The Experts below are selected from a list of 46335 Experts worldwide ranked by ideXlab platform
Heinrich M Jaeger - One of the best experts on this subject based on the ideXlab platform.
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the intertwined roles of particle shape and surface roughness in controlling the shear strength of a Granular Material
Granular Matter, 2019Co-Authors: Kieran A Murphy, Arthur K Mackeith, Leah K Roth, Heinrich M JaegerAbstract:Both the shape of individual particles and their surface properties contribute to the strength of a Granular Material under shear. Here we show the degree to which these two aspects can be intertwined. In experiments on assemblies of 3D printed, convex lens-shaped particles, we measure the stress–strain response under repeated compressive loading and find that the aggregate’s shear strength falls rapidly when compared to other particle shapes. We probe the Granular Material at mm-scales with X-ray computed tomography and $$\upmu $$ m-scales with high-resolution surface metrology to look for the cause of the degradation. We find that wear due to accumulated deformation smooths out the lens surfaces in a controlled and systematic manner that correlates with a significant loss of shear strength observed for the assembly as a whole. The sensitivity of lenses to changes in surface properties contrasts with results for assemblies of 3D printed tetrahedra and spheres, which under the same load cycling are found to exhibit only minor degradation in strength. This case study provides insight into the relationship between particle shape, surface wear, and the overall Material response, and suggests new strategies when designing a Granular Material with desired evolution of properties under repeated deformation.
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a positive pressure universal gripper based on the jamming of Granular Material
IEEE Transactions on Robotics, 2012Co-Authors: John R Amend, Heinrich M Jaeger, Eric Brown, Nicholas Rodenberg, Hod LipsonAbstract:We describe a simple passive universal gripper, consisting of a mass of Granular Material encased in an elastic membrane. Using a combination of positive and negative pressure, the gripper can rapidly grip and release a wide range of objects that are typically challenging for universal grippers, such as flat objects, soft objects, or objects with complex geometries. The gripper passively conforms to the shape of a target object, then vacuum-hardens to grip it rigidly, later utilizing positive pressure to reverse this transition-releasing the object and returning to a deformable state. We describe the mechanical design and implementation of this gripper and quantify its performance in real-world testing situations. By using both positive and negative pressure, we demonstrate performance increases of up to 85% in reliability, 25% in error tolerance, and the added capability to shoot objects by fast ejection. In addition, multiple objects are gripped and placed at once while maintaining their relative distance and orientation. We conclude by comparing the performance of the proposed gripper with others in the field.
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universal robotic gripper based on the jamming of Granular Material
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Eric Brown, Nicholas Rodenberg, John R Amend, Annan Michael Mozeika, E Steltz, Mitchell R Zakin, Hod Lipson, Heinrich M JaegerAbstract:Gripping and holding of objects are key tasks for robotic manipulators. The development of universal grippers able to pick up unfamiliar objects of widely varying shape and surface properties remains, however, challenging. Most current designs are based on the multifingered hand, but this approach introduces hardware and software complexities. These include large numbers of controllable joints, the need for force sensing if objects are to be handled securely without crushing them, and the computational overhead to decide how much stress each finger should apply and where. Here we demonstrate a completely different approach to a universal gripper. Individual fingers are replaced by a single mass of Granular Material that, when pressed onto a target object, flows around it and conforms to its shape. Upon application of a vacuum the Granular Material contracts and hardens quickly to pinch and hold the object without requiring sensory feedback. We find that volume changes of less than 0.5% suffice to grip objects reliably and hold them with forces exceeding many times their weight. We show that the operating principle is the ability of Granular Materials to transition between an unjammed, deformable state and a jammed state with solid-like rigidity. We delineate three separate mechanisms, friction, suction, and interlocking, that contribute to the gripping force. Using a simple model we relate each of them to the mechanical strength of the jammed state. This advance opens up new possibilities for the design of simple, yet highly adaptive systems that excel at fast gripping of complex objects.
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reversibility and irreversibility in the packing of vibrated Granular Material
Powder Technology, 1997Co-Authors: E R Nowak, James B Knight, Heinrich M Jaeger, Michelle L Povinelli, Sidney R NagelAbstract:Abstract We report on the settling of loosely packed, cohesionless Granular Material under mechanical vibrations. Monodisperse spherical beads were confined to a long vertical cylinder that was driven by an electromagnetic vibration exciter. Under vibrations the bead packing evolves from an initial, low-density configuration towards higher density. Ramping the vibration intensity repeatedly up and back down again reveals the existence of both an irreversible and a reversible branch in the response. The reversible branch represents a steady state in which the packing density depends monotinically on the vibration intensity. We have investigated the bead size, depth, and ramp rate dependence of the compaction process. Our results indicate how the occupied volume fraction can be optimized by slowly reducing the vibration intensity along the reversible branch.
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density relaxation in a vibrated Granular Material
Physical Review E, 1995Co-Authors: James B Knight, Christopher G Fandrich, Chun Ning Lau, Heinrich M Jaeger, Sidney R NagelAbstract:We report measurements of the density of a vibrated Granular Material as a function of time. The Material studied consists of monodisperse spherical glass particles confined to a long, thin cylindrical tube. Vibrations cause the pile to evolve from a low density initial configuration toward a steady state with a final density that depends on the intensity of the vibrations. We find a complex time evolution that is incompatible with a single exponential relaxation. There appears to be a characteristic value of the acceleration that separates two regimes of packing behavior. The results are compared to current theories of compaction.
Sidney R Nagel - One of the best experts on this subject based on the ideXlab platform.
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reversibility and irreversibility in the packing of vibrated Granular Material
Powder Technology, 1997Co-Authors: E R Nowak, James B Knight, Heinrich M Jaeger, Michelle L Povinelli, Sidney R NagelAbstract:Abstract We report on the settling of loosely packed, cohesionless Granular Material under mechanical vibrations. Monodisperse spherical beads were confined to a long vertical cylinder that was driven by an electromagnetic vibration exciter. Under vibrations the bead packing evolves from an initial, low-density configuration towards higher density. Ramping the vibration intensity repeatedly up and back down again reveals the existence of both an irreversible and a reversible branch in the response. The reversible branch represents a steady state in which the packing density depends monotinically on the vibration intensity. We have investigated the bead size, depth, and ramp rate dependence of the compaction process. Our results indicate how the occupied volume fraction can be optimized by slowly reducing the vibration intensity along the reversible branch.
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density relaxation in a vibrated Granular Material
Physical Review E, 1995Co-Authors: James B Knight, Christopher G Fandrich, Chun Ning Lau, Heinrich M Jaeger, Sidney R NagelAbstract:We report measurements of the density of a vibrated Granular Material as a function of time. The Material studied consists of monodisperse spherical glass particles confined to a long, thin cylindrical tube. Vibrations cause the pile to evolve from a low density initial configuration toward a steady state with a final density that depends on the intensity of the vibrations. We find a complex time evolution that is incompatible with a single exponential relaxation. There appears to be a characteristic value of the acceleration that separates two regimes of packing behavior. The results are compared to current theories of compaction.
James B Knight - One of the best experts on this subject based on the ideXlab platform.
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reversibility and irreversibility in the packing of vibrated Granular Material
Powder Technology, 1997Co-Authors: E R Nowak, James B Knight, Heinrich M Jaeger, Michelle L Povinelli, Sidney R NagelAbstract:Abstract We report on the settling of loosely packed, cohesionless Granular Material under mechanical vibrations. Monodisperse spherical beads were confined to a long vertical cylinder that was driven by an electromagnetic vibration exciter. Under vibrations the bead packing evolves from an initial, low-density configuration towards higher density. Ramping the vibration intensity repeatedly up and back down again reveals the existence of both an irreversible and a reversible branch in the response. The reversible branch represents a steady state in which the packing density depends monotinically on the vibration intensity. We have investigated the bead size, depth, and ramp rate dependence of the compaction process. Our results indicate how the occupied volume fraction can be optimized by slowly reducing the vibration intensity along the reversible branch.
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density relaxation in a vibrated Granular Material
Physical Review E, 1995Co-Authors: James B Knight, Christopher G Fandrich, Chun Ning Lau, Heinrich M Jaeger, Sidney R NagelAbstract:We report measurements of the density of a vibrated Granular Material as a function of time. The Material studied consists of monodisperse spherical glass particles confined to a long, thin cylindrical tube. Vibrations cause the pile to evolve from a low density initial configuration toward a steady state with a final density that depends on the intensity of the vibrations. We find a complex time evolution that is incompatible with a single exponential relaxation. There appears to be a characteristic value of the acceleration that separates two regimes of packing behavior. The results are compared to current theories of compaction.
Alain De Ryck - One of the best experts on this subject based on the ideXlab platform.
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Effect of the particle size and the liquid content on the shear behaviour of wet Granular Material
Powder Technology, 2017Co-Authors: Haithem Louati, Driss Oulahna, Alain De RyckAbstract:The size of particle is a relevant parameter in the study of the Granular Material behaviour.,For wet Granular Materials, it affects the capillary force and the number of liquid bridges. We present quantitative and qualitative investigations of the effect of the particle size on the steady-state shear behaviour of partially wet Granular Material. Two sizes of glass beads have been used: 12-40 mu m and 70-110 mu m in diameter and the shear behaviour was studied using an annular shear cell. The results show different regimes of the shear-normal stresses relationship depending on the particle size, with a general increase of the magnitude of the shear stress for a decrease in the particle size. Most studies of wet Granular Material behaviour have focused on the pendular state of saturation with liquid bridge formed between particles. In this study, the states of saturation are explored going up to completely filling the space between beads of 70-110 mu m. Different regimes are identified depending on the liquid fraction and the applied normal stress. A theoretical approach was used to estimate the tensile strength for the different states of saturation. An agreement between both experimental and theoretical data was observed and discussed.
Hod Lipson - One of the best experts on this subject based on the ideXlab platform.
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a positive pressure universal gripper based on the jamming of Granular Material
IEEE Transactions on Robotics, 2012Co-Authors: John R Amend, Heinrich M Jaeger, Eric Brown, Nicholas Rodenberg, Hod LipsonAbstract:We describe a simple passive universal gripper, consisting of a mass of Granular Material encased in an elastic membrane. Using a combination of positive and negative pressure, the gripper can rapidly grip and release a wide range of objects that are typically challenging for universal grippers, such as flat objects, soft objects, or objects with complex geometries. The gripper passively conforms to the shape of a target object, then vacuum-hardens to grip it rigidly, later utilizing positive pressure to reverse this transition-releasing the object and returning to a deformable state. We describe the mechanical design and implementation of this gripper and quantify its performance in real-world testing situations. By using both positive and negative pressure, we demonstrate performance increases of up to 85% in reliability, 25% in error tolerance, and the added capability to shoot objects by fast ejection. In addition, multiple objects are gripped and placed at once while maintaining their relative distance and orientation. We conclude by comparing the performance of the proposed gripper with others in the field.
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universal robotic gripper based on the jamming of Granular Material
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Eric Brown, Nicholas Rodenberg, John R Amend, Annan Michael Mozeika, E Steltz, Mitchell R Zakin, Hod Lipson, Heinrich M JaegerAbstract:Gripping and holding of objects are key tasks for robotic manipulators. The development of universal grippers able to pick up unfamiliar objects of widely varying shape and surface properties remains, however, challenging. Most current designs are based on the multifingered hand, but this approach introduces hardware and software complexities. These include large numbers of controllable joints, the need for force sensing if objects are to be handled securely without crushing them, and the computational overhead to decide how much stress each finger should apply and where. Here we demonstrate a completely different approach to a universal gripper. Individual fingers are replaced by a single mass of Granular Material that, when pressed onto a target object, flows around it and conforms to its shape. Upon application of a vacuum the Granular Material contracts and hardens quickly to pinch and hold the object without requiring sensory feedback. We find that volume changes of less than 0.5% suffice to grip objects reliably and hold them with forces exceeding many times their weight. We show that the operating principle is the ability of Granular Materials to transition between an unjammed, deformable state and a jammed state with solid-like rigidity. We delineate three separate mechanisms, friction, suction, and interlocking, that contribute to the gripping force. Using a simple model we relate each of them to the mechanical strength of the jammed state. This advance opens up new possibilities for the design of simple, yet highly adaptive systems that excel at fast gripping of complex objects.
