JP3350113B2 - Incident light amount monitor circuit for laser length measuring machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an incident light amount monitor circuit for a laser length measuring machine.

[0002]

2. Description of the Related Art As a length measuring machine capable of measuring a length with high accuracy, a laser length measuring machine is known.
Technical document "Hikari Alliance" (March 1991, p. 29-33)
Discloses a length measuring machine of this type. The laser measuring machine shown in this technical document has a laser tube that emits light in a predetermined polarization state, light emitted from this laser tube is incident, the incident light is divided, and the target is measured and referred to. An interferometer that projects light onto an optical target and receives and combines the reflected light from each of these targets. A polarization process is performed on the output light from the interferometer to convert it into a sinusoidal electric signal having a phase difference of 90 degrees. And the measurement resolution is 1 / 8λ
(≒ 0.079 μm).

By the way, when actually measuring a length with this type of laser length measuring machine, if the distance between the interferometer and the target to be measured becomes longer, the intensity of the light emitted from the interferometer becomes lower, resulting in an inaccurate measurement. Measurement becomes difficult. Therefore, conventionally, the amplitude of a sine wave electric signal having a phase difference of 90 degrees obtained by polarization processing is obtained, and this is used as a monitor signal. Or not.

FIG. 5 shows an example of an incident light amount monitoring circuit for a laser length measuring device which has been conventionally employed. The incident light amount monitoring circuit shown in FIG.
A sine wave signal of B is inputted and an amplitude signal Y is detected. A diode a for rectifying the input signals A and B, and -A and -B are inputted with the signals A and B as inputs.
A pair of inverting circuits b for generating a signal (indicating one of the signals complementary to each other with a sign-) and an inverting circuit b
A rectifying diode c connected to the output side of
The four diodes a and c are connected together on the output side.

[0005] In the incident light amount monitoring circuit thus configured, as shown in FIG.
When acos θ is input as θ and the sine wave signal B, the rectified signals A and B and the rectified inverted signals −A and −B of the same signals are added to form a pulsating flow. An output signal Y is obtained. However, such a conventional incident light amount monitoring circuit has a technical problem described below.

[0006]

That is, in the above-described incident light amount monitoring circuit, the output signal Y has a pulsating flow as shown in FIG. Therefore, it fluctuates between a and a / square root 2. For example, if the amplitude a of the input signals A and B is 1v,
The output signal Y becomes 0.7 to 1 V, and a fluctuation of 0.3 V occurs. The present inventors have actually input such a signal into the meter and measured it.As a result, it is difficult to obtain an accurate amplitude value because the pointer of the meter fluctuates, and therefore, it is possible to accurately judge the quality of the measurement. There was a problem of not being able to.

[0007] The present invention has been made in view of such a conventional problem, and an object of the present invention is to obtain an accurate output signal without fluctuation, thereby making it possible to accurately judge the quality of a measurement state. It is an object of the present invention to provide an incident light amount monitoring circuit for a laser length measuring device which can be used.

[0008]

In order to achieve the above object, the present invention provides a laser tube for emitting light of a predetermined polarization state, a light emitted from the laser tube being incident, and splitting the incident light. And interferometers that project light onto the target to be measured and the reference light target and receive and combine the reflected light from each of these targets. Polarization processing is performed on the light emitted from the interferometer to produce a phase difference of 90 degrees. in the laser measuring instrument to obtain a measurement pulse is converted into a plurality of sinusoidal electrical signal having the sine wave electric signal converted photoelectrically, light intensity
Relates degrees as input a plurality of sine wave signals having a phase difference of the 90 degrees, 2 having a phase difference of 90 degrees
An addition and subtraction circuit that outputs two sine wave signals, a pair of squaring circuits that receive the output of the addition and subtraction circuit, receive the sine wave signal having the phase difference of 90 degrees as an input, and output a square signal thereof; An addition circuit connected to the output side of the squaring circuit for outputting an added value signal obtained by adding the square value signal; and a square root connected to the output side of the addition circuit for outputting a square root value of the added value signal. And determining whether the measurement of the laser length measuring device is good or not from the output signal value of the square root circuit .
Characterized in that that.

[0009]

According to the incident light amount monitoring circuit for a laser length measuring device having the above-described structure, for example, the input sine wave signals X and Y
And acos θ, the square value signal that is the output of the squaring circuit is X ² = a ² sin ² θ, Y ² = a ² cos ²
θ, and the added value signal of the adder circuit obtained by adding these square value signals is X ² + Y ² = a ² sin ² θ + a ² cos
² θ = a ² (sin ² θ + cos ² θ), and sin
Since ^{2 θ} + cos ^{2 θ} 1, after all addition value signal becomes a ^2. When the sum signal is calculated by a square root circuit, an output signal a is obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIGS. 1 to 4 show an embodiment of an incident light amount monitor circuit for a laser length measuring apparatus according to the present invention. FIG. 1 shows the overall configuration of a laser length measuring apparatus to which the incident light amount monitoring circuit of the present invention is applied. Is shown. First, the laser length measuring machine shown in FIG.
The laser length measuring machine is a light of a predetermined polarization state, for example, 45 °
, A laser tube 1 that emits linearly polarized light, an interferometer 2, a target prism 3 to be measured, a target prism 4 for reference light, and a polarization processing unit 5.

[0011] Between the laser tube 1 and the interferometer 2,
A polarizing beam splitter 6 for extracting a signal for monitoring the light emission state of the laser tube 1 and a photodiode 7 are provided, and a beam for expanding light emitted from the laser tube 1 into a beam suitable for long-distance measurement. An expander 8 is provided. The interferometer 2 splits the light incident from the beam expander 8 in two directions, irradiates the split light to the target prism 3 for measurement, and the target prism 4 for reference, respectively.
Receives reflected light from and synthesizes.

The polarization processing unit 5 includes first and second polarization beam splitters 5a and 5b, a λλ plate 5c provided between the polarization beam splitters 5a and 5b,
First of which receives the light separated by the polarizing beam splitter 5a
It is composed of a polarizing plate 5d and a second polarizing plate 5e that receives the light split by the second polarizing beam splitter 5b.
The photodiodes 9a, 9b, 9c receive the light passing through the first and second polarizing plates 5d, 5e and the light separated by the second polarizing beam splitter 5b, respectively, and convert the received light into an electric signal. Is provided.

[0013] In the laser length measuring machine thus configured,
Photodiode 9a, 9b, the light 9c detects intensity of each I _a, I _b, and I _c, when the phase and [delta], which are respectively _{I a α (1-sinδ)} , I b α (1 + s
in δ) _, I _c ∝ (1 + cos δ), which is shown in FIG. 2, and as shown in FIG. 2, these light intensities become sine wave signals having a phase difference of 90 degrees. In the actual length measurement, electrical processing is performed from the output signal shown in FIG. 2 to obtain a length measurement pulse having a length measurement resolution of 1 / 8λ.
The distance is calculated from this pulse.

On the other hand, the incident light amount monitor for judging whether the length measurement is good or not.
The details of the circuit 20 are shown in FIG. In the figure
The incident light amount monitoring circuit 20 shown includes a photodiode 9a,
9b output signal I_a,I_bAs an input signal, I_a−
I_bIs calculated, the signal of X = asinθ is
A subtracting circuit 20a for sending out, photodiodes 9a, 9
b, output signal I from 9c_a,I_b, I_cIs the input signal
And 2I_c− (I_a+ I _b)
An addition / subtraction circuit 20b for transmitting a signal of Y = acos θ
Have.

The subtraction and addition / subtraction circuits 20a, 20
A pair of squaring circuits 20c and 20d, to which sine wave signals of these circuits are input and output their square signals, respectively, are connected to the output side of 0b. An output side of each of the squaring circuits 20c and 20d is connected to an adding circuit 20e which receives a square value signal as an input signal and outputs an added value signal. Further, on the output side of the addition circuit 20e, a square root circuit 2 that receives the addition value signal as an input signal and outputs the square root value signal thereof
0f is connected.

The incident light amount monitoring circuit thus configured
At 20, the subtraction and addition / subtraction circuits 20a, 2
0b and X = as respectively.
If inθ, Y = acosθ, this is used as an input signal.
Square value signals output from the squaring circuits 20c and 20d,
Is X^Two= A^Twosin^Twoθ, Y^Two= A^Twoco
s^Twoθ. Next, this squared value signal is used as an input.
, The output of the adder circuit 20e for adding them.
The value signal is X^Two+ Y^Two= A^Twosin^Twoθ + a ^Twocos
^Twoθ = a^Two(Sin^Twoθ + cos^Twoθ) and sin
^Twoθ + cos ^TwoSince θ is 1, X is eventually^Two+ Y^Two= A
^TwoBecomes

The square root circuit 13 calculates the sum signal, that is, the square root of X ² + Y ² = a ² , so that the finally obtained square root signal becomes the amplitude a of the input sine wave signal. . Now, according to the incident light amount monitoring circuit 20 configured as described above, the finally output signal does not include the function of θ as a fluctuation factor, and therefore, this type of conventional type Unlike a circuit, the output signal does not fluctuate with a change in the input signal, and a stable and accurate output signal is always obtained. Therefore,
If the quality of the measurement by the laser length measuring device is judged based on the output signal of the incident light amount monitor circuit 20, it is possible to make an accurate and accurate judgment.

As a criterion for determining the quality at this time, for example, an allowable value of the return light amount (for example, 50
%), And if it falls below that tolerance, the measurement can be rejected.

[0019]

As described above in detail in the embodiments,
According to the incident light amount monitoring circuit for a laser length measuring device according to the present invention, the output signal does not fluctuate with a change in the sine wave input signal, and is always stable and accurate. Can be accurately determined.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a laser length measuring machine to which an incident light amount monitoring circuit according to the present invention is applied.

FIG. 2 is a waveform diagram of an output signal of the laser length measuring machine.

FIG. 3 is a block diagram illustrating a configuration of an incident light amount monitoring circuit.

FIG. 4 is a waveform diagram of input / output signals of the incident light amount monitor circuit of FIG. 4;

FIG. 5 is a circuit diagram showing an example of a conventional incident light amount monitoring circuit.

FIG. 6 is a waveform diagram of input / output signals of the incident light amount monitor circuit shown in FIG.

[Explanation of symbols]

 Reference Signs List 20 incident light amount monitor circuit 20a subtraction circuit 20b addition / subtraction circuit 20c square circuit 20d square circuit 20e addition circuit 20f square root circuit

Claims (1)

(57) [Claims] 1. A laser tube that emits light of a predetermined polarization state, light emitted from the laser tube is incident, the incident light is divided and projected onto a measurement target and a reference light target. An interferometer that receives and combines the reflected light from each target, and obtains a length measurement pulse by converting the output light from the interferometer into a plurality of sinusoidal electric signals having a phase difference of 90 degrees. In the laser measuring machine, the photoelectrically converted sine wave electric signal relates to the light intensity.
A shall, as input a plurality of sine wave signals having a phase difference of the 90 degrees, a subtraction circuit which outputs two sinusoidal signals having a phase difference of 90 degrees, receiving the output of the subtraction circuit, the A pair of squaring circuits for inputting a sine wave signal having a phase difference of 90 degrees and outputting a squared value signal, and connected to the output side of these squaring circuits, for adding the squared value signal an adding circuit for outputting a value signal is connected to the output side of the adder circuit, and a square root circuit for outputting a square value of the sum value signal, measured from the output signal value of the square root circuit of the laser length measuring machine
An incident light amount monitor circuit for a laser length measuring device, which determines whether or not a constant is acceptable .