DE3425476A1 - Length measuring device in accordance with the two-beam laser interferometer principle - Google Patents

Abstract

Length measuring device having a position detector (12) in accordance with the two-beam laser interferometer principle, having a laser light source (16) supplied from a current source (48), a beam splitter (18), arranged in the optical axis of said light source, for splitting the light beam into a measuring light beam and a reference light beam aligned at an angle thereto, a movable mirror (19) which reflects the measuring light beam with a transverse offset parallel to the optical axis and is connected to the position detector (12), and having an at least partially reflecting further optical element (20). This optical element (20) can be constructed either as a second mirror or as a second beam splitter. Situated in the interference region of the beam paths is at least one photodetector (21) whose output or output is/are applied to an evaluation circuit (37) having a counting device for counting the bright/dark sequences including directional detection, and having a digital display system (3). According to the invention, the laser light source is a laser diode (16) for generating, simultaneously laterally, transversely and longitudinally, essentially monomode laser light having a coherence length which corresponds at least to the length to be measured. Furthermore, the evaluation circuit (37) has at least one device for eliminating the influences of operating and environmental parameters of the length measuring device. The device is of exceptionally compact design ... Original abstract incomplete. <IMAGE>

Description

"Length measuring device according to the two-beam

Laser interferometer principle The invention relates to a length measuring device with position indicator based on the two-beam laser interferometer principle with one of one Power source supplied laser light source, one arranged in its optical axis Beam splitter for splitting the light beam into a measuring light beam and a at an angle to this aligned reference light beam, with a measuring light beam movable with transverse offset parallel to the optical axis reflective, with the Position indicator connected mirror, with an at least partially reflective further optical element (second mirror or second beam splitter) and at least a photodetector located in the interference area of the beam paths, its output or the outputs of an evaluation circuit with a counter for counting the light / dark sequences including a directional recognition and with a digital one Display system are activated.

The moving part of the measuring device is called a position indicator, that detects the position of the measurement object, so for example a stylus that is on a workpiece surface can be placed on it, or a moving part of a machine tool, to which the movable mirror of the interferometer is attached.

Such measuring devices are with different exemplary embodiments in the article by Kunzmann '"Application of the laser interferometer in production metrology" in Annais of the CIRP Vol. 28/1/1979 ", pages 311 to 316. It is included possible to use either a beam splitter and two reflectors, or else two beam splitters and a reflector. This is a very well-known measuring device so-called Michelson interferometer, which is also mentioned in the literature reference mentioned is described.

In such interferometers, a light beam is split into two sub-beams split, of which one as a reference light beam and the other as a measuring light beam can be designated. A semitransparent mirror can be used as a beam splitter used, which is arranged at an angle of 45 degrees in the beam path is, or a cube that is cemented together from two prisms, the cemented surface is also arranged at an angle of 45 degrees in the beam path.

The measuring and reference light beams become more independent after they have been covered Paths re-merged into an interference ray and interfered with it Way. Depending on the phase of the two partial beams with respect to one another, the interference beam can an amplitude value between the sum of the individual amplitudes (constructive interference) and assume zero (destructive interference). With a continuous movement of the movable mirror, the remote signal passes through a sequence of signals of different types Brightness (called interference lenses or fringes) as seen by a photodetector can be detected and converted into an electrical pulse sequence. Divided by two Photodetectors that are offset from one another in relation to the phase position are not only the light-to-dark transitions are recorded, but also the direction of displacement of the movable mirror evaluates the displacement S, t of the movable mirror results from the number of zero crossings "m" and the light wavelength 2'R. " to s = m.

The number of light-ouncle transitions is therefore a measure of the displacement of the movable mirror relative to the fixed optical elements. These Method of interferometric length measurement is in the group of incrementals To classify measurements.

For a clean interference signal, the structure must be aligned in this way be that the two partial beams are exactly parallel and with the same polarization direction meet. The use of so-called retro-reflectors as mirrors, for example of so-called triple mirrors, ensures that the incident beam is always parallel to the reflected beam is oriented. It is also necessary to prevent reflected light back in by suitable parallel offset reaches the light source and causes interference there.

The above considerations assume that the used Light source emits an infinitely long wave train of exactly one frequency. In practice, a light source supplies a mixture of localized light particles, so-called photons of different polarization and frequency. Even strictly monochromatic Light sources such as lasers have a certain bandwidth in terms of frequency. This bandwidth is. the reason why the photons of the light beam are not spatially arbitrary far have the fixed phase relationship necessary for interference.

The distance over which this fixed phase relationship exists is called Called coherence length. It is greater, the narrower the frequency bandwidth of the laser is. The coherence length thus forms the maximum limit of the path length difference of the two partial beams, i.e. twice the travel of a mirror or Reflector.

If the path length difference exceeds the permissible value, it decreases the contrast in the interference signal decreases so far that a counting of the light-dark transitions is no longer possible. A similar but spatially periodic effect in contrast causes the emission of several discrete, each narrowband frequency modes. the location of the individual modes and the contour of the so-called amplification curve (= Envelope curve of the intensity maxima) are due to the temperature and other external parameters strongly influencing. Especially the temperature susceptibility of the frequency stability leads to the need to control the output power of the light source through a control loop keep constant. It is therefore desirable to significantly oppose the individual fashion to reinforce the neighboring fashions.

Another prerequisite for good contrast in the interference signal is the approximate equality of intensity of the two partial beams. Since the optical Path lengths of the two partial beams are different from one another, the light source must emit a beam of light that is as well bundled as possible.

The reference by Kunzmann cited at the beginning mentions on page 311 a helium-neon laser, i.e. a so-called gas lasers.

Such lasers are, however, for practical use in manufacturing metrology afflicted with some disadvantages: the thermal influences, the heating of the laser tube, and the encapsulation of the relatively large aggregates results in measuring devices with large dimensions and of great weight, which can no longer be used for manual measurements. The known gas lasers require extensive facilities or auxiliary units for Regulation, and in particular for cooling, which further increase the construction volume. the when using the well-known gas lasers emerging problems in the measuring section due to steam, dust particles and other impurities a disruptive influence on the measurement result.

The invention is therefore based on the object of a measuring device of the type described at the outset to be used in a reliable measurement according to the interferometer principle also over longer distances, i.e. in the decimeter and meter range, has dimensions that are much smaller than those the known measuring devices with gas lasers and the no extensive auxiliary units for the actual laser operation.

The task at hand is solved with the one specified at the beginning Length measuring device according to the invention in that the laser light source is a laser diode for the production of lateral, transversal and longitudinal essentially simultaneously mono-mode laser light with a coherence length that is at least that to be measured Length corresponds, and that the length measuring device has at least one device for Eliminate the effects of operating and environmental parameters.

The use of semiconductor or laser diodes in some special Measuring devices, which do not include length measuring devices, are known per se: By DE-OS 31 31 232 a semiconductor ring laser device is known, which is a so-called Gyroscope forms.

In such a device, two laser light beams run in opposite directions in a circle or polygon with an initially fixed phase relationship. If the Circle or polygon is rotated, then there is an extremely small phase shift, which is smaller than a wavelength, so that a count of the light / dark transitions is not provided. Rather, the phase shift is the actual measured variable. A greater coherence length is also not desirable in such gyroscopes, since then interference from scattering and overlay would occur. The waiver to a greater coherence length is achieved in that the reflector surfaces the ends of the waveguide at an angle significantly different from 90 degrees are aligned to the longitudinal axis of the waveguide. In this way there is no mono-mode laser light, and the coherence length is well below one millimeter. The well-known laser is a custom-made product and cannot be used for length measuring devices.

Published by the Taylor et al. Article "Fiber Optic Sensors" on the occasion of the "First European Conference on Integrated Optics"> by The Institution of Electrical Engineers, 1981, pages 99 to 101, it is known to use mono-mode laser diodes in connection with fiber optics for the measurement of sound pressures, magnetic fields, To use accelerations, temperatures and rotations.

The media used here are those listed above Influences suffer extremely slight changes in length, so that again path differences occur between the interfering rays that are smaller than one wavelength are, so that in turn, small coherence lengths should be aimed for in order to avoid interference are. In this case, too, it is a matter of length or length. Phase changes that are play in pm or 2w -erei di, so that the described arrangements are suitable for length measurements is not given.

In the article by Petermann "Semiconductor Laser Mode in an Interferometer System, "published in IEEE Journal of Quantum Electronics, July 1981, pages 1251 to 1256, as well as "Single-mode diode laser phase noise" by Dandridge in Appl Phys. Lett., January 1981,> Pages 77/78 are measuring arrangements for measurement of laser noise, which, among other things, make use of the Michelson principle. Petermann describes a multimode laser that is also used for length measurements is useless. Dandridge describes the use of a mono-mode laser diode the name Hitachi 1400 CSP, which according to the data sheet has an emission wavelength has between 820 and 880 nm. The laser diode, however, was in an unstabilized state respectively.

operated freely, and the noise level was a function of the path length difference was examined, which was up to 40 cm. Because of the way it works the coherence length was on the order of 30 µm, making it suitable for length measuring devices likewise not can be seen. The displacement path of the mirror of up to 40 cm does not contain any information about the coherence length. rush basically leads to a lack of contrast in the interference phenomena, so that a counting of the light / dark transitions is neither possible nor even provided is.

Laser diodes are, for example, called 'tCollimator-Pen " CQL 13 A from VALVO and under the serial names HLP 1000, HLP 2000 and HLP 3000 sold by Hitachi. However, as areas of application are alien subject areas specified. The well-known laser diodes are used as light sources for glass fiber optics> as well as for scanning video and audio disks, data transmission and storage, alarm systems, etc. are provided.

The solution according to the invention has proven to be particularly suitable the laser diode sold by Hitachi under the name HLP 7801 E proven. It is also offered for scanning video and audio disks and has a coherence length of approx 2 to 3 meters and is also extremely cheap because its price is less than 10 % of the price of the laser diodes mentioned above. The laser diode HLP 7801 E has the advantage that its operating conditions (operating temperature, Injection current) can be set to values that lead to an emission wavelength of lead practically exactly 800 nm. This wavelength can also be orderly simply process it in a binary system and add it without a great deal of computational effort counting results that can be evaluated immediately.

It has surprisingly been found that such laser diodes that including a built-in collimator length dimensions of about 20 mm with diameters of 6 to 8 mm, excellent as laser light sources suitable for length measuring devices based on the two-beam interferometer principle. she In spite of the simple structure and the simple operating conditions, the above are sufficient requirements described for the laser light sources required for measuring devices. In particular, they also have the large size, which is indispensable for such measuring devices Coherence length.

The Hitachi HLP 7801 E laser diode emits at an output power of about 5 mm-watt predominantly a mode of the wavelength around 800 nm, i.e. the maximum this mode stands out many times over from the maxima of the neighboring mode. The light beam lies in the infrared range and is invisible to the eye.

For length measurements, their relative and absolute errors are extremely small must be maintained, there are also other influencing factors that must be taken into account; The emission wavelength of laser diodes depends on their operating temperature and the so-called injection current (Operating current). So basically these are operating parameters within to set specific, as narrow limits as possible to defined and constant values respectively.

to regulate. It will be shown later that the relevant The effort can be kept within limits, if necessary additionally or exclusively the effects of intensity and wavelength changes within the laser diode compensated by the evaluation circuit.

Furthermore, the density of the Medium in the beam path, which in turn is determined by pressure, temperature and humidity is determined.

In addition to the laser diode described, the solution according to the invention therefore has at least one device for eliminating the effects of operating and environmental parameters. For this purpose there are the examples explained in more detail below: Once The laser diode can easily be fixed with a device to stabilize it Operating temperature provided. For example, the laser diode can be made with a Peltier element get connected. Here the temperature of the laser diode is measured with a temperature sensor detected and the Peltier element controlled accordingly via an assigned control circuit. With the current state of the art, the temperature can easily be increased to ' Stabilize 0.1 K, if necessary even to 0.01 K. In the latter In this case, the absolute measurement error would be related to a measurement path from 100 mm below 0.1 pm.

The injection current can be kept constant that the diode is connected to a current-stabilized, controllable power source. The dependence the emission wavelength of the Hitachi laser diode HLP 7801 E is around 6.4 x 10 10 nm / mA. This influence is not very important for the absolute measurement, however, higher frequency interference can create the contrast required for counting influence significantly.

The subject matter of the invention can thereby be made even more advantageous configure that the laser diode for intensity measurement is another photodetector is assigned, the output signal of which is sent to a microcomputer via an analog-to-digital converter is switched on, in which a comparison with a predetermined intensity target value is feasible, and that the corresponding output signal as a correction signal over a digital-to-analog converter can be supplied to the current source for the current of the laser diode is.

Any fluctuations in the intensity of the laser radiation are divided up in this way the further photodetector that is directly assigned to the laser diode can be, so that due to any current fluctuations going back to intensity fluctuations can be recorded and corrected immediately.

With regard to the states in the beam path of the device, it is in accordance with Another embodiment of the invention is particularly advantageous when the output signals of sensors for temperature, pressure and humidity in the beam path via an analog-digital converter are connected to a microcomputer, in which a compensation operation for the mentioned sizes is feasible. This compensation operation is purely computational Measure, i.e. the mentioned influences on the counting result are shown in the computer the forwarding to the digital display system is compensated.

It has already been shown above that the subject of the invention Devices for stabilizing the operating temperature and the injection flow can have the operating parameters and thus the emission wavelength in as possible keep tight limits constant. Current stabilized, controllable or adjustable Current sources, so-called "current constants", are certainly available today, however has already been shown that it is through appropriate control measures according to claim 5 is also possible to generate a corresponding correction signal and any deviations regulate with regard to the injection flow. These measures are considered alternative To see opportunities that, in particular, also support one another can.

An alternative way of focusing on the optical processes in the beam paths as well as on the electronic one Data processing the counting results refer, is according to a further embodiment of the invention characterized in that in addition to the interferometer system with the movable Mirrors. a reference interferometer system with an opposed to the rest of the optical Ele ments fixed mirror is present, the reference interferometer system is acted upon by the light of the same laser diode, and that the output of the reference interferometer system another counting device for counting the light / dark sequences and detecting the direction of travel switched on for the purpose of a compensation operation for the wavelength changes is.

This reference interferometer system naturally detects such changes the laser radiation, which is due to a change in the operating parameters (temperature, injection current) are due in the same or analogous way. The reference interferometer system but also detects changes in the density of the medium in the beam path (Pressure, temperature, humidity). In other words, any change in the emission wavelength and the wavelength in the beam path up to the movable mirror leads to a corresponding one Change in the beam path up to the fixed mirror.

This also results in the reference interferometer system depending on the size the change of state to a light / dark sequence with a corresponding counting process, although these changes are orders of magnitude slower than for example the movement of the moving mirror. By corresponding mathematical processing of the two counting results can be a Achieve compensation of the mentioned influencing variables without this being a complicated one Regulation of the operating parameters of the laser diode in connection with the acquisition of measured values for pressure, temperature and humidity in the beam path.

It should be noted, however, that the rules described and compensation measures, all of which are measures to eliminate the influences of operating and environmental parameters can also be combined with one another, which minimizes the circuitry effort and the accuracy of the display can be maximized.

The solution according to the invention is in particular also in comparison to see with other known incremental encoders that take the handy form of have so-called dial gauges, i.e. the execution of manual measurements on workpieces enable. Such encoders include, for example, dial gauges in which the shifting of glass scales with line grids in connection with light sources and photoreceivers supplies pulse trains that are in downstream signal processing devices converted into the desired measurement results and preferably digitally displayed will. The subject of the invention has now, despite about the same handiness as the known manual measuring devices the extraordinary advantage that the absolute accuracy is a power of ten higher than that of the glass scales. Such glass scales work with a line grating that divides from 10 to 10 pm and leads to sinusoidal pulses. With the subject matter of the invention, a half leads Light wavelength into a sinusoidal pulse, which increases the significantly Accuracy is achieved. In addition, the absolute measurement accuracy is not a reference temperature to be assigned, for example in the form of the expansion coefficient of the material for which glass scales is required.

The subject of the invention is not limited to manual length measuring devices limited, but also and with particular advantage applicable to length measuring systems, which interact with machine controls and measuring machine controls for Use. The subject of the invention is characterized by the extremely small dimensions also advantageous in such measuring systems. Retrofitting is also possible in this way mechanical production machines with the subject matter of the invention possible, since this only takes up a small amount of space, but has all the functions of the expensive known Has laser measuring devices.

Compared to these, however, the subject matter of the invention has because of the exclusive use of semiconductor components a longer service life and Insensitivity, so that even when used under harsh operating conditions no malfunctions occur in the area of machine controls. Same is a Use Height measuring devices, also known as "vertical length measuring devices" as well as scribers with scribers for scoring Contour lines over a reference platform (measuring plate) possible. It is also possible the linear grid scales used in handling devices and robot controls to be replaced by the subject matter of the invention.

To ensure a high speed of movement of the position knife or the movable To enable mirror with reliable signal evaluation, it is particularly advantageous to if the at least one photodetector is followed by a counter block whose Outputs of a signal processing device for converting the counter pulses into digital display signals corresponding to the travel path of the movable mirror are activated for the digital display system. With such, commercially available Counter modules are allowed counting frequencies in the MHz range.

A signal that is 90 degrees out of phase (e.g. can be obtained by an X / 4 plate) and two receiver diodes, which are used to detect the direction of travel are required anyway, can be added to the circuit using an exclusive-OR link (exor link) in connection with a downstream edge detector die Counting frequency quadrupled and thus a corresponding increase in resolution be effected. The resolving power receives an increase with the same Effect as if using instead of the laser diode an emission wavelength of 800 nm, one with an emission wavelength of only 200 nm would be used.

It is particularly advantageous to have the laser diode inside.: Half of a To accommodate the housing, arranged in the opposite wall of a guide tube is.t, the axis of which is parallel to the optical axis of the collimator and in where the stylus (position indicator) is mounted to be longitudinally displaceable with the movable mirror is. Such a device can include all for the acquisition of the measured values and the display required functional groups are inserted manually, i.e. in the Hand held. Here are the beam paths of the measuring and reference light beams hermetically encapsulated within the same housing or within the guide tube, so that a disruptive influence of the beam paths by external influences is not can be done. In particular, it is possible for the housing itself and the guide of the stylus sealed in the guide tube, so that the entire inner Structure of the device is reliably protected. By filling with a protective gas and maintenance: 9 ;;; $ of an overpressure, the protective effect can still be inherited.

As already stated above, the subject matter of the invention is suitable also for length measuring systems that interact with machine controls and; Measuring machine controls come into use. Such a measuring device is according to the further invention dadur ~ t +.

characterized in that the laser diode with the collimator in a housing is housed, which is connected to a first part of a machine that the Position indicator with the movable mirror with a relatively movable mirror to the first part second part of the machine is connected and that position indicator and housing via a The length-adjustable protective device enclosing the optical axis is connected. In a particularly advantageous manner, the protective device consists of telescopic tubes.

It is with regard to the fixed spatial allocation of the individual optical elements of the interferometer system particularly advantageous when the laser diode and the collimator are housed in an adapter sleeve, at the end of which in the area of the intersection point "K of the measuring and reference light beam of the beam splitter, the at least partially reflective optical element and the at least one photodetector are arranged.

It is an essential feature that the coherence length is at least corresponds to the length to be measured. Since the laser rays in the beam path are about the cover twice the distance, it is therefore particularly useful if the coherence length corresponds to at least twice the value of the length to be measured. With increasing The coherence length increases the contrasts with regard to the light / dark transitions, see above that with regard to an evaluation or counting of the interference effect as possible long coherence length is to be aimed for with reasonable effort.

Further advantageous refinements of the subject matter of the invention result from the other subclaims.

The measuring principle, the basic signal processing and two exemplary embodiments of the subject matter of the invention are explained in more detail below with reference to FIGS. 1 to 6.

They show: FIG. 1 a front view of a measuring device for manual use, FIG. 2 shows a longitudinal section through the object according to FIG 1 along the optical axis of the collimator, Figure 3 is a schematic diagram of a Two-beam laser interferometer system in connection with an electrical signal processing device, FIG. 4 shows a longitudinal section through a measuring device for use in a Machine control, Figure 5 is a schematic diagram of a variant of Figure 3, Figure 6 is a perspective view of an external display device.

In Figure 1 is an external view of a housing is shown on its front 2 a digital display system 3 with three digits in front and three Places after the decimal point 4. The externally visible part of the display system is an LCD.

Below the display system 3 there is a keypad 5 with an ON-OFF button 6, a start button 7, a delete button 8 and a conversion button 9 for the optional display of the measurement result in inches and in millimeters. It understands that the keypad 5 also contain a much larger number of keys can, for example, also numerical values and predefined programs for certain To be able to enter arithmetic operations or program sequences.

Such a keypad 5a is shown in FIG.

The housing 1 has in the lower part a wall 10 into which a guide tube 11 is firmly inserted. A position indicator 12 is sealed in this guide tube guided. There is another one between the position indicator and the guide tube Telescopic tube 13 through which the entire displacement path of the position indicator 12 is still corresponding is enlarged.

Figure 3 is shown reduced in scale, the same parts however, provided with the same reference numerals.

The housing 1 has an upper wall 14 on which an adapter sleeve 15, the laser diode 16 according to the invention is attached. It is a laser diode with the type designation HLP 7801 E from Hitachi with a arranged in the front part and only shown in dashed lines collimator 17. Der The collimator defines an optical axis A-A, which is the axis of the whole System is. The adapter sleeve 15 made of aluminum has a lateral one Flattening to which a device 90 (Peltier element) for stabilizing the Operating temperature and a heat sensor 91 are set to conduct heat well.

In the axis A-A a beam splitter 18 is arranged through which the Light beam into a measuring light beam running parallel to the optical axis and a reference light beam aligned at 90 degrees to this is split. in the The beam path of the measuring light beam is a mirror at the inner end of the position indicator 12 19 arranged, which is designed as a so-called triple mirror and which the light always reflected offset parallel to the direction of the incident light. In the direction of the reference light beam deflected by 90 degrees is a stationary optical one Element 20 arranged, which also in the embodiment described here designed as a triple mirror. Have measuring light beam and reference light beam due to the permeability of the beam splitter, each about half the intensity of the light beam emerging from the collimator 17.

The light reflected from the mirror 19 is reflected by the beam splitter 18 in the same proportion to a photodetector 21 deflected. Of the the same photodetector is also acted upon by that part of the reference light beam, which is reflected by the optical element 20 in the direction of the beam splitter 18 and passes through it in the same direction. Beam splitter 18, optical Element 20 and photodetector 21 are firmly in the interior in the spatial position shown Installed at the end of the guide tube 11, in the area of the intersection point "K" of measuring and reference light beam. In this way, before the photodetector 21 is through Superposition of measuring and reference light beam formed an interference beam, the when the mirror 19 is displaced in the direction of the axis A-A the further above has described influence on the photodetector 21. The embodiment according to Figure 2 corresponds to the Michelson interferometer.

In the housing 1 is through a pressure-tight wall 22, which in the present Case is formed from a metallic bellows, partitioned off a sub-space 23, which communicates with the interior space 24 of the guide tube 11.

By reducing the volume of the subspace 23 - since this is sealed to the outside - a pressure is built up, which is on the inner end faces of position indicator 12 and telescopic tube 13 transmits and these to extend or to brings a contact with the measurement object. Such an extended position is labeled 12a. The interference process on the photodetector 21 creates a rapid sequence of light / dark transitions that are at the Output of the photodetector 21 is expressed as an electrical pulse train in the downstream Signal processing device according to FIG. 3 can be converted into measured values to be displayed is.

According to Figure 2, the subspace 23 is surrounded by a bellows, in which also houses the laser diode 16. One end of the bellows is connected to the wall 14 of the housing 1 in a pressure-tight manner, while the other end is likewise is pressure-tightly connected to a movable annular flange 25, which the guide tube 11 surrounds.

An equally pressure-tight connection between the ring flange and the guide tube is effected by a rolling membrane 26, which like the bellows is commercially available as a standardized component. It turns out in this way that a movement of the annular flange 15 parallel to the axis A-A, its main plane otherwise perpendicular to the axis A-A, a corresponding reduction in Volume within the subspace 23 results, so that the desired extension movement of the position indicator 12 takes place.

In order to be able to bring about the movement of the annular flange 25 from the outside, this is connected to a drive device 27, which consists of a hydraulic Pressure transmitter 28 and three pressure sensors 29 distributed equidistantly on the circumference. The pressure transducers 29 are supported on the wall 10 of the housing 1 and are with the Pressure transmitter 28 connected by a line 30 each. The pressure transmitter 28 consists of one not designated cylinder and a piston 28a, the can be actuated from the outside by means of a mechanical trigger 31 again made of bellows, but it goes without saying that a piston drive is also used here can be used; conversely, the pressure transducer 28 can also be formed by a bellows realize. By transmitting the same pressure from the pressure transmitter 28 to several A corresponding force transmission can be achieved by pressure transducer 29.

In Figure 2, the display system 3 (LCD) are shown in dashed lines, the keypad 5 and a signal processing device 32, which are based on FIG 3 will be explained in more detail. A battery 33 is arranged in a battery compartment; by means of an external connection 34 (multiple plug connection), connections on machine controls, external program memories, computers and printers will.

In Figure 3 are again the same parts or parts with the same function provided with the same reference numerals. The arranged in the area of the interference beam, however, the photodetector 21, which is shown considerably larger, contains two phototransistors 21a and 21b, which are offset in the direction of displacement of the position indicator 12 by such an amount are arranged that the light / dark pulses with a phase shift of 90 Degrees occur. The two signal sequences are used for direction detection in a directional circuit 35 which, like a counter block 36, is part of a counter module 37 is. The preferred counter blocks are up and down counters CMOS type 4516 and TDL Type 74 LF 193 can be used. Several outputs lead from the counter module 37 38 to a microcomputer 39, which is under the type designation "80 C 49" from the company NEC> Japan is manufactured. This is an 8-bit computer, also when more extensive arithmetic operations (measurement and control) are required can be replaced by a corresponding 16-bit computer. The microcomputer 39 has a processor 39ab, a parallel input 39b, decoder 39c and 39d as well as memory blocks designated by their functions ROM, EAROM and RAM are.

The microcomputer 39 receives its time pulses from a clock generator 40. All counters can be reset by means of a reset button 41. The external connection 34 has already been explained with reference to FIG. 2; another external connection 42 can be connected to a computer (not shown).

The microcomputer 39 already receives its input commands via the described keypad 5a. It is via a display control circuit 43 with the Display system 3 connected.

In accordance with Figure 3, the laser diode 16 is a good heat conductor Connection a device 90 for stabilizing the operating temperature and a Warmth ~ sensor 91 attached. A signal line leads from the heat sensor 91 to an analog regulator 92, which receives its supply voltage via a terminal 93. The controller 92 is in turn connected to the device via two lines, not shown in detail 90 connected, so that it is possible in this way, the operating temperature of the Laser diode 16 to a constant value within extremely narrow limits to regulate.

The light beam 16a coming from the laser diode 16 still becomes In front of the beam splitter 18, a partial beam 16b is masked out, which leads to a further Photo detector 44 is performed. This is used to measure the intensity and is there Output signal via a line 45 and an analog-to-digital converter 46 into the microcomputer 39 a.

In this there is a comparison with a predetermined intensity value instead, and any deviations are recognized by a digital-to-analog converter 47 as Correction signal supplied to a current source 48 controllable to a constant current, the output of which is connected to the laser diode 16 via a line 49. On the indicated way the laser diode 16 is on constant emission data (wavelength, Intensity).

The microcomputer 39 are still the outputs of sensors 50, 51 and 52 switched on, which in reality are arranged in the beam path, i.e. in the guide tube 11 are, namely the sensor 50 is a temperature sensor, the sensor 51 is a pressure sensor and sensor 52 a humidity sensor.

The connection of the outputs of these sensors takes place in the same way as the the output of the photodetector 44 via a multiplexer 53, i.e. the interrogation takes place at time intervals. In the microcomputer 39, a compensation operation is performed carried out for the stated measured values.

In the embodiment of Figure 4, the laser diode 16 is with the collimator 17 housed in a housing 54 with a cover 55 The housing is with a first part 56 of a machine, for example with the machine bed connected via a mounting flange 57. In this way, the Housing 54 held stationary. The position indicator 12 is in the present case as extreme Guide tube for Tel es koprohre 58 and 59 formed.

The position indicator 12 is in a further housing 60 with a cover 61 housed, which via a fastening flange 62 with a second part 63 connected to the machine. This second part 63 is in the present case in the direction of the double arrow 64 displaceable in the direction of the axis A-A; however, it comes here only on the relative movement between the individual assemblies. In which Part 63 is, for example, the support of a machine tool.

The movable mirror 19 is at the inner end of the position indicator 12 in mounted so that the light reflected from it in the direction of the axis A-A (Collimator axis) or is reflected parallel to it. From the- was standing this mirror consequently corresponds exactly to the position of the movable part 63. The telescopic tubes 58 and 59 are coaxial with the axis A-A and are well sealed one inside the other as well as in the position indicator 12, which is also designed as a tube.

The telescopic tube that can be moved farthest from the position indicator 12 59 has a flange 65 by means of a union nut 66 with the Housing 54 is connected. Position indicators 12 and telescopic tubes 58, 59 form together a protective device 67 for the measuring light beam on its way to the mirror 19 and back.

As can also be seen from FIG. 4, there are laser diode 16 and collimator 17 arranged in an adapter sleeve 68, at the end of which in the area of the intersection point "K" of the measuring and reference light beam of the beam splitter 18, at least partially reflective optical element 20 and the at least one photodetector 21 arranged are. The adapter sleeve 68 is aligned with the protective device 67. The adapter sleeve 68 is connected via a flange 69 to a partition 70 in the housing 54, behind which is a circuit board 71 with the signal processing device (not shown) is located. Both the laser diode 16 is connected to this circuit board via a plug connection 72 and the photodetector 21 are connected via a line 73. From the board 74 lead unspecified lines to an external connection 34.

In the upper part, FIG. 5 shows a device similar to FIG. 4 but with the difference that the position indicator 12 is in the form of a radial arm is formed, which is passed through the protective device 67. The situation reporter 12 carries the sliding mirror 19 at its inner end and at its outer end free end. a sensing device 74 for detecting the position of a workpiece Etc.

According to Figure 5 is the interferometer system with the movable ichen mirror 19 shows a reference z interferometer system 75 with an optical system compared to the other Elements fixed mirror 76 arranged. The remaining optical elements are in an analogous manner by a beam splitter T7 and another stationary one Mirror 78 is formed. The reference interferometer system 75 receives laser light from the same laser diode 15 by corresponding, not shown in detail optical elements a further beam path 16c is hidden. To the reference interferometer system 75 also belongs to a photodetector 79, which works in an analogous manner to the photodetector 21 consists of two phototransistors 79a and 79b. which the passage of light-dark transitions recognize as well as their direction of travel.

The referent interferometer system makes it possible to do all To recognize changes in the interferometer system in a proportional manner and thus to compensate for the processes in the interferometer system.

For this purpose the output of the reference interferometer system is used connected to the microcomputer 39 via a line 80, by doing another, not shown here, counting device for counting the light / dark sequences and the direction of travel detection is arranged, the counting result of which is taken into account of the sign is added to the count of the main interferometer system will. In the present case, only one cooling body 94 is assigned to the laser diode 16, which allows a temperature rise within certain limits, but excessive temperatures the laser diode 16 prevents. Such cooling bodies are made of semiconductor circuits known and are therefore not explained in more detail.

The laser doodle 16 receives its operating current (injection current) a power source 48, which is not regulated here, but only on one constant current is set. The power source 48 receives the operating current via a terminal 95. The signal processing device is correct in other features according to FIG. 5 corresponds to that according to FIG. 3, so that the same reference numerals were used. It can be seen, however, that sensors 50-52 and any Control interventions for the laser diode 16 are missing here, and that a compensation action only carried out via the reference interference system 75 and the microcomputer 39 will.

Figure 6 shows an external display device 81, for example with the external outputs 34 of three sub ferometer systems according to Figures 4 and 5 is connected.

Their axes are arranged on a machine in the X-Y-Z coordinate system, so that a spatial detection of measurement objects is possible. The device has a Housing 82 with a front side 83, in the three display fields 84, 85 and 86 for the coordinates X, Y and Z are arranged.

To the right there are reset buttons 87 for resetting of the individual advertisements. Again to the right of it is a keypad 88, with the setpoints for the coordinates X, Y and Z entered and certain programs and arithmetic operations can be triggered.

Finally, the front side has a selector switch 89 for the setting of the required coordinates.

The external display device can be very easily attached to a machine attach and enables a central monitoring of the measurement results on the smallest Space.

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Claims (17)

Claims: 1. Length measuring device with position indicator based on the two-beam laser interferometer principle with one laser light source supplied by a power source, one in its optical one Axis arranged beam splitter for splitting the light beam into a measuring light beam and a reference light beam aligned at an angle thereto, with a measuring light beam movable with transverse offset parallel to the optical axis reflective, with the Position indicator connected mirror with at least partially reflective further optical element (second mirror or second beam splitter). as well as at least a photodetector located in the interference area of the beam paths, its output or the outputs of an evaluation circuit with a counter for counting the light / dark foloen including a directional recognition and with a digital one Display system are switched on, characterized in that the laser light source a laser diode (16) for the generation of lateral, transversal and simultaneously longitudinal is essentially mono-mode laser light with a coherence length, which corresponds at least to the length to be measured, and that the length measuring device at least one device for eliminating the effects of operating and environmental parameters owns. 2. Length measuring device according to claim 1, characterized in that the laser diode (16) is one with an emission wavelength of 800 nm. 3. Length measuring device according to claim 1, characterized in that the laser diode (16) a device for stabilizing its operating temperature having. 4. Length measuring device according to claim 1, characterized in that the laser diode (16) is connected to a current-stabilized, controllable current source (48) is. 5. Length measuring device according to claim 4, characterized in that a further photodetector (44) is assigned to the laser diode (16) for intensity measurement is, whose output signal via an analog-to-digital converter (46) to a microcomputer (39) is switched on, in which a comparison with a predetermined intensity setpoint value is feasible, and that the corresponding output signal as a correction signal over a digital-to-analog converter (47) of the current source (48) for the current of the laser diode (16) can be supplied. 6. Length measuring device according to claim, characterized in that the output signals from sensors (50, 51, 52) for temperature (50), pressure (51) and Moisture (52) in the beam path via an analog-digital converter (46) to a microcomputer (39) are activated, in which a compensation operation for the named large is feasible. 7. Length measuring device according to claim 1, characterized in that that in addition to the interferometer system with movable mirror (19) a reference interferometer system (75) with a mirror (76) which is fixed in relation to the other optical elements is present, which reference interferometer system (75) from the light of the same Laser diode (16) is applied, and that the output of the reference interferometer system (75) a further counter for counting the light / dark sequences and the direction of travel detection for the purpose of a compensation operation for the change in wavelength is activated. 8. Length measuring device according to claim 1, characterized in that that the signal processing device comprises a microcomputer (39) which in is designed and switched in such a way that optionally a display of the maximum, of the minimum or an optimized measured value or the relation of the measured value to a tolerance field is feasible. 9. Length measuring device according to claim 8, characterized in that that the microcomputer (39) has a program memory for at least one measuring program and its measured value processing. 10. Length measuring device according to claim 9, characterized in that that the program memory for receiving computer programs for signal processing is designed. 11. Length measuring device according to claim 1, characterized in that that three length measuring devices are arranged in an X-Y-Z coordinate system and that their outputs are connected to a common display device (81). 12. Length measuring device according to claim 1, characterized in that that the laser diode (16) is housed within a housing (1) in which opposite wall (10) a guide tube (11) is arranged, the axis of which to the optical axis (A-A) of the collimator (17) runs parallel and in which the Position indicator (12) designed as a stylus with the movable mirror (19) is longitudinally displaceable is stored. 13. Length measuring device according to claim 12, characterized in that that the beam splitter (18), the at least partially reflective optical element (20) and the at least one photodetector (21) at the inner end of the guide tube (11) arranged in the area of the intersection point "K" of the measuring and reference light beams are. 14. Length measuring device according to claim 12, characterized in that that the digital display system (3) is integrated into the housing (1) with the laser diode (16) is. 15. Length measuring device according to claim 1, characterized in that that the laser diode (16) is housed with the collimator (17) in a housing (54) is that is connected to a first part (56) of a machine that the position indicator (12) with the movable mirror (19) with a relative to the first part (56) movable second part (63) of the machine is connected, and that position indicator (12) and housing (54) via a length-adjustable protective device enveloping the optical axis (A-A) (67) are connected. 16. Length measuring device according to claim 15, characterized in that that the position indicator (12) is housed in a further housing (60) that with the second part (63) of the machine is connected. 17. Length measuring device according to claim 15, characterized in that that laser diode (16) and collimator (17) housed in an adapter sleeve (68) are, at the end in the area of the intersection point K "of the measuring and reference light beam the beam splitter (18), the at least partially reflective optical element (20) and the at least one photodetector (21) are arranged.