Eiichi Saito

Vibration suppression of resonant system by using wave compensator

Vibration control of resonant system is an important problem in industry applications. The reason is that degradation of task accuracy and destruction of materials are caused by vibration. Under such a background, state feedback control, H∞ control, and resonant ratio control based on lumped parameter system have been researched for vibration suppression of system with flexible mechanism. On the other hand, methods in distributed parameter model need a lot of calculation in time domain design. In this paper, to suppress vibration of resonant system, a novel position controller based on a transfer function of wave equation is proposed. Superposition of a traveling wave and the reflection wave causes ordinary wave and vibration occurs. Therefore, a method of reflected wave rejection is proposed. Moreover, the proposed method is applied to a two-mass resonant system and three-mass resonant system. Because the proposed method is based on a distributed parameter model, all vibration modes can be suppressed. The effectiveness of the proposed method is verified by experimental results in a 2-mass and 3-mass resonant system.

A filter design method in disturbance observer for improvement of robustness against disturbance in time delay system

Control of time delay system has been researched for a long time. In time delay system, feedback including time delay sometimes makes transient response of a system worse. In the worst case, the system becomes unstable. As time delay compensation method, various methods have been proposed, for example, smith predictor, communication disturbance observer, and so on. In particular, communication disturbance observer is superior than smith predictor in terms of no using a time delay model. However, if an error in plant model exists or disturbance is applied to the system, steady-state error occurs. As disturbance rejection method, communication disturbance observer with an disturbance observer and an integrator in outer loop was proposed in conventional research. But using this method, time delay compensation and disturbance rejection can not be designed independently. Therefore, in this paper, an integrator is not used and two degrees of freedom control is conducted by communication disturbance observer and disturbance observer. For eliminating disturbance, a novel filter design method is proposed. Using proposed filter, the effect of disturbance is suppressed. Finally, the validity of the proposed method is verified by simulation results.

Vibration control of resonant system by using reflected wave rejection with fractional order low-pass filter

This paper proposes a novel vibration control of a resonant system by using a reflected wave rejection with a fractional order low-pass filter. In a conventional research, a vibration control using a reflected wave rejection based on wave equation was proposed. From the viewpoint of the wave, vibrations are suppressed by eliminating a reflected wave. The conventional method can suppress the all resonances by using a reflected wave rejection. However, the conventional reflected wave rejection assumes that poles of the resonant system are located on the imaginary axis at regular intervals. Considering real industry application, there is few case that the above assumption is realized. Therefore, in this paper, the resonant system is modeled as a wave equation including not only spring but also damper. Considering the damper effect, the proposed method is not restricted by the above assumption. In addition, based on the wave equation including the damper effect, this paper presents the method of eliminating the reflected wave. The reflected wave is eliminated by a novel reflected wave rejection with a fractional order low-pass filter. Finally, the validity of the proposed method is verified by simulation and experimental results.

Vibration control of flexible system with communication delay using wave compensator

Recently, teleoperated robots have been researched for working in ultimate environment actively. Developing performance of teleoperated robots, it will be possible for human to work in such a ultimate environment with safety. However, in the actual case, as gears are used for amplifying output, stiffness of connection part reduces and vibration occurs. Moreover, communication delay causes vibration, too. In addition, in the worst case, the system becomes unstable. Therefore, in this paper, for suppression of the vibration, vibration control using wave compensator is proposed. In the proposal, there are two important control structures. Firstly, reflected wave in the resonant system is eliminated by reflected wave rejection. Transfer function of wave equation without reflected wave is composed of a time delay. Therefore, resonant system can be regarded as time delay system. Next, vibrations from flexible mechanism and communication delay are simultaneously suppressed by wave compensator. Finally, the validity of the proposal is verified by experimental results.

Force control of two-mass resonant system with vibration suppression based on modal transformation

This paper proposes a force control of a two-mass resonant system based on modal transformation. In the conventional force-control method in resonant system, the control goals are not clearly defined from the point of the view of control stiffness. Moreover, there is a problem that it is needed to know value of an environmental stiffness for setting force gain. Therefore, in this paper, the control stiffness in the case of force control of the two-mass resonant system is defined on the modal spaces which are composed of rigid and torsional modes. Concretely speaking, in the force control, it is defined that a control stiffness of a rigid mode should be zero. Based on the control stiffness, a force control of the two-mass resonant system is designed. Vibration suppression is conducted in torsional mode. On the other hand, in rigid mode, force control is conducted. The validity of the proposed method is verified by both simulation and experimental results.

Reaction-torque-based reflected wave rejection for vibration suppression of integrated resonant and time-delay system

The vibration suppression on a resonant system, based on the reflected wave rejection, has been recently proposed. In the method, the resonant system is modeled through a wave equation, in order to consider high order vibrations and vibration suppression is achieved by eliminating a reflected wave. However, it is difficult to implement such method when there are input and output time-delays, because it requires the implementation of the inverse of a time delay. Under such background, vibration suppression on the integrated resonant and time-delay system by using a modified reflected wave rejection has been proposed. However, a problem still remains, which is to need to use load-position information. Therefore, this paper proposes a novel vibration suppression method for systems including time delays by using a reaction-torque-based reflected wave rejection, which does not use the load position information. The novel reflected wave rejection can estimate and compensate the reflected wave by using motor position and reaction-torque information which is estimated by a reaction-torque observer. The validity of the proposed method is confirmed by experimental results.

Per hop data encryption protocol for transmission of motion control data over public networks

Bilateral controllers are widely used vital technology to perform remote operations and telesurgeries. The nature of the bilateral controller enables control objects, which are geographically far from the operation location. Therefore, the control data has to travel through public networks. As a result, to maintain the effectiveness and the consistency of applications such as teleoperations and telesurgeries, faster data delivery and data integrity are essential. The Service-oriented Router (SoR) was introduced to maintain the rich information on the Internet and to achieve maximum benefit from networks. In particular, the security, privacy and integrity of bilateral communication are not discoursed in spite of its significance brought by its underlying skill information or personal vital information. An SoR can analyze all packet or network stream transactions on its interfaces and store them in high throughput databases. In this paper, we introduce a hop-by-hop routing protocol which provides hop-by-hop data encryption using functions of the SoR. This infrastructure can provide security, privacy and integrity by using these functions. Furthermore, we present the implementations of proposed system in the ns-3 simulator and the test result shows that in a given scenario, the protocol only takes a processing delay of 46.32 μs for the encryption and decryption processes per a packet.

Vibration suppression of integrated resonant and time delay system by reflected wave rejection

The vibration suppression on a resonant system, based on the reflected wave rejection, has been recently proposed. In the method, the resonant system is modeled through a wave equation, in order to consider high order vibrations and vibration suppression is achieved by eliminating a reflected wave from the resonant system. However, it is impossible to implement such method when there are input and output time delays, because it would require the implementation of the inverse of a time delay. This paper proposes a new vibration suppression scheme for a resonant systems, affected by time delay, by using a modified reflected wave rejection. The proposed reflected wave rejection can be applied even in presence of time delays, as long as some conditions on the value of such delays are satisfied. The validity of the proposed method is confirmed by simulations and experimental results.

Control of bilateral force feedback system with flexible mechanism based on resonant ratio control

Recently, real-world haptics has been researched for tele-operation system. Conventional bilateral control can achieved corresponding master and slave position and action-reaction law. However, if system has flexible mechanism, performance of conventional bilateral control is degraded. Firstly, vibration occurs at slave load side by its flexibility. Secondly, an error between motor position and position of load occurs and synchronism position is not achieved. Thirdly, action-reaction law is not realized as well as position error. In this paper, the structure of bilateral force feedback control in the case of the slave system including the flexibility is proposed. Therefore, the proposed control structure has three important components in the slave system. Firstly, in order to suppress the vibration, resonant ratio control is implemented. Secondly, for corresponding to master and slave position, a modified control goal which is added reaction force estimated by load disturbance observer is proposed. Moreover, action-reaction law between master and slave load is accomplished by positive feedback of load reaction force multiplied inverse system. The effectiveness of the proposed method is verified by actual experiment.

An approach for heat flux sensor-less heat inflow estimation based on distributed parameter system of Peltier device

Peltier device has recently been attracting attention as a suitable device to produce thermal sensation. For the information obtainment of the heat exchanged between the device and external environment, heat flux sensor is generally utilized. However, heat flux sensor has drawbacks from the viewpoints of thermal capacitance and cost compared with temperature sensor. In order to address the problems, heat flux sensor-less estimation method of the heat flow should be developed. This research focuses on the distributed parameter system of Peltier device, and constructs a heat inflow observer based on the system. The derived model has the infinite number of poles and zeros, and the observer is approximated with the consideration on the poles and zeros for the simplicity in implementation. As shown in the experiments, the proposed observer shows its capacity of estimating heat inflow without using a heat flux sensor.