Force-Closure Grasps With Two Palms

This paper studies force-closure grasps of rigid objects by using two palms. The two palms are instrumented with tactile sensors capable of detecting the presence of contacts, and are assumed to be respectively installed on two robotic manipulators capable of motion and force control. Established in this paper is an existence condition under which the two palms form a force-closure grasp. The salient feature of this condition is that it does not require the information on the shape of the object and the contact locations. A configuration of the two palms in contact with the object satisfying this condition is called a force-closure grasp configuration (FCGC). Further an algorithm is developed to check the condition for FCGC in terms of the position and orientation of the palms

A Distributed System for Robot Manipulator Control, NSF Grant ECS-11879 Fourth Report

This is the fourth annual report representing our last year\u27s work under the current grant. This work was directed to the development of a distributed computer architecture to function as a force and motion server to a robot system. In the course of this work we developed a compliant contact sensor to provide for transitions between position and force control; developed an end-effector capable of securing a stable grasp on an object and a theory of grasping; developed and built a controller which minimizes control delays; explored a parallel kinematics algorithms for the controller; developed a consistent approach to the definition of motion both in joint coordinates and in Cartesian coordinates; developed a symbolic simplification software package to generate the dynamics equations of a manipulator such that the calculations may be split between background and foreground

Spin-Cooling of the Motion of a Trapped Diamond

Observing and controlling macroscopic quantum systems has long been a driving force in research on quantum physics. In this endeavor, strong coupling between individual quantum systems and mechanical oscillators is being actively pursued. While both read-out of mechanical motion using coherent control of spin systems and single spin read-out using pristine oscillators have been demonstrated, temperature control of the motion of a macroscopic object using long-lived electronic spins has not been reported. Here, we observe both a spin-dependent torque and spin-cooling of the motion of a trapped microdiamond. Using a combination of microwave and laser excitation enables the spin of nitrogen-vacancy centers to act on the diamond orientation and to cool the diamond libration via a dynamical back-action. Further, driving the system in the non-linear regime, we demonstrate bistability and self-sustained coherent oscillations stimulated by the spin-mechanical coupling, which offers prospects for spin-driven generation of non-classical states of motion. Such a levitating diamond operated as a compass with controlled dissipation has implications in high-precision torque sensing, emulation of the spin-boson problem and probing of quantum phase transitions. In the single spin limit and employing ultra-pure nano-diamonds, it will allow quantum non-demolition read-out of the spin of nitrogen-vacancy centers under ambient conditions, deterministic entanglement between distant individual spins and matter-wave interferometry.Comment: New version with a calibration of angular resolution and sensitivity. Fig. 1 is also replaced to show an ODMR when the diamond is static to avoid spin-torque induced distortion

A Distributed System for Robot Manipulator Control

This is the final report representing three years of work under the current grant. This work was directed to the development of a distributed computer architecture to function as a force and motion server to a robot system. In the course of this work we developed a compliant contact sensor to provide for transitions between position and force control; we have developed an end-effector capable of securing a stable grasp on an object and a theory of grasping; we have built a controller which minimizes control delays, and are currently achieving delays of the order of five milliseconds, with sample rates of 200 hertz; we have developed parallel kinematics algorithms for the controller; we have developed a consistent approach to the definition of motion both in joint coordinates and in Cartesian coordinates; we have developed a symbolic simplification software package to generate the dynamics equations of a manipulator such that the calculations may be split between background and foreground

Rolling-based manipulation for multiple objects

This paper discusses the manipulation of multiple objects under rolling contacts. For manipulating multiple objects, the following two key issues do not arise in the manipulation of a single object: 1) each object's motion is restricted by the other objects and 2) the contact force among objects is not controlled directly. As for 1), we first formulate the motion constraint for the whole grasp system, and then provide a necessary condition for manipulating multiple objects uniquely. As for 2), we provide a condition for determining the contact forces among objects uniquely. We further show a sufficient condition for manipulating multiple objects within the object motion constraint. Under this sufficient condition, we propose a control scheme for object motion by taking the motion constraint into account. Simulation and experimental results are provided to confirm our idea

Two-Handed Grasping With Two-Fingered Hands

This paper analyzes two-handed grasping of a rigid object in the two-dimensional (2-D) space. The two hands under consideration have two fingers, and each finger is equipped with a tactile sensor. The hands are assumed to be respectively installed on two robotic manipulators capable of motion and force control. In a separate paper [1], a necessary condition for proper grasping configurations of two two-fingered hands are obtained. A proper grasping configuration is a configuration of the two hands at the initial contact with the object guaranteeing that a stable grasp can be achieved. A detailed study of the properties of contacts with the two fingers of a hand, and a method to determine if a proper grasping configuration has been reached by the two hands, are provided

Reflexive obstacle avoidance for kinematically-redundant manipulators

Dexterous telerobots incorporating 17 or more degrees of freedom operating under coordinated, sensor-driven computer control will play important roles in future space operations. They will also be used on Earth in assignments like fire fighting, construction and battlefield support. A real time, reflexive obstacle avoidance system, seen as a functional requirement for such massively redundant manipulators, was developed using arm-mounted proximity sensors to control manipulator pose. The project involved a review and analysis of alternative proximity sensor technologies for space applications, the development of a general-purpose algorithm for synthesizing sensor inputs, and the implementation of a prototypical system for demonstration and testing. A 7 degree of freedom Robotics Research K-2107HR manipulator was outfitted with ultrasonic proximity sensors as a testbed, and Robotics Research's standard redundant motion control algorithm was modified such that an object detected by sensor arrays located at the elbow effectively applies a force to the manipulator elbow, normal to the axis. The arm is repelled by objects detected by the sensors, causing the robot to steer around objects in the workspace automatically while continuing to move its tool along the commanded path without interruption. The mathematical approach formulated for synthesizing sensor inputs can be employed for redundant robots of any kinematic configuration

Free Nano-Object Ramsey Interferometry for Large Quantum Superpositions

We propose an interferometric scheme based on an untrapped nano-object subjected to gravity. The motion of the center of mass (c.m.) of the free object is coupled to its internal spin system magnetically, and a free flight scheme is developed based on coherent spin control. The wavepacket of the test object, under a spin-dependent force, may then be delocalized to a macroscopic scale. A gravity induced dynamical phase (accrued solely on the spin state, and measured through a Ramsey scheme) is used to reveal the above spatially delocalised superposition of the spin-nano-object composite system that arises during our scheme. We find a remarkable immunity to the motional noise in the c.m. (initially in a thermal state with moderate cooling), and also a dynamical decoupling nature of the scheme itself. Together they secure a high visibility of the resulting Ramsey fringes. The mass independence of our scheme makes it viable for a nano-object selected from an ensemble with a high mass variability. Given these advantages, a quantum superposition with 100 nm spatial separation for a massive object of 109 amu is achievable experimentally, providing a route to test postulated modifications of quantum theory such as continuous spontaneous localisation

AMP-CAD: Automatic Assembly Motion Planning Using C AD Models of Parts

Assembly with robots involves two kinds of motions, those that are point-to-point and those that are force/torque guided, the former kind of motions being faster and more amenable to automatic planning and the latter kind being necessary for dealing with tight clearances. In this paper, we describe an assembly motion planning system that uses descriptions of assemblies and CAD models of parts to automatically figure out which motions should be point-to-point and which motions should be force/torque guided. Our planner uses graph search over a potential field representation of parts to calculate candidate assembly paths. Given the tolerances of the parts and other uncertainties, these paths are then analyzed for the likelihood of collisions. Those path segments that are prone to collisions are then marked for execution under force/torque control. The calculation of the various motions is facilitated by an object-oriented and feature-based assembly representation. A highlight of this representation is the manner in which tolerance information is taken into account: Representation of, say, a part contains a pointer to the boundary representation of the part in its most material condition form. As first defined by Requicha, the most material condition form of a geometric entity is obtained by expanding all the convexities and shrinking all the concavities by relevant tolerances. An integral part of the assembly motion planner is the execution unit. Residing in this unit is knowledge of the different types of automatic EDR (error detection and recovery) strategies. Therefore, during the execution of the force/torque guided motion, this unit invokes the EDR strategies appropriate to the geometric constraints relevant to the motion. This system, called AMP-CAD, has been experimentally verified using a Cincinnati Milacron T3-726 robot and a Puma 762 robot on a variety of assemblies

Cooperative Manipulation using a Magnetically Navigated Microrobot and a Micromanipulator

The cooperative manipulation of a common object using two or more manipulators is a popular research field in both industry and institutions. Different types of manipulators are used in cooperative manipulation for carrying heavy loads and delicate operations. Their applications range from macro to micro. In this thesis, we are interested in the development of a novel cooperative manipulator for manipulation tasks in a small workspace. The resultant cooperative manipulation system consists of a magnetically navigated microrobot (MNM) and a motorized micromanipulator (MM). The MNM is a small cylinder permanent magnet with 10mm diameter and 10mm height. The MM model is MP-285 which is a commercialized product. Here, the MNM is remotely controlled by an external magnetic field. The property of non-contact manipulation makes it a suitable choice for manipulation in a confined space. The cooperative manipulation system in this thesis used a master/slave mechanism as the central control strategy. The MM is the master side. The MNM is the slave side. During the manipulation process, the master manipulator MM is always position controlled, and it leads the object translation according to the kinematic constraints of the cooperative manipulation task. The MNM is position controlled at the beginning of the manipulation. In the translation stage, the MNM is switched to force control to maintain a successful holding of the object, and at the same time to prevent damaging the object by large holding force. Under the force control mode, the motion command to the MNM is calculated from a position-based impedance controller that enforces a relationship between the position of the MNM and the force. In this research, the accurate motion control of both manipulators are firstly studied before the cooperative manipulation is conducted. For the magnetic navigation system, the magnetic field in its workspace is modeled using an experimental measurement data-driven technique. The developed model is then used to develop a motion controller for navigating of a small cylindrical permanent magnet. The accuracy of motion control is reached at 20 µm in three degrees of freedom. For the motorized micromanipulator, a standard PID controller is designed to control its motion stage. The accuracy of the MM navigation is 0.8 µm. Since the MNM is remotely manipulated by an external magnetic field in a small space, it is challenging to install an on-board force sensor to measure the contact force between the MNM and the object. Therefore, a dual-axial o_-board force determination mechanism is proposed. The force is determined according to the linear relation between the minimum magnetic potential energy point and the real position of the MNM in the workspace. For convenience, the minimum magnetic potential energy point is defined as the Bmax in the literature. In this thesis, the dual-axial Bmax position is determined by measuring the magnetic ux density passing through the workspace using four Hall-effect sensors installed at the bottom of an iron pole-piece. The force model is experimentally validated in a horizontal plane with an accuracy of 2 µN in the x- and y- direction of horizontal planes. The proposed cooperative manipulator is then used to translate a hard-shell small object in two directions of a vertical plane, while one direction is constrained with a desired holding force. During the manipulation process, a digital camera is used to capture the real-time position of the MNM, the MM end-effector, and the manipulated object. To improve the performance of force control on the MNM, the proposed dual-axial force model is used to examine the compliant force control of the MNM while it is navigated to contact with uncertain environments. Here, uncertain refers to unknown environmental stiffness. An adaptive position-based impedance controller is implemented to estimate the stiffness of the environment and the contact force. The controller is examined by navigating the MNM to push a thin aluminum beam whose stiffness is unknown. The studied cooperative manipulation system has potential applications in biomedical microsurgery and microinjection. It should be clarified that the current system setup with 10mm ×10 mm MNM is not proper for this micromanipulation. In order to conduct research on microinjection, the size of the MNM and the end-effector of the MNM should be down-scaled to micrometers. In addition, the navigation accuracy of the MNM should also be improved to adopt the micromanipulation tasks