A microstep controller of a DC servomotor

A microstep controller of a DC servomotor is developed for accurate positioning and smooth movement at low-speed rotation. It consists of digital and analog positioning loops. Dividing one period of quadrature sinusoidal signals generated by an incremental encoder attached to a motor shaft into quarter sections, the digital loop controls the movement between the sections. The analog loop divides each section further into N equiangle segments to control the movement within each section. The effective angle resolution is thus 90°/MN with M being the number of slits etched on an incremental encoder. A prototype controller assembled using monolithic and hybrid integrated components has confirmed the principles of operation. Positioning accuracy was 0.009°±0.002°. A further improvement is possible with this controller by increasing the number of slits on the encoder and reducing the interpolation step size. Positioning accuracy is dominated ultimately by the amplitude fluctuation of quadrature sinusoidal outputs, and thus an automatic amplitude control should be incorporated into the encoder. The controller was first intended for applications such as crystal-pulling apparatus, astronomical observation systems, and tracking radars, which require smoothly rotating mechanisms, but it can also be applied to fine-positioning mechanisms in scanning electron and tunneling microscopes and semiconductor manufacturing equipment     

不同分辨率下增量式光栅编码器测量误差研究

为了研究增量式光栅编码器在不同分辨率下的测量误差,构建了一套基于旋转角加速度测量的编码器误差检测系统。首先介绍了永磁式角加速度传感器的工作原理,以及增量式光栅编码器的角加速度测量原理;然后采用角加速度传感器和增量式光栅编码器,对同一正弦振动源实际轴上的旋转角加速度进行检测,根据实验结果剖析了光栅编码器在不同分辨率下的误差产生原因;最后讨论了在进行角参数测量时,选择增量式光栅编码器分辨率的参考依据。     

Magnetic angular encoder using an offset compensation technique

Quality and resolution of integrated microsystems using Hall sensors dedicated to an angular encoder are strongly dependent on the accuracy of the relative position of Hall sensors and on the offset of electronic front end circuitry. In this paper, we describe a CMOS microsystem built on two integrated circuits. This contactless encoder microsystem gives three sine and square signals with a phase shift of 120/spl deg/ and provides an angular error of less than 4/spl deg/ without external trimming or feedback. The Hall sensor assembly with the engine consists of fixing a small permanent magnet on the rear axis of the motor. Then, the sensor is positioned in front of this magnet.     

Antialiasing Encoder Interface With Sub-Nyquist Sampling

A technique is presented for reconstructing absolute position or angle from time-sampled outputs of incremental encoders. Unlike existing techniques, the new method is able to track analog quadrature outputs with frequency contents higher than the Nyquist frequency. The algorithm is described in detail, and both the existing and new methods are tested using a linear position sensor and a high-speed hydraulic actuator. The results from these tests demonstrate aliasing and incorrect tracking for the existing algorithm and correct tracking for the new algorithm. The technique is an excellent complement to resolution-enhancing encoder interfaces that sample raw analog encoder outputs     

Instantaneous phase method for readout signal processing of body dithered ring laser gyro

The readout signal of a body dithered ring laser gyro contains both useful information and the dither component. The dither component must be removed to get the useful information. The dither stripping method can get the useful information without latency. But the quadrature demodulator only has 1/4 pulse resolution, which means that the quantization noise will limit the short-term accuracy. The effect and the property of quantization noise are analyzed in detail. Taking advantage of high-speed analog-to-digital conversion (ADC), the analog values of the two beat frequency signals in quadrature are sampled. A novel instantaneous phase method is introduced, which can get the residual phase besides 4× resolution and the quantization noise can be removed radically. The Allan variance analysis of experimental results shows that the quantization noise coefficient using this method is only 1/7 of that using the original 4× resolution method.     

An Approach Method to Calibrate the Autocollimator with Small Angle Measurement Range

A new method to calibrate the autocollimator with small angle measurement range has been developed. This method used a system based on rotary encoder for angle measurements with self-calibration function (SelfA47). The SelfA47 has 18,000 graduation lines with angle interval of 0.02°, corresponds to 72 arcsec. Thereby this system cannot be used to calibrate the autocollimator with measurement range <72 arcsec. On the other hand, SelfA47 can be used to calibrate an electronic level. The deviation of electronic level shaped linear gradient. Therefore a small nominal gradient of electronic level can be approximated by interpolation. Since the gradient of a curve corresponds to the angle quantities, it is feasible to calibrate the autocollimator with nominal angle <72 arcsec using SelfA47 and an electronic level. In this proposed method, SelfA47 is placed horizontally on the same plane with electronic level and mirror reflector position. The electronic level value that have been corrected by SelfA47 is used as a reference. This reference value was converted to the angle, thus the angle deviation of autocollimator can be determined. The prominent uncertainty of angle measurement using this new technique derived from the uncertainty of electronic level and rotary encoder. Using this method, the expanded uncertainty of 0.36 arcsec is obtained from calibration of autocollimator with measuring range of ±20 arcsec and it is consistent statistically with the manufacturer calibration result shown by E _n value is <1. In conclusion, this approach method can be applied to calibrate the autocollimator with a resolution smaller than SelfA47 as standard, but it is not recommended for the calibration of highly accurate autocollimator.     

Resolving quadrature fringes in real time

In many interferometers, two fringe signals can be generated in quadrature. The relative phase of the two fringe signals depends on whether the optical path length is increasing or decreasing. A system is developed in which two quadrature fringe signals are digitized and analyzed in real time with a digital signal processor to yield a linear, high-resolution, wide-dynamic-range displacement transducer. The resolution in a simple Michelson interferometer with inexpensive components is 5 x 10(-13) m Hz(-1/2) at 2 Hz.     

A wideband analog continuum correlator for radio astronomy

Design details for a 1-GHz bandwidth analog continuum cross-correlator for the Owens Valley Millimeter Array are presented. The correlator uses a pair of microwave mixers fed in phase quadrature to realize a complex multiplier for each baseline in the array. Very fast 180° phase switching is included to reject spurious signals     

Fiber bragg grating strain sensor demodulation with quadrature sampling of a mach-zehnder interferometer

A simple and highly sensitive phase-demodulation technique is proposed, and its use for a fiber Bragg grating strain sensor is experimentally demonstrated. Sampling a phase-modulated Mach-Zehnder output with controlled time delay produced two quadrature data streams that have relative quadrature phase difference (90 degrees ). The Bragg wavelength-dependent phase information is extracted by application of digital arctangent function and phase unwrapping to the quadrature signals. By use of this technique with a reference grating, strain sensing at as much as a 30-kHz sampling rate was obtained with strain resolution of 3.5 microstrains and 6 nanostrains/ Hz in quasi-static and dynamic strain measurements, respectively.     

Analysis of mismatch effects among A/D converters in atime-interleaved waveform digitizer

High-speed A/D conversion can be achieved by employing a parallel array of M A/D converters interleaved in time, each working at 1/Mth of the sampling rate. Theoretically, the resolution of the structure is given by the resolution of the A/D converters in the array (subconverters). In practice, however, mismatches among the subconverters lead to a decrease in the resolution. The effect of such mismatches is analyzed in terms of a signal-to-noise ratio defined as the ratio between the energy of the input analog signal and the energy of the error signal due exclusively to these mismatches. The analysis shows that the distortion is comparable to that generated by nonuniform sample timing in the analog demultiplexer when converting a single high-speed signal into several low-speed sampled-and-held signals. The results of the analysis can be used to specify the degree of precision to be achieved in an actual monolithic implementation     

Intensity-modulated, stepped frequency cw lidar for distributed aerosol and hard target measurements

A compact frequency-modulated, continuous wave (FM-cw) lidar system for measurement of distributed aerosol plumes and hard targets is presented. The system is based on intensity modulation of a laser diode and quadrature detection of the return signals. The advantages of using laser diode amplitude modulation and quadrature detection is a large reduction in the hardware required for processing and storing return signals as well as the availability of off-the-shelf integrated electronic components from the wireless and telecommunication communities. Equations to invert the quadrature signal components and determine spatial distributions of multiple targets are derived. Spatial scattering intensities are used to extract aerosol backscatter coefficients, which can then be directly compared to microphysics aerosol models for environmental measurements. Finally, results from laboratory measurements with a monostatic FM-cw lidar system with both hard targets and aerosols are discussed.     

A New Low Cost Linear Resolver Converter

A new low cost converter topology is proposed for sinusoidal position encoders. The converter enables determination of the angle from the sine and cosine signals of the encoder. When used with resolvers, the implementation of the present scheme takes advantage of the available excitation signal used to operate the device. This trigonometric reference signal is optimally used to generate an analogue signal equivalent to a digital look-up table (LUT). This enables determination of the mechanical angle without using LUT, A/D, and D/A converters. The scheme is optimized in order to achieve highest possible precision. Beside simplicity of its implementation, the proposed converter offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal. The converter was implemented using ordinary low-cost analog components. The theory of operation, computer simulation, and experimental results are given.      

混凝土结构健康检测的声发射圆阵波束形成仿真分析

采用了声发射(Acoustic Emission,AE)均匀圆阵并分析其波束形成特性,通过仿真分析了阵元数目及声发射模拟信号频率的变化对波束模式的影响.结果表明,当频率不变,阵元数目为4~32时,随着阵元数目的增加,角分辨率保持不变,最高旁瓣降低,可达-8 dB左右.混凝土结构内部缺陷声发射信号的超声频段一般在25~200 kHz,当阵元数目不变时,随着频率的升高,角分辨率随之升高,最高旁瓣也随之增大.另外,文中提出如何设计一个性能相对稳定的阵列,并通过从噪声信号中提取有用信号的实例说明声发射均匀圆阵空间匹配滤波性能.     

A method of improving the resolution and accuracy of rotaryencoders using a code compensation technique

A method of improving the resolution and accuracy of incremental type rotary encoders using a phase encoding and code compensation system is described. Applying this system to an optical incremental encoder whose scale pitch is 1/3600 rotation, results in a resolution of up to 1/920000 rotation, and better than ±1/300000 rotation (±0.0012°) precision is obtained     

Polar nephelometer based on a rotational confocal imaging setup

Rapid measurement of the angular distribution of light scattered by particles, the scattering phase function, is achieved by using a new type of polar nephelometer, a device for measuring the angular scattered-light intensity distribution, with a high angular precision and across many orders of magnitude of intensity. The design offers high-speed measurements and avoids many of the problems often associated with traditional goniometers when they are used for measurements of light scattering from small particles or biological cells in suspension. Our system relies on confocal imaging of the test space with off-axis parabolas, using a rotating mirror to scan the angular field of view at the second focus of a pair of conjugated parabolic mirrors, with the test space located at the first focus. The angular resolution of the system is limited mainly by the data-acquisition sampling frequency. In this proof-of-principle demonstration the system performs multiple scans of a 55 deg field of view in a very short time (<1 s). To significantly increase the signal-to-noise ratio, we averaged the successively acquired scans during this time. Polystyrene spheres dispersed in water at low concentrations were used to test the system. The scattering patterns obtained were found to be in good agreement with Mie theory calculations.     

Digital generation of coherent sweep signals

The authors describe a digitally implemented coherent sweep generator, i.e. a sweep generator in which sweep rate, start frequency, and start phase can be specified. By carrying out a digital integration twice, using a counter and an accumulator as integrators, a quadratic phase function of a linear sweep is produced. The desired start frequency and start phase are introduced by presetting the counter and accumulator. The mod (2π) of the quadratic phase function is extracted and used as an address for a sine look-up table whose output is applied to a digital-to-analog converter. The system is capable of producing sweep signals from DC up to the lower megahertz range, and the sweep rate can be verified over several orders of magnitude. By operating several digital sweep generators from the same clock, multiple coherent sweep signals may be produced, or quadrature signals can be produced with two modules. The digital sweep generator has been implemented with transistor-transistor logic (TTL). Generated waveforms are presented     

Some Aspects of Fringe Counting in Laser Interferometers

A number of arrangements are possible for deriving signals in phase quadrature from interferometers, so that bi-directional counting of the interference fringe movements can be carried out. Arrangements which avoid splitting the image field are preferred for laser light sources, and can give a better signal-to-noise ratio. In environments where the interferometer is subjected to vibration, the fringe counting system may be required to handle rapid reversals in the direction of movement. In these circumstances the rate of production of rapid counting signals of alternate direction may be considerably reduced by using an appropriate logic system between the interferometer and the counter.     

Focal plane detector for the Oxford MDM-2 spectrometer

A “hybrid” focal plane counter comprising a gridded ionization chamber with position sensitive proportional counters, 300 mm long, 510 mm deep and with an active height of 60 mm, is described. The detector is designed for use with the Oxford MDM-2 magnetic spectrometer and is suitable for both light and heavy ions. Typical results obtained are 0.6 mm position resolution and 1% total energy resolution. Two energy loss, a veto and two position signals are available as well as provision for height and timing signals. Techniques are described for the reduction of capacitive noise, correction of electric field nonuniformities, and the reduction of interference from positive ions on the ionization signals.     

Diffractive incremental and absolute coding principle for optical rotary sensors

Rotary sensors are an essential component in numerous applications where a rotation movement has to be detected. With optical encoders, a high angular resolution can be achieved. As a disadvantage, the resolution enhancement is associated with increasing cost. To overcome this issue, a coding principle is presented that uses a diffractive solid measure on a microstructured plastic disc. Like a DVD, this encoder disc can be manufactured in a cost effective injection molding process. For this approach, a differential incremental code, as well as an absolute code, has been developed.