JPH07295651A - Acceleration and deceleration controller for robot - Google Patents

Abstract

PURPOSE:To provide the acceleration and deceleration controller which takes the influence of the relation between the operation directions of respective arms upon the torque applied to actuators into consideration. CONSTITUTION:This acceleration and deceleration controller for the robot which has two horizontal rotary arms is provided with a track generation part and an acceleration/deceleration correction rate determination part in a control part; and the acceleration/deceleration correction rate determination part is provided with a correction rate calculation part 28 which calculates a correction rate (r) a turning direction relation judgement part 32 which corrects acceleration by using a correction rate (r) calculated as to the angle theta2 between the two arms at a start point and deceleration by using a correction rate (r) calculated as to the angle theta2 at an end point when the two arms are in the same rotating direction, but corrects the acceleration and deceleration by using a correction rate previously set above the correction rate (r) without exceeding the output limit of the actuators.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a robot controller, and more particularly to an acceleration / deceleration controller for controlling the acceleration / deceleration of robot operation.

[0002]

2. Description of the Related Art In an industrial robot, it is necessary to move an end effector of the robot to a target point in space in the shortest possible time in order to shorten the cycle time of a production system using the robot. That is, it is necessary to speed up the operation of the robot.

The speed of movement of the end effector of the robot,
Acceleration is determined by the balance between the maximum output of the actuator that drives the joint and the inertial moment and mass of the robot arm, end effector, and work that are loads. That is, making the robot arm, etc., lighter and making the actuator as powerful as possible will cause the robot to operate faster and move the end effector faster, but from the standpoint of strength and accuracy of the robot. There is a limit due to. Therefore, it is necessary to operate the robot so as to make maximum use of the output of the actuator. Particularly, in the case of a rotary joint type robot, the inertia moment and the interference torque between joints change depending on the posture of the robot. Adopting a corresponding control method is one means for operating the robot at a higher speed, and several means are conventionally known.

(First Method) According to Japanese Unexamined Patent Publication No. 62-61104, in a method of controlling acceleration / deceleration of a horizontal joint type robot having a plurality of horizontally rotating arms, a reference point at the tip of the arm of the robot is used. The motion acceleration / deceleration of the reference point at the tip of the arm of the robot is changed according to the distance from the position of to the center of rotation of the horizontally rotating arm to effectively utilize the capability of the drive source.

(Second Method) In Japanese Patent Laid-Open No. 4-315205, two arms are rotatably connected by a shaft, and a first arm is rotatably connected to a fixed portion by another shaft. The two arms are movable in a horizontal plane according to the configuration described above, the moving shaft is provided in the vertical direction at the tip of the second arm that is far from the fixed portion, and the hand is provided at the tip of this moving shaft for control. A robot with an attached part, the acceleration / deceleration correction ratio determination part and the trajectory generation part are provided in the control part, and the coefficients a, b, c, d determined by the dynamic characteristics of the arm are stored in the control system, and the deceleration Mass transferred by the robot by the correction ratio determination unit m
And the angle θ ₂ formed by the two arms, the correction ratio r is calculated by the following equation: r = (a + b × m) + (c + d × m) × θ ₂ ² , and the trajectory generator sets it in advance in the control system. There is disclosed an acceleration / deceleration control method for a robot, which outputs a position command based on an appropriate acceleration / deceleration by correcting the existing acceleration / deceleration curve using the correction ratio r.

(Third Method) Japanese Patent Publication No. 2-55803 discloses a work robot hand in which a servomotor, which is an actuator, is driven based on a command speed curve calculated and generated from desired parameters. In the control method of the articulated robot that controls the posture and position of the robot, the entire work area of the robot hand is subdivided into a plurality of areas, and the command speed curve is set for each combination of the area to which the start point and the end point of the robot hand belong The calculation parameter of is set in advance in consideration of the load inertia fluctuation information of the servo motor,
Using this parameter, the speed command curve that is the input to the servo system is calculated. This discloses a method that enables high-speed control of the posture and position of the robot hand regardless of the posture of the robot arm.

[0007]

In the first and second methods, a mechanism for determining the acceleration / deceleration of the robot operation based on the amount that can be uniquely determined from the position of the reference point of the arm tip at the start point and the end point of the operation. Has become. As a result, the ability of the drive source can be effectively utilized by modifying the acceleration / deceleration in consideration of the change in the inertia moment and the change in the interference torque depending on the posture. However, the motor torque required when operating the robot is not only related to the amount that can be determined from the position of the reference point of the arm tip at the start and end points of the operation. Unless a non-interfering arm structure is adopted, the robot's actuator adds torque that resists the interference torque caused by the motion of other joints to the acceleration / deceleration torque required to accelerate / decelerate the joint that the actuator directly rotates. Must output. The interference torque may be a torque in the same direction (that is, a direction that supports acceleration / deceleration) as a direction in which the actuator directly rotates the actuator depending on the acceleration / deceleration direction of other joints. There are none. This is determined by the relationship of the rotation directions of the plurality of arms. When the rotation directions are the same, the torque is in the direction of hindering acceleration / deceleration, and when the rotation directions are different, the torque is in the direction of assisting acceleration / deceleration. .
The former method does not consider that the relationship of the rotational directions of multiple arms affects the load torque applied to the actuator, and therefore the worst condition must be considered when estimating the required torque. There is a problem that there is room for more effectively using the output of the actuator for the non-operation.

The third method also has the same problem as the former, because the relationship of the motion directions among a plurality of joints is not specified. However, in the latter case, if the meaning of the area to which the start point and the end point of the robot hand belong is expandedly interpreted as a divided area in the joint coordinate system of the robot, the relationship between the motion directions of the plurality of joints becomes clear. However, in order to realize this, even if the position of the same hand is different, if the posture of the robot is different, it must be distinguished as different regions. Therefore, there arises a problem that a huge amount of calculation parameters of the velocity curve corresponding to a huge amount of area divisions and combinations thereof must be stored.

In order to solve the above two problems, an object of the present invention is an acceleration / deceleration control method corresponding to the change of the moment of inertia and the interference torque depending on the posture of the robot, and stores a huge amount of calculation parameters. You do n’t have to
An object of the present invention is to provide an acceleration / deceleration control device in consideration of the fact that the relationship of the rotation directions of a plurality of arms affects the torque applied to the actuator.

[0010]

In a robot acceleration / deceleration control apparatus according to the present invention, two arms are rotatably connected by a shaft, and a first arm is rotatably connected to a fixed portion by another shaft. Two arms are movable in a horizontal plane due to the connected structure, and a moving shaft is provided in the vertical direction at the tip of the second arm farther from the fixed portion, and a hand is provided at the tip of this moving shaft. A robot with a control unit attached, wherein the control unit is provided with an acceleration / deceleration correction ratio determination unit and a trajectory generation unit, and the coefficients a, b, c, and d determined by the dynamic characteristics of the arm are stored in the control system and reduced. The speed correction ratio determination unit calculates the correction ratio r by the calculation formula r = (a + b × m) + (c + d × m) × θ ₂ ² regarding the mass m carried by the robot and the angle θ ₂ formed by the two arms. However, the trajectory generation unit has an acceleration / deceleration curve preset in the control system. In an acceleration / deceleration control device for a robot that outputs a position command based on an appropriate acceleration / deceleration by correcting using the correction ratio r, the acceleration / deceleration correction ratio determination unit includes a rotation direction of the first arm and a second arm. When the rotation direction of the arm is the same, the acceleration is corrected using the correction ratio r calculated for the angle θ _{2 at the} start point, and the deceleration is corrected using the correction ratio r calculated for the angle θ ₂ at the end point. If the rotation direction of the first arm and the rotation direction of the second arm are different, use a correction ratio that is set to a value equal to or larger than the correction ratio r and that is preset so as not to exceed the output limit of the actuator. A rotational direction relationship determination unit that determines to correct the acceleration and deceleration is provided.

[0011]

According to the present invention, when the rotation direction of the first arm and the rotation direction of the second arm are the same, the correction ratio r calculated for the angle θ _{2 at the} starting point is applied to the acceleration / deceleration correction ratio determination unit. If the acceleration direction is corrected by using the correction ratio r calculated with respect to the angle θ ₂ at the end point and the rotation direction of the first arm and the rotation direction of the second arm are different, By providing a rotation direction relation determination unit that determines that the acceleration and deceleration are corrected using a correction ratio that is set in advance so as not to exceed the output limit of the actuator and that is greater than or equal to the correction ratio r, When the rotation direction of the first arm and the rotation direction of the second arm are different, the correction ratio r is set to a value equal to or larger than the correction ratio and the correction ratio is set in advance so as not to exceed the output limit of the actuator. However, the interference torque becomes the torque in the same direction as the torque required for acceleration / deceleration of each arm, and the actuator output (torque) is small, so the actuator capacity is effectively Available. The rotation direction of the first arm and the second
When the rotation direction of the arm of is the same, the interference torque becomes a torque in the direction opposite to the torque required for acceleration / deceleration of each arm, and the actuator must also output the torque against this interference torque. Maximum acceleration using the correction ratio r calculated for the angle θ _{2 at the} start point and end point,
By modifying the maximum deceleration, the actuator operates at the maximum acceleration and maximum deceleration so that the limit of the actuator capacity is not exceeded.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below with reference to the drawings. FIG. 2 is a side view of a robot embodying the present invention. The robot is a so-called scalar type, and one end of the first arm 6 is rotatably connected to the fixed portion 2 by an axis perpendicular to the fixed portion 2, and the fixed portion 2 has a servo motor 4 for driving the first arm 6 built therein. . The other end of the first arm 6 has a second
One end of the arm 10 is rotatably connected by a vertical axis, and a servo motor 8 that drives the second arm 10 is attached to the first arm 6. A ball screw 14 is attached to the other end of the second arm 10 so that it can be vertically moved up and down by a drive system (not shown). A hand 18 is attached to the lower end of the ball screw 14.
The hand 18 holds the work 20 to be conveyed.

FIG. 1 is a block diagram of the control unit. A movement command 34 is sent to the trajectory generation unit according to the operation program 30 stored in the storage unit in the controller attached to the robot. The movement command 34 includes the target position X _r , the maximum acceleration α _a , and the maximum deceleration α _d . X _r , α _a , α _d
Is a two-dimensional vector quantity whose elements are values for the first arm 6 and the second arm 10. On the other hand, the transport mass m is set by the operator, and the acceleration / deceleration correction ratio determination unit 26
Sent to. Further, the angle θ _1a of the first arm 6 at the start point (current position), the angle θ _{2a of} the second arm 10, the angle θ _1d of the first arm 6 at the end point (target position X _r ), the angle θ of the second arm 10 _2d is sent from the trajectory generation unit 24 to the acceleration / deceleration correction ratio determination unit 26. The angle of the arm is the first
When the arm 6 and the second arm 10 are aligned and the front of the robot is 0 radian, the first arm 6 measures the angle around the fixed portion 2 and the second arm 10
Measures an angle around the connection with the first arm, which is the center of rotation of the second arm. Each is measured counterclockwise when viewed from above.

The acceleration / deceleration correction ratio determination unit 26 is composed of a correction ratio calculation unit 28 and a rotational direction relation determination unit 32.
The correction ratio calculation unit 28 calculates the function f of the transport mass m and the angle θ _2a .
The correction ratio r _a0 is calculated as (m, θ _2a ), and the transport mass m
And the correction ratio r _d0 is calculated as a function f (m, θ _2d ) of the angle θ _2d . A specific example of the function f is described in Japanese Patent Application Laid-Open No. 4-315205 by the present applicant. f (m, θ ₂ ) = (a + b × m) + (c + d × m) × θ
₂ ² Function f is determined so that the required torque does not exceed the maximum torque of the servo motor of each arm. The interference torque is taken into consideration under the worst condition (when the rotation directions of the first arm and the second arm are the same), and a, b, c, d in the above equation are considered.
Is a numerical value (constant) determined in relation to the dynamic characteristics of the robot. The value of the function f becomes smaller as the transport mass m becomes larger, and becomes larger as θ ₂ becomes larger.

The rotation direction relation judging section 32 determines the angles θ _1a and θ.
_2a , θ _1d , and θ _2d are used for the trajectory generation unit 2 by the following procedure.
Fixed ratio r _a as data to be transmitted to 4, obtaining a r _d. Step 1: If (θ _1d −θ _1a ) × (θ _2d −θ _2a ) ≦
If 0, execute step 3. Step 2: r _a = r _a0 , r _d = r _d0 End. Step 3: r _a = r _max (m), r _d = r _max
(M) The end. Where r _max (m), which is a function of the transport mass m
Is set by the following formula, for example. r _max (m) = f (m, maximum angle that the second arm 10 can take) The function f (m, θ ₂ ) increases as θ ₂ increases, so r _max (m) is the transport mass m. Will take the maximum value in the case of.

The trajectory generating unit 24 modifies the acceleration and deceleration curve set in advance corrected ratios r _a, the r _d, e.g. 5
Servo drivers 21, 22 at a fixed cycle such as msec
The position commands 35 and 36 are sequentially sent to. Servo driver 2
1, 22 rotate the servomotors 4, 8 respectively,
The first arm 6 and the second arm 10 are moved to position commands 35, 36.
Move according to. The maximum acceleration α _am and the maximum deceleration α _dm in the corrected acceleration / deceleration curve are represented by the following equations. α _am = α _a × r _a α _dm = α _d × r _d α _am , α _dm is a vector amount similar to α _a , α _d , r _a ,
r _d is a scalar quantity. If a trapezoidal curve (the velocity changes into a trapezoidal shape over time) is used as the acceleration / deceleration curve, the acceleration is accelerated at a constant acceleration and decelerated at a constant speed.
_It becomes _am and the constant deceleration becomes α _dm .

Now, the operation of this embodiment will be described with reference to FIG. FIG. 3 is a simplified view of the state in which the SCARA robot has four postures, as viewed from above. Four postures are shown around the fixed portion 2. The posture 4 is a posture in which the first arm 6 and the second arm 10 are close to a straight line.
Angle is -0.24 radians and the angle of the second arm is-
It is 0.34 radians. Consider that the robot operates up to this posture 4. In posture 1, the angle of the first arm 6 is −1.33 radians and the angle of the second arm 10 is −.
Since it is 0.83 radians, in the movement from the posture 1 to the posture 4, the rotation directions of both arms are the same, the step 2 is executed in the rotation direction relation determining unit 32, and the correction ratio obtained by the function f is To be selected. Posture 3
The position of the hand is the same as the posture 1, but the postures are different and the angle of the first arm 6 is −2.1 radians and the angle of the second arm 10 is 0.83 radians.
In the movement from the posture to the posture 4, the rotation directions of the both arms are different, the step 3 is executed in the rotation direction relation judging section 32, the maximum correction ratio is selected, and the ability of the servo motor is effectively utilized.

The angle of the first arm 6 is 1.33 radians,
Even in the movement from the posture 2 to the posture 4 in which the angle of the second arm 10 is −2.31 radians, the rotation directions of both arms are different, and the rotation direction relationship determination unit 32 executes the above step 3 and The correction ratio is selected to effectively utilize the servo motor's ability.

[0019]

According to the present invention, in the acceleration / deceleration correction ratio determining unit, when the rotation direction of the first arm and the rotation direction of the second arm are the same, the correction ratio calculated with respect to the angle θ _{2 at the} starting point. If the acceleration is corrected using r, the deceleration is corrected using the correction ratio r calculated with respect to the angle θ ₂ at the end point, and if the rotation direction of the first arm and the rotation direction of the second arm are different, A rotation direction relationship determination unit that determines whether to correct the acceleration and deceleration using a correction ratio that is preset so as not to exceed the output limit of the actuator and that is larger than the correction ratio r. As a result, the correction ratio for correcting the acceleration / deceleration can be changed in consideration of the decrease in the load torque applied to the servo motor when the rotation direction is opposite, and operation is performed at the maximum acceleration / deceleration. Therefore, unlike the method using a table, it is not necessary to store a huge amount of calculation parameters, and it is possible to perform acceleration / deceleration control in consideration of the fact that the relationship between the rotation directions of a plurality of arms affects the torque applied to the actuator. Furthermore, the cycle time of the production system using the robot can be shortened.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a control unit of the present invention.

FIG. 2 is a schematic view of a SCARA type robot to which the present invention is applied.

FIG. 3 is a simplified diagram of the state in which the SCARA robot of FIG. 1 has four postures as viewed from above.

[Explanation of symbols]

 2 Fixed part 4 Servo motor 6 1st arm 8 Servo motor 10 2nd arm 14 Ball screw 18 Hand 20 Work 21 Servo driver 22 Servo driver 24 Orbit generation part 26 Acceleration / deceleration correction ratio determination part 28 Correction ratio calculation part 30 Operation program 32 rotation Directional relationship determination unit 34 Movement command 35 Position command 36 Position command

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Claims (1)

[Claims] 1. A structure in which two arms are rotatably connected by a shaft and a first arm is rotatably connected to a fixed portion by another shaft, so that the two arms are movable in a horizontal plane. A robot in which a moving shaft is provided in the vertical direction at the tip of the second arm farther from the fixed portion, and a hand is provided at the tip of this moving axis, and a controller is attached to the robot. An acceleration / deceleration correction ratio determination unit and a trajectory generation unit are provided,
Coefficients a, b, c, and d determined from the dynamic characteristics of the arm are stored in the control system, and the deceleration correction ratio determining unit calculates the mass m carried by the robot and the angle θ ₂ formed by the _two arms. = (A + b × m) + (c + d × m) × θ ₂ ² to calculate the correction ratio r, and the trajectory generator corrects the acceleration / deceleration curve preset in the control system using the correction ratio r. Thus, in the robot acceleration / deceleration control device that outputs a position command based on an appropriate acceleration / deceleration, when the rotation direction of the first arm and the rotation direction of the second arm are the same in the acceleration / deceleration correction ratio determination unit. Corrects the acceleration using the correction ratio r calculated for the angle θ _{2 at the} start point, and corrects the deceleration for the correction ratio r calculated for the angle θ ₂ at the end point. The direction of rotation of the arm In this case, the rotation direction relation determining unit determines that the acceleration and deceleration are corrected by using a correction ratio that is set in advance so as not to exceed the output limit of the actuator and that is larger than the correction ratio r. An acceleration / deceleration control device for a robot, characterized by being provided with.