Application of the hottest DELTA servo system in C

Application of DELTA servo system in CNC engraving machine

Abstract: Based on the analysis of the automatic processing performance requirements of CNC engraving machine, combined with inertia matching, this paper discusses how to reasonably apply DELTA servo system to CNC engraving machine

key words: CNC engraving machine; inertia; rigidity; DELTA servo

1 introduction

with the launch of China's manufacturing brand construction project, the demand for high-speed and high-precision engraving machines in hardware, advertising products and other industries is increasing day by day. For example, in economically developed East China, the market demand reaches thousands of high-speed and high-precision engraving machines. High speed and high precision engraving machine equipment has increasingly become the application field of CNC (computer digital control) technology

engraving machine is a special processing equipment for the production and processing of advertising and mold products. Due to the frequent market changes of products, the engraving machine requires not only one-time purchase price and initial function, but also the upgrading and application ability of products. Market demand is volatile. Only products with leading technological development ability and appreciation potential can extend the service life of products and expand the scope of use of products

2 CNC engraving machine feeding system

2.1 introduction to feeding system

the company will purchase

cnc engraving machine feeding system. The main task is to move the sliding parts (workbench or driving head, column, etc.) along the guide rail and smoothly at the commanded rate. In addition to the design of mechanical transmission components, the feeding system also involves servo positioning control. Therefore, in essence, the feed system is an electromechanical integrated system, which enables the processing workpiece or tool to move with high precision according to the established speed, position, as shown in Figure 1

Figure 1 control flow chart and system framework

a good CNC engraving machine should have the characteristics of good stability, high precision and fast response. Then, in order to achieve such conditions, the important links to be considered are: inertia matching and rigidity of feeding system

2.2 mechanical inertia and robust (robust) control

transmission inertia has an impact on the accuracy, stability and dynamic response of the servo system. Large inertia, large mechanical constant of the system and slow response will reduce the natural frequency of the system and easily produce resonance, which limits the servo bandwidth and affects the servo accuracy and response speed. Therefore, in the mechanical design, under the condition of not affecting the system stiffness, we should try to reduce the mechanical inertia and pay attention to the inertia matching, so as to select the appropriate inertia motor and obtain the inertia ratio

required torque of feeding system t = system transmission inertia J × angular acceleration θ； The total inertia of the feed shaft J = the rotational inertia of the servo motor JM + the converted load inertia of the motor shaft JL. So how does the inertia of CNC engraving machine feed system match? When the measuring machine automatically calculates the dynamic characteristics of the mechanical system, such as the maximum air force, upper and lower yield strengths, hysteresis ring method, gradual approximation method, non proportional extension strength, tensile strength, compressive strength, constant extension strength at any point, constant load extension at any point, elastic modulus, elongation, maximum value, minimum value, average value, bending modulus, etc. at the end of the test, the smaller the inertia, the better the dynamic characteristic response of the system; The greater the inertia, the greater the load of the motor and the more difficult it is to control, but the inertia of the mechanical system needs to match the inertia of the motor. Different mechanisms have different choices for the inertia matching principle and have different functions. When CNC engraving machine performs high-speed cutting through servo motor, when the load inertia increases, the following situations will occur:

(1) when the control command changes, the motor takes more time to meet the speed requirements of the new command

(2) when the machine table performs arc curve rapid cutting along the two axes, large errors will occur

and 2. Poor activity. Under normal conditions, when JL ≤ 3jm, the above problems will not occur; When JL ≥ 5 × JM, the controllability of the motor will be significantly reduced, especially in high-speed curve cutting. In this regard, DELTA servo introduced robust (robust) control, which can tolerate the large inertia change claimed by PCI company, and the requirement for inertia ratio is greatly reduced

2.3 electromechanical rigidity and robust control

the rigidity of the feed system refers to the ability of the feed system to resist deformation when under load. The rigidity of NC feed system can be divided into mechanical rigidity of mechanical system and servo rigidity of servo system

(1) rigidity of mechanical system. The mechanical rigidity of the feeding system refers to the force required by mechanical components such as screws to produce unit deformation, which reflects the ability of mechanical components to resist deformation. Definition of mechanical (static) rigidity:

k=f/△ x (kgf/um); Where f: force (KGF); △ X: deformation (UM)

(2) servo system rigidity refers to the entire feed servo system, that is, the ability to resist the position deviation caused by load interference from the controller to the workbench. The rigidity of servo system is more important, while DELTA servo adopts robust control, which has outstanding ability to resist the interference of load change

3 DELTA servo system application

DELTA servo is composed of three closed-loop structures, including position outer loop, speed middle loop and current inner loop. See Figure 2. The robust and simple mode of DELTA servo has become the technical feature of delta

Figure 2 DELTA servo three loop structure

3.1 robust control (robust control --robust control)

robust control enables delta CNC to maintain excellent performance in the face of rapidly changing load inertia

robust control is a modern control law that tolerates its own variation. Fix the selected non PI controller to maintain robust stability and performance. In a wide range of load inertia changes, the system still retains excellent performance. There are different compensation controls for command and interference; Excellent damping rigidity and dynamic characteristics at low speed; The stability is fully guaranteed; The overshoot is very small

3.2 high response bandwidth

in view of the contradiction that high gain setting brings high torque but easy to cause oscillation at low speed, and low gain setting will cause motor creep operation, delta CNC uses high sampling rate (>15khz) to obtain high response bandwidth, making low speed have high rigidity and very stable operation effect

3.3 gain debugging of CNC on engraving machine

(1) jog mode. Jog mode is used for on-board commissioning test and preliminary inertia ratio estimation without upper control. See Figure 3

Figure 3 jog inertia test control flow chart

(2) automatic gain mode. The automatic gain mode is used for continuous adjustment, see Figure 4

Figure 4 automatic gain mode control flow chart

(3) manual gain adjustment (position mode) see Figure 5

Figure 5 manual gain adjustment control flow chart

(4) key points for debugging:

· after the feed speed is increased, the tracking error of the servo system will increase with the increase of the speed, affecting the dynamic accuracy of the moving parts (generally, the servo gain of each axis is set to the same size, especially the X and Y axes). The servo setting time of delta is short, and the dynamic accuracy is protected to the greatest extent

· machine components have their natural frequencies. When resonance occurs, noise, vibration and response are limited. Use the software of DELTA servo to confirm the resonance point, set software traps to eliminate mechanical resonance and improve the responsiveness of the machine tool

· choose the appropriate inertia motor, the machine tool and motor inertia match, DELTA servo has robust control, the requirements for inertia matching are greatly reduced, and it has its own inertia estimation function, which saves the complex calculation process

· traditional manual debugging of servo and auxiliary service parameters is highly empirical and difficult to debug to the best state. DELTA servo provides special debugging software, which is not only simple to operate but also has excellent debugging effect

4 conclusion

the current proportion in the CNC engraving machine industry is rising steadily every year. The excellent quality, good stability and powerful control function of the system make DELTA servo system have a wide application prospect in the high-end engraving machine industry. (end)