METHOD FOR ADJUSTING A SELF MIXING LASER SENSOR SYSTEM FOR MEASURING THE VELOCITY OF A VEHICLE

• US 20120016615A1
• Filed: 01/18/2010
• Published: 01/19/2012
• Est. Priority Date: 01/20/2009
• Status: Active Grant

• Current Assignee: TRUMPF Photonic Components GmbH (TRUMPF SE + Co. KG)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Carpaij, Mark, Van Der Lee, Alexander Marc, Engelbrecht, Bernd, Schemmann, Marcel, Moench, Holger, Heinks, Carsten
• Granted Patent: US 9,229,024 B2
• Time in Patent Office: Days
• US Class Current: 702/96
• CPC Class Codes: B60T 2250/04 Vehicle reference speed; Vehicle body speed
• CPC Class Codes: G01C 22/00 Measuring distance traversed on the ground by vehicles, persons, animals or other moving solid bodies, e.g. using odometers, using pedometers
• CPC Class Codes: G01P 13/00 Indicating or recording presence, absence, or direction, of movement electric switches H01H; counting moving objects G06M7/00
• CPC Class Codes: G01P 21/02 of speedometers
• CPC Class Codes: G01P 3/366 by using diffraction of light for measuring speed of fluids G01P5/26
• CPC Class Codes: G01S 1/00 Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith position fixing by co-ordinating a plurality of determinations of direction or position lines G01S5/00
• CPC Class Codes: G01S 13/60 wherein the transmitter and receiver are mounted on the moving object, e.g. for determining ground speed, drift angle, ground track G01S13/64 takes precedence
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/875 for determining attitude
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4916 using self-mixing in the laser cavity
• CPC Class Codes: G01S 7/4972 Alignment of sensor

Abstract

The method is based on a determination of the orientation of the sensor to the surface moving with respect to the sensor and then acquiring data where the lateral velocity is small and the forward velocity is large. Then, the orientation of the sensor with respect to the direction of the forward velocity is determined and the velocity data subsequently measured are corrected using the measured orientation of the sensor with respect to the reference surface and the forward velocity direction.

Claims

1. A method of adjusting a self mixing laser sensor for measuring the velocity of a vehicle moving relative to a reference surface, the method comprising the steps of:

determining the frequency of self-mixing intensity oscillations caused by Doppler-induced phase shift of the laser light reflected back from the surface and re-entering the cavity of the at least one laser,

calculating a velocity from said frequency of self-mixing intensity oscillations,

determining the orientation of the sensor in relation to the reference surface and a predetermined direction of movement using at least a first laser beam of said self mixing laser sensor, said step of determining the orientation of the sensor comprising the steps of determining, whether the direction of movement of the vehicle coincides with a predetermined direction of movement, obtaining velocity data for a movement of said vehicle along said predetermined direction of movement, and calculating a transformation based on said velocity data for a movement of said vehicle along said predetermined direction of movement, and

adjusting velocity data determined by means of the self mixing laser sensor based on the determined orientation of the sensor, said step of adjusting velocity data comprising applying said transformation to measured velocity data.

2. The method of claim 1, further comprising determining the orientation of the sensor by measuring the vertical velocity of the vehicle perpendicular to the reference surface and adjusting the velocity data by means of a coordinate transformation so that the adjusted average vertical velocity is zero.

3. The method of claim 1, further comprising determining the orientation of the vehicle by at least a second laser beam and a third laser beam being emitted in linear independent directions with respect to each other and the first laser beam and the velocity data is adjusted by means of a coordinate transformation which compensates the mismatch in orientation of the sensor and the reference surface.

4. The method of claim 1, comprising determining the predetermined direction of movement of the vehicle by means selected from the group consisting of a steering wheel sensor, an acceleration sensor, a compass, a comparison of rotation speed data of wheel speed sensors, and a GPS unit.

5. The method of claim 1, comprising determining the predetermined direction of movement of the vehicle by storing measured velocity data and averaging said data, said averaged data representing said predetermined direction of movement.

6. The method according to claim 1, wherein the step of obtaining velocity data for a movement of the vehicle along the predetermined direction of movement is carried out in response to the measurement of a velocity component exceeding or falling below a predetermined threshold.

7. The method according to claim 1, wherein the step of calculating a transformation based on said velocity data for a movement of said vehicle along said predetermined direction of movement comprises the steps of

determining a first transformation that aligns a plane of the sensor coordinate system parallel to the reference surface, and

determining a second transformation which rotates the plane of the sensor coordinate system around its perpendicular direction so that the amount of the lateral velocity is minimised.

8. The method according to claim 1, wherein the step of calculating a transformation based on said velocity data for a movement of said vehicle along said predetermined direction of movement comprises the steps of

determining a first transformation which minimises the component of the forward velocity in the direction of the sensor coordinate system perpendicular to the reference surface or the amount of the velocity perpendicular to the reference surface,

determining a second transformation which minimises the component of the lateral velocity, and

determining a third transformation which minimises the correlation between the lateral and perpendicular components of movement.

9. The method according to claim 1, wherein the step of calculating a transformation based on said velocity data for a movement of said vehicle along said predetermined direction of movement comprises determining the three distances between laser and said reference surface and calculating a transformation from said three distances, said transformation aligning the sensor the velocities in the center coordinates to the velocities of the reference surface.

10. A laser self-mixing velocity sensor for determining the velocity moving relative to a reference surface, comprising

at least one laser,

circuitry for determining the frequency of self-mixing intensity oscillations caused by Doppler-induced phase shift of the laser light reflected back from the surface and re-entering the cavity of the at least one laser,

circuitry for determining the velocity along at least one predetermined direction from said self-mixing intensity oscillations, and

circuitry for determining the orientation of the sensor in relation to the reference surface using at least a first laser beam of said self mixing laser sensor, said circuitry comprising circuitry for determining, whether the direction of movement of the vehicle coincides with a predetermined direction of movement, obtaining velocity data for a movement of said vehicle along said predetermined direction of movement, and calculating a transformation based on said velocity data for a movement of said vehicle along said predetermined direction of movement, the laser self-mixing velocity sensor further comprising circuitry for adjusting velocity data determined by means of the self mixing laser sensor based on the determined orientation of the sensor by applying said transformation to measured velocity data.

11. The laser self-mixing velocity sensor according to the preceding claim 10, comprising

at least two lasers,

circuitry for determining the velocity along at least one predetermined direction from said self-mixing intensity oscillations,

circuitry for detecting phase jumps or minima of the self-mixing Doppler induced intensity oscillation of at least one of the at least three laser beams at interfaces of speckle induced intensity oscillations and

circuitry for correcting a deviation of a signal derived from the frequency of the Doppler induced intensity oscillation at the interfaces of speckle induced intensity oscillations, the deviation resulting from the phase jumps.

12-15. -15. (canceled)