U.S. patent application number 11/211485 was filed with the patent office on 2007-11-01 for sensor node for impact detection.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Kei Suzuki, Hidetoshi Tanaka.
Application Number | 20070251294 11/211485 |
Document ID | / |
Family ID | 37015225 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070251294 |
Kind Code |
A1 |
Tanaka; Hidetoshi ; et
al. |
November 1, 2007 |
SENSOR NODE FOR IMPACT DETECTION
Abstract
The invention is intended to provide a technique regarding
sensor nodes for impact detection to enable the intensities of
impacts to be determined in a multi-value or analog mode and to
reduce the power consumption of sensor nodes. The sensor node is
provided with a shock detection sensor comprising a piezoelectric
element unit which generates an electric charge corresponding to an
external impact, a capacitor which rectifies and accumulates the
electric charge so generated, and a voltage detector which operates
on the accumulated power and externally outputs a signal when the
accumulated voltage reaches a preset level; a stand-by control
object section which is caused by the external signal to return
from a stand-by state and to operate; and a power supply which
feeds power to the stand-by control object section, wherein the
operation of the stand-by control object section is triggered by
the signal of impact detected by the piezoelectric element
unit.
Inventors: |
Tanaka; Hidetoshi;
(Kokubunji, JP) ; Suzuki; Kei; (Kokubunji,
JP) |
Correspondence
Address: |
Stanley P. Fisher;Reed Smith LLP
Suite 1400
3110 Fairview Park Drive
Falls Church
VA
22042-4503
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
37015225 |
Appl. No.: |
11/211485 |
Filed: |
August 26, 2005 |
Current U.S.
Class: |
73/12.01 |
Current CPC
Class: |
G01P 15/0891 20130101;
G01P 15/0922 20130101 |
Class at
Publication: |
073/012.01 |
International
Class: |
G01N 3/30 20060101
G01N003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2005 |
JP |
2005-085441 |
Claims
1. A sensor node for impact detection, comprising: a shock
detection sensor including a piezoelectric element unit which
generates an electric charge corresponding to an external impact, a
capacitor which rectifies and accumulates the electric charge so
generated, and a voltage detector which operates on the accumulated
power and externally outputs a signal when the accumulated voltage
reaches a preset level; a stand-by control object section which is
caused by said external signal to return from a stand-by state and
to operate; and a power supply which feeds power to said stand-by
control object section, wherein the operation of said stand-by
control object section is triggered by the signal of impact
detected by said piezoelectric element unit, and wherein said
stand-by control object section measures an intensity of an impact
by measuring a time length of a signal outputted by said shock
detection sensor.
2. The sensor node for impact detection according to claim 1,
wherein said shock detection sensor and said stand-by control
object section are in a stand-by state until any impact is detected
by said piezoelectric element unit.
3. (canceled)
4. The sensor node for impact detection according to claim 1,
wherein said piezoelectric element unit is provided with a planar
piezoelectric element member, a plate which fixes one end of said
piezoelectric element member and a mass installed at an end of a
free end, which is the other end of said piezoelectric element
member, and an impulse working on said plate deforms said
piezoelectric element member to generate an electric charge.
5. The sensor node for impact detection according to claim 1,
wherein said stand-by control object section has means which,
triggered by the signal of impact detected by said piezoelectric
element unit, senses ambient information unevenly distributed in
the environment, and processes the sensed information to perform
wireless communication.
6. A sensor node for impact detection, comprising a shock detection
sensor including a piezoelectric element unit which generates an
electric charge corresponding to an external impact, a capacitor
which rectifies and accumulates the electric charge so generated,
and a voltage comparator which compares the accumulated voltage
with a reference voltage and externally outputs a signal when the
accumulated voltage has surpassed the reference voltage; a stand-by
control object section which is caused by said external signal to
return from a stand-by state and to operate; and a power supply
which feeds power to said voltage comparator and said stand-by
control object section, wherein the operation of said stand-by
control object section is triggered by the signal of impact
detected by said piezoelectric element unit, wherein said stand-by
control object section measures an intensity of an impact by
measuring a time length of a signal outputted by said shock
detection sensor.
7. The sensor node for impact detection according to claim 6,
wherein said shock detection sensor and said stand-by control
object section are in a stand-by state until any impact is detected
by said piezoelectric element unit.
8. (canceled)
9. The sensor node for impact detection according to claim 6,
wherein said piezoelectric element unit is provided with a planar
piezoelectric element member, a plate which fixes one end of said
piezoelectric element member and a mass installed at an end of a
free end, which is the other end of said piezoelectric element
member, and an impulse working on said plate deforms said
piezoelectric element member to generate an electric charge.
10. The sensor node for impact detection according to claim 6,
wherein said stand-by control object section has means which,
triggered by the signal of impact detected by said piezoelectric
element unit, senses ambient information unevenly distributed in
the environment, and processes the sensed information to perform
wireless communication.
11. A sensor node for impact detection, comprising: a shock
detection sensor including a piezoelectric element unit which
generates an electric charge corresponding to an external impact,
and a voltage comparator which compares the voltage so generated
with a preset reference voltage and externally outputs a signal
when the generated voltage has surpassed the reference voltage; a
stand-by control object section which is caused by said external
signal to return from a stand-by state and to operate; and a power
supply which feeds power to said voltage comparator and said
stand-by control object section, wherein the operation of said
stand-by control object section is triggered by the signal of
impact detected by said piezoelectric element unit, and wherein
said stand-by control object section measures an intensity of an
impact by counting a number of times a signal is outputted by said
shock detection sensor.
12. The sensor node for impact detection according to claim 11,
wherein said shock detection sensor and said stand-by control
object section are in a stand-by state until any impact is detected
by said piezoelectric element unit.
13. (canceled)
14. The sensor node for impact detection according to claim 11,
wherein said piezoelectric element unit is provided with a planar
piezoelectric element member, a plate which fixes one end of said
piezoelectric element member and a mass installed at an end of a
free end, which is the other end of said piezoelectric element
member, and an impulse working on said plate deforms said
piezoelectric element member to generate an electric charge.
15. The sensor node for impact detection according to claim 11,
wherein said stand-by control object section has means which,
triggered by the signal of impact detected by said piezoelectric
element unit, senses ambient information unevenly distributed in
the environment, and processes the sensed information to perform
wireless communication.
Description
CLAIM OF PRIORITY
[0001] The present invention claims priority from Japanese
application JP 2005-085441 filed on Mar. 24, 2005, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a sensor node technique and
more particularly to a sensor node for detecting impacts.
[0003] A sensor node senses information unevenly distributed in its
environment at designated intervals of time, and transmits the
sensed information values by wireless communication. On account of
its intrinsic function to sense and transmit by wireless
communication information unevenly distributed in its environment,
a sensor node has to be able to operate on a battery for a long
period.
[0004] Conventional devices for detecting impacts arising at
irregular intervals of time for use in sensor nodes detect such
impacts with a mechanical switch or a switch using electric power
generated by electromagnetic inductance or a piezoelectric element,
or through the measurement of variations in acceleration with an
acceleration sensor which is kept operating all the time.
[0005] A conventional impact detecting sensor using a piezoelectric
element utilizes the trend of the vibration, which accompanies the
operation of the device, to increase when an abnormality arises,
and detects a signal which is generated when the vibration has
surpassed a certain amplitude (see, for instance, Japanese Patent
Application Laid-Open Nos. 8-145783 and 9-264778).
[0006] In another conventional sensor, when the acceleration
working on the piezoelectric element is at or above a certain
level, a voltage is applied to the gate of a MOS-FET to turn it on
and detect a signal, and the duration of its being kept on can be
adjusted with a resistor (see, for instance, Japanese Patent
Application Laid-Open No. 10-260202).
SUMMARY OF THE INVENTION
[0007] Any such sensor node using a conventional impact detection
involves a problem that, where a switch of the aforementioned type
is used, only a two-value determination can be made, namely whether
or not the sensed intensity of the impact has surpassed a
threshold, but no multi-value or analog determination can be
made.
[0008] Or where the aforementioned acceleration sensor is used,
though analog determination is possible, measuring the acceleration
by keeping the sensor in operation all the time involves another
problem of greater power consumption, which makes it impossible to
use the sensor node for a long continuous period.
[0009] An object of the present invention, therefore, is to provide
a technique regarding sensor nodes for impact detection to enable
the intensities of impacts to be determined in a multi-value or
analog mode and to reduce the power consumption of sensor
nodes.
[0010] In order to achieve the object stated above, according to
the invention, an electric charge is generated by having a
piezoelectric element distorted by an external impact, and a sensor
node in a waiting state is returned to an active state, trigged by
this charge. By measuring the wattage corresponding to the
generated charge with the sensor node, it is made possible to
evaluate the intensity of the impact in a multi-valued or analog
mode.
[0011] Since this enables power consumption by the sensor node in
its waiting mode to be dramatically reduced, it is made possible to
realize a sensor node for impact detection consuming very little
power.
[0012] Typical examples of configuration of the sensor node for
impact detection according to the invention will be summarized
below.
[0013] (1) A configuration is characterized by being provided with
a shock detection sensor comprising a piezoelectric element unit
which generates an electric charge corresponding to an external
impact, a capacitor which rectifies and accumulates the electric
charge so generated, and a voltage detector which operates on the
accumulated power and externally outputs a signal when the
accumulated voltage reaches a preset level; a stand-by control
object section which is caused by the external signal to return
from a stand-by state and to operate; and a power supply which
feeds power to the stand-by control object section, wherein the
operation of the stand-by control object section is triggered by
the signal of impact detected by the piezoelectric element
unit.
[0014] (2) A configuration is characterized by being provided with
a shock detection sensor comprising a piezoelectric element unit
which generates an electric charge corresponding to an external
impact, a capacitor which rectifies and accumulates the electric
charge so generated, and a voltage comparator which compares the
accumulated voltage of the capacitor with a reference voltage and
externally outputs a signal when the accumulated voltage has
surpassed the reference voltage; a stand-by control object section
which is caused by the external signal to return from a stand-by
state and to operate; and a power supply which feeds power to the
voltage comparator and the stand-by control object section, wherein
the operation of the stand-by control object section is triggered
by the signal of impact detected by the piezoelectric element
unit.
[0015] (3) A configuration is characterized by being provided with
a shock detection sensor comprising a piezoelectric element unit
which generates an electric charge corresponding to an external
impact, and a voltage comparator which compares the voltage so
generated with a preset reference voltage and externally outputs a
signal when the generated voltage has surpassed the reference
voltage; a stand-by control object section which is caused by the
external signal to return from a stand-by state and to operate; and
a power supply which feeds power to the voltage comparator and the
stand-by control object section, wherein the operation of the
stand-by control object section is triggered by the signal of
impact detected by the piezoelectric element unit.
[0016] (4) In a sensor node for impact detection of any of the
configurations stated in (1) through (3), the shock detection
sensor and the stand-by control object section are in a stand-by
state until any impact is detected by the piezoelectric element
unit.
[0017] (5) In a sensor node for impact detection of any of the
configurations stated in (1) through (3), the stand-by control
object section measures the intensity of an impact by measuring the
time length of a signal outputted by the shock detection
sensor.
[0018] (6) In a sensor node for impact detection of any of the
configurations stated in (1) through (3), the piezoelectric element
unit is provided with a planar piezoelectric element member, a
plate which fixes one end of the piezoelectric element member and a
mass installed at an end of a free end, which is the other end of
the piezoelectric element member, and an impulse working on the
plate deforms the piezoelectric element member to generate an
electric charge.
[0019] (7) In a sensor node for impact detection of any of the
configurations stated in (1) through (3), the stand-by control
object section has means which, triggered by the signal of impact
detected by the piezoelectric element unit, senses ambient
information unevenly distributed in the environment, and processes
the sensed information to perform wireless communication.
[0020] According to the invention, detection of the intensities of
impacts in a multi-value or analog mode is realized, and further a
technique to realize a sensor node for impact detection that can
significantly reduce power consumption is achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a block diagram illustrating the configuration of
a sensor node for impact detection, which is a preferred embodiment
of the present invention.
[0022] FIG. 2 is a block diagram illustrating the configuration of
a sensor node for impact detection, which is another preferred
embodiment of the invention.
[0023] FIGS. 3(a) and 3(b) are profiles illustrating examples of
piezoelectric element unit for use in the invention.
[0024] FIG. 4 shows one example of capacitor for use in the
configurations shown in FIG. 1 and FIG. 2.
[0025] FIG. 5 shows one example of shock detection sensor for use
in the configuration shown in FIG. 1.
[0026] FIG. 6 shows one example of shock detection sensor for use
in the configuration shown in FIG. 2.
[0027] FIG. 7 is a time chart also showing waveforms which occur
when an impact is applied to the sensor node of FIG. 1 or FIG. 2,
wherein a capacitor is used.
[0028] FIG. 8 is a time chart also showing waveforms which occur
when an impact is applied to the sensor node of FIG. 2, wherein
neither a capacitor nor an impact detect circuit is used.
[0029] FIG. 9 shows another example of configuration of the sensor
node for impact detection according to the invention.
[0030] FIG. 10 shows one example of configuration of a sensor
network system for impact detection using sensor nodes of the type
shown in FIG. 1 or FIG. 2.
[0031] FIG. 11 shows one example of configuration of a power
supply-free wireless communication node for impact detection using
the sensor node shown in FIG. 1 or FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Preferred embodiments of the present invention will be
described in detail below with reference to the accompanying
drawings.
Embodiment 1
[0033] FIG. 1 is a block diagram illustrating the configuration of
a sensor node for impact detection, which is a preferred embodiment
of the invention.
[0034] A sensor node 101 comprises a shock detection sensor 102
configured of a piezoelectric element unit 105, a capacitor 106 and
a voltage detector 107; a stand-by control object section 103
configured of a wake up signal generator 108, an impact detect
circuit 113, a microcomputer 109, a radio frequency transceiver
circuit 110, an A/D converter 111, a sensor 112 and other elements;
and a power supply 104.
[0035] Referring to FIG. 1, the shock detection sensor 102 requires
no power supply, while the stand-by control object section 103 is
supplied with power by the power supply 104. Until any impact is
detected, power supply is either off or in a waiting state for the
radio frequency transceiver circuit 110, the A/D converter 111 and
the sensor 112, in a waiting state for the microcomputer 109, and
in a state of awaiting a signal from the shock detection sensor 102
for the wake up signal generator 108 and the impact detect circuit
113. These states constitute a stand-by state for the sensor node.
As the microcomputer 109 consumes only about a few .mu.W of power
when in its waiting state while the wake up signal generator 108
and the impact detect circuit 113 also consume only a few .mu.W or
less even when operating, the sensor node can realize low power
consumption in its stand-by state.
[0036] Next will be described how an impact is detected.
[0037] When an impact works on the sensor node 101, the
piezoelectric element in the piezoelectric element unit 105 is
distorted to generate an electric charge. The charge generated by
the piezoelectric element unit 105 is rectified and accumulated by
the capacitor 106 to provide a charge corresponding to the external
impact and, when accumulated to a certain voltage, is transmitted
by the voltage detector 107 to the stand-by control object section
103 as the impact detection signal sensed by the shock detection
sensor 102. The signal transmitted by the shock detection sensor
102 is inputted into the wake up signal generator 108 and the
impact detect circuit 113, and the wake up signal from the wake up
signal generator 108 causes a signal to be transmitted to the
microcomputer 109, which is thereby awakened from a stand-by state
to an active state. The microcomputer 109 in the active state
captures the signal from the impact detect circuit 113, measures
the intensity of the impact, and performs predetermined control.
For the predetermined control, ambient information is sensed by the
A/D converter 111 and the sensor 112, the sensed information is
processed by the microcomputer 109, and communication is performed
by the radio frequency transceiver circuit 110. Upon completion of
the predetermined processing, the sensor node 101 returns to the
stand-by state.
Embodiment 2
[0038] FIG. 2 is a block diagram illustrating the configuration of
a sensor node for impact detection, which is another preferred
embodiment of the invention.
[0039] A sensor node 201 comprises a shock detection sensor 202
configured of a piezoelectric element unit 205, a capacitor 206 and
a voltage comparator 207; a stand-by control object section 203
configured of a wake up signal generator 208, an impact detect
circuit 213, a microcomputer 209, a radio frequency transceiver
circuit 210, an A/D converter 211, a sensor 212 and other elements;
and a power supply 204. As will be described afterwards, the
capacitor 206 in the shock detection sensor 202 may not be required
depending on the method of shock detection.
[0040] In this embodiment, power is fed by the power supply 204 to
the voltage comparator 207 and the stand-by control object section
203 in the shock detection sensor 202. The piezoelectric element
unit 205 and the capacitor 206 in the shock detection sensor 202
require no power supply. Until any impact is detected, power supply
is either off or in a waiting state for the radio frequency
transceiver circuit 210, the A/D converter 211 and the sensor 212,
in a waiting state for the microcomputer 209, and in a state of
awaiting a signal from the shock detection sensor 202 for the wake
up signal generator 208, the impact detect circuit 213 and the
voltage comparator 207. These states constitute a stand-by state
for the sensor node. As the microcomputer 209 consumes only about a
few .mu.W of power when in its waiting state while the wake up
signal generator 208, the impact detect circuit 113 and the voltage
comparator 207 also consume only a few .mu.W or less even when
operating, the sensor node can realize low power consumption in its
stand-by state.
[0041] Next will be described how an impact is detected. When an
impact works on the sensor node 201, the piezoelectric element in
the piezoelectric element unit 205 is distorted to generate an
electric charge. The charge generated by the piezoelectric element
unit 205 is rectified and accumulated by the capacitor 206 to
provide a charge corresponding to the external impact and, when
accumulated to a certain voltage, is transmitted by the voltage
comparator 207 to the stand-by control object section 203 as the
impact detection signal sensed by the shock detection sensor
202.
[0042] Where the capacitor 206 is not used as referred to above, as
the piezoelectric element unit 205 generates an AC voltage
corresponding to the quantity of the generated charge, the AC
voltage of the piezoelectric element unit 205 is inputted directly
into the voltage comparator 207; when the voltage from the
piezoelectric element unit 205 reaches a certain level, it is
transmitted to the stand-by control object section 203 by the
voltage comparator 207 as the impact detection signal sensed by the
shock detection sensor 202. The signal transmitted by the shock
detection sensor 202 is inputted into the wake up signal generator
208 and the impact detect circuit 213, and the wake up signal from
the wake up signal generator 208 causes a signal to be transmitted
to the microcomputer 209, which is thereby awakened from a stand-by
state to an active state. The microcomputer 209 in the active state
captures the signal from the shock detection sensor 202, measures
the intensity of the impact, and performs predetermined control.
For the predetermined control, ambient information is sensed by the
A/D converter 211 and the sensor 212, the sensed information is
processed by the microcomputer 209, and communication is performed
by the radio frequency transceiver circuit 210. Upon completion of
the predetermined processing, the sensor node 201 returns to the
stand-by state.
[0043] FIGS. 3(a) and 3(b) are profiles illustrating examples of
piezoelectric element unit for use in the invention. The
piezoelectric element unit shown in FIG. 3(a) is configured of a
piezoelectric element 301, a metal plate 302, a mass 303, a fixed
plate 304, a fixed face 305 and electrodes 306a and 306b.
[0044] FIG. 3(b) shows a piezoelectric element unit shown in FIG.
3A with the mass 303 omitted. The piezoelectric element 301 is to
be made of a material having a piezoelectric effect such as lead
zirconate titanate ceramic, lead titanate ceramic or lead
metaniobate ceramic. The metal plate 302 is to have a bimorph
shape, sandwiched between the layers of the piezoelectric element
301. The metal plate 302 is intended to increase the durability of
the piezoelectric element 301 or increasing the distortion of the
piezoelectric element 301 by external forces, but it can be
dispensed with. The mass 303 should have the optimum size that is
determined by the materials and sizes of the piezoelectric element
301 and the metal plate 302 and the intensity of the external
impact to be measured. Depending on the intensity of the external
impact, a shape which does not require the mass 303, as shown in
FIG. 3(b) can be selected. When an impact works from outside, an
electric charge corresponding to that external impact is generated
between the electrodes 306a and 306b. As will be described
afterwards, this charge is used for measuring the intensity of the
impact and the sensor node is returned from its stand-by state.
[0045] FIG. 4 shows one example of capacitor for use in the
configurations shown in FIG. 1 and FIG. 2. A capacitor 410 is
configured of rectification diodes 402 through 405, a charging
capacitor 406, a discharging resistance 407, a Zener diode 408 for
protection from breakdown voltage and output terminals 409a and
409b. The piezoelectric element unit 401, such as the one described
with reference to FIGS. 3A and 3B, is connected to rectification
diodes. As described with reference to FIG. 1 and FIG. 2, the
piezoelectric element unit 401 performs rectification with the
diodes 402 through 405 to generate electric charges corresponding
to the external impact, and accumulates the charges in the charging
capacitor 406. The resistance 407, as will be described afterwards,
is a resistance for adjusting the duration of discharge, and the
Zener diode 408 for protection from breakdown voltage is intended
to prevent surpassing of the breakdown voltage of the charging
capacitor 406 and the breakdown voltage of an additional circuit
connected between the output terminals 409a and 409b.
[0046] FIG. 5 shows one example of shock detection sensor for use
in the configuration shown in FIG. 1. This shock detection sensor
is configured of a piezoelectric element unit 500, a capacitor 501,
a voltage detector 502, terminals 503a and 503b for connecting the
capacitor 501 and the voltage detector 502, and terminals 504a and
504b for transmitting signals to the stand-by control object
section shown in FIG. 1. The voltage detector 502 outputs from the
terminals 504a and 504b a voltage (equal to either the input
voltage or to the detect voltage) when the voltage of the capacitor
501 has surpassed the detect voltage.
[0047] Since the current required for operating the voltage
detector 502 is only about a few .mu.W, the size of piezoelectric
element unit of the type described with reference to FIG. 4
(denoted by 401 in FIG. 4) and its capacitor (denoted by 406 in
FIG. 4) are designed to optimally match the operating power of the
voltage detector 502. The shock detection sensor in this
embodiment, as is evident from the foregoing description, consumes
no power when standing by. Nor does it require any power supply
when in operation because it relies on power generated by the
piezoelectric element unit.
[0048] FIG. 6 shows one example of shock detection sensor for use
in the configuration shown in FIG. 2. It is configured of a
piezoelectric element unit 600, a capacitor 601, a voltage
comparator 602, terminals 603a and 603b for connecting the output
terminals of the piezoelectric element unit shown in FIG. 3 (306a
and 306b) or the output terminals of the capacitor 410 (409a and
409b) to the voltage comparator 602, terminals 604a and 604b for
transmitting signals to the stand-by control object section shown
in FIG. 1, a reference voltage generator 607, a power supply 605
and another power supply 606 (corresponding to the power supply 204
shown in FIG. 2). The voltage comparator 602 outputs from the
terminals 604a and 604b a certain voltage when the voltage of the
reference voltage generator 607 has surpassed the reference
voltage.
[0049] Further, as described with reference to the embodiment shown
in FIG. 2, as the piezoelectric element unit 600 generates an AC
voltage when no capacitor is used, the AC voltage from the
piezoelectric element unit 600 is directly inputted into the
voltage comparator 602, and when the voltage of the piezoelectric
element unit 600 reaches the reference voltage, the voltage
comparator 602 outputs a certain voltage from the terminals 604a
and 604b.
[0050] Since power is externally fed to the voltage comparator 602,
it is sufficient for a voltage for impact detection to be supplied
from the capacitor 601 or, where no capacitor is used, from the
piezoelectric element unit 600. For this reason, the size of
piezoelectric element of the piezoelectric element unit and the
capacitor shown in FIG. 4 (denoted by 406 in FIG. 4) can be smaller
than in the case shown in FIG. 5.
[0051] FIG. 7 is a time chart also showing waveforms which occur
where the capacitor 206 is used in the sensor node of FIG. 1 or
FIG. 2 and an impact is applied to the sensor node. In the
following description and drawings, parenthesized numerals or
phrases refer to a case in which the capacitor 206 is used in the
sensor node of FIG. 2.
[0052] When an impulse-form impact 701 is applied to the sensor
node 101 (201) of FIG. 1, the output signal of the piezoelectric
element 114 (214) supplied from the piezoelectric element unit 105
(205) manifests a repetitive attenuating waveform denoted by 702.
Here, to is uniquely determined by the size of the piezoelectric
element unit in FIGS. 3A and 3B and FIG. 9 to be referred to below.
The waveform of 702 is converted by the capacitor 106 (206) into a
waveform denoted by 703 as the output signal of the capacitor 115
(215). The waveform denoted by 703 is converted by the voltage
detector 107 (the voltage comparator 207) into the output signal of
the voltage detector 116 (the output signal of the voltage
comparator 216) having the waveform denoted by 704. Here the
waveform of 704 is generated from the waveform of 703 by using a
detection voltage (comparison voltage) V.sub.ref. The t.sub.d of
704 can be determined by appropriately selecting the size of the
piezoelectric element unit 105 (205), the resistance of the
capacitor 106 (206) and the charge capacity according to the
intensity of the impact to be detected. By measuring the length of
this t.sub.d, the intensity of vibration can be detected in an
analog value.
[0053] When the output signal of the voltage detector 116 (216) has
surpassed V.sub.ref, which is the detection voltage (comparison
voltage), the wake up signal 117 (217) is transmitted by the wake
up signal generator to the microcomputer 109 (209) according to the
part of the time chart denoted by 705. This wake up signal brings
the microcomputer 109 (209) into an awaken state. Also, as
described earlier, the output signal of the voltage detector 116
(216) and the impact detect circuit 113 (213) give an impact level
signal 119 (219) of the form denoted by 707 in the time chart. As
an example of this impact detect circuit 113 (213), a counter
circuit can be used. In this case, as long as the voltage detect
signal is on, the clocks of the stand-by control object section 103
(203) are inputted into the counter, which counts the pulses
generated during the period of time t.sub.d to detect the intensity
of the impact.
[0054] The microcomputer 109 (209) captures the intensity of the
impact from the impact detect circuit 113 (213); after completing
other predetermined steps of processing, it transmits reset signals
118 and 120 (218 and 220) in accordance with the 706 part of the
time chart and, after resetting the wake up signal generator 108
(208) and the impact detect circuit 113 (213), enters into a
stand-by state. A time chart regarding the operating state of the
microcomputer 109 (209) is shown as denoted by 708.
[0055] The method for analog detection of the impact intensity
charted in FIG. 7 is one example, and any other appropriate method
can be used as well.
[0056] FIG. 8 is a time chart also showing waveforms which occur
when an impact is applied to the sensor node of FIG. 2, wherein
neither the capacitor 206 nor the impact detect circuit 213 is
used.
[0057] When an impulse-form impact 801 denoted by 801 is applied to
the sensor node of FIG. 2, the output signal of the piezoelectric
element 214 supplied from the piezoelectric element unit 205 of
FIG. 2 manifests a repetitive attenuating waveform denoted by 802.
Here, to is uniquely determined by the size of the piezoelectric
element unit in FIGS. 3A and 3B and FIG. 9 to be referred to below.
The waveform of 802 takes on a waveform denoted by 803, and the
output signal of the voltage comparator 216 takes on the pulse
waveform denoted by 804. Here the waveform of 804 is generated from
the waveform of 802 by using a comparison voltage V.sub.ref. When
the output signal of the voltage comparator 216 has surpassed
V.sub.ref, which is the comparison voltage, the wake up signal 217
is transmitted by the wake up signal generator to the microcomputer
209 according to the part of the time chart denoted by 805. This
wake up signal brings the microcomputer 209 into an awaken
state.
[0058] Further, the output signal of the voltage comparator 216 is
directly inputted into the microcomputer 209 as described above,
and the microcomputer 209 counts the number of pulses to detect the
intensity of the impact. The judgment by the microcomputer 209 that
the output signal of the voltage comparator 216 has ended is based
on the lapse of a period of time not less than a certain length
(t>t.sub.0) after the waveform 804 ceases to manifest any pulse
as denoted by 806 of the time chart. The microcomputer 209, upon
completing the detection of the intensity of the impact and other
predetermined steps of processing, transmits a reset signal 220
and, after resetting the wake up signal generator 208, enters into
a stand-by state. A time chart regarding the operating state of the
microcomputer 209 is shown as denoted by 807.
[0059] The method for analog detection of the impact intensity
charted in FIG. 8 is one example, and any other appropriate method
can be used as well.
[0060] FIG. 9 shows another example of configuration of the sensor
node for impact detection according to the invention. The sensor
node for impact detection of this example is configured of a
piezoelectric element 901, a metal plate 902, a mass 903, a fixed
plate 904, a fixed face 905 and electrodes 906a and 906b. The shape
of the mass 903 differs from its counterpart in the configuration
of the piezoelectric element unit shown in FIG. 3A.
[0061] Regarding the mass, it was stated with reference to the
example shown in FIG. 3A that its size should be appropriate
relative to the external vibration and the size of the
piezoelectric element. However, depending on conditions, the mass
903 may be so large as to swell beyond the size of the
piezoelectric element 901 at the other end than the fixed plate
904, or may extend in the direction of the fixed plate 904 and the
fixed face 905, resulting in an increased size of the case to
protect the piezoelectric element unit. In this embodiment, the
protective case for the piezoelectric element unit can be made
smaller by folding back the mass 903 toward the fixed plate
904.
Embodiment 3
[0062] FIG. 10 shows one example of configuration of a sensor
network system for impact detection using sensor nodes of the type
shown in FIG. 1 or FIG. 2. This embodiment is configured of sensor
nodes 1004 through 1006, base stations 1007 through 1009 for
wireless reception of various items of information from the sensor
nodes, a network 1010 to which the base stations are connected, a
system control device 1011 for receiving information from the base
stations via the network 1010 and processing the information into
desired data, and a control information database 1012 for storing
the data processed by the system control device 1011. In this
embodiment, each of the sensor nodes 1004 through 1006 is installed
on the object of intended detection, such as a door 1001, a cargo
1002 or a lid 1003. These objects of intended detection are mere
examples, and many other items can be objects of detection.
[0063] Each of the sensor nodes 1004 through 1006, when detecting
any external impact, actuates itself to perform predetermined
control, and transmits the intensity of the impact, the time of
detection of the impact, the value measured by the sensor and
information to identify the sensor among other items of
information.
[0064] Each of the base stations 1007 through 1009, when receiving
from a sensor node information on the items referred to above, adds
supplementary information including the time of receiving a
wireless packet and information to identify the base station having
received the wireless packet to the intensity of the impact, the
time of measurement, the value measured by the sensor, information
to identify the sensor and so forth, and transmits these items of
information to the network 1010. These items of information are
processed by the system control device 1011, and stored into the
control information database 1112. The sensor nodes may either
operate only when any impact is detected, or operate intermittently
in normal times to sense various items of information and perform
node operation, not intermittent, when there is any external
impact.
Embodiment 4
[0065] FIG. 11 shows one example of configuration of a power
supply-free wireless communication node for impact detection using
the sensor node shown in FIG. 1 or FIG. 2. This embodiment
comprises a wireless communication node for impact detection 1101
configured of a piezoelectric element unit 1102, a capacitor 1103
and a radio frequency transceiver circuit 1104, a base station 1105
for wireless reception of various items of information from the
wireless communication node for impact detection, and a display
device 1106 for receiving the information from the base station and
display its state. Since the radio frequency transceiver circuit
operates only on the wattage generated by the piezoelectric element
system 1102 in response to an external impact, here is realized a
wireless communication node for impact detection requiring no power
supply.
[0066] As hitherto described in detail, according to the present
invention, it is made possible to save power consumption by
measuring the intensity of an external impact in a multi-valued or
analog mode according to the level of electric power generated by
the distortion of a piezoelectric element by the impact and actuate
a sensor node in a waiting mode by the generated power.
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