KR100571346B1 - Each encoder - Google Patents

Abstract

An angle sensor is disclosed that includes a body 1 rotatable about an axis of rotation 8 fixed to an enclosing housing 5. The body 1 has a grating element 2 comprising a plane of rotation about an axis of rotation, the plane of rotation 21 of a pseudo-random distribution of high EMR reflectance arranged in the form of an endless series of individual binary barcodes and A region of low EMR reflectance 22, wherein each position sensor also has an array 9 of EMR sensitive detectors fixed relative to the EMR source 10 and the housing, the EMR source roughening the plane of rotation and the array being Receives the reflected incident EMR, and a pattern is generated by the incident EMR on the array from alternating high and low reflectance regions on the rotating surface, which pattern is generated by the processor 11 to obtain the absolute angular position of the region with respect to the housing. And provide a measurement of the absolute angular position of the rotor relative to the housing.

Absolute angular position, grating element, EMR source, EMR reflectance, EMR sensitive detector, pattern, processor, rotor, housing, binary barcode

Description

Each encoder {ANGLE ENCODER}

The present invention relates to an angular position sensor, and more particularly to a sensor for detecting the absolute rotation angle of the rotating body without the need to count from the reference mark.

Conventionally, each position sensor has been used to detect the rotation angle of the rotating body. Each such position sensor conventionally consists of a detector device and a scale scale made of a material with a contrasting bar formed of alternating transparent and opaque or reflective bars, the displacement of the bar being in a detector device comprising light emission, photodetection and optical means. Is detected.

The scale scale is illuminated by light emitting means, which is an EMR source that generates a pattern on one or more arrays of photodetectors that are sensitive to electromagnetic radiation (EMR), usually UV, visible or IR light. Such arrays include CCD devices, VLSI vision chips, one or two dimensional photodetector arrays and side effect photodiodes (commonly referred to as PSD devices or position sensitive devices). The outputs of one or more arrays are processed to estimate measurements of each position of the rotor. The scale scale may be arranged axially or radially around the axis of rotation of the rotor, and may have the property of enabling continuous output of the array regardless of each position of the rotor, while the limited array dimensions are arbitrary It does not allow the complete circumferential or radial plane to be seen by the array at one point.

Such sensors usually provide a signal based on the incremental angular position of the scale, and the absolute angular position is determined by counting from known reference positions. Incremental sensor accuracy is often substantially improved by using well-known techniques such as quadrature interpolation. Such quadrature interpolation methods require an invariant bar angular spacing.

Alternatively, the sensor can provide an absolute position based signal by using a barcode attached to the scale. These barcodes usually do not have a fixed angle of bar spacing because each set of barcodes is unique to each location where they are detected, and such absolute position sensors usually do not measure the position provided by the incremental sensor because it cannot use quadrature interpolation techniques. Does not provide accuracy.

However, if an absolute position sensor with high accuracy is needed, two scales are needed. The first scale measures the coarse absolute position by interrogation of the barcode, and the second scale provides fine relative position by orthogonal interpolation of the regular bar pattern.

Prior art that provides a high accuracy absolute position measurement and is most closely associated with each encoder of the present invention is described in US Pat. No. 5,235,181 (Durana et al.). It describes a sensor consisting of two scales, pseudo-random barcode scales for coarse absolute position, and regularly spaced scales for fine position.

The position sensor described in US Pat. No. 5,235,181 has some inherent drawbacks. The use of two scales requires the use of multiple photodetector arrays of increased cost compared to a single array. In addition, the scale and the array need to be positioned very precisely with respect to each other, which also increases cost and limits the maximum accuracy of the sensor. In addition, the inevitable changes in mechanical deflection and assembly clearance during use cause uncertainties in the relative position of the two arrays, which further limits the maximum accuracy possible.

The essence of the present invention is to provide both absolute resolution of coarse resolution and incremental position detection of fine resolution on a single scale providing all the necessary information. Preferably this is accomplished by using a bar code having a constant bar pitch and various bar widths or alternatively a special type of bar code with various bar pitches. Thus, the bar code provides the binary information needed for absolute position detection and also provides a regular bar pattern that enables interpolation of fine resolution of the position. Further, the sensor is preferably in accordance with the reflection principle, wherein the light emitting means and the light detecting means are located on the same side of the rotating body, and the scale includes an area of high and low reflectance.

Compared to that described in US Pat. No. 5,235,181, this design has several advantages. First, using only a single scale requires only one photodetector array, reducing costs. Secondly, when both scales are combined, inaccuracies due to relative scale misalignment are eliminated to provide better measurement accuracy. Third, the combination of the two scales into a single form makes the sensor less susceptible to mechanical torsion, tolerances or bearing clearances, since variations in the relative positions of the two scales and arrays described in the prior art are eliminated. Fourthly, the use of reflective scales allows for simpler and more compact structures since the light emitting and photodetecting means can be packaged in the same assembly with additional savings in space and cost of the sensor. Fifth, another advantage of using a reflective scale over a transmissive scale is that edge scattering as in the case where the EMR is reflected from the surface of the scale and has an opening, or a transparent material where the EMR must pass through the mediator in the transmissive region It is not affected by internal reflections, refractions or other problems due to deterioration with time, as in the case of having. Such effects limit the maximum resolution of the sensor in other ways. Finally, combined scales are less complex than two separate scales and can be produced faster and at lower cost, especially when direct writing techniques such as laser marking are applied.

The invention relates to at least one body having a grid element at least partially enclosed by the housing, rotatable about a fixed axis of rotation relative to the housing and attached to or integrally formed with the housing; A source and an array of at least one EMR sensitive detector, the grating element comprising a plane of rotation about an axis of rotation, the plane of rotation comprising a pseudo-random distribution of high EMR arranged in the form of a series of discrete binary barcodes A region of reflectance and low EMR reflectivity, wherein the EMR source irradiates the plane of rotation and the array receives an incident EMR reflected from the plane of rotation, the EMR source and the array being fixed relative to the housing, the grating From alternating low and high reflectance regions on the plane of rotation of the element A pattern is generated by an incident EMR on the ray, and the pattern on the array is processed by a processor to obtain an absolute angular position of the area relative to the housing, thus providing a measure of the absolute angular position of the rotor relative to the housing. Each position consists of a sensor.

In one embodiment at least one body comprises two rotors, each rotor having a respective grating element, the two rotors being connected by a member having a predetermined torsional rigidity, the at least one The array of EMR sensitive detectors receives an incident EMR reflected from the plane of rotation of the grating element, and the pattern is processed to obtain an absolute angular position of the area on the plane of rotation of the grating element relative to the housing, and between absolute angular positions The difference is further processed to obtain the relative angular displacement of the grating elements, thus providing a measure of the torque transmitted by the member. There are two arrays of EMR sensitive detectors, each of which is associated with a respective grid element. The number of EMR sources is two, and each of the two EMR sources is associated with each lattice element.

The rotating surface is preferably at least partially cylindrical or partially conical.

Either the region of high EMR reflectance or the region of low EMR reflectance preferably includes bars having constant centerline pitch and various thicknesses. The bars of various thicknesses preferably consist of bars having at least two distinct thicknesses. The bars preferably have only two thicknesses, i.e. wide bars and narrow bars.
Alternatively, either the high EMR reflectance region or the low EMR reflectance region comprises bars having various centerline pitches, wherein the pitch is an integer multiple of the base pitch. Alternatively, the bars with the various centerline pitches are preferably of constant thickness. The bars of various thicknesses preferably consist of bars having at least two distinct thicknesses. The bars preferably have only two thicknesses, i.e. wide bars and narrow bars.

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In some embodiments, the rotating surface has a plurality of castels that project radially therefrom. The high reflectance region corresponds to the largest protruding regions of the castellation, and the low reflectance region is preferably angularly aligned with the less protruding regions between the castels. Maximum protruding zones can be machined smoothly, molded or sintered to impart high reflectivity, or surfaced with paint or a stack of materials, and discrete gap zones or less protruding zones can be machined to give low reflectivity It is preferred to be molded or sintered, or to be surface treated with a paint or certain material stack.

The areas of high reflectivity are preferably metal coated, shiny or brightly colored, and the areas of low reflectivity are substantially transparent, matte, roughened or dark colored, forming a reflection scale.

At least one array of EMR detectors is located radially inward or outward of the plane of rotation.

The array of at least one EMR detector preferably comprises a one or two dimensional array, a CCD, a VLSI vision chip or a side effect photodiode.

It is also desirable to process the pattern with a processor to obtain the angular velocity of the rotor relative to the housing.

1A is a schematic cross-sectional view of each position sensor according to a first embodiment of the present invention showing a rotating body and a radially arranged photodetector array composed of low reflectance and high reflectance regions provided by radially projecting castellation;

FIG. 1B is an enlarged partial view of the grid element shown in FIG. 1A;

FIG. 2A is a schematic cross-sectional view of an angular position sensor similar to that shown in FIG. 1A using an axially projecting castellation and an axially arranged photodetector array; FIG.

FIG. 2B is an enlarged partial view of the grating element shown in FIG. 2A;

3A is a schematic cross-sectional view of each position sensor according to a second embodiment of the present invention showing a rotating body composed of a cylindrical scale surface having an area of high and low reflectivity and a radially arranged photodetector array;

3b is an enlarged partial view of the grating element shown in FIG.

4A is a schematic cross-sectional view of an angular position sensor similar to that shown in FIG. 3A using a disk shaped surface with an array of photodetectors arranged axially;

4b is an enlarged partial view of the grating element shown in FIG. 4a;

FIG. 5 shows a technique used to provide both an absolute angle measurement of a pattern and a coarse resolution and an interpolated incremental measurement of fine resolution, incident on a photodetector array, and

6 is a schematic cross-sectional view of each position sensor according to a third embodiment of the present invention in which a sensor provided for the measurement of the torque transmitted by the torsional member comprises two rotating bodies coupled by the torsional member.

1A and 1B show each position sensor according to the first embodiment of the present invention. The rotor 1 comprises a grating element 2 having a discontinuous outer cylindrical face 14 composed of low and high EMR reflectance regions arranged alternately in the form of a series of individual binary barcodes. The grating element 2 comprises a radially projecting castellation 3 interposed between the radially extending cavities 4. The region of high reflectivity on the cylindrical surface 14 corresponds to the region 12 of the maximum radius of the castel 3 with respect to the axis of rotation 8 of the rotor 1 and is machined smoothly to give the required high reflectivity. It may be molded, molded or sintered, or surface treated with paint or with a stack of certain materials. The low reflectance region on the cylindrical surface 14 corresponds to the discontinuous gap region 13 and is the region of minimum radius which is substantially antireflective due to the presence of the cavity 4 and is disposed at a smaller radius than the region 12 described above ( 15) and are ideally machined, molded or sintered, or surface treated with paint or some material laminates to impart low reflectance. The rotor 1 is enclosed in the housing 5 and supported in the bearings 6, 7 and can rotate about the axis of rotation 8. The EMR source 10 and the EMR sensitive photodetector array 9 are fixed and arranged in the housing 5 such that the EMR source 10 irradiates the discontinuous surface 14, which discontinues the EMR. This reflects to the array 9 arranged radially. A pattern is thus produced on the array 9, which is processed by the processor 11 to provide a measure of the absolute angular position of the rotor 1 with respect to the housing 5. The words "reflection", "reflected" and "reflectivity" herein refer to mirrors and / or diffuse reflections.

2A and 2B show an alternative angular position sensor according to the first embodiment of the invention. The rotating body 1 comprises a grating element 2 having discontinuous radially oriented flat disk faces 14 composed of alternating high and low EMR reflecting regions arranged in the form of a series of individual binary barcodes. do. The grating element 2 comprises an axially projecting castellation 3 interposed between the cavities 4 extending axially. The high reflectance region corresponds to the maximum axial protruding region 12 of the castellation 3 about the axis of rotation 8 of the rotor 1 and is smoothly machined, molded or sintered to give the required high reflectivity. Or it may be surface treated with paint or a stack of certain materials. The low reflectance region corresponds to the discontinuous gap region 13 and is virtually antireflective due to the presence of the cavity 4. The rotor 1 is enclosed in the housing 5 and supported in the bearings 6, 7 and can rotate about the axis of rotation 8. The EMR source 10 and the EMR sensitive photodetector array 9 are fixed and arranged in the housing 5 so that the EMR source 10 irradiates the discontinuous surface 14, which discontinuous surface 14 is substantially axis. EMR is radiated again to the array 9 arranged in the direction. A pattern is thus produced on the array 9, which is processed by the processor 11 to provide a measure of the absolute angular position of the rotor 1 with respect to the housing 5.

3A and 3B show each position sensor according to the second embodiment of the present invention. The grating element 2 of the rotor 1 comprises a continuous cylindrical surface in the form of a scale scale 20 consisting of a high EMR reflectance region and a low EMR reflectance region arranged alternately in the form of a series of individual binary barcodes. . Metallic coatings, or other shiny or brightly colored materials or surface treatments, provide substantially reflective axially aligned regions 21 of high reflectivity. Substantially transparent roughened or dark colored material or surface treatment provides a region 22 between low reflectivity. The rotor 1 is enclosed in the housing 5 and supported in the bearings 6, 7 and can rotate about the axis of rotation 8. The EMR source 10 and the EMR sensitive photodetector array 9 are fixed and arranged in the housing 5 so that the EMR source 10 irradiates the regions 21 and 22 of high and low reflectivity, and the regions 21 and 22. Reradiates EMR into the array 9 arranged substantially radially. A pattern is thus produced on the array 9, which is processed by the processor 11 to provide a measure of the absolute angular position of the rotor 1 with respect to the housing 5.

4a and 4b show an alternative angular position sensor according to a second embodiment of the invention. The grid element 2 of the rotor 1 is a continuous radially oriented flat in the form of a scale scale 20 consisting of high and low EMR reflectance regions arranged alternately in the form of a series of individual binary barcodes. Includes disk facets. A metallic coating, or other shiny or brightly colored material or surface treatment, provides a substantially radially aligned area 21 of high reflectivity. Substantially transparent, roughened or dark colored material or surface treatment provides a region 22 between low reflectivity. The rotor 1 is enclosed in the housing 5 and is supported in the bearings 6, 7 and can rotate about the axis of rotation 8. The EMR source 10 and the EMR sensitive photodetector array 9 are fixed and arranged in the housing 5 so that the EMR source 10 irradiates the regions 21 and 22 of high and low reflectivity, and the region 21. (22) radiates EMR to the array (9) substantially arranged in the axial direction. A pattern is thus produced on the array 9, which is processed by the processor 11 to provide a measure of the absolute angular position of the rotor 1 with respect to the housing 5.

In both the case of the first and second embodiments, the rotary body 1 with respect to the housing 5 can be easily programmed or wired in order to calculate the rate of change of the absolute angular position of the rotary body 1 as a function of time. It also provides a measure of the absolute angular velocity of.

5 shows an example of a pattern generated by the incident EMR on the array 9 according to the first or second embodiment of the present invention (also according to the third embodiment described below). Individual bits 30a-e are dark regions of the pattern on the array 9 caused by reduced levels of reflection from regions of low reflectivity 13 (first embodiment) or 22 (second embodiment). Indicates. Array 9 is a one-dimensional "linear" array, for example a Texas Instruments TSL 1410 Black & White Linear Array chip with 128 pixels and an active window length of about 8 mm. Such an array is intended to provide both absolute angular position measurements and incremental angular position measurements of fine resolution. Absolute angular positioning is performed by reading at least one word (in this case word 31 comprising 5 bits) formed by a predetermined number of consecutive bits, so as to determine the absolute random position of the words in the pseudorandom sequence. Enable verification. The placement and use of such pseudorandom sequences is well known in the field of image analysis and is described in US Pat. No. 5,576,535 with reference to absolute linear displacement measurements. Another example of a combination of such sequences is described as Ouroborean ring in "Game, Set and Math" by Ian Stewart of Penguin Books, 1989.

However, the arrangement of the low and high EMR reflectance regions employed in this embodiment of the present invention is such that the pattern generated on the array 9 has a constant centerline pitch while having different widths "p" and "q". It differs because it contains a sequence of bits of "a" (ie, the distance distance between the centerlines of adjacent bars). 5 shows a 5-bit word 31 having binary " 1 " represented by bits 30a, 30d having a width " p " and binary " 0 " represented by bits 30b, 30c, 30e having a width " q " Is showing. Thus, the complete word 31 is 10010 (i.e., 18 in base 10, the base 10), which is processed by the processor 11 to provide a unique absolute angular position of the rotor 1. Importantly, the placement of the high and low EMR reflectance regions resulting in a pattern on the array 9 with a constant pitch allows the same pattern and thus the array to be used for the measurement of incremental angular positions of fine resolution. One such interpolation technique is also shown in FIG. 5. The EMR intensity pattern on the array 9 is represented by the horizontal scale where x represents the angular displacement and P is represented by P (x) which is a function of x.

If the EMR intensity pattern is sinusoidal,

P (x) = sin [2л (x-d) / a]

Where a is the pitch of the pattern,

d is the displacement of the pattern.

The pattern P (x) is sampled by the individual pixels of the array 9. Let P _i be the i th sample. So the "pattern vector" of n samples is equal to P = [P ₁ , P ₂ , P ₃ , ... P _n ].

Two weighting functions are now defined as sine and cosine weight vectors:

K _1i = sin (2лi / a) where i = 1 ... n

K _2i = cos (2лi / a) where i = 1 ... n

So the phase angle α is

α = arctan [(ΣP _i K _1i ) / (ΣP _i K _2i )] where i = 1 ... n

Is given by

The resulting phase angle α is a measure of the incremental displacement of the pattern with respect to the sine and cosine weight vectors and provides a measure of each position of resolution that is several times finer than the width of one bit of the pattern. The coarse resolution absolute angular position measurement and the fine resolution incremental angular position measurement are combined to provide an absolute angular position detector with fine resolution and low sensitivity to machine deflection and misalignment requiring only one detector array.

The use of other kinds of barcodes with a constant pitch can be similarly handled according to, for example, a "convolution algorithm" where binary bit information is coded as a difference in the length of the bar rather than the width. In addition, the binary bit information can be encoded as a difference in the attenuation level of the reexamined EMR, such as by the use of a grayscale code. Furthermore, while this embodiment describes a convolution algorithm based on bar codes with constant bar pitch and various bar widths, if the selected bar pitching is an integer multiple of the "base pitch", the algorithm is also equally successful for the case of various bar pitches. It should be understood that it will function. For example, referring to the terminology used in FIG. 5, the centerline pitching separating the bits 30a-e is greater than the constant pitch of "a" as shown in FIG. 5, respectively "a", "3a", " 2a "and" a "(with a basic pitch of" a "). In fact, any integer multiple of "a" can be used as the centerline pitch between successive bits. When such various pitch formats of barcodes are selected, barcode encoding can be achieved through various pitch intervals rather than by the bar width (as shown by the bit pattern in FIG. 5), and in this case a constant bar Using width it is still possible to achieve satisfactory barcode encoding for absolute angular position measurements of coarse resolution.

It should also be noted that the sequencing of the barcodes may have retroreflectivity compared to the described embodiment, which is a high reflectance region placed on the low reflectance background.

Also herein "high reflectance" and "low reflectance" are broadly defined in relation to the particular EMR source selected. For example, if red light EMR was used, the high and low reflectance regions of the surface of the reflective grating may consist of regions that are respectively painted (or otherwise colored by some means) with red and blue surface coatings.

6 shows each position sensor according to the third embodiment of the present invention. Each position sensor includes two rotating bodies 1a and 1b connected by a torsion bar 23 having a predetermined torsional rigidity. The grating elements 2a and 2b are attached or integral to the rotors 1a and 1b, respectively, and the arrays 9a and 9b receive the incident EMR reradiated from the surfaces 20a and 20b respectively. In some other embodiments (not shown), the arrays 9a and 9b may be combined as a single array. So this single array will inevitably be a 2D array and will receive EMR reflected from both surfaces 20a and 20b. Similarly, in some other embodiments (not shown), the EMR sources 10a, 10b may be combined as a single EMR source.

Surfaces 20a and 20b are shown to be similar to surface 20 in FIGS. 3a and 3b, ie, these surfaces are cylindrical and have high EMR reflectance regions and low EMR reflectances arranged alternately in the form of an endless series of binary barcodes, respectively. Contains a scale scale consisting of regions. Instead of these continuous cylindrical surfaces 20a, 20b, other types of "rotating surfaces", for example continuous flat disk surfaces (similar to the surface 20 in Figures 4a, 4b), discontinuous cylindrical surfaces (surfaces in Figures 1a, 1b) It will be appreciated that similar to 14), or discontinuous flat disk face (similar to surface 14 of FIGS. 2A, 2B) may alternatively be used. The "rotational surface" of the body of the present specification is defined as a surface uniformly arranged around the axis of rotation in which the body rotates about the center.

The patterns on the arrays 9a and 9b, or the patterns on a single array (not shown) mentioned above, are processed by the processor 11 to provide the surface (surface) of the respective grating elements 2a and 2b with respect to the housing 5, respectively. Absolute angular positions of regions of high and low reflectivity (or transmittance in other embodiments) on 20a, 20b) are obtained. The difference between these absolute angular positions is further processed by the processor 11 to obtain the relative angular displacements of the grating elements 2a, 2b, thus providing a measure of the torque transmitted by the torsion bar 23.

This third embodiment of the angular position sensor thus only provides a measure of the absolute angular position (and potentially their angular velocity as described above) of each of the two rotors 1a, 1b with respect to the housing 5. In addition, the measurement value of the torque (reaction by the torsion bar 23) applied between the rotating bodies 1a and 1b is also provided.

It will be understood by those skilled in the art that numerous changes and modifications can be made without departing from the spirit and scope of the invention.

Claims (21)

At least one body, at least partially enclosed by the housing, having at least one body rotatable about a fixed axis of rotation relative to the housing and having a grating element attached or integrally formed with the housing, at least one EMR source and at least An array of one EMR sensitive detector, the grating element comprising a rotational plane about an axis of rotation, the rotational plane having a high EMR reflectance and low pseudorandom distribution arranged in the form of a series of discrete binary barcodes A region of EMR reflectance, wherein the EMR source irradiates the plane of rotation and the array receives an incident EMR reflected from the plane of rotation, and the EMR source and the array are fixed relative to the housing to rotate the grating element. On the array from alternating low and high reflectance regions on the face A pattern is generated by an incident EMR, and the pattern on the array is processed by a processor to obtain an absolute angular position of the area relative to the housing, thus providing a measure of the absolute angular position of the rotor relative to the housing. Each position sensor. The apparatus of claim 1, wherein at least one body comprises two rotors, each rotor having a respective grid element, the two rotors being connected by a member having a predetermined torsional rigidity, the at least An array of one EMR sensitive detector receives an incident EMR reflected from the plane of rotation of the grating element, and the pattern is processed to obtain an absolute angle position of an area on the plane of rotation of the grating element relative to the housing, and also an absolute angle position. And the difference between them is further processed to obtain a relative angular displacement of the grating elements, thereby providing a measure of the torque transmitted by the member. 3. The position sensor of claim 2, wherein the number of arrays of EMR sensitive detectors is two and each of the two arrays is associated with a respective grating element. 3. The position sensor of claim 2, wherein the number of EMR sources is two, and each of the two EMR sources is associated with a respective grid element. 2. The position sensor of claim 1, wherein the rotating surface is at least partially cylindrical. The position sensor of claim 1, wherein the rotation surface is at least partially conical. The position sensor of claim 1, wherein either the high EMR reflectance region or the low EMR reflectance region comprises bars having a constant centerline pitch and varying thicknesses. 8. The position sensor of claim 7, wherein the bars having various thicknesses comprise at least two distinct thickness bars. 9. The position sensor of claim 8, wherein the bars have only two thicknesses. 2. The position sensor of claim 1, wherein either the high EMR reflectance region or the low EMR reflectance region comprises bars having various centerline pitches and the pitch is an integer multiple of the base pitch. The position sensor of claim 10, wherein the bars having various centerline pitches are bars having a constant thickness. 11. The position sensor of claim 10, wherein the bars have various thicknesses. 13. The position sensor of claim 12, wherein the bars having various thicknesses comprise at least two distinct thickness bars. 14. The position sensor of claim 13, wherein the bars have only two thicknesses. The position sensor as set forth in claim 1, wherein said rotating surface has a plurality of castels projecting radially from said rotating surface. 16. An angle according to claim 15, wherein the high reflectance region corresponds to the largest protruding regions of the plurality of castels and the low reflectance region is angularly aligned with the less protruding regions between the plurality of castels. Position sensor. 17. The method of claim 16, wherein the maximum protruding zones are smoothly machined, molded or sintered, or surface treated with a paint or material stack to impart high reflectivity, and discontinuous gap zones or less protruding zones have low reflectivity. Each position sensor characterized in that it is machined, molded or sintered, or surface treated with a layer of paint or certain materials to impart a seal. The method of claim 1, wherein the high reflectance regions are metallic coated, shiny or colored brightly, and the low reflectance regions are substantially transparent, matte, roughened or dark colored to form a reflection scale. Each position sensor, characterized in that. The position sensor of claim 1, wherein the at least one array of EMR sensitive detectors is located inside or outside the reflection image of the rotating surface. 2. The position sensor of claim 1, wherein the array of at least one EMR detector comprises a one or two dimensional array, a CCD, a VLSI vision chip or a side effect photodiode. The angular position sensor of claim 1, wherein the pattern is further processed by a processor to obtain an angular velocity of the rotor relative to the housing.

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