How should the positioning accuracy of CNC turning machine be tested? Without further ado let’s take a look!
1, linear motion positioning accuracy detection
Linear motion positioning accuracy is generally carried out under no-load conditions on CNC turning machines and tables. According to the national standards and the provisions of the International Organization for Standardization (ISO standards), the detection of CNC turning machine, should be subject to laser measurement. In the absence of a laser interferometer, for the general user can also use a standard scale with an optical reading microscope for comparative measurements. However, the accuracy of the measuring instrument must be 1 to 2 levels higher than the accuracy being measured. In order to reflect the entire error in multiple positioning, the ISO standard stipulates that each positioning point is calculated as the average of five measurements and scatter, and the scatter band constitutes the scatter band of the positioning point.
2、Repeat positioning accuracy testing of linear motion
The instruments used for testing are the same as those used for testing positioning accuracy. The general test method is to measure any three positions near the midpoint of each coordinate stroke and at both ends, each position is positioned with rapid movement, the positioning is repeated seven times under the same conditions, the stop position value is measured and the maximum difference between the readings is found. One half of the maximum difference in the three positions, with positive and negative signs attached, is used as the repeat positioning accuracy of the coordinate, which is the most basic indicator of the stability of the axis movement accuracy.
3、Return accuracy of linear motion
Origin return accuracy is essentially the repeat positioning accuracy of a special point on the coordinate axis, so it is detected in the same way* as repeat positioning accuracy.
4、Reverse error detection of linear motion
The reverse error of linear motion, also known as the amount of loss of motion, it includes the axis feed drive chain drive parts (such as servo motors, hydraulic motors and stepper motors, etc.) of the reverse dead zone, the mechanical motion drive vice of the reverse clearance and elastic deformation and other errors of the comprehensive reflection. The larger the error, the lower the positioning accuracy and repeat positioning accuracy. The method of detecting reverse error is to move a distance in advance within the stroke of the measured coordinate axis in the forward or reverse direction and use the stop position as a reference, then give a certain movement command value in the same direction to move a distance, then move the same distance in the opposite direction and measure the difference between the stop position and the reference position. In the midpoint of the trip and the two ends of the three positions were measured several times (generally 7 times), to find out the average value of each position, to obtain the average value of the maximum value of the reverse error.
5, rotary table positioning accuracy testing
Measurement tools are standard rotary table, angle polyhedra, circular grating and parallel light tube (collimator), etc., can be selected according to the specific circumstances. Measurement method is to make the table forward (or reverse) turn an angle and stop, locking, positioning, the position as a benchmark, and then to the same direction of rapid rotation of the table, every 30 locking positioning, for measurement. Forward and reverse rotation are measured for one week each, and the maximum value of the difference between the actual angle of each positioning position and the theoretical value (command value) is the indexing error. If it is a CNC rotary table, every 30 should be a target position, for each target position from the positive and negative direction for rapid positioning 7 times, the actual position reached and the difference between the target position that is the position deviation, and then according to GB10931-89 “digital control of machine tool position accuracy assessment methods” method to calculate the average position deviation and standard deviation, all average position deviation and standard deviation The difference between the maximum value and the minimum value of all average position deviation and standard deviation is the positioning accuracy error of CNC rotary table. Considering the dry-type transformer to the actual use requirements, generally for 0, 90, 180, 270 and so on several right angle equal points to focus on the measurement, require the accuracy of these points compared to other angular position to improve a grade.
Post time: Mar-14-2023