Angular position measurement test

1. Test Objective

Test the measurement repeatability, measurement accuracy, and resolution of the axis of turntable at any angular position within the 360° range where an output is displayed.

2. Test Instruments

Small angle measuring instrument:

Photoelectric autocollimator (hereinafter referred to as optical tube), resolution not less than 0.1";

A 360-tooth multi-tooth indexing table (hereinafter referred to as the 360-tooth disk) and a plane mirror;

A 391-tooth multi-tooth indexing table (hereinafter referred to as the 391-tooth disk) and a plane mirror;

23-faceted prism, Level 1;

24-faceted prism, Level 1.

3. Test Environment Conditions

Ambient temperature: 20±2℃;

Relative humidity: ≤70%;

Vibration isolation requirements: The turntable under test shall be placed on a vibration isolation foundation, with no severe vibrations or impacts around it;

Electromagnetic field requirements: There should be no strong electromagnetic interference in the vicinity of the test site.

4. Test Methods

Before the test, install the multi-faceted prism or multi-tooth disk and plane mirror at the center of rotation of the shaft being measured on the turntable. Install the optical tube on the stationary part of the shaft being measured or on a well-isolated foundation, ensuring that the optical axis of the optical tube is perpendicular to the prism face or plane mirror. Start the turntable angle measurement system and ensure it is working normally and stably.

4.1 Repeatability of Angular Position Measurement

The experiment uses a 23-faceted prism or a 391-tooth disk and a plane mirror. Starting from an arbitrary angle position θ₁ of the measured axis, align face I of the prism or the plane mirror with the light tube and record the light tube reading a11 . Using the digital display of the angular position measurement system as a reference, rotate the measured axis sequentially by the specified angle θi of the prism , and record the corresponding reading a1i of the optical tube . Starting from θ1 , rotate the measured axis in the opposite direction and repeat the above test, recording the corresponding reading a2i of the optical tube . When using a multi-tooth disk, rotate the disk in the opposite direction by the angle rotated by the axis, so that the plane mirror is aligned with the optical tube.

4.2 Angular position measurement accuracy

4.2.1 Component Test Method

4.2.1.1 Indexing accuracy

The experiment uses a 24-faceted prism or a 360-tooth disk and a plane mirror. Starting from 0 on the digital display of the measured shaft angle position measurement system, record the reading a₁ of the optical tube. Using the digital display as the reference, rotate the shaft 15° sequentially and record the corresponding optical tube readings a₁, ..., a₂₄ . When using a multi-tooth disk, reverse the disk 15° sequentially to align the plane mirror with the optical tube.

4.2.1.2 Subdivision Accuracy

a. The subdivision accuracy test uses a small-angle measuring instrument. Depending on the specific requirements of the selected small-angle measuring instrument, its rotating part is mounted on the shaft being measured, and its stationary part is mounted on the stationary part of the turntable or on a well-isolated foundation.

b. Within 360° of the measured axis, select three angular positions for subdivision testing. The angular position measurement system digitally displays the 0° position, and the angular positions θm (maximum positive error) and θn (maximum negative error) derived from the graduation accuracy. The selection of the subdivision angle interval: When using a 720-pole inductive synchro as the angular measuring element, the subdivision angle interval is 1° with 17 subdivision points; when using other angular measuring elements, the angle interval is selected as one cycle of subdivision, with no less than 9 subdivision points.

c. The 0° position subdivision test starts from the 0 position on the digital display. Record the reading of the small angle measuring instrument b0.1 . Based on the digital display of the angular position measuring system, rotate the rotation shaft at 1°/17 angle intervals and record the readings of the small angle measuring instrument b0.2 … , b0.17 respectively .

θm and θn is the same as above. The corresponding readings of the small angle measuring instrument are recorded as b1.1…,b1.17 ; b2.1 , …,b2.17 , respectively . 

4.2.2 Comprehensive Test Method 

The experiment uses a 23-faceted prism or a 391-tooth disk and a plane mirror. Starting from position 0 on the digital display of the measured shaft angle position measurement system, record the initial reading c₁ of the optical tube. Using the digital display as a reference, rotate the shaft by the specified angle of the prism face and record the corresponding optical tube readings c₂, ..., c₂₃ .

When using a multi-tooth disk, the disk should be rotated in reverse order through the angle of the axis being measured, so that the plane mirror is aligned with the light tube.

Note: When using the component test method and the comprehensive test method, if the instrument accuracy cannot meet the inspection requirements, the comparative ranking method shall be used. See Appendix B.

4.3 Angular position measurement resolution

The measuring axis is finely adjusted using the fine-tuning mechanism of the turntable, and the angular position of the measuring axis is observed visually using the digital display. The smallest increment is the resolution of the angular position.

5. Data Processing and Result Evaluation

5.1 Repeatability of Angular Position Measurement

5.1.1 Data Processing

In the formula: e1.i — the difference between the measured values of adjacent test points when the measured shaft rotates forward;

e2.i — The difference between the measured values of adjacent test points when the measured axis is reversed (");

N – Number of angular position measurement points.

5.2 Angular position measurement accuracy

5.2.1 Component Testing Method

5.2.1.1 Data Processing

a. Indexing error

In the formula: e ai——circumferential indexing error based on the digital display of the angular position measurement system at 0, unit: (");

Δi — Correction value for the corresponding face of the prism, unit: (").

Take the positive maximum indexing error e₁ + and the negative maximum graduation error e₁ - in eai , and determine the corresponding angular positions θ₁ and θ₂ of the measured axis based on these.

b. Subdivision error

In the formula: eb0.i ——0 ° position subdivision error, (");

eb1.i ——θ₁ position subdivision error, (");

eb2.i ——θ₂ position subdivision error,(");

θ₁——Subdivision of angular intervals, (");

N — Number of subdivision points.

Take the positive maximum subdivision error e₂ + and the negative maximum subdivision error e₂- from eb0.i ; eb1.i ; eb2.i.

5.2.1.2 Result Evaluation

The angular position measurement accuracy is + Uα , -Uα .

5.2.2 Comprehensive Test Method

5.2.2.1 Data Processing

In the formula: eai — angular position error of each test point, (");

Δi —— Correction value for the corresponding face of the prism, (").

5.2.2.2 Result Evaluation

Take the maximum positive error e 0+and the maximum negative error e 0- in eai.

The angular position measurement accuracy is + Uα , -Uα .