DE102018117878A1 - Safety Light Curtain - Google Patents

Abstract

Safety light grid 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 arranged opposite one another and between them a protective field (2) is formed by the light beams of the light transmitters, at least one light transmitter (S) of the one transmitting / receiving bar (3; 3 ') and at least one light receiver (E) of the other transmitting / Receiving bar (3, 3 ') form a transmitting / receiving pair, with means for synchronizing the transmitting / receiving bars (3, 3') and with a control and evaluation unit, at least one of the light transmitters (S) being one of the transmitting / Receiving bar (3; 3 ') with at least one of the light receivers (E) of the same transmitting / receiving bar (3; 3') forms a light button, the light button being designed as a light transit time button, with the control and evaluation unit being formed by the L Evaluate the non-running time of received light signals or light pulses from the light receiver (E), the light receiver (E) having at least one single photon avalanche diode.

Description

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

Safety-related optoelectronic sensors are subject to high requirements with regard to the required reliability in accordance with 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 optoelectronic sensors are divided into safety categories, which are specified in the standard "Safety-related parts of control systems"
EN 954 or its successor standard EN 13849 are defined.

Standardized safety levels are necessary because such sensors act as protective measures on dangerous machines, such as presses, punching tools, robots and the like. are used and thus the life and health of operating personnel depends 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 zone of a machine tool in order, if necessary, to detect the entry into 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 contain a number of self-test options for their measuring chain in order to demonstrate their functionality and to achieve a certain security category or a certain security level in accordance with a security standard.

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

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

Today's safe light grids and light barriers with opposing transmitters and receivers are based on the closed-circuit principle. 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. by windshield soiling, transmitter degradation, etc. show up 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 detected and a warning or stop signal can be issued accordingly.

The type of self-testing according to the quiescent current principle used in the light grid according to the prior art cannot be used with free-touching light grids / light buttons, since the direct opposite side is missing.

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

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

One object of the invention is to provide a scanning light grid or safety light grid which has extensive possibilities for self-testing in order to obtain the highest possible safety category. Another object is to provide a light curtain and a method which, on the one hand, allows simple protection zone monitoring and, on the other hand, enables geometrical detection 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 transmission / reception strips with at least one light transmitter and with at least one light receiver, the transmission / reception strips being arranged opposite one another, and between them by the light beams of the light transmitters a protective field is formed, in each case at least one light transmitter of the one transmission / reception strip and at least one light receiver of the other transmission / reception strip forming a transmission / reception pair, with means for synchronizing the transmission / reception strips and with a control and evaluation unit, wherein at least one of the light transmitters of the transmission / reception bar forms a light scanner with at least one of the light receivers of the same transmission / reception bar, the light scanner being designed as a time-of-flight sensor, the control and evaluation unit being designed to receive the time of flight light To evaluate light signals or light pulses from the light receiver, the light receiver having at least one single photon avalanche diode.

By using pulsed light signals, the light propagation time elapsed from the transmission 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 curtain with the advantages of sensing systems. The double arrangement of two scanning transmit / receive bars, in addition to the classic security function, which can be implemented both with two scanning transmit / receive bars separately and with a transmitter-receiver pairing of opposite transmit / receive bars, also implements a high-quality measurement function. A penetrating object is measured on both sides within the protection level. If the measuring plane is inclined relative to the direction of passage, the 3D contour can also be reconstructed from a series of measurements.

The double arrangement allows the realization of the protection function on the basis of the closed-circuit principle and enables the mutual testing of all sensor components. This enables high levels of security to be achieved, which are required for many security light curtain applications.

According to the invention, two preferably identically keying transmit / receive bars are used, which, however, can also be used individually. Comparable to classic safety light grids, these scanning transmit / receive strips are attached opposite 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 transmit - and reception 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 to a configured value in order to protect the arrangement against manipulation. In addition, the measurement of the object can take place when an object passes through the measurement / protection level. In addition, protective fields can be defined, the intactness of which is monitored independently. The double arrangement also has the advantage that objects can be localized and tracked without having disadvantageous concealment areas.

In addition, mutual optical communication can be established between the two send / receive bars. This can be used for data transmission, avoidance of third-party transmitter interference or plausibility tests. A wired connection of the two transmit / receive bars is no longer necessary. Communication can also be used to implement an alignment aid.

Furthermore, a safeguarding function can be implemented that is identical to classic safety light grids, in which opposite transmitter-receiver pairs define a beam, the uninterruptibility of which is monitored. In addition to the high security levels that such an arrangement allows, a range can also be achieved that is significantly greater than with one-sided, touching safety light grids. In combination with the distance measurement function, the "Object too dark for a tactile measurement" error case can be detected and mastered 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), 'Geiger Mode Avalanche Photon Diode' or 'Single Photon Counting Diode'. Single-photon avalanche diodes are photosensitive detectors which can be implemented using standard CMOS technology and, similar to avalanche photo diodes, convert incident photons into current pulses. In contrast to avalanche photo diodes, single photon avalanche diodes are operated via a breakdown voltage. A single incident photon thus triggers an avalanche effect that can be detected as a current pulse. Gain factors from 10 ⁵ to 10 ⁶ enable high sensitivity and thus the detection of individual 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 are provided for the pulse method by providing each individual photon event with a time stamp. Several time stamps therefore occur correlated in the case of a useful signal. The measurement value is generated statistically. Backlight, however, creates randomly distributed timestamps.

This is a transmission / reception bar or a safety light grid based on the time-of-flight principle with at least one light transmitter that sends successive light pulses into a measuring range and with at least one light receiver that receives the light pulses that are thrown out of the measuring range and 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 the transmission and reception of the light pulse, determines a distance signal representative of the distance from objects to the safety light curtain, the light receiver having at least one single photon avalanche diode.

Known phase measurement methods can also be used, in which a modulated light signal is used. In these methods, 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 counter readings.

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

When evaluating using the time-of-flight method, an amplitude value can be generated in addition to the distance value, e.g. B. by a histogram of the timestamp, by the counting rate or by the voltage amplitude in an analog evaluation. A plausibility check can be carried out using the amplitude value, in particular in safety-related applications.

The safety light curtain according to the invention has the advantage that it is 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. The safety light curtain is thus highly integrable, e.g. B. using ASIC devices. 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 curtain is less expensive than previously used safety light curtains with photosensitive receivers. Very compact systems are possible due to the multiple arrangement of light buttons, consisting of at least one light transmitter and at least one light receiver. The use of single-photon avalanche diodes provides high sensitivity down to individual photons. This means that optional optics can 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 propagation 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 emitting an alarm signal, for outputting measured values or for storing measured values.

The safety light curtain according to the invention initially makes it easy to detect object interventions over large ranges. If an object enters the protective field between the transmission / reception strips, at least one transmission / reception pair detects an interruption in the light beam, as a result of which an object detection signal is generated and, as a result, a safety switching signal. Such a light beam interruption can be easily evaluated and detected. This ensures a short response time for the safety light curtain. A light beam interruption is easy to detect even for 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 using the number of interrupted, adjacent light beams and the spacing of the light beams from one another.

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

If, for example, an object is transported on a conveyor belt through the safety light curtain, a height profile of the object can be determined and saved on the one hand by interrupting the individual transmitting / receiving pairs and on the other hand the distance contour data of one of the respective transmitting / Receiving bar facing side of the object can be detected and saved. By means of the safety light grid according to the invention, a height profile and a lateral distance contour can thus be detected at the same time and used to assess the object.

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

The juxtaposition of two scanning transmitter / receiver strips makes it possible to uncover fault cases very reliably and to react in a safety-related manner. This enables a safety function to 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 reflectance below a detection threshold can be detected with the present double system due to the lack of light pulses from the opposite send / receive bar.

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.

A change in the distance can be recognized by teaching and storing the distance.

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

If, however, larger distances than the taught distance are measured on one or both sides, one of the following error cases occurs, for example: Firstly, manipulation by turning one or both transmission / reception bars. Secondly, a reflection or the introduction of a reflective object. Third, a systematic drift of a measured value of a send / receive bar.

The distance measured values of the opposite send / receive strips can also be checked. The comparison of opposite channels can be used in addition to the consistency check in the company to verify and support the alignment. Since a touching safety light curtain must use more collimated light than a conventional safety light curtain for energy reasons, alignment becomes more difficult and support with the help of the measurement data is desirable. In any case, the measured value of opposite measurement channels of the transmit / receive strips must match within a narrow tolerance range, otherwise the measurement beams are not on top of one another and the transmit / receive strips are not sufficiently aligned with one another.

In summary, the presence of the opposite signal can be checked by comparing two scanning transmit / receive bars 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. The absence of jamming transmitters 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 a comparison with a learned reference value allows the evaluation of a receiver sensitivity. A comparison with the opposite reception signal allows the evaluation of contamination.

An object with remission below a detection threshold can also be the cause of this signal dropout. In this case, the signal level on one or both sides is not sufficient for detection. In this case, however, the absence of the opposite transmission signal leads to the switch-off 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 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 occur can be corrected, e.g. B. with temperature influences.

In the phases in which no light is emitted, the ambient light level can be measured on 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, with optional other scaling, can be used to check the necessary signal-to-noise ratio in the actual measurement channel.

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

A direct measurement of the extraneous light level on the light receiver and possibly on the reference light receiver enables 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.

In this way, a failure or a signal loss of one or more measuring channels can be determined. If a signal from an opposite light transmitter is detected, but not the light pulse from a light transmitter on the same side, then it is assumed that the light transmitter has failed or that it is contaminated locally.

As a result, the reception channel can be tested for the timing or timing as well as signal height-dependent effects.

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

Oversteer measurements in particular can be easily carried out 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 height of the light transmitter.

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

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

Secondly, 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. Override measurements can be 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, 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 single-photon avalanche diode, for example using a comparator or an analog-digital converter. However, the avalanche signals can also be directly digitally processed if the signal is already sufficiently high.

To cover the possibility of a larger angular range through the safety light curtain and still the necessary spatial resolution for detection z. B. to get a leg, the single photon avalanche diode array can be divided into so-called macropixels. In this case, several spatially adjacent single-photon avalanche diode cells are associated with a common evaluation and evaluate the light received from a certain angular range using 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 single-photon avalanche diode arrays, the signal level can either be determined directly via the counting rates of the photons, if the signals are digitized directly at the pixel level, or by measuring the amplitude of the total current of all pixels. In the monitoring state, both values are continuously measured and compared with the learned setpoint. If there are deviations in one of the two values, this deviation becomes Plausibility check of the second measured value and possibly 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 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, which is a main source of thermal noise, which is common in the classic reception path, is not required. On the single photon avalanche diode array, the extraneous light level can be determined in the transmission pauses of the measuring system via the number of incident extraneous light photons 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 during the corresponding transmission pauses.

For the 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 recognized 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 interfering object and must be switched off in a safety-related manner.

The light transmitter and / or light receiver is preferably both part of the transmitter / receiver pair and part of the light button. One and the same light transmitter or light receiver is therefore necessary in order to form both a transmitter / receiver pair and a light sensor. After the light beam is interrupted by an object, the light beam remitted by the object is directed to an associated receiving element of the same transmitting / receiving bar 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 transmission / reception strips. A plurality of light transmitters and light receivers is preferably arranged. This ensures a uniform resolution of the safety light curtain over the entire protective field length. The light sensors are also advantageously located directly adjacent to one another and evenly distributed over the entire protective field length.

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

In a further embodiment, a plurality of non-adjacent light transmitters can be activated at the same time.

In order to achieve a low 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 sensors or light barriers are activated at the same time.

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

This means that neighboring light sensors can be activated in parallel at the same time without crosstalk occurring between the channels.

In a further development of the invention, the transmit / receive strips are constructed identically. This means that only a single module, namely the transmission / reception bar, has to be manufactured in order to provide a safety light grid consisting of two such transmission / reception bars located opposite one another. For maintenance of the safety light curtain, only a single transmission / reception bar needs to be kept in stock, so that in the event of a failure or malfunction of a bar, a functional replacement bar is at hand.

Electrical connections for both transmit / receive strips are also identical. This simplifies a connection technique, since only one type of connector has to be provided. This allows the send / receive bars can also be easily connected, as it is not necessary, as with previous safety light grids, consisting of a transmitter bar and separate receiver bar, to provide different connections for the transmitter bar and receiver bar.

According to a further embodiment, characteristic contours of the permissible objects are taught in, by teaching in the distance values that result from the reflection of the emitted light signals 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 permitted objects within a specified tolerance range.

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

In a further development of the invention, a reference surface is provided, the light signals or light pulses from the light transmitter hitting the reference surface and the reflected light signals or light pulses hitting the light receiver. However, an existing contour can optionally 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 taught in compared to a natural reference surface. Here, the safety light grid measures any deviation from these learned values, namely 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 curtain is easier 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 curtain, for example aging of the light transmitter, influence of extraneous light and / or contamination leads to a deviating measured value either when monitoring the amplitude or the distance.

Secondly, the distances for each measuring channel can be configured with appropriate software. Here, the safety light curtain measures freely in the room and every fall below the configured distance value leads to a protective field violation. Variable protective field geometries can be realized, which can also be done by switching the protective field, for example muting or blanking z. B. can be changed in a clock mode. In this case, safety-related sensor testing is more difficult because it cannot be expected.

By briefly interrupting the measuring cycle, it is also possible to determine a level by means of external light radiation using the light receiver. When measuring the signal level, fluctuations on longer time scales, for example due to temperature changes or changes in ambient light, can be continuously logged and the setpoints 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 able to be activated in succession.

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

To save costs, a single light receiver can be used in series with the scanning safety light curtain for the evaluation of two or more light transmitters adjacent to it. This saves some of the light receivers. 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 security in the safety light grid by a parallel evaluation of two neighboring light receivers, which receive light impulses from a single light transmitter. This can redundancy can be achieved in the entire safety light grid.

In one embodiment of the invention, the light transmitter is preceded by a transmission 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, particularly in the case of large quantities.

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

Different monitoring optics and different ranges can be realized through different transmission optics.

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

The receiving optics are optionally integrated on a chip or in the chip housing in order to achieve an inexpensive 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.

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

Different monitoring optics 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 curtain can be used as an independent safety sensor or safety light curtain even with higher demands on the safety level to be achieved.

This enables the safety light curtain itself to carry out a large number of self-tests and to ensure its own functionality in a comprehensive manner.

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

For example, it may be sufficient if each individual light sensor on the common bus only reports when its measured values violate or exceed previously taught-in thresholds or have diagnosed a problem with self-diagnosis.

In a further development of the invention, the light sensor is an integrated light sensor 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 one chip. With this technology, all components of the measuring chain of the light sensor can be integrated in a single ASIC. The ASIC is able to measure distance values independently and to pass the final result on to the central controller via a suitable bus.

Using 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 sensor module. The reference light receiver and / or the reference light transmitter can also be provided in the integrated light sensor module.

A modular structure serves as the basis for the safety light curtain. 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 control.
The measuring core preferably consists of a highly integrated CMOS-ASIC. A construction from discrete components is also possible.

Due to the good directional characteristics of light, various optics modules can be used to implement different variants of the safety light curtain with different opening angles and ranges, which are adapted to different requirements of different applications. The light beams can be collimated by optical elements or expanded further.

To limit the incidence of extraneous light, the light receiver can be equipped with a filter element, for example with a bandpass filter.

The invention is explained in detail below using exemplary embodiments with reference to the drawing.

• 1 und 2 eine schematische Darstellung eines erfindungsgemäßen Sicherheitslichtgitters.

The drawing shows:

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

1 shows a safety light curtain 1 for monitoring a protected area with at least two transmit / receive strips 3 . 3 ' with at least one light transmitter S and with at least one light receiver e , with the send / receive bars 3 . 3 ' are arranged opposite each other, and between them by the light rays 4 the light transmitter S a protective field 2 is formed, with at least one light transmitter S 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 bars 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 bar 3 . 3 ' with at least one of the light receivers e same send / receive bar 3 . 3 ' forms a light scanner, the light scanner being designed as a light transit time probe, the control and evaluation unit being embodied, the light transit time 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 pulsed light signals, the light propagation time elapsed from the transmission 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 bars 3 . 3 ' is in addition to the classic security function, which has both tactile send / receive strips 3 . 3 ' separately as well as through a transmitter-receiver pairing of opposite transmit / receive bars 3 . 3 ' a high-quality measurement function can be implemented. A penetrating object is measured on both sides within the protection level. If the measuring plane is inclined relative to the direction of passage, the 3D contour can also be reconstructed from a series of measurements.

According to 1 are two preferably identical tactile transmit / receive bars 3 . 3 ' used, which can also be used individually. These groping send / receive bars 3 . 3 ' - comparable to classic safety light grids - are placed opposite each other and aligned with each other, 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 within the transmission and reception range 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 to a configured value in order to protect the arrangement against manipulation. In addition, the measurement of the object can take place when an object passes through the measurement / protection level. And in addition, protective fields 4 be defined, the intactness of which is monitored independently. The double arrangement also has the advantage that objects can be localized and tracked without having disadvantageous concealment areas.

Furthermore, a safeguarding function can be implemented that is identical to classic safety light grids, in which opposite transmitter-receiver pairs define a beam, the uninterruptibility 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, touching safety light grids. In combination with the distance measurement function, the "Object too dark for a tactile measurement" error case can be detected and mastered in terms of safety.

Penetrates an object into the protective field 2 so that at least one of the emitted light beams 4 interrupted and reflected or remitted, the light propagation 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 emitting an alarm signal, for outputting measured values or for storing measured values.

Through the safety light grid 1 At first, object interventions can be recognized easily and over a wide range. An object enters the protective field 2 between the send / receive bars 3 . 3 ' , at least one pair of transmitters / receivers detects an interruption in the light beam, as a result of which an object detection signal is generated and, as a result, a safety switching signal, if appropriate. Such a light beam interruption can be easily evaluated and detected. This means that the safety light curtain has a short response time 1 guaranteed. A light beam interruption is easy to detect even for long ranges.

For the detection of objects of different sizes, the transmit / receive pairs are arranged at equal distances from one another. An object height can be determined using the number of interrupted, adjacent light beams and the spacing of the light beams from one another.

In addition, it is due to the formed light switch with the safety light curtain 1 it is also possible to obtain precise information about an object contour that could not be detected by simply interrupting the beam. However, an object can now be measured using the light scanners or the object can be classified as a permissible or impermissible object based on the detected object contour and an object detection signal or safety switching signal can be generated depending on this result. With the safety light curtain 1 it is therefore possible to determine not only the object height, but also the lateral contour of the object while the object is passing through the protective field.

If an object is, for example, on a conveyor belt through the safety light curtain 1 transported, a height profile of the object can be determined and saved on the one hand by interrupting the individual transmit / receive pairs, and on the other hand the distance contour data of a side of the object facing the respective transmit / receive bar can also be recorded and saved at the same time by the light sensors formed. Through the safety light grid 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, permissible objects can pass through the protected area without a safety switching signal being generated. 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 when an impermissible object, for example a person, is being conveyed through the protected area - even if the person is to the side of the permissible object and does not tower above it - A corresponding safety switching signal is triggered.

The comparison of two groping transmitter / receiver bars 3 . 3 ' enables very reliable detection of errors and a safety-related reaction. This enables a safety function to 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 the distance between the opposite transmitter / receiver bars 3 . 3 ' taught-in 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, that is to say redundantly, during commissioning and is monitored cyclically or continuously during operation. If smaller distances are measured during operation, there is an object in the protected area. There is therefore no fault.

If, however, larger distances than the taught distance are measured on one or both sides, there is, for example, an error.

The distance measured values of the opposite transmission / reception strips can also be used 3 . 3 ' be checked. The comparison of opposite channels can be used in addition to the consistency check in the company to verify and support the alignment.

In summary, by comparing two groping transmit / receive bars 3 . 3 ' to form a safety light curtain 1 and pairwise alignment of the individual measurement channels, the presence of the opposite signal can be 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. The absence of jamming transmitters 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. So it is one and the same light transmitter S or light receiver e necessary to form both a transmit / receive pair and a light switch. After the light beam is interrupted by an object, the light beam reflected by the object is transferred 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 receiver e individually alternately one after the other in the send / receive bars 3 . 3 ' arranged. A plurality of light transmitters is preferred S and light receivers e arranged. This ensures a uniform resolution of the safety light curtain 1 guaranteed over the entire protective field length. The light sensors are also advantageously located directly adjacent to one another and evenly distributed over the entire protective field length.

Becomes a send / receive bar 3 . 3 ' along according 1 and 2 rotated by 180 ° compared to the opposite send / receive bar 3 ' . 3 mounted, so the light transmitters lie S and the light receivers e to form the transmit / receive pairs directly opposite, which creates a homogeneous protective field with parallel light beams. The light transmitter S and the light receivers e to form the light button lie directly next to each other.

According to 2 form adjacent light transmitters S and light receiver e a light switch. This is a particularly simple construction of the safety light curtain 1 guaranteed and the light scanners formed are as a unit with uniform distances from each other along a send / receive bar 3 . 3 ' arranged. This arrangement allows the safety light curtain 1 can be constructed modularly for different protective field heights. Depending on the protective field height, a certain number of adjacent light transmitters S and light receivers e arranged to form light buttons. Due to the adjacent arrangement of the light scanners, the measured distance values can also be directly assigned to a respective pair of transmitters / receivers, so that when a light beam is interrupted, an associated distance of the light beam is also directly related 4 interrupting object is determined.

According to 1 and 2 are the send / receive bars 3 . 3 ' for example, constructed identically. This means that only 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 bars 3 . 3 ' provide.

Also electrical connections for both transmit / receive strips 3 . 3 ' are identical. This simplifies a connection technique, since only one type of connector has to be provided. The send / receive bars 3 . 3 ' can also be easily connected because, as with previous safety light grids, consisting of a transmitter bar and separate receiver bar, different connections for the transmitter bar and receiver bar do not have to be provided.

The described embodiments can also be combined with one another, so that the light sensors of the light grid according to the invention can perform 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 documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

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

Claims (10)

Safety light grid (1) for monitoring a protective 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 transmitters (S), at least one light transmitter (S) each of the one transmitting / receiving strip (3; 3 ') and at least one Light receivers (E) of the other transmission / reception bar (3 ', 3) form a transmission / reception pair, with means for synchronizing the transmission / reception bars (3, 3') and with a control and evaluation unit, at least one of the Light transmitter (S) of the transmission / reception bar (3, 3 ') with at least one of the light receivers (E) of the same transmission / reception bar (3, 3') forms a light switch, the light switch being designed as a light transit time switch, the control and evaluation unit is to evaluate the light transit time of received light signals or light pulses from the light receiver (E), characterized in that the light receiver (E) has at least one single photon avalanche diode. Safety light curtain (1) after Claim 1 , characterized in that the distance between the opposite transmission / reception bar (3, 3 ') has been taught in and stored, and the stored value is compared cyclically with currently recorded 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-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 transmitter / receiver pair and part of the light switch. Safety light curtain (1) according to at least one of the preceding claims, characterized in that the light transmitters (S) and the light receivers (E) are individually arranged alternately one after the other in the transmission / reception strips (3, 3 '). Safety light grid (1) according to at least one of the preceding claims, characterized in that in each case adjacent light transmitters (S) and light receivers (E) form a light scanner. Safety light curtain (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 correspond 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 transmission / reception strips (3, 3 ') are constructed identically.

Images