CN113932908A - Measuring system and measuring method for vibration parameters of MEMS scanning galvanometer - Google Patents
Measuring system and measuring method for vibration parameters of MEMS scanning galvanometer Download PDFInfo
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Abstract
The application discloses measurement system and measurement method of MEMS scanning galvanometer vibration parameter, this measurement system includes: the collimating light source is used for emitting collimated light to the back of the MEMS scanning galvanometer in the same direction, and the MEMS scanning galvanometer with a preset turning angle is parallel to the emitting direction of the collimated light and has a constant distance with the collimating light source; the MEMS scanning galvanometer comprises a plurality of different reflecting areas formed by a grating structure, wherein the plurality of reflecting areas are distributed on the back surface of the MEMS scanning galvanometer, and the different reflecting areas respectively receive the irradiation of collimated light at a turnover angle of the MEMS scanning galvanometer and emit echoes to a fixed position; a photodetector for receiving an echo at a fixed position and converting the echo into an electrical signal; and the signal processor is connected with the photoelectric detector and used for determining the vibration parameters based on the electric signals. The structure of the vibration parameter measuring system is simplified.
Description
Technical Field
The invention relates to the technical field of optical measurement, in particular to a system and a method for measuring vibration parameters of an MEMS scanning galvanometer.
Background
The MEMS (Micro-Electro-Mechanical System) scanning galvanometer is a vector scanning device, has the characteristics of small volume, easy integration, large scanning angle, high speed, low power consumption and the like, and has wide application requirements in the fields of laser marking, laser radar, laser projection, structured light, face recognition, laser imaging, three-dimensional measurement and the like.
The MEMS scanning galvanometer is easily influenced by external environments (such as thermal convection, temperature change, humidity change, air disturbance, environmental vibration and the like), and has simple harmonic vibration in different states in different environments, so that vibration parameters do not completely depend on the manufacture of manufacturers, and the vibration parameters can be accurately determined by measurement. The current measurement methods of vibration parameters mainly include: the method comprises the steps of capturing reflected light rays of a scanning galvanometer in the vibration process by utilizing a plurality of photoelectric detectors, generating electric signals for marking the positions of the photoelectric detectors, and finally determining the vibration amplitude of the scanning galvanometer to be detected by combining the electric signals with the position relations of the photoelectric detectors.
The measurement method cannot be separated from the arrangement of a plurality of photoelectric detectors, wherein if the vibration parameters of the one-dimensional scanning galvanometer are measured, at least two photoelectric detectors arranged at different positions are required; if the vibration parameters of the two-dimensional scanning galvanometer are measured, more photoelectric detectors are required to be arranged at different positions. The arrangement of the multiple photodetectors entails a complication in the structure of the measurement system.
Disclosure of Invention
In view of this, the present invention provides a measurement system and a measurement method for measuring a vibration parameter with a single photodetector for a MEMS scanning galvanometer.
According to a first aspect of the present invention, there is provided a system for measuring vibration parameters of a MEMS scanning galvanometer, comprising:
the collimating light source is used for emitting collimated light to the back surface of the MEMS scanning galvanometer in the same direction in the vibrating process of the MEMS scanning galvanometer, wherein the MEMS scanning galvanometer with a preset turning angle is parallel to the emitting direction of the collimated light and has a constant distance with the collimating light source;
the MEMS scanning galvanometer comprises a plurality of different reflecting areas formed by a grating structure, wherein the plurality of reflecting areas are distributed on the back surface of the MEMS scanning galvanometer, and the different reflecting areas respectively receive the irradiation of collimated light at a turnover angle of the MEMS scanning galvanometer and emit echoes to a fixed position;
a photodetector for receiving the echo at the fixed position and converting the echo into an electrical signal;
and the signal processor is connected with the photoelectric detector and used for analyzing the time of receiving the echo by the photoelectric detector and the turning angle of the MEMS scanning galvanometer marked by the echo based on the electric signal and determining the vibration parameter according to the turning angle and the receiving time.
Optionally, the plurality of light reflecting regions are a mirror region and at least one grating region, and different grating regions are distinguished by different grating structures.
Optionally, in a case that the MEMS scanning galvanometer has one rotation axis, the plurality of light reflecting areas are a mirror area and two grating areas distributed on two sides of the mirror area;
under the condition that the MEMS scanning galvanometer has two mutually perpendicular rotating shafts, the plurality of light reflecting areas are nine light reflecting areas which are arranged in an array form, and only one light reflecting area in the center of the nine light reflecting areas is a mirror area.
Optionally, the grating structure adopted by each grating region is a blazed grating structure.
Optionally, the grating parameters of the blazed grating structure adopted by each grating region are determined according to the turning angle corresponding to the grating region, the turning angle corresponding to the mirror region, and the distance between each of the collimated light source and the photodetector and the target plane;
and the target plane is the plane where the MEMS scanning galvanometer with the preset turning angle is located.
Optionally, the corresponding flip angle of the mirror area is in a range of 0 ° to 90 °.
Optionally, the grating structure is formed by processing the back surface of the MEMS scanning galvanometer;
or the grating structure is adhered to the back of the MEMS scanning galvanometer.
Optionally, the photodetector is a single pixel photodetector.
Optionally, the photodetector receives 1 st order diffracted light of each grating structure, and the photodetector includes:
a signal conversion unit for converting an echo incident to the photodetector into an electric signal;
the comparison unit is connected with the signal conversion unit and used for comparing the electric signal with a reference value and triggering the signal processor to analyze the turnover angle and the receiving time under the condition that the electric signal is larger than the reference value;
and the reference value is an electric signal value corresponding to a photosensitive threshold value, and the photosensitive threshold value is determined according to the 1-order diffraction light intensity of each grating structure.
According to a second aspect of the present invention, there is provided a method for measuring a vibration parameter of a MEMS scanning galvanometer, the method being performed by any one of the measurement systems of the first aspect, the method comprising:
the collimating light source emits collimated light to different reflecting areas in the same direction in the vibration process of the MEMS scanning galvanometer so that the different reflecting areas emit echoes to fixed positions at a turning angle of the MEMS scanning galvanometer respectively;
the photoelectric detector receives an echo at the fixed position and converts the echo into an electric signal;
the signal processor analyzes the time of receiving the echo by the photoelectric detector and the turning angle of the MEMS scanning galvanometer marked by the echo based on the electric signal, and determines the vibration parameter according to the turning angle and the receiving time;
the MEMS scanning galvanometer with the preset turning angle is parallel to the incidence direction of collimated light and has a constant distance with the collimated light source.
The embodiment of the invention has the following beneficial effects:
the measuring system for the vibration parameters of the MEMS scanning galvanometer provided by the embodiment of the invention not only comprises a collimation light source, a photoelectric detector and a signal processor, but also comprises a plurality of reflecting areas, wherein the plurality of reflecting areas are distributed on the back surface of the MEMS scanning galvanometer, the plurality of reflecting areas are scanned by collimation light in the vibration process of the MEMS scanning galvanometer, and the turnover angles of the MEMS scanning galvanometer are different when the different reflecting areas are irradiated by the incident collimation light; the reflection areas are distinguished by means of the grating structures and the angles of emergent light rays are adjusted by utilizing the grating structures, so that incident collimated light rays of different reflection areas can emit echo waves to fixed positions respectively in the vibration process of the MEMS scanning galvanometer, the echo waves emitted by the MEMS scanning galvanometer at different turnover angles can be detected by placing one photoelectric detector on the fixed positions, and the purpose of measuring vibration parameters by using the single photoelectric detector is achieved. The measuring system achieves the technical effect of simplifying the measuring system by reducing the number of the photoelectric detectors.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.
FIG. 1 illustrates a top view of a MEMS scanning galvanometer of the related art;
FIG. 2 illustrates a front view of the MEMS scanning galvanometer of FIG. 1;
FIG. 3 is a schematic plan view of a measurement system according to an embodiment of the present invention;
FIG. 4 is a perspective view showing a partial structure of the measuring system of FIG. 3;
FIG. 5 shows a plurality of reflective regions disposed on the backside of a one-dimensional MEMS scanning galvanometer in a first embodiment of the present invention;
FIG. 6 illustrates a plurality of reflective regions disposed on the backside of a two-dimensional MEMS scanning galvanometer in accordance with one embodiment of the present invention;
FIG. 7 is a diagram illustrating a usage scenario of a measurement system according to an embodiment of the present invention;
FIG. 8 shows a schematic view of the plurality of retroreflective regions of FIG. 5;
FIG. 9 is a diagram illustrating another usage scenario of a measurement system in accordance with an embodiment of the present invention;
fig. 10 shows an optical path diagram of collimated light incident on a blazed grating structure X1 and diffracted by the blazed grating structure X1;
FIG. 11 is a diagram illustrating another scenario for use of the measurement system in accordance with one embodiment of the present invention;
fig. 12 shows an optical path diagram of collimated light incident to the blazed grating structure X2 and diffracted by the blazed grating structure X2;
FIG. 13 is a graph showing the relationship between the flip angle and the receiving time in the first embodiment of the present invention;
FIG. 14 is a schematic diagram showing the change of the electrical signal with time during the vibration of the MEMS scanning galvanometer in the first embodiment of the invention;
FIG. 15 illustrates a scanning trajectory for a two-dimensional MEMS scanning galvanometer in a first embodiment of the present invention;
FIG. 16 illustrates another scan trajectory for a two-dimensional MEMS scanning galvanometer in accordance with an embodiment of the present invention;
FIG. 17 illustrates a scan trajectory for a two-dimensional MEMS scanning galvanometer in a first embodiment of the present invention;
fig. 18 is a schematic flow chart of a measurement method according to a second embodiment of the present invention.
Detailed Description
The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. Moreover, certain well-known elements may not be shown in the figures.
Fig. 1 is a plan view of a MEMS scanning galvanometer in the related art, and fig. 2 is a front view of the MEMS scanning galvanometer shown in fig. 1. Referring to fig. 1 and 2, the MEMS scanning galvanometer 110 includes a MEMS substrate 111, a MEMS driver 112, and a MEMS mirror 113. The MEMS mirror 113 is connected to the MEMS substrate 111 through the MEMS actuator 112, and when a different voltage is applied to the MEMS actuator 112, the MEMS actuator 112 deforms and turns the MEMS mirror 113, and the vibration of the MEMS mirror 113 starts.
For the one-dimensional MEMS scanning galvanometer 110, the MEMS driver 112 makes the MEMS mirror 113 turn around the X-direction rotation axis 114 only, and the MEMS mirror 113 performs one-dimensional vibration around the X-direction rotation axis 114; for the two-dimensional MEMS scanning galvanometer 110, the MEMS actuator 112 causes the MEMS mirror surface 113 to flip around the X-direction rotation axis 114 and the Y-direction rotation axis 115, and the MEMS mirror surface 113 is vibrated two-dimensionally around the X-direction rotation axis 114 and the Y-direction rotation axis accordingly.
The MEMS mirror 113 itself includes a front surface a and a back surface B, and during the scanning process of the MEMS scanning galvanometer 110, incident light beams from the same direction irradiate the front surface a, and the incident light beams may have different incident angles along with the vibration of the MEMS mirror 113. The front surface A reflects incident light through the metal-plated film layer, so that the incident light from the same direction can correspond to reflected light from different directions along with the vibration of the MEMS mirror surface 113, thereby realizing the scanning function.
The vibration of the MEMS scanning galvanometer 110 is described by a vibration equation expressed by formula (1), where α denotes a flip angle at time t at which the MEMS mirror 113 vibrates around the rotation axis, a denotes an angular amplitude of the vibration, ω denotes a frequency, and ψ denotes an initial phase, where a, ω, and ψ are vibration parameters, and accurate determination of these vibration parameters is of great significance for various application systems using the MEMS scanning galvanometer 110.
α＝A·sin(ω·t+ψ) (1)
Embodiments of the present invention are directed to measuring the vibration parameter by a measurement system having a relatively simple structure. For convenience of description, the MEMS substrate 111 and the MEMS driver 112 are not considered in the following, and the MEMS mirror 113 may also be replaced by the MEMS scanning galvanometer 110.
Fig. 3 is a schematic plan view of a measurement system according to an embodiment of the present invention, and fig. 4 is a perspective view of a part of the measurement system shown in fig. 3. Referring to fig. 3 and 4, the measurement system 200 includes not only a collimated light source 210, a photodetector 220 and a signal processor 230, but also a plurality of different reflective regions 240 formed by a grating structure, wherein the collimated light source 210 may be a semiconductor laser, a fiber laser, a solid laser or an LED including a configuration of a collimating system; the plurality of light-reflecting regions 240 and the collimated light source 210 and the photo detector 220 have light rays (shown by dotted lines) propagating therebetween, and the signal processor 230 and the photo detector 220 are electrically connected (shown by a connecting line). Further, the signal processor 230 may also be electrically connected to the collimated light source 210 as shown in FIG. 3, so that the signal processor 230 can control the collimated light source 210 accordingly.
The plurality of light reflecting regions 240 are formed by improving the back surface B of the MEMS mirror 113, and the back surface B may be processed or bonded with a grating structure to form the plurality of light reflecting regions 240, wherein the processing mode facilitates the position fixing of the plurality of light reflecting regions 240, and the bonding mode facilitates the flexible configuration of the plurality of light reflecting regions 240 for the same MEMS scanning galvanometer 110.
Each retroreflective region 24i (i ═ 1, 2, …, n, n is the total number of retroreflective regions 240) has the function of reflecting light, which can be achieved by a metallized film layer, similar to the front surface a. The plurality of light reflecting areas 240 are distributed on the back surface B of the MEMS scanning galvanometer perpendicular to the rotation axis of the MEMS scanning galvanometer 110, wherein for the one-dimensional MEMS scanning galvanometer 110, the plurality of light reflecting areas 240 are dispersed in a direction perpendicular to the X-direction rotation axis 114; for the two-dimensional MEMS scanning galvanometer 110, the plurality of light reflecting regions 240 are dispersed along two mutually perpendicular directions considered to be perpendicular to one of the X-direction axis of rotation 114 and the Y-direction axis of rotation 115, respectively.
The plurality of light reflecting areas 240 may be a mirror area and at least one grating area, different grating areas are distinguished by different grating structures, and the mirror area is configured to facilitate the calculation process of the vibration parameter to be simplified. The more the total number of the at least one grating region is, the higher the measurement accuracy of the vibration parameter is, regardless of the one-dimensional MEMS scanning galvanometer 110 or the two-dimensional MEMS scanning galvanometer 110.
Fig. 5 exemplarily shows a plurality of light reflecting regions 240 corresponding to the one-dimensional MEMS scanning galvanometer 110, where the plurality of light reflecting regions 240 are mirror regions 242, and grating regions 241 and 243 distributed on both sides of the mirror regions. It is emphasized that for the one-dimensional MEMS scanning galvanometer 110, the total number of the plurality of light reflecting regions 240 is not limited to two, nor is the plurality of light reflecting regions 240 limited to the position shown in fig. 5. In the actual measurement process of the vibration parameters, the measurement accuracy and the calculation difficulty are comprehensively considered, the total number of the plurality of light reflecting areas 240 can be any one within the range of 2-5, and the positions of the plurality of light reflecting areas 240 can be dispersed as long as the positions are perpendicular to the rotating shaft 114 in the X direction.
Fig. 6 exemplarily shows one of the plurality of light reflecting regions 240 corresponding to the two-dimensional MEMS scanning galvanometer 110, where the plurality of light reflecting regions 240 are arranged in an array, and the plurality of light reflecting regions 240 are a mirror region 249 located in the center of the array and a grating region 241, a grating region 242, a grating region 243, a grating region 244, a grating region 245, a grating region 246, a grating region 247, and a grating region 248 arranged around the mirror region 249. It should also be emphasized that for the two-dimensional MEMS scanning galvanometer 110, the total number of the plurality of light reflecting regions 240 is not limited to nine, nor is the plurality of light reflecting regions 240 limited to the position shown in fig. 6. In the actual measurement process of the vibration parameters, the measurement accuracy and the calculation difficulty are comprehensively considered, the total number of the plurality of light reflecting regions 240 may be any one within the range of 5 to 25, and the positions of the plurality of light reflecting regions 240 may be dispersed so as to be perpendicular to the X-direction rotation axis 114 and the Y-direction rotation axis.
It should be understood that the grating structure belongs to a reflective grating structure, and particularly, a blazed grating structure can be selected, and the blazed grating structure is formed by engraving a series of saw-toothed groove surfaces on a polished metal plate or a glass plate plated with a metal film; of course, other materials can be used to form a common grating, such as a common reflective grating formed by parallel silicon trenches or parallel oxide strips. The blazed grating structure can stagger the single-groove diffraction 0 order and the inter-groove interference 0 order, so that the light energy is transferred and concentrated on a required first-order spectrum, and the photoelectric detector 220 can fully receive collimated light emitted by the collimated light source 210, thereby being beneficial to the photoelectric detector 220 to separate the collimated light emitted by the collimated light source 210 from interference light in the surrounding environment.
The grating parameters of the blazed grating structure include the grating center position, the blazed angle, and the groove length, and after the distribution positions of the plurality of reflective areas 240 are determined, the grating parameters are determined, and then the plurality of reflective areas 240 included in the measurement system 200 are determined in detail. In particular, a blazed grating junction on a certain grating regionThe grating parameters of the structure can be determined according to the turning angle corresponding to the grating region (i.e., the turning angle of the MEMS scanning galvanometer 110 when the grating region receives the illumination of the collimated light and emits the echo to the fixed position), the turning angle corresponding to the mirror region (i.e., the turning angle of the MEMS scanning galvanometer 110 when the mirror region receives the illumination of the collimated light and emits the echo to the fixed position), and the distances from the collimated light source 210 and the photodetector 220 to the target plane; wherein the target plane is a preset turning angle alpha0The plane of the MEMS scanning galvanometer 110 is preset with a turning angle alpha0The MEMS scanning galvanometer 110 is parallel to the collimated light incidence direction and has a constant spacing from the collimated light source 210.
The following description will mainly use the one-dimensional MEMS scanning galvanometer 110 as an example.
Fig. 7 is a schematic diagram illustrating a measurement system 100 for measuring a vibration parameter of a one-dimensional MEMS scanning galvanometer 110 according to an embodiment of the invention, wherein a predetermined flip angle α is used for simplifying the calculation 00; the thick dotted line represents the position of the MEMS scanning galvanometer 110 corresponding to the flipping angle α 1, the thick solid line represents the position of the MEMS scanning galvanometer 110 corresponding to the flipping angle α 2, and the thick dotted line represents the position of the MEMS scanning galvanometer 110 corresponding to the flipping angle α 3; the target plane is designated as plane P in fig. 7.
Referring to fig. 7, the collimated light source 210 enters the collimated light to the back surface B of the MEMS scanning galvanometer 110 in the same direction, and the irradiation position of the collimated light on the back surface B changes with the vibration of the MEMS scanning galvanometer 110, specifically, in the process that the MEMS scanning galvanometer 110 rotates clockwise from the flip angle α 1 to the flip angle α 3, the irradiation position moves from a position closer to the X-direction rotation axis 114 to an edge position of the back surface B, as can be seen: the irradiation position moves perpendicular to the X-direction rotation axis 114 with the vibration of the MEMS scanning galvanometer 110.
The same light reflecting area 24i is a mirror area or a grating area with the same grating structure, the same light reflecting area 24i only has one reflection angle or one diffraction angle for collimated light in the same incident direction, and the same light reflecting area 24i has different reflection angles or different diffraction angles for collimated light in different incident directions. As described above, the vibration of the MEMS scanning galvanometer 110 causes the irradiation position to move perpendicular to the X-direction rotation axis 114 with the change of the flip angle, each of the reflective regions 24i can correspond to one flip angle α i by reasonably setting the distribution position of the plurality of reflective regions 24i and the grating parameters of the grating structure in the grating region, and when the MEMS scanning galvanometer 110 vibrates to the flip angle α i, the reflective regions 24i are irradiated by collimated light and cause the reflected echo to be incident on the photodetector 220, so that a single photodetector can detect the echoes at a plurality of different flip angles.
As an example, the back surface B of the MEMS mirror 113 shown in fig. 7 is provided with a plurality of light reflecting regions 240 shown in fig. 5, and the plurality of light reflecting regions 240 correspond to 3 flip angles α i as shown in fig. 5, wherein the light reflecting regions 241 correspond to the flip angle α 1, the light reflecting regions 242 correspond to the flip angle α 2, and the light reflecting regions 243 correspond to the flip angle α 3. Fig. 8 shows a structure of 3 light-reflecting regions 240, in which a blazed grating structure X1 is distributed on the grating region 241, and a blazed grating structure X2 is distributed on the grating region 243.
(first) the grating parameters of the blazed grating structure X1 are explained with reference to FIGS. 9 and 10
Fig. 9 shows the MEMS scanning galvanometer 110 rotated counterclockwise from the position of the flip angle α 2 to the position of the flip angle α 1, and fig. 10 shows the optical path diagram of collimated light incident on the blazed grating structure X1 and diffracted by the blazed grating structure X1. For simplicity of calculation, the flip angle α 2 shown in fig. 9 is 45 °, so that collimated light enters the mirror region 242 in the horizontal direction and exits to the photodetector 220 in the vertical direction. In practice, if the arrangement of the measurement system 200 is limited by space, the flip angle α 2 corresponding to the mirror surface region can be set within a range of 30 ° to 60 °, i.e. the interference between the incident light and the reflected light or the diffracted light of the MEMS scanning galvanometer 110 can be effectively avoided.
Assuming that the distance between the collimated light source 210 and the target plane P in the vertical direction is h, the distance L1 (see fig. 5) between the center position of the grating region 241 and the X-direction rotation axis 114 is expressed by equation (2):
L2＝h/sin(α2) (2)
the distance L2 (see fig. 5) between the center position of the mirror surface region 242 and the X-direction rotation axis 114 is expressed by the formula (3):
L1＝h/sin(α1) (3)
let m be the distance between the photodetector 220 and the target plane P in the vertical direction, and let m be the diffraction angle of the light with the maximum diffraction principal of the grating region 241
The incident angle of the diffracted light on the photodetector 220 is θ 1, then
θ 1 has what angular relationship is represented by equation (4):
wherein θ 1 satisfies the relationship shown in formula (5):
based on the formula (4) and the formula (5),
has the expression shown in formula (6):
when the groove length of the blazed grating structure X1 is d1 and the incident angle of the incident light with respect to the normal of the blazed grating structure X1 is i1, the expression shown in formula (7) is obtained according to the blazed grating formula:
the relationship between i1 and α 1 is shown in formula (8):
in this embodiment, if the 1 st order diffracted light is the diffraction principal maximum light, that is, if j is 1, d1 is obtained based on equation (7) and equation (8) and has the expression shown in equation (9):
when the blaze angle of the blazed grating structure X1 is γ 1, γ 1 satisfies the relationship shown in formula (10) when the incident light and the diffracted light are located on the opposite side from the grating:
by transforming equation (10), γ 1 is obtained having the expression shown in equation (11):
in summary, the expressions (2), (3), and the expressions (9) and (11) in combination with the expression (6) give expressions of the position of the mirror region 242, the position of the grating region 241, and the groove length and the blaze angle of the blazed grating structure X1 in the grating region 241. The equations (2), (3) and the equations (9), (11) substituted into the equation (6) are four equations in total, in which the grating parameters L1, L2, d1 and γ 1 of the plurality of light reflection areas 240 are involved, and the configuration parameters h, m, α 1 and α 2 in the vibration parameter measurement process are involved, as can be seen: the grating parameters L1, L2, d1 and gamma 1 can be determined according to the configuration parameters h, m, alpha 1 and alpha 2.
(II) the grating parameters of the blazed grating structure X2 will be described with reference to FIGS. 11 and 12
Fig. 11 is a diagram showing an optical path of the MEMS scanning galvanometer 110 rotated clockwise from the position of the flip angle α 2 to the position of the flip angle α 3, and fig. 12 shows a diagram showing a case where collimated light is incident on the blazed grating structure X2 and is diffracted by the blazed grating structure X2. For simplicity of calculation, the flip angle α 2 shown in fig. 11 is 45 °, so that collimated light enters the mirror region 242 in the horizontal direction and exits to the photodetector 220 in the vertical direction.
Assuming that the distance between the collimated light source 210 and the target plane P in the vertical direction is h, the distance L3 between the center position of the grating area 243 and the X-direction rotation axis 114 is expressed by the following formula (12):
L3＝h/sin(α3) (12)
let m be the distance between the photodetector 220 and the target plane P in the vertical direction, and the diffraction angle of the light ray with the maximum diffraction principal of the grating area 243 be
The incident angle of the diffracted light on the photodetector 220 is θ 2, then
θ 2 has what angular relationship is represented by equation (13):
where θ 2 satisfies the relationship shown in formula (14):
based on the formula (13) and the formula (14),
has the expression shown in formula (15):
when the groove length of the blazed grating structure X2 is d2 and the incident angle of the incident light with respect to the normal of the blazed grating structure X2 is i2, the expression shown in formula (16) is obtained according to the blazed grating formula:
i2 and α 3 have a relationship shown by the formula (17):
in this embodiment, if the 1 st order diffracted light is the diffraction principal maximum light, that is, if j is 1, d2 is obtained based on equation (16) and equation (17) and has the expression shown in equation (18):
when the blaze angle of the blazed grating structure X2 is γ 2, γ 2 satisfies the relationship shown in formula (19) when the incident light and the diffracted light are located on the opposite side from the grating:
transforming equation (19), then γ 2 is obtained with the expression shown in equation (20):
in summary, the equations (2), (12), and the equations (18) and (20) in combination with the equation (15) give expressions of the position of the mirror region 242, the position of the grating region 243, and the groove length and the blaze angle of the blazed grating structure X2 in the grating region 243. The equations (2), (12) and the equations (18), (19) substituted into the equation (15) are four equations in total, in which the grating parameters L1, L3, d2 and γ 2 of the plurality of light reflection areas 240 are involved, and the configuration parameters h, m, α 2 and α 3 during the measurement of the vibration parameter are involved, as can be seen: the gratings L1, L3, d2 and γ 2 are determined according to the configurations h, m, α 2 and α 3.
The foregoing describes how the plurality of retro-reflective regions 240 are determined, including the determination of the distribution of the plurality of retro-reflective regions 240 and the determination of the grating parameters to which the plurality of retro-reflective regions 240 relate. The plurality of retroreflective regions 240 required by the measurement system 200 can be determined by the above description.
In the above description, h, m, α i are used as preset values to determine the settings of the plurality of light reflecting regions 240, and the signal processor 230 can directly call each α i to match the corresponding α i to the echo received at each time. It should be understood that, for the plurality of light reflecting regions 240 with fixed structures, even if the signal processor 230 cannot know the preset values of the respective flip angles α i, the signal processor 230 may first determine the incident angle θ i of the diffracted light on the photodetector 220 according to the direction of the incident light, the direction of the reflected light or the diffracted light, and the irradiation position of the collimated light on the back surface B of the MEMS scanning galvanometer 110, and then calculate the flip angles α i by using the above formula (5) or formula (14) in combination with the configured m, h, and α 2 in the measurement process.
The signal processor 230 receives the electrical signal converted by the photodetector 220, and analyzes the receiving time t of the echo and the flip angle α i marked by the echo based on the electrical signal, where the receiving time t and the flip angle α i have a one-to-one correspondence relationship; then, the signal processor 230 also determines each vibration parameter in formula (1) from the flip angle α i and the reception time t. Referring to equation (1), three sets of t and α i corresponding to the same vibration period can be determined such that a, ω, and ψ are determined. It should be understood that the initial phase ψ is related to the zero time referenced by the receiving time t, which is different from the initial phase ψ, wherein the zero time can be selected one when the MEMS scanning galvanometer 110 is vibrated stably and the collimated light source 210 is stably illuminated to the back of the MEMS scanning galvanometer 110, illustratively, the time when the MEMS scanning galvanometer 110 is vibrated to the flip angle α 2 so that the photodetector 220 receives the echo.
Referring to fig. 13, the MEMS scanning galvanometer 110 vibrates for a period T, and the plurality of light reflecting regions 240 shown in fig. 5 enable the photodetector 220 to receive echoes at time points T1, T2, T3, T4, T5 and T6, respectively, which indicates that the plurality of light reflecting regions 240 shown in fig. 5 can generate six sets of corresponding T and α i in a vibration period, and the six sets of corresponding T and α i are sufficient to enable the signal processor 230 to fit a good vibration curve (as shown by a thick solid line in fig. 13), so as to determine the vibration parameters a, ω and ψ. It should be noted here that, in theory, three sets of corresponding t and α i in the same vibration period may enable a, ω, and ψ to be determined, but the measurement is inevitably subject to errors, and fitting a vibration curve based on the sets of corresponding t and α i can enable the errors to be reduced.
In an alternative embodiment, the photodetector 220 receives the 1 st order diffracted light from each grating structure as described above, and the photodetector 220 includes: a signal conversion unit for converting an echo incident to the photodetector 220 into an electric signal, and a comparison unit; the comparing unit is connected to the signal converting unit, and is configured to compare the electrical signal with the reference value, and trigger the signal processor 230 to analyze the flip angle and the receiving time by the signal processor 230 when the electrical signal is greater than the reference value. The reference value is an electrical signal value corresponding to the light sensing threshold, and the light sensing threshold is determined according to the 1-order diffraction light intensity of each grating structure, specifically, the light sensing threshold is smaller than the 1-order diffraction light intensity of each grating structure and is larger than the 2-order diffraction light intensity of each grating structure.
Illustratively, the signal conversion unit includes a photoresistor converting the echo into a current signal and a transimpedance amplifier converting the current signal into a voltage signal; the comparison unit comprises a comparator which compares the voltage value Vc of the voltage signal with a reference value V0.
Due to the plurality of light reflecting areas 240 arranged in the above manner, the photodetector 220 can detect 1 st order diffracted light when the MEMS scanning galvanometer 110 is flipped over to the flipping angle α i, and the diffracted light larger than 1 st order is incident on the photodetector 220 when the MEMS scanning galvanometer 110 is flipped over to the vicinity of the flipping angle α i, so that the photodetector 220 generates a voltage signal as shown in fig. 14 according to the received echo, and the setting of the reference value V0 distinguishes the 1 st order diffracted light intensity and the other orders diffracted light intensity.
In the embodiment of the present invention, the photodetector 220 is provided with the comparison unit, so that the signal processor 230 performs the analysis of the flip angle and the receiving time only when the photodetector 220 receives the light intensity of the 1 st order diffraction of each grating structure, and the light intensity of the 1 st order diffraction of each grating structure is received by the photodetector 220 only when the MEMS scanning galvanometer 110 is flipped to the flip angle α i, that is, the echo receiving time for determining the vibration parameter is limited to a small range so as to be only one moment, thereby facilitating the accurate determination of the vibration parameter.
In another alternative embodiment, the photo detector 220 is a single-pixel photo detector, i.e. the range of receiving light by the photo detector 220 is spatially narrowed, especially in the case that the photo detector 220 is provided with the comparison unit as described above, the 1 st order diffracted light of each grating structure is not incident on the photo detector 220 when the MEMS scanning galvanometer 110 is flipped to the vicinity of the flip angle α i, i.e. the photo detector 220 receives the 1 st order diffracted light only when the MEMS scanning galvanometer 110 is flipped to the flip angle α i, further, the echo receiving time for determining the vibration parameter is limited to a small range so as to be only one moment, thereby facilitating the precise determination of the vibration parameter.
For a two-dimensional MEMS scanning galvanometer 110, the measurement principle of the vibration parameters may be referred to as the one-dimensional MEMS scanning galvanometer 110 as described above. The plurality of retroreflective regions 240 distributed in the array shown in fig. 6 is described here as a simple example.
Referring to fig. 6, grating regions 241, 242, 243, 244, 245, 246, 247, and 248 are surface-processed with periodic saw-tooth grooves to realize a blazed grating function.
When the turning angle of the two-dimensional MEMS scanning galvanometer 110 is (α 1, 0), the outgoing beam of the collimated light source 210 is irradiated onto the grating region 241;
when the turning angle of the two-dimensional MEMS scanning galvanometer 110 is (α 2, 0), the outgoing beam of the collimated light source 210 is irradiated onto the mirror surface region 249;
when the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 3, 0), the outgoing beam of the collimated light source 210 is irradiated onto the grating region 242;
when the turning angle of the two-dimensional MEMS scanning galvanometer 110 is (α 2, β 1), the outgoing beam of the collimated light source 210 is irradiated onto the grating region 243;
when the turning angle of the two-dimensional MEMS scanning galvanometer 110 is (α 2, β 2), the outgoing beam of the collimated light source 210 is irradiated onto the grating region 244;
when the turning angle of the two-dimensional MEMS scanning galvanometer 110 is (α 1, β 1), the outgoing beam of the collimated light source 210 is irradiated onto the grating region 245;
when the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 1, β 2), the outgoing beam of the collimated light source 210 is irradiated onto the grating region 246;
when the turning angle of the two-dimensional MEMS scanning galvanometer 110 is (α 3, β 1), the outgoing beam of the collimated light source 210 is irradiated onto the grating region 247;
when the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 3, β 2), the outgoing beam of the collimated light source 210 impinges on the grating region 248.
To simplify the calculation, the direction in which the collimated light source 210 emits the collimated light is parallel to the two-dimensional MEMS scanning galvanometer 110 with the flip angle of (0, 0), and the flip angles α 1, α 2, and α 3 and the flip angles β 1, β 2, and β 3 are determined with respect to the plane in which the two-dimensional MEMS scanning galvanometer 110 with the flip angle of (0, 0) is located.
For the two-dimensional mems scanning galvanometer 110, the measurement relates to a spatial three-dimensional structure, and thus is described in a vector manner, wherein the direction of the collimated light emitted by the collimated light source 210 is always unchanged and is recorded as
The spatial position of the photodetector 220 is unchanged, denoted as b; when the two-dimensional MEMS scanning galvanometer 110 is respectively flipped at different angles, the collimated light source 210 emits collimated light at the irradiation positions of the plurality of light reflecting regions 240, respectively m1, m2, m3, m4, m5, m6, m7, m8, m9, that is,
when the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 1, 0), the illumination position is m1, which together with the position b of the photodetector 220 determines the diffraction direction vector
When the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 2, 0), the irradiation position is m2, and the irradiation position and the spatial position b confirm the diffraction direction vector
When the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 3, 0), the irradiation position is m3, and the irradiation position and the spatial position b confirm the diffraction direction vector
When the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 2, β 1), the irradiation position is m4, and the irradiation position confirms the diffraction direction vector together with the spatial position b
When the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 2, β 2), the irradiation position is m5, and the irradiation position confirms the diffraction direction vector together with the spatial position b
When the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 1, β 1), the irradiation position is m6, and the irradiation position confirms the diffraction direction vector together with the spatial position b
When the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 1, β 2), the irradiation position is m7, and the irradiation position confirms the diffraction direction vector together with the spatial position b
When the two-dimensional MEMS scanning galvanometer 110 has a flip angle of (alpha 3, beta 1)The irradiation position is m8, and the diffraction direction vector is confirmed together with the spatial position b
When the flip angle of the two-dimensional MEMS scanning galvanometer 110 is (α 3, β 2), the irradiation position is m9, and the irradiation position confirms the diffraction direction vector together with the spatial position b
In the process of measuring the vibration parameters, the turning angle corresponding to the mirror surface region, and the distance between the collimated light source 210 and the photodetector 220 and the target plane P can be determined according to the construction process of the measurement system 200. Knowing the direction vector of the collimated light emitted from the collimated light source
And diffraction direction vector
Thereafter, the angle θ i at which the diffracted light is incident on the photodetector can be determined. With reference to the above equations (5) and (14), after the flip angle corresponding to the mirror region, the distance between the collimated light source 210 and the photodetector 220 and the target plane P, respectively, and the angle θ i at which the diffracted light is incident on the photodetector are determined, the flip angle (α i, β i) corresponding to the grating region 24i can be determined. From the correlation analysis of the one-dimensional MEMS scanning galvanometer 110, it can be known that: after the flip angle corresponding to the mirror surface region, the distance between the collimated light source 210 and the photodetector 220 and the target plane P, and the flip angle (α i, β i) corresponding to the grating region 24i are determined, the grating parameters of the grating structure in the grating region 24i can be determined, so that a plurality of reflective regions 240 required by the measurement system 200 are prepared, so that diffraction/reflection light rays can be irradiated on the photodetector 220 when the two-dimensional MEMS scanning galvanometer 110 is respectively flipped to 9 fixed angles, the photodetector 220 senses light signals, and the signal processor 230 acquires the reception time t of the echo therewith.
By the turning angle (α i, β i) of the two-dimensional MEMS scanning galvanometer 110 and the corresponding trigger time t, a relation curve of the turning angle (α i, β i) and the time t can be fitted, so that the vibration parameter of the two-dimensional MEMS scanning galvanometer 110 can be measured.
The relation curve between the turning angle and the time of the two-dimensional MEMS scanning galvanometer 110 is set independently according to the actual use environment. Different vibration modes of the two-dimensional MEMS scanning galvanometer 110 correspond to different scanning tracks of the plurality of reflective regions 240, and the different scanning tracks generate different relationship curves between the flip angle and the time, wherein the scanning tracks are multiple, and fig. 15 shows one scanning track, specifically: scanning the plurality of light reflecting regions 240 line by line and scanning the adjacent two lines end to end; fig. 16 shows another scanning trajectory, which specifically includes: scanning the plurality of light reflecting regions 240 in columns and scanning between two adjacent columns in a head-to-tail phase-grounded manner; fig. 17 shows another scanning trajectory, which specifically includes: the two-dimensional MEMS scanning galvanometer 110 simultaneously oscillates in simple harmonic fashion about an X-direction axis of rotation 114 and a Y-direction axis of rotation 115 to produce a scanning trajectory. In fig. 15, 16, and 17, the abscissa represents the flip angle of the two-dimensional MEMS scanning galvanometer 110 about the X-direction rotation axis 114, and the ordinate represents the flip angle of the two-dimensional MEMS scanning galvanometer 110 about the Y-direction rotation axis 115.
After the vibration parameters are determined, the vibration equation shown in formula (1) is determined. Based on the determined vibration equation, after a time point t is obtained (the time point t is an initial time taking a zero time corresponding to the initial phase ψ in formula (1) as a timing time), the flip angle of the MEMS scanning galvanometer 110 can be accurately determined, that is, the MEMS scanning galvanometer 110 is accurately positioned, so that the measurement system 200 provided by the embodiment of the present invention can also be used in a positioning system of the MEMS scanning galvanometer 110. For the MEMS scanning galvanometer 110 with vibration parameters susceptible to external environment, the measurement system 200 in combination with a vibrating timing device can accurately position the MEMS scanning galvanometer 110 used in various environments in real time.
Corresponding to the above-mentioned measuring system 200 for the vibration parameter of the MEMS scanning galvanometer, the second embodiment of the present invention further provides a measuring method for the vibration parameter of the MEMS scanning galvanometer, which is implemented by applying any one of the measuring systems described in the first embodiment, and the measuring system has a simpler structure. Fig. 18 is a flowchart showing a measurement method, and referring to fig. 18, the measurement method includes:
step S110, the collimated light source 210 emits collimated light to different light reflecting areas 24i in the same direction in the vibration process of the MEMS scanning galvanometer 110, so that the different light reflecting areas 24i emit echoes to fixed positions respectively at a turning angle alpha i of the MEMS scanning galvanometer 110, wherein the MEMS scanning galvanometer 110 with a preset turning angle alpha 0 is parallel to the incident direction of the collimated light and has a constant distance with the collimated light source 210;
step S120, the photodetector 220 receives the echo at the fixed position and converts the echo into an electrical signal;
in step S130, the signal processor 230 analyzes the time t of receiving the echo by the photodetector 220 and the flip angle α i of the MEMS scanning galvanometer 110 marked by the echo based on the electrical signal, and determines the vibration parameter according to the flip angle α i and the receiving time t.
It should be noted that, for the specific implementation of the measurement method provided in the embodiment of the present invention, reference may be made to the above description of the measurement system 200, and details are not described here.
In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.
Claims (10)
1. A measurement system for vibration parameters of a MEMS scanning galvanometer is characterized by comprising:
the collimating light source is used for emitting collimated light to the back surface of the MEMS scanning galvanometer in the same direction in the vibrating process of the MEMS scanning galvanometer, wherein the MEMS scanning galvanometer with a preset turning angle is parallel to the emitting direction of the collimated light and has a constant distance with the collimating light source;
the MEMS scanning galvanometer comprises a plurality of different reflecting areas formed by a grating structure, wherein the plurality of reflecting areas are distributed on the back surface of the MEMS scanning galvanometer, and the different reflecting areas respectively receive the irradiation of collimated light at a turnover angle of the MEMS scanning galvanometer and emit echoes to a fixed position;
a photodetector for receiving the echo at the fixed position and converting the echo into an electrical signal;
and the signal processor is connected with the photoelectric detector and used for analyzing the time of receiving the echo by the photoelectric detector and the turning angle of the MEMS scanning galvanometer marked by the echo based on the electric signal and determining the vibration parameter according to the turning angle and the receiving time.
2. The measurement system of claim 1, wherein the plurality of light-reflecting regions are a mirror region and at least one grating region, and wherein different grating regions are distinguished by different grating structures.
3. The measurement system of claim 2,
under the condition that the MEMS scanning galvanometer has one rotating shaft, the plurality of light reflecting areas are mirror areas and two grating areas distributed on two sides of the mirror areas;
under the condition that the MEMS scanning galvanometer has two mutually perpendicular rotating shafts, the plurality of light reflecting areas are nine light reflecting areas which are arranged in an array form, and only one light reflecting area in the center of the nine light reflecting areas is a mirror area.
4. A measuring system according to claim 3, wherein the grating structure adopted by each grating region is a blazed grating structure.
5. The measurement system of claim 4,
determining grating parameters of a blazed grating structure adopted by each grating area according to the turning angle corresponding to the grating area, the turning angle corresponding to the mirror area, and the distance between each collimated light source and the corresponding photoelectric detector and the target plane;
and the target plane is the plane where the MEMS scanning galvanometer with the preset turning angle is located.
6. The measurement system of claim 5, wherein the mirror region has a corresponding flip angle in a range of 0 ° to 90 °.
7. The measurement system of claim 1,
the grating structure is formed by processing the back of the MEMS scanning galvanometer;
or the grating structure is adhered to the back of the MEMS scanning galvanometer.
8. The measurement system of claim 1, wherein the photodetector is a single pixel photodetector.
9. The measurement system of claim 1, wherein the photodetector receives 1 st order diffracted light from each grating structure, the photodetector comprising:
a signal conversion unit for converting an echo incident to the photodetector into an electric signal;
the comparison unit is connected with the signal conversion unit and used for comparing the electric signal with a reference value and triggering the signal processor to analyze the turnover angle and the receiving time under the condition that the electric signal is larger than the reference value;
and the reference value is an electric signal value corresponding to a photosensitive threshold value, and the photosensitive threshold value is determined according to the 1-order diffraction light intensity of each grating structure.
10. A method for measuring vibration parameters of a MEMS scanning galvanometer, performed using the measurement system of any one of claims 1-9, the method comprising:
the collimating light source emits collimated light to different reflecting areas in the same direction in the vibration process of the MEMS scanning galvanometer so that the different reflecting areas emit echoes to fixed positions at a turning angle of the MEMS scanning galvanometer respectively;
the photoelectric detector receives an echo at the fixed position and converts the echo into an electric signal;
the signal processor analyzes the time of receiving the echo by the photoelectric detector and the turning angle of the MEMS scanning galvanometer marked by the echo based on the electric signal, and determines the vibration parameter according to the turning angle and the receiving time;
the MEMS scanning galvanometer with the preset turning angle is parallel to the incidence direction of collimated light and has a constant distance with the collimated light source.
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