Patent Publication Number: US-2011050667-A1

Title: Multistable display system and method for writing image data on multistable display

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 098129514, filed on Sep. 2, 2009, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application relates in general to a multistable display system and in particular to a multistable display system capable of image updating. 
     2. Description of the Related Art 
     Multistable displays may hold images on a screen without applying voltage thereto. Thus, multistable displays are power efficient and suitable for e-books or large electronic displays which do not require frequent updating of image data. Referring to  FIG. 1 , a writehead W for a bistable medium  1  has been disclosed in US 2006/0170981 A1. The writehead W has a plurality of alignment protrusions W 2  on an outer surface thereof, corresponding to a plurality of perforated alignment features  6  which are formed on the bistable medium  1 . When the writehead W contacts and moves along the bistable medium  1 , the alignment protrusions W 2  engage with the perforated alignment features  6  for positioning therebetween. As shown in  FIG. 1 , an electrode W 1  is disposed below the bistable medium  1  and respectively applies a driving voltage signal to each of the contact electrodes  9  above the bistable medium  1 , so as to update the image data on the bistable medium  1 . 
     BRIEF SUMMARY OF INVENTION 
     The application provides a multistable display system, including a multistable display, a writehead, and a sensor. The writehead includes a plurality of electrodes for writing the pixels of the multistable display, wherein each of the pixels corresponds to at least two of the electrodes. The sensor can detect the position of the writehead relative to the multistable display. The electrodes are charged with driving voltage signals according to the relative position between the multistable display and the writehead for updating the pixels of the multistable display. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a perspective diagram of a conventional multistable display with a writehead; 
         FIGS. 2A˜2C  are perspective diagrams of a multistable display system according to an embodiment of the invention; 
         FIGS. 3A˜3B  are perspective diagrams of a multistable display system according to another embodiment of the invention; 
         FIG. 4  is a perspective diagram of a multistable display system according to another embodiment of the invention; 
         FIG. 5  is a perspective diagram of a multistable display system according to another embodiment of the invention; 
         FIG. 6  is a perspective diagram of a multistable display system according to another embodiment of the invention; and 
         FIG. 7  is a perspective diagram of a multistable display system according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring to  FIGS. 2A-2C , an embodiment of a multistable display system S primarily comprises a data writing device  10 , a multistable display  20 , and a sensor  30 . The data writing device  10  comprises a driving unit  11  and a writehead  12 . The driving unit  11  includes a driving circuit  110  and a plurality of brushes  111  electrically connected to the driving circuit  110 . The writehead  12  is rotatable around an axis A, comprising a plurality of annular electrodes  121  and insulating portions  122  between the electrodes  121 , wherein the electrodes  121  are insulated from each other by the insulating portions  122 . The brushes  111  respectively contact and electrically connect to the electrodes  121 . An independent electrode  123  is disposed at an end of the writehead  12  and electrically connected to a conductive portion  205  of the multistable display  20 . 
     As shown in  FIG. 2A , the multistable display  20  comprises a protection layer  201 , an electrode layer  202  disposed on the protection layer  201 , a multistable medium layer  203  disposed on the electrode layer  202 , and a plurality of contact electrodes  204  disposed on the multistable medium layer  203 . The electrode layer  202  is electrically connected with the independent electrode  123  through the conductive portion  205  disposed thereon. In some embodiments, the electrodes  121  may be block-shaped and comprise elastic conductive material for writing data on the multistable display  20 . The insulating portions  122  may comprise elastic material such as rubber, and the multistable medium layer  203  may comprise cholesterol liquid crystal material. Additionally, the contact electrodes  204  may comprises silver, and the electrode layer  202  may comprise transparent ITO material. 
     In  FIG. 2A , the contact electrodes  204  are arranged in a matrix form and electrically independent from each other, thus defining each pixel of the multistable display  20 . When writing or updating image data on the multistable display  20 , the multistable display  20  is moved along the X direction, as the arrow indicates in  FIG. 2A . Hence, the electrodes  121  moves along the multistable display  20  and sequentially contact the contact electrodes  204  line by line, such that the electrodes  121  can provide a driving voltage signal to each contact electrode  204 . The image data of each pixel is therefore updated by applying an electric field between the contact electrode  204  and the electrode layer  202 . 
     In this embodiment, the sensor  30  is disposed beside the multistable display  20  to detect the position of the writehead  12  relative to the multistable display  20 . The sensor  30  can transmit a control signal to the driving circuit  110  according to the positions of the writehead  12  and the multistable display  20 . Subsequently, the driving circuit  110  provides a driving voltage signal to each of the electrodes  121  according to the control signal for rapidly and precisely updating the image on the multistable display  20 . As shown in  FIGS. 2A-2C , the control signal is transmitted from the sensor  30  to the driving circuit  110  through a wire C. However, the control signal can also be transmitted by wireless data transmission. In some embodiments, the driving circuit  110  may communicate with a storage medium which contains a specific image through wire or wireless transmission, so that the image data in the storage medium can be shown on the multistable display  20 . 
     Referring to  FIG. 2A , the adjacent electrodes  121  have a first distance d, and the adjacent contact electrodes  204  (the adjacent pixels) have a second distance D, wherein D&gt;d. In this arrangement, each contact electrode  204  corresponds to at least two of the electrodes  121 . Namely, each pixel can be charged by at least two of the electrodes  121 . When the writehead  12  deviates from a desired position relative to the multistable display  20 , such as a deviated horizontal position along the Y axis, the sensor  30  can detect the deviation (offset) of the writehead  12  and transmit a control signal to the driving circuit  110 . Subsequently, the driving circuit  110  provides a driving voltage signal to each of the electrodes  121  according to the control signal. Since the first distance d is less than the second distance D, some of the driving voltage signals can be shifted and reassigned to the electrodes  121 , so as to compensate for the deviated horizontal position between the writehead  12  and the multistable display  20 . 
     As mentioned above, each of the contact electrodes  204  in the multistable display system S corresponds to several electrodes  121  for writing or updating the image data of the multistable display  20 . Since the sensor  30  can detect the positions of the writehead  12  and the multistable display  20 , conventional rails and perforated alignment features are not necessary. Thus, manufacturing of the multistable display  20  of the invention is less complicated and costs less than conventional multistable displays. 
     To prevent frictional wear between the brushes  111  and the electrodes  121 , another embodiment of the driving circuit  110  is fixed in the writehead  12 , as shown in  FIGS. 3A and 3B . In this embodiment, the driving circuit  110  and the electrodes  121  are electrically connected through wires, so as to transmit the driving voltage signals to the electrodes  121 . Additionally, the driving circuit  110  can communicate with the sensor  30  or other storage media by wireless data transmission to display images on the multistable display  20 . 
     Referring to  FIG. 4 , another embodiment of the writehead  12  comprises a block-shaped circuit board B. A plurality of block-shaped electrodes  121  (such as conductive rubbers) and insulating portions  122  are connected to the circuit board B, such that the electrodes  121  are insulated from each other by the insulating portions  122 . In  FIG. 4 , the driving circuit  110  is electrically connected to the electrodes  121  via the wires L 1 . The driving circuit  110  is further electrically connected to the conductive portion  205  via the wire L 2 . Similarly, each of the contact electrodes  204  in the multistable display system S corresponds to several electrodes  121  to write or update the image data of the multistable display  20 . 
     In some embodiments, the data writing device  10  can be disposed across the multistable display  20  to produce a driving electric field from the upper and lower sides thereof. Moreover, the driving circuit  110  can update and save desired image data by one time download or wireless data transmission. According to the required resolution and the detection result from the sensor  30 , the circuit  110  provides a corresponding driving voltage signal to each of the electrodes  121 . In some embodiments, resolution of the multistable display  20  can also be adjusted by altering the writing frequency of the data writing device  10 . Referring to  FIG. 5 , another embodiment of a multistable display system S further comprises an erase head  40  to completely remove the image data of the multistable display  20  by moving therealong. 
     The data writing device  10  can also be applied to the multistable display  20  without the contact electrodes  204 . Namely, the multistable display  20  forms a first non-electrode surface toward the data writing device  10  without the contact electrodes  204  disposed thereon. With regard to this configuration, the driving electric field is directly produced by the data writing device  10  and the electrode layer  202  of the multistable display  20 . In some embodiments, the electrode layer  202  may be omitted from the multistable display  20  so that a second non-electrode surface is formed under the multistable display  20 . Two data writing devices  10  may be respectively disposed on the upper and lower sides of the multistable display  20  to produce the driving electric field. 
     Referring to  FIG. 6 , another embodiment of a data writing device  50  comprises a hollow writerhead with a driving circuit  510  disposed therein. The driving circuit  510  electrically connects to a lower electrode layer of a multistable display  60  through the conductive wire  520  or a probe to generate a reference voltage. A plurality of electrodes  51  are arranged in a matrix form on the outer surface of the writerhead. The electrodes  51  in  FIG. 6  are elastic, electrically independent from each other, and connected to the driving circuit  510 . In this embodiment, the data writing device  50  can move along a first non-electrode surface  61  of the multistable display  60 . The image data of the multistable display  60  can be updated by the electrodes  51  directly contacting the non-electrode surface  61 . 
     Referring to  FIG. 7 , another embodiment of a data writing device  70  comprises a writerhead with a caterpillar mechanism. A plurality of elastic electrodes  71  are arranged in a matrix form on a caterpillar band  72  of the writerhead. A driving circuit  74  is received in the caterpillar band  72  and electrically connected to the electrodes  71  to respectively provide a driving voltage signal to each of the electrodes  71 . As shown in  FIG. 7 , the driving circuit  74  further connects to a lower electrode layer of a multistable display  80  to generate a reference voltage. 
     In this embodiment, the caterpillar band  72  is driven by two rollers  73 , such that the data writing device  70  progresses through a non-electrode surface  81  of the multistable display  80 . Hence, the image data of the multistable display  80  can be rapidly updated by the electrodes  71  directly in contact with the non-electrode surface  81 . As shown in  FIG. 7 , the caterpillar band  72  has at least an exhaust hole  721  in communication with a vacuum pump. When the electrodes  71  contact the non-electrode surface  81 , the vacuum pump evacuates the air from the gap between the caterpillar band  72  and the non-electrode surface  81 . Hence, negative pressure is produced between the caterpillar band  72  and the non-electrode surface  81  to ensure close contact therebetween. 
     The invention provides a multistable display system and a method for writing image data on a multistable display. The multistable display system comprises a multistable display, a data writing device, and a sensor. The data writing device comprises a plurality of electrodes for writing the pixels of the multistable display, wherein each of the pixels corresponds to at least two of the electrodes. The sensor can detect a position of the writehead relative to the multistable display, and the electrodes of the data writing device can provide a corresponding driving voltage signal to each of the pixels, so as to update the image data of the multistable display. Since the invention does not need complex mechanisms for alignment, manufacturing costs are saved. Additionally, the invention can rapidly update the image data according to the required resolution, thus improving efficiency and flexibility of a multistable display. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.