Vehicular radar device
Provided is a vehicular radar device which is capable of reducing an operation resource quantity necessary for a process of estimating an axis deviation angle in a radar measurement coordinate system, to thereby reduce a device size. The vehicular radar device includes: a measurement unit that measures an azimuth angle and a relative Doppler velocity; an extraction/accumulation unit that extracts target information satisfying conditions related to the relative Doppler velocity, a travel speed and a turning velocity, and accumulates the azimuth angle and a velocity ratio obtained by dividing the relative Doppler velocity by the travel speed of the subject vehicle among the extracted target information; and an axis deviation angle estimate unit that reads the target information accumulated in the extraction/accumulation unit, and estimates an axis deviation angle of the measurement coordinate system of a radar based on a second-order polynomial expression of the azimuth angle of the target.
1. A vehicular radar device, comprising:
a measurement unit that measures an azimuth angle and a relative Doppler velocity of a target as target information;
a travel speed detection unit that detects a travel speed of a subject vehicle;
an angular velocity detection unit that detects a turning velocity of the subject vehicle;
an extraction/accumulation unit that extracts target information satisfying conditions related to the relative Doppler velocity of the target, the travel speed of the subject vehicle, and the turning velocity of the subject vehicle, and accumulates the azimuth angle and a velocity ratio obtained by dividing the relative Doppler velocity by the travel speed of the subject vehicle among the extracted target information as new target information; and
an axis deviation angle estimate unit that reads the target information accumulated in the extraction/accumulation unit, and estimates an axis deviation angle of a measurement coordinate system of a radar based on a second-order polynomial expression of the azimuth angle of the target.
2. A vehicular radar device according to claim 1 , wherein when it is assumed that the azimuth angle of the target is θ, the velocity ratio obtained by dividing the relative Doppler velocity by the travel speed of the subject vehicle is γ, and a velocity error ratio included in the relative Doppler velocity and the travel speed of the subject vehicle is 1, the axis deviation angle estimate unit approximates a right-hand side of
γ=cos(θ+ψ)
that is an expression satisfied by a reference axis deviation angle ψ in the measurement coordinate system of the radar by the second-order polynomial expression of the azimuth angle θ of the target to obtain the following approximate expression, and estimates the axis deviation angle based on the approximate expression,
γ=cos(θ+ψ)≈− a (θ) 2 +b (θ)+ c
where a, b, and c are coefficients.
3. A vehicular radar device according to claim 2 , wherein the axis deviation angle estimate unit approximates a binomial coefficient a by an invariant fixed value in the approximate expression to obtain only a monomial coefficient b, and calculates the axis deviation angle to be estimated by b/2a.
4. A vehicular radar device according to claim 1 , wherein the extraction/accumulation unit extracts, as the target information that satisfies extraction conditions, target information that a travel turning radius of the subject vehicle which is calculated from the travel speed of the subject vehicle from the travel speed detection unit and the turning velocity of the subject vehicle from the angular velocity detection unit falls within a predetermined range being regarded as a straight travel, and an absolute velocity of the target which is calculated from the travel speed of the subject vehicle from the travel speed detection unit and the relative Doppler velocity from the measurement unit falls within a predetermined range being regarded as a stationary object.
5. A vehicular radar device according to claim 1 ,
wherein the extraction/accumulation unit accumulates, as new target information, a predetermined number of the azimuth angles and a predetermined number of the velocity ratios, and
wherein the axis deviation angle estimate unit reads a plurality of the azimuth angles and a plurality of the velocity ratios each being the new target information from the extraction/accumulation unit, and estimates the axis deviation angle of the measurement coordinate system of the radar.
6. A vehicular radar device according to claim 1 , wherein the measurement unit corrects the azimuth angle of the target information which is measured by the radar by using the axis deviation angle estimated by the axis deviation angle estimate unit.
7. A vehicular radar device according to claim 6 , further comprising a control unit that transmits, when the axis deviation angle estimated by the axis deviation angle estimate unit falls within a predetermined range, the axis deviation angle estimated by the axis deviation angle estimate unit to the measurement unit and controls so as to correct the azimuth angle of the target information which is measured by the radar and notifies, when the estimated axis deviation angle is beyond the predetermined range, a driver of an abnormality of an output result from the vehicular radar device.