The measurement of the six degrees of freedom (6-DOF) is crucial in industrial manufacturing, enabling efficient operation of machinery. The combination of 6-DOF and the quaternion coordinate system offers a robust framework for accurately representing and controlling the motion and orientation of objects in 3D space. Electro-optical measurement systems are commonly used in these cases due to their advantages such as compact design, fast measurement speed, high stability, and accuracy, as well as the ability to directly measure displacement parameters of the object. The proposed autocollimator optic-electronic system is designed to provide accurate measurements of the position and motion coordinates of industrial objects. It consists of an autocollimator, reflector, radiation marks, lenses, CMOS matrix photoreceivers, and a computer for calculations. By combining the equations related to the quaternion coordinates, reflected images, and image distances, a system of equations is formed to determine the six motion coordinates of the object. The proposed autocollimator optic-electronic system offers a practical solution for accurate measurement of industrial objects' motion coordinates, optimizing both accuracy and efficiency. It can be applied in various applications where precise measurements are required. The autocollimator measuring system outperforms the three-point optic-electronic system in terms of measurement accuracy for all six coordinates encompassing rotational motion and linear displacement. The autocollimator system offers higher precision, particularly in linear displacements, angular rotation, and rotational axis position.
In this paper we propose an algorithm for autocollimators with cylindrical surfaced reflectors. We discuss it’s flow and how it can be achieved. Optimal flow can contain the following steps in the order, they should be performed: noise filtering, line width reduction, line separation, clustering, determination of an angle for each line.
A microelectromechanical system (MEMS) gyroscope mounting error calibration platform composed of autocollimator and manual turntable were proposed. In order to achieve the dynamic angular range reflected in the mounting error of MEMS gyroscope, the range of the NIKON-6D autocollimator has been extended from ±15' to ±9°by exploiting the relationship between the angular range and the structure of the reflector. In addition, in the software design, a common data acquisition serial port between CMOS camera and MEMS gyroscope was built. By integrating the angular rate measurements of the MEMS gyroscope with the sampling time, a uniformity of magnitude was obtained between the angular readings of the autocollimator and the angular rate readings of the MEMS gyroscope. Experimental verification shows that compared with precision three-axis angular rate output turntable, the relative calibration deviation of the MEMS gyroscope mounting error coefficient is less than 0.6%, and the platform benefits from the traceable reference of the autocollimator, which has the advantages of low maintenance evaluation rate and high stability, and can serve the long-cycle and high-efficiency MEMS gyroscope mounting error calibration and calibration process.
A novel trihedral reflector (also known as hollow cube-corner reflector) with two cylindrical surfaces is proposed. This reflector has bottom side represented by two cylindrical surfaces, which axes constitute a 45° angle. Novel reflector solves the problem of an objects pitch measurement using singular cylindrical cube-corner reflector. Main benefit is that an image of this reflector consists of three lines, allowing to differ more consistently and to measure all three angles of object rotation.
Nowadays, linear displacement and angle measuring devices are widely used in the assembly, calibration and deformation monitoring of industrial structures. The Optic-electronic autocollimators for non-contact measurements are highly effective in these cases, since the measurement has a large measuring distance and high accuracy, but the existing autocollimation sensor for measuring angular and linear coordinates consists of two separate measuring systems and two reflectors, respectively. This disadvantage is a major obstacle for determining 6 motion coordinates at a point of the object. Autocollimator is suggested, capable of determining 6 object motion parameters (3 3 rotation angles and 3 linear displacements). The two main components of the autocollimator are the special reflector at the track point of the monitored object and radiating-receiver unit at the rigid base. A specially constructed tetrahedral prism is used as a reflector. Two emission marks are placed directly in front of the radiation receiver objective. Each emission mark after reflecting through the faces of the reflector produces 6 images, so with two emission marks 12 images are produced behind the reflector. The displacement of the object is calculated from the coordinates of the images obtained on the sensor. Mathematical models that determine the displacement of the object based on the image coordinates on the matrix photo receiver have been built. A comparative analysis between the optic-electronic autocollimators and the existing schemes was performed by computer simulation. The simulation results show that the proposed scheme has a smaller error. In addition, the simple and compact structure is also one of their outstanding advantages.
Microwave frequency measurement (MFM) is to estimate frequencies of intercepted microwave signals, which is critical to modern military and civil radio-frequency (RF) systems, such as wireless communications, electronic countermeasure (ECM), radar warning and electronic intelligence systems. In this paper, a photonic-assisted MFM method based on harmonic down-conversion with semiconductor optical amplifiers (SOAs) is proposed. Two optical harmonic intensifiers consisting of an electro-optic intensity modulator and a SOA are used to generate high-order optical harmonics based on cascaded four-wave mixing in the SOA, which has low-frequency and tunable spacing. It enables ultra-wide harmonic down-conversion of microwave signals under test in the electrical domain with low-frequency local oscillator (LO). The microwave frequency is therefore unequivocally determined by cross-referencing two pairs of harmonic down-converted tones within the LO frequency. It enables multi-tone frequency measurement and eliminates the trade-off between the measurement range and frequency-resolution. Moreover, it avoids the limitation of deadband by the cross-referenced frequency discrimination.
Although autocollimators enable noncontact measurement, their performance is limited in large-scale and long-distance applications because of errors caused by nonideal point light sources. Therefore, we analyze this type of measurement error, including the error source and the equations used to describe the irradiance distribution of the light spot. A two-dimensional exponential approximation formula is used to express the light irradiance distribution and compensate the spot imaging errors. Experimental results show that the measurement error could be reduced by sixfold. Therefore, the proposed compensation algorithm can be applied to autocollimator measurements over distances.
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