Projection type display system

Abstract

The present invention suppresses color mixture in a projection image, in a projection type display system in which a light source unit and a projection unit are separated.　A first control unit 110 of a light source unit 100 causes a serial video signal (LVDS VideoS) to be transmitted to a projection unit 300 and measures a delay amount for one way in a communication cable 210. An optical element drive unit 116 drives a plurality of optical elements 117-119 on the basis of a light emission enable signal (R / G / B Enable) transmitted from the projection unit 300. A second control unit 313 of the projection unit 300 transmits a light emission enable signal synchronized with video bit stream data VBSD corresponding to the received video digital signal VD to the light source unit 100, and imparts a delay of the measured delay amount to the video bit stream data VBSD. An optical modulation device 322 modulates, in synchronization with the delayed video bit stream data VBSD, the light transmitted through an optical fiber 220.

Description

Projection Display System

[0001] The present invention relates to a projection display system that is mounted on a vehicle such as an automobile and projects an image onto a road or the like.

[0002] Projection display devices in which the light source unit and the projection unit are separated are described in, for example, Patent Documents 1 and 2.

[0003] JP 2010-78622 A JP 2023-97755 A

[0004] The inventors' research has revealed the following problems. (1) In both the projection display device of Patent Document 1 and the projection display system of Patent Document 2, light for forming a projection image output from a light source unit is supplied to a projection unit via an optical fiber, and the projection unit forms a projection image by modulating (spatial light modulation) the light for forming the projection image using a light modulation device such as a DMD (digital mirror device). Here, if there is a mismatch between the light emission timing of the light source in the light source unit (the output timing of light for forming the projection image) and the modulation timing of the light modulation device in the projection unit, there is a high possibility of color mixing in the projection image. For example, if a red light source is also emitting light during a blue image display period, blue and red colors will be mixed and a magenta image will be displayed. If a blue light source is also emitting light during a green image display period, green and blue colors will be mixed and a cyan image will be displayed. If a green light source is also emitting light during a red image display period, red and green colors will be mixed and a yellow image will be displayed. This can cause display color distortion, color imbalance, etc. (2) One cause of the aforementioned synchronization error is delays in the communication of electrical signals via a communication cable between the light source unit and the projection unit. (3) Furthermore, the amount of delay in electrical signals in the communication cable varies depending on the ambient temperature (ambient temperature) in which the projection display device (projection display system) is placed. For example, the delay length of electrical signals in the communication cable increases at high temperatures compared to low temperatures. Therefore, it is preferable to take measures against the aforementioned synchronization error while also taking the ambient temperature (ambient temperature) into consideration. (4) The aforementioned Patent Documents 1 and 2 do not mention at all the problem of color mixing resulting from the aforementioned synchronization error, which reduces the quality of the displayed image, and do not mention any measures to address this issue.

[0005] Such a problem was made clear through investigations by the inventors of the present invention.

[0006] One of the objects of the present invention is to suppress color mixing in a projected image in a projection display system in which a light source section and a projection section are separated.

[0007] Other objects of the present invention will become apparent to those skilled in the art by referring to the following exemplary aspects and best modes, as well as the accompanying drawings.

[0008] In order to facilitate an understanding of the outline of the present invention, the following examples are given of embodiments according to the present invention.

[0009] In a first aspect, a projection display system is a projection display system in which a light source unit and a projection unit are separated, the light source unit and the projection unit are electrically connected via a communication cable, and light for forming a projection image output by the light source unit is supplied to the projection unit via an optical fiber, and a projection image is formed by the projection unit, wherein the light source unit comprises a first control unit having a function of causing the projection unit to transmit a video signal, a function of causing the projection unit to transmit an outgoing signal for delay measurement, and a function of performing a delay measurement process that measures a one-way delay of the communication cable based on a time difference between a timing at which the outgoing signal for delay measurement is instructed to be transmitted and a timing at which a return signal for delay measurement transmitted from the projection unit is detected, and a function of notifying the projection unit of the delay amount obtained by the delay measurement process; an optical element unit having a plurality of optical elements with different emission colors that generates the light for forming the projection image; and a function of causing the projection unit to emit light for forming the projection image. and a light element driving unit that drives the plurality of light elements based on a light emission enable signal sent thereto, wherein the projection unit has a second control unit that has the functions of generating video bit stream data based on the video signal sent from the light source unit, generating the light emission enable signal synchronized with the video bit stream data and transmitting it to the light source unit, generating a return signal for delay measurement and transmitting it to the light source unit, and setting a first delay amount notified by the light source unit and equivalent to the delay amount acquired by the delay measurement process in the delay unit, and imparting a delay of the first delay amount to the video bit stream data by the delay unit; and a light modulation device that modulates the light for forming the projection image sent from the light source unit via the optical fiber based on the video bit stream data to which the first delay amount has been imparted, thereby forming the projection image.

[0010] In a first aspect, the projection display system has a system configuration in which a light source unit and a projection unit are separate and connected by a communication cable (electrical cable) and an optical fiber cable (hereinafter sometimes simply referred to as optical fiber), and the light source unit and the projection unit are each equipped with a first and second control unit (e.g., a processor). In this projection display system, a video signal is transmitted from the light source unit to the projection unit, and the projection unit generates video bitstream data based on the transmitted video signal. The video bitstream data is a video data string composed of bits consisting of "1" and "0" arranged in chronological order on a time axis.

[0011] The modulation timing of the light modulation device provided in the projection unit is controlled based on (in synchronization with) this video bitstream data. Meanwhile, the second control unit in the projection unit generates a light emission enable signal synchronized with the video bitstream data and transmits the generated light emission enable signal to the light source unit. Here, the light emission enable signal is a light emission control signal (light element control signal) that enables multiple light elements provided in the light source unit to emit light. The light element driving unit of the light source unit causes the multiple light elements to emit light based on (in synchronization with) the light emission enable signal sent, thereby generating light for forming a projection image.

[0012] With this configuration, both the light output timing for forming a projection image from the light source unit and the light modulation timing from the projection unit are controlled based on the video bitstream data, which theoretically ensures synchronization. However, in reality, propagation delays occur when transmitting the light emission enable signal through a communication cable. This delay delays the output timing of the light for forming a projection image, resulting in synchronization errors and color mixing. Note that, because communication via optical fiber is fast, the delay is negligible. Therefore, in this aspect, the first control unit on the light source unit performs a delay measurement process to measure the one-way delay of the communication cable (the delay amount of the light emission enable signal), and notifies (transmits) the projection unit of the delay amount information obtained through this measurement. The second control unit on the projection unit delays the video bitstream data by the notified delay amount and controls the light modulation timing of the light modulation device using the delayed video bitstream data. This effectively suppresses synchronization errors.

[0013] In this aspect, the first and second control units (processors, etc.) mounted on the light source unit and the projection unit, respectively, perform their own functions and cooperate with each other, thereby reliably suppressing synchronization errors.

[0014] In a second aspect dependent on the first aspect, the communication cable may be provided with a first communication line for an outbound signal for delay measurement and a second communication line for a return signal for delay measurement.

[0015] In the second aspect, a dedicated line is used as the communication line for the outgoing signal and the return signal for delay measurement used in the delay measurement process, which simplifies the configuration and the algorithm used in the delay measurement process.

[0016] In a third aspect dependent on the first aspect, in the communication cable, a communication line included in the communication line of the video signal may also be used as a communication line for at least one of the outbound signal for delay measurement and the return signal for delay measurement.

[0017] According to the third aspect, the communication lines included in the communication path used for transmitting the video signal are also used as the communication lines for the outgoing signal and the return signal for delay measurement, which eliminates the need for dedicated communication lines and simplifies the configuration of the communication lines.

[0018] In a fourth aspect dependent on any one of the first to third aspects, a temperature sensor for measuring an ambient temperature may be provided in at least one of the light source unit and the projection unit, and when at least one of the temperature sensors detects that a difference between the ambient temperature and a reference temperature is equal to or greater than a first threshold, or when at least one of the temperature sensors detects that a temperature change in the ambient temperature is equal to or greater than a second threshold, the delay measurement process by the first control unit and the process of applying a delay of the first delay amount to the video bitstream data by the second control unit may be performed.

[0019] In a fourth aspect, a temperature sensor (e.g., a thermistor) is provided in at least one of the light source unit and the projection unit, and this temperature sensor measures the ambient temperature (environmental temperature) of the projection display system. In this aspect, when performing delay measurement processing in the light source unit and delay correction processing (processing for delaying video bitstream data) in the projection unit, the ambient temperature (environmental temperature) of the projection display system is taken into consideration to determine whether to perform each of the above processes. One of the main causes of delay in the communication cable described above is change in ambient temperature (environmental temperature). For example, delay is greater at high temperatures than at low temperatures. For example, when the projection display system is installed in a vehicle, the vehicle's driving environment may change suddenly, so measures that take temperature changes into account are necessary. Situations in which temperature changes become a problem include "when the difference between the ambient temperature and a reference temperature (e.g., 25°C) is equal to or greater than a first threshold (e.g., 5°C)" and "when the ambient temperature changes suddenly, and the change is equal to or greater than a second threshold (e.g., 5°C)." In either case, it is assumed that the delay amount of the electrical signal in the communication cable will vary considerably. According to this aspect, in the above cases, the delay measurement process and the delay correction process can be performed quickly, thereby effectively suppressing degradation of the quality of the projected image.

[0020] In a fifth aspect that is dependent on the fourth aspect, the light source section has a heat dissipation section that dissipates heat generated by the light element section, which is a heat source, and the temperature sensor is provided only in the projection section, or if the temperature sensor is provided in both the light source section and the projection section, the temperature measurement result of the temperature sensor provided in the projection section may take priority.

[0021] In the fifth aspect, in order to prevent a decrease in accuracy in measuring the ambient temperature (environmental temperature), the temperature sensor is provided in a projection unit that does not have a large-sized heat dissipation unit (such as a heat sink, which can be a heat source), or if a temperature sensor is provided in both the light source unit and the projection unit, the measurement results of the temperature sensor provided in the projection unit that does not have a large-sized heat dissipation unit are given priority in determining the temperature.

[0022] This reduces the influence of the heat source of the light source unit, and prevents a decrease in the measurement accuracy in temperature measurement.

[0023] In a sixth aspect dependent on any one of the first to fifth aspects, the projection display system may be an in-vehicle projection display system mounted on a vehicle.

[0024] When a projection display system is installed in a vehicle, the ambient temperature varies depending on the vehicle's driving environment, and the ambient temperature may also change suddenly. According to this aspect, the delay measurement process and delay correction process can be quickly performed in response to changes in the vehicle's driving environment, and degradation of the quality of the projected image can be effectively suppressed. Therefore, high performance can be achieved in an in-vehicle projection display system (e.g., a road projector that displays an image on the road surface).

[0025] Those skilled in the art will easily understand that the exemplified embodiments according to the present invention can be further modified without departing from the spirit of the present invention.

[0026] FIG. 1 shows an example of the external appearance of a projection display system and an example of the basic internal configuration of a light source unit and a projection unit that was considered by the present inventors prior to the present invention. FIG. 2 shows an example of a synchronization error between the actual light emission timing of an optical element and the modulation timing (i.e., the timing of video bitstream data) in the projection display system of FIG. 1. FIG. 3 shows an example of an internal configuration of a light source unit and a projection unit (a configuration for performing delay correction) in the projection display system of the present invention. FIG. 4 shows an example of a process for measuring the amount of delay in a communication cable (using timestamps). FIG. 5 shows an example of a case in which a synchronization error does not occur between the actual light emission timing of an optical element and the modulation timing (i.e., the timing of video bitstream data) in the projection display system of the present invention of FIG. 3. FIG. 6 is a flowchart showing an example of a main procedure for performing delay correction processing.

[0027] The best mode described below is used to facilitate understanding of the present invention, and therefore, those skilled in the art should be aware that the present invention is not unduly limited by the embodiments described below.

[0028] First Embodiment Please refer to Fig. 1. Fig. 1 is a diagram showing an example of the external appearance of a projection display system and an example of the basic internal configuration of a light source unit and a projection unit that was considered by the inventors prior to the present invention.

[0029] In the example of FIG. 1, the projection display system 10 is an in-vehicle projection display system that is mounted on a vehicle (not shown).

[0030] In recent years, there has been a demand for higher brightness in in-vehicle projection display systems (in-vehicle projectors) to improve visibility. However, in order to make the light source shine brighter, it is necessary to efficiently dissipate the heat generated by the light source, and the size of heat sinks and other devices used for heat dissipation tends to increase. As a result, in-vehicle projectors are becoming larger, and it is possible that they will no longer be able to be installed in the limited space of a vehicle.

[0031] Therefore, in the present invention, optical fiber optical transmission technology is used to separate the light source unit and the projection unit, and a separate projection display system (projector system) 10 is constructed. By separating the light source unit 100 and the projection unit 300, the light source unit, which dissipates a large amount of heat, can be installed in an available space in a vehicle, etc., while the projection unit, which forms the projected image, can be installed freely in an appropriate location, separated from the heat source, making it easier to install the projection display system 10 in a vehicle.

[0032] A specific description will be given below with reference to the drawings. As shown in A-1 of Fig. 1, in a projection display system 10, a light source unit 100 and a projection unit 300 are arranged separately, and the light source unit 100 and the projection unit 300 are electrically connected via a communication cable 210. Light for forming a projection image output by the light source unit 100 is supplied to the projection unit 300 via an optical fiber cable (hereinafter sometimes simply referred to as an optical fiber) 220, and a projection image is formed by the projection unit 300. The communication cable 210 can be used to transmit power, control signals, video signals, etc.

[0033] The light source unit 100 has a heat sink 101 as a heat dissipation unit, a control board 102, an integrated circuit device (IC) 103 mounted on the control board 102 and including a microcontroller (MCU: reference numeral 110 in A-2 of FIG. 1) as a first control unit, and a plurality of mirrors 120-122 as optical elements. On the other hand, the projection unit 300 has a projection aperture (exit aperture) 323 that projects (exits) display light for an image.

[0034] 1A-2, the light source unit 100 includes an MCU 110 as a first control unit, a serializer (parallel / serial converter) 112, a deserializer (parallel / serial converter) 114, an optical element drive unit (LC driver) 116, a plurality of optical elements 117-119 emitting different light colors (here, laser diodes corresponding to the colors R (red), G (green), and B (blue)), a plurality of mirrors 120-122, a photodiode (PD) 123 for monitoring optical output, an optical output interface 124, and a power circuit (power supply circuit) 130. The MCU (microcontroller) 110 as the first control unit is an integrated circuit device that integrates a processor that functions as a main CPU (host CPU) with peripheral circuits such as memory.

[0035] An optical element section 125 is configured by a plurality of optical elements 117 to 119 that emit light of different colors, a plurality of mirrors 120 to 122, a photodiode (PD) 123 for monitoring the optical output, and an optical output interface .

[0036] The serializer 112 and the deserializer 114 form a first serial interface unit SIF1.

[0037] The projection unit 300 has a deserializer (serial / parallel converter) 312, a display controller (display control device) 313 as a second control unit, a serializer (parallel / serial converter) 314, an optical input interface 320, an optical modulation device (here, a DMD (digital mirror device) is used) 322, a photodiode (PD) 324 for monitoring optical output, and a power circuit (power supply circuit) 325. The display controller 313 as the second control unit is equipped with a sub-CPU (not shown) and is a dedicated integrated circuit device that performs display control in place of the MCU 110.

[0038] The deserializer 312 and the serializer 314 form a second serial interface unit SIF2.

[0039] The optical modulation device 322 includes a main body 319 incorporating an optical modulation element, an input terminal 321 of the optical modulation device to which video bitstream data VBSD supplied from the display controller 313 is input, and a projection port (exit port) 323 from which display light of the image is projected (exited).

[0040] The optical input interface 320 receives light for forming a projection image transmitted from the light source unit 100 via the optical fiber 220, and supplies the received light (light of each color R, G, and B) to the main body unit 319 of the optical modulation device 322.

[0041] Next, the contents of communication of video signals and control signals via the first serial interface unit SIF1 and the second serial interface unit SIF2 will be described.

[0042] The serial communication signals transmitted and received between the first serial interface unit SIF1 and the second serial interface unit SIF2 include, for example, a serial video signal (LVDS VideoS) transmitted from the light source unit 100 to the projection unit 300 using an LVDS (Low Voltage Differential Signal) transmission method, a light emission enable signal (LDE: specifically, LEDR / G / B LD Enable for each color) which is transmitted from the light source unit 100 to the projection unit 300 and enables the light elements 117 to 119 to emit light, and various communication signals (Communication S1, Communication S2).

[0043] Next, an example of various communication signals will be described. For example, a vehicle-side controller 90 mounted on a vehicle (not shown) can transmit various request commands C1 based on user settings to an MCU (first control unit) 110 of the light source unit 100. Possible request commands include, for example, request commands to change the display brightness, change the color balance, change the image size, change the image position, correct projection distortion, turn the display on / off, etc.

[0044] The MCU 110 sends the received request command as a communication signal C2 to the serializer 112, and the serializer 112 performs parallel / serial conversion on the received communication signal C2 to generate a communication signal Communication S1 and transmits this communication signal Communication S1 to the projection unit 300 via the communication cable 210. The deserializer 312 of the projection unit 300 performs serial / parallel conversion on the received communication signal Communication S1 to generate a communication signal C3 and sends this communication signal C3 to a display controller (second control unit) 313.

[0045] The display controller (second control unit) 313 performs processing in response to various requests from the MCU (first control unit) 110 of the light source unit 100, and generates a signal C4 indicating the results of the processing (for example, a signal indicating that the processing was successful, or a signal indicating a parameter value obtained as a result of the processing) and sends it to the serializer 314. The serializer 314 performs parallel-to-serial conversion of the communication signal C4 to generate a communication signal Communication S2, and transmits this communication signal Communication S2 to the light source unit 100 via the communication cable 210. The deserializer 114 of the light source unit 100 performs serial-to-parallel conversion of the received communication signal Communication S2 to generate a communication signal C5, and sends this communication signal C5 to the MCU (first control unit) 110.

[0046] In this way, the MCU (first control unit) 110 and the display controller (second control unit) 313 can transmit and receive various signals via the first and second serial interface units SF1 and SF2.

[0047] Next, transmission of a video signal will be described. The vehicle-side controller 90 transmits a video signal VideoS to the serializer 112 of the light source unit 100. The serializer 112 generates an LDVS video signal LDVS VideoS based on the received video signal VideoS and transmits it to the projection unit 300 via the communication cable 210. The deserializer 312 of the projection unit 300 converts the received LDVS video signal LDVS VideoS into a parallel digital video signal VD and transmits the digital video signal VD to a display controller (second control unit) 313.

[0048] Next, a method for ensuring synchronization between the output timing of light for forming a projection image in the light source unit 100 (light emission timing of the optical elements 117 to 119) and the light modulation timing in the light modulation device 322 in the projection unit 300 will be described.

[0049] The display controller (second control unit) 313 of the projection unit 300 generates video bit stream data VBSD, in which digital bits of "1" and "0" are arranged in time series on the time axis, based on the received video digital signal VD, and supplies this video bit stream data VBSD to an input terminal 321 of the optical modulation device 322. The optical modulation operation in the optical modulation device 322 is performed in synchronization with this video bit stream data VBSD.

[0050] On the other hand, the display controller (second control unit) 313 generates a light emission enable signal LDE, which is a control signal that is synchronized with the video bitstream data VBSD and that enables the light elements 117 to 119 of the light source unit 100 to emit light. The light emission enable signal LDE may also be referred to as a light emission control signal or a light element control signal.

[0051] The light emission enable signal LDE is sent to the serializer 314, and the serializer 314 transmits the light emission enable signal LDE (specifically, R / G / B LD Enable that controls the light emission of the laser diodes of each color) to the light source unit 100 via the communication cable 210.

[0052] The deserializer 114 of the light source unit 100 supplies the received light emission enable signal LDE (R / G / B LD Enable that controls the light emission of the laser diodes of each color) directly to the light element driving unit 116 so as not to cause any extra delay.

[0053] The optical element driver 116 drives the optical elements (laser diodes) 117 to 119 of each color in the optical element unit 125 based on (in synchronization with) the light emission enable signal LDE. This generates light for forming a projection image. The light for forming a projection image is sent to the projection unit 300 via an optical fiber 220.

[0054] In this way, the light modulation timing of the light modulator 322 in the projection unit 300 is controlled based on (in synchronization with) the video bitstream data VBSD, while the output timing of light for forming a projection image in the light source unit 100 is controlled based on (in synchronization with) the light emission enable signal LDE synchronized with the video bitstream data VBSD.

[0055] In other words, since both the output timing of light for forming the projection image in the light source unit 100 and the light modulation timing in the projection unit 300 are controlled based on the video bitstream data VBSD, synchronization between the transmitting and receiving sides in optical communication via the optical fiber 220 is theoretically ensured.

[0056] Furthermore, power supply PS is supplied from the vehicle-side controller 90 to a power circuit 130 of the light source unit 100. The power circuit 130 supplies a power supply voltage to a power circuit 325 of the projection unit 300 via a communication cable 210. The power circuit 325 supplies the power supply voltage to each unit within the projection unit 300.

[0057] According to the above configuration, both the output timing of light for forming a projection image in the light source unit 100 and the light modulation timing in the projection unit 300 are controlled based on the video bitstream data VBSD, so that synchronization is theoretically ensured. However, in reality, a propagation delay occurs when the light emission enable signal LDE is transmitted via the communication cable 210, and the output timing of light for forming a projection image is delayed by the amount of this delay, causing a synchronization error and resulting in color mixing. Note that, because communication via the optical fiber 220 is fast, the delay can be ignored.

[0058] Next, the cause of color mixing will be explained with reference to Figure 2. Figure 2 is a diagram showing an example of a synchronization error between the actual light emission timing of the optical elements and the modulation timing (in other words, the timing of the video bitstream data) in the light modulation device in the projection display system of Figure 1.

[0059] In FIG. 2, each of the "RLD enable signal (RLDE)," "BLD enable signal (BLDE)," and "GLD enable signal (GLDE)" indicates a light emission enable signal LDE (however, in a state before being transmitted via the communication cable 210) for each laser diode (LD) emitting light of red (R), blue (B), or green (G), which is generated by the display controller 313 of the projection unit 300 shown in A-2 of FIG. 1.

[0060] Furthermore, "RLD power", "BLD power", and "GLD power" each indicate the actual light emission power of the laser diodes (LD) 117 to 119 provided in the light source unit 100 and emitting light of R, B, or G, respectively.

[0061] In the figure, Δt indicates the amount of delay that occurs when transmitting each of the “RLD enable signal (RLDE)”, “BLD enable signal (BLDE)”, and “GLD enable signal (GLDE)” via the communication cable 210.

[0062] Due to this delay, the timing of each of the "RLD power", "BLD power", and "GLD power" is delayed by Δt relative to the timing of each of the "RLD enable signal (RLDE)", "BLD enable signal (BLDE)", and "GLD enable signal (GLDE)". This delay causes color mixing.

[0063] For example, let us focus on the period from time t3 to time t6. During this period, the video bit stream data is "B data," so the blue LD 119 is actually emitting light during this period, and this light emission period corresponds to point Z2 (the first half of the BLD power period) indicated by the dashed ellipse in FIG. 2.

[0064] However, in reality, from time t3 to time t4, the red LD 117 emits light at a normal light emission level in the on state (see point Z1 indicated by the dashed oval).

[0065] In other words, points Z2 and Z1 indicated by the dashed ellipses overlap on the time axis, and therefore, during the period from time t3 to t6 (the period during which the blue image is normally displayed), the red LD 117 emits light at its normal light emission level from time t5 to t6, and the blue LD 119 emits light at its normal light emission level from time t5 to t6, resulting in color mixing over time, and the user's eyes perceive a magenta image as a mixture of red and blue.

[0066] Similarly, during the period from time t6 to t9 (the period during which a green image is normally displayed), points Z4 and Z3 indicated by dashed ellipses overlap on the time axis, and therefore, from time t6 to t7, blue LD 119 emits light at its normal light emission level, and from time t8 to t9, green LD 118 emits light at its normal light emission level, causing color mixing over time, and the user's eyes perceive a cyan image as a mixture of blue and green.

[0067] Similarly, during the period from time t9 to t12 (the period during which the red image is normally displayed), points Z5 and Z6 indicated by the dashed ellipses overlap on the time axis, and therefore, from time t9 to t10, green LD 118 emits light at its normal light emission level, and from time t10 to t12, red LD 117 emits light at its normal light emission level, causing color mixing over time, and the user's eyes perceive a yellow image as a mixture of green and red.

[0068] In this way, color mixing occurs due to the delay of Δt. Therefore, measures to suppress color mixing are required. This point will be explained below.

[0069] Next, reference is made to Fig. 3. Fig. 3 is a diagram showing an example of the internal configuration of the light source unit and the projection unit (configuration for performing delay correction) in the projection display system of the present invention. In Fig. 3, parts common to Fig. 1 are assigned the same reference numerals.

[0070] The basic configuration has been explained in A-2 of FIG. 1, so here, only the new configuration added in FIG. 3 will be explained.

[0071] 3, the light source unit 100 is provided with a temperature sensor 111, and the projection unit 300 is provided with a temperature sensor 311, but this will be described in the second embodiment. In the following description, the temperature sensors 111 and 311 will not be mentioned.

[0072] 3, the MCU 110 serving as the first control unit of the light source unit 100 performs a delay measurement process to measure the amount of delay (the amount of delay of the light emission enable signal) for one way along the communication cable 210, and notifies (transmits) information about the amount of delay obtained by this measurement to the projection unit 300 via the communication cable 210. The display controller 313 serving as the second control unit of the projection unit 300 delays the video bitstream data VBSD by the notified amount of delay using the delay unit 315, and controls the optical modulation timing of the optical modulation device 322 using the delayed video bitstream data VBSD. This makes it possible to sufficiently suppress synchronization errors.

[0073] Next, the delay amount measurement process will be described in detail. The MCU (first control unit) 110 of the light source unit 100 changes the voltage of the A terminal from L level to H level to transmit (output) a transmission instruction signal OT1 for an outbound signal for delay measurement. In response to this transmission instruction signal OT1, the serializer 112 outputs an outbound signal for delay measurement (hereinafter, sometimes simply referred to as an outbound signal) outwardTS, and this outbound signal for delay measurement outwardTS is transmitted to the projection unit 300 via the dedicated line L1 of the communication cable 210.

[0074] A received signal OT2 obtained by receiving the outward signal outwardTS is output from the deserializer 312 of the projection unit 300, and this received signal OT2 is sent to a display controller (second control unit) 313. The display controller (second control unit) 313 sends a transmission instruction signal OT3 for a return signal for delay measurement to the serializer 314.

[0075] A return signal for delay measurement (sometimes simply referred to as a return signal) returnTS is output from the serializer 314. This return signal for delay measurement returnTS is transmitted to the light source unit 100 via the dedicated line L2 of the communication cable 210.

[0076] A received signal RT1 indicating that a return path signal returnTS for delay measurement has been received is output from the deserializer 114 of the light source unit 100, and this received signal RT1 is input to the B terminal of the MCU (first control unit) 110. At this input timing, the return path signal returnTS for delay measurement has been detected by the MCU (first control unit) 110.

[0077] Here, reference will be made to Fig. 4. Fig. 4 is a diagram showing an example of a process for measuring the amount of delay in a communication cable (using timestamps).

[0078] 4, at time t20, the voltage level of the A terminal of the MCU (first control unit) 110 changes from L to H (in other words, a transmission instruction signal OT1 for the outbound signal for delay measurement is output). At this timing, the MCU 110 acquires (records) the first timestamp TS.

[0079] Also, at time t21, the voltage level of the B terminal of the MCU (first control unit) 110 changes from L to H. In other words, a reception signal RT1 indicating that the return signal returnTS for delay measurement has been received is input. At this input timing, the return signal returnTS for delay measurement is detected by the MCU (first control unit) 110. At this timing, the MCU 110 acquires (records) a second timestamp TE.

[0080] Here, time t20 is the output timing of the transmission instruction signal OT1 for the outward signal outwardTS for delay measurement, and time t21 is the timing when the return signal returnTS for delay measurement is detected by the MCU (first control unit) 110. In this case, the value obtained by dividing the time difference between the second timestamp TE and the first timestamp TS in half is set to Δt (Δt = (TE - TS) / 2). Note that the division by 2 is done to convert the delay time for the round-trip wiring into the delay time for a one-way trip.

[0081] This Δt is the amount of delay for one way in the communication cable 210. In other words, this Δt is the amount of delay when the light emission enable signal LDE is transmitted from the projection unit 300 to the light source unit 100 via the communication cable 210.

[0082] Now, returning to Fig. 3, the description will continue. The MCU (first control unit) 110 transmits the measured delay amount Δt to the projection unit 300 using, for example, the communication signal Communications1 described above.

[0083] The display controller (second control unit) 313 of the projection unit 300 sets the delay amount in the delay unit 315 to be the same (equivalent) to the notified delay amount Δt.

[0084] The video bit stream data VBSD is delayed by Δt by the delay unit 315, and this delayed video bit stream data VBSD is input to the input terminal 321 of the optical modulation device 322. In other words, an optical modulation operation is performed based on (in synchronization with) this delayed video bit stream data VBSD.

[0085] This reduces misalignment between the output timing of light for forming a projection image (the light emission timing of each optical element) and the light modulation timing of the light modulation device, and sufficiently reduces the color mixing caused by the delay Δt described above in Figure 2. This prevents a decrease in display quality.

[0086] Please refer to Fig. 5. Fig. 5 is a diagram showing an example in which there is no misalignment between the actual light emission timing of the optical elements and the modulation timing in the light modulation device (in other words, the timing of the video bit stream data) in the projection type display system of the present invention shown in Fig. 3.

[0087] In Fig. 5, a delay of Δt is also applied to the video bitstream data, so that the timing of the video bitstream data for each color and the timing of the actual light emission power of the LD for each color are aligned, eliminating the inconsistency that occurred in Fig. 2.

[0088] For example, during the period from time t4 to t7, the video bitstream data is "B data," so this is the period during which the blue LD 119 is supposed to emit light, and this light emission period corresponds to point Z12 (almost the entire period of the BLD power) indicated by the dashed ellipse in Figure 5.

[0089] Here, if we focus on point Z11 (almost the entire period of RLD power) indicated by the dashed ellipse, points Z12 and Z11 do not overlap on the time axis. Therefore, the blue and red do not mix to form magenta, as occurs in the example of Figure 2, and an image of the original blue color can be formed.

[0090] Similarly, the period from time t7 to t10 is the period during which the green LD 118 emits light, since the video bitstream data is "G data." This light emission period corresponds to point Z13 (almost the entire period of the GLD power) indicated by the dashed ellipse in Figure 5.

[0091] Here, if we focus on point Z12 (almost the entire period of BLD power) indicated by the dashed ellipse, points Z13 and Z12 do not overlap on the time axis. Therefore, the green and blue do not mix to form cyan, as occurs in the example of Figure 2, and the original green image can be formed.

[0092] Similarly, during the period from time t10 to t13, the video bitstream data is "R data," so this is the period during which the red LD 117 is supposed to emit light, and this light emission period corresponds to point Z14 (almost the entire period of RLD power) indicated by the dashed ellipse in Figure 5.

[0093] Here, if we focus on point Z13 (almost the entire period of GLD power) indicated by the dashed ellipse, points Z14 and Z13 do not overlap on the time axis. Therefore, the red and green do not mix to turn yellow, as in the example of Figure 2, and the original red image can be formed.

[0094] In this way, according to this embodiment, color mixing is sufficiently suppressed, and degradation of display quality is prevented.

[0095] In this embodiment, the dedicated lines L1 and L2 are used as communication lines for the outward signal (outward TS) and the return signal (return TS) for delay measurement, which simplifies the configuration. The algorithm used in the delay measurement process can also be simplified.

[0096] However, the present invention is not limited to this, and if possible, a communication line (wiring) included in a communication line for a serial video signal (for example, an LVDS communication line) in the communication cable 210 may also be used as the communication line (wiring) for at least one of the outward signal outwardTS and the return signal returnTS for delay measurement. This eliminates the need for a dedicated communication line (wiring), simplifying the configuration of the communication line (wiring).

[0097] (Second embodiment) In this embodiment, a temperature sensor consisting of a thermistor or the like is provided in at least one of the light source unit and the projection unit, and based on the measurement result (detection result) of the temperature sensor, it is determined whether or not to perform the above-mentioned delay measurement process and delay correction process.

[0098] Referring again to Fig. 3, in the example of Fig. 3, a temperature sensor 111 is provided in the light source unit 100, and a temperature sensor 311 is provided in the projection unit 300. In the example of Fig. 3, these temperature sensors 111 and 311 detect (measure) the ambient temperature (environmental temperature) of the projection display system 10.

[0099] A detection signal TM1 indicating the detection result of the temperature sensor 111 is supplied to the MCU (first control unit) 110, and a detection signal TM2 indicating the detection result of the temperature sensor 311 is supplied to the display controller (second control unit) 313.

[0100] 3, when the light source unit 100 performs the delay measurement process and the projection unit 300 performs the delay correction process (a process of delaying video bitstream data), a determination is made as to whether or not to perform each of the above processes, taking into consideration the ambient temperature (environmental temperature) of the projection display system 10. In the example of FIG. 3, this determination is made by each of the MCU (first control unit) 110 and the display controller (second control unit) 313.

[0101] One of the main causes of the delay in the communication cable 210 described above is a change in the ambient temperature (environmental temperature).

[0102] For example, when the projection display system 10 is installed in a vehicle, the driving environment of the vehicle may change suddenly, so measures must be taken to take temperature changes into account.

[0103] Furthermore, when projecting an image onto the road surface, outdoor light can make the image difficult to see, so a projected image with higher brightness is required, and as shown in A-1 of Fig. 1, a fairly large heat dissipation unit 101 is provided in the light source unit 100. This heat dissipation unit 101 functions as a heat source, and it is conceivable that the heat emitted by this heat dissipation unit 101 will cause a change in the ambient temperature (environmental temperature).

[0104] Possible situations where temperature changes become a problem are "a situation (first situation) where the difference between the ambient temperature and a reference temperature (e.g., 25°C) is equal to or greater than a first threshold (e.g., 5°C)" and "a situation (second situation) where the ambient temperature changes, for example, suddenly and the change is equal to or greater than a second threshold (e.g., 5°C)." In either case, it is expected that the amount of delay of the electrical signal in the communication cable 210 will become too large to ignore.

[0105] In the example of Figure 3, when at least one of the first and second situations described above is detected by either the MCU (first control unit) 110 or the display controller (second control unit) 313, a delay measurement process and a delay correction process are performed.

[0106] According to this embodiment, when a change in the temperature environment occurs that exceeds a threshold, delay measurement processing and delay correction processing can be performed quickly, thereby effectively suppressing degradation of the quality of the projected image.

[0107] Furthermore, as shown in A-1 of Figure 1, when the light source unit 100 has a heat dissipation unit (heat sink, etc., which can be a heat source) 101 that dissipates heat generated by the optical element unit (heat source), in order to prevent a decrease in accuracy in measuring the ambient temperature, a configuration may be adopted in which the temperature sensor is provided only in the projection unit 300 that does not have a heat dissipation unit (in other words, in Figure 3, the only temperature sensor to be installed is temperature sensor 311).

[0108] 3, when temperature sensors 111 and 311 are provided in both the light source unit 100 and the projection unit 300, a configuration may be adopted in which the measurement result of the temperature sensor 311 provided in the projection unit 300, which does not have a heat dissipation unit, is used preferentially to determine the temperature. For example, when there is a difference between the temperature measurement results of the temperature sensors 111 and 311, the measurement result of the temperature sensor 311 may be used preferentially.

[0109] This reduces the influence of the heat source of the light source unit 100, and prevents a decrease in the accuracy of temperature measurement.

[0110] Third Embodiment Next, reference will be made to Fig. 6. Fig. 6 is a flowchart showing an example of a main procedure when delay correction processing is performed.

[0111] In step S1, it is determined whether the difference between the ambient temperature and the reference temperature is equal to or greater than a first threshold value, or whether the change in the ambient temperature is equal to or greater than a second threshold value. If the answer is yes, the process proceeds to step S2, and if the answer is no, the process continues with step S1.

[0112] In step S2, the signal level (e.g., voltage level) of the A terminal of the MCU (first control unit) is changed. This change in signal level essentially instructs transmission of an outbound signal for delay measurement. In other words, a transmission instruction signal for an outbound signal for delay measurement is output. A first timestamp TS is acquired (recorded) according to the output timing of this transmission instruction signal.

[0113] In step S3, the serializer of the light source unit outputs a forward path measurement signal.

[0114] In step S4, it is determined whether a change in the signal level due to the return signal for delay measurement sent from the projection unit is detected at terminal B of the MCU. In other words, it is determined whether the return signal for delay measurement is detected. If the answer is Y, proceed to step S5, and if the answer is N, continue with step S4.

[0115] In step S5, a second timestamp TE is acquired (recorded) in accordance with the detection timing of the return path signal for delay measurement.

[0116] In step S6, the one-way delay Δt of the communication cable (the wiring that transmits the outgoing and return signals) is calculated. In other words, Δt is calculated as (TE-TS) / 2. The reason for dividing by 2 is to convert the delay time of the round-trip wiring into the one-way delay time.

[0117] In step S7, the calculated delay amount Δt is transmitted from the MCU to the display controller.

[0118] In step S8, a delay of the notified Δt (the same delay amount) is imparted to the video bit stream data supplied to the optical modulation device.

[0119] In step S9, it is determined whether the display has ended. If yes, the delay correction process ends, and if no, the process returns to step S1.

[0120] As described above, according to this embodiment, it is possible to suppress color mixing in a projected image in a projection display system in which the light source section and the projection section are separated.

[0121] Furthermore, when a projection display system is installed in a vehicle, the ambient temperature varies depending on the vehicle's driving environment, and the ambient temperature may change suddenly. According to this embodiment, for example, the delay measurement process and delay correction process can be quickly performed in response to changes in the vehicle's driving environment, thereby effectively suppressing degradation in the quality of the projected image. Therefore, high performance can be achieved in an in-vehicle projection display system (for example, a road projector that displays an image on the road surface).

[0122] The present invention is not limited to the above-described exemplary embodiments, and those skilled in the art will be able to easily modify the above-described exemplary embodiments to the extent that they fall within the scope of the claims.

[0123] 10...Projection type display system, 90...Vehicle side controller, 100...Light source unit, 101...Heat sink (heat dissipation unit), 102...Control board, 103...Integrated circuit device (IC), 110...Microcontroller (MCU) (first control unit), 112...Serializer (parallel / serial converter), 114...Deserializer (parallel / serial converter), 116...Optical element driving unit (LC driver), 117-119...Multiple optical elements with different luminous colors (laser diodes corresponding to each color of R, G, B), 120-122...Multiple mirrors, 123...Photodiode (PD) for monitoring optical output, 124...Optical output interface, 125...Optical element unit, SIF1...First serial interface interface unit, 130... power circuit (power supply circuit), 210... communication cable, 220... optical fiber cable (optical fiber), 300... projection unit, 312... deserializer (serial / parallel converter), 314... serializer (parallel / serial converter), 313... display controller (display control device) (second control unit), 320... optical input interface, 321... input terminal of optical modulation device, 322... optical modulation device (DMD (digital mirror device)), 323... projection port (output port), 324... photodiode (PD) for monitoring optical output, 325... power circuit (power supply circuit), SIF2... second serial interface unit, VideoS... video signal, LVDS VideoS...serial video signal transmitted using the LVDS transmission method, VD...video digital signal, VBSD...video bit stream data, LDE (R / G / B LD Enable)...light emission enable signal, CommunicationS1, CommunicationS2...various communication signals, OT1...send instruction signal for outgoing signal for delay measurement, outwardTS...outgoing signal for delay measurement (outgoing signal), OT2...received signal obtained by receiving outgoing signal outwardTS, OT3...send instruction signal for return signal for delay measurement, returnTS...return signal for delay measurement (return signal), RT1...received signal indicating that return signal returnTS for delay measurement has been received, L1, L2...dedicated wiring (wiring,Communication line), PS...power supply.

Claims

1. A projection type display system in which a light source unit and a projection unit are separated and electrically connected to each other via a communication cable, and light for forming a projection image output by the light source unit is supplied to the projection unit via an optical fiber, and a projection image is formed by the projection unit, wherein the light source unit has: a first control unit having a function of causing the projection unit to transmit a video signal, a function of causing the projection unit to transmit an outgoing signal for delay measurement, and a function of performing a delay measurement process for measuring a one-way delay of the communication cable based on the time difference between the timing at which the outgoing signal for delay measurement is instructed to be transmitted and the timing at which a return signal for delay measurement transmitted from the projection unit is detected, and a function of notifying the projection unit of the amount of delay obtained by the delay measurement process; a light element unit having a plurality of light elements with different light emission colors that generates light for forming the projection image; and a light element drive unit that drives the plurality of light elements based on a light emission enable signal transmitted from the projection unit, wherein the projection unit has: a second control unit having a function of generating video bitstream data based on the video signal sent from the light source unit, a function of generating the light emission enable signal synchronized with the video bitstream data and transmitting it to the light source unit, a function of generating a return signal for delay measurement and transmitting it to the light source unit, and a function of setting a first delay amount in the delay unit that is equivalent to the delay amount obtained by the delay measurement process and notified from the light source unit, and imparting a delay of the first delay amount to the video bitstream data by the delay unit; and an optical modulation device that modulates the light for forming the projection image sent from the light source unit via the optical fiber based on the video bitstream data to which a delay of the first delay amount has been imparted, thereby forming the projection image.

2. The projection display system according to claim 1, wherein the communication cable is provided with a first communication line for an outgoing signal for delay measurement, and a second communication line for a return signal for delay measurement.

3. The projection display system according to claim 1, wherein in said communication cable, a communication line included in the communication path for said video signal is also used as a communication line for at least one of said outbound signal for delay measurement and said return signal for delay measurement.

4. The projection display system of claim 1, wherein at least one of the light source unit and the projection unit is provided with a temperature sensor for measuring an ambient temperature, and when at least one of the temperature sensors detects that a difference between the ambient temperature and a reference temperature is equal to or greater than a first threshold, or when at least one of the temperature sensors detects that a temperature change in the ambient temperature is equal to or greater than a second threshold, the delay measurement process by the first control unit and the process of applying a delay of the first delay amount to the video bit stream data by the second control unit are performed.

5. The projection type display system according to claim 4, wherein the light source section has a heat dissipation section that dissipates heat generated by the light element section, which is a heat source, and the temperature sensor is provided only in the projection section, or, when the temperature sensor is provided in both the light source section and the projection section, the temperature measurement result of the temperature sensor provided in the projection section takes priority.

6. The projection display system according to claim 1, wherein the projection display system is an in-vehicle projection display system mounted on a vehicle.

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