Gripper element for use in robotics and cobotics

Abstract

The invention relates to a gripper element for use in robotics and cobotics, the gripper element (5a, 5b) being at least partly in the form of a multi-bending beam (9, 19) so that an essentially parallel gripping and in particular direct measuring of the gripping force and a fiber reinforcement is made possible. The invention also relates to a method of producing such a gripper element.

Description

[0001] Gripping element for use in robotics and cobotics

[0002] The invention relates to a gripping element for use in robotics and cobotics (collaborative robotics) and a method for producing such a gripping element.

[0003] In robotics and cobotics, gripping elements are already used to safely grasp, hold and move objects.

[0004] Depending on the object, it may be necessary to use sensitive gripper jaws with sensors manufactured using 3D printing (additive manufacturing). Such sensors consist of a non-conductive and a conductive material. Plastics are typically used as the non-conductive material. Plastics mixed with carbon or graphite, or silver inks, are used as the conductive material (see, for example, W02020 / 041221 A1, DE102019102913 A1, JP2020128083 A, and US 2016 / 0198576 A1).

[0005] 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).

[0006] The present invention is therefore based on the object of creating a gripping element and a manufacturing method for such a gripping element that reduces, ideally avoids, the aforementioned disadvantages and enables precise force measurement during gripping, as well as preventing 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.

[0007] 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, rigidity, linearity and viscoelastic behavior).

[0008] 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, fivefold, sixfold, sevenfold 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), ie for example a few degrees, preferably a fraction of a degree, in particular less than 0.15°, most preferably less than 0.05°.

[0009] This advantageously avoids any significant bending of the gripping element during gripping, thus ensuring a more precise measurement.

[0010] 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.

[0011] 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 just 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 a carrier material for a gripping element, sufficient stability of the gripping element can be ensured without impairing the measuring accuracy of the force measurement of, for example, several Newtons, preferably at least 10 Newtons, in particular at least 40 Newtons.

[0012] 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 improving linearity and viscoelastic properties). Furthermore, embedding at least one strain gauge, preferably in each individual rod or beam of a multiple bending beam, enables not only force measurement but also mechanical reinforcement of the component.

[0013] 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 for purely mechanical reinforcement without electrical evaluation.

[0014] According to the manufacturing method according to the invention, the gripping element is manufactured by means of an additive manufacturing process, in particular by means of 3D printing.

[0015] 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 saves 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, thereby mechanically reinforcing the gripping element.

[0016] The strain gauges can preferably be embedded in a layer on the top and bottom of each bending beam during 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.

[0017] 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.

[0018] In a further embodiment of the invention, the strain gauges themselves are not manufactured by 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.

[0019] In addition, the strain gauge can be formed into its shape, size, and number of turns during insertion or embedding, rather than prefabricated. 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 in a newly created layer (using 3D printing). The inventive solution enables individual adaptation of gripper jaws to the gripped objects, as well as process monitoring and damage prevention through gripping force measurement directly on the component.

[0020] 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.

[0021] Furthermore, the invention prevents warping of the gripper jaws during and after printing. Furthermore, it ensures cost-effective and easy recycling by simply separating the plastic and wire.

[0022] The inventive additive manufacturing based on plastics also enables a reduction in the price of sensitive gripper jaws.

[0023] Further advantageous embodiments arise from the dependent claims.

[0024] The invention is explained in more detail below with reference to embodiments of gripping elements according to the invention shown in the drawing.

[0025] The drawing shows:

[0026] Fig. 1 is a perspective view of a gripping device with a gripping element according to the invention;

[0027] Fig. 2a is a side view of a gripping element structure in the form of a multiple bending beam;

[0028] Fig. 2b is a side view of an example of a gripping element structure in the form of a simple bending beam, not belonging to the invention;

[0029] Fig. 3a is a side view of the gripping element structure in the form of the multiple bending beam according to Fig. 2a in the deflected position; Fig. 3b is an enlarged view of a detail from Fig. 3a;

[0030] Fig. 4 is a side view of the gripping element structure in the form of the multiple bending beam according to Fig. 1 in the non-deflected position with embedded strain gauges;

[0031] Fig. 5a is a sectional view along the line AA in Fig. 4;

[0032] Fig. 5b is a sectional view along the line BB in Fig. 4;

[0033] Fig. 6 a circuit diagram of a measuring circuit and

[0034] Fig. 7 is a sectional view along the line CC in Fig. 5a with a schematic representation of a layer structure of the individual bar of a bending beam.

[0035] The gripping device shown in Fig. 1 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 are provided which are complementary to one another or identical in design but rotated by 180°. 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 an appropriately controlled movement towards one another, preferably without damaging the egg 7.

[0036] The movement is controlled by a control device (not shown in the drawing), which can be used to adjust the applied contact pressure or force to the desired level. To ensure that the contact pressure is applied as parallel as possible, the gripping elements, as shown, are at least partially designed as multiple bending beams (in the example, as a sevenfold bending beam).

[0037] As explained using the example of a gripping jaw in the form of a quadruple bending beam 9 shown in Fig. 2a, 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, remains essentially parallel to the original, undeflected or undeflected position shown in dashed lines in Fig. 2a. Accordingly, the angle of inclination a during this deflection (deformation) is minimal or amounts to a fraction of a degree, in particular less than 0.15°, preferably less than 0.05°.

[0038] In contrast, the angle of inclination ß is significantly greater when a simple bending beam shown in Fig. 2b (with similar or identical dimensions, in particular the same length and thickness) is deflected by a (preferably similar or identical) distance w when a (same) force F is applied, so that essentially parallel gripping can no longer be spoken of within the meaning of the invention. Upon deflection, the engagement surface of the gripping jaw in the form of a simple bending beam assumes a significantly changed, oblique position instead of an essentially parallel position to the original position - shown in dashed lines in Fig. 2b - which is not deflected or deformed.

[0039] 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.

[0040] As shown in Fig. 3a and Fig. 3b, in the case of parallel gripping, i.e. gripping with at most a minimal angle of inclination a, 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 (Fig. 2b).

[0041] Each individual rod 9a, 9b, 9c, 9d has, in the deflected position or in the deformed state of the gripping jaw 9, as shown in Fig. 3b, in relation to its outer side (or viewed from the inner center outwards), a tensile area o z , a pressure region Od and an intermediate linear reversal region U (without deformation).

[0042] The outer sides, i.e., the top and bottom sides of a single bar, as shown in Fig. 3b using the fourth bar 9d, have correspondingly complementary regions. Thus, in the lower right-curved region of bar 9d, the top side (on the left in the drawing) is subjected to tension (tension region o) during the deformation shown (movement to the right in the drawing). z ), whereas the underside (on the right in the drawing) is subjected to compression (compression area Od). In the upper left-curved area of ​​beam 9, however, the upper side (on the left in the drawing) is subjected to compression (compression area Od), whereas the underside (on the right in the drawing) is subjected to tension (tension area o z ). The oppositely curved areas (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.

[0043] The side view of a sevenfold bending beam with seven bars 19a, 19b, 19c, 19d, 19e, 19f, 19g shown schematically in Fig. 4 naturally also applies to other embodiments with a different number of bars.

[0044] The bars 19a, 19b, 19c, 19d, 19e, 19f, and 19g have strain gauges or measuring grids embedded on their top and bottom surfaces. Thus, Fig. 5a shows the top side and Fig. 5b the bottom side of the (third) bar 19c. For clarity, the layers in Fig. 4 and Fig. 5a and Fig. 5b are shown extending beyond the actual bars 19a, 19b, 19c, 19d, 19e, 19f, and 19g.

[0045] 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, so that the strength and stiffness of the bars are increased. Even if the strain gauges extend over the reversal area, the respective tensile area is always measured. z and the respective pressure range Od is also 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.

[0046] 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 the printing process, to print non-prefabricated strain gauges, or to subsequently adhere prefabricated strain gauges.

[0047] 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.

[0048] All strain gauges 25 subjected to tensile stress (of the tensile areas o z ) of all bars 19a, 19b, 19c, 19d, 19e, 19f, 19g are connected in series to a resistor Rz ug connected to each other. Likewise, all strain gauges 25 subjected to compression (of the compression ranges Od) of all bars 19a, 19b, 19c, 19d, 19e, 19f, 19g are connected in series to form a resistance Roruck, 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.

[0049] By embedding several, preferably four, strain gauges per rod, the resistance change and thus the accuracy of the force measurement is increased considerably.

[0050] The measurement is carried out, for example, via a measuring bridge, as shown in Fig. 6. When the voltage Uo is applied, the voltage U maccording to the resistance Roruck and resistance Rz ug changed partial voltage. Of course, it is also conceivable to use a full bridge as a measuring device instead of a half bridge, as shown, in which case instead of fixed resistors R, resistance Roruck and resistance Rz ug in the right branch of the measuring bridge can be used in reverse to the left branch of the measuring bridge.

[0051] As shown in Fig. 7 as an 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.

[0052] 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.

[0053] 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.

[0054] List of reference symbols

[0055] I Gripping device

[0056] 3 housings with drive

[0057] 5a gripping jaw

[0058] 5b gripping jaw

[0059] 7 eggs

[0060] 9 Gripping jaw in the form of a quadruple bending beam in deformed position

[0061] 9a first beam or bar of the quadruple bending beam 9

[0062] 9b second beam or bar of the quadruple bending beam 9

[0063] 9c third beam or bar of the quadruple bending beam 9

[0064] 9d fourth beam or bar of the quadruple bending beam 9

[0065] II non-deformed position of gripping jaw 9

[0066] 13 simple bending beam in deformed position

[0067] 15 non-deformed position of 13

[0068] 17 Bending beam area

[0069] 19 Gripper jaw in the form of a sevenfold bending beam

[0070] 19a first beam or bar of the sevenfold bending beam 19

[0071] 19b second beam or bar of the sevenfold bending beam 19

[0072] 19c third beam or bar of the sevenfold bending beam 19

[0073] 19d fourth beam or bar of the sevenfold bending beam 19

[0074] 19e fifth beam or bar of the sevenfold bending beam 19

[0075] 19f sixth beam or bar of the sevenfold bending beam 19

[0076] 19g seventh beam or bar of the sevenfold bending beam 19

[0077] 21a front or distal part of the gripping jaw 19

[0078] 21b rear or proximal part of the gripping jaw 19

[0079] 23 DMS

[0080] 23a left connection

[0081] 23b right connection

[0082] 25 strain gauges

[0083] 25a left connection

[0084] 25b right connection

[0085] 27 embedded wire

[0086] 29 printed plastic a angle ß angle a z Train area

[0087] Od pressure range

[0088] D Detail

[0089] F Force

[0090] R resistance oruck Bridge resistance of all strain gauges connected in series and subjected to compression

[0091] Rzug Bridge resistance of all series-connected strain gauges subjected to tensile stress

[0092] U reversal area

[0093] Uo fixed voltage

[0094] To measure voltage

[0095] W Distance of bending / deflection

Claims

Patent claims 1. 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 a substantially parallel gripping is possible.

2. 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.

3. 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).

4. 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).

5. Gripping element according to claim 4, characterized in that the Strain gauges (23, 25) made of resistance wire, in particular Constantan wire.

6. 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.

7. Method according to claim 6, characterized in that the multiple bending beam (9, 19) is manufactured from individual beams (9a, 9b, 9c, 9d; 19a, 19b, 19c, 19d, 19e, 19f, 19g) which are thin compared to their elongated extent.

8. Method 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).

9. Method according to one of claims 6 to 8, characterized in that the gripping element (5a, 5b) is produced by additive manufacturing in the form of a one-piece component.

10. Method according to one of claims 6 to 9, characterized in that During the layer-by-layer additive manufacturing of the gripping element (5a, 5b), several 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.

11. Method 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.

12. Method 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.

Images