1 Present situation of feeding system of CNC punch press
1. 1 Type of existing feeding system
The feed system of CNC punching machine belongs to mechatronics products, including mechanical part, control part, power supply, detection part and execution element. According to the structure of the control system and the controller, the existing automatic feeding system can be roughly divided into the following categories:
1) special numerical control system. There are CNC systems such as Fanuc and Siemens abroad; Domestic products are Wuhan, Central China and guangzhou cnc. The special numerical control system has the advantages of high control precision, strong programming ability, high system reliability and multi-functions. But for the punching machine, because it is point-to-point control, the control is relatively simple. If you choose a special system with high cost, it is undoubtedly a waste of resources, and its control may not have an advantage for the feeding device with specific significance.
2) Relay control. The obvious feature of relay logic control is low cost, but it also has obvious shortcomings, because in modern production equipment, there are often a large number of control devices for switching value, digitizer, pulse value and analog value, such as the start and stop of motor, the opening and closing of solenoid valve, and the counting of products. This control scheme has complex connection, large volume and high power consumption. Once the system is built, it is difficult to change or add functions. In addition, the number of relay contacts is limited, and the flexibility and expansibility are poor. Secondly, in terms of control speed, the relay control logic relies on the mechanical action of the contact to realize control, which has low working frequency, slow natural control speed, jitter of the mechanical contact and unstable work.
3) Single chip microcomputer control. Single-chip microcomputer has the advantages of simple structure, convenient use and low price. Better at data calculation and data processing, generally more widely used in data acquisition and central control room control, completely controlled by single chip microcomputer. In particular, the sports console is also directly controlled by a single chip microcomputer. In this way, the load of single chip microcomputer is particularly heavy. In addition, the electromagnetic field in the industrial field is equal to the interference signal, which will cause strong interference to the single chip microcomputer. Therefore, it is also a problem that we have to consider to use single chip microcomputer to win and enter the field control for anti-interference processing.
4) PLC control. This is also the commonly used control mode of automatic feeding system at present, with simple scheme, wide range of hardware selection, easy software programming and generally no serious problems in debugging. However, this scheme also has some inevitable shortcomings, such as relatively poor flexibility, it is difficult to choose a system that is completely consistent with the application for a specific application, which often wastes system resources, and in some special applications, some technical details are difficult to achieve.
1.2 actuator
In the existing automatic feeding system, stepping motors are widely used as driving actuators. The open-loop numerical control system composed of stepping motor and driving circuit is simple, cheap and very reliable. However, the stepping motor can not directly use AC power supply and DC power supply, and its own noise and vibration are large, and its ability with inertial load is poor. Moreover, there are oscillation and out-of-step phenomena, and the control accuracy is not high. If it is not properly controlled, it is easy to produce * * * vibration, and it is difficult to run to a higher speed.
2. Improvement plan
With the development of China's stamping industry, the performance of stamping equipment is in line with the world, and the automation of stamping production is further improved, which puts forward higher and higher requirements for the feeding technology of stamping production to meet the matching with stamping equipment.
2. 1 embedded CNC punch vibration system
Aiming at some shortcomings of the current automatic feeding system, an embedded CNC punch feeding system based on ARM is proposed. Generally speaking, embedded computer systems have the following advantages:
1) specificity. Embedded systems are usually application-oriented, so embedded CPUs are mostly designed for specific user groups, and usually have the characteristics of low power consumption, small size and high integration.
2) Real-time response. According to the definition of embedded system, it is used in the core process of a technological process to meet the time limit requirements of the technological process, and naturally has the characteristics of real-time processing.
3) Solid and reliable. The users of embedded products are mostly non-computer professionals, and the environmental conditions are harsh. Its robustness and reliability are the necessary conditions for this kind of products.
2.2 Selection of servo motor
The system uses linear motor to drive X-axis and Y-axis feed. In the machine tool feeding system, the biggest difference between the linear motor and the original rotary motor drive is that all mechanical intermediate links from the motor to the workbench (carriage) are cancelled, and the length of the machine tool feeding transmission chain is shortened to zero (this transmission mode is called "zero transmission"). This "zero-drive" mode brings performance indicators and advantages that the original rotating motor drive mode can't achieve.
1) high-speed response. Because some mechanical transmission parts (such as lead screws) with large response time constants are directly cancelled in the system, the dynamic response performance of the whole closed-loop control system is greatly improved, and the response is extremely sensitive and fast.
2) high accuracy. The linear drive system counteracts the transmission gap and error caused by mechanical mechanisms such as lead screw, and reduces the tracking error caused by the lag of the transmission system in interpolation movement. Through the feedback control of linear position detection, the positioning accuracy of machine tools can be greatly improved.
3) High transmission rigidity. Due to the adoption of "direct drive", the phenomenon of motion lag caused by elastic deformation, friction and wear and reverse clearance of the intermediate transmission link during starting, speed change and commutation is avoided, and the transmission stiffness is also improved.
4) Fast speed and short acceleration and deceleration process. When the linear motor is used to drive the machine tool, it is not the same problem to meet the maximum feed speed (60- 100 m/min or higher) of its ultra-high speed leopard cutting. Due to the high-speed responsiveness of the above-mentioned "zero drive", the acceleration and deceleration process is greatly shortened, and the high speed can be reached at the moment of starting, and the high-speed operation can be stopped at the moment. Higher acceleration can be obtained, generally reaching 2- 10g. Generally, the maximum acceleration of ball screw drive is only 0.1-0.5g. ..
5) The stroke length is not limited. The linear motor is connected in series on the guide rail, and the stroke length can be extended indefinitely.
6) Quiet exercise and low noise. Because the mechanical friction of transmission screw and other parts is cancelled, the guide rail can be a rolling guide rail or a magnetic pad suspension guide rail (without mechanical contact), so the noise will be greatly reduced during movement.
7) High efficiency. Because there is no intermediate transmission link, the energy loss caused by mechanical friction is eliminated and the transmission efficiency is greatly improved.
2.3 Series Pure Hardware Design
The hardware structure block diagram of the improved system is shown in Figure L. The upper computer is a PC, which communicates with the lower computer ARM through serial port, and the lower computer controls the touch screen and linear motor.
The control part adopts the microprocessor S3C24 10 with low cost, high performance and low power consumption as the core controller. It is a 32-bit RISC architecture processor with low cost, high performance and low power consumption. Its main frequency is 200MHz, including 1 LCD controller (supporting STN and' rFT LCD with touch screen), SDRAM controller, 3 channels of ART, 4 channels of DMA, 4 timers with PWM function, 1 internal clock and 8 channels of 65438+. S3C24J O quotient integration simplifies the hardware design of the application system and improves the reliability and stability of the application system. The operation part uses the touch screen as the operation unit, with intuitive and convenient human-computer interaction, friendly interface and simple operation, which realizes the automatic, manual, start and stop operations of feeding and the setting of some system parameters. In the moving part, the DDL series coreless linear servo motor of Kollmorgen Company is selected for the X axis and Y axis. The motor stator adopts U-shaped structure, and the rotor adopts coreless design. The linear motor has simple structure, safe and reliable operation, and omits the middle mechanical link, so the positioning accuracy is high. The grating ruler is selected as the position detection element, which has high detection accuracy. The whole system adopts closed-loop control, which greatly improves the system accuracy.
2.4 System software design
System software mainly includes upper computer software and lower computer software, as shown in Figure 2. The upper computer software is mainly responsible for the generation and translation of NC codes and the communication with lower computers and other PCs. The lower computer software mainly includes five modules: basic control module, data communication module, motion control module, human-computer interaction module and transaction processing module.
In the whole software system, the lower computer software is the core of the whole system. We chose the Linux real-time operating system with open source code, good portability and easy learning as software operating environment, completed the management and scheduling of five task modules, and combined with the hardware equipment of the system to realize the function of the feeding system. The basic control module manages some basic operations of the system, including the management of device drivers and the management of system hardware initialization settings. The data communication module is responsible for data receiving and proper data processing; Motion control module includes interpolation operation, motor acceleration and deceleration control and position control, which is the core of system control. Man-machine interaction module includes LCD display and touch screen input. The interface design of this paper adopts Qt/Embedded. Qt-based embedded graphics library development tool is a graphics library framework between user application and kernel. In order to ensure the integrity of the system, a transaction processing module is set up to manage alarms and some abnormal transactions.
The communication and scheduling among the five modules are completed under the management of the operating system. Each module is defined as a specific task in the system, usually called thread mode or process mode. The function of embedded operating system is to decide which process the system should run at a certain moment. There are three states of a process in a general system: running state, ready state and waiting state. Switching between these states is accomplished through the message mechanism provided by the operating system, such as mailbox, semaphore, message queue, etc. There is no other coupling between modules. If it is necessary to increase or decrease system functions, the system can be multifunctional and diversified by adding or deleting modules in the corresponding tasks, thus making the system open and extensible.
3 Conclusion
In this paper, the present situation of the existing feed system of CNC punch is analyzed from two aspects: controller and servo drive, and an embedded system scheme based on ARM is put forward in view of the shortcomings of these feed systems. Linear motor is used as X and Y axis control motor, which saves human resources and raw materials, improves reliability, and greatly improves control accuracy and modernization.