1. Linear motion positioning accuracy detection
The accuracy of linear motion positioning is generally carried out under no-load conditions of machine tools and workbenches. According to national standards and the provisions of the International Organization for Standardization (ISO standards), the testing of CNC machine tools should be based on laser measurement. In the absence of a laser interferometer, for ordinary users, a standard scale can also be used with an optical reading microscope for comparative measurement. However, the accuracy of the measuring instrument must be 1-2 levels higher than the measured accuracy.
In order to reflect all errors in multiple positioning, the ISO standard specifies that each positioning point should be calculated based on the average of five measurements and a scatter band of -3 to form a scatter band for the positioning point.
2. Detection of Repetitive Positioning Accuracy in Linear Motion
The instruments used for detection are the same as those used for detecting positioning accuracy. The general detection method is to measure at any three positions near the midpoint and ends of each coordinate stroke. For each position, rapid movement positioning is used, and the positioning is repeated 7 times under the same conditions. The stop position value is measured and the maximum difference in reading is calculated. One half of the maximum difference between the three positions, accompanied by positive and negative symbols, is used as the repeated positioning accuracy of the coordinate, which is the most basic indicator reflecting the stability of axis motion accuracy.
3. Accuracy detection of origin return in linear motion
4. Reverse Error Detection of Linear Motion
The detection method for reverse error is to move forward or backward by a certain distance within the stroke of the measured coordinate axis, and use this stop position as a reference. Then, give a certain movement command value in the same direction to move it by a certain distance, and then move the same distance in the opposite direction to measure the difference between the stop position and the reference position. Conduct multiple measurements (usually 7 times) at three positions near the midpoint and ends of the stroke, and calculate the average value at each position. The maximum value of the obtained average value is the reverse error value.
5. Positioning accuracy detection of rotary worktable
Measurement tools include standard turntables, angle polyhedra, circular gratings, and collimators (collimators), which can be selected according to specific situations. The measurement method is to rotate the workbench forward (or backward) by an angle and stop, lock, and position it, using this position as a reference. Then, quickly rotate the workbench in the same direction and lock the position every 30 seconds for measurement. Measure forward and reverse rotation once each, and the maximum difference between the actual rotation angle at each positioning position and the theoretical value (command value) is the indexing error. If it is a CNC rotary worktable, the target position should be set every 30, and each target position should be quickly positioned 7 times from the positive and negative directions. The actual difference between the position and the target position is the position deviation. Then, the average position deviation and standard deviation should be calculated according to the method specified in GB10931-89 "Evaluation Method for Position Accuracy of Digital Control Machine Tools", The difference between the maximum value of all average position deviations and the minimum value of all average position deviations and the standard deviation is the positioning accuracy error of the CNC rotary worktable.
Considering the practical usage requirements of dry-type transformers, it is generally important to focus on measuring several right angle equal points such as 0, 90, 180, 270, etc. The accuracy of these points is required to be improved by one level compared to other angle positions.
6. Repetitive indexing accuracy detection of rotary worktable
The measurement method is to select three positions within one week of the rotary worktable and repeat the positioning three times, respectively, and perform the detection in the forward and reverse directions of rotation. The maximum value division accuracy of the difference between the theoretical value at the corresponding position and all read values. If it is a CNC rotary worktable, a measurement point should be taken every 30 as the target position, and each target position should be quickly positioned 5 times from the positive and negative directions. The difference between the actual position and the target position should be measured, which is the position deviation. Then, the standard deviation should be calculated according to the method specified in GB10931-89. Six times the maximum standard deviation of each measurement point is the repeated indexing accuracy of the CNC rotary worktable.
7. Precision detection of origin restoration for rotary workbenches
The measurement method is to perform one origin reset from 7 arbitrary positions, determine their stopping positions, and use the maximum difference read as the accuracy of the origin reset.
It should be pointed out that the current detection of positioning accuracy is measured under fast and positioning conditions. For some CNC machine tools with poor feed system wind speed, different positioning accuracy values will be obtained when using different feed rates for positioning. In addition, the measurement results of positioning accuracy are related to the ambient temperature and the working state of the coordinate axis. Currently, most CNC machine tools use a semi closed loop system, and position detection components are mostly installed on the drive motor. It is not surprising that an error of 0.01-0.02mm occurs within a 1m stroke. This is an error caused by thermal elongation, and some machine tools use pre stretching (pre tightening) methods to reduce the impact.
