RU2467285C1 - Device for twist angle measurement - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention may be used to align optoelectronic systems, assemble bulky devices, define parameters of shafts rigidity, measure remotely and transfer a twist angle value, etc. The device comprises a radiator installed on the object and on the optical axis of the device matching the axis of object rotation, a matrix photodetector and a joined calculating unit. On the object, along with the radiator beam direction, there is a mark shaper installed additionally to shape a mark in the form of a linear interference structure of high contrast confined in space between the shaper and the photodetector and lying in the plane perpendicular to the optical axis. The radiator is made in the form of a coherent source of radiation.

EFFECT: invention provides for high-accurate measurement with constant error as distance to an object changes within large limits without retuning (focusing, scale change), and also simplicity of manufacturing and using standard unified units.

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Description

The invention relates to the field of measuring equipment, to measuring devices characterized by optical measuring instruments, and can be used to solve a wide range of technical problems, such as aligning optoelectronic systems, assembling large-sized structures, determining the parameters of shaft rigidity, remote measurement and remote transmission of values twisting angle, etc.

Known auto-collimation device for transmitting horizontal direction from one horizon to another [US Pat. RU, No. 2204116, IPC G01C 15/00, prior. 06/14/2001], consisting of located on the optical axis, coinciding with the axis of rotation of the object, the radiation source, the shaper brand in the form of a matrix of round windows (MCO), a beam splitting prism separating the lighting and measuring channels, a lens, a reflector in the form of a prism AR -90, located on the object, and the CCD matrix, while the brand and the CCD matrix are installed in the focal plane of the lens, and the CCD matrix is connected to the information processing unit.

The radiation source illuminates the mark in the form of an MCO, the radiation passes through a beam-splitting prism, then a parallel light beam after passing through the lens enters the reflector installed in the object in the form of a prism AR-90, is reflected from it, the lens passes in the reverse direction, the beam-splitting prism and hits the CCD matrix. An MCO image appears on the CCD matrix, the rotation of which around the optical axis is equal to twice the angle of rotation of the reflector. The rotation of the MCO image leads to the rotation of the brand image relative to the coordinates of the CCD matrix. The torsion angle is calculated from the displacement of the MCO image in the information processing unit. The algorithm for calculating the twist angle by the displacement of the brand image is known.

The autocollimator allows measurements at significant longitudinal displacements of the reflector along the optical axis (changes in the distance from the photodetector to the object) without refocusing the lens and with a constant measurement error (without taking into account the influence of disturbances in the air duct).

However, such a device has a complex design and includes a high-quality telephoto lens with a large field of view, a high-quality beam-splitting prism-cube, and a high-quality prism AP-90.

Known we have chosen as a prototype device for measuring the angle of twisting [Pat. RU No. 2152591, IPC G01C 15/00, prior. 06/09/1999], consisting of a radiation source and a mark in the form of a matrix of round windows (MCO) located on the object and located coaxially with the mark of the photodetector, consisting of a lens and a CCD matrix installed behind it, and the CCD is installed as that the image of the brand is projected on a CCD matrix, while the optical axis of the system coincides with the axis of twisting.

A stamp in the form of a matrix of round windows (MCO) is projected by the lens into the plane of the CCD matrix. In the information processing unit, the coordinates of the centers of the image of the windows are determined, the coordinates of the centers of the image of the windows lead to the center of the image of the matrix of round windows. When the MCO is rotated around the axis, the image is rotated by the same angle, which can be determined by changing the coordinates of the windows.

The disadvantage of this device is the variable error of measurement of the angle of twist when using the lens of a photodetector with a constant focal length. In the case of increasing the distance from the photodetector to the object, the measurement error increases in proportion to the increase in the distance, since the measurement error depends on the diameter of the image of the matrix of windows on the CCD matrix, i.e. from image scale. Another disadvantage is the complexity of the device due to the presence of a lens focusing system when changing the distance to the object. When refocusing, the lens should not change the aberration characteristics and the position of the optical axis in space.

We have proposed a high-precision device for measuring with a constant error in the torsion angle, which works when the distance to the object changes within large limits and does not require adjustment (focusing, zooming). The device is easy to manufacture and contains standard unified nodes.

We achieved such a technical result when, in a device for measuring the angle of torsion, including an emitter placed on an object, mounted on the optical axis of the device coinciding with the axis of rotation of the object, the photodetector array and the associated computing unit, it is new that the object along the way of the emitter’s beam, a brand shaper is additionally installed, forming a brand in the form of a linear interference structure of high contrast localized in the space between the shaper and the photodetector and lying in a plane perpendicular to the optical axis, and the emitter is designed as a coherent radiation source.

Approaches to solving the problem of brand formation in the form of a linear interference structure of high contrast with desired properties are known.

Figure 1 shows a schematic diagram of a torsion angle meter, where: a coherent radiation source 1 and a shaper 2 of a linear interference structure, a photodetector 3, a computing unit 4, located on an object rotating around an optical axis

Figure 2 shows an example of a specific embodiment of the device, where: placed on an object rotating around the optical axis, a coherent radiation source 1 and a linear interference structure former 2, a photodetector array 3, a computing unit 4, a single-mode optical fiber 5, a splitter 6, a lens 7 The lens 7, the splitter 6 and the single-mode optical fiber 5 form a shaper 2 of a linear interference structure.

The device operates as follows.

The radiation of the coherent source 1 is introduced into the shaper 2 of the linear interference structure, at the output of which interference bands are created in the planes perpendicular to the axis, which are displayed on the photodetector 3.

Shaper 2 of the linear interference structure (brand) is a device at the output of which two plane wave fronts interfere, inclined relative to each other at a certain angle, on which the frequency of the interference fringes depends. With spatial and temporal coherence of the radiation source, a high contrast interference structure will exist at any distance in the zone of intersection of the apertures of the fronts.

As mentioned above, approaches to solving the problem of brand formation in the form of a linear interference structure of high contrast with desired properties are known and can be performed, for example, using fiber, hologram, polarization and other optical elements.

It is fundamental that the image of interference fringes on the matrix photodetector 3 at a variable distance to the object is obtained without using a focusing lens. This eliminates the additional measurement error associated with aberrations and distortion of the lens with a large field of view, determined by the format of the matrix, as well as the tilt of the optical axis during refocusing. The range of working distances to the object depends on the diameter of the shaper and the frequency of the interference fringes, the format of the receiver and can be calculated for the selected system parameters.

Due to the fact that the shaper is placed on the object and changes its position with it, the angle of rotation of the image of the stripes will correspond to the angle of rotation of the object with the linear interference structure forming unit installed on it. In the computing unit 4, the angle of rotation of the image of the interference bands relative to the coordinates of the matrix photodetector 3 is calculated. The algorithm for calculating the angle of rotation (twisting) is known.

Concrete example

According to the scheme shown in figure 1, created a mock device for measuring the angle of twisting (figure 2). For reasons of minimizing coherent noise, a circuit with a fiber light source giving an almost perfect spherical front was chosen as a shaper of the interference structure. A semiconductor laser (λ = 0.635 μm) with a fiber output was chosen as a coherent light source, and a digital CCD matrix of 1280 × 1024 elements with an element size of 5 μm was used as a photodetector. As a computing unit 4, a Pentium-4 type computer is used.

The radiation of a semiconductor laser 1 with a single-mode optical fiber at the output is divided into two channels using a splitter 6. The ends of the output single-mode optical fibers 5 are point sources that are located in the focal plane of the lens 7 at a certain distance from each other. The splitter 6, the single-mode optical fibers 5 and the lens 7 form a shaper of the linear interference structure in a section perpendicular to the axis of the lens. Each point source (end of optical fibers 5), placed in the focal plane of the lens 7, gives a flat wave front at the output. The frequency of the interference structure obtained by the interference of two plane wave fronts that come out of the lens at an angle to each other depends on the distance between the point sources (fiber ends) and the focal length of the lens, and in this case is 3.1 mm ^-1 (angle 7 angles. min).

The interference structure is localized in all planes between the lens 7 and the photodetector 3 in the zone of intersection of plane wave fronts. The zone of intersection of the fronts determines the maximum distance of the device. In this case, with a lens diameter of 30 mm, the maximum distance is about 4 m (with a margin of lateral displacement of the matrix photodetector).

The initial orientation angle of the image of interference fringes on the CCD matrix is set to close to zero degrees relative to the columns of the matrix.

Fiber optic lasers and splitters are commercially available products. The requirements for the lens 7 of the shaper are significantly lower than for the lens of the photodetector device of the prototype. The shaper lens, for example, in comparison with the prototype lens, has a significantly smaller linear field of view (0.25 mm and 10 mm), a smaller focal length (100 mm and 500 mm at a distance of 4 m), it does not have requirements for the presence of focusing movement .

The task of zooming at a variable distance to the object to maintain a constant measurement error in devices such as a prototype could be solved using a high-quality lens with a variable focal length. However, there are high technical requirements for it. The lens should have a large field of view, determined by the matrix used, small aberrations, small distortion, preservation of small aberrations and distortions when refocusing and changing the focal length, preserving the direction of the optical axis when refocusing and changing the focal length. The cost of such a lens is incommensurably higher than the total cost of the remaining elements of the device.

The measuring range of the device was ± 6 angles. hail, the error in measuring the angle of twist in laboratory conditions was 4 angles. sec when changing the distance to the object from 0.1 m to 4 m.

Currently, the design study of the system is underway. It is supposed to use the proposed technical solution in the system of remote transmission of angular coordinates.

Claims (1)

A device for measuring the twist angle, including a radiator located on the object, mounted on the optical axis of the device, coinciding with the axis of rotation of the object, a matrix photodetector and an associated computing unit, characterized in that a brand shaper is additionally installed on the object along the emitter beam, forming a brand in the form of a linear interference structure of high contrast, localized in the space between the shaper and the photodetector and lying in a plane perpendicular to the optical axis, and the emitter is made in the form of a coherent radiation source.

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