DE9321459U1 - Laser distance determination device - Google Patents

Description

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Description·

The invention relates to a laser distance determination device according to the preamble of claim 1.

Such a laser distance determination device is known from the German patent application DE 38 08 972 A1. This patent application relates to a device for the continuous tracking and position measurement of an object in a three-dimensional space. For this purpose, two light transmitters are provided, each of which emits light lines that are drawn out in one direction and narrow in a direction perpendicular to this. The two light lines emitted by the light transmitters run vertically to each other. Both light lines are periodically deflected by a deflection device in a direction vertical to their longitudinal extension, so that both light lines sweep over a common search field. The deflection devices each comprise a rotating, transparent plane plate which, according to the generally known optical laws, causes a different parallel offset between the incoming and outgoing light depending on its angular position. If an object is in the search field, it reflects the emitted light back to the measuring device, where it is fed to a receiver via a lens. The distance between the measuring device and the object is calculated from the light travel time between the measuring device and the reflecting object. The angular position of the object is determined from the current angular position of the two rotating plane plates. As soon as an object is detected and its position is determined, a tracking device is activated.

1 a

which aligns the measuring device to the detected object.

US Patent 4,475,035 discloses a device by means of which the surface of an object can be scanned, whereby the object is transported on a conveyor belt at a constant distance from the device along a predetermined path. The intensity of the light reflected from the surface to be scanned can be evaluated or the distance of the surface to be scanned from the device can be determined using a laser distance determination system.

From the German patent application DE 3 9 23 281 A1, a dirt sensor for motor vehicle windows, in particular for motor vehicle headlights, is known, which works with a reflection light barrier arranged in a specific area of the respective window. The reflection light barrier suitable for measuring dirt covers a specific area of the respective window, which is disadvantageous, so that this area cannot be used, for example, to emit headlight light.

In the method for measuring contamination, which is known at least according to the applicant's internal state of the art and is based on the principle of useful light backscattering, useful light is emitted through a pane and the proportion of the useful light that is backscattered due to contamination of the pane is quantitatively recorded. This method has the disadvantage that dirt particles on the pane can have different reflectivities, so that, for example, a small amount of white dust can lead to the same result as a large amount of black dust. By determining the useful light backscattering, it is therefore not possible to determine in which

1 b

the manner in which the existing contamination actually hinders the emission of useful light through the pane to be monitored.

The object of the present invention is to further develop a device of the type mentioned at the outset in such a way that negative effects of soiling of the windscreen can be avoided, whereby in particular soiling should be reliably detected and the windscreen should not be partially covered by devices for measuring soiling.

To solve this problem, the features of the characterising part of claim 1 are provided.

The invention thus creates a laser radar by means of which not only the distance of objects hit by the pulsed light can be determined from the device, but also the angle at which the object is arranged relative to any basic direction in space, whereby contamination of the windscreen can be monitored and detected by means of a plurality of light barrier beams.

For automatic detection of dangerous contamination of the windscreen and for issuing a contamination or error signal in the event of excessive contamination, the device can be expediently designed according to claims 2 or 3. The inclination of the main part of the windscreen simultaneously serves to reflect away the reflection from the surface of the windscreen.

Due to the design according to claims 4 or 5, contamination in the form of a liquid film, in particular oil film, on the windscreen, which in itself does not or only insignificantly affect the passage of light, can trigger a contamination signal by exploiting the property of such films that they form a smooth surface even when they are applied to a rough surface. Due to safety requirements, at least two oil measuring channels should be provided in order to be able to detect in the evaluation electronics even the case that one of the light transmitters or light receivers fails.

Preferably, the front screen is curved according to the scanning.

Preferred dimensions of the laser radar are defined by patent claims 8 to 11.

The embodiment according to claim 10 ensures that an angular range of approximately 1° is covered by the light deflection device in 50 to 150 and in particular 100 ßs .

On the other hand, if according to claim 11 a light pulse of short duration is emitted approximately every 50 με , this means that a light pulse is emitted approximately every 1/2° or, with a total scanning range of 180°, 360 pulses. This is completely sufficient for the angular resolution required in the safety area.

The time between two emitted light pulses of approximately 50 με is used for the tests described below.

The embodiments according to claims 12 to 28 are particularly advantageous, because they ensure scanning of a desired spatial area in a structurally compact and optically very effective manner, whereby the scanning angle can be up to 360°, but is normally only 180°.

Of particular advantage is the concentric formation of transmit and receive pulse light beams according to claims 17 and 18. This achieves in particular a clean geometric beam separation as well as sensitivity in the close range.

The rotational speeds according to claim 27 are particularly advantageous because, in conjunction with the pulse repetition frequencies used, they achieve sufficient angular and temporal resolution.

In connection with the following embodiments, the use of a computer according to claim 2 9 is of great importance. This allows in particular the various self-monitoring functions of the system to be carried out.

The further developments of the invention according to claims 30 and 31 ensure a distance resolution of the order of 5 cm/bit that is fully sufficient for the intended monitoring purposes, whereby a bit is defined by one or half a period of the clock frequency.

The resolution given by the clock frequency can be halved by the embodiment according to claims 3 2 and 3 3.

A particular advantage, however, is that the use of two individual meters connected in parallel enables error

monitoring according to claims 34 to 36 can be carried out.

A further error test, which is additionally used in particular in the embodiment according to claim 36, is defined in claim 37.

Furthermore, it is advantageous if, according to claims 38 to 41, the noise level on which the useful pulse signal is superimposed is also taken into account, since both the brightness in the monitored rooms and the degree of reflection of the monitored objects can fluctuate greatly.

A further advantageous embodiment is characterized by claim 43. In particular, this development of the invention enables a measurement accuracy of up to 5 cm/bit to be achieved.

By means of the embodiment according to claim 44, errors in the transmitting and receiving system of the device can be determined.

The further development according to claim 45 also makes it possible to check the proper functioning of the preferably used avalanche receiving diode.

All desired navigation and error signals can be converted and retrieved in a suitable manner via an interface provided according to claim 46.

Advantageous applications of the device according to the invention can be found in claim 47.

The particular advantage of the laser radar device according to the invention is that it is protected against any system error

This applies to errors in the optical area as well as in the evaluation electronics.

The invention is described below by way of example with reference to the drawing, in which:

Fig. 1 is a schematic view of a laser radar according to the invention,

.jyij Fig. 2 a schematic plan view of the rotating mirror

according to Fig. 1 and the scanning angle range,

Fig. 3 is a block diagram of the laser radar according to the invention ,

Fig. 4 shows a more detailed cross-section of the laser radar according to Fig. 1,

Fig. 5 is a block diagram of the counter preferably used according to the invention with the components connected to it,

(pf Fig. 6 a signal voltage-time diagram of different strengths

Light reception light pulses,

Fig. 7 a view similar to Fig. 1 with the rotating mirror rotated by 90° to illustrate the function of a test body introduced into the beam path,

Fig. 8 is a view similar to Fig. 7, showing a light emitting diode for testing the receiving system,

Fig. 9 shows a schematic section through the front panel of the device according to the invention and one of the

Light barrier arrangement for contamination monitoring with the corresponding block diagram and the

Fig. 10 to 14 are schematic plan views of various applications of the laser radar according to the invention.

According to Fig. 1, a motor 31 drives a horizontal rotary table 28 to a continuous rotational movement around a vertical axis 17. On the circumference of the rotary table 28 there is an angle sensor 29, which is designed as a fork light barrier and is connected via a line 32 (see also Fig. 3) to a control stage 40 within the associated evaluation circuit.

A circular cylinder body 27 is arranged on the rotary plate 28 in such a way that its upper end face, designed as a rotating mirror 16, is arranged at an angle of 45° to the axis of rotation 17. The rotating mirror 16 can also be formed on a mirror plate in a manner not shown, which is attached to the rotary plate 28 via a mirror carrier.

Above the rotating mirror 16 there is a much narrower, also flat deflecting mirror 19, whose mirror surface has an angle of 45° to the axis of rotation 17 and can also be realized as a circular cylinder body. According to Fig. 4, the deflecting mirror 19 is also designed as a flat mirror plate. A central area 24 of the deflecting mirror 19 receives light from a pulse laser 11 via a transmitting lens 33 and the deflecting mirror 19. The initially horizontal light beam is deflected downwards at the deflecting mirror 19, in order to then be deflected by the rotating mirror 16 in a horizontal direction to the front screen 41 of the device. From there the transmitted light beam 21 reaches the measuring area 13, in which, for example, a light-reflecting object 14 is assumed, from which scattered light acts as a receiving light.

light bundle 20 passes through the front panel 41 in the sense of an autocollimation beam path back to the rotating mirror 16. The received light 20 strikes a ring area 47 of the rotating mirror 16 to the side of the central area 24, onto which the transmitted light 21 and in particular the central incident light beam 18 strike, in order to be reflected past the deflection mirror 19 to an interference filter 26, behind which there is a receiver lens 25 which has areas 25', 25" of different focal lengths in order to be able to clearly recognize objects arranged very close to the device.

The receiver lens 25 concentrates the received light on a photoreceiver 23 and together with the photoreceiver 23 forms a photoreceiving arrangement 22. The rotating mirror 16, the rotating plate 28 and the motor 31 together represent a light deflection device 15 which allows the transmitted pulse light bundles 21 and received pulse light bundles 20 to rotate around the axis 17. In this way, a scanning angle range of up to 360° can be realized. According to Figs. 2 and 5, however, the front window 41 only extends over an angle of approximately 180°, which is sufficient, for example, for the complete monitoring of the area in front of a vehicle. In addition to the top view according to Fig. 1, Fig. 2 also shows two further angular positions of the rotating mirror 16 and the transmitted pulse light bundle 21. The transmitted pulse light beam 21 performing an angular scan defines a scanning plane 53. The maximum scanning angle range 54 extends over 180° according to Fig. 2.

According to Fig. 3, the control stage 40 causes the pulse laser 11 to emit light pulses with a duration of 3 to 4 nanoseconds via lines 42, 43 and the rotation of the light deflection device 15 at a speed of 1500 rpm. The control stage 40 is controlled by the angle sensor 29 via line 32 in

the angular position of the light deflection device 15 is communicated at any moment.

Light pulses 12 are sent into the measuring area 13 via the transmitting lens 33 and the mirrors 19, 16 (Fig. 1, 4). After a transit time t, they are received as reception pulses 12' (Fig. 3) by the photoreceiver arrangement 22. The photoreceiver 23, in particular an avalanche diode, forms a corresponding electrical signal from this, which is applied via a comparator 34 to a counter 30 clocked by a frequency generator 52. The output of a noise level meter 36 is fed to the reference input 35 of the comparator 34, the input of which is also connected to the output of the photoreceiver arrangement 22. The noise level meter 36 also reports the noise level present at any given time to a computer 38 via a line 44.

The output signal of the photoreceiver 23 is also fed to the input of a peak detector 37, the output of which is also applied to the computer 38.

A control line 45 leads from the pulse laser 11 to the counter fg-, 30 in order to trigger it each time a light pulse is emitted. As soon as the light pulse 12' is received by the photo-receiving arrangement 22, the counter 30 is stopped due to the connection of the photo-receiving arrangement 22 via the comparator 34. The counting result is then communicated to the computer 38 via the control line 46. The computer 38 determines the running time t from this and calculates the distance d of the object 14 according to the formula

d = c-t/2 (1)

where c is the speed of light.

Since the computer 38 knows the current angular position of the light deflection device 15 via the line 32 and the control stage 40, information about the

Polar coordinates of the object 14 are passed on to the interface 3 9 where they are available for further use, e.g. as a navigation signal or error signal.

The operation of the described device is as follows:

When the rotating mirror 16 is driven by the motor 31 to a constant rotational movement, the control stage 40 causes the pulse laser 11 to emit a light pulse 12 of 3.5 nanoseconds duration. The light pulse 12 is sent into the measuring area 13 via the light deflection device 15 and is reflected according to Fig. 1 by an object 14, which is only indicated by dashed lines in Fig. 3, so that finally a reception pulse 12' reaches the reception arrangement 22. In this way, the light reaches the photo reception arrangement 22 after a light travel time of 2.d/c (where d is the distance of the object 14 from the device and c is the speed of light).

The time t between the emission and reception of the light pulse is measured using the time interval counter 30. When the light pulse 12 is emitted, the counter is started via the control line 45 and stopped again when the light pulse 12' that has passed back and forth across the measuring range 13 is received by the photo receiver 23 via the comparator 34. With a time resolution of the counter of 330 ps, the distance measurement accuracy is 5 cm.

The task of the noise level meter 36 is to adjust the detection threshold depending on the receiver noise level. This adjustment ensures a constant false alarm rate in changing lighting situations and object reflection factors. The noise level meter

3 6 provides a trigger threshold at the reference input 35 of the comparator 34, which ensures that, for example, only those received light pulses 12' trigger a counter signal at the comparator 34 which is seven times as high as the noise level present shortly before the appearance of the light pulse 12'. The noise level meter 3 6 constantly forms an average of the received signal over a time which is much longer than the length of a single light pulse. However, the averaging time is significantly shorter than, for example, the 50 μεε time interval between two consecutive transmitted light pulses 12. In this way, the measuring transmitted light pulses 12 have no influence on the mean value, and when a received light pulse 12' appears at the input of the comparator 34, the noise level meter 36 provides a trigger threshold at the reference input 35 which - multiplied by a factor of, for example, seven - is representative of the statistically maximum noise level present immediately before the arrival of the received light pulse 12'.

The task of the peak value detector 37, which is made up of a chain of fast ECL comparators with self-holding, is to generate correction values to compensate for the time measurement errors that occur as a result of signal dynamics, which is explained below with reference to Fig. 6. Fig. 6 shows three different light reception pulses 12' arriving at the photo reception arrangement 22 according to Fig. 3, which reach a maximum signal voltage of 80, 81 and 82 respectively. Due to a correspondingly low noise level, all of the received light pulses 12' exceed the trigger threshold 79 set by the noise level meter 36 at the reference input 35 of the comparator 34, but the time t at which the rising edge of the three different received light pulses exceeds the trigger threshold 79 is different. In the example shown

The time difference can be up to 1.2 ns, which corresponds to a measurement error of approx. 20 cm.

According to the invention, the time measurement errors (for example 84, 85 for the maximum signals 80, 81) relative to the base time 83, which is assumed for the largest occurring maximum 82, are stored in the computer 38, where they are available for correction purposes.

The peak value detector 37 determines whether the signal voltage U _s occurring at the output of the photoreceiver 23 is within, for example, six predetermined signal levels 1 to 6 and emits a corresponding signal via the control line 100 to the computer 38, where the corresponding correction value (for example 84 or 85) is called up for the currently determined signal voltage and a corrected time signal is determined therefrom.

In this way, corresponding measurement errors are eliminated and an overall accuracy of, for example, 5 cm/bit is achieved.

The elimination of time errors by means of the peak value detector 37 is important because the total measuring range of the device according to the invention is 4 m, so that, for example, a measuring error of 20 cm can normally no longer be tolerated.

Since the control stage 40 controls the pulse laser 11 and the light deflection device 15, the computer 38 can assign a distance measurement value to each angular position of the light deflection device 15. The evaluation of the measurement data in the computer 38 consists of monitoring a protective field 122" previously stored in polar coordinates, as shown in Fig. 12, for example, for a driverless, self-steering vehicle 120.

■' the laser radar 121 according to the invention mounted on the front of the vehicle 120 is shown schematically. Whenever the protective field 122" detects the road edge 101 or another obstacle 123 (Fig. 11) that can be detected by the laser radar 121, a corresponding counter-steering movement can be triggered, whereby the sector S1 to S16 where the obstacle is located is also determined.

Fig. 10 shows the simplest application case for a self-steering vehicle 120 equipped with a laser radar 121 according to the invention on the front, whereby the protective field 122 responds to two roadway boundaries 101. As soon as the protective field 122 detects one of the boundaries 101, the laser radar 121 initiates a counter-steering movement.

Fig. 11 shows an example where the protective field 122' in front of the laser radar 121 arranged on the front of a vehicle 120 is set according to the invention so that it reacts to obstacles 123 located at a predetermined distance r, for example by means of a switch-off or braking signal.

tlf According to Fig. 12, the protective field 122" in front of the vehicle 120 is designed in such a differentiated manner that different critical distances Sl to S16 can be provided for different angular sectors, so that not only obstacles can be detected, but also their angle and distance from the location of the laser radar 121 can be determined.

Fig. 13 shows a self-navigating vehicle 120, the navigation device 125 of which is connected to the laser radar according to the invention via an information line 102, whereby the laser radar 121, by means of its detection range 124, from time to time updates the navigation device 125 to the current status at locations where the coordinates of the surroundings are known.

can correct.

The application shown in Fig. 14 consists in the fact that the laser radar device 121 according to the invention defines an approximately rectangular, distance-limited protection area 127, at one corner of which it is arranged so that the bisector of the scanning angle area 54 lies approximately on the diagonal of the rectangular protection area. In the diagonally opposite corner area there is a dangerous work machine 126, from which people approaching the machine are to be protected by the laser radar device 121 according to the invention. It is important that the protection area 127 can be limited by the laser radar device 121 according to the invention so that a person located, for example, in a safe place at 103 is not detected even though he or she is in the scanning angle area 54, while a person located, for example, in a dangerous place at 104 is detected, which then leads, for example, to the dangerous work machine 126 being switched off.

The laser radar according to the invention has a range of 4 to 6 m and a resolution of better than 7 cm. The detection time is approximately 40 ms and the detection angle is 180° in all cases.

In the case of the application according to Fig. 11, for example, an obstacle distance signal r is generated at the interface 39 (Fig. 3), which can be used, for example, for a stop signal in the vehicle 120.

In the embodiment according to Fig. 12, a minimum distance signal can be set for each sector S1 to S16.

With the navigation support according to Fig. 13, a measuring

rate of 360 measurements in 40 ms. The lateral resolution can be 0.5° in all cases, while the distance resolution can be reduced to ±5 cm.

The distance-limited protection zone 127 according to Fig. 14 can be 3 to 4 m, in which case the detection time is 80 to 120 ms at a resolution of 5 cm.

äHj According to the invention, the counter 3 0 is made up of two asynchronous individual counter chains, with one counter incrementing on the positive edge and one counter on the negative edge of the 1.5 GHz clock, so that adding both counter readings results in a resolution of 33 0 ps. How this happens in detail is explained below:

According to Fig. 5, the counter 30 according to the invention contains two asynchronously operating individual counters 50, 51, whose clock inputs 105, 106 are controlled via an OR gate 71. It is important that the output 72 for the clock input 106 of the individual counter 51 is inverted compared to the output 72' for the clock input of the individual counter 50. The two inputs of the ^SF OR gate 71 are connected via a test counting pulse input 55 to the computer 38 or to the output of an AND gate 73, the two inputs of which are connected to the switching output of a flip-flop 76 or to a high frequency voltage input 59, which is supplied with a high frequency voltage of 1.5 GHz by the frequency generator 52.

The switching input of the flip-flop 76 is connected to the output of an OR gate 75, both inputs of which are supplied by the pulse laser 11 via the line 45 (see also Fig. 3), while the other input is connected to a test start input 58 which is connected to the computer 38 via a control line 65.

The output of the comparator 34 (Fig. 3) is connected according to Fig. 7 via the line 62 to the measurement stop input 61 of the counter 30, which in turn is connected to one input of an OR gate 74. The other input of the OR gate 74 is connected to the overflow output 107 of the second individual counter 51.

A control line 66 leads from the computer 3 8 to a multiplexer switching input 67, which is connected to the switching input 108 of a multiplexer 68.

The counter output signals of the individual counters 50, 51 are applied to the two inputs of an addition stage 69 , which forms the sum from the two input count signals and feeds this to an output stage 70 via the multiplexer 68.

The counting signal of the second individual counter 51 is also applied directly to a second input of the multiplexer 68 via the control line 109. The output of the addition stage 69 or the output of the second individual counter 51 can be switched through to the output stage 70 via the control input 108.

The test counting pulse input 55 is controlled by the computer 38 via a control line 56. The test start input 58 is also controlled by the computer 38 via a control line 65.

The two individual counters 50, 51 also have reset inputs 110, 111, which are controlled by the computer 3 8 via a reset input 63 and a control line 64.

The counter 3 0 explained in Fig. 5 is used to

during operation of the laser radar device according to the invention -'' the following functions are carried out:

While the rotating mirror 16 sweeps over the useful scanning angle range 54 (Fig. 2, 14, 16), each light pulse 12 emitted by the pulse laser 11 triggers a switching of the flip-flop 76 at the moment of its emission via the line 45 and the OR gate 75, so that the connected AND gate 73 passes the maximum frequency voltage of 1.5 GHz present at its other input to the OR gate 71. From there, the maximum frequency voltage now reaches the counting inputs 105, 106 of the individual counters 50, 51, whereby the counting signal reaching the counter input 106 of the second counter 51 is phase-shifted by 180° compared to the counting signal at the input 105 due to the inverted output 72 of the OR gate 71. In other words, counter 50 now counts the rising edges of the positive half-waves, and individual counter 51 counts the falling edges of the negative half-waves. As a result, during each period of the maximum frequency voltage from frequency generator 52, two bits are generated by individual counters 50, 51, each of which is phase-shifted by 180°.

The counting of the half-waves of the maximum frequency voltage from the frequency generator 52 is now continued until a light pulse 12' (Fig. 3) is received by the photo-receiving arrangement 22 and a stop signal is sent to the reset input 112 of the flip-flop 76 via the comparator 34, the line 62, the measurement stop input 61 and the OR gate 74. The flip-flop 76 is then reset to its initial state, whereupon the AND gate 73 blocks and the maximum frequency generator 52 is separated from the OR gate 71. The counting of the individual counters 50, 51 is thus stopped, and now the computer 38, which has been informed of this via the line 4 6 (Fig. 3), can not only send the measured counter readings after summation in the addition stage 69 via the

Not only do we not only call up the multiplexer 68 and the output stage 70, but we also carry out two tests.

Since two bits are generated during each period of the high frequency voltage, a temporal resolution of 33 0 ps in the time of flight measurement (t) is achieved at a frequency of 1.5 GHz, thus achieving a distance measurement accuracy of 5 cm/bit.

After a runtime measurement has been carried out in this way, the computer 38 switches the multiplexer 68 over the control line 66 and the multiplexer switching input 67 so that it can now send the counter reading of the second counter 51, which is present over the line 10 9, to the computer 3 8. There, a comparison of the total output signal of the addition stage 69 with twice the counter reading of the second counter 51 takes place. If all components are working properly, the two numerical values may differ by a maximum of one bit. If this is determined by the computer 38, this is a sign that all components have worked properly. However, if this comparison results in a difference of several bits, the computer 3 8 generates an error signal and, for example, stops the dangerous work machine 96 according to Fig. 16.

The aforementioned test can, for example, be carried out once after each received light pulse 12' and the corresponding evaluation. In general, however, it is sufficient if such a test is only carried out after the scanning angle range 54 has been completely scanned.

In the latter case, the computer 38 also carries out a further safety test in that test counting pulses are sent to the test counting pulse input 55 via the supply line 56, which are counted via the OR gate 71.

triggers in the individual counters 50, 51, whereby this test counting takes place approximately 300 times slower, i.e. at a frequency of 5 MHz, than in the actual measuring process.

The counting process is triggered by the computer via the control line 65, the test start input 58, the OR gate 75, the flip-flop 76 and the AND gate 73 in a similar way to the actual measuring process via the measuring start input.

Once a test counting process has been triggered, it continues until the counters 50, 51 are full, whereupon a stop signal is sent to the reset input 112 of the flip-flop 76 via the overflow output 107 of the second individual counter 51, the reset line 77 and the OR gate 74. It can now be checked via the addition stage 69 and the line 109 as well as the multiplexer 68, which is again controlled in a suitable manner by the computer 38, whether the actual counter readings match the target value.

This second test, which is also only carried out once after each scan, can be used to check whether the logical functions are working correctly. Since the computer 3 8 generates the positive and negative edges that trigger the counting at the test input 55, it can easily check that everything is working properly by comparing the counter readings received with the number of edges output. Logical malfunctions and damaged signal lines can be reliably detected in this way.

The arrangement of two individual counters 50, 51 in counter 3 0 not only has the advantage of doubling the time resolution, but also enables the two safety tests described above.

Figures 4 and 7 show that test devices can be arranged in the area of the 360° scan of the rotating mirror 16 which lies outside the scanning angle range 54 (Figure 2). One of these test devices consists of a test body 86 arranged in the area of the transmitted light pulse bundle 21, which preferably consists of a light-scattering material. This can be a sintered glass pane (glass frit) in which the light is scattered by the crystalline particles. A blackened ring diaphragm 87 around the area where the transmitted pulse light bundle 21 strikes reduces undesirable scattered light effects.

Since the scattering properties of the test body 86 are known and stable, the proper functioning of the pulse laser 11 and the reception system can be tested by evaluating the reception signal of the photo receiver 23, which is preferably designed as an avalanche receiver diode.

The reception signal Us of the photoreception arrangement 22 is calculated according to the following formula:

Us = Ps · Rr · Rq ■ M · Rt (2)

In this formula:

Us: Receive signal

Ps: Transmission power

Rr: test target reflectance

Rq: quantum efficiency

M : Multiplication factor of the avalanche diode used

23
Rt: Transimpedance of the avalanche diode 23 (effective working resistance of the diode)

The computer now checks whether the received signal Us reaches at least the value of a predefined limit constant Kl. If this is the case, the transmitting-receiving arrangement is assessed as being faultless and the measurement is continued. However, if the received signal Us falls below Kl in the test described above, the computer 38 reports an error and switches off, for example, the dangerous working machine 126 according to Fig. 14.

According to Fig. 9, a further test can be carried out in the same angular range that is ineffective for the actual measurement by providing a light-emitting diode 88 either inside the test body 86 or next to it (Fig. 4), which is imaged by the imaging receiving system or the photoreceiver arrangement 22 onto the photoreceiver 23, which is again assumed to be an avalanche diode. The direct current I generated in the avalanche diode 23 as a result leads to quantum noise (shot noise) due to the laws of physics, which is quantitatively determined by the noise level meter 36 (Fig. 3). An evaluation allows the calculation of the so-called excess noise index of the avalanche photodiode 23 with a known receiver direct current I, which is a direct measure of the quality or functionality of the avalanche photodiode 23. Together with the measurement result of the test described in Fig. 7, the system sensitivity under all ambient light situations can be indirectly demonstrated.

The noise level determined by the noise level meter 3 6 is calculated using the following formula

Ur = (2-qIM ^1+k -f _g ) ^M -Rt (3)

The computer 3 8 then checks whether the following requirement is met:

• · · ft ·

Us (I) ¹¹ 1

> ^: = K2 (4)

Ur-Kl (2-qM ^1+k -f _g )*-Rt

In the above formulas:

I: Photocurrent in the photodiode 23

Ur: Noise voltage due to the illumination by the

ßk LED 8 8

M: Multiplication factor of the avalanche diode 23

q: elementary charge (1.6-ICT ¹⁹ Coulomb)

Rt: Transimpedance of the Laverne Diode 23

f : cutoff frequency of the noise

K2: second limit constant

According to Fig. 4 and 9, light-emitting diodes 91 are arranged evenly distributed over the scanning angle range 54 below the lower end face 89 of the front pane 41. Each of these emits a light barrier beam 98 upwards, which passes through a lower part of the front pane 41 angled as shown in Fig. 4 and 9 and then passes through the inclined main part of the front pane 41 to an associated photoreceiver 92 arranged above it. The inclined position of the main part of the front pane 41 not only serves the purpose of creating a passage for the vertical light barrier beams 98, but also of keeping the inner side reflection from the front pane 41 away from the photoreceiver arrangement 22.

According to the invention, the lower angled part of the front pane 41 has two matte or roughened areas .41' distributed over the circumference on its outer surface, through which the sharply focused light 131 emanating from the associated light transmitter 91 passes in the absence of a light source shown in Fig.4.

drawn smoothing oil film 128 is scattered into a much larger solid angle area 129, so that the associated light receiver 92 receives only a small amount of light from the light transmitter 91.

If, for example, an oil film 128 is deposited on the roughened outer surface of the frosted area 41', this cancels out the strong light scattering of the beam 131 due to the only slight difference in the refractive index to the underlying material of the front screen 41, so that a concentrated light beam 130 now hits the associated light receiver 92 and triggers a significantly stronger light reception signal at the light receiver 92. The strong increase in the output signal of the light receiver 92 is therefore a measure of the fact that a smoothing liquid film has deposited on the roughened surface of the frosted area 41'.

Of the light transmitter-light receiver pairs 91, 92 distributed over the circumference of the front screen 41, at least two are assigned a frosted area 41' in order to create redundancy in the event of a defective optoelectronic component.

According to Fig. 9, the LEDs 91 are connected to a series of outputs 113 of a multiplexer 93, which is controlled by the computer 38 and is supplied with rectangular pulses via a pulse former 95.

The receiving diodes 92 are connected to the various inputs 114 of a further multiplexer 94, which is also controlled by the computer 38 and is connected to the computer 38 via an amplifier 96 and an analog-digital converter 97.

•••ft- ·* ·* ·· ··

The described arrangement of LEDs 91 and receiving diodes 92 serves to monitor the contamination of the windscreen 41. It works as follows:

The computer 38 clocks the multiplexer 93 so that it successively emits a rectangular pulse via the pulse former 95 to the transmitting diodes 91, which are evenly arranged around the circumference of the scanning angle range 54. The receiving diodes 92 opposite each other are activated in the same rhythm by the multiplexer 94 being clocked by the computer 38 in the same way as the multiplexer 93, whereby the outputs of the individual receiving diodes 92 are successively applied to the amplifier 96 and the analog-digital converter 97. The computer 38 therefore continuously receives signals from the individual receiving diodes 92. By comparing a predetermined target reception strength with the actual reception strength of the light beams 98, the computer 38 can thus detect dirt on the windshield 41. If excessive contamination is detected at least in one place, the computer 38 reports this to the interface 39 and a warning or shutdown signal can then be issued, for example.

When evaluating the received signals from the light receivers 92, which are assigned to a frosted area 41', the computer 38 distinguishes between a decrease and an increase in the received signal, so that both darkening dirt and an oil film in the light beam running between the light transmitter 91 and the light receiver 92 can be recognized. However, it is also possible that the light transmitter-light receiver pair 91, 92 assigned to the frosted area 41' only serves to detect liquid films, so that the computer 38 only responds to an increased light reception when such a light transmitter-light receiver pair 91, 92 is connected.

In addition to the - preferably four - measuring light barrier beams 98, there should be two redundant reference branches whose beam path does not lead through the window, whereby the temperature response of the transmitting diodes and the pulse current source can be eliminated by corresponding signal comparison in the computer 38. By designing the reference branches as two channels, the circuit is designed in such a way that every malfunction is detected.

Furthermore, according to the invention, the computer monitors the engine speed and the system timing. The program sequence is monitored in terms of time and logic.

According to the invention, the monitoring of the electronic functions is carried out by a RAM, ROM, ALU, watchdog test, A/D converter (contamination measurement, noise level measurement), D/A converter (comparator test),
Peak detector,
Stop comparator and
Oscillators for the computer 38 and the 1.5 GHz counter.

According to the invention, two opto-decoupled, dynamic, read-back intervention lines are provided. The verification of the system line is based on a worst-case power balance. The laser is controlled in a single-fault-safe manner (eye safety). Furthermore, access protection for the setup mode can be achieved using passwords. The light grid described ensures contamination detection and warning.

There is a defined start-up behavior of the system or interface. After the device is switched on, all of the above-mentioned tests are run through.

The sensitivity of the transmitter-receiver arrangement is set so that objects with a reflection factor of down to 2% can be detected.

According to Fig. 4, the laser radar device is housed in a housing 115 which is closed off at the front by a cover cap 116, in the lower area of which the front screen 41 curved over 180° is provided. According to Fig. 4, the transmitter and receiver are housed in a transmitter-receiver unit 49 designed as a compact structural unit, for example in the form of a cylindrical housing.

Claims (47)

risprüche 1. Laser distance determination device according to the pulse transit time method with a pulse laser (11) which sends controlled light pulses (12) into a measuring area (13), a photoreceiving arrangement (22) which receives the light pulses (12') reflected by an object (14) located in the measuring area (13), an evaluation circuit (23, 30, 34, 36, 37, 38, 39, 40) which, taking into account the speed of light, determines a distance signal characteristic of the distance of the object (14) from the pulse laser (11) from the time between the emission and reception of a light pulse (12, 12'), wherein a light deflection device (15) is arranged between the measuring area (13) and the pulse laser (11), which deflects the successive light pulses (12) into the measuring area (13) at increasingly changing angles and simultaneously feeds them to the evaluation circuit (23, 30, 34, 36, 37, 38, 39, 40) emits an angular position signal representative of its current angular position, and wherein the evaluation circuit (23, 30, 34, 36, 37, 38, 39, 40) determines the location of the object (14) within the measuring range (13) from the distance signal and the angular position signal,
marked by a housing (115) which is closed off in the region of the passage of the transmitted pulse light beam and the received pulse light beam by a front panel (41), the front panel (41) being traversed at a plurality of points along its circumference by light barrier beams (98) which are emitted by light transmitters (91) arranged on the front side (89) and are received by light receivers (92) arranged in the region of the other front side (90). 2. Device according to claim 1,
characterized-, that the light transmitters (91) for sequential control with pulses and the light receivers (92) for corresponding evaluation of the received pulses are connected via multiplexers (93 or 94) to the computer (38), which, if at least one received signal has fallen below a predetermined minimum value, emits a contamination signal. 3. Device according to one of the preceding claims, characterized in that the front pane runs obliquely from top to bottom in the direction of the rotating mirror (16) and is preferably angled at its lower end in the opposite direction by a significant angle, which can be approximately 90°, in order to bring about a double passage of the light barrier beam (98) through the front pane (41), first from the inside of the housing (115) into the outside space and then from there again into the inside of the housing (115). 4. Device according to claim 3,
characterized, that at least one area (41') of the front screen (41), which is preferably located near a light transmitter (91) and far from the associated light receiver (92), is matt on its outer surface, such that when the area (41') of the associated light receiver (92) is uncontaminated, a weakened by light scattering receives a predetermined amount of light and, in the presence of a liquid, in particular oil film (128) on the area (41'), the associated light receiver (92) receives an increased amount of light, and that a contamination signal is emitted when the light reception at the associated light receiver (92) exceeds a predetermined value. 5. Device according to claim 4,
characterized, that on the front screen (41) there are two frosted areas (41') distributed around the circumference and light transmitters (91) and light receivers (92) assigned to them. 6. Device according to one of the preceding claims, characterized in that the front panel (41) is curved around the axis of rotation (17) and extends in the scanning direction at least over the scanning angle range (54). 7. Device according to one of the preceding claims, characterized in that the distance angle range (54) is preferably greater than 90° and in particular less than 270° and is preferably approximately 180° and expediently the pulsed light beams define a preferably horizontal scanning plane (53). 8. Device according to one of the preceding claims, characterized in that the light pulse duration is so short that the light deflection device (15) can be considered to be practically stationary during this time. 9. Device according to one of the preceding claims, characterized in that the light pulse duration is a few nanoseconds, expediently 1-5, preferably 2-4 and in particular about ns. 10. Device according to one of the preceding claims, characterized in that the angular velocity of the light deflection device (15) is 0.5.10 ⁴ to 2.10 ⁴ , in particular about 1.10 ⁴ °/sec. 11. Device according to one of the preceding claims, characterized in that the distance between successive transmitted light pulses (12) is several orders of magnitude greater than the pulse length, preferably by an order of magnitude of 4 orders of magnitude greater than the pulse length and/or that the pulse repetition frequency is preferably between 5 and 50, expediently 10 to -40, and in particular approximately 20 kHz. 12. Device according to one of the preceding claims, characterized in that the light deflection device (15) comprises a preferably planar rotating mirror (16). 13. Device according to claim 12, characterized in that the rotating mirror (16) is rotatable about one of the incident light beams, preferably the central incident light beam (18). 14. Device according to claim 13, characterized in that the axis of rotation (17) or the central incident light beam (18) extends at 30 to 60, preferably 40 to 50 and in particular 45° to the surface of the rotating mirror (16), wherein the rotating mirror (16) advantageously has a circular disk shape when viewed in the direction of the axis of rotation (17). 15. Device according to one of the preceding claims, characterized in that the rotating mirror (16) receives a transmitted pulse light beam (21) essentially from above and emits it essentially horizontally. 16. Device according to one of the preceding claims, characterized in that the pulsed light emitted preferably horizontally by the pulsed laser (11) is deflected by a fixed, preferably flat deflection mirror (19) by preferably 90° to the rotating mirror (16), in particular downwards. 17. Device according to one of the preceding claims, characterized in that a transmitting lens (33) forming a parallel transmitting pulse light beam (21) is connected upstream of the pulse laser (11). 18. Device according to one of the preceding claims, characterized in that the light deflection device (15) also receives a received pulse light beam (20) and directs it to the photoreceiving arrangement (22), wherein the transmitted pulse light beam (21) and the received pulse light beam (20) beyond the rotating mirror (16) are preferably coaxial with one another and wherein in particular the transmitted pulse light beam (21) runs centrally and has a circular cross-section and the received pulse light beam (22) is arranged around the transmitted pulse light beam and has a circular cross-section and both beams (20, 21) adjoin one another, so that the rotating mirror (16) has a central region (24) where the transmitted pulse light beam (21) impinges and a peripheral region (47) where the received pulse light beam (20) impinges. 19. Device according to one of claims 12 to 18, characterized in that that the deflection mirror (19) for the pulsed light coming from the pulsed laser (11) or the transmitting lens (33) is arranged opposite, in particular above a central region (24) of the rotating mirror (16) and the received pulsed light bundle (20) passes the deflection mirror (19) to the photoreception arrangement (22), the deflection plane mirror (19) preferably having a circular cross-section in the direction of the received pulsed light bundle (20) passing by it. 20. Device according to one of the preceding claims, characterized in that the photoreceiving arrangement (22) comprises a receiver lens (25) which concentrates the received light onto a photoreceiver (23). 21. Device according to claim 19 and 20, characterized in that that the diameter of the receiver lens (25) is so large that it receives the received pulse light beam (20) striking the peripheral region (47) of the rotating mirror (16) next to the central region (24). 22. Device according to one of the preceding claims, characterized in that an interference filter (26) tuned to the spectrum of the light emitted by the pulse laser (11) is arranged at the input of the photoreceiving arrangement (22). 23. Device according to one of the preceding claims, characterized in that the receiving lens (25) has two areas (25', 25") with different focal lengths, which are preferably concentric with each other. 24. Device according to one of the preceding claims, characterized in that the rotating mirror (16) is formed on an oblique section plane of a circular cylinder body (27) whose cylinder axis coincides with the axis of rotation (17). 25. Device according to one of claims 1 to 23, characterized in that that the rotating mirror (16) is formed on a flat mirror plate (78) which is attached to a rotatable mirror carrier (48). 26. Device according to one of the preceding claims, characterized in that that the light deflection device (15) covers a 360° deflection angle and preferably rotates continuously in one direction of rotation. 27. Device according to one of the preceding claims, characterized in that the rotating mirror (16) is arranged on a rotary plate (28) which is driven by a motor (31) for continuous rotation at a preferably predetermined speed, the speed expediently 1000 to 3000, in particular about 1500 rpm. 28. Device according to one of the preceding claims, characterized in that an angle sensor (29) is arranged in the area of the turntable (28), which reports the current angular position of the turntable (28) to the evaluation circuit (38, 40). 29. Device according to one of the preceding claims, characterized in that the evaluation circuit contains a computer (3 8) in which all necessary calculation operations, in particular the calculation of the distance of the object (14) from the pulse transit time (t) are carried out. 30. Device according to one of the preceding claims, characterized in that the evaluation circuit comprises a counter (30) with a preferably fixed clock frequency, which is connected to the pulse laser (11) or its trigger circuit in such a way that it is triggered when a light pulse (12) is emitted, and is connected to the photoreceiving arrangement (22) in such a way that it is stopped when the same light pulse (12') is received by the photoreceiving arrangement (22), and that the transit time (t) and preferably the distance of the object (14) are calculated from the counter reading. 31. Device according to claim 30,
characterized, that the counter (3 0) is acted upon by a frequency generator (52) which expediently operates with a clock frequency of 0.5 to 3.0, in particular 1 to 2 and preferably about 1.5 GHz. 32. Device according to claim 31,
characterized, that the counter (30) is constructed from two asynchronous individual counters (50, 51), one of which responds to the positive half-waves, in particular the rising edges of the positive half-waves, and the other to the negative half-waves, in particular the falling edges of the negative half-waves, of a maximum frequency voltage output by the frequency generator (52). 33. Device according to claim 31,
characterized, that the two individual counter readings generated by the transit time (t) of a light pulse (12, 12') are added and used as a measure for the transit time (t·). 34. Device according to claim 32 or 33, characterized in that that the sum of the individual counter readings is compared with the doubled counter reading of one of the individual counters (50, 51) and an error signal is emitted if the comparison results in a difference of more than a few bits, preferably one bit. 35. Device according to claim 34,
characterized, that the comparison is carried out after each evaluation of a light pulse (12, 12'). 36. Device according to claim 34,
characterized, that the comparison is carried out in the pause between the end of a scan of the scanning angle range (54) and the beginning of the next scan of the scanning angle range (54). 37. Device according to one of claims 3 2 to 36, characterized in that that in the pause between two scans of the scanning angle range (54) the computer (38) supplies controlled counting pulses to the individual counters (50, 51), checks the counting result and emits an error signal if the counting result does not match the entered number of counting pulses. 38. Device according to one of the preceding claims, characterized in that the photoreceiving arrangement (22) is connected to the counter (30) via a comparator (34), to whose reference input (35) defining the trigger threshold for the received signals is supplied the output signal of a noise level meter (36) representative of the noise level immediately before the signal is received, to whose input the output signal of the photoreceiving arrangement (22) is applied. 39. Device according to claim 38,
¹ ^ characterized by that the noise level meter (36) continuously detects the basic brightness via the photoreceiving arrangement (22) and averages it over a predetermined time which is long compared to the duration of a light pulse (12, 12') and short compared to the time between two consecutive transmitted light pulses (12), and that this average value is used as the average noise level. 40. Device according to claim 39,
characterized, that the averaging time is approximately 30% of the time interval between two adjacent transmitted light pulses (12) carries. 41. Device according to one of claims 38 to 40, characterized in that that the trigger threshold (79) determined by the output signal of the noise level meter (36) is several times, preferably 2 to 10 times, in particular 4 to 8 times and particularly preferably about 7 times, greater than the determined average noise level. 42. Device according to one of the preceding claims, characterized in that a peak value detector (37) is also connected to the output of the photoreceiving arrangement (22), the output signal of which is used to generate correction values to compensate for the time measurement errors occurring as a result of signal dynamics. 43. Device according to claim 42,
characterized, that the peak value detector (37) detects the respective maximum of a received light pulse (12') and emits a corresponding maximum signal to the computer (38), that the time measurement errors (84, 85) occurring depending on the height of the maximum (80, 81, 82) are stored in the computer (38) and that depending on the determined maximum (80, 81, 82) a corresponding correction value is determined and the measured time is corrected according to this correction value. 44. Device according to one of the preceding claims, characterized in that outside the scanning angle range (54) a light-reflecting or -scattering test body (86) is in the path of the transmitting pulse light beam carrying out the scanning movement. dels (21) and the computer (38) checks, during the scanning of the test body (86) by the transmitted pulse light beam (21), whether the signal received by the photoreceiving arrangement (22) is at least equal to a predetermined limit value (Kl). 45. Device according to one of the preceding claims, characterized in that outside the scanning angle range (54) a light-emitting diode (88) is arranged in the path of the transmit pulse light beam (21) carrying out the scanning movement and the computer (38) checks whether the signal-to-noise ratio is at least equal to a predetermined limit value (K2) while the light-emitting diode (88) is being scanned by an area of the rotating mirror (16) corresponding to the receive pulse light beam (20). 46. Device according to one of claims 28 to 45, characterized in that that an interface (39) is connected to the computer (38), at the output of which the desired output signals and values including error signals can be taken and fed for further use. 47. Laser distance measuring device according to one of the preceding claims, characterized,
that it is applied - in the case of self-control of vehicles (12 0) to create a defined protection area (122) in front of the vehicle (12 0); - by arrangement on the front of a vehicle (120) for collision protection with obstacles (123) by defining a corresponding protection area (122 ¹ ); - by arrangement on the front of a vehicle (120) to create a collision protection area (122") which is divided into several sectors (S1 to S16) of the scanning angle range (54), each of which defines its own and well-defined safety distance; - by arranging it at the front of a vehicle (120) for the purpose of defining a detection area (124) on the basis of which a navigation device (125) arranged in the vehicle can be checked for its proper functioning and, if necessary, corrected; - when protecting persons (104) on dangerous work machines (126) by defining a distance-limited protection area (127), wherein the dangerous work machine (126) is expediently located in the end region of the protection area (127) facing away from the device (121) according to the invention or under the machine.