The application requires by inventor Jahja I.Trisnadi, Clinton B.Carlisle, Charles B.Roxlo and David A.LeHoty submitted on May 21st, 2004, exercise question is the U.S. Provisional Application No.60/573 of " Opticalposition sensing device using telecentric imaging ", 316 rights and interests.The disclosure of above-mentioned U.S. Provisional Application all is combined in herein by reference.
The application also requires the A.LeHoty by inventor David, Douglas A.Webb, CharlesB.Roxlo, C1inton B.Carlisle and Jahja I.Trisnadi are in U.S. Provisional Application No.60/573 that submit to, that be entitled as " Optical position sensing device having a detector array usingdifferent combinations of shared interlaced photosensitive elements " on May 21st, 2004,075 rights and interests.The disclosure of above-mentioned U.S. Provisional Application all is combined in herein by reference.
Embodiment
Spot " boiling " problem
The problem of existing OPD based on spot relates to the change of speckle patterns, or spot " boiling ".In general, mobile thereupon from the speckle patterns on surface when the surface is mobile, and direction is identical, and speed is identical.But in many optical systems, from the phase front that send on the surface, have additional change.For example, change if participate in the light group that speckle patterns forms on the detecting device when the apparent surface of system moves, then the speckle patterns that is detected just is not simple displacement but changes (or " boiling ") in the mode of having a few at random.This just makes (from displacement) to detect the surface and moves employed signal degradation, causes the degree of accuracy of system and susceptibility to descend.
As detailed below, one aspect of the present invention provides a kind of OPD, and its spot boiling can ignore or be reduced.
OPD embodiment disclosed herein
Present disclosure relates generally to be used for the sensor of optical positioning apparatus (OPD), and based on the random strength distribution patterns from the light of surface reflection, and the displacement that is called spot the method that relatively moves between detection sensor and the surface.OPD includes but not limited to be used for importing to personal computer the optical mouse or the tracking ball of data.
Mention " embodiment " or " embodiment " and be meant in instructions, concrete property, structure or a feature illustrating in conjunction with this embodiment are included among at least one embodiment of the present invention.Each local phrase " in one embodiment " that occurs not necessarily all refers to same embodiment in instructions.
In general, the sensor that is used for OPD comprises: irradiator, and it has light source and illumination optics with the illuminated portion surface; Detecting device, it has a plurality of light activated elements and image optics device; And signal Processing or blended signal electronic circuit, be used to make up signal, to produce the output signal of detecting device from each light activated element.
In one embodiment, detecting device and blended signal electronic circuit are to use standard CMOS process and device fabrication.Preferably, sensor of the present invention and method provide a kind of optics efficient detection architecture, that is: the structured illumination of (phase-front) and heart stigmatic image far away before the use generation homogeneous phase, and use the simplification signal Processing of analog-and digital-electronic circuit combination to dispose.This architecture has reduced the signal Processing that is exclusively used in the sensor and the electric power amount of offset estimation.Find, use the spot detection technology and can meet or surpass all properties standard desired usually, comprise maximum displacement speed, degree of accuracy and % tracking error rate OPD according to the sensor that the present invention suitably disposes.
Displacement transducer introduction based on spot
The principle of work that this section discusses that the applicant understood and believed based on the displacement transducer of spot.Though these principle of work are for understanding of great use, embodiments of the invention should unnecessarily not be subjected to the restriction of these principles.
Consult Figure 1A, shown in the laser optical of wavelength be illustrated as being mapped to lip-deep first incident wave 102 and second incident wave 104, each all is formed into firing angle θ with surface normal.Produce diffraction pattern 106, the periodicity that it has is λ/2sin θ.
What form contrast is, consults Figure 1B, and any have size and tend to make light 114 to scatter to four corner to be similar to the Lambertian form greater than the irregular general surface of form of optical wavelength (promptly approximately>1 μ m).If use coherent source such as laser instrument, then when being detected by the square-law detector with finite aperture, the scattered light of spatial coherence can produce complicated interference figure 116.This complex interference pattern 116 of clear zone and dark space is called spot.The exact nature of speckle patterns 116 and contrast depend on surfaceness, light wavelength and spatial coherence degree thereof and optically focused or image optics device.Though usually be high complexity, the obvious characteristic of speckle patterns 116 is one section any rough surface to be arranged by the optical device imaging, so just can be used to it is discerned when the relative laser instrument in lip-deep position and optical device-detector module transverse shift.
The expectation spot has all sizes, and the spatial frequency up to the effective aperture by optical device sets conventionally defines with its numerical aperture NA=sin θ, shown in Figure 1B.According to Goodman[J.W.Goodman, " Statistical Properties of Laser SpecklePatterns " in " Laser Speckle and Related Phenomena " edited by J.C.Dainty, Topics in Applied Physics volume 9, Springer-Verlag (1984)-specifically sees the 39-40 page or leaf], the size statistical distribution is represented with the automatic coherence of spot intensity." on average " spot diameter may be defined as:
(formula 1)
What is interesting is and to point out that the spatial frequency spectrum density of spot intensity according to the Wiener-Khintchine rule, is exactly the automatic coherence's of intensity Fourier transform.The most tiny possible spot a
Min=λ/2NA is set by following unlikely situation, that is: main effect comes from the outermost rays 118 (promptly ± θ ray) of Figure 1B, and from the effect of " interior " ray destructive interference is arranged.So by spatial frequency is f
Co=1/ (λ/2NA) or 2NA/ λ.
Note that numerical aperture for along a dimension (for example " x ") with can be different along the spatial frequency in the image of its orthogonal dimensions (" y ").This may be since optical aperture on a dimension than the length on another dimension (for example oval rather than justify) or owing to anamorphote causes.In these cases, speckle patterns 116 also can be anisotropic, and average blob size can be different on two dimensions.
An advantage based on the laser instrument displacement transducer of spot is that it can come work in order to the irradiates light that nearly normal incidence angle arrives.Adopt the image optics device and also can be used for the transversal displacement sensing with the sensor that the grazing incidence angle arrives the incoherent light of rough surface.But, because the grazing incidence angle of irradiation is used for producing the suitable big light-dark shade of image topographical surface, this system optically efficient itself is just low, and is because light reflexes to outside the detecting device with the minute surface form greatly, therefore inoperative to formed image.On the contrary, can effectively be used to the irradiates light of the major part of self-excitation light source, thereby allow exploitation optics displacement transducer efficiently based on the displacement transducer of spot.
Disclosed design based on the displacement transducer of spot
The architecture that is used for a this laser instrument displacement transducer based on spot has been described in following detailed description, it uses the CMOS photodiode, and simulating signal combinational circuit, an amount of digital signal processing circuit and low power sources, for example 850nm vertical cavity surface emitting laser (VCSEL) arranged.Though being discussed in the following detailed description, some realizes details, but those skilled in the art will appreciate that, under the prerequisite that does not deviate from the spirit and scope of the present invention, different light sources, detecting device or light activated element and/or the different circuit that are used for composite signal also can use.
Now consult Fig. 2 and 3 pairs of mouses based on spot according to the embodiment of the invention are illustrated.
Fig. 2 illustrates the functional diagram based on the system 200 of spot according to the embodiment of the invention.System 200 comprises lasing light emitter 202, illumination optics 204, image optics device 208, a plurality of CMOS photodiode arrays 210 of at least two groups, front-end electronics 212, signal processing circuit 214 and interface circuit 218.Photodiode array 210 can be configured to provide the displacement measurement along two orthogonal axes x and y.Can use the passive electric components in the front-end electronics 212 that the many groups photodiode in each array is made up, to produce group signals.Group signals can be carried out algebraic combination by signal processing circuit 214 subsequently, and (x, y) signal are provided at the amplitude of OPD displacement on x and the y direction and the information of direction to produce.(x, y) signal can convert x, y data 220 to by interface circuit 218, and it can be exported by OPD.Use the sensor of this detection technique can have the interleaved set array of linear photodiode, be called " difference comb arrays ".
Fig. 3 illustrates a general configuration (along an axle) of this photodiode array 302, wherein surface 304 is by coherent source, for example vertical cavity surface emitting laser (VCSEL) 306 and illumination optics 308 irradiations, and wherein in the array 302 combination of interleaved set with the periodic optical filter of work to the light-dark signal space frequency that spot image produced.
The spot that is produced by rough surface 304 is mapped to the detector plane with image optics device 310.Preferably, image optics device 310 is hearts far away, in the hope of optimum performance is arranged.
In one embodiment, in two independent orthogonal arrays, carry out comb arrays and detect, to obtain the offset estimation on x and y.A small-sized this array 302 is shown in Fig. 3.
Each array in the detecting device comprises N photo diode sets, and every group has M photodiode (PD), lines up to form the MN linear array.In the embodiment shown in fig. 3, every group comprises four photodiodes (4PD), is called 1,2,3,4.PD1 in every group is electrically connected (line and) and forms one group, PD2, PD3 and PD4 obtain four signal line of coming out from array too.Electric current of their correspondences or signal are I
1, I
2, I
3And I
4These signals (I
1, I
2, I
3And I
4) can be described as group signals.By using difference analogue circuit 312 to produce homophase differential current signal 314 (I
13)=I
1-I
3, and use difference analogue circuit 316 to produce orthogonal differential current signal 318 (I
24)=I
2-I
4, can realize that background suppresses (and signal increases the weight of).These homophases and orthogonal signal can be described as the line signal.Compare I
13And I
24Phase place just can detect mobile direction.
Preferably, for suppressing the introducing of phase error, because of it can directly be converted to displacement error, sensor of the present invention uses a plurality of comb arrays.In addition, though the embodiment of this paper explanation uses " 4N " scheme to each array, this system design ultimate principle (suitably changing the back) is applicable to other array configurations or scheme, as 3N, 5N, 6N, 7N, 8N or the like.Term " 4N " is meant with each the 4th detecting device line together and resulting four detector arrays that photo-signal is subtracted each other each other, as described in people's such as Dandliker the patent (U.S. Patent No. 5,907,152).But the suitable scheme with composite signal also has many other groupings.
Telecentric imaging is to reduce spot boiling problem
Speckle patterns, example as shown in Figure 1 can be used as the basis of displacement measurement, and wherein surperficial relative measurement device such as spot mouse carry out displacement.This displacement can the displacement of speckle patterns be derived (considering after effective optics amplification coefficient) from detecting device.So successfully a factor of measuring is, speckle patterns carries out almost pure flat moving for little displacement (it is little promptly comparing with the detecting device field of view (FOV)), and pattern itself has only very little change relatively.In this case, coherence or other signal processing algorithms can be used to determine physical displacement.
Speckle patterns change to rare two sources.First source that changes be because: when the detector system apparent surface was shifted, part surface left detecting device FOV, and new a part of surface enters detecting device FOV.This source that speckle patterns changes is inevitably, but estimated displacement just can make this effect minimize in faster time used time by moving on its FOV at ratio sensor.
Second source that speckle patterns changes be because: when surface displacement, the visual angle of each point has changed on the rough surface relatively.As described in the present patent application, the applicant notices: if the image optics device is the non-heart far away at object side (scattering surface), this second changes the source and will take place, and the inclined degree that is to say light depends on visual field point-for example see Fig. 4.
The inclined degree of Fig. 4 illustrates several (five) the illustrative light that works, these light below object side is the lens 404 of imaging system of the non-heart far away from surface 402 each point several points launch.Light shown in the consideration passes the system aperture (not shown) of non-telecentric imaging system, and the intermediate rays of also considering the every group of light that works is a chief ray, and promptly it passes the center of system aperture.As seen from Figure 4, the angle each picture point chief ray apparent surface depends on this position in the visual field.In other words, relevant at the work inclined degree of light of each picture point with visual field point.
When the displacement of the detecting device of the non-telecentric imaging of object side system, from set visual field point image is worked that organize light and just change.Under undesirable extreme case, when the twice that tilt to change more than or equal to the lens numerical aperture, complete incoherent spot will take place.In order to keep translation invariant comparatively speaking speckle patterns, tilting to change should be less than lens numerical aperture (NA).
Object side is that the imaging system of the heart far away is shown in Fig. 5 A and 5B.In the object side telecentric imaging, irrelevant with visual field point basically at the work inclined degree of light of each picture point, and for being in a ratio of little displacement with imaging system FOV, speckle patterns is translation invariant basically.In other words, the chief ray from each picture point is parallel.
First example of Fig. 5 A illustrates the lens 502 that are used for object side telecentric imaging system, and this system configuration becomes to make chief ray perpendicular to surface 402.
Second example of Fig. 5 B illustrates the lens 504 of object side telecentric imaging system, and this system configuration becomes to make 402 one-tenth non-normal angles of chief ray and surface.This embodiment allows same lens 504 to be used for irradiation and imaging function.In this configuration, except imaging function, lens also can be used for guiding irradiation light 506 on the visual field from different perspectives.
Chief ray is the light by the system aperture center.When using in this disclosure, if be parallel or almost parallel from all or most basically chief ray of object (or surface), then imaging system is the heart far away at object side.Equally, if all of directive image (or detecting device) or most basically chief ray are parallel or almost parallel, then imaging system is the heart far away in image-side.
In the object side telecentric system, move axially object (along the z axle move so that body surface is more close or further from imaging system) on the enlargement factor of image, should not produce and change or seldom change.This is parallel because of chief ray, as mentioned above.Move axially object and may make image defocus, but when the mobile tracking based on speckle patterns moved, this not defocusing should become problem.
According to embodiments of the invention, if the optical position sensing system is the heart far away at object side, and if its illumination beam before getting to the surface, have the phase front on plane basically, then this system just can be adapted to the spot boiling with remarkable minimizing.On the contrary, before not having the object side telecentric optics and/or not having the homogeneous phase of illumination beam, significant spot boiling will take place.Non-homogeneous phase front for example can be dispersed.
Object side be the heart far away and getting to the surface before have a phase front on plane basically (promptly have homogeneous phase before) basically imaging system during translation, will cause the spot boiling that reduces.On the other hand, not to be that the imaging system of the heart far away can not reduce the spot boiling during translation at object side but in the imaging side.
Fig. 6 and 7 illustrates by selecting the aperture location in the imaging system can determine mood condition far away.
Imaging system shown in Fig. 6 is configured to make system aperture 604 to be positioned at and is right after after the lens 602.This is a non-telecentric system, because chief ray (thicker light) is with angle scioptics 602, this angle is all different for each picture point on the surface 402.
It is the imaging system of the heart far away that Fig. 7 is illustrated in lens 702 object sides.In the configuration of Fig. 7, system aperture 704 is positioned at back focal plane, and on body surface 402 all or basically all chief rays all be parallel (being vertical in the case).Back focal plane is positioned at the optical range place that equals focal length of lens f apart from the distance of lens 702.At medium is under the situation of air or vacuum, and optical range equals the actual range between lens 702 and the back focal plane, as shown in Figure 7, if but the use refractive index is not 1 material, then the actual range between lens 702 and the system aperture 704 need be done corresponding adjusting.
Object side telecentric system shown in Figure 7 has the aperture that is positioned at back focal plane.So, should effectively be focused on and transmit by the aperture from the collimated light beam of object side.In other words, most of basically collimated light beams should pass the back focal plane aperture of object side telecentric system, but just not necessarily like this for non-telecentric system.
Though the object side telecentric system embodiment shown in Fig. 7 is configured to make chief ray perpendicular to surface 402, alternative also can be configured to for example make chief ray and surperficial 402 one-tenth non-normal angles, as above in conjunction with as described in Fig. 5 B.
Fig. 7 is illustrated in the imaging system that object side is the heart far away, and Fig. 8 is illustrated in the imaging system that image-side is the heart far away.In Fig. 8, aperture 804 is positioned at the front focal plane of lens 802.The system of Fig. 8 does not reduce the spot boiling during translation.
In object side and image-side all is that the system of the heart far away is shown in Fig. 9.F1 and f2 are respectively the focal lengths of left side (object side) lens 902 and right side lens 904 among the figure.The focal length of front lens 902 is f1, and the focal length of rear lens 904 is f2.In this configuration, aperture 906 is positioned at the back focus place of front lens 902, and it overlaps with the front focus of rear lens 904.Can select these focal lengths,, and satisfy virtually any size restriction total length f1+f2 so that enlargement factor=f2/f1 meets is required.
According to embodiments of the invention, for the spot image of keeping translation does not change or few the change, when object (surface) translation, a picture point on the detecting device can be by forming with a branch of light.In other words, when surface translation took place, the inclined degree of the light that works should be constant or almost constant.If it is optical system is the heart far away at object side, for example shown in Fig. 7 or 9, this constant with regard to existence.Because aperture and lens move with detecting device, the mood condition far away of image-side may have some advantages, but does not need.
In above-mentioned discussion, the numerical aperture that the plane of system aperture is positioned at image is defined the place.This aperture can comprise the opaque structure with transparent part of intentional introducing, for example shown in Fig. 7 and 9.Alternative is that the aperture can comprise the lens in the system, maybe can comprise other members that are used to define this aperture.
The optical device layout
As mentioned above, telecentric imaging optical device (for example, shown in Fig. 7 or 9) does not have the strong speckle signal of change basically when can be used to produce translation.This image optics device can make up with illumination optics, to form a holonomic system.
An embodiment of this combination of illumination optics 1002 and image optics device 1004 is shown in Figure 10.In this embodiment, illumination optics 1002 be configured to make the irradiation 1006 normal vectors with apparent surface 402 be that non-zero incident angle θ enters.
The above-mentioned explanation of specific embodiment of the present invention and example is to propose in order to illustrate with illustrative purposes, though and the invention has been described by some previous examples, should not think that the present invention is limited.Illustrate and illustrate and be not intended to exhaustive or limit the invention to disclosed precise forms, many change, improvement and variations within the scope of the invention can be arranged according to foregoing.Scope of the present invention should comprise disclosed herein, and by this paper appended claims and the included general field of their equivalent.