7 Methods to Detect the Positioning Accuracy of CNC Machine Tools
The positioning accuracy of CNC machine tools identifies the positional accuracy that may be achieved by the movement of each coordinate axis of the machine tool beneath the control of the numerical control device. The positioning accuracy of CNC machine tools could be understood as the motion accuracy of the machine tool. Ordinary machine tools are manually fed. The positioning accuracy is principally determined by the reading error. The movement of the CNC machine tool is realized by digital program instructions, therefore the positioning accuracy is set by the numerical control system and mechanical transmission error.Hit on CNC Machine Tool Accuracy Calculation to explore more about our services and sites. Hope you ll like our more services.
CNC machine tool is the abbreviation of digital control machine tool, which is a computerized machine tool with an application control system. The control system is effective at logically processing an application having control code or other symbolic instructions and decoding it, using coded digital representations, and Nanjing Fourth Machine Tool Co., Ltd. inputs the numerical control device through the info carrier. Through the arithmetic processing, various control signals are issued by the differential control device to control the movement of the machine tool, and the parts are automatically processed in line with the shape and size required by the drawings.
The movement of each moving the main machine tool is completed beneath the control of the numerical control device. The precision that every moving part can achieve beneath the control of this system command directly reflects the precision that the machined part can make. Therefore, the positioning accuracy is an essential test. Content.
1. Linear motion positioning accuracy detection Linear motion positioning accuracy is generally performed under no-load conditions on machine tools and benches. Based on the national standards and the provisions of the International Organization for Standardization (ISO standards), the detection of CNC machine tools should be predicated on laser measurements. In the absence of a laser interferometer, it is also easy for the typical user to use a standard scale with an optical reading microscope for comparative measurements. However, the accuracy of the measuring instrument should be anyone to two levels higher compared to the accuracy of the measurement.
To reflect all the errors in multiple positioning, the ISO standard stipulates that every positioning point calculates the typical value and the dispersion difference predicated on five measurement data, and the dispersion difference band formed by the dispersion band.
2, linear motion repeat positioning accuracy detection The instrument useful for the test is exactly like that used to detect thepositioning accuracy. The typical detection method would be to measure at any three positions close to the midpoint and the 2 ends of each coordinate stroke. Each position is quickly moved, and the positioning is repeated 7 times beneath the same conditions. The stop position value is measured, and the most reading difference is obtained. Taking one-half of the most significant difference among the three positions, the positive and negative signs are attached as the repeated positioning accuracy of the coordinates, which is probably the most basic index reflecting the stability of the axis motion accuracy.
3, linear motion origin return accuracy detection The origin return precision is essentially the repeat positioning accuracy of a unique point on the coordinate axis, so its detection method is wholly exactly like the repeat positioning accuracy.
4. Reverse error detection of linear motion The contrary error of the linear motion also called losing amount, includes the reverse dead zone of the drive position (such as servo motor, servo motor, and stepping motor) on the coordinate axis feed chain, and each mechanical motion transmission pair An extensive reflection of errors such as for instance backlash and elastic deformation. The larger the error, the lower the positioning accuracy and the repeat positioning accuracy.
The detection way of the reverse error is to go a range forward or backward in the stroke of the measured coordinate axis and utilize the stop position as a research, and then give a specific movement command value in the same direction to make it move a distance. Then run the same distance in the opposite direction and measure the difference involving the stop position and the reference position. The measurement has performed a plurality of times (generally seven times) at three points close to the midpoint and both ends of the stroke, and the typical value at each position is obtained, and the most value among the obtained average values is the reverse error value.
5. Positioning accuracy detection of rotary table Measuring tools include standard turret, angle polyhedron, circular grating and collimator (collimator), etc., which can be selected in line with the specific conditions. The measurement method is to help make the table forward (or reverse) to an angle and stop, lock, and position. Make use of this position as a research, then quickly turn the table in the same direction and measure every 30 locks. All the forward rotation and the reverse rotation is measured for one week, and the most value of the difference between the actual rotation angle of each positioning position and the theoretical value (command value) is the division error.If it is really a CNC rotary table, it should be a target position every 30, for every target position to quickly locate 7 times from the positive and negative directions, the difference between the region and the mark position is obviously reached, and then based on GB10931- 89 The strategy specified in the “Method for Evaluating the Position Accuracy of Digital Control Machines” calculates the typical position deviation and standard deviation, the difference between the most value of all the average position deviations and the conventional deviation and the sum of all the average position deviations and the conventional deviation. It's the positioning accuracy error of the CNC rotary table.
Thinking about the dry-type transformer to the actual use requirements, it's generally important to measure several equal-angle points such as for instance 0, 90, 180, 270, etc., and the accuracy of those points is needed to be improved by one level compared with other angular positions.
6. Repeated indexing accuracy detection of rotarytable The measurement method is repeated three times in three places in one week of the rotary table, and the detection is performed in the forward and reverses directions respectively. The most value of the difference involving the values of most readings and the theoretical value of the corresponding position. If it is a CNC rotary table, take one measurement point every 30 as the mark position, and perform five fast positionings for every target position from the positive and negative directions respectively, and measure the difference between the actual arrival position and the mark position. That is, the career deviation, and then calculate the conventional deviation in line with the method specified in GB10931-89, which is six times of the most value of the conventional deviation of each measuring point, which is the repeating indexing precision of the numerical control rotary table.
7. The origin return accuracy detection of the rotary table The measurement method is to do the origin return from 7 arbitrary positions, measure the stop position, and utilize the maximum difference read as the origin return accuracy.
It should be remarked that the detection of the existing positioning accuracy is measured beneath the condition of fast and positioning. For many CNC machine tools whose feeding system is of low quality, different positioning accuracy values will soon be obtained when positioning with varying speeds of feed. Also, the measurement result of the positioning accuracy relates to the ambient temperature and the working state of the coordinate axis. At present, a lot of the numerical control machine tools adopt a semi-closed loop system, and the career detecting components are mostly attached to the driving motor, which generates an error of 0.01 to 0.02 mm in a swing of 1 m. It's not strange. That is an error caused by thermal elongation, and some machines use a pre-stretch (pre-tightening) method to cut back the impact.
The repeating positioning accuracy of each coordinate axis reflects probably the most basic accuracy index of the shaft, which reflects the stability of the motion accuracy of the axle, and it cannot be assumed that the machine tool with poor precision could be stably useful for production. At present, as a result of increasing number of functions of the numerical control system, system errors such as for instance pitch accumulation error and backlash error could be compensated for the motion accuracy of each sitting injector. Only the random error cannot be paid, and the repeat positioning accuracy is repeated. It reflects the absolute random error of the feed drive mechanism. It can't be corrected by the CNC system compensation. When it is found to be out of tolerance, only the fine adjustment of the feed drive chain is performed. Therefore, if the machine tool is allowed to be selected, it is better to select a device with high repeatability.
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