Based on the analysis of traditional sandblasting glass processing techniques, and combined with computer graphics imaging principles, this paper utilizes computer numerical control (CNC) technology to automate sandblasting glass engraving, providing a new technical method for the production of sandblasted glass products. The paper details the technical principles of CNC sandblasting glass processing, presents a preliminary design of the machine's overall structure and the hardware and software structure of the CNC system, and illustrates the practical processing application effects of this technology. 1. Introduction Sandblasting glass products combine the practicality and artistry of glass, are simple to process, inexpensive, and possess high artistic decorative value. They are widely used in various industries such as interior architectural decoration, arts and crafts, furniture, signage, lighting, advertising, gardening, and glassware. For many years, this method of mechanically processing decorative glass products, primarily based on manual operation, remains one of the most popular surface treatment technologies in various cold-working processes for decorative glass. Currently, computer numerical control (CNC) technology, computer graphics, image processing technology, and mechatronics technology have been highly developed and widely applied. This article introduces the author's innovative design and development of a sandblasting glass engraving machine system based on PC computer numerical control technology. It attempts to combine traditional glass sandblasting methods with computer numerical control technology, providing a new technology for the digital and automated production of sandblasted glass products. The article also presents some key technologies and implementation methods for this system. 2. Analysis of Traditional Sandblasting Glass Processing Methods Traditional sandblasting uses compressed air nozzles to spray fine particles of quartz sand or corundum, forming a high-speed jet of mixed abrasive gas that impacts and etches the workpiece surface, thus removing material. This is a special mechanical processing method, particularly suitable for decorative processing of hard and brittle materials such as glass and stone. Sandblasting glass engraving is based on traditional sandblasting. A nozzle is used to spray fine abrasive particles at a directional, high-speed airflow onto the glass surface, causing intersecting micro-cracks that peel off in small, shell-like patterns, resulting in an opaque or semi-transparent matte surface. Because the matte surface scatters light, different roughness levels result in different light scattering effects, creating layered, three-dimensional artistic patterns and text on the glass surface. The traditional processing method for sandblasted glass involves the following steps: First, a mask (adhesive paper) is manually applied to the surface of the glass product. Then, referring to a sample image (or design pattern), the engraving pattern is traced onto the mask with a pencil. Next, a knife is used to carve out the design according to the traced pattern. Finally, the glass product with the mask attached is placed in a sealed container, and a handheld spray gun connected to compressed air and abrasive pipes is used for sandblasting. This process creates a rougher, frosted glass surface in the areas where the mask is cut out, while the areas protected by the mask retain the original gloss and transparency of the glass. Analysis of this traditional sandblasting method reveals that the patterns, text, and markings on the surface of sandblasted glass are composed of a rough, frosted glass surface and a glossy, transparent glass surface. From a digital imaging perspective, these rough, opaque, or semi-transparent frosted glass surfaces, with varying degrees of roughness, are essentially a series of dense pixel arrays created by the impact and etching of high-speed abrasive particles. Therefore, glass art patterns engraved using traditional sandblasting techniques are similar in imaging principle to ordinary black and white photographs and black and white images printed on paper by computer dot matrix printers; both are two-dimensional planar images represented by a dense dot matrix. 3. Principles and Process Planning of CNC Sandblasting Technology for Glass 3.1 Principles of CNC Sandblasting Technology for Glass As we know from computer graphics, an image is a two-dimensional matrix composed of graphic elements, namely pixels. An image is composed of many pixels, each containing information reflecting the brightness and color changes of the image at that point. In MS Windows, this type of image is called a "bitmap," and any character or complex graphic can be considered as a bitmap image composed of a set of points. Therefore, characters and graphics of various sizes can be composed of pixel dot matrices. [IMG=Figure 1 Correspondence between pixel array and engraving nozzle, image data byte]/uploadpic/THESIS/2007/11/2007111411365029233O.jpg[/IMG] Figure 1 Correspondence between pixel array and engraving nozzle, image data byte [IMG=Figure 2 Schematic diagram of CNC sand carving glass engraving machine structure layout]/uploadpic/THESIS/2007/11/2007111411401187462I.jpg[/IMG] Figure 2 Schematic diagram of CNC sand carving glass engraving machine structure layout The CNC sand carving glass engraving machine adopts a two-dimensional mechanical motion mechanism equipped with a pneumatic abrasive jet engraving head device. The jet engraving head has 8 nozzles, which are arranged in a straight line at even intervals. The opening and closing working state of each nozzle is controlled by a pneumatic solenoid valve. The eight nozzles on the engraving nozzle correspond to the coordinates of eight pixels, and the on/off state of each nozzle corresponds to the brightness information of the corresponding pixel. Based on the principle of forming an image by scanning a pixel matrix, image processing technology is first used to transform the graphics, text, and patterns to be engraved on the glass into a Windows bitmap format. Then, the converted bitmap is binarized to become a black and white image. Next, the binarized bitmap pixel matrix is ​​recombined according to binary byte data format, so that the eight binary bits (0 or 1) in each byte correspond one-to-one with the "on" and "off" working states of the eight nozzles on the nozzle head. The CNC engraving machine borrows from the traditional sandblasting method for glass engraving, mimicking the scanning operation of a dot matrix printer, scanning the pixel matrix according to the row and column order of the image. The CNC machining software controls the eight nozzles of the engraving nozzle, controlling the corresponding nozzle to spray or not spray abrasive airflow at the coordinate position of each pixel. At the coordinates of the points requiring engraving, the nozzle opens and ejects a fine abrasive stream under high pressure, impacting and etching opaque, rough points onto the glass surface. At the coordinates of the points not requiring engraving, the nozzle closes, preserving the original bright and transparent points of the glass. By repeatedly scanning the pixel array of the entire image, a frosted glass pattern consisting of a series of dense pixel arrays with varying brightness can be obtained. The correspondence between the pixel array of the engraved image, the engraving head nozzle, and the image data bytes is shown in Figure 1. 3.2 Process Planning for CNC Frosted Glass The process of CNC frosted glass processing can be divided into two steps: the first step is to preprocess the CNC engraving data. In a Windows environment, image processing software such as Photoshop is used to convert the graphic and text image files to be engraved on the glass surface into Windows bitmap format. The converted image file is then binarized into a discrete binary pixel (dot matrix) matrix. Using specialized image data processing software programmed in a high-level language, the brightness ("1" or "0") information of each pixel is read sequentially according to its coordinates and recombined in binary byte data format. This ensures that the 8 bits in each byte correspond one-to-one with the "on" and "off" working status information of the 8 nozzles on the nozzle head. Finally, the recombined image data file is directly sent to the next step for CNC engraving, or saved as an engraving data file for later use. The second step is CNC automatic sandblasting engraving. The computer numerical control system directly receives or opens the engraving data file processed in the first step, continuously reading 8 bits of binary information in byte data format. The CNC system then sends engraving instructions to the stepper motors driving the X and Y direction motion mechanisms and the pneumatic control valves controlling the opening and closing of the eight nozzles. The two-dimensional mechanical motion mechanism begins to perform continuous scanning at equal intervals in row and column order. At the same time, the pneumatic abrasive engraving nozzle, based on the row and column coordinates of the pixel array and the brightness information of each pixel, immediately opens the corresponding nozzle at the position where the pixel needs to be engraved, ejecting a high-speed abrasive airflow to impact and etch the image dots at that coordinate point; otherwise, the nozzle closes and does not eject. This scanning cycle is repeated until all pixels of the entire image array are scanned, and the glass engraving process is completed. 4 Structure of the Computer Numerical Control Sand Engraving Glass Engraving Machine 4.1 Structure of Mechanical Motion Components The mechanical motion structure of the CNC glass engraving machine consists of mechanical components such as stepper motors, synchronous toothed belts, machine bases, worktables, gantry frames, and cylindrical linear rolling guides. A two-dimensional mechanical motion system, consisting of X-axis and Y-axis moving parts (the Z-axis only adjusts distance and does not move), provides X-axis and Y-axis motion for the pneumatic abrasive jet engraving head, enabling scanning and engraving processing. The layout of the mechanical motion structure is shown in Figure 2. The X-axis moving parts mainly consist of a gantry, an X-axis stepper motor, two cylindrical linear rolling guides, a synchronous toothed belt and pulleys, and an X-axis motion bracket. The stepper motor, as the drive element, transmits motion to the connected X-axis motion bracket via the synchronous toothed belt, thus enabling the pneumatic abrasive jet engraving head mounted on the bracket to move in the X-axis direction. The Y-axis moving parts mainly consist of a Y-axis stepper motor, two cylindrical linear rolling guides, a synchronous toothed belt and pulleys, and a machine base. Driven by the stepper motor, the motion is transmitted to the connected gantry via the synchronous toothed belt, thus enabling the pneumatic abrasive jet engraving head mounted on the gantry to move in the Y-axis direction. 4.2 Scheme Selection of Open CNC System With the rapid development of computer technology, the development of open CNC system using PC microcomputer has become a trend in CNC system technology development and a hot topic in the research of open CNC system at home and abroad. Currently, there are three ways to implement PC microcomputer open CNC system. [IMG=Figure 3 Hardware structure principle block diagram of CNC system]/uploadpic/THESIS/2007/11/2007111411445422770T.jpg[/IMG] Figure 3 Hardware structure principle block diagram of CNC system [IMG=Figure 4 Human-machine interface (carving data file preview state)]/uploadpic/THESIS/2007/11/2007111411485736774T.jpg[/IMG] Figure 4 Human-machine interface (carving data file preview state) (1) PC embedded NC: The PC board is installed inside the CNC, and the PC and CNC are connected by a dedicated bus. Such systems are complex in structure and powerful in function, but expensive. (2) NC embedded in PC: using a general-purpose microcomputer as the platform and a standard plug-in open programmable motion controller as the control core, the PC and the motion controller form a master-slave, upper and lower computer control mode. The general-purpose PC is responsible for functions such as CNC program editing and human-machine interface management, while the motion controller is responsible for the real-time control tasks of the machine tool's motion, logic and other functions. The motion control card has a dedicated CPU and does not need to occupy PC resources. (3) Pure software NC: using software to complete the real-time control tasks in the machining process, replacing the NC hardware module with software, and controlling the servo drive through the interface card. Since it does not depend on NC hardware, this mode has high flexibility and versatility, but because the real-time performance of the PC operating system is not strong and the NC module has high requirements for software programming, only some large manufacturers are currently conducting research. Based on the above analysis, under the current technical conditions, the NC embedded in PC method is selected, and the PC + motion controller mode is adopted to develop the CNC system of the sand carving glass engraving machine. This dual-CPU open CNC system based on upper and lower computers can give full play to the characteristics of fast computer processing speed and user-friendly human-machine interface, and has great practical value. 4.3 Hardware Structure of the PC-Based Open CNC System The hardware structure principle of the open CNC system developed based on the PC + motion controller mode is shown in Figure 3. The host of the CNC system is a PC, and the operating system is Windows 98/2000. The motion controller uses a domestically produced (Shenzhen Leisai Electromechanical Technology Development Co., Ltd.) DMC1000 motion control card and a (Taiwan Advantech) PCI-1762 digital input/output control card as the lower-level controller for real-time control. Two BYG series permanent magnet induction stepper motors are selected as servo drive motors for the two-dimensional mechanical motion mechanism. Both the DMC1000 and PCI-1762 cards used as lower-level controllers communicate with the upper-level PC via the PCI bus. No jumper settings are required on the cards, and all resources are automatically configured. External interfaces use SISC connectors and multi-core high-density shielded cables for convenient and compact signal connections, improving the reliability and anti-interference capabilities of the control cards. On the software side, both are equipped with dynamic link libraries and feature-rich function libraries under Windows 98/2000/NT, supporting users to independently program and develop open CNC systems for specific applications according to their specific process requirements. [IMG=Figure 5 Basic Flowchart of CNC Engraving Software]/uploadpic/THESIS/2007/11/2007111411522846085C.jpg[/IMG] Figure 5 Basic Flowchart of CNC Engraving Software. The DMC1000 is mainly used for controlling the stepper motors in the X and Y axes. It receives instructions from the PC's main CPU and processes all motion control details: automatic acceleration/deceleration calculation, stroke control, pulse and direction signal output, etc., to complete the motion control of the engraving machine system. The PCI-1762 card is mainly used for the automatic opening and closing control of pneumatic solenoid valves and pneumatic jet engraving head devices, as well as the input and output control of other digital information. On the one hand, it receives instructions from the PC and completes automatic engraving tasks; on the other hand, it also detects the system's output status, motion position status, electrical switch status, compressed air pressure status, abrasive box level status, origin and limit switch signals, etc. Furthermore, it feeds this information back to the PC in a timely manner to complete various real-time control tasks of the engraving machine system. 4.4 The CNC system software of the sand-carving glass engraving machine was developed using Visual Basic 6.0 under the Windows 2000 operating system. The motion control, digital input/output control function library and dynamic link library provided by DMC1000 and PCI-1762 card were utilized to develop an open CNC system based on PC according to the specific processing requirements of the sand-carving glass engraving machine system. (1) Human-machine interface of CNC system software The CNC system software of the engraving machine mainly includes three major functions: screen operation, parameter setting and image display. Screen operation function: The software virtualizes the hardware panel of the CNC system to realize emergency stop, continue, return to origin, manual operation of the machine tool, reading, selecting and saving image data files and other operation functions. Parameter setting function: During glass engraving, the relevant working parameters and working status selections must be determined in advance for the control system. For example, the setting of parameters such as the engraving start position coordinates, proportional coefficient, servo motor start speed, drive speed, acceleration time, and quantitative pulse and interval delay of the feed amount (step distance) of the control mechanical motion mechanism. Image display function: mainly includes the display functions of information such as engraving graphic preview, screen simulation processing, real-time dynamic tracking of engraving trajectory and fault alarm. The human-machine interface of the CNC system is shown in Figure 4. (2) Screen simulation processing and real-time dynamic trajectory tracking display Applying the principles of computer graphics technology, the actual processing process of the CNC engraving machine is simulated, and the computer screen simulation processing and real-time dynamic tracking display program module is developed using VB language. Before glass engraving processing, the glass engraving pattern can be simulated on the computer screen in advance to verify the correctness of the engraving data; during the operation of the CNC glass engraving machine, the computer screen tracks and displays the movement trajectory of the engraving nozzle. The image of the movement trajectory always maintains a corresponding relationship with the actual processing process. The operator can observe the actual processing progress of the engraving machine and monitor the working status of the system in real time by observing the computer screen. This is very necessary to ensure the safe operation of the CNC engraving machine, improve the processing quality of sand-carved glass products, and avoid the generation of waste products. (3) Basic process of CNC engraving processing software The basic content of CNC engraving processing control software mainly includes reading the engraving data file, reciprocating cyclic scanning of pixel dot matrix, nozzle "open" and "close" state control, and simulation of the processing process. First, select and open the dedicated image engraving data file that has already undergone pixel-level processing. The host computer (PC) sends drive commands and "on" and "off" control commands for each engraving nozzle to the slave computer (DMCl000, PCI1762 control card). It then begins a reciprocating cyclic scan according to the row and column order of the pixel matrix until all pixel matrix scans are completed, automatically returning to the engraving machine system origin. To improve the efficiency of glass engraving, the CNC glass engraving machine uses an 8-nozzle engraving head device, requiring 64 rows of large-cycle and 8 rows of small-cycle scanning motions, along the X-axis, using a bidirectional reciprocating motion. The basic flowchart of the CNC glass engraving software is shown in Figure 5. 5. Example of CNC Sand Engraving Glass Processing Figure 6 shows an example processed using the aforementioned CNC sand engraving glass engraving machine. Among them, (a) is a regular image acquired by a scanner and binarized and inverted, and (b) is a sand-carved glass test sample carved using a CNC sand-carving glass engraving machine based on the bitmap pixel data of the original image shown in (a). 6 Conclusion and Outlook The traditional sand-carved glass processing method using sandblasting technology remains very popular in the current domestic decorative and interior glass processing market due to its simple production equipment and the wide availability and low price of sandblasting abrasives. However, this manual production process, from mask drawing and engraving to glass sandblasting, mainly relies on manual operation. The artistic effect and quality level of the sand-carved glass products depend entirely on the operator's aesthetic literacy and technical level, making it difficult to guarantee the quality of glass carving. In addition, the carving image materials used in this processing method mainly come from copying samples, but the number of sample patterns is limited, and the pattern content is monotonous and outdated, making it difficult to meet users' requirements for diversified, personalized, fashionable, and refined glass carving patterns. Moreover, this processing method is labor-intensive and has a long production cycle, making it unsuitable for mass production and causing serious environmental pollution. [IMG=Fig. 6 Original Image and Glass Engraving Sample Photo]/uploadpic/THESIS/2007/11/2007111412120466620U.jpg[/IMG] Fig. 6 Original Image and Glass Engraving Sample Photo (1) Image materials are widely available and can be obtained through scanning, digital camera photography, or directly selected from a large number of computer image files. Furthermore, they can be arbitrarily artistically processed using popular digital image processing software such as Photoshop. (2) CNC sandblasting glass engraving technology eliminates the mask production process that is indispensable in traditional sandblasting glass processing, simplifies the engraving process of sandblasted glass, and realizes that what you see is what you get when you see the glass engraving pattern. In particular, since the engraving process of sandblasted glass has been digitized, it makes the simulation engraving of elegant landscapes, figures, calligraphy and paintings, patterns, borders, celebrity handwriting, flowers and animals and other artistic masterpieces quite convenient and easy. (3) In the CNC sand-carving glass engraving process, the air consumption and abrasive consumption are very low, which not only saves energy and abrasive, but also shortens the production cycle, reduces the labor intensity of workers, and is beneficial to environmental protection. Moreover, the speed of CNC processing is better than that of manual processing, and the quality of CNC processing is more stable, which can meet the needs of mass production. With the further improvement of computer numerical control sand-carving glass processing technology, the resolution of engraved images can be further improved in the future, thereby improving the image quality of sand-carved glass. Due to the wide variety and wide application of glass products, computer numerical control sand-carving glass processing technology has good promotion and application value and market development prospects. Proceedings of the Second Servo and Motion Control Forum Proceedings of the Third Servo and Motion Control Forum