Rui Weng

Spray-coating process in preparing PTFE-PPS composite super-hydrophobic coating

In order to improve the performance of a liquid-floated rotor micro-gyroscope, the resistance of the moving interface between the rotor and the floating liquid must be reduced. Hydrophobic treatment can reduce the frictional resistance between such interfaces, therefore we proposed a method to prepare a poly-tetrafluoroethylene (PTFE)-poly-phenylene sulphide (PPS) composite super-hydrophobic coating, based on a spraying process. This method can quickly prepare a continuous, uniform PTFE-PPS composite super-hydrophobic surface on a 2J85 material. This method can be divided into three steps, namely: pre-treatment; chemical etching; and spraying. The total time for this is around three hours. When the PTFE concentration is 4%, the average contact angle of the hydrophobic coating surface is 158°. If silicon dioxide nanoparticles are added, this can further improve the adhesion and mechanical strength of the super-hydrophobic composite coating. The maximum average contact angle can reach as high as 164° when t...

Friction Reduction for a Rotational Gyroscope with Mechanical Support by Fabrication of a Biomimetic Superhydrophobic Surface on a Ball-Disk Shaped Rotor and the Application of a Water Film Bearing

Friction between contacting surfaces of metal materials restricts the application of mechanical support in the high-precision inertial device of a rotational gyroscope. Instead, a disk- or ring-shaped rotor is electrostatically or magnetically suspended. However, stability of the rotor suspension restricts further improvement of the measurement precision. In the developed rotational gyroscope, a stable mechanical rotor supporting scheme with low friction is achieved by fabrication of a superhydrophobic surface with similar nanostructures of the lotus leaf on the carbon steel ball of the ball-disk-shaped rotor and the addition of a water film between the rotor ball and bronze hemispherical supporting bowl, which forms a water film bearing. The special design of the ball-disk-shaped rotor makes it possible for the application of a low-friction water bearing in the gyroscope, with rotor tilting motion. With a superhydrophobic surface, friction is further decreased and the rated spinning speed increases 12.4%, resulting in approximately the same proportion of increase in the scale factor. Moreover, superhydrophobic surface reduces mechanical damping torque for precessional motion to one order smaller than electrostatic feedback torque. Thus, through close-loop control, stable damping characteristics for precessional motion are obtained. The gyroscope exhibits excellent performance with the parameters of the measurement range, scale factor, nonlinearity, resolution, bias stability, and dynamic setting time tested to be −30°/s to 30°/s, −0.0985 V/(°/s), 0.43%, 0.1°/s, 0.5°/h, 0.1 s, respectively.

Fabrication and drag reduction of the superoleophobic surface on a rotational gyroscope

ABSTRACT Surface tension and friction are dominant forces at microscale. The friction and wear of solid–solid or solid–liquid contacts affect the performance and lifetime of a microgyroscope. In this paper, we propose a novel superoleophobic liquid-bearing microgyroscope, and present a simple method to fabricate a superoleophobic surface on a 2J85 ferromagnetic alloy substrate through hydrofluoric acid etching. The superoleophobic surfaces exhibit reduced viscous drag because of the ‘slip’ associated with a layer of air trapped at the liquid/solid interface. In addition, a drag reduction ratio of approximately 10.7% was observed at a high velocity.

A Rotational Gyroscope with a Water-Film Bearing Based on Magnetic Self-Restoring Effect

Stable rotor levitation is a challenge for rotational gyroscopes (magnetically suspended gyroscopes (MSG) and electrostatically suspended gyroscopes (ESG)) with a ring- or disk-shaped rotor, which restricts further improvement of gyroscope performance. In addition, complicated pick-up circuits and feedback control electronics propose high requirement on fabrication technology. In the proposed gyroscope, a ball-disk shaped rotor is supported by a water-film bearing, formed by centrifugal force to deionized water at the cavity of the lower supporting pillar. Water-film bearing provides stable mechanical support, without the need for complicated electronics and control system for rotor suspension. To decrease sliding friction between the rotor ball and the water-film bearing, a supherhydrophobic surface (SHS) with nano-structures is fabricated on the rotor ball, resulting in a rated spinning speed increase of 12.4% (under the same driving current). Rotor is actuated by the driving scheme of brushless direct current motor (BLDCM). Interaction between the magnetized rotor and the magnetic-conducted stator produces a sinusoidal rotor restoring torque, amplitude of which is proportional to the rotor deflection angle inherently. Utilization of this magnetic restoring effect avoids adding of a high amplitude voltage for electrostatic feedback, which may cause air breakdown. Two differential capacitance pairs are utilized to measure input angular speeds at perpendicular directions of the rotor plane. The bias stability of the fabricated gyroscope is as low as 0.5°/h.

Fabrication of superhydrophobic surface by oxidation growth of flower-like nanostructure on a steel foil

Energy saving has drawn attention all around the world. The fluidic drag reduction effect of superhydrophobic surfaces has been investigated both theoretically and experimentally. However, there has been little experimental analysis on the drag reduction of superhydrophobic steel surfaces. Here, we present a novel method to fabricate the superhydrophobic surface with a 3D flower-like micro-nanostructure on the steel foil using the method of high-temperature oxidation. The wettability of the oxide films can be easily changed from super hydrophilic to superhydrophobic with chemical modification. We measure the liquid/solid friction of the as-prepared superhydrophobic surface using the self-assembly system. The drag reduction ratio for the superhydrophobic steel surface is 20–30% at low velocity. The superhydrophobic steel surface has numerous technical applications in drag reduction field.

Micro-angle tilt detection for the rotor of a novel rotational gyroscope with a 0.47″ resolution

Differential capacitive detection has been widely used in the displacement measurement of the proof mass of vibratory gyroscopes, but it did not achieve high resolutions in angle detection of rotational gyroscopes due to restrictions in structure, theory, and interface circuitry. In this paper, a differential capacitive detection structure is presented to measure the tilt angle of the rotor of a novel rotational gyroscope. A mathematical model is built to study how the structure’s capacitance changes with the rotor tilt angles. The relationship between differential capacitance and structural parameters is analyzed, and preliminarily optimized size parameters are adopted. A lownoise readout interface circuit is designed to convert differential capacitance changes to voltage signals. Rate table test results of the gyroscope show that the smallest resolvable tilt angle of the rotor is less than 0.47″ (0.00013°), and the nonlinearity of the angle detection structure is 0.33%, which can be further improved. The results indicate that the proposed detection structure and the circuitry are helpful for a high accuracy of the gyroscope.

Superhydrophobic Drag-Reduction Spherical Bearing Fabricated by Laser Ablation and PEI Regulated ZnO Nanowire Growth

The resistance of the bearing is a significant factor affecting the performance of the ball-disk rotor gyroscope. The micro and nano combined surface with low surface energy material modifications can be hydrophobic. This can reduce the drag when the bearing is lubricated by deionized water. Laser ablation method is utilized to form micron-scaled structures on the surface of the stainless steel rotor ball. And the nanostructures are formed by PEI (Polyetherimide) regulated ZnO nanowires growth. After low surface energy material modification, the water contact angle of processed surface was 163° and the sliding angle was less than 4°. The maximum rotational speed was enhanced by up to 82.77% at 1.5 W driving power. Experiments show that the superhydrophobic drag-reduction spherical bearing has good short-term reliability. At 5 V drive voltage, the bearing can extend the rotational speed of ball-disk rotor gyroscope to 35000 rpm, and maintain the normal operation for longer than 40 minutes. This is quite meaningful for short-term-work or one-time-use rotor gyroscopes.

Ball-disk rotor gyroscope adaptive quick-start technique

Rotating speed is a critical parameter affecting the performance of rotor gyroscopes. Rotor gyroscopes must operate at the rated rotating speed. To shorten the start time of the ball-disk rotor gyroscope, this paper presents a new design of the drive system for a ball-disk rotor gyroscope. The drive system is monitored by a microcontroller. First, the microcontroller generates a sine pulse width modulation signal to drive the permanent magnet rotor. Second, the position of the rotor is detected according to the back electromotive force in the non-energized coil. Third, a piecewise closed-loop control algorithm is implemented to keep the angular acceleration of the rotor within the safe range automatically during the acceleration process and when running at a constant speed. This control algorithm can avoid rotor stalling due to loss of steps. Experimental result shows that with the help of adaptive quick-start technique, the start time of the device can be shortened by up to 36.6%.

Design of detection electrode on contactless conductivity detection in capillary electrophoresis microchip

Contactless conductivity detection has attained great attention in the last decade in capillary electrophoresis. But contactless conductivity detection is restricted by its sensitivity, how to improve detection sensitivity has become the key of contactless conductivity. In this paper a novel extended model for the detection cell consisting of a network of resistors and capacitors is proposed according to the structure of contactless conductivity detection. The effect of the detector geometry on the sensitivity of contactless conductivity is studied. By simulation, the optimal parameters are obtained. Sandwich electrode structure was established to improve the performance of the detector and minimize the stray capacitance between the electrodes. Using the optimal electrode structure, the two peaks corresponding to K+ and Mg2+ are clearly resolved with complete separation.

Liquid-Suspended Rotor Gyroscope Multiphase Driving Technology

Liquid-suspended rotor micro-mechanical gyroscope uses a high-speed rotating hollow rotor in response to the density of the liquid as the mass to do the angular velocity detection. In order to improve the liquid-suspended gyroscopes performance, this paper suggested a new high performance magnetic driving technology. In this technology, the driving performance is optimized by applying six-phase overlapped driving signal to the twelve driving coils of the stator. With this driving technology, the rotating speed of rotor in 3# industrial white oil can go up to 8700rpm.