Patent Publication Number: US-9886914-B2

Title: Flexible display device disposed in a housing

Description:
FIELD 
     The present invention relates to a display device. 
     BACKGROUND 
     The current so-called “rigid” display devices are mainly Liquid Crystal Display (LCD). Such displays inevitably have certain weight and volume, which cannot be bent and need to be placed in a fixed frame, thus ease of use is limited. 
     Unlike the indeformable “rigid” display device described above, a flexible display device has an essential member of a flexible display panel. A flexible display panel typically refers to a display panel with a display unit formed on a flexible substrate such as polyimide and having flexibility. Since the flexible display panel has the characteristics such as thin, bendable and low power consumption, and the deformation enables reduced volume for easy carrying, therefore there is a great application potential. A conventional flexible display panel typically includes a housing and a panel wrapped inside the housing, and one end of the panel is pulled out from the housing for viewing in use. 
     However, in some cases, it is only required to pull a portion of the flexible display panel out from the housing. Since the entire display area of the flexible display panel is in an active display state at this time, a portion of the flexible display panel located inside the housing in the wrapped state is also in the active display state. In this case, since the panel located inside the housing is in the wrapped state, the wrapped flexible panel in the active display state will cause heat accumulation inside the housing, leading to a higher temperature inside the housing. If the panel is in a high temperature condition for a long time, the operation performance of the panel will be deteriorated and thus shortening the lifetime of the panel. 
     SUMMARY 
     The present invention provides a display device which can improve the lifetime of the flexible display panel. 
     According to one aspect, a display device in embodiments of the present invention comprising: a housing having an outlet; a flexible display panel located inside the housing, wherein at least a portion of the flexible display panel can be pulled out from the outlet, and in a case where the flexible display panel is pulled out, a region located outside the housing is a front end region of the flexible display panel, and a region located inside the housing is a rear end region of the flexible display panel, an extending direction from the front end region to the rear end region is a direction from front to rear of the flexible display panel; a detection calculation unit configured to detect and calculate an area of the front end region; and a controller signally connected with the detection calculation unit and the flexible display panel, and configured to receive the area of the front end region output from the detection calculation unit and control only the front end region displaying images. 
     In an example, the flexible display panel includes at least one discrete mark region disposed along the direction from front to the rear of the flexible display panel; the detection calculation unit includes a detection unit disposed at the outlet, and the detection calculation unit determines the area of the front end region according to a number of the mark regions detected by the detection unit. 
     In an example, the mark region is at least one luminant region formed on the flexible display panel by control of the controller, and the luminant regions and non-luminant regions separating the luminant regions have a total number of at least three; the detection unit is a light intensity detection unit configured to detect intensity of light. 
     In an example, in a case where an Nth luminant region opposes the light intensity detection unit directly, the light intensity detection unit detects an optical signal of the Nth luminant region, the detection calculation unit determines that the Nth luminant region is located at the outlet, and the detection calculation unit determines that a flexible display panel region in front of the Nth luminant region is the front end region, and feeds the area information of the front end region to the controller; in a case where an Nth non-luminant region opposes the light intensity detection unit directly, the light intensity detection unit detects an optical signal corresponding to the Nth non-luminant region, the detection calculation unit determines that the Nth non-luminant region is located at the outlet, and the detection calculation unit keeps the area information of the front end region detected at a previous time; where N is a positive integer. 
     In an example, a width of the luminant regions is equal to a width of the non-luminant regions in the direction from front to rear of the flexible display panel. 
     In an example, a width of the luminant region is smaller than a width of the non-luminant region in the direction from front to rear of the flexible display panel in a case where the width of the luminant region and the width of the non-luminant region abutting the luminant region have a constant sum. 
     In an example, a region of the flexible display panel pulled out from the outlet firstly is the luminant region. 
     In an example, the flexible display panel is an active light emitting type flexible display panel or a passive emitting type flexible display panel. 
     In an example, the flexible display panel is the passive emitting type flexible display panel, and the display device further includes a light source disposed near the light intensity detection unit and emitting lights which are not incident onto the light intensity detection unit directly, and the luminant region reflects the lights from the light source, and the non-luminant region transmits the lights from the light source. 
     In an example, the flexible display panel is a passive matrix type flexible display panel with a column scanning mode. 
     In an example, the detection calculation unit is located inside the housing, and the controller is located outside the housing. 
     In an example, in a case where the detection calculation unit determines that a region of the flexible display panel in front of the Nth luminant region is the front end region, the controller further controls a (N+1)th luminant region after the Nth luminant region to be luminant. 
     In an example, the controller is configured to control at most two luminant regions in a luminant state. 
     In an example, in a case where the detection calculation unit determines that the region of the flexible display panel in front of the Nth luminant region is the front end region, the controller is configured to control only the Nth luminant region and the (N+1)th luminant region after the Nth luminant region to be luminant. 
     In an example, the controller is configured to control all the luminant regions on the flexible display panel in a luminant state when the display device has been just powered on. 
     By using the display device according to the embodiments of the present invention, the detection calculation unit can detect the area size of the front end region of the display panel outside the housing and feed the area information corresponding to the front end region back to the controller. The controller can control only the front end region of the flexible display panel to display images based on the information, and control the rear end region of the flexible display panel to keep an original state in which no image is displayed. In this case, the temperature of the rear end region is low with less heat generation, so that the temperature within the housing is low. Thus, the operation performance of the panel will not be affected or less affected and the lifetime of the panel is lengthened. 
     Compared with prior art, during operation of the display device, since the rear end region of the display panel located inside the housing is the regions with no images displayed, the temperature of the region is low and less heat is generated, and the temperature inside the housing is also low. Therefore, the rear end region of the display panel wrapped inside the housing would not cause heat accumulation. The operation performance of the panel will not be deteriorated by heat accumulation, and the lifetime of the display panel could be extended. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to explain the technical solution in the embodiments of the present invention more clearly, the accompanying drawings needed to be used in the embodiments will be briefly introduced below. It is obvious that the drawings described below are only some embodiments of the present invention, and other drawings can also be obtained based on these drawings for those skilled in the art without any inventive work. 
         FIG. 1  is a schematic view of a display device according to an embodiment of the present invention; 
         FIGS. 2A-2C  are schematic views showing configuration states of the display device in  FIG. 1 ; 
         FIG. 3  is a schematic view of a configuration state of the display device in  FIG. 1 ; 
         FIG. 4  is a schematic view of a configuration state of the display device in  FIG. 1 ; 
         FIG. 5  is a schematic view of another display device according to an embodiment of the present invention; 
         FIG. 6  and  FIG. 7  are schematic views of configuration states of the display device according to the embodiments of the present invention; and 
         FIG. 8  is a schematic view of state transition of the cholesteric liquid crystal in the cholesteric liquid crystal display panel under different applied pressure in a case where the display panel in the display device is cholesteric liquid crystal display panel. 
     
    
    
     DETAILED DESCRIPTION 
     The technical solution of the embodiments of the present disclosure will be described clearly and fully in connection with the drawings of the embodiments of the present disclosure. It is obvious that the described embodiments are just a part but not all of the embodiments of the present disclosure. Based on the described embodiments of the present disclosure, those skilled in the art can obtain all other embodiments without any inventive work, which all fall into the scope of the claimed disclosure. 
     Unless otherwise defined, technical terms or scientific terms used herein shall have a common meaning known by those skilled in the art of the present disclosure. Terms and expressions such as “first”, “second” and the like used in the description and claims of the patent application of the present disclosure do not denote any sequence, quantity or importance, but distinguish different components. Likewise, words such as “a”, “an” and the like do not denote quantitative restrictions, but denote the presence of at least one. Words such as “connected”, “connecting” and the like are not restricted to physical or mechanical connections, but can include electrical connections, regardless of direct or indirect connections. Words such as “up”, “below”, “left”, “right”, etc., are only used to denote the relative positional relationship. Upon the absolute position of the described object changes, the relative positional relationship change correspondingly. Thicknesses and shapes of various layers of films in the drawings do not reflect the true scale, which are just for purposes of illustrating schematically the contents of the present invention. 
       FIG. 1  is a display device according to the first embodiment of the present invention. As shown in  FIG. 1 , the display device includes a housing  01  and a flexibility display panel  02  located inside the housing  01 . The housing  01  can be a box having various geometric shapes and ventilation openings can be disposed on the box. Flexible display panel  02  is a display panel which is formed on a flexible substrate and can undergo bending deformation and still achieve display function. The flexible display panel  02  is wrapped when it is not in operation. The housing  01  has an outlet  06 . During operation, the display panel  02  is pulled out from the outlet  06 . As shown in  FIG. 1 , a portion of the flexible display panel  02  is pulled out from the housing  01 . In this state, a region located outside the housing  01  is a front end region  02   a  of the flexible display panel  02 , and a region located inside the housing  01  is a rear end region  02   b  of the flexible display panel  0 . An extending direction from the front end region  02   a  to the rear end region  02   b  is a direction from front to rear of the flexible display panel  02 . An end of the front end region  02   a  opposite to the rear end region  02   b  is connected with a cover  08 . A direction in which the flexible display panel  02  is pulled out is a length direction of the display panel  02  such as a row direction, and a direction perpendicular to the direction in which the flexible display panel  02  is pulled out is a width direction of the display panel  02  such as a column direction. 
     The display device described above further includes a detection calculation unit  03  and a controller  04 . The detection calculation unit  03  detects and calculates an area size of the front end region  02   a , and the area size of the front end region  02   a  is output to the controller  04 . The controller  04  is signally connected with the detection calculation unit  03  and the display panel  02 . The controller  04  receives the area size of the front end region  02   a  output from the detection calculation unit  03 , and controls only the front end region  02   a  in an active display state in which images are displayed. 
     By using a display device according to a first embodiment of the present invention, the detection calculation unit  03  can detect the area size of the front end region  02   a  of the flexible display panel  02  outside the housing  01 , and the detected area information corresponding to the front end region  02   a  is output to the controller  04 . The controller  04  controls only the flexible front end region  02   a  of the display panel  02  to display images based on the information, and controls the rear end region  02   b  of the flexible display panel  02  in a non-display state. In this case, the temperature of the rear end region  02   b  is low with less heat generation. Therefore the temperature within the housing  01  is low. Thus, the operation performance of the flexible the display panel  02  will not be affected or be less affected, such that the lifetime of the flexible display panel  02  will be lengthened. 
     During operation of the display device, since the rear end region of the flexible display panel  02  located inside the housing does not display images, the temperature of the region is low and very small amount of heat is generated, thus the temperature inside the housing is also low. Therefore, even if the rear end region of the flexible display panel is wrapped inside the housing, heat accumulation will not occur. The operation performance of the flexible display panel will be not deteriorated by heat accumulation, and the lifetime of the flexible display panel could be extended. 
     In the embodiment described above, the controller is signally connected with the detection calculation unit and the display panel. The “signally connected” herein includes connecting via signal lines and wireless signals. 
     Based on the display device described above, for the detection calculation unit detects the area of the front end region, the controller controls the display panel such that mark regions for example luminant regions for signal detection and non-mark regions for example non luminant regions are arranged alternatively along the direction from the front end region to the rear end region during operation. The mark regions and the non-mark regions have a total sum of at least three. That is, in this embodiment, the luminant region is formed on the display panel as the mark region, thereby the detection calculation unit determines the area size of the front end region by detecting the luminant region. The area size of the front end region is mainly determined based on the number of luminant regions detected by the detection calculation unit. 
     It is noted that the luminant regions in the present embodiment are used for detecting signals by the detection calculation unit and do not perform normal image display. The luminant region in the present embodiment includes active luminant region such as light emitting region, and passive luminant region such as reflective region under illumination. Correspondingly, the non-luminant region in the present embodiment includes a non-light emitting region separating active luminant regions, and a light transmissive region separating reflective luminant regions. 
     The detection calculation unit determines the area of the front end region by detecting the number of the luminant regions. The non-luminant region divides the luminant regions into a plurality of discrete regions with a predetermined spacing. Specifically, as shown in  FIG. 2A , the detection calculation unit  03  includes a light intensity detection unit (not shown) provided at the outlet  06 . The light intensity detection unit detects the light intensity. The light intensity detection unit can be located inside the housing  01 , or located outside the housing  01 . When a luminant region  07  opposes the light intensity detection unit, the light intensity detection unit detects an optical signal from the luminant region  07 , thereby the detection calculation unit  03  identifies that the luminant region  07  is at the outlet  06 . The detection calculation unit  03  determines that the display surface region in front of the luminant region  07  is a front end region. At this point, the front end region does not include the luminant region  07  itself. The area information of the front end region is fed to the controller (not shown). When the flexible display panel  02  is further pulled out such that a non-luminant region adjacent to the luminant region  07  and located after the luminant region  07  opposes the light intensity detection unit, the light intensity detection unit detects an optical signal corresponding to the non-luminant region, thereby the detection calculation unit  03  keeps the area information of the front end region detected at the previous time. 
     In the present embodiment, the luminant regions can be configured as a plurality of discrete regions with a predetermined spacing, that is, the flexible display panel  02  includes a plurality of the luminant regions  07  at different positions so as to distinguish different sizes of the front end region  02  of the display panel which is pulled out from the housing  01 . The luminant regions  07  located at different positions of the flexible display panel  02  indicate the front end regions  02   a  with different sizes which in turn corresponds to area information of different front end regions  02   a . The detection calculation unit  03  obtains the area information of different front end regions by detecting the light emission regions located at different positions of the display panel. After each detection, the detection calculation unit  03  outputs the area information of the front end regions  02   a  to the controller. After receiving the area information of the front end regions  02   a  from the detection calculation unit  03 , the controller will control pixels of the corresponding front end regions  02   a  to display image according to the area information of different front end regions  02   a . The front end regions  02   a  can display a complete image being scaled down or a part of the complete image. At the same time, the controller controls the rear end regions  02   b  in an original state where images are not displayed. Temperature of the rear end region  02   a  as non-image display region is low, and very small amount of heat is generated, so that the temperature inside the housing  01  is also low. 
     In an embodiment of the present application, other types of regions or structures indicating the area of the front end regions  02   a  can be formed on the flexible display panel, which are not repeated herein. 
     In the present embodiment, the width of the luminant region  07  and the width of the non-luminant region are equal in a direction where the flexible display panel is pulled out so that a control strategy of the controller is relatively simpler. 
     In some cases, as shown in  FIG. 2B , due to space limitation, one of the luminant regions  07  on the flexible display panel  02  is outside the housing  01  after the flexible display panel  02  is pulled out from the outlet  06  of the housing  01 . When the non-luminant region adjacent to the light-emitting region  07  is located at the outlet  06  and opposes the light intensity detection unit, the light intensity detection unit detects an optical signal corresponding to the non-luminant region. At this point, the detection calculation unit  03  keeps the area information of the front end region detected at the previous time, that is, the controller will not control to refresh the active display region of the enlarged front end region  02   a . Therefore the luminant region  07  located outside the housing  01  and closest to the outlet  06  does not display images. In order to improve user experience, the width of the luminant region  07  which do not display images should be as smaller as possible. In the present embodiment, for this purpose, the width of the luminant region  07  is less than that of the non-luminant region in a case where the width of the luminant region  07  and the width of the non-luminant region adjacent have a constant sum value in the direction where the flexible display panel  02  is pulled out. Thus, the non-active display region on flexible display panel  02  outside the housing  01  will be relatively small, and user experience can be improved. In the present embodiment, the flexible display panel  02  is configured such that a region firstly pulled out from the outlet  06  is a non-luminant region, that is, the region of the flexible display panel  02  adjacent to the cover  08  is a non-luminant region. Before the flexible display panel  02  is further pulled out so that the second luminant region  07  opposes the light intensity detection unit, the area of the front end region  02   a  outside the housing  01  is the sum of the area of one luminant region  07  and the area of two non-luminant regions, rather than only one non-luminant region for displaying images. 
     In order to further improve user experience, in another example of the present embodiment, the flexible display panel  02  can be configured such that a region firstly pulled out from said outlet  06  is a luminant region  07 , that is, the region of the flexible display panel  02  adjacent to the cover  08  is the luminant region  07 , as shown in  FIG. 2C . In this embodiment, in a state where the second luminant region  07  opposes the light intensity detection unit, the area of the front end region  02   a  of the display panel  02  outside the housing  01  is the sum of the area of one luminant region  07  and the area of one non-luminant region, and both the one luminant region  07  and the one non-luminant region display images, therefore the display device configured according to the present example can improve user experience compared to the configuration of  FIG. 2B . 
     In the embodiments described above, the flexible display panel  02  can include an active light emitting type display panel or a passive light emitting type display panel. 
     Specifically, the active light emitting type display panel can include an active matrix type active light emitting display panel which is driven in an active matrix driving mode, in which each pixel has only one TFT (Thin Film Transistor) or two, three TFTs. A part of regions of the panel can be controlled to emit lights to be luminant regions of the panel, without involving other regions on the panel. For example, in the present embodiment, the controller  04  controls a plurality of pixels corresponding to the luminant regions to emit lights having light intensity satisfying detection threshold of the light intensity detection unit via control circuits, without affecting other regions of the display panel. The luminant regions and the non-luminant regions can have any shapes, preferably regular shape such as rectangular, circular, oval and polygonal and so on. In a case where the light intensity of lights emitted from the plurality of the pixels in the luminant regions detected by the light intensity detection unit reaches the detection threshold of the light intensity detection unit, the detection calculation unit  03  identifies that the luminant region  07  detected by the light intensity detection unit is located at the outlet  06 , and that display panel region in front of the luminant region  07  is the front end region  02   a . The detection calculation unit  03  sends the area information of the front end region  02   a  to the controller  04 . And in a case where the light intensity of lights emitted from the plurality of the pixels in the luminant regions detected by the light intensity detection unit does not reach the detection threshold of the light intensity detection unit, the detection calculation unit  03  identifies that the luminant region  07  is not located at the outlet  06 , therefore the area information of the front end region  02   a  detected at the previous time is kept constant. For example, in both cases shown in  FIG. 3  and  FIG. 4 , the luminant region  07  is not aligned perfectly with the light intensity detection unit included in the detection calculation unit  03 , a portion of the lights emitted from the luminant region  07  is not received by the light intensity detection unit, and the light intensity detected by the light intensity detection unit does not reach the detection threshold thereof. At this point, the controller  04  will not update the area size of the front end region  02   a . Thus the accuracy of the controller  04  can be improved, and only in a case where each of the luminant regions  07  opposes the light intensity detection unit included in the detection calculation unit  03 , the controller  04  can control to refresh the active display region of the front end region  02   a , for ensuring that the image displayed in the front end region  02   a  outside the housing  01  is continuously and stably refreshed during the display panel  02  is pulled out from the housing  01 . 
     As an alternative and preferred manner, the active light emitting type display panel can further include a passive matrix type active light emitting display panel, which is driven in a passive matrix driving mode. In the embodiments of the present invention, the display panel in the passive matrix driving mode employs row scanning. The detection calculation unit  03  can be provided at a substantially central position in the width direction of the display panel  02 . For ensuring that the detection calculation unit  03  can detect each luminant regions  07 , in the present embodiment, the passive matrix driving mode is modified as column scanning, and the direction of column scanning is the direction from the front to the rear of the display panel. The controller  04  can control a part of the columns of the display panel  02  to be luminous as the luminant region  07 , without involving other regions of the display panel. 
     In the embodiment of the present invention, the passive light emitting type display panel can include a cholesteric liquid crystal display panel in either an active matrix driving mode or a passive matrix driving mode. During operation, the controller  04  can control partial regions of the cholesteric liquid crystal display panel to be reflective regions, partial regions of that to be transmissive regions. At this point, the reflective regions function as the aforementioned luminant regions, and the transmissive regions function as the aforementioned non-luminant regions, and the driving mode of the reflective regions is the same as the active matrix driving mode and the passive matrix driving mode of the active light emitting type display panel. As shown in  FIG. 5 , the display panel  02  is a passive light emitting type display panel, and the display device further includes a light source  05  located inside the housing  01 . The detection calculation unit  03  including the light intensity detection unit is also disposed inside the housing  01  to prevent ambient light from affecting the detection result. The light source  05  is disposed near the detection calculation unit  03 . During operation, lights emitted by the light source  05  will be not incident directly into the light intensity detection unit, but on the display panel  02 . The reflective region of the display panel  02  reflects lights from the light source  05 , and the transmissive region of the display panel  02  transmits the lights from the light source  05 , and the detection calculation process of the detection calculation unit  03  and the control of the controller  04  are the same as those of the active light emitting type display panel described above, which are not repeated herein. 
     The characteristics of the cholesteric liquid crystal employed in the cholesteric liquid crystal display panel are briefly introduced herein. According to different voltages applied, states of the cholesteric liquid crystal can be classified into three forms, namely a planar texture (P state), focal conic texture (FC state) and homeotropic texture (H state). The P state cholesteric liquid crystal has a Bragg reflection characteristic capable of reflecting lights with a wavelength the same or similar as a pitch of a helical structure of the cholesteric liquid crystal helical structure. The FC state cholesteric liquid crystal presents a scattering effect. The H state cholesteric liquid crystal can transmit lights completely.  FIG. 8  is a transition diagram among P state, FC state and H state of the cholesteric liquid crystal when different voltages are applied. As shown in  FIG. 8 , P state and FC state can be transformed to each other, and FC state and H state can be transformed to each other, while the transition between H state and P state is only from H state to P state. Specifically, the voltage applied to the P state liquid crystal is V P , and the voltage applied to the FC state liquid crystal is V FC , and the voltage applied to the H state liquid crystal is V H . When V P &gt;V FC , the P state liquid crystal is transformed to the FC state liquid crystal, and the transformation time is a few milliseconds. When V FC &gt;V H , the FC state liquid crystal is transformed to the H state liquid crystal, and the transformation time is also a few milliseconds. The voltage V H  applied to the H state liquid crystal is reduced rapidly, and the H state liquid crystal is transformed rapidly to the P state liquid crystal in less than 1 ms; whereas the voltage V H  applied to the H state liquid crystal is reduced slowly, the H state liquid crystal is transformed rapidly to the FC state liquid crystal in a few milliseconds. In summary, the states of the cholesteric liquid crystal are different when external electric fields with different intensities are applied, that is, the helical structure of the cholesteric liquid crystal molecules is changed and the display panel exhibits different bright or dark states. In particular, when the cholesteric liquid crystal is P state, the helical axis of the liquid crystal molecules is substantially perpendicular to the substrate surface where the pixels of the display panel are located. At this time, if the pitch of the helical structure of the liquid crystal is similar or same as the wavelength of the incident lights to satisfy the Bragg reflection condition, the incident lights of the wavelength will be reflected, that is, the P state has Bragg reflection characteristic. 
     In the present embodiment, in a case where the display panel  02  is a cholesteric liquid crystal display panel, the controller  04  is enabled to control the liquid crystals of some regions in the display panel  02  to become the P state liquid crystals during operation, thus the regions are reflective regions, while control the liquid crystals of other regions separating the reflective regions to become the H state liquid crystals, thus the other regions become the transmissive regions. Lights from the light source  05  are irradiated on the reflection region  07 , and the detection calculation unit  03  receives the lights reflected from the reflection region  07  of the liquid crystal panel to determine the front end region  02   a  of the display panel  02 . If the lights from the light source  05  are irradiated on the transmissive region, the detection calculation unit  03  will not receive the lights from the light source  05 . Thus, in the present embodiment, the function of the transmissive region is equivalent to the function of the non-luminant region in the active light emitting type display panel described above. 
     The cholesteric liquid crystal has a characteristic of selective wavelength of reflection. Accordingly, the wavelength of reflection of the cholesteric liquid crystal molecules is λ, and the average value of the birefringence is n, and the pitch is P, then the relationship among λ, n and P is:
 
λ= n×P  
 
Further, the wavelength of reflection has a bandwidth of:
 
Δλ=Δ n×P  
 
where Δn is refractive index anisotropy, and the pitch is P=1/(HTP×Xc), where Xc is concentration of the chiral agent, and HTP is twisting force constant of the chiral agent, the concentration of the chiral agent and the twisting force constant of the chiral agent are depended on the characteristics of chiral molecules themselves.
 
     It can be seen according to the formula above, in the present embodiment including the cholesteric liquid crystal display panel, the wavelength of reflection λ of the cholesteric liquid crystal can be adjusted by adjusting the pitch P of the liquid crystal molecules. That is, the wavelength range of the lights emitted by the light source is large. Even if the display device can include light sources emitting lights with different wavelengths, by adjusting the pitch of the liquid crystal molecules in the liquid crystal display panel so that it is similar or the same as the wavelength of the lights from the light source, the reflection regions can be luminous thereby the detection calculation unit  03  detects the front end region  02   a  to improve the robustness of the display device. 
     Preferably, the detection calculation unit  03  is disposed inside the housing  01  for easy carrying in a condition for satisfying operation requirements. Therefore, this can prevent the ambient lights outside the housing  01  from interfering with detection results of the detection calculation unit  03 , and prevent the detection calculation unit  03  from erroneous detection and feeding back erroneous signals to the controller  04 . However, during the operation of the device, the controller  04  will generate a small amount of heat. And because of poor ventilation inside the housing  01 , if the controller  04  is placed inside the housing  01 , the operational performance and lifetime of the controller  04  will be affected. Therefore, the controller  04  is disposed outside the housing  01 . 
     Further, in order to enable the processes for the detection calculation unit detecting and determining the front end region of the display panel and the controller controlling the display process of the front end region to progress successively, the controller also controls the (N+1)th luminant region after the Nth luminant region luminous while the detection calculation unit determines that the display panel region in front of the Nth luminant region is the front end region. Thus, the user can pull the display panel to a desired size for viewing at any time during operation. 
     Preferably, in the display device, the controller is configured to control at most two luminant regions in the luminous state. Alternatively, the controller is configured to control all luminant regions on the display panel in the luminant state after the display device is just powered on for simplifying the operation of the controller. Here, as described above, the luminant regions on the display panel will not display images normally in the luminant state, and the luminant regions on the display panel will display images normally when they are not in the luminant state. 
     If the controller controls at most two luminant regions in the luminant state, the display device is configured as follows. For example, as shown in  FIG. 6 , when the display device described above is just powered on, the controller sends signals to control the first luminant region  71  and the second luminant region  72  on the display panel to be luminant. Since when the first luminant region  71  is luminant, the detection calculation unit receives an optical signal of the first luminant region  71  and determines that the region in front of the first luminant region  71  is the front end region, while the area information of this front end region is fed back to the controller. The controller then controls the second luminant region  72  to be luminant. The display panel  02  is pulled out continually from the housing  01 , and the first luminant region  71  and a first non-luminant region are located outside the housing when the second luminant region  72  is aligned with the detection calculation unit  03 . The controller controls the front end region including the first luminant region  71  and the first non-luminant region in front of the second luminant region  72  to re-display images, and the controller controls a third luminant region to be luminant. At this point, only the second and third luminant regions are luminant. By such analogy, as shown in  FIG. 7 , a (N−1)th luminant region (N−1) and a (N−1) non-luminant region are pulled out from the housing  01  when a Nth luminant region N is aligned with the detection calculation  03 . The controller controls the front end region in front of the Nth luminant region N to display images, and the controller controls a (N−1) luminant region (N+1) to be luminant. Therefore, each time after the detection calculating unit  03  detects the front end region  02   a  and feeds the information of the front end region  02   a  of the information back to the controller, the controller controls the next luminant region to be luminant, and the controller is configured to control at most two luminant regions to be luminant. 
     If the controller controls all luminant regions t in the luminant state, the display device is configured as follows. When the display device described above os just powered on, the controller sends signals to control all luminant regions on the display panel to be luminant. When the first luminant region is luminant, the detection calculation unit receives an optical signal of the first luminant region and determines that the region in front of the first luminant region is the front end region, while the area information of this front end region is fed back to the controller. The controller then controls the front end region in front of the first luminant region to display images. The display panel continues to be pulled out from the housing, and the detection calculation unit receives an optical signal of the second luminant region and determines that the region in front of the second luminant region is the front end region, while the area information of this front end region is fed back to the controller, then the controller controls the front end region in front of the second luminant region to display images. Thus, when the Nth luminant region N is aligned with the detection calculation unit, the controller controls the front end region in front of the Nth luminant region N to display images so as to simplify the control strategy of the controller. 
     The above embodiments are only for illustrating the present disclosure, and not intended to limit the present disclosure. Those skilled in the art can make various variations and modifications without departing from the spirit and scope of the present disclosure, so all equivalent technical solutions also fall into the scope of the present disclosure. It is intended that the scope of the present disclosure should be defined by the claims appended.