Granular gripper

Abstract

Granular gripper (1), in particular for a robot arm, comprising - a carrier (2), - a membrane (4) attached to the support (2) which encloses an interior space (6) in a balloon-like manner, - a granulate (10) filled into the interior (6), - a fluid connection (12) which leads into the interior (6) and, during normal operation, serves to convey fluid from or into the interior (6), wherein the granulate (10) comprises two different materials, of which the first material has a comparatively low formability and the second material has a comparatively high formability, and wherein the granulate (10) is formed from two-phase particles (18), each having a core (14) formed from the first material and a shell (16) formed from the second material, or wherein the first and the second material are each used in separate particles (20, 22) which together form a mixture which cannot be demixed under mechanical stimulation.

Description

[0001] The invention relates to a granular gripper which is designed and intended in particular for use as a gripping device for a robot arm.

[0002] Grippers (or “gripping devices”) are usually attachments for handling equipment (particularly robots or “industrial robots”) and are often also referred to as “robot hands” or similar. Such grippers are usually used, for example, to grip components during assembly or manufacturing processes, to “manipulate” them (i.e. in particular to handle them, e.g. to move them into predetermined positions, particularly by changing their orientation to another object), and the like. A robot hand is often understood to be a relatively detailed articulated device that usually has a large number of fingers and / or finger joints in order to mimic a human hand. This often allows the external structure of a very wide variety of objects to be gripped.In contrast, there are usually comparatively "simple" grippers, which are often specifically adapted to an object and sometimes have only two or three rigid "fingers" or even just a number of one type of suction cups, for example, to handle sheet goods using negative pressure. Despite their usually comparatively complex and therefore expensive design, robot hands can offer cost advantages, especially for frequently changing object geometries.

[0003] Novel gripping systems feature a type of balloon formed by a membrane, the interior of which is filled with a medium (also known as "filler") that solidifies when a vacuum is applied. Typically, the medium is a granulate, which is why such a gripper is also referred to as a granular gripper, membrane gripper, granulate gripper, or similar. The gripping principle is based on the filled balloon being partially "slipped" over the component to be gripped and then "frozen" in the shape it assumes by applying a vacuum. This allows a simple gripper structure to grip and hold a multitude of different geometric structures. Adaptation to objects of different sizes is optionally achieved using "balloons" of different sizes.

[0004] In FITZGERALD, Seth G.; DELANEY, Gary W.; HOWARD, David. A review of jamming actuation in soft robotics. In: Actuators. MDPI, 2020. p. 104, AMEND, John, et al. Soft robotics commercialization: Jamming grippers from research to product. Soft robotics, 2016, Volume 3, No. 4, pp. 213-222, AMEND, John R., et al. A positive pressure universal gripper based on the jamming of granular material, IEEE transactions on robotics, 2012, Vol. 28, No. 2, pp. 341-350 and JIANG, Allen, et al. Design of a variable stiffness flexible manipulator with composite granular jamming and membrane coupling. In: 2012 IEEE / RSJ International Conference on Intelligent Robots and Systems. IEEE, 2012. Pp. 2922-2927 discusses granular grippers and the principles underlying them.

[0005] The invention is based on the object of improving a granular gripper.

[0006] This object is achieved according to the invention by a granular gripper having the features of claim 1. Advantageous and partly inventive embodiments and further developments of the invention are set out in the subclaims and the following description.

[0007] The granular gripper according to the invention (in short: gripper) is preferably designed and intended for use with (in particular on) a robot arm. The gripper has a carrier and a membrane fastened to the carrier, which encloses an interior space like a balloon. The gripper further has granules filled into the interior space and a fluid connection which leads into the interior space and, during normal operation, serves to convey fluid from or into the interior space. In addition, the granules have two different materials, of which the first material has a comparatively low deformability (i.e., compared to the other, second material) and the second material has a comparatively high deformability.

[0008] Preferably, the two materials are selected such that they have a significant difference, preferably of at least one, optionally also two or more orders of magnitude, in their deformability.

[0009] Further preferably, the two materials are not alloyed, compounded or the like together to form a common material.

[0010] A granulate designed in this way has the advantage that the positive effects of the "soft", comparatively highly deformable material can be used, while at the same time disadvantages resulting from such a material can be at least partially compensated for. A soft granulate has the advantage that a higher holding force can be achieved compared to an exclusively hard granulate, particularly for gripping cases in which there is no geometric claw formation of the membrane on the back of the object to be gripped, i.e. there is no form-fitting gripping around or engagement with the object. In such cases, friction (i.e. force connection) is the key factor in whether the object can be gripped and held sufficiently. In order to generate sufficient friction, the membrane of the gripper must be in close contact with the surface of the object to be gripped.Tests and simulations have shown that soft particles (soft granules) are squeezed during gripping (particularly when fluid is pumped out of the interior), thus improving the adhesion of the membrane. In contrast, with hard particles, when they stiffen (i.e. when fluid is pumped out of the interior), their movement can be hindered by other particles (of a similar type and therefore almost undeformable, at least for the forces typically encountered here), so that the transfer of pressure caused by the stiffening to the membrane and / or the object to be gripped is at least locally prevented. Simulations have shown that when granulate particles with a Young's modulus greater than 10 are used, 9Pascal (Pa), only a small, purely frictional holding force can be exerted on the object to be grasped. A sphere was used as the object, which – to avoid mechanical claws – was to be grasped only at its upper half (hemisphere). For granulate particles with an E-modulus of less than 10 8 Pa, up to about 10 5 Pa, an increase in the purely friction-related holding force in the ratio of approximately 1 / E could be shown.

[0011] However, soft granules have the disadvantage that the holding force is limited to the force required to deform the individual (granule) particles (so-called limiting holding force). By using the first, harder material in the granules (in addition to the second material), this disadvantage can be compensated. Thus, the invention described above enables grippers with increased gripping force.

[0012] For this purpose, in one embodiment according to the invention, the granulate is formed from two-phase particles, each comprising a core formed from the first, particularly hard, material and a shell formed from the second, particularly soft, material. These particles are also referred to below as "core-shell particles." The core thus limits the deformation of the shell during pumping out of the fluid (hereinafter referred to simply as "evacuation"), so that the aforementioned positive effects are apparent, but the limit holding force is also increased.

[0013] In an alternative embodiment of the invention (i.e., as an alternative to the core-shell particles described above), the first and second materials are each used in separate particles of the granulate. These two types of particles together form a mixture that cannot be demixed under mechanical stimulation (in particular, a solid mixture, i.e., one formed from solids). Specifically, the two types of particles are selected such that such a non-deixable mixture is present. The latter prevents the particles from separating into coherent groups during movements that usually inevitably occur during operation, in particular vibrations of the entire mixture - e.g., due to pressure changes in the interior or when the robot moves.

[0014] In optional variants, the fluid can be air or another gas mixture as well as a liquid.

[0015] Preferably, the particles are at least approximately (ie exactly or within manufacturing tolerances) spherical.

[0016] In a practical embodiment, the two materials are selected with regard to their elastic deformability. Preferably, the second, soft material is selected such that it has a high elastic deformability and the lowest possible plastic deformability in the range of the pressures required for sufficient holding force (and the resulting forces acting between the particles). For example, for the second material, elastic moduli in the range between 10 5 and 10 8 Pa. A low plastic deformation capacity makes it possible, in particular, to reduce or prevent mechanical aging effects caused by the changing loads during operation.

[0017] Preferably, the shell of the core-shell particles has a thickness between at least 1 and approximately (particularly within the scope of standard tolerances) 25 percent of the total thickness—and, in the case of at least approximately spherical particles, also of the diameter. In particular, the thickness of the shell is between 1 and 25 percent of the total thickness.

[0018] In a further advantageous embodiment, the granulate comprises, in addition to the core-shell particles, further particles formed from the first, second, or a third material, wherein the third material has a deformability, in particular an elastic one, comparable to that of the first or second material. In other words, the granulate (comparable to that already described) is formed from a mixture of the core-shell particles and another type of (preferably single-phase) particles, preferably one that cannot be separated under mechanical stimulation.

[0019] In order to prevent the different particles from segregating under mechanical excitation, in one advantageous embodiment the material properties (e.g. mass density, coefficient of restitution, coefficient of friction) and / or the geometric properties (e.g. diameter, sphericity) of the particles of the non-segregable mixture are coordinated with one another. For example, the different particles of the granulate are selected to be approximately the same size. Optionally, additionally or alternatively, the materials from which the different particles are formed are selected so that they have approximately the same mass density. In this context, “approximately the same size” is understood in particular to mean that the particles are exactly the same size and / or have exactly the same mass density or can also lie within a predetermined tolerance range in which segregation is still sufficiently avoided despite the difference.

[0020] In a practical embodiment, the first material is a thermoplastic, a thermoset, a glass, a metal, or a mineral. The second material, on the other hand, is an elastomer or a foamed thermoplastic or thermoset. Expanded polystyrene (EPS), for example, is used as a foamed thermoplastic.

[0021] In a further expedient embodiment, the proportion of particles made of the second material in the total number of all particles in the granulate is between at least 20 and a maximum of 80 percent, preferably between 25 and 75 percent.

[0022] In the case of a mixture of core-shell particles and other particles, their mixing ratio is advantageously of a comparable order of magnitude as described above.

[0023] The conjunction “and / or” is to be understood here and in the following in particular in such a way that the features linked by means of this conjunction can be formed both together and as alternatives to one another.

[0024] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In the drawings: Fig. 1 shows a schematic sectional view of a granular gripper, Fig. 2 in a schematic sectional view of a particle of the granulate, and Fig. 3 in view according to Fig. 2 another embodiment of the granulate as a mixture of different particles.

[0025] Corresponding parts are always provided with the same reference symbols in all figures.

[0026] In Fig. 1 schematically shows a granular gripper 1. The gripper 1 has a carrier 2 and a membrane 4, which is attached to the carrier 2 and encloses an interior space 6 like a balloon. The carrier 2 also serves to attach the gripper 1 to a robot arm. To attach the membrane 4 to the carrier 2, the gripper 1 in the illustrated embodiment has a clamping ring 8. In addition, the gripper 1 has a granulate 10, which is filled into the interior space 6. The operating principle of the gripper 1 is based on the fact that in order to grip an object, the membrane 4 is pressed onto the object, while ambient pressure is (usually) present in the interior space 6. The granulate 10, which is loosely arranged in the membrane 4, can flow around the object (within the membrane 4). To support this process, the interior space 6 can optionally also be pressurized. The interior space 6 is then subjected to a negative pressure (also: “evacuated”).This "freezes" the granulate 10. For evacuation (or optionally for pressurizing the interior 6), the gripper 1 has a fluid connection 12 leading into the interior 6. In its intended use, a (vacuum) pump (not shown) is connected to the interior 6 via the fluid connection 12.

[0027] In addition to the granulate 10, the interior 6 usually contains air or a gas as a fluid.

[0028] In Fig. Figure 2 shows an embodiment of the particles of the granulate 10 in more detail, showing a cross-section of a single particle. The particle has a core 14 and a shell 16, each formed from different materials. The particle is therefore also referred to as a "core-shell particle 18." The material of the core 14 (also referred to as the "first material") has a lower deformability than the material ("second material") of the shell 16. In the present embodiment, the shell 16 is made of EPS and the core 14 is made of glass.

[0029] In Fig.Figure 3 shows an alternative embodiment of the granulate 10. Here, the granulate 10 is formed from a mixture of first particles 20 and second particles 22. The mixture is adjusted in such a way that demixing of the two particle types due to mechanical agitation is prevented. To this end, the particles 20 and 22 are matched to one another in their material properties and / or geometric properties. In the present embodiment, the particles 20 and 22 are specifically designed to be the same size. The first particles 20 are made of the first material, i.e., glass, and the second particles 22 are made of the second material, i.e., EPS.

[0030] In a further embodiment not shown, the granulate 10 is formed by a mixture of the core-shell particles 18 and further particles, for example, the first particles 20. In this case, too, the core-shell particles 18 and the further particles 20 are matched to one another in their material properties and / or geometric properties to prevent segregation; in this embodiment, they are particularly designed to be the same size.

[0031] The subject matter of the invention is not limited to the exemplary embodiments described above. Rather, further embodiments of the invention can be derived by those skilled in the art from the above description. In particular, the individual features of the invention and their design variants described with reference to the various exemplary embodiments can also be combined with one another in other ways. List of reference symbols 1 gripper 2 carriers 4 Membran 6 Interior 8 clamping ring 10 granules 12 Fluid connection 14 core 16 coat 18 core-shell particles 20 particles 22 particles

Claims

[1] Granular gripper (1), in particular for a robot arm, comprising - a carrier (2), - a membrane (4) attached to the support (2) which encloses an interior space (6) in a balloon-like manner, - a granulate (10) filled into the interior (6), - a fluid connection (12) which leads into the interior (6) and, during normal operation, serves to convey fluid from or into the interior (6), wherein the granulate (10) comprises two different materials, of which the first material has a comparatively low formability and the second material has a comparatively high formability, and wherein the granulate (10) is formed from two-phase particles (18), each having a core (14) formed from the first material and a shell (16) formed from the second material, or wherein the first and the second material are each used in separate particles (20, 22) which together form a mixture which cannot be demixed under mechanical stimulation. [2] Granular gripper (1) according to claim 1, wherein the two materials are selected with respect to an elastic deformability. [3] Granular gripper (1) according to claim 1 or 2, wherein the shell (16) of the two-phase particles (18) has a thickness of at least 1 up to 25 percent of the total thickness of the two-phase particles (18). [4] Granular gripper (1) according to one of claims 1 to 3, wherein the granulate (10) comprises, in addition to the two-phase particles (18), further particles (20) which are formed from the first, the second or a third material, wherein the third material has a, in particular elastic, deformability comparable to the first or the second material. [5] Granular gripper (1) according to one of claims 1 to 4, wherein the particles (18, 20, 22) of the non-separable mixture are matched to one another in their material properties and / or their geometric properties. [6] Granular gripper (1) according to one of claims 1 to 5, wherein the first material is a thermoplastic, a thermosetting plastic, a glass, a metal or a mineral, and wherein the second material is an elastomer or a foamed thermoplastic or thermosetting plastic. [7] Granular gripper (1) according to claim 1, wherein a proportion of the particles (20) made of the first material in the total number of all particles (20, 22) in the granulate (10) is between at least 20 and a maximum of 80 percent, preferably between 25 and 75 percent.

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