GB2457155A

GB2457155A - Projection method where the two periodic control signals and the light modulation signal are synchronised by a clock generator

Info

Publication number: GB2457155A
Application number: GB0901761A
Authority: GB
Inventors: Frank Freund
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-02-08
Filing date: 2009-02-04
Publication date: 2009-08-12
Also published as: FR2927426A1; DE102008008565A1; GB0901761D0; DE102008008565B4

Abstract

A projection method and system comprising a signal generator 2 for generating two periodic control signals 3,4 to excite a biaxial deflection unit, a modulation signal generator 8 for producing a light modulation signal 5 to modulate an intensity of a light beam which is deflected by the biaxial deflection unit, and a clock generator 8 for synchronising the signal generator 2 and the modulation signal generator 8. An image memory 6 may be arranged to store brightness values for pixels of an image to be projected and to output them to the modulation signal generator 8 in response to a clock signal 9 from the clock generator 8, wherein the light modulation signal 5 is generated in response to the output brightness values. The image memory 6 may be a ring buffer wherein the pixels are stored in a sequence corresponding to a Lissajous figure (Figure 2), which is predetermined by the periodic control signals 3,4. The image memory may provide a memory region for storing the pixels and an access table 7 to the memory region wherin entries are sorted in a sequence of the associated pixels as the associated pixels are disposed along a Lissajous figure.

Description

Projection method and control device for a projection device The present invention relates to a projection method and a conirol device for a projection device.

A projection device for an image is known from US 6,843,568. The projection is based on a laser light beam which is deflected along a Lissajous figure by a mirrorpivoting about two axes.

Each point along the Lissajous figure can be used as an pixel of the image by a modulation in the intensity ofthe laser light beam. A deflection device of the mirror detects reversal points of the minor in order to synchronise the modulation unit.

The projection method in accordance with the invention provides the following steps: generating two periodic control signals to excite a biaxial deflection unit; producing a light modulation signal to modulate an intensity of a light beam which is deflected by the biaxial deflection unit; wherein a clock generator synchmnises the two periodic control signals and the light modulation signal.

The method permits simple addressing of all possible points of the Lissajous figure by a simple clock generator.

A control device in accordance with the invention provides: a signal generator for generating two periodic control signals which serve to excite a biaxial deflection unit; a modulation signal generator for producing a light modulation signal for modulating an intensity of a light beam which is deflected by the biaxial deflection unit; and a clock generator for synchmnising the signal generator and the modulation signal generator.

By way of example only, specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a block diagram of a first embodiment of control device for a projection device; Fig. 2 shows a Lissajous figure;

I

Fig. 3 shows a block diagram of a second embodiment of control device for a projection device.

Fig. 1 shows a block diagram of a first embodiment of a control device 1 for a projection system.

A signal generator 2 produces two periodic control signals 3,4. Both control signals 3,4 can serve to drive actuators of a gimbal-mounted mirror. The mirror then begins to pivot about two orthogonal axes with the period of the two control signals 3,4. The deflection of the mirror over time preferably takes place in an approximately sinusoidal manner.

A light beam, e.g. from a laser, is deflected onto a projection screen by the mirror. The two sinusoidal deflections cause the light beam to be guided along a Lissajous curve or figure over the projection surface. A corresponding Lissajous figure is shown in Fig. 2.

The Lissajous figure is repeated periodically by reason of the periodic control. The repetition rate of the Lissajous figure is determined by the largest common fctor of the periods of the control signals 3,4.

The control signals 3,4 can be sinusoidal but can also comprise another periodic signal form. If the excited pivoting of the mirror about its respective axes does not comprise sinusoidal deflection over time then there will be no Lissajous figure 30 in accordance with its mathematical definition but there will still be a closed periodically repeating figure. In the context of this invention such figures should also be considered as Lissajous figures.

In Fig. 2 a raster of pixels of an image is laid under the Lissajous figure 30. Each pixel 31 to be depicted is swept at least once by the Lissajous figure 30. For each pixel 31 the intensity of the light beam is modulated according to the brightness values ofthe pixel 31 when the light beam is guided overthe region of the Lissajous figure 30 corresponding to the pixel 31. The modulation of the intensity of the light beam is controlled by a light modulation signal 5.

The light modulation signal 5 is determined in dependence upon the Lissajous curve and the image to be depicted. The image can first be rasterised into pixels. The pixels are sorted into a sequence which corresponds to the time sequence with which the Lissajous figure is guided over the respective pixels. The pixels are stored in this sequence in an image memory 6.

The light modulation signal 5 is generated by the image memory 6. A clock generator 8 causes the image memory 6 to output the pixels in the sorted sequence. The conversion of the brightness values into a light modulation signal 5 can be effbcted by a modulation signal generator 8.

During sorting of the pixels it is possible to take into account that the Lissajous figure 30 sweeps some pixel more than once until the Lissajous figure is repeated. The frequency of sweeping a single pixel 31 per repetition of the Lissajous figure can be taken into account in the brightness values of the pixels 31 stored in the image memoiy 6. A first variation divides the brightness value, to be depicted, of the pixel 31 by the frequency of sweeping and stores the divided value in the image memory 6. After the first sweep another variation zeros the brightness value for each further sweep.

An alternative provides for producing an access table 7 to the pixels. The entries of the access table 7 are sorted according to the occurrence of the respective pixels in the Lissajous figure.

The actual pixels are not sorted. Access to the pixels is effected via the access table 7. With each clock signal 9 of the clock generator there is a switch to the next entry in the access table 7 and the associated pixel is output to the entry as a light modulation signal 5. In this way single sorting of the access table is sufficient. Sorting of each image to be depicted is no longer necessary at least as long as the properties of the Lissajous figure are maintained.

In addition, the clock signal 9 is used to control the signal generator 2. The signal generator 2 is synchronised with the clock signal 9 so that synchronisation of the modulation signal 5 and of the control signals 3, 4 is ensured.

The synchronisation can use a counter 10, a comparator 11, a value table 12 and a reset signal 13. The counter 10 is clocked by the clock generator 8. The comparator 11 outputs a reset signal 13 to the signal generator 2 when the counter 10 reaches the value(s) stored in the value table 12. The values in the value table 12 can be, amongst other things, the number of clock pulses until a complete Lissajous figure is projected. Other values are the number of clock pulses corresponding to the period ofone orboth of the control signals 3,4.

Figure 3 shows a block diagram of a second embodiment. A signal generator 20 generates two periodic control signals 21,22. The control signals 21, 22 serve to control actuators of a mirror.

The two output control signals 21,22 are supplied to a data processing device which determines the associated pixel 31 of the Lissajous figure 30 with respect to the two control signals 21,22.

The brightness value of the pixel 31 is output to a light modulation device in the fonn of a control signal, e.g. light modulation signal 28. The data processing device can take into account, amongst other things, that a mirror pivots in the event of non-resonant excitation in a time-oflet manner with respect to the control signals 21,22.

Allocation of the control signals 21, 22 to the pixels 31 can also be effected according to the fbllowing process. The two output control signals 21,22 are supplied to an address generator 23. On the basis of the control signals 21,22 and the associated Lissajous figure 30 the address generator determines the associated pixel 31 and its associated address 24 in the image memory 25. The address 24 is supplied to an image memory 25. In the image memoiy2s the brightness values for each pixel of an image are stored. The image memory 25 outputs the brightness value 26 appertaining to the address 24 as a light modulation signal 28. For individual addresses blanking of the light beam may be efThcted. A correction device 27 may possibly carry out the corresponding blanking of the light modulation signal 28.

As with the first embodiment, the signal generator 20 is controlled by a clock generator 8, a counter 10, a comparator 11, a value memory 12 and a reset signal 13. The clock signal 8 is supplied directly to the signal generator 20, whereby the control signals 21, 22 are synchronous to the clock signal 8. The image memory 8 and/or the address generator are controlled indirectly by the clock signal 8 since both control signals 21, 22 are supplied to them. The control process is not dependent upon the projection means used, e.g. mirror, electra-optical modulators, acousto-optic modulators. The synchronisation is effected in a self-sustaining manner.

An external calculation of the association between the Lissajous figure 30 and the raster of the pixels 31 can be omitted. Furthermore, it may be possible to vary the frequencies for the control signals without impairing an allocation of the pixels 31 to be depicted.

A colour projection can be achieved by a plurality of colour light beams and associated projections.

Claims

Claims 1 A projection method comprising the following steps: generating two periodic control signals (3,4; 21, 22) to excite a biaxial deflection unit; producing a light modulation signal (5; 28) to modulate an intensity of a light beam which is deflected by the biaxial deflection unit; wherein a clock generator (8) synchronises the two periodic control signals (3, 4; 21, 22) and the light modulation signal (5; 28).
2 A projection method as claimed in claim 1, wherein in an image memory (6; 25) brightness values for pixels of an image to be projected are stored, which are output as a light modulation signal (5; 28) in response to a clock signal (9) of the clock generator (8).
3 A projection method as claimed in claim 2, wherein the pixels are stored in a sequence corresponding to a Lissajous figure which is predetermined by the periodic control signals (3,4; 21, 22).
4 A projection method as claimed in claini 2, wherein the pixels are stored in a memory region and an access table (7) to the memory region is produced, wherein the entries of the access table (7) are sorted in a sequence of the associated pixels as the associated pixels are disposed along a Lissajous figure which is predetermined by the periodic control signals (3, 4; 21; 22).
A projection method as claimed in claim 2, wherein the two periodic control signals (21, 22) are supplied to an address generator which, on the basis of the control signals (21, 22), determines an address of a pixel which is allocated to the control signals (21,22), and the image memory (25) outputs the brightness value for the pixel detennined by the address.
6 A control device lbr a projection system comprising: a signal generator (2; 20) for generating two periodic conimi signals (3, 4; 21,22) which serve to excite a biaxial deflection unit; a modulation signal generator (8) for producing a light modulation signal (5; 28) for modulating an intensity of a light beam which is deflected by the biaxial deflection unit; and a clock generator (8) for synchronising the signal generator (2; 20) and the modulation signal generator (8).
7 A ontrol device as claimed in claim 6, thrther comprising: an image memory (6; 25) arranged to store brightness values for pixels of an image to be projected and to output them to the modulation signal generator (8) in response to a clock signal (9) of the clock generator (8), wherein the modulation generator (8) is arranged to generate a light modulation signal (5; 28) in response to the output brightness values.
8 A control device as claimed in claim 7, wherein the image memory (6; 25) is a ring buffer, wherein the pixels are stored in a sequence corresponding to a Lissajous figure, which are predetermined by the periodic control signals (3, 4; 21, 22).
9 A control device as claimed in claim 7, wherein the image memory (6; 25) provides a memory region for storing the pixels (31) and an access table (7) to the memory region, wherein entries in the access table (7) to the pixels (31) in the memory region are sorted in a sequence of the associated pixels (31) as the associated pixels are disposed along a Lissajous figure which is predetermined by the periodic control signals (3,4; 21, 22).
A control device as claimed in claim 6, further comprising: an image memory (25) which is arranged to store brightness values for pixels of an image to be projected and to output an associated brightness value to the modulation signal generator (8) in response to an address signal (24), wherein the modulation generator (8) is arranged to generate a light modulation signal (5; 28) in response to the output brightness value, and an address generator (23) which is coupled to the signal generator (20) to detect the two periodic control signals (21, 22), wherein the address generator (23) is arranged to determine, on the basis of the control signals (21,22), an address of a pixel (31) in the image memory (25) which is allocated to the control signals (21, 22), and to output an address signal (24) with the address.
11. A projection method substantially as herein described with reference to, and as illustrated in, the accompanying drawings.
12. A control device for a projection system substantially as herein described with reference to, and as illustrated in, the accompanying drawings.