DE3219452A1 - Arrangement for controlling the dynamic range of a range finder - Google Patents

Abstract

In a measuring instrument for determining the range of a target object from the transit time of a measurement light pulse which is emitted towards the target object, reflected there and received by the measuring instrument, it is necessary, in order to achieve a high measuring accuracy, to adapt the intensity of the measuring light pulse to the range and reflectivity of the target object and to the transparency of the medium between the target object and the measuring instrument, which is done by an optical attenuation of the measuring light pulse initially generated at the highest possible intensity. According to the invention, this optical attenuation can be carried out in range finders which have a light path change-over switch (10) in order to feed a light pulse generated by the transmitter (1) either into a transmit measuring light path (15) or into a reference light path (11), by the fact that the times at which the transmitter (1) emits a light pulse in each case are controlled as a function of the movement of the light path change-over switch (10) in such a manner that only a desired proportion of the quantity of light output by the transmitter (1) in a light pulse reaches the receiver (23). <IMAGE>

Description

The invention relates to a distance measuring device based on the principle of measuring the transit time of a measuring light pulse according to the preamble of claim 1.

Such a distance measuring device is described, for example, in the earlier German patent application P 31 03 567.1. There the branching point is static, i.e. each light pulse emitted by the transmitter is split into two parts, one of which is emitted as a measuring light pulse to the target object and the other is fed directly to the detector device as a reference light pulse, with the latter for starting and the former for stopping at large measuring distances dt.-r transit time measurement is used. The problem of adapting the intensity of the emitted measuring light pulse to the reflectivity and distance of the target object and the intensity of the reference light pulse to that of the reflected measuring light pulse is solved with the help of damping devices that are switched into the light path between the receiving optics and the detector device or into the reference light path and in principle can be of any type. The adjustments just mentioned are necessary because the intensity of the received measuring light pulse can fluctuate within wide limits due to the causes mentioned as well as the influences of the respective light permeability of the medium lying between the measuring device and the target object. Since the receiver of the detector device has a low dynamics compared to this amplitude range of the reflected light pulse, it is necessary to achieve a high measurement accuracy to attenuate the high intensity of the light pulses emitted by the transmitter for a large measuring range, if very small distances and / or the distances of very good reflecting target objects are to be measured. Since , moreover, the response behavior of the receiver can change as a function of the intensity of the light pulse falling on the photodetector, it is necessary to achieve the most uniform possible processing of measuring light pulse and

Reference light pulse required that the latter has approximately the same amplitude as the light pulse reflected from the target object. In the case of very distant and / or poorly reflecting target objects , it is therefore necessary to reduce the amplitude of the reference light pulse accordingly.

Known damping devices such as iris diaphragms or retractable filters can be used for this

are either comparatively large and unresponsive and therefore unsuitable for high measuring frequencies, or they are expensive and cannot be used without further ado.

In contrast, the invention is based on the object of developing a distance measuring device of the type mentioned at the outset in such a way that the required attenuation of the light pulse intensities can be carried out in a simple, inexpensive and reliable manner at high speed. At a distance measuring device of the type mentioned e, is now different than beschrieten in German Patent Application P 31 03 567.1, not possible to start the transit time measurement with a branched off from the measuring light reference light pulse but by the output by the trigger generator electrical trigger pulse of the transmitter to submit a Light pulse caused, so that here, strictly speaking, no light pulse but a signal transit time measurement is made, the signal first appearing in electrical form, then as a light pulse and then again as an electrical signal. The influence of the signal delays occurring during the two "electrical" phases and their fluctuation and drift phenomena on the measurement result is eliminated by adding a reference light pulse to the measurement light immediately before and / or after the measurement light pulse, which is passed on to the target object

device-internal reference light path is steered, whereby the signal transit time measurement described above is also carried out. In this case the time is Length of the "optical" phase known exactly, so that the signal delays in the two "electrical" phases are determined and because of the shortness of the time in the measuring shot and Successive calibration shots, with the signal delays that occurred during the measuring shot of the "electrical" Phases can be equated or eliminated by subtracting the measured values obtained in this way.

For the necessary feeding of the light pulse emitted by the transmitter once into the measuring light path and once into the A light path switch is provided for the reference light path, which moves and thereby corresponding measuring light positions (feeding the light pulse into the measuring light path) and calibration light positions (feeding the light pulse into the calibration light path) passes through.

This light path turbo switch, which is required in any case, can now, according to claim 1, also serve to solve the problem of the invention underlying task can thereby be used.

In the context of the concept according to the invention, namely the times at which the light pulses hit the movable one To control light path switch so that due to the current position of the light path switch, the desired Attenuation is achieved, there are the following three preferred variants:

a) In the output area of the light path switch, which is from a periodically oscillating mirror, a mirror prism rotating at an approximately constant angular velocity or a deflecting mirror rotating at / constant angular speed and having light passage openings can be formed, there is only one disc

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further 'Feed section of the measuring light path and / or a only further feed section of the reference light path. To achieve one example 50% attenuation is ensured that a light pulse hits the mirror at such a point in time the mirror prism or the rotating disk hits that due to the current position of the light path switch, only half of the amount of light contained in the light pulse falls into the entrance window of the further light path, while the other half passes it and / or is absorbed. To achieve greater or lesser attenuation, other points of impact are correspondingly required for the light pulse on the light path switch to increase the amount of light falling into the further light path or to zoom out. The advantage of such an arrangement, which works with a variable partial covering of the light paths at the moment a light pulse passes through the separation point, is that with you can carry out a continuous damping within wide limits. There are difficulties here, however when the light pulse has a spatio-temporal dispersion, because then the temporal focus of the forwarded part of a light pulse against the temporal focus of the undivided light pulse in Depending on the selected degree of damping can be shifted in different ways, which is immediately affects the transit time measurement to be carried out to determine the distance.

b) This last-mentioned problem can be solved by having several functionally parallel to one another for the measuring light path and / or for the reference light path Provides feed-in sections which are then merged again in the further course into a single measuring or reference light path and each of which

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comprises a damping device having a fixed damping factor which is different from the damping factors in each of the other sections. A desired attenuation can thus be achieved in that the entire light pulse is directed with the aid of the light path switch in each case into that feed section in which a filter or the like effecting this attenuation is arranged. In this way, although the damping only gradually verMnde can _j Ch'i ^ but leads to no particular problems, since / the photoelectric receiver can handle a certain amplitude range over and the attenuation factors of different damping devices can be coordinated so that the product of the The damping factor is smaller in each case and, due to the dynamics of the receiver, is somewhat larger than the next larger damping factor, so that a slightly overlapping connection of the individual damping areas results in a complete total damping area. If, in addition, the transmitter power can be changed, the dynamic factor available can also be included in this product, so that there are correspondingly larger differences between the attenuation factors of the individual filters and, with the overall attenuation range remaining the same, a smaller number of Filter results.

In those cases in which the structure of the light pulses allows this, according to the invention it is also possible here to work with partial overlap of the light paths , whereby the number of functionally parallel light path sections and thus also the required attenuation devices can be reduced, c) A particularly preferred and advantageous variant combines parts of variants a) and b) in such a way that that a plurality of feed sections parallel to one another are not required for the respective light path and yet it is not necessary to work with a partial covering of the light paths. This is done by that by the permanent periodic movement of the light path switch in the light path in which the light pulses are to be damped, continuously damping elements ^ at-

are brought play filters with different attenuation factors, and generates the light pulses so that they arrive at the time the optical-path switcher, wherein them the desired damping element is provided is.

Here, too , you can also work with partial coverage of light paths. If this is not the case, then only a gradual change in the damping factors is also possible. For the reasons already mentioned under b), however, this does not give rise to any particular difficulties.

In all three variants it is possible in principle to carry out the attenuation of the measuring light pulses either before they are transmitted to or after they return from the target object. The latter case is preferred because the ambient light directed by the target object or its surroundings into the receiving light path is attenuated in the same way as the measuring light and thus errors that occur due to different ambient light in the avalanche diode are eliminated, and at the same time the signal-to-noise ratio is significantly improved. To achieve this attenuation on the receiving side, it is only necessary to coordinate the light path switch and the received light path in their structural design so that not only the transmitted light but also the received light strikes the light path switch and from this to the receiver is forwarded.

A rotating disk provided as a light path switch according to the invention to implement variant c) preferably has a large number of openings which allow the light coming from the transmitter to pass through in a straight line and without partial overlap as measuring light, and a large number of mirrors with the same radial distance from the axis of rotation , each of which is suitable for deflecting the light coming from the transmitter into the reference light path. On the other hand, the disc has

be with a different radial distance from the axis of rotation a further multiplicity of openings, which extend through the path of the move through the measuring light returning from the target object and which contain the filters providing the various attenuation values. There are both the openings allowing the transmitted light to pass through, as well as the mirrors and the reference light Passing openings are each combined into groups of the same size, with all the different attenuation values present being represented in a group of receiving light openings. Each group of transmitting light openings and each group of mirrors is assigned a group of receiving light openings in such a way that one through one certain transmission light opening exiting measuring light pulse on its return from the target object passes through a certain receiving light opening, or that when one of the arrives a certain mirror reflected reference light pulse at the receiver there at the same time by a certain Receiving light opening impinges ambient light that has passed through. As a result, on the one hand, by selecting the "correct" transmission light opening for a measuring light pulse, the desired attenuation is determined and on the other hand, by "correct" selection of the mirror for the associated reference light pulse, it is ensured that the lighting conditions at Receiver for both pulses are as similar as possible to each other, assuming that one is in the reference light path arranged damping device, which comprises an unchangeable damping element and a controllable optical damper, the amplitude of the reference light pulse as closely as possible to that of the measuring light pulse arriving at the receiver is aligned.

If the above-mentioned groups of transmitting light openings and mirrors or associated receiving light openings are arranged on the Disc so alternately that in the receiving light openings the different filters, which are in the same way in each Group are present, also have the same order in each group, so it can be, after experimental

measurements the correct attenuation has been found, to obtain several individual measured values for both the measuring light transit time as also the reference light transit time, from which then to achieve a single particularly accurate distance measurement value before or after the subtraction mean values are formed, operate the whole arrangement strictly periodically so that with A measuring light pulse and a reference light pulse are always alternately received at exactly the same time intervals at the receiver.

The analog circuits that process these pulses, like all analog circuits, have the property that the size of the error impressed by them on the measurement signal to be processed from the time interval between two successive similar signal processing operations depends. Due to the periodicity of the control now achieved according to the invention that these errors are of the same size in the transit time values of both the measuring light pulses as well as the associated reference light pulses and thus stand out in the subsequent difference formation.

In addition, a distance measuring device under discussion here generally has a timing device Time base signal use that is used in a wide variety of places and therefore inevitably occurs practically all lines as, albeit a very small, periodically fluctuating interference signal.

If the arrangement is not operated with any periodicity, but with a repetition frequency that is an integral multiple of the frequency of the time base signal, then the interference voltages caused by the time base signal also go into the analog signals with the same Amplitude decreases and therefore drop out again in the subsequent differential formations, and the time measurement process is simplified.

If a sufficiently high frequency, for example 15 MHz, is selected for the time base signal, then the periodic operation described above can easily be carried out under the condition that the light pulses the openings of the rotating disk with full overlap with the preceding and following beam paths should go through.

If such a distance measuring device is supplied with power from a battery, there is a problem that the different voltages required in the device must be generated with the help of a chopper, the edges of which if they coincide with the generation of a signal that starts or ends a run-time measurement, an exact measurement to make impossible.

To avoid this source of error, it is advantageous to control the time of the trigger generator so that the light pulses not only hit the light path switch at the correct times for the desired attenuation, but also so that the start and end of the signal transit time measurements fall in periods in which no disturbances caused by chopper edges occur.

If one wants to use the distance measuring device in the manner described above in order to achieve a particularly high measurement accuracy operate periodically and synchronously with the time base signal, this condition can no longer be realized. In this case, it is provided according to the invention, in the periods in which the start or end of a transit time measurement occurs, to blank the chopper, i.e. to suppress its oscillations for a short time and instead to feed the power supply from a buffer capacitor even in the case of long distances, periods of time in the order of magnitude of GO to 70 μs are only involved, this is possible without great technical effort.

The invention is described below using exemplary embodiments with reference to the drawing; in this shows:

Fig. 1 is a schematic block diagram of a distance measuring device in which, according to the invention, the dynamics control with the aid of a in the transmission and reception Optical switching and damping unit arranged in light paths can be carried out,

FIG. 2 shows the schematic representation of a first embodiment for an optical switching and damping unit according to FIG. 1,

Fig. 3 shows a second, particularly preferred embodiment for an optical switching and damping unit according to Fig. 1 and

FIG. 4 is a front view of the damping disk shown in section in FIG. 3.

As shown in FIG. 1, a distance measuring device operating on the principle of light pulse transit time measurement has a transmitter 1 which, for example, supplies a laser transmitter diode and a transmitter diode which supplies energy Circuit arrangement can comprise, which essentially consists of a "slowly" chargeable energy store in the form of a There is capacity and a controllable electronic switch, which is used to control the energy accumulated in the energy store To discharge energy quickly via the transmitter diode to generate a laser light pulse.

This switch is controlled by a trigger generator 3, the output signal of which also serves to start or as a preparation signal for the start of the respective signal transit time measurement. There is a delay between the trigger generator 3 and the transmitter 1

Switching element 2 , which ensures on the one hand that, for example, even when measuring a very short Ent distance, the stop signal for the transit time measurement has a sufficiently large time interval from the start signal, so that these two signals from one and the same timing channel easily one after the other can be processed, and on the other hand, that the signal transit time measurement is started before the point in time and thus trouble-free, in which the transmitter reacts to the trigger signal with the generation of a very fast and comparatively large surge by the transmitter diode, with very strong Störsig signals are generated, which would make it extremely difficult to capture a precisely simultaneously with or shortly after the light pulse generation emitted by the transmitter 1 start signal for the signal transit time measurement exactly in time.

The light pulses generated by the transmitter 1 are transmitted via a

Transmitter light path 7 of an optical switching and attenuation

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Unit 8 supplied, which / contains a mechanically movable light path switch 10 which, depending on its position, directs a light pulse emerging from the transmitter light path 7 either into a transmitted measuring light path 15 or into a device-internal reference light path 11.

The light pulses fed by the light path switch 10 in its measuring light position into the transmission measuring light path 15 are forwarded to a transmission optics 16, which is shown in simplified form as a single lens and emits the light pulses to the target object whose distance is to be measured .

The light reflected from the target object part of each light pulse is from the also schematically as a single lens shown in Fig. 1, receiving optical system 18 via a receiver angs -Meßlichtweg 19, a included in the optical switching and damping unit 8, the variable optical

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Attenuator 20 and a Qnpfangslichtvyeg 21, 22 fed to a receiver 23, which, for example, as a photoelectric converter comprises a photodiode with a downstream amplifier and signal generation circuit, which serves to send a signal generated by it when a light pulse is received via a line 24 of a measuring device 25 as a stop signal to end the signal transit time measurement carried out by this timing device for the light pulse in question. As mentioned above, this signal transit time measurement was started in a correlated manner with the trigger signal emitted by the trigger generator 3, which can be fed to the time measuring device 25 via the line 27.

In the event that the output signals of the trigger generator 3 are synchronized with a time base signal generated in the time measuring device 25 are to be, a line 29 is provided through which the corresponding signals are transmitted from the timing device 25 to the trigger generator 3 can be.

The timing results obtained by the timing device 25 are transmitted via the lines 28 to a central sequence control, computing and Out-waiting unit 30 is supplied, which on the one hand determines the corrected measured distance values from these runtime measured values and displays them brings and on the other hand controls the functional processes in the entire measuring device. This sequence control, computing and evaluation unit 30 can preferably comprise a microprocessor.

The light pulses fed into the reference light path 11 by the light path switch 10 in its reference light position pass through an optionally controllable optical damper 33 and are at a branch point 35 in the guided to the receiver 23 leading part 22 of the received light path. The on this way from the transmitter 1 to the receiver 23 The current reference light pulse is subject to the same delay or signal processing times as that on the transmitter side with regard to the trigger signal and on the receiver side until the stop signal is generated for the time measuring device 25 Measuring light pulses, of which they differ essentially only in terms of the length of the light path switch between the light path switch

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and the branch point 35 differentiate the light path traversed. Since the length of this reference light path 11 and so that the time required for it to pass through is known very precisely, the above-mentioned can also be used with the aid of the signal transit time measurement over the reference light path in the case of the signal transit time measurements over the measurement path, effective delay and signal processing times through a The formation of the difference between the respective measured values can be eliminated.

A signal exchange between the optical switching and damping unit 8 and the sequence control, computing and Evaluation unit 30 takes place via line 39, which can be multi-core or bidirectional, so that, for example, via line 40, the current position of the Information relating to the optical path switch 10 is transmitted to the sequence control, arithmetic and evaluation circuit 30, and command signals adapted to the respective operating state are transmitted via the lines 41 and 42 from the sequence control, Computing and evaluation unit 30 can be delivered to the optical attenuator 20 and 33, respectively.

According to the invention, the light path switch 10 can now either. can be used directly to determine the intensity of the vom To change the light pulses generated by the transmitter 1 and emerging from the transmitter light path 7, before they are transmitted to the transmitter optics 16 reach or be fed into the Referenζlichtweg 11, or it can be in an extremely advantageous manner with the for Dynamic control serving optical damper 20 to achieve a particularly simple, optimally operable and dynamics control arrangement can be combined very quickly to give extremely precise measurement results.

The direct intensity control with the aid of the light path switch 10 will now be explained with reference to the exemplary embodiment shown in FIG. In Fig. 2, the light path switch 10 is formed by an oscillating mirror 45, the between a measuring light position 46 and a reference light position 47 represented by a dashed line

is periodically movable back and forth, which is to be indicated by the curved arrow 48. The angular distance between the two positions mentioned is shown greatly exaggerated in FIG. 2 for the sake of clarity. In fact, the two positions can be much closer together so that the switching process can be carried out very quickly. The oscillating mirror 45 is controlled by a control unit 49, as indicated by the arrow 50. The measuring light position 46 and the reference light position 47 of the oscillating mirror 45 are characterized in that a maximum proportion of the light energy emerging from the transmitter light path 7 when a light pulse is emitted is fed into the associated transmitter measurement light path 15 or reference light path 11. In order to ensure this maximum light feed despite the permanent periodic movement of the oscillating mirror 45, the times at which the trigger generator 3 emits a trigger signal must be precisely correlated with the movement of the oscillating mirror 45 so that the transmitter 1 that responds with a delay is precisely timed Light pulses impinge on the oscillating mirror 45 at the right moment. If the points in time at which the trigger signals are generated are shifted towards these optimal points in time, the oscillating mirror 45 only ever directs part of the amount of light of a light pulse emerging from the transmitter light path 7 into the relevant light path 15 or 11 appropriate time control change the amplitude of the transmitted light pulses within wide limits. For this purpose it is advantageous if the control unit 49 supplies information relating to the current position of the oscillating mirror 45 via the line 40 and the receiver 23 supplies information relating to the current amplitude of the corresponding signals via the line 43 to the sequence control, computing and evaluation unit which can then forward control signals causing a corresponding time shift of the trigger signals to the trigger generator 3 via the line 51.

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In this case it is then possible to rely on the variability of the optical attenuator located in the reference light path 11 33 and to provide a filter with a fixed attenuation ratio, which determines the intensity of the reference light pulses reduced so far that with the oscillating mirror 4 5 only within the dynamic range that can be processed by the receiver 23 an adaptation of the reference light intensity to the measuring light intensity must be carried out.

The optical attenuator 20 can then, if not only the intensity of the reference light pulses, but also that of the measuring light pulses is controlled with the aid of the oscillating mirror 45, can be omitted. To achieve a good signal / noise ratio However, it is advantageous not to use those emitted by the measuring device for dynamics control, but rather those emitted by the Target object to attenuate reflected light impulses, since at the same time the ambient brightness and that through it is reduced due to noise. This attenuation of the reflected light pulses takes place with the help of the optical Attenuator 20 takes place, which also occurs when performing the signal run-time measurements via the reference light path 11 serves to attenuate the ambient light received by the receiving optics 18 at these times and reaching the receiver 23 to the same extent as in each case associated signal transit time measurement takes place over the measuring light path.

When using a periodically moving oscillating mirror 4 5 as a light path switch 10, for example with operates at a frequency of 5 kHz to 10 kHz, the ends of the transmission measuring light path 15 or the optical fibers forming the reference light path 11 are arranged so that the measuring light position 46 or the reference light position 47 does not coincide with the reversal points of the oscillating mirror. This allows both the measurement frequency as well as the repetition frequency of the reference light pulses

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double, because with each full oscillation of the mirror 45, both the measuring light position 46 and the reference light stel ment 47 is passed through twice.

Instead of the oscillating mirror 45 shown in FIG. 2, a mirror prism can be used according to the invention to achieve a higher light pulse repetition frequency which rotates uniformly about an axis perpendicular to the plane of the drawing. From the controller 49 of the angular velocity has made then only for an approximate consistency and produces a the position Continuity of each mirror surface by a certain angle indicative signal and passed via line 40 to the sequential control, computation and evaluation unit 30th

The light paths 7, 11, 15, 19 and 21 are shown in FIGS. 1 and 2 exclusively as optical fibers, condenser or imaging lenses to be provided in front of or behind the end faces of these optical fibers being omitted for the sake of simplicity . According to the invention, the optical fibers can also be at least partially replaced by other known optical fiber and imaging means such as mirrors, lenses, etc.

In the previous description of the mode of operation of an oscillating mirror 45 b «w. a rotating mirror prism formed Lichtwegumechalters 10 was assumed wor the that only in those cases where the maximum transmitter power must be used because of very large Ent distance and / or very low reflectivity of the target , the trigger generator 3 is timed so that through the light path switch 10, the entire amount of light contained in a light pulse is directed into the entrance opening of the respective further light paths . In all other cases, however, the trigger generator 3 is time- controlled for the required optical signal attenuation

that the light pulses generated by the transmitter 1 impinge on the light path switch 10 at a time in which this occupies such a position that only a desired part of the amount of light contained in the light pulse in the further light path arrives, while the rest of the light path is deflected past the entrance window of the light path and somewhere in the Meter is absorbed.

This form of optical signal attenuation, which is based on a momentary partial overlap of the light paths, can be used only use a distance measuring device that measures the transit time of a light pulse in a meaningful way, if it is ensured that the light pulse is emitted by a quasi point light source, or that In the case of a flat light source, different surface areas do not light up one after the other and their light with them feed different angles into a subsequent optical fiber, for example. Isn't that condition fulfilled, optical attenuation through partial overlap can lead to the temporal focus of the transmitted light pulse depending on the selected Attenuation, i.e. depending on the extent of the respective partial overlap, experiences a time shift that for measuring light pulse and reference light pulse can be different and thus does not stand out in the subtraction of the signal transit times, resulting in considerable measurement errors can arise.

If the above condition cannot be met, according to the invention, when using an oscillating mirror or a rotating prism as a light path switch for the measuring or reference light pulses to be damped, several Functionally parallel * light paths are provided, each of which has a different, unchangeable attenuation value delivers and depending on the requirements of the trigger generator depending on the movement or momentary

Position of the light path switch 10 timed so that the oscillating mirror 45 or the rotating mirror prism feeds the incident light pulse completely into the correct light path, where the light pulse is then subjected to the desired attenuation without a temporal shift in the center of gravity occurring. With such an arrangement, in contrast to partial overlap , it is not possible to change the damping value continuously, but rather only in stages. But since the sensitivity of the avalanche photodiode of the receiver 23 can be influenced by changing the supply voltage (D attenuation value for example 1: 5.5) and the amplifier contained in the receiver 23, the avalanche photodiode downstream, for example, a dynamic range of 1: 6.6 can have a dynamic range of approx. 1: 3 (>) for the channel, so that the individual attenuation levels in the parallel light paths can differ from one another by a factor of between 1:30 and 1:35 for example with six parallel light paths and dynamics

he makes rich 10: the amplifier an overall dynamic range of more than the first

In the event that the output power of the transmitter even in a ratio of 1: 5 is changed, the channel dynamics increased to 1: 180. This results in a corresponding Ver enlargement factor between the individual attenuator stages In Figures 3 and 4 is another. Embodiment of an optical switching and damping unit 8 according to the invention is shown, in which a rotating disk 55 is used , which is arranged in a particularly advantageous manner both the light path switch 10 located behind the transmitter light path 7 and between the received measuring light path 19 and the received light path 21 , changeable optical attenuator 20 combined in a single component .

How to FIG. 3 extracts in which the rotating disc is displayed in a line III-III in Fig. 4 following section 55, the disk 55 is driven via a shaft 56 by a motor 57 so as to be resistant in Rich direction of the arrow R rotates.

The / $ or? S £ ^r num CTER angular velocity of this rotation can be either through a circuit located at the engine 57 known rule or monitored by the central and sequential control, computing and evaluation unit 30 ensures that then the motor 57 line 58 exchanges corresponding information and command signals.

The rotating disk 55 is arranged so that it engages with its outermost circumferential area in the beam path of the light that emerges from the transmitter light path 7 shown here as an optical fiber and from a lens 59 indicated only symbolically in FIG. 3 by its central axis with reduced Divergence is passed on.

In this outermost region, the disk 55 has alternating groups of openings 60 to 65 and mirrors 70 to 75. The two first openings 60 and 61 of each group are designed as holes elongated in the circumferential direction of the disk 55. If the trigger generator 3 is controlled so that , taking into account the corresponding delays, it causes the Sen of the 1 to emit a light pulse when one of these openings 60, 61 is in the beam path behind the transmitter light path 7, this light pulse arrives completely undamped via the transmitting light path 15, shown as a free beam path, to the transmitting optics 16 and from there on to the target object. The remaining openings 62 to 65 each contain an attenuation filter which provides a comparatively low attenuation factor of, for example, 1:10 and intersects the optical axis of the beam path 15 at an angle other than 90 °.

These attenuation filters have the following purpose: In those cases in which the distance measuring device is to be used to measure a target object which is located at a comparatively short distance and which carries a retroreflector, it can contribute

unfavorable position of the retroreflector happens that that part of a light pulse that at the receiving optics 18 and in particular at the end face of the optical fiber 21, which here forms the part of the receiving light path leading to the branch point 35, is reflected back via the retroreflector to the transmitting optics 16 and from there on the end of the optical fiber that forms the transmitter light path 7 is focused. Without the in the openings 62 there 65 provided attenuation filter, the part of the light pulse that is reflected again at this end face would have a sufficient large amplitude over the entire measuring light path to the receiver 23 to be there as a delayed interference light pulse to disturb the signal processing process triggered by the actual measuring light pulse in such a way that incorrect measurements result comes or a perfect time interval measurement is made completely impossible. This is due to the in the openings 62 to 65 attached, inclined damping filter prevents. These openings are used to send out Measurement shots are always used when no very large distances are to be measured, i.e. when there is a risk that the interference pulse just described will be sufficient to disrupt the measurement without further measures Has amplitude. In those cases in which the light emitted by the transmitter 1 must be attenuated anyway, it is There is no problem in attenuating the transmitter light by the factor 1:10 caused by the attenuation filter in question before it emerges from the measuring device. If the light component reflected by the optical receiving devices then comes back to the transmitting optics 16, so When it is projected onto the end face of the optical fiber 7, it passes through the attenuation filter located in its light path for the first time, with it as well as during the reflection at the front end of the optical fiber 7 and when it passes through the damping filter again in relation to each other 1: 10 is weakened, so that there is an overall attenuation of a factor of 10 - the weakened in this way

StorIichtimpuls is no longer able to cause a disturbance of the signal processing of the previous measuring light impulse at the receiver 2 3. Through the Inclination of the attenuation filters in the openings 62 to 65 prevents light components reflected on the surface of the filter from reaching the transmission optics 16 and thus can themselves become interfering signals.

The two holes 60 and 61, which are each used to send out measuring shots for distant target objects, do not have such a damping filter, since the above-described formation of interfering reflections does not play a role here because of the great distance. The läny.liehe formation of these two openings 60 and 61 also enables the measuring shots for these large distances to be generated so early that, despite the large distance, the light pulses reflected on the target object on the part of the rotating disk 55 forming the optical damper 20 and in particular on the receiver 23 arrive at the right time, as will be explained in more detail below.

Each group of holes 60 to 65 is followed by a group of the same size in the outer region of the rotating disk 55 of mirrors 70 to 75, which, as can be seen in particular from FIG. 3, are attached to the disk 55 in such a way that their reflective surface when passing through the beam path 15 at an angle of 45 ° to the optical axis this beam path is. If the trigger generator 3 is controlled so that it causes the transmitter 1 to in a time to emit a light pulse in which one of the mirrors 70 to 75 is in the just described and 3 is the position shown for the mirror 7 1, this light pulse is deflected by 90 ° on the mirror and focused by a lens 77 on the front end of an optical fiber 32 which forms the front section of the reference light path 11 in FIG. 3.

The reference light pulse generated in this way emerges at the other end of the optical fiber 32, is converted by a lens 78 into a parallel light beam and passes through a controllable optical DMmofex 31 ,. the hXer is formed by a gray wedge disk 80, which can be adjusted in both directions with the aid of a stepping motor 81 around its axis 82, as indicated by the double arrow S, in order to achieve a desired damping value. Behind the variable optical attenuator 33, the reference light pulse passes through an attenuation filter 83, which has a fixed, predetermined attenuation ratio, and then at the branch point 35 with the help of a partially transparent mirror via an interference filter or an interference filter 87 tunable in the center frequency into the part leading to the receiver 23 22 of the receiving light path to be coupled. For this purpose, the parallel light bundle is focused with the aid of a lens 86 onto the end of the optical fiber forming this part of the receiving light path.

The optical attenuator 33 can also be formed by a PLZT or a PLMNZT disk.

In a region lying further radially inward, the rotating disk 55 has successive groups of openings 90 to 95, each of these groups comprising six openings, i.e. as many openings as the above opening or mirror groups described have openings or mirrors in the outer edge region of the pane 55.

The openings 90 to 95 located further inside are arranged so that when the disk 55 is rotated they pass through the receiving / measuring light path 19 leading from the receiving optics 18 to part 21 of the receiving light path at a point where the cross section of the beam path is certain smaller than the diameter of the openings up to 95. A lens 96 is arranged behind the rotating disk 55 in the direction in which the pulse is running. The measuring light emerging at the other end of this optical fiber 21

is converted into a parallel light beam by a further lens 97 in the same way as above for the reference light and lens 78 has been described.

The measuring light then passes through the inclined, partially transparent mirror 85 in a straight line, i.e. with a very

Slight attenuation via the interference filter 87 and arrives at / to the lens 86, from which it is focused on the end face of the optical fiber which forms the part 22 of the receiving light path leading to the receiver 23.

Each of the openings 90 allows an undamped passage of the received light, while in the openings 91 to 95 filters with different attenuation ratios are attached. It is essential that from group to Group of all holes 91, all holes 92, all holes 93, all holes 94 and all holes 95 each have a filter with the same attenuation value.

When using this rotating disk, the measuring light, which is attenuated for dynamic control on the receiver side, only passes through a single light path that is transmitted by the Transmit measuring light path 15 via the transmitting optics 16, the target object, the receiving optics 18, the receiving measuring light path 19 and the front part 21 of the receiving light path 21, 22 to the branch point 35 and from there on to the receiver 23 leads. Nevertheless, attenuation is not achieved here with a partial overlap of light paths at the moment of passage of the respective light pulse worked.

Instead, the trigger generator 3 is timed so that it sends the transmitter 1 to emit measuring light pulses caused precisely at such a point in time at which not only one of the openings 60 up to 65 fully covering in the beam path of the transmission / measuring light path 15 but also one of the openings 90 to 95 fully covering

is in the beam path of the receiving measuring light path 19. In the case of short and medium distances, this full coverage is given practically at the same time, since the disk 55 practically does not move further at a preferred speed of approx. 130 rev / s in the time that the measuring light pulse needs to pass through these short and medium distances. Only at long and very long distances (up to 10 km) does the rotary movement of the disk 55 play a role with regard to the transit time of the measuring light pulses. This is also one of the reasons why the openings 60 and 61 of each group used for emitting the measuring light pulses for large and very large distances are so elongated in the circumferential direction of the disk 55 that one with a lead of approx ° emitted light pulse can pass through these openings unimpeded. This makes it possible to emit the measuring light pulse so early that it hits the corresponding opening 90 or 91 in its fully covering position when it returns from the target object.

The different attenuations required for dynamic control are generated in this embodiment by the fact that the rotational movement of the disk 55 forming the light path switch 10 is permanently in and out the same light path filters with different attenuation factors are brought and that the trigger generator is timed as a function of the movement of the disk 55 so that it triggers the transmitter at times which ensure that the subsequently emitted measuring light pulse does just that when it returns from the target object finds the currently desired attenuation factor supplying filter in one of the holes 90 to 95. So that the measuring light pulse also passes through the rotating disk 55 on the transmitter side at the respective point in time can, a number of openings 60 to 65 is provided there, which corresponds to the number of the various attenuations

32 13452

delivering openings 90 to 95 per group on the receiving end .

In an arrangement in which, as shown in Fig. 3, transmission-measuring light path 15 and receiving-measuring light path 19 are exactly diametrically opposed with respect to the center of rotation of the disc 55, are because of the above- mentioned "simultaneity" with each one of the transmission light openings 60 to 65 and the associated receiving light openings 90 to 95 achieve full coverage with the associated beam paths, in each case the center of a transmitting light opening 60, 61, 62, 63, 64, 65 and the center of the associated receiving light opening 90, 91, 92, 93, 94, arranged on a common disk diameter, as is indicated in FIG. 4 for one of the openings 62 and the associated opening 92 by a dot-dash line 101 . The received light opening 92 located radially directly inside the transmitted light opening 62 is not assigned to this transmitted light opening but to the diametrically opposite mirror 72.

The other mirrors 70, 71 and 73 to 75 of each group are each assigned a diametrically opposed receiving light opening 90, 91 and 93 to 95, each of these receiving light openings containing a filter with the same attenuation factor as the correspondingly numbered receiving light opening that of an opposite one Sending light opening is assigned.

The purpose of this arrangement is to also trigger the reference light pulses at very specific points in time, which again depend on the movement or the current position of the rotating disk 55. A basic principle of the device according to the invention is for measuring light pulses and reference light pulses, their transit times for obtaining the sought distance values from one another

should be deducted, the running time measurements should be carried out under conditions that are as identical as possible. This includes not only a very extensive adjustment of the light intensity of the reference light pulses to that of the associated measuring light pulses, which is done with the help of the controllable optical damper 33's, but also an adaptation of the respective background brightness. For this purpose , the reference light pulses are not triggered when any of the mirrors 70 to 75 is in the exit beam path of the transmitter light path 7; rather, that one of the mirrors 70 to 75 is always used, to which a received light opening is assigned on the opposite side of the disk 55 , which contains the same filter as the one received light opening through which the associated measuring light pulse passes. This ensures that the receiver 23 "sees" the same environmental brightness when receiving the reference light pulse and thus has the same response behavior over time as when receiving the associated measuring light pulse.

Similarly as described in the above also non-operating with partial overlaps dynamics control in which the light pulses but are directed into different functional parallel with different attenuation filters equipped light paths of the disk is also 55 possible to only a gradual change of the damping means, but , as already explained above, does not present any particular difficulties because of the dynamics of the receiver 23 which are available in any case.

In order to determine the instantaneous position of the disk 55 and thus also the driving timing for the trigger generator 3 to be able to choose the right, 55, the disk radially further inwardly a plurality of holes 98, one of which is associated with a respective one of the radial beam, on the the center of one of the openings 90 to 95 and the openings

60 to 65 or the mirror 70 to 75 is. These holes 98 are used with the help of the shown in Fig. 3, formed by a light source 99 and a differential photodiode 100 light barrier via the line 40 the respective Position of the rotating disk 55 characterizing signals to the central sequence control, computing and To output evaluation unit 30, which in turn sends trigger generator 3 via line 51 shown in FIG. 1 timed correctly.

One of the holes 98 can, as shown in FIG. 4 , have a different distance from the axis of rotation 56 than the other holes 98 and can be scanned by a separate, not shown light barrier through which a clear position signal for the Sequence control, computing and evaluation unit 30 is generated. If the initially completely unknown distance of a target object with unknown reflectivity is to be determined with a distance measuring device constructed according to the invention, the correct attenuation must first be found by the measuring device itself so that exact measurement results (accuracy + 1 mm for distances up to 10 km) can be obtained can.

If one assumes that the amplifier connected downstream of the receiving photodiode in the receiver 23 can amplify signals between 175 mV and 1150 mV with sufficient linearity and feed them to further processing, which corresponds to a dynamic range of approx. 1: 6.6, and that the sensitivity of the receiving photodiode by varying the supply voltage by a factor of 1: 5,5 is variable, then a processable by the receiver 23 results in dynamic range of about 1: 36.3, and it must pass through a corresponding attenuation of the light as possible selected for achieving a wide range Meßlichtimpulse it must be ensured that the signals arriving at the receiver 23 are in this processable brightness range. This attenuation takes place on the one hand through the measuring section and the reflectivity of the target object (external attenuation) and on the other hand to compensate for the possible differences, which can be in the order of magnitude of 1: 10 ⁹ to 1: 10 ¹⁰ , through the time control according to the invention -

tion of the trigger generator 3 as a function of the movement of the disc 55 (internal damping), and possibly with With the help of a change in the power output by transmitter 1 (additional channel attenuation).

If the transmitter power cannot be changed, the measuring device first goes to find out the correct internal attenuation

from a very large distance of the target object and a high external attenuation and sends a test light pulse through one of the openings 60 with a lead corresponding to a large distance, so that the reflected light pulse comes back through the associated opening 90, which does not cause any attenuation. The receiving photodiode is switched to maximum sensitivity.

The receiver 23 comprises, in a manner known per se, a comparator which monitors whether the output signal to be amplified from the receiving photodiode or from an oscillating circuit connected downstream thereof exceeds the upper limit of 1150 mV. If this is not the case, this means that a very distant and / or poorly reflecting target object has actually been appropriate and that the correct internal attenuation value, namely 1: 1, has already been found.

The time measurement value obtained in this manner, however, the comparator an override signal from because the 1150 mV were exceeded, on the one hand rejected by the central sequential control, accountability and evaluation because it is fraught _v fault certainly with too large a measurement , and on the other hand, the sensitivity of the receiving photodiode is reduced in the ratio 1: 5.5. This takes place so quickly that a second measuring light pulse can be emitted through the next opening running through the transmitting light path 15, which then again reaches the receiver 23 through the associated opening 90 which does not cause any attenuation.

If the overdrive comparator responds again, this measured value is also discarded, the sensitivity of the Receiving photodiode is switched back to the high value and the next measuring light pulse is sent out so that it that the measuring device leaves through one of the openings 61 and returns through the associated opening 91, in which a Filter with a damping factor of 1:30. In the event that the threshold value of 1150 mV was only slightly exceeded in the preceding measuring light pulse, it is ensured that the 2 3 The amplifier contained is now not too small, i.e. falling below the lower limit of 175 mV, but receives a signal lying within the desired work area.

If the overload comparator responds in this third attempt as well, the next measuring light pulse is triggered emitted again through one of the openings 61 and received the associated opening 91, although the The sensitivity of the receiving photodiode is reduced again in a ratio of 1: 5.5.

If this also leads to an overload of the receiver amplifier, the sensitivity of the receiving photodiode is increased again and the next measuring light pulse discharged through one of the opening 62, which, as described in detail above, for the suppression of disruptive Light reflections contains an inclined filter with an attenuation factor of 1:10. This attenuation of the emitted measuring light is therefore easily justifiable, because the previous measurement tests have shown that a damping of 1:30 is not sufficient to achieve a Avoid overloading the receiver amplifier. The reflected light pulse then passes through the opening 92 belonging to the receiver 23, in which a filter with a damping factor of 1: 100 is arranged.

net , so that this light pulse has experienced a total internal attenuation of 1: 1000. This attenuation value is currently selected such that it is slightly smaller than the product of the attenuation value of the preceding reception light opening, in this case, the light receiving opening 91 and out of the dynamic range of the receiver 23rd The same also applies to the attenuation values in the following receiving light openings 93 to 95, which each contain a filter with an attenuation factor of 1: 3 * 10 ³ , 1: 10 ⁵ or 1: 3 - 10 ⁶ , which in connection with the in the associated transmission light openings 63, 64 and 65 contained attenuation

filter total internal attenuation factors of 1 : 3 · 10,

6 7
1:10 or 1 : 3 · 10 results, so that taking into account the dynamic range of the receiver 23 is a

Overall dynamics of more than 1:10 can be achieved.

If the override comparator also responds to the measuring light pulse emitted through the transmitting light opening 62 and received by the associated receiving light opening 92, the sensitivity of the receiving photodiode can initially be reduced again and the above- described method can be continued in the subsequent openings 93 to 95 using ever higher attenuation levels , until finally the override comparator no longer responds and the correct damping value has been found.

If the transmitter power can also be changed, for example in the ratio 1: S _t , every time the overdrive comparator responds to a damping given by one of the openings 90 to 95 and the receiving diode is switched to minimum sensitivity, the sensitivity and the use of the next stronger attenuation filter in one of the openings 91 until a further measurement attempt with reduced transmitter power is undertaken. Since by switching the receiver

;: 21 j452

gers and the transmitter can achieve a dynamic range of 1: 180 overall, the attenuation values in the window 55 in the openings 91 to 95 can vary accordingly filters that differ more from one another are provided and thus an even larger overall dynamic range can be covered. If the overall dynamic range remains the same, the Number of openings with different damping filters, i.e. the number of openings per group is reduced and a correspondingly higher number of measuring and reference light pulses per revolution of the disk 55 are emitted.

In addition to the circuits already mentioned, the receiver 23 also has an amplitude amplification and rectification circuit provided, to which the amplified output signal of the resonant circuit connected downstream of the receiving photodiode is fed. Is the right one for the measuring light pulse Attenuation is found, the DC voltage signal emitted by this rectifier is held in a sample-and-hoid circuit until it is through a Analog / digital converter has been converted into a digital numerical value, which is then fed back to the central sequence control, computing and evaluation unit 30 and is saved there.

According to a particularly preferred method, a particularly exact distance measurement value is now determined with the attenuation found, a measuring light pulse and a reference light pulse are always alternatively generated, and moreover A calibration measurement is carried out in the time measuring device 25 between each two successive light pulse running time measurements.

As already mentioned above, the reference light pulses are deflected via that of the mirrors 70 to 75, to which that one of the openings 90 to 95 is assigned that has a damping filter with the same damping factor, which is also used in the Meeiicht transit time measurement, so that the environmental brightness in the measuring light pulses and is attenuated in the same way for the reference light pulses.

To adapt the amplitude of the reference light pulses to the amplitude of the measuring light pulses, as already mentioned, In the reference light path 11 a fixed attenuation filter 83 with an unchangeable attenuation factor and an optical one Damper 33 arranged with a variable damping factor.

For the measuring light pulses / as already mentioned, the internal attenuation must be changed within a very large range, since the external attenuation can change in a correspondingly large range. The desired objective is always _7, the ratio of the smallest to the maximum incident on the receiver In the photodiode light intensity in the processable by the receiver 23 dynamic range of 1: hold 36, which, if appropriate, with the ratio (1: 5) is to be multiplied by said Switching of the transmitter line can be achieved; this is achieved in that with high external attenuation a correspondingly small internal attenuation and possibly a high transmitter power and vice versa with small external attenuation a correspondingly large internal attenuation and possibly a small transmitter line is selected.

n / A-

For this reason , the change in the amplitude of the measuring light pulses arriving at the receiving photodiode can at most

or 1: 180

in a range of 1: 36 / and the controllable optical attenuator 33 built into the reference light path only needs to be able to attenuate the reference light pulses in this ratio, while the remaining load

range of 1: 3 · 10 can be done by the fixed damping filter 83 and the inclined, partially transparent mirror 85. If one assumes, for example , that the inclined mirror, which is necessary for the lowest possible attenuation of the measuring light, accounts for 99% of the

The incident light is straight, transmits and only 1% for the reference light

articulated, i .e. thus / supplies a damping factor of 1: 100, the damping filter 83 must have a damping factor of about 3 · 10 "*.

or 1: 180

In the remaining range of 1: 36 / the amplification of the reference light pulses is matched to that of the measuring light pulses by also storing and digitizing the DC voltage signal emitted by the above-mentioned rectifier when a reference light pulse is received in the sample-and-hold circuit the digital value thus obtained is compared with the previously obtained digital value of the associated measuring light pulse. If the deviation is greater than a predetermined tolerance range, the stepping motor 81 is adjusted with the corresponding command signals supplied via the line 41 so that the gray wedge disk 80 attenuates the next reference light pulse in the correct manner.

If the correct attenuation values have been found for both the measuring light pulses and the reference light pulses, the above-mentioned series of measuring

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light and reference light transit time measurements and calibration

it can

and / from the individual measured values obtained in the process, mean values are formed, from which the sought-after distance value can then be calculated.

It is of particular importance that the entire receiving channel and in particular also the time measuring circuit 25 are operated strictly periodically so that the measuring accuracy can be brought to the values given above. A particular advantage of the above-described embodiment of the light path switch 10 is that the rotating disk 55 actually enables such a strictly periodic operation of the receiving channel and the downstream time measuring device once the correct attenuation has been found. The disk 55 has , as can be seen in particular from FIG. 4, three groups of transmitting light openings 60 to 65 and mirrors up to 75 and the associated receiving light openings 90 to 95. This means that with each rotation of the disk, three measuring light pulses at exactly the same intervals and in between, three nested reference light pulses can be emitted and the associated signal propagation times can be measured. Although the time interval between the time of transmission and the time of reception of a measuring light pulse is dependent on the distance of the target object , this can be easily compensated for by a corresponding time reserve for the control of the irigger generator 3. For this purpose, the centra le sequential control, Kechen- and evaluation unit 30 with a no strict periodicity of the further test routines having first MeBversuch determined the approximate distance of the target object, which because of the aperiodicity of measurement sequences even with a target in comparison to the attached accuracy of ^ 1 mn can be liable to considerable errors. Nevertheless, this distance determination is

sufficiently accurate to then be able to calculate the time allowance required for a strict periodicity of the further measuring and reference shots. Since, as already mentioned, for short and medium distances the transit time of the measuring light pulse does not play a role in comparison to the rotational speed of the disk 55 , the condition of full coverage of the transmitting and receiving light openings with the transmitting measuring light path is established by the time allowance just mentioned or the received measuring light path is not disturbed. For large and very large distances, because of the elongated design of the transmitting light openings 60 and 61, the necessary time reserve can also be carried out while observing the above condition.

Regarding the gray wedge disk 80 or a corresponding PLZT or PLMNZT disk forming the controllable optical damper 3 3 , it should be noted that it is advantageous to have its attenuation range, for example 1: 72 or 1: 360, twice as large as that provided by the Receiver 2 3 ge possibly together with the transmitter 1 predefined dynamics

select a range of 1: 36 or 1: 180. This makes it possible to take into account the fact that the power of the transmitting diode generally decreases by half over the course of time. Apart from a corresponding shortening of the maximum measurable distance, this further has no disadvantageous consequences if the above measure in the reference light path 11 ensures a corresponding compensation.

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Claims (1)

V : ···· = | ^: · * _: .; ··; * .- ^: 3219452 URI & STRASSER patent attorneys M 72 - S / Sv Munich, the £ 4 _{Mfi |} ^ Dr. Ludwig Bölkow OberfeldalIee 9 8022 Grünwald Dynamic control arrangement for a distance measuring device Claims 1. Dynamics control arrangement for a distance measuring device according to the principle of time-of-flight measurement of a measuring light pulse generated by a transmitter controlled by a trigger generator, via transmission optics to the Target object sent, reflected by this and received by the measuring device by means of receiving optics and is directed to an electro-optical receiver, which in response to this generates an electrical signal to terminate the transit time measurement / with the from the transmitter to the transmission optics leading light path has a branch point at which light coming from the transmitter into a can be fed in device-internal reference light path leading directly to the receiver, characterized in that a Lichtwegunechalter (10) is arranged through which a light pulse generated by the transmitter (1) with each measurement shot the transmission measurement light path (15) leading to the transmission optics (16) and with each reference light path (11) can be fed and that the trigger generator (3) the measuring shots and / or the reference shots can be time-controlled in such a way that in each case a predeterminable part of the The amount of light emitted by the transmitter (1) in a light pulse reaches the receiver (23). Arrangement according to Claim 1, characterized in that the light path switch (10) is movable. Arrangement according to Claim 2, characterized / that the light path switch (10) is periodic Movement. Arrangement according to Claim 2 or 3, characterized in that the trigger generator (3) is temporal can be controlled in such a way that, through the corresponding effective position of the light path switch (10), a part that can be predetermined to achieve the desired attenuation the amount of light contained in the respective light pulse into a single continuing section (15 or 32) of the measuring light path (15, 19) or the reference light path (11) can be fed. Arrangement according to Claim 2 or 3, characterized in that the trigger generator (3) is temporal can be controlled in such a way that, through the corresponding effective position of the light path switch (10) to achieve the desired attenuation, the entire amount of light contained in the respective light pulse in one selected of several functionally parallel sections of the measuring light path or the Reference light path can be fed in, each of these sections having a damping element with another Has damping factor. 6. Arrangement according to claim 2 or 3, characterized in that the trigger generator (3) in time Is controllable in such a way that the entire Amount of light contained in the respective light pulse into a single continuing section (15 or 32) of the measuring light path (15, 19) or the reference light path (11) can be fed into the measuring light path (15, 19) or the reference light path (11) depending on the current position of the light path switch (10) a different damping filter with a damping factor of the desired size can be brought in each case. 7. Arrangement according to one of claims 3 to ⁵ , characterized in that a periodically reciprocating mirror (45) is provided as the light path switch (10), the measuring light position (46) and the reference light position (47) being selected so that they do not coincide with the reversal points of the mirror (45). 8. Arrangement according to one of claims 3 to 5, characterized in that as a light path switch (10) a rotating prism with reflective side surfaces is provided, the axis of rotation of which is perpendicular to the optical axes of the light paths ending at the prism. Claims 3 to 6, 9. An arrangement according to one of the / characterized in that the light path switch (10) is a constant rotating disk (55) is provided, whose axis of rotation (56) is parallel to the optical axes of the Disc (55) ending light paths (7,15,19,21) and the light path (7) coming from the transmitter (1) area covering at least one opening (60 to 65) which allows the transmitter light to pass through in a straight line and has at least one mirror (70 to 75) which deflects the transmitter light by a predetermined angle, and that the transmission measuring light path (15) for receiving the light transmitted in a straight line through the disc (55) and the reference light path (11) are arranged for receiving the deflected light. 10. The arrangement according to claim 9, characterized in that the disc (55) has several openings (60 to 65) which pass through the transmitter light and several mirrors (70 to 75) which deflect the transmitter light, that all openings (60 to 65) and mirrors (70 to 75) have the same distance from the axis of rotation (56) of the disk (55) and that a filter which attenuates the transmitter light is arranged in at least one (62 to 65) of the openings (60 to 65). 11 . Arrangement according to claim 9 or 10, characterized in that the disc (55) has an area which covers the receiving measuring light path (19) leading from the receiving optics (18) to the photoelectric receiver (23) and that in this area a multiplicity of the receiving light-transmitting openings (90 to 95) are provided, which all have the same distance from the axis of rotation (56) of the disc (55), and that at least in some (91 to 95) of these openings (90 to 95) in each case one of the receiving light damping filter is arranged, the damping factors of the various filters partially differ from each other. 2. Arrangement according to claim 11, characterized in that in each case η of the openings (90 to 95) of the disc (55) which allow the received light to pass through are combined to form a group which includes the Received light has undamped permeable opening (90) and n-openings (91 to 95) in which in each case a filter with a different damping factor is arranged, and that in each group the attenuation-free opening (90) and the openings (91 to 95) with the filters with different Attenuation factors are arranged in the same order. 13. The arrangement according to claim 12, characterized in that the damping factors of the in Corresponding openings (90 to 95) of different groups arranged filters one another are equal and that the attenuation factors of the filters belonging to a group differ from one another by a factor that is smaller as the ratio of the largest to the smallest signal amplitude that can be processed by the photoelectric receiver (23) and the downstream channel is. 14. The arrangement according to claim 12, characterized in that the damping factors of the in Corresponding openings (90 to 95) of different groups arranged filters are identical to one another and that the attenuation factors of the filters belonging to a group each differ from one another by a factor distinguish which is smaller than the product of the ratio of the largest to the smallest of the photoelectric receiver (23) and the channel connected downstream of it processable signal amplitude and from the ratio of the greatest to the smallest power that can be emitted by the transmitter (1). 3 213 4 15. Arrangement according to one of claims 11 to 14, characterized in that the transmitter light through openings (60 to 65) of the disk (55) are combined to form groups comprising η openings, between which η mirror (70 to 75) comprehensive groups of the transmitter light deflecting mirrors are, that each of the groups of openings (60 to 65) comprises at least one opening (60, 61) which is elongated in the circumferential direction and in which no filter is arranged, and that in the other openings (62 to 65) below an angle different from 90 ° obliquely to the optical axis (15a) standing attenuation filters are arranged, all of which have the same damping factor. 1 6 . Arrangement according to one of Claims 10 to 1 5, characterized in that there is always an opening (60 to 65) which allows the transmitter light to pass through or a mirror (70 to 75) which deflects the transmitter light and an opening (90 to 95) which allows the received light to pass through Centers are arranged on a common radial ray emanating from the axis of rotation (56) of the disk (55), and that the disk (55) has at least one hole (98) which is at a different distance from the axis of rotation (56) than the openings (60 to 65 and 90 to 95) and the mirrors (70 to 75) and through which a light barrier (99, 100) can be released once with each revolution of the disk (55), the signal of which is used to determine the current position of the disk (55 ) and is used to monitor their speed of rotation. ■ '- D I 17. The arrangement according to claim 16, characterized in that at a predetermined angular distance in front of each of the center of two openings or an opening and a mirror interconnecting radial rays a light barrier exposing hole (98) is provided and that the at Passing these holes (98) through the light barrier (99,100) emitted signals to prepare the Triggering a light pulse are used. 18. Arrangement according to one of claims 9 to 17, characterized in that in the receiving light path (19, 21) between the rotating disc (55) and the photoelectric receiver (23) a partially transparent mirror (85) at an angle to the optical axis of the received light path is arranged through which the received light passes in a straight line and through the the light coming from the reference light path (11) can be deflected and into the part (21) leading to the receiver (23) of the receiving light path (19,21) can be coupled. 19. Arrangement according to one of the preceding claims, characterized in that in the reference light path (11) serially one behind the other an attenuator (83) with a fixed attenuation factor and a controllable attenuator (33) are arranged with a variable damping factor. 20. The arrangement according to claim 19, characterized in that the ratio of the maximum to the minimum damping factor of the controllable attenuator (33) is at least equal to the product of a numerical value that takes into account the aging-related decrease in the transmitter power and the ratio of the maximum to the minimum signal amplitude that is derived from the photoelectric Receiver (23) and its downstream channel can still be processed. 21. Arrangement according to claim 19 , characterized in that the ratio of the maximum to the minimum damping factor of the controllable attenuator (33) is at least equal to the product of a numerical value that takes into account the aging-related decrease in the transmitter power, the ratio of the maximum to the minimum signal amplitude generated by the photoelectric receiver (23) and its downstream channel can still be processed, and the ratio of the maximum to the minimum power that can be emitted by the transmitter (1). up to 21, 22. Arrangement according to one of claims 19 / characterized in that the controllable damping element (33) is a gray wedge disk (80) which can be rotated by a stepping motor (81). 23. Arrangement according to one of claims 19 to 21, characterized in that the controllable attenuator (33) is a PLZT or PLMNZT disk. Arrangement according to one of Claims 19 to 23, characterized in that the control signal for the controllable attenuator (33) can be obtained by comparing the amplified and rectified signal amplitudes that the photoreceiver (23) receives when receiving a measuring light pulse on the one hand and when receiving a reference light pulse on the other hand gives away. 25. Arrangement according to one of the preceding claims with a chopper serving to generate the various required voltages, characterized in that the trigger generator (3) in : 21: -52 Depending on the chopper vibrations, it can be controlled so that the beginning and end of the signal-run Zeitmes solutions fall in periods in which no disturbances caused by the chopper flanks occur. 26. Arrangement according to one of claims 1 to 25 with a chopper serving to generate the various required voltages, characterized in that a circuit arrangement for suppressing the vibrations of the chopper in the periods in which the beginning and end of a signal transit time measurement can fall , and a buffer capacitor that takes over the power supply of the device during these periods is provided. 27. Arrangement according to one of the preceding claims, characterized in that an interference filter (87) which can be tuned in the center frequency is arranged in a parallel light path in front of the receiver (23) to optimize the signal / noise ratio.