Ball Screw Return Error Elimination Method
Question: Is the return error of the ball screw large? Can it be completely eliminated?
Answer: There are several grades, P1.P2.P3.P4 four grades, P1 accuracy is 2.5+, P2 accuracy is 7+, P3 accuracy is +12. The general error cannot be eliminated, the unit is micron level.
Question: The allowable error of the average stroke in the ball screw ep=2×Lu/300×v300p, what does the following number symbol represent?
Answer: ep is the actual accumulated lead error, which represents the nut moving distance. V300P is the lead change of any 300mm stroke.
Q: When the ball screw nut pair is installed on the CNC machine tool, the pre-tensioning method is often used to eliminate the thermal elongation error. Why?
Answer: After using for a long time, the lead screw will heat up, causing elongation and pre-stretching, which is to eliminate the axial error after elongation. Generally, after the nut at one end of the lead screw is locked, use a dial indicator on the end of the lead screw and then lock it. Nuts, about three to five wires are pre-pulled. It is an exaggeration to think that after you install the lead screw, the lead screw will deform and bend when it is hot, because the two ends of the lead screw are locked. When you pre-pull it down, it won't bend, because it has a pulling force to the sides.
Ball screw pair selection calculation
1.1 Precision selection
Generally, in the preliminary design, the variation of any 300mm stroke of the lead screw should be less than 1/3—1/2 of the positioning accuracy value of the target setting position.
1.2 Determination of lead screw
1.3 Preliminarily determine the specifications of the ball screw according to the rated dynamic load
2. Check calculation of ball screw pair
2.1 Stability check of pressure bar
When the axially fixed long lead screw is subjected to compressive load, the stability of the pressure rod should be checked.
2.2 Checking the critical speed of the lead screw
The long lead screw works under the command, in order to prevent bending resonance, the critical speed should be beautiful.
2.3 Accuracy check, that is, stiffness check
The lead error of the lead screw, the error of the servo system, and the error caused by the elastic deformation of each mechanical link are the factors that affect the positioning accuracy of the machining center.
In general, the order in which the elastic deformation is affected in the above links is: the compressive stiffness Ktmin of the ball screw itself; the axial stiffness Kba of the support bearing; the contact stiffness between the ball and the raceway in the ball screw pair Kc; converted to the stiffness KR of the servo system on the ball screw pair; converted to the stiffness K1 of the coupling on the ball screw pair; torsional stiffness Kk of the ball screw pair; stiffness Kh of the nut seat and the bearing seat.
The elastic deformation of the lead screw is: δ= Ff /K.