Frequency deviation detecting circuit and measuring apparatus using the frequency deviation detecting circuit

A hardness measuring apparatus in which a frequency deviation detecting circuit is used has a contact element, an oscillator, a self-oscillating circuit and a gain variation compensating circuit. The self-oscillating circuit feeds back oscillation information of the oscillator to generate a resonant state. The gain variation compensating circuit is disposed in the self-oscillating circuit. The gain variation compensating circuit has a central frequency different from that of the self-oscillating circuit, and increases gain in response to a change in frequency.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a frequency deviation detecting circuit 
and a measuring apparatus using the frequency deviation detecting circuit, 
particularly to a hardness measuring apparatus, which is equipped with a 
contact element which is suitable for a hardness measuring apparatus, 
oscillated by an oscillator and brought into contact with a measuring 
subject in order to measure the hardness of the subject. A hardness 
measuring apparatus provided by the present invention has advantages in 
measuring the hardness of soft subjects, such as rubber, resin, food, and 
that of biological tissue subjects, such as human skin and internal 
organs, whose hardness has not been accurately determined. In addition, 
the present invention is applicable to an acceleration measuring 
apparatus, fluid pressure measuring apparatus or fluid viscosity measuring 
apparatus in which a frequency deviation detecting circuit is used. 
2. Description of the Related Art 
Many measuring apparatuses which detect a change in the frequency of an 
applied signal to determine a property of a subject have been known. For 
example, Japanese Patent Publication No. Sho 40-27236, Japanese Patent 
Laid-Open Publication No. Hei 1-189583 and Japanese Patent Laid-Open 
Publication No. Hei 2-290529 disclose hardness measuring apparatuses which 
determine the hardness of a subject using frequency deviation. The 
hardness measuring apparatuses disclosed in these publications have an 
ultrasonically oscillating probe which is brought into contact with a 
subject (sample to be subjected to measurement), and determine the 
hardness of the subject by detecting a change in the resonance frequency 
or oscillation amplitude of the probe. In such a hardness measuring 
apparatus, a self-oscillating circuit in which an oscillation system 
including a subject contacting oscillator in contact with the subject 
forms a feedback loop causes resonance. When the subject contacting 
oscillator or a contact element mechanically coupled with the subject 
contacting oscillator comes into contact with a subject in a resonant 
state, the impedance of the subject brings about changes in the 
oscillating frequency and detection voltage of the self-oscillating 
circuit. These changes give information about the hardness of the subject. 
This kind of hardness measuring apparatus has the following advantages: 
(1) The hardness of a subject can be quantitatively measured. 
(2) The hardness of a subject can be electrically measured, requiring a 
short measuring time. 
(3) The hardness of a subject can be non-destructively measured without any 
damage to a subject. 
A hardness measuring apparatus having these advantages is promising for 
determining the elasticity (hardness) of human tissue, such as skin and 
internal organs, and that of biological tissues of animals and plants, and 
for being used as a tactile sensor of an industrial robot. 
A circuit having a feedback loop is formed by a self-oscillating circuit or 
the like. 
When an oscillator oscillating in a resonant state due to the circuit comes 
into contact with a subject, a mechanical impedance is added, leading to 
changes in the resonance frequency and detection voltage of the 
oscillator. This phenomenon is already known and described by T. Akatsuka 
and O. Takatani in Journal of the Society of Instrument and Control 
Engineers, Vol. 14, No. 3, pp. 281-292 (1975). According to the general 
frequency-gain (current amplification factor) characteristic of a 
self-oscillating circuit including an oscillator, the gain increases with 
the increase in frequency, has a peak at a resonance frequency (central 
frequency), and decreases with further increase in frequency. When a 
contact probe coupled with such an oscillating circuit is applied to a 
soft and elastic subject, such as biological tissues of human skin or 
internal organs, with a certain area, both the resonance frequency and 
gain decrease, as shown by S. Omata in "Technical Digest of the 9th Sensor 
Symposium" pp. 257-260 (1990). In particular, the hardness of a biological 
tissue is changed when a pathological lesion exists in the tissue. The 
presence of the pathological lesion can be easily detected by measuring 
the hardness of the tissue. Therefore, this method is expected to be 
applied in the field of medicine. 
When the hardness of such a soft subject as a biological tissue is 
measured, however, neither a change in the resonant frequency nor that in 
the oscillation amplitude is detected as a sufficient detection voltage, 
due to a decreased gain. This prevents the hardness of such a biological 
tissue from being precisely measured. In particular, hardness information 
extracted by a subject contacting oscillator or contact element of a 
hardness measuring apparatus has a lot of noise, which is added to the 
detection voltage. Consequently, it is difficult to obtain accurate 
hardness information. In addition, the hardness is varied even among soft 
subjects, and the frequency characteristic and the variation in gain are 
different among the soft subjects. Therefore, it has been difficult to 
accurately obtain the hardness information of various subjects. 
SUMMARY OF THE INVENTION 
In order to solve the above problems, the present invention has the 
following objects: 
(1) The first object of the present invention is to provide a frequency 
deviation detecting circuit which has a simple structure, is fabricated 
with low cost, and can accurately detect oscillation information of an 
oscillator in a wide frequency range. 
(2) The second object of the present invention is to provide a hardness 
measuring apparatus which can obtain hardness information of soft and hard 
subjects in a wide hardness range. 
(3) The third object of the present invention is to provide a hardness 
measuring apparatus which achieves the second object, has a simple 
structure, and is fabricated with low cost. 
(4) The fourth object of the present invention is to provide a hardness 
measuring apparatus which achieves the third object, and whose size can be 
reduced. 
(5) The fifth object of the present invention is to provide a hardness 
measuring apparatus by which the hardness of a biological tissue, 
particularly that of a human living tissue, can be easily and accurately 
measured, and a medical diagnosis can be easily performed for preventing a 
disease. 
(6) The sixth object of the present invention is to provide various 
apparatuses equipped with the frequency deviation detecting circuit, such 
as an acceleration measuring apparatus, fluid pressure measuring apparatus 
and fluid viscosity measuring apparatus. 
In order to solve the above problems, a frequency deviation detecting 
circuit provided by the invention comprises an oscillator for generating 
oscillation, a self-oscillating circuit for feeding back oscillation 
information of the oscillator to generate a resonant state, and a gain 
variation compensating circuit which is disposed in the self-oscillating 
circuit, has a central frequency different from that of the 
self-oscillating circuit, and increases gain in response to a change in 
frequency, wherein the oscillator and self-oscillating circuit form an 
electromechanical oscillation system, and the effective resonance 
frequency band of the electromechanical oscillation system is expanded. 
According to the invention, the gain variation compensation circuit 
increases the gain in response to a change in the resonance frequency of 
the electromechanical system. Since the detection voltage as the 
oscillation information of the oscillator can be increased by an increase 
in the gain, the oscillation information can be accurately detected. In 
addition, since the gain can be increased in response to a change in the 
resonance frequency of the oscillator, the oscillation information of the 
oscillator can be accurately detected in a wide frequency range. 
The invention provides a frequency deviation detecting circuit, wherein the 
gain variation compensating circuit has a phase transfer function for 
adjusting the difference between the input and output phases, called phase 
difference, of the self-oscillating circuit to zero, and of promoting 
feedback oscillation, shifts the frequency so that the phase difference 
becomes zero, and increases the gain. In the invention, the gain variation 
compensating circuit has the phase transfer function, can further change 
the central frequency by a frequency corresponding to the phase difference 
of the electromechanical oscillation system when the frequency of the 
electromechanical oscillation system is changed, and can increase the gain 
in response to the change in the central frequency. Therefore, the 
detection voltage of the oscillator as oscillation information is 
increased by the further increased gain. This enables the oscillation 
information to be precisely detected. Since the gain can be increased in 
response to a change in the resonant frequency of the oscillator, the 
oscillation information of the oscillator can be precisely detected in a 
wide frequency range. 
A hardness measuring apparatus provided by the invention comprises a 
contact element coming into contact with a subject, an oscillator for 
oscillating the contact element, a self-oscillating circuit which feeds 
back oscillation information of the oscillator in contact with the subject 
to generate a resonant state, and a gain variation compensating circuit 
which is disposed in the self-oscillating circuit, has a central frequency 
different from that of the self-oscillating circuit, and increases gain in 
response to a change in frequency, wherein the contact element, oscillator 
and self-oscillating circuit form an electromechanical oscillation system, 
and the effective resonance frequency band of the electromechanical 
oscillation system is expanded. According to the invention, when the 
contact element is in contact with a subject, the resonance frequency of 
an electromechanical oscillation system is changed in response to a change 
in mechanical impedance representing the hardness of the subject. The gain 
variation compensating circuit increases the gain in response to the 
change in the resonance frequency. Since the detection voltage as hardness 
information of the subject can be increased by the increase in the gain, 
the hardness of the subject can be accurately measured. In addition, when 
various hardnesses of subjects are measured, the gain can be increased in 
response to changes in resonance frequency. This enables the measurement 
of hardness to be accurate in a wide hardness range. 
The invention further provides a hardness measuring apparatus, wherein the 
hardness of a subject is measured using a change in the frequency of the 
electromechanical oscillation system. 
The invention further provides a hardness measuring apparatus, wherein the 
hardness of a subject is measured using a change in the phase of the 
electromechanical oscillation system. 
The invention further provides a hardness measuring apparatus, wherein the 
gain compensating circuit increases the gain with a decrease in frequency, 
and the effective resonance frequency band of the electromechanical 
oscillation system is expanded in a frequency range used for measuring the 
hardnesses of soft subjects. 
The invention further provides a hardness measuring apparatus, wherein the 
oscillator is any one of a piezoelectric ceramic oscillator, a layered 
ceramic oscillator, a PVDF-based oscillator, a magnetostrictive element, a 
bimorph oscillator, a quartz oscillator or a surface acoustic wave (SAW) 
element. 
The invention provides a hardness measuring apparatus, wherein the 
self-oscillating circuit has an amplifying circuit for amplifying the 
oscillation information of the oscillator. 
The invention provides a hardness measuring apparatus, wherein the gain 
variation compensating circuit comprises any of a band-pass filter 
circuit, a low-pass filter circuit, a high-pass filter circuit, a notch 
filter circuit, an integrating circuit, a differentiating circuit, a 
peaking amplifying circuit, an active filter circuit or a passive filter 
circuit. 
The invention further provides a hardness measuring apparatus, wherein the 
gain variation compensating circuit is disposed between an output terminal 
of the oscillator and an input terminal of the amplifying circuit of the 
self-oscillating circuit, or between an output terminal of the amplifying 
circuit of the self-oscillating circuit and an input terminal of the 
oscillator. 
A hardness measuring apparatus provided by the invention further comprises 
a contact element becoming in contact with a subject, an oscillator for 
oscillating the contact element, a self-oscillating circuit which feeds 
back oscillation information of the oscillator in contact with the subject 
to generate a resonant state, a gain variation compensating circuit which 
is disposed in the self-oscillating circuit, has a central frequency 
different from that of the self-oscillating circuit, and increases gain in 
response to a change in frequency, an electromechanical oscillation system 
formed by the contact element, oscillator and self-oscillating circuit and 
a frequency measuring circuit for detecting a change in the frequency of 
the electromechanical oscillation system. 
The invention further provides a hardness measuring apparatus, wherein the 
gain variation compensating circuit has a phase transfer function of 
adjusting the difference between the input and output phases, called phase 
difference, of the self-oscillating circuit to zero, and of promoting 
feedback oscillation, shifts the frequency so that the phase difference 
becomes zero, and increases the gain. In the invention, the gain variation 
compensating circuit has the phase transfer function, can further change 
the central frequency by a frequency corresponding to the phase difference 
of the electromechanical oscillation system when the frequency of the 
electromechanical oscillation system is changed, and can increase the gain 
in response to the change in the central frequency. Therefore, the 
detection voltage of the oscillator as oscillation information is 
increased by the further increased gain. This enables the oscillation 
information to be precisely detected. Since the gain can be increased in 
response to a change in the resonant frequency of the oscillator, the 
hardness of a soft subject or hard subject can be precisely determined in 
a wide range. 
The invention also provides a hardness measuring apparatus, further 
comprising a detecting element for detecting the oscillation information 
of the oscillator, wherein the oscillator includes a layered piezoelectric 
ceramic oscillator formed by stacking a plurality of piezoelectric ceramic 
layers, and the detecting element comprises a film-shaped bimorph 
oscillator. 
The invention provides a hardness measuring apparatus, further comprising a 
detecting element for detecting the oscillation information of the 
oscillator, wherein both the oscillator and detecting element comprise a 
layered piezoelectric ceramic oscillator formed by stacking a plurality of 
piezoelectric ceramic layers. 
The invention provides a hardness measuring apparatus, further comprising a 
detecting element for detecting the oscillation information of the 
oscillator, wherein both the oscillator and detecting element comprise a 
film-shaped piezoelectric material. 
A hardness measuring apparatus provided by the invention comprises a 
contact element becoming in contact with a subject, an oscillator for 
oscillating the contact element, a phase lock loop circuit which feeds 
back oscillation information of the oscillator in contact with the subject 
to generate a resonant state, and a gain variation compensating circuit 
which is disposed in the phase lock loop circuit, has a central frequency 
different from that of the phase lock loop circuit, and increases gain in 
response to a change in frequency, wherein the contact element, oscillator 
and phase lock loop circuit form an electromechanical oscillation system, 
and the effective resonance frequency band of the. electromechanical 
oscillation system is expanded. 
The invention provides a hardness measuring apparatus, wherein the subject 
is a biological tissue, and the contact element is made to come into 
contact with the biological tissue when the hardness of the biological 
tissue is measured. 
The invention provides a hardness measuring apparatus, wherein the 
biological tissue is any of skin, internal organs, body cavities, bones, 
teeth or nails, and its hardness is measured. 
The invention also provides a hardness measuring apparatus, further 
comprising a main probe in which the oscillator is contained, and the 
contact element is fixed, and a monitor for displaying hardness 
information based on the oscillation information. 
The invention also provides a hardness measuring apparatus, further 
comprising a fiberscope unit, wherein an observation image obtained by the 
fiberscope unit is displayed on the monitor. 
The invention also provides a hardness measuring apparatus, further 
comprising a contact needle and outer needles for puncturing a biological 
tissue, wherein the contact needle is used as the contact element, and the 
outer needles are disposed around the contact needle to form the tip 
portion of the main probe. 
The invention further provides a hardness measuring apparatus, wherein the 
tip portion of the main probe is formed by a soft tube. 
An acceleration measuring apparatus for measuring a change in the 
acceleration of a moving substance, provided by the invention, further, 
comprises an oscillator which is placed on the moving substance to 
generate oscillation, a self-oscillating circuit which feeds back 
oscillation information of the oscillator to generate a resonant state, 
and a gain variation compensating circuit which is disposed in the 
self-oscillating circuit, has a central frequency different from that of 
the self-oscillating circuit, and increases gain in response to a change 
in frequency, wherein the oscillator and self-oscillating circuit form an 
electromechanical oscillation system, and consequently the effective 
resonance frequency band of the electromechanical oscillation system is 
expanded. 
A fluid viscosity measuring apparatus for measuring a change in the 
viscosity of a fluid, provided by the invention, further any of an 
oscillator for generating oscillation in the fluid or an oscillator for 
oscillating a fluid contacting element put into the fluid, a 
self-oscillating circuit which feeds back oscillation information of the 
oscillator to generate a resonant state, and a gain variation compensating 
circuit which is disposed in the self-oscillating circuit, has a central 
frequency different from that of the self-oscillating circuit, and 
increases gain in response to a change in frequency, wherein the 
oscillator and self-oscillating circuit form an electromechanical 
oscillation system, and the effective resonance frequency band of the 
electromechanical oscillation system is expanded. 
A fluid pressure measuring apparatus for measuring a change in the pressure 
of a fluid, provided by the invention, further comprises a fluid 
contacting element whose shape is changed in response to the pressure of 
the fluid, an oscillator which generates oscillation, and the position of 
which is moved in response to the change in the pressure of the fluid, a 
self-oscillating circuit which feeds back oscillation information of the 
oscillator to generate a resonant state, and a gain variation compensating 
circuit which is disposed in the self-oscillating circuit, has a central 
frequency different from that of the self-oscillating circuit, and 
increases gain in response to a change in frequency, wherein the 
oscillator and self-oscillating circuit form an electromechanical 
oscillation system, and the effective resonance frequency band of the 
electromechanical oscillation system is expanded. 
The invention further provides a measuring apparatus, wherein the gain 
variation compensating circuit has a phase transfer function of adjusting 
the difference between the input and output phases, called phase 
difference, of the self-oscillating circuit to zero, and of promoting 
feedback oscillation, shifts the central frequency so that the phase 
difference becomes zero, and increases the gain.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
System Structure of a Hardness Measuring Apparatus! 
In Embodiment 1 of the present invention, a hardness measuring apparatus 
utilizing a frequency deviation circuit is described. FIG. 1 shows the 
overall structure of a hardness measuring apparatus according to 
Embodiment 1 of the present invention. The hardness measuring apparatus 
has a hand piece 1 and a control unit disposed outside the hand piece 1. 
The hand piece 1 has a casing 2 formed in a substantially cylindrical shape 
having a bottom. An oscillator 3 is disposed inside the middle portion of 
the casing 2. The oscillator 3 has a cylindrical shape. In this 
embodiment, a piezoelectric ceramic oscillator is used as the oscillator 
3. FIG. 2 shows a cross-sectional view of the main part of the oscillator 
3. The oscillator 3 comprises a first electrode 3A used as an anode, a 
second electrode 3C used as a cathode, and a piezoelectric crystal 3B 
formed between the first and second electrodes 3A and 3C. The 
piezoelectric crystal 3B has a cylindrical shape. The first electrode 3A 
is formed on the inner surface of the piezoelectric crystal 3B in a 
cylindrical shape. The second electrode 3C is formed on the outer surface 
of the piezoelectric crystal 3B in a cylindrical shape, and grounded. In 
the oscillator 3, a voltage varying with time is applied between the first 
and second electrodes 3A and 3C, causing mechanical oscillation of the 
piezoelectric crystal 3B. In a hardness measuring apparatus according to 
this embodiment, any of a quartz oscillator, a PVDF-based oscillator, a 
magnetostrictive element or a surface acoustic wave (SAW) element can be 
used as the oscillator 3, instead of the piezoelectric ceramic oscillator. 
The oscillator 3 is mechanically coupled with a contact element 5 via an 
oscillation conducting member 4. An end portion of the oscillation 
conducting member 4, which extends inside the casing 2 toward its open 
end, is coaxially fixed on the inner surface of the second electrode 3C at 
a middle portion of the oscillator 3 with adhesive. The other end of the 
oscillation conducting member 4 is coupled with the contact element 5 with 
adhesive. As shown in FIG. 1, the contact element 5 is a cylinder having 
one closed end (tip portion), which is in contact with a subject H. The 
contact element 5 has a hole 5A at the center of the tip portion. The 
oscillation conducting member 4 is inserted into the hole 5A. The hole 5A 
of the contact element 5 and oscillation conducting member 4 are fixed 
with adhesive. 
The contact element 5 is disposed inside an oscillation maintaining hole 2A 
formed at the end portion of the casing 2 facing toward the subject H. The 
tip portion of the contact element 5 facing toward the subject H projects 
from the end portion of the casing 2. The contact element 5 disposed 
inside the oscillation maintaining hole 2A can freely oscillate in the 
axial direction. A groove 2B is form ed on the inner surface of the 
oscillation maintaining hole 2A along its circumference. An elastic member 
6 is put in the groove 2B. The contact element 5 is retained in the 
oscillation maintaining hole 2A of the casing 2 via the elastic member 6. 
The oscillation to be conducted to the contact element 5 from the 
oscillator 3 via the oscillation conducting member 4 is absorbed by the 
elastic member 6, and consequently it is not conducted to the hand piece 
1. For example, an O-ring is used as the elastic member 6. In a hardness 
measuring apparatus according to this embodiment, the elastic member 6 
works as a node of the oscillation of an electromechanical oscillation 
system described later. The node is formed at a connecting point of the 
oscillation conducting member 6 and the contact element 5, between the 
casing 2 and the contact element 5. The elastic member 6 is not always 
disposed at this position, and can be disposed between the 
electromechanical oscillation system and casing 2 at such a position that 
the oscillation of the electromechanical oscillation system is not 
conducted to the casing, and the casing 2 does not adversely affect the 
oscillation of the electromechanical oscillation system. 
A detecting element 7 is placed on the outer surface of the oscillator 3 
inside the casing 2. The detecting element 7 comprises a first electrode 
7A used as a cathode, a second electrode 7C used as an anode, and a 
piezoelectric crystal 7B formed between the first and second electrodes 7A 
and 7C. An electrode cylindrically formed on the outer surface of the 
oscillator 3 is commonly used as the first electrode 7A of the detecting 
element 7 and the second electrode 3C of the oscillator 3. The 
piezoelectric crystal 7B is formed on the outer surface of the first 
electrode in a cylindrical shape. The second electrode 7C is formed on the 
outer surface of the piezoelectric crystal 7B in a cylindrical shape. The 
detecting element 7 basically comprises piezoelectric ceramic, as the 
oscillator 3. The detecting element 7 oscillates in synchronism with the 
oscillation of the oscillator 3, and is used as a sensor for detecting the 
oscillation as an electrical signal. The detecting element 7 outputs 
hardness information capable of monitoring the oscillation amplitude, 
frequency and phase of the oscillator 3 as a detection voltage. 
A control unit 10 of the hardness measuring apparatus comprises a 
self-oscillating circuit 11, a gain variation compensating circuit 13, a 
voltage measuring circuit 14 and a frequency measuring circuit 15. The 
self-oscillating circuit 11 has an amplifying circuit 12, whose input 
terminal is connected to the output terminal (second electrode 7C) of the 
detecting element 7. The output terminal of the amplifying circuit 12 is 
connected to the input terminal (first electrode 3A) of the oscillator 3 
via the gain variation compensating circuit 13. 
The self-oscillating circuit 11 has the oscillator, detecting element 7 and 
amplifying circuit 12. The detecting element 7 detects oscillation 
information of the oscillator 3, and converts it into an electrical 
signal. The amplifying circuit 12 amplifies the electrical signal. The 
amplified electrical signal is fed back to the oscillator 3, leading to 
the formation of a feedback loop. The self-oscillating circuit 11 feeds 
back the oscillation information of the oscillator 3 via the detecting 
element 7 and amplifying circuit 12, forming an electrical oscillation 
system setting the oscillator 3 in a resonant state. The oscillator 3, 
oscillation conducting member 4 and contact element 5 form a mechanical 
oscillation system in which the oscillation information of the oscillator 
3 is conducted to a subject H via the oscillation conducting member 4 and 
contact element 5. In a hardness measuring apparatus according to this 
embodiment, the electrical and mechanical oscillation systems are combined 
into an electromechanical oscillation system. The gain of the 
self-oscillation circuit 11 is almost proportional to the driving voltage 
of the self-oscillation circuit 11. The input terminal of this 
self-oscillating circuit 11 (input terminal of the electromechanical 
oscillation system) corresponds to the output terminal of the oscillator 
3. The output terminal of the self-oscillating circuit 11 (output terminal 
of the electromechanical oscillation system) corresponds to the input 
terminal of the oscillator 3. 
The gain variation compensating circuit 13 increases the gain in response 
to a change in the resonance frequency of the electromechanical 
oscillation system, and has a function of increasing a detection voltage 
with an increase in the gain. In addition, the gain variation compensating 
circuit 13 has a phase transfer function of adjusting the difference 
between the input and output phases, called phase difference, of the 
self-oscillating circuit 11 to zero, and of promoting feedback 
oscillation, shifts the central frequency so that the phase difference 
becomes zero, and increases the gain in response to the change in the 
central frequency. In this embodiment, a filter circuit having a 
frequency-gain characteristic realizing a change in the gain in response 
to a change in frequency is used as the gain variation compensating 
circuit 13. FIG. 3 shows the structure of an example of the filter circuit 
used as the gain variation compensating circuit 13. This filter circuit 
has resistance elements R1, R2, R3 and R4, capacitance elements C1, C2, C3 
and C4 and an amplifying circuit AMP. The resistance of the resistance 
element R1 is set at 10 k.OMEGA., that of the resistance element R2 at 220 
.OMEGA.. that of the resistance element R3 at 470 k.OMEGA., and that of 
the resistance element R4 at 2.2 k.OMEGA.. A voltage of 12 V is supplied 
to the power terminal V1 of the amplifying circuit AMP. A reference supply 
voltage of -12 V is supplied to a reference supply voltage terminal V2. 
V.sub.in shown in FIG. 3 denotes the input terminal for a signal, and 
V.sub.out the output terminal. This filter circuit can work as a band-pass 
filter circuit. The input terminal V.sub.in of the filter circuit is 
connected to the output terminal of the amplifying circuit 12 included in 
the self-oscillating circuit 11. The output terminal V.sub.out is 
connected to the first electrode 3A (input terminal) of the oscillator 3. 
The gain variation compensating circuit 13 can be disposed between the 
oscillator 3 and amplifying circuit 12 of the self-oscillating circuit 11. 
In this case, the input terminal V.sub.in of the filter circuit is 
connected to the second electrode 7C (output terminal of the oscillator 3) 
of the detecting element 7. The output terminal V.sub.out is connected to 
the input terminal of the amplifying circuit 12. 
In a hardness measuring apparatus according to this embodiment, the gain 
variation compensating circuit 13 is not limited to the band-pass filter 
circuit. Since any circuit having such a characteristic that it changes 
the gain in response to a change in frequency, and then increases the 
detection voltage with the increase in the gain, can be used as the gain 
variation compensating circuit 13, any of a low-pass filter circuit, 
high-pass filter circuit, notch filter circuit, integrating circuit, 
differentiating circuit or peaking amplifying circuit can be used. 
The voltage measuring circuit 14 and frequency measuring circuit 15 of the 
control unit 10 shown in FIG. 1 are respectively connected to the gain 
variation compensating circuit 13. The voltage measuring circuit 14 and 
frequency measuring circuit 15 is connected to the output terminal 
V.sub.out of the filter circuit (gain variation compensating circuit 13). 
The voltage measuring circuit 14 is used for measuring a change in the 
voltage of the electromechanical oscillation system, and the frequency 
measuring circuit 15 for measuring a change in the frequency of the 
electromechanical oscillation system. In a hardness measuring apparatus 
according to this embodiment, the hardness of a subject can be determined 
by the change in the frequency of the electromechanical oscillation system 
formed as described above. The gain is increased by the gain variation 
compensating circuit 13, leading to an increased detection voltage. In 
addition, the hardness information of a subject can be monitored by the 
voltage measuring circuit 14 and frequency measuring circuit 15 of the 
control unit 10. The voltage measuring circuit 14 and frequency measuring 
circuit 15 are not always connected to the output terminal of the gain 
variation compensating circuit 13. They may be coupled with the 
electromechanical oscillation system in any manner. 
Basic Principle of Hardness Measurement! 
The basic principle of a hardness measuring apparatus provided by the 
present invention will be described. FIG. 4 shows a total gain-frequency 
characteristic and a total phase-frequency characteristic, which are 
obtained by combining the gain-frequency characteristics, and the 
phase-frequency characteristics of the self-oscillating circuit 11 and 
gain variation compensating circuit 13. In FIG. 4, the horizontal axis 
represents frequency, and the vertical axes gain and phase, respectively. 
The characteristic curve TG shows a gain-frequency characteristic of the 
self-oscillating circuit 11 in which a signal is outputted from the output 
terminal of the oscillator 3 (actually the output terminal of the 
detecting element 7), and fed back to the oscillator 3 via the gain 
variation compensating circuit 13. The gain-frequency characteristic curve 
TG shows a total frequency characteristic obtained by combining the 
frequency characteristic of the self-oscillating circuit 11 with that of 
the gain variation compensating circuit 13. The gain-frequency 
characteristic curve TG shows that the gain increases with the increase in 
frequency in a lower frequency band, has a peak at a resonance frequency 
f.sub.0, and then decreases with the increase in frequency in a higher 
frequency band, making an arched curve. The phase characteristic curve 
.theta..sub.11 shows the difference between the input and output phases 
(phase difference) of the self-oscillation circuit 11. 
In a hardness measuring apparatus according to this embodiment, the 
difference between the input and output phases of the self-oscillation 
circuit 11 is adjusted to zero at a resonance frequency f.sub.0 at which 
the gain-frequency characteristic curve TG shows a maximum value TGP. In 
the self-oscillating circuit 11, the phase difference .theta..sub.11 
between the phase .theta..sub.1 (input phase) of a signal outputted from 
the oscillator 3 at a resonance frequency and phase .theta..sub.2 (output 
phase) of a signal which is outputted from the gain variation compensating 
circuit 13, and fed back to the input terminal of the oscillator 3 after 
increasing the gain of the signal, is adjusted to zero (.theta..sub.11 
=.theta..sub.1 +.theta..sub.2 =0). When the phase difference between the 
input phase .theta..sub.1 and output phase .theta..sub.2 is not equal to 
zero, the feedback is repeatedly carried out until the phase difference 
becomes zero. The oscillation is performed at a phase difference of zero. 
Consequently, the feedback oscillation of the self-oscillating circuit 11 
including the gain variation compensating circuit 13 is ensured and 
promoted by the adjustment of the phase difference .theta..sub.11, to 
zero. In a hardness measuring apparatus according to this embodiment, the 
gain variation compensating circuit 13 carries out the adjustment of the 
phase difference .theta..sub.11, and can easily adjust the phase 
difference .theta..sub.11 by shifting the central frequency in the 
frequency characteristic. 
FIG. 5 shows characteristic curves representing gain-frequency and 
phase-frequency characteristics of the self-oscillating circuit 11 and 
gain variation compensating circuit 13. The horizontal axis represents 
frequency, and the vertical axes represent gain and phase, respectively. 
The characteristic curve 13G shows a gain-frequency characteristic of the 
gain variation compensating circuit 13. In the gain-frequency 
characteristic curve 13G, the gain increases with the increase in 
frequency in a lower frequency band, reaches a maximum value, and then 
decreases in a higher frequency band, showing an arched curve. The 
characteristic curve .theta..sub.13 shows a phase difference between the 
input and output phases of the gain variation compensating circuit 13. The 
characteristic curve MG shows a gain-frequency characteristic of the 
self-oscillating circuit, that is, the electromechanical oscillation 
system itself, not including a characteristic of the gain variation 
compensating circuit 13. The gain-frequency characteristic curve MG is 
also an arched curve as the frequency characteristic of the gain variation 
compensating circuit 13, although the central frequency and maximum value 
of the gain are different. This gain-frequency characteristic curve MG is 
obtained when the contact element 5 is not in contact with a subject H. 
In a hardness measuring apparatus according to this embodiment, as shown by 
the gain-frequency characteristic curves MG and 13G, the central frequency 
f.sub.1 (resonance frequency) of the electromechanical oscillation system, 
at which the gain has a maximum value P1, and the central frequency 
f.sub.2, at which the gain of the gain variation compensating circuit 13 
has a maximum value 13GP, are intentionally set in different frequency 
bands. When the contact element 5 is in contact with a soft subject H, 
such as human skin or a human internal organ, the total gain should be 
increased. Therefore, the central frequency f.sub.2 of the gain of the 
gain variation compensating circuit 13 is set at a lower frequency than 
the central frequency f.sub.1 of the gain of the electromechanical 
oscillation system. When the contact element 5 is in contact with a hard 
subject H, such as metal, bone or tooth, the central frequency f.sub.2 of 
the gain of the gain variation compensating circuit 13 is set at a higher 
frequency than the central frequency f.sub.1 of the gain of the 
electromechanical oscillation system in order to increase the total gain. 
When the contact element 5 of a hardness measuring apparatus according to 
this embodiment comes into contact with a soft subject H, the mechanical 
or acoustic impedance of the soft subject is increased. This causes a 
change in the oscillation mode of the oscillator 3, leading to a change in 
the frequency characteristic of the electromechanical oscillation system. 
All the oscillation frequency, gain, phase and oscillation amplitude 
included in the oscillation information can be varied. The oscillation 
frequency is shifted toward a lower frequency due to the impedance of the 
soft subject H. A maximum value of the gain is originally decreased in 
general but in contrast, it is increased in a hardness measuring apparatus 
according to this embodiment due to the gain increasing function of the 
gain variation compensating circuit 13. The maximum value of the gain 
increases from the maximum value P1 along the gain-frequency 
characteristic curve 13G of the gain variation compensating circuit 13. At 
the instant the contact element 5 comes into contact with a soft subject 
H, the central frequency f.sub.1 of the electromechanical oscillation 
system is changed to a resonance frequency f.sub.11 determined by the 
impedance of the subject H. The gain-frequency characteristic curve MG of 
the electromechanical oscillation system is shifted to a gain-frequency 
characteristic curve MG1. As shown in the gain-frequency characteristic 
curve MG1, the maximum value P1 of the gain is changed to a maximum value 
P11, and the gain G1 to G11, leading to an increase in the gain. 
Oscillation information, including the changes in the frequency and gain, 
is detected by the detecting element 7. This oscillation information 
detected by the detecting element 7 is fed back to the oscillator 3 by the 
feedback loop of the self-oscillating circuit 11. 
The feedback loop of the self-oscillating circuit 11 has a circuit in which 
a combination of resistance and capacitance elements is used. Therefore, 
the phase difference .DELTA..theta. between the input phase .theta..sub.1 
and output phase .theta..sub.2 is always non-zero. The gain variation 
compensating circuit 13 has a phase transfer function of adjusting the 
phase difference .theta..sub.11 between the input and output phases of the 
feedback loop including itself to zero. Therefore, the frequency further 
changes, and the gain increases until they both reach a stable point in 
the feedback oscillation at a phase difference .theta..sub.11 of zero. The 
gain-frequency characteristic curve MG1 of the electromechanical 
oscillation system is changed to a gain-frequency characteristic curve 
MG2, and the resonance frequency f.sub.11 to a resonance frequency 
f.sub.12. The maximum value P11 of the gain is changed to a maximum value 
P12, and the gain G11 to a gain G12 in response to the change in the 
resonance frequency to f.sub.12, leading to a further increase in the 
gain. The central frequency f.sub.1 of the electromechanical oscillation 
system is continuously varied to the resonance frequency f.sub.12 by a 
frequency corresponding to the phase difference .DELTA..theta., and the 
gain G1 is continuously increased to G12. Consequently, a variation 
.DELTA.f in the frequency and a variation .DELTA.G in the gain are 
obtained in the electromechanical oscillation system. When the variation 
.DELTA.f and variation .DELTA.G are obtained, the phase difference 
.theta..sub.11 between the input and output phases becomes zero, enabling 
the self-oscillation circuit to carry out feedback oscillation. 
A hardness measuring apparatus according to this embodiment detects the 
variation .DELTA.f between the frequencies before and after contacting the 
contact element 5 with a soft subject H, as hardness information. This 
enables the hardness of a soft subject H to be measured. Similarly, the 
hardness measuring apparatus according to this embodiment detects the 
phase difference .DELTA..theta. between the phases before and after 
contacting the contact element 5 with a soft subject H, as hardness 
information. This also enables the hardness of a soft subject H to be 
measured. In addition, the hardness measuring apparatus according to this 
embodiment enables the gain to be increased in response to the variation 
.DELTA.f and phase difference .DELTA..theta. (a sufficient variation 
.DELTA.G in the gain to be obtained), obtaining a detection voltage 
sufficient for hardness measurement. 
In a hardness measuring apparatus according to this embodiment, when 
contacting the contact element 5 with a hard subject H, the frequency, 
gain, phase and oscillation amplitude are changed, but the gain is not 
increased, because an adjustment appropriate to measuring the hardness of 
a soft subject H is made. FIG. 6 shows gain-frequency characteristic 
curves and phase-frequency characteristic curves of the self-oscillating 
circuit 11 and gain variation compensating circuit 13. The characteristic 
curve MG3 shows a gain-frequency characteristic of the electromechanical 
oscillation system when contacting the contact element 5 with a hard 
subject H. When contacting the contact element 5 with a hard subject H, 
the resonance frequency is changed to a frequency determined by the 
impedance of the subject H at the instance of contacting. Subsequently, 
the frequency is changed by a frequency corresponding to the phase 
difference .DELTA..theta. to a resonance frequency f.sub.3 at which the 
phase difference 0.sub.11 between the input and output phases becomes 
zero, enabling feedback oscillation to be carried out. The change in the 
frequency is shifted toward a higher frequency, and then the variation 
.DELTA.f in the frequency is increased until the phase difference 
.theta..sub.11 becomes zero, leading to a larger value. Consequently, the 
gain-frequency characteristic curve MG1 of the electromechanical 
oscillation system is shifted to a gain-frequency characteristic curve 
MG3. The maximum value P1 of the gain is changed to a maximum value P3 at 
which feedback oscillation is stably carried out. 
The gain variation compensating circuit 13 of a hardness measuring 
apparatus according to this embodiment has both the gain increasing 
function and phase transfer function. In the present invention, the gain 
variation compensating circuit 13 may have only the gain increasing 
function. 
The relationship between the resonance frequency of an oscillator and the 
mechanical properties of a material with which the oscillator is to be in 
contact with is described by S. Omata in "Measurements of the hardness of 
a soft material with a piezoelectric vibrometer and their analysis" 
Iyodenshi to Seitaikogaku (Journal of the Japan Society of Medical 
Electronics and Biological Engineering), Vol. 28, No. 1, pp. 1-4 (1990). 
Use of a Hardness Measuring Apparatus! 
The use of a hardness measuring apparatus according to this embodiment will 
be described. In the above mentioned hardness measuring apparatus shown in 
FIG. 1, an electromechanical oscillation system, which includes the 
oscillator 3, detecting element 7, oscillation conducting member 4 and 
contact element 5, is oscillated in a resonant state by the 
self-oscillating circuit 11, so that the hardness measuring apparatus is 
set in operation. Oscillation information, that is, the frequency, gain, 
phase and oscillation amplitude, of this electromechanical oscillation 
system, is outputted from the output terminal of the gain variation 
compensating circuit 13. The detection voltage is monitored by the voltage 
measuring circuit 14, and the frequency is monitored by the frequency 
measuring circuit 15. A person measuring the hardness holds the hand piece 
I by hand, and contacts the tip of the contact element 5 oscillating in a 
resonant state with a subject H. 
At this time, the detection voltage and frequency for the electromechanical 
oscillation system detected by the voltage measuring circuit 14 and 
frequency measuring circuit 15 respectively, are changed in response to 
the hardness of the subject H, as follows: 
A highly elastic and soft subject, such as a biological soft tissue (human 
skin, human internal organs) or rubber, has a low mechanical or acoustic 
impedance, reducing the resonance frequency of the electromechanical 
oscillation system. As shown in FIG. 5, the electromechanical oscillation 
system has a gain-frequency characteristic shown by the characteristic 
curve MG having a maximum value P1 of the gain at a central frequency 
f.sub.1 before contacting the contact element 5 with the subject H. A 
hardness measuring apparatus according to this embodiment has the gain 
variation compensating circuit 13 which increases the gain in response to 
a change in the resonance frequency. In the gain variation compensating 
circuit 13, the gain is set to be increased in response to a change in the 
frequency when contacting the contact element 5 with a soft subject H. The 
gain-frequency characteristic curve MG of the electromechanical 
oscillation system is corrected by the gain-frequency characteristic curve 
13G of the gain variation compensating circuit when bringing the contact 
element 5 into contact with a soft subject H. Consequently, the 
gain-frequency characteristic curve MG of the electromechanical 
oscillation system is shifted in the direction indicated by the arrow Q1 
shown in FIG. 5. In addition, the gain variation compensating circuit has 
the phase transfer function, and the phase difference .theta..sub.11 
between the input and output phases in the feedback (closed) loop formed 
by the self-oscillating circuit 11 is adjusted to zero, enhancing the 
variation in the frequency by a frequency corresponding to a phase 
difference .DELTA..theta.. The increase in the gain is enhanced by this 
change in the frequency. At an appropriate stable point of feedback 
oscillation, the change in the frequency and the increase in the gain 
stop, and the feedback oscillation of the electromechanical oscillation 
system occurs. The gain-frequency characteristic curve MG is changed into 
a gain-frequency characteristic curve MG2, and the maximum value P1 of the 
gain is increased to a maximum value P12. 
A hardness measuring apparatus according to this embodiment is set to be 
suitable for measuring the hardness of a soft subject H. When measuring 
the hardness of a hard subject H, such as iron or an alloy at room 
temperature, the frequency is changed, but the gain is not increased. As 
shown in FIG. 6, the gain-frequency characteristic curve MG of the 
electromechanical oscillation system is shifted in the direction indicated 
by the arrow Q2 to a gain-frequency characteristic curve MG3. Although the 
gain is decreased, the variation in the frequency is enhanced by the phase 
transfer function. The hardness of a hard subject H can be determined by 
monitoring this variation in the frequency using the frequency measuring 
circuit 15. In order to set the gain to be increased when measuring the 
hardness of a hard subject H, the central frequency of the 
electromechanical oscillation system is set in a lower frequency band, in 
which the gain is increased with an increase in the frequency, in the 
gain-frequency characteristic curve 13G of the gain variation compensating 
circuit 13. 
In a hardness measuring apparatus according to this embodiment, a change in 
the voltage of the electromechanical oscillation system is monitored by 
the voltage measuring circuit 14, and a change in the resonance frequency 
is monitored by the frequency measuring circuit 15, in order to determine 
the hardness of a subject. 
Results of the Measurement of Hardness! 
FIG. 7 shows the structure of an actual system for measuring the hardness 
of a subject H. The hand piece 1 of a hardness measuring apparatus is 
coupled with a holding stand 31 via a load cell 30 to be used for 
measuring the hardness of a subject H. The compressive force applied to 
the subject H by the contact element 5 can be measured by the load cell 
30. 
FIG. 8 shows variations in the frequency and detection voltage of a 
hardness measuring apparatus according to this apparatus and those in a 
conventional one, which are plotted against the compressive force. The 
horizontal axis indicates a compressive force F measured by the load cell 
30, and the vertical axis indicates a variation in the resonance frequency 
.DELTA.f or in the detection voltage .DELTA.V. Two subjects H.sub.A and 
H.sub.B having different hardnesses are used as the subject H. The curves 
S.sub.1 and S.sub.2 show variations in the frequency and voltage in a 
hardness measuring apparatus according to this embodiment, plotted against 
the compressive force. The curve S.sub.1 shows the variation for the 
subject H.sub.A, and the curve S.sub.2 the variation for the subject 
H.sub.B. The curves T.sub.1 and T.sub.2 show variations in the frequency 
and detection voltage in a conventional hardness measuring apparatus, 
plotted against the compressive force. The curve T.sub.1 shows the 
variation for the subject H.sub.A, and the curve T.sub.2 the variation for 
the subject H.sub.B. 
As shown in FIG. 8, the variations in the frequency and detection voltage 
increase with the increase in compressive force to a small extent in a 
conventional hardness measuring apparatus, and the difference between the 
variations for the subjects H.sub.A and H.sub.B is small, even when the 
hardnesses (acoustic impedance) of the subjects H.sub.A and H.sub.B are 
different. Sufficient variations in the frequency and detection voltage 
for measuring the hardnesses of the subjects H.sub.A and H.sub.B cannot be 
obtained. In contrast, the variations in frequency and detection voltage 
increase with the increase in compressive force to a much larger extent in 
a hardness measuring apparatus according to this embodiment than the 
variations in a conventional hardness measuring apparatus, and the 
difference between the variations for the subjects H.sub.A and H.sub.B is 
large. A hardness measuring apparatus according to this embodiment can 
enhance a slight difference between variations in the resonance frequency 
or detection voltage which is derived from the difference between the 
hardnesses (acoustic impedances) of subjects. 
When a hardness measuring apparatus has the gain variation compensating 
circuit 13, and the resonance frequency of the electromechanical 
oscillation system is set in a frequency band in which the gain is 
increased in response to a change in the frequency of the gain variation 
compensating circuit 13, the gain is increased in response to a change in 
the frequency due to a slight difference between the hardnesses of 
subjects H. When the hardness of a subject H with a similar hardness and 
having a similar frequency characteristic is measured, the phase transfer 
function of the gain variation compensating circuit 13 enhances the 
variation in the frequency until the phase difference is cancelled to 
zero, and further increases the gain. This enables a sufficient detection 
voltage for determining the hardness of a subject to be obtained. In 
addition, when the hardnesses of various subjects H are measured, the 
variation in the frequency is enhanced, enabling the measurement of 
hardness for soft and hard subjects H to be realized in a wide range. The 
effective resonance frequency band of the electromechanical oscillation 
system of a hardness measuring apparatus is expanded, realizing 
measurement of the hardness of various subjects H in a wide range. 
In a hardness measuring apparatus according to this embodiment, the gain 
variation compensating circuit 13 can be easily achieved by a filter 
circuit comprising a simple combination of resistance elements, 
capacitance elements and the like. Complicated circuitry is not necessary 
for the gain variation compensating circuit 13, enabling a simple 
structure and fabrication with low cost. 
Modification 1! 
FIGS. 9 and 10 show gain-frequency characteristic curves of a hardness 
measuring apparatus according to Modification 1 of Embodiment 1. FIG. 9 
shows gain-frequency characteristic curves when a low-pass filter is used 
as the gain variation compensating circuit 13. A gain-frequency 
characteristic curve 13G1 of the gain variation compensating circuit 13 
and gain-frequency characteristic curve MG of the electromechanical 
oscillation system are shown. In this hardness measuring apparatus, a 
variation in frequency is basically amplified in a similar manner to that 
in a hardness measuring apparatus including a band-pass filter circuit 
(see FIG. 3). In particular, when the contact element 5 is in contact with 
a soft subject H, the frequency is changed. The variation in the frequency 
is enhanced, and the gain is increased by the variation in the frequency. 
As described before, the gain variation compensating circuit 13 has both 
the gain increasing function and the phase transfer function. Having both 
functions enables a larger variation in the frequency and a larger gain. 
FIG. 10 shows gain-frequency characteristic curves when a high-pass filter 
circuit is used as the gain variation compensating circuit 13. A 
gain-frequency characteristic curve 13G2 of the gain variation 
compensating circuit 13 and gain-frequency characteristic curve MG of the 
electromechanical oscillation system are shown. This hardness measuring 
apparatus is suitable for measuring the hardness of a hard subject H, such 
as a metal like iron or an alloy, and a human hard tissue such as a bone 
or tooth. In this hardness measuring apparatus, when the contact element 5 
comes into contact with a soft subject H, the frequency is changed, the 
variation in the frequency is enhanced, and the gain is increased by the 
variation in the frequency. In FIG. 10, a gain-frequency characteristic 
curve MG when the contact element 5 is not in contact with a hard subject 
is shifted to a gain-frequency characteristic curve MG3. A detection 
voltage sufficient for the measurement of hardness can be obtained by 
increasing the gain. In this hardness measuring apparatus, when the 
contact element 5 is in contact with a soft subject H, the gain-frequency 
characteristic curve MG of the electromechanical oscillation system is 
shifted to a gain-frequency characteristic curve MG1, decreasing the gain. 
Modification 2! 
FIG. 11 shows the overall structure of a hardness measuring apparatus 
according to Modification 2 of Embodiment 1. This hardness measuring 
apparatus includes an oscillator 3 comprising a layered piezoelectric 
ceramic oscillator and a detecting element 7 comprising a film bimorph 
oscillator. These oscillator 3 and detecting element 7 form the 
electromechanical oscillation system. In the layered piezoelectric ceramic 
oscillator 3, a ring-shaped piezoelectric ceramic is fixed around an 
oscillation conducting member 4 with adhesive, and is layered numerous 
times in the axial direction of the oscillation conducting member 4. The 
size of the layered piezoelectric ceramic oscillator is small, and an 
input voltage of large amplitude can be obtained. 
The detecting element 7 comprising the bimorph oscillator is fixed on the 
outer surface of the oscillator 3 (layered piezoelectric ceramic 
oscillator). The detecting element 7 fabricated in a film form has a small 
weight, and only requires a small space in the casing 2 of the hand piece 
1 for disposition. An oscillator comprising a PVDF film can be used in the 
detecting element 7 instead of the bimorph oscillator. 
A hardness measuring apparatus having such a structure includes the 
oscillator 3 comprising a layered piezoelectric ceramic oscillator and the 
detecting element 7 comprising a film bimorph oscillator. Therefore, it 
has the advantage obtained by the hardness measuring apparatus shown in 
FIG. 1, and also its oscillator 3 outputs a sufficiently large amplitude, 
enabling the size and weight to be reduced. The detecting element 7 of the 
hardness measuring apparatus is fabricated in a film form, also enabling 
its size and weight to be reduced. Consequently, the size and weight of 
composite elements inside the hand piece 1 can be reduced, enabling the 
size and weight of the hand piece 1 itself to be reduced. The operability 
of the hand piece 1, that is, of the hardness measuring apparatus, can be 
improved. 
Modification 3! 
FIG. 12 shows the overall structure of a hardness measuring apparatus 
according to Modification 3 of Embodiment 1. This hardness measuring 
apparatus includes an oscillator 3 comprising a layered piezoelectric 
ceramic oscillator, a detecting element 7 comprising a layered 
piezoelectric ceramic oscillator and an insulation material 3D. These 
oscillator 3 and detecting element 7 form the electromechanical 
oscillation system. In the layered piezoelectric ceramic oscillator of the 
oscillator 3, a ring-shaped piezoelectric ceramic is fixed around an 
oscillation conducting member 4 with adhesive, and is layered numerous 
times in the axial direction of the oscillation conducting member 4. As 
mentioned above , the size of the layered piezoelectric ceramic is small, 
and an input voltage of large amplitude can be obtained. 
The layered piezoelectric ceramic oscillator comprising the detecting 
element 7 is disposed closer to the contact element 5 than to the 
oscillator 3. As in the oscillator 3, a ring-shaped piezoelectric ceramic 
is fixed around an oscillation conducting member 4 with adhesive, and is 
layered numerous times in the axial direction of the oscillation 
conducting member 4. 
The insulation material 3D is disposed between the oscillator 3 and 
detecting element 7. The oscillator 3 of the layered piezoelectric ceramic 
oscillator, insulation material 3D and detecting element 7 are fabricated 
as an integrated assembly. 
A hardness measuring apparatus having such a structure includes the 
oscillator 3 comprising layered piezoelectric ceramic oscillator and the 
detecting element 7 comprising a film bimorph oscillator. Therefore, it 
has the advantage obtained by the hardness measuring apparatus shown in 
FIG. 1, and also its oscillator 3 outputs a sufficiently large amplitude, 
enabling the size and weight to be reduced. The detecting element 7 of the 
hardness measuring apparatus is fabricated in a film form, also enabling 
its size and weight to be reduced. Consequently, the size and weight of 
composite elements inside the hand piece 1 can be reduced, enabling the 
size and weight of the hand piece 1 itself to be reduced. The operability 
of the hand piece 1, that is, of the hardness measuring apparatus, can be 
improved. 
Modification 4! 
FIG. 13 shows the overall structure of a hardness measuring apparatus 
according to Modification 3 of Embodiment 1. This hardness measuring 
apparatus includes a cylindrical-shaped casing 2 of a hand piece 1. A 
hemi-spherical tip of a contact element 5 fits into an end of the casing 
2. An oscillator 3 is disposed on a flat surface of the contact element 5 
facing toward the casing 2, and then a detecting element 7 is disposed on 
the oscillator 3. The oscillator 3 comprises a first electrode 3A used as 
an anode, a second electrode 3C used as a cathode and a piezoelectric 
crystal 3B formed between the first and second electrodes 3A and 3C, as in 
the hardness measuring apparatus shown in FIG. 1. A detecting element 7 
comprises a first electrode 7A used as a cathode, a second electrode 7C 
used as an anode and a piezoelectric crystal 7B formed between the first 
and second electrodes 7A and 7C. Each layer of these first electrode 3A, 
piezoelectric crystal 3B, second electrode 3C, first electrode 7A, 
piezoelectric crystal 7B and second electrode 7C can be easily fabricated 
with a fine pattern by a film fabricating method, such as sputtering used 
in semi-conductor production. The sequence of the layers of the oscillator 
3 and detecting element 7 can be reversed. Alternatively, the oscillator 3 
can be easily made by laminating a sheet-formed piezoelectric material, 
such as piezoelectric ceramic or oscillating quartz, with adhesive. 
A hardness measuring apparatus having such a structure includes the 
hemi-spherical contact element 5. The oscillator 3 and detecting element 7 
are directly fabricated on the flat surface of the contact element facing 
toward the casing 2 as an integrated assembly. The mechanical oscillation 
part of the electromechanical oscillation system, which is in contact with 
a subject H, can be significantly reduced in size and weight. When a 
semiconductor producing technique is used for fabricating the oscillator 3 
and detecting element 7, the measuring section can be fabricated in a 
small size, enabling the hardness measuring apparatus to be used for 
measuring the hardness of a small subject, such as a biological tissue. 
In a hardness measuring apparatus according to this embodiment, the contact 
element 5 and oscillator 3 can be formed as an integrated assembly. In 
this structure, the oscillation of the oscillator 3 is directly conducted 
to a subject H. In addition, the feedback loop of a phase-lock loop (PLL) 
circuit can be used instead of the feedback loop of the self-oscillating 
circuit 11. 
Embodiment 2 
In Embodiment 2, a hardness measuring apparatus for measuring the hardness 
of a biological tissue in a human living body, in which a frequency 
deviation circuit is used, will be described. 
System Structure of a Hardness Measuring Apparatus for Palpation of 
Internal Organs! 
FIG. 14 shows the overall structure of a hardness measuring apparatus for 
palpation of internal organs according to Embodiment 2. The hardness 
measuring apparatus has a main probe 1 used for palpation of internal 
organs and a control unit 10 placed outside the main probe 1. The main 
probe 1 of the hardness measuring apparatus for palpation of internal 
organs has a casing 2, which is formed by a tubular pipe insertable into a 
living body (for example, a human body). The casing 2 has a touch section 
2C which is brought into contact with a subject H (living body), a middle 
section in its middle portion and a hold section 2E held by a person 
carrying out the measurement. The outer diameters of the touch and hold 
sections 2C and 2E are a little larger than that of the middle section 2D. 
Since the casing 2 is inserted into a living body, it is made of a highly 
rigid and corrosion resistive material, such as stainless steel. 
An oscillator 3 for generating ultrasonic oscillation and a detecting 
element 7 for detecting oscillation are disposed inside the touch section 
2C of the casing 2. The oscillator 3 comprises a piezoelectric ceramic 
oscillator, as in the hardness measuring apparatus according to Embodiment 
1. The oscillator 3 is brought into contact with a subject H of a 
biological tissue in a living body. A contact element 5 (touch member) is 
mechanically coupled with the subject H whose hardness is to be measured. 
The tip of the contact element 5 sticks out from an opening formed at the 
end of the touch section 2C of the casing 2. The tip of the contact 
element has a hemi-spherical shape. Therefore, the contact element 5 is 
widely usable for contacting with a subject H both at a point and over an 
area. The detecting element 7 is fixed on the oscillator 3, and detects 
the oscillation of the oscillator 3. The detecting element 7 comprises 
piezoelectric ceramics, as the oscillator 3. The detecting element 7 is 
integrated with the oscillator 3, as in the hardness measuring apparatus 
according to embodiment 1. Alternatively, the detecting element 7 can be 
separately fabricated, and then mechanically coupled with the oscillator 
3. 
Inside the touch section 2C of the casing, an elastic member 6 is disposed 
between the inner surface of the touch section 2C and oscillator 3, or 
detecting element 7. The elastic member 6 retains the electromechanical 
oscillation system comprising the oscillator 3, detecting element 7 and 
contact element 5, and absorbs the oscillation generated by the 
electromechanical oscillation system and proceeding toward the casing 2. 
The elastic member 6 is made of silicone rubber. Any oscillation absorbing 
material of urethane resin, fluororubber or nitrile rubber (NBR) can be 
used as the elastic member 6. 
The control unit 10 has a self-oscillating circuit 11, a gain variation 
compensating circuit 13, a frequency counter circuit 15, a controller 
circuit 16, a monitor 17 and a fiberscope unit 18. The self-oscillating 
circuit 11 of the control unit 10 has an amplifying circuit 12. The 
amplifying circuit 12 is disposed inside the hold section in a hardness 
measuring apparatus for palpation of internal organs according to this 
embodiment. The input terminal of the amplifying circuit 12 is connected 
to the output terminal of the detecting element 7. The output terminal is 
connected to the input terminal of the oscillator 3 via the gain variation 
compensating circuit 13. The amplifying circuit 12 amplifies oscillation 
information outputted from the detecting element 7. The amplified 
oscillation information is fed back to the oscillator 3 to form a feedback 
loop. The mechanical oscillation system comprising the oscillator 3, 
detecting element 7 and contact element 5, and the electrical oscillation 
system comprising the self-oscillating circuit 11 form an 
electromechanical oscillation system. In this electromechanical 
oscillation system, the self-oscillating circuit 11 oscillates the 
oscillator 3 in a resonant state, and the oscillator 3 oscillates the 
contact element 5. When the contact element 5 is brought into contact with 
a subject H, the mechanical or acoustic impedance of the subject H changes 
the oscillation mode of the oscillator 3. This causes a change in the 
frequency characteristic of the electromechanical oscillation system. The 
hardness of the subject H can be determined by the change in the frequency 
characteristic. 
The gain variation compensating circuit 13 is connected between the 
amplifying circuit 12 and oscillator 3. The gain variation compensating 
circuit 13 has a gain increasing function of increasing the gain in 
response to a change in the frequency characteristic of the 
electromechanical oscillation system according to a principle of basic 
operation similar to that of the hardness measuring apparatus according to 
Embodiment 1. The gain variation compensating circuit 13 also has a phase 
transfer function of adjusting the difference between the input and output 
phases (phase difference) of the self-oscillating circuit 11, and of 
promoting feedback oscillation. 
The input terminal of the frequency counter circuit 15 is connected to the 
output terminal of the gain variation compensating circuit 13. The 
frequency counter circuit measures the frequency of the electromechanical 
oscillation system. 
The input terminal of the controller circuit 16 is connected to the output 
terminal of the frequency counter circuit 15. The controller circuit 16 
generates an image. The frequency counter circuit 15 measures the 
difference between the frequencies of the electromechanical oscillation 
system before and after the contact element 5 in a resonant state becomes 
in contact with a subject H. The controller circuit 16 detects the 
difference in the frequency of the electromechanical oscillation system 
from the data measured by the frequency counter circuit 15. Hardness 
information representing the mechanical property of the subject H is 
obtained in the controller circuit 16. 
The fiberscope unit 18 and monitor 17 are connected to the controller 
circuit 16. The fiberscope unit 18 images a location whose hardness is to 
be measured. Obtained image data (image data generated by endoscopic image 
or observation image) are outputted to the controller circuit 16. In a 
hardness measuring apparatus for palpation of internal organs according to 
Embodiment 2, an endoscope is used as the fiberscope unit 18. The monitor 
17 combines the image data from the fiberscope unit 18 and hardness 
information based on the measured data from frequency counter circuit 15. 
The monitor 17 displays the combined hardness information as an image. 
FIG. 15 shows an image displayed on the monitor 17. In a hardness 
measuring apparatus for palpation of internal organs according to this 
embodiment, the screen of the monitor 17 is divided into two areas 17A and 
17B, one is an endoscopic image display area 17A, the other is a hardness 
information display area 17B. In the endoscopic image display area 17A, an 
endoscopic image taken by the fiberscope unit 18 is displayed. As shown in 
FIG. 15, an image showing that the main probe 1 is in contact with a 
subject H is displayed in the endoscopic image display area 17A. In the 
hardness information display area 17B, a graph representing the hardness 
of the subject H is displayed. FIG. 16 shows another image displayed in 
the monitor 17. As shown in FIG. 16, the monitor 17 has the endoscopic 
image display area 17A and hardness information display area 17B, and a 
specific part of the endoscopic image display area 17A (for example, a 
lower-left part) overlaps the hardness information display area 17B. 
FIG. 17 shows gain-frequency and admittance-frequency characteristic curves 
of the electromechanical oscillation system and gain variation 
compensating circuit 13. In FIG. 17, the horizontal axis indicates 
frequency, and vertical axes respectively indicate gain and admittance of 
the oscillation system. The characteristic curve MG shows a gain-frequency 
characteristic (admittance-frequency characteristic) of the 
electromechanical oscillation system excepting the gain variation 
compensating circuit 13 when the contact element 5 is not in contact with 
a subject H. The characteristic curve 13G shows a gain-frequency 
characteristic of the gain variation compensating circuit 13. In the gain 
variation compensating circuit 13 of a hardness measuring apparatus for 
palpation of internal organs according to Embodiment 2, a band-pass filter 
circuit is used, as in a hardness measuring apparatus according to 
Embodiment 1. The gain-frequency characteristic curve 13G of the gain 
variation compensating circuit 13 is set in a frequency band in which the 
gain of the electromechanical oscillation system is changed in response to 
a change in the frequency. A central frequency f.sub.2, at which the gain 
has a maximum value 13GP in the gain-frequency characteristic curve 13G of 
the gain variation compensating circuit 13, is lower than a central 
frequency f.sub.1 at which the gain in the characteristic curve MG of the 
electromechanical oscillation system has a maximum value P1 (maximum value 
of the admittance). Therefore, the electromechanical oscillation system 
resonantly oscillates at a frequency lower than the central frequency 
f.sub.1, and higher than the central frequency f.sub.2, when the contact 
element 5 is in contact with subject H. 
When the contact element 5 of the main probe 1 is brought into contact with 
a soft subject with an area the gain-frequency characteristic curve MG of 
the electromechanical oscillation system is changed to a gain-frequency 
characteristic curve MG4 in a conventional hardness measurement apparatus 
without the gain variation compensating circuit 13. In the gain-frequency 
characteristic curve MG4, because the acoustic impedance is low, the 
resonance frequency f.sub.4 at which the gain has the maximum value P4 is 
lowered, and the gain is also decreased. Such a phenomenon has been 
reported by S. Omata in "Development of piezoelectric transducer for 
measuring contact compliance of a soft body" Iyodenshi to Seitaikogaku 
(Journal of the Japan Society of Medical Electronics and Biological 
Engineering), Vol. 24, No. 5, pp. 38-42 (1986). 
A hardness measuring apparatus for palpation of internal organs according 
to Embodiment 2 has a characteristic shown by a gain-frequency 
characteristic curve MG5, when the contact element 5 of the main probe 1 
is not in contact with anything. The gain-frequency characteristic curve 
MG5 has a maximum value P5 at a central frequency f.sub.5. When bringing 
the contact element 5 into contact with a subject H having an area, the 
gain-frequency characteristic curve MG5 is changed to a gain-frequency 
characteristic curve MG6. Because the acoustic impedance of the subject H 
is low, the central frequency f.sub.5 is shifted toward a lower frequency, 
and becomes stable at a frequency f6. The gain is increased along the 
gain-frequency characteristic curve 13G of the gain variation compensating 
circuit 13 by the gain increasing and phase transfer functions of the gain 
variation compensating circuit 13, leading to the obtaining of a maximum 
value P5 of the gain. This increased gain enables a sufficient detection 
voltage for hardness measurement to be obtained. 
Use of a Hardness Measuring Apparatus for Palpation of Internal Organs! 
The use of a hardness measuring apparatus for palpation of internal organs 
according to this embodiment will be described. A lung in a human thoracic 
cavity is used as a subject, and its hardness is measured for medical 
investigation. FIG. 18 shows the system structure of a hardness measuring 
apparatus for palpation of internal organs according to this embodiment. 
The fiberscope unit 18 is inserted into the thoracic cavity X of a human 
body (subject) through an opening formed on the surface of a thoracic 
part. The fiberscope unit 18 sends an endoscopic image in the thoracic 
cavity to the controller circuit 16 as image data, the controller circuit 
16 generates an endoscopic image, which is displayed in the endoscopic 
image display area 17A of the monitor 17. A person carrying out the 
measurements can observe the endoscopic image in a field of view by 
looking at the endoscopic image displayed in the endoscopic image display 
area 17A of the monitor 17. 
Another opening is formed on the surface of the thoracic part of the 
subject. A probe guide 19 is inserted through the opening. The main probe 
1 of the hardness measuring apparatus for palpation of internal organs is 
inserted into the thoracic cavity X via the probe guide 19. The measurer 
contacts the contact element 5 disposed at the tip of the main probe 1 
inserted into the thoracic cavity with the objective subject H (lung) in 
the human body, while observing the endoscopic image display area 17A of 
the monitor 17. In the endoscopic image display area 17A, an endoscopic 
image showing that the contact element 5 is in contact with the objective 
subject H can be observed. Using a hardness measuring apparatus for 
palpation of internal organs according to this embodiment, at the instant 
the contact element 5 is brought into contact with a subject H, the 
hardness of the subject H can be measured from a change in the frequency 
of the electromechanical oscillation system. A result of this, a hardness 
measurement is displayed in the hardness information display area 17B of 
the monitor as hardness information. 
FIG. 19 shows a cross-sectional view of a biological tissue (subject H) for 
explaining the operation of the main probe 1. FIG. 20 shows a magnified 
view of the hardness information display area 17B representing the 
hardness information corresponding to a cross-section of a biological 
tissue. As shown in FIG. 19, the contact element 5 of the main probe is 
slid in the direction indicated by the arrow, keeping contact with the 
subject H. The hardness measuring apparatus for palpation of internal 
organs measures the hardness of the subject H in the range of the sliding. 
When a tumor Y such as a cancer exists on the surface of a lung (subject 
H) or in a deeper part of a pulmonary tissue, the tissue is usually harder 
than a normal pulmonary tissue. Therefore, when the contact element 5 of 
the main probe 1 moves from a normal tissue to the tumor, the hardness of 
the subject H shown in the hardness information display area 17B 
increases, as shown in FIG. 20. The tumor Y located in the pulmonary 
tissue can be detected, and its position can also be identified. 
A hardness measuring apparatus for palpation of internal organs can be used 
for measuring the hardness of a liver (for example, a liver suffering from 
cirrhosis) or a muscle tissue. The biological tissue in a living body to 
which the hardness measuring apparatus for palpation of internal organs is 
applied is not limited. In addition, a hardness measuring apparatus for 
palpation of internal organs can be used for measuring the hardness of 
animal or plant tissues. 
As a hardness measuring apparatus according to Embodiment 1, a hardness 
measuring apparatus for palpation of internal organs has the gain 
variation compensating circuit 13. The gain increasing and phase transfer 
functions of the gain variation compensating circuit 13 increases the gain 
in response to a change in the frequency. This enables a sufficient 
detection voltage for hardness measurement to be obtained. A slight 
difference in the hardness of a subject can be detected to precisely 
determine the hardness. When the hardness of different materials, which 
have similar hardnesses resulting in similar resonance frequencies, is 
measured, the phase transfer function of the gain variation compensating 
circuit 13 changes the frequency, and increases the gain until a slight 
difference between the phases becomes zero, where the feedback oscillation 
is stably carried out. This enables a sufficient detection voltage for 
hardness measurement to be obtained. When the hardness of various soft and 
hard subjects H is measured, the frequency is changed, a variation in the 
frequency is enhanced, and then the gain is increased in response to the 
enhanced variation in the frequency. This enables a detection voltage 
sufficient for hardness measurement to be obtained. Therefore, the 
hardness of various soft and hard subjects can be measured in a wide range 
of hardness. In this hardness measuring apparatus, the effective resonance 
frequency band of the electromechanical oscillation system is widened, and 
the hardness of various soft and hard subjects H can be measured. 
In a hardness measuring apparatus for palpation of internal organs, the 
gain variation compensating circuit 13 can be easily realized by a filter 
circuit comprising a simple combination of resistance elements and 
capacitance elements. This does not require a complicated circuit 
structure, enabling the system to be simple and fabricated with low cost. 
A hardness measuring apparatus for palpation of internal organs according 
to this embodiment can detect a tumor Y located on the surface or at a 
deeper position of a biological tissue by bringing the contact element 5 
of the main probe 1 inserted into a living body into contact with a 
biological tissue (subject H) in the living body, and identifying the 
position of the tumor Y. Therefore, medical diagnosis of a disease, such 
as cancer, a tumor or cirrhosis, can be easily carried out. In addition, 
when a physician cannot directly touch an affected part of a biological 
tissue, the hardness measuring apparatus for palpation of internal organs 
easily realizes palpation similar to that conducted by a physician with 
high accuracy. This enables an early prophylaxis. 
Since a hardness measuring apparatus for palpation of internal organs 
according to this embodiment has the endoscopic image display area 17A and 
hardness information display area 17b in the monitor 17 of the control 
unit 10, the contact of the main probe 1 with a biological tissue (subject 
H) in a living body is confirmed by an endoscopic image displayed in the 
endoscopic image display area 17A. At the same time, measurement of the 
hardness (diagnosis) of the biological tissue can be carried out. This 
always enables the measurement of hardness to be performed at a correct 
location safely and with high efficiency. 
Application of a Hardness Measuring Apparatus for Palpation of Internal 
Organs! 
The hardness measuring apparatus for palpation of internal organs according 
to Embodiment 2 can be used for measuring the hardness of a biological 
tissue located not only within a living body, but also that located on the 
surface of the living body, such as skin, as a hardness measuring 
apparatus for ectal organs. The hardness of an ectal biological tissue 
(subject H), such as skin, which is treated with an electrical cautery, 
laser treatment device or microwave treatment device can be measured by 
this hardness measuring apparatus for ectal organs. The postoperative 
healing of the treated tissue can be easily monitored by continuously 
measuring the hardness of the treated tissue. 
In both hardness measuring apparatus for palpation of internal organs and 
hardness measuring apparatus for ectal organs according to this 
embodiment, a layered piezoelectric ceramic oscillator, bimorph 
oscillator, quartz oscillator, PVDF-based oscillator, magnetostrictive 
element or SAW element can be used as the oscillator 3 instead of the 
piezoelectric ceramic oscillator, as in a hardness measuring apparatus 
according to Embodiment 1. A layered piezoelectric ceramic oscillator, 
bimorph oscillator, quartz oscillator, PVDF-based oscillator, 
magnetostrictive element or SAW element can also be used as the detecting 
element 7. A low-pass filter circuit, high-pass filter circuit, notch 
filter circuit, integrating circuit, differentiating circuit or peaking 
amplifying circuit can be used as the gain variation compensating circuit 
13. In addition, an active filter circuit or passive filter circuit can be 
used as the gain variation compensating circuit 13. 
Modification 1! 
In a hardness measuring apparatus for palpation of internal organs 
according to Modification 1 of Embodiment 2, a main probe 1 is used 
instead of the hand piece 1. The shape of the tip of the main probe 1 and 
that of the contact element 5 are changed. FIG. 21 shows a partial 
cross-sectional view of the tip of the main probe 1 of a hardness 
measuring apparatus for palpation of internal organs. The contact element 
5 of the hardness measuring apparatus for palpation of internal organs is 
formed as a contact needle that can puncture a biological tissue. An outer 
needle 2F having a lumen is formed surrounding the contact needle 5 of the 
main probe 1, which is to be brought into contact with a subject H, in 
order to protect the contact needle 5. A puncture edge 2G is formed at the 
tip of the outer needle 2F by cutting at a sharp angle to the longitudinal 
axis, and can puncture a biological tissue in a living body. Only the tip 
of the contact needle 5 (contact element) sticks out of the puncture edge 
2G of the outer needle 2F. The contact element 5 is disposed inside the 
outer needle 2F except its tip, which can be brought into contact with a 
subject H (biological tissue). 
A supporting member 6A is disposed in a middle portion of the lumen of the 
outer needle 2F. The contact element 5 is held at the central axis of the 
outer needle 2F by the supporting member 6A, and prevents the contact 
element 5 from coming into contact with the outer needle 2F. The 
supporting member 6A blocks the inside of the outer needle 2F in order to 
prevent an unnecessary substance from entering the inside of the main 
probe 1. The supporting member 6A is disposed so that it is a node of the 
resonance oscillation of the electromechanical system, as it is disposed 
between the oscillator 3, and detecting element 7 and the casing 2. This 
enables the oscillation not to be conducted to the casing 2, such as the 
outer needle 2F, and only the contact element is oscillated. In this 
hardness measuring apparatus for palpation of internal organs, the overall 
structure is the same as that according to Embodiment 2 described before, 
except for the contact element 5, outer needle 2F, puncture edge 2G and 
supporting member 6A. The hardness measuring apparatus for palpation of 
internal organs will be described. FIG. 22 shows cross-sectional views of 
the main probe 1 and the main part of a subject H (biological tissue) in 
the respective steps of palpation. In the hardness measuring apparatus for 
palpation of internal organs, the hardness of the subject H (biological 
tissue) is measured according to the sequence of the steps (A), (B) and 
(C). The outer needle 2F of the main probe 1 punctures the subject H 
(biological tissue) from the surface a living body, and then the hardness 
of the subject is measured. Since the outer needle 2F has the puncture 
edge 2G at its tip, puncture of the biological tissue is smoothly carried 
out. In a hardness measuring apparatus for palpation of internal organs 
according to Modification I of Embodiment 2, the contact element 5 
(contact needle) is placed inside the outer needle 2F, and the hardness of 
a part of the biological tissue in contact with it is measured. The step 
(C) shows that the contact element 5 reaches a tumor Y located in a deeper 
part of the biological tissue. As in the hardness measuring apparatus for 
palpation of internal organs according to Embodiment 2, when the hardness 
of a biological tissue in contact with the contact element 5 is changed, 
the frequency of the electromechanical oscillation system is changed. The 
gain variation compensating circuit 13 increases the gain in response to 
the change in the frequency of the electromechanical oscillation system, 
leading to the obtaining of a sufficient detection voltage for measuring 
the hardness of the biological tissue. The hardness of the biological 
tissue is finally displayed in the hardness information display area 17B 
of the monitor 17 as a graph. 
FIG. 23 shows a graph displayed in the hardness information display area 
17B of the monitor 17. The vertical axis rep resents the hardness of a 
subject H (biological tissue), and the horizontal axis the depth of the 
subject H from the surface of a living body. In the step (A) in which the 
puncture edge 2G of the outer needle 2F has just begun to puncture, the 
surface of the biological tissue is pressed by the outer needle 2F and 
elongated. This makes the surface harder. Since the contact element 5 is 
in contact with the hardened surface, an increased hardness is measured. 
In the step (B) during which the puncture of the outer needle 2F into the 
subject H proceeds, the contact element 5 stays in contact with an 
internal tissue. A constant and small hardness is measured during this 
step. In the step (C), the contact element 5 reaches a tumor Y and is 
further inserted into it. As in the step (A), at the boundary between the 
tumor Y and normal tissue, the puncture edge 2G of the outer needle 2F 
presses the surface of the tumor Y, which is elongated. This makes the 
surface harder. Since the contact element 5 is in contact with the 
hardened surface, an increased hardness is measured. After that, the 
contact element 5 further proceeds into the tumor Y. A constant hardness 
larger than that measured for the normal tissue is measured. The hardness 
of the tumor Y is slightly larger than that of the surrounding normal 
tissue. The difference between these hardnesses can be surely detected by 
a hardness measuring apparatus for palpation of internal organs according 
to Embodiment 2. 
The contact of the outer needle 2F of the main probe 1 with a biological 
tissue (subject H) is monitored by observing an endoscopic image which is 
sent from the fiberscope unit 18 and displayed in the endoscopic image 
display area 17A of the monitor 17 (see FIGS. 14, 15 and 18), for example, 
when puncturing a biological tissue located on the surface of a lung with 
the outer needle 2F. The puncture position of the outer needle 2F on the 
surface of a lung is displayed in the endoscopic image display area 17A. 
The hardness of the lung in the depth direction at the puncture position 
can be measured while observing the puncture region. Therefore, a tumor Y 
can be surely detected and both the position and depth of the tumor Y can 
be identified. 
In such a hardness measuring apparatus for palpation of internal organs, a 
contact needle is used as the contact element 5 of the main probe 1, and 
it is surrounded by the outer needle 2F having the puncture edge 2G at the 
tip. This enables the contact element 5 to puncture a deeper part of a 
biological tissue. Hardness information of the deeper part of a biological 
tissue can be directly obtained. As described before, the hardness 
measuring apparatus for palpation of internal organs according to 
Embodiment 2 can obtain a sufficient detection voltage for measuring the 
hardness of a biological tissue, even when the difference between the 
hardnesses is slight. The hardness of a deeper part of a biological tissue 
can be directly measured by the contact element 5, enabling an affected 
part of a biological tissue to be detected with high accuracy. This 
realizes an effective medical prophylaxis. 
In a hardness measuring apparatus for palpation of internal organs 
according to this embodiment, the monitor 17 has the two endoscopic image 
display area 17A and hardness information display area 17B. An actual 
contact position, at which the contact element 5 is in contact with a 
biological tissue via the outer needle 2F, can be confirmed by observing 
an endoscopic image displayed in the endoscopic image display area 17A. 
While observing the endoscopic image, the hardness of a biological tissue, 
in particular that of a deeper part of the biological tissue, can be 
measured. This enables a diagnosis of a biological tissue at a correct 
position safely and with high efficiency. 
A hardness measuring apparatus for palpation of internal organs according 
to Embodiment 2 is not restrictively used for measuring the hardness of a 
lung or liver as described before, but can be also used for measuring the 
hardness of a living tissue of a thyroid gland. When the hardness of a 
living tissue of a thyroid gland is measured, the outer needle 2F is 
inserted toward the thyroid gland with puncture, and the contact element 
is brought into contact with a thyroid gland tissue. When the contact 
element 5 is in contact with the thyroid gland tissue, hardness 
information of the thyroid gland tissue is displayed in the hardness 
information display area 17B of the monitor 17. In measurement of the 
hardness of a thyroid gland tissue, the fiberscope unit is not needed. 
Modification 2! 
A hardness measuring apparatus for palpation of internal organs according 
to Modification 2 of Embodiment 2 is the same as one described in 
Modification 1 except that a soft main probe 1 used instead of the main 
probe 1. FIG. 24 shows the overall structure of a hardness measuring 
apparatus for palpation of internal organs according to Modification 2 of 
Embodiment 2. This hardness measuring apparatus for palpation of internal 
organs has a soft main probe 1 insertable into a cavity in a human body. 
The touch section 2C of the soft main probe 1 is formed by a flexible 
(soft) tube which can be inserted into a cavity. A fluororesin tube is 
used as the flexible tube. A polyvinyl chloride tube, polyurethane tube or 
coil sheath tube can be used as the flexible tube. 
The soft main probe basically has the touch section 2C and holding section 
2E. The amplifying circuit 12 of the self-oscillating circuit 11 is 
disposed inside the holding section 2E, as in the hardness measuring 
apparatus for palpation of internal organs according to Embodiment 2. FIG. 
25 shows a magnified cross-sectional view of the touch section 2C of the 
soft main probe 1. In the touch section 2C formed by a soft tube, the 
oscillator 3 for generating ultrasonic oscillation is disposed at the tip 
facing a subject H on the central axis of the soft tube. The contact 
element 5 to be brought into contact with the subject H is placed at the 
tip of the touch section 2C. The contact element 5 has a hemi-spherical 
shape, and sticks out from the tip toward the subject H. The contact 
element 5 is coupled with the oscillator 3, and the ultrasonic oscillation 
of the oscillator 3 is conducted to the contact element 5. 
The oscillator 3 is connected to the detecting element 7 detecting the 
oscillation of the oscillator 3. The detecting element 7 is connected to 
the amplifying circuit 12 of self-oscillating circuit 11 placed inside the 
holding section 2E of the soft main probe 1. 
In the touch section 2C formed by a soft tube, the supporting member 6 for 
supporting the electromechanical oscillation system including the 
oscillator 3, detecting element 7 and contact element 5 is placed. As in 
the hardness measuring apparatus for palpation of internal organs 
according to Embodiment 2, the supporting member 6 holds the 
electromechanical oscillation system at the axial center of the touch 
section 2C, and prevents the oscillation of the mechanical oscillation 
system from being conducted to the touch section 2C. In the hardness 
measuring apparatus for palpation of internal organs described here, a 
round ring-shaped supporting member is used as the supporting member 6. 
The contact areas between the oscillator 3 and supporting member 6, and 
the supporting member 6 and the inner surface of the touch section 2C are 
set smaller. The oscillator 3 is fairly flexibly supported to enable it to 
follow the bending of the touch section 2C to some extent. This keeps the 
oscillator 3 from being excessively pressed and adversely affected from 
outside. The supporting member 6 is made of a rubber material, such as 
silicone rubber or NBR, or of a resin material, such as polyurethane resin 
or fluororesin. 
FIG. 26 shows a cross-sectional view of the fiberscope unit 18 having the 
soft main probe 1 and a biological tissue into which the fiberscope unit 
18 is inserted. The touch section 2C of the hardness measuring apparatus 
for palpation of internal organs, formed by a soft tube, is inserted into 
an instrument guide channel 18A of the fiberscope unit 18, and introduced 
to a cavity through the instrument guide channel 18A. A fiberscope unit 
having a flexible structure, such as a digestive tract videoscope or 
digestive tract fiberscope, is used as the fiberscope 18. The fiberscope 
unit 18 has an insertion section 18B which can be inserted into a cavity. 
A tip section 18D is coupled with the tip of the insertion section 18B 
facing the cavity via a flexible tube section 18C. The flexible tube 
section 18C connects the insertion section 18B and tip section 18D, and 
permits the tip section 18D to freely turn around the insertion section 
18B. The end surface of the tip section 18D has an exit of the instrument 
guide channel 18A, an illumination window 18E of a light guide for 
introducing illumination light and an observation window 18F coupled with 
observation optics. The touch section 2C of the soft main probe 1 is 
formed by a soft tube, and has such an outer diameter that it can be 
inserted into the instrument guide channel 18A of the fiberscope unit 18 
having a flexible structure. 
The structure of this hardness measuring apparatus for palpation of 
internal organs is the same as that of the hardness measuring apparatus 
for palpation of internal organs according to Embodiment 2 except for the 
soft main probe and fiberscope unit 18 having a soft structure. 
The use of this hardness measuring apparatus for palpation of internal 
organs will be described. The hardness of the inner surface (subject H) of 
an esophagus suffering from esophageal varices is measured by this 
hardness measuring apparatus for palpation of internal organs. As shown in 
FIG. 26, the insertion section 18B of the soft fiberscope unit 18 is 
inserted into the esophagus of a patient from his mouth. The inner surface 
of the esophagus is observed by looking at an endoscopic image displayed 
in the endoscopic image display area 17A. When varices Z are found on the 
inner surface of the esophagus by the observation, the touch section 2C of 
the soft main probe 1 is inserted into the instrument guide channel 18A of 
the insertion section 18B of the fiberscope unit 18. The tip of the touch 
section 2C of the soft main probe 1 is stuck out into the esophagus from 
the exit of the instrument guide channel in the end surface so that the 
contact element 5 is brought into contact with the varix Z (subject H). In 
the fiberscope unit 18 having a flexible structure, the flexible tube 
section 18C is so flexibly bent that the tip section 18D freely turns 
around. This enables the tip section 18D to freely turn to a place to be 
observed, and the contact element 5 to freely turn to a place to be 
diagnosed. 
When the contact element 5 is in contact with a varix, the frequency 
counter circuit 15 shown in FIG. 24 measures the frequency of the 
electromechanical oscillation system. The controller circuit 16 detects a 
change in the frequency of the electromechanical oscillation system, in 
which the contact element 5 is in contact with the varix Z, by data 
measured by the frequency counter circuit 15 to obtain hardness 
information of the varix Z. Data of an endoscopic image of the inner 
surface of the esophagus, which are sent from the fiberscope unit 18, and 
the hardness information of the varix Z obtained by the data measured by 
the frequency counter circuit 15 are combined in the controller circuit 
16. The endoscopic image and hardness information are displayed in the 
monitor 17, respectively. As the monitor 17 of the aforementioned hardness 
measuring apparatus for palpation of internal organs (see FIGS. 15 and 
16), the monitor 17 has the two endoscopic image display area 17A and 
hardness information display area 17B. The endoscopic image including the 
varix Z is displayed in the endoscopic image display area 17A, and the 
hardness information of the varix Z in the hardness information display 
area 17B. 
A hardness measuring apparatus for palpation of internal organs according 
to Modification 2 of Embodiment 2, can be used not only for measuring the 
hardness of an esophagus, but also for measuring the hardness of a 
biological tissue of a prostate. The contact element 5 of the soft main 
probe 1 is brought into contact with the prostate (subject H) using a 
urethroscope. A change in the frequency of the electromechanical 
oscillation system, in which the contact element 5 is in contact with the 
prostate, is measured by the frequency counter circuit 15. The hardness of 
a biological tissue of the prostate can be determined by measuring the 
change. A result of the hardness measurement is displayed in the hardness 
information display area 17B of the monitor 17. In the endoscopic image 
display area 17A, an endoscopic image of the inner surface of the bladder 
is displayed. 
In addition, this hardness measuring apparatus for palpation of internal 
organs can be used for measuring the hardness of a biological tissue of a 
bladder. The contact element 5 of the soft main probe 1 is inserted into 
the inside of a bladder (subject H) using an urethroscope, so that the 
contact element 5 is brought into contact with the inner surface of the 
bladder. A change in the frequency of the electromechanical oscillation 
system, in which the contact element 5 is in contact with the inner 
surface of the bladder, is measured by the frequency counter circuit 15. 
The hardness of a biological tissue of the bladder can be determined by 
measuring the change. A result of the hardness measurement is displayed in 
the hardness information display area 17B of the monitor 17. In the 
endoscopic image display area 17A, an endoscopic image of the inner 
surface of the bladder is displayed. When the hardness of biological 
tissues of the prostate and bladder is measured by the hardness measuring 
apparatus for palpation of internal organs according to Embodiment 2, the 
progress of prostatomegaly can be diagnosed. A hardness measuring 
apparatus for palpation of internal organs according to Embodiment 2 can 
be used for measuring the hardness of any biological tissues in a human 
body, as well as those of a human lung, lever, esophagus, prostate and 
bladder, and for medically diagnosing the tissues. The obtained diagnosis 
results are useful for treatment and prophylaxis. 
A hardness measuring apparatus for palpation of internal organs having such 
a structure comprises the soft main probe 1, in which the touch section 2C 
is formed by a flexible tube, so that the touch section freely turns 
around. The contact element 5 can be inserted into a cavity via the 
instrument guide channel 18A of the insertion section 18B of the 
fiberscope unit 18 having a flexible structure. The fiberscope section 18 
has the flexible tube section 18C at the tip of the insertion section 18B. 
The flexible tube section 18C enables the tip section 18D to freely turn 
around. The contact element 5 can freely move in the cavity due to the 
free turning of the tip section 18D. The illumination window 18E and 
observation window 18F disposed in the end surface of the tip section 18D 
of the fiberscope unit 18 can freely turn to a pathological part. The 
contact element 5 can be surely set in contact with the pathological part 
to measure the hardness of the pathological part. This hardness measuring 
apparatus for palpation of internal organs easily enables a precise 
diagnosis of a biological tissue in a cavity. 
This hardness measuring apparatus for palpation of internal organs has the 
soft main probe 1 which can be inserted into a cavity, enabling the 
hardness of a biological tissue in the cavity to be measured without 
performing a painful surgical operation on a patient. 
This hardness measuring apparatus for palpation of internal organs has the 
endoscopic image display area 17A and hardness information display area 
17B in the monitor 17. The hardness of an affected part of a biological 
tissue in a cavity, with which the contact element 5 should be in contact, 
can be measured while identifying the actual position of the affected part 
by observing an endoscopic image. This enables a safe diagnosis of a 
biological tissue at the correct position with high efficiency. 
Modification 3! 
A hardness measuring apparatus for palpation of internal organs according 
to Modification 3 of Embodiment 2 has a structure of the control unit 10 
partly different from that in the hardness measuring apparatus for 
palpation of internal organs according to Embodiment 2. FIG. 27 shows the 
overall structure of a hardness measuring apparatus for palpation of 
internal organs according to Modification 3 of Embodiment 2. This hardness 
measuring apparatus for palpation of internal organs has an amplitude 
voltage measuring circuit 20 instead of the frequency counter circuit 15. 
When the contact element 5 of the main probe 1 is brought into contact 
with a subject H, the resonance frequency and resonance amplitude voltage 
of the electromechanical oscillation system are changed due to the 
acoustic impedance of the subject H. The amplitude voltage measuring 
circuit 20 measures the amplitude voltage of the electromechanical 
oscillation system. 
In FIG. 17 (gain-frequency and admittance-frequency characteristic curves) 
shown before, the central frequency f.sub.2 of the gain variation 
compensating circuit 13 shown in the gain-frequency characteristic curve 
13G is set lower than the central frequency f.sub.1 of the 
electromechanical oscillation system shown in the gain-frequency 
characteristic curve MG. Therefore, when the contact element 5 is brought 
into contact with the subject H, the frequency of the electromechanical 
oscillation system is changed, the gain is increased in response to this 
change in the frequency, and then the amplitude voltage is increased. 
A hardness measuring apparatus for palpation of internal organs having such 
a structure has advantages similar to those provided by the aforementioned 
hardness measuring apparatus for palpation of internal organs according to 
Embodiment 2. The frequency counter circuit 15 in the respective hardness 
measuring apparatuses for palpation of internal organs according to 
Modifications 1 and 2 of Embodiment 2 can be replaced with the amplitude 
voltage measuring circuit 20. 
Modification 4! 
In a hardness measuring apparatus for palpation of internal organs 
according to Modification 4 of Embodiment 2, a low-pass filter circuit is 
used as the gain variation compensating circuit 13 instead of the 
band-pass filter circuit. FIG. 28 shows gain-frequency and 
admittance-frequency characteristic curves of the electromechanical 
oscillation system and gain variation compensating circuit 13 in a 
hardness measuring apparatus for palpation of internal organs according to 
Modification 4 of Embodiment 2. The horizontal axis represents frequency, 
and the vertical axes respectively represent gain and admittance of the 
oscillation system. As the gain-frequency and admittance-frequency 
characteristic curves shown in FIG. 17, the characteristic curve MG shows 
a gain-frequency characteristic (admittance-frequency characteristic) of 
the electromechanical oscillation system excepting the gain variation 
compensating circuit 13, when the contact element 5 is not in contact with 
a subject H. The characteristic curve 13G1 shows a gain-frequency 
characteristic of the gain variation compensating circuit 13. In the gain 
variation compensating circuit 13 of a hardness measuring apparatus for 
palpation of internal organs according to Modification 4 of Embodiment 2, 
a low-pass filter circuit is used. The gain-frequency characteristic of 
the gain variation compensating circuit 13 is set in a frequency band in 
the gain-frequency characteristic curve 13G1, in which the gain of the 
electromechanical oscillation system is changed in response to a change in 
the frequency. A central frequency f.sub.2, at which the gain has a 
maximum value 13GP in the gain-frequency characteristic curve 13G of the 
gain variation compensating circuit 13, is set lower than a central 
frequency f.sub.1 at which the gain in the characteristic curve MG of the 
electromechanical oscillation system has a maximum value P1 (maximum value 
of the admittance). Therefore, the electromechanical oscillation system 
resonantly oscillates at a frequency lower than the central frequency 
f.sub.1, and higher than the central frequency f.sub.2, when the contact 
element 5 is in contact with subject H. 
When the contact element 5 of the main probe 1 (see FIG. 14) is in contact 
with a biological tissue (subject H), the gain-frequency characteristic 
curve MG of the electromechanical oscillation system is changed to a 
gain-frequency characteristic curve MG4 in a conventional hardness 
measuring apparatus. In this gain-frequency characteristic curve MG4, the 
resonance frequency given by the maximum value P4 is changed to a 
frequency f.sub.4 because the acoustic impedance of the subject H is low. 
A hardness measuring apparatus for palpation of internal organs according 
to Embodiment 2 shows a gain-frequency characteristic curve MG5 when the 
contact element 5 of the main probe 1 is not in contact with anything. The 
gain-frequency characteristic curve MG5 has a maximum value P5 at a 
central frequency f.sub.5. When contacting the contact element 5 with a 
subject H, the gain-frequency characteristic curve MG5 is changed to a 
gain-frequency characteristic curve MG6. Because the acoustic impedance of 
the subject H is low, the central frequency f.sub.5 is shifted to a 
frequency f.sub.6. The gain is increased along the gain-frequency 
characteristic curve 13G1 of the gain variation compensating circuit 13 by 
the gain increasing and phase transfer functions of the gain variation 
compensating circuit 13, leading to obtaining a maximum value P5 of the 
gain. This increased gain enables a sufficient detection voltage for 
hardness measurement to be obtained. 
A hardness measuring apparatus for palpation of internal organs having such 
a structure has advantages similar to those provided by the aforementioned 
hardness measuring apparatus for palpation of internal organs according to 
Embodiment 2. 
Modification 5! 
In a hardness measuring apparatus for palpation of internal organs 
according to Modification 5 of Embodiment 2, a high-pass filter circuit is 
used as the gain variation compensating circuit 13 instead of the 
band-pass filter circuit. FIG. 29 shows gain-frequency and 
admittance-frequency characteristic curves of the electromechanical 
oscillation system and gain variation compensating circuit 13 in a 
hardness measuring apparatus for palpation of internal organs according to 
Modification 5 of Embodiment 2. The horizontal axis represents frequency, 
and the vertical axes respectively represent gain and admittance of the 
oscillation system. The characteristic curve MG shows a gain-frequency 
characteristic (admittance-frequency characteristic) of the 
electromechanical oscillation system excepting the gain variation 
compensating circuit 13, when the contact element 5 is in contact with a 
subject H. The characteristic curve 13G2 shows a gain-frequency 
characteristic of the gain variation compensating circuit 13. In the gain 
variation compensating circuit 13 of a hardness measuring apparatus for 
palpation of internal organs according to Modification 5 of Embodiment 2, 
a high-pass filter circuit is used. The slope of the gain-frequency 
characteristic curve 13G2 of the gain variation compensating circuit 13 is 
opposite to that of the gain-frequency characteristic curves 13G and 13G1, 
which are obtained by using band-pass and low-pass filter circuits, 
respectively. A central frequency f.sub.2, at which the gain has a maximum 
value 13GP in the gain-frequency characteristic curve 13G2 of the gain 
variation compensating circuit 13, is set higher than a central frequency 
f.sub.1 at which the gain in the characteristic curve MG of the 
electromechanical oscillation system has a maximum value P1. Therefore, 
the electromechanical oscillation system resonantly oscillates at a 
frequency higher than the central frequency f.sub.1, and lower than the 
central frequency f.sub.2, when the contact element 5 is in contact with 
subject H. 
A hardness measuring apparatus for palpation of internal organs is 
particularly suitable for measuring the hardness of a hard subject H. 
Therefore, the hardness of a relatively hard biological tissue, such as a 
human bone, tooth or nail, can be measured by this hardness measuring 
apparatus for palpation of internal organs. When the contact element 5 of 
the main probe 1 (see FIG. 14) is in contact with a hard subject H, the 
gain-frequency characteristic curve MG of the electromechanical 
oscillation system is changed to a gain-frequency characteristic curve MG4 
in a conventional hardness measuring apparatus. In this gain-frequency 
characteristic curve MG4, the resonance frequency f.sub.4 at which the 
maximum value P4 is given is shifted toward a higher frequency, because 
the acoustic impedance of the subject H is high. 
A hardness measuring apparatus for palpation of internal organs according 
to Embodiment 2 shows a gain-frequency characteristic curve MG5 when the 
contact element 5 of the main probe 1 is not in contact with anything. The 
gain-frequency characteristic curve MG5 has a maximum value P5 at a 
central frequency f.sub.5. When bringing the contact element 5 into 
contact with a hard subject H, the gain-frequency characteristic curve MG5 
is changed to a gain-frequency characteristic curve MG6. Because the 
acoustic impedance of the subject H is high, the central frequency f.sub.5 
is shifted to a resonance frequency f.sub.6. The gain is increased along 
the gain-frequency characteristic curve 13G2 of the gain variation 
compensating circuit 13, leading to the obtaining of a maximum value P5 of 
the gain. This increased gain enables a sufficient detection voltage for 
hardness measurement to be obtained. A hardness measuring apparatus for 
palpation of internal organs having such a structure has advantages 
similar to those provided by the aforementioned hardness measuring 
apparatus for palpation of internal organs according to Embodiment 2. 
The hardness measuring apparatus for palpation of internal organs can 
detect a slight change in the hardness of a hard biological tissue in a 
patient's body. The fiberscope unit 18 (for example, an arthroscope) is 
inserted into a knee joint. When the contact element 5 of the main probe 1 
is brought into contact with periosteum on a synovial membrane in the knee 
joint, the hardness of the synovial membrane can be measured. A medical 
diagnosis of the knee joint can be conducted based on a result of this 
hardness measurement. The hardness of a relatively hard biological tissue, 
such as a bone, cartilage or synovial membrane, can be easily measured 
with high accuracy by a hardness measuring apparatus for palpation of 
internal organs according to Modification 5 of Embodiment 2. 
The hardness of a tooth can be measured by this hardness measuring 
apparatus for palpation of internal organs. The tooth has enamelum and 
dentinum, whose hardnesses can be measured. Soft teeth easily suffer from 
dental caries. When results of the measurement of their hardnesses show 
that the tooth is soft, fluoridization is carried out for the tooth, 
preventing the tooth from being decayed. 
Modification 6! 
A hardness measuring apparatus for palpation of internal organs according 
to Modification 6 of Embodiment 2 has a structure of the main probe 1, 
which is partly different from that in a hardness measuring apparatus for 
palpation of internal organs according to Embodiment 2 shown in FIG. 14. 
FIG. 30 shows a magnified cross-sectional view of the main part of the 
main probe 1 of a hardness measuring apparatus for palpation of internal 
organs according to Modification 6 of Embodiment 2. The main probe 1 of 
this hardness measuring apparatus for palpation of internal organs has the 
oscillator 3 comprising a layered piezoelectric ceramic oscillator and the 
detecting element 7 comprising a bimorph oscillator. The oscillator 3 and 
detecting element 7 form the electromechanical oscillation system. The 
layered piezoelectric ceramic oscillator of the oscillator 3 is formed by 
stacking plural piezoelectric ceramic sheets in the direction of the 
longitudinal axis of the casing 2. The oscillator 3 is mechanically 
coupled with the contact element 5. The layered piezoelectric ceramic 
oscillator has a small size, and outputs a large amplitude for an input 
voltage. 
The detecting element 7 comprising the bimorph oscillator is fixed on the 
outer surface of the oscillator 3 (layered piezoelectric ceramic 
oscillator). The detecting element 7 is formed in a film shape. This 
causes the detecting element 7 to be light in weight, and to require only 
a small space for its disposition inside the casing 2 of the main probe 1. 
A film-shaped PVDF-based oscillator can be used as the detecting element 7 
instead of the bimorph oscillator. 
A hardness measuring apparatus for palpation of internal organs having such 
a structure has the oscillator 3 comprising a layered piezoelectric 
ceramic oscillator and the detecting element 7 comprising a bimorph 
oscillator. Therefore, it has advantages similar to those provided by the 
aforementioned hardness measuring apparatus for palpation of internal 
organs according to Embodiment 2. In addition, the size of the oscillator 
3 can be reduced since a sufficient amplitude is obtained. The size of the 
detecting element 7 can be also reduced since the detecting element 7 is 
formed in a film shape. These enable the size of components inside the 
main probe 1 to be reduced, realizing a reduced size and weight of the 
main probe 1 itself. Consequently, the operability of the main probe 1 can 
be improved, realizing improved operability of the hardness measuring 
apparatus for palpation of internal organs. 
Modification 7! 
A hardness measuring apparatus for palpation of internal organs according 
to Modification 7 of Embodiment 2 has a structure of the main probe 1, 
which is partly different from that according to Embodiment 2 shown in 
FIG. 14. FIG. 31 shows a magnified cross-sectional view of the main part 
of the main probe 1 of a hardness measuring apparatus for palpation of 
internal organs according to Modification 7 of Embodiment 2. The main 
probe 1 of this hardness measuring apparatus for palpation of internal 
organs has the oscillator 3 comprising a layered piezoelectric ceramic 
oscillator, the detecting element 7 comprising a layered piezoelectric 
ceramic oscillator and an insulation material 3D. The oscillator 3 and 
detecting element 7 form the electromechanical oscillation system. The 
layered piezoelectric ceramic oscillator of the oscillator 3 is formed by 
stacking plural piezoelectric ceramic sheets in the direction of the 
longitudinal axis. This layered piezoelectric ceramic oscillator is small 
in size, and a large amplitude can be obtained for an input voltage. 
The layered piezoelectric ceramic of the detecting element 7 is also formed 
by stacking plural piezoelectric ceramic sheets in the direction of the 
longitudinal axis, as that of the oscillator 3. This detecting element 7 
is fixed around the oscillator 3. 
The insulation material 3D is formed between the oscillator 3 and detecting 
element 7. The layered piezoelectric ceramic oscillator of the oscillator 
3, layered piezoelectric ceramic of the detecting element 7 and insulation 
material 3D are fabricated as an integrated assembly. 
A hardness measuring apparatus for palpation of internal organs having such 
a structure has both the oscillator 3 and detecting element 7 comprising a 
layered piezoelectric ceramic oscillator. Therefore, the size of the 
oscillator 3 can be reduced since a sufficient amplitude is obtained. The 
size of the detecting element 7 can be also reduced since the detecting 
element 7 is formed in a film shape. These enable the size of components 
inside the main probe 1 to be reduced, realizing a reduced size and weight 
of the main probe 1 itself. Consequently, the operability of the main 
probe 1 can be improved, realizing improved operability of the hardness 
measuring apparatus for palpation of internal organs. 
Modification 8! 
A hardness measuring apparatus for palpation of internal organs according 
to Modification 8 of Embodiment 2 has a structure of the soft main probe 
1, which is partly different from that according to Embodiment 2 shown in 
FIGS. 24, 25 and 26. FIG. 32 shows a magnified cross-sectional view of the 
main part of the soft main probe 1 of a hardness measuring apparatus for 
palpation of internal organs according to Modification 8 of Embodiment 2. 
The soft main probe 1 of the hardness measuring apparatus for palpation of 
internal organs is formed by a soft tube. A supporting member 2H is 
inserted and fitted into an opening of the soft main probe 1 at the tip 
facing toward a subject H. The supporting member 2H has a cylindrical 
shape with a closed end, and is formed by an electroconductive material, 
such as a metal. The oscillator 3 is fixed to the supporting member 2H on 
the surface facing to the contact element 5. The detecting element 7 is 
fixed to the supporting member 2H on the opposite surface facing to the 
touch section 2C. Both the oscillator 3 and detecting element 7 may 
comprise a plate-shaped piezoelectric ceramic oscillator. Although details 
are not shown in FIG. 32, the oscillator has a layer structure in which an 
electrode (anode), a piezoelectric crystal and an electrode (cathode) are 
stacked. The detecting element 7 has a similar structure in which an 
electrode (cathode), a piezoelectric crystal and an electrode (anode) are 
stacked. 
The contact element 5 is mechanically coupled with the oscillator 3 to 
conduct oscillation generated by the oscillator 3. The contact element 5 
has a hemi-spherical shape, and is disposed on the supporting member 2H. 
This contact element 5 has a function of separating a subject (biological 
tissue), the oscillator 3 and supporting member 2H. A wiring cable passing 
aperture 2I for a cable electrically connecting the output terminal 
(anode) of the oscillator 3 and the output terminal of the gain variation 
compensating circuit is formed. The supporting member 2H is also used as a 
common reference potential plate, to which the cathodes of the oscillator 
3 and detecting element 7 are electrically connected. The output terminal 
(anode) of the detecting element 7 is electrically connected to the 
amplifying circuit 12 of the self-oscillating circuit 11. 
A hardness measuring apparatus for palpation of internal organs having such 
a structure has advantages similar to those provided by the aforementioned 
hardness measuring apparatus for palpation of internal organs according to 
Modification 2 of Embodiment 2. In addition, in this hardness measuring 
apparatus for palpation of internal organs, the supporting member 2H is 
fixed to an opening at the tip of the touch section 2C of the soft probe 
1, enabling the size of the electromechanical oscillation system to be 
reduced. The flexibility of the tip of the touch section 2C is not 
adversely affected by the oscillator 3 and detecting element 7. Therefore, 
the touch section 2C can be smoothly inserted into the instrument guide 
channel 18A of the fiberscope unit 18 having a soft structure. 
Consequently, the operability of the soft main probe 1 can be improved, 
realizing improved operability of the hardness measuring apparatus for 
palpation of internal organs. 
Modification 9! 
A hardness measuring apparatus for palpation of internal organs according 
to Modification 9 of Embodiment 2 has a structure of the main probe 1, 
which is partly different from that according to Modification 1 of 
Embodiment 2 shown in FIGS. 21, 22 and 23. FIG. 33 shows a magnified 
cross-sectional view of the main part of the main probe 1 of a hardness 
measuring apparatus for palpation of internal organs according to 
Modification 9 of Embodiment 2. The main probe 1 of this hardness 
measuring apparatus for palpation of internal organs has the outer needle 
2F in the touch section 2C. The outer diameter of the puncture edge 2G at 
the tip of the outer needle 2F is gradually decreased toward the tip, 
making the puncture edge very sharp. The contact element 5 included in the 
outer needle 2F is stuck out from the opening at the tip of the puncture 
edge 2G of the outer needle 2F, and is not in contact with puncture edge 
2F. 
A hardness measuring apparatus for palpation of internal organs having such 
a structure has advantages similar to those provided by the aforementioned 
hardness measuring apparatus for palpation of internal organs according to 
Modification 1 of Embodiment 2. In addition, in this hardness measuring 
apparatus for palpation of internal organs, the puncture edge 2G having a 
sharp shape is formed in the outer needle 2F of the main probe 1, 
realizing smooth puncturing of the outer needle 2F into a biological 
tissue. The shape of the outer needle 2F including the puncture edge 2G 
becomes symmetrical. Therefore, the contact of the contact element 5 with 
the biological tissue is stable, irrespective of puncturing conditions 
into the biological tissue. In addition, the space between the outer 
needle 2F and contact element 5 can be made small. This prevents an 
unnecessary substance, such as a biological tissue, from being put in the 
space or entering the inside of the outer needle 2F, and then realizes 
stable hardness measurement. 
Embodiment 3 
In Embodiment 3 of the present invention, an acceleration measuring, fluid 
viscosity measuring apparatus and fluid pressure measuring apparatus in 
which a frequency deviation circuit is used will be described. 
Acceleration Measuring Apparatus! 
FIG. 34 shows the system structure of an acceleration measuring apparatus 
(gyroscope) according to Embodiment 3 of the present invention. The 
acceleration measuring apparatus basically has a structure similar to that 
of the aforementioned hardness measuring apparatuses. It has an 
acceleration measuring section comprising an oscillator 3 and a detecting 
element 7, and a control unit 10. The oscillator 3 is fixed to a moving 
body. The oscillation mode in the oscillator 3 is changed by an 
acceleration (Coriolis force) acting on the moving body. The detecting 
element 7 detects a change in the oscillation mode of the moving body. 
The control unit 10 has a self-oscillating circuit 11 including an 
amplifying circuit 12, a gain variation compensating circuit 13 and an 
acceleration measuring circuit 21. The gain variation compensating circuit 
13 has a gain increasing function and phase transfer function, and 
increases the gain in response to a change in the frequency. The 
acceleration measuring circuit 21 detects a change in the acceleration 
from the change in the frequency. An acceleration measuring apparatus 
having such a structure can detect an acceleration acting on a moving body 
as a change in the oscillation mode of the oscillator 3. A change in the 
acceleration can be determined by a change in the frequency of an 
electromechanical oscillation system. In addition, since the gain 
variation compensating circuit 13 can increase the gain of the 
electromechanical oscillation system, a sufficient detection voltage for 
acceleration measurement can be obtained. 
Fluid Viscosity Measuring Apparatus! 
FIG. 35 shows the system structure of a fluid viscosity measuring apparatus 
according to Embodiment 3 of the present invention. The fluid viscosity 
measuring apparatus basically has a structure similar to that of the 
aforementioned hardness measuring apparatuses. It has a viscosity 
measuring section comprising an oscillator 3 and a detecting element 7, 
and a control unit 10. The oscillator 3 is directly in contact with a 
fluid 23 whose viscosity is to be measured, or indirectly in contact with 
the fluid 23 via a fluid contact element (not shown in FIG. 35). The 
oscillation mode in the oscillator 3 is changed by the viscosity of the 
fluid 23. The detecting element 7 detects a change in the oscillation mode 
of the moving body. 
The control unit 10 has a self-oscillating circuit 11 including an 
amplifying circuit 12, a gain variation compensating circuit 13 and a 
fluid viscosity measuring circuit 21. The gain variation compensating 
circuit 13 has a gain increasing function and phase transfer function, and 
increases the gain in response to a change in the frequency. The fluid 
viscosity measuring circuit 21 detects the viscosity of the fluid 23 from 
the change in the frequency. 
In a fluid viscosity measuring apparatus having such a structure, the 
oscillation mode of the oscillator 3 is changed by the viscosity of a 
fluid 23. Therefore, the viscosity of the fluid 23 can be determined by a 
change in the frequency of an electromechanical oscillation system. In 
addition, since the gain variation compensating circuit 13 can increase 
the gain of the electromechanical oscillation system, a sufficient 
detection voltage for acceleration measurement can be obtained. 
FIG. 36 shows the system structure of a fluid viscosity measuring apparatus 
according to a modification of Embodiment 3. In this fluid viscosity 
measuring apparatus, the oscillator 3 and detecting element 7 are bimorph 
oscillators, and an insulation material 3D is disposed between them. 
Fluid Pressure Measuring Apparatus! 
FIG. 37 shows the system structure of a fluid pressure measuring apparatus 
(pressure sensor) according to Embodiment 3 of the present invention. The 
fluid pressure measuring apparatus basically has a structure similar to 
that of the aforementioned hardness measuring apparatuses. It has a fluid 
pressure measuring section comprising a fluid contact element 5, an 
oscillator 3 and a detecting element 7, and a control unit 10. The fluid 
contact element 5 is directly in contact with a fluid 25. The shape of the 
fluid contact element 5 is changed by a pressure F generated in the fluid 
25. A diaphragm or the like is used as the fluid contact element 5. The 
oscillator 3 is coupled with the fluid contact element 5, and then the 
position of the oscillator 3 is changed in response to a change in the 
shape of the fluid contact element 5. As shown in FIG. 37, when a fluid 25 
flows upward from the bottom, the fluid contact element 5 is deformed by a 
pressure F. The position of the oscillator 3 is changed up and down in the 
vertical direction. The oscillation mode of the oscillator 3 is changed by 
the change in the position. The detecting element 7 detects a change in 
the oscillation mode. 
The control unit 10 has a self-oscillating circuit 11 including an 
amplifying circuit 12, a gain variation compensating circuit 13 and a 
fluid pressure measuring circuit 24. The gain variation compensating 
circuit 13 has a gain increasing function and phase transfer function, and 
increases the gain in response to a change in the frequency. The fluid 
pressure measuring circuit 24 detects a change in the fluid pressure from 
the change in the frequency. 
In a fluid pressure measuring apparatus having such a structure, the 
position of the oscillator 3 is changed by the pressure F of a fluid 25, 
and then the oscillation mode of the oscillator 3 is changed. Therefore, a 
change in the pressure of the fluid 25 can be determined by a change in 
the frequency of an electromechanical oscillation system. In addition, 
since the gain variation compensating circuit 13 can increase the gain of 
the electromechanical oscillation system, a sufficient detection voltage 
for acceleration measurement can be obtained. 
FIG. 38 shows the system structure of a fluid pressure measuring apparatus 
according to a modification of Embodiment 3 of the present invention. This 
fluid pressure measuring apparatus comprises an oscillator 3 having a 
cylindrical shape. A fluid contact element 5, which is deformed by a fluid 
pressure F, is disposed at an end of the cylindrical-shaped oscillator 3. 
A moving body 26 which moves in response to a change in the shape of the 
fluid contact element 5 is stored in a space formed by the 
cylindrical-shaped oscillator 3 and fluid contact element 5. A diaphragm 
or the like is used as the fluid contact element 5. A liquid, such as 
water or mercury, gas, such as an inert gas, or fine particles, such as 
sand or powder, is used as the moving body 26. 
In a fluid pressure measuring apparatus having such a structure, when a 
pressure is applied to the fluid contact element, the fluid contact 
element 5 is deformed 5, and then the moving body 26 stored inside the 
oscillator 3 moves. The position of the oscillator 3 is relatively changed 
by the movement of the moving body 26, and then the oscillation mode of 
the oscillator 3 is changed. As in the aforementioned fluid pressure 
measuring apparatus, a change in the pressure of the fluid 25 can be 
determined by a change in the frequency of an electromechanical 
oscillation system. In addition, since the gain variation compensating 
circuit 13 can increase the gain of the electromechanical oscillation 
system, a sufficient detection voltage for acceleration measurement can be 
obtained. 
While there has been described what are at present considered to be 
preferred embodiments of the present invention, it will be understood that 
various modifications may be made thereto, and it is intended that the 
appended claims cover all such modifications as fall within the true 
spirit and scope of the present invention.