JP2005059048A - Electric spot welding gun - Google Patents

Abstract

A ball screw is used to smoothly advance and retract a rod, and a circulation path of a first ball group that exerts a power transmission action, and a circulation path of a second ball group that acts as a rotation stop of components. Set each route appropriately.
A rod having a hollow portion, a cylindrical anti-rotation portion 30a fixed to an end of the rod, a ball spline shaft 32 having spline grooves 31a, 31b, and 31c, and a ball screw groove on an inner wall. In the electric spot welding gun having the formed hollow rotor, the rotation preventing unit 30a includes three first circulation paths 59a, 59b, 59c in which the first ball group is inserted and circulated, and the second ball group. Are inserted and circulated and three second circulation paths 60a, 60b, 60c are provided. The second circulation paths 60a, 60b, and 60c are arranged radially in cross section around the axis of the rotation preventing unit 30a.
[Selection] Figure 4

Description

  The present invention relates to an electric spot welding gun that welds a workpiece by energizing the workpiece while the workpiece is sandwiched between electrode tips, and more particularly, to an electric spot welding gun that can open and close an electrode tip with a motor.

  Conventionally, spot welding is used for welding of workpieces, but recently, an electric spot welding gun using a servo motor is becoming widespread from the viewpoint of controlling an electrode tip. According to the electric spot welding gun, it is possible to flexibly cope with workpieces having different thicknesses.

  On the other hand, the electric spot welding gun is sometimes used as an end effector of an articulated robot. From the viewpoint of the operation performance of the articulated robot, the electric spot welding gun is desired to be small and light.

  From such a background, there has been proposed an electric spot welding gun which is formed such that a ball screw groove and a ball spline groove cross on a rod provided with an electrode tip and has an advance / retreat function and a detent function (for example, a patent) Reference 1). Such an electric spot welding gun can shorten the overall length.

  A spot welding gun having a hollow rotor structure has been proposed (see, for example, Patent Document 2). Thus, it is preferable that the rotor has a hollow structure because the entire electric spot welding gun can be made compact.

  Further, as a mechanism for smoothly moving the rod forward and backward, for example, it is considered to apply a ball screw spline unit (see, for example, Patent Document 3).

JP 2001-314972 A JP 2002-28788 A Japanese Utility Model Publication No. 6-84776

  By the way, in the technique of Patent Document 1, a ball screw groove and a ball spline groove are formed on the rod, and in the technique of Patent Document 2, a non-rotating spline groove is formed on the rod. Therefore, when the rod is extended from the housing, the ball screw groove and the ball spline groove are also exposed to the outside. In order to protect the ball screw grooves and ball spline grooves from foreign matter such as spatter, moisture, dust, etc., it is necessary to cover them with a stretchable protective material such as bellows, but these spatters scattered during welding are hot. The cover will be damaged and will not be adequately protected.

  When the rod does not have a ball spline groove, for example, it is necessary to provide a guide member as a rod detent. However, when such a guide member is provided, the entire spot welding gun becomes larger, and is smaller and lighter. Contrary to the request for conversion.

  Further, in the technique of Patent Document 3, the ball inserted into the spiral ball groove circulates through a guide passage on the outer diameter side of the ball screw groove. Therefore, when the rod on the inner diameter side of the rotor is advanced and retracted by rotating the rotor, it is necessary to provide a ball guide passage in the rotor on the outer diameter side of the rod, and the rotor structure is complicated. The moment of inertia increases. Thereby, the control responsiveness of the rotor and the rod is lowered.

  Furthermore, the ball inserted into the spiral ball groove has a power transmission function. On the other hand, in addition to these balls, a ball having a function of preventing rotation of the component may be used. No technology has been proposed that can be set compactly without causing interference between the circulation paths of the two types of balls.

  The present invention has been made in consideration of such a problem, and uses a ball screw to smoothly advance and retract the rod and to transmit power, and the circulation path of the first group of balls and the rotation of the components. It is an object of the present invention to provide an electric spot welding gun capable of appropriately setting each path of the circulation path of the second ball group that exerts a stopping action.

  The electric spot welding gun according to the present invention is an electric spot welding gun that performs welding by holding a workpiece between a fixed electrode tip and a movable electrode tip, and includes the movable electrode tip at one end and a hollow portion at the other end. A rod, a cylindrical anti-rotation portion fixed to the other end of the rod, and a plurality of spline grooves fixed in the housing and extending in the axial direction, are inserted into the anti-rotation portion and the hollow portion of the rod A ball spline shaft and a hollow rotor that is rotated by receiving electromagnetic force from a stator provided in the housing and has a ball screw groove formed on the inner wall, and the rotation preventing portion is formed on the outer wall. A plurality of spiral recesses and a plurality of first internal passages communicating with both end portions of the spiral recesses, the first circulation path in which the first ball group is inserted, and an axial direction formed on the inner wall An inner surface recess, and a plurality of second circulation passages, each of which includes a second internal passage communicating with both ends of the inner surface recess, into which the second ball group is inserted, and the spiral recess of the first ball group Is inserted from the outer wall of the anti-rotation portion and is engaged with the ball screw groove, and the second ball group inserted into the inner surface recess is the anti-rotation portion. It protrudes from the inner wall and engages with the spline groove, and the first ball group and the second ball group circulate in the first circulation path and the second circulation path as the rod advances and retreats, respectively. The plurality of second circulation paths are arranged in a radial cross section around the axis of the rotation preventing portion.

  Thereby, it is possible to appropriately set each path of the first circulation path in which the first ball group circulates and the second circulation path in which the second ball group circulates. Further, since the second circulation path is radially arranged in section around the axis of the rotation preventing portion, it can be engaged with the ball spline shaft in a balanced manner.

  In this case, on the projection plane perpendicular to the axis of the rotation preventing portion, at least a part of the first internal passage is at least part of the fan-shaped arc portion having sides adjacent to the second internal passage. When intersecting, the first internal passage can be disposed in the fan-shaped space between the second circulation paths, and the space inside the rotation preventing portion can be used effectively. Therefore, the outer diameter of the rotation preventing portion can be reduced to reduce the moment of inertia, and the control response of the rotor and the rod can be further improved.

  On the projection plane perpendicular to the axis of the rotation prevention unit, the first internal passage may be set as a path that advances in the forward direction in the circumferential direction, once returns in the reverse direction, and then advances in the forward direction again. Thereby, a smooth substantially S-shaped passage can be formed by effectively using the space between two adjacent second internal passages, and the first ball group can be passed smoothly.

  The minimum distance of the first internal passage with respect to the axis is larger than the maximum distance of the second internal passage with respect to the axis on a projection plane perpendicular to the axis of the rotation prevention unit, and the first distance with respect to the axis When the angle occupied by one internal passage is set to be larger than the angle occupied by the fan-shaped portion having adjacent sides of the second internal passage as sides, the first internal passage becomes a gentle path with a small degree of bending, and the first ball group Can pass smoothly.

  Furthermore, the second circulation path is divided into a plurality along the extending direction of the spline groove, and the first internal passage passes between the divided second circulation paths. In this way, the first internal passage becomes a gentle path with a small degree of bending, and can smoothly pass the first ball group. Also, the moment of inertia can be reduced by reducing the outer diameter of the rotation preventing portion, and the control response of the rotor and the rod can be further improved.

  According to the electric spot welding gun according to the present invention, each path of the first circulation path in which the first ball group circulates and the second circulation path in which the second ball group circulates is appropriately set. Can do. Further, since the second circulation path is radially arranged in section around the axis of the rotation preventing portion, it can be engaged with the ball spline shaft in a balanced manner.

  Hereinafter, an embodiment of an electric spot welding gun according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the electric spot welding gun 10 according to the present embodiment is a so-called C-shaped welding gun, and is provided as an end effector at the tip of the articulated robot 12. The electric spot welding gun 10 has a function of welding the workpiece W under the control of the control unit 14, and can be moved to various positions and take various postures by the operation of the articulated robot 12. Further, the electric spot welding gun 10 includes a rod advance / retreat mechanism 90, and the rod 24 advances / retreats by the action of the rod advance / retreat mechanism 90.

  The electric spot welding gun 10 includes a C-shaped yoke 18 attached to the articulated robot 12, a fixed electrode tip 20 attached to one end of the yoke 18, and an electric drive unit 16 provided at the other end. Have The yoke 18 may have an equalizing function that can move in the direction of arrow A with respect to the articulated robot 12.

  Below the electric drive unit 16 (points in the direction of the arrow A1 and the direction of the arrow A2 in the opposite direction is referred to as the top), a rod 24 that advances and retreats under the action of the built-in servo motor 40 (see FIG. 2) protrudes. . A movable electrode tip 26 is attached to the lower end of the rod 24 so as to face the fixed electrode tip 20.

  Next, the configuration of the electric drive unit 16 will be described with reference to FIGS. 2 and 3.

  The electric drive unit 16 is configured based on a housing 28 which is a main body, the rod 24, a cylindrical anti-rotation portion 30 a fixed to the upper end of the rod 24, and a ball whose upper portion is fixed to the housing 28. It has a spline shaft 32 and a rotor 36 that is hollow and has ball screw grooves 35a, 35b, and 35c formed in a spiral shape on the inner wall. As will be described later, the rotation preventing unit 30 a prevents the rod 24 from rotating with respect to the ball spline shaft 32 and also serves to transmit a thrust force that causes the rod 24 to advance and retreat from the servo motor 40.

  An upper portion of the ball spline shaft 32 is fixed to the housing 28 by a nut 25, and a D-cut surface 33 (see FIG. 3) is formed on the fixed portion, thereby providing a detent function for the housing 28. An appropriate sealing process is applied to the connection portion between the ball spline shaft 32 and the housing 28.

  The housing 28 can be divided into members 28a, 28b, 28c, 28d and 28e. Seals 37a, 37b, 37c and 37d are provided at the connecting portions of these members 28a, 28b, 28c, 28d and 28e.

  The stator 34 and the rotor 36 constitute a servo motor 40. The rotor 36 includes a plurality of magnets 36b on the outer wall, and rotates by receiving electromagnetic force from the stator 34 provided on the housing 28. The stator 34 is energized from the control unit 14 (see FIG. 1) to generate electromagnetic force, and can rotate the rotor 36 forward and backward depending on the energization direction. The rotor 36 is pivotally supported by bearings 42 and 44 on the upper side and the lower side, respectively, and can rotate smoothly. A rotation detection unit 46 such as a resolver is provided at the upper end of the rotor 36, and a signal related to the rotation angle of the rotor 36 can be transmitted to the control unit 14.

  The signal lines and power lines of the rotation detection unit 46 and the servo motor 40 are connected to the control unit 14 via a wire connector 49 having a sealing function. The connector 49, the ball spline shaft 32 and the housing 28 are sealed (annular seal 51, which will be described later), and the seals 37a, 37b, 37c, and 37d make the entire housing 28 waterproof and dust-proof. It is possible to prevent foreign substances such as the like from entering, and to protect the internal servo motor 40, the rotation detector 46, the bearings 42 and 44, and the like.

  The rod 24 includes the movable electrode chip 26 on the lower side via an insulator 48, and includes a hollow portion 24a on the upper side. The movable electrode chip 26 can be supplied with power by connecting a power cable to the terminal 26a.

  Of the rod 24, the outer wall 24c of the portion that is exposed when extended and is housed in the housing when retracted has a cylindrical shape. Accordingly, it is possible to reduce the adhesion and biting of foreign matters such as spatter, water droplets and dust, and the rod 24 can be easily manufactured.

  The rod 24 is slidably supported by a member 28e constituting the housing 28 via a cylindrical metal bush (slide bearing) 50. The rod 24 can be reliably held by supporting the outer wall 24c by the metal bush 50.

  A grease nipple 52 for supplying grease to the hollow portion 24a through the passage 24b is provided at the distal end portion of the rod 24. A grease nipple 54 for supplying grease to the metal bush 50 is provided on the outer wall of the member 28 e in the vicinity of the metal bush 50. An annular seal 51 that contacts the outer wall 24 c of the rod 24 is provided at the lower end of the member 28 e constituting the housing 28.

  On the outer wall of the ball spline shaft 32, three spline grooves 31a, 31b, 31c are provided at equal intervals so as to extend in the axial direction. The ball spline shaft 32 is inserted into the rotation preventing portion 30a. Further, when the rod 24 is retracted, the ball spline shaft 32 is inserted into the hollow portion 24 a of the rod 24.

  As shown in FIGS. 3 and 4, in the rotation preventing portion 30a, a plurality of balls (first ball group) 56 are rotatably inserted into three spiral recesses 55a, 55b, and 55c provided on the outer wall. , Part protrudes from the outer wall. Portions protruding from the outer wall of the ball 56 are inserted into the ball screw grooves 35a, 35b, and 35c, and transmit the rotational force of the rotor 36 to the rotation preventing portion 30a. The spiral concave portions 55a, 55b, and 55c are formed in a spiral shape on the outer wall of the rotation preventing portion 30a, and end portions 70a and 70b of the spiral concave portion 55a, end portions 72a and 72b of the spiral concave portion 55b, and end portions of the spiral concave portion 55c. The parts 74a and 74b communicate with each other by three first internal passages 57a, 57b, and 57c (see FIG. 5) provided inside the rotation preventing part 30a.

  The first internal passage 57a enters the rotation preventing portion 30a so as to draw a smooth arc starting from the end portion 70a, proceeds in the forward direction in the circumferential direction, and once in the substantially axial direction while slightly reversed in the reverse direction. It extends, further reverses and reaches the end portion 70b while proceeding in the positive direction. As described above, the first internal passage 57a effectively uses the space between the two adjacent second circulation passages 60a and 60c to form a smooth substantially S-shaped passage and allows the ball 56 to pass smoothly. be able to. Similarly, the first internal passage 57b forms a smooth substantially S-shaped passage between the end portions 72a and 72b, and the first internal passage 57c forms a smooth substantially S-shaped passage between the end portions 74a and 74b.

  As described above, the spiral recesses 55a, 55b, 55c and the first internal passages 57a, 57b, 57c form three first circulation paths 59a, 59b, 59c, and the ball 56 has the first circulation path 59a, It is tightly inserted into 59b and 59c.

  As a result, the rotational force of the rotor 36 is converted into a force that advances and retracts the rotation preventing portion 30a, and the rotation preventing portion 30a and the rod 24 advance and retract. As the rod 24 advances and retreats, the ball 56 circulates while rolling along the first circulation paths 59a, 59b, and 59c, and the sliding resistance between the rotation preventing portion 30a and the rotor 36 is reduced. Therefore, the rod 24 can smoothly advance and retreat, and the rotational force can be transmitted very smoothly.

  The rotation preventing portion 30a includes three inner recesses 62a, 62b, 62c extending in the axial direction, and second inner passages 61a, 61b, 61c communicating with both ends of the inner recesses 62a, 62b, 62c, respectively. Two circulation paths 60a, 60b and 60c are provided, and a plurality of balls (second ball group) 58 are densely arranged in the second circulation paths 60a, 60b and 60c. Each ball 58 can circulate while rolling in the second circulation paths 60a, 60b, 60c. Some of the balls 58 in the inner surface concave portions 62a, 62b, 62c on the inner wall side of the rotation preventing portion 30a protrude from the inner wall and are inserted into the spline grooves 31a, 31b, 31c, respectively. The ball 58 protruding from the inner wall of the rotation preventing portion 30a acts as a detent when the rod 24 moves back and forth. In other words, the rotation preventing portion 30a receives a rotational force from the rotor 36 via the outer ball 56, but prevents rotation because a part of the inner ball 58 is inserted into the spline grooves 31a, 31b, 31c. The rotation of the portion 30a is prevented, and as a result, the outer ball 56 moves up and down along the ball screw grooves 35a, 35b, and 35c, and the rotation preventing portion 30a and the rod 24 move forward and backward with respect to the housing 28. .

  Further, since the ball 58 can roll while being in contact with the second circulation paths 60a, 60b, 60c and the spline grooves 31a, 31b, 31c, the sliding friction is prevented, and the rod 24 can advance and retreat very smoothly. It is.

  As shown in FIG. 5, when the rotation preventing part 30a is viewed on the projection plane perpendicular to the axis C, the fan-shaped arc part 98a having two adjacent second circulation paths 60a and 60c as sides and the first inner part The passages 57a intersect with each other, and the first internal passages 57a are set as paths that enter the fan shape 98. Similarly, the first internal passage 57b enters the fan-shaped interior with the second circulation paths 60a and 60b as sides, and the first internal passage 57c is the fan-shaped interior with the second circulation paths 60b and 60c as sides. I'm stuck in. That is, the minimum distance R2 of the first internal passages 57a, 57b, 57c with respect to the axis C is set smaller than the longest distance R1 of the second internal passages 61a, 61b, 61c with respect to the axis C.

  In this way, at least a part of the first internal passages 57a, 57b, 57c intersects the fan-shaped arc portion having the adjacent sides of the second circulation paths 60a, 60b, 60c as sides. By setting, the first internal passages 57a, 57b, and 57c can be disposed in the space between the second circulation paths 60a, 60b, and 60c, and the space inside the rotation prevention unit 30a can be effectively used. Can do. Therefore, the moment of inertia can be reduced by reducing the outer diameter of the rotation preventing portion 30a.

  As is apparent from FIG. 5, the three second circulation paths 60 a, 60 b and 60 c are set radially about the axis C and can be engaged with the ball spline shaft 32 in a well-balanced manner.

  The configuration of the electric spot welding gun 10 and the rod advance / retreat mechanism 90 has been described above. However, as described above, the rod advance / retreat mechanism 90 is incorporated in the electric spot welding gun 10 and is electrically driven spot welding. In the gun 10, the rod 24, the rotation prevention unit 30 a, the ball spline shaft 32, the rotor 36, and the balls 56 and 58 correspond to the rod advance / retreat mechanism 90.

  Next, the operation of the electric spot welding gun 10 and the rod advance / retreat mechanism 90 configured as described above will be described.

  First, the articulated robot 12 (see FIG. 1) is operated to move the electric spot welding gun 10 to the vicinity of the workpiece W. The electric spot welding gun 10 is disposed at a position where the fixed electrode tip 20 of the yoke 18 contacts one surface of the workpiece W.

  Next, the controller 14 extends the rod 24 by rotating the servo motor 40 in a predetermined positive direction. As described above, the movable electrode tip 26 at the tip of the rod 24 is moved to grip the workpiece W together with the fixed electrode tip 20, and then energized to weld the workpiece W.

  At this time, as described above, when the rotor 36 constituting the servo motor 40 rotates, the rotational force is transmitted to the rotation preventing unit 30 a via the ball 56. Since a part of the ball 58 protrudes from the inner wall of the rotation preventing portion 30a and is inserted into the spline grooves 31a, 31b, 31c of the ball spline shaft 32 fixed to the housing 28, the rotation preventing portion 30a rotates. The rotation preventing part 30a and the rod 24 extend (see FIG. 6).

  Further, the sliding resistance is reduced by the action of the balls 56 and 58, and the rotation preventing portion 30a and the rod 24 can be smoothly extended.

  The extended rod 24 exposes the outer wall 24c, but the outer wall 24c has a smooth cylindrical shape, and is less likely to be spattered or dusted.

  Since the control unit 14 can detect the amount of extension of the rod 24 based on the signal from the rotation detection unit 46, the control unit 14 can appropriately perform advance / retreat control according to the thickness of the workpiece W. Further, the control unit 14 can perform control while switching between position control for controlling the position of the rod 24 and force control for controlling the clamping force for gripping the workpiece W.

  After the welding is completed, the control unit 14 rotates the servo motor 40 in the reverse direction to retract the rod 24. At this time, even when spatter, water droplets, dust or the like adheres to the rod 24, the spatter and dust can be prevented from entering the electric drive unit 16 by the annular seal 51 and the metal bush 50.

  Next, the anti-rotation parts 30b and 30c which are the 1st and 2nd modification of the anti-rotation part 30a used for the electric spot welding gun 10 will be described with reference to FIGS. In addition, in the rotation prevention parts 30b and 30c, the same code | symbol is attached | subjected about the same location as the said rotation prevention part 30a, and the detailed description is abbreviate | omitted.

  As shown in FIG. 7, in the rotation preventing portion 30b as the first modified example, the first internal passages 92a and 92c corresponding to the first internal passages 57a and 57c are located outside the second internal passages 61a and 61c. It is set to pass through the radial side. Although not shown in FIG. 7, the first internal passage 92b corresponding to the first internal passage 57b is set so as to pass the outer diameter side of the second internal passage 61b. That is, as shown in FIG. 8, the maximum distance R1 of the second internal passages 61a, 61b, 61c with respect to the axis C on the projection plane perpendicular to the axis C of the rotation preventing unit 30b is the first internal to the axis C. It is set to be larger than the minimum distance R2 of the passages 92a, 92b, and 92c. Further, the angle occupied by the first internal passages 92a, 92b, and 92c with respect to the axis C is 180 °, and the angle occupied by the fan-shaped 98 having two adjacent second circulation paths 60a and 60c as sides is 120 °. It is set larger. Therefore, the first internal passages 92a, 92b, and 92c become a gentle path with a small degree of bending, and the ball 56 can pass smoothly.

  Further, since the longest distance R1 is smaller than the minimum distance R2, the outer cylindrical portion having the first inner passages 92a, 92b, and 92c is formed with the rotation preventing portion 30b as a boundary with the diameter R3 where R1 <R3 <R2. It is also possible to divide it into an inner cylindrical part having the second internal passages 61a, 61b, 61c. In this case, the two cylindrical portions can be individually manufactured. In FIG. 8, since the three first internal passages 92a, 92b, and 92c partially overlap each other, only the first internal passage 92a is represented by a solid line for easy understanding, and the remaining first internal passages are shown. The passages 92b and 92c are indicated by broken lines.

  Next, a rotation preventing unit 30c as a second modification will be described with reference to FIGS.

  As shown in FIG. 9, in the rotation preventing unit 30c, the circulation paths corresponding to the second circulation paths 60a and 60c (see FIG. 5) are each provided in the axial direction so as to be divided into two. The paths 78a and 80a correspond to the second circulation path 60a, and the second circulation paths 78c and 80c correspond to the second circulation path 60c. Although not shown in FIG. 9, the circulation paths corresponding to the second circulation path 60 b (see FIG. 5) are provided by being divided into two in the axial direction, and the second circulation paths 78 b and 80 b are provided. This corresponds to the second circulation path 60b.

  The second circulation paths 78a and 80a are provided side by side along the direction in which the spline groove 31a extends. Similarly, the second circulation paths 78b and 80b are provided along the direction in which the spline groove 31b extends. The second circulation paths 78c and 80c are provided along the direction in which the spline groove 31c extends.

  As shown in FIGS. 9 and 10, the first internal passage 94a corresponding to the first internal passage 57a (see FIG. 5) is provided so as to pass through a space 82a between the second circulation passages 78a and 80a. ing. Similarly, the first internal passage 94b corresponding to the first internal passage 57b passes through the space 82b between the second circulation passages 78b and 80b, and the first internal passage 94c corresponding to the first internal passage 57c. Passes through a space 82c (not shown) between the second circulation paths 78c and 80c. Thus, by setting the first internal passages 94a, 94b, 94c so as to pass through the spaces 82a, 82b, 82c, the space inside the rotation prevention unit 30c can be used effectively, and the rotation prevention unit 30c. The moment of inertia can be reduced by reducing the outer diameter of the.

  Further, the angle (for example, 180 °) occupied by the first internal passages 94a, 94b, and 94c with respect to the axis C is adjacent to the second circulation passages 78a (and 80a), 78b (and 80b), and 78c (and 80c). It can be set to be larger than 120 ° which is the two interval angles. Therefore, the first internal passages 94a, 94b, and 94c become a gentle path with a small degree of bending, and the ball 56 can pass smoothly.

  In FIG. 10, since the three first internal passages 94a, 94b, and 94c partially overlap each other, only the first internal passage 94a is shown by a solid line for easy understanding, and the remaining first internal passages 94a, 94b, and 94c overlap each other. The passages 94b and 94c are indicated by broken lines.

  As described above, according to the electric spot welding gun 10 according to the present embodiment, the rod 24 provided with the movable electrode tip 26 does not require a groove for driving back and forth or a groove for preventing rotation, and the outer wall 24c can be formed in a smooth cylindrical shape. Therefore, an accordion mechanism or the like for protecting the rod 24 is unnecessary.

  Further, the rod 24 is disposed so as to be inserted into the inner diameter side of the rotor 36, and the ball spline shaft 32 is disposed so as to be inserted into the inner diameter side of the rod 24. On the other hand, the stator 34 is provided on the outer periphery of the rotor 36. That is, the stator 34, the rotor 36, the rod 24, and the ball spline shaft 32 are arranged coaxially, and the electric drive unit 16 can be made a compact structure that is short in the axial direction.

  Furthermore, since the outer wall 24c of the rod 24 has a columnar shape, a cylindrical metal bush 50 or an annular seal 51 can be applied. Thereby, it is possible to reliably hold the rod 24 and prevent backlash. Moreover, entry of foreign matters such as spatter, water droplets, and dust can be prevented.

  In addition, according to the electric spot welding gun 10 according to the present embodiment, the rotor 36 is light in weight because it has a hollow structure, and also has good control responsiveness because the rotational moment is small.

  Furthermore, since the load applied to the ball spline shaft 32 is only a weak reaction force for preventing the rotation of the rotation preventing portion 30a and the rod 24, the ball spline shaft 32 can be set to have a small diameter. Since the rod 24 is disposed on the inner diameter side of the rotor 36 and the ball spline shaft 32 inserted into the hollow portion 24a can be set to a small diameter, the rod 24 can also be set to a relatively small diameter.

  Since the ball spline shaft 32 and the rod 24 can be set to have a small diameter, the electric drive unit 16, the electric spot welding gun 10, and the rod advance / retreat mechanism 90 can be made lighter.

  Further, since the rod 24 can be smoothly advanced and retracted by the action of the balls 56 and 58 of the rotation preventing portion 30a, the servo motor 40 is sufficient in a small capacity, and the weight can be reduced.

  Furthermore, the ball 56 inserted into the spiral recesses 55a, 55b, 55c circulates and moves through the first internal passages 57a, 57b, 57c on the inner diameter side of the spiral recesses 55a, 55b, 55c. That is, the ball 56 circulates only in the first circulation paths 59a, 59b, 59c in the rotation preventing unit 30a, and is not supplied to the rotor 36 on the outer side. Therefore, since it is not necessary to provide the guide path for the ball 56 in the rotor 36, the rotor 36 can be made thin, and the moment of inertia can be set small, whereby the control response of the rotor 36 and the rod 24 can be reduced. Will be improved.

  According to the electric spot welding gun 10 according to the present embodiment, each path of the first circulation path in which the first ball group circulates and the second circulation path in which the second ball group circulates is prevented from rotating. It can be set compactly in the part 30a. Further, since the first circulation paths 59a, 59b, 59c and the second circulation paths 60a, 60b, 60c can be set so as to overlap in the axial direction, the dimension of the electric spot welding gun 10 in the axial direction is shortened. can do.

  Further, since the second circulation paths 60a, 60b, and 60c are arranged in a radial cross section around the axis C of the rotation preventing portions 30a, 30b, and 30c, they can be engaged with the ball spline shaft 32 in a balanced manner. it can.

  In the above embodiment, the example in which the three spiral recesses 55a, 55b, and 55c are provided on the outer walls of the rotation preventing portions 30a, 30b, and 30c has been shown. An appropriate number can be set based on the speed and thrust required for operation. For example, in order to set the speed of the rod 24 to be slow, the number of spiral recesses may be set to 1, and the number of ball screw grooves corresponding to the ball screw grooves 35a, 35b, and 35c may be set to 1.

  Moreover, although the example which has the three 1st circulation paths 59a, 59b, 59c according to the three spiral recessed parts 55a, 55b, 55c in the rotation prevention parts 30a, 30b, and 30c was shown, three spiral recessed parts 55a were shown. , 55b, 55c may form one circulation path by the path of the internal passage. That is, by connecting the end portion 70a and the end portion 72b, the end portion 72a and the end portion 74b, and the end portion 74a and the end portion 70b with the internal passages, respectively, these internal passages and the spiral concave portions 55a, 55b, and 55c Thus, one circulation path is formed.

  The electric spot welding gun according to the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

It is a perspective view in the state where the electric spot welding gun concerning this embodiment was connected to the articulated robot. In the electric drive unit of the electric spot welding gun according to the present embodiment, it is a cross-sectional side view of a state in which the rod is retracted. It is a principal part disassembled perspective view of the electric drive unit of the electric spot welding gun which concerns on this Embodiment. It is a partial cross section perspective view of a rotation prevention part. It is the schematic diagram which looked at the 1st circulation path and 2nd circulation path of the rotation prevention part on the projection surface perpendicular | vertical to an axis | shaft. It is a section side view in the state where the rod extended in the electric drive unit of the electric spot welding gun concerning this embodiment. It is a partial cross section perspective view of the rotation prevention part concerning the 1st modification. It is the schematic diagram which represented the 1st circulation path and 2nd circulation path of the rotation prevention part which concerns on a 1st modification on the projection surface perpendicular | vertical to an axis | shaft. It is a partial cross section perspective view of the rotation prevention part concerning the 2nd modification. It is the schematic diagram which represented the 1st circulation path and 2nd circulation path of the rotation prevention part which concerns on a 2nd modification on the projection surface perpendicular | vertical to an axis | shaft.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric spot welding gun 12 ... Articulated robot 14 ... Control part 16 ... Electric drive unit 24 ... Rod 24a ... Hollow part 24c ... Outer wall 26 ... Movable electrode tip 26a ... Terminal 30a-30c ... Anti-rotation part 31a-31c ... Spline groove 32 ... Ball spline shaft 34 ... Stator 35a-35c ... Ball screw groove 36 ... Rotor 36b ... Magnet 40 ... Servo motor 50 ... Metal bush 51 ... Ring seal 55a-55c ... Spiral recess 56, 58 ... Balls 57a-57c, 92a -92c, 94a-94c ... 1st internal passage 59a-59c ... 1st circulation path 60a-60c, 78a-78c, 80a-80c ... 2nd circulation path 61a-61c ... 2nd internal passage 62a-62c ... Inner surface recessed part 70a , 70b, 72a, 72b, 74a, 74b ... end 8 a~82c ... space 90 ... rod reciprocating mechanism 98 ... fan-shape 98a ... arcuate portion

Claims (5)

In an electric spot welding gun that performs welding by sandwiching a workpiece with a fixed electrode tip and a movable electrode tip,
A rod provided with the movable electrode tip at one end and a hollow part at the other end;
A cylindrical anti-rotation portion fixed to the other end of the rod;
A ball spline shaft fixed to the housing and provided with a plurality of spline grooves extending in the axial direction, and inserted into the rotation prevention portion and the hollow portion of the rod;
A hollow rotor that rotates by receiving electromagnetic force from a stator provided in the housing, and has a ball screw groove formed on an inner wall;
Have
The rotation prevention unit includes a plurality of spiral recesses formed on an outer wall, and a first circulation path including a plurality of first internal passages communicating with both end portions of the spiral recesses, and the first ball group is inserted therein;
A plurality of second circulation paths formed of an inner surface recess formed in the inner wall and extending in the axial direction, and a second inner passage communicating with both ends of the inner surface recess, into which the second ball group is inserted;
With
The first ball group inserted into the spiral recess protrudes from the outer wall of the rotation prevention portion and engages with the ball screw groove, and the inner surface recess of the second ball group The inserted one protrudes from the inner wall of the rotation preventing portion and engages with the spline groove,
The first ball group and the second ball group respectively circulate in the first circulation path and the second circulation path as the rod advances and retreats,
The electric spot welding gun, wherein the plurality of second circulation paths are arranged radially in section around the axis of the rotation preventing portion. The electric spot welding gun according to claim 1,
On the projection plane perpendicular to the axis of the rotation preventing part, at least a part of the first internal passage intersects a fan-shaped arc portion having sides adjacent to the second internal passage. Electric spot welding gun characterized by The electric spot welding gun according to claim 2,
On the projection plane perpendicular to the axis of the rotation preventing unit, the first internal passage is set to a path that proceeds in the forward direction in the circumferential direction, and once again returns to the reverse direction and then travels in the forward direction again. Electric spot welding gun. The electric spot welding gun according to claim 1,
On the projection plane perpendicular to the axis of the rotation preventing unit, the minimum distance of the first internal passage relative to the axis is greater than the maximum distance of the second internal passage relative to the axis, and the first internal passage relative to the axis. An electric spot welding gun characterized in that an angle occupied by the passage is larger than an angle occupied by a fan shape having adjacent sides of the second internal passage. The electric spot welding gun according to claim 1,
The second circulation path is divided into a plurality along the extending direction of the spline groove,
The electric spot welding gun, wherein the first internal passage is provided so as to pass between the divided second circulation paths.

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