DE102023134831A1 - Gripping element for use in robotics and cobotics - Google Patents

Abstract

The invention relates to a gripping element for use in robotics and cobotics, wherein the gripping element (5a, 5b) is at least partially designed as a multiple bending beam (9, 19), thus enabling essentially parallel gripping and, in particular, direct measurement of the gripping force, as well as fiber reinforcement. Furthermore, the invention relates to a method for producing such a gripping element.

Description

The invention relates to a gripping element for use in robotics and cobotics (collaborative robotics) and a method for producing such a gripping element.

In robotics and cobotics, gripping elements are already used to safely grasp, hold and move objects.

Depending on the object, it may be necessary to use sensitive gripper jaws with sensors manufactured using 3D printing (additive). Such sensors consist of a non-conductive and a conductive material. Plastics are usually used as the non-conductive material. Plastics mixed with carbon or graphite, or silver inks, are used as the conductive material (see, for example, WO2020/041221 A1 , DE102019102913 A1 , JP2020128083 A and US 2016/0198576 A1 ).

Disadvantages of these additively manufactured sensors include their low strength, low stiffness, and their viscoelastic properties. Viscoelasticity is a time-dependent expansion of the material under sudden load. This distorts the sensor's measured value at the beginning of the gripping process, as the final expansion, and thus the force, only develops over time. Furthermore, plastics exhibit high thermal expansion (for example, a factor of 10 compared to metals).

The present invention is therefore based on the object of creating a gripping element and a manufacturing method for such a gripping element which reduces the aforementioned disadvantages, at best avoids them and enables an exact force measurement during gripping and prevents damage to the objects to be gripped.

This object is achieved according to the invention by a gripping element having the features of claim 1 and a manufacturing method for such a gripping element having the features of claim 6.

According to the invention, a sensitive gripping element, in particular a gripping jaw made of plastic, can be manufactured additively, i.e. by means of 3D printing, which has improved mechanical and electrical properties (strength, stiffness, linearity and viscoelastic behavior).

For this purpose, the gripping element is at least partially designed as a multiple bending beam, for example as a double, preferably as a quadruple, five-fold, six-fold, seven-fold or multiple bending beam, so that a substantially parallel gripping is possible, wherein the gripping element deforms during gripping substantially parallel to the starting position, so that only a small angle of inclination arises during this deflection (deformation), i.e. for example a few degrees, preferably a fraction of a degree, in particular less than 0.15°, most preferably less than 0.05°.

This advantageously avoids significant bending of the gripping element during gripping, thus ensuring a more precise measurement.

According to the invention, the force application point at which the component is gripped is uncritical for parallel gripping. However, for non-parallel gripping, the lever length is also crucial.

In a preferred embodiment of the invention, the multiple bending beam preferably consists of at least two, three, four, five, six, or seven, in particular identically designed, individual beams that are thin in relation to their length (e.g., several centimeters), for example, a few millimeters or even only one millimeter thick. The thickness-to-length ratio is advantageously at most 1:5, preferably at most 1:10, in particular at most 1:15.

This advantageously makes it possible to increase the stability of the gripping element, in particular of the plastic finger, while simultaneously optimizing the parallelism of the gripping action. Even when using plastic as the carrier material for a gripping element, sufficient stability of the gripping element can be ensured without compromising the measurement accuracy of the force measurement of, for example, several Newtons, preferably at least 10 Newtons, in particular at least 40 Newtons.

In a further embodiment of the invention, several strain gauges, preferably made of resistance wire, in particular constantan wire, are embedded in each bending beam of the multiple bending beam, resulting in mechanical reinforcement (fiber reinforcement) of the gripping element. By embedding a 3D-printed force sensor in the form of at least one strain gauge, the force acting on the gripping jaw or causing the deformation (bending of the bending beam) can be measured (direct measurement of the gripping force on the component to be gripped or gripped, as well as improvement of the linearity and viscoelastic properties). In addition, the embedding of at least one strain gauge in preferably each individual bar or beam of a multiple bending beam enables not only force measurement but also mechanical reinforcement of the component.

It is therefore also conceivable to use strain gauges not as force sensors, but solely for the purpose of reinforcing the multiple bending beam. In this case, the strain gauges can also be used passively, purely for mechanical reinforcement without electrical evaluation.

According to the manufacturing method according to the invention, the gripping element is manufactured by means of additive manufacturing, in particular by means of 3D printing.

In a particularly preferred embodiment of the invention, the gripping element is manufactured as a one-piece component using additive manufacturing. This simplifies the manufacturing process and reduces costs.

In a further embodiment of the invention, several strain gauges are embedded in each bending beam during the layer-by-layer additive manufacturing of the gripping element, so that the gripping element is mechanically reinforced.

The strain gauges can preferably be embedded in a layer on the top and bottom of each bending beam during the layer-by-layer additive manufacturing of the gripping element, preferably with at least one protective layer overlying them. This advantageously further increases the stability of the gripping element.

In a particular embodiment of the invention, at least two strain gauges for compressive and tensile loads are located on the top and bottom sides (optionally provided with a protective layer), which are preferably arranged on the other side and on this side of a reversal point of the multiple bending beam.

In a further embodiment of the invention, the strain gauges themselves are not manufactured using 3D printing, but consist of a resistance wire, preferably a continuous wire, in particular a constantan wire. This wire, for example, drawn, rolled, etc., can be embedded into a layer, preferably a layer located far outward, in particular by ironing, i.e., heated and/or introduced with pressure. By using a continuous wire, preferably embedding it in the form of several meandering loops or windings (with straight sections in the direction of the elongated extension of the gripping element), the strength and rigidity are significantly increased.

In addition, instead of prefabricated, the strain gauge can be shaped in shape, size, and number of turns during insertion or embedding. This advantageously allows for individual adaptation to the size and shape of the gripping element and the desired strain gauge during additive manufacturing by embedding it into a newly created layer (using 3D printing).

The solution according to the invention enables individual adaptation of gripping jaws to the gripped objects as well as process monitoring and damage prevention by measuring gripping force directly on the component.

In addition, the solution according to the invention enables an improvement in linearity, viscoelastic behavior and service life compared to previously additively manufactured sensors based on plastic carriers.

Furthermore, the invention prevents warping of the gripper jaws during and after printing. Furthermore, cost-effective and easy recycling is ensured by simply separating the plastic and wire.

The inventive additive manufacturing based on plastic also enables a reduction in the price of sensitive gripper jaws.

Further advantageous embodiments arise from the dependent claims.

The invention is explained in more detail below with reference to embodiments of gripping elements according to the invention shown in the drawing.

• 1 eine perspektivische Ansicht einer Greifvorrichtung mit einem erfindungsgemäßen Greifelement;
• 2a eine Seitenansicht auf eine Greifelementstruktur in Form eines mehrfachen Biegebalkens;
• 2b eine Seitenansicht auf ein nicht zur Erfindung gehöriges Beispiel einer Greifelementstruktur in Form eines einfachen Biegebalkens;
• 3a eine Seitenansicht auf die Greifelementstruktur in Form des mehrfachen Biegebalkens nach 2a in ausgelenkter Position;
• 3b eine vergrößerte Ansicht eines Details aus 3a;
• 4 eine Seitenansicht auf die Greifelementstruktur in Form des mehrfachen Biegebalkens nach 1 in nicht ausgelenkter Position mit eingebetteten Dehnungsmessstreifen;
• 5a eine Schnittansicht entlang der Linie A-A in 4;
• 5b eine Schnittansicht entlang der Linie B-B in 4;
• 6 einen Schaltplan einer Messschaltung und
• 7 eine Schnittansicht entlang der Linie C-C in 5a mit einer schematischen Darstellung eines Schichtaufbaus des einzelnen Stabes eines Biegebalkens.

The drawing shows:

• 1 a perspective view of a gripping device with a gripping element according to the invention;
• 2a a side view of a gripping element structure in the form of a multiple bending beam;
• 2b a side view of an example not belonging to the invention of a gripping element structure in the form of a simple bending beam;
• 3a a side view of the gripping element structure in the form of the multiple bending beam according to 2a in deflected position;
• 3b an enlarged view of a detail from 3a ;
• 4 a side view of the gripping element structure in the form of the multiple bending beam according to 1 in undeflected position with embedded strain gauges;
• 5a a sectional view along the line AA in 4 ;
• 5b a sectional view along the line BB in 4 ;
• 6 a circuit diagram of a measuring circuit and
• 7 a sectional view along the line CC in 5a with a schematic representation of a layer structure of the individual bar of a bending beam.

The 1 The gripping device shown shows one of many ways in which the gripping elements according to the invention, for example in the form of gripping jaws, can be used and employed. In the example shown, two gripping elements in the form of inward-facing gripping jaws 5a and 5b that are complementary to one another or identical in design but rotated by 180° are provided. These gripping jaws 5a, 5b can be moved linearly via a drive arranged in a housing 3 (for example electrically, in particular by means of an activator in the form of a servomotor, stepper motor, etc., or pneumatically). As shown, an object, for example an egg 7, can be gripped by a correspondingly controlled movement towards one another, preferably without damaging the egg 7.

The movement is controlled by a control device not shown in the drawing, with which the applied contact pressure or the applied contact force can be regulated in the desired manner.

In order to exert the contact force as parallel as possible, the gripping elements are, as shown, at least partially designed as multiple bending beams (in the example as a sevenfold bending beam).

As shown by the example of a 2a As explained in the example of the gripping jaw shown in the form of a quadruple bending beam 9, a predominantly linear deformation or displacement of the gripping surface of the gripping jaw (parallel gripping) occurs when a force F is applied by a distance w, so that its gripping surface, despite deflection, continues to be essentially parallel to the original, in 2a remains in the non-deflected or non-deformed position shown by the dashed line. Accordingly, the angle of inclination α at this deflection (deformation) is minimal or amounts to a fraction of a degree, in particular less than 0.15°, preferably less than 0.05°.

In contrast, the angle of inclination β for a deflection of a simple, 2b The deflection of the bending beam shown (with similar or identical dimensions, in particular the same length and thickness) when a (same) force F is applied is significantly greater by a (preferably similar or identical) distance w, so that in the sense of the invention, it can no longer be referred to as a substantially parallel gripping. The contact surface of the gripping jaw in the form of a simple bending beam decreases during deflection instead of a - in 2b The original position, essentially parallel to the non-deflected or non-deformed position shown in dashed lines, assumes a significantly changed, oblique position.

Of course, it is also conceivable to arrange two or more gripping elements in a different shape. For example, the gripping jaws can be directed outward (particularly radially) to allow for a spread grip into a cavity and thus gripping with the outer surfaces instead of the inner surfaces.

How 3a and 3b As shown, in the case of parallel gripping, i.e. gripping with a minimal angle of inclination α, a deformation of individual bars 9a, 9b, 9c, 9d of the bending beam 9 occurs differently than in the case of a simple bending beam ( 2b) .

Each individual rod 9a, 9b, 9c, 9d has in the deflected position or in the deformed state of the gripping jaw 9, as in 3b shown, in relation to its outer side (or from the inner center to the outside) a tensile region σ _z , a compressive region σ _d and an intermediate linear reversal region U (without deformation).

The outer sides, i.e. top and bottom of a single bar, as in 3b illustrated using the fourth bar 9d, have correspondingly complementary regions. Thus, in the lower right-curved region of the bar 9d, the upper side (left in the drawing) is subjected to tension (tensile region σ _z ) during the deformation shown (movement to the right in the drawing), whereas the underside (right in the drawing) is subjected to compression (compression region σ _d ). In the upper left-curved region of the beam 9, however, the upper side (left in the drawing) is subjected to compression (compression region σ _d ), whereas the underside (right in the drawing) is subjected to tension (tensile region σ _z ). The oppositely curved regions (right- and left-curved) cancel each other out. so that the upper part of the gripping jaw 9 assumes a position parallel to the starting position.

The 4 The schematically illustrated side view of a sevenfold bending beam with seven bars 19a, 19b, 19c, 19d, 19e, 19f, 19g naturally also applies to other embodiments with a different number of bars.

The bars 19a, 19b, 19c, 19d, 19e, 19f, 19g have strain gauges or measuring grids embedded on the top and bottom. 5a the top and 5b the underside of the (third) bar 19c. For better understanding, the layers are 4 and 5a , 5b shown extending beyond the actual bars 19a, 19b, 19c, 19d, 19e, 19f, 19g.

The actual bars 19a, 19b, 19c, 19d, 19e, 19f, 19g—and not the (compression) layers extending beyond them—are preferably provided along their entire length on the top and bottom with two adjacent strain gauges 23 and 25, or 25 and 23, respectively, thus increasing the strength and stiffness of the bars. Even if the strain gauges extend across the reversal region, the respective tensile region σ _z and the respective compression region σ _d are always covered.

As shown, the strain gauges 23 and 25 have a meandering structure with long, linear regions extending in the longitudinal direction of the rod 19c and with a tight curvature, so that as many linear or straight wire regions as possible exist in order to be able to absorb the resulting compressive and tensile stresses when the rod 19c is deformed.

The strain gauges are inserted during the printing of the corresponding layer using a device not shown in the drawing, preferably unwound from a wire reel, in the desired number and shape of the lamellae, adapted to the length and width of the rod 19c. The wire, in particular constantan wire, can be heated to facilitate melting into the existing layer. Of course, it is also conceivable to insert prefabricated strain gauges during the manufacturing process, in particular during printing, to print non-prefabricated strain gauges, or to subsequently adhere prefabricated strain gauges.

The starting and end points of the strain gauges 23 and 25 are led outwards in the lower area of the rod 19c or the corresponding printed layer of the beam 19 as connections 23a, 23b and 25a, 25b.

All strain gauges 25 subjected to tensile stress (of the tensile ranges σ _z ) of all bars 19a, 19b, 19c, 19d, 19e, 19f, 19g are connected in series to form a resistance R _tensile . Likewise, all strain gauges 25 subjected to compressive stress (of the compressive ranges σ _d ) of all bars 19a, 19b, 19c, 19d, 19e, 19f, 19g are connected in series to form a resistance R _compression , so that the bridge resistance is increased, in particular multiplied by the number of bending beams, and the requirements for an evaluation unit not shown in the drawing are reduced.

By embedding several, preferably four, strain gauges per rod, the resistance change and thus the accuracy of the force measurement is increased considerably.

The measurement is carried out, for example, as in 6 shown, via a measuring bridge. When a voltage U ₀ is applied, the voltage U _m changes according to the partial voltage changed between resistance R _compression and resistance R _tension . Of course, it is also conceivable to use a full bridge as the measuring device instead of a half bridge, as shown, in which case, instead of fixed resistors R, resistance R _compression and resistance R _tension are used in the right branch of the measuring bridge in reverse to the left branch of the measuring bridge.

As in 7 As shown by way of example for other designs of multiple bending beams, a single bar 19c of a bending beam 19 has a structure consisting of several layers in the profile.

The rod 19c, which consists, for example, of eight (1-8) layers, has a wire 27 embedded in layer 2 on its underside and layer 7 on its upper side, preferably made of printed plastic. The wire 27, in particular constantan wire, can be heated to facilitate insertion (for example, by ironing). As shown, these layers are each surrounded by an outer layer (first and eighth layers). This outer layer (first and eighth) acts as a protective layer against external mechanical influences (damage, jumping out/loosening of the wire), as well as against moisture penetration and to prevent short circuits.

Of course, it is also conceivable to provide several, in particular two, outer layers as a protective layer instead of as shown, or even to dispense with the protective layer altogether.

List of reference symbols

1

gripping device

3

Housing with drive

5a

gripping jaw

5b

gripping jaw

7

egg

9

Gripping jaw in the form of a quadruple bending beam in deformed position

9a

first beam or bar of the quadruple bending beam 9

9b

second beam or bar of the quadruple bending beam 9

9c

third beam or bar of the quadruple bending beam 9

9d

fourth beam or bar of the quadruple bending beam 9

11

non-deformed position of gripping jaw 9

13

simple bending beam in deformed position

15

non-deformed position of 13

17

Bending beam area

19

Gripping jaw in the form of a sevenfold bending beam

19a

first beam or bar of the sevenfold bending beam 19

19b

second beam or bar of the sevenfold bending beam 19

19c

third beam or bar of the sevenfold bending beam 19

19d

fourth beam or bar of the sevenfold bending beam 19

19e

fifth beam or bar of the sevenfold bending beam 19

19f

sixth beam or bar of the sevenfold bending beam 19

19g

seventh beam or bar of the sevenfold bending beam 19

21a

front or distal part of the gripping jaw 19

21b

rear or proximal part of the gripping jaw 19

23

DMS

23a

left connection

23b

right connection

25

DMS

25a

left connection

25b

right connection

27

embedded wire

29

printed plastic

α

angle

β

angle

σz

Train area

σd

Print area

D

detail

F

Power

R

Resistance

RPrint

Bridge resistance of all strain gauges connected in series and subjected to compression

Train

Bridge resistance of all strain gauges connected in series and subjected to tensile stress

U

Reversal area

U0

fixed voltage

To

Measuring voltage

W

Path/distance of bending/deflection

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2020/041221 A1 [0003]
• DE 102019102913 A1 [0003]
• JP 2020128083 A [0003]
• US 2016/0198576 A1 [0003]

Claims (12)

Gripping element for use in robotics and cobotics, characterized in that the gripping element (5a, 5b) is at least partially designed as a multiple bending beam (9, 19), so that essentially parallel gripping is possible. Gripping element according to Claim 1 , characterized in that the multiple bending beam (9, 19) consists of individual beams (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g) which are thin compared to their elongated extent. Gripping element according to Claim 1 or 2 , characterized in that the multiple bending beam (9, 19) consists of at least three individual beams (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g). Gripping element according to one of the preceding claims, characterized in that a plurality of strain gauges (23, 25) are embedded in each beam (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g) of the multiple bending beam (9, 19), so that this results in a mechanical reinforcement of the gripping element (5a, 5b). Gripping element according to Claim 4 , characterized in that the strain gauges (23, 25) consist of resistance wire, in particular constantan wire. Method for producing a gripping element according to one of the preceding claims by means of additive printing/3D printing, characterized in that the gripping element (5a, 5b) is at least partially designed as a multiple bending beam (9, 19), so that a substantially parallel gripping is made possible. Procedure according to Claim 6 , characterized in that the multiple bending beam (9, 19) is made of individual beams (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g) which are thin compared to their elongated extent. Procedure according to Claim 6 or 7 , characterized in that the multiple bending beam (9, 19) is formed from at least three individual bending beams (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g). Method according to one of the Claims 6 until 8 , characterized in that the gripping element (5a, 5b) is manufactured by additive manufacturing in the form of a one-piece component. Method according to one of the Claims 6 until 9 , characterized in that during the layer-by-layer additive manufacturing of the gripping element (5a, 5b) a plurality of strain gauges (23, 25) are embedded in each beam (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g), so that a mechanical reinforcement of the gripping element (5a, 5b) takes place. Procedure according to Claim 10 , characterized in that during the layer-by-layer additive manufacturing of the gripping element (5a, 5b), strain gauges (23, 25) are embedded on the top and bottom of each beam (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g), preferably with at least one protective layer lying thereover. Procedure according to Claim 10 or 11 , characterized in that the strain gauges (23, 25) are made of a resistance wire, preferably endless wire, in particular constantan wire.

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