Kaiji Sato

Self-alignment of microparts using liquid surface tension—behavior of micropart and alignment characteristics

Abstract The purpose of this research is to establish a self-alignment technique for microparts assembly using liquid surface tension. The factors that influence alignment performance are examined and ways of performance improvement are discussed experimentally and theoretically. First, the relationship between the alignment accuracy and the behavior of the micropart and the water droplet is examined in the alignments with six different water droplet volumes. The experimental results show that the volume influences the alignment accuracy and the behavior. Next, the relationship between restoring force induced theoretically and the experimental alignment accuracy is discussed. Then, the effect of pattern change of the boundary between different wettability areas on the alignment accuracy is examined experimentally. In the experiments, the micropart with the hexagonal boundary pattern demonstrates smaller alignment error than those with the square, triangular, cross and star patterns.

Characteristics of practical control for point-to-point (PTP) positioning systems: Effect of design parameters and actuator saturation on positioning performance

In this study, a nominal characteristic trajectory following (NCTF) controller for point-to-point (PTP) positioning systems is introduced and its performance is evaluated. The NCTF controller consists of a nominal characteristic trajectory (NCT) and a compensator. The objective of the NCTF controller is to make the object motion follow the NCT and end at its origin. Therefore, the NCT is used as an intended object motion and the compensator is used to make the motion of the controlled object follow the NCT. The NCTF controller is designed based on a simple open-loop experiment of the object and no information except the NCT is necessary for controller design. The effectiveness of the NCTF controller is evaluated and discussed through simulations and experiments using an experimental rotary positioning system. The effect of the design parameters on the robustness of the NCTF controller to inertia and friction variations is evaluated and the influence of saturation on the positioning performance is examined. Moreover, the effects of the saturation on the positioning performance and robustness are compared with those of conventional PID ones. It is proved that the NCTF controller is much more accurate and robust to inertia and friction variations than the PID controllers, even if the saturation occurs.

X-Y-θ Nano-Positioning Table System for a Mother Machine

Abstract Within recent manufacturing environment, there is an increasing demand for nanometer positioning table system with high stiffness, high resolution and high repeatability. In this study, therefore, a high-stiffness X-Y-6 nano-positioning table system has been developed for ultraprecision machine tools. The table is levitated by high-stiffness aerostatic bearings with porous material and driven by six voice coil motors in a non-contact condition. The table system is designed symmetrically about the driving axis and consequently free from nonlinear behavior and direction dependency. The performance of the developed table system has been verified through a series of nano-positioning experiments.

Fabrication of thin film metallic glass and its application to microactuators

Metallic glasses are kinds of amorphous alloys. They are free from defects resulting from crystalline structures. Metallic glasses soften in a certain temperature range called the supercooled liquid region, which makes metallic glasses easily be formed into a 3D shape. This paper first describes a fabrication method for a thin film metallic glass (TFMG) using RF magnetron sputtering. Secondly A micro beam of TFMG is introduced. Although the fabricated micro beams bent due to the internal stress caused by stress was related by annealing the beams in the supercooled liquid region, and straight beams were fabricated. Secondly, curved micro beams of TFMG were micro formed by heating the straight beams again into the supercooled liquid state. Finally, a new type electrostatic microactuator of a conical spring shape was made of TFMG. CSLA was capable of stepwise motion vertical to the substrate. The 10 micrometers step height and 30 micrometers total height were realized.

Ultrahigh-Acceleration Moving-Permanent-Magnet Linear Synchronous Motor With a Long Working Range

This paper describes a linear motor design for ultrahigh acceleration and high velocity, as well as the driving performance of the motor. First, because of its ease of control, a moving-permanent-magnet linear synchronous motor (MPM LSM) was selected. The overall structure of the motor, which consists of a table to which the permanent magnets (PMs) are attached and two fixed electromagnet (EM) lines between which the PMs move, was selected based on the simplicity of the structure and the ease of gap adjustment. The dimensions of the EMs and PMs are optimized numerically to achieve a high thrust density that can provide an acceleration of 100G or greater to the mover, which comprises PMs, spacers, and a frame. The prototype MPM LSM has a working range of 1.5 m. The mover, including the guide parts, has a length of 444 mm and a mass of 4.79 kg. The measured peak thrust was greater than 5 × 103 N, and the measured average thrust was 4.03 × 103 N. The prototype driven by a rectangular current command produced a maximum acceleration of greater than 100G and a velocity higher than 12 m/s for a moving distance of 0.6 m.

Robustness evaluation of three friction compensation methods for point-to-point (PTP) positioning systems

Abstract Friction is one of the major contributing factors to problems associated with accuracy in positioning systems. The positioning accuracy problem becomes more complicated because of variations in the friction. In this paper, three simple friction compensation methods for the point-to-point (PTP) positioning system, which are easily applied in practical applications, are compared and evaluated experimentally on an experimental rotary positioning system. The first controller is the nominal characteristic trajectory following (NCTF) controller and the other two are the PD controller with a discontinuous non-linear proportional feedback (DNPF) compensator and the smooth robust non-linear feedback (SRNF) compensator. All of the controllers are compared in terms of the effectiveness of the controller to compensate for the friction as well as robustness against inertia and friction variations. The results demonstrate that the NCTF controller is more robust against friction variation than the PD controller with the DNPF or SRNF compensator.

Thrust Ripple Reduction in Ultrahigh-Acceleration Moving-Permanent-Magnet Linear Synchronous Motor

This paper describes thrust ripple reduction in an ultrahigh-acceleration moving-permanent-magnet linear synchronous motor (MPM LSM). The pole pitch of the permanent magnet (PM) is adjusted to reduce thrust ripple because this technique is effective and is easily applicable for many design procedures of PM LSMs. However, in addition to reducing the thrust ripple, this adjustment affects parameters such as the number of driving phases, the average thrust, the mover mass, and the working range. These parameters influence the performance and the usability of linear motors. In this study, the PM pole pitch of an MPM LSM is adjusted. The MPM LSM produces an average thrust of 4030 N, but the ratio of the peak-to-peak thrust ripple to the average thrust exceeds 80%. The influences on the properties of the MPM LSM are numerically investigated and discussed. The PM pole pitch of the MPM LSM is determined based on the numerical analysis and an improved mover whose pitch was numerically determined is fabricated. The improved mover has a light frame and 18 PMs for realizing a high thrust-to-mover mass ratio (thrust per mover mass). The experimental results demonstrate that the improved MPM LSM can generate 4.56 × 103 N with a peak-to-peak thrust ripple of 7.04%.

Robustness evaluation of new practical control for PTP positioning systems

This paper presents robustness evaluation of a new practical control for point-to-point (PTP) positioning systems. The proposed controller consists of a nominal characteristic trajectory as an intended motion trajectory and PI elements which are used to restrict the plant motion along the trajectory. The nominal characteristic trajectory is determined with measured open-loop responses of the plant and is also used to determine PI coefficients. Thus the proposed controller does not require an exact model of the plant and its parameters, and is easily applicable to practical systems. The robustness of the proposed controller is evaluated and compared experimentally with conventional PID controllers using an experimental rotary positioning system. It is proved that the proposed controller is better than the conventional PID controllers in robustness to parameter variation.

Practical control of non-friction mechanism for precision positioning

This paper describes the practical control of non-friction mechanism for precision positioning. Non-friction mechanism is often used for precision positioning. Even though it has a simple structure, still, plant identification is compulsory needed during designing a conventional controller. This makes the controller non-user-friendly and non-practical-used in industry. For overcoming this problem, practical controller design procedure based on NCTF (nominal characteristic trajectory following) controller is proposed. NCTF controller consists of a nominal characteristic trajectory (NCT) and a PI compensator, which is free from exact modeling and parameter identification. The NCT is determined using an open-loop time responses of the mechanism. The PI compensator is used to make the mechanism motion to follow the NCT and it is tuned without given model parameters. Non-friction mechanism has non-damping a characteristic and often has a short-working range. A suitable current input to stop the non-damping mechanism within a short working range in open-loop condition and to be able to improve the damping characteristic of the mechanism is necessary. The positioning performances of two different current inputs are examined and discussed. The positioning performance of NCTF control system is evaluated based on simulation and experimental results.

An Active Air Journal Bearing with Ultraprecision, Infinite Static Stiffness, High Damping Capability and New Functions

Summary The aim of the paper is to develop an Active Air Journal Bearing (AAJB), AAJB is a rotary air bearing of a controlled type with following features: (1) ultra precision. (2) infinite static stiffness. (3) high vibration damping capability. (4) new functions such as the positioning of the rotating axis and the dynamics stiffness control. Such features are realized by positioning the axis with an active air bearing (AAB). AAB is composed of a static air bearing mechanism a non-contact sensor, a piezoelectric actuator, a controller and an objective mass to be controlled ie. the axis. First, the basic configuration of AAJB as well as its dynamic model and controller design is shown. Then the compliance and the axis positioning characteristics are examined. Finally the radial positions of the axis rotating at 1000rpm is controlled and the rotation accuracy of the axis less than 25nm is accomplished.