JP6569066B2 - Strain gauge, strain sensor and force transducer having the same - Google Patents

Description

The present invention relates to a strain gauge, a strain sensor that measures strain of a measurement object using the strain gauge, a load cell that is a force transducer that measures force and load, and the like.

  Conventionally, in a strain gauge for measuring the force applied to a strain generating body, a metal foil having a large electric resistance value is laminated on an insulating film, and a conductive pattern is produced on the foil using an etching technique.

By attaching the strain gauge to the strain generating body, strain is generated when force is applied to the strain generating body, and the electric resistance value is changed. By utilizing this characteristic, that is, the characteristic that the electrical resistance value of the strain gauge changes, a Wheatstone bridge circuit is formed, and a voltage is applied to the circuit to measure the output voltage. It was possible to measure.

In addition, the strain gauge is provided with a conductive pattern of filament-shaped wiring that is folded back and forth so that a large change in electrical resistance value can be captured, and the direction in which the electrical resistance value changes significantly depending on the magnitude of the strain received It is common to stick (that is, the sensitivity direction) in parallel with the direction in which the strain generated in the strain generating body is measured. However, the electric resistance value of the strain gauge varies individually even if the conductor pattern is manufactured in the same process by the etching technique. As a result, when the Wheatstone bridge circuit was formed, the initial output voltage did not become 0 V, and a problem that an offset of a level that cannot be ignored occurred.

Therefore, in order to set the initial output voltage of the Wheatstone bridge circuit to 0 V, a method of providing an adjustment margin at the time of manufacture is used as means for matching the electric resistance value of the strain gauge constituting the Wheatstone bridge circuit with a desired value. In this case, the width of the filament-shaped conductor pattern is made slightly larger so that the electrical resistance value of the strain gauge becomes smaller than the desired value during the etching process, and the conductor is subjected to additional etching, polishing, etc. Adjustments were made to reduce the cross section of the pattern and bring the electrical resistance value closer to the desired value.

Further, as another method for matching the electrical resistance value of the strain gauge with a desired value, as shown in Patent Document 1, in a form in which a plurality of conductor patterns on the strain gauge are turned back and forth, An arbitrary portion is provided with several short-circuited portions, and the short-circuiting is cut off in a timely manner to adjust the electric resistance value so as to approach the desired electric resistance value.

Further, in the measurement of the force applied by the strain sensor, a creep phenomenon occurs because the strain gauge has a configuration in which a conductive pattern made of a metal foil that is folded back and forth is provided on an insulating film made of a synthetic resin. The creep phenomenon here refers to a phenomenon in which the output voltage from the Wheatstone bridge circuit changes with the lapse of time from the time when the force is applied when a state where a constant force (load) is applied is maintained. ing. It is known that the cause of the creep phenomenon is related to a strained body, a strain gauge, an adhesive for bonding them, and a coating material for protecting an electric circuit including the strain gauge.

The normal strain gauge exhibits a negative creep phenomenon as described in the prior art of Patent Document 2. Therefore, the end tab ratio of the conductor pattern that is folded back and forth in the strain gauge, that is, the length D of the end tab portion (folded portion) that plays the role of the end tab in the sensitivity direction X of the conductor pattern shown in FIG. The creep characteristics are adjusted by adjusting the ratio (D / d) of the length d in the Y direction. Specifically, when the conditions such as the shape and size of the strain-generating body, the material and thickness of the base member in the strain gauge are set to be the same, and only the end tab ratio in the conductor of the strain gauge is changed, the end tab is changed. Using the characteristic that the creep phenomenon swings more positively as the ratio increases, the adjustment is made by selecting the optimal end tab ratio of the end tab portion.

Japanese Patent Publication No. 06-103213 Japanese Patent Laid-Open No. 11-64125

  However, the strain gauge conductor pattern is usually produced by an etching process in many cases, and it has been difficult to obtain a desired end tab ratio accurately due to variations in the etching amount such as overetching and underetching.

  Especially when measuring a small force, the strain gauge becomes smaller and the strain gauge conductor pattern to be adhered becomes extremely fine. Therefore, it becomes more strict to manufacture the end tab portion to a desired end tab ratio. End up.

  Therefore, the present invention does not increase the accuracy requirement at the time of manufacturing, and, for example, even when a Wheatstone bridge circuit is configured by a strain gauge conductor pattern that can be manufactured by a normal etching process, the initial voltage is set to 0 V and a desired value It is an object of the present invention to provide a strain gauge capable of simultaneously obtaining an end tab ratio, a strain sensor using the strain gauge, and a force transducer.

In order to achieve the solution of the above problem, the strain gauge according to claim 1
A sensing part consisting of a plurality of linear wires with the extending direction as the sensitivity direction;
A first end tab part for connecting each wiring of the sensing part at both ends in the sensitivity direction;
A strain gauge for detecting distortion by forming a folded conductor pattern with
A breakable short-circuit portion that extends in a direction crossing the sensitivity direction and short-circuits a part of the conductor pattern between at least one adjacent end tab portion or between adjacent wirings. Have
The end tab ratio of the second end tab portion that plays the role of an end tab is connected to each wiring in which the detection of strain is activated by cutting the short-circuit portion, and is configured to be higher than the end tab ratio of the first end tab portion. .

In order to achieve the solution of the above problem, the strain gauge according to claim 2
A sensing part consisting of a plurality of linear wires with the extending direction as the sensitivity direction;
A first end tab part for connecting each wiring of the sensing part at both ends in the sensitivity direction;
A strain gauge for detecting distortion by forming a folded conductor pattern with
Cutting by cutting a short-circuit portion that extends in a direction intersecting the sensitivity direction and short-circuits a part of the conductor pattern between at least one adjacent end tab portion or between adjacent wirings. Part
The end tab ratio of the second end tab portion that plays the role of an end tab is connected to each wiring in which the detection of strain is activated by cutting the short-circuit portion, and is configured to be higher than the end tab ratio of the first end tab portion. .

The strain gauge according to claim 3 is configured such that the second end tab portion is provided at a position separated from the central portion of the sensing portion in order to achieve the solution of the above-described problem.

In the strain gauge according to claim 4, in order to achieve the solution of the above-mentioned problem, the second end tab portion is line-symmetrically or linearly received with a straight line parallel to the sensitivity direction passing through the central portion of the sensitive portion as a symmetry axis. They are arranged symmetrically with respect to the center of the sensitive part.

The strain gauge according to claim 5 is configured such that the end tab ratio of the second end tab portion is in a range of 1.5 to 3 times the end tab ratio of the first end tab portion in order to achieve the solution of the above problem. Has been.

A strain sensor according to a sixth aspect includes the strain gauge according to any one of the first to fifth aspects, in order to achieve the solution of the above-described problem.

A force transducer according to a seventh aspect comprises the strain gauge according to any one of the first to fifth aspects, in order to achieve the solution of the above-mentioned problem.

According to the strain gauge according to claim 1 and 2, a short-circuit portion is provided between adjacent end tab portions of the conductor pattern of the strain gauge, and the short-circuit portion is cut to adjust to a desired electric resistance value. Thus, it is possible to easily set the initial voltage of the Wheatstone bridge circuit to 0 V, and at the same time, a desired end tab ratio can be obtained. The fact that the short-circuit portion needs to be cut indicates that the electrical resistance value of the strain gauge is smaller than a desired value, and for example, the conductor pattern width is larger than the design value as a whole. At this time, the strain gauge has a lower end tab ratio than the desired end tab ratio.

In the present invention, the sensitive portion and the end tab portion of the conductor pattern, which until then did not flow due to cutting of the short-circuit portion and were inactive with respect to detection of distortion, become active with respect to detection of distortion. I use that. The end tab ratio of the end tab part connected to the sensitive part that becomes active by cutting the short circuit part is made larger than the end tab ratio of the end tab part connected to the sensitive part that is in the active state and is not opposed to this short circuit part. Thus, the overall average value of the end tab ratio can be increased. Therefore, the resistance adjustment of the strain gauge and the adjustment of the overall end tab ratio can be performed simultaneously.

Further, a short-circuit portion is provided between adjacent wiring portions of the conductor pattern of the strain gauge, and the short-circuit portion is cut to adjust to a desired electric resistance value so that the initial setting of the initial voltage of the Wheatstone bridge circuit is facilitated. At the same time, a desired end tab ratio can be obtained. By providing variations in the position of the short-circuit portion in the sensitivity direction, the resistance value and the end tab ratio can be adjusted stepwise.

According to the strain gauge of claim 3, in addition to the above-described effect, the short-circuit portion is located at a position away from the center of the sensing portion, and therefore when a bending moment or the like in a direction perpendicular to the sensitivity direction is applied. Even if it is, accurate measurement is possible.

According to the strain gauge of the fourth aspect, in addition to the above effect, since the short circuit portion is in a symmetrical position, even when a bending moment or the like in a direction perpendicular to the sensitivity direction is applied, Measurement is possible.

According to the strain gauge according to claim 5, in addition to the above-described effect, the end tab ratio of the end tab portion connected to each wiring where the detection of strain is activated by cutting the short-circuit portion is set to a desired end tab of the strain gauge. By designing the end tab ratio in the range of 1.5 to 3 times the ratio, a strain gauge that facilitates resistance adjustment and end tab ratio adjustment can be realized.

According to the strain sensor of the sixth aspect, since the Wheatstone bridge circuit is configured by including the strain gauge according to any one of the first to fifth aspects, the strain can be easily adjusted in resistance and end tab ratio. A sensor can be realized.

According to the force transducer of claim 7, since the strain gauge according to any one of claims 1 to 5 is provided, it is possible to realize a force transducer that facilitates resistance adjustment and end tab ratio adjustment.

Illustration of strain gauge end tab ratio The top view of 1st Embodiment of the strain gauge of this invention The top view of 1st Embodiment of the strain gauge of this invention Configuration diagram of a strain sensor including a strain gauge of the present invention and forming a Wheatstone bridge circuit The perspective view of the force transducer which stuck the strain gauge of this invention to the strain body The top view which shows the non-operation state area | region of 1st Embodiment of the strain gauge of this invention The top view after the short circuit part cutting | disconnection of 1st Embodiment of the strain gauge of this invention The top view which shows the non-operation state area | region of 2nd Embodiment of the strain gauge of this invention Plan view of a third embodiment of the strain gauge of the present invention The top view which shows the non-operation state area | region of 3rd Embodiment of the strain gauge of this invention The top view which shows the non-operation state area | region after the short circuit part cutting | disconnection of 3rd Embodiment of the strain gauge of this invention The graph of explanation concerning the magnification of the end tab ratio of the strain gauge of the present invention

  Hereinafter, embodiments of the strain gauge of the present invention will be described with reference to the drawings.

2 and 3 are plan views of the strain gauge G according to the first embodiment of the present invention, and are diagrams showing a conductor pattern of the strain gauge G. FIG. In the strain gauge G, a conductor is patterned on a film base material serving as a base, and the conductor pattern includes a sensing part S including a plurality of wires extending in a straight line parallel to the sensitivity direction X; It is formed in a folded shape by end tab portion regions T1 and T2 that connect each wiring in the sensitivity direction X of the sensing portion S at both ends thereof. Furthermore, connection terminals 101 and 102 are provided at the end of the conductor pattern.

In this embodiment, the film base material used as a base is a polyimide film, for example, and a resistor is a metal and uses the alloy of copper and nickel. If necessary, an insulating layer may be applied or laminated as a protective layer covering a part of the surface of the conductor pattern.

Further, in the end tab portion regions T1 and T2, at least one or more conductor patterns are formed in a direction in which the short-circuitable portions 11a and 11b capable of short-circuiting between some adjacent end tab portions intersect the sensitivity direction X. Elongated and provided. The short-circuit portions 11a and 11b can be cut by laser irradiation or the like. The first end tab portion 10 in the sensing portion S where the short-circuit portions 11a and 11b are not provided is formed with a design length D1 that provides a desired end tab ratio of the strain gauge G. On the other hand, the length D2 in the sensitivity direction X of the second end tab portions 12a, 12b connected to the short-circuit portions 11a, 11b in the sensitivity direction X is long, compared with the length D1 of the above design. The length is set to about 1.5 to 3 times. Details of this will be described later.

FIG. 4 shows a strain sensor 3 in which a strain gauge G (G1, G2, G3, G4) of the present invention is arranged to constitute a Wheatstone bridge circuit. Here, the four gauges are configured with strain gauges G (G1, G2, G3, G4) on all four sides, but the invention is not limited to this, and one gauge or two gauges may be used. By applying the voltage E, the strain sensor 3 can output the strain applied to the strain gauge G (G1, G2, G3, G4) at the output voltage Vout.

FIG. 5 shows a force transducer 1 in which a strain gauge G (G1, G2, G3, G4) of the present invention is arranged to constitute a Wheatstone bridge circuit, and is a double beam type load cell as an example. The force transducer 1 includes an upper beam B1 and a lower beam B2 that form part of the strain generating body 2, and are provided with elastic body strain generating portions e1, e2, e3, and e4 which are thinned, respectively. A strain gauge G1, G2, G3, G4 is attached to each of the strain generating portions e1, e2, e3, e4, and a total of four strain gauges G (G1, G2, G3, G4) are shown in FIG. 4 functions as a strain sensor 3 and constitutes a force transducer 1 containing the strain sensor 3.

When a voltage E is applied to the strain sensor 3 shown in FIG. 4 with no force applied to the force transducer 1, the output voltage Vout needs to indicate 0V. For this purpose, it is necessary to make the electrical resistance values of the strain gauges G (G1, G2, G3, G4) the same as desired values. Therefore, as in the above-described prior art, the electrical resistance value of the strain gauge G (G1, G2, G3, G4) is prepared in advance so as to have a small value with respect to a desired electrical resistance value. This is because although the resistance value can be increased by cutting such as trimming, it is very difficult to increase the resistance value because it increases the cross-sectional area of the resistor. Therefore, if the electrical resistance value is smaller than the desired electrical resistance value, the electrical resistance value is increased by cutting the short-circuit portions 11a and 11b as appropriate so as to approach the desired electrical resistance value.

Next, details will be described with reference to FIG. 6 showing the strain gauge G before cutting the short-circuit portion and FIG. 7 showing after cutting the short-circuit portion 11a in the first embodiment. Before the short-circuit portions 11a and 11b are cut, the short-circuit portions 11a and 11b are the main current paths. Therefore, the wiring of the sensing portion S connected to the short-circuit portions 11a and 11b and extending in the sensitivity direction X. The second end tab portions 12a and 12b are not involved in distortion detection. In the present invention, this is defined as a non-action state, and is shown by a shaded area in FIG. Accordingly, conversely, a state in which distortion is detected by the sensing part S is defined as an action state.

With this strain gauge G, the number of wires of the sensing part S that is in an operating state before cutting is 26. When the short-circuit portion 11a is cut here, this becomes a cut portion and the state shown in FIG. 7 is reached, and the number of wires of the sensing portion S in the active state increases by 2 to 28. Therefore, the ratio of the increased two to the whole is approximately 2/28 = 0.07. Cutting the short-circuit portion 11a means increasing the total resistance value because it is small, and cutting the short-circuit portion 11a can increase the resistance value by 7%.

When trying to increase the resistance value of the strain gauge G, it can be considered that, for example, the width of the produced conductor pattern is generally wider than the design value. Therefore, it means that the overall end tab ratio is made smaller as the conductor pattern becomes wider. For example, when the desired end tab ratio Rt is 10, assuming that Rt = D / d = 10/1, the conductor pattern width is actually wide by δa (assuming d is 1), so (D + δa) / (D + δa) is the actual end tab ratio. Assuming that the conductor pattern width is increased by a resistance increase rate of 7% increased by cutting the short-circuit portion 11a, that is, assuming that δa = 0.07, the actual end tab ratio Rr of the manufactured strain gauge G is 9 .41.

On the other hand, before the short-circuit portion 11a is cut, there are 27 end tabs having a length D1. When the short circuit portion 11a is cut, the number increases by two to 29. There are 28 end tabs aiming at a desired end tab ratio Rt = 10 (from the above, the actual end tab ratio is estimated to be 9.41), and there is one end tab of the adjustment length D2. Therefore, since the dimension of the length D2 may be determined so that the average value of the end tab ratio of each end tab portion becomes the desired end tab ratio Rt = 10, D2 = 27.2. Therefore, the ratio between D2 and D1 is D2 / D1 = 27.2 / 10 = 2.72, and D2 is larger than D1 and should be approximately 2.7 times the length. This magnification is determined by the number of wires and a desired end tab ratio, and FIG. 12 is a graph showing the relationship relating to this magnification. The horizontal axis is the number of wires of the sensing part S, and the respective vertical magnifications of the desired end tab ratios between 2 and 100 are indicated by the vertical axis. As can be seen from this graph, when the number of wirings is increased for each desired end tab ratio, this magnification saturates at a certain value for each desired end tab ratio, and as a whole, approximately 1.5 to 3 times as a whole. Between.

  In addition, the second end tab portions 12 a and 12 b connected to the short-circuit portions 11 a and 11 b are disposed at positions separated from the central portion of the sensing portion S. Usually, the strain gauge G is pasted so that the central part of the sensing part S comes to the place to be measured. For example, as shown in FIG. 5, when the force F is applied to 1 in the force transducer, the surface of the upper beam B1 is distorted in the H direction, so that the second end tab portion 12a is not in the same wiring shape as the central portion of the sensing portion S. , 12b are located away from the central part of the sensitive part S so as to reduce this influence, and further pass through the central part of the sensitive part S with a symmetry axis ML that is a straight line parallel to the sensitivity direction X. They are arranged symmetrically with respect to the axis of symmetry. Further, as a modification, the same effect can be obtained even if the second end tab portions 12a and 12b are point-symmetric with respect to the central portion of the sensing portion S.

  FIG. 8 is a diagram showing an operating state / non-operating state before cutting of the strain gauge G of the second embodiment of the present invention. In the second embodiment, in addition to the first embodiment, the short-circuit portions 11a and 11b and the second end tab portions 12a and 12b are reversed and arranged next to each other in the sensitivity direction X. That is, in the second embodiment, there are four short-circuit portions 11a, 11b, 11c, and 11d, and the number of adjustment points is increased. The dimensions in the sensitivity direction X of the second end tab portions 12a, 12b, 12c, and 12d can be set in the same way as in the first embodiment. Of course, the length in the sensitivity direction X of the second end tab portions 12c and 12d is slightly different from that of the second end tab portions 12a and 12b, so that the strain gauge can be selected according to the finished state of the pattern production process. It is also possible to bring the end tab ratio of G as a whole closer to a desired one.

  Further, the second end tab portions 12a, 12b, 12c, and 12d are located at positions separated from the central portion of the sensitive portion S, and are symmetric that are straight lines parallel to the sensitivity direction X through the central portion of the sensitive portion S. The axes ML are arranged symmetrically about the axis of symmetry. These effects are the same as those of the first embodiment. The same effect can be obtained even if the second end tab portions 12a, 12b, 12c, and 12d are point-symmetric with respect to the central portion of the sensing portion S.

  FIG. 9 is a plan view of a strain gauge G according to the third embodiment of the present invention. In the third embodiment, the short circuit portion is provided in the area of the adjacent wiring of the sensing part S, and is extended from the adjacent wiring of the sensing part S in the direction intersecting the sensitivity direction X. It consists of short-circuit parts 13e, 13f and second-stage short-circuit parts 14e, 14f. And the end tab parts 15e and 15f are arrange | positioned at the termination | terminus side connected with the 2nd stage short circuit parts 14e and 14f.

  FIG. 10 is a plan view of the strain gauge G according to the third embodiment of the present invention before cutting the short-circuited portion, and shows an operating state / non-operating state. Before the first stage short circuit parts 13e, 13f and the second stage short circuit parts 14e, 14f are cut, the first stage short circuit parts 13e, 13f are shortcuts. The included part serves as an end tab. By setting the dimension in the sensitivity direction X of the first stage short-circuit portions 13e and 13f to D1, the end tab ratio of the strain gauge G is set to a desired value. Therefore, it can be considered that this first stage short-circuited portion 13e, 13f is an end tab and this portion is equivalent to a strain gauge having a shorter turn-back pattern than the other wires of the sensing portion S.

  FIG. 11 is a plan view of an example after cutting the short-circuit portion of the strain gauge G according to the third embodiment of the present invention, and shows an active state / non-active state. The first-stage short-circuit portion 13e is cut and the second-stage short-circuit portion 14e remains, and in this case, the portion including the second-stage short-circuit portion 14e having the length D3 serves as a second end tab portion as a role of the end tab It changes to make. On the other hand, when the first-stage short circuit portion 13f and the second-stage short circuit portion 14f are cut, the end tab portion 15f having the length D2 changes so as to serve as an end tab as the second end tab portion.

  That is, as in the third embodiment, the short-circuit portion is provided in the area of the adjacent wiring of the sensing portion S, and a plurality of the short-circuit portions are provided, and the design in which variations in the dimension of the sensitivity direction X are provided is performed. Thus, a strain gauge G having a desired end tab ratio and a desired resistance value can be realized.

  Further, the end tab after the first stage short circuit part and the second stage short circuit part are cut is located away from the central part of the sensitive part S, and further passes through the central part of the sensitive part S in the sensitivity direction X. They are arranged symmetrically with respect to a symmetry axis ML which is a parallel straight line. Of course, these effects are the same as those of the first embodiment and the second embodiment.

  Further, in the present embodiment, the example in which the conductor pattern is patterned by the etching technique is shown, but the same is effective in the case where the conductor pattern is performed by the additive technique or the like.

The preferred embodiments of the present invention have been described above. The present invention is not limited to the one described in the drawings, and design changes can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Force transducer 2 ... Strain body 3 ... Strain sensor 10 ... 1st end tab part 11a, 11b, 11c, 11d ... Short-circuit part 12a, 12b, 12c, 12d ... 2nd end tab part (folding part)
13e, 13f ... 1st stage short circuit part 14e, 14f ... 2nd stage short circuit part 15e, 15f ... End tab part (folding part)
101, 102 ... terminals e1, e2, e3, e4 ... strain generating parts G, G1, G2, G3, G4 ... strain gauge ML ... symmetry axis S ... sensitive parts T1, T2 ... end tab part region (folded part region)
X: Sensitivity direction

Claims (7)

A sensing part consisting of a plurality of linear wires with the extending direction as the sensitivity direction;
A first end tab portion for connecting the respective wires of the sensing portion at both ends in the sensitivity direction;
A strain gauge for detecting distortion by forming a folded conductor pattern with
Cutting is possible to extend between the adjacent first end tab portions or between the adjacent wirings in a direction crossing the sensitivity direction to short-circuit a part of the conductor pattern. A short circuit,
The end tab ratio of the second end tab portion that plays the role of an end tab connected to each of the wirings in which the detection of strain is activated by cutting the short circuit portion is higher than the end tab ratio of the first end tab portion. A strain gauge characterized by A sensing part consisting of a plurality of linear wires with the extending direction as the sensitivity direction;
A first end tab portion for connecting the respective wires of the sensing portion at both ends in the sensitivity direction;
A strain gauge for detecting distortion by forming a folded conductor pattern with
A short-circuit portion that extends in a direction crossing the sensitivity direction and short-circuits a part of the conductor pattern between adjacent first end tab portions or between adjacent wirings. Has a cutting part cut,
The end tab ratio of the second end tab portion that plays the role of an end tab connected to each of the wirings in which the detection of strain is activated by cutting the short circuit portion is higher than the end tab ratio of the first end tab portion. A strain gauge characterized by 3. The strain gauge according to claim 1, wherein the second end tab portion is provided at a position separated from a central portion of the sensing portion. The second end tab portion is arranged line-symmetrically about a straight line parallel to the sensitivity direction through the central portion of the sensitive portion, or point-symmetrically about the central portion of the sensitive portion. The strain gauge according to claim 1 or 2, wherein   5. The end tab ratio of the second end tab portion is in a range of 1.5 to 3 times the end tab ratio of the first end tab portion. 6. Strain gauge.   A strain sensor comprising the strain gauge according to any one of claims 1 to 5 and constituting a Wheatstone bridge circuit. A force transducer comprising the strain gauge according to any one of claims 1 to 5.