JP2010179323A - Straight motion actuator for resistance welding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance precision in welding quality through high-speed control by reducing frictional resistance produced in a sliding part, by obtaining a mechanical strength that can fully deal with compound overturning torque in vertical, horizontal, cross, rotating, and twisting directions acting on the same coaxial center line of a ball screw and a ball nut driven by a servomotor. <P>SOLUTION: A straight motion actuator comprises: a body case having a nearly recessed cross section; a bearing support plate integrally attached to the body case; a ball screw arranged in the body case and freely rotatably supported; a guide rod fixed in parallel with the ball screw in the body case; a ball nut which is incorporated in the ball screw, converts the rotary motion of the ball screw to a linear motion and slides on the outer periphery of the guide rod; and a guide device by which a cam follower projectingly attached to the symmetric positions of both sides of the ball nut is incorporated in a cam groove formed along the longitudinal direction of the side plate of the body case and is slid and guided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention belongs to the technical field of linear motion actuators, and more specifically, is useful for an electrode pressurizing device of a resistance welding machine that generates a torque for applying pressure necessary for resistance spot welding between a pair of positive and negative electrode tips. The present invention relates to an electric linear actuator.

A resistance spot welder (C type, X type servo spot gun for robot welding) for mounting a robot using an electric linear actuator is used in an assembly line of an automobile body or the like.

As shown in FIGS. 6 and 7, a linear motion actuator used in an electrode pressurizing device of a conventional spot welder has a guide rail 72 arranged in the longitudinal direction of the rail body 71 of the drive unit 70. A raceway surface 75 is formed on the inner surfaces of both sides, and the ball screw 73 is disposed along the guide rail 72.

The ball nut 74 is incorporated in the ball screw 73, and a plurality of balls 76 housed in a ball circulation system path 77 formed inside the ball nut 74 are formed along a raceway surface 75 formed on the guide rail 72. It is guided smoothly (Patent Document 1-2).

According to this type of conventional device, it is possible to mount each unit based on the rail body of the linear actuator, and it is evaluated for realizing lightweight and compact design by simplifying the structure and standardizing assembly parts.

However, the pressurizing linear motion actuator used in the conventional servo spot gun has a plurality of balls 76 (rolling elements) precisely processed in the ball circulation path 77 inside the ball nut 74, and the ball The ball circulation path 77 of the nut 74 requires high-precision processing, and a sealing cover for constructing prevention of entry of foreign matters such as dust is indispensable.

A conventional servo spot welding gun using this type of direct acting actuator is guided to the workpiece hitting position at a high speed by a robot or the like, and the inertial impact and vibration due to the weight of the gun due to the change of the gun posture during the movement are caused by the ball screw 73. And is forced to the movable part of the ball nut 74. Also, in this case, since the ball screw 73 (pressure shaft) for driving the electrode tip to press and the welding point position are in an eccentric position (offset position), the robot can operate at a high speed and millions of times under high pressure. While the number of welding hit points is repeated, the vertical direction (arrow a in FIG. 6), the horizontal direction (arrow b), the front-rear direction (arrow c in FIG. 7), the rotational direction between the ball screw 73 and the ball nut 74. (D arrow), when a complex high torque load from the twist direction (e arrow) is forced, the surface of the ball 76 that circulates in the ball nut directly wears on the raceway surface of the guide rail due to the falling torque. The wear resistance gradually increases, and the wear resistance of the ball 76 is often increased.

In this case, damage to precision processed parts such as the ball 76 is difficult to maintain and is fatal, and the problem remains that the expensive actuator body must be replaced.

US Pat. No. 5,299,465

Utility Model Registration No. 3079838

Therefore, the problem to be solved by the present invention is that the advantage of the conventional linear actuator is not changed as much as possible, and maintenance such as replacement of parts is made effective as a standard part of the electric pressure type spot welding gun, and the ball driven by the electric motor is used. To obtain a mechanical strength that can sufficiently oppose the combined load from the vertical direction, the horizontal direction, the front-rear direction, the rotational direction, and the torsional direction acting on the pressure shaft of the screw and the ball nut, especially the overturning torque for the ball screw. Thus, the frictional resistance of the sliding part between the ball screw and the ball nut is reduced, thereby improving the deflection between the arms and the electrodes, the misalignment of the electrode pressing point, the pressing response, etc. Along with improving durability, the electric spot welding gun can be made lighter, more compact, and faster when guiding the welding gun. While providing dynamic actuator is that a simplified sealing cover structure without any actuator internal relationship with the movement of the ball nut can be prevented foreign matter entry always dust or the like.

The present invention has been developed to achieve the above-mentioned object, and the linear motion actuator according to claim 1 includes a rectangular base plate and side plates rising substantially at right angles from both longitudinal sides of the base plate. A formed body case having a substantially concave cross section;
A bearing support plate integrally attached to the front end and the rear end of the main body case;
A ball screw disposed in the main body case in the longitudinal direction of the case and having both ends rotatably supported by bearing support plates at the front end portion and the rear end portion;
A guide rod disposed in parallel to the ball screw in the main body case and having both ends fixed to the bearing support plates at the front end portion and the rear end portion;
A ball nut incorporated in the ball screw and sliding on the outer peripheral surface of the guide rod by converting the rotational motion of the ball screw into a linear motion;
And an electric motor that is detachably attached to one bearing support plate side of the main body case and that rotates the ball screw directly or via a power transmission mechanism;
Cam followers protruding from both sides of the ball nut and attached respectively;
Furthermore, a guide device that slides and guides a cam follower that protrudes and attaches to both sides of the ball nut into a cam groove having a substantially concave cross section formed along the longitudinal direction of the side plate of the main body case; To suppress frictional resistance caused by a complex torque load from the vertical direction, the horizontal direction, the front-rear direction, the rotational direction, and the twist direction with respect to the ball screw and the ball nut incorporated therein. And

The linear motion actuator according to claim 2 is characterized in that a plurality of the cam followers are arranged at symmetrical positions on both sides of the ball nut.

The linear motion actuator according to a third aspect is characterized in that the guide device having the cam groove has a cover function of the side plate in addition to a rotation preventing function of the ball nut.

The linear motion actuator according to claim 4, wherein the cam groove of the guide device is constituted by a rail having a substantially concave cross section, and the cross section width of the rail is the cross section width of the side plate of the main body case. The bottom plate of the rail is configured as a cover plate including flanges extending in the longitudinal direction on both sides.
And it is detachably attached to the step portion of the fitting groove of the guide device formed on the side plate of the main body case so that the outer surface of the cover plate is in the same plane as the side plate. To do.

The linear actuator according to claim 5, wherein the ball screw is disposed on the base plate side of the main body case, and the guide rod is disposed on the opening side of the main body case in parallel to the axial center line of the ball screw. It is characterized by being.

The linear actuator according to claim 6, wherein the cam follower disposed on both sides of the ball nut is perpendicular to a line connecting the central axes of the ball screw and the guide rod, The ball screw and the guide rod are arranged approximately in the middle of parallel lines connecting the two central axes.

The linear motion actuator according to claim 7 is positioned as a pressure driving device for an electrode tip having a polarity that forms a positive / negative pair of a resistance welder, and the electrode tip having the one polarity is disposed on the first arm, The electrode tips having the other polarity are attached to the second arm so as to face each other, and the second arm is attached to a part of the main body case or a base plate or a gun bracket attached to the base plate. One arm is attached to the ball nut, a fixed cover having an opening that allows a movement range of the ball nut is extended in the longitudinal direction of the main body case, and the first nut is disposed on the ball nut side. A slide cover that moves together with the arm is disposed, and the slide cover moves within the movement range of the ball nut. Characterized in that to cover the opening of the cover at all times.

The linear motion actuator according to claim 8, wherein the fixed cover and the slide cover are made of a non-magnetic material having a substantially cross-sectional shape and are overlapped with an outer inclined surface of the opening of the main body case. It is characterized by that.

In the linear actuator of the present invention, the ball screw and the guide rod are arranged in parallel in the main body case, and cam followers having appropriate intervals are attached to both sides of a ball nut incorporated in the ball screw. A cam follower is slidably incorporated in a cam groove having a substantially concave cross section formed along the longitudinal direction of the side plate of the main body case. Thus, the mechanical strength can sufficiently cope with the combined overturning torque in the vertical direction, the horizontal direction, the front-rear direction, the rotational direction, and the torsional direction acting on the same axis of the ball screw and the ball nut driven by the electric motor. Is obtained. As a result, the frictional resistance generated at the sliding portion can be reduced, the linear high-speed drive control by the servo motor can be facilitated, and the welding quality accuracy can be improved.

In addition, the direct acting actuator of the present invention can be easily maintained, extend its life, and can be manufactured at low cost.

In this linear motion actuator, multiple pairs of cam followers are arranged at symmetrical positions on both sides of the ball nut with distances (spans) in the vertical, horizontal, and diagonal directions to effectively prevent rotation of the ball nut. Can function.

The linear actuator has a concave body that is always in cross section regardless of the opening / closing operation (welding operation) of the electrode tip, because the guide device having the cam groove has both the rotation prevention function of the ball nut and the cover function of the side plate. The cam groove of the case can be completely covered. As a result, sliding parts such as ball screws and ball nuts can be completely protected from foreign matters such as spatter and dust scattered during welding.

The linear actuator is formed on the side plate of the main body case so that the guide device is composed of a rail having a substantially concave cross section and the cover plate including the flange is in the same plane as the side plate. By detachably attaching to the stepped portion of the fitting groove, it is possible to easily attach and remove the rails and replace parts, thereby improving maintenance efficiency.

In the linear actuator, the ball screw is disposed on the base plate side of the main body case, and the guide rod is disposed on the opening side of the main body case in parallel with the axis of the ball screw. Since the guide rod is disposed at a distance from the pressing center line that is eccentric from the driving center line of the pressing shaft, the misalignment between the electrode tips due to the eccentric load can be suppressed, and the welding quality accuracy can be improved.

The linear actuator has a direction in which a rotation axis of a cam follower disposed on both sides of the ball nut intersects at right angles to a line connecting the central axes of the ball screw and the guide rod, and the ball screw and the guide By being positioned approximately in the middle of the parallel line connecting the two central axes of the rod, it is possible to reduce the load applied directly to the cam follower and to obtain mechanical strength, and to improve the durability of the cam follower. it can.

The linear motion actuator is positioned as a pressure driving device for electrode tips having a polarity that forms a positive / negative pair of a resistance welder, and the first arm is attached to the ball nut to allow a movement range of the ball nut. A fixed cover having an opening to extend in the longitudinal direction of the body case opening of the actuator, and a slide cover is disposed on the first arm or ball nut side, and the slide cover moves the ball nut. Since the opening of the fixed cover is completely covered within the range, the length of the slide cover can be shortened to the minimum necessary.

Therefore, even if the slide cover slightly protrudes forward and rearward in the longitudinal direction of the actuator as the first arm moves, there is no problem of interference with the servo motor, workpiece or jig, and operability and safety can be improved.

Since the cover structure is simple, it can be manufactured at low cost. Moreover, it is easy to attach and remove. By configuring the cover in this way, foreign matters such as spatter, dust, and water can be completely blocked against sliding parts such as a ball screw, a ball nut, a guide rod, and a bearing in the opening of the linear motion actuator.

In the linear motion actuator, the fixed cover and the slide cover are made of a non-magnetic material having a substantially cross-sectional shape and are arranged so as to overlap the inclined surface outside the opening of the main body case. It is possible to efficiently seal ingress of foreign matter from both sides of the opening and to prevent spattering or the like from adhering to the surface of the cover.

In addition, the linear actuator according to the present invention has to replace all of the expensive linear actuators as in the conventional case, even if each component is damaged, it is necessary to replace the individual parts with the minimum necessary parts. Solve a problem. The use of the conventional actuator can be omitted, which is advantageous in terms of cost.

FIG. 1 is a front view showing a concept when the linear actuator of the present invention is applied to an electric pressurizing robot welding gun. FIG. 2 is an AA arrow view of FIG. FIG. 3 is a front view showing an embodiment of a linear motion actuator. FIG. 4 is a view taken along the line BB in FIG. FIG. 5 is a plan view showing the structure of the cover of the present invention. FIG. 6 is a cross-sectional view schematically showing a conventional linear actuator. FIG. 7 is a cross-sectional view schematically showing the internal structure of the conventional ball nut shown in FIG.

The present invention exemplifies a pressure welding machine, particularly a servo spot welding gun pressure actuator, and operates in the vertical direction, the horizontal direction, and the longitudinal direction acting on the same axis of the ball screw and the ball nut driven by the servo motor. Friction resistance generated in the sliding part can be reduced by obtaining mechanical strength that can sufficiently cope with the combined overturning torque in the rotation direction and twist direction, and linear drive by the servo motor can be easily controlled at high speed. A linear actuator that improves quality accuracy has been realized.

Embodiments of the present invention will be described below with reference to FIGS.

The linear actuator 2 is formed of a rectangular base plate 4 and side plates 5 that rise substantially perpendicularly from both sides of the base plate in the longitudinal direction. The body case 3 having a substantially concave cross section is formed by extruding a non-ferrous metal made of aluminum. It is comprised from the material (refer FIG. 4).

Bearing support plates 8 and 9 are integrally attached to the front end portion 6 and the rear end portion 7 of the main body case 3 by bolts B1 (see FIG. 3).

The ball screw 10 is disposed inside the main body case 3 in the longitudinal direction of the case, and both ends of the bolt screw 10 are respectively supported by bearing support plates 8 and 9 of the front end portion 6 and the rear end portion 7 of the main body case. 12 is rotatably supported via 12.

The guide rod 11 is disposed in the main body case so as to extend in parallel with the ball screw 10 in a vertically positioned relationship with a line perpendicular to the axis of the ball screw 10. Both ends of the guide rod 11 are fixed to the front end portions 6 and 7 and the bearing support plates 8 and 9 at the rear end portion by screwing.

A ball nut 13 is incorporated in the ball screw 10, and an outer cylinder of a linear motion bearing 14 (also referred to as a linear bush) that slides on the outer peripheral surface of the guide rod 11 by converting the rotational motion of the ball screw 10 into linear motion. (See FIG. 4).

The electric motor M that rotationally drives the ball screw 10 is detachably attached to one bearing support plate 9 side of the main body case 3. In general, the motor output shaft Q and the ball screw 10 side are provided in the box case. The pulley PL is connected with the timing belt TB to transmit the power of the electric motor M to the ball screw 10 (see FIG. 2).

In this case, the main body of the electric motor M is attached to the base plate 4 of the box case so as to be folded back. The electric motor M may be directly connected to the ball screw 10 via a coupling to the output shaft depending on the specification conditions.

The servo motor M has an encoder (not shown), converts the rotation speed of the output shaft of the servo motor into the number of pulses, and the value obtained by counting the number of pulses is the position of the electrode chip E1, that is, the movement distance. The moving distance is detected at the timing when the number of corresponding pulses matches. Therefore, speed control and positioning control of the movable electrode tip are performed by detecting with the signal of the encoder.

The servo motor M is connected to a force sensor that detects a pressurizing force based on an armature current flowing through the motor. The force sensor executes a current feedback control to generate a torque for the pressurizing force required for welding.

The guide device 15 slides and guides the cam follower 16 along a cam groove 18 having a substantially concave cross section formed along the longitudinal direction of the side plate of the main body case, and the ball screw 10 during operation of the ball nut 13. This resists the load applied to the ball nut 13 (see FIGS. 3 and 4).

The cam follower 16 protrudes from both sides of the ball nut 13 and is attached thereto. In this case, the cam follower 16 is attached at four places on the one side of the ball nut 13 at the front and rear, and a total of eight places symmetrically with the other side.

Although the ball screw 10 driven by the electric motor and the ball nut 13 are loaded in the same axial direction from the vertical direction, the left-right direction, the front-rear direction, the rotation direction, and the twist direction, both sides of the ball nut 13 are applied. The cam follower 16 guides along the cam groove 18 and guides along the guide rod 11 in parallel with the ball screw 10 of the ball nut 13, so that the ball nut 13 and the ball screw 10 are compounded in all directions. It has a structure that can handle mechanical loads sufficiently.

The guide device 15 including the cam groove 18 has both a function of preventing rotation of the ball nut 13 and a function of covering the side plate 5.

The cam groove 18 of the guide device 15 is composed of one rail body 17 having a substantially concave cross section. The rail has a cross-sectional width that is substantially the same as the cross-sectional width of the side plate 4 of the main body case 3, and a flange cover plate 20 extending in the longitudinal direction on both sides is provided on the bottom plate 19 of the rail main body 17. (See FIG. 4).

Further, in the step portion 21 of the fitting groove of the guide device 15 formed on the side plate 4 of the main body case 3 so that the outer surface of the flange cover plate 20 and the side plate 4 of the main body case 5 are in the same plane. The bolt hole of the flange cover plate 20 is overlapped on the formed screw hole, and the stepped portion and the flange cover plate 20 are detachably and firmly attached by the bolt B2.

The ball screw 10 of the linear actuator 2 is arranged near the base plate of the main body case 3, and one of the guide rods 11 is arranged near the opening of the main body case 3 in parallel to the axis of the ball screw 10. Has been.

When the cam follower 16 is disposed on both sides of the ball nut 13 in the linear motion actuator 2, the axial center line XX of the cam follower 16 connects the center points of the axes of the ball screw 10 and the guide rod 11. It is configured so as to be perpendicular to the vertical line and to be positioned at a substantially middle point between the two center points of the ball screw 10 and the guide rod 11 (see FIG. 4). As a result, the cam followers 16 arranged on the axial center line XX are arranged on a triangle connecting the three central points of the ball screw 10 and the guide rod 11, so that each cam follower 16 is firmly supported by a tripod. Will be. Therefore, even when a local or eccentric load is applied to the movable part of the actuator, it is dispersed and suppressed in the direction of the triangle connecting each cam follower 16, the ball screw 10, and the guide rod 11, so that when the ball nut is running, And the sliding performance is maintained by the symmetrical cam follower 16.

In this embodiment, the linear actuator 2 is positioned in a pressure drive device of a resistance welder. The first arm 22 is detachably attached to an arm attachment surface N (N in FIG. 5) on the ball nut 13 side by means of a bolt B3 with an insulating plate 26 interposed. The electrode tip E1 having one polarity is attached to the tip of a tip holder 23 attached to the tip of the first arm 22.

The electrode tip E2 having the other polarity is attached to the tip of a tip holder 25 attached to the tip of the second arm 24 so as to face the electrode tip E1.

The fixed cover 28 is screwed in a form in which the opening side of the body case 3 of the actuator 2 extends in the longitudinal direction and is wrapped with the side plate 5 of the body case 3. The fixed cover 28 is formed with an opening U that allows the movement range of the ball nut 13 corresponding to the movement of the first arm 22 (see FIG. 5).

The slide cover 29 disposed on the ball nut side is configured to cover the opening U (shaded portion in FIG. 5) of the fixed cover 28 within the movement range of the ball nut 13.

The fixed cover 28 and the slide cover 29 of the linear motion actuator 2 have a substantially cross-sectional shape made of a non-magnetic material. For example, a lightweight material with a low friction coefficient such as glass fiber (fiber carbon material), plastic, rubber material, or other synthetic resin material is preferable.

On both sides in the longitudinal direction of the two-sheet covers 28, 29, edges that are bent with an equal opening angle are formed on both outer inclined surfaces of the opening 3U of the main body case 3, and the bent edges overlap. (See FIG. 3).

The slide cover 29 can always completely cover the body case opening 3U having a concave cross section regardless of the position within the allowable movement range of the first arm 22 when the first arm 22 moves forward and backward by the actuator 2. As a result, it is possible to realize a sealing structure that completely protects the sliding parts such as the ball screw 10 and the ball nut 13 from foreign matters entering from the outside such as spatter and dust scattered during welding.

The second arm 24 is made of an aluminum-based or high-strength brass-based material, and is attached to a part of the main body case 3 or the base plate 4 with an insulating plate 27 interposed between the gun-based bracket BT. It is detachably attached to the side attachment surface with bolts (see FIG. 1).

An inverter welding transformer T is mounted on the bracket BT. The output terminal T1 of the transformer and the first arm 22 on the movable side are substantially U-shaped so as to flexibly cope with the movement of the electrode tip when the pressure is released. A mold movable copper plate 30 is connected through a secondary conductor 31. The other fixed-side second arm 24 is connected to the other output terminal T2 via a secondary conductor 32 (see FIGS. 1 and 2).

In this embodiment, as an example when the linear actuator is used for an X-type servo spot gun, the electrode tip E1 of the first arm 22, the second arm 24, the electrode pressing point of the electrode tip E2, and the ball screw 10 (electrode addition) Although the pressurization source of the servo motor in which the pressurization center line of the pressure shaft is eccentric is described, the present invention is not limited to this.

For example, in the case of a C-type servo spot gun, one end of a C-shaped gun arm is detachably attached to the body case 3 side or the bracket BT side with an insulating plate sandwiched by bolts, and the other gun arm is a tip holder ( (It is also referred to as a point holder) and is detachably attached by a bolt with an insulating plate sandwiched between ball nuts 13.

A pair of opposing electrode tips are supported on the tips of the C-shaped gun arm and tip holder. Therefore, it is possible to easily cope with the change to the X-type and C-type.

The cooling water does not flow into the actuator but circulates through a reciprocating water passage formed in the electrode tips E1 and E2 of the first arm and the second arm.

An operation of the servo spot welding gun of the present invention having such a configuration will be described as an example.
The spot welding gun 1 is usually mounted at the tip of an arm of an articulated industrial robot for 6 axes, and has one axis (pressure axis) necessary for the pressurizing operation for feeding one opposing electrode tip and the opening operation for lifting. Driven with multiple joints.

The robot controller includes a robot trajectory control function including the welding gun pressure axis, and controls the welding power source by opening and closing an electronic switching circuit (contactor) such as a thyristor and controlling the welding current energization time by the timer unit. The welding power source control function is integrated, and the movements necessary for robot welding are reproduced while synchronizing the pre-teached trajectory movement, welding movement, and welding conditions.

The welding gun 1 calls the robot trajectory and the hit point position from the recorded data. The trajectory motion to the workpiece set on the work jig moves at high speed, and the servo motor M of the actuator rotates in response to a command from the robot controller. Then, the reduction gear (pulley, timing belt, etc.) is rotated by the motor torque, whereby the ball screw is driven to rotate.

The rotational movement is converted into a linear movement by the ball nut 13 and fixed, and the electrode tip E1 of the first arm 22 is sent out in a pressing direction opposite to the electrode tip E2 supported by the second arm 24 on the fixed side. In addition, the electrode tips E1 and E2 are inserted at an appropriate angle at the strike position of the workpiece while the stroke positions of the electrode tips E1 and E2 are arbitrarily changed during the movement.

During this time, the cam followers 16 arranged on both sides of the ball nut 13 are guided along the cam grooves 18 on both sides, and the ball nut 13 moves on the parallel axis of the ball screw 10 and the guide rod 11.

As soon as the electrode tips E1 and E2 reach the welding spot position, the opening stroke between the electrode tips and the feeding of the movable electrode tip E1 move in the pressurizing direction at a high speed and immediately before the contact with the workpiece, the descending speed is reduced to a low speed. The electrode tip is pressed by a soft touch.

When the movable-side electrode tip E1 sandwiches a workpiece, an applied pressure is detected by an armature current flowing through the servo motor M between the electrode tips, current feedback control is executed, and torque for the applied pressure required for welding is generated.

  In this case, the front, rear, left and right cam followers 16 are guided and moved along the cam grooves 18 on the left and right rails. The plurality of cam followers 16 are guided in the cam groove 18 with a span between the left and right cam followers (lateral direction), a span between the front and rear cam followers (vertical direction), and a span between the front and rear left and right cam followers (diagonal direction).

A plurality of cam followers 16 are arranged on the ball screw 10 and the ball nut 13 with spans in the vertical and horizontal and diagonal lines even when a load is applied in a combined manner from the vertical direction, the horizontal direction, the rotational direction, and the twisting direction. And at least one guide rod 11 can be sufficiently mechanically accommodated.

Thus, when the predetermined welding pressure is reached, the electronic switching circuit opens and closes by the energization start signal from the robot controller, a predetermined value of welding current is supplied from the welding power source by the timer unit for a predetermined time, and after a predetermined holding time after energization, the spot Welding is performed.

The welding current flows from the terminal T1 of the welding transformer T through the secondary conductor 31 to the electrode tip E1 through the flexible conductor 30 and the first arm 22 supported by the ball nut 13, and then to the electrode tip E2 through the workpiece.

The current returns to the terminal T2 of the welding transformer T through the second arm 24, the secondary conductor 32, and the like. In this cycle, the welding point position of the work is such that the welded portion sandwiched between the electrode tip E1 and the electrode tip E2 raises the temperature by the resistance heat generation of the current and melts the metal to form a nugget and are joined.

Thus, when the welding is completed, the servo motor M is reversed by the welding end signal from the timer unit of the robot controller, and the ball screw 10 is driven to pull up the first arm 22 in the backward direction (right direction in the figure). The distance between E1 and E2 is released, and welding at a predetermined position is completed.

When the welding gun is moved to the next welding position, the actuator 2 is operated so as to be in a free state before welding as described above, so that the robot can quickly move the welding gun to the next spot position. It will move lightly with low speed.

In this embodiment, the X-type robot welding gun is described as the actuator of the present invention. However, the basic idea of the present invention is not limited to these models, and it is not limited to the C-type robot welding gun. The range of application can be easily expanded to a welding machine.

1 Spot welding gun
2 Linear Actuator 3 Body Case 3U Body Case Opening 4 Base Plate 5 Pressure Rod 6 Front End 7 Rear End 8, 9 Bearing Support Plate 10 Ball Screw 11 Guide Rod 12 Bearing 13 Ball Nut 14 Bearing 15 Guide Device 16 Cam Follower 17 Rail body 18 Cam groove 19 Bottom plate 20 Stepped portion 21 Flange cover plate 22 First arm 23 Chip holder 24 Second arm 25 Chip holder 26 Insulating plate 27 Insulating plate 28 Fixed cover 29 Slide cover 30 Flexible conductor 31 Secondary conductor 32 Secondary conductor BT Bracket E1 Electrode tip E2 Electrode tip

Claims (8)

The linear motion actuator includes a main body case having a substantially concave cross section formed from a rectangular base plate and side plates rising substantially at right angles from both longitudinal sides of the base plate;
A bearing support plate integrally attached to the front end and the rear end of the main body case;
A ball screw disposed in the main body case in the longitudinal direction of the case and having both ends rotatably supported by bearing support plates at the front end portion and the rear end portion;
A guide rod disposed in parallel to the ball screw in the main body case and having both ends fixed to the bearing support plates at the front end portion and the rear end portion;
A ball nut incorporated in the ball screw and sliding on the outer peripheral surface of the guide rod by converting the rotational motion of the ball screw into a linear motion;
An electric motor which is detachably attached to one bearing support plate side of the main body case and which rotates the ball screw directly or via a power transmission mechanism;
Furthermore, a guide device that slides and guides a cam follower that protrudes and attaches to both sides of the ball nut into a cam groove having a substantially concave cross section formed along the longitudinal direction of the side plate of the main body case; Thereby suppressing frictional resistance caused by a combined torque load from the vertical direction, the horizontal direction, the front-rear direction, the rotational direction, and the twist direction with respect to the ball screw and the ball nut. 2. The linear actuator according to claim 1, wherein a plurality of the cam followers are arranged at symmetrical positions on both sides of the ball nut. 2. The linear actuator according to claim 1, wherein the guide device including the cam follower and the cam groove has a function of preventing the rotation of the ball nut and a cover function of the side plate. 4. The linear motion actuator according to claim 1, wherein the cam groove of the guide device corresponding to the side plate is composed of a rail having a substantially concave cross section and the cross section width of the rail is the body case. The bottom plate of the rail is configured as a cover plate including a flange extending in the longitudinal direction on both sides, and the cover plate is in the same plane as the side plate. Thus, it is attached to the level | step-difference part of the fitting groove formed in the side plate of the said main body case so that attachment or detachment is possible. 2. The linear actuator according to claim 1, wherein the ball screw is disposed on the base plate side of the main body case, and the guide rod is disposed on the opening side of the main body case in parallel with the axial center line of the ball screw. It is characterized by. 2. The linear actuator according to claim 1, wherein an axial center line of the cam follower disposed on both sides of the ball nut is perpendicular to a line connecting the central axes of the ball screw and the guide rod, It is characterized by being located approximately in the middle of a parallel line connecting the two central axes of the screw and guide rod. The linear motion actuator according to claim 1 is positioned as a pressure driving device for an electrode tip having a polarity that forms a positive / negative pair of a resistance welder, and the electrode tip having the one polarity is disposed on the first arm and the other. Electrode tips having the following polarities are respectively attached to the second arms opposite to each other;
The second arm is attached to a part of the main body case or a base plate or a gun bracket attached to the base plate;
The first arm is attached to the ball nut, and a fixed cover having an opening that allows a movement range of the ball nut is extended in the longitudinal direction of the main body case;
A slide cover that moves together with the first arm is disposed on the ball nut side, and the slide cover always covers the opening of the fixed cover within the movement range of the ball nut. To do. 8. The linear motion actuator according to claim 7, wherein the fixed cover and the slide cover have a substantially cross-sectional shape [made of a non-magnetic material and overlapped with the inclined surface outside the opening of the main body case. It is arranged.

Images