RU2340872C1 - Monostatic method of determining distance to object, its direction and speed - Google Patents

Abstract

FIELD: physics; measurements.

SUBSTANCE: proposed method can be used in tracking and detection devices and allows for obtaining information on the distance to an object with unknown linear dimensions, as well as information on the direction and speed of the object. Determination of the distance to an object, its direction and speed is done at discrete time intervals using an optical imaging device, with an adjustable optical system with two known limiting focal distances (for example, a zoom lens). Two images of the object are obtained, distinguished by scale. The distance to the object is determined from the expression

where f₁ and f₂ are the limiting focal distances of the optical system, y₁' and y₂' are the dimensions of the image of the object for f₁ and f₂ respectively. The direction and the speed of the object are determined through comparison of the position of the object on the images of one scale, obtained from the current and preceding measurements of the distance to the object, taken after known time intervals.

EFFECT: obtaining information on the distance to an object with unknown linear dimensions, as well as information on the direction and speed of the object.

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Description

The invention relates to measuring technique and can be used in tracking devices and registration of objects and allows to obtain information about the distance to objects with unknown linear dimensions, as well as information about the direction and speed of their movement.

A known method that implements the system [1], designed for passive determination of the coordinates of the radiation source (horizontal angle, elevation angle and distance) using two television CCD cameras. The cameras in the system [1] are located on one common vertical axis, around which they can rotate synchronously, and at a known distance from each other so that their optical axes are always in the same vertical plane. In this case, the distance is determined by the method of triangulation from the angles of the apparent displacement of the radiation source received from each of the cameras. The disadvantages of this method are the need for spacing CCD cameras a certain distance from each other, which increases the dimensions of the system, and the presence of mechanical vertical and horizontal rotary devices, which reduces the accuracy of the vertical and horizontal angles of the optical axes of the CCD cameras. In addition, the need to use two photodetectors significantly increases the cost of the system and reduces its reliability.

Closest to the proposed one is the prototype method for determining the distance to an object using an optical device [2], which includes measuring the image size of an object in the image plane of an optical device before and after moving the optical device towards the object (or away from it) along the line of sight of the optical device at a fixed distance, after which the distance to the object is determined by the formula.

The disadvantages of this method are the need to determine the distance of the mechanical movement of the optical device and compliance with the requirements for moving the optical device strictly along its optical axis, which significantly reduces accuracy and makes measurement difficult.

The problem to which this invention is directed is to eliminate the influence of mechanical movement of the photodetector on the accuracy of measuring the distance to the object.

The technical result is to increase the reliability and accuracy of measurements and expand the functionality in determining the spatial coordinates of an object with previously unknown linear dimensions.

The specified technical result in the implementation of the invention is achieved by the fact that in the known method, the distance to the object is determined using a photodetector by measuring the image size of the object in the image plane, the photodetector is additionally moved along its optical axis towards the object (or away from it) and the dimensions are measured again image of the object in the image plane of the photodetector, after which the distance to the object is determined according to the formula

where s is the distance over which the optical device was moved;

y ₁ 'is the size of the image of the object before moving;

y ₂ 'is the size of the image of the object after moving.

In contrast to the method known in the proposed method, using an optical photodetector having a tunable optical system with two known boundary focal lengths (for example, a zoom lens or a zoom lens), two different-sized images of the selected object are obtained and the distance to it is determined by the formula:

where ₁ 'is the size of the image of the object at f ₁ ,

y ₂ 'is the image size of the object with f ₂ ,

f ₁ and f ₂ are the boundary focal lengths of the optical system.

The direction and speed of the object is determined by comparing the position of the object on the images of the same scale, obtained in the current and previous measurements of the distance to the object, made after a known period of time.

Comparison of the proposed method with the prototype made it possible to establish compliance with their condition of "novelty." When comparing the proposed method with other known technical solutions, no similar signs were revealed, which allows us to conclude that the condition "inventive step" is met.

The method is illustrated by drawings. Figure 1 explains the relative position of the object and its image at the boundary focal lengths f ₁ and f _{2 of the} optical system. Figure 2 illustrates a method for determining the direction and speed of an object.

Example. The optical photodetector has a tunable optical system with known boundary focal lengths f ₁ and f ₂ .

At a certain point in time t _i-2 , an image of an object is obtained at a focal length f ₁ , the optical system is rebuilt, and at time t _i-1 , an image of an object is obtained at a focal length f ₂ . Taking into account that the tuning time of the optical system is insignificant, i.e. t _i-2 -t _i-1 ≈ 0, it can be assumed that both images of the object were obtained simultaneously at time t _i-1 , while both images of the object differ only in scale.

According to [3] we have (figure 1):

(1)

(one)

(2)

(2)

whence follows

(3)

(3)

where β ₁ is a linear increase in the optical system at f ₁ ,

β ₂ - a linear increase in the optical system at f ₁ ,

y is the linear size of the object. In addition, according to [3], we have the following relations:

(4)

(four)

where a is the distance from the optical system to the object,

a 'is the distance from the optical system to the image plane and

(5)

(5)

Substituting (5) in (4) we obtain:

(6)

(6)

After which the expression (3) takes the form:

(7)

(7)

whence we get that the distance to the object can be determined by the following formula:

(8)

(8)

To determine the direction and speed of the object on the image obtained at time t _i-1 , the coordinates x _i-1 and _{i-1 of} object C are determined (Fig. 2).

At the next discrete time instant t _i , the coordinates x _i and y _{i of the} object C are re-determined. Knowing the distance to the object, the time interval between measurements Δt = t _i -t _i-1 and the coordinate difference Δx = x _i -x _i-1 and Δy = y _i -y _i-1 , determine the components of the speed V _x and V _y and then the speed V

(9)

(9)

and the direction of motion φ of the object C (figure 2)

(10)

(10)

Thus, the proposed method allows to obtain information about the distance to the object, its direction and speed. An advantage of the invention is that the measurement accuracy is improved due to the absence of mechanical movement of the photodetector during the measurement and the use of a tunable optical system having one optical axis at different focal lengths.

Used sources

1. European patent No. EP 0379425, IPC G01C 3/18, G01S 11/12, for the invention "System for determining the position of at least one target by means of triangulation".

2. RF patent No. 2095756, IPC G01C 3/32, for the invention "Method for determining the distance to an object using an optical device".

3. Applied optics. Ed. Zakaznova N.P. - M.: Mechanical Engineering, 1988 .-- 312s.

Claims (1)

A monostatic method for determining the distance to the object, its direction and speed, at which the image size of the object is measured twice in the plane of the photodetector images, characterized in that the image of the object is obtained in different scales by rebuilding the optical system of the photodetector, which has two known focal lengths, then determine the distance to the object according to the formula

where f ₁ and f ₂ are the boundary focal lengths of the optical system; y ₁ 'and y ₂ ′ are the sizes of the image of the object at f ₁ and f _2, respectively, and the direction and speed of movement of the object is determined by comparing the position of the object on images of the same scale obtained in the current and previous measurements of the distance to the object made after a known period of time .

Images