CN102650535A - Method for eliminating influence of vibration over measurement of incremental optical encoder - Google Patents

Abstract

The invention aims to provide a method for eliminating the influence of vibration over the measurement of an incremental optical encoder, so as to solve the technical problem of poor anti-vibration ability of the incremental optical encoder in the prior art. The method is characterized in that on the basis of the existing incremental optical encoder, the number of photoelectric read heads of the optical encoder is increased to four; the four photoelectric read heads are evenly settled along the circumference of an indicating circular grating disc; and each read head is distributed at an angle of 90 DEG relative to a circle center. Stacked grating fringe phases in the positions of the four read heads are solved through the four read heads, an analog-digital (AD) conversion circuit and a phase detection algorithm; then the vibration direction and the vibration amplitude of a scale circular grating disc are calculated on the basis of the phase information of the four specific positions, so as to determine error terms produced during the vibration; and the vibration direction and the vibration amplitude are inversely substituted into an expression of stacked grating fringe phase changes caused by the rotation of the optical encoder, so as to eliminate the influence of the vibration. By adopting the method, phase detection errors of the optical encoder are greatly reduced during the vibration, and the measurement accuracy of the optical encoder is improved when the vibration exists.

Description

A kind of method of eliminating vibrations to increment type optical encoder measurement influence

Technical field

The present invention relates to a kind of method that improves the optical encoder measurement stability, be specifically related to a kind of influence is measured in vibrations to the increment type optical encoder method of eliminating.

Background technology

Optical encoder is that circle grating Moire fringe and photoelectric conversion technique are combined; The angle value of mechanical rotation is converted into a kind of modern sensor of amount of digital information output; Be a kind of precision measurement instrument, belong to photoelectric device, in many angle measurement instruments; The angle measurement accuracy of optical encoder is the highest, can reach a second level.

The increment type optical encoder has two amplitude grating disks, is respectively scale circle grating dish and indication circle grating dish, and two grating disk circumference are carved with the uniform grating groove; The groove of the groove of scale circle grating dish and indication circle grating dish is also not parallel; But exist very little inclination angle, like this, when two circle gratings are taken inventory when relatively rotating; Can form Moire fringe (claiming Moire fringe again) in the interference field of two grating dishes; The photoelectricity read head converts certain some light intensity in the interference field into electric signal, forms sine wave, can learn the angle that relatively rotates of two circle gratings through measuring sinusoidal wave phase changing capacity.Therefore, eliminate the influence to this sine wave of environmental factor and noise, the degree of accuracy that improves the sine wave phase measurement is the key of measurement of angle.

In general, manufacturer adopt to improve the phase-detecting of optical encoder and divided method, improvement grating line processing technology, improve the performance that method such as illuminator strengthens optical encoder.At present, best increment type optical encoder measurement resolution can reach 0.1 ", measuring accuracy can reach 0.036 " (" optical electric axial angle encoder analysis of development situation and prospect " seen the 27th the 1st phase of volume of " optical instrument " periodical, in February, 2005).But; High-precision optical encoder has very high requirement to alignment error and environment for use; As setting-up eccentricity amount, the optical encoder serviceability temperature environment of the installation site of photoelectricity read head, two grating dishes, install rotating shaft effects limit such as vibrations the application of optical encoder, make its some occasions performances not high-precision performance.

The increment type optical encoder is employed in the grating dish basically path position is installed two photoelectricity read heads; When phase-detecting, the phase place reading addition of two read heads is reduced the eccentric influence (" code-disc off-centre is to the theoretical analysis of Moire fringe signal phase influence " with vibrations of optical encoder divided by 2 method again; See " optics journal " the 23rd the 8th phase of volume, in August, 2003).In addition; Also the someone adopts the method for changing grating dish material and improving the optical encoder illuminator to strengthen the anti-vibration adaptability (" a kind of based on the novel absolute photoelectric shaft encoder of metal code disk " of optical encoder; See " sensing technology journal ", the 23rd the 5th phase of volume, in May, 2010; Domestic patent 99250599.2, " a kind of absolute photoelectric shaft encoder illuminator "), these measures hour have obtained good anti seismic efficiency in vibration amplitude, but when vibration amplitude is big, still can not realize the high precision performance of optical encoder.To justify the grating diameter is 50mm, and the grating line number is 16200, and the segmentation number is that 80 increment type optical encoder is an example, and when amplitude of vibration had surpassed 15 μ m, above-mentioned measure just can not reach the normal accuracy rating of optical encoder.

Summary of the invention

The present invention aims to provide a kind of method of eliminating vibrations to increment type optical encoder measurement influence, to solve the technical matters of increment type optical encoder shock resistance difference in the prior art.

Technical scheme of the present invention is following:

A kind of method of eliminating vibrations to increment type optical encoder measurement influence adopts four photoelectricity read heads, may further comprise the steps:

(1) four photoelectricity read heads is evenly settled along indication circle grating dish circumference, made each read head become 90 degree to distribute with respect to the center of circle;

(2) the actual measurement Moire fringe phase place of four read head positions is resolved out through A/D change-over circuit and phase-detecting algorithm by four photoelectricity read heads;

The actual measurement Moire fringe phase place of four read head positions that (3) obtain with step (2) is the basis, calculates scale circle grating dish vibrations direction and vibration amplitude, and then obtains the error term with respect to desirable Moire fringe phase place that produces because of vibrations;

(4) with the mean value of four read head positions of the said error term correction of step (3) Moire fringe phase place, calculate, then eliminated the influence of vibrations basically the Moire fringe phase measurement according to revised mean value expression formula;

If indication grating has identical grating constant δ with the scale grating, indication circle grating radius is R, and the actual measurement Moire fringe phase place that each position read head is read is respectively p ₁, p ₂, p ₃And p ₄,

The calculating formula of the said vibrations direction of step (3) does

$\mathrm{\ϵ}=-\arctan \frac{\tan \frac{\mathrm{\δ}}{2\mathrm{\π}}(p_1-p_3)}{\tan \frac{\mathrm{\δ}}{2\mathrm{\π}}(p_2-p_4)};$

The calculating formula of said vibration amplitude does

${\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">e</figure-callout>}}_2=\frac{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000047623110000022.png,HDA0000047623110000031.png"\; state="\{\{state\}\}">R</figure-callout>}\sqrt{1+{\mathrm{<figure-callout\; id="2"\; label="tan"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">tan</figure-callout>}}^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_1-p_3)+{\mathrm{<figure-callout\; id="2"\; label="tan"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">tan</figure-callout>}}^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_2-p_4)}-\mathrm{<figure-callout\; id="2"\; label="R\; tan"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">R</figure-callout>}}{\sqrt{{\tan }^{}}};$

Said error term with respect to desirable Moire fringe phase place does

The mean value of the actual measurement Moire fringe phase place of four read head positions does

The said revised mean value expression formula of step (4) does

Phase-detecting algorithm in the above-mentioned steps (2) is to adopt tangential method to resolve the actual measurement Moire fringe phase place of four read head positions.In fact, conventional phase-detecting algorithm has multiple, and tangential method is just wherein a kind of, and other phase-detecting algorithm also is applicable to this employing Error Feedback compensating measure result's method.

Beneficial effect of the present invention is; The phase-detecting error of optical encoder when greatly having reduced vibrations; Improved the measuring accuracy of optical encoder when having vibrations; With respect to the current diameter read head method of reading that generally adopts, can more effectively eliminate the influence that optical encoder scale circle grating dish is eccentric and shake; In actual use, make optical encoder can adapt to bigger installation shaft vibrations, thereby expanded the usable range of optical encoder, the precise angle measurement when shaking greatly for rotating shaft provides measurement means.Simultaneously, this method also can be relaxed the requirement to the eccentric debugging of optical encoder, has reduced debugging difficulty, makes it under normal circumstances, promptly shakes when little, also has bigger using value.

Description of drawings

Fig. 1 is an increment type optical encoder eccentric shaking analytical model of the present invention;

The Measurement Phase error of Fig. 2 when adopting traditional single read head;

The error of the synthesis phase that Fig. 3 obtains when being employing traditional double read head;

Fig. 4 is the error of the synthesis phase that adopts four read heads and obtain with the traditional measurement mode;

Fig. 5 is for using the revised error of the present invention's four read head phase places;

Fig. 6 is the duplicate measurements precision contrast (moment of torsion-torsion angle is measured the repeatable accuracy curve) of the present invention's four read head corrections and traditional double read head optical encoder;

Embodiment

The present invention is on the basis of existing increment type optical encoder, the photoelectricity read head quantity of optical encoder is increased to four, and four photoelectricity read heads are evenly settled along indication circle grating dish circumference, makes each read head become 90 degree to distribute with respect to the center of circle.Through four read heads and A/D convertor circuit and phase-detecting algorithm the Moire fringe phase place of four read head positions is resolved out; Phase information with these four ad-hoc locations is the basis again; Calculate scale circle grating dish vibrations direction and vibration amplitude; Thereby error term and the inverse iteration of obtaining this vibrations generation are gone into the Moire fringe phase change expression formula that the rotation of optics scrambler causes, eliminate the influence of vibrations.

The rationale of technical scheme of the present invention and error term derivation are following:

Set up rectangular coordinate system, true origin O is rotating shaft fixed mechanism center, shown in Fig. 1 increment type optical encoder eccentric shaking analytical model, and O ₁For indicating round grating center, O ₂Be scale circle grating center, and indication grating has identical grating constant δ with the scale grating, the angle of promptly adjacent two grid lines is δ.

Each grid line all has the phase place of oneself, is referred to as folded grid phase place, the moving δ angle of then round grating revolution, and this phase change 2 π, as shown in Figure 1, establish indication grating and scale grating and be respectively e with respect to the offset of rotating shaft center of rotation ₁And e ₂, the angle of eccentric direction and x axle is respectively α ₀And ε, and establish and indicate the reference grid line of circle grating parallel with the x axle, the reference grid line of scale grating and the angle of x axle are θ ₀Scale circle grating together rotates with rotating shaft, and when rotating shaft rotation θ, no matter there is bias free at scale circle grating center and rotating shaft center, and the reference grid line of scale grating all can rotate θ thereupon.

The phase place of the detected Moire fringe signal of increment type optical encoder read head D is relevant with the folded grid phase place of indication grating that participate in to form Moire fringe in the read head position and scale grating, the folded grid phase place of establishing the indication grating grid line for

scale grating grid line folded grid phase place is

then the phase place of Moire fringe signal be:

If indication grating is motionless, the scale grating rotates the θ angle, then by geometric relationship, any coordinate points in the interference field (x y) locates, and has:

In the formula, is respectively in the indication grating of participating in the formation of this Moire fringe and the folded grid phase place of scale grating.

If indication circle grating radius is R, the line at read head position and indication circle grating center and indication grating are α with reference to the angle of grid line, and then the read head coordinate is:

X＝Rcosα+e ₁cosα ₀ (4)

Y＝Rsinα+e ₁sinα ₀ (5)

The read head coordinate is brought in (2) formula and (3) formula:

Then the Moire fringe phase place of read head detection is:

Obviously, if indication grating and scale grating are with respect to the rotating shaft center all without acceptance of persons, e then ₁=e ₂=0, α ₀=ε, the Moire fringe phase place should be:

Formula (9) is under the ideal situation, the folded grid phase place that read head detects.

Adopt each read head reading addition again divided by 4 method when handling if be respectively α=0,

α=π and,

phase information along indication circle four read heads of grating dish and indication grating with reference to the angle of grid line, process calculates:

Wherein: $S({\mathrm{<figure-callout\; id="1"\; label="e"\; filenames="HDA0000047623110000022.png,HDA0000047623110000031.png"\; state="\{\{state\}\}">e</figure-callout>}}_1,e_2)={\mathrm{<figure-callout\; id="1"\; label="e"\; filenames="HDA0000047623110000022.png,HDA0000047623110000031.png"\; state="\{\{state\}\}">e</figure-callout>}}_1^2\mathrm{<figure-callout\; id="2"\; label="Sin"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">Sin</figure-callout>}2{\mathrm{\&alpha;}}_0+e_2^2\mathrm{<figure-callout\; id="2"\; label="Sin"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">Sin</figure-callout>}2\mathrm{\&epsiv;}-2e_1{e}_2\mathrm{Sin}(\mathrm{\&epsiv;}+{\mathrm{\&alpha;}}_0)---\left(11\right)$

$C(e_1,e_2)=e_1^2\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">cos</figure-callout>}2{\mathrm{\&alpha;}}_0+e_2^2\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&epsiv;}-2e_1{e}_2\cos (\mathrm{\&epsiv;}+{\mathrm{\&alpha;}}_0)---\left(12\right)$

Omit e ₁And e ₂The quadravalence dimensionless, then:

So at e ₁And e ₂Under the little situation, adopt the eccentric error that also can eliminate optical encoder along four read head readings addition of indication circle grating circle spacing 90 ° of distributions again divided by 4 method effectively.

After optical encoder is debug completion, e ₁Size do not rotate and change with rotating shaft, as long as guarantee to debug quality, can be with e ₁Revise very for a short time, e ₂Vibrations with optical encoder change, and its value is indefinite, so formula (8) can be written as:

Formula (10) can be written as:

With α=0,

α=β with,

Substitution formula (10), and establish the phase place that each position read head reads and be respectively p ₁, p ₂, p ₃And p ₄, then have:

$\mathrm{\&theta;}+{\mathrm{\&theta;}}_0=\arctan \frac{-{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">e</figure-callout>}}_2\sin \mathrm{\&epsiv;}}{R-{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">e</figure-callout>}}_2\cos \mathrm{\&epsiv;}}+\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}{p}_1---\left(16\right)$

$\mathrm{\&theta;}+{\mathrm{\&theta;}}_0=\arctan \frac{R-{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">e</figure-callout>}}_2\sin \mathrm{\&epsiv;}}{-e_2\cos \mathrm{\&epsiv;}}+\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}{p}_2-\frac{\mathrm{\&pi;}}{2}---\left(17\right)$

$\mathrm{\&theta;}+{\mathrm{\&theta;}}_0=\mathrm{<figure-callout\; id="2"\; label="arctan\; e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">arctan</figure-callout>}\frac{e_{}}{}\frac{{}_2\sin \mathrm{\&epsiv;}}{R+{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">e</figure-callout>}}_2\cos \mathrm{\&epsiv;}}+\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}{p}_3-\mathrm{\&pi;}---\left(18\right)$

$\mathrm{\&theta;}+{\mathrm{\&theta;}}_0=\arctan \frac{R+{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">e</figure-callout>}}_2\sin \mathrm{\&epsiv;}}{e_2\cos \mathrm{\&epsiv;}}+\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}{p}_4-\frac{3\mathrm{\&pi;}}{2}---\left(19\right)$

Simultaneous formula (16)～formula (19) can solve:

The vibrations direction: $\mathrm{\&epsiv;}=-\mathrm{Arctan}\frac{\mathrm{Tan}\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_1-p_3)}{\mathrm{Tan}\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_2-p_4)}---\left(20\right)$

Vibration amplitude: ${\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="HDA0000047623110000012.png,HDA0000047623110000021.png"\; state="\{\{state\}\}">e</figure-callout>}}_2=\frac{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000047623110000022.png,HDA0000047623110000031.png"\; state="\{\{state\}\}">R</figure-callout>}\sqrt{1+{\mathrm{Tan}}^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_1-p_3)+{\mathrm{Tan}}^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_2-p_4)}-R}{\sqrt{{\mathrm{Tan}}^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_1-p_3)+{\mathrm{Tan}}^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_2-p_4)}}---\left(21\right)$

Adopt folded grid phase place that four read head phase signal additions calculate divided by 4 method again relatively and the folded grid phase place under the ideal situation, promptly

with respect to the phase error of the folded grid phase place of ideal

is:

With vibrations direction that calculates and vibration amplitude substitution formula (22) and obtain phase error term, revise with this error term

Can obtain working as e ₁When very little, the eccentric revised folded grid phase place of indication circle grating:

In practical application, at first become 90 degree evenly to install along indication circle grating dish circumference four read heads; Then when optical encoder scale circle grating dish rotates, at a time, the phase-detecting that writes down four read heads is p as a result ₁, p ₂, p ₃And p ₄, through type (20)～(22) calculate vibrations direction, vibration amplitude and vibrations error term respectively; Again with p ₁, p ₂, p ₃And p ₄The phase adduction obtains divided by 4

Last through type (23) obtains revised folded grid phase place.Through with the folded grid bit comparison mutually of previous moment optical encoder, draw the rotational angle of scale circle grating dish.

In order to further specify the usefulness of this method, designed the test battery model and carried out emulation.If the optical encoder diameter is 50mm, grating constant is 0.2mrad, scale circle grating eccentric amount e ₂Be 20 μ m, indication circle grating eccentric amount e ₁Be 2 μ m, θ is a scale grating rotational angle, and slewing area is 0～2 π, as indication circle grating eccentric angle α ₀When between 0～2 π, changing, calculate the revised phase-detecting error of single read head, two read head, four read heads and four read heads.

The phase error

that single read head is read is as shown in Figure 2.

Divided by after 2,

is as shown in Figure 3 for the error of synthesis phase again in diameter read head (two read head) reading addition.

Divided by after 4,

is as shown in Figure 4 for the error of synthesis phase again in four read head reading additions.

After employing formula (22) was carried out error correction to four read head synthesis phases, was as shown in Figure 5 for revised phase error.

Can find out that from Fig. 2～Fig. 4 the phase error that single read head is read is bigger, reach the 10rad magnitude, in actual engineering, can not use basically.Under the similarity condition, divided by after 2, the error of synthesis phase is 10 again for the addition of diameter read head reading ^-2The rad magnitude, under accuracy requirement was not very high situation, two read heads can meet the demands.After adopting four read head readings, phase error is 10 ^-9The rad magnitude, with respect to two read heads, precision has improved 10 ⁷Doubly, promptly under same accuracy requirement, adopt four read head methods can reduce debugging requirement to the optical encoder offset.

After employing formula (22) is revised four read head reading phase places, can the vibration effect error magnitude under this simulated conditions be reduced to 10 ^-12Rad, simultaneously, because the vibration of optical encoder installation shaft can be considered e ₁Random variation, four read head methods have been eliminated e ₁Influence, so eliminated optical encoder the influence of rotating shaft vibrations to measuring is installed.

Experimental verification of the present invention

Because the angle measurement accuracy of optical encoder is the highest in the angle measuring instrument; Can't adopt other instruments that its measuring accuracy is demarcated; Promptly can't adopt other instruments that the angle error of this patented method and commonsense method is demarcated; For the actual utility of this method is described, enumerate an application example here.

In a rotating shaft torsion angle measuring system; Assemble a cover optical encoder respectively at the rotating shaft two ends; Optical encoder scale grating dish is connected in the rotating shaft and rotates with rotating shaft; Indication grating is installed on the rotating shaft bracing frame, and countershaft loads different moments of torsion, calculates the torsion angle of rotating shaft through the difference of two cover optical encoder scale circle grating disc spins angles.Testing procedure is following:

(1) the good diameter read head optical encoder of place's Installation and Debugging in fixed position, rotating shaft two ends;

(2) in a certain moment that rotating shaft is rotated, adopt tangential method that the sine wave phase of each read head is carried out phase-detecting, with the phase place addition of two read heads divided by 2 phase places as Moire fringe;

(3) countershaft loads different moments of torsion, loads under the moment of torsion in difference, calculates the Moire fringe phase differential of two cover optical encoders, and the phase differential when loading with no moment of torsion relatively is scaled the torsion angle of rotating shaft;

(4) read head with two cover optical encoders all is changed to equally distributed four read heads, debugs well and be installed in original position;

(5) in a certain moment that rotating shaft is rotated; Adopt tangential method to calculate the phase-detecting result of four read heads; Vibrations direction, vibration amplitude and the vibrations error term of this moment are calculated in through type (20)～(22), and are adapted in the mean value of four read head phase places, obtain the signal of Moire fringe;

(6) countershaft loads different moments of torsion, loads under the moment of torsion in difference, calculates the Moire fringe phase differential of two cover optical encoders, and the phase differential when loading with no moment of torsion relatively is scaled the torsion angle of rotating shaft;

(7), compare the measuring accuracy of two kinds of methods with respect to the theoretical value of torsion angle.

, do not adopt sealed bead bearing between rotating shaft and the bracing frame here, the bearing ball gap is bigger, causes rotating shaft when rotating, to have vibration, can contrast the shock absorbing effect that embodies the increment type optical encoder so better.When adopting traditional double read head and the present invention's four read head optical encoders, its partial test data are as shown in table 1, and it is as shown in Figure 6 to measure repeatable accuracy.

Table 1 is revised the moment of torsion angular measurement value of back optical encoder

In this torsion angle measuring system, the factor that influences the torsion angle measuring accuracy also has the error in length, diameter error, loading moment of torsion error of torsion angle etc. except optical encoder self measuring accuracy.From table 1 and Fig. 6, can find out; When adopting two read head optical encoders to read the rotating shaft torsion angle; Its maximum error of measuring approaches 50 "; and optical encoder can be controlled at 10 with measuring error after the four read head corrections " in, visible four read head methods have tangible effect on eliminating optical encoder off-centre and vibrating.

Claims (2)

1. a method of eliminating vibrations to increment type optical encoder measurement influence adopts four photoelectricity read heads, may further comprise the steps:

(1) four photoelectricity read heads is evenly settled along indication circle grating dish circumference, made each read head become 90 degree to distribute with respect to the center of circle;

(2) the actual measurement Moire fringe phase place of four read head positions is resolved out through A/D change-over circuit and phase-detecting algorithm by four photoelectricity read heads;

The actual measurement Moire fringe phase place of four read head positions that (3) obtain with step (2) is the basis, calculates scale circle grating dish vibrations direction and vibration amplitude, and then obtains the error term with respect to desirable Moire fringe phase place that produces because of vibrations;

(4) with the mean value of four read head positions of the said error term correction of step (3) Moire fringe phase place, calculate, then eliminated the influence of vibrations basically the Moire fringe phase measurement according to revised mean value expression formula;

If indication grating has identical grating constant δ with the scale grating, indication circle grating radius is R, and the actual measurement Moire fringe phase place that each position read head is read is respectively p ₁, p ₂, p ₃And p ₄,

The calculating formula of the said vibrations direction of step (3) does

$\mathrm{\&epsiv;}=-\arctan \frac{\tan \frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_1-p_3)}{\tan \frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_2-p_4)};$

The calculating formula of said vibration amplitude does

$e_2=\frac{R\sqrt{1+{\tan }^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_1-p_3)+{\tan }^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_2-p_4)}-R}{\sqrt{{\tan }^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_1-p_3)+{\tan }^2\frac{\mathrm{\&delta;}}{2\mathrm{\&pi;}}(p_2-p_4)}};$

Said error term with respect to desirable Moire fringe phase place does

The mean value of the actual measurement Moire fringe phase place of four read head positions does

The said revised mean value expression formula of step (4) does

2. elimination vibrations according to claim 1 are measured the method for influence to the increment type optical encoder, it is characterized in that: said phase-detecting algorithm is to adopt tangential method to resolve the actual measurement Moire fringe phase place of four read head positions.

Images