Noboru Wakatsuki

Relay contacts of multi-electrodes with timely controlled operation for arc discharge suppression

We propose a new electric contact device for stable arc discharge suppression. The functions of conventional electric contacts are categorized into the energizing contacts and the switching contacts. A capacitor is connected in series to switching contacts. Arc discharge suppression was experimentally measured and theoretically analyzed using equivalent circuits. The V-I characteristics of breaking contacts were introduced with a time dependent resistor R(t) into the circuit. The transient responses at contact were numerically derived by SPICE, and compared to the minimum discharge current and the minimum discharge voltage, clarifying the function of the parallel capacitor for stable arc discharge suppression. Using two conventional relay contacts, no stable arc break operation was confirmed for a 42 V/3 A. For the reliability examination, contact resistances were measured over many breaking operations, and the contact surfaces were observed.

LiTaO 3 crystal fork vibratory gyroscope

A new vibratory gyroscope using a LiTaO3 crystal is proposed for a miniature angular rate sensor. A fork with a 130° rotated Y-cut plate has high electromechanical coupling factors and low temperature coefficients in both modes, the fx mode and the f y mode which are orthogonal to each other. Our trial fork has cuboid arms that are 7.0 mm long 1.0 mm wide, and 1.0 mm thick with a 0.3 mm gap. The fork has a high-Q resonance at 16 KHz in the two modes. The driving mode gives effective and stable self-oscillation as a resonator. The detecting mode slightly couples to the holder and its Q is about 500. This Q value is convenient for frequency adjustment during fabrication and as a sensor, for a quick rotation response. As a loading mass on the holder changes only the resonance frequency in the detecting mode, we can adjust the two resonance frequencies to within 1 Hz of each other. Our experimental results showed that a LiTaO3 fork gyroscope can potentially be used as a miniaturized and sensitive angular rate sensor

Arc discharge and surge suppression during a breaking operation of a magnetic relay

In a switching circuit with an inductive load, arc discharge and surge generated during a breaking operation are big problems. We proposed an electric method for arc discharge suppression using a timely controlled transient current switch and a capacitor arranged in parallel to the energizing switch. In this paper, we propose an improvement. We replaced the capacitor with two capacitors. One to suppress arc ignition and the other is to suppress surge. Using electrical measurements of the relay contact operation, adequate capacitance values and series resistance were derived numerically. The capacitance to suppress arc ignition does not depend on load inductance but only on load resistance. However, the capacitance and its series resistance to suppress surge depend on the load inductance and its resistance. For the break operation (50 V/8 A) of a conventional magnetic relay (HH62P) with an inductive load (84 mH), a 1muF capacitor can suppress arc ignition and a 100 muF capacitor and a resistance of 8Omega is sufficient to suppress surge. No arc ignition and surge controlled to less than 30 V were confirmed experimentally.

Suppression of null signals in LiTaO/sub 3/ crystal fork vibratory gyroscope

A LiTaO/sub 3/ tuning fork vibratory gyroscope has a high sensitivity, because of its high electromechanical coupling for the bending f/sub x/ mode and its orthogonal f/sub x/ mode, and high Q value for driving and adjustable Q value for detecting f/sub y/ mode. Our trial LiTaO/sub 3/ fork with cuboid arms (7.0 mm long, 1.0 mm wide, 1.0 mm thick, 0.3 mm gap) has a high sensitivity of 0.5 mV/deg/sec for 1 V pp input at 16.5 KHz. But the sensitivity is often reduced by spurious driving and detection modes coupling due to electrostatic coupling, electromechanical coupling and mechanical coupling. We experimentally analyzed the leakage couplings separately and proposed a new configuration of driving and detection electrodes for functional laser trimming. Also we proposed the additional slit formed by laser at an arm-edge of fork to achieve orthogonal vibrations for the f/sub x/ mode and the f/sub y/ mode. These functional YAG laser trimmings can suppress the leakage coupling or leakage signal voltage to -50 dB of driving voltage.

Melting and Discharge Phenomena of Breaking Ag Contacts Using a Precisely Controlled Piezoelectric Actuator

Using a laminated ceramic piezoelectric actuator for a very slow (4 m/s) precisely controlled make/break operation, contact voltage Vc and contact current Ic, residue of melt surface and discharge for breaking hinge relays with Ag contacting electrodes are measured. To control mechanical conditions, the movable electrode had a finely shaped convex surface (curvature radius: 0.5 mm) and a flat fixed electrode. Make/break operation was attempted only once due to transformation of contact surface. Then, Vc and Ic were measured at 1.5 to 25 V and 0.1 to 5 A. Fusion spots and residue of electric discharge on the contact surface were quantitatively measured using a laser microscope. Even when Vc and Ic were larger than the minimum arc voltage and minimum arc current, respectively, a continuous arc discharge occasionally did not occur. For the case of Vc=25 V and Ic=1 A, electric discharge was spontaneously suppressed to less than 100 s. The displacement of the movable electrode was estimated to be several nanometers for the discharging time interval. The residues of discharge were multiple damaged spots in the range of 100 m in radius, which had a black and/or white rectangular convex and concave shape.

Equivalent Circuit Analysis for Transient Phenomena from Elastic Contact to Breaking Contact through Metal Melting

This paper explores the proposal of equivalent circuits of electric breaking contacts to analyze the transient phenomena from elastic metal contact to rupture. The time dependency of elastic contact resistance is derived from the actual measurement values with the low current condition. The equivalent circuit for the phenomena is divided into the three stages: the first stage from the energizing to the softening voltage Us, the second stage from Us to the beginning of the latent heat, and the third stage from the start of the latent heat to the melting at the melting voltage Um. The accumulation of Joule heat at the contacts is shown with the capacitor in the circuits. The analytical result was able to qualitatively explain the complicated contact transient response characteristic of the Au crossing 1.0 mm φ rod experiment with source voltage 25 V, load current 2.5 A. Experimental results are compared with the fusion phenomena of conventional current fuse.

Melting Phenomena and Arc Ignition of Breaking Relay Contacts

Using the transient current switch circuit in parallel with the energizing switching contacts and the driving delay lines for timely control of breaking operations, the increase of contact voltage is suppressed as well as arc ignition at the last stage of the breaking electric contacts. Therefore, the melting phenomena can be slowly controlled and the electric characteristics can be accurately measured. Breaking contact voltage Vc and current Ic of conventional electromagnetic relays with Ag contacts were measured for two hinge springs (Spring constants; 2 N/mm and 0.2 N/mm), for 12.5~50 V energizing power-supply voltage and for 0.1~20 A contact current. The current-decreasing process was clearly measured at the melting voltage Um. After the melting voltage, the breaking time of contact current did not depend on mechanical conditions due to the two springs and energizing power-supply voltage, but did depend on the contact current. A new melting model of breaking mechanical contact is proposed. Using the model, a numerical equivalent circuit analysis of electric characteristics confirmed the measured data. For the conventional breaking operation (50 V/1A), arc ignition was measured after the melting break operation. The top of the metal contact had a finely shaped hemisphere and arc was ignited only once. The residue of arc ignition was observed as a black concentric circle, which was clearly separated from the melt contact point.

Melting phenomena of electric contacts during current interruption

The physical phenomena related to the melting of electric contacts are classified and the relations to electric characteristics are examined. The solid phase and/or the liquid phase exist at melting temperature. Joule heats from the electric circuit accumulate the latent heat till the melting of the contacts. We studied how the phase changes are ruled by electric circuit. The melting phenomena at the contact current interruption were observed electrically and optically.

Time-coordinated nonarcing breaking operation of reed switches for higher current

At the 50th IEEE Holm conference, we proposed a method for suppressing arc ignition in mechanical contact devices using a transient current switch and a capacitor. We applied the method to conventional reed switches. For the electric circuit analysis, we clarified the momentary voltage-current characteristics at the reed switch breaking operation by FEM analysis. We were able to estimate the nonarc ignition breaking condition using SPICE simulation. It was experimentally confirmed with the capacitor of 9.4/spl mu/F for 24V/15A breaking operation.

Study of LiTaO/sub 3/ shear wave resonator for viscosity sensor of polymer liquid in MHz range

We are studying the response of LiTaO/sub 3/ shear wave resonator in polymer liquid in MHz range. The element size is small (1.0 /spl times/ 7.4 /spl times/ 0.49 mm/sup 3/). The side faces of the resonator were covered with a highly viscous silicone rubber material. Using Newton fluid theory, the characteristic mechanical impedance of the shear wave in the liquid was derived for the equivalent circuit of the resonator. The analytical values of glycerin were roughly consistent with the experiment using only 0.1cc. the polymer liquid used for the measurement was silicone oil. The static viscosity is from 9.8 to 94,720 mPa/spl middot/s. The resonance frequency change was from 0.05% to 0.07%. The resonance resistance change was from 57 ohm to 190 ohm. The experimental results were examined using Masons equivalent circuit with Maxwell model of a viscoelastic polymer.