In the servo control system of CNC machine tools, the transmission rigidity is one of the main determinants of the high speed positioning repeated accuracy. The transmission rigidity and accuracy are mainly determined by the rigidity of the transmission ball screw and its supporting structure.
Methods for improving the transmission rigidity of the CNC machine tools ball screw:
1, Using appropriate coupling
The large torque and wide speed regulation DC motor generally can be directly coupled with the ball screw, which can be used the conical clamping ring anti-backlash coupling or flexible coupling, in order to eliminate the transmission gap and improve the transmission rigidity. If the use of small inertia DC motor, the need to gear deceleration, the large gear can be directly mounted on the ball screw end.
2, Improve the rigidity of the ball screw and its support
Integrated tension and compression of the ball screw transmission mainly composed of ball screw tension and compression rigidity, support rigidity, nut rigidity and others three parts. Tension and compression rigidity of the ball screw can be improved by using the bearing manner of axial fixed at both ends. And over the entire operating stroke range smaller stiffness change, which is favorable to reduce the positioning error caused by the change of the transmission rigidity. This support way when the nut is in the middle position the stiffness minimum, but still 4 times of the minimum stiffness of one end axial support.
Support stiffness includes bearing stiffness itself and bearing seat stiffness, according to experience, in addition to tension and compression stiffness of the ball screw, the bearing stiffness is one of the weak links. The stiffness of the bearing itself can using Contact Angle of 60 degrees of thrust angular contact ball bearing, double thrust angular contact ball bearing, ball bearing and thrust roller bearing and other measures to improve the axial rigidity of the bearing. To enhance the rigidity of the support seat, the design should pay attention to avoid using the narrow and thin gaskets and middle spacer sleeve. To improve the contact stiffness of the bearing seat, the mating surfaces must be grinding. And in the direction of the force arranged appropriate reinforcing rib.
3, Ball screw nut assembly preload and ball screw prestretching
Ball screw nut assembly preload general use various forms of double nut mechanism and ball screw nut with preload. Require the preload value should be 1/3 times greater than the maximum axial force.
Ball screw prestretching can compensate for ball screw thermal deformation and improve the tension and compression stiffness of the ball screw. General require the prestretching force should be greater than the 0.35 times of maximum working load.
Source: http://www.machineballscrew.com Ball Screw Nut Assembly.
No comments:
Post a Comment