DE20022683U1 - Optoelectronic device - Google Patents

Description

Φ m ···

&Rgr;0131900

Leuze electronic GmbH + Co.
73277 Owen/Teck

Optoelectronic device

The invention relates to an optoelectronic device according to the preamble of claim 1.

Such an optoelectronic device is known from DE 43 41 080 Cl. To locate objects in a monitoring area, the optoelectronic device has a transmitter that emits transmitted light beams and a receiver designed as a spatially resolving detector that receives received light beams, which are integrated in a common housing. The transmitted light beams are deflected by a deflection unit and thus periodically guided within a monitoring area. The distance of objects in the monitoring area is determined using a phase measurement. Based on the phase measurement, the transit time difference of the received light beams reflected by an object with respect to the transmitted light beams emitted by the transmitter is determined.

A test object is arranged inside the housing outside the monitoring area. The L transmitted light beams reflected back to the receiver from the test object as received light beams are evaluated in an evaluation unit for functional testing of the optoelectronic device with regard to their amplitude.

This can be used, for example, to check whether the transmitter or receiver is functioning properly. Faults caused by aging or contamination of components can also be detected using the test measurement against the test object.

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However, the test measurement against the test object does not provide any information about whether the distance measurement for locating the objects in the monitoring area is carried out correctly. In fact, any errors that may occur during the distance measurement cannot be eliminated by the test measurement.

The invention is based on the object of designing an optoelectronic device of the type mentioned at the outset in such a way that the most accurate and verifiable detection of objects in the surveillance area is ensured.

To solve this problem, the features of claim 1 are provided. Advantageous embodiments and expedient further developments of the invention are described in the subclaims.

The optoelectronic device according to the invention has a distance sensor that operates according to the pulse transit time method. The distances of the objects to the optoelectronic device are determined by determining the transit time t of the transmitted light pulses emitted by the transmitter and the transmitted light pulses reflected back by objects within the monitoring area to the receiver of the distance sensor as received light pulses.

According to the invention, a portion of the light quantity is extracted from the transmitted light pulses as a reference transmitted light pulse and guided to the receiver via a reference path.

The evaluation unit of the optoelectronic device determines the transit time tR of the reference transmitted light pulse that is sent to the receiver as a reference received light pulse. The transit time difference to - tR is then used to determine the distance of an object.

The basic idea of the invention is therefore to transfer all distance measurements carried out with the transmitted light pulses to a

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Reference measurement carried out on the reference transmitted light pulse, whereby the length of the reference path is known in advance and advantageously stored in the evaluation unit.

By evaluating the transit time difference t0 - tR, internal measurement errors that occur during distance measurement are largely eliminated. One reason for such measurement errors is that the emission of a transmitted light pulse does not occur at the same time as the activation of the transmitter by a trigger pulse or the like. Rather, the emission of the transmitted light pulse occurs with a slight delay due to the finite transit times of the electrical signals in the individual components, whereby these transit times fluctuate as a result of temperature fluctuations, operating voltage fluctuations or as a result of aging of components.

The same applies to the registration of the received light pulses at the receiver. Their conversion into electrical reception signals and their amplification are subject to delay times, which are also subject to fluctuations caused by interference.

When determining the travel times to for determining the distance of objects in the monitoring area and when determining the travel times tR for the reference measurement, the same fluctuating delay times eii are superimposed on the distance measurement values. These interference-prone delay times are eliminated when the travel time difference ^ - tR is formed, which significantly increases the accuracy and reproducibility of the distance measurement.

It is particularly exemplary that the referencing of the distance measurement is carried out continuously for all transmitted light pulses fed into the monitoring area.

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This advantage is particularly present when the transmitted light pulses are periodically guided within the monitoring area by means of a deflection unit. Then, for each deflection position of the deflection unit, a reference transmitted light pulse for a reference measurement is coupled out from a transmitted light pulse guided into the monitoring area.

What is particularly advantageous here is that the decoupling of the reference transmitted light pulse does not limit the usable monitoring area.

If the deflection unit is formed, for example, by a deflection mirror that periodically guides the transmitted light pulses within a full circle in the angular range from 0° to 360°, no separate angular range needs to be left out for the reference measurement. Instead, the full angular range covered by the transmitted light pulses is available for object detection.

A further significant advantage of the device according to the invention is that the distance measurement within the entire monitoring area is continuously monitored by means of the continuous referencing of the object detection by means of the reference measurements carried out with the reference transmitted light pulses.

This makes it easy to meet the requirements for the use of the optoelectronic device in the field of security technology and personal protection. A particularly advantageous feature here is that the reference measurements according to the invention mean that a multi-channel structure of the components for determining the propagation time differences is not necessary.

The invention is explained below with reference to the drawings. They show:

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Figure 1: Longitudinal section through the optoelectronic device according to the invention.

Figure 2: Cross section through the optoelectronic device according to Figure

1.
5

Figure 3: Longitudinal section through the exit window of the device according to Figures 1 and 2 with a reflection surface for coupling out a reference transmitted light pulse.

Figure 4: First diagram for evaluating the propagation times of the transmitted light pulses and reference transmitted light pulses of the device according to Figures 1-3.

Figure 5: Second diagram for evaluating the runtimes of the transmitted light pulses and reference transmitted light pulses of the device

according to figures 1-3.

Figure 1 shows a schematic representation of the structure of an embodiment of the optoelectronic device 1 according to the invention for detecting objects in a surveillance area. In addition to objects, objects in the surveillance area also include people who enter the surveillance area.

The optoelectronic device 1 has a distance sensor operating according to the pulse transit time method with a transmitter 3 emitting transmitted light pulses 2 and a receiver 5 receiving received light pulses 4. The transmitter 3 is formed, for example, by a laser diode. A photodiode or the like is provided as the receiver 5.

A transmitting optics 6 is arranged downstream of the transmitter 3 for beam shaping of the transmitted light pulses 2. A receiving optics 7 is arranged upstream of the receiver 5 for focusing the received light pulses 4 on the receiver. The transmitter 3 and the receiver

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Receivers 5 are connected to an evaluation unit (not shown) which is formed by a microprocessor or the like.

To determine the distances of objects in the monitoring area, the transit time t of the received light pulses 4 directed to an object and reflected back to the receiver 5 as received light pulses 4 is determined. The corresponding distance values are calculated from the transit times in the evaluation unit.

The transmitted light pulses 2 and the received light pulses 4 reflected from an object back to the device 1 are guided via a deflection unit 8. In the present embodiment, the transmitted light pulses 2 are guided to the deflection unit 8 via a stationary mirror 9. In the present example, the deflection unit 8 consists of a deflection mirror 10 which sits on a base 11 which can rotate about an axis of rotation D running in a vertical direction. The base 11 is set in a rotary movement at a constant speed by means of a motor (not shown). Both the transmitted light pulses 2 emitted by the transmitter 3 and the received light pulses 4 reflected from an object are guided via the deflection mirror 10. In principle, the deflection unit 8 can also have several deflection mirrors 10, whereby in particular the transmitted light pulses 2 and received light pulses 4 can be guided via separate deflection mirrors 10.

The optoelectronic device 1 is integrated in a housing 12 which has an exit window 13 on its front side through which the transmitted light pulses 2 are guided into the monitoring area and through which the received light pulses 4 are guided back to the device 1.

As can be seen from Figure 2, the exit window 13 runs in the circumferential direction of the housing 12 along a circular arc and extends over an angular range of Δα = 180°. The transmitting beams deflected at the deflection unit 8

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light pulses 2 are guided periodically within the full angular range of 360°.

The transmitted light pulses 2 are guided through the exit window 13 into the monitoring area lying in a horizontal plane within the angular range Δα between 0° and 180°. Within the angular range between 180° and 360°, however, the transmitted light pulses 2 are sensed inside the housing 12.

According to the invention, a portion of the light quantity is extracted from each transmitted light pulse 2 as a reference transmitted light pulse 2', which is used for a reference measurement. For this purpose, the reference transmitted light pulse 2' is fed back to the receiver 5 as a reference received light pulse 4'.

An example of such a coupling out of a reference transmitted light pulse is shown in Figure 3. For this purpose, a reflection surface 14 is provided in the center of the exit window 13. The width of the reflection surface 14 is considerably smaller than the beam diameter of the transmitted light pulses 2. The reflection surface 14 extends in the circumferential direction over the entire length of the exit window 13. The reflection surface 14 is formed, for example, by the surface of a coating applied to the inside of the exit window 13. Alternatively, the exit window 13 can be locally roughened to produce the reflection surface 14. In any case, the part of a transmitted light pulse 2 striking the reflection surface 14 is diffusely reflected and guided via the deflection unit 8 to the receiver 5. Since the reflection surface 14 extends over the entire length of the exit window 13, in each angular position of the deflection unit 8 the same portion of a transmitted light pulse 2 is coupled out by reflection from the reflection surface 14 and guided to the receiver 5 as a reference received light pulse 4'.

In principle, the reference transmitted light pulses 2' can also be transmitted via a not shown optical waveguide or the like from the transmitter 3 to the receiver

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5. The optical waveguide, which is designed as an optical fiber, for example, has a light entry surface arranged downstream of the transmitter 3, via which a defined part of the amount of light of a transmitted light pulse 2 is coupled into the optical waveguide. The advantage here is that the reference transmitted light pulse 2' does not have to be guided via the deflection unit 8 and is guided directly from the transmitter 3 to the receiver 5.

In any case, the reference transmitted light pulses 2' are guided completely within the housing 12, whereby the reference distance that a reference transmitted light pulse 2' travels from the transmitter 3 to the receiver 5 is known and stored as a parameter in the evaluation unit.

According to the invention, to determine the distance of objects in the surveillance area, it is not the transit time to of the transmitted light pulses 2 that is evaluated directly, but rather the transit time difference to - tR of a transmitted light pulse 2 and the respective associated reference transmitted light pulse 2'. If the light path of the reference transmitted light pulse 2' is known, the object distance can then be determined from this transit time difference in the evaluation unit.

Figures 4 and 5 show schematically two embodiments for evaluating the runtime differences to - tR, each in a diagram.

In both cases, the analogue reception signals generated by the reception light pulses 4 or reference reception light pulses 4' arriving at the receiver 5 are quantized. The quantized reception signal sequence E corresponding to the temporal progression of the reception signal is then read into the individual registers R of a memory element (not shown). The memory element can be formed by a semiconductor memory or a CCD array.

As shown in Figures 4 and 5, the receiving light pulse 4 and the associated reference receiving light pulses 4' are each

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Received signal sequence E is read into the registers R of the memory element. The signal values of the quantized received signal sequence E stored in the individual registers R are read out in cycles using an oscillator clock and evaluated in the evaluation unit. To determine the propagation time difference t0 - tR, the register positions defining the positions of the received light pulse 4 or the reference received light pulse 4' are determined. The difference between the register positions of the received light pulse 4 and the associated reference received light pulse 4' results in the propagation time difference t0 - t _R when the clock rate at which the received signal sequence E is read into the registers R is known.

Figure 4 shows a first embodiment of such an evaluation. In this case, the analogue received signal is converted into a binary signal sequence by means of a threshold value unit (not shown). If a received light pulse 4 or a reference received light pulse 4' is present, the received signal sequence E quantized in this way takes on the value 1, while otherwise it takes on the value 0. The register position defining the position of the received light pulse 4 or reference received light pulse 4' is preferably predetermined by the center of the respective received light pulse 4 or reference received light pulse 4'.

Figure 5 shows a second embodiment of such an evaluation. In this case, the analogue received signal is quantized by means of an analogue-digital converter (also not shown). In accordance with the word width η of the analogue-digital converter, the amplitude of the analogue received signal is mapped to 2 ⁿ discrete amplitude values of the quantized received signal sequence E. Preferably, an analogue-digital converter with a word width of η = 8 is used.

Figure 5 shows schematically the amplitude curves of the received signal sequence E generated by the analog-digital converter and running in discrete steps.

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with a received light pulse 4 and an associated reference received light pulse 4'.

To determine the transit time differences t0 - tR, either the positions of the maxima or the positions of the centers of gravity of the received light pulse 4 and the reference received light pulse 4' are determined. The differences between the corresponding registration positions in turn provide the transit time difference t0 - tR.

Since the quartization of the analogue received signal by means of an analogue-digital converter with a sufficiently large word width results in a far more detailed profile of the amplitudes of the received light pulses 4 and reference received light pulses 4' than is possible when using a threshold unit, this type of determination of the propagation time difference is considerably more accurate.
15

Alternatively, a time measuring module (not shown) can be used to determine the transit time difference t0 - tR. The received light pulse 4 and a reference received light pulse 4' assigned to it are read in via separate inputs of this time measuring module. These two inputs are preferably formed by the start and stop inputs of this time measuring module.

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P0131900

Leuze electronic GmbH + Co. 73277 Owen/Teck

List of reference symbols

(1) Optoelectronic device

(2) Transmitted light pulse

(2') Reference transmitted light pulse

(3) Sender

(4) Received light pulse

(4') Reference received light pulse

(5) Recipient

(6) Transmission optics

(7) Receiving optics

(8) Deflection unit

(9) Mirror

(10) Deflecting mirror

(11) Base (12) Housing

(13) Exit window

(14) Reflection surface

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Claims (15)

1. Optoelectronic device for detecting objects in a surveillance area with a transmitter emitting transmitted light, a receiver receiving received light and with an evaluation unit in which the transit time t _o of the transmitted light guided in the surveillance area and reflected back by the object as received light is evaluated to determine the distance of an object, characterized in that the transmitter ( 3 ) emits the transmitted light in the form of a sequence of transmitted light pulses ( 2 ), that a part of the amount of light of a transmitted light pulse ( 2 ) is coupled out as a reference transmitted light pulse ( 2 ') and guided over a reference path to the receiver ( 5 ), that the transit time t _R of the reference transmitted light pulse ( 2 ') guided to the receiver ( 5 ) as a reference received light pulse ( 4 ') is determined in the evaluation unit, and that the transit time difference t _o -t _R is used to determine the distance of an object. 2. Optoelectronic device according to claim 1, characterized in that the transmitted light pulses ( 2 ) are periodically guided within the monitoring area by means of a deflection unit ( 8 ). 3. Optoelectronic device according to claim 2, characterized in that for each deflection position of the deflection unit ( 8 ) a reference transmitted light pulse ( 2 ') is coupled out from a transmitted light pulse ( 2 ) guided into the monitoring area. 4. Optoelectronic device according to one of claims 2-3, characterized in that it is integrated in a housing ( 12 ), that the transmitted light pulses ( 2 ) deflected at the deflection unit ( 8 ) are guided into the monitoring area via an exit window ( 13 ) integrated in the housing ( 12 ), and that a reflection surface ( 14 ) is arranged on the exit window ( 13 ), on which a part of the amount of light of the transmitted light pulses ( 2 ) is reflected as a reference transmitted light pulse ( 2 ') to the receiver ( 5 ). 5. Optoelectronic device according to one of claims 1-3, characterized in that the reference transmitted light pulses ( 2 ') are coupled into an optical waveguide arranged downstream of the transmitter ( 3 ) and are guided via this to the receiver ( 5 ). 6. Optoelectronic device according to one of claims 4 or 5, characterized in that the reference transmitted light pulses ( 2 ') are guided completely inside the housing ( 12 ). 7. Optoelectronic device according to one of claims 1-6, characterized in that to determine the transit time difference t _o -t _R between a transmitted light pulse ( 2 ) reflected back from an object as a received light pulse ( 4 ) and a reference received light pulse ( 4 '), the amplitudes of the analog received signal present at the output of the receiver ( 5 ) are quantized, that the quantized received signal sequence is read into the registers of a memory element at a predetermined rate, and that to determine the transit time difference, the difference between the register positions of the received light pulse ( 4 ) and reference received light pulse ( 4 ') is determined. 8. Optoelectronic device according to claim 7, characterized in that the analogue received signals are converted into a binary received signal sequence by means of a threshold unit. 9. Optoelectronic device according to claim 7, characterized in that the analog received signals are quantized by means of an analog-digital converter having a word width of n-bit. 10. Optoelectronic device according to claim 9, characterized in that the analog-digital converter has a word width of 8 bits. 11. Optoelectronic device according to one of claims 9 or 10, characterized in that to determine the register positions of the received light pulse ( 4 ) and the reference received light pulse ( 4 '), the position of the maximum or the center of gravity of the quantized received light pulse ( 4 ) or reference received light pulse ( 4 ') is determined. 12. Optoelectronic device according to one of claims 7-11, characterized in that the memory element is formed by a semiconductor memory or CCD array. 13. Optoelectronic device according to one of claims 1-6, characterized in that a time measuring module is provided for determining the transit time difference t _o -t _R , wherein a received light pulse ( 4 ) and the associated reference received light pulse ( 4 ') are read in via separate inputs of the time measuring module. 14. Optoelectronic device according to claim 13, characterized in that the inputs of the time measuring module are formed by a start input and a stop input. 15. Optoelectronic device according to one of claims 1-14, characterized in that it can be used as a safety device in the field of personal protection, wherein the components for determining the transit time difference t _o - t _R have a single-channel structure.