RU2642975C2 - Device for measuring instant angular movements of swinging platform - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: device for measuring instant angular movements of the swinging platform consists of a measured instant flat angle sensor and a fixed reading device. The angle sensor is designed as a multivalued holographic angle measures, each forming stable flat fan of diffracted beams under the influence of external optical radiation with known angles between the beams. The reading device is made on the basis of CCD-rulers, equipped with a time scale and connected to an external computer.

EFFECT: increased measurement accuracy.

3 tbl, 2 dwg

Description

The proposed device relates to the field of measurement technology.

For testing high-precision inertial devices, swinging platforms are widely used, which, in turn, are subject to certification. Most of the certification procedures for such platforms, due to the operating principles of the angle sensors used, are based on measuring the angle of rotation of the platform shaft. However, due to the need to install the device under test in any part of the platform and not to the absolute rigidity of the platform, the problem arises of measuring the angle of rotation of the swinging platform at the location of the device.

Numerous precision optical angle sensors are known, the so-called encoders using code and raster transforms.

Examples of such devices are:

1) optical angular encoders (Renishaw pic, UK, specifications are given on the website http://www.renishaw.ru);

2) sensors for measuring angular displacements (DR. JOHANNES Heidenhain GmbH, Germany, the characteristics are given on the website http://www.heidenhain.ru);

3) angular displacement transducers and angular position sensors (OJSC SKB IS, Russia, characteristics are given on the website http://www.skbis.ru);

4) a device for measuring a flat angle (Yu.E. Dukarevich, M.Yu. Dukarevich, Yu.M. Ivanov. A method of measuring a flat angle and a device for its implementation // RF Patent No. 2451903);

5) angle meter (A.N. Korolev, A.Ya. Lukin, G.S. Polishchuk, Angle meter // Utility Model Patent of the Russian Federation No. 109847);

6) a device for reproducing angular velocity (V. A. Granovsky, M. D. Kudryavtsev, A. I. Ryskin, A. S. Shcheulin. Device for reproducing angular velocity (measure of angular velocity) // RF Patent No. 2429490);

7) measuring angular velocities and accelerations (LS Priver. Optoelectronic measuring angular velocities and accelerations // RF Patent No. 94042213).

Angle measurement in known devices is as follows:

1) in encoders produced by Renishaw plc and DR. JOHANNES Heidenhain GmbH »the determination of the angle occurs by photoelectric scanning of the scale, which is a long bar code, or by using an ultrafast miniature digital camera that takes pictures of the scale;

2) in the encoders produced by SKB IS, the definition of the angle is based on recording the fraction of the optical radiation flux that passed through the conjugation of a regular raster of the scale and raster of the analyzer windows as a coordinate-periodic function of the mutual angular position of the specified rasters;

3) in a device for measuring a flat angle (RF patent No. 2451903) and an angle meter (RF patent No. 109847), a flat angle is measured by encoding the measuring range of the device using an optical mark mounted on the rotor of the object and forming a recording CCD image matrix in the plane signal labels that occur when light passes through the code holes of the brand;

4) in the device for reproducing angular velocity (RF patent No. 2429490), the measurement of the instantaneous angle of rotation of the table is carried out on a dial, the formation of which used the angles between the rays of the fan.

The main disadvantages of these devices are:

- limited measurement accuracy due to the influence of backlash and vibration;

- the impossibility of measuring the angle in an arbitrary part of the platform.

The closest in technical essence and adopted for the prototype device is a device for measuring a flat angle (RF Patent No. 2451903).

The prototype device consists of a control element, rigidly fixed to a controlled object, a measuring unit and an information processing device. The control element contains an LED, a pinhole, a capacitor and a signal mask located in the focal plane of the lens. The measuring unit contains a lens and a receiving CCD matrix, the signal from which is transmitted via a high-speed USB-2.0 port to an information processing device - a personal computer (PC). The PC performs the necessary computational operations and generates a digital code of the measured angle of rotation of the control element relative to the measuring unit. The control element and the measuring unit are mounted coaxially with respect to one another.

The prototype device works as follows.

An LED, a pinhole, and a capacitor form a uniform parallel light stream that illuminates the signal mask. The lens of the control element collimates the signal light flux passing through the signal slots of the mask and directs it to the measuring unit. The receiving lens builds in its focal plane an image of the signal mask, which falls on the CCD matrix installed in the image plane. Using the CCD, the optical image is converted into a digital video signal and is sent to a PC. In the PC using special information processing algorithms, the angle of rotation of the control element relative to the measuring unit is calculated.

An essential feature of the prototype is the presence of a dual-count coding scheme for the measuring range of the device. The coarse channel is represented as a single signal slit located in the central zone of the mask, and the exact channel is represented as N signal slots (N >> 1) located in the peripheral zone of the mask.

The measurement error is estimated by the authors analytically (and more simply), and is not determined by comparison with the standard. At the same time, a number of factors affecting the accuracy of measurements, in particular, quantization and sampling noise, optics parameters that determine the image quality of a control element, are not taken into account.

The disadvantages of the prototype device are:

- the quality of the “light source - mask” system substantially depends on the characteristics of the source and the stability of these characteristics with respect to temperature and supply voltage, as well as on the stability of the mutual spatial position of the light source and the mask due to the materials from which the control part is made;

- the need to mount the device near the axis of the platform (due to the limited size of the measuring unit), which does not allow to measure angles in an arbitrary part of the platform.

The problem that is solved by the invention is to improve the accuracy and expand the functionality of the device, namely the possibility of fixing it outside the axis of the object and, therefore, the ability to observe the deformation of the platform.

Technical result: improved measurement accuracy. The problem is solved by using the composition of the proposed device:

a) a sensor - a set of multi-valued holographic measures of a flat angle - holographic prisms (hereinafter - GP) (Granovsky V.A., Kudryavtsev M.D., Ryskin A.I., Shcheulin A.S. Multivalued holographic measure of a flat angle // Patent RF No. 2332638);

b) reading device - photodetector.

The GP is based on a crystal with a system of superimposed holograms recorded in it, which are excited by a reference laser beam and induce a fan of diffracted rays. The angles between the diffracted beams have the stability of a hologram system (RF Patent No. 2332638), sufficient to provide the required level of accuracy of the proposed device. The diffracted rays can be located in a plane with uniform or uneven angular pitch. In fact, they are analogues of the normals to the side faces of a quartz prism. In the functional aspect, a GP is considered as a movable multipath (multi-reference) optical indicator of a special type, the angles between the rays of which are no worse than the angles between the normals of a quartz prism.

The sensor consists of several GPs mounted on a common base so that the planes of the fans are parallel. The sensor is mounted on the platform, orienting the planes of the fans of these rays perpendicular to the axis of rotation. When the platform rotates, the rays of the fans move along the photodetector, which allows you to register this movement.

Due to the relatively small overall dimensions, the sensor can be mounted with clamps and magnets in any part of the platform, provided that the planes of the fans are perpendicular to the axis of rotation.

The photodetector is stationary relative to the axis of rotation and performs the function of a scale carrier, the formation of which uses the values of the angles stored by the GP.

Thus, the GP performs two functions: the carrier of the reference angles and the sensor of the instantaneous angle of rotation of the platform.

The photodetector consists of rows of successive CCD arrays placed on a fixed base, and the number of rows does not exceed the number of GPs. During measurements, the photodetector is parallel to the axis of rotation and, therefore, perpendicular to the planes of the fans so that the rays of the fans fall into the sensitive areas of the CCD arrays. For registration and visual display of the realized angle of rotation of the platform, a personal external computer (PC) is used to interrogate the photodetector elements. Also, the external PC performs the function of processing the primary signals of these elements - determining the coordinates of the centers of the exposure zones, forming a time scale and a number of service functions: setting up photodetector elements and displaying their activity, starting and stopping the transmission of primary data, setting the time for recording primary data in automatic mode. The formation of the time scale occurs using the PC system clock, in contrast, for example, to the approach described in the patent (RU 94042213), in which the time scale is set by an optocoupler and slots in the scanning disk. All service functions are carried out by setting the necessary command in special software and transmitting the corresponding signal to the microprocessor of the photodetector. The specified service functions do not affect the performance of the signal processing functions and, ultimately, the measurement accuracy.

Two important circumstances should be emphasized. Firstly, the device implements potentially the most accurate of the measurement methods - the method of comparison with the measure. Secondly, due to the ambiguity of the angle measure used, there is redundancy in the measurements of the angles in the indicated way.

The ability to mount the sensor in different parts of the platform and the immobility of the recorder make it possible for a variety of recorded data related to the same angular position of the platform, and with different locations of the sensor on the platform to monitor the deformation of the platform. A condition for observing the deformation is that the linear parameter of the deformation exceeds the error of the angle sensor installed in the platform axis and the backlash of the platform axis.

Thus, the proposed device contains two main components: 1) fixed to the object sensor measured instantaneous flat angle; 2) a reading device mounted motionless on a support (foundation) common with the object and allowing to register the movement of the rays of the fan.

There are three significant differences of the proposed device from the prototype:

1) the proposed device does not need access to the axis of rotation of the platform, which expands the list of turntables, in particular pitching stands, for certification of which the proposed device can be used;

2) the device has the ability to self-control by conducting internal calibration;

3) due to the possibility of the location of the proposed device in different parts of the platform, it can be used to observe the deformation of the platform during rotation.

Based on the foregoing, the claimed combination of features allows to obtain a device for measuring instantaneous angular displacements of a swinging platform, consisting of a set of multi-valued measures of a flat angle and a reading device based on CCD-arrays, characterized by advanced functionality, as well as the possibility of its internal calibration during operation without use of additional funds.

The invention is illustrated by the presented figures 1 and 2, which shows a generalized structure of the device and the following notation:

FIG. 1 - a schematic diagram of the location of the components of the device: 1 - reference laser; 2 - reference beam; 3 - a crystal with a system of superimposed holograms; 4 - rotary platform; 5 - a fan of diffracted rays; 6 - photodetector; 7 - external PC;

FIG. 2 - scheme of a photodetector with diffracted rays illuminated on it: 6 - photodetector; 8 - CCD line; 9 - sensitive area of the CCD line; 10 - zones of illumination by diffracted rays.

Laser 1 with beam 2 and crystal 3 form a GP.

The photodetector 6, connected to an external PC 7, forms a reading device.

The device operates as follows. When the platform 4 is rotated, the fan of diffracted rays 5 moves along the photodetector 6, with the help of which the position of each beam is fixed, namely, the pixel number on one or another CCD line 8. The photodetector 6 captures the diffracted rays 5 in any position of the turntable 4. When the platform is rotated 4, each of the diffracted beams 5 rotates at the same angle, but at the photodetector 6, the diffracted beams 5 are moved at different distances. Knowing the distances over which the diffracted rays 5 move and the angles between these rays allows you to set the angle-distance relation. Thus, the portion of the linear scale between adjacent beams is calibrated in angular units and, as a result, the next time you turn the platform 4, the rays 5 will move along the calibrated angle scale.

Thus, the determination of the angle of inclination of the platform 4 is based on a comparison of the measured flat angle with the angles between the diffracted rays 5. This comparison is mediated by the above-mentioned calibration of the recorder, taking into account the orbital movement of the center of the fan of diffracted rays 5. The coordinates of the center of the fan of diffracted rays 5 are calculated based on the coordinates of the centers illumination zones 10 of the reading device (photodetector) with 6 diffracted beams 5. To find the center of the fan 5, it is necessary to know at least the coordinates of the three centers of the zones 10 branches.

As elements of the reading device (photodetector) 6, CCD arrays 8 are used. Each CCD array 8 has its own sensitive zone 9, which forms the so-called local scale. The scale of the photodetector 6 is formed as a result of "stitching" of the local scales, which is carried out at the stage of calibration of the installation.

The processing of the primary signals of CCD arrays 8 in order to form a reference (angle of rotation) on the scale of the photodetector 6, as well as a number of service functions, including the formation of the time scale necessary for temporal reference of fixed instantaneous angles, is performed by an external PC 7, on which the corresponding software is installed .

An example of a specific implementation of the proposed device is the installation, consisting of:

- two GPs forming two fans of six rays parallel to each other and perpendicular to the axis of rotation of the stand;

- two motionless relatively prisms low-power reference lasers with power sources;

- a stationary photodetector, which includes two parallel rows of CCD arrays, ten samples in each row;

- external PC with special software.

The use of two parallel rows of CCD arrays is due to the fact that the connection of CCD arrays closely, without dead zones, is not possible. To exclude dead zones, the rows of CCD arrays are shifted relative to each other. In connection with the presence of two rows of CCD arrays, two GPs have to be used.

As reference ones, gas lasers of the LGN-226A type (JSC NII SRP “Plasma”, Russia, www.plasmalabs.ru) were selected with parameters according to the table. one.

* - built-in power supply

As CCD rulers, devices of the type SONY ILX 751 V with parameters according to the table are used. 2. Due to the fact that CCD arrays have dead zones, in order to obtain a single continuous scale of the photodetector, the arrays in rows are staggered relative to each other.

For registration and data processing, a PC with characteristics according to the table is used. 3.

Due to the features of the device and the required high accuracy, the calibration is divided into several stages:

1) checking the stability of the device as a whole;

2) calibration of the photodetector;

3) calibration of each GP and their assembly as a whole;

4) calibration of the device as a whole.

At the first stage, the stability of the device readings is checked when the platform returns to the same position. The purpose of calibrating the photodetector (second stage) is to form the scale of the photodetector. In the third stage, the angles between the diffracted beams are measured with high accuracy. The purpose of calibrating the device as a whole (the fourth stage) is to compile its calibration table.

The measurement error of a flat angle using the proposed device depends on:

- stability of pixel sizes on CCD arrays;

- the accuracy of determining the coordinates of the centers of the exposure zones;

- Accuracy of “stitching” of the local scales of CCD arrays into the scale of the photodetector;

- the accuracy of determining angles in the fan of diffracted rays;

- stability of the relative position of the photodetector and the base of the platform;

- stability of the position of the GP on the platform during the measurement process;

- the accuracy of the exposure of the plane of the fan of diffracted rays relative to the axis of rotation of the platform;

- the accuracy of the exposure of the photodetector relative to the plane of the fan of diffracted rays.

The pixel size is a fairly stable value, so its change can be considered insignificant for measurements. The accuracy of determining the coordinates of the centers of the exposure zones is due to the properties of CCDs and the primary information processing path. The accuracy of “stitching” and determining angles is quite high due to the equipment used with errors of the order of a few micrometers and fractions of arc seconds.

The stability of the relative positions of the components relative to each other is determined by the angular vibrations of the base. A prerequisite for the operability of the device is the absence of angular vibrations exceeding 7 '.

The developed sample has no requirement for the availability of the swing axis of the platform. The sample has the ability to self-control by conducting internal calibration and observing the deformation of the platform. These facts allow us to talk about achieving the claimed technical result.

Claims (1)

A device for measuring instantaneous angular displacements of a swinging platform, consisting of a sensor of the measured instantaneous flat angle and a stationary reading device, characterized in that the sensor is a set of multi-valued holographic measures of the angle, each forming a stable flat fan of diffracted rays with known angles under the influence of external optical radiation between the rays; the fans are located in parallel planes and are shifted relative to each other by predetermined angles, and a photodetector based on CCD arrays arranged in parallel rows, the number of which equals the number of holographic measures, serves as a reading device; the photodetector is connected to an external personal computer, which forms a timeline.

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