Introduction to linear and nonlinear programming

Mobile manipulators operating in field environments will be required to perform tasks on uneven terrain which may cause the system to approach, or achieve, a dangerous tipover instability. To avoid tipover in an automatic system, or to provide a human operator with an indication of proximity to tipover, it is necessary to define a measure of stability margin. This work presents a new tipover stability measure (the force-angle stability measure) which is easily computed and sensitive to topheaviness. The proposed metric is applicable to systems subject to inertial and external forces, operating over even or uneven terrains. Performance of the measure is demonstrated using a forestry vehicle simulation.

A new measure of tipover stability margin for mobile manipulators

This paper introduces a novel and general real-time adaptive motion planning (RAMP) approach suitable for planning trajectories of high-DOF or redundant robots, such as mobile manipulators, in dynamic environments with moving obstacles of unknown trajectories. The RAMP approach enables simultaneous path and trajectory planning and simultaneous planning and execution of motion in real time. It facilitates real-time optimization of trajectories under various optimization criteria, such as minimizing energy and time and maximizing manipulability. It also accommodates partially specified task goals of robots easily. The approach exploits redundancy in redundant robots (such as locomotion versus manipulation in a mobile manipulator) through loose coupling of robot configuration variables to best achieve obstacle avoidance and optimization objectives. The RAMP approach has been implemented and tested in simulation over a diverse set of task environments, including environments with multiple mobile manipulators. The results (and also the accompanying video) show that the RAMP planner, with its high efficiency and flexibility, not only handles a single mobile manipulator well in dynamic environments with various obstacles of unknown motions in addition to static obstacles, but can also readily and effectively plan motions for each mobile manipulator in an environment shared by multiple mobile manipulators and other moving obstacles.

Real-Time Adaptive Motion Planning (RAMP) of Mobile Manipulators in Dynamic Environments With Unforeseen Changes

.SUMMARY Mobile manipulators operating in field environments will be required to apply large forces, or manipulate large loads, and to perform such tasks on uneven terrain which may cause the system to approach, or reach, a dangerous tipover instability. To avoid tipover in an automatic system, or to provide a human operator with an indication of proximity to tipover, it is necessary to define a measure of available stability margin. This work presents a new tipover stability measure the Force-Angle . stability measure which has a simple geometric interpretation, is easily computed, and is sensitive to changes in Center of Mass height. The proposed metric is applicable to systems subject to inertial and external forces, operating over even or uneven terrains. Requirements for computation and implementation of the measure are described, and several different categories of application of the measure are presented along with useful normalizations. Performance of the Force-Angle measure is demonstrated and compared with that of other stability margin measures using a forestry vehicle simulation. Results show the importance of considering both center-of-mass height and system heaviness, and confirm the effectiveness of the Force-Angle measure in monitoring the tipover stability margin.

The Force-Angle Measure of Tipover Stability Margin for Mobile Manipulators

This research is aimed at the development of bipedal humanoid robots working in a human living space, with a focus on its physical construction and motion control method. At the first stage, we developed the bipedal humanoid robot WABIAN (Waseda bipedal humanoid), and proposed a control method for dynamic cooperative biped walking. In this paper, we present a follow-walking control method with a switching patterns technique for a bipedal humanoid robot to follow human motion by hand contact. By a combination of both algorithms, the robot is able to perform dynamic stepping and walking forward and backward in a continuous time while someone is pushing or pulling its hand. In this paper, the authors describe the control methods for the realization of physical interaction between a human and a bipedal humanoid robot.

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Physical interaction between human and a bipedal humanoid robot-realization of human-follow walking

Many future applications of robotic systems will require manipulators to operate from moving vehicles. However, vehicle-mounted mobile manipulators might be unstable and even tip over. The authors assume that the stability of such a mobile manipulator has a close relationship with the vehicle's motion, the manipulator's posture and motion, and the endpoint's force. They present the concepts of the stability degree and the valid stable region based on the ZMP zero moment point criterion, which can be used as effective stability criteria in controlling mobile manipulators. Finally, the concepts are illustrated by computer simulation.

Stability criteria in controlling mobile robotic systems

Many future applications of robotic systems will require that manipulators perform operations while being carried by moving vehicles. However, such a vehicle mounted mobile manipulator can be unstable or even tip over. Previous work on stability control hardly considered the dynamics and environmental disturbances. The stability of a mobile manipulator has a close relation with the vehicle motion, manipulator motion and posture, and end-effector force. To evaluate the stability for a mobile manipulator, the concepts about stability, such as the stability degree and the valid stable region based on the zero moment point (ZMP) criterion have already been proposed. In this paper, as a control scheme for maintaining or recovering stability, the method of ZMP path planning by a stability potential field is presented, in which the concepts of the goal state and prohibitive state of stability are outlined. A motion planning algorithm is then formulated, which controls the manipulator in order to maintain the stability of the whole system while the vehicle is moving along a given trajectory. >

Stability control for a mobile manipulator using a potential method

It is desired that a vehicle-mounted mobile manipulator can move with stability and can operate tasks in various environments in the presence of disturbances. In this paper, a mobile manipulator cooperative motion planning algorithm is proposed, consisting of a rough motion planning and a local motion modification. As a step to realize the cooperative motion, the vehicle motion planning is discussed, given the end-effector trajectory. First, the vehicle path is planned. Then the optimal problem of determining the passing time of the vehicle along the planned path is formulated, considering the vehicle acceleration, the manipulator workspace and the system stability. Using a gradient projection method, the vehicle motion is derived. Finally, the effectiveness of this method is illustrated by simulation.

Q. Huang

Papers

Stability criteria in controlling mobile robotic systems

Stability control for a mobile manipulator using a potential method

Motion planning of stabilization and cooperation of a mobile manipulator-vehicle motion planning of a mobile manipulator