1. High efficiency of CNC machine tool factory and reversibility of transmission
Since the contact point between the ball screw pair screw and the nut of the CNC machine tool factory is rolling motion, the friction coefficient is small, and the friction coefficient can be up to 0.0025 after experimental measurement, so its efficiency can reach more than 90%, and the motor driving torque is about 1/3 of the trapezoidal sliding screw: Compared with the trapezoidal sliding screw, the ball screw of the CNC machine tool factory can also realize reverse transmission, that is, the nut driving the screw in a linear motion does a rotary motion, and the ball screw pair cannot realize self-locking. of. Figure 253 shows the comparison of the forward and reverse transmission efficiency of the ball screw pair and the trapezoidal sliding screw pair in the CNC machine tool factory. The abscissa in the figure is the helix angle of the pitch diameter, and the pitch diameter of the ball screw pair of the CNC machine tool factory is the diameter of the cylindrical surface where the ball center of the CNC machine tool factory is located. The formula for calculating the helix angle of the pitch diameter of the ball screw pair is as follows: is the lead of the ball screw pair;
do is the pitch diameter of the ball screw pair.
2 CNC machine tool factory accuracy
The processing of the ball screw pair in the CNC machine tool factory is made by grinding with a high-precision grinding machine in a factory with strict temperature control. The accuracy of the thread lead must be tested by a laser lead measuring instrument. The various indicators of thread lead accuracy are shown in Figure 264, and the meaning of each symbol is introduced as follows:
Z is the total length of the thread;
Z,, is the effective stroke: the stroke part with the specified accuracy requirements (ie the stroke plus the total length of the nut);
f. is the remaining distance: the part of the stroke that does not specify the accuracy requirement;
c is the stroke compensation value: the compensation value within the effective stroke, which is also called the cumulative reference lead target value or the cumulative target lead. The size of the value is determined by the specific use situation. For example, the effective stroke of a machining center screw is iOOOmrrJ. In order to cope with the elongation caused by the temperature rise, a pulling force needs to be applied to the screw during installation. The magnitude of the pulling force is equivalent to the temperature rise. The elongation of 2~3°C is due to the elongation of the lead screw per meter for every 1°C rise in temperature. . 012mm, so the stretch of the lead screw is 0 024~0 036mm. That is, the stroke compensation value of the lead screw is -0.024. -0 036mm, that is to say, during grinding, within the effective stroke, the cumulative lead of the lead screw is one smaller than the nominal value iOOOmm. . 024~ -0.036mm.
e. is the target travel tolerance: half of the difference 2e, between the maximum and minimum allowable actual average travel.
K. is the effective stroke variation: parallel to the actual stroke and including the allowable bandwidth value of the actual stroke curve.
V30,. It is any 300mm stroke variation: it is parallel to the actual stroke of 300mm and includes the allowable bandwidth value of the actual stroke curve.
V2np is an arbitrary 27rrad stroke variation: parallel to the actual stroke of a lead, and including the allowable bandwidth value of the actual stroke curve.
In my country’s standard GB/T 17587.3-1998, the thread lead accuracy grades are divided into seven grades. Among them, Pl-P5 grades are ball screw pairs for positioning, and Iy7 and Pl0 are ball screw pairs for transmission.
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