Design of hardware for industrial robot AC servo drive control system
Since the 1970s, the number of industrial robots in China has been relatively large, and some of the technologies of robots have reached the world's advanced level. However, industrial robot technology in western developed countries still leads China for many years. . The reason is not difficult to find: the method adopted by China to study industrial robots is mainly to introduce foreign advanced technology and then carry out secondary development. This has caused China's own innovative technology to be less, which seriously restricts China's industrial robot industry. Development.
In order to break the foreign technology monopoly of industrial robots in China, we must be self-reliant, master the key technologies of high-performance industrial robots, and innovate on the basis of the original. Since the actuator of the industrial robot joint is a motor, it is very important to obtain a good control effect of the motor. In order to obtain excellent motor control performance, a high-performance AC servo drive system is required, so a high-performance AC servo drive system is developed. It is one of the key technologies of industrial robots.
The hardware of the AC servo drive system is the basis of software design, so the main task of this paper is to design the hardware of the system according to the characteristics of the industrial robot servo drive system.
1, hardware design
1.1 DSP selection
DSP system hardware design includes control chip selection, main circuit drive and protection, peripheral equipment, logic circuit, etc. It is the basis of the entire control system design, DSP chip is the top priority. TMS320C5000 series DSP has the lowest power consumption and is designed for the consumer digital market. The minimum power consumption is only 0.33mA/MHz, so it is mostly used in daily life consumer products such as cameras and mobile phones. TI's TMS320C6000 series has the highest processing power and is a digital processor suitable for programming in high-level languages ​​such as C++/C. It is mainly used in high-end fields such as military defense. Compared with the C5000 and C6000 series of DSPs, the TMS320C2000 series of DSPs are the most powerful processors in the control field due to their fast speed, high precision and high integration. Among them, C28 series DSP is a new member of TMS320C2000 platform. It is improved by C24 series DSP. It is a chip that supports C/C++ language design. C28 series DSP is very suitable for industrial control and has unique control in algorithm control. The advantage is a rare microprocessor that is efficient enough to replace any other processor. C2000 series DSP does not contain Flash memory, only contains read-only memory ROM; F2000 series DSP not only contains ROM read-only memory, but also includes Flash memory, which can be repeatedly erased and written, suitable for application in the initial development stage of the product. If the TMS320C281x is used, the code needs to be delivered to the manufacturer, and the program is solidified into the ROM of the TMS320C281x, which increases the cost, so the TMS320F281xDSP chip is selected. Among them, TMS320F2812 as TI's first chip, has a high cost performance. In summary, the final selection of the DSP model is TMS320F2812.
1.2 position detection circuit design
The encoder used in the AC servo motor is a 17-bit absolute encoder of TS5668N21 produced by Tamagawa. The general practice is to use a dedicated chip provided by the manufacturer for data processing. However, this method has a disadvantage, that is, it is dedicated. The cost of the chip is very expensive, which is contrary to the purpose of developing an economical industrial robot. In order to reduce the cost, this paper designs a serial signal circuit that can convert the absolute encoder signal into DSP.
The inductor and optocoupler can function as filtering and anti-surge. Since the absolute encoder outputs a differential signal, the differential signal of the absolute encoder needs to be converted into DSP by the chip SN65176BD (BDR) G4. The serial port signal identified is TTL signal. In addition, the power supply voltage of the chip is 5V DC, so the drive system should also provide 5V DC power. Because the industrial robot servo drive system uses a DSP to control two permanent magnets. The idea of ​​the motor is to reduce the cost and make full use of the TMS320F2812's fast computing speed and rich peripheral resources. Therefore, the encoder signals of the two motors are input to the same DSPTMS320F2812 through the serial port SCIA and SCIB.
1.3 Low-speed external input signal conversion circuit design
Since the input signal of an external input signal such as a parameter setting button needs to be collected into the DSP, only the 3.3V TTL level can be recognized by the DSPTMS320F2812, so a signal conversion circuit is required, and a bidirectional optical coupling is used in the circuit. It plays a good role in isolation protection. Once the voltage is too large, it only needs to replace the optocoupler to prevent the interface of the DSP from being burned out. The bidirectional optocoupler used in this circuit is TLP280-4/SOP-16 manufactured by Toshiba Corporation, in which SOP-16 is packaged. The bidirectional optocoupler common terminal can be connected to either 24V or 0V. Conveniently, the circuit can convert the low-speed signal into a 3.3V TTL signal to complete the signal conversion, wherein the capacitance in the circuit acts as a filter.
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