GB2112961A

GB2112961A - Corner angle portion detecting apparatus

Info

Publication number: GB2112961A
Application number: GB08200058A
Authority: GB
Inventors: Akira Tsuchihashi
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1982-01-04
Filing date: 1982-01-04
Publication date: 1983-07-27
Also published as: GB2112961B

Abstract

A corner angle portion detecting apparatus detects a corner angle portion (23,24,25,26) of an object (21,22). There are provided a pair of sensors (14,16) for detecting the position of the object from different directions and a driving means (18) for changing the relative positional relation between the sensors, so that it is possible to freely change the relative positional relation between the working tool (12) and the sensors. Therefore, when the object is detected by the sensors, a torch (12) can aim at any position on the corner angle portion of the object. This can be used in a robot operating in teach/playback cycles for welding, painting or coating adhesive. <IMAGE>

Description

SPECIFICATION Corner angle portion detecting apparatus This invention relates to a corner angle portion detecting apparatus having two sensors placed close to or in contact with an object to detect a corner angle portion of the object, and particularly to a corner angle portion detecting apparatus having a driving device for changing the relative positional relation between the two sensors.

A corner portion detecting apparatus is used for industrial robots for automatic welding. For example, in the U.S. Pat. No. 4,042,161 issued on August 16, 1977 which was assigned to this applicant, there is disclosed an automatic welding system in which the detecting apparatus has two sensors fixed to a torch. These sensors are arranged in a fixed mutual positional relationship, and are able to detect the corner angle portion of an object in only a predetermined positional relationship between the corner and the sensors.

These sensors are for example of contact type.

The U.S. Pat. No. 4,205,217 to Araya et al issued on May 27, 1980 and assigned to the same applicant discloses a non-contact type magnetic sensors. These sensors are also positioned close to the object to detect the position of the object.

However, these two fixed sensors sometimes cannot detect the corner angle portion. In other words, when the position of the object to be detected and its corner angle portion are not in a constant relative positional relation, the corner angle portion of the object cannot be detected by these sensors.

Thus, it is an object of this invention to provide a corner angle portion detecting apparatus capable of changing freely the relative positional relationship between the corner angle portion and at least one of the sensors.

According to the present invention, there is provided a corner angle portion detecting apparatus comprising a working tool, first and second position detecting sensors disposed to hold the working tool therebetween and to detect the position of an object from different detecting directions, respectively, driving means for driving at least one of the sensors to change the relative positional relation between the sensors, command signal for generating a command signal to determine the relative positional relatitionship between at least one of the sensors and the working tool, detecting means for generating a detected output indicative of the position of the drive means, and servo means for comparing the detected output of the detecting means and the command signal from the command means, to operate the driving means to cause a difference therebetween to be a particular value.

In one aspect of the present invention, since a driving means is provided to drive at least one sensor with respect to the other sensor in order to change the relative positional relation between the two sensors, it is possible to detect the corner angle portions of objects of different shapes. For example, even if the object has projections or recesses which are not in a predetermined positional relationship with the corner angle portion, the corner angle portion can be detected precisely by moving at least one of the sensors to an appropriate position.

In another aspect of the present invention, multilayer welding at the corner angle portion can be performed effectively.

These and other objects, features and advantages of the present invention will be more apparent from the following descriptions taken in conjunction with the accompanying drawings, in which: Fig. 1 is one embodiment of a welding robot employing a corner angle portion detecting apparatus of this invention; Fig. 2 is a block diagram of a control apparatus for allowing the welding robot of Fig. 1 to learn welding steps and to automatically perform the welding; Fig. 3 is a view explaining a driving method for changing target positions at which the welding robot aim; Fig. 4 is a flow chart of welding steps which the welding robot performs on the basis of the control apparatus of Fig. 2; Fig. 5 is a modification of the control apparatus of Fig. 2;; Fig. 6 is a part of a flow chart of welding steps which the welding robot performed on the basis of the control apparatus of Fig. 5; and Figs. 7A and 7B are side and plan views of another embodiment of a corner angle portion detecting mechanism, respectively.

Referring to Fig. 1 , there is shown a carrying holder 1 for an industrial welding robot, which can be moved in the vertical direction with respect to the drawing (or in the X-direction) by an actuator for the carrying holder (not shown). A numeral 2 is a detector for detecting the position of the carrying holder 1, 3 an up/down moving device, 4 an oil pressure cylinder mounted on the carrying holder 1 to drive the up/down moving device 3 in the Z-direction perpendicular to the Xdirection, 5 a rack for detecting the position of the up/down moving device 3, 6 a detector having a gear (not shown) engaged with the rack 5 and which detects the position of the up/down moving device 3, 7 a forward/backward arm that is driven in the Y-direction perpendicular to X- and Zdirections by an actuator (not shown) such as an oil pressure cylinder fixed to the up/down moving device 3, 8 a rack provided to detect the position of the forward/backward arm 7, 9 a detector having a gear (not shown) engaged with the rack 8 and which detects the position of the forward/backward arm 7, 10 an oil pressure motor mounted at the tip end of the forward/backward arm 7, 1 1 a detector for detecting the rotational position of the oil pressure motor 10, 12 a torch provided at the tip end of an oil pressure motor 13 for changing the target angle of the torch 12, and 14 a forward/backward sensor.

The sensor 14 is of the known contact type or non-contact type. The non-contact type sensor draws near the surface of an object to an extent of, for example, 4 mm to detect the position of the object. This sensor 14 generates a signal necessary for positioning the tip end of the torch 12 in the Y-direction with respect to the object to be welded. Designated at 15 is a withdrawing device for drawing the sensor 14 back. The sensor 14 is put out in the case of detecting the position of the object, but withdrawn when the object is welded or when the sensor 14 is not necessary.

Designated at 16 is an up/down sensor which generates a signal for positioning the tip end of the torch 12 in the Z-direction with respect to the object to be welded, and 17 a withdrawing device for drawing the sensor 16 back.

A numeral 18 is a drive means formed of, for example, an oil pressure cylinder fixed to the rotatable shaft of the oil pressure motor 10. The withdrawing device 15 is fastened to the oil pressure cylinder 18. To a piston of the oil pressure cylinder 18, is fixed a support member 20 to which the oil pressure motor 13 and the withdrawing device 17 are fixed. The oil pressure cylinder 18 operates to cause the positional relationship between the sensor 14 and the torch 12 or up/down sensor 16 to be changed.

Designated at 19 is a position detector mounted on the oil pressure cylinder 18. This position detector detects the position of the piston of the oil pressure cylinder 18 thereby to detect the relative positional relation between the sensor 14 and the torch 12 # or sensor 16. A numeral 21 is a horizontal plate to be welded, 22 a vertical plate to be welded, and 23, 24, 25 and 26 positions at which the torch 12 aims for multilayer welding.

The operation will be described hereinbelow.

The carrying holder 1 is driven in the Xdirection perpendicular to the drawing by an oil pressure cylinder (not shown). The position of the carrying holder 1 with respect to the floor is detected by the detector 2.

On the carrying holder 1 there is provided a square post having the rack 5 mounted thereon, and the up/down moving device 3 is moved up or down along the square post in the Z-direction by driving the oil pressure cylinder 4. The position of the up/down moving device 3 is detected by the detector 6 directly connected to the gear rotating on the rack 5.

The oil pressure cylinder (not shown) mounted on the up/down moving device 3 allows the forward/backward arm 7 to be moved in the Y-direction, and the position of the forward/backward arm 7 is detected by the detector 9 directly connected to the gear rotating on the rack 8. The oil pressure motor 10 mounted on the tip end of the forward/backward arm 7 can rotate the corner angle portion detecting mechanism including the sensors 14 and 16 and the torch 12.

In order to detect the vertical plate 22 by the sensor 14, first the sensor 14 is drawn out of the withdrawing device 15 to a take a forward position. Then, the oil pressure motor 10 is rotated to move the sensor 14 to face the surface of the vertical plate 22 at right angles. The position at which the sensor 14 is at right angles to the surface of the vertical plate 22 is detected by the detector 11 for detecting the rotational angle. After the position is detected, the sensor 14 is moved in the X- and Y-directions at the same time by the forward/backward arm 7 and the carrying holder 1 until the sensor 14 detects the vertical plate 22.Since the sensor 14 and the torch 12 are in a desired positional relation depending on the position at which the piston of the oil pressure cylinder 18 is located, the tip end of the torch 12 can be located at a fixed position with respect to the surface of the vertical plate 22. For single layer welding, the distance between the tip end of the vertical plate 22 on the XY-plane is normally selected to be 2 mm, while for multilayer welding, it is necessary to change the position to be aimed at, as 23, 24, 25 and 26.

Thus, for welding at each layer, the oil pressure cylinder 18 is driven to change the distance between the torch 12 and the sensor 14 and then the forward/backward arm 7 and the carrying holder 1 are driven to make the distance between the vertical plate 22 and the sensor 14 at constant, so that the tip end of the torch 12 is automatically brought to a desirable position with respect to the vertical plate 22.

The up/down sensor 16 is used for determining vertical position of the torch 12. The sensor 16 is moved by the up/down moving device 3 until it detects the horizontal plate 21, where a distance between the sensor 16 and the horizontal plate 21 is kept at constant and the tip end of the torch 1 2 is adjusted to contact the surface of the horizontal plate 21. Thus, when the tip end of the torch 12 is desired to be positioned at 23, 24 and 25, the withdrawing device 17 is put in the forward state to operate the sensor 16 so that the tip end of the torch 12 is controlled to always contact the surface of the horizontal plate 21.

When the tip end of the torch 12 is desired to be at location 26, it is enough to drive the up/down moving device 3 to move in the Zdirection by the distance between the position 26 to be aimed at and the horizontal prate 21.

Fig. 2 shows a control apparatus for causing the welding robot of Fig. 1 to learn the welding steps and to perform the welding automatically.

There is shown a teaching box 30 which is used for causing the welding robot to learn the welding steps. The operation by which the robot learns the welding steps will hereinafter be referred to as a manual mode. Designated at 32 is a console for issuing commands to automatically operate the robot after the completion of the manual mode.

The automatic welding operation of the robot after the learning of the welding steps will hereinafter be referred to as an automatic mode.

Shown at 34 is a change-over switch for the manual and automatic modes, 36 a central processing unit (hereinafter, referred to as CPU), 38 a memory having a core memory for storing the welding steps and a RAM (Random Access Memory) for storing the momentary outputs from various different detectors, 40 a command memory for issuing commands to drive each drive portion of the robot, and which is formed of a RAM, and 42 a comparator for comparing a drive command from the command memory 40 and a detected signal indicative of a current position detected by a detector. In addition, shown at 44 is a D/A converter, 46 a servo valve operating in response to the output of the D/A converter 44, and 48 an actuator corresponding to, for example, the oil pressure cylinder 4.The actuator 48 may also show either of an oil pressure cylinder (not shown) for driving the carrying holder, an oil pressure cylinder (not shown) for driving the forward/backward arm 7, the oil pressure motor 10 and the oil pressure cylinder 18. It should be understood that for each actuator, the comparator 42, the D/A converter 44, the servo valve 46 and a detector 50 are similarly connected. Therefore, the detector 50 is the detector 2 for the oil pressure cylinder 4, and also detectors 6, 9, 11 and 18 for other actuators. The sensors 14 and 16 are connected to the memory 38 through a sensor control circuit 49 which serves to improve output characteristics of each sensor to raise accuracy of positioning of each actuator. The control circuit 49 also converts outputs of the sensors to digital values.

If a store command is issued from the teaching box 30 to perform the manual mode, the CPU 36 causes the memory 38 to store at certain addresser data from the position detectors of the industrial robot including the detectors 2, 6, 9, 11 and 19. When another store command is again issued from the teaching box 30, the CPU 36 similarly allows the memory 38 to store at next addresses other data from the position detectors 2, 6, 9, 11 and 19. In addition, the teaching box 30 sends a command to the CPU 36 so as to drive the oil pressure actuators 4, 10, 18 ... by the electric oil pressure servo valve 46... through the command memory 40. If the oil pressure actuator 4, 10, 18 ... is moved, the position to which it is moved is detected by the corresponding detectors 2, 6, 9, 11, 19.

Thus, the oil pressure actuators 4, 10, 18... of the industrial robot are moved by a command from the CPU under the teaching mode, and when the robot arrives at the most appropriate positions, the information detected by the detectors or the command information in the CPU at such optimum positions can be stored in the memory 38 by a store command from the teaching box 30. In this way, if the movement of the oil pressure actuators 4, 10, 1 8.. and the storing of the optimum position information in the memory 38 are continuously made, the industrial robot is able to learn the positions at which it works and the working steps.That is, when the position 23 at which the torch aims is memorized by robot, the up/down and the horizontal directions of the torch 12 or determined by the oil pressure motors 13 and 10, respectively and the robot is driven in the X, Y and Z directions, while the oil pressure cylinder 18 is driven to determine a predetermined positional relation between the support member 20 and the sensor 14. In this condition, if the store command is issued from the teaching box 30, the positions of the detectors 2, 6, 9, 11 and 19 or the command value in the CPU at this instant are stored in the memory 38. When the torch is desired to be aimed at positions 23, 24 and 25, the robot is driven in the same manner as above while the relative positions of the sensor 14 and the support member 20 are changed by a certain distance by the oil pressure cylinder 18.In this condition, if the store command is issued from the teaching box, the outputs of the detectors 2, 6, 9, 11 and 19 (or the command value in the CPU), which indicate the positions of the robot at this moment, are stored in the memory 38.

In addition, in order that the robot is caused to learn the position 26 to be aimed at, the sensor 14 and the support member 20 are brought to a predetermined positional relation, and the robot is moved by a predetermined distance in the Zdirection to attain an accurate positioning without using the sensor 16. In this condition, when the store command is issued from the teaching box 30, positions of the detectors 2, 6, 9, 11 and 19 (or the command value in the CPU) are stored in the memory 38.

As well as storing of the optimum positions, operations of the industrial robot at that point can also be stored. In other words, it is possible to store a speed at which the robot moves from the optimum position to the next one, whether the sensors 14 and 16 should be drawn in or out by the oil pressure cylinders 15 and 17, and whether welding should be made at the optimum position.

It is also possible to store a path along which the robot moves from the optimum position to the next one, such as a straight path or circular arc path.

The automatic mode in which the industrial robot is automatically operated by the data stored in the memory 38 will hereinafter be described.

The automatic mode is brought about by connecting the CPU 36 to the console 32 through the change-over switch 34.

When a command from the console 32 is supplied to the CPU 36, the CPU 36 reads the data in the memory 38, and computes the momentary positions of the oil-pressure actuators 4, 10, 18 ... on the basis of information of position, speed and path. The resulting data at constant intervals of time are stored in the command memory 40. Then, when a command from the command memory 40 is sent to the D/A converter 44, servo valve 46..., the oil pressure actuators 4, 10, 18 ... operate in accordance with the information in the memory 38.

The operation that the robot is driven from target position P, to P2 will be described with reference to Fig. 3. First, the oil pressure cylinder is driven so that the output of the detector 19 coincides with the value stored in the memory 38, thereby determining the relative positions of the sensor 14 and the torch 12. In addition, the oil pressure motor 10 is driven to determine the orientation of the sensor 14 which coincides with the stored data. Then, the carrying holder 1, the up/down moving device 3 and the forward/backward arm 7 are driven until the sensors 14 and 16 detect the object 21 to be welded and the vertical plate 22. Since detected outputs from the sensors 14 and 1 6 serve to stop the robot, the movement of the robot from Pt to P2 has been completed.In other words, in the above operation, the CPU 36 first reads the points P1 and P2, computes the equation given by

and then computes L (2) 1 where L represents the distance between P, and P2, and Al a predetermined value.

Subsequently, the CPU 36 computes the following equations:

The resulting values of xl, y1 and zl are sent to the command memory 40. These values are outputted from the command memory 40 as command outputs to the comparator 40... at a certain interval to drive the robot at a speed stored previously. Thus, the robot can be driven from point (X1, Y1, Z1) to (X2, Y2, Z2) through point (x1, y,, z1). Therefore; if the relative positions of the tip end of the torch 12 and the sensor 14 are determined previously and the robot is driven, the tip end of the torch 12 can be brought to any position in the corner angle portion, thereby enabling the multilayer welding. Fig. 4 is a flow chart of the operation of the robot.In the figure, steps 58 to 61 show that the robot is driven in the X and Y directions and then driven in the Z direction. Alternatively, steps 60#6 1 #5 8#59 can be applied.

When the angle of the oil pressure motor 13 is changed in Fig. 1, mutual positional relation between the tip end of the torch 12 and the sensor 14 is changed in the forward or backward direction. However, there is a case where no change in the mutual positional relation between the tip end of the torch 12 and the sensor 14 is desired even though the angle of the oil-pressure motor 13 is changed. To this end, the oil pressure cylinder 18 is moved by a distance corresponding to the change of the angle of the oil pressure motor 13.Thus, even though the angle of the oil pressure motor 13 is changed the oil pressure cylinder 18 can be moved in response to the movement of the oil pressure motor 13 and the positions of the cylinder 18 at that point can be stored, to assure a constant mutual positional relationship in the forward or backward direction between the torch 12 and the detecting surface of the sensor 14.

While only the forward or backward positional relationship between the tip end of the torch 12 and the sensitive surface of the sensor 14 is described above, the upward or downward positional relationship between the tip end of the torch 12 and the sensitive surface of the sensor 16 can be controlled by providing another oil pressure cylinder, capable of changing the mutual positional relationships in the upward and downward direction, which corresponds to the oil pressure cylinder 18.

Fig. 5 shows a modification of the control apparatus of Fig. 2. In this figure, the comparator 42 is not used, and instead the CPU 36 compares the command output of the command memory 40 and the position signal from the detector 50, thereby deciding whether outputting of the drive command to the D/A converter 44 is required or not The other arrangements are the same as in Fig. 2.

Fig. 6 is a flow chart of part of the welding steps in which the robot performs welding operations under the control of the control apparatus of Fig. 5. The other steps are the same as in Fig. 5, and thus will not be described. From Fig. 6, it will be seen that the steps 53, 54, 55 and 56 are replaced by steps 53', 55' and 56'.

Figs. 7A and 7B show another embodiment of the corner angle portion detecting mechanism. In this embodiment, there are shown a motor 62 for driving the forward/backward sensor 14 fixed to the torch 12, a guide 66 which is fixed to the sensor 14 and moved by driving the motor 12, a detector 64 for detecting the position of the motor 62, a motor 68 for driving the up/down sensor 16 fixed to the torch 12, and a detector 70 for detecting the position of the motor 68. In this embodiment, the sensors 14 and 16 can be moved independently with respect to the torch 12. The driving motors 62 and 68 in this embodiment also serve as withdrawing devices and may be hydraulic motors, pneumatic motors or stepping motors.

While in this invention the driving devices or the actuators for the welding robot are described as the hydraulic cylinders, they may be electric motors, pneumatic cylinders or stepping motors.

When a stepping motor is used, the feedback control of the actuator as shown in Fig. 2 is not performed, but the stepping motor as the actuator is controlled in an open loop, or by a command directly issued from the CPU.

Moreover, the apparatus of the invention is not limited to the welding works, but may be applied to coating of adhesive on the opposite surfaces of plates to be bonded, painting works and so on.

Claims

1. A corner angle portion detecting apparatus comprising: a working tool; first and second position detecting sensors disposed to hold said working tool therebetween and to detect position of an object from different detecting directions, respectively; driving means for driving at least one of said sensors to change a relative positional relationship between said sensors; command means for generating a command signal to determine the relative positional relationship between at least one of said sensors and said working tool; detecting means for generating a detected output indicative of the position of said drive means; and servo means for comparing the detected output of said detecting means and said command signal from said command means to operate said driving means to cause a difference therebetween to be a particular value.

2. A corner angle portion detecting apparatus comprising: a working tool; first and second position detecting sensors disposed to hold said working tool therebetween and to detect position of an object from different detecting directions; driving means for driving at least one of said sensors to change a relative positional relationship between said sensors; detecting means for generating a detected output indicative of said driving means; and drive command means for generating a drive command to said driving means to drive at least one of said sensors by a distance corresponding to a predetermined relative positional relationship between the at least one of said sensors and said working tool.

3. A corner angle portion detecting apparatus according to Claim 1 or 2, further comprising rotation driving means for rotating said working tool and said first and second sensors simultaneously.

4. A corner angle portion detecting apparatus according to Claim 1 or 2, wherein said first sensor is fixed to said driving means and said working tool and said second sensor are moved relative to said first sensor by said driving means.

5. A corner angle portion detecting apparatus according to Claim 1 or 2, wherein said driving means includes first and second driving means for independently driving said first and second position detecting sensors.

6. A corner angle portion detecting apparatus according to Claim 1 or 3, wherein said driving means is fixed to said working tool and said at least one sensor is moved relative to said working tool by said driving means.

7. A corner angle portion detecting apparatus according to Claim 1, wherein said driving means is one selected from a group consisting of a hydraulic cylinder, a pneumatic cylinder, and an electric motor.

8. A corner angle portion detecting apparatus according to Claim 2, wherein said driving means is a stepping motor.

9. A welding robot comprising: a corner angle portion detecting mechanism having a working tool, a pair of object position detecting sensors disposed to hold said working tool therebetween and to detect position of an object from different detecting directions, and sensor-torch driving means for driving at least one of said sensors to change a relative positional relationship between said sensors; driving means provided respectively to drive said corner angle portion detecting mechanism in the X, Y, Z and rotational directions, independently; command means for generating position command signals to the sensor-torch driving means, and the X, Y, Z and rotational directions driving means to instruct positions of respective driving means;; position detecting means provided respectively to detect the position of said sensor-torch driving means and said X, Y, and Z rotational direction driving means; and servo control means provided respectively to compare each of the detected outputs of said position detecting means and each of said position command signals from said command means to operate said driving means to cause each difference therebetween to be a particular value.

10. A welding robot comprising: a corner angle portion detecting mechanism having a working tool, a pair of object position detecting sensors disposed to hold said working tool therebetween and to detect position of an object from different detecting directions, and sensor-torch driving means for driving at least one of sensors to change a relative positional relationship between said sensors; driving means provided respectively to drive said corner angle portion detecting mechanism in the X, Y, Z and rotational directions, independently; position detecting means provided respectively to detect the positions of said sensor-torch driving means and the X, Y, Z and rotational directions driving means; and drive command means for generating drive commands to said sensor-torch drive means and the X, Y, Z and rotational directions driving means to cause said working tool to be moved by a distance corresponding to a value that said working tool arrives at a target position.

1 A corner angle portion detecting apparatus constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

12. A welding robot constructed and arranged to operate substantially as hereinbefore decribed with reference to and as illustrated in the accompanying drawings.