JPH066273B2 - Swing prevention device for industrial robots - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an industrial robot, and more particularly to means for suppressing vibration of its arm.

BACKGROUND OF THE INVENTION Generally, when a cantilevered arm is moved in a direction perpendicular to its longitudinal direction, a kinematically troublesome phenomenon occurs. The phenomenon is a delay in the movement of the arm tip portion due to the weight and inertia of the arms themselves and the robot head attached to them when the acceleration of the base suddenly changes due to start-stop or other movements.

This delay phenomenon is based on an inertial rotational force centered on the base of the arm when the acceleration of the arm suddenly changes.
The members that support the arm against this rotational force are the guide rails attached to the gantry, the guides that are slidably fitted to the gantry, and the pedestal and the arm base itself to connect the various parts. It is a member. Further, a finite clearance is usually formed between the guide rail and the sliding body, and they are composed of rolling elements having limited rigidity.

This portion is the weakest portion in terms of rigidity among the members that support the rotational force of the arm. Moreover, since the constituent members of the robot are always made of a material having a finite elasticity, regardless of the material, when the speed of the arm suddenly changes, vibration always occurs at the tip portion of the arm.

When the change in the acceleration of the arm is small, this vibration
Since it is absorbed by the damping property of the material, it is not a practical problem.

However, when the change in acceleration is large, vibration occurs due to the resonance frequency of the entire mechanical system, resulting in resonant damped vibration according to the damping capacity of the entire mechanical system.

On the other hand, in the case of performing a predetermined work with this type of industrial robot, in the work of positioning from point to point, it is guided to a predetermined position by a fast-forward motion, but in that case, acceleration at the time of starting and stopping is sufficient. If it is made small and moved in a so-called slow-up or slow-down state, kinematic vibration can be suppressed to the minimum limit.

However, when cutting various curves at high speed using a plasma jet or a laser beam, it is inevitably made to move at a constant velocity along the curves, and in the cutting area of a small arc or an angled corner, the arm In spite of the constant velocity motion along the curve, the acceleration of the arm becomes large and exceeds the limit of vibration generation. As a result, a cutting line that is far from the expected cutting shape appears, resulting in a decrease in processing accuracy regardless of the high positioning accuracy of the industrial robot.

In the cutting processing using a plasma jet or a laser beam, the processing method itself is non-contact processing, the processing speed is fast, and today a speed of 10 meters per minute is not uncommon. When the ratio of the width of the supporting portion of the cantilever type arm to the length of the arm increases, the natural frequency of the arm reaches 3 to 7 times per second. For this reason, there is a vibration that takes 1 second before the vibration attenuates.
Practical processing accuracy cannot be expected at all.

2. Description of the Related Art Conventionally, such vibration prevention means have already been proposed.

First of all, the rigidity of mechanical members constituting the industrial robot is increased, the weight of the arm is reduced, the vibration displacement is reduced, and the natural frequency is increased at the same time to prevent the resonance phenomenon. Is. A dimensional measure against this is to increase the width of the sliding portion of the cantilevered arm, reduce the length of the arm, and increase the proportion of those dimensions. Such measures inevitably increase the weight of the sliding parts, the base of the arm, the guide rails, the pedestal, and the like, which increases the manufacturing cost of the industrial robot and causes a large economic problem. Further, in order to reduce the weight of the arm itself and the robot head, a light material such as a light alloy or a resin has to be used, which also causes a high cost.

Next, the second measure for preventing vibration was to move the long robot arm in a two-sided holding state instead of one side, while driving it at both ends thereof. According to this measure, a pedestal is provided on the opposite side, and two or more sets of drive units and their movement mechanisms are required. Since all of the displacements must be driven in perfect synchronization, a high level of control technology is required,
The cost of the control device was high. In addition, if this is done, it is necessary to provide guide rails and pedestals on both ends of the arm, so in order to approach the work area of the industrial robot, it is necessary to detour from the remaining two directions. However, there is a significant disadvantage in terms of workability such as replacement of a work piece or a jig for mounting. Therefore, workability is poor on the side of using this industrial robot.

Therefore, the present invention provides, instead of the conventional solution, from the viewpoint of kinematics, when a sudden change in the acceleration of a cantilevered arm is given a weight motion in the opposite direction to the sudden change in the acceleration. This is to suppress the resonant vibration of the arm tip portion and prevent the motion from being delayed.

SUMMARY OF THE INVENTION Therefore, according to the present invention, a first acceleration sensor and a second acceleration sensor are attached to a drive-side base portion of an arm of an industrial robot and a tip end side of the arm, respectively.
These acceleration sensors detect acceleration in the movement direction alternating with the longitudinal direction of the arm and send it as an acceleration signal to the control device. Furthermore, in the present invention, as the most characteristic part, a weight that is movable in the movement direction of the arm and is driven by a servomotor is attached to the tip of the arm. This weight acts in a direction in which the damping characteristic of the arm is kept kinematically small by moving in a direction that cancels the movement due to the inertia of the arm when the acceleration in the movement direction of the arm suddenly changes. Such control of the servomotor is performed by the above control device. That is, the control device receives the acceleration signals from the first acceleration sensor and the second acceleration sensor as input, and in the moving direction of the weight and the required acceleration so that the difference between them is always minimized. Rotate the servo motor. In such control, even if the direction of movement of the robot head changes, or even if the natural frequency of the arm changes due to material dynamics of products or parts, it always follows these changes. Stable control can be realized.

Configuration of Embodiments FIGS. 1 and 2 show an example in which a rocking prevention device 1 for an industrial robot of the present invention is incorporated in a rectangular coordinate type industrial robot 2.

The industrial robot 2 as a whole has a pair of guide rails 3 in the X-axis direction, a robot arm 4 supported by the guide rails 3 in a so-called cantilever state at a base end portion thereof, and a Y-axis direction in the robot arm 4. The robot head 5 is movably supported by the robot head 5.

The pair of guide rails 3 are attached in parallel to the X-axis direction on a pedestal 6 installed at the installation position of the industrial robot 2, and an arm base attached to the base end portion of the robot arm 4. It is fitted in the dovetail-shaped guide groove 8 of the table 7 in a sliding pair state. A drive motor 9 with a reducer for driving in the X-axis direction is attached to the upper surface of the arm base 7, and a gear 10 on the output side thereof is a rack gear 11 attached in the X-axis direction on the upper surface of the pedestal 6. It is in mesh.

The robot arm 4 is attached at its base end portion to the upper surface of the arm base 7 in a so-called cantilever state in a state orthogonal to the guide rail 3, and has a base end portion and a tip end portion. The bearing 13 rotatably supports the feed screw 12 in the Y-axis direction. The feed screw 12 is driven by a drive motor 14 with a speed reducer attached to the base end portion of the robot arm 4 in the Y-axis direction.

The robot head 5 has a guide groove 1 on the back side thereof.
The guide surface 18 of the robot arm 4 in the Y-axis direction at the portion 9
It is slidably attached to the feed screw 12 by means of the feed nut 17 on the rear side and is fitted to the feed screw 12 under a screw pair. Further, the robot head 5 supports a vertically moving shaft 15 in the vertical direction, that is, the Z-axis direction so as to be vertically movable, and can be set at a position of an appropriate height by a drive motor 16 thereof. Further, the tip portion of the vertical movement shaft 15 is connected to the robot wrist 22 by an A axis 20 in the same direction and a B axis in the intersecting direction. The robot head 5 includes a drive motor 23a for driving the A-axis 20, and the vertical shaft 15 has a drive motor 23b for rotating the B-axis 21 of the robot wrist 22 therein. Is equipped with.

By the way, the rocking prevention device 1 of the present invention is incorporated in the part of the industrial robot 2 as a first acceleration sensor 24, a second acceleration sensor 25, a weight 26, and a servo motor for driving the same. It is equipped with 27.

The first acceleration sensor 24 is attached to the base end portion of the robot arm 4, for example, the side surface of the arm base 7, detects the acceleration α1 in the X-axis direction at the base end portion of the robot arm 4, and detects it. It is converted into an electrical signal and sent to the control device 30 described later. In addition, the second acceleration sensor 25
Is attached to the tip of the robot arm 4, detects the acceleration α2 of the robot arm 4 in the X-axis direction, and sends it to the control device 30 as an electrical signal in the same manner as described above.

Further, the weight 26 is swingably attached to, for example, the tip end portion of the connecting shaft 28 in the Y-axis direction so as to be movable in the movement direction of the robot arm 4, that is, the X-axis direction. The tip end portion of the connecting shaft 28 is rotatably supported by a support plate 29 attached to the tip end of the robot arm 4, and the base end portion is connected to the servo motor 27. The servo motor 27 is controlled by the control device 30, and the rotation amount thereof is electrically detected by the encoder 31 and becomes a speed system feedback signal of the control device 30.

Next, FIG. 4 shows the configuration of the control system. As described above, the control device 30 constitutes, for example, a digital servo system, and is connected to the first acceleration sensor 24 and the second acceleration sensor 25 at its two input sides,
The output side is connected to the servo motor 27 via the servo driver 32. In addition, this servo motor 27
The encoder 31 connected to the
It is also connected to the other input terminal of the control device 30.

Operation of the Embodiment The desired movement is given to the industrial robot 2 by the positioning control. During this movement, when the robot arm 4 moves in the X-axis direction, it is supported in a so-called cantilever state at the base end portion. Therefore, when the acceleration α1 suddenly changes, the displacement of the tip end portion of the robot arm 4 is The robot arm 4 is not exactly aligned with that of the end portion, and the material elastic force of the robot arm 4 makes the vibration easily occur.

FIG. 5 shows a state of motion of the robot arm 4 when the rocking preventive device 1 of the present invention is not operated. When the robot arm 4 is moving at a constant velocity in the X-axis direction, the displacement S1 of the base end portion and the displacement S2 of the tip end portion thereof change in direct proportion to the time T. Moreover, in the constant velocity motion, the acceleration is 0, so that the base end portion and the tip end portion of the robot arm 4 do not show a displacement shift in the X-axis direction.
However, when the robot arm 4 approaches the target position and its speed is reduced, the base end portion of the robot arm 4 becomes
Although the drive source, that is, the speed V1 of the drive motor 9 during deceleration is accurately followed, the inertial force acts on the tip portion thereof, so that the speed V2H of the tip portion is slower than that of the base end portion of the robot arm 4. It will decrease with a slow slope and with a time delay. During this period, the acceleration α1 of the base end portion of the robot arm 4 changes into an approximately trapezoidal shape, but the acceleration α2 of the tip end portion of the robot arm 4 depends on the inertia force and the material elastic force in the returning direction of the robot arm 4. The state becomes 0 only after a certain time elapses while causing damping vibration. During this period, the tip of the robot arm 4
Similarly, damping vibration is occurring.

On the other hand, FIG. 6 shows the motion characteristics of the rocking preventive device 1 of the present invention. When the robot arm 4 enters the deceleration region while the robot arm 4 is moving in the X-axis direction, the tip portion thereof continues to move in the displacement direction due to the inertial force, as described above. The acceleration α1 at the base end portion and the acceleration α2 at the tip end portion of the robot arm 4 at this time are detected by the respective first acceleration sensor 24 and second acceleration sensor 25, and as a signal of electrical acceleration, the control device 30 Entered in. Therefore, the control device 30 detects the difference between the two accelerations α1 and α2, discriminates the value of the difference and the positive / negative sign, drives the servomotor 27 based on the value and the sign, and determines The weight 26 is driven in a direction in which the difference in acceleration signals is always the minimum.

For example, when the acceleration α1 at the base end portion of the robot arm 4 is smaller than the acceleration α2 at the tip end portion, it is given to the weight 26 as a rotational force in the counterclockwise direction in FIG. At this time, the reaction of the weight 26 causes the acceleration α3 to act on the tip portion of the robot arm 4 by the reaction force in the direction opposite to the inertial force. As a result, the inertial force of the tip portion when the robot arm 4 is damped is canceled by the acceleration α3 of the reaction force. In this way
Even in the deceleration area, the tip portion of the robot arm 4 stops at the target position with almost no displacement from the base end portion. Further, the acceleration α1 at the tip end portion is in the deceleration region, and the acceleration α2 at the base end portion is
Although the time delay is shown, in the stop region of the robot arm 4 in the X-axis direction, it is settled to be 0 at a low frequency and a small peak value and a short settling time.

Although the above description of the operation shows the motion characteristics in relation to the deceleration area, such motion characteristics similarly occur in the acceleration area of the robot arm 4. FIG. 8 shows vectors of accelerations α1 and α2 in the acceleration region. In the acceleration region, the acceleration α1 at the base end portion of the robot arm 4 is larger than the acceleration α2 at the tip end portion thereof. Therefore, the control device 30 applies the rotational force in the clockwise direction to the weight 26 by the servo motor 27, contrary to the case of the deceleration region.

Thus, although the robot arm 4 is supported in the cantilever state in the acceleration / deceleration area of the robot arm 4 and is driven only by the base end portion thereof, the tip end portion of the robot arm 4 is Accurately follows the movement of the end part,
The target position is reached within a short time without causing a large damping vibration as in the conventional case.

Modified Example of the Invention The above-described embodiment is the Cartesian coordinate type industrial robot 2 of the present invention.
However, the target industrial robot 2 is not limited thereto, and can be commonly used for cantilevered robot arms such as a cylindrical coordinate type robot or an articulated robot.

Further, the control device 30 may be either a digital servo or an analog servo, and practically,
It is also realized in the field of software for microcomputers.

Further, in the above-described embodiment, the reaction force is generated by applying the rotational movement to the weight 26, but the movement of the weight 26 may of course be linear.

Advantageous Effects of Invention According to the present invention, during acceleration / deceleration motion of a robot arm, a displacement in a direction that cancels an inertial force or a material restoring force of the robot arm with respect to a weight that can be displaced in a motion direction at a tip end portion of the robot arm. Since it is given, even if the robot arm is in a so-called cantilever state, with the base end part on the drive side,
There is no difference in the amount of displacement from the tip end on the driven side, and the vibrationally damped wave during acceleration / deceleration is contained in a smaller range than the conventional one. As a result, the rigidity of the robot arm and the parts related to it may be smaller than the conventional ones, and therefore the mechanical structure of the industrial robot can be lightweight and simplified, and its drive source can have a small capacity. Further, the positioning accuracy is also improved as compared with the conventional one.

Moreover, these effects can be obtained by following changes in motion, and can be expected to be stable even with variations in parts. Therefore, positioning control of the industrial robot becomes easy.

[Brief description of drawings]

FIG. 1 is a plan view of a swing prevention device for an industrial robot according to the present invention, FIG. 2 is a front view thereof, FIG. 3 is a front view of a part of a weight portion, and FIG. 4 is a block line of a control system. FIG. 5 is a characteristic diagram of the motion of a conventional industrial robot, FIG. 6 is a characteristic diagram of the motion of the present invention, and FIGS. 7 and 8 are the magnitude and direction of acceleration and the motion direction of a weight. It is explanatory drawing which shows the relationship of. 1. ・ Rotation prevention device for industrial robots, 2 ・ ・ Industrial robots, 3 ・ ・ Guide rails, 4 ・ ・ Robot arms,
5 ... Robot head, 7 ... Arm base, 24 ... First acceleration sensor, 25 ... Second acceleration sensor, 26
..Weights, 27 ... Servo motors, 28..Connection shafts, 2
9 ... Support plate, 30 ... Control device, 31 ... Encoder, 32 ... Servo driver

Claims (2)

[Claims] 1. An industrial robot provided with an arm that moves in a predetermined direction by a drive source, wherein a weight which is movable in the movement direction of the arm and is driven by a servomotor is attached to the tip of the arm, and the arm is attached. Of the industrial robot, wherein a control device for rotating the servo motor at a moving direction of the weight so that the difference between the base acceleration and the tip acceleration is always minimized and the required acceleration is installed. Rocking prevention device. 2. As a means for always minimizing the difference between the base acceleration and the tip acceleration, a first acceleration sensor in the movement direction of the arm is fixed to the base on the drive side of the arm, and the tip of the arm is fixed. The second acceleration sensor for the movement direction of the arm is fixed to, and the first acceleration sensor and the second acceleration sensor are connected to the control device,
The rocking prevention device for an industrial robot according to claim 1, wherein control is performed so that a difference between acceleration signals of the first acceleration sensor and the second acceleration sensor is always minimized.