Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P3/00—Measuring linear or angular speed; Measuring differences of linear or angular speeds
  • G01P3/36—Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light
  • G01P3/38—Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light using photographic means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02094—Speckle interferometers, i.e. for detecting changes in speckle pattern
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/0201—Interferometers characterised by controlling or generating intrinsic radiation properties using temporal phase variation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02012—Interferometers characterised by controlling or generating intrinsic radiation properties using temporal intensity variation
  • G01B9/02014—Interferometers characterised by controlling or generating intrinsic radiation properties using temporal intensity variation by using pulsed light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02015—Interferometers characterised by the beam path configuration
  • G01B9/02029—Combination with non-interferometric systems, i.e. for measuring the object
  • G01B9/0203—With imaging systems
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02041—Interferometers characterised by particular imaging or detection techniques
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02041—Interferometers characterised by particular imaging or detection techniques
  • G01B9/02045—Interferometers characterised by particular imaging or detection techniques using the Doppler effect
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
  • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P3/00—Measuring linear or angular speed; Measuring differences of linear or angular speeds
  • G01P3/36—Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light
  • G01P3/366—Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light by using diffraction of light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
  • G01B2290/45—Multiple detectors for detecting interferometer signals

Definitions

• the present invention relates to a method and system for monitoring at least one parameter of a moving object.
• Orientation and position of a device is known and may comprise six degrees of freedom (three of translation and three of rotation).
• a speckle pattern is a micro-pattern of illumination generated by a coherent light source, such as a laser, when it passes through a diffuser or when it scatters from a surface which has irregularities larger than the wavelength of the illumination.
• Streams of laser speckle images are used in some types of computer mice to calculate 2D velocity vectors tracking motion of the mouse. Disparities between corresponding speckles in images of the same speckle pattern taken at different times give information about 2D displacement.
• the invention relates to a method and system for monitoring at least one parameter of an object.
• object may be a single element, a subject, a body's part of at least one individual people, or a group of elements or subjects or a surface thereof.
• the body's part may be a passive soft tissue.
• the object may be a back reflecting surface being uniform or not.
• the parameters may be physiological parameters/conditions of an individual.
• an imaging system for monitoring at least one parameter of movement of a moving object, the system comprises at least one imaging unit comprising an optical transformer configured and operable for applying spatial image space transformation of at least one parameter of movement into geometric relation, by translating different components of six degrees of freedom of movement in a three - dimensional space into a lateral translation; wherein the imaging unit is configured and operable for imaging the moving object on an image plane and generating image data indicative of the moving object in an x-y plane; the imaging system generating motion data indicative of the six degrees of freedom of movement. Therefore, the imaging unit is configured to generate x-y plane information and to apply direct transformation of movement within the object into an imaging plane.
• the optical transformer applies at least one of Fourier transform, Mellin transform, coordinate transform such as Cartesian coordinates transform into (log(r), ⁇ ) when r is a radial coordinate and ⁇ is an angular coordinate or circular harmonic transform.
• a motion of a surface can be split into such components as transversal motion, axial motion, and tilt (the axis connects the surface of interest with the imaging unit).
• the technique of the invention has an enhanced sensitivity to the tilt, which on the imager sensing plane (PDA) primarily causes speckle pattern shifting.
• the transversal motion of the surface of interest causes shifts and changes of the speckle pattern image, but in cases when imaging utilizes focusing on a displaced (e.g. forward or downward displaced) plane (i.e. unfocused image) thus caused shifts are often significantly smaller than the shifts caused by the tilt.
• the spatial image space transformation is a Fourier transformation.
• the imaging unit is selectively operable to provide an unfocused image of the object in the object plane, collect a sequence of secondary speckle patterns and determine at least one shift between regions of the object which appear in the sequence of secondary speckle patterns, to thereby provide motion data indicative of motion of the object along a tilt dimension and image data in an x-y plane.
• the unfocused imaging may be performed by the imaging unit configured for imaging the moving object on an image plane, or by another imaging unit being unfocused on the object in the object plane.
• the system further comprises a pinhole for collecting a portion of the secondary speckle patterns.
• an imaging system for monitoring at least one parameter of movement of a moving object, the system comprises an imaging unit comprising a detector having certain detection sessions; a source of at least partially coherent light generates a beam of at least partially coherent light having a predetermined frequency modulation.
• the frequency modulation of the source is selected to overcome the detector limited frame per second rate, due to the increased frequency changes of the interference fringe pattern.
• the frequency modulation of the source is selected with respect to the frequency range of the surface movement of the object.
• the coherent illumination is in the form of pulsed light having a modulation frequency selected to enable correlation between illumination and detection sessions (sampling rate). Therefore, the pulsation of the source allows the detection of fast vibrations by slow camera.
• an imaging system for monitoring at least one parameter of movement of a moving object, the system comprises an imaging unit comprising a detector; an interferometric module configured and operable to detect an interference pattern indicative of phase shifts of the object being indicative of temporal changes along a z-axis; the interferometric module comprises at least one beam splitter/combiner configured for receiving at least partially coherent light beam, splitting the beam into object and reference beams propagating along substantially identical optical paths; and at least one mirror arrangement located in the reference beam path and configured for reflecting the reference beam towards the detector through the beam splitter/combiner where it interferes with an object response to interaction with the object beam, wherein the at least one mirror arrangement is configured for displacement at a predetermined frequency to induce controllable temporal modulation of the interference pattern.
• the interferometric module provides an interference pattern indicative of temporal changes at a surface of the object in the z- axis.
• a Mach-Zehnder interferometer is used.
• the interferometric module may be a stand alone module of the imaging system or may be integrated in the imaging unit.
• the system comprises an illumination source generating a beam of at least partially coherent light having a predetermined frequency modulation.
• the frequency modulation of the source is selected to overcome the detector limited frame per second rate, due to the increased frequency changes of the interference fringe pattern. Moreover, the frequency modulation of the source is selected with respect to the frequency range of the surface movement.
• the coherent illumination is in the form of pulsed light having a modulation frequency selected to enable correlation between illumination and detection sessions (sampling rate). Therefore, the pulsation of the source allows the detection of fast vibrations by slow camera.
• the system comprises a filter placed in the reference path and configured for equalizing intensities of light propagating along the reference and object paths.
• the system comprises a feedback circuit placed between the detector downstream of the reference path, the feedback circuit being configured for correcting frequency multiplication.
• the system is configured such that the tilt and z-axis data are concurrently obtained on the same imaging unit/detector.
• the imaging unit utilizes the object path as an imaging channel to produce unfocused image of the object by receiving a reflected secondary speckle pattern originated at the object (due to movement /vibrations in at least a part of the object) and provides image data indicative of the changes in the speckle pattern in the x-y plane, i.e. tilt with respect to x-y plane.
• the collection of the tilt and z-axis data can be time separated.
• the mirror of the interferometric module may be controllably moved to induce controllable temporal modulation of the interference pattern. This enables to separate between the tilt and z-axis data in the detected image.
• the technique provides a detection of a surface movement in the x-y plane having a tilt component with the detection of temporal changes of the surface in the z-axis.
• the technique of the present invention combines imaging of a coherent speckle pattern of a surface movement with detection of interference changes being indicative of vibrations of the surface in the z-axis at the same scan time.
• the technique includes imaging of a coherent speckle pattern formed by an object or subject or, generally, a surface of interest.
• the pattern can be formed by illumination of the still or moving surface of interest by coherent light of a laser or another light source.
• the surface movement can be for example of vibration type.
• the vibration can be caused by a sound or vibration itself can produce a sound, thus making the motion of the surface of interest associated with the sound.
• the system comprises a support surface for supporting the object and applying a periodic stimulation to the object.
• a method for monitoring at least one parameter of movement of a moving object comprises applying a spatial image space transformation to at least one parameter of a movement into geometric relation, by translating different components of six degrees of freedom of movement in a three-dimensional space into a lateral translation; imaging the moving object on an image plane; and generating motion data being indicative of six degrees of freedom of movement.
• a method for monitoring at least one parameter of movement of a moving object comprises imaging the moving object on an image plane; detecting an interference pattern indicative of phase shifts of the object being indicative of temporal changes along a z-axis; and controllably inducing controllable temporal modulation of the interference pattern.
• the method comprises illuminating the moving object with at least partially coherent electromagnetic beam.
• a coherence length for the coherent beam may be selected to provide a desired ratio between a size of an illumination spot and size of the speckles in a captured set of patterns.
• the method comprises applying a stimulation field of a periodically changing stimulation frequency to an object.
• the method comprises concurrently imaging the interference pattern onto the imaging plane.
• the method comprises timely separating between the interference pattern and the motion data. In some embodiments, the method comprises measuring at least one of velocity and frequency of the moving object along the z-axis.
• the coherence length of illumination is selected to be shorter than a typical distance between the object and such surface. Therefore, in some embodiments, the method comprises separating between the moving object and a reflecting surface at least partially surrounding the object by selecting the coherence length of the at least partially coherent electromagnetic beam to be shorter than a typical distance between the object and the reflected surface.
• Fig. 1 represents a schematic illustration of the main modules of the imaging system of the present invention, according to a broad aspect of the present invention
• Fig. 2a represents a schematic illustration of the main modules of the imaging system of the present invention, according to another broad aspect of the present invention
• Fig. 2b represents a specific and non-limiting schematic illustration of the operation of a possible configuration of the imaging system according to some embodiments of the present invention
• FIG. 3 representing an example of a configuration of the imaging system according to some embodiments of the present invention
• Fig. 4 shows speckle pattern and the fringes pattern
• Fig. 5 represents an optical configuration of an embodiment of the imaging system in which the mirror arrangement is configured for displacement at a predetermined frequency to induce controllable temporal modulation of the interference pattern;
• Fig. 6 shows the correlation between illumination and detection sessions in which spectral replications of the detection sessions are acquired due to pulses of the laser
• Fig. 7 represents a specific and non-limiting example of an imaging system of the present invention
• Figs. 8a-8g show laser modulation results
• Figs. 9a-9b show mirror modulation results
• Fig. 10 shows laser and mirror arrangement modulation results.
• the position and orientation of a rigid body in space is defined by six degrees of freedom: three components of translation (x-, y-, and z-) and three components of rotation (roll-, pitch-, and yaw-rotations).
• a motion of a surface can be split into such components as transversal motion, axial motion, and tilt (the axis connects the surface of interest with the imaging unit).
• an optical transformation is applied to at least one parameter of a movement to provide a geometric relation between the parameter of the movement and a spatial image space, by translating different components of six degrees of freedom of movement in a three- dimensional space into a lateral translation.
• the moving object is then imaged on an image plane and motion data being indicative of six degrees of freedom of movement is generated.
• the optical transformation comprises at least one of Fourier transform, circular harmonic transform, Mellin transform, coordinate transform such as e.g. Cartesian (x,y) coordinates into (log(r), ⁇ ) when r is a radial coordinate and ⁇ an angular coordinate.
• Fig. 1 representing a schematic illustration of the main modules of the imaging system of the present invention, according to a broad aspect of the present invention.
• the imaging system 100 is aimed at monitoring at least one parameter of movement of a moving object.
• the system 100 comprises at least one imaging unit 10 configured and operable for imaging the moving object on an image plane and generating image data indicative of the moving object in an x-y plane.
• the imaging unit 10 comprises an optical transformer 12 configured and operable for applying an optical transformation of at least one parameter of movement into geometric relation between the parameter of the movement and a spatial image space, by translating different components of six degrees of freedom of movement in a three- dimensional space into a lateral translation.
• the optical transformer 12 is configured and operable to convert different movement characteristics into geometric relations.
• the optical transformer 12 is an optical element, placed in the aperture plane of the imaging unit 10 configured to apply an optical transformation and to therefore detect the different components of the movement of the inspected tissue/object. Therefore, the imaging system 100 generates motion data indicative of the six degrees of freedom of movement.
• the optical transformer 12 applies at least one of Fourier transform, Mellin transform, coordinate transform such as Cartesian coordinates transform into (log(r), ⁇ ) when r is a radial coordinate and ⁇ is an angular coordinate or circular harmonic transform. Therefore, the system and method of the present invention provides modified optical transformations for remote sensing of six degrees of freedom of any general movement.
• the optical transformer 12 may be a coordinate transformation filter or any general linear optical transformer described for example in Z. Zalevsky and D. Mendlovic, "Optical implementation of the Bode transform," Appl. Opt. 34, 828-831 (1995), Zalevsky, D. Mendlovic and G.
• the imaging unit 10 is selectively operable to provide an unfocused image of the object in the object plane, collect a sequence of secondary speckle patterns and determine at least one shift between regions of the object which appear in the sequence of secondary speckle patterns, to thereby provide motion data indicative of motion of the object along a tilt dimension and image data in an x-y plane.
• the sequence of secondary speckle patterns is focused on a plane displaced from the moving object.
• the speckle pattern method is based upon temporal tracking of a secondary reflected speckle by imaging the speckle through properly defocused optics.
• the tilting changes of the object surface reflect the movement of the speckle pattern in the x-y plane.
• the spatial image space transformation is a Fourier transformation (far field defocused imaging) which converts tilting changes into movement of the speckle patterns.
• the system 100 comprises a speckle pattern collecting unit 14 being unfocused on the object in the object plane and collecting a plurality of sequential secondary speckle patterns thereby generating data indicative of an image of the object in an x-y plane and determining at least one shift between regions of the object which appear in at least first and second images of the object, to thereby provide data indicative of motion of the object along a tilt dimension and image data in an x-y plane.
• the imaging unit 10 may comprise a processing utility 16 configured to determine the shift between the sequence of secondary speckle patterns and provide motion data indicative of motion of the object along a tilt dimension and image data in an x-y plane.
• the processing utility 16 may be a DSP, microcontroller, FPGA, ASIC, etc., or any other conventional and/or dedicated computing unit/system.
• the term "processing utility” should be expansively construed to cover any kind of electronic device with data processing capabilities, including, by way of non-limiting example, personal computers, servers, computing systems, communication devices, processors (e.g. digital signal processor (DSP), microcontrollers, field programmable gate array (FPGA), application specific integrated circuit (ASIC), etc.) and other electronic computing devices.
• DSP digital signal processor
• FPGA field programmable gate array
• ASIC application specific integrated circuit
• the processor utility may comprise a general-purpose computer processor, which is programmed in software to carry out the functions described hereinbelow.
• processing utility 16 is shown in Fig. 1, by way of example, as an integrated unit of the imaging unit 10, some or all of the processing functions of processing utility 16 may be performed by suitable dedicated circuitry within the housing of the imaging unit 10 or otherwise associated with the imaging unit 10 or may be a separate stand alone utility.
• suitable dedicated circuitry within the housing of the imaging unit 10 or otherwise associated with the imaging unit 10 or may be a separate stand alone utility.
• operations in accordance with the teachings herein may be performed by a computer specially constructed for the desired purposes or by a general purpose computer specially configured for the desired purpose by a computer program stored in a computer readable storage medium.
• the software may be downloaded to processing utility 16 in electronic form, over a network, for example, or it may alternatively be provided on tangible media, such as optical, magnetic, or electronic memory media.
• some or all of the functions of the processing unit 16 may be implemented in dedicated hardware, such as a custom or semi-custom integrated circuit or a programmable digital signal processor (DSP). Therefore, the system and the method of the present invention provide a remote sensing of six degrees of freedom of any general movement.
• DSP programmable digital signal processor
• the imaging unit 10 or the speckle pattern collecting unit 14 are selectively operable to provide an unfocused image of the object in the object plane (far field imaging).
• the processing utility 16 analyses the temporal changes of the speckle patterns and convert the movement of the speckles into the tilting information of the movement while the x-y information as well as the z-axis movement will not modify the speckle patterns.
• focused image of the object is performed by the imaging unit 10 (not speckles but regular imaging)
• the x-y movement and probably also the z-axis movement can be determined.
• the imaging system 100 provides a modified sensing system having two image channels having both a defocused image in which the speckle patterns are analyzed and a regular focused image of the object (regular image and not speckle patterns analysis).
• the combination of the far field speckle pattern and of a near field image provides the capability to extract more information about the movement characteristics.
• the near field image gives information about movement in the x-y plane and possible also about z-axis movement and the far field speckle pattern analysis gives angular tilting dimension.
• Another technique to monitor at least one parameter of movement of the moving object comprises imaging the moving object on an image plane; detecting an interference pattern indicative of phase shifts of the object being indicative of temporal changes along a z-axis; and; controllably inducing controllable temporal modulation of the interference pattern.
• Fig. 2a representing a schematic illustration of the main modules of the imaging system of the present invention, according to another broad aspect of the present invention.
• the imaging system 200 comprises an imaging unit 20 comprising a detector 22 and an interferometric module 24 configured and operable to detect an interference pattern indicative of phase shifts of the object being indicative of temporal changes along a z- axis.
• the interferometric module 24 is used to detect the temporal changes of the surface in the z-axis.
• the interferometric module 24 is represented as a stand alone unit, which may comprise its own detector as illustrated for example in Fig. 3, the interferometric module 24 may be integrated with the imaging unit 20 such that the interference pattern is concurrently imaged onto an imaging plane of the imaging unit 20. Therefore, in some embodiments, imaging unit 20 comprises interferometric module 24.
• a Mach- Zehnder interferometer configuration can be used. The at least partially coherent light beam is split into two similar paths when only one path is reflected from the moving object. The result is phase shifts between the two beams caused by a change in length of one of the paths.
• the vibration of the surface in the z-axis changes the path length of one of the Mach- Zehnder laser paths. These changes reflect in the interference pattern (fringes) of the two joined beams on the detector and camera plane. The number of wavelength contained in the path's length difference changes the fringes oscillating frequency.
• LDV laser Doppler vibrometer
• the velocity of the object surface vibration in the z-axis is measured. The vibration velocity and frequency are extracted from the Doppler shift of the reflected partially coherent beam due to the motion of the surface as will be detailed further below. Therefore, the technique of the present invention measures at least one of velocity and frequency of the moving object along the z-axis to thereby enable to timely separating between the interference pattern and the motion data.
• the imaging system receives an at least partially coherent light beam being indicative of at least one parameter of movement of a moving object.
• the at least partially coherent light beam is separated in two paths: an object path and a reference path.
• the at least partially coherent light beam of the object path is received by the imaging unit being selectively operable to provide an unfocused image of the object in the object plane which generates motion data indicative of motion of the object along a tilt dimension.
• the method comprises positioning the imaging unit to provide an unfocused image of the object in the object plane and collecting at the imaging unit a sequence of secondary speckle patterns and determining at least one shift between regions of the object appearing in the sequence of secondary speckle patterns.
• the imaging unit may thus be selectively operable to provide an unfocused image of the object in the object plane, collect a sequence of secondary speckle patterns and determine at least one shift between regions of the object which appear in the sequence of secondary speckle patterns, to thereby provide motion data indicative of motion of the object along a tilt dimension and image data in an x-y plane.
• the sequence of secondary speckle patterns is focused on a plane displaced from the moving object.
• the speckle pattern method is based upon temporal tracking of a secondary reflected speckle by imaging the speckle through properly defocused optics.
• the tilting changes of the object surface reflect the movement of the speckle pattern in the x-y plane.
• the object path and the reference path are introduced into an interferometric module configured and operable to detect an interference pattern indicative of phase shifts of the object being indicative of temporal changes along a z-axis.
• the imaging system 300 comprises an interferometer module 302 including at least one beam splitter/combiner 304 configured for receiving at least partially coherent light beam, splitting the beam into object and reference beams noted Oi and R respectively propagating along substantially identical optical paths and at least one mirror arrangement 306 located in the reference beam path and configured for reflecting the reference beam R towards a detector 308 through beam splitter/combiner 304 where it interferes with an object response noted O3 to interaction with the object beam.
• the imaging system 300 may include a source of at least partially coherent light 310. The speckle pattern and the fringes pattern are shown in Fig. 4.
• Fig. 5 illustrating an optical configuration of an embodiment of the imaging system 400 in which the mirror arrangement 306 is configured for displacement at a predetermined frequency f 2 to induce controllable temporal modulation of the interference pattern.
• the illumination source 310 may generate pulsed light having a modulation frequency fi selected to enable correlation between illumination and detection sessions.
• the secondary speckle patterns created by direct illumination of an object are acquired for extracting tilting information.
• the correlation of each of the sequential speckles images is measured.
• relative tilting movement of the object is extracted.
• the relative shift ⁇ of the speckle pattern is proportional to the change in the spatial position of the speckle pattern due to the object temporal tilting movement: P ⁇ I
• ⁇ is the illumination wavelength.
• the temporal tilting movement of the object is proportional to the change in the speckle pattern.
• an interferometer operated with phase shift measurements provides z- axis information. Therefore, in order to monitor the z-axis vibration interference, behavior measurements were used.
• the constructive and destructive interferences pattern of the fringes imaging is according to the length difference between the two paths:
• AL the two paths length difference
• n the number of the illumination wavelength.
• the modulation frequency is such that the difference between it and the object frequency bandwidth is in the detector limited frame rate:
• the imaging system of the present invention is capable to perform pulsation of the illumination source at frequency fi and/or modulation of the interferometer mirror at frequency of ⁇ 2.
• a sequence of secondary speckle patterns are collected at the detector plane.
• a speckle pattern has a frequency of ⁇
• fringes of the interference pattern has a frequency of ⁇ 2.
• Fig. 6 schematically demonstrates how due to the pulsation of the illumination source 310 high temporal frequencies e.g.
• this embodiment of the imaging system provides a modified interference based configuration for remote sensing of six degrees of freedom of any general movement.
• the imaging system 500 comprises inter alia an illumination source 510 generating an at least partially coherent light beam.
• the imaging system 500 also comprises a beam splitter 504 configured for receiving at least partially coherent light beam, splitting the beam into object and reference beams noted O and R respectively propagating along substantially identical optical paths and a mirror arrangement located in the reference beam path and including in this example three adjustable mirrors noted as 506a and 506b.
• Adjustable mirrors 506a are configured for reflecting the reference beam R towards a camera 509 where it interferes with an object response noted O to interaction with the object beam through a second beam splitter/combiner 505.
• the mirror arrangement can change the length of the reference path in order to calibrate the interferometer with two similar paths and according with its coherence length. Since the at least partially coherent light beam in the reference path gets to the camera 509 directly, while the at least partially coherent light beam in the object path is acquired by reflection from the object, thus the intensities of the at least partially coherent light beams from the two paths on camera 509 are not the same. For that reason a filter 511 may be placed in the reference path to equal the two path intensities of light propagating along the reference and object paths.
• the imaging system 500 also comprises a detector 508.
• camera 509 is configured and operable to monitor the tilting shift by tracking the speckle movement (or imaging the object), while detector 508 is configured and operable to monitor the axial movement of the object. These two functions may be performed by the same imaging element.
• the detector 508 is configured to receive/collect the speckle patterns and the interference fringes in order to perform the movement estimation.
• a pinhole 513 may be used for collecting a portion of the secondary speckle patterns and may be attached to the detector 508.
• the pinhole is of 200 ⁇ .
• system 500 further comprises a feedback circuit 512 placed between detector 508 downstream of the reference path.
• the feedback circuit 512 is thus placed from the detector 508 back to the reference path and is configured for correcting frequency multiplication. It should be understood that for stabilization of the fringes pattern imaging, the frequency multiplication caused by the number of wavelengths contained in the object path difference should be corrected.
• the feedback circuit 512 comprises a differentiator amplifier through which the output signal from the detector 508 passes with negative feedback.
• the differentiator amplifier may be powered by a DC power supply.
• the output derived signal from the amplifier derived an analogue amplifier driver controls a piezoelectric actuator 507 attached to a controlled mirror 506b of the mirror arrangement 506 in the reference path.
• the controlled mirror movement compensates the instability of the frequency multiplication due to the number of wavelength in the path length changes.
• the system 500 comprises a support surface for supporting the object and applying a periodic stimulation to the object. In this way, a stimulation field of a periodically changing stimulation frequency can be applied to an object.
• the illumination source 510 is controlled to select a coherence length for the at least partially coherent beam to provide a desired ratio between a size of an illumination spot and size of the speckles in a captured set of patterns.
• the system 500 enables the separation between different movements of the various components of the object. More generally, by using a degree of partial coherence and/or a plurality of wavelengths more information about the inspected object (e.g. having a back reflecting surface) may be extracted.
• a degree of partial coherence and/or a plurality of wavelengths more information about the inspected object (e.g. having a back reflecting surface) may be extracted.
• back reflections of the laser beam are originated from the surface of the shirt as well as from the tissue of his body underneath the shirt (e.g. from his chest).
• the technique of the present invention generates such a separation by using a controlled partial coherence of the illumination source 501 (spatial or temporal).
• the coherence length of the at least partially coherent beam may be selected to be shorter than the distance between the tissue and the shirt to prevent the interference between the two different speckle patterns.
• the two different speckle patterns can be separate via image processing as each one of them has different temporal dynamics. This may be implemented by the processing utility 16 shown in Fig. 1. Therefore, the technique of the invention comprises separating between the moving object and a reflecting surface at least partially surrounding the object by selecting the coherence length of the at least partially coherent electromagnetic beam to be shorter than a typical distance between the object and the reflected surface.
• the technique of the invention comprises separating between the moving object and a reflecting surface at least partially surrounding the object by generating at least two wavelengths having different linear mixture coefficients.
• the illumination source 510 was a laser diode of the firm Phot op Suwtech of the type DPGL-2100F having a wavelength of 532 nm and a power of max 300 mW operated with a driver (Photop LDC-2500S);
• the detector 508 was a Si switchable gain detector of the type Thorlabs PDA100A-EC, 340-1100 nm, 2.4 MHz BW, 100 mm2;
• the camera 509 was of the type PixelLink PL-B761U;
• the piezoelectric actuator 507 was a low voltage piezoelectric actuator controlled by an analogue amplifier of the type Piezomechanik SVR 1000-1 ;
• the DC power supply powering the differentiator amplifier was of the type Lion LE-3003D-3;
• the support surface was a speaker of the type OSC LS13C050, 2 1/4" Diameter, 50 ohm 0.5 Watt controlled by a signal generator (Tektronix AFG1022).
• the system 500 also
• an imaging system for monitoring at least one parameter of movement of a moving object comprises an imaging unit comprising a detector having certain detection sessions and a source of at least partially coherent light generating a beam of at least partially coherent light having a predetermined frequency modulation.
• the frequency modulation of the source is selected to overcome the detector limited frame per second rate, due to the increased frequency changes of the interference fringe pattern.
• the frequency modulation of the source is selected with respect to the frequency range of the surface movement of the object.
• the coherent illumination is in the form of pulsed light having a modulation frequency selected to enable correlation between illumination and detection sessions (sampling rate). Therefore, the pulsation of the source allows the detection of fast vibrations by slow camera.
• the laser parameters were as follows: the wavelength was about 532 nm, the power (on detector and camera) was in the range of about 5-13 ⁇ ; the driver current was about 0.35 A; the modulation signal was about 25% on pulse; the frequency range was about 0-220 Hz; the voltage (Pk2Pk) was about 10 V and the offset was about 0 V.
• the detector parameters were as follows: the gain set was about 40 dB, the bandwidth was about 225 kHz; the FFT Offset was about -110 dBV.
• the object parameters were as follows: the object signal was a sinusoidal signal, the frequency range was about 0-220 Hz; the voltage (Pk2Pk) was about 10 V and the offset was about 0 V.
• Figs. 8a-8g The laser modulation results are illustrated in Figs. 8a-8g.
• the high frequency of the object is modulated by the laser frequency to low frequencies.
• Fig. 8a shows the laser frequency at 250Hz and its harmonics
• Figs. 8b-8d show the object frequency, its harmonics and the 50Hz line noise at 120Hz, 170 Hz and220 Hz respectively
• Figs. 8e-8g show the object frequencies with laser modulation at 250 Hz.
• the object frequency is 120 Hz
• Fig. 8f the object frequency is 170 Hz
• Fig. 8g the object frequency is 220 Hz.
• the results show that the high frequency object signal is modulated to low frequencies within the detector frame rate window according to the frequencies difference but the frequencies had many harmonics frequencies due the convolution of the laser modulation.
• an imaging system for receiving an at least partially coherent light beam being indicative of at least one parameter of movement of a moving object
• the system comprises an imaging unit comprising a detector; an interferometric module configured and operable to detect an interference pattern indicative of phase shifts of the object being indicative of temporal changes along a z-axis;
• the interferometric module comprises at least one beam splitter/combiner configured for receiving at least partially coherent light beam, splitting the beam into object and reference beams propagating along substantially identical optical paths; and at least one mirror arrangement located in the reference beam path and configured for reflecting the reference beam towards the detector through the beam splitter/combiner where it interferes with an object response to interaction with the object beam, wherein the at least one mirror arrangement is configured for displacement at a predetermined frequency to induce controllable temporal modulation of the interference pattern.
• the camera parameters were as follows: the exposure time was about 0.2 msec; the frame rate was about 100; the number of frames acquired was about 1000; the scan time was about 10 sec; the signal gain was about 0 dB and the gamma of the camera was about 2.2.
• the mirror arrangement parameters were as follows: the analogue amplifier output voltage was about 180 V; the modulation signal was a saw tooth signal; the frequency range was about 0-220 Hz; the voltage (Pk2Pk) was about 4.9 V and the offset was about 0 mV.
• the object parameters were as follows: the object signal was a sinusoidal signal, the frequency range was about 0-220 Hz; the voltage (Pk2Pk) was about 8 V and the offset was about 0 mV.
• Figs. 9a-9b The mirror modulation results are illustrated in Figs. 9a-9b.
• the high frequency of the object is modulated by a piezoelectric mirror frequency to low frequencies.
• Fig. 9a shows the object and modulation frequencies and their difference and addition frequencies when the object frequency is 20Hz and the frequency of the piezoelectric mirror arrangement is 22 Hz;
• Fig. 9b shows the difference frequency and the cut frequencies (by 100Hz of the detector) of the object and piezoelectric mirror object frequency when the object frequency is 110Hz and the frequency of the piezoelectric mirror arrangement is 141 Hz.
• the results show that the high frequency object signal is modulated to low frequencies within the detector frame rate window according to the frequencies difference.
• the inventors of the present invention have made some experiment to test the laser and the mirror arrangement modulations together using an open circuit without feedback.
• the laser parameters were as follows: the wavelength was about 532 nm, the power (on detector and camera) was in the range of about 5-13 ⁇ ; the driver current was about 0.35 A; the modulation signal was about 25% on pulse; the frequency range was about 0-220 Hz; the voltage (Pk2Pk) was about 10 V and the offset was about 0 V.
• the detector parameters were as follows: the gain set was about 40 dB, the bandwidth was about 225 kHz; the FFT Offset was about -110 dBV.
• the camera parameters were as follows: the exposure time was about 0.2 msec; the frame rate was about 200; the number of frames acquired was about 1000; the scan time was about 5 sec; the signal gain was about 0 dB and the gamma of the camera was about 2.2.
• the mirror arrangement parameters were as follows: the analogue amplifier output voltage was about 180 V; the modulation signal was a saw tooth signal; the frequency range was about 0-220 Hz; the voltage (Pk2Pk) was about 4.9 V and the offset was about 0 mV.
• the object parameters were as follows: the object signal was a sinusoidal signal, the frequency range was about 0-220 Hz; the voltage (Pk2Pk) was about 10 V and the offset was about 0 V.
• Fig. 10 shows the object and modulation frequencies and their difference and addition frequencies when the object frequency is 67 Hz, the frequency of the piezoelectric mirror arrangement is 18 Hz and the laser modulation frequency is 24 Hz.
• the difference and addition frequencies of the object and the modulation frequencies gave many combination frequencies such as: 6 Hz (laser-piezo), 42 Hz (laser+piezo), 43 Hz (object-laser), 48, 54, 72 Hz (harmonics of laser and piezo frequencies), 85 Hz (object +piezo) etc.
• the results show that the high frequency object signal is modulated to low frequencies within the detector frame rate window according to the frequencies difference.

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• 2017
  • 2017-02-07 WO PCT/IL2017/050146 patent/WO2017145145A1/en not_active Ceased
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