Three-component force measuring device and multi-component force measuring table

Abstract

This invention provides a method to suppress measurement errors due to temperature drift, even when the temperature changes between multiple piezoelectric elements differ. [Solution] A three-component force measuring device is provided, which uses multiple shear force measuring elements with different measurement directions, by combining two surfaces of concentric Y-cut piezoelectric elements that output positive charges via electrodes, and includes a shear force measuring element 1 positioned to detect shear force in the rightward direction with a detection part on its upper surface, a shear force measuring element 2 positioned approximately parallel to the shear force measuring element 1 and on the upper surface in contact with the shear force measuring element 1, so as to detect shear force in the depth direction with a detection part on its upper surface, a shear force measuring element 3 positioned approximately vertically below and to the left of the shear force measuring element 1, so as to detect shear force downward with a detection part on its right surface, and a shear force measuring element 4 positioned approximately vertically below and to the right of the shear force measuring element 1 and further approximately parallel to the shear force measuring element 3, so as to detect shear force downward with a detection part on its left surface.

Description

Technical Field

[0001] The present invention relates to a multi-component force measuring device having a piezoelectric element for measuring a plurality of shearing forces and having a structure for suppressing a measurement error due to the influence of temperature, so-called temperature drift.

Background Art

[0002] As an old technology for measuring multi-components, there is a measuring device for measuring multi-component forces in which several multi-component force sensors are sandwiched between a base plate and a top plate and a pressing force is applied and fixed to them by screws (Patent Document 1). However, in this structure, when a temperature change occurs in the measuring device, due to the difference in the thermal expansion coefficients of the constituent members such as the multi-component force sensors and the screws, a change in the pressing load occurs due to the difference in the amount of expansion due to the temperature change. As a result, an error (temperature drift) occurs in the output of the sensor that measures in the same direction as the pressing direction.

[0003] Therefore, in the invention related to the "force and (or) inertia measuring device" (Patent Document 2), in order to suppress the measurement error due to the temperature change of the sensor that measures in the same direction as the pressing direction, so-called temperature drift, the screw for applying the pressing force is installed horizontally, and the polarities in the pressing direction of the two force measuring cells installed on the same screw for applying the pressing force are opposite to each other. By adding up the outputs of these two force measuring cells, the stress components to the two force measuring cells generated by the temperature change can be canceled out. However, in this method, since the error due to temperature drift can be canceled out only when the temperature changes of the two force measuring cells are the same, there is a problem that it is not effective when the temperature changes are different, such as when the installation distance between the two force measuring cells is large.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] The present invention aims to provide a method for suppressing measurement errors due to temperature drift, even when the temperature changes between multiple piezoelectric elements differ. [Means for solving the problem]

[0006] The present invention relates to a three-component force measuring device and a multi-component force measuring table that solve the above problems by having the following configuration. [1] The device comprises two Y-cut piezoelectric elements that are concentric, with one side emitting a negative charge and the other side emitting a positive charge. The two positive charge-emitting surfaces of the concentric Y-cut piezoelectric element are aligned. By using multiple shear force measuring elements with different measurement directions, which are combined via electrodes, The device includes a shear force measuring element 1 (Type A for Fy) positioned to detect shear force in the rightward direction using a detection section on its upper surface, and a shear force measuring element 2 (Type C for Fx) positioned substantially parallel to the shear force measuring element 1 and on its upper surface in contact with the shear force measuring element 1, positioned to detect shear force in the depth direction using a detection section on its upper surface. The shear force measuring element 3 (Type A for Fz) is positioned approximately vertically below and to the left of the shear force measuring element 1 (Type A for Fy), and is configured to detect the shear force downwards with a detection unit on its right side. A three-component force measuring device characterized by comprising a shear force measuring element 4 (Type B for Fz) positioned approximately vertically below and to the right of the shear force measuring element 1 (Type A for Fy), and further positioned approximately parallel to the shear force measuring element 3 (Type A for Fz), such that the shear force is detected downward by a detection unit on the left side. [2] The device comprises two Y-cut piezoelectric elements that are concentric, with one side emitting a negative charge and the other side emitting a positive charge. The two positive charge-emitting surfaces of the concentric Y-cut piezoelectric element are aligned. By using multiple shear force measuring elements with different measurement directions, which are combined via electrodes, A shear force measuring element 1 (Type A for Fy) is positioned to detect shear force in the rightward direction at the detection section on the top surface, The device comprises a shear force measuring element 1 (Type A for Fy), a shear force measuring element 2 (Type D for Fx) positioned approximately vertically below and to the left to detect shear force in the depth direction, and further to the left of that, a shear force measuring element 3 (Type A for Fz) positioned to detect shear force downwards with a detection unit on its right side. A three-component force measuring device characterized by comprising: a shear force measuring element 4 (Type C for Fx) positioned approximately vertically below and to the right of the shear force measuring element 1 (Type A for Fy), and further positioned approximately parallel to the shear force measuring element 2 (Type D for Fx), so as to detect the shear force in the depth direction with a detection unit on its left side; and a shear force measuring element 5 (Type B for Fz) positioned to the right of the shear force measuring element 4 (Type C for Fx) so as to detect the shear force downward with a detection unit on its left side. [3] A multi-component force measuring table incorporating multiple three-component force measuring devices as described in {1} and / or {2} above. A multi-component force measuring table according to {3}, wherein multiple three-component force measuring devices according to {1} and / or {2} above are incorporated near the four corners of a {4} rectangular table. [Effects of the Invention]

[0007] According to the present invention [1], it is possible to provide a three-component force measuring device that has the remarkable effect of suppressing measurement errors due to temperature drift, even when the temperature changes between piezoelectric elements are different.

[0008] According to the present invention [2], it is possible to provide a three-component force measuring device that has the remarkable effect of suppressing measurement errors due to temperature drift even when the temperature changes between piezoelectric elements are different.

[0009] According to the present invention [3], it is possible to provide a multi-component force measuring table that has the remarkable effect of suppressing measurement errors due to temperature drift, even when the temperature changes between the three-component force measuring devices are different. [Brief explanation of the drawing]

[0010] [Figure 1] This is a diagram illustrating an example of Pattern A, a three-component sensor with temperature drift reduction using a shear force measuring element. [Figure 2] This is a diagram illustrating an example of Pattern B, a three-component sensor with temperature drift reduction using a shear force measuring element. [Figure 3] This diagram shows two Y-cut piezoelectric elements, arranged in concentric circles, with one side emitting a negative charge and the other side emitting a positive charge, and one electrode. [Figure 4] This is a diagram of shear force measuring elements of types A to D. [Figure 5] This is a diagram illustrating an example of a multi-component force measuring table incorporating multiple three-component force measuring devices. [Figure 6] This diagram shows an embodiment of a unit in which multiple three-component force measuring devices are incorporated into the spindle case to measure the multi-component forces acting on the spindle unit. [Figure 7] This is an electrical diagram of an embodiment of a unit for measuring the multi-component force acting on a spindle unit. [Modes for carrying out the invention]

[0011] The three-component force measuring device of the present invention 1 comprises two Y-cut piezoelectric elements that are concentric, with one surface emitting a negative charge and the other surface emitting a positive charge. The two positive charge-emitting surfaces of the concentric Y-cut piezoelectric element are aligned. By using multiple shear force measuring elements with different measurement directions, which are combined via electrodes, The device includes a shear force measuring element 1 (Type A for Fy) positioned to detect shear force in the rightward direction using a detection section on its upper surface, and a shear force measuring element 2 (Type C for Fx) positioned substantially parallel to the shear force measuring element 1 and on its upper surface in contact with the shear force measuring element 1, positioned to detect shear force in the depth direction using a detection section on its upper surface. The shear force measuring element 3 (Type A for Fz) is positioned approximately vertically below and to the left of the shear force measuring element 1 (Type A for Fy), and is configured to detect the shear force downwards with a detection unit on its right side. The shearing force measuring element 4 (type B for Fz) is provided, which is substantially vertically downward and to the right of the shearing force measuring element 1 (type A for Fy) and is arranged so as to detect the shearing force downward at the detection part on the left surface substantially parallel to the shearing force measuring element 3 (type A for Fz).

[0012] First, FIG. 3 shows a diagram of combining two Y-cut piezoelectric elements which are concentric circles, where one surface outputs negative charges and the other surface outputs positive charges. As shown in FIG. 3, the Y-cut piezoelectric element with the surface that outputs positive charges and the Y-cut piezoelectric element with the surface that outputs positive charges are combined with an electrode sandwiched therebetween. In the present invention, a Y-cut piezoelectric element of a crystal single crystal is used, but in addition to quartz, those that exhibit a piezoelectric effect such as lead zirconate titanate (PZT) of ceramics may also be used.

[0013] FIG. 4 shows shearing force measuring elements of type A to type D. In the present invention, the types in the direction in which charges are generated with respect to the shearing force are defined as type A to type D shown in FIG. 4. Inside the measuring element, a washer-shaped quartz plate Y-cut from a quartz ingot is incorporated.

[0014] According to this method, since each measuring element can be fixed with a short pressure bolt, the structure can be simplified and various combinations can be realized, so that it becomes easy to incorporate into various devices.

[0015] When the temperature of the environment where the sensor is installed changes due to heat generated by the device to be incorporated or the like, compared with a conventional piezoelectric sensor using an element for measuring compressive / tensile force, the temperature drift of the sensor according to the present invention is very small. When a rapid large temperature change is applied, the sensor according to the present invention shows some temperature drift, but the degree to which the temperature drift decreases over time is very fast compared with a conventional piezoelectric sensor.

[0016] For measuring shear force, only washer-shaped measuring elements that respond only to shear force (Y-cut elements in the case of quartz) are used, and these measuring elements are fixed by applying pre-pressure only in the axial direction. By adopting this assembly method, even if axial stress occurs, the measuring element (sensor) that responds only in the shear direction (radial direction) will not react to changes in axial stress due to the difference in thermal expansion coefficients between the member used to apply pre-pressure and the measuring element. Therefore, only the force to be measured can be measured without being affected by thermal changes. By using this method of assembling the measuring element, it is possible not only to measure three-component forces, but also to combine units that can measure multiple three-component forces and calculate moment values ​​from the relationship with their installation distances to obtain moment values ​​from one-axis to three-axis directions. Furthermore, while the structure of the present invention suppresses the influence of measurement errors due to temperature drift, by using pre-pressure bolts made of the same material as the case surrounding the measuring element, the occurrence of crosstalk due to differences in thermal expansion coefficients can be suppressed, and accuracy can be further improved. In addition, although the measuring element is shown as an independent part in each drawing, further miniaturization can be achieved by integrating it with the surrounding parts.

[0017] Figure 1 shows an example of a three-component temperature drift reduction sensor pattern A using shear force measuring elements. This will be explained in the lower part of Figure 1. A shear force measuring element 1 (Type A for Fy) is positioned to detect shear force in the rightward direction at the detection part on its upper surface. A shear force measuring element 2 (Type C for Fx) is provided on the upper surface that is approximately parallel to the shear force measuring element 1 and in contact with the shear force measuring element 1, so as to detect shear force in the depth direction at the detection part on its upper surface. The shear force measuring element 1 (Type A for Fy) and the shear force measuring element 2 (Type C for Fx) are fastened together with pre-pressure bolts and nuts of the top plate, which also serves as the shear force measuring element for Fx and Fy, and fixed to the inner connecting block.

[0018] Furthermore, a shear force measuring element 3 (Type A for Fz) is positioned approximately vertically below and to the left of shear force measuring element 1 (Type A for Fy), so as to detect the shear force downwards with a detection unit on its right side. Then, a shear force measuring element 4 (Type B for Fz) is positioned approximately vertically below and to the right of shear force measuring element 1 (Type A for Fy), and approximately parallel to shear force measuring element 3 (Type A for Fz), so as to detect the shear force downwards with a detection unit on its left side. Shear force measuring elements 3 (Type A for Fz) and 4 (Type B for Fz) are fixed between the inner connecting block and the two base blocks, respectively, by the pre-pressurizing bolts of the Fz shear force measuring elements.

[0019] The configuration shown in Figure 1 provides a three-component force measuring device that has the remarkable effect of suppressing measurement errors due to temperature drift, even when the temperature changes between each shear force element are different.

[0020] The three-component force measuring device of the present invention 2 comprises two Y-cut piezoelectric elements that are concentric, with one surface emitting a negative charge and the other surface emitting a positive charge. The two positive charge-emitting surfaces of the concentric Y-cut piezoelectric element are aligned. By using multiple shear force measuring elements with different measurement directions, which are combined via electrodes, A shear force measuring element 1 (Type A for Fy) is positioned to detect shear force in the rightward direction at the detection section on the top surface, The device comprises a shear force measuring element 1 (Type A for Fy), a shear force measuring element 2 (Type D for Fx) positioned approximately vertically below and to the left to detect shear force in the depth direction, and further to the left of that, a shear force measuring element 3 (Type A for Fz) positioned to detect shear force downwards with a detection unit on its right side. The present invention is characterized by comprising a shear force measuring element 4 (Type C for Fx) positioned approximately vertically below and to the right of the shear force measuring element 1 (Type A for Fy), and further positioned approximately parallel to the shear force measuring element 2 (Type D for Fx), with the shear force detected in the depth direction by a detection unit on its left side, and a shear force measuring element 5 (Type B for Fz) positioned to the right of the shear force measuring element 4 (Type C for Fx) positioned with the shear force detected downward by a detection unit on its left side.

[0021] Figure 2 shows an example of a three-component temperature drift reduction sensor pattern B using a shear force measuring element. This will be explained in the lower part of Figure 2. The two Y-cut piezoelectric elements are the same as in Invention 1. A shear force measuring element 1 (Type A for Fy) is used as the reference, positioned to detect shear force in the rightward direction at the detection section on the top surface. The shear force measuring element 1 (Type A for Fy) is fastened with a pre-pressure bolt and pre-pressure nut of the top plate / Fy shear force measuring element and fixed to the inner connecting block.

[0022] A shear force measuring element 1 (Type A for Fy) is provided, and a shear force measuring element 2 (Type D for Fx) is positioned approximately vertically below and to the left of it to detect shear force in the depth direction. Further to the left of that, a shear force measuring element 3 (Type A for Fz) is provided to detect shear force downwards with a detection unit on the right side. The shear force measuring element 2 (Type D for Fx) and the shear force measuring element 3 (Type A for Fz) are fixed to the inner connecting block by pre-pressure bolts of the Fx and Fz shear force measuring elements, so as to be held in place from the outside by the base block.

[0023] Shear force measuring element 4 (Type C for Fx) is positioned approximately vertically below and to the right of shear force measuring element 1 (Type A for Fy), and approximately parallel to shear force measuring element 2 (Type D for Fx), so as to detect shear force in the depth direction with a detection unit on its left side. Further to the right of this, shear force measuring element 5 (Type B for Fz) is positioned so as to detect shear force downwards with a detection unit on its left side. Shear force measuring elements 4 (Type C for Fx) and 5 (Type B for Fz) are fixed to the inner connecting block by pre-pressure bolts for the Fx and Fz shear force measuring elements, so as to be held in place from the outside by the base block. [Examples]

[0024] The present invention will be described with reference to examples, but the present invention is not limited to these examples.

[0025] Figure 5 shows an example of a multi-component force measuring table incorporating multiple three-component force measuring devices. As shown in Figure 5, near one corner, the Type D shear force measuring elements for Fx and Type B shear force measuring elements are fixed between the top plate and the inner connecting block using pre-pressure bolts for the Fx and Fy shear force measuring elements. The Type B shear force measuring element for Fz is fixed between the inner connecting block and the base block using pre-pressure bolts for the Fz shear force measuring element. By fixing the shear force measuring elements in a similar manner near the four corners, a multi-component force measuring table is constructed.

[0026] In this configuration, all measuring elements measure shear force. All pre-pressure bolts that fix these shear force measuring elements expand / contract with temperature changes, applying tensile / compressive forces to the measuring elements, but the shear force measuring elements are hardly affected. Therefore, even if temperature changes occur within the three-component force measuring table, temperature drift can be suppressed.

[0027] Figure 6 shows an example of an embedded multi-component force measuring unit in which multiple three-component force measuring devices are incorporated into the spindle of a machining center. As shown in Figure 6, near one corner, one Fz-type E, one Fy-type E, and one Fx-type E shear force measuring element are fixed between the spindle case and the spindle flange via a connecting block using pre-pressure bolts for the Fx and Fy shear force measuring elements and pre-pressure bolts for the Fz shear force measuring element. By fixing the shear force measuring elements in a similar manner near the four corners, the multi-component force measuring unit is incorporated into the spindle of the machining center. Here, the Type E shear force measuring element generates an electric charge when a shear force is applied in the direction of the arrow in the explanatory diagram shown on the right of Figure 6.

[0028] In this configuration, all measuring elements measure shear force. All pre-pressure bolts that fix these shear force measuring elements expand / contract with temperature changes, applying tensile / compressive forces to the measuring elements, but the shear force measuring elements are hardly affected. Therefore, even if temperature changes occur within the built-in multi-component force measuring unit, temperature drift can be suppressed.

[0029] Figure 7 shows an electrical diagram of an embodiment of the embedded multi-component force measurement unit. The circuit shown in this electrical diagram suppresses temperature drift even when temperature changes occur within the multi-component force measurement table. Furthermore, by using the calculation formula shown below, it was possible to accurately determine not only the three-component force but also the moment values ​​in the three axial directions. Fx = Fx1 + Fx2 + Fx3 + Fx4 (1) Fy = Fy1 + Fy2 + Fy3 + Fy4 (2) Fz = Fz1 + Fz2 + Fz3 + Fz4 (3) Mx = c(-Fz1 - Fz2 + Fz3 + Fz4) (4) My = a(-Fz1 + Fz2 + Fz3 - Fz4) (5) Mz = b(-Fx1 - Fx2 + Fx3 + Fx4) +a(-Fy1+Fy2+Fy3-Fy4) (6) Here, the symbols Fx1 to Fz4 indicate the output from each type E shear force measuring element in Figure 6, where X, Y, and Z represent the measurement direction (X, Y, and Z axes), and 1, 2, 3, and 4 represent the position of the type E shear force measuring element in Figure 6. Furthermore, a represents the distance from the centerline of the type E shear force measuring element in the X-axis direction to the centerline of the spindle, and b and c represent the distance from the centerline of the type E shear force measuring element in the Y-axis direction to the centerline of the spindle. [Industrial applicability]

[0030] This system can accurately measure three-component forces without being affected by ambient temperature or the heat generated by the device it is incorporated into. In addition, it can accurately obtain moment values ​​from one-axis to three-axis directions calculated from these forces. Therefore, process monitoring and control based on this information can be performed with high precision.

Claims

1. The system comprises two Y-cut piezoelectric elements that are concentric, with one side emitting a negative charge and the other side emitting a positive charge. The two positive charge-emitting surfaces of the concentric Y-cut piezoelectric element are aligned. By using multiple shear force measuring elements with different measurement directions, which are combined via electrodes, The device includes a shear force measuring element 1 (Type A for Fy) positioned to detect shear force in the rightward direction using a detection section on its upper surface, and a shear force measuring element 2 (Type C for Fx) positioned substantially parallel to the shear force measuring element 1 and on its upper surface in contact with the shear force measuring element 1, positioned to detect shear force in the depth direction using a detection section on its upper surface. The shear force measuring element 3 (Type A for Fz) is positioned approximately vertically below and to the left of the shear force measuring element 1 (Type A for Fy), and is configured to detect the shear force downwards with a detection unit on its right side. A three-component force measuring device characterized by comprising a shear force measuring element 4 (Type B for Fz) positioned approximately vertically below and to the right of the shear force measuring element 1 (Type A for Fy), and further positioned approximately parallel to the shear force measuring element 3 (Type A for Fz), such that the shear force is detected downward by a detection unit on the left side.

2. The system comprises two Y-cut piezoelectric elements that are concentric, with one side emitting a negative charge and the other side emitting a positive charge. The two positive charge-emitting surfaces of the concentric Y-cut piezoelectric element are aligned. By using multiple shear force measuring elements with different measurement directions, which are combined via electrodes, A shear force measuring element 1 (Type A for Fy) is arranged so as to detect shear force in the rightward direction at the detection section on the top surface, The device comprises a shear force measuring element 1 (Type A for Fy), a shear force measuring element 2 (Type D for Fx) positioned approximately vertically below and to the left to detect shear force in the depth direction, and further to the left of that, a shear force measuring element 3 (Type A for Fz) positioned to detect shear force downwards with a detection unit on its right side. A three-component force measuring device characterized by comprising: a shear force measuring element 4 (Type C for Fx) positioned approximately vertically below and to the right of the shear force measuring element 1 (Type A for Fy), and further positioned approximately parallel to the shear force measuring element 2 (Type D for Fx), so as to detect the shear force in the depth direction with a detection unit on its left side; and a shear force measuring element 5 (Type B for Fz) positioned to the right of the shear force measuring element 4 (Type C for Fx) so as to detect the shear force downward with a detection unit on its left side.

3. A multi-component force measuring table incorporating a plurality of three-component force measuring devices according to claim 1 and / or claim 2.

4. A multi-component force measuring table according to claim 3, wherein a plurality of three-component force measuring devices according to claim 1 and / or claim 2 are incorporated near the four corners of a rectangular table.

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