Metal spinning is a plastic forming process in which a relatively ductile metal sheet is forced onto a rotataing mandrel by using a roller tool. This study is aimed at developing a versatile and intelligent forming process and expand the application area of robotic manufacturing processes. In this research, the metal spinning process has been accomplished with an industrial robot. Trajectory control algorothms have been implemented. The effectiveness and the applicability of the proposed method have been experimentally verified. In addition, wrinkle occurences have been experimentally analyzed with repect to spinning conditions.

Metal spinning is a plastic forming process that forms a metal sheet by forcing the metal onto a rotating mandrel using a roller tool. A novel metal spinning machine was designed in which the roller is directly driven by linear motors. We aim to form non-axisymmetric products by controlling the pushing force of the roller so that the roller can quickly track the changing radius of the mandrel. Our experimental results show that the linear motors substantially improve response of the force control and non-axisymmetric products can be rapidly formed. Open-loop force control without a force sensor was also studied. It exhibited a comparable performance to closed-loop control with regard to the forming time

Metal spinning is a plastic forming process that forms a metal sheet by forcing the metal onto a rotating mandrel using a roller tool. Products formed by metal spinning have been inherently limited to round shapes. In this paper, we propose metal spinning of non-axisymmetric products by applying hybrid position/force control. The pushing force of the roller is regulated so that the roller can track the changing radius of the mandrel. Our forming experiment demonstrates that a thin aluminum sheet can be formed into a non-axisymmetric shape.

Metal spinning is a plasticity forming process that forms a metal sheet or tube by forcing the metal onto a rotating mandrel using a roller tool. This is a study on metal spinning applying robot control techniques such as force feedback control with the aim to develop flexible and intelligent forming processes, and to expand a new application area for robot control. An experimental setup was developed for gathering basic data on the forming process. Some results of preliminary experiments are presented. The influence of the clearance between the roller and mandrel is also discussed. The author proposes applying hybrid position/force control for shear spinning, which is free from fine adjustment of the clearance. The effectiveness of the proposed method was experimentally verified.

We present a method for controlling mobile manipulators for assist systems. The mobile manipulator should provide good manipulability and stability at any time. Most of mobile assist systems have a heavy mobile base for stability. We propose an approach for motion control of a mobile manipulator to remove unnecessary movement of the mobile base. In our proposed scheme, the mobile base does not move until the manipulator tip position or the mobile base goes over the preferred operating area which compensates the manipulability and the stability. The boundary of the area is the virtual impedance wall consisting of a spring and a damper by impedance control. If the manipulator tip position or the mobile base reaches the boundary, the mobile base starts to move by a repulsive force from the virtual wall and recovers the system conditions. To verify the validity of the proposed scheme, we have carried out experiments employing a graphic simulator and a real robot. The experimental result shows the effectiveness of the proposed scheme.

Humans can easily maneuver some types of nonholonomic systems, e.g. wheeled vehicles, while other types, e.g. space robots, are difficult to handle intuitively. We propose a human interface to simplify the operation of "difficult" nonholonomic systems, which utilizes the human ability to maneuver "easy" systems. The difficult real system is converted into an easy virtual system using coordinate and input transformation. The input from the human operator to the virtual system is converted into input to the real system, while the state of the real system is converted into that of the virtual system which is displayed to the operator. The operator can then steer the real system feeling as if maneuvering the virtual system. Our experiments show that the operating performance is improved by this method.

Deals with human-robot cooperative handling of a long object in 3-D space. We assume that the operator and the robot grasp each end of the object and carry it cooperatively. In this task, it is difficult for the human operator to apply a large torque to give a translational force at the robot hand. Thus, we propose to assign a virtual nonholonomic constraint to the robot hand. In this method, the robot behaves like a unicycle and we only use translational force to manipulate it. The controllability is assured based on nonholomony and the operator can transport the object to the desired position and posture in 3-D space by a similar skill using a wheelbarrow. The effectiveness of our method is experimentally verified.

Biped robots have better mobility than conventional wheeled robots, but they tend to tip over easily. To be able to walk stably in various environments, such as on rough terrain, up and down slopes, or in regions containing obstacles, it is necessary for the robot to adapt to the ground conditions with a foot motion, and maintain its stability with a torso motion. When the ground conditions and stability constraint are satisfied, it is desirable to select a walking pattern that requires small torque and velocity of the joint actuators. We first formulate the constraints of the foot motion parameters. By varying the values of the constraint parameters, we can produce different types of foot motion to adapt to ground conditions. We then propose a method for formulating the problem of the smooth hip motion with the largest stability margin using only two parameters, and derive the hip trajectory by iterative computation. Finally, the correlation between the actuator specifications and the walking patterns is described through simulation studies, and the effectiveness of the proposed methods is confirmed by simulation examples and experimental results.

A robotic assistance system for handling long objects that are difficult to manipulate with only one point of support is presented. The robot grasps one end of the object and helps the human operator to carry at the other end. Such cooperative manipulation in a horizontal plane is considered here. The control method proposed uses a virtual nonholonomic constraint. The movement of the object is constrained as if it were being carried on a wheel attached to the object. This method can prevent the object from slipping sideways and simplify the carrying operation. The experimental results show that an operator can easily handle a long object when aided by the robot.

Since a biped robot tends to tip over easily, stable and reliable biped walking is a very important achievement. In this paper, we propose a balance control method based on an off-line planned walking pattern with real-time modification. First, a method of generating a highly stable, smooth walking pattern is presented. Then, a method of real-time modification consisting of body posture control, actual zero moment point control and landing time control based sensor information is proposed. By combining the proposed off-line walking pattern with real-time modification, the biped robot can walk smoothly and adapt to unknown environments. The effectiveness of the proposed method is confirmed by dynamic simulator such as walking on unexpected irregular rough terrain, soft ground and in environments in the presence of disturbances.

Since a biped humanoid inherently suffers from instability and always risks to tipping over, stable and reliable biped walking is the most important goal. The simulator is a significant tool to pursue this goal. In this paper, we first present a method for constructing a humanoid simulator that can closely model and predict the motion of an actual humanoid. We then propose a balance controller consisting of an off-line walk-pattern generator and a real-time modification. Using the simulator, we can predict the humanoid's physical capability subject to the constraints of actuators, and clarify the required specifications of actuators to execute a desired task. The functions of the developed simulator and the effectiveness of the proposed balance controller were evaluated through simulated walks on an unknown rough terrain, soft ground, and an environment in the presence of disturbances.

We discuss a robotic system that assists a human to carry a long object. The operator and the robot grasp each end of the object and carry it cooperatively. We extend the concept of virtual nonholonomic constraint to the motion in a vertical plane, in which the robot wrist behaves like a wheel and the operator can maneuver the object like a wheelbarrow. The operator and the robot can cooperatively lift the object to the desired height and inclination. Furthermore, we combine the vertical motion and the horizontal motion to carry the object to the desired position and posture in 3D space. The effectiveness of our method is experimentally confirmed.

Biped robots have better mobility than conventional wheeled robots, but they tip over easily. In order to walk stably in various environments such as rough terrain, up and down slopes, or regions containing obstacles, it is desirable to adapt to such ground conditions with a suitable foot motion, and maintain the stability of the robot by a smooth hip motion. We propose a method to plan a walking pattern consisting of a foot trajectory and a hip trajectory. First, we formulate the constraints of a foot trajectory, and generate the foot trajectory by 3rd order spline interpolation. By setting the values of constraint parameters, it is easy to produce different types of foot motion. Then, we formulate a hip trajectory using a 3rd order periodic spline function, and derive the hip trajectory with high stability. Finally, the effectiveness of the proposed method is illustrated by simulation examples.

Deals with an assist system for carrying a long object with a human operator. When we carry such an object, we often grasp both ends and move it cooperatively. Our purpose is to establish how to design the assist system which can achieve such a task. It is difficult to apply conventional control laws. On the other hand, humans can achieve such a task. Therefore, we measure the human cooperative behaviors and analyze them to find the cooperative rules. Based on the rules, we propose a control law of the assist system. Furthermore, we construct a prototype system and verify the validity of the control law.

Since most conventional robots cannot easily be adapted to environments designed for humans, a human-size biped robot is expected to be able to play an important role in assisting human activities. The selection of suitable joint actuators is an important point when developing a human-size biped robot. In order to select suitable actuators and effectively utilize the selected actuators, it is necessary to clarify the relationship between walking patterns and the specifications of each joint actuator, and this is the issue tackled in the paper. First, a method of generating a high stability, smooth walking pattern is presented, and it is shown how various walking patterns can be produced by setting a series of defined walking parameters. Then, the dynamics of the robot, including the reaction force between the feet and the ground, are formulated. Finally, by simulation studies, the correlation found between actuator specifications and walking patterns is described, and the effectiveness of the proposed method is suggested.

Position control of an underactuated manipulator that has one passive joint is investigated. The dynamic constraint caused by the passive joint is second-order nonholonomic. Time-scaling of the active joint trajectory and bi-directional motion planning from the initial and the desired configurations provide an exact solution of the positioning trajectory. The active and passive joints can be positioned to the desired angles simultaneously by swinging the active joints only twice. Feedback control constrains the manipulator along the planned path in the configuration space. Simulation and experimental results show the validity of the proposed methods.

Studies motion planning from one zero velocity state to another for a three-joint robot in a horizontal plane with a passive revolute third joint. Such a robot is small-time locally controllable on an open subset of its zero velocity section, allowing it to follow any path in this subset arbitrarily closely. However some paths are "preferred" by the dynamics of the manipulator in that they can be followed at higher speeds. We describe an algorithm that plans collision-free paths in the robot's configuration space, where the motions correspond to dynamically preferred robot motions. Thus the problem of planning fast trajectories in the robot's six-dimensional state space is reduced to the computationally simpler problems of planning paths in the three-dimensional configuration space and time-scaling the paths according to the manipulator dynamics. Implementation on an underactuated manipulator is described.

We study the juggler skill called the "butterfly". Starting with a ball resting on the palm of his/her open hand, a skilled juggler can accelerate and shape his/her hand so that the ball rolls up the fingers, over the top, and back down to the back of the hand. This paper describes a robotic implementation of the butterfly. The combined hand shape and motion set the rolling motion of the ball, and we find that the shape and motion parameters enter the dynamic equations in a similar way. We define parametrized spaces of hand shape and motion, and using a simulation based on the rolling equations, we identify shape and motion solutions that roll the ball from one side of the hand to the other. We describe an implementation of the butterfly on our planar dynamic manipulation testbed FLATLAND. This example is our first step toward exploring the roles of shape and motion in dynamic manipulation.

Control of a manipulator with a passive joint which has neither an actuator nor a holding brake is investigated. The manipulator has three degrees of freedom in a horizontal plane, with the third joint being passive. The dynamic constraint on the free link is shown to be second-order nonholonomic. Controllability of the system is proved by constructing examples of the input trajectories from arbitrary initial states to arbitrary desired states, considering the motion of the center of percussion of the link. Trajectories for positioning are composed of simple translational and rotational trajectory segments. The trajectory segments are stabilized by nonlinear feedback control. Simulations and experimental results show the effectiveness of the planned trajectory and the feedback control law.

Feedback control of a manipulator with a passive joint which has neither an actuator nor a holding brake is investigated. The manipulator has three degrees of freedom in a horizontal plane, with the third joint being passive. The dynamic constraint on the free link is 2nd-order nonholonomic. A trajectory for positioning is composed of simple translational and rotational trajectory segments. The trajectory segments are stabilized by nonlinear feedback, considering the motion of the center of percussion of the free link. Simulation results show the effectiveness of the feedback control.

This paper present the design concept of a power assist system. In such system, when the controller is designed without considering the maximum torque of the actuators, the actuators can sometimes become saturated, resulting in a loss of stability and manoeuvrability. We propose a method for dealing with this problem. The load force is divided into gravitational and dynamic component, and each component is attenuated by an individual ratio. These ratios are determined considering the maximum power of the operator and the actuators.

Controllability of a manipulator with a passive joint which has neither an actuator nor a holding brake is investigated. The manipulator has 3 degrees of freedom in a horizontal plane and the third joint is passive. The dynamic constraint on the third link is 2nd-order nonholonomic. The controllability is proved by constructing examples of the input trajectories from arbitrary initial slates to arbitrary desired slates. The proof is intuitively understandable, and the construction of the input directly leads to the trajectory planning. Simulations show that the manipulator can reach the desired position and velocity by the constructed input.

Position control of a manipulator with a passive joint which has neither an actuator nor a holding brake is investigated. The manipulator has three degrees of freedom in a horizontal plane, with the third joint being passive. The dynamic constraint on the free link is 2nd-order nonholonomic. Trajectories from initial configurations to desired configurations are planned by combining simple translational and rotational trajectory segments, considering motion of the center of impact of the free link. This planning method is very fast because it requires no iteration. Feedback control using the passive joint angle is applied. Experimental results of positioning are presented.

When the minimum-time trajectory of a manipulator along a geometrically prescribed path is planned, considering the manipulator's dynamics and actuators' torque limits, at least one of the joints is at the torque limit. The execution of such a trajectory by a conventional feedback scheme results in torque saturation. Consequently, the tracking error cannot be suppressed and the manipulator may deviate from the desired path. We propose a feedback control method for path tracking which takes the torque saturation into account. A "path coordinate system" is defined, which is composed of the component along the desired path and the components normal to the path. Control of the components normal to the path is given priority in order to keep the motion of the manipulator on the path. A disturbance observer is used to estimate nonlinear dynamics instead of calculating them directly. This method can reduce real-time computations and can also reject unmodeled disturbances. The simulations of a two-degree-of-freedom manipulator show the effectiveness of the method.>

A method for controlling a manipulator with passive joints, which have no actuators, in operational space is presented. The equation of motion is described in terms of operational coordinates. The coordinates are separated into active and passive components. The acceleration of the active components can be arbitrarily adjusted by using the coupling characteristics of manipulator dynamics. This method is also extended to path tracking control of a manipulator with passive joints. A desired path is geometrically specified in operational space. The position of the manipulator is controlled to follow the path. In this method, a path coordinate system based on the path is defined in operational space. The path coordinates consist of a component parallel to the path and components normal to the path. The acceleration of the components normal to the path is controlled according to feedback based on tracking error by using the dynamic coupling among the components. This in turn keeps the manipulator on the path. The effectiveness of the method is verified by experiments using a two-degree-of-freedom manipulator with a passive joint.>

When the minimum-time trajectory of a manipulator along a geometrically prescribed path is planned taking into consideration the manipulator's dynamics and actuator's torque limits, at least one of the joints should be at the torque limit. The execution of such a trajectory by a conventional feedback control scheme results in torque saturation. Consequently, the tracking error cannot be suppressed and the manipulator may deviate from the desired path. In this paper, the author's propose a feedback control method for path tracking which takes the torque saturation into account. Based on the desired path, a coordinate system called path coordinates is defined. The path coordinates are composed of the component along the path and the components normal to the path. The equation of motion is described in terms of the path coordinates. Control of the components normal to the path is given priority in order to keep the motion of the manipulator on the path. Simulations of a two-degree-of-freedom manipulator show the effectiveness of this method. >

A method for controlling the tip position of a manipulator with passive joints, which have no actuators, in an operational coordinate space is presented. The equations of motion are described in terms of operational coordinates. The coordinates are separated into controlled coordinates and compensating coordinates. The accelerations of the controlled coordinates can be arbitrarily adjusted by using dynamic coupling of the manipulator. The effectiveness of the method is verified by experiments using a two-degree-of-freedom manipulator with a passive joint. The experiments show that the controlled coordinates of the position of the manipulator can be controlled precisely by means of the proposed method.>

A method is proposed of path tracking control of a manipulator with passive joints, i.e. having no actuators. A desired path is geometrically specified in operational space. The position of the manipulator is controlled to follow the desired path. In this method, a path coordinate system based on the desired path is defined in operational space. The path coordinates consist of a component parallel to the desired path and components normal to the desired path. The equation of motion of the manipulator is described in terms of the path coordinates. The acceleration of the components normal to the desired path is controlled according to the feedback based on tracking errors by using the dynamic coupling among the components. This in turn keeps the manipulator on the desired path. Results of path tracking experiments using a two-degree-of-freedom manipulator with a passive joint are presented.>

A method of controlling the position of a manipulator composed of active and passive joints is described. The active joints have actuators and position sensors. The passive joints have holding brakes instead of actuators. While the brakes are released, the passive joints are indirectly controlled by the motion of the active joints using the coupling characteristics of manipulator dynamics. While the brakes are engaged, the passive joints are fixed and the active joints are controlled. The position of the manipulator is controlled by combining these two control modes. The basic principle of the control method and the conditions that ensure the controllability of the passive joints are described. An algorithm for point-to-point control of the manipulator is presented. The feasibility of the method is demonstrated by simulations for a manipulator with two degrees of freedom.>