Yuichi Tsumaki

Stiffness Analysis and Design of a Compact Modified Delta Parallel Mechanism

In our previous work, we developed a compact 6-DOF haptic interface as a master device which achieved an effective manual teleoperation. The haptic interface contains a modified Delta parallel-link positioning mechanism. Parallel mechanisms are usually characterized by a high stiffness, which, however, is reduced by elastic deformations of both parts and bearings. Therefore, to design such a parallel mechanism, we should analyze its structural stiffness, including elastic deformations of both parts and bearings. Then we propose a simple method to analyze structural stiffness in a parallel mechanism using bearings. Our method is based on standard concepts such as static elastic deformations. However, the important aspect of our method is the manner in which we combine these concepts and how we obtain the value of the elasticity coefficient of a rotation axis in a bearing. Finally, we design a modified Delta mechanism, with a well-balanced stiffness, based on our method of stiffness analysis.

Singularity-consistent kinematic redundancy resolution for the S-R-S manipulator

A kinematic redundancy resolution approach for the S-R-S manipulator is introduced which uses arm plane orientation as the redundancy resolution criterion. The approach can handle both kinematic and algorithmic singularities in a consistent way, without introducing motion instabilities, yielding thereby motions that can be predicted easily by a human operator. The method is verified by experiments with a seven-DOF Mitsubishi Heavy Industries PA10-7C arm and data from both simulations and experiments is presented.

Static Walk of a Humanoid Robot Based on the Singularity-Consistent Method

This paper addresses the problem of naturally looking and energy efficient walk of biped humanoids. We presuppose that such walk requires motion control capability around kinematic singularities, such that the knee can be fully extended. This problem is tackled by adopting the singularity-consistent method developed for manipulator motion control at and around kinematic singularities. We implemented the method with a HOAP-2 humanoid robot, demonstrating stable static walk as a first step in this direction

A Walking Pattern Generator around Singularity

Humans utilize the extended-knee configuration to achieve efficient walk. A humanoid robot, however, cannot do so, since this posture is a singular one, and hence, an extremely large joint velocity would be generated, provided a conventional control method is used. Some other methods exist, though, that are able to handle motion control at such postures. One example is the singularity consistent (SC) approach, which we used in a previous work to generate a static walk for a humanoid robot. In this paper, we propose a new method to generate a dynamic walking pattern through the singularity neighborhood, by using proper ankle control and pattern generation based on a spherical inverted pendulum model. Experimental results show the effectiveness of this approach

Development of a skincare robot

With aging, human skin develops a dry condition called senile xerosis. The skin lesion can be prevented by daily skin care such as applying an ointment containing moisturizing factors several times a day. Aged persons, however, have difficulties in accessing the back and rely therefore on nursing care for such treatment. Unfortunately, in underpopulated areas such nursing care may not always be available. To tackle this problem, the concept of a skincare robot is proposed. The feasibility of the concept is then confirmed by designing a real skincare robot and by performing experiments for applying ointment on humans back. The robot developed is able to recognize the shape of the body, to plan the appropriate motion paths for the hand, and to execute the task without applying any excessive forces.

Motion analysis of a kinematically redundant seven-DOF manipulator under the singularity-consistent method

The SC method is applied to a 7-DOF manipulator arm with a spherical wrist and zero joint offsets, such as the Mitsubishi Heavy Industries PA-10 arm. We obtain two vector fields for driving the positioning subchain and one vector field for the wrist, in analytical form. The former two vector fields are used to realize decoupled motion control of the end-effector and the arm plane, respectively. No additional singularities are introduced, and motion through kinematic singularities is stable and cyclic.

Design of a Compact 6-DOF Haptic Device to Use Parallel Mechanisms

We present design of a compact haptic device in which parallel mechanisms are utilized. The design realizes a large workspace of orientational motion in a compact volume of the device. The device is a parallel-serial mechanism consisting of a modified DELTA mechanism for translational motion and a spatial five-bar gimbal mechanism for orientational motion. We derive an analytical model of stiffness for the modified DELTA mechanism which we utilize for the design of a stiff platform for translational motion. The model shows that the compliance matrix is a function of kinematic parameters as well as elastic parameters of each mechanical element. Configuration dependency of the compliance matrix is therefore an important point to be noticed.

Biped walk based on vertical pivot motion of linear inverted pendulum

Typical human walking patterns include extended-knee postures. Humanoid robots, however, walk with bended knees in order to avoid controlling motion in the presence of kinematic singularities, appearing at the extended-knee postures. Hence, the walking motion patterns of humanoid robots are not as natural and as efficient as those of humans. We have addressed the problem in previous works and shown that, for a static walking pattern, it is possible to include the extended-knee postures, provided control is based on the singularity-consistent (SC) approach, which can ensure stable control in the neighborhood of kinematic singularities. In this paper, we propose a method to generate a dynamic walking pattern including up-and-down waist motion, such that the support leg enters the singularity neighborhood in the middle of each support phase. The basic motion pattern is generated with the help of a linear inverted pendulum model, whose pivot is controlled in the vertical direction to ensure the up-and-down waist motion, independently of the horizontal motion of the pendulum. Experimental results show the effectiveness of our approach.

Walking control using the SC approach for humanoid robot

Conventional humanoid robots cannot achieve human like walking patterns. The reason is that human walking patterns include singularity configurations, i.e. configurations with the extended knees. Such kinematic singularities cause spurious joint motions. In other words, a humanoid robot cannot handle the singularity problem. On the other hand, humans make use of singularity configurations, because at such configurations large forces in certain directions can be generated. Therefore, singularities play an important roll for creating efficient walking patterns. In our previous work, we proposed the singularity consistent (SC) approach that can handle the singularity problem without instabilities. Until now, the approach has been applied to various manipulators. In this paper, we implement the SC approach into a walking pattern generator for a humanoid. Some issues and resolutions addressed. Experimental results show the effectiveness of our approach

Walking control around singularity using a Spherical Inverted Pendulum with an Underfloor Pivot

Humans utilize the configuration with extended knees to achieve efficient walk. A humanoid robot, however, cannot do so, since this posture is a singular configuration. In order to tackle this problem, in our previous work, a walking pattern generator based on the spherical inverted pendulum model has been proposed. It enables to generate up-and-down waist motions and utilizes the singularity neighborhood in the middle of each support phase. However, the spherical inverted pendulum model cannot move the ZMP during each single support phase. In this paper, we propose a new approach to generate a walking pattern based on a Spherical Inverted Pendulum model with an Underfloor Pivot (the SIPUP method). With this method, the ZMP gains mobility during each singleleg support phase, and walking with a smaller acceleration is achieved. In addition, it becomes easy to utilize the singularity neighborhood. As a result, the knee joint can be almost fully extended (to less than 0.01 rad). Experimental results show the effectiveness of our approach.