ECR ion source high vacuum trim needle valve control system

The ECR opens from the structure of the needle on the f source. Measured load torque of this needle valve: The maximum value is 0.0588Hm. 3 Index of control system According to the need of ECR ​​ion source to adjust the working gas, the control system should reach the following index: Adjustment range: 0~15 laps, 0~30! Arc (Note: The needle valve can rotate 18 laps, but actually the needle valve is fully open at 13 laps, so we can choose 15 laps as the end position to meet the requirements.) Speed: No strict requirements on the speed, about 7~8 laps / Minute; 4 The structure of the control system The entire control system through the shaft encoder to collect needle valve position information to achieve closed-loop control. The axis encoder outputs digital quantities and does not require analog-to-digital conversion.

As an actuator, the stepper motor drives the needle valve through the mechanical transmission to realize the adjustment of the working gas of the ECR ion source.

This control system is divided into two parts (for example), one part is located on the low voltage side, and the other part is located on the high voltage side. In the middle, two optical paths are used to achieve electrical insulation and transmit control information. The control process of the entire control system is as follows: First, the target position of the needle valve is set, and then transmitted through the optical path. After the receiver receives the setting information, the comparator passes the set value of the needle valve and the shaft encoder. The current position of the needle valve is compared and the result obtained is sent to the stepper motor driver. The driver determines the direction of rotation, stoppage and rotation of the stepper motor according to the comparison result. The stepper motor drives the needle valve and the position of the needle valve is fed back through the shaft encoder. At the same time, the output of the shaft encoder is transmitted to the low-voltage side through the transmitter, and is received by the receiver at the low-voltage side and displayed by the digital tube. The light path is always in working condition, and the current position information of the needle valve is always displayed to monitor the status of the needle valve. The alarm device is an alarm when the high-voltage transmitter is not working properly.

The entire control system adopts digital circuits, which are of good reliability and high precision. The ECR is separated from the Y-source vacuum fine-tuning needle valve with the lemon system structure and connected to the computer, which has good scalability.

5 Control system module function The target position adopts the keypad input, the input information is the absolute position of the needle valve.

We use absolute position to simplify the entire control system and improve the reliability of the system. If the relative position is used as the position input, the difference and positive and negative between the position reached by the needle valve and the current position need to be calculated to determine the rotation angle and rotation direction of the needle valve. In this way, two signals need to be sent to the implementing agency to complicate the circuit. With the absolute position, the light path only needs to transmit one kind of signal, namely the position signal, and the rotation angle and steering of the needle valve are all realized by the circuit.

The system uses the optical path to achieve the electrical insulation of the high-voltage and low-voltage sides, and it is also the channel for information transmission.

When designing an optical system, it is firstly considered which transmission medium to use, which often depends on the insulation requirements of the system and the insulating properties of the medium. According to the needle valve at the high voltage end of 30kV, the transmission distance is not strictly limited. We use the atmosphere as the transmission medium to achieve the pressure resistance requirements.

Since the infrared light is invisible light, it has little effect on the environment. The wavelength of the infrared light wave is much smaller than the wavelength of the radio wave and will not affect the adjacent radio equipment; the wavelength is less than 1.5! The near-infrared light of m has a much better transmission characteristic in the transparent atmosphere than visible light, so we use infrared to transmit information.

Infrared rays are close to the red light edge of visible light, and their physical properties such as straight line transmission, reflection, refraction, and absorption by substances are very similar to visible light. Therefore, it can use an optical device such as a focusing lens similar to visible light, and the transmission distance is generally several meters to several tens of meters or more. Therefore, we designed a set of optical transmission devices so that the transmitter and the corresponding receiver are basically in a straight line. And use the focusing lens to increase the transmission distance, increase the signal strength, and improve the anti-jamming performance.

Because the optical signal is directly transmitted in the air, the optical loss is large. In order to ensure the correct transmission and reception of the signal, we use high-power infrared light-emitting diodes and sensitive phototransistors. After comparison, the method of transmission of raw optical information from Suzhou Semiconductor Factory is adopted. : Sometimes the optical signal does not cause the turn-off and turn-on of the phototransistor, and the information is contained in the frequency of the presence or absence of the optical signal. The triode's linearity need not be considered at this time, but its sensitivity should be considered.

The optical signal is alternately changed according to a certain frequency. The input of the optical signal has a certain frequency. The upper cutoff frequency (preferably the best operating frequency) of the phototransistor must be larger than the frequency of the input signal to measure the change of the input signal.

The amplitude information of the optical signal is included in the amplitude of the optical signal. In order to accurately measure the change in amplitude, a photo-transistor with good linearity and fast response must be used.

The difference in chromaticity of the optical signal utilizes the difference in chromaticity of the optical signal to transmit information, and optoelectronic devices with appropriate spectral characteristics should be selected.

In the above four optical signal transmitters, the first type is the easiest to realize, and the effect is very good, because whether the optical signal frequency, amplitude, or the difference in chromaticity, the light receiving device is difficult to distinguish, and the presence or absence of optical signals It is the most extreme two situations, the light receiving device is easy to distinguish, so the first method is used.

Infrared light emitting diodes are current driven devices. The basic driving methods include constant direct current drive, pulsed direct current drive, and alternating current drive. In order to reduce the transmitter power consumption, extend the life of infrared light-emitting diodes, in order to improve the control of the launch distance, infrared light-emitting diodes generally use pulsed DC current drive, but also can improve the anti-interference performance of the optical system 637. transmitter and transmitter The circuit is the same, the function is to transmit the position information of the needle valve, the transmitter emits the target position of the needle valve, and the transmitter emits the current position of the needle valve. The transmitter uses a multivibrator with an oscillation frequency of 5kHz and a duty ratio of 1:1 to control the transistor to drive the infrared light emitting diode, and converts the electric pulse into a light pulse to emit it. The number of positions is set, how many light pulses are emitted.

The receiver and receiver circuits are basically the same. The phototransistor constitutes a photoelectric converter. When pulsed infrared light shines on the phototransistor, the current of the phototransistor will correspond to the change of the same frequency of the light pulse. Under the action of the load resistance of the phototransistor, the light pulse will be generated at the output end. Frequency voltage signal. Since this electrical signal is very weak, it needs to be amplified and reshaped. The receiver takes the amplified, shaped pulse signal as a count pulse, calculates the number of received pulses, and finally sends the accumulated result to a register, taking note of the position of the needle valve emitted from the low pressure side.

The target position information of the needle valve received from the low pressure side in the control system, ie the value latched by the latch, is compared with the current position of the needle valve. The positive and negative result of the comparison result in the direction signal of the stepping motor. The stepping pulse of the stepping motor is sent by the multi-harmonic oscillator. When the comparison result is not equal, the multi-harmonic oscillator issues the step pulse. When the target position is equal to the current position, the multivibrator stops working.

Data Acquisition and Execution System In this control system, the feedback channel employs 13 contact angle encoders (13 encoders for short). When the input shaft of the 13-bit encoder rotates through 256 revolutions, thirteen full-scale binary Gray codes are continuously output, and a total of 8192 different numbers are output. The axis encoder corresponds to 32 codes per revolution, and the 13-bit Gray code output from the 13-bit coder is converted into a BCD code, which facilitates decoding display and composition feedback system.

Since the needle valve can rotate 15 turns, we set the entire needle valve to 0 to 15 turns. The stepper motor directly drives the shaft encoder to operate. The gear ratio between the needle valve and the stepper motor is designed to be 15. That is, the stepping motor drives the needle valve to rotate 15 revolutions, and the axis encoder rotates 75 revolutions, ie, turns over 2400 codes. number. Satisfy the accuracy better than one-thousandth.

The stepper motor is controlled by the driver and emits a pulse to the driver. The driver controls the motor to produce a constant amount of step motion, ie a constant amount of angular or linear displacement. Based on the measured load torque of the needle valve, we chose the 42BYGH101 hybrid stepper motor from Beijing Startech. This stepping motor is a two-phase motor with a rated torque of 0.44 cm, which is much larger than the load torque of the needle valve. The step angle is 0.9, the phase current is 1.7 A, and the driving voltage is 24 V DC. 6 Conclusion Based on the EC2 ion A high vacuum trimming needle valve control system was designed for the control requirements of the source high-voltage end device. The system transmits signals in a pulsed manner and uses an infrared transmission and receiving system through the optical path to achieve electrical insulation between the high-voltage end and the low-voltage end and achieve control. Transmission of information. The entire system has been successfully completed from design, production to off-line debugging, and has stable operation, high reliability, and all performances have reached the expected targets.

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