Title: GRIPPING SYSTEM FOR GRIPPING PROCESSED PARTS AND METHOD FOR DETECTING WHETHER A PROCESSED PART HAS BEEN CUT

The present invention relates to a gripping system for gripping parts of a workpiece processed in a processing system and a method for detecting whether a processed part of a workpiece processed in a processing system has been completely cut.

In the processing industry, in particular in the metalworking industry, a high proportion of the processing steps and/or manufacturing steps are carried out fully automatically. These steps also include the fully automatic loading and unloading of processing systems, in particular cutting systems, which reduces set-up times and maximises machine utilisation. For the loading and unloading of cutting systems, a changing table can be used as a transport unit for transporting the raw material (workpiece) into the cutting system and a gripping system for unloading the parts cut from the workpiece after processing. In order to avoid faults and/or downtimes in the cutting system, in particular during unloading, it is necessary to check the processed (cut) parts for correct processing, in particular complete cuts, before unloading from the changing table. An incomplete cut between the processed part and the workpiece, the so-called scrap skeleton, can result in the processed part jamming when it is gripped by the gripping system. The entire workpiece or scrap skeleton would be lifted out of the changing table, which can lead to a fault of the gripping system and the processing system.

In this regard, solutions known in the prior art provide for an inspection of the cuts between the processed part(s) and the scrap skeleton by an optical sensor, for example a surface scanner. Surface scanners have the disadvantage that they are sensitive to extraneous light exposure, for example sunlight, which can influence the measurement result or lead to a fault in the surface scanner. In addition, when using surface scanners to check remaining material webs (residual material in the event of an incomplete cut) between the processed part and the scrap skeleton, due to the mode of operation it is necessary to lift the processed part to a predetermined height of at least 50 mm using a gripping system so that a surface field generated by the surface scanner can be mapped onto the processed part and evaluated. Raising the processed part to this predetermined height can, however, lead to jamming and thus lifting of the entire scrap skeleton if there are material webs between the processed part and the scrap skeleton. In this regard, the position of the scrap skeleton on the changing table can be changed so that further processed parts can no longer be gripped/lifted off. The unloading process is disrupted and the entire processing system can go into a fault state, which leads to a loss of production and increased production costs. The other processed parts may also be damaged. Furthermore, lifting to the specified height and checking must be carried out for each processed part of the processed workpiece, which increases the processing time of the processing system and reduces productivity or machine utilisation.

Thus, the object of the present invention is to ensure a fault-free inspection of the processed parts of the workpiece and to at least partially overcome the disadvantages known in the prior art.

This object is achieved according to the invention by a gripping system for gripping parts of a workpiece processed in a processing system and by a method for detecting whether a processed part of a workpiece processed in a processing system has been completely cut with the features specified in claims 1 and 15.

According to a first aspect, the invention thus provides a gripping system for gripping parts processed in a processing system:

- having a gripping arm;

- having a gripping tool for lifting the processed parts out of the workpiece, wherein the gripping tool is arranged on the gripping arm;

- having a control unit which communicates with the gripping system.

For the purposes of the present invention, a processing system is understood to mean a cutting system, in particular a laser cutting system. The laser cutting system comprises the actual laser cutting unit in which a workpiece or a workpiece to be processed, for example a metal sheet is processed into individual parts, for example cut into individual sheet metal parts or from which individual contours are cut out. In addition, the processing system may comprise a transport system, for example a changing table for transporting the workpiece from a loading and unloading area into and out of the laser cutting unit. The changing table can be moved into the laser cutting system and out of the laser cutting system. On the changing table, the workpiece to be processed (sheet metal) from which the parts to be processed (individual contours) are cut out by the laser cutting system.

The present invention is based on the knowledge that there is a need for an improved checking of the cuts between the processed parts and the workpiece before the processed parts are actually lifted by the gripping system. Advantageously, the parts to be processed can be checked for contact with the workpiece before the actual lifting. This contact represents a material connection, for example a material web between the processed part and the workpiece, which is detected before lifting, thus preventing the processed part from jamming or snagging during lifting, and thus the entire workpiece or the scrap skeleton is not moved onto the changing table. The processing system and the entire processing process are therefore less prone to failure. In addition, the process time for checking the processed parts is advantageously reduced since the present invention can detect at any time whether the processed part is still in contact with the workpiece or the scrap skeleton and the changing table (material web) as soon as the gripping tool touches the processed part.

Advantageous embodiments and further developments result from the subclaims and from the description with reference to the figures.

In an advantageous embodiment, the gripping system has an analogue input which is designed to receive an analogue electrical signal. An analogue electrical signal can advantageously be received by the gripping system. An electrical voltage can be applied to the analogue input and can advantageously be evaluated for its voltage value. The evaluated voltage value can be used to control or manage electronic units.

In an advantageous embodiment, the control unit comprises a detector unit which has a 0 volt potential and which is designed to detect a voltage drop at the analogue input. For the purposes of the present invention, a voltage drop is understood to mean the reduction from a previously applied voltage value to a lower voltage value caused by an event. The detector unit can be designed, for example, as a measuring device, in particular a voltage measuring device, via which a voltage or a contiguous or decreasing voltage can be determined. The voltage measuring device is connected in parallel to a consumer, component or to the voltage source. When measuring at the voltage source, the current voltage value is measured. The voltage drop at this one consumer is measured at a consumer. This voltage drop corresponds to a partial voltage from the total voltage of the voltage source. In order not to influence the circuit to be measured, the internal resistance of the voltage measuring device should be as high-resistance as possible. An infinitely high internal resistance would be ideal. A voltage drop with reference to the same potential can thus advantageously be determined and evaluated. In an advantageous embodiment, the detector unit is designed as an analogue input card of the control unit. The analogue input card can be designed to be configurable, so that it has a different function behaviour/output behaviour in relation to changing voltage drops. In an advantageous embodiment, the gripping system is a gripping robot. In the sense of the present invention, a gripping robot is to be understood as a universal, programmable machine for handling processed parts. The gripping system can be designed as a gripping robot with several axes which can be controlled differently and with separate drive units. The drive units can comprise electrical, pneumatic and/or hydraulic drives. With a gripping robot, a work sequence can be carried out autonomously, precisely, repeatable at high speed and automatically. The gripping system can comprise one or more gripping tools. The gripping tools are interchangeable and can be exchanged or replaced automatically or by manual input using the gripping system.

In an alternative embodiment, the gripping system can be designed as a Cartesian robot system. The Cartesian robot system comprises linear drives and can be designed as a single-axis, two-axis or three-axis Cartesian robot system.

In an advantageous embodiment, the gripping tool comprises at least one electrically conductive gripping tool. For the purposes of the present invention, an electrically conductive gripping tool is to be understood as a gripping tool with which objects can be gripped or held and transported from a first position by the gripping system to a second position. The electrically conductive gripping tool is designed such that it conducts an electrical current. Advantageously, the electrically conductive gripping tool can thus be connected to a voltage source via an electrical connection, for example an electrical line. The electrically conductive gripping tool has a resistance with a specific, material-dependent resistance value, as a result of which a voltage across the electrically conductive gripping tool drops when a current flows through the electrically conductive gripping tool. The resistance value also depends on the size of the electrically conductive gripping tool.

In an advantageous embodiment, the gripping tool can be modularly interchangeable.

Processed parts of a wide variety of shapes, sizes, masses, materials and/or material thickness can thus be gripped and transported with a gripping tool designed for this purpose. The gripping system may have a storage/changing station for storing and changing a plurality of modularly interchangeable gripping tools.

In an advantageous embodiment, the electrically conductive gripping tool is designed as an electrically conductive suction device, preferably as an electrically conductive vacuum suction device. In an advantageous manner, electrically conductive suction devices are available in different materials with different Shore hardnesses so that a corresponding suction device can be selected and used for each processed part with a wide range of shapes, sizes, masses, materials and/or material thicknesses. The electrically conductive vacuum suction device thus forms the interface or interfaces to the processed part. The electrically conductive vacuum suction device can be designed in a round and in an oval design. The round electrically conductive vacuum suction device is suitable for handling flat workpieces. The oval, electrically conductive vacuum suction device can be used for narrow, elongated workpieces. In one embodiment, the electrically conductive vacuum suction device can be designed as a flat or bellows suction device. Flat suction devices have the advantage of a low overall height and a small internal volume. The small volume ensures short blow-off times. In addition, flat suction devices in this design have good inherent stability and ensure high positional accuracy. Flat suction cups can be used in highly dynamic processes.

Bellows suction devices with one or more bellows have the advantage that height differences can be compensated for. The bellows also provide a damping effect when the gripping system touches the part of the processed workpiece. Sensitive parts of the processed workpiece can thus be gripped gently with a bellows suction device. In a further embodiment, the electrically conductive vacuum suction device can be designed as a flat suction device with a spring plunger. The height can advantageously be compensated for.

In one embodiment, the electrically conductive vacuum suction device has a diameter of 40 mm, 50 mm, 60 mm or 80 mm. As the size changes, the resistance value of the electrically conductive vacuum suction device also changes.

In one embodiment, the electrically conductive gripping tool can have a plurality of vacuum suction devices, in which one vacuum suction device is designed as an electrically conductive vacuum suction device. Processed parts with a wide range of different shapes, sizes, dimensions, materials and/or material thickness can thus be sucked in (gripped).

In a further embodiment, the electrically conductive gripping tool can have a plurality of vacuum suction devices, in which at least two vacuum suction devices are designed as electrically conductive vacuum suction devices. Processed parts with a wide range of different shapes, sizes, dimensions, materials and/or material thickness can thus be sucked in (gripped). Furthermore, the functionality of the electrically conductive vacuum suction device is designed in a redundant manner.

In an advantageous embodiment, the electrically conductive vacuum suction device lifts the processed parts out of the workpiece by the lifting height of the vacuum suction device. The lifting height represents the height at which the processed part is lifted or gripped from the workpiece when a vacuum is applied. The height corresponds to the suction volume of the electrically conductive vacuum suction device, in particular the height corresponds to the movement potential of the suction material up to the suction nozzle. The electrically conductive vacuum suction device is used to grip and move the processed part out of the workpiece. The electrically conductive vacuum suction device does not suck onto the part, but the ambient pressure (atmospheric pressure) presses the part against the electrically conductive vacuum suction device or the electrically conductive vacuum suction device against the processed part of the workpiece being processed. For this, the surrounding pressure (ambient pressure) must be higher than the pressure between the electrically conductive vacuum suction device and the processed part. This pressure difference can be achieved by connecting the electrically conductive vacuum suction device to a vacuum generator. The vacuum generator sucks the air between the electrically conductive vacuum suction device and the processed part. The air is thus evacuated. As soon as contact occurs between the electrically conductive vacuum suction device and the surface of the processed part and the electrically conductive vacuum suction device seals the workpiece surface against the ambient pressure, the necessary negative pressure is generated. The holding force of an electrically conductive vacuum suction device is obtained by multiplying the pressure difference by the effective suction area of the electrically conductive vacuum suction device. The holding force F results from the following formula:

F = Dr c A.

Here, the parameter Dr is the difference between the ambient pressure and the system pressure and the parameter A is the effective suction area (the effective area of an electrically conductive vacuum suction device which is subjected to vacuum). The holding force F is therefore proportional to the pressure difference and the area. The holding force F is greater, the higher the difference between ambient pressure and pressure in the electrically conductive vacuum suction device or the larger the effective suction area. The holding force F can be varied by changing the parameters of pressure difference and area.

In an advantageous embodiment, the electrically conductive gripping tool can be connected to a voltage source, in particular a DC voltage source. The electrically conductive gripping tool is advantageously conductive and has a resistance, as a result of which a voltage across the conductive gripping tool drops when the circuit is closed. This voltage drop can be detected and measured.

In an advantageous embodiment, the voltage source provides the electrically conductive gripping tool with a voltage in a range from 0.1 to 24 volts, in particular in a range from 8 to 12 volts, preferably of 10 volts. Advantageously, safely reduced voltages in a range of 0.1 to 24 volts can be applied to the electrically conductive gripping tool via a voltage source. The safely reduced voltages are preferably reduced via a voltage divider in such a way that 10 volts are present at the analogue input and in parallel to the electrically conductive gripping tool. Here, safely reduced voltages are to be understood as those voltages which are present in electrical systems due to a corresponding type of protective separation of different voltage levels. A distinction is made between separated extra-low voltage (SELV), protected extra- low voltage with electrically safe isolation (PELV) and functional extra-low voltage without electrically safe isolation (FELV).

In an advantageous embodiment, the analogue input can be connected to the same voltage source in parallel with the electrically conductive gripping tool. The analogue input with the same voltage source is advantageously connected in parallel to the electrically conductive gripping tool. Thus, the voltage provided by the voltage source at the analogue input drops as long as there is no electrical connection between the processed part and the workpiece. If there is an electrically conductive connection between the processed part and the workpiece and the electrically conductive gripping tool grips the processed part, a current flows from the electrically conductive gripping tool via the processed part to the workpiece, which has a connection to the changing table. The changing table has the corresponding ground potential for this. By connecting the electrically conductive gripping tool and the analogue input to a shared voltage source in parallel, a voltage drop at the analogue input can be generated and detected in the event of a faulty cut of the processed part.

In an advantageous embodiment, the workpiece with the processed parts is stored on a changing table of the processing system and the changing table has the same potential as the detector unit. A current flow across the electrically conductive gripping tool thus advantageously occurs when there is an electrically conductive connection between the processed part and the workpiece and the electrically conductive gripping tool is in contact with the processed part. A voltage drop can be detected by the same potential of the detector unit, including the analogue input.

In an advantageous embodiment, the detector unit detects a voltage drop at the analogue input if a processed part has an electrical connection to the workpiece. For the purposes of the present invention, a voltage drop is understood to mean the reduction from a previously applied voltage value to a lower voltage value caused by an event. A faulty processed part can thus be advantageously detected. The event can represent, for example, the electrical connection between the processed part and the workpiece, as well as the changing table. According to a further aspect, the invention provides a method for detecting whether a processed part of a workpiece processed in a processing system has been completely cut, having the following method steps:

- detecting the workpiece with processed parts on a changing table of the processing system;

- lifting a processed part of the workpiece with a gripping tool of a gripping system; and

- detecting a voltage drop at an analogue input of the gripping system if a processed part has an electrical connection to the workpiece.

In an advantageous embodiment, the gripping tool comprises at least one electrically conductive gripping tool which can be connected to the analogue input.

In an advantageous method embodiment, the electrically conductive gripping tool is designed as an electrically conductive suction device, preferably as an electrically conductive vacuum suction device.

The invention also provides a computer program with program code for executing a method according to any one of the preceding method claims when the computer program is executed on an electronic device. The computer program can be provided as a signal by download or can be stored in a memory unit of a portable device with the computer-readable program code contained therein in order to cause a gripping system to execute instructions in accordance with the above-mentioned method. The implementation of the invention by means of a computer program product has the advantage that already existing electronic devices, for example computers, portable devices can easily be used by software updates in order to detect, as proposed by the invention, whether a processed part has been completely cut from a workpiece processed in a processing system.

The computer program can be executed in a distributed manner so that, for example, isolated method steps are carried out on a first computing unit and other method steps are carried out on a second computing unit.

The above embodiments developments can, if appropriate, be combined with one another as desired. Further possible embodiments, developments and implementations of the invention also include combinations of features of the invention described above or below with reference to the exemplary embodiments, which are not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention. Brief description of the figures

In the following detailed description of the figures, non-limiting exemplary embodiments with the features and further advantages thereof will be discussed with reference to the drawings. In the drawings:

Fig. 1 shows a block diagram to show a possible exemplary embodiment of a gripping system according to the invention;

Fig. 2 shows a flowchart to show a possible exemplary embodiment of a method according to the invention;

Fig. 3 shows a block diagram to show a further possible exemplary embodiment of a gripping system according to the invention;

Fig. 4 shows a block diagram to show a further possible exemplary embodiment of a gripping system according to the invention.

The accompanying drawings are intended to provide further understanding of the

embodiments of the invention. They illustrate embodiments and, in connection with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the advantages mentioned result from the drawings. The elements of the drawings are not necessarily shown to scale with respect to one another.

In the figures of the drawing, elements, features and components which are the same, have the same function and have the same effect - unless otherwise stated - are provided with the same reference symbols.

Detailed description of the invention

Fig. 1 shows a block diagram to show a possible exemplary embodiment of a gripping system 10 according to the invention. In Fig. 1 , reference numeral 10 denotes the gripping system according to the present invention. The gripping system 10 is designed to grip a processed part 41 (cf. Fig. 4) of a workpiece 40 and to transport and deposit it, for example, to a further transportation system. The workpiece 40, for example a metal sheet, is processed in a processing system 30. In one embodiment, the processing system 30 comprises a laser cutting system in which a processed part 41 , for example a contour, is cut from the workpiece 40. The workpiece 40 can comprise different sheet thicknesses and/or sheet area contents with different external dimensions corresponding to the processing system 30, which can be processed by the processing system 30. A contour or a plurality of contours can be cut from a workpiece 40.

The workpiece 40 is deposited on a changing table 31 for processing. The changing table 31 can be moved into the processing system 30 for the processing of the workpiece 40 and can be moved out of the processing system 30 for the removal of the processed part 41 by the changing table 31. In one embodiment, the changing table 31 is designed in a redundant form. This enables a workpiece 40 to be processed simultaneously in the processing system 30 and a previously processed workpiece 40 to be unloaded by the gripping system 10. The changing tables 31 are exchanged outside the processing system 30 in such a way that the already loaded changing table 31 is lowered outside the processing system 30 and the changing table 31 is moved with the processed workpiece 40 from the processing system 30 via the lowered changing table. Both changing tables 31 located outside the processing system are raised and the processed parts are unloaded by the gripping system 10. The lower changing table 31 is moved into the processing system 30 and a previously placed new workpiece 40 can be processed inside the processing system 30. This is merely an exemplary and not a restrictive embodiment of the changing table 31 and its movement sequences. Rather, further sequences with possibly further and/or different steps are also conceivable.

The gripping system 10 can be designed as a gripping robot. In one embodiment, the gripping system 10 has a gripping arm 11. In an advantageous embodiment, the gripping system 10 has at least one gripping arm 11 with a plurality of axes which can be controlled differently to one another. The mobility, precision and range of the gripping system 10 can be increased by the different axes.

The gripping system 10 has a gripping tool 12 for lifting the processed parts 41 out of the workpiece 40. The gripping tool 12 is arranged on the gripping arm 11 of the gripping system 10. In an advantageous embodiment, the gripping tool 12 is designed as a modularly interchangeable gripping tool 12. In one embodiment, the gripping system 10 has a gripping tool change system in which predefined gripping tools are stored corresponding to specific requirements, activities and work processes. The gripping system 10 can automatically change the gripping tool 12 corresponding to the requirements, activities and work processes. The gripping system 10 has a control unit 13 which communicates with the gripping system 10. A control unit 13 refers to any electronic device that includes a processor, such as a main processor (CPU), a dedicated processor, or a microcontroller. The processor is adapted to perform a dedicated computing task, namely to detect a voltage drop. The control unit 13 can receive data (an input), then perform a sequence of predetermined operations and thereby generate a result in the form of information or signals (an output). Depending on the context, the computer unit either means a processor or, more generally, can refer to a processor in conjunction with an assembly of interconnected elements contained in a single housing or housings. In one embodiment, the control unit 13 can represent a programmable logic controller (PLC) or a software implementation of a PLC on a processor. Furthermore, the control unit 13 can run as an entity on another system.

In one embodiment, the control unit 13 has a detector unit 15. In one embodiment, the detector unit 15 can be designed as a voltage measuring device, via which a falling voltage can be determined. In one embodiment, the detector unit 15 also has an analogue input card (not shown) which is connected to the analogue input 14 for evaluating the voltage drop at the analogue input 14. The analogue input 14 is designed to receive an analogue electrical signal, in particular a DC voltage signal. The analogue electrical signal is evaluated by the analogue input card and can be converted into a digital signal usable for control by an analogue-digital conversion integrated on the analogue input card by an AD converter. This usable digital signal can be used in accordance with the value for controlling the processing system 30 and/or for displaying it to an operator of the processing system 30. In one embodiment, the analogue input 14 and the detector unit 15 are integrated in the gripping system 10 designed as a gripping robot, and the control unit 13 is an external component which communicates with the gripping system 10 via a communication link. This has the advantage that the voltage losses in the connecting lines, in particular between the electrically conductive gripping tool and the analogue input 14 or the detector unit 15, can be minimised or limited. Lines that are too long lead to an increased voltage drop at the connecting lines, which falsifies the detection of the voltage drop at the analogue input 14 and can lead to a measurement error.

In addition, the gripping system 10 has a voltage supply via a voltage source 20, in particular via a DC voltage source. The voltage source 20 can provide a voltage in a voltage range from 0.1 to 20 volts, in particular in a range from 8 to 12 volts, preferably from 10 volts. In embodiments with a voltage higher than 10 volts, the 10 volt voltage can be provided via a voltage divider. The voltage source 20 is connected to the electrically conductive gripping tool 12. The voltage source 20 is also connected in parallel to the electrically conductive gripping tool 12 to the analogue input 14. A DC voltage of 10 volts is preferably applied to both the electrically conductive gripping tool 12 and the analogue input 14.

In one embodiment, the detector unit 15 and the changing table 31 have the same ground potential. If a processed part 41 has an electrical connection 50 (cf. Fig. 4) via a material web (residual material in the case of a faulty cut), the ground potential of the changing table 31 via the workpiece 40 is also present at the processed part 41 when the electrically conductive gripping tool 12 has raised the processed part 41 above the level of the suction volume. This leads to a voltage drop of 10 volts at the analogue input, which can be evaluated in an advantageous manner and provides information about the processed part 41 to be lifted, for example which processed part 41 of the workpiece 40 is defective.

The gripping system 10 has a gripping tool 12. In one embodiment, the gripping tool 12 comprises at least one electrically conductive gripping tool 12. The electrically conductive gripping tool 12 is constructed from a material that conducts the electrical current and has an electrical resistance with a resistance value. The resistance value depends on the material and the size of the electrically conductive gripping tool 12.

In one embodiment, the electrically conductive gripping tool 12 of the gripping system 10 is modularly interchangeable. For the purposes of the present invention, modular is to be understood to mean that different gripping tools are interchangeable in accordance with the requirements in terms of size and weight of the processed parts 41 to be lifted, as well as the type of use and area of use.

The electrically conductive gripping tool 12 comprises an electrically conductive suction device, preferably an electrically conductive vacuum suction device. In one embodiment, the electrically conductive gripping tool 12 comprises at least one suction device or a plurality of suction devices and one electrically conductive suction device or a plurality of electrically conductive suction devices. Differently processed parts 41 with different requirements can thus advantageously be lifted. There is also redundancy for the electrically conductive suction device and for the voltage drop at the analogue input 14. This is advantageous if there is a second analogue input 14 and a second analogue input card. This results in redundant monitoring of the measurement and evaluation of the voltage drop.

Fig. 2 shows a flowchart to show a possible exemplary embodiment of a method according to the invention. In the exemplary embodiment shown, the method 1 comprises a plurality of steps. In a first step S1 , the workpiece 40 with the processed parts 41 is detected on a changing table 31 belonging to the processing system 30. The step S1 takes into account the cutting information of the processed parts 41 provided by the processing system 30, for example a cutting plan. The positions of the processed parts 41 that are to be removed are thus known.

In a further step S2, a processed part 41 of the workpiece 40 is lifted using a gripping tool 12 of a gripping system 10. In one embodiment of the present invention, the gripping tool 12 comprises an electrically conductive gripping tool, in particular an electrically conductive suction device, preferably an electrically conductive vacuum suction device. For the purposes of the present invention, lifting is to be understood to mean the lifting of a processed part 41 by the lifting height of the vacuum suction device from the workpiece 40.

In one embodiment, the lifting height corresponds to a suction volume of the vacuum suction device.

In a further step S3, a voltage drop at an analogue input 14 of the gripping system 10 is detected if a processed part 41 has an electrical connection 50 (of. Fig. 4) to the workpiece. The voltage drop at the analogue input 14 can then be detected when the electrically conductive gripping tool 12 lifts the processed part 41 out of the workpiece 40.

Fig. 3 shows a block diagram to show a further possible exemplary embodiment of a gripping system 10 according to the invention. Fig. 3 shows a gripping system 10 which lifts a processed part 41 out of the workpiece 40 by means of an electrically conductive gripping tool 12, preferably by means of an electrically conductive vacuum suction device. The gripping system 10 performs the method 1 (cf. Fig. 2) according to the present invention. The electrically conductive vacuum suction device 12 has a resistance value. The resistance value of the electrically conductive vacuum suction device 12 can be measured. A voltage, preferably of 10 volts, can be applied to the electrically conductive vacuum suction device 12 via the voltage source 20 (cf. Fig. 1). The voltage of 10 volts from the voltage source 20 is applied in parallel to an analogue input 14. The analogue input 14 has a connection to a detector unit 15 for detecting the voltage drop. In one embodiment, the detector unit 15 comprises an analogue input card. The changing table 31 and the detector unit 15 have a ground potential. If the electrically conductive vacuum suction device 12 comes into contact with the changing table 31 via a processed part 41 that is in electrical contact with the workpiece 40 during the lifting, the voltage at the analogue input 14 drops at an originally applied voltage of, for example, 10 volts to 2 volts. If, as shown in Fig. 3, the processed part 41 is suctioned or raised by the electrically conductive vacuum suction device 12 and there is no contact between the processed part 41 and the workpiece 40 and thus the changing table 31 , the 10 volts are still connected to the analogue input 14 and can be measured and evaluated.

Fig. 4 shows a block diagram to show a further possible exemplary embodiment of a gripping system 10 according to the invention. Fig. 4 shows a gripping system 10 which lifts a processed part 41 out of the workpiece 40 by means of an electrically conductive gripping tool 12, preferably an electrically conductive vacuum suction device. The gripping system 10 performs the method 1 (cf. Fig. 2) according to the present invention. A voltage, preferably of 10 volts, can be applied to the electrically conductive vacuum suction device 12 via the voltage source 20 (cf. Fig. 1). The voltage of 10 volts from the voltage source 20 is applied in parallel to an analogue input 14. The analogue input 14 has a connection to a detector unit 15 for detecting the voltage drop. In one embodiment, the detector unit 15 comprises an analogue input card. The changing table 31 and the detector unit 15 have a ground potential. If the electrically conductive vacuum suction device 12 comes into contact with the changing table 31 via a processed part 41 that is in electrical contact with the workpiece 40 during the lifting, the voltage at the analogue input 14 drops at an originally applied voltage of, for example, 10 volts to 2 volts. If, as shown in Fig. 4, the processed part 41 is now suctioned or raised by the electrically conductive vacuum suction device 12 and there is an electrical contact or an electrical connection 50 between the processed part 41 and the workpiece 40 and thus the changing table 31 , the 10 volt voltage previously present at the analogue input 14 drops, for example, to a voltage value of 2 volts. This voltage drop can be evaluated by the detector unit 15 and appropriate measures can be implemented. For example, the gripping system 10 can issue a fault message or warning and show which processed part 41 has an electrical connection 50 to the workpiece 40.

In an advantageous embodiment, the analogue input 14 is designed to be configurable. In an advantageous manner, the analogue input 14 can be configured to changing values for the voltage drop, which may result from the materials for the parts 41 to be processed due to the conductivity value. For example, copper has a better conductivity coefficient than steel, which makes copper a better conductor than steel. In this regard, the voltage drop for a 10 volt output voltage for copper is higher than that for steel. The higher voltage drop can be predetermined by the configurable input 14, whereby different types of material can be checked with the present invention. Finally, it should be noted that the description of the invention and the exemplary embodiments are not to be understood as limiting in terms of a particular physical realisation of the invention. All of the features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the subject matter according to the invention to simultaneously realise their advantageous effects.

The scope of protection of the present invention is given by the claims and is not limited by the features illustrated in the description or shown in the figures.

REFERENCE SYMBOLS

1 Method

10 Gripping system 11 Gripping arm

12 Gripping tool

13 Control unit

14 Analogue input

15 Detector unit 20 Voltage source

30 Processing system

31 Changing table

40 Workpiece

41 Processed parts 50 Electrical connection

S1-S3 Method steps