DE102012109888B4 - Suction gripper, suction gripper system and control device for controlling at least one suction gripper - Google Patents

Abstract

Suction grippers (9, 9 ') for sucking and holding workpieces, in particular pliable, air-permeable semi-finished products, comprising a housing with at least one air inlet and at least one air outlet and a plurality of suction openings (13) in a suction surface (11) for sucking in at least one workpiece , characterized in that the suction surface (11) has at least two electrodes (15, 17; 15 ', 17') connected to a voltage measuring device (5) on its side facing the workpiece to be sucked on.

Description

The invention relates to a suction gripper for sucking in and holding workpieces according to the preamble of claim 1, a suction gripper system according to the preamble of claim 18 and a control device for controlling a suction gripper according to the preamble of claim 19.

Suction grippers for sucking in and holding workpieces in order to transport them, for example, in a production process, are generally known from the prior art. So shows the DE 10 2009 047 089 B4 a compressed air-operated vacuum generator, which works to generate a vacuum and the resulting suction of a workpiece according to the so-called Coanda principle. Furthermore, from the DE 10 2010 029 662 A1 a vacuum generator operated with compressed air with an air inlet and an air outlet and a suction opening opening into a suction chamber is known, which can work according to the Bernoulli, Coanda, Vortex, jet nozzle or Venturi principle. Suction grippers of the type mentioned above are used in particular for gripping and transporting carbon or fiberglass semi-finished products, assembled circuit boards, porous and highly absorbent workpieces, thin glass, veneers, foils or other sensitive materials that should be handled gently, efficiently and automatically.

From the DE 10 2010 040 686 B3 a method for operating a suction gripper is known in which the suction body has a circumferential sealing lip on the side facing the workpiece, the wear of which is to be determined and continuously displayed by means of electrical measurement of its depth.

the DE 101 40 248 B4 shows and describes a suction gripper called a negative pressure treatment device with a device for controlling negative pressure and / or volume flow, which monitors the status data on the suction gripper with a sensor and evaluation electronics in order to allow the device to work as required and to prevent the negative pressure from tearing off.

In the DE 198 47 314 C5 discloses a suction device with a tool designed as a cup for attracting and holding a workpiece. In the foot of the cup, electrodes are arranged at a distance, via which a detection signal for establishing the electrically conductive state in the pressure-sensitive rubber cup is to be established.

From the DE 10 2010 034 720 A1 a surface gripper made up of several layers for, in particular, pliable, flat objects is known, which gripper is intended to grip the objects by means of negative pressure generated between the layers.

Suction grippers of the type described above usually have a control device which controls the volume flow of the air to be sucked in or the supplied compressed air and thus the resulting negative pressure in the suction gripper in order to hold a workpiece to be sucked on a suction surface of the suction gripper. The control device is essentially based on empirical values that have to be evaluated separately for different applications. With the known suction grippers, it can happen that a workpiece is not securely held by the suction gripper, so that interruptions in the production process occur if a workpiece becomes detached from the suction surface due to incorrect gripping. If the suction gripper is to grip a single work piece from a stack of several stacked workpieces, it can also happen that the suction gripper grips not only a single workpiece but several workpieces at the same time when sorting the stack of workpieces. Overall, the problem is that the known suction grippers do not have any information as to whether the suction gripper has safely gripped a target workpiece and how many workpieces have been gripped. Another problem with the known suction cups is the high air consumption, which can be around 250 l / min. In the case of suction gripper systems, which, depending on the application, can have up to 1000 or more individual suction grippers, there is consequently an enormous consumption of air and energy.

The object of the present invention is therefore to create a suction gripper which ensures safe handling of a workpiece and which is also designed to be energy-efficient.

To solve the above-mentioned problem, a suction gripper with the features of claim 1 is proposed. The suction pad is used to suck in and hold workpieces, in particular pliable, air-permeable semi-finished products. The suction gripper has a housing which can be constructed in several parts and which has at least one air inlet and at least one air outlet as well as a plurality of suction openings in a suction surface for sucking workpieces. The suction gripper is characterized in that the suction surface has at least two electrodes.

An essential point of the invention is therefore that by means of the electrodes, a sensor-based feedback of status data of a workpiece to be gripped can take place in a simple manner. By the electrodes, which are arranged in the area of the suction surface or the suction surface form, it is thus not only possible to obtain information about the state of one or more gripped air-permeable workpieces, but at the same time the air consumption can be regulated in such a way that a minimum air consumption can be dynamically set for safe handling of a workpiece. At the same time, the suction gripper according to the invention does not require any significant additional expenditure in production. In any case, the saving of resources far outweighs the additional effort resulting from the electrodes and the implementation of the regulation.

Particularly preferred is a suction gripper in which the at least two electrodes can be or are connected to a voltage measuring device. The tension measuring device can be integrated into the suction gripper or arranged externally. By changing the measured voltage drop between the at least two electrodes, it is possible to determine in “real time” during the gripping process whether a workpiece and, in particular, how many workpieces were gripped by the suction gripper. The voltage drop between the at least two electrodes allows a conclusion about the existing resistance between the electrodes, which changes depending on the state and position of the gripped workpiece and depending on the number of gripped workpieces. The at least two electrodes preferably each have at least one electrical connection for connection to the voltage measuring device.

As already indicated above, the at least two electrons can be arranged on the side of the suction surface facing the workpiece to be sucked on. In particular, the suction surface can be formed from an insulating material. The electrodes can be applied to the suction surface, for example in the form of a coating. In principle, it is also conceivable that the electrodes form at least part of the suction surface. It is crucial that the electrodes are designed to be electrically insulated from one another. If the electrodes are applied to the suction surface, this can serve as insulation between the two electrodes. On the other hand, it is conceivable to design the suction surface in several parts. For example, the suction surface can have at least three areas, of which at least two are made from a conductive material and a third area is made from an insulating material that electrically isolates the two conductive areas from one another.

In principle, a change in the voltage drop when a workpiece is gripped can then be determined between the at least two electrodes if it is a workpiece made of a conductive material. In order to be able to determine a change in the voltage drop between the at least two electrodes when gripping a non-conductive workpiece, an electrically conductive and air-permeable intermediate layer, for example a carbon fiber fabric, can be arranged on the side of the at least two electrodes facing the workpiece to be sucked on. When the suction gripper is in operation, the electrically conductive intermediate layer is arranged between the electrodes or the suction surface and the workpiece to be gripped. Because a non-conductive workpiece also exerts a greater normal force on the electrically conductive intermediate layer, as a result of which the resistance between the electrodes changes, a voltage drop between the at least two electrodes can also be measured in this case. It is particularly advantageous here if the conductive intermediate layer has openings which are aligned with the suction openings of the suction surface. In this way, the functioning of the suction pad is not impaired by the conductive intermediate layer. On the other hand, it can also be provided that the conductive intermediate layer is formed from a porous, air-permeable material. The suction gripper is thus designed to suck in a porous workpiece that is sucked through, in particular an air-permeable fabric or scrim made of glass, aramid or carbon fibers.

The at least two electrodes can be designed such that a first point-shaped electrode is arranged centrally with respect to the suction surface, which is surrounded by a second ring-shaped electrode. The suction surface is preferably designed to be essentially circular. On the other hand, a first and a second electrode can also be provided, both of which are annular and are arranged concentrically to one another. In principle, it is also conceivable to provide more than two electrodes which are designed in the form of a ring and are arranged concentrically to one another. The electrodes can cover the major part of the suction surface or form the major part of the suction surface. In order not to block the suction openings and thus the functioning of the suction gripper, the electrodes are preferably arranged in the area between the suction openings. If the electrodes form at least part of the suction surface, the suction openings are arranged to penetrate the electrodes.

The suction gripper can work according to the Bernoulli, Coanda, Vortex, jet nozzle or Venturi principle. It is crucial that a workpiece can be gripped by the negative pressure. To generate the negative pressure, the suction gripper can be designed to be operated by compressed air. However, it is also conceivable to integrate an air delivery device, in particular a propeller, into the suction gripper to generate a negative pressure. Accordingly, the Suction grippers have an integrated or an external vacuum generating device.

A suction gripper system with the features of claim 18 is also proposed to solve the above-mentioned object. The suction gripper system is characterized by several suction grippers according to the invention. To create a suction gripper system, these can be connected to one another in such a way that large-area workpieces can be sucked in and held by up to approx. 1000 individual suction grippers.

In order to achieve the above-mentioned object, a regulating device for regulating one or more suction grippers with the features of claim 19 is also proposed. The regulating device is preferably designed such that it regulates the operating pressure and / or the operating volume flow of the suction gripper as a function of a measured voltage drop between the at least two electrodes. This makes it possible in an advantageous manner to set a minimum air consumption required for safe handling of the workpiece.

The control device can have a microprocessor which is arranged either externally or also integrated in the suction gripper. A program can be executed on the microprocessor which dynamically regulates the operating pressure and / or the operating volume flow of the suction gripper on the basis of the measured voltage drop between the at least two electrodes. The regulating device thus preferably interacts with the tension measuring device and regulates the gripping process on the basis of the measured tension values.

• 1 eine Prinzipdarstellung einer Kontaktwiderstandsmessung zwischen einer ersten und einer zweiten Fläche;
• 2 ein Prinzipschaltbild zur Durchführung einer Kontaktwiderstandsmessung gemäß der Erfindung;
• 3 eine schematische Stirnseitenansicht eines erfindungsgemäßen Sauggreifers nach einer ersten Ausführungsform der Erfindung;
• 4 eine schematische Stirnseitenansicht eines Sauggreifers nach einer weiteren Ausführungsform der Erfindung;
• 5 ein Schaubild der Messspannung, des Betriebsvolumenstroms und des Betriebsdrucks des Sauggreifers;
• 6 ein Schaubild der Messspannung, des Betriebsvolumenstroms und des Betriebsdrucks des Sauggreifers beim Greifen von unterschiedlich vielen Werkstücken;
• 7 ein Schaubild der Messspannung, des Betriebsvolumenstroms und des Betriebsdrucks, bei einer dynamischen Regelung des Betriebsvolumenstroms und des Betriebsdrucks, und
• 8 ein Schaubild der Messspannung, des Betriebsvolumenstroms und des Betriebsdrucks, bei einer dynamischen Ausgleichsregelung des Betriebsvolumenstroms und des Betriebsdrucks bei Ausübung einer Quer- und/oder Normalkraft auf ein angesaugtes Werkstück.

The invention is explained in more detail below with reference to the drawing. Show it:

• 1 a schematic diagram of a contact resistance measurement between a first and a second surface;
• 2 a basic circuit diagram for performing a contact resistance measurement according to the invention;
• 3 a schematic end view of a suction gripper according to the invention according to a first embodiment of the invention;
• 4th a schematic end view of a suction gripper according to a further embodiment of the invention;
• 5 a diagram of the measuring voltage, the operating volume flow and the operating pressure of the suction pad;
• 6th a diagram of the measuring voltage, the operating volume flow and the operating pressure of the suction gripper when gripping different numbers of workpieces;
• 7th a diagram of the measurement voltage, the operating volume flow and the operating pressure, with a dynamic control of the operating volume flow and the operating pressure, and
• 8th a diagram of the measurement voltage, the operating volume flow and the operating pressure, with a dynamic compensation control of the operating volume flow and the operating pressure when a transverse and / or normal force is exerted on a workpiece that is sucked in.

$${\text{R}}_{\text{Eng}}=\frac{\text{E}\ast \cdot \rho \cdot {\text{R}}_{\text{A}}}{\mathrm{3,7}{\text{F}}_{\text{N}}}$$

The present invention uses the principle of contact resistance measurement between a first surface and a second surface, which is described below with reference to FIG 1 is explained in more detail. the 1 shows a schematic diagram of a contact point between a first surface 1 and a second face 3 . The contact resistance between the two surfaces 1 and 3 is measured according to the following formulas: $${\text{R.}}_{\text{Contact}}={\text{R.}}_{\text{Closely}}+{\text{R.}}_{\text{Strange}}$$

$${\text{R.}}_{\text{Closely}}=\frac{\text{E.}\ast \cdot \rho \cdot {\text{R.}}_{\text{A.}}}{3.7{\text{F.}}_{\text{N}}}$$

E * is the effective modulus of elasticity, p is the specific electrical resistance, R _{A is} the roughness of the surface and F _{N is} the normal force exerted on the contact point. The so-called narrow resistance R _Eng arises from the microscopic unevenness of a contact surface, while the so-called foreign layer _{resistance R foreign} arises from oxidation or corrosion on the contact surface. This foreign layer increases the resistance between the first and the second surface.

The present invention makes use of the dependence of the contact resistance R _contact on the normal force F _N. This normal force changes as soon as a workpiece is gripped by the suction gripper, which consequently rests on the electrodes in the area of the suction surface and creates an electrically conductive connection between them. Furthermore, the normal force in the contact area changes if more than one workpiece was gripped by the suction gripper. The change in normal force, on the other hand, results in a change in the measurable resistance in the contact area, which in turn results in a changed voltage drop in the contact area.

the 2 shows a basic circuit diagram of a measuring arrangement for performing a resistance measurement according to the invention. The basic circuit diagram shows a two-point _measurement for determining the voltage U Mess, which drops across a measuring resistor R _Mess. The measuring circuit according to 2 is explained below with reference to a suction gripper according to the invention with a suction surface which has two electrodes arranged isolated from one another. When the suction gripper is in use, it sucks a workpiece onto the suction surface, which consequently rests on the two electrodes. As a result of the workpiece being supported, a contact resistance R _contact is produced in the contact area with the electrodes. In the area between the contact points, the workpiece forms a resistance R _HZ (semi-finished product resistance). The one from a tension measuring device 5 The measured voltage U _Mess is obtained when a constant voltage is supplied from a current source 7th generated electricity measured, with the power source 7th also in the voltage measuring device 5 can be integrated. The voltage dropped across the two contact resistors R _Kontakt and the resistance of the workpiece R _{HZ corresponds to the measurement} voltage U Mess. The measuring voltage consequently depends on the current strength of the known constant current I _const and the measuring resistor R _Mess and thus, according to equation (2), also on the normal force F _N on the contact between the workpiece and the electrodes. So the following applies: $${\text{U}}_{\text{Mess}}\left({\text{F.}}_{\text{N}}\mathrm{,\; ...}\right)\sim {\text{I.}}_{\text{const}}\times {\text{R.}}_{\text{Mess}}\left({\text{F.}}_{\text{N}}\mathrm{,\; ...}\right)$$

The dependency of the measurement voltage on the normal force F _N exerted on the contact point results essentially from the contact resistance R _contact , which, as described above, varies with the normal force exerted on the contact point between the workpiece and the electrode. The resistance of the workpiece R _HZ, on the other hand, corresponds to the ohmic resistance of the workpiece and is consequently to be regarded as essentially constant for a specific workpiece type. The decisive factor is therefore the fact that the contact resistance R _contact between the workpiece and the electrodes changes with the normal force F _N acting on the contact point. Depending on how strongly the workpiece is pressed onto the electrodes, the contact resistance R _contact consequently also changes. This change in resistance is reflected in the measuring voltage U _Mess , which measures the voltage that drops _{across the measuring resistor R Mess.}

By using two electrodes on or next to the suction surface, which are connected to a voltage measuring device, a change in the measured voltage drop U _Mess between the two electrodes can be used to determine whether and how many workpieces are held by the suction surface.

the 3 shows an end view of a suction gripper 9 according to a first embodiment, the one suction surface 11 with a variety of suction openings 13th having. The suction cup 9 is preferably designed as a Coanda suction cup and is therefore particularly suitable for gripping and holding pliable and air-permeable semi-finished fiber products. The number of suction openings can vary depending on the application and field of application of the suction gripper, and can be between 50 and 150, for example. The suction surface 11 is circular in the present embodiment and has a first circular electrode 15th on, which is concentric by a second annular electrode 17th is surrounded. The two electrodes 15th and 17th are through an annular isolation area 19th electrically isolated from each other. The two electrodes 15th and 17th are like that with an in 3 connected voltage measuring device, not shown, that a voltage drop between the electrodes can be measured.

The two electrodes 15th and 17th can be applied to the suction surface in a coating process 11 be upset. The suction surface can 11 be made of an insulating material, so that during the coating process the insulating area 19th can be left out, which is part of the original suction surface in this embodiment 11 is. The two electrodes 15th and 17th which are made of a conductive, in particular metallic material, are electrically insulated from one another in this way. the 3 also makes it clear that the electrodes 15th and 17th preferably in the area between the suction openings 13th are arranged so that the suction openings 13th So are not covered and the functioning of the suction pad 9 so that it is not impaired.

the 4th Figure 3 shows yet another embodiment of the invention. There is also an end view of a suction gripper 9 ' shown, which has a suction surface 11 with a variety of suction openings 13th having. The regularly arranged suction openings 13th serve to suck in a workpiece, in particular a pliable, air-permeable material such as a carbon fiber semi-finished product. The suction openings 13th are connected to the air inlet and the air outlet (not shown in the figures) of the suction cup 9 ' connected in such a way that the negative pressure created in the suction gripper a workpiece by means of the suction openings 13th sucks. The negative pressure can be generated in various ways, for example by means of compressed air.

In the embodiment according to 4th is also a first electrode 15 ' provided that but centrally and essentially point-like on the circular suction surface 11 is arranged. This first point-shaped electrode 15 ' is from a second annular electrode 17 ' surrounded concentrically. The ring-shaped second electrode 17 ' is in this way on the suction surface 11 formed that they are at the very edge of the suction surface 11 is arranged and thus has a radius which corresponds to the radius of the suction surface 11 .

A comparison of the embodiment of the invention according to FIGS 3 and 4th shows that in the embodiment according to 3 a predominant part of the suction surface 11 from the first and second electrodes 15th and 17th is covered. The area of the first and second electrodes 15th and 17th essentially agree. The isolation area 19th however, only takes up a very small part of the total area of the suction area 11 on.

In the embodiment according to 4th however, take the first and second electrodes 15 ' and 17 ' only a small part of the total surface of the suction surface 11 on. It also becomes clear that the total area of the second electrode 17 ' is larger than the total area of the first electrode 15 ' . The isolation area 19 ' that is between the first electrode 15 ' and the second electrode 17 ' is arranged for electrical insulation of the two electrodes, takes up a major part of the suction surface 11 on.

Instead of a coating, the electrodes can also be integral with the suction surface 11 be trained. It is conceivable here, for example, to use the suction surface 11 , which can be part of a cap of the suction pad, to produce with different material areas. In the area of the electrodes, the cap can be made entirely of an electrically conductive material, for example. In the isolation areas 19th , 19 ' however, an insulating material would have to be used. The electrodes 17th , 17 ' and 19th , 19 ' can consequently also be integrated in the suction pad 9 , 9 ' or in the suction area 11 be designed so that a coating for producing the electrodes is not necessary in this case. In this way, existing suction grippers can also be easily retrofitted with electrodes according to the invention.

In the embodiments according to 3 and 4th these are merely exemplary and particularly advantageous configurations of the electrodes. It is also conceivable to arrange and design the electrodes completely differently in the area of the suction surface or also next to the suction surface. Furthermore, more than two electrodes can be used in order to further improve the reliability of the suction gripper.

In order to explain the functional principle of the present invention, it is assumed below that a negative pressure in the suction gripper 9 a workpiece, for example a pliable, air-permeable and conductive carbon fiber fabric, is sucked in. The workpiece then lies on the suction surface 11 and thus on the first electrode 15th and second electrode 17th on. The electrodes 15th and 17th are equipped with a voltage measuring device 5 connected, which conducts a constant measuring current through the electrodes to determine the voltage drop between the two electrodes. So if a workpiece is on the electrodes 15th and 17th is arranged, the current flows from one electrode to the other, for example from the electrode 15th over the workpiece to the electrode 17th . The measured voltage drop or the _measurement voltage U Mess between the two electrodes can be determined from this. As with reference to the 1 and 2 has been explained, this measured voltage drop depends on the contact resistance R _contact between the sucked workpiece and the second electrode 17th (in 2 with reference number 21 marked), from the ohmic resistance R _{HZ of} the workpiece (in 2 with reference number 22nd characterized) and from the contact resistance R _contact between the workpiece and the first electrode 15th (in 2 with reference number 23 marked).

The behavior of the operating volume flow V , the operating pressure P. and the measuring voltage U _Mess during operation of the suction gripper 9 , 9 ' is explained below using the graphs according to 5 until 8th explained. The operating volume flow is the amount of air flow conveyed to generate a specific negative pressure in the suction gripper. The operating pressure changes with the amount of air conveyed in the suction gripper and determines the negative pressure created in the suction gripper. On the y-axis of each diagram is the operating pressure in bar, that in the suction pad 9 existing operating volume flow V plotted in 100 l / min and the measured voltage U _Mess in volts, while the number of sampling points of the aforementioned values is shown on the x-axis.

the 5 shows a diagram of the voltage U Mess measured between the electrodes, the operating _{volume flow} V and the operating pressure P. in the suction cup 9 in the event that the suction gripper has picked up a conductive workpiece and is holding it. It becomes clear that with a falling pressure and a resulting decrease in the volume flow, the _measurement voltage U Mess between the electrodes increases. With a falling pressure and a resulting falling negative pressure in the suction gripper 9 the held workpiece is pressed onto the two electrodes with less force than it would be with a greater negative pressure in the suction gripper 9 the case is. The lower negative pressure results in a contact area between _{the normal force F N} acting on the workpiece and the electrodes, which is less than in the case of a greater negative pressure. The normal force F _N is consequently dependent on the negative pressure generated by the suction gripper. Furthermore, the _{measurement voltage U Mess is} dependent on the normal force F _N. So when the workpiece is applied to the first and second electrodes with less force 15th , 17th is sucked in, the contact resistances R _contact ( 21 , 23 ), as a result of which the measuring resistance R _Mess becomes larger overall. Due to equation (3), this results in an increase in the _measurement voltage U Mess, as shown in FIG 5 can be seen.

The present invention makes use of the dependence of the _{measurement voltage U Mess on the normal force F N} acting on the contact surface between a workpiece and the electrodes _{, in that it can be determined on the basis of the measurement} voltage U Mess whether and, if so, how many workpieces are sucked in by the suction gripper and be held. This is particularly based on the 6th clearly which a characteristic curve of the measured voltage U Mess, the operating _{volume flow} V and the operating pressure P. for the case shows that, one after the other, first a first workpiece and then a second workpiece are sucked in by the suction gripper.

The operating pressure P. and the operating volume flow V are in the embodiment according to 6th kept essentially constant. During the operating pressure P. is approx. 6 bar, the operating volume flow is kept constant at approx. 290 l / min. The measurement voltage U _Mess, on the other hand, has a stepped profile which is between 9 and 10 V ^{in the range between 0 and approximately 1.3 * 10 4 sample values.} This corresponds to the no-load case between the electrodes. In this voltage range lies on the electrodes 15th and 17th consequently no workpiece, ie the suction pad 9 has not sucked in a workpiece. Starting from this first range, the voltage drops after approx. 1.3 * 10 ⁴ sampling points to a voltage value in the range of 2 and 3 V. This measured value results from the suction of the suction gripper 9 of a workpiece, which is consequently on the two electrodes 15th and 17th rests. The resistance between the two electrodes 15th and 17th is reduced by the connection of the two electrodes with the workpiece, so that overall the measuring resistance R _Mess decreases and consequently the measuring voltage U _{Mess also} decreases. After approx. 2.6 * 10 ⁴ sampling points, the measured voltage U _Mess drops to a value between 0 and 1 V. This further step-like decrease in the _measurement voltage U Mess results from a further workpiece being sucked onto the suction surface 11 . On the suction surface 11 then consequently not only one workpiece, but two workpieces are arranged one behind the other. By having two workpieces on the electrodes 15th and 17th the total air permeability of the stack of semi-finished products decreases and the negative pressure on the suction surface increases. This results in an increase in the normal force F _N in the contact areas between the workpiece that was sucked in first and the electrodes, so that the resistance R _{contact is} subsequently reduced. As a result, the measuring resistance R _{Mess is} reduced overall, which at the same time results in a reduction in the measured voltage U _Mess .

the 6th makes it clear that by means of the present invention using two in the area of the suction surface 11 attached electrodes with a voltage measuring device 5 are connected, it can be determined in an advantageous manner whether a workpiece and how many workpieces by the suction gripper 9 was sucked in. Corresponding voltage threshold values can be defined for this purpose, which _{are compared by an evaluation unit with the measured voltage values U Mess} and which consequently allow a conclusion to be drawn about the number of workpieces sucked in. The evaluation unit can, for example, generate a warning signal if no workpiece or too many workpieces have been sucked in. This is made possible by the fact that the normal force in the contact areas of the electrodes and the workpiece at constant operating pressure P. and constant volume flow V changes, so that it can advantageously be determined on the basis of the measured voltage U _Mess whether a workpiece is being removed from the suction gripper 9 was sucked in and how many workpieces are involved.

However, the present invention not only makes it possible, as in FIG 6th shown at a constant pressure curve P. and volume flow V determine how many workpieces from the suction pad 9 were sucked in, but it also enables the implementation of a dynamic control to minimize the required volume flow.

the 7th shows a characteristic curve of the measured voltage U _Mess , the operating pressure P. and the operating volume flow V with dynamic regulation of the average air consumption of the suction pad.

the 7th makes it clear that in an initial state the operating volume flow V and the operating pressure P. have essentially constant values. _{The measurement} voltage U Mess is in the range between 9 and 10 V, which corresponds to idling operation, so that no workpiece is removed from the suction gripper 9 is held. As soon as the suction cup 9 a workpiece grips, which consequently in that on the suction surface 11 and thus on the electrodes 15th and 17th is applied, the measured voltage U _Mess drops at approx. 3000 sampling points due to the change in resistance to a value between 2 and 3 V. The control device according to the invention then calculates the minimum average air consumption that is necessary for the workpiece being gripped on the suction surface 11 to keep. The operating volume flow conveyed in the suction gripper V and thus the operating pressure P. are significantly reduced, as in the 7th is clearly visible. By reducing the operating pressure, the negative pressure in the suction gripper is also reduced 9 so that the normal force F _N in the area between the workpiece and the electrodes 15th and 17th decreases. This increases the contact resistance R _contact ( 21 , 23 ) between the workpiece and the electrodes, which leads to an increase in the measured voltage U _Mess due to the increased resistance. This course is also clear in the 7th recognizable in the range between 6000 and 8000 sampling points.

To prevent the workpiece from being completely removed from the suction surface 11 of the suction cup 9 replaces, the negative pressure and thus the operating volume flow V can be increased again slightly. This in turn brings the workpiece closer to the suction surface due to the stronger negative pressure 11 sucked in, whereby the normal force F _N in the contact area between the workpiece and the electrodes 15th and 17th again increases. As a result, the contact resistance R _contact is also reduced ( 21 , 23 ) between the electrodes and the workpiece, which leads to a reduction in the measured voltage U _Mess . The operating volume flow can then be reduced, which in turn leads to an increase in the measured voltage U _Mess . This control strategy is continued continuously, with the control device for an average air consumption 25th which is much lower than with a constant volume flow of approx. 290 l / min (see 6th ). the 7th shows that the average air consumption can be reduced to approx. 50 l / min and thus to a fifth of the conventional value with the aid of the control device according to the invention. At the same time it is ensured that the gripped workpiece is safe from the suction gripper 9 is held.

Corresponding threshold values for the measured voltage U _Mess can be defined within the regulating device, within which a reliable gripping of the workpiece or also of several workpieces is guaranteed. For example, it can be specified that the measured voltage U _Mess must not fall below a value of 3 V in order to prevent the workpiece from detaching from the suction surface. If the measuring voltage approaches this value, the operating volume flow and thus the negative pressure must consequently be increased until the voltage is again in an acceptable range.

the 8th shows another diagram of the volume flow V the operating pressure P. and the measured voltage U _Mess in the event that a transverse force acts on a suction pad 9 sucked workpiece is exercised. Such a transverse force can be exerted, for example, by pulling on the workpiece. In this case, the normal force suddenly decreases, which increases the resistance between the electrodes and consequently also the measurement voltage. _{This results in a deflection of the measurement} voltage U Mess, shown in the range from 4 to 6 * 10 ⁴ sampling points, which, as a result of the control device according to the invention, directly increases with a steeply increasing operating volume flow V and consequently a greater negative pressure is compensated. The increase in the operating volume flow and the operating pressure exists as long as the transverse force is exerted on the workpiece. As the 8th clearly shows, the control device returns to its original control goal of minimal air consumption as soon as transverse force is no longer exerted on the workpiece (cf. range between 7 and 9 * 10 ⁴ scanning points).

In order to be able to actively regulate the air consumption by the regulating device according to the invention, knowledge of the parameter relationships described above is required. A controller can then be designed from this. The regulation depends on many influencing factors. In particular, the regulation is to be adapted to a corresponding workpiece to be gripped. This can be, for example, a semi-finished product, such as a fabric or scrim, which preferably consists of an air-permeable and conductive material such as carbon fiber. Other parameters relate to the type of weave of the semi-finished product, a handicap, the design of the electrodes, the yarn count, the operating pressure and the normal force. Because the regulation of the air consumption presented here requires the workpiece to be air permeable, the present invention is particularly suitable for workpieces that are permeable to air.

The suction gripper according to the invention and the corresponding control device can advantageously also be used for a suction gripper system which has a plurality of individual suction grippers according to the invention. It goes without saying that a control device according to the invention can also be used in a suction gripper system in such a way that the total _{air consumption can be controlled as a function of the measured voltage U Mess in} such a way that a minimum air consumption can be set.

In addition, a defined normal or transverse force between the suction surface and the semi-finished product can be set through the interaction of the control device with the electrodes. This is necessary, for example, when draping semi-finished products, since here the semi-finished products have to slide off the suction surface of the gripper with defined normal and transverse forces during the forming process, but should nevertheless be held securely.

Overall, the present invention creates an advantageous suction gripper which, with the aid of at least two electrodes that can be connected to a voltage measuring device, can work much more reliably and energy-efficiently. In particular, the invention makes it possible to determine whether a workpiece has been safely sucked in by the suction gripper and is being held by it. It is also possible to determine how many workpieces are being held by the suction gripper. In addition, a control device is able to regulate the volume flow and the operating pressure of the suction gripper based on the measured values in such a way that a minimum average air consumption can be set.

List of reference symbols

1

first surface

3

second face

5

Voltage measuring device

7th

Power source

9, 9 '

Suction cups

11

Suction surface

13th

Suction openings

15, 15 '

first electrode

17, 17 '

second electrode

19, 19 '

Isolation area

21

Contact surface of the first electrode

22nd

Resistance workpiece

23

Second electrode contact surface

25th

average air consumption

P.

operating pressure

V

Volume flow

UMess

Measuring voltage

Claims (21)

Suction grippers (9, 9 ') for sucking and holding workpieces, in particular pliable, air-permeable semi-finished products, comprising a housing with at least one air inlet and at least one air outlet and a plurality of suction openings (13) in a suction surface (11) for sucking in at least one workpiece , characterized in that the suction surface (11) has at least two electrodes (15, 17; 15 ', 17') connected to a voltage measuring device (5) on its side facing the workpiece to be sucked on. Suction cup after Claim 1 , characterized in that the at least two electrodes (15, 17; 15 ', 17') are arranged on the suction surface (11) or are formed integrally therewith. Suction cup after Claim 1 or 2 , characterized in that the at least two electrodes (15, 17; 15 ', 17') each have at least one electrical connection for connection to the voltage measuring device. Suction gripper according to one of the preceding claims, characterized in that the suction surface (11) is at least partially made of an electrically insulating material. Suction gripper according to one of the preceding claims, characterized in that the suction surface (11) for generating the at least two electrodes (15, 17; 15 ', 17') is coated at least in some areas with a conductive material. Suction gripper according to one of the preceding claims, characterized in that the at least two electrodes (15, 17; 15 ', 17') are electrically isolated from one another, in particular by the suction surface (11). Suction gripper according to one of the preceding claims, characterized in that an electrically conductive intermediate layer, in particular a carbon fiber fabric, is arranged on the side of the at least two electrodes (15, 17; 15 ', 17') facing the workpiece to be sucked on. Suction cup after Claim 7 , characterized in that the electrically conductive intermediate layer has openings which are aligned with the suction openings (13) of the suction surface (11). Suction gripper according to one of the preceding claims, characterized in that a first punctiform electrode (15 ') is arranged centrally with respect to the suction surface (11), which is surrounded by a second annular electrode (17). Suction gripper according to one of the preceding claims, characterized in that a first and a second electrode are ring-shaped and are arranged concentrically to one another. Suction gripper according to one of the preceding claims, characterized in that a first circular electrode (15) of one second annular electrode (17) is surrounded concentrically. Suction gripper according to one of the preceding claims, characterized in that the at least two electrodes (15, 17; 15 ', 17') cover or form a predominant part of the suction surface (11). Suction gripper according to one of the preceding claims, characterized in that the at least two electrodes (15, 17; 15 ', 17') are arranged in the areas between the suction openings (13). Suction gripper according to one of the preceding claims, characterized in that it works according to the Bernoulli, Coanda, Vortex, jet nozzle or Venturi principle. Suction gripper according to one of the preceding claims, characterized in that it is designed to suck in a porous workpiece that is sucked through, in particular an air-permeable fabric or scrim made of glass, aramid or carbon fibers. Suction gripper according to one of the preceding claims, characterized in that it is operated by compressed air or propeller and has an integrated negative pressure generating device. Suction gripper system, comprising several suction grippers (9, 9 ') according to one of the Claims 1 until 16 . Control device for controlling one or more suction grippers (9, 9 ') according to one of the Claims 1 until 16 . Control device according to Claim 18 , characterized in that it is integrated into a suction gripper (9, 9 '). Control device according to Claim 18 or 19th , characterized in that it comprises a microprocessor. Control device according to one of the preceding Claims 18 until 20th , characterized in that the regulating device regulates the operating pressure (P) and / or the operating volume flow (V) of the suction gripper (9, 9 ') as a function of a measured voltage drop between the at least two electrodes.

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