Apparatus for interferometric distance measurement.

Abstract

To provide a device for interferometric interval measurement.SOLUTION: A device for interferometric interval measurement includes a multi-wavelength light source that supplies a bundle of rays of at least three different wavelengths. The device includes an interferometer unit that splits the bundle of rays into a measurement bundle of rays and a reference bundle of rays. The measurement bundle of rays propagates to a measuring reflector movable along a measurement axis and the reference bundle of rays propagates to a fixed reference reflector, and both are reflected backward. The backward-reflected measurement bundle of rays and reference bundle of rays overlap while interfering in an interference bundle of rays. The interference bundle of rays is divided by a detection unit, a plurality of phase-shifted partial interference signals for each wavelength are generated. A signal processing unit determines absolute position information about the measuring reflector from the partial interference signals with different wavelengths and an additional rough position signal. In order to generate the additional rough position signal, the device has a modulation unit. The modulation unit applies phase modulation to an emitted wavelength, and a phase-modulated bundle of rays propagates in a direction of the interferometer unit and induces a spacing-dependent modulation in the partial interference signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus for interferometric distance measurement, which is particularly suitable for determining the absolute distance between two objects that are movable relative to one another. [Background technology]

[0002] A general-purpose device for determining the absolute distance between two movable objects by interferometry is known from DE 10 2017 213 258 A1. This device is based on the so-called multi-wavelength method, in which one or more beat phases are determined from the differential formation of interference phases of different wavelengths, which allows for unambiguous absolute position determination over a relatively large distance range.

[0003] In this regard, corresponding devices can also be configured in a cascaded manner and can generate multiple beat phases from multiple different wavelengths. The device known from DE 10 2017 213 258 A1 includes a multi-wavelength light source that provides a ray bundle with at least three different wavelengths. The multi-wavelength light source is configured as a fiber laser including at least three different Bragg gratings, the grating constants of which are tuned to the wavelengths to be generated. Furthermore, an interferometer unit is provided that splits the ray bundle into a measurement ray bundle and a reference ray bundle. The measurement ray bundle propagates in the measurement arm toward a measurement reflector and is reflected back there. The reference ray bundle propagates in the reference arm toward a fixed reference reflector and is reflected back there. The measurement ray bundle and the reference ray bundle, reflected back by the measurement reflector and the reference reflector, overlap in an interference ray bundle while interfering. The detection unit splits the interference ray bundle so that a plurality of phase-shifted partial interference signals are generated for each wavelength. A signal processing unit determines absolute position information about the measurement reflector from the partial interference signals of different wavelengths and an additional coarse position signal. To generate the coarse position signal, a time-of-flight measurement method has been proposed, in which the time of flight of a light pulse to a measurement reflector and back is determined, and the coarse position signal is derived from the time-of-flight. Such a time-of-flight measurement method requires additional optical and electronic components for light generation, coupling and decoupling, detection, amplification, and time measurement for each measurement axis. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] DE102017213258A1 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem underlying the invention is to provide an apparatus for absolute interferometric distance measurement, which is capable of generating a coarse position signal with as little additional effort as possible. [Means for solving the problem]

[0006] This problem is solved according to the invention by a device having the features of claim 1. Advantageous embodiments of the device according to the invention are evident from the measures recited in the dependent claims. The device according to the present invention is used for interferometric distance measurement. The device includes a multi-wavelength light source that provides a beam of rays with at least three different wavelengths. Furthermore, at least one interferometer unit is provided that splits the beam of rays into a measurement beam and a reference beam. The measurement beam propagates in the measurement arm toward a movable measurement reflector along a measurement axis and is reflected back there. The reference beam propagates in the reference arm toward a fixed reference reflector and is reflected back there. The measurement beam and the reference beam reflected back by the measurement reflector and the reference reflector interfere with each other and overlap in an interference beam. Furthermore, at least one detection unit is provided, which splits the interference beam so that a plurality of phase-shifted partial interference signals are respectively generated for each wavelength. At least one signal processing unit is configured and adapted to determine absolute position information about the measurement reflector from the partial interference signals of different wavelengths and an additional coarse position signal. To generate the coarse position signal, the modulation unit applies a phase modulation to the at least one emitted wavelength, whereby the phase-modulated ray bundle propagates in the direction of the at least one interferometer unit and causes a spacing-dependent modulation in the at least one partial interference signal.

[0007] In an advantageous embodiment, the modulation unit comprises an electro-optical modulator and a sine wave generator, which controls the electro-optical modulator with a defined modulation frequency and a defined voltage amplitude.

[0008] In this regard, it is preferable that the modulation frequency of the sine wave generator is selected to be greater than the generated mechanical and acoustic frequencies. For example, the modulation frequency of the sine wave generator can be selected within the frequency range [100 kHz...10 MHz].

[0009] The electro-optical modulator can then be formed as an integrated fiber-coupled modulator. Preferably, spacing-dependent phase and amplitude modulation results in at least one partial interference signal.

[0010] In an advantageous embodiment, the signal processing unit processes the coarse position signal (L G ) are formed and adapted to produce In this case, the signal processing unit - determining a modulated phase value from the at least one evaluated partial interference signal; and - determining a position phase amplitude from the modulated phase value; and The position phase amplitude and the optical phase amplitude applied to the phase-modulated ray bundle can be formed and adapted to determine a coarse position signal.

[0011] The approximate position signal is expressed as follows:

[0012]

number

[0013] Advantageously, the value is determined based on the formula: L G := approximate position signal c: = speed of light in the measurement medium f PM :=modulation frequency A λi ;i=1, 2, 3:=position phase amplitude A λiPM ;i=1, 2, 3:=optical phase amplitude is.

[0014] Furthermore, it is possible that the optical phase amplitude determination unit can be formed and adapted to determine the optical phase amplitude applied to the phase modulated ray bundle. In addition, - determining an unmodulated phase value for each wavelength from the phase-shifted electrical partial interference signal; and - forming a plurality of differential phases from the unmodulated phase values, each of which is assigned to a different synthetic wavelength; and - Determine high-resolution absolute position information about the measurement reflector from the coarse position signal and the differential phase A signal processing unit configured and adapted for this purpose may be envisaged.

[0015] moreover, a splitting element for splitting the phase-modulated ray bundle into a plurality of phase-modulated partial ray bundles; - a number of interferometer units for assigning different measurement axes, each capable of transmitting one phase-modulated partial beam, each of which is followed by a detection unit and a signal processing unit in order to determine absolute position information for the respective measurement reflector for each measurement axis; But it is possible.

[0016] In this regard, phase-modulated partial beams can be envisaged that can be sent to an optical phase amplitude determination unit that sends the optical phase amplitudes determined from the partial beams to a signal processing unit in each measurement axis for further processing.

[0017] In a preferred embodiment, the interferometer unit includes a beam splitting unit, a measurement reflector movable along at least one measurement direction, a fixed reference reflector, and a beam combining unit, wherein the beam splitting unit splits the phase-modulated beam into a measurement beam and a reference beam, and the beam combining unit superimposes the measurement beam and the reference beam reflected back by the measurement reflector and the reference reflector into an interference beam.

[0018] It has proven particularly advantageous that the costs for generating a coarse position signal can be significantly reduced in the device according to the invention, in particular because no additional optical components for coupling and decoupling of light pulses are required, and no additional electronic components for light generation, detection, amplification and time measurement are required.

[0019] In addition, since the coarse position signal is generated using the same components as the high-resolution interferometer signal, the time consistency of the different position information is guaranteed without any additional measures. Furthermore, this modulated multi-wavelength light source can provide multiple measurement axes if required, whereas if time-of-flight measurements are used to generate a coarse position signal, this requires separate optical and electronic components for each measurement axis.

[0020] Further details and advantages of the invention will be explained on the basis of the following description of an exemplary embodiment of the device according to the invention in conjunction with the drawings. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a highly schematic view of one exemplary embodiment of an apparatus according to the present invention; [Figure 2] FIG. 2 is a schematic diagram of a detection unit from the exemplary embodiment in FIG. 1; [Figure 3] FIG. 2 is a schematic diagram of a signal processing unit from the exemplary embodiment in FIG. 1; [Figure 4] 2 is a graph showing sampled phase values ​​during constant velocity movement of the measurement reflector from the example of FIG. 1; [Figure 5] 2 is a graph illustrating the complex amplitude of the resulting phase modulation and amplitude modulation in the exemplary embodiment of FIG. 1; [Figure 6] FIG. 2 is a detailed diagram of an optical phase amplitude determination unit from the example of FIG. 1. [Figure 7] FIG. 7 is a detailed diagram of the signal processing unit of the optical phase amplitude determination unit from FIG. 6. [Figure 8] 1 is a highly schematic diagram of a multi-axis measurement configuration associated with an apparatus according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0022] 1 shows a schematic diagram of one exemplary embodiment of an apparatus according to the invention for interferometric distance measurement. The apparatus includes a light source unit 10, an interferometer unit 30, a detection unit 40, a signal processing unit 50, and an optical phase amplitude determination unit 80. Using the apparatus according to the invention, this exemplary embodiment allows for highly accurate determination of absolute position information L or absolute distance between two objects (not shown) that are movable relative to one another. In this example, one of the two objects is coupled to a measurement reflector 33 that is part of the interferometer unit 30 and is movable along a measurement direction x, and the other of the two objects is coupled to other components of the interferometer unit 30 that are arranged fixedly relative to it.

[0023] The two objects can be, for example, machine parts that are movable relative to one another, and the absolute distance between these machine parts can be determined using the device according to the invention. The information about the absolute position information L generated by the device according to the invention can be further processed by a superordinate machine control.

[0024] Furthermore, the device according to the invention can also be used in a laser tracker or tracer, in which case the absolute distance between a fixed component of the interferometer unit 30 and a measurement reflector 33 movable in space is determined.

[0025] Such a system can be used in connection with a wide variety of measurement and / or calibration tasks, but there are of course still further possibilities for use of the device according to the invention.

[0026] The approximate position signal L is shown below. G Before describing in detail the procedure according to the invention for determining .times. ...

[0027] The light source unit 10 of the device according to the invention comprises a multi-wavelength light source 11, which emits light at at least three different wavelengths λi (i=1, 2, 3) emits a bundle of rays S with wavelengths λ i (i=1, 2, 3) each have a small spectral linewidth. As the multi-wavelength light source 11, a fiber laser including at least three different Bragg gratings is intended here, and the lattice constants of these Bragg gratings are set to λ = 1 / ... i (i=1, 2, 3). Further details of the multi-wavelength light source 11 and the appropriate wavelengths λ i For the selection of (i=1, 2, 3), reference is expressly made to document DE102017213258A1 already mentioned at the outset.

[0028] The light beam S provided by the multi-wavelength light source 11 is phase modulated by a modulation unit 15, in which at least one emitted wavelength λ i (i=1, 2, 3), although in the illustrated exemplary embodiment it is intended that such phase modulation is applied not only to this but also to all three emitted wavelengths λ1, λ2, λ3. To this end, the modulation unit 15 controls the electro-optical modulator 12 to a defined modulation frequency f PM and the specified voltage amplitude A PM The electro-optic modulator 12 includes a sine wave generator 13 controlled by a sine wave generator 14. The electro-optic modulator 12 is configured in this exemplary embodiment as an integrated fiber-coupled modulator.

[0029] The modulation frequency f of the sine wave generator 13 PM is preferably selected within the frequency range [100 kHz...10 MHz], and in this regard, furthermore, the modulation frequency f PM is considered to be greater than the mechanical (several kHz) and acoustic (hundreds of kHz) frequencies occurring in the system. In one specific exemplary embodiment, the modulation frequency f PM =1.5625MHz is intended.

[0030] Therefore, the light source unit 10 generates a phase-modulated beam of light S PM are emitted at different wavelengths λi (i=1, 2, 3) is the applied optical phase amplitude A λiPM (i=1, 2, 3), and this optical phase amplitude A λiPM (i=1, 2, 3) are in the range of multiples of π (=180°). In the course of the following explanation, it will be noted that the applied phase modulation, among other things, G This section explains in more detail how the .DELTA..times ...

[0031] A beam splitter 100 in the form of a fiber optic splitter downstream of the light source unit 10 splits the phase-modulated beam S PM Part of S PM_R is branched and sent to the optical phase amplitude determination unit 80. The optical phase amplitude determination unit 80 determines the optical phase amplitude A applied by the modulation unit 15. λiPM (i=1, 2, 3) are determined and available to the signal processing unit 50, which processes the coarse position signal L G To generate the optical phase amplitude A λiPM (i=1, 2, 3). See also the discussion below for details on determining and processing this quantity.

[0032] Phase modulated wavelength λ iPM A phase-modulated ray bundle S with (i=1, 2, 3) PM The unsplit part of the beam reaches the interferometer unit 30, where it is split into a measurement beam M PM and the reference ray bundle R PM The measurement beam M PM After splitting, the reference ray bundle R propagates in the direction of a measurement reflector 33 movable in the measurement arm at least along the measurement direction x, where it is reflected back towards the incident direction. PMAfter splitting, the measurement and reference beams M propagate in the reference arm towards a fixed reference reflector 34, where they are also reflected back towards the incident direction. The measurement and reference reflectors 33 and 34 are formed as retroreflective three-way mirrors in the illustrated example. The measurement and reference beams M reflected back by the measurement and reference reflectors 33 and 34 are PM , R PM then reaches the beam combining unit 31, which is made as a polarizing beam splitter, where it interferes to form an interfering beam IF PM In the illustrated exemplary embodiment of Fig. 1, only one component in the form of a cube beam splitter is intended as the beam splitting unit 31 or the beam combining unit 31, in which both units are formed together. At the beam splitting or beam combining surface 32 of the cube beam splitter, the phase-modulated beam of rays S PM The measured ray flux M PM and the reference ray bundle R PM and the measurement beam M PM and the reference ray bundle R PM Interference beam IF PM The subscript PM used in this context allows us to denote the reference ray bundle R, which depends on the interval or absolute position information L. PM and the measurement ray flux M PM In addition to the incremental phase difference between the two, it is clarified that there is an interval-dependent modulation of the phase difference, and in the course of the following explanation, the approximate position signal L G How is determined will be explained in more detail. PM passes through a further λ / 4 plate 35 at the output of the interferometer unit 30, which divides the interfering ray bundle IF PM The s-polarized and p-polarized components of the light are superimposed into a rotating electric field vector, the rotation angle of which is taken into account for the evaluation. Thus, in this exemplary embodiment, the interferometer unit 30 is formed as a polarization-encoded interferometer.

[0033] It should be pointed out that the interferometer unit 30 is in no way essential to the present invention in the form of a Michelson interferometer as depicted diagrammatically in FIG. 1 . Therefore, alternative interferometer variants and / or components may also be used in the interferometer unit 30 of the device according to the present invention. Thus, for example, spheres with a refractive index of n=2 may be used as reflectors between which the absolute distance is measured. Furthermore, other types of measurement and reference reflectors may of course also be used, such as plane mirrors. Similarly, a Mach-Zehnder interferometer with separate beam splitting and beam combining units for splitting and combining the measurement and reference beams could also be used, etc.

[0034] The interference beam IF generated by the interferometer unit 30 PM then propagates towards the detection unit 40, which outputs a phase-modulated wavelength λ iPM (i=1, 2, 3) for each of a plurality of electrical phase-shifted partial interference signals S90 λiPM , S210 λiPM , S330 λiPM (i=1, 2, 3) is the phase-modulated wavelength λ iPM Three partial interference signals S90 shifted by 120° for each (i = 1, 2, 3) λiPM , S210 λiPM , S330 λiPM (i=1, 2, 3) so that the interfering ray bundle IF PM In this case, three phase-modulated wavelengths λ iPM In this example with (i=1, 2, 3), there are a total of nine partial interference signals S90 at the output of the detection unit 40. λiPM , S210 λiPM , S330 λiPM (i=1, 2, 3), which partial interference signals are then further processed for position determination. Regarding possible configurations of the detection unit 40, see the description of FIG. 2 below.

[0035] As shown in FIG. 2, the interference beam IF generated by the interferometer unit consists of a rotating linearly polarized electric field after passing through the λ / 4 plate 35. PM impinges on the detection unit 40, where it is split by a first splitting element 41 and a subsequent polarizing element 43 into an interference beam IF PM Three mutually phase-shifted interfering beams IF PM90 , IF PM210 , IF PM330 In this case, the first dividing element 41 divides the incident interference beam IF PM The polarizing element 43 includes three linear polarizing filters each having a polarization direction rotated by 60° relative to one another, and is configured as a reflective phase grating that first splits the three interfering beams separated by the splitting element 41 into three partial interfering beams IF PM90 , IF PM210 , IF PM330 The first dividing element 41 and the polarizing element 43 convert the three phase-shifted partial interference beams IF PM90 , IF PM210 , IF PM330 The splitting into three phase-shifted partially coherent ray bundles IF is performed perpendicular to the drawing plane, i.e., in the representation of FIG. 2, three phase-shifted partially coherent ray bundles IF exist after the polarizing element 43. PM90 , IF PM210 , IF PM330 The three phase-shifted partially coherent beams IF PM90 , IF PM210 , IF PM330 The first beam then strikes a second dividing element 42, which is also formed in the form of a reflective phase grating. The second dividing element 42 divides the first beam into three phase-shifted partially coherent beams IF PM90 , IF PM210 , IF PM330 There is a wavelength-dependent division of iPMThere are three phase-shifted partial coherent beams for each of the beams (i=1, 2, 3), i.e., nine partial coherent beams in total, which are not shown individually in FIG. 2. The partial coherent beams then pass via deflection element 44 and imaging optics 45 to detector array 46, which here comprises nine electro-optical detector elements 46.1 to 46.3, only some of which are visible in the representation in FIG. 2. Imaging optics 45 is here configured as a single lens or as a lens array, or alternatively may be configured in a single component in combination with deflection element 44. Detector array 46 or its detector elements 46.1 to 46.9 capture the nine partial coherent beams and generate nine electrical partial coherent signals S90. λiPM , S210 λiPM , S330 λiPM (i=1, 2, 3), and these partial interference signals are then further processed in the signal processing unit. In this regard, in FIG. 2, a total of nine generated partial interference signals S90 λiPM , S210 λiPM , S330 λiPM Three partial interference signals S out of (i=1, 2, 3) λ1_90 , S λ2_90 , S λ3_90 Only this is shown.

[0036] Next, the partial interference signal S90 λiPM , S210 λiPM , S330 λiPM Further processing of the different phase modulated wavelengths λ (i=1, 2, 3) takes place in a signal processing unit 50, which is only indicated schematically in FIG. iPM Partial interference signal S90 (i=1, 2, 3) λiPM , S210 λiPM , S330 λiPM (i=1, 2, 3), one approximate position signal L for the movable measuring reflector 33 is obtained. G and to determine the absolute position information L step by step by a multi-wavelength beat method.

[0037] The approximate position signal L according to the present invention will be described below.G A procedure for determining the coarse position signal L is now described. What is important in this respect is the phase modulation applied to the ray bundle S, which causes a spacing-dependent modulation of phase and amplitude in the position signal of the interferometer unit 30 to be evaluated. This means that both the amplitude and the phase of the modulation on the control signal of the electro-optical modulator 12 depend on the spacing. In this case, the coarse position signal L G The determination of λ can be substantially performed by the existing hardware components of the interferometer unit 30, the detection unit 40, and the signal processing unit 50. In addition to this, only an optical phase amplitude determination unit 80 is further contemplated in the exemplary embodiment of FIG. i The optical phase amplitude A applied by the modulation unit 15 at (i=1, 2, 3) λiPM (i=1, 2, 3), and this optical phase amplitude A λiPM (i=1, 2, 3) is the approximate position signal L G are taken into consideration to determine

[0038] Approximate position signal L G The procedure according to the present invention for determining is described in detail below. Reference ray flux R PM Wavelength λ i the time-dependent modulated phase component P generated by the modulation unit 15 for one of i=1, 2, 3; λiR (t)

[0039]

number

[0040] Assume that: In the following, A λiPM (i=1, 2, 3) represents the optical phase amplitude applied by the modulation unit 15, and f PM denotes the modulation frequency of the electro-optic modulator 12.

[0041] Measuring ray flux M PM The time-dependent modulated phase component P in λiM(t) is the reference ray bundle R PM The phase position in the measurement arm is delayed by the light flight time required for the path length 2 × L in the measurement arm.

[0042]

number

[0043] This becomes: In this equation, c denotes the speed of light in the measurement medium, and L denotes the absolute position information for the measurement reflector 33 or the absolute distance between the measurement reflector 33 and the beam splitting unit 31 as suggested in FIG. 1.

[0044] Therefore, the reference ray bundle R PM and the measurement ray flux M PM The time-dependent modulated phase difference ΔP between λi (t) is

[0045]

number

[0046] This becomes: Trigonometric Formulas

[0047]

number

[0048] and by replacing the parameters a, b, α, β, and x in this equation as follows:

[0049]

number

[0050] and

[0051]

number

[0052] Position phase amplitude A depends on absolute position information L λi but,

[0053]

number

[0054] This is what happens. This formula is

[0055]

number

[0056] can be simplified to The following formula

[0057]

number

[0058] By applying λi Regarding

[0059]

number

[0060] is derived. Therefore, the phase position δ of the time-dependent phase difference with respect to the control signal of the electro-optic modulator 12 λi (i=1, 2, 3) is

[0061]

number

[0062] is brought about based on This formula furthermore

[0063]

number

[0064] can be simplified to In this case, further deformation

[0065]

number

[0066] This becomes: This allows the measurement beam M PM and the reference ray bundle R PM In addition to the incremental, interval-dependent phase difference between λi (t);i=1, 2, 3 is the following equation

[0067]

number

[0068] is derived based on. In the detection unit 40, the individual wavelengths λ i (i=1, 2, 3) are separated, and the wavelength λ i Three electrical 120° phase-shifted partial interference signals S90 for each (i=1, 2, 3) λiPM , S210 λiPM , S330 λiPM (i=1, 2, 3) are generated. These signals are available to the signal processing unit 50.

[0069] In the signal processing unit 50, the partial interference signal S90 λiPM , S210 λiPM , S330 λiPM (i=1, 2, 3) are first amplified by amplifiers 51.1 to 51.3 and digitized by A / D converters 52.1 to 52.3. Then, each phase-modulated wavelength λ iPM (i=1, 2, 3), the phase calculation units 53.1 to 53.3 calculate the modulated phase value ΦλiPM (i=1, 2, 3) is calculated. λiPM (i=1, 2, 3) are modulated by the phase modulation of light, with modulation frequency f PM and position phase amplitude A λi (i=1, 2, 3) modulated components or sinusoidal time- and length-dependent phase difference ΔP λi (t);i=1, 2, 3. In the demodulation units 53a.1 to 53a.3, the position phase amplitude A λi (i=1, 2, 3) are determined and the unmodulated phase value Φ λi (i=1, 2, 3) are generated. Then, in the coarse position determination unit 56, the position phase amplitude A λi (i=1, 2, 3) to obtain the absolute rough position signal L G is determined, and the absolute rough position signal L G is sent to the position determination unit 55.

[0070] The subsequent determination of the absolute position information L is performed using the unmodulated phase value Φ λi (i=1, 2, 3) and the approximate position signal L G , based on the procedure already proposed in DE 10 20 17 21 3 25 8 A1, to which reference is explicitly made in this connection. λi (i=1, 2, 3), the differential phase calculation units 54.1 to 54.3 calculate the differential phases ΔΦ attributed to various synthetic wavelengths. 12 , ΔΦ 23 , and ΔΦ are determined and sent to the position determination unit 55 .

[0071] Thereafter, in the position determination unit 55, the transmitted signal L G and ΔΦ, ΔΦ 23 , and Φ λ3 The absolute position information L is determined in a cascaded manner based on the above. Reference is again expressly made to DE 10 2017 213 258 A1 for a detailed description of this procedure.

[0072] In the following, the modulated phase value Φ λiPM (i=1, 2, 3) to position phase amplitude A λi (i=1, 2, 3) is determined. λi (i=1, 2, 3) is the approximate position signal L G and for this purpose is sent to the coarse position determination unit 56.

[0073] Each of the phase calculation units 53.1 to 53.3 in the signal processing unit 50 calculates a modulated phase value Φ λiPM 4 exemplarily gives the sampled modulated phase values ​​Φ (n) (i=1, 2, 3) at the sampling instant n when the measurement reflector 33 moves at a constant speed. λiPM (n) (i=1, 2, 3) and the unmodulated phase value Φ λi (n) (i=1, 2, 3). The sampling frequency f A In this example, A =32 f PM were selected based on

[0074] Here, in general,

[0075]

number

[0076] During the ceremony,

[0077]

number

[0078] should be applied. Thus, the following equation

[0079]

number

[0080] Using the in-phase value I λi (n) (i=1, 2, 3) and quadrature value Q λi (n) (i=1, 2, 3) can be calculated. In this case, the in-phase value I λi (n) (i=1, 2, 3) represents the real part of the complex amplitude, and the quadrature value Q λi (n) (i=1, 2, 3) means the imaginary part of the complex amplitude. Figure 5 shows an example using 32 sampling values ​​in the complex plane, that is, the so-called IQ plane. Therefore, the position phase amplitude A at sampling time n is λi (n)(i=1, 2, 3)

[0081]

number

[0082] is. Similarly, the phase position δ of the modulation with respect to the control signal of the electro-optical modulator 12 at the sampling instant n λi (n) (i=1, 2, 3) is

[0083]

number

[0084] can be calculated from In this case, δ' λi (n) (i=1, 2, 3) is the I at sampling time n λi (n) and Q λi (n) represents the angle of the phasor.

[0085] A λi (n) and δ λi In order to be able to calculate (n) based on the above formula, an additional condition must be met: sampling must be performed equidistantly in time and simultaneously for all signals. Furthermore, the sampling frequency f A and modulation frequency f PMmust be phase-locked with respect to each other, which can be ensured, for example, by deriving both frequencies from a common reference frequency.

[0086] In addition, noise can be reduced by appropriate averaging of multiple complex amplitude values ​​at different sampling times. The demodulation units 53a.1 to 53a.3 then produce the unmodulated phase values ​​Φ for further processing in the differential phase calculation units 54.1 to 54.3. λi (n) (i=1, 2, 3) is the modulated phase value Φ λiPM We will explain how it can be obtained from (n) (i=1, 2, 3).

[0087] For example, the unmodulated phase value Φ λi f(n) (i=1, 2, 3) is calculated for each sampling point n by the following rule:

[0088]

number

[0089] can be determined by In the following, the amplitude value A is sent to the coarse position determination unit 56. λi (i=1, 2, 3) or A λiPM The required coarse position signal L from (i=1, 2, 3) G Explain the decision.

[0090] The following formula

[0091]

number

[0092] is solved based on L to obtain the approximate position signal L G Regarding

[0093]

number

[0094] is derived. This equation is used to calculate the coarse position signal L in the coarse position determination unit 56. G are taken into consideration to determine

[0095] In principle, the approximate position signal L G To determine the wavelength λ i (i=1, 2, 3) position phase amplitude A λi (i=1, 2, 3) would be sufficient. However, for all three wavelengths λ i (i=1, 2, 3) position phase amplitude A λi It has proven advantageous to evaluate (i=1, 2, 3) and, on the basis of this, calculate the arithmetic mean value of the obtained coarse position, which results in a coarse position signal L G The noise can be reduced.

[0096] Position phase amplitude A λi (i=1, 2, 3) approximate position signal L G The equation that expresses the relationship to

[0097]

number

[0098] It is clear from the position phase amplitude A λi Approximate position signal L from (i=1, 2, 3) G The unambiguous determination of is only possible when the sign argument is between 0 and π / 2.

[0099] therefore

[0100]

number

[0101] Therefore

[0102]

number

[0103] applies. However, the approximate position signal L G phase angle δ λi It may be determined from the following formula:

[0104]

number

[0105] is solved based on the measured length or absolute position information L,

[0106]

number

[0107] Approximate position signal L G can be calculated. Naturally, the very small position phase amplitude A λi In the case of (i=1, 2, 3), the phase cannot be determined, so the phase angle δ λi Approximate position signal L from G The decision L G >0~L G <c / 2f PM The most accurate phase determination is possible only for values ​​of L G =c / f PM This is possible in the range of the position phase amplitude A λi (i=1, 2, 3) is the largest.

[0108] Therefore, in this case, the approximate position signal L G is the position phase amplitude A λi or phase angle δ λi It can be determined from either This results in a rough position signal L G The unambiguous measurement range for e.g.

[0109]

number

[0110] can be expanded to The formula already given above

[0111]

number

[0112] Approximate position signal L G To determine the optical phase amplitude A applied by the modulation unit 15 for each wavelength, λiPM (i=1, 2, 3) need to be known accurately. In the exemplary embodiment of Fig. 1, the determination of these quantities is performed by continuous measurements using an optical phase amplitude determination unit 80. The optical phase amplitude determination unit 80 may also be integrated into the light source unit as an alternative to the representation of Fig. 1.

[0113] Based on the representation in FIG. 6, the structure and function principle of the optical phase amplitude determination unit 80 used in this exemplary embodiment will be explained below. As already mentioned, the beam splitter 100 splits the phase-modulated beam S PM A portion of the optical power is decoupled from the ray bundle S PM_R 6, the optical phase and amplitude determination unit 80 includes a reference interferometer unit 60, a detection unit 40.R, and a signal processing unit 70. The functioning of the reference interferometer unit 60 corresponds in principle to the functioning of the interferometer unit 30 from FIG. 1, except that the measurement beam M PM_R However, the optical path length is 2 × L due to the fiber coupler 66. R and decoupled again by a fiber collimator 67, in which R corresponds to the optical path length difference between the measurement beam and the reference beam in the reference interferometer unit 60. Instead, the measurement beam M PM_R and the reference ray bundle RPM_R The reference interferometer unit 60 is followed by a detection unit 40.R and a signal processing unit 70, which detects the position, phase, and amplitude A of each wavelength. λi_R (i=1, 2, 3) is determined. This is the position phase amplitude A λi (i=1, 2, 3). The structure of the signal processing unit 70 used for this purpose is shown in Fig. 7, and the signal processing intended to be carried out by this signal processing unit 70 corresponds substantially to the procedure already explained above in connection with the signal processing unit 50 and with reference to Fig. 3.

[0114] The signal processing unit 70 then processes the individual wavelengths λ i (i=1, 2, 3) the optical phase amplitude A applied by the modulation unit 15 λiPM (i=1, 2, 3) is determined, and for this purpose the formula

[0115]

number

[0116] But, A λiPM is solved based on Subsequently, the optical phase amplitude A applied by the modulation unit 15 λiPM (i=1, 2, 3) is expressed as follows:

[0117]

number

[0118] and can be provided at the output of the optical phase amplitude determination unit 80 for further processing. It is advantageous to perform signal conditioning within the reference interferometer unit 60 to minimize interpolation errors due to component and alignment tolerances. In this regard, the optical path length difference L Rmust be changed by at least half a wavelength. This can be done, for example, by changing the force applied to the reference fiber 68 or by changing the temperature of the reference fiber 68.

[0119] The device according to the invention can be used, for example, in a measurement setup for absolute length measurements consisting of multiple laser trackers. With such a measurement setup, the absolute position or absolute orientation of an object in space can be determined by the known multilateration method. A corresponding measurement setup is shown in highly schematic form in FIG. 8. In this case, the phase-modulated ray bundle S generated by the light source unit 10 is PM first reaches a splitting element 90 in the form of a fiber splitter, which splits the beam into a plurality of phase-modulated partial beams S PM_R and S PM_j (j=1, 2, ...N). Then, the partial ray bundle S PM_R is sent to the optical phase amplitude determination unit 80, and the remaining partial ray bundle S PM_j (j=1, 2, ...N) are sent to a number N of interferometer units 30.1...30.N, each assigned to a different measurement axis or laser tracker. Each interferometer unit 30.1...30.N is followed by one detection unit 40.1...40.N and one signal processing unit 50.1...50.N, respectively, in accordance with the exemplary embodiment described above, so that for each measurement axis, absolute position information L1...L2 for the respective measurement reflector is obtained. N is determined.

[0120] In addition to the described exemplary embodiments and variants of the device according to the invention, there are of course still other configuration possibilities within the scope of the invention. That is, the optical phase amplitude A using the optical phase amplitude determination unit explained above λiPM Instead of continuous determination of (i=1, 2, 3), the amplitude A applied by phase modulation λiPM(i=1, 2, 3) are determined once in a suitable manner before the measurement operation, and then these quantities are available to the signal processing unit as constants for further processing. Such determination can be performed, for example, during production, and periodic recalibration can be performed later.

[0121] Furthermore, the amplitude A applied by phase modulation λiPM (i=1, 2, 3) can also be determined during the measurement operation. For this, at least two different lengths or absolute positions L_1 and L_2 must be adjusted. During the movement between both absolute positions L_1 and L_2, no beam interruption in the interferometer must occur, and therefore the unmodulated phase value Φ λi The measurement of the imputed unmodulated phase value Φ remains undisturbed. λi _1(i=1, 2, 3) and Φ λi _2(i=1, 2, 3) and position phase amplitude A λi _1(i=1, 2, 3) and A λi _2 (i=1, 2, 3) are measured and stored. In this case, the following simultaneous equations are

[0122]

number

[0123] can be established. In addition to this,

[0124]

number

[0125] can be set. where L_0 is the unknown difference between the incremental and absolute position information.

[0126] In this case, the simultaneous equations

[0127]

number

[0128] is derived as a result. This system of equations has two unknowns, L_0 and A λiPM It only contains the unknowns L_0 and A λiPM This procedure can be applied repeatedly during the measurement operation, and thus the optical phase amplitude A λiPM It can also be applied to correct for slow changes in (i=1, 2, 3). [Explanation of symbols]

[0129] 12 Electro-optic modulator 13 Sine Wave Generator 15 Modulation Unit 30;30.1, 30.2, ...30.N Interferometer Unit 31 Beam splitting unit, beam merging unit 33 Measuring reflector 34 Reference reflector 50;50.1, 50.2, ...50.N signal processing unit 40;40.1, 40.2, ...40.N detection unit 80 Optical Phase Amplitude Determination Unit 90 split elements A PM Voltage Amplitude A λi ;i=1...3 Position Phase Amplitude A λiPM ;i=1...3 Optical phase amplitude f PM Modulation Frequency IF PM Interfering beam L;L1, L2, ... L N Absolute location information L G rough position signal M PM Measuring ray flux R PM reference ray bundle S PM Phase-modulated ray bundle S PM_R , S PM_j;j=1, 2, ...N phase-modulated partial ray bundles S90 λiPM , S210 λiPM , S330 λiPM ;i=1,2,3;S90 λiPM_j , S210 λiPM_j , S330 λiPM_j ;i=1,2,3;j=1,2,...N partial interference signals x measurement direction ΔΦ 12 , ΔΦ 23 , and ΔΦ differential phase λ i ;i=1, 2, 3 wavelength Λ j ;i=1, 2, 3 combined wavelength Φ λi ;i=1, 2, 3 Unmodulated phase value Φ λiPM ;i=1, 2, 3 modulated phase value

Claims

1. a multi-wavelength light source providing a bundle of rays providing at least three different wavelengths; at least one interferometer unit for splitting the light beam into a measurement light beam and a reference light beam, the measurement light beam propagating in a measurement arm towards a measurement reflector movable along a measurement axis and being reflected back therefrom, and the reference light beam propagating in a reference arm towards a fixed reference reflector and being reflected back therefrom, the measurement light beam and the reference light beam reflected back by the measurement reflector and the reference reflector interferingly overlapping in an interference light beam; at least one detection unit in which the division of the interference ray bundle is effected in such a way that a plurality of phase-shifted partial interference signals respectively result for each wavelength; at least one signal processing unit configured and adapted to determine absolute position information about the measurement reflector from the partial interference signals of different wavelengths and an additional coarse position signal; 1. An apparatus for interferometric distance measurement, comprising: The approximate position signal (L Ｇ A modulation unit (15) arranged downstream and adjacent to the multi-wavelength light source (11) modulates at least one emitted wavelength (λ) to generate a ｉ ; i = 1, 2, 3), thereby generating a phase-modulated ray bundle (S ＰＭ ;S ＰＭ＿１ , S ＰＭ＿２ ,...S ＰＭ＿Ｎ ) propagates in the direction of said at least one interferometer unit (30; 30.1, 30.2, ... 30.N) and produces at least one partial interference signal (S90 λｉＰＭ , S210 λｉＰＭ , S330 λｉＰＭ ;i=1,2,3;S90 λｉＰＭ＿ｊ , S210 λｉＰＭ＿ｊ , S330 λｉＰＭ＿ｊ ; i=1, 2, 3; j=1, 2, ... N), the modulation caused in said intervals depends on said intervals.

2. The modulation unit (15) includes an electro-optical modulator (12) and a sine wave generator (13), and the sine wave generator (13) modulates the electro-optical modulator (12) at a predetermined modulation frequency (f ＰＭ ) and the specified voltage amplitude (A ＰＭ 2. The device according to claim 1, wherein the control is performed by a

3. The modulation frequency (f ＰＭ 3. The device of claim 2, wherein the frequency of the vibration is selected to be greater than the mechanical and acoustic frequencies generated.

4. The modulation frequency (f ＰＭ 3. The device according to claim 2, characterized in that the frequency range [100 kHz...10 MHz] is selected.

5. 3. The device according to claim 2, characterized in that the electro-optical modulator (12) is formed as an integrated fiber-coupled modulator.

6. At least one partial interference signal (S90 λｉＰＭ , S210 λｉＰＭ , S330 λｉＰＭ ;i=1,2,3;S90 λｉＰＭ＿ｊ , S210 λｉＰＭ＿ｊ , S330 λｉＰＭ＿ｊ 3. The device according to claim 2, wherein the modulations caused in (i=1, 2, 3; j=1, 2, . . . N) are phase and amplitude modulations.

7. The signal processing unit (50) processes the approximate position signal (L Ｇ 7. The device according to claim 1, wherein the device is configured and adapted to generate a signal.

8. The signal processing unit (50) at least one evaluated partial interference signal (S90 λｉＰＭ , S210 λｉＰＭ , S330 λｉＰＭ ;i=1,2,3;S90 λｉＰＭ＿ｊ , S210 λｉＰＭ＿ｊ , S330 λｉＰＭ＿ｊ ; i = 1, 2, 3; j = 1, 2, ... N) to obtain the modulated phase value (Φ λｉＰＭ ; i=1, 2, 3), and - the modulated phase value (Φ λｉＰＭ ; i = 1, 2, 3), the position phase amplitude (A λｉ ; i = 1...3), and - the position phase amplitude (A λｉ ; i = 1...3) and the phase-modulated ray bundle (S ＰＭ ) is the optical phase amplitude (A λｉＰＭ ; i = 1, 2, 3) and the approximate position signal (L Ｇ 8. The apparatus of claim 7, configured and adapted to determine

9. The approximate position signal (L Ｇ ) is expressed as follows: [Equation 36] is determined based on the formula L Ｇ := Approximate position signal c: = speed of light in the measurement medium f ＰＭ : = modulation frequency A λｉ ; i=1, 2, 3:=position phase amplitude A λｉＰＭ i = 1, 2, 3: = optical phase amplitude 9. The device according to claim 8, wherein:

10. An optical phase amplitude determination unit (80) determines the phase modulated beam of light (S ＰＭ ) is applied to the optical phase amplitude (A λｉＰＭ 9. The device according to claim 8, characterized in that it is configured and adapted to determine:

11. In addition, the signal processing unit (50) the phase-shifted electrical partial interference signal (S90 λｉＰＭ , S210 λｉＰＭ , S330 λｉＰＭ ;i=1,2,3;S90 λｉＰＭ＿ｊ , S210 λｉＰＭ＿ｊ , S330 λｉＰＭ＿ｊ ; i = 1, 2, 3; j = 1, 2, ... N) to obtain the wavelength (λ １ , λ ２ , λ ３ ), the unmodulated phase value (Φ λｉ ; i=1, 2, 3), and - the unmodulated phase value (Φ λｉ ; i = 1, 2, 3), each with a different synthetic wavelength (Λ ｊ ; i = 1, 2, 3) １２ , ΔΦ ２３ , and ΔΦ), and - the approximate position signal (L Ｇ ) and the differential phase (ΔΦ １２ , ΔΦ ２３ , and ΔΦ) to determine high-resolution absolute position information (L) for the measurement reflector (33).

9. A device according to claim 7 or 8, characterized in that it is configured and adapted for

12. said phase-modulated ray bundle (S ＰＭ ) into a plurality of phase-modulated partial ray bundles (S ＰＭ＿Ｒ , S ＰＭ＿ｊ ; j=1, 2, ... N), - each assigned to a different measurement axis and each having one phase-modulated partial beam (S ＰＭ＿ｊ ; j=1, 2, ... N) with a number of interferometer units (30.1, 30.2, ... 30.N) capable of transmitting absolute position information (L １ , L ２ ,...L Ｎ a number of interferometer units (30.1, 30.2, ... 30.N), each of which is followed by one detection unit (40.1, 40.2, ... 40.N) and one signal processing unit (50.1, 50.2, ... 50.N) for determining the 12. The device according to claim 1, wherein:

13. Partial ray bundle (S ＰＭ＿Ｒ ) and the optical phase amplitude (A λｉＰＭ ; i=1, 2, 3) to an optical phase amplitude determination unit (80) which sends the phase modulated partial beams (S ＰＭ＿Ｒ 13. The device according to claim 10 or 12, characterized in that

14. The interferometer unit (30) includes a beam splitting unit (31), the measurement reflector (33) movable along at least one measurement direction (x), the fixed reference reflector (34), and a beam combining unit (31), and the beam splitting unit (31) splits the phase-modulated beam (S ＰＭ ) measurement ray flux (M ＰＭ ) and the reference ray bundle (R ＰＭ ), and the measurement light beam (M ＰＭ ) and the reference beam (R ＰＭ ) with the interference beam (IF ＰＭ 14. The device according to claim 1, wherein the superposition is performed on the image signal.

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