CN100447694C - A Large Stroke Nano-precision Positioning Control System - Google Patents

Abstract

The invention relates to a positioning control system used in high-precision measurement or experiment. The purpose is to overcome the deficiencies in the prior art and provide a positioning control system capable of monitoring the positional relationship changes between measuring or experimental instruments and recovering them in time. The system includes a light source, two semi-reflective half-lenses, an interferometer, a half-wave plate, a quarter-wave plate, an analyzer, and an analysis control system. After that, it is divided into two beams of light, which are respectively incident on the two arms of the interferometer. The light passing through the arm passes through the half-wave plate and then merges with the light passing through the arm in the second semi-reflective half-lens to form a beam of light, which passes through the quarter-wave After the film is injected into the optical sensor of the analysis control system, in order to realize high-precision positioning of a large stroke, the present invention installs one arm of the interferometer on a multi-level precision stepping motor, and the minimum stroke accuracy of the stepping motor is Nanoscale, control side analysis control system connection.

Description

A Large Stroke Nano-precision Positioning Control System

technical field

The invention relates to a positioning control system used in high-precision measurement or experiment, more specifically a control system capable of positioning with nanometer precision.

technical background

In high-precision measurement or experimental systems, there are often high requirements for the stability of the entire system, especially the positional relationship between instruments, even if there is a small disturbance, it will lead to completely different measurement or experimental results. Therefore, in a high-precision measurement or experiment system, the requirements for the measurement or experiment environment are very high, and generally it needs to be carried out in a highly isolated environment, such as an ultra-clean laboratory. But even in a highly isolated environment, due to the movement of personnel, the operation of instruments, and even the flow of air, there are disturbances to measurements or experiments. Ultra-clean vacuum laboratories are expensive to build and difficult to maintain. Therefore, various monitoring and positioning systems have appeared in the prior art, which are used to track the positional relationship between the instruments in the measurement or experiment. Once the relative position of the instruments changes, the monitoring and positioning system can restore the system in time. The initial position plays the role of real-time monitoring. However, because the interference that generally exists in high-precision measurement or experimental systems is very weak, how to measure such weak interference, timely feedback information and amplify the weak interference signal to push the system back to the original position is a problem. An important indicator of a monitoring and positioning system with excellent performance. None of the existing monitoring and positioning systems can fully meet these indicators, and can only make up for its defects through mathematical methods, and it is even more incompetent in realizing high-precision positioning with large interference.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, to provide a positioning control system capable of monitoring changes in the positional relationship between measuring or experimental instruments and recovering them in time, especially a positioning control system capable of realizing large-stroke and high-precision positioning system.

The present invention realizes its object of invention through the following technical solutions.

The present invention designs a large-stroke nanometer-precision positioning control system, which uses light sensing to perform system positioning, including a light source, two semi-reflective half-lenses, an interferometer, a half-wave plate, a quarter-wave plate, and a Analytical mirror, analysis and control system, the light path starts from the light source and enters the first half-mirror, and then is divided into two beams of light, which are respectively incident on the two arms of the interferometer. The light passing through the first arm passes through the half-wave plate and passes through the The light from the second arm is merged into a beam of light by the second semi-reflective lens, and then enters the optical sensor of the analysis and control system after passing through the quarter-wave plate and the analyzer, in order to achieve high-precision positioning with a large stroke. , the present invention installs one of the arms of the interferometer on a multi-level precision stepping motor, the minimum travel precision of the stepping motor is nanometer level, and the control terminal is connected to an analysis control system. The interferometer used in the present invention is a Michelson interferometer, which monitors the position change between the two arms by monitoring the phase difference between the two beams of circularly polarized light caused by the light passing through the two arms of the Michelson interferometer. The stepper motor moves one of the arms to track the other, so as to achieve the purpose of controlling the position between the two arms. The present invention adopts the multi-level precision stepping motor to realize the high-precision control of the large stroke. Generally, the multi-level precision stepping motor is composed of a small-stroke stepping motor and a large-stroke stepping motor. The small-stroke stepping motor and the large stroke The control ends of the stroke stepper motors are respectively connected with the analysis control system. When the required stroke reaches the maximum stroke of the small-stroke stepping motor, the large-stroke motor can be moved to supplement, and then the specific position can be adjusted through the small-stroke stepping motor, so the stroke accuracy of the large-stroke stepping motor cannot be greater than that of the small-stroke stepping motor 2 times the maximum stroke of the motor. It is necessary to be able to adjust the length of one arm of the Michelson interferometer within the precision range of nanometers, and the response speed must also be on the order of milliseconds. To meet such requirements, the small-stroke stepping motor can only use piezoelectric micro-stroke devices.

In order to realize the control of the whole system, the analysis control system of the present invention includes: a feedback module for detecting weak optical signals and converting them into corresponding digital signals; an execution module for adjusting the position of the interferometer arm; and The control module realizes the central control and data transmission; the control module is connected with the feedback module and the execution module respectively. The feedback module includes: a photodiode amplification and filtering part for light intensity signal extraction and amplification; a V/F conversion part that converts the amplified voltage into a frequency; and is responsible for processing commands from the control module to control the first and second digital Potentiometer, and the control and data transmission part that converts the frequency into a number and transmits it to the control module.

In order to be able to amplify the detected weak light signal and convert it into a corresponding digital signal, the amplifying circuit of the photodiode amplifying and filtering part of the present invention includes a current amplifying amplifying circuit composed of a photodiode and a first operational amplifier. A digital zeroing circuit composed of a digital potentiometer and a buffer, and an adder with reverse amplification function composed of a second digital potentiometer and a second operational amplifier; the filter circuit of the photodiode amplification and filtering part adopts a second-order high-pass filter .

In order to push the piezoelectric micro-stroke device to move and the response speed can reach the order of milliseconds, the execution module must include a DA converter, which is responsible for communication with the control module and a microcontroller that controls the DA converter for amplification. There are three parts of the high-voltage expansion circuit of the output voltage of the DA converter.

The advantages of using a computer as a control module are obvious. Various algorithms can be implemented very easily, the interface is friendly, easy to debug, data can be stored, and a large number of other data processing software are available. The computer of the invention adopts the PID control method to control the operation of the small stroke stepping motor and the large stroke stepping motor in real time. PID control method is an electronic control method that has been used for a long time. This method has many advantages: it is the most mature and widely used method in continuous systems. Its structure is flexible, not only can be adjusted by conventional PID, but also various PID variants can be used according to the requirements of the system, such as PI, PD control, incomplete differential control, integral separation PID control, PID control with dead zone , Variable speed integral PID control, proportional PID control and so on. In the PID control system, the system parameter setting is convenient, and the effect is relatively good in most industrial production processes. Powerful and a control method that can be applied to objects that are more obscure. So far, there are still many industrial objects that cannot or are difficult to obtain accurate mathematical models. Therefore, it is difficult or even impossible to apply direct digital control methods. At this time, we can only turn to the PID algorithm. Simple and practical, the key to the use of PID control method is to adjust its various parameters. The adjustment process is a process of accumulating experience, and now you can master the range of each parameter proficiently. The control effect is better, although the computer control is discrete, but for the system with relatively large time constant, it is close to continuous change. Therefore, the analog regulator can be completely replaced by a digital PID, and more satisfactory results can be obtained.

The present invention can be applied in various measuring and experimental systems, controls the relative position between two instruments, has following outstanding substantive effect and remarkable progress with respect to prior art present invention:

1. The positioning control system is designed using the principle of light interference, which can sense small changes in the system and has high sensitivity;

2. It can realize the nano-precision positioning of a large stroke, which ensures that the measurement or experiment system can maintain the stability between the positions under general interference;

3. It can amplify the detection of weak interference signals to a sufficient strength, and the response speed of the stepping motor should also be able to reach the order of milliseconds;

4. Using a computer as the control module can flexibly control the operation of the system, and the processing speed is fast;

5. The use of PID control method can well realize the control of nonlinear control objects, so it can control various external disturbances in the measurement or experimental system;

6. The overall structure is simple, the application is convenient, and the construction cost of the measurement or experiment environment is greatly reduced.

Description of drawings

Fig. 1 is the optical path diagram of the system of the present invention;

Fig. 2 is the control flowchart of the present invention;

Fig. 3 is the system block diagram of analysis control system of the present invention;

Fig. 4 is the control system block diagram of Fig. 3;

Fig. 5 is the circuit diagram of the amplifying circuit of photodiode amplifying and filtering part;

Fig. 6 is the circuit diagram of the filter circuit of photodiode amplification filter part;

Fig. 7 is the circuit diagram of V/F conversion part;

Fig. 8 is a circuit diagram of a high voltage extension circuit;

Fig. 9 is a graph showing the variation of the photosensitive current when the experimental system of the present invention is impacted.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The present invention provides a long-stroke nano-precision positioning control system for monitoring system stability. This system uses light intensity to reflect the control method of optical path difference information. The optical path diagram of this method is shown in Figure 1. With a horizontally polarized He-Ne laser light source 1, a polarizer can be added to obtain linearly polarized light, which is incident on the first half-mirror 2 from the left and then divided into two beams a and b, respectively incident on the Michelson interference The two arms 91, 92 of the instrument add a half-wave plate 4 and a quarter-wave plate 5 in the optical path, as shown in the figure, then after the two beams of light pass through the quarter-wave plate 5, they will respectively Become a left-handed circularly polarized light and a right-handed circularly polarized light, and enter the light sensor 7 of the analysis control system 8, and the two circularly polarized lights can be expressed as vectors respectively:

${\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Where δ is the optical path difference between two beams of circularly polarized light caused by the two arms 91 and 92 of the Michelson interferometer, and the value of δ is controlled by the position of the movable arm 91 of the interferometer. After the two circularly polarized lights are superimposed, the x-direction and y-direction components of the resulting vector can be written as:

E _x ＝E ₁ cosωt+E ₂ sin(ωt+δ) (1-3)

E _y ＝E ₁ sinωt+E ₂ cos(ωt+δ) (1-4)

Then through an analyzer 6, the angle between the vibration transmission direction and the x direction is Then the projections of the two components on the through-vibration direction can be written as:

Add the formula (1-5) and formula (1-6) vectorially to get the electric field vector of the light wave after passing through the analyzer:

Therefore, the light intensity that the light sensor 7 can receive is:

Because what the light sensor 7 actually receives is the signal integrated over time, the (1-8) formula is integrated over time, considering that all items containing ωt are all zero, and δ is changed into -δ, the detector received The signal is expressed as:

Finally we get their relationship as:

有关的一余弦函数的平方。假设检偏镜是保持静止的，这样就可以认为I就只同光程差δ有关。由于外界的干扰使光程差在瞬间的变化很难跳出某一个单调区间，所以只考虑余弦函数某一个增区间或者减区间，就可以根据光强I的变化来判断光程差的变化。It can be seen from the relationship (1-9) that the light intensity I detected by the light sensor 7 is composed of two parts, the first part is a DC voltage. The second part of the intensity I is the optical path difference δ between the two arms 91, 92 of the Michelson interferometer and the orientation angle of the final analyzer

related to the square of a cosine function. Assuming that the analyzer is kept static, it can be considered that I is only related to the optical path difference δ. Due to external interference, it is difficult for the instantaneous change of the optical path difference to jump out of a certain monotonic interval, so only a certain increasing or decreasing interval of the cosine function is considered, and the change of the optical path difference can be judged according to the change of the light intensity I.

As shown in Figure 1, the arm 91 of the interferometer of the present invention is installed on the stepping motor of multi-level precision, and the stepping motor of multi-level precision is made of a small stroke stepping motor 10 and a large stroke stepping motor 11, and the large stroke The stroke accuracy of the stroke stepper motor 11 is not greater than twice the maximum stroke of the small stroke stepper motor 10, and the control terminals of the small stroke stepper motor 10 and the large stroke stepper motor 11 are respectively connected with the analysis control system 8. The system is monitored through the control method shown in FIG. 2 , so that the arm 91 can track the change of the position of the arm 92 in real time and maintain the stability of the system. After starting the positioning control system, first set the locking state required by the system, then enter real-time monitoring, and monitor the positional relationship between the arms 91 and 92 by determining whether the light intensity I changes. If it is found that the light intensity I changes, then adjust the small stroke stepping motor 10 to restore the locked state, if the adjusted range exceeds the maximum stroke of the small stroke stepping motor 10, then adjust the large stroke stepping motor 11 to supplement , and then continue to adjust the small-stroke stepper motor 10 for precise positioning until the positional relationship between the arms 91 and 92 returns to the locked position.

In order to realize the control as shown in Figure 2, the present invention designs an analysis control system as shown in the system block diagram of Figure 3. The control module 83 is respectively connected with the feedback module 81 and the execution module 82. The optical signal is received by the optical sensor 7 and transmitted to the photodiode amplification and filtering part 811 for amplification and filtering, and is converted into a frequency signal by the V/F conversion part 812. The control and data transmission part 813 feeds back to the control module 83 . The control module 83 can be implemented by a computer. The control module 83 establishes communication with the DA converter 821 through the microcontroller 822 and controls the DA converter. The high-voltage expansion circuit 823 is used to amplify the signal output by the DA converter, so that it is enough to drive the small-stroke stepping motor 10 and the large-stroke stepping motor 10. Into the operation of the motor 11. In conjunction with the control block diagram of Figure 4, it can be seen that the light intensity signal detected by the photodiode is amplified, filtered, and V/f converted by the feedback module 81, and the RS232 sends data to the control module 83, which is processed by the control module 83 according to a certain algorithm, and then Send an order to the execution module 82 again. After the execution module 82 is executed, the optical path difference will be changed, which will change the feedback light intensity, and the feedback light intensity will be detected by the photodiode. The feedback module 81, the execution module 82 and the control module 83 form a closed-loop control.

Specific to the actual circuit implementation, in order to convert the light intensity signal into an electrical signal, the light sensor 7 uses a photodiode, but the voltage output by the photodiode is very low, only in the millivolt level, and the signal-to-noise ratio is very low. Such a small signal AD conversion cannot be performed directly, it must be amplified. For this reason, the circuit diagram of the amplifying circuit of the photodiode amplification and filtering part 811 shown in Figure 5 has been designed. The photodiode is a kind of photoelectric conversion device that converts the incident light intensity into a current proportional to it. Reverse bias is often required, as shown in Figure 5, the bias voltage provided to the photodiode is -15 volts. Since the output current of the photodiode is very small, it needs to be further amplified. The amplifying part of the photodiode is composed of three parts. The first is the current amplification amplifier circuit composed of the photodiode and the operational amplifier U1. The reason why R1 is 56 ohms is to make the photodiode work in the linear region, that is, the output current I _o is proportional to the light intensity. Capacitor C1 can filter out the high-frequency noise signal from the photodiode. The output voltage after the first stage of amplification is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Secondly, it is a digital zero-adjustment circuit composed of digital potentiometer X9C503 and buffer OP07, U3 in the figure. Its function is to output a negative voltage -V _ref (V _ref > 0), and then V _o and V _ref are input together to The last level consists of

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 9</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="104"\; label="C"\; filenames="C20041009182000171.png"\; state="\{\{state\}\}">C</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 104</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

In the adder with reverse amplification function composed of digital potentiometer X9C104 and operational amplifier _U2 . The output voltage is:

Where R _x9c104 is the resistance value of digital potentiometer X9C104.

的关系为：In the closed-loop control to be realized, it is necessary to collect the interference signal intensity of two laser beams that have undergone special polarization processing, and then use it as a criterion for closed-loop control. The phase difference between the intensity I _total of the interference light signal to be collected and the two beams of light to be controlled

The relationship is:

I _total ＝I _const +I(φ)-----(1-12)

是同相位差

有关的光强度变化部分。为了提高控制的灵敏度和精度，我们希望

同I_const的比值越大越好，而上面的电路可以帮助我们比较完美地解决这个问题。Among them, I _const is a light intensity constant generated because the light beam splitter in the experimental light path cannot split the beams with equal intensity.

is the same phase difference

Sections related to light intensity changes. In order to improve the sensitivity and precision of the control, we hope

The larger the ratio to I _const, the better, and the above circuit can help us solve this problem perfectly.

即：From formula (1-12), we can think that the amplified voltage V _o of the photocurrent converted by the photodiode is composed of two parts V _const and

Right now:

V _o ＝V _const +V(φ)-----(1-13)

Substituting formula (1-13) into formula (1-11), we can get:

Properly adjusting the digital potentiometer X9C503 to change the zeroing voltage V _ref can make the first bracket in the above formula

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="V\; const\; R"\; filenames="C20041009182000141.png"\; state="\{\{state\}\}">V</figure-callout></span><figure-callout\; id="3"\; label="V\; const\; R"\; filenames="C20041009182000141.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; const</span>}}}{{}_{}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 9</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="104"\; label="C"\; filenames="C20041009182000171.png"\; state="\{\{state\}\}">C</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 104</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 9</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="104"\; label="C"\; filenames="C20041009182000171.png"\; state="\{\{state\}\}">C</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 104</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

The first and third terms of the offset and almost only for to zoom in. Right now:

According to the above parameters, properly adjust the digital potentiometer R _x9c503 to offset the constant light intensity part I _const in the optical signal, and then select the appropriate resistance value of R _x9c104 to just amplify the changing part of the optical signal into the range of 0 ~ -10V, which can be Make full use of the precision of V/F conversion.

Due to the interference caused by the external micro-vibration of the system, the change of the intensity of the feedback light is low-frequency, so the amplified voltage needs to be further filtered. This system uses a second-order high-pass filter. The schematic diagram is as follows Figure 6 shows.

V/F conversion is to convert the voltage into a frequency proportional to it. It is a special AD conversion method. This conversion method has many advantages. The biggest reason for using this method when collecting optical signals is: V/F The conversion process is to continuously integrate the input signal, which has the advantage of balancing random or high-frequency variables caused by noise in the optical signal. The circuit of the V/F conversion part 812 is shown in Figure 7, the input analog voltage range of this circuit is 0-10V, the output frequency is 0-200KHz, and the nonlinearity is 0.03%. It is mainly composed of chips LM331 and TL082, and the full-scale frequency can be adjusted by properly adjusting the resistance of the above 2K rheostat during use. In order to obtain the best linearity, the rheostat R16 should be adjusted so that the potential of the second pin of TL082 is 0. If the capacitance of the integral capacitor C4 or the resistance value of the resistor _R14 is changed, the conversion gain can be adjusted, and the integral capacitor C4 should use a highly stable polyester ene capacitor. If you want to obtain a higher full-scale frequency, you can use AD652 as a V/F conversion device, its full-scale output frequency can reach 2M, and the nonlinear error at this time is only 0.02%.

Since the control module 83 is implemented by a computer, the control and data transmission part 813 is composed of a single-chip microcomputer 89C2051 and a MAX232, which is a very traditional hardware combination method connected with a computer. The frequency output by the V/F converter is counted periodically by the counter T0 of 89C2051 to complete the AD conversion. In fact, changing the period of frequency measurement will change the accuracy of AD conversion. The measurement period can be set by sending commands from the computer to the microcontroller, so it is easy to freely change the accuracy of AD conversion through appropriate microcontroller and computer programming. The improvement of the accuracy of VF conversion is at the cost of reducing the conversion speed, so if the conversion accuracy can be changed freely during the experiment, the best combination point can be found that the accuracy meets the requirements and the conversion speed is as high as possible. During the experiment, when it is only necessary to know the stability of the laser light power, the conversion resolution can be increased so that the conversion module works in a state similar to a high-precision optical power meter; Sometimes, the resolution can be appropriately lowered and the conversion speed can be increased to achieve control. In addition, it is also very easy to realize the change of the value of the two digital potentiometers by computer command 89C2051. A relatively simple software implementation method is to make the single-chip microcomputer in the continuous V/F conversion cycle, and use the serial interrupt method to execute the computer's commands.

The piezoelectric micro-displacement device used as the small stroke stepping motor 10 of this system is purchased from the German PI company. The open-loop precision of piezoelectric ceramics is 1 nanometer, the maximum elongation is 60 microns, the voltage is 100 volts, and its capacitance is 7.6 μf. Its capacitance is quite large, and the fast charge and discharge of such a large capacitance requires the drive circuit to be able to provide a large enough current. The driving circuit must be able to meet the upper limit of the driving requirement, which is assumed to be: 60 microns of piezoelectric ceramic elongation in 1 ms. The current required for this is

I＝Q/T＝CU/T＝0.76(A) (1-16)

It is difficult for current commercial devices to directly measure such parameters. In addition, the current that the driving circuit can provide must also be able to reach 100 volts, which is a voltage range that is far beyond the reach of existing operational amplifiers. In this way, the upper limit instantaneous power requirement of the driving circuit can reach 76 watts, and this must be a digitally controlled power supply, and its voltage step accuracy must be able to meet nanometer level adjustments, that is, its step accuracy should reach 100/(60000) =0.0016 volts, so the DA converter 821 requires 16 bits. It can be seen that the drive circuit must meet the following three conditions:

1. The peak current can reach 0.76 amperes;

2. The voltage swing can reach 100 volts;

3. The accuracy of the voltage step can reach 0.0016 volts, that is, the accuracy of DA conversion can be 16 bits.

DA converters with 16-bit precision are available, but the voltage amplitude output by the DA converter 821 is generally 5 volts, and the maximum current does not exceed 10 mA. Therefore, we must re-amplify the voltage converted by DA, which requires the use of a high-voltage expansion circuit 823 . The high-voltage expansion circuit 823 uses an ordinary operational amplifier as the core of the amplification, and uses two pairs of transistors TIP41C, TIP42C, MJ15025, MJ15024 to increase its voltage, expand its voltage output range and amplify the current, and the current it provides can be as high as one Amperes, the magnitude of the voltage can exceed one hundred volts.

The execution module 82 is actually a digital control power supply, and the structure of the digital control power supply is composed of a microcontroller 89c51, a DA converter, and a high voltage expansion circuit. Among them, the microcontroller 822 is responsible for the communication with the computer and the control of the DA converter 821; the output voltage of the DA converter 821 is in the range of 0 to 5V, and the current is only a few milliamps, which requires further amplification to reach the upper limit. 100 volts. The schematic diagram of the high voltage extension circuit 823 is shown in FIG. 8 . This is composed of an ordinary operational amplifier and two sets of triode pairs. The voltage of the operational amplifier is provided by the emitters of the transistors T1 and T2, and the value of the voltage of the power supply applied to both ends is determined by R2/R7 and R1/R6. The voltage across the amplifier can be calculated as:

V ₊ ＝(60*3.6k/(3.6k+10k)-V _be )≈15V (1-17)

This is within the normal operating voltage range of common op amps. When the output current of the operational amplifier changes, the currents of its power supply voltages V ₊ and _V- change accordingly, so the collector currents of transistors T3 and T4 will also change accordingly. The voltage drop of this changing current on the collector 1K resistance of R5 and R4 is added between the base and emitter of T3 and T4 respectively. Since the emitters of T3 and T4 are respectively connected to +60V and -60V power supplies, the voltage change at both ends of the load is close to plus or minus 60V, here it is plus or minus 59V. Theoretically speaking, the expansion of the output voltage range of this circuit is not limited by the components. Since Q3 and Q4 also have the effect of current amplification, the output power of the circuit increases. Capacitor C has the effect of improving the high frequency response of the circuit, and can improve the dynamic stability of the circuit.

The computer of the invention adopts the PID control method to control the operation of the small stroke stepping motor and the large stroke stepping motor in real time. If no PID control is performed, the acquired data will be irregular, because the phase difference changes irregularly with external interference, so it is reasonable to obtain a graph of irregular light intensity changing with time. But if PID control is performed, the phase difference will be locked, so the feedback light intensity will basically not change, and the measured data should be a straight line. As shown in Figure 9, if a sudden impact from the outside causes the phase difference to deviate from the equilibrium value, the system will quickly return to the equilibrium position under the action of PID control. Back to full balance.

Claims (7)

1. control system of large stroke nanometer precision location, comprise light source (1), two half-reflecting half mirrors (2) (3), interferometer, a half-wave plate (4), a quarter-wave plate (5), an analyzer (6), analysis and Control system (8), (1) was divided into two-beam after inciding first half-reflecting half mirror (2) to light path from light source, incide two arms (91) (92) of interferometer respectively, merge into a branch of light by the light of the first arm (91) light back by half-wave plate (4) and at second half-reflecting half mirror (3) by second arm (92), inject the optical inductor (7) of analysis and Control system (8) afterwards by quarter-wave plate (5) and analyzer (6), second arm (92) that it is characterized in that interferometer is installed on the stepper motor of multi-stage accuracy, the minimum stroke precision of stepper motor is a nanoscale, and control end is connected with analysis and Control system (8);

The stepper motor of described multi-stage accuracy is made of a little stroke stepper motor (10) and a big stroke stepper motor (11), the stroke accuracy of big stroke stepper motor (11) is not more than 2 times of little stroke stepper motor (10) range, and little stroke stepper motor (10) is connected with analysis and Control system (8) respectively with the control end of big stroke stepper motor (11);

Described analysis and Control system (8) comprising:

Be used to the feedback module (81) surveying weak one and convert thereof into digital signal corresponding;

Be used to adjust the execution module (82) of interferometer second arm (92) position;

Be used for the control module (83) that control of realization center and data transmit;

Control module (83) is connected with execution module (82) with feedback module (81) respectively.

2. control system of large stroke nanometer precision location according to claim 1 is characterized in that described little stroke stepper motor (10) is the piezoelectric micromotor stroke device of nanometer for precision.

3. control system of large stroke nanometer precision location according to claim 2 is characterized in that feedback module (81) comprising:

Be used for the optical diode amplification filtering part (811) that light intensity signal extracts and amplifies;

The V/F conversion portion (812) that the back voltage transitions becomes frequency will be amplified;

Be responsible for the order that processing and control module (83) transmits, control first and second digital regulation resistances, and become numeral to pass to the control and the tcp data segment (813) of control module (83) frequency inverted.

4. control system of large stroke nanometer precision location according to claim 3, the amplifying circuit that it is characterized in that optical diode amplification filtering part (811) comprises the electric current scale-up version amplifying circuit of being made up of with first amplifier optical diode, digital zero setting circuit of being made up of first digital regulation resistance and impact damper and the totalizer of being made up of second digital regulation resistance and second amplifier that reverse enlarging function is arranged; The filtering circuit of optical diode amplification filtering part (811) adopts bivalent high-pass filter.

5. control system of large stroke nanometer precision location according to claim 2, it is characterized in that execution module (82) comprises DA converter (821), be responsible for the communication between the same control module (83) and the microcontroller (822) of control DA converter, be used to amplify the high voltage expanded circuit (823) of DA converter output voltage.

6. control system of large stroke nanometer precision location according to claim 2 is characterized in that described control module (83) is computing machine.

7. control system of large stroke nanometer precision location according to claim 6 is characterized in that described control module (83) is to adopt pid control law to control the computing machine of little stroke stepper motor (10) and big stroke stepper motor (11) operation.

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