Abstract:
A liquid crystal projector that has a plurality of light sources for providing light to a light crystal panel, which functions as an image forming unit in the projector. A plurality of light source driving power sources are connected to the plural light sources individually by means of a light source lighting control circuit. As the light source lighting control circuit, a delay circuit, a counter circuit, or a programmed microcomputer is used. By controlling the light source driving power sources, each one of the plural light sources lights up sequentially or alternately in time. The light emitted from the light sources is modulated by the liquid crystal panel to produce a light image, and the light image is projected through the projector lens.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a liquid crystal projector having a light source, a liquid crystal panel, and a projector lens. 
     An example of a conventional liquid crystal projector is shown in FIG. 9 from Japanese Laid-open Patent Publication NO. 5-313115. FIG. 9 is a structural diagram depicting the basic concept of a liquid crystal projector. In FIG. 9, a power source  10  of a liquid crystal projector main body supplies electric power to a light source driving power source  20 . The light source driving power source  20  converts the electric power supplied from the power source  10  into a state optimum for driving a light source  30 , and supplies the electric power to the light source  30 . As the light source  30 , a halogen lamp or the like is used. A condenser lens  40  is used to condense the rays of light from the light  30 , and to transform the rays into parallel light. The transformed rays of light are fed into a liquid crystal panel  50 , which functions as an image forming unit to form an image. The image is later magnified by a projector lens  60 , and a magnified image is projected on a screen  70 . 
     In the conventional constitution, as shown in FIG. 9, since the light efficiency of the light source is extremely low, the image becomes dark when a large image is projected. Accordingly, by using a plurality of light sources, a method for producing a brightness sensation of a large image hag been proposed. However, the problem in this case is that the electric power consumed by one light source is as much as hundreds of watts. Therefore, when plural light sources are lit up or put out simultaneously, the stress to load fluctuations of the power source feeding electric power to the light sources is large, which may lead to breakdown of power source or the like. 
     SUMMARY OF THE INVENTION 
     The liquid crystal projector of the present invention comprises plural light sources, a liquid crystal panel for modulating the light emitted from the lighting light source out of the plural light sources, corresponding to image information, and a projector lens for projecting a light image modulated by the liquid crystal panel. Each one of the plural light sources emits light sequentially in time. The emitted light is modulated by the liquid crystal panel, and a light image is produced. The light image is projected by a projector lens. The liquid crystal panel is a valve for controlling the transmission of light. 
     With this arrangement, the fluctuation width of the load of the power source supplying electric power to the light source is decreased, the occurrence of troubles, such as a breakdown of the power source or light source is prevented, and a bright image is obtained. 
     In the present invention, preferably, when a switch of a power source is switched on, each one of the plural light sources starts emitting light sequentially delayed in time. Such a constitution has the advantage of a providing a bright image without fluctuations in power and breakdowns of the power and light sources. 
     The liquid crystal projector, according to the present invention further comprises, plural light-source-driving-power-sources connected to the plural light sources individually, and light-source-lighting-control-means for sending a light-source-lighting-control-signal to the plural light-source-driving-power-sources, whereby each one of the plural light sources lights up or emits light sequentially by means of the light-source-lighting-control-means. 
     Another liquid crystal projector, according to the present invention comprises, plural light sources, a liquid crystal panel for modulating the light emitted from the plural light sources corresponding to image information, and a projector lens for projecting a light image modulated by the liquid crystal panel. At least two of the plural light sources emits light alternately. This arrangement provides the advantage of improving the life of the light sources. 
     In the present invention, the light-source-lighting-control-means is a delay circuit, and each one of the plural light sources lights up sequentially by the delay circuit, which provides time controlled signals to each of the light-source-driving-power-sources. 
     As a variation, the light-source-lighting-control-means is a counter circuit that provides time controlled signals to each of the light-source-driving-power-sources. 
     In another variation, the light-source-lighting-control-means is a programmed microcomputer that provides time controlled signals to each of the light-source-driving-power-sources. 
     The present invention provides the advantages of decreasing the fluctuation width of the load of the power source for supplying electric power up to the light source, preventing the occurrence of troubles such as the breakdown of the power source or light source, and results in a bright image. 
     The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block structural diagram of a liquid crystal projector of an embodiment of the invention. 
     FIG. 2 is a structural diagram of a light source lighting control circuit in FIG. 1 using a delay circuit. 
     FIG. 3 is a structural diagram of a light source lighting control circuit in FIG. 1 using a counter circuit. 
     FIG. 4 is a structural diagram of the light source lighting control circuit in FIG. 1 using a microcomputer. 
     FIG. 5 is an example of a timing chart of a light source lighting control circuit shown in FIG. 2, FIG. 3, and FIG. 4 
     FIG. 6 is another example of a timing chart of a light source lighting control circuit shown in FIG. 2, FIG. 3, and FIG.  4 . 
     FIG. 7 shows an example of a flickered for the embodiment in FIG.  4  and FIG.  5 . 
     FIG. 8 shows an example of a flickered for the embodiment in FIG.  4  and FIG.  6 . 
     FIG. 9 is a structural diagram of a conventional liquid crystal projector. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     FIG. 1 is a structural block diagram of a power source, light source and control circuit for a liquid crystal projector according to a first embodiment of the invention. In this embodiment the light source comprises a plurality of light sources. 
     In FIG. 1, a power source  11  of a liquid crystal projector main body supplies electric power to light source driving power source  21  comprising a plurality of sources a to d. As the light source  31 , the same number of light sources a to d are provided as the number of light source driving power sources a to d. Each of the light source driving power sources a to d are individually connected to the light sources a to d, respectively. The light source driving power sources a to d transform the electric power supplied from the power source  11  of the liquid crystal projector main body into an optimum state for driving the light sources a to d. A light source lighting control circuit  81  is light source lighting control means used to control the light source driving power source  21 . The supply of electric power to the light sources a to d is on/off controlled by light source lighting control signals B 1  to B 4 , which are released from the light source lighting control circuit  81 . Each of the light source lighting control signals B 1  to B 4  is connected to one of the corresponding light source driving power sources a to d, respectively. 
     In particular, when a light source on/off signal (key signal A), which is generated by an external switch or the like, is fed into the light source lighting control circuit  81 , the light source lighting control circuit  81  generates a light source lighting control signal B 1 , delayed by T 1 , from the key signal A, as shown in an example of a timing chart in FIG.  5 . As further depicted in FIG. 5, the light source lighting control circuit  81  also generates a light source lighting control signal B 2  delayed by T 2  from the key signal A etc. In this way, the light source lighting control signals B 1  to B 4  are created on the basis of key signal A, and these signals are transmitted to the light source driving power sources a to d. 
     The delay time T 1  to T 4  may be varied. As shown in FIG. 6, the light source lighting control circuit  81  may generate light source lighting control signal B 1  delayed by T 11  from a key signal A, and generate light source lighting control signal B 2  delayed by T 12  from light source lighting control signal B 1 , and thereafter in the same manner, light source lighting control signals B 3 , B 4  delayed by T 13 , T 14  may be generated. 
     The delay time T 1  to T 4 , T 11  to T 14  may be set freely depending on the requirement. 
     The light source driving power sources  21   a  to  21   d , upon receiving the light source lighting control signals B 1 , to B 4  sequentially, start to supply electric power to the light sources  31   a  to  31   d.  In this manner, a sequential lighting control of the light sources  31   a  to  31   d  is realized. 
     As a variation, five or more light sources may be used. With such an arrangement, each one of the plural light sources emits light sequentially in time. 
     A liquid crystal projector provided with power and light sources according to the first embodiment has the advantage of providing brighter images, reducing the load fluctuation width of the power source  11 , and preventing breakdown and other troubles. 
     Embodiment 2 
     FIG. 2 shows a structural example of the light source lighting control circuit  81  in FIG.  1 . As shown in FIG. 2, the delay circuits  91   a  to  91   d , respectively, have circuit time constants T 1  to T 4 . The light source lighting control signals B 1  to B 4  are generated by the delay circuits with the timing as shown in FIG. 5, or any other time setting, depending on the requirement. 
     In particular, with the arrangement shown in FIG. 5, a key signal A generated by an external switch or the like is simultaneously entered in the delay circuits  91   a  to  91   d.  The delay circuits  91   a  to  91   d  generate light source lighting control signals B 1  to B 4  so that the timing may be as shown in FIG. 5, and transmit the control signals to the light source driving power sources  21   a  to  21   d.  The light source driving power sources  21   a  to  21   d , upon receiving the light source lighting control signals B 1  to B 4  sequentially start to supply electric power to the light sources  31   a  to  31   d , so that a sequential control of the lighting of the light sources  31   a  to  31   d  is realized. 
     Hence, according to the present invention, the load fluctuation width of the power source  11  becomes smaller, and the breakdown of the power source  11  and other troubles can be prevented. 
     Embodiment 3 
     FIG. 3 is a structural example of the light source lighting control circuit  81  in FIG. 1 in the form of a counter circuit  92 . As shown in FIG. 3, a counter circuit  92  may be employed as the control circuit and the time setting set depending on the application requirement. The light source lighting control signals B 1  to B 4  may be generated with the time settings shown in FIG. 5 or FIG. 6 with a counter circuit  92 . 
     In this embodiment, a key signal A, which is generated by an external switch or the like, is applied to the counter circuit  92 . The counter circuit  92  counts the time of T 1  to T 4 , or T 11  to T 14 , or any other time setting desired, so that the timing may be as shown in FIG. 5 or FIG. 6, and generates light source lighting control signals B 1  to B 4  that are transmitted to the light source driving power sources  21   a  to  21   d.    
     The light source driving power sources  21   a  to  21   d , upon receiving the light source lighting control signals B 1  to B 4 , sequentially start to supply electric power to the light sources  31   a  to  31   d , so that the light sources  31   a  to  31   d  are controlled sequentially. 
     Hence, the present invention provides the advantage of smaller load fluctuations of the power source  11 , and in preventing the breakdown of the power source  11  and other troubles. 
     Embodiment 4 
     FIG. 4 depicts another variation for realizing the light source lighting control circuit  81  in FIG.  1 . In this embodiment, a microcomputer  93  is used to generate the sequentially time delayed control signals. As shown in FIG. 4, when key signal A that is generated by an external switch or the like is fed into the microcomputer  93 , the microcomputer  93  starts up a program according to an example of a flickered as clearly shown in FIG. 7 or FIG.  8 . The microcomputer generates the light source lighting control signals B 1  to B 4  according to the timing shown in FIG. 5 or FIG. 6, and transmits the control signals in a sequential to the light source driving power sources  21   a  to  21   d.    
     The light source driving power sources  21   a  to  21   d , upon receiving the light source lighting control signals B 1  to B 4 , sequentially start to supply electric power to the light sources  31   a  to  31   d , in a time delayed sequential manner so that the light sources  31   a  to  31   d  are lit on/off in a sequential manner. 
     Hence, the load fluctuation width of the power source  11  becomes smaller, and the breakdown of the power source  11  and other troubles can be prevented. 
     In this way, the liquid crystal projector of the invention employs a plurality of light sources, which light up sequentially in order to obtain bright images. 
     According to the invention, when turning on and off a plurality of power sources, the load fluctuation width of the power source  11  becomes smaller, and a breakdown of the power source  11  and other troubles can be prevented. 
     Embodiment 5 
     A fifth embodiment is a variation of Embodiment 1. In the fifth embodiment, the light source block  31  comprises: (i) a first group of light sources including the first light source  31   a  and the second light source  31   b;  and (ii) a second group of light sources including the third light source  31   c  and the fourth light source  31   d.  The light source lighting control circuit functions to control the first and second groups of light sources alternately. In particular, when the first group of light sources  31   a ,  31   b  is emitting light, the second group of light sources  31   c ,  31   d  is not emitting light. With this arrangement, an improvement in the life of the light sources is obtained. 
     Of course, it should be understood that a wide range of changes and modifications can be made to the preferred embodiment described above and that the foregoing description be regarded as illustrative rather than limiting. It is therefore intended that it is the following claims, including all equivalents, which are intended to define the scope of this invention.