The three-axis multi-function position card is the key hardware for realizing the speed and position control of the numerical control system. It has the following functions: three-axis fully independent servo control, three-axis linear interpolation control, two-axis circular interpolation control, and DDA interpolation time. 2ms to 2s, servo parameter update to 1ms time, can be programmed in C and other advanced languages, direct operation of registers, 2, 4 multiplier setting selection function for counting pulses, built-in F/V converter, output Digital servo function such as voltage 10V (12-bit D/A) and homing. Each axis has a dedicated position chip control that forms a servo position loop and a speed loop. Communication between the location card and the computer takes place via the ISA data and control bus.
In order to keep the axes interlocked, each axis simultaneously transmits a position pulse at time T1 and simultaneously outputs at the time T2. This period of time is defined as the interpolation time or DDA period. The length of the DDA cycle can be set by software.
The location card continuously issues an interrupt with the interpolation time as the cycle, requesting the CPU to place the number of pulses output in the next cycle in the buffer. A continuous pulse train is output to the servo motor drive for a smooth position response. The position card utilizes a position and speed double closed loop control system to ensure smooth and accurate positioning of each axis. It provides two interrupt signals, and the DDA interrupt is an interrupt. An interpolation interrupt occurs, indicating that the next interrupt time begins. An overflow interrupt (OV interrupt) occurs, indicating that the position error feedback count exceeds the threshold. The position card issues an overflow interrupt alarm, indicating that there is a problem with the photoelectric code wheel pulse measurement circuit.
Three-axis multi-function position card DDA interpolation cycle 3 software design This CNC system is designed for each special equipment, and the requirements of each special equipment are different, so the system is mainly to provide users with the underlying software, and the control software is Written for each device. The underlying software mainly has multi-axis linear interpolation control, multi-axis circular interpolation control, DDA interpolation time setting, setting of parameters such as Gain gain of each axis, and programming with Visual and other high-level languages.
The module mainly includes the following sub-modules: finding the origin module; status display module; parameter setting, correction module; instruction interpretation execution module, instruction editing module and task file editing module. These modules are highly independent of each other. In the implementation of the program, each module corresponds to one or more C classes.
(1) Finding the origin of the original sub-module is the reference point of the CNC machine. The accuracy of the origin positioning directly affects the accuracy of the CNC system. Therefore, finding the origin is a very important process. The main function of finding the origin program is to drive each axis back to the mechanical zero position and the zero position of the photoelectric code wheel.
(2) Current state sub-module CNC system software structure relationship diagram The current state module provides the motion state information of each axis of the numerical control system. This module is implemented and managed by a CSTATUSWND class. CSTATUSWND is a derived class of the dialog class CDIALOG in the MFC class. In the corresponding resource window, the prompt information and error information of the running status are displayed. The timely refresh of the status window, using the threading technology under Windows95. In the processing function of the state refresh thread, the system constantly monitors the motion of the CNC system.
(3) Parameter setting and correction sub-module This module consists of two mode dialogs and several corresponding VC classes, enabling the user to modify various parameters. The module uses the tag-type attribute table class CPROPERTYSHEET to implement maintenance and management of multi-dialog pages (multi-parameter parameter sets).
Tabbed attribute table classes are a common form of user interface in Windows-style software systems, including the extensive use of this interface technology in operating systems such as WINDOW95 and Windows NT. Its expression is clear and concise, the user is very convenient to use, and each label property page shares a form, which can effectively streamline and clear the window interface. From the perspective of inheritance, the attribute table class is not derived from the CDIALOG class, but is a direct derived class of the window class CWND, indicating that the attribute table class is the concept of the management mode dialog class. From the compositional structure, a property sheet (CPROPERTRSHEET) consists of one or more property page objects (CPROPERTYPAGE), and the main data exchange work is concentrated in the property page class. These property pages are actually modal dialogs. From the point of view of usage, the creation and management of the property sheet is similar to the dialog class. It is worth noting that in each property sheet, the system automatically sets four common buttons for determining, canceling, applying and helping, which are simple and clear. In addition, customize the property sheet to the wizard mode that you usually see. At this time, it provides browsing and forward and backward sequences for each page. Integrate some parameter classifications into several relatively independent modal dialog classes (such as speed classes, acceleration classes, etc.), and then use a property sheet class to manage these dialog classes. In this way, both in the structure of the program and on the interface, it is very clear.
(4) Instruction Interpretation Execution Submodule This submodule is one of the key parts of the system. The main function is to interpret the machined part file that executes the CNC commands. During the execution of the file, the user can stop, interrupt and continue the operation of the instruction at any time. This sub-module again uses the threading technology of Windows 95. The program opens two threads with multiple events.
Ending the hardware platform using the industrial computer as the robot controller, and using Windows95 as the software platform to develop the numerical control system, this will be a quick and feasible solution. The versatile platform will make the CNC system versatile, compact, versatile and scalable.
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