PROJECTION DEVICE AND METHOD FOR PROJECTING AT LEAST ONE IMAGE ONTO A PROJECTION SURFACE

Abstract

A projection device for projecting at least one image onto a projection surface is provided. According to the present disclosure, a control device of the projection device is designed, on the basis of an evaluation of at least one measured value of a measuring device of the projection device determined during a drive of a discharge lamp of the projection device with a current waveform to be checked, to check the current waveform in respect of its suitability for minimizing an electrode burn-back of a first electrode and a second electrode, and in the case of a positive check result, to retain the checked current waveform, and in the case of a negative check result, depending on a checked commutation vector characterizing the checked current waveform, to create, by means of a specifiable algorithm, a modified commutation vector that characterizes a modified current waveform.

Claims

1. A projection device for projecting at least one image onto a projection surface, comprising: at least one discharge lamp operated by alternating current with a first electrode and a second electrode, a control device for driving the discharge lamp, wherein the control device is designed to drive the discharge lamp in such a way that the at least one image is projected with a specifiable refresh rate onto the projection surface, wherein the control device is designed to provide at least one base current waveform for driving the discharge lamp, wherein the base current waveform exhibits a current commutation scheme that is described by a commutation vector that comprises a binary value for specifiable locations of a possible current commutation which states whether a current commutation takes place at the location concerned, and a measuring device for determining a measured value correlated to a state variable of the discharge lamp, wherein the control device is designed, on the basis of an evaluation of at least one measured value of the measuring device determined during a drive of the discharge lamp with a current waveform to be checked, to check the current waveform in respect of its suitability for minimizing an electrode burn-back of the first electrode and the second electrode, and in the case of a positive check result, to retain the checked current waveform, and in the case of a negative check result, depending on a checked commutation vector characterizing the checked current waveform to create, by means of a specifiable algorithm, a modified commutation vector that characterizes a modified current waveform.

2. The projection device as claimed in claim 1, further comprising a color wheel with a specifiable number of color segments, through which each position of a possible current commutation is determined, wherein the projection device is implemented as a DLP projector.

3. The projection device as claimed in claim 1, wherein the projection device is implemented as an LCD projector which is designed to provide the individual color components for projecting at least one image onto a projection surface simultaneously.

4. The projection device as claimed in claim 1, wherein the control device is designed to perform the evaluation of at least one measured value of the measuring device in the form of a determination of a rate of change within a specifiable test time interval.

5. The projection device as claimed in claim 1, wherein the control device is designed to perform the evaluation of at least one measured value of the measuring device in the form of a trend analysis of a specified number of measured values over a specifiable time interval.

6. The projection device as claimed in claim 1, wherein the control device is designed to perform the testing of the current waveform in respect of its suitability for minimization of an electrode burn-back of the first electrode and the second electrode in a dimmed operating state of the discharge lamp, in which the power currently being drawn by the discharge lamp is at most 90% of the rated power of the discharge lamp.

7. The projection device as claimed in claim 1, wherein the control device is designed to carry out the drive of the discharge lamp during a test phase with a direct current for the detectability of an electrode tip state of whichever of the first electrode or the second electrode is being operated as the anode during the test phase.

8. The projection device as claimed in claim 1, wherein the measuring device is designed to determine an electrical voltage between the first electrode and the second electrode as the state magnitude of the discharge lamp.

9. The projection device as claimed in claim 8, wherein the control device is designed to provide the positive test result in respect of the suitability of the current waveform for the minimization of an electrode burn-back of the first electrode and of the second electrode when a voltage change, as a change in the electrical voltage in the course of a specifiable measuring time interval, adopts at least the value of a lower voltage threshold and at most the value of an upper voltage threshold, and to provide the negative test result when the voltage change adopts a value outside a range specified by the lower voltage threshold and by the upper voltage threshold.

10. The projection device as claimed in claim 1, wherein the control device is designed to set an uneven number of commutations when generating a modified commutation vector.

11. The projection device as claimed in claim 10, wherein the control device is designed to set a specifiable frequency modulation factor of the modified current waveform when generating the modified commutation vector.

12. The projection device as claimed in claim 10, wherein the control device is designed to set a mean frequency generated by the commutations within a frequency range defined by a specifiable minimum frequency and/or by a specifiable maximum frequency when generating the modified commutation vector related to individual segments or to the entire sequence of the modified current waveform.

13. The projection device as claimed in claim 10, wherein the control device is designed to evaluate a configuration vector that is designed to identify specifiable positions of a possible commutation as the positions of an unwanted commutation or as the positions of a preferred, active commutation when generating the modified commutation vector.

14. The projection device as claimed in claim 1, wherein the control device is designed to determine, on the basis of the checked commutation vector, the modified commutation vector from the checked commutation vector in such a way that an inactive first position of the checked commutation vector which is adjacent to an active second position of the checked commutation vector is set to active in the modified commutation vector, and the active second position of the checked commutation vector is set to inactive in the modified commutation vector.

15. The projection device as claimed in claim 1, wherein the control device is designed to determine, on the basis of the checked commutation vector, the modified commutation vector from the checked commutation vector in such a way that either an inactive first position of the checked commutation vector which is adjacent to an active second position of the checked commutation vector is set to active in the modified commutation vector, or an active first position of the checked commutation vector which is adjacent to an active second position of the checked commutation vector is set to inactive in the modified commutation vector.

16. A control device of a projection device for projecting at least one image onto a projection surface, the projection device comprising: at least one discharge lamp operated by alternating current with a first electrode and a second electrode, a control device for driving the discharge lamp, wherein the control device is designed to drive the discharge lamp in such a way that the at least one image is projected with a specifiable refresh rate onto the projection surface, wherein the control device is designed to provide at least one base current waveform for driving the discharge lamp, wherein the base current waveform exhibits a current commutation scheme that is described by a commutation vector that comprises a binary value for specifiable locations of a possible current commutation which states whether a current commutation takes place at the location concerned, and a measuring device for determining a measured value correlated to a state variable of the discharge lamp, wherein the control device is designed, on the basis of an evaluation of at least one measured value of the measuring device determined during a drive of the discharge lamp with a current waveform to be checked, to check the current waveform in respect of its suitability for minimizing an electrode burn-back of the first electrode and the second electrode, in the case of a positive check result, to retain the checked current waveform, and in the case of a negative check result, depending on a checked commutation vector characterizing the checked current waveform, to create, by means of a specifiable algorithm, a modified commutation vector that characterizes a modified current waveform.

17. A method for projecting at least one image onto a projection surface by means of a projection device, which comprises at least one discharge lamp with a first electrode and a second electrode, and a control device for driving the discharge lamp, wherein the control device is designed to drive the discharge lamp in such a way that the at least one image is projected with a specifiable refresh rate onto the projection surface, wherein the control device is designed to provide at least one base current waveform for driving the discharge lamp, wherein the base current waveform exhibits a current commutation scheme that is described by a commutation vector that comprises a binary value for each location of a specifiable current commutation which states whether a current commutation takes place at the location concerned, as well as a measuring device for determining a measured value correlated to a state variable of the discharge lamp, the method comprising: determining at least one measured value of the measuring device during a drive of the discharge lamp with a current waveform to be checked, checking the current waveform with respect to its suitability for minimizing an electrode burn-back of the first electrode and the second electrode, on the basis of an evaluation of the at least one measured value, and in the case of a positive check result, retaining the checked current waveform, and in the case of a negative check result, depending on a checked commutation vector characterizing the checked current waveform generating a modified commutation vector that characterizes a modified current waveform by means of a specifiable algorithm.

18. The projection device as claimed in claim 1, wherein the control device is designed to perform the testing of the current waveform in respect of its suitability for minimization of an electrode burn-back of the first electrode and the second electrode in a dimmed operating state of the discharge lamp, in which the power currently being drawn by the discharge lamp is at most 80% of the rated power of the discharge lamp.

19. The projection device as claimed in claim 1, wherein the control device is designed to perform the testing of the current waveform in respect of its suitability for minimization of an electrode burn-back of the first electrode and the second electrode in a dimmed operating state of the discharge lamp, in which the power currently being drawn by the discharge lamp is at most 90% of the rated power of the discharge lamp.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The invention is to be explained in more detail below with reference to exemplary embodiments. In the figures:

[0049] FIG. 1 shows a simplified, schematic illustration of a form of embodiment of the operating method according to the invention;

[0050] FIG. 2 shows an exemplary base current waveform WF.sub.0;

[0051] FIG. 3 shows an exemplary series of measurements at a first time point;

[0052] FIG. 4 shows an exemplary series of measurements at a second time point;

[0053] FIG. 5 shows an exemplary first current waveform WF.sub.1;

[0054] FIG. 6 shows an exemplary series of measurements at a third time point;

[0055] FIG. 7 shows an aging characteristic as a curve of the lamp voltage U against the duration of operation t.sub.op;

[0056] FIG. 8 shows an exemplary series of measurements at a first time point at reduced power;

[0057] FIG. 9 shows an exemplary series of measurements at a second time point at reduced power;

[0058] FIG. 10 shows an exemplary series of measurements at a third time point at reduced power.

PREFERRED EMBODIMENT OF THE INVENTION

[0059] A simplified schematic illustration of an operating method according to the invention is illustrated in FIG. 1. The starting point is a base current waveform WF.sub.0, which has previously been determined by the manufacturer by means of extensive series of tests, for example in endurance tests with a specific number of test items in order to determine the aging behavior and/or the synchronization of an ensemble of lamps, in appropriate cases with the assistance of direct measurement methods for assessing the electrode geometry in that, for example, the discharge arc is projected by means of a suitable lens onto an observation screen.

[0060] FIG. 2 shows an exemplary current waveform WF.sub.0; the second curve, with a rectangular shape, shows a synchronization signal SCI, which inverts its value with every rotation of a color wheel. Usually, an image refresh frequency/frame rate is 60 hertz (NTSC) or 50 hertz (PAL), wherein, in a preferred form of embodiment, a DLP projector with a color wheel is used, wherein the color wheel makes two rotations for each video frame. Thus, for example, with a 60 hertz image refresh rate and two color wheel rotations, in the example illustrated with one commutation for each rotation of the color wheel, a lamp frequency of 60 hertz results.

[0061] The base current waveform WF.sub.0 used as the starting point has a symmetrical structure, to the extent that the anode and cathode phase of a first electrode are always of equal length. Following the start, a running index i is at first 0, and the current waveform WF.sub.0 corresponding to WF.sub.i (i=0) is made available for a specifiable first time T.sub.1 for output to the lamp.

[0062] Based on a drive of the lamp with this current waveform WF.sub.0, at the beginning of operation (T=0 hours) a lamp voltage U can now, for example, be 75 volts, a lamp power P can be 190 watts, and a lamp current I can be 2.53 amperes.

[0063] In the example illustrated, the first time T.sub.1=10 hours. As a rule, a time that is sufficiently long to obtain a reliable conclusion about a voltage trend should be chosen. After the waiting time Δt=T.sub.1 has elapsed, the current waveform now being provided, WF.sub.i (i=0), is checked. This check is carried out according to the illustration in FIG. 1 by a first function block WF-Check, for example in the form of a measurement of six sequential measurements of the lamp voltage U at intervals of 10 minutes.

[0064] FIG. 3 shows an exemplary measurement on a scatter plot, in which the time t is plotted schematically on the abscissa, and the lamp voltage U on the ordinate. In addition to the six measurement points, a linear regression line, with which a gradient dU/dt can be determined, is also drawn for illustration. The linear regression line drawn here stands in representatively for a possible implementation for calculation of the value of dU/dt. This can, for example, be 0.05 volts/hour.

[0065] As a possible criterion for checking the suitability for minimization of an electrode burn-back, a maximum permitted voltage change rate is defined as dU/dt=+/−0.1 volts/hour. The measured rate of change of 0.05 volts/hour thus lies in the defined range, as a consequence of which the present current waveform WF.sub.0 is retained, and a check is made again after the first time T.sub.1 has elapsed.

[0066] At T=10 hours, for example, the lamp voltage U is 77 volts, the lamp power P is 190 watts, and the lamp current I is 2.47 amperes. After a further waiting time Δt=T.sub.1 has elapsed, a further check is made of the current waveform WF.sub.i (i=0) presently being provided, at an operating time of T=20 hours.

[0067] FIG. 4 shows for this purpose a scatter plot of an exemplary measurement. In comparison with the similar illustration of FIG. 3, the linear regression line has a significantly higher gradient, being for example 0.125 volts/hour.

[0068] The criterion for the test of suitability for minimization of an electrode burn-back (dU/dt=+/−0.1 volts/hour) would thus not be satisfied, and the flow branches to a second function block, WF-Change. This changes the current waveform WF.sub.0 used most recently for drive of the lamp in such a way that it modifies a commutation vector K.sub.0 that characterizes the current waveform WF.sub.0 in that it inserts a further commutation.

[0069] Different forms of embodiment of the second function block WF-Change, which may include at least one of the following features in any combination, are conceivable here. With n segments, 2.sup.n waveform schemes are theoretically possible (typically: 8 to 12 segments, meaning between 256 and 4096 waveforms).

[0070] It should be noted here that useful secondary constraints can significantly reduce the number of possibilities, for example the requirement for an uneven number of commutations within one periodicity interval of the current waveform, so that a direct component is not present in the lamp current. The relevant periodicity interval correlates here with the above-mentioned image refresh frequency/frame rate.

[0071] In addition, it may be that a particular modulation factor is to be maintained, determined, for example, according to the teaching of DE 10 2011 089 592 A1.

[0072] Minimum or maximum frequencies that are to be maintained, averaged over individual waveform sections or over the entire current waveform, may also be specified.

[0073] The individual positions of the commutation vector can, furthermore, be marked by a flag indicating whether, at the corresponding location, no commutation is to take place or that preferably a commutation is to take place. Such a preferencing can also be expressed as a vector, for example in the form

(0 +1 0 0 −1 0 +1 0)

where 0 stands for indifferent weighting, −1 for a commutation to be suppressed, and +1 for a commutation to be preferentially activated.

[0074] With purely binary representation, the preferencing can be performed by a 2*n matrix, where

[00002]$\left(\begin{array}{c}0\\ 0\end{array}.Math.\begin{array}{c}1\\ 0\end{array}.Math.\begin{array}{c}0\\ 0\end{array}.Math.\begin{array}{c}0\\ 0\end{array}.Math.\begin{array}{c}0\\ 1\end{array}.Math.\begin{array}{c}0\\ 0\end{array}.Math.\begin{array}{c}1\\ 0\end{array}.Math.\begin{array}{c}0\\ 0\end{array}\right)$

describes the same configuration as before.

[0075] In a first pass, the current waveform WFi can be changed in such a way that one of the commutations is shifted to a neighboring position of the commutation vector, meaning that a commutation vector

K.sub.i=(0 1 1 0 0 0 1 0)

can be changed to a commutation vector

K.sub.i+1=(0 1 1 0 0 0 0 1).

[0076] During a shift in the opposite direction, the following commutation vector would also be conceivable:

K.sub.i+1=(0 1 1 0 0 1 0 0).

[0077] The modified commutation vector K.sub.i+1 is to be verified, and to be rejected if necessary, in accordance with the secondary constraints that are to be taken into account, as described above. If rejected, another commutation vector K.sub.i+1 is to be determined. Known algorithms, such as for example the “random walk” or the “downhill simplex”, can be used to determine the modified commutation vector K.sub.i+1.

[0078] A first current waveform WF.sub.1 derived from the base current waveform WF.sub.0 is illustrated in FIG. 5. Here, in an interval given by two color wheel rotations, a third commutation is added to the two commutations that already exist. The two current waveforms WF.sub.0 and WF1 are arranged directly under one another in FIGS. 2 and 5, and have been given vertical orientation lines which, at locations with a communication of the same phase, meaning with a change in current direction of the current waveform WF.sub.0 and of the current waveform WF1 simultaneously from a positive direction into a negative direction, or simultaneously from a negative direction into a positive direction, are labeled with DIR, and at a counter-phase commutation, meaning that with an opposing change in current direction of the two current waveforms WF.sub.0 and WF.sub.1, wherein one of the two current waveforms changes from a positive direction into a negative direction and at the same time the other from a negative direction into a positive direction, are labeled with REV. The locations of the newly added third commutation are labeled with ADD.

[0079] In addition to the generation of new frequencies with a markedly asymmetric current waveform WF.sub.1, it can furthermore be seen that as a result of the insertion of commutations, the mean lamp frequency rises, in the example illustrated from 60 Hz to 90 Hz. The mean lamp frequency is here given as ½ times the number of commutations per frame, times the frame frequency. For this reason, the current waveform WF.sub.1 leads to a changed growth behavior of peaks on the electrodes of the discharge lamp as compared with the current waveform WF.sub.0.

[0080] The advantages of the uneven number of commutations in terms of a current waveform that, as a matter of principle, does not contain a DC component, must therefore be weighed against the possible disadvantages that arise through the introduction of visually perceptible refresh frequencies of individual color segments (scintillations). The previously-named secondary constraints in terms of minimum or maximum frequencies can here advantageously be considered to prevent further unwanted disturbances.

[0081] Based on a drive of the lamp with the current waveform WF.sub.1, at, for example, T=20 hours, the lamp voltage U can be 80 volts, the lamp power P can be 190 watts, and the lamp current I can be 2.375 amperes.

[0082] As a result of the change of the current waveform used for drive of the lamp from the current waveform WF.sub.0 to the current waveform WF.sub.1, the transfer of the current waveform is henceforth not carried out after a relatively long waiting time Δt=T.sub.1, but after a second time T.sub.2, which is preferably significantly shorter than the first time T.sub.1, wherein the second time T.sub.2 can, for example, be 20 minutes.

[0083] After the waiting time Δt=T2 has elapsed, the current waveform now being provided, WF.sub.i (i=1), is checked.

[0084] This check can, for example, be carried out in the form of a measurement of six sequential measurements of the lamp voltage U at intervals of 10 minutes, as already described above. The number of individual measurements can be reduced, and/or the interval between the individual measurements can be reduced, for the sake of a more quickly available result.

[0085] In this connection, FIG. 6 shows a scatter plot of an exemplary measurement. In comparison with the similar illustration of FIG. 3, the linear regression line has a gradient of a similar magnitude, being for example 0.06 volts/hour. The measured rate of change of 0.06 volts/hour thus lies in the defined range, as a consequence of which the present current waveform WF.sub.1 is retained, and a check is made again after a waiting time Δt, which now again receives the value of the first time T.sub.1, has elapsed.

[0086] Alternatively or in addition to a pure measurement of ΔU/Δt.sub.m during a check interval, an intermediate storage of n voltage values can also be made every x seconds, and the evaluation of the voltage trend can be performed (trend analysis). Preferably, here, a ring buffer to be described cyclically can be used. Through this, a more precise diagnosis of the electrode behavior is possible, in particular including immediately after a change in the commutation vector K on which the drive of the lamp is based.

[0087] A yet deeper analysis of the electrode state can be done through the deliberate introduction of DC test phases for assessment of the tip state in accordance with the teaching of WO 2013/131802 A1.

[0088] In particular, a further measuring device can be present, by means of which a further state magnitude of the lamp is detected and made available for evaluation by the first function block WF-Check, for example the lamp current I or the lamp power P, which is preferably determined indirectly through the power transferred via a direct voltage intermediate circuit of a ballast containing the drive of the discharge lamp.

[0089] In an advantageous form of embodiment, the first function block WF-Check can perform an evaluation of a rate of change ΔU/Δt.sub.m of the lamp voltage U during a check interval Δt.sub.m=T.sub.check in a dimmed state of the discharge lamp, wherein the power presently taken up by the discharge lamp is at most 90% of the rated power of the discharge lamp, preferably at most 80%, in particular at most 70%.

[0090] Since, as a result of the reduction of the electric power supplied, the brightness of the image projected through the projector also reduces, an operating state of this sort can preferably be run in the switching-off process of the lamp, thereby being “hidden”, unnoticed by the user of the projector. Alternatively or in addition, an operating state of the projector of this sort can also be run in a so-called dynamic dimming mode.

[0091] For example, in a normal operating state of the projector, the lamp voltage U can be 75 volts, the lamp power P can be 190 watts, and the lamp current I can be 2.53 amperes. Correspondingly, in an eco-operating state of the projector, the lamp voltage U can be 78 volts, the lamp power P can be 160 watts, and the lamp current I can be 2.05 amperes.

[0092] A typical aging characteristic is shown in FIG. 7 as a curve of the lamp voltage U over an operating period t.sub.op, wherein the operating period is plotted, scaled in the unit of hours, on the abscissa, and the lamp voltage U is plotted, scaled in the unit of volts, on the ordinate. The lamp current I=2.05 amperes which is present in the eco-operating state of the projector is achieved in the normal operating state of the projector at a lamp voltage U=190 watts/2.05 amperes=92.7 volts, in relation to a typical service life this would correspond to an operating period t.sub.op of approximately 700 hours. This means that the electrode behavior of a discharge lamp operated in a dimmed state can be thought of as comparable to that of an aged lamp that is being operated at its rated power.

[0093] To check the current waveform WF.sub.0 that is provided for drive of the lamp after the start in respect of its suitability for minimizing an electrode burn-back, a change is henceforth made in accordance with the above-described aspect of the invention at a time T=0 hours, at which, as in the first example, the lamp voltage U is 75 volts, the lamp power P is 190 watts and the lamp current I can be 2.53 amperes, into a dimming mode which can, for example, be the 160 watt eco-mode.

[0094] A schematic illustration of a corresponding voltage curve is illustrated in FIG. 8. When dimming, the lamp voltage U jumps suddenly from 100% to 84%, and a constant rate of change is then visible in the further continuation in the dimmed state. Six measured values are, for example, evaluated over an evaluation interval Δt.sub.m of 3 minutes. The change in the voltage determined from the linear regression line is, for example, ΔU=−0.1 volts. A specifiable criterion for ΔU=+0.1 to −0.3 volts is thus satisfied. The current waveform WF.sub.0 is thus retained, and a return is made to 100% operation.

[0095] Following a waiting time Δt=T.sub.1, where in this example the first time T.sub.i can be 5 hours, the lamp voltage U is, for example, 78 volts, the lamp power P is 190 watts, and the lamp current I is 2.43 amperes. The power is now again reduced to 84% for the check by the first function unit WF-Check. The following measurement is illustrated, by way of example, in FIG. 9. Following the same evaluation process as was described before, it is found that ΔU=+0.15 volts. This ΔU is outside the specified range for ΔU of +0.1 to −0.3 volts, as a result of which a change in the current waveform WF.sub.0 is initiated according to the method already described. After the evaluation interval has elapsed, a return is made, as before, to 100% operation (normal operating state), and after a waiting time Δt=T2, which can, for example, be 5 hours, a further check cycle takes place.

[0096] With the current waveform WF.sub.1 used for drive of the discharge lamp, at T=10 hours the lamp voltage U is, for example, is 76 volts, the lamp power P is 190 watts, and the lamp current I is 2.5 amperes. The voltage curve of the lamp voltage U after the change to 84% operation is illustrated in FIG. 10. The evaluation of the voltage change AU by means of the linear regression line here yields −0.2 volts. This value satisfies the specified criteria, according to which the value should be in the range from +0.1 volts to −0.3 volts.

[0097] The current waveform WF.sub.1 is therefore retained, and the return is made to 100% operation. A new check is made according to the method already known after a further waiting time Δt=T.sub.1.

[0098] The advantage of this method is that the reaction of the electrodes to the current waveform used for drive of the lamp takes place significantly more quickly, and thus an assessment of whether a concrete current waveform WF.sub.i is suitable for a lamp-protecting operation, meaning one that is aimed at achieving the longest possible service life.

[0099] The above-mentioned methods for obtaining information about the state of the electrodes and/or the development of the electrode geometry under the influence of a current waveform WF.sub.i for drive of the discharge lamp defined by a particular commutation vector K.sub.i can be combined together in any desired way.

[0100] The embodiment only has the purpose of explaining the invention, and does not restrict it. The advantages and features, as well as forms of embodiment, described for the method according to the invention are equally applicable to the projection device according to the invention, and vice versa. Consequently, corresponding device features can be provided for method features, and vice versa.

[0101] Finally it is thus shown how through the use of adaptive current waveforms for the operation of P-VIP lamps, an improved service life performance, a constant voltage trend and a lower scatter in an ensemble of lamps can all be achieved.