WO2001013029A1

WO2001013029A1 - Device for protecting a danger zone, especially the danger zone of an automatic machine

Info

Publication number: WO2001013029A1
Application number: PCT/EP2000/007531
Authority: WO
Inventors: Claus Brenner
Original assignee: Pilz Gmbh & Co.
Priority date: 1999-08-14
Filing date: 2000-08-03
Publication date: 2001-02-22
Also published as: AU6161400A; DE19938639B4; DE19938639A1

Abstract

The invention relates to a device for protecting a danger zone (26), especially the danger zone (26) of an automatic machine (28). The inventive device (10) comprises first means (12, 16) for producing an optically monitored, virtual barrier (30) and second means for generating a switch signal that stops the machine (28) when said barrier (30) is broken through (24). The first means (12, 16) are provided with an image recording element (12) and a defined target (16) the image of which is recorded by the image recording element (12). The second means contain a comparative element that compares the recorded image with a value that is characteristic of a reference image. The inventive device is further characterized in that the defined target (16) contains position marks that are used to determine its present position.

Description

Device for protecting a danger zone, in particular the danger zone of an automated machine

The present invention relates to a device for securing a danger zone, in particular the danger zone of an automated machine, with first means for generating an optically monitored, virtual barrier and with second means for generating a switching signal for stopping the machine when the barrier is broken, the the first means have an image recording unit and a defined target, the image of which the image recording unit records, and wherein the second means have a comparison unit which compares the recorded image with a variable characteristic of a reference image. Such a device is known from DE 196 44 278 AI.

The barrier created is referred to here as virtual, since it does not have to contain any real mechanical obstacle, such as a fence or a protective grille. A breakdown of the virtual barrier can be detected solely on the basis of the optical monitoring. With earlier barriers of this type, such as, for example, light barriers, light curtains or light grids, the switching or alarm signal is triggered when one or more light beams between a transmitter and a receiver are interrupted. A disadvantage of light barriers, light grids, etc., however, is that they require a large number of light beams, which generally run parallel to one another, to monitor a virtual barrier that is extended over a large area. The distance between the parallel light beams is determined by the size of the smallest, still detectable object. For example, in order to detect an object the size of a finger, which is often required to secure a machine, a large number of transmitting and receiving elements arranged in parallel with one another is necessary, which means considerable installation and cost expenditure. In addition, light barriers etc. are susceptible to faults in the area of highly reflective environments or in areas with strong flashes of light. This is the case, for example, with large press brakes or with welding robots. Furthermore, light barriers etc. can be overridden quite simply by conscious or unconscious manipulations by deflecting the light beam (s) on their way from the transmitter to the receiver, for example with a mirror. In order to eliminate these disadvantages, the above-mentioned DE 196 44 278 A1 discloses the device described in the introduction, in which the virtual barrier is generated by the comparison device comparing the image of a recorded pattern field with a reference image. In the simplest case, the reference image corresponds to the undisturbed image of the defined target. This has distinctive features that are easy to recognize and evaluate. It is therefore also referred to below as a cooperative goal. A deviation of the recorded image from the reference image is caused in particular by an object that obscures at least part of the defined target in the field of view of the image recording unit. The change in the recorded image compared to the reference image can be easily recognized on the basis of the known features of the defined target. As a result, an optically monitored, virtual barrier can be generated with the aid of the image recording unit in combination with the defined target.

The characteristic size can include the reference image as a whole. Alternatively, it can also be limited to one or more characteristic features that can be extracted from the reference image. In addition, the reference image or its characteristic features can be stored in a memory of the comparison unit. Alternatively, it is possible to carry out the comparison in relation to an external reference.

In practice, however, difficulties arise with the known device if, on the one hand, one wants to reliably and without fail to secure a machine with regard to smaller objects, for example the size of a finger or hand on the other hand, you want to largely rule out false alarms. Since only a small tolerance with regard to possible changes in the recorded image may be allowed for the detection of smaller objects, even small shifts in the spatial position of the image recording unit and / or the defined target can trigger a false alarm. The known device must therefore be adjusted very precisely at the beginning, and the adjustment must also be repeatedly checked and corrected when the device is in operation. In principle, this can be automated with the aid of modern electronic image processing methods, but with the known device this involves considerable additional effort. It is therefore an object of the present invention to provide a device of the type mentioned at the outset which enables simplified monitoring of the virtual barrier, especially with regard to smaller objects.

This object is achieved in the device mentioned at the outset in that the defined target contains position marks for determining its current position.

The device according to the invention is very flexible in several respects. For example, the shape and orientation of the virtual barrier is no longer determined by a fixed mechanical arrangement of transmitting or receiving elements, but above all by the extent and position of the defined target within the field of view of the image recording unit. This makes it possible to change the shape or position of the virtual barrier simply by changing the defined target if the position and orientation of the image recording unit remain unchanged. In addition, virtually any shape, including curvilinear virtual barriers can be generated in the device according to the invention by appropriate design of the defined target. If there are several defined targets in the field of view of the image recording unit, one can be determined by a corresponding selection in the comparison unit. This can only be done by changing the software of the comparison unit, i.e. without mechanical installation effort. As a result, a device according to the invention can be adapted very easily and quickly to new tasks.

It is also possible to monitor several defined targets at the same time with a single image acquisition unit. This results in the possibility of generating several virtual barriers that are used together or as an alternative to one another. For example. In this way, several virtual barriers arranged one behind the other can be created with increasing security priority and optionally activated. Furthermore, several danger areas that are independent of one another can be monitored with only one image recording unit in combination with several defined targets.

The overall installation effort of the device according to the invention is very low. It is sufficient here to roughly align the image recording unit so that the defined target is in its field of vision. The exact alignment then takes place within the framework of the image processing with the aid of the position marks, which can be identified very easily during the image evaluation. Furthermore, the comparison unit can always take into account the current position of the defined target in a simple manner when comparing with the reference image, in order to, for example, to recognize an offset of the defined target. This can prevent false alarms during operation. Vibrations or oscillations of the defined target or of the image recording unit can also be compensated for very easily on the basis of this measure in the comparison unit.

Overall, the device according to the invention is therefore very flexible and at the same time easy and inexpensive to install.

In addition, the device according to the invention can also be used to monitor manipulations on existing mechanical barriers. For example, it is possible to monitor part of a mechanical protective grille that blocks the danger zone of the machine as a defined target. The distance of this protective grille with the defined target would be recognized by the image acquisition unit.

In one embodiment of the invention, the image recording unit has a flat image sensor with a large number of pixels.

The image sensor can be constructed, for example, using CCD or CMOS technology. All light rays that reach the image recording unit are collected by the image sensor. In contrast to the known light grids, in which a multiplicity of light beams run parallel to one another from a transmitting element to a receiving element, all of the light beams recorded meet here at an image sensor. A fixed assignment of one transmitting element to exactly one receiving element is neither available nor necessary. The image of the defi- Rather, the nominated target is recorded together with all pixels. This has the advantage that the failure of one or more individual pixels of the image sensor does not necessarily result in a gap being created in the virtual barrier.

The greater the number of pixels of the image sensor with the same size of the monitored area, the greater the resolution of the image recording unit. Since this also increases the accuracy of the image, the accuracy and also the flexibility of the device is increased by a large number of pixels.

In a further embodiment, the defined target has at least one artificial area, which is highlighted in comparison to its surroundings for the image recording unit.

The measure mentioned differs from an alternative embodiment of the invention, in which a natural object is evaluated as a target. In contrast to this, the defined goal in this embodiment has at least one area that is highlighted in a defined manner. This can be done, for example, with a colored coating or a reflective film. This measure simplifies the comparison of the image of the defined target with the reference image. As a result, the effort and costs involved in implementing the comparison unit are reduced, and the comparison of the image with the reference image can be carried out more quickly and reliably. In a further embodiment, the defined target has a structured, high-contrast pattern of areas that are visually stronger and less strongly emphasized.

In this embodiment of the invention it is achieved that an object which breaks through the virtual barrier can be recognized independently of its own color or its reflection properties. If the penetrating object has optical properties that resemble one of the high-contrast pattern areas, this object is recognized against the background of the other pattern area. Overall, this measure increases the reliability and safety of the device according to the invention.

In a further embodiment, the structured pattern contains a code for uniquely identifying the defined target.

This code can be implemented in the form of a bar code, for example. The measure mentioned has the advantage that different targets can be clearly recognized in the field of view of the image recording unit and can thus be assigned to a specific monitoring function. In addition, this measure makes it considerably more difficult to manipulate the monitoring device by introducing a “wrong target” or by moving the defined target. The monitoring of mechanical protective grilles already mentioned can also be further improved in this way in order to prevent dismantling of the protective grille. In a further embodiment of the measures mentioned above, the highlighted area is more light-reflecting than its surroundings.

The highlighting of the area can then be achieved, for example, by means of light-reflecting foils or lacquers, or else by attaching reflectors, such as, for example, “cat's eyes”. The measure mentioned has the advantage that the defined goal can be achieved in a very simple and inexpensive manner. In addition, the defined goal in this embodiment is purely passive, so that there is no wiring effort.

In a further embodiment of the measure mentioned above, the more reflective area is retroreflective.

Retroreflective materials are known per se in the prior art. These are materials that reflect a light beam in the direction from which it strikes the corresponding material. In contrast, other materials reflect either diffusely, ie in all directions, or according to the law "angle of incidence equals angle of reflection", ie deviating from the direction of incidence. The measure has the advantage that the efficiency of the reflection is particularly high, as a result of which the device is particularly well protected against extraneous light interference. An example of a retroreflective element are the "cat eyes" already mentioned, which are used, inter alia, as reflectors in motor vehicles. In an alternative embodiment of the aforementioned measures, the highlighted area is self-illuminating.

This can be achieved with actively illuminating foils, for example fluorescent foils, or with the aid of light-emitting diodes. The measure has the advantage that the device according to the invention is independent of the ambient light and can therefore also be used in dark areas. In addition, the efficiency of the light generation is particularly good, since the light only has to travel the simple way from the defined target to the image recording unit.

In a further embodiment of the invention, the first means furthermore have a light source for illuminating the defined target.

This measure also has the advantage that the device according to the invention is independent of the ambient light. As a result, safe operation can be ensured even in poorly lit areas or in the event of ambient lighting failing. In addition, the comparison unit always finds determined, constant lighting conditions, which increases the reliability of the comparison.

In a further embodiment of the measure mentioned above, the light source is an infrared light source.

The use of infrared light sources, such as, for example, infrared LEDs, is known per se in the prior art. With regard to the present invention, the measure has the advantage that the lighting, which is not for the human eye is visible, the surrounding area is not affected. In addition, the use of an infrared light source allows the image recording unit to be restricted to the corresponding frequency range by using a blocking filter, so that disturbing influences by reflections of the visible light in the surroundings are reduced.

In a further embodiment of the aforementioned measures, the light source is arranged in the area of the image recording unit.

In connection with the use of retroreflective materials for the defined goal, this measure has the advantage that the efficiency and thus the sensitivity of the device is particularly good. In addition, the image recording unit in this embodiment of the invention can be realized as a particularly compact and therefore easy to install unit.

In a further embodiment, the light source has a directional characteristic that is adapted to the course of the defined target.

This measure is particularly advantageous if the defined target is designed to generate a flat virtual barrier in the form of an elongated strip. In this case, a light source without a directional characteristic results in a very unfavorable energy balance with regard to the complete illumination of the defined target. In addition, a light source with a directional characteristic also causes disturbing reflections. xions from the environment can be reduced. This in turn increases the functional reliability of the entire device.

In a further embodiment, the light source has light-emitting semiconductors.

Light-emitting semiconductors, so-called LEDs, are known per se as light sources in the prior art. With regard to the present invention, however, they have the advantage that their long service life enables a particularly reliable and safe function of the protective device. This is of particular advantage with regard to the safety aspect associated with the device according to the invention.

In a further embodiment, the light from the light source is modulated.

Modulated means that the intensity of the light source is deliberately controlled differently during operation. In a particularly preferred embodiment, the light from the light source is pulsed, i.e. the light source only emits individual light pulses. The measure has the advantage that disturbing reflections from the surrounding area can be eliminated by comparing the reference image in the comparison unit with both an unilluminated and an illuminated image of the defined target. This can also be done by forming a difference.

In a further embodiment of the invention, the image recording unit has optics that influence the image. This measure has the advantage that the field of view of the image recording unit can be specifically adapted to different, possibly changing environmental conditions. In particular, the device according to the invention can hereby be adapted to environments which are extensive and / or have obstacles.

In one embodiment of the measure mentioned above, the optics contain a mirror, via which the image of the defined target is deflected onto the image recording unit.

This measure has the advantage that the image recording unit is given the ability to look around the corner. As a result, it is possible with the measure mentioned to set up a virtual barrier even where there are mechanical obstacles in the room.

In a further embodiment of the measure mentioned above, the mirror is a concave mirror.

This measure is particularly advantageous since the beam path of the light beams that are focused on the image recording unit can be converted to a parallel beam path with a concave mirror. This makes it particularly easy to give the virtual barrier an approximately rectangular area. In addition, a very long monitoring area can be realized with a concave mirror.

In a further embodiment, the optics contain a prism, via which the image of the defined target is deflected onto the image recording unit. This measure is particularly advantageous in order to monitor different, separate areas with a single image acquisition unit. With this measure, too, it is therefore very simple and inexpensive to generate, for example, a rectangular virtual barrier.

In a further embodiment of the aforementioned measures, the optics are anamorphic.

Anamorphic optics are characterized in that the imaging scale of the optics differs in two directions perpendicular to one another and in each case to the optical axis. This distorts the image. Within the scope of the present invention, the measure has the particular advantage that a very "thin" and nevertheless very elongated and large-area virtual barrier, in particular with a rectangular area, can be realized with only one image recording unit.

In a further embodiment of the invention, the defined target is extended in a line.

This measure has the advantage that very large and at the same time thin virtual barriers can be created in the manner of a curtain. The lines can also be curved.

In a further embodiment of the invention, the second means furthermore have a device for the non-volatile storage of the recorded image. This measure is particularly advantageous for documenting a breakthrough of the virtual barrier, which inevitably leads to an object entering the secured danger area. When securing machines, documentation is possible in this way, which is advantageous for researching the causes of accidents and also with regard to approval by the responsible supervisory authorities. The measure gives the device according to the invention a function which cannot be realized with the light grids etc. used hitherto.

In a further embodiment of the invention, the comparison unit has means for the non-volatile storage of an arrangement of defined targets.

This measure further develops the features of the invention already discussed above, with which the installation outlay of the device according to the invention is considerably reduced. With the measure at hand, it is possible to store different configurations of virtual barriers in such a way that they can be easily selected for a specific operating environment. The measure therefore increases the flexibility of the device used considerably. In addition, the measure has the advantage that a change in the environment in a period in which the virtual barrier is not required and in which the device is therefore switched off can be reliably detected. Malfunctions and the resulting security gaps can be avoided in this way. In a further embodiment of the invention, the comparison unit has means for compensating for vibrations of the defined target.

The means mentioned can include, for example, software that determines the current position of the defined target and then ignores changes in the current position within predetermined tolerance ranges. The measure is particularly advantageous when the device according to the invention is used in the area of heavy machinery, such as a hydraulic press, in the vicinity of which vibrations inevitably occur due to the heavy moving machine parts.

In a further embodiment of the invention, the comparison unit has means for compensating for soiling of the defined target.

Such means include, for example, a memory in which a long-term average of the recorded images is stored. The comparison of a currently recorded image with this long-term mean value makes it possible to distinguish a gradual contamination of the defined target from shadowing by an object. The measure is particularly advantageous in order to ensure reliable and error-free long-term operation of the device according to the invention even in dusty environments. Incorrect switching reactions of the device can be avoided due to the measure mentioned. In a further embodiment of the invention, the comparison unit has a blocking filter for suppressing extraneous light.

This measure has the advantage that disturbing light reflections or flashes from the environment are suppressed particularly well. This increases the functional reliability of the device.

In a further embodiment of the invention, the comparison unit has a two-channel redundant structure.

It is particularly preferred if the two channels of the comparison unit are diversified, i.e. are realized with different components. The measure mentioned has the advantage that errors or malfunctions of the comparison unit can be identified in good time, which is particularly advantageous with regard to the safety-critical function of the virtual barrier. In a particularly preferred embodiment of the invention, the results from each channel of the comparison unit are compared with one another using a dual-ported RAM, in order to ensure error-free operation of the entire device. Such a measure is technically particularly simple and inexpensive to implement.

In a further embodiment of the invention, the first means have a plurality of image recording units whose fields of vision adjoin one another.

With this measure, virtual barriers of any size and shape can be created, so that a particularly large one Flexibility with regard to the possible uses is achieved.

In a further embodiment of the invention, the first means generate a plurality of virtual barriers which are spatially staggered one behind the other.

On the one hand, this measure has the advantage that the danger zone is still protected if one of the virtual barriers fails due to an error. For others, protection with increasing security level can be implemented in this way, for example first a pre-warning and only in the second level a shutdown of the machine. The staggered barriers running parallel to one another can be implemented in a particularly simple and cost-effective manner with an image recording unit and several defined targets.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination indicated in each case, but also in other combinations or on their own without departing from the scope of the present invention.

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

1 is a schematic representation of a first embodiment of the invention, 2 shows the embodiment of FIG. 1 in a plan view along the line II-II,

3 different images of the defined target in the embodiment according to FIG. 1,

4 shows a perspective view of an image recording unit according to the invention,

5 shows the block diagram of an image recording and evaluation unit according to the invention,

6 - 8 embodiments of defined goals,

9 shows a schematic illustration of a second exemplary embodiment of the invention,

10 shows a schematic illustration of a third exemplary embodiment of the invention,

11 shows the monitored area of the virtual barrier in the exemplary embodiment according to FIG. 1,

12 shows an exemplary embodiment for generating a rectangular virtual barrier,

13 shows a further exemplary embodiment for generating a rectangular virtual barrier, 14 shows a schematic illustration to explain the functioning of an anamorphic optics,

15 shows an embodiment of the invention with a concave mirror,

16 shows a further exemplary embodiment of the invention with a concave mirror,

17 shows an exemplary embodiment of the invention with two image recording units, the monitoring areas of which complement one another,

Fig. 18 shows an embodiment of the invention with two prisms and

Fig. 19 is a flowchart explaining the operation of the device according to the invention.

1 and 2, a device according to the invention is designated in its entirety by reference number 10.

The device 10 has a combined image acquisition and evaluation unit 12, which in the following is referred to simply as a camera. The camera 12 records, via a lens 14, the image of a defined target in the form of a marking 16, which is explained in more detail below with reference to FIGS. 6 to 8.

The reference number 18 denotes a light source which in the present case contains a plurality of infrared LEDs Reference number 20 denotes individual light beams which are reflected by the marking 16 towards the camera 12. The reference numeral 22 denotes the light cone which emanates from the light source 18 and which illuminates the marking 16 in such a way that the reflected light beams 20 reach the camera 12.

As can be seen from the illustration in FIGS. 1 and 2, the light source 18 has a directional characteristic such that the light cone 22 is focused approximately on the extent of the marking 16. In the case of the linear marking 16, which is linear here, this is achieved in that the light source 18 has individual LEDs which are arranged next to one another parallel to the extension of the marking 16.

The reference numeral 24 denotes a rod which is held in the space between the camera 12 and the marking 16 in such a way that it interrupts at least some of the light beams 20 and therefore changes the image of the marking 16 recorded by the camera 12.

The reference number 26 in FIG. 2 denotes a danger zone which surrounds a machine 28 in the form of a robot arm in a circle.

The light beams 20 with which the camera 12 records the image of the marking 16, in combination with the evaluation explained in more detail below, form a virtual barrier 30, the breakthrough of which can be detected by an object or by a person. 3 shows four different images 34a to 34d, which the camera 12 records from the marking 16 in different situations. The image 34a shows the marking 16 in the initial state after the device 10 has been started up. The image 34a thus corresponds to the reference image with which the subsequently recorded images of the marking 16 for monitoring the virtual barrier 30 are compared.

In the image 34b, the marking 16 is shifted in comparison to the image 34a. Such a shift can be the result of a snapshot when the marking 16 vibrates, for example due to heavy movements of the machine 28. The offset of the marking 16 that occurs in this case must, however, move within predetermined limits. If the offset exceeds these predetermined limits or if there is no vibration compensation when evaluating the recorded image 34, the evaluation unit of the camera 12 determines that the image 34b does not correspond to the expected reference image according to image 34a. This can be the result, for example, of an unintentional or deliberately manipulative displacement of the marking 16. In both cases, the evaluation unit of the camera 12 will generate a switching or alarm signal.

The mark 16 in the image 34c has completely disappeared. This can be the result of excessive contamination of the marking 16 or a failure of the light source 18, for example. In any case, the deviation of the image 34c from the reference image according to image 34a indicates a malfunction that endangers the security of the virtual barrier 30. Also in this case, the evaluation unit of the camera 12 will therefore generate a switching signal.

In the image 34d, the marking 16 is overlaid by the rod 24. This situation also means a change compared to the reference image according to image 34a. The evaluation unit of the camera 12 will therefore also generate a switching or alarm signal in this case. This example clearly shows that the camera 12 can detect a breakdown of the virtual barrier 30 by comparing the recorded image 34d with the expected reference image.

In the description of the following figures, the same reference numerals designate the same elements which have already been explained with reference to the preceding FIGS. 1 to 3.

FIG. 4 shows a preferred embodiment of the camera 12, in which the light source 18 has individual infrared LEDs which are arranged concentrically with the lens 14 of the camera. Furthermore, in this exemplary embodiment, the entire image recording and evaluation electronics are accommodated within the housing 38 of the camera 12.

As can be seen from the block diagram in FIG. 5, the camera 12 has, in addition to the components already explained, a control circuit 42 and, in the present case, two comparison units 44a and 44b which are redundant to one another. The control circuit 42 controls the light source 18, which is pulsed modulated in the present case. This is shown by way of example using a flash of light 46. The control circuit 42 also controls the actual image acquisition and for this purpose is connected to a flat image sensor 48 with a large number of pixels not shown here. The image sensor 48 is an example of a CCD (charge coupled device) image sensor. Alternatively, this can be an image sensor using CMOS technology.

Finally, the control circuit 42 is connected to two mutually redundant processors 50a and 50b, to which it supplies the signals from the image sensor 48 and further control information. The processors 50a, 50b each form the core of the comparison units 44a, 44b.

Reference numbers 52a, 52b each designate a memory in which a variable characteristic of the image 34 of the marking 16 is stored. The characteristic size can include, for example, all the pixels of the reference image corresponding to the image 34a. As an alternative to this, however, only characteristic features which are extracted from the reference image of the marking 16 are stored in the present exemplary embodiment.

Reference numerals 54a, 54b each denote a non-volatile memory in which the comparison units 44a, 44b store the image 34 last recorded when they detect a breakdown of the virtual barrier 30. The saved image can later be used to evaluate possible causes of accidents or for documentation. In addition, configurations of different markings 16 in the field of view of the camera 12 can be stored in the non-volatile memories 54a, 54b and can optionally be activated. The reference numeral 56 denotes an interface to a safe bus system. In this way, the camera 12 can be integrated into an existing security system. In addition, the camera 12 can be configured via this interface 56 and switching or alarm signals can be transmitted.

The reference number 58 denotes a switching and / or alarm signal which is triggered by each of the comparison units 44a, 44b if either a breakdown of the virtual barrier 30 is detected or if an error is found within the camera 12. The two processors 50a, 50b are connected via a dual-ported RAM for mutual monitoring and control of the comparison units 44a, 44b. This is a memory that can be accessed by each of the two processors 50a, 50b so that the stored data can be compared. The dual-ported RAM is represented here by an arrow 60.

In a departure from the exemplary embodiment shown here, the camera 12 has, in other exemplary embodiments, two mutually redundant image sensors 48 and mutually redundant light sources 18. The two image sensors 48 are then either provided with their own optics or combined with a common stereo optic.

6 to 8, exemplary embodiments of the marking 16 are shown in more detail. All of the exemplary embodiments have in common that the marking 16 has a structured, high-contrast pattern of highly reflective regions 66 and weakly reflective regions 68. In the exemplary embodiment in FIG. 6, the marking 16 is extended linearly and is sits an elongated, linear region 66 that is highly reflective. This area consists of a retroreflective sheeting. The surrounding area 68 is weakly reflective and consists of a very dark film. The reference number 70 designates two reflective position marks which, in the case of the marking 16, stand out from the dark area 68 in an identifiable manner. The position marks 70 are arranged at a defined distance from one another and enable the position 16 of the mark 16 to be determined exactly.

A circular or point-shaped marking 16 is shown in FIG. 7 as a further exemplary embodiment. It has a highly reflective central area 72 and also concentrically arranged, also highly reflective angular marks 74. The area 68 which surrounds the central area 72 and the angular marks 74 is weakly reflective. The arc length of the angle marks 74 represents a code with which the marking 16 in this exemplary embodiment can be distinguished from other, similar markings 16. Moreover, with the aid of the marking 16 according to FIG. 7 it is possible to create a virtual barrier, the shape of which roughly corresponds to that of a light barrier. As an alternative to this, however, a multiplicity of punctiform markings 16 according to FIG. 7 can be lined up to form a linear marking.

FIG. 8 shows a section of a further exemplary embodiment of a linear, elongated marking 16. In addition to the already strongly reflecting area 66 and the weakly reflecting area 68, this marking 16 has a bar code 76 which is defined by a defined sequence of strongly and weakly reflecting areas. areas is formed. With the aid of the barcode 76, the marking 16 of this exemplary embodiment can be clearly distinguished from other markings in the field of view of the camera 12.

All of the markings 16 shown have in common that, due to the combination of a strongly and a weakly reflecting area, the breaking through of the virtual barrier 30 with objects of different intensities can be detected. If, for example, it is an object that itself has a highly reflective surface, there is the possibility that this object will not be detected by the camera 12 against the background of the highly reflective areas 66. In this case, however, the camera 12 recognizes this object against the background of the weakly reflecting areas 68. Conversely, a rather dark object is easily recognized against the background of the highly reflecting and therefore bright areas 66.

In a further exemplary embodiment, which is not shown here, the marking 16 has at least two mutually parallel, highly reflective regions 66, which are separated from one another by at least one weakly reflective region 68. With such an arrangement, the direction of movement of an object that breaks through the virtual barrier 30 can be determined.

In further exemplary embodiments of the invention, the highly reflective regions 66 of the markings 16 are realized with the aid of reflective lacquers or with the aid of actively illuminating elements, for example luminescent foils or LED strips. 9 shows an exemplary embodiment of a device 80 according to the invention, in which the camera 12 is arranged vertically above a floor 82. There is a wall 84 on one side which prevents access to a danger zone below the camera 12. The remaining three sides, from which access to the danger zone is possible, are secured by a virtual barrier 30. For this purpose, there is a U-shaped marking 16 on the bottom 82, the open side of which lies on the wall 84. Overall, a pyramid-shaped, virtual barrier 30 is thus created, which secures access to the danger area from three sides. The fourth side is secured by wall 84.

10 shows a further exemplary embodiment of the invention with the aid of a device 86. In this case, the virtual barrier 30 runs approximately horizontally and parallel to the floor 82. The camera 12 is located diagonally opposite the corner 87 of the two walls 84 at the level of the marking 16.

A special feature of this exemplary embodiment of the invention is that here the two legs 88, 90 of the L-shaped marking can be used mutually as a reference image. However, in this case too, a variable characteristic of the reference image is preferably used in the memory 52 of the camera 12.

In FIG. 11, the virtual barrier 30 of the exemplary embodiment is again shown in order to explain the following figures Fig. 1 shown. As can be seen, the virtual barrier 30 in this arrangement has a triangular shape.

Often, however, a triangular protection rather than a triangular protection is required to secure a danger zone. The following exemplary embodiments therefore show possibilities of how rectangular virtual barriers 30 can also be generated on the basis of the present invention.

12, the camera 12 is arranged above a U-shaped marking 16. The opening angle of the camera 12 is 180 °, i.e. the field of view of the camera 12 covers the entire U-shaped marking 16. As can be seen, a rectangular virtual barrier 30 is hereby generated.

FIG. 13 shows an arrangement which corresponds approximately to the exemplary embodiment according to FIG. 10. It is understood that this arrangement can not only be used to create a horizontal barrier 30. In the present case, the marking 16 is L-shaped and the camera 12 is arranged diagonally opposite the corner point of the L-shaped marking 16. A rectangular virtual barrier 30 is also produced with this embodiment.

A difficulty with this arrangement as well as with the arrangement according to FIG. 12 is that a very large length range of the marking 16 has to be monitored here. In FIG. 14, this length range is shown “developed” as it is recorded by the camera 12. If the two legs of the L-shaped marking 16 have the dimensions H and B, the overall effective length range recorded by the camera 12 is 1.41 (B + H). Assuming H with 2 m and B with 4 m, for example, the total length to be recorded is approx. 8.5 m. In contrast, to build up a virtual barrier in the form of a thin curtain, the width of the line or strip-shaped marking 16 is only a few centimeters, for example 5 cm. In this case, the image sensor 48 must therefore detect 8.5 m in one direction and at the same time be able to resolve 0.5 cm in the other direction. In order to compensate for these differences in scale, the camera 12 in this exemplary embodiment has an anamorphic optics which has different imaging scales in the two directions mentioned. An anamorphic appearance is achieved in particular with the help of cylindrical lenses.

Alternative exemplary embodiments for realizing a substantially rectangular virtual barrier 30 are shown in FIGS. 15 to 18.

In the exemplary embodiment according to FIG. 15, the camera 12 views the marking 16 via a concave mirror 94, ie the beam path of the reflected light rays 20 is deflected and bundled on the way from the marking 16 to the camera 12 via the concave mirror 94. The light beams 20 therefore run from the marking 16 to the concave mirror 94 first along a parallel first beam path 96 and then on their way from the concave mirror 94 to the camera 12 along a focused second beam path 98. The concave mirror 94 is symmetrical to the optical axis 100 of the camera 12 arranged. In this embodiment of the invention, the virtual barrier 30 can have a very large extension L up to 12 m and more. A special feature of this exemplary embodiment is that the marking 16 is arranged here next to or at least in the region of the camera 12, which enables the marking 16 to be illuminated particularly efficiently.

In the exemplary embodiment according to FIG. 16, the concave mirror 94 with the camera 12 is arranged in a common housing 102. Accordingly, the beam path 98 is shortened compared to the exemplary embodiment according to FIG. 15. This embodiment of the invention has the advantage over the example according to FIG. 15 that the adjustment of the arrangement during installation is not critical. Furthermore, the recorded image only has to pass through the distance L here once.

In the exemplary embodiment according to FIG. 17, a rectangular virtual barrier 30 is generated by a combination of two triangular monitoring areas 104, 106. According to the present invention, each of the triangular monitoring areas 104, 106 is formed with the aid of a camera 12, 12 'and a marking 16, 16' which cooperates with it. The two monitoring areas 104, 106, which in the present case are characterized by different hatching, overlap along the diagonal of the rectangle in order to exclude a gap within the virtual barrier 30. This embodiment of the invention is characterized in that the cameras 12, 12 'can be constructed very simply, since no additional optics are required.

A further exemplary embodiment is shown in FIG. 18, in which a rectangular virtual barrier 30 is formed by a combination of two monitoring areas 104, 106. The special feature of this exemplary embodiment is that the two monitoring areas 104, 106 are each imaged on one half of the image sensor 48. This is achieved with the aid of two prisms 108, 110, via which the image of one leg of the again L-shaped marking 16 is directed. This exemplary embodiment is characterized in that the image sensor 48 only has to record half of the entire longitudinal extent of the marking 16 across its width, as a result of which a gain in resolution is achieved.

The functional sequence of the device according to the invention can be seen from the illustration in FIG. 19. After the device has been switched on, a self-test is first carried out in step 120 in order to detect existing errors with regard to the safety aspect of the device at an early stage. Then, in step 122, the switching signal 58 is switched to the "red" state, ie the virtual barrier 30 is not yet ready for operation. In step 124, an image 34 is first recorded. In step 126, markings 16 are then searched for at the positions stored in the non-volatile memory 54. If no marking is found at the expected positions, the device remains in the "red" state according to step 128. If, on the other hand, the expected markings are found, their position, orientation and internal geometry are checked in accordance with step 130 using the known reference image. If these values have changed to such an extent that they lie outside a defined tolerance, the device remains in the "red" state according to step 132. If, on the other hand, the defined tolerances are observed, the virtual barrier 30 is checked in accordance with step 134 by comparing the recorded images 34 of the markings 16 with the reference images become. In particular, the images 34 of the markings 16 are checked for shadowing from an intruding object. As long as there are no interruptions, the device remains in the "green" state according to steps 136, 138, ie the danger area 26 of the machine 28 is reliably secured.

The installation of the device according to the invention can also be carried out simply using the method shown in FIG. 19, since the device automatically searches for markings 16 in the field of view of the camera 12 in accordance with step 126. Found markings 16 can then be stored in the non-volatile memory 54 in the context of a configuration mode. However, manual teaching of the device is also possible.

In a further exemplary embodiment of the invention, which is not shown here, the light beams 20 are deflected to the camera 12 with the aid of a spherical mirror. Such an arrangement is characterized in that a complete area of the room can be monitored with a camera.

In a further embodiment of the invention, which is also not shown, two virtual barriers 30 are formed with the aid of two cameras 12, which are essentially parallel to one another, i.e. spatially staggered, run. The two cameras can be housed in a common housing. Alternatively, a camera with stereo optics can also be used here.

Such an arrangement is characterized in that there is also redundancy with regard to the image recording unit. This makes it possible, for example, to detect shading of the lens 14 of only one of the two cameras 12, for example by an insect, without triggering a false alarm. In addition, staggered virtual barriers 30 can be realized with increasing security level. For a complete redundancy, two defined targets 16 are preferably also used.

Claims

claims

1. Device for securing a danger zone (26), in particular the danger zone (26) of an automated machine (28), with first means (12, 16, 18) for generating an optically monitored, virtual barrier (30) and with second means (44a, 44b) for generating a switching signal (56; 58) for stopping the machine (28) when the barrier (30) is broken, the first means (12, 16, 18) having an image recording unit (12) and a defined target (16), the image (34a - 34d) of which records the image recording unit (12), and wherein the second means have a comparison unit (44a, 44b) which compares the recorded image (34a - 34d) with a variable characteristic of a reference image , characterized in that the defined target (16) contains position marks (70) for determining its current position.

2. Apparatus according to claim 1, characterized in that the image recording unit (12) has a flat image sensor (48) with a plurality of pixels.

3. Apparatus according to claim 1 or 2, characterized in that the defined target (16) has at least one artificial area (66; 72, 74) which is visibly highlighted in comparison to its surroundings (68) for the image recording unit (12) ,

4. Device according to one of claims 1 to 3, characterized in that the defined target (16) is a struc- rated, high-contrast pattern from optically stronger and less strongly emphasized areas (66, 68).

5. The device according to claim 4, characterized in that the structured pattern includes a code (74; 76) for uniquely identifying the defined target.

6. Device according to one of claims 3 to 5, characterized in that the highlighted area (66; 72, 74) is more light reflecting than its surroundings (68).

7. The device according to claim 6, characterized in that the more reflective region (66; 72, 74) is retroreflective.

8. Device according to one of claims 3 to 5, characterized in that the highlighted area (66; 72, 74) is self-illuminating.

9. Device according to one of claims 1 to 8, characterized in that the first means (12, 16, 18) further comprise a light source (18) for illuminating the defined target (16).

10. The device according to claim 9, characterized in that the light source (18) is arranged in the region of the image recording unit (12).

11. The device according to claim 9 or 10, characterized in that the light source (18) has a directional character Stik has, which is adapted to the course of the defined target (16).

12. Device according to one of claims 9 to 11, characterized in that the light source (18) has light-emitting semiconductors.

13. Device according to one of claims 9 to 12, characterized in that the light (46) of the light source (18) is modulated.

14. Device according to one of claims 1 to 13, characterized in that the image recording unit (12) has an image-influencing optics (14; 94; 108, 110).

15. The apparatus according to claim 14, characterized in that the optics includes a mirror (94) via which the image (34) of the defined target (16) is deflected onto the image recording unit (12).

16. The apparatus according to claim 15, characterized in that the mirror (94) is a concave mirror.

17. Device according to one of claims 14 to 16, characterized in that the optics includes a prism (108, 110) via which the image (34) of the defined target (16) is deflected onto the image recording unit (12).

18. Device according to one of claims 14 to 17, characterized in that the optics (14) is anamorphic.

19. Device according to one of claims 1 to 18, characterized in that the defined target (16) is linear.

20. Device according to one of claims 1 to 19, characterized in that the second means (44a, 44b) further comprise a device (54a, 54b) for non-volatile storage of the recorded image (34).

21. Device according to one of claims 1 to 20, characterized in that the comparison unit (44a, 44b) has a device (54a, 54b) for the non-volatile storage of an arrangement of defined targets (16).

22. Device according to one of claims 1 to 21, characterized in that the comparison unit (44a, 44b) has means (50a, 50b) for compensating for vibrations of the defined target (16).

23. Device according to one of claims 1 to 22, characterized in that the comparison unit (44a, 44b) has means (50a, 50b) for compensating for contamination of the defined target (16).

24. Device according to one of claims 1 to 23, characterized in that the comparison unit (44a, 44b) has a blocking filter for suppressing extraneous light.

25. Device according to one of claims 1 to 24, characterized in that the comparison unit (44a, 44b) is constructed in two-channel redundancy.

26. Device according to one of claims 1 to 25, characterized in that the first means (12, 16, 18) have a plurality of image recording units (12, 12 ') whose fields of view adjoin one another.

27. The device according to one of claims 1 to 26, characterized in that the first means (12, 16, 18) generate a plurality of virtual barriers (30) which are spatially staggered one behind the other.