Since the feed servo system uses the servo motor as the power drive component, the servo system can realize the automatic stepless speed regulation of the feed speed without mechanical shifting, so the feed drive chain is greatly shortened. For actuators that move in a straight line, the servo motor is usually connected only via a pair of drive pairs (gear, toothed timing pulley) or directly to the screw (linear motion conversion element). Shortening the drive chain greatly improves the transmission accuracy and rigidity. Nevertheless, in order to ensure the transmission performance requirements of the feed servo system, in the design of the mechanical transmission structure, in addition to the selection of higher precision transmission components, the transmission clearance must be reduced and eliminated in the structure.
(1) Gear transmission
The role of the gear transmission: change the direction of motion, reduce the speed, increase the torque, adapt to the different screw pitch and the matching of different pulse equivalents.
The gear drive has a backlash that causes a reverse motion dead zone and must be eliminated.
Double gear misalignment anti-backlash structure:
For spur gears: divide the large gears in a pair of gears into two gears and put them together. Install four screws with lugs on the same side of the two gears, and use springs (tension springs). The two screws are connected, and the two gears are naturally staggered by the tension of the spring. Thus, the two large gears are always meshed with the two sides of the tooth gap of the pinion gear during transmission, thereby eliminating the purpose of eliminating the backlash. The tension of the spring is adjusted to meet the requirements of the transmission torque.
For helical gears: divide a helical gear into two thin gears, add a spacer between the two thin gears, change the thickness of the gasket, and make the spiral of the two thin helical gears misaligned, respectively, with two of the wide gear slots. The sides are engaged to eliminate the backlash. The relationship between the amount of backlash elimination Δ and the amount of increase or decrease of the gasket Δt. It can be calculated by:
Δt=Δctgβ
(2) Synchronous (toothed) belt drive
The timing belt drive is a transmission consisting of a closing tape with an equally spaced tooth on the inner circumferential surface and a corresponding pulley. When driving, the timing belt and the pulley multi-tooth meshing have the advantages of gear transmission, chain transmission and belt transmission. No relative sliding, smooth and uniform transmission, no meshing clearance. Due to the metal skeleton in the middle of the tape, the elastic elongation is small and the transmission rigidity is good. It is a good seamless drive, so it is used in servo feed drives.
(3) Gear or pulley connection to the shaft
When the gear or pulley is connected to the shaft, it is also necessary to eliminate the transmission gap.
Use double keys to eliminate the gap: use the set screw to tighten the key on the side of the key, so that the key is close to the keyway, eliminating the gap, and the two keys respectively drive different rotation directions.
Cone ring pair connection: The cone ring pair consists of a ring with an inner cone and a ring with an outer cone. When connecting, a plurality of (general position 2) secondary cone ring pairs are placed between the shaft and the wheel hole, and the outer cone ring has a small clearance with the outer circumference of the shaft and the inner cone ring and the wheel hole. Tighten the end cap screws so that the end caps are close to the end faces of the wheels, and the end caps push the inner cone ring so that the inner and outer cone rings are pressed against each other. At this time, the inner taper rings are narrowed, the shaft is tightened, and the outer diameter of the inner taper ring is tightened. Inflate, expand the hole, and realize the keyless connection between the shaft and the wheel.
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