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This paper proposes a high-precision permanent magnet (PM) motor primarily used for the satellite attitude control. Considering aerospace applications, the dynamic response, weight and torque ripple are primarily concerns. To achieve the fast response and low ripple, a stator with slotless windings is designed to achieve the ripple free torque production. However, slotless windings contain visible leakage fluxes which might decrease the torque production. In this paper, several design methods are proposed to decrease leakage fluxes by concentrating the flux linkage under slotless topology. First, leakage fluxes caused by slotless windings are minimized through the radial-flux dual-rotor topology. This topology results in the flux linkage concentration in the air gap because two rotors are used separately for flux transmitter and receiver. It is concluded that the dual-rotor is well suited for a slotless windings motor to maximize the air gap flux linkage. Second, Halbach array magnets are chosen to realize the sinusoidal flux linkage distribution. Different array angles are analyzed to minimize the torque ripple. It is shown that the 22.5deg array angle results in the lowest torque ripple among three different Halbach magnets. More importantly, the average torque output is higher comparing to conventional radial magnet magnetization. Although several optimization methods have been developed on the motor geometric design, very few researches focus on the design of dual-rotor slotless windings and air gap length. This design approach further decreases leakage fluxes. In this paper, finite element analysis (FEA) is used for the satellite motor design. In addition, a motor prototype is built for experimental tests.

This paper proposes the fault-tolerant control of Hall-sensor-based field oriented control (FOC) motor drive. To overcome the transient current spikes at the fault instant, both Hall sensor state reversal and zero voltage vector are used to achieve the instantaneous fault identification and transient current compensation. This method realizes faster fault detection time and minimum transient current effect. A 3kW surface permanent magnet motor is used for experimental verification.

This paper improves the surface permanent magnet (PM) machine position sensorless drive at low speed. Considering the surface PM machine (SPM) drive, EMF voltage or flux linkage should be estimated for the sensorless drive. Different from EMF voltage, the flux linkage based on the voltage integration is theoretically independent to speed which is suited for the low speed position estimation. In this paper, several improvements on the flux-based sensorless drive are proposed to enhance the low speed dynamic performance. First, a modified voltage integration is develop to remove the flux estimation drift caused by voltage or current offset. This integration contains a high-pass filter (HPF) for the DC drift elimination. In addtion, the filter delay is compensated to maintain the flux phase. Second, inverter deadtime harmonics are decoupled with the knowledge of actual machine phase voltages. It is shown that the position estimation error is decreased for the better low speed performance. According to experimental results, SPM machine sensorless drive is enhanced at 4%~6% speed region from many aspects. They include position signal SNR, position error and drive dynamic response. More importantly, the overall current regulation bandwidth can increase to 1kHz at low speed. It is compatible to standard encoder-based field oriented control (FOC) drives.

For pulse width modulation (PWM) inverter drives, an LC filter can cascade to a permanent magnet (PM) machine at inverter output to reduce PWM-reflected current harmonics. Because the LC filter causes resonance, the filter output current and voltage are required for the sensorless field-oriented control (FOC) drive. However, existing sensors and inverters are typically integrated inside commercial closed-form drives, it is not possible for these drives to obtain additional filter output signals. To resolve this integration issue, this paper proposes a sensorless LC filter state estimation using only the drive inside current sensors. The design principle of the LC filter is first introduced to remove PWM current harmonics. A dual-observer is then proposed to estimate the filter output current and voltage for the sensorless FOC drive. Compared to conventional model-based estimation, the proposed dual-observer demonstrates robust estimation performance under parameter error. The capacitor parameter error shows a negligible influence on the proposed observer estimation. The filter inductance error only affects the capacitor current estimation at high speed. The performance of the sensorless FOC drive using the proposed dual-observer is comparable to the same drive using external sensors for filter voltage and current measurement. All experiments are verified by a PM machine with only 130 μH phase inductance.

A FePt(B, Ag, C) granular film was formed from post-annealed B4C(1.0 nm)/FePt(Ag, C) layers at a substrate temperature of 470 °C for 2 min. The 6 nm thick FePt(B, Ag, C) film demonstrates high perpendicular magnetic anisotropy (Ku = 2.83 × 107 erg/cm3 at 100 K) and out-of-plane coercivity (Hc = 38.0 kOe at 100 K). The Ku and out-of-plane Hc are respectively increased from 38% and 46% between 350 K and 50 K. The sample with a thickness of 8 nm also shows a similar trend for magnetic properties, however, the tiny magnetization kink which may come from rare Fe-B or disordered FePt grains was observed in the easy axis loop. The intrinsic (ΔHint = 12.6 kOe) and extrinsic switching field distribution (ΔHext = 1.62 kOe) were characterized by major and minor loops to correlate the microstructural grains. The coupled FePt grains grown on a single MgTiON grain were observed in a high-resolution transmission electron microstructure (HRTEM) image. This small intergranular exchange coupling was defined by estimating the magnetic cluster size (46.6 nm) from ΔHext and the average grains size (28.2 nm) from TEM images. The temperature dependence of coercivity was fitted to further understand the magnetization reversal process. The lower microstructural parameter was evidenced in the imperfect grain morphology.

Saliency-based position sensorless drive with the pulse width modulation (PWM) switching frequency injection can achieve the high position estimation bandwidth. However, in order to obtain the rotor position, multiple currents should be sampled every PWM cycle to calculate the saliency reflected current difference. Considering the low-cost inverter using shunt resistors for phase current sensing, it is not possible to obtain this saliency current difference because machine current can only be measured once the low-side switch is ON. To implement the PWM injection sensorless drive on shunt-based sensing inverters, this paper proposes two modified PWM voltage controls for the measurement of saliency reflected current difference. The first modified PWM is based on the asymmetric PWM for both the field-oriented control (FOC) and position estimation. This proposed PWM requires only a single interrupt service routine (ISR); however, the current total harmonic distortion (THD) is higher. By contrast, the second modified PWM consists of both discontinuous PWM (DPWM) for FOC and asymmetric PWM for the position estimation. Although two ISR’s are required for this proposed PWM pattern, the current THD is reduced through the separated PWM control. All the proposed PWM patterns are experimentally verified on an interior PM machine where the inverter with shunt resistors is used for current sensing.

The microstructural and magnetic properties of perpendicular anisotropic CoCrPt films deposited on Ru or RuCoCrX (X = Ti, Re) intermediate layers were studied. The c-axis of CoCrPt grains were promoted by (0002) textured RuCoCr, and RuCoCrX (X = Ti, Re) intermediate layers due to smaller lattice misfit as compared to Ru. The narrower rocking width (&Delta, &theta, 50 = 3.76&deg, ) in RuCoCrRe intermediate layer and CoCrPt shows higher out of plane coercivity (Hc = 6.2 kOe), magnetic anisotropy constant (Ku = 6.2 &times, 106 erg/cm3) and nucleation field (HN = &minus, 2.8kOe) as compared to the Ru intermediate layer (Hc = 5.4 kOe, Ku = 5.9 &times, 106 erg/cm3, HN = &minus, 1.6 kOe). The partial intergranular exchange decoupling of CoCrPt grains was observed. The grain boundaries oxides were formed by the residual oxygen in targets and sputtering processes. The minor Cr2O3, CoO, TiO2, ReO3 oxides were investigated by surface analysis. Due to the minor oxides and Cr segregation at grains boundaries, the CoCrPt films present high coercivity. Samples CoCrPt/RuCoCr and CoCrPt/RuCoCrTi present a minimum at 45&deg, but the values are much higher than the ideal Stoner-Wohlfarth theoretical value 0.5 which could be due to fewer natural oxides for magnetic grains separation. In sample CoCrPt/RuCoCrRe, there is an increase of intergranular interaction as indicated by the large asymmetry and the shift of the minimum at lower angles.

Structural, morphological and magnetic properties of CoCrPt@(TiO2,CoO) granular thin films deposited on Ru/NixPd100-x/NiTa intermediate layers were investigated as a function of the NixPd100-x composition (x = 20, 50, 80). Using a Ni20Pd80 buffer-layer leads to a significant improvement of the crystallographic texture, grain separation and easy-axis angular distribution with respect to conventional systems using Ru/NiTa as intermediate layers. As a result, a meaningful enhancement of magnetic properties (anisotropy constant, K = 4.1 x 10(5) J/m(3), out-of-plane coercivity, H-c perpendicular to = 470 kA/m, nucleation field, H-N = -115 kA/m) with respect to conventional systems (K = 3.7 x 10(5) J/m(3), H-c perpendicular to = 374 kA/m, H-N = -71.6 kA/m) was achieved, thus indicating that Ni20Pd80 can potentially be used as buffer-layer to enhance the recording density of conventional Hard Disk Drives.

This paper proposes a high-precision permanent magnet (PM) motor primary used for the small satellite attitude control. A radial-flux type motor is designed to achieve the high demanded smooth torque production for satellite applications. On the basis, a slotless stator is used to improve flux harmonics by removing the stator steel component. Several design methods are proposed to increase the torque output while minimizing the ripples under the slotless topology. First, leakage fluxes caused by slotless stator are reduced by designing the radial-flux distribution with dual rotors. In this structure, two rotors can be used respectively for flux transmitter and flux receiver to concentrate the flux linkage across air gap. Second, rotor magnets are designed with Halbach array for the sinusoidal magnet flux distribution. Halbach array results in more torque production at low ripples. In this paper, finite element analysis (FEA) is used as the simulation tool for the motor design. A prototype is fabricated for the experimental evaluation.

This paper analyzes current sampling issues on the saliency-based position sensorless drive for permanent magnet (PM) machines using the pulse width modulation (PWM) voltage injection. On the basis, PWM voltage with the switching frequency is persistently injected into the machine. The rotor position is estimated through the spatial signal from the PWM voltage reflected current ripples. Because the rotor position is estimated every PWM cycle, multiple transient currents instead of single average current should be sampled per PWM. It leads to the issue on the selection of current sampling points with respect to different PWM patterns. In this paper, an asymmetric current sample is proposed for the position estimation using PWM voltage injection. By directly sampling phase currents during the injection period, the better signal-to-noise ratio (SNR) of position signal is concluded comparing to conventional symmetric current sample. In addition, shunt resistors are typically installed for the current sensing in inverters at low cost. A modified PWM control is also proposed for the position estimation compatible with low-side shunt current sensing. According to preliminary experimental results, the position estimation error is decreased using the proposed asymmetric current sample for the inverter with Hall-effect current sensors. More importantly, the inverter with low-side shunt sensors can be used for the saliency-based drive using the proposed PWM voltage pattern.

This paper improves a flux-based position sensorless drive for surface permanent magnet (PM) machines. On the basis, the rotor position is obtained from the spatial information in the magnet flux. The flux estimation is realized based on the integration of EMF voltage. In this paper, several implementation issues on the flux estimation are considered to improve the position sensorless drive. First, the machine phase voltage is measured for the flux estimation. By obtaining the actual inverter voltage outputs, the inverter deaditme effect is negligible on the flux and position estimation. Second, a modified integration is proposed to remove the flux estimation drift due to the voltage offset. Because the flux linkage is theoretically independent to the rotor speed, the signal-to-noise (SNR) ratio of postion estimation greatly increases at low speed. According to experimental results, the PM machine sensorless drive is improved at ~6% rated speed among the spaital signal SNR and drive dynamic response. More importantly, the overall current regulation bandwidth can be increased to 1kHz which is compatible to standard encoder-based drives.

Considering the field oriented control (FOC), low inductance permanent magnet (PM) machine drive usually contains the LC filter cascaded to the inverter in order to reduce the inverter reflected current harmonics. For position sensorless FOC drive with LC filter, the inductor current and capacitor voltage are required for the position estimation. However in standard machine drives, only phase current signals before LC filter can be obtained. It leads to implementation issues on sensorless FOC drive with LC filter. This paper concentrates on the LC filter implmentaiton for sensorless FOC drives with only inverter existing current sensors. First, filter parameters are designed to reduce PWM reflected harmonics on low inductance PM machines. Second, a dual-observer is developed to estimate the capacitor voltage and machine current for the position estimation. Considering the low inductance machine at high speed, this dual-observer is implemented in discrete-time with sample delay. In addition, the influence of machine inductance cross-coupling on LC filter is compensated from the observer to stabilize FOC drive at high speed. According to experimental results, sensorless FOC drive is realized on a low inductance PM machine with LC fitler by using the proposed active damping and observer esitmation.

This paper investigates digital implementation issues on high speed permanent magnet (PM) machine drives. The machine operating speed is designed beyond 30krpm where the ratio of controller sample frequency $\mathrm{f}_{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{ple}}$ over rotor electrical frequency $\mathrm{f}_{\mathrm{e}}$ is less than 5. Because microcontrollers are used in variable frequency drives to realize the field oriented control (FOC), the discretized effects must be considered to maintain the controller stability under low ratios of $\mathrm{f}_{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}/\mathrm{f}_{\mathrm{e}}$ . In this paper, the FOC based on different current controllers are compared specifically at low $\mathrm{f}_{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}/\mathrm{f}_{\mathrm{e}}$ . It is shown that current controllers using forward difference and bilinear approximation are able to maintain the drive stability if the voltage delay and indcutance cross-coupling are compensated. However, the drive performance strongly depends on the accuracy of inductance parameter. By contrast, the controller using direct digital design achieves the better FOC performance independent to machine specifications. In this paper, different types of controllers are experimentally compared to find a suited high speed FOC drive.

The FePt film above 10 nm critical lattice relaxation thickness was prepared and the ultrathin MgTiTaON layer was interleaved in between FePt film and the multilayer stack is FePt(6 nm)/[MgTiTaON(1 nm)/FePt(4 nm)]2. Next, the FePt films were co-sputtered with (Ag, C) segregants during deposition and the layer stacks is FePt(6 nm)(Ag, C)(x vol %)/[MgTiTaON (1 nm)/FePt(4 nm)(Ag, C) (x vol %)]2 (x = 0, 10, 20, 30, 40). After high temperature deposition at 470 &deg, C, the granular FePt(Ag, C, MgTiTaON) film illustrated perpendicular magnetization and the out-of-plane coercivity (Hc) was increased with (Ag, C) segregants and the highest Hc is 18.3 kOe when x = 40. From cross-section images, the FePt layer are more continuous with 0 and 10 vol% (Ag, C) segregants and changed to an island structure when the (Ag, C) segregants increase to 20&ndash, 40 vol %. The FePt grains were grown in separated islands in 20, 30 vol % (Ag, C) and changed to dense columnar-like morphology in 40 vol%. The second nucleated grains which contribute the in-plane magnetization are found in FePt (Ag, C) (40 vol %) film. The FePt islands are reached by inserting the ultrathin MgTiTaON layer and the island heights of FePt(Ag, C) (30, 40 vol %) are around 31&ndash, 38 nm and the aspect ratios are 0.6&ndash, 0.8.

The in-plane magnetic component in FePt-40 vol% (Ag, C) granular film was caused by lower ordering degree which lower the magnetic anisotropy field and out-of-plane coercivity (Hc = 23.6 kOe). To inhibit the FePt grains with second nucleation, random texture and in plane c-axis, the ultrathin B4C layer with thickness of 1 nm was capped. After surface modification, the FePt-40 vol% (Ag, C) film illustrates high perpendicular magnetic anisotropy (Ku = 1.75 × 107 erg/cm3) and out-of-plane coercivity (Hc = 28.8 kOe). The in-plane remanence magnetic moment is small and the tiny magnetization kink at zero field was not observed in easy-axis loop of 6 nm thick FePt-40 vol% (Ag, C) film. The ordering degree and the average surface roughness of FePt-(Ag, C) films were improved by surface diffusion of B4C which deposited at 470 °C and post-annealed for 2 min. Further, the perpendicular magnetic anisotropy and out-of-plane coercivity of FePt-(Ag, C) films were enhanced significantly. The TiOx are more favorable than TiN in MgTiON layer due to formation enthalpy, part of N atoms was diffused and incorporated in the FePt lattice evidenced in high angle angular dark field mapping. After post annealing, the released N atoms cause lots of vacancies and defects inside FePt film which promote the ordering degree.

The microstructure and magnetic properties of FePt(BN, Ag, C) granular films grown on the MgTiON intermediate layer with and without the MoC inserting layer were studied. Without the MoC inserting layer, the 6 nm thick FePt film is continuous, which favors the domain wall motion magnetization reversal process and shows a lower out-of-plane coercivity (Hc) value of 6.7 kOe. The FePt(BN, Ag, C) granular film was grown in ball- and square-like grains with an almost vertical contact angle, and the out-of-plane coercivity (Hc) was increased to 15.5 kOe. When the MoC with a thickness of 3 nm was capped on the MgTiON intermediate layer, the FePt grains with and without (BN, Ag, C) segregants were both formed in large trapezoidal islands with a low contact angle morphology. The out-of-plane Hc value changed from 14.9 to 13.2 kOe and the reduced coercivity was due to larger grain sizes and a lower ordering degree of the FePt(BN, Ag, C) film.

Fabrication of crystalline indium-tin-oxide (c-ITO) nanogratings and smooth line patterns on amorphous ITO (a-ITO) thin films by femtosecond laser-induced structuring and simultaneous crystallization followed by chemical etching is demonstrated. Three types of c-ITO structures are obtained merely by controlling the laser pulse energy of a high-repetition rate femtosecond laser at wavelength 532 nm: nanogratings perpendicular to laser polarization direction with period of 130 ± 11 nm, smooth c-ITO line patterns as well as nanogratings parallel to laser polarization direction with period of 390 ± 10 nm. Large area c-ITO patterns and nanograting structures are fabricated, which are expected to be used in optoelectronic and micro-electronic devices.

During the last decade, industrial robots have been applied to various field of science from computer-assisted surgery to space exploration. In recent years, autonomous service robots are increasingly finding their way into our daily lives. In this paper, we present the design of the robot, and the robot arm path planning combined with several sensors: motor encoder, CCD camera and laser range finder. Using information of CCD-cameras that provide information of the robot's environment which serves as an input for a robust object recognition algorithm: SURF (Speeded Up Robust Features). However, image information provided by cameras is strongly affected by environmental influence. In order to reduce environmental influence, we integrate distance information provided from a laser range finder. The integrated sensory system locates the object using distance information and then identifies the target using image information. Ultimately the dexterous manipulator system integrated with visual servo system and eye-in-hand laser scanner feedback, it can perform object fetching towards contributions in flexible automation.