Fig. 1 Schematic diagram of a traditional gear processing machine chain
Fig. 2 Schematic diagram of the transmission chain of non-full-function CNC gear machining
Fig. 3 Based on software interpolation gear machine CNC system structure
Traditional gear machining machines have complex movement relationships. For example, gear hobbing machines (or worm gear grinding machines) exist in the gear machine tools, such as the display of degree chains, differential chains, and feed transmission chains, as shown in Fig. 1. Adjustment is complicated and time consuming. The positions and distances for rapid approach, advancement, and retreat must be carefully adjusted or tested to complete, and more accessories are needed. In order to improve the processing precision and machining efficiency of gears, after the 1980s, domestic and foreign companies began to carry out numerical control transformation of gear processing machines and produce CNC gear processing machine tools. Especially in recent years, due to the rapid development of microelectronics technology and the emergence of high-precision, high-speed responsive AC servo systems based on modern control theory, it provides good conditions and opportunities for the development of gear processing CNC systems. We divide the gear processing CNC system into two categories, full-function and non-full-function. 1 The structure of the non-full-function gear processing CNC system The NC axis is used as the feed axis of this type of CNC system, and servo systems are often used. Since the numerical control of gear machining began in the 1980s, the numerical control technology was unable to meet the high synchronization requirements of the component chain of the gear processing machine. Therefore, the component chain and differential chain were still traditional mechanical transmissions (Fig. 2). For example, the YKS3120 gear hobbing machine of Nanjing No. 2 Machine Tool Plant, the YKX3132 hobbing machine of Chongqing Machine Tool Works, and the YK520 gear shaping machine of Tianjin No. 1 Machine Tool Plant are all 2- to 3-axis NC gear machining machines. This kind of numerical control processing method is much more convenient than the mechanical gear processing machine tool. They can realize the processing of the tooth-tooth-shaped gears through the linkage of several coordinate axes, eliminating the need for fixtures and other devices required for conventional machining of the modified gears, improving productivity and machining accuracy. However, this kind of gear processing numerical control system is an economical numerical control system. Because its exhibition component chain and differential chain are still traditional mechanical types, the accuracy of gear processing depends on the precision of the mechanical transmission chain. At present, this kind of gear machining numerical control system is mostly used for the numerical control transformation of the existing mechanical gear processing machine tools. 2 In recent years, full-function gear machining CNC system structure, due to the rapid development of computer technology and the emergence of high-precision, high-speed response servo system, full-function CNC gear processing machine tools have become mainstream products in the international market. Full-featured CNC means that not only the feed motion of each axis of the gear machine tool is numerical control, but also the generative motion and differential motion of the machine tool are numerical control. At present, numerical control methods for the display of the component chain and the differential chain are not the same, and there are two types based on software interpolation and hardware control. Gear interpolation based on software interpolation Numerical control system The tool spindle of this kind of numerical control system is generally controlled by the frequency conversion device. The workpiece spindle is directly driven by the servo motor through the numerical control instruction (Figure 3). At present, the numerical control systems of domestically-made CNC gear processing machines are mostly universal numerical control systems of well-known foreign brands, and thus all of them are based on software-based interpolation. Determine the motion relationship between the tool and the workpiece according to the parameters in the gear machining process. For example, when machining a spur gear on a gear hobbing machine, satisfy: nB = zC nC zB (1) where: nB, nC—are machine tool spindles ( The rotational speed of the B axis and the workpiece spindle (C axis), r/min zB, zC—the number of teeth of the machine tool (number of heads) and the number of teeth of the workpiece gear, respectively, when diagonal gears are processed using the “differential method†When the feed line feeds the cutting teeth, the worm wheel grinding machine deeply cuts the grinding process. The machine tool workpiece spindle and the tool spindle need not only realize the strict development of component gear movement, but also need to complete the Z, Y axis or Z. Additional synthetic movements related to the axis and Y axis feed. The equation of motion is nC = ZB nB ± sinb vZ ± cosl vY ZC pmnZC pmnzC (2) where: vY, vZ - are the moving speeds of the Y and Z axes, respectively, mm/min b, l - respectively The installation angle mn of the gear and tool is the normal module of the gear, mm The advantage of the software-based interpolation method is that the rotational speed of the workpiece spindle is completely controlled by the software of the numerical control system. Therefore, the appropriate software can be used to prepare general-purpose software. The cutters process high-precision and non-circular gears and modified gears with high precision, and the machining accuracy is much higher than that of conventional mechanical cams. For example, the STAR-930E CNC system developed by CIMS Institute of Hefei University of Technology for the Chongqing Machine Tool Plant YK3480CNC non-circular gear hobbing machine is a software interpolation method that successfully realizes high-speed and high-precision hobbing and gear cutting of non-circular gears. At present, because of the control precision, dynamic response and other reasons, the gear processing CNC system based on software interpolation is not yet able to meet the requirements of high-speed and high-precision gear grinding machines. With the continuous improvement of computer speed, the emergence of new control methods and the improvement of control accuracy, the application of this method will become wider and wider.
Figure 4 Based on hardware control gear CNC system structure
Gear control CNC system based on hardware control In the development component chain of the traditional gear machine tool, the tool and the workpiece are dragged by the same motor. The transmission chain is very long, and often it is necessary to use a transmission element (such as a cone) whose accuracy is not easily improved. Gears, universal joints, etc., so the accuracy of the machine is limited. At present, the use of photoelectric disk pulse frequency division drive chain. The grinding wheel spindle rotates at a fixed rotation speed and drives a transmission element (such as a photoelectric disk). After the frequency division of the photoelectric disk signal, the workpiece shaft servo motor is controlled to rotate at a certain rotation speed to achieve an accurate indexing transmission relationship. At the same time, the differential chain of the machine tool is also included in the control system. The system structure is shown in Figure 4. The IPC is responsible for controlling the speed of the tool spindle and the movement of the workpiece feed axes. The workpiece spindle is completely controlled by hardware. The control circuit realizes the indexing and differential motion, that is to realize the formula (2), in which the ratio of the differential coefficient and the display component ratio in the control circuit is adjustable, and is modified by the IPC. During gear cutting, the relationship between the rotary motion of the workpiece, the rotary motion of the tool, and the feed axis is strictly described by formula (2). Convert the rotation speed to the pulse frequency of each axis, substituting the formula (2) to obtain the relationship between the pulse frequencies of each axis as fC = ZBNC fB ± sinbNC fZ ± coslNC fY KBfB + KfNY + KZfZ ZCNB pmnZCNZ pmnzCNY (3) where: NC, NC— —The number of pulses fed back by each axis of B and C axes, NY and NZ, respectively, is the number of pulses fed back by Y and Z axes each moving 1 mm. Formula (3) is implemented by a phase-locked servo system, and its structure is shown in FIG.
Figure 5 Phase-locked servo system
The advantages of gear control CNC system based on hardware control: using hardware control, especially high-precision phase-locked servo control, high accuracy and fast response. Disadvantages: The structure is more complex, and there is one more hardware control circuit than software interpolation. The hardware controlled electronic gear ratio [differential coefficient, main gear ratio, ie the relevant coefficient in formula (3)] cannot be modified in real time, ie, the spindle speed cannot be changed in real time, and thus cannot be used to process non-circular gears Wait. At present, gear control CNC machine tools such as Gleason, Reishauer, Pfauter and other well-known foreign brands have adopted this control system. 3 Conclusions and prospects The non-full-function CNC system is due to the processing accuracy depends on the mechanical transmission chain, there are still exchange hanging wheels, the operation is more complicated, has been less used, is currently used for the transformation of the existing mechanical gear processing machine CNC transformation; based on the software The interpolated gear processing CNC system has the advantages of great flexibility, can be conveniently controlled by programs, can process non-circular gears and various modified gears, and is therefore widely used in gear hobbing machines and gear shaping machines with low machining accuracy; Based on the hardware control of the gear processing CNC system, due to the emergence of the movement is directly using the hardware control, especially when using high-precision tracking servo technology, can well ensure that the gear machine differential and generate movement accuracy, response speed Fast, but with poor flexibility, suitable for grinding machines with high machining accuracy. At present, the fully functional gear processing CNC system is a mainstream product in the world and will also become a mainstream product in China. The development direction of the display component chain of full-function CNC gear processing machine tool is a combination of soft and hard, that is, the electronic gear ratio of the phase-locked servo system can be modified by software in real time, so that the software has the flexibility of interpolation, can process non-circular gears and each The modified gears, in turn, maintain the advantages of hardware-controlled, high-precision speed response. This will be our next research direction.
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