Simple End Effectors Research Articles

Robotic Edge-Rolling Manipulation: A Grasp Planning Approach

This letter presents a novel robotic manipulation technique that we call robotic edge rolling. It refers to transporting a cylindrical object by rolling on its circular edge, as human workers might maneuver a gas cylinder on the ground. Our robotic edge rolling is achieved by controlling the object to both roll on its bottom edge in contact with the ground and slide on the surface of the robot's end effector. It can thus be regarded as a form of robotic dexterous, in-hand manipulation with nonprehensile grasps. We address the problem of grasp planning for edge rolling by studying how to design appropriately shaped end effectors with zero internal mobility and how to find feasible grasps for stably rolling the object quasi-dynamically with our simple end effectors. An extensive set of experiments is performed with a conventional manipulator arm on not only flat surfaces but also a U-shaped half-pipe track. Long-range edge rolling is demonstrated with a modular mobile manipulator that is capable of active steering control.

Object Picking Through In-Hand Manipulation Using Passive End-Effectors With Zero Mobility

This letter presents a new method for picking objects through quasistatic in-hand manipulation with end-effectors that have no degrees of freedom. Our stable manipulation/grasp planning is achieved with two contacts at fixed distance and the force of gravity, and is provably complete and correct. Practically, our robotic in-hand manipulation technique can facilitate low-cost manipulation and render simple end-effectors such as the parallel-jaw gripper more dexterous in picking, placing, and handing-off objects in case, for example, failing actuated grippers become frozen and it is impossible to exert sufficiently large internal forces. Our picking technique can also be applied to placing objects. Implementation and experimentation on a custom-made direct-drive manipulator and a conventional manipulator are presented. Many experiments were performed for both picking and placing and the results demonstrate usefulness of this method for manipulating a variety of common objects, with different geometries and surface conditions.

Getting to grips with automated prepreg handling

Automated manufacturing of composite parts based on prepreg material is receiving increased interest with the rising use of composite materials for high-performance applications. The two main automation alternatives for prepreg layup, automated tape layup and fiber placement, are not cost-effective for all types of products, and manual labor is common for the manufacturing of complex parts in low manufacturing volumes. Alternatives to the two dominant automation solutions have been pursued, but so far these have had a limited impact in industrial applications. This paper presents four different solutions for automated layup of prepreg plies to flat laminates that can be formed in a subsequent forming process, which decrease the system complexity. The solutions target products where the layup of flat laminates today is done manually due to technical limitations or cost considerations. The layup solutions must manage challenges caused by material properties such as low material rigidity and tack, and be able to handle a high number of ply shapes. All four solutions are designed for prepreg that is covered with a stiff backing paper. The aim of the paper is to analyze and compare the four solutions. It can be concluded that the most versatile solution is a dual-arm robot equipped with simple end effectors. The dual-arm solution presents a possibility to control the pick-up and lay-down motions that make peeling motions possible, which is advantageous when picking material that has tacked to the pickup surface.

OCOG: A common grasp computation algorithm for a set of planar objects

This paper addresses the problem of defining a simple End-Effector design for a robotic arm that is able to grasp a given set of planar objects. The OCOG (Objects COmmon Grasp search) algorithm proposed in this paper searches for a common grasp over the set of objects mapping all possible grasps for each object that satisfy force closure and quality criteria by taking into account the external wrenches (forces and torque) applied to the object. The mapped grasps are represented by feature vectors in a high-dimensional space. This feature vector describes the design of the gripper. A database is generated for all possible grasps for each object in the feature vector space. A search algorithm is then used for intersecting all possible grasps over all parts and finding a common grasp suitable for all objects. The search algorithm utilizes the kd-tree index structure for representing the database of the sets of feature vectors. The kd-tree structure enables an efficient and low cost nearest-neighbor search for common vectors between the sets. Each common vector found (feature vector) is the grasp configuration for a group of objects, which implies the future end-effector design. The final step classifies the grasps found to subsets of the objects, according to the common vectors found. Simulations and experiments are presented for four objects to validate the feasibility of the proposed algorithm. The algorithm will be useful for standardization of end-effector design and reducing its engineering time.