Mechanical transmission structure of the hottest f

The mechanical transmission structure of the feed servo system

because the feed needs the tilt support of the national policy more, the servo system uses the servo motor as the power driving element, and the servo system can realize the automatic stepless speed regulation of the feed speed without mechanical speed change, so the feed transmission chain is greatly shortened. For the actuator of linear motion, the servo motor is usually connected only through a pair of transmission pairs (gears, toothed synchronous pulleys) or directly to the lead screw (linear motion conversion element). Shortening the transmission chain greatly improves the transmission accuracy and stiffness. Nevertheless, in order to ensure the transmission performance requirements of the feed servo system, in the design of mechanical transmission structure, in addition to selecting high-precision transmission components, it is also necessary to reduce and eliminate the transmission gap in the structure

I. connection structure between motor and lead screw

(1) gear transmission

the role of gear transmission: changing the direction of motion, reducing speed, increasing torque, adapting to the matching of different lead screw pitches and different pulse equivalents

there is side clearance in gear transmission, which causes the dead zone of reverse movement, which must be eliminated

double gear staggering and backlash elimination structure:

spur gear: divide the big gear in a pair of gears into two gears and put them together. Install four screws with lugs evenly on the same side of the two gears, connect the two screws with springs (tension springs), and naturally stagger the two gears through the tension of springs. In this way, the two big gears will always mesh with the two sides of the pinion's tooth slots during transmission, So as to achieve the purpose of eliminating side clearance. Adjust the tension of the spring to meet the requirements of transmission torque

opposite helical gear: divide a helical gear into two thin gears, add shims between the two thin gears, change the thickness of the shims, so that the spiral lines of the two thin helical gears are misaligned, and mesh with the two sides of the wide tooth groove respectively, so as to eliminate the side clearance. Clearance elimination Δ And gasket increase and decrease Δ T. It can be calculated by the following formula:

Δ t= Δ ctg β

(2) synchronous (toothed) belt transmission

synchronous belt transmission is composed of a closed tape with equidistant teeth on the inner circumference surface and the corresponding pulley. During transmission, the synchronous belt and pulley mesh with multiple teeth, which has the advantages of gear transmission, chain transmission and belt transmission. No relative sliding, stable and uniform transmission, no meshing clearance. Due to the metal framework in the middle of the tape, the elastic elongation is very small, and it has good transmission stiffness. It is a good gapless transmission, so it is applied in servo feed transmission

(3) connection between gear or pulley and shaft

when the gear or pulley is connected with the shaft, it is also necessary to eliminate the transmission clearance

use double keys to eliminate the gap: use the set screw to top tightly on the side of the key to draw the experimental curve key, so that the key is close to the keyway to eliminate the gap. The two keys drive different rotation directions respectively

connected by cone ring pair: the cone ring pair is composed of a ring with inner cone and a ring with outer cone. When connecting, place several (general position 2) pairs of cone rings between the shaft and the wheel hole, and the hole of the outer cone ring fits with the shaft, and the outer circle of the inner cone ring fits with the wheel hole with a small gap. Tighten the end cap screws so that the end cap is close to the end face of the wheel. The end face of the end cap pushes the inner cone ring so that the inner and outer cone rings squeeze each other. At this time, the inner hole of the outer cone ring shrinks, hugs the shaft, and the outer diameter of the inner cone ring expands, expanding the hole, realizing the keyless connection between the shaft and the wheel

(4) coupling

when the motor is directly connected with the lead screw, the coupling is used

sleeve plus taper pin connection. Elastic coupling

II. Ball screw nut pair

(I) circulation mode of ball

external circulation: the ball is sometimes separated from the screw during the circulation. Simple manufacturing process; Large radial size, low stiffness, easy to wear, high noise

internal circulation: the ball always contacts the lead screw during the circulation. Compact structure, good rigidity, reliable positioning, not easy to wear, low friction loss. Complex structure and difficult manufacturing

(II) pre tightening of ball screw nut pair

ball screw nut pair must be pre tightened to work normally. Pre tightening: eliminate the gap between the ball and the raceway to ensure the precision of the transmission after precise measurement; Make the ball contact with the raceway slightly into micro surface contact, and improve the transmission stiffness. Double nuts are often used to make the two nuts produce axial displacement, so as to eliminate the gap. The experimental machines with different materials mentioned above need different speed gaps and preloads. There are three kinds of pre tightening structures: