1. Gear transmission
Gear transmission is a kind of mechanical transmission that is widely used. Almost all kinds of machine tool transmissions have gear transmission. There are two purposes of using gear transmission device in CNC machine tool servo feed system. One is to change the output of high-speed torque servo motors (such as stepper motors, DC and AC servo motors, etc.) to the input of low-speed high-torque actuators; The moment of inertia has a relatively small proportion in the system. In addition, the required motion accuracy can be guaranteed for open-loop systems.
In order to minimize the influence of the tooth side clearance on the machining accuracy of CNC machine tools, structural measures are often taken to reduce or eliminate the space error of the gear pair. For example, the double-plate gear staggered tooth method is used, the center distance of the gear pair is adjusted by using the eccentric sleeve, or the gear backlash is eliminated by the axial gasket adjustment method.
Compared with the use of synchronous toothed belts, the use of gear reduction devices in the feed drive chain of CNC machine tools is more likely to generate low-frequency oscillations. Therefore, dampers are often configured in the reduction mechanism to improve dynamic performance.
2. Timing belt
Synchronous toothed belt drive is a new type of belt drive. It uses the teeth of the toothed belt to mesh with the teeth of the pulley to transmit motion and power, so it has the advantages of belt transmission, gear transmission and chain transmission, and there is no relative slip, the average transmission is relatively accurate, and the transmission precision is high. 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 parameters and specifications of the synchronous toothed belt are as follows:
1) Tooth pitch The tooth pitch p is the distance between two adjacent teeth on the pitch line. Since the length of the tension layer does not change during work, the center line of the tension layer is specified as the pitch line (neutral layer) of the toothed belt, and the perimeter L of the pitch line is used as the nominal length of the toothed belt.
2) Modulus The modulus is defined as m=p/π, which is a main basis for calculating the size of the toothed belt.
3) Other parameters The other parameters and dimensions of the toothed belt are basically the same as those of the involute rack. The calculation formula of the tooth profile of the toothed belt is different from that of the involute rack, because the pitch line of the toothed belt is on the strong layer, not in the middle of the tooth.
The marking method of the toothed belt is: modulus*width*number of teeth, that is, m*b*z.