DE10233155A1 - Systematic error correction method for rotation angle measurement instrument in which one-off automated calibration is carried out against reference sensor with resultant correction values stored in analysis unit - Google Patents

Abstract

Method for correction of systematic geometrical errors in an angle of rotation measurement instrument, whereby after assembly of a sensor (1) the absolute angle determined by the sensor is measured and at the same time the same angle measured with a reference sensor (14) that is rigidly coupled to the sensor rotation axle. The systematic errors so determined are stored in the analysis unit (2) of the sensor and used in subsequently to correct actual measurements.

Description

The invention relates to a method for the correction of systematic geometry errors in a rotation angle measuring device. such Rotary angle encoders are regularly in the Factory automation, instrumentation or process control for the controls of actuators, the automatic reading of mechanical display devices, for Determination of the shaft position of machines and for controls in the robotics area used.

Such rotation angle measuring devices are in different versions, Measuring ranges, resolutions and accuracy, both as an absolute and an incremental encoder known.

Depending on the area of application different principles of angle measurement are used. On a known analogous method is, for example, the resolver method, where that is from a magnetic dipole or a multipole, AC excited rotor generated magnetic field of two orthogonal arranged magnetic field sensors or stator windings evaluated according to the sine-cosine method becomes. Other analog methods use capacitive or potentiometric Principles.

Working according to analog procedures Rotary angle encoders are regularly from simple construction and robust and therefore insensitive to industrial environmental influences such as contamination or temperature change. However, it is disadvantageous their limited measurement accuracy. So far a sufficiently high one Accuracy is achievable, this requires a complex adjustment and / or manual adjustment. About that In addition, the measuring range is regularly less than the full circle limited.

Known digital rotation angle measuring devices usually have a rotatable code disk attached to an axis, on which the angle information along of the circumference in radially arranged bit patterns, which are typically follow the Gray code, or in the case of incremental encoders as a radial stripe pattern is encoded. The angle information is dependent on the position of a fixed, optical reading head that consists of an arrangement can consist of several sensors, read, and electronics into an angle-proportional, digital or analog output signal converted. To achieve high mechanical accuracy the angle plates are made of glass or a dimensionally stable, made of transparent plastic. As an information carrier one applied to the surface, opaque layer used, either lithographically, by Exposure and development of a photoresist layer and subsequent chemical etching, structured or printed on. The information is bundled, visible or read infrared light in transmission.

With digital sensors are high Measuring accuracy achievable. However, the production is disadvantageous the code and plate washers very complex and for mass production not very suitable. Glass panes also have the disadvantage that they are sensitive to strong shocks, and because of their great Heat capacity also against Are condensation.

Such rotation angle measuring devices are with systematic inaccuracies in the form of layer inhomogeneities potentiometric sensors, mechanical deviations in the electrode geometry with capacitive sensors, acentricity of the angle disc or faulty Alignment of the read head afflicted, which adversely affects the measurement accuracy influence.

Depending on the type of sensor, the specific influences or lead due to specimen scatter these inaccuracies to different dependencies Δϕ (ϕ) of the angular error in the output signal. While the function Δ? (?) in some cases random History shows, in others, the form of the main contributor Error proportions predictable.

The invention is therefore the object based on a method for correcting systematic geometry errors in a rotation angle measuring device specify.

According to the invention this task with the Steps of claim 1 solved.

Advantageous embodiments of the Invention are referenced in the claims specified.

The invention is based on one Angular Torque Gauge consisting of a rotatable data carrier attached to an axis with an information track and a sensor for scanning the information track, which is connected to an evaluation unit.

The essence of the invention now exists in that the systematic angular errors after mounting the Sensor as a function of the absolute angle determined by the sensor automatically recorded, stored in the evaluation unit of the sensor and during the actual measurement is used to correct the output signal become.

For this purpose, the actual angle values are determined parallel to the measurement of the output signal of the actual sensor using a highly precise reference sensor that is rigidly coupled via the axis of rotation and recorded synchronously via an additional digital interface. The rotation angle sensor for recording the actual angle values is preferably driven by a motor and the process the recording is controlled fully automatically by a computer.

With known and mathematically describable Functional course of the error signal is a small number n of over Measuring range distributed reference measurements sufficient. This will the additionally required for storing the reference measurement values required for correction Data storage kept low. There are n pairs of values from a measured value of the angle of rotation sensor and the reference sensor determined and stored in the evaluation unit of the rotation angle sensor. These variable pairs then become the variable parameters the function stored in the sensor. The determination of Functional parameters can either be solved by exact number of equations corresponding to the number of pairs of values determined take place, or - in a mathematically overdetermined system - by means of of a method for minimizing the squares of errors. This can the influence of any noise components present in the measurement signal is reduced become. With the intended rotation angle measurement is the measured angle of rotation according to the mathematically described Functional course of the error signal based on the stored Functional parameters corrected.

If the function history is unknown of the error signal is according to the required measurement accuracy for each Measured value the associated Determined reference measured value and a parameter set consisting of each the measured value of the angle of rotation sensor and the reference sensor in one Saved table. With the intended rotation angle measurement for each Measured value of the angle of rotation sensor and the associated reference measured value from the table determined and output.

According to a further feature of the invention if the function of the error signal is unknown, a predeterminable one Number n of pairs of values determined whose resolution is less than the angular resolution of the Data carrier. With the intended rotation angle measurement the measured angle of rotation is based on local interpolation corrected on the stored n value pairs. To do this, the stored parameters the parameters of an interpolation model for themselves known method determined. The measured angle of rotation becomes the corrected angle of rotation is determined by means of this interpolation.

The measurement accuracy is advantageously corresponding scalable to the respective requirements from the application. The measurement accuracy can be specified by the number of stored value pairs. The required computing power during the Intended rotation angle measurement is low.

The invention is illustrated below of embodiments explained in more detail. The necessary drawings show:

1 a schematic diagram of a rotation angle measuring device

2 a graphic representation of the error function of a systematic geometry error

3 a schematic diagram for the determination of correction values

4 a graphic representation of the error function of a systematic geometry error with sampling points

5 a schematic diagram of an evaluation unit

In 1 the basic structure of a rotation angle measuring device is shown in two views. Using the same reference numerals for the same means 1a a view of the stub shaft of a rotatable shaft 13 and 1b a sectional view through the rotation angle measuring device along the section line AA 'in 1a ,

The rotation angle measuring device consists of a on the shaft 13 attached, rotatable disk 16 with an information trail 17 and a sensor 1 for scanning the information track 17 , The sensor 1 is to an evaluation unit 2 connected.

Ideally, the information track 17 on the disk 16 concentric to the axis of rotation of the shaft 13 arranged. As a result of manufacturing tolerances, the rotation angle measured value is the information track when the position is eccentric 17 systematically buggy. In 2 is the error function Δ? (?) of a systematic geometry error when the information track is eccentric 17 represented graphically over the angle of rotation. Is the error-free measured angle of rotation Δϕ (0) = 0 arbitrarily based on the initial value of the angle of rotation? set. Due to the eccentric location of the information track 17 The error function Δϕ (ϕ) is sinusoidal over the angle of rotation.

The rotation angle measuring device, which is subject to a geometry error, is calibrated in a single operation. In 3 a basic device for determining the correction value is shown. The sensor data carrier 1 is about a wave 13 rigid with the data carrier of a reference sensor 14 coupled. The reference sensor 14 is to the evaluation unit 2 of the sensor 1 connected. By rotating the shaft 13 sweep the sensor 1 and the reference sensor 14 the information traces at the same time 17 the respective data carrier over the entire measuring range.

The actual angle values at predetermined scanning locations are parallel to the measurement of the output signal of the actual sensor 1 with the highly precise, rigid over the axis of rotation 13 coupled reference sensor 14 determined and synchronized in the evaluation unit 2 recorded and in the form of Value pairs saved. The scanning location is defined by the angle of rotation.

The rotation angle sensors are preferred 1 and 14 from an engine 15 driven and the process of recording is controlled fully automatically by a computer.

A small number n of reference measurements uniformly distributed over the measuring range is sufficient for a known and mathematically describable function course of the error signal. In 4 are for a sinusoidal error function Δ? (?) of a systematic geometric error with an eccentric position of the information track 17 over the rotation angle three samples evenly over the circumference of the information track 17 applied spread.

As a result, the for storage of Correction of necessary reference measurement values and additional data storage kept low. Three pairs of values are made up of each a measured value of the angle of rotation sensor and the reference sensor and the derived parameters of the correction function in the Evaluation unit of the angle of rotation sensor saved. From these pairs of values are then determines the variable parameters of the function stored in the sensor. It can be provided that this determination is outside of the sensor takes place in the computer controlling the reference measurement. In this case, the pairs of values are not stored in the sensor required. Only the values of the function parameters are transferred and stored in the sensor. With the intended rotation angle measurement is the measured angle of rotation using the stored Correction function corrected.

In an alternative embodiment of the Invention is made when the function curve of the error signal is unknown according to the required measuring accuracy for each measured value associated The reference measured value is determined and the pair of values is stored in a table. With the intended rotation angle measurement is the measured angle of rotation for each measured value of the angle of rotation sensor associated Reference measured value determined from the table and output. alternative With a smaller number of stored value pairs, the corrected Value can also be determined by interpolation.

The measurement accuracy is advantageously corresponding scalable to the respective requirements from the application. The measurement accuracy can be specified by the number of stored value pairs. The required computing power during the Intended rotation angle measurement is low.

In 5 is the evaluation unit 2 of the rotation angle measuring device shown in principle. The heart of the evaluation unit 2 is an arithmetic unit 4 , which is preferably designed as a microprocessor, microcontrollers, PIC or gate array and with which the sensor data are read in and processed. In the case of an analog sensor signal, an analog / digital converter (not shown) is also connected upstream. The evaluation unit 2 has an interface 5 for recording the signal of the reference sensor 14 during calibration, and for later connection to a digital control bus 6 for remote control and reading out the data.

To the calculator 4 is a non-volatile memory 7 for storing the parameter sets or the value pairs for the correction of the measured values. For outputting an analog output signal at the signal output 11 is the calculator 4 a digital / analog converter 10 downstream. In addition, there is a power supply 12 intended.

The evaluation unit 2 is prepared for the integration of advanced functions. So is a reset button 8th provided with which the current angle value can be set as the zero point after installation of the angle of rotation measuring device at the destination. The offset can thus be variably corrected. It also has a tap changer 9 flexible measuring range selection provided. This is an advantage for high-resolution digital sensors, in which a single code disk replaces a large number of previous analog sensors with different measuring ranges. This advantageously reduces the number of variants and reduces the effort for warehousing. In an advantageous embodiment of the invention, it can be provided that all of the described functions are additionally carried out in the same way via the control bus 6 to control.

Another advantage of the invention is the waiver of manual adjustment as a result of the described automatic calibration of the measuring device.

Advantageously, with the invention increased Measurement accuracy achieved with reduced manufacturing and adjustment effort.

In addition, the Invention using cheaper methods and materials the production of angle code disks.

1

sensor

2

evaluation

3

signal input

4

calculator

5

interface

6

control bus

7

Storage

8th

Reset button

9

step switch

10

D / A converter

11

signal output

12

power supply

13

Rotation axis / shaft

14

reference sensor

15

engine

16

disk

17

information track

Claims (6)

Method for correcting systematic geometry errors in a rotation angle measuring device consisting of a rotatable data carrier attached to a shaft with an information track and an optical scanning device for scanning the information track, which is connected to an evaluation unit, characterized in that the systematic angle errors after mounting the sensor ( 1 ) as a function of the sensor ( 1 ) determined absolute angle recorded once, in the evaluation unit ( 2 ) of the sensor ( 1 ) saved and used during the actual measurement to correct the output signal. A method according to claim 1, characterized in that the actual angle values parallel to the measurement of the output signal of the actual sensor ( 1 ) with a highly precise, rigid over the axis of rotation ( 13 ) coupled reference sensor ( 14 ) determined and synchronized via an additional digital interface ( 5 ) of the evaluation unit ( 2 ) are recorded. A method according to claim 2, characterized in that the rotation angle sensor ( 1 ) to record the actual angle values of a motor ( 15 ) driven and the process of recording is controlled fully automatically by a computer. Method according to one of claims 1 to 3, characterized in that - in the case of a known and mathematically describable function curve of the error signal, at least three pairs of values distributed over the measuring range, each consisting of a measured value of the rotation angle sensor ( 1 ) and the reference sensor ( 14 ) is determined and from these the parameters of the correction function are calculated and in the evaluation unit ( 2 ) of the rotation angle sensor ( 1 ) are stored and - that during the intended rotation angle measurement the measured rotation angle is corrected by calculation according to the mathematically defined function course of the error signal based on the stored parameter set. Method according to one of claims 1 to 3, characterized in that - if the function curve of the error signal is unknown, the associated reference measured value is determined once for each measured value in accordance with the required measurement accuracy and a pair of values consisting of the measured value of the angle of rotation sensor ( 1 ) and the reference sensor ( 14 ) stored in a table and - that in the intended rotation angle measurement for each measured value of the rotation angle sensor ( 1 ) the associated reference measured value is determined from the table and output. Method according to one of claims 1 to 3, characterized in that - if the function of the error signal is unknown, a predeterminable number n of value pairs is determined, the resolution of which is less than the angular resolution of the data carrier ( 16 ), - that the corrected angle of rotation is determined by interpolation from the stored value pairs during the intended rotation angle measurement.