WO2004018986A1 - Force or pressure sensor and method for applying the same - Google Patents

Force or pressure sensor and method for applying the same Download PDF

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Publication number
WO2004018986A1
WO2004018986A1 PCT/FI2003/000604 FI0300604W WO2004018986A1 WO 2004018986 A1 WO2004018986 A1 WO 2004018986A1 FI 0300604 W FI0300604 W FI 0300604W WO 2004018986 A1 WO2004018986 A1 WO 2004018986A1
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WO
WIPO (PCT)
Prior art keywords
sensor
diaphragm
cover
set forth
frame
Prior art date
Application number
PCT/FI2003/000604
Other languages
French (fr)
Inventor
Heikki Ruotoistenmäki
Original Assignee
Ruotoistenmaeki Heikki
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ruotoistenmaeki Heikki filed Critical Ruotoistenmaeki Heikki
Priority to US10/525,703 priority Critical patent/US7726209B2/en
Priority to DE60313796T priority patent/DE60313796T2/en
Priority to AU2003251019A priority patent/AU2003251019A1/en
Priority to DK03792435T priority patent/DK1563268T3/en
Priority to EP03792435A priority patent/EP1563268B1/en
Publication of WO2004018986A1 publication Critical patent/WO2004018986A1/en
Priority to US12/076,399 priority patent/US7862523B2/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6887—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient mounted on external non-worn devices, e.g. non-medical devices
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • A61B5/1102—Ballistocardiography
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • A61B5/113—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb occurring during breathing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/16—Measuring force or stress, in general using properties of piezoelectric devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
    • G01L1/2206—Special supports with preselected places to mount the resistance strain gauges; Mounting of supports
    • G01L1/2231—Special supports with preselected places to mount the resistance strain gauges; Mounting of supports the supports being disc- or ring-shaped, adapted for measuring a force along a single direction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
    • G01L9/008—Transmitting or indicating the displacement of flexible diaphragms using piezoelectric devices
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0247—Pressure sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
    • A61B5/0816—Measuring devices for examining respiratory frequency

Definitions

  • the invention relates to a force or pressure sensor, comprising a substantially rigid, mechanical-load resistant frame, a flexible diaphragm secured over its peripheral rim to the frame, and a piezoelectric sensor diaphragm applied to the surface of the flexible diaphragm.
  • the invention relates also to a method for applying this method, such that a sleeping or lying person can be measured for his or her heart rate and respiratory amplitude, as well as frequency.
  • Patent publications US-4,570,097, US-4,567,395, US-4,590,400 and US- 5,353,633 disclose a piezoelectric pressure sensor for measuring changes of a cylinder pressure in an internal combustion engine during ignition.
  • the cylinder pressure is supplied by means of a separate transmitter body to a piezoelement, which is subjected to compression according to a pressure change occurring in the engine cylinder. Since the piezocrystal is compressed and its surface area is relatively small, the sensor remains comparatively low in responsivity.
  • the sensor is not structurally designed to provide simultaneously a high load rating and a high sensitivity.
  • WO 99/47044 discloses a piezoelectric pressure sensor for measuring blood pressure changes in a blood vessel.
  • the pulse of a blood vessel is delivered by means of a transmitter diaphragm and a rod to a piezoelement, which is subjected to deflection according to a pressure change occurring in the blood vessel. Since the load is received by a sensitive transmitter diaphragm, the sensor has a remarkably low static resistance to pressure.
  • the sensor's piezoelement is structurally asymmetrical.
  • Patent publication US-5,365,937 describes a piezoelectric sensor for measuring cardiomuscular rate on skin surface.
  • Some of the sensor's housing structure consists of a piezoelement. Since some of the sensor's housing structure consists of a piezoelement, the sensor's static resistance to pressure is relatively modest. The movement applied to a piezoelement in the sensor is transmitted over the entire surface area of the piezoelement.
  • Patent publication US-4,803,671 discloses a sensor for acoustic pressure wave pulses, wherein a piezoelectric measuring diaphragm is disposed in a space between two coupling diaphragms filled with a coupling medium. This sensor is not capable of handling major external loads, either.
  • a sensor of the invention i.e. a high load rating and responsivity
  • it can be applied with particular benefits in a method, by which a sleeping or lying person is measured for his or her heart rate and respiratory amplitude, as well as frequency.
  • the features characteristic of the method are set forth in the appended claim 12.
  • Implementing options for the method are set forth in claims 13 and 14.
  • FIG. 1 shows a force or pressure sensor of the invention in a sectional view
  • Fig. 2 shows a variant for the sensor of fig. 1, which can be used for measuring changes in fluid or gas pressure
  • Fig. 3 depicts a sensor application method for measuring a sleeping or lying person for his or her heart rate and respiratory amplitude, as well as frequency, and
  • Fig. 4 shows a method otherwise similar to fig. 3 except for an alternative disposition of the sensor.
  • the sensor to be described hereinafter has properties like a high resistance to force or pressure, a high sensitivity, a trouble-free operation, a simplicity of required electronics, and a broad frequency repetition. Surprisingly, all these qualities are achieved with a sensor assembly to be described hereinbelow.
  • a sensor frame 1 is substantially rigid and resistant to mechanical loading. Therefore, the frame 1 is made e.g. from stainless steel.
  • a sensor cover 4 is also substantially rigid and resistant to mechanical loading, and preferably made from stainless steel or another suitable metal.
  • the frame 1 and the cover 4 are metal blocks in the shape of bodies of revolution. They can also be made of a plastic or composite material or some other rigid, durable material.
  • the actual sensor element comprises a piezoelectric ceramic diaphragm 3, which is applied to a thin, flexible metal diaphragm 2. The flexible metal diaphragm is in turn attached by its peripheral rim between the frame 1 and the cover 2.
  • the frame 1 and the cover 2 define therebetween a closed, hermetically sealed housing chamber, the flexible diaphragm 2 and the sensor diaphragm 3 being located thereinside.
  • the piezoceramic sensor diaphragm 3 is smaller than the metal diaphragm 2, which is why the sensor diaphragm 3 has its peripheral rims left at a distance from the inner periphery of the housing chamber.
  • Such combination of a metal diaphragm and a piezoceramic sensor diaphragm is prior known and generally used in piezoelectric loudspeakers for producing sound by conducting an electric signal to the diaphragm.
  • Such a piezoelectric loudspeaker is prior known e.g. from patent publication US- 2002/0067840A1.
  • the cover 4 functioning as a loading element, is provided with a protrusion or shoulder 4a, bearing against the flexible diaphragm 2 in its mid-section, and hence prestressing the flexible diaphragm 2 and the sensor diaphragm 3 attached thereto.
  • a sensor-signal transmitting contact spring 5 is in contact with the sensor diaphragm 3 opposite to the cover protrusion 4a.
  • the frame 1, the cover 4, and the diaphragms 2 and 3 are all rotationally symmetrical with respect to the cover protrusion or shoulder 4a.
  • the cover has a load rating or load carrying capacity which is very high, typically more than 50 kg and preferably more than 100 kg, the sensor has an extremely high responsivity to changes in a force F or a pressure p.
  • the sensor provides a clear and highly decipherable output signal as the change of a load applied to the cover 4 is less than 10' 6 , even less than IO" 9 x load rating of the cover 4.
  • the load rating of the cover refers to its elastic loading section, over which the sensor retains its functionality and high responsivity.
  • An amplifier 6 and its circuit board 7 are located within the housing chamber defined by the frame 1 and the cover 4.
  • the amplifier 6 has its input impedance matched to provide a desired settling time, during which the amplifier's 6 output sets essentially to zero as the loading applied to the cover 4 remains unchanged.
  • the input impedance of the amplifier 6 is used for making the sensor applicable to various applications, in which the measured fluctuation of force or pressure can happen at a low or a high frequency.
  • the sensor's output cable 8, extending from the amplifier 6, comprises a single- or multi-wire screened cable.
  • Fig. 2 differs from the embodiment of fig. 1 in that the cover 4 has its threaded sleeve 9 fitted with an adapter element 10, 11, by way of which the cover 4 can be loaded with changes in a fluid or gas pressure.
  • the member 10 defines a pressure chamber, and the member 11 is e.g. a threaded fitting piece.
  • the cover 4 is also provided in the middle with an upward protrusion 4b, which is subjected to mechanical loading.
  • the cover plate 4 has a thickness between a curb collar 4c and the central protrusions 4a, 4b in the order of e.g. 1 mm, and the sensor diameter can be in the order of 2-3 mm.
  • the sensor's operation is based on the fact that, as a compressive force is applied to the protruding part 4b in the mid-section of the cover plate 4, the cover element 4 depresses slightly inward and deflects the piezo-diaphragm 3 with its protrusion 4a.
  • the deflection of the cover element 4 must be very slight indeed, as the ceramic piezo-diaphragm 3 is easily ruptured.
  • the piezo-diaphragm 3 Upon deflection, the piezo-diaphragm 3 generates a potential, which is conducted by way of the contact spring 5 to the high-impedance amplifier 6.
  • the amplifier 6 turns the output impedance lower, thus improving the output signal's immunity to interference.
  • a sleeping or lying person is measured for his or her heart rate and respiratory amplitude, as well as frequency.
  • a sleeping person can be measured, without having any wires or transducers connected to the person, for his or her heart rate and respiration, regardless of a person's lying posture (on his or her back, side or belly).
  • the method utilizes a ballisto-cardiographic signal generated by the heart and a weight change in a person at rest, resulting from pulmonary movements and strains.
  • the measurement has been enabled by a sensor of the invention, which is concurrently provided with a high load rating and a high responsivity.
  • Fig. 3 illustrates a first alternative of the method, wherein under the post or posts of a bed is placed a responsive sensor 13 as described above, identifying a change in force or pressure.
  • the sensor identifies, through the intermediary of a bed frame 16, a weight change caused by the heart as well as respiration.
  • the signal processing is effected by using a filter 17 for the filter-separation of a higher-rate frequency component coming from the sensor 13, thereby enabling the measurement of a person's heart rate for its amplitude and frequency.
  • An oscilloscope 18 is provided with a graph representative of cardiac function.
  • a filter 19 for the filter-separation of a low frequency component coming from the sensor 3, it is possible to measure the amplitude as well as the frequency of human respiration, a graph representing the same being displayable on an oscilloscope 20.
  • the oscilloscopes 18 and 20 are optionally replaceable with a plotter or an electronic memory, from which the graphs can be transferred onto a computer screen.
  • the sensor 13 is placed between a top mattress 14 and an actual mattress 15 in a bed 12 in line with the thorax of a person.
  • the sensor 13 is prevented from sinking in the top mattress 14 and/or the actual mattress 15 by means of panels 21 and 22, which are more rigid than the mattresses and between which the sensor 13 is positioned.
  • panels 21 and 22 which are more rigid than the mattresses and between which the sensor 13 is positioned.
  • under the top mattress 14 lies a resilient panel 20, extending essentially across the width of the mattresses, and thereunder a rigid backing panel 22, whose surface area is confined within a section of the upper body, such that the function of the actual mattress 15 is not substantially impeded.
  • the panels 21, 22 of an appropriate surface area it is possible to identify the heart rate, as well as respiration, reliably over a more extensive area (and, if desired, a change in the sleeping posture of a sleeping person during sleep). Hence, the comfort of a sleeping platform is not impaired by the sensor system.
  • the method can be used in monitoring or attending to heart patients, lung patients, demented patients, sleep apnea patients, a child's sleep, etc.
  • - Sensor can also be used for measuring a fluid or air pressure by modifying the cover plate design.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Animal Behavior & Ethology (AREA)
  • Public Health (AREA)
  • General Physics & Mathematics (AREA)
  • Biophysics (AREA)
  • Pathology (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Medical Informatics (AREA)
  • Molecular Biology (AREA)
  • Surgery (AREA)
  • Veterinary Medicine (AREA)
  • General Health & Medical Sciences (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Physiology (AREA)
  • Dentistry (AREA)
  • Cardiology (AREA)
  • Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
  • Measuring Fluid Pressure (AREA)
  • Push-Button Switches (AREA)
  • Pressure Welding/Diffusion-Bonding (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)
  • Force Measurement Appropriate To Specific Purposes (AREA)
  • Measuring And Recording Apparatus For Diagnosis (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

Abstract

The invention relates to a force or pressure sensor and a method for applying the same. The pressure sensor comprises a substantially rigid, mechanical-load resistant frame (1), a flexible diaphragm (2) secured over its peripheral rim to the frame (1), and a piezoelectric sensor diaphragm (3) applied to the surface of the flexible diaphragm (2). The sensor diaphragm (3) loading element comprises a substantially rigid, mechanical-load resistant cover (4), having its protrusion or shoulder (4a) bearing against a middle section of the flexible diaphragm (2) and thereby prestressing the flexible diaphragm (2) and the piezoelectric sensor diaphragm (3) attached thereto. The frame (1) and the cover (4) define therebetween a closed, hermetically sealed housing chamber, the flexible diaphragm (2) and the piezoelectric sensor diaphragm (3) being located thereinside. The placement of one or more responsive, yet load-resistant sensors in contact with a bed enables measuring a sleeping or lying person for his or her heart rate and respiratory amplitude, as well as frequency.

Description

Force or pressure sensor and method for applying the same
The invention relates to a force or pressure sensor, comprising a substantially rigid, mechanical-load resistant frame, a flexible diaphragm secured over its peripheral rim to the frame, and a piezoelectric sensor diaphragm applied to the surface of the flexible diaphragm.
The invention relates also to a method for applying this method, such that a sleeping or lying person can be measured for his or her heart rate and respiratory amplitude, as well as frequency.
Patent publications US-4,570,097, US-4,567,395, US-4,590,400 and US- 5,353,633 disclose a piezoelectric pressure sensor for measuring changes of a cylinder pressure in an internal combustion engine during ignition. The cylinder pressure is supplied by means of a separate transmitter body to a piezoelement, which is subjected to compression according to a pressure change occurring in the engine cylinder. Since the piezocrystal is compressed and its surface area is relatively small, the sensor remains comparatively low in responsivity. The sensor is not structurally designed to provide simultaneously a high load rating and a high sensitivity.
Published application WO 99/47044 discloses a piezoelectric pressure sensor for measuring blood pressure changes in a blood vessel. The pulse of a blood vessel is delivered by means of a transmitter diaphragm and a rod to a piezoelement, which is subjected to deflection according to a pressure change occurring in the blood vessel. Since the load is received by a sensitive transmitter diaphragm, the sensor has a remarkably low static resistance to pressure. In addition, the sensor's piezoelement is structurally asymmetrical.
Patent publication US-5,365,937 describes a piezoelectric sensor for measuring cardiomuscular rate on skin surface. Some of the sensor's housing structure consists of a piezoelement. Since some of the sensor's housing structure consists of a piezoelement, the sensor's static resistance to pressure is relatively modest. The movement applied to a piezoelement in the sensor is transmitted over the entire surface area of the piezoelement.
Patent publication US-4,803,671 discloses a sensor for acoustic pressure wave pulses, wherein a piezoelectric measuring diaphragm is disposed in a space between two coupling diaphragms filled with a coupling medium. This sensor is not capable of handling major external loads, either.
It is an object of the invention to provide a force or pressure sensor, which is highly capable of handling major external loads, yet at the same time is extremely responsive even to very slight changes in force or pressure.
This object is achieved by a force or pressure sensor of the invention, which is provided with the characterizing features set forth in the appended claim 1. The dependent claims disclose preferred structural solutions of the invention, which assist in reaching the above objective.
By virtue of the features of a sensor of the invention, i.e. a high load rating and responsivity, it can be applied with particular benefits in a method, by which a sleeping or lying person is measured for his or her heart rate and respiratory amplitude, as well as frequency. The features characteristic of the method are set forth in the appended claim 12. Implementing options for the method are set forth in claims 13 and 14.
The inventive force or pressure sensor and its application will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 shows a force or pressure sensor of the invention in a sectional view,
Fig. 2 shows a variant for the sensor of fig. 1, which can be used for measuring changes in fluid or gas pressure,
Fig. 3 depicts a sensor application method for measuring a sleeping or lying person for his or her heart rate and respiratory amplitude, as well as frequency, and
Fig. 4 shows a method otherwise similar to fig. 3 except for an alternative disposition of the sensor.
The sensor to be described hereinafter has properties like a high resistance to force or pressure, a high sensitivity, a trouble-free operation, a simplicity of required electronics, and a broad frequency repetition. Surprisingly, all these qualities are achieved with a sensor assembly to be described hereinbelow.
A sensor frame 1 is substantially rigid and resistant to mechanical loading. Therefore, the frame 1 is made e.g. from stainless steel. A sensor cover 4 is also substantially rigid and resistant to mechanical loading, and preferably made from stainless steel or another suitable metal. The frame 1 and the cover 4 are metal blocks in the shape of bodies of revolution. They can also be made of a plastic or composite material or some other rigid, durable material. The actual sensor element comprises a piezoelectric ceramic diaphragm 3, which is applied to a thin, flexible metal diaphragm 2. The flexible metal diaphragm is in turn attached by its peripheral rim between the frame 1 and the cover 2. The frame 1 and the cover 2 define therebetween a closed, hermetically sealed housing chamber, the flexible diaphragm 2 and the sensor diaphragm 3 being located thereinside. In terms of its diameter, the piezoceramic sensor diaphragm 3 is smaller than the metal diaphragm 2, which is why the sensor diaphragm 3 has its peripheral rims left at a distance from the inner periphery of the housing chamber. Such combination of a metal diaphragm and a piezoceramic sensor diaphragm is prior known and generally used in piezoelectric loudspeakers for producing sound by conducting an electric signal to the diaphragm. Such a piezoelectric loudspeaker is prior known e.g. from patent publication US- 2002/0067840A1.
The cover 4, functioning as a loading element, is provided with a protrusion or shoulder 4a, bearing against the flexible diaphragm 2 in its mid-section, and hence prestressing the flexible diaphragm 2 and the sensor diaphragm 3 attached thereto. A sensor-signal transmitting contact spring 5 is in contact with the sensor diaphragm 3 opposite to the cover protrusion 4a. The frame 1, the cover 4, and the diaphragms 2 and 3 are all rotationally symmetrical with respect to the cover protrusion or shoulder 4a. Despite the fact that the cover has a load rating or load carrying capacity which is very high, typically more than 50 kg and preferably more than 100 kg, the sensor has an extremely high responsivity to changes in a force F or a pressure p. It has been discovered in practical experiments that the sensor provides a clear and highly decipherable output signal as the change of a load applied to the cover 4 is less than 10'6, even less than IO"9 x load rating of the cover 4. In this conjunction, the load rating of the cover refers to its elastic loading section, over which the sensor retains its functionality and high responsivity.
An amplifier 6 and its circuit board 7 are located within the housing chamber defined by the frame 1 and the cover 4. The amplifier 6 has its input impedance matched to provide a desired settling time, during which the amplifier's 6 output sets essentially to zero as the loading applied to the cover 4 remains unchanged. Thus, the input impedance of the amplifier 6 is used for making the sensor applicable to various applications, in which the measured fluctuation of force or pressure can happen at a low or a high frequency. The sensor's output cable 8, extending from the amplifier 6, comprises a single- or multi-wire screened cable.
Fig. 2 differs from the embodiment of fig. 1 in that the cover 4 has its threaded sleeve 9 fitted with an adapter element 10, 11, by way of which the cover 4 can be loaded with changes in a fluid or gas pressure. The member 10 defines a pressure chamber, and the member 11 is e.g. a threaded fitting piece.
In the embodiment of fig. 1, the cover 4 is also provided in the middle with an upward protrusion 4b, which is subjected to mechanical loading. The cover plate 4 has a thickness between a curb collar 4c and the central protrusions 4a, 4b in the order of e.g. 1 mm, and the sensor diameter can be in the order of 2-3 mm.
The sensor's operation is based on the fact that, as a compressive force is applied to the protruding part 4b in the mid-section of the cover plate 4, the cover element 4 depresses slightly inward and deflects the piezo-diaphragm 3 with its protrusion 4a. The deflection of the cover element 4 must be very slight indeed, as the ceramic piezo-diaphragm 3 is easily ruptured. Upon deflection, the piezo-diaphragm 3 generates a potential, which is conducted by way of the contact spring 5 to the high-impedance amplifier 6. The amplifier 6 turns the output impedance lower, thus improving the output signal's immunity to interference.
The application of a sensor of the invention will now be described in connection with a method, whereby a sleeping or lying person is measured for his or her heart rate and respiratory amplitude, as well as frequency. In the method, a sleeping person can be measured, without having any wires or transducers connected to the person, for his or her heart rate and respiration, regardless of a person's lying posture (on his or her back, side or belly). The method utilizes a ballisto-cardiographic signal generated by the heart and a weight change in a person at rest, resulting from pulmonary movements and strains. The measurement has been enabled by a sensor of the invention, which is concurrently provided with a high load rating and a high responsivity.
Fig. 3 illustrates a first alternative of the method, wherein under the post or posts of a bed is placed a responsive sensor 13 as described above, identifying a change in force or pressure. As a person is lying, the sensor identifies, through the intermediary of a bed frame 16, a weight change caused by the heart as well as respiration. The signal processing is effected by using a filter 17 for the filter-separation of a higher-rate frequency component coming from the sensor 13, thereby enabling the measurement of a person's heart rate for its amplitude and frequency. An oscilloscope 18 is provided with a graph representative of cardiac function. By using a filter 19 for the filter-separation of a low frequency component coming from the sensor 3, it is possible to measure the amplitude as well as the frequency of human respiration, a graph representing the same being displayable on an oscilloscope 20. The oscilloscopes 18 and 20 are optionally replaceable with a plotter or an electronic memory, from which the graphs can be transferred onto a computer screen.
In the alternative of fig. 4, the sensor 13 is placed between a top mattress 14 and an actual mattress 15 in a bed 12 in line with the thorax of a person. The sensor 13 is prevented from sinking in the top mattress 14 and/or the actual mattress 15 by means of panels 21 and 22, which are more rigid than the mattresses and between which the sensor 13 is positioned. In the illustrated case, under the top mattress 14 lies a resilient panel 20, extending essentially across the width of the mattresses, and thereunder a rigid backing panel 22, whose surface area is confined within a section of the upper body, such that the function of the actual mattress 15 is not substantially impeded. By using the panels 21, 22 of an appropriate surface area, it is possible to identify the heart rate, as well as respiration, reliably over a more extensive area (and, if desired, a change in the sleeping posture of a sleeping person during sleep). Hence, the comfort of a sleeping platform is not impaired by the sensor system.
The method can be used in monitoring or attending to heart patients, lung patients, demented patients, sleep apnea patients, a child's sleep, etc.
Other possible applications for a sensor of the invention include:
- Wearing of engine bearings (audibility range)
- Pressure changes in the combustion chamber of an engine cylinder
- Dynamic stress of bearing supports (measurement at low frequencies; stresses and torques applied to axles etc.)
- Wobbling of building structures (swaying of tall buildings and smokestack structures, e.g. as a result of wind action)
- As a seismographic sensor for controlling an earthquake alarm system (apartment-specific alarm like a fire alarm)
- As a surveillance device in buildings (capable of detecting depression of floor)
- Sensor can also be used for measuring a fluid or air pressure by modifying the cover plate design.

Claims

Claims
1. A force or pressure sensor, comprising a substantially rigid, mechanical- load resistant frame (1), a flexible diaphragm (2) secured over its peripheral rim to the frame (1), and a piezoelectric sensor diaphragm (3) applied to the surface of the flexible diaphragm (2), characterized in that the sensor diaphragm (3) loading element comprises a substantially rigid cover (4) capable of carrying mechanical loading of more than 50 kg, preferably more than 100 kg, that the cover (4) has a protrusion or shoulder (4a), bearing against a middle section of the flexible diaphragm (2) and thus, by deflection, prestressing the flexible diaphragm (2) and the piezoelectric sensor diaphragm (3) attached thereto, and that the frame (1) and the cover (4) define therebetween a closed housing chamber, the flexible diaphragm (2) and the piezoelectric sensor diaphragm (3) being located thereinside.
2. A sensor as set forth in claim 1, characterized in that the frame (1), the cover (4), and the diaphragms (2, 3) are rotationally symmetrical relative to the cover protrusion or shoulder (4a).
3. A sensor as set forth in claim 1 or 2, characterized in that the flexible diaphragm (2) comprises a thin metal diaphragm, having its peripheral rim secured between the edges of the frame (1) and the cover (4).
4. A sensor as set forth in any of claims 1-3, characterized in that the sensor diaphragm (3) comprises a piezoceramic diaphragm, having a diameter smaller than that of the metal diaphragm (2), and that the sensor diaphragm (3) has its peripheral rim at a distance from the inner periphery of the housing chamber.
5. A sensor as set forth in any of claims 1-4, characterized in that a sensor- signal transmitting contact spring (5) is in contact with the sensor diaphragm (3) opposite to the cover protrusion or shoulder (4a).
6. A force or pressure sensor as set forth in any of claims 1-5, characterized in that an amplifier (6) and its circuit board (7) are located in said housing chamber.
7. A sensor as set forth in any of claims 1-6, characterized in that the frame (1) and the cover (4) comprise elements in the shape of bodies of revolution.
8. A sensor as set forth in any of claims 1-7, characterized in that the sensor has a responsivity, such that the sensor provides an output signal when the change of a load applied to the cover (4) is less than IO"6, preferably less than IO"9 x load rating of the cover (4).
9. A sensor as set forth in any of claims 5-8, characterized in that the amplifier (6) has its input impedance matched to provide a desired settling time, during which the amplifier (6) has its output set substantially to zero, while the loading applied to the cover (4) respectively remains essentially unchanged.
10. A sensor as set forth in any of claims 1-9, characterized in that the closed housing chamber is hermetically sealed.
11. A sensor as set forth in any of claims 1-10, characterized in that the cover (4) is provided with an adapter element (10, 11), which enables loading of the cover with changes in a fluid or gas pressure.
12. A method for applying a force or pressure sensor as set forth in any of claims 1-11, characterized in that one or more sensors (13) are disposed in contact with a bed (12), and a sleeping or lying person is measured for his or her heart rate and respiratory amplitude, as well as frequency.
13. A method as set forth in claim 12, characterized in that the measurement is implemented with one or more sensors (13) placed under a bed post or posts.
14. A method as set forth in claim 12, characterized in that the measurement is implemented with one or more sensors (13) placed in contact with a bed mattress (14, 15), especially between a top mattress (14) and an actual mattress (15), and the sensor is prevented from sinking in the top mattress and/or the mattress with panels (21, 22), which are more rigid than the mattresses and between which the sensor (13) is positioned.
PCT/FI2003/000604 2002-08-21 2003-08-15 Force or pressure sensor and method for applying the same WO2004018986A1 (en)

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AU2003251019A AU2003251019A1 (en) 2002-08-21 2003-08-15 Force or pressure sensor and method for applying the same
DK03792435T DK1563268T3 (en) 2002-08-21 2003-08-15 Power or pressure sensor and use of the same
EP03792435A EP1563268B1 (en) 2002-08-21 2003-08-15 Force or pressure sensor and use of the same
US12/076,399 US7862523B2 (en) 2002-08-21 2008-03-18 Force or pressure sensor and method for applying the same

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ATE362099T1 (en) 2007-06-15
AU2003251019A1 (en) 2004-03-11
FI116097B (en) 2005-09-15
EP1563268B1 (en) 2007-05-09
FI20021508A0 (en) 2002-08-21
US7726209B2 (en) 2010-06-01
US20060129047A1 (en) 2006-06-15
DK1563268T3 (en) 2007-09-17
DE60313796T2 (en) 2007-09-06
EP1563268A1 (en) 2005-08-17
FI20021508A (en) 2004-02-22
US20080167561A1 (en) 2008-07-10
US7862523B2 (en) 2011-01-04
DE60313796D1 (en) 2007-06-21

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