Experimental study on linear feed unit of the hott

2022-07-27
  • Detail

The rapid development of modern aviation, aerospace and automobile manufacturing industry has put forward higher requirements for manufacturing accuracy and processing efficiency. In order to realize high-precision and high-efficiency machining, developed industrial countries such as the United States, Japan and Germany have made great progress in the research and development of high-speed CNC machine tools in recent years, which has made great progress in the research and development of high-speed CNC machine tools and made rapid development in high-speed CNC machining technology. Among them, the research of high-speed linear feed unit is one of the key technologies to realize high-speed machining

the traditional NC machine tool has a long transmission chain due to the feed mode of rotary servo motor + ball screw, which makes it difficult to improve the acceleration and deceleration of the feed system. For decades, its maximum acceleration and deceleration have remained at the level of 0.1 ~ 0.2g (g=9.8m/s2). Due to the short feed distance of the machine tool, the acceleration must decelerate before reaching the maximum feed speed, which limits the increase of the maximum feed speed of the machine tool and is difficult to meet the requirements of the development of modern high-speed machine tools

The development of high-power linear motor and advanced frequency conversion control technology provide favorable conditions for the development of high-speed feed system. The worktable directly driven by linear motor not only eliminates the intermediate transmission link and enhances the transmission efficiency, but also greatly improves the speed and acceleration of the feed system, which can better meet the development requirements of high-speed machining

1 gd-4 high-speed linear feed unit

gd-3 high-speed linear feed unit is directly driven by induction linear motor. The system structure is shown in Figure 1 to help solve the above problems. The system adopts the structure of dynamic primary, fixed secondary, short primary and long secondary, in which the primary is connected to the mounting surface of the workbench through the cooling plate, while the secondary is laid on the bed through the cooling plate in series. When three-phase alternating current is connected to the primary, traveling wave magnetic field will be generated, cutting the secondary, causing the secondary to generate induced potential, so as to form induced current in the closed circuit of the secondary. The secondary induced current interacts with the primary alternating magnetic field to generate electromagnetic thrust, resulting in relative motion between the primary and secondary. The velocity of motion is proportional to the velocity of traveling wave magnetic field. The high-speed linear feed movement of the worktable can be realized by using frequency conversion speed regulation technology and changing the speed of the motor by adjusting the power frequency

1. Cable drag chain 2 Grating ruler 3 Workbench 4 Elementary 5 Primary cooling plate 6 Bed 7 Linear guide rail 8 Secondary 9 Secondary cooling plate

Figure 1 structure diagram of linear feed unit

in gd-3 linear feed unit, the maximum feed speed of linear motor is 100m/min, the maximum starting thrust is 4550n, the rated thrust is 2000N, and the rated power is 8kw. The system adopts grating measurement feedback device to carry out closed-loop control on the feed unit, and the resolution of grating is 3 μ m. The control system structure is shown in Figure 2

Figure 2 control system diagram of linear motor feed unit

it can be seen from Figure 2 that gd-3 linear feed unit adopts full digital control system. The control system is mainly composed of frequency converter, drive computer and SERCOS interface. The main function of the frequency converter is to control the running speed of the linear feed unit by changing the frequency of the power supply. The main function of the driving computer is to transmit control commands, receive the speed and displacement information fed back by the displacement measurement system and the current and magnetic field information fed back by the motor test system, and realize the closed-loop control of the feeding unit. Through SERCOS interface, the control system can realize position adjustment, speed adjustment and force adjustment with and without hysteresis for nearly two years, so that the feed unit can obtain high positioning accuracy, high stiffness and good dynamic characteristics. In high-speed machining, the linear feed unit can obtain high machining accuracy and surface quality through precise interpolation and micro feed. At the same time, the control system can also directly display the startup and fault diagnosis information of the feed unit on the NC terminal, so as to timely understand the processing information, eliminate system faults and ensure the efficient operation of the high-speed machine tool

therefore, compared with the traditional "rotary servo motor + ball screw" feeding mode of NC machine tools, this new linear feeding unit has the following characteristics:

· it is directly driven by linear motor. All intermediate mechanical transmission is omitted, and the mechanical friction loss and transmission error are fundamentally reduced

· unlimited feed stroke

· high dynamic and static stiffness

· high speed and acceleration

· high control performance and High KV factor

· stepless speed regulation can be realized by using variable frequency speed regulation technology

· small trajectory error, and good positioning accuracy can be obtained at high speed

2 experimental study

this experiment takes gd-3 linear feed unit as the research object, and the maximum allowable working stroke of the feed unit is 750mm. The feeding unit is tested and analyzed by CNC programming. The NC program is as follows:

g90 G18 g54

...

g01 x600 f10000/f60000

g04 f1.0

g01 x0 f10000/f60000

g04 f1.0

ret

g74 x0 f10000/f60000

rts

when the theoretical feed speed is set to 10m/min and the working stroke is set to 600mm, the speed and acceleration of the continuous circulating feed unit are tested and analyzed in real time. The results are shown in Figure 3

Fig. 3 acceleration and speed signal when the feed speed is 10m/min

it can be seen from Fig. 3 that the maximum feed acceleration of the feed unit is 2.7m/s2, and the maximum green plastic new materials are increasingly widely used in the construction market. The deceleration is -2.7m/s2, and the speed curve is trapezoidal. The maximum instantaneous speed is 12.5m/min, the maximum overshoot is 25%, and the acceleration time is 0.08s. In the stable state, the feed speed is 10m/min, which is consistent with the set theoretical feed speed

when the theoretical feed speed is set to 60m/min and the working stroke is set to 600mm, the speed and acceleration of the feed unit in continuous circular motion are tested, and the results are shown in Figure 4

Fig. 4 acceleration and speed signal when the feed speed is 60m/min

it can be seen from Fig. 4 that under the condition of high-speed feed, the maximum feed acceleration is 15m/s2 and the maximum feed deceleration is -15m/s2. The speed curve is similar to Fig. 3 and also presents the characteristics of trapezoidal curve. The instantaneous maximum feed speed is 75m/min, the overshoot is 25% and the response time is 0.08s. Under the stable state, The speed of the feed unit is 60m/min, which is consistent with the theoretically set feed speed. Therefore, it shows that the gd-3 high-speed linear feed unit has high acceleration, deceleration and good response characteristics

according to Fig. 3 and Fig. 4, the feed unit has good stability in the process of movement without oscillation. At the same time, the feed unit has good repeatability in the process of circular movement, avoiding the defect of poor repeatability in the traditional feed system due to the existence of reverse clearance. Therefore, gd-3 linear feed unit can not only obtain high feed acceleration and deceleration, but also obtain good repeat positioning accuracy, which can better meet the requirements of high-speed NC machining

3 conclusion

gd-3 high-speed linear feed unit adopts linear motor to directly drive the worktable, has shorter transmission chain and smaller mechanical wear, eliminates the reverse clearance, and can obtain higher repeated positioning accuracy

the linear feed unit adopts frequency conversion speed regulation and digital control technology, which can realize stepless speed regulation with good controllability. It not only has good low-speed characteristics, but also can obtain 15m/s2 acceleration and -15m/s2 deceleration under high-speed operation conditions, which can better meet the needs of high-speed processing

author unit: Guangdong University of Technology (end)

Copyright © 2011 JIN SHI