Application Research of Stepper Motor in NC Reform of CT5235 Lathe

There is a CT5235 vertical lathe at the Yingxiuwan Hydropower Plant Repairing Plant, which is mainly used for the processing tasks of the overcurrent components commissioned by the Yuzixi, Yuda, Yingxiuwan and other power stations. The lathe has a turning diameter of 35 meters and can be used for turning planes, turning circles, limited cones and boring round holes. However, with the need for the transformation of power stations in recent years, irregular surface design often occurs in the overcurrent components. For example, the bottom surface of the turbine is a revolving surface formed by discrete spline curves, and then it is incapable of processing with the machine tool. It is. In order to solve the problem that CT5235 can't process such a surface, the research on numerical control transformation with stepping motor and single chip is now carried out.

1 Selection of stepping motor in numerical control transformation In order to realize the irregular surface of CT5235 vertical lathe, it is necessary to make the tool holder of lathe can carry out the feeding movement in the X and Y directions according to the requirements of numerical control interpolation operation. In order to reduce the cost of retrofitting, it is decided to adopt open-loop control and use a stepping motor as the driving force for the feed motion.

A stepper motor is an actuator that uses an electrical pulse signal to control and convert an electrical pulse signal into a corresponding angular displacement. The angular displacement is proportional to the number of electrical pulses, and its rotational speed is proportional to the electrical pulse frequency. The rotational speed of the motor can be adjusted by changing the pulse frequency. If the windings of some phases remain energized after shutdown, they also have self-locking capability.

The biggest disadvantage of stepper motors is that they are prone to step out. Especially in the case of high load and high speed, out of step is more likely to occur. However, the constant current chopper drive, microstep drive, and ultramicro drive developed in recent years, and their comprehensive application, have greatly improved the high frequency output of the stepper motor, and the low frequency oscillation has been significantly improved, especially in The development of intelligent ultra-micro step drive technology has taken the performance of stepper motors to a new level. It has been widely used. At present, the stepping motor is mainly used for the feed drive of the economical CNC machine tool, and generally adopts an open loop control structure. There are also CNC machine tools driven by stepping motors that use position detection components to form a feedback-compensated drive control structure. In order to improve the precision of machining, the "three-phase six-shot" reactive stepping motor with small step angle is used on the CT5235 vertical car.

1 Stepper motor for feed drive machining rotary surface interpolation method Turbine over-flow components processed on the vertical car, such as the bottom ring flow surface, can be rotated 360 degrees around the axis of the unit by the curve y=f(t) Get the desired surface. The basic principle of processing such a surface can be explained by function integration. From the geometric concept of differential, the integral formula can be used when calculating the area enclosed by the curve of the function y=f(t) from time t=0 to t: if it will be 0 The time of ~t is divided into finite intervals with time interval of At. When At is small enough, the approximation formula can be obtained: the process is approximated by the accumulation of numbers. The geometric meaning is approximated by the sum of a series of tiny rectangles. The area below the function f(t). In the case of digital operations, if At? is taken as the smallest basic unit "1", the above formula is called a rectangular formula, and is simplified to satisfy the accuracy we need if At is sufficiently small. It can be seen that during the processing from the start point to the end point, each coordinate axis is at least one unit time At, and the two accumulators are simultaneously accumulated in the controller in increments. An overflow occurs when the accumulated value exceeds a received date: (1) 4-09~29 coordinate units (pulse equivalent). The overflow pulse drives the servo system to feed a pulse equivalent to get out of a given curve. Therefore, finding "incremental" is the key to solving such surfaces.

Any complex curve can always be regarded as a small straight line or arc. In CNC machining, complex curves can be processed by linear or circular interpolation. For the flow surface of the turbine component, the processing method of the arc is discussed below.

x, y are variables with time t as a parameter.

The two sides of the equation simultaneously derivate the derivative of t, and the feed velocity component of the moving point along the coordinate axis in the first quadrant inverse circle processing can be derived: from equation (5), the velocity components Vx and Vy are the follow-up points. The change of the displacement of the two axes in the feed direction is as follows: the expression in the counterclockwise processing in the first quadrant is: the expression in the clockwise machining of the first quadrant is: the determination of the end point of the arc machining: calculated by The position of the moving point coordinate axis is compared with the end point coordinate of the arc. When a certain coordinate axis reaches the end point, the axis no longer has a feed pulse. When both axes reach the end point, the operation ends.

3 Control the stepping motor motion and the path JZLOOP0 based on the single-chip microcomputer; the control code is 0 (H to ACALLYANS; the delay time subroutine INCR3; the pointer points to the next control code DJNZR2LOOP1; the number of steps is not completed, continue POPBC; the recovery scene is known by the aforementioned analysis, As long as the stepping motor outputs the timing pulse according to the specified control model, the stepping motor can rotate in a certain direction, and the rotation direction and the rotation angle are calculated by the MCU according to the displacement increment, and then the tool holder is driven. The rams are respectively moved according to the above displacement increments. In the numerical control machining, the stepping motor is often required to change the moving direction at any time to meet the needs of machining.

The main task of the stepper motor running control program design is to judge the direction of motion, send out the control pulses in sequence, and judge whether the pulse to be sent is sent. The block diagram is shown in the following. The source code of the MCU assembly language of the motion control is as follows: 4 Conclusion DB01H; Reverse rotation control code DB05H; Stepper is used as the feed drive of the tool holder and ram for controlling the lathe and the MCU is used as the motion controller. Transform the existing CT5235 vertical car to achieve simple CNC. It is only necessary to use the single-chip microcomputer to calculate the "displacement increment" according to the specific geometry, and then control the stepper to control the feed of the tool holder and the ram, and the desired surface can be processed. The modification scheme not only has low cost, but also can satisfy the over-flow surface processing of the turbine with a curved surface, and the modification scheme is simple and feasible.


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