DE102021130619A1 - Device and assembly for generating images on a projection surface - Google Patents

Abstract

Shown is a device (200) for generating images on a projection surface (202), with at least one light source (204) for generating illumination light; a liquid crystal unit (208) with at least two segments (214a, 214b, 214c), each comprising two electrodes (400, 402a, 402b, 402c) and a liquid crystal (316) arranged between the two electrodes, which can each be transilluminated by the illumination light and whose respective transparency can be controlled by means of AC voltages applied to the electrodes (400, 402a, 402b, 402c); imaging optics (210), which images the illumination light, which shines through the segments (214a, 214b, 214c), to generate the images onto the projection surface (202); and a control unit (222) which is designed to determine the temperature of the liquid crystal unit (208) and the frequencies and the potential differences of the AC voltages present at the electrodes (400, 402a, 402b, 402c) as a function of the temperature of the liquid crystal unit (208) to control. The light source (204) is designed in such a way that the luminous flux density on a surface (226) of the liquid crystal unit (208) facing the light source (204) has a value between 7 lm/mm2 and 80 lm/mm2, in particular between 36 lm/mm2 and 48 lm/mm2. mm2, has.

Description

technical field

The invention relates to a device for generating images on a projection surface. The invention also relates to an assembly for a vehicle with a device of the aforementioned type.

Background of the Invention

So-called logo lights are used in the automotive sector, which can project a number of static, i.e. still images or a sequence of images to generate a short animation onto an area on the side of a vehicle, for example in front of a door of the vehicle. The functionality of these logo lights corresponds to that of a film projector. In order to be able to produce such logo lights particularly inexpensively and compactly, a liquid crystal unit is used for image generation. The liquid crystal unit has several segments that can be individually switched to be transparent, which are illuminated by a light source like a mask and are imaged onto a projection surface by imaging optics for generating images.

In order to switch the individual segments transparent or opaque, a voltage is applied to the segments. By applying the voltage, the molecules of the liquid crystal are aligned in the respective segment and become transparent or opaque to light. The higher the voltage applied, the higher the transparency of the segment. An AC voltage is used so that the molecules of the liquid crystal are not permanently aligned and the liquid crystal is not damaged.

The transparency of the segments also depends on the temperature of the liquid crystal unit. The transparency of a segment increases with increasing temperature and constant voltage. In particular, the transparency of non-transparent switched segments also increases with increasing temperature. In order to achieve a constant contrast even at high temperatures, in known liquid crystal units the voltage present at the electrodes is reduced as the temperature rises. The voltage reduction prevents crosstalk between the segments and neighboring areas. For this voltage adjustment, however, a complex electronic control is required, which is expensive and is associated with a high space requirement. Additional electronic components may also be required for voltage adjustment.

It is therefore an object of the invention to specify a device for generating images on a projection surface and an assembly with a device of the aforementioned type that delivers a high-contrast image over a wide temperature range and is compact and inexpensive.

The object is achieved by a device and an assembly with the features of the independent claims. Advantageous developments are specified in the dependent claims.

Summary

The proposed device comprises at least one light source for generating illuminating light, a liquid crystal unit with at least two segments, each comprising two electrodes and a liquid crystal arranged between the two electrodes, which can each be transilluminated by the illuminating light and whose respective transparency is controlled by means of AC voltages applied to the electrodes is controllable. The device has imaging optics, which images the illumination light, which shines through the segments, onto the projection surface in order to generate the images. The device also includes a control unit which is designed to determine the temperature of the liquid crystal unit and to control the frequencies and the potential differences of the AC voltages present at the electrodes as a function of the temperature of the liquid crystal unit.

The higher the frequency of the AC voltage applied to the respective segment, the more voltage drops across the resistance of the conductor tracks and the lower the effective voltage between the two electrodes of the driven segments. The two electrodes represent a capacitance that, together with the resistance of the conductor tracks, forms an electrical low-pass filter at high frequencies. The effective voltage that is present at the segments can therefore be adjusted via the frequency of the alternating voltage present at the electrodes. Consequently, by controlling the frequency, the transparency of the segments can be adjusted. In order to obtain a constant contrast as the temperature of the liquid crystal unit rises, only the frequency of the AC voltage applied to the electrodes is increased in the proposed device. Changing the frequency of the AC voltage can be achieved with simpler electronic circuitry than changing the voltage levels of the AC voltage. On the one hand, the proposed device can thus be manufactured more cost-effectively. On the other hand, the proposed device can be realized with smaller electronic components, whereby the device can also be installed in small spaces.

In particular, the control unit is designed to control the frequencies and the potential differences of the AC voltages present at the two electrodes of a segment independently of one another.

The light source is designed in such a way that the luminous flux density on a surface of the liquid crystal unit facing the light source has a value between 7.75 lm/mm ² and 77.5 lm/mm ² , in particular between 36 lm/mm ² and 48 lm/mm ² , has. At low temperatures, in particular below 0°C, the response time of typical liquid crystal units decreases sharply - up to the point where the segments freeze completely. Integrated heaters are commonly used to bring the liquid crystal unit up to its operating temperature. However, these take up additional space and require their own electronic control. In this embodiment, the liquid crystal unit is heated to its operating temperature by means of the luminous flux.

In particular, the control unit is designed to control the light source in such a way that the luminous flux density on a surface of the liquid crystal unit facing the light source is increased when the temperature of the liquid crystal unit is below a predetermined value. The heating of the liquid crystal unit to its operating temperature can thus be accelerated at particularly low temperatures, in particular at temperatures below 0°C.

In a further preferred embodiment, the control unit is designed to set the frequency of the alternating voltage applied to the electrodes to a first frequency value when the temperature of the liquid crystal unit has a value below a predetermined temperature value, and to a second frequency value when the temperature of the Liquid crystal unit has a value that is greater than the predetermined temperature value. In summary, in this embodiment, the frequency of the AC voltage applied to the electrodes and thus the temperature-dependent transparency of the segments is regulated in at least two stages. Such a control can be implemented simply and inexpensively.

In an alternative embodiment, the frequency of the AC voltage applied to the electrodes is steplessly, i.e. continuously, regulated. Such a stepless regulation can take place, for example, on the basis of a functional relationship between the temperature of the liquid crystal unit and a frequency of the AC voltage applied to the electrodes.

In a further preferred embodiment, the control unit is designed to set the frequency of the AC voltage applied to the electrodes to the second frequency value when the temperature of the liquid crystal unit has a value between the first predetermined temperature value and a second predetermined temperature value, and towards a third frequency value set when the temperature of the liquid crystal unit is at a value greater than the second predetermined temperature value. In this embodiment, the frequency of the AC voltage applied to the electrodes and thus the transparency of the segments is regulated in three stages. This allows control over the contrast of the device, but is still simple and inexpensive to implement. More than three levels can also be used to enable even more precise control of the contrast. Alternatively, stepless, continuous control of the frequency value as a function of the temperature can also take place, in particular on the basis of a functional relationship.

Preferably, the first predetermined temperature value is in the range between -5°C and 10°C. In this range, the response time of the liquid crystal unit begins to decrease as the temperature decreases. Driving at a frequency higher than the inverse of the response time would lead to undesired flickering of the liquid crystal unit and thus to a reduction in image quality.

In a further preferred embodiment, the control unit controls the frequency of the AC voltage applied to the electrodes in such a way that the frequency has a value between 1 Hz and 40 Hz when the temperature of the liquid crystal unit is between -40°C and 0°C. From a temperature of about 0°C, the response time of the liquid crystal unit begins to decrease with decreasing temperature up to a value of about 1 Hz before the liquid crystal unit freezes. Choosing these parameters thus prevents flickering of the liquid crystal unit at low temperatures.

In a further preferred embodiment, the control unit controls the frequency of the AC voltage applied to the electrodes in such a way that the frequency has a value between 40 Hz and 100 Hz when the temperature of the liquid crystal unit is between 0°C and 60°C. In this temperature range, the frequency of the AC voltage roughly corresponds to a refresh rate that is fluid for the human eye Display of an animation allowed. In addition, the frequency of the AC voltage is selected in such a way that the effective voltage applied to the respectively driven segments generates a high-contrast image.

In a further preferred embodiment, the control unit controls the frequency of the AC voltage applied to the electrodes in such a way that the frequency has a value between 100 Hz and 100 kHz when the temperature of the liquid crystal unit is between 40° C. and 200° C., in particular between 60° C and 130°C. At higher temperatures, the voltage applied to the segments that are switched transparent must be lowered in order to prevent crosstalk to neighboring segments. In order to generate a high-contrast image on the projection surface even in this temperature range, the frequency of the AC voltage is adjusted accordingly.

In a further preferred embodiment, the control unit is designed to measure the level and duration of the potential difference between a first voltage which is present at a first electrode of the liquid crystal unit and is assigned to all segments, and at least one second voltage which is present at a second electrode of the liquid crystal unit and associated with at least one segment depending on the temperature of the liquid crystal unit. The first electrode is common to all segments, so the first electrode is also called the common electrode. Each segment also has a second electrode. The liquid crystal is arranged between the two electrodes. By creating a potential difference between the common electrode and the individual electrode of a segment, that segment is controlled in its transmission rate.

Typically, liquid crystal units are operated with a square-wave AC voltage. A first square-wave AC voltage is applied to the first electrode and a second square-wave AC voltage is applied to the second electrodes, respectively. The difference between the two AC voltages corresponds to the potential difference that is present at the corresponding segment. A phase shift between the two AC voltages changes the effective voltage applied to the respective segment. Thus, a phase shift can be used in addition to the frequency change to control the effective voltage and hence the transmission rate of the segments. In particular, the phase can be changed individually for each segment. A phase shift is also possible when the frequency of the AC voltage cannot be increased any further because, for example, the clock frequency of the control unit cannot be increased any further or cannot be changed at all. In particular, this allows the use of inexpensive electronics.

Alternatively or additionally, the device comprises a temperature sensor for measuring the temperature of the liquid crystal unit or the environment of the liquid crystal unit. The temperature of the liquid crystal unit can be determined from the temperature of the surroundings of the liquid crystal unit, in particular by the control unit. A thermistor is particularly suitable as a temperature sensor. The temperature can be determined very reliably using a temperature sensor. This is a condition for effectively adjusting the frequency of the AC voltage to achieve consistent contrast. In this embodiment, a particularly uniform contrast and thus a constant image quality is thus achieved over a wide temperature range.

In another preferred embodiment, the liquid crystal unit is a passive LCD unit. Passive and active LCD units differ in the way they are controlled. With a passive LCD unit, each segment is controlled via an individual conductor track, which means that the control can be implemented particularly easily and therefore inexpensively.

In a further preferred embodiment, the device can be connected to a bus system of a motor vehicle, in particular to a LIN bus or a CAN bus. Both LIN buses and CAN buses are fieldbuses that are widespread in the automotive sector and connect various sensors and actuators in a vehicle to a central control unit. The device can thus be controlled by the central control unit of the vehicle.

The invention also relates to an assembly for a vehicle, in particular a motor vehicle, with a device of the type mentioned above. The assembly is designed in particular in such a way that it can be installed in a door of the vehicle, a side mirror, a side skirt of the vehicle or in a space that is required for a reversing camera is provided, can be arranged.

Alternatively, the assembly is designed in such a way that it can be arranged in an installation space that is provided for a lamp in the vehicle. In this alternative embodiment, the device is designed in particular to project at least one image onto the projection surface, which represents a permissible signal light function or is part of a permissible signal light function, for example a tail light or a direction indicator.

However, the use of the assembly is not limited to the exterior of the vehicle. For example, the assembly can also be arranged as dynamic reading or room lighting in the interior of the vehicle.

character list

Further features and advantages emerge from the following description, which explains exemplary embodiments in more detail in conjunction with the attached figures.

• 1 einen Graph, der die Abhängigkeit der Transparenz eines beispielhaften Flüssigkristalleinheit von einer angelegten Spannung zeigt;
• 2 eine schematische Darstellung einer Vorrichtung zum Erzeugen von Bildern auf einer Projektionsfläche gemäß einem Ausführungsbeispiel;
• 3 eine Explosionsdarstellung der Vorrichtung zum Projizieren von Bildern auf die Projektionsfläche gemäß einem weiteren Ausführungsbeispiel;
• 4 eine schematische Darstellung der Flüssigkristalleinheit der Vorrichtung zum Erzeugen von Bildern auf einer Projektionsfläche;
• 5 ein Ersatzschaltbild eines Segments der Flüssigkristalleinheit; und
• 6 ein Phasendiagramm zur Verdeutlichung der Funktionsweise der Flüssigkristalleinheit.

Show it:

• 1 a graph showing the dependency of the transparency of an exemplary liquid crystal device on an applied voltage;
• 2 a schematic representation of a device for generating images on a projection surface according to an embodiment;
• 3 an exploded view of the device for projecting images onto the projection surface according to a further embodiment;
• 4 a schematic representation of the liquid crystal unit of the device for generating images on a projection surface;
• 5 an equivalent circuit of a segment of the liquid crystal unit; and
• 6 a phase diagram to clarify the operation of the liquid crystal unit.

Detailed description

1 10 is a graph 100 showing the dependency of the transparency of an exemplary liquid crystal device on an applied voltage.

The abscissa 102 indicates the value of the voltage in volts applied to a transparent switchable segment of the liquid crystal unit. The ordinate 104 indicates the transparency of the segment in percent. Diagram 100 includes two graphs 106a, 106b, each showing the dependency of the transparency of the exemplary liquid crystal unit on the applied voltage for two different temperatures. A first graph 106a is represented by a solid line and shows the behavior of the example liquid crystal device at a low temperature. A second graph 106b is represented by a dotted line and shows the behavior of the example liquid crystal device at a high temperature.

how to get in 1 As can be seen, the segment is not completely opaque even with a low applied voltage. For typical liquid crystal units, both segments that can be switched transparent individually and the so-called non-luminous areas between individual segments have this basic transparency because the liquid crystal lies over the entire surface of the liquid crystal unit and is only switched in the area of the segments. In the example shown, the basic transparency is 20% or 30%. From an applied voltage of about 1.7 V, the transparency of the liquid crystal unit increases rapidly with increasing voltage and asymptotically approaches the maximum value of 100%.

However, the transparency of the liquid crystal unit depends not only on the applied voltage but also on the temperature of the liquid crystal unit. With increasing temperature, the basic transparency of the liquid crystal unit increases. The second graph 106b is compressed compared to the first graph 106a. In known liquid crystal units, in order to produce a constant contrast between the segments and the non-luminous areas at high temperatures, the voltage applied to the segments is reduced. This voltage reduction reduces crosstalk from a driven segment to an adjacent segment or non-luminous area. Thus, the areas of the liquid crystal unit remain clearly separated from each other even with increasing temperatures.

Also, as the temperature decreases, the response time of the liquid crystal unit decreases. This means that the time it takes to switch the segments from an opaque state to a transparent state increases. In typical liquid crystal units, the refresh rate drops from a temperature of around 0°C to values below 1 Hz with decreasing temperature. At particularly low temperatures, the liquid crystal unit can freeze completely, at which point it is no longer possible to switch the segments. It is therefore necessary to heat liquid crystal units to a certain operating temperature. In known liquid crystal units, this is done with the aid of heating devices.

2 shows a schematic representation of a device 200 for generating images on a projection surface 202 according to an embodiment.

The projection surface 202 is in 2 indicated by a dashed line. The device 200 has a light source 204, condenser optics 206, a liquid crystal unit and imaging optics 210. The light source 204 generates illumination light which is directed through a condenser lens 212 of the condenser optics 206 onto the liquid crystal unit 208. The liquid crystal unit 208 comprises two or more segments 214a, 214b sandwiched between two glass plates 216,218. The segments 214a, 214b can be switched to be transparent individually and independently of one another and are each assigned to one of the images. The respective segment 214a, 214b switched transparent is transilluminated by the light source 204 and forms a mask of the image assigned to the segment 214a, 214b. In order to generate the image that is assigned to the segment 214a, 214b that has been switched to transparent, the segment 214a, 214b is imaged onto the projection surface 202 by an imaging lens 220 of the imaging optics 210. On the one hand, the device 200 can be used to project a plurality of images onto the projection surface 202 . On the other hand, a short animation composed of the images can be projected onto the projection surface 202 by successively switching the segments 214a, 214b transparent.

The device 200 further comprises a control unit 222 which is connected to the liquid crystal unit 208 and the light source 204 . The control unit 222 is designed to switch the individual segments 214a, 214b of the liquid crystal unit 208 transparent by applying an AC voltage. For this purpose, the control unit 222 is connected to the segments 214a, 214b directly via conductor tracks 224. Alternatively, a multiplex unit can also be used in order to address a plurality of segments 214a, 214b via a conductor track 224. The frequency of the alternating voltage is controlled by the control unit 222 depending on the temperature of the liquid crystal unit 208. If the liquid crystal unit 208 is operated at a higher frequency than intended, the liquid crystal unit 208 acts like an electrical low-pass filter. This means that more voltage is dropped across the electrical resistance of the conductor tracks 224 and the effective voltage present across the segments 214a, 214b decreases. Consequently, the voltage present at the segments 214a, 214b decreases with higher frequency. This is shown below using the 4 and 5 described in more detail. The control unit 222 also controls a potential difference between the AC voltages which are applied to different electrodes 400, 402 (cf. 4 ) of the segments 214a, 214b. The effective voltage applied to the segments 214a, 214b can also be controlled by means of this phase shift, which is explained below on the basis of 4 and 6 is described in more detail.

The control unit 222 is also designed to control the light source 204 such that a luminous flux on a surface 226 of the liquid crystal unit 208 facing the light source 204 has a specific value. In particular, the control unit 222 is designed to control the light source 204 as a function of the temperature of the liquid crystal unit 208 . In other words, the control unit 222 controls the luminous flux density as a function of the temperature of the liquid crystal unit 208. At low temperatures, for example below 0° C., the luminous flux density is increased. Thereby, the liquid crystal unit 208 can be heated and the frame rate can be prevented from being lowered.

In order to determine the temperature of the liquid crystal unit 208, the device 200 can have a temperature sensor which measures the temperature at the liquid crystal unit 208 or in the immediate vicinity of the liquid crystal unit 208.

3 shows an exploded view of the device 300 for projecting images onto the projection surface 202 according to a further exemplary embodiment.

The device 300 includes a housing 302, which in the embodiment according to 3 is embodied as a two-part assembly, for example. The housing 302 consists of a first housing part 304a and a second housing part 304b and is used to fix and adjust the other units of the device 300. The housing 302 is light-absorbing and thus shields off scattered light. The first housing part 304a has a light entry opening 306 directed towards the light source 204. The second housing part 304b has a light exit surface 308 through which the imaging optics 210 images the segments 214a, 214b of the liquid crystal unit 208 onto the projection surface 202 in order to generate the images.

The light source 204 is arranged below the first housing part 304a. The light source 204 includes a circuit carrier 310 on which two LED elements 312a, 312b are arranged, for example. The LED elements 312a, 312b can be dimmed individually, for example by controlling the keying of the voltage present at the LED elements 312a, 312b. Furthermore, the LED elements 312a, 312b can be switched on and off individually. The luminous flux density on the surface 226 of the liquid crystal unit 208 facing the light source 204 can be controlled both by dimming and by switching individual LED elements 312a, 312b on or off.

The liquid crystal unit 208 comprises a first polarizer 314, a liquid crystal 316 and a second polarizer 318. The first polarizer 314 only allows illumination light of a predetermined direction of polarization to pass. The individually controllable segments 214a, 214b are formed in the liquid crystal 316. The liquid crystal 316 rotates the direction of polarization of transmitted light by 90°. The second polarizer 318 only allows light that has passed through the liquid crystal 316 pass a predetermined polarization direction.

The liquid crystal unit 208 is connected to an LCD control unit 320 via the conductive traces 224 . The LCD control unit 320 and the circuit carrier 310 of the light source 204 together form a control unit 222 of the device 300. In the embodiment according to FIG 3 the LCD control unit 320 and the circuit carrier 310 of the light source 204 are each arranged on a separate circuit board. In an alternative embodiment, the LCD control unit 320 and the circuit carrier 310 of the light source 204 can be arranged on a common circuit board.

In the embodiment after 3 the imaging optics 210 includes three optical elements 322a, 322b, 322c. The holding elements 324 are formed on the optical element 322a arranged directly on the liquid crystal unit 208 and are each connected to the liquid crystal unit 208 at a contact surface. The condenser optics 206 are designed in one piece.

4 shows a schematic representation of the liquid crystal unit 208 of the device 200, 300 for generating images on a projection surface 202.

The liquid crystal unit 208 includes the liquid crystal 316 sandwiched between the two glass plates 216,218. In 4 A first electrode 400 is arranged below the liquid crystal 316 and is connected to the control unit 222 via one of the conductor tracks 224 . In 4 Second electrodes 402a, 402b, 402c are arranged above the liquid crystal 316, which are each connected to the control unit 222 via one of the conductor tracks 224 and can be controlled individually by the control unit 222. The areas lying between the first electrode 400 and one of the second electrodes 402a, 402b, 402c are called the segments 214a, 214b, 214c. The areas not lying between the first electrode 400 and one of the second electrodes 402a, 402b, 402c are called non-luminous areas 404. Segments 214a, 214b, 214c and non-luminous areas 404 are in 4 marked by different hatching. The first electrode 400 is common to all segments 214a, 214b, 214c, it is therefore also referred to as the common electrode 400.

By applying an AC voltage to the first electrode 400 and to one of the second electrodes 402a, 402b, 402c, the segment 214a, 214b, 214c lying between the two electrodes is switched to be transparent. If the applied voltage is too high, crosstalk can occur, that is, the non-driven region 404 lying next to a driven segment 214a, 214b, 214c is also switched to be transparent or partially transparent. This leads to a degraded contrast of the device 200, 300.

5 Figure 12 is an equivalent circuit diagram of a segment 214 of liquid crystal unit 208.

Two poles 500a, 500b on the left side of 5 correspond to two poles of the control unit 222. The voltage output by the control unit 222 is denoted by Ue. Two poles 502a, 502b on the right side of 5 correspond to the electrodes of the segment 214a, 214b, 214c. The effective voltage present at the electrodes of the segment 214a, 214b, 214c is denoted by Ua. Between the electrodes 400, 402 the liquid crystal 316 is arranged. This arrangement forms a capacitor 504, the capacitance of which is denoted by C in the equivalent circuit diagram. The electrical resistance of the traces 224 between the control unit 222 and the segment is in 5 denoted by R.

If the control unit 222 outputs an AC voltage Ue with a correspondingly high frequency, the liquid crystal unit 208 in connection with the conductor tracks 224 acts like an electrical low-pass filter. As the frequency of the AC voltage Ue output by the control unit 222 increases, more voltage drops across the resistance R of the conductor tracks 224 . The voltage drop across the capacitance C drops, which means that the effective voltage Ua present at the electrodes of the segment 214a, 214b, 214c also drops. The effective voltage Ua present at the electrodes of the segment 214a, 214b, 214c can thus be controlled by controlling the frequency of the alternating voltage Ue output by the control unit 222.

6 FIG. 6 is a phase diagram 600 of the AC voltage applied to the segments 214a, 214b, 214c to illustrate the mode of operation of the liquid crystal unit 208.

The abscissa corresponds to the time, and the voltage level is shown on the ordinate. A first line 602 represents the voltage curve of a clock signal of the control unit 222. The individual clocks are in 6 indicated by vertical dashed lines and numbered from 0 to 19. A second line 604 represents the voltage profile of a square-wave AC voltage applied to the common electrode 400 . Up to and including clock 9, the voltage level of the common electrode 400 is at a high level, with typical microcontrollers this is typically 5 V, after which the voltage pe gel to a low level, typically 0 V.

A third row 606 represents the voltage waveform of a square-wave AC voltage applied to the second electrode of the first segment 214a. Up to and including clock 8 the voltage level is at the high level, after which the voltage level is lowered to the low level for clock 9, raised again to the high level for clock 10 and finally lowered to the low level. This results in a voltage difference between the common electrode 400 and the electrode 402a of the first segment 214a in cycles 9 and 10, and the segment is switched to be transparent. This voltage difference is shown in a fourth line 608 . Measured against the 20 clock pulses shown, the first segment 214a has a duty cycle of 10%.

A fifth line 610 represents the voltage waveform of a square-wave AC voltage applied to the second electrode of the second segment 214b. Up to and including clock 7 the voltage level is at the high level, after which the voltage level is lowered to the low level for clocks 8 and 9, raised again to the high level for clocks 10 and 11 and finally lowered to the low level. This results in a voltage difference between the common electrode 400 and the electrode 402b of the second segment 214b in cycles 8 to 11. This voltage difference is shown in a sixth line 612 . Measured against the 20 clock cycles shown, the second segment 214b has a duty cycle of 20%.

A seventh line 614 represents the voltage waveform of a square-wave AC voltage applied to the second electrode 402c of the third segment 214c. Up to and including clock 9 the voltage level is at the low level, after which the voltage level is increased to the high level. The voltage profile of the second electrode 402c is therefore anticyclic to the voltage profile of the common electrode 400. This results in a permanent voltage difference between the common electrode 400 and the second electrode 402c of the third segment 214c and the segment 214c remains switched transparent. This voltage difference is shown in your eighth line 216. Consequently, the third segment 214c has a 100% duty cycle.

A phase shift and/or a potential difference between the AC voltages applied to the common electrode 400 and a second electrode 402a, 402b, 402c changes the effective voltage applied to the segment 214a assigned to the respective second electrode 402a, 402b, 402c , 214b, 214c. Thus, a phase shift and/or a potential difference control can be used in addition to the frequency change to control the effective voltage and hence the transmission rate of the segments 214a, 214b, 214c. In particular, the phase can be changed individually for each segment 214a, 214b, 214c. A phase shift and/or a potential difference control is also still possible when the frequency of the AC voltage cannot be increased any further because, for example, the clock frequency of the control unit 222 cannot be increased any further.

Reference List

100

diagram

102

abscissa

104

ordinate

106a, 106b

graph

200

contraption

202

projection surface

204

light source

206

condenser optics

208

liquid crystal unit

210

imaging optics

212

condenser lens

214, 214a, 214b, 214c

segment

216,218

glass plates

220

imaging lens

222

control unit

224

trace

226

Surface

300

contraption

302

Housing

304a, 304b

housing part

306

light entry opening

308

light exit surface

310

circuit carrier

312a,312b

LED element

314

polarizer

316

liquid crystal

318

polarizer

320

LCD control unit

322a, 322b, 322c

optical element

324

holding element

400, 402, 402a, 402b, 402c

electrode

404

non-luminous areas

500a, 500b, 502a, 502b

pole

504

capacitor

600

phase diagram

602, 604, 606, 608, 610, 612, 614, 616

Line

P

Arrow

Claims (13)

Device (200, 300) for generating images on a projection surface (202), with at least one light source (204) for generating illuminating light; a liquid crystal unit (208) with at least two segments (214a, 214b, 214c), each comprising two electrodes (400, 402a, 402b, 402c) and a liquid crystal (316) arranged between the two electrodes, which can each be transilluminated by the illumination light and whose respective transparency can be controlled by means of alternating voltages applied to the electrodes (400, 402a, 402b, 402c); imaging optics (210), which images the illumination light, which shines through the segments (214a, 214b, 214c), to generate the images onto the projection surface (202); and a control unit (222) which is designed to determine the temperature of the liquid crystal unit (208) and the frequencies and the potential differences between the AC voltages present at the electrodes (400, 402a, 402b, 402c) as a function of the temperature of the liquid crystal unit (208 ) to control; wherein the light source (204) is designed in such a way that the luminous flux density on a surface (226) of the liquid crystal unit (208) facing the light source (204) has a value between 7 lm/mm ² and 80 lm/mm ² , in particular between 36 lm/mm 2 mm ² and 48 µm/mm ² . device (200, 300). claim 1 , wherein the control unit (222) is designed to control the light source (204) in such a way that the luminous flux density on a surface (226) of the liquid crystal unit (208) facing the light source (204) is increased when the temperature of the liquid crystal unit (208) is below a predetermined value. device (200, 300). claim 1 or 2 , wherein the control unit (222) is designed to set the frequency of the AC voltage present at the electrodes (400, 402a, 402b, 402c) to a first frequency value when the temperature of the liquid crystal unit (208) has a value below a predetermined temperature value, and set to a second frequency value when the temperature of the liquid crystal unit (208) is at a value greater than the predetermined temperature value. device (200, 300). claim 3 , wherein the control unit (222) is designed to set the frequency of the AC voltage present at the electrodes (400, 402a, 402b, 402c) to the second frequency value when the temperature of the liquid crystal unit (208) has a value between the first predetermined temperature value and has a second predetermined temperature value and set to a third frequency value when the temperature of the liquid crystal unit (208) has a value greater than the second predetermined temperature value. device (200, 300). claim 3 or 4 , wherein the first predetermined temperature value is in the range between -5°C and 30°C. Device (200, 300) according to one of the preceding claims, wherein the control unit (222) controls the frequency of the AC voltage applied to the electrodes (400, 402a, 402b, 402c) such that the frequency has a value between 1 Hz and 40 Hz , when the temperature of the liquid crystal unit (208) is between -40 C and 0°C. Device (200, 300) according to one of the preceding claims, wherein the control unit (222) controls the frequency of the AC voltage applied to the electrodes (400, 402a, 402b, 402c) such that the frequency has a value between 40 Hz and 100 Hz , when the temperature of the liquid crystal unit (208) is between 10°C and 40°C. Device (200, 300) according to one of the preceding claims, wherein the control unit (222) controls the frequency of the AC voltage applied to the electrodes (400, 402a, 402b, 402c) in such a way that the frequency has a value between 100 Hz and 100 kHz , when the temperature of the liquid crystal unit (208) is between 40°C and 200°C, in particular between 60°C and 130°C. Device (200, 300) according to one of the preceding claims, wherein the control unit (222) is designed to measure the level and duration of the potential difference between a first voltage which is present at a first electrode (400) of the liquid crystal unit (208) and all segments ( 214a, 214b, 214c) and at least one second voltage applied to a second electrode (402a, 402b, 402c) of the liquid crystal unit (208) and which is assigned to at least one segment (214a, 214b, 214c) depending on the temperature of the liquid crystal unit (208). A device (200, 300) according to any one of the preceding claims comprising a temperature sensor for measuring the temperature of the liquid crystal unit (208) or the environment of the liquid crystal unit (208). A device (200, 300) according to any one of the preceding claims, wherein the liquid crystal unit (208) is a passive LCD unit. Device (200, 300) according to one of the preceding claims, wherein the device (200, 300) can be connected to a bus system of a motor vehicle, in particular to a LIN bus or a CAN bus. Subassembly for a vehicle, in particular a motor vehicle, with a device (200, 300) according to one of the preceding claims.

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