Takahiro Nozaki

Decoupling Strategy for Position and Force Control Based on Modal Space Disturbance Observer

This paper extends the diagonalization method on the basis of the modal space disturbance observer (MDOB) for application to a multidegree-of-freedom (DOF) system. The aim of this method is to suppress the interference between the position and force control systems and realize a bilateral control system. The utility of the proposed method is experimentally verified by using a multi-DOF manipulator. It is confirmed that the MDOB-based decoupling method has better performance than oblique coordinate control. Conventional oblique coordinate control causes oscillation in cases where the modeling error is large and the cutoff frequency of an observer is not high enough to change the system dynamics. On the other hand, the MDOB-based decoupling method becomes unstable when the difference in mass is large.

Heartbeat Synchronization With Haptic Feedback for Telesurgical Robot

Motion-canceling bilateral control, a teleoperation method, is proposed and implemented for telesurgical robots. Telesurgical robots have difficulty in achieving control owing to a lack of haptic feedback and the beating motion of organs. Hence, this study aims to provide a surgeon with the means for feeling the tactile sensation of the remote organ, as well as synchronizing with its motion. Therefore, a surgeon can treat the target using a master robot as if the organ is not moving even though it actually moves. The proposed method basically consists of acceleration-based bilateral control to achieve haptic feedback, and visual servoing is used to compensate for organ motion. The frequency characteristics and root locus of the proposed method are analyzed to evaluate its performance and stability, respectively. The proposal is validated through experiments using telesurgical forceps robots.

Motion Expression by Elemental Separation of Haptic Information

This study aims to reveal the concealed features of human motions. For this purpose, a method of elemental separation (ES method) of human motions is proposed. First, human motions are extracted as haptic information through a bilateral control system. Then, by using the proposed method, the haptic information is divided into basic elements: 1) transformation matrices; 2) hybrid angles; 3) pure position commands; and 4) pure force commands. The proposed method is validated through simulations as well as experiments with robotic and human operators. The obtained results clearly reveal the features of human motions, although it is difficult to recognize the differences from the original responses. Nonetheless, this study provides a motion expression that should contribute toward a greater understanding of human skill.

Recognition of Grasping Motion Based on Modal Space Haptic Information Using DP Pattern-Matching Algorithm

Human motion recognition systems play an important role in improving the ability of robots to support human life. This paper proposes a novel motion recognition method based on haptic data (i.e., position and force information). First, haptic data are obtained using a bilateral control system. Second, the haptic data are divided into action components, using modal transformation. Finally, both the position and the force information in each action component are compared with recorded data. A dynamic programming pattern-matching algorithm is used to recognize the desired motion, and the validity of the proposed method is verified experimentally. In the experiments, the proposed method is applied to a grasping motion. The proposed method can trigger scaled bilateral control and assist the operator in real time.

Stiffness Transmission of Scaling Bilateral Control System by Gyrator Element Integration

Bilateral control is one of the methods to transfer remote environmental haptic sense to the operator. The conventional bilateral control design contains a problem in transmitting correct environmental haptic sense when velocity information is transferred in a scaling manner. This paper proposes a novel bilateral control design integrating gyrator element to improve tactile sense transmission under velocity scaling. The problem is explained in two velocity scaling values, namely, constant value scaling and scaling with derivation. The proposed method is effective in both of the scaling methods. Analyses and experiments are performed to clarify the effect of the proposal.

The power factor in mechanical system

This paper represents a analytical, simulation and experimental study of power factor in mechanical system. In electrical system, power factor is often used to evaluate how intense we can use the electrical power as a active electrical power. It is useful when considering the power consumption of the electrical system. However, this kind of approach did not exist in mechanical system. In mechanical system, we consider mechanical loss of energy, however we did not consider the amount of power used in the phase change. Thus this study introduces the power factor in the mechanical system and investigates how much power is actually used in the motion. Power factor of certain frequency of the motion was analyzed and compared with the simulation results. Experiments were conducted to further study the behavior of power factor in many situations. Experimental results signify power factor changes due to the speed of the motion and also path of the motion.

Power factor analyses in mechanical system focusing on trajectory and environment

This paper examines two approaches to determine power factor of the mechanical system. First approach is vector expression approach. This method is based on analogy of mechanical system and electrical system, especially focusing on phase characteristic of environment. Another approach is mathematical analysis approach. This method is based on power factor determination method focusing on active power and apparent power. Comparison suggests vector expression approach has advantage in simplicity, though it is only valid in pure cosine wave. Cosine wave with DC component and ramp velocity case is also analyzed to show how they differ from vector expression approach. Experiment and simulation results supports validity of analyses in this paper.

Development of 16-DOF telesurgical forceps master/slave robot with haptics

Minimally invasive surgery (MIS) has attracted attention recently. MIS such as endoscopic surgery considers a patients quality of life. In endoscopic surgeries, bilateral control systems are strongly required to apply. It is necessary to develop the multi Degrees Of Freedom (DOF) robot to achieve various operation procedures including endoscopic surgery. In this paper, 16-DOF haptic telesurgery master/slave robot is developed. This master/slave robot has two arms, and each arm has 8-DOF. The bilateral control using 4ch controller is implemented in the master/slave robot. Experiments of peeling motion and suturing motion are performed by a surgeon to evaluate the development robot.

A controller design method for multirobot systems based on task projection matrix

Future motion systems should interact with other systems and unstructured environments. Therefore, a realization of multirobot systems and impedance control systems is necessary in order to adapt to various environments. This paper proposes a task projection control in an attempt to achieve a unified control of multirobot systems. First, the interactions are abstracted by using a quarry matrix. Then, the center of the motion is changed based on a task projection matrix. The task projection matrix consists of a quarry matrix, normalization matrix, and a projection matrix. Each desired motion can be designed and achieved independently, though the target object is an entirely-unknown object. This paper also proposes a novel control index named “hybrid angle”. The hybrid angle is defined as a ratio of an effect of a position control system and a force control system. The relationship between the hybrid angle and the control stiffness is clarified in this paper. The proposed task projection control is applied for grasping motion by multirobot systems. Two kinds of experiments are conducted. One is a motion division based on the task projection matrix, and the other is an impedance control based on the hybrid angle. The experimental results show the viability of the proposed method.

Environmental Robust Position Control for Compact Solenoid Actuators by Sensorless Simultaneous Estimation of Position and Force

This paper aims to realize compact actuation systems by sensorless approach. This study adopts solenoid actuators which have advantageous characteristics from the view point in inexpensive cost, simple structure, and high-output force in spite of difficulty in low cost position and force sensing. Some sensorless position estimation techniques for solenoid actuators were reported. However, position and force simultaneous estimation has not sufficiently been achieved. In addition, any real-time feedback control has not been reported. This paper proposes sensorless feedback position control for compact solenoid actuators. The force generation and position/force estimation are conducted by using a dc supply power superposed by an ac component. This control technique has three main features: 1) separation of the power supply into ac and dc components for the position estimation, 2) simultaneous real-time estimation of position and force, and 3) robust feedback position control. Simulations and experiments were conducted for verification of the proposed control with the above three features, and the results indicated that error between the estimation and actual positions was within 0.2 mm. This proposed system offers a new avenue for compact and inexpensive application field.