ELECTROSTATIC DISPLAY APPARATUS

Abstract: A display panel (21) is formed by a large number of electro­ statically operated display units (20) arranged to form a matrix. Each display unit (20) basically has two fixed electrodes (1, 2) and a movable electrode (3), between which a high-tension voltage is supplied to bend the movable electrode (3) by elec­ trostatic force so as to cover one of the fixed electrodes (1, 2). With the fixed electrode covered or uncovered, each of the display units has its appearance changed, and serves as one of the dots constituting a pattern to be displayed. The display can present a static or a moving or flowing pattern in a positive image mode and in a negative image mode. Each display unit (20) is driven by a thyristor of a drive circuit (22) which is con­ trolled by a display register (23) consisting of shift registers. A control unit (24) receives control instruction signals from a memory (20), and includes an address counter (27) which reads out display patterns from the memory (30) which are transmitted through a data transmitter (29) to the display register (23).

Description: The present invention relates to an electrostatic display apparatus capable of displaying a pattern, said apparatus comprising: a display panel constituted by a plurality of electrostatic display units arranged in a plane, each of said electrostatic display units having a fixed electrode, a movable electrode made capable of being attracted and repelled from the surface of said fixed electrode, a dielectric layer provided at least on the surface of said fixed electrode or the surface of said movable electrode, and lead wires for said fixed electrode and said movable electrode whereby the appearance of said electrostatic display unit is changed when voltage is applied through the lead wires so as to cause said movable electrode to be electrostatically attracted to and cover the surface of said feed electrode; a display register loadable with display data bits corresponding to said electrostatic display units and adapted to be driven by shift pulses; memory means including RAM for storing a plurality of display data bits and control commands for determining display speed and positive or negative display image; a transmitting means for transmitting display data bits from said memory means to said display register; and pulse generating means having a shift pulse output stage for supplying shift pulses to the display register. A known electrostatic display apparatus comprises a display board which is constituted by many electrostatic display units arranged to form a display matrix. Each of the elctrostatic display units is made up of a pair of electrodes: one is fixed and the other is movable. The fixed electrode is coated with a dielectric substance having a particular color. The movable electrode is, for instance, made of a metal-coated plastic thin film so as to be bent over the fixed electrode by an electrostatic force produced when a high-tension voltage is imposed between the two electrodes. The movable electrode, when bent over the fixed electrode, covers its dielectric surface and thus changes the apparent color of the fixed electrode, that is, the appearance of the display unit is changed. The display board can thus be made to display a predetermined pattern by selecting the distribution of high voltage supply to the electrostatic display units. An example of an electrostatic display unit is shown in perspective in Fig. 1 and in cross-section in Fig. 2, in which an electric circuit to supply voltage is also shown. In this example two electrode plates 1 and 2 constitute fixed electrodes, while an aluminium coated polyester or polycarbonate film 3 is the movable electrode. The upper portions 1C, 2C and lower portions 1A, 2A of the two electrode plates 1 and 2 are flat and set up opposite to each other in parallel, while the middle portions protrude inside forming semi-cylindrical prominences 1B and 2B. The film-like movable electrode 3 runs through a shim inserted in the narrowest clearance 4 made between the semi-cylindrical prominences 1B and 2B. The lower portion of the movable electrode 3 is fixed to an electrode holder 6, which doubles as a terminal 14. The holder 6 of the movable electrode 3 is fixed between the lower portions 1A and 2A of the two electrode plates by means of male and female spacers 5, 6 and bolts 9 and 8. The spacers 5 and 6 are made of an insulating material. The inner surfaces of the electrode plates 1 and 2, at least the area above the narrowest space 4 between them, are coated with insulating paints of different colors. In addition to the above arrangement of the electrodes, an A.C voltage is supplied, as is shown in Fig. 2, between the movable electrode 3 (via the terminal 14) and one of the electrode plates 1 and 2 (via the terminals 12 and 13) from a voltage source 10, with the polarity of the movable electrode 3 changed by a switch 11. In the described electrostatic display unit, the movable electrode 3 is attracted, in accordance with its polarity, by either the electrode plate 1 or the electrode plate 2, and covers the inner surface of that electrode plate 1 or 2. Thus the appearance of the display unit seen from above can be switched between the two colors applied to the inside surfaces of the fixed electrodes. An electrostatic display apparatus of the type defined at the beginning is described at page 88 of Vol. 20, No. 195, March 1983, of the J.E.E. Journal of Electronic Engineering, Tokyo, Japan, and uses display units of the kind described with reference to Figs. 1 and 2. The main display unit incorporates a shift register for transmitting display signals to the display panel. The drive method involves storing a character or picture as digital signals in a RAM pack, then serially reading the signals. Page 59 of Vol. 19, No. 189, of J.E.E. Journal of Electronic Engineering, Tokyo, Japan, September 1982, briefly describes a similar display apparatus using the same type of display units, and US-A-4336536 describes an electrostatic display apparatus having a panel of electrostatically operated display units controlled by the contents of a shift register fed with a video signal. An object of the present invention is to provide, by using the above mentioned electrostatic display units, a display apparatus capable of displaying not only a fixed pattern but also a moving pattern like a series of flowing characters giving a message or news. Another object of the present invention is to provide a display apparatus capable of reversing a displayed pattern between a positive and a negative image. According to the invention, an electrostatic display apparatus of the type defined at the beginning is characterised by controlled pulse generating means for generating drive pulses at a selected frequency; and decoding means coupled to the memory means for receiving said control commands in the form of instruction code bits and supplying mode control signals to the controlled pulse generating means and said transmitting means, said pulse generating means being so coupled to the memory means that the selected frequency of the said drive pulses determines the rate of addressing in the memory means, the decoding means being so coupled to the pulse generating means as to select the frequency of generation of the drive pulses in dependence upon the presence of predetermined combinations of values of said instruction code bits and being so coupled to the transmitting means as to determine whether a display has a positive image or a negative image in dependence upon the value of one of the instruction code bits, the shift pulse output stage supplying shift pulses to the display register in synchronism with the drive pulses, the decoding means being so coupled to the shift pulse output stage as to block the supplying of shift pulses during the presence of one predetermined combination of values of the instruction code bits at the decoding means corresponding to a selected low frequency of generation of the drive pulses, the shift pulse output stage being enabled to supply shift pulses during the presence of other predetermined combinations of values of the instruction code bits corresponding to a selected high frequency of drive pulses to which the movable electrodes of the display units are unable to respond, and a selected lower frequency of drive pulses to which the movable electrodes of the display units are able to respond, and the memory means having a matrix-type RAM storing the display data bits and the control instruction code bits in columns corresponding to columns of the display panel, each column of bits being composed of a plurality of display data bits and a plurality of control instruction code bits selecting a frequency of generation of drive pulses and a positive or negative image. The invention will now be described by way of example with reference to the attached drawings, in which: Fig. 1 shows a perspective view of an electrostatic display unit used in the present invention; Fig. 2 shows a cross-sectional view of the above electrostatic display unit; Fig. 3 shows a block diagram illustrating the constitution of an embodiment of the present invention; Fig. 4 shows an example of the formats stored in the memory 30 in Fig. 3; Fig. 5 shows in detail part of the embodiment of Fig. 3; Figs. 6 and 7 show time charts for explaining the function of the circuit shown in Fig. 5; and Fig. 8 shows in detail another part of the embodiment of Fig. 3. Detailed Description of the Invention In Fig. 3, which shows an embodiment of the present invention, a display panel 21 is constituted by many electrostatic display units 20 (shown in Figs. 1 and 2) arranged in the form of a matrix. The number of the display units is, for example, 20x200. A driving circuit 22 is formed with thyristors, each thyristor corresponding to a respective one of the display units 20 in the display panel 21. A display register 23 consists of shift registers shifted by shift pulses CK' generated by a shift pulse generator 26 in a control unit 24 . Each bit of the display register 23 corresponds to a respective pixel (a display unit) in the display panel 21. The control unit 24 comprises an oscillator 25 for generating clock pulses at a fundamental frequency, the shift pulse generator 26 for generating the shift pulses CK' and address pulses CK by dividing the fundamental frequency output from the oscillator 25, an address pulse counter 27 for counting the address pulses CK, a decoder 28 for controlling the shift pulse generator 26 in accordance with control instruction signals C₁ and C₂, and a data transmitter 29, controlled by a control instruction signal C₀, for transmitting data signals from a memory 30 to the display register 23. The memory 30, which consists of a RAM, stores all display data and the control instructions C₀, C₁, and C₂. The control instructions are three bits C₀, C₁ and C₂ assigned to each column in the display data storing part of the memory 30. These instructions specify various modes as shown in Table 1. In Table 1, "Reversed display" means display with contrast reversed. The RAM is a matrix type with 24 bits per column: 4 bits out of the 24 bits are assigned to control data and the remaining 20 bits are assigned to display data. Fig. 4 shows a bit format in the memory 30. In Fig. 4 the white-ground portions represent logic "0", while the black-dotted portions represent logic "1". In this example, data for the display of "DAIWA SHINKU" is stored. The control instructions C₁=1 and C₂=0 are stored above the display data for "DAIWA". This combination specifies the High-speed shift mode. The control instruction corresponding to the next display data "SHINKU" is again C₁=1 and C₂=0. The control instruction in the RAM matrix columns corresponding to the blanks just after the display data "DAIWA" and "SHINKU" is C₁=0 and C₂=1. This logic combination specifies the Stop mode. Fig. 5 shows in detail the shift pulse generator 26 and its connections, and illustrates control instructions decoded by the decoder 28 and supplied to the shift pulse generator 26. The shift pulse generator 26 includes a binary counter acting as a frequency divider 32 which successively divides the frequency of the fundamental clock oscillation CL generated by the oscillator 25. Outputs Q₁, Q₉ and Q₁₂ are respectively the outputs from 1st stage, 9th stage and 12th stage of the binary counter. If the frequency of the fundamental clock oscillation be f₀, then the frequencies of Q₁, Q₉ and Q₁₂ are f o x 1/2, f o x (1/2)⁹ and f o x (1/2)¹², respectively. The outputs Q₁ Q₉ and Q₁₂ are provided for High-speed shift, Flowing display, and Stop, respectively. NAND gates 33, 34 and 35 open with C₁=1, C₂=0, with C₁=0, C₂=0, and with C₁=0, C₂=1, respectively. The outputs from the NAND gates 33, 34 and 35 are inputted to an AND gate 36. The output from the AND gate 36 is supplied both to the reset terminal of the frequency divider 32 through an inverter 38, and to a flip-flop 37 which shapes the input pulse into an output pulse having a definite pulse width. The address pulse counter 27 proceeds step by step in response to the output pulse from the flip-flop 37, and can output 4096 (=2¹²) state-signals through 12 output terminals Q₁, Q₂, ..., Q₁₂. Addresses in the RAM 30 are selected by these state-signals. The data stored in the RAM 30 are outputted from data output terminals D₀, D₁, ..., D₁₉. The output from the flip-flop 37 is also supplied to a NAND gate 39 to drive a transistor 40 which supplies the shift pulses to the display register 23 (Fig. 3). In the Stop mode, C₁=0 and C₂=1 and no shift pulse CK' is generated since the NAND gate 39 is blocked. Now suppose that the RAM 30 has stored, together with display data, the code (C₁=1, C₂=0) specifying the High-speed shift mode. Fig. 6 shows voltage waveforms at various parts in the mode of High-speed shift. The NAND gates 34 and 35 are set to output "1". As soon as the output Q₁ of the frequency divider 32 turns to H (high level) from L (low level), the frequency divider 32 is reset by the output of the inverter 38, and the output from the AND gate 36 to the flip-flop 37 become a sharp negative-going pulse. The flip-flop 37 outputs a square wave at half the frequency of the negative-going pulses. Each cycle of the square wave output advances the address in the RAM 30 by one step, and therefore the display data contents of the display register 23 advance by one column synchronously with that step. However, the frequency of the pulses CK and CK' is 5 kHz, so the movable electrodes of the electrostatic display units 20 cannot respond, and instead keep the previous display unchanged. In this mode the frequency divider 32 is inevitably reset after outputting Q₁ so it cannot proceed to output Q₉, Q₁₂. If the data in the column addressed in the RAM 30 proceeds from the High-speed shift mode to the Stop mode (C₁=0, C₂=1), the NAND gate 35 is held open, while the NAND gates 33 and 34 are set to output "1". The output Q₁₂ of the frequency divider 32 is outputted at 2048 (=2¹¹) times the period of Q₁. As soon as the NAND gate 35 and the AND gate 36 respond to the Q₁₂ output the frequency divider 32 is reset by the output of the inverter 38, as in the case of the High-speed shift node. The AND gate 36 according supplies a sharp negative-going pulse. Fig. 7 shows voltage waveforms at various parts in the present mode. Fig. 7 is drawn with the time scale very much compressed in comparison with Fig. 6. The number of addresses in which the Stop instruction code is written is,for instance, four as shown in Fig. 4. The time needed for the counter 27 to advance by four addresses is, for instance, 1 second. During this time, the display register is not supplied with shift pulses, and therefore the previous pattern "DAIWA" is displayed. When the control instruction code returns to the High-speed shift mode, the contents of the display register 23 change from "DAIWA" to "SHINKU" at a high speed. However, during the short time in which this change takes place, the electrostatic display units 20 continue to display "DAIWA" because, as mentioned above, they can not respond. When the memory column addressed contains the Stop code following "SHINKU", the movable electrodes of the display units 20 finally respond, and change the display from "DAIWA" to "SHINKU". In the following the Flowing display mode is described. This display mode is specified by C₁=0 and C₂=0. In this case the NAND gate 34 is held open, and the output Q₉ of the frequency divider 32, which has a period 256 (=2⁸) times the period of Q₁, is supplied. The address in the memory advances at the rate of Q₉, to which the electrostatic display units can respond. Synchronously with the advancing of the address, the columns in the display shift one by one. Fig. 8 shows an example of the data transmission circuit 29 in Fig. 3. The display data D₀, D₁, .., D₁₉ from the memory 30 are transmitted to the input terminals of the display register 23 through exclusive OR gates 41. In this case, one input line of each exclusive OR gate is connected to a common line supplied with a control instruction code C₀. As is shown in Table 1, C₀=0 is the condition for Normal display as in Fig. 4 and C₀=1 is the condition for Reversed display. The truth table for an exclusive OR gate is shown in Table 2 below. As is understood from this truth table, if C₀=0, D i (i=0, 1, 2, ..., 16) are outputted as they are, whereas if C o =1, D i are inverted to D i ' and outputted. This implementation of the data transmission circuit is simple, and is not accompanied by time delay. The return code of the control instruction is specified by C₁=1 and C₂=1. This code is usually specified just after the final data of a data series in the memory. In Fig. 5 the decoder 28, detecting C₁=C₂=1, supplies a reset signal to the address pulse counter 27 to return the address to 0. As a result the display 21 repeats the display of the same program.

Claims: An electrostatic display apparatus capable of displaying a pattern, said apparatus comprising: a display panel (21) constituted by a plurality of electrostatic display units (20) arranged in a plane, each of said electrostatic display units (20) having a fixed electrode (1, 2), a movable electrode (3) made capable of being attracted and repelled from the surface of the said feed electrode (1, 2), a dielectric layer provided at least on the surface of said fixed electrode (1, 2) or the surface of said movable electrode (3), and lead wires for said fixed electrode (1, 2) and said movable electrode (3) whereby the appearance of said electrostatic display unit (20) is changed when voltage is applied through the lead wires so as to cause said movable electrode (3) to be electrostatically attracted to and cover the surface of said fixed electrode (1, 2); a display register (23) loadable with display data bits corresponding to said electrostatic display units (20) and adapted to be driven by shift pulses; memory means (27, 30) including RAM (30) for storing a plurality of display data bits and control commands for determining display speed and positive or negative display image; a transmitting means (29) for transmitting display data bits from said memory means (27, 30) to said display register (23); and pulse generate means (25, 26) having a shift pulse output stage (39, 40) for supplying shift pulses (CK') to the display register (23); characterised by the pulse generating means (25, 26) being controlled to generate drive pulses (CK) at a selected frequency; and decoding means (28) coupled to the memory means (27, 30) for receiving said control commands in the form of instruction code bits (C₀, C₁, C₂) and supplying mode control signals to the controlled pulse generating means (25, 26) and said transmitting means (29), said pulse generating means being so coupled to the memory means (27, 30) that the selected frequency of the said drive pulses (CK) determines the rate of addressing in the memory means (27, 30), the decoding means (28) being so coupled to the pulse generating means (25, 26) as to select the frequency of generation of the drive pulses (CK) in dependence upon the presence of predetermined combinations of values of said instruction code bits (C₀, C₁, C₂) and being so coupled to the transmitting means (29) as to determine whether a display has a positive image or a negative image in dependence upon the value of one of the instruction code bits (C₀), the shift pulse output stage (39, 40) supplying shift pulses (CK') to the display register (23) in synchronism with the drive pulses (CK), the decoding means (28) being so coupled to the shift pulse output stage (39, 40) as to block the supplying of shift pulses (CK') during the presence of one predetermined combination ( C ₁.C₂=1) of values of the instruction code bits at the decoding means (28) corresponding to a selected low frequency of generation of the drive pulses (CK), the shift pulse output stage (39, 40) being enabled to supply shift pulses (CK') during the presence of other predetermined combinations of values of the instruction code bits corresponding to a selected high frequency of drive pulses (CK) to which the movable electrodes (3) of the display units (20) are unable to respond, and a selected lower frequency a drive pulses (CK) to which the movable electrodes (3) of the display units (20) are able to respond, and the memory means (27, 30) having a matrix-type RAM (30) storing the display data bits and the control instruction code bits in columns corresponding to columns of the display panel (21), each column of bits being composed of a plurality of display data bits and a plurality of control instruction code bits selecting a frequency of generation of drive pulses and a positive or negative image.

Inventors: HATA, KAZUO, TOGO, HIDEHIKO
Applicants: DAIWA SHINKU CORPORATION
Application year: 1985
Main classification: G09F9
IPC codes: G09F9, G09G3