Recent availability of encoder with millions of counts per revolution makes it possible to enlarge the bandwidth of the torque disturbance observer (TDO) equipping a servo drive. As a consequence, the TDO dynamics are no more decoupled from those of current and the behavior of the torque disturbance compensator (TDC) is influenced by the current dynamics as well as by the discrete-time implementation of TDO. The purpose of this paper is to analyze the TDC performance under the above-mentioned circumstances. The main outcome is the underdamped or even unstable behavior of TDC. Another outcome is the limited range of values allowable for the parameter mismatch to preserve stability. The conditions on the TDO bandwidth and the parameter mismatch for TDC to be stable and to be damped are provided. Experimental tests are given, which substantiate the theoretical findings.
"Disturbance observer (DOB) technique was originally presented by Ohnishi in 1987 . Disturbance observer based control schemes for linear and nonlinear systems have been put forward and applied successively in many other control fields, e.g., robotic systems   , hard drive systems   , position system , missile system , general systems    , etc. DOB has fine abilities in dealing with model mismatches and strong external disturbances. It does not rely on precise disturbance models. "
[Show abstract][Hide abstract] ABSTRACT: Ball mill grinding circuits are essentially multi-variable systems characterized with couplings, time-varying parameters and time delays. The control schemes in previous literatures, including detuned multi-loop PID control, model predictive control (MPC), robust control, adaptive control, and so on, demonstrate limited abilities in control ball mill grinding process in the presence of strong disturbances. The reason is that they do not handle the disturbances directly by controller design. To this end, a disturbance observer based multi-variable control (DOMC) scheme is developed to control a two-input-two-output ball mill grinding circuit. The systems considered here are with lumped disturbances which include external disturbances, such as the variations of ore hardness and feed particle size, and internal disturbances, such as model mismatches and coupling effects. The proposed control scheme consists of two compound controllers, one for the loop of product particle size and the other for the loop of circulating load. Each controller includes a PI feedback part and a feed-forward compensation part for the disturbances by using a disturbance observer (DOB). A rigorous analysis is also given to show the reason why the DOB can effectively suppress the disturbances. Performance of the proposed scheme is compared with those of the MPC and multi-loop PI schemes in the cases of model mismatches and strong external disturbances, respectively. The simulation results demonstrate that the proposed method has a better disturbance rejection property than those of the MPC and PI methods in controlling ball mill grinding circuits.
Journal of Process Control 07/2009; 19(7-19):1205-1213. DOI:10.1016/j.jprocont.2009.02.004 · 2.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper proposes an analysis method about bilateral tele-operation. The bilateral tele-operation is the key technology to the tele-communication. At this point, the bilateral tele-operation treats 2 systems and each system is controlled position and force information. Thus, force information which is attained to a system affects position and force information of another system. These effects are affected by values of gains in position regulator and force servoing, mass, cut-off frequency and so on. To analyze these effects, this paper defines transmissibility about position and force information. The proposed method enables to analyze the behavior of a system when external force is added to another system. The viability of the proposed method is confirmed by some experiments.
[Show abstract][Hide abstract] ABSTRACT: Artificial acquisition and reproduction of human sensations are basic technologies of communication engineering. For example, auditory information is obtained by a microphone, and a speaker reproduces it by artificial means. Furthermore, a video camera and a television make it possible to transmit visual sensation by broadcasting. On the contrary, since tactile or haptic information is subject to the Newton's "law of action and reaction" in the real world, a device which acquire, transmit, and reproduce the information has not been established. Real-world haptics is the key technology for future haptic communication engineering. This paper proposes a novel acquisition method of haptic information named "haptograph". The haptograph visualizes the haptic information like photograph. Since temporal and spatial analyses are conducted to represent haptic information as the haptograph, it is possible to be recognized and to be evaluated intuitively. In this paper, the proposed haptograph is applied to haptic recognition of the contact environment. A linear motor contacts to the surface of the environment and its reaction force is used to make a haptograph. A robust contact motion and sensor-less sensing of the reaction force are attained by using a disturbance observer. As a result, an encyclopedia of contact environment is attained.
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