SI26348A - Circular position encoder and method for correcting assembly errors - Google Patents

Abstract

The subject of the invention is a circular position encoder (2), whose output information contains information about the position of the rotary measured system (1), and a method for correcting an error in the output information caused by inaccurate mounting of the circular position encoder (2) on the rotary measured system (1) ). The circular position encoder (2) includes a primary measuring assembly (2a) and a secondary measuring assembly (2b), which are connected by a mechanical connection (3) that enables mutual rotational movement of the measuring assemblies (2a, 2b) around the axis (A'). The primary measuring assembly (2a) is fixedly connected to the primary main part (1 a) of the measured system (1), the secondary measuring assembly (2b) is flexibly connected to the secondary main part (1 b) of the measured system (1) via limiting connecting means ( 6), the lever (4) and the correction measuring element (5), which enables the primary measuring assembly (2a) to move circularly together with the primary main part (1a). When axis (A) and axis (A') are not aligned, the secondary measuring assembly (2b) moves relative to the secondary main part (1b) of the measured system (1), which is generally static, in such a way that the circular movement of the circular converts the position encoder (2) into linear movement of the correction measuring element (5) or its corresponding measuring point (M), the movement of which is measured with a linear sensor (7).

Description

Circular position encoder and method for correcting assembly errors

The invention in question relates to a circular position transmitter whose output information contains information about the position of a rotary measured system, and a method for correcting an error in the output information caused by inaccurate mounting of the circular position transmitter on a rotary measured system.

Circular position encoders are known, which are mounted on rotary measured systems, for example on a machine with a rotating robotic arm, and are intended to detect the position of one of the main parts of the measured system, for example the robotic arm, with respect to another of the main parts of the measured system, on example, with respect to the static part of the machine to which the robotic arm is attached, and giving the position in the output information in the desired form, for example in analog or digital form. Usually, the position in the output information is expressed or expressible in the form of an angle between the main parts of the measured system or a change in the angle resulting from the circular movement of one of the main parts of the measured system relative to another of the main parts of the measured system. For example, circular position encoders are disclosed in, inter alia, US4319188.

In practice, the exact mechanical assembly of circular position encoders on the systems being measured each time is very demanding, and if the circular position encoder is not additionally calibrated after assembly, significant errors in the output information often occur. When mounting a circular position encoder on a rotary measured system, an inaccuracy occurs, namely that the axis A of rotation of the measured system does not completely match the axis A' of rotation of the circular position encoder, which causes the output information to contain the wrong position of the measured system. For example, circular position encoders often contain a ring with magnetic recording and a readhead with magnetic sensors, where the ring is attached to a rotating robotic arm and the readhead is attached to a static part of the machine. The robotic arm, as the primary main part of the measured system, moves circularly around the A axis relative to the static part of the machine, as the secondary main part of the measured system. When mounting the ring on the robot arm, there is almost always an inaccuracy, namely that the axis A' of the ring's rotation after assembly does not completely match the mentioned axis A of the measured system, therefore the information about the position (angle) of the measured system in the output information of the circular encoder contains an error, which is unwanted.

The circular position encoder and the method according to the relevant invention are intended to detect and correct the error in the output information due to inaccurate mounting of the circular position encoder on the measured system.

The invention is described in more detail below and presented with an example and in pictures:

Figure 1: an embodiment of the circular position transmitter according to the invention, when it is mounted on the measured system;

Figure 2: an embodiment of the circular position transmitter according to the invention, when it is mounted on the measured system in a vertical section;

Figure 3: The xy plane of the coordinate system with relevant points to show the error in the output information due to the misalignment of the A and A' axes.

In general, rotationally measured systems, for example robotic machines or other automatically controlled systems, comprise a primary main part and a secondary main part, where one of these parts, for example the primary main part, rotates around an axis A with respect to the other, for example secondary main part. The reverse is also possible, namely that the secondary main part moves circularly with respect to the primary main part, but for the purposes of the relevant description we will assume that the primary main part moves circularly with respect to the secondary main part. In order to operate robotic machines or other automatically controlled systems, we need information about the position of individual parts of the machine. Therefore, information about the position, more specifically the angle or the change of the angle, between the primary main part and the secondary main part of the measured system is generally required, for which circular position encoders are used.

Circular position sensor 2 according to the invention in question for determining the position of one of the main parts 1a, 1b of the measured system 1 relative to the other of the main parts 1a, 1b of the measured system 1, preferably for determining the angle or changing the angle between the main parts 1a, 1b of the measured system 1, contains two measuring assemblies: a primary measuring assembly 2a and a secondary measuring assembly 2b, whereby the primary measuring assembly 2a is adapted to be connected to the primary main part 1a of the measured system 1, and the secondary measuring assembly 2b is adapted to be connected to the secondary main part 1b of the measured of system 1.

One of the mentioned measuring units 2a, 2b has the function of an information measuring unit, while the other of the mentioned measuring units 2a, 2b has the function of a reading measuring unit. In the known state of the art, circular position transmitters are disclosed which contain an information measuring assembly, for example one or more circular magnetic traces on a ring, the magnetic record of which changes depending on the position, and a reading measuring assembly for reading the information measuring assembly, for example a reading head with Hall magnetic sensors. In addition to magnetic circular position transmitters, optical circular position transmitters are also known, in which the information measuring unit is implemented as an optical ring, which contains, for example, an optical track with divisions of different optical reflectance arranged in a certain grid. The reading measuring unit is implemented as an optical reading head, which contains a light source that illuminates the optical track, apertures with divisions of the same raster as the optical track, and a photodetector for detecting the proportion of light that, after reflection on the optical track, comes through the aperture. For the light source, infrared LEDs are mostly used, because the wavelength of infrared light is sufficiently different from the wavelengths of visible light that the operation of the reading measuring unit is almost completely independent of the presence or absence of visible light from the environment.

One of the main ideas of the invention in question is to produce an improved circular position encoder 2, wherein, even before the circular position encoder 2 is mounted on the rotary measuring system 1, the primary measuring assembly 2a and the secondary measuring assembly 2b are rotationally connected to each other so that enabled free circular movement around axis A' of one of the two measuring assemblies 2a, 2b around the other of the two measuring assemblies 2a, 2b. For example, when the primary measurement assembly 2a is a magnetic recording ring and the secondary measurement assembly 2b is a reading head, free circular movement of the reading head around the magnetic recording ring is enabled. This allows us to use known methods to calibrate the circular position encoder 2 to the desired accuracy of position measurement, preferably angle or angle change, as a result of the circular movement of one of the measuring units 2a, 2b relative to the other of the measuring units 2a, 2b around axis A ', the position encoder 2 is first mounted on the measured system 1. Then the circular position encoder 2 is mounted on the rotary measured system 1 with the axis of rotation A, namely the primary measuring assembly 2a of the position encoder 2 is fixedly attached to the primary main part 1a of the measured system 1, and the secondary measuring assembly 2b is flexibly connected to the secondary main part Ib of the measuring system 1 in a special way, explained in more detail below, in such a way that the circular movement of the axis A' of the position transmitter 2 around the axis A due to inaccurate - eccentric mounting, when axis A is not completely aligned with axis A', it transforms into a linear movement, which can be measured in known ways and the error in the output information can be calculated using mathematical methods, which is a result of the circular movement of axis A' around axis A.

The circular position sensor 2 according to the invention, the embodiment of which is shown in Figure 1 and in cross-section in Figure 2, in addition to the above-mentioned measuring units, namely the primary measuring unit 2a, which is adapted for a fixed connection to the primary main part 1a of the measured system 1, and secondary measuring assembly 2b, also contains the following elements:

- Mechanical connection 3 between the primary measuring assembly 2a and the secondary measuring assembly 2b, which enables mutual rotational movement of one of the two measuring assemblies relative to the other of the two measuring assemblies around the axis A'.

Lever 4, which is fixed in relation to the secondary measuring assembly 2b and moves circularly around the axis A' in relation to the primary measuring assembly 2a.

The correction measuring element 5 with the measuring point M, which is attached to the handle 4, so that the movement of the correcting measuring element 5 or the measuring point M with the handle 4 around the axis A' at a distance d1 is enabled.

- Limiting connecting means 6, which are adapted to be attached to the secondary main part 1b of the measuring system 1 and to cooperate with the correction measuring element 5 in such a way as to enable the movement of the correction measuring element 5 essentially only in the linear direction, preferably in the radial direction with respect to on the A axis or in the x direction of the xyz coordinate system, which is shown in Figure 3 and which is determined so that the measuring point M lies on the x coordinate axis and the xy plane is perpendicular to the A axis, with the starting point of the coordinate system being point C, in which axis A intersects said plane; thus creating a flexible connection between the secondary measuring assembly 2b and the secondary main part Ib of the measured system 1.

The linear sensor 7, which converts the linear mechanical displacement into a displacement signal, either analog or digital, and cooperates with the correction measuring element 5, so that it measures the displacement of the measuring point M in a linear direction, preferably in the direction of the x-axis of the defined coordinate system. The linear sensor 7 is fixedly fixed with respect to the secondary main part 1b of the measured system 1.

It is essential for the mechanical connection 3 that it enables a reliable and repeatable rotational movement of the primary measuring assembly 2a with respect to the secondary measuring assembly 2b, because only in this way does the circular position encoder 2 enable the desired results.

The displacement signal of the linear sensor 7 is used to calculate the error in the determination of the position, preferably the angle or the change of the angle, in the output information, using mathematical methods that will be described below for example, and consequently to correct the position in the output information, namely the error that occurs due to the above-described inaccurate mounting of the circular position encoder 2 on the measured system 1, namely inaccurate mounting that causes a mismatch between axis A and axis A'. As mentioned, point C represents the point where axis A intersects the xy plane of the coordinate system defined above. Point C' represents the point where axis A' intersects the xy plane of the coordinate system defined above.

Before the circular position sensor 2 according to the invention in question is mounted on the measured system 1, the primary measuring assembly 2a and the secondary measuring assembly 2b, which are interconnected by a mechanical connection 3, are calibrated to the desired position measurement accuracy in known ways. For example, in one of the implementation examples, the desired measurement accuracy is achieved in such a way that the mechanical connection 3 is manufactured and mounted between the measuring assemblies 2a, 2b with small enough mechanical tolerances to enable the desired accuracy of the circular movement of one of the measuring assemblies 2a, 2b around the axis A', for example the reading head 2b at a constant distance to the magnetic recording ring 2a. In a different embodiment, when the mechanical connection 3 does not provide sufficiently small mechanical tolerances of circular movement, we calibrate the circular position encoder 2 to the desired measurement accuracy by comparing the output information with a sufficiently accurate reference circular position encoder and, if necessary, additionally processing the output information.

When the circular position transmitter 2 according to the relevant invention is calibrated to the desired position measurement accuracy, it is mounted on the measured system 1 in the following manner. The primary measuring assembly 2a is fixedly attached to the primary main part 1a of the measured system 1. The secondary measuring assembly 2b is flexibly connected to the secondary main part 1b of the measured system 1 via the limiting connecting means 6 and the correcting measuring element 5 in the manner described above. Such mounting of the circular position encoder 2 according to the invention in question allows the primary measuring assembly 2a to move circularly together with the primary main part 1a. When axis A and axis A' are not aligned, due to the flexible connection, the secondary measuring assembly 2b moves with respect to the secondary main part 1b of the measured system 1, which is generally static, in such a way that the circular movement of the circular encoder of position 2 or point C' around C is converted into a linear movement of the correction measuring element 5 or the measuring point M belonging to it, the movement of which is measured with the linear sensor 7.

Calibration method

When the circular position encoder 2 according to the invention in question is mounted on the measured system 1 in the manner described above, the circular position encoder 2 is calibrated in such a way that the primary main part 1a and with it the primary measuring assembly 2a rotates and in the process monitors the output information of the circular of the position transmitter 2 and the displacement signal of the linear sensor 7. During calibration, the rotation of the measured system 1 can be performed for a whole revolution, for a part of a revolution, or even for several revolutions. By knowing the construction of the circular encoder of the position 2 and the method of mounting on the measured system 1, we can calculate the error in the position of the measured system 1, which is expressed or expressible in the output information, using mathematical methods, which will be described below with reference to Figure 3. Using mathematical methods in the calibration process, it is possible to calculate in the first step the amplitude of the eccentricity, which is represented in Figure 3 as the distance e between points C and C, and the phase of the eccentricity, which is expressed in Figure 3 in the angle β enclosed by the CCG points or HCB. From the amplitude e and the phase β of the eccentricity, it is then possible to calculate in the second step the measurement error due to the eccentricity, which in Figure 3 is expressed in the angle a, which is subtracted from the measured value of the angle <p _mer of the circular position encoder in order to calculate the correct rotation angle φ of the measured system despite inaccurate eccentric mounting:

Ψ = Vmer ’ «

As mentioned, figure 3 represents the xy plane of the coordinate system defined above and the most important points in it to represent one of the possible methods for use in one of the implementation examples where the circular position encoder 2 measures the angle of the measured system 1. The primary measuring assembly 2a in this case is an information measuring assembly, for example a magnetic ring, which is fixedly attached to the primary main part 1a of the measured system 1, while the secondary measuring assembly 2b is implemented as a reading measuring assembly, for example a magnetic reading head, which is flexibly connected to the secondary main part 1b of the measured system 1 as described above.

In the embodiment, when an optical position encoder is used instead of a magnetic circular position encoder, the primary measuring unit 2a or the information measuring unit is implemented as a ring with an optical track, while the secondary measuring unit 2b or the reading measuring unit is implemented as an optical reader with an optional light source .

Figure 3 does not represent the real relations between the dimensions, but the amplitude of the eccentricity e is intentionally exaggerated for clarity. Point C represents the center of rotation of the measured system 1, where axis A pierces the xy plane, while point C' represents the center of rotation of the circular position encoder 2, where axis A' pierces the xy plane. Due to the eccentricity, when the primary main part 1a of the measured system 1 rotates, the point C' will orbit around the point C at a distance e, which represents the amplitude of the eccentricity. The smaller circle has its center at point C and represents the circulation of the measured system 1. The larger circle has its center at point C' and represents the circulation of the circular position encoder 2. Point J represents the current position of the secondary measuring assembly 2b (reading head). The starting point B symbolically represents the physical point on the primary measuring assembly 2a (magnetic ring), above which the reading head 2b or the circular position encoder 2 measures the angle ^ _mer = 0· The angle β represents the eccentricity phase and is bounded by the points CCG, with the distance CG parallel to the distance C'B. The measuring point M is located on the correction measuring element 5, whose movement is limited in such a way that it can only move in the direction of the x axis and is at a constant distance d1 from the point C, because this distance is determined by the geometry of the lever 4. Points M is a limited movement in the direction of the y axis, so its value in the direction of the y coordinate is equal to zero throughout the calibration.

The geometry of the eccentricity is described by the triangle CCM. In the first calibration step, the measured system 1 is preferably rotated for one circle around point C, whereby the circular position encoder 2 measures the angle <p _mer (BCJ), and the linear sensor 7 measures the linear displacement of the measuring point M along the x coordinate.

The cosine equation belongs to the triangle CCM:

dl ² = e ² + m ² — 2 em εοε(φ + β), where d1 represents the length of the lever 4, e represents the amplitude of the eccentric (distance between C and C), β represents the phase of the eccentric and m represents the current distance of the point M from coordinate origin (x coordinate of point M).

If the equation is solved for m, we get the equation:

m = e cos(<p + /?) + ^/dl ² + ε ² (εο3 ² (φ + β) - 1))

We expand the entire term with the root into a Taylor series:

e ² e ⁴ //1 \ ⁴ m = e cos(<p + β} + dl + — (cos(2(<p + /?)) + 3) + —j(εο3 ² (φ + /?) + l) ² + O (— 4al 8al ^J \\dl/

Two conclusions can be drawn from the obtained results:

- already the second term of the equation is of order —, which is practically negligible for small e and large d1, and the third term is even much smaller; and

- linear coefficients can be calculated from the measurement using Fourier transformation. All terms of the Taylor series have a frequency higher than the fundamental one, so they can be easily removed by Fourier transformation.

With these justifications, the above equation can be simplified for calculation purposes to:

m = e οοδ(φ + β) + CONST.

Whereas CONST. represents a constant value that does not change with the angle φ.

In the first step of the calculation of the first approximation of the eccentric amplitude and phase, it is assumed that the correct angle of the measured system angle φ (GCM or BCF) is equal to the angle <p _mer (BOJ). When a Fourier transformation is performed on the signal mv of the dependence on the rotation of the measured system and the measurement (p _mer) , from the results we get the amplitude e of the eccentric, or its first approximation, and the phase β of the eccentric, or its first approximation, since the amplitude and the phase of the eccentric are equal to the amplitude and phase of the first harmonic of the Fourier transform.

In the second step, the error angle a is calculated, which represents the difference between the correct rotation angle φ and the measured angle of the reference system <p _mer , in the following way. In Figure 3, the angle a is shown between the points JCF, but since the distance C'F is by definition parallel to the x axis, this is also the angle between the points CMC.

Even in this first calculation of the approximation of the angle a, it is assumed that the correct angle of the measured system φ (GCM or BCF) is equal to the angle <p _mer (BCJ). Using the sine theorem:

dl e είη(φ + β) sin(a) the equation for the angle a is derived:

a - sin ^-1 είη(φ + β)^

Although the equation is easy enough to calculate, it can be expanded into a Taylor series for better representation:

α = - ₅ ΐη(φ + ^+-(-) ₅ ίη ³ (φ + β) +0^(-) J

From the latter equation, it can be seen that for small amplitudes of the eccentric e and large lengths dl of the lever, only the first term is dominant, so the ratio e to dl is very important. With a longer handle d1, the accuracy of the error calculation or calibration increases.

For the calculation of the first approximation of the error angle a, as already mentioned above, the measured angle φmer' P° is taken as the angle φ, and if necessary, one or more subsequent iterations of the calculation can be performed, whereby in each subsequent iteration the measured angle is taken as the angle φ , which is corrected by the error angle a from the previous iteration <P = <Pref - a.

In general, it can be written that the angle φ in iteration n is taken as: φ _π - φ _π _ _τ - .

In this way, it is possible for all values of the angle Q _mer to calculate the corresponding error angles a, and consequently the correct rotation angle φ of the measured system, and in this way to calibrate the circular position encoder 2 to sufficient accuracy after mounting on the measured system 1.

All mathematical calculations in the method described above are performed in known ways with memory processing capabilities added to the circular position encoder 2 according to the present invention.

Implementation example

Figures 1 and 2 show an implementation example of the circular position encoder 2, which is mounted on the measured system 1. The difference between axis A and axis A' is highlighted in figures 1 and 2 for clarity. In actual cases, this difference is much smaller, and would not be visible in pictures with this scale. The primary main part 1a of the measured system 1 is shown schematically and is a static part of the machine in a concrete embodiment. The secondary main part 1b is a rotating robot arm in this embodiment.

The primary measuring assembly 2a is implemented as an optical ring, for example a ring with the commercial name REX by Renishaw, and the secondary measuring assembly 2b is an optical reading head, for example a reading head with the commercial name VIONiC™ by Renishaw. The selected optical ring and optical reading head achieve sufficient accuracy, better than two arc seconds.

The mechanical connection 3 is implemented as a system of ball bearings 3c, which connects and enables circular movement between the primary mechanical part 3a and the secondary mechanical part 3b. The 3c ball bearing system consists of two sets of prestressed steel ball bearings to ensure sufficient rotational stability. The primary mechanical part 3a is attached to the primary measuring assembly 2a (optical ring) on one side and connected to the ball bearing system 3c on the other side. The secondary mechanical part 3b is attached to the secondary measuring unit 2b (optical reader) on one side and connected to the ball bearing system 3c on the other side. The lever 4, on which the correction measuring element 5 is installed, is in this embodiment integrated with the mechanical connection 3, specifically fixedly integrated with the secondary mechanical part 3b, since the lever 4 ensures the rotation of the correction measuring element 5 around the axis A' at a distance d1, the secondary and the mechanical part 3b ensures the rotation of the secondary measuring assembly 2b (optical reader) around axis A, both with respect to the primary measuring assembly 2a (optical ring). In this embodiment, the mechanical connection 3 is made of steel, but it can also be made of other materials, such as aluminum.

The correction measuring element 5 is implemented as a standard sapphire ball for use on measuring devices with the commercial name Stylus, manufactured by Renishawv. The deviation from the spherical shape must be minimal, as deviations result in measurement error. The measuring point M is in the center of the ball. The ball can also be made of other materials, such as ruby, steel and other materials that allow sufficient strength and durability of the material as well as the reliability and precision of the shape.

In this case, the limiting connecting means 6 are implemented as a steel table 6a with a smooth surface, on which the correction measuring element 5 slides, and a spring 6b, which is attached on one side to the table 6a and on the other side to the lever 4 or to the secondary mechanical part 3b of mechanical connections 3. The table 6a and the spring 6b, which presses the correction measuring element 5 against the surface of the table 6a, limit the movement of the measuring element 5 (and point M) in the y direction of the coordinate system, as shown in Fig. 3. The limiting connecting means 6 are via the tables 6a are fixedly attached to the secondary main part Ib of the measured system 1. The limiting connecting means 6 therefore, on the one hand, limit the movement of the correction measuring element 5 in all directions except the x direction, and on the other hand, they provide a flexible connection between the secondary main part Ib and the secondary measuring set 2b.

In a different embodiment, the limiting connecting means 6 can also be implemented in other ways, for example, with linear bearings that are fixedly attached to the secondary main part 1b and that limit the movement of the correction measuring element 5 in the y direction and allow movement only in the x, which also creates a flexible connection between the secondary measuring assembly 2b or correction measuring element 5 and the secondary main part 1b of the measured system 1.

In this embodiment, the linear sensor 7 consists of a body 7a of the linear sensor 7 and a measuring arm 7b, for example a linear sensor with the commercial name Metro of the manufacturer Heidenhain. The body 7a of the linear sensor 7 is fixedly fixed with respect to the secondary main part 1b of the measured system 1, and the measuring arm 7b cooperates with the correction measuring element 5, so that it can measure its linear displacement in the x-axis direction of the defined coordinate system. The measurement accuracy of the linear sensor is better than one micrometer, preferably better than 0.5 micrometer.

In the illustrated example (in Figures 1 and 2) it is very important that the surface of the table 6a is very smooth and clean, as unevenness or impurities cause unwanted movement of the correction measuring element 5 in the direction of the y axis, which causes significant measurement errors.

The circular position encoder according to the invention can be used as an independent improved circular position encoder, the calibration of which after assembly is simpler than with circular position encoders known so far, and which remains on the measured system after calibration.

The circular position encoder according to the invention can also be used as a reference circular position encoder, which is used to calibrate a conventional circular position encoder, after the latter is mounted on the measured system, whereby the reference circular position encoder is disassembled after calibration and used for other installations . In this case, a reference circular position encoder and a conventional circular position encoder are first mounted on the measured system. Then, a reference circular position encoder is calibrated, whose output information, corrected to the desired accuracy, is used to calibrate a conventional circular position encoder. After the latter calibration, the reference circular encoder can be disassembled and used for the next assembly and calibration.

The circular position encoder according to the invention can be improved by adding linear sensors (not shown in the figures) that measure any displacement of the measuring point M in other directions. For example, one additional linear sensor measures the unwanted movement of the correction measuring element 5 in the direction of the y axis, which is caused, for example, by the unevenness of the surface of the table 6a or impurities on the table 6a, which allows this movement to be taken into account when calculating the error due to assembly. Furthermore, one more linear sensor (not shown in the pictures) can be added, which measures any unwanted displacements of the correction measuring element 5 in the z-axis direction, which allows this displacement to be taken into account when calculating or correcting the error due to assembly.

Claims (16)

Patent claims 1. Circular position encoder (2) for determining the position of one of the main parts (1a, 1b) of the measured system (1) with respect to the other of the main parts (la, Ib) of the measured system (1), whereby one of the main parts (1a, 1b) of the measured system (1) rotates around the axis (A) with respect to the second of the main parts (1a, 1b) of the measured system (1), includes a primary measuring assembly (2a) which is adapted to be connected to the primary main part (1a) of the measured system (1), and the secondary measuring assembly (2b), which is adapted for connection with the secondary main part (1b) of the measured system (1), whereby one of the measuring assemblies (2a, 2b) has the function of an information measuring assembly, and the second of the mentioned measuring assemblies (2a, 2b) has the function of a reading measuring assembly, characterized by the fact that the circular position encoder (2) additionally includes: a mechanical connection (3) between the primary measuring assembly (2a) and the secondary measuring assembly (2b), which enables mutual rotational movement of one of the two measuring assemblies relative to the other of the two measuring assemblies around the axis (A ¹ ); the lever (4), which is fixed in relation to the secondary measuring unit (2b) and moves circularly around the axis (A ¹ ) in relation to the primary measuring unit (2a); correction measuring element (5) with a measuring point (M), which is attached to the lever (4), so that the movement of the correcting measuring element (5) or the measuring point (M) with the lever (4) around the axis (A') is enabled at distance (d1); - limiting connecting means (6), which are adapted to be attached to the secondary main part (1 b) of the measured system (1) and to cooperate with the correction measuring element (5) in such a way as to enable the movement of the correction measuring element (5) substantively only in the linear direction, preferably in the radial direction with respect to the axis (A) or in the direction (x) of the coordinate system (xyz), which is determined so that the measuring point (M) lies on the (x) coordinate axis and is the plane (xy) perpendicular to the axis (A), where the starting point of the coordinate system is the point (C) in which the axis (A) intersects the mentioned plane; wherein the limiting connecting means (6) create a flexible connection between the secondary measuring assembly (2b) and the secondary main part (1b) of the measured system (1); and a linear sensor (7) which is fixed with respect to the secondary main part (1b) of the measured system (1) and cooperates with the correction measuring element (5) so as to measure the displacement of the measuring point (M) in a linear direction, preferably in the direction axes (x) of the defined coordinate system. 2. Circular position sensor (2) according to claim 1, characterized in that the primary measuring unit (2a) has the function of an information measuring unit and is designed as a ring with an optical track, while the secondary measuring unit (2b) has the function of a reading measuring unit and is implemented as an optical reading head. 3. Circular position sensor (2) according to claim 1, characterized in that the primary measuring unit (2a) has the function of an information measuring unit and is designed as a ring with magnetic recording, while the secondary measuring unit (2b) has the function of a reading measuring unit and is implemented as a magnetic sensor. 4. Circular position encoder (2) according to claims 1 to 3, characterized in that the mechanical connection (3) includes a ball bearing system (3c), a primary mechanical part (3a) and a secondary mechanical part (3b), wherein the ball bearing system of bearings (3c) connects and enables circular movement between the primary mechanical part (3a) and the secondary mechanical part (3b), and wherein the primary mechanical part (3a) is attached to the primary measuring assembly (2a), and the secondary mechanical part (3b) is attached to the secondary measuring assembly (2b). 5. Circular position encoder (2) according to claims 1 to 4, characterized in that the lever (4) is integrated with the secondary mechanical part (3b). 6. Circular position encoder (2) according to claims 1 to 5, characterized in that the correction measuring element (5) is designed as a sapphire ball. 7. Circular position transmitter (2) according to claims 1 to 6, characterized in that the limiting connecting means (6) are implemented as a steel table (6a) with a smooth surface on which the correction measuring element (5) slides, and a spring ( 6b), which are attached on one side to the table (6a) and on the other side to the lever (4) or to the secondary mechanical part (3b) of the mechanical connection (3). 8. Circular position sensor (2) according to claims 1 to 6, characterized in that it contains at least one additional linear sensor that measures the movement of the correction measuring element (5) in other directions, preferably in the direction of the (y) axis. 9. The method of calibration of the circular position encoder (2), which includes the determination of the position measurement error in the output information of the circular position encoder (2), which is caused by the misalignment of the axes (A) and (A') due to the eccentric mounting of the circular position encoder (2) on measured system (1), characterized by containing the following steps: a. monitoring the angle (<p _mer ) in the output information and the signal (m) of the movement of the linear sensor (7) during the rotation of the measured system (1) for a part of the plant, the entire plant, or several plants, preferably for one plant; b. calculation of the amplitude of the eccentricity, which is reflected in the distance (e), and the phase of the eccentricity, which is expressed in the angle (β) from the data on the change of the angle (<p _mer ) and the displacement signal of the linear sensor (7); c. calculation of different values of the angle (a), which represents the error in the measurement, depending on the change of the angle (<p _mer ). 10. The method according to claim 9, characterized by the fact that for the calculation of the approximation of the amplitude of the eccentricity (e) and the approximation of the phase of the eccentricity (/?) in step b, a Fourier transformation is used, which is carried out over the signal (m), whereby the approximation of the amplitude is eccentricity (e) is equal to the amplitude of the first harmonic of the Fourier transform, and the approximation of the eccentricity phase (/?) is equal to the phase of the first harmonic of the Fourier transform. 11. The method according to claims 9 and 10, characterized by the fact that in step c the first approximation of the angle (a) is calculated according to the following equation a= sin ^-1 ^5ίη(φ+), whereby the calculation is simplified that the angle (φ ) equal to the measured angle (<p _mer ). 12. The method according to claim 11, characterized by the fact that the calculation of the angle (a) in step c is carried out in several iterations, whereby in the first iteration we assume that the angle (φ) is equal to the measured angle ^ _mer ), in each subsequent iteration n, for the angle (φ), the result from the previous iteration is taken into account according to the following equation: Φη ⁼ Φη-l ^— ^n-1 13. The method according to claims 9 to 12, wherein the displacement signal of the additional linear sensors is used in the calculation of the eccentricity amplitude (e), the eccentricity phase (/?) and the angle (a). 14. A method of calibrating other circular position encoders using the circular position encoder (2) according to claims 1 to 8 as a reference circular position encoder, comprising the steps of: a. mounting of the second circular position encoder and the reference circular position encoder (2) on the measured system (1); b. calibration of the reference circular position transmitter (2) to the desired measurement accuracy according to the method according to claims 9 to 13; c. calibration of the second position encoder by comparing the output information of the second position encoder with the output information of the calibrated reference circular position encoder (2). 15. Calibration method according to claim 14, characterized in that step c is followed by an additional step of removing the reference circular position encoder (2). 16. Use of the circular position encoder (2) according to claims 1 to 8 as a reference circular position encoder for calibrating other circular position encoders.