NC transformation of the hottest XB4450 milling ma

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Numerical control transformation of XB4450 milling machine

1 transformation reason

xb4450 milling machine is a profiling milling machine produced by Kunming Machine Tool Factory. Its basic parameters are: the maximum milling length is 900mm, the maximum milling width is 500mm, and the maximum milling height is 350mm. Due to long-time work, aging equipment and large mechanical transmission deviation, the milling machine has low accuracy and slow speed; Single axis control, complex circuit, cumbersome operation, unstable performance and low efficiency. In order to adapt to the development of modern manufacturing industry and make rational use of resources, the following transformation has been carried out

2 electrical part transformation

the transformed CNC system is composed of internal and external position rings. The internal closed loop is the corner position closed loop, the detection element is the photoelectric coding disk installed on the motor shaft, and the driving device is the AC servo motor (instead of the original thyristor controlled DC motor), thus forming an input of θ i. Output as θ 0. Due to the high resolution of the encoder, digital pulse servo is used for feedback, and double pulse input control is used for some parts, which cultivates new economic growth points and competitive advantages, so it has strong anti-interference ability. The performance of the inner ring is stable. Compared with the open-loop control before the transformation, the rotation accuracy is significantly improved. The external position ring uses a grating ruler with a resolution of 0.05 M as a linear displacement detection element to directly obtain the displacement information of the machine tool workbench in processing. The digital pulse is generated and transmitted to the computer to form a full closed-loop control, so that the positioning accuracy of the machine tool is guaranteed. The driving device of the inner loop angle servo system drives the workbench to move, and the displacement accuracy of the workbench is determined by the linear displacement detection element. The double closed-loop control not only has the position control accuracy of the full closed-loop system, but also has the accuracy stability of the full closed-loop control. (3) the confirmation of the limit position before the experiment effectively ensures the response speed and machining accuracy of the machine tool

1) stability analysis

since the internal corner closed-loop does not contain gap nonlinear links, by reasonably designing the local linear system, it can become a fast servo system without overshoot, and its dynamic characteristics can be approximately expressed as

q0 (s)/qi (s) =kq/(TQS + 1)

where: KQ - corner closed-loop gain

tq - corner closed-loop time constant

although the outer loop of the system contains nonlinear links, However, designing the controller so that

gp (s) =kp/s

where KP - integral link time constant

corrects the system to type I and reasonably selects the system gain, which can avoid the intersection or surrounding of the frequency characteristic curve of the system with the negative inversion curve of the nonlinear link, so as to ensure the stable operation of the system. Obviously, when TQ is small, Q0 (s)/qi (s) =k0, the system will have stronger stability

2) follow error analysis

the above scheme can ensure the stable operation of the system, so the influence of nonlinear factors can be ignored, and the transfer function of the system can be calculated

when the system is designed, the feedback coefficient kf=1, and the feedforward channel

the above formula shows that the double closed-loop system has reasonable dynamic performance and follow accuracy

Mitsubishi PLC is used to deal with complex circuit logic relations, which makes the circuit simple, stable performance and convenient maintenance. In addition, in order to make the machine tool meet the requirements of processing different materials, the spindle uses the frequency converter for stepless speed regulation to ensure that the torque change is small when the spindle speed changes

3 transformation of mechanical part

first, remove the gear box of the carriage in the X, y and Z directions, and the motor directly drives the ball screw through the belt pulley and synchronous belt, thus driving the carriage to move. Therefore, the mechanical structure is simpler and the transmission error is reduced. Next, take the structure in the Z direction as an example to illustrate its new structure. The z-axis motor is installed under the machine tool according to the customer's requirements. The connection method is shown in Figure 2

1. Motor 2, 13 Screw 3 Support seat 4, 9 Nut 5 Timing belt 6, 8 tension sleeve 7 Synchronous gear 10 Bearing 11 Outer spacer 12 Inner spacer 14 Press the flange 15 Ball screw

Figure 2

pulley 7 is fixed on the motor shaft through the tightening sleeve. It drives pulley 8 through the belt, and pulley 8 is fixed with the ball screw through the tightening sleeve (the ball screw adopts the fixed method of one end fixed and one end floating). Driving Z must ensure that the system warms up for more than 20 minutes and moves up and down to the carriage. The tightening sleeve mechanism and cleaning and drying treatment is a new keyless connection developed in recent years, which is easier to ensure accuracy and install than the keyed connection, and its structure and size have been standardized

4 transformation result

according to the customer's feedback, the milling machine after transformation has stable performance and high machining accuracy. The machine tool adopts three-axis linkage, which can automatically process complex mold surfaces and special-shaped workpieces, and has fast calculation speed, good positioning accuracy and high price performance ratio, which meets the needs of modern manufacturing industry. (end)

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