DE2012946B2 - Device for determining the distance of an object in relation to a defined position with the aid of an interferometer - Google Patents

Description

system is frequency-modulated according to a '' tgelegten relationship of 20 sensitive Detektorsystein connected meter Δω, and in that the number is set.

In this way, a very simple structure results the device, which with a minimum of op-

the zero crossings (N) of the modulation corresponding, changing partial signal ( B1) of the table elements in the radiation-sensitive detector system and the implementation

(8, 25, 27) generated electrical signal while 25 enables very precise measurements

the time of a period (T) of the frequency (<·>) of the radiation emitted by the radiation source (1) is determined and is set in a counter (9, 26) connected to the radiation-sensitive detector system (8, 25, 27).

2. Apparatus according to claim 1, characterized in that the radiation emitted by the radiation source (1) is polarized and that in one of the arms of the interferometer a (2 «+ 1)

^ -Plate (21) (n - integer) is added.

3. Apparatus according to claim 1 or 2, characterized in that the radiation source (1) emits two bundles of radiation, the frequency difference of which fluctuates around an average value.

4. Apparatus according to claim 2 or 3, characterized characterized in that the radiation source (1) emits circularly polarized radiation.

The invention relates to a device for determining the distance of an object in relation on a defined position with the help of an interferometer, the emitted by a radiation source Radiation divided into two spatially separated partial beams with the help of a radiation stator of which one on a reflector connected to the object of one of the dividers low-ferometer hits, is reflected back and from Das am

The radiation splitter is reunited with the partial radiation bundle of the other interferometer arm, and the combined radiation then. Expedient embodiments of the device according to the invention emerge from the subclaims.

The invention is based on the drawing, for example explained in more detail, the in 1 i g. 1 shows a first embodiment of a device according to the invention and in Fig. Figure 2 illustrates a second embodiment.

According to FIG. 1 hits the avs of a radiation source 1

Radiation bundles originating in the radiation splitter 3 of an interferometer. That reflected on the radiation splitter 3 Teilstrahlungsbündcl is reflected by a first reflector 11, which consists of a lens 4 and a concave mirror 5 arranged in the focal plane of the lens 4. The reflector 11 is located at a relatively short distance from the radiation splitter 3.

The partial radiation beam which is let through by the radiation splitter 3 is transmitted to a second rectifier 12, which consists of a lens 6 and a concave mirror 7 arranged in its focal plane. The reflector 12 is located at a relatively large distance from the beam splitter 3 and is rigid with the item (not shown)

so connected, its distance from a defined Point to be measured. This defined point lying in a plane 2 is in one optical distance from beam splitter 3 equal to the optical distance of reflector 11 from radiation

First reflector 11 is reflected beam from the beam splitter 3 partially to a radiation-sensitive detector system 8 allowed through; the same is done on the second reflector 12

• uf a radiation-sensitive, an output signal 60 deflected beam bundle from the radiation splitter 3 partially delivering Detector system falls. way to the radiation-sensitive detector system 8

reflected.
The radiation amplitude of the radiation-sensitive

Such a device is e.g. B. from DT-OS 73 541 known. This known device requires however, a relatively high cost of optical elements.

Similar devices are also known from DT-PS 19 09 728 and the journal »Naturwissenschaftliche Rundschau «22nd year, 1969, borrowed detector system 8 incoming beam can be as a function of time / by the formula

A = sin (ot + sin ω ti - τ)
= 2 sin co (/ - τ / j) cos <;> (τ / ₂ )

being represented. Here, w / 2 π denotes the light frequency and τ the time during which the partial bundle fed to the 7th reflector 12 is between plane 2 and reflector 12, i.e.: x = 2z / f, if ζ is the distance between plane 2 and the reflector 12, and c is the speed of propagation of the radiation.

The electrical signal B generated in the radiation-sensitive detector 8, which is proportional to the square of the amplitude of the incoming radiation, is proportional to

cos ² ωτ / 2, i.e. to 1 · + ■ cos ωτ.

If the angular frequency ω of the radiation emitted by the radiation source 1 is changed in accordance with the relationship ω = ω ₉ (1 + / sin Ω ί), the changing part B _{1 of} the signal B becomes

cos 2 π ™ (1 + / sin Ω /), where λ * = ---.

^ O'-og

In it is w _? the mean angular frequency of the radiation emitted by the radiation source 1 and Ω the frequency with which ω is changed.

The number of zero crossings N of the partial signal Bl during the time t of a sinusoidal period

T = 2π / Ω is: N = ~ f.

«0

If N is set in a counter 9 connected to the radiation-sensitive element 8, then the distance ζ can be calculated with a known value of /.

In one embodiment: A ₀ = 0.5 μπι,

/ = - "- = 0.1 and Λ ¹ " = 1.6 -10 ⁷ . Calculated from this

the distance ζ = 5 m.

Instead of a sinusoidal change in the angular frequency Q you can also make a sawtooth change, e.g. B. according to the relationship

1 + /

The changing part S, de *. Signal B then becomes

During the time / = T of the sawtooth period, the number of zero crossings of the partial signal is B _x

¹¹ -

One can in the device according to FIG. 1 also replace the radiation source 1 with a radiation source which emits radiation bundles of ζν / ή circular frequencies ο and ω ₂ , these bundles of radiation having the same polarization state. At the location of the radiation-sensitive element 8, the amplitude of the radiation can pass through

Λ = 2 sin Ci) ₁ (f - τ / 2) cos o>, τ / 2
+ 2 sin ω ₂ (/ - τ / 2) cos «>" τ / 2

can be specified.

The electrical signal B generated in the detector 8 is proportional to the time mean value of the square of the amplitude of the radiation.

One calculates
B = (l -f- cos Δω ~] (1 + cos ω _ο τ) + (l - cos Δω ^

(1 - cos ω _ο τ) = 2 (1 4- m cos ω _ο τ). It is

2ω ₀ = Oj ₁ 4- coj, Δω = CO ₁ - ö> _a and m = cos Δω - ^.

It should be noted that Δω with respect to the cutoff frequency of the detector 8 is large.

If you now change the circular frequency of the Radiation source emitted radiation beam according to the relationship

Δω = ω ₀ / sin Ω f, so becomes

BI2 - 1 + cos f ω ₀ / ^ sin Ω t \ cos ω _ο τ = 1 + m _x cos ω _ο τ. The modulation depth m changes periodically. Not the zero crossings of cos ω _ο τ, but the

from cos ίω ₀ / · = ■ sin Ω ί J are counted.

In the device according to FIG. 1, radiation source 1 can also be replaced by two radiation sources with mutually perpendicular polarization planes. In this case, an analyzer is arranged in the radiation path between the radiation splitter 3 and the radiation-sensitive system 8, the plane of polarization of which encloses an angle γ with the radiation with angular frequency i ·) leaving the radiation source. The electrical signal B generated in the radiation-sensitive system 8 is then given by

B - 1 4- cos UJ ₁ T cos ² γ + cos Ct ₂ τ sin ² γ. At γ - 0 we have: B = - 1 + cos W ₁ τ; at γ - 90 "we have S = Ii coso) ₂ t; and at y -45 ° we have: ß− 1 -fcos ^r ₂ - τ ■

₀ T. Here 2 <t) ₀ - «ο, + fojund If) = O) ₁ -Ci ₂ . The device according to FIG. 2 is the one according to FIG. 1 very similar. Corresponding items have the same reference numbers in both figures. The radiation source 1 emits linearly polarized radiation which is split up by the radiation splitter 3 of the interferometer into white partial radiation bundles. A λ 4 plate 21 is attached in the short section of the interferometer. The angle between the optical axis of the λ / 4 plate and the plane of polarization of the incident partial bundle is 45 °. After reflection at the first reflector 11, the sub-bundle again passes through the λ / 4 plate 21. Overall, this sub-bundle has thus passed through a λ / 2-plate, so that the plane of polarization of the sub-bundle D ₁ returning in the short section 7um the radiation splitter 3 by 90 in is rotated with respect to the radiation beam leaving the radiation source 1. In contrast, the plane of polarization of the partial bundle D ₂ reflected on the second reflector 12 does not change. _{The partial bundle D 1 which} is transmitted by the beam splitter 3 and coming from the reflector 11 therefore has a plane of polarization which is perpendicular to that of _{the partial bundle D 2 reflected from the reflector 12 and reflected on the beam splitter 3.} After leaving the beam splitter 3, the sub-bundles D ₁ and D ₂ pass through a further λ / 4 plate 28, the main direction of which forms an angle of 45 ° with the polarization direction of each of the sub-bundles D ₁ and Z) ₂ . The λ / 4 plate 28 now converts the two linearly polarized partial bundles D ₁ and D ₂ into a clockwise and counterclockwise polar-

5 6

ized radiation beam. When joining together, the position of the plane of polarization of this radiation bundle can result from a linearly or almost linearly polarilinearly polarized radiation bundle emerging from the Λ / 4 plate 28, its position of the siert radiation bundle and thus the polarization plane to be measured from the mutual phase of the distance Z as well determine other way. For this purpose circularly polarized radiation beam depends, ie a 5 must be between the P./4 plate 28 and the radiation displacement of the reflector 12 and thus of the divider 22 the series connection of two λ / 4 plates with a measuring distance 12 extremely in the form of an equal Orientation can be attached, between rotation of the plane of polarization. The polarized linearly which an electro-optic crystal having a Orientiesierte radiation beam hits now another approach direction is arranged, which is a difference beam splitter 22, which with the comprises a part of the linearly polarized io of 45 ° the // 4-plate, wherein this terraced The radiation beam passes through and another crystal reflects an appropriate electrical alternating voltage. The part that has passed through is fed into a voltage. Relatively slow polarizer 23, whose plane of polarization includes an angle changes in the position of the plane of polarization of the γι with a selected A'-axis, so that the λ / 4 plate 28 emerging linearly polarized amplitude of a downstream radiation-sensitive 15 radiation beam can then measure comfortably,
Liches element 25 striking radiation beam by an advantage of the embodiment according to FIG. 2 is

that absorption losses in one of the four arms of the

cos (ait - yO + eis 1 (ωί - τ) + ^ ₁ ] ferometer has no influence on the position of the plane of polarization of the polarization ellipse of the relevant

and the electrical signal generated in the element 25 exert 20 radiation beam.

by In the device according to FIG. 2 can

1 -1- cos (o) t - 2 ν) lungsquclle 1 also replaced by a radiation source

that emits circularly polarized radiation,

can be represented. The ¼ plate 28 must then be omitted.

The part reflected on the beam splitter 22 passes 35. In the device according to FIG. 2, the one polarizer 24, whose plane of polarization includes a radiation source 1 also by a radiation angle y _g with the mentioned A'-axis, so replace source, the two polarized radiation beams that the amplitude of a downstream further with two angular frequencies W ₁ and a ₂ sends out. The radiation-sensitive element 27 striking the beam polarization planes of both radiation bundles can be bundles through 30 the same or are perpendicular to each other.

cos ((ot -tf + cos [((Ot -r) + γ>] ^W l ^{rd dcr W 'nkel} * = °° ^{and the angle?} * _K = ⁴⁵ °

selected, it can be in the radiation-sensitive

and the electrical signal generated in the radiation-sensitive system 27 he system 25 through
transmitted electrical signal through

1 + cos M - 2 _yi ) ^3S 1 + cos Λω - COSO) ₀ T

can be represented.

If you choose y = 0 ° and y _t = 45 °, this can be done

in the element 25 generated by the signal generated in the radiation-sensitive system 27

1 + cos ωτ ⁴ ° ^zcu ^ ^e signal through

and the signal generated by the element 27, _sm ^ _ω 2

1 ■ + ■ sin ωτ 2

indicate. 45 must be specified.

Instead of a signal as in the device according to Here, 2 ω ₀ = ω _Λ 4- aij and Λα - <·> _Λ - o> ₂ .
F i g. 1 one then has two signals, whose changing one then has two amplitude-modulated signals. Borrowed parts have a 90 ° phase difference. whose amplitude-modulated parts have a phase. The angular frequency is now ο that of the radiation difference of 90 °. The number of radiation sources 1 coming in according to FIG. 1 then N of the amplitude-modulated parts, changed the manner described, so that a number is processed in the counter 26 is twice greater than zero crossings N, which is twice greater than the number of according to FIG. 1 resulting zero number of according to F i g. 1 resulting zero passages when using one of two circular passages. The speed changes N are in turn processed in a counter 26 _{in frequencies Co 1} and a> _{2 to be emitted radiation.} 55 source 1.

1 sheet of drawings

Claims (1)

Patent claims: 1. Device for determining the distance of an object in relation to a defined position with the help of an interferometer, the radiation emitted by a radiation source being divided into two spatially separated partial radiation beams with the help of a radiation splitter, one of which is directed to a reflector connected to the object of one interferometer arm hits, is reflected back and is reunited by the radiation splitter with the partial radiation beam of the other interferometer arm, and the combined radiation then falls on a radiation-sensitive detector system which provides an output signal, characterized in that the frequency (ω) corresponds to that of the radiation source ( 1) sent out Strah-Heftl, pp. 8 to 16. The devices known from these two publications are even more complex than the device mentioned at the beginning, because they even require two radiation sources. The object of the present invention is therefore to provide a device of the type mentioned at the beginning to improve that it is much simpler and still a very accurate measurement of Distances enabled. This is done according to the invention in that the frequency of the emitted by the radiation source Radiation is frequency modulated according to a fixed relationship of / It «, and that the number of Zero crossings of the modulation corresponding, changing partial signal of the radiation-sensitive Detector system generated electrical signal during the time-liner period of the frequency (w) the radiation emitted by the radiation source is determined and sent to the radiation