Method for operating a MEMS system and MEMS system

Abstract

Method for operating a MEMS system (1) with at least one projection unit (8) for providing an image by means of at least one light beam and a deflection unit (6) for two-dimensionally deflecting the at least one light beam, comprising the steps: - driving (T1) the deflection unit (6) by means of at least one reference signal (S1, S2) so that the deflection unit (6) deflects the at least one light beam periodically at least two-dimensionally, - measuring (T2) at least one controlled variable of the deflection unit (6) which corresponds to an actual position of the deflected light beam, - determining (T3) a current deviation of the at least one controlled variable from a target variable corresponding to a target position of the light beam, - Calculating (T4) at least one compensation value based on the determined deviation, - Controlling (T5) the deflection unit (6) with respect to the deflection based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position by means of a repetitive controller as the control unit (3, 7) and / or the projection unit (8) with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position by means of the repetitive controller as the control unit (3, 7), wherein for controlling the deflection unit (6) the at least one compensation variable is additionally calculated based on an earlier deviation in at least one earlier period.

Description

Technical area

[0001] The invention relates to a method for operating a MEMS system having at least one projection unit for providing an image by means of at least one light beam and a deflection unit for two-dimensional deflection of the at least one light beam.

[0002] The invention further relates to a MEMS system comprising a projection unit for providing an image by means of at least one light beam and a deflection unit which is designed to deflect a light beam incident on the deflection unit in two dimensions. State of the art

[0003] Although the present invention is generally applicable to any projection units, the present invention will be described with reference to projection units in the form of lasers.

[0004] Although the present invention is generally applicable to any deflection units, the present invention will be explained with reference to deflection units in the form of micromirrors.

[0005] US 2015 / 0249809 A1 discloses a system for controlling or correcting a projected image exhibiting an undesirable convex curvature in the lateral edge area. The image projection system comprises a laser module and a micromirror module with a periodically driven 2-DOF micromirror that can be tilted in two orthogonal directions. The control system comprises the image projection system and a controller. The controller performs pulse-width modulation of the control signal to correct the deflection angle of the micromirror.

[0006] EP 2 711 916 A1 discloses a system for controlling or correcting a projected image exhibiting a trapezoidal distortion. The image projection system comprises three lasers whose light is combined by dichroic mirrors, and a periodically driven 2-DOF micromirror that can be tilted in two orthogonal directions. The control system comprises the image projection system, a controller for controlling the color or intensity of the laser light, and a controller for controlling the mirror orientation. The control system corrects a trapezoidal distortion.

[0007] From the documents DE 10 2013 217 105 A1 and US 2012 / 0 170 639 A1, control methods of a deflection unit are known, which partially have features of the method for operating a MEMS system according to claim 1. Disclosure of the invention

[0008] In one embodiment, the present invention provides a method for operating a MEMS system having at least one projection unit for providing an image by means of at least one light beam and a deflection unit for two-dimensionally deflecting the at least one light beam, comprising the steps: - driving the deflection unit by means of at least one reference signal so that the deflection unit periodically deflects a light beam at least two-dimensionally, - Measuring at least one control variable of the deflection unit, which corresponds to an actual position of the deflected light beam, - Determining a current deviation of the at least one controlled variable from a target value corresponding to a target position of the light beam, - Calculating at least one compensation value based on the determined deviation, - Controlling the deflection unit with respect to the deflection and / or the projection unit with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position, wherein for controlling the deflection unit the at least one compensation variable is additionally calculated based on a previous deviation in at least one previous period.

[0009] In a further embodiment, the present invention provides a MEMS system comprising a projection unit for providing an image by means of at least one light beam, a deflection unit configured to two-dimensionally deflect a light beam incident on the deflection unit based on at least one reference signal, a measuring unit for measuring at least one controlled variable of the deflection unit, which corresponds to an actual position of the deflected light beam, a deviation measuring unit designed to determine a current deviation of the at least one controlled variable from a target variable corresponding to a target position of the light beam, a predictor unit configured to calculate at least one compensation value based on the determined deviation, and a control unit configured to control the deflection unit with respect to the deflection and / or the projection device with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position, wherein, for controlling the deflection unit, the at least one compensation variable is additionally calculated by the predictor unit based on an earlier deviation in at least one earlier period.

[0010] One of the advantages achieved is that deviations between a reference or target position of a projected pixel and the actual projected position of the pixel can be minimized in a simple and reliable manner using the deflection unit. Another advantage is that the robustness against disturbances on the deflection unit or the projection unit can be increased. Another advantage is the compensation of dead times, which result, for example, from analog-to-digital or digital-to-analog conversion. Another advantage is that, when controlling the deflection unit, prior knowledge of previous deviations is used to carry out current control of the deflection unit, which overall improves the performance of the MEMS system.Using this prior knowledge, an almost temporally perfect match between the reference position or target position of the projected pixel and the position of the pixel actually provided by the deflection unit is possible.

[0011] In other words, either a) the deflection unit can be controlled separately with respect to the deflection based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position, or b) the projection unit can be controlled separately with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position. Furthermore, both a) the deflection unit can be controlled with respect to the deflection and b) the projection unit can be controlled with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position.

[0012] Further features, advantages and further embodiments of the invention are described below or will become apparent thereby.

[0013] According to an advantageous development, the at least one reference signal is provided in the form of a periodic, preferably wave-like, bandwidth-limited signal. The advantage of this is that it enables a simple and reliable periodic control of the deflection unit and thus a periodic deflection of the light beam incident on the deflection unit.

[0014] According to a further advantageous development, the at least one compensation variable is calculated within a predetermined frequency control interval, wherein the at least one reference signal is provided from at least one fundamental harmonic of a sawtooth signal, wherein the at least one fundamental harmonic is provided within the frequency control interval. The advantage of this is that deviations from the reference signal caused by the deflection unit can be compensated for in a simple and reliable manner within the frequency control interval. A fundamental harmonic is understood to mean, in particular, the fundamental oscillation with a frequency f or an oscillation with an integer multiple of the frequency f. A sawtooth signal can, for example, be represented by a fundamental oscillation and an infinite number of harmonics, i.e. integer multiples of the frequency of the fundamental oscillation.

[0015] According to a further advantageous development, the at least one compensation variable is calculated using a predictor, in particular a Smith predictor. In this way, control errors of the deflection unit can be dynamically compensated for in a simple and rapid manner. The advantage of a Smith predictor is the compensation of control errors resulting from the neglect of dead times, for example, during the digital-to-analog conversion of a control signal for the deflection unit.

[0016] According to a further advantageous development, the brightness of the deflected light beam is adjusted depending on its actual position using an adjustment unit. This allows a projected image to be displayed even more reliably using the MEMS system.

[0017] According to a further advantageous development, the light beam is deflected by the deflection unit at least two-dimensionally by deflection around at least two different axes at different speeds. This increases the flexibility in displaying the image using the deflection unit.

[0018] According to a further advantageous development, the deflection unit is driven by two reference signals, wherein the two reference signals have different frequencies, and wherein deflection by means of the deflection unit occurs in such a way that the first of the two reference signals results in a deflection about one of the two different axes, and the second of the two reference signals results in a deflection about the second of the two different axes. This increases the flexibility with regard to the representation of the projected image.

[0019] According to a further advantageous development of the MEMS system, the deflection unit comprises a MEMS mirror that is movable about at least two axes or at least two MEMS mirrors that are each movable about one axis, wherein the at least two axes have different orientations. The advantage of this is that a deflection of a light beam in two dimensions can be provided in a simple and reliable manner.

[0020] According to a further advantageous development of the MEMS system, the control unit comprises an integrator and an anti-windup unit. The advantage of this is that the integrator in the control unit is limited if control variables for the deflection unit are set outside the corresponding limits. An anti-windup unit is therefore generally used to limit one or more integrators of a linear controller in the event that the controller's control variables are calculated or requested outside of the specified limits.

[0021] According to a further advantageous development of the MEMS system, the predictor unit is designed to perform the calculation using a Smith predictor. The advantage of a Smith predictor is that it compensates for control errors resulting from neglecting the dead time.

[0022] Further important features and advantages of the invention emerge from the subclaims, from the drawings, and from the associated description of the figures based on the drawings.

[0023] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0024] Preferred embodiments and embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components or elements. Short description of the drawings

[0025] In schematic form Fig. 1 a MEMS system according to an embodiment of the present invention; Fig. 2 a MEMS system according to an embodiment of the present invention; and Fig. 3 a method for operating a MEMS system according to an embodiment of the present invention. Embodiments of the invention

[0026] Fig. 1 shows in schematic form a MEMS system according to an embodiment of the present invention.

[0027] In detail, Fig. 1 shows a MEMS system 1. The MEMS system 1 comprises a reference generator 2, which generates a reference signal S1. The MEMS system 1 further comprises a linear controller 3, which generates a control signal MS for controlling a deflection unit 6. The control signal MS for the deflection unit 6 is transmitted to the latter. For deflecting a light beam incident on the deflection unit 6, the deflection unit 6 comprises a drive unit 6a for one or more micromirrors 6b, which are each movable about one axis or about two axes and which are then moved, in particular periodically, according to the control signal MS in order to deflect a light beam accordingly.

[0028] Connected to the deflection unit 6 is a measuring unit 9, which measures the position of the micromirror(s) 6b. Based on the measured position, a deviation measuring unit 10 determines the current deviation of a controlled variable of the deflection unit 6—in this case, the controlled variable for controlling the position of the micromirror 6b—from a predetermined target value based on the reference signal S1. This deviation is then transmitted to both a repetitive controller 7 and the linear controller 3.

[0029] The MEMS system 1 further comprises two anti-windup devices 4a, 4b, which are arranged in parallel with the linear controller 3. Furthermore, a Smith predictor 5 is arranged in parallel with the input and output of the linear controller 3. The linear controller 3 serves to control and stabilize the micromirror 6b in the largest possible continuous frequency control band or control range. The linear controller 3 is initially configured accordingly, neglecting the dead time of the controlled system of the MEMS system 1. The Fig. The MEMS system 1 shown in Figure 1 comprises a control system which includes the movable axis(es) of the micromirror 6b, the measuring unit 9 for position determination and - in Fig. 1 (not shown) – comprises an analog-to-digital / digital-to-analog conversion including analog filters. The Smith predictor 5, in turn, serves to dynamically compensate for control errors resulting from the neglect of dead time. The anti-windup devices 4a, 4b, in turn, serve to limit the integrators of the linear controller 3 in the event that control variables for the deflection unit 6 are calculated or requested outside of given limits. Furthermore, the repetitive controller 7 compensates for control errors occurring periodically, i.e., over at least one previous period.

[0030] The reference signal S1 provided by the reference generator 2 is in Fig. 1 a wavy, bandwidth-limited signal. Using the signal S1, the pixel of an image provided by a projection device (not shown here) is then projected at different speeds for the different axes of the micromirror 6b. This makes it necessary to adapt or readjust the brightness of the pixel. The wavy, bandwidth-limited reference signal S1 can be limited to a few, for example, five fundamental harmonic frequencies of a fundamental signal, for example a rectangular or sinusoidal signal, with which the deflection unit 6, in particular the micromirror 6b, is to be excited. This enables reliable control of deviations. In particular, the reference signal S1 can consist of a finite number of fundamental harmonics of a sawtooth signal.The fundamental harmonics can be selected such that they lie within the control range or interval of the linear controller 3. The repetitive controller 7 compensates for dead times caused by the analog-to-digital conversion. For this purpose, the repetitive controller 7 has a memory device 7a in which a control error is stored over at least one excitation period of the reference signal or of the micromirror 6b, from which future control errors and corresponding control variables can be derived. Periodic disturbances can thus be efficiently compensated, even if, for example, the mirror's natural frequencies of the micromirror 11 change.

[0031] Fig. 2 shows a MEMS system according to an embodiment of the present invention.

[0032] Fig. Figure 2 shows a MEMS system 1 with a linear controller 3 and a deflection unit 6. A sawtooth-shaped, periodic reference signal S1 is fed to the linear controller 3, which then provides a corresponding periodic control signal MS for the deflection unit 6. Based on the measured controlled variable of the deflection unit 6 by means of a measuring unit 9 and a corresponding deviation measuring unit 10, the linear controller 3 then controls the deflection unit 6 based on the comparison with the periodic reference signal S1 and generates the corresponding periodic control signal MS for the deflection unit 6.

[0033] The measured deviation MSA is stored in a memory 7a. The memory 7a stores not only the current deviation of the current period of the reference signal S1, but also the deviation over at least one previous period. The memory 7a provides this information to an image processing device 8b of a projection device 8, which comprises an image provision device 8a for providing an image. The image processing device 8b receives, on the one hand, as information, for example, a sinusoidal high-frequency signal S2 on one axis and the signal S1 on the other axis. The image processing device 8b then determines a two-dimensional image with a corresponding pixel function p for each pixel to be projected, taking the deviation into account, and projects the pixel function p via a projector 8c to project the image.In other words, the image processing device 8b considers not only the two reference signals S1, S2 for displaying the image, but also the measured deviations MSA at at least one different point in time. Control errors of a deflection unit 6, in particular of a micromirror 6b, which are periodic within a certain time window, are used to correct projected image content, thus enabling consistency between the control of the deflection unit 6, in particular a micromirror position, and the image content to be projected, even if control errors are constantly changing.

[0034] The reference signals S1, S2 serve - as explained above - to control the deflection unit 6 about different axes. The movement of the micromirror 6b of the deflection unit 6 can occur at different speeds about different axes, corresponding to different periods of the respective reference signals S1, S2. The image processing device 8b, in turn, uses these signals S1, S2 to determine the pixel in the image to be projected that is to be displayed at a specific time by the projector 8c of the projection device 8. The memory 7a is designed in particular as a ring buffer, preferably for the "slower" axis, which stores the measured deviation between a reference position of the micromirror 6b of the deflection unit 6 and the actual position of the micromirror 6b over a period of time.Assuming that this deviation is the same between two consecutive periods, this deviation is used to correct the reference signal S2 of the image processing device 8b and thus the image to be projected.

[0035] Furthermore, this can lead to the Fig. 1 described procedure and the Fig. 2 can be combined, which further improves the control accuracy of the deflection unit 6 and the image processing unit 8b. The memory 7a can be used by both the repetitive controller 7 and the image processing unit 8b.

[0036] Fig. 3 schematically shows a method according to an embodiment of the present invention.

[0037] In detail, Fig.3 a method for operating a MEMS system with at least one projection unit for providing an image by means of at least one light beam and a deflection unit for two-dimensional deflection of the at least one light beam. The procedure includes the following steps:

[0038] In a step T1, the deflection unit is driven by means of at least one reference signal so that the deflection unit periodically deflects a light beam at least two-dimensionally.

[0039] In a further step T2, at least one controlled variable of the deflection unit is measured, which corresponds to a position of the deflected light beam.

[0040] In a further step T3, a current deviation of the at least one controlled variable from a target variable corresponding to a target position of the light beam is determined.

[0041] In a further step T4, at least one compensation value is calculated based on the determined deviation.

[0042] In a further step T5, the deflection unit is controlled with respect to the deflection and / or the projection unit with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position, wherein, for controlling the deflection unit, the at least one compensation variable is additionally calculated based on an earlier deviation in at least one earlier period.

[0043] In summary, at least one of the embodiments of the invention has at least one of the following advantages: • Control over a wide control range • greater accuracy in the display of images • greater flexibility • Compensation of dead times

[0044] Although the present invention has been described using preferred embodiments, it is not limited thereto but can be modified in many ways.

Claims

[1] Method for operating a MEMS system (1) with at least one projection unit (8) for providing an image by means of at least one light beam and a deflection unit (6) for two-dimensionally deflecting the at least one light beam, comprising the steps: - driving (T1) the deflection unit (6) by means of at least one reference signal (S1, S2) so that the deflection unit (6) deflects the at least one light beam periodically at least two-dimensionally, - measuring (T2) at least one controlled variable of the deflection unit (6) which corresponds to an actual position of the deflected light beam, - determining (T3) a current deviation of the at least one controlled variable from a target variable corresponding to a target position of the light beam, - Calculating (T4) at least one compensation value based on the determined deviation, - Controlling (T5) the deflection unit (6) with respect to the deflection based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position by means of a repetitive controller as the control unit (3, 7) and / or the projection unit (8) with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position by means of the repetitive controller as the control unit (3, 7), wherein for controlling the deflection unit (6) the at least one compensation variable is additionally calculated based on an earlier deviation in at least one earlier period. [2] Method according to claim 1, wherein the at least one reference signal (S1, S2) is provided in the form of a periodic, preferably wavy, bandwidth-limited signal. [3] Method according to one of claims 1-2, wherein the at least one compensation variable is calculated within a predeterminable frequency control interval, and wherein the at least one reference signal is provided from at least one fundamental harmonic of a sawtooth signal (S1), wherein the at least one fundamental harmonic is provided within the frequency control interval. [4] Method according to one of claims 1-3, wherein the calculation (T4) of the at least one compensation variable is carried out by means of a predictor (5), in particular a Smith predictor. [5] Method according to one of claims 1-4, wherein the brightness of the deflected light beam is adjusted by means of an adjustment unit (8c) depending on its actual position. [6] Method according to one of claims 1-5, wherein the light beam is deflected by the deflection unit (6) at least two-dimensionally by means of deflection about at least two different axes at different speeds. [7] Method according to claim 6, wherein the driving (T1) of the deflection unit (6) is carried out by means of two reference signals (S1, S2), wherein the two reference signals (S1, S2) have different frequencies, and wherein the deflection is carried out by means of the deflection unit (6) in such a way that with the first (S1) of the two reference signals (S1, S2) a deflection about one of the two different axes takes place and with the second (S2) of the two reference signals (S1, S2) a deflection about the second of the two different axes takes place. [8] MEMS system (1), comprising a projection unit (8) for providing an image by means of at least one light beam, a deflection unit (6) which is designed to periodically deflect a light beam incident on the deflection unit (6) around two axes based on at least one reference signal (S1), a measuring unit (9) for measuring at least one controlled variable of the deflection unit (6), which corresponds to an actual position of a deflected light beam, a deviation measuring unit (10) designed to determine (T3) a current deviation of the at least one controlled variable from a target variable, which corresponds to a target position of the light beam, a predictor unit (5) designed to calculate (T4) at least one compensation variable based on a determined deviation, and a control unit (3, 7) designed to control (T5) the deflection unit (6) with respect to the deflection based on a calculated at least one compensation variable for reducing the deviation of the light beam from the target position and / or a projection device (8) with respect to the image provision based on the calculated at least one compensation variable for reducing the deviation of the light beam from the target position, wherein for controlling (T5) the deflection unit (6), the at least one compensation variable is additionally calculated by the predictor unit (5) on the basis of an earlier deviation in at least one earlier period, wherein the control unit (3, 7) is designed as a repetitive controller with a memory device (7a). [9] MEMS system according to claim 8, wherein the deflection unit (6) comprises a MEMS mirror (11) which is movable about at least two axes or at least two MEMS mirrors (11) which are each movable about one axis, wherein the at least two axes have different orientations. [10] MEMS system according to claim 8 or 9, wherein the control unit (3,7) comprises an integrator and an anti-windup unit (4a,4b). [11] MEMS system according to one of claims 8-10, wherein the predictor unit (5) is designed to perform the calculation (T4) using a Smith predictor (5).

Images