Method and control device for trajectory adjustment of micro-scanner in Lissajin

Abstract

In a method for trajectory adjustment of a biaxial Lissajin microscanner, a drive device for the microscanner is controlled in the sense of adjustment in such a way that, in each of a plurality of consecutive time periods, the drive frequencies of the two axes form a frequency pair for the respective duration thereof, and the respective corresponding pairs of frequencies of the directly contiguous time periods differ at least with respect to at least one frequency. For a corresponding time period, according to a value of at least one physical parameter which is detected by a sensing technology and has a dependency relationship with the corresponding resonant frequency relative to the at least one vibration axis, a frequency pair corresponding to the time period is selected from a predetermined discrete set of a plurality of different frequency pairs according to a selection rule, so that the frequency pair corresponding to the time period is selected relative to the same vibration axis. The selected frequency pair has a corresponding frequency deviation on at least one of the two frequencies thereof from the resonant frequency corresponding to the value of the detected at least one variable according to the dependency.

Description

Technical Field

[0001] The present invention relates to a method and a control device for operating a Lissajous microscanner system, a computer program (product) for operating the control device, and a beam deflection system based on the control device. Background Art

[0002] Microscanners, also referred to in technical language as "MEMS scanners", "MEMS mirrors" or "micromirrors" or in English as "microscanners" or "microscanning mirrors" or "MEMS mirrors", belong to microelectromechanical systems (MEMS) or, more precisely, micro-opto-electro-mechanical systems (MOEMS) of the type of micromirror actuators for dynamic modulation of electromagnetic beams, in particular visible light. Depending on the configuration, the modulation movement of the individual mirrors can be carried out translationally or rotationally about at least one axis. In the first case, a phase shift effect is achieved, in the second case a deflection (Ablenkung) of the incident electromagnetic beam. Also to be considered are microscanners in which the modulation movement of the individual mirrors is at least also carried out rotationally. In contrast to the modulation of the incident light in mirror arrays by the cooperation of a plurality of mirrors on a single MEMS component, in microscanners the modulation is usually produced by individual mirrors of the respective MEMS component (microscanner).

[0003] Thus, a microscanner can be used in particular to deflect an electromagnetic beam in order to modulate the electromagnetic beam incident thereon with respect to its deflection direction by means of a deflection element ("mirror"). This can be used in particular to produce a Lissajous projection of the beam in an observation field or projection field. This can, for example, be used to perform imaging sensing tasks or to implement display functions. Furthermore, such a microscanner can also be used to irradiate materials in an advantageous manner, in particular to process them. Other possible applications include the field of illuminating (Beleuchtung) or lighting up (Ausleuchtung) certain open or closed spaces or spatial regions using electromagnetic beams, for example in the context of headlight applications.

[0004] In many cases, microscanners consist of mirror plates (deflection plates) that are laterally suspended on elastically stretchable springs. A distinction is made between single-axis mirrors, which should preferably be suspended rotatably only about a single axis, and dual-axis mirrors and multi-axis mirrors, in which rotation, in particular rotational oscillation, can take place about a corresponding number of different axes, in particular simultaneously.

[0005] Thus, the microscanner system for deflecting the electromagnetic beam can in particular have a two-axis microscanner, i.e. a microscanner with two different, in particular mutually orthogonal vibration axes, or a combination of a plurality of single, in particular two, uniaxial microscanners, which are arranged in such a way that the incident beam can be deflected successively by different single microscanners of the microscanner system. In a microscanner system having a combination of two or three uniaxial microscanners, their vibration axes can in particular be orthogonal to one another in pairs.

[0006] Whether in the case of an imaging sensor or in the case of a display function, a multi-axis microscanner is used to deflect an electromagnetic beam, such as a laser beam or a shaped beam from any other electromagnetic beam source, at least two-dimensionally (e.g. horizontally and vertically) in order to scan or illuminate an object surface within the field of observation. This can be done in particular in such a way that the scanning laser beam is swept over a rectangular area on the projection surface in the projection field. Therefore, in these applications, a microscanner system with at least a two-axis microscanner or with a plurality, in particular two, of single-axis microscanners connected in series in the beam path is used. The wavelength range of the beam to be deflected can in principle be selected from the entire spectrum of short-wave UV beams, through the VIS range, the NIR range, the IR range, the FIR range to long-wave terrestrial and radar beams.

[0007] The drive is usually based on electrostatic, electromagnetic, piezoelectric, thermal and other actuator principles. The mirror movement can be carried out in particular quasi-statically (especially non-resonantly) or resonantly, the latter in particular in order to achieve larger amplitudes, larger deflections and higher optical resolution. In resonant operation, in principle, energy consumption can also be minimized, or advantages can be achieved in particular with regard to stability, robustness, throughput, etc. The scanning frequency is usually from 0 Hz (quasi-static) to more than 100 kHz (resonant).

[0008] Although the microscanner system and microscanner described here can in principle be reasonably and successfully used in many different fields, their application in the field of laser projection displays will be discussed in particular below for the purpose of illustrating the technical solution only, which should not be regarded as limiting the scope of application.

[0009] In many known cases, laser projection displays based on microscanners are so-called raster scan displays, in which a first beam deflection axis is operated resonantly at high frequencies (typically 15 kHz to 30 kHz) (fast axis) to produce horizontal deflections, while a second axis is operated quasi-statically at low frequencies (typically 30 Hz to 60 Hz) to produce vertical deflections. The trajectory of the beam deflected in this way therefore corresponds to a fixedly set grid-like linear pattern. This is typically reproduced 30 to 60 times per second.

[0010] Another approach is the use in so-called Lissajous microscanners or Lissajous microscanner systems, in particular also in Lissajous scanning displays. There, the two axes are usually operated in a resonant manner, and a trajectory in the form of a Lissajous diagram is generated as a result. In this way, larger amplitudes can be achieved on both axes. In particular, the vertical deflection can thus be much larger than in a raster scanner. Accordingly, in a Lissajous microscanner, in particular a Lissajous scanning display, a significantly higher optical resolution can usually be achieved than in a raster scanning display, in particular in the vertical direction.

[0011] Patent document EP 2 514 211 B1 discloses a deflection device of a projection system for projecting a Lissajous figure onto an observation field, which is designed to deflect a light beam about at least a first and a second deflection axis to generate a Lissajous figure. Summary of the invention

[0012] The object of the present invention is to further improve the control of the operation of a Lissajous microscanner, in particular with regard to applications in the field of projection displays, in particular to illuminate the observation field as uniformly as possible.

[0013] The object of the invention is achieved by the teaching of the independent claim. Various embodiments and developments of the invention are given by the dependent claims.

[0014] A first aspect of the invention relates to a method for trajectory control in a multi-axis microscanner system. The method comprises: controlling a drive device for the microscanner system so that a deflection element of the microscanner system is driven to a first rotational oscillation around a first vibration axis by means of an excitation having a first drive frequency, and simultaneously a deflection element of the microscanner system is driven to a second rotational oscillation around a second vibration axis orthogonal to the first vibration axis by means of an excitation having a second drive frequency. In this case, the control is carried out in a plurality of consecutive time periods in the sense of control as follows:

[0015] (i) in each time period, for its respective duration, the first driving frequency and the second driving frequency are respectively stably maintained at the respective set first target frequency or second target frequency, in particular through a phase adjustment loop, wherein the two target frequencies form a frequency pair corresponding to the time period, and the frequency pairs corresponding to at least two consecutive time periods are different from each other with respect to the first target frequency and / or the second target frequency; and

[0016] (ii) For each time period, based on the value of at least one physical parameter detected by the sensing technology (the physical parameter has a dependency relationship with the corresponding resonant frequency with respect to at least one vibration axis), a frequency pair corresponding to the time period is selected from a discrete set of a plurality of pre-set different frequency pairs according to a selection rule, so that with respect to the same vibration axis, the selected frequency pair has a corresponding frequency deviation with respect to at least one of its two frequencies and the resonant frequency corresponding to the value of the at least one parameter detected according to the dependency relationship.

[0017] The term "microscanner system" (and its variants) as used herein is to be understood as a device or a system of a plurality of cooperating devices, which has at least one microscanner. In particular, both a single, in particular biaxial, microscanner and a device with two or more, in particular uniaxial, microscanners (which is configured to sequentially deflect an incident electromagnetic beam by means of two or more microscanners) are corresponding microscanner systems.

[0018] The term "deflection element" (and its variants) used in this document is particularly understood to be an object with a sufficiently smooth reflecting surface (mirror) so that an electromagnetic beam (e.g. visible light) reflected on the mirror surface according to the law of reflection can maintain its parallelism and thereby produce an image. To this end, the roughness of the mirror surface must be less than approximately half of the wavelength of the electromagnetic beam. The deflection element can be constructed in particular as a mirror plate having at least one mirror surface or having such a mirror plate. In particular, the mirror surface itself can be composed of a material different from the other body of the deflection element, for example, composed of a metal, in particular composed of a metal deposited (e.g. by chemical vapor deposition (CVD) or sputtering). In the above-mentioned microscanner system based on the present technical solution, the first oscillation and the second oscillation either involve the same, in this case multi-axis, deflection element in the microscanner system, or involve different deflection elements arranged in the same optical path, in particular deflection elements of a single-axis microscanner of the microscanner system.

[0019] The term "Lissajous projection" (and its variants) used in this document is particularly understood to be a scanning of an observation field by means of an electromagnetic beam, which is caused by at least two mutually orthogonal sinusoidal vibrations (oscillations) of a deflection device, in particular of at least a two-axis microscanner system, which deflects the beam into the observation field.

[0020] The term "nonlinear Lissajous projection" (and its variants) as used herein is to be understood as a special case of a Lissajous projection (and therefore also within the scope of the term "Lissajous projection"), in particular by scanning or illuminating an observation field with the aid of an electromagnetic beam which is caused by at least two mutually orthogonal sinusoidal oscillations about the respective corresponding oscillation axes of a deflection device, in particular at least a two-axis microscanner system, which deflects the beam into the observation field. In this case, at least a first of the oscillations about a first oscillation axis can be modulated in terms of its amplitude as a function of the instantaneous amplitude of the oscillation about at least one other oscillation axis, so that at least the first oscillation does not behave as a linear oscillation and therefore does not follow Hooke's law with an amplitude-independent spring constant.

[0021] The term "axis" or the synonymous "vibration axis" (and its variants) used herein is to be understood as the axis of rotation (rotation axis) of a particularly oscillating rotational movement. It is therefore a straight line that defines or describes a rotation or a rotation.

[0022] The term "drive device" (and variants thereof) as used herein is to be understood in particular as a device having one or more actuators for driving a deflection unit, i.e., for causing a deflection element of a multi-axis microscanner to oscillate in rotation relative to a support structure on which the deflection element is suspended in a vibrating manner and about at least a first vibration axis and a second vibration axis and possibly a third vibration axis simultaneously. In the case of a microscanner system having a plurality of microscanners, the drive device may also be understood in particular as a device having one or more actuators for driving a respective deflection unit of the microscanner.

[0023] The term "phase period" (and its variants) as used herein is understood to mean in particular a time period which is defined as the time period between the occurrence of a specific, identical phase pair formed by the phase of the first and second oscillation and the first subsequent occurrence. In particular in the case of a closed trajectory of an electromagnetic beam deflected by a microscanner system, one phase period corresponds exactly to a complete phase period through the associated Lissajous figure.

[0024] The term "dependency" between two variables (and its variants) as used herein is to be understood as meaning that at least one of the two variables depends on the other variable. This dependence can be expressed in particular in the sense of a mathematical function or more generally in the sense of a relationship or correlation. It is essential that the resonant frequency associated with at least one variable can be inferred from the measured value of the at least one variable. This dependence can be unilateral or mutual.

[0025] A discrete set of frequency pairs can be defined explicitly, in particular by its elements (frequency pairs or their corresponding frequency deviation pairs relative to a reference frequency pair), or implicitly by a generation rule that can generate the elements of the set.

[0026] The term "selection rule" (and its variants) used in this document is to be understood in particular as a fixed rule according to which an element of a discrete set of frequency pairs, i.e. a specific frequency pair, can be unambiguously selected depending on the value of a physical variable detected by the sensing technology. The selection rule can be implemented in particular in the sense of a tabular relationship, wherein each element of a set of possible values ​​or value ranges of the physical variable corresponds to a frequency pair from the discrete set of frequency pairs. However, the selection rule can also be determined in particular in the sense of a calculation rule, with the aid of which an output variable can be calculated using the corresponding value of the physical variable or, if necessary, each of the multiple physical variables used as input variable, which output variable unambiguously corresponds to a specific frequency pair from the discrete set of frequency pairs, for example as an index to the discrete set or itself already being a selected frequency pair.

[0027] The terms "comprises," "including," "involving," "having," "with," "having" or any other variations thereof as may be used herein are intended to cover a non-exclusive inclusion. For example, a method or apparatus that includes or has a list of elements is not necessarily limited to those elements but may include other elements not expressly listed or inherent in such method or such apparatus.

[0028] In addition, unless expressly specified to the contrary, "or" refers to an inclusive "or" rather than a non-inclusive "or". For example, one of the situations in which condition A or B is satisfied is: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); and both A and B are true (or exist).

[0029] The terms "a" or "an", as used herein, are defined as "one / one or more." The terms "another" and "another" and any other variations thereof should be construed to mean "at least another."

[0030] The term "plurality" as used herein should be understood as "two or more".

[0031] In the sense of the present invention, "configured to" or "configured", "designed" or variations thereof are to be understood as meaning that the corresponding device is designed or can be adjusted, i.e. configured to fulfill a specific function. The configuration or design can be achieved, for example, by correspondingly adjusting parameters of the process or by hardware or software-implemented switches for activating or deactivating functions or settings. In particular, the device can have a plurality of predefined configurations or operating modes, so that the configuration can be performed by selecting one of these configurations or operating modes.

[0032] While in conventional methods of operating a Lissajous microscanner system, in most cases a phase adjustment circuit is used for each vibration axis to resonantly maintain the oscillation relative to the associated vibration axis, in the method according to the first aspect the operation is such that a drive frequency is used at least for one vibration axis, which differs from the associated resonant frequency for the same vibration axis by a frequency deviation. By appropriately defining a discrete set of frequency pairs and corresponding selection rules, on the one hand, the characteristics of the generated trajectory that deviate from pure resonant operation, in particular double resonant operation, can be adjusted in a targeted manner, and on the other hand, these characteristics can be maintained by adjustment even if the resonant frequency changes over time. Such a time-varying resonant frequency of the vibration axis can, for example, be due to temperature changes and thus to the inertia moment of the deflection element. caused by changes in the suspension system or due to the characteristics of its suspension system.

[0033] In particular, it can be achieved that Lissajous trajectories which have omitted image regions in the observation field to be illuminated in a certain time period are purposefully moved to precisely these previously omitted image regions in the immediately following time period. This can be achieved in particular by allowing, in principle, only those trajectories which are known in advance, in the sense of a permission list (Positivliste) established on the basis of a discrete set, in particular for the relevant observation period which is usually guided by human perception and the image repetition rate (Bildwiederholrate) of conventional video formats. Since a more uniform density of trajectories can be achieved and thus a more uniform illumination of the observation field which is illuminated as a whole by the Lissajous pattern, the achievable image quality is improved.

[0034] Preferred embodiments of the method will be described below. Unless explicitly excluded or technically infeasible, these embodiments may be arbitrarily combined with each other and with other aspects of the further description of the present invention.

[0035] In some embodiments, according to the selection rule of the corresponding time period, such a frequency pair is selected from the set: with respect to the same vibration axis, the frequency pair has a frequency deviation different from zero and the smallest frequency within the set with respect to at least one of its two frequencies and the resonant frequency, and the frequency deviation corresponds to the value of the at least one parameter detected according to the dependency. Such a selection is particularly advantageous because the shape of the Lissajous figure generated for the new time period in this way is highly similar to the shape of the Lissajous figure in the previous time period, so that it can be accurately embedded in the image area vacated by the previous Lissajous figure. Therefore, the overall achievable illumination level (Ausleuchtungsgrad) over the entire time period is significantly improved after the two time periods.

[0036] In some embodiments, the respective duration of each time segment is equal to at least 90%, in particular at least 50%, preferably at least 80%, and more preferably at least 95% of the duration of the phase period of the Lissajous locus according to the frequency pair corresponding to the time segment, which Lissajous locus is generated in the observation field by the reflected deflection of the electromagnetic beam incident on the microscanner system during the simultaneous oscillation. In this way, a high achievable illumination level and, therefore, a high imaging quality are also facilitated. In some embodiments, the method further comprises determining at least one frequency pair {f1; f2} of the set according to the following conditions:

[0037] - The resonance frequency f of the microscanner system for the first vibration axis r,1 ;

[0038] -The resonant frequency f of the microscanner system for the second vibration axis r,2 ;as well as

[0039] At least one predetermined line spacing value or an upper limit specified therefor, which represents the maximum line spacing between adjacent lines of the Lissajous locus occurring during a complete phase period.

[0040] In particular, corresponding upper limits can be determined for the line spacing along a direction parallel to the first oscillation axis and / or the line spacing along a direction parallel to the second oscillation axis. In a Lissajous projection, the maximum line spacing usually occurs at or near the center of the projected image.

[0041] These embodiments are characterized in particular in that they not only achieve good illumination homogeneity in the respectively considered observation period (image frame), but also here reach at least the majority, in particular all, of the pixels or image areas within a very short time, so that a very high image quality can be achieved in the associated Lissajous projection.

[0042] In particular, at least one frequency pair {f1; f2} can be determined from the phase cycle frequency f res Initially, the phase cycle frequency is related to the possible resonant frequency pair {f 0,1 ,f 0,2 The determination of at least one frequency pair {f1; f2} comprises:

[0043] (i) determining the lower limit of the first factor n1 corresponding to the first vibration axis and / or the second factor n2 corresponding to the second vibration axis based on the line spacing values ​​corresponding to the corresponding vibration axes or the upper limits specified therefor, wherein n1, n2 ≥ 1 are respectively integers; and

[0044] (ii) determining at least one frequency pair {f1; f2} by: i.e., for the frequency pair or each of these frequency pairs, the following condition applies: f1 ≤ f 0,1 / n1; f2≤f 0,2 / n2; and n1 and n2 are coprime.

[0045] In some alternative or incremental embodiments (different frequency pairs can also be determined using different embodiments), the method further comprises: from a resonant frequency pair {f 0,1 ,f 0,2 The closed Lissajous locus of the phase cycle frequency f res Initially, determine at least one frequency pair {f1; f2} of the set, and |n Δ |>1, applicable:

[0046] f1=f 0,1 +Δf1, where

[0047] f2=f 0,2 +Δf2, where Among them, n1, n2 ≥ 1 are integers and relatively prime (teilerfremd), so it applies:

[0048] f 0,1 =n1·f res and f 0,2 =n2·f res .

[0049] By means of the above-described manner and method, without considering it as limiting, particularly suitable frequency pairs can be determined, which are characterized in particular in that an advancement of the trajectory from time period to time period can be achieved, wherein in a time period those image areas in the observation field are first illuminated which have not yet been reached by the trajectory in the immediately preceding time period.

[0050] Here, |n Δ The higher the value of | is chosen, the smaller the drop in trajectory displacement from time segment to time segment. Δ In the case of |=2, in particular a trajectory can be obtained which is substantially located in the center of the image area which has not been illuminated in the immediately preceding time period.

[0051] In some embodiments, the microscanner system has a deflection element that is suspended in a vibratory manner so that it can perform a first rotational oscillation about a first vibration axis and simultaneously perform a second rotational oscillation about a second vibration axis. During these two simultaneous oscillations, the electromagnetic beam is directed onto the deflection element so that a Lissajous projection of the beam is formed in the observation field by its reflection on the deflection element. Accordingly, such a microscanner system can in particular be designed with only a single multi-axis microscanner.

[0052] In other embodiments, the microscanner system has a first deflection element and a second deflection element, wherein the first deflection element is suspended in a vibratory manner so that it can perform a first rotational oscillation about a first vibration axis, and the second deflection element is suspended in a vibratory manner so that it can perform a second rotational oscillation about a second vibration axis simultaneously with the first oscillation. During the two simultaneous oscillations, the electromagnetic beam is directed onto the first deflection element in order to form a Lissajous projection of the beam in the observation field by its sequential reflection first at the first deflection element and then at the second deflection element. Accordingly, such a microscanner system can in particular have two single-axis microscanners, which can be used in the above-described manner for sequential deflection of the electromagnetic beam, in particular for causing a Lissajous projection.

[0053] In some embodiments, the method further comprises: modulating the electromagnetic beam, in particular with respect to intensity or wavelength, by means of an image signal, in dependence on the real-time deflection of the beam, so that a Lissajous projection with a certain image resolution formed by N matrix-arranged pixels images a two-dimensional digital image or a sequence of such images in the observation field. Here, according to a selection rule, for at least one time period, preferably for each time period, the frequency pairs corresponding to each of them are selected from the set, so that within a maximum of five, preferably a maximum of three consecutive phase periods, each of the N pixels corresponding to the image resolution is imaged on the observation surface (illumination conditions).

[0054] Therefore, selection rules and / or discrete sets are defined here, by means of which such frequency pairs are respectively selected for one or more time periods in order to meet the above-mentioned lighting conditions. The setting of the selection rules or the selection of the frequency pairs according to the detected physical variables can be carried out in particular in advance, for example within the framework of a series of tests or characterization of the microscanner system, when it is known in advance that these frequency pairs meet the above-mentioned lighting conditions when one or more corresponding values ​​of the physical variables detected by one or more sensor technologies occur. Therefore, in these embodiments, compliance with the above-mentioned lighting conditions can be ensured in advance.

[0055] In particular, within the respective duration of each time segment, the duration of the phase period of the Lissajous trajectory based on the frequency pair corresponding to the respective time segment can be (selected to be) shorter than the minimum projection duration of each image that occurs during the Lissajous projection by the microscanner system within the respective time segment. This allows for projection images or possibly projection image sequences of high image quality, since each image is projected over at least one complete phase period and thus covers at least a majority of the pixels, in particular all N pixels.

[0056] In some embodiments for image formation, according to a selection rule, for at least one, preferably each time period, a frequency pair corresponding to the time period is selected from the set, so that the selected frequency pair corresponds to a Lissajous locus generated during the Lissajous projection process, which passes through the Lissajous locus within a complete phase cycle. At least 90%, preferably at least 95%, of the N pixels. In particular, it can be achieved that a substantially uniform illumination can be achieved with only a single phase period or a phase period. The frequency pair or pairs that meet this condition can in turn be predetermined for a specific microscanner system, in particular based on its known resonant frequency and its dependence on at least one physical variable.

[0057] In some embodiments, the physical parameter characterizes or depends on one of the following states of the microscanner system (in particular a part or component thereof) or a combination of at least two such states or state changes: (i) a shift in the resonant frequency of at least one oscillation measured; (ii) temperature; (iii) mechanical stress or strain; (iv) the amplitude of the deflection element; (v) a phase instability occurring in at least one oscillation; (vi) exceeding a corresponding control variable of a phase regulation loop for the phase of at least one oscillation. (vii) a phase difference between a drive signal for controlling a drive device and a measurement signal representing the measured deflection of the deflection element; (viii) a change in the power of an incident electromagnetic beam received by the deflection element by absorption; (ix) a vibration state of a reference oscillator in the microscanner system or a change thereof, wherein the vibration state of the reference oscillator or a change thereof is related to the vibration state of at least one deflection element or a change thereof, in particular in a specific dependency relationship. Thus, for example, after a previous calibration, the vibration state of at least one deflection element can be inferred from the detected vibration state of the reference oscillator or a change thereof. In particular, the amplitude, frequency and / or phase of the individual oscillations or a combination of two or more of these quantities can be regarded as the vibration state.

[0058] All these states or state changes have in common that, on the one hand, they can be detected easily by sensor technology and, on the other hand, they are dependent on the current resonance frequency of the microscanner system and are therefore suitable as input variables for regulating one or more drive frequencies.

[0059] In some embodiments, according to the selection of the relevant frequency pair for a corresponding time period, the value of the at least one physical variable is detected in the time period immediately before the time period. In this way, the time interval between the selection of the frequency pair and its application to drive the microscanner system is shortened as much as possible, so that the selected frequency pair is particularly well matched to the current resonance frequency of the microscanner system, in particular with a view to achieving a good illumination effect, in particular an optimal track density adjustment to achieve the goal of keeping the track density as constant as possible despite the change of the resonance frequency.

[0060] In some embodiments, the switching between the time periods that follow each other takes place in the control framework at a time point when the trajectory of the Lissajous projection has a distance from the center of the observation field illuminated by the trajectory during its complete phase period, which distance corresponds to at least 80%, preferably at least 90%, of the maximum distance of a point on the trajectory from the center. This has the advantage that the switching takes place in the outer region of the Lissajous figure and is usually not noticeable to the observer at all, or, if noticeable, at least less slightly or less disturbingly than near the center of the illuminated observation field.

[0061] In some such embodiments, the switching between the adjacent time periods occurs in the control framework, in particular, when the trajectory of the Lissajous projection passes through the outer turning point ( In this case, the switching is usually barely perceptible to the observer, so that despite the frequency jumps and the resulting changes in trajectory, the achievable image quality is still particularly high.

[0062] In some embodiments, the frequency pairs of the discrete set are stored in advance ("offline") in a preferably non-volatile storage device, and the corresponding frequency pairs are selected for at least one time period according to the selection rule for each time period based on the value of at least one physical variable detected by the sensor technology. Thus, the frequency pairs of the discrete set can be predetermined, for example, within the framework of a measurement or characterization of a specific microscanner system operated according to the method, and can be stored in a readable manner in the storage device and retained (vorgehalten) during the operation of the microscanner system for subsequent use. This makes it possible, in particular, to achieve very high-performance operation, since the frequency pairs do not need to be calculated only during the operation. In addition, suitable frequency pairs can also be determined very accurately as elements of the discrete set, since for measuring or characterizing the microscanner system under different conditions (e.g. different temperatures or mechanical load conditions), more accurate measurement methods and devices are used, for example under manufacturing or laboratory conditions, while in the later operational operation, complex measurement devices are usually not available and only the measurement devices of the microscanner system itself can generally be used, which often have lower accuracy.

[0063] In some embodiments, in the control framework, based on the value of at least one physical variable detected by the sensor technology, the corresponding frequency pair is dynamically ("online") determined during the method for at least one time period by means of a calculation rule set by a selection rule (which defines the discrete set). In this case, the above-mentioned storage of the predetermined frequency pair can be omitted, so that in particular the storage capacity required for this and the step of predetermining the frequency pair before putting into operation (in particular for display applications) can be omitted.

[0064] In some embodiments, in addition to selecting a corresponding frequency pair for each time period, a target amplitude gain corresponding to the time period is selected for at least one of the two vibration axes. Furthermore, the control of the drive device during the corresponding time period also includes configuring a corresponding amplitude gain for the at least one vibration axis according to the corresponding target amplitude gain. In this way, a reduction in the size of the illuminated observation field (in particular perpendicular to the imaging optical axis) that may be caused by a frequency deviation caused by the selection of a frequency pair in one or more frequency pairs can be fully or at least partially compensated by a corresponding amplitude adjustment.

[0065] In some embodiments, the microscanner system can be configured such that it is able to adjust (verstimmt) the corresponding resonant frequency of at least one vibration axis by correspondingly adjusting at least one configuration parameter of the microscanner system. Within the framework of the method, for at least one time period, in addition to selecting the respective corresponding frequency pair, the resonant frequency of at least one vibration axis of the microscanner system is also adjusted by adjusting at least one configuration parameter. This adjustment of the resonant frequency of the relevant vibration axis can be used in particular instead of or in addition to the above-mentioned amplitude gain. In particular, the configuration parameter can relate to a configurable characteristic of the inertia moment of the relevant deflection element of the microscanner system or a configurable characteristic of the suspension of the deflection element. For example, the configuration can be achieved at least in part by adjusting the microscanner system to a specific temperature level, which corresponds to a specific resonant frequency of the microscanner system. Alternatively or in addition to this, it can also be considered to configure the suspension of one or more deflection elements to change the effective spring stiffness of the suspension.

[0066] A second aspect of the present invention relates to a control device for trajectory control of a microscanner system, wherein the control device is designed to actuate a drive device of the microscanner system according to the method according to the first aspect of the present invention.

[0067] According to some embodiments, the control device can have, in particular for at least one of the two vibration axes: (i) a phase control loop for stabilizing, in particular avoiding a phase difference between the phase corresponding to the first or second oscillation of the vibration axis and the control signal output by the phase control loop for the drive device of the vibration axis; and (ii) a frequency adjustment device for the phase control loop, in particular a frequency adjustment device controlled by a computer program, which is configured to adjust the guide parameter of the phase control loop according to the target frequency for the vibration axis determined for the time period according to the method according to the first aspect of the present invention. In this way, a combination, in particular an integration, of frequency regulation and phase control according to the method according to the invention can be achieved particularly efficiently.

[0068] The third aspect of the present invention relates to a computer program having instructions for causing the above-mentioned control device, in particular its frequency adjustment device, to execute the method according to the first aspect of the present invention.

[0069] The computer program can be stored in particular on a non-volatile data carrier. Preferably, such a non-volatile data carrier is an optical data carrier or a data carrier in the form of a flash memory module. This can be advantageous if the computer program itself is to be processed independently of the processor platform on which the program or programs are running. In another embodiment, the computer program can be stored as a file on a data processing unit, in particular a server, and can be downloaded via a data connection, such as the Internet or a dedicated data connection, such as a private network or a local area network. Furthermore, the computer program can have a plurality of independent program modules that work together.

[0070] The control device according to the second aspect can accordingly have a program memory in which the computer program (according to the third aspect) is stored. Alternatively, the control device can also be designed to access an external computer program available, for example, on one or more servers or other data processing units via a communication connection, in particular to exchange data with the external computer program, which data are used during the operation of the method or the computer program or represent the output of the computer program.

[0071] A fourth aspect of the present invention relates to a beam deflection system comprising: (i) a multi-axis microscanner system having at least one deflection element capable of performing a first rotational oscillation around a first vibration axis, and having at least one deflection element capable of performing a second rotational oscillation around a second vibration axis orthogonal to the first vibration axis simultaneously with the first oscillation, so as to generate a Lissajous projection in an observation field by deflecting the reflection of an electromagnetic beam incident on the microscanner system during the simultaneous oscillations; (ii) a drive device for driving at least one oscillation of the microscanner system; and (iii) a control device according to the second aspect for controlling the drive device according to the method of the first aspect.

[0072] In some embodiments of the beam deflection system, the quality factor (often also referred to as "Q factor") of the microscanner system with respect to at least one of the two oscillations is at least 1000. This can be achieved in particular if one or more of the associated microscanners of the microscanner system are hermetically packaged, wherein the various oscillating components, in particular the corresponding deflection element and its suspension, are arranged together in an interior space defined by the package, the gas pressure in the interior space being below atmospheric pressure, in particular in a vacuum. There, the oscillations of the deflection element are damped only accordingly, and during the oscillations of the deflection element, in particular large deflection angles of the deflection element and thus a stable, large illuminated observation field can be achieved.

[0073] The features and advantages described with respect to the first aspect of the present invention also apply accordingly to the other aspects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] More advantages, features and possible applications of the present invention will be described in detail below with reference to the accompanying drawings.

[0075] 1A-C show various exemplary trajectories and trajectory segments of Lissajous trajectories on a projection surface in an observation field to be illuminated in a two-axis microscanner according to the prior art;

[0076] Figure 2 A flow chart showing a preferred embodiment of the method according to the present invention when using a micro scanner system having a dual-axis micro scanner;

[0077] Figure 3 Various exemplary tabular illustrations of discrete sets of frequency and amplitude pairs are shown;

[0078] Figure 4 In each case, (i) a closed output trajectory, (ii) a series of trajectory segments of consecutive phase periods of a control trajectory, and (iii) a control trajectory formed by connecting these trajectory segments to each other are shown by way of example when a Lissajous projection is performed on a projection surface in an observation field to be illuminated by means of an exemplary microscanner system according to the invention having a two-axis microscanner;

[0079] Figure 5 shows three temporally consecutive exemplary partial images of a control trajectory with only very small frequency deviations during Lissajous projection onto a projection surface in the observation field to be illuminated by means of an exemplary microscanner system according to the invention having a two-axis microscanner;

[0080] Figure 6 Three temporally consecutive exemplary partial images of the adjustment trajectory are shown during a Lissajous projection onto a projection surface in the observation field to be illuminated by means of an exemplary microscanner system according to the invention with a two-axis microscanner, with a comparison to Figure 5 Optimized frequency deviation;

[0081] Figure 7 respectively show two different frequency deviations during Lissajous projection on a projection surface in an observation field to be illuminated by means of an exemplary microscanner system according to the invention having a two-axis microscanner, each showing an exemplary trajectory segment of a series of consecutive phase periods of a control trajectory and a control trajectory formed by connecting these trajectory segments to one another;

[0082] Figure 8 schematically illustrates an exemplary beam deflection system according to an exemplary embodiment of the present invention;

[0083] Fig. 9An exemplary block diagram showing a circuit for generating control signals for a drive device of a Lissajous microscanner without trajectory regulation according to the invention; and

[0084] Fig.10 Shown based on Fig. 9 An exemplary block diagram of a circuit constructed for generating control signals for a drive device of an exemplary Lissajous microscanner system having trajectory control according to the invention. DETAILED DESCRIPTION

[0085] In the following, unless otherwise specified, it is exemplarily assumed that the micro-scanner system has a dual-axis micro-scanner, but this should not be understood as a whole that the present invention is limited to this specific micro-scanner system.

[0086] Laser projection systems based on Lissajous microscanners usually work as follows: The intensity- and / or color-modulated laser projects light onto a deflection element of a multi-axis microscanner system, in particular, in the case of a multi-axis microscanner, onto a deflection element (mirror) that is suspended and deflectable in two axes. The deflection element, or in the case of a plurality of microscanners, a plurality of deflection elements, is in turn driven by a suitable drive device, which may in particular have one or more piezoelectric actuators. As a result, the deflection element or elements are vibrated in two axes, so that the image projected by the deflection element appears to a human observer as an illuminated surface, in particular a rectangular surface.

[0087] However, the trajectory followed by the laser spot actually corresponds to a Lissajous figure which, due to the ratio of the vibration frequencies of the two axes, is so complex that an observer would no longer be able to distinguish individual lines in an ideal situation. In known technical solutions, when a single two-axis microscanner is used as the microscanner system, the vibration frequency usually corresponds to the corresponding resonant frequency, i.e. the natural frequency, of the suspended mirror (the vibrating system) relative to the corresponding vibration axis, since in this operating mode, known as "double resonance", the maximum deflection and therefore the maximum illumination or image area can be achieved.

[0088] However, if the drive frequency is made consistent with the resonant frequency by adjusting the corresponding phase of the vibration using a phase adjustment loop to maintain stable resonance, especially double resonance operation, the projection trajectory will change continuously over time, because in most applications the resonant frequency of the system may change over time, especially under the influence of temperature. Even very small deviations in one or the other axis with respect to frequency or phase may have a huge impact on the trajectory, as shown in the exemplary trajectory generated by simulation in FIG1A . Here, the line corresponds to the path of the laser spot on the rectangular projection surface to be illuminated, which is perpendicular to the imaging optical axis. The calculated time periods are (1 / 60) s, i.e., about 16.66 ms (which corresponds exactly to one image (frame) to be projected at a conventional image repetition rate of 60 Hz).

[0089] FIG. 1A(a) shows a first example of a trajectory 100 calculated based on the vibration frequencies or drive frequencies f1 and f2 (f1=26314 Hz and f2=557 Hz) of two orthogonal vibration axes. On the other hand, in the second example shown in FIG. 1A(b), the vibration frequencies or drive frequencies are f1=26314 Hz and f2=557.1 Hz, i.e., the frequency f2 of the second axis is adjusted by 0.1 Hz compared to the first example. The dimensions of the Lissajous figure on the projection surface or on it corresponding to these two axes are marked with the underlying pixel grid. For this purpose, a typical resolution of 1920×1080 pixels should be used, i.e., 1920 pixels for the horizontal first axis with frequency f1 and 1080 pixels for the horizontal second axis with frequency f2.

[0090] In order to more clearly show the difference between the two tracks in FIG. 1A in the following discussion, an enlarged view of the middle portion of each track in FIG. 1A is shown in FIG. 1B . Here, it can be clearly seen that a shift of only 0.01 Hz in the drive frequency of the second axis will have a significant impact on the line density. Although the track in FIG. 1B(b) is not uniform, it at least covers almost the entire image area, while the left track in FIG. 1B(a) is obviously extremely unfavorable for image projection because it does not cover a large number of entire rows of pixels at all.

[0091] As mentioned above, if the drive frequencies of the two axes always follow their own changing resonant frequencies, regardless of the other axis, the projected Lissajous locus is not constant in time, but varies according to the current resonant frequency, which may be particularly temperature-dependent. For example, a 0.1 Hz adjustment of the second axis described above may result in such a shift in the resonant frequency of the axis. Thus, over time, due to the time-dependent change of the resonant frequency of one or both axes, almost arbitrary trajectories may occur, including those exemplarily shown in FIG. 1B (a), where individual lines become very apparent to the observer and the projected image is mostly unilluminated.

[0092] Therefore, the time variation curve of this Lissajous locus is somewhat random, because it depends on the time variation ratio of the resonant frequencies of the two axes. ), and the line density may therefore be subject to strong fluctuations over time, which can sometimes also be perceived by the observer with the naked eye.

[0093] The Lissajous loci can be described mathematically, that is, the vibration frequency f1 or f2 of the two axes is expressed as an integer factor n1 or n2 and the repetition rate f of the loci, respectively. res (Trajectory repetition rate):

[0094] f1=n1·f res Or f2=n2·f res (1)

[0095] If the vibration frequency is solved in this way, and the two integer factors n1 and n2 are relatively prime, then a stable trajectory will be formed that moves at time T res (duration of the phase period) will then be exactly reproduced

[0096]

[0097] Therefore, in each cycle T res However, from a purely mathematical point of view, not all possible pairs of vibration frequencies can be represented in this way, but only those pairs of frequencies whose ratio is a rational number, namely:

[0098] f1 / f2=n1 / n2 (3)

[0099] The other frequency pairs are connected to the nearest frequency by means of the corresponding difference frequencies Δf about one and / or the other axis. The frequency of the stable trajectory is different. These trajectories that deviate from the stable trajectory leave such an optical impression that they initially approximately imitate the trajectory of the closest stable situation, but then move ("wander") at a certain speed according to Δf. Therefore, depending on the value of Δf, the trajectory will be more or less strongly offset in its m-th trajectory segment generated in any m-th phase cycle relative to the (m+1)-th trajectory segment generated during the immediately following (m+1)-th phase cycle.

[0100] In this context, Figures 1A and 1B can be interpreted as follows: Case (a) forms a trajectory where the two vibration frequencies are very close to each other with a high repetition rate f res , so each trajectory runs almost identically to the previous one, and the individual lines (as seen in Figure 1B(a)) almost overlap. Therefore, such a trajectory ignores most of the pixels. In contrast, case (b) produces a trajectory with stronger "wandering" over time between images, where a more uniform illumination is achieved within the observation time of about 16.6 ms (which corresponds to one phase cycle and here also to the duration of a single image), which may however also change towards unfavorable illumination conditions in subsequent time periods or images.

[0101] In conventional technical solutions, if the image repetition rate (Bildwiederholrate) is different from the trajectory repetition rate f res , there will be another problem. Now refer to FIG. 1C to explain this situation, where an image material with an image repetition rate of 60 Hz is taken as an example.

[0102] FIG. 1C shows, with its sub-figures (a) and (b), two segments of a stable Lissajous trajectory (a complete phase cycle) in a manner corresponding to FIG. 1B , whose duration corresponds to the time period of three consecutive images (frames) of the image material. The three frames 1, 2 or 3 are shown with different line types. In the case of FIG. 1C (a), as a result of the phase adjustment of the respective axis, the drive frequencies corresponding to the resonance frequency are: f1=26314 Hz and f2=557.5 Hz, from which it can be derived from the above relation (1) that the trajectory repetition rate is f res =111.5Hz, where n1=256 and n2=5. In the case of FIG1C(b), the resonant frequency or driving frequency is f1=26314.753Hz and f2=557.194Hz, respectively. The resulting trajectory repetition rate is significantly lower than that of FIG1C(a), which is f res=25.327Hz, where n1=1039 and n2=22, n1 and n2 are relatively prime.

[0103] In the case of FIG. 1C (a), the trajectory misses the main image content due to its high repetition rate within its complete phase period, so that only a part of the first frame is shown in the projection during the observation time, while neither the second frame nor the third frame is shown. In the opposite case of FIG. 1C (b), the trajectory repetition rate is very low, so that even some rows are not sampled at all within the duration of a frame (e.g., frame 1). Thus, for example, the row shown at the bottom is only reached from the second frame (frame 2).

[0104] For this reason, currently known solutions focusing on solving the problem of trajectory density are mostly aimed at projecting stable Lissajous trajectories whose trajectory repetition rate is roughly equivalent to the image repetition rate of the image material to be projected. This only allows a trajectory repetition rate f res has a relatively small range and the range of the driving frequency pairs is also strongly restricted. Furthermore, since a stable trajectory necessarily always misses the same image content, even in this seemingly ideal case, i.e., the trajectory is repeated at approximately the frame rate of the image material, image content may still appear to the observer as being clearly not illuminated, if the resonant frequency of the microscanner system is not set high enough during manufacturing so that the generated trajectory covers all pixels within one phase period.

[0105] Reference now Figure 2 An exemplary embodiment 200 of a method for trajectory control of a microscanner system having a two-axis microscanner according to the present invention is described. The method 200 is described starting from the static state of the microscanner. Therefore, the microscanner is first started, thereby generating an oscillation process ("oscillation") in which the amplitude gradually increases to a maximum value.

[0106] Here, the oscillating movement of the vibrating part of the microscanner, in particular the deflection element (mirror) including its suspension, is driven by a suitable drive device, which can in particular have one or more piezoelectric actuators, and as a result of the oscillation, a first oscillation axis and a second oscillation axis orthogonal thereto are caused to vibrate biaxially and resonantly (biaxialedoppeltresonante Schwingung) of the deflection element. That is, the microscanner is operated during the oscillation so that the microscanner vibrates at the respective current resonant frequency with respect to each of the two axes at least at the end of the oscillation process. This can be done in particular for each axis by conventional phase adjustment (without the addition of additional trajectory adjustment), which will be referred to later. Fig. 9 and Fig.10When a laser beam is directed onto a vibrating deflection element and reflected there to form a projection, a closed, stable track is formed in the observation field. Figure 4 A simple example of such a stable trajectory is shown in image 401 in FIG.

[0107] During the start-up, or when the start-up process has ended and a stable trajectory already exists, at least one physical variable G is measured in step 210, which physical variable has a dependency on the current resonance frequency of the microscanner about the two axes at this time. This dependency can be in particular such that (i) the physical variable G depends on the resonance frequency, (ii) conversely, the resonance frequency depends on the physical variable G, or (iii) there is a mutual dependency. Ideally, the dependency corresponds to a mathematical function. It is important that the resonance frequency can be inferred from the measured G value. In the case of measuring multiple physical variables (the number is n), these physical variables can be measured in particular as a set of values ​​or vectors {G1, ..., G n} form a multidimensional parameter G.

[0108] In step 215, a frequency pair for the drive frequency of the two axes in the subsequent time period can now be determined according to a predetermined selection rule as a function of G. This can be done, for example, by selection from a discrete set of frequency pairs stored, for example, in a memory device, or such a frequency pair can also be determined, in particular calculated, directly in the method sequence according to a selection rule, which in this case can in particular include a corresponding calculation rule.

[0109] Reference now Figure 3 Step 215 is explained more clearly. Here, each selection rule according to step 215 is explained by way of example based on three value tables (Wertetabellen), which are stored as explained above or can be implemented according to calculation rules. In this example, for Figure 3 In the first two tables (a) and (b), the temperature of the microscanner is used as a scalar physical variable G, which can be determined in particular contactlessly, for example by infrared measurement or by an NTC measuring element in or on the microscanner. Each table assigns each value of G to a corresponding frequency pair {f1; f2}. To illustrate this, one row in each table is shown in a different color. That is, if the temperature resulting from the value of the variable G is, for example, -7°C, then according to Figure 3 The selection rule of (a) selects the frequency pair {f1; f2} = {20000.3 Hz; 10000.7 Hz}. In this example, the closest achievable resonant frequency of the microscanner, at least in theory, is: 0,1 =20,000Hz, second axis f 0,2= 10,000 Hz, thus always ensuring that the frequency pair {f1; f2} obtained in the table is consistent with the frequency pair {f 0,1 ;f 0,2} One of the two vibration frequencies or axes is different (i.e., f1≠f 0,1 and / or f2≠f 0,2 ).

[0110] exist Figure 3 (b) shows the same selection rule again, but in a different form, which is particularly suitable for the selected frequency pairs and the frequency pair {f 0,1 ;f 0,2} in the presence of an expected systematic deviation. Instead of directly giving the frequency value of the selected frequency pair, here it is given by relative to the frequency pair {f 0,1 ;f 0,2} to indirectly give the frequency value. Therefore, from Figure 3 The frequency deviation obtained from the table in (b) is Δf1 = +0.3 Hz or Δf2 = +0.7 Hz. Therefore, at the resonant frequency {f 0,1 ;f 0,2} are known, these two representations are equivalent, they both define the same selection rule, and therefore each selection process also defines the corresponding selected frequency pair {f1; f2}.

[0111] exist Figure 3 (c) describes the situation where instead of measuring a single physical parameter, a set of multiple different physical parameters is measured, and the set of parameters G = {G1, ..., G n} Determine the frequency pair to be selected. That is, here, if the measured parameter group G falls into the range defined by the parameters G1,…,G n In the spatial region corresponding to a certain frequency pair in the multidimensional (mathematical) space (if G is regarded as a vector, the space can be regarded as an n-dimensional vector space), the frequency pair is selected here. In addition or in addition to the temperature, such physical variables can be, in particular, mechanical stress or strain of the microscanner, amplitude or phase instability occurring in at least one oscillation, etc. In addition or as an alternative, in particular, one or more of the following variables can also be used: a control variable that exceeds the trajectory regulation according to the method; a phase difference between a drive signal for controlling a drive device and a measurement signal characterizing the measured deflection of the deflection element; a shift in the resonance frequency of each corresponding axis; a change in the power of the incident electromagnetic beam, which the deflection element receives by absorption; a change in the amplitude, frequency or phase of a reference oscillator for the vibration of the deflection element.

[0112] Considering that in the framework of trajectory regulation of this method, in addition to frequency regulation, amplitude regulation may also be possible, Figure 3 In the three tables of , in addition to the discrete set M of corresponding frequency pairs, there are also sets of corresponding discrete amplitude pairs {V1; V2} or {ΔV1; ΔV2}, which are in the form of voltage amplitudes for controlling the drive, expressed as amplitude values ​​or amplitude deviation values ​​with respect to a reference amplitude, which can correspond in particular to the amplitude in the case of double resonance. As well as frequency pairs, amplitude pairs are also possible, or overall mixed forms are also possible, in which, within the framework of the selection rule, on the one hand, absolute frequency values ​​or amplitude values ​​are determined, and on the other hand, corresponding deviation values ​​with respect to the corresponding reference values ​​are determined.

[0113] Now refer to Figure 2 , after step 215, the next step 220 is followed, in which it is checked whether the frequency pair selected according to step 215 is consistent with the frequency pair currently in effect, that is, whether a frequency adjustment is not required or has already been performed. If the two frequency pairs are consistent (220-yes), the method branches back to step 210 for a new round. Otherwise (220-no), in step 225, the drive frequency of the drive device of the microscanner is changed to the new frequency pair selected in step 215 and, if necessary, a new amplitude pair, which specifies a corresponding increase or decrease in amplitude (= negative increase in amplitude). This change has the same meaning as the beginning of a new time period, because the term "time period" here coincides with a specific frequency pair or a time period between two consecutive frequency pair changes, during which this specific frequency pair is used to drive the microscanner.

[0114] Then, the process branches back to step 210 for the next round. Steps 210 to 225 represent, in addition to any pure phase control, a trajectory control 230 by means of which the microscanner or the beam deflection system based thereon is adjusted as a function of at least one physical variable G and thus as a function of the time curve of the current resonance frequency (see Figure 8 ) The direction of the tracks generated during the operation of the spectral imager. In particular, by appropriately determining the frequency pairs and the selection rule, a track density regulation can be achieved, which can provide a substantially uniform illumination of the observation field and thus provide a high-quality image projected into the observation field.

[0115] Figure 4 shows that in use especially according to Figure 2 4. An exemplary sequence 400 of trajectory segments 401 to 409 that can be generated when using the trajectory control method of FIG. 4, each trajectory segment corresponds to a complete phase cycle of the trajectory. In another image 410, a control trajectory formed by connecting the trajectory segments 401 to 409 to each other is shown. Figure 4All the diagrams in the figure are obtained by Lissajous projection of the microscanner onto the projection surface in the field to be illuminated (see Figure 8 ). The following will refer to Figure 2 The illustrated embodiment 200 of the method is provided for better illustration, but is not intended to be limiting.

[0116] The image 401 shows a stable trajectory, such as may be obtained in particular at the end of a start-up process according to step 205 of the method 200. Such a Lissajous trajectory is obtained, for example, by a mirror at the (current) resonance frequency f 0,1 =10kHz and f 0,2 = 20kHz for projection. The basic parameters of this trajectory can be calculated based on the known Lissajous trajectory vibration equation.

[0117] x1(t)=sin(2πn1f res t) (4a)

[0118] x2(t)=sin(2πn2·tf res ) (4b)

[0119] Get and calculate as follows:

[0120]

[0121] The parameters n1 and n2 basically describe the nodes, and thus the line density and frequency f of the trajectory res , or better yet: its reciprocal The duration (phase period) during which the path of the trajectory is completely traversed once. The resonant frequency ratio is f 0,1 :f 0,2 = n1:n2 = 1:2, will permanently project the stable trajectory shown in image 401 as long as the driving frequency pair {f1; f2} accurately satisfies this ratio and the resonant frequency remains constant over time.

[0122] However, if the resonant frequency adjusts over time, for example due to temperature changes of the microscanner, then according to the currently valid selection rule, the frequency adjustment 230 can now select another frequency pair {f1; f2} from the discrete set M (see Figure 3 ) is defined as the driving frequency of the driving device driving the micro scanner to replace the original frequency pair that is consistent with the initial resonant frequency value. According to the definition of set M, the new frequency pair has at least one of its two frequencies deviating from the current resonant frequency, that is, it satisfies: f1≠f 0,1 and / or f2≠f 0,2 .

[0123] The stable trajectory shown in image 401 obviously does not illuminate most of the image, so it is necessary to improve it by frequency shifting n1 and n2 to: when projecting a digital two-dimensional image, it can be in the same changing time period T′ res Ideally, T′ res should be less than the duration of the image display, so for common video formats less than about or However, this is often difficult to achieve in practice, so that the resulting trajectory usually has a significantly longer cycle time but still reaches as many pixels as possible in each sub-image and does not miss the same pixels in consecutive images, thereby creating the impression of an at least largely uniformly illuminated projected image after multiple phase cycles.

[0124] Accordingly, in Figure 4 , images 402 to 409 show eight consecutive, each complete, phase cycles for a new "offset" frequency pair {f1; f2}, which is shifted from {f 0,1 ;f 0,2}, and the second axis driving frequency is constant (Δf2 = 0 Hz), and is defined by the frequency deviation Δf1 = 312.5 Hz. Thus, using the newly obtained driving frequency f1 = 10,312.5 Hz, we obtain Figure 4 Images 402 to 409 in FIG.

[0125] The trajectory is no longer stable, but changes from one phase cycle to another, so that the trajectory changes its shape as a whole during the observation period and thus appears to wander, thereby increasing the trajectory density (line density). Here, the frequency pair {f1; f2} is defined so that the trajectory will specifically reach the image area that was not reached in the previous pass in each of its next passes. Over the entire observation period corresponding to images 401 to 490, a trajectory course as shown in image 410 is formed, which provides a nearly uniform illumination of the rectangular projection surface in the observation field, thereby providing a satisfactory image quality when the trajectory repetition rate is so high as to be unable to distinguish the individual images by the observer as described above.

[0126] That is, the track is "pushed" into the previously omitted area, so that the newly formed track is significantly more suitable for image projection. The optimal frequency deviation, which determines the extent of the track shift, obviously depends on the proportion of the area that was omitted in the initial track. In principle, the frequency change can be carried out separately in both axes or also in both axes simultaneously.

[0127] Figure 4The example just shown in is characterized by a very high frequency deviation of Δf1 = 312.5 Hz. This causes the drive frequency to deviate far from the resonant frequency of the axis, which, especially in the case of mirrors with a high quality factor (Q factor), would no longer make it possible to project an image, since the amplitude of the axis would drop significantly or even collapse completely. The frequency deviation must therefore be sized so as to maximize the track density or (here equivalent) line density on the one hand, while not allowing an unacceptable reduction in the range or size of the projected image, in particular without changing the position of the pixels, on the other hand. In individual cases, however, depending on the specific application, a certain reduction in the image range may be acceptable, in particular if only a local image (in the sense of a "region of interest") is required.

[0128] However, if a certain image expansion is required or must be observed, then within the framework of trajectory regulation (see Figure 2 , trajectory adjustment 230), the maximum frequency deviation will be determined in the following way: the resulting (alone) reduction in expansion can be compensated by the amplitude adjustment (especially the amplitude gain) that reacts thereto.

[0129] Will Figure 4 Compared with the above example in the other example, in which the selected frequency deviation is only Δf1=1 Hz, it is relatively easy to achieve this requirement, especially by compensating amplitude adjustment. However, the trajectory deviation from phase cycle to phase cycle will be much smaller, so that for the observer, each consecutive phase cycle (with an initial cycle duration T res =0.1ms) can no longer be distinguished by the naked eye.

[0130] So, for this example, Figure 5 As shown, it is more intuitive to image the trajectory 500 in discrete time periods that roughly match human perception and common image repetition rates. exist Figure 5 The illustrations 501 to 503 of the image area to be illuminated show corresponding trajectory segments occurring in three such consecutive time periods.

[0131] Here we can see a phenomenon that can often be noticed in practice. It is rare that a long-term stable trajectory appears there, as in image 401. Instead, the observer has the visual impression that such a trajectory is gradually rotating. Therefore, the frequency deviation is preferably selected so that the human observer with the naked eye cannot perceive the trajectory as such, neither as completely static nor as movable. This trajectory 500 is also characterized in that it is clear that it can only display the entire image area and therefore all pixels in the case of a two-dimensional digital image after a plurality of the above-mentioned time periods have passed.

[0132] Although the resonant frequency given here is f 0,1 =10kHz and f 0,2 =20kHz shows an unfavorable initial condition, but with sufficient offset in both axes, a situation can still be established where the typical requirements for illumination uniformity and maintaining illumination range are met well, or at least come close to them, depending on the degree of the requirements. With Δf1=3.92Hz and Δf2=-1.92Hz, in three consecutive, each duration In the time period of Figure 6 The three trajectory segments shown in the diagram 601 to 603 of the rectangular image area to be illuminated together complete the substantially complete illumination of the image area 600. Thus, at least in the case of digital images, after three consecutive time periods, all pixels have been reached, wherein after two intervals almost all pixels have been displayed, i.e. projected, and thus a projection situation favorable to the resonance frequencies exists.

[0133] A) In order to determine a set of suitable frequency pairs from the discrete set M, the first embodiment can be suitably adopted, that is, starting from the maximum line spacing between adjacent trajectory lines, to determine the set of frequency pairs.

[0134] This embodiment can be particularly advantageously used in combination with Lissajous projection when the frequency pairs are determined such that the repetition rate of the trajectories to which they correspond is (particularly significantly) lower than the image repetition rate of the image material to be projected (e.g. a video). For example, in the case of an image repetition rate of 30 Hz, the frequency pairs can be determined such that the repetition rate of the trajectories to which they correspond is in the range of 5 Hz to 15 Hz. For such trajectories, it can be pre-established that they will be from image to image, i.e. changes during the observation time.

[0135] The line spacing between adjacent trajectory segments of the Lissajous figure is greater in the center of the Lissajous figure than at its edges in the cross section. Similarly, the maximum line spacing d max Usually appears at or near the center of the Lissajous figure. max There is the following relationship, where the subscript "1" represents the distance associated with the image range caused by the first vibration axis, and the subscript "2" represents the distance associated with the image range caused by the second vibration axis:

[0136]

[0137]

[0138] That is, if the maximum line spacing d is predetermined 1,max and d 2,max, the target values ​​of the factors n1 and n2, which are already known from the relation (1), can be determined from these spacings. For example, in the case of a full HD resolution with 1920 pixels in the horizontal image direction and 1080 pixels in the vertical image direction, it can be specified that the maximum line spacing in each direction corresponds to one pixel. If the image height and image width are normalized to the value 1, it can be obtained that:

[0139] and

[0140] Then, according to equations (6a) and (6b), the lower thresholds of n1 and n2 can be obtained, which are natural numbers:

[0141] n x ≥1696 and n y ≥3016. (8)

[0142] Now, given that these thresholds are met, value pairs (n1; n2) can be identified that simultaneously meet the criterion of n1 and n2 being mutually prime. Preferably, a set of discrete, restricted and finite value pairs (n1; n2) is searched and determined in this way, or according to the relationships (1) and (3) for the corresponding frequency pairs (f1; f2), which are as close as possible to the thresholds of the relationship (8), because otherwise the track transit time becomes very large and, in particular, approaches or even exceeds the image repetition rate.

[0143] In particular, for microscanner systems that at least approximately provide a raster scan structure for the projection trajectory, it has been observed that only d 2,max criterion (6b), since the traces run approximately horizontally and can still reach all pixels. Now at a resonant frequency of approximately f 0,1 =18418Hz, f 0,2 =631Hz micro-scanner system is used as an example.

[0144] If the fast axis resonant frequency f is 0,1 Dividing by the above factor 1696, we get approximately f res = 10.86 Hz. Now, according to the method described previously, frequency pairs (f1; f2) can be determined for the set M, which form a repetition rate f as close as possible to the trajectory. res The trajectory repetition rate satisfies the coprime property of the two factors n1 and n2, and the trajectory repetition rate f res On both axes, approximately at the above resonant frequency f 0,1 or 0,2In these trajectories, although the image is constructed more frequently depending on the choice of the frequency pair (f1; f2) than with a trajectory repetition rate of f res The "ideal" trajectory of is slower, or no longer reaches every pixel, but a good approximation to the ideal trajectory can be obtained.

[0145] B) To determine a set of suitable frequency pairs for the discrete set M, a second embodiment may be suitably employed, wherein one or more potential resonant frequency pairs {f 0,1 ,f 0,2}, using their own perfectly stable and therefore closed trajectories (see Figure 4 The corresponding correlation trajectory repetition rate f in the image 401) res , determine one or more relatively cheap frequency pairs to be determined in the set M according to the following relationship:

[0146] f1=f0,1+Δf1, where

[0147] f2=f0,2+Δf2, where in, And |nΔ|>0, preferably |nΔ|>1; n1, n2≥1, are integers and are mutually prime, satisfying the following relationship:

[0148] f0,1=n1·f res and f0,2=n2·f res . (6)

[0149] It should be noted here that the frequency deviations Δf1 and Δf2 in the relationships (5a) and (5b) are identical to the frequency deviations Δf1 and Δf2 in the relationships (5a) and (5b) which are based on theoretical assumptions and are relative to the corresponding resonant frequency pairs {f 0,1 ,f 0,2}, while the actual existing resonant frequency may deviate from it. Therefore, the frequency deviations Δf1 and Δf2 in the relations (5a) and (5b) must be distinguished from the difference frequencies between the corresponding drive frequencies that occur during the actual operation of the microscanner according to the method and the corresponding actual existing current resonant frequencies about each axis.

[0150] n Δ The higher the value of , and therefore the smaller the value of Δf1 or Δf2, the smaller the trajectory shift from phase cycle to phase cycle, and thus for those trajectories that already have a very high line density, a small shift is sufficient to fill in the current phase cycle at least to a large extent the image parts that were missed in the previous phase cycle. Thus, such a discrete set M can be obtained by selecting different n with the corresponding trajectories corresponding to its frequency pairs. Δ The values ​​of these nΔ is suitable for forming such a trajectory: it will continuously slide to the initial assumed double resonance trajectory relative to the corresponding frequency pair {f 0,1 ,f 0,2} in the image area that is omitted.

[0151] The same applies to the tracks formed at the actual resonant frequency. In a sense, if the tracks are moved towards those that are a priori guaranteed to continuously slide to the image areas that were not reached before within a predetermined period of time, then the tracks formed at the current resonant frequency are automatically guaranteed to slide to the image parts that they missed. However, the proposed method is only one possible way to ensure that this is achieved.

[0152] By cleverly constructing the set M and thereby forming the desired trajectory, it can be ensured that the frequency pairs of the set M and their corresponding trajectories satisfy the above conditions and substantially do not deviate significantly from the resonant frequency, thereby producing a stable image. Therefore, it is particularly advantageous not only to construct the desired trajectory according to the relations (5a), (5b) and (6), but also to determine a trajectory spectrum that is as wide as possible for the trajectory that can be continuously slid into the initially omitted image region.

[0153] Parameter n Δ The value of can be specifically chosen to satisfy |n Δ |∈{2,3,4,…}, where smaller values ​​are preferred. Figure 7 The special case shown in Δ = 2, in each phase cycle, pixels that were not reached in the previous phase cycle tend to be reached, as shown in the illumination 700 of the image area. If the corresponding trajectory segments of two adjacent phase cycles are observed, it can be seen that the lines of the second phase cycle are located between the lines of the first phase cycle.

[0154] From this, two frequency pairs can be determined as described in detail below, Figure 7 The example of (A) is f1=26314.5806 Hz and f2=557.2761 Hz, Figure 7 (b) is an example of a frequency pair of f1 = 26314.2620 Hz and f2 = 558.6104 Hz, which are in phase cycle time T res Or the corresponding trajectory repetition rates have good comparability and are close to the trajectories shown in Figures 1A to 1C. Figure 7 The trace in (a) is based on a trace repetition rate f of approximately 111 Hz. res ,and Figure 7The traces in (b) are based on a trace repetition rate of approximately 29 Hz. They were also studied at a repetition rate of 60 Hz at the frame rate of the underlying image material.

[0155] Depend on Figure 7 It can be directly seen that the continuous shifting of the trajectory over time ensures that the image from one frame to the next actually tends to reach the previously omitted image part. In the time period of the three images displayed respectively, there are no longer any large image contents that are not reached. The trajectory direction is here controlled by the special selection n Δ =2 is determined as follows: the trajectory formed after frequency adjustment within the framework of trajectory adjustment 230 is different from the initial trajectory of Figure 1A(a) or Figure 1B(a), and the lines of the second phase period tend to be located exactly between the lines of the first phase period, while the lines of the third phase period are located between the lines of the second phase period.

[0156] exist Figure 7 In the example of (a), the trajectory repetition rate is set to f res =111,50246 Hz. From this we get f1=236·111,5025 Hz=26314,5806 Hz and f2=5·111,5025 Hz=557,5123 Hz. If this frequency pair is selected as the driving frequency pair, an (undesirable) image of a stable trajectory is obtained, in which, Figure 7 The different highlighted lines in (a) would overlap as in FIG1C(a). Instead, the frequency f2 is corrected by a frequency deviation This results in the actual driving frequency f2 = (557,5123-0,2362) Hz = 557,2761 Hz, which gives Figure 7 Here, for achieving the optimized trajectory, whether adding or subtracting Δf2 according to different variations, or adding or subtracting f1 instead of or in addition to f1 It's all irrelevant.

[0157] exist Figure 7 In another example of (b), assume that the repetition rate of the trajectory is f res =29.40141Hz. From this, we get f1 = 895·29.40141Hz = 26314.2620Hz and f2 = 5·29.40141Hz = 558.6268Hz. If we now correct the frequency f2 by a frequency deviation Then the optimized driving frequency f2 = (558.6268-0.0164) Hz = 558.6104 Hz is obtained. Figure 7Here, according to different variations, it is also possible to selectively add or subtract Δf2 to f2, and / or add or subtract Δf2 to f1.

[0158] like Figure 7 The use of trajectory repetition rates of approximately 111 Hz and approximately 29 Hz, as used or shown in (a) and (b), results in a relatively high line density, so that ultimately the range of values ​​available for the drive frequency on both axes can be significantly increased compared to projection using a stable trajectory. The simulation results confirm the above impression: the illumination calculated as a percentage (i.e., the ratio of the number of pixels involved to the number of all pixels in the image at a given resolution in the case of a digital image) is approximately the same within a given time period of, for example, 1 / 30 s. As a result, not only a significantly higher flexibility is obtained, but also a more uniformly illuminated image compared to conventional methods due to this continuous trajectory offset.

[0159] By using the first and / or second embodiment described above to determine a set of frequency pairs of the discrete set M, the phase control loop can be well combined with the trajectory control, in particular the line density control. In particular, it is possible to avoid the requirement of line density control from placing too strong a restriction on the phase control or making it infeasible. That is, compared to the conventional pure phase control of the drive signal, it is no longer just about resonating the two vibration axes of the microscanner independently of each other, but rather adjusting the entire system so that the Lissajous trajectories all meet the described requirements to a sufficient extent, in particular approximately the same. It can also be stated as follows: that is, the phase control with respect to the two axes is discretized according to the scheme described by line density control, i.e. with the goal of maximum illumination.

[0160] The change between frequency pairs (ie between time periods that are respectively associated within the context of trajectory control) is ideally performed when the trajectory is in the outer image region, since there is generally a higher trajectory line density there (see FIG. 1A ), and changes in the trajectory shape are generally not visible to the observer.

[0161] If the resulting drive frequency deviates in frequency from the actual current resonant frequency to such an extent that an image of constant size can no longer be displayed due to the resulting reduction in amplitude, it is possible either to supplement the amplitude control loop by supplying the system with more or less energy accordingly (e.g. by adjusting the drive voltage), or to adjust the resonators of one or both axes, e.g. by targeted temperature changes, so that the resonant frequency again corresponds to the selected drive frequency.

[0162] Furthermore, a trajectory with a relatively low trajectory repetition rate, but not too low below 30 Hz, can be used so that the trajectory is closed only after passing through a small number of visible sub-images and at an image repetition rate of 30 Hz, each pass does not cover a complete image frame. Figure 6 The example shown is formed according to this scheme. Figure 4 By moving the initial track in the image 401 in the direction of the track, it is ensured that the initial track moves to the image portion previously missed by it.

[0163] In summary, the aim is to ensure that Lissajous trajectories which miss image parts in a certain observation period are precisely slid into these areas in a targeted manner in the next observation period. This is achieved in that in principle only trajectories which are precisely known in advance are permitted in the sense of a permission list defined by the set M, in particular for observation periods which are generally guided by human perception and the image repetition rates of common video formats.

[0164] Figure 8 Schematically shown is a beam deflection system 800 according to an exemplary embodiment of the invention, which can be used in particular for projecting images or image sequences (e.g. moving images, videos, etc.). The beam deflection system 800 has a radiation source 805, which can be in particular a laser source, wherein the wavelength of the emitted beam L1 can be in particular in the visible spectral range, although other spectral ranges can also be used depending on the application, for example within the framework of a material inspection method. Unless otherwise stated, it will be assumed hereinafter by way of example that the beam L1 is emitted as a laser beam in the visible spectral range.

[0165] The laser beam L1 is directed toward a microscanner having a deflection element 810 in the form of a mirror plate, which is suspended on a surrounding frame 820 via two crossed spring pairs 815, each of which defines an oscillation axis. At the deflection element 810, the beam L1 is reflected (mirrored) in the sense of optical imaging and directed as a reflected beam L2 toward a projection surface 840 in the field of view of the microscanner.

[0166] The beam deflection system 800 also has a control device 825, which is designed to provide at least one modulation signal to the radiation source, according to which the laser beam is modulated. The modulation can particularly relate to its temporal or spatial intensity distribution. However, depending on the type of radiation source, other types of modulation are also conceivable, in particular a modulation of the wavelength (e.g. color) or wavelength distribution of the beam emitted by the radiation source 805. When projecting an image, the modulation is correspondingly carried out according to the instantaneous deflection direction, so that a corresponding image point with a corresponding pixel value of the corresponding image point of the image to be displayed is generated on the projection surface by the modulation. .

[0167] The control device 825 is also designed to control the drive device of the micro scanner so as to Figure 2 The method causes the deflection element 810 of the microscanner to oscillate simultaneously around its two vibration axes, so that the light spot or radiation spot generated by the reflected beam L2 on the projection surface 840 passes through a trajectory or path in the form of a Lissajous figure 835 adjusted by the trajectory, which trajectory or path completely illuminates the area on the projection surface set as the image surface within a short observation time period. In the case of projecting a digital image composed of pixels, this means that all pixels are reached or displayed by the trajectory within the observation time period. The drive device can in particular have at least one actuator, in particular a piezoelectric actuator 830. In Figure 8 In the embodiment, two piezoelectric actuators 830 are exemplarily shown installed on each spring 815 of each spring pair according to a possible implementation. Other piezoelectric actuators 830 of this type can also be respectively arranged on two other springs 815.

[0168] The control device 825 provides a phase adjustment loop for each vibration axis, which is used to stabilize the phase difference between the phase of the first or second oscillation corresponding to the vibration axis and the corresponding control signal output by the phase adjustment loop for the drive device with respect to the vibration axis. In addition, the device has a frequency adjustment device for the phase adjustment loop, so that for the corresponding time period, by adjusting the frequency of the control signal for the vibration axis, the vibration frequency is adjusted according to the time period according to the control signal. Figure 2 The frequency error determined by the method shown (or by another embodiment of the method according to the invention) is adjusted.

[0169] In order to carry out the method, the control device 825 may in particular have a data processing device 825a and a storage device 825b, the data processing device having one or more processors. In the storage device 825b, in particular, a computer program may be stored, which is configured to cause the control device to carry out the method when it is run on the data processing device or at least one of its processors. In particular, the frequency adjustment device may be implemented completely or partially in the form of software. In addition, the storage device may also be used to store the preset frequency pairs of the set M and, if necessary, the associated amplitude pairs (see Figure 3 ).

[0170] However, the beam deflection system 800 can also be operated in reverse in order to sample the beam emitted or reflected by the object to be observed via a Lissajous figure and thereby reflect it on the correspondingly oscillating deflection element 810 and image it in the direction of the unit 805, where, in addition to or instead of the laser source, a sensor device, in particular an image sensor, can be provided in order to detect the beam by sensor technology.

[0171] Fig. 9An exemplary control device 900 for trajectory control of a microscanner is shown in the form of an exemplary circuit block diagram for generating control signals for a drive device of a Lissajous microscanner, but does not yet include trajectory control according to the present invention.

[0172] exist Fig. 9 In the block diagram, box 910 represents the actual control device, and various input signals (Input) are shown on the left side. Fig. 9 The three boxes arranged side by side at the bottom show, on the one hand, detailed views of boxes 912 and 917 in the superordinate box 910 , and, on the other hand, list output signals (Output) of the control device 900 at the bottom right.

[0173] The control device 900 has two control paths, namely, one for a first oscillation about a first oscillation axis A1 of the deflection element 810 and one for a second oscillation about a second oscillation axis A2 of the deflection element 810. Since the oscillation frequencies of the two oscillations are usually different, the first oscillation axis A1 is referred to here as the fast axis (FAST) and the second oscillation axis A2 as the slow axis (“SLOW”) without loss of generality. The same applies to the corresponding signals and oscillations.

[0174] First, the circuit part of the fast axis is discussed. For this purpose, the control device 900 has a bandpass filter 911 on the input side for filtering the input signal ADC_FAST. The input signal is a sensor signal or a derivative signal thereof, which characterizes the measured position, i.e. direction or deflection, such as the deflection angle, of the deflection element (micromirror) 810. Therefore, it describes the actual vibration process of the deflection element 810 about the fast axis A1 and can be a digital signal, in particular as described herein. By filtering with the bandpass filter 911, on the one hand, unwanted noise is removed, and on the other hand, the signal is limited to a band limit (Bandbegrenzung) within a defined frequency band range for subsequent signal processing.

[0175] Filtered signal ADC down The signal now enters the digital down-converter (DDC) 925 as input, which has a QAM block 912 (QAM = Quadrature Amplitude Modulation) and two down-samplers connected downstream, one of which is a down-sampler 913 for the real part Re and the other is a down-sampler 914 for the imaginary part Im, which each reduce the clock rate by a factor of 32. Fig. 9 The input signal ADC is shown in detail again in the lower left area. downThe real part Re and the imaginary part Im are obtained as the output signal of the QAM block 912 and as the input signal of the downsampler 913 or 914. In general, the DDC 925 converts the input signal ADC into the real part Re and the imaginary part Im. down The conversion into two sub-signals with lower frequencies and sampling rates is particularly advantageous in order to simplify the subsequent circuit stages. The two sub-signals, which represent the real part and the imaginary part respectively, together form a complex output signal which represents the actual course of the measured vibration of the deflection element 810 about the first fast vibration axis A1.

[0176] Now, based on the complex output signal of DDC 925, its phase is determined in block 915. On the other hand, the values ​​|x| are determined in block 916 and are fed to subsequent blocks 917, which are referred to here as "PLL", although they themselves are not PLLs (Phase-Locked-Loop or Phase Control Loop) in the conventional sense. Fig. 9 The lower middle part of FIG. 8 is shown in more detail. It mainly comprises a PI regulator 940 (proportional integral regulator) and a fixed phase (here set to 0°) oscillator 941 connected downstream, which is used to generate drive signals DRIVE-FAST and PHASE_FAST of a drive device (e.g. a piezoelectric drive) to drive the fast first oscillation of the deflection element 810. The oscillator is a so-called numerically controlled oscillator (NCO). In addition, in the signal path between the PI regulator 940 and the oscillator 941, the frequency NCO_FREQ of the output signal of the PI regulator 940 is intercepted as a frequency signal and fed back to the QAM block 912 in the loop as its other input signal, thereby forming a PLL (phase-locked loop, phase regulation loop) as a whole, wherein this fed-back frequency signal represents the frequency NCO_FREQ (and therefore also referred to as NCO_FREQ) as a control variable of the phase regulation loop PLL.

[0177] Each module or block of the circuit (eg PLL block 917) is connected to a clock signal (Clock-Signa) CLK100. The entire circuit is traversed once per (usually) rising edge, so that the output signal is also clocked accordingly.

[0178] If the reset signal RST is positive with a rising edge, ie, is 1 instead of 0, the reset signal RST resets the circuit with state-dependent output, thereby resetting the state of the block or all blocks.

[0179] When the microscanner is started, the vibration of the deflection element 810 is first approached to the resonant frequency "manually" (i.e., by determining visible vibrations with the naked eye, or by electronically detecting vibrations until a threshold amplitude is exceeded), wherein the frequency NCO_FREQ is also set accordingly without the aid of the regulation function of the regulator 940.

[0180] The control function of block 917 is then activated as a whole and thus the PLL or phase control loop is activated, in particular the phase is determined in block 915 as described above. The phase The phase position of the actual vibration process used as a control guide variable relative to the first vibration axis A1 is described, which is represented by the complex output signal of the DDC 925 and is related to the constant (reference) phase position 0° of the drive oscillator 941.

[0181] Leaving aside signal propagation time and similar distortions, phase (Compare here with the Bode diagram of the PT2 element) At the resonant frequency, it should ideally be exactly 90°. If not, the frequency (not the phase, as the phase is constant) of the drive oscillator 941 is increased or decreased in the right direction by the PI regulator until the target phase of 90° is reached.

[0182] The circuit parts for the slow axis A2 are in principle constructed in the same way and function accordingly. However, the difference is that, due to the lower vibration frequency of the slow axis, a lower frequency reduction (Heruntertaktung) is provided, so that the downsampler 920 only reduces the clock by a factor of two. The bandpass filter 918 can also be designed for a corresponding frequency band lower than the corresponding bandpass filter 911 for the fast axis, and the QAM block 919 and optionally the PLL block 924 can also be frequency-adjusted accordingly. Blocks 922 and 923 for determining the phase or value of the DDC output signal with respect to the slow axis can usually correspond to blocks 915 and 916 respectively without change, although frequency-related adjustments may also be considered here.

[0183] Fig.10 Shown based on Fig. 9 An exemplary block diagram 1000 of a circuit constructed to generate control signals for a drive device of a Lissajous microscanner having trajectory adjustment according to the present invention is shown.

[0184] Since the design and function of the corresponding circuit parts of the fast axis and the slow axis are also corresponding here, only the circuit parts of the fast axis (A1 or FAST) are discussed as an example below. Fig. 9 In the circuit of FIG. 1 , the input signal ADC_FAST is delivered to a bandpass filter 911 and then to a DDC block 925 having a QAM block 912 and two downsampling blocks 913 or 914 for the real or imaginary part. Then, following along the signal route are a block 915 for determining the phase and a block 916 for determining the value of the complex output signal of the DDC block 925.

[0185] Relative to Fig. 9 The downstream connected PLL block 1017 is modified to additionally receive the frequency correction control signal CORR_FREQ_FAST as an input signal. The signal CORR_FREQ_FAST is generated in an additional frequency correction block 1042, which is connected in Fig. 9 It is not present in , and is responsible for the control action according to the invention of circuit 1000 for controlling the drive of fast axis A1 .

[0186] The frequency correction block 1042 receives the frequency control signal NCO_FREQ_FAST intercepted from the PLL block 1017 as an input signal for the fast axis, and uses the signal to control the NCO of the PLL block 1017. The frequency control signal NCO_FREQ_FAST is converted into the adjustment frequency control signal CORR_FREQ_FAST in the frequency correction block 1042 as follows: that is, according to NCO_FREQ_FAST, for the adjustment frequencies for the fast axis A1 and the slow axis A2, a matching frequency pair is read from a memory, in particular a ROM, and the adjustment frequency control signal CORR_FREQ_FAST is generated so that it represents the adjustment frequency in the frequency pair designated for the fast axis A1.

[0187] This also happens for the slow axis, where the frequency control signal NCO_FREQ_SLOW is based on Figure 2 The method is converted in the frequency correction block 1042 into adjusting the frequency control signal CORR_FREQ_SLOW so that the read frequency pair is now represented by the signal pair (CORR_FREQ_FAST; CORR_FREQ_SLOW).

[0188] The adjustment frequency read from the ROM and represented by CORR_FREQ_FAST is supplied to the QAM block 912 as an input variable in the sense of a feedback loop modified by the frequency adjustment as described above. Since the deflection element 810 is driven with this corrected frequency, in order to correctly determine the phase in block 915 This frequency must be used beforehand for demodulation in the QAM block 912. However, this would theoretically result in a phase The deviation from the ideal value of 90° is due to the frequency CORR_FREQ_FAST always slightly deviating from the current resonance frequency of the fast axis A1 due to the frequency adjustment in block 1021 described above. However, this deviation is usually so small that it usually has no effect in practice. The adjustment frequency represented by CORR_FREQ_FAST is also fed to the PLL block 1017.

[0189] What has been said here about the fast axis also applies correspondingly to the slow axis. Overall, therefore, the drive frequencies NCO_FREQ_FAST and NCO_FREQ_SLOW for driving the deflection element 810 are discretized, wherein only preselected frequency pairs stored in advance in the ROM are allowed to be used, which are known in advance: compared with the case without frequency adjustment, a better, in particular more uniform, track density and thus better imaging results can be achieved. This applies in particular to longer observation periods, during which regular temperature changes or other influencing factors may have an impact on the resonance frequency.

[0190] Although at least one exemplary embodiment has been described above, it should be noted that a large number of variations thereof are possible. In this case, it should also be noted that the exemplary embodiments described are merely non-limiting examples and are not intended to limit the scope, applicability, or configuration of the apparatus and methods described herein. Instead, the foregoing description will provide guidance to those skilled in the art for implementing at least one exemplary embodiment, wherein it should be understood that various changes may be made in the operation and arrangement of the elements described in the exemplary embodiments without departing from the subject matter defined in the appended claims and their legal equivalents.

[0191] Reference numerals list

[0192] 100The trajectory in Figure 1

[0193] 200 Method for trajectory adjustment

[0194] 205-230 Steps or method steps of method 200

[0195] 400 Sequence of trajectory segments 401 to 409

[0196] 401-409 trace fragment

[0197] 500 Figure 5 The trajectory in

[0198] 600 Figure 6 Illumination of the image area in

[0199] 700 Figure 7 Illumination of the image area in

[0200] 800 beam deflection system

[0201] 801 Micro scanner system, especially a dual-axis micro scanner

[0202] 805 Radiation Source

[0203] 810 deflection element

[0204] 815 spring pair

[0205] 820 frame

[0206] 825 Control Device

[0207] 825a Data processing device

[0208] 825b storage device

[0209] 830 Piezoelectric Actuator

[0210] 835 Lissajous figure or Lissajous locus

[0211] 840 projection surface

[0212] 900 has no track adjustment controls

[0213] 910 box (controller)

[0214] 911 Bandpass Filter

[0215] 912 QAM Block

[0216] 913, 914 downsampler

[0217] 915 Block for determining phase

[0218] 916 Block 916 for determining the value of the complex output signal of the DDC block 925

[0219] 917 PLL Frame

[0220] 918 Bandpass Filter

[0221] 919 QAM Box

[0222] 920, 921 downsampler

[0223] 922Block for determining phase

[0224] 923 Block 916 for determining a value

[0225] 924 PLL Frame

[0226] 925 DDC Frame

[0227] 930, 933 Oscillator

[0228] 931, 932 mixer

[0229] 934, 935 low pass filter

[0230] 940 PI Regulator

[0231] 941 Drive Oscillator

[0232] 1000 Control device with trajectory adjustment

[0233] 1010 Box (Control)

[0234] 1017 PLL Block

[0235] 1024 PLL Block

[0236] 1042 Frequency correction block.

Claims

1. A method (200) for performing trajectory adjustment in a multi-axis micro-scanner system (801), wherein: The method (200) comprises: controlling (205, 225) a drive device for the microscanner system (801) so that a deflection element (810) of the microscanner system (801) is driven to a first rotational oscillation around a first vibration axis by means of an excitation having a first drive frequency, and simultaneously with the first oscillation, a second rotational oscillation around a second vibration axis orthogonal to the first vibration axis by means of an excitation having a second drive frequency, wherein the control is performed in a regulated manner in a plurality of consecutive time periods as follows: In a corresponding time period, for its corresponding duration, the first driving frequency and the second driving frequency are respectively stably maintained at a correspondingly set first target frequency or second target frequency, wherein the two target frequencies form a frequency pair corresponding to the time period, and the frequency pairs corresponding to at least two consecutive time periods are different from each other with respect to the first target frequency and / or the second target frequency; and For a corresponding time period, the value of at least one physical parameter is detected (210) according to the sensing technology, wherein the physical parameter is dependent on the corresponding resonant frequency with respect to at least one of the vibration axes, and according to a selection rule, a frequency pair corresponding to the time period is selected (215) from a discrete set of a plurality of pre-set different frequency pairs, so that with respect to the same vibration axis, the selected frequency pair has a corresponding frequency deviation at at least one of its two frequencies from the resonant frequency corresponding to the value of the at least one parameter detected according to the dependency.

2. The method (200) according to claim 1, wherein: According to the selection rules of the corresponding time period, the following frequency pair is selected (215) from the set: for the same vibration axis, the frequency pair has a frequency deviation from the resonant frequency that is different from zero and is the smallest within the set at least in at least one of its two frequencies, and the frequency deviation corresponds to the value of at least one detected parameter according to the dependency.

3. The method (200) according to any one of the preceding claims, wherein: The respective duration of each time period is equal to at least 50%, in particular at least 80%, preferably at least 90% of the duration of a phase period of a Lissajous locus (835) corresponding to the frequency of the respective time period, the Lissajous locus being generated in the observation field by the reflected deflection of an electromagnetic beam incident on the microscanner system (801) during simultaneous oscillations.

4. The method (200) according to any one of the preceding claims, further comprising: At least one frequency pair {f1; f2} in the set is determined according to the following conditions: - the resonant frequency f of the microscanner system (801) for the first vibration axis r,1 ; - the resonant frequency f of the microscanner system (801) for the second vibration axis r,2 ;as well as - at least one predetermined line spacing value or an upper limit defined therefor, which represents the maximum line spacing between adjacent lines of the Lissajous locus (835) occurring during a complete phase period.

5. The method (200) according to claim 4, wherein: The at least one frequency pair {f1; f2} is determined from the phase cycle frequency f res Initially, the phase cycle frequency and the possible resonant frequency pair {f 0,1 ,f 0,2 } corresponds to a closed Lissajous locus (835) of , and the determination of the at least one frequency pair comprises: Determining a lower limit of a first factor n1 corresponding to the first vibration axis and / or a second factor n2 corresponding to the second vibration axis according to line spacing values ​​corresponding to the corresponding vibration axes or upper limits specified therefor, wherein n1, n2≥1 are integers, respectively; and The at least one frequency pair {f1; f2} is determined in the following manner: for the frequency pair or each of the frequency pairs, the following condition is satisfied: -f1≤f 0,1 / n1 -f2≤f 0,2 / n2; and -n1 and n2 are coprime.

6. The method (200) according to any one of the preceding claims, further comprising: From the possible resonant frequency pairs {f 0,1 ,f 0,2 The closed Lissajous locus (835) of the phase cycle frequency f res Initially, at least one frequency pair {f1; f2} of the set is determined, and |n Δ |>1, satisfying: f1=f 0,1 +Δf1, where f2=f 0,2 +Δf2, where Among them, n1 and n2≥1 are integers and relatively prime, so they satisfy: f 0,1 =n1·f res and f 0,2 =n2·f res .

7. The method (200) according to any one of the preceding claims, further comprising: Relying on the real-time deflection of an electromagnetic beam, said beam is modulated by means of an image signal so that a two-dimensional digital image or a sequence thereof is imaged in said observation field by a Lissajous projection with a certain image resolution formed by N matrix-arranged pixels; Wherein, according to the selection rule, for at least one of the time periods, their respective corresponding frequency pairs are selected from the set, so that within a maximum of five consecutive phase periods, each of the N pixels corresponding to the image resolution is imaged on the observation surface.

8. The method (200) of claim 7, wherein: During the corresponding duration of each time period, the duration of the phase cycle of the Lissajous trajectory (835) based on the frequency pair corresponding to each time period is shorter than the minimum projection duration of each image that appears when the Lissajous projection is performed by the microscanner system (801) during the corresponding time period.

9. The method (200) according to claim 7 or 8, wherein: According to the selection rule, for at least one of the time periods, a frequency pair corresponding to the time period is selected from the set, so that the selected frequency pair corresponds to the Lissajous trajectory (835) generated in the Lissajous projection, and the Lissajous trajectory passes through at least 90% and preferably at least 95% of the N pixels within a complete phase cycle.

10. The method (200) according to any one of the preceding claims, wherein: The physical variable characterizes or depends on one of the following states of the microscanner system (801) or a combination of at least two such states or state changes: - a shift in the measured resonant frequency of at least one oscillation; -temperature; - Mechanical stress or strain; - the amplitude of the deflection element (810); - a phase instability occurring in at least one of said oscillations; - a corresponding controlled variable of a phase control loop for a phase of at least one oscillation; - a phase difference between a drive signal for controlling the drive device and a measurement signal representing the measured deflection of the deflection element (810); - a change in the power of an incident electromagnetic beam, the deflection element (810) receiving the incident electromagnetic beam power by absorption; - a change in the vibration state of a reference oscillator in the microscanner system (801), which change is correlated with the vibration state of at least one of the deflection elements (810).

11. The method (200) according to any one of the preceding claims, wherein: Depending on the selection of the relevant frequency pair for the respective time period, the value of at least one of the physical variables is detected in the time period immediately preceding this time period.

12. The method (200) according to any one of the preceding claims, wherein: Switching between adjacent time periods occurs within the control framework at points in time at which the trajectory (835) of the Lissajous projection has a distance relative to the center of the observation field illuminated by the trajectory during its complete phase cycle, which distance corresponds to at least 80% of the maximum distance of a point on the trajectory (835) from the center.

13. The method (200) of claim 12, wherein: The switching between the adjacent time segments takes place in each case within the control framework at the time when the trajectory (835) of the Lissajous projection passes through an outer turning point of the trajectory (835).

14. The method (200) according to any one of the preceding claims, wherein: The discrete set of frequency pairs is pre-stored in a storage device, and based on the value of at least one physical parameter detected by the sensing technology, a corresponding frequency pair is selected for at least one time period according to the selection rules of each time period.

15. The method (200) according to any one of the preceding claims, wherein: In the control framework, based on the value of at least one physical variable detected by sensor technology, corresponding frequency pairs are dynamically determined during the method for at least one of the time periods by means of calculation rules defined by the selection rules and defining the discrete sets.

16. The method (200) according to any one of the preceding claims, wherein: In addition to selecting the frequency pairs corresponding to each time period, a target amplitude gain corresponding to the time period is selected for at least one of the two vibration axes; as well as Controlling the driving device in the corresponding time period includes: configuring a corresponding amplitude gain for the at least one vibration axis according to the corresponding target amplitude gain.

17. The method (200) according to any one of the preceding claims, wherein: The micro-scanner system (801) can be configured to adjust a corresponding resonant frequency of at least one vibration axis by correspondingly adjusting at least one configuration parameter of the micro-scanner system (801); and For at least one time period, in addition to selecting the respective corresponding frequency pair, the resonant frequency of at least one vibration axis of the microscanner system (801) is adjusted by adjusting the at least one configuration parameter.

18. A control device (825; 1000) for trajectory adjustment of a micro scanner system (801), wherein: The control device (825; 1000) is configured to control a drive device of the microscanner system (801) according to the method (200) of any one of the preceding claims.

19. The control device (825; 1000) according to claim 18, comprising for at least one of the two vibration axes: a phase control circuit for stabilizing a phase difference between a phase of a first oscillation or a second oscillation corresponding to the vibration axis and a control signal output by the phase control circuit for the drive device; and A frequency adjustment device for the phase control loop, the frequency adjustment device being configured to adjust a control variable of the phase control loop according to a target frequency determined for the time period in accordance with the method (200) with respect to the vibration axis.

20. A computer program having instructions for causing a control device (825; 1000) according to claim 18 or 19 to execute a method (200) according to any one of claims 1 to 17.

21. A beam deflection system (800), comprising: A multi-axis microscanner system (801) having at least one deflection element (810) capable of performing a first rotational oscillation about a first vibration axis and having at least one deflection element (810) capable of performing a second rotational oscillation about a second vibration axis orthogonal to the first vibration axis simultaneously with the first oscillation, so as to generate a Lissajous projection in an observation field by deflecting the reflection of an electromagnetic beam incident on the microscanner system (801) during the simultaneous oscillation; A driving device for driving at least one oscillation of the micro-scanner system (801); as well as A control device (825; 1000) according to claim 18 or 19, for controlling the drive device according to the method (200) according to any one of claims 1 to 17.

22. The beam deflection system (800) of claim 21, wherein: The microscanner system (801) has a quality factor of at least 1000 with respect to at least one of the two oscillations.

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