SYSTEM FOR MONITORING ARC SENSOR PROTECTING WINDOW

Abstract: An object of the title system is to appropriately determine a replacement time for arc sensor protecting windows by use of a function originally provided to an arc sensor. The system for monitoring an arc sensor protecting window according to the present invention is constructed such that an unused (new) arc sensor protecting window (28) is mounted on an arc sensor unit (20), and a reference reflecting surface (30) is provided at a position a predetermined distance apart from the front surface of the arc sensor protecting window (28). In this state, a laser beam (26) scans the reference reflecting surface (30) to receive a reflected light (27). The received light is stored in a memory as a first received light amount. Subsequently, the arc sensor protecting window (28) is used as it is for arc welding, and thereafter, similarly to the case of the unused arc sensor protecting window, the reflected light (27) is received from the reference reflecting surface (30). This received light amount is stored as a second received light value. A degree of contamination of the arc sensor protecting window (28) is discriminated on the basis of the first and second received light amounts, whereby it is determined whether the replacement time for the arc sensor protecting windows (28) is reached or not.

Description: Apparatus for Monitoring a Guard Window of an Arc Sensor TECHNICAL FIELD The present invention relates to an apparatus for monitoring a guard window of an arc sensor mounted on a welding torch of an arc welding robot, and relates more particularly to an apparatus for monitoring a guard window of an arc sensor, which determines the replacement time of the guard window. BACKGROUND ART An arc sensor, such as that disclosed in Week 9033, Derwent Publications Ltd., AN90-253902, used for searching a welding line of an arc welding robot and otherwise, is mounted on a welding torch of the robot, and because of this, the arc sensor experiences internal structure damage or accumulates stains on the lens as a result of spatterings and lampblack generated during welding. Therefore the arc sensor is provided with a replaceable guard window to guard the internal structure from spatterings and lampblack. However, this guard window is sometimes burned black by the spatterings and accumulates stains as a result of lampblack etc. in proportion to the number of welding operations, so that an incident beam and a reflected beam of a laser beam cannot easily penetrate the window. When penetration of the incident beam and reflected beam through the window becomes difficult, the detecting capability of the arc sensor is reduced and the detecting accuracy of the same is also reduced. Therefore, the guard window is usually replaced at determined intervals or as required, or the stains on the window are wiped clean after discerning the accumulated stains on the window with the naked eye. However, if the guard window is replaced at determined intervals, stains accumulate and replacement thereof is quite often too late, in the case of a large number of welding operation, and as a result, the detecting capability of the arc sensor is reduced. On the other hand, replacement thereof can be too early, and a window is unnecessarily replaced in the case of a small number of welding operation during the determined interval. Replacement of the guard window as required is indiscriminate and unreliable depending on individual operators thereof, for instance, by discerning the naked eye, thereby posing the same problem as the case when the windows are replaced at determined intervals. DISCLOSURE OF THE INVENTION Accordingly, it is an object of the present invention to provide an apparatus for monitoring a guard window of an arc sensor, capable of determining the proper replacement time by using an original function of the arc sensor, in the light of the above-mentioned problem. In order to solve the above-mentioned problem, the apparatus for monitoring the guard window of the arc sensor according to the present invention, which determines the replacement time of the guard window, characterized in that it includes a standard reflecting plate located at a position a determined distance from the front surface of the guard window of the arc sensor; a detecting means that detects the first quantity of light reception from the light reflected when a laser beam scans the standard reflecting plate before the guard window is used for arc welding, and that detects the second quantity of light reception from the light reflected when the laser beam scans the standard reflecting plate after the guard window is used for arc welding; and a judging means to determine the replacement time of the guard window of the arc sensor based on a comparison of the first quantity of light reception and the second quantity of light reception. First, an unused (brand new) guard window is mounted on an arc sensor, and a standard reflecting plate is then located at the position a pre-determined distance from the front surface of the guard window. The reflected light is detected when the laser beam scans the standard reflecting plate in that state, and data concerning the quantity of light reception is stored in a memory as the first quantity. Then after using the guard window for arc welding operation, the standard reflecting plate is located at a position a pre-determined distance from the front surface of the guard window of the arc sensor. The data concerning the quantity of light reception is stored in a memory as the second quantity, and based on the data of the first and the second quantities of light reception, the condition of the guard window is determined and a decision is made regarding whether the guard window should be replaced or not, thereby providing a suitable replacement time for the guard window of the arc sensor. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a block diagram showing the structure of an apparatus for monitoring a guard window of an arc sensor of the present invention; Figure 2 is an outline drawing of an arc welding robot; Figure 3 is a flow chart of a process for the apparatus (for monitoring a guard window of an arc sensor of the present invention) before the guard window is used for welding operation; and, Figure 4 is a flow chart of a process for determining the replacement time of the guard window of the apparatus. BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be explained hereinafter, referring to the attached drawings. Figure 1 is a block diagram showing a structure of an apparatus for monitoring a guard window of an arc sensor of the present invention. An arc sensor control unit 10 is composed of a mirror scanning unit 11, a laser drive 12 and a signal detecting unit 13. On the other hand, an arc sensor unit 20 is composed of a laser oscillator 21, a scanner 22 and an oscillation mirror 23 oscillated by the scanner 22. The arc sensor unit 20 is also composed of a lens 24 and a light receptive element 25. And, for example, a C.C.D. or a P.S.D. (position sensing device) is used for a light receptive element 25. An arc sensor guard window 28 is also provided on the front surface of the arc sensor unit 20. This arc sensor guard window 28 is, for example, composed of a heat resisting glass or a special resin, and protects internal constitutions of the arc sensor unit 20 from spatterings and lampblack generated during welding operation. The laser oscillator 21 oscillates after receiving drive power from the laser drive 12 and outputs a laser beam 26. The scanner 22 is driven by a drive current generated from the mirror scanning unit 11 and oscillates the oscillation mirror 23. Generally, the oscillation mirror 23 scans the laser beam 26 onto a workpiece (not shown), and the reflected light is detected by the light receptive element 25. Data detected by the element 25 are sent to a robot controller 7, hereinafter mentioned, via the signal detecting unit 13. The robot controller 7 detects a welded point of the workpiece or others based on the data. Figure 2 is an outline drawing of an arc welding robot. A torch 3 is connected at the tip of a hand 2 of a robot 1. The arc sensor unit 20 is provided with the torch 3. The arc sensor control unit 10 is also provided on an arm 4. The arc sensor control unit 10 controls the behavior of the arc sensor unit 20 in accordance with command signals output from the robot controller 7. The robot controller 7 is mainly composed of a processor 71. The processor 71 outputs the command signals in accordance with a system program stored in a ROM 72, and controls the robot 1 and the arc sensor control unit 10. In the ROM 72, a system program for controlling the robot behavior, a system program for controlling the arc sensor control unit 10 and a program for the process of the apparatus for monitoring the guard window of the arc sensor, hereinafter explained, are stored. In a RAM 73, a program for processing the operations of the robot 1, system parameters, data necessary for the arc sensor, data on the quantity of light reception detected by the apparatus for monitoring, and data involving the average value of the same are stored. Next, operations of the apparatus for monitoring the guard window of the arc sensor will be explained hereinafter. First of all, after mounting an unused (brand new) guard window 28 of an arc sensor to the arc sensor unit 20, a standard light reflecting plate 30 is located at a position a determined distance from a front surface of the guard window 28. The standard reflecting plate 30 has a standard surface of which roughness and reflection rate are uniform, for example, the plate 30 is composed of a plaster board so that a uniform irregular reflection can be obtained when the laser beam 26 is projected. The reflected light 27 is detected by the light receptive element 25 after penetrating the lens 24 when the laser beam 26 is projected to the standard reflecting plate 30. Data obtained by the detection are sent to the robot controller 7 via the signal detecting unit 13 of the arc sensor control unit 10, and are input via an interface 74. The detected input data are stored in the RAM 73. The laser beam 26 scans the whole scanning surface area of the standard reflecting plate 30, and the whole detected data are stored at the RAM 73. The average value of all the detected data is calculated and also stored in the RAM 73. Next, after arc welding while maintaining the guard window 28 of the arc sensor mounted at the arc sensor unit 20 as it is, the standard reflecting plate 30 is located at a position a determined distance from the front surface of the guard window 28 as in the above explained case. The laser beam 26 is projected to the standard reflecting plate 30, and detected data of the reflected light 27 are then sent to the robot controller 7 as in the above explained case. The processor 71 of the robot controller 7 compares the sent detected data with the detected data previously memorized before the guard window 28 is used for welding, and determines whether the detected data sent exceeds the determined level or not. This is determined, for example, based on the calculated differences between the two detected data, and when the difference is large, the processor 71 judges that there is a stain or lampblack generated by the spatterings on the surface of the guard window 28 through which the laser beam 26 passes when the quantities of light reception are detected. The result of the judgement is displayed as a message so that operators can discern that the guard window 28 is partly stained. On the other hand, when the difference is small, the processor 71 determines that there are not stains or otherwise on the guard window 28 and that the window 28 does not require replacement. When the laser beam 26 scans the whole standard reflecting surface 30 and the detected data are obtained, the average value of the whole detected data is also calculated. This average value is compared with the previously stored average value of the detected data detected before the guard window 28 is used for an arc welding operation. When the difference between the two average values is large, the processor 71 determines that there are stains on the guard window 28 by the lampblack, and the result of the determination is displayed as a message, and the operator discerns that there are stains or otherwise on the whole guard window 28 of the arc sensor based on the display. On the other hand, when the difference is small, the processor 71 discerns that there are no stains on the whole guard window 28. Figure 3 and Figure 4 are flow charts of a process for the apparatus for monitoring a guard window of an arc sensor of the present invention. In the drawings, the numbers following after alphabet "s" indicate step numbers. Figure 3 shows a process flow chart of the apparatus before the guard window of the arc sensor is used for arc welding, whereas a process flow chart of the same shown in Figure 4 is based on the detected data before the guard window is used for an arc welding operation. (S1): Mount an unused guard window 28 of the arc sensor in the arc sensor unit 20. (S2): Lay the standard reflecting plate 30 at a position a determined distance from the front surface of the guard window 28. (S3): Let the laser beam 26 scan on the standard reflecting plate 30, and detect the quantity of light reception from the reflected light 27. (S4): Memorize the quantity of light reception. (S5): Determine whether or not the whole scanning area on the standard reflecting plate 30 has been scanned and detected. If the whole area has been scanned and detected, go to step S6, and if not, go back to step S3. (S6): Calculate the average value of the quantity of the reflected light reception from the whole scanning area on the standard reflecting plate 30, and memorize the calculated data. Figure 4 is a flow chart of a process for determining the replacement time of the guard window of the apparatus after arc welding, with the guard window used in the process explained by referring to Figure 3. (S10): Lay the standard reflecting plate 30 at a position a determined distance from the front surface of the guard window 28 of the arc sensor. (S11): Let the laser beam 26 scan, and detect the quantity of light reception from the reflected light 27. (S12): Calculate a difference between the data of the detected quantity of light reception and the memorized data of the same stored before the guard window is used for an arc welding operation. (S13): Determine whether the difference is small or not, and if it is small, go to step S14, and if it is large, go to step S18 respectively. (S14): Determine whether the light reflected from the whole scanning area on the standard reflecting plate 30 is detected or not. If it is detected, go to step S15, and if not, go back to step S11. (S15): Calculate the data of an average value of the quantity of light reception detected for the whole scanning area. (S16): Determine whether the difference between the calculated average value and previously memorized average value of the quantity of light reception detected before using the guard window is small or not, and if it is determined to be small, go to step S17, and if it is determined to be large, go to step S19, respectively. (S17): Discern that there are no stains or otherwise on the guard window 28 of the arc sensor, thereby determining that the guard window is normal, and finish the execution of the program. (S18): Discern that there are stains or lampblack as a result of the spatterings on the guard window 28 of the arc sensor when it is detected, quickly display same as a message, and go to step S14. (S19): Discern that there are stains or otherwise as a result of lampblack on the whole area of the guard window 28, display same as a message, and finish the execution of the program. In this way, the quantity of light reception detected before using the guard window 28 for an arc welding operation is compared with the same detected after using it for an arc welding operation, and the condition of the guard window is determined based on the results of the comparison, and the replacement time of the guard window is determined. By this, the replacement time of the guard window 28 can be properly determined using an original function of the arc sensor; the function of which detects the quantity of light reception from the reflected light. Therefore, a suitable replacement time of the guard window 28 of the arc sensor can be determined. If said process is executed at the beginning of every arc welding operation, the replacement time of the guard window can be accurately determined. As explained above, an apparatus for monitoring a guard window of an arc sensor according to the present invention compares the quantity of detected light reception before using the guard window for an arc welding operation with the quantity of detected light reception after using the guard window for an arc welding operation discerns the condition of the guard window of the arc sensor, and determines whether it is acceptable or not based on the result of the said comparison, and determines the replacement time of the guard window. Therefore, the proper replacement time of the guard window can be determined using an original function of the arc sensor, which detects the quantity of light reception from the reflected light, so that the guard window can be replaced at an appropriate time.

Claims: A welding robot apparatus including guard window monitoring apparatus for an arc sensor guard window (28) of the robot, said apparatus comprising: robot controller means (7); an arc sensor unit (20) having laser scanner means (22) controlled by arc sensor control means (10) said scanner means (22) directing a laser beam to scan a welding area of an object being worked , said arc sensor unit (20), further including a light receptive element (25) providing signals to signal detecting means (13) representing quantity of reflected light from said object being worked to detect a welded point of said object; a standard reflecting plate (30) located at a position having a pre-determined distance from a front surface of said guard window (28) at the side of said guard window (28) opposite from the position of said light receptive element (25); means in said controller means (7) selectively operable to cause said laser scanner means (22) to direct said laser beam to scan a surface of said standard reflecting plate (30) through said guard window (28) such that said light receptive element (25) provides a first signal to said signal detecting means (13) representing a first quantity of light reflected from a scanned area of the surface of said standard reflecting plate (30) through said guard window (28) before using said guard window (28) in an arc welding operation and provides second a signal to said signal detecting means (13) representing a second quantity of light reflected from the scanned area of the surface of said standard reflecting plate (30) after using said guard window (28) in an arc welding operation and means in said robot controller means (7) for storing first and second signals from said detecting means (13) representative of said first and second quantities of light, and for determining the time for a replacement of said guard window based upon the magnitude of a difference between said signals representing said first quantity of light and said second quantity of light. An apparatus as recited in claim 1, wherein said time for replacement determination is made by comparison of signals representing first and second quantities of light corresponding to light reflected from a portion of the scanned area of said standard reflection plate (30). An apparatus as recited in claim 1, wherein said time for replacement determination is made by a comparison of signals representing average values of said first quantity of light and said second quantity of light reflected from the whole scanned area of said standard reflecting plate (30).

Inventors: NIHEI RYO FANUC MANSION HARIMO, TORII NOBUTOSHI, WAKIO HIROSHI FANUC DAI- VIRA-, NIHEI, RYO, FANUC MANSION HARIMOMI 7-210, TORII, NOBUTOSHI, WAKIO, HIROSHI, FANUC DAI-3 VIRA-KARAMATSU
Applicants: FANUC LTD, FANUC LTD.
Application year: 1992
Main classification: G01J1
IPC codes: G01J1, B23K9, G01N21