Ferroelectric liquid crystal touch panel

A ferroelectric liquid crystal touch panel includes a ferroelectric liquid crystal panel including counterposed electrodes and a ferroelectric liquid crystal positioned between the electrodes; a position detector for detecting a pushed position on the ferroelectric liquid crystal through the electrodes by means of an electromotive force generated when the ferroelectric liquid crystal is pushed; a display control circuit for controlling a display state of the ferroelectric liquid crystal through the electrodes; a sound generation control circuit for supplying a sound generation signal to the electrodes so that the ferroelectric liquid crystal panel generates a sound in correspondence thereto; and a selection circuit for selectively connecting the position detector, the display control circuit and the sound generation control circuit to the electrodes.

BACKGROUND OF THE INVENTION 
The present invention relates to a ferroelectric liquid crystal touch 
panel. 
In recent years, accompanying the increase in the amount and complication 
of information treated in information devices, there is the related 
tendency that various devices are becoming too large and complicated. 
Therefore, in order to make the entire device compact, a device has been 
proposed which has both an input function and another function, such as a 
display function. 
For example, a device provided with such plural functions is a panel using 
a liquid crystal as will more specifically be shown hereinafter. 
A first such device includes a liquid crystal panel equipped with an input 
function and which determines the change of distance between electrodes of 
the panel in the case when the display surface of the liquid crystal panel 
is pushed as a change of the electrical capacity, and the pushed position 
of the liquid crystal panel is detected thereby. 
The second such device includes a liquid crystal panel equipped with an 
input function and which effects heat writing with a light pen comprising 
a semiconductor laser and a focussing lens into the liquid crystal display 
device using a thermoelectric optical effect. The difference of the 
display state is determined as a change of the electric capacity, and the 
position thermally written on the liquid crystal panel is detected 
thereby. 
In the above-described first liquid crystal panel, since the liquid crystal 
shows dielectric constant anisotopy, the electric capacity changes also by 
the display state of the liquid crystal (on, off, or intermediate state). 
It is therefore necessary to separate the change of electric capacity in 
the case when the display surface of the panel is pushed and there is a 
change of electric capacity due to the display state. Therefore, the 
construction of the detecting circuit becomes complicated, and together 
with that, there is the problem that separation of the above-described 
respective capacities becomes extremely difficult. 
In the above-described second liquid crystal panel, since the change of the 
writing-in state is detected as a change of electric capacity, there is 
the problem that the input cannot be effected without changing the display 
state. Further, since a special device such as a light pen and the like is 
required, there is also the problem that the device becomes expensive. 
As described above, it was impossible heretofore to obtain an effective 
liquid crystal panel equipped with both an input function and another 
function, such as a display function. 
An object of the present invention is to obtain a liquid crystal panel 
equipped with a plural number of functions, including an input function. 
The present invention utilizes the piezoelectric effect of a ferroelectric 
liquid crystal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following, embodiments of the present invention will be explained by 
referring to drawings. 
The present invention relates to a device which carries out, for example, 
the key input and display by use of a single ferroelectric liquid crystal 
panel. 
Referring to the drawings, a ferroelectric liquid crystal panel 1 has the 
construction shown in FIGS. 1 and 2. Specifically, on the counterposed 
surfaces of the counterposing substrates 1c and 1d, there are formed 
transparent electrodes 1a and 1b, and alignment layers 1f and 1g using 
polyimide or the like, and a ferroelectric liquid crystal 1e is sealed 
between the substrates 1c and 1d. For the above-described substrate 1c, it 
is preferable to use a flexible transparent body such as a plastic (PET 
film and the like) or the like, and for the above-described substrate 1d, 
it is preferable to use a transparent body such as glass or the like. The 
electrodes 1a and 1b constitute a matrix as shown in FIG. 1. The numeral 
1h denotes a seal material using epoxy resin or the like, and numerals 1i 
and 1j denote polarizing plates. 
The above-described ferroelectric liquid crystal panel 1 has the following 
characteristics: 
(1) The alignment layers are subjected to a homogeneous alignment 
treatment. 
(2) The alignment layers are shifted with respect to each other out of a 
parellel or antiparallel arrangement and have been subjected to a 
homogeneous alignment treatment. 
(3) At least one alignment layer has been subjected to a homogeneous 
alignment treatment by a strong rubbing method. 
(4) The ferroelectric liquid crystal is in a phase showing 
ferroelectricity. 
(5) The distance between the counterposed electrodes is as narrow as 
possible. 
(6) The alignment layer at one side is formed with a material attracting 
spontaneous polarization of the ferroelectric liquid crystal, and the 
alignment layer at the other side is formed with a material repulsing 
spontaneous polarization of the ferroelectric liquid crystal. 
(7) For the ferroelectric liquid crystal, one having a large spontaneous 
polarization is used. 
Referring back to FIG. 1, position detecting means 2a and 2b are provided 
for detecting the pushed position through electrodes 1a and 1b by the 
electromotive force generated between electrodes 1a and 1b when the side 
of substrate 1c in the above-described ferroelectric liquid crystal panel 
1 is pushed. Position detecting means 2a and 2b are mainly constituted by 
operational amplifiers for voltage detecting use. 
Display control means 3a and 3b are provided for controlling the display 
state of the above-described ferroelectric liquid crystal panel 1 through 
the electrodes 1a and 1b. Display control means 3a and 3b are mainly 
constituted by driving circuits for driving the liquid crystal. 
Selection means 5a and 5b are provided for selecting the connection of the 
above-described position detecting means 2a and 2b and display control 
means 3a and 3b to the above-described electrodes 1a and 1b in a 
time-sharing manner. Specifically, the connection of position detecting 
means 2a and 2b and display control means 3a and 3b to the same electrodes 
1a and 1b changes over in a time-sharing manner. Selection means 5a and 5b 
are constituted by array-like switching elements. When position detecting 
means 2a and 2b are connected to electrodes 1a and 1b by selection means 
5a and 5b, the connection of display control means 3a and 3b to electrodes 
1a and 1b is cut off. Conversely, when display control means 3a and 3b are 
connected to electrodes 1a and 1b by selection means 5a and 5b, the 
connection of position detecting means 2a and 2b to electrodes 1a and 1b 
is cut off. 
Further, a control means 6 is provided for sending control signals to the 
above-described selection means 5a and 5b. 
Next, an explanation will be given on the operation of the ferroelectric 
liquid crystal touch panel by use of the above-described elements. 
From control means 6, for example, a control signal for changing over 
between logic level "1" and logic level "0" is sent to selection means 5a 
and 5b at each period of 1 msec. 
When the control signal is at logic level "1", position detecting means 2a 
and 2b are connected to electrodes 1a and 1b by the above-described 
selection means 5a and 5b . When ferroelectric liquid crystal panel 1 is 
pushed, the pushed position is detected in this period. The cross point of 
the largest electromotive force is judged as the pushed position, from 
among the electromotive forces generated at the plural number of cross 
points of the electrodes constituting the matrix. 
On the other hand, when the control signal is at logic level "0", display 
control means 3a and 3b and electrodes 1a and 1b are connected by the 
above-described selection means 5a and 5b. At this time, a predetermined 
electrode 1a is selected and a selection signal is applied by the display 
control means 3a, and a non-selective signal is applied on the other 
electrode. Further, the display signals are applied by display control 
means 3a and 3b to all electrodes 16 in synchronization to the selection 
signal. Next, when the control signals become logic level "0", an 
electrode 1a other than the above-described predetermined electrode 1a is 
selected. Specifically, for the display control, only one electrode 1a is 
selected each time that the control signal becomes logic level "0", and 
scanning is effected successively as is performed in a conventional liquid 
crystal display device. 
In the above-described embodiment, although only one electrode 1a was 
selected each time that the control signal became logic level "0", several 
or all electrodes 1a may be successively selected during the period when 
the control signal is at logic level "0", and these electrodes may be 
scanned continuously. 
Although ferroelectric liquid crystal panel 1 shown in FIG. 2 has been 
premised to have a double refraction display using two polarization 
plates, it is also possible to apply a guest host mode for effecting such 
display by mixing two dichroic dyes into the ferroelectric liquid crystal, 
and in this case, one polarization plate may be used. 
Referring now to FIG. 3, a key input device is shown, as an example of a 
concrete use of the above-described embodiment. 
As shown in FIG. 3, the display of various input keys such as characters, 
numbers, marks, etc., is carried out at the cross points of electrodes 1a 
and 1b. In order to carry out the display, in the same manner as in a 
conventional liquid crystal display panel, electrodes 1a and 1b may be 
pattern formed in a desired shape. The user may push desired keys while 
seeing the characters, numbers, marks, etc., displayed on the 
ferroelectric liquid crystal panel. Also, when the input key is pushed, it 
is more effective to supply sound-generating signals from sound generation 
control means 4a and 4b to the electrodes corresponding to the keys 
accepting the input to let them generate sound. 
It is noted that at the plural number of cross points of electrodes 1a and 
1b, display of the characters, numbers, marks, etc., may be carried out. 
Next, an explanation will be given of other embodiments of the present 
invention. 
In addition to position detecting means 2a and 2b and display control means 
3a and 3b in the above-described embodiment, sound generation control 
means 4a and 4b are provided, and in the same manner as in the 
first-described embodiment, all of these are connected successively to the 
electrodes in a time-sharing manner. In other words, in FIG. 3, sound 
generation control means 4a and 4b are connected to selection means 5a and 
5b, in addition to position detecting means 2a and 2b and display control 
means 3a and 3b. An explanation will now be given in which sound 
generation control means 4a and 4b are added to the system shown in FIG. 
1. 
FIG. 4 is a timing diagram for showing an example of the operation in the 
present instance. 
In the same Figure, in the period t1, sound generation control means 4a and 
4b and electrodes 1a and 1b are connected by selection means 5a and 5b. 
Then AC voltage of a frequency f (about 4096 Hz) is applied between 
electrodes 1a and 1b by sound generation control means 4a and 4b, and 
sound is generated from ferroelectric liquid crystal panel 1 by the 
piezoelectric effect of the ferroelectric liquid crystal. 
In the period t2 (about 62.5 msec), position detecting means 2a and 2b and 
display control means 3a and 3b are selected by selection means 5a and 5b. 
The performance at this time is the same as that in the already-described 
first embodiment. 
As described above, in the example of FIG. 4, modulation of 1/t3 Hz (about 
8 Hz) is applied for the sound generation, and in the rest period t2 of 
the sound generation, position detection and display control are effected. 
The modulation is not limited to the example described above. For example, 
for the fundamental frequency of 4096 Hz, a modulation of 8 Hz and 256 Hz, 
etc., may be applied. In such as case, it is also preferable that the 
position detection is effected in the rest period of 256 Hz, and the 
display control is effected in the rest time of 8 Hz. 
Next, another embodiment of the present invention will be explained by 
referring to FIG. 5. 
In the stationary state, position detecting means 2 and electrodes 1a and 
1b are connected by selection means 5c and 5d, and sound generation 
control means 4 and electrodes 1a and 1b are not connected. When 
ferroelectric liquid crystal panel 1 is pushed, and the pushed position is 
detected by position detecting means 2, the states of the above-described 
selection means 5c and 5d are reversed. In other words, position detecting 
means 2 and electrodes 1a and 1b are not connected, and sound generation 
control means 4 and electrodes 1a and 1b are connected. As a result, after 
generation of the sound, in that predetermined sound generation signals 
are sent from the sound generation control means to electrodes 1a and 1b, 
the device returns to the stationary state, that is, only when 
ferroelectric liquid crystal panel 1 is pushed, sound is generated. 
Numeral 6a denotes the control means. 
In the above-described embodiment, the position detecting means, display 
control means, and sound generation control means were suitably selected 
with a selecting means, and the above-described respective means were 
connected to common electrodes. 
However, in the present invention, it is not necessarily required that the 
above-described respective means use the same electrode, and the 
above-described respective means may be connected to electrodes different 
from each other. 
According to the present invention, since the pushed position of the panel 
is detected from the electromotive force by use of the piezoelectric 
effect of the ferroelectric liquid crystal, the pushed position can be 
positively detected without relation to the fluctuation of the cell 
thickness and the display state. 
Also, since a plural number of functions such as the position detection, 
display, and sound generation can be obtained, miniaturization and thin 
type formation of the whole device can be attained. 
Also, by providing a selection means, since the position detection, display 
control and sound generation can be individually effected, respective 
functions can be positively performed. 
Although the present invention has been described through specific terms, 
it should be noted here that the described embodiments are not necessarily 
exclusive and that various changes and modifications may be imparted 
thereto without departing from the scope of the invention, which is 
limited solely by the appended claims.