DE102018117878B4 - Safety light curtain - Google Patents

Abstract

Safety light grid (1) for monitoring a protected 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') being mutually exclusive are arranged opposite one another, and between them a protective field (2) is formed by the light beams (4) of the light transmitter (S), at least one light transmitter (S) of the one transmitter / receiver strip (3; 3 ') and at least one light receiver (E) the other transmitting / receiving strip (3 ', 3) form a transmitting / receiving pair, with means for synchronizing the transmitting / receiving strips (3, 3') and with a control and evaluation unit, with at least one of the light transmitters ( S) one of the transmitting / receiving strips (3, 3 ') forms a light button with at least one of the light receivers (E) of the same transmitting / receiving strip (3, 3'), the light button being designed as a time-of-flight button, the control and Evaluation unit is formed, the Li to evaluate the 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, the distance between the opposite transmitting / receiving strip (3, 3 ') being learned and stored, and the stored value cyclically is compared with currently recorded values, with reciprocal optical communication between the two transmitting / receiving strips.

Description

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

Safety-related optoelectronic sensors are subject to high requirements with regard to the required reliability according to various standards, such as the standard "Safety of machines - non-contact protective devices (ESPE)", EN / IEC 61496 or the European standard "Functional safety of safety-related electrical, electronic, programmable electronic systems" , EN 61508. The photoelectric sensors are subdivided into safety categories that are specified 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 are used as protective measures on dangerous machines such as presses, punching tools, robots and the like. and thus the life and health of operating personnel depend on the functionality of the sensors so that the sensors can emit a safety-related switching signal in the event of danger.

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

Optical safety sensors must contain a number of self-test options for their measuring chain in order to prove their functionality and to achieve a certain safety category or a certain safety level according to a safety standard.

Depending on the desired category, the testing must go in different depths. For example, according to DIN EN 61496, a loss of detection capability in response time and a restriction in detection capability must be recognized in four seconds.

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

Today's safe light grids and light barriers with opposing transmitters and receivers are based on the closed-circuit principle. Here, the light signal is sent directly from the transmitter to the receiver and runs through a complete measuring chain. An interruption of this direct light path is detected. Changes in the received signal, e.g. B. due to windscreen contamination, transmitter degradation, etc. are shown directly in the amplitude of the received signal and can be detected directly.

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

The type of self-test used in the light curtain according to the state of the art according to the closed-circuit principle cannot be used with free-sensing light curtains / light scanners because the direct opposite side is missing.

In free-sensing systems, the amplitude of the received signal in the measuring channel is primarily dependent on the distance and the remission of the target, or is completely absent when the sensor looks into "infinity".

Sensing light grids are from the EP 2 180 348 A1 and the EP 3 091 272 B1 known.

One object of the invention is to provide a tactile light grid or safety light grid which has extensive 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, allow simple protection area monitoring and, on the other hand, enable geometric detection of the penetrating objects.

The object is achieved according to claim 1 by a safety light grille for monitoring a protected area with at least two transmitting / receiving strips with at least one light transmitter and with at least one light receiver, the transmitting / receiving strips being arranged opposite one another, and between them through the light beams of the light transmitter a protective field is formed, with at least one light transmitter of one transmitting / receiving strip and at least one light receiver of the other transmitting / receiving strip forming a transmitting / receiving pair, with means for synchronizing the transmitting / receiving strips and with a control and evaluation unit, wherein at least one of the light transmitters of one of the transmitting / receiving strips forms a light button with at least one of the light receivers of the same transmitting / receiving strip, the light button being designed as a time-of-flight button, the control and evaluation unit being designed to measure the time of flight of received light signals, etc. of the light pulses from the light receiver the light receiver has at least one single photon avalanche diode, the distance between the opposite transmitting / receiving strips being learned and stored, and the stored value being compared cyclically with currently recorded values, and reciprocal optical communication between the two transmitting / receiving strips being present.

By using pulse-shaped light signals, the light transit time which has elapsed from the emission of the light signals to the reception of the light signals can be determined, 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 scanning transmitter / receiver strips, a high-quality measurement function is implemented in addition to the classic protection function, which can be implemented both with two scanning transmitter / receiver strips separately and by a transmitter-receiver pairing of opposing transmitter / receiver strips. A passing object is measured on both sides within the protection level. With the measuring plane inclined with respect to the direction of passage, the 3-D contour can also be reconstructed from a sequence of measurements.

The double arrangement enables the protection function to be implemented on the basis of the closed-circuit current principle and enables the mutual testing of all sensor components. This enables high levels of safety, as required for many safety light curtain applications, to be achieved.

According to the invention, two preferably identically scanning send / receive strips are used, but they can also be used individually. These scanning transmitter / receiver strips - comparable to classic safety light grids - are placed opposite one another and aligned so that the individual TOF elements (e.g. SPAD sensors with integrated transmitter and receiver or TOF imager) are oriented in pairs so that they are transmitting - and reception area of the other are ( ).

In this way, a distance measurement can be carried out on both sides with each TOF element. This distance value can be compared with a configured value in order to protect the arrangement against manipulation. In addition, when an object passes through the measurement / protection plane, the object can be measured. In addition, protective fields can be defined, the integrity of which is monitored independently. The double arrangement also has the advantage that objects can be localized and tracked without having disadvantageous areas of coverage.

In addition, two-way optical communication can be set up between the two transmitting / receiving strips. This can be used for data transmission, avoidance of external transmitter interference or plausibility tests. A wired connection between the two send / receive strips is no longer necessary. The communication can also be used to implement an alignment aid.

Furthermore, a safeguarding function can be implemented identically to classic safety light grids, in which opposite transmitter-receiver pairs define a beam, the absence of which is monitored. In addition to the high level of security that such an arrangement allows, a range can be achieved that is significantly greater than with one-sided scanning safety light grids. In combination with the distance measurement function, the “object too dark for a tactile measurement” error can be detected and controlled from a safety point of view.

Single photon avalanche diodes are also referred to synonymously as 'single photon avalanche diodes' for short. Other common names are Silicon Photomultiplier '(SiPM), Geigermode Avalanche Photon Diode' or 'Single Photon Counting Diode'. Single photon avalanche diodes are photosensitive detectors that can be implemented in standard CMOS technology and convert incident photons into current pulses, similar to avalanche photo diodes. In contrast to avalanche photo diodes, single-photon avalanche diodes are operated above a breakdown voltage. A single incident photon triggers an avalanche effect, which can be detected as a current pulse. Gain factors of 10 ⁵ to 10 ⁶ enable a high level of sensitivity and thus the detection of even single photons.

Various time-of-flight methods with a corresponding evaluation can be implemented for distance measurement.

A pulse method can be provided. For example, one or more time-to-digital converters (time-to-digital converters) are provided for the pulse method in that each individual photon event is provided with a time stamp. In the case of a useful signal, several time stamps therefore occur in a correlated manner. The measured values are generated statistically. Background light, on the other hand, generates randomly distributed time stamps.

This is a send / receive strip or a safety light curtain the light transit time principle with at least one light transmitter that emits successive light pulses into a measuring area and with at least one light receiver that picks up the light pulses thrown back from the measuring area and feeds them in the form of electrical reception signals to a control and evaluation unit, which, taking into account the speed of light from the time between Transmission and reception of the light pulse determine a distance signal representative of the distance between objects and the safety light grid, the light receiver having at least one single photon avalanche diode.

Known phase measurement methods in which a modulated light signal is used can also be used. In this method, for example, the single photon events are divided into two counters via a gating signal and a phase is calculated from the ratio of the counters.

Analog signals from the single photon diode can also be evaluated. These are compared with a threshold value, are sampled or are evaluated using statistical methods.

When evaluating according to the time-of-flight method, an amplitude value can also be generated in addition to the distance value, e.g. B. 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, particularly in the case of safety-related applications.

The safety light grid according to the invention has the advantage that it is designed to be 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. This means that the safety light curtain can be highly integrated, e.g. B. using ASIC modules. 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 control can also be integrated on the chip.

The safety light grid is more cost-effective than the safety light grid with photosensitive receivers that has been customary in security technology. The multiple arrangement of light scanners, consisting of at least one light transmitter and at least one light receiver, enables very compact systems. The use of single-photon avalanche diodes ensures high sensitivity down to single photons. This means that optional optics can be made very compact.

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

With the safety light grid according to the invention, object intrusions can initially be recognized simply and over large ranges. If an object enters the protective field between the transmitting / receiving strips, at least one transmitting / receiving pair detects a light beam interruption, which generates an object detection signal and, as a result, a safety switching signal. Such a light beam interruption can easily be evaluated and detected. This ensures a short response time for the safety light curtain. An interruption in the light beam is easy to detect, even over long ranges.

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

In addition, the light scanner formed according to the invention with the safety light grid also makes it possible to obtain precise information on an object contour which could not be detected by a simple beam interruption. However, an object can now be measured by the light scanner or, based on the detected object contour, the object can be classified as a permissible or impermissible object 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 the protective field.

If an object is transported through the safety light grid, for example on a conveyor belt, on the one hand a height profile of the object can be determined and stored by interrupting the individual transmit / receive pairs and, on the other hand, the distance contour data of one of the side of the object facing the respective transmission / reception bar can be detected and stored. With the safety light grid according to the invention, a height profile and a lateral distance contour can thus be recorded at the same time and used to assess the object.

In certain applications, it is provided that predefined, permitted objects can pass the protection area without a safety switching signal being generated. For example, when permissible objects cross the protected area, for example by means of a conveyor belt, no safety switching signal is triggered, while when conveying an impermissible object, for example a person, through the protected area - even if the person is to the side of the permitted object and does not protrude beyond it - a corresponding safety switching signal is triggered.

The comparison of two scanning transmitter / receiver strips makes it possible to detect errors very reliably and to react in a safety-oriented manner. As a result, a safety function can achieve a higher level of safety than would be the case with a single system. The detection capability can also be expanded. A very dark object with a remission below a detection threshold can be detected with the present double system due to the lack of light pulses from the opposite transmitting / receiving strip.

In a further development of the invention, the distance between the opposite bar is taught in and stored, and the stored value is compared cyclically with currently recorded values.

By teaching in and saving the distance, a change in the distance can be recognized.

The distance or the measured distance value is determined, for example, on both sides, i.e. redundantly, during commissioning and monitored cyclically or continuously during operation. If smaller distances are measured during operation, there is an object in the protection area. There is therefore no fault.

If, however, distances greater than the taught-in distance are measured on one or both sides, one of the following error cases is present, for example: Firstly, manipulation by twisting one or both transmitter / receiver strips. Second, a reflection or the introduction of a reflective object. Third, a systematic drift of a measured value from a transmit / receive strip.

In addition, the measured distance values of the opposing transmitting / receiving strips can be checked. In addition to checking the consistency during operation, the comparison of opposing channels can also be used to verify and support alignment. Since a tactile safety light grid has to use more strongly collimated light than a conventional safety light grid for energy reasons, alignment becomes more difficult and support with the aid of the measurement data is desirable. In any case, the measured value of opposing measuring channels of the transmitter / receiver strips must match within a narrow tolerance range, otherwise the measuring beams will not lie on top of each other and the transmitter / receiver strips are not sufficiently aligned with each other.

In summary, the presence of the opposite signal can be checked by juxtaposing two scanning send / receive strips to form a safety light curtain and aligning the individual measuring channels in pairs. The measured values of overlapping beams can be compared with each other and with taught reference values. The signal strengths of opposing beams can be compared with each other and with taught reference values. The absence of jammers is also possible in this way, since their signal energy does not correspond to expectations due to the greater distance.

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 taught-in 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 remission below a detection threshold. In this case, the signal level is insufficient for detection on one side or on both sides. However, in this case the absence of the opposite transmit signal still leads to shutdown and thus allows the detection of very dark objects that would not be detectable with a single transmit / receive strip.

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

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

The exact time behavior or timing of the light transmitter can be monitored and any offsets that may occur can be corrected, e.g. B. in the case of temperature influences.

In the phases in which no light is emitted, the external light level can be measured at the reference light receiver. 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 can be used with optional other scaling 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 assessment of the functionality.

A direct measurement of the external light level on the light receiver and, if necessary, on the reference light receiver enable 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 a reference light transmitter for safety-related self-testing.

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

In this way, the receiving channel can be tested for the time behavior or timing as well as signal level-dependent effects.

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

Overload measurements in particular can be carried out easily in this way. The time behavior, i.e. the timing of the distance measuring chain, can be tested via a programmable variable delay in front of the light transmitter.

The dynamics of the light receiver can be tested via an adjustable signal level of the light transmitter.

• Erstens kann eine Linearität und eine Integrität der Empfangssignale des Lichtempfängers für verschiedene Verzögerungen bzw. Lichtlaufzeiten gewährleistet werden. Damit kann indirekt die Abstandsmessung überprüft werden.

The reference light transmitter enables the following tests, for example:

• Firstly, a linearity and an integrity of the received signals of the light receiver can be guaranteed for different delays or light transit times. This allows the distance measurement to be checked indirectly.

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

Third, e.g. B. overdrive measurements can be carried out if necessary.

In a further 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, e.g. 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 individual photon avalanche diode, for example using a comparator or an analog-digital converter. However, the avalanche signals can also be processed further digitally if the signal is already sufficiently high.

In order to cover the possibility of a larger angular range through the safety light grid and still have the necessary spatial resolution for detection z. B. a leg, the single-photon avalanche diode array can be divided into so-called macropixels. Here, several spatially adjacent single photon avalanche diode cells belong to a common evaluation and evaluate the received light from a certain angular range via appropriate optics. The arrangement can be linear or flat.

The dynamics and / or the external light behavior can be scaled via the various single-photon avalanche diodes or single-photon avalanche diode arrays.

In the case of single-photon avalanche diode arrays, the signal level can either be determined directly via the count rates of the photons, if the signals are digitized directly at the pixel level, or via the measurement of the amplitude of the total current of all pixels. In the monitoring state, both values are continuously measured and compared with the taught-in setpoint. If deviations occur in one of the two values, this deviation is checked for plausibility using the second measured value and, if necessary, detected as an intervention.

The possibility of a background light measurement in the single photon avalanche diode array is interesting for a safety sensor. In the case of a single-photon avalanche diode, the extraneous light is a dominant source of noise via the 'shot noise'. The thermal noise is significantly lower than that of classic photodiode receivers, since the transimpedance converter common in the classic receiving path, which is a main source of thermal noise, is not required. On the single-photon avalanche diode array, the external light level can be determined during the transmission pauses of the measuring system via the number of external light photons incident on the light receiver. For example, in the case of the phase measurement method mentioned, by means of a further gating signal which adds up the individual photon events in a counter in the corresponding transmission pauses.

For a safe detection of objects in a safe safety light grid, a necessary signal-to-noise ratio can be defined beforehand, at which an object must be detected under all circumstances. By determining the level of extraneous light during the measurement cycle, it can be monitored whether the noise level is too high compared to an expected signal from the intervening object and whether it has to be switched off accordingly in a safety-oriented manner.

The light transmitter and / or light receiver is preferably both part of the transmitter / receiver pair and part of the light scanner. One and the same light transmitter or light receiver is therefore necessary in order to form both a transmitter / receiver pair and a light switch. After the light beam is interrupted by an object, the light beam reflected by the object is directed to an associated receiving element of the same transmitting / receiving strip as the light transmitter and a distance signal is determined.

In a further development of the invention, the light transmitters and light receivers are individually arranged alternately one after the other in the transmitting / receiving strips. A plurality of light transmitters and light receivers is preferably arranged in this case. This ensures a uniform resolution of the safety light grid over the entire length of the protective field. Advantageously, the light scanners are also directly adjacent to one another, evenly distributed over the entire length of the protective field.

If a bar is rotated lengthways by 180 ° opposite the opposite bar, the light transmitter and light receiver are directly opposite to form the transmitter / receiver pairs, creating a homogeneous protective field with parallel light beams. The transmitters and receivers for forming the light switch are also right next to each other.
In a further development of the invention, adjacent light transmitters and light receivers each form a light switch. This ensures a particularly simple structure of the safety light grid and the light sensors formed are arranged as a unit with uniform distances from one another along a transmitting / receiving strip. With this arrangement, the safety light grid can be set up modularly for different protective field heights. Depending on the height of the protective field, a certain number of adjacent light transmitters and light receivers are arranged to form light sensors. Due to the adjacent arrangement of the light scanners, the measured distance values can also be assigned directly to a respective transmit / receive pair, so that when a light beam is interrupted, an associated distance of the object interrupting the light beam is determined directly.

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

In order to achieve a short response time, several light scanners or several light barriers can be operated in parallel, preferably in an arrangement without overlapping transmission lobes or reception lobes. For example, neighboring light buttons or light barriers are activated at the same time.

Here, different light transmitters have different pulse repetition frequencies, modulation frequencies or different phases.

This means that neighboring light switches can be activated in parallel without crosstalk occurring between the channels.

In a further development of the invention, the transmission / reception strips are constructed identically. This means that only a single assembly, namely the transmission / reception strip, has to be produced in order to provide a safety light grid consisting of two such opposite transmission / reception strips. To maintain the safety light grid, only a single send / receive strip needs to be stored in order to have a functional replacement strip to hand in the event of failure or malfunction of a strip.

Electrical connections for both transmission / reception strips are also identical. This simplifies connection technology, since only one type of plug connector has to be provided. The transmission / reception strips can therefore also be easily connected, since different connections for the transmission strip and reception strip do not have to be provided as with previous safety light grids, consisting of transmission strip and separate reception strip.

According to a further embodiment, characteristic contours of the permissible objects are taught-in by teaching-in the distance values that result when the emitted light signals are reflected on 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 switching signal is generated, and no safety switching signal is generated if the measured distance values match the distance values of permissible objects within a specified tolerance range.

Depending on the shape of the permissible objects, several permissible distance values can be stored, which are different depending on the point of incidence of the light beams, especially when using several light sensors. If an impermissible object enters the protected area or if a permitted object is not correctly positioned, the determined distance does not match the permitted distance, so that in this case a safety switching signal is generated.

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

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

First, the distances and signal amplitudes can be learned in relation to a natural reference surface. The safety light curtain measures any deviation from these learned values, namely distances that are too large or too small, or too large or too small signal amplitudes lead to a protective field violation and an object detection signal.

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

Second, the distances for each measurement channel can be configured with the appropriate software. Here, the safety light grid measures freely in the room and any undershooting of the configured distance value leads to a protective field violation. In this way, variable protective field geometries can be implemented, which can also be achieved by switching protective fields, for example muting or blanking e.g. B. can be changed in a cycle operation. The safety-related sensor testing is more difficult in this case, since expected values cannot be assumed.

By briefly interrupting the measuring cycle, it is possible to use the light receiver to determine a level caused by extraneous light. When measuring the signal level, fluctuations on longer time scales, for example due to temperature changes or changes in the ambient light, can be continuously logged and the setpoint values can be adjusted accordingly.

In a further development of the invention, a first light receiver with a first light transmitter forms a first light switch and the first light receiver with a second light transmitter forms a second light switch, the first light transmitter and the second light transmitter being activated one after the other.

In the case of safety light grids according to the state of the art, the geometric resolution is specified by the beam spacing. With the scanning safety light grid according to the invention, the distance between the collimated light transmitters is used to define the geometric resolution.

In order to save costs, a single light receiver can be used serially for the scanning safety light grid for the evaluation of two or more light transmitters adjacent to it. This allows some of the light receivers to 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 forms a first light switch and a second light receiver with the first light transmitter forms a second light switch.

This offers a further possibility for higher detection reliability in the safety light grid through a parallel evaluation of two adjacent light receivers that receive light pulses from a single light transmitter. This enables redundancy to be achieved in the entire safety light grid.

In one embodiment of the invention, transmission optics, in particular a lens, are arranged upstream of the light transmitter. The transmission optics are optionally integrated on a chip or in the chip housing in order to achieve a cost-effective and compact solution, especially for large quantities.

Thanks to a high level of integration and the small size of the transmitter optics, the safety light curtain is very compact.

Different monitoring angles and different ranges can be implemented using different transmission optics.

In a further embodiment, receiving optics, in particular a lens, are arranged in front of the light receiver.

The receiving optics are optionally integrated on a chip or in the chip housing in order to achieve a cost-effective and compact solution, especially for large quantities.

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

The safety light grid is very compact thanks to a high level of integration and the small size of the receiver optics.

Different monitoring angles and different ranges can be implemented using different receiving optics.

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

Thanks to the two-channel control and evaluation unit, the safety light grid can be used as an independent safety sensor or safety light grid, even if there are higher demands on the safety level to be achieved.

As a result, the safety light grid itself is able to carry out a large number of self-tests and to ensure its own functionality in a comprehensive manner.

Furthermore, several light buttons can also communicate via a common bus and a central safety controller or safety controller is used to configure the individual light buttons, query their status and, if necessary, feed in suitable test signals, evaluate and compare the received signals, signal warnings and in the event of danger to stop a machine to be secured or a self-driving vehicle to be secured.

For example, it can be sufficient if each individual light button on the shared bus only reports when its measured values violate or exceed previously learned thresholds or have diagnosed a problem during a self-diagnosis.

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

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

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

A modular structure serves as the basis for the safety light grid. The safety light curtain has, for example, the following components: optics 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 control.
The measuring core preferably consists of a highly integrated CMOS ASIC. However, a construction from discrete components is also possible.

Due to the good directional characteristics of light, different variants of the safety light grid with different opening angles and ranges can be implemented using appropriate optical modules, which are adapted to different requirements of different applications. The light rays can through optical elements are collimated or expanded further.

To restrict the incidence of external light, the light receiver can be provided with a filter element, for example with a bandpass filter.

In the following, the invention is explained in detail on the basis of exemplary embodiments with reference to the drawing.

• 1 und 2 eine schematische Darstellung eines erfindungsgemäßen Sicherheitslichtgitters.

In the drawing shows:

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

1 shows a safety light curtain 1 for monitoring a protected area with at least two transmitter / receiver strips 3 , 3 ' with at least one light transmitter S. and with at least one light receiver E. , with the send / receive strips 3 , 3 ' are arranged opposite to each other, and between them by the light rays 4th the light transmitter S. a protective field 2 is formed, with at least one light transmitter in each case 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 synchronizing the transmit / receive strips 3 , 3 ' and with a control and evaluation unit, according to 2 at least one of the light transmitters S. one of the send / receive bars 3 , 3 ' with at least one of the light receivers E. the same send / receive bar 3 , 3 ' forms a light switch, the light switch being designed as a time-of-flight switch, the control and evaluation unit being designed to measure the time of flight of received light signals or light pulses from the light receiver E. evaluate, the light receiver E. has at least one single photon avalanche diode.

By using pulse-shaped light signals, the light transit time which has elapsed from the emission of the light signals to the reception of the light signals can be determined, which is representative of the distance to the object.

Due to the double arrangement of two scanning send / receive strips 3 , 3 ' is in addition to the classic protection function, which is both with both tactile transmitter / receiver strips 3 , 3 ' separately as well as through a transmitter-receiver pairing of opposing transmitter / receiver strips 3 , 3 ' can be realized, in addition, a high-quality measurement function is implemented. A passing object is measured on both sides within the protection level. With the measuring plane inclined with respect to the direction of passage, the 3-D contour can also be reconstructed from a sequence of measurements.

According to 1 are two preferably identically groping send / receive strips 3 , 3 ' used, but they can also be used individually. These groping send / receive strips 3 , 3 ' are - comparable to classic safety light grids - attached opposite one another and aligned with one another so that the individual TOF elements (e.g. SPAD sensors with integrated transmitter and receiver or TOF imager) are oriented in pairs so that they are in the sending and receiving area of the other lie.

In this way, a distance measurement can be carried out on both sides with each TOF element. This distance value can be compared with a configured value in order to protect the arrangement against manipulation. In addition, when an object passes through the measurement / protection plane, the object can be measured. And protective fields can also 2 can be defined, the integrity of which is monitored independently. The double arrangement also has the advantage that objects can be localized and tracked without having disadvantageous areas of coverage.

Furthermore, a safeguarding function can be implemented identically to classic safety light grids, in which opposite transmitter-receiver pairs define a beam, the absence of which is monitored. In addition to the high level of security that such an arrangement allows, a range can also be achieved that is significantly greater than with one-sided scanning safety light grids. In combination with the distance measurement function, the “object too dark for a tactile measurement” error can be detected and controlled from a safety point of view.

If an object penetrates the protective field 2 one so that at least one of the emitted light beams 4th 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, depending on the application, leads to a desired follow-up action. This can be, for example, the output of a safety switching signal for stopping a machine to be monitored, for outputting an alarm signal, outputting measured values or also storing measured values.

Through the safety light curtain 1 object tampering can initially be recognized easily and over a large range. If an object enters the protective field 2 between the send / receive strips 3 , 3 ' on, at least one transmit / receive pair detects a light beam interruption, whereby an object detection signal is generated and as a result, possibly a safety switching signal. Such a light beam interruption can easily be evaluated and detected. This results in a short response time for the safety light curtain 1 guaranteed. An interruption in the light beam is easy to detect, even over long ranges.

To detect objects of different sizes, the transmit / receive pairs are arranged at equal distances from one another. An object height can be determined by means of the number of interrupted, adjacent light beams and the distance between the light beams.

In addition, it is through the formed light buttons 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 the light scanner or, based on the detected object contour, the object can be classified as a permissible or impermissible object and an object detection signal or safety switching signal can be generated depending on this result. With the safety light grid 1 it is thus possible to determine not only the object height but also the lateral contour of the object while the object passes the protective field.

For example, if an object is on a conveyor belt through the safety light curtain 1 transported, on the one hand a height profile of the object can be determined and stored by interrupting the individual transmit / receive pairs and on the other hand the distance contour data on a side of the object facing the respective transmit / receive strip can be recorded and stored at the same time. Through the safety light curtain 1 a height profile and a lateral distance contour can thus be recorded at the same time and used to assess the object.

In certain applications, it is provided that predefined, permitted objects can pass the protection area without a safety switching signal being generated. For example, when permissible objects cross the protected area, for example by means of a conveyor belt, no safety switching signal is triggered, while when conveying an impermissible object, for example a person, through the protected area - even if the person is to the side of the permissible object and does not protrude beyond it - a corresponding safety switching signal is triggered.

The comparison of two scanning transmitter / receiver strips 3 , 3 ' enables error cases to be detected very reliably and to react in a safety-oriented manner. As a result, a safety function can achieve a higher level of safety than would be the case with a single system. The detection capability can also be expanded.
According to 1 and 2 becomes the distance between the opposing transmitter / receiver strips 3 , 3 ' learned and saved, and the saved value is compared cyclically with currently recorded values.

The distance or the measured distance value is determined, for example, on both sides, i.e. redundantly, during commissioning and monitored cyclically or continuously during operation. If smaller distances are measured during operation, there is an object in the protection area. There is therefore no fault.

If, however, greater distances than the taught-in distance are measured on one or both sides, an error has occurred, for example.

The measured distance values of the opposite transmit / receive strips can also be used 3 , 3 ' be checked. In addition to checking the consistency during operation, the comparison of opposing channels can also be used to verify and support alignment.

In summary, by comparing two scanning send / receive strips 3 , 3 ' to form a safety light curtain 1 and pairwise alignment of the individual measuring channels, the presence of the opposite signal can be checked. The measured values of overlapping beams can be compared with each other and with taught reference values. The signal strengths of opposing beams can be compared with each other and with taught reference values. The absence of jammers is also possible in this way, since their signal energy does not correspond to expectations due to the greater distance.

The light transmitter is preferably 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 transmitter is S. or light receiver E. necessary to create both a transmit / receive pair and a light button. After the light beam is interrupted by an object, the light beam reflected by the object is sent 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 transmitters S. and light receivers E. individually alternating one after the other in the send / receive bars 3 , 3 ' arranged. A plurality of light transmitters is preferably used S. and light receivers E. arranged. This ensures a uniform resolution of the safety light curtain 1 Guaranteed over the entire length of the protective field. Advantageously, the light scanners are also directly adjacent to one another, evenly distributed over the entire length of the protective field.

Becomes a send / receive bar 3 , 3 ' lengthways according to 1 and 2 rotated by 180 ° in relation to the opposite send / receive strip 3 ' , 3 mounted, so are the light transmitters S. and the light receivers E. to form the transmit / receive pairs directly opposite, creating a homogeneous protective field with parallel light beams. The light transmitter S. and the light receivers E. to form the light button are also right next to each other here.

According to 2 form neighboring light transmitters S. and light receivers E. a light button. This results in a particularly simple construction of the safety light grid 1 guaranteed and the formed light buttons are as a unit with uniform distances from one another along a transmitting / receiving strip 3 , 3 ' arranged. This arrangement allows the safety light curtain 1 can be set up modularly for different protective field heights. Depending on the height of the protective field, a certain number of neighboring light transmitters S. and light receivers E. arranged to form light sensors. Due to the adjacent arrangement of the light scanners, the measured distance values can also be assigned directly to a respective transmit / receive pair, so that when a light beam is interrupted, an associated distance of the light beam is also directly assigned 4th interrupting object is determined.

According to 1 and 2 are the send / receive strips 3 , 3 ' for example constructed identically. This means that only one module, namely the transmit / receive strip, needs to be installed 3 or. 3 ' be made to a safety light curtain 1 , consisting of two such opposing transmit / receive strips 3 , 3 ' to provide.

Also electrical connections for both transmitter / receiver strips 3 , 3 ' are designed identically. This simplifies connection technology, since only one type of plug connector has to be provided. The send / receive strips 3 , 3 ' can therefore also be easily connected, as there is no need to provide different connections for the sending bar and receiving bar, as was the case with previous safety light grids, consisting of a transmitter bar and a separate receiver bar.

The described embodiments can also be combined with one another, so that the light scanners of the light grid according to the invention can fulfill various functions.

List of reference symbols

1

Safety light curtain

2

Protective field

3, 3 '

Send / receive strips

4th

Rays of light

S.

Light transmitter

E.

Light receiver

Claims (9)

Safety light grid (1) for monitoring a protected 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') are arranged opposite one another, and between them a protective field (2) is formed by the light beams (4) of the light transmitter (S), with at least one light transmitter (S) of the one transmitting / receiving strip (3; 3 ') and at least one Light receiver (E) of the other transmitting / receiving strip (3 ', 3) form a transmitting / receiving pair, with means for synchronizing the transmitting / receiving strips (3, 3') and with a control and evaluation unit, at least one of the Light transmitter (S) of one of the transmission / reception strips (3, 3 ') forms a light switch with at least one of the light receivers (E) of the same transmission / reception strip (3, 3'), the light switch being designed as a time-of-flight switch - and evaluation unit is formed to evaluate the light travel 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, the distance between the opposite transmitting / receiving strip (3, 3 ') being learned and stored, and the The stored value is compared cyclically with the currently recorded values, with reciprocal optical communication between the two transmitting / receiving strips. Safety light curtain (1) Claim 1 , rather characterized in that a further light receiver (E) is provided as a reference light receiver as a second receiving channel for safety-related 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 switch. Safety light grille (1) according to at least one of the preceding claims, characterized in that the light transmitters (S) and the light receivers (E) are arranged individually and alternately one after the other in the transmitting / receiving strips (3, 3 '). Safety light grid (1) according to at least one of the preceding claims, characterized in that adjacent light transmitters (S) and light receivers (E) each form a light switch. Safety light grid (1) according to at least one of the preceding claims, characterized in that a plurality of light transmitters (S) and a plurality of light receivers (E) each have an optical coding in pairs, which leads to adjacent pairs of light transmitters (S) and light receivers (E ) is different, so that a plurality of light transmitters (S) and a plurality of light receivers (E) can be controlled and evaluated simultaneously. Safety light grid (1) according to at least one of the preceding claims, characterized in that the transmitting / receiving strips (3, 3 ') are constructed identically.

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