Daisuke Yashiro

Performance Analysis of Bilateral Control System With Communication Bandwidth Constraint

It is difficult to realize a transparent bilateral control over network because communication time delay, jitter, or packet loss deteriorates transparency and stability. Although many dead time compensation methods have been considered, each approach does not realize both high transparency and stability. To solve the problem, our previous work has proposed a multirate sampling method for bilateral control systems. In this approach, packet-sending period tp is set to larger than the control period of the master/slave robot control tc. This method has an advantage to improve the transparency because large tp often reduces communication delays. However, that work has not shown the relationship between the transparency and the value of tp. Therefore, this paper analyzes the relationship between the transparency and tp by introducing frequency characteristic of an ideal sampler and a zero-order holder. In addition, the validity of the analysis is shown by experimental results.

Abstraction of Action Components Unconstrained by Alignment of Haptic Sensing Points

This paper proposes an abstraction method of independent components of human action from haptic information. First, the haptic information is obtained using a haptic device (haptic bilateral system). Second, the action components can be abstracted from the haptic information by using the proposed method. The proposed method achieves abstraction of the action components unconstrained by the alignment of sensing points with simple calculations. The proposed method is applied for grasping and manipulation motions by two- and three-finger robots. The validity of the proposed method is shown by the experimental results.

Motion control systems with network delay

In this paper motion control systems with delay in measurement and control channels are discussed and a new structure of the observer-predictor is proposed. The feature of the proposed system is enforcement of the convergence in both the estimation and the prediction of the plant output in the presence of the variable, unknown delay in both measurement and in the control channels. The estimation is based on the available data — undelayed control input, the delayed measurement of position or velocity and the nominal parameters of the plant and it does not require apriori knowledge of the delay. The stability and convergence is proven and selection of observer and the controller parameters is discussed. Experimental results are shown to illustrate the theoretical predictions.

Design of a PID controller based on H ∞ loop shaping method using frequency responses

Robust control is used for a system with perturbations of a plant and disturbances. Above all, H∞ loop shaping method is known as a method showing a good control performance. However, this method takes designing cost because it needs a mathematical model of the actual plant. In order to reduce the identification cost, we propose a fixed-order controller design method which only uses frequency responses. The proposed method can derive a controller satisfying the better control performance with non-linear optimization.

Multirate sampling method for bilateral control with communication bandwidth constraint

This paper proposes a multirate sampling method for bilateral control systems over network. In the proposed structure, packet-sending period is larger than control period of motor control. This packet contains position and force information that is transmitted between master side and slave side. In general, packet sending period is equal to control period. The reason comes from the fact that data size of this packet is so small that communication bandwidth between master and slave has not been considered. However, we confirmed a phenomenon that the smaller the packet-sending period, the larger the communication delay. Therefore relationship between packet-sending period and control period should be considered in order to design high transparent bilateral control systems. The validity of the proposed multirate sampling method is shown by numerical and experimental results.

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.

Wireless Haptic Communication Under Varying Delay by Switching-Channel Bilateral Control With Energy Monitor

A switching-channel bilateral control with energy monitor (EM) is newly proposed to realize haptic communication through a wireless network. The varying delay in the communication line and the situation of duplex operation are considered. In such a system, human operators on two sides of the master-slave robots system feel the hardness of the remote environment placed on the contralateral side. The EM approach is presented to judge the role of the robot (manipulated by an operator or contacting an environment), which provides a beacon for the switching algorithm. The position tracking of the system is improved by switching off the channel of force control in the human manipulated robot. The problem of position drift in traditional methods is overcome. Disturbance observer is applied to simplify the design of the bilateral control law, and to guarantee the efficient force switching. Because of improved position tracking and satisfactory force fidelity, the proposed approach achieves more vivid haptic transmission. By experiments, the validity is verified.

Central controller based hybrid control with communication delay compensator

This paper proposes a structure for a position/force hybrid control through network. In the case of most conventional structures, each terminal controller transmits a position/force interactively. Then these terminals calculate acceleration references by themselves. In contrast, our previous research proposed a novel structure for a position/force hybrid control through network. In this approach, a position/force is transmitted from each terminal controller to a central controller. Then, the central controller calculates acceleration references that are feedback to the terminals. This structure makes it possible to achieve mode-based hybrid controls through networks. However, this structure causes measurable steady-state error that is induced by a delay time compensator. To solve this problem, this paper introduces a delay time compensator that does not require a delay model. This compensator is applied to the central controller based hybrid control system. The validity of the proposed controller is confirmed by experiments.

Feedback Controller With Low-Pass-Filter-Based Delay Regulation for Networked Control Systems

This paper proposes a novel traffic shaping algorithm for jitter buffers. Jitter buffers are effective in reducing jitter and therefore constitute an important technique used to improve the quality of real-time communication. Traffic shaping regulates the interval between packets received at the destination. Although the well-known dynamic jitter buffer needs to identify the maximum one-way delay and current one-way delays in the network, it is not necessary for our proposed approach to supply this information. Our algorithm utilizes a feedback controller to adjust the queuing delay in the jitter buffer to avoid packet overrun and underrun. In addition, a constant packet-receiving interval is achieved by employing a low-pass filter. The validity of our proposed method is confirmed through experiments of position control over a network.

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.