31 results about "Laser doppler velocimeter" patented technology

A double-optical path laser Doppler velocimeter includes a laser source, a light source beam splitter, a photoelectric receive and electronic process system and a focusing system, among which, the laser source, the beam splitter, the photoelectric receive and electronic process display system, a mobile lens and a fixed lens in the focusing system are set on the optical axis of the propagating direction of the laser source beam orderly from left to right to compose a measurement system. The moving direction of the object and the axis of the test system are vertical to the optical axis of the laser ranger, a step motor controller drives the step motor to drive the ballscrew based on the distance of the tested moving object to regulate the distance between the mobile and the fixed lenses to let the laser beam focus drop on the tested moving object accurately.

The invention discloses a non-contact dynamic stiffness measurement system and a method thereof. The non-contact dynamic stiffness measurement system includes a base, a test bar, an exciter, a force sensor, a laser Doppler velocimeter, and a controller. The force sensor is connected to the exciter and the base. The exciter is located between the test bar and the force sensor. The controller is electrically connected to the force sensor and the laser Doppler velocimeter. The test bar is detachably set in a holder of the main shaft under test. The exciter provides an electromagnetic force to thetest bar. The force sensor measures the acting force of the exciter. The laser Doppler velocimeter provides a first laser beam and a second laser beam. The laser Doppler velocimeter measures a vibration response with reflected laser beams. The controller determines an equivalent main shaft stiffness value of the main shaft under test according to the acting force and the vibration response.

The invention discloses a measuring system for particle velocity of an impact surface and a free surface of a light transmission material. The system comprises an emission device, an impact object, a target plate, a target frame and an all-fiber laser doppler velocimeter; the impact object is emitted through the emission device; the target plate is prepared from the light transmission material; an all-reflection film is plated on the impact surface of the target plate; a semi-reflection film is plated on the free surface of the target plate; the target plate is fixed on the target frame and directly faces the impact object; a laser lens of the all-fiber laser doppler velocimeter is directly arranged one side plated with the semi-reflection film of the target plate and has a certain distance from the semi-reflection film; the laser lens is connected with a main body part of the all-fiber laser doppler velocimeter through optical fibers. With the adoption of the system, the problems that the particle velocity of the free surface of the target plate cannot be accurately measured by the existing flat impact test, and the particle velocity of the impact surface of the target plate cannot be synchronously measured, can be solved; the system has the advantages of being accurate in measuring result, high in precision, and difficultly interfered by the environment.

A laser Doppler velocimeter uses self-mixing amplification of backreflections from scatterers below the surface of a flow. A time domain signal is divided into segments that are roughly equal to a transit time of particles through a focus of a laser beam. The segments are connected to a frequency domain through the use of an FFT algorithm to produce frequency domain data segments. Signal-to-noise ratio is enhanced through signal processing techniques using the segments to produce a final enhanced signal spectrum.

The invention discloses a non-intrusive experimental device used for researching underwater bubble plumes. The non-intrusive experimental device comprises a power system, an experimental system and adata collection system; the power system comprises an air compressor and a gas buffer tank which are connected with each other; the experimental system comprises a wave maker, a background plate, a water tank and a steel pipeline arranged at the interior of the water tank; the gas buffer tank is connected with the inlet of the steel pipeline through a gas transportation soft tube, the outlet of the steel pipeline is connected to a gas outlet soft tube and stretches out of the water tank and a leakage hole is formed in the steel pipeline; and the data collection system comprises a high-speed camera and a compact type laser doppler velocimeter. The experimental device can measure upward floating time of the gas, bubble plume dimension and horizontal migration distance, flow and pressure of the gas before after the leakage hole and speed of the gas at any measuring point of the flow field; and the parameters provide verification path for a numerical simulation method and perfect underwater bubble plume theory.

The invention discloses a LDV / INS (Laser Doppler Velocimeter / Inertial Navigation System) combination-based vehicle-mounted height measurer and a method thereof. The vehicle-mounted height measurer comprises an inertial navigation system, a laser Doppler velocimeter, a signal solving unit and a height information display unit, wherein the inertial navigation system and the laser Doppler velocimeterare arranged on a vehicle; the inertial navigation system is used for measuring a real-time pitch angle of the vehicle in the driving process and transmitting the measured real-time pitch angle information to the signal solving unit; the laser Doppler velocimeter is used for measuring a real-time speed in the vehicle driving process and transmitting the measured real-time speed information to thesignal solving unit; the signal solving unit is used for solving to obtain an elevation height increment of the vehicle in a set unit time interval according to the speed information and the pitch angle information, accumulating all height increments from an initial point to a to-be-measured point, and finally solving the elevation of the to-be-measured point. The vehicle-mounted height measurerdisclosed by the invention has the characteristics of being capable of avoiding influence of meteorological changes, small in influence of atmospheric refraction, high in working efficiency, high in measurement accuracy and the like.

The invention relates to a laser Doppler velocimeter-based initial alignment method of an inertial navigation system during advancing. The method comprises the following steps: under a geocentric inertial coordinate system and a local navigation coordinate system, establishing a process model and a measurement model of the alignment process of the strapdown inertial navigation system based on a speed measurement value, a specific force equation and attitude direction cosine matrix estimation of the laser Doppler velocimeter; constructing a state vector by taking an attitude error of inertial navigation equipment, zero offset drift of a gyroscope, zero offset drift of an accelerometer, and a mounting angle error and a scale coefficient error of a laser Doppler velocimeter as components, establishing a robust square root unscented quaternion estimator, and obtaining a predicted value of the state vector to carry out initial alignment between marches on the strapdown inertial navigation system. The process model and the measurement model of the method utilize the high-precision speed output of the laser Doppler velocimeter, and the error of the inertial measurement unit and the installation inclination angle and the scale coefficient of the laser Doppler velocimeter are considered in initial alignment, so that the attitude estimation precision can be improved.

A motion member (1) urged by an application spring (4) is made to collide with a surface of a sheet material supported by a support member (14) so as to be deflectable and deformable. The velocity of the motion member (1) during the collision process is detected every second by a measuring portion (17) of a laser Doppler velocimeter. A control circuit (121) measures the velocity of the motion member (1) immediately before the collision of the motion member (1) with the sheet material, the time period of deflection deformation until the sheet material collides with an opposing member (15), and the time period of compression deformation after the collision of the sheet material with the opposing member (15), and outputs a result thereof as sheet material information to a control portion (120). The timing at which the sheet material collides with the opposing member (15) is detected by an output of a piezoelectric element (16) connected to the opposing member (15).

The invention relates to the technical field of laser measurement, and in particular, relates to a device for calibrating a micro anemograph through laser measurement and a use method thereof, and aims to overcome the defect that no special equipment for calibrating the micro anemograph exists at present. A laser Doppler velocimeter irradiates a transparent air channel, tracer particle smoke moving along with wind in the air channel is measured, namely the wind speed in the air channel and serves as a wind speed calibration value, then the wind speed calibration value is compared with the wind speed obtained by an anemograph measuring head after blockage ratio calculation and correction, and thus the accuracy of the anemograph is displayed. The device has the beneficial effects that the laser measurement technology is utilized to solve the problems of low calibration quality and low calibration efficiency of an existing micro anemograph, and the accuracy of the micro anemograph is greatly improved.

The invention provides a new goaf solid phase structure based on LDA and a flow field regression method, and relates to the technical field of mine ventilation. The method comprises the following steps: firstly, establishing a new goaf experimental model, and arranging observation points in the model; and testing the model through a laser Doppler velocimeter to obtain actual measurement speed values of observation points; randomly generating a plurality of binary method arrays; and calculating the gas flow state of each sample by adopting a lattice Boltzmann method, matching the positions ofthe observation points in the model in the samples, and extracting the calculation results of the corresponding positions; and finally, calculating an adaptive value, judging whether the adaptive value meets a termination condition or not, if so, outputting the binary array and the flow field flow state thereof, and if not, selecting, crossing and mutating individuals in the sample set and repeating the step 5. The invention solves the problem that the porous medium is not suitable for the new goaf, can process the complex geometric boundary of the new goaf, and accurately obtains the internalsolid phase structure and gas flow state of the new goaf.

A double-optical path laser Doppler velocimeter includes a laser source, a light source beam splitter, a photoelectric receive and electronic process system and a focusing system, among which, the laser source, the beam splitter, the photoelectric receive and electronic process display system, a mobile lens and a fixed lens in the focusing system are set on the optical axis of the propagating direction of the laser source beam orderly from left to right to compose a measurement system. The moving direction of the object and the axis of the test system are vertical to the optical axis of the laser ranger, a step motor controller drives the step motor to drive the ballscrew based on the distance of the tested moving object to regulate the distance between the mobile and the fixed lenses to let the laser beam focus drop on the tested moving object accurately.

A vehicle laser Doppler velocimeter based on a scanning galvanometer comprises a reference beam type laser Doppler velocity measurement probe, a coaxial cable, a signal processing unit and a display screen, and a scanning galvanometer is arranged on a laser path before a laser of the reference beam type laser Doppler velocity measurement probe is incident to the ground. The scanning galvanometer is provided with a first working position and a second working position. When the scanning galvanometer is located at the first working position, the laser of the reference beam type laser Doppler velocity measurement probe is directly incident to the ground; and when the scanning galvanometer is located at the second working position, the laser of the reference beam type laser Doppler velocity measurement probe is incident onto the scanning galvanometer, the laser reflected by the scanning galvanometer is incident to the ground. According to two Doppler frequencies measured when the scanning galvanometer is rotated to the first working position and the second working position, the variation of the emission inclination angle can be calculated to obtain the motion speed of the vehicle and eliminate the influence of the emission inclination angle variation on the velocity measurement precision when the vehicle is bumped.

The invention provides a method for measuring the average Mach number of a nozzle outlet. The method is used to indirectly measure the average Mach number Ma of the nozzle outlet based on measured pressure, temperature and mass flow, and obtain the average Mach number Ma of the nozzle outlet by measuring the total temperature T0 * of airflow of a nozzle inlet, static pressure P1 of airflow of thenozzle outlet and the mass flow m of airflow flowing through the nozzle. A measuring instrument does not need to be inserted into a high-speed flow field of the nozzle outlet, and disturbance to the flow field is reduced. Compared with a method for obtaining the average Mach number Ma of the nozzle outlet through a laser Doppler velocimeter LDV and a particle image velocimeter PIV, the method onlyneeds to arrange an inlet total temperature measuring point at the nozzle inlet, arrange a static pressure measuring point at the nozzle outlet and measure the flow passing through the nozzle; the measurement cost is relatively low, and solid particles do not need to be added into the flow field. The maximum deviation between the nozzle outlet average Mach number Ma calculated according to the method and the CFD numerical calculation result does not exceed 6.2%.

The invention discloses a speed measurement method and system applied to a laser Doppler velocimeter, and the method comprises the steps: collecting a motion signal of a measured object through the laser Doppler velocimeter, and carrying out the parameter setting according to the motion signal; filtering and segmenting the motion signal according to the set parameters, converting the signal of each segment into a frequency domain through fast Fourier transform, and performing spectral analysis to obtain a frequency search range of the signal of each segment; performing wavelet transform on the signals in the paragraphs through the set parameters and the frequency search range, and obtaining an instantaneous frequency estimation curve fragment of each paragraph signal by extracting a wavelet ridge line; and splicing the instantaneous frequency estimation curve segments of each paragraph, and reconstructing a time-frequency signal to obtain a speed-time curve of the measured object. According to the invention, wavelet transform is utilized to process signals, and the time resolution and data processing speed of the system are effectively improved by combining fast Fourier transform.

The invention provides an integrated navigation method and device based on double laser Doppler velocimeters and an inertial navigation system. The integrated navigation method comprises the following steps: firstly, constructing output speeds and speed error models of the two laser Doppler velocimeters under a carrier coordinate system; establishing a state equation of a filtering system by taking scale coefficient errors and installation angle errors of the two laser Doppler velocimeters and inertial navigation attitude errors, speed errors, position errors, gyroscope measurement errors and accelerometer measurement errors of the inertial navigation system as state vectors; taking the difference between the displacement increment of the inertial navigation system in the carrier coordinate system and the displacement increment of the two laser Doppler velocimeters under the carrier coordinate system and the difference between the course angle obtained by the inertial navigation system and the course angles obtained by the two laser Doppler velocimeters as observed quantities, and constructing an observation equation of the filtering system; and performing feedback correction on the dual-laser Doppler velocimeter and the inertial navigation system by using the state vector obtained by filtering, and outputting a corrected positioning result. The precision of integrated navigation can be improved.

The invention relates to an online calibration method and device for a laser Doppler velocimeter based on an inertial measurement unit. The method comprises the following steps: using inertial navigation data in an initial time period, carrying out coarse calibration on a mounting angle and a transmitting inclination angle of a laser Doppler velocimeter based on a parameter analysis method, establishing a state equation of a combined navigation system, establishing an observation equation by taking a difference value between a speed error of the laser Doppler velocimeter and a speed error of inertial navigation equipment as an observed quantity, and carrying out calculation on the observed quantity; obtaining the installation angle error estimation value and the emission angle error estimation value of the laser Doppler velocimeter, correspondingly compensating the rough calibration value, and obtaining a high-precision online calibration result of the laser Doppler velocimeter. According to the method, the characteristics of inertial navigation equipment are fully utilized, online high-precision calibration is carried out on the laser velocimeter in real time without depending on a satellite navigation system, the equipment cost is reduced, the method has the characteristics of high autonomy, good environmental adaptability and the like, and the maneuverability of a carrier can be improved.

The invention discloses a LDV / INS (Laser Doppler Velocimeter / Inertial Navigation System) combination-based vehicle-mounted height measurer and a method thereof. The vehicle-mounted height measurer comprises an inertial navigation system, a laser Doppler velocimeter, a signal solving unit and a height information display unit, wherein the inertial navigation system and the laser Doppler velocimeterare arranged on a vehicle; the inertial navigation system is used for measuring a real-time pitch angle of the vehicle in the driving process and transmitting the measured real-time pitch angle information to the signal solving unit; the laser Doppler velocimeter is used for measuring a real-time speed in the vehicle driving process and transmitting the measured real-time speed information to thesignal solving unit; the signal solving unit is used for solving to obtain an elevation height increment of the vehicle in a set unit time interval according to the speed information and the pitch angle information, accumulating all height increments from an initial point to a to-be-measured point, and finally solving the elevation of the to-be-measured point. The vehicle-mounted height measurerdisclosed by the invention has the characteristics of being capable of avoiding influence of meteorological changes, small in influence of atmospheric refraction, high in working efficiency, high in measurement accuracy and the like.

The invention discloses a simulation method of 'wave current-structure-seabed' dynamic coupling experiment. The method utilizes a simulated experimental water tank, sinks the simulated structure on the simulated seabed in the simulated experimental tank, and controls the structure through a sensor. The dynamic load on the object, the dynamic response of key parts, and its dynamic displacement change are detected, and the wave height meter, PIV particle image velocimeter, and Doppler laser velocimeter are set up to measure the wave height and the velocity of the flow field around the structure. The dynamic response of the soil is detected through the pore water pressure sensor and the earth pressure cell, and finally the detection data is collected and processed synchronously through the multi-channel data acquisition system to truly reproduce the actual stress status of the structure . The invention also discloses a simulated experiment water tank. A seabed simulated tank is arranged at the bottom of the simulated experiment tank, and the simulated tank is filled with simulated seabed soil. This method can truly reproduce the actual stress state of the structure.

The invention discloses a pile foundation penetration measuring device. The pile foundation penetration measuring device comprises a fixing frame, a laser Doppler velocimeter, a control display and a cleaning device, wherein the fixing frame is used for being installed on the side edge of a pile foundation, the laser Doppler velocimeter is installed on the fixing frame and used for emitting first detection laser and second detection laser to the surface of the peripheral wall of the pile foundation and receiving reflected light emitted by the surface of the peripheral wall of the pile foundation, the control display is electrically connected with the laser Doppler velocimeter and is used for displaying the moving speed and the moving amount of the pile foundation, and the cleaning device is used for cleaning the peripheral wall surface of the pile foundation. According to the technical scheme, the pile foundation penetration measuring device can accurately monitor the penetration of a pile foundation through the laser Doppler velocimeter, high-precision automatic monitoring is achieved, the cleaning device is beneficial to guaranteeing the measurement accuracy and the construction quality, the labor cost is reduced, and meanwhile, the use safety of the laser Doppler velocimeter can be ensured by using the fixing frame, and the service life of the device is prolonged.

The invention discloses a pipeline two-dimensional flow field flow velocity measurement system and method based on laser Doppler velocity measurement, and the system comprises a laser which is used for outputting a laser beam; the beam splitter is positioned behind the laser and is used for splitting the laser beam into two parallel measuring light beams which are propagated at equal intensity and equal optical path; the focusing reflection assembly is positioned behind the beam splitter and is used for reflecting and converging the two parallel measurement light beams at a flow field to-be-measured point in the pipeline and returning part of scattered light carrying flow field motion information along an original path to form scattered light to be measured; and the detection assembly is located on the light path of the to-be-detected scattered light and is used for collecting the to-be-detected scattered light. The device is applied to the technical field of pipeline flow velocity measurement, interference of a contact type measuring device on a flow field can be avoided, the problem of complex correction caused by a light incident angle when a traditional laser Doppler velocimeter measures two-dimensional flow field flow velocity distribution can also be avoided, the structure is simple, universality is better, and multi-point measurement is convenient.

The invention relates to a laser Doppler velocimeter for middle and long distance velocity measurement. After the laser Doppler velocimeter determines component parameters of an optical module according to detection requirements, the beam waist position of measuring light output by the optical module is adjusted by adjusting the distance between a positive lens group and a negative lens group in the optical module; an optical signal formed by interference of reference light and signallight is converted into a current signal containing Doppler frequency information, the current signal is processed through a signal processing system, so that the speed of a object to be measured is obtained, and middle and long distance speed measurement is achieved. With the laser Doppler velocimeter provided by the invention adopted, the problem of short measurement distance of a current velocimeter can be solved, and high precision and high signal-to-noise ratio of a measurement result can be ensured in middle and long distance measurement.

The invention discloses a tight combination method for calculating a pseudo range / pseudo range rate by using a Doppler velocimeter. The method comprises: step 1, installing a strapdown inertial navigation system, a laser Doppler velocimeter, and a Beidou satellite navigation system at a moving carrier, and electrifying the combined navigation system for starting up; step two, carrying out initial position parameter binding; step three, keeping the moving carrier to be still for five minutes, carrying out initial alignment to obtain an initial attitude angle; step four, starting a tight combination mode and starting the moving carrier; and step five, carrying out calculation to obtain a pseudo range value and a pseudo range rate value, and carrying out tight combination navigation by using differences between the pseudo range value and pseudo range rate value and pseudo range and pseudo range rate values outputted by a Beidou satellite navigation system as observation values of the combined navigation system. According to the invention, tight combination with the Beidou satellite navigation system is carried out by using the pseudo range value and pseudo range rate value calcualtd by the laser Doppler velocimeter and function complementation is realized; and the pseudo range value and pseudo range rate value of the moving carrier are deduced based on the location of the moving carrier and the Beidou satellite, so that high-precision navigation is realized.

The invention relates to a motion starting point automatic positioning method applied to a laser Doppler velocimeter. The motion starting point automatic positioning method solves the two defects of atraditional laser Doppler velocimeter: 1, the speed measurement precision in the initial motion stage is low; 2, and a relationship between an absolute moment and a movement speed of a measured object cannot be obtained. The motion starting point automatic positioning method comprises the following steps of (1) data acquisition and (2) calculation of a moment t1 when a measured object starts to move from a static state. The motion starting point automatic positioning method can automatically position to the absolute moment when the measured object starts to move from the static state, is convenient to obtain the relation between the absolute moment and the object movement speed, and improves the speed measurement precision in the initial movement stage.

The present application relates to an initial alignment method of an inertial navigation system based on a laser Doppler velocimeter. The method includes: in the earth-centered inertial coordinate system and the local navigation coordinate system, based on the speed measurement value of the laser Doppler velocimeter, the specific force equation and the estimation of the cosine matrix of the attitude direction, the alignment process of the strapdown inertial navigation system is established. Process models and measurement models. Construct the state vector with the attitude error of the inertial navigation equipment, the gyroscope zero offset drift, the accelerometer zero offset drift, and the installation angle error and scale coefficient error of the laser Doppler velocimeter as components, and establish a robust square root unscented quaternion estimation device, and get the predicted value of the state vector to carry out the initial alignment of the strapdown inertial navigation system during travel. The process model and measurement model of the above method utilizes the high-precision velocity output of the laser Doppler velocimeter, considers the inertial measurement unit error in the initial alignment, and the installation inclination and scale coefficient of the laser Doppler velocimeter, which can improve the attitude estimation precision.

The invention provides a calibration device and method for a laser Doppler velocimeter based on a lithium niobate modulator. The calibration device and method mainly solve the problem that in the prior art, detection and calibration of the laser Doppler velocimeter in a high speed measurement range are difficult to meet. The calibration device comprises a lithium niobate modulator, a radio frequency signal amplifier, a signal source, an optical fiber isolator, a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler and an optical fiber beam expander. According to the device and the method, the standard speed is generated through a Doppler signal simulation method, the measurement precision can be obtained according to the standard speed and the measurement speed, the detected laser Doppler velocimeter is calibrated, and the highest standard speed which can be simulated theoretically exceeds 10km / s.

The invention relates to a motion starting point automatic positioning method applied to a laser Doppler velocimeter. The motion starting point automatic positioning method solves the two defects of atraditional laser Doppler velocimeter: 1, the speed measurement precision in the initial motion stage is low; 2, and a relationship between an absolute moment and a movement speed of a measured object cannot be obtained. The motion starting point automatic positioning method comprises the following steps of (1) data acquisition and (2) calculation of a moment t1 when a measured object starts to move from a static state. The motion starting point automatic positioning method can automatically position to the absolute moment when the measured object starts to move from the static state, is convenient to obtain the relation between the absolute moment and the object movement speed, and improves the speed measurement precision in the initial movement stage.

The invention discloses a particle velocity measurement system of the impact surface and the free surface of a light-transmitting material, which includes a launch device, an impact object, a target plate, a target frame, and an all-fiber laser Doppler velocimeter, and the impact object is controlled by the launch device. The target plate is made of light-transmitting material, the impact surface of the target plate is coated with a total reflection film, the free surface of the target plate is coated with a semi-reflective film, the target plate is fixed on the target frame, and is facing the impact object, so The laser lens of the all-fiber laser Doppler velocimeter is directly arranged on the side of the target plate coated with a semi-reflective film, and is at a certain distance from the semi-reflective film. connected to the main body of the instrument. The invention solves the problem that the existing flat plate impact experiment device cannot accurately measure the particle velocity of the free surface of the target plate, and cannot simultaneously measure the particle velocity of the impact surface of the target plate, and has the advantages of accurate measurement results, high precision, and less susceptible to environmental interference The advantages.

A motion member (1) urged by an application spring 4 is made to collide with a surface of a sheet material supported by a support member (14) so as to be deflectable and deformable. The velocity of the motion member (1) during the collision process is detected every second by a measuring portion (17) of a laser Doppler velocimeter. A control circuit (121) measures the velocity of the motion member (1) immediately before the collision of the motion member (1) with the sheet material, the time period of deflection deformation until the sheet material collides with an opposing member (15), and the time period of compression deformation after the collision of the sheet material with the opposing member (15), and outputs a result thereof as sheet material information to a control portion (120). The timing at which the sheet material collides with the opposing member (15) is detected by an output of a piezoelectric element (16) connected to the opposing member (15).

The invention discloses an electric control system of a water tunnel type swimming machine and a control method thereof. The rotating speed of a motor is adjusted in a digital frequency driving manner. The rotating speed of a propeller impeller is adjusted through hydraulic or mechanical transmission, so that the water flow speed is controlled continuously and precisely. A water flow driving system comprises a driver, a motor and a propeller impeller. The driver controls the rotating speed of the motor through digital frequency and drives a hydraulic transmission device or a mechanical transmission device to drive propeller blades to rotate, thereby pushing water flow circulation and changing the water flow speed. An intelligent electric control system calibrates the speed of the water flow through a laser Doppler velocimeter LDV to obtain non-linear characteristics of the water flow speed and the rotation speed of the motor; the data are stored in a monitoring program of the electriccontrol system; and the water flow speed is adjusted in real time. Under the cooperation of electrical appliances like a circulating pump, a jet pump, a heater, a sterilizer, and a laser Doppler velocimeter, the comprehensive performance of the water tunnel type swimming machine can be intelligentized in multiple aspects.

The invention relates to an eye movement tracking device (20) comprising: a camera (2) configured to take an image of an eye (10) at a first scan rate; a laser velocimeter (3) configured to capture an eye velocity of the movement of the eye (10) at a second scanning rate by means of a laser Doppler velocimeter; and a control device (4) configured to determine an absolute eye position based on the image and to track a gaze direction of the eye (10) based on the absolute eye position and the eye speed.