JP2002066969A - Mobile robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mobile robot capable of preventing an automated guided vehicle from being raised even when a tip of a robot arm is forcibly pressed or collided. SOLUTION: This mobile robot operates the force applied by the tip of the robot arm by each hinge torque including the force applied to each axis of the robot arm, and limits the current for a servo motor provided on each hinge in order to limit the hinge torque if the hinge torque reaches the limit value to raise the mobile robot. The mobile robot can be prevented from being raised and the automated guided vehicle can be prevented from being positionally deviated or broken even when the robot arm of the mobile robot is forcibly pressed against any facility or collided therewith.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile robot having a robot arm connected to a joint mounted on an automatic guided vehicle.

[0002]

Conventionally, in a mobile robot of this type, a base cannot be fixed as in a normal industrial robot, so that an excessively large amount of force or collision with equipment by a robot arm is required. When a load occurs, a problem arises in that the mobile robot is lifted up with the wheels as a fulcrum, causing displacement.

When the mobile robot is lifted in this way, an unexpected load due to the lifting is applied to a device associated with a moving mechanism such as a suspension mechanism of the automatic guided vehicle, causing a problem to the mobile robot. This may occur.

In general, when an installation type industrial robot is used, the base is fixed with bolts or the like, and when the robot tip is forcibly pressed or collides due to an error such as an interlock, the robot is detected by overcurrent detection. I try to stop it. In other words, the purpose of detecting overcurrent in a stationary industrial robot is to prevent the destruction of the robot or the work, and does not consider the position shift of the robot itself, and responds to the lifting of the automatic guided vehicle. The fact is that you cannot do it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible for an automatic guided vehicle to float even when the tip of a robot arm is forcedly pressed or collides against equipment. It is an object of the present invention to provide a mobile robot that can prevent the mobile robot from being lost.

[0006]

According to the first aspect of the present invention, when the control device moves the robot arm and the robot arm presses or collides with the facilities unreasonably, the mobile robot lifts up. Try to. At this time,
The control device obtains a joint torque when the mobile robot attempts to float, and executes a current limitation on the servomotor when the joint torque reaches a predetermined limit value or before the joint torque reaches the limit value. As a result, the joint torque of the robot arm is reduced, and the pressing force and the collision force of the robot arm are reduced, so that it is possible to reliably prevent the mobile robot from floating.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a side view of the mobile robot. In FIG. 2, the mobile robot 1
A robot arm 3 of, for example, a vertical articulated (6-axis) type is provided on the automatic guided vehicle 2.

Although not shown in detail, the mobile robot 1 is used, for example, in a production line for automobile parts, and this production line includes a plurality of facilities (work stations) along a traveling route on which the mobile robot 1 travels. ). The mobile robot 1 sequentially stops at a predetermined stop position in front of each facility while a plurality of mobile robots are traveling on the traveling route, and performs various operations such as delivery of a workpiece by the robot arm 3, assembly of parts, processing, and inspection. To perform the work.

FIG. 3 shows the bottom of the automatic guided vehicle. In FIG. 3, the automatic guided vehicle 2 is formed in a rectangular box shape that is slightly longer in the front-rear direction (traveling direction), and a traveling mechanism 4 for traveling on a traveling route is provided at the bottom. The traveling mechanism 4 includes a pair of drive wheels 5 and 6 on the left and right of the front-rear direction intermediate portion of the automatic guided vehicle 2, and includes casters (corresponding to wheels) 7 located at substantially four corners. I have.

FIG. 4 shows an electric configuration of the mobile robot 1. In FIG. 4, the drive wheels 5 and 6 are driven to rotate by drive motors 8 and 9 via a speed reducer (not shown), respectively. The drive motors 8 and 9 are provided with encoders 10 and 11 for detecting the rotation speed (rotational position) thereof and providing the encoders with feedback control. Further, these drive motors 8, 9
Are independently controlled by a traveling controller 12 described later via a motor drive circuit 13.

Returning to FIG. 3, guide sensors 14 and 15 are provided before and after the automatic guided vehicle 2. The guide sensors 14 and 15 are configured by arranging a plurality of magnetic sensor elements in a lateral direction (lateral direction), and detect a position of a guide line (not shown) for guiding the automatic guided vehicle 2. ing. Further, a stop marker sensor 16 is provided adjacent to the drive wheel 6, and the stop marker sensor 16 detects a stop marker (not shown) laid at a stop point of the automatic guided vehicle 2. I have.
The detection signals of the front and rear guide sensors 14 and 15 and the stop marker sensor 16 are input to the traveling controller 12.

The traveling controller 12 includes a CPU, an RO,
The microcomputer mainly includes a microcomputer including an M, a RAM, an input / output circuit, and the like. The drive motors 8 and 9 are controlled on the basis of the detection signal to cause the automatic guided vehicle 2 to travel along the traveling route and to stop at a predetermined stop position. At this stop position, the center point (reference point) of the automatic guided vehicle 2 is
The X-axis, Y-axis, θ
By agreeing on all of the (rotational) axes,
It is said to have stopped at the regular position.

At this time, when the traveling controller 12 drives the automatic guided vehicle 2, the traveling sensor 12
Based on the detection signals 4 and 15, the traveling posture of the automatic guided vehicle 2 is controlled (steered) so that the center point (reference point) of the automatic guided vehicle 2 passes on the guide line.
This attitude control is performed by giving a difference in speed between the drive motors 8 and 9. The traveling controller 12 stops the automatic guided vehicle 2 when the stop marker sensor 16 detects the stop marker.

As shown in FIG. 4, the robot arm 3 is controlled by a robot controller (corresponding to a control device) 17 provided in the automatic guided vehicle 2. The robot controller 17 is also configured mainly by a microcomputer, and is configured to execute a task by the robot arm 3 based on a previously input task program and a taught operation point. At this time, the operation point is taught (set) assuming that the mobile robot 1 (the automatic guided vehicle 2) has accurately stopped at a predetermined stop position.

As shown in FIG. 5, a robot controller 17 for controlling the mobile robot 1 includes a main controller 18
A servo control unit 19 and a drive unit 20 are provided. The main control unit 18 stores an operation program set using the teaching pendant 21 or the like. The operation program includes an operation start position and its direction, an operation end position and its direction, a path position halfway from the start position to the end position, and an end position of the robot arm 3 for each operation of the robot arm 3. Data such as the direction and parameters such as a speed coefficient and an acceleration / deceleration coefficient are recorded. The speed coefficient and acceleration / deceleration coefficient are
The maximum allowable speed of the operation and the ratio to the maximum allowable acceleration / deceleration are defined.

The main control unit 18 determines a speed pattern by applying a speed pattern to, for example, a trapezoidal pattern from the data and parameters in the above operation program for one operation, and determines the position (angle) and the position of each joint from the speed pattern. The speed (angular speed) is obtained every predetermined sampling time, for example, every 10 msec. The position of the joint is obtained by integrating the speed of the joint. Then, the main control unit 18 converts the position and speed of each joint obtained from the speed pattern into the position and speed of each servo motor 22 and gives the position and speed command values to the servo control unit 19. It has become. On the other hand, the servo control unit 19 detects the current position and the rotation speed of each servo motor 22 from the position information and the speed information from the rotary encoder 23 provided for the servo motor 22, and
Is compared with the position command value of each servo motor 22 given from the main control unit 18 to obtain a position deviation, and the position deviation is multiplied by a position loop gain to obtain a speed command value.

Further, the servo control unit 19 compares the speed command value given from the main control unit 18 with the current rotational speed for each servo motor 22 to obtain a speed deviation, and calculates a speed loop gain to the speed deviation. Multiply to obtain the torque command value. Then, the servo controller 19 controls each servo motor 2
2 is given to the drive unit 20, and the drive unit 20
The drive current is output so that each servo motor 22 has an output torque corresponding to the torque command value. As a result, each robot arm 3 is driven by each servo motor 22, so that the distal end of the robot arm 3 operates by following an operation trajectory determined by the operation program, and performs a predetermined operation.

In practice, the servo control unit 19 divides the difference between the current position command value and speed command value from the previous position command value and speed command value by 10 and divides it by 1 msec. A process (feedback control) of dividing the current position and the current speed of the servo motor 22 with the position command value and the speed command value and finally calculating the output torque of each servo motor 22 is performed every 1 msec. It is configured to do so.

FIG. 1 shows the principle of feedback control by the robot controller 17. In this FIG.
Gravity compensation means that a moment based on the weight of the robot arm 3 acts on each joint connecting each axis of the robot arm 3. A torque having the same magnitude as the above-mentioned moment and the opposite direction is applied. This torque is referred to as gravity estimation torque, and the main control unit 18 calculates the gravity estimation torque based on the posture of each robot arm 3 and gives the torque to the servo control unit 19.

Then, the servo controller 19 sets a torque command value (Tm) of each servo motor 22 by adding the drive torque obtained by the normal feedback control to the estimated gravity torque.

In order to obtain the position command value and the speed command value of each servo motor 22 every time the sampling time elapses, it is necessary to first obtain the position and speed of each joint with respect to the portion supporting each robot arm 3. is there. On the other hand, the operation start position and its direction, the operation end position and its direction recorded in the operation program, the path position and its direction on the way from the start position to the end position,
Robot arm 3 in the reference coordinate system of robot 1
It is recorded as the tip one.

Therefore, since the speed pattern obtained from each position and its direction recorded in the operation program is the one at the tip of the robot arm 3, each servo motor 22
In order to obtain the position command value and the speed command value, the position and speed of each joint must first be calculated from the position and speed of the tip of the robot arm 3 in the reference coordinate system. Then, the position and speed of each joint are converted into relative positions and speeds between the joints. Finally, each servo is determined based on the relative position and speed of each joint and the reduction ratio of the transmission mechanism. The position and speed of the motor 22 must be determined.

For this purpose, a three-dimensional coordinate system is set for each joint. Among these, the coordinate system of the base unit is immovable as the reference coordinate system of the robot 1, and the position and orientation of the other coordinate systems change due to the rotation of the joint.

The speed of each joint is obtained from the speed at each sampling time for the tip of the robot arm 3 obtained from the speed pattern as described above, using an inverse Jacobian matrix as is well known. It is performed by calculation. In this case, the inverse Jacobian matrix is a 6-by-6 determinant for translational movement in three coordinate axes of the reference coordinate system and rotational movement around each coordinate axis. In the reference coordinate system, when the position and speed of each joint at each sampling time are obtained using the inverse Jacobian matrix, coordinate conversion is then performed to calculate the relative position and speed of each joint. .
Then, the position command value and the speed command value of each servomotor 22 are obtained from the relative position and speed of each joint and the reduction ratio of the transmission mechanism.

Here, the main control unit 18 determines the torque of each joint, and when determining that the torque of each joint has reached a predetermined limit value, the main control unit 18 limits the torque to the servo control unit 19. Command. When a torque limit is instructed, the servo control unit 19 reduces the torque command value for the drive unit 20, and the drive unit 20 performs a current limit in accordance with the torque command value. It is a feature of the form.

Next, the operation of the above configuration will be described. The mobile robot 1 moves according to the guideline, and stops at a stop point in front of a predetermined facility and executes a predetermined operation based on a program. At this time, the tip of the robot arm 3 may be forcibly pressed against the equipment or collide with the equipment due to a shift in the stop position of the mobile robot 1 or a mistake in the program. In such a case, an excessive load is generated on the robot arm 3, and a force is exerted on the mobile robot 1 to float on the wheels as fulcrums. For this reason, there is a possibility that the automatic guided vehicle 2 may move from the stop position, or an unexpected load may be applied to a suspension mechanism of the automatic guided vehicle 2 or the like, and malfunctions may occur.

Therefore, in the present embodiment, the floating of the mobile robot 1 is prevented as follows. FIG. 6 shows a force relationship acting on the mobile robot in a state where the tip of the robot arm 3 is pressed against the equipment 24. In FIG. 6, lg is the distance between the caster 7 located on the side opposite to the direction in which the robot arm 3 extends and the contact point at the tip of the robot arm 3; M is the mass of the mobile robot 1; The force for rotating the caster 7 located on the opposite side to the extension direction of the robot arm 3 as a fulcrum due to the mass, lo is the distance between the caster 7 located on the opposite side to the extension direction of the robot arm 3 and the center of mass of the mobile robot 1 The distance, F, is the force that the tip of the robot arm 3 receives from the equipment 24, and the Fv is the force (M) that causes the tip of the robot arm 3 to rotate around the caster 7 located on the opposite side to the direction in which the robot arm 3 extends.
gv), the rotation direction is opposite to gv.
At the time of o · Fv, the mobile robot 1 tries to float around the caster 7 as a fulcrum. That is, when the force in the counterclockwise direction shown in FIG. 6 becomes larger than the force in the clockwise direction with respect to the caster 7 on the opposite side of the extension direction of the robot arm 3 of the mobile robot 1 as a fulcrum, the mobile robot 1 rises. Attempting force acts. Although Mgv is fixed, Fv changes depending on the magnitude and direction of the force exerted by the mobile robot 1 on the equipment.

Here, assuming that the rotational force Fv when the mobile robot 1 is about to float is Fvlimit, lo · Fv
limit = lg · Mgv.

If the limit value of the joint torque when the mobile robot tries to float is τlimit, τlimit
= J ^T · Fvlimit = J ^T · (lg / lo).

Therefore, the main controller 18 of the robot controller 17 determines that τlimit = J ^T · (lg / lo) · Mgv
When the torque is satisfied or before the torque is satisfied, the servo controller 19 is instructed to limit the torque, so that the mobile robot 1 can be prevented from floating.

According to such an embodiment, the mobile robot 1 calculates the force exerted on the other end by the robot arm 3 based on each joint torque, and the calculated joint torque is applied to the distal end of the robot arm 3. When the limit value is such that the mobile robot 1 is lifted by pressing or collision, the joint torque is limited, so that the mobile robot 1 can be reliably prevented from lifting. In this case, without using any special means,
Since this can be handled by software processing, it can be easily implemented without significantly increasing costs.

The present invention is not limited to the embodiments described above and shown in the drawings, and applicable robots are not limited to those of the vertical articulated type and the rectangular coordinate type, and do not depart from the gist of the present invention. Various changes can be made within the scope of the invention.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a current limiting function according to an embodiment of the present invention.

FIG. 2 is a side view of a mobile robot.

FIG. 3 is a bottom view of the automatic guided vehicle.

FIG. 4 is a block diagram showing an electric configuration of the mobile robot.

FIG. 5 is a functional block diagram showing a configuration of a robot controller.

FIG. 6 is a diagram showing a force relationship acting on a mobile robot.

[Explanation of symbols]

1 is a mobile robot, 2 is an automatic guided vehicle, 3 is a robot arm, 5 and 6 are drive wheels, 7 is a caster (wheel), and 17 is a robot controller (control device).

Claims (1)

[Claims] An automatic guided vehicle movably supported by wheels, a robot arm mounted on the automatic guided vehicle and connected by a joint, and controlling a current to a servomotor that drives the joint by controlling the current. And a control device for controlling the torque of the joint.The control device, when moving the tip of the robot arm according to the position and attitude control with respect to the tip of the robot arm, the limit value of the joint torque A mobile robot, wherein current limiting is performed on the servomotor when or before the following expression is satisfied. τlimit = J ^T · (lg / lo) · Mgv where τlimit is the limit value of the joint torque, J ^T is the Jacobian matrix, and lg is the contact point between the wheel located on the side opposite to the direction in which the robot arm extends and the tip of the robot arm. The distance between,
lo is the distance between the wheel located on the opposite side to the extension direction of the robot arm and the center of mass of the mobile robot, M is the mass of the mobile robot, and Mgv is the opposite side to the extension direction of the robot arm due to the mass of the mobile robot. The rotation force is shown with the rotating wheel as a fulcrum.