CN101922909A - A high-precision capacitive displacement sensor that directly detects the height difference of the mirror surface without contact - Google Patents

Abstract

A high-precision capacitive displacement sensor that directly detects the height difference of the mirror surface without contact. The mirror surfaces of each sub-mirror to be detected are installed on the truss of the support system. On the side of the reference plate facing the sub-mirror and corresponding to the sub-mirror, a capacitor plate is installed; at the same time, the reflective metal film layer of the corresponding detected sub-mirror or the metal mirror itself is used as the other pole of the capacitor plate; connect the two capacitive plates with the detection circuit of the capacitive displacement sensor. The invention can directly realize the height difference detection of spliced mirror surfaces. It has the advantages of clear principle, compact structure, simple process and high height difference detection accuracy; compared with traditional classic sensors, it can directly and non-contact obtain the mirror height difference without introducing other stray light. The invention is applicable to the height difference detection of mirror surfaces of various optical or radio systems.

Description

The high-precision capacitance-type displacement sensor of direct non-contact detection of mirror surface high-low difference

Technical field

The present invention relates to a kind of for the direct high-precision capacitance-type displacement sensor that detects of splicing mirror surface high-low difference noncontact, be used to be particularly useful for needs and realize that splicing astronomical telescope mirror surface high-low difference detects the occasion of (comprise that optical system requires confocal and common phase, even use in enormous quantities).

Background technology

The high-precision sensor technology is the inevitable choice of scientific and technical high development.The common sensor that detects the minute surface height when can be used for splicing astronomical telescope mirror minute surface has a variety of, mainly is divided into contact and contactless, direct-detecting mode and indirect detection formula or the like; Contact mainly is included in displacement transducers such as the electric capacity the minute surface back side or side installed, inductance, current vortex, detects the minute surface height by calibration in advance; And contactless optical fibre displacement sensor and other pupil detection and the image planes detection method based on optical system of mainly containing; Directly detect the displacement that is meant direct acquisition difference of height and express, indirect detection then needs detection angles or other physical quantity to obtain displacement indirectly by formula or method.

Above-mentioned several different methods and the displacement transducer of being realized thereof all have various shortcomings.Contact type measurement needs often to use Other Instruments carry out the transducer calibration of high and low position at the minute surface back side or installation position, side displacement sensor, such as Keck telescope splicing primary mirror etc.; Though and optical fibre displacement sensor can directly reflect the height of minute surface, because adopt optical energy to detect, so can bring influence of various factors such as veiling glare to optical system, fiber end face and minute surface influence measuring accuracy apart from meeting in addition; Pupil face based on the optical detection system detects and the image planes detection method, can be subjected to the influence that the various environmental factors of atmospheric turbulence, temperature variation, noise or the like change, and precision is limited and detection is limited in batches, and use occasion is limited.

Summary of the invention

The high-precision capacitance-type displacement sensor that the purpose of this invention is to provide a kind of direct non-contact detection of mirror surface high-low difference, this condenser type mirror surface high-low difference displacement transducer can directly be measured the difference of height of minute surface, and principle is clear, compact conformation and technology are simple.With respect to the sensor of traditional classical, this condenser type mirror surface high-low difference displacement transducer can obtain mirror surface high-low difference in direct, non-contact manner, does not introduce other parasitic light.The present invention is applicable to that the mirror surface high-low difference of various optics or radio system detects.

The scheme of finishing the foregoing invention task is, a kind of high-precision capacitance-type displacement sensor of direct non-contact detection of mirror surface high-low difference, the sub-mirror minute surface of detected each is installed on the truss of support system, it is characterized in that, the truss of described support system is provided with a datum plate, this datum plate facing to the one side of sub-mirror, the position corresponding with sub-mirror minute surface on, capacitor plate is installed; Simultaneously, with the reflective metals rete or the metallic mirror surface itself of the detected sub-mirror minute surface of correspondence, as another pole plate of electric capacity; These two capacitor plates are connected with the testing circuit of capacitance displacement sensor.

In the above scheme, on the datum plate of two adjacent sub-mirror minute surface correspondences, a capacitor plate or two capacitor plates can be installed respectively.Also can will the capacitor plate of two homalographics of symmetry be installed all on the datum plate on two sub-mirrors, the error of inclination be installed to eliminate, thus the way of realization of pie graph 2.

Principle of work of the present invention is:

At first propose a kind of high-precision capacitance-type displacement sensor, and be referred to as condenser type mirror surface high-low difference displacement transducer for the direct detection of splicing mirror surface high-low difference.As shown in Figure 1.With the reflective metals rete or the metallic mirror surface of minute surface, form capacitive transducer with the homalographic capacitor plate on the reference field; On a minute surface, arrange two capacitive transducers, and arrange a capacitive transducer on the minute surface in addition, install caused error to eliminate reference field; Homalographic capacitor plate on minute surface and the reference field connects resonant circuit or other testing circuit, for fear of mirror metal reflectance coating or metallic mirror surface heating, can adopt the incomplete driving amplifier testing circuit of minute surface ground connection; The size of capacitor plate area can calibrate proportionate relationship by other surveying instrument.For example, receive in the circuit simultaneously a utmost point of two electric capacity respectively, other one extremely corresponding same enough big pole plate, the pole span of two electric capacity guarantees identical and parallel by installation or reference block, by determining capacitance size and proportionate relationship thereof, calibrate correlation proportion coefficients such as pole plate area to the detection of electric capacity or interlock circuit parameter.

Technical in above two mirror surface high-low difference detecting sensors, (sexangle splices then N is 6 if to adjacent N sub-mirror, quadrilateral splices then, and N is 4), N-2 sensor probe (each minute surface respectively comprises a minute surface capacitive transducer) be can stretch out in addition, thereby the detection and the demarcation of adjacent whole sub-mirror differences of height realized.

The testing circuit of capacitance displacement sensor has bridge diagram, resonant circuit, FM circuit, operational amplification circuit, difference pulse width modulation circuit, incomplete driving amplifier testing circuit etc.

Be object hereinafter, it is carried out Theoretical Calculation and its characteristic is described further with Fig. 1 condenser type mirror surface high-low difference displacement transducer.

1, condenser type mirror surface high-low difference displacement transducer displacement detecting and precision analysis

$C=\frac{{\mathrm{\ϵ}}_0\mathrm{\ϵS}}{\mathrm{\δ}}---\left(1\right)$

$\mathrm{dC}=-\frac{{\mathrm{\ϵ}}_0\mathrm{\ϵS}}{{\mathrm{\δ}}^2}\mathrm{d\δ}---\left(2\right)$

$K=\frac{\mathrm{dC}}{\mathrm{d\δ}}=-\frac{{\mathrm{\ϵ}}_0\mathrm{\ϵS}}{{\mathrm{\δ}}^2}=-\frac{C}{\mathrm{\δ}}---\left(3\right)$

When measured δ, S or ε change, all can cause changes in capacitance.If keep two parameter constants wherein, and only change another parameter, just can be transformed to the variation of this parameter the variation of single electric capacity.Change the parameter difference according to it, capacitance type sensor can be divided into following three kinds: the medium type sensor that changes the specific inductive capacity (ε 0) of the pole span type sensor of the distance (δ) of pole plate, the area type sensor that changes pole plate masked area (s), change dielectric.Pole span formula capacitive transducer.Calculate as can be known its sensitivity K and pole span square and be inversely proportional to, pole span is littler, and sensitivity is height more.Generally improve sensitivity by reducing initial pole span (δ 0).But pole span reduces to be subjected to the restriction of voltage breakdown between capacitor plate.Because electric capacity C and pole span δ are nonlinear relationship, so this will cause nonlinearity erron.When Δ δ/δ 0 ≈ 0.1, can obtain approximate linear.In order to reduce this error, usually specifying measurement range delta δ＜＜δ 0.Generally getting the pole span variation range is Δ δ/δ 0 ≈ 0.01～0.1, and at this moment, the sensitivity of sensor is approximately constant.About general δ 0=0.1～1mm.This type of electric capacity only is suitable for the measurement (0.01 micron～hundreds of microns) of micro-displacement.

Classical pole span formula capacitive displacement displacement transducer in actual applications, for the sensitivity that improves sensor, increase linear working range and overcome the influence of the variation of external condition (as supply voltage, environment temperature etc.) measuring accuracy, usually adopt two capacitance serially connected differential-type capacitance type sensors.

Condenser type mirror surface high-low difference displacement transducer can realize overcoming the influence of the variation of external condition to measuring accuracy equally by the straight line distribution form of three electric capacity.

Before installing, demarcate by the capacitance detecting of on two-frequency laser interferometer, carrying out the same pole distance, can obtain the proportionate relationship of S of three capacitor plate areas and the distance proportion relation between three electric capacity.After the sensing adjustment of the splicing minute surface of optical system was finished, be difference of height fully this moment between the minute surface.By measuring three pole span δ ₅, δ ₆, δ ₇, utilize the relation of the area S that demarcates can calculate three pole span δ accurately ₅₀, δ ₆₀, δ ₇₀Then datum plate with respect to the tilt quantity of minute surface is:

$\mathrm{\θ}=\frac{{\mathrm{\δ}}_{60}-{\mathrm{\δ}}_{50}}{d_{56}}---\left(4\right)$

The d here ₅₆Be the spacing of sensor 5 and 6 on the line.The sub-mirror in electric capacity 7 places then can be expressed as with respect to the difference of height of the sub-mirror of electric capacity 5 and 6 places:

$\mathrm{\Δd}={\mathrm{\δ}}_{70}-{\mathrm{\δ}}_{50}-\frac{({\mathrm{\δ}}_{60}-{\mathrm{\δ}}_{50})\×d_{57}}{d_{56}}---\left(5\right)$

d ₅₇Be the spacing of sensor 5 and 7 on the line.

As can be seen from the above equation, difference of height can transmit the precision that keeps capacitance displacement sensor equally.

Can adopt the incomplete driving amplifier testing circuit mode of minute surface ground connection, then can be by amplifier open loop enlargement factor being adjusted to enough big (generally more than 85～90dB), the influence of electric cable capacitance is reduced to enough little, circuit is simple, and cost is low.

The invention has the beneficial effects as follows: condenser type mirror surface high-low difference displacement transducer can directly be realized splicing mirror surface high-low difference and detect.Have that principle is clear, compact conformation, technology is simple and difference of height accuracy of detection advantages of higher; With respect to the sensor of traditional classical, can obtain mirror surface high-low difference in direct, non-contact manner, do not introduce other parasitic light.The present invention is applicable to that the mirror surface high-low difference of various optics or radio system detects.

Description of drawings

Fig. 1 minute surface condenser type difference of height displacement sensor structure figure;

Fig. 2 symmetry minute surface condenser type difference of height displacement sensor structure figure;

Fig. 3 is a kind of circuit theory diagrams of resonance testing circuit of electric capacity.

Among the figure 1, capacitive transducer places the benchmark base plate, 2, place the minute surface of two capacitive transducers, 3, place the minute surface of a capacitive transducer, 4, the bindiny mechanism between benchmark base plate and truss; 5, capacitor 5,6,7, the 8 minute surface wiring of capacitor 6,7 capacitors, 9, sub-mirror sub-truss, 10, capacitor, 11, capacitive detection circuit.

12,15,17 are respectively common electric capacity among Fig. 3, and 16 is variable capacitance, and 13 and 14 is common inductance, and 18 is oscillator, and 19 for amplifying and demodulator probe.

Embodiment

Embodiment 1, with reference to Fig. 1: two minute surfaces 2 in the drawings, dispose two capacitive transducer positive plates 5 on the datum plate 1 of 3 tops respectively, 6, (promptly there are two for symmetrical expression herein with a capacitive transducer positive plate 7, be respectively 7 and 10), along rectilinear direction, to eliminate the droop error of reference seat, the negative plate of capacitive transducer then utilizes the metallic reflective coating or the metallic mirror surface itself of minute surface, the reference seat of capacitive transducer is connected on the truss 9 of minute surface support system, determine the systematic error of this sensor by the method for calibration in advance, mainly from the area of capacitor plate and electric capacity spacing etc., and before installation, adjust electric capacity reference seat 1 and truss bindiny mechanism 4 approximate vertical (sensor plate and minute surface almost parallel, error is little) and by bindiny mechanism 4 can coarse adjustment electric capacity two die openings to scope 0.1～0.2 millimeter of sensor.The minute surface electrode is by cable 8 connection circuits 11 or direct ground connection, and capacitance electrode 5,6,7,10 cables are directly from truss bindiny mechanism 4 cablings.The external testing circuit 11 of whole sensor system.

Embodiment 2, with reference to Fig. 2: and substantially the same manner as Example 1, but institute's configuration capacitive transducer positive plate is two on the datum plate 1 of two minute surface 2,3 tops, is respectively 7 and 10.

Claims (6)

1. A high-precision capacitive displacement sensor that directly detects the height difference of the mirror surface without contact, each sub-mirror mirror surface to be detected is installed on the truss of the support system, and it is characterized in that a datum is arranged on the truss of the support system plate, on the side of the reference plate facing the sub-mirror and at the position corresponding to the sub-mirror mirror surface, a capacitor plate is installed; at the same time, the reflective metal film layer or the metal mirror surface of the corresponding detected sub-mirror mirror surface is used as a capacitor The other plate; the two capacitive plates are connected to the detection circuit of the capacitive displacement sensor. 2. the high-accuracy capacitive displacement sensor of non-contact direct detection mirror level difference according to claim 1, it is characterized in that, the capacitance polar plate installed on the reference plate corresponding to the mirror surface of two adjacent sub-mirrors is Install one and two capacitor plates respectively. 3. the high-accuracy capacitive displacement sensor of non-contact direct detection mirror level difference according to claim 1, it is characterized in that, the capacitance polar plate installed on the reference plate corresponding to the mirror surface of two adjacent sub-mirrors is Both capacitor plates are installed. 4. The high-precision capacitive displacement sensor for non-contact direct detection of mirror level difference according to claim 1, characterized in that, the detection circuit of the capacitive displacement sensor is: a bridge circuit, a resonant circuit, a frequency modulation circuit, an operation Amplifying circuits, differential pulse width modulation circuits, or partially driven amplifier detection circuits. 5. The high-precision capacitive displacement sensor for non-contact and direct detection of the height difference of the mirror surface according to any one of claims 1 to 4, characterized in that, the detection circuit of the capacitive displacement sensor adopts an incomplete drive amplifier grounded on the mirror surface detection circuit. 6. The high-precision capacitive displacement sensor for non-contact direct detection of mirror level difference according to claim 5, characterized in that, the open-loop magnification of the amplifier in the incomplete drive amplifier detection circuit of the capacitive displacement sensor is at 85 ~90dB or more to reduce the influence of cable capacitance.

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