Practical and robust control for precision motion: AR-CM NCTF control of a linear motion mechanism with friction characteristics

This study presents the framework of the acceleration reference continuous motion nominal characteristic trajectory following (AR-CM NCTF) control system, and its effectiveness in a linear motion mechanism with friction characteristics is experimentally demonstrated in comparison with the other control methods. The overall control system comprises the feedback-loops for velocity reference and acceleration reference following controls. The AR-CM NCTF control is an enhanced continuous motion NCTF (CM NCTF) control that has been proposed for high-precision motion. It has the same structure as the CM NCTF controller with additional elements for high-precision motion. The design procedure of the AR-CM NCTF controller remains easy and is independent of friction characteristics. The usefulness and advantages of the proposed controller are shown in the experimental studies. Besides, this study also highlights the robustness of the AR-CM NCTF controller by examining its performances in point-to-point and tracking motions in the presence of mass and disturbance force variations. In the robust performance, the AR-CM NCTF controller is compared with two types of proportional derivative control systems with disturbance observers (PDDOs). The comparative experimental results illustrate that the AR-CM NCTF controller shows the higher motion performances the higher robustness to plant parameter variations than the PDDO controllers

Force Characterization of a Rotary Motion Electrostatic Actuator based on Finite Element Method (FEM) Analysis

Two types of rotary motion electrostatic actuators were designed and analyzed using Finite Element Method (FEM) analysis. This paper discussed the comparisons and detailed thrust force analysis of the two actuators. Both designs have similar specifications; i.e the number of rotor’s teeth to stator’s teeth ratio, radius and thickness of rotor, and gap between stator and rotor. Two structures were designed & evaluated; (a) Side-Driven Electrostatic Actuator and (b) Bottom-Driven Electrostatic Actuator. The paper focuses on comparing & analyzing the generated electrostatic thrust force for both designs when the electrostatic actuator’s parameters are varied. Ansys Maxwell 3D software is used to design and analyze the generated thrust force of the two rotary motion electrostatic actuators. The FEM analyses have been carried out by (i) varying the actuator size; (ii), varying the actuator thickness and (iii) varying the actuator teeth ratio. The FEM analysis shows that the Bottom-Drive Electrostatic Actuator exhibit greater thrust force, 4931.80N compared to the Side-Drive Electrostatic Actuator, 240.96N; when the actuator’s radius is 700m, thickness is 50m, gap between the stator and rotor is 2m and the teeth ratio is 16:12

Experiments on meteor burst communications in the Antarctic

Two kinds of experiments on the meteor burst communication(MBC) are now being conducted in the Antarctic to study the ability of MBC as a communication medium for data collection systems in that region. In the first one, continuous tone signal is transmitted from Zhongshan Station. The received signal at Syowa Station about 1400km apart is recorded and analyzed. This experiment is to study basic properties of the meteor burst channel in that high latitude region. From the data available thus far, we can see that 1) the sinusoidal daily variation in the meteor activity typical in mid and low latitude regions can not be clearly seen, 2) non-meteoric propagations frequently dominate the channel, etc. On the other hand, the second experiment is to estimate data throughput of a commercial MBC system in that region. A remote station at Zhongshan Station tries to transfer data packets each consists of 10 data words to the master station at Syowa Station. Data packets are generated with five min interval. We are now operating the system only five min in each ten min interval. About 60% of the generated data packets are constantly transferred to the master station within two hours delay

VHF data transmission experiments using MBC equipment conducted during the period from JARE-43 to JARE-45

In order to study the ability of meteor burst communications (MBC) as a new medium of data collection networks in Antarctica, we have performed a series of VHF data transmission experiments. In the experiment during the period of JARE-43 (the 43rd Japanese Antarctic Research Expedition), a remote station at Zhongshan Station sent data packets to a master station at Syowa Station using a commercial MBC system. Together with meteor burst propagations, non-meteoric propagations were frequently observed during local nighttime. We found that they worked effectively for packet transmissions and greatly increased the data throughput. Overall data throughput obtained by this experiment was 0.63bps. In JARE-44, we added another remote station at Dome Fuji Station. Since the transmitted power from the master unit was split into two directions, data throughput from Zhongshan Station was reduced to 0.36bps. That from Dome Fuji Station was only 0.13bps. For the experiment in JARE-45, we replaced the commercial MBC system with a RANDOM (RAdio Network for Data Over Meteor) system developed by the authors. The experiment is being conducted between Syowa and Zhongshan Stations. The estimated data throughput during the period from April 1st, 2004 to August 31st, 2004 was 2.9bps

Characteristic switching of a multilayer thin electrostatic actuator by a driving signal for an ultra-precision motion stage

The present paper describes the characteristic switching of a multilayer thin electrostatic actuator supported by only lubricating oil and its application in the control of an ultra-precision fine stage. Friction forces often deteriorate the response and positioning accuracy of a control system. However, they generate a large holding force, which is needed to precisely maintain the stage position in fine stages. When the lightweight electrode layers in the electrostatic actuator are supported by only lubricating oil, the contact condition between the electrode layers can be changed by the attractive forces resulting from the driving signal, which consequently influences the frictional effect. Thus, suitable driving signals have the potential to adjust the frictional effect for fine motion with a large holding force and a wide and fast motion. In this paper, suitable driving signals for switching between two frictional conditions (i.e., low friction for the wide and fast motion and high friction for the fine motion with a large holding force) are examined and clarified. First, the relationship between the driving signals and the working range of the actuator is explained. Then, the holding force characteristics and the driving signals for switching between the frictional conditions are discussed. Finally, the actuator control system is designed based on the findings. The control system includes a PID compensator and a driving signal unit that generates two driving signals. One driving signal provides a driving mode with a holding force for a working range smaller than 250 nm. The other driving signal provides a wide driving mode for a working range wider than 250 nm under low-friction conditions. The driving signal is determined so as to quickly change the frictional effect. A combination of these modes (referred to as the dual driving mode) is implemented in the actualmultilayer electrostatic actuator, and its effectiveness is validated experimentally. The actuator exhibits a positioning error of less than 14 nm with a continuous holding force of 0.205 N