Method for driving liquid crystal element employing ferroelectric liquid crystal

Abstract

A method for driving a liquid crystal element including a ferroelectric liquid crystal sandwiched between a pair of substrates having electrodes on their opposite surfaces is disclosed. A pulse voltage for defining the light transmitting state of the liquid crystal element is applied to the ferroelectric liquid crystal. Before and/or after the application of the pulse voltage, the ferroelectric liquid crystal is applied with a voltage signal which renders the average value of voltages applied to the ferroelectric liquid crystal equal to zero.

We claim: 
     
       1. A method for driving a liquid crystal element including a ferroelectric liquid crystal interposed between a pair of substrates which have electrodes on their confronting surfaces, said method comprising: a first step of applying to said ferroelectric liquid crystal a pulse voltage which defines the light transmitting state of said liquid crystal element; and   a second step of applying to said ferroelectric liquid crystal before and/or after said first step a voltage signal which renders the average value of voltages applied to said ferroelectric liquid crystal equal to zero.   
     
     
       2. A method according to claim 1, wherein the DC component of said voltage signal having an opposite polarity and the same absolute value as compared with said pulse voltage. 
     
     
       3. A method according to claim 2, wherein said voltage signal has an opposite polarity, the same pulse width and the same pulse height as compared with said pulse voltage. 
     
     
       4. A method according to claim 1, wherein the pulse height of said voltage signal is smaller than the threshold voltage of said ferroelectric liquid crystal. 
     
     
       5. A method according to claim 1, wherein a period during which said pulse voltage is applied is relatively longer than that during which said voltage signal is applied. 
     
     
       6. A method according to claim 1, wherein said ferroelectric liquid crystal includes one selected from a group consisting of chiral smectic C-phase liquid crystal and chiral smectic H-phase liquid crystal. 
     
     
       7. A method according to claim 1, wherein a dichroic dye is mixed into said ferroelectric liquid crystal. 
     
     
       8. A method according to claim 1, wherein a polarizer is placed adjacent to at least one of said substrates. 
     
     
       9. A method according to claim 8, wherein the polarization direction of said polarizer adjacent to one of said substrates is made to nearly coincide with the direction of the long molecular axis of said ferroelectric liquid crystal when an electric field exceeding the threshold voltage of said ferroelectric liquid crystal is applied. .Iadd. 
     
     
       10.  A method for driving a liquid crystal element including a liquid crystal interposed between a pair of substrates which have electrodes on their confronting surfaces, said method comprising the steps of: applying to said liquid crystal a first voltage signal of one polarity which defines a light transmitting state of said liquid crystal element; and   applying a second voltage signal to said liquid crystal before and/or after the application of said first voltage signal, said second voltage signal having an opposite polarity to that of said first voltage signal and enabling maintenance of the light transmitting state of said liquid crystal element defined by the application of said first voltage signal. .Iaddend. .Iadd.11. A method according to claim 10, wherein said liquid crystal is a ferroelectric liquid crystal. .Iaddend. .Iadd.12. A method according to claim 10, wherein said liquid crystal element is driven dynamically. .Iaddend. .Iadd.13. A method according to claim 10, wherein said step of applying the second voltage signal includes applying the second voltage signal immediately before and/or immediately after the application of said first voltage signal. .Iaddend. .Iadd.14. A method according to claim 10, further comprising the step of periodically repeating the application of said first and second voltage signals.   
     
     
        .Iaddend. .Iadd.15.  A method according to claim 14, further comprising the step of periodically repeating the application of said first and second voltage signals. .Iaddend. .Iadd.16. A method according to claim 10, wherein the step of applying the second voltage signal includes applying the second voltage signal having a height at least equal to that of a threshold voltage of said liquid crystal. .Iaddend. .Iadd.17. A method according to claim 13, wherein the step of applying the second voltage signal includes applying the second voltage signals having a height less than that of a threshold voltage of said liquid crystal. .Iaddend. .Iadd.18. A method according to claim 17, further comprising the steps of periodically repeating the application of said first and second voltage signals. .Iaddend. .Iadd.19. A method according to claim 10, further comprising the steps of applying to said liquid crystal a third voltage signal of a polarity which changes the light transmitting state of said liquid crystal element as defined by the application of said first voltage signal, and applying a fourth voltage signal to said liquid crystal before and/or after the application of said third voltage signal, said fourth voltage signal having an opposite polarity to that of said third voltage signal and enabling maintenance of the changed light transmitting state of said liquid crystal element as obtained by the application of said third voltage signal. .Iaddend. .Iadd.20. A method according to claim 19, wherein the step of applying said fourth voltage signal includes applying said fourth voltage signal immediately before and/or immediately after the application of said third voltage signal. .Iaddend. .Iadd.21. A method according to claim 19, further comprising the step of periodically repeating at least one of the application of said first and second voltage signals and the application of said third and fourth pulse signals. .Iaddend. .Iadd.22. A method according to claim 19, wherein the steps of applying the second voltage signal and the fourth voltage signal includes at least one of applying the second voltage signal having a height at least equal to that of a threshold voltage of said liquid crystal and applying the fourth voltage signal having a height at least equal to that of a threshold voltage of said liquid crystal. .Iaddend. .Iadd.23. A method according to claim 22, further comprising the step of periodically repeating at least one of the application of said first and second voltage signals and the application of said third and 
     
     
        fourth voltage signals. .Iaddend. .Iadd.24.  A method according to claim 22, wherein the steps of applying the second voltage signal and the fourth voltage signal includes at least one of applying the second voltage signal having a height less than that of a threshold voltage of said liquid crystal and applying the fourth pulse voltage having a height at least equal to that of a threshold voltage of said liquid crystal. .Iaddend. .Iadd.25. A method according to claim 24, further comprising the step of periodically repeating at least one of the application of said first and second voltage signals and the application of said third and fourth voltage signals. .Iaddend. .Iadd.26. A method for driving a liquid crystal element including a liquid crystal interposed between a pair of substrates which have electrodes on their confronting surfaces, said method comprising the steps of: applying to said crystal a first voltage signal of one polarity which defines a light transmitting state of said liquid crystal element; and   applying a second voltage signal of an opposite polarity to said liquid crystal before and/or after the application of said first voltage signal so as to reduce an average value of the voltage applied to said liquid crystal. .Iaddend. .Iadd.27. A method according to claim 26, wherein said   
     
     
        liquid crystal is a ferroelectric liquid crystal. .Iaddend. .Iadd.28.  A method according to claim 26, wherein the liquid crystal is a ferroelectric liquid crystal and the step of applying said second voltage signal enables suppression of occurrence of an electrochemical reaction and deterioration of said ferroelectric liquid crystal. .Iaddend. .Iadd.29. A method according to claim 26, wherein said liquid crystal element is driven dynamically. .Iaddend. .Iadd.30. A method according to claim 26, wherein the the step of applying the second voltage signal includes applying the second voltage signal immediately before and/or immediately after the application of said first voltage signal. .Iaddend. .Iadd.31. A method according to claim 26, further comprising the step of periodically repeating the application of said first and second voltage signals. .Iaddend. .Iadd.32. A method according to claim 26, wherein the step of applying the second voltage signal includes applying the second voltage signal having a height at least equal to that of a threshold voltage of said liquid crystal. .Iaddend. .Iadd.33. A method according to claim 32, further comprising the step of periodically repeating the application of said first and second voltage signals. .Iaddend. .Iadd.34. A method according to claim 26, wherein the step of applying the second voltage signal includes applying the second voltage signal having a height less than that of a threshold voltage of said liquid crystal. .Iaddend. 
     
     
        .Iadd.35.  A method according to claim 34, further comprising the step of periodically repeating the application of said first and second voltage signal. .Iaddend. .Iadd.36. A method according to claim 26, further comprising the steps of applying to said liquid crystal a third voltage signal of a polarity which changes the light transmitting state of said liquid crystal element as defined by the application of said first voltage signal, and applying a fourth voltage signal to said liquid crystal before and/or after the application of said third voltage signal and having an opposite polarity to that of said third voltage signal so as to reduce an average value of the voltage applied to said liquid crystal. .Iaddend. .Iadd.37. A method according to claim 36, wherein the step of applying said fourth voltage signal includes applying said fourth voltage signal immediately before and/or immediately after the application of said third voltage signal. .Iaddend. .Iadd.38. A method according to claim 36, further comprising the step of periodically repeating at least one of the application of said first and second voltage signals and the application of said third and fourth voltage signals. .Iaddend. .Iadd.39. A method according to claim 36, wherein the steps of applying the second voltage signal and the fourth voltage signal includes at least one of applying said second voltage signal having a height at least equal to that of a threshold voltage of said liquid crystal and applying said fourth voltage signal having a height at least equal to that of a threshold voltage of said liquid crystal. .Iaddend. .Iadd.40. A method according to claim 39, further comprising the step of periodically repeating at least one of the application of said first and second voltage signals and said third and fourth voltage signals. .Iaddend. .Iadd.41. A method according to claim 36, wherein the steps of applying said second voltage signal and said fourth voltage signal includes at least one of applying said second voltage signal having a height less than that of a threshold voltage of said liquid crystal and applying said fourth voltage signal having a height at least equal to that of a threshold voltage of said liquid crystal. .Iaddend. .Iadd.42. A method according to claim 41, further comprising the step of periodically repeating at least one of the application of said first and second voltage signals and the application of said third and fourth voltage signals. .Iaddend.