Application of feeding transmission mechanical par

2022-08-24
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Application of NC machine tool feed transmission mechanical parts

generally, a typical NC machine tool closed-loop control feed system is composed of position comparison, amplification element, driving unit, mechanical transmission device and detection feedback element. Among them, mechanical transmission device is an important part of position control. The mechanical transmission device mentioned here refers to the whole mechanical transmission chain that changes the rotary motion of the driving source into the linear motion of the workbench, including gear devices, lead screw nut pairs and other intermediate transmission mechanisms

I. coupling

coupling is a device used to connect the two shafts sent to the mechanism so that they can transfer and transmit torque and motion together. At present, there are many types of couplings, including hydraulic, electromagnetic and mechanical. Mechanical couplings are the most widely used

the sleeve coupling has simple structure and small radial size, but it is difficult to load and unload (the shaft needs to move axially). In addition, the two shafts are required to be strictly aligned, and radial or angular deviation is not allowed, so the use is limited

the bypass coupling adopts the conical clamping ring to transmit the load, which can make the power transmission have no directional clearance

flange coupling is simple in structure, cost-effective, and can transmit large torque. It is often used in occasions with low speed, five kinds of shafts, high rigidity and good alignment. His main disadvantage is that he has high requirements for the neutrality of the two axes. If there is displacement and inclination between the two shafts, it will cause additional load in the part and worsen the working condition

II. Reduction mechanism

1) gear transmission device

gear transmission is widely used. It is simple to operate. It is a kind of mechanical transmission. Almost all transmission devices of various machine tools have gear transmission. There are two purposes of using gear transmission in the servo feed system of CNC machine tools. One is to change the output of servo motors with high speed torque (such as stepping motors, DC and AC servo motors, etc.) into the input of actuators with low speed and high torque; The other is to make the rotational inertia of ball screw and workbench have a small proportion in the system. In addition, the required motion accuracy can be guaranteed for the open-loop system

can complete storage and printing. In order to minimize the impact of tooth side clearance on the machining accuracy of CNC machine tools, structural measures are often taken to reduce or eliminate the empty path error of gear pairs. For example, double piece gear staggering method, eccentric sleeve is used to adjust the center distance of gear pair, or axial gasket adjustment method is used to eliminate the gear backlash

compared with the use of synchronous toothed belt, the use of gear reduction device in the feed transmission chain of CNC machine tools is more likely to produce low-frequency oscillation, so the reduction mechanism is often equipped with dampers to improve the dynamic performance

2) synchronous toothed belt

synchronous toothed belt transmission is a new type of belt transmission. He uses the tooth shape of the toothed belt to mesh with the teeth of the pulley in turn to transmit motion and power, so it has the advantages of belt transmission, gear transmission and chain transmission. There is no relative sliding, the average transmission is relatively accurate, the transmission accuracy is high, and the toothed belt has high strength, small thickness and light weight, so it can be used for high-speed transmission. The toothed belt does not need special tension, so the load acting on the shaft and bearing is small, and the transmission efficiency is also high. It has been widely used in CNC machine tools. The main numbers and specifications of synchronous toothed belts are as follows:

· pitch pitch P is the distance between two adjacent teeth on the pitch line. Since the strength layer does not change during operation, the center line of the strength layer is specified as the pitch line (neutral layer) of the toothed belt, and the circumference l of the pitch line is taken as the nominal length of the toothed belt

In particular, there are few reports on the influence of grain size on small crack propagation

· modulus modulus is defined as m=p/π, which is a main basis for the calculation of the size of toothed belt

· other parameters other parameters and dimensions of the toothed belt are basically the same as those of the involute rack. The calculation formula of the tooth shape of the toothed belt is different from that of the involute rack, because the pitch of the toothed belt is on the strength layer, not in the global director of marketing and innovation management of Benecke kaliko company under ContiTech group of toothed high school, Dominik Beckman said

the marking method of toothed belt is: modulus × width × Number of teeth, i.e. M × b × z。

III. ball screw nut pair

in order to improve the sensitivity, positioning accuracy and prevent creeping of the feed system, it is necessary to reduce the friction of the CNC machine tool feed system and reduce the difference between static and dynamic friction coefficients. Therefore, ball screw pairs are often used to form linear motion mechanisms that are not too long

the transmission efficiency of ball screw pair is as high as 85%-98%, which is times that of ordinary sliding screw pair. The friction angle of the ball screw pair is less than 1 °, so it is not self-locking. If the ball screw pair drives the lifting movement (such as the lifting of the main axle box or lifting table), there must be a braking device

there is practically no difference between the static and dynamic friction coefficients of ball screws. It can eliminate the reverse clearance and apply preload, which is helpful to improve the positioning accuracy and stiffness. Ball screws are manufactured by specialized factories

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