Nonprehensile Dynamic Manipulation: A Survey

Nonprehensile dynamic manipulation can be reason- ably considered as the most complex manipulation task. It might be argued that such a task is still rather far from being fully solved and applied in robotics. This survey tries to collect the results reached so far by the research community about planning and control in the nonprehensile dynamic manipulation domain. A discussion about current open issues is addressed as well

Closed-loop Control of a Nonprehensile Manipulation System Inspired by the Pizza-Peel Mechanism

A nonprehensile manipulation system consisting of a dexterous plate (e.g., a peel) which is intended to induce a rotating movement on a disk (e.g., a pizza) is studied. A dynamic model based on the Euler-Lagrange equations is first derived. Then, a controllability analysis of this model is carried out, which shows some intrinsic limitations of the proposed system. Later, a closed-loop control strategy is proposed to induce the desired rotating speed in the disk, while maintaining the position of both the disk and the plate as close to zero as possible. A stability analysis is performed to show the boundedness of all the states, the oscillatory response of all of them, and the maximum amplitude of these oscillations. A numerical simulation is employed to verify the proposed controller and the predicted behavior found in the stability analysis

Nonprehensile Manipulation of Deformable Objects: Achievements and Perspectives from the RoDyMan Project

The goal of this work is to disseminate the results achieved so far within the RODYMAN project related to planning and control strategies for robotic nonprehensile manipulation. The project aims at advancing the state of the art of nonprehensile dynamic manipulation of rigid and deformable objects to future enhance the possibility of employing robots in anthropic environments. The final demonstrator of the RODYMAN project will be an autonomous pizza maker. This article is a milestone to highlight the lessons learned so far and pave the way towards future research directions and critical discussions

Nonprehensile Manipulation of Deformable Objects: Achievements and Perspectives from the RobDyMan Project

International audienceThe goal of this work is to disseminate the results achieved so far within the RODYMAN project related to planning and control strategies for robotic nonprehensile manipulation. The project aims at advancing the state of the art of nonprehensile dynamic manipulation of rigid and deformable objects to future enhance the possibility of employing robots in anthropic environments. The final demonstrator of the RODYMAN project will be an autonomous pizza maker. This article is a milestone to highlight the lessons learned so far and pave the way towards future research directions and critical discussions

Variable structure dynamics in a bouncing dimer

Systems with unilateral constraints usually possess a variable structure dynamics, in which systems can switch from one mode to another due to contacts and impacts. In particular, friction participating into contacts and impacts will extremely complicate the dynamics, and even result in some singularities when using rigid body models. In this paper, we develop a method that can well deal with the difficulties involved in the variable structure systems, such as the multiple impacts with friction (i.e. the occurrence of simultaneous impacts), the superstatic problems in rigid body systems, the multivalued graph in the stick mode of the Coulomb's friction, and the inelastic collapse in impacts. The transition rules to monitor the switches from one mode to another are also established, in which the normal states at each contact point are controlled by the complementary conditions for a contact process and by the potential energy at contact points for an impact process, while the tangential states at the contact point will be governed by a correlative coefficient of friction defined by the tangential differential equations. A system elaborated in \cite{Dorbolo-05} with precise experimental results serves as an example to illustrate the theoretical developments, in which a dimer consisting of two spheres rigidly connected by a light glass rod bounces on a vibrating plate. This system, even though simple enough, exhibits profuse physical phenomena under different initial and driving conditions, and may spur different ordered persistent motions, such as the drift, jump and flutter modes. In particular, each mode of the persistent motion is synthesized by a periodically complicated motion that may involve single and double impacts, contacts with or without slip, {\em etc}. Based on the theory proposed in this paper, we clearly explain the regime of persistent motions in the dimer and find that the peculiar property of friction with discontinuity plays a significant role for its formation. Plenty of numerical simulations are carried out, and precise agreements between the numerical and experimental results are obtained. Furthermore, a simplified model for the dimer in drift mode is developed and theoretical analysis is implemented. An approximate formula for the mean horizonal velocity is obtained that also coincides well with the experimental findings. This may be beneficial for the study of complex systems dynamics, in which there exists an intrinsic connection between the ordered behaviors of the systems and the microsize parameters of its ingredients

The application of oscillation to the deformation of an elastoviscoplastic material

The research reported in this thesis demonstrates the benefits of applying coaxial vibration to forming tools in soft solid forming processes using Plasticine as a model material. In the study of vibration assisted upsetting and indentation (conical and spherical), finite element models under kinematic loading were first developed to gain insight into interface mechanics. FE simulation of the model material included the effects of elasticity, viscoplasticity, strain rate, large strains and a coulombic stress boundary condition in the presence of a lubricant. Agreement was achieved between the FE results and those obtained from upsetting and indentation experiments with respect to the force-displacement curves and deformed configurations for a range of friction coefficients, specimen sizes and platen velocities. The FE models, subsequently developed to simulate processes under superimposed vibration loading of the forming tool, predicted an apparent reduction in the mean forming force. The reduction in mean force is largely dependent on the vibration amplitude and shows a weak dependence on frequency. The results illustrate the phenomenon of stress superposition, where a cyclic stress is superimposed on a non-oscillatory stress. However, a reduction in the mean force alone is not necessarily beneficial since the maximum stress under idealised superimposed vibration loading will follow the same stress-strain curve as under static loading, with both the mean and minimum stresses following paths parallel to the non-oscillatory stress-strain curve. In fact, in the case of strain rate dependent materials, the maximum stress can be greater under vibration loading, and this overstress is correctly predicted by the FE model. However, more importantly, experiments under vibration loading using Plasticine have shown both a reduction in the mean forming force, and a maximum stress which is less than the static stress. The reduction in maximum stress achieved is related to the friction condition at the die/specimen interface. The relationship between vibration condition and soft solid material flow is investigated. It is established that vibration assisted forming can result in a significant reduction in resistance of the forming material to deformation, by a combination of stress superposition effect and a reduction in interface friction

Driven colloidal particles in optical potential energy landscapes

The structure and dynamics of colloidal particles in optical potential energy landscapes is studied. Experiments use paramagnetic or optically anisotropic colloidal particles interacting with lines or pairs of time-dependent optical traps. First, the pairwise interactions of the paramagnetic particles are measured using pairs of optical traps. We test a novel data analysis method under various conditions and calculate the magnetic susceptibility of the particles. Next, we measure the structure and dynamics of chains of paramagnetic colloids in a sinusoidal optical potential of varying depth. At well defined chain lengths, we observe a transition from an asymmetric, strongly pinned state to a free-sliding, symmetric state as the optical potential decreases. We then analyse the frictional dynamics of the same system under a constant driving force and observe a transition from low to high friction as the optical potential increases. We model the dynamics of the chains in the low and high friction regimes. The simple hard sphere model developed for the high friction regime is used to derive an equation which predicts the transition point from low to high friction. Next, we drive the chains through a time-dependent optical potential with an oscillating depth. We analyse the synchronisation of the chain’s motion to the oscillations of the potential and characterise the dynamics, observing a novel mode of motion involving the simultaneous nucleation of kinks and anti-kinks. Finally, we study the dynamics of a single optically anisotropic dumbbell particle interacting with a repulsive optical trap controlled by a time-delayed feedback protocol. We observe a transition from diffusive to driven dynamics which is modelled using delay-differential equations. We find that this transition coincides with the maximum work done on the particle and a local minimum in the mutual information between the particle and the trap

TIP trajectory tracking of flexible-joint manipulators

In most robot applications, the control of the manipulator’s end-effector along a specified desired trajectory is the main concern. In these applications, the end-effector (tip) of the manipulator is required to follow a given trajectory. Several methods have been so far proposed for the motion control of robot manipulators. However, most of these control methods ignore either joint friction or joint elasticity which can be caused by the transmission systems (e.g. belts and gearboxes). This study aims at development of a comprehensive control strategy for the tip-trajectory tracking of flexible-joint robot manipulators. While the proposed control strategy takes into account the effect of the friction and the elasticity in the joints, it also provides a highly accurate motion for the manipulator’s end-effector. During this study several approaches have been developed, implemented and verified experimentally/numerically for the tip trajectory tracking of robot manipulators. To compensate for the elasticity of the joints two methods have been proposed; they are a composite controller whose design is based on the singular perturbation theory and integral manifold concept, and a swarm controller which is a novel biologically-inspired controller and its concept is inspired by the movement of real biological systems such as flocks of birds and schools of fishes. To compensate for the friction in the joints two new approaches have been also introduced. They are a composite compensation strategy which consists of the non-linear dynamic LuGre model and a Proportional-Derivative (PD) compensator, and a novel friction compensation method whose design is based on the Work-Energy principle. Each of these proposed controllers has some advantages and drawbacks, and hence, depending on the application of the robot manipulator, they can be employed. For instance, the Work-Energy method has a simpler form than the LuGre-PD compensator and can be easily implemented in industrial applications, yet it provides less accuracy in friction compensation. In addition to design and develop new controllers for flexible-joint manipulators, another contribution of this work lays in the experimental verification of the proposed control strategies. For this purpose, experimental setups of a two-rigid-link flexible-joint and a single-rigid-link flexible-joint manipulators have been employed. The proposed controllers have been experimentally tested for different trajectories, velocities and several flexibilities of the joints. This ensures that the controllers are able to perform effectively at different trajectories and speeds. Besides developing control strategies for the flexible-joint manipulators, dynamic modeling and vibration suppression of flexible-link manipulators are other parts of this study. To derive dynamic equations for the flexible-link flexible-joint manipulators, the Lagrange method is used. The simulation results from Lagrange method are then confirmed by the finite element analysis (FEA) for different trajectories. To suppress the vibration of flexible manipulators during the manoeuvre, a collocated sensor-actuator is utilized, and a proportional control method is employed to adjust the voltage applied to the piezoelectric actuator. Based on the controllability of the states and using FEA, the optimum location of the piezoelectric along the manipulator is found. The effect of the controller’s gain and the delay between the input and output of the controller are also analyzed through a stability analysis