Mechanical ultrasonic scanner

A mechanical ultrasonic scanner includes a transducer element which is swingably supported in a housing, and a sensor for detecting a swinging angle of the transducer element. The sensor includes a permanent magnet swung together with the transducer element, and a magnetoresistive element fixed to the housing to be opposite to a swinging locus of the permanent magnet. The permanent magnet generates a magnetic field between the permanent magnet and the magnetoresistive element. The magnetoresistive element detects a strength of the magnetic field which changes in correspondence with a swinging angle of the magnet, so that the swinging angle of the transducer element is detected on the basis of the change in the strength of the magnetic field. Even if the housing contains a sound transmitting medium, the magnetic field generated by the sensor is not adversely affected by the sound transmitting medium. Therefore, the swinging angle of the transducer element can be accurately detected to accurately obtain a radiating/returning direction of an ultrasonic beam, thus accurately reconstructing an image. In addition, the position of the transducer element can be controlled with high precision.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a mechanical ultrasonic scanner for 
mechanically swinging a transducer element, thereby scanning the interior 
of a living body by a ultrasonic beam emitted from the transducer element, 
so that an image of the structure and movement of internal organs of the 
living body is displayed in real time. 
2. Description of the Related Art 
In a mechanical ultrasonic scanner, a transducer element is swingably 
supported in a housing. This transducer element radiates an ultrasonic 
beam while being swung by, e.g., a motor. Therefore, the inside of a 
living body is scanned by the ultrasonic beam. After scanning, the 
ultrasonic beam returned from the living body is detected by the 
transducer element. The detected ultrasonic beam reconstructs an image to 
obtain a tomogram. 
The housing contains a liquid sound transmitting medium (e.g., a mineral 
oil). The transducer element is dipped in the sound transmitting medium. 
This sound transmitting medium has a property of easily transmitting an 
ultrasonic beam in a frequency range incident on a living body. Therefore, 
the ultrasonic beam radiated from the transducer element can be 
transmitted without being obstructed in the housing, and can be incident 
on the living body. 
In order to reconstruct an image by the detected ultrasonic beam, a 
direction in which the ultrasonic beam is radiated and returned from/to 
the transducer element must be detected. Therefore, a swinging angle of 
the transducer element is conventionally detected by an optical encoder to 
obtain a radiating/returning direction of the ultrasonic beam. 
In a liquid sound transmitting medium, however, light emitted from the 
optical encoder may be irregularly reflected. In addition, swinging of the 
transducer element causes the sound transmitting medium to flow, and 
irregular reflection of the light is enhanced. Furthermore, straight 
propagation of the light may often be interrupted by dust which floats in 
the sound transmitting medium. For these reasons, the light is not 
accurately detected, and the swinging angle of the transducer element is 
not often detected accurately. Therefore, a radiating/returning direction 
of the ultrasonic beam cannot be accurately obtained, and a reconstructed 
image may often be inaccurate. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a mechanical ultrasonic 
scanner for accurately detecting a swinging angle of a transducer element 
to accurately obtain a radiating/returning direction of an ultrasonic 
beam, thus accurately reconstructing an image. 
According to the present invention, there is provided a mechanical 
ultrasonic scanner, comprising: 
a housing; 
a transducer element arranged in said housing; 
means for swinging said transducer element; and 
means for detecting a swinging angle of said transducer element, said 
detecting means including a first member which is swung together with said 
transducer element, and a second member attached to said housing to be 
opposite to a part of a swinging locus of the first member, said detecting 
means causing one of the first and second members to generate a magnetic 
field between them, causing the other of the first and second members to 
detect a strength of the magnetic field which changes in correspondence 
with a swinging angle of the first member, and detecting the swinging 
angle of said transducer element on the basis of the change in strength of 
the detected magnetic field. 
In the present invention, a swinging angle of the transducer element is 
detected by a magnetic detecting means. For this reason, even if he 
housing contains a sound transmitting medium, a magnetic field radiated 
from the detecting means is not adversely affected by the sound 
transmitting medium. Therefore, in the present invention, the swinging 
angle of the transducer element can be accurately detected to accurately 
obtain a radiating/returning direction of the ultrasonic beam, thus 
accurately reconstructing an image. In addition, the position of the 
transducer element can be controlled with high precision. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 to 4 show a mechanical ultrasonic scanner according to the first 
embodiment of the present invention. This scanner includes a housing 4. 
The housing 4 includes a spherical shell-like cap 1 through which an 
ultrasonic beam is transmitted, a shielding case 2 to which the cap 1 is 
fixed, and a holding case 3 for supporting the shielding case 2. 
A chamber 16 defined by the cap 1 and the shielding case 2 contains a sound 
transmitting medium. In addition, a transducer element 11 and a swinging 
motor 8 for swinging the transducer element 11 are arranged in the chamber 
16. More specifically, the transducer element 11 is supported by a support 
member 10, and an extending member 10-1 which extends from the support 
member 10 is fixed to a rotating shaft 9 rotatably supported by bearings 
27 of the shielding case 2. 
The swinging motor 8 includes a stator 6 fixed to the shielding case 2, an 
exciting coil 5 wound around the stator 6, and a rotor 7 which is disposed 
between a pair of opposite surfaces 6-1 and 6-2, and is fixed to the 
rotating shaft 9. The stator 6 is made of, e.g., a soft magnetic iron 
(SUSYB material), a rolled steel for general structure (SS41), or silicon 
steel (S-10). The rotor 7 is made of a permanent magnet having north and 
south poles polarized by a plane including the center of the rotating 
shaft 9. 
In the swinging motor 8, when a current is periodically supplied to the 
exciting coil 5, a pair of opposite surfaces 6-1 and 6-2 of the stator 6 
are periodically excited. As a result, the pair of opposite surfaces 6-1 
and 6-2 are periodically magnetized to the north and south poles to swing 
the rotor 7 and the rotating shaft 9. 
An operation of the swinging motor 8 will be described below in detail with 
reference to FIGS. 5A to 5E. 
Referring to FIG. 5A, when a current is supplied to the exciting coil 5 in 
a direction indicated by an arrow, the pair of opposite surfaces (magnetic 
poles) 6-1 and 6-2 are magnetized to the north and south poles, 
respectively. The rotor (permanent magnet) 7 is opposite to the magnetic 
poles in the manner of N--N, and S --S, and a direction of a magnetomotive 
force of an armature coincides with that of a permanent magnet. Therefore, 
an attractive force between the permanent magnet and the magnetic poles is 
set to be "0" (cogging torque). 
FIG. 5B shows a case wherein the permanent magnet is rotated clockwise by 
45.degree.. Since the direction of the magnetomotive force of the armature 
has a phase difference of 45.degree. from that of the permanent magnet, a 
clockwise torque is generated by the vertical components thereof. However, 
since the magnetic center of the magnetomotive force of the permanent 
magnet is shifted from that of the north magnetic pole by 45.degree., a 
torque in a direction to match the magnetic centers, i.e., a 
counterclockwise torque is also generated. As a result, a rotational 
torque is generated in a direction obtained by synthesizing the clockwise 
and counterclockwise rotational torques. 
In FIG. 5C, since the direction of the magnetomotive force of the armature 
is perpendicular to that of the permanent magnet, a maximum clockwise 
torque can be obtained. Since the magnetic center of the permanent magnet 
is shifted from that of the magnetic poles by 90.degree., a force between 
the permanent magnet and the magnetic pole is set to be "0". Therefore, 
the synthetic torque includes only a torque generated by the magnetomotive 
force of the armature. 
FIG. 5D shows a case wherein the permanent magnet is further rotated 
clockwise by 45.degree.. Since the direction of the magnetomotive force of 
the armature is shifted from that of the permanent magnet by 45.degree. as 
in FIG. 5B, a clockwise torque is generated by the vertical components 
thereof. However, since the magnetic center of the magnetomotive force of 
the permanent magnet is shifted from that of the south magnetic pole by 
45.degree., a torque in the direction to match the magnetic centers, i.e., 
a clockwise torque is also generated. As a result, a rotational torque is 
generated in the direction obtained by synthesizing the clockwise and 
counterclockwise rotational torques. 
In FIG. 5E, the permanent magnet is opposite to the magnetic poles in the 
manner of N--S, and S--N, unlike in FIG. 5A, and the direction of the 
magnetomotive force of the armature coincides with that of the permanent 
magnet. A torque is not generated by excitation of the armature, and the 
magnetic center of the direction of the magnetomotive force of the 
permanent magnet also coincides with that of the magnetic poles. 
Therefore, a cogging torque is set to be "0". 
When the permanent magnet is set in the state shown in FIG. 5E, and the 
direction of a current supplied to the exciting coil 5 is reversed, a 
torque in the opposite direction can be obtained. Therefore, the swinging 
motor 8 can swing the rotor (permanent magnet) 7. 
FIG. 6 shows a generated torque relative to the rotational angle of the 
permanent magnet. It is seen from FIG. 6 that when a swinging range is 
properly selected from a range of 0.degree. to 180.degree., torques in the 
same direction are generated in this swinging range. 
When the rotating shaft 9 is swung by the swinging motor 8, the transducer 
element 11 is swung within a sector-shaped range represented by reference 
symbol S in FIG. 1. Therefore, a living body is scanned by an ultrasonic 
beam radiated from the transducer element 11 in a sector shape. When a 
timing to reverse a direction of the current supplied to the exciting coil 
5 is changed, the scanning region S can be arbitrarily set, as a matter of 
course. Note that power required to drive the motor, power required to 
generate an ultrasonic beam from the transducer element, and a control 
signal for the motor and the transducer element are supplied through a 
cable 12. 
In the first embodiment, there is provided a magnetic sensor 15 for 
detecting a swinging angle of the transducer element 11. The sensor 15 
includes a permanent magnet (first or second member) 13 fixed to the 
distal end of the extending member 10-1 of the support member 10, and a 
pair of magnetoresistive elements (first or second members) 14-1 and 14-2 
each of which has an arcuated shape to be opposite to a swinging locus of 
the permanent magnet 13, is fixed to the shielding case 2, and changes a 
resistance in correspondence with a change in strength of a magnetic field 
(see FIGS. 2 and 3). 
A magnetic field generated by the permanent magnet 13 is applied to the 
magnetoresistive elements 14-1 and 14-2. In this state, if the permanent 
magnet 13 is swung in the clockwise direction in FIG. 3, the strength of 
the magnetic field applied to the magnetoresistive element 14-1 is 
increased. On the other hand, the strength of the magnetic field applied 
to the magnetoresistive element 14-2 is decreased. Therefore, a resistance 
of the magnetoresistive element 14-1 is largely changed. On the other 
hand, a resistance of the magnetoresistive element 14-2 is slightly 
changed. When a difference between these resistances is detected, a 
swinging angle of the permanent magnet 13, i.e., a swinging angle of the 
transducer element 11, is detected. 
Even if the housing 4 contains a sound transmitting medium, therefore, a 
magnetic field generated by the detecting means is not adversely affected 
by the sound transmitting medium. Therefore, a swinging angle of the 
transducer element can be accurately detected, and hence a 
radiating/returning direction of an ultrasonic beam can be accurately 
detected, thus accurately reconstructing an image. 
In addition, since the swinging angle of the transducer element is 
accurately detected, the position of the transducer element can be 
controlled with high precision. When the precision of control is low, the 
support member 10 may often collide with the stator 6. In the first 
embodiment, however, there is no possibility of such a collision, and a 
long service life of the ultrasonic scanner can be achieved. 
Furthermore, when a swinging angle of the transducer element is 
magnetically detected, power consumption of the sensor is small as 
compared with a case wherein the swinging angle is optically detected. 
Therefore, power cost can be saved in the first embodiment. 
FIGS. 7 to 10 show a modification of the first embodiment. In this 
modification, as is most apparent from FIGS. 8 and 9, the permanent magnet 
13 is mounted at one end of the rotating shaft 9, and the pair of 
semicircular magnetoresistive elements 14-1 and 14-2 are mounted to the 
shielding case to be opposite to the permanent magnet 13. An operation of 
the sensor including the permanent magnet 13 and the magnetoresistive 
elements 14-1 and 14-2 is the same as that in the first embodiment. In 
this case, a swinging locus of the permanent magnet 13 is decreased, and 
the size of each magnetoresistive element 14-1 or 14-2 is also decreased. 
Therefore, a space for the sensor 15 can be saved. In addition, since the 
swinging locus of the permanent magnet 13 is decreased, bubbles are not 
easily formed in the sound transmitting medium (a reason for this merit 
will be described hereinafter). 
In addition, the permanent magnet may be mounted on the shield case 2 and 
the magnetoresistive elements may be mounted on the extending member 10-1 
or the rotating shaft 9. 
As shown in FIGS. 1 to 4, the ultrasonic scanner according to the first 
embodiment includes a means for compressing the sound transmitting medium 
filled in the chamber 16. 
More specifically, a bellows 17 is mounted at a bottom portion of the 
shielding case 2. The internal space of the bellows 17 is filled with a 
sound transmitting medium. This internal space defines a supplement medium 
container. This internal space communicates with the inside of the chamber 
16 through two holes 21 formed in the bottom portion of the shielding case 
2. In addition, a plurality of support shafts 18 are fixed to the bottom 
portion of the shielding case 2. A lower end of each support shaft 18 is 
formed into a male screw. The lower end of each male screw extends through 
a support plate 19 mounted at the bottom portion of the bellows 17, and is 
threadably engaged with a corresponding nut 20. 
When the nut 20 is fastened to the male screw at the lower end of each 
support shaft 18 after the sound transmitting medium is filled in the 
chamber 16 and the internal space of the bellows 17, an internal capacity 
of the bellows 17 is decreased. Therefore, the sound transmitting medium 
in the chamber 16 is compressed. 
Conventionally, when the transducer element is swung in the sound 
transmitting medium at high speed, heat is generated by swinging. As a 
result, bubbles may often be formed in the sound transmitting medium Since 
the bubbles interrupt transmission of ultrasonic beams, a high-quality 
image cannot be obtained. Conventionally, therefore, an operation to 
eliminate bubbles is frequently performed. However, it is difficult to 
perfectly eliminate bubbles. 
In contrast to this, in the first embodiment, the bellows 17 always 
compresses the sound transmitting medium filled in the space surrounded by 
the cap 1 and the shielding case 2 by an urging pressure thereof. 
Therefore, a liquid pressure of the sound transmitting medium is increased 
to increase an air saturation pressure of the transmitting medium. For 
this reason, formation of bubbles is suppressed. Therefore, an image 
having a quality higher than that of the conventional image can be 
obtained without interruption for transmission of an ultrasonic beam. 
In addition, when the nut 20 is adjusted with respect to the male screw at 
the lower end of the support shaft 18, the internal capacity of the 
bellows 17 is changed. Therefore, a compression pressure can be 
controlled. For example, when the compression pressure is decreased by a 
change in bellows 17 with the passage of time, the nut 20 is adjusted to 
set the compression pressure to be a predetermined pressure. 
Even if an amount of the sound transmitting medium in the chamber 16 is 
decreased by formation of bubbles, the bellows is filled with a supplement 
medium, and hence a new medium is not required. In addition, since an 
amount of the sound transmitting medium is increased in accordance with 
the capacity of the bellows 17, a cooling effect for the exciting coil 5 
can be enhanced. 
FIGS. 7 to 10 show a modification of the first embodiment. The means for 
changing the internal capacity of the bellows in this modification is 
slightly different from that in the first embodiment. More specifically, 
the support shaft 18 has a cylindrical shape, and a female screw is formed 
inside the cylinder. This female screw is threadably engaged with a male 
screw shaft 22 fixed to the bottom portion of the shielding case 2. The 
lower end of the cylindrical support shaft 18 is fitted on and fixed to a 
pin 23 which extends through a hole formed in the support plate 19. At 
this time, the lower end of the cylindrical support shaft 18 and the pin 
23 are not fixed to the support plate 19. 
When the cylindrical support shaft 18 is rotated, therefore, the position 
of the support plate 19 is moved to change the internal capacity of the 
bellows 17. Note that FIG. 8 shows a state in which the support shaft 18 
is perfectly in contact with the bottom portion of the shielding case 2, 
i.e., a state wherein the internal capacity of the bellows is minimum. 
Therefore, the internal capacity of the bellows can be freely changed 
within the range of the length which extends from the shielding case 2 of 
the total length of the male screw shaft 22. Note that the lower end of 
the support shaft 18 may be inserted in the hole formed in the support 
plate 19 without being fixed. 
FIG. 11 shows the second modification of the compressing means. In this 
modification, a first sleeve 24 having an outer surface on which a male 
screw is formed is arranged at the bottom portion of the shielding case 2. 
A second sleeve 25 having an inner surface on which a female screw is 
formed is threadably engaged with the first sleeve 24. An elastic plate 26 
consisting of, e.g., a rubber is disposed at a lower portion of the second 
sleeve 25 An O-ring 28 seals between the first and second sleeves 24 and 
25. 
When the second sleeve 25 is moved with respect to the first sleeve 24 
after the chamber 16 and the internal space of the first and second 
sleeves 24 and 25 are filled with a sound transmitting medium, therefore, 
the capacities of the internal spaces of the first and second sleeves are 
decreased. At this time, the elastic plate 26 is expanded in a direction 
opposite to the moving direction of the second sleeve 25. However, since a 
restoring force of the elastic plate 26 is affected by the sound 
transmitting medium in the chamber 16, the sound transmitting medium in 
the chamber 16 is compressed. 
Thus, the restoring force of the elastic plate 26 always compresses the 
sound transmitting medium filled in the chamber 16. Therefore, formation 
of bubbles is suppressed. In addition, when the second sleeve 25 is moved 
with respect to the first sleeve 24, the capacities of the internal spaces 
of the first and second sleeves 24 and 25 are changed, and hence the 
compression pressure can be controlled. 
As shown in FIG. 12, the bellows 17 can be used in place of the elastic 
plate 26. An operation in this case is the same as that in FIG. 9. 
FIG. 13 shows the fourth modification of the compressing means. In this 
modification, a spring 29 is inserted between the bellows 17 and the 
holding case 3. In this case, the sound transmitting medium in the chamber 
16 is compressed by a biasing force of the spring 29 in addition to the 
urging pressure of the bellows 17. Therefore, even if the urging pressure 
of the bellows 17 is degraded over time, a predetermined compression 
pressure can always be assured. 
FIGS. 14 to 18C show an ultrasonic scanner according to the second 
embodiment of the present invention. In the second embodiment, a 
transducer element is not directly swung by a swinging motor, but a drive 
force of swinging movement generated by the swinging motor is transmitted 
by a parallel link mechanism 40 to the transducer element, thereby 
swinging it. 
In this embodiment, a swinging motor 8 includes an exciting coil 5, a 
stator 6, and a rotor 7, as in the first embodiment. A drive shaft 31 
fixed to the center of the rotor 7 is rotatably supported by a pair of 
bearings 33 (FIG. 15) fixed to a braket 32 (FIG. 15). Note that the rotor 
7 and the drive shaft 31 may be integrally formed. 
On the other hand, a transducer element 11 is supported by a support member 
10. The support member 10 is rotatably supported by a stationary shaft 34 
(or support shaft), fixed to a shielding case 2, using a pair of bearings 
35. The stationary shaft 34 is disposed to be parallel to the drive shaft 
31. 
In FIG. 14, reference numeral 71 denotes a ring to mount the cap 1 to the 
shielding case 2. An O-ring 72 seals between the cap 1 and the shielding 
case 2. Referring to FIGS. 14 and 16, a signal transmission cable 73 
supplies an ultrasonic signal to the transducer element 11. An electric 
cable 74 supplies a current to the exciting coil 5. In addition, in FIG. 
15, a supply port 75 is formed in the shielding case 2 to fill a sound 
transmitting medium in a chamber 16. An O-ring 76 and a plug 77 are 
mounted at the supply port 75. 
As is most apparent from FIGS. 17A and 17B, the parallel link mechanism 40 
includes a first link member 41 having a proximal end fixed to the drive 
shaft 31, a second link member 42 having a proximal end rotatably coupled 
to the distal end of the first link member 41, and a third link member 43 
having a proximal end rotatably coupled to the distal end of the second 
link member 42 and a distal end rotatably coupled to the stationary shaft 
34. Therefore, when the drive shaft 31 is swung, the link members 41 to 43 
are moved. As a result, the support member 10 is swung. Note that the 
shielding case 1 to which the drive shaft 31 and the stationary shaft 34 
are mounted defines a stationary link. 
More specifically, a pin 44 is mounted at the distal end of the first link 
member 41. The pin 44 is rotatably supported by a pair of bearings 45 
mounted at the proximal end of the second link member 42. On the other 
hand, the third link member 43 is fixed to the support member 10, and a 
pin 46 is mounted at the proximal end of the third link member 43. The pin 
46 is rotatably supported by a pair of bearings 47 mounted at the distal 
end of the second link member 42. Note that the second link member 42 is 
shifted from the first and third link members 41 and 43 in a direction 
which is perpendicular to the surface of the sheet of FIG. 17A. Therefore, 
interference of the second link member 42 with respect to the first and 
third link members 41 and 43 is prevented. In addition, two ends of the 
second link member 42 are formed to be substantially circular to prevent 
interference of the second link member 42 with respect to the support 
member 10 and the stator 6. 
Assuming that the central axes of the drive shaft 31, the pins 44 and 46, 
and the stationary shaft 34 are A, B, C, and D, respectively, AB=CD, and 
BC=DA. When the parallel link mechanism 40 is driven, a quadrilateral ABCD 
always constitutes a parallelogram. 
An operation of the second embodiment will be described hereinafter. The 
swinging motor 8 is swung in the same manner as in the first embodiment. 
More specifically, the drive shaft 31 is continuously swung. Therefore, a 
drive force of swinging movement is transmitted to the support member 10 
by the parallel link mechanism 40. More specifically, as shown in FIGS. 
18A to 18C, the first link member 41 is continuously swung, and the second 
link member 42 is continuously and vertically moved. Therefore, the third 
link member 43 and the support member 10 are continuously swung. As a 
result, the transducer element 11 is swung about the stationary shaft 34 
within a sector-shaped range S shown in FIG. 14. As shown in FIGS. 18A and 
18C, the transducer element and the support member 10 are swung through an 
angle of S/2 with respect to the central line. For example, therefore, the 
transducer element can be swung clockwise through an angle of only S/2 
from the central line. On the contrary, the transducer element can be 
swung counterclockwise through an angle of only S/2 from the central line. 
In addition, the swinging range S can be freely changed. 
Furthermore, the drive shaft 31 and the stationary shaft 34 are coupled to 
each other by the parallel link mechanism, and AB.parallel.CD and 
BC.parallel.DA even if the drive shaft 31 has any swinging angle. 
Therefore, AB and CD are always swung at the same angular velocity, and 
hence the swinging angle of the support member 10 is always equal to that 
of the drive shaft 31. For this reason, in this embodiment, the swinging 
angle of the support member 10 is not directly detected by a sensor, but 
the swinging angle of the drive shaft 31 is detected by the sensor, thus 
obtaining the swinging angle of the support member 10. 
Conventionally, a cable or a pulley is used as a means for transmitting a 
drive force of swinging movement from the swinging motor to the transducer 
element. In this case, bending stress is generated in the cable. The 
smaller the diameter of the pulley is, the larger the bending stress. 
Therefore, it is difficult to decrease the diameter of the pulley in 
consideration of a service life of the cable. As a result, it is difficult 
to decrease the size of the ultrasonic scanner. A gear is often used as a 
transmitting means in place of the cable or pulley. In this case, the gear 
teeth must be formed with high manufacturing precision, and it is 
difficult to decrease the size of the ultrasonic scanner. In addition, the 
gear teeth are worn and degraded with the passage of time. As a result, 
backlash of the gear teeth occurs to shorten the service life of the 
ultrasonic scanner. 
In contrast to this, the parallel link mechanism 40 is used as a 
transmitting means in the second embodiment. Therefore, bending stress of 
the cable is negligible, unlike in a case wherein a cable or pulley is 
used as a transmitting means, thus achieving a small-sized ultrasonic 
scanner. In addition, high precision of the manufacture of the 
transmitting means is not required, unlike in the case wherein a gear is 
used as a transmitting means. Therefore, a change with the passage of time 
such as backlash does not occur to achieve a long service life of the 
scanner. 
In addition, the swinging center (i.e., the stationary shaft 34) of the 
support member 10 can be arbitrarily set. For this reason, a swinging 
radius of the support member 10 can be sufficiently decreased. Therefore, 
a load inertia obtained when the support member 10 is swung can be easily 
reduced to minimize generation of vibrations. Furthermore, since a 
swinging radius of the support member is decreased, the diameter of the 
scanner is necessarily decreased to easily achieve a compact scanner, and 
to improve its operability. In addition, since a swinging radium of the 
support member is decreased, a swinging range of the transducer element 
can be wider than that of the conventional scanner even if the swinging 
range of the support member is equal to that of the conventional scanner 
Therefore, an ultrasonic beam radiating range of the transducer element is 
increased, and an amount of data of a living body image can be largely 
increased. For this reason, in particular, this scanner is advantageous in 
a B-mode operation. 
Note that although the parallel link mechanism is arranged on only one side 
of the rotor 7 in this embodiment, the parallel link mechanisms may be 
arranged on both sides of the rotor 7. 
FIGS. 19A to 19C show the first modification of the second embodiment. In 
this modification, an anti-parallel link mechanism 50 is used in place of 
the parallel link mechanism. More specifically, the pins 44 and 46 are 
positioned on the opposite sides with respect to a central line 51. 
Assuming that the central axes of the drive shaft 31, the pins 44 and 46, 
and the stationary shaft 34 are A, B, C, and D, respectively, a line which 
connects the point B to the point C intersects with a line which connects 
the point A to the point D, and AB=CD, and BC=DA. For this reason, in this 
case, when the drive shaft 31 is continuously swung, the first link member 
41 is continuously swung, and the second link member 42 is continuously 
and vertically moved and swung. Therefore, as shown in FIGS. 19A and 19C, 
the third link member 43 and the support member 10 are continuously swung. 
Therefore, this modification can exhibit the same effect as in the second 
embodiment. 
In this modification, however, the first and third link members 41 and 43 
are swung in opposite directions at different angular velocities. At this 
time, a speed ratio i=DA/AE, where E is the intersecting point between the 
axis of the second link member 42 and the central line 51. Therefore, in 
order to swing the transducer element at a constant speed, the swinging 
speed of the drive shaft 31 must be controlled in consideration of the 
speed ratio i. 
Therefore, the transmitting means is not limited to the parallel link 
mechanism, and various link mechanisms can be applied to the second 
embodiment. 
FIGS. 20 to 23 show the second modification of the second embodiment. In 
this modification, the swinging center (i.e., a central axis of the 
rotatory shaft or support shaft 34) of the support member 10 coincides 
with the swinging center of an ultrasonic beam radiated from the 
transducer element 11. As is most apparent from FIGS. 20 and 23, the 
rotatory shaft 34 extends from a portion of the support member 10 
corresponding to the center of the transducer element 11. The second link 
member 42 is shifted in the extending direction of the rotatory shaft 34 
to prevent interference between the support member 10 and the second link 
member 42 of the parallel link mechanism 40. 
In this modification, therefore, the swinging center of the support member 
10 coincides with the swinging center of an ultrasonic beam radiated from 
the transducer element 11, and hence a swinging radius of the support 
member 10 can be sufficiently decreased. Therefore, a load inertia 
obtained when the support member 10 is swung is reduced to minimize 
generation of vibrations. In addition, since the swinging radius of the 
support member is decreased, the diameter of the scanner is necessarily 
decreased, thus easily achieving a compact scanner. Furthermore, since the 
swinging radius of the support member is decreased, the swinging range of 
the transducer element can be wider than that in the second embodiment 
even if the swinging range of the support member is equal to that in the 
second embodiment. As a result, an ultrasonic beam radiating range of the 
transducer element can be increased to further increase an amount of data 
of an image. Therefore, a conventional drawback that radiation of an 
ultrasonic beam is interrupted by ribs when, e.g., a heart is diagnosed 
can be solved. 
FIGS. 24A to 24C show various arrangements of the stator of the swinging 
motor. In the stator shown in FIG. 24A, a pair of opposite surfaces 6-1 
and 6-2 which respectively define magnetic poles are coupled to each other 
by a thin-wall portion 61 (closed slot shape). In the stator shown in FIG. 
24B, a gap 62 is formed between the pair of opposite surfaces 6-1 and 6-2 
(open slot shape). In the stator shown in FIG. 24C, the gap 62 is formed 
between the pair of opposite surfaces 6-1 and 6-2 (open slot shape), and 
projecting and recessed portions (internal teeth) 63 are formed on the 
pair of opposite surfaces 6-1 and 6-2. 
These swinging motors have response performance which is better than that 
of the conventional swinging motor. More specifically, in the conventional 
swinging motor used in the ultrasonic scanner, a cylinder positioned 
outside a stationary shaft is swung with respect to the stationary shaft 
positioned at the center of the motor. Therefore, an inertia moment of the 
swung cylinder is relatively large. For this reason, when the cylinder is 
swung, a long time period may often be required until the cylinder is 
swung at a predetermined speed. In addition, when the cylinder is stopped, 
the cylinder may not be stopped at a predetermined position, but the 
cylinder often exceeds the predetermined position. The conventional 
swinging motor has, therefore, poor response performance. 
In contrast to this, in each swinging motor shown in FIGS. 24A to 24C, the 
rotor 7 having a relatively small inertia moment is swung. Therefore, this 
swinging motor achieves good response performance of the rotor 7 when the 
rotor 7 is swung or stopped. 
In addition, the magnitude of a cogging torque (a torque obtained when 
magnetomotive force =0) generated from each swinging motor shown in FIGS. 
24A to 24C will be considered hereinafter. 
FIGS. 25 to 27 show contour lines representing a product of a current 
supplied to the exciting coil 5 and the number of turns of the exciting 
coil 5. The axis of ordinate represents a torque generated in the rotor 7, 
and the axis of abscissa represents a rotational angle of the rotor 7. 
In the stator having a closed slot shape shown in FIG. 25, a curve obtained 
when a product (magnetomotive force) of a current supplied to the exciting 
coil 5 and the number of turns of the exciting coil 5 is "0" coincides 
with an axis wherein a generated torque is "0" at any rotational angle of 
the rotor 7. This means that an attractive force is not generated between 
the rotor 7 serving as a permanent magnet and the stator 6, when a current 
is not supplied to the exciting coil 5. If current supply to the exciting 
coil 5 is stopped when the transducer element reaches a desired position 
in M-mode control, the transducer element can always be stopped and held 
at the desired position. 
In contrast to this, in the stator having an open slot shape shown in FIG. 
26, a cogging torque is generated. It is, therefore, considered that 
generation of the cogging torque depends on the presence/absence of the 
thin-wall portion 61 which couples the pair of opposite surfaces 6-1 and 
6-2 to each other. In this stator having the open slot shape, even if 
current supplying to the exciting coil is stopped when the transducer 
element reaches the desired position, the transducer element is not 
stopped at this position, but stops exceeding the position. 
In addition, in the stator having an open slot shape with the projecting 
and recessed portions (internal teeth) 63 shown in FIG. 27, a cogging 
torque is present. However, the magnitude of the cogging torque is smaller 
than that in FIG. 26. Furthermore, the number of angles at which the 
cogging torque is set to be "0" is larger than that in FIG. 26. This is 
because a cogging torque is dispersed to decrease a peak value as a result 
of addition of the projecting and recessed portions (internal teeth) 63. 
Therefore, in order to improve controllability in an M mode in the stator 
having the open slot shape, the projecting and recessed portions (internal 
teeth) 63 need only be additionally arranged on the pair of opposite 
surfaces 6-1 and 6-2, and more preferably, the number of projecting and 
recessed portions (internal teeth) 63 is increased as much as possible to 
disperse a cogging torque. 
As described above, it is understood that a stator having a closed slot 
shape is most preferable from a view point of prevention of generation of 
a cogging torque. Even if the stator has an open sot shape, addition of 
the projecting and recessed portions (internal teeth) 63 suppresses 
generation of a cogging torque. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, representative devices, and illustrated examples 
shown and described. Accordingly, departures may be made from such details 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.