Robot controlling method and apparatus using laser sensor

• US 5,799,135 A
• Filed: 06/22/1995
• Issued: 08/25/1998
• Est. Priority Date: 06/28/1994
• Status: Expired due to Fees

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Terawaki, Fumikazu
• Primary Examiner(s): Downs, Robert W.
• Assistant Examiner(s): SHAH, SANJIV
• Application Number:
  US08/493,618
• Time in Patent Office: 1,160 Days
• Field of Search: 395/93, 395/94, 395/88, 395/89, 219/124.35, 219/125.1, 219/121.6, 250/559, 228/102, 318/568.22, 356/5.01, 364/571.01
• US Class Current: 700/258
• CPC Class Codes: B25J 9/1679 characterised by the tasks executed
• CPC Class Codes: G05B 2219/34088 Chamfer, corner shape calculation
• CPC Class Codes: G05B 2219/37571 Camera detecting reflected light from laser
• CPC Class Codes: G05B 2219/45104 Lasrobot, welding robot
• CPC Class Codes: G05B 2219/49384 Control of oscillatory movement like filling a weld, weaving

Abstract

A robot controlling method and apparatus using a laser sensor in which an optimum moving path is realized even if the accuracy of positioning workpieces is low. While a laser sensor is operated, a robot is started to move toward a taught position corresponding to the start position of a welding line. When the workpieces W1 and W2 are detected, a three-dimensional position of the points Q1-Q4 are calculated. The equations of a straight line Q1Q2 and a straight line Q3Q4 are obtained from position data of points Q1-Q4, and a corner position Q0 is calculated as a crossing point of these two straight lines. Then, access is made to a register, which is designated by an address designation counter value i, to read position shift data. When i=1, Δx=Δy=Δ is read and a position shifted from the position Q0 by Δ respectively along the straight lines Q1Q2 and Q3Q4 is calculated as a target position to which the robot movement is performed. In the first moving cycle for forming the first welding layer, a path a is realized. Likewise, in the subsequent moving cycles, different position shift data are read to realize the paths a-f successively.

Claims

1. A method of controlling a robot by consecutively modifying a taught path designated by an operation program, using an output from a laser sensor which has a sensing area in the vicinity of and in a moving direction of a tool mounted on the robot, said method comprising the steps of:

(a) obtaining data representing a position of a workpiece by said laser sensor during a playback operation of the operation program to operate the robot;

(b) calculating a reference position for determining a target position for the robot movement based on said data obtained in said step (a);

(c) determining a shift direction and a shift amount with respect to said reference position in accordance with a position shift pattern designated by the operation program;

(d) calculating the target position by shifting said reference position in said shift direction determined in said step (c) and by said shift amount determined in said step (c); and

(e) modifying said taught path based on said target position determined in said step (d),

wherein said steps (a)-(e) are periodically executed.

2. A robot controlling method according to claim 1, wherein said step (c) includes a step of reading data stored in one position shift pattern register, designated by the operation program, of a plurality of position shift pattern registers for storing said shift direction and shift amount with respect to said reference position.

3. A method of controlling a welding robot for performing multi-layer welding on a workpiece by repeatedly executing a moving cycle of a welding torch mounted on the welding robot while consecutively modifying a taught path designated by an operation program, using an output from a laser sensor which has a sensing area in the vicinity of and in a moving direction of the welding torch, said method comprising the steps of:

(a) obtaining data representing a position of the workpiece by said laser sensor during the playback operation of the operation program to operate the robot;

(b) calculating a reference position for determining a target position of the robot movement based on said data obtained in said step (a);

(c) determining a shift direction and a shift amount with respect to said reference position in accordance with a position shift pattern designated by the operation program;

(d) calculating the target position by shifting said reference position in said shift direction determined by said step (c) and by said shift amount determined in said step (c); and

(e) modifying said taught path based on said target position determined in said step (d),

wherein said steps (a)-(e) are periodically executed and said step (c) includes a step of reading data stored in one position shift pattern register, designated by the operation program, of a plurality of position shift pattern registers for storing said shift direction and shift amount with respect to said reference position, in dependence upon the current moving cycle of the welding torch for the corresponding layer of the multi-layer welding.

4. A method of controlling a welding robot for performing multi-layer welding on a workpiece by repeatedly executing a moving cycle of a welding torch mounted on the welding robot while consecutively modifying a taught path designated by an operation program, said method comprising the steps of:

(a) determining positions of first and second workpieces by irradiating light beams from a laser sensor in a vicinity of and in a moving direction of the welding torch;

(b) determining a reference position based on the positions determined in said step (a), wherein the reference position is a position of a corner line on a cross section of the first and second workpieces;

(c) determining a shift direction and a shift amount relative to said reference position in accordance with a preset position shift pattern designated by the operation program;

(d) determining a target position of the robot movement by shifting the reference position based upon the shift direction and shift amount;

(e) modifying the taught path based upon said target position determined in said step (d); and

(f) repeating said steps (a)-(e) for a plurality of moving cycles of the welding torch, wherein each moving cycle produces another layer of the multi-layer welding.

5. A method as claimed in claim 4, wherein said (b) further comprises the steps of:

designating a first set of two points based upon the position of the first workpiece;

designating a second set of two points based upon the position of the second workpiece;

sampling detection outputs of the laser sensor at points in time when the light beams are formed at each of the points of the first and second sets to determine light spot coordinates of each of the points of the first and second sets;

determining three-dimensional positions of each of the points of the first and second sets based upon the light spot coordinates and date representing a position of a laser beam scanning surface determined by the robot position at each sampling time;

determining equations for straight lines between the two points of each set; and

determining the reference point as an intersection between the two straight lines.

6. A method as claimed 5, wherein said step (c) further comprises retrieving a distinct shift direction and shift amount for each moving cycle of the welding torch, wherein the shift directions and shift amounts are determined based upon a coordinate system using the two straight lines as axes.

7. A method as claimed in claim 6, wherein the shift directions are only in a direction parallel to a first one of the two straight lines, parallel to a second one of the two straight lines, and at a 45 degree angle to the two straight lines.

8. A method of controlling a welding robot for performing multi-layer welding on a workpiece by repeatedly executing a moving cycle of a welding torch mounted on the welding robot while consecutively modifying a taught path designated by an operation program, said method comprising the steps of:

(a) determining a position of a workpiece by irradiating light beams from a laser sensor in a vicinity of and in a moving direction of the welding torch;

(b) determining a reference position based on the position determined in said step (a), wherein the reference position is a welding-line position of the welding torch;

(c) determining a shift direction and a shift amount relative to said reference position in accordance with a preset position shift pattern designated by the operation program;

(d) determining a target position of the robot movement by shifting the reference position based upon the shift direction and shift amount; and

(e) modifying the taught path based upon said target position determined in said step (d); and

(f) repeating said steps (a)-(e) for a plurality of moving cycles of the welding torch, wherein each moving cycle produces another layer of the multi-layer welding.

9. A sensor for controlling a welding robot which performs multi-layer welding on a workpiece by repeatedly executing a moving cycle of a welding torch mounted on the welding robot while consecutively modifying a taught path designated by an operation program, the sensor comprising:

a laser generator to produce laser light;

a pivotal mirror which pivots to scan the laser light on the workpiece;

an optical system to receive and focus the laser light reflected from the workpiece;

a light receiving element to receive the focused laser light passing through the optical system;

a controller to control the laser generator and the pivotal mirror;

wherein a coordinate position (X,Y) at which the laser light strikes and the workpiece is determined by the following equations;

##EQU2## wherein L1 is a distance from an origin of the sensor to a center of the optical system, L2 is a distance from the center of the optical system to a center point of the light receiving element, D is a distance from the origin to a pivot point of the pivotal mirror in the X axis direction, L0 is a distance from the origin to the pivot point in the Y axis direction, θ

is an angle between the laser light reflected from the workpiece and a Y-axis, and xa is a light receiving position on the light receiving element in the X axis direction.

10. A sensor as claimed in claim 9, wherein the light receiving element is a charge coupled device and a scanning cycle of the charge coupled device is shorter than a scanning cycle of the pivotal mirror.

11. A sensor as claimed in claim 10, wherein the charge coupled device includes cells, and an output of the charge coupled device is determined in terms of cell position of maximum output.