Friction stir welding device and friction stir welding method

A friction stir welding device includes: a control device which causes a pin part to be inserted into members to be joined while causing a joining tool to rotate and which causes a joining head to move along a joint line via a robot main body; and an image pickup device which detects a junction deviation that is a deviation between the joining head and a direction along the joint line. Also, when a junction deviation is generated, this control device causes the joining head to move in a direction toward the joint line and thus resolves the junction deviation.

TECHNICAL FIELD

The present invention relates to a friction stir welding device and a friction stir welding method.

BACKGROUND ART

Patent Literatures 1 to 3 each disclose a friction stir welding device (FSW device) which generates, with a rotating joining tool, a plastic flow in members to be joined and thus joins together the members to be joined.

Patent Literature 1 discloses a friction stir welding device having a structure suitable for three-dimensional joining in which a tool (joining tool) is attached to a five-axis machining center.

Patent Literature 2 discloses a friction stir welding device in which the depth of insertion or the like of a tool (joining tool) is controlled in such a way that the load and current of a main shaft motor for rotating the tool fall within a predetermined range, thus making it less susceptible to the influence of deformation of members to be joined.

Patent Literature 3 discloses a friction stir welding device configured in such a way that a distal end part of a joining tool inserted in members to be joined is swung, thus increasing the width of a plastic flow region and increasing the joining strength.

CITATION LIST

Patent Literatures

Patent Literature 1: JP 2004-136331 A

Patent Literature 2: JP 2003-080380 A

SUMMARY OF INVENTION

Technical Problem

In friction stir welding, a joining tool is moved along a joint line (boundary line formed at a part to be joined) on members to be joined. Also, the joining tool, while rotating, is inserted into the members to be joined. Thus, the joining tool receives a reaction force (rotational reaction force) to the rotation, from the members to be joined. Therefore, an external force (Coriolis force) directed in a direction away from the joint line acts on the joining tool moving along the joint line.

A large friction stir welding device can restrain the Coriolis force with its large mass and can move the joining tool along a joint line. That is, by increasing the mass of the joining tool and peripheral apparatus and by moving the joining tool by a large and powerful drive device, it is possible to move the joining tool without being influenced by the Coriolis force. However, a small and lightweight friction stir welding device cannot sufficiently restrain the Coriolis force with its mass. Therefore, the moving joining tool may move away from a joint line and generate misalignment between the joint line and the joining tool (junction deviation).

In order to improve the quality of friction stir welding with a small friction stir welding device, it is necessary to correct the junction deviation caused by the Coriolis force.

However, Patent Literatures 1 to 3 include no description of a technique for correcting the junction deviation generated between the moving joining tool and the joint line.

For example, the correction mechanism disclosed in Patent Literature 1 is configured to change the position of the tool (joining tool) into a direction parallel to the axis of rotation of the tool, but is not configured to correct the junction deviation generated between the moving tool and the joint line.

The friction stir welding device of Patent Literature 2 is configured to change the depth of insertion of the tool (joining tool) according to the load factor of the main shaft of the main shaft motor for rotating the tool, but is not configured to correct the junction deviation generated between the joint line and the tool.

Also, the joining device (friction stir welding device) of Patent Literature 3 is configured to increase the joining strength by tilting the joining tool and thus broadening the plastic flow region, but is not configured to correct the junction deviation generated between joint line and the tool.

In this way, the friction stir welding devices disclosed in Patent Literatures 1 to 3 are not configured to be able to correct the junction deviation between the joint line and the joining tool caused by the Coriolis force acting on the rotating joining tool, and to move the joining tool accurately along the joint line to achieve high-quality friction stir welding. Therefore, there is room for improvement.

Thus, an object of the invention is to provide a friction stir welding device and a friction stir welding method that enable accurate movement of a joining tool and high-quality friction stir welding.

Solution to Problem

In order to solve the foregoing problems, according to the invention, a friction stir welding device includes: a joining head attached to a wrist head of a robot main body having multi-axis degrees of freedom; a drive device having the robot main body and capable of moving the joining head along a joint line where two members to be joined are joined together; a control device which supplies a motor drive current to an electric motor provided for the joining head, thus inserts a pin part of a joining tool into the members to be joined while rotating the joining tool, and also controls the drive device in such a way that the joining head moves along the joint line, thus performing friction stir welding of the two members to be joined; and a deviation detection device which detects a junction deviation which is a deviation between the joining head that is moving and a direction along the joint line. If the junction deviation exceeds a deviation limit value which is a predetermined maximum deviation at the time of the friction stir welding, the control device outputs to the drive device a position correction signal with a different polarity according to a difference indirection of misalignment between the joining head and the joint line, for moving the joining head in a direction toward the joint line and resolving the junction deviation, and thus moves the joining head toward the joint line, until the next time the junction deviation becomes zero. If the junction deviation becomes zero, the control device stops outputting the position correction signal to the drive device until the next time the junction deviation exceeds the deviation limit value. Also, a friction stir welding method is executed when the friction stir welding device performs friction stir welding of members to be joined.

Advantageous Effects of Invention

According to the invention, a friction stir welding device and a friction stir welding method that enable accurate movement of a joining tool and high-quality friction stir welding can be provided.

DESCRIPTION OF EMBODIMENTS

Hereinafter, friction stir welding devices according to examples of the invention will be described in detail with reference to the drawings as appropriate. In the drawings shown below, the same members are denoted by the same reference signs and duplicate explanation will be omitted as appropriate.

FIG. 1is a view showing a friction stir welding device.FIG. 2is a view showing a joining head of the friction stir welding device.

A friction stir welding device1in Example 1 is configured by having a joining head20attached to a robot main body10. Then, the robot main body10is a drive device which moves the joining head20.

As shown inFIG. 1, the robot main body10has a pedestal part10a, a lower arm10b, an upper arm10c, a wrist10d, and a wrist head10e. The joining head20is attached to the wrist head10e.

The lower arm10bis attached to the pedestal part10a. The lower arm10bcan swivel about an S-axis with respect to the pedestal part10a. Also, the lower arm10bcan tilt about an L-axis with respect to the pedestal part10a. The S-axis is an axis extending in a direction perpendicular to an installation surface G where the pedestal part10ais installed.

The upper arm10cis attached in such a way as to be able to swing about a U-axis with respect to the lower arm10b. The L-axis and the U-axis are axes parallel to each other and both orthogonal to the S-axis.

The wrist10dis attached to the upper arm10cin such a way as to be rotatable about an R-axis. The R-axis and the U-axis are axes orthogonal to each other and extending in the direction of extension of the upper arm10c.

The wrist head10eis attached to the distal end of the wrist10d. The wrist head10eis attached in such a way as to be rotatable about a B-axis. The B-axis is an axis orthogonal to the R-axis and rotates about the R-axis together with the wrist10d.

Also, the wrist head10eis rotatable about a T-axis. The T-axis is an axis orthogonal to the B-axis and rotates about the B-axis together with the wrist head10e.

The lower arm10bis attached with two degrees of freedom (about the S-axis, about the L-axis) with respect to the pedestal part10a. The upper arm10cis attached with one degree of freedom (about the U-axis) with respect to the lower arm10b. The wrist10dis attached with one degree of freedom (about the R-axis) with respect to the upper arm10c. The wrist head10eis attached with one degree of freedom (about the B-axis) with respect to the wrist10d. Then, the wrist head10erotates about the T-axis with one degree of freedom.

In this way, the robot main body10is a six-axis robot having degrees of freedom about the six axes (S-axis, L-axis, U-axis, B-axis, R-axis, and T-axis). Thus, the wrist head10e, to which the joining head20(seeFIG. 1) is attached, has six degrees of freedom with respect to the installation surface G.

The robot main body10and the joining head20are controlled by a control device30.

It should be noted that the robot main body10may be a widely used six-axis industrial robot or its equivalent. Also, the robot main body10may be driven by electric power or may be driven by oil pressure or air pressure.

As shown inFIG. 2, a joining tool2is attached to the distal end of a main body part20a, thus forming the joining head20. An electric motor (main shaft motor3) is housed inside the main body part20a, and the joining tool2is rotated at the distal end of the main body part20aby the main shaft motor3. The axis of rotation of the main shaft motor3is provided parallel to the T-axis. Thus, the joining tool2rotates about an axis of rotation parallel to the T-axis. For example, a configuration in which a chuck part20brotated by the main shaft motor3is arranged at the distal end and in which this chuck part20bholds the joining tool2may be employed.

The main shaft motor3is controlled by the control device30(seeFIG. 1) controlling the robot main body10shown inFIG. 1.

The joining tool2has a shoulder part2aand a pin part2b. The shoulder part2ais cylindrical. The pin part2bis shaped by reducing the diameter of the shoulder part2aand is formed coaxially with the shoulder part2a.

When the pin part2bis inserted into members to be joined4and the shoulder part2acomes in contact with surfaces4aof the members to be joined4, friction stir welding proceeds as the joining tool2rotates in this state.

The control device30(seeFIG. 1) moves the joining tool2to a boundary (referred to as a joint line4b) where the two members to be joined4which are to be joined by friction stir welding are butted against each other, and causes the main shaft motor3to rotate. The joint line4bis the boundary where the two members to be joined4are joined together. Then, the joining tool2is pressed against the members to be joined4so that the pin part2bis inserted into the members to be joined4. The two members to be joined4are fixed to a work table (not illustrated) with a fixing measure, not illustrated, so as not to break away from each other on the joint line4bat the time of friction stir welding.

Then, the control device30causes the joining tool2to move along the joint line4bin the state where the pin part2bof the rotating joining tool2is inserted in the members to be joined4. At this time, the control device30controls the robot main body10to move the joining tool2.

Moreover, the joining head20is held by the robot main body10with degrees of freedom about six axes. Then, the robot main body10is configured to be able to move the joining head20in a direction along the joint line4b. Also, the robot main body10is configured to be able to move the joining head20in directions toward and away from the members to be joined4.

Moreover, the friction stir welding device1can also perform friction stir welding of superimposed parts of the two members to be joined4.

For example, the control device30(seeFIG. 1) controls the robot main body10(seeFIG. 1), based on the shape of the joint line4binputted in advance as numerical data, and causes the joining tool2, inserted in the members to be joined4while rotating, to move along the joint line4b.

In this way, the friction stir welding device1in Example 1 is configured by having the joining head20shown inFIG. 2attached to the wrist head10eof the robot main body10shown inFIG. 1, and is controlled by the control device30shown inFIG. 1.

The main body part20aof the joining head20is provided with an image pickup device20c. The image pickup device20cis provided so as to pick up an image of the joint line4bon the members to be joined4at the time of friction stir welding. The image pickup device20cmay be, for example, an image pickup device utilizing a CMOS (complementary metal-oxide semiconductor) image sensor or a CCD (charged-coupled device) image sensor.

The image pickup device20cpicks up an image of the joint line4bwhen the friction stir welding device1performs friction stir welding of the members to be joined4.

FIGS. 3A and 3Bare views showing the state where the image pickup device picks up an image of the joint line.FIG. 3Ais a view showing the state where the two members to be joined are butted against each other.FIG. 3Bis a view showing the state where the two members to be joined are superimposed on each other.

As shown inFIG. 3A, when the two members to be joined4which are to be joined together by friction stir welding come in contact with and butted against each other on one side, the boundary between the two members to be joined4is the joint line4b. The control device30controls the robot main body10(seeFIG. 1) and thus moves the joining head20along the joint line4b. The image pickup device20cis arranged forward in the direction of movement of the joining head20and picks up an image of the joint line4bthat is ahead of the joining head20in the direction of movement. A signal (video signal SigV) of the image of the joint line4bpicked up by the image pickup device20cis inputted to the control device30.

Meanwhile, as shown inFIG. 3B, in the case of performing friction stir welding of the members to be joined4superimposed on each other, the joint line4bis formed at the part where the two members to be joined4are superimposed. In this case, the image pickup device20cpicks up an image of an edge of the one member to be joined4arranged on the side of the image pickup device20c, as the joint line4b.

FIG. 4is a functional block diagram of the control device.FIG. 5is a view showing ON/OFF of a position correction signal and the direction of movement of the joining head.

As shown inFIG. 4, the control device30has a control unit30a, a motor drive unit30b, an ammeter30c, and an image processing unit30d. The control unit30ais a computer device configured of a CPU (central processing unit), a memory, and an interface or the like, none of which is illustrated. The CPU executes a predetermined program and thus controls the friction stir welding device1(seeFIG. 1).

The motor drive unit30boutputs a current (motor drive current Im) supplied to the main shaft motor3of the joining head20in response to a command from the control unit30a. The ammeter30cinputs, to the control unit30a, a measurement signal (current detection signal Sig1) obtained by measuring the motor drive current Im supplied to the main shaft motor3.

The control unit30acalculates the motor drive current Im supplied to the main shaft motor3, based on the current detection signal Sig1.

Also, the control unit30acauses the main shaft motor3to rotate at a predetermined rotational speed. For example, the control unit30ais configured to maintain the rotational speed of the main shaft motor3at a predetermined rotation speed by feedback control based on a signal inputted from a rotational speed meter (not illustrated) which measures the rotational speed of the main shaft motor3.

The video signal SigV of the image picked up by the image pickup device20cis inputted to the image processing unit30d. The image processing unit30dperforms image processing on the inputted video signal SigV and extracts the joint line4b(seeFIG. 2). Then, the image processing unit30ddetects misalignment generated between the joint line4band the joining head20with respect to the direction of movement of the joining head20(seeFIG. 2).

Between the joint line4band the joining head20, misalignment is generated due to the rotation of the joining tool2(seeFIG. 2).

The control device30controls the robot main body10(seeFIG. 1) in such a way as to move the joining head20in a direction along the joint line4bas its direction of movement, as shown inFIG. 5. Since the joining tool2is rotating (in the example shown inFIG. 5, rotating clockwise) in the joining head20, a Coriolis force P1directed in a direction (in the example shown inFIG. 5, to the left, facing the direction of movement) away from the direction of movement (direction along the joint line4b) is generated in the joining head20. With the Coriolis force P1, the direction of movement of the joining head20changes to the left and the joining head20becomes misaligned from the joint line4b. In this way, due to the Coriolis force P1generated by the rotation of the joining tool2, misalignment is generated between the joint line4band the joining head20.

For example, at the time of friction stir welding, the control device30(seeFIG. 1) decides the direction of movement of the joining head20according to the shape of the joint line4binputted in advance. At this time, the control device30causes the wrist head10e(seeFIG. 1) to rotate about the T-axis so that the image pickup device20c(seeFIG. 2) is situated forward in the direction of movement of the joining head20. When there is no misalignment of the joint line4bfrom the direction of movement of the joining head20, the joint line4bextracted by the image processing unit30d(seeFIG. 4) is situated at the center (center of the image) of the image pickup range of the image pickup device20c.

If the joint line4bis misaligned from the direction of movement of the joining head20, the joint line4bextracted by the image processing unit30dshown inFIG. 4is misaligned from the center of the image by the image pickup device20c. The image processing unit30ddetects the misalignment (junction deviation ΔX) of the joint line4bfrom the center of the image, and outputs a position correction signal Sig2when this junction deviation ΔX exceeds a predetermined level. The position correction signal Sig2is inputted to the control unit30a. When the position correction signal Sig2is inputted, the control unit30acorrects the direction of movement of the joining head20so as to resolve the junction deviation ΔX of the joint line4bfrom the direction of movement of the joining head20.

In Example 1, the junction deviation ΔX is the misalignment (deviation) between the moving joining head20and the direction along the joint line4b.

Also, in Example 1, a deviation detection device which detects the junction deviation ΔX is formed by the image pickup device20cshown inFIG. 2and the image processing unit30dshown inFIG. 4.

FIG. 6is a flowchart showing a procedure for the image processing unit to output the position correction signal. The image processing unit30dof the control device30shown inFIG. 4executes the procedure shown inFIG. 6, as appropriate, and thus outputs the position correction signal Sig2.

The image processing unit30dof the control device30calculates the misalignment of the joining head20from the joint line4b(junction deviation ΔX shown inFIG. 5) (Step S1).

Moreover, the image processing unit30ddetermines whether the junction deviation ΔX is within a predetermined proper range (proper deviation) or not (Step S2). When the junction deviation ΔX reaches a predetermined level (deviation limit value ΔXmax), as indicated by a point Px inFIG. 5, the image processing unit30ddetermines that the junction deviation ΔX is not a proper deviation (No in Step S2), outputs the position correction signal Sig2(Step S3), and proceeds to Step S4.

As the image processing unit30doutputs the position correction signal Sig2, the position correction signal Sig2turns ON, as indicated by a bold dashed line inFIG. 5. Meanwhile, when the junction deviation ΔX is less than the deviation limit value ΔXmax, the image processing unit30ddetermines that the junction deviation ΔX is a proper deviation (Yes in Step S2) and ends this procedure without outputting the position correction signal Sig2.

The image processing unit30doutputs the position correction signal Sig2until the junction deviation ΔX becomes zero (No in Step S4). When the junction deviation ΔX becomes zero, the image processing unit30dstops outputting the position correction signal Sig2(Step S5) and ends this procedure. As the image processing unit30dstops outputting the position correction signal Sig2, the position correction signal Sig2turns OFF, as indicated by a bold dashed line inFIG. 5.

When the position correction signal Sig2is inputted (when the position correction signal Sig2is turned ON), the control unit30acontrols the robot main body10(seeFIG. 1) to move the joining head20forward along the direction of the joint line4band to move the joining head20in the direction such that the junction deviation ΔX is resolved. That is, when the position correction signal Sig2is inputted, the control device30(control unit30a) causes the joining head20to move in the direction toward the joint line4b.

As shown inFIG. 5, after the point Px, the joining head20moves forward toward the joint line4band the junction deviation ΔX decreases.

Also, the control unit30astops the movement of the joining head20in the direction toward the joint line4bat the time point when the output of the position correction signal Sig2is stopped (at the time point when the position correction signal Sig2turns OFF).

Also, the image processing unit30dmay be configured to stop the output of the position correction signal Sig2, for example, slightly before the junction deviation ΔX becomes zero. With this configuration, the joining head20avoids exceeding the joint line4bdue to inertia and the position of the joining head20can be accurately aligned with the joint line4b.

Also, as shown inFIG. 5, a position correction signal Sig2having different polarities (for example, positive (+) and negative (−) signal levels) depending on the difference in the direction of the misalignment of the joining head20from the joint line4b(left-right direction with respect to the direction of movement of the joining head20) may be employed. With such a position correction signal Sig2, the control unit30acan acquire the direction of the misalignment (junction deviation ΔX) of the joining head20from the joint line4b, based on the position correction signal Sig2.

As an example, as shown inFIG. 5, a configuration may be employed in which a position correction signal Sig2with a positive (+) polarity is generated when a junction deviation ΔX of leftward misalignment from the direction of movement of the joining head20is generated and in which a position correction signal Sig2with a negative (−) polarity is generated when a junction deviation ΔX of rightward misalignment from the direction of movement of the joining head20is generated. The control unit30acan determine the direction (left/right) of the junction deviation ΔX from the direction of movement of the joining head20, based on the polarity (positive/negative) of the position correction signal Sig2.

Also, when controlling the friction stir welding device1shown inFIG. 2to perform friction stir welding of the members to be joined4, the control device30in Example 1 monitors the motor drive current Im, based on the current detection signal Sig1inputted from the ammeter30c(seeFIG. 4). Moreover, the control device30controls the robot main body10(seeFIG. 1) in such a way that the motor drive current Im reaches a predetermined reference value (proper range of current).

FIG. 7is a view showing the relationship between the amount of insertion of the tool and torque.

The main shaft motor3shown inFIG. 2rotates the joining tool2. Also, at the time of friction stir welding, the pin part2bof the joining tool2is inserted into the members to be joined4while rotating. Therefore, the pin part2breceives resistance (torque P) to the rotation from the members to be joined4. As shown inFIG. 7, as the amount of insertion of the joining tool2(pin part2b) into the members to be joined4(amount of insertion of the tool λ) increases, the resistance (torque P) received by the joining tool2from the members to be joined4increases.

Also, the resistance (torque P) received by the joining tool2from the members to be joined4is a load to the rotation of the main shaft motor3. Therefore, as the torque P received by the joining tool2from the members to be joined4increases, the load to the rotation of the main shaft motor3increases and the motor drive current Im supplied to the main shaft motor3increases.

In other words, as the amount of insertion of the tool λ increases, the motor drive current Im increases. Therefore, the control device30(seeFIG. 4) can monitor the amount of insertion of the tool λ by monitoring the motor drive current Im.

For example, as shown inFIG. 7, if a proper range (proper range of insertion) for the amount of insertion of the tool λ into the members to be joined4is set, it is possible to set an upper limit value (upper limit of torque PT) and a lower limit value (lower limit of torque PL) of the torque P corresponding to the proper range of insertion.

Thus, the control device30can maintain the amount of insertion of the tool λ within the proper range of insertion by controlling the robot main body10(seeFIG. 1) in such a way that the motor drive current Im falls between a current corresponding to the upper limit of torque PTand a current corresponding to the lower limit of torque PL.

If the range between the current corresponding to the upper limit of torque PTand the current corresponding to the lower limit of torque PLis set as a proper range of current for the motor drive current Im, the control device30can maintain the amount of insertion of the tool λ within the proper range of insertion by maintaining the motor drive current Im within the proper range of current.

If the motor drive current Im is greater than the proper range of current, the control device30determines that the amount of insertion of the tool λ is greater than the proper range of insertion, and controls the robot main body10to reduce the amount of insertion of the tool λ. The amount of insertion of the pin part2binto the members to be joined4decreases, and the pressing force with which the shoulder part2apresses the members to be joined4drops. Thus, the torque P received by the joining tool2from the members to be joined4decreases, the load on the main shaft motor3is reduced, and the motor drive current Im drops.

Meanwhile, if the motor drive current Im is smaller than the proper range of current, the control device30determines that the amount of insertion of the tool λ is smaller than the proper range of insertion, and controls the robot main body10to increase the amount of insertion of the tool λ. The amount of insertion of the pin part2binto the members to be joined4increases, and the pressing force with which the shoulder part2apresses the members to be joined4increases. Thus, the torque P received by the joining tool2from the members to be joined4increases, the load on the main shaft motor3increases, and the motor drive current Im increases.

Also, when reducing the amount of insertion of the tool λ or when increasing the amount of insertion of the tool λ, the control device30controls the robot main body10in such a way that the joining tool2moves in a direction perpendicular to the members to be joined4, by a combination of movements of the lower arm10b, the upper arm10c, the wrist10d, and the wrist head10e.

In this way, at the time of friction stir welding, the control device30(seeFIG. 4) in Example 1 monitors the motor drive current Im, based on the current detection signal Sig1inputted from the ammeter30c(seeFIG. 4). Then, the control device30controls the robot main body10in such a way that the motor drive current Im falls within the proper range of current. That is, the control device30maintains the amount of insertion of the tool λ within the proper range of insertion, based on the motor drive current Im. Thus, the amount of insertion of the tool λ is maintained within the proper range of insertion, based on the motor drive current Im, and the quality of friction stir welding is improved.

Also, the relationship between the torque P received by the joining tool2from the members to be joined4(load on the main shaft motor3) and the motor drive current Im is decided, based on characteristics of the main shaft motor3, and the proper range of current corresponding to the upper limit of torque PTand the lower limit of torque PLis decided, based on the characteristics.

Moreover, the proper range of insertion for the amount of insertion of the tool λ, and the upper limit of torque PTand the lower limit of torque PLcorresponding to the proper range of insertion are suitably set, based on the material or the like of the members to be joined4.

As described above, in the friction stir welding device1in Example 1 shown inFIGS. 1 and 2, when the joining head20is misaligned from the direction of movement along the joint line4bon the members to be joined4(when the junction deviation ΔX shown inFIG. 5is generated), the joining head20moves in such a way as to resolve the misalignment. Therefore, the joining head20moves forward accurately along the joint line4b. Thus, the position accuracy at the time of performing friction stir welding of the members to be joined4is improved and the quality of friction stir welding is improved.

Also, the control device30can maintain the amount of insertion of the tool λ within the proper range of insertion by maintaining the motor drive current Im supplied to the main shaft motor3within the proper range of current. Thus, at the time of performing friction stir welding, the joining tool2(pin part2b) is inserted properly into the members to be joined4. Therefore, the quality of friction stir welding is improved.

FIG. 8is a view showing a joining head according to Example 2.FIG. 9is a view showing the relationship between a proper range of insertion for the amount of insertion of the tool and pressing load.

As shown inFIG. 8, the joining head20in Example 2 is attached to the wrist head10evia a load sensor (load cell21).

Moreover, the friction stir welding device1in Example 2 has the same configuration as the friction stir welding device1in Example 1 shown inFIGS. 1 and 2, except for having the load cell21. Also, the control device30(seeFIG. 4) resolves the misalignment (junction deviation ΔX shown inFIG. 5) of the joining head20from the joint line4b, as in Example 1.

The load cell21detects the load when the joining head20is pressed against the wrist head10e, and outputs a detection signal (load signal Sig3). The load signal Sig3is inputted to the control unit30a(seeFIG. 4) of the control device30.

The control unit30a(seeFIG. 4) of the control device30calculates the load (pressing load W) with which the joining head20presses the wrist head10e, based on the load signal Sig3. As the pressing load W increases, the amount of insertion of the tool λ increases. Therefore, the control device30can adjust the amount of insertion of the tool λ by adjusting the pressing load W. The relationship between the pressing load W and the amount of insertion of the tool λ is decided as a characteristic due to the material of the members to be joined4.

For example, as shown inFIG. 9, if a proper range (proper range of insertion) for the amount of insertion of the tool λ into the members to be joined4is set, it is possible to set an upper limit value (upper limit of load WT) and a lower limit value (lower limit of load WL) of the pressing load W corresponding to the proper range of insertion.

Thus, the control device30(seeFIG. 4) can maintain the amount of insertion of the tool λ within the proper range of insertion by controlling the robot main body10(seeFIG. 1) in such a way that the pressing load W falls between the upper limit of load WTand the lower limit of load WL.

If the range between the upper limit of load WTand the lower limit of load WLis set as a proper range of load for the pressing load W, the control device30can maintain the amount of insertion of the tool λ within the proper range of insertion by maintaining the pressing load W within the proper range of load.

If the pressing load W is smaller than the proper range of load, the control device30controls the robot main body10to increase the amount of insertion of the tool λ. The pressing force with which the shoulder part2apresses the members to be joined4increases. Thus, the load received by the joining tool2from the members to be joined4increases and the pressing load W increases.

Meanwhile, if the pressing load W is greater than the proper range of load, the control device30controls the robot main body10to reduce the amount of insertion of the tool λ. The pressing force with which the shoulder part2apresses the members to be joined4decreases. Thus, the load received by the joining tool2from the members to be joined4decreases and the pressing load W decreases.

In this way, at the time of friction stir welding, the control device30(seeFIG. 4) in Example 2 monitors the pressing load W, based on the load signal Sig3inputted from the load cell21(seeFIG. 8). Then, the control device30controls the robot main body10in such a way that the pressing load W falls within the proper range of load. Thus, the amount of insertion of the tool λ is maintained within the proper range of insertion and the quality of friction stir welding is improved.

FIG. 10is a view showing a joining head according to Example 3.FIG. 11is a view showing the relationship between a proper range of insertion for the amount of insertion of the tool and the height of the head.

As shown inFIG. 10, the joining head20in Example 3 is provided with a distance meter22(distance measuring device).

Moreover, the friction stir welding device1in Example 3 has the same configuration as that of the friction stir welding device1in Example 1 shown inFIGS. 1 and 2, except for having the distance meter22. Also, the control device30(seeFIG. 4) resolves the misalignment (junction deviation ΔX shown inFIG. 5) of the joining head20from the joint line4b, as in Example 1.

The distance meter22measures the distance from the joining head20to the surfaces4aof the members to be joined4, converts the measured distance into a measurement signal (distance signal Sig4), and outputs the measurement signal. The distance signal Sig4is inputted to the control unit30a(seeFIG. 4) of the control device30. The structure of the distance meter22(distance measuring device) is not limited. For example, a contactless distance meter22which casts a laser beam onto the members to be joined4and measures the distance to the surfaces4a, based on its reflected light, may be used. Alternatively, a contact distance meter22which has a rod (not illustrated) directed toward the members to be joined4and measures the distance to the surfaces4a, based on the amount of displacement of the rod, may be used.

The control unit30a(seeFIG. 4) of the control device30calculates the height of the joining head20(height of the head Hd) from the surfaces4aof the members to be joined4, based on the distance signal Sig4. As the height of the head Hd decreases, the amount of insertion of the tool λ increases. The relationship between the height of the head Hd and the amount of insertion of the tool λ is decided as a characteristic due to the material of the members to be joined4. Therefore, the control device30can adjust the amount of insertion of the tool λ by adjusting the height of the head Hd.

For example, as shown inFIG. 11, if a proper range (proper range of insertion) for the amount of insertion of the tool λ into the members to be joined4is set, it is possible to set an upper limit value (upper limit of height HdT) and a lower limit value (lower limit of height HdL) of the height of the head Hd corresponding to the proper range of insertion.

Thus, the control device30(seeFIG. 4) can maintain the amount of insertion of the tool λ within the proper range of insertion by controlling the robot main body10(seeFIG. 1) in such a way that the height of the head Hd falls between the upper limit of height HdTand the lower limit of height HdL.

If the range between the upper limit of height HdTand the lower limit of height HdLis set as a proper range of height for the height of the head Hd, the control device30can maintain the amount of insertion of the tool λ within the proper range of insertion by maintaining the height of the head Hd within the proper range of height.

If the height of the head Hd is higher than the proper range of height, the control device30controls the robot main body10to bring the joining head20closer to the members to be joined4and increase the amount of insertion of the tool λ. The distance between the joining tool2and the members to be joined4decreases and the height of the head Hd decreases. Meanwhile, if the height of the head Hd is lower than the proper range of height, the control device30controls the robot main body10to move the joining head20away from the members to be joined4and reduce the amount of insertion of the tool λ. The distance between the joining tool2and the members to be joined4increases and the height of the head Hd increases.

In this way, at the time of friction stir welding, the control device30(seeFIG. 4) in Example 3 monitors the height of the head Hd, based on the distance signal Sig4inputted from the distance meter22(seeFIG. 10). Then, the control device30controls the robot main body10in such a way that the height of the head Hd falls within the proper range of height. That is, the control device30in Example 3 maintains the amount of insertion of the tool λ within the proper range of insertion, based on the distance signal Sig4outputted from the distance meter22(distance measuring device). Thus, the amount of insertion of the tool λ is maintained within the proper range of insertion and the quality of friction stir welding is improved.

FIG. 12is a view showing a friction stir welding device according to Example 4.

As shown inFIG. 4, in a friction stir welding device1aaccording to Example 4, the joining head20is attached to the robot main body10via a lift device50.

The structure of the lift device50is not limited. For example, the lift device50may be configured of a servo motor50a, a ball screw50b, and a lift head50c.

The ball screw50bis provided, extending in a direction (direction of an H-axis) of moving the joining head20in a straight line, and is rotated about an axis by the servo motor50a. The lift head50cis attached to the ball screw50bby a ball screw mechanism, and moves in its axial direction according to the rotation of the ball screw50b. Then, the joining head20is attached to the lift head50c.

Also, in Example 4, the direction of the axis of rotation of the joining tool2, that is, of the axis of rotation of the main shaft motor3, is defined as the direction of the H-axis.

Moreover, though not illustrated, a lift device in which the lift head50cis moved in a straight line in the direction of the H-axis by an actuator which is driven by oil pressure or air pressure may be used.

The friction stir welding device1ain Example 4 has the same configuration as that of the friction stir welding device1in Example 1 shown inFIGS. 1 and 2, except for having the lift device50. Also, the control device30(seeFIG. 4) resolves the misalignment (junction deviation ΔX shown inFIG. 5) of the joining head20from the joint line4b, as in Example 1.

Moreover, while, inFIG. 12, the main shaft motor3is arranged outside of the main body part20a, the main shaft motor3may be housed within the main body part20a, as in Example 1.

In the friction stir welding device1ain Example 4, the one-axis degree of freedom (movement in the H-axis direction) provided for the lift device50is added to the six-axis degrees of freedom provided for the robot main body10. Therefore, the joining head20has seven-axis degrees of freedom with respect to the installation surface G. In this way, in the friction stir welding device1ain Example 4, the joining head20is held on the robot main body10with the seven-axis degrees of freedom. Then, the lift device50is configured to be able to move the joining head20in directions toward and away from the members to be joined4.

In the friction stir welding device1ain Example 4, the control device30controls the robot main body10, based on a video signal SigV inputted from the image pickup device20c, and causes the joining head20to move along the joint line4b(seeFIG. 2).

Also, the control device30performs friction stir welding of the members to be joined4while changing the amount of insertion of the tool λ in such a way that the motor drive current Im supplied to the main shaft motor3falls within a proper range of current.

At this time, the control device30according to Example 4 drives the lift device50and thus changes the amount of insertion of the tool λ. If the motor drive current Im is greater than the proper range of current, the control device30drives the servo motor50a, thus causes the joining head20to move away from the members to be joined4, and reduces the amount of insertion of the tool λ. The torque P received by the joining tool2from the members to be joined4decreases, the load on the main shaft motor3is reduced, and the motor drive current Im drops. Meanwhile, if the motor drive current Im is smaller than the proper range of current, the control device30drives the servo motor50a, thus causes the joining head20to move toward the members to be joined4, and increases the amount of insertion of the tool λ. The torque P received by the joining tool2from the members to be joined4increases, the load on the main shaft motor3increases, and the motor drive current Im increases.

In this way, the control device30according to Example 4 performs friction stir welding of the members to be joined4while controlling the lift device50to maintain the motor drive current Im within the proper range of current.

When the motor drive current Im departs from the proper range of current, the friction stir welding device1ain Example 4 can return the motor drive current Im to the proper range of current simply by driving the lift device50. Therefore, the motor drive current Im can be adjusted with less energy (electric power) than for driving the robot main body10.

Also, in the case where the joining head20is moved by the lift device50, inertia can be made smaller than in the case where the joining head20is moved by the robot main body10. Therefore, the accuracy of position control of the joining head20is improved.

FIG. 13is a view showing a joining head of a friction stir welding device according to Example 5.

As shown inFIG. 13, the joining head20of the friction stir welding device1ain Example 5 is attached to the lift head50cvia a load sensor (load cell21).

Moreover, the friction stir welding device1ain Example 5 has the same configuration as that of the friction stir welding device1ain Example 4 shown inFIG. 12, except for having the load cell21. Also, the control device30(seeFIG. 4) resolves the misalignment (junction deviation ΔX shown inFIG. 5) of the joining head20from the joint line4b, as in Example 1.

The load cell21detects the load when the joining head20is pressed against the lift head50c, and outputs a load signal Sig3. The load signal Sig3is inputted to the control unit30a(seeFIG. 4) of the control device30.

Then, as in Example 2, the control device30(seeFIG. 4) calculates the pressing load W based on the load signal Sig3. Moreover, the control device30controls the lift device50in such a way that the calculated pressing load W falls between the upper limit of load WTand the lower limit of load WLshown inFIG. 9.

In this way, if the pressing load W is smaller than the proper range of load, the control device30(seeFIG. 4) of the friction stir welding device1aaccording to Example 5 controls the lift device50to increase the amount of insertion of the tool λ. The load received by the joining tool2from the members to be joined4increases and the pressing load W increases. Meanwhile, if the pressing load W is greater than the proper range of load, the control device30controls the lift device50to reduce the amount of insertion of the tool λ. The load received by the joining tool2from the members to be joined4decreases and the pressing load W decreases. Thus, the amount of insertion of the tool λ is maintained within the proper range of insertion and the quality of friction stir welding is improved.

Also, as in Example 4, the amount of insertion of the tool λ can be adjusted with less energy. Moreover, since the inertia with respect to the movement of the joining head20can be reduced, the accuracy of position control of the joining head20is improved.

FIG. 14is a view showing a joining head of a friction stir welding device according to Example 6.

As shown inFIG. 14, the joining head20of the friction stir welding device1ain Example 6 is provided with a distance meter22.

Moreover, the friction stir welding device1ain Example 6 has the same configuration as that of the friction stir welding device1ain Example 4 shown inFIG. 12, except for having the distance meter22. Also, the control device30(seeFIG. 4) resolves the misalignment (junction deviation ΔX shown inFIG. 5) of the joining head20from the joint line4b, as in Example 1.

The distance meter22measures the distance (height of the head Hd) from the joining head20to the surfaces4aof the members to be joined4and outputs a distance signal Sig4. The control device30(seeFIG. 4) calculates the height of the head Hd, based on the distance signal Sig4. Moreover, the control device30controls the lift device50in such a way that the calculated height of the head Hd falls between the upper limit of height HdTand the lower limit of height HdL(proper range of height) shown inFIG. 11.

If the height of the head Hd is lower than the proper range of height, the control device30(seeFIG. 4) controls the lift device50to reduce the amount of insertion of the tool λ. The joining head20and the members to be joined4are moved away from each other and the height of the head Hd increases. Meanwhile, if the height of the head Hd is higher than the proper range of height, the control device30controls the lift device50to increase the amount of insertion of the tool λ. The joining head20and the members to be joined4are moved closer to each other and the height of the head Hd decreases.

In this way, the control device30(seeFIG. 4) of the friction stir welding device1ain Example 6 performs friction stir welding of the members to be joined4while controlling the lift device50to maintain the height of the head Hd within the proper range of height. Thus, the amount of insertion of the tool λ is maintained within the proper range of insertion and the quality of friction stir welding is improved.

Also, as in Example 4, the amount of insertion of the tool λ can be adjusted with less energy. Moreover, since the inertia with respect to the movement of the joining head20can be reduced, the accuracy of position control of the joining head20is improved.

FIG. 15is a view showing a joining head in a friction stir welding device according to Example 7.

As shown inFIG. 15, the friction stir welding device1ain Example 7 is provided with an ammeter (lift device ammeter50d) which measures the current (position control current Is) supplied to the servo motor50aof the lift device50. The lift device ammeter50dmeasures the position control current Is supplied to the servo motor50aand outputs a measurement signal (lift current signal Sig5). The lift current signal Sig5is inputted to the control device30(seeFIG. 12). The control unit30a(seeFIG. 4) of the control device30calculates the position control current Is supplied to the servo motor50a, based on the lift current signal Sig5.

Moreover, the friction stir welding device1ain Example 7 has the same configuration as that of the friction stir welding device1ain Example 4 shown inFIG. 12, except for having the lift device ammeter50d. Also, the control device30(seeFIG. 4) resolves the misalignment (junction deviation ΔX shown inFIG. 5) of the joining head20from the joint line4b, as in Example 1.

After driving the servo motor50aand deciding the position of the lift head50c(joining head20), the control device30(seeFIG. 4) supplies the position control current Is to the servo motor50ain order to maintain the lift head50cat that position. Thus, the position of the lift head50cis maintained and hence the position of the joining tool2of the joining head20attached to the lift head50cis maintained. Then, at the time of performing friction stir welding of the members to be joined4, the distance between the joining head20and the members to be joined4(height of the head Hd) is maintained and the amount of insertion of the tool λ is maintained.

At the time of friction stir welding, if the height of the head Hd changes, the load applied to the servo motor50achanges and therefore the position control current Is changes. In other words, if the position control current Is is constant, the height of the head Hd is constant. Also, the relationship between the position control current Is and the height of the head Hd is decided as a characteristic of the friction stir welding device1a(seeFIG. 12).

For example, as shown inFIG. 11, if a proper range of insertion for the amount of insertion of the tool λ into the members to be joined4is set, it is possible to set an upper limit value (upper limit of height HdT) and a lower limit value (lower limit of height HdL) of the height of the head Hd corresponding to the proper range of insertion.

If the position control current Is calculated based on the lift current signal Sig5becomes greater than the current at the time when the height of the head Hd is equal to the upper limit of height HdT, the control device30(seeFIG. 4) controls the lift device50to move the joining head20away from the members to be joined4and thus increase the height of the head Hd. Meanwhile, if the position control current Is calculated based on the lift current signal Sig5becomes smaller than the current at the time when the height of the head Hd is equal to the lower limit of height HdL, the control device30controls the lift device50to move the joining head20closer to the members to be joined4and thus reduce the height of the head Hd.

In this way, the control device30of the friction stir welding device1aaccording to Example 7 can maintain the amount of insertion of the tool λ within the proper range of insertion by adjusting the height of the head Hd, based on the position control current Is. Thus, the amount of insertion of the tool λ is maintained within the proper range of insertion and the quality of friction stir welding is improved.

Also, as in Example 4, the amount of insertion of the tool λ can be adjusted with less energy. Moreover, since the inertia with respect to the movement of the joining head20can be reduced, the accuracy of position control of the joining head20is improved.

As described above, the friction stir welding device1in Example 1 shown inFIGS. 1 and 2is configured to be able to correct misalignment (junction deviation ΔX shown inFIG. 5) between the joining head20and the joint line4bif such misalignment is generated, when moving the joining head20along the joint line4bformed as the boundary between the two members to be joined4which are to be jointed together. That is, the friction stir welding device1in Example 1 can bring the junction deviation ΔX generated between the joining head20and the joint line4b, close to zero.

The control device30controlling the friction stir welding device1performs image processing on the video signal SigV inputted from the image pickup device20cand extracts the joint line4b. Then, when the misalignment (junction deviation ΔX) between the center of the image and the joint line4bexceeds a predetermined level, the control device30determines that the junction deviation ΔX is generated between the joining head20and the joint line4b, and corrects the junction deviation ΔX. Specifically, the control device30controls the robot main body10to move the joining head20in the direction of the joint line4b. Thus, the junction deviation ΔX is converged toward zero and the joining head20moves accurately along the joint line4b. Therefore, the members to be joined4are joined together by friction stir welding along the joint line4b. That is, since the area where friction stir welding is performed is not largely away from the joint line4b, high-quality friction stir welding is achieved.

In friction stir welding, the joining head20moves along the joint line4bin the state where the joining tool2attached to the joining head20shown inFIG. 2is rotating and where the pin part2bformed in the joining tool2is inserted in the members to be joined4. Then, due to the reaction force received by the rotating pin part2bfrom the members to be joined4, the Coriolis force P1(seeFIG. 5) causing the junction deviation ΔX between the joining head20and the joint line4bis generated.

If the friction stir welding device1is large, the friction stir welding device1can restrain the Coriolis force P1with its large mass and can move the joining head20without generating the junction deviation ΔX between the joining head20and the joint line4b(or in the state where the junction deviation ΔX is small).

For example, in the friction stir welding device1in Example 1, the joining head20is attached to the robot main body10. The robot main body10is small-sized and lightweight in order to efficiently move the moving parts such as the lower arm10band the upper arm10c. Therefore, the joining head20tends to be displaced by the Coriolis force P1generated by the rotation of the pin part2b, and the junction deviation ΔX tends to occur between the joining head20and the joint line4b.

Thus, the control device30in Example 1 is configured to be able to correct the junction deviation ΔX generated between the joining head20and the joint line4b. Thus, even with the friction stir welding device1(seeFIG. 1) in which the joining head20is attached to the small-sized and lightweight robot main body10, friction stir welding accurately along the joint line4bis possible and high-quality friction stir welding is possible.

Also, since the miniaturization of the friction stir welding device1is possible, for example, a portable friction stir welding device1with a high degree of freedom in installation can be provided.

Also, the control device30controlling the friction stir welding device1in Example 1 monitors the amount of insertion of the tool λ by monitoring the current (motor drive current Im) supplied to the main shaft motor3. Then, friction stir welding of the members to be joined4can be performed in such a way that the amount of insertion of the tool λ is maintained within a predetermined proper range of insertion. Therefore, the amount of insertion of the pin part2binto the members to be joined4is kept constant and high-quality friction stir welding is possible.

Also, as shown inFIG. 12, the friction stir welding device1ain Example 4 has the lift device50. Then, the joining head20is attached to the robot main body10via the lift device50. Therefore, the control device30can maintain the amount of insertion of the tool λ at a constant level by controlling the lift device50.

Since the lift device50can be driven with less energy (electric power) than the robot main body10, the energy that is needed to maintain the amount of insertion of the tool λ at a constant level is reduced.

It should be noted that the invention is not limited to the examples above. For example, the examples above are described in detail in order to explain the invention intelligibly. The invention is not necessarily limited to having all of the configurations described above.

Also, a part of the configuration in one example can be replaced by the configuration in another example. Moreover the configuration in one example can be added to the configuration in another example.

In addition, the invention is not limited to the examples above and suitable design changes can be made without departing from the scope of the invention.

For example, the joining head20(seeFIG. 2) of the friction stir welding device1(seeFIG. 1) described in Examples 1 to 3 is provided with the image pickup device20c(seeFIG. 2). Also, the image processing unit30d(seeFIG. 4) of the control device30detects the misalignment between the joint line4b(seeFIG. 2) and the joining head20, based on the video signal SigV inputted from the image pickup device20c.

This configuration is not limiting. A configuration in which a laser beam is cast onto the members to be joined4(seeFIG. 2) so as to detect the joint line4b(seeFIG. 2) can be employed.

For example, a contactless distance meter (not illustrated) which casts a laser beam onto the members to be joined4(seeFIG. 2) and thus measures the distance from the members to be joined4is provided forward in the direction of movement of the joining head20(seeFIG. 2). Since the joint line4b(seeFIG. 2) is a recessed part on the surfaces4a(seeFIG. 2) of the members to be joined4, the distance from this part to the distance meter is longer. The control device30(seeFIG. 4) can detect the misalignment between the joint line4band the joining head20by extracting the part (recessed part) with a longer distance from the distance meter, as the joint line4b.

With such a configuration, the image pickup device20c(seeFIG. 2) and the image processing unit30d(seeFIG. 4) are not needed and the structure of the friction stir welding device1(seeFIG. 1) can be simplified.

Also, the image processing unit30d(seeFIG. 4) outputs the position correction signal Sig2when the junction deviation ΔX reaches the deviation limit value ΔXmax, as shown inFIG. 5. This configuration is not limiting. The image processing unit30dmay be configured to output the position correction signal Sig2indicating the magnitude of the junction deviation ΔX when the junction deviation ΔX becomes greater than zero. In this case, the control unit30a(seeFIG. 4) can acquire the magnitude of the junction deviation ΔX, based on the position correction signal Sig2. Therefore, the control device30(seeFIG. 4) can move the joining head20(seeFIG. 2) in such a way that the junction deviation ΔX is constantly zero, and can effectively resolve the misalignment generated between the joint line4b(seeFIG. 2) and the joining head20.

Also, the robot main body10(seeFIG. 1) in Examples 1 to 7 has six-axis degrees of freedom. This configuration is not limiting and the degree of freedom of the robot main body10is not limited. For example, the robot main body10may have five-axis or fewer degrees of freedom, or may have seven-axis or more degrees of freedom.

REFERENCE SIGNS LIST