Satoshi Makita

3D multifingered caging: Basic formulation and planning

In this paper, three-dimensional caging by a multifingered hand (3D multifingered caging) is studied. Caging is a method of object constraining in which robot bodies surround an object and make it inescapable from the ldquocagerdquo composed of the robot bodies. In 3D multifingered caging, position-controlled robot hands can constrain objects and transport them, and force control is not necessary. Furthermore, even a robot hand with low degrees of freedom can constrain an object to manipulate. We show some examples of 3D multifingered caging. Then, we derive sufficient conditions for caging objects, and propose a method to plan configurations of a robot hand for caging with the sufficient conditions.

Analysis of indeterminate contact forces in robotic grasping and contact tasks

In this paper, we analyze indeterminate contact forces in robotic grasping and contact tasks. Previous studies by Omata and Nagata showed that there is a constraint on static friction forces, which is derived from contact kinematics, in rigid-body power grasps. The set of possible contact forces can be calculated using the constraint. This approach can be applied to not only mechanical analysis of power grasps but also that of other robotic contact tasks. However, there are some cases where Omata and Nagatas formulation generates paradoxical results on contact forces. In this paper, we investigate this problem and propose a modified method to calculate the set of possible indeterminate contact forces. We also study how to reduce the computation.

3D two-fingered caging for two types of objects: sufficient conditions and planning

Caging is a method to capture an object geometrically by robots. Position-controlled robots can make the object inescapable from the robot formation. Moreover less number of mobile robots or a robot hand with low degrees of freedom can constrain the object with considering concavity of the object. In this paper, we propose two types of caging: ring-type and waist-type, which both can be accomplished by a two-fingered hand. We derive sufficient conditions for caging of the two types and construct RRT-based motion planner for caging by a robotic arm/hand system. In motion planning, we find one of final configurations that satisfy the sufficient conditions and produce a path of robot configuration to the goal. With object recognition using AR picture markers, we can acquire geometrical information of objects and plan robot motion for caging. We show some experimental results of planning and execution of planned caging motion for four objects.

A quantitative test for the robustness of graspless manipulation

In this paper, the robustness of graspless manipulation (or nonprehensile manipulation) is investigated. We derive some new constraints for static frictional forces in graspless manipulation, which gives us more accurate evaluation of the robustness of graspless manipulation than previous studies. We also present a procedure to calculate a measure of the robustness based on linear programming. Numerical examples are shown to prove that our new method works well even when previous methods make an inappropriate evaluation

Motion planning for 3D multifingered caging with object recognition using AR picture markers

Caging is a method to capture an object geometrically by position-controlled robots without any force and tactile sensors. Many previous researches focused on caging constraints of objects, and those on planning are few. In this paper, we present a motion planner for caging by a multifingered hand and a manipulator to produce whole motion which includes approaching to a target object and capturing it without any collisions. We derive sufficient conditions required for the caging tasks about three caging patterns. Since the planner requires the object properties including the position and orientation of the object, we adopt an object recognition using AR picture markers. We apply the proposed method to caging about four target objects: a cylinder, a ring, a mug and a dumbbell. Some experimental results shows that each motion are successfully planned, and executed by the arm/hand system.

Manipulation of submillimeter-sized electronic parts using force control and vision-based position control

This paper presents manipulation of small electronic parts whose size is submillimeter order or smaller. For assembly of small parts which are components of electronic devices, we need two key technologies: accurate position control and force control in handling them. In this paper, we utilize a four-degree-of-freedom assembly robot with a camera for position control. This vision-based assembly system gives us positioning accuracy of micrometer order. We also control the pressing load of the robot in pick-and-place of small objects indirectly with mechanical springs and a displacement sensor by changing resilience force of springs actively. We execute some experiments to handle small electronic parts using above-mentioned active force control and vision-based position control.

Evaluation of finger configuration for partial caging

In caging, an object is geometrically confined by position-controlled robots and never escapes from the constraint. Caging has some advantages over conventional grasping, and its applications have been performed not only in 2D but also in 3D scenes with various actual robots. However, the conditions of complete caging are not always satisfied due to limited robot configuration. This paper studies partial caging, in which an object is incompletely confined by robots or obstacles and is able to escape from the constraint. As an example of partial caging, a circular object moving in the planar hand is considered. We investigate an effect of arrangement of its fingertips, which prevents the object from escaping outside through the gap between the fingertips. Some simulation results show differences of difficulty of escaping for the object according to width of the gap and angle of the fingers. In addition, ease of entering the hand through the gap of the fingers is also evaluated. From these two scores on partial caging, we define an ability index for the hand, which represents the hand can easily capture an object and confine it without any finger motion.

Joint torque optimization for quasi-static graspless manipulation

Graspless manipulation is easily interfered by external disturbances because the manipulated object is not completely held by a robot hand and supported by an environment such as a floor. Thus it is important to ensure the manipulation is executed robustly against some disturbances. In our works, a rigid-body-based analysis of indeterminate contact forces for quasi-static graspless manipulation has been proposed, and also joint torque optimization for robotic hands. The joint torques of the robot is determined in consideration of some robustness of manipulation against disturbances, which include changes or estimation errors of friction. In the analysis of contact forces in quasi-statics, a kinematic constraint on static friction is considered to exclude infeasible sets of frictional force, with considering treatment of kinetic friction. Additionally, new objective functions for computing optimal joint torques in both static and quasi-static graspless manipulation are proposed. Some numerical samples of both applications are shown to verify our proposed methods.

Evaluation of quality of partial caging by a planar two-fingered hand

In partial caging, an object is partially constrained by robots and is able to escape from there. Although complete caging ensures the hand never releases the confined object, insufficient degrees of freedom of robots does not often satisfy the conditions for caging. Partial caging, however, can be accomplished even by robots having such mechanical restriction. We consider a case that an object moves in the semi-closed region formed by a planar robot hand with two fingers, as an example of partial caging in two-dimensional space. Then the parameters of fingers: joint angles interfere in the object motion to escape from the hand through the gap between the fingertips. Some simulation results show differences of difficulty of escaping according to arrangement of fingers, and factors interfering in the difficulty are analyzed. Additionally, we also evaluate ease of entering the hand through the gap and define an ability index of robot hand for partial caging with the above two evaluation scores. Then a high index score indicates that the hand assumed to be able to capture objects easily and confine it without any finger motion. It can be utilized for mechanical design and controlling strategies of robots in capturing objects. Graphical Abstract

A new formulation for indeterminate contact forces in rigid-body statics

Friction forces play an important role in analysis of robotic contact tasks. In most of related studies, only “local” constraint on friction forces imposed by, for example, Coulombs law is considered. However, when contact forces are indeterminate, such local constraint is not enough to assess possible friction forces appropriately. Although Omata and Nagata derived additional “global” constraint on indeterminate friction forces from rigid-body kinematics, it is not accurate in some cases. Thus we propose a modified formulation for indeterminate friction forces in rigid-body statics in this paper. It solves two major problems in Omata and Nagatas formulation. Its validity is successfully demonstrated in numerical examples for evaluation of the robustness of grasping.