Light detection device and optical encoder

Abstract

The present application relates to the technical field of photoelectric detection. Disclosed are a light detection device and an optical encoder. The light detection device comprises: a plurality of first-level detection arrays, each first-level detection array comprising at least one light detection unit, and an electrical signal output by the light detection unit in each first-level detection array being used as a first-level electrical signal output by the first-level detection array. The plurality of first-level detection arrays are divided into a plurality of second-level detection arrays, each of the plurality of second-level detection arrays comprising t2 first-level detection arrays, and the coordinate difference between corresponding points of two adjacent first-level detection arrays belonging to the same second-level detection array being x×P / N+(t1×P) / (t2×N). The corresponding first-level electrical signals of the t2 first-level detection arrays belonging to the same second-level detection array are added, so as to suppress N-th order harmonic components and harmonic components of orders of integer multiples of N. The optical encoder comprises the light detection device. The present application can better suppress harmonic components and is easy to design and manufacture.

Description

Optical detection device and optical encoder TECHNICAL FIELD

[0001] The present application relates to the technical field of photoelectric detection, and in particular to an optical detection device and an optical encoder. BACKGROUND

[0002] An optical encoder is a sensor that can convert mechanical displacement on an output shaft into pulses or digital quantities through photoelectric conversion, and is widely used in devices such as numerical control machine tools, motors, robots, and radars to detect angles, speeds, or linear displacements.

[0003] An optical encoder generally includes a light source, a grating disc or grating (hereinafter referred to as a grating), and a light detection unit. The grating has a plurality of slits, i.e., transmissive portions, and portions not provided with slits, i.e., non-transmissive portions. The transmissive portions and the non-transmissive portions are arranged at equal distances, and the arrangement period of the transmissive portions and the non-transmissive portions is P. The light from the light source forms a periodic light signal through the grating, and the light detection unit detects the light signal and converts it into an electrical signal. However, since the light transmitted through the grating and irradiated onto the light detection unit is equivalent to a square wave of light, the square wave contains a large number of high-order harmonic components, and therefore the electrical signal output by the light detection unit also contains a large number of high-order harmonic components. These high-order harmonic components affect the processing accuracy of the subsequent signal processing circuit, affect the accuracy of the detection result, and are also not conducive to the simplification of the signal processing circuit.

[0004] Chinese Patent No. CN202410143700.X discloses a photoelectric detection unit, a photoelectric encoder system, and a motor. The photoelectric detection unit has a specific design, and the geometry of the photoelectric detection unit is described by a mathematical description function. This geometry can effectively suppress high-order harmonic components in the electrical signal generated by the photoelectric detection unit after receiving light, thereby improving the detection accuracy. However, this high-order harmonic component suppression depends on the geometry of the photoelectric detection unit, which requires the geometry to include a curved segment, making it difficult to manufacture the photoelectric detection unit.

[0005] Therefore, there is a need for a photoelectric detection unit for an optical encoder that is easy to manufacture and can better suppress high-order harmonic components. SUMMARY

[0006] The present application provides an optical detection device and an optical encoder for an optical encoder, which are easy to manufacture and can better suppress harmonic components.

[0007] In a first aspect, the application provides a light detection device for an optical encoder, which comprises a first pattern obtained by rectangular-fan-shaped transformation of a second pattern, and the second pattern comprises: a plurality of first-level detection arrays, wherein: each first-level detection array comprises at least one light detection unit, each light detection unit outputs an electrical signal, and the electrical signals output by the at least one light detection unit comprised in a first-level detection array are directly or combined as a first-level electrical signal output by the first-level detection array; the plurality of first-level detection arrays are divided into a plurality of second-level detection arrays, each of the plurality of second-level detection arrays comprises t2 first-level detection arrays, and the coordinates of corresponding points of any two first-level detection arrays belonging to the same second-level detection array differ by x×P / N+(t1×P) / (t2×N), t1 is a natural number greater than or equal to 1, t2 is a natural number greater than or equal to 2, t1 and t2 are relatively prime, P is a value determined in advance based on the total number of grating slits used by the optical encoder, N is an odd number greater than or equal to 3, and x is a natural number, and x is selected to avoid the first-level detection arrays from overlapping with each other in space; and each of the plurality of second-level detection arrays outputs at least one second-level electrical signal, each second-level electrical signal is generated by adding a group of t2 corresponding first-level electrical signals, and the group of t2 corresponding first-level electrical signals are t2 corresponding first-level electrical signals output by the t2 first-level detection arrays belonging to the same second-level detection array, so as to suppress the Nth harmonic component and the harmonic components with frequencies being integer multiples of N in the second-level electrical signal.

[0008] In a second aspect, the application provides a light detection device for an optical encoder, which comprises a second pattern, and the second pattern is the same as the "second pattern" in the first aspect. The reason for the difference is that the light detection device in the second aspect is generally used in cooperation with a linear grating, and the second pattern can be directly made on the light detection device; the light detection device in the first aspect is generally used in cooperation with a disc grating, and in this case, the second pattern needs to be subjected to rectangular-fan-shaped transformation before being made on the light detection device.

[0009] In a third aspect, the application provides an optical encoder. The technical scheme adopted is as follows:

[0010] An optical encoder comprises: a grating having a plurality of slits, the period of the slits being P; a light source for forming a periodically varying fringe spot through the grating; and a light detection device as described above for detecting the fringe spot and converting it into an electrical signal.

[0011] The application has the following technical effects: by adjusting the coordinate difference of the corresponding points of the first-level detection arrays, the harmonic components can be well suppressed, and the light detection device is easy to design and manufacture. Attached Figure Description

[0012] Figures 1 and 2 are schematic diagrams illustrating the working principle of an optical encoder.

[0013] Figure 3 is a schematic diagram of the arrangement of optical detection units according to an embodiment of the present invention.

[0014] Figure 4 is a schematic diagram of the arrangement of optical detection units according to another embodiment of the present invention.

[0015] Figure 5 is a schematic diagram of the arrangement of optical detection units according to another embodiment of the present invention.

[0016] Figure 6 is a schematic diagram of the arrangement of optical detection units according to another embodiment of the present invention.

[0017] Figure 7 is a schematic diagram of the arrangement of optical detection units according to another embodiment of the present invention.

[0018] Figure 8 is a schematic diagram of the arrangement of optical detection units according to another embodiment of the present invention.

[0019] Figure 9 is a schematic diagram of the arrangement of optical detection units according to another embodiment of the present invention.

[0020] Figure 10 is a schematic diagram of the arrangement of light detection units according to another embodiment of the present invention.

[0021] Figure 11 is a schematic diagram of the arrangement of optical detection units in an actual optical detection device according to another embodiment of the present invention.

[0022] Figure 12 is a spectrum simulation diagram of the output electrical signal of the time detection device in one embodiment of the present invention without taking any measures to suppress harmonic components.

[0023] Figure 13 is a spectrum simulation diagram of the output electrical signal of the photodetector after suppressing the 3rd, 5th, and 7th harmonic components using the method shown in Figure 7 of this application.

[0024] Figure 14 is a spectrum simulation diagram of the output electrical signal of the photodetector after suppressing the 3rd, 5th, 7th and 11th harmonic components using the method shown in Figure 8 of this application.

[0025] Figure 15 is a spectrum simulation diagram of the output electrical signal of the optical detection device after suppressing the 3rd, 5th, 7th, 11th and 13th harmonic components using the method shown in Figure 10 of this application. Detailed Implementation

[0026] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0027] The terms "first", "second", "third", etc. are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or an ordered ranking of the indicated technical features. Thus, features defined with "first", "second" or "third" can explicitly or implicitly include one or more of such features. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly specified otherwise.

[0028] In addition, it should be noted that, in order to more clearly illustrate the technical solutions, the sizes in the drawings of the present patent application are not necessarily drawn to scale, and they are only schematic. Embodiments

[0029] Referring to FIG. 1 and FIG. 2, FIG. 1 and FIG. 2 are schematic diagrams of the working principle of a light detection device in an optical encoder. In an optical encoder, the light detection device 1 is a key part to realize sensing. Generally, the light emitted by the light source 8 passes through the collimator, then passes through the grating 9, and finally projects a stripe light spot on the light detection device 1. The light detection device 1 includes a plurality of light detection units, each of which outputs an electrical signal. After the electrical signals are processed by the signal processing circuit 6, various physical quantities associated with the detected relative motion can be obtained.

[0030] In order to detect the relative motion between two components, the grating 9 and the light detection device 1 are usually fixed on two components that move relative to each other, so that the grating 9 and the light detection device 1 also form relative motion. If the physical quantities to be detected are linear displacement, linear displacement speed, etc. between two components, the grating 9 is a linear grating, as shown in FIG. 1, and the relative motion between the grating 9 and the light detection device 1 is shown as V1. If the physical quantities to be detected are angular displacement, rotational speed, etc. between two components, the grating 9 is a disc grating, as shown in FIG. 2, and the relative motion between the grating 9 and the light detection device 1 is shown as V2, and L is the rotation axis around which the relative motion occurs.

[0031] The grating 9 includes slits 91 and non-transmission parts 92 arranged side by side. When the grating 9 and the light detection device 1 form relative motion, the stripe light spot projected on the light detection device 1 also forms relative motion with respect to the light detection units, resulting in a periodic change in the light intensity sensed by each light detection unit over time. In this way, the electrical signal output by each light detection unit also periodically changes. By detecting these periodically changing electrical signals, the relative motion speed, relative motion displacement, etc. between two components can be measured.

[0032] When the grating 9 is a linear grating, the light projected onto the light detection unit can be regarded as "square wave" light. This "square wave" light can be expanded as the superposition of a fundamental light wave and an odd harmonic component:

[0033] .........

[0034] wherein A0 is the average value of the square wave after time integration, A i is the amplitude of each odd harmonic component, and the angular velocity of the fundamental light wave is as follows:

[0035] .

[0036] wherein P is the period of the slits of the grating, which essentially represents a spatial frequency, which can be calculated by H / I, H is the total length occupied by all the slits 91 of the grating 9, and I is the total number of slits.

[0037] When the grating 9 is a disc-shaped grating, the above harmonic decomposition still holds, only the quantity representing the spatial frequency is replaced by the angular velocity of rotation per unit time, and the projected "square wave" light can still be expanded into the superposition of the fundamental light wave and the odd harmonic components.

[0038] Each light detection unit on the light detection device 1 can be regarded as a combination of an infinite number of extremely small light detection points. For each light detection point, after being irradiated by the "square wave" light, an electrical signal close to the "square wave" is inevitably generated, which can also be expanded into the superposition of the fundamental component and the odd harmonic components, and the fundamental frequency of the fundamental component is the same as that of the "square wave" light. Therefore, the main components of the electrical signal output by each light detection unit include the fundamental component and the odd harmonic component. Generally, the fundamental component is the electrical signal required for detection. Therefore, in order to improve the detection accuracy, it is necessary to remove the odd harmonic component.

[0039] Next, how to set the shape, position and other parameters of the light detection unit on the light detection device 1 to remove the odd harmonic component will be discussed. It should be noted that the method disclosed in the present patent application is not limited to the odd harmonic component, i.e., it can not only remove the odd harmonic component. Those skilled in the art can understand that if the even harmonic component in the electrical signal output by the light detection unit needs to be removed in some application scenarios, the method disclosed in the present patent application can also be applied after appropriate adjustment.

[0040] It should be noted that when used with a disc-shaped grating, the arrangement scheme of the light detection unit disclosed in the embodiments of the present patent application needs to be subjected to a rectangular-fan-shaped graphical transformation to obtain the pattern actually made on the light detection device 1. After the rectangular-fan-shaped graphical transformation, the shape, position and other parameters of the light detection unit will be slightly deformed.

[0041] If used with a straight-line grating, the arrangement scheme of the light detection unit disclosed in the embodiments of the present patent application does not need to be subjected to a rectangular-fan-shaped transformation, and can be made on the light detection device 1.

[0042] Rectangular-fan transform method and its inverse transform (i.e. fan-rectangular transform) are common techniques in the field of figure transform, which are used to transform the figure of optical encoder between rectangular coordinate system and polar coordinate system. The specific algorithm for transforming the figure between rectangular coordinate system and polar coordinate system is disclosed in the US patent with patent number US7268883B2 and title "Optoelectronic harmonically filtered detector system for a scanning unit".

[0043] It should be noted that the "rectangular-fan transform" and "fan-rectangular transform" methods mentioned in this patent application do not refer to any figure transform method that can transform the figure between rectangular coordinate system and polar coordinate system, but refer to the figure transform method that meets the requirements of optical encoder. The core requirement is that the effective light sensing ability of each part of the light detection unit remains unchanged after figure transform. The algorithm disclosed in the above-mentioned US patent US7268883B2 is only one possible transform algorithm, and according to its teachings, those skilled in the art can easily design other variant algorithms. The "rectangular-fan transform" method mentioned in this patent application refers to any figure transform method suitable for transforming the figure of optical encoder from rectangular coordinate system to polar coordinate system; the "fan-rectangular transform" method mentioned in this patent application refers to any figure transform method suitable for transforming the figure of optical encoder from polar coordinate system to rectangular coordinate system.

[0044] In actual production of light detection device used in cooperation with circular grating, the technical personnel usually first determines the total number of slits I required by the grating to be used in a circumference, takes the center point of the light detection device 1 as the reference point, and determines a rough P = 2πR0 / I with the distance from the reference point to the center of the rotating shaft L as R0. The reference point can also be determined in other ways, for example, taking an arbitrary point on the light detection device 1 as the reference point. Then, the figure of the light detection unit in rectangular coordinate system is designed with this P as the period, and the position of the above-mentioned reference point in rectangular coordinate system is x = 0, y = R0. Then, the designed figure of the light detection unit is transformed into polar coordinate system through rectangular-fan transform.

[0045] The rectangular-fan conversion algorithm used above needs to satisfy certain boundary conditions, for example, in the polar coordinate system, the radial coordinate r = R0, any arc length is equal to the corresponding length in the x-axis direction in the rectangular coordinate system. Those skilled in the art can understand that there are many choices for the specific algorithm and boundary conditions actually used, which are conventional techniques in the art and will not be described here. The setting of these algorithms and boundary conditions essentially satisfies the condition that the light intensity obtained by any part of the light detection device 1 remains unchanged before and after coordinate transformation. In summary, in the actual manufacture of the light detection device used in cooperation with the disc-type grating, P is a pre-set value, which is essentially determined based on the total number of slits I of the grating used by the optical encoder.

[0046] In order to facilitate the explanation of the technical solutions, the following content will be explained in cooperation with the light detection device used with the linear grating. Those skilled in the art can understand that the same content is also applicable to the light detection device used in cooperation with the disc-type grating, except that the relevant arrangement scheme needs to be converted by rectangular-fan conversion and then applied to manufacture the light detection device.

[0047] In this application, the "width" refers to the width in the transverse direction (x-axis direction shown in the figure), specifically referring to the distance between the two points obtained by intersecting a straight line drawn in the transverse direction with the two edges of the light detection unit. The "pitch" and "coordinate difference of corresponding points" also refer to the distance in the transverse direction, and the "transverse direction" refers to the relative movement direction of the grating and the light detection device.

[0048] Referring to FIG. 3, FIG. 3 is a schematic diagram of the arrangement of the light detection unit according to an embodiment of the present application, which shows the arrangement of the light detection unit for suppressing the 3rd harmonic component. As shown in FIG. 3, the grating has a slit period P, and after the light passes through the grating, it falls on the light detection device as a stripe light spot 7, as shown by the dashed box in FIG. 3.

[0049] The light detection device includes a plurality of light detection units, and FIG. 3 only shows light detection units 151H-156H, which output electrical signals 91a-96a, respectively. The pitch (x-axis direction) between each light detection unit is the same. Two identical light detection units are arranged side by side within one period P, and both light detection units are uniformly distributed within the period P. As shown in FIG. 3, two identical light detection units 151H and 152H are arranged within one period P, and the shape of the two light detection units is rectangular, with a width (x-axis direction) of P / 3. The two light detection units 151H and 152H have two identical pitches (x-axis direction) within the period P, both of which are P / 6, so that one period P contains the light detection units 151H and 152H and the two pitches between them.

[0050] In this arrangement, two light detecting units output one electrical signal in one period P, for example, light detecting units 151H and 152H output electrical signals 91a and 92a respectively. If the odd harmonic component signal and the interference signal are filtered out, leaving only the fundamental component signal, the two electrical signals 91a and 92a are opposite to each other (i.e. the phase difference is 180°), because the coordinate difference of the corresponding points of light detecting units 151H and 152H is half of the fundamental period. The two electrical signals 91a and 92a are input to the subsequent signal processing circuit, which helps to obtain how much relative displacement occurs between the grating and the light detecting device.

[0051] To suppress the 3rd harmonic component in the output electrical signal, the width of each light detecting unit in the transverse direction is set to be one period of the harmonic component to be suppressed. The period of the 3rd harmonic component is P / 3, and the transverse dimension of each light detecting unit completely covers one period of the 3rd harmonic component in the electrical signal. Therefore, at a specific moment, the phase change of the 3rd harmonic component output by any point on cross section 3 in single light detecting unit 154H covers exactly one period. If single light detecting unit 154H is regarded as a collection of numerous small light detecting points, the electrical signal 94a output by light detecting unit 154H should be the collection of the electrical signals output by each light detecting point. Therefore, the integral of the 3rd harmonic component output by each light detecting point on single cross section 3 is zero. Further, if light detecting unit 154H is regarded as being composed of numerous small cross sections 3, the integral of the 3rd harmonic component in the electrical signal output by each light detecting point over the entire light detecting unit is also zero. Therefore, the 3rd harmonic component in the electrical signal output by the photoelectric conversion of the stripe light spot 7 by single light detecting unit should be zero. Even if there is still a 3rd harmonic component due to some imperfections in the device manufacturing or external interference, the main source of the 3rd harmonic component has been eliminated, so the 3rd harmonic component is suppressed.

[0052] In FIG. 3, light detecting unit 154H is white and other light detecting units 151H-153H, 155H and 156H are black, which is to facilitate the illustration of cross section 3 in light detecting unit 154H and does not mean that there is any essential difference in material or other aspects between the light detecting units. The subsequent drawings of this patent application also use a similar description method.

[0053] It can be seen that by setting the width of the light detecting unit in the transverse direction to be one period or an integer multiple of the period of the harmonic component to be suppressed, the harmonic component can be suppressed in the electrical signal output by the light detecting unit. This principle is also applicable to the suppression of 5th, 7th and higher harmonic components. That is, the Wth harmonic component can be eliminated by setting the width of the light detecting unit to be P / W (W is the order of the harmonic component to be suppressed) or an integer multiple of P / W.

[0054] It should be noted that in this case, the electrical signals 91a-96a output by the light detecting units can be connected as desired, because the light detecting units achieve the filtering of the harmonic components by virtue of their shape alone, i.e. the electrical signals 91a-96a already have the harmonic components to be suppressed filtered out, without the need for a combination or operation of the electrical signals output by different light detecting units to achieve the filtering of the harmonic components.

[0055] Referring to Fig. 4, Fig. 4 shows a light detecting unit of arbitrary shape, the width of which in the lateral direction is constant and equal to A. As shown in Fig. 4, the shape of the light detecting unit 154K is not fixed, but each cross section 3' of the light detecting unit 154K has a width of A in the lateral direction, A being one period of the harmonic component to be suppressed, for example A = P / 3. The phase of the third harmonic component of the electrical signals output by the individual light detecting points on a single cross section 3' varies exactly over one period. The electrical signal 94'a output by the light detecting unit 154K is the sum of the electrical signals output by the individual light detecting points, if the light detecting unit 154K is regarded as a collection of an infinite number of light detecting points. Therefore, the third harmonic component of the electrical signals output by the individual light detecting points is integrated over a single cross section 3' and the result is zero. Further, if the light detecting unit is regarded as being composed of an infinite number of cross sections 3', the third harmonic component of the electrical signals output by the individual light detecting points is integrated over the entire light detecting unit and the result is also zero. Therefore, the method for suppressing harmonic components described with reference to Fig. 3 does not require the individual light detecting units to be rectangular, but it is sufficient if the width of the individual light detecting units is equal to one period of the harmonic component to be suppressed. In the present document, the "width" is defined as follows: a cross section 3' is drawn across the light detecting unit in the lateral direction, the cross section 3' intersects the outer edge of the light detecting unit at two points, the length between these two points is the width. The two points are also the two end points of the cross section 3'.

[0056] It should be noted that the method described with reference to Figs. 3 and 4 for suppressing the third harmonic component also suppresses harmonic components whose order is an integer multiple of 3. This is because, if the width of the light detecting unit is P / 3, this width is also an integer multiple of the sixth, ninth, twelfth, etc. harmonic component, and the integral of these harmonic components over the width of the individual light detecting unit is also zero, so that the sixth, ninth, twelfth, etc. harmonic component is also suppressed in the electrical signal. Similarly, when the method is used to suppress the fifth, seventh, eleventh, etc. harmonic component, harmonic components whose order is an integer multiple of the order of the harmonic component to be suppressed are also suppressed.

[0057] It should be noted that the method introduced in FIG. 3 and FIG. 4 for suppressing the 3rd harmonic component, the number of light detection units arranged in one period P is not necessarily two, but can be three, four or more, or one. Arranging different number of light detection units in one period P will affect the difficulty of subsequent signal processing circuit for signal processing, but as long as the width of each light detection unit is one period or an integer multiple of the period of the harmonic component to be suppressed, it can suppress the harmonic component. However, arranging different number of light detection units in one period P, while the width of a single light detection unit is required, it should be noted whether these light detection units can be placed in one period P without overlapping. For example, in some scenarios, it is advantageous to arrange four light detection units in one period P, at this time the method cannot be used to suppress the 3rd harmonic component, because four P / 3 width light detection units cannot be placed in one period P. At this time, the width of the light detection unit can be used to suppress higher harmonic components, for example, the 5th harmonic component, and other methods can be used to suppress the 3rd harmonic component.

[0058] It should also be noted that the stripe light spot 7 and the light detection units will appear repeatedly in the transverse direction (x-axis direction), and FIG. 3 and FIG. 4 only show part of them; the length of the stripe light spot 7 in the vertical direction (y-axis direction) can be much larger than the length of the light detection unit in the vertical direction, and only a part of the stripe light spot 7 is shown in FIG. 3 and FIG. 4; the light detection units can also appear repeatedly in the vertical direction, and different light detection units that appear repeatedly in the vertical direction can also be connected to each other, and only part of them is shown in FIG. 3 and FIG. 4.

[0059] However, the method introduced in FIG. 3 and FIG. 4 can only suppress a single harmonic component and harmonic components with an integer multiple of the harmonic component, and cannot suppress multiple harmonic components without an integer multiple relationship, but there are countless harmonic components in the light detection unit output electrical signal that need to be suppressed, even if only the more influential ones are considered, the 5th, 7th, 11th, 13th harmonic components need to be suppressed, and the more harmonic components that can be suppressed, the better.

[0060] Referring to FIG. 5, FIG. 5 is a schematic diagram of the arrangement of light detection units according to another embodiment of the present application, which shows the arrangement of light detection units for simultaneously suppressing the 3rd and 5th harmonic components. As shown in FIG. 5, the period of the grating slit is P, and the light after passing through the grating falls on the light detection device as a stripe light spot 7.

[0061] The light detecting device includes a plurality of light detecting units, each of which is a parallelogram. FIG. 5 only shows light detecting units 811H-822H, and the intervals (x-axis direction) between the light detecting units are the same, satisfying that four identical light detecting units are arranged side by side in one period P, and the four light detecting units are uniformly distributed in the period P. As shown in the figure, four identical light detecting units 811H-814H are arranged in one period P, and the four light detecting units 811H-814H have four identical intervals (x-axis direction) in the period P, so that one period P contains the light detecting units 811H-814H and the four intervals between them.

[0062] In this arrangement, the four light detecting units in one period P output one electrical signal respectively, for example, the light detecting units 811H-814H output electrical signals 81a-84a respectively. If the odd harmonic component signals and interference signals are filtered out, only the fundamental component signals are left, then the phases of the electrical signals output by the adjacent two light detecting units are different by 90°, because the coordinates of the corresponding points of the adjacent two light detecting units in the light detecting units 811H-814H are different by one quarter of the fundamental period. The four electrical signals 81a-84a are input to the subsequent signal processing circuit, which helps to obtain how much relative displacement occurs between the grating and the light detecting device.

[0063] To suppress the 5th harmonic component in the output electrical signal, the width of each light detecting unit is set to P / 5, and the principle is as described in the description of FIGS. 3 and 4.

[0064] To suppress the 3rd harmonic component in the electrical signal at the same time, the inclination of each light detecting unit in the transverse direction is specially designed. The transverse inclination offset C of a single light detecting unit 821H is the period of the 3rd harmonic component to be suppressed, i.e. P / 3. As shown in FIG. 5, the "transverse inclination offset" C describes the inclination degree of the two edges of the parallelogram arranged in the transverse direction, which specifically refers to the difference in the transverse coordinates of the two end points of one of the two edges.

[0065] The single light detection unit 821H can be regarded as a combination of a large number of thin slanted strips 2 with a width tending to zero. A single thin slanted strip 2 just spans one period of the third harmonic component, i.e. P / 3. The single light detection unit 821H can be regarded as a collection of a large number of thin light detection points. The output electrical signal 79a of the single light detection unit 821H should be a collection of the output electrical signals of the light detection points. Therefore, the third harmonic component in the output electrical signal of each light detection point should be integrated over the thin slanted strip 2 and the result should be zero. This is true for each thin slanted strip 2 and therefore for the whole light detection unit 821H. Therefore, the third harmonic in the output electrical signal of the single light detection unit should be zero after photoelectric conversion of the fringe pattern 7. Even if there is still a third harmonic component due to some imperfections in the device fabrication or external disturbances, the main source of the third harmonic component has been eliminated and the third harmonic component is suppressed.

[0066] It can be seen that by keeping the width of the single light detection unit unchanged and designing the single light detection unit to be slanted in the lateral direction with a lateral slanting offset C of one period or an integer number of periods of the harmonic component to be suppressed, the harmonic component can be suppressed in the electrical signal. This principle is also applicable to the suppression of the 5th, 7th and higher order harmonic components. That is, the Uth order harmonic component can be eliminated by setting the lateral slanting offset C of the single light detection unit to be P / U (U is the order of the harmonic component to be suppressed) or an integer multiple of P / U.

[0067] It should be noted that the light detection unit shape shown in Fig. 5 can suppress the 3rd and 5th harmonic components simultaneously. Other combinations of harmonic components can also be suppressed simultaneously by designing the light detection unit shape accordingly, for example, the 5th and 7th harmonic components can be suppressed simultaneously by adjusting the width of the light detection unit and the lateral slanting offset parameter accordingly. For example, if the 5th and 7th harmonic components are to be suppressed simultaneously, four light detection units can be placed within one period P with a width of P / 5 and a lateral slanting offset of P / 7, or a width of P / 7 and a lateral slanting offset of P / 5. For another example, if the 3rd and 7th harmonic components are to be suppressed simultaneously, four light detection units can be placed within one period P with a width of P / 7 and a lateral slanting offset of P / 3, or two light detection units can be placed within one period P with a width of P / 3 and a lateral slanting offset of P / 7. Those skilled in the art can understand that the light detection unit shape can be designed according to actual requirements to suppress different combinations of harmonic components.

[0068] Referring to FIG. 6, FIG. 6 shows another light detecting unit 811K-822K with a width B and a lateral tilt offset C. As shown in FIG. 6, the light detecting unit 818K is an irregular quadrilateral, which is composed of four edges 191-194. Two of the edges 191, 192 are arranged opposite to each other in the lateral (x) direction, and the other two edges 193, 194 are arranged opposite to each other in the vertical (y) direction. The four edges 191-194 form a closed shape. The two edges 191, 192 arranged opposite to each other in the lateral direction are straight lines arranged in a lateral tilt and parallel to each other, and the lateral tilt offset of each of the two edges is C. The two edges 193, 194 arranged opposite to each other in the vertical direction are not fixed in shape, but are the same in shape. The width of the quadrilateral is B, and the width is taken in the manner shown in the figure. As shown in FIG. 6, the "lateral tilt offset" C describes the degree of tilt of the two edges arranged opposite to each other in the lateral direction, and specifically refers to the coordinate difference in the lateral direction of the two endpoints of one of the edges.

[0069] In this way, the single light detecting unit 818K can be decomposed into an infinite number of thin slanted strips 2', each of which has a width tending to zero. Since the two edges 193, 194 arranged opposite to each other in the vertical direction are the same in shape, all the thin slanted strips 2' are the same in length. The lateral tilt offset of each of the thin slanted strips 2' is C, and each of the thin slanted strips 2' maintains a uniform slope within the lateral tilt offset C. The lateral tilt offset C is the period of the third harmonic component in the electrical signal, i.e., P / 3. The single light detecting unit 818K is regarded as a collection of an infinite number of thin light detecting points, and the output electrical signal 88'a of the light detecting unit 818K should be a collection of the output electrical signals of the light detecting points. Therefore, the third harmonic component in each of the output electrical signals of the light detecting points is integrated over the thin slanted strip 2', and the result is zero. This is true for each of the thin slanted strips 2', and therefore the third harmonic component in each of the output electrical signals of the light detecting points is integrated over the entire light detecting unit 818K and is also zero. Therefore, in the method of suppressing harmonic components described in FIG. 5, it is not required that the single light detecting unit must be a parallelogram. As long as the shape of the single light detecting unit is as shown in FIG. 6, the effect of suppressing harmonic components can be achieved. The shape of the single light detecting unit shown in FIG. 6 is not necessarily a quadrilateral. For example, the two edges 193, 194 arranged opposite to each other in the vertical direction can be broken lines, which increases the number of edges and makes the shape a hexagon or a polygon with more sides.

[0070] It should be noted that the method described using FIG. 5 and FIG. 6 suppresses the third harmonic component, and at the same time, suppresses the harmonic components with an order of 3 times. This is because, if the lateral tilt offset of the light detecting unit is P / 3, this tilt offset is also an integer multiple of the periods of the sixth harmonic component, the ninth harmonic component, the twelfth harmonic component, etc. These harmonic components are also integrated to zero over the single light detecting unit, and are therefore suppressed. This is also true for the fifth, seventh, eleventh, etc. harmonic components suppressed using the method.

[0071] It should be noted that the stripe light spot 7 and the light detecting units are repeated in the horizontal direction (x-axis direction), and only a part of them is shown in FIGS. 5 and 6. The length of the stripe light spot 7 in the vertical direction (y-axis direction) can be much larger than the length of the light detecting units in the vertical direction, and only a part of the stripe light spot 7 is shown in FIGS. 5 and 6. The light detecting units can also be repeated in the vertical direction, and different light detecting units repeated in the vertical direction can also be connected to each other, and only a part of them is shown in FIGS. 5 and 6.

[0072] However, the method introduced in FIGS. 5 and 6 can only suppress two harmonic components and integer multiple harmonic components of the two harmonic components by setting the shape and position of the light detecting units, and cannot suppress other harmonic components at the same time. However, there are still multiple harmonic components that need to be suppressed in the electrical signal generated by the light detecting units, such as 7th, 11th, 13th, and 17th harmonic components.

[0073] Referring to FIG. 7, which is a schematic diagram of the arrangement of light detecting units according to another embodiment of the present application, the arrangement of light detecting units that can suppress the 7th harmonic component is shown. As shown in FIG. 7, the period of the slit of the grating is P, and the light passing through the grating falls on the stripe light spot 7 on the light detecting device. The light detecting device includes a plurality of light detecting units, and only the light detecting units 111H-114H, 121H-124H, 131H-134H, and 141H-144H are shown in FIG. 7. The plurality of light detecting units are arranged in the horizontal direction (x-axis direction shown in FIG. 7). The relative movement direction between the grating and the light detecting device is the horizontal direction.

[0074] It should be noted that the stripe light spot 7 and the light detecting units are repeated in the horizontal direction (x-axis direction), and only a part of them is shown in FIG. 7. The length of the stripe light spot 7 in the vertical direction (y-axis direction shown in FIG. 7) can be much larger than the length of the light detecting units in the vertical direction (y-axis direction), and only a part of the stripe light spot 7 is shown in FIG. 7. The light detecting units can also be repeated in the vertical direction (y-axis direction), and different light detecting units repeated in the vertical direction can also be connected to each other, and only a part of them is shown in FIG. 7.

[0075] In FIG. 7, four identical light detection units are arranged side by side in one period P, and the four light detection units are uniformly distributed in the period P. As shown in FIG. 7, four identical light detection units 111H-114H are arranged in one period P, and the shape of each light detection unit is parallelogram. The shape of each light detection unit is identical, and the four light detection units 111H-114H are uniformly distributed in the period P. Therefore, one period P contains the light detection units 111H-114H and the four intervals (x-axis direction) between them. In this arrangement, the four light detection units in one period P output an electrical signal, for example, the light detection units 111H-114H output first-level electrical signals 11a-14a, respectively. If the odd harmonic component signals and interference signals are filtered out, only the fundamental component signals are left, and the first-level electrical signals output by adjacent two light detection units are 90° out of phase, because the coordinate difference between the corresponding points of adjacent two light detection units in the light detection units 111H-114H is one-fourth of the fundamental period. The four first-level electrical signals 11a-14a are input to the subsequent signal processing circuit, which helps to obtain how much relative displacement occurs between the grating and the light detection device.

[0076] Further, every four light detection units form a first-level detection array. For example, the light detection units 111H-114H form a first-level detection array 11M, the light detection units 121H-124H form a first-level detection array 12M, the light detection units 131H-134H form a first-level detection array 13M, and the light detection units 141H-144H form a first-level detection array 14M. A certain number of first-level detection arrays further form a second-level detection array. For example, the first-level detection arrays 11M and 12M form a second-level detection array 101N, and the first-level detection arrays 13M and 14M form a second-level detection array 102N. In this way, the multiple light detection units contained on the entire light detection device are divided into multiple second-level detection arrays, and each second-level detection array contains two first-level detection arrays.

[0077] In the first-stage detection array 11M, the light-detecting units 111H-114H each output an electric signal 11a-14a, which directly becomes a first-stage electric signal output by the first-stage detection array 11M as a whole. In other cases, the electric signals 11a-14a output by the light-detecting units 111H-114H each can be combined, for example, two by two with each other to become an output electric signal, to become the first-stage electric signal output by the first-stage detection array 11M as a whole. That is, the electric signals 11a-14a output by the light-detecting units 111H-114H included in the first-stage detection array 11M directly become or become, after being combined, the first-stage electric signal output by the first-stage detection array 11M. For two first-stage detection arrays belonging to the same second-stage detection array, the first-stage electric signals directly becoming and the first-stage electric signals becoming, after being combined, the electric signals output by the corresponding light-detecting units are called "corresponding" first-stage electric signals. For example, the first-stage electric signals 11a, 15a directly becoming the electric signals output by the corresponding light-detecting units 111H, 121H in the first-stage detection arrays 11M, 12M are called "corresponding" first-stage electric signals.

[0078] In order to suppress the 7th harmonic component in the electric signal output by the light-detecting unit, the coordinate difference of the corresponding points in the adjacent two first-stage detection arrays belonging to the same second-stage detection array is set to P+P / 14. For example, in the adjacent first-stage detection array 11M and the first-stage detection array 12M of the second-stage detection array 101N, the light-detecting unit 111H and the light-detecting unit 121H correspond to each other, and the coordinate difference of the corresponding points of the light-detecting unit 111H and the light-detecting unit 121H is set to P+P / 14.

[0079] The "coordinate difference of the corresponding points" means the coordinate difference of any pair of corresponding points in the corresponding light-detecting units in the adjacent two first-stage detection arrays belonging to the same second-stage detection array. For example, as shown in FIG. 7, the light-detecting unit 111H and the light-detecting unit 121H correspond to each other, and the upper left vertex of the light-detecting unit 111H and the upper left vertex of the light-detecting unit 121H are corresponding points, and the coordinate difference of these two points is P+P / 14.

[0080] Since the period of the 7th harmonic component is P / 7, the coordinate difference between the corresponding points of the light detection unit 111H and the light detection unit 121H is P+P / 14, which is exactly 7 and a half periods of the 7th harmonic component. If the single light detection unit 111H, 121H is regarded as a collection of numerous tiny light detection points, the first-level electrical signals 11a, 15a output by the light detection unit 111H, 121H should be a collection of electrical signals output by each light detection point. The amplitude of the 7th harmonic component in the electrical signals output by each pair of corresponding light detection points in the corresponding light detection units 111H, 121H in the adjacent two first-level detection arrays 11M, 12M is the same, and the phase difference is 7x360°+180°, i.e., the phase difference is 180°. Therefore, after the first-level electrical signals 11a, 15a output by the light detection units 111H, 121H are added, the 7th harmonic component in the second-level electrical signal 11b generated is cancelled.

[0081] As shown in FIG. 7, in the first-level detection array 11M and the first-level detection array 12M, the first-level electrical signals 11a, 15a output by the corresponding two light detection units, i.e., the light detection unit 111H and the light detection unit 121H, are added to obtain a second-level electrical signal 11b. The first-level electrical signals 11a, 15a are a group of corresponding first-level electrical signals, and their addition obtains a second-level electrical signal 11b. In the second-level electrical signal 11b, the 7th harmonic component is cancelled. Similarly, the 7th harmonic component in the second-level electrical signals 12b, 13b, 14b is also cancelled.

[0082] Similarly, in the first-level detection array 13M and the first-level detection array 14M of the second-level detection array 102N, the corresponding first-level electrical signals 21a, 25a output by the corresponding two light detection units, i.e., the light detection unit 131H and the light detection unit 141H, are added to obtain a second-level electrical signal 21b. The first-level electrical signals 21a, 25a are a group of corresponding first-level electrical signals, and their addition obtains a second-level electrical signal 21b. In the second-level electrical signal 21b, the 7th harmonic component is cancelled. Similarly, the 7th harmonic component in the second-level electrical signals 22b, 23b, 24b is also cancelled.

[0083] As can be seen from the above, after the corresponding first-level electrical signals in all the first-level detection arrays belonging to the same second-level detection array are added, the 7th harmonic component in the added second-level electrical signal is eliminated. Even if there is still a 7th harmonic component due to some imperfections in device manufacturing or external interference, the main source of the 7th harmonic component has been eliminated, so the 7th harmonic component is suppressed.

[0084] The above principle is also applicable to suppressing 3rd, 5th, 11th and higher harmonic components, that is, the 3rd, 5th, 11th and Nth harmonic components can be eliminated respectively by setting the coordinate difference of the corresponding points in the adjacent two first-level detection arrays belonging to the same second-level detection array as P+P / 6, P+P / 10, P+P / 22 or P+P / (2xN) (N is the order of the harmonic component to be suppressed).

[0085] In FIG. 7, the lines of the first-level electric signals output by the light detection units are connected, which shows that the corresponding first-level electric signals are added. In fact, for the current signals, the connection of the lines of the electric signals can play the role of adding the corresponding electric signals. For the voltage signals, an adder can be added to realize the adding operation.

[0086] It should also be noted that, in order to suppress the 7th harmonic component using the method introduced in FIG. 7, the coordinate difference of the corresponding points in the adjacent two first-level detection arrays belonging to the same second-level detection array does not necessarily have to be P plus half of the period of the 7th harmonic component (the harmonic component to be suppressed), that is, P+(P / 7)x(1 / 2), but can also be P plus 1 / 3, 1 / 4, 1 / 5, 1 / 6, etc. of the period of the 7th harmonic component (the harmonic component to be suppressed), that is, the coordinate difference of the corresponding points in the adjacent two first-level detection arrays belonging to the same second-level detection array is P+P / (t2xN), where t2 is the number of the first-level detection arrays in the same second-level detection array, t2 is a natural number greater than or equal to 2, N is the order of the harmonic component to be suppressed, and N is an odd number greater than or equal to 3, and N is not the same as the order of the harmonic component that has been suppressed. At this time, the first-level electric signals output by the corresponding light detection units in the t2 first-level detection arrays belonging to the same second-level detection array need to be added, and then the second-level electric signal obtained by the addition is zero for the Nth harmonic component to be suppressed.

[0087] If the 7th harmonic component is to be suppressed, N=7. If t2=3, the same second-level detection array contains three first-level detection arrays, and the coordinate difference of the corresponding points in the adjacent two first-level detection arrays belonging to the same second-level detection array is P+P / 21. Therefore, the phase difference of the 7th harmonic component contained in the first-level electric signals output by the corresponding light detection units in the adjacent two first-level detection arrays is 120°, and thus the three first-level electric signals output by the corresponding light detection units in the three first-level detection arrays belonging to the same second-level detection array are added, and then the second-level electric signal obtained by the addition is zero for the 7th harmonic component.

[0088] If the 7th harmonic component is to be suppressed, N = 7. If t2= 4, the same second-level detection array contains four first-level detection arrays, and the coordinate difference of the corresponding points between the adjacent two first-level detection arrays belonging to the same second-level detection array is P + P / 28. In the first-level electric signals output by the corresponding light detection units in the adjacent two first-level detection arrays, the phase difference of the 7th harmonic components contained is 90°. Therefore, when the four first-level electric signals output by the corresponding light detection units in the four first-level detection arrays belonging to the same second-level detection array are added, the 7th harmonic component in the second-level electric signal obtained by the addition is zero.

[0089] If the 7th harmonic component is to be suppressed, N = 7. If t2= 6, the same second-level detection array contains six first-level detection arrays, and the coordinate difference of the corresponding points between the adjacent two first-level detection arrays belonging to the same second-level detection array is P + P / 42. In the first-level electric signals output by the corresponding light detection units in the adjacent two first-level detection arrays, the phase difference of the 7th harmonic components contained is 60°. Therefore, when the six first-level electric signals output by the corresponding light detection units in the six first-level detection arrays belonging to the same second-level detection array are added, the 7th harmonic component in the second-level electric signal obtained by the addition is zero.

[0090] To suppress the Nth harmonic component, the coordinate difference of the corresponding points between the adjacent two first-level detection arrays belonging to the same second-level detection array can be set as x × P / N + P / (t2 × N), where N is the order of the harmonic component to be suppressed, t2 is a natural number greater than or equal to 2, and x can take many values as long as x is a natural number, but the selection of x should avoid the mutual overlap of the first-level detection arrays in space. Since the period of the Nth harmonic component of the light wave is P / N, the Nth harmonic components of the light waves sensed by the light detection points of the light detection units with a distance of "x × P / N" are the same. The phase difference of the Nth harmonic components of the light waves sensed by the light detection points of the light detection units with a distance of P / (t2 × N) is 360° / t2, and the phase difference of the Nth harmonic components in the first-level electric signals output by the light detection units is also 360° / t2. Therefore, when the first-level electric signals of the corresponding light detection units in the t2 first-level detection arrays belonging to the same second-level detection array are added, the result of the Nth harmonic component in the second-level electric signal obtained by the addition is zero, that is, the Nth harmonic component can be suppressed.

[0091] It should be noted that the "adjacent" in the above-mentioned "between the adjacent two first-level detection arrays belonging to the same second-level detection array" does not mean that the two first-level detection arrays must be adjacent in the physical space, but means that the two first-level detection arrays are adjacent in the sense of belonging to the same second-level detection array. The "adjacent" first-level detection arrays belonging to the same second-level detection array do not have to be adjacent in the physical space in the lateral direction (x-axis direction), but other first-level detection arrays belonging to another second-level detection array can be inserted between the two first-level detection arrays. In this regard, reference can be made to the embodiment described in connection with FIG. 9.

[0092] For example, in FIG. 7, the first-level detection arrays 11M and 12M belong to the same second-level detection array 101N, and the coordinate difference of the corresponding points between the two first-level detection arrays is x×P / N+P / (t2×N). When x is large, the distance between the adjacent two first-level detection arrays among the t2 first-level detection arrays belonging to the same second-level detection array 101N is large, and in this case, one or more first-level detection arrays belonging to another second-level detection array can be inserted in the physical space between the two adjacent first-level detection arrays belonging to the same second-level detection array. For example, in FIG. 7, when x=14, N=7, and t2=2, the coordinate difference of the corresponding points between the first-level detection arrays 11M and 12M is 2P+P / 14. In this case, a first-level detection array 13M belonging to another second-level detection array 102N can be inserted in the physical space between the two adjacent first-level detection arrays 11M and 12M belonging to the same second-level detection array 101N. In this case, although the first-level detection arrays 11M and 12M are not adjacent in the physical space, they belong to the same second-level detection array 101N, and thus they are adjacent in the second-level detection array 101N. The "adjacent k-level detection arrays" in the present patent application means that the two first-level detection arrays are adjacent in the same k+1-level detection array.

[0093] It should also be noted that in FIG. 7, the elimination of the 7th harmonic is completed within a single second-level detection array (for example, the second-level detection arrays 101N and 102N). Therefore, the distance J between the adjacent two second-level detection arrays 101N and 102N does not need to be specially set, and the distance J does not affect the suppression of the 7th harmonic component. The distance J can be close to zero, or can be other suitable values. In the embodiment shown in FIG. 7, the distance J is P / 14.

[0094] In the above distance x x P / N + P / (t2 x N), the value of x in x x P / N needs to avoid the first level detection array overlapping each other in the lateral direction (x-axis direction). For example, in the embodiment shown in FIG. 7, the value of x x P / N needs to be greater than or equal to the sum of the width of four light detection units in a first level detection array and the four spacings (x-axis direction). In other embodiments, the value of x x P / N needs to take into account the size of the first level detection array of another second level detection array that needs to be placed between. For this, please refer to the embodiment described in conjunction with FIG. 9.

[0095] It is also noted that in the above coordinate difference x x P / N + P / (t2 x N) of the corresponding points, the part P / (t2 x N) can also be an integer multiple of P / (t2 x N), i.e. (t1 x P) / (t2 x N), t1 is a natural number greater than or equal to 1, and t1 and t2 are co-prime. At this time, it is still that t2 first level detection arrays form a second level detection array. In the t2 first level detection arrays belonging to the same second level detection array, the coordinate difference of the corresponding points of the adjacent two first level detection arrays is x x P / N + (t1 x P) / (t2 x N). In this way, a fixed phase difference (t1 / t2) x 360° is introduced for the Nth harmonic component in the output electrical signal of the corresponding light detection units in the adjacent two first level detection arrays. The output electrical signal of the corresponding light detection units directly or after combination becomes the first level electrical signal output by the first level detection array as a whole. Therefore, after adding the corresponding first level electrical signals in the t2 first level detection arrays belonging to the same second level detection array, the Nth harmonic component is also cancelled or suppressed in the second level electrical signal obtained by adding.

[0096] It is noted that using the method introduced in FIG. 7 to suppress the 7th harmonic component also suppresses the harmonic components with an integer multiple of 7. This is because if the coordinate difference of the corresponding points of the adjacent two first level detection arrays belonging to the same second level detection array is x x P / 7 + (t1 x P) / (t2 x 7), this coordinate difference is also an integer multiple of the 14th, 21st, etc. harmonic components in the first level electrical signal, and the integrals of these harmonic components are also zero under such a coordinate difference, so the 14th, 21st, etc. harmonic components in the second level electrical signal are also suppressed. This is also applicable to the use of this method to suppress the 3rd, 5th, 11th, etc. harmonic components.

[0097] The method introduced in FIG. 7 can suppress a harmonic component and harmonic components whose orders are integer multiples of the order of the harmonic component. If 3rd and 5th harmonic components in the first-stage electrical signal output by the light detection unit are to be suppressed simultaneously, the specific shape of the light detection unit in FIG. 7 can be set simultaneously. For example, the horizontal tilting offset C of the parallelogram can be set to the period of the 3rd harmonic component to be suppressed, i.e. P / 3, and the width of each parallelogram (x-axis direction) can be set to P / 5, and the principle is as described in conjunction with the content described in FIGS. 3-6.

[0098] It should be noted that if only the method introduced in FIG. 7 is used to suppress a harmonic component and harmonic components whose orders are integer multiples of the order of the harmonic component, the specific shape of the light detection unit can not be limited. The position setting and electrical signal connection mode between the light detection units can be suppressed. It is also not necessary for all light detection units to have the same shape, but only those light detection units whose output electrical signals are added to suppress the harmonic components need to have the same shape. It is also not necessary for the spacing between the light detection units to be uniform. Only when all light detection units have the same shape and the spacing between them is uniformly distributed, it is the easiest to design and helpful for subsequent signal processing, so the embodiments of the present application are all based on this case, but this does not mean a limitation on the present application.

[0099] When the specific shape of the light detection unit is set, the arrangement of the light detection unit shown in FIG. 7 can simultaneously suppress multiple harmonic components and harmonic components whose orders are integer multiples of the orders of the harmonic components. In addition to the above-mentioned manner, the shape, size and coordinate difference parameter of the corresponding points of the adjacent two first-stage detection arrays belonging to the same second-stage detection array of the light detection unit can be designed to simultaneously suppress other harmonic component combinations, for example, to simultaneously suppress 5th, 7th and 11th harmonic components, only the corresponding adjustment of the shape, size parameters of the light detection unit and the coordinate difference parameter of the corresponding points is needed.

[0100] Moreover, the same group of harmonic component combinations, such as 3rd, 5th and 7th harmonic components, can be suppressed in different ways as needed. For example, as described above, the 3rd and 5th harmonic components can be suppressed using the shape design of the light detection unit, and the 7th harmonic component can be suppressed using the setting of a certain coordinate difference between the adjacent two first-stage detection arrays belonging to the same second-stage detection array; the 3rd and 7th harmonic components can be suppressed using the shape design of the light detection unit, and the 5th harmonic component can be suppressed using the setting of a certain coordinate difference between the adjacent two first-stage detection arrays belonging to the same second-stage detection array; there can be other combinations. Those skilled in the art can understand that the specific suppression method can be designed according to actual needs.

[0101] Figure 12 is a simulation of the frequency spectrum of the electrical signal output by the light detection device when no measures are taken to suppress the harmonic components, and Figure 13 is a simulation of the frequency spectrum of the electrical signal output by the light detection device after the 3rd, 5thand 7thharmonic components have been suppressed using the method shown in Figure 7. As can be seen from Figure 13, the 3rd, 5thand 7thharmonic components of the second stage electrical signal 11b-14b, 21b-24b and so on output by the light detection device have been completely eliminated.

[0102] However, the method introduced in Figure 7 can only suppress three harmonic components at the same time and the number of harmonic components must be an integer multiple of the number of the three harmonic components. It cannot suppress four or more harmonic components at the same time, for example, it cannot suppress the 3rd, 5th, 7thand 11thharmonic components at the same time.

[0103] Referring to Figure 8, Figure 8 is a schematic diagram of the arrangement of the light detection unit according to another embodiment of the present application, which shows the arrangement of the light detection unit that can suppress the 7thand 11thharmonic components at the same time. As shown in Figure 8, the period of the slit of the grating is P, and the light passing through the grating projects a fringe pattern 7. The light detection device comprises a plurality of light detection units, and Figure 8 only shows the light detection units 211H-214H, 221H-224H, 231H-234H and 241H-244H. The plurality of light detection units are arranged in the horizontal direction (x-axis direction as shown in Figure 8). The relative movement direction between the grating and the light detection device is the horizontal direction.

[0104] It should be noted that the fringe pattern 7 and the light detection units will repeat in the horizontal direction (x-axis direction), and Figure 8 only shows part of them; the length of the fringe pattern 7 in the vertical direction (y-axis direction as shown in Figure 8) can be much greater than the length of the light detection units in the vertical direction (y-axis direction), and Figure 8 only shows part of the fringe pattern 7; the light detection units can also repeat in the vertical direction (y-axis direction), and different light detection units that repeat in the vertical direction can also be connected to each other, and Figure 8 only shows part of them.

[0105] In Figure 8, four identical light detection units are arranged side by side in one period P, and the four light detection units are uniformly distributed in the period P. For example, four identical light detection units 211H-214H are arranged in one period P, and the shape of the four light detection units is a parallelogram, and the shape of each light detection unit is the same, and the four light detection units 211H-214H are uniformly distributed in the period P, so that the light detection units 211H-214H and the four spacings between them (in the x-axis direction) are contained in one period P.

[0106] In this arrangement, four light detecting units output one electrical signal in one period P, for example, light detecting units 211H-214H output first level electrical signals 31a-34a respectively. If the odd harmonic component signal and the interference signal are filtered out, only the fundamental component signal is left, then the phase difference between the electrical signals outputted by two adjacent light detecting units is 90°. Because the coordinate difference between the corresponding points of two adjacent light detecting units in light detecting units 211H-214H is one fourth of the fundamental period. The four first level electrical signals 31a-34a are inputted into the subsequent signal processing circuit, which is helpful to obtain how much relative displacement occurs between the grating and the light detecting device.

[0107] Further, four light detecting units form a first level detecting array, for example, light detecting units 211H-214H form a first level detecting array 21M, light detecting units 221H-224H form a first level detecting array 22M, light detecting units 231H-234H form a first level detecting array 23M, and light detecting units 241H-244H form a first level detecting array 24M. A certain number of first level detecting arrays further form a second level detecting array, for example, first level detecting arrays 21M and 22M form a second level detecting array 201N, and first level detecting arrays 23M and 24M form a second level detecting array 202N. The second level detecting arrays 201N and 202N are shown as the parallelogram drawn by the solid line in FIG. 8. In this way, the multiple light detecting units contained in the light detecting device are divided into multiple second level detecting arrays 201N, 202N, … (not completely shown), and each second level detecting array contains two first level detecting arrays.

[0108] In order to suppress the 7th harmonic component in the electrical signal outputted by the light detecting unit, the coordinate difference between the corresponding points of two adjacent first level detecting arrays belonging to the same second level detecting array is set to P+P / 14. For example, in the adjacent first level detecting arrays 21M and 22M belonging to the same second level detecting array 201N, light detecting unit 211H corresponds to light detecting unit 221H, then the coordinate difference between the corresponding points of light detecting unit 211H and light detecting unit 221H is set to P+P / 14. Moreover, the first level electrical signals outputted by the corresponding light detecting units in the adjacent first level detecting arrays 21M and 22M are added, for example, the first level electrical signal 31a outputted by light detecting unit 211H and the first level electrical signal 35a outputted by light detecting unit 221H are added to obtain a second level electrical signal 31b, and the 7th harmonic component in the second level electrical signal 31b is suppressed or eliminated. The principle can be referred to the description in the present patent application document in combination with FIG. 7. In this way, the 7th harmonic component in the second level electrical signals 31b-34b is suppressed or eliminated.

[0109] Similarly, the positional relationship and connection relationship between the two adjacent first-level detection arrays 23M and 24M belonging to the same second-level detection array 202N are also set as the relationship between the first-level detection arrays 21M and 22M, so that the 7th harmonic components in the second-level electrical signals 41b-44b are suppressed or eliminated.

[0110] Further, a certain number of second-level detection arrays further form a third-level detection array, for example, the second-level detection arrays 201N and 202N form a third-level detection array 2001R. In this way, the plurality of light detection units contained on the entire light detection device are divided into a plurality of third-level detection arrays, each third-level detection array can contain two second-level detection arrays, each second-level detection array can contain two first-level detection arrays, and each first-level detection array can contain four light detection units.

[0111] In this way, a multi-level detection array and a corresponding electrical signal connection structure are formed. The four light detection units 211H-214H in the first-level detection array 21M respectively output first-level electrical signals 31a-34a, the four light detection units 221H-224H in the first-level detection array 22M respectively output first-level electrical signals 35a-38a, the four light detection units 231H-234H in the first-level detection array 23M respectively output first-level electrical signals 41a-44a, and the four light detection units 241H-244H in the first-level detection array 24M respectively output first-level electrical signals 45a-48a. Among them, the first-level electrical signal 31a and the first-level electrical signal 35a are added to generate the second-level electrical signal 31b, the first-level electrical signal 32a and the first-level electrical signal 36a are added to generate the second-level electrical signal 32b, the first-level electrical signal 33a and the first-level electrical signal 37a are added to generate the second-level electrical signal 33b, the first-level electrical signal 34a and the first-level electrical signal 38a are added to generate the second-level electrical signal 34b, the first-level electrical signal 41a and the first-level electrical signal 45a are added to generate the second-level electrical signal 41b, the first-level electrical signal 42a and the first-level electrical signal 46a are added to generate the second-level electrical signal 42b, the first-level electrical signal 43a and the first-level electrical signal 47a are added to generate the second-level electrical signal 43b, and the first-level electrical signal 44a and the first-level electrical signal 48a are added to generate the second-level electrical signal 44b.

[0112] If the first-level detection array 21M and the first-level detection array 22M are regarded as a whole, that is, to form a second-level detection array 201N, the second-level electrical signals 31b-34b can be regarded as the electrical signals output by the second-level detection array 201N. Similarly, the second-level electrical signals 41b-44b can be regarded as the electrical signals output by the second-level detection array 202N. In the second-level electrical signals 31b-34b and 41b-44b, there are no 7th harmonic components, but there are 11th harmonic components.

[0113] To suppress the 11th harmonic component in the second-stage electrical signal outputted by the second-stage detection array, the coordinate difference between the corresponding points of the two adjacent second-stage detection arrays belonging to the same third-stage detection array is set to 24P / 11+P / 22. For example, in the two adjacent second-stage detection arrays 201N and 202N belonging to the same third-stage detection array 2001R, the light detection unit 211H corresponds to the light detection unit 231H, and the coordinate difference between the corresponding points of the light detection unit 211H and the light detection unit 231H is set to 24P / 11+P / 22. Meanwhile, the second-stage electrical signals corresponding to the second-stage detection arrays 201N and 202N are added to obtain a third-stage electrical signal. For example, the second-stage electrical signals 31b and 41b are added, and the second-stage electrical signals 31b and 41b are referred to as a group of corresponding second-stage electrical signals, and the addition results in a third-stage electrical signal 31c. Similarly, other third-stage electrical signals 32c-34c are obtained. The third-stage electrical signals 31c-34c are regarded as the electrical signal outputted by the third-stage detection array 2001R composed of the second-stage detection arrays 201N and 202N.

[0114] The "coordinate difference between the corresponding points" means the coordinate difference between any pair of corresponding points in the corresponding light detection units of the two adjacent second-stage detection arrays belonging to the same third-stage detection array. For example, as shown in FIG. 8, the light detection unit 211H corresponds to the light detection unit 231H, and the left upper vertex of the light detection unit 211H corresponds to the left upper vertex of the light detection unit 231H, and the coordinate difference between the two corresponding points is 24P / 11+P / 22.

[0115] FIG. 8 shows the specific positional relationship of the light detection units. The D line indicates the starting position of the first-stage detection array 21M, i.e., the position of the left upper vertex of the light detection unit 211H. The E line indicates the ending position of the first-stage detection array 22M, i.e., the position of the right upper vertex of the light detection unit 224H plus the distance between the adjacent light detection units in the first-stage detection array. Between the D line and the E line, the space position occupied by the second-stage detection array 201N can be regarded. The F line indicates the position 24P / 11 away from the D line, and this distance is an integer multiple of the period P / 11 of the 11th harmonic component in the light wave. The G line indicates the starting position of the second-stage detection array 202N, i.e., the position of the left upper vertex of the light detection unit 231H. Between the D line and the G line, the coordinate difference 24P / 11+P / 22 between the corresponding points of the second-stage detection array 201N and the second-stage detection array 202N is obtained.

[0116] Since the period of the 11th harmonic component is P / 11, the coordinate difference between the corresponding points of the light detecting unit 211H and the light detecting unit 231H is 24P / 11+P / 22, which is exactly 24 and a half periods of the 11th harmonic component. If the single light detecting unit 211H, 231H is regarded as a collection of numerous tiny light detecting points, the first stage electric signal 31a, 41a outputted by the light detecting unit 211H, 231H should be a collection of the electric signals outputted by each light detecting point. Since the corresponding light detecting points in the light detecting unit 211H, 231H belonging to the adjacent second stage detecting array 201N and the second stage detecting array 202N of the same third stage detecting array 2001R output the electric signals with the same amplitude and a phase difference of 24x360°+180°, i.e. a phase difference of 180°. Therefore, the phase difference between the 11th harmonic components in the first stage electric signals 31a, 41a generated by the light detecting unit 211H and the light detecting unit 231H is 180°. Similarly, the phase difference between the 11th harmonic components in the first stage electric signals 35a and 45a is 180°. Since the second stage electric signals 31b is composed of the first stage electric signals 31a, 35a, and the second stage electric signals 41b is composed of the first stage electric signals 41a, 45a, the phase difference between the 11th harmonic components in the second stage electric signals 31b, 41b is also 180°. Therefore, the 11th harmonic component in the third stage electric signal 31c obtained by adding them should be zero. This achieves the effect of removing or suppressing the 11th harmonic component. Similarly, the 11th harmonic components in the third stage electric signals 32c-34c are also cancelled.

[0117] As can be seen from the above, the 11th harmonic component in the added third stage electric signal is eliminated after the corresponding second stage electric signals in all the second stage detecting arrays belonging to the same third stage detecting array are added. Even if the 11th harmonic component still exists due to some imperfections in the device manufacturing or external interference, the main source of the 11th harmonic component has been eliminated, so the 11th harmonic component is suppressed.

[0118] The embodiment shown in Fig. 8 has other implementation methods. To suppress the 11th harmonic component, the coordinate difference between the corresponding points of the adjacent second-level detection arrays 201N, 202N belonging to the same third-level detection array 2001R can also be y x P / M + P / (s2 x M), where M is the order of the harmonic component to be suppressed, and M is not the same as the order of the harmonic component that has been suppressed, s2 is the number of second-level detection arrays in the same third-level detection array, s2 is a natural number greater than 2, and y is a natural number and can take many values, but the selection of y should avoid the second-level detection arrays overlapping each other in space. That is, on the basis of the integer multiple of the period P / 11 of the 11th harmonic component in the electrical signal, the distance P / (s2 x 11) is added, thereby introducing a fixed phase difference of 360° / s2 for the 11th harmonic component sensed by each pair of corresponding light detection units in the adjacent second-level detection arrays 201N, 202N.

[0119] Correspondingly, the corresponding second-level electrical signals of each of the s2 second-level detection arrays in the same third-level detection array are added, and in the third-level electrical signal obtained by the addition, the 11th harmonic component is zero. For example, when s2 = 2, as shown in Fig. 8, the corresponding second-level electrical signals in the second-level detection arrays 201N, 202N in the same third-level detection array 2001R are added respectively, that is, the second-level electrical signals 31b and 41b are added, the second-level electrical signals 32b and 42b are added, the second-level electrical signals 33b and 43b are added, and the second-level electrical signals 34b and 44b are added, thereby obtaining third-level electrical signals 31c, 32c, 33c, and 34c respectively. In the third-level electrical signals 31c-34c, the 11th harmonic component is zero. When s2 = 3, in the embodiment shown in Fig. 8, the same third-level detection array 2001R needs to contain three second-level detection arrays, and the corresponding second-level electrical signals in the three second-level detection arrays are added respectively, that is, each of the three corresponding second-level electrical signals is added to obtain a third-level electrical signal. In each of the third-level electrical signals obtained in this way, the 11th harmonic component is zero.

[0120] Here, the "corresponding" second-level electrical signal refers to the second-level electrical signal output by each second-level detection array in a third-level detection array, which is composed of the first-level electrical signals output by the corresponding light detection units. For example, in Fig. 8, between the second-level detection arrays 201N, 202N, the second-level electrical signals 31b and 41b are composed of the first-level electrical signals output by the corresponding light detection units 211H and 221H and the corresponding light detection units 231H and 241H respectively, so the second-level electrical signals 31b and 41b are two corresponding second-level electrical signals in the second-level detection arrays 201N, 202N.

[0121] Similarly, the "adjacent" in the "adjacent second-level detection array" in the present embodiment refers to the "adjacent" in the sense of belonging to the same third-level detection array, rather than the physical adjacency. The "adjacent" second-level detection arrays belonging to the same third-level detection array are not necessarily physically adjacent in the lateral (x-axis) direction, but other second-level detection arrays belonging to another third-level detection array can be inserted therebetween.

[0122] In FIG. 8, the transmission lines of the first-level electrical signals output by the first-level detection arrays are connected or the transmission lines of the second-level electrical signals output by the second-level detection arrays are connected, indicating that the corresponding electrical signals are added. In fact, the transmission lines of the current signals are connected to achieve the effect of adding the corresponding electrical signals. For voltage signals, an adder can be added to achieve the addition operation.

[0123] In the above distance y x P / M + P / (s2 x M), the value of y in y x P / M needs to avoid the second-level detection arrays from overlapping with each other in the lateral (x-axis) direction. For example, in the embodiment shown in FIG. 8, the value of y x P / M needs to be greater than or equal to the sum of the widths (x-axis direction) of the two first-level detection arrays 21M and 22M and the spacing therebetween. In other embodiments, the value of y x P / M also needs to take into account the size of the second-level detection arrays belonging to other third-level detection arrays that need to be placed therebetween. For this, please refer to the embodiment described in conjunction with FIG. 9.

[0124] It should be noted that when the coordinate difference of the corresponding points of the second-level detection arrays is the above distance y x P / M + P / (s2 x M), the phase difference of the Mth harmonic components in the second-level electrical signals output by the adjacent second-level detection arrays belonging to the same third-level detection array is 360° / (s2 x M). This phase difference can also be an integer multiple of P / (s2 x M), i.e., (s1 x P) / (s2 x M), s1 is a natural number greater than or equal to 1, s1 and s2 are co-prime, and each s2 second-level detection arrays form a third-level detection array. At this time, the coordinate difference of the corresponding points of the adjacent two second-level detection arrays belonging to the same third-level detection array is y x P / M + (s1 x P) / (s2 x M). In this way, a fixed phase difference (s1 / s2) x 360° is introduced for the Mth harmonic components in the electrical signals output by the corresponding light detection units in the adjacent two second-level detection arrays belonging to the same third-level detection array. The electrical signals output by the corresponding light detection units are finally combined into the second-level electrical signals output by the second-level detection arrays. Therefore, after the corresponding second-level electrical signals in the s2 second-level detection arrays belonging to the same third-level detection array are added, the Mth harmonic components are also cancelled or suppressed in the third-level electrical signals obtained by the addition.

[0125] It should be noted that the method introduced in Figure 8 suppresses the 11th harmonic component, and also suppresses the harmonic components with integer times of 11. This is because the coordinate difference is also an integer times of the 22nd, 33rd, etc. harmonic components in the second order electric signal. Based on the same coordinate difference, if the integral of the 11th harmonic component in the third order electric signal is zero, the integrals of the 22nd, 33rd, etc. harmonic components in the third order electric signal are also zero, so the 22nd, 33rd, etc. harmonic components in the third order electric signal are also suppressed. This is also applicable to the suppression of the 3rd, 5th, 7th, etc. harmonic components using the method.

[0126] The principle of the embodiment shown in Figure 8 is also applicable to the suppression of the 3rd, 5th, 13th, etc. harmonic components, which can be achieved by setting the parameter M in the above y x P / M + (s1 x P) / (s2 x M).

[0127] The method introduced in Figure 8 can suppress two harmonic components and their integer times harmonic components. If the 3rd, 5th, etc. harmonic components in the output electric signal of the light detection unit also need to be suppressed, the specific shape of the light detection unit in Figure 8 can be set at the same time. For example, the horizontal tilting offset C of the parallelogram is set to the period of the 3rd harmonic component to be suppressed, i.e. P / 3, and the width of each parallelogram (x-axis direction) is set to P / 5, and the principle is as described in conjunction with the contents described in Figures 3-6.

[0128] It should be noted that if only the method introduced in Figure 8 is used to suppress two harmonic components and their integer times harmonic components, the specific shape of the light detection unit can not be limited. The position setting between the light detection units and the electric signal connection mode can suppress two harmonic components and their integer times harmonic components. It is also not required that all light detection units have the same shape, only those light detection units whose output electric signals are added to suppress the harmonic components need to have the same shape. It is also not required that the spacing between the light detection units is uniform. This is also applicable to the embodiments shown in Figures 9 and 10. Only when all light detection units have the same shape and the spacing between them is uniformly distributed if not specifically set, it is the easiest to design and helpful for subsequent signal processing, so the embodiments of the present application are based on this case, but this does not mean a limitation of the present application.

[0129] When the specific shape of the light detection unit is set, the arrangement of the light detection unit shown in Fig. 8 can simultaneously suppress multiple harmonic components and harmonic components whose orders are integer multiples of their orders. This can be achieved by designing the shape, size and coordinate difference parameters of the corresponding points in the two adjacent first-level detection arrays of the light detection unit. For example, to simultaneously suppress the 5th, 7th, 11th and 13th harmonic components, only the shape, size and coordinate difference parameters of the corresponding points of the light detection unit need to be adjusted accordingly. Moreover, to suppress the same group of harmonic components, such as the 3rd, 5th, 7th and 11th harmonic components, different methods can be selected as needed.

[0130] For example, as described above, the 3rd and 5th harmonic components can be suppressed by designing the shape of the light detection unit, the 7th harmonic component can be suppressed by setting a certain coordinate difference between the two adjacent first-level detection arrays belonging to the same second-level detection array, and the 11th harmonic component can be suppressed by setting a certain coordinate difference between the two adjacent second-level detection arrays belonging to the same third-level detection array. Alternatively, the 3rd and 7th harmonic components can be suppressed by designing the shape of the light detection unit, the 5th harmonic component can be suppressed by setting a certain coordinate difference between the two adjacent first-level detection arrays belonging to the same second-level detection array, and the 11th harmonic component can be suppressed by setting a certain coordinate difference between the two adjacent second-level detection arrays belonging to the same third-level detection array. There can be other combinations. Those skilled in the art can understand that the specific suppression method can be designed according to actual needs.

[0131] Fig. 12 is a simulation diagram of the frequency spectrum of the electrical signal output by the light detection device without taking any measures to suppress the harmonic components, and Fig. 14 is a simulation diagram of the frequency spectrum of the electrical signal output by the light detection device after suppressing the 3rd, 5th, 7th and 11th harmonic components using the method shown in Fig. 8. As can be seen from Fig. 14, the 3rd, 5th, 7th and 11th harmonic components of the third-level electrical signal 31c-34c output by the light detection device are completely eliminated.

[0132] In the above embodiments, the "adjacent" in the "adjacent two second-level detection arrays" does not necessarily mean physically adjacent, but means "adjacent" in the sense of belonging to the same third-level detection array. The "adjacent" second-level detection arrays belonging to the same third-level detection array do not necessarily have to be physically adjacent in the lateral (x-axis) direction, but can be inserted between other second-level detection arrays belonging to another third-level detection array.

[0133] For example, in FIG. 8, the second-level detection arrays 201N, 202N belong to the third-level detection array 2001R, and the coordinate difference of the corresponding points between them is y x P / M + (s1 x P) / (s2 x M). If M = 11, y = 44, s1 = 1, and s2 = 2, the coordinate difference of the corresponding points between the second-level detection arrays 201N, 202N is 4P + P / 22. At this time, there is enough space between the second-level detection arrays 201N, 202N, and a second-level detection array belonging to another third-level detection array can be placed (not shown in FIG. 8). However, for the third-level detection array 2001R, the second-level detection arrays 201N, 202N are still "adjacent" second-level detection arrays.

[0134] Referring to FIG. 9, FIG. 9 is a schematic diagram of an arrangement of light detection units according to another embodiment of the present application, which shows another implementation capable of simultaneously suppressing 3rd, 5th, 7th, and 11th harmonic components. The light detection device includes a plurality of light detection units (not shown in FIG. 9), and a fixed number of light detection units are combined into a first-level detection array. FIG. 9 only shows the first-level detection arrays 51M-53M, 61M-63M. For example, in FIG. 9, the first-level detection arrays 51M-53M, 61M-63M each include 4 light detection units, and the 4 light detection units have the same shape and are uniformly distributed in the first-level detection array.

[0135] It should be noted that each first-level detection array repeats in the lateral direction (x-axis direction), and FIG. 9 only shows part of them.

[0136] In FIG. 9, the first-level detection arrays 51M-53M belong to the second-level detection array 501N, and the first-level detection arrays 61M-63M belong to the second-level detection array 601N. The first-level electrical signals 49a-60a output by the sequentially adjacent first-level detection arrays 51M, 52M, 53M are added correspondingly. The first-level electrical signals 61a-72a output by the sequentially adjacent first-level detection arrays 61M, 62M, 63M are added correspondingly.

[0137] As can be seen, in the second-level detection array 501N, the first-level detection array 61M belonging to the second-level detection array 601N is inserted between the adjacent first-level detection arrays 51M, 52M. Similarly, the first-level detection array 62M is inserted between the adjacent first-level detection arrays 52M, 53M. In the second-level detection array 601N, the first-level detection array 52M belonging to the second-level detection array 501N is inserted between the adjacent first-level detection arrays 61M, 62M. Similarly, the first-level detection array 53M is inserted between the adjacent first-level detection arrays 62M, 63M.

[0138] In the second-level detection array 501N, the coordinate difference of the corresponding points between the adjacent first-level detection arrays 51M and 52M and between the adjacent first-level detection arrays 52M and 53M is 3P+P / 21. In order to clearly illustrate the technical solutions, the left upper corner of each block indicating the first-level detection arrays 51M-53M and 61M-63M can be regarded as the corresponding point of the first light detection unit in each first-level detection array. The light detection units in the first-level detection array 51M output first-level electric signals 49a-52a, respectively, the light detection units in the first-level detection array 52M output first-level electric signals 53a-56a, respectively, and the light detection units in the first-level detection array 53M output first-level electric signals 57a-60a, respectively. In these first-level electric signals, the corresponding first-level electric signals are added to obtain second-level electric signals 51b-54b, respectively, and the 3rd, 5th and 7th harmonic components in the second-level electric signals 51b-54b are suppressed or eliminated. The principle can be referred to the description in the patent application file in combination with FIGS. 3-8.

[0139] Similarly, in the second-level detection array 601N, the coordinate difference of the corresponding points between the adjacent first-level detection arrays 61M and 62M and between the adjacent first-level detection arrays 62M and 63M is 3P+P / 21. The first-level detection arrays 61M, 62M and 63M output first-level electric signals 61a-64a, 65a-68a and 69a-72a, respectively. In these first-level electric signals, the corresponding first-level electric signals are added to obtain second-level electric signals 61b-64b, respectively, and the 3rd, 5th and 7th harmonic components in the second-level electric signals 61b-64b are suppressed or eliminated. The principle can be referred to the description in the patent application file in combination with FIGS. 3-8.

[0140] In FIG. 9, two second-level detection arrays 501N and 601N constitute a third-level detection array, and the coordinate difference of the corresponding points between the second-level detection arrays 501N and 601N is P+P / 22. For example, the coordinate difference of the corresponding points between the first-level detection array 51M and the first-level detection array 61M is P+P / 22, the coordinate difference of the corresponding points between the first-level detection array 52M and the first-level detection array 62M is P+P / 22, and the coordinate difference of the corresponding points between the first-level detection array 53M and the first-level detection array 63M is P+P / 22. The corresponding second-level electric signals output by the second-level detection arrays 501N and 601N are added, for example, the corresponding second-level electric signals 51b and 61b are added, and in the third-level electric signal 51c obtained, the 11th harmonic component should be zero. Similarly, in the third-level electric signals 52c-54c, the 11th harmonic component is suppressed or eliminated. The principle can be referred to the description in the patent application file in combination with FIGS. 3-8.

[0141] According to the technical principles disclosed in FIGS. 3-9, if five or more harmonic components are to be suppressed simultaneously, the third-level detection arrays can be combined into higher-level detection arrays, and the coordinate difference between corresponding points of two adjacent third-level detection arrays belonging to the same higher-level detection array is set appropriately. For example, r2third-level detection arrays are combined as a fourth-level detection array, thereby forming a plurality of fourth-level detection arrays, and corresponding third-level electric signals in the r2third-level detection arrays belonging to the same fourth-level detection array are added respectively, thereby forming r2fourth-level electric signals, in which the fifth harmonic component is suppressed.

[0142] Referring to FIG. 10, which is a schematic diagram of an arrangement of light detection units according to another embodiment of the present application, an implementation that can suppress the 7th, 11th, and 13th harmonic components simultaneously is shown. In FIG. 10, each of the first-level detection arrays 15M-18M and 25M-28M contains a plurality of light detection units, and the number and arrangement of the light detection units in each first-level detection array are the same. Each first-level detection array outputs four first-level electric signals, for example, the first-level detection array 15M outputs first-level electric signals 1’a, 2’a, 3’a, and 4’a. The number of first-level electric signals can be other numbers, which depends on the number of light detection units in a first-level detection array and the manner of electrical connection between them.

[0143] t2first-level detection arrays can form a second-level detection array. For example, taking t2=2, the two adjacent first-level detection arrays 15M and 16M form a second-level detection array 105N, the two adjacent first-level detection arrays 17M and 18M form a second-level detection array 106N, the two adjacent first-level detection arrays 25M and 26M form a second-level detection array 205N, and the two adjacent first-level detection arrays 27M and 28M form a second-level detection array 206N. The coordinate difference between corresponding points of two adjacent first-level detection arrays (for example, the first-level detection arrays 15M and 16M) belonging to the same second-level detection array is set to x×P / N+(t1×P) / (t2×N), and N=7, thereby introducing a phase difference (t1 / t2)×360° between the 7th harmonic components of the electric signals output by the two adjacent first-level detection arrays. For example, taking x=7, t1=1, and t2=2, the coordinate difference between the corresponding points is set to P+P / 14, thereby introducing a phase difference of 180° between the 7th harmonic components of the electric signals output by the two adjacent first-level detection arrays. In order to make the technical solution clearer, the upper left corner of each of the dashed boxes indicating the first-level detection arrays 15M-18M and 25M-28M can be regarded as the corresponding point of the first light detection unit in each first-level detection array.

[0144] The corresponding first-level electrical signals outputted by the t2 first-level detection arrays belonging to the same second-level detection array are added to obtain a second-level electrical signal, and the second-level electrical signal is taken as the second-level detection array output electrical signal. For example, the first-level electrical signals 1’a and 5’a are corresponding, and are added to obtain the second-level electrical signal 1’b; the first-level electrical signals 2’a and 6’a are corresponding, and are added to obtain the second-level electrical signal 2’b; the first-level electrical signals 3’a and 7’a are corresponding, and are added to obtain the second-level electrical signal 3’b; and the first-level electrical signals 4’a and 8’a are corresponding, and are added to obtain the second-level electrical signal 4’b. In the second-level electrical signals 1’b, 2’b, 3’b and 4’b, the 7th harmonic component is suppressed or eliminated. Similarly, in the second-level electrical signals 5’b-16’b, the 7th harmonic component is suppressed or eliminated.

[0145] Further, the s2 second-level detection arrays adjacent to each other can constitute a third-level detection array. For example, taking s2=2, the two second-level detection arrays 105N and 106N adjacent to each other constitute the third-level detection array 1005R, and the two second-level detection arrays 205N and 206N adjacent to each other constitute the third-level detection array 2005R. The coordinate difference of the corresponding points of the two second-level detection arrays (for example, the second-level detection arrays 205N and 206N) belonging to the same third-level detection array is set to y×P / M+(s1×P) / (s2×M), and M=11, so as to introduce a phase difference (s1 / s2)×360° between the 11th harmonic components of the second-level detection array output electrical signals of the two second-level detection arrays. For example, taking y=24, s1=1 and s2=2, the coordinate difference of the corresponding points is set to 24 / 11+P / 22, so as to introduce a phase difference 180° between the 11th harmonic components of the second-level detection array output electrical signals of the two second-level detection arrays.

[0146] The corresponding second-level electrical signals outputted by the s2 second-level detection arrays belonging to the same third-level detection array are added to obtain a third-level electrical signal, and the third-level electrical signal is taken as the third-level detection array output electrical signal. For example, the second-level electrical signals 1’b and 5’b are corresponding, and are added to obtain the third-level electrical signal 1’c; the second-level electrical signals 2’b and 6’b are corresponding, and are added to obtain the third-level electrical signal 2’c; the second-level electrical signals 3’b and 7’b are corresponding, and are added to obtain the third-level electrical signal 3’c; and the second-level electrical signals 4’b and 8’b are corresponding, and are added to obtain the third-level electrical signal 4’c. In the third-level electrical signals 1’c, 2’c, 3’c and 4’c, the 11th harmonic component is suppressed or eliminated. Similarly, in the third-level electrical signals 5’c, 6’c, 7’c and 8’c, the 11th harmonic component is suppressed or eliminated.

[0147] Further, the adjacent r2 third-level detection arrays can constitute a fourth-level detection array. For example, taking r2=2, the adjacent two third-level detection arrays 1005R and 2005R constitute a fourth-level detection array 10005S. In FIG. 10, only one fourth-level detection array 10005S is shown, and in fact, a plurality of fourth-level detection arrays can be included on the light detection device, each of which is arranged in the same manner. The corresponding third-level electrical signals output by the r2 third-level detection arrays belonging to the same fourth-level detection array are added to obtain a fourth-level electrical signal, which is the fourth-level detection array output electrical signal. For example, the third-level electrical signals 1’c and 5’c correspond to a group of corresponding third-level electrical signals, which are added to obtain the fourth-level electrical signal 1’d. Similarly, the third-level electrical signals 2’c and 6’c correspond to each other and are added to obtain the fourth-level electrical signal 2’d, the third-level electrical signals 3’c and 7’c correspond to each other and are added to obtain the fourth-level electrical signal 3’d, and the third-level electrical signals 4’c and 8’c correspond to each other and are added to obtain the fourth-level electrical signal 4’d.

[0148] Further, in the plurality of third-level detection arrays described above, the coordinates of the corresponding points of the adjacent two third-level detection arrays belonging to the same fourth-level detection array differ by z×P / Q+(r1×P) / (r2×Q), where r1 and z are natural numbers, r2 is a natural number greater than 2, r1 and r2 are coprime, r2 is the number of third-level detection arrays belonging to the same fourth-level detection array, z can take many values as long as it is a natural number, but the selection of z should avoid the mutual overlap of third-level detection arrays in space, Q is the order of the harmonic component to be suppressed, Q is an odd number greater than or equal to 3, and Q is not the same as the order of the harmonic component that has been suppressed. That is, on the basis of an integer multiple of the period P / Q of the Qth harmonic component, the distance (r1×P) / (r2×Q) is added, thereby introducing a fixed phase difference (r1 / r2)×360° for the Qth harmonic component in the electrical signals output by the corresponding light detection units in the adjacent two third-level detection arrays belonging to the same fourth-level detection array. Correspondingly, the corresponding third-level electrical signals output by the r2 third-level detection arrays belonging to the same fourth-level detection array are added, and the Qth harmonic component in the fourth-level electrical signal obtained by the addition is zero, and the Qth harmonic component is suppressed or eliminated.

[0149] For example, in FIG. 10, the 13th harmonic is to be suppressed, i.e. Q is 13. Take r1=1, r2=2, z=57, and set the coordinate difference between the corresponding points of the two adjacent third-level detection arrays belonging to the same fourth-level detection array to be 57P / 13+P / 26, so as to introduce a 180° phase difference for the 13th harmonic components in the corresponding third-level electric signals output by the two adjacent third-level detection arrays. The corresponding third-level electric signals output by all the third-level detection arrays belonging to the same fourth-level detection array are added to obtain a fourth-level electric signal. For example, in the third-level electric signals output by the two adjacent third-level detection arrays 1005R and 1006R belonging to the same fourth-level detection array 10005S, the third-level electric signals 1'c and 5'c correspond, and they are added to obtain a fourth-level electric signal 1'd. Similarly, fourth-level electric signals 2'd, 3'd and 4'd are obtained. In the fourth-level electric signals 1'd-4'd, the 13th harmonic components are suppressed or eliminated.

[0150] In FIG. 10, if the 3rd and 5th harmonic components are to be removed, the shape of each light detection unit (not shown in FIG. 10) can be set to be a parallelogram as shown in FIG. 8. For example, the width of the parallelogram can be set to be P / 5, and the transverse inclination offset can be set to be P / 3. Any one of the first-level detection arrays 15M-18M and 25M-28M includes four light detection units, which have the same shape and are uniformly distributed in the first-level detection array. With this setting, in the embodiment shown in FIG. 10, the 3rd, 5th, 7th, 11th and 13th harmonic components and their integer multiple harmonic components in the output electric signals can be removed at the same time. This can achieve a good measurement accuracy in most optical encoders.

[0151] If only three harmonic components are to be removed, in the embodiment shown in FIG. 10, the specific shape of the light detection unit can not be limited. If only four harmonic components are to be removed, in the embodiment shown in FIG. 10, only one geometric dimension of the light detection unit can be limited, for example, the light detection unit can be set to have the shape as shown in FIG. 4 or FIG. 6. As to which harmonic components are to be removed and which size setting is to be used to remove these harmonic components, those skilled in the art can design according to the needs based on the teachings provided in the present patent application.

[0152] FIG. 12 is a frequency spectrum simulation diagram of the electric signals output by the light detection device without taking any measures to suppress the harmonic components, and FIG. 15 is a frequency spectrum simulation diagram of the electric signals output by the light detection device after the 3rd, 5th, 7th, 11th and 13th harmonic components are suppressed by the method shown in FIG. 10. As can be seen from FIG. 15, the 3rd, 5th, 7th, 11th and 13th harmonic components in the fourth-level electric signals 1'd-4'd output by the light detection device are completely eliminated after being processed by the above method.

[0153] Referring to Fig. 11, Fig. 11 is a schematic diagram of the arrangement of the light detecting units on the light detecting device actually made according to another embodiment of the present application. The grating used in cooperation with the light detecting device is a disc grating. The pattern shown in Fig. 11 can be the pattern actually made after the rectangular-fan conversion of the arrangement of any of the embodiments disclosed in Figs. 3-10. 911 is one of the columns of the light detecting units, and the light detecting unit 911 includes a plurality of segments 116-119, each of which is arranged in mirror symmetry in the vertical direction. Each segment can be one of the light detecting units in any of the embodiments disclosed in Figs. 3-10, for example, can be a parallelogram as shown in Fig. 8. In this way, a plurality of parallelograms arranged in mirror symmetry in the vertical direction (y-axis direction) and repeatedly arranged adjacent to each other form one column of the light detecting units.

[0154] In Fig. 11, the light detecting units 911H-914H, 915H-918H, 919H-922H, 923H-926H are combined into the first-level detecting arrays 91M, 92M, 93M, 94M, respectively, and the first-level detecting arrays 91M-92M, 93M-94M are combined into the second-level detecting arrays 901N, 902N, respectively. The second-level detecting array 901N is additionally provided with the light detecting unit 930H outside the second-level detecting array 901N, which is horizontally spaced apart from the light detecting unit 911H by a distance of P / 22, and the second-level detecting array 902N is additionally provided with the light detecting unit 940H outside the second-level detecting array 902N, which is horizontally spaced apart from the light detecting unit 926H by a distance of P / 22. The above-mentioned distance P / 22 is the horizontal distance between the second-level detecting arrays 901N, 902N. The provision of the two additional light detecting units 930H, 940H can avoid the inconsistency in the light conversion rates of the light detecting units 911H-926H due to the difference in the environments of the light detecting units 911H-926H in the main structure of the light detecting device, and thus can make the working environments of all the light detecting units 911H-926H as consistent as possible. That is, the two additional light detecting units 930H, 940H are used to reduce or eliminate the inconsistency in the working environments of all the light detecting units 911H-926H. The two additional light detecting units 930H, 940H can not be connected to the main structure of the light detecting device and the signal processing circuit.

[0155] In summary, the above-mentioned only the preferred embodiments of the present application, any equivalent changes and modifications made in accordance with the disclosure of the present application, should be included in the scope of the present application.

Claims

1. A light detection device for an optical encoder, characterized by, The light detection device comprises a first pattern, which is obtained by a rectangular-fan conversion of a second pattern, and the second pattern comprises: a plurality of first-level detection arrays, wherein each first-level detection array comprises at least one light detection unit, each light detection unit outputs an electrical signal, and the electrical signals output by the at least one light detection unit in a first-level detection array are directly or combined as a first-level electrical signal output by the first-level detection array, wherein: the plurality of first-level detection arrays are divided into a plurality of second-level detection arrays, each of the plurality of second-level detection arrays comprises t2 first-level detection arrays, and the coordinates of corresponding points of adjacent two first-level detection arrays in the t2 first-level detection arrays belonging to the same second-level detection array differ by x×P / N+(t1×P) / (t2×N), t1 is a natural number greater than or equal to 1, t2 is a natural number greater than or equal to 2, t1 and t2 are co-prime, P is a value determined in advance based on the total number of grating slits used by the optical encoder, N is an odd number greater than or equal to 3, x is a natural number, and x is selected to avoid the first-level detection arrays from overlapping with each other in space; and each of the plurality of second-level detection arrays outputs at least one second-level electrical signal, each second-level electrical signal is generated by adding a group of t2 corresponding first-level electrical signals, the group of t2 corresponding first-level electrical signals are t2 corresponding first-level electrical signals output by the t2 first-level detection arrays belonging to the same second-level detection array, thereby suppressing Nth harmonic components and harmonic components with a frequency that is an integer multiple of N in the second-level electrical signal.

2. The light detecting device according to claim 1, wherein Wherein: the plurality of second-level detection arrays are divided into a plurality of third-level detection arrays, each of the plurality of third-level detection arrays comprises s2 second-level detection arrays, and the coordinates of corresponding points of adjacent two second-level detection arrays in the s2 second-level detection arrays belonging to the same third-level detection array differ by y×P / M+(s1×P) / (s2×M), s1 is a natural number greater than or equal to 1, s2 is a natural number greater than or equal to 2, s1 and s2 are co-prime, M is an odd number greater than or equal to 3, and M is not equal to N, y is a natural number, and y is selected to avoid the second-level detection arrays from overlapping with each other in space; and each of the plurality of third-level detection arrays outputs at least one third-level electrical signal, each third-level electrical signal is generated by adding a group of s2 corresponding second-level electrical signals, the group of s2 corresponding second-level electrical signals are s2 corresponding second-level electrical signals output by the s2 second-level detection arrays belonging to the same third-level detection array, thereby suppressing Mth harmonic components and harmonic components with a frequency that is an integer multiple of M in the third-level electrical signal.

3. The light detecting device according to claim 2, wherein Wherein: The third-level detection arrays are divided into fourth-level detection arrays, each of the fourth-level detection arrays comprises r2 third-level detection arrays, the coordinates of the corresponding points of two adjacent third-level detection arrays in the r2 third-level detection arrays belonging to the same fourth-level detection array are different by z×P / Q+(r1×P) / (r2×Q), r1 is a natural number greater than or equal to 1, r2 is a natural number greater than or equal to 2, r1 and r2 are relatively prime, Q is an odd number greater than or equal to 3, Q is not equal to M or N, and z is a natural number, and z is selected to avoid the third-level detection arrays from overlapping in space; and each of the fourth-level detection arrays outputs at least one fourth-level electrical signal, each fourth-level electrical signal is generated by adding a group of r2 corresponding third-level electrical signals, the group of r2 corresponding third-level electrical signals are r2 corresponding third-level electrical signals output by the r2 third-level detection arrays belonging to the same fourth-level detection array, so that the Qth harmonic component and the harmonic component with a frequency that is an integer multiple of Q in the fourth-level electrical signal are suppressed.

4. The light detecting device according to any one of claims 1 to 3, wherein The transverse direction is defined as the relative movement direction of the grating of the optical encoder and the light detection device, the widths of all the light detection units in the transverse direction are equal, and the width of each light detection unit in the transverse direction is equal to an integer multiple of the period of the Wth harmonic component, that is, an integer multiple of P / W, W is an odd number greater than or equal to 3, and W is not equal to the frequency of the harmonic component that has been suppressed.

5. The light detecting device according to any one of claims 1 to 3, wherein The transverse direction is defined as the relative movement direction of the grating of the optical encoder and the light detection device, the at least one light detection unit is an irregular quadrilateral, one group of opposite sides of the irregular quadrilateral are arranged opposite to each other in the transverse direction and are parallel to each other, the irregular quadrilateral is inclined in the transverse direction by an amount that is an integer multiple of the period of the Uth harmonic component, that is, an integer multiple of P / U, U is an odd number greater than or equal to 3, and U is not equal to the frequency of the harmonic component that has been suppressed, the other two opposite sides are arranged opposite to each other in the vertical direction, the vertical direction is perpendicular to the transverse direction in the plane on which the light detection unit is located, and the two opposite sides arranged opposite to each other in the vertical direction have the same shape.

6. The light detecting apparatus according to any one of claims 1 to 3, wherein The transverse direction is defined as the relative movement direction of the grating of the optical encoder and the light detection device, the at least one light detection unit is a parallelogram, and one group of opposite sides of the parallelogram extend in the transverse direction.

7. A light detection device for an optical encoder, characterized in that The light detection device comprises a second pattern, and the second pattern comprises: a plurality of first-level detection arrays, wherein each first-level detection array comprises at least one light detection unit, each light detection unit outputs an electrical signal, and the electrical signals output by the light detection units in one first-level detection array are directly or combined to be first-level electrical signals output by the first-level detection array; and a plurality of first-level detection arrays, wherein each first-level detection array comprises at least one light detection unit, each light detection unit outputs an electrical signal, and the electrical signals output by the light detection units in one first-level detection array are directly or combined to be first-level electrical signals output by the first-level detection array; and The multiple first-level detection arrays are divided into multiple second-level detection arrays, each of the multiple second-level detection arrays comprises t2 first-level detection arrays, in the t2 first-level detection arrays belonging to the same second-level detection array, the coordinate difference of corresponding points of adjacent two first-level detection arrays is x×P / N+(t1×P) / (t2×N), t1 is a natural number greater than or equal to 1, t2 is a natural number greater than or equal to 2, t1 and t2 are relatively prime, P is the slit period of a grating used in the optical encoder, N is an odd number greater than or equal to 3, x is a natural number, and x is selected to avoid the first-level detection arrays from overlapping with each other in space; and Each of the multiple second-level detection arrays outputs at least one second-level electrical signal, each second-level electrical signal is generated by adding a group of t2 corresponding first-level electrical signals, the group of t2 corresponding first-level electrical signals are t2 corresponding first-level electrical signals output by the t2 first-level detection arrays belonging to the same second-level detection array, so as to suppress the Nth harmonic component and the harmonic component with a frequency being an integer multiple of N in the second-level electrical signal.

8. The light detecting device according to claim 7, wherein Wherein: The multiple second-level detection arrays are divided into multiple third-level detection arrays, each of the multiple third-level detection arrays comprises s2 second-level detection arrays, in the s2 second-level detection arrays belonging to the same third-level detection array, the coordinate difference of corresponding points of adjacent two second-level detection arrays is y×P / M+(s1×P) / (s2×M), s1 is a natural number greater than or equal to 1, s2 is a natural number greater than or equal to 2, s1 and s2 are relatively prime, M is an odd number greater than or equal to 3, and M is not equal to N, y is a natural number, and y is selected to avoid the second-level detection arrays from overlapping with each other in space; and each of the multiple third-level detection arrays outputs at least one third-level electrical signal, each third-level electrical signal is generated by adding a group of s2 corresponding second-level electrical signals, the group of s2 corresponding second-level electrical signals are s2 corresponding second-level electrical signals output by the s2 second-level detection arrays belonging to the same third-level detection array, so as to suppress the Mth harmonic component and the harmonic component with a frequency being an integer multiple of M in the third-level electrical signal.

9. The light detecting device according to claim 8, wherein Wherein: The third-level detection arrays are divided into fourth-level detection arrays, each of which contains r2 third-level detection arrays, and the coordinates of the corresponding points of two adjacent third-level detection arrays in the same fourth-level detection array differ by z×P / Q+(r1×P) / (r2×Q), r1 is a natural number greater than or equal to 1, r2 is a natural number greater than or equal to 2, r1 and r2 are co-prime, Q is an odd number greater than or equal to 3, Q is not equal to M or N, z is a natural number, and z is selected to avoid the third-level detection arrays from overlapping in space; and each of the fourth-level detection arrays outputs at least one fourth-level electrical signal, each fourth-level electrical signal is generated by adding a corresponding set of r2 third-level electrical signals, the corresponding set of r2 third-level electrical signals are r2 corresponding third-level electrical signals output by the r2 third-level detection arrays in the same fourth-level detection array, thereby suppressing the Qth harmonic component and the harmonic components with frequencies that are integer multiples of Q in the fourth-level electrical signal.

10. An optical encoder characterized by, Comprise: a grating having a plurality of slits, the period of the slits being P; a light source forming a periodically varying fringe pattern through the grating; a light detection device as claimed in any one of claims 1-9 for detecting the fringe pattern and converting into an electrical signal.

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