Force-closure Grasps Research Articles

A Fast Grasp Planning Algorithm for Humanoid Robot Hands.

Grasp planning is crucial for robots to perform precision grasping tasks, where determining the grasp points significantly impacts the performance of the robotic hand. Currently, the majority of grasp planning methods based on analytic approaches solve the problem by transforming it into a nonlinear constrained planning problem. This method often requires performing convex hull computations, which tend to have high computational complexity. This paper proposes a new algorithm for calculating multi-finger force-closure grasps of three-dimensional objects based on humanoid multi-fingered hands. Firstly, sufficient conditions for the multi-finger force-closure grasps of three-dimensional objects are derived from a point contact model with friction. These three-dimensional force-closure conditions are then transformed into two-dimensional plane conditions, leading to a simple algorithm for multi-finger force-closure determination. This method is purely based on geometric analysis, resulting in low computational demands and enabling the rapid assessment of force-closure grasps, which are beneficial for real-time applications. Finally, the algorithm is validated through two case studies, demonstrating its feasibility and effectiveness.

Fast Force-Closure Grasp Synthesis With Learning-Based Sampling

Anthropomorphic robotic hands have been widely investigated to dexterously manipulate objects because of their anatomical similarity to the human hand. However, the large dimension of configuration space challenges the real-time performance of existing grasp planning methods and drastically limits the application of anthropomorphic hands. In this letter, we propose a fast force-closure grasp synthesis (FFCGS) method for the anthropomorphic hand to efficiently grasp unknown objects. The FFCGS is implemented by using a signed distance field (SDF) as input. Firstly, a network that samples feasible 6D wrist poses is trained in an end-to-end fashion to reduce the dimension of search space. Furthermore, a fast optimization algorithm is presented to find finger configurations for force-closure precision grasp based on the differentiable Q-distance metric. We validate our method in both a simulated and a real-world environment. Experiment results show that the proposed FFCGS achieves a significantly improved performance in terms of time efficiency (5 times faster), grasp quality metrics, and success rate (5%-10% improvement) over benchmark methods. The outcomes of this study have great significance in promoting the motion planning of robot hand-arm systems and upper-limb prostheses.

Grasping and Object Reorientation for Autonomous Construction of Stone Structures

Building large and stable structures from highly irregular stones is among the most challenging construction tasks with excavators. In this letter, we present a method for grasp planning and object manipulation that enables the world's first autonomous assembly of a large-scale stone wall with an unmanned hydraulic excavator system. Our method utilizes point clouds and mesh surface reconstruction of stones in order to plan grasp configurations with a 2-jaw gripper mounted on the excavator. Besides considering the geometry of the stone to sample force closure grasps, the grasp planner also takes into account collision constraints during object pick and place, informed by a LiDAR based point cloud map. Furthermore, we show an approach to reorient arbitrarily shaped objects that are not feasible to be directly placed at the desired location without violating collision constraints. Using a physics engine, we find a settled intermediate pose that allows direct placement and is reachable from the initial stone pose. The applicability of the proposed grasp planning method is demonstrated with the construction of a dry stone wall composed of over one hundred boulders using an autonomous excavator. We show a high primary grasp success rate (82.2%) and illustrate how the system recovers from slippage by relocating the object and re-planning the grasp correspondingly.

Self-adaptive Stable Grasp of Two-finger End-effector: A Review

There have been growth demands for two-finger end-effector in agricultural and industrial because of the simple structure and control strategy. This paper reviews the human grasp behaviour, design of two-finger end-effectors, and research on self-adaptive stable grasp control. Human grasp behaviors such as grasp pattern and self-adaptive grasp provide useful information for humanoid two-finger end-effector. Most of the two-finger gripper and intelligent grasp strategy are focused on the stable grasp for regular object at present time. The self-adaptive stable grasp strategies of two-finger end-effector are presented by force-closure grasps strategy, contact stability grasp strategy and grasp synthesis strategy. Self-adaptive stable grasp synthesis strategy should consider the influence factor include geometric of contact surface and interaction of center of mass. In addition, the future work on two-finger self-adaptive stable grasp for 3D irregular object and 3D soft object is also reviewed.

Shallow-Depth Insertion: Peg in Shallow Hole Through Robotic In-Hand Manipulation

This letter presents a novel robotic manipulation technique suitable for shallow-depth insertion , which refers to the assembly of a relatively thin peg-like object into a hole with a shallow depth, as can be seen in a cell phone battery insertion for example. Our technique features dexterous manipulation actions that combine into a complete insertion operation, as also commonly demonstrated by humans performing the battery insertion task. The quasistatic stability of the presented insertion process is shown by constructing the space of force-closure grasps and manipulation primitives to navigate the space by changing the grasps. Our technique is directly applicable to a simple hardware setting with the conventional parallel-jaw gripper installed on an industrial robot arm. A set of experiments performed with our software demonstrates the effectiveness of our technique with a high success rate.

A Randomized Approach in Identifying High Quality Force Closure Grasp from Contact Points in Real Time

We proposed a randomized algorithm that can effectively identify a large number of high quality force closure grasps in short time. This task is very important when we consider grasping in real time where a large number of force closure grasps are needed as a candidate for planning in higher level. The key idea of our method is that a concurrent grasp is usually a high quality grasp and a concurrent grasp can be quickly identified by providing heuristic in choosing a concurrent point. A comparison of our method with other methods was performed and the result indicates that our method outperforms other methods.

Covering Folded Shapes

Can folding a piece of paper flat make it larger? We explore whether a shape S must be scaled to cover a flat-folded copy of itself. We consider both single folds and arbitrary folds (continuous piecewise isometries \(S\to\mathbb{R}^2\)). The underlying problem is motivated by computational origami, and is related to other covering and fixturing problems, such as Lebesgue's universal cover problem and force closure grasps. In addition to considering special shapes (squares, equilateral triangles, polygons and disks), we give upper and lower bounds on scale factors for single folds of convex objects and arbitrary folds of simply connected objects.

Output-Sensitive Computation of Force-Closure Grasps of a Semi-Algebraic Object

We propose a technique which significantly simplifies the computation of frictionless force-closure grasps of a curved planar part <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$P$</tex></formula> . We use a colored projection scheme from the three-dimensional wrench space to two-dimensional screens, which allows us to reduce the problem of identifying combinations of arcs and concave vertices of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$P$</tex></formula> that admit frictionless force-closure grasps, to colored intersection searching problems in the screens. We show how to combine this technique with existing intersection searching algorithms to obtain efficient, output-sensitive algorithms to compute all force-closure grasps of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$P$</tex></formula> , where at most four hard, frictionless point contacts exert exactly four wrenches on <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$P$</tex></formula> . If the boundary of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$P$</tex></formula> consists of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$n$</tex></formula> algebraic arcs of constant complexity and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$m$</tex></formula> concave vertices, we show how to compute all force-closure grasps with: <orderedlist continuation="restarts" numeration="bullet" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <listitem><para>four contacts along four arcs in <formula formulatype="inline"> <tex Notation="TeX">$O(n^{8/3}\log ^{1/3}n+K)$</tex></formula> time;</para></listitem></orderedlist>

A new strategy combining empirical and analytical approaches for grasping unknown 3D objects

This paper proposes a novel strategy for grasping 3D unknown objects in accordance with their corresponding task. We define the handle or the natural grasping component of an object as the part chosen by humans to pick up this object. When humans reach out to grasp an object, it is generally in the aim of accomplishing a task. Thus, the chosen grasp is quite related to the object task. Our approach learns to identify object handles by imitating humans. In this paper, a new sufficient condition for computing force-closure grasps on the obtained handle is also proposed. Several experiments were conducted to test the ability of the algorithm to generalize to new objects. They also show the adaptability of our strategy to the hand kinematics.

Procedimiento Geométrico para la Síntesis Automática de Prensiones con Equilibrio de Fuerzas de Cuatro Dedos sobre Objetos Poliédricos

The synthesis of Force-Closure Grasps is one of the fundamental problems in the grasp and manipulation of objects by means of mechanical hands. In this work a geometric method to determine force-closure grasps on polyhedral objects is presented. First the sets of faces whose relative orientations and positions allow obtaining force-closure grasps (concurrent prensiones, flat-pencils and regulus) are determined. Second, these sets are evaluated using a quality function and the best one is selected for the grasp; and third, on the selected set faces the fingertip contact points are determined such that they assure the force-closure property. This method is based on geometric operation in the 3D physical space and do not present iterative loops. The article includes a comparison of the resulting grasps with the optimum ones in different cases.

Finding locally optimum force-closure grasps

This paper presents an iterative procedure to find locally optimum force-closure grasps on 3D objects, with or without friction and with any number of fingers. The object surface is discretized in a cloud of points, so the approach is applicable to objects with any arbitrary shape. The approach finds an initial force-closure grasp that is then iteratively improved through an oriented search procedure. The grasp quality is measured considering the largest perturbation wrench that the grasp can resist with independence of the direction of perturbation. The efficiency of the algorithm is illustrated through numerical examples.

Positive Span of Force and Torque Components in Three-Dimensional Four-Finger Force-Closure Grasps

Testing whether a given grasp achieves force closure is a fundamental problem in grasping. Unfortunately, most of the force-closure testing methods avoid dealing with the true quadratic friction cones by resorting to some linear approximation which unavoidably sacrifices completeness and accuracy. This paper presents a method, considering the true nonlinear friction cone, that can be used as a filter that quickly rejects non-force-closure grasps. The method is based on a necessary condition stating that a force-closure grasp must be able to generate wrenches that positively span the force space and the torque space separately. The geometric relationship between the friction cones and the corresponding force space and torque space is analyzed to help construct an efficient test of the condition. Due to the superior speed of the test over a complete method, the overall performance improvement is paramount. In our experiment, a speed-up factor of 20 or greater can be achieved when testing a large number of grasps on various test objects.

Dynamic Analysis and Control Synthesis of Grasping and Slippage of an Object Manipulated by a Robot

Grasping an object by a cooperating system such as multi-fingered hands and multi-manipulator robotic system has received much attention. Research has focused on analysis of force-closure grasps and the synthesis of optimal grasping, when there is no slipping condition. Although the control system is designed to keep the contact force in the friction cone and avoid the slipping condition, slippage can occur for many reasons. In this research, dynamics analysis and control synthesis of a manipulator moving an object on a horizontal surface using the contact force of an end-effector are performed considering the slipping condition. Equality and inequality equations of frictional contact conditions are replaced by a single second-order differential equation with switching coefficients in order to facilitate the dynamic modeling. Accuracy of this modeling is verified by comparing the results of the model with those of SimMech. Using this modeling of friction, a set of reduced order form is obtained for equations of motion of the system. A new method is proposed to control the object motion and the end-effector undesired slippage based on the reduced form. Finally, performance of the method is evaluated both numerically and experimentally.

Computation of force-closure grasps: an iterative algorithm

Computation of grasps with form/force closure is one of the fundamental problems in the study of multifingered grasping and dextrous manipulation. Based on the geometric condition of the closure property, this paper presents a numerical test to quantify how far a grasp is from losing form/force closure. With the polyhedral approximation of the friction cone, the proposed numerical test can be formulated as a single linear program. An iterative algorithm for computing optimal force-closure grasps, which is implemented by minimizing the proposed numerical test in the grasp configuration space, is also developed. The algorithm is computationally efficient and generally applicable. It can be used for computing form/force-closure grasps on 3-D objects with curved surfaces, and with any number of contact points. Simulation examples are given to show the effectiveness and computational efficiency of the proposed algorithm.

GRASP PLANNING WITH FOUR FRICTIONAL CONTACTS ON POLYHEDRAL OBJECTS

This paper addresses the problem of computing force-closure grasps with four non-coplanar contact points. The proposed approach in this work to determine force-closure grasp, is valid for sets of four faces with coplanar or non-coplanar normal, and is based on geometric operations. First, the sets of four object faces that due to their relative orientations and positions allow concurrent, flat-pencil and regulus types of grasp are determined; second, these sets are evaluated with a quality function and the best one is selected for the grasp; Finally, on the selected faces, according to the possible types of non-planar grasp, four contact points assuring a force-closure grasp are determined.

GraspIt!

A robotic grasping simulator, called Graspit!, is presented as versatile tool for the grasping community. The focus of the grasp analysis has been on force-closure grasps, which are useful for pick-and-place type tasks. This work discusses the different types of world elements and the general robot definition, and presented the robot library. The paper also describes the user interface of Graspit! and present the collision detection and contact determination system. The grasp analysis and visualization method were also presented that allow a user to evaluate a grasp and compute optimal grasping forces. A brief overview of the dynamic simulation system was provided.

On Quality Functions for Grasp Synthesis, Fixture Planning, and Coordinated Manipulation

Planning a proper set of contact points on a given object/workpiece so as to satisfy a certain optimality criterion is a common problem in grasp synthesis for multifingered robotic hands and in fixture planning for manufacturing automation. In this paper, we formulate the grasp planning problem as optimization problems with respect to three grasp quality functions. The physical significance and properties of each quality function are explained, and computation of the corresponding gradient flows is provided. One noticeable property of some of these quality functions is that the optimal solutions are also force-closure grasps if they do exist for the given object. Furthermore, when specialized to two-fingered or three-fingered grasps on a spherical object, the optimal solutions become the familiar antipodal grasp, or the symmetric grasp, respectively. Thus, by following the gradient flows with arbitrary initial conditions, the optimal grasp synthesis problem is solved for objects with smooth geometries manipulated by hands with any number of fingers. Also, note that our solutions do not involve linearization of the friction cones. We discuss two simplified versions of these problems when real-time solutions are needed, e.g. coordinated manipulation of a robotic hand with contact points servoing. We give simulation and experimental results illustrating validity of the proposed approach for optimal grasp planning. Note to Practitioners: This paper presents three new quality functions for comparing and planning grasps and fixtures. These measures improve on the traditional measure of force closure. We propose a method for computing the optimal solutions of these functions, and a method for reducing their computation time through reasonable simplification/approximation. Preliminary experiments with a three-fingered robotic hand demonstrate that the proposed functions can be used to optimize the grasp quality during manipulation/manufacturing, and keep the optimal grasp configuration once it is reached. However, we only obtain the local optimal solutions for the functions without simplification except for some special cases. We also assume that the object/workpiece is ideally rigid in all three functions. In future research, we will improve these limitations through a compliance model.

A Pseudodistance Function and its Applications

By using the concept of gauge function, a pseudodistance function is defined for quantifying the clearance or the penetration depth of two convex point sets, depending on whether they separate or intersect. The linear programming formulations (for convex polyhedra) and the nonlinear constrained optimization formulations (for general convex objects) are presented for its calculation. For a pair of convex polyhedra, the pseudodistance function is differentiable almost everywhere with respect to the coordinate vectors of their vertices. Sufficient conditions for the differentiability and the characterization of its derivative are presented. By applying the pseudodistance function to the wrench space, a numerical measure of multifingered grasps is defined, which can be used for qualitative test and quantitative analysis of the force-closure property. On this basis, two algorithms for planning optimal force-closure grasps on general three-dimensional objects are developed. In addition, the application of the pseudodistance function in robot path planning is also demonstrated.

Heuristic approach to construct 3-finger force-closure grasps for polyhedral objects

In this paper a heuristic approach for the generation of force closure grasps with a three-finger mechanical hand is presented. First, the sets of three object faces that allow a force closure grasp are detennined considering their relative orientations and positions; second, these sets are evaluated using a quality function; and third, the contact points of the fingers on the object faces with the best quality are detennined using a heuristic that allows a fast computation and ensures a force-closure grasp.

Synthesis of force-closure grasps on 3-d objects based on the Q distance

The synthesis of force-closure grasps on three-dimensional (3-D) objects is a fundamental issue in robotic grasping and dextrous manipulation. In this paper, a numerical force-closure test is developed based on the concept of Q distance. With some mild and realistic assumptions, the proposed test criterion is differentiable almost everywhere and its derivative can be calculated exactly. On this basis, we present an algorithm for planning force-closure grasps, which is implemented by applying descent search to the proposed numerical test in the grasp configuration space. The algorithm is generally applicable to planning optimal force-closure grasps on 3-D objects with curved surfaces and with arbitrary number of contact points. The effectiveness and efficiency of the algorithm are demonstrated by using simulation examples.