JPH11165282A - Force control robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently work while dealing with variation of a working load without interrupting the working by tentatively changing a working course when a working load is increased and a feed speed is lowered under the lowest feed speed, and returning the moving course of a tool to the initial working course after completing the working. SOLUTION: A feed speed judging part 29 judges whether or not a feed speed is lowered under the lowest feed speed. A working course changing part 30 tentatively changes an initial working course to a working course so as to decrease the working load. A tentative working course control part 31 gives command data as to the changed working course to a working course control loop 26 through a working completion judging part 32 instead of a teaching data 24, and at the same time it gives feed speed command data to a feed speed control loop 27. The working completion judging part 32 judges completion of working along the changed working course, and a return course control part 33 controls a moving course so as to return a grinder 15 to the position directly before changing the working course, after completing the working.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a force control robot, for example, to a force control robot that performs a cutting operation of a weld bead using a grinder as an end effector.

[0002]

2. Description of the Related Art When machining with a machine tool or an industrial robot, the feed speed of a tool is almost always set to a constant speed. However, even if the feed speed of the tool is constant, the processing load increases or decreases with the feed of the tool due to irregularities of the workpiece.

[0003] If the machining load is excessively increased, the tool may be damaged or an abnormal stop may occur due to an overload exceeding the capability of the feed actuator. For this reason, the following control of the feed speed according to the processing load has been conventionally performed in order to prevent the occurrence of an excessive processing load.

One of them is to monitor the increase and decrease of the processing load while detecting the current value of the drive motor and the current value of the feed actuator, and to increase and decrease the feed speed while comparing with the set value of the current. If the height becomes abnormally high, the feed of the tool is stopped.

There is also a method of detecting an increasing machining load with a load cell or the like, and, if the machining load is large, moving the tool in a direction in which the machining load is reduced, that is, in a direction in which the cutting depth is reduced.

[0006] In recent years, in the bead finishing work for shaving a weld bead after joining steel sheets by welding and in the chamfering work of a workpiece after fusing, automation has been advanced by introducing an industrial robot instead of a manual grinder work. ing. Industrial robots that perform this type of work
It has a force control function that can control not only the position of the tool but also the processing action of the tool such as the force pressing the tool against the workpiece.

[0007]

When such a force control robot performs a machining operation such as cutting a welding bead, the machining load naturally fluctuates during the machining process.

However, in the machining operation by the force control robot, simply controlling the feed speed of the tool according to the variation of the machining load may not be effective for the variation of the load.

In most cases, an industrial robot having a force control function is applied to a grinder operation by dry grinding. In dry grinding, to reduce the increased processing load,
When the feed rate is reduced, the grinding time at a specific location on the workpiece increases, so the temperature of the workpiece increases,
Along with this, the temperature of the grindstone also rises. After this temperature rises, the grinding ability of the grindstone may be extremely reduced, making it impossible to continue processing. In such a situation, it is necessary to temporarily suspend the processing to reshape and sharpen the grindstone which has been blinded to restore the grinding ability of the grindstone.

On the other hand, if machining is performed with a target pressing force set to a large value in order to prevent a decrease in the feed rate, the rotation of the grindstone of the grinder stops and machining becomes impossible or the tool is damaged. There is a problem.

As described above, in the operation of removing a weld bead by introducing a robot, the size, shape,
There is a characteristic that the processing load varies greatly depending on the weld bead because of its different height, which is an obstacle to the improvement of the processing efficiency.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a force control capable of efficiently performing machining while coping with variations in machining load without interrupting machining. To provide a robot.

[0013]

In order to achieve the above object, the present invention detects a processing load acting on a tool held by a robot, and controls a feed rate of the tool according to a change in the processing load. A force control robot with a function to perform
A means for monitoring the magnitude of the machining load acting on the tool from the workpiece and a minimum feed rate at which the machining load increases and the feed rate is set in advance in the process of machining along the initial machining path taught to the robot in advance. Means for determining the situation where the machining path needs to be changed from the following, and when the machining path needs to be changed, temporarily change the machining path so that the feed speed does not drop below the minimum feed speed. And a means for returning the moving path of the tool to the initial processing path after finishing the processing along the changed processing path.

According to the present invention, not only the processing load is monitored, but also the processing path is changed based on the decrease in the feed speed caused by the increase in the processing load. In the temporarily changed machining path, the machining load is reduced and the feed rate is restored. In this way, fluctuations in the machining load are monitored from both the machining load and the feed rate. Since it is prevented, the processing is performed smoothly without stopping.

In order to reduce the processing load, it is preferable to change the height of the processing path so as to reduce the contact area between the tool and the object to be processed. Now, based on the reduction of machining load,
The end of machining along the changed machining path is determined.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a force control robot according to the present invention will be described below with reference to the accompanying drawings. FIG. 2 shows a grinder working robot to which the force control robot according to the present invention is applied. The grinder working robot 10 includes a base 11, a column 12, an arm 13, and a wrist 14. The grinder working robot 10 has six control axes. That is, the column 12 is pivotable on the base 10, and the arm 13 moves up and down along the column 12. Also,
The wrist 14 at the tip of the arm 13 expands and contracts in the axial direction of the arm 14.

A grinder 15 is mounted on the wrist 14 as an end effector. This grinder 1
Reference numeral 5 denotes a tool having a disk-shaped grindstone that is rotationally driven by air or electricity. In this case, the grinder 15
Can rotate on the wrist 14 about three axes orthogonal to each other.

The wrist 14 has a force which can detect the magnitude of the force acting on the grinder 15 with respect to the X, Y, and Z axes and the six axes A, B, and C, which are the directions of rotation around these axes. A sense sensor 16 is provided. The grinder working robot 10 has a force control function of detecting the processing load applied to the grinder 15 by the force sensor 16 and controlling the feed speed of the grinder 15 and the magnitude of the pressing force according to the fluctuation of the processing load. ing.

The operation of the grinder working robot 10 is performed by the controller 2 in accordance with the taught data.
Controlled by 0. Reference numeral 22 denotes an operation pendant for instructing the grinder work robot 10 in advance a machining path, a speed, a work command, and the like.

Next, FIG. 1 shows a grinder working robot 1.
FIG. 3 is a block diagram of a control system that controls the operation of the control system 0.

Reference numeral 24 denotes teaching data given from the operation pendant 22. In order to move the grinder 15 at the commanded speed along the machining path instructed by the teaching data 24, the controller 20 includes a machining path control loop 26 for controlling a robot driving device 25 and a feed speed control loop 27. Is provided. The processing path control loop 26 continuously controls the path along which the grinder 15 moves according to the commanded processing path. In the feed speed control loop 27, the actual feed speed of the grinder 15 is fed back from the driving device 25 via the feed speed determination unit 29, and the machining load monitoring unit 28 and the feed speed determination unit 29 are transmitted from the force sensor 16 to the feed speed control loop 27. A processing loop is fed back via the controller, and a control loop is configured to control the feed speed of the grinder 15 so as to maintain the processing load at a predetermined value or less based on the commanded feed speed.

The processing load monitoring unit 28 detects the processing load from the signal output from the force sensor 16 and, while the processing object 40 is ground by the grinder 15, sets a predetermined maximum processing load value. To avoid this, the magnitude of the processing load is monitored. Processing load detection data is
This is given to the feed speed judging section 29.

The feed speed judging section 29 receives a signal from a speed detecting section (not shown) provided in the driving device 25 from the grinder 15.
Feed rate is introduced. This feed speed determination unit 29
Based on the feed speed and the processing load given from the processing load monitoring unit 28, it is determined whether or not the change of the processing path is necessary because the feed speed has fallen below the preset minimum feed speed. The machining path changing unit 30
When it is determined that the processing path needs to be changed, the initial processing path is provisionally changed to a processing path that reduces the processing load. The data on the changed provisional machining path is provided to the provisional machining path control unit 31. The provisional machining path control unit 31 transmits the teaching data 2
4, the command data about the changed machining path via the machining completion determination unit 32 is transmitted to the machining path control loop 2.
6 and feed speed command data to a feed speed control loop 27.

The machining completion judging unit 32 controls the machining load monitoring unit 28 while the grinder 15 moves on the changed machining route.
It is determined that the machining along the changed machining path has been completed based on the decrease in the machining load given by. The determination of the processing end is introduced to the processing path control loop 26 and the return path control unit 33.

The return path control unit 33 returns the grinder 15 to the position immediately before the change of the processing path in order to return the moving path to the initial processing path after the processing along the changed processing path is completed. In addition, the movement route can be controlled.

Next, the operation of the present embodiment will be described with reference to an example of the object to be processed 40, which is an operation of removing a weld bead excess. FIG. 3 is a diagram illustrating the movement route of the grinder 15 in a time-series order. FIG. 3A shows a weld bead 44 to be removed from the base material 42 using the grinder 15. The weld bead 44 rises from the surface of the base material 42, and the cross section of the weld bead 44 cut parallel to the surface of the base material 42 decreases as the height increases.

In FIGS. 3B to 3D, reference numeral 15a
Indicates a disk-shaped grindstone of the grinder 15.

Therefore, as shown in FIG. 3B, the initial machining path 46 previously taught by the grinder working robot 10 is provided on the surface of the base material 42 so that the weld bead 44 can be almost removed from the base material 42. It is set to a slightly higher height.

The grindstone 15a of the grinder 15 is shown in FIG.
In (b), the weld bead 44 is ground and removed while moving rightward. During this time, the processing load monitoring unit 28 monitors the magnitude of the processing load. The feed speed of the grindstone 15a is sent to the feed speed determining unit 29. In the case of this embodiment, the minimum feed rate is set to 5 mm / s,
The feed speed judging section 29 compares the detected feed speed of the grindstone 15a with the minimum feed speed.

The minimum feed speed is set according to the processing conditions such as the object to be processed, the type of tool to be used, and the feed speed. In general, when the welding bead 44 is dry-ground by the grinder 15 by an industrial robot as in this embodiment, the feed rate of 5 mm / s is a limit feed rate for maintaining the grinding ability of the grindstone 15. Have found.

Assuming that the machining load suddenly increases at the position A during the grinding and the feed speed of the grindstone 15a decreases, the machining load is larger than the set maximum machining load, and the feed speed is set at the minimum speed. If the speed drops below the feed rate,
It is determined that the machining path should be changed.

Next, in FIG. 3C, the processing path is changed by the processing path changing unit 31 to the initial initial processing path 46.
Is temporarily changed to the secondary machining path 48 that has been translated to a higher position. In the secondary machining path 48 whose height has been changed, the welding bead 44 is attached to the grindstone 1 of the grinder 15.
Since the area in contact with 5a is small, the processing load is reduced, and the feed speed is restored to the initially taught command speed. As a result, a temperature increase at the processing point due to a remarkable decrease in the feed rate accompanying an increase in the processing load, and an extreme decrease in the grinding ability of the grindstone 15a due to the temperature increase are prevented.

In this way, when the grinding proceeds along the provisional secondary machining path 48, reaches the machining end point B, and when it is detected that the machining load has decreased to a predetermined value or less, the machining completion determining unit 32 The end of the machining along the secondary machining path 48 is determined.

Thereafter, as shown in FIG. 3D, the grinder 15 is returned to the return path 50 by the return path control unit 33.
Is controlled to move along. This return route 50
Along the line A, the load is initially retracted to the position A on the initial machining path 46 where the feed rate has decreased below the minimum feed rate due to an increase in load.

Thereafter, the grinder 15 moves the initial machining path 4
6 and if there is no increase in load and a decrease in feed rate beyond the limit, grinding is continued while moving to the final processing end point C as taught, and the operation is completed.

In the above processing example, the change of the processing path is performed by A
Although it is only once at a point, the load increases and the feed rate becomes lower than the minimum feed rate during the change of the processing path or during the processing of the initial processing path 46 after the return, and the processing path needs to be changed again. Is determined, the machining path is repeatedly changed. In this way, since the fluctuation of the processing load is monitored from both the processing load and the feed speed, a decrease in the grinding ability of the grindstone is avoided beforehand, and the feed of the grinder 15 stops and the processing is interrupted. Work can be carried out efficiently and continuously without any trouble.

[0037]

As is apparent from the above description, according to the present invention, even if the processing load varies, the processing can be efficiently performed without interrupting the processing and coping with the fluctuation of the processing load. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram of a controller for controlling the operation of a grinder working robot according to an embodiment of the present invention.

FIG. 2 is an external view showing a grinder working robot to which the force control robot according to the present invention is applied.

FIG. 3 is an explanatory diagram showing a moving path of a grindstone of a grinder with time in an example in which the present invention is applied to grinding of a weld bead.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Grinder work robot (force control robot) 11 Base 12 Column 13 Arm part 14 Wrist part 15 Grinder 15a Whetstone 16 Force sensor 20 Controller 22 Operation pendant 42 Base material 44 Weld bead 46 Initial processing path 48 Secondary processing path 50 Return path

Claims (4)

[Claims] An object of the present invention is to provide a force control robot having a function of detecting a processing load acting on a tool held by a robot and controlling a feed speed of the tool according to a change in the processing load. Means for monitoring the magnitude of the processing load acting on the workpiece, and that during the processing along the initial processing path taught to the robot in advance, the processing load has increased and the feed rate has dropped below the preset minimum feed rate. Means for judging a situation where the machining path needs to be changed, and means for temporarily changing the machining path so that the feed speed does not drop below the minimum feed speed when the machining path needs to be changed. And a means for returning a tool movement path to the initial processing path after finishing the processing along the processed processing path. 2. The force control robot according to claim 1, wherein the height of the machining path is changed so that the machining load is reduced. 3. The force control robot according to claim 1, wherein the end of the machining along the changed machining path is determined based on a decrease in the machining load. 4. The tool comprises a grinder having a dry grinding wheel, and a set value of the minimum feed rate is 5 mm /
The force control robot according to any one of claims 1 to 3, wherein s.