Seven Ways to Detect Positioning Accuracy of Machining Center (Part 2)

5. Detection of positioning accuracy of the rotary table

Measuring tools include a standard rotary table, angle polyhedron, circular grating and collimator (collimator), etc., which can be selected according to specific conditions. The measurement method is to rotate the worktable forward (or reverse) by an angle and stop, lock, and position, using this position as a reference, and then quickly rotate the worktable in the same direction, locking and positioning every 30th, and measuring. The forward rotation and the reverse rotation are measured for one week, and the maximum value of the difference between the actual rotation angle of each positioning position and the theoretical value (command value) is the indexing error. If it is a CNC rotary table, each 30 should be a target position, and each target position should be quickly positioned 7 times from the forward and reverse directions. The difference between the actual position and the target position is the position deviation, and then press GB10931- 89 "Evaluation Methods for Positional Accuracy of Digitally Controlled Machine Tools" calculates the average position deviation and standard deviation, the difference between the maximum value of all average position deviations and the standard deviation and the sum of all average position deviations and the minimum value of standard deviation Is the positioning accuracy error of the CNC rotary table.

Considering the requirements of dry-type transformers to actual use, it is generally important to measure the right-angle bisectors such as 0, 90, 180, 270, etc., and the accuracy of these points is required to be improved by one level compared to other angular positions.

6. Repeated indexing accuracy detection of the rotary table

The measurement method is to repeat the positioning at any three positions within a week of the rotary table 3 times, and detect under the rotation of the forward and reverse directions respectively. The maximum indexing accuracy of the difference between all readings and the theoretical value of the corresponding position. If it is a CNC rotary table, take a measurement point every 30 as the target position, and perform five quick positionings on each target position from the forward and reverse directions, and measure the difference between the actual position and the target position. That is, the position deviation, and then calculate the standard deviation according to the method specified in GB10931-89. The standard deviation of each measurement point is 6 times the maximum value, which is the repeating index accuracy of the CNC rotary table.

CNC Lathe Machine

7. Accuracy detection of the return-to-origin of the rotary table

The measuring method is to perform a return-to-origin from each of 7 arbitrary positions, measure the stop position, and use the maximum difference read as the return-to-origin accuracy.

It should be pointed out that the detection of the existing positioning accuracy is measured under the condition of rapid and positioning. For some CNC lathe machines with poor feed system, the positioning will be different when using different feed speed Positioning accuracy value. In addition, the measurement result of the positioning accuracy is related to the ambient temperature and the working state of the coordinate axis. At present, most CNC machine tools use a semi-closed loop system, and the position detection elements are mostly installed on the drive motor, resulting in an error of 0.01 ~ 0.02mm within a 1m stroke. It is not strange. This is an error caused by thermal elongation. Some machine tools use pre-stretching (pre-tensioning) to reduce the impact.

The repeated positioning accuracy of each coordinate axis is the most basic accuracy index reflecting the axis. It reflects the stability of the motion accuracy of the axis. It cannot be assumed that machine tools with poor accuracy can be used stably in production. At present, due to more and more functions of the CNC system, system errors such as pitch accumulation error and backlash error can be compensated systematically for each sitting injector standard motion accuracy. Only random errors cannot be compensated, while repeated positioning accuracy It reflects the comprehensive random error of the feed drive mechanism. It cannot be corrected by CNC system compensation. When it is found to be out of tolerance, only the feed drive chain is fine-tuned and corrected. Machining center manufacturing believes that if machine tool selection is allowed, it is better to choose a machine with high repeat positioning accuracy.