Device and method for control of a safety device - Patents.com

Abstract

A device for controlling a safety device comprises at least one OSSD type output, preferably a pair of outputs, having output terminals connected to corresponding inputs of the safety device for detecting signals coming from said at least one OSSD output, said at least one OSSD output being capable of supplying maximum and minimum thresholds of a supply voltage suitable for determining the on and off conditions of said at least one output, respectively; and a control circuit suitable for testing the operation of said at least one OSSD output by sending a test micropulse to switch said output terminal to said minimum threshold, and for sending an error signal to the safety device if a value different from said minimum threshold is detected, said control circuit generating a test micropulse having a variable or adjustable duration depending on a defined load of a circuit located downstream of said at least one OSSD output.

Description

[Technical field]

[0001] The invention finds application in the field of industrial electrical devices and has as its object in particular a device and method for the control of safety devices used in the control of industrial machines or plants, such as safety sensors, safety switches and / or safety modules. [Background technology]

[0002] As is known, the acronym OSSD (Output Signal Switching Device) denotes a safe switching output of a safety device intended to safely signal an event related to a safety condition in the operation of a machine or system.

[0003] Generally, a safety device with OSSD outputs, such as a safety sensor, a safety switch, or a safety module, has two OSSD outputs, which need to be analyzed separately from each other.

[0004] These devices are then used for safety purposes, such as monitoring the operation of access to potentially dangerous areas of a machine or plant or to moving parts of a machine or plant.

[0005] For example, a safety device with OSSD outputs used to control access could be placed at the access and, if open access is detected, the OSSDs could signal the event via output terminals to the system's safety control circuitry, thereby stopping the machine or plant and avoiding potential risk to people inside or close to the safety boundary.

[0006] To meet high safety levels, OSSDs typically include at least one pair of redundant electrical output terminals.

[0007] In the absence of any safety-relevant events (eg, in the case of closed access), both the first output terminal and the second output terminal are powered with the highest voltage level, eg, 24V.

[0008] When a security-relevant event (eg opening of access) needs to be reported to a safety control system, the OSSDs switch the first and second output terminals to a low level, eg 0V.

[0009] This voltage fluctuation is detected by a safety control system which can intervene to shut down the plant or controlled machine.

[0010] By using two redundant output terminals, even if an error occurs in one of the output terminals, a switch to a low level is transmitted to the control system via the intact output terminal, allowing safe information transmission from the OSSDs to the safety control system.

[0011] Generally, to detect such faults at the safety output, i.e. at the two output terminals, so-called test pulses are used, i.e. tests are carried out by generating test pulses which are applied to the output terminals.

[0012] These test pulses switch each output terminal to a low voltage level for a very limited period of time, on the order of a few hundred microseconds, and the test pulses are monitored to verify the presence of unwanted connections, such as shorts or electrical interconnects between the first and second output terminals.

[0013] EP 3358592 discloses a device with an OSSD output, comprising a first output terminal and a second output terminal, voltage reducing means providing a first voltage having a magnitude less than a supply voltage, and second voltage reducing means providing a second voltage having a magnitude less than the first voltage, the second voltage being applied to the first terminal output and the first voltage being applied to the second output terminal, and switching means being provided for switching the second voltage from the first output terminal and / or the first voltage from the second output terminal when the magnitude of the voltage at the second output terminal is equal to or greater than the magnitude of the supply voltage and / or when the magnitude of the voltage at the first terminal output is equal to or greater than the magnitude of the first voltage.

[0014] WO2004059677 discloses a safety control device comprising two controllable switching circuits having output terminals interconnected to form an output of a safety switching device, capable of periodically sending a first test switching pulse to a first said switching circuit and periodically supplying a second test switching pulse offset from the first test switching pulse to the other said switching circuit, said switching circuits being designed such that, upon receiving simultaneous test pulses, the output voltage of the safety switching device varies to cause an intervention of the safety system upon receipt of test pulses offset by an amplitude that deviates from the amplitude of the output voltage upon receipt of the simultaneous test pulses.

[0015] A limitation of the known solutions consists in the need to adjust the length of the micropulse at the OSSD output depending on the load of the device detecting the OSSD signal, which may also vary depending on the technical specifications adopted by a particular manufacturer.

[0016] As a result, the safety device associated with the control device risks failure if the load differs from the load for which the OSSD outputs are calibrated. Summary of the Invention

[0017] The object of the present invention is to overcome the aforementioned drawbacks by providing a device and method for controlling safety equipment, in particular provided with OSSD outputs, which is characterized by high efficiency and relatively cost-effectiveness.

[0018] One particular object is to provide a device and method for controlling safety devices, in particular provided with OSSD outputs, which is constituted by a device for detecting OSSD signals and which can automatically adapt to the type of load.

[0019] Yet another specific object is to provide a device and method for controlling a safety device, especially one provided with OSSD outputs, where the safety device is not subject to errors due to different loads due to different devices that may be on the market.

[0020] Yet another specific object is to provide a device and method for controlling a safety device, in particular provided with OSSD outputs, which makes it possible to set the duration of micropulsations in a personalized way for the user, without modifying the hardware.

[0021] These objects, as well as others that will become more apparent hereinafter, are achieved by a control device for a safety device, which according to claim 1 comprises at least one OSSD-type output, preferably a pair of outputs, having output terminals connected to corresponding inputs of the safety device detecting signals coming from said at least one OSSD output, said at least one OSSD output being powered with maximum and minimum thresholds of a supply voltage in order to determine, respectively, the on and off conditions of said at least one output, and a control circuit which performs a test of the operation of said at least one OSSD output by sending test micropulses for switching said output terminals to said minimum threshold and which, in case of detecting a value different from said minimum threshold, sends an error signal to the safety device, said control circuit generating test micropulsations having a variable or modifiable duration depending on a defined load of the circuit located downstream of said at least one OSSD output.

[0022] Thanks to this feature, the device automatically adapts to the type of load constituted by the device detecting the OSSD signals, preventing failure of the safety device due to different loads due to different devices that may be on the market.

[0023] According to a further aspect of the invention there is provided a safety apparatus comprising a control device according to claim 7.

[0024] According to a further aspect of the present invention there is provided a safety device control method according to claim 9.

[0025] Advantageous embodiments of the invention are obtained according to the dependent claims. [Brief description of the drawings]

[0026] Further features and advantages of the present invention will become more apparent in the light of the detailed description of some preferred, but not exclusive, device embodiments, illustrated as non-limiting examples with the aid of the accompanying drawings.

[0027] [Figure 1] FIG. 1 is a schematic illustration of a device according to the present invention. [Diagram 2] FIG. 2 shows pulse diagrams for three different operating modes of the device associated with three different loads. [Diagram 3] FIG. 3 represents a first sampling operation mode of the control circuit. [Figure 4] FIG. 4 represents a second operating mode for sampling the control circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The control device according to the invention will be designed in particular to be associated with safety equipment used for the control of industrial machines or plants, or parts thereof.

[0029] In particular, the control device may be applied to an access door of a safety barrier or boundary of a machine or industrial plant or other system used to control a safety boundary, and may be applied to a safety sensor or safety switch designed to signal a potentially dangerous condition, such as an open access door condition or an unauthorized position of a moving part of the machine or plant, inside the boundary or corresponding to a moving part of the machine or plant, in order to allow safe access at all times.

[0030] The control device could also be applied in a safety module which can be inserted in a safety circuit for the control of a machine or industrial plant.

[0031] These safety arrangements are not limiting of the invention and will not be described in further detail below.

[0032] FIG. 1 shows diagrammatically the logical structure of a control device, generally indicated at 1, which essentially comprises at least one output 2 of the OSSD type, preferably a pair of outputs.

[0033] As is known, each OSSD output 2 has an output terminal which is connected to a corresponding input of a safety device which detects the signal coming from the OSSD output 2 .

[0034] Typically in this type of device the OSSD outputs 2 may be powered with a supply voltage at two different voltage levels, a maximum threshold typically being 24V and a minimum threshold typically being 0V.

[0035] Corresponding to these maximum and minimum threshold values ​​will determine the ON and OFF switching conditions of the OSSD outputs 2, respectively, which correspond to dangerous and safe states of the machine or plant or relevant part controlled by the safety device.

[0036] The device 1 also comprises a control circuit 3 for providing a voltage supply for the OSSD outputs 2 and a control circuit 4 suitable for carrying out a test of the operation of the OSSD outputs 2 by sending test micro-pulses which switch the output terminals at a minimum threshold value.

[0037] The purpose of this test is to verify that under safe conditions the OSSD output 2 is indeed outputting a pulse at the minimum voltage state and that there is no condition associated with a dangerous situation, i.e. a value exceeding the minimum threshold, in which case an error signal can be sent to the safety device to stop the machine or system or any controlled relatively moving parts.

[0038] According to one unique feature of the present invention, the control circuit 4 is adapted to generate test micro-pulsations having a variable or modifiable duration depending on the defined load of the circuitry downstream of the OSSD outputs 2.

[0039] In particular, according to the first mode of operation, the control circuit 4 may dynamically vary the duration of the test micropulsations to suit the particular load.

[0040] The load may be capacitive, inductive, resistive, or the like.

[0041] More precisely, the duration of the micropulsations will not be predetermined, but may start from a minimum duration value and extend up to a predetermined maximum value for a particular appropriately programmed interval.

[0042] In this mode of operation, low loads can be detected with micropulsations of minimum duration, as in the leftmost image of Figure 2.

[0043] At higher loads, the duration of the micropulsations will be extended to a maximum interval, as shown in the right image of the same Figure 2.

[0044] If after a micropulsation of maximum duration the control circuit does not find the minimum threshold, ie the value is lower than the minimum threshold, an error signal will be generated.

[0045] In practice, after the line has been switched off, periodic sampling is performed by sending micropulsations of a minimum duration to see if it has actually been switched off. If the test after this minimum period fails, the micropulsations are extended to a maximum value and only then, in the absence of detection, an error signal is generated.

[0046] Dynamic modulation of the micropulsation amplitude can eliminate the possibility of erroneous error reporting associated with the use of too short a micropulsation in combination with a pulsation of OSSD output 2 having a relatively less steep decline curve, which may lead one to believe that OSSD output 2 is not switched to its minimum value because the micropulsation may block the signal on the decline curve.

[0047] This allows the device 1 thus programmed to be adapted to any type of safety device that may be advantageously classified according to several categories according to the various standards or technical specifications used in the industry.

[0048] For example, according to the ZVEI (Association of the German Electrical and Electronics Industry) specifications defined in the position paper CB24I "Classification of binary 24 V interfaces - Functional safety aspects covered by dynamic tests" edition 2.0.1, the same safety equipment may be classified as class A, B or C.

[0049] From a theoretical point of view, there are no upper or lower limits on the extreme values ​​of the time interval.

[0050] For example, if you want to stay within the ZVEI specifications mentioned above, the minimum interval is 250 μs and the maximum is 1000 μs.

[0051] According to a further mode of operation, the control circuit 4 may be programmed to set a fixed duration of the test micropulsations, but always in a programmable manner, either by the user or directly by the manufacturer.

[0052] Similarly, the minimum power supply voltage threshold may be user and / or manufacturer programmable.

[0053] The control circuit 4 will also be programmed to sample the instantaneous voltage value one or more times within the interval of the micropulsation duration to see if the instantaneous value is below or above a set threshold value.

[0054] Generally, a single sampling near the end of the micropulsation interval may be sufficient.

[0055] According to a further operational aspect, outlined in FIG. 3, sampling may be performed at regular time intervals T having a period of a constant value.

[0056] According to yet another variant not shown, multiple samplings can be carried out for each period T into which the interval of micropulsation duration is divided.

[0057] On the other hand, FIG. 4 represents a further operating mode in which the control circuit 4 performs substantially continuous sampling, i.e. with very short intervals between one sampling and the next, e.g. not allowing any gaps between subsequent samplings to be evaluated.

[0058] However, in this case it would be appropriate for the control circuit 4 to have an analogue type input for reading a voltage value, as opposed to the previous configuration where the input would be digital.

[0059] Advantageously, all modifications made to the control circuit 4 may be performed via firmware, without any hardware modifications.

[0060] From the above, it is clear that the device according to the invention achieves the stated objects.

[0061] It will be understood, however, that many modifications and variations can be made to the devices, apparatus and methods according to the present invention, all of which are within the scope of the inventive concept as expressed in the appended claims.

Claims

1. 1. A device for controlling a safety device, comprising: at least one OSSD output, preferably a pair of outputs, having output terminals connected to corresponding inputs of the safety device for detecting signals coming from said at least one OSSD output, said at least one OSSD output being capable of supplying maximum and minimum thresholds of a supply voltage suitable for determining, respectively, on and off conditions of said at least one OSSD output; a control circuit adapted to perform a test of the operation of said at least one OSSD output by sending a test micro-pulse to switch said output terminal to said minimum threshold value and to send an error signal to a safety device if a value different from said minimum threshold value is detected, The control circuitry generates a test micro-pulse having a variable or adjustable duration depending on a defined load of a circuit downstream of the at least one OSSD output.

2. 2. The device of claim 1, wherein the control circuitry is adapted to dynamically adjust the duration of the test micro-pulse within a range of values ​​having predetermined minimum and maximum values.

3. 3. The device of claim 1 or 2, wherein the control circuit samples an instantaneous voltage value one or more times within the interval of the duration of the test micro-pulse to verify that the instantaneous voltage value is not below the minimum threshold and not above the maximum threshold.

4. The device of claim 3 , wherein the sampling is performed at regular time intervals having a period of a constant value.

5. 4. The device of claim 3, wherein the control circuitry comprises an analog input for substantially continuous sampling within the interval of the duration of the test micropulse.

6. 2. The device of claim 1, wherein the control circuitry is adapted to set a fixed duration of the test micro-pulse in a manner programmable by a user or manufacturer.

7. 7. The device of claim 1, wherein the minimum threshold value of the supply voltage is programmable by a user and / or a manufacturer.

8. 8. The device according to claim 1, wherein the load is of the capacitive type.

9. 8. A device according to claim 1, wherein the load is of the inductive, resistive or similar type.

10. A safety device having an input terminal connected to an OSSD type output terminal associated with a control device according to any one of claims 1 to 9.

11. 11. The safety device of claim 10, wherein the safety device is selected from the group comprising a safety sensor, a safety switch, and a multi-function safety module.

12. 1. A method of controlling a security device provided with one or more OSSD outputs, comprising the steps of: each said OSSD output having an output terminal connected to a corresponding input terminal of a security device for detecting a signal coming from said OSSD output; the OSSD outputs are provided with respective maximum and minimum thresholds of supply voltage suitable for determining on and off conditions of the outputs, respectively; said method comprising a test phase of said OSSD outputs, sending test micro-pulses to said output terminals which switch said output terminals to their respective minimum thresholds and sending an error signal to said security device if a value different from said minimum threshold is detected; A method in which the test micro-pulse has a variable or modifiable duration depending on a defined load of circuitry downstream of at least one OSSD output.

13. 13. The method of claim 12, wherein the duration of the test micropulse is dynamically variable within a range having predetermined minimum and maximum values.

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