Laser Goniometer Research Articles

Inertial information based star detection for airborne star sensor

Star sensors are among the most promising attitude measurement devices owing to their high accuracy. Insufficient star detection ability during daytime is a major issue in airborne applications because of the highly dynamic and strong sky background present. A star detection algorithm for a medium field-of-view star sensor combined with a zero-lock laser goniometer is proposed in this paper. The star sensor employs a high-frame-rate detector that shortens the exposure time to obtain an undistorted star spot under dynamic conditions. To improve the low signal-to-noise ratio of the star image influenced by the strong sky background, a technique for multi-frame image accumulation was introduced, prior to which attitude compensation for each star image frame was carried out by using the inertial information related to the reference frame measured by zero-lock laser gyro goniometers. Both simulations and laboratory experiments were conducted. The simulation results show that the proposed algorithm effectively enhances the stability of the star spot and signal-to-noise ratio of the star image. The experimental results demonstrate a fine star spot centroid extraction performance for the medium field of view star sensor with an extraction error of less than 0.2 pixels or 2 arc-second under four different types of one-dimensional angular motion after compensation. Based on this, the multi-frame accumulation of star images demonstrates little star spot dispersion compared with no compensation and exhibits a higher signal-to-noise ratio than a single-frame star image. In the real situation experiments, a K0 spectrum star with magnitude +3.0 was successfully observed under dynamic condition during daytime. The signal-to-noise ratio is up to 20, which is more than 5 times than that by the traditional method.

Laser goniometer: smartphone goniometer with laser guidance for range of motion measurement in musculo- skeletal medicine

Laser goniometer: smartphone goniometer with laser guidance for range of motion measurement in musculo- skeletal medicine

Validity and Intra-Rater Reliability of Laser Goniometer Versus Electro-Goniometer in Measuring Shoulder Range of Motion

Background: Providing new objective valid and reliable methods of assessment of a range of motion is always a persistent need for clinical practitioners and researchers in physical therapy for obtaining precised and realistic diagnostic and treatment decisions. So this study was carried out to test the validity and intra-rater reliability of the laser goniometer via comparing repeated measures of laser and electro-goniometers in measuring a range of motion of shoulder movements considering the electro-goniometer as the reference standard.Methods: one hundred healthy males with ages ranging between 20-30 years shared in this study. Three consecutive measures of bilateral shoulder flexion, abduction, internal and external rotation range of motion were performed by the same examiner on each subject by each of the laser and electro-goniometer, with standardized measurement procedures, subjects’ positions, and stabilizations.Results: Pearson (r), paired T-test, and intra-class (ICC) correlation coefficients were used to test the validity and intra-rater reliability of the laser goniometer in comparison to the electro-goniometer. And the results of the validity testing showed a very strong relationship between readings by both devices (r=0.84 to 0.93) and also no significant differences between means of readings of both devices with the p-value ranging between 0.13 and 0.97. Also, ICC revealed high intra-rater reliability of laser goniometer on repeated measures of shoulder range of motions (ICC=0.98-0.99).Conclusion: laser goniometer can be used as a new valid, reliable digital objective method of measurement of shoulder range of motion.

Implementation of the dynamic laser goniometer for noncontact measurement of angular movement

The dynamic laser goniometer (LG) implementation for noncontact measurements of an object’s angular position is presented. One of the possible implementations involves determining the time dependence of the scanning mirror’s angular position. Another application is aimed at determining the oscillatory movement parameters on the test table. The results obtained in the course of the research show that the dynamic LG makes it possible to calibrate various kinds of test beds making angular oscillations or angular movement of arbitrary law.

Noncontact measurement of angular position and angular movement by means of laser goniometer

The results of analysis and experimental investigation of a laser goniometer (LG), working in the mode of the noncontact measurement of an object’s angular position, are presented. The important feature of this approach is the very wide range of high-accuracy measurements. In this case, the LG, characterized by the accuracy of ∼0.1 arc sec, has big advantages in comparison to photoelectrical autocollimators which have a rather narrow range of measured angular positions. Our results indicate that the use of a laser dynamic goniometer makes it possible to measure constant angles with an accuracy of 0.05 to 0.1 arc sec in the range of possible angles of 15 to 20 deg. If the measured angle is varying, the residual measurement error contains an additional component, which is equal to ∼0.2 arc sec, induced by the nonflatness of the optical polygon’s faces and by the problems with statistical averaging of the measurement results.

Development of precision laser goniometer systems

The concept of constructing precision laser goniometer systems, based on integrating a ring laser and an optical angle sensor with the holographic principle of angular scale recording is considered. The concept implies the application of the cross-calibration procedure, aimed at determination of systematic components of the errors of angle sensors, used in the system. The results of the presented system studies demonstrate the error of angular measurements amounting to ∼0.01''. The results of implementing the proposed concept in the creation of a standard system of the planeangle unit of rigid rotation and the measuring and computing complex for automated control of digital angle transducers with high digit capacity are briefly presented.

A method of eliminating the influence of magnetic field in a dynamic laser goniometer linear and angular measurements

A method of eliminating the systematic error of a ring laser induced by the influence of magnetic field, based on the reversible nature of the rotation of the laser, is proposed. Results of experimental studies that have demonstrated the effectiveness gained from the use of the method of reverse rotation are presented.

Modeling of Micropitch Shift of a Magnetoelectrical Sensor During Laser Solder Ball Bonding Process

With the development of optoelectronics and microelectromechanical systems (MEMS) packaging, laser soldering has become an extensively used interconnection technique in electronic manufacturing industry. Postsolder shift in assembling of such components is the most challenging issue to affect the packaging yields. To maintain a high coupling efficiency or accuracy, tight control of postsolder shift is required. In the present work, a 3-D thermal-mechanical coupled finite element model was developed to investigate the time-dependent pitch shift induced by the laser solder ball bonding process. This model accounted for the laser interaction, the heat conduction, the thermal induced deformation and the phase change of the solder and could reflect the actual laser soldering process. The modeling results show different deformation mechanisms in the prebumping and reflow processes. The pitch shift is mainly induced by the thermal shrinkage of solder. The pitch angles obtained from the finite element analysis are in good agreement with those from the measurement using laser goniometer.

A method of reducing the random error of a dynamic laser goniometer

The noise generated by a dynamic laser goniometer is considered and a method of reducing the random error of the device based on compensation of the generalized shift of the zero of a ring laser and suppression of the noise of the dynamic laser goniometer is proposed. Results of experimental studies are presented.

Dynamic angle measurement by means of a ring laser

A ring laser goniometer was investigated in different applications of precision angle measurement, such as the calibration of optical polygons and optical encoders, external angle measurement of rotating objects and inertial angle measurement by rotation of the goniometer itself. The results agree with standard methods of angle measurement to about 0,5 µrad (0,1 ). Further improvement in accuracy is expected mainly from the reduction of noise in the mechanical and electrical setup of the measurement system.

Photoelectric device for stroke induction in the control of dials and coded disks

Currently photoelectric devices for stroke induction are widely used in systems for controlling dials (coded disks). As a rule the induction is effected with the aid of a photoelectric microscope (PEM) with a movable slit, located in the plane of analysis, i.e., in the plane of the sensitive area of the phototransducer. To eliminate error associated with variation in the width of the stroke, the induction is performed on its center [1]. Stroke induction using a PEM requires special conditions and accessories. First, they place strict requirements on the initial exposure of the optical axis of the PEM relative to the axis of rotation of the attachment and on the focusing of the microscope on the surface of the piece being tested. Second, when the axis of rotation of the attachment is not parallel to the optical axis of the PEM (the inclination of the reading microscope) an additional error appears due to wobble in the axes of the rotating attachment and sphericity in the dial, since these factors cause variation in the distance of the diaI from the microscope [2]. Third, the PEM have significant structural parameters (mass, dimensions) and should be equipped with complex electronic units [3]. These factors to a significant degree limit application of PEM in systems for the dynamic control of dials and coded disks constructed, for example, on the basis of a laser goniometer [4] the speed of rotation of the rotating base of which is equal to 90~ Fiber optics has permitted development of light field intensity distribution gauges for relative motion of the gauge and the field. Figure 1 shows a measurement diagram of such a device. Fiber light conductor 2 is mounted on carrier 3. The input end of the light conductor is optically treated and transparent to the wavelength of the field being tested. The output end of the light conductor is connected optically to the sensitive area of phototransducer 1 and mechanically to its chassis. The design incorporates special measures to exclude the incidence of background radiation onto the sensitive area of the phototransducer. Moreover, the gauge is equipped with a device 5 for rotation around two mutually orthogonal axes and a device 4 for translation along a third axis which is perpendicular to the first two axes and which coincides with the axis of the fiber light conductor. This light field intensity gauge permits practical application of classical diffraction theory to problems of dial stroke (coding path window) induction. The dial is a plane-parallel plate with strokes the dimensions of which may vary within broad limits for different dials. Independently of the method of applying the stroke to the surface of the dial the stroke may be regarded as an opaque screen with finite dimensions and, without loss of generality, the rectilinearity of the edge of any stroke may be assumed. The portion of the dial with the strokes is shown in Fig. 1. Here 2h is the width of the stroke, 2H is its height, M is the distance between neighboring strokes along the diameter of the graduated circumference. Let us introduce a rectangular coordinate system X, Y, Z, the center of which is the point O which coincides with the center of symmetry of the stroke, while the axes OX and OY are directed along the short 2h and the long 2H sides of the stroke, respectively. The OZ axis is perpendicular to the surface of the stroke (screen). Let us connect a linear laser equipped with a collimating system and generating in space a light field of intensity E to the gauge in such a way that the optical axes of the laser and the gauge coincide and coincide with the O'Z" of the fixed rectilinear coordinate system X'Y'Z" associated with the gauge. The input end of the fiber light conductor lies in the X'O'Y" plane. The gauge registers the field intensity I r determined by the square of the modulus I El 2 as a constant quantity. Into the gap between the laser mirror and the input end of the fiber light conductor we introduce the dial in such a way that the axes of the XYZ and X'Y'Z" coordinate systems are collinear and the distance OO" is equal to L. Then, taking into account that for dials and coding disks 2H >> 2h in accordance with [5] we write the field intensity beyond the stroke in the near diffraction zone (taking into account that Ir(Y') = const) as