Preservation and Reproduction of Human Motion Based on a Motion-Copying System

Introduction

Multimedia technology has been the basis for human communication and industry applications. Auditory and visual information is obtained through human ears and eyes, respectively. Artificial acquisition and reproduction of auditory and visual sensations are basic technologies in communication engineering and have been commercialized in various forms. Auditory information is obtained by a microphone, and a speaker reproduces it by artificial means. A video camera and a display make it possible to transmit visual sensation through television broadcasting. Multimedia technologies such as these can connect a human with another human located at a remote site. Furthermore, it is possible to preserve, process, and analyze information through the development of digital signal processing technology.

Haptic information has received attention as a third type of multimedia information. The directional properties of human sensations are shown in Figure 1.

Figure 1.

Directional properties of human sensations

A touching motion is inherently bilateral, as an action of this sort is always accompanied by a reaction. Furthermore, the recognition of the contact environment is attained only after touching it. This means that the artificial realization of touching requires a very fast controller to keep the time-delay as small as possible. Thus, conventional model-based environmental recognition will not always be suitable for future applications. Environmental recognition in the real world should be based on action, and it is necessary for future modes of communication to have force feedback ability. As a result, real-world haptics is the key technology that will enable future haptic communication engineering.

Background

It is possible to extend human sensation through remote environments by bilateral tele-operation. There has been extensive research on how bilateral tele-operation can attain force feedback from a remote environment. One of the major objectives in designing bilateral control systems is achieving transparency, which is defined as a correspondence of positions and forces between a master and a slave (Yokokohji, 1994) or a match between the impedance perceived by an operator and an environmental impedance (Lawrence, 1993). To attain bilateral force feedback between a master and slave system, it is important to control their forces and positions simultaneously. As both controllers are represented by oppositely controlled stiffness, it is difficult to attain them using a conventional minor-loop-based servo system. In addition, the frequency range of the force signal is also important for the vivid sensation needed to achieve higher transparency (Katsura, 2006a; 2007). An acceleration controller brings a wide-band controller, which satisfies the above requirements (Katsura, 2005a; 2008).

A disturbance observer is a good method for achieving acceleration control (Ohnishi, 1996). A disturbance observer can observe the disturbance as quickly as possible. Once a measurement of disturbance can be obtained as the inner variable, it is easy to compensate for it, and thus a robust motion system controlling for stiffness is attained. As a result, robust motion control turns a motion system into an acceleration control system (Tomizuka, 2004; Sabanovic, 2008).

The merits of a disturbance observer extend beyond robust motion control and include force sensing. It is possible to obtain wide-band force information without the use of force sensors (Murakami, 1993). General force sensors obtain force information using strain gauges. This leads to mechanical weakness resulting in the generation of resonance in the structure. Furthermore, sensor information may result in noise due to the amplification of small signals emanating from the strain. Thus, frequency bandwidth is limited because it is necessary to use filters. As a result, the use of force sensors affects not only force feedback sensation, but also total control stability.