CN102049717A - Controlling computerized numerical control (CNC) high-quality aspheric surface forming control method and hardware system - Google Patents

Abstract

The invention is a digital control method and a hardware system for realizing high-order aspheric surface forming by tangential method through three-axis linkage based on the principle of speed interpolation. The hardware control system adopts the UMAC controller with multi-axis linkage function, and uses the electronic cam algorithm to obtain accurate time intervals to ensure the synchronization of the three-axis linkage. At the same time, the PVT speed interpolation algorithm is adopted so that the actual processing curve does not have an inflection point at the node. Smooth transition, the position does not overshoot, and the continuous change of the grinding wheel feed speed is maintained at all times between the interpolation nodes, and the moving direction of the grinding wheel is consistent with the tangent direction of the point, thereby forming a high-precision continuous smooth aspheric surface, and finally The processing efficiency of the aspheric surface can be improved and the processing cost can be reduced.

Description

A control method and hardware system for high-order aspheric surfaces formed by numerical control

technical field

The invention relates to a digital control method and a hardware system for realizing high-order aspheric surface forming by tangential method through three-axis linkage based on the principle of speed interpolation.

Background technique

Numerical control technology has been widely used in various control fields, such as aerospace, automobiles, transportation, communications, electronics, positioning and tracking systems, robots, high-precision processing equipment, and assembly lines. In the field of optical parts processing, technologies such as CNC turning, CNC grinding and CNC polishing have been used to process high-precision aspheric optical parts. A variety of CNC machining optical aspheric machine tools have been developed at home and abroad to be applied. At present, the processing efficiency of CNC processing optical aspheric surface technology has been greatly improved compared with the traditional manual processing of aspheric surface technology, but the processing efficiency is still very low. , only suitable for single-piece small-scale production. With the rapid development of the optical industry, the demand for optical aspheric optical parts continues to increase. There is an urgent need for equipment with high processing efficiency and capable of batch and variable batch production of optical aspheric parts.

At present, the main reason for the low processing efficiency of CNC forming optical aspheric machine tools is that the aspheric surface after turning, grinding or polishing always produces small corrugation errors, and it takes a long time to remove such corrugation errors, so the processing efficiency is low. Processing costs are high. The reasons for this situation include the principle of CNC forming, the geometric factors and physical factors of the processing method, etc. The error caused by the NC forming principle is a theoretical error. At present, the NC forming principles of the existing domestic and foreign machine tools for processing aspheric surfaces are all two-axis linkage position interpolation NC principles. This NC forming principle itself has theoretical errors in the formation of surface corrugations. There are three interpolation methods in the position interpolation numerical control principle, namely, pulse incremental interpolation, digital sampling interpolation, and a mixed interpolation method of digital sampling interpolation and pulse incremental interpolation. The trajectory curves obtained according to the above three interpolation methods are all tiny broken lines close to the aspheric trajectory curve given by the optical design. Such a broken line, the smaller the interpolation interval is, the smaller the approximation error, but theoretically it is always a broken line, and the broken line always forms tiny ripples on the entire surface. On the basis of this theoretical micro-ripple, the geometric and physical factors of the ripple will be superimposed, and more complex micro-ripples of different frequency bands will be obtained. Aiming at the above-mentioned status quo, a new control method of high-order aspheric surface for NC forming is proposed to achieve the purpose of eliminating tiny ripples on the forming surface of aspheric surface. The specific control method proposed is based on the three-axis linkage based on the principle of speed interpolation to realize the digital control method of tangential method forming high-order aspheric surface.

Contents of the invention

The purpose of the present invention is to improve the processing efficiency of aspheric optical parts, and propose a three-axis linkage tangent method forming numerical control method based on the principle of speed interpolation. The three-axis CNC linkage of the grinding wheel shaft moving along the X-axis and the grinding wheel shaft moving along the Y-axis, the speed interpolation refers to the single-axis motion in which the motion of each of the three axes is decomposed from the trajectory curve equation given by the optical design The equation rotates at different angles and moves at different distances. The tangent method refers to the fact that the grinding point on the grinding wheel always moves along the tangent direction of each point on the curve.

The three-axis linkage of the speed interpolation principle is realized by using the UMAC controller hardware with multi-axis linkage function. The speed interpolation control of each axis is realized by the PVT speed interpolation method carried by the UMAC controller. Accurate motion control The time is based on the electronic cam algorithm.

v_mxi＝v_mx(i-1)+a_mxiΔt_i，

如果z轴以ω_m匀速旋转，其速度变化规律是一条恒速直线，x轴分段为匀加速运动，速度时间曲线单调上升；y轴为分段匀速运动，速度时间曲线单调下降。通过以上编程计算，最终获得曲线上各节点的位置、速度、加速度、时间以及各变量的单调变化关系。The specific linkage parameters, that is, the processing parameters are to divide the workpiece diameter of the given part equation into N equal parts, and calculate the movement of the grinding wheel axis along the x-axis and y-axis Δx _mi , Δy _mi linear displacement and the grinding wheel axis around the rotation axis Z through the program. Δθ _mi angular displacement of axis rotation. According to the requirements of the processing technology, the rotational angular velocity of the grinding wheel shaft ω _m is given, then the processing time Δt _i can be obtained by the program calculation, where Δt _i = (Δθ _mi ×60)/(ω _m ×2π); t _i =t _{i- 1} +Δt _i , t ₀ =0. Then calculate the speed v _mxi , v _myi and acceleration a _mxi of each split node through program calculation, where

v _mxi = v _mx(i-1) + a _mxi Δt _i ,

If the z-axis rotates at a constant speed _{of ωm} , its speed change law is a constant speed straight line, the x-axis moves at a uniform acceleration in segments, and the speed-time curve monotonically increases; the y-axis moves at a segmented uniform speed, and the speed-time curve monotonically decreases. Through the above programming calculations, the position, velocity, acceleration, time of each node on the curve and the monotonous change relationship of each variable are finally obtained.

The hardware system of the technical solution of the present invention is a UMAC-based tangent method for processing high-order aspheric three-axis linkage speed servo control method, which is characterized in that the control system uses a UMAC-based PC+NC hierarchical structure, adopts zero transmission drive technology and The analog linear drive constitutes a self-controlled variable frequency synchronous motor feed servo system to realize three-axis linkage control. The software design scheme of the control system is composed of upper and lower computers. The software system of the upper computer is designed using the Microsoft Visual C++6.0 development environment. Communication and lower computer motion control adopt UMAC's PVT speed interpolation control method and electronic cam algorithm to realize precise control of the feed speed of the grinding wheel between interpolation nodes, that is, based on UMAC's PVT speed interpolation three-axis linkage servo control method, and finally use The grinding wheel is always located in the tangent direction of the required curve during the processing process.

Through the motion parameters pre-processed by the above-mentioned host computer, the three-axis linkage control is carried out with the PTV speed interpolation of UMAC and the electronic cam algorithm. The PVT control method is based on the controlled trajectory node position (P), speed (V), adjacent nodes These parameters are based on the initial list file generated by the preprocessing calculation results of the host computer. After taking out a set of PVT parameters from this list file, it will automatically walk out of a position according to the motion program. Trajectory curve, and corresponding speed curve and acceleration curve, in addition, you can also set the acceleration time (TA) and motion time (T) to be equal to get the whole acceleration curve. In the motion control process between interpolation nodes, the continuous change of speed is kept consistent with the tangent direction at all times. At the same time, the acceleration and deceleration forward control is adopted in the motion control process. At least 4 nodes must be input for advance calculation, so that the actual processing speed There is no inflection point at the node of the curve, the position curve transitions smoothly, the speed gradually increases or decreases, and the position does not produce overshoot. Finally, a high-precision aspheric surface that requires surface accuracy and continuous smoothness is processed through three-axis linkage. This method is actually based on UMAC's PVT fine interpolation speed servo control method.

The electronic cam algorithm described above, that is, the calculated T value cannot be directly used in the motion control process using PVT, but the electronic cam algorithm of the UMAC motion controller is required. Use an external time base instead of the calculated T value in PVT motion control. When the oscillating axis is used as the time base axis, when it moves to generate n pulses, the x and y axes follow the base axis to move for the time corresponding to n pulses. This kind of time base control is to make the "time" proportional to the distance that the base axis turns, and It is not expressed as a function of "time" through language, so as to complete the coordination and synchronization of three-axis positions and realize high-precision three-axis linkage.

Beneficial effects of the present invention

The invention ensures the synchronization of the three-axis linkage through the electronic cam algorithm. The time base control neither changes the time of the servo cycle nor the dynamic performance of the control system. It only defines the trajectory control as a function of the position of the base axis, so the motion trajectory Nothing has changed. Secondly, the PVT speed interpolation algorithm is adopted, so that the speed curve does not have an inflection point at the node during actual processing, the position curve transitions smoothly, the speed gradually increases or decreases, and the position does not overshoot. During the motion control process between interpolated nodes, Keeping the continuous change of the feed speed of the grinding wheel and consistent with the tangential direction at all times can form a high-precision, continuous and smooth aspheric surface, thereby improving the processing efficiency of the aspheric surface.

Description of drawings

Preferred embodiments of the present invention are described in detail below in conjunction with accompanying drawings, wherein:

Accompanying drawing 1 is the curve trajectory that pulse incremental interpolation principle forms;

Accompanying drawing 2 is the curve locus that data sampling interpolation principle forms;

Accompanying drawing 3 is the curved trajectory that hybrid interpolation principle forms;

Accompanying drawing 4 is pulse incremental interpolation trajectory and grinding wheel forming trajectory;

Accompanying drawing 5 is data sampling interpolation trajectory and grinding wheel forming trajectory;

Accompanying drawing 6 is the schematic diagram of the three-axis linkage control principle of the speed interpolation principle;

Accompanying drawing 7 is θmi, xmi and ymi displacement change relation curve with time ti;

Accompanying drawing 8 is a structural block diagram of the total control system based on UMAC;

Accompanying drawing 9 is the block diagram of three-axis linkage servo system.

Accompanying drawing 1 is to approach the interpolated curve with a unit length straight line segment parallel to the coordinate axis or its composite line segment. Among the figures, 1 is the interpolated curve and 2 is the interpolation track, which is the principle of pulse increment interpolation.

Accompanying drawing 2 is in each interpolation cycle, approximates the interpolated curve with the straight line segment, among the figure 1 is the interpolated curve, 2 is the interpolation trajectory, 3 is the interpolation point, is the digital sampling interpolation principle.

Attached drawing 3 is a mixed interpolation process using the principle of data sampling interpolation and pulse incremental interpolation. In the figure 1 is the interpolated curve, 2 is the straight line segment for rough interpolation, 3 is the rough interpolation point, and 4 is the fine interpolation Complementing points is the principle of mixed interpolation.

Accompanying drawing 4 is the pulse increment interpolation trajectory and the grinding wheel forming trajectory, in which 1 is the outer circle of the grinding wheel, 2 is the forming trajectory, 3 is the interpolation trajectory, and 4 is the workpiece.

Accompanying drawing 5 is the curved trajectory formed by the principle of data sampling interpolation, in which 1 is the outer circle of the grinding wheel, 2 is the forming trajectory, 3 is the interpolation trajectory, and 4 is the workpiece.

Accompanying drawing 6 is a schematic diagram of the three-axis linkage control principle of the speed interpolation principle. In each time period, the grinding wheel shaft moves along the X axis and moves along the Y axis for a certain distance while rotating a certain angle at the center to form a continuous Smooth and high-precision optical design given the aspheric schematic.

Detailed ways

As shown in Figure 1, Figure 2 and Figure 3, the current position interpolation numerical control principle can obtain the principle of the broken line close to the given curve of the optical design. The figure illustrates that the position interpolation numerical control principle cannot obtain a continuous smooth curve trajectory in theory. .

As shown in Figure 4 and Figure 5, on the trajectory formed by the pulse increment interpolation principle and digital sampling interpolation principle with theoretical ripple error, the ripple caused by the geometric factors of the grinding wheel will be superimposed to produce more complex ripples.

As shown in Figure 6, in the method of the present invention, in each time period, the grinding wheel shaft rotates at the center at a certain angle, moves along the X axis, and moves along the Y axis to form a continuous smooth and high-precision optical design. fixed aspheric surface. Figure 6 is a schematic diagram of forming a convex aspheric surface. The forming principle of forming a concave aspheric surface is exactly the same as that of a convex aspheric surface, except that the rotation direction of the grinding wheel shaft is opposite to that of the convex one, and the section of the grinding wheel is arc-shaped.

v_mxi＝v_mx(i-1)+a_mxiΔt_i，

分析得到z轴以ω_m匀速旋转，其速度变化规律是一条恒速直线，x轴做分段匀加速运动，速度时间曲线单调上升；y轴做分段匀速运动，速度时间曲线单调下降。通过以上编程计算，最终获得曲线上各节点的位置、速度、加速度、时间以及各变量的单调变化关系。As shown in Figure 7, with the time t _i as the abscissa, the change law of x _mi is approximately parabolic, the change law of y _mi is approximately linear (determined by the equal division of the y axis), and the change law of θ _mi is approximately linear. . The synthetic trajectory of θ _mi , x _mi , y _mi forms the motion trajectory of the center of the grinding wheel. The specific calculation process is to first divide the workpiece diameter into N equal parts according to the processing parameters, and calculate the linear displacement of the grinding wheel shaft along the x-axis and y-axis Δx _mi , Δy _mi linear displacement and the angular displacement of the grinding wheel around the grinding wheel center Δθ _mi through the program, according to the processing The requirements of the process determine the rotational angular velocity of the grinding wheel shaft ω _m , then the processing time Δt _i can be obtained according to the programming calculation, where Δt _i = (Δθ _mi ×60)/(ω _m ×2π); t _i =t _i-1 +Δt _i , t ₀ =0. Then the velocity v _mxi , v _myi and acceleration a _mxi of each node are calculated by programming, where

v _mxi = v _mx(i-1) + a _mxi Δt _i ,

The analysis shows that the z-axis rotates at a constant speed _{of ωm} , and its speed change law is a constant speed straight line. The x-axis moves at a uniform acceleration in segments, and the velocity-time curve rises monotonously; the y-axis moves at a segmented uniform speed, and the velocity-time curve decreases monotonously. Through the above programming calculations, the position, speed, acceleration, time of each node on the curve and the monotonous change relationship of each variable are finally obtained.

As shown in Figure 8, the principle of speed interpolation is three-axis linkage to realize the tangential method forming high-order aspheric digital control hardware system. The hardware system is a PC+NC hierarchical structure based on UMAC. The upper computer software system uses Microsoft Visual C+ +6.0 development environment for design, PC (host computer) mainly completes human-computer interaction function module design, preprocessing calculation, motion program compilation, upper and lower computer communication and dynamic display, etc., and coordinates and manages the operation of the entire system, etc. Real-time control. NC (UMAC controller) mainly completes real-time control such as trajectory planning, trajectory interpolation, switching value control (PLC), drive control, etc., and forms the functional modules required by the NC system (such as CPU basic card, analog axis interface card, I/O interface card).

As shown in Figure 9, through the preprocessing process of the upper computer, the second is to use the PTV speed interpolation of UMAC and the electronic cam algorithm to carry out the schematic diagram of three-axis linkage control. The PVT control method is based on the controlled trajectory node position (P), speed (V ), the time segment (T) between adjacent nodes and other parameters to realize trajectory motion control, these parameters are based on the initial list file generated by the preprocessing calculation results of the host computer, after taking out a set of PVT parameters from this list file, according to the motion program Automatically walk out a position trajectory curve, and there are corresponding speed curves and acceleration curves corresponding, and the acceleration time (TA) and motion time (T) can be set to be equal to obtain the full acceleration curve (for the x-axis). An example of a program fragment is as follows:

INC; Incremental mode, specify movement with distance

PVT200; enter PVT exercise mode, exercise time 200ms

X100: 1500; Translate 100 units long at the end speed of 1500 units/second

PVT100; enter PVT exercise mode, exercise time 100ms

X500: 3000; Translate 500 units long at the end speed of 3000 units/second

In addition, when using acceleration and deceleration look-ahead control in the motion control process, at least 4 nodes must be input for advance calculation, so that the speed curve does not appear at the node inflection point during actual processing, the position curve transitions smoothly, the speed gradually increases or decreases, and the position does not appear. overshoot. In the process of motion control between interpolation nodes, the continuous change of speed is kept at all times and is consistent with the tangential direction. At the same time, the high-precision UMAC controller also meets the position error requirements, and finally achieves the required surface accuracy and continuous smoothness. high-order aspheric optical components.

Finally, as shown in Figure 9, the electronic cam algorithm is introduced on the basis of the PVT speed interpolation algorithm as the time base of the three-axis linkage. The time base control of the electronic cam is a complex method of synchronous coordination with independent axes. In the design, z The axis is used as the time base axis, and the time base is set through the known processing conditions, and the three-axis synchronous action is completed according to the number of pulses generated by the base axis movement, that is, the base axis rotates to generate n pulses, and the x and y axes follow the base axis to move n The time corresponding to the pulse, because the pulse period of the ultra-precision CNC system is microsecond level, it can meet the setting of the motion time segment during PVT programming. This kind of time base control is to make the "time" proportional to the distance passed by the base axis, rather than expressing it as a function of "time" through language, so as to complete the coordination and synchronization of the three axis positions. Time-base control neither changes the time of the servo cycle nor the dynamic performance of the control system, but defines the trajectory control as a function of the position of the base axis, so the motion trajectory does not change.

Through the comprehensive application of the above methods, the high-order aspheric optical parts that meet the required surface accuracy and are continuous and smooth are finally processed. The method used in this process is the three-axis linkage tangent method control method based on the PVT speed interpolation principle of UMAC.

The above descriptions are preferred embodiments of the present invention, and are not intended to limit the implementation scope of the present invention. All equivalent changes and modifications made according to the scope of the claims of the present invention fall within the protection scope of the present invention.

Claims (5)

1. A three-axis linkage based on the principle of speed interpolation to realize the high-order aspherical digital control method of tangent method forming, which is characterized in that the three-axis linkage refers to the rotation of the grinding wheel shaft with the rotation axis Z axis in the same period of time, grinding The three-axis CNC linkage of the wheel shaft moving along the X-axis and the grinding wheel shaft moving along the Y-axis. The referent speed interpolation means that the movement of each of the three axes is rotated at different angles and moved at different distances by the single-axis motion equation decomposed from the trajectory curve equation given by the optical design. The referent tangent method is on the grinding wheel The grinding point always moves along the tangent to each point on the curve. The three-axis linkage of the speed interpolation principle is realized by using the UMAC controller hardware with multi-axis linkage function. The speed interpolation control of each axis is realized by the PVT speed interpolation method carried by the UMAC controller. Accurate motion control The time is based on the electronic cam algorithm. 2. According to the speed interpolation principle described in claim 1, the parameters required for the three-axis linkage motion control are to divide the workpiece diameter of the given part equation into N equal parts, and calculate the grinding wheel shaft to move Δx along the x-axis and y-axis through the program. _mi , Δy _mi linear displacement and Δθ _mi angular displacement of the grinding wheel shaft rotating around the Z axis of rotation. Given the rotational angular velocity ω _m of the grinding wheel shaft required by the processing technology, then the processing time Δt _i is calculated by the program, where Δt _i =(Δθ _mi ×60)/(ω _m ×2π); t _i =t _i-1 + Δt _i , t ₀ =0. Then calculate the speed v _mxi , v _myi and acceleration a _mxi of each split node through program calculation, where

v _mxi = v _mx(i-1) + a _mxi Δt _i ,

If the z-axis rotates at a constant speed _{of ωm} , its speed change law is a constant speed straight line, the x-axis moves at a uniform acceleration in segments, and the speed-time curve monotonically increases; the y-axis moves at a segmental uniform speed, and the speed-time curve monotonically decreases. Through the above programming calculations, the position, speed, acceleration, time of each node on the curve and the monotonous change relationship of each variable are finally obtained. 3. The digital control method according to claim 1, in order to realize the three-axis linkage tangent method of speed interpolation to process high-order aspheric surfaces, the hardware system of the technical solution of the present invention is a PC+NC hierarchical structure based on UMAC, The zero transmission drive technology and analog linear drive are used to form a self-controlled variable frequency synchronous motor feed servo system to realize three-axis linkage control. The software design scheme of the control system is composed of upper and lower computers. The software system of the upper computer is designed using the Microsoft Visual C++6.0 development environment. Communication and lower computer motion control adopt UMAC's PVT speed interpolation control method and electronic cam algorithm to realize precise control of the feed speed of the grinding wheel between interpolation nodes, that is, based on UMAC's PVT speed interpolation three-axis linkage servo control method, and finally use The grinding wheel is always located in the tangent direction of the required curve during the processing process. 4. PVT speed interpolation control mode as claimed in claim 1 realizes trajectory motion control according to parameters such as controlled trajectory node position (P), speed (V), time segment (T) between adjacent nodes, and these parameters It is an initial list file generated based on the preprocessing calculation results of the host computer. After taking out a set of PVT parameters from this list file, a position trajectory curve is automatically created according to the motion program, and there are corresponding speed curves and acceleration curves. In addition, it can also be Set the Acceleration Time (TA) and Motion Time (T) to be equal to get the full acceleration curve. In the motion control process between interpolation nodes, the continuous change of speed is kept consistent with the tangent direction at all times. At the same time, the acceleration and deceleration forward control is adopted in the motion control process. At least 4 nodes must be input for advance calculation, so that the actual processing speed There is no inflection point at the node of the curve, the position curve transitions smoothly, the speed gradually increases or decreases, and the position does not produce overshoot. Finally, a high-precision aspheric surface that requires surface accuracy and is continuously smooth is processed through three-axis linkage 5. The electronic cam algorithm as claimed in claim 1, that is, the calculated T value cannot be directly used in the motion control process using PVT, but the electronic cam algorithm of the UMAC motion controller needs to be used. Use an external time base instead of the calculated T value in PVT motion control. When the oscillating axis is used as the time base axis, when it moves to generate n pulses, the x and y axes follow the base axis to move for the time corresponding to n pulses. This kind of time base control is to make the "time" proportional to the distance that the base axis turns, and It is not expressed as a function of "time" through language, so as to complete the coordination and synchronization of three-axis positions and realize high-precision three-axis linkage.

Images