Classifications

• • 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
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
  • G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres
• • 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
  • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
  • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
  • G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
  • G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
  • G01L11/025—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means using a pressure-sensitive optical fibre
• • 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
  • A61B2562/0261—Strain gauges
  • A61B2562/0266—Optical strain gauges

Definitions

• THIS INVENTION relates to an optical transducer and, more specifically, an optical displacement sensor which uses deformation or deflection of a tubular optical element to detect small displacements, typically of the order of 1 to 5 mm.
• Optical displacement sensors or motion detectors are particularly useful in applications in which a degree of isolation, either physical or electrical, from the measurand is required.
• the force or work required to displace or otherwise operate an optical sensor is extremely small, thereby allowing greater accuracy and sensitivity to be achieved.
• optical sensors are described in which the transmission of light through the fibre is affected by the bending of the fibre, primarily the loss of higher modes, i.e. the light rays which are internally reflected at angles close to the critical angle.
• optical fibre sensors have limited application and require complex and sensitive detection equipment.
• such sensors are typically used for detecting very small displacements of the order of microns, but are not suitable for detecting larger displacements of the order of millimetres.
• optical fibre sensors normally require some reliable form of intensity referencing. The need for such highly sensitive and complex equipment limits the practical uses of such optical fibre sensors.
• the first type of optical displacement sensor comprises two optical fibres each having an end cut to provide an end face substantially perpendicular to the fibre axis.
• the fibre ends are positioned so that the faces are opposed and parallel, and closely spaced apart.
• the fibre axes lie on a common straight line, light propagating in one fibre will couple with maximum intensity into the other fibre.
• the amount of light coupled between the fibres will be reduced. If the end of one fibre is held stationary, the displacement of the end of the other fibre can be measured by reference to the amount of light coupled between the two.
• An example of this type of sensor can be found in U.S. Patent No. 4,293,188.
• the end of an optical fibre is positioned in front of a reflective surface. Displacement of the reflective surface relative to the end of the fibre is measured by the amount of light reflected from the reflective surface into the optical fibre.
• a third group of optical displacement sensors uses a shutter, fringe or variable aperture member connected to the measurand. Displacement of the measurand is measured by the amount of light which the shutter, fringe or aperture member allows into the optical fibre.
• the strain on a photoelastic material changes the axis of polarisation, which in turn affects the amount of light transmitted through the material.
• This type of optical displacement sensor is particularly suitable for use in strain gauge applications.
• optical displacement sensors A common disadvantage of known optical displacement sensors is the requirement of precise setup arrangements. Some sensors also require additional complex optical devices or components, such as micro lenses, polarisers, shutters or birefringent materials. Further, contamination of optical transmission surfaces with dust or corrosive agents limits the performance of the sensors, particularly in industrial or harsh environments.
• the present invention provides an optical displacement sensor comprising an elongate flexible optical element suitable for the passage of light axially therethrough, the optical element being deformable by displacement of a first portion thereof relative to another portion; a light source optically coupled to one end of the optical element for transmitting light radiation into the optical element; and a light detector for detecting the light radiation after passage through the optical element, the light detector providing an output indicative of the intensity of light detected, wherein the detector output is responsive to variation in the intensity of light transmitted through the optical element as a result of deformation thereof, characterised in that the optical element is a tubular member.
• light as used in this specification and claims is intended to include not only visible light, but also infrared or ultraviolet radiation, unless stated otherwise or the context does not permit.
• the tubular member is a thin polymer tube having a reflective internal surface.
• the surface may be mirrored, but not necessarily so. Light is transmitted through the tube by a combination of direct radiation and reflection from the internal surface.
• the intensity or amount of light output from the tubular member will vary with deflection or bending of that member.
• This property or characteristic enables the flexible member to be used as an optical displacement sensor.
• one end of the tubular member may be fixed to a reference point and the other end may be connected, either directly or indirectly to the measurand. Any displacement of the end connected to the measurand caused by movement of the measurand can be detected by variation in the output of the light detector. Other fixing arrangements can be used.
• both ends of the flexible tubular member may be fixed to reference points, and an intermediate portion connected, either directly or indirectly to the measurand.
• several measurands may be connected to points on the tubular member thereby permitting the sensor to detect movement of one or all of a plurality of measurands.
• Multiple sensor tubes may be used in any one displacement sensor. Such tubes can be coupled optically in series by optical fibre.
• the light source is typically a light emitting diode which is optically coupled to one end of the flexible member via an optical fibre. Appropriate focusing and coupling means are provided, if required. A coherent light source is not necessarily required.
• the light detector is typically an optoelectric device such as a commonly available photodiode or phototransistor which provides an electrical output dependent on the light received. This output can be connected to appropriate electronic circuitry containing filtering, amplification and signal processing circuits.
• the light detector is preferably coupled to the other end of the flexible member via an optical fibre.
• the light source and light detector are typically at opposite ends of the sensor tube.
• both the light source and light detector are located at the same end of a tubular optical fibre which acts as the sensor. .
• light radiation from the light source passes through the tubular fibre and is reflected back to the detector, i.e. the light passes twice through the sensor tube.
• the flexible tubular sensor fibre can be mounted in cantilever fashion with one end fixed to a reference point and its free end movable in response to the measurand.
• the optical displacement sensor of this invention has several advantages. First, it is simple and inexpensive to construct and install, and does not require complex light transmission or detection equipment.
• the senor has high sensitivity and can be used to detect small displacements.
• the simple basis of operation of the sensor results in a high degree of reliability.
• the sensor has all the advantages of optical fibre instrumentation, such as noise immunity, electrical isolation and ease of miniaturisation.
• Fig.l is a schematic sectional diagram of the optical displacement sensor of this invention, showing various modes by which light may be attenuated by the sensor tube;
• Fig.2 is a schematic diagram of a one embodiment of the optical displacement sensor
• Fig.3 is a schematic diagram of a second embodiment
• Fig.4 is a diagram illustrating one application of the sensor of Fig.3; and Fig.5 is a sample output of the sensor of Fig.4.
• the optical displacement sensor 10 of a first embodiment of this invention comprises a sensor tube 13 joined to a pair of optical fibres 11,.12 at its opposite ends.
• the optical fibres 11, 12 are typically 1mm diameter polymer optical fibres (with protective sleeves), although the length, size and type of optical fibres may be varied to suit particular applications.
• the sensor tube 13 is a flexible compliant tube with an internal diameter matching that of the core of each optical fibre 11, 12. In this manner, the cores of optical fibres 11, 12 may be easily coupled to opposite ends of the sensor tube 13.
• the sensor tube 13 is reflective on its internal surface and provides only minimal attenuation to the passage of light when not distorted due to internal reflection.
• the reflective internal surface may be provided either by inherent nature or by specific manufacture, i.e. a metallised coating.
• Suitable flexible materials for the sensor tube include plastics such as vinyl and rubbers, both natural and synthetic.
• the outer surface of the tube is typically opaque to shield the sensor from ambient light.
• a light source typically an infrared or visible light emitting diode 14, is optically coupled to the free end of optical fibre 11.
• the output of the detector 15 is connected to an electronic circuit providing the necessary amplification, filtering, and an output display, if required.
• the output of the detector electronics can also be used to control dependent apparatus.
• any deflection or distortion of the flexible sensor tube 13 caused by deforming forces A, B, or difference in pressures pi, p2 outside and within the tube 13, will affect the transmission of light therethrough, namely by changing the number of internal reflections which the light undergoes. More specifically, if the number of internal reflections is increased as a result of a change in the configuration of the tube 13, the intensity of light transmitted through the tube 13 will be decreased as each reflection is less than 100% efficient. Thus, any deflection of the sensor tube 13 caused by displacement of one portion thereof relative to another will be detected by variation in the amount of light received by optodetector 15.
• Variations (if any) in the intensity of light emitted by diode 14 can be avoided by an electronic light intensity referencing circuit connected to the diode, or accommodated by a second parallel optical fibre between diode 14 and light detector 15, acting as a reference beam.
• optical displacement sensor 10 is the ability to detect small deflections or displacements, while being electrically isolated from the measurand or deflecting member. Further, the pliant sensor 10 is highly sensitive to displacement forces, yet robust in construction.
• FIG.2 A modified version of the embodiment of Fig.l is shown in Fig.2.
• light from a light source 21 is focused by lens 22 for transmission through a tubular fibre 23.
• the light is reflected at the distal end of the tube 23, and is detected by an optodetector 25 which typically is a photodiode or phototransistor. Discrimination of the incident light from the reflected light is performed optically as shown in the arrangement of Fig.2.
• Light from the light source 21 passes twice through the tubular sensor fibre 23 before detection by the optodetector 25. Any distortion 24 of the tubular sensor fibre will attenuate the amount of light received by optodetector 25.
• the intensity of light detected by optodetector 25 provides an indication of the deflection or displacement 24 of the free end of tubular sensor fibre 23.
• Deflection or displacement of the sensor tube or fibre may be either direct or indirect.
• Direct distortion can occur, for example, when the sensor tube is adherent at an intermediate point to the measurand and anchored to two reference points on either side thereof. Further, the sensor tube may be adhered to the measurand at several points, with its ends anchored to reference points. In this manner, complex deflection curves may be sensed.
• the embodiment of Fig.2 is particularly suitable for this type of application.
• Indirect distortion can occur through the transmission of force through a system of levers or other interconnecting components in order to introduce some mechanical gain (or loss) or alter the linearity (or otherwise) of the optical sensing system.
• FIG.3 An embodiment of the optical sensor, adapted for the specific purpose of angular displacement sensing, is shown in Fig.3.
• a light source (not shown) is optically coupled to one end of an optical fibre 31, the other end of which is connected to one end of a flexible sensor tube 32, e.g. in the manner shown in the top portion of Fig.l.
• the optical fibre 31 (provided with a protective sleeve) is held within a channel in a rigid strip member 36.
• sensor tube 32 is connected to a second optical fibre 33, the other end of which is connected to a second sensor tube 34.
• the second optical fibre 33 (in its protective sleeve) is held in a U-shaped channel in a second rigid flap member 35.
• the other end of the second sensor tube 34 is connected to a third optical fibre 37 which is similarly located (in its protective sleeve) within a channel in rigid strip member 36, parallel to optical fibre 31.
• the distal end of optical fibre 37 is optical coupled to a optodetector device (not shown).
• the connections between the optical fibres and the sensor tubes are generally as shown in Fig.l.
• the sensor tubes 32, 34 form connecting bridges between strip 36 and flap 35.
• the sensor tubes 32, 34 are flexible, they form a hinge-like connection between the flap 35 and strip 36, permitting the flap 35 to pivot about that hinge connection. As the flap 35 pivots about the hinge connection formed by sensor tubes 32, 34, the tubes are deformed by bending, thereby affecting the passage of light therethrough. The angular displacement of flap 35 is thereby detected by the change of intensity in light received from optical fibre 37.
• the optical sensor 30 is used to detect respiratory movements in small animals, e.g. a mouse 41.
• the optical fibre 31 is optically coupled to a light source (not shown), suitably via a SWEET SPOTTM housing and connector.
• the light source is typically a 660 nm (red) light emitting diode with an integral lens to permit optical coupling to one end of the optical fibre 31.
• the end of the fibre 37 is connected to, and optically coupled with a light detector (not shown).
• the rigid strip 36 is fixed relative to the probe on which the mouse rests, but the flap 35 is pivotable relative to the strip 36.
• the flap 35 is lightly biased against the abdomen of the mouse.
• the optical sensor 30 of Fig.4 derives from the abdomen of the animal 41 a motional signal indicative of the respiratory movement of the animal.
• Intensity modulation is preferred in distinction to more complex frequency and phase modulation commonly used in (solid) optical fibre sensing.
• Light in the visible range of the spectrum is preferred due to lower attenuation in the tubular fibre and ease of troubleshooting.
• the animal 41 is anaesthetised.
• the source and detector fibres 31, 37 are then connected to the light source and optodetector, respectively.
• Light from the source passes through the sensor tubes 32, 34 and into detector fibre 37 where it is detected by the optodetector.
• the output of the optodetector provides the electrical signal source for further amplification and filtering.
• the respiratory movement sensor described above has been trialled on adult Wistar rats and adult Quackenbush mice, and a gatable or trigger signal suitable for use in imaging, for example, has been acquired reliably with both species. Trials in excess of three hours have been performed.
• the output signal has been displayed on an oscilloscope, after appropriate amplification and filtering. A representative oscilloscope trace is shown in
• Fig.5. It is to be noted that the output display indicates movements due to inspiration and expiration, hence providing an indication of when the abdominal organs are stationary.
• the abovedescribed optical sensor provides a relatively inexpensive and simple means of monitoring respiration of small animals. Other uses or applications of the optical sensor of this invention are described briefly below. 1. Apnoea Alarm
• Apnoea or the cessation of breathing, is a relatively common problem in acute care situations for both children and adults.
• Paediatric apnoea alarms are used extensively in intensive care units where prematurity or other illness predeposes infants to apnoeic episodes.
• Known apnoea alarms use instrumentation to monitor respiration in the spontaneously breathing infant by measuring chest wall (e.g. electrical) impedance or by using various forms of a movement responsive blanket placed under the infant.
• chest wall e.g. electrical
• the optical displacement sensor can be used as a "stand alone” unit, or as a component module of more comprehensive monitors used in intensive 20 care units.
• optical displacement sensor of this invention can be used as a simple and reliable alternative
• the electrical output of the optical sensor is appropriately gated to provide a trigger signal indicative of respiratory movement.
• the optical displacement sensor of this invention can be used to monitor both inspiration and expiration phases of the respiratory cycle, and to provide the appropriate timing signal for imaging.
• the optical fibre sensor is particularly advantageous when used with nonverbal or preverbal subjects.
• a similar application is in the field of nuclear medicine where repeated signal acquisitions are averaged to improve image quality.
• One or more displacement sensors appropriately placed can indicate the degree of mobility of a subject. Such an implementation may be of use in the study of hyperactivity or movement disorders.
• Impotence or the failure to achieve an erection, is typically first investigated by NPT studies in a sleep study lab.
• the subject is observed for nocturnal erections usually associated with REM sleep. Failure to produce results delineates organic or physiological disease from a psychological cause.
• the optical displacement sensor of this invention for example the embodiment of Fig.3, can be easily adapted for use in NPT monitoring.
• Flexion and extension of most joints can be monitored using the optical displacement sensor of this invention.
• the rate of flexion can be
• the optical displacement sensor of this invention 20 can be used as a pressure transducer by detecting pressure sensitive movement. For example, if the sensor tube is hermetically sealed, the tube will be deformed by a pressure differential between the fluids inside and outside the tube. Such 25 deformation will be detected by the optical sensor. In this manner, the sensor can be used as a pressure transducer.
• the flexibility of the sensor tube material as well as the internal pressure are chosen to suit the particular 30 application of the pressure transducer.This mode of use is not limited to in vivo monitoring but can encompass domestic and industrial applications.
• Deformation of structures or vessels in remote or hazardous environments may be performed with the aforementioned sensor.
• the sensing tube may be attached to the structure along its entire length or in a number of points.
• the sensor therefore acts as a safety device in signalling failure of critical structures and rupture (or pending rupture) of vessels or conduits. Illicit deformation of elements may occur through vandalism or forced entry to premises. Vulnerable portals may be implemented with such a sensor to detect displacement of component elements.
• the sensor may be concealed in a compliant material thus forming a pressure sensitive mat. Such a device will produce an optical signal similar to that described above.
• the optical displacement sensor of this invention has widespread use as a movement detector. Any displacement or deformation of the sensor tube as a result of movements as small as 1mm (or even less) can be reliably detected.
• the optical displacement sensor therefore finds general application as a limit switch, movement detector for burglar alarms, position feedback indicator in closed loop control systems, etc.
• the output of the optodetector would normally be fed to an electrical circuit for filtering, amplification and/or level discrimination.
• the detector output may be fed to a microprocessor-based circuit to provide automatic gain and level triggering, as well as software-based self diagnostic facilities.
• the degree of reflectivity of the internal surface of the sensor tube may be varied to vary the sensor's characteristics and performance.

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• 1993
  • 1993-05-05 EP EP93911687A patent/EP0639260A4/fr not_active Withdrawn
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