PMAC-based linear motor speed acceleration feedforward control
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Since the conventional "rotary motor + ball screw" servo feed method is difficult to meet the machining accuracy and speed requirements, the precision feed machining method of the linear motor has begun to appear. Although the linear motor is greatly simplified in terms of mechanical structure, there is no intermediate transmission link, the rigidity of the servo system is greatly improved, and the error caused by the intermediate transmission link is also improved, but the corresponding electrical control zone is also provided. Come to a higher demand. How to make full use of computer control technology to achieve precise control of linear AC servo system on the basis of traditional control methods becomes more important and urgent. Based on the above analysis, this paper proposes a PMAC-based linear motor speed/acceleration feedforward control.
The 2PMAC motion controller implements the machine motion control and logic control functions by an independent motion controller. The motion controller usually forms a system in the form of a PC hardware plug-in. The CNC upper-layer software (CNC program editing, man-machine interface, etc.) runs on Windows and other mainstream operating systems based on PC. This has become the mainstream structure mode for the development of open CNC systems.
The PMAC (ProgrammableMutli-axes Con-troller) open multi-axis motion controller is introduced. DELTATAU uses NGC, OMAC and other protocols, and adopts PMAC open CNC system composed of PC plus PMAC controller, which has achieved good application prospects.
PMAC motion controller provides numerical control functions such as motion control, discrete control, housekeeping, and host interaction. It can control 1~8 axes at the same time by Motorola's DSP 56001/56002 digital signal processing chip. Its speed, The resolution, bandwidth and other indicators are far superior to the general controller. The servo control includes PID plus NOTCH and feedforward control such as speed and acceleration. It can even connect to the high-speed ring network of the NACRO field bus to directly control the linkage of the production line.
In general, servo control capabilities can only be measured with operations performed per h or qualified parts produced. Today, product quality requirements exceed productivity requirements, so every part of the system is best when designing the system, and for PMAC motion controllers, regardless of processing power, trajectory characteristics, and input bandwidth characteristics. In terms of performance, its performance is far superior to traditional motion controllers.
In addition, PMAC provides users with greater flexibility, allowing the same control software to run on three different buses (PC-XT and AT, VMESTD), thereby providing multi-platform support features and each axis can be configured to Different servo types and multiple feedback types. It is embodied in the following points.
The servo interface is available in both analog and digital versions and can be connected to different servo systems.
Can be connected to different detection components: tachogenerator, photoelectric encoder, grating, resolver, etc.
The realization of PLC and interface functions: There is a built-in software fund project: the National Natural Science Foundation funded project (59775064) PLC, and can be customized according to user needs.
PMAC can communicate with PCs in serial, parallel and dual-port RAM.
3PMAC-based linear motor speed/acceleration feedforward control linear motor control In the high-precision micro-feed CNC machine servo drive system, due to the relatively high control requirements for linear AC servo motor, some more subtle factors must be considered. System performance requirements, such as system nonlinearity, coupling and load disturbances, noise detection, etc., especially thrust changes caused by end effects, will deteriorate the performance of the servo system, and it is difficult to meet the requirements of high precision micro feed. . Therefore, effective control strategies must be taken to suppress these disturbances, effectively achieving precise and micro feeds, in order to achieve precision and ultra-precision machining.
In the linear AC servo system, traditional control strategies such as PID feedback control and decoupling control have been widely used in AC servo systems. However, in high-performance micro-feeding high-performance applications, it is necessary to take into account the changes in the structure and parameters of the object, the effects of various nonlinearities, changes in the operating environment, and environmental disturbances, etc., in order to obtain satisfactory control results. . Therefore, modern control strategies have received great attention in the research of linear servo motor control. For systems with complex control objects, environments and tasks, it is best to use intelligent control methods. Fuzzy logic control, neural network and expert control are three typical intelligent control strategies.
When the PMAC-based control algorithm adopts various control methods, based on the understanding of the structure of the object model, it is necessary to start from the characteristics of the linear AC servo motor transmission system which is a highly dynamic dynamic system. A very complex control algorithm is implemented during the short dynamic adjustment process. At the same time, it is necessary to deal with the particularity of the different causes of the disturbance, with the correspondingly well-known control strategy. Another important feature of the servo system is its ability to track commands. Ideally, the output can track changes in input commands without delay or overshoot. A successful control strategy must be tailored to the characteristics of the specific object, while meeting the main requirements, while taking into account the tracking ability and anti-interference ability.
In this case, and taking into account the powerful servo control function of PMAC, based on the traditional PID control algorithm, plus the feedforward of speed and acceleration, use speed feedforward to reduce the differential gain or tachogenerator ring. The following error caused by road damping uses acceleration feedforward to compensate for the following error due to inertia, and a notch filter is added to prevent resonance to cancel the resonance. Based on the above analysis, a linear motor speed/acceleration feedforward control based on PMAC is proposed. The algorithm is shown in the figure.
The first position feedback is based on the PMAC linear motor speed/acceleration feedforward control algorithm. In the above control algorithm, the variables represented by each parameter are as follows: IM: integral mode (/*34) Kf speed feedforward gain (/*32) Acceleration gain (/*35)n1: band-stop filter coefficient (/*36)n2: band-stop filter coefficient (/*37); 1: band-pass filter coefficient (/*38); 2: band pass Filter coefficient (/*39).
The performance analysis and parameter adjustment of the control algorithm are in the state of the machine state, and the control loop of the system needs to be adjusted and corrected.
In the entire mechatronic system, the influence of the control loop on the system is enormous. Therefore, when the basic characteristics of the system are determined, the control loop of the system needs to be adjusted, that is, through the adjustment of the servo filter, according to the controlled physical system. The dynamic performance of the servo loop parameters is adjusted and set so that the rigidity of the servo system is good, the system is stable and the tracking error is small.
In the above-mentioned PMAC controller for the linear motor speed/acceleration feedforward control loop algorithm, in the adjustment electric integration system of each parameter, in order to obtain the sharp state characteristics and the influence of the correction on the system, it cannot be ignored. the following. Net describes the parameters and their adjustments in the system. As the P parameter, I*30 is the proportional gain of the system. I*33 as the I parameter is the integral gain in the algorithm; I*31 as the D parameter is the differential gain in the algorithm; /*32 is the speed before Feeding, through which it can reduce the following error caused by the introduction of differential. For specific adjustment, I*32 should be equal to or slightly larger than I*31 for the current loop, and I*32 should be much larger than I*31 for the speed loop. ; / * 35 is the acceleration feedforward, which reduces the following error caused by the inertia of the system, especially when the reaction lag is particularly obvious, I * 35 should be increased; * 34 is the integral mode, through which the integral gain is determined Valid or valid when the control speed is zero. In the adjustment, when I*34 is 0, the integral gain is valid all the time. When I* plus the appropriate speed feedforward, the speed parabolic motion conclusion follows the demand of modern production for small batches and personalized products, high speed and super high speed. Precision machining is becoming more and more important. As a new type of linear drive technology, the precise control of linear AC servo system is receiving more and more attention and attention. Based on PMAC, the speed/acceleration feedforward control of linear motor is used, and the feedforward control of speed and acceleration is utilized. The following error is compensated well by the motor damping circuit and inertia, so that the performance of the system is greatly improved. When the value is further increased by 34, the integral gain is only effective when the control speed is zero. When the speed feedforward I*32 is too large, it will bring too much following error. In the actual adjustment, it should be made slightly larger than or equal to the differential gain I*31. At the same time, proper acceleration feedforward will make the performance of the motor better. The speed/following error plot after increasing the appropriate speed feedforward and acceleration feedforward is shown. It can be seen from the figure that the correlation between the following error and the speed is weakened due to the introduction of suitable speed feedforward and acceleration feedforward, and the following error is also greatly reduced, so that the control performance of the whole system is improved. Great improvement.
The accuracy of the electromechanical system of the parabolic motion diagram after the appropriate acceleration feedforward is added.