DE4340756A1 - Laser range finder, e.g. for driverless transport system - measures distance using pulse travel time and light deflection angle to determine position of object in measuring region - Google Patents

Abstract

The laser appts. includes a pulse laser (11) which transmits controlled light pulses (12) to a measuring region (13). A photoreceiver (22) intercepts light reflected from an object (14) in the measuring region, and a processor circuit (23,30,34,36-40) delivers a distance signal according to the speed of light and the time between transmission and reception of the light pulses (12,12'). A light deflector (15), disposed between the pulsed laser and the measuring region, deflects successive light pulses into different angles in the measuring region. The deflector also sends corresp. angular position signals to the processor circuit. The processor uses the angle and distance signals to determine the object position within a 90 to 270 degree radius. USE/ADVANTAGE - Laser radar detects distance from pulsed light and detects angle w.r.t. any basis direction in surveyed area.

Description

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

The pulse transit time method for distance measurement is basic additionally known (DE-PS 34 29 062, DE-PS 40 02 356).

The aim of the present invention is this Pulse transit time method for the position determination of Use objects in spatial areas, e.g. B. together Menhang with the protection of driverless transport systems general area safeguards.

To solve this problem, the characteristics of the characteristic ning part of claim 1 provided.

The invention thus creates a laser radar by means of which not just the distance from the counter hit by the pulse light stands can be determined by the device, but also the angle at which the object is relative to any one Base direction is arranged in the room.

Preferred dimensions of the laser radar are the Claims 2 to 5 defined.

The embodiment according to claim 4 achieves that in 50 to 150 and in particular 100 µs an angular range of about 1 ° swept by the light deflecting device becomes.

If, on the other hand, according to claim 5 a light every 50 µs is emitted for a short duration, this means that a light pulse is emitted approximately every 1/2 ° or at a total scanning range of 180 ° 360 pulses. This is enough  for an angular resolution required in the security area completely out.

The time between two emitted light pulses of about 50 µs is used for tests described below uses.

The embodiments according to FIGS Claims 6 to 22, because this is a structural compact and optically very effective way of scanning a desired area, where the Scanning angle can go up to 360 °, but usually only Is 180 °.

The concentric formation is particularly advantageous formation of transmit and receive pulse light bundles according to Claims 11 and 12. This is particularly a clean re geometric beam separation and sensitivity in the near area achieved.

The speeds according to claim 21 are particularly advantageous because of this in connection with the pulse used repetition frequencies sufficient angular and temporal Resolution is achieved.

In the context of the following embodiments, the Use of a computer according to claim 23 of large size interpretation. In this way, in particular, the different Self-monitoring functions of the system perceived who the.

The developments of the invention according to claims 24 and 25 ensure one for the intended monitoring purposes fully adequate distance resolution in the order of magnitude 5 cm / bit, with one bit separated by one or half Period of the clock frequency is defined.  

The resolution given by the clock frequency can halved by the embodiment according to claim 26 and 27 become.

Of particular advantage, however, is that through the use one error from two individual counters connected in parallel be carried out according to claims 28 to 30 can.

Another error test, especially during execution example according to claim 30 is additionally used defined in claim 31.

It is also advantageous if according to claims 32 to 35 also the noise level to which the useful pulse signal is stored, is taken into account, since both the brightness in the monitored spaces as well as the reflectance of the over objects can fluctuate strongly.

Another advantageous embodiment is by claim 37 marked. In particular through this training The invention can measure accuracy up to 5 cm / bit be enough.

Errors can be caused by the embodiment according to claim 38 who is determined in the transmission and reception system of the device the.

The development according to claim 39 also enables the proper functioning of the preferred used Check avalanche receiver diode.

The device according to the invention is more expedient wise in a housing which in the area of the outlet of the  Send pulse light bundle and the receive pulse light bundle through a windscreen curved in accordance with the scanning is completed.

To also Ver dangerous for the function of the device Detect dirt on this windscreen automatically can and in case of excessive pollution Issuing a contamination or error signal can Device expedient according to claims 41 to 43 be educated. Tilting the main part of the front disc also serves to mirror away the disc surface reflex.

Due to the design according to claims 44 or 45 also contamination in the form of a liquid, in particular special oil film on the windscreen, which in itself the light Do not affect passage or only marginally Trigger pollution signal by the property of such Films are exploited so that they have a smooth surface too then form when placed on a rough surface be brought. Due to safety requirements at least two oil measuring channels should be provided to also the case that one of the light transmitters or light receivers fails to be able to record in the evaluation electronics.

Via an interface provided according to claim 46 all desired navigation and error signals in suitable ter be converted and accessed.

Advantageous applications of the device according to the invention one takes from the claim 47.

The particular advantage of the laser radar according to the invention direction is that it is against any system error  is secured. This applies to both errors in the optical Area as well as in evaluation electronics.

The invention is described below, for example, with the aid of Drawing described; in this shows

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

Fig. 2 is a schematic plan view of the turning mirrors of FIG. 1 and the scan angle range,

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

Fig. 4 is a more detailed cross-section of the laser radar shown in FIG. 1,

Fig. 5 is a block diagram of the present invention preferably counter used with the components connected thereto,

Fig. 6 is a signal voltage-time diagram of various degrees of light receiving light pulses,

Fig. 7 is a view analogous to FIG. 1 in a 90 ° twist th position of the rotary mirror to illustrate the function of an introduced in the beam path of the test body,

A view similar to Fig. 7 view, with a light-emitting diode is shown for testing the receiving system Fig. 8,

Fig. 9 is a schematic section through the front panel of the device according to the invention and a light barrier arrangement used for monitoring pollution with the associated block diagram and

Figs. 10 to 14 are schematic top views of different applications of the laser radar according to the invention.

According to Fig. 1, an engine 31 drives a horizontal rotary plate 28 to a continuous rotational movement about an axis 17 Tikale ver. On the periphery of the turntable 28 there is an angle sensor 29 which is configured 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.

On the turntable 28 , a circular cylinder body 27 is arranged so 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 in a manner not shown on a mirror plate which is attached to the turntable 28 via a mirror carrier.

Above the rotating mirror 16 there is a substantially narrower, likewise planar deflecting mirror 19 , the mirror surface of which is at an angle of 45 ° to the axis of rotation 17 and can also be realized as a circular cylinder body. According to Fig. 4 and the deflecting mirror 19 is formed as a planar 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 downward on the deflecting mirror 19 , in order then to be deflected by the rotating mirror 16 in a horizontal direction to the front pane 41 of the device. From there, the transmitted light beam 21 arrives in the measuring area 13 , in which, for example, a light-reflecting object 14 is assumed, from the scattered light as the received light beam 20 through the windshield 41 in the sense of an autocollimation beam path back to the rotating mirror 16 . The receiving light 20 strikes the side of the central area 24 , on which the transmitted light 21 and in particular the central incidence light beam 18 strike a ring area 47 of the rotating mirror 16 , in order to be reflected past the deflecting mirror 19 to an interference filter 26 , behind which a receiver lens 25 is located, the areas 25 ', 25 ''of different focal lengths, in order to be able to recognize objects arranged very close to the device.

The receiver lens 25 focuses the received light on a photoreceptor 23 and forms, together with the photoreceptor 23 is a photoreceptor array 22nd The rotating mirror 16 , the turntable 28 and the motor 31 together constitute a light deflecting device 15 which allows the transmit pulse light beam 21 and receive pulse light beam 20 to rotate about 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 windscreen 41 extends only over an angle of about 180 °, z. B. is sufficient for the complete monitoring of the area in front of a vehicle. In Fig. 2, in addition to the top view of FIG. 1, two further angular positions of the rotary mirror 16 and the transmit pulse light beam 21 are illustrated. The angular scanning performing transmit pulse light bundle 21 defines a scanning plane 53 . The maximum scanning angle range 54 extends according to FIG. 2 over 180 °.

According to FIG. 3, the control section 40 causes via lines 42, 43 the pulse laser 11 deflection device for emitting light pulses of a duration of 3 to 4 nanoseconds, and the circulation of the light 15 at a speed of 1500 rpm. Via the line 32 , the control stage 40 from the angle sensor 29 communicates the angular position of the light deflecting device 15 at every moment.

Via the transmitting lens 33 and the mirror 19 , 16 ( Fig. 1, 4) who sent the light pulses 12 in the measuring area 13 . You who after a running time t as receive pulses 12 '( Fig. 3) received by the photo receiving arrangement 22 . The photodetector 23 , in particular an avalanche diode, forms a corresponding electrical signal, which is applied via a comparator 34 to a counter 30 clocked by a frequency generator 52 . The reference input 35 of the comparator 34 is the output of a noise level meter 36 , the input of which is also connected to the output of the photo receiving arrangement 22 . The noise level meter 36 also reports the present noise level to a computer 38 via a line 44 .

The output signal of the photoreceiver 23 is also fed to the input of a peak value 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 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 . This determines the transit time t and calculates the distance d of the object 14 according to the formula

d = ct / 2 (1)

where c is the speed of light.

Since the computer 38 is aware of 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 can now be passed on to the interface 39 , where it can be used for further use. B. is available as a navigation signal or error signal.

The operation of the device described is how follows:

When driven by the motor 31 to a constant rotary motion rotating mirror 16 , the control stage 40 causes the pulse laser 11 to emit a light pulse 12 of 3.5 nanoseconds in duration. About the light deflecting device 15 , the light pulse 12 is sent into the measuring area 13 and, according to FIG. 1, is reflected by an object 14 , which is only indicated by dashed lines in FIG. 3, so that a receiving pulse 12 'finally reaches the receiving arrangement 22 . In this way, the light reaches the photo-receiving arrangement 22 after a light propagation 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 transmission and reception of the light pulse is measured using the time interval counter 30 . When emitting the light pulse 12 , the counter is triggered via the control line 45 and stopped when receiving the light pulse 12 'passed back and forth across the measuring range 13 ' by the photo receiver 23 via the comparator 34 . With a temporal resolution of the counter of 330 ps, a distance measuring accuracy of 5 cm results.

The task of the noise level meter 36 is to track the detection threshold as a function of the receiver noise level. This tracking ensures a constant false alarm rate in the event of changing lighting situations and object reflection factors. The noise level meter 36 provides a trigger threshold at the reference input 35 of the comparator 34 , which ensures that, for. B. only such received light pulses 12 'trigger a counter signal at the comparator 34 , which is seven times the size of the shortly before the appearance of the light pulse 12 ' existing noise level. The noise level meter 36 constantly averages the received signal over a time that is much greater than the length of a single light pulse. However, the averaging time is significantly smaller than the time interval between two consecutive transmit light pulses 12, for example 50 µs. In this way, the measurement-transmit light pulses 12 have no influence on the mean value, and when a receive light pulse 12 'appears at the input of the comparator 34 , the noise level meter 36 at the reference input 35 provides a trigger threshold which - multiplied by a factor of e.g. B. seven - representative of the immediately before the arrival of the received light pulse 12 'available NEN statistically maximum noise level.

The task of the peak value detector 37 , which is built up from a chain of fast self-latching ECL comparators, is the generation of correction values for compensating the time measurement errors occurring as a result of signal dynamics, which is explained below with reference to FIG. 6. In Fig. 6 three different arriving at the photo receiving arrangement 22 of FIG. 3 incoming light receiving pulses 12 'are shown, which che chen chen a maximum signal voltage of 80, 81 and 82. Due to a suitably low noise level all receive light pulses exceed 12 ', although the by the noise level meter 36 at the reference input 35 of the comparator 34 set trigger threshold 79, but the time t at which the rising edge of the three difference union receiving light pulses, the trigger threshold 79 exceeds , differently. 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 ) are stored in the computer 38 relative to the base time 83 , which is assumed for the largest occurring maximum 82 , 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 for the currently detected signal voltage the corresponding correction value (for example 84 or 85 ) is called up and a corrected time signal is determined therefrom.

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

The time error elimination 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 accepted.

Since the control stage 40 controls the pulse laser 11 and the light deflecting device 15 , the computer 38 can assign each distance position of the light deflecting device 15 to a measured distance value. The evaluation of the measurement data in the computer 38 consists of monitoring a protective field 122 '' previously stored in polar coordinates, as shown schematically in FIG. 12 for a driverless, self-controlling vehicle 120 in front of the laser radar 121 according to the invention mounted on the front of the vehicle 120 is. Whenever the protective field 122 '' detects the lane edge 101 detectable by the laser radar 121 or another obstacle 123 ( FIG. 11), a corresponding countermovement movement can be triggered, the sector S1 to S16 also determining where the obstacle is located becomes.

Fig. 10 shows the simplest case of application at a equipped on the front with an inventive laser radar 121 autonomously controlled vehicle 120, in which the protective field 122 responsive to two lane boundaries one hundred and first As soon as the protective field 122 detects one of the limitations 101 , the laser radar 121 initiates a countermovement movement.

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

According to Fig. 12, the protective field 122 '' in front of the vehicle 120 is so differentiated that different critical distances S1 to S16 can be provided for different angle sectors, so that not only obstacles he knows, but also their angle and their distance from the Location of the laser radar 121 can be determined.

Fig. 13 shows a self-navigating vehicle 120 , the navigation device 125 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 area 124 from time to time, where the coordinates of the environment are known, the navigation device 125 can correct to the current status.

The application shown with reference to FIG. 14 is 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 such 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 , against which 121 people who approach the machine are to be protected by the laser radar device according to the invention. It is essential that the protection area 127 can be limited by the laser radar device 121 according to the invention so that a person at 103, for example, at a non-hazardous location, although it is in the scanning angle range 54, is not recognized, while one, for example, at 104 a person at risk is recognized, which then z. B. leads to switching off the dangerous machine 126 .

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

At the interface 39 ( FIG. 3), for example, in the case of the application according to FIG. 11, an obstacle removal signal r is generated which, for. B. can be used 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.

In the navigation support of FIG. 13 may be at a measurement rate of 360 measurements in 40 ms to work. The lateral resolution can be 0.5 ° in all cases, while the distance resolution can be reduced to ± 5 cm.

The distance-limited protection area 127 according to FIG. 14 can be 3 to 4 inches, in which case the detection time is 80 to 120 ms with a resolution of 5 cm.

According to the invention, the counter 30 is constructed from two asynchronous individual counter chains, with one counter on the positive and one counter on the negative edge of the 1.5 GHz clock incremented, so that a resolution of 330 ps results from adding the two counter readings. How this happens in detail is explained below:

According to FIG. 5, the counter 30 has two asynchronously operating invention contains single counter 50, 51, the clock inputs 105, 106 is driven through an OR gate 71. It is important that the output 72 for the clock input 106 of the individual counter 51 is inverted with respect to the output 72 'for the clock input 105 of the individual counter 50 . The two inputs of the OR gate 71 are connected via a test count 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 maximum frequency voltage input 59 , which is acted upon by the frequency generator 52 with a maximum frequency voltage of 1.5 GHz.

The switching input of the flip-flop 76 is present at the output of an OR gate 75 , the two inputs of which are acted upon by the pulse laser 11 via the line 45 (see also FIG. 3), while the other input is present at a test start input 58 which is connected via a Control line 65 is connected to the computer 38 .

The output of the comparator 34 ( FIG. 3) is shown in FIG. 7 via the line 62 to the measurement stop input 61 of the counter 30 , which in turn is connected to the 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 38 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 of the two input count signals and feeds them to an output stage 70 via the multiplexer 68 .

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

The test count pulse input 55 is controlled by the computer 38 via a control line 56 . The test start input 58 is also struck by a 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 38 via a reset input 63 and a control line 64 .

The counter 30 explained with reference to FIG. 5 performs the following functions during operation of the laser radar device according to the invention:

While the rotating mirror 16 sweeps over the useful scanning angle range 54 (FIGS . 2, 14, 16), each light pulse 12 emitted by the pulse laser 11 triggers a switchover of the flip-flop 76 at the moment it is emitted 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 applied to its other input to the OR gate 71 . From there, the maximum frequency voltage now reaches the counter inputs 105 , 106 of the individual counters 50 , 51 , but the count signal reaching the counter input 106 of the second counter 51 is shifted by 180 ° in relation to the count signal at the input 105 due to the inverted output 72 of the OR gate 71 is. In other words, the counter 50 counts the rising edges of the positive half-waves, the individual counter 51 the falling edges of the negative half-waves. As a result, two bits are generated by the individual counters 50 , 51 from the frequency generator 52 during each period of the maximum frequency voltage, in each case 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 via the comparator 34 , the line 62 , the measurement stop input 61 and the OR gate 74 a stop signal is given to the reset input 112 of the flip-flop 76 . 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 , to which this has been reported via line 46 ( FIG. 3), not only the measured counters would be available after summation in the addition stage 69 via the multiplexer 68 and call the output stage 70 , but also perform two tests.

After during each period of the maximum frequency voltage two bits will be generated at a frequency of 1.5 GHz a temporal resolution in the runtime measurement (t) of 330 ps and thus a distance measuring accuracy of 5 cm / bit achieved.

After a runtime measurement has been carried out in this way, the computer 38 switches over the control line 66 and the multiplexer switching input 67 to the multiplexer 68 , so that the latter can now deliver the counter present on the line 109 to the computer 38 via the second counter 51 . There is now a comparison of the sum output signal of the addition stage 69 with twice the counter status of the second counter 51 takes place. If all components work properly, the two numerical values may differ by at most one bit. If this is determined by the computer 38 , this is a sign that all components have worked properly. However, if this comparison reveals a difference of several bits, the computer 38 generates an error signal and, for example, stops the dangerous work machine 96 according to FIG. 16.

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

In the latter case, the computer 38 also carries out a further security test such that test counts are given to the test count input 55 via the feed line 56 , which trigger 71 counting processes in the individual counters 50 , 51 via the OR gate 71 , but these Test counting is about 300 times slower, for example with 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 manner similar to that which takes place in the actual measuring process via the measuring start input 57 .

A test counting process which has been triggered once is continued until the counters 50 , 51 are full, whereupon a stop signal is sent to the reset input 112 of the via the overflow output 107 of the second individual counter 51 , the reset line 77 and the OR gate 74 Flip-flops 76 is issued. More 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 , to determine whether the actual meter readings match the target value.

This second test, which is also only performed once after each scan, can be used to check whether the logic functions are working correctly. Since the computer 38 generates the positive and negative flanks triggering the count at the test input 55 , it can easily check the correct function by comparing the counter readings obtained with the number of flanks issued. Logical malfunctions and destroyed signal lines can be reliably detected in this way.

The arrangement of two individual counters 50 , 51 in the counter 30 therefore not only has the advantage of doubling the time resolution, but also enables the two security tests described above.

FIGS. 4 and 7 show that in that region of the 360 ° scan of the rotary mirror 16, which angular range outside of the sample 54 (Fig. 2), the test devices may be angeord net. One of these test devices consists of a test body 86 arranged in the region of the transmitted light pulse bundle 21 , which preferably consists of a light-scattering material. It can be a sintered glass pane (glass frit) in which the light is scattered on the crystalline particles. A blackened ring aperture 87 around the area where the transmission pulse light bundle 21 strikes reduces unwanted stray light effects.

Since the scattering properties of the test body 86 are known and stable, the faultless operation of the pulse laser 11 and the receiving system can be tested by evaluating the received signal of the photoreceiver 23 , which is preferably designed as an avalanche receiver.

The received signal Us of the photo receiving arrangement 22 is calculated using the following formula:

Us = PsRrRqMRt (2)

In this formula:

Us: reception signal
Ps: transmission power
Rr: test target reflectance
Rq: quantum efficiency
M: multiplication factor of the avalanche diode 23 used
Rt: transimpedance of avalanche diode 23 (effective load resistance of the diode)

The computer now checks whether the received signal Us reaches at least the value of a predetermined limit constant K1. If this is the case, the transceiver arrangement is rated as faultless and the measurement is continued. If, however, the received signal Us drops in the above-described test under K1, the computer 38 reports an error and switches off, for example, the dangerous work machine 126 according to FIG. 14.

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

The noise level determined by the noise level meter 36 is calculated using the following formula

Ur = (2q iM ^{1 + kf} _g ) ^1/2 Rt (3)

The computer 38 then checks whether the following requirement is met:

In the above formulas:

I: photocurrent in photodiode 23
Ur: noise voltage due to the illumination by the LED 88
M: multiplication factor of the avalanche diode 23
Elementary charge (1.6 · 10 ^-19 Coulomb)
Rt: Transimpedance of the avalanche diode 23
f _g : cut-off frequency of the noise
K2: second limit constant

FIGS. 4 and 9 of the windshield 41 are below the lower end face 89 uniformly distributed over the scan angle 54 light emitting diodes arranged 91, which each emit a light barrier beam 98 upward, the one shown in FIGS. 4 and 9 angled lower part of the windscreen 41 traverses and then passes through the inclined main part of the front window 41 to an associated photo receiver 92 arranged above it. The inclination of the main part of the front window 41 not only makes sense to create a passage for the vertical right light barrier rays 98 , but also to keep the inside reflex of the front window 41 away from the photo receiving arrangement 22 .

According to the invention, the lower angled part of the front pane 41 is distributed over the circumference of two areas 41 'matted or roughened on its outer surface, through which the sharply focused light 131 emanating from the associated light transmitter 91 in the absence of a smoothing oil film shown in FIG. 4 128 is scattered into a western larger solid angle region 129 , so that the associated light receiver 92 receives only a small amount of light from the light transmitter 91 .

Now strikes on the roughened outer surface of the matted area 41 ', for example an oil film 128 never, this cancels the strong light scattering of the bundle 131 due to the low refractive index compared to the underlying material of the front window 41 , so that now a concentrated light bundle 130 meets the assigned light receiver 92 and triggers a much 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 matted 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 matted area 41 'in order to create redundancy in the event of a defective optoelectronic component.

According to FIG. 9, the light-emitting diodes 91 are transitions from a range of 113 of a multiplexer connected to 93, which is controlled by the computer 38 and is fed via a pulse shaper 95 with rectangular pulses.

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

The described arrangement of LEDs 91 and receiving diodes 92 is used to monitor the contamination of the front window 41st They work as follows:

The computer 38 clocks the multiplexer 93 in such a way that it successively outputs a rectangular pulse via the pulse shaper 95 to the transmitter diodes 91, which are arranged uniformly on the circumference of the scanning angle region 54 . The opposite reception diodes 92 are activated in the same rhythm by the multiplexer 94 being clocked by the computer 38 in the same way as the multiplexer 93 , as a result of which the outputs of the individual reception diodes 92 are sent to the amplifier 96 and the analog-digital converter 97 one after the other be created. As a result, the computer 38 continuously receives signals from the individual receiving diodes 92 . By comparing a predetermined target reception strength with the actual reception strength of the light rays 98 , the computer 38 can thus recognize dirt on the front window 41 . If excessive contamination is detected at at least one point, the computer 38 reports this to the interface 39 , and a warning or switch-off signal can then be emitted, for example.

When evaluating the received signals of the light receiver 92 , which are assigned a matted area 41 ', the computer 38 distinguishes between a decrease and an increase in the received signal, so that both darkening Ver pollution and an oil film in the between the light sensor of 91 and the light beam 92 extending light bundle can be recognized. But it is also possible that the matted area 41 'assigned light transmitter-Lichtempfän ger pair 91 , 92 is used only for the detection of liquid films, so that the computer 38 when connecting such a light transmitter-light receiver pair 91 , 92 only on one appeals to increased light reception.

In addition to the preferably four measuring light barrier beams 98 , two redundantly constructed reference branches are to be provided, the beam path of which does not lead through the pane, where the temperature response of the transmitting diodes and the pulse current source can be eliminated by appropriate signal comparison in the computer 38 . By two-channel design of the reference branches, the circuit is designed so that any malfunction is revealed.

According to the invention, the engine speed is also determined by the computer and monitors the system timing. There is a temporal and logical program flow monitoring.

The electronic functions are monitored according to the invention by means of a RAM, ROM, ALU, watchdog test, A / D converter (contamination measurement, noise level measurement), D / A converter (comparator test), peak value 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 provided. Evidence of System management is based on a worst-case current account. The laser is controlled in a fail-safe manner (Eye safety). Access protection for the Setup mode can be reached via pass words. By the Light curtain described is a contamination detection and warning guaranteed.

There is a defined startup behavior of the system or the interface. After turning on the device all of the above Go through tests.  

The sensitivity of the transmitter-receiver arrangement is so set that objects with a reflectivity up to down to 2% can be recognized.

The laser radar device is housed in FIG. 4 in a housing 115 , which is closed at the front by a cover cap 116 , in the lower region of which the windshield 41 curved over 180 ° is provided. According to FIG. 4, for example, Sen housed and receiver in a compact unit as ausgebil Deten transmitter-receiver unit 49 in the form of a cylindrical housing.

Claims (47)

1. Laser distance determination device according to the pulse-on-time method with a pulse laser ( 11 ), which sends controlled light pulses ( 12 ) into a measuring area ( 13 ), a photo receiving arrangement ( 22 ) which the object ( 14 ) located in the measuring area ( 13 ) recovered Light pulses ( 12 ') receives and an evaluation circuit ( 23 , 30 , 34 , 36 , 37 , 38 , 39 , 40 ) which, taking into account the speed of light from the time between transmission and reception of a light pulse ( 12 , 12 ') a for the distance of the object ( 14 ) from the pulse laser ( 11 ) characteristic distance signal determined, characterized in that between the measuring area ( 13 ) and the pulse laser ( 11 ) a light deflection device ( 15 ) is arranged, which the successive light pulses ( 12 ) among themselves increasingly changing angles in the measuring range ( 13 ) and at the same time to the evaluation circuit ( 23 , 30 , 34 , 36 , 37 , 38 , 39 , 40 ) an angular position signal representative of their current angular position, and that the evaluation circuit ( 23 , 30 , 34 , 36 , 37 , 38 , 39 , 40 ) from the distance signal and the angular position signal signals the location of the object ( 14 ) within the measuring range ( 13 ), the distance angle range ( 54 ) preferably being greater than 90 ° and in particular smaller than 270 ° and preferably being approximately 180 ° and expediently the pulse light rays preferably define a horizontal scanning plane ( 53 ). 2. Device according to claim 1, characterized in that the light pulse duration is so short that during this time the light deflecting device ( 15 ) can be regarded as practically stationary. 3. Device according to claim 1 or 2, characterized, that the light pulse duration a few nanoseconds, expedient sometimes 1-5, preferably 2-4 and in particular about 3 is ns. 4. Device according to one of the preceding claims, characterized in that the angular velocity of the light deflection device ( 15 ) 0.5 · 10 ⁴ to 2 · 10 ⁴ , in particular about 1 · 10 ⁴ ° / sec be. 5. Device according to one of the preceding claims, characterized in that the distance between successive transmitted light pulses ( 12 ) by several powers of ten, preferably by magnitudes 4 powers of ten greater than the pulse length and / or that preferably the pulse sequence frequency between 5 to 50th , expediently 10 to 40, and in particular about 20 kHz. 6. Device according to one of the preceding claims, characterized in that the light deflecting device ( 15 ) comprises a preferably planar rotating mirror ( 16 ). 7. The device according to claim 6, characterized in that the rotating mirror ( 16 ) about one of the incident light rays, preferably the central incident light beam ( 18 ) is rotatable. 8. The device according to claim 7, characterized in that the axis of rotation ( 17 ) or the central incident light beam ( 18 ) at 30 to 60, preferably 40 to 50 and in particular 45 ° to the surface of the rotating mirror ( 16 ), the rotating mirror ( 16 ) seen in the direction of the axis of rotation ( 17 ) has a circular disc shape. 9. Device according to one of the preceding claims, characterized in that the rotating mirror ( 16 ) receives a transmission pulse light beam ( 21 ) substantially from above and radiates essentially union union horizontally. 10. Device according to one of the preceding claims, characterized in that the pulse light emitted preferably horizontally by the pulse laser ( 11 ) via a fixed, preferably planar deflecting mirror ( 19 ) by 90 ° to the rotating mirror ( 16 ), in particular is deflected downwards . 11. Device according to one of the preceding claims, characterized in that the pulse laser ( 11 ) is preceded by a transmission lens ( 33 ) forming a parallel transmission pulse light bundle ( 21 ). 12. Device according to one of the preceding claims, characterized in that the light deflecting device ( 15 ) also receives a received pulse light beam ( 20 ) and directs to the photo receiving arrangement ( 22 ), the transmit pulse light beam ( 21 ) and the receive pulse light beam ( 20 ) beyond the rotating mirror ( 16 ) are preferably coaxial to one another, and in particular the transmission pulse light bundle ( 21 ) runs centrally and has a circular cross section and the reception pulse light bundle ( 22 ) is arranged around the transmission pulse light bundle and has an annular shape Has cross section and both bundles ( 20 , 21 ) adjoin each other, so that the rotating mirror ( 16 ) has a central area ( 24 ) where the transmitted pulse light beam ( 21 ) meets and a peripheral area ( 47 ) where the receiving Impulse light beam ( 20 ) strikes, has. 13. Device according to one of claims 6 to 12, characterized in that the deflecting mirror ( 19 ) for the pulse light coming from the pulse laser ( 11 ) or the transmitting lens ( 33 ) opposite, in particular over a central region ( 24 ) of the rotating mirror ( 16 ) is arranged and the receive pulse light bundle ( 20 ) past the deflecting mirror ( 19 ) passes to the photo receiving arrangement ( 22 ), the deflecting plane mirror ( 19 ) in the direction of the receiving pulse light bundle ( 20 ) passing by it preferably having a circular cross section owns. 14. Device according to one of the preceding claims, characterized in that the photo receiving arrangement ( 22 ) comprises a receiving light on a photo receiver ( 23 ) concentrating the receiving lens ( 25 ). 15. The apparatus according to claim 13 and 14, characterized in that the diameter of the receiver lens ( 25 ) is so large that it next to the central region ( 24 ) on the peripheral region ( 47 ) of the rotating mirror ( 16 ) impinging the receiving Pulse light bundle ( 20 ) takes. 16. Device according to one of the preceding claims, characterized in that an interference filter ( 26 ) which is matched to the spectrum of the light emitted by the pulse laser ( 11 ) is arranged at the input of the photo-receiving arrangement ( 22 ). 17. Device according to one of the preceding claims, characterized in that the receiving lens ( 25 ) has two regions ( 25 ', 25 '') with different focal lengths, which are preferably concentric to one another. 18. 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 ), the cylinder axis of which coincides with the axis of rotation ( 17 ). 19. Device according to one of claims 1 to 17, characterized in that the rotating mirror ( 16 ) is formed on a flat mirror plate ( 78 ) which is attached to a rotatable mirror carrier ( 48 ). 20. Device according to one of the preceding claims, characterized in that the light deflecting device ( 15 ) sweeps a 360 ° deflection angle and preferably rotates continuously in one direction of rotation. 21. Device according to one of the preceding claims, characterized in that the rotating mirror ( 16 ) is arranged on a turntable ( 28 ) which is driven by a motor ( 31 ) to a continuous rotation with a preferably predetermined speed, the speed is expediently 1000 to 3000, in particular approximately 1500 rpm. 22. Device according to one of the preceding claims, characterized in that an angle transmitter ( 29 ) is arranged in the region of the turntable ( 28 ) and reports the instantaneous angular position of the turntable ( 28 ) to the evaluation circuit ( 38 , 40 ). 23. Device according to one of the preceding claims, characterized in that the evaluation circuit contains a computer ( 38 ) in which all the necessary arithmetic operations, in particular the calculation of the distance of the object ( 14 ) from the pulse transit time (t) are carried out. 24. Device according to one of the preceding claims, characterized in that the evaluation circuit comprises a counter ( 30 ) with preferably fixed clock frequency, which is so verbun with the pulse laser ( 11 ) or its trigger circuit that it is when a light pulse is emitted (12) is triggered, and is connected to the photoreceiver assembly (22) so that it is stopped on receipt of the same pulse of light (12 ') by the photo-receiving device (22), and that from the count the running time (t), and preferably the Distance of the object ( 14 ) is calculated. 25. The device according to claim 24, characterized in that the counter ( 30 ) is acted upon by a frequency generator ( 52 ), which expediently with a clock frequency of 0.5 to 3.0, in particular 1 to 2 and preferably about 1.5 GHz is working. 26. The apparatus according to claim 25, characterized in that the counter ( 30 ) is constructed from two asynchronous individual counters ( 50 , 51 ), one of which on the positive half-waves, in particular the rising edges of the positive half-waves, and the other on the nega tive half waves, in particular the falling edges of the negative half waves of a frequency generator ( 52 ) output maximum frequency voltage. 27. The apparatus according to claim 25, characterized in 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 of the transit time (t). 28. The apparatus of claim 26 or 27, characterized in that the sum of the individual counts with the doubled th count of one of the individual counters ( 50 , 51 ) compared and an error signal is emitted if the comparison is a difference by more than a few bits preferably results in one bit. 29. The device according to claim 28, characterized in that the comparison is carried out after each evaluation of a light pulse ( 12 , 12 '). 30. The device according to claim 28, characterized in that the comparison is carried out in the pause between the end of a scan of the scanning angle range ( 54 ) and the start of the next scanning of the scanning angle range ( 54 ). 31. The device according to any one of claims 26 to 30, characterized in that in the pause between two scans of the scanning angular range ( 54 ) the computer ( 38 ) delivers 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 number of counting pulses entered. 32. Device according to one of the preceding claims, characterized in that the photo receiving arrangement ( 22 ) via a comparator ( 34 ) is applied to the counter ( 30 ), the reference input ( 35 ) which defines the trigger threshold for the received signals, which directly for the noise level before the signal reception representative output signal of a noise level meter ( 36 ) is supplied, at the input of which the output signal of the photo receiving arrangement ( 22 ) is applied. 33. Apparatus according to claim 32, characterized in that the noise level meter ( 36 ) on the photo receiving arrangement ( 22 ) continuously detects the basic brightness and over a predetermined time that is large compared to the duration of a light pulse ( 12 , 12 ') and small compared to Time between two successive transmit light pulses ( 12 ) is averaged and that this average value is used as the average noise level. 34. Apparatus according to claim 33, characterized in that the averaging time carries about 30% of the time interval between two adjacent transmitted light pulses ( 12 ) be. 35. Device according to one of claims 32 to 34, characterized in that the trigger threshold ( 79 ) determined by the output signal of the noise level meter ( 36 ) by a multiple, preferably 2 to 10 times, in particular 4 to 8 times and particularly preferably approximately is 7 times greater than the average noise level found. 36. Device according to one of the preceding claims, characterized in that a peak value detector ( 37 ) is also applied to the output of the photo receiving arrangement ( 22 ), the output signal of which is used to generate correction values for compensating for the time measurement errors occurring as a result of signal dynamics. 37. Apparatus according to claim 36, characterized in 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 in the computer ( 38 ) which is dependent from the height of the maximum ( 80 , 81 , 82 ) occurring time measurement errors ( 84 , 85 ) are stored and that a corresponding correction value is determined as a function of the determined maximum ( 80 , 81 , 82 ) and the measured time is corrected accordingly to this correction value. 38. 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 arranged in the path of the scanning movement transmitting pulse light beam ( 21 ) and the computer ( 38 ) during the sweep of the test body ( 86 ) by the transmission pulse light bundle ( 21 ) checks whether the signal received by the photo receiving arrangement ( 22 ) is at least equal to a predetermined limit value (K1). 39. 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 transmitting pulse light beam ( 21 ) and the computer ( 38 ) during the scanning of the light-emitting diode ( 88 ) by an area corresponding to the received light pulse bundle ( 20 ) of the rotating mirror ( 16 ) checks whether the signal / noise ratio is at least equal to a predetermined limit value (K2). 40. Device according to one of the preceding claims, characterized in that the front screen ( 41 ) is curved around the axis of rotation ( 17 ) and extends in the scanning direction at least over the scanning angle range ( 54 ). 41. Apparatus according to claim 40, characterized in that the front pane ( 41 ) is traversed at a plurality of locations along its circumference by light barrier beams ( 98 ) which emanate from light transmitters ( 91 ) arranged in the region of one end face ( 89 ) thereof and from in the area of their other end face ( 90 ) arranged th light receivers ( 92 ) are received. 42. Apparatus according to claim 41, characterized in that the light transmitter ( 91 ) for sequential control with pulses and the light receiver ( 92 ) for appropriate evaluation of the received pulses via multiplexers ( 93 and 94 ) to the computer ( 38 ) ruled out which, when at least one received signal has dropped below a predetermined minimum value, emits a contamination signal. 43. Device according to one of the preceding claims, characterized in that the windshield runs obliquely from top to bottom in the direction of the rotating mirror ( 16 ) and preferably at its lower end by a clear angle, which can be approximately 90 °, in the opposite direction is angled in order to bring about a double passage of the light barrier beam ( 98 ) through the windshield ( 41 ), first from the inside of the housing ( 115 ) to the outside and then from there back to the inside of the housing ( 115 ) . 44. Apparatus according to claim 43, characterized in that at least a region ( 41 ') of the windshield ( 41 ), which is preferably near a light transmitter ( 91 ) and far from the associated light receiver ( 92 ), is formed matt on its outer surface , in such a way that when the area ( 41 ') of the assigned light receiver ( 92 ) is not contaminated it receives a quantity of light weakened by light scattering and in the presence of a liquid, in particular oil film ( 128 ) on the area ( 41 ') the assigned light receiver ( 92 ) receives an increased amount of light, and that a pollution signal is emitted when the light reception at the associated light receiver ( 92 ) exceeds a predetermined value. 45. Apparatus according to claim 44, characterized in that on the front window ( 41 ) distributed over the circumference two matted areas ( 41 ') and associated light transmitter ( 91 ) and light receiver ( 92 ) are available. 46. Device according to one of claims 22 to 45, characterized in that to the computer ( 38 ) an interface ( 39 ) is ruled out, at the output of which the desired output signals and values, including error signals, are accepted and supplied for further use can. 47. Laser distance determination device according to one of the preceding claims, characterized in that it is applied

• - In the self-control of vehicles ( 120 ) to create a defined protection area ( 122 ) in front of the vehicle ( 120 );
• - By arrangement on the front of a vehicle ( 120 ) for collision protection with obstacles ( 123 ) by defining a corresponding protection area ( 122 ');
• - 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 on 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 correct functioning and corrected if necessary;
• - machine in the protection of persons (104) to dangerous work (126) by defining a entfernungsbe excluded scope (127), wherein the dangerous work machine (126) is suitably in the side facing away from the inventive device (121) end portion of the scope (127) or located under the machine.