Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-04-08
2001-06-26
Chapman, John E. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C310S334000
Reexamination Certificate
active
06250162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic sensor for radiating and/or detecting ultrasonic energy, and more particularly to an ultrasonic sensor to detect the existence of objects or to measure a distance to an object, used as, for example, an obstacle detecting sensor, a vehicle back sonar or corner sonar, etc.
2. Description of the Related Art
There has been known an ultrasonic sensor which radiates (or transmits) ultrasonic pulses intermittingly and detects (or receives) the ultrasonic pulses reflected by an object, thereby detecting the existence of the object or measuring the distance to the object.
FIG. 1
shows a conventional ultrasonic sensor used in vehicles as a back sonar or a corner sonar. The ultrasonic sensor
1
comprises a metallic case member
2
. The case member
2
has a hollow having a circular cross section, thereby forming a circular cylindrical shape. A flat piezoelectric element
4
, accommodated in the hollow
3
, is affixed to the inside surface of a bottom portion
2
a
of the case member
2
. one of the signal wires
6
of a connector cable
5
is connected to one of the electrodes of the piezoelectric element
4
, while the other signal wire
6
is in electrical conduction with the other of the electrodes of the piezoelectric element
4
, through the case member
2
. A soundabsorbing material
7
such as felt covers the piezoelectric element
4
, and an insulating resin
8
such as silicone rubber or urethane rubber seals the piezoelectric element
4
and the sound-absorbing material
7
.
Such ultrasonic sensors are mounted to, for example, an automobile bumper (not shown) to be used as back sonars or corner sonars for obstacle detection. When the ultrasonic sensor is being mounted to the bumper, the bottom portion of the case member to which the piezoelectric element
4
is affixed, is set substantially perpendicular to the surface of roads or the ground, so as to be positioned to face a direction from which ultrasonic energy is radiated. In such ultrasonic sensors, when the ultrasonic radiation range and the detection range in the horizontal direction is too narrow, a dead angle occurs in the detecting range, whereas when the ultrasonic radiation range and the detection range in the vertical direction is too wide, the reflected ultrasonics from the ground become too noisy. Therefore, in the above-described ultrasonic sensor
1
, an ultrasonic horn
9
is mounted to the outer side of the case member
2
from outside the case member
2
in order to control the ultrasonic wave radiation and detection range such that the ultrasonic radiation and detection range is wide in the horizontal direction and narrow in the vertical direction.
However, when the directional properties of ultrasonic sensors are controlled by mounting an ultrasonic horn thereto, rain water and mud (splashed from the road by tires of vehicles), dust, or the like, may accumulate and get clogged in the ultrasonic horn, resulting in malfunctioning of the ultrasonic sensor. In addition, when the ultrasonic horn gets deformed, the directional properties of the ultrasonic sensor change. Further, the use of ultrasonic horns results in large ultrasonic sensors.
To overcome the above-described problems, Japanese Laid-Open Patent Publication No. 9-284896 discloses a structure for controlling the directional properties without the use of ultrasonic horns. As shown in
FIGS. 2A and 2B
, an ultrasonic sensor
11
has a case member
12
in which an oblong or elliptical cylindrical hollow
13
is provided. A disk-shaped piezoelectric element
15
is affixed to a bottom portion
14
of the case member
12
. When the case member
12
with such a structure is used, the ultrasonic energy spreads wider in the longitudinal direction of the oblong or elliptical cross section than in the transverse direction. Therefore, the ultrasonic radiation and detection range can be made wide in the horizontal direction and narrow in the vertical direction.
For example, when the ultrasonic sensor has an outside diameter D of 18 mm, the ultrasonic wave radiation and detection range becomes 80 degrees in the horizontal direction and 60 degrees in the vertical direction, thereby exhibiting an anisotropic radiation and detection range without using an ultrasonic horn.
However, when the ultrasonic sensor with the above-described structure is made small, the ultrasonic radiation and detection range in the vertical direction becomes wide, causing the difference between the ultrasonic radiation and detection range in the horizontal direction and that in the vertical direction to be small, so that the small ultrasonic sensor is not very anisotropic.
In
FIG. 2A
, the vertically formed inside wall surfaces at the edges of the hollow
13
are made to extend in the longitudinal direction of the oblong such that each has an overall length H of 13 mm and a width W of 8 mm. The case member
12
, in which the hollow 13 is formed, has an outside diameter D of 14 mm. The piezoelectric element
15
, with a diameter d of 7 mm, is accommodated in the casing member
12
, and affixed to the inside surface of the bottom portion
14
. In
FIG. 2B
, the bottom portion
14
of the case member
12
has a uniform thickness T of 0.7 mm. The minimum thickness of each of the side walls of the case member
12
is 0.5 mm. The directional properties, in the horizontal and vertical directions, of such an ultrasonic sensor with the aforementioned dimensions are as shown in FIG.
3
.
FIG. 3
shows that the ultrasonic radiation and detection range (a half-decay angle) in the horizontal direction is 80 degrees, while that in the vertical direction is wide at 70 degrees. Therefore, the ultrasonic sensor with an outside diameter D of 14 mm is less anisotropic, in the horizontal and vertical directions, than the ultrasonic sensor with an outside diameter D of 18 mm. It is to be noted that the half-decay angle used to evaluate the ultrasonic radiation and detection range is the angle between directions in which the ultrasonic radiation and detection sensitivity is less than 20 log 0.5 dB (approximately 60 dB) of the radiation and detection sensitivity at the front face (or at the zero degree direction).
SUMMARY OF THE INVENTION
In view of the above-described problems, it is an object of the present invention to provide an ultrasonic sensor which has anisotropic radiation and detection characteristics with respect to the horizontal and vertical directions, even when the ultrasonic sensor is made small.
The ultrasonic sensor comprises a case member and an piezoelectric element. The case member has a hollow therein and a bottom portion provided at one end of the hollow. The bottom portion has a thick portion which extends along a first direction and a pair of thin portions which have a smaller thickness than the thick portion and are provided on opposite sides of the bottom portion along a second direction different than the first direction. The piezoelectric element radiates and/or detects ultrasonic energy and is provided at a center of the thick portion on an inner surface of the bottom portion.
The bottom portion may have a circular shape. Alternatively, the bottom portion may have an oblong or elliptical shape. In such a case, a longitudinal direction and a transverse direction of the oblong or elliptical shape preferably corresponds to the second direction and the first direction of the bottom portion, respectively.
The thin portions may have a thickness smaller than the thickness of a side wall surrounding the hollow. The outer surface of said bottom portion of said case member may be flat. Further, the ultrasonic sensor may comprise an insulating resin provided on the thin portions.
According to the present invention, the radiation and detection range of the ultrasonic sensor is made relatively narrower in the direction along which the thin portions of the bottom portion are provided due to the difference in the thicknesses between the thin portion and the thick portion. This is accomplished
Amaike Shinji
Ota Junshi
Chapman John E.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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