Area suction grippers for suction and handling of objects with pressure sensors

Abstract

A surface suction gripper (10) for sucking up and handling objects (16), comprising a base module (12) in which a vacuum chamber (14) to which negative pressure can be applied is provided, wherein the base module (12) has suction openings (18) on a suction side (20), wherein an elastically compressible structure (22) having through-openings (26) corresponding to the suction openings (18) and having a contact surface (30) for contacting the object (16) to be sucked is assigned to the suction side (20), wherein during operation of the surface suction gripper (10), the structure (22) or a partial section of the structure (22) in which no objects (16) are held by suction on the contact surface (30) assumes a neutral state, and wherein during operation, the structure (22) or a partial section of the structure in which objects (16) are held by suction on the contact surface (30) assumes a compressed state, characterized in thatthat pressure sensors (32) are provided between the base module (12) and the structure (22) or in the structure (22), which pressure sensors are configured such that, in the compressed state, they generate sensor signals that represent the pressure forces acting on the structure (22), wherein the structure (22) is arranged on the suction side (20), wherein the pressure sensors (32) are provided in or on a pressure sensor mat (34) or pressure sensor film or are formed by such a pressure sensor mat (34).

Description

The invention relates to a surface suction gripper for sucking in and handling objects, having a basic module in which a negative pressure chamber to which negative pressure can be applied is provided, wherein the basic module has suction openings on a suction side, wherein the suction side is assigned an elastically compressible structure having through openings corresponding to the suction openings and having an abutment surface for abutment of the object to be sucked in, wherein, during operation, the structure or a subsection of the structure in which no objects are held sucked in on the abutment surface assume a neutral state, and wherein, during operation, the structure or a subsection of the structure in which objects are held sucked in on the abutment surface assume a compressed state.Such surface suction grippers serve in particular for the positional gripping and lifting of articles which have irregular and complex surfaces, in particular positionally stable flat materials, such as, for example, boards or plates, or of smaller articles, such as, for example, cans, cups, trays or the like. The surface suction gripper has a flexible structure, in particular a covering, which is usually placed on the upper side of the objects to be gripped. A structure made of foam or sealing foam has proven to be advantageous, since it fits well against the surface, which is sometimes uneven.DE 10 2006 050 970 A1 discloses surface suction grippers in which the structure in the form of a foam covering is provided with a cover layer which has suction openings whose flow cross section is exactly matched to the objects to be gripped.Similar surface suction grippers with a foam-like structure are known from DE 10 2013 201 249 B4.EP 3 153 282 A1 discloses surface suction grippers with an electrically conductive plate as a contact surface, wherein the capacitance of the plate with respect to the basic module is measured. An elastically compressible structure is not provided. Such a surface suction gripper can be used in particular to grip objects, such as metal sheets, which have a uniform metallic surface. Articles having an irregular or complex surface are difficult or impossible to handle. In addition, the electric field is easily influenced by the machine environment, which leads to incorrect results.DE 20 2017 101 333 U1 discloses surface suction grippers in which a flow sensor in the form of a flow meter is provided in each flow opening. The arrangement and maintenance of the flow meters is comparatively complicated.DE 10 2010 034 720 A1 discloses a surface gripper for the targeted picking up, handling and depositing of objects.EP 3 626 412 A1 discloses a suction gripper and a method for monitoring the functioning of a suction gripper.The object of the present invention is to provide a surface suction gripper with which the gripping process is carried out in a functionally reliable manner and can be monitored.This object is achieved by a surface suction gripper having the features of claim 1. Consequently, it is provided in particular that pressure sensors are provided between the base module and the structure or in the structure, which pressure sensors are configured such that they generate sensor signals in the compressed state, which sensor signals represent the pressure forces acting on the structure.The sensor signals can be analog or digital signals and represent the pressure force acting on the structure at the respective location of the structure. The pressure force acting on the structure at the respective location preferably corresponds linearly to the holding force with which the suctioned object is held. The higher the holding force, the higher the compressive force acting on the structure. If a high compressive force is consequently detected, a high holding force can be deduced therefrom. If only a low pressure force is detected on the basis of the sensor signals representing the pressure, the holding force is correspondingly lower.Overall, this makes it possible to draw conclusions as to the respectively present holding force, as a result of which the gripping process can be carried out in a functionally reliable manner and can be monitored reliably.Advantageously, a plurality of pressure sensors is provided, which are arranged distributed in a plane, in particular at uniform distances from one another. In this case, the plane preferably runs parallel to the suction surface. Depending on the desired local resolution of the pressure forces, and thus a pressure profile acting on the structure, a different number of pressure sensors can be used. If a comparatively high local resolution is to be provided, a comparatively large number of sensors are to be provided; if a comparatively low local resolution is sufficient, a smaller number of sensors may be sufficient.According to the invention, the pressure sensors are provided in or on a pressure sensor mat or pressure sensor foil or are formed by such a mat. It is conceivable for a mat or film to be provided on or in the structure which provides perforations in the region of the suction openings. It is also conceivable that several mats or foils are used in the areas between the suction openings.The pressure sensors of the pressure sensor mat or pressure sensor foil can be formed in particular by threads provided in textiles with sensory properties. Such threads with sensory properties are known, for example, from WO 2007 / 059 971 A2.A preferred embodiment of the invention provides that an evaluation unit evaluating the sensor signals is provided, which is configured to determine one or more variables from the sensor signals. These variables include, in particular, a 2- or 3-dimensional pressure profile of the compressive forces acting on the structure. Such a profile can have a base surface extending parallel to the contact surface, in the X and Y directions, and a Z direction running perpendicular thereto, in which the height of the respective compressive forces is reproduced. From such a pressure profile it can be derived at which locations or partial sections of the structure which holding force is applied and whether in particular a sufficient holding force is provided. It can also be established which partial sections of the suction surface grip an object and which do not grip an object. In addition, the occupancy level of the contact surface can be determined, in particular also whether all objects to be gripped are actually gripped. It is also conceivable to determine the compression depth of the structure when the objects are being suctioned in. This can be effected in particular in that, with a known force / travel, the ratio (error rate) of the structure can be deduced from the measured pressure forces on the compression path. If the compression depth is very low, it is conceivable that the object is not sucked in as intended. It is furthermore advantageous if the change in the compression depth or the compression state is determined during handling. The compression state may change in particular due to weight forces or inertial forces during the movement of the surface suction gripper. If the compression state falls below a critical threshold value during the gripping process and the handling, then detachment of the object from the contact surface cannot be ruled out. The evaluation unit can then take appropriate countermeasures, for example increase the suction pressure, deposit the gripped objects or initiate appropriate measures accordingly. In addition, the evaluation unit can determine the number of compression states at a predefined point in time. It is conceivable that the aging or wear of the structure is deduced via the number of compression states, so that the structure can be replaced in good time.It is furthermore advantageous if the evaluation unit is configured and provided to output signals and / or take measures depending on at least one of the plurality of variables. Such measures can be, for example, an increase in the negative pressure, a decrease in the negative pressure, an acceleration of the flat suction gripper, a deceleration of the flat suction gripper or an emergency operation of the flat suction gripper.The evaluation unit can be provided in or on the flat suction gripper. However, it is also conceivable for the evaluation unit to be provided externally and in particular to be coupled to a superordinate machine controller.It is particularly advantageous if the evaluation unit is provided in such a way and is configured to actuate a vacuum generator for generating the vacuum in the vacuum chamber as a function of the sensor signals. If low pressure forces acting on the structure are detected, the vacuum generator can be activated in particular to generate a higher vacuum. If comparatively high pressure forces are detected on the structure and thus a comparatively high holding force, the vacuum generator can be actuated, for example, in such a way that a lower, but still sufficient vacuum is generated.An advantageous embodiment of the invention provides that the structure is formed by foam, in particular foam or technical sealing foam. It is conceivable that the foam is formed from a plurality of layers, in particular running parallel to the suction side. In such an embodiment, the pressure sensors may be disposed between the layers. In particular, it is also conceivable for a pressure sensor mat or pressure sensor films to be provided between the layers. As a result, the pressure sensors are protected from disruptive environmental influences.In another embodiment of the invention, it is provided that the structure is formed by a matrix of bellows or flat suckers. Such bellows or flat suckers have an elastic, flexible suction cup and therefore a compressible suction cup.The object mentioned at the beginning is also achieved by a method for operating a surface suction gripper according to the invention, wherein the negative pressure in the negative pressure chamber is provided as a function of the sensor signals which represent the pressure forces acting on the structure. As a result, a regulation of the negative pressure in the negative pressure chamber, which is dependent in particular on pressure forces acting on the structure, can be provided.It is conceivable that the provision of the negative pressure is such that a minimum negative pressure that is just still permissible is provided in the compressed state. Overall, this makes it possible to achieve a comparatively energy-saving operation of the surface suction gripper.It is furthermore conceivable that the provision of the negative pressure is such that a maximum permissible negative pressure is provided in the compressed state. As a result, a maximum holding force can be achieved, whereby maximum accelerations of the gripped object become possible. Overall, this allows time-optimized handling to be achieved.The provision of the negative pressure is such that the negative pressure can be constant or can vary during the handling of the object, in particular depending on the spatial orientation and / or the acceleration of the object.Further details and advantageous embodiments of the invention can be found in the following description, on the basis of which an exemplary embodiment is described in more detail.FIG. 1 shows a schematic structure of a surface suction gripper 10 which has a basic module 12 in which a vacuum chamber 14 to which vacuum can be applied is provided. In the basic module 12 a corresponding valve technology can be accommodated (not shown in the figures), with which suction openings 18 on a suction side 20 of the basic module 12 can be opened or closed. On the suction side 20, an elastically compressible structure 22 is provided, which is formed in particular from a foam 24, in particular from a technical sealing foam. The structure 22 can also be formed from a matrix of bellows or flat suckers.As is clear from FIG. 1, the structure 22 has through-openings 26 which correspond to the suction openings 18. A valve foil can also be arranged between the suction side 20 and the structure 22.For the suction and handling of objects 16, the structure 22, or its contact surface 30, is brought into contact with the object 16 to be gripped. Due to the negative pressure (indicated by arrows) which is present in the through openings 26 and is generated by a negative pressure generator 28, the object 16 is attracted in the direction of the basic module 12 and the elastically compressible structure 22 is brought from a neural state into a compression state in the subsection in which the object 16 bears against the contact surface 30.Pressure sensors 32 are provided between the basic module 12 and the structure 22, which are configured such that, in the compressed state, they generate sensor signals which represent the pressure forces acting on the structure 22. The pressure sensors 32 are distributed at uniform intervals in a plane E running parallel to the suction side 20. The pressure sensors 32 are furthermore provided in or on at least one pressure sensor mat 34 or pressure sensor foil which has apertures in the regions of the suction openings 18 or of the passage openings 26.As is clear from FIG. 1, an evaluation unit 38 is provided on or in the base body 12 and evaluates the sensor signals generated by the pressure sensors 32. The evaluation unit 38 is connected via a line 40 to the pressure sensor mat 34, and thus to the pressure sensors 32.The evaluation unit 38 is configured such that it can determine which subsection the structure 22 assumes a compressed state on the basis of the sensor signals or the compressive forces applied to the structure 22, and can deduce therefrom whether or that the component 16 is gripped there. The evaluation unit 38 can also determine the level of the gripping force from the applied pressure forces. It is conceivable that the evaluation unit 38 generates a pressure profile which displays the pressure forces in the Z direction above the contact surface 30, which extends in the X direction and the Y direction. In the regions in which objects 16 are gripped, correspondingly large holding forces are present, the pressure profile in the Z direction shows correspondingly high values.Advantageously, the printing profile can be output on an output unit, such as a monitor, so that the operator is presented with an optical image about the gripping state of the surface suction gripper 10.The evaluation unit 38 can also determine the total occupancy level of the contact surface 30. It is also conceivable for the evaluation unit 38 to determine a change in the compressive forces, and thus in the compression state, during the handling of the articles 40. The number of pressure changes in a provided period of time or a change in the compression behavior upon aging or closing of the structure can also be determined.Furthermore, it is provided that the evaluation unit 38 evaluating the sensor signals is also configured to actuate the vacuum generator 28 as a function of the sensor signals, so that a sufficiently high vacuum, and thus a sufficiently high gripping force, is always available. This can be done in such a way that in the compressed state a minimum vacuum which is just still permissible is provided in order to enable energy-saving gripping. It is also conceivable that a maximum permissible negative pressure is provided, and a secure gripping can be achieved even at maximum accelerations and speeds of the object 16.

Claims

A surface suction gripper (10) for sucking in and handling objects (16), comprising a base module (12) in which a negative pressure chamber (14) to which negative pressure can be applied is provided, wherein the base module (12) has suction openings (18) on a suction side (20), wherein the suction side (20) is assigned an elastically compressible structure (22) having through openings (26) corresponding to the suction openings (18) and having an abutment surface (30) for abutment of the object (16) to be sucked in, wherein during operation of the surface suction gripper (10) the structure (22) or a subsection of the structure (22) in which no objects (16) are held sucked in on the abutment surface (30) assume a neutral state, and wherein during operation the structure (22) or a subsection of the structure in which objects (16) are held sucked in on the abutment surface (30), A compressed state, characterized in that pressure sensors (32) are provided between the basic module (12) and the structure (22) or in the structure (22), which pressure sensors are configured in such a way that they generate sensor signals in the compressed state, which sensor signals represent the pressure forces acting on the structure (22), wherein the structure (22) is arranged on the suction side (20), wherein the pressure sensors (32) are provided in or on a pressure sensor mat (34) or pressure sensor foil or are formed by such a mat.Surface suction gripper (10) according to Claim 1, characterized in that the pressure sensors (32) are arranged distributed at uniform distances in a plane E.Surface suction gripper (10) according to one of the preceding claims, characterized in that the pressure sensors (32) are formed by threads provided in textiles with sensory properties.Surface suction gripper (10) according to one of the preceding claims, characterized in that an evaluation unit (38) is provided which evaluates the sensor signals and is designed to determine one or more of the following variables from the sensor signals: - an in particular 2- or 3-dimensional pressure profile of the pressure forces acting on the structure (22); - the subsection of the structure (22) which assumes the compression state and / or does not assume the compression state; - the degree of occupancy of the contact surface (30); - the compression depth when objects (16) are being sucked in, - the change of the compression state during the handling of the objects (16), - the number of compression states in a provided period of time, and / or - the changes of the compression behavior for the same process sequence over a plurality of process cycles.Surface suction gripper (10) according to Claim 4, characterized in that an evaluation unit (38) which evaluates the sensor signals is provided and is configured to output signals and / or take measures as a function of at least one of the plurality of variables.Surface suction gripper (10) according to one of the preceding claims, characterized in that an evaluation unit (38) evaluating the sensor signals is provided, which is configured to actuate a vacuum generator (28) for generating the vacuum in the vacuum chamber (14) as a function of the sensor signals.Surface suction gripper (10) according to one of the preceding claims, characterized in that the structure (22) is formed by foam (24), in particular by sealing foam.The surface suction gripper (10) according to any one of claims 1 to 6, characterized in that the structure (22) is formed by a matrix of bellows or flat suction devices.Method for operating a surface suction gripper (10) according to one of the preceding claims, wherein the negative pressure is provided in the negative pressure chamber (14) as a function of the sensor signals which represent the pressure forces acting on the structure (22).Method according to Claim 9, characterized in that the provision of the negative pressure is such that a minimum negative pressure which is just still permissible is provided in the compressed state.Method according to Claim 9, characterized in that the provision of the negative pressure is such that a maximum permissible negative pressure is provided in the compressed state.Method according to one of Claims 9 to 11, characterized in that signals are output and / or measures are taken as a function of the sensor signals which represent the compressive forces acting on the structure (22).

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