Akihiro Suzumura

Real-Time Motion Generation and Control Systems for High Wheel-Legged Robot Mobility

A wheel-legged mobile robot (WLMR) has both leg and wheel structures. WLMRs have adaptability advantages because they can change locomotion methods depending on the terrain. However, the location of a WLMRs center of gravity (CoG) is very high; thus, almost all existing WLMRs move statically. In this paper, whole body motion generation and various control systems are studied to facilitate higher WLMR mobility. To this end, a zero moment point (ZMP) is introduced as a stability index. In addition, WLMRs are modeled as single point mass linear inverted pendulums. Subsequently, online CoG pattern generation methods are proposed; one is a preview control approach, and a second is an approach that realizes the desired ZMP pattern using a zero-phase low-pass filter. It is then possible to generate the desired CoG patterns more easily and faster than with a preview control approach. The CoG patterns based on the single point model are constructed via the resolved-momentum-control approach. Finally, the effectiveness of the whole body motion pattern generated by the proposed methods is validated by simulations and experiments.

High mobility control for a wheel-legged mobile robot based on resolved momentum control

This paper deals with realization of both rapidity and stabilities for four-wheel-legged locomotion. To achieve these aims, two control approaches are proposed. First, we show the kinematic modeling of constraint for wheel-legged mechanism to achieve the three-dimensional locomotion. Then, the proposed constraint is applied to the resolved momentum control. This method realizes the dynamic locomotion by considering the center of mass and angular momentum directly affecting the stability of dynamic locomotion. Second, a trajectory generating method by using zero-phase low pass filter based on a cart-table model is applied. These schemes can control the robot by stabilizing the zero moment point which is the criteria of dynamic locomotion. In this paper, we focus on the realization of fast and stable wheeled locomotion. Finally, the effect of proposed methods is confirmed by simulations and experiments.

Control of dynamic locomotion for the hybrid wheel-legged mobile robot by using unstable-zeros cancellation

In this paper, a new method of center of mass trajectory planning using the zero-phase low pass filter is proposed. This method is based on a table-cart model which simply describes the relationship between center of mass and zero moment point. Generally, zero moment point should be controlled to realize dynamic motion. This method can easily generate the center of mass trajectory which realizes the desired zero moment point. In our study, this method is applied to wheel-legged locomotion. We will show the result that zero moment point can be sufficiently controlled even if quadruped wheel-legged mobile robot is approximated to a table-cart model. The effectiveness of the idea is validated by simulation and experiment.

Workspace control of a wheel-legged mobile robot for gyrating locomotion with movable leg

We discuss motion generation problems of a wheel-legged mobile robot (WLMR) with movable legs. We consider and solve two problems of inverse kinematics of WLMRs. The first problem occurs in the generation of steering commands for WLMRs, which is due to the mechanism of the structure of the wheels. In general, inverse kinematics for WLMRs are applied in the velocity level. However, in our case, it is not possible to generate the proper steering motion. To solve this problem, we show that for WLMRs, the application of inverse kinematics in the acceleration level is effective. The second problem addressed is a singularity problem that occurs when controlling the contact point of legs during the wheeled locomotion of the WLMR. We show that this singularity problem can be avoided by utilizing the redundancy present in the wheel-leg mechanism. Finally, the effectiveness of our motion generation schemes is validated by conducting precise, three-dimensional simulations.

A General Framework for Designing SISO-Based Motion Controller With Multiple Sensor Feedback

This paper proposes N-degree-of-freedom (N-DoF) control for single-input and single-output based systems. This method relaxes the water-bed effect, which limits the capacity to suppress disturbances and noise using multiple sensors. The systems design procedure for the control system and nominal stability conditions are introduced. N-DoF control is then compared with classical two-DoF control and with Kalman filter using simulations and experiments of motor systems with an encoder and an accelerometer. The results indicate that N-DoF control achieves an enhanced disturbance and an oscillation suppressing performance simultaneously. Moreover, N-DoF control is applied to two-mass systems and verified by using numerical simulation. The characteristics are introduced and compared with several conventional approaches. The results suggest that N-DoF control incorporates all the characteristics of the other methods, and its disturbance and vibration suppression capability is demonstrated.

Three-degree-of-freedom control and its application to motion control systems

This paper proposes a Three-degree-of-freedom (Three-DoF) control that is extended from a Two-degree-of-freedom (Two-DoF) control. In a classical Two-DoF control, the command input response and the disturbance suppression characteristics can be determined independently. However, the disturbance suppression characteristic and the noise suppression characteristic have a trade-off relation. Thus, if the disturbance suppression property sets high, the noise suppression property becomes low, and vice versa. In Three-DoF control scheme, command input response, disturbance suppression, and noise suppression property can be determined independently. To realize above capability, the controlled plant is divided by utilizing its linearity and an additional controller is used. In this paper, the control system architecture and the controller design methodology are shown and its effectiveness are validated by position control simulations of a 1DoF DC motor model.

On explicit implementation of multiple disturbance observers derived from three-degree-of-freedom control

This paper analyzes three-degree-of-freedom (Three-DoF) control based multiple disturbance observers (TDoF-DOB). Three-DoF control has multiple DOBs equivalently; therefore, its explicit implementation is verified in this paper for the force estimation problem. As the comparative study, differences between TDoF-DOB and position and acceleration integrated disturbance observer (PAIDO) are analyzed. TDoF-DOB has one advantage in terms of a noise sensitivity performance in the case of being applied for two-inertia systems. Finally, the analysis is verified by simulations and fundamental experiments for one and two-inertia systems.

Three-degree-of-freedom control for impedance control using encoder and accelerometer

This paper stated a problem of dilemma among accuracy, robustness, and noisiness in an impedance control. Additionally, applying Three-degree-of-freedom (Three-DoF) control for the problem is proposed as a solution. By using Three-DoF control, the performance is improved in terms of the noisiness compared with a conventional framework. The effectiveness is verified by preliminary simulations and experiments. As a result, the proposed method improved the accuracy/robustness and noisiness simultaneously.