Kazuto Yokoyama

A simple 3D straight-legged passive walker with flat feet and ankle springs

To date, most passive walkers have been designed with arc-shaped feet rigidly attached to the legs. We developed a simple 3D straight-legged passive walker with flat feet and ankle springs. The flat feet are connected to the legs with springs at the ankles that produce torsional force while the stance leg is on the ground, mimicking the motion of simple 3D passive walkers with arc-shaped feet. This helps to prevent slipping and to handle the disturbance behavior of the robot. Flat feet are particularly advantageous for yaw stability. Our 3D passive-walker robot with a 0.84-m leg can walk the full length of a 1.8-m slope at about 0.44 m/s.

Dynamics-Based Nonlinear Acceleration Control With Energy Shaping for a Mobile Inverted Pendulum With a Slider Mechanism

A nonlinear controller to accelerate a mobile inverted pendulum (MIP) with a slider mechanism is proposed. The concept of this paper is to control translational acceleration and deceleration of the MIP in a dynamically reasonable manner. The body angle and slider displacement are controlled to maintain reference states where the MIP is statically unstable but dynamically stable, which leads to a constant translational acceleration due to instability of the vehicle. The accelerating motion is like a sprinter moving from the crouch start, and it fully exploits the dynamics of the MIP. To achieve it, the total energy of the system is shaped to have the minimum at the given reference states and the system is controlled to converge to them. The controller can achieve various properties through the energy-shaping procedure. In particular, an energy function that will lead to safe operation of the MIP is proposed. The function ensures that motion of the MIP is restricted within predefined regions. The controller also returns the system back to the reference states with state-dependent gains that become large if the system comes close to falling over. The effectiveness of the controller is verified in simulations. Finally, a new physical MIP was constructed, and experiments were carried out with an additional friction compensation method. The results show that the proposed controller works well in the presence of uncertainty, such as noise and modeling errors.

An Experimental Study of Three-Dimensional Passive Dynamic Walking with Flat Feet and Ankle Springs

Passive dynamic bipeds were first studied by McGeer (McGeer, 1990) as inspired by a bipedal toy described in (McMahon, 1984). Passive dynamic walkers can walk down a shallow slope without actuators and controllers(McGeer, 1990; 1993). McGeer has built passive walkers that exhibit steady motion using a Poincare map, which he called as a stride function, to analyze the gaits(McGeer, 1990; 1993). This method is quite useful and is independent of the biped model. The key idea that he examined is the stability of the entire step-to-step motion, and not the local stability at every instance. This analysis is also rather useful for actuated bipeds (Hobbelen and Wisse, 2007). Firstly, McGeer studied two elementary passive walkingmodels derived from awagonwheel. One model was a rimless wheel model on a slope, and the other a synthetic wheel model on level ground as shown in Fig. 1. The motion of the models is constrained to the sagittal plane. Each model captures the fundamental mechanism of passive dynamic walking.

Energy shaping non-linear acceleration control for a pendulum-type mobility and experimental verification

A dynamics-based non-linear controller with energy shaping to accelerate a pendulum-type mobility is proposed. The concept of this study is to control translational acceleration of the vehicle in a dynamically reasonable manner. The body angle is controlled to maintain a reference state where the vehicle is statically unstable but dynamically stable, which leads to a constant translational acceleration due to instability of the system. The accelerating motion is like a sprinter moving from crouch start and it fully exploits dynamics of the vehicle. To achieve it, the total energy of the system is shaped to have the minimum at a given reference state and the system is controlled to converge to it. The controller can achieve various properties through the energy shaping procedure. Especially, an energy function that will lead to safe operation of the vehicle is proposed. The effectiveness of the controller is verified in simulations and experiments.

Inverted Pendulum-type Personal Mobility Considering Human Vibration Sensitivity

An inverted pendulum-type PM (personal mobility) has been attracting attention as a low-carbon vehicle. For many people who like to use the PM, ride comfort is important. However, ride comfort of PM has not been focused on in previous studies. The vibration is one of causes that make riders feel uncomfortable. The PM is unstable system and horizontal vibration may be caused by a stabilizing control. Additionally, vertical vibration may also be caused by road disturbances. This study analyzes the vibration of the rider’s head in these two directions when the PM runs on a road with disturbances in numerical simulations, and evaluates ride comfort with the frequency characteristics of the vibration. To consider human vibration sensitivity, the frequency weighting proposed in ISO 2631-1 is used as an evaluation standard. The improvement methods are proposed from both software and hardware, and it is confirmed that the proposed method can improve ride comfort.

Proposal of an Inverted Pendulum-Type PMV Considering the Characteristics of Human Vibration Sensitivity

An inverted pendulum-type PMV (personal mobility vehicle) has been attracting attention as a low-carbon vehicle. For many people who like to use the PMVs, ride comfort is important. However, the problem of ride comfort has not attracted much attention in previous studies. The vibration is one of the important indicators for evaluating ride comfort. The PMV is unstable system. Therefore, the vibration may be generated when the PMV is stabilized. This study investigates the horizontal and vertical vibration of the head of the occupant when the PMV runs on a road with disturbances in numerical simulations. Frequency characteristics of the inverted pendulum-type PMV is analyzed to verify what vibrational factors that worsens ride comfort are. To consider human vibration sensitivity, the frequency weighting proposed in ISO2631-1 is used as the evaluation standard. The improvement methods are proposed from both software and hardware, and it is confirmed that the proposed method can improve ride comfort.© 2012 ASME