FIELD

The present invention relates to a device for an image projection and to a method for projecting an image. More specifically, the present invention relates to a laser scanner projector such as for a portable device.

BACKGROUND INFORMATION

Laser scanners provided with micromirrors can be used for the projection of images, in which case the micromirrors deflect the emitted laser beam. For instance, a micromirror which is pivotable about two axes that are orthogonal to each other may be used to generate a two-dimensional image. Toward this end, the micromirror is normally resonantly set into oscillations at a rapid frequency about a first axis, while the micromirror is deflected in a quasi-static manner at a slow frequency about the second axis. Two mutually perpendicular sinusoidal oscillations having different frequencies are superimposing one another in this way. This results in an essentially linear movement of the laser, and a line is scanned during the half period of the fast deflection, and a frame having a multitude of lines is scanned during the half period of the slow deflection.

An exemplary micromirror device having a two-dimensionally deflectable micromirror is described in German Patent Application No. DE 10 2008 054784 A1.

Instead of a single micromirror, it is also possible to provide two micromirrors, each being pivotable about a pivot axis, with the pivot axes being orthogonal to each other. The frequencies of the deflections of the micromirrors differ, so that linear scanning is possible once again.

When employing such projectors, eye safety has to be taken into account because of the used lasers. The lasers are subdivided into different classes according to DIN EN 60825-1, which differ with regard to the risk to the human eye. For example, the maximum power output by a laser of the 3R class is greater by a factor of 5 than that of a laser of Class 2. The maximum permissible exposure (MPE), which denotes the highest power or energy density that is still classified as safe for the human eye, may be examined for the classification of the lasers.

To ascertain the maximally permissible energy or power of a laser of a scanning unit, different scanning configurations of the scanning unit have to be taken into account.

According to a first criterion, the output energy is calculated while the laser beam executes a single sweep across the pupil. According to a second criterion, the laser beam sweeps twice across the eye or multiple times. According to a third criterion, the energy emitted to the pupil during a full frame is considered. According to a fourth criterion, the energy emitted during a period of time up to the maximum exposure time is taken into account. For laser class 2, for example, the maximum exposure time may amount to 0.25 seconds.

Corresponding calculations are carried out for different distances between the pupil and the scanning unit, which begin at approximately 100 millimeters. The greatest restrictions result when the eye is focused on the scanning unit.

The different criteria are of different importance for different angular positions of the micromirrors, i.e., for different solid angles of the scanned region.

SUMMARY

The present invention provides a device for projecting an image and a method for projecting an image.

According to a first aspect, the present invention provides a device for projecting an image using a laser device and a micromirror device. In one example embodiment of the present invention, the laser device emits a laser beam and furthermore has a modulation unit which modulates image data onto the laser beam. The micromirror device deflects the laser beam in a linear manner. In addition, the modulation unit is developed to modulate the laser beam in such a way that a predefined optical warning signal is emitted in a region around reversal points of the linear deflection.

According to a second aspect, the present invention provides a method for projecting an image. In one example embodiment of the present invention, a laser beam is emitted with the aid of a laser device, with image data being modulated onto the laser beam. The laser beam is deflected in a linear manner by a micromirror device. The laser beam is modulated in such a way that a predefined optical warning signal is emitted in a region around reversal points of the linear deflection.

Preferred embodiments of the present invention are described herein.

One recognition on which the present invention is based is that the edge regions of the scanned solid angle region are particularly hazardous to the human eye. The edge regions are the particular regions in which the laser beam changes direction and a new line is scanned.

However, by emitting an optical warning signal in this outer region, a person who walks into the area being scanned will close the eyes because of the eyelid closure reflex already as a result of the warning signal. In this way, the eyes of such a person will not be exposed to the dangerous radiation in the first place. The eye safety is able to be increased in this way.

According to one preferred further development of the example device according to the present invention, the modulation unit is developed to carry out the modulation of the laser beam for the emission of the optical warning signal as a function of the modulated image data. For example, the emitted image may pose a particular hazard to the eye, for instance in the presence of large white regions of high intensity. In this case, the warning signal is preferably emitted continuously. The warning signal may particularly be emitted at the reversal point of each line. The region around the reversal point at the time when the warning signal is emitted may also depend on the intensity of the image data and preferably be greater the stronger the intensity of the image data. In addition, the warning signal may be emitted only if an intensity calculated on the basis of the image data exceeds a predefined threshold value. For example, the total intensity during a frame may be calculated and compared with the predefined threshold value.

According to one preferred further development of the present invention, the example device has an arithmetic device, which calculates the energy of the laser beam during the deflection along at least one line. The modulation unit is developed to carry out the modulation of the laser beam for the emission of the optical warning signal as a function of the calculated energy. For instance, the energy of the laser beam may be calculated during a predefined number of lines to be scanned next. More specifically, the two lines to be scanned next may be taken into account. If the ascertained energy exceeds a predefined threshold value, then a warning signal is output at the end of the next scanned line by a modulation of the laser beam. In the other case, no warning signal will be output. The threshold value, for example, is able to be specified based on an accessible energy limit (accessible emission limit, AEL). In particular, the threshold value may be equal to a predefined percentage of the accessible emission limit such as 90%. The modulation unit thus emits the optical warning signal at the end of the line if the energy of the laser beam during the deflection along this line and/or along adjacent lines exceeds a predefined threshold value.

According to a preferred further development of the example device in accordance with the present invention, the modulation unit modulates the image data onto the laser beam in such a way that edge regions of the lines are shielded, with the exception of the warning signal. Shielding the edge regions makes it possible to correct distortions. In addition, a clearance is created between the region of the displayed image and the region in which the warning signal is displayed. Since the warning signal already triggers the eyelid closure reflex, a person who moves into the scanned region has already closed the eyes or averted the eyes before reaching the actual image content. This makes it possible to avoid eye injuries.

According to a preferred further development of the example device in accordance with the present invention, the modulation unit is developed to carry out the modulation of the laser beam for the emission of the optical warning signal as a function of a size of the shielded edge region. The greater the distortion, the greater the shielded edge region. Since the danger from the laser beam to the eyes decreases from the edge in the direction of the center, the laser thus poses less of a risk. Accordingly, the warning signal may be displayed only when the size of the shielded edge region drops below a predefined threshold value.

According to a preferred further development of the present invention, the example device has a sensor device which outputs a detection signal if a person is approaching a solid angle region scanned by the micromirror device. The modulation unit carries out the modulation of the laser beam for the emission of the optical warning signal as a function of the detection signal. The optical warning signal may thus be displayed only if a person who is moving into the scanned solid angle region is detected. This avoids an unnecessary display of warning signals and bothers observers to a lesser degree.

According to one specific embodiment of the present invention, the warning signal may be made up of individual pulses or pixels directly at the reversal points or in the vicinity of the reversal points. For example, the laser device may have a green, a blue and a red laser. The warning signal may be emitted only by the red laser. The observer therefore sees a line-shaped red region at the edge of the scanned solid angle region.

According to one further development of the example device in accordance with the present invention, the modulation unit is developed to modulate the laser beam in such a way that a band-shaped region of a predefined color and/or a predefined intensity along the reversal points of the linear deflection is continuously emitted as an optical warning signal. The band-shaped region may preferably be generated by the red laser again.

The modulation unit preferably modulates the laser beam in such a way that the optical warning signal poses no risk to the human eye.

