JPS62127686A - Laser doppler speed indicator - Google Patents

Abstract

PURPOSE:To reduce an error in speed measurement due to variation in measured distance by measuring the quantity of variation in the measured distance between an optical transmission system and a moving body from reference distance and correcting the error in speed measurement. CONSTITUTION:An optical displacement meter 11 which uses the principle of triangulation measures the quantity DELTAlp of variation in the measured distance between optical transmission systems 5a and 5b and moving body 1 from the reference distance l0 and the quantity DELTAlp of variation outputted by the displacement meter 11 and a speed measured value v' outputted by a speed computing element 10 are inputted to a measured distance correcting circuit 13. The measured distance correcting circuit 13 performs arithmetic operation shown by an equation. When a proportional constant (k) is set equal to an error in measurement per unit measured distance variation, the output v'' of the measured distance correcting circuit 13 becomes equal to the speed (v) of the moving body 1 and the error in speed measurement due to variation in measured distance is reduced.

Description

[Detailed description of the invention] [Industrial application field] This invention utilizes the Doppler effect of light to produce steel.

This invention relates to a laser Doppler velocimeter that non-contactly measures the speed of moving objects on a production line for non-ferrous metals.

[Conventional technology]

Generally, a laser Doppler velocimeter having a configuration as shown in FIG. 2 has been used to measure the speed of a moving object using the Doppler effect of light. FIG. 2 is a configuration diagram of a conventional laser Doppler velocimeter shown in, for example, the optical fiber sensor laser interferometer described in Mitsubishi Electric Branch Axis Voz, 5B No. 7, 1984, pages 34 to 38. +11 is a moving object.

(2) is a laser beam, (3) is a beam splitter that splits the laser beam into two, (4a), (4b) is an optical system (5a) that transmits the laser beam that is split into two by the beam splitter (3).
), (51)),
(4) is an optical fiber cable that transmits the received light of the receiving optical system (described later), (6) is the receiving optical system that receives the light scattered from the moving object (1), and (7) is the optical fiber cable that transmits the received light. A photodetector that converts into an electrical signal, (8) is an amplifier, (9
) is a frequency tracker, and αO is a speed calculator.

As shown in Figure 2, the laser beam (2) transmitted to the moving object (1) is split into two by the beam splitter (3), and each beam is sent to the optical fiber cable (4a) (4b).
When the transmitting optical systems (5a) and (5b) cross-irradiate the moving object (1) from opposite directions, the wavelength of the scattered light from the moving object (11) corresponding to each transmitted light beam is:

A so-called positive and negative Doppler shift occurs depending on the speed mv of the moving object (11). The scattered light that has undergone these two positive and negative Doppler shifts is received by the receiving optical system (6).

When the optical fiber cable (4C) leads to the photodetector (7) and converts it into an electrical signal, some of the electrical signals.

There are a DC signal proportional to the intensity of received light and an AC signal (hereinafter referred to as a Doppler signal) having a Doppler frequency fcl shown in equation (1).

where V: velocity of the moving object λ; wavelength ψ of the laser beam; intersection angle of the two transmitted light beams. By measuring the Doppler frequency fd with the second frequency tracker (9) and calculating the speed with the speed calculator On according to equation (1), the moving object f can be detected.
The velocity ■ of il can be found. This is a known fact.

Figure 3 is a diagram showing the intersection of two beams from the transmission optical system (5a) and (5b), and the beam diameter,
Δθ beam spread, point A, point B, and point 0 indicate the intersection of two beams, respectively.

Indicates the intersection of the lower, middle, and upper limits of the beam.

t is transmission optical system (5a), (5b) or moving object +1
The measurement distance to 1, 2・Δt is the distance between the intersection A and 0 of the two beams, and the beam intersection angle at point ψ and B.

ψ1 is the beam intersection angle at point A, and ψ2 is the beam intersection angle at point 0.

In a laser Doppler velocimeter, in order to obtain a Doppler signal by receiving scattered light that has undergone a Doppler shift from each of the two beams, the moving object (1)
between the points).

Usually, the traveling line P (hereinafter referred to as a path line) of the moving object (1) or the intersection Bf of two beams).

The transmitting optical systems (5a) and (5b) are arranged perpendicular to the center line where the two beams intersect, and the measured distance to at this time is used as the reference distance, and the speed measurement value V of the speed calculator α
' is calibrated to be equal to the velocity V of the moving object (1).

In this case, even if the path line P of the moving object il+ moves in parallel, if it does not exceed point A or point 0, a Doppler signal will be obtained and the velocity V of the moving object (11) can be measured. In other words, the beam intersection The length 2·Δt indicates the variation range of the allowed path line P in which the speed of the moving object (1) can be measured.

If the moving object (1+ path line P passes through point B,
Since the beam intersection angle is ψ, the Doppler frequency fd is given by the fi1 equation for the velocity V. However, when the path line P fluctuates and passes through point A, the beam spread is
Since the beam crossing angle ψ1 becomes ψ1-ψ+2·Δθ due to θ, the Doppler frequency f+H is given by the following equation.

Similarly, when the path line P fluctuates and passes through the 0 point, the beam intersection angle ψ2 times ψ2 = ψ-2Δθ, which is given by the Doppler frequency fd2 order equation.

As is clear from equations (11 to 31), when the moving object fi1 causes a change in the path line P, the moving object (1)
The Doppler frequency obtained for the velocity V of [ is a different value, and the velocity meter + 1111 f direct V' of the velocity calculator H that calculates the velocity of the moving object (1) from the Doppler frequency contains an error. That will happen.

Now, the measurement error rate ε when the path line P changes to point A or point ko is based on the Doppler frequency fd when the path line passes through point B from equations (1) to (3). is given by the following equation.

2・sin (Δθ) m−・・・−Song (4) jan ((L) Length of beam intersection 2・ΔtId”, beam radius and beam intersection angle ψ or I− are approximated by the following equation can.

Therefore, the measurement error δ of the path line Pni distance variation υ
is given by the following equation from equations (41 and (5)).

δ = □ 2・Δt (6) Normally, the beam spread Δθ is designed to be less than the number mrad, and the wide beam intersection angle is less than 10°, so the angle Δθ slope Δθ,
cos (71ζ1), equation (6) is approximated by the following equation.

For example, the beam spread Δθ is 3 and the beam diameter is 41.
'', the measurement error δ is 2X3X10 r
ad 4 city m-1・5X10 (,;ゝ =-=-(Fil
This results in a constant error of 611 for the pass line P fluctuation (approximately -0,15←). Here, the sign of formula 181 is ←).

This indicates that when the path line P changes in the direction of increasing the measurement distance l, a negative measurement error is given.
A measurement error approximately equal to f11 is given to the measurement distance variation.

If the path line P passing through point B in FIG. 3 is used as a reference and the amount of path line variation from the measured distance io at this time is Δtp, then the speed measurement value V' of the speed calculator is given by a quadratic equation.

v'=v(1+δ,Δtp)---9-f9
) The pass line variation amount Δtp is determined when the measured distance t is the reference distance t.
Let the direction in which the force is longer than o be (-1-), and the direction in which the force is shorter than 9, on the contrary, be ←).

Generally, the PH of a moving object such as a steel line (bus line 11) fluctuates by several nm to several tens of vm due to the flap of the plate during threading. Therefore, the transmission optical system (5a), (5b) and the moving object (1 The measured distance between them will change.

This causes an error in the speed measurement value.

[Problem that the invention seeks to solve]

The conventional laser Doppler speedometer described above has a problem in that it produces a speed measurement error that is approximately proportional to the amount of variation Δtp of the measurement distance from the reference distance Ao due to the path line variation of the moving object (1). there was.

The present invention has been made to solve these problems, and an object thereof is to obtain a laser Doppler speedometer that reduces speed measurement errors caused by fluctuations in measurement distance.

[Failure to solve the problem]

The laser Doppler velocimeter according to the present invention uses transmission optical systems (5a) and (5b), a displacement meter that measures a variation meter Δtp of the measurement distance of a moving object filJf from a reference distance to, and the output of the displacement meter. A measurement distance correction circuit is provided to correct speed measurement errors.

[Effect]

In this invention, the transmission optical system (5a), (5b)
A displacement meter for measuring the amount of variation Δtp in the measured distance from the reference distance to between the moving object and the moving object (11) and a measured distance correction path are provided at the output end of the speed calculator O1, and the speed is adjusted approximately in proportion to the measured distance variation. The speed output of the speed calculator σ which causes the measurement error is corrected using the output of the displacement meter that measures the measurement distance variation Δtp so as to reduce the measurement error.

〔Example〕

FIG. 1 is a block diagram of a "laser Doppler speed converter" showing one embodiment of this invention, and will be described below with reference to the drawings.

In the figure, (1) to Q0 are the same as the above-mentioned conventional device. +1
11 is a triangle 611] A non-contact displacement meter, represented by an optical displacement meter that uses the principle of quantity, is a transmission optical system (5a), (
5b).

A probe that integrates the receiving optical system (6) and displacement meter 01+.

03) is a measurement distance correction path that corrects the output of the speed calculator 00.

PB to the laser Doppler speedometer with the above configuration.

The displacement meter (II) measures the amount of variation Δtp of the measurement distance between the transmission optical system (5a), csb) and the moving object (1) from the reference distance to, and calculates the amount of variation Δtp which is the output of the displacement meter (11).
tp and the speed measurement value V' which is the output of the speed calculator θ1 are respectively input to the measured distance correction circuit o; 3). The measured distance correction circuit α performs the calculation shown in Equation 01.

■! Proportionality constant V'': Output of the measurement distance correction circuit (I3) Now, if the proportionality constant kf of the OI equation is set to be equal to the measurement error δ per unit measurement distance change shown in the equation (8), then Section (9),
From equation Q1, the output V" of the measurement distance correction circuit (13) is equal to the velocity V of the moving object fll, and it is determined that the laser Doppler velocimeter is a laser Doppler velocimeter that reduces speed measurement errors due to measurement distance fluctuations.

〔Effect of the invention〕

As described above, according to the present invention, the transmission optical system (5a)
, (5b) Measured distance variation ΔA between moving objects (1)
A displacement meter that measures l) and a measurement distance correction l path 0ait are installed at the output end of the speed calculator α, and the measurement distance variation amount Δtp
and the speed measurement value V' which is the output of the speed calculator 01.
By performing the correction shown in Equation 1, it is possible to provide a laser Doppler speedometer that reduces speed measurement errors due to fluctuations in measurement distance.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a laser Doppler velocimeter showing an embodiment of the present invention, FIG. 2 is a block diagram of a conventional laser Doppler velocimeter, and FIG. 3 is a diagram showing a beam intersection of a transmitting optical system. In the figure, 01) is a displacement meter, 62 is a probe, and (13 is a measurement distance correction circuit. The same reference numerals in the figure indicate the same or equivalent parts.

Claims (1)

[Claims] A laser that outputs a specific wavelength, a beam splitter that splits the output beam of the laser into two, an optical fiber cable that transmits the laser beam that is split into two, and a cable that receives the transmitted laser beam and is mounted on a moving object opposite to each other. two transmitting optical systems that emit radiation from different directions, a receiving optical system that simultaneously receives scattered light that has undergone a Doppler shift in accordance with the speed of the moving object for each of the two irradiated beams, and the receiving optical system. an optical fiber cable that transmits the scattered light including the Doppler signal received by the receiver, a photodetector that electrically converts the transmitted scattered light, an amplifier that amplifies the output of the photodetector, and a In a laser Doppler velocimeter that includes a frequency tracker that detects a Doppler frequency and a speed calculator that calculates the speed of a moving object from the Doppler frequency that is an output signal of the frequency tracker, there is a distance between the moving object and the transmitting optical system. a displacement meter that detects the amount of variation in the measurement distance; and a measurement distance that corrects the output of the speed calculator that causes a speed measurement error due to the variation in the measurement distance so as to reduce the speed measurement error using the output of the displacement meter. A laser Doppler velocimeter characterized by comprising a correction circuit.