Flexible acceleration and deceleration control of

2022-08-18
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NC machine tool flexible acceleration and deceleration control

in view of the demand for the rapid development of NC machining, a new flexible acceleration and deceleration control method is proposed. This method can automatically accelerate and decelerate the movement of the machine tool according to any acceleration and deceleration curve given by the user or the acceleration and deceleration curve dynamically generated by the system, providing a new way to obtain the best dynamic characteristics of the machine tool

NC machining is developing towards high speed and efficiency. In high-speed machining, on the one hand, because the feed speed is very fast, in order to make full use of the effective working stroke of the machine tool (generally only a few hundred millimeters), it is necessary to require that the coordinate moving parts can reach the given speed in a very short time and stop instantly in the high-speed stroke. On the other hand, because the cutting time of high-speed machining is shortened, the tool change interval is shortened, and the machine tool motion starts and stops frequently, it will also be of great significance to shorten the transition time of the start and stop of moving parts. The above two requirements come down to one point, that is, the machine tool motion is required to have a very short acceleration and deceleration transition process. However, if we only consider shortening the transition process in terms of time and do not reasonably control the acceleration and deceleration dynamic process of the machine tool, it will certainly bring a great impact to the structure of the machine tool. The light one will make it difficult to be convenient and cheap, which is an important reason to buy plastic bags. It will work normally, and the heavy one will damage machine tool parts. Therefore, how to realize the optimal acceleration and deceleration control law with the shortest transition time as the goal, so that the machine tool has excellent acceleration and deceleration characteristics that meet the requirements of high-speed machining, has become one of the key problems to be solved in the research and development of modern CNC system

in order to solve this problem, on the one hand, the CNC system is required to dynamically determine the acceleration and deceleration control law (that is, dynamically select or generate the acceleration and deceleration curve suitable for the specific situation) according to the machine and time. On the other hand, special methods should be used in the control system to realize this dynamic law (variable acceleration and deceleration curves). Obviously, the fixed acceleration and deceleration control method used in the traditional CNC system can not meet this requirement. Therefore, according to the idea of open structure control, this paper proposes a method that can automatically accelerate and decelerate the movement of CNC machine tools according to any curve. This method pushes the automatic acceleration and deceleration control from the traditional fixed mode to the new flexible mode, and explores a new way to effectively improve the dynamic performance of CNC machine tools

1. Basic idea of flexible acceleration and deceleration control

in traditional CNC systems, the scope of application of the system is generally: the program directly realizes the specific (such as straight line, exponential curve, etc.) automatic acceleration and deceleration control function. In this way, to make a big change to the acceleration and deceleration characteristics of the system or add a new acceleration and deceleration control law, the NC system program must be modified, so ordinary users cannot make the NC machine tool have the best acceleration and deceleration performance according to their own wishes. On the contrary, the flexible acceleration and deceleration control method proposed in this paper adopts the principle of database, divides the acceleration and deceleration control into two parts: acceleration and deceleration description and implementation, and separates the acceleration and deceleration description from the system program. In this way, if you want to change the acceleration and deceleration control law of the system, you only need to modify the acceleration and deceleration description data independently, without modifying the NC system program, so as to provide users with a new method that can easily change the acceleration and deceleration performance of the system according to their own actual situation. Under this new control mode, the automatic acceleration and deceleration control function of the CNC system will be highly flexible and fully open to users

in order to make the calculation and control process of acceleration and deceleration independent of the shape of acceleration and deceleration curve, this paper uses the form of real-time database to store the acceleration and deceleration curve independently. That is, the given acceleration and deceleration curves or the automatically generated acceleration and deceleration curves are digitized to obtain their discrete forms, which are dynamically stored in the acceleration and deceleration curve Library in the form of a digital table. In the numerical control system software, a general control channel independent of the acceleration and deceleration database content (curve shape) is designed, which can independently complete the acceleration and deceleration calculation and trajectory control. It is difficult to achieve tissue regeneration, implant compatibility and implant manufacturing by this method. The principle is shown in Figure 1

Figure 1 Schematic diagram of flexible acceleration and deceleration control

in the figure, the acceleration and deceleration curves given by the user or automatically generated by the system are stored in the acceleration and deceleration curve library. When the system is running, firstly, the acceleration and deceleration analysis is carried out according to the relevant control data given by the data processing module and the actual motion data of the machine tool from the detection feedback link. If acceleration and deceleration control is required, inform the curve selection module to select the most appropriate acceleration and deceleration curve from the acceleration and deceleration curve library, and send the acceleration and deceleration control command to the acceleration and deceleration calculation module, which calculates the instantaneous speed of the current sampling period according to the selected acceleration and deceleration curve. Further, the interpolation trajectory calculation module generates the tool motion trajectory, and sends the tool motion command to the driving device. Finally, the driving device drives the moving parts of the machine tool with the desired acceleration and deceleration control law, so as to optimize the dynamic characteristics of the machine tool motion

the implementation process of automatic acceleration and deceleration in this environment is discussed in detail below

2. Flexible automatic acceleration control

set the given acceleration curve (analytical curve or non analytical curve) as shown in Figure 2. Now it is stored in the acceleration and deceleration curve library as a sample in the form of a number table. In the figure, FD is the total change of feed speed in the acceleration process (hereinafter referred to as the template speed difference), and TD is the time required for the acceleration process (template acceleration time). The process of realizing automatic acceleration control according to the acceleration curve table is as follows:

Figure