JP2012207960A - Strain gauge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain gauge capable of reducing thermally-induced apparent strain caused by a thermal gradient, even when a strain gauge material having particularly high sensitivity and a large resistance temperature coefficient is employed.SOLUTION: A strain gauge 10 is constituted by a main-strain sensing element 11 and sub-strain sensing elements 12 and 13. The direction in which the main-strain sensing element 11 is arranged and the direction in which the pair of sub-strain sensing elements 12 and 13 are arranged are orthogonal to each other. The pair of sub-strain sensing elements 12 and 13 are disposed symmetrically above and below the main strain sensing element 11. Consequently, the apparent strain due to heat from directions of the sub-strain sensing elements 12 and 13 on both sides is offset.

Description

  The present invention relates to a strain gauge, and more particularly to a strain gauge that detects strain of a tie bar in a mold clamping device of an injection molding machine, for example.

  Conventionally, for example, a strain gauge for detecting strain of a tie bar in a mold clamping device of an injection molding machine is known (for example, Patent Document 1).

  The invention described in Patent Document 1 discloses a detachable sensor for a tie bar, which has a pair of strain gauges orthogonal to each other on a single gauge base and is attached so as to face each other in the 180 ° direction. It is characterized in that the output is increased by the Poisson's ratio as compared with a single gauge bridge circuit.

JP 2004-309400 A

  By the way, since the strain generated in the tie bar originally is very small, it has been desired to improve the output of the strain gauge for tie bars.

  Therefore, when a strain gage material having high sensitivity and a large temperature coefficient of resistance is used to increase the output, the sensitivity is high, but at the same time, the temperature coefficient of resistance increases. The tie bar has a temperature gradient due to heat during injection molding.

  For example, when a strain gauge material having a high sensitivity and a large temperature coefficient of resistance is adopted for a pair of strain gauges orthogonal to each other on a single gauge base described in Patent Document 1, a slight temperature at a minute part particularly during a temperature transient is obtained. When the gradient is generated across a pair of strain gauges, there is a problem that a thermal apparent strain is generated due to the temperature difference between the two direct elements, which causes an error and decreases the measurement accuracy.

  The present invention has been made in view of the above problems, and provides a strain gauge capable of reducing the apparent thermal strain caused by a temperature gradient even when a strain gauge material having a high sensitivity and a large temperature coefficient of resistance is employed. The purpose is to do.

  In order to solve the above-mentioned problems, the present invention provides a strain gauge formed by an element that receives a main strain and an element that receives a sub-strain, and is paired with the element that receives the main strain. The sub-strain-sensitive element is composed of two directions orthogonal to each other, and a pair of sub-strain-sensitive elements are arranged symmetrically above and below the main strain-sensitive element, The present invention is characterized in that the apparent strain due to heat from the direction of the element receiving the strain is offset.

  The present invention is characterized in that a half-bridge circuit is constituted by an element that senses the main strain and a pair of elements that sense the sub-strain.

  Further, the present invention is characterized in that a full bridge circuit including at least two sheets is configured by a strain gauge including an element that receives the main strain and a pair of elements that receive the sub-strain.

  Further, the present invention is characterized in that it can be attached to and detached from a strain measurement target.

  Further, the present invention is characterized in that it can be attached to and detached from a tie bar which is a strain measurement target.

  Further, the present invention is characterized in that an element that receives the main strain and a pair of sub-strains arranged above and below the element that receives the main strain are arranged in a line in the axial direction of the tie bar. .

  According to the present invention, it is possible to provide a strain gauge capable of reducing the apparent thermal strain caused by a temperature gradient even when a strain gauge material having a high sensitivity and a large resistance temperature coefficient is employed.

It is a top view which shows the pattern of one Embodiment of the strain gauge by this invention. It is a figure which shows an example of the circuit diagram of the strain gauge 10 shown in FIG. It is a figure which shows the example different from FIG. 2 of the circuit diagram of the strain gauge 10 shown in FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a plan view showing a pattern of an embodiment of a strain gauge according to the present invention.

  The strain gauge 10 of the present embodiment is not particularly limited with respect to the material of the pattern, but when a strain gauge material having high sensitivity and a large resistance temperature coefficient is used, the effect is more remarkable. Examples of the strain gauge material having high sensitivity and a large temperature coefficient of resistance include Fe—Ni alloys, Fe—Cr alloys, and the like.

  The strain gauge 10 is formed on, for example, a flexible substrate in which a polyimide resin material is formed into a sheet shape, but the type of the substrate material is not particularly limited. However, when the strain gauge 10 of the present embodiment is used as, for example, a strain gauge for detecting strain of a tie bar in a mold clamping device of an injection molding machine, it is required to be detachable from the tie bar and the outer periphery of the tie bar. Therefore, it is preferable to use a flexible substrate as the strain gauge 10 so that the substrate can be bent according to the outer diameter of the tie bar.

  The strain gauge 10 of this embodiment includes electrodes 14, 15 and 16 formed on a substrate, and includes elements 11, 12 and 13 which are gauge resistance elements (sensitive elements). One end of the element 13 is connected to the electrode 14, and the other end of the element 13 is connected to one end of the element 12. The other end of the element 12 is connected to the electrode 16 and to one end of the element 11. The other end of the element 11 is connected to the electrode 15.

  When the strain gauge 10 is attached to a tie bar (not shown), an attachment tool (not shown) is used to closely contact the outer periphery of the tie bar. The direction of the strain gauge 10 at this time is such that the vertical direction in FIG. 1 coincides with the axial direction of the tie bar.

  The element 11 is an element that senses the main strain of the tie bar, and the elements 12 and 13 are elements that sense the sub strain of the tie bar. That is, the element 11 is arranged in a direction that coincides with the axial direction of the tie bar, and the elements 12 and 13 are arranged in a direction orthogonal to the axial direction of the tie bar. In addition, the element 12 and the element 13 are provided as a pair on the upper and lower sides with the element 11 interposed therebetween, and are arranged at symmetrical positions.

  FIG. 2 is a diagram showing an example of a circuit diagram of the strain gauge 10 shown in FIG.

  The example of FIG. 2 is an example in which a half bridge circuit is configured by the strain gauge 10 of the present embodiment.

  In FIG. 2, resistors R <b> 1 and R <b> 2 are resistors having a predetermined resistance value determined so as to form a Wheatstone bridge together with the elements 11, 12, and 13.

  In the half-bridge circuit of FIG. 2, an input voltage 21 is applied between predetermined electrodes according to the known Wheatstone bridge principle, an output is obtained from between the predetermined electrodes, and is amplified by, for example, an amplifier 22 and used as a distortion detection result. .

  FIG. 3 is a diagram showing an example different from FIG. 2 of the circuit diagram of the strain gauge 10 shown in FIG.

  In the example of FIG. 3, in addition to the strain gauge 10 of the present embodiment, another strain gauge 10 a having the same configuration as that of the strain gauge 10 is further provided and attached to a tie bar in the same manner as the strain gauge 10. This is an example in which a full bridge circuit is constituted by the strain gauge 10a.

  In FIG. 3, the strain gauge 10 a has the same configuration as the strain gauge 10, and has a predetermined resistance value determined so as to form a Wheatstone bridge together with the strain gauge 10.

  In the full bridge circuit of FIG. 3, an input voltage 21 is applied between predetermined electrodes according to the known Wheatstone bridge principle, an output is obtained from between the predetermined electrodes, and is amplified by an amplifier 22, for example, and used as a distortion detection result. .

  According to the present embodiment described above, the elements 12 and 13 for detecting the sub-strain are arranged symmetrically above and below the element 11 for detecting the main strain, so that even when a temperature gradient is generated in a plane. The apparent distortion of the adjacent sides that calibrate the bridge becomes equivalent, and the thermal output of the bridge can be offset to compensate for the temperature.

  For example, when there is a temperature gradient in the vertical direction in FIG. 1, there is a temperature difference at each of the planar positions of the elements 11, 12, and 13, but the elements 12 and 13 that detect the secondary strain are the elements 11 that detect the main strain. Therefore, the average temperature of the elements 11, 12 and 13 is the same as that of the element 11 that senses the main strain, and the apparent strain due to heat shows an equivalent value and is offset.

  Further, according to the present embodiment, the elements 12 and 13 that sense two sub-strains are arranged above and below the element 11 that senses main strain, and these are arranged in a line in the axial direction of the tie bar. Therefore, the same applies to the case where the applied pressure is not affected by the curvature of the tie bar and the strain gauge 10 (10a) is attached and the tie bar is replaced with a plurality of tie bars having different curvatures.

  The present invention described above is not limited to this description, and it goes without saying that various modifications and combinations can be made without departing from the spirit of the present invention.

10 Strain gauge 11, 12, 13 Sensitive element (gauge resistance element)
14, 15, 16 Electrode 21 Input voltage 22 Amplifier

Claims (6)

An element sensitive to the main strain;
An element that senses sub-strain;
A strain gauge formed by
The element that receives the main strain and the pair of elements that receive the sub-strain are composed of two orthogonal directions,
A pair of elements that receive the sub-strain are arranged symmetrically above and below the element that receives the main strain,
A strain gauge configured to cancel apparent strain due to heat from the direction of an element that senses the sub-strain on both sides. An element sensitive to the main strain;
A pair of elements that receive the sub-strain;
The strain gauge according to claim 1, wherein a half-bridge circuit is configured. An element sensitive to the main strain;
A pair of elements that receive the sub-strain;
The strain gauge according to claim 1, wherein a full bridge circuit comprising at least two pieces is configured.   The strain gauge according to any one of claims 1 to 3, wherein the strain gauge can be attached to and detached from a strain measurement target.   The strain gauge according to any one of claims 1 to 4, wherein the strain gauge can be attached to and detached from a tie bar which is a strain measurement target.   6. The element that receives the main strain and the pair of sub-strains arranged above and below the element that receives the main strain are arranged in a line in the axial direction of the tie bar. Strain gauge.

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