Shigenori Sano

Model-Reference Control Approach to Obstacle Avoidance for a Human-Operated Mobile Robot

Because the obstacle-avoidance function is indispensable for providing the safe and easy operation of human-operated robotic systems, this paper deals with the obstacle-avoidance control for a human-operated mobile robot in unknown environments. A general type of two-wheeled mobile robot with inexpensive distance sensors to detect obstacles is considered. Because the robot cannot move in arbitrary directions due to a nonholonomic constraint, we propose a model-reference control approach, in which a reference model generates the desired trajectory to satisfy the nonholonomic constraint, and the robot follows the desired trajectory. The reference model has the steering-like and brake-like functions that are adjusted according to the distance-sensor information. The stability of the proposed control system is analyzed with a linear model. The effectiveness of the proposed method is confirmed by experiments in which several operators handle the robot in an environment with obstacles.

Reduction of Electrical Energy Consumed by Feed-Drive Systems Using Sliding-Mode Control With a Nonlinear Sliding Surface

The large amount of energy consumed in machining by feed-drive systems has become an important issue in recent years because machine tools are extensively used worldwide. This paper presents a novel sliding-mode controller with a nonlinear sliding surface (NLSS) to improve the machining accuracy of ball-screw feed-drive systems. Unlike the conventional sliding-mode control design, the proposed NLSS varies according to the output (controlled variable) so that the damping ratio of the system changes from its initial low value to its final high value as the output changes from its initial value to the reference point. Hence, the proposed algorithm allows a closed-loop system to simultaneously achieve low overshoot and a small settling time, resulting in a smaller error. Experiments to verify the effectiveness of the proposed approach are carried out for a ball-screw feed-drive system for two perspectives. The first perspective is to show the effectiveness of the proposed NLSS in reducing the tracking error, while the second one is to verify the ability of the proposed approach to reduce the consumed energy and control input variation. For the first case, sliding-mode controllers with and without the nonlinear term are compared under the same parameters. The mean of the tracking error magnitude was reduced by 35% without additional electrical energy or control input variation in the controller with NLSS. In the second case, the linear gain is increased for the controller with the linear surface to obtain similar tracking performance. By using the controller with an NLSS, the consumed energy and control input variation were reduced by about 12.9% and 19.1%, respectively.

Point-contact type foot with springs and posture control for biped walking on rough terrain

This paper proposes a new foot system to achieve stable biped walking on rough terrain. The new foot system, which is named point-contact type foot with springs (PCFS), has four passive joints each of which equips a spring and a sensor. The proposed foot system has the following advantages: 1) The geometrical adaptability to rough terrain. 2) The measurability of the posture of the robot. 3) The absorption of the influence of disturbances. The index of stability like ZMP and the posture of the robot can be estimated from the displacement of each spring. The foot system can also absorb not only the impact at the foot landing but also the influence of irregularities on the ground and unexpected disturbances. However, because the biped walking by use of the foot with springs corresponds to walking on a soft ground, posture control is indispensable. Therefore we consider an appropriate walking pattern generation and present feedback control for the proposed foot system. The effectiveness of the proposed foot system is demonstrated by simulation results.

Energy Saving in Feed Drive Systems Using Sliding-Mode-Based Contouring Control With a Nonlinear Sliding Surface

Reduction of contour error, which is defined as the shortest distance between the actual position of the cutting tool and the reference trajectory, is an essential requirement in machining by multiaxis feed drive systems. In addition, because these machines operate all the time in industrial applications all over the world, reduction of the consumed energy in these machines contributes to environmental, natural resources, and energy problems. This paper presents a novel sliding mode contouring controller with a nonlinear sliding surface to improve the machining accuracy of the biaxial feed drive systems. Because the contour error is more important than the tracking error with respect to each feed drive axis, the contour error component is included in the proposed sliding surface. The advantage of including the contour error in the proposed sliding surface is that the damping ratio of the system changes from its initial low value to final high value as the contour error changes from high value to small value and vice versa. Hence, the proposed algorithm allows a closed-loop system to simultaneously achieve low energy consumption and small settling time, resulting in a smaller error. By using the proposed method, experimental results for a biaxial feed drive system show a significant performance improvement in terms of the contour error. In addition, the proposed approach reduces the control input variance by about 41.2 % and 14.9 % for x - and y-axis, respectively, and consumed energy by about 23.7 % and 5.5 % for the respective axis from the conventional method with a linear sliding surface.

Real-time trajectory generation for mobile robots in a corridor-like space using Bézier curves

This article deals with trajectory generation for teleoperated wheeled mobile robot using piecewise Bézier curves that are well-known to have useful properties. We develop an algorithm for generating motion trajectories with continuous curvature (C2 continuity). We consider a teleoperated wheeled mobile robot in an indoor environment having ceiling cameras for operators visibility. The motion trajectory is constrained by via points and path width designated by the operator. The Bézier subdivision method is employed and quintic Bézier segment is inserted in the high curvature area to improve the trackability by mobile robots. Simulation results demonstrate the feasibility of the proposed method.

Design of point-contact type foot with springs for biped robot

This paper presents a new foot system for biped walking on rough terrain and its design flow. To achieve the stable biped walking on rough terrain, the following functions are required. 1) Stabilization of contact states between foot and ground. 2) Landing to unknown terrain. The conventional rigid and flat foot changes its contact states and is separated from the ground easily. In addition, the impulsive impact force at landing on rough terrain must be suppressed. We propose a point-contact type foot with springs (PCFS). The proposed foot has the following advantages. 1) Stabilization of contact state. 2) Estimation of stability index, and 3) Absorption of landing impact. A design method of primary parameters for PCFS is presented to increase the stability of the robot and reduce the impact force at the landing. The validity of the proposed design method is shown experimentally.

Collision avoidance control for a human-operated four-wheeled mobile robot

Because the collision avoidance function is indispensable for providing safe and easy operation of human-operated robotic systems, this paper deals with the collision avoidance control for a human-operated mobile robot in unknown environments. A typical four-wheeled mobile robot with infrared distance sensors for detecting obstacles is considered. The robot cannot move in an arbitrary direction owing to a nonholonomic constraint. Therefore, we propose a simple control approach in which a human operator’s control input is modified in real time to satisfy the nonholonomic constraint and avoid collision with obstacles. The proposed controller has steering- and brake-like functions that are adjusted according to the distance sensor information. The stability of the proposed control system is analyzed with a linear model. The effectiveness of the proposed method is confirmed by experiments in which several operators control the robot in an environment with obstacles.

Second order sliding mode control for a quad-rotor helicopter with a nonlinear sliding surface

This paper presents a novel second order sliding mode control strategy for a robust tracking controller of a quad-rotor helicopter by utilizing a nonlinear sliding surface. The nonlinear sliding surface enables the closed loop dynamics to have a variable damping ratio, and therefore the transient time to reach the sliding mode can be shorten. The effectiveness of the proposed control strategy is proven experimentally.

Residual vibration suppression and energy saving in industrial machines using a trapezoidal velocity profile

A trapezoidal velocity profile is widely used in industrial machines all over the world in particular for point-to-point motion. This paper deals with residual vibration suppression and energy saving for industrial machines operated by such a simple trapezoidal velocity profile. Because many industrial machine controllers currently in use allow to implement only such a simple motion trajectory, the proposed method has significant advantage on the implementation to these machines all over the world, and can contribute to recent environmental and energy-shortage problems. This paper first derives necessary and sufficient conditions for suppressing residual vibration by using a trapezoidal velocity profile for industrial machines that have typical second-order dynamics. Next, an equation for calculating energy consumed in point-to-point motion based on a trapezoidal velocity profile is presented. Simulation and experiment demonstrate the effectiveness of the proposed analytical results.

Sound source tracking considering obstacle avoidance for a mobile robot

Sound source tracking is an important function for autonomous robots, because sound is omni-directional and can be recognized in dark environment. This paper presents a new approach to sound source tracking for mobile robots using auditory sensors. We consider a general type of two-wheeled mobile robot that has wide industrial applications. Because obstacle avoidance is also an indispensable function for autonomous mobile robots, the robot is equipped with distance sensors to detect obstacles in real time. To deal with the robots nonholonomic constraint and combine information from the auditory and distance sensors, we propose a model reference control approach in which the robot follows a desired trajectory generated by a reference model. The effectiveness of the proposed method is confirmed by experiments in which the robot is expected to approach a sound source while avoiding obstacles.