The latest intelligent position finding CNC system

2022-08-16
  • Detail

As a new type of processing technology, intelligent locating processing technology greatly shortens the production preparation cycle of enterprises, accelerates the speed of products to market, and greatly improves the agility of manufacturing enterprises. In order to make this technology widely used in manufacturing enterprises and further improve the market dynamic response ability of enterprises, it needs to be supported from the equipment and system level. This paper introduces the CNC system in detail

first, basic functional requirements

the main difference between intelligent positioning processing technology and traditional processing technology lies in two points: ① replace passive positioning with active positioning; ② To adapt to the reality of flexible processing instead of forced processing according to the established relationship

this requires that the CNC system is completely different from the traditional way, which is also an important and unique function of the new intelligent position finding CNC system introduced in this paper

according to the actual needs, the new CNC system introduced in this paper should have at least the following basic functions in addition to the functions of the traditional CNC system:

① it can carry out active position finding control, and carry out position finding motion control for the active position finding equipment, including the motion control of tactile and visual measurement systems

② it can automatically generate NC machining instructions according to the position finding information. According to the actual state information of the workpiece in the information flow, it can generate the tool motion path control instructions of the workpiece for this in-line machining through real-time planning, and control the machining equipment to process according to the reality

③ network communication function, because the intelligent numerical control system is only a component of the intelligent position finding processing system, the transmission of information flow between various components or systems needs to have the basic function of network communication, which also requires that the numerical control system must have corresponding network interfaces

II. Architecture

the overall structure of the intelligent position finding CNC system based on CAN bus is shown in Figure 1, which mainly includes drive control module (generating drive control instructions according to the reality of the workpiece), information acquisition module (vision combined with tactile active information acquisition control), network communication module (can bus network communication), information processing module (multi-sensor fusion information processing), etc

Figure 1 overall architecture

III. key links

information acquisition

active information acquisition is the most critical link in intelligent position finding processing technology. It mainly uses macro and micro measurement (vision combined with touch) to achieve rapid and accurate information acquisition. Its block diagram is shown in Figure 2

Figure 2 information acquisition block diagram

for example,

for the visual system, the numerical control system needs simple point operation, analyzes the results measured by the visual system, calculates the displacement difference with the predetermined target, automatically generates control instructions, adjusts the relevant variables of the visual system, controls the workbench to move to a new position, and repeats the visual measurement and control movement process, Until the workpiece position meets the basic requirements of visual measurement, and then carry out the final visual measurement of workpiece pose

for tactile measurement, after knowing the visual macro pose information, under the guidance of measuring point and path planning, drive the workbench to make multi coordinate movement relative to the probe. In the process of movement, the continuous detection link continuously obtains the actual position information of the probe. When the probe touches the surface of the workpiece and makes its switch act to send out sampling pulse signals, the computer samples the continuous motion information fed back by the grating system, obtains the accurate coordinates of the contact point between the probe and the workpiece, and promotes the transaction information

information processing

the function of the information processing system is to process the workpiece information obtained by the visual and tactile system, and then solve the current state of the workpiece in real time, so as to guide the driving system to automatically generate machining control instructions according to the actual situation of the workpiece. Its structural block diagram is shown in Figure 3

Figure 3 structural block diagram of information processing system

the working process is as follows: first, the macro image information of the workpiece from the visual system is processed, and the macro state of the workpiece (the approximate position and posture of the workpiece in the machine coordinate system) is solved through image recognition and fuzzy matching with the tightening of China's waste paper import policy. Then, guided by the macro state information of the workpiece, the micro measurement planning is carried out and the corresponding measurement control instructions are generated. Thirdly, the motion control software in the computer controls the operation of the tactile system according to the control instructions, accurately measures the coordinates of the key points on the workpiece, the regular protection inspection of the electrical control system, and feeds back the measurement results to the tactile information processing module in the system. After the information is processed, the micro state of the workpiece is solved by the micro state solution module with an accurate positioning algorithm. Finally, the actual state of the workpiece in the machine coordinate system is accurately solved by the workpiece state calculation module, which integrates the macro and micro information

drive control

conventional CNC systems need to be programmed offline to generate tool motion paths in advance according to the established state of the workpiece, which cannot meet the requirements of intelligent positioning processing technology to generate tool paths and control tracks in real time according to the actual state of the workpiece. The intelligent position finding CNC system adopts the real-time correction method to realize the basic functional requirements, and its basic structure block diagram is shown in Figure 4

Figure 4 basic structure of the drive control system

this link first preprocesses the part geometry information and processing technology information transmitted by the superior computer through the CAN bus, and maps the elements to be processed on the workpiece from the design space to the actual processing space according to the actual state information of the workpiece (from the information processing system); Then, the cutting path generation module generates the cutting path on the machined element of the workpiece in real time according to the actual state of the workpiece; Further, the tool path calculation module calculates the tool compensation and path interpolation of the cutting path according to the tool information; Finally, according to the desired path of the tool and the feedback information of each coordinate, the position servo control of the coordinate movement is carried out, and the coordinate movement of the machine tool is driven by the servo system to complete the machining of the workpiece

network communication

in this numerical control system, due to the large amount of data exchange of multiple devices, network communication function is required between various devices or multiple numerical control systems. At present, most of the existing CNC systems in the domestic market do not have the connection function. Even if a few products can be connected, they are more limited to Ethernet, map and BITBUS

Due to its strong performance advantages in reliability, real-time, transmission speed, transmission distance, etc., can bus has been applied in network numerical control since the 1990s. In China, our school adopted can bus for network communication earlier, developed a new network numerical control based on CAN bus, and cooperated with enterprises for practical application. Its functional module structure is shown in Figure 5

Figure 5 can bus communication module structure

the communication function of this module is completed by processor 80c188 (embedded microprocessor, 12Mhz) and SJA1000CAN controller. 80c188 and SJA1000 jointly complete the data communication and coordination management between CAN node and PC, which greatly reduces the communication burden of host PC. At the same time, there is 2KB high-speed dual port RAM on the module, which is directly mapped to the memory space of the host in the way of memory mapping, so as to realize the high-speed data exchange between the communication module and the host PC. Dual port RAM can reduce the number of data exchange. In addition, it can not only meet a small amount of data, but also meet the storage of a large amount of data, and enhance the versatility of the communication module

IV. application research

based on the self-developed economic NC system, an intelligent position finding NC system is developed, and the machining experiment is carried out with the domestic skx23-jsj/1632 milling machine as the driving control object

the actual verification results show that the control system can reliably, quickly and accurately measure the actual position and posture of the workpiece on the workbench, and can automatically generate machining control instructions to carry out NC machining control according to the actual state of the workpiece, so as to process products that meet the requirements. (end)

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