Monitoring device

Abstract

A monitoring device 12 for monitoring an access region 13 comprises at least one optical sensor 1 for monitoring a protection field and at least one control unit 17, 18 in which sensor signals of the

Description

The present invention relates to a monitoring device and has particular reference to, especially, a monitoring device for securing or safeguarding access to a plant. Such a monitoring device comprises at least one security sensor. Access to the plant via an access region can be monitored by the sensor. In that case a protection field extending over the entire access region is monitored by the sensor. If an object, particularly a person, is recognised in the protection field by the sensor a safety function is triggered which transfers the plant into a secure state so that no risks can emanate therefrom. In particular, the plant can be shut down. In the case of, for example, performance of work operations by means of the plant it is necessary to feed transportable goods, items or materials to the plant. On passing the access region a safety function triggered by the sensor in the case of detection of goods in the protection field would lead to unnecessary shutdown of the plant. For that reason, muting sensors arranged upstream of the security sensor in the transport direction of the transported goods are provided in known monitoring devices. The muting sensors are typically formed by optical barrier arrangements. These optical barrier arrangements can distinguish transported goods from persons or other safety-critical objects by way of characteristic sequences of beam interruptions by optical barriers. If the goods are recognised by the muting sensors the security sensor is bypassed, i.e. muted, so that during muting operation the penetration of an object into the protection field of the sensor does not lead to triggering of the safety function. The goods can thus pass the security sensor without the safety function being triggered and the plant shut down. After the transported goods have passed the security sensor the muting operation is concluded and the sensor resumes its monitoring function. A problem with muting of that kind is that the entire security sensor is bypassed and thus no monitoring function whatsoever takes place. This can lead to, in particular, risk situations if the transported goods do not extend over the entire width of the access region. A person standing near the goods can then traverse the access region and move unnoticed into a risk area of the plant. This results in unchecked risk situations. EP 4 151 899 A1 relates to a monitoring device for securing access to a plant by an arrangement of security sensors, which are each configured for detection of objects within a protection field, wherein a safety function is triggered on detection of an object in at least one protection field. Moreover, the monitoring device comprises an arrangement of distance sensors by means of which the position and width of transported goods, which can be fed across the access of the plant, are detectable, as well as a control and evaluating unit by means of which a normal operation is provided in which the security sensors monitor protection fields that combine to form an entire protection field extending over the entire width of the access. It is thereby possible to preset by the control and evaluating unit a muting operation of such a kind that depending on the position and width of the goods determined by the distance sensors the security sensors monitor protection fields which combine to form an entire protection field in which in the region of the access there is present a gap so adapted to the position and width of the goods that these can pass the access without penetrating the entire protection field. Transfer from normal operation to muting operation is carried out by a time control in such a way that goods are detected by distance sensors and, depending on signals of the distance sensors, the muting operation is activated shortly before entry of the goods into the region of the security sensors. In that case it is disadvantageous that the distance sensors represent a substantial constructional outlay. In addition, the time control has to be adapted to the speed of the goods, which represents an additional cost. The invention has the object of improving a monitoring device of the afore-described kind with respect to the functionality thereof. According to the invention there is provided a monitoring device as defined in independent claim 1 and a method as defined in independent claim 15. Advantageous embodiments and expedient developments are defined in the subclaims. In a preferred embodiment the monitoring device for monitoring an access region comprises at least one optical sensor for monitoring a protection field and at least one control unit for evaluation therein of sensor signals of the optical sensor. The control unit is operable to trigger a safety function if an object is detected in the protection field by means of the optical sensor. In an initial state, the optical sensor is operable to monitor an entire protection field extending over the entire access region. The control unit is configured so that, on entry of an object into the entire protection field, triggering of the safety function is suppressed and a timer is started in the control unit if the object has a given minimum size. The control unit is further configured so that, depending on the sensor signals of the optical sensor, after starting of the timer an adapted protection field and a warning field which are adapted to the detected object are activated in place of the entire protection field and after the timer has run down the safety function is triggered only if the object has not been recognised in the warning field as a permissible object in accordance with, for example, a recognition criterion or recognition criteria or if object entry into the adapted protection field is registered, in particular detected by the sensor. A method of monitoring the access region by the monitoring device comprises corresponding operation of the device in accordance with the stated capabilities of the components thereof. An access region to a plant can be safeguarded by such a monitoring device embodying the invention. For this purpose use is made of at least one optical sensor which monitors the access region and at least one control unit which controls the optical sensor and evaluates sensor signals thereof. The monitoring device is configured as a safeguarded or secure device if risks for persons can derive from the plant. For this purpose the or each optical sensor is configured as a safeguarded or secure sensor. In addition, the or at least one control unit is configured as a safeguarded or secure control unit. The safeguarded sensor or sensors as well as the safeguarded control unit each have a fail-safe construction which can be realised by, for example, redundantly configured, multi-channel computer structuring. In normal operation of the monitoring device an entire protection field extending over the entire access region, specifically over the entire width of the access region, is monitored by the optical sensor or optical sensors. The entire protection field is preset by the control unit. The optical sensor or sensors detects or detect whether or not object entry into the entire protection field is present, this being reported to the control unit. If there is no object entry into the entire protection field the control unit sets the plant in operation. If there is object entry into the entire protection field the control unit triggers a safety function, which advantageously consists of shutting down the plant. In order to be able to transport a non-safety-critical object - such as, for example, a box containing transported goods or work materials for the plant - through the access region to the plant without triggering the safety function the monitoring device can be operated in muting operation. For preference initiation of the muting operation takes place solely by way of the optical sensor or sensors monitoring the access region. Additional sensors monitoring the foreground of the access region are not required. Moreover, in the case of a monitoring device embodying the invention muting operation is initiated not by a time control prior to movement of the non-safety-critical object into the access region, but when the object has already moved into the access region. The muting is then initiated in dependence on the sensor signals of the optical sensor or sensors monitoring the access region and in that case detecting the non-safety-critical object. The starting point for initiation of the muting operation is normal operation in which the entire protection field extending over the entire access region is monitored by the optical sensor or sensors. If an object then penetrates the entire protection field it is checked in a first step on the basis of the sensor signals of the optical sensor or sensors whether the object has a minimum size. The minimum size, especially a minimum width, is preferably >500 millimetres. As a result, a non-safety-critical object such as a box can be securely distinguished from a person. If this is not the case, the object is classified as safety-critical and the control unit immediately triggers the safety function. Triggering of the safety function thus takes place almost without delay so that unsafe states are avoided. If the size of the object is greater than or equal to the minimum size, a timer is started which then runs for a predetermined time typically lying between 0.5 seconds and 1 second. During the running time of the timer an adapted protection field and a warning field are calculated in the control unit in dependence on the sensor signals of the optical sensor or sensors. The adapted protection field and the warning field are sub-regions of the entire protection field. The warning field comprises the region in which the object was detected. The adapted protection field adjoins the warning field on one side or both sides. The control unit then activates the adapted protection field and the warning field by reading these into the optical sensor or sensors so that the optical sensor or sensors then no longer monitors or monitor the entire protection field, but instead the adapted protection field and the warning field. It is then checked in the control unit on the basis of the sensor signals of the optical sensor or sensors whether an object in the warning field is recognised as permissible. Recognition of a permissible object can be carried out on the basis of predetermined features which have to be recognised at the object by the warning field. Alternatively, an object is regarded as recognised to be permissible if the contour thereof corresponds with a reference contour predetermined in the control unit. In a boundary case even the warning field itself can form a reference contour. Advantageously, the control unit stops the timer as soon as the object in the warning field is recognised as permissible. The muting operation thereafter commences. Alternatively, the muting operation can also start the running down of the timer. In this muting operation safety switching-off is suppressed if the object is recognised at least once in the warning field as permissible and if no object is registered in the adapted protection field. A high degree of safety with, at the same time, a high level of serviceability of the plant are thereby achieved. The permissible object, as a recognised non-safety-critical object, moves in the warning field and can thus pass the access region without the control unit triggering the safety function. In order to avoid triggering of the safety function, it can be required that the permissible object has to be constantly recognised in the warning field. In the case of more complex permissible objects with apertures and / or cut-outs this requirement can be mitigated in such a way that the permissible object is identified as such only once in the warning field. At the same time the adapted protection field is active adjacent to the warning field. In the adapted protection field the monitoring function of the monitoring device is maintained in such a way that the safety function is immediately triggered if object entry into the adapted protective field is registered by the optical sensor or sensors. The adapted protection field preferably directly adjoins the warning field at both sides. This prevents a person from being able to traverse the access region unnoticed together with the permissible object, since for that purpose the person has to penetrate the adapted protection field, in which case the safety function is immediately triggered. The muting operation is concluded when the permissible object has left the warning field. The entire protection field is then reactivated and normal operation resumed. In principle, the monitoring device can comprise only a single optical sensor. With advantage, however, the monitoring device comprises two optical sensors respectively arranged at two mutually opposite side edges of the access region. A permissible object passing the access region is then detected by the optical sensors at opposite sides, whereupon the warning field is defined in the region of this permissible object. A respective sub-region of the adapted protection field then adjoins each of the two sides of the warning field and is monitored by a respective optical sensor. Advantageously, the or each optical sensor is an area distance sensor, i.e. a scanning distance sensor, by which an areal monitoring region is detected. Alternatively, the or each optical sensor can be a time-of-flight camera, i.e. a camera in which distance measurements are performed in accordance with a pulse transit time procedure. In the simplest case the monitoring device comprises only a single control unit, which is configured as a safeguarded or secured control unit. Alternatively, the monitoring device comprises two control units, wherein one control unit is a safeguarded control unit and the other control unit is a non-safeguarded control unit. In this case the non-safeguarded control unit calculates the adapted protection field and the warning field on the basis of sensor signals of the optical sensor or sensors. The safeguarded sensors generate the safety function. The non-safeguarded control unit can then transmit the co-ordinates of the adapted protection field and the warning field to the safeguarded control unit, which then activates the adapted protection field and the warning field for the optical sensors. Alternatively, the non-safeguarded control unit can directly control the optical sensors and communicate the adapted protection field and the warning field to the optical sensors. Preferred embodiments of the monitoring device and preferred examples of the method according to the invention will now be more particularly described with reference to the accompanying drawings, in which: Fig. 1 is a diagram of a security sensor of a first embodiment of the monitoring device; Fig. 2 is a diagram of a security sensor of a second embodiment of the monitoring device; Fig. 3 is a diagrammatic plan view of a monitoring device embodying the invention for securing an access region; Fig. 4 is a schematic side view of the access region monitored by the security sensor of the monitoring device of Fig. 1; and Figs. 5 to 9 are diagrams showing different phases of monitoring of the access region by a monitoring device embodying the invention. Referring now the drawings, Figs. 1 and 2 respectively show two different forms of security sensor 1, each configured as a distance-measuring optical sensor, in two embodiments of a monitoring device according to the invention, wherein distance measurements are advantageously carried out in accordance with a pulse transit time method or a phase measuring method. Fig. 1 shows an example of an optical security sensor 1 in the form an areal distance sensor, i.e. a scanning distance sensor 12. For performance of distance measurements the optical sensor comprises a transmitter 3 emitting light beams 2 and a receiver 4 receiving light beams 2. The transmitter 3 emits light beams 2 in the form of light pulses. As Fig. 1 shows, the light beams 2 are reflected at a target object 5 to be detected, in which case the corresponding light transit time of the light pulse to the target object 5 and back to the optical sensor is evaluated for the determinations of distance. As Fig. 1 shows, the sensor components of the optical sensor are integrated in a housing 6, wherein the transmitter 3 and the receiver 4 together with an upstream transmitting optical system and an upstream receiving optical system 7, respectively, are arranged in stationary position in the housing 6. Object detection in an areal detection region is carried out by the optical sensor in such a way that the light beams 2 are periodically deflected by means of a deflecting unit 8. The deflecting unit 8 is motor-driven and comprises an angled mirror 9 which is rotatable about an axis D of rotation and at which the light beams 2 are deflected. Fig. 2 shows a variant of the areal distance sensor of Fig. 1. In this case the periodic deflection of the light beams 2 takes place in such a way that the transmitter 3 and the receiver 4 are arranged in a measuring head 10 rotatable about an axis D of rotation, wherein the measuring head 10 is rotatably mounted on a pedestal 11. In general, the security sensor 1 comprises an evaluating unit (not illustrated) in which the received signals of the receiver 4 can be evaluated. According to Figs. 1 and 2 the security sensor 1 has, for use in the field of safety, a failsafe construction which can be realised by, for example, a redundantly configured evaluating unit in the form of two processors cyclically monitoring one another. Fig. 3 schematically shows in plan view an embodiment of the monitoring device 12 for safeguarding the access region 13 to a plant 14. Access to the plant 14 is protected towards three sides by fencing 15. An open front side forms the access region 13 of the plant 14. A respective security sensor 1 in the form an optical sensor, which is executed in accordance with Fig. 1 or Fig. 2, is disposed at each of two opposite edges of the access region 13. Fig. 4 shows monitoring regions 16 which are monitored by the optical sensors and which are formed by a part of the detection regions. The monitoring regions 16 extend in a vertical plane so that the protection field monitoring actions performed by the optical sensors also take place in a vertical plane. A non-safeguarded control unit 17 and a safeguarded control unit 18 form a control unit for controlling the monitoring device 12. The safeguarded control unit 18 has a fail-safe construction in that it has redundantly configured, particularly twin-channel, computer structuring. The non-safeguarded control unit 17 is not fail-safe and has single-channel computer structuring. The safeguarded control unit 18 controls the plant 14. The non-safeguarded control unit 17 serves for evaluation of sensor signals of the optical sensors, wherein for this purpose the optical sensors are connected with the non-safeguarded control unit 17. The nonsafeguarded control unit 17 is connected with the safeguarded control unit 18. The optical sensors are also directly connected with the safeguarded control unit 18 so that evaluation of sensor signals of the optical sensors can also be carried out thereat, in particular so as to generate a safety-relevant output signal for control of the plant 14. The mode of functioning of the monitoring device 12 embodying the invention is explained hereinafter with reference to Figs. 5 to 9. Fig. 5 shows normal operation of the monitoring device 12. In normal operation an entire protection field 19 extending over the entire width of the access region 13 is monitored by the optical sensors 1. If there is no entry of an object into the entire protection field 19 then depending on the sensor signals of the optical sensors an output signal by which operation of the plant 14 is released is generated in the safeguarded control unit. If entry of an object into the entire protection field 19 is registered by the optical sensors then depending on the sensor signals of the optical sensors an output signal by which a safety function is triggered, in particular to shut down the plant 14 so that no risks can emanate therefrom, is generated in the safeguarded control unit. Fig. 5 shows, as an example of a non-safety-critical object, a box 20 which moves forward in arrow direction towards the access region 13. The box 20 is to be able to pass the access region 13 without the safety function being triggered. For this purpose a muting region is initiated, as illustrated in Figs. 6 and 7. Fig. 6 shows entry of the box 20 into the entire protection field 19, so that this is detected by the optical sensors. In a first step it is checked, particularly in the non-safeguarded control unit, whether the box 20 has a predetermined minimum size. If this is not the case, a corresponding report is issued to the safeguarded control unit 18 and this triggers the safety function. If the size of the box 20 is greater than or equal to the minimum dimension, a timer, which runs for a preset time typically in the range of 0.5 seconds to 1 second, is started in the safeguarded control unit 18. In addition, on the basis of the sensor signals of the optical sensors an adapted protection field 21 and a warning field 22 are calculated, the fields 21 and 22 being adapted to the position and size of the box 20 and, in particular, in such a way that the warning field 22 extends over the region of the box 20 and the adapted protection field 21 adjoins the warning field 22 at both sides in the form of two protection sub-fields, as illustrated in Fig. 7. The adapted protection field 21 and the warning field 22 are calculated in the nonsafeguarded control unit 17 and communicated to the safeguarded control unit 18, which communicates the adapted protection field 21 and the warning field 22 to the optical sensors and activates them. Alternatively, this can also be carried out directly by the nonsafeguarded control unit 17. It is checked in one of the control units whether the object in the warning field 22 is recognised as a permissible object, which can be carried out on the basis of predetermined features of the object. Alternatively, an object can be treated as recognised to be permissible if the contour thereof corresponds with a reference contour preset in the control unit. If this is the case and characterises the object in the adapted protection field 21 the timer is stopped and the muting operation started. If, on the other hand, during running down of the timer one of the aforesaid conditions is not fulfilled the safety function is triggered. In muting operation and as illustrated in Fig. 7 it is monitored whether the permissible object is present in the warning field 22. If this at least temporarily the case and there is no object entry into the adapted protection field 21 the box 20 can pass the access region 13 without the safety function being triggered. As soon as the box 20 has left the access region 13 (Fig. 8) the muting operation is changed and transfer to normal operation takes place, in which the entire protection field 19 is again monitored. Fig. 9 accordingly shows resumption of monitoring of the entire protection field 19 by the sensors 1.

Claims

1. Monitoring device for monitoring an access region, the device comprising at least one optical sensor configured for monitoring a protection field and at least one control unit for evaluation therein of sensor signals of the optical sensor, wherein a safety function in the control unit can be triggered on detection of an object in the protection field by means of the optical sensor and wherein in an initial state an entire protection field extending over the entire access region is monitored by the optical sensor, triggering of the safety function is suppressed and a timer started in the control unit if an object enters the entire protection field and the object has a minimum size, after starting of the timer and depending on the sensor signals of the optical sensor an adapted protection field and a warning field which are adapted to the detected object are activated in place of the entire protection field, and after the timer has run down the control unit triggers the safety function only if the object is not recognised in the warning field as a permissible object or if object entry into the adapted protection field is registered.

2. Monitoring device according to claim 1, wherein the safety function is suppressed if the object is recognised at least once in the warning field as permissible and if no object is registered in the adapted protection field.

3. Monitoring device according to either claim 1 or claim 2, wherein the control unit stops the timer as soon as the object has been recognised in the warning field as permissible.

4. Monitoring device according to any one of the preceding claims, wherein the control unit triggers the safety function if the size of the object detected in the entire protection field is smaller than the minimum size.

5. Monitoring device according to any one of the preceding claims, wherein an object is recognised as permissible if the contour thereof corresponds with a reference contour preset in the control unit.

6. Monitoring device according to any one of the preceding claims, wherein the entire protection field is reactivated as soon as the object recognised as permissible has left the warning field.

7. Monitoring device according to any one of the preceding claims, wherein the adapted protection field and the warning field are sub-regions of the entire protection field.

8. Monitoring device according to any one of the preceding claims, wherein the entire protection field extends over the entire width of the access region.

9. Monitoring device according to any one of the preceding claims, wherein the device comprises two such optical sensors respectively arranged at two opposite side edges of the access region.

10. Monitoring device according to any one of the preceding claims, wherein the or each optical sensor is an areal distance sensor.

11. Monitoring device according to any one of the preceding claims, wherein the or each optical sensor is a safeguarded sensor.

12. Monitoring device according to any one of the preceding claims, wherein the device comprises a single control unit, which is configured as a safeguarded control unit.

13. Monitoring device according to any one of claims 1 to 11, wherein the device comprises two such control units, one of which is a safeguarded control unit and the other of which is a non-safeguarded control unit.

14. Monitoring device according to claim 13 when dependent on claim 11, wherein the non-safeguarded control unit calculates the adapted protection field and the warning field on the basis of sensor signals of the optical sensor or sensors and the safeguarded sensor generates the safety function.

15. Method of operating a monitoring device for monitoring an access region, the device comprising at least one optical sensor configured for monitoring a protection field and at least one control unit for evaluation therein of sensor signals of the optical sensor,wherein a safety function can be triggered in the control unit on detection of an object in the protection field by means of the optical sensor and wherein in an initial state an entire protection field extending over the entire access region is monitored by the optical sensor, triggering of the safety function is suppressed and a timer started in the control unit if an object enters the entire protection field and the object has a minimum size, after starting of the timer and depending on the sensor signals of the optical sensor an adapted protection field and a warning field which are adapted to the detected object are activated in place of the entire protection field, and after the timer has run down the control unit triggers the safety function only if the object has not been recognised in the warning field as a permissible object or if object entry into the adapted protection field is registered.A

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