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Home > Processor/DSP > Circuit design of galvanometer laser marking controller based on TMS32

Circuit design of galvanometer laser marking controller based on TMS320F2812 high-speed processor

Update Time: 2020-05-18 17:17:40

With the continuous expansion of the application range of laser marking machines, the requirements for the speed and accuracy of laser marking are becoming higher and higher. TI's TMS320F2812DSP is a high-speed processor designed specifically for industrial control applications. It is of practical significance to use it to develop laser marking controllers. The laser marking controllers designed in this paper have broad application prospects.

1. The working principle of the controller

The upper computer of the galvanometer laser marking controller is a computer with marking software installed. Text and graphics are processed into a large amount of marking data through images, and the rendering effect is displayed on the marking software interface. The marking data is transferred from the USB bus to the expansion memory RAM, and then taken out by the DSP and sent to the D / A conversion chip. The D / A chip converts and outputs an analog voltage of -5 to 5 V to drive the scanning galvanometer and control. The power of the laser power supply, and the switch of the laser energy is controlled by a GPIO (general input / output) pin. The x, y-axis galvanometer controls the laser focus to move in an orderly manner on the two-dimensional plane to complete various forms of text and graphics. Mark.

2. Hardware circuit design of galvanometer laser marking controller

The functional block diagram of the system is shown in Figure 1. The galvanometer laser marking controller mainly includes USB communication circuit, extended memory circuit, D / A conversion circuit and CPLD circuit.

2.1 USB communication interface

The USB communication module adopts Cypress's CY7C68013. There are two connection methods between USB and DSP: FIFO and GPIF. In this system, FIFO is used. The read and write signals are provided by CPLD and DSP. The SLOE of the USB chip is connected to the external interrupt of the DSP, and other control signals are decoded by the CPLD through the CPLD and connected to the USB chip, and the DSP data line and two address lines are directly connected to the USB.

2.2 High-speed D / A conversion circuit

The digital-to-analog conversion part is the key part of the controller. Three D / A channels are required in this system to control the galvanometer x-axis and galvanometer y-axis and laser power respectively. The main technical parameters of this system AD7836 meet the requirements:

(1) Single-chip 4-channel 14-bit D / A conversion; (2) Voltage output, the maximum voltage output range is ± 10 V; (3) The typical settling time of the output voltage is 16 μs.

The D / A voltage resolution is: 5 V / 213 = O.61 mV. Compared with bipolar and unipolar voltage output, the circuit omits the operational amplifier that changes the voltage polarity, which simplifies the circuit.

Ad7836 supports interfaces with 16-bit microprocessors and DSPs, including 14-bit data lines, 3-bit address lines A0, A1, A2, control signals CS, CLR, WR, SEL. AD7836 is selected when CS is at a low level; the value of the internal data register of the D / A converter can control the output value of the analog voltage only when CLR is at a high level; WR is at a low level and can be combined with CS to write data into the input buffer . When SEL is high, the value of register E set by the user is output to VOUT, so it can be grounded. When the system is working, because the external interface XINTF is used, the operation of the D / A chip is the same as reading and writing data from the SRAM, and the starting address of the external interface 2 area of the control D / A chip is 0X08 0000. You can change the corresponding value at any time in the program to control the voltage value of the D / A conversion, and then control the position of the marking point. If you want to mark the picture, you can output the position and laser energy of each marking point in a progressive scan.

The pin connection of DSP and AD7836 is shown as in Fig. 2.

Figure 2 Connection of DSP and AD7836

Since the driving voltage range of the galvanometer used is also ± 5 V, the reference voltages VREF (+) and VREF (-) of each channel in this system are connected to ± 2.5 V, respectively. Accurate ± 2.5 V reference voltage is used in the hardware circuit design of Microehip's special 2.5 V voltage reference source MCPl525 and OP operational amplifier MCP606. As shown in Figure 3, after the voltage reference of +2.5 V is generated by MCP1525, in order to reduce noise, RC low-pass filtering and MCP606 are used, where MCP606 is used as a voltage follower. As shown in Figure 4, the -2.5 V voltage is generated by +2.5 V through a voltage divider formed by two equivalent resistors and MCP606.

Figure 3 +2.5V voltage reference  Figure 4-2.5V voltage reference

The pin voltages of AD7836 and DSP are different, so they cannot be directly connected. The SN74ALVCl64245 chip is selected in the system to isolate the data bus on both sides. The output enable control pins OE1 and OE2 are both connected to a low level, and the direction of the data line DIR1 and DIR2 are both connected to a high level to ensure that the output end of the chip changes instantly with the input end.

2.3 Extended data storage

The memory is used to temporarily store the marking data transmitted from the upper computer. The external expansion memory uses IS61LV51216, which is 512 kB, 16-bit SRAM memory, a total of 19-bit address bus, 16-bit data bus. SARAM access time in this system is 10 ns, CMOS process, 3.3 V power supply, input and output are TTL compatible, suitable for external expansion memory of DSP. The memory is expanded through the external interface XINTF of the DSP, and the / XZCS6AND7 pin of the F2812 is used as a chip select, so it corresponds to the external area 6 of the memory map, and the address range is 0X10 0000 ~ 0X17FFFF.

2.4 CPLD system

In this system, CPLD uses Altera's MAX3000A series EPM3256A chip, and the CPLD firmware is designed with software MAX + plusII. CPLD is mainly used to control the data transmission of the USB chip, and the interrupt key and the liquid crystal display module are extended by it. In addition, the DSP system reserves a multi-channel GPIO interface, which can control the multi-dimensional motion control platform composed of stepper motors. By reserving the GPIO port and using the CPLD chip, the scalability of the system is enhanced.

3. Controller system software development

The software of the control system is composed of two parts. The upper computer is designed with visual object-oriented language VB 6.0. It is mainly responsible for the generation and packaging of marking data, as well as the user interface for human-computer interaction. The lower computer DSP is written by C ++ / C ++ The program is developed with the efficient C compiler and integrated development environment: Code Studio (CCS) provided by TI. The main flow chart of the control system is shown in Figure 5.

After the marking machine is turned on, the lower computer program initializes each chip and memory according to the parameters on the user interface. The parameters include laser energy, scanning times, and text filling methods. Then wait for the host computer to transmit the marking data from the USB interface. The marking data is first stored in the data memory. At this time, no matter whether the marking instruction is issued from the user interface or the keyboard, the DSP takes out the marking data from the data memory and sends it to the D / A chip. The D / A chip outputs the corresponding voltage to drive the galvanometer until this marking is completed. The same marking graphics only need to transfer the data once, select the start processing button from the software or the keyboard.

When performing graphic marking, import the graphic file and perform image processing, and then convert it into marking position data; when text marking, call the Windows API function GetGly-phOutline in Visual Basic to get the outline of the text, which can be zoomed, rotated, etc. The operation does not affect the text display quality, and its display effect is displayed on the user interface through the DrawGlyph function.

4 Conclusion

A laser marking controller based on TMS320F2812 DSP is introduced in this article. A 4-output D / A converter is used to control the galvanometer and laser power supply. The high-performance D / A conversion module enables the speed and accuracy of laser marking. Greatly improved, the use of USB interface makes the marking controller plug and play, and improves the stability of data transmission. The upper computer of the system is programmed with Visual Basic, the lower computer is programmed with C language, and the program transplantation is easy. The marking system developed has achieved ideal results in terms of speed and accuracy. 


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