WO2002099505A1 - Procede et dispositif permettant de controler un arrangement de miroirs - Google Patents

Procede et dispositif permettant de controler un arrangement de miroirs Download PDF

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Publication number
WO2002099505A1
WO2002099505A1 PCT/SE2002/001051 SE0201051W WO02099505A1 WO 2002099505 A1 WO2002099505 A1 WO 2002099505A1 SE 0201051 W SE0201051 W SE 0201051W WO 02099505 A1 WO02099505 A1 WO 02099505A1
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WO
WIPO (PCT)
Prior art keywords
mirror arrangement
estimated
time interval
control signals
values
Prior art date
Application number
PCT/SE2002/001051
Other languages
English (en)
Inventor
Rune Axelsson
Andreas Axelsson
Original Assignee
Airborne Hydrography Ab
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 Airborne Hydrography Ab filed Critical Airborne Hydrography Ab
Publication of WO2002099505A1 publication Critical patent/WO2002099505A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/18—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors
    • G02B7/182—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for mirrors
    • G02B7/1821—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for mirrors for rotating or oscillating mirrors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems

Definitions

  • the invention concerns a method and a device for controlling a mirror arrangement to enable laser radiation reflected by the mirror arrangement to execute a sweeping motion in accordance with an essentially deterministic scheme.
  • the method and device are intended in particular for a laser bathymetry application.
  • the system comprises a laser system, which emits pulsed radiation in the infrared range while simultaneously emitting pulsed radiation in the range of visible light.
  • the infrared radiation is reflected from the surface of the water, while a significant portion of the visible light penetrates down into the water and is reflected from the bottom.
  • the system further comprises a receiver with a detector that is arranged to register the intensity of the reflected, received radiation.
  • a calculating unit connected to the detector calculates the time difference between the reception of the radiation reflected from the water surface and the reception of the radiation reflected from the bottom, whereupon the water depth is calculated as one-half the time difference multiplied by the speed of light, with compensation for the angle of incidence of the radiation relativejo the water surface.
  • the laser bathymetry system it is possible to perform depth measurements relatively quickly over an area if the helicopter or airplane flies at a speed of, e.g. 30 - 130 knots and at an altitude of 200 - 500 meters above the water surface.
  • the laser system included in the laser bathymetry system is fixedly mounted in the laser bathymetry system and aimed toward a bidirectionally (x-direction and y-direction) servo-controlled mirror arrangement.
  • the mirror arrangement is controlled to enable the laser radiation to sweep across the water surface within an area of 100 - 200 m transverse to the direction of flight.
  • the servo characteristically comprises a PD regulator for each direction.
  • One purpose of the invention is to improve the control of the mirror arrangement so that the laser pulses are distributed uniformly across the water surface during the sweeping motion.
  • Another purpose is to minimize the peak currents in the driving means for controlling the mirror arrangement.
  • a method according to a first aspect of the invention for controlling a mirror arrangement to enable laser radiation reflected by the mirror arrangement to execute a sweeping motion according to an essentially deterministic scheme comprises the following steps, which are not necessarily performed in the order given.
  • a setpoint value for the position of the mirror arrangement is determined in at least one direction, in which direction an estimated or measure actual value for the position of the mirror arrangement is also determined, and a control signal is calculated based on the determined setpoint and actual values in order to guide the position of the mirror arrangement toward the setpoint value.
  • the method is characterized in that
  • control signals for the mirror arrangement are estimated for said time interval based on the predicted setpoint values
  • the control signals for the time interval are selected in such a way that the magnitude of said control signals and the magnitude of the distances between the predicted setpoint values and the associated estimated actual values for the time interval are minimized, whereupon the first of the estimated control signals for the interval is selected as the current control signal.
  • One particular embodiment is characterized in that the distance values are squared, whereupon a first sum of the squared distance values is generated.
  • the calculated control signal values for the interval are squared, whereupon a second sum of the squared control signal values is generated.
  • the control signals for the interval are thus chosen in such a way as to minimize the first and the second sums.
  • the invention also comprises a device for a laser for controlling a mirror arrangement so that incident radiation striking the mirror arrangement is reflected so that it executes a sweeping motion in accordance with an essentially deterministic scheme.
  • the device comprises means for driving the mirror arrangement in at least one direction, and control means arranged so as to: determine a setpoint value for the current position of the mirror arrangement, determine an estimated or measured actual value for the position of the mirror arrangement and calculate a control signal for the driving means based on the determined setpoint and actual values in order to guide the position of the arrangement toward the setpoint value.
  • the device is characterized in that the control means are further arranged so as to predict future setpoint values for the sweeping motion for a selected time interval, and comprises a regulator part arranged so as, during calculation of the control signal, to optimize same in order to minimize the magnitude of future control signals estimated for the time interval and the magnitude of the distances between predicted setpoint values and associated actual values calculated based on the estimated control signals for the time interval and a system model for the mirror arrangement and the driving means for the mirror arrangement.
  • the device is preferably arranged in a laser bathymetry system, in which laser pulses are sent toward the water surface in the aforedescribed sweeping motion in order to create a scanning pattern on the surface.
  • the driving means of the laser bathymetry system consist of, e.g., an electric servomotor.
  • a number of advantages are associated with the use of a regulator part according to the invention.
  • a more uniform scanning pattern can be achieved without overshooting, while at the same time the peak currents for the servomotor need not be increased, and the scanning frequency can simultaneously be maintained.
  • the scanning frequency can alternatively be increased while maintaining the peak currents to the servomotor and the uniformity of the scanning pattern. It is also conceivable to choose to reduce the peak currents, whereupon a smaller servomotor is required, while still maintaining the scanning frequency and the uniformity of the scanning pattern.
  • the method and device according to the invention further enable the scanning pattern uniformity requirement to be set up versus the requirement regarding motor currents as an optimization problem, where the requirements can be counterposed and a choice made as to whether to prioritize more highly either the scanning pattern uniformity requirement or the low motor current requirement.
  • the new regulator is thus highly flexible, and the choice of weighting factor can be made based on the application in question.
  • FIGURES Figure 1 shows a diagram of measurements of water depth being made using a helicopter- based laser bathymetry system.
  • Figure 2 shows a block diagram of the design of the laser bathymetry system in Figure 1 according to an exemplary embodiment of the invention.
  • Figure 3 shows an example of a sweep pattern on the water surface in connection with measurements of water depth as per Figure 1.
  • Figure 4 shows a graph of angular positions as a function of time for the mirror arrangement for the laser bathymetry system.
  • Figure 5 shows a feedback control system for controlling the mirror arrangement
  • Figure 6 shows a control signal for a motor for driving the mirror arrangement.
  • Reference number 1 in Figure 1 designates a helicopter with a helicopter-based laser bathymetry system 2 for measuring water depths in seas, lakes, rivers and other watercourses.
  • Reference number 3 designates the water surface, while reference number 4 designates the bottom of the sea, lake or other watercourse.
  • the laser bathymetry system 2 comprises a laser arrangement 5, which emits pulsed radiation in the infrared range while simultaneously emitting pulsed radiation in the visible light range.
  • the laser arrangement consists of an IR laser with a frequency-doubling crystal that converts a portion of the IR radiation into visible green light.
  • the laser arrangement consists of twin lasers, one for each wavelength used, which lasers are mounted in connection with one another so that the radiation from both lasers has the same beam direction.
  • the pulse frequency for the beam from the laser arrangement is characteristically 0.2 - 2 kHz, and preferably 1 - 2 Hz.
  • a mirror arrangement 6 is disposed in front of the laser arrangement 5 so as to direct the laser radiation toward the water surface in a chosen direction, as will be described below.
  • the mirror arrangement 6 comprises, e.g. a bi-directionally (x-direction and y-direction) rotatable mirror placed in the beam path from the laser arrangement 5, the rotation of which mirror in the x-direction is driven by a first motor 7, and the rotation of which mirror in the y-direction is driven by a second motor 8.
  • a first control unit 9 is connected to the first motor 7 and arranged so as to send a control signal to the first motor 7 for controlling the rotation of the mirror in the x-direction.
  • a second control unit 10 is connected to the second motor 8 and arranged so as to send a control signal to the second motor 8 for controlling the rotation of the mirror in the y-direction.
  • the system 2 further comprises a receiver 11 for receiving the radiation reflected from the water surface 3 and the radiation reflected from the bottom 4.
  • the receiver 11 is connected to a calculating unit 12 for calculating the water depth based on the reception times for the radiation reflected from the surface and from the bottom.
  • the lower portion of the depiction shows how the laser beam is intended to sweep across the water surface during the measurements of water depth, wherein the x-axis indicates the position on the water surface laterally in relation to the helicopter's direction of travel, while the y-axis indicates the position on the water surface in a forward direction.
  • the distance between the pulses striking the water surface depends on the pulse frequency of the lasers, the speed of the helicopter and the width of the sweep.
  • the required distance between the pulses depends of course on the structure of the bottom where the depth measurements are being made, but it is generally appropriate for the distance between two measurement points not to exceed 1 - 2 m in connection with measurements of water depth.
  • each respective control unit consists of a feedback system with a PD regulator for controlling the currents to the motor in order to achieve the angles of rotation shown in Figure 4, and thus the sweeping motion shown in the lower portion of Figure 3.
  • a PD regulator for controlling the currents to the motor in order to achieve the angles of rotation shown in Figure 4, and thus the sweeping motion shown in the lower portion of Figure 3.
  • the PD regulator it is not possible to control the angles of rotation of the mirror arrangement in such a way as to achieve the sweep pattern shown in the lower portion of Figure 3; the pattern shown in the upper portion of Figure 3 is instead obtained, with irregularities and overshooting at the turning points in the sweeping motion.
  • One way of eliminating such irregularities and overshooting is to use a very large motor with high motor currents. Another option is to improve the regulator.
  • FIG. 5 shows one of the control units 9, 10.
  • the control units 9, 10 can be identically realized, and receive an input signal in the form of a setpoint value r(t) for the rotational position of the mirror arrangement.
  • the received setpoint value signal r(t) is compared to the current rotational position y(t) of the mirror arrangement to generate an error signal e(t).
  • the error signal is processed by an improved regulator 13, which generates a control signal u(t) for the motor associated with the control unit.
  • the control signal u(t) is also input to a model 14 of the motor/mirror arrangement to calculate the rotational position of the mirror arrangement y(t) based on the control signal used.
  • the setpoint value signal r(t) for the control unit 9 consists of the setpoint value r x (t) shown in Figure 4, while the regulator 13 and the model 14 are adapted to control the mirror arrangement in the x- direction.
  • a modified version of r x (t) is input to the control unit 9, compensated for the current roll attitude of the helicopter.
  • the signal r(t) for the control unit 10 consists of the setpoint value signal r y (t) shown in Figure 4, and the regulator and the model are adapted to control the mirror arrangement in the y-direction.
  • r y (t) can also be compensated for the position of the helicopter.
  • each regulator is to generate a control signal u x (t), u y (t) for each mirror motor 7, 8 so that the angle of rotation y x (t) of the mirror arrangement in the x-direction and the angle of rotation y y (t) in the y-direction are kept close to their respective setpoint values r x (t), r y (t).
  • control system 9 for rotating the mirror arrangement in the x-direction.
  • control system 10 for rotation in the y- direction can be identical.
  • Gd is the aforedescribed function G(s) in a time-discrete form and R[k] is the setpoint value signal r x (t) sampled at a time interval T.
  • x[nT + T] Ax[nT] + Bu[nT] + NvrfnT]
  • y[nT] Cx[nT] + v 2 [nT]
  • A, B, C and N are matrices that describe the dynamic model and x is a state vector.
  • V ⁇ describes the system noise and v describes the measurement noise.
  • the way in which the matrices A, B, C and N are to be set up may be found in any text book on advanced control technology. This means that procedures known to one skilled in the art are all that is necessary to use this information to build matrices to create a state description of the feedback system with the dynamic model G d of the motor/mirror arrangement.
  • the state vector x can be estimated by using an observer in the form of, e.g. a Kalman filter. Now a linear relation can be formed between the predicted output signal Y t , the future control signals U t and the current state x(t) . wher g
  • M should lie between 1 and 100 and N between 1 and 10, depending on how well the model 14 describes the system, and also on the available processor capacity, since large dimensions for the matrices M and N impose a heavier calculation load.
  • the prediction interval is 7 x T seconds.
  • the prediction interval is preferably 1 - 100 ms, and typically 10 ms.
  • V(U ) - ⁇ t - R ⁇ + ⁇ U ⁇ is minimized for a selected prediction interval
  • V(U t ) is the standard function
  • R is a vector that here indicates the predicted setpoint values for the interval
  • Q y and Q u are weight matrices chosen for the application in question so that the requirements of a position error (Y t -R) in the scanning pattern and the predicted level of the motor currents U t are met.
  • R may thus indicate a prediction of the continuation of the setpoint value signal based on the desired scanning pattern shown in the lower portion of Figure 4.
  • the vector R can thus be described by r x (t) in Figure 3, sampled during the chosen prediction interval, which starts from the current position.
  • the vector values in R can be modified to compensate for the current attitude of the helicopter in the air plus a change in attitude predicted within the selected prediction interval.
  • a roll attitude is estimated to be constant during the prediction interval, while in another simple embodiment a roll motion is estimated to be occurring at constant speed and in a constant direction during the prediction interval.
  • K p q u /q y that indicates the behavior of the system.
  • a large K p penalizes the control signal downward, while a smaller K p penalizes the position error.
  • the magnitude of K p depends on the units in which the control signal and output signal are measured. Using the values of K p given below, the control signal U t is expressed in Nm, and the output signal Y t in radians.
  • V(U t ) U QU t + 2c ⁇ U t +b
  • control signal U(t+2) that is to be used for the ensuing time step is calculated using the above procedure, predicting the setpoint values for a new time interval advanced one time step in relation to the preceding interval and minimizing the standard function of the new time interval to obtain an updated vector U t where u(t+l) is again used as a control signal for the associated motor.
  • the aforedescribed regulator is described for the control unit 9, which controls the mirror arrangement in the x-direction, but it can also be implemented advantageously in the control unit 10 that controls the mirror arrangement in the y-direction.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Optical Radar Systems And Details Thereof (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

L'invention concerne un procédé de contrôle d'arrangement de miroirs (6), au moins dans une direction, qui permet au rayonnement laser réfléchi par un arrangement de miroirs de produire un mouvement de balayage selon un schéma essentiellement déterministe. On peut prévoir les valeurs de consigne futures du mouvement, pour un intervalle de temps donné. Les signaux de contrôle de l'arrangement sont estimés pendant cet intervalle, sur la base des valeurs prévues, et les valeurs effectives correspondant à l'intervalle de temps considéré sont estimées sur la base d'un modèle de système et des signaux de contrôle estimés. Pour l'estimation des signaux de contrôle relatifs à l'intervalle visé, on choisit les signaux de manière à réduire au minimum leur valeur et la valeur des distances comprises entre les valeurs de consigne prévues et les valeurs effectives correspondantes estimées dans ledit intervalle. Ensuite, on choisit le signal de contrôle estimé pour l'intervalle suivant, en tant que signal de contrôle courant pour le contrôle de l'arrangement de miroirs.
PCT/SE2002/001051 2001-06-07 2002-06-03 Procede et dispositif permettant de controler un arrangement de miroirs WO2002099505A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0102084-1 2001-06-07
SE0102084A SE0102084L (sv) 2001-06-07 2001-06-07 Metod och anordning för att styra ett spegelarrangemang

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WO2002099505A1 true WO2002099505A1 (fr) 2002-12-12

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003064970A1 (fr) * 2002-02-01 2003-08-07 Tenix Lads Corporation Pty Ltd Appareil et procede pour faire osciller un faisceau laser de lumiere emis a l'interieur d'un champ de vision (fov) dans un systeme de reception de lumiere
WO2010029544A1 (fr) 2008-09-11 2010-03-18 Kilolambda Technologies Ltd. Identification d'échos marins à l'aide d'un capteur laser pour détecter une cible marine distante

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5187364A (en) * 1989-03-22 1993-02-16 National Research Council Of Canada/Conseil National De Recherches Du Canada Scanning device with waveform generator optimizer
US5594556A (en) * 1993-03-28 1997-01-14 Scitex Corporation Ltd. Scanner having a misalignment detector
US6037583A (en) * 1997-01-27 2000-03-14 Carl Zeiss Jena Gmbh Control system for a scanner drive

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5187364A (en) * 1989-03-22 1993-02-16 National Research Council Of Canada/Conseil National De Recherches Du Canada Scanning device with waveform generator optimizer
US5594556A (en) * 1993-03-28 1997-01-14 Scitex Corporation Ltd. Scanner having a misalignment detector
US6037583A (en) * 1997-01-27 2000-03-14 Carl Zeiss Jena Gmbh Control system for a scanner drive

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003064970A1 (fr) * 2002-02-01 2003-08-07 Tenix Lads Corporation Pty Ltd Appareil et procede pour faire osciller un faisceau laser de lumiere emis a l'interieur d'un champ de vision (fov) dans un systeme de reception de lumiere
US7248341B2 (en) 2002-02-01 2007-07-24 Tenix Lads Corporation Pty Ltd Apparatus and method for oscillating a transmitted laser beam of light within the field of view (FOV) of a light receiving system
WO2010029544A1 (fr) 2008-09-11 2010-03-18 Kilolambda Technologies Ltd. Identification d'échos marins à l'aide d'un capteur laser pour détecter une cible marine distante
US8638426B2 (en) 2008-09-11 2014-01-28 Israel Aerospace Industries Ltd. Sea clutter identification with a laser sensor for detecting a distant seaborne target

Also Published As

Publication number Publication date
SE517479C2 (sv) 2002-06-11
SE0102084D0 (sv) 2001-06-07
SE0102084L (sv) 2002-06-11

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