This paper presents an energy regeneration-based hybrid control method for transfemoral prosthetic legs using a four-bar linkage mechanism. To do that, we consider a model of transfemoral prosthetic leg with three-degrees of freedom that employs a knee mechanism using a four-bar linkage mechanism. We also focus on suggesting a practical strategy for effective implementation rather than a complex algorithm. In this point of view, we devise a hybrid controller for the prosthetic leg. Actually, the motions of the hip mechanism of the leg are controlled by a PID control method and the knee joint is controlled by an impedance control method. We also consider an electrical energy regeneration module for effective energy utilization. Through an exemplary walk simulation, we show the availability of the hybrid controller for such a transfemoral prosthetic leg and also address the advantages of using such a four-bar mechanism and an energy regeneration module for effective driving the knee joint. It is finally concluded that the proposed hybrid controller can be applied for effective control of transfemoral prosthetic legs using such a four-bar mechanism.

This paper characterizes the dynamic deformation of soft fingertips applied to multi-fingered object manipulations of humanoid robots and analyzes its significance for multi-fingered operations. To this end, we present a dynamic model for soft-fingered object manipulations. For analyzing the control performance of soft-fingered manipulating tasks, we present a dynamic manipulation control scheme that considers the deformation effects of soft fingertips. The simulation results validate the influence of the dynamic deformation of soft fingertips during manipulation in a two-fingered operation, and will enable us to recognize its significance for precise manipulating tasks.

This paper provides the fundamental dynamic deformation features for soft-fingered object manipulation tasks. To this end, we present a dynamic model for an object manipulation system by a two-fingered hand using soft fingertips. The model reveals that soft fingertips employed in a multi-fingered hand lead to certain deformation effects during object manipulation that are closely related to the motion control of the manipulated object. Through several experimental works, we discuss on the deformational influence of soft fingertips during manipulation in a two-fingered operation.

In this paper, a hemisphere-shaped soft fingertip for soft fingers is developed and its modeling based on force distribution is presented. We first analyze the geometrical relation of the soft fingertip when it is deformed. Secondly, the force distribution of the soft fingertip is investigated by using a compressional strain mechanism. And then, we propose a nonlinear model of the soft fingertip which enables us to obtain the total contact force at the contact surface of each finger in manipulating tasks. Finally, the proposed force function is verified by experiment, where a tactile sensor is used to measure the contact force distribution in the contact surface and its total force. The developed soft fingertip and its force function can be usefully applied to soft-fingered manipulations.

This paper focuses on the fundamental deformation effect of soft fingertips as applied in soft-fingered object manipulations. In order to analyze the deformation effect, we first describe the dynamic relation of a two-fingered object manipulation using soft fingertips. From the dynamic relation, we show that the fundamental deformation effect of soft fingertips is essential for soft-fingered manipulations. A dynamic manipulation control method considering the deformation effect is also proposed. Simulation results show that the deformation effect of soft fingertips during the manipulation process is crucial for stable manipulation. Finally, we conclude that the deformation effect of soft fingertips is desirable to be properly considered in a manipulation control law for successful soft-fingered manipulation tasks.

In this paper, a modified two-step compliance control method for robot hands is proposed: resolved interfinger decoupling solver (RIFDS) and resolved interjoint decoupling solver (RIJDS). For this, we first investigate how many fingers are necessary to successfully implement stiffness characteristics in the operational space. RIFDS is then proposed to decompose the desired compliance characteristic specified in the operational space into the compliance characteristic in the fingertip space without interfinger coupling, and RIJDS is also proposed to decompose the compliance characteristic in the fingertip space without interjoint coupling. It is found in the process of RIFDS that some nondiagonal stiffness elements specified in the operational space cannot be planned arbitrarily, due to grasping geometry. Similar to independent finger control, RIJDS aims at independent joint control. This scheme facilitates the joint servo control. To show the effectiveness of the proposed compliance control method, some experimental results are illustrated for a compliant task by using two- and three-fingered hands, which consist of five-bar finger mechanisms. It is concluded that grasping geometry and finger structure are crucial to successfully performing multifingered hands operations.

In this paper we discuss the design and implementation of a concurrency control manager for Tachyon, a main-memory DBMS. Since a main-memory DBMS, unlike a disk-resident DBMS, performs all data updates or data retrievals by accessing main-memory only the portion of the cost for the concurrency control manager in the total cost for a data update or a data retrieval is fairly high. Thus, the development of an efficient concurrency control manager greatly accelerates the performance of the entire main-memory DBMS. Our concurrency control manager employs the two-phase locking protocol, and has the following characteristics. First, it adapts the partition as a locking granule, and thus effectively adjusts the trade-off between system concurrency and locking cost. Second, it enjoys low locking costs by maintaining lock information directly in the partition itself. Third, it provides the latch as a mechanism for physical consistency of system data. Our latch supports both shared and exclusive modes. and maximizes CPU utilization by combining the Bakery algorithm and the Unix semaphore facility. Fourth, for solving the deadlock problem, it periodically examines whether a system is in a deadlock state based on lock waiting information. In addition, we discuss various issues arising in development such as mutual exclusion of a transaction table, mutual exclusion of indexes and system catalogs, and phantom problem handling.

Based on the analysis of the stiffness relation between the operational space and the fingertip space of multifingered hands, this paper provides a guideline of task-based compliance planning for multifingered hands. 2D and 3D examples are illustrated to show the characteristics of the task-based stiffness matrix. It is shown that some of coupling stiffness elements cannot be planned arbitrarily due to grasping geometry. Through the analytical results, it is concluded that the operational stiffness matrix should be carefully specified by considering the location of compliance center and the grasp geometry of multifingered hands for successful grasping and manipulation tasks.

We provide a guideline for specifying compliance characteristics in the operational space of multifingered hands. From the analysis of the stiffness relation between the operational space and the fingertip space of multifingered hands, it is shown that some of the coupling stiffness elements cannot be planned arbitrarily. An independent finger-based compliance control method to achieve the given compliance characteristics is presented. Through the analytical results, it is concluded that the operational stiffness matrix should be carefully specified by considering the grasp geometry of multifingered hands for successful grasping and manipulation tasks, and the three-dimensional compliance control can also be achieved by a five-fingered human-like hand.

For a multi-fingered hand to grasp an object, there are numerous ways to grasp it stably, and thus an optimal grasp planning is necessary to find the optimal grasp point for achieving the objective of the given task. First, we define several grasp indices to evaluate the quality of each feasible grasp. Since the physical meanings of the defined grasp induces are different from each other, it is not easy to combine those indices to identify the optimal grasping. In this paper, we propose a new generalized grasping performance index to represent all of the grasp indices as one measure based on a non-dimensional technique. Through simulations, we show that the proposed optimal grasp planning is resemblant to the physical sense of human grasping.

For an object grasped by a robot hand to work in the compliance control domain, we first analyze a necessary condition for successful stiffness modulation in the operational space. Next, we propose a compliance control method for robot hands which consist of two steps: the RIFDS (resolved inter-finger decoupling solver) decomposes the desired compliance characteristic specified in the operational space into the compliance characteristic in the fingertip space without inter-finger coupling; and the RIJDS (resolved inter-joint decoupling solver) decomposes the compliance characteristic in the fingertip space into the compliance characteristic in the joint space without inter-joint coupling. According to the analysis results, the finger structure should be biomimetic in the sense that either kinematic redundancy or force redundancy are required to implement the proposed compliance control scheme. Five-bar fingered robot hands are treated as illustrative examples to implement the proposed compliance control method. To show the effectiveness of the proposed compliance control method, simulations are performed for two-fingered and three-fingered robot hands.

This paper deals with stiffness analysis for effective peg-in/out-hole tasks using multifingered robot hand without inter-finger coupling. We first observe the fact that some coupling stiffness elements cannot be planned arbitrary. Then, we analyze the conditions of the specified stiffness matrix in the operational space to successfully and more effectively achieve the given peg-in/out-hole tasks. It is concluded that the location of compliance center on the peg and the coupling stiffness element between the translational and the rotational direction play important roles for successful peg-in/out-hole tasks. Simulation results are included to verify the feasibility of the analytic results.

A compliance control strategy for robot manipulators is proposed by employing a self-adjusting stiffness function. To be specific, each entry of the diagonal stiffness matrix corresponding to task coordinate in Cartesian space is adaptively adjusted during contact along the corresponding axis based on the contact force with its environment. It can also be used for both unconstrained and constrained motions without any switching mechanism which often causes undesirable instability and/or vibrational motion of the end-effector. The experimental results show the effectiveness of the proposed method by employing a two-link direct drive manipulator interacting with an unknown environment.