The shadowless lamp is an indispensable important device for illuminating the surgical site, and it is required to optimally observe objects of different depths, sizes, and contrasts in the incision and the body cavity. Therefore, in addition to the need for "no shadow", it also needs uniform illumination and good light quality, which can well distinguish the color difference between blood and other tissues and organs of the human body. In addition, the shadowless lamp must be able to continue working for a long time without emitting excessive heat, because overheating can make the operator uncomfortable and dry the tissue in the surgical field.
At present, surgical lamps generally use circular energy-saving lamps or halogen lamps. However, with the continuous development of LED technology, especially the development of high-brightness white LEDs, LED shadowless lamps have completely solved the inherent defects of the ring-shaped energy-saving lamps themselves. Upgrade of the lamp. At present, the superiority of the LED shadowless lamp is gradually understood and accepted by the microscope user, and the use cost is lower than that of the ring-shaped energy-saving lamp, which reduces the trouble of replacing the ring-shaped lamp tube every 1-2 months.
At present, the technology has successfully solved the problems of packaging, constant current driving, heat dissipation and illumination control of high-power LEDs, which can realize multi-level regulation of illumination of the shadowless lamp, and the dimming is flexible and convenient. The advantages of LED shadowless lamps are:
(1) Excellent cold light effect: Using the new LED cold light source as the surgical illumination, it is a real cold light source, and there is almost no temperature rise in the doctor's head and wound area.
(2) Good light quality: White LED has the characteristics of chromaticity that is different from ordinary surgical shadowless light source. It can increase the color difference between blood and other tissues and organs of the human body, making the doctor's vision clearer during surgery, flowing and infiltrating blood. The various tissues and organs of the human body are more easily distinguished, which is not available in ordinary surgical shadowless lamps.
(3) Stepless adjustment of brightness: The brightness of the LED can be steplessly regulated by digital method. The operator can adjust the brightness according to the adaptability of brightness to achieve the most ideal comfort, so that the eyes working for a long time are not easy to fatigue. sense.
(4) No stroboscopic: Because the LED shadowless lamp is pure DC power supply, there is no stroboscopic light, it is not easy to cause fatigue to the eyes, and it will not cause harmonic interference to other equipment in the working area.
(5) Uniform illumination: With a special optical system, 360° uniform illumination on the object to be observed, no ghosting, high definition.
(6) Long life: LED shadowless lamp has a long average life (35 000 h), which is much larger than the ring-shaped energy-saving lamp (1 500~2 500 h), and its life span is more than ten times that of energy-saving lamps.
(7) Energy saving and environmental protection: LED has high luminous efficiency, impact resistance, not easy to be broken, no mercury pollution, and the light emitted by it does not contain radiation pollution of infrared and ultraviolet components.
1 system structure
1.1 Overall structure
Since the luminous efficiency of a single LED cannot meet the requirements of the illumination intensity and uniformity of the surgical shadowless lamp, it is necessary to form an array with a plurality of LEDs, and it is required to have a reasonable arrangement and a uniform distribution, so that the illumination of each target plane meets the requirements, thereby determining The number of LEDs and the distribution rules.
Although the LED has high luminous efficiency and generates less heat, so many LEDs will generate a lot of heat in a sealed box, and the temperature will even be as high as 60 ° C ~ 80 ° C, so the radiator and heat dissipation channel must be properly designed. To effectively reduce the thermal resistance of the system.
The LED surgical shadowless lamp consists of a plurality of lamp caps, which are petal-shaped and fixed on the balance arm suspension system. The positioning is stable and can be moved vertically or cyclically to meet the different heights and angles of the operation. The entire shadowless lamp has 144 high-brightness white LEDs, and 8 are connected in series, which is called High Brightness Lighting Emitting Diode, which is made up of 18 groups in parallel. Each group is independent of each other. If there is a group of damage, the other can continue to work, so the impact on the surgery is small. Each group is independently driven by a LM3402 and accepts a PWM pulse width adjustment control of a microprocessor (CMU) P89LPC932 according to user needs. It can be steplessly adjusted, and the current flowing through each LED is about 120 ~ 320 mA. . The electrical schematic diagram of the LED shadowless lamp is shown in Figure 1. 
Figure 1 Electrical schematic diagram of LED shadowless lamp.
1.2 operation panel
There are 4 buttons (ambient lighting, off, brightening and dimming buttons) and 8 LED indicators on the operator panel. Pressing the ambient illumination button means that only the ambient illumination of the cavity is required, leaving only one of the three LEDs for illumination and turning off the remaining LED strings; pressing the close button will extinguish all eight LED strings. Press this button again, you can return to the original illuminance display state, power down or restart can also return to the set illuminance state; Brighten and dim buttons are used to change the illuminance of the shadowless lamp, corresponding to 8 indicators, indicating 8 blocks Brightness, an additional LED is lit for each additional block from left to right. When the shadowless lamp is off, the two right LEDs are lit. All operational information is transmitted to the driver board MCU via the RS485 bus.
1.3 driver board
The driver board is the core of the entire shadowless controller. It consists mainly of an MCU P89LPC932 and 18 LM2402 constant current regulator circuits. It also includes RS485 communication circuit.
The P89LPC932 is a low-power MCU manufactured by Philips. It has a power supply voltage of 3.3 V and can operate at low power. It is suitable for many applications requiring high integration and low cost, and can meet various performance requirements.
The P89LPC932 features a high-performance processor architecture that requires only 2 to 4 clock cycles of instruction execution and 6 times the standard 80C51 device. In addition, the P89LPC932 integrates many system-level functions, which greatly reduces component count, board area, and system cost. There are two internal timers that can be used as a PWM generator with 256 timer clock cycles. .
The LM3402 is a step-down regulator derived from a controllable current source that drives a series of high-power, high-brightness LED strings that accept input voltages ranging from 6 V to 42 V. When using the pin-compatible LM3402HV, the input voltage can be up to 75 V. The output voltage of the converter is adjusted to maintain a constant current level through the LED array as needed for the surgical contrast. Figure 2 shows a typical application circuit diagram of the LM3402. RSNS is the current setting resistor. The average current is IF≈0.2/RSNS. The value of RON is related to the number of LEDs in the LED string. The value of 300 LEDs can be 300 kΩ for 8 LEDs. After testing, the constant current is nominally 250 mA (RSNS=0.8 Ω), and the current fluctuation is within ±20 mA, which can fully meet the surgical light requirements. 
Figure 2 shows a typical application circuit for the LM3402.
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1.4 Safety measures
Taking into account the particularity of the safety requirements of medical instruments, every link of the system should consider taking appropriate safety measures. First of all, the operating room is an environment with strong electromagnetic interference. It is very important to prevent the MCU from crashing. Therefore, the following measures must be taken: (1) The hardware reset circuit design and internal reset procedure must be carefully handled; (2) The error interference signal must be eliminated, so The entire system is fully electrically isolated to prevent interaction between the various parts of the circuit. In addition, Modbus redundancy check method is adopted; (3) The price of high-brightness white LED is high. In order to avoid damage, the influence of grid and power supply damage on the system must be eliminated. Therefore, the overvoltage and overcurrent automatic protection circuit is adopted in this paper. When the voltage or current exceeds 20% of the set value, the system automatically cuts off the power to ensure the safety of the system circuit and high-brightness LED.
2 programming
2.1 Program structure
The program mainly consists of two independent programs: panel controller and driver board.
The panel controller program sends a switch or illuminance adjustment command to the engine board according to the input status of the four buttons, and displays the command status on the eight LEDs. After the driver board program is initialized, the interrupt receiving operation information is mainly received through the serial port. After the Modbus data redundancy check is performed, different PWM signals are issued according to the command indication. The engine board program flow block diagram is shown in Figure 3. 
Figure 3 shows the block diagram of the program board of the driver board.
2.2 PWM occurs
The current of the high-brightness LED string is mainly PWM regulated by the DIM port of the LM3402. The ratio of the actual current to the set current value depends on the duty cycle of the PWM. The PWM output of P89LPC932 internal timer T0/T1 occupies the same pin as the count input and timer trigger output, and the port output is automatically triggered when a timer overflow occurs.
This function enables timers 0 and 1 respectively via control bits ENT0 and ENT1 in the AUXR1 register. When this mode is on, the output of the port is logic 1 before the first timer overflows. For this mode to take effect, the C/T bit must be cleared to select PCLK as the clock source for the timer. The timer initialization setting reference program is as follows:
Void Timer1_init(void)
{
TMOD|=0x20 ; //Timer works in mode 6
*OD|=0x10;
TH1=256-n ; //n is the duty cycle
AUXR1|=0x20 ; // Timer enabled
TR1=1; //Start timer
}
The duty cycle duty cycle = 256-TH1, the overflow of Timer 1 will cause the P1.2 or P0.7 port to flip, so the output frequency is 1/2 of the Timer 1 overflow rate.
2.3 Energy saving mode
Energy consumption control is of great importance throughout the shadowless control system. Most of the time, HBLEDs are off and the control system is in standby, minimizing power consumption. When the power control register PCONA is set to 0xFF, the external function module is powered down. When the power control register PCON is set to 03H, the MCU can be completely powered down. Only when the interrupt is triggered can it wake up, and then the external function module is given. At power-on, the MCU starts working. The MCU on the engine board is woken up by the serial port receiving interrupt, and the MCU on the panel wakes up through the keyboard interrupt. The keyboard interrupt reference program is as follows:
Void KEY_ISR( ) interrupt 7
{
Key_push=1 ; // has a key press mark
PCONA=0x00 ; //The external function module is powered on.
KBCON=0x00; //Clear keyboard interrupt flag
}
The market demand for shadowless lamps in China is more than 20,000 per year. At the same time, due to the demand for low-carbon economy development, energy-saving renovation is needed. Therefore, the market prospect of LED shadowless lamps is very broad.
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