This paper proposes a safe emergency stop control for collision avoidance of gantry cranes. The crane mechanism is widely used for handling heavy load. A big problem is that the suspended load swings easily. This leads to possibilities of collision of load with obstacle during the crane work. Emergency stop for collision avoidance is, however, also dangerous. Because residual sways after the stop is easy to be caused by the stop. Therefore, this paper presents an anti-sway control method when the emergency stop. The method is based on inverse dynamics of the crane system. Thus the inverse dynamics problem is also discussed. Using the inverse dynamics calculation and a real time obstacle detection system, a feed-forward based emergency stop control method is proposed. Experiments of emergency stop control using the method are shown.

This paper presents a development of a cleaner robot for vertical type air conditioning duct. The air conditioning duct is used for ventilation and air conditioning. After years use of the duct without cleaning, much dust is gathered inside the duct. That leads scattering the dust into rooms. This is not desirable in the view point of sanitation or health. Thus, periodic cleaning of the duct is requested. For the cleaning work, an air hose type cleaner robot is developed. An air nozzle is attached with the tip of the hose type robot. Compressed air blows off the dust from the air nozzle, then the dust inside the duct is collected by a dust collector with a filter. The part of nozzle is manipulated by wires' constraint using two DC motors. By watching TV monitor which shows inside of the duct, the cleaning work is done remotely using a control stick operation. To control the nozzle of the hose robot, the paper discusses a relation between position of nozzle (tip of hose robot) and wire length. Discussions on wire force for the position are also given. An experiment of the motion for the hose robot is presented, then theoretical solutions and experimental results are compared.

This paper discusses parallel wire mechanisms where an end-effector of the mechanism is suspended by multiple wires. The mechanisms enable not only three-dimensional (3-D) positioning but also 3-D orienting of the end-effector, unlike typical wire suspension-type mechanisms such as overhead crane. To discuss the parallel-wire-suspended mechanisms generally, two forms of basic dynamic equations are presented. Then the parallel wire mechanisms are classified into two types based on the basic equations. Dynamical properties of the two types of wire-suspended positioning mechanism are discussed. In this paper, one of the wire-suspended mechanism, incompletely restrained-type parallel wire mechanism, is mainly discussed on its inverse dynamics problem and its trajectory control problem. The inverse dynamics problem for the incompletely restrained-type mechanism plays an important role on its control problem, because the mechanism has low stiffness based on incomplete constraints on the suspended object which is governed by its dynamics. The paper proposes an antisway control method for the suspended object. In the method, the inverse dynamics calculation is used for nonlinear dynamics compensation to control the suspended object of the incompletely restrained parallel wire mechanism.

This paper presents methods of trajectory planning for a mobile manipulator with stability considerations. The proposed trajectory planning method is to generate a trajectory for the mobile manipulator from a given path of the end-effector considering stability. Then, we derive a dynamics model of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. ZMP criterion is used as an index for the system stability. The trajectory planning problem is formulated as an optimal control problem with some constraints. To solve the problem, we use a hierarchical gradient method which synthesizes the gradient function in a hierarchical manner based on the order of priority. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

This paper proposes a new type of two wheels caster type odometer to estimate the current position and orientation of omni-directional vehicles. The proposed odometer is composed of two passive wheels and one passive rotational axis. The two wheels rotate independently, and the rotational axis changes the odometer's orientation as the omni-directional vehicle moves. Three rotary encoders using a gear train measure angular velocities of the two wheels and rotational axis. A mechanism of the gear train is proposed to prevent the encoder from being entangled with it. Using measured values of the three encoders, the current velocity vector of an omni-directional vehicle is calculated by kinematics of the odometer. Using the velocity vector, the current position and orientation of the omni-directional vehicle are estimated by dead reckoning. Results of localization experiments by the developed odometer are shown.

In this paper, we propose the trajectory planning method of multiple mobile manipulators which carry a common object in cooperation. We derive a dynamic equation considering dynamic characteristics of mobile manipulators and the object. The dynamic equation consists of equations of motion of mobile manipulators and the object, nonholonomic constraints of mobile platforms, and geometrical constraints between end-effectors and the object. The trajectory planning problem is formulated as an optimal control problem. A simulation result is given to show the effectiveness of the proposed method.

A feedback control method of Omni-Directional Vehicles (ODV) is proposed by using a caster type odometer. The odometer which is called the Two Wheels Caster Type Odometer (TWCTOdometer) is specially designed for ODVs. Driving wheels of typical ODVs are easy to slip. When an odometer is connected directly with the shafts of driving wheels, the slip of the driving wheels causes much dead-reckoning error. Thus the TWCTOdometer is attached independently to the driving wheels of the ODV in order to avoid the influence of slips of the driving wheels. The TWCTOdometer has a characteristic of passive omni-directional motion, which is to follow the omni-directional motion of the ODV. The ODV's current position and orientation are estimated accurately from the measurement values of the TWCTOdometer. The proposed control method uses the estimated current position and orientation that allow the accurate trajectory control of the ODV along desired trajectories. Experimental results show effectiveness of the proposed control method by using the TWCTOdometer.

For the motion planning problem, an iterative algorithm has been proposed as a general method. However, when we apply the algorithm to the problem of under-actuated mechanical systems, there are many cases when the convergence performance becomes too poor and we can not obtain the solution. We investigate the reason why the performance becomes poor and propose a method to improve the convergence performance. The effectiveness of the proposed method is shown by using an index that expresses the convergence performance.

Proposes a feedback control method for wire-suspended mechanisms. The wire-suspended mechanisms are classified into two types, which are completely restrained type mechanisms and incompletely restrained type mechanisms. The paper discusses mainly incompletely restrained type mechanisms form the viewpoint of actual control. The incompletely restrained type wire-suspended mechanism has the merit that it enables three dimensional positioning and orientation of suspended object with simple mechanism using a small number of wires. However it also has the drawback that the manipulated object is easy to swing as seen in overhead crane which is a simple incompletely restrained type mechanism. For this reason, an anti-sway control method for incompletely restrained type mechanisms is needed. To resolve the problem of swing, inverse dynamics for general incompletely restrained type wire-suspended mechanism is discussed, then a feedback control method based on dynamics compensation is presented.

In this paper, we consider cooperative multiple manipulators with passive joints and study the effect of a combination of active and passive joints. This kind of manipulator system may restrict the direction of the end-effector's force depending on which joints are set to passive ones. In the case of operating and transferring a common object, this restriction may give a less effective force and excessive internal force to the object. To use driving force effectively, the question of which joints are set to passive ones must be considered. Therefore, we show the effect of the joint configurations by case studies.

This paper discusses a feedback control method for incompletely restrained wire-suspended mechanisms. The incompletely restrained wire-suspended mechanism has a merit that it enables three dimensional positioning and orientating of suspended object with simple mechanism using a small number of wires. However it also has a drawback that the manipulated object is easy to swing as seen in overhead crane which is one of the simplest incompletely restrained mechanism. For this reason, anti-sway control method for incompletely restrained type mechanisms is needed. A key point of our method is exact linearization using inverse dynamics of the system. Feedback control method with exact linearization and measuring method for the suspended object are presented, and effectiveness of proposed methods are shown by an experiment.

A trajectory planning method of a mobile manipulator is presented. We derive the dynamics of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. The planning problem is formulated as an optimal control problem. To solve the problem, we use the concept of the order of priority. A gradient-based iterative algorithm which synthesize the gradient function in a hierarchical manner based on the order of priority is used. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

Discusses an inverse dynamics problem and proposes a trajectory generation method for wire-suspended mechanisms. The wire-suspended mechanisms are classified into two types, which are completely restrained type mechanisms and incomplete by restrained type mechanisms. For the incompletely restrained type mechanisms, consideration of dynamics is important, because the motion of this mechanism is governed by its dynamics and kinematics, whereas the motion of the completely restrained type mechanism is determined by only its kinematics. The paper discusses mainly the incompletely restrained type mechanisms from the viewpoint of dynamical properties. The incompletely restrained type wire-suspended mechanism has a merit that it enables three dimensional positioning and orientating of suspended object with simple mechanism using a small number of wires. However it also has a drawback that the manipulated object is easy to swing as seen in overhead crane which as a simple incompletely restrained type mechanism. To overcome the problem, inverse dynamics for general incompletely restrained type wire-suspended mechanism is discussed, then a condition on desired trajectory of manipulated object is presented on the basis of the inverse dynamics analysis. Using the desired trajectory, an online trajectory modification method for the control of manually operated overhead crane is proposed.

In this paper, a trajectory planning method of a mobile manipulator with the end-effector's specified path is presented. We derive the dynamics of the mobile manipulator considering it as the combined system of the manipulator and the mobile platform. The planning problem is formulated as an optimal control problem. To solve the problem, we use the concept of the order of priority. A gradient-based iterative algorithm which synthesize the gradient function in a hierarchical manner based on the order of priority is used. The simulation results of the 2-link planar nonholonomic mobile manipulator are given to show the effectiveness of the proposed algorithm.

Proposes a control method for a crane using inverse dynamics calculation of the system. The load of a crane is generally easy to swing and thus the work using the crane is dangerous. For preventing the unfavorable swing of the load, it is desirable to feedback the actual position of the load in a control method. As such a control law, state-feedback control based on linearization of the crane system is often used. However the method reduces control performance when rope length is changed, because of nonlinearity of the system. In the paper, a feedback control method is proposed where the inverse dynamics calculation is involved to compensate non-linear dynamics of the system. In the control system, an observer is used to get higher order derivatives of the position of load, which is needed for the inverse dynamics calculation. By using the control method, control performance is unchangeable for changing rope length. Numerical simulation and experiment are shown to verify the effectiveness of the proposed control method.

In this paper, an optimal motion planning scheme using time-axis transformation and gradient method is proposed for nonholonomic systems. The motion planning of nonholonomic systems can be formulated as a nonlinear optimal control problem. However, the optimal control problem is too difficult to solve due to peculiar difficulty in the control of the nonholonomic systems. To alleviate the difficulty, we first convert the optimal control problem to a bidirectional, fixed-domain optimal control problem by using quasi-time variable. Then, a numerical algorithm which is based on the gradient method is developed for the optimal control problem and its convergence property with respect to final state error is proved. The optimal motion planning scheme is also applied to a 2-link planar free-joint manipulator. The simulation results show the effectiveness of the proposed optimal motion planning scheme.

This paper proposes an algorithm to determine suboptimal paths and trajectories for cooperative multiple manipulators with passive joints. The problem of operating and transferring the object from a given start point to a given goal point is considered. In this case, in general, degrees of freedom of the manipulators are larger than that of the object, and thus this manipulator system involves redundancy. Several joints can be changed to passive ones. We use remaining redundant degrees of freedom to refine trajectories. We apply this algorithm to a two-manipulators system. Simulation results show the effectiveness of the algorithm.

This paper discusses the optimal trajectory planning problem of nonholonomic systems in the presence of obstacles. The problem can be formulated as an optimal control problem by incorporating final state errors and obstacle avoidance conditions in the cost function. To solve the highly nonlinear optimal control problem, we introduce the concept of the order of priority into the trajectory generation procedure. We place the first priority on the convergence of the state to a desired state. The second priority is given to obstacle avoidance and the third priority is given to trajectory optimization. Then, a gradient-based iterative algorithm which synthesizes the gradient function in a hierarchical manner considering the order of priority is proposed. The simulation results of the 3-link planar free-joint manipulator are given to show the effectiveness of the proposed algorithm.

This paper discusses parallel wire mechanisms where an end-effector of the mechanism is suspended by multiple wires. This mechanism enables not only three dimensional positioning but also three dimensional orientating of the end-effector, unlike typical wire suspension type mechanism such as overhead crane. To discuss the parallel wire mechanism, two forms of basic dynamic equations are presented. Then dynamical properties of the mechanism is described based on the basic equations. This paper mainly issues an inverse kinematics problem for general incompletely restrained type parallel wire mechanism. To distinguish some parallel wire mechanisms including the incompletely restrained type, the paper first defines constraint states of the end-effector, then parallel wire mechanisms are classified into three categories based on the definition. Each characteristic of the mechanism corresponding to the categories is described. Especially, incompletely restrained type parallel wire mechanism is mainly discussed in the view point of inverse kinematics problem. After arguing a general solution for the inverse kinematics problem of the incompletely restrained type parallel wire mechanism, an actual mechanism of the incompletely restrained type mechanism is presented and the inverse kinematics problem for this mechanism is analyzed.

This paper addresses a problem of optimal motion planning of mobile platforms amidst obstacles, considering the mobile platform dynamics. Due to nonholonomic constraints, actuator constraints, and state constraints by obstacle avoidance, the planning problem of mobile platform with two independently driven wheels is a complicated one. In this study, a dynamical model for the mobile platform is presented, including nonholonomic kinematic constraints. The idea of a path parameter is introduced to simplify the planning problem by considering the dynamics and nonholonomic constraints. Using the path parameter, the optimal motion planning problem is divided into two sub-problems: 1) time-optimization of trajectory along specified path, and 2) search for optimal path. Then two methods are proposed the solve the problems using the path parameter and parametrization by B-spline function. Finally, quasi-time-optimal solution for the original problem are planned by combining the two methods. Numerical examples show effectiveness of the motion planner.

Discusses the optimal trajectory planning problem of classical nonholonomic systems. Most conventional studies have discussed the nonholonomic motion planning problem considering only kinematics. However, when a trajectory is required to minimize the traveling time or the energy used in performing tasks, the dynamics must be taken into consideration. In this paper, a trajectory planning method that considers the full nonlinear dynamics of the system is proposed. This method is based on the concept of geometric phase and the minimum cost trajectory planning algorithm which were previously developed for motion planning of robotic manipulators. Simulation results show the effectiveness of the proposed method.

This paper discusses an inverse dynamics problem for a parallel wire mechanism with multi-degrees of freedom. Firstly, a crane-type parallel wires mechanism which has three trolleys and three wires is proposed for handling heavy objects. This handling mechanism enables not only three dimensional positioning but also orientating of objects, unlike typical crane mechanism. A dynamical model using wire force vector is derived. Based on the dynamical model with wire force vector, inverse dynamics problem is analytically solved by a linear equation in terms of the wire force vector. The trajectory of end-effector of the crane-type manipulator can be transformed into the trajectory of wire length and trolley position by the calculation method. Using the trajectory of wire length and trolley position, the end-effector of the crane-type manipulator is controlled. Two dimensional experimental crane-type manipulator is also developed to verify an effectiveness of the inverse dynamics calculation and the trajectory control method.

Feedforward control design of flexible robot can take advantage of planning algorithm. In this paper two such algorithms have been presented, one for static case and the other for dynamic case. Both the algorithms are iterative in nature and are computationally based on the minimization of position or tracking error defined at the end-effector level. The algorithms are simple but computationally expensive. The performance is tested on a planar two-link arm through simulation and the results show the capability of the methods to compensate error due to deflection of the flexible links at the time of static condition of positioning and to track a given trajectory effectively at the time of dynamic condition of tracking under end kinematic constraints.

A motion planning problem of a cooperative multiple manipulator system carrying out grinding work or similar works to the object is considered. One manipulator holds the object rigidly and the other holds the tool and works on the object's surface. At the contact point between the object and the tool there exists friction, so that interaction forces must be taken into consideration in the dynamics of manipulators and the object. We only specify the tool task on the object's surface, so the object and manipulators can move arbitrary paths in the world coordinates frame. We propose an algorithm to generate joint trajectories for cooperative multiple manipulators to accomplish the specified task effectively.

Motion planning under fixed travelling time between start and goal point along a specified path is considered in this study. The structure between the actuator and the end point of the robot arm is assumed flexible and is the main cause of positioning error because of residual vibration. An algorithm is developed to generate motion of the manipulator arm along the specified path that significantly reduces the residual vibration, at the goal point configuration. The problem also considers the full nonlinear dynamics of the manipulator arm. The dynamics are described by finite element method using Lagrange's equation and are expressed by the time scale factor. The performance index is optimized successfully through off-line computation for a two link flexible manipulator, one example of which is described in detail.

The tracking error of robot manipulators based on flexible arm models are presented in this study. The number of actuator is equal to the dimension of the task space which is usually equal to the rigid body degrees of freedom. Actuator torques required for a flexible arm to track a given trajectory are formulated and computed by an iterative algorithm which is based on path planning method. The formulation is complete in the sense that it also considers the full nonlinear dynamics of the manipulator arm. The Euler-Bernoulli beam theory is used to model the dynamics of flexible links and the resulting equations of motion are derived by Lagrange's equation using finite element discretization technique. The algorithm is simple to implement but computationally expensive. The performance and capabilities of the proposed method are tested on a two-link arm through simulation and the results show the potential use of this method not only for feedforward open-loop control but also for closed-loop control strategies.

Addresses a problem of time-optimal motion planning of skid-steer mobile robots amidst obstacles. Due to nonholonomic constraints, actuator constraints, and state constraints by obstacle avoidance, the planning problem is a complicated one. In this study, the problem is divided into two sub-problems: (1) time-optimization of trajectory along specified path, (2) search for the optimal path, to alleviate the difficulties of the original problem. Then two methods to solve the problems are proposed, using an idea of path parameter and parametrization by B-spline function. Finally, quasi-optimal solutions for the original problem are obtained by combining the two algorithms. A simulation result shows an effectiveness of the proposed motion planner.

Two methods are presented to design the joint trajectory for a two-link flexible manipulator: 1) a combined Fourier series and polynomial function; and 2) a B-spline function. In both cases, the path satisfies the start and end kinematic constraints of motion. Using the energy approach for the above two cases, the final path is generated optimizing kinetic and strain energy at the goal point that reduces the residual vibration significantly. The present study is to compare the two methods and to predict that the B-spline curve has faster convergence property and at the same time, minimizes the performance index by six-fold and thus gives further reduction of residual vibration compared to the combined Fourier series and polynomial function. The dynamics of the manipulator arm, during its motion as well as free vibration after reaching the goal, are described by finite element analysis using Lagrange's equation of motion.

Rapid end point positioning along a specified path is considered in this study. The structure between the actuator and the end point of the robot arm is assumed flexible and is the main cause of positioning error because of residual vibration. An algorithm, based on optimization of residual energy at the goal point and the fundamental property of time scaling of manipulator dynamics, is developed that iteratively determines the time optimal trajectory along the specified path under given start and end point conditions. It also considers the full nonlinear dynamics of the manipulator arm and its actuator saturation limit, The dynamics are described by finite element method using Lagrange's equation and are expressed by the time scale factor. The performance index is optimized successfully through off-line computation for a two link flexible manipulator, one example of which is described in detail.

This paper proposes a method of planning collision free joints paths for two cooperative manipulators. When two manipulators hold a common object and execute specified tasks, there are problems related to handling and collision. To move two manipulators effectively, all of them must be considered together. There are redundancy aspects peculiar to the cooperative two manipulators. We use this redundancy and the potential function method to avoid collisions between the object and the link, the link and the link, the link and the obstacle and so on. Simulation results show the effectiveness of the proposed method.

This paper proposes a method for planning the collision free trajectory of a manipulator. In this method, geometrical constraints to avoid obstacles are represented by restrictive potential functions. The dynamic equation of the manipulator is expressed by a path parameter 's' which is the generalized length along the path. The driving torque/force is improved by taking shorter travelling time and collision avoidance into considerations. Finally, the proposed method is applied to a manipulator with three links and is shown to be effective.

A method for a time optimal collision free trajectory planning problem is proposed. In this paper, the dynamics of manipulator and obstacles are considered. This type of optimal trajectory planning problem is very difficult and complicated one because of the nonlinearity of manipulator dynamics and existence of obstacles. Generally, it results in a multimodal optimization problem. The proposed method is basically an iteratively improving one based on a gradient method. Firstly, two global methods (a genetic algorithm or an exact cell decomposition method) are used to search multiple initial feasible spatial paths for the gradient method. Next, the gradient method searches the time optimal solution locally with the multiple initial feasible solutions. Simulation results show that this is an effective approach to the time optimal collision free trajectory planning problem.>

Proposes a method of planning collision-free trajectories for two manipulators considering dynamic constraints. This algorithm is composed of two planning stages. In the first stage, minimum time trajectories for two manipulators are searched with limits of input torques/forces. In the second stage, if there is interference between two obtained trajectories, motion priority is given to two manipulators in order to avoid collision. Collision-free trajectories are obtained along the paths generated in the first stage and their traveling times are shortened, too.>

A pattern recognition method using an artificial hand to identify the pattern of a grasped object and to locate its position relative to the hand coordinates is discussed. In the proposed recognition method, an object is recognized as a pile of two-dimensional slices, namely, a pile of plane closed curves. Each curve (i.e., contour) is described as the distribution pattern of unit-vectors, called the unit-vector distribution (UVD). The proposed recognition method using UVD functions is as follows. 1) Given the a priori information about the contours of objects to be grasped, the UVD's of their contours are calculated and memorized. These are called the original patterns (OP's). 2) Then a sampled UVD is formed from real tactile data and called the data pattern (DP). 3) The DP is compared with the memorized patterns (MP's), which are obtained by blurring the corresponding OP, so as to make it easier to single out the best fitted OP. 4) Finally, the contour is regenerated in the hand coordinate system by using the UVD of the singled out pattern. An experiment using a trial sensor and a model hand has shown the effectiveness of the proposed method in the recognition of several kinds of objects having cylindrical and prismatic contours.