Optical encoder comprising a width of at least one optical sensor array corresponds to an interpolation period of the encoder

An optical encoder includes an encoding disk and an optical detector disposed to correspond to the encoding disk. The optical detector includes a plurality of optical sensors arranged to form an optical sensor array. The optical detector is provided to receive light. The optical detector includes at least one optical sensor arranged to form at least one sensor array. The width of the sensor array corresponds to an interpolation period of the optical encoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 108148533 filed in Taiwan, R.O.C. on Dec. 31, 2019, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to an encoder, more particularly to an optical encoder having high resolution.

BACKGROUND

An encoder uses optical, magnetic or mechanical contact to sense a position, converts the information of position into an electrical signal, and outputs the electrical signal to a driver as a feedback signal for controlling position. The encoder can be classified into a rotary encoder or a linear encoder according to a movement mode. The rotary encoder can convert a rotational position or a rotation quantity into analog or digital electrical signal, and the rotary encoder is generally mounted on a rotary object such as a motor shaft. The linear encoder can convert a linear position or linear displacement into electrical signal in a similar manner. Nowadays, encoders are widely used in machine tools, robots and semiconductor devices as sensing modules for servo motor positioning, and the accuracy and precision of encoders would directly affect the positioning performance of mechanical device.

For an optical encoder, there is an encoding disk (grating disk) having patterned area for light to pass through. While the encoding disk is irradiated by the light source, the optical detector receives different amounts of light due to the relative movement between the optical detector and the encoding disk, and linear displacement or the rotation angle is determined according to the change of amount of received light. The resolution of an optical encoder is determined by the quantity and the pattern of the light-intransmissive and light-transmissive regions. However, there is a physical limitation on enhancement of the resolution by increasing the quantity of light-transmissive regions because overly small light-transmissive regions may cause diffraction interference.

Among the conventional optical encoders, the optical detector would be utilized with silicon-based photodiodes (PDs) to analyze light power signals since silicon-based photodiodes have good quantum efficiency and photoelectric response in the infrared wavelength range. In a high-order encoder, the silicon-based photodiode in the optical detector is divided into two groups: a group in a coding area and another group in an interpolating area. The code track (binary code or gray code) on the encoding disk blocks light from transmitting and/or allows light to pass through. According to amount of received light, we could know the PD receives light with high luminous flux or low luminous flux. This can match with logic decoding on the system end to covert the current angle. The PDs in the interpolating area can be designed according to the period of the PD with smallest coding in the coding area so as to generate a sinusoidal signal. Then, the signal is interpolated to obtain total bits of the encoder. The total bits of encoder is a result of superposition of the resolutions of coding area and interpolating area. The conventional method of analyzing the interpolating area is to convert an analog sinusoidal signal received by PDs in the interpolating area into a digital signal through high-order analog-to-digital converter (ADC) to analyze a finer angular position. Since different ADCs is applicable to specifications of different encoders, a relatively high-order ADC is needed if it is necessary to achieve higher interpolating resolution (e.g., 24-bit/rev). For example, when the coding area provides the resolution of 10 bits, the interpolating area is required to provide the resolution of 14 bits, and thus an ADC with a resolution of at least 14 bits must be used. However, as the price of ADCs rises with resolution, the problem of increased cost arises.

SUMMARY

In view of the abovementioned problem, the present disclosure provides an optical encoder which helps to solve that high-resolution optical encoders are difficult to be widely used in related field due to high manufacturing cost of high-order ADCs.

The present disclosure provides an optical encoder including an encoding disk and an optical detector that are disposed corresponding to each other. The optical detector is configured to receive light. The optical detector includes at least one optical sensor arranged to form at least one optical sensor array. The width of the optical sensor array corresponds to an interpolation period of the optical encoder.

According to one aspect of the present disclosure, an optical encoder includes an encoding disk, an optical detector and a sensing circuit. The optical detector is configured to receive light and is disposed to correspond to the encoding disk. The optical detector includes a plurality of optical sensors arranged to form a plurality of optical sensor arrays. Each of the optical sensors has digital grayscale characteristics, and amount of light received by the optical sensors is quantified.

According to the optical encoder discussed above, the optical encoder includes optical sensors such as CMOS or CCD which can achieve high-density element arrangement and can be integrated. Taking CMOSs as an example, they can form an optical sensor array to receive light signals. Compared with the conventional optical encoder equipped with silicon-based photodiodes, CMOSs can be highly integrated into a circuit and can easily achieve high SNR, and CMOS can be manufactured by skilled manufacturing process. With the improvement of manufacturing process in recent years, the response rate of CMOS in non-visible spectrum also raises to the level of silicon-based photodiodes. Therefore, a high-resolution optical encoder equipped with CMOS optical sensors could be competitive in market.

In addition, the optical encoder may further include a sensing circuit. The sensing circuit is electrically connected to the optical sensor arrays such that the optical sensor has digital grayscale characteristics, and amount of light received by each optical sensor can be quantified so as to output electrical signals obtained according to light power signals superposed by the optical sensor arrays. Compared with the conventional silicon-based photodiode that receives analog electrical signals and then converts them into digital signals through the ADC, although the optical sensor of the present disclosure still generates electrical signals of analog signals, each optical sensor, each row of optical sensors, or each column of optical sensors can be utilized with an ADC element by designing the integrated circuit. Or alternatively, it can be simplified to take each row or each column as a standard. By doing so, when the corresponding optical sensors in the row or column are scanning in a manner of circuit scanning, the optical sensors in each row or each column can be utilized with an ADC element which captures analog signals and then converts them into digital signals. That is, the ADC converts analog signals, generated by corresponding optical sensor, into digital signals sequentially, and the superposition of these digital signals is implemented in a power amp counting circuit to obtain a full-digitalized power result. The advantage of scanning in each row or column is favorable for simplifying the quantity of ADCs.

DETAILED DESCRIPTION

According to one embodiment of the present disclosure, an optical encoder includes an encoding disk and an optical detector. Please refer toFIG. 1toFIG. 5, whereFIG. 1is a schematic view of an optical encoder according to the first embodiment of the present disclosure,FIG. 2is a partially enlarged view of the optical encoder inFIG. 1,FIG. 3is a partially enlarged view of an optical detector of the optical encoder inFIG. 2,FIG. 4is a schematic view of an optical sensor array located in an encoding light sensing part of the optical detector inFIG. 3, andFIG. 5is a schematic view of an optical sensor array located in an interpolating light sensing part of the optical detector inFIG. 3. In this embodiment, an optical encoder1includes an encoding disk10, an optical detector20and a light source30. The optical encoder1shown inFIG. 1is a rotary encoder, but it may be a linear encoder in some other embodiments.

The encoding disk10includes two encoding code track parts110and an interpolating code track part120. For simplicity drawings, the encoding code track parts110and the interpolating code track part120are not shown inFIG. 1. The encoding code track part110includes encoding tracks which have a plurality of opening patterns111configured for light passing through. The encoding method of the encoding code track part110may be, for example, gray code, binary code, M-sequence or other encoding method applicable to an absolute encoder. The interpolating code track part120is located between the two encoding code track parts110, and the interpolating code track part120has a plurality of slits121that are spaced apart from one another and configured for light passing through. The quantity of the encoding code track parts110is not intended to limit the present disclosure. In addition, the positions of the encoding code track parts110and the interpolating code track part120shown inFIG. 2are not intended to limit the present disclosure. In some embodiments, an encoding code track part is located between two interpolating code track parts; or alternatively, an encoding code track part is aligned with an interpolating code track part.

The optical detector20is disposed to correspond to the encoding disk10. The optical detector20includes two encoding light sensing parts210corresponding to the encoding code track parts110, respectively, and an interpolating light sensing part220corresponding to the interpolating code track part120. The optical detector20further includes a plurality of optical sensors230. Some optical sensors230are located in the encoding light sensing parts210and configured to receive light passing through the opening patterns111of the encoding code track parts110. Some other optical sensors230are located in the interpolating light sensing part220and configured to receive light passing through the slits121of the interpolating code track part120. In the interpolating light sensing part220, the optical sensors230are arranged to form a plurality of optical sensor arrays240. In this embodiment, each of the optical sensors230is, for example, a complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD). The CMOSs worked as the optical sensors230can be highly integrated into a circuit and can easily achieve high signal-to-noise ratio (SNR), which is a skilled manufacturing process and thus the manufacturing cost of the optical detector20can be reduced. For easy understanding the figures, only the optical sensor arrays240are shown whereas the optical sensors230are not shown inFIG. 2andFIG. 3. The quantities of the optical sensors230and the optical sensor arrays240are not intended to limit the present disclosure.

The light source30disposed opposite to the encoding disk10, and the optical detector20and the light source30are respectively located at opposite sides of the encoding disk10, but the present disclosure is not limited to the aforementioned arrangement. In some embodiments, the optical detector20and the light source30may be located at the same side of the encoding disk10. The light source30is, for example but not limited to, a light-emitting diode or a laser diode. Light emitted from the light source30passes through the opening patterns111of the encoding code track parts110and the slits121of the interpolating code track part120and can be received by the optical sensors230of the optical detector20. Further, the optical sensors230can receive light within infrared wavelength range from 760 nm to 1000 nm, but the aforementioned wavelength range are not intended to limit the present disclosure. In addition, there can be one or more optical lenses31disposed in front of the light source30, such that an approximately parallel light field is generated when light passes through the optical lens31.

According to one embodiment of the present disclosure, the optical sensor arrays may be in a shape of non-rectangular. That is, the optical sensor arrays may be in polygon shapes such as trapezoid shapes, rhombus shapes and parallelogram shapes, or fan shapes, ellipse shapes or other irregular shapes. Please refer toFIG. 3toFIG. 5, in this embodiment, the optical sensor arrays240located in the interpolating light sensing part220are in trapezoid shapes. As shown inFIG. 5, one of the optical sensor arrays240located in the interpolating light sensing part220has an upper row and a lower row, the upper row includes more optical sensors230, and the lower row includes less optical sensors230. The upper row can be considered as the long base241of the trapezoid-shaped optical sensor array240, and the lower row can be considered as the short base242of the trapezoid-shaped optical sensor array240. A distance between two of the optical sensors230that are adjacent to each other in each optical sensor array240is smaller than the distance T between two optical sensor arrays240that are adjacent to each other; specifically, the distance between adjacent optical sensors230is smaller than the minimum distance between adjacent optical sensor arrays240.

In this embodiment, the long base241of the said optical sensor array240is defined by the distance from the leftmost optical sensor230to the rightmost optical sensor230in the upper row, and the short base242is defined by the distance from the leftmost optical sensor230to the rightmost optical sensor230in the lower row. As shown inFIG. 5, the distance D1from the left side231aof the leftmost optical sensor230to the right side231bof the rightmost optical sensor230in the upper row is defined as the long base241of the optical sensor array240. The distance D2from the left side232aof the leftmost optical sensor230to the right side232bof the rightmost optical sensor230in the lower row is defined as the short base242of the optical sensor array240.

According to one embodiment of the present disclosure, theses optical sensor arrays are arranged side by side in the interpolating light sensing part. Please refer toFIG. 3andFIG. 5, the trapezoid-shaped optical sensor arrays240located in the interpolating light sensing part220are arranged side by side. For some optical sensor arrays240, the short bases242of respective optical sensor arrays240face the same direction, and the long bases241face the opposite direction. These optical sensor arrays240together form an optical sensor array group250, and each optical sensor array group250is spaced apart from other optical sensor array groups250.

InFIG. 3, the short bases242of the optical sensor arrays240in each optical sensor array group250face the same direction, but the present disclosure is not limited thereto. In some embodiments, the optical sensor arrays240in each optical sensor array group250can be arranged in a manner that the long bases241and the short bases242are alternatively arranged; that is, the short base242of one of the optical sensor arrays240and the short base242of adjacent one of the optical sensor arrays240face opposite directions.

InFIG. 5, all the optical sensors230in each optical sensor array240are square-shaped, and thus the trapezoid-shaped optical sensor array240has zigzag edges, but the present disclosure is not limited thereto. In some embodiments, for one optical sensor array240, the optical sensors230on the outermost side of the optical sensor array240may be trapezoid-shaped or polygon-shaped to smoothen the contour of the optical sensor array240from having zigzag edges.

Light emitted from the light source30passes through the encoding code track parts110and the interpolating code track part120to respectively reach the optical sensors230located in the encoding light sensing parts210and the optical sensors230located in the interpolating light sensing part220, and the optical sensors230receive light to output electrical signals. Herein, one optical sensor230receives an analog electrical signal that related to the change of light intensity and outputs a digital signal via an analog-to-digital converter (ADC) or a comparator connected thereto. When the encoding disk10moves relative to the optical detector20or the optical detector20moves relative to the encoding disk10, the quantity of the optical sensors230that can receive light changes. As such, the digital signals converted by the optical encoder1changes, and the amount of displacement or rotation angle is determined according to the change of the digital signals.

The optical sensor arrays240shown inFIG. 3andFIG. 5are not intended to limit the present disclosure. In some embodiments, the interpolating code track part of the encoding disk can be designed to includes non-rectangular slits corresponding to rectangular optical sensor arrays. Alternatively, the slits of the interpolating code track part and the optical sensor arrays may be both rectangular so as to work with a light source of a non-parallel light field. An embodiment of non-parallel light field can be a reflective encoder including a light source and an optical detector that are located on the same side thereof.

According to one embodiment of the present disclosure, the optical sensors have digital grayscale characteristics, and amount of light received by the optical sensors can be quantified. The quantification of the optical sensors can be accomplished by electrical connection between optical sensor and ADC. According to the present disclosure, multiple ADCs are electrically connected to at least one optical sensor of respective optical sensor arrays. Please further refer toFIG. 6, which is a schematic view of optical sensor arrays and a sensing circuit of an optical encoder according to the first embodiment of the present disclosure. As shown inFIG. 1andFIG. 3, in this embodiment, the optical encoder1further includes a sensing circuit40disposed on the optical detector20. As shown inFIG. 6, the sensing circuit40includes a plurality of simultaneous-sampling ADCs410, and the optical sensors230in each column are electrically connected to one of the simultaneous-sampling ADCs410. For one of the optical sensor arrays240, the optical sensors230are arranged in columns, and the optical sensors230in each column are electrically connected to one of the simultaneous-sampling ADCs410. The ADC410can sequentially read power of each optical sensor230in corresponding column in a manner of scanning and converts analog signals into digital signals. If there are N columns of the optical sensors230in one optical sensor array240, N simultaneous-sampling ADCs410are provided to be electrically connected to respective N columns of the optical sensors230. For one of the optical sensor array groups250, the simultaneous-sampling ADCs410in each optical sensor array240are electrically connected to respective columns of the optical sensors230, and the simultaneous-sampling ADCs410in the optical sensor arrays240are connected in parallel so as to output electrical signals according to light power signals superposed by the optical sensor arrays240. As such, the electrical signals generated by the optical sensors230can indicate not only whether amount of light is received, but also the amount of power of received light, such that it is considered that the optical sensors have grayscale digital characteristics. The optical sensors230of each column in this embodiment are exemplarily electrically connected to one of the simultaneous-sampling ADCs410, but the present disclosure is not limited thereto. In some embodiments, the optical sensors of each row may be electrically connected to one of ADCs. Or alternatively, each optical sensor corresponds to one ADC or one comparator; that is, the comparator can be used instead of the simultaneous-sampling ADC410.

Similarly, the sensing circuit40can further include a simultaneous-sampling ADC or a comparator circuit that is electrically connected to the optical sensors230in the encoding light sensing parts210, such that amount of light received by the optical sensors230in the encoding light sensing parts210can be quantified.

In summary, each optical sensor array240is formed by arranging the optical sensors230, and each optical sensor230can be connected to the sensing circuit (ADC or comparator). By superposition of the digital signals from the optical sensors230, the purpose of increasing resolution can be easily achieved.

For a conventional optical encoder using silicon-based photodiodes, a single silicon-based photodiode is connected to a high-order sensing circuit (e.g., an ADC with a resolution of 10 bits or more) to achieve high resolution. In some embodiments of the present disclosure, the optical sensors230may be CMOS optical sensors. Since CMOS belongs to skilled integrated circuit process, in the case that the optical sensor array240has the same sensing area as the silicon-based photodiode, the optical sensors230of the optical sensor array240can be connected to a middle-order sensing circuit (e.g., an ADC with a resolution of 5-10 bits) or a low-order sensing circuit (e.g., a comparator), and the manufacturing cost of the sensing circuit can be reduced while signal-to-noise ratio (SNR) in the integrated circuit process is improved.

Please refer toFIG. 7, which is a schematic view of an interpolation period of the optical encoder inFIG. 6. The optical resolution of the encoding disk10depends on the widths of the slits121and the distances between adjacent slits121in the interpolating code track part120. Herein, in the encoding disk10, one slit121has a width W1, a light-intransmissive area between adjacent slits121has a width W2, and the sum of the width of the slit121and the width of the light-intransmissive area (W1+W2) is defined as an interpolation period of the interpolating light sensing part of the optical encoder, also called the smallest encoding bit of the encoding light sensing part. Please refer toFIG. 5toFIG. 7, each optical sensor array240has a width (distance D1) corresponding to an interpolation period. Specifically, the maximum width (distance D1) of the optical sensor array240is smaller than or equal to the size of an interpolation period. In some embodiments, the sum of the width of one optical sensor array240and the distance T (please refer toFIG. 3again) between adjacent optical sensor arrays240is equal to an interpolation period.

According to the resolution of the encoding disk, the size of the optical sensor array would be adjusted. Please refer toFIG. 8, which is a partially enlarged view of an optical detector of an optical encoder according to the second embodiment of the present disclosure. In this embodiment, the optical detector of the optical encoder includes an encoding light sensing part210and an interpolating light sensing part220. An optical sensor array240aincluding optical sensors230is located in the encoding light sensing part210, and an optical sensor array240bincluding optical sensors230is located in the interpolating light sensing part220. The optical resolution of the encoding disk in this embodiment is higher than that of the encoding disk in the first embodiment; that is, an interpolation period of this embodiment is relatively small. In order to match the width of the optical sensor array240bwith an interpolation period, the optical sensor array240bin the interpolating light sensing part220is formed by four optical sensors230, and the optical sensor array240ain the encoding light sensing part210is formed by sixteen optical sensors230. The optical sensor array240bprovided in this embodiment is rectangular, and each optical sensor230in the optical sensor array240bcan be electrically connected to an ADC such that the optical sensors have digital grayscale characteristics.

Please refer toFIG. 9, which is a partially enlarged view of an optical detector of an optical encoder according to the third embodiment of the present disclosure. The optical resolution of the encoding disk in this embodiment is higher than that of the encoding disk in the second embodiment; that is, an interpolation period of this embodiment is further relatively small. In order to match the width of the optical sensor array240bwith an interpolation period, the optical sensor array240bin the interpolating light sensing part220is formed by one optical sensor230, and the optical sensor array240ain the encoding light sensing part210is formed by four optical sensors230.

FIG. 8andFIG. 9illustrate one optical sensor array240bin the interpolating light sensing part220. Actually, there may be a plurality of optical sensor arrays240bin the interpolating light sensing part220, and the optical sensor arrays240bcan be connected in parallel to increase resolution.

Hereinafter, other designs of the optical encoders in the present disclosure would be further described in specific embodiments.

Embodiment I

Embodiment I provides a rotary optical encoder1as shown inFIG. 1toFIG. 6, and the rotary optical encoder1includes an encoding disk10, an optical detector20, a light source30and a sensing circuit40. An interpolating code track part120of the encoding disk10has a plurality of slits121that are spaced apart from one another and configured for light passing through. The width of the slits121may be 60 micrometers (μm), and the total quantity of the slits121is 1024. The specific widths and the quantity of the slits are only exemplary, and they would vary based on the resolution requirement of the interpolating code track part120.

The optical detector20includes a plurality of optical sensors230located in the encoding light sensing parts210and an interpolating light sensing part220. The optical sensors230located in the interpolating light sensing part220are arranged to form a plurality of trapezoid-shaped optical sensor arrays240, and adjacent eight optical sensor arrays240together form an optical sensor array group250. Each optical sensor array240includes2960optical sensors230that are arranged in 25 columns (n=25). The lowermost row of one optical sensor array240includes 7 optical sensors230, and the uppermost row thereof includes 25 optical sensors230. The long base241(distance D1) of one optical sensor array240is 121.25 μm, and the short base242(distance D2) thereof is 33.95 μm.

The light source30can emit infrared light with a wavelength of 850 nm. The optical sensors230are CMOS photodiodes which have a response rate of 0.41 amps/watt (A/W) under the emission of infrared light with a wavelength of 850 nm.

The sensing circuit40includes a plurality of ADCs410. For one of the optical sensor arrays240, there are 25 ADCs410electrically connected to the optical sensors230of respective 25 columns. In addition, in one optical sensor array group250, the ADCs410in the eight optical sensor arrays240are connected in parallel; therefore, a total of 200 analog-to-digital converters (ADCs)410are connected in parallel.

Embodiment II

Embodiment II provides a rotary optical encoder1, and the rotary optical encoder1includes an encoding disk10, an optical detector20, a light source30and a sensing circuit40. An interpolating code track part120of the encoding disk10has a plurality of slits121that are spaced from one another and configured for light passing through. The total quantity of the slits121is 1024.

The optical detector20includes a plurality of optical sensors230located in encoding light sensing parts210and an interpolating light sensing part220. The optical sensors230located in the interpolating light sensing part220are arranged to form a plurality of trapezoid-shaped optical sensor arrays240, and adjacent eight optical sensor arrays240together form an optical sensor array group250. Each optical sensor array240includes2960optical sensors230that are arranged in 25 columns. The lowermost row of one optical sensor array240includes 7 optical sensors230, and the uppermost row thereof includes 25 optical sensors230. The long base241of one optical sensor array240is 121.25 μm, and the short base242thereof is 33.95 μm.

The light source30can emit infrared light with a wavelength of 850 nm. The optical sensors230are CMOS photodiodes which have a response rate of 0.41 amps/watt (A/W) under the emission of infrared light with a wavelength of 850 nm.

The sensing circuit40includes a plurality of comparators. For one of the optical sensor arrays240, each optical sensor230corresponds to one comparator, and all comparators are connected in parallel.

The difference between the Embodiment II and the Embodiment I is that the optical encoder1of the Embodiment II is equipped with simple comparators instead of ADCs. As such, each optical sensor230only provides a binary output result of 0 or 1. Then, by superposition of the signals from each optical sensor array240, the digitalized result of the optical sensor array group250is obtained.

[Resolution of Optical Encoder]

In the Embodiments I and II, the encoding disk10having 1024 slits121provides 10-bit resolution. When the quantity of the optical sensors230in each optical sensor array240is 2960, and a total of eight optical sensor arrays240are connected in parallel, a circuit design of pair of differential analog signals Sin+ and Sin− can be used to double the resolution. Therefore, the total quantity of the optical sensors can reach 2960×8 (units)×2 (areas)=47360 optical sensors. If each optical sensor is connected to one comparator and has independent output result of 0 or 1, the resolution is approximately 15 bits (the quantity is larger than 32768), and the optical encoder can achieve at least 25-bit/rev. resolution. If each optical sensor230is utilized with an ADC of 10 bits grayscale instead, the optical encoder of the Embodiment I can achieve 35-bit/rev. resolution. Therefore, the optical encoder of the Embodiment I has a resolution of up to 35-bit, and the optical encoder of the Embodiment II has a resolution of 25-bit/rev.

[Design of Light Source and Optical Detector]

In the Embodiments I and II, CMOS photodiodes (optical sensors230) have a response rate of 0.41 amps/watt under the emission of infrared light with a wavelength of 850 nm. According to an optical encoder of one comparative embodiment, CMOS optical sensors are replaced with silicon-based photodiodes which have a response rate of 0.46 amps/watt under the emission of infrared light with a wavelength of 850 nm.

Therefore, under the emission of infrared light with a wavelength of 850 nm, the optical encoder equipped with CMOS photodiodes and the conventional photodiodes equipped with silicon-based photodiodes have similar response rates.

[Design of Trapezoid-Shaped Optical Sensor Array for Compensation of Photoelectric Signal]

In the optical encoder1of the Embodiment I, the optical sensor arrays240receive an optical signal passing through the slits121. When the encoding disk10or the optical detector20rotates, the optical detector20can obtain an electrical signal approximate to a sinusoidal waveform (including sine waveform and cosine waveform). However, if the optical detector20is not optimized in design, the waveform of this electrical signal would be in a non-standard sinusoidal waveform, or even in a non-sinusoidal waveform, which has a significant impact on the signal quality. In order to prevent deterioration of signal quality, there is a particular shape design for the trapezoid-shaped optical sensor array240in the Embodiment I. In Embodiment I, the optical sensor array240has a long base241approximate to 121.25 μm and a short base242approximate to 33.95 μm. Such trapezoid-shaped optical sensor array240satisfy an angular deviation of less than 1.0. The angular deviation represents the standard deviation between the output result of the analyzed angle and the ideal angle. Taking a circular encoding disk as an example, if 360 degrees of the circular encoding disk are divided into 1024 resolution, each ideal angle is approximately 0.352 degrees, and the angle deviation is used for describing the difference between the design result and the ideal angle.

When the encoding disk or the optical detector rotates, the intensity of light received by the optical sensor array groups250in different regions can be changed by designing the phase difference in different interpolating regions. As shown inFIG. 3, electrical signals of the four optical sensor array groups250represent four sinusoidal signals Sin+, Cos+, Cos−, Sin−. Two sinusoidal waves with a phase difference of 90 degrees can be obtained by differently pairing Sin+with Sin− and Cos+ with Cos−. According to the lissajous figure obtained by superposing the two sinusoidal waves, this circular figure can be further interpolated in angle.

Please refer toFIG. 10andFIG. 11, whereFIG. 10is a sine wave signal and a cosine wave signal generated by an optical encoder according to one embodiment of the present disclosure, andFIG. 11is a lissajous figure obtained based on incorporating the sine wave signal and the cosine wave signal inFIG. 10. It can be seen that the four optical sensor array groups250in the Embodiment I generates signals having phase differences of 90 degrees or its multiple from one another. By differently pairing, two sine and cosine waves can be obtained. By superposing the electrical signals, the lissajous figure approximate to a circle is obtained. This indicates that differently paired trapezoidal optical sensor arrays generate electrical signals with relatively good signal quality.

According to the present disclosure, the optical encoder includes optical sensors such as CMOS or CCD which can achieve high-density element arrangement and can be integrated. Taking CMOSs as an example, they can form an optical sensor array to receive light signals. Compared with the conventional optical encoder equipped with silicon-based photodiodes, CMOSs can be highly integrated into a circuit and can easily achieve high SNR, and CMOS can be manufactured by skilled manufacturing process. With the improvement of manufacturing process in recent years, the response rate of CMOS in non-visible spectrum also raises to the level of silicon-based photodiodes. Therefore, a high-resolution optical encoder equipped with CMOS optical sensors could be competitive in market.

In addition, the optical encoder disclosed in the present disclosure may further include a sensing circuit. The sensing circuit is electrically connected to the optical sensor arrays such that the optical sensor has digital grayscale characteristics, and amount of light received by each optical sensor can be quantified so as to output electrical signals obtained according to light power signals superposed by the optical sensor arrays. Compared with the conventional silicon-based photodiode that receives analog electrical signals and then converts them into digital signals through the ADC, although the optical sensor still generates electrical signals of analog signals, each optical sensor, each column of optical sensors, or each row of optical sensors can be utilized with an ADC element by designing the integrated circuit. By doing so, when the corresponding optical sensors in the row or column are scanning in a manner of circuit scanning, the optical sensors in each row or each column can be utilized with an ADC element which captures analog signals and then converts them into digital signals. That is, the ADC converts analog signals, generated by corresponding optical sensor, into digital signals sequentially, and the superposition of these digital signals is implemented in a power amp counting circuit to obtain a full-digitalized power result. The advantage of scanning in each row or column is favorable for simplifying the quantity of ADCs.

The embodiments are chosen and described in order to best explain the principles of the present disclosure and its practical applications, to thereby enable others skilled in the art best utilize the present disclosure and various embodiments with various modifications as are suited to the particular use being contemplated. It is intended that the scope of the present disclosure is defined by the following claims and their equivalents.