DE202018104258U1 - Safety Light Curtain - Google Patents

Abstract

Safety light grid (1) for monitoring a protected area with at least two transmitting / receiving strips (3, 3 '), with at least one light transmitter (S) and at least one light receiver (E), the transmitting / receiving strips (3, 3') facing each other a protective field (2) is formed between them by the light beams (4) of the light emitter (S), wherein in each case at least one light emitter (S) of the one transmitting / receiving strip (3; 3 ') and at least one light receiver (E) the other transmit / receive bar (3 ', 3) form a transmit / receive pair, with means for synchronization of the transmit / receive bars (3, 3') andwith a control and evaluation unit, wherein at least one of the light transmitters ( S) one of the transmission / reception strip (3, 3 ') with at least one of the light receiver (E) of the same transmission / reception strip (3, 3') forms a light sensor, wherein the light sensor is designed as a light cycle time, the control and Evaluation unit is formed, d the light transit time of received light signals or light pulses of the light receiver (E), characterized in that the light receiver (E) comprises at least one single photon avalanche diode.

Description

The invention relates to a safety light grid according to the preamble of claim 1.

Safety-related optoelectronic sensors are subject to stringent requirements regarding required reliability in accordance with various standards, such as the standard "Safety of Machinery - Non-Contact Guards (ESPE)", EN / IEC 61496 or the European Standard "Functional safety of safety-related electrical, electronic, programmable electronic systems" , EN 61508. The optoelectronic sensors are subdivided into safety categories as defined in the standard "Safety related parts of control systems"
EN 954 or its successor standard EN 13849.

Standardized safety levels are necessary because such sensors can be used as protective measures on dangerous machinery such as presses, stamping tools, robots, etc. are used and thus life and health of operating personnel on the functionality of the sensors depends, so that the sensors can deliver a safety-related switching signal in case of danger.

Such optoelectronic sensors are used, for example, at the edge of a danger zone of a machine tool in order to detect, if appropriate, the entry of this danger zone and to trigger an optical or acoustic warning signal or a switch-off signal for the machine tool.

Optical safety sensors must include a range of self-test capabilities of their measurement chain to demonstrate their functionality and to achieve a certain safety category or safety level according to a safety standard.

Depending on the desired category, the test must be different. For example, according to DIN EN 61496, a loss of detection capability in the response time and a limitation of the detection capability must be detected in four seconds.

Today's safety light grids are designed with transmitters and receivers in separate housings. The detection principle is the interruption of the light path between transmitter and receiver.

Today's safe light grids and light barriers with opposite transmitters and receivers are constructed according to the quiescent current principle. Here, the light signal is sent directly from the sender to the receiver and passes through a complete measuring chain. An interruption of this direct light path is detected. Changes of the received signal, z. As by windshield contamination, transmitter degradation, etc. show up directly in the amplitude level of the received signal and can be detected directly.

Since the safety decision is made on the basis of an amplitude threshold, any critical deterioration in the measuring path can be detected and a warning or stop signal can be output accordingly.

The type of self-testing according to the quiescent current principle used in the light grid according to the prior art is not applicable to frangible light grids / light sensors, since the direct opposite side is missing.

In the case of scanning systems, the amplitude of the received signal in the measuring channel depends above all on the distance and the remission of the target, or is completely absent if the sensor looks into the "infinite".

Tasting light grids are out of the EP 2 180 348 A1 and the EP 3 091 272 B1 known.

An object of the invention is to provide a momentary light grid or safety light grid which has comprehensive possibilities for self-testing in order to obtain the highest possible safety category. A further object is to provide a light grid and a method which, on the one hand, permits simple monitoring of the protected area and, on the other hand, enables geometric recognition of the penetrating objects.

The object is achieved according to claim 1 by a safety light grid for monitoring a protective area with at least two transmitting / receiving strips with at least one light transmitter and with at least one light receiver, wherein the transmission / reception bars are arranged opposite to each other, and between them by the light beams of the light emitter a protective field is formed, wherein in each case at least one light transmitter of one transmit / receive bar and at least one light receiver of the other transmit / receive bar form a transmit / receive pair, with means for synchronization of the transmit / receive bars and with a control and evaluation unit, wherein at least one of the light emitter of one of the transmission / reception strip forms a light sensor with at least one of the light receivers of the same transmission / reception strip, wherein the light button is designed as a light transit time button, wherein the control and evaluation unit is designed to receive the light transit time Evaluate light signals or light pulses of the light receiver, wherein the light receiver has at least one single photon avalanche diode.

Through the use of pulse-shaped light signals, it is possible to determine the light transit time which has elapsed from the emission of the light signals until the light signals have been received, which is representative of the distance to the object.

The invention combines the advantages of the classic safety light grid with the advantages of tactile systems. Due to the double arrangement of two tactile transmit / receive strips, a high-quality measurement function is implemented in addition to the classic safety function, which can be implemented separately with both tactile transmit / receive strips as well as by a transmitter / receiver pairing of opposite transmit / receive strips. A passing object is measured on both sides within the protective plane. If the measurement plane is inclined relative to the direction of passage, the 3D contour can also be reconstructed from a sequence of measurements.

The double arrangement allows the realization of the protection function based on the closed-circuit principle and allows the mutual testing of all sensor components. This can achieve high levels of safety, as required for many safety light grid applications.

According to the invention, two preferably identically tentative transmission / reception strips are used, which, however, can also be used individually. These tactile transmit / receive strips are - opposite to conventional safety light curtains - mounted opposite and aligned, so that the individual TOF elements (eg SPAD sensors with integrated transmitter and receiver or TOF imager) are paired so that they are in the transmit and receiving range of the other ( ).

In this way, a distance measurement can be carried out on both sides with each TOF element. This distance value may be compared to a configured value to protect the device from tampering. In addition, when an object passes through the measurement / protection level, the measurement of the object can take place. And in addition, protective fields can be defined whose uninjuredness is independently monitored. The double arrangement also has the advantage that objects can be located and tracked without having detrimental occlusion areas.

Furthermore, a mutual optical communication between the two transmission / reception strips can be established. This can be used for data transmission, avoidance of external transmitter interference or plausibility tests. A wired connection of the two transmit / receive strips is therefore no longer necessary. The communication can also be used for the realization of an alignment aid.

Furthermore, a safety function identical to conventional safety light curtains can be realized, in which respective opposite transmitter-receiver pairs define a beam whose freedom from interruptions is monitored. In addition to the high safety levels, which allows such an arrangement, so that a range can be realized, which is significantly greater than with one-sided momentary safety light curtains. In combination with the distance measuring function, the error case "Object too dark for a tentative measurement" can thus be detected and controlled in terms of safety.

Single photon avalanche diodes are also referred to synonymously as 'single photon avalanche diode' or SPAD for short. Other common names are Silicon Photomultiplier '(SiPM) ,, Geigermode Avalanche Photon Diode' or, Single Photon Counting Diode '. Single-photon avalanche diodes are standard photosensitive detectors using standard CMOS technology, which, like avalanche photodiodes, convert incident photons into current pulses. Unlike avalanche photodiodes, however, single-photon avalanche diodes operate over a breakdown voltage. Thus, even a single incident photon triggers an avalanche effect, which can be detected as a current pulse. Gain factors of 10 ⁵ to 10 ⁶ allow a high sensitivity and thus the detection of single photons.

For distance measurement, different light transit time methods can be implemented with a corresponding evaluation.

It may be provided a pulse method. For example, one or more time-to-digital converters for the pulse method are provided by timestamping each single-photon event. For a useful signal, therefore, multiple timestamps occur correlated. The measured value is generated statistically. Background light, however, generates randomly distributed timestamps.

This is a transmission / reception strip or a safety light grid according to the time of flight principle with at least one light transmitter which emits successive light pulses into a measuring range and with at least one light receiver which receives the light pulses reflected back from the measuring range and in the form of electrical received signals to a control and evaluation unit, which determines taking into account the speed of light from the time between transmission and reception of the light pulse representative of the distance of objects to the safety light grid distance signal, wherein the light receiver has at least one single photon avalanche diode.

Furthermore, known phase measuring methods can also be used in which a modulated light signal is used. In these methods, for example, the single-photon events are distributed in two counters via a gating signal, and a phase is calculated from the ratio of the counter readings.

Furthermore, analog signals of the single photon diode can be evaluated. These are compared with a threshold, sampled or evaluated using statistical methods.

In the evaluation according to the time of flight method, an amplitude value can be generated in addition to the distance value, for. Example by a histogram of the time stamp, by the count rate or by the voltage amplitude in an analog evaluation. The amplitude value can be used to carry out a plausibility check, in particular in safety-related applications.

The safety light grid according to the invention has the advantage that this is configured compact and can be accommodated in a small housing.
The use of single-photon avalanche diodes offers the following advantages: Single-photon avalanche diodes can be produced in a standard CMOS process. Thus, the safety light grid is highly integrated, z. B. using ASIC blocks. The light transmitter, for example a VSCEL, a laser diode or a light emitting diode and the control and evaluation unit or a separate light transmitter drive can also be integrated on the chip.

The safety light curtain is less expensive than safety light grids with photosensitive receivers which were previously customary in safety technology. By multiple arrangement of light sensors, consisting of at least one light transmitter and at least one light receiver, very compact systems are possible. The use of single-photon avalanche diodes provides high sensitivity down to individual photons. This allows an optional optics to be made very compact.

If an object penetrates into the protected area, so that at least one of the emitted light beams is interrupted and reflected or remitted, the light transit time of the corresponding light signal is determined, so that an object contour is detected, which leads to a desired follow-up action depending on the application. This can be, for example, the output of a safety switching signal for stopping a machine to be monitored, for outputting an alarm signal, for outputting a measured value or also for storing measured values.

By means of the safety light grid according to the invention, it is initially possible to detect object interventions simply and over long ranges. If an object enters the protective field between the transmission / reception strips, then at least one transmission / reception pair detects a light beam interruption, whereby an object detection signal is generated and, as a result, optionally a safety switching signal. Such a light beam interruption can be easily evaluated and detected. This ensures a short response time of the safety light curtain. Even for long ranges, a light beam interruption is easy to detect.

To detect objects of different sizes, the transmit / receive pairs are arranged at regular intervals from one another. By means of the number of interrupted, adjacent light beams and the distance of the light beams to each other, an object height can be determined.

In addition, it is also possible by the inventively formed light sensor with the safety light grid to obtain accurate information on an object contour that could not be detected by a simple beam interruption. However, an object can now be measured by means of the light scanner or the object can be classified as a permissible or impermissible object on the basis of the detected object contour, and an object detection signal or safety switching signal can be generated depending on this result. With the safety light grid according to the invention, it is thus possible to determine not only the object height but also the lateral contour of the object while the object passes through the protective field.

If an object is transported through the safety light grille, for example, on a conveyor belt, a height profile of the object can be determined and stored on the one hand by the interruption of the individual transmit / receive pairs and, on the other hand, the spacing contour data of one of the respective transmitters / detectors can also be simultaneously formed by the light sensors formed. Receiving bar facing side of the object are detected and stored. By means of the safety light grid according to the invention, a height profile and a lateral distance contour can thus simultaneously be detected and used to evaluate the object.

In certain applications, predefined allowable objects may pass through the protected area without generating a safety switch signal. Thus, for example, when crossing the protected area of permissible objects, for example by means of a conveyor belt, no safety switching signal is triggered, while conveying an impermissible object, for example a person, through the protected area - even if the person is laterally of the permissible object and this does not tower - A corresponding safety switch signal is triggered.

The juxtaposition of two tactile transmitter / receiver strips makes it possible to reliably detect faults and react in a safety-related manner. As a result, a security function can achieve a higher level of security than would be the case with a single system. Furthermore, the detection capability can be extended. A very dark object with a remission below a detection threshold can be detected with the present double system due to the missing light pulses of the opposite send / receive bar.

In a development of the invention, the distance between the opposing strip is taught and stored, and the stored value is cyclically compared with currently detected values.

By teaching and storing the distance, a change in the distance can be detected.

The distance or the distance measured value is determined, for example, on both sides, ie redundantly, during commissioning and monitored cyclically or continuously during operation. If smaller distances are measured during operation, an object is located in the protected area. There is thus no error case.

If, however, larger distances than the taught-in distance are measured on one side or on both sides, then one of the following error cases exists, for example: First, a manipulation by twisting one or both of the transmit / receive strips. Secondly, a reflection or an introduction of a specular object. Third, a systematic drift of a measured value of a transmit / receive bar.

Furthermore, the distance measurement values of the opposite transmission / reception bars can be checked. The comparison of opposing channels can be used in addition to the consistency check in operation for the verification and support of the alignment. Since a momentary safety light grid must use more collimated light for energetic reasons than a conventional safety light grid, the alignment becomes more difficult and support with the aid of the measured data is desirable. In any case, the measured value of opposite measuring channels of the transmitting / receiving strips must match within a narrow tolerance range, otherwise the measuring beams are not on top of each other and the transmitting / receiving bars are not sufficiently aligned with each other.

In summary, the presence of the opposite signal can be tested by comparing two probing transmit / receive strips to form a safety light grid and pairwise alignment of the individual measurement channels. The measured values of overlapping beams against each other and with learned reference values can be compared. The signal strengths of opposing beams against each other and with learned reference values can be compared. Even the absence of jammers is possible in this way, since their signal energy due to the greater distance does not coincide with expectations.

In a further development of the invention, a further light receiver is provided as a reference light receiver as a second receiving channel for safety-related self-testing.

An evaluation of the signal strength and the comparison with a learned reference value allows the evaluation of a receiver sensitivity. A comparison with the opposite received signal allows the assessment of contamination.

The cause of this signal failure can also be an object with a response below a detection threshold. In this case, the signal level on one or both sides is insufficient for detection. The absence of the opposite transmission signal but in this case still leads to shutdown and thus allows the detection of very dark objects that would not be detectable with a single transmission / reception bar.

The reference light receiver is preferably an already existing light receiver of the safety light grid.

The reference light receiver allows, for example, the following self-tests.

It can be monitored the exact timing of the light emitter and possibly occurring offsets can be corrected, for. B. at temperature influences.

It can be measured at the reference light receiver of the extraneous light levels in the phases in which no light is emitted. The corresponding measurement signal can be compared with the signal of the light receiver, whereby the sensitivity of the light receiver can be verified and with optional other scaling can be used to check the necessary signal-to-noise ratio in the actual measurement channel.

Additional measured values, which are generated on the light receiver and the reference light receiver, allow a safety-related evaluation of the functionality.

A direct measurement of the external light level on the light receiver and possibly on the reference light receiver allow a good determination of the signal-to-noise ratio and a safety-related sensitivity of the system.

In a further development of the invention, a further light transmitter is provided as reference light transmitter for safety-related self-testing.

As a result, a failure or signal loss of one or more measurement channels can be detected. If a signal from an opposite light transmitter is detected, but not the light pulse of a light transmitter of the same side, then it can be assumed that the light transmitter has failed or local contamination.

In this way, a test of the receiving channel on the timing or timing and signal level-dependent effects can be performed.

To test the light receiver, optical test pulses with different time profiles and amplitudes can be used and a light transit time can be imitated via a controllable delay relative to the start time of the measurement.

In particular, overmodulation measurements can be carried out easily in this way. Via a programmable variable delay in front of the light transmitter, the time behavior, ie the timing of the rangefinder, can be tested.

The dynamic response of the light receiver can be tested via an adjustable signal height of the light transmitter.

This allows the reference light transmitter, for example, the following tests:

First, a linearity and integrity of the received signals of the light receiver can be ensured for different delays or light propagation times. Thus, the distance measurement can be checked indirectly.

Secondly, by measuring the signal level with different reference amplitudes of the reference transmitter, the dynamics and the sensitivity of the light receiver can be checked. The measurements can also be used to compensate for aging effects or degradation or to compensate for temperature effects.

Third, z. B. over-steering measurements are performed if necessary.

In a development of the invention, the light receiver has at least one array consisting of single photon avalanche diodes.

So that the light receiver with the at least one single photon avalanche diode is not already saturated by individual photons, z. B. by extraneous light, many single photon avalanche diodes are arranged and evaluated together. In principle, the analog signals of the single photon avalanche diode pixels or single photon avalanche diode elements can be added here. It is also possible to digitize and digitally evaluate the avalanches of each single photon avalanche diode, for example, via a comparator or via an analog-to-digital converter. However, the avalanche signals can also be processed directly digitally if the signal is already sufficiently high.

To cover the possibility of a larger angle range through the safety light grid and still provide the necessary spatial resolution for detection z. As a leg, the single photon avalanche diode array can be divided into so-called macropixels. Here, a plurality of spatially adjacent single photon avalanche diode cells are associated with a common evaluation and evaluate the received light from a certain angular range via a corresponding optics. The arrangement can be linear or planar.

The dynamics and / or the external light behavior is scalable via the various single-photon avalanche diodes or single-photon avalanche diode arrays.

The signal level can be determined in single-photon avalanche diode arrays either directly via the count rates of the photons, if the signals are digitized directly at the pixel level, or by measuring the amplitude of the sum current of all pixels. In the monitoring state, both values are continuously measured and compared with the learned setpoint. If deviations occur at one of the two values, this deviation becomes Plausibilisiert over the second measured value and possibly detected as an intervention.

Interesting for a safety sensor is the possibility of background light measurement in the single photon avalanche diode array. The extraneous light is a dominant noise source in a single photon avalanche diode via the shot-noise. The thermal noise is much smaller compared to classical photodiode receivers, since the usual in the classical reception path transimpedance converter, which is a major source of thermal noise, is not needed. On the single photon avalanche diode array, the extraneous light level can be determined in the transmission pauses of the measuring system by the number of incident extraneous light photons on the light receiver. For example, in the case of the stated phase measurement method by another Gating signal, which adds the single photon events in a counter in the corresponding transmission breaks.

For a safe detection of objects in a safe safety light grid, a necessary signal-to-noise ratio can be defined beforehand in which an object must be detected under all circumstances. By determining the ambient light level during the measurement cycle, it is possible to monitor whether the noise level is too large in comparison with an expected signal from the intervening object and must accordingly be switched off in a safety-related manner.

Preferably, the light emitter and / or light receiver is both part of the transmit / receive pair and part of the light button. Thus, one and the same light emitter or receiver is necessary to form both a transmit / receive pair and a light scanner. After interruption of the light beam by an object of the remitted by the object light beam is directed to an associated receiving element of the same transmission / reception bar as the light emitter and determines a distance signal.

In a further development of the invention, the light emitter and light receiver are arranged individually one after the other alternately in the transmission / reception strips. Preferably, a plurality of light emitters and light receivers is arranged. This ensures a uniform resolution of the safety light curtain over the entire protective field length. Advantageously, the light scanners are also directly adjacent to each other evenly distributed over the entire protective field length.

If a strip is rotated longitudinally by 180 ° relative to the opposite strip, the light emitters and light receivers lie directly opposite each other to form the emitter / receiver pairs, resulting in a homogeneous protective field with parallel light beams. The transmitters and receivers for forming the light sensor are also located directly next to each other.
In a further development of the invention, adjacent light transmitters and light receivers each form a light scanner. As a result, a particularly simple construction of the safety light grid is ensured and the light sensors formed are arranged as a unit with uniform distances from one another along a transmission / reception bar. Due to this arrangement, the safety light curtain can be modularly constructed for different protective field heights. Depending on the protective field height, a specific number of respectively adjacent light emitters and light receivers are arranged to form light sensors. As a result of the adjacent arrangement of the light sensors, the measured distance values can also be assigned directly to a respective transmission / reception pair, so that an interruption of a light beam also directly determines an associated distance of the object interrupting the light beam.

In a further embodiment, a plurality of non-adjacent light transmitters can be activated simultaneously.

In order to achieve a low response time, multiple light sensors or multiple light barriers can be operated in parallel, preferably in an arrangement without overlap of transmitting lobes or receiving lobes. For example, adjacent light sensors or light barriers are activated simultaneously.

In this case, different light transmitters have different pulse repetition frequencies, modulation frequencies or different phases.

As a result, adjacent light sensors can be activated in parallel at the same time, without crosstalk between the channels occurring.

In a further development of the invention, the transmission / reception strips are constructed identically. Thus, only a single assembly, namely the transmit / receive bar must be made to provide a safety light grid consisting of two such opposite send / receive bars. To maintain the safety light grid, only a single transmit / receive bar needs to be stored in order to have a functional spare bar at hand in the event of a malfunction or malfunction of a bar.

Also electrical connections for both transmit / receive strips are identical. This simplifies a connection technique, since only one type of connector must be provided. The send / receive bars can thereby also easy to be connected, since not as in previous safety light curtains, consisting of transmission bar and separate reception bar, different connections for transmission bar and reception bar must be provided.

In accordance with a further embodiment, characteristic contours of the permissible objects are learned by teaching the distance values which result upon reflection of the emitted light signals at the respective object and storing them in a memory. If an object enters the protected area, the measured distance values are compared with the stored distance values before the safety switch signal is generated, and no safety switch signal is generated if the measured distance values coincide with the distance values of permissible objects within a predetermined tolerance range.

Depending on the form of the permissible objects, a plurality of permissible distance values may be stored, which differ in particular when multiple light buttons are used, depending on the location of the light beams. If an inadmissible object enters the protected area or if a permissible object is not positioned correctly, the determined distance does not coincide with the permissible distance, so that in this case a safety switching signal is generated.

In a further development of the invention, a reference surface is provided, wherein the light signals or light pulses of the light transmitter strike the reference surface and strike the reflected light signals or light pulses on the light receiver. However, an existing contour can optionally also serve as a reference surface.

The protective field dimensions or measuring range dimensions can be defined in two ways.

First, the distances and signal amplitudes can be learned against a natural reference surface. In this case, the safety light grid measures any deviation from these taught-in values, ie too large or too small distances, or too large or too small signal amplitudes lead to a protective field violation and to an object detection signal.

Safety-related testing of the safety light grid is simpler than in the prior art since the measured value is operated with two different expected values. Any deviation due to an incorrect measurement or an environmental influence of the safety light curtain, for example aging of the light emitter, extraneous light influence and / or contamination leads to a different measured value either in the monitoring of the amplitude or the distance.

Second, the distances for each measurement channel can be configured with appropriate software. In this case, the safety light curtain measures in the room with a sense of proximity and every falling below the configured distance value leads to a protective field violation. In this case, variable protective field geometries can be realized, which also by protective field switching, such as muting or blanking z. B. can be changed in a clock mode. The safety-related sensor test is more difficult in this case, since it can not be expected from expected values.

By short interruptions of the measuring cycle, it is possible to determine a level by external light irradiation by means of the light receiver. In the measurement of the signal level, fluctuations on longer time scales, for example due to temperature changes or changes in the ambient light, can be recorded continuously and the setpoints can be adjusted accordingly.

In a development of the invention, a first light receiver with a first light transmitter forms a first light sensor and the first light receiver with a second light transmitter forms a second light sensor, wherein the first light transmitter and the second light transmitter can be activated one after the other.

In safety light curtains according to the prior art, the geometric resolution is given by the beam spacing. In the momentary safety light grid according to the invention, the distance of the collimated light transmitters is used to define the geometric resolution.

In order to save costs, with the momentary safety light grid, a single light receiver can be used serially in time for the evaluation of two or more light transmitters adjacent to it. As a result, a part of the light receiver can be saved. The receiving lobe of the light receiver covers both light transmitters.

In a further embodiment, a first light receiver with a first light transmitter form a first light sensor and a second light receiver with the first light transmitter form a second light sensor.

This offers a further possibility for a higher detection reliability in the safety light grid by a parallel evaluation of two adjacent light receivers which receive light pulses from a single light transmitter. This can a redundancy in the entire safety light curtain can be achieved.

In one embodiment of the invention, the light transmitter is preceded by a transmitting optics, in particular a lens. The transmission optics are optionally integrated on a chip or in the chip housing in order to achieve a cost-effective and compact solution, in particular in high quantities.

Due to a high integration and a small size of the transmitter optics, the safety light grid is very compact.

By different transmission optics different monitoring angles and different ranges can be realized.

In a further embodiment, a receiving optical system, in particular a lens, is arranged in front of the light receiver.

Optionally, the receiving optics are integrated on a chip or in the chip housing in order to achieve a cost-effective and compact solution, in particular in the case of large quantities.

An optical bandpass filter can also be arranged directly on the chip or the light receiver, in particular vapor-deposited, in order to attenuate background light.

Due to a high integration and a small size of the receiver optics, the safety light grid is very compact.

By different receiving optics different monitoring angles and different ranges can be realized.

In a development of the invention, the control and evaluation unit is designed with two channels.

Due to the dual-channel control and evaluation unit, the safety light grid can be used as an independent safety sensor or safety light grid even with higher demands on the safety level to be achieved.

As a result, the safety light grid itself is able to perform a large number of self-tests and to ensure its own functionality comprehensively.

In addition, however, several light sensors can also communicate via a common bus and a central safety controller or safety controller is used to configure the individual light sensors, query their status and, if appropriate, feed suitable test signals, evaluate and compare the received signals, signal warnings and in case of danger to stop a machine or a self-propelled vehicle to be protected.

It may be sufficient, for example, if each individual light sensor only reports on the shared bus, if its measured values violate or exceed previously learned thresholds or if a self-diagnosis has diagnosed a problem.

In a further development of the invention, the light scanner is an integrated light scanner module.

By using a CMOS process, it is possible to integrate additional components such as the control and evaluation unit, the laser driver, the power supply and / or a temperature control logic together with the photosensitive receiver on a chip. With this technology, all components of the light probe measuring chain can be integrated in a single ASIC. The ASIC is able to autonomously measure distance values and pass the final result to the central controller via a suitable bus.

By means of a hybrid technology, the light transmitter, for example a laser, a VCSEL or a light-emitting diode can also be integrated with the chip on the integrated light scanner module. The reference light receiver and / or the reference light transmitter can also be provided in the integrated light scanner module.

The basis for the safety light grid is a modular design. The safety light grid has, for example, the components: optical module with transmitting optics and receiving optics, measuring core with light transmitter and light receiver and / or back-end with control and evaluation unit, I / O drivers, bus interface and / or safety controller.
The measuring core preferably consists of a highly integrated CMOS ASIC. However, a structure of discrete components is also possible.

Due to the good directional characteristic of light, different variants of the safety light grid with different opening angles and ranges can be realized by means of corresponding optical modules, which are adapted to different requirements of different applications. The light rays can be collimated or further expanded by optical elements.

To restrict the extraneous light incidence, the light receiver with a filter element, For example, be provided with a bandpass filter.

In the following, the invention will be explained with reference to exemplary embodiments with reference to the drawing in detail.

• 1 und 2 eine schematische Darstellung eines erfindungsgemäßen Sicherheitslichtgitters.

In the drawing shows:

• 1 and 2 a schematic representation of a safety light curtain according to the invention.

1 shows a safety light grid 1 for monitoring a protection area with at least two transmission / reception strips 3 . 3 ' with at least one light transmitter S and with at least one light receiver e , wherein the transmit / receive bars 3 . 3 ' are arranged opposite to each other, and between them by the light rays 4 the light transmitter S a protective field 2 is formed, wherein in each case at least one light transmitter S the one send / receive bar 3 . 3 ' and at least one light receiver e the other send / receive bar 3 ' . 3 form a transmit / receive pair, with means for synchronization of the transmit / receive bars 3 . 3 ' and with a control and evaluation unit, according to 2 at least one of the light emitters S one of the send / receive bar 3 . 3 ' with at least one of the light receivers e the same send / receive bar 3 . 3 ' forms a light sensor, wherein the light sensor is designed as a light time-stamp, wherein the control and evaluation unit is formed, the light transit time of received light signals or light pulses of the light receiver e evaluate, wherein the light receiver e has at least one single photon avalanche diode.

Through the use of pulse-shaped light signals, it is possible to determine the light transit time which has elapsed from the emission of the light signals until the light signals have been received, which is representative of the distance to the object.

Due to the double arrangement of two momentary transmit / receive strips 3 . 3 ' is in addition to the classic hedge function, both with both momentary transmit / receive bars 3 . 3 ' separately as well as through a transmitter-receiver pairing of opposing transmit / receive bars 3 . 3 ' can be realized, additionally implemented a high-quality measurement function. A passing object is measured on both sides within the protective plane. If the measurement plane is inclined relative to the direction of passage, the 3D contour can also be reconstructed from a sequence of measurements.

According to 1 become two preferably identically groping send / receive bars 3 . 3 ' used, but which can also be used individually. These tentative transmit / receive bars 3 . 3 ' are - compared to classic safety light curtains - mounted opposite and aligned, so that the individual TOF elements (eg SPAD sensors with integrated transmitter and receiver or TOF imager) are pairwise oriented so that they are in the transmission and reception range of each other lie.

In this way, a distance measurement can be carried out on both sides with each TOF element. This distance value may be compared to a configured value to protect the device from tampering. In addition, when an object passes through the measurement / protection level, the measurement of the object can take place. And in addition, protective fields 4 whose uninjuredness is independently monitored. The double arrangement also has the advantage that objects can be located and tracked without having detrimental occlusion areas.

Furthermore, a safety function identical to conventional safety light curtains can be realized, in which respective opposite transmitter-receiver pairs define a beam whose freedom from interruptions is monitored. In addition to the high level of security that allows such an arrangement, so that a range can be realized, which is significantly larger than one-sided momentary safety light curtains. In combination with the distance measuring function, the error case "Object too dark for a tentative measurement" can thus be detected and controlled in terms of safety.

Penetrates an object into the protective field 2 a, so that at least one of the emitted light rays 4 is interrupted and reflected or remitted, the light transit time of the corresponding light signal is determined, so that an object contour is detected, which leads to a desired follow-up action depending on the application. This can be, for example, the output of a safety switching signal for stopping a machine to be monitored, for outputting an alarm signal, for outputting a measured value or also for storing measured values.

Through the safety light grid 1 At first it is easy to detect object interventions over long ranges. If an object enters the protective field 2 between the send / receive bars 3 . 3 ' at least one transmit / receive pair detects a light beam interrupt, thereby generating an object detection signal and, as a result, optionally a safety switch signal. Such a light beam interruption can be easily evaluated and detected. This is a short response time of the safety light curtain 1 guaranteed. Even for long ranges, a light beam interruption is easy to detect.

To detect objects of different sizes, the transmit / receive pairs are arranged at regular intervals from one another. By means of the number of interrupted, adjacent light beams and the distance of the light beams to each other, an object height can be determined.

In addition, it is due to the formed light scanners with the safety light grid 1 It is also possible to obtain precise information on an object contour that could not be captured by a simple beam interruption. However, an object can now be measured by means of the light scanner or the object can be classified as a permissible or impermissible object on the basis of the detected object contour, and an object detection signal or safety switching signal can be generated depending on this result. With the safety light grid 1 Thus, it is possible to determine not only the object height but also the lateral contour of the object while the object passes the protective field.

If, for example, an object is being transported on a conveyor belt through the safety light grid 1 transported, it can be determined and stored on the one hand by interrupting the individual send / receive pairs a height profile of the object and on the other hand by the light sensor formed at the same time the distance contour data of the respective send / receive bar facing side of the object are recorded and stored. Through the safety light grid 1 Thus, at the same time a height profile and a lateral distance contour can be detected and used to assess the object.

In certain applications, predefined allowable objects may pass through the protected area without generating a safety switch signal. Thus, for example, when crossing the protected area of permissible objects, for example by means of a conveyor belt, no safety switching signal is triggered, while conveying an impermissible object, for example a person, through the protected area - even if the person is laterally of the permissible object and this does not tower - A corresponding safety switch signal is triggered.

The juxtaposition of two tactile transmitter / receiver strips 3 . 3 ' makes it possible to detect fault cases very reliably and to react in a safety-oriented manner. As a result, a security function can achieve a higher level of security than would be the case with a single system. Furthermore, the detection capability can be extended.
According to 1 and 2 is the distance of the opposite transmitter / receiver strips 3 . 3 ' is learned and stored, and the stored value cyclically compared with currently detected values.

The distance or the distance measured value is determined, for example, on both sides, ie redundantly, during commissioning and monitored cyclically or continuously during operation. If smaller distances are measured during operation, an object is located in the protected area. There is thus no error case.

If, however, larger distances than the taught-in distance are measured on one side or on both sides, there is, for example, a fault.

Further, the distance measurements of the opposite transmit / receive bars 3 . 3 ' be checked. The comparison of opposing channels can be used in addition to the consistency check in operation for the verification and support of the alignment.

In summary, the juxtaposition of two momentary transmit / receive strips 3 . 3 ' for forming a safety light grid 1 and pairwise alignment of the individual measurement channels the presence of the opposite signal are checked. The measured values of overlapping beams against each other and with learned reference values can be compared. The signal strengths of opposing beams against each other and with learned reference values can be compared. Even the absence of jammers is possible in this way, since their signal energy due to the greater distance does not coincide with expectations.

Preferably, the light emitter S and / or the light receiver e both part of the transmit / receive pair and part of the light button. Thus, one and the same light emitter S or light receiver e necessary to form both a transmit / receive pair and a light scanner. After interruption of the light beam by an object of the remitted by the object light beam to an associated light receiver e the same send / receive bar 3 . 3 ' like the light transmitter S steered and determined a distance signal.

According to 1 and 2 are the light emitters S and light receiver e individually one after the other in the send / receive bars 3 . 3 ' arranged. Preferably, there is a plurality of light emitters S and light receivers e arranged. This results in a uniform resolution of the safety light grid 1 guaranteed over the entire protective field length. Advantageously, the light scanners are also directly adjacent to each other evenly distributed over the entire protective field length.

Will be a send / receive bar 3 . 3 ' along according to 1 and 2 rotated 180 ° relative to the opposite send / receive bar 3 ' . 3 mounted, so are the light emitters S and the light receivers e to form the send / receive pairs directly opposite, creating a homogeneous protective field with parallel light beams. The light emitter S and the light receivers e to form the light sensor are also here next to each other.

According to 2 each form adjacent light emitters S and light receiver e a light sensor. This is a particularly simple construction of the safety light curtain 1 guaranteed and the light sensors formed are as a unit with equal distances to each other along a transmission / reception bar 3 . 3 ' arranged. By this arrangement, the safety light grid 1 modular for different protective field heights. Depending on the protective field height, there will be a certain number of neighboring light transmitters S and light receivers e arranged to form light sensors. As a result of the adjacent arrangement of the light sensors, the measured distance values can also be assigned directly to a respective transmission / reception pair, so that when the light beam is interrupted, an associated distance of the light beam is also directly present 4 interrupting object is determined.

According to 1 and 2 are the send / receive bars 3 . 3 ' for example, identical. This only has to be a single module, namely the send / receive bar 3 respectively. 3 ' be made to a safety light curtain 1 consisting of two such opposite send / receive strips 3 . 3 ' provide.

Also electrical connections for both transmit / receive bars 3 . 3 ' are identical. This simplifies a connection technique, since only one type of connector must be provided. The send / receive bars 3 . 3 ' This means that they can also be easily connected, since unlike previous safety light curtains, consisting of a transmitter bar and a separate receiver bar, different connections for the transmitter bar and the receiver bar must be provided.

The described embodiments can also be combined with each other so that the light sensors of the light grid according to the invention can fulfill various functions.

LIST OF REFERENCE NUMBERS

1

Safety Light Curtain

2

protection field

3, 3 '

Transmitting / receiving strips

4

light rays

S

light source

e

light receiver

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• EP 2180348 A1 [0012]
• EP 3091272 B1 [0012]

Claims (10)

Safety light grid (1) for monitoring a protection area with at least two transmission / reception strips (3, 3 '), with at least one light transmitter (S) and with at least one light receiver (E), the transmission / reception strips (3, 3') a protective field (2) is formed between them by the light beams (4) of the light emitter (S), wherein in each case at least one light emitter (S) of a transmitting / receiving strip (3; 3 ') and at least one Light receiver (E) of the other transmission / reception strip (3 ', 3) form a transmission / reception pair, with means for synchronization of the transmission / reception strips (3, 3') and with a control and evaluation unit, wherein at least one of Light transmitter (S) one of the transmission / reception strip (3, 3 ') with at least one of the light receiver (E) of the same transmission / reception strip (3, 3') forms a light sensor, wherein the light sensor is designed as a light transit time, the control Form and evaluation unit t is to evaluate the light transit time of received light signals or light pulses of the light receiver (E), characterized in that the light receiver (E) has at least one single photon avalanche diode. Safety light grid (1) after Claim 1 , characterized in that the distance of the opposite transmitting / receiving bar (3, 3 ') is taught and stored, and the stored value is cyclically compared with currently detected values. Safety light grid (1) according to at least one of the preceding claims, characterized in that a further light receiver (E) is provided as a reference light receiver as a second receiving channel for safety-oriented self-testing. Safety light grid (1) according to at least one of the preceding claims, characterized in that a further light transmitter (S) is provided as a reference light transmitter for safety-related self-testing. Safety light grid (1) according to at least one of the preceding claims, characterized in that the light receiver (E) has at least one array consisting of single photon avalanche diodes. Safety light grid (1) according to at least one of the preceding claims, characterized in that the light transmitter (S) and / or the light receiver (E) is both part of the transmit / receive pair and part of the light sensor. Safety light grid (1) according to at least one of the preceding claims, characterized in that the light emitter (S) and the light receiver (E) are arranged individually one after the other alternately in the transmission / reception strips (3, 3 '). Safety light grid (1) according to at least one of the preceding claims, characterized in that each adjacent light transmitter (S) and light receiver (E) form a light sensor. Safety light grid (1) according to at least one of the preceding claims, characterized in that a plurality of light emitters (S) and a plurality of light receivers (E) in pairs each have an optical coding which is adjacent to pairs of light emitters (S) and light receivers (E ) is different, so that a plurality of light emitters (S) and a plurality of light receivers (E) can be simultaneously controlled and evaluated. Safety light grid (1) according to at least one of the preceding claims, characterized in that the transmission / reception strips (3, 3 ') are constructed identically.

Images