Light emitting device, driving method thereof, and image forming apparatus
View Patent ↗A light emitting device includes: a plurality of light emitting elements that emit light to have luminosity depending on the magnitude of a driving signal; a plurality of holding units that are respectively disposed in the plurality of light emitting elements, and respectively hold the driving signal to maintain a magnitude regulated such that the luminosity of the plurality of light emitting elements becomes uniform; and a plurality of supply units that are respectively disposed in the plurality of light emitting elements, and supply the driving signal, which is held by the holding units to have a certain magnitude for a period of time according to a gradation of light to be emitted, to a corresponding light emitting element.
1. A light emitting device comprising:
a plurality of light emitting elements that emit light to have luminosity depending on the magnitude of a driving signal;
a plurality of holding units that are respectively disposed in the plurality of light emitting elements, and respectively hold the driving signal to maintain a certain magnitude to be supplied to a corresponding light emitting element;
a plurality of supply units that are respectively disposed in the plurality of light emitting elements, and supply the driving signal, which is held by the holding units for a period of time according to a gradation of light to be emitted, to the corresponding light emitting element;
a memory unit that respectively stores signal data indicating the magnitude of the driving signal, which is regulated so that luminosity of the plurality of light emitting elements becomes uniform for the plurality of light emitting elements;
a setting unit that sequentially reads the signal data from the memory unit, and generates a setting signal based on the signal data; and
an input circuit that sequentially supplies the driving signal having a magnitude depending on the magnitude of the setting signal to the holding units when the setting signal is supplied, and holds the driving signal.
2. The light emitting device according to claim 1 , wherein the holding unit is a volatile memory, and the memory unit is a non-volatile memory.
3. The light emitting device according to claim 1 , wherein the setting signal is a current signal or a voltage signal.
4. The light emitting device according to claim 1 , comprising:
a designated data generator that generates designated data for designating a period of time for the light emitting elements to emit light based on image data; and
a plurality of light emitting controllers that are respectively disposed in the plurality of light emitting elements, and generate a light emission control signal which is valid for a period of time for the light emitting elements to emit light based on the designated data,
wherein the supply unit supplies the driving signal, which is held by the holding units for a period of time for the light emission control signal to be valid, to the corresponding light emitting element.
5. The light emitting device according to claim 4 , comprising:
a measurement unit that respectively measures luminosity of the plurality of light emitting elements; and
a controller that performs a process of sequentially selecting the plurality of light emitting elements, a process of controlling the light emitting controller so that the designated data that allows the selected light emitting element to emit light, a process of generating signal data so that luminosity of the selected light emitting element is in a specific range, and a process of inputting the signal data to the memory unit.
6. The light emitting device according to claim 5 , wherein:
the plurality of light emitting elements are arranged in a single line or in multiple lines;
the measurement unit includes at least two optical sensors disposed at both ends of the plurality of light emitting elements; and
the controller measures luminosity of the selected light emitting element according to the sum of output signals output from at least the two optical sensors.
7. The light emitting device according to claim 5 , wherein, when usage frequencies of the plurality of light emitting elements respectively reach a predetermined usage frequency, the controller performs a process of receiving a specific data that specifies a light emitting element of which usage frequency reaches the predetermined usage frequency, a process of selecting the light emitting element of which usage frequency reaches the predetermined usage frequency based on the specific data, a process of controlling the light emitting controller so that the designated data that allows the selected light emitting element to emit light is generated, a process of generating signal data so that luminosity of the selected light emitting element is in a specific range, and a process of inputting the signal data to the memory unit.
8. The light emitting device according to claim 1 , wherein:
the setting unit generates the setting signal having a magnitude indicated by the signal data read from the memory unit; and
the input circuit sequentially supplies the driving signal having the same magnitude as the setting signal to the holding units, and holds the driving signal to maintain the magnitude.
9. The light emitting device according to claim 1 , further comprising a temperature measurement unit that measures present temperature, and outputs a temperature signal, wherein:
the memory unit respectively stores the signal data that indicates the magnitude of the driving signal, which is regulated such that luminosity of the plurality of light emitting elements becomes uniform at a reference temperature, for the plurality of light emitting elements;
the setting unit performs an operation process for the signal data read from the memory unit according to a difference between the present temperature indicated by the temperature signal and the reference temperature, and generates the setting signal; and
the input circuit sequentially supplies the driving signal having the same magnitude as the setting signal to the holding units, and holds the driving signal to maintain the magnitude.
10. The light emitting device according to claim 9 , wherein:
the memory unit stores temperature data indicating the reference temperature along with the signal data; and
the setting unit performs the operation process for the signal data according to a difference between the present temperature and the referenced temperature indicated by the temperature data.
11. The light emitting device according to claim 9 , wherein:
the memory unit respectively stores signal data, which indicates the magnitude of the driving signal regulated such that luminosity of the plurality of light emitting elements becomes uniform at the plurality or reference temperatures, for the plurality of light emitting elements; and
the setting unit generates the setting signal by interpolating the signal data at the plurality of reference temperatures read from the memory unit according to the difference between the present temperature indicated by the temperature signal and the plurality of reference temperatures.
12. The light emitting device according to claim 1 , further comprising a temperature compensation circuit that compensates for the setting signal according to the present temperature wherein:
the setting unit generates the setting signal having a magnitude indicated by the signal data read from memory unit; and
the input circuit sequentially supplies the driving signal, which has the same magnitude as the setting signal compensated for by the temperature compensation circuit, to the holding units, and holds the driving signal to maintain the magnitude.
13. The light emitting device according to claim 1 , comprising:
a plurality of integrated circuit chips respectively having at least one of the plurality of holding units and at least one of the plurality of supply units;
a control circuit chip that supplies the setting signal;
a first substrate in which the plurality of light emitting elements are arranged along a long side thereof, and the plurality of integrated circuits are arranged in a line along the plurality of light emitting elements; and
a second substrate on which the control circuit chip is fixed,
wherein:
the second substrate is connected to a short side of the first substrate; and
the setting signal is supplied from the short side of the first substrate towards another short side thereof.
14. The light emitting device according to claim 1 , comprising:
a plurality of integrated circuit chips respectively having at least one of the plurality of holding units and at least one of the plurality of supply units;
a control circuit chip that supplies the setting signal;
a first substrate in which the plurality of light emitting elements are arranged along a long side thereof, and the plurality of integrated circuits are arranged in a line along the plurality of light emitting elements; and
a second substrate on which the control circuit chip is fixed,
wherein:
the second substrate is connected to a center portion of the long side of the first substrate; and
the setting signal is supplied from the center portion of the long side of the first substrate towards not only a short side thereof but also another short side thereof.
15. The light emitting device according to claim 13 , wherein a flexible substrate, on which a wire for transmitting the setting signal is formed, is included between at least one of the adjacent integrated circuit chips.
16. An image forming apparatus comprising:
a light emitting device according to claim 1 ; and
an image carrier on which an electrostatic latent image is formed by light respectively irradiated from the plurality of light emitting elements.
17. A method of driving a light emitting device having: a plurality of light emitting elements that emit light to have luminosity depending on the magnitude of a driving signal; a plurality of holding units that are respectively disposed in the plurality of light emitting elements, and respectively hold the driving signal to maintain a magnitude regulated such that the luminosity of the plurality of light emitting elements becomes uniform; a plurality of supply units that are respectively disposed in the plurality of light emitting elements, and supply the driving signal, which is held by the holding units to have a certain magnitude for a period of time according to a gradation of light to be emitted, to a corresponding light emitting element; and a memory unit that respectively stores signal data indicating the magnitude of the driving signal, which is regulated so that luminosity of the plurality of light emitting elements becomes uniform, respectively, for the plurality of light emitting elements, the method comprising:
sequentially reading the signal data from the memory unit when power is supplied;
generating a setting signal based on the read signal data; and
sequentially supplying the driving signal having a magnitude depending on the magnitude of the generated setting signal to the holding units, and holding the driving signal to maintain the magnitude.
18. The method according to claim 17 , comprising:
sequentially selecting the plurality of light emitting elements;
allowing the selected light emitting element to emit light;
measuring luminosity of the selected light emitting element;
generating signal data so that the luminosity of the selected light emitting element is in a specific range; and
inputting the generated signal data to the memory unit.
19. The method according to claim 18 , comprising, after the signal data is input to the memory unit:
respectively determining whether usage frequencies of the plurality of light emitting elements reach a predetermined usage frequency, and specifying the light emitting element of which usage frequency reaches the predetermined usage frequency;
allowing the specified light emitting element to emit light;
measuring luminosity of the specified light emitting element;
generating signal data so that the luminosity of the specified light emitting element is in a specific range; and
inputting the generated signal data to the memory unit.
20. The method according to claim 17 , wherein:
the setting signal has a magnitude indicated by the signal data; and
the driving signal sequentially supplied to the holding units has the same magnitude as the setting signal.