JP4753617B2 - Energizing pressure sensor - Google Patents

Description

  The present invention relates to an apparatus for measuring a pressurizing force for resistance welding, and more particularly to an energization pressure sensor for measuring a pressurizing force while allowing energization between welding electrodes.

  In resistance welding, the applied pressure is one of the three major welding conditions that influence the welding result as well as the welding current and energization time. Generally, a resistance welder presses a welding electrode to a welded portion or welded portion of a material to be welded, applies a pressure to the welded portion through the welding electrode, and causes an electric current to flow. I'm trying to cool it down. Therefore, in order to measure the pressure for resistance welding, it is preferable to place the welding electrode in direct pressure contact with the load sensor instead of the workpiece, and to measure the pressure during energization, the load sensor It is preferable to have such a conductivity and current capacity that it can flow. The energization pressurization sensor is a load sensor having both a conductivity capable of flowing a large current for resistance welding and a pressure measurement function.

  A conventional energization pressure sensor has a conductive block made of copper or a copper alloy formed in a U-shaped longitudinal section and is elastically deformable, and a welding electrode in a direction to narrow the gap at both ends of the conductive block. The U-shaped intermediate part or the body part is elastically deformed in response to the applied pressure, and a current flows between the welding electrodes while bypassing the U-shaped body part. A pair of strain gauges that are respectively sensitive to displacement in two orthogonal directions are attached to the position on the center line on the outer surface of the U-shaped body portion of the conductive block, that is, the position closest to the current path. A strain gauge converts the deformation of the U-shaped intermediate portion into an electrical signal.

  However, the conventional energizing pressure sensor as described above has low reliability of the pressure measurement accuracy. In particular, it is easily susceptible to thermal distortion generated in the conductive block when energized. That is, when energized, the inside of the conductive block is thermally expanded along the current path by Joule heat. Conventional energizing pressure sensors are sensitive not only to the pressure strain that the strain gauge receives from the welding electrode, but also to thermal expansion strain due to resistance heat generation in the conductive block. There is a problem that it tends to shift in an increasing direction. In addition, there is also a problem that an error is likely to occur in the measured pressure value even when the position where the welding electrode is in pressure contact with both ends of the conductive block is shifted.

  The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a highly reliable energization pressure sensor that can measure the applied pressure during energization with high accuracy.

  Another object of the present invention is to provide a highly reliable energization pressure sensor that can accurately measure the applied pressure even if the position of the welding electrode in contact with pressure is shifted.

In order to achieve the above object, an energization pressurization sensor of the present invention is an energization pressurization sensor for measuring a pressurizing force while allowing energization between welding electrodes of a resistance welder, through a gap. First and second electrode receiving portions for receiving the first and second welding electrodes, respectively, are provided at both end portions facing each other, and the first and second electrode receiving portions are provided in accordance with the applied pressure from the first and second welding electrodes . The barrel extending between the first electrode receiving portion and the second electrode receiving portion is elastically deformed, and the barrel is interposed between the first electrode receiving portion and the second electrode receiving portion when energized. A conductive block through which a current flows, and a portion of the body of the conductive block that is off the route where current flows most easily between the first electrode receiving portion and the second electrode receiving portion. One or more strain gates pasted at Have.

  In the above configuration, each strain sensor is affixed at a position off the side where the current flows most easily in the body of the conductive block made of, for example, copper or copper alloy. Even if thermal expansion distortion occurs due to Joule heat, the thermal expansion distortion hardly affects the strain sensors disposed far from the current path or only slightly. For this reason, each strain sensor is able to measure the applied pressure with high accuracy in response to the distortion in the block caused by the applied pressure received from the welding electrode.

According to a preferred aspect of the present invention, the strain gauge includes a first gauge that is sensitive to a longitudinal strain of the body portion of the conductive block at the pasting position, and a body portion of the conductive block at the pasting position. And a second gauge sensitive to the strain in the width direction. In this case, it is preferable that a pair of first and second gauges are provided on each of the left and right sides of the current route. In particular, it is preferable that the first strain gauge and the second strain gauge provided on the left side of the current route (the center line) and the first strain gauge and the second strain gauge provided on the right side of the current route (the center line). The two strain gauges constitute a Wheatstone bridge circuit in which the change in resistance value of the left gauge and the change in resistance value of the right gauge cancel each other. In such a configuration, even if the welding electrode deviates from the set position of the electrode receiving portion, the applied pressure can be measured with high accuracy by compensating for the offset load from the welding electrode. Note that a Wheatstone bridge circuit may be assembled with a strain gauge to generate an electric signal representing the pressure applied from the welding electrode.

  Moreover, in the energization pressurization sensor of this invention, the distortion which arises in the longitudinal direction of a block trunk | drum with respect to the applied pressure from a welding electrode is larger than the distortion which arises in the width direction of a block trunk | drum. For this reason, the first gauge is more sensitive than the second gauge and is sensitive to the applied pressure. According to a preferred aspect of the present invention, the first gauge is provided outside the second gauge with respect to the shortest route in the body portion of the conductive block, whereby the current is measured in the applied pressure measurement during energization. The effect of heat generation due to can be reduced more effectively.

  In the present invention, the conductive block can have any shape, and the strain gauge may be attached to any surface of the conductive block. According to a preferred aspect of the present invention, the conductive block is formed in a U-shaped longitudinal section, and a strain gauge is attached to the top surface of the upper side or the lower surface of the lower side. In the present invention, a toroidal coil for current detection can be attached to an arbitrary portion of the conductive block.

  According to the energization pressurization sensor of the present invention, it is possible to measure the applied pressure during energization with high accuracy by the above-described configuration and operation, and further, the position where the welding electrode is in press contact is shifted. It is also possible to accurately measure the applied pressure.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 and FIG. 2 show the appearance and usage of an energization pressure sensor in one embodiment of the present invention. 3 and 4 are a plan view and a longitudinal sectional view showing a configuration of a main part of the energization pressure sensor in the embodiment.

  The illustrated resistance welder 10 is a direct spot welder, and includes a pair of welding electrodes 12 and 14 facing vertically in the vertical direction. The upper welding electrode 12 is moved up and down via an upper electrode support arm 18 by a pressurizing mechanism 16 having a pneumatic cylinder, for example. The lower welding electrode 14 is fixed to the main body via the lower electrode support arm 20. Both welding electrodes 12 and 14 are electrically connected to a welding power source (not shown), and more specifically, are electrically connected to a secondary terminal of the welding transformer.

  In order to measure the applied pressure and current at the time of energization in the resistance welding machine 10 using the energization pressurization sensor 22 according to this embodiment, the energization pressurization sensor 22 is replaced with both welding electrodes in place of the workpiece (not shown). 12 and 14 and the resistance welding machine 10 is operated under exactly the same welding conditions and sequence as when resistance welding is actually performed. That is, the pressurizing mechanism 16 applies a pressurizing force having the same magnitude as that applied during actual resistance welding to the energizing pressurizing sensor 22 via the welding electrodes 12 and 14, and the welding power source supplies both the welding electrodes 12 and 14. A current having the same magnitude as the welding current that flows during resistance welding is passed through the energizing pressure sensor 22. The pressure detection signal and the current detection signal obtained by the energization pressure sensor 22 are sent to the monitor device body 26 via the electric cable 24, and the measured values of the pressure and current are displayed on the display unit of the monitor device body 26, respectively. It has become so.

  As shown in FIGS. 2, 3, and 4, the energization and pressure sensor 22 has a block or body 30 having a U-shaped vertical section (or U shape) attached to the tip of the handle 28. The block 30 is made of a metal having high conductivity and high thermal conductivity, such as copper or a copper alloy, and has recesses 32a and 32b for receiving electrodes on outer surfaces (upper surface and lower surface) of both ends opposed to each other through a gap G. have. Both the recesses 32 a and 32 b are formed in the central portion of the block 30 in the body width direction (Y direction).

  On the top surface of the upper side portion of the U-shaped block 30, a pair (34L, 34R) of X-direction strain sensor 34 and Y-direction strain sensor 36 are respectively disposed on both sides of a center line C indicated by a one-dot chain line in FIG. 36L, 36R). Here, the center line C is a line that extends in the body longitudinal direction (X direction) through each center point in the body width direction (Y direction) of the block 30. Each strain sensor is made of, for example, a metal resistance wire, the X direction strain sensors 34L and 34R are sensitive to the strain in the X direction, and the Y direction strain sensors 36L and 36R are sensitive to the strain in the Y direction.

  In the U-shaped block 30, the distortion when receiving pressure from the welding electrodes 12 and 14 is much larger in the X direction (trunk longitudinal direction) than in the Y direction (trunk width direction). Therefore, the X direction strain sensors 34L and 34R are more sensitive to the electrode pressure with higher sensitivity than the Y direction strain sensors 36L and 36R. In this embodiment, the X-direction strain sensors 34L and 34R are arranged outside the Y-direction strain sensors 36L and 36R on the top surface of the upper side portion of the U-shaped block 30 when viewed from the center line C.

  As shown in FIG. 5, these four strain sensors (34L, 34R) and (36L, 36R) constitute a Wheatstone bridge circuit. When the U-shaped block 30 is deformed so that the gap G at both ends is narrowed by receiving pressure from the welding electrodes 12 and 14, the resistance values of the X-direction strain sensors 34L and 34R are positive according to the magnitude of the pressure. The direction changes greatly. On the other hand, the resistance values of the Y-direction strain sensors 36L and 36R change only slightly. Thereby, the output voltage v of the Wheatstone bridge circuit changes according to the magnitude of the applied pressure, and the applied pressure detection signal is obtained.

  As described above, in this embodiment, both the X-direction strain sensor 34 and the Y-direction strain sensor 36 are attached to the top surface of the upper side portion of the U-shaped block 30 at a position off from the center line C. . When energized, as shown in FIGS. 3 and 4, most of the current flows between the upper electrode receiving recess 32a and the lower electrode receiving recess 32b of the block 30 through the central route in the block. Here, the center route is a route extending along the center line C.

  In this way, the strain sensors 34 and 36 are pasted at positions where they are off the current route in the U-shaped block 30, that is, positions on the top surface of the upper side of the U-shaped block 30. Therefore, even if a thermal expansion distortion occurs due to Joule heat in the current route in the middle part of the block during energization, the thermal expansion distortion is applied to each of the strain sensors 34 and 36 disposed at a position far from the current path. Is less or less. Therefore, each of the strain sensors 34 and 36 can measure the pressurizing force with high accuracy in response to the strain in the block generated by the pressurizing force received from the welding electrodes 12 and 14. In particular, in this embodiment, the X-direction strain sensors 34L and 34R that are sensitive to the distortion in the longitudinal direction (X direction) of the block 30 are connected to the Y-direction strain that is sensitive to the distortion in the width direction (Y direction) of the block 30. Since it is arranged outside the sensor 36L, 36R (the edge of the upper side of the U-shaped block 30), it is possible to more effectively reduce the influence of the current in the measurement of the applied pressure during energization.

  In this regard, in the conventional energization pressure sensor, as shown by the one-dot chain line 40 in FIG. 3, the strain sensor is arranged at the position on the center line C, that is, at the center route in the block intermediate part or the position closest to the current path. For this reason, the distortion of thermal expansion that occurs during energization easily reaches the strain sensor, and the measurement accuracy of the applied pressure is affected (error).

FIG. 6 shows the waveform of the applied pressure (solid line 42) obtained by the energization / pressurization sensor 22 of this embodiment in comparison with the waveform of the applied pressure (chain line 44) obtained by the comparative example. In the figure, t ₁ on the time axis is the pressurization start point, t ₂ is the start point of energization, t ₃ is the end point of energization, t ₄ is the monitor point, t ₅ is the end point of pressurization, and T _W (t ₁ ~t ₅₎ is an energizing time. Here, the comparative example is a case where the X-direction strain sensor 34 and the Y-direction strain sensor 36 are attached to a position 40 (FIG. 3) indicated by a virtual line on the center line C of the U-shaped intermediate portion of the block 30. .

As shown, in the energization time T _W distortion occurs due to thermal expansion of the Joule heat, the influence of the distortion of the thermal expansion on the measurement of pressure applied by the strain sensor 34 and 36 out, and the degree Example There are significant differences between the comparative examples. As an example, using the measured pressure immediately before energization as a reference (100%), it was confirmed that the variation rate during energization was 33.3% in the comparative example, whereas the embodiment could be improved to 13.4%. It has been confirmed that the variation rate at the monitoring time point t ₄ 3 seconds after the end of energization is 12.5% in the comparative example, whereas the embodiment can be improved to 2.4%.

  Further, in this embodiment, a pair of (34L, 34R), (34L, 34R), (on both sides of the center line C on both sides of the X-direction strain sensor 34 and the Y-direction strain sensor 36 on the top surface of the upper side portion of the U-shaped block 30 ( 36L, 36R). According to such a configuration, even when the position where the upper welding electrode 12 is in pressure contact within the upper electrode receiving recess 32a deviates from the set position on the center line C, or the lower welding electrode 14 is lower electrode receiving. Even when the pressure contact position in the recess 32b deviates from the setting position of the center line C, the offset force can be compensated and the applied pressure can be measured with high accuracy.

  That is, if the upper welding electrode 12 in FIG. 3 deviates from the center line C toward the left strain sensor (34L, 36L), for example, the deformation or resistance change of the left strain sensor (34L, 36L) increases relatively. The deformation or resistance value change of the right strain sensor (34R, 36R) is relatively reduced, and as a result, the increase / decrease (error) of both is canceled in the Wheatstone bridge circuit (FIG. 5). The same effect is exhibited when the upper welding electrode 12 is shifted to the right side of the strain sensor (34R, 36R) from the center line C, and the same operation is performed when the lower welding electrode 14 is shifted to the left or right side from the center line C. The effect is played.

  Although it is not possible to compensate for the eccentric load as described above, only one X direction strain sensor 34 and one Y direction strain sensor 36 are attached to one side of the center line C on the top surface of the upper side portion of the U-shaped block 30. A configuration to attach is also possible. In that case, circuit elements other than the strain sensors 34 and 36 in the Wheatstone bridge circuit (FIG. 5) may be configured with fixed resistors.

  As shown in FIG. 2, a toroidal coil 46 is attached to the lower side of the block 30. At the time of energization, an electric signal representing the differential waveform of the current is output from the output terminal of the toroidal coil 46. The output signal of the toroidal coil 46 is also sent to the monitor apparatus body 26 via the cable 24. Such a toroidal coil or a current sensor can be attached to an arbitrary portion of the block 30, and for example, can be attached to the upper side of the block 30. Moreover, the structure which affixes the strain sensors 34 and 36 on surfaces other than the top surface of the upper side part of the block 30 is also possible. For example, a configuration in which strain sensors (34L, 36L) and (34R, 36R) are attached to the lower surface of the lower side of the block 30 on both the left and right sides of the center line C in the same layout as in FIG. Alternatively, although the sensitivity is somewhat lowered, it is also possible to attach the strain sensors (34L, 36L), (34R, 36R) to the inner side surface (lower surface) of the upper side of the block 30 or the inner side surface (upper surface) of the lower side. is there.

It is a side view which shows the external appearance and usage condition of the energization pressurization sensor in one Embodiment of this invention. It is a perspective view which shows the principal part of FIG. It is a top view showing the pasting position of the strain sensor in the energization pressurization sensor of an embodiment. It is a longitudinal section showing the current passage at the time of energization in the energization pressurization sensor of an embodiment. It is a circuit diagram showing a Wheatstone bridge circuit formed by a strain sensor in the energization pressure sensor of an embodiment. It is a wave form diagram showing contrast of the waveform of the pressurization measurement value obtained by the energization pressurization sensor of an embodiment with the waveform of the pressurization measurement value obtained by a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Resistance welding machine 12 Upper welding electrode 14 Lower welding electrode 16 Pressurization mechanism 22 Current supply pressurization sensor 30 Conductive block 32a Recess for receiving upper electrode 32b Recess for receiving lower electrode 34 (34L, 34R) X direction strain gauge 36 (36L, 36R) Y direction strain gauge 46 Toroidal coil

Claims (10)

An energization and pressure sensor for measuring a pressurizing force while enabling energization between welding electrodes of a resistance welder,
First and second electrode receiving portions for receiving the first and second welding electrodes, respectively, are provided at both ends facing each other through a gap, and the applied pressure from the first and second welding electrodes is In response, the body extending between the first electrode receiving portion and the second electrode receiving portion is elastically deformed, and when energized, the first electrode receiving portion and the second electrode receiving portion A conductive block through which current flows through the barrel,
One or a plurality of affixed at positions adjacent to a route where current flows most easily between the first electrode receiving portion and the second electrode receiving portion in the body portion of the conductive block. Energized pressure sensor with strain gauge. The strain gauge is attached to the conductive block at a position deviating from a center line extending in the longitudinal direction of the trunk through each central point in the trunk width direction of the conductive block. The energizing pressure sensor described. In the body of the conductive block, said strain gauge is provided on the left and right sides of the current route, current pressure pressure sensor according to claim 1 or claim 2. The strain gauge is sensitive to the strain in the longitudinal direction of the body portion of the conductive block at the pasting position and the strain gauge is sensitive to the strain in the width direction of the body portion of the conductive block at the pasting position. and a second gauge, energizing pressure sensor according to any one of claims 1 to 3. Wherein the first and second gauges are provided in pairs on the left and right sides of the current route, current pressure pressure sensor according to claim 4. Said first gauge is provided on the outer side than the second gauge current pressure pressure sensor according to claim 5 with respect to the current route. The resistance of the left gauge by the first strain gauge and the second strain gauge provided on the left side of the current route and the first strain gauge and the second strain gauge provided on the right side of the current route. The energization pressurization sensor according to claim 5 or 6 in which a Wheatstone bridge circuit in which a change in value and a change in resistance value of the right gauge cancel each other is configured . The conductive block is formed in the longitudinal sectional U-shape, the said strain gauges on the top surface of the upper side portion is attached, energizing pressure sensor according to any one of claims 1-7. The conductive block is formed in the longitudinal sectional U-shape, the said strain gauge on the lower surface of the lower portion is attached, energizing pressure sensor according to any one of claims 1-7. The toroidal coil for detecting a current in the conductive block is mounted, energization pressure sensor according to any one of claims 1-9.

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