Redirected walking (RDW) allows users to navigate a large virtual world in a small physical space. At this time, if the applied redirection is below the detection threshold, the human hardly notice. However, some papers reported that users perceived changes in curvature gain even when redirections smaller than the detection threshold were applied. This means that the change in curvature gain caused human perception. Therefore, in this paper, we identified a threshold for the change in curvature gain, which was found to be 3.06°/m. Further experiments using different variation methods for variations in curvature gain will follow.

In a cable-driven suspension system developed to simulate the reduced gravity of lunar or Martian surfaces, we propose to manipu-late/reduce the physical cues of forward jumps so as to overcome the limited workspace problem. The physical cues should be manipulated in a way that the discrepancy from the visual cues provided through the HMD is not noticeable by users. We identified the extent to which forward jumps can be manipulated naturally. We combined it with visual gains, which can scale visual cues without being noticed by users. The test results obtained in a prototype application show that we can use both trajectory manipulation and visual gains to overcome the spatial limit. We also investigated the user experiences when making significantly high and far jumps. The results will be helpful in designing astronaut-training systems and various VR entertainment content.

This paper presents flotation simulation in a cable-driven virtual environment. For this, a virtual parasailing system was developed, where the visual stimulus was provided through a VR headset and the physical stimulus was given by wires. In order to prevent the user from moving out of the limited workspace of the cable-driven system, the visual acceleration was washout-filtered to produce the physical acceleration. In the parasailing trajectory, we focused on the stages of vertical acceleration/deceleration and conducted an experiment to identify how much gain can be applied to the visual acceleration, which makes the user feel the natural self-motion when integrated with physical stimulus. Then, the results were tested using several types of full-course virtual parasailing. The results showed that fairly large differences between visual and physical stimuli would be accepted and different gains could be assigned depending on the user's altitudes.

The reduced gravity experienced in lunar or Martian surfaces can be simulated on the earth using a cable-driven system, where the cable lifts a person to reduce his or her weight. This paper presents a novel cable-driven system designed for the purpose. It is integrated with a head-mounted display and a motion capture system. Focusing on jump motion within the system, this paper proposes to scale the jump and reports the experiments made for quantifying the extent to which a jump can be scaled without the discrepancy between physical and virtual jumps being noticed by the user. With the tolerable range of scaling computed from these experiments, an application named retargeted jump is developed, where a user can jump up onto virtual objects while physically jumping in the real-world flat floor. The core techniques presented in this paper can be extended to develop extreme-sport simulators such as parasailing and skydiving.

In this paper, we propose a new parallel mechanism of biped robots, each of its legs is composed of two 3-DOF parallel platforms linked serially. The thigh possesses three active linear actuators with a constraint bar and seven passive joints, the shank has two linear actuators to operate pitch and roll motion at the ankle and a rotational actuator for the pitch at the knee. To generate locomotion trajectory for the proposed robot, we adopt the genetic algorithm for minimizing energy consumption. For the fast convergence and efficiency, the RCGA (real coded genetic algorithms) is used. A trajectory is represented by 4-th order polynomials whose coefficients are chromosomes. Equality conditions reflect the start and end position of swing leg and the repeatability condition for stable walking is used with inequality conditions to describe kinematics constraints for swing motion and ZMP (zero moment point) conditions. To demonstrate the effectiveness and performance of the proposed structure and trajectories, computer simulations were executed using SimMechanicsreg

In this paper, we propose optimal trajectories of biped robots to move a staircase up and down using genetic algorithms and computed-torque controller to be dynamically stable. Firstly, in order to minimize the total energy efficiency, the real-coded genetic algorithm (RCGA) which of operators are composed of the reproduction, crossover and mutation is used. Constraints are divided into equalities and inequalities: equality constraints consist of position conditions at the start and end of stride period and repeatability conditions related to each joint angle and angular velocity. Next, inequality constraints include the collision avoidance conditions of swing leg at the face and edge of a stair, the knee joint conditions with respect to the singular avoidance, and the zero moment point condition with respect to the stability into the going direction. Finally, in order to approximate the walking gait, each joint angle trajectory is defined as a 4th order polynomial of which coefficients are chromosomes. In the computer simulation used 6 degree of freedom biped robot model that consists of seven links, we analyze the energy efficiency of proposed optimal trajectories about the following cases: walking on ground, ascending stairs, and descending stairs.

In this paper, we propose a gait transition algorithm between walking and running for fast movement of a biped robot. Firstly, considering that walking and running differ in the oscillations of the body and legs that occur during each step or stride, the transitionary trajectory is constructed by the transformations of the velocities of hip link, the step height and stride of the feet, and the duration of the step using interpolating polynomials. And in order to increase the compliance about the environment and to absorb the impact force in the landing event, the impedance controller is designed for walking and running biped robot. The effectiveness and the performance of the proposed gait patterns are shown in computer simulations with a 19-DOF biped robot and a 6-DOF elastic pad model.

Biped robots are expected to walk on many different and previously unknown terrains, and thus they may walk on a slippery surface with low friction with no information on the surface a priori. Any fall-down due to unexpected slipping could cause costly damage to the robot and thus should be avoided. The paper proposes a reflex control method for biped robots to quickly recover their posture from a slip soon after a detection of the slip. Computer simulations with a 12-DOF biped robot and a 6-DOF environment model that consists of nonlinear dampers, and linear and nonlinear springs, show that the proposed method is very effective in preventing a fall-down of biped robots on a slippery surface.