Projection system for projecting LISSAJOUS figures and microscanner with coupled oscillators

Description

[0001] The present invention relates to a projection system for projecting Lissajous figures onto an observation field, and to a microscanner for such a projection system.

[0002] Microscanners, also known in technical terminology as "MEMS scanners," "MEMS mirrors," or "micromirrors," are micro-electromechanical systems (MEMS), or more precisely, micro-optoelectromechanical systems (MOEMS) from the class of micromirror actuators used for the dynamic modulation of electromagnetic radiation, particularly visible light. Depending on their design, the modulating movement of a single mirror can be translational or rotational around at least one axis. In the first case, a phase-shifting effect is achieved; in the second, the deflection of the incident electromagnetic radiation. The following discussion focuses on microscanners in which the modulating movement of a single mirror is rotational.In microscanners, the modulation is generated by a single mirror, in contrast to mirror arrays where the modulation of incident light is achieved through the interaction of several mirrors.

[0003] Microscanners can be used, in particular, to deflect electromagnetic radiation. A deflecting element (a "mirror") is used to modulate the direction of deflection of an incident electromagnetic beam. This can be used, in particular, to create a Lissajous projection of the beam into a field of view. This allows, for example, the solution of imaging sensor tasks or the implementation of display functionalities. Furthermore, such microscanners can also be used to advantageously irradiate and thus process materials. Other possible applications include the illumination of specific open or closed spaces or areas with electromagnetic radiation, for example, in the context of spotlight applications.

[0004] In both the case of imaging sensors and in the case of a display function, a beam deflection system, in particular a microscanner, serves to deflect electromagnetic radiation such as a laser beam or a shaped beam from any other source of electromagnetic radiation at least two-dimensionally, e.g. horizontally and vertically, in order to scan or illuminate object surfaces within an observation field.

[0005] From EP 2 514 211 B1, a deflection device for a projection system for projecting Lissajous figures onto an observation field is known, which is configured to deflect a light beam around at least a first and a second deflection axis to generate the Lissajous figures. The deflection device has a deflection unit for generating oscillations around the deflection axes and a control device for generating control signals for the deflection unit with a first and second control frequency corresponding to the resonance frequencies of the deflection unit. The deflection unit has a quality factor greater than 3,000.The control device comprises a first control loop configured to regulate the first and / or second control frequency based on a measured phase of the deflection unit's oscillations, ensuring that the maximum amplitude of the oscillations remains within the deflection unit's resonance range. The control frequencies do not exhibit a fixed integer ratio. The control device also includes a second control loop configured to influence the resonance frequency of the first and / or second deflection axes based on a line density of the Lissajous figures determined by the control frequencies, ensuring that the line density remains within a predetermined tolerance range.The two deflection axes are decoupled by means of a gimbal suspension, so that the associated oscillations around the two axes are completely decoupled from each other and are also completely independent of each other with the aim of keeping each of the two axes in resonance.

[0006] The following relationship applies to the deflection device from EP 2 514 211 B1 f 1 R ≠ f 2 R , where f1R denotes the resonant frequency of the first axis and f2R the resonant frequency of the second axis. The mechanical torque T1 and T2, respectively, generated by the deflected spring of the first and second axis, respectively, is given by: T 1 = k 1 * θ 1 und T 2 = k 2 * θ 2 , where θ1 and θ2 denote the respective mechanical amplitude (deflection angle) of the mirror in the first axis and in the second axis, respectively, and k1 and k2 denote the respective spring constant of the spring of the first axis and the second axis, respectively. Due to the decoupling of the oscillation axes, it is particularly easy with such gimbal-based microscanners to achieve at least an approximately rectangular illumination of the observation field using Lissajous figures.

[0007] Besides gimbal-based microscanners with completely decoupled axes, there are also types of microscanners without a gimbal (so-called "gimballess mirrors" or "gimballose" microscanners or mirrors) that implement two or more axes of vibration without using a gimbal suspension of the mirror and in which a non-negligible, and in particular a strong, coupling between the individual axes of vibration can occur. The strength of such coupling can be amplitude-dependent.

[0008] One example of a microscanner type is constructed with a deflection unit containing a mirror plate suspended from a surrounding frame by three rotationally symmetrical spring elements, resulting in a biaxial microscanner. A variant of this type of microscanner, which is described in Fig. 3 The illustrated mirror is known as the "Minifaros" mirror and is described in particular in Hofmann et al.: Resonant biaxial 7-mm MEMS mirror for omnidirectional scanning; J. Micro / Nanolith. MEMS MOEMS, 3-11 Jan-Mar 2014 / Vol. 13(1).

[0009] Due to the couplings between the oscillation axes and the corresponding oscillations of the mirror around each of these axes, gimballess mirrors tend to rapidly converge their resonant frequencies with respect to the different oscillation axes during oscillation. This results in a Lissajous illumination of the observation field that is essentially elliptical (and therefore linear, not planar). In particular, this makes achieving an even approximately planar, and especially an even approximately rectangular, illumination of the observation field difficult or even impossible.

[0010] Further microscanners are disclosed in the following documents: US 2012 / 0320379 A1 describes a deflection device for a Lissajous scanning scanner with a micromirror oscillating in at least two deflection axes, comprising a frame and a mirror plate movably mounted on a suspension, and a control device for generating control signals for resonant operation of the micromirror in the at least two deflection axes. The suspension of the mirror plate has at least one spring connected on one side to the mirror plate and on the other side to the stationary frame. The frequencies of the control signals for the resonant operation of the micromirror in the at least two deflection axes are essentially the same, but differ by at least the specified sampling rate.The resonance frequencies of the deflection axes, and thus the frequencies of the control signals, are determined by a predetermined sampling resolution and a predetermined sampling rate.

[0011] EP 3447560 A1 describes a compact and robust microelectromechanical reflector system comprising a support, a reflector, a circumferential edge of the reflector with edge points, and suspensions with piezoelectric actuators that suspend the reflector from the support. Two pairs of suspensions are attached to the support from two attachment points, such that in each pair of suspensions, the first ends of one suspension are attached to a common attachment point of the pair. A first axis of rotation is aligned with a line passing through the two attachment points and divides the reflector into a first reflector part and a second reflector part. In each pair of suspensions, a second end of one suspension is connected to the first reflector part, and a second end of the other suspension is connected to the second reflector part.

[0012] EP 3173843 A1 describes a MEMS device comprising: a fixed structure, a movable structure including a reflecting element; a first deformable structure, and a second deformable structure arranged between the fixed structure and the movable structure. Each of the first and second deformable structures includes a corresponding number of principal piezoelectric elements. The principal piezoelectric elements of the first and second deformable structures can be electrically controlled to cause vibrations of the movable structure about a first axis and a second axis, respectively. The first deformable structure further includes a corresponding number of secondary piezoelectric elements, which can be electrically controlled to change a first resonant frequency of the movable structure about the first axis.

[0013] EP 3751328 A1 describes a microelectromechanical system, in particular a mirror system, which can be used, for example, in LiDAR (Light Detection and Ranging), wherein the MEMS mirror system uses four suspensions, each of which is connected to the reflector body at two separate connection points that can be moved independently of each other by piezoelectric actuators. By actuating adjacent and opposite pairs of piezoelectric actuators, the reflector body can be excited to oscillate about two orthogonal axes.

[0014] US 2019 / 0162948 A1 describes a device comprising a reflector system and a feedback circuit. The reflector system includes a support, a reflector, and a spring structure that suspends the reflector from the support for scanning movement of the reflector in two orthogonal oscillation modes. Each oscillation mode has a frequency response that peaks at a natural resonant frequency with an initial bandwidth. The reflector system includes a first transducer structure for mechanically actuating the reflector and a second transducer structure for generating one or more sensing signals that represent a mechanical movement of the reflector. The feedback circuit is configured to receive a sensing signal from a transducer of the second transducer structure and to generate a drive signal based on the received sensing signal at a transducer of the first transducer structure.For each of the two oscillation modes, the feedback circuit is configured to adjust the amplitude and frequency of the drive signal to a non-linear oscillation range where the peak frequency shift is at least ten times the initial bandwidth; to vary the amplitude of the drive signal relative to a waveform of a modulation signal; and to set the frequency of the modulation signal component to be smaller than the peak frequency shift. This configuration provides a simple way to widen the image area of ​​a scanning micromirror.

[0015] The present invention is based on the objective of providing an improved gimbal-less microscanner with coupled vibration axes and a projection system equipped therewith, with which planar Lissajous illumination of the observation field is possible. In particular, it is desirable to create a means of achieving at least approximately rectangular illumination with such a microscanner.

[0016] The solution to this problem is achieved according to the teaching of the independent claims. Various embodiments and further developments of the invention are the subject of the dependent claims.

[0017] A first aspect of the invention relates to a microscanner for a projection system for projecting Lissajous figures onto an observation field. The microscanner comprises a deflection unit with (i) a deflection element for deflecting, in particular by reflection, an incident electromagnetic beam, (ii) a support structure, and (iii) a spring assembly. The spring assembly may comprise one or more spring elements. The deflection element is gimbal-less (i.e., without any deflection) by means of the spring assembly.(non-gimbal) suspended on the support structure in such a way that it can perform a first rotational oscillation around a first axis of oscillation and a second rotational oscillation around a second axis of oscillation orthogonal to it simultaneously relative to the support structure, in order to produce a non-linear Lissajous projection into an observation field by deflecting an electromagnetic beam incident on the deflection element during the simultaneous oscillations.

[0018] The microscanner also has a control device configured to drive a drive unit for the deflection unit in such a way that a respective, in particular resonant, drive effect with respect to at least one of the oscillations of the deflection element can be individually adjusted.

[0019] Furthermore, the spring mechanism is designed in such a way that it mediates an amplitude-dependent mutual coupling between the oscillations.

[0020] The control device is also designed to control the drive device depending on at least one detected state variable of the first oscillation in order to produce a driving effect on the second oscillation by influencing at least one state variable of the second oscillation, so that the driving effect counteracts a predetermined minimum frequency difference between the respective instantaneous oscillation frequencies of the first oscillation and the second oscillation.

[0021] The respective state variable of each oscillation is determined by its amplitude, frequency, or phase, or as a function of at least one of these variables. In particular, at least one of the measured state variables can be determined by the amplitude of the oscillation. This is particularly advantageous because, in a non-linear oscillation, the spring stiffness k(θ) and thus also the frequency f(θ) with respect to an axis are each a function of the amplitude θ with respect to that axis, and thus modulating the other oscillation as a function of the measured amplitude θ of that axis enables a direct, particularly dynamic, assurance of the minimum frequency spacing.

[0022] A "Lissajous projection" within the meaning of the invention is to be understood in particular as a scanning of an observation field using electromagnetic radiation, which is effected by at least two mutually orthogonal harmonic oscillations of a deflection element that deflects the radiation into the observation field.

[0023] A "nonlinear Lissajous projection" within the meaning of the invention is a special case of a Lissajous projection, namely the scanning or illumination of an observation field using electromagnetic radiation. This scanning is achieved by at least two mutually orthogonal, non-harmonic oscillations about an associated axis of oscillation of a deflecting element that deflects the radiation into the observation field. In particular, at least one of these oscillations with respect to a first axis of oscillation can have its amplitude modulated as a function of the instantaneous amplitude of an oscillation with respect to at least one other axis of oscillation, such that at least the first oscillation does not represent a linear oscillation, i.e., it does not follow Hooke's law with an amplitude-independent spring constant.

[0024] In the context of the invention, an "axis" or, synonymously, "axis of vibration" is understood to be an axis of rotation of a rotary motion. It is a straight line that defines or describes a rotation.

[0025] A "drive device" within the meaning of the invention is understood to be a device comprising one or more actuators for driving the deflection unit, i.e. the simultaneous rotary oscillations of the deflection element relative to the support structure and with respect to at least the first and the second, and optionally also a third axis of oscillation.

[0026] Any terms used herein, such as "comprises," "includes," "features," "has," "with," or any other variant thereof, are intended to cover non-exclusive inclusion. For example, a method or apparatus that includes or features 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 apparatus.

[0027] Furthermore, unless explicitly stated otherwise, "or" refers to an inclusive or and not an exclusive "or". For example, a condition A or B is satisfied by any of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0028] The terms "ein" or "eine," as used here, are defined as "one or more." The terms "ein anderer" and "ein Weitere," as well as any other variant thereof, are to be understood as "at least one more."

[0029] The term "plural", as used here, is to be understood in the sense of "two or more".

[0030] The aforementioned microscanner offers one or more of the following advantages, thereby solving the aforementioned problem: Due to the special control of the drive unit in the aforementioned microscanner, it is possible, despite the existing coupling between the various oscillations or vibration axes, to ensure that the respective vibration frequencies, especially resonance frequencies, of the individual oscillations maintain a minimum frequency separation from one another. This prevents frequency synchronization of these frequencies to different axes, which would ultimately result in elliptical Lissajous figures. This, in turn, enables a consistently uniform, and especially a substantially rectangular, illumination of the observation field during projection, particularly with gimballess mirrors.Among other things, this makes it possible to achieve a Lissajous-like excitation of the deflection element (mirror) in the microscanner even when the resonance frequencies of different axes are close together, despite this circumstance, even with many gimballess mirrors, where this would not be possible without control of the aforementioned type.

[0031] Since gimballess mirrors, for the same mirror size, generally have a smaller overall design than gimbal-based mirrors, a reduction in the required installation space can be achieved with comparable projection results.

[0032] Because at least one of the oscillators (corresponding to the oscillation around a specific axis of oscillation) has a non-linear characteristic, i.e., it does not correspond to Hooke's law with an amplitude-independent spring constant across its entire amplitude range, a wider tuning range (frequency bandwidth), especially with high quality, can be achieved, particularly compared to gimbal-based mirrors.

[0033] The microscanner also enables the maintenance of defined frequency ratios across wide temperature ranges, as temperature-related fluctuations in the oscillator properties can be compensated to ensure the minimum frequency separation between the frequencies of the different oscillation axes. With gimbal-less mirrors, temperature-related fluctuations in the oscillator properties typically occur with the same intensity, in the same direction, and simultaneously for both oscillator axes, in contrast to gimbal-mounted mirrors, where this typically occurs sequentially and to varying degrees.

[0034] Even with strongly coupled axes and thus pronounced nonlinear microscanners, the aforementioned control system can usually enable oscillation in at least two dimensions and with different resonant frequencies for the various axes.

[0035] Preferred embodiments of the microscanner according to the first aspect are described below, which, unless expressly excluded or technically impossible, can be combined with each other and with the other described aspects of the invention as desired.

[0036] According to some embodiments, the control device is further configured to additionally control the drive device depending on at least one detected state variable of the second oscillation in order to cause a driving effect on the first oscillation by influencing at least one state variable of the first oscillation, which counteracts a falling below a predetermined minimum frequency difference between the respective instantaneous oscillation frequencies of the first oscillation and the second oscillation.While the basic microscanner design described above allows for a "primary-secondary" operation in the sense that only one of the oscillations (secondary oscillation) is influenced by at least one detected state variable of the other oscillation (primary oscillation), the embodiments described here allow both the first and second oscillations to be influenced by at least one detected state variable of the other oscillation, particularly in an equal manner. This enables, among other things, a greater variety of control options and a particularly effective, and especially fast, automatic dynamic control of the oscillations involved, while avoiding frequency synchronization of the amplitude-dependent operating frequencies, especially resonance frequencies.

[0037] According to some alternative embodiments, the control device is configured to control the drive unit independently of any state variable of the second oscillation, in order to produce a driving effect on the first oscillation by influencing at least one state variable of the first oscillation. These embodiments thus enable, in particular, the aforementioned "master-slave" operation. Since only one of the oscillations (specifically the second oscillation) needs to be controlled by the control device depending on at least one state variable of the other (first) oscillation, a particularly simple implementation of the control device is possible.

[0038] According to some embodiments, the control device is configured to control the drive unit to generate the respective drive effect on at least one oscillation driven by it, in the sense of a closed-loop control, depending on at least one repeatedly, and in particular continuously, measured control variable, which is a state variable of the other oscillation or is determined depending on it. With the aid of such a control system, dynamic control of the drive unit for the purpose of ensuring the minimum frequency spacing can be achieved particularly effectively and efficiently, and in particular, it can also react to unforeseen disturbances, which would generally not be possible to the same extent with a simple control system without feedback.Furthermore, this opens up the possibility of targeted compensation for, in particular, periodic changes in amplitude-dependent spring stiffnesses of the spring assembly with respect to at least one axis, especially for nonlinear coupling effects that could otherwise cause distortions, such as constrictions in the planar area of ​​the observation field illuminated by the microscanner. On the other hand, such nonlinear coupling effects can also be amplified or selectively modulated, particularly depending on the application, to achieve specific shapes of the illuminated planar area, especially those that deviate from an elliptical or rectangular shape. For headlight applications, this can be used in particular for the static or dynamic shaping of the illuminated area (planar in cross-section) generated by a headlight system based on the microscanner.Consider, for example, a glare-free high beam for a motor vehicle, in which the light cone of the headlight is dynamically shaped in such a way that road users at risk of being blinded in the traffic area (which is also the observation field) are automatically excluded from the high beam distribution.

[0039] According to some embodiments, the acquisition of this controlled variable, particularly when the controlled variable for the drive control of the respective driven oscillation is defined as a frequency or phase of the other oscillation or as a function of at least one of these state variables, can always occur at the same amplitude of this other oscillation, for example, always at a zero crossing of the oscillation's amplitude profile. In this way, a control system that is particularly robust against disturbances can be achieved, which, due to the consistently identical measurement conditions with respect to the amplitude, typically exhibits lower measurement errors.

[0040] According to some embodiments, the control device can also be configured to perform both the first and the second oscillations in the sense of a control based on at least one repeatedly, and in particular continuously, detected control variable, which is a state variable of the other oscillation or is defined as a function of it. These respective control mechanisms for the first and second oscillations are dynamically configurable with respect to their respective steepness and control speed depending on the steepness and control speed of the other control mechanism.This tuning is advantageous because it ensures that the axes oscillate at approximately the same rate, thereby shifting their original resonant frequencies at roughly the same rate, particularly towards higher frequencies, as spring stiffness increases with amplitude (spring stiffening). This approximate synchronization of frequency shifts makes it particularly easy and reliable to ensure the minimum frequency spacing for the difference between the shifting frequencies.Thus, such a coordinated configuration of the control loops can, in particular, prevent one of the control loops from regulating significantly faster than the other, thereby avoiding the risk of an undesirable overlap of the resonance ranges, especially the resonance frequencies of the oscillations, resulting in the minimum frequency separation being undesirably undershot and consequently only a linear, especially elliptical, Lissajous projection occurring instead of the planar, especially rectangular, illumination desired for the task.

[0041] According to some embodiments, the control device is configured to actuate the drive unit to generate the respective drive effect on the oscillation it drives, in the sense of feedbackless control, depending on at least one detected state variable of the other oscillation. Here, a pure "open-loop control" of the drive unit, in the sense of control engineering, can be employed. Such a control system can advantageously be implemented with less effort compared to the aforementioned control systems. In particular, it is also conceivable to combine such a control system with at least one of the aforementioned control systems. Specifically, one oscillation could be controlled and another oscillation controlled.

[0042] According to some of these control-based embodiments, the control device is configured to actuate the drive device to produce the respective drive effect on the oscillation being driven, such that the drive device causes a stepwise increase in the respective amplitude or frequency of the first and second oscillations, alternating between them. For example, the oscillation of the microscanner, more precisely its deflection element, could be set in motion by first incrementing the frequency f1 of the first oscillation (i.e., increasing it by a defined frequency step), then incrementing the frequency f2 of the first oscillation, then further incrementing f1, then further incrementing f2, and so on, until the desired drive frequencies are reached.Thus, even using a simple control system, a microscanner oscillation can be achieved without unwanted overlap of resonance ranges, particularly resonance frequencies of the oscillations. This ensures the minimum frequency separation and, consequently, avoids purely elliptical Lissajous projections instead of the desired planar, especially rectangular, illumination. The increment sequence can also be stored in memory and, in particular, determined based on a prior calibration process. This allows for configuration of the oscillation by defining and storing the desired increment sequence, either in addition to or instead of calibration.

[0043] According to some embodiments, the control device is further configured to control (i.e., regulate) the drive device such that the respective frequency of at least one of the oscillations, in particular one oscillation primarily driven by this control, is maintained within a predetermined, limited resonance range surrounding the current resonance frequency of that oscillation. The resonance frequency is, as usual, given by the frequency fR at which the maximum amplitude occurs. The limits of the resonance range for a resonance frequency fR can be determined, in particular, by the values ​​fR ± 70%, preferably fR ± 40%, more preferably fR ± 20%, and even more preferably fR ± 10% of the frequency value fR of the resonance frequency. (The percentages here refer in each case to the value fR).This has the particular advantage that in the resonance range, especially at the value f, maximum amplitudes and thus the largest possible extents of the illuminated area of ​​the observation field can be achieved, which is particularly relevant for large-area illumination.

[0044] In some embodiments, the minimum frequency spacing is defined as a constant value. This allows for a particularly simple implementation, since once this value is defined, no further dependencies need to be considered for determining it, especially not dynamically.

[0045] According to some alternative embodiments, the minimum frequency spacing is defined as a variable that depends on the current amplitude of the first or second oscillation, or on the current amplitudes of both oscillations. This allows for better adaptation to different system states. In particular, it enables more precise control of the microscanner's oscillation and effectively avoids unwanted overlap of resonance ranges on different axes, especially when the frequency changes of these axes do not occur at the same rate as the oscillation progresses.

[0046] According to some alternative embodiments, the spring assembly is designed such that the strength of the amplitude-dependent mutual coupling between the first and second oscillations increases continuously with increasing amplitude of at least one of these two oscillations. This can be achieved in particular by designing the spring assembly as a whole, or optionally its individual springs, such that their respective spring stiffness k increases with increasing amplitude, i.e., when k = k θ mit k θ a > k θ b für θ a > θ b .

[0047] This is also known as "spring stiffening" or "stress stiffening." This allows for the following advantages in particular: Through this deliberately induced stiffening, the frequency bandwidth or the width of the resonance can be increased as desired. The more pronounced this effect, the more suitable such a two-axis microscanner with bilateral spring stiffening behavior is for unregulated and very easy-to-implement open-loop operation (pure control). If only one oscillator exhibits this pronounced spring stiffening and the second oscillator does not, it may be necessary to equip at least one oscillator with a control circuit, as the bandwidth for stable open-loop control might then be insufficient. This situation is not as advantageous as the situation with two oscillator suspensions exhibiting pronounced spring stiffening.If the suspensions are designed so that the oscillation with the higher resonant frequency exhibits "spring stiffening" and the other "spring lowering" behavior, it can be ensured, whether using pure control, regulation, or a combination thereof, that the oscillations do not approach and synchronize. If the suspension of the oscillator with the lower resonant frequency is designed with "spring stiffening" behavior and that of the oscillator with the higher resonant frequency with "spring lowering" behavior, amplitude increases can only be achieved by bringing the oscillation frequencies closer together. This case is generally undesirable, as it offers few usable properties.If both oscillators exhibit "spring lowering" behavior, which is relatively difficult to achieve from a design perspective and therefore less common, a suitably simple implementation based on pure control can be achieved if the behavior is sufficiently pronounced, since the frequency bandwidth of the respective resonances then allows for sufficient stability of the state. According to the invention, the control system must be designed such that the desired frequency spacing is maintained. This state can then be stabilized by appropriate control loops.

[0048] According to some embodiments, the microscanner is designed as a biaxial microscanner in which the deflection unit comprises a deflection element suspended from a surrounding frame, serving as a support structure, by means of three rotationally symmetrically arranged spring elements. The microscanner can, in particular, have a deflection unit of the "Minifaros mirror" type. Microscanners according to these embodiments regularly exhibit very strong coupling between the oscillations of the different axes and therefore a strongly non-linear resonance. This, in turn, enables large tuning ranges, i.e., a large bandwidth (e.g., approximately 200 Hz for some Minifaros mirror variants) within which the deflection element can oscillate in resonance (resonance range).

[0049] According to some alternative embodiments, the microscanner is designed as a biaxial gimballess microscanner in which: (i) the deflection unit has a deflection element that is rigidly clamped at two opposite sides and suspended by means of a bending spring from a rigid frame serving as a support structure, in particular a chip frame made of a semiconductor material; and (ii) the bending springs each have two arc-shaped sections connected to each other at their end faces and otherwise spaced apart, which extend around the deflection element, wherein the respective section of each bending spring adjacent to the deflection element is connected to the deflection element and the respective section of each bending spring adjacent to the frame is connected to the frame. The deflection element and the bending springs, and optionally also the frame, can in particular be formed in one piece, i.e., made from a single substrate.In such a microscanner, the spring stiffness with respect to each axis depends both on the instantaneous amplitude of the deflection element relative to that axis and on the instantaneous amplitude of the deflection element relative to the other axis. Thus, during operation of the microscanner, the first oscillation periodically modulates the second oscillation and vice versa. Furthermore, the two oscillations continuously exchange vibrational energy and temporarily store it. With such a mirror, it is particularly possible to achieve area-like illumination of the observation field, which has the form of deformed, especially constricted, rectangles. With appropriate control of the drive unit to compensate for the mutual modulation, an at least approximately rectangular area-like illumination can also be achieved.

[0050] According to some embodiments, the control device is configured, within the framework of controlling the drive unit for the deflection unit, to individually adjust at least one corresponding state variable of the first oscillation, the second oscillation, or each of these two oscillations to a specific setpoint by means of amplitude adjustment, frequency adjustment, or phase adjustment. In particular, phase adjustments, especially phase control, are well suited to effect a control-based, partial or complete compensation of the mutual modulations of the different oscillations and also to maintain resonant operation of the microscanner.

[0051] According to some embodiments, the deflecting element is suspended from the support structure by means of the gimballos spring device in such a way that it can simultaneously perform a third rotational oscillation relative to the support structure with respect to a third axis of oscillation that is orthogonal to the first and second axes of oscillation. This is achieved by deflecting an electromagnetic beam incident on the deflecting element during the three simultaneous oscillations, thereby producing a nonlinear Lissajous projection into the observation field. Furthermore, the spring device is designed to provide an amplitude-dependent mutual coupling between the third oscillation and the first oscillation, the second oscillation, or both. Thus, by utilizing the third axis of oscillation, or...Third oscillation, in particular, more complex projection images can be made, in which, for example, the intensity or phase of the deflected radiation can be (additionally) modulated by the movement around the third oscillation axis through a correspondingly inhomogeneous design of the reflectance or the structure of the reflecting surface.

[0052] According to some embodiments, the control device is further configured to control the drive unit depending on at least one detected state variable of the first or second oscillation in order to produce a driving effect on the third oscillation by influencing at least one state variable of the third oscillation. This effect counteracts the failure to fall below a predetermined minimum frequency difference between the respective instantaneous oscillation frequencies of the first and second oscillations on the one hand and the third oscillation on the other. Thus, the frequency decoupling of the different axes can also be extended to the third axis, and therefore, undesirable imaging disturbances that would otherwise occur during projection can be compensated for or avoided by such coupling.

[0053] In some embodiments, the microscanner further comprises an encapsulation by means of which at least the deflection element and the spring assembly are hermetically sealed in such a way that the deflection element is suspended within the encapsulation in a manner capable of performing oscillations, and is oscillatively mounted on the spring assembly. The encapsulation includes a capsule section bridging the deflection element, through which the radiation to be deflected can be introduced into the space enclosed by the encapsulation and, after being deflected by the deflection element, re-emitted from it. The encapsulation or the capsule section can, in particular, consist of or contain a glass material that is at least predominantly, preferably largely, transparent to electromagnetic radiation in a spectral range relevant for the use of the microscanner.

[0054] The use of such encapsulation makes it possible, in particular, to reduce the pressure in the hermetically sealed, encapsulated space, and especially to evacuate this space, in order to reduce or even largely eliminate gas friction losses, especially air friction losses, or other disturbances to the oscillations of the deflecting element. This is particularly advantageous when using the microscanner for Lissajous display applications, where the deflecting element and its spring suspension are not operated in ambient air, but at reduced pressure, especially in a vacuum, because this allows friction losses due to air damping to be circumvented very efficiently, and as a result, the microscanner can achieve, for example, oscillation amplitudes up to 100 times greater than in air at atmospheric pressure.Accordingly, the achievable optical resolution can also be increased accordingly, for example up to 100 times, in one or each of the first and second vibration axes.

[0055] In some of these embodiments, the capsule section has a dome-shaped, planar, or U-shaped cross-section. The dome shape has the particular advantage that incident and outgoing electromagnetic beams, especially laser beams, are hardly deflected by the wiring. If incident beams are reflected by the dome-shaped capsule section, this regularly occurs in a different direction than the direction of the outgoing beam reflected by the deflecting element, thus effectively avoiding unwanted interactions or superpositions of the beams. The planar shape and the U-shaped cross-section, on the other hand, are characterized by their particularly simple manufacturability and handling during the production of the microscanner.The U-shaped cross-section, which is rectangular in cross-section, can also offer the advantage that any additional intermediate layers (spacer layers) that would otherwise be required in the substructure of the encapsulation for the formation of a sufficiently large enclosed space area for the movement of the deflection element can be avoided or reduced in number or thickness.

[0056] A second aspect of the invention relates to a projection system for projecting Lissajous figures onto an observation field, wherein the projection system comprises a microscanner according to the first aspect of the invention, in particular according to one of the embodiments and variants described herein.

[0057] According to some embodiments, the projection system may in particular include a radiation source for generating the electromagnetic beam to be deflected (and thus "incident") by the micro-scanner.

[0058] According to some embodiments, the control device can further be configured to supply the radiation source with at least one modulation signal, depending on which the incident electromagnetic beam is modulated. The modulation can, in particular, affect its temporal or spatial intensity profile. Depending on the type of radiation source, however, other types of modulation are also conceivable, especially modulations of the wavelength (e.g., color) or wavelength distribution of the radiation emitted by the radiation source. When projecting images, the modulation is carried out accordingly, depending on the current deflection direction, so that corresponding pixels on the projection surface are generated by modulation with the associated pixel value of the corresponding pixel of the image to be displayed.

[0059] The features and advantages explained in relation to the first aspect of the invention also apply accordingly to the aforementioned projection system according to the second aspect of the invention.

[0060] Further advantages, features and applications of the present invention will become apparent from the following detailed description in conjunction with the figures.

[0061] This shows: Fig. 1 schematically an exemplary setup of a microscanner according to some embodiments of the invention; Fig. 2 schematically an exemplary setup of a projection system for projecting Lissajous figures onto an observation field according to some embodiments of the invention; Fig. 3 schematically a top view of a deflection unit with a gimbal-less minifaron mirror, which is particularly evident in the microscanner made of Fig. 1 usable; Fig. 4 an exemplary frequency response of the gimbal-less Minifaros mirror Fig. 3 ; Fig. 5 Schematic view of a deflection unit of an exemplary further gimbal-less mirror variant ("KOLA") using arc-shaped bending springs as a spring device, which is particularly used in the microscanner made of Fig. 1 usable; Fig. 6 An exemplary image of the cross-section of a non-compensated, constricted and deformed area of ​​illumination in relation to a rectangle in a microscanner with a deflection unit according to Fig. 5 ; Fig. 7 a frequency response diagram to illustrate an example of maintaining a required minimum frequency separation during the oscillation of a microscanner according to the invention, in order to avoid self-synchronization occurring as the amplitude increases and thus resulting in rigid phase and frequency coupling; Fig. 8(A) a block diagram of an exemplary combined control / regulation system (open-loop for one axis, closed-loop for another axis) of the microscanner Fig. 1 , according to some embodiments of the invention; Fig. 8(B) shows an example frequency response for the two oscillations during the oscillation of the microscanner. Fig. 8(A) ; Fig. 9 a block diagram of an exemplary dual control system (closed-loop for both axes) of the microscanner Fig. 1 according to one embodiment of the invention, wherein, however, signal-based feedback between the two control systems is only unidirectional; and Fig. 10 a block diagram of an exemplary dual control system (closed-loop for both axes) of the microscanner Fig. 1 according to an embodiment of the invention, wherein a signal-based bidirectional feedback exists between the two control systems.

[0062] The same reference numerals are used throughout the figures for the same or corresponding elements of the invention.

[0063] Fig. 1 Figure 1 schematically illustrates an exemplary embodiment 100 of a microscanner according to an exemplary embodiment of the invention with a drive device 105 for driving the microscanner 100 in a side cross-sectional view.

[0064] The microscanner 100 features a piezo actuator 105 as its drive unit, which also forms a base plate on which a stacked, multilayered structure of various stacked substrates is arranged, forming a deflection unit 101 of the microscanner. The core of this multilayered structure is a first substrate 120 (chip) made of a semiconductor material, structured into various interconnected sub-areas. These sub-areas include a frame sub-area 125, a mirror sub-area ("mirror") 130 serving as a deflection element, and several spring elements 135, designed as connecting bridges, that connect the mirror sub-area 130 to the frame sub-area.

[0065] The mirror section 130 is movably mounted in the frame section 125 via spring elements 135, which are capable of twisting, such that the mirror section 130 can perform a two-dimensional, in particular biaxial, oscillatory movement relative to the frame section 125. The connecting webs 135 thus constitute a spring suspension of the mirror section 130. The connecting webs or spring elements 135 together form a spring assembly of the deflection unit 101. This spring assembly is designed such that it provides an amplitude-dependent mutual coupling between the oscillations to the individual axes of vibration. This results in a non-linear spring characteristic of the spring assembly as a whole.

[0066] The mirror section 130 is provided on one of its main surfaces with a metallic coating 140 such that this metallic layer 140 forms a mirrored reflective surface for deflecting incident electromagnetic radiation, in particular a laser beam, e.g., in the visible or infrared range of the electromagnetic spectrum. The mirror section 130 with its coating 140 thus forms a deflection element of the deflection unit 101.

[0067] The metal layer 140 can, in particular, contain one or more of the following materials: Al, Ti / Au, Ti / Pt / Au, Ta / Pt / Au, Cr / Au, Ta / Au, Ti / Ag, Ta / Ag, Ta / Pt / Ag, Ti / Pt / Ag, Ti / TiW / Au, Ti / W / Au, Ti / W / Ag, Ti / TiW / Ag, etc. In particular, additional dielectric layers can be used above or below the metal layers to improve the quality of the layers or to protect the metal layers from corrosion. In other cases, the mirror layer can be composed entirely of dielectric layer stacks in order to achieve particularly high reflectivities for a specific wavelength range. The aforementioned materials can exhibit both high long-term durability and good mirror properties. The shape of the mirrored reflective surface 140 can be, in particular, as shown in Fig. 3 and 5Each shape shown is circular, but this should not be understood as a limitation. In particular, rectangular or other polygonal shapes are also conceivable. The following refers to the Figuren 3 and 5 Various exemplary implementations of such deflection elements, or in particular of first substrates, will be discussed in detail below.

[0068] The deflection unit 101 optionally includes a second substrate 145 made of a glass material. The second glass substrate has a dome shape and is hermetically connected to the frame section 125 of the first substrate 120 by means of a substrate bonding material 150, e.g., a glass-frit material, in order to form a first (in Fig. 1 to form the "upper") sub-area 175a of a cavity 175 surrounding the mirror sub-area 130 on both sides.

[0069] On the side of the first substrate 120 opposite the second substrate 145, a third substrate 110 serving as a base plate is located in the multilayer structure 101, as well as a fourth substrate 115 between the first and third substrates, which is designed as a spacer layer. The third and fourth substrates can each be made of a semiconductor material.

[0070] The fourth substrate 115 is structured in such a way that it has a cavity which is arranged below the mirror part area 130 in such a way that, together with its bottom boundary given by the base plate 110, it forms a second (in Fig. 1 (a) "lower") part area 175b of the cavity 175.

[0071] The adjacent individual substrates are hermetically sealed to one another, for example, by means of a substrate bonding material 150 or 155, so that the cavity 175 is hermetically sealed when the second substrate 145 is used. It is preferably evacuated, so that a residual gas pressure prevails within it, preferably significantly below normal conditions (101.325 kPa = 1013.25 mbar), preferably below 10 kPa / 10 ± 1 < kPa (10 ± 1 < mbar), and particularly preferably below 10 ± 1 < kPa (10 ± 3 < mbar). Typically, the first to fourth substrates 110, 115, 120, 145 each have the same basic shape, in particular a rectangular shape, although other shapes are also possible.

[0072] The piezo actuator 105 is configured to generate vibrational motion when electrically actuated and to transmit this motion to the deflection unit 101, and in particular to its mirror section 130. In one variant, the vibrational motion is multidimensional, so that several oscillations about different orthogonal axes of vibration can be excited simultaneously when the vibration frequency(ies) enter the resonance range of the respective oscillation. Alternatively, the drive unit, in particular the piezo actuator 105 in this example, can also be configured such that each of the oscillations can be selectively excited separately via a corresponding special motion component, in particular a tilting of the actuator about an axis parallel to the corresponding axis of vibration.

[0073] In these and other ways, the mirror section 130 with its mirror surface 140 can be excited to perform an oscillatory motion, in particular a resonant or forced multidimensional oscillatory motion such as a biaxial Lissajous motion relative to the frame section 125. The uniaxial oscillation components about each of the corresponding axes of oscillation are hereinafter referred to as oscillations. During these oscillations, the mirror section 130 can move out of the plane of the first substrate 120 by tilting (rotating) about the respective axis of oscillation and thereby immerse itself on both sides in the subsections 175a and 175b of the cavity 175. Due to the evacuation of the cavity 175, the remaining friction in the gas is very low, so that only a small, in particular a negligible, damping occurs.

[0074] Furthermore, the microscanner 100 features a capacitive position detection device. This device comprises two electrodes between which an electrical capacitance measurement is performed to determine the current amplitude position, and in particular the orientation, of the mirror section 130. The first of the two electrodes is formed by the metallic mirror surface 140, which is thus designed to perform a dual function (deflection of incident electromagnetic radiation; electrode). The second electrode is located on the inside of the base plate 110 in the cavity 175 as a corresponding metallic coating 180 of the base plate 110. In this example, this base electrode 180 is designed as a multi-layered structured metal layer.The shape of this bottom electrode 180 corresponds in its nature and preferably at least approximately also in size essentially to the shape of the mirror part 130, or of its reflective layer or mirror surface 140, which lies parallel to it in the non-displaced rest state of the mirror part 130.

[0075] The base electrode 180 is electrically contacted via one or more so-called vias, i.e., connecting tunnels filled with electrically conductive (conductivity >10⁶ < S / m), usually metallic, material, which extend from the base electrode 180 through the base plate 110 to corresponding connection pads 190 on the piezo actuator 105. The mirror electrode 140, in turn, is electrically connected via a rewiring layer to a connection pad 165 located on the first substrate 120 outside the dome formed by the second (glass) substrate, and from there electrically connected by means of a bond wire 160 to another connection pad 170 on the piezo actuator 105. Thus, the mirror electrode 140 is electrically contacted via the connection pad 170. Consequently, an electrical capacitance measurement used to determine the position of the mirror section 130 can be performed between the connection pads 190 and 170.

[0076] The microscanner 100 further comprises a control device 195, which is specifically designed to control the piezo actuator 105 for driving the deflection unit by means of corresponding electrical control signals 198 (in the sense of controlling or regulating) in such a way that a respective, in particular resonant, driving effect with respect to at least one of the oscillations of the deflection element 130, 140 can be individually adjusted.Specifically, the control unit is configured, and in particular programmed, to control the piezo actuator 105 depending on at least one detected state variable of an oscillation along a first oscillation axis A1 ("first oscillation") in order to induce a driving effect on the oscillation towards the second, first orthogonal, oscillation axis A2 ("second oscillation") by influencing at least one state variable of the second oscillation, which counteracts a predetermined minimum frequency difference fTH between an instantaneous oscillation frequency f1,i of the first oscillation and an instantaneous oscillation frequency f2,i of the second oscillation. Furthermore, the control unit 195 is configured to receive measurement signals 199 from the deflection unit based on the aforementioned electrical capacitance measurement, in particular measurement signals indicating an instantaneous position of the deflection unit with respect to the axes A1 and A2.The amplitude, frequency, and phase of the respective oscillations are particularly relevant as state variables in this context.

[0077] Optionally, the control device 195 can also be configured to perform control in the opposite direction, i.e., to control the piezo actuator 105 depending on at least one detected state variable of the second oscillation in order to produce a driving effect on the first oscillation by influencing at least one state variable of the first oscillation, which counteracts a fall below the predetermined minimum frequency difference between an instantaneous oscillation frequency f1,i of the first oscillation and the instantaneous oscillation frequency f2,i of the second oscillation. Details of the control and regulation of the oscillations that can be carried out in this context by means of the control device 195 are described below, in particular with reference to the Figuren 7 bis 10 will be explained. Fig. 2 Figure 1 schematically shows an exemplary setup of a projection system 200 for projecting Lissajous figures onto an observation field 220. The microscanner 100 can be used for this purpose. Fig. 1 a beam L1 of incident light is generated on its mirrored surface 140, which serves as a reflective surface, by means of a laser 210 serving as a source of electromagnetic radiation, in particular visible light, and directed onto the reflective surface 140 to be reflected there and projected as a deflected beam L2 onto the observation field 220 in order to illuminate it, at least partially. The observation field can be defined by a projection surface, such as a smooth surface like a screen, a floor, or a road surface. In addition to the Fig. 2 In the simplest case of pure reflection shown, in addition to the deflecting element or mirror 130 / 140, one or more further optical elements may be provided to determine the image, in particular in the form of mirrors or optical lenses.

[0078] Fig. 3 schematically shows a top view of a deflection unit 300 with a gimbal-less minifaron mirror, which is used in particular in the microscanner 100. Fig. 1 or in the projection system 200 from Fig. 2 can be used. Fig. 4 shows a corresponding frequency response of the amplitude of the deflection element when excited with respect to an oscillation axis.

[0079] In this embodiment, the microscanner can be configured in particular as a biaxial microscanner 300. Its deflection unit 101 here has a deflection element 130, 140 designed as a mirror plate. It is suspended on a surrounding frame section 125 of the substrate 120, which serves as a support structure, by means of three rotationally symmetrically arranged spring elements 135, which together form a spring assembly.The suspension is configured such that the deflection element 130, 140 (mirror) is suspended from the frame section 125 in a spring-loaded manner, enabling it to simultaneously perform a first rotational oscillation about a first axis of oscillation A1 and a second rotational oscillation about a second axis of oscillation A2 orthogonal to the first. This deflection of an electromagnetic beam L1 incident on the deflection element during these simultaneous oscillations produces a nonlinear Lissajous projection into the observation field 220. The orientation of the two mutually orthogonal axes of oscillation A1 and A2 depends on the excitation pattern due to the rotational symmetry with respect to the three suspensions, which are spaced 120 degrees apart along the circumference of the mirror.

[0080] The oscillations around the two axes A1 and A2 are strongly coupled here due to the specific configuration of the spring assembly, meaning they are no longer independent. In fact, unlike a harmonic oscillator, the effective spring stiffnesses k1 and k2 are time-dependent functions of the actual mechanical amplitudes (displacements) θ1,i(t) and θ2,i(t) with respect to the two oscillation axes A1 and A2, respectively. k 1 = k 1 θ 1 , i t , θ 2 , i t und k 2 = k 2 θ 1 , i t , θ 2 , i t .

[0081] In the Minifaros mirror type, the coupling or interaction between the two oscillations is usually very clear. Both axes of oscillation are defined by all three springs 135. This means that all three springs 135 are involved in both axes A1 and A2, unlike in the gimbal-mounted mirror. In the latter, each axis of oscillation has its own pair of torsional suspensions.

[0082] If the MiniFaros mirror is driven conventionally, i.e., without the use of the special control system according to the invention, by internal or external forces, it initially begins to oscillate linearly around one axis, A1 or A2. As the frequency f is increased and the resonant frequency of the second axis is approached, more and more vibrational energy is transferred from the first oscillation around axis A1 to the second oscillation around axis A2, and the 130 / 140 mirror no longer oscillates linearly but elliptically. This ellipse becomes increasingly larger in diameter and simultaneously takes on a more circular shape. This means that, due to the strong interaction between the two axes, more and more of the applied vibrational energy is transferred from one axis to the other.

[0083] In this process, the second axis synchronizes itself with respect to its phase, because there is then no oscillation with an arbitrary phase relationship between the axes, but rather an ellipse or a circle, which is equivalent to a synchronized phase relationship of the two axes A1 and A2, even though the energy was only supplied via one axis.

[0084] An interesting and important feature of the strongly interacting axes are the non-linearly operating spring suspensions 135. These result in a pronounced non-linear resonance – in the case of MiniFaro mirrors, this is so-called "stress stiffening" or "spring stiffening" with a "tilted peak" towards higher frequencies, as shown in Fig. 4 as frequency responses of the vibration amplitude, e.g., to axis A1.

[0085] The spring stiffnesses k1 and k2, according to the aforementioned equation (3), increase with increasing amplitude as a function of both the first amplitude θ1 and the second amplitude θ2. This means that the microscanner 100 can only be driven into resonance from lower to higher frequencies in order to achieve the maximum amplitude occurring at the resonance point. Furthermore, one must start at the lower of the two resonance frequencies to excite oscillations about both axes A1 and A2. If one starts at the higher of the two resonance frequencies, the oscillation remains uniaxial.

[0086] Fig. 4 Figure 1 shows a series of corresponding frequency responses for three different drive voltages of 40 V, 80 V, and 120 V for the drive device 105, where a higher drive voltage corresponds to a larger maximum amplitude under otherwise identical operating conditions. It is clearly evident that during the oscillation phase with an increasing frequency response ("up"), the aforementioned angular amplitude curves with only one pronounced maximum result, which suggests the synchronized axes (f1,i ≈ f2,i or f1R ≈ f2R ≈ fR).

[0087] Instead of a nearly vertical, narrow resonance peak, the resonance curve broadens considerably towards higher frequencies as the oscillation amplitude increases. The greater the oscillation amplitude, the stiffer the suspension becomes, i.e., the spring stiffness k increases, and the more the resonance frequency fR changes. This leads to a broadening of the bandwidth (frequency tuning range).

[0088] However, if one were to perform the oscillation with decreasing excitation frequency ("ab"), significantly different frequency responses would result with separate and less pronounced maxima corresponding to the then separate permanent resonance frequencies f 1R and f 2R of the two axes A 1 and A 2 respectively.

[0089] Nonlinear 2D microscanners without gimbal mounting almost always exhibit very strong coupling. This highly nonlinear resonance results in a large tuning range—that is, a wide bandwidth within which the microscanner can resonate. For the MiniFaros mirror, this can be as high as 200 Hz, depending on the specific model, which is significantly higher than the typical bandwidth of less than 1 Hz for high-quality gimbal scanners.

[0090] These nonlinear coupled 2D mirrors are no longer a combination of two harmonic oscillators, because according to equation (3) there is no longer a spring force increasing linearly with the amplitude based on a "spring constant", i.e., no harmonic behavior. Rather, it is a spring force that is strongly nonlinearly dependent on the amplitude, which can be described as a so-called "Duffing oscillator".

[0091] It should be noted that, despite the potential circular / elliptical shape of the resulting Lissajous projection, the Minifaros mirror typically exhibits two different resonant frequencies, not identical ones. These frequencies can differ by approximately 100 Hz in the ground state (low oscillation amplitude). However, as the axis with the lower resonant frequency oscillates, the oscillator detunes so significantly towards higher frequencies that the frequencies of the two axes gradually converge until they eventually overlap (f1R ≈ f2R), enabling complete energy exchange. Therefore, the deflection unit 300 is not readily suitable for projecting an area of ​​light onto a field of view using Lissajous projection, beyond simply imaging elliptical, and especially circular, lines instead of the desired area of ​​light.

[0092] If, on the other hand, a control device according to the invention is used to control the drive unit of the microscanner 100, an area-wide, and in particular at least approximately rectangular, illumination is possible by tuning the amplitude. Even when oscillating with increasing frequency, the frequency maxima for the two oscillations or axes can be maintained, since these frequencies are always set with respect to their frequency separation such that they cannot fall below a predetermined minimum frequency separation f TH, thus resulting in illumination patterns that deviate from an elliptical shape.

[0093] Fig. 5 Figure 1 schematically shows a top view of a deflection unit 500 with a gimbal-less mirror (here designated as type "KOLA") according to another embodiment of the deflection unit 101, in particular of the substrate 120. This embodiment can also be used in particular in the microscanner 100. Fig. 1 or in the projection system 200 from Fig. 2 be used.

[0094] The KOLA microscanner is a biaxial gimbal-less microscanner in which the deflection unit 500 has a deflection element (mirror) 130, 140, which is suspended on two opposite sides by means of a rigidly clamped bending spring 135a, 135b on a (rigid) frame section 125, in particular a chip, which serves as a support frame. The bending springs 135a, 135b each have two arc-shaped sections connected to each other at their end faces and otherwise spaced apart, which extend around the deflection element 130, 140. The respective section of each bending spring adjacent to the deflection element 130, 140 is connected to the deflection element 130, 140 by means of an internal connecting web 136a or 136b. The respective section of each bending spring 135a, 135b adjacent to the frame section 125 is connected to the frame section 125 by means of an outer connecting web 137a or 137b.

[0095] The bending springs 135a, 135b can be designed in such a way that they are as long and wide as possible and run along the outer contour of the deflecting element, preferably extending perpendicularly away from the axis of rotation A 1 (approximately a quarter circle to each side) and then returning to this axis A 1. This arrangement of the bending springs allows the deflecting element 130, 140 to be movable in both mutually orthogonal axes of rotation A 1 and A 2, the respective bearing of which is determined by the structure of the spring assembly with the described suspension.

[0096] The two axes, or rather the associated oscillations, exhibit strong coupling and thus a pronounced interaction when the oscillation amplitudes are very large. In particular, every amplitude of the deflection element 130, 140 about the first axis A1 immediately leads to a stiffening of the entire bending spring 135a or 125b, which, however, affects both oscillation axes A1 and A2. As a result, the relevant spring constant or amplitude-dependent spring function k1 is not only periodically detuned for the oscillation of the first axis A1, but simultaneously also the relevant spring function k2 for the perpendicular second axis A2, and vice versa. Thus, both spring functions are time-dependent functions according to equation (3).

[0097] This periodic stiffening results in a periodic shift of the respective resonant frequencies f1R and f2R of the two oscillations relative to axes A1 and A2, respectively. This means that the oscillation of the first axis A1 periodically detunes the resonant frequency f2R of the second axis A2, and conversely, the oscillation of the second axis A2 periodically detunes the resonant frequency f1R of the first axis A1. Furthermore, the two axes A1 and A2 continuously transmit, exchange, and store vibrational energy.

[0098] This results in modulated mirror vibration amplitudes θ1(t) and θ2(t) in the KOLA microscanner. The scan pattern generated during projection in the observation field 220 therefore, if no control system according to the invention is used, does not have a completely rectangular cross-section, but rather exhibits a distinct constriction, particularly along one axis. This is shown schematically in Fig. 6 illustrated.

[0099] If, on the other hand, a control device according to the invention is used to control the drive unit of the microscanner 100, an area-wide, and in particular at least approximately rectangular, illumination is possible by tuning the amplitude. Furthermore, when the oscillation increases with frequency, the frequency maxima for the two oscillations or axes can be maintained, since these frequencies are always set with respect to their frequency difference f1,i - f2,i (or |f1,i - f2,i|) such that they do not fall below a predetermined minimum frequency difference fTH.

[0100] Fig. 7 Figure 1 shows a frequency response diagram to illustrate an example of maintaining a required minimum frequency separation during the oscillation of a microscanner according to the invention, in order to avoid self-synchronization occurring as the amplitude increases and thus resulting in rigid phase and frequency coupling.

[0101] The three lower curves show the actual frequency response of the amplitude of the deflection element's oscillation (with respect to any one of the two axes) at various successive times t1, t2, and t3 of the oscillation process. The uppermost curve, shown with a dashed line, in Fig. 7 This represents the state when the amplitude of the oscillator with the lower resonant frequency has increased to such an extent that the resonance of one axis overlaps with that of the other axis (with the higher resonant frequency). In this state, the first oscillator attempts to synchronize the second. This "merging" can only be prevented if the two resonators maintain their separation by oscillating simultaneously and thus exhibiting synchronized stress stiffening. Here, f1 (abbreviation for f1R) denotes the instantaneous (amplitude-dependent) resonant frequency for the first oscillation axis A1, and f2 (abbreviation for f2R) denotes the instantaneous (amplitude-dependent) resonant frequency for the second oscillation axis A2. When using a microscanner according to the invention, strong couplings occur between the different oscillations, partly due to the gimbal-less deflection unit used.associated oscillation axes A1 and A2. On the other hand, the control unit 195 actively counteracts any synchronization of these oscillations or short-wave oscillation axes in order to maintain a minimum frequency difference fTH and thus prevent the two resonance frequencies f1 and f2 (or f1R and f2R) from converging. Consequently, the resulting Lissajous figures are not mere ellipses, as would be the case with f1 = f2 (or f1R = f2R), but, with a suitable choice of excitation by the drive unit 105, can produce differently shaped, planar, and in particular even rectangular illumination areas in the observation field 220.

[0102] Fig. 8(A) shows a block diagram of an exemplary embodiment 800 of the microscanner. Fig. 1 with combined control / regulation (open-loop for one axis, closed-loop for another axis).

[0103] The control device 195 comprises, on the one hand, a control unit 196 (open-loop) for the first oscillation with respect to the first axis A1 and, on the other hand, a control unit 197 (closed-loop) for the second oscillation with respect to the second axis A2. The control unit 196 provides a first control signal in the form of a time-dependent voltage V1(t) for controlling the piezo actuator 105 with respect to the first oscillation. The control unit 197, in contrast, provides a second control signal (more precisely, a control variable signal) in the form of a time-dependent voltage V2(t) for controlling the piezo actuator 105 with respect to the second oscillation. The two voltages V1(t) and V2(t) correspond to the control signals 199 or control variable signals 199. Fig. 1 or Fig. 2 . Due to this control, the piezo actuator 105 performs movements acting on the first and second oscillation axes A 1 and A 2 and, due to its mechanical coupling to the deflection unit 101, exerts corresponding mechanical forces F 1 (t) and F 2 (t) respectively in order to drive the first and second oscillations respectively, in particular resonantly, i.e. according to their respective instantaneous resonance frequencies f 1R and f 2R respectively. Since the deflection unit 101 is of the gimbal-less type, there are non-negligible mechanical couplings between the two oscillation axes A 1 and A 2, which depend on the actual amplitudes θ 1,i (t) and θ 2,i (t) and are therefore also time-dependent, K 1 (θ 1,i (t); θ 2,i (t)) on the first oscillation and K 2 (θ 1,i (t); θ 2,i (t)) on the second oscillation.

[0104] The control unit 196 includes a control controller 196a for the first oscillation, which can access a lookup table 196d containing control data representing a time-dependent setpoint profile θ1,s(t) of the amplitude of the first oscillation during the oscillation of the microscanner 800. Based on the control data, the control controller 196a generates the time-dependent voltage V1(t) for controlling the piezo actuator 105 with respect to the first oscillation and outputs this voltage to the piezo actuator 105 for its control.

[0105] While the aforementioned control of the first oscillation is an open-loop control, the control for the second oscillation features a closed-loop feedback loop. This loop feeds back to the control unit 197 an input signal indicating the instantaneous position of the deflection element (mirror) 130,140, ​​which is detected by the ground electrode 180 of the deflection unit 101 and given by the instantaneous actual amplitudes θ1,i(t) and θ2,i(t). The feedback amplitude θ1,i(t) is fed to a control controller 197a of the control unit 197. Taking into account the (optionally time-dependent) minimum frequency offset fTH, the control unit determines a setpoint θ2,s(t) for the amplitude of the second oscillation. Since the amplitude is related to the frequency of the second oscillation, as described in Fig. 7 As illustrated by example, and since the two are mutually dependent, a target value for the current frequency of the second oscillation is also determined.

[0106] The setpoint θ 2,s (t) is fed to a differential detector 197b for the second oscillation, which may in particular be configured to detect a phase difference Δ φ The system is designed to detect the amplitude of the second oscillation between the setpoint θ2,s(t) and the feedback value θ2,i(t), and to generate a control signal V2(t) determined for phase synchronization via a downstream controller or loop filter and output it to the piezo actuator 105. Alternatively, or additionally, amplitude control or direct frequency control can be implemented in an analogous manner.

[0107] Fig. 8(B) shows an example frequency response for the two oscillations during the oscillation of the microscanner. Fig. 8(A) If, according to this example, the controlled first oscillation behaves such that its actual frequency f1,i follows the step-like curve represented by the solid characteristic, the control for the second oscillation can be designed to follow the step-like curve represented by the dashed characteristic, while always maintaining the minimum frequency spacing fTH. The oscillation of the microscanner thus alternates over time with respect to the two oscillations. In this way, by using the control for the second oscillation, which is dependent on the first oscillation via the coupling K2 (θ1,i(t); θ2,i(t)), a biaxial oscillation can be achieved while maintaining the minimum frequency spacing fTH.

[0108] Fig. 9 shows a block diagram of an exemplary dual control system (closed-loop for both axes) of the microscanner from Fig. 1 according to a further embodiment 900 of the invention, wherein, however, signal-based feedback between the two control systems is only unidirectional.

[0109] The Microscanner 900 is derived from the Microscanner 800. Fig. 8 (A) This is evident in that, instead of a control unit for the first oscillation, a control unit, in particular a phase control unit, is now also provided there. Accordingly, the control unit is replaced by a control unit 196 and the actual amplitude θ 1,i (t) of the first oscillation is also measured at the deflection element and fed back to the control unit 196 in order to close a control loop for the first oscillation as well.

[0110] As a result, each of the two oscillations now has its own control system. The control system for the first oscillation acts as the master control system, meaning it does not take the control system for the second oscillation into account and therefore does not receive feedback of the actual amplitude θ₂,i(t) of the second oscillation. In contrast, the control system for the second oscillation acts as a slave control system, whose setpoint determination depends on the feedback of the actual amplitude θ₁,i(t) of the first oscillation and the minimum frequency spacing fTH, which serves as an additional input variable. Ensuring compliance with the minimum frequency spacing thus depends on the control system for the second oscillation, while each of the two control systems additionally ensures that the respective drive signals V₁(t) and V₂(t) are in phase with the actual waveform of their respective oscillations, thereby supporting corresponding resonant operation of the deflection unit 101.

[0111] Fig. 10 shows a block diagram of an exemplary dual control system (closed-loop for both axes) of the microscanner from Fig. 1 according to a further embodiment 1000 of the invention, wherein a bidirectional signal coupling of the controls is present.

[0112] The microscanner 1000 originates from the microscanner 900. Fig. 9 This is further enhanced by the fact that the control system for the first oscillation now additionally receives feedback of the actual amplitude θ2,i(t) of the second oscillation as well as the minimum frequency spacing fTH as input signals. This results in a symmetrical setup in which the control system for the first oscillation is influenced by the second oscillation, and vice versa. Ensuring compliance with the minimum frequency spacing thus depends on the respective control systems of both oscillations, while each of the two control systems additionally ensures that the respective drive signals V1(t) and V2(t) are in phase with the actual waveform of their respective oscillations, thereby supporting corresponding resonant operation of the deflection unit 101.

[0113] The respective control mechanisms for the first and second oscillations are dynamically configured, or configurable, with respect to their respective steepness and control speed, depending on the steepness and control speed of the other control mechanism. This coordination is advantageous because it ensures that the axes oscillate at approximately the same rate, thereby shifting the original resonant frequencies of the axes at approximately the same rate, particularly towards higher frequencies as the spring stiffness increases with increasing amplitude.

[0114] To reduce or ideally eliminate the risk of control instabilities from the outset, the maximum rate at which frequencies or amplitudes can change can be limited in the control loops, possibly through calibration resulting from a calibration process. Since the frequencies are typically very high, e.g., several kilohertz, a highly controlled and safe approach can be implemented within very short timeframes for this purpose.

[0115] While at least one exemplary embodiment has been described above, it should be noted that a large number of variations exist. It should also be noted that the described exemplary embodiments are merely non-limiting examples, and it is not intended to restrict the scope, applicability, or configuration of the devices and methods described herein. Rather, the preceding description will provide the person skilled in the art with guidance for implementing at least one exemplary embodiment. It is understood that various modifications to the function and arrangement of the elements described in an exemplary embodiment can be made without deviating from the subject matter defined in the appended claims. REFERENCE MARK LIST

[0116] 100 Microscanner 101 Deflection unit 105 Drive unit, in particular piezo actuator 110 Third substrate, base plate 115 Fourth substrate, spacer layer 120 First substrate 125 Frame section 130 Mirror section 135 Spring element 135a,b Bending springs 136a,b Inner connecting webs 137a,b Outer connecting webs 140 Metallic mirror coating, mirror electrode 145 Second substrate, dome-shaped 150 Substrate bonding material 155 Further substrate bonding material 160 Bonding wire 165 Connection pad on first substrate 120 for connecting the upper electrode (top electrode) 140 170 Connection pad on piezo actuator 105 for connecting the upper electrode 140 175a Upper area of ​​the cavity 175 175b Lower area of ​​the Cavity 175 180 structured, if necessary.Multi-part ground electrode 185 Vias with solder bumps for contacting the piezo actuator 190 Connection pads on piezo actuator 105 for connecting the ground electrode 195 Control device 196 Control unit or regulation unit for first oscillation 196a Control controller for first oscillation 196b Differential detector for first oscillation 196c Controller or loop filter (in phase-locked loop) for first oscillation 196d Look-up table 197 Control unit for second oscillation 197a Control controller for second oscillation 197b Differential detector for second oscillation 197c Controller or loop filter (in phase-locked loop) for second oscillation 198 Measurement signals for feedback in control loop(s) and position measurement 199 Control signals orControl signals 200 Projection system 210 Light source, in particular laser 220 Observation field, in particular projection surface 300 Deflection unit with a gimbal-less mini-mirror 400 Frequency response of the gimbal-less mini-mirror 500 Deflection unit with a gimbal-less KOLA mirror 600 Constricted and deformed planar illumination area 700 Frequency response 800 Block diagram of a mixed control (open-loop) / control (closed-loop) 900 Block diagram of a unidirectionally coupled two-axis control (closed-loop) 1000 Block diagram of a bidirectionally coupled control (closed-loop) A1 First oscillation axis A2 Second oscillation axis F1, F2 Axis-specific drive forces from drive unit to deflection element K1 (...) Mechanical axis coupling to the first axis K2 (...)mechanical axis coupling onto the second axis L 1 incident light beam L 2 light beam reflected at the mirror V 1 , V 2 control voltages for controlling the drive device fFrequency f 1 Target frequency of the first oscillation f 2 Target frequency of the second oscillation ΔfFrequency difference f TH Minimum frequency difference θ 1,i Actual amplitude of the first oscillation with respect to the first axis of oscillation A 1 θ 1,s Target amplitude of the first oscillation with respect to the first axis of oscillation A 1 θ 2,i Actual amplitude of the second oscillation with respect to the first axis of oscillation A 2 θ 2,s Target amplitude of the second oscillation with respect to the first axis of oscillation A 2 ΔθAmplitude difference . φ Phase Δ φ Phase difference tTime

Claims

1. A microscanner (100) for a projection system (200) for projecting Lissajous figures onto an observation field, wherein the microscanner (100) comprises: a deflection unit (101) having a deflection element (130,140) for deflecting an incident electromagnetic beam (L1), a support structure (125), and a spring device (135; 135a,b), wherein the deflection element (130,140) is suspended in a gimballess manner by means of the spring device (135; 135a, b) on the support structure (125) in such a way that, relative to the support structure (125), it can simultaneously perform a first rotary oscillation around a first axis of oscillation (A1) and a second rotary oscillation around a second axis of oscillation (A2) orthogonal thereto to cause a non-linear Lissajous projection in an observation field (220) by deflecting an electromagnetic beam (L1) incident on the deflection element (130, 140) during the simultaneous oscillations; and a control device (195), which is configured to control a drive device (105) for driving the deflection unit (101) in such a way that a respective drive effect (F1; F2) with respect to at least one of the oscillations of the deflection element (130, 140) is adjustable individually; wherein the spring device (135; 135a, b) is furthermore designed in such a way that it mediates an amplitude-dependent mutual coupling (K1; K2) between the oscillations; characterized in that the control device (195) is also configured to control the drive device (105) as a function of at least one detected state variable (θ1,i, f1,i, φ1,i) of the first oscillation in order to cause a drive effect (F2) on the second oscillation thereby influencing at least one state variable (θ2,i, f2,i, φ2,i) of the second oscillation, so that the drive effect (F2) counteracts the respective instantaneous oscillation frequencies (f1,i, f2,i) of the first oscillation and the second oscillation falling below a predetermined minimum frequency spacing (fTH); wherein the respective at least one state variable of a respective oscillation is determined by its amplitude (θ1,i; θ2,i), frequency (f1,i, f2,i), or phase (φ1,i, φ2,i) or as a function of at least one of these variables.

2. The microscanner (100) of claim 1, wherein the control device (195) is further configured to additionally control the drive device (105) as a function of at least one detected state variable (θ2,i, f2,i, φ2,i) of the second oscillation in order to cause a drive effect (F1) on the first oscillation thereby influencing at least one state variable (θ1,i, f1,i, φ1,i) of the first oscillation, which counteracts the respective instantaneous oscillation frequencies (f1,i, f2,i) of the first oscillation and the second oscillation falling below a predetermined minimum frequency spacing (fTH).

3. The microscanner (100) of claim 1, wherein the control device (195) is configured to control the drive device (105) independently of a state variable (θ2,i, f2,i, φ2,i) of the second oscillation in order to cause a drive effect on the first oscillation thereby influencing at least one state variable (θ1,i, f1,i, φ1,i) of the first oscillation.

4. The microscanner (100) of any one of the preceding claims, wherein the control device (195) is configured to control the drive device (105) to cause the respective drive effect on at least one oscillation driven thereby in the sense of a closed-loop control as a function of at least one repeatedly detected controlled variable which is a state variable (θ1,i, f1,i, φ1,i; θ2,i, f2,i;, φ2,i) of the respective other oscillation or is defined as a function thereof.

5. The microscanner (100) of any one of claims 1 to 3, wherein the control device (195) is configured to control the drive device (105) to cause the respective drive effect (F1, F2) on the respective oscillation driven thereby in the sense of an open-loop control as a function of the at least one detected state variable (θ1,i; θ2,i) of the respective other oscillation.

6. The microscanner (100) of any one of the preceding claims, wherein the control device (195) is further configured to control the drive device (105) in such a way that the respective frequency of at least one of the oscillations is kept within a predetermined, limited resonance range surrounding a current resonant frequency (f1R, f2R) of this oscillation.

7. The microscanner (100) of any one of the preceding claims, wherein the minimum frequency distance (fTH) is defined as a constant value.

8. The microscanner (100) of any one of claims 1 to 6, wherein the minimum frequency distance (fTH(t)) is defined as a variable value that depends on the respective current amplitude (θ1,i; θ2,i) of the first oscillation or the second oscillation or on the respective current amplitudes (θ1,i; θ2,i) of these two oscillations.

9. The microscanner (100) of any one of the preceding claims, wherein the spring device (135; 135a,b) is designed such that the strength of the amplitude-dependent mutual coupling (K1; K2) between the first oscillation and the second oscillation steadily increases with increasing amplitude (θ1,i; θ2,i) of at least one of these two oscillations.

10. The microscanner (100) of any one of the preceding claims, wherein the microscanner (100) is designed as a biaxial microscanner, in which the deflection unit (101) comprises a deflection element (130,140) that is suspended on a frame (125), which is used as a support frame and surrounds it, by means of three rotationally symmetrically arranged spring elements (135).

11. The microscanner (100) of any one of claims 1 to 8, which is designed as a biaxial gimballless microscanner (100), in which: the deflection unit (101) comprises a deflection element (130, 140) which is suspended, firmly clamped on two opposite sides in each case by means of a flexible spring (135a, 135b), on a frame (125) used as a support frame; and the flexible springs (135a, 135b) each have two curved sections which are connected to one another at their end faces and otherwise extend spaced apart adjacent to one another and which extend around the deflection element (130, 140), wherein the respective section of each flexible spring (135a, 135b) adjacent to the deflection element (130, 140) is connected to the deflection element (130, 140) and the respective section of each flexible spring (135a, 135b) adjacent to the frame (125) is connected to the frame (125).

12. The microscanner (100) of any one of the preceding claims, wherein the control device (195) is configured, in the context of the controlling of the drive device (105) to drive the deflection unit (101) in the sense of an amplitude adjustment, a frequency adjustment, or a phase adjustment, to set at least one corresponding state variable of the first oscillation, the second oscillation, or each of these two oscillations individually to a specific setpoint value.

13. The microscanner (100) of any one of the preceding claims, wherein: the deflection element (130, 140) is suspended in a gimballess manner on the support structure (125) by means of the spring device (135; 135a,b) in such a way that it can simultaneously additionally execute a third rotational oscillation relative to the support structure (125) with respect to a third oscillation axis that is orthogonal in each case to the first and second oscillation axes, in order to, by deflecting an electromagnetic beam (L1) incident on the deflection element (130,140) during the three simultaneous oscillations, cause a non-linear Lissajous projection in the observation field (220), wherein the spring device (135; 135a, b) is further designed in such a way that it mediates an amplitude-dependent mutual coupling between the third oscillation and the first oscillation, the second oscillation, or both.

14. A projection system (200) for projecting Lissajous figures on an observation field (220), wherein the projection system (200) comprises a microscanner (100) of any one of the preceding claims.

15. The projection system (200) of claim 14, wherein the control device is further configured to supply a radiation source with at least one modulation signal as a function of which the incident electromagnetic beam (L1) is modulated.