At the end of the 20th century robot technology became well established as a reliable and economic source in industrial automation. On the other hand, it is claimed that even a general six or seven degree of freedom robot arm or a multifingered robot hand designed carefully and manufactured with very high precision lacks versatility in its use in a variety of tasks that must be done instead of a human. The lack of versatility or the clumsiness of present industrial robots is not due to the fine mechanism of such robots. Rather, the clumsiness shows a lack of our knowledge of everyday physics, in particular, a lack of knowledge of physics involving grasping and handling of various kinds of things and manipulating them with certain dexterity, in which tactile and vision sensings must be well coordinated.

A new approach to the control of indirect simultaneous positioning of deformable objects is presented. Many manufacturing processes that deal with deformable objects such as clothes and rubber sheets involve a positioning of multiple points on a deformable object. The multiple points should be guided simultaneously to the desired locations. Moreover, these positioned points cannot be manipulated directly. This operation is referred to as indirect simultaneous positioning. In this article, we will propose a new control law for indirect simultaneous positioning of a deformable object based on its uncertain model and will show the robustness of the proposed control law. First, a simplified physical model of a deformable object is developed for its positioning operation. Second, indirect simultaneous positioning of an extensible object is formulated. Based on a linearized model of an extensible object, we will propose a novel control law for indirect simultaneous positioning. Next, we will prove the robustness of the proposed control law theoretically. Finally, experimental results will show the robustness of our proposed control law against the discrepancy between a real fabric and its uncertain model.

A new type of a parallel wire-driven robot is proposed in order to reach ultra-high speed. The driving principle of parallel wire systems is described. Since wires can only pull and not push on an object, at least n+1 wires are needed in order to move the object in a n-dimensional space. In this paper, taking account of the effect of such redundancy on actuation, the motion stability in wire length coordinates is analyzed by using a Lyapunov function. Using “Vector Closure”, it is proven that the hand position and orientation converge to the corresponding desired values and the internal force also converges to the desired one. Moreover, by making good use of non-linear elasticity of parallel wire driven robots, it is claimed that the internal force arising from redundant actuation can effectively reduce vibration when the high-speed robot stops at desired points. As a result, ultra-high speed with more than 40 g(g:gravitational acceleration) can be attained by using relatively small actuators.

We present a general framework for modeling a class of mechanical systems for robotic manipulation, consisting of articulated limbs with redundant tendinous actuation and unilateral constraints. Such systems, that include biomorphically designed devices, are regarded as a collection of rigid bodies, inter-acting through connections that model both joints and contacts with virtual springs. Methods previously developed for the analysis of force distribution in multiple whole-limb manipulation are generalized to this broader class of mechanisms, and are shown to provide a basis for the control of co-contraction and internal forces that guarantee proper operation of the system. In particular, in the presence of constraints such as those due to limited friction between surfaces or object fragility, the choice of tendon tensions is crucial to the success of manipulation. An algorithm is described that allows to evaluate efficiently set-points for the control of tendon actuators that “optimally” (in a sense to be described) comply with the given constraints.

This paper proposes a grasp planning for a multifingered hand-arm robot in the presence of obstacles. When the hand grasps an object, neither the hand nor the arm should collide with obstacles. However, it is very difficult to generate a collision-free grasp configuration of the hand-arm robot due to its abundant degrees of freedom of motion. To overcome this difficulty, we first decompose the hand-arm robot into the multifingered hand part and the arm part. We develop two methods of the grasp planning. In one method, a collision-free configuration of the hand part is planned first. Then, the arm configuration is planned so as to enable the hand configuration. In the other method, the collision-free configuration of the arm part is planned first and the multi-fingered hand configuration second. The best method is selected according to the space structure of the environment. Various heuristics are developed to improve the efficiency of the planning and implementation of the system. Simulation results are presented.

This paper mainly concerns a vibrotactile sensor capable of generating impulsive high-frequency signals for exclusively distinguishing a slip phase from various other contact phases. We describe the structure of the vibrotactile sensor with surface ridges and, after analyzing the slip signals, conclude that the output signal originates in the free vibration of the ridge. By using a two-fingered robot hand with the sensor attached to its compliant endtips, we verify that the vibrotactile sensor has a slip phase isolating function and demonstrate object regrip control in real time.

This paper presents a new formulation of computing three-dimensional (3-D) frictional form-closure grasps of n robotic fingers. As 3-D form-closure grasps involve 6-D wrench space, we first propose a recursive reduction technique to transform the complicated problem in the 6-D space into a simpler 3-D one. Next, we rewrite the sufficient and necessary condition for form-closure grasps into its equivalent form of two sets of linear inequalities. Then, according to the linear inequality theory, the problem is transformed to searching for a set of points which ensure the inconsistency of each of the two linear inequality systems. To search for such points, we proposed two methods: The first one is based on testing whether the convex region formed by each linear inequality system is empty, while the second one relies on the potential field method. We have implemented the algorithm and confirmed their efficiency for the synthesis of 3-D form-closure grasps.

This paper deals with the stability of a rigid body under multiple contact forces. First, the problem is considered at the force planning level, and the stability of a force distribution is formulated. For this problem, the stiffness tensor is derived, and its basic properties are analyzed. Necessary and sufficient conditions for stability of a force distribution are established in an analytical form. These conditions, considered under unilateral frictional constraints, are studied on an illustrative example. Next, it is shown that stabilization of an unstable force distribution can be done by a simple control law. The stability conditions for this control law are formulated by transforming the stiffness tensor to the center of stiffness. Finally, conclusions on the contradiction between the Liapunov stability and the contact stability of the objects are drawn.

This paper attempts firstly to derive a mathematical model of the dynamics of a set of dual fingers with soft and deformable tips which grasps and manipulates a rigid object with some dexterity. To gain a physical insight into the problem, consideration is restricted to the case that the motion of the whole system is confined to a horizontal plane. Secondly on the basis of the derived model it is shown that the rotation of the object can be indirectly controlled by the change of positions of the center points of both contact areas on the object. Then, each of the center points of contact areas can be positioned by inclining the last link of each corresponding finger against the object. It is further shown that, when both forces of pressing the object becomes almost equal, the equation of motion of the object in terms of rotational angles assumes the form of a harmonic oscillator with a forcing term, which can be regulated coordinately by the relative angle between the two last links contacting with the object. It is also shown that dynamics of this system satisfy passivity. Finally, design problems of control for dynamic stable grasping and enhancing dexterity in manipulating things are discussed on the basis of passivity analysis.

GECCO-99 STUDENT WORKSHOP

(13th July, 1999)

The Genetic and Evolutionary Computation Conference (GECCO-99) in Orlando, Florida, USA was the biggest ever conference on evolutionary computation. It was a joint meeting of the long standing biannual International Conference on Genetic Algorithms (ICGA) which has been running since 1985 and the more recent annual Genetic Programming (GP) conference (which started in 1996). Before the start of each GP conference there has been a workshop for PhD students research in GP. This year Dr. O'Reilly (MIT AI lab) organized a joint graduate student workshop for research students principally concerned with any aspect of evolutionary computation, Evolvable Hardware, DNA computation, Artificial Life or Agents.

This paper describes the design of a small-scale three degree-of-freedom compliant-mechanism-based manipulator with an approximately 2 cm×2 cm×2 cm cubic workspace. The manipulator exhibits a significantly larger range of motion and better spatial structural properties than a conventional compliant mechanism, due primarily to a unique flexure joint developed by the authors. A brief description of the mechanics of the flexure joint is followed by a description of the design of the manipulator. Following the mechanical description, the design of the low-level manipulator controller is discussed. Finally, data is presented that demonstrates manipulator performance.

This paper approaches the design problem of suitable grippers for a robotic arm to pick up horticulture products. General considerations have been pointed out and main concepts and mechanical designs have been discussed and proposed by sketches and drawings for an easy understanding of “on-field” problems and feasible solutions. Pneumatic actuation has been proposed with suitable grasp force control by using commercial components. Specific attention has been focused on tomato horticulture for a practical design and prototyping of a device for laboratory experiments.