Yasutaka Fujimoto

Simulation of an autonomous biped walking robot including environmental force interaction

This autonomous biped walking control system is based on reactive force interaction at the foothold. The precise 3D dynamic simulation presented includes: 1) a posture controller which accommodates the physical constraints of the reactive force/torque on the foot with quadratic programming; 2) a real-time COM (center of mass) tracking controller for foot placement, with a discrete inverted pendulum model; and 3) a 3D dynamic simulation scheme with precise contact with the environment. The proposed approach realizes robust biped locomotion because environmental interaction is directly controlled. The proposed method is applied to a 20 axes simulation model, and stable biped locomotion with velocity of 0.25 m/sec and a stepping time of 0.5 sec/step is realized.

A Novel Nine-Switch Inverter for Independent Control of Two Three-Phase Loads

Industrial applications require large numbers of motors. For example, motors are used to manipulate industrial robots, an electric vehicles with in-wheel motors and electric trains. Two methods exist for controlling PM motors providing an inverter to control each motor, and connecting the motors in parallel and driving them with a single inverter. The first method makes an experimental apparatus complex and expensive; the second does not allow independent control of each motor because of differences in rotor angle between the two motors. Thus, we propose a novel nine-switch inverter that can independently control two three-phase loads. This paper introduces the structure of the nine-switch inverter, which is made from nine switches. The validity of the proposed inverter is verified through simulations and experiments.

Robust biped walking with active interaction control between foot and ground

Describes a biped walking control system based on the reactive force interaction control at the foothold: 1) robust control of reactive force/torque interaction at the foothold based on Cartesian space motion controller: 2) posture control considering the physical constraints of the reactive force/torque at the foothold by quadratic programming. The proposed approach realizes robust biped locomotion because the environmental interaction is directly controlled. The control is applied to the 20 axes simulation model, and the stable biped locomotion is realized even if an unknown small slope exists. Stable attitude control is confirmed by 14-axis biped robot experiments.

Development and Analysis of a High Thrust Force Direct-Drive Linear Actuator

This paper presents the design and analysis of a novel high thrust force linear actuator with high backdrivability. This motor consists of a mover and a stator with spiral (helical) structure. The mover moves spirally in the stator, and the linear motion is extracted to drive the load. This motor is a direct-drive system and highly backdrivable. In this paper, a basic model and thrust-force/torque equations are proposed, and finite-element method analysis and experimental results of a prototype are presented. From experiments, the designed spiral motor achieves 2000-N rated thrust force. The thrust-force capabilities of the spiral motor are compared with other linear motors. It is confirmed that the spiral motor is almost close to the latest state of the art in linear motor technology.

Control System With High-Speed and Real-Time Communication Links

Technological advances have enabled distributed control systems to be implemented via networks. This allows feedback control loops to be closed over a communication channel. This paper develops a control system with high speed and real time communication links. The two-degree-of-freedom control is utilized in this servo control system and delta-sigma modulation is employed to compress data and transmit the signal over the transmission channels between the controller and the servomotor. Simulations and experimental results show that it is possible to compensate the noise in signal transmission channels. In addition, FPGA is used in the control system and the communication system to realize high-speed control system with 0.6 mus sampling period and latency. The data is also compressed and transmitted with FPGA in the experiments

Inverter with Reduced Switching-Device Count for Independent AC Motor Control

This paper proposes a novel inverter named nine-switch inverter. The inverter has nine switching devices and can control two loads. First, the configuration of the inverter is introduced. Then, a PWM method for the inverter is elaborated. The validity of the inverter is verified by simulations and experiments. In addition, this paper proposes a 3N + 3-switch inverter, which is an extension of the nine-switch inverter. This inverter has 3N + 3 switches and can control N loads independently. The validity of the 3N + 3-switch inverter is also verified by simulations.

Proposal of biped walking control based on robust hybrid position/force control

This paper describes a novel biped walking control based on a force control. The proposed control system can stabilize the contact force between the foot and the ground under the proposed restrictions. As a result, a hierarchical control is proposed by which the legged locomotion can be realized. The proposed control system is applied to the 19 axes simulation model and the results of stable walking are shown.

Three dimensional digital simulation and autonomous walking control for eight-axis biped robot

First, the three dimensional precise simulation method for biped robot has been proposed, which is the extension of the open link manipulator simulation method and the contact simulation method of rigid body mechanics. The proposed simulation model can be said to be mathematically exact, thus this approach enables the essential investigation for control algorithms of biped locomotion. This approach has advantages in the less cost compared with the experimental demonstration. Second, the autonomous walking control with hierarchical structure has been proposed in which three dimensional inverted pendulum model is considered as the motion of gravity center, and the tip position of nonsupport leg are controlled autonomously. Both of references can be simultaneously transformed to the joint space reference, then they are accurately realized by the robust-servo controller. Third, the proposed walking control is investigated by the proposed simulation method, and the stable walking motion is confirmed.

Trajectory generation of biped running robot with minimum energy consumption

The exact and general formulation of optimal control for biped robots based on a numerical representation of the motion equation is proposed. We can solve exactly the minimum energy consumption trajectories for a biped running motion. Through the numerical study of a five link planar biped robot, it is found that big peak power and torque is required for the knee joints but its consumption power is small and the main work is done by the hip joints.

Development, Analysis, and Experimental Realization of a Direct-Drive Helical Motor

Safety issue is a great concern for rehabilitation robots that are expected to contribute to future aging society. Appropriate compliance is required for their joints. However, combination of servomotors and high-ratio gears, such as harmonic gears, makes the joint of robots nonbackdrivable. The nonbackdrivability causes lack of adaptability and safety. On the other hand, conventional direct-drive systems, including linear motors, are relatively big for such application. This paper presents the development and analysis of compact high-backdrivable direct-drive linear actuator. The motor consists of a helical structure stator and mover. The mover does not contact the stator and moves helically in the stator under a proper magnetic levitation control. Thus, the motor realizes direct-drive motion without mechanical gears. Decoupling control is proposed and integrated with disturbance observer to achieve robustness against model uncertainties and input disturbance. The main contribution of this paper is to experimentally realize the direct-drive feature of the helical motor.