DE202020101055U1 - Device for monitoring a protected area - Google Patents

Abstract

Device (10) for monitoring a protected area (12) with
- At least one time of flight sensor (14, 14.1, ..., 14.n), the at least one transmitter (16, 16.1, ..., 16.n) for emitting light beams (24, 24.1, ..., 24. n) in the protected area (12), and at least one receiver (18, 18.1, ..., 18.n) for receiving reflected or remitted light beams (28, 28.1, ..., 28.n),
- A delimitation element (20) which lies opposite the time-of-flight sensor (14, 14.1, ..., 14.n) at a first distance (22) and at least partially delimits the protected area (12),
- A reference element (26) opposite the time-of-flight sensor (14, 14.1, ..., 14.n) at a second distance (30) for reflecting or remitting the emitted light beams ((24, 24.1, ..., 24.n) ),
- At least one evaluation unit (32) for determining a light transit time between emission of the light beams (24, 24.1, ..., 24.n) and reception of the reflected or remitted light beams (28, 28.1, ..., 28.n), and
- A monitoring unit (36) for evaluating the determined light transit time, characterized in that the second distance (30) is greater than the first distance (22).

Description

The invention relates to a device for monitoring a protected area according to the preamble of claim 1.

Such protective devices are used in a variety of ways according to the state of the art, for example to be able to initiate measures in the event of unauthorized access by persons to a danger area so that injury or damage is avoided.

The variety of optoelectronic protective devices used for these tasks is very broad due to the respective application conditions and ranges from single-beam light barriers and multi-beam light grids to scanners or camera solutions. The functional principle of all of these optoelectronic protective devices is that a protected area, for example a route, a surface or a room, is penetrated by light beams and these light beams are then detected by one or more light-sensitive receivers. If an object gets into one or more of these light beams, these are influenced, i.e. H. interrupted, distracted, weakened or the like. This influence is then recognized by the light-sensitive receiver or receivers. The signals supplied by the light receiver are processed in a downstream evaluation unit so that the protective devices can output a corresponding status message.

An optoelectronic protective device in the form of a multi-beam light grid or light curtain is shown in, for example EP 1 089 030 B1 described. There, several light transit time sensors consisting of transmitter-receiver pairs, also called time-of-flight sensors, are arranged in a common housing that is arranged on one side of a protected area, while on the other side of the protected area there is a protected area limit for reflecting or remitting of the light beam emitted by the transmitters is formed on the respective receiver.

The distance between the transmitter-receiver pairs on the one hand and the reflective protection zone limit on the other hand is known, so that this distance or the position of the delimitation element can be taught into the system.

If an object penetrates the protected area, so that at least one of the emitted light beams is interrupted, the determined light transit time of the corresponding light beam changes, so that an interrupt signal is generated which, depending on the application, triggers a desired follow-up action. This can be, for example, shutting down a machine to be monitored, outputting an alarm signal, outputting measured values or even storing measured values.

The protective device described is essentially intended to detect relatively large objects such as a person or a pallet with box-shaped elements.

The depth resolution, i.e. the smallest detectable change in distance in the direction of the light beam of such time-of-flight sensors, is limited. This leads in particular to the fact that objects that are smaller than the depth resolution of the TOF sensor cannot be reliably detected in the vicinity of the reflective protection area limit of the protection area, since when evaluating the light transit time it cannot be reliably recognized whether the change in transit time due to the occurrence of a Object or a fluctuation due to the limited depth resolution.

Time of flight sensors with sufficient depth resolution to reliably detect objects with object sizes smaller than 20 mm near a protection area limit and are therefore suitable for applications in which objects the size of a finger are to be detected, for example as protection against intrusion in a danger area, are usually very complex and use in the protective devices described above is therefore not economical.

In order to meet the requirement of reliable object recognition of objects with object sizes smaller than 20 mm, the prior art, for example from the DE 10 2006 048 098 A1 Imaging devices are known which have a lighting device for illuminating an area to be monitored and an image recording camera that generates an image of at least one surface delimiting the area to be monitored on a spatially resolving light receiver and supplies corresponding image signals to an evaluation unit as a function of the image on the light receiver that generates a switching signal if there are not permitted objects within the area to be monitored, the area having an elongated pattern in the form of a reference strip forming the boundary on a background, so that the pattern extends over the entire length of the area viewed by the camera Area extends. However, such systems require relatively complex image recording and processing systems. In addition, the reference strips (eg reflector foils) can be susceptible to contamination. Furthermore, when only one camera is used, only the presence of an object, but not its position, can be detected.

The object of the invention is therefore to develop an optoelectronic protective device based on time-of-flight sensors in such a way that it can reliably detect objects with a size smaller than the depth resolution of the time-of-flight sensors.

A device according to the invention for monitoring a protected area, for example a route, a surface or a space through which light rays penetrate, which are detected by one or more light-sensitive receivers after reflection or remission, has at least one time-of-flight sensor for this purpose. The time of flight sensor contains at least one transmitter for emitting light beams into the protected area and at least one receiver for receiving light beams reflected or remitted from the protected area.

An evaluation unit determines a light transit time between transmission and reception of the light beams. A monitoring unit evaluates the determined light transit time. If the determined light transit time deviates from a predetermined maximum light transit time at least by a predetermined threshold value, the monitoring unit can send an interrupt signal, for example to a robot in a danger area, which can then be stopped or switched off when an object enters the protected area.

The protection area is at least partially delimited on a side of the protection area opposite the time-of-flight sensor by a delimitation element which is arranged at a first distance from the time-of-flight sensor. The first distance thus essentially determines the dimension of the protected area in the direction of the light beam.

For reflecting or remitting the emitted light rays, a reference element is arranged at a second distance on the side of the protection area opposite the light transit time sensor, which is greater than the first distance, i.e. the distance between the light transit time sensor and the delimiting element delimiting the protection area. The light beams are therefore not reflected or remitted on the delimiting element delimiting the protected area and thus, as in the prior art, at the protected area boundary, but rather on the more distant reference element. In the area between the delimitation element and the reference element, reaching into a danger area is preferably not possible.

The difference between the second distance and the first distance is preferably at least as large as a depth resolution of the time-of-flight sensor, i.e. the smallest change in distance detectable by the light-travel sensor, particularly preferably greater than the depth resolution of the time-of-flight sensor. Thus, when the light beam is interrupted, a change in the time of flight is always measured which corresponds to a distance that is greater than the depth resolution of the time of flight sensor.

This has the advantage that time-of-flight sensors can be used with a depth resolution that is worse than the smallest object size to be detected. Less complex time-of-flight sensors and evaluation units can therefore be used, which are correspondingly inexpensive.

The difference between the second distance and the first distance can be at least 15 mm, preferably at least 25 mm, so that commercially available, inexpensive time-of-flight sensors can be used in the device.

To monitor a planar protection area, a plurality of time-of-flight sensors can be arranged in a line and thus form a light grid or a light curtain. The time of flight sensors can be connected to a central evaluation unit that determines the time of flight of the individual sensors. In an alternative embodiment, each time-of-flight sensor can have its own evaluation unit for determining the time of flight.

In a further embodiment, the time-of-flight sensors can be arranged in a matrix for monitoring a volumetric, that is to say three-dimensional, protection area. As in the previously described embodiment, the time-of-flight sensors can be connected to a central evaluation unit, or each time-of-flight sensor can have its own evaluation unit for determining the time of flight.

In the case of a linear or matrix-shaped arrangement of the time-of-flight sensors, a beam spacing of the light beams from adjacent time-of-flight sensors can be less than 15 mm, preferably less than 10 mm. This means that objects the size of a finger can be reliably detected in the protected area.

The device according to the invention cannot only be used for a simple detection of an object in a protected area. Even more complex detection tasks such as recognizing previously taught-in object shapes and generating an interrupt signal depending on the recognized object, such as in the EP 1 089 030 B1 are possible.

• 1 eine schematische Darstellung einer erfindungsgemäß ausgebildeten Vorrichtung zur Überwachung eines Schutzbereichs
• 2 eine schematische Darstellung einer erfindungsgemäß ausgebildeten Vorrichtung zur Überwachung eines Schutzbereichs mit linienförmiger Anordnung einer Vielzahl von Lichtlaufzeitsensoren

The invention is explained below on the basis of exemplary embodiments with reference to FIG Drawing explained in more detail. The same reference symbols identify elements that are the same or have the same function. In the drawing show:

• 1 a schematic representation of a device designed according to the invention for monitoring a protected area
• 2 a schematic representation of a device designed according to the invention for monitoring a protected area with a linear arrangement of a plurality of time-of-flight sensors

1 shows a schematic representation of a device 10 for monitoring a protection area 12th . The protection area 12th is on one side by at least one time-of-flight sensor 14th with a transmitter 16 and a recipient 18th and on the opposite side by a delimiting element 20th limited. Time of flight sensor 14th and limiting element 20th are at a first distance 22nd arranged from each other. The transmitter 16 sends pulsed light beams 24 in the protection area 12th out. The rays of light 24 are on a reference element 26th , for example a reflective film, so reflected or remitted that they are reflected or remitted light rays 28 back to the recipient 18th of the time of flight sensor 14th reach. The reference element 26th is the time of flight sensor 14th at a second distance 30th across from.

By using pulsed light beams 24 , 28 can die from sending out the rays of light 24 until the reflected or remitted light rays are received 28 elapsed time of flight can be determined, which is representative of the second distance 30th is. The time of flight is determined by an evaluation unit 32 who have favourited part of the time-of-flight sensor 14th or can be designed as a separate unit.

When an object penetrates 34 (in the example a hand) into the protection area 12th , are the rays of light 24 from the object 34 remitted or reflected. Due to the shortened path of the light rays 24 , 28 from the transmitter 16 to the recipient 18th the light transit time is reduced accordingly, which is determined by the evaluation unit 32 can be determined. The determined light transit time is provided by a monitoring unit 36 evaluated. Based on the evaluation, the monitoring unit can 36 output an interrupt signal, for example to stop a machine 38 (in the example a robot) in a danger area 50 or to activate a warning signal 40 (in the example a warning light).

The difference 42 between the second distance 30th and the first distance 22nd is at least as big as a depth resolution 44 of the time of flight sensor 14th . This ensures that there is interference by an object 34 in the protection area 12th is always reliably detected, even if the extent of the object 34 in the direction of the light rays ( 24 , 28 ) is smaller than the depth resolution 44 because the measured change in distance when an object enters the protected area is always at least the difference 42 between the second distance 30th and the first distance 22nd corresponds to.

The area 46 between boundary element 20th and reference element 26th is designed so that in the area 46 no access in the direction of the machine 38 in the danger area 50 is possible.

2 shows a schematic representation of a device for monitoring a protected area 12th with a linear arrangement of a large number of time-of-flight sensors 14.1, ..., 14.n . Due to the linear arrangement, the emitted light beams form 24.1, ..., 24.n and reflected or remitted light rays 28.1, ..., 28.n a flat protection area by means of a light grille or a light curtain 12th .

The beam spacing 48 that of the time-of-flight sensors 14.1, ..., 14.n emitted light rays 24.1, ..., 24.n to each other is determined by the size of the smallest object that occurs when entering the protected area 14th should still be detected. In applications in which, for example, the engagement of a finger is to be detected, these are preferably no larger than 15 mm

The protection area 12th is on one side by time of flight sensors 14.1, ..., 14.n with transmitters 16.1, ..., 16.n and recipients 18.1 ..., 18.n and on the opposite side by a delimiting element 20th limited. Time of flight sensors 14.1, ..., 14.n and the delimitation element 20th are at a first distance 22nd arranged. The transmitters 16.1, ..., 16.n send pulsed light beams 24.1 ..., 24.n in the protection area 12th out. The rays of light 24.1, ..., 24.n are on a reference element 26th , for example a reflective film, so reflected or remitted that they are reflected or remitted light rays 24.1, ..., 24.n back to the recipients 18.1 ..., 18.n the time of flight sensors 14.1, ..., 14.n reach. The reference element 26th is the time of flight sensor 14.1, ..., 14.n at a second distance 30th across from.

By using pulsed light beams 24 can die from sending out the rays of light 24.1, ..., 24.n until the reflected or remitted light rays are received 24.1 , ..., 24.n elapsed time of flight can be determined, which is representative of the second distance 30th is.

The time of flight sensors 14.1, ..., 14.n are with a central evaluation unit 32 connected, which determines the time of flight of the light rays. Alternatively, each of the time-of-flight sensors 14.1, ..., 14.n have their own evaluation unit. The determined light transit times are monitored by a monitoring unit 36 evaluated. Based on the evaluation, the monitoring unit can 36 output an interrupt signal, for example to stop a machine or to activate a warning signal

When an object penetrates the protected area 12th , becomes at least part of the light rays 24.1, ..., 24.n remitted or reflected from the object. Due to the shortened travel distance of the light beams from the transmitter to the receiver, the light transit time is reduced accordingly, which is determined by the evaluation unit 32 can be determined. The determined light transit time is provided by a monitoring unit 36 evaluated. Based on the evaluation, the monitoring unit can 36 output an interrupt signal, for example to stop a machine 38 (in the example a robot) or to activate a warning signal 40 (in the example of a warning light).

The difference 42 between the second distance 30th and the first distance 22nd is at least as big as a depth resolution 44 the time of flight sensors 14.1, ..., 14.n . This ensures that there is interference by an object 34 in the protection area 12th is always reliably detected, even if the extent of the object 34 in the direction of the light rays ( 24 , 28 ) is smaller than the depth resolution 44 because the measured change in distance when an object enters the protected area is always at least the difference 42 between the second distance 30th and the first distance 22nd corresponds to.

The area 46 between boundary element 20th and reference element 26th is designed so that in the area 46 no access in the direction of the machine 38 in the danger area 50 is possible.

Analogous to the in 2 The exemplary embodiment shown can also be used to monitor a volume-shaped protection area with a matrix-shaped arrangement of time-of-flight sensors.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the 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 assumes no liability for any errors or omissions.

Patent literature cited

• EP 1089030 B1 [0004, 0022]
• DE 102006048098 A1 [0010]

Claims (9)

Device (10) for monitoring a protected area (12) with - at least one time of flight sensor (14, 14.1, ..., 14.n), the at least one transmitter (16, 16.1, ..., 16.n) for transmitting Light rays (24, 24.1, ..., 24.n) into the protected area (12), and at least one receiver (18, 18.1, ..., 18.n) for receiving reflected or remitted light rays (28, 28.1, ..., 28.n), - a delimitation element (20) which lies opposite the time-of-flight sensor (14, 14.1, ..., 14.n) at a first distance (22) and at least partially delimits the protected area (12), a reference element (26) opposite the time-of-flight sensor (14, 14.1, ..., 14.n) at a second distance (30) for reflecting or remitting the emitted light beams ((24, 24.1, ..., 24.n)) - At least one evaluation unit (32) for determining a light transit time between emission of the light beams (24, 24.1, ..., 24.n) and reception of the reflected or remitted light beams (2 8, 28.1, ..., 28.n), and - a monitoring unit (36) for evaluating the determined light transit time, characterized in that the second distance (30) is greater than the first distance (22). Device (10) according to Claim 1 , wherein a difference between the second distance (30) and the first distance (11) is at least as great as a depth resolution (44) of the time-of-flight sensor (14, 14.1, ..., 14.n). Device (10) according to Claim 1 wherein a difference between the second distance (30) and the first distance (22) is at least 15 mm, preferably at least 25 mm Device (10) according to one of the preceding claims, wherein a plurality of time-of-flight sensors (14.1, ..., 14.n) are arranged in a line for monitoring a planar protection area (12). Device (10) according to one of the Claims 1 to 3 , wherein a plurality of time-of-flight sensors (14.1, ..., 14.n) for monitoring a volumetric protection area are arranged in a matrix. Device (10) according to one of the Claims 4 or 5 , wherein adjacent time-of-flight sensors (14.1, ..., 14.n) have a beam spacing (48) of the light beams (24.1, ..., 24.n) of less than 15 mm, preferably of less than 10 mm. Device (10) according to one of the Claims 4 to 6th with a central evaluation unit (32) for determining the light transit times of the plurality of light transit time sensors (14.1, ..., 14.n) Device (10) according to one of the Claims 4 to 6th , each time-of-flight sensor (14.1, ..., 14.n) being assigned its own evaluation unit. Device (10) according to one of the preceding claims, wherein a monitoring unit (36) is set up to generate an interrupt signal if the determined light transit time of at least one light transit time sensor (14, 14.1, ..., 14.n) of a predetermined light transit time is at least one specified threshold deviates.

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