DE202023101662U1 - Optoelectronic sensor - Google Patents

Abstract

Optoelectronic sensor (1), in particular safety laser scanner, for fail-safe detection and distance determination of objects in a monitoring area (ÜB), with
a light transmitter (2) for emitting a transmitted light beam (2a),
a light receiver (3) for receiving a received light beam (2b) formed by light remitted or reflected by objects in the monitoring area (ÜB) and for generating a received signal, an evaluation unit (4) for determining the presence of an object and a distance to it in the monitoring area (ÜB) from the received signal,
a humidity sensor (13) for determining the relative humidity (F) in the monitoring area (ÜB),
a temperature sensor (12) for determining the air temperature (T),
wherein the evaluation unit (4) is designed to receive an air temperature value provided by the temperature sensor (12) and a relative air humidity value (F) provided by the humidity sensor (13) from the monitoring area (ÜB), and to calculate a dew point temperature value (τ) of the monitoring area (ÜB) and to carry out a comparison between the obtained air temperature value (T) and the calculated dew point temperature value (τ) in order to derive therefrom a presence of fog in the monitoring area (ÜB).

Description

The present invention relates to an optoelectronic sensor, in particular a safety laser scanner, for detecting and determining the distance of objects in a monitoring area according to claim 1.

An optoelectronic sensor, in particular a laser scanner, is used in many areas of everyday industrial life and is particularly well suited for distance measurements that require a large horizontal angle range of a monitoring area. In particular, the laser scanner is provided on preferably autonomously driving vehicles in order to deliver data regarding a monitoring area around the vehicle to a control system of the vehicle, so that collision-free navigation of the vehicle is possible.

In this case, a light beam generated by a light transmitter, such as a laser, periodically sweeps over the monitoring area as transmitted light. The transmitted light beam is remitted by objects in the monitoring area and received by a light receiver. The received light, referred to below as received light, is evaluated in the laser scanner using electronics. The light transmitter and the light receiver together form a signal detection unit of the laser scanner.

Such laser scanners are used in safety technology to monitor a source of danger, such as a dangerous machine. Such a safety laser scanner is known from the DE 43 40 756 A1 known. A protective field is monitored that the operating personnel must not enter while the machine is in operation. If the laser scanner detects an inadmissible intrusion into the protective field, such as an operator's leg, it triggers an emergency stop of the machine. Sensors used in safety technology must work particularly reliably and therefore meet high safety requirements, for example the EN13849 standard for machine safety and the EN61496 device standard for non-contact protective devices (ESPD). To meet these safety standards, a number of measures must be taken, such as secure electronic evaluation using redundant, diverse electronics, function monitoring or special monitoring of the contamination of optical components, in particular a front screen, and/or the provision of individual test targets with defined degrees of reflection that must be detected at the corresponding scanning angles.

When used outdoors, environmental influences, especially fog, rain and snow, pose particular challenges for reliability and trouble-free operation. While these weather influences can be excluded indoors as intended, they are inevitably present outdoors and cannot be controlled, but are very relevant for productive processes in the logistics or production environment. Complete freedom from interaction between the optical sensor and the weather influences is generally not possible with reasonable effort.

Laser scanners for pure automation and measurement tasks can largely suppress fog effects by reducing their sensitivity to such an extent that fog only becomes disruptive in extreme cases of very high density. Even then, there is at most a loss of usable measurement data, but no safety-relevant detection, so no further measures to control fog attenuation need to be provided.

In contrast, there are currently no satisfactory concepts for outdoor safety laser scanners, nor are there any other sensor technologies that provide data for secure monitoring on their own. Conventional safety laser scanners are mainly used indoors. Operation under the influence of rain and fog is excluded from the safety concept. For safe outdoor applications, such as autonomous or semi-autonomous driving, data from different sensors is merged.

If you simply use a conventional indoor laser scanner outdoors, the only problem that arises in the event of dense fog or severely impaired visibility is availability. The fog echo is sufficiently strong and the fog is treated as a safety-relevant object. Therefore, there is no safety-critical failure, just an unnecessary shutdown. At medium visibility, however, there is also the possibility that the fog itself does not cause a suprathreshold light echo, but its damping effect prevents the detection of a safety-relevant object because the object echo is too weak. The fog "swallows" the light. This is then even a dangerous error case, as the light echo is not sufficiently strong, even if objects are present in the protection area. A safe laser scanner must provide an error control measure for this error case.

In the EP 2 541 273 A1 The received signal is split into two paths for a high and a low frequency component at a splitter element The high-frequency component is used to detect hard targets or objects, while the low-frequency component is used to determine the visibility. This requires a double evaluation path that begins in the analog part of the evaluation.

According to the EP1980871B1 Safety is achieved by providing external reference cells that must be detected at a specific location. Such a solution is only possible for stationary applications and cannot be used for mobile applications, such as autonomous vehicles.

The EP3588139B1 describes a solution in which two distance measurements are taken at different sensitivities and a conclusion is drawn about the limitation of visibility from the comparison of the two distance measurements. This solution may be able to detect the onset of fog, but does not solve the problem of the error case in which fog absorbs the light.

It is an object of the invention to enable the use of an optoelectronic sensor outdoors.

The object is achieved according to the invention by an optoelectronic sensor having the features of claim 1.

Here, the optoelectronic sensor, in particular a safety laser scanner, for the fail-safe detection and distance determination of objects in a monitoring area, comprises a light transmitter for emitting a transmitted light beam, a light receiver for receiving a received light beam formed by light remitted or reflected by objects in the monitoring area and for generating a received signal, an evaluation unit for determining the presence of an object and a distance to it in the monitoring area from the received signal, a humidity sensor for determining the relative humidity in the monitoring area and a temperature sensor for determining the air temperature in the monitoring area, wherein the evaluation unit is designed to receive an air temperature value provided by the temperature sensor and a relative air humidity value provided by the humidity sensor from the monitoring area, and to calculate a dew point temperature value of the monitoring area and to carry out a comparison between the received air temperature value and the calculated dew point temperature value in order to derive therefrom the presence of fog in the monitoring area.

The advantage here is that critical fog with low visibility is reliably detected and a corresponding fog status bit is set as an output signal for protective field monitoring or a fog warning. If fog is detected, the vehicle speed can be reduced via a control of the autonomously driving vehicle and/or the protective field can be adjusted accordingly, so that availability is increased and detection capability is not restricted. The error safety is increased because the critical error case mentioned above, when the fog "swallows" the transmitted light, is recognized as such.

According to a preferred embodiment, the evaluation unit is designed to consider the results of the comparison over a defined period of time or over a predetermined number of measurements of the optoelectronic sensor in order to rule out incorrect deduction of the presence of fog. The evaluation over a predetermined period of time ensures that fog is always detected in order to initiate an error control measure if necessary.

The evaluation unit is advantageously designed to adapt a configuration of the optoelectronic sensor according to a result of the comparison. In particular, the evaluation unit is designed to change the monitoring area and/or to issue a warning signal if, after the defined period of time and/or after the specified number of measurements, the air temperature value is less than or equal to the dew point temperature value. This allows the monitoring area of the sensor to be adapted for improved availability, for example if fog is present but this does not yet have to lead to a shutdown, but a reduction in the size of the monitoring area would be sufficient to maintain operation.

Preferably, the evaluation unit is designed to cancel a change in the monitoring area and/or the warning signal if the air temperature value is greater than the dew point temperature value after the defined period of time and/or after the specified number of measurements. This means that if the temperature value is high, the presence of fog can be ruled out, so that, for example, the monitoring area is then set back to the size configured for fog-free conditions.

Furthermore, according to an alternative embodiment, the temperature and humidity sensors are combined in a thermo-hygrometer. The temperature and/or humidity The temperature sensor or the thermo-hygrometer can be integrated into the optoelectronic sensor, whereby the temperature/humidity sensor or thermo-hygrometer must be connected to the external climate that prevails in the monitoring area. This can be done, for example, by means of an air and moisture-permeable membrane or a grid. Alternatively, the sensors are arranged outside the laser scanner, for example on its housing. Both arrangements have the advantage that the environmental sensors form a compact unit together with the laser scanner.

If the temperature and humidity sensors are located outside the laser scanner housing, the required temperature and relative humidity values may be able to be measured at a greater distance from the sensor, which can better reflect the environmental conditions of the sensor, especially the monitoring area.

The air temperature and relative humidity values of the monitoring area can then advantageously be transmitted to the evaluation unit by means of a radio signal. A radio antenna is preferably provided in order to transmit and receive the air temperature value and the relative humidity value to the evaluation unit.

The optoelectronic sensor is preferably designed as a safety laser scanner, solid-state LIDAR sensor, camera or light grid.

Preferred embodiments and further developments as well as further advantages of the invention can be found in the dependent claims, the following description and the drawings.

• 1 eine schematische Schnittdarstellung eines bevorzugten Ausführungsbeispiels eines optoelektronischen Sensors; und
• 2 eine schematische Schnittdarstellung eines weiteren bevorzugten Ausführungsbeispiels des optoelektronischen Sensors.

The invention is explained in detail below using exemplary embodiments with reference to the drawing. In the drawing:

• 1 a schematic sectional view of a preferred embodiment of an optoelectronic sensor; and
• 2 a schematic sectional view of another preferred embodiment of the optoelectronic sensor.

1 shows a schematic sectional view of a preferred embodiment of an optoelectronic sensor 1 according to the invention, which is intended for detecting and determining the distance of objects (not shown) in a monitoring area ÜB. The sensor 1 preferably comprises a safety laser scanner, in particular a LIDAR sensor, very particularly a solid-state LIDAR sensor.

In the preferred embodiment shown, the sensor 1 has a light transmitter 2, a light receiver 3 and an evaluation unit 4. The light transmitter 2, which is preferably designed in the form of a laser diode or a vertical cavity surface emitting laser (VCSEL), emits a transmitted light beam 2a, which is preferably periodically amplitude modulated or preferably has at least one short light pulse. The transmitted light beam 2a is directed via a deflection mirror 5 and a movable deflection unit 6 as an emitted transmitted light beam 2a into the monitoring area ÜB and there by a possibly present - in the 1 not shown - object remitted or reflected.

A portion of the emitted transmitted light beam 2a returns to the sensor 1 as incident remitted transmitted light 2b and is deflected by the movable deflection unit 6 to a receiving optics 7. The remitted transmitted light 2b is bundled by the receiving optics 7 onto the light receiver 3, wherein the light receiver 3 is formed, for example, from at least one photodiode, avalanche photo diode (APD) or single-photon avalanche diode (SPAD).

The deflection unit 6 is generally a rotating mirror which rotates continuously, in particular by driving a motor 8. Alternatively, no rotating mirror is provided as the deflection unit 6, but the deflection unit 6 is designed as a rotating measuring head including a light transmitter 2 and a light receiver 3.

The respective angular position of the deflection unit 6 is recorded via an encoder 9. The transmitted light beam 2a generated by the light transmitter 2 thus covers the monitoring area ÜB generated by the movement of the deflection unit 6. If a remitted transmitted light 2b from the monitoring area ÜB is received by the light receiver 3, the angular position of the object in the monitoring area ÜB can be deduced from the angular position of the deflection unit 6 by means of the encoder 9. The described embodiment is based on a rotating signal-emitting unit whose transmitted light beam 2a covers the monitoring area ÜB.

The sensor 1 can also be designed as a so-called (not shown) solid-state sensor, in particular a solid-state LIDAR sensor, in which a large number of transmitted light beams 2a are directed into the monitoring area ÜB in different X and Y directions, which then allow the monitoring area to be covered with only a transmitted light beam. The remitted or reflected transmitted light 2b is received by an image sensor with numerous pixels designed as a light receiver 3. The spatial resolution is thus achieved by a large number of light beams. This means that moving parts in the sensor 1 can be dispensed with.

In addition, a light transit time is determined from the emission of the transmitted light beam 2a to the reception of the remitted transmitted light 2b after reflection on the object in the monitoring area ÜB. All light transit time methods are conceivable for this, in particular phase methods, pulse methods or pulse averaging methods, with pulse-based methods preferably being used in security applications. The distance of the object from the sensor 1 is determined from the light transit time using the speed of light. The evaluation takes place in the evaluation unit 4, which is connected to the light transmitter 2, the light receiver 3, the motor 8 and the encoder 9.

Two-dimensional polar coordinates of all objects in the monitoring area ÜB are then available via the angle and distance. In the monitoring area ÜB, for example, two-dimensional protective fields can be defined into which unauthorized objects such as operators or their body parts are not allowed to intervene. If the evaluation unit 4 detects an unauthorized intervention in the protective field, a safety-related shutdown signal is output via a safe output Out (OSSD, Output Signal Switching Device) in order to stop a monitored dangerous machine, for example the autonomously driving vehicle, or to bring it into a safe position. This is just one possible application of the sensor 1. Alternatively, measurement data is output via the output Out, for example.

All of the functional components mentioned are arranged in a housing 10, which has an optical window 11 in the area of the light exit and light entry. The optical window 11 in a laser scanner is often, but not necessarily, designed as a rotating body and does not necessarily have to extend over 360°, so that a certain angular range remains as a dead zone. Deviating from 1 Instead of a straight contour in cross-section, a curvature is also conceivable.

The evaluation unit 4 is designed to receive an air temperature and a relative humidity value T and F of the monitoring area ÜB. The air temperature and the relative humidity value T and F of the monitoring area ÜB can be detected by a temperature sensor 12 and a humidity sensor 13 or a thermo-hygrometer 14, wherein the temperature sensor 12 and the humidity sensor 13 or the thermo-hygrometer 14 transmit the detected air temperature T and relative humidity values F to the evaluation unit 4.

From the obtained air temperature values T and relative air humidity values F, the evaluation unit 4 calculates a dew point temperature value τ prevailing in the monitoring area ÜB. The evaluation unit 4 compares the obtained air temperature value T and the calculated dew point temperature value τ. From the comparison, the evaluation unit 4 deduces the presence of fog in the monitoring area ÜB. This means that if the air temperature value T recorded in the monitoring area ÜB is below the calculated dew point temperature value τ, this is evaluated as fog detection in the evaluation unit 4 and the presence of fog in the monitoring area ÜB is output as a suitable signal. If the recorded air temperature value T is greater than the calculated dew point temperature value τ, there is no fog in the monitoring area ÜB.

If the presence of fog in the monitoring area ÜB is inferred because the dew point temperature value τ is undershot, the evaluation unit 4 is designed, for example, to output a warning signal for the presence of fog for all protective fields. Additionally or alternatively, the speed of the autonomously driving vehicle (not shown) can be reduced. In this case, the evaluation unit 4 is particularly designed to adapt a configuration of the optoelectronic sensor 1 according to the result of the comparison, for example by reducing the protective fields according to the presence of fog. In the case of autonomously driving vehicles, this would typically be a reduction of the monitoring area boundary to, for example, less than or equal to 2 m. This improves the reliable scanning of the monitoring area ÜB by the sensor 1 and the availability of the sensor 1, since the effect of the signal attenuation by the fog on the receiving light 2b is recognized and a complete shutdown can be prevented by taking appropriate measures, such as shifting the monitoring area boundary.

Since fog is basically a slow weather phenomenon, the evaluation unit 4 is advantageously designed to consider results of the comparison over a defined period of time or over a predetermined number of measurements of the optoelectronic sensor 1 in order to exclude an erroneous deduction of the presence of fog. In other words, the evaluation unit 4 comprises in particular a low-pass filter set to a time period with which a temperature difference between the obtained air temperature value T and the calculated dew point temperature value τ is considered over the defined period of time of, for example, greater than or equal to one second. If, over this entire period of time, the air temperature value T at the recorded relative humidity value F is lower than the calculated dew point temperature value τ, then the evaluation unit 4 can conclude with a high degree of certainty that fog is present.

Alternatively, the low-pass filter can also be set in such a way that the comparison is considered over a predetermined number of measurements from sensor 1. If the air temperature value T is, for example, below the calculated dew point temperature value τ over 100 measurements from sensor 1 or, for example, over 100 of 200 measurements from sensor 1, on average, then the evaluation unit 4 can conclude with certainty that fog is present in the monitoring area ÜB. This has the advantage that if there is a brief, incorrect determination of the absence of fog, sensor 1 can still provide safe protective fields for the monitoring area ÜB.

The temperature sensor 12 and the humidity sensor 13 are advantageously provided on the sensor 1, with the temperature sensor 12 recording the air temperature value T and the humidity sensor 13 recording the relative humidity value F of the monitoring area ÜB and transmitting it to the evaluation unit 4. In particular, the temperature sensor 12 and the humidity sensor 13 can be integrated in the sensor 1. The temperature sensor 12 and the humidity sensor 13 are in contact with the monitoring area ÜB through a membrane (not shown), the membrane being semi-permeable in order to prevent water from penetrating the optoelectronic sensor 1. As an alternative to a membrane, a mechanical grid to protect the temperature and humidity in the sensor would also be conceivable. In an alternative, these sensors can also be located unprotected on the outer housing. The sensors can be read out via connecting wires that are sealed into the interior of the housing.

The temperature 12 and the humidity sensor 13 can, as in 2 shown, in particular as a thermo-hygrometer 14. In the preferred embodiment, the thermo-hygrometer 14 is arranged outside the optoelectronic sensor 1 and transmits the air temperature value T and the relative humidity value F by means of radio signals 14a to the evaluation unit 4 of the optoelectronic sensor 1. For this purpose, in particular a radio antenna 15 is provided on the thermo-hygrometer 14 and on the optoelectronic sensor 1.

The thermo-hygrometer 14 can preferably also be arranged on the optoelectronic sensor 1 and connected to the evaluation unit 4 by means of an electrical line.

Furthermore, the optoelectronic sensor 1 can be connected to an additional sensor, such as a pressure sensor or an optical sensor for determining visibility, so that the derived result of the optoelectronic sensor 1 can be verified or checked for plausibility taking into account a measurement result of the additional sensor. This makes the fog detection of the optoelectronic sensor 1 even more reliable and precise.

List of reference symbols

1

optoelectronic sensor

2

Light transmitter

2a

Transmitted light beam

2 B

Received light or remitted transmitted light

3

Light receiver

4

Evaluation unit

5

Deflecting mirror

6

movable deflection unit

7

Reception optics

8th

engine

9

Encoders

10

Housing

11

optical window

12

Temperature sensor

13

relative humidity sensor

14

Thermo-hygrometer

14a

Radio signal

15

Radio antenna

F

relative humidity value

T

Air temperature value

τ

Dew point temperature value

Out

safe exit

ÜB

Monitoring area

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 4340756 A1 [0004]
• EP 2541273 A1 [0009]
• EP1980871B1 [0010]
• EP 3588139 B1 [0011]

Claims (9)

Optoelectronic sensor (1), in particular a safety laser scanner, for fail-safe detection and distance determination of objects in a monitoring area (ÜB), with a light transmitter (2) for emitting a transmitted light beam (2a), a light receiver (3) for receiving a received light beam (2b) which is formed by light remitted or reflected by objects in the monitoring area (ÜB) and for generating a received signal, an evaluation unit (4) for determining the presence of an object and a distance to it in the monitoring area (ÜB) from the received signal, a humidity sensor (13) for determining the relative air humidity (F) in the monitoring area (ÜB), a temperature sensor (12) for determining the air temperature (T), wherein the evaluation unit (4) is designed to receive an air temperature value provided by the temperature sensor (12) and a relative air humidity value (F) provided by the humidity sensor (13) from the monitoring area (ÜB) and to calculate a dew point temperature value (τ) of the monitoring area (ÜB) and to make a comparison between the obtained air temperature value (T) and the calculated dew point temperature value (τ) in order to deduce the presence of fog in the monitoring area (ÜB). Optoelectronic sensor (1) according to Claim 1 , wherein the evaluation unit (4) is designed to consider results of the comparison over a defined period of time or over a predetermined number of measurements of the optoelectronic sensor (1) in order to exclude an erroneous derivation of the presence of fog. Optoelectronic sensor (1) according to Claim 1 or 2 , wherein the evaluation unit (4) is designed to adapt a configuration of the optoelectronic sensor (1) according to a result of the comparison. Optoelectronic sensor (1) according to Claim 3 , wherein the evaluation unit (4) is designed to change the monitoring area (ÜB) and/or to issue a warning signal if, after the defined period of time and/or after the predetermined number of measurements, the air temperature value (T) is less than or equal to the dew point temperature value (τ). Optoelectronic sensor (1) according to Claim 4 , wherein the evaluation unit (4) is designed to cancel a change in the monitoring area (ÜB) and/or the warning signal if, after the defined period of time and/or after the predetermined number of measurements, the air temperature value (T) is greater than the dew point temperature value (τ). Optoelectronic sensor (1) according to one of the preceding claims, wherein the temperature and/or humidity sensor (12 and/or 13) or the thermo-hygrometer (14) are integrated in the optoelectronic sensor (1) or arranged outside the optoelectronic sensor (1). Optoelectronic sensor (1) according to at least one of the preceding claims, wherein the air temperature and the relative humidity value (T and F) of the monitoring area (ÜB) can be transmitted to the evaluation unit (4) by means of a radio signal (14a). Optoelectronic sensor (1) according to Claim 7 , wherein a radio antenna (15) is provided to transmit and receive the air temperature value and the relative humidity value (T and F) to the evaluation unit (4). Optoelectronic sensor (1) according to at least one of the preceding claims, wherein the optoelectronic sensor (1) is designed as a safety laser scanner, LIDAR sensor, camera or light grid.

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