CN101408409A - High precision digital type linear displacement transducer - Google Patents

Abstract

The invention discloses a high-precision digital linear displacement sensor comprising a grate disk driven by a motor. A photolithographic beam is arranged on the grate disk; a linear track is arranged above the grate disk; a reflective infrared photoelectric sensor is respectively arranged at two ends of the linear track and the other reflective infrared photoelectric sensor is connected with movable objects on the linear track; the face of the grate disk facing the reflective infrared photoelectric sensor is a bright face. The high-precision digital linear displacement sensor has the advantages that the measurement range is wide; the structure is simple; the mounting is convenient; the cost is low; the measurement precision and the resolving power are high; zero-regulation can be avoided; and the direction can be directly judged through software.

Description

High precision digital type linear displacement transducer

Technical field:

The present invention relates to a kind of linear displacement transducer, specifically, relate to a kind of very high-precision digital type linear displacement transducer that has.

Background technology:

In commercial production, especially require straight-line displacement to detect and have higher precision and resolution in fields such as Aero-Space, automatic armament equipments, this just strengthens greatly to the requirement of linear displacement transducer.It is current that to be used for straight-line displacement measured sensor kind a lot, but existing sensors more or less all exists some problems in actual applications, the equipment complexity that has, cost height, have to the environmental requirement height, the precision that has is low, the range of linearity is little, the complex structure that has, technological requirement height.Simple as capacitive sensor structure, dynamic response is fast, but is subjected to stray capacitance and external interference easily.Inductance type transducer is simple in structure, output power is big, and output impedance is little, and antijamming capability is strong, but its dynamic response is slow, is subject to magnetic interference.Magnetic induction sensor is easy to install, and cost is low, and single precision is not high, need shield poor anti jamming capability during use.Optical grating ruler measurement precision height, controllability is good, is generally adopted.The linear displacement grating chi precision and the resolution of producing as companies such as German HEIDENHAIN, Japanese MITUTOYO are very high.But it is high that the grating chi requires environment for use, requires grating to operate steadily, do not have sudden change and relative low speed, and polluted by industry spot dust, greasy dirt and aqueous vapor.Homemade grating sensor deal is heavy, low, the unstable properties of precision, and the high precision grating chi of import costs an arm and a leg.All there are the high problem of cost in this infrared optical fiber linear displacement transducer and laser sensor.

Summary of the invention:

The invention provides a kind of simple in structure, easy for installation, cost is low, measuring accuracy and the high high precision digital type linear displacement transducer of resolution.

The technical solution adopted for the present invention to solve the technical problems is:

A kind of high precision digital type linear displacement transducer, it is characterized in that: comprise motor-driven grating dish, the grating dish is provided with a printing opacity groove, grating dish top is provided with rectilinear orbit, the rectilinear orbit two ends install a reflective infrared photoelectric sensor respectively, other has a reflection infrared sensor to be connected with mobile object on the rectilinear orbit, and the grating card is a wet look to the one side of reflection infrared sensor.

The beneficial effect of high precision digital type linear displacement transducer of the present invention mainly shows:

1. simple in structure, the grating dish is made simple, need only open a printing opacity groove, and live width does not need very narrow, as long as can make the reflective photoelectric sensor work of being adopted just passable.Easy for installation, realize the digitizing non-contact detection.

2. cost is low, and measurement range is big.

3. precision and resolution height keeping adopting the high-frequency impulse completion method under the stable prerequisite of motor speed, can obtain very high precision.

4. need not return to zero before measuring, need not direction judgment circuit, can by software directly declare to, made things convenient for testing process.

Description of drawings:

The invention will be further described below in conjunction with drawings and Examples.

Fig. 1 is a high precision digital type linear displacement transducer structural drawing of the present invention;

Fig. 2 is a linear displacement transducer measuring principle diagrammatic top view 1 of the present invention;

Fig. 3 is a linear displacement transducer measuring principle sequential chart 1 of the present invention;

Fig. 4 is a linear displacement transducer measuring principle diagrammatic top view 2 of the present invention;

Fig. 5 is a linear displacement transducer measuring principle diagrammatic top view 3 of the present invention;

Fig. 6 is a linear displacement transducer measuring principle sequential chart 2 of the present invention.

Fig. 7 is a linear displacement transducer measuring principle diagrammatic top view 4 of the present invention;

Fig. 8 is a sensor interface circuitry structured flowchart of the present invention;

Fig. 9 is a sensor interface circuitry of the present invention high-frequency impulse counting circuit schematic diagram when adopting 74HC4040 as counter.

Embodiment:

A kind of high precision digital type linear displacement transducer, comprise the grating dish 5 that motor 6 drives, the grating dish is provided with a printing opacity groove 7, grating dish top is provided with rectilinear orbit 4, the rectilinear orbit two ends install a reflective infrared photoelectric sensor 1,2 (quiet sensor) respectively, other has a reflection infrared sensor 3 (dynamic sensor) to be connected with mobile object on the rectilinear orbit, and the grating card is a wet look to the one side of reflection infrared sensor.

The round grating that uses only has a printing opacity groove, and the grating dish adopts material such as the inferior preferably light aluminium of reflecting properties, and its one side towards reflective photoelectric sensor is a wet look.When printing opacity groove process reflective photoelectric sensor, sensor is exported a low level pulse.When groove during without reflective photoelectric sensor, the light that the infrared transmitting tube of sensor sends is through the reflection of grating card, receiving end output high level.4 is object linear running track (track), and testee is along track (track) linear running, and reflective photoelectric sensor 1,2 is fixed on the track two ends, and reflective photoelectric sensor 3 is followed the testee motion.For easy analysis, below abbreviate trans photoelectric sensor 1,2 as " quiet sensor " (wherein photoelectric sensor 1 is called the quiet sensor of work, photoelectric sensor 2 and is called auxiliary quiet sensor), reflective photoelectric sensor 3 abbreviates " dynamic sensor " as, and the rotating speed of small synchronous motor abbreviates " synchronous rotational speed " as.

1. the testee moving direction is away from the quiet sensor of work

The measuring principle vertical view as shown in Figure 2, be clockwise direction if turn to synchronously, n is a synchronous rotational speed, the testee initial position is at the A0 place, before measurement, start synchronous motor earlier and drive the rotation of grating dish, after grating printing opacity groove passes through quiet sensor 1, dynamic sensor, quiet sensor 2 respectively, can export three pulse signals (supposing to be after treatment undersuing) according to this.

Sensor measurement principle sequential chart as shown in Figure 3.Before measuring, after synchronous motor rotated, the pulse signal of the output of quiet sensor 1, dynamic sensor, quiet sensor 2 was respectively shown in pulse A, B and D among Fig. 3.Quiet sensor 1 is θ with the initial phase difference of dynamic sensor ₁This moment we at two interpulse filling high-frequency impulses, start the high-frequency impulse counting at quiet sensor 1 pulse negative edge, stop counting (shown in the pulse C among Fig. 3) at the dynamic sensor negative edge, then count high-frequency impulse number N ₁With θ ₁Be directly proportional.In like manner, export interpulse filling high-frequency impulse, establish θ=θ at two quiet sensors ₁+ θ ₂+ θ ₃+ θ ₄, then high-frequency impulse is counted N ₂Be directly proportional with θ.When grating line continues rotation, when contacting once more, can obtain 360 ° of high-frequency impulses of counting of synchronous motor rotation and count N with quiet sensor 1 ₈Can get:

${\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="A20081023632800161.png,A20081023632800171.png"\; state="\{\{state\}\}">L</figure-callout>}}_1=\frac{{\mathrm{<figure-callout\; id="5"\; label="L"\; filenames="A20081023632800161.png,A20081023632800201.png"\; state="\{\{state\}\}">L</figure-callout>}}_5\mathrm{Sin}{\mathrm{\&theta;}}_1}{\mathrm{Sin}(180-{\mathrm{\&theta;}}_1-{\mathrm{\&theta;}}_5)}$ (establish θ ₅, L ₅Known) (2)

When measured object has produced displacement of the lines, then drive the same moved further of dynamic sensor, establish from position A ₀Move to position A ₁, this moment, quiet sensor output pulse was constant, and dynamic sensor output pulse is shown in the F among Fig. 3.At this moment, we at two interpulse filling high-frequency impulses shown in figure G, pulse number H then ₅With θ ₁+ θ ₂Be directly proportional N ₄=N ₅-N ₁With θ ₂Be directly proportional.Can get:

${\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="A20081023632800201.png"\; state="\{\{state\}\}">L</figure-callout>}}_2=\frac{{\mathrm{<figure-callout\; id="5"\; label="L"\; filenames="A20081023632800161.png,A20081023632800201.png"\; state="\{\{state\}\}">L</figure-callout>}}_5\mathrm{Sin}({\mathrm{\&theta;}}_1+{\mathrm{\&theta;}}_2)}{\mathrm{Sin}(180-{\mathrm{\&theta;}}_1-{\mathrm{\&theta;}}_2-{\mathrm{\&theta;}}_5)}-L_1---\left(4\right)$

In like manner, when measured object with A ₁Be initial point, from position A ₁Move to position A ₂, the output pulse waveform of dynamic sensor is shown in the H of Fig. 3, by counting the high frequency between two pulse negative edges at this moment

Umber of pulse is N ₇(shown in figure I).The umber of pulse N of the angular displacement representative that this is stylish ₆=N ₇-N ₅The angular displacement that moves of measured object then ₃:

Then the straight-line displacement of object of which movement is:

${\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="A20081023632800161.png,A20081023632800201.png"\; state="\{\{state\}\}">L</figure-callout>}}_3=\frac{{\mathrm{<figure-callout\; id="5"\; label="L"\; filenames="A20081023632800161.png,A20081023632800201.png"\; state="\{\{state\}\}">L</figure-callout>}}_5\mathrm{Sin}({\mathrm{\&theta;}}_1+{\mathrm{\&theta;}}_2+{\mathrm{\&theta;}}_3)}{\mathrm{Sin}(180-{\mathrm{\&theta;}}_1-{\mathrm{\&theta;}}_2-{\mathrm{\&theta;}}_3-{\mathrm{\&theta;}}_5)}-L_1-L_2---\left(6\right)$

Can adopt said method to obtain the linear movement measuring general formula:

$L=\frac{L_G\mathrm{Sin}({\mathrm{\&theta;}}_C+\mathrm{\&theta;})}{\mathrm{Sin}(180-{\mathrm{\&theta;}}_C-\mathrm{\&theta;}-{\mathrm{\&theta;}}_G)}-L_Q---\left(7\right)$

In the formula, the tested displacement of the lines of L-; L _G-electrical axis in the heart distance in the quiet sensor 1; θ _CInitial time phase differential between-dynamic and static sensor; θ _GThe angle of-quiet sensor 1 center and formed line of electrical axis and rectilinear orbit; θ-dynamic sensor straight line moves the phasing degree that the back produces; L _QDistance between the quiet dynamic sensor of-initial time; N _BHigh-frequency impulse number between quiet dynamic sensor of-this moment; N _CHigh-frequency impulse number between the quiet dynamic sensor of-initial time; N-360 degree scope high-frequency impulse number.

Be noted that here " high-frequency impulse number between the quiet dynamic sensor of initial time " is not a fixing number.As initial time is defined in A ₀N then ₁Be " high-frequency impulse number between the quiet dynamic sensor of initial time "; As constantly being defined in A at the beginning of the handle ₁, N then ₄Be " high-frequency impulse number between the quiet dynamic sensor of initial time ".This will need to decide on measurement, can realize different functions by software in interface routing.

What here use is dynamic measurement method, and not stall of synchronous motor just is moving, and controller constantly writes down the high-frequency impulse number between quiet dynamic sensor, constantly according to formula update calculation result and demonstration.By showing, the regularly straight-line displacement of Measuring Object and observe the dynamic process that the measured object straight line moves.

The precision of measurement result and resolution depend on the frequency of high-frequency impulse and the at the uniform velocity degree that synchronous motor rotates, as long as the frequency of high-frequency impulse is enough high, the synchronous motor uniform rotation can obtain very high measuring accuracy and Measurement Resolution in theory.

At this we also as can be seen, the effect redundancy of quiet sensor 2 only needs a quiet sensor (the quiet sensor of working) and a dynamic sensor just can finish the displacement of the lines detection.We still adopt two quiet sensors in design, can make things convenient for the user to adopt different detection modes to finish greater functionality.

And the position of rectilinear orbit and grating disk can not have influence on measurement, as long as rectilinear orbit without the center of circle and in the disk scope, can detect.As shown in Figure 4, rectilinear orbit (track) at an arbitrary position, adopt the single-lens reflex infrared sensor to detect, formula 7,8 is suitable equally.

2. the testee moving direction is near the quiet sensor of work

When the quiet sensor of the approaching gradually work of testee moving direction, as shown in Figure 5.The dynamic sensor initial position is at A ₀The place, the printing opacity groove can be exported two pulses, shown in the A among Fig. 6, B after passing through dynamic sensor again through quiet sensor.The phase differential of two pulses is two sensors initial phase difference θ=θ ₁+ θ ₂+ θ ₃Start high-frequency impulse counting at quiet sensor pulse negative edge this moment, stops counting (shown in the pulse C among Fig. 6) at the dynamic sensor negative edge, then count high-frequency impulse number N ₁Be directly proportional with θ.If initial distance L=L between quiet dynamic sensor ₁+ L ₂+ L ₃

When measured object has produced displacement of the lines, then drive dynamic sensor and be synchronized with the movement, establish from position A ₀Move to position A ₁, this moment, quiet sensor output pulse was constant, and dynamic sensor output pulse is shown in the D among Fig. 6.At this moment, we two interpulse filling high-frequency impulses as figure E shown in, count high-frequency impulse number N ₃With (θ ₂+ θ ₃) be directly proportional.

Can obtain N by subtraction ₂=N ₁-N ₃, shown in C among the figure.N ₂With angular displacement ₁Be directly proportional.And can obtain synchronous motor turns over 360 ° of high-frequency impulses of counting and counts N ₆Then computing formula is as follows:

L ₁＝L-L ₂-L ₃ (13)

In like manner, when measured object with A ₁As reference position, from position A ₁Move to position A ₂, the output pulse waveform of quiet sensor and dynamic sensor is N by the high-frequency impulse number of counting between two pulse negative edges shown in D, F among the figure at this moment ₅(shown in G among the figure).Can get:

L ₂＝L ₂+L ₃-L ₃ (17)

Can adopt said method to obtain the linear movement measuring general formula:

$L=L_Q-\frac{L_G\mathrm{Sin}{\mathrm{\&theta;}}_B}{\mathrm{Sin}(180-{\mathrm{\&theta;}}_G-{\mathrm{\&theta;}}_B)}---\left(18\right)$

The tested displacement of the lines of L-; L _G-electrical axis to quiet transducer spacing from; θ _GThe angle of-quiet center sensor and formed line of electrical axis and rectilinear orbit; L _QDistance between the quiet dynamic sensor of-initial time; N _BHigh-frequency impulse number between quiet dynamic sensor of-this moment; N _GHigh-frequency impulse number between the quiet dynamic sensor of-initial time; N-360 degree scope high-frequency impulse number; θ _B-dynamic sensor straight line moves phase differential between the dynamic and static sensor of back.

3. the testee moving direction is unknown or indefinite

Turning to synchronously by synchronous motor in the sensor provides, direction immobilize (supposing to be fixed as clockwise direction).And be unknown or indefinite under a lot of situations of testee moving direction.At first to differentiate in the case by the thing moving direction.Method of discrimination is very simple: when grating line the N-1 time through having obtained the high-frequency impulse number between them behind quiet, the dynamic sensor, in interface circuit software, be recorded as " high-frequency impulse number between last quiet dynamic sensor " with register.Then grating line the N time is recorded as " high-frequency impulse number between quiet dynamic sensor of this moment " through the high-frequency impulse number that obtains behind quiet, the dynamic sensor.Deduct " high-frequency impulse number between last quiet dynamic sensor " with " high-frequency impulse number between quiet dynamic sensor of this moment ", if for just just illustrating that measured object moves to the direction away from the quiet sensor of work, adopts 7,8 formulas to calculate displacement of the lines at this moment.If for negative explanation object moves to the direction near the quiet sensor of work, adopt 18,19 formulas to calculate displacement of the lines this moment.When grating line the N+1 time during, the N time " high-frequency impulse number between quiet dynamic sensor of this moment " calculated as the N+1 time " high-frequency impulse number between last quiet dynamic sensor " and differentiate through quiet dynamic sensor.In the time of need not knowing moving direction if only need calculate displacement of the lines, there is no need so loaded down with trivial detailsly, only need use formula 7,8 or 18,19 all the time, the result takes absolute value and gets final product.

In a more general case, synchronous rotational speed is indefinite, and situation as shown in Figure 7 can appear in the not timing of movement of objects direction: initial angle is greater than 180 ° between quiet dynamic sensor.Turn to synchronously oppositely in order to use formula 7,8 or 18,19 to calculate, should to make.Therefore the sensor that can obtain inventing uses flow process:

1. before detecting small synchronous motor is rotated, in the interface circuit microcontroller, pass through procedure identification, make grating line pass through the resulting pulse of quiet sensor for the first time as initial pulse, the output pulse that remains dynamic sensor lags behind quiet sensor output pulse.And calculate when initial distance and corresponding angle between quiet dynamic sensor.

2. then do not process less than 180 ° as initial angle between quiet dynamic sensor, turn to as then changing synchronous motor greater than 180 °, and the work of repeating step " 1. ".

3. differentiate the movement of objects direction.If object moves towards the direction near the quiet sensor of work, then adopt formula 18,19 to calculate displacement of the lines.Move towards direction as object, then adopt formula 7,8 to calculate displacement of the lines away from the quiet sensor of work.

When measuring, also can adopt two high-frequency impulse numbers between quiet sensor as benchmark, replace 360 degree scope high-frequency impulses to count N.

4. sensor performance and strengths and weaknesses analysis

4.1 sensor precision, accuracy and resolution analysis

For linear movement pick-up, precision of measurement, accuracy and resolution are most important technical indicators.Precision of measurement is meant under the same terms, to measured repeatedly repeated measurement, the unanimity between the measured value (meeting) degree of carrying out.From the angle of measuring error, what precision reflected is the stochastic error of measured value.In native system, precision of measurement depends primarily on the degree of uniformity of synchronous rotational speed.

Measuring accuracy (accuracy) is meant the degree of closeness of measured measured value and its " true value ".From the angle of measuring error, what correctness reflected is the systematic error of measured value.This moment, we came accessible resolution of system and precision on the theory of computation, supposes that the synchronous motor rotating speed is 200r/min (3.3r/s) in the sensor, and then the driven by motor grating line rotates 360 and spends the high-frequency impulse number of being remembered and be: $\frac{1/3.3}{1/(25\&times;{10}^6)}\&ap;7575757$ Individual.Then minimum in theory distinguishable angle is

The pairing displacement of the lines of this angle also is very little, so linear movement measuring resolution and precision are all very high.And motor speed is slow more, and systemic resolution is high more, and precision is also high more.But motor rotation speed is more little, and system responses is slow more.In order to improve system response time, should make the motor fast rotational, can improve system accuracy and resolution this moment by increasing the high-frequency impulse frequency.

4.2 the strengths and weaknesses analysis of novel linear displacement transducer system

This novel linear displacement transducer advantage is as follows:

(1) measurement range is big, only needs to guarantee that the movement of objects scope gets final product in the circle that with the grating line is radius, increases grating line length and can increase range.

(2) simple in structure, easy for installation, cost is low.

(3) measuring accuracy and resolution height.

(4) need not return to zero before the measurement.

(5) do not need to add in addition direction judgment circuit, by software directly declare to.

Also there is shortcoming in this system design and improves one's methods:

(1) there is certain systematic error

Be mainly electrical error and synchronous rotational speed error.Electrical error is made up of two parts, the controller that adopts in the system enters interruption after receiving the dynamic sensor signal, sending latch signal simultaneously reads the high-frequency impulse number and needs certain hour, this time can be caused the high-frequency impulse number the read umber of pulse more than reality, form the measuring system error, can be by improving controller (as selecting for use CPLD, FPGA or DSP etc. to reduce error) as controller.In addition, when controller carries out sinusoidal calculations, generally adopt look-up table can have certain error, can be by improving algorithm and adopting high side controller to reduce error.The synchronous rotational speed error causes the high-frequency impulse counting error mainly due to the inhomogeneous meeting of synchronous rotational speed, can reduce error by selecting the high motor of rotating speed uniformity coefficient for use.

(2) response speed is slow

After measured object produced straight-line displacement, sensor can not make an immediate response, and could respond but will wait until that light is deleted when groove turns to new displacement place.Can improve response speed by improving synchronous rotational speed.Maybe this sensor is used for the regularly occasion of measurement.

(3) be unsuitable for measuring the high speed ohject displacement

5. sensor interface circuitry design

5.1 hardware design The general frame

In design, the mode that adopts the AT89S51 single-chip microcomputer to combine with high-speed counter 74HC4040 or CPLD can effectively reduce system cost, the expandability of enhanced system.The interface circuit The general frame as shown in Figure 8.

5.2 signal processing module

As adopt reflection infrared sensor as position transducer, can adopt comparers such as LM339 that sensor output signal is carried out shaping.

5.3 high-frequency count module

The 74HC4040 frequency of operation can reach 50MHZ.The high-frequency impulse counting circuit of this problem design as shown in Figure 9.Counting unit adopts the active crystal oscillator of 25M to import as high-frequency impulse, triggers 74HC4040 by the pulse negative edge and begins counting.Because 74HC4040 is 12 binary counters, so system adopts the mode of two cascades, and first most significant digit is connected to second CLK end, thereby with first Gao Siwei low four 16 binary counters of composition jointly with second.If but only adopted 16 countings can not satisfy system requirements, because the full required time of 16 digit counter meters would be $\frac{1}{25\&times;{10}^6}\&times;2^{16}=0.002621$ Second, this means that sensor grating groove must be less than 0.002621 second through the time interval between dynamic sensor and quiet sensor, synchronous motor does not reach so high speed.So we count full 2 with the T0 end that the Q4 of second 74HC4040 receives single-chip microcomputer ¹⁶Negative edge appears in Q4 after the number, triggers the T0 counting.Because T0 then can constitute 32 binary counters by above structure originally as 16 binary counters.If the full required time of meter is $\frac{1}{25\&times;{10}^6}\&times;2^{32}=171.8$ Second, can meet the demands.The 25M clock is through 2 simultaneously ¹⁶Frequency division, the count frequency of T0 end is 381HZ, this also can meet the demands.

In addition, also can adopt CPLD as the high-frequency count module, CPLD has that frequency height, integrated level height, antijamming capability are strong, good reliability, maintainable characteristics such as strong.Though use CPLD to increase system cost, realized the lifting of system performance.The present invention selects for use the EPM7032 of ALTERA company production as the CPLD module in the hardware design.Adopt CPLD to finish tally function in the experiment, single-chip microcomputer is finished computing and is shown memory function.

5.4 display module and data memory module

Adopt the charactron dynamic display types, the I/O mouth of 8255 expansion single-chip microcomputers.Wherein the PA mouth is exported segment encode, PB mouth and PC mouth output bit code.The bit scan mouth adds reverse driven 75452 so that enough drive currents to be provided, and the segment data mouth is received each section of LED again through driver 7407 in the same way.The historical data of the straight-line displacement of measuring in the native system will be preserved, so that the user inquires about, has used nonvolatile memory 24C04 to preserve these information in the hardware system for this reason, and single-chip microcomputer passes through I ²The software package of C agreement is read and write 24C04.

Claims (1)

1, a kind of high precision digital type linear displacement transducer, it is characterized in that: comprise motor-driven grating dish, the grating dish is provided with a printing opacity groove, grating dish top is provided with rectilinear orbit, the rectilinear orbit two ends install a reflective infrared photoelectric sensor respectively, other has a reflection infrared sensor to be connected with mobile object on the rectilinear orbit, and the grating card is a wet look to the one side of reflection infrared sensor.

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