SENSOR ARRANGEMENT AND METHOD FOR SAFEGUARDING A MONITORED ZONE

Abstract

The invention relates to a sensor arrangement and to a method for safeguarding a monitored zone at a machine. The sensor arrangement comprises a camera continuously generating 3D images, a control and evaluation unit for the position detection of objects in the monitored zone and, in the case of a hazardous position, initiating a safety-directed response of the machine, with a buffer memory unit being provided for storing last recorded images and with a 3D reference map being prepared from the stored images when the safety-directed response was initiated, a voxel identification unit being provided for flagging those voxels in the current 3D image whose coordinates differ by a specified distance from those of the corresponding voxels of the reference map, a movement recognition unit being provided in which the voxels thus identified are examined as to whether they display position changes that are above a fixed threshold in the course of a fixed number of further current images, and independently thereof, a restart signal for the machine being able to be output at an output.

Claims

1. A sensor arrangement for safeguarding a monitored zone at a machine that defines a hazard site, the sensor arrangement comprising at least one camera continuously generating 3D images for the detection of objects in the monitored zone; a control and evaluation unit that is configured to determine the presence or position of detected objects in the monitored zone and to initiate a safety-directed response of the machine in the case of a hazardous position, a buffer memory unit for the storage of last recorded images; —the control and evaluation unit is configured to prepare a 3D reference map from the stored images when the safety directed response has been initiated; a voxel identification unit for the flagging of those voxels in the current 3D image whose coordinates differ by a specified difference from those of the corresponding voxels of the reference map; and a movement recognition unit in which the voxels thus identified are examined as to whether they display position changes that are above a fixed threshold in the course of a fixed number of further current images; and independently thereof, a restart signal for the machine can be output at an output.

2. The sensor arrangement in accordance with claim 1, wherein the threshold amounts to 10 mm.

3. The sensor arrangement in accordance with claim 1, wherein the control and evaluation unit is configured to output a person recognition signal when a movement has been recognized by the movement recognition unit, that is the position changes are above the fixed threshold.

4. The sensor arrangement in accordance with claim 1, wherein the absolute values of the position changes of an identified voxel from image to image are summed in the movement recognition unit and wherein the threshold is a fixedly stored voxel threshold to output the movement recognition signal and/or to suppress the restart signal if the sum of the absolute values of the position changes is above the voxel threshold.

5. The sensor arrangement in accordance with claim 1, wherein the absolute values of the position changes of all the identified voxels from image to image are summed in the movement recognition unit and that the threshold is a fixedly stored sum threshold to output the movement recognition signal and/or to suppress the restart signal if the sum of the absolute values of the position changes is above the sum threshold.

6. The sensor arrangement in accordance with claim 1, wherein the 3D camera is configured to detect an additional optical feature that serves as an additional criterion for identifying the voxels in the voxel identification unit.

7. The sensor arrangement in accordance with claim 1, wherein the buffer memory unit, the voxel identification unit, and the movement recognition unit are parts of the control and evaluation unit.

8. The sensor arrangement in accordance with claim 1, that has a safety control in which at least a part of the control and evaluation unit is implemented

9. The sensor arrangement in accordance with claim 1, further comprising an additional sensor that detects movements of objects in the monitored zone.

10. The sensor arrangement in accordance with claim 9, wherein the additional sensor is a radar sensor.

11. The sensor arrangement in accordance with claim 1, wherein the 3D camera is configured as failsafe according to safety standards.

12. The sensor arrangement in accordance with claim 1, wherein the control and evaluation unit is configured as failsafe.

13. The sensor arrangement in accordance with claim 1, wherein N images are stored in the buffer memory unit and the variable N is equal to 10 or more.

14. The sensor arrangement in accordance with claim 1, wherein the continuous detection of 3D images takes place in a fixed time pattern.

15. A method of safeguarding a monitored zone at a machine, the method comprising the steps continuously generating 3D images with at least one camera for the detection of objects in the monitored zone; determining the position of detected objects; and in the case of a hazardous position, initiating a safety-directed response of the machine; storing last recorded images in a buffer memory unit; preparing a 3D reference map from the stored images when the safety-directed response has been initiated; flagging those voxels in the current 3D image whose coordinates differ by a specified difference from those of the corresponding voxels of the reference map in a voxel identification unit; examining the voxels thus identified in a movement recognition unit as to whether they display position changes that are above a fixed threshold in the course of a fixed number of further current 3D images; and outputting a restart signal for the machine at an output when the position changes are not above the fixed threshold.

Description

[0030] The invention will be explained in more detail in the following also with respect to further features and advantages by way of example with reference to embodiments and to the enclosed drawing. The Figures of the drawing show in:

[0031] FIG. 1 a schematic three-dimensional representation of a 3D camera and its monitored zone;

[0032] FIG. 2 a schematic representation of the monitoring; and

[0033] FIG. 3 a schematic representation of the monitoring in a different situation.

[0034] FIG. 1 shows in a schematic three-dimensional representation the general setup of a sensor arrangement 10 in accordance with the invention with a 3D camera for recording a depth map in a typical monitoring system. At least one 3D camera 11 continuously detects objects 14 and 16 in its field of vision 12 and generates 3D images of the field of vision 12. Various technologies are known for a 3D camera such as time of flight principle with a direct time of flight measurement of light signals or a phase measurement or a distance estimate from brightness levels or focal positions (depth from focus, depth from defocus) or a triangulation principle in which two camera images of a moving camera or of a stereo camera are correlated with one another or alternatively an illumination pattern is correlated with a camera image to thus estimate disparities and to determine distances therefrom. The 3D camera 11 is preferably configured as failsafe, that is, it is designed for a safety engineering application and satisfies the standards named in the introduction or corresponding standards to safeguard a hazardous machine.

[0035] A control and evaluation unit 18 evaluates the 3D images and determines the positions of the detected objects 14 and 16, in particular from the received signal of a light receiver 20 of the 3D camera 11. The control and evaluation unit 18 can be implemented in the most varied hardware, for example digital modules such as microprocessors, ASICS (application specific integrated circuits), FPGAs (field programmable gate arrays), GPUs (graphics processing units) or mixed forms thereof that can preferably be located in the 3D camera 11, but that can also be distributed over any desired internal and external components, with external components also being able to be integrated via a network or cloud provided that latencies can be managed or tolerated. Since a 3D evaluation, that is the generation of the depth map and its evaluation, is very processor intensive, an at least partly parallel architecture is preferably formed.

[0036] A monitored zone 22 is defined within the field of vision 12 and, for example a person, an object 14 here, may not be present therein because otherwise the person 14 would come too close to the hazard site, that is the machine 16. If the person 14 nevertheless enters the monitored zone 22, the instantaneous position is evaluated as dangerous and a safety-directed response of the machine 16 is initiated via a machine control 24. For this purpose, the control and evaluation unit 18 has a safety output 26 via which a safety signal can be conducted to the machine control 24.

[0037] The control and evaluation unit 18 here designates analog circuits or digital evaluation modules of the 3D camera 11 itself or of other devices of the sensor arrangement. A minimal configuration of the sensor arrangement is accordingly a single 3D camera having an internal control and evaluation unit such as is schematically shown in FIG. 1.

[0038] The heart of the invention is a restart function after a triggering of a safety-directed response of the machine 16, for example a shutdown. A buffer memory unit 28 is provided for this purpose, in the control and evaluation unit 18, for example. A specific number N of the last recorded 3D images is continuously stored in the buffer memory unit 28 in ongoing operation. The buffer memory unit 28 can be configured, for example, in the manner of a ring memory.

[0039] If the safety directed response was initiated because an unpermitted object, for example a person 14, was detected in the monitored zone 22, as indicated in FIG. 2, a 3D reference map of the monitored zone 22 is prepared from the stored N images in the control and evaluation unit 18. The situation is thus recorded so-to-say directly before the safety-directed shutdown. That is the configuration such as is shown in FIG. 2. In this case, a part of a permitted object 30, for example a pallet loaded with material, is also still in the monitored zone 22. The variable N is preferably equal to 10 or more. This is a sensible compromise between a fast storage of as few images as possible and an accuracy of the reference map due to as many images as possible.

[0040] After the shutdown, 3D images are further continuously recorded by the 3D camera 11. These new 3D images are further processed together with the reference map in a voxel identification unit 32 and those voxels are identified or flagged whose coordinates differ by a specified distance from those of the corresponding voxels of the reference map.

[0041] FIG. 3 is intended to show the situation of FIG. 2 at a somewhat later time. Only the position of the person 1 has changed in the monitored zone 22 between the time of the shutdown (FIG. 2) and the later time (FIG. 3). This object 14, or rather the part regions of this object that are disposed in the monitored zone 22, are therefore identified in the voxel identification unit 32 because their positions have changed after the safety-directed response. All the other regions or objects in the monitored zone are static and thus permitted in the monitored zone because they have not led to the safety-directed response.

[0042] In a movement recognition unit 34, the previously identified voxels are then examined as to whether they display position changes that are above a fixed threshold in the course of a fixed number of further current images. It is therefore thus determined whether the objects or at least part regions of the objects 14 move. A distinction between static objects 30 and persons 14 thus becomes possible. This is therefore a person recognition. This works because a person cannot remain static. Even if the person in the monitored zone falls and remains lying “motionless”, smaller movements will nevertheless occur simply by breathing that the sensor arrangement in accordance with the invention identifies. The threshold for the recognition of a movement is preferably at 10 mm. Movements are thus recognized that amount to a least a position change of 10 mm.

[0043] If it is found that a person 14 is or at least part regions of this person 14 or is/are not is is/are no longer present in the monitored zone, the machine 16 can be restarted without risk. A restart signal for the machine 16 is then output at an output 28. The machine control 24 then causes the machine 16 to restart.

[0044] In addition to the restart signal, in a further development of the invention, a person recognition signal can be output if the movement recognition unit 34 has recognized a person, that is has recognized movements that are above the fixed threshold.

[0045] The buffer memory unit 28, the voxel identification unit 32, and the movement recognition unit 34 are preferably parts of the control and evaluation unit 18. This not only shortens the signal distances, but also increases the compactness. The control and evaluation unit 18 can be integrated in the 3D camera for a further increase in compactness.

[0046] A splitting of the units over a separate safety control and the 3D camera is possible, as presented in the introduction.

[0047] In an embodiment of the invention, the sensor arrangement 10 comprises an additional sensor, in particular a radar sensor, that only detects movements of objects in the monitored zone 22. The functional safety, which is synonymous with movement safety, can thereby be increased because a radar sensor having a different measurement technology, that is diversely redundant, likewise carries out a movement recognition.

[0048] All the components of the sensor arrangement 10, and in particular the control and evaluation unit 18 with the buffer memory unit 28, the voxel identification unit 32, and the movement recognition unit 34, are preferably configured as failsafe.