With the flexible inter-task communication capability of the μC/OS II, the message mailbox Mbox is used to transfer print data from the data generation task to the print job. In different tasks, the task that does not need to work temporarily is suspended, and the task that needs to work is resumed, and the fast and precise control of the three-dimensional printing is satisfactorily realized.
0 Preface
3D printing manufacturing is one of the hot technologies in the field of rapid manufacturing in recent years. According to the research of this group, the development of 3D printers using μC/OSII operating system can decompose the various tasks of the printer into different tasks, each task completing a specific task. Some work, from the division of program modules, the task is clear, the level is clear. The key is the synchronization and communication between different tasks. With the flexible inter-task communication capability of the μC/OS II system, it has been carefully designed and debugged to successfully realize the communication between tasks. The coordinated and orderly work of each task enables fast and precise control of 3D printing.
1 Introduction to 3D printing principle and control system
The print head of the 3D printer is fixed at a certain height, the printed parts are placed on the workbench under the print head, the parts are printed layer by layer from the bottom layer, the layer is printed, and the workbench is moved down one layer. Print the previous layer of the part. The up and down movement of the table is called Z-direction movement. It is driven by a motor that controls the Z-direction movement. When printing a part, there are two wire feeding motors, one for feeding the thick wire for the basic skeleton printing and the other for the filament. Used for printing of fine parts of parts. Data processing of 3D printing of parts on a PC computer before printing, the parts are divided into several layers, each layer has a thickness of Δh, and each layer is divided into several closely adjacent hatching lines according to the optimal direction, and the printer prints these sections. line. When printing a certain layer, the movement of the print head is a two-dimensional plane motion. The printing of each line is performed by the X-direction drive motor and the Y-direction drive motor to complete the printing of one line. This prints line by line until all lines of the layer are printed, and the printing of this layer is completed. In this way, a total of five motors of X, Y, and Z directions and two wire feed motors are required for real-time control in order to realize three-dimensional printing. Therefore, 3D printing can be regarded as a five-axis linkage system.
As a result of research on its control system, the CPU of the ARM Cortex M3 with the latest version of the current V7 architecture as the master is a good choice. The STM32F103VE6T from STMicroelectronics based on the ARM Cortex M3 core is used. The MCU is 32-bit, clocked at 72 MHz and contains 512 KB of FLASH flash memory. It can store up to 512 KB of program code with 64 KB. RAM, 8 multi-function timers. The other resources on the chip are abundant, and its speed and resources can well meet the control requirements of 3D printers. Five general-purpose timers are selected as the controllers for the X, Y, and Z direction motion motors and the two wire feed motors, and the timer T6 is selected as the total time timer for each line segment print. After comparing several embedded operating systems, the μC/OS II system with the best real-time performance, the smallest code size and powerful functions was selected. The design, development and debugging of software and hardware systems were completed on the Keil integrated simulation platform.
2 3D printing task division
All work that needs to be done before printing is completed in the initialization section, such as initialization of I/O port, initialization of serial communication, initialization of LCD display, initialization of 6 timers required for print control, initial position of print head OK, printhead warm-up, print mode settings, and more.
The work in the printing process is divided into four user tasks, as shown in Table 1.
Together with two system tasks - the idle task OSIdleTask () and the statistical task OSStatTask (), a total of six tasks run in the system.
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