Foreword
Medical treatment instrument provides services to people, which determines its transmission control system requires rigor, especially in the treatment device for the treatment of cervical spondylosis and lumbar disc herniation, safety and accuracy of the transmission system proposed Higher requirements: stalling is absolutely not allowed, offside is not allowed, and parking is accurate. At the same time, in order to simplify the design of the mechanical part and reduce the related sensors, most of the control functions are electrically controlled by the principle of mechatronics.
The therapeutic device transmission system requires the motor speed to be controlled between 100 and 250 r/min, and then decelerated by a 50:1 mechanical reducer with a transmission torque of 1.5 Nm. The amplitude of the swing is required to be cervical vertebra: ±30° to ±60°; lumbar vertebra: ±60° to ±100°; the starting point should be controlled at the center position. The speed and swing should be adjustable according to the specific case.
2Intelligent design of all-digital dedicated inverter
(1) Taking into account the special requirements of medical therapeutic instruments, in order to improve the operational reliability and control accuracy of the frequency converter, intelligent digital design is adopted, and also combined with the characteristics of miniaturization, the main power device adopts the IGBT intelligent power module of Mitsubishi Electric of Japan. (IPM) PM20CSJ060. The input is single-phase 220V AC, and is supplied to the intelligent power module after being rectified by the single-phase full-bridge rectifier. The output is three-phase 220V AC, and the 0.5kW three-phase asynchronous motor is connected to the â–³ connection method.
(2) Using INTEL's 16-bit single-chip 80C196KC as the system CPU, it has the characteristics of fast computing speed, high precision and strong command function. With 8 10-bit A/D converters, it can detect analog and digital signals. Control calculation and data processing, logic judgment of protection function, send setting and control data to PWM generation circuit SA4828, and manage functions such as keyboard and digital display.
(3) The SPWM wave generator adopts the enhanced motion control large-scale integrated circuit SA4828 from MITEL of the United Kingdom. The chip works as a microprocessor-independent peripheral, but it can be controlled by any type of microprocessor with little or no additional logic. The pin configuration makes it suitable for most bus formats, including multiplexed address/data bus formats and RD/WR or R/W control modes. Since the intervention of the microprocessor is required only when the operating state is changed, the chip hardly occupies the resources of the CPU during operation.
The SA4828 is fully digital and operates at carrier frequencies up to 24 kHz. There are three optional output power waveforms in the internal ROM, and harmonic suppression technology reduces power device losses. 16-bit frequency control accuracy, three independent amplitude registers for three-phase unbalance compensation. The hardware structure of the inverter designed with SA4828 is shown in Figure 1.
3SA4828 features and working principle
3.1SA4828 pin diagram and pin function description
The pin diagram of SA4828 is shown in Figure 2. The pin function description is shown in Table 1.
3.2 SA4828 internal structure block diagram and working principle
Figure 1 shows the hardware structure of the inverter using SA4828
Figure 2SA4828 pin diagram
Figure 3 internal block diagram of the SA4828 chip
Figure 3 is a block diagram of the internal structure of the SA4828. It can be seen from the figure that the SA4828 is mainly composed of three parts:
(1) Receive and store the microprocessor command (control word) part, which is mainly controlled by bus, bus decoding, register R0, R1...R5, virtual register R14, R15 and 32-bit initialization register and 48-bit control Register composition;
(2) reading a portion of the modulated waveform from the waveform ROMS, which is composed of an address generator and a waveform decompression buffer;
(3) Three-phase output control circuit and output pulse latch circuit, each phase output control circuit is composed of pulse deletion circuit and pulse delay circuit.
The SA4828 chip has a parallel interface to communicate with the microprocessor. This interface is compatible with almost all industry standard microprocessors such as 8051, 0096, 6805, 68000 and TMS320 without regard to the width of the bus and the addition of additional logic. Most data bus structures can be divided into a multiplexed address/data bus and a separate address/data bus, while most microprocessors are not WR/RD structures or R/W structures; and the chip is designed to work with the above four Any combination of the combinations is used. All bus formats are distinguished by the status of one configuration pin (MUX) and one register select pin (RS).
More importantly, in the case of system anomalies (overcurrent or overvoltage), an emergency shutdown input (SETTRIP) can quickly shut down all PWM outputs without the control of the microprocessor, which is a good solution to the frequency conversion. The fast protection of the device avoids the delay caused by the CPU interrupt service instruction cycle.
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