Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
1998-11-30
2001-11-20
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C700S245000, C700S249000, C700S252000, C700S254000, C700S255000, C700S258000, C700S259000, C701S029000, C219S124340
Reexamination Certificate
active
06321139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of detecting a position of an operation line when starting tracking of the operation line using a robot/sensor system in which an operation line on an object is detected by a sensor so as to perform a predetermined operation by moving a tool along the detected operation line, and also relates a robot/sensor system with such detecting function. The present invention is applicable to a robot/laser sensor system for performing various operations such as arc welding, deburring and sealing.
2. Description of Related Art
A technique of operating a robot to move along an operation line such as a weld line while sensing a position of the operation line in advance using a laser sensor mounted on the robot is applied to various robot operations including a welding operation as a real-time tracking technique, the robot having a tool such as an arc welding torch attached to a distal end thereof. This technique enables the robot to move along an actual operation line even when individual objects of operation (for example, fillet welding workpieces) are not positioned precisely. Thus, the technique is widely used as means for improving operation accuracy.
FIG. 1
is a schematic perspective view showing an example of an arrangement of a robot/laser sensor system performing an arc welding on a corner portion WD formed by fillet welding workpieces W
1
and W
2
. As shown in
FIG. 1
, a welding torch
2
as an operation tool and a laser sensor (a body thereof)
10
are attached to a robot
1
(only a distal portion thereof is shown). The laser sensor
10
scans for sensing surfaces of the workpieces W
1
and W
2
with a laser beam
4
. In the following description, it is supposed that a point
3
representing the position of the robot agrees with an distal end of the tool.
Sign Q
0
indicates an initial position of the robot
1
, P
1
a welding start point which is taught, and P
2
a welding end point which is taught. In general cases where positioning of the objects of operation, for example, such as the workpieces W
1
, W
2
to be jointed by welding is not so precise, an actual start point Q
1
of the corner portion
4
does not necessarily agree with the taught welding start point P
1
.
When the robot
1
starts regenerative operation, the robot starts to move the tool tip
3
from the initial position Q
0
to the taught point P
1
, and the laser sensor
10
is turned on to start sensing. Around the time when the tool tip
3
reaches the taught point P
1
, the laser beam
4
starts to scan the surfaces of the workpieces W
1
and W
2
to be welded in such a manner as crossing the weld line (corner line) WD to thereby detect the position of the point Q
1
on the weld line WD.
Then, after correcting its position to the point Q
1
, the robot
1
moves along the weld line WD by known real-time tracking. The torch
2
is ignited at an appropriately determined point of time, and welding is performed from the point Q
1
to the point Q
2
. Also when applied to operation other than welding, the robot is guided to the operation start point Q
1
by a similar manner of approach, and starts to move along the operation line (a deburring line, a sealing line and the like).
In order that the operation as described above can be started and performed smoothly, it is necessary that positioning of the workpieces W
1
and W
2
to be welded (objects of operation) be performed with relatively high accuracy (relatively small error) with respect to the range of scanning by the laser beam
4
. Since the laser sensor
10
is primarily a sensor for narrow-range sensing, the range of scanning by the laser beam
4
cannot be considered a large one. Therefore, if the positioning of the workpieces W
1
and W
2
to be welded (objects of operation) is not accurate adequately, there is a possibility that the weld line (operation line) WD cannot be detected.
The most popular method which has been conventionally adopted to deal with this problem is outputting an alarm signal to stop operation if an operation line is not detected within a predetermined time, or before the robot travels a predetermined distance. Such method, however, is one of the causes of drop of operation efficiency.
Another method proposed is designed so that the robot is made to retry its operation when an operation line cannot be detected. The problem is that such method is burdensome since it needs preparation of complicated programs.
Further, in conventional methods, the probability of false detection is high, if an obstacle F (external to the objects of operation) or an obstructively-shaped portion G (belonging to the objects of operation) which hinders normal detection of a position of the operation line lies in the vicinity of the operation start point Q
1
and if the objects of operation W
1
and W
2
are erroneously positioned, causing the taught point P
1
to become closer than a normal position to the obstructively-shaped portion G.
SUMMARY
A first object of the present invention is to improve a robot/laser sensor system having a laser sensor for detecting an operation line so that searching motion for finding the position of an operation line can be performed in a rationalized manner and that, even if positioning of objects of operation is not performed with high precision, the position of the operation line can be detected with high precision and intended an operation can be started.
A second object of the present invention is to increase the possibility of unhindered approach to the work even if an obstacle or a portion of work having an obstructive shape which hinders normal detection of the position of the operation line lies in the vicinity of an operation start point, by avoiding such obstacle or obstructive portion of work.
The present invention is an improvement of a method of searching an operation line in performing a predetermined operation by moving a tool supported by a robot along the operation line based on a signal outputted from a sensor using a robot/sensor system having the robot, a robot controller and the sensor mounted on the robot for detecting the operation line of an object of operation.
The method of the present invention includes the steps of: determining a search motion for finding a position of the operation line using the sensor by moving the tool closer to a predetermined start position of operation, to include a component of motion in a direction crossing an extending direction of the operation line in the vicinity of the start point of the operation line; starting the determined search motion; and terminating the search motion when the sensor detects a shaping element of the object of operation during the search motion, said shaping element defining the operation line. The robot/sensor system of the present invention has means for performing the above steps.
In a preferred embodiment of the present invention, a plurality of searching motion path patterns, each having in the vicinity of the start point of the operation line a component of motion in a direction crossing an extending direction of the operation line, are provided in advance, and one search motion path pattern is selected from these searching motion path patterns.
The following methods can be adopted for determining the search motion, (I) the search motion is determined by relating the search motion to the direction of a coordinate axis of a coordinate system specified for the robot; (II) the search motion is determined by teaching the robot; and (III) the search motion is determined based on predetermined calculation using parameters which are provided in advance for the robot/sensor system to describe the path patterns
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patent: 4998050 (1991-03-01), Nishiyama et al.
patent: 5111401 (1992-05-01), Everett, Jr. et al.
patent: 5297238 (1994-03-01), Wang et al.
patent: 5347463 (1994-09-01), Nakamura et al.
patent: 5429682 (1995-07-01), Harlow, Jr. et al.
patent: 5544282 (1996-08-01), Chen et al.
patent: 55827
Okuda Mitsuhiro
Terada Akihiro
Cuchlinski Jr. William A.
Fanuc Ltd.
Marc McDieunel
Staas & Halsey , LLP
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