JP3257563B2 - Hardness measuring device and hardness measuring probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hardness measuring device for evaluating mechanical properties of a surface of an object to be measured such as a living body surface, in particular, hardness, and a hardness measuring probe used therein.

[0002]

2. Description of the Related Art The mechanical properties of the surface of an object to be measured, such as the surface of a living body, can be evaluated by measuring mechanical impedance. This mechanical impedance is expressed as a complex number Z (ω) as a function of the angular frequency ω. From the force F (ω) applied to the surface and the velocity V (ω) of the surface in response, Z (ω) = F (ω) ) / V (ω), and using the acceleration A (ω) = jωV (ω), it is expressed as Z (ω) = jωF (ω) / A (ω) (1).

[0003] Japanese Patent Application No. 2-180546 filed by the present applicant.
Discloses an apparatus capable of calculating the mechanical impedance Z (ω) and a probe used therein.

[0004]

In the above-described apparatus, the mechanical impedance Z (ω) is calculated over a predetermined frequency range, and then various parameters for evaluating the mechanical characteristics are calculated. Measurements of the applied force and the acceleration as a response are obtained in the time domain as a function of time. Therefore, in order to calculate the mechanical impedance by the equation (1), it is necessary to perform a Fourier transform operation for transforming the force and acceleration obtained in the time domain into the frequency domain. It becomes something.

[0005] Since the measurement is performed while holding the probe by hand and pressing it against various parts of the object to be measured, it is desirable that the probe be small and lightweight. Therefore, the first of the present invention
It is an object of the present invention to provide a hardness measuring device that can easily obtain a parameter for evaluating the hardness of a measurement object with a simple configuration.

A second object of the present invention is to provide a small and lightweight measuring probe used in the hardness measuring device.

[0007]

A hardness measuring apparatus according to the present invention, which achieves the first object, changes its magnitude on a surface of an object with a constant amplitude at a constant frequency of 30 Hz or more and 500 Hz or less. Vibration generating means for applying a force to vibrate the surface of the object, acceleration detecting means for detecting the acceleration of the surface vibrating by the vibration generating means, and proportional to the amplitude of the acceleration detected by the acceleration detecting means And an amplitude proportional amount calculating means for calculating an amount to be calculated.

A hardness measuring probe according to the present invention, which achieves the second object, measures a vibrator to be pressed against an object and a static pressure of the vibrator pressed against the object. A static pressure measuring device, a first piezoelectric element for applying a force to the vibrator in accordance with the applied voltage, and a piezoelectric bimorph structure together with the first piezoelectric element, the voltage being proportional to the acceleration of the vibrator And a second piezoelectric element that outputs the same.

[0009]

As will be described in detail later in the embodiment section,
The absolute value of the mechanical impedance at one point within ５００500 Hz, particularly around 200 Hz, is a good indicator of the hardness of the living body surface. When a force that changes at a constant amplitude at this frequency is applied, the amplitude or effective value of the detected acceleration is proportional to the reciprocal of the absolute value of the mechanical impedance. Therefore, the amount proportional to the detected amplitude of the acceleration is an index for evaluating the hardness of the surface of the object.

Further, by using the first piezoelectric element as an actuator for generating vibration and the second piezoelectric element having a piezoelectric bimorph structure as an acceleration detecting sensor, the hardness measuring probe can be reduced in size and weight. can do.

[0011]

EXAMPLE As a result of measuring the mechanical impedance of each part of the living body surface using the device disclosed in Japanese Patent Application No. 2-180546, as shown in FIG. , A soft part characteristic A, an intermediate part characteristic B, a hard part characteristic C
Were found to be classified into three types of patterns
(Oka H. and Yamamoto T .: "Dependence of biomechani
cal impedance uponliving body structure ", Med. & Bi
ol., Eng. & Comput., 25, pp. 631-637 (1987).

Among the living body surfaces, the soft part characteristic A is the largest, but the characteristic shows a particularly low impedance in the frequency range of 30 to 500 Hz. The difference between the three impedance values is particularly prominent in this range. Therefore, one point within this range of 30 to 500 Hz, especially 20 points
If the mechanical impedance is obtained at around 0 Hz, an index for evaluating the hardness of the living body surface can be obtained.

From equation (1), the complex mechanical impedance Z (ω ₀ ) at a specific frequency ω ₀ is Z (ω ₀ ) = jω ₀ F (ω ₀ ) / A (ω ₀ ). Taking the absolute values of both sides, | Z (ω ₀ ) | = ω ₀ | F (ω ₀ ) | / A (ω ₀ ) |, and if ω ₀ and | F (ω ₀ ) | , | Z (ω ₀ ) | = k / | A (ω ₀ ) |; k = constant (2) Equation (2) is obtained by measuring the absolute value or the effective value of the acceleration when a constant amplitude and frequency vibration is applied, and obtaining an amount inversely proportional to the mechanical impedance at that frequency. This means that an amount proportional to the impedance is obtained. Therefore, the parameter SH (SkinHardness) representing the hardness of the living body surface
Is defined as SH = 1 / Ae. Here, Ae is the effective value of the measured acceleration.

FIG. 2 is a block diagram showing an embodiment of a hardness measuring apparatus for automatically calculating and displaying SH on the surface of a living body based on the above principle. Probe 1 for hardness measurement
Reference numeral 0 denotes a vibrator 14 that is in contact with the measurement object 12, a piezoelectric plate 16 for exciting the vibrator 14, a piezoelectric plate 18 for detecting the acceleration of the vibrator 14, and It comprises a load cell 20 for measuring the static pressure when pressed against the object 12, and a grip 22 for holding the probe 10 by hand and pressing the vibrator 14 at the tip of the probe 10 against the object 12 to be measured.

The voltage corresponding to the static pressure output from the load cell 20 is amplified by the distortion amplifier 24 and
Is displayed as a bar graph. An oscillator 28 is connected to the piezoelectric plate 16.
And a sine wave voltage of a constant amplitude and constant frequency amplified by the amplifier 30 is applied. The voltage corresponding to the acceleration output from the piezoelectric plate 18 is amplified by the charge amplifier 32,
It is input to the operation output circuit 34.

As will be described later in detail, the arithmetic output circuit 34
Also receives a static pressure signal from the distortion amplifier 24, calculates the reciprocal of the effective value of the acceleration signal, takes in this signal when the static pressure signal indicates a predetermined static pressure, and calculates an average (total) of 10 times. And outputs it to the display 36. The buzzer 38 is provided for notifying the timing of signal capture and the completion of the ten captures.

FIG. 3 is a block diagram showing the configuration of operation output circuit 34 of FIG. The comparator 40 compares the static pressure signal with a voltage V ₀ corresponding to a predetermined static pressure, and the control pulse generator 42 detects the edge of the comparison signal from the comparator 40, that is, at the timing when the static pressure signal crosses the voltage V ₀ . And outputs two pulse signals having a pulse width of 0.5 seconds and 0.7 seconds.

The acceleration signal from the charge amplifier 32 (FIG. 2) is converted to an rms / dc converter (rms: root mean square) 4.
At 4, the voltage is converted to a DC voltage corresponding to the effective value, and the reciprocal thereof is calculated at a divider 46. The rms / dc converter 44 and the divider 46 are realized by commercially available ICs AD536 and AD534, respectively. The sample / hold circuit 48 samples the input from the divider 46 while the 0.7-second pulse width is not output from the control pulse generator 42, and outputs a 0.7-second pulse. Hold the last sample value while The V / F converter 50 is a sample / hold circuit 4
And outputs a pulse signal having a frequency proportional to the voltage from step 8. The AND gate 52 allows the pulse from the V / F converter 50 to pass only while a pulse having a width of 0.5 seconds is output from the control pulse generator 42. The counter 54 is A
The number of pulses passing through the ND gate 52 is counted.

The counter 56 counts the number of pulses having a width of 0.5 seconds from the control pulse generator 42 and outputs a signal for holding the count value of the counter 54 after counting 10 times. The OR gate 58 passes a 0.5-second pulse from the control pulse generator 42 and a signal indicating the end of counting from the counter 56, and causes the buzzer 38 (FIG. 2) to sound.

The columns (a), (b), (d)... (J) in FIG.
The waveforms of the signals at the locations indicated by a, b, d... J in FIG. 3 are shown, and the column (c) shows the signals inside the control pulse generator 42. The operation of the circuit shown in FIG. 3 will be described with reference to FIGS. FIG. 4A shows a static pressure signal input to the comparator 40. The level of the reference voltage V ₀ is indicated by a broken line. From the comparator 40,
As shown in column (b), an H level signal is output when the static pressure signal is higher than the reference voltage V ₀ , and an L level signal is output when the static pressure signal is lower than the reference voltage V ₀ . The control pulse generator 42 generates a pulse having a very short width at the timing when the level of the signal in the column (b) changes as shown in the column (c), and uses this pulse as a trigger to generate the pulse shown in the column (d). A 0.5-second positive pulse and a 0.7-second negative pulse shown in column (e) are output.

FIG. 4F shows a waveform of the acceleration signal input to the rms / dc converter 44. The rms / dc converter 44 outputs a DC voltage corresponding to the effective value of the input signal, as shown in column (g). This voltage is reciprocal in a divider 46 and 0.7 in a sample and hold circuit 48.
Since the pulse is held while the second pulse is being output, the output is as shown in column (h), and the output of the V / F converter 50 is as shown in column (i). As shown in the column (j), the AND gate 52 allows this pulse to pass only while the 0.5-second pulse is being output.
A digital value proportional to the reciprocal of the effective value of the acceleration is obtained. By calculating the digital value ten times, an average value of the ten times is displayed on the display.

FIG. 5 is a diagram showing a detailed structure of a piezoelectric plate 16 as an actuator and a piezoelectric plate 18 as a sensor incorporated in the probe 10 (FIG. 2). The donut-shaped piezoelectric plates 16 and 18 have a bimorph structure attached to both surfaces of a metal plate 60. Normally, a bimorph-structured piezoelectric element has a force to bend the entire piezoelectric plate or to bend both piezoelectric plates by applying a voltage to extend one piezoelectric plate and contract the other. Is used to extract a voltage from both piezoelectric plates.In the present invention, however, by using one piezoelectric plate of a bimorph structure piezoelectric element as an actuator and using the other piezoelectric plate as a sensor, ,
A small and lightweight probe is realized. The vibration of the vibrator 14 is obtained by fixing the shaft 62 of the piezoelectric element to the vibrator 14 (FIG. 2) and fixing the metal plate 60 to the load cell 20.

SH measured in the apparatus according to the present invention
The value is obtained as being proportional to the sum of the mechanical impedance Z _{s of the} object to be measured and the mechanical impedance Z _p of the vibrating portion of the probe, that is, the mechanical impedance Z _m given by Z _m = Z _s + Z _p . Therefore, as Z _p is smaller, Z _m ≒ Z
_s , and high measurement accuracy can be obtained. The probe used in the present invention has a resonance frequency f _p = 205 as shown in FIG.
The mechanical impedance is minimum at Hz. By measuring at this frequency, highly accurate and highly sensitive measurement is possible.

To examine the reproducibility of the measurement, three types of silicon materials having different hardnesses (Toyo Medical Research Institute, LTV rubber)
The experiment was performed using. Silicone is used for acupuncture and moxibustion education, and has a suitable hardness as a biological tissue simulator. Silicon is assumed to be H, M, S in order of hardness. The hardness values of silicon H, M, and S measured by an industrial Asker hardness meter (F type) are 50, 45, and 40, respectively. Table 1 shows the results obtained by measuring three types of silicon 10 times. It can be seen that sufficient reproducibility of the measurement was obtained in any of the silicons. In addition, SH increases (hardens) in the order of silicon S, M, and H, which is equal to the evaluation of hardness by the Asker hardness tester.

Table 1 Reproducibility of measurement Silicon H (50) Silicon M (45) Silicon S (40) Average value 14439 13481 11909 Standard deviation 146.9 162.9 198.2 Error (%) 1.02 1.21 1.67 Error (%) = (standard deviation / average value) × 100 Using this apparatus, measurement was performed three times at each of five sites on the body surface of an adult male, and the average value was obtained.
Table 2 shows the results. The difference between the forehead where the largest value was obtained and the thigh where the smallest value was obtained is about four times. Considering that the reproducibility of this apparatus is within about 2%, it is considered that the hardness of the living body surface can be sufficiently evaluated.

Table 2 Example of measurement on living body surface Measurement site SH Forehead 43552 Chest 13651 Above rib 14620 Thigh 11646 Calf 13887

[0027]

The features of the hardness measuring device and the hardness measuring probe according to the present invention are as follows. (1) A sinusoidal vibration is applied to the surface of the living body, and the acceleration at that time is detected and the result is displayed.
Real-time measurement is possible. (2) By using a handy-type measurement probe to detect vibration and acceleration on a living body surface, it is possible to perform measurement at almost all parts of the living body surface. In addition, since amplifiers, indicators, and the like can be housed in a small case, they are portable and can be used anywhere. (3) By using a small bimorph type piezoelectric ceramic having a resonance frequency close to the resonance frequency of the soft part of the living body in place of the electrodynamically driven vibrator or impedance head, an inexpensive, small and lightweight handy type measurement probe can be obtained. Production is possible. (4) Measurement can be performed with a constant contact force, and the display of the result is an integrated value of ten times, so that the reliability of the measurement result is high. (5) The SH proposed as an index of the hardness of a living body is not a simple index, but can have a physical meaning of an amount proportional to the impedance.

[Brief description of the drawings]

FIG. 1 is a graph showing three characteristic characteristics of frequency characteristics of mechanical impedance of each part of a living body surface.

FIG. 2 is a block diagram showing an embodiment of a hardness measuring device according to the present invention.

FIG. 3 is a block diagram showing a detailed configuration of an arithmetic output circuit 34 of FIG.

FIG. 4 is a diagram for explaining the operation of the circuit of FIG. 3;

FIG. 5 is a diagram showing a structure of a piezoelectric element used in a hardness measuring probe of the present invention.

FIG. 6 is a graph showing frequency characteristics of mechanical impedance of a probe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Probe 12 ... Measurement object 14 ... Vibrator 16, 18 ... Piezoelectric plate 20 ... Load cell

Continuation of the front page (56) References JP-A-4-71533 (JP, A) JP-A-61-240140 (JP, A) JP-A-3-81641 (JP, A) JP-A-50-81382 (JP, A) JP-A-58-138456 (JP, A) JP-A-1-189583 (JP, A) JP-A-4-160341 (JP, A) JP-A-60-90536 (JP, A) Irie, Oka , Yamamoto, Portable Biomechanical Impedance Measuring Device, Transactions of the Institute of Electronics, Information and Communication Engineers, Japan, The Institute of Electronics, Information and Communication Engineers, February 20, 1992, J75-DII No. 2, P. 432-434 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 3/40 A61B 5/00 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A constant amplitude of 30 Hz or more on the surface of a living body.
Vibration generating means (14, 14) for vibrating the living body surface by applying a force whose magnitude changes at a constant frequency of 00 Hz or less.
16, 28, 30), acceleration detecting means (14, 18) for detecting the acceleration of the surface vibrating by the vibration generating means, and calculating an amount proportional to the amplitude of the acceleration detected by the acceleration detecting means. Proportional amount calculating means (44, 48, 5)
0,54) and the reciprocal of the amplitude proportional amount calculated by the amplitude proportional amount calculating means
Reciprocal calculating means for calculating and evaluating the hardness value of the living body surface
(46) An apparatus for measuring hardness of a living body surface, comprising: 2. The vibration generating means includes: a vibrator (14) pressed against a surface of a living body with a predetermined static pressure; and a force that applies the changing force to the vibrator and applies the changing force to the surface of the living body. An acceleration detector for applying an acceleration to the surface of the living body by detecting an acceleration of the vibrator. The hardness measuring device according to claim 1, comprising: