JP2007315840A - Device and method for measuring mechanical impedance of flexible deformable object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method capable of determining a mechanical impedance of a flexible deformable object without using various sensors. <P>SOLUTION: Since a high speed camera 40 as a photographing means for acquiring images before and after deformation of the flexible deformable object 100 is provided, the mechanical impedance such as rigidness, viscosity or elasticity of the flexible deformable object 100 can be determined without using sensors, by determining its displacement and by using an equation of motion of a known object (rigid body 30) which is a displacement applicator. Consequently, stable and highly-accurate measurement can be performed without requiring as hitherto much labor in order to clear problems such as calibration accuracy of various sensors, synchronization of a measuring signal, or noises. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for measuring mechanical impedance such as inertia, rigidity, and viscosity of a flexible deformation material such as polyurethane foam and rubber.

For example, many studies have been reported on the estimation of the viscoelasticity from the frequency response of a sample load test for polyurethane foams that are widely used in various industrial products. Non-Patent Document 1 proposes a viscoelasticity estimation method using a fractional differential model, and Non-Patent Document 2 actually estimates the viscoelasticity of polyurethane foam using a fractional differential model. Has been reported.
RL Bagley, PJ Torvik: A Theoretical Basis for the Application of Fractional Calculus to Viscoelasticity, Journal of Rheology, Vol. 27, No. 3, 201/210 (1983) R. Deng, P. Davies, AK Bajaj: Application of Fractional Derivatives to Modeling the Quasi-Static Responce of Polyurethane Foam, Proceedings of ASME 2003 Design Engineering Technical Conferences, VIB-48397 (2003)

  However, the conventional method requires a plurality of sensors such as an acceleration sensor and a load sensor in order to measure the external force applied to the flexible deformation and the amount of displacement of the surface. Accordingly, it is necessary to clear problems such as calibration accuracy of each sensor, synchronization of measurement signals, noise, and the like, and much labor is required to realize high-accuracy and stable measurement.

  This invention is made | formed in view of said point, and makes it a subject to provide the measuring device and measuring method which can obtain | require the mechanical impedance of a flexible deformation | transformation, without using the above-mentioned various sensors. .

In order to solve the above-described problem, in the present invention according to claim 1, a displacement imparting body that deforms a flexible deformation object that is a measurement object;
An imaging unit that captures at least images before and after the deformation of the flexible deformation product when the flexible deformation product is deformed by the displacement imparting body;
Image processing calculation means for obtaining a displacement amount of the flexible deformation object from an image acquired by the photographing means and obtaining a mechanical impedance of the flexible deformation object using the displacement amount and an equation of motion of the displacement imparting body. There is provided a mechanical impedance measuring device for a flexible deformed material.
According to the second aspect of the present invention, the displacement imparting body is an object having a known mechanical impedance that is caused to collide at a predetermined speed from a predetermined position with respect to a flexible deformation object as a measurement object. A mechanical impedance measuring device for a flexible deformation according to claim 1 is provided.
In this invention of Claim 3, the said known object is a rigid body which deform | transforms a flexible deformation | transformation by being supported by the support frame in the predetermined position above the flexible deformation | transformation object which is a measuring object, and making it fall freely. A mechanical impedance measuring device for a flexible deformation according to claim 2 is provided.
In this invention of Claim 4, a flexible deformation | transformation object is changed with a displacement provision body,
Acquire at least images before and after the deformation of the flexible deformation object by the photographing means,
A flexible deformation object characterized in that a displacement amount of the flexible deformation object is obtained from an image acquired by the photographing means, and a mechanical impedance of the flexible deformation object is obtained using the displacement amount and an equation of motion of the displacement imparting body. Provide a method for measuring the mechanical impedance of
In this invention of Claim 5, the said displacement imparting body is an object with known mechanical impedance, and it is made to collide with the flexible deformation body which is a measuring object from a predetermined position at a predetermined speed, and the said flexible deformation body. The method of measuring a mechanical impedance of a flexible deformed object according to claim 4 is provided.
6. The flexible deformation according to claim 5, wherein the known object is a rigid body, and the flexible deformation is deformed by freely dropping from a predetermined position above the flexible deformation. A method for measuring mechanical impedance of an object is provided.

  According to the present invention, since the photographing means for acquiring the images before and after the deformation of the flexible deformation object is provided, the displacement amount is obtained and the deformation equation is used without using the sensor by using the equation of motion of the displacement imparting body. Mechanical impedance such as inertia, rigidity, and viscosity of an object can be obtained. Therefore, highly accurate and stable measurement can be performed without taking the trouble of clearing problems such as calibration accuracy of various sensors, synchronization of measurement signals, and noise as in the past.

  Hereinafter, the present invention will be described in more detail based on the embodiments shown in the drawings. FIG. 1 is a diagram illustrating an overall configuration of a mechanical impedance measuring apparatus according to the present embodiment. A sample mounting table 10 for supporting a flexible deformable object 100 that is a measurement object, and a support frame attached to the sample mounting table. 20, a displacement imparting body supported by the support frame 20 at a predetermined height above the flexible deformation body 100 on the sample mounting table 10, and a rigid body 30 that is an object having a known mechanical impedance, and an imaging unit. The image processing unit 50 includes a high-speed camera 40 and a computer connected to the high-speed camera 40. Note that “mechanical impedance” means parameters (inertia, rigidity, viscosity) for converting motion into force.

  A rigid body 30, which is a known object supported by the support frame 20 via the support portion 31, is allowed to freely fall from a predetermined height and collide with the flexible deformation object 100. The high-speed camera 40 photographs the marker attached to the rigid body 30 at least at two positions before and after the collision with the flexible deformable object 100 (before and after the deformation), and preferably a plurality of markers continuously from before the collision of the rigid body 30 to after the collision. Take a picture. Note that the rigid body 30 is not allowed to fall freely, but is caused to collide with a flexible deformation object, which is a measurement object, from a predetermined position at a predetermined speed, for example, in a horizontal direction with respect to the flexible deformation object 100. It is also possible to cause a collision at a predetermined speed from a position separated by a predetermined distance and capture the behavior with the high-speed camera 40 as described above.

  The image data acquired by the high speed camera 40 is transmitted to the image processing calculation means 50 and processed. In the image processing calculation means 50, first, the subtraction amount (displacement amount) dX of the flexible deformable object 100 due to the collision of the rigid body 30 is obtained from the position information before the collision of the marker attached to the rigid body 30 and the position information after the collision. Next, from the displacement dX and the equation of motion of the rigid body 30, the speed and acceleration of the rigid body 30 from immediately after the collision to the lowest point (the most depressed position) are obtained. And the mechanical impedance of the flexible deformation | transformation object 100 is calculated | required by the least square method using displacement dX, speed, and acceleration.

FIG. 2 is a diagram for explaining the principle of obtaining the mechanical impedance by the image processing calculation means 50. First, consider a case where a known object of mechanical impedance having a sufficiently large mass M ₀ performs free fall motion vertically and collides with a flexible deformation object 100 as a measurement object at time t ₀ to deform the surface. Assuming that the upward direction in the vertical direction is positive, a forced displacement dX (t) = X (t ₀ ) −X (t) (X (t) is the value of the known object due to the collision of the known object. The characteristic after the fall is added as a function of the displacement dX using the rigidity (K (dX)) and the viscosity (B (dX)), which are mechanical impedances of the flexible deformable body 100. It is expressed by the formula. In the formula, F (t) is the restoring force of the flexible deformable body 100.

  On the other hand, the equation of motion of a known object is expressed by the following equation.

  From equations (1) and (2), based on the shape and mass of a known object, the motion of the rigid body 30 that has collided with the flexible deformable object 100 is measured with high sampling using a photographing means such as a high-speed camera 40. Thus, the displacement dX, the speed, and the acceleration can be calculated.

When the stiffness (K ₀ (dX ₀ )) and viscosity (B ₀ (dX ₀ )) of the known object is sufficiently larger than the flexible deformable material 100 (in the case of a rigid body), the deformation amount dX ₀ is sufficiently small. Therefore, the equation (2) can be transformed as the following equation.

(Test example)
On the sample mounting table 10 shown in FIG. 1, a cushion material (seat back portion) of an automobile seat was placed as the flexible deformation object 100 as a measurement object, and the viscoelastic characteristics were obtained. The seat back has a structure in which polyurethane and fabric are stacked on a metal spring material, and its mechanical properties change nonlinearly with the amount of displacement caused by pressing from the surface. It has been. From this, the viscoelastic characteristics (stiffness (K (dX)) and viscosity (B (dX))) of the seat back part are modeled by the following equation as a nonlinear polynomial related to the displacement dX.

Here, a _i and b _j (i = 0, 1, 2,..., M; j = 0, 1, 2,..., N) are weighting coefficients. Substituting Equation (4) into Equation (1), the viscoelastic characteristics of the seat back portion are estimated using the behavior of the collision object (the rigid body 30 in FIG. 1) of the image information obtained from the high-speed camera 40. In this test example, the order of the viscoelastic model was set to m = 6 and n = 5. In addition, in order to realize stable estimation of viscoelastic properties, the coefficient of the stiffness function estimated in a quasi-static pressurization test performed in advance was set as an initial value.

  The rigid body 30 that is a known object has a diameter of 165 mm, and the combined weight of the rigid body 30 that freely falls by the support frame 20 and the support portion 31 that supports the rigid body 30 was 6.8 kg. The rigid body 30 was set to a height of 300 mm from the surface of the seat back portion, and was allowed to vertically fall and collide. The support portion 31 of the rigid body 30 in the support frame 20 is movable in the same direction as the rigid body 30 is freely dropped. As shown in FIG. 1, the high-speed camera 40 was installed on the extension of the center line in the width direction of the seat back portion, and the marker attached to the rigid body 30 was photographed at a sampling frequency of 1 kHz immediately after dropping. For verification, an acceleration sensor (sampling frequency: 10 kHz) was attached to the support portion 31.

  FIG. 3 shows the displacement dx, speed, and acceleration from immediately after the rigid body 30 collides with the surface of the seat back portion to the lowest point, obtained by the image processing calculation means 50 based on the obtained image information. (A) to (c). In each case, the results of the last five consecutive trials of the ten consecutive trials are drawn with thin lines, and the acceleration graph in FIG. 3C shows the acceleration of the tenth trial measured by the acceleration sensor. Is indicated by a broken line.

  As shown in FIG. 3, as the amount of displacement from the surface of the seat back portion increases, the acceleration slightly varies so as to be proportional to this, but immediately after the collision using the image data taken by the high-speed camera 40. It can be seen that the behavior of the rigid body 30 can be measured with high reproducibility. In addition, regarding the acceleration waveform in FIG. 3C, the acceleration (thin line) obtained from the image data of the high-speed camera 40 by the image processing calculation means 50 is substantially coincident with the acceleration (dashed line) measured by the acceleration sensor. It has been verified that the behavior of the rigid body 30 can be accurately measured by the method of the present invention using the high-speed camera 40.

  Next, using the displacement dx, velocity, and acceleration obtained from the measurement data of the five trials, the image processing calculation unit 50 calculates the above formulas (1) to (4) to obtain viscoelastic characteristics (rigidity ( K (dX)) and viscosity (B (dX))) were determined (estimated). The results are shown in FIGS. In these figures, the horizontal axis represents the displacement dX. FIG. 4 shows an initial stiffness function (broken line) used in calculating the stiffness in addition to the average (solid line) of the estimated stiffness (K (dX)). FIG. 5 shows the average of the estimated viscosity (B (dX)). FIG. 6 shows the restoring force (broken line) obtained by using the average of the restoring force (solid line) of the seat back portion obtained from the estimation result and the acceleration data of the 10th trial measured by the high-speed camera.

  From FIG. 4, the estimated stiffness approximates the initial stiffness, and the viscosity of FIG. 5 also shows some variation near the maximum displacement, but the estimated viscosity variation as a whole. Is small and can be estimated with high reproducibility. Further, as shown in FIG. 6, the sheet restoring force obtained from the estimation result almost coincides with the restoring force measured by the high-speed camera 40, so that the accuracy of the estimation result can be confirmed. . Therefore, it has been verified that the mechanical impedance of the flexible deformable object can be estimated by using the imaging means such as the high-speed camera 40 and the motion equation of a known object (for example, the rigid body 30) as the displacement imparting body.

  In the above embodiment, the seat back portion of the automobile seat is taken up as the flexible deformation, but this is only an example, and in addition to the cushioning material for the vehicle seat such as an automobile, train, airplane, etc. Needless to say, the present invention can also be applied to the estimation of the mechanical impedance of cushion materials for office chairs, cushion materials used for bedding such as bed pads, and other flexible deformations (for example, human bodies that are difficult to attach sensors or the like).

FIG. 1 is a diagram showing an overall configuration of a mechanical impedance measuring apparatus according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the principle of obtaining the mechanical impedance. FIG. 3A is a diagram showing the amount of displacement obtained by the image processing calculation means from immediately after the rigid body collides with the surface of the seat back portion to the lowest point, and FIG. FIG. 3C is a diagram showing the acceleration of the rigid body at that time. FIG. 4 is a diagram showing an initial stiffness function (broken line) used in calculating the stiffness in addition to the estimated average stiffness (solid line) in the test example. FIG. 5 is a diagram showing the estimated average viscosity. FIG. 6 is a diagram showing the average of the restoring force (solid line) of the seat back portion obtained from the estimation result and the restoring force (broken line) obtained using the acceleration data measured by the high-speed camera.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sample mounting base 20 Support frame 30 Rigid body 31 Support part 40 High-speed camera 50 Image processing calculating means 100 Flexible deformation | transformation object

Claims (6)

A displacement imparting body for deforming a flexible deformation object as a measurement object;
An imaging unit that captures at least images before and after the deformation of the flexible deformation product when the flexible deformation product is deformed by the displacement imparting body;
Image processing calculation means for obtaining a displacement amount of the flexible deformation object from an image acquired by the photographing means and obtaining a mechanical impedance of the flexible deformation object using the displacement amount and an equation of motion of the displacement imparting body. An apparatus for measuring mechanical impedance of a flexible deformed material.   2. The flexible deformation object according to claim 1, wherein the displacement imparting body is an object having a known mechanical impedance that collides at a predetermined speed with respect to the flexible deformation object that is a measurement object. Mechanical impedance measuring device.   3. The known object is a rigid body that is supported by a support frame at a predetermined position above a flexible deformed object that is a measurement object, and that deforms the flexible deformed object by being freely dropped. Mechanical impedance measuring device for flexible deformation. Deform the flexible deformation by the displacement imparting body,
Acquire at least images before and after the deformation of the flexible deformation object by the photographing means,
A flexible deformation object characterized in that a displacement amount of the flexible deformation object is obtained from an image acquired by the photographing means, and a mechanical impedance of the flexible deformation object is obtained using the displacement amount and an equation of motion of the displacement imparting body. Mechanical impedance measurement method.   The displacement imparting body is an object having a known mechanical impedance, and causes the flexible deformation object to be deformed by colliding with a predetermined speed from a predetermined position with respect to the flexible deformation object as a measurement object. Item 5. A method for measuring mechanical impedance of a flexible deformation according to Item 4.   6. The method of measuring a mechanical impedance of a flexible deformation according to claim 5, wherein the known object is a rigid body, and the flexible deformation is deformed by freely dropping from a predetermined position above the flexible deformation.

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