Image forming apparatus and driving method therefor

• US 4,884,079 A
• Filed: 01/19/1989
• Issued: 11/28/1989
• Est. Priority Date: 04/25/1984
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Inoue, Yutaka, Inoue, Hiroshi, Yamakawa, Tadashi, Osada, Yoshiyuki, Satomura, Hiroshi, Omata, Satoshi
• Primary Examiner(s): Hartary, Joseph W.
• Application Number:
  US07/300,698
• Time in Patent Office: 313 Days
• Field of Search: 346/1.1, 346/107 R, 346/108, 346/160, 350/331 R, 350/333, 350/356
• US Class Current: 347/247
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G06K 15/1238 simultaneously exposing more than one point

Abstract

An image forming apparatus comprising an exposure light source, a printer head which comprises a group of micro-shutters each controlling the transmission or interruption of light from the exposure light source, and an image bearing so disposed to be irradiated with light signals transmitted through the printer head. The group of micro-shutters are arranged in a matrix comprising a plurality of rows and a plurality of columns. The group of micro-shutters are formed by a substrate having thereon a plurality of segment electrodes each forming a shutter and connected to a drain of a thin film transistor, another substrate having thereon a common electrode, and a liquid crystal interposed between the substrates. The image forming apparatus further comprises means for applying a scanning signal to the gate of the thin film transistor and applying an electric signal corresponding to image information in synchronism with the scanning signal.

Claims

1. In an image forming apparatus comprising an exposure light source, a printer head which comprises a plurality of microshutters arranged in at least one line and each controlling the transmission or interruption of light from said exposure light source, and an image bearing member so disposed to be irradiated with light signals transmitted through the printer head;

the improvement wherein

each of said plurality of microshutters is connected to one of a plurality of thin film transistors,

said plurality of thin film transistors are divided into a plurality of groups each comprising a prescribed number of thin film transistors which are connected in common to one source line and are connected separately to different gate lines; and

each of said different gate lines is commonly connected to a plurality of thin film transistors each belonging to one of said plurality of groups.

2. An image forming apparatus according to claim 1 wherein said plurality of microshutters are formed on a substrate having thereon a plurality of segment electrodes each forming a shutter and connected to a drain of a thin film transistor, another substrate having thereon a common electrode, and a liquid crystal interposed between the substrates.

3. An image forming apparatus according to claim 1, wherein an electric field strength of 5×

10⁵ V/cm or below is applied to a gate insulating film at the channel of said thin film transistor.

4. An image forming apparatus according to claim 2, wherein said thin film transistors are formed outside of a sealing member for sealing said liquid crystal between said substrates.

5. An image forming apparatus according to claim 2, wherein said thin film transistors and the segment electrodes of the microshutters are on the same substrate.

6. An image forming apparatus according to claim 4, wherein said thin film transistors are formed on an exterior circuit board.

7. An image forming apparatus according to claim 1, wherein said thin film transistors comprise a semiconductor of amorphous silicon.

8. An image forming apparatus according to claim 2, which further comprises means for applying gate-on pulses sequentially to the gate electrodes of said plurality of thin film transistors.

9. An image forming apparatus according to claim 2, wherein said liquid crystal is a nematic liquid crystal.

10. An image forming apparatus according to claim 1, which further comprises pre-charging means by which said image bearing member is pre-charged, so that the pre-charged image bearing member is exposed with the optical signal from said printer head to form an electrostatic image thereon, and developing means for developing the electrostatic image.

11. An image forming apparatus according to claim 1, which further comprises pre-charging means by which said image bearing member is pre-charged so that the pre-charged image bearing member is exposed with the optical signal from said printer head to form an electrostatic image thereon, developing means for developing the electrostatic image to form a toner image, and means for transferring the toner image.

12. An image forming apparatus according to claim 1, wherein said image bearing member is a rotatable photosensitive drum.

13. An image forming apparatus according to claim 12, wherein said photosensitive drum comprises a photosensitive layer formed of an organic photoconductive material.

14. An image forming apparatus according to claim 12, wherein said photosensitive drum comprises a photosensitive layer formed of amorphous silicon.

15. A driving method for an image forming apparatus of the type comprising an exposure light source, a printer head which comprises a group of micro-shutters each controlling the transmission or interruption of light from said exposure light source, and an image bearing member so disposed to be irradiated with light signals transmitted through the printer head;

said group of micro-shutters are arranged in a matrix comprising a plurality of rows and a plurality of columns;

said group of micro-shutters are formed by a substrate having thereon a plurality of the segment electrodes each forming a shutter and connected to a drain of a thin film transistor, another substrate having thereon a common electrode, and a liquid crystal interposed between the substrates;

said driving method comprising, during a period for writing in a selected row among said plurality of rows,

a first period for applying an electric voltage providing a light interrupting state between segment electrodes corresponding to said selected row and the common electrode, and

a second period for applying an electric voltage providing a light transmitting state between a selected segment electrode among the segment electrodes corresponding to said selected row.

16. A driving method according to claim 15, wherein immediately before said first period, said exposure light source is caused to emit a light pulse or the quantity of light emitted therefrom is increased.

17. A driving method according to claim 15, wherein an electric signal having a pulse duration equal to the sum of said first period and said second period is applied sequentially to the gate lines of thin film transistors.

18. A driving method according to claim 15, wherein electric signals are alternately applied to gate lines during said first period and said second period.

19. A driving method for an image forming apparatus of the type comprising an exposure light source, a printer head which comprises a group of micro-shutters each controlling the transmission or interruption of light from said exposure light source, and an image bearing so disposed to be irradiated with light signals transmitted through the printer head;

said group of micro-shutters are arranged in a matrix comprising a plurality of rows and a plurality of columns;

said group of micro-shutters are formed by a substrate having thereon a plurality of segment electrodes each forming a shutter and connected to a drain of a thin film transistor, another substrate having thereon a common electrode, and a liquid crystal interposed between the substrates;

said image forming method comprising;

a first period for applying a scanning signal to gate lines of the thin film transistors and applying an electric signal providing a light interrupting state to data lines in synchronism with the scanning signal, and

a second period, after the first period, for applying a scanning signal to gate lines of thin film transistors corresponding to a row and applying, in synchronism with the scanning signal, an electric signal providing a light transmitting states to data lines connected to selected segment electrodes among the segment electrodes corresponding to said row to which the scanning signal is applied.

20. A driving method for an image forming apparatus of the type comprising an exposure light source, a printer head which comprises a group of micro-shutters each controlling the transmission or interruption of light from said exposure light source, and an image bearing so disposed to be irradiated with light signals transmitted through the printer head;

said group of micro-shutters are arranged in a matrix comprising a plurality of rows and a plurality of columns;

said group of micro-shutters are formed by a substrate having thereon a plurality of segment electrodes each forming a shutter and connected to a drain of a thin film transistor, another substrate having thereon a common electrode, and a liquid crystal interposed between the substrates;

said driving method comprising;

a first period for applying a scanning signal to gate lines of the thin film transistors;

applying, in synchronism with the scanning signal, an electric signal corresponding to image information to data lines thereby to form a light transmitting state at selected micro-shutters among the group of micro-shutters and produce a light signal; and

irradiating the image bearing member with the light signal for a predetermined period; and

a second period, after the first period, for applying to the liquid crystal a voltage of a polarity opposite to that of the voltage applied to the liquid crystal during the first period.

21. A driving method for an image forming apparatus of the type comprising an exposure light source, a printer head which comprises a group of micro-shutters each controlling the transmission or interruption of light from said exposure light source, and an image bearing so disposed to be irradiated with light signals transmitted through the printer head;

said group of micro-shutters are arranged in a matrix comprising a plurality of rows and a plurality of columns;

said group of micro-shutters comprise electrodes connected to scanning lines, electrodes connected to data lines and a liquid crystal;

said driving method comprising;

a first period for applying a scanning signal to the scanning lines and applying an electric signal providing a light interrupting state to data lines in synchronism with the scanning signal, and

a second period, after the first period, for applying a scanning signal to the scanning lines and applying an electric signal providing a light transmitting state to selected data lines in synchronism with the scanning signal.

22. A driving method for an image forming apparatus of the type comprising an exposure light source, a printer head which comprises a group of microshutters each controlling the transmission or interruption of light from said exposure light source, and an image bearing so disposed to be irradiated with light signals transmitted through the printer head;

said group of micro-shutters are arranged in a matrix comprising a plurality of rows and a plurality of columns;

each micro-shutter comprises a liquid crystal interposed between a pair of electrodes;

said driving method comprising;

a first phase for applying an electric signal providing a light interrupting state to a selected row of micro-shutters among said group of micro-shutters,

a second phase for applying an electric signal providing a light transmitting state to selected micro-shutters among the micro-shutters in the light interrupting state, and

a third phase interposed between the first and second phases for applying an electric signal providing a light transmitting state to another row of microshutters.

23. A driving method according to claim 22, wherein one of said pair of electrodes is connected to a drain of a thin film transistor.

24. A driving method for a transistor array of the type in which capacitance type load elements are arranged in a matrix comprising n rows and m columns and transistors are arranged in a matrix comprising n rows and m columns, each of said capacitance type load elements having a capacitance C between a segment electrode connected to the drain of a transistor and an opposing electrode;

wherein, when the frame frequency of gate-on pulses applied to said transistors is represented by f and an electrical signal applied to the source of each transistor has a voltage Vs, the ratio W/L (where L is the channel length and W is the channel width in the channel of each transistor) is correlated with said frame frequency f of gate-on pulses and said input signal voltage Vs so as to satisfy the following relationship;

##EQU10##

25. A driving method according to claim 24, wherein said transistors are thin film transistors.

26. A driving method according to claim 25, wherein each of said thin film transistors comprises a semiconductor of amorphous silicon.

27. A driving method according to claim 24, wherein said input signal voltage Vs is 15 volts or higher.

28. A driving method according to claim 24, wherein said input signal voltage Vs is between 20 and 60 volts.

29. A driving method according to claim 24, wherein said W/L ratio is between 1.4 and 290.

30. A driving method according to claim 24, wherein said W/L ratio is between 10 and 80.

31. A driving method according to claim 24, wherein said capacitance type load element is a liquid crystal.

32. A driving method for a transistor array of the type in which capacitance type load elements are arranged in a matrix comprising n rows and m columns and transistors are arranged in a matrix comprising n rows and m columns, each of said capacitance type load elements having a capacitance C between a segment electrode connected to the drain of a transistor and an opposing electrode;

wherein, a parasitic capacitance Cgd between the gate and drain in the channel of each transistor is correlated with said capacitance C and said capacitance CE so as to satisfy the following relationship;

##EQU11## where Δ

Vg;

the variation in the gate voltage;

Δ

V₀ ;

the variation in the voltage on the opposite electrode; and

Vs;

the maximum input signal.

33. A driving method according to claim 32, wherein said parasitic capacitance Cgd is 45 pF (picofarads) or less.

34. A driving method according to claim 32, wherein said parasitic capacitance Cgd is between 0.2 and 1.5 pF.

35. A driving method according to claim 32, wherein said transistors are thin film transistors.

36. A driving method according to claim 35, wherein said thin film transistors comprise a semiconductor of amorphous silicon.

37. A driving method according to claim 32, wherein said capacitance type load element is a liquid crystal.

38. A driving method according to claim 32, wherein the maximum value Vs of said input signal voltage is 15 volts or higher.

39. A driving method according to claim 32, wherein the maximum value Vs of said input signal voltage is between 20 and 60 volts.