic brake 9 is fitted into this cylindrical hole concentrically with the shaft 10,
It is fixed to the fourth link 4 with bolts 13.

The first link 1 rotatably supports an intermediate portion of the fourth link 4 at its other end, and an end effector (such as a welding torch, a fusing torch, etc.) (not shown) is attached to the other end of the fourth link 4. ) is provided. Furthermore, the base end of the first link 1 and the second link 2
Detects the rotational position of each link at the base end of the
A first rotational position detector and a second rotational position detector (not shown) are respectively attached, and like the first and second direct drive motors M1 and M2, electrical wiring is connected between them and a control device (not shown). has been applied.

Driving the first link 1 and the second link 2 by driving either or both of the first direct drive motor M1 and the second direct drive motor M2 according to a program in the control device. Then, move the end effector (not shown) to a desired position. During this time, the brakes 8 and 9 are released, but are activated as each link stops operating.

The implementation of this invention is not limited to the above-mentioned embodiments, but can also be applied to robots with 2 degrees of freedom or robots with 3 or more degrees of freedom, and it is possible to use not only vertical links but also horizontal links, and also to robots other than robots. It is also possible to implement

(Effects) As mentioned above, this invention uses a direct drive motor for the drive part and stops the rotation of the second link 2 in parallel drive parallel links with a link length of (l ₁ > l ₂ ). Since _the brake necessary for
Even without changing the shape of the fourth link 4, the center of gravity of the fourth link 4 is closer to the shaft support 7, which satisfies m ₄ / m ₃ · g ₄ / g ₃ = l ₂ / l ₁ , making it lightweight. A well-balanced mechanism can be obtained.

[Brief explanation of drawings]

The drawings show the configuration and embodiments of this invention, with FIG. 1 being a schematic diagram, FIG. 2 being a schematic diagram, and FIG. 3 being a sectional view. In the drawings, 1 is the first link, 2 is the second link, 3 is the third link, 4 is the fourth link, 5 is the axis, 8 is the first brake, 9 is the second brake, M1
is the first direct drive motor, and M2 is the second direct drive motor.

Claims (1)

[Scope of utility model registration request] a support member having first and second direct drive motors disposed on the same axis; a first link having a proximal end pivotally supported via the first direct drive motor; A second link supported via a drive motor,
a third link having a proximal end rotatably supported on the other end of the second link; a proximal end rotatably supported on the other end of the third link; and an intermediate portion being rotatably supported on the other end of the first link; A parallel drive parallel link is formed by a fourth link rotatably supported by a fourth link, and the length of the first link is made larger than the length of the second link, and furthermore, the first link and the The shaft support of the support member is provided with a first brake that operates when the parallel drive parallel link is not driven, and the shaft support of the third link and the fourth link is provided with a first brake that operates when the parallel drive parallel link is not driven. An inertial balance mechanism of parallel drive parallel links, which is equipped with a second brake.