Device and method for deflecting a light beam in order to scan a solid angle range

A device and a method for deflecting a light beam to scan a solid angle range. The device includes: a deflection device having an adjustable micromirror, which is configured to periodically deflect a light beam in accordance with an actuating signal, in order to periodically scan a solid angle range, using the micromirror; a control device to receive a control signal that indicates a currently preferred solid angle in the solid angle range to be scanned, and to generate the actuating signal based on the received control signal; and the control device is configured to generate the actuating signal so that a maximum of a location probability density of the periodically deflected light beam is situated at the solid angle.

FIELD OF THE INVENTION

The present invention relates to a device and a method for deflecting a light beam, in particular, a laser beam, in order to scan a solid angle range.

BACKGROUND INFORMATION

Laser scanners are used for a multitude of applications, for example, for image projection, in headlights, or for scanning surrounding areas of vehicles. In this context, a laser scanner is to be understood, in particular, as a device, in which a laser beam is directed onto a deflection device and controlled by this, in accordance with an actuating signal, in such a manner, that the reflected laser beam scans a solid angle range of interest, e.g., a screen. Scanning is to be understood as covering the solid angle range or the screen in a traversing manner, for example, in zigzag patterns; a desired scanning density being able to be a function of the specific application.

By way of example, a laser scanner, as is explained in more detail in the following, in light ofFIG. 6, is discussed in US 2010/079 836 A1.FIG. 6shows a customary laser scanner1, which includes a light source2that is configured to generate a laser beam3and direct it onto a micromirror4. The laser beam3striking micromirror4is deflected, as a deflected laser beam5, in the direction of a screen6; micromirror4being controlled by a regulating device7so as to scan screen6.

To that end, micromirror4rotates about a first axis of rotation, which may also be referred to as a rapid axis of rotation, so that screen6is traversed in a horizontal direction from left to right and back again in a periodic manner. In addition, micromirror4rotates about a second axis of rotation, which may also be referred to as a slow axis of rotation, in such a manner, that light beam5traverses screen6periodically from top to bottom and back again. The zigzag pattern shown inFIG. 6results from superimposing the movements about the first and the second, that is, the slow and the rapid, axes of rotation. Regulating device7receives position signals8, which indicate a respective position of deflection device4, and, on the basis of them, adapts control signals9for controlling deflection device4.

The scanning is normally implemented in a periodic, in particular, a sinusoidal, motion, as represented, for example, inFIG. 7.FIG. 7shows a graph, which represents a deflection angle α of a micromirror4as a function of time t within one period, in the form of a sine function. In the case of a motion as shown inFIG. 7, maxima of a location probability density for the deflected light beam result in accordance with the deflection angle of micromirror4, as shown inFIG. 8. Accordingly, there are maxima of the location probability density at the maximum deflection angle in the negative direction, αmin, as well as at the maximum deflection angle in the positive direction, αmax.

SUMMARY OF THE INVENTION

The present invention provides a device having the features described herein and a method having the features described herein.

Accordingly, a device for deflecting a light beam, in order to scan a solid angle range, is provided, including: a deflection device having an adjustable micromirror, which is configured to deflect a light beam in accordance with an actuating signal, in order to periodically scan a solid angle range, using the micromirror; a control device, which is configured to receive a control signal that indicates a currently preferred solid angle in the solid angle range to be scanned; the control device further being configured to generate the actuating signal for the deflection device on the basis of the received control signal; and the control device being configured to generate the actuating signal in such a manner, that a maximum of a location probability density of the periodically deflected light beam is situated at the currently preferred solid angle. In particular, this is achieved in that a location probability density and/or residence time of the micromirror at a deflection angle corresponding to the preferred solid angle, as well as in a range of deflection angles about the corresponding deflection angle, determined by a half width b of the maximum, is increased in comparison with conventional laser scanners.

The control device may be configured to generate the control signal in such a manner, that the maximum has a predefined and/or adjustable width, in particular, half width, of the density of the location probability density.

The solid angle currently preferred is to be understood as the solid angle, at which, during the course of a period of the periodic scanning, the greatest level of available optical power, the so-called light center, should be directed. This may be, for example, a solid angle, at which an object of interest is situated, and which should be scanned with a particularly high reliability. A location probability density is to be understood as a function, which indicates a probability of the light beam per differential solid angle (or angle), so that integration of the location probability density over the entire solid angle range (or angular range) yields one.

A solid angle range and a preferred solid angle in it may also be understood as a deflection angle range and a preferred deflection angle in it, for example, if the deflection device is configured only to deflect the light beam in accordance with a single axis of rotation.

In addition, a method for deflecting a light beam, in order to scan a solid angle range, is provided with the steps: deflecting a light beam in accordance with an actuating signal, in order to periodically scan a solid angle range; receiving a control signal, which indicates a currently preferred solid angle in the solid angle range to be scanned; and generating the actuating signal on the basis of the received control signal, in such a manner, that a maximum of a location probability density of the, in particular, periodically deflected light beam is situated at the preferred solid angle.

The control signal may be generated in such a manner, that the maximum has a predefined and/or adjustable width, in particular, half width, of the density of the location probability density.

The finding underlying the present invention is that in the case of conventional light scanning systems, the location probability density of the light beam deflected for the scanning is always unchangeable at the reversal points or reversal zones, that is, at the edges of the solid angle range to be scanned, where, however, the objects of most interest within the solid angle range are rarely expected to be.

Now, the idea forming the basis of the present invention is to take this finding into account and to provide a device and a method to deflect a light beam for scanning a solid angle range, which allow the maximum of the location probability density of the deflected light beam to be set arbitrarily within the solid angle range to be scanned, and to be changed as required. In this manner, maxima of the light distribution over the to-be-scanned solid angle range of the light, which is deflected by the device or in accordance with the method, may be shifted away, as needed, from the edges of the solid angle range to be scanned.

Advantageous specific embodiments and further refinements are derived from the dependent claims, as well as from the specification, with reference to the figures.

According to one further refinement, the control device is configured to generate and/or adapt the actuating signal in such a manner, that in at least one first section of its periodic domain, an angular velocity function of the micromirror includes, or is made up of, a first term constant in time and a first term periodic in time. The angular velocity function of the micromirror indicates an angular velocity of the micromirror as a function of a time within a period of the periodic scanning. The time within the period may be specified as a fraction of a period duration T of the period. In other words, the angular velocity function indicates the angular velocity (magnitude and direction), which the micromirror has during its motion, in each instance, sequentially from a starting point (at a time t=0), via its maximum positive deflection (or maximum negative deflection) at a time t=T/4, via the starting point again at a time t=T/2, via a maximum negative deflection (or maximum positive deflection) at a time t=¾ T, back to the starting point at t=T or, again, t=0, in accordance with the periodic motion.

A term periodic in time should be understood as a term, which is describable by a periodic function, in particular, a trigonometric function, particularly, by a sine or cosine function, even if a complete period of the periodic function (which may be different from the period of the periodic scanning of the micromirror) is not run through within the specific section of the domain.

In other words, a deflection angle function of the micromirror, which indicates a deflection angle of the micromirror as a function of time t within the period of the periodic scanning, includes, in at least the first section of the periodic domain, a term linear in time (whose derivative with respect to time yields the first term of the angular velocity function constant in time) and a periodic term (whose derivative with respect to time yields the first term of the angular velocity function periodic in time), or is made up them. This yields an advantageous form of the location probability density of the light beam periodically deflected.

According to an additional further refinement, the control device is also configured to generate the control signal in such a manner, that in a second section of its periodic domain, the angular velocity function of the micromirror includes, or is made up of, a second term constant in time and a second term periodic in time. The first and the second portions are each disjoint, as are all of the further sections of the domain described in the following, as well. The first term constant in time may differ from the second term constant in time, and the first term periodic in time may differ from the second term periodic in time, namely, even without taking into account the different sections of the domain. The domain may be covered completely by the first and the second sections, that is, be made up of them. At any transition between the first and the second section (and/or vice versa), the angular velocity function may change abruptly.

According to an additional further refinement, the angular velocity function in the first section is equal to the angular velocity function in the second section, multiplied by negative one, if the argument of the angular velocity function in the first section is multiplied by negative one. In other words, the angular velocity function in the first section may be referred to as a point reflection, at the coordinate origin, of the angular velocity function in the second section. This yields a further advantageous form of the location probability density of the light beam deflected periodically.

According to an additional further refinement, a third section of the periodic domain is defined at a first transition between the first section and the second section of the periodic domain of the angular velocity function, and a fourth section of the periodic domain is defined at a second transition between the second section and the first section of the periodic domain. In the third section, the angular velocity function of the micromirror is a continuous function and may include a first term linear in time t or, particularly, is made up of a first-order polynomial in time. In the fourth section, the angular velocity function of the micromirror is a continuous function and includes a second term linear in time t or, particularly, is made up of a first-order polynomial in time. Due to this, the movements of the micromirror are less abrupt, which allows gentler operation of the device.

According to another further refinement, the angular velocity function assumes the value of zero once in the third section, and/or the angular velocity function assumes the value of zero once in the fourth section. In other words, during its periodic motion to scan the solid angle range periodically, in each instance, the micromirror is controlled, in the region of its reversal points, in accordance with an angular velocity function having a linear term, in particular, made up of a first-order polynomial in time t. In this manner, particularly gentle control of the micromirror may be implemented.

According to another further refinement, the control signal further indicates a half width of a peak of the location probability density of the periodically deflected light beam about the maximum situated at the preferred solid angle. The control device is advantageously configured to adapt the actuating signal to the forming of the peak of the location probability density having the half width indicated by the control signal.

According to another further refinement, the device includes a provision device, which is configured to generate the light beam in accordance with a light-provision control signal. The control signal advantageously indicates a desired light intensity of the light beam at the preferred solid angle, as well. The control device may be configured to generate the light-provision control signal on the basis of the light intensity indicated by the control signal. Thus, a light distribution in the solid angle range may be adapted even more precisely to varied requirements.

According to an additional further refinement, the control device is configured to generate the actuating signal in such a manner, that the micromirror is deflected, in particular, in a parabolic motion, in order to deflect the light beam over boundaries of the solid angle range to be scanned.

The method of the present invention is implementable by, in particular, the device of the present invention, and is therefore adaptable in accordance with all of the modifications and further refinements described with reference to the device of the present invention.

The present invention is explained in greater detail in the following, with reference to the exemplary embodiments depicted in the schematic figures of the drawings.

Unless otherwise indicated, identical or functionally equivalent elements and devices are provided with the same reference numerals in all of the figures. The numbering of method steps is used for clarity, and unless otherwise indicated, does not imply, in particular, a certain chronological order. In particular, a plurality of method steps may also be implemented simultaneously.

DETAILED DESCRIPTION

FIG. 1shows a schematic block diagram of a device10to deflect a light beam50for scanning a solid angle range51, according to a specific embodiment of the present invention.

Device10includes a deflection device12, which has a micromirror14and an actuator13, with the aid of which micromirror14is deflectable, in order to deflect a light beam50for periodically scanning a solid angle range51. Actuator13may be configured to move micromirror14in quasi-static or in resonant operation. The moving of micromirror14may include rotation of micromirror14about one or more axes of rotation. Alternatively, or in addition, the moving of micromirror14may also include deformation of micromirror14, in particular, of a reflecting surface of micromirror14. Deflection device12is configured to deflect light beam50in accordance with an actuating signal60, in order to periodically scan solid angle range51with the aid of micromirror14.

Device10may include a provision device11, which is configured to provide light beam50and direct it to deflection device12. For example, provision device11may include, or be made up of, a light source or a device for coupling a light beam50externally generated into device10. In addition, provision device11may include, for example, a number of optical elements, for example, lenses, diaphragms, optical fiber lines, and the like. Alternatively, by positioning device10relative to an external light beam, an externally generated light beam in the form of light beam50may also be directed onto deflection device12. Light beam50may be a laser beam. The light beam50provided, in particular, a laser beam, strikes deflection device12and is deflected by micromirror14in accordance with a current position, that is, alignment, or a current deformation, of micromirror14. Light beam50may be provided with a light intensity temporally constant over at least one period of the scanning.

Device10further includes a control device16, which is configured to receive an external or internal control signal62that indicates a currently preferred solid angle52in the solid angle range51to be scanned. Solid angle range51to be scanned may be, in particular, a one-dimensional deflection angle range, that is, a deflection angle range describable by a deflection angle as a single parameter, if, namely, e.g., adjustable micromirror14is rotatable about only one single axis of rotation. An external control signal62may indicate, for example, requests of a further device, e.g., requests of a headlight control system, a lidar system, or the like.

In the following, for reasons of clarity, in the description, focus is given partially to a deflection angle range to be scanned as a subtype of a solid angle range to be scanned, as well as to a currently preferred deflection angle in the deflection angle range to be scanned, as a subtype of the solid angle currently preferred. It should be understood that the principles and modifications described here, as well as the described forms of construction of device10, may equally be used for scanning a solid angle range.

In order to scan a solid angle range, for example, the light beam50to be deflected may scan, that is, sweep over or screen, an azimuthal angle range and an elevation angle range periodically; the solid angle range51to be scanned being scanned by superimposing the azimuthal angular motion and the elevational angular motion of deflected light beam50. By setting a currently preferred azimuthal deflection angle in the azimuthal angle range to be scanned and a currently preferred elevation deflection angle in the elevation angle range to be scanned, currently preferred solid angle52may be defined as the solid angle, which is reached by deflected light beam50, when light beam50is deflected both at the preferred azimuthal deflection angle and at the preferred elevational deflection angle.

Control device16is further configured to generate actuating signal60on the basis of received control signal62. By that, it should be understood that control device16is able to check received control signal62in real time, continuously or regularly, and, in each instance, to adapt generated actuating signal60continuously to currently received control signal62. Consequently, a change in currently preferred solid angle52may always be carried out immediately with particularly little delay. Control device16is configured to generate and/or adapt actuating signal60in such a manner, that a maximum of a location probability density of periodically deflected light beam50is situated at currently preferred solid angle52. In a manner analogous to the location probability density of periodically deflected light beam50, a location probability density of adjustable micromirror14may also be considered a function of deflection angles of adjustable micromirror14within the deflection angle range of micromirror14, between a maximum positive deflection and a maximum negative deflection.

Deflection device12may further include a detector15, which is configured to ascertain an angular position, that is, a deflection angle, and/or an angular velocity of micromirror14, and to output a feedback signal on the basis of it. The feedback signal may be transmitted to control device16; control device16being able to function in a regulating mode (closed-loop operation with feedback) on the basis of the feedback signal. In this case, control device16may also be referred to as a regulating device or include an automatic controller.

Different variants of the manner, in which control device16may be configured for generating actuating signal60, are explained in light of the followingFIGS. 2 through 5. In the context of descriptions of device10according to the present invention, it should be understood that a description of the analogous method of the present invention, which is adaptable to all of the further refinements, modifications and variants described with regard to device10, is always given, as well. In the description ofFIGS. 2 through 5, another simplifying assumption is made, that deflection device12is configured in such a manner, that the deflection angle of light beam50corresponds to the deflection angle of micromirror14. Of course, deflection device12may also include further optical elements, such as additional micromirrors, etc. Accordingly, the deflection angle of light beam50may also differ from the deflection angle of micromirror14in a defined manner.

According to one possible specific embodiment of the present invention, which is explained below in light ofFIGS. 2 and 3, regulating device16is configured to generate actuating signal60in such a manner, that a deflection angle function of micromirror14, having the value α(t), is of the following form:

if time t is in a first section71of periodic domain75of the periodic scanning; first section71being situated between t=−T/4 and t=T/4 (that is, t=¾ T and t=T/4). In this connection, T represents the period of the periodic scanning, αmaxis a (maximum) deflection amplitude of the micromirror, and a0, a1 and α0are adjustable parameters. Furthermore, regulating device16is configured to generate actuating signal60in such a manner, that the deflection angle function of micromirror14, having the value α(t), is of the following form:

if time t is in a second section72of periodic domain75of the periodic scanning; second section72being situated between t=T/4 and t=¾ T. Thus, in second section72, the deflection angle function is derived from the deflection angle function in first section71, using axial reflection at the t=0 axis.

Consequently, in first section71, an angular velocity function {dot over (α)}(t) is given, according to actuating signal60, by:

and in second section72, by:

That is to say, angular velocity function {dot over (α)}(t) in first section71is the angular velocity function {dot over (α)}(t) in second section72, point-reflected at the coordinate origin; the point reflection being characterized by f(t)=−f(−t).

FIG. 2shows a schematic graph, which represents a normalized deflection angle function83of light beam50or, analogously, the deflection angle function of micromirror14, as a function of time t, within one period of the periodic scanning, as well as an angular velocity function84of light beam50or, analogously, of micromirror14, as a function of time t, within the same period, in accordance with the above formulas. A left vertical axis shows the normalized deflection angle of micromirror14, which, in the present specific embodiment, is equal to a normalized deflection angle85of light beam50. Currently preferred deflection angle86is drawn in on the left vertical axis, as an example.

FIG. 3shows a schematic graph, which includes a location probability density82of light beam50as a function of normalized deflection angle85of light beam50. As is apparent fromFIG. 3, according to the formulas given above, actuating signal60results in a maximum81of location probability density82at currently preferred deflection angle86; maximum81being surrounded by a peak having a half width b.

To that end, parameter α0introduced above may be selected as the arcsine of a preferred shift of maximum81from the center of the deflection angle range on; the shift lying between −1 and 1, corresponding to a shift of maximum81between a maximum negative deflection and a maximum positive deflection of light beam50, and corresponding to a maximum negative deflection of micromirror14and a maximum positive deflection of micromirror14.

The remaining parameters may be determined from specified boundary conditions:

In this connection, γ is a light intensity parameter of light beam50, which may be adjustable with the aid of provision device11of device10. Light intensity parameter γ may be parameterized as

where γ0is a set or adjustable light intensity parameter at the light center, that is, at maximum81of location probability density82of light beam50. Parameter γ0may be set with the aid of provision device11. To that end, external control signal62may indicate a currently desired value for parameter γ0. Computing device16may be configured to generate or adapt a light-provision control signal64on the basis of the value of parameter γ0indicated in accordance with control signal62, and to transmit it to provision device11. Provision device11may optionally be configured to generate light beam50in accordance with light-provision control signal64, in order to produce or adapt light intensity parameter γ of light beam50accordingly (seeFIG. 1).

Further values for adjustable parameters may be indicated by external control signal62, in particular, for frequency 1/T of the periodic scanning and for deflection amplitude αmaxof micromirror14. In the same way, using external control signal62, a desired half width b for the peak formed about maximum81of location probability density82may be indicated, and the actuating signal60for forming it may be generated or adapted.

Half width b is influenced considerably by light intensity parameter γ. Since the area underneath the location probability density fromFIG. 3corresponds to a value of one, the height of maximum81is also indirectly determined by half width b of the peak, and consequently by light intensity parameter γ. The greater the half width b of the location probability density, the lower the peak. Alternatively or additionally, a desired value of maximum81, which may be, in particular, an absolute or global maximum, may also be transmitted to provision device11and/or control device16, in order to generate the maximum81having the desired value.

In one variant, light-provision control signal64may be generated and/or adapted so that provision device11generates the light beam50having a temporally modulated light intensity, in such a manner, that maximum81of location probability density82is situated at preferred solid angle52by a combination of deflecting light beam50in accordance with actuating signal60, with generating light beam50in accordance with light-provision control signal64. Alternatively, light beam50is provided to have a light intensity temporally constant over at least one period of the scanning.

A further possible functioning method of the device fromFIG. 1is explained with the aid of the followingFIG. 4.

In the case of the further possible method of functioning, in a first section171of periodic domain175, an angular velocity function184of micromirror14is given in accordance with actuating signal60, by:

first section171extending between a time t=Td, which lies between t=¾ T and t=T (or t=0), and a time t=Ta, which lies between t=0 and t=T/4. In a second section172of periodic domain175, which extends between a time t=Tb, which lies between t=T/4 and t=T/2, and a time t=Tc, which lies between t=T/2 and t=¾ T, angular velocity function184is given in accordance with actuating signal60, by:

that is, by the negative of angular velocity function184in first section171.

Between first and second sections171,172, a third section173is defined between times Ta and Tb, and a fourth section174is defined between times Tc and Td. In third and fourth sections173,174, the angular velocity of the micromirror does not change stepwise, as between the first and second sections171,172shown inFIGS. 2 and 3, but with a linear path of the function, and it experiences, in particular, a sign change. This produces a smooth deflection angle function183of light beam50, as shown inFIG. 4. The definitions of angular velocity function184in third section173and fourth section174are selected to produce an altogether continuous, albeit not generally continuously differentiable, angular velocity function184, as shown inFIG. 4. In this context, micromirror14may be deflected across boundaries of the solid angle range51to be scanned, which are denoted by the values 1 and −1 on the left vertical axis inFIG. 4.

FIG. 5shows a schematic flow chart for explaining a method to deflect a light beam50for scanning a solid angle range51, according to another further specific embodiment of the present invention.

The method of the present invention according toFIG. 5is implementable, using, in particular, the device10of the present invention, and is therefore adaptable, in particular, to all of the modifications and further refinements described with reference to the device10of the present invention, in particular, to the specific form of angular velocity functions84;184.

In a step S02, a light beam50is periodically deflected according to an actuating signal60, in order to scan a solid angle range51periodically. In an optional step S01, the light beam50used for that may be provided, in particular, generated, by a provision device11, to have a light intensity temporally constant over at least one period of the scanning. In a step S03, a control signal62, which is, in particular, externally generated and indicates a currently preferred solid angle52in the solid angle range51to be scanned, is received. In a step S04, actuating signal60is generated on the basis of received control signal62in such a manner, that a maximum81of a location probability density82of periodically deflected light beam50is situated at preferred solid angle52. This may be accomplished, in particular, as described above with reference toFIGS. 2 through 4.

As described with regard to device10, the method may include, as an optional step, generating a light-provision control signal64on the basis of a light intensity at preferred solid angle52, indicated by control signal62, and controlling provision device11with the aid of generated light-provision control signal64. In addition, the method may include, as an optional step, generating or adapting actuating signal60on the basis of a half width b for a peak of location probability density82of light beam50about maximum81, the half width being indicated by control signal62.