Shigeki Nakaura

Balance control analysis of humanoid robot based on ZMP feedback control

Balance control analysis of humanoid robot based on Zero Moment Point (ZMP) feedback control is presented. ZMP is mostly used as standard evaluation of stability of humanoid robot, and balance control is conducted by controlling ZMP position so that it is always in convex hull of the foot-support area. To simplify the design of controller, it is mainly used as one mass inverted pendulum model which represents lower body of humanoid robot model. However this model causes system to become non-minimum phase and performance limitation of the system occurrs, because of the presence of Waterbed effect in frequency domain and unavoidable undershoot in time domain. This paper proposes ZMP feedback control using two masses inverted pendulum model which represents lower and upper body of humanoid robot and creates minimum phase system. The design of the controller based on the proposed model using linear quadratic by considering output is described and confirmed using simulation.

Locomotion control of a snake robot with constraint force attenuation

We deal with the locomotion control of a snakelike articulated robot with passive wheels. The robot gains propulsion by means of constraint forces on the wheels caused by actuating the joints. The so-called serpentine movement is known to be an effective gait on a flat ground. Our goal is to achieve such motion by autonomous gait generation, i.e., without giving any winding gait beforehand. Therefore we utilize a notion of manipulability to evaluate the locomotability and propose a control method capable of reducing the constraint forces. The results of simulations show that smooth motion is generated.

Inverse optimal control problem for bilinear systems: Application to the inverted pendulum with horizontal and vertical movement

Inverse optimal design for bilinear systems is considered. The main result is that a nonlinear optimal feedback control law which minimizes a new quadratic cost function with nonlinear weight is obtained based on an inverse optimal control problem for bilinear systems. This inverse optimal control design is applied to the problem of the stabilization of the inverted pendulum on the cart which moves not only in the horizontal direction but also in the vertical direction. This inverted pendulum system can be transformed into a bilinear system by using input transformation and coordinate transformation focused on the center of percussion of the pendulum. It is theoretically shown that the proposed nonlinear optimal feedback controller has higher control performance than a conventional linear optimal controller for the linear approximation system. Furthermore, it is shown by numerical simulations that the control performance of the pendulum is improved by utilizing the vertical movement of the pendulum.

Throwing motion control based on output zeroing utilizing 2-link underactuated arm

This paper deals with motion control of throwing generated by dexterous action. Dexterous actions can be seen in many sports. In baseball pitching, dexterous throwing seems to use energy transfer and a physical constraint at the elbow joint. To implement the dexterous throwing, two types of two-link underactuated manipulator are presented. One model has a spring at 2nd joint which represents an arms stiffness and a constraint at elbow joint, another model has a physical absolute constraint at elbow joint. For these models, throwing motion control method based on output zeroing which specifies the path of the ball held by an end-effector is proposed. The proposed control strategy realizes the energy efficient motion for throwing to the desired direction. Simulation and experimental results show the effectiveness of the proposed control method.

Throwing motion control of the springed Pendubot via unstable zero dynamics

This paper describes a control strategy for throwing motion of the springed Pendubot based on the concept of unstable zero dynamics. An underactuated two-link planar robot called the Pendubot is investigated to realize dexterous actions of the superior limb in human throwing motion. A torsion spring is mounted on the passive joint of the Pendubot representing the flexibility of the cubital joint. In the proposed control strategy, the zero dynamics is intentionally destabilized when the end-effector of the springed Pendubot is constrained on a geometric path via output zeroing control for the deviation between the end-effector and the geometric path. The unstable zero dynamics drives the end-effector along the geometric path to achieve a fast and accurate throw in a desired direction when the input is devoted to constrain the end-effector on the geometric path. The unstable zero dynamics is analytically derived to guarantee the divergence of the end-effector along the geometric path. Numerical simulations confirm the effectiveness of the proposed control strategy.

Throwing motion control experiment utilizing 2-link arm passive joint

This paper describes the throwing motion control experiment utilizing a 2 link arm with a passive joint. In throwing, dexterous actions can be seen. Dexterous throwing uses energy transfer from a trunk of the body to a hand and a physical constraint at the elbow joint. However, human throwing is very difficult to analyze all features, because throwing motion performs in three dimensions. Therefore, under-actuated 2 link model is applied in this paper. Proposed model has a spring joint which is represented as an armpsilas stiffness and a constraint at elbow joint. For this model, the control method based on output zeroing which specifies the path of the ball at the end-effector is proposed. By developing an experimental equipment and carrying out experiments of throwing motion control, the effectiveness of the proposed control method is verified.

Control of a snake robot in consideration of constraint force

This paper deals with an autonomous locomotion of a snakelike articulated robot with passive wheels. Using the non-slip condition of the wheels, the robot gains propulsion by means of constraint forces on the wheels caused by bending the joints. Our goal is to achieve the so-called serpentine movement known to be an effective gait on a flat ground with automatic gait generation, i.e., without giving any winding gait beforehand. We utilize a notion of manipulability to evaluate the locomotability and propose a controller capable of reducing the constraint forces. The results of simulations show that smooth winding motion is achieved.

Throwing Motion Control of the Springed Pendubot

This brief describes a control strategy for the throwing motion of an underactuated two-link planar robot called the Pendubot. The springed Pendubot is built based on the concept of unstable zero dynamics, and our investigation uses it as a dynamic model of superior limbs to imitate human throwing motion. In the proposed control strategy, the zero dynamics is intentionally destabilized when a ball held by the end-effector is constrained on a geometric path in a vertical plane, using output zeroing control for the deviation between the ball and geometric path. The unstable zero dynamics drives the ball along the geometric path to achieve fast and accurate throw in a desired direction. The unstable zero dynamics is analytically derived to guarantee the dynamic acceleration of the ball along the geometric path. Numerical simulations and experimental results confirm the effectiveness of the proposed control strategy.

The Control of a Bipedal Running Robot based on Output Zeroing considered Rotation of the Ankle Joint

For the bipedal robot, this paper investigates natural running motion like human running, without performing tracking control to the optimal trajectory of such a motion. The bipedal robot considered in this paper is planar and has revolute joints which actuate ankle, knee and hip. The running motion is assumed to consist of two successive phases which are composed of a flight phase and a stance phase: the flight phase where the bipedal robot floats, the stance phase where either a heel or a toe keeps contact with the ground. In order to realize the natural motion of the human, an output function which is easily understood in the physical aspect is designed on the basis of the human actual motion. Running motion of bipedal robot is generated autonomously by zero dynamics which appears by zeroing output function. Some parameters of this output function are re-configured online in order to suppress disturbance caused by unstable zero dynamics. Through a numerical simulation it is confirmed that running motion becomes stable

Position control of surface vessel with unknown disturbances

This paper describes dynamic position control of surface vessel with disturbances such as waves and wind. A smooth time-varying controller is proposed that performs both in presence and absence of disturbances. Using this controller, position of the vessel converges to neighborhood about zero that can be made arbitrarily small. In addition, if disturbance is small, orientation of the vessel converges to neighborhood about zero that is as small as possible. Effectiveness of proposed control law is demonstrated by simulation.