JP3310831B2 - Pressure detector for spot welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure detecting device for a spot welding machine for detecting a pressing force of an electrode tip on a work.

[0002]

2. Description of the Related Art An apparatus of this kind is disclosed in Japanese Patent Laid-Open No. 2-84.
According to Japanese Patent Publication No. 276, a ram guide is fixed to an upper arm of a resistance welding machine, and a pressurizing cylinder having a piston rod inserted therein is provided. 2. Description of the Related Art There is known a device which is connected so as to be able to float and detects a displacement generated between a piston rod and a ram when an electrode is pressed by a sensor provided in a hollow portion of the ram. This makes it possible to measure the electrode pressing force during energization, instead of setting the necessary pressing force before the welding operation.

[0003]

However, there is a problem in that a cylindrical ram guide is provided around the piston rod, and the measuring device is housed inside the ram guide. Further, the lead wire derived from the pressure sensor also moves in conjunction with the elevation of the piston, and it is necessary to take care to avoid disconnection.

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides a pressure detecting device for a spot welding machine which is juxtaposed with a piston rod without being bulky and requires only a small amount of displacement as the piston rod moves up and down. With the goal.

[0005]

In order to achieve the above object, the present invention provides, according to claim 1, an outer cylinder provided in a cylinder side by side with a piston rod, inserted into the outer cylinder, and A driven body held slidably up and down by a ring-shaped elastic body mounted on the inner circumference of the outer cylinder, and the driven body is pushed through a cushioning spring by an upper end portion being pressed downward by a descending piston. A rod to be pressed, a pressure sensor attached to the rod to detect a pressure applied by the rod to press the driven body, and project downward from the bottom surface of the outer cylinder,
And an operating rod that pushes the inner cylinder that has been slid downward by pressing the rod upward, and the spring force of the spring is such that when the rod is pressed by the piston, the spring is held in a state where the driven body is held by the elastic body. It is characterized in that compression is set.

[0006] By setting the position of the operating rod in the vertical direction, the driven member held upward by the elastic body is displaced downward to such an extent that the rod can be displaced downward while the piston rod is lowered to the position where the work is pressed. Set the position. During spot welding, during the process in which the piston rod descends and presses the work between the electrode tips, the driven body is gradually pressurized via the spring, and the level of the pressure detection signal of the pressure sensor gradually increases. When the lowering of the piston rod is restrained,
The driven body attempts to displace downward or follows the displacement, and the level of the pressure detection signal of the pressure sensor rises and becomes constant. By generating an energization start signal at this constant timing, the lowering of the piston rod is stopped, energized, and then increased.

When the descending position where the piston rod is restrained is displaced downward due to the wear of the electrode tip, the rod follows and descends correspondingly, and the driven body is driven. Similarly, the pressure detection signal becomes a constant level. At the time, an energization start signal is generated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A pressure detecting device for a spot welding machine according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 2, the upper arm 1b of the arm 1 is provided with a cylinder 2 for driving the piston 4 up and down. An electrode tip 3a is supported at a lower end of a piston rod 5 provided below the cylinder 2, and a flange portion 7 of a work 7 is provided between the electrode tip 3 and an electrode tip 3 supported by a lower arm 1a.
a, and welding is performed by energizing the electrode tip 3 in a state where the electrode tip 3 a is pressed against the electrode tip 3 to perform spot welding. The arm 1 is attached to, for example, a robot arm. In the cylinder 2, a pressure detecting device 9 according to the present invention is juxtaposed independently of the piston rod 5.

As shown in FIG.
An outer cylinder 10 provided below the bottom surface of the cylinder 2 and a driven body inserted in the outer cylinder and held slidably in parallel with the piston rod 5 by a ring-shaped elastic body 11 mounted on the inner periphery thereof. An inner cylinder 12, a rod 15 inserted into the inner cylinder, slidably guided by a guide member 16 with a bearing, and whose upper end is pressed from a predetermined lower position by the piston 4; The coil spring 17 is mounted between the spring seat 15a and the bottom surface 12b of the inner cylinder 12 and urges the rod 15 toward the piston 4, and the inner cylinder 12 displaced downward is pushed to return to the upper position. , Through hole 10 in bottom surface 10b of outer cylinder 10
c, and an operating rod 19 held by an elastic ring 19a and having a rear portion protruding outward.

The rod 15 is provided with a stopper 12a for restricting the upward movement of the spring seat 15a. A piezoelectric element 14 as a pressure sensor is interposed in the middle of the stopper 12a. The cable 14a is led out through a cable outlet 12d provided in the cable 14a. An escape groove 10b is formed in the outer cylinder 10 to allow air in a cylinder chamber formed below the outer cylinder 10 to escape into the cylinder 2 when the inner cylinder 12 descends. The portion of the inner cylinder 12 held by the elastic body 11 needs to have a vertical width corresponding to at least the amount of wear of the electrodes 3 and 3a, and a similar relief groove 12c is formed.

The spring constant of the coil spring 17 is
With the upper end of the spring seat 15 released from the piston 4, the spring seat 15
When the rod 15 is pressed downward by the piston 4, the inner cylinder 12 is compressed while being held by the elastic body 11, and the lower end portion 15 b of the rod 15 is moved to the bottom surface 12 b. It is set small enough to directly contact the The elastic ring 19a has a holding force enough to hold the operation rod 19 with almost no opposition to the displacement of the inner cylinder 12.

The operation of the pressure detecting device thus constructed will be described with reference to FIGS. Electrode tips 3, 3
As shown in FIG. 3A, the piston rod 5 moves the work 7
The inner cylinder 12 is positioned at an upper position where the lower end portion 15b can be securely pressed against the bottom surface 12b while the flange portion 7a is lowered to a position where the flange portion 7a is pressed between the electrode chips 3 and 3a. In this state, the rod 15 is positioned by the stopper 12a, the cable 14a reaches the upper surface of the cable outlet 12d, and the pressure detection signal of the piezoelectric element 14 remains at a minute level.

At the time of spot welding, a welding start signal (FIG. 4)
In response to A), the piston rod 5 descends. When the piston 4 starts pressing the rod 15 on the way (see the two-dot chain line in FIG. 1), the coil spring 17 is gradually compressed, and the piezoelectric element 1
4, the level of the pressure detection signal (FIG. 4C) gradually increases. In the process of further lowering the piston rod 5, the flange portion 7a is pressed between the electrode tips 3 and 3a so that the lowering is restrained and, as shown in FIG.
b directly presses against the bottom surface 12b through the inside of the coil spring 17 and is driven immediately before or slightly following the downward movement, so that the pressing force becomes constant. Therefore, the detection signal level also becomes constant, and by generating an energization start signal (FIG. 4D) at the timing when the detection signal level becomes constant, the lowering drive of the piston rod 5 is stopped (FIG. 4B), and energization is performed (FIG. 4B). (FIG. 4E). Thereafter, the piston rod 5 moves up.

In the subsequent welding step, the rod 15 also interlocks with the piston rod 5 to detect the pressure detection signal again at the position of the inner cylinder 12 positioned in the previous welding step. When the lowering position where the piston rod 5 is restrained is slightly displaced downward due to the wear of the electrode tips 3 and 3a, the rod 15 correspondingly displaces the bottom surface 12b downward and the pressure detection signal is constant at that time. Level to generate an energization start signal. FIG. 3C shows a state in which the electrode tips 3 and 3a have been greatly worn.
Is operated downward, and the operating rod 19 is also operated downward in conjunction with the operation. When the electrode tips 3 and 3a are replaced, the inner cylinder 12 is pushed back by the knob 19b of the operating rod 19, and the lower end portion 15b of the rod 15 is set to be pressed against the bottom surface 12b of the inner cylinder 12 at the first operation. Keep it.

FIG. 5 shows another embodiment, and the same or equivalent parts as those in the above-described embodiment are denoted by the same reference numerals. The driven body is configured as a round bar 33 integrally formed with the operation rod 19, and the ring-shaped elastic body 1 is provided in the outer cylinder 10.
1 is held movably downward by pressure. At the upper end of the round bar 33, a disk-shaped spring 37 made of, for example, rubber is attached for cushioning. The rod 15 is supported in the outer cylinder 10 by a bearing 36 so as to be slidable up and down. Accordingly, when the rod 15 is pressed by the descending piston 4, the round bar 33 is pressurized while gradually compressing the spring 37, and the round bar 33 is moved in conjunction with the lowered position where the piston rod 5 is restrained. It is driven in a pressurized state. As a result, the pressure detection signal becomes a constant level at a position where the lowermost position of the rod 15 is gradually lowered while the electrode tips 3, 3a are gradually worn.

[0016]

According to the first aspect of the present invention, the pressure detecting device is miniaturized by providing a rod with a pressure sensor which is pressed at a predetermined lower position by the piston together with the piston rod, and the slide stroke of the rod is reduced. Only a little,
Derivation of the lead wire from the piezoelectric sensor is also facilitated.

According to the second aspect of the present invention, the driven body is formed in a cylindrical shape into which the rod is inserted, and the bottom surface is directly pressed by the rod through a coil spring mounted on the bottom surface of the driven member. Is stabilized, and a highly stable pressure detection signal is obtained. By mounting the coil spring in the cylinder, the vertical dimension can be saved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a pressure detecting device of a spot welding machine according to an embodiment of the present invention.

FIG. 2 is a side view of a spot welding machine provided with the pressure detection device.

FIG. 3 is a cross-sectional view of a main part for explaining the operation of the pressure detection device.

FIG. 4 is a waveform chart for explaining the operation of the pressure detection device.

FIG. 5 is a sectional view of a main part of a pressure detection device according to another embodiment.

[Explanation of symbols]

 2 Cylinder 4 Piston 5 Piston rod 7 Work 10 Outer cylinder 11 Elastic body 12 Inner cylinder 14 Piezoelectric element 15 Rod 17 Coil spring 19 Operating rod 37 Spring 33 Round rod

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-237580 (JP, A) JP-A-2-284773 (JP, A) JP-A-2-84276 (JP, A) 36369 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 11/24 B23K 11/11 G01L 5/00

Claims (2)

(57) [Claims] 1. A piston rod is provided below a piston which is pressed and driven by a cylinder provided on an upper arm,
Spot welding that detects the pressing force of the electrode tip against the workpiece when conducting electricity and performing spot welding while holding the workpiece between the electrode tip supported by the piston rod and the electrode tip supported by the lower arm In the pressurization detection device of the machine, an outer cylinder installed in the cylinder side by side with the piston rod,
The driven body is held by a ring-shaped elastic body mounted on the inner periphery of the outer cylinder, and can be driven downward by pressurization from above, and the upper end is pressed downward by a descending piston, whereby A rod that presses the driven body via a shock-absorbing spring, a pressure sensor that is attached to the rod and that detects a pressing force that presses the driven body, a rod that projects downward from the bottom surface of the outer cylinder, and An operating rod that pushes the inner cylinder that has been slid downward by pressing the rod upward, and the spring force of the spring is such that when the rod is pressed by the piston, the driven body is held by the elastic body. A pressure detecting device for a spot welding machine, wherein the spring is set to be compressed in a state where the spring is compressed. A driven body which is held by a ring-shaped elastic body mounted on the inner periphery of the outer cylinder so as to be able to be driven downward by pressurization from above, and is constituted as an inner cylinder into which a rod is inserted; A buffer coil spring is mounted on the bottom surface of the inner cylinder, and the spring force is such that when the rod is pressed by a piston, the coil spring is compressed while the inner cylinder is held by the elastic body. The pressure detecting device for a spot welding machine according to claim 1, wherein a lower end portion of the rod is set so as to be able to directly press the bottom surface through the inside of the coil spring.