JP3471938B2 - Method of determining light intensity adjustment data for LED print head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining light intensity adjustment data of an LED print head for correcting variations in the light intensity of each LED element by a light emission time. 2. Description of the Related Art In an LED print head used for a printer, a facsimile machine, or the like, each LED element of a plurality of LED array chips constituting the LED print head is subject to various factors in a manufacturing process of the LED array chip. In addition, since the relationship between the supply current value and the light amount is different, it is necessary to correct the variation so that the average light amount of each LED array chip is substantially equal, and the light amount of each LED element in the LED array chip is also substantially equal. There is. As one example of such correction, individual LEs
Regarding the variation of the average light amount of the D array chip, LE
A method of correcting by the current value supplied to all the LED elements of the D array chip, and for the variation of the light amount of each LED element in the LED array chip, only the LED element to be corrected emits light separately for a certain period of time. There is. When such correction is performed, data of a current value to be supplied to the LED elements is determined for each LED array chip, and which LED element should emit light for a certain period of time separately for correction is determined. Although the data also needs to be determined in advance, in the conventional method of determining the light amount adjustment data of the LED print head, first, the LED of each LED array chip is set so that the average light amount of the LED array chip becomes a predetermined target light amount. The current value to be supplied to the element is determined, and thereafter, the LED element to be corrected is determined from the light amount of each LED element in the LED array chip. [0005] However, the conventional LED
In the print head light amount adjustment data determination method, the current value to be supplied to the LED elements in order to equalize the average light amount of the LED array chip is determined before the LED elements to be corrected are determined. The average light amount of the array chip varies, and in order to correct the variation, it is necessary to additionally determine an LED element to emit light for a certain period of time. In some cases, this separate light emission had to be performed a plurality of times in addition to the first correction. As a result, when the LED print head is used, a process of causing a specific LED element to emit light for correction must be repeated a plurality of times. There has been a problem that the circuit becomes complicated and the manufacturing cost becomes high. [0007] The present invention has been proposed in view of the above points, and it is possible to perform a process of causing a specific LED element to emit light for correction only once when using an LED print head. It is an object of the present invention to provide a method for determining light amount adjustment data of a print head. Means for Solving the Problems In order to solve the above problems, the present invention takes the following technical means. That is, the present invention is a method for determining light amount adjustment data of an LED print head for correcting variations in the light amount of each LED element by a light emission time.
A light amount measuring step of measuring a light amount of each LED element by flowing a constant current to each LED element of the D array chip for a predetermined time; and calculating a deviation of a light amount between adjacent LED elements from the light amount measured in the light amount measuring step. Light intensity variation
Is one of a plurality of preset patterns.
A pattern determining step of determining whether or not the LED is to be corrected, and a correction element determining step of determining an LED element to correct the light amount based on a predetermined determination condition according to the pattern determined in the pattern determining step, LED when the light amount of the LED element determined in the correction element determination step is corrected under a predetermined correction condition
Calculating a virtual average energy of the light quantity of the entire array chip, and determining whether or not the calculated average energy matches a predetermined target average energy. Is determined, the above-described series of steps are similarly performed on the next LED array chip, and when it is determined that they do not match, the value of the current flowing through each LED element is changed to execute the above-described series of steps. By repeating this, for each LED array chip, the data of the current value flowing through the LED element and the LE to be corrected
And determines the D element of the data, these data
Non-volatile memory mounted on the LED print head
It is characterized by being stored in . That is, according to the present invention, first, in the light quantity measuring step, a constant current is applied to all the LED elements of the LED array chip for a predetermined time. And each L
The light amount of the ED element is measured. Next, in a pattern determination step, a deviation of the light amount between adjacent LED elements is obtained from the light amount measured in the light amount measurement step, and a variation pattern of the light amount is determined from the result. Next, in a correction element determination step, based on a determination condition predetermined according to the pattern determined in the pattern determination step,
The LED element whose light quantity is to be corrected is determined. Next, in the coincidence determination step, the virtual average energy of the light amount of the entire LED array chip when the light amount of the LED element determined in the correction element determination step is corrected under a predetermined correction condition is calculated. It is determined whether or not the target average energy matches the determined target average energy. If it is determined in the matching determination step that they match, the LED
When the print head is used, the LED elements to be corrected emit light separately for a predetermined period of time, and the light amount of the entire LED array chip after the correction is performed reaches a predetermined target value. Is completed, and the above-described series of steps are similarly performed on the next LED array chip. If it is determined that they do not match, when the LED print head is used, the amount of light of the entire LED array chip after the LED element to be corrected emits light for another predetermined time and is corrected does not reach the predetermined target value. Therefore, the value of the current flowing through the LED element is changed, and the above-described series of steps is repeated until the values match. If they match, the above-described series of steps is similarly performed for the next LED array chip. Thus,
The above-mentioned series of steps are executed for all the LED array chips of the LED print head, and for each LED array chip, data of a current value flowing through the LED element and data of the LED element to be corrected are determined. Is written to a nonvolatile memory such as a ROM. As described above, after determining the LED element to be corrected, it is determined whether or not the average light amount of the LED array chip coincides with the target value, including the light amount as a result of the correction. As a result, the average light amount of the LED array chip varies as a result of the correction as described above, and in order to correct it, it is not necessary to determine another LED element that emits light for a certain period of time. When the print head is used, a separate light emission for correction can be performed only once. As a result, when the LED print head is used, it is not necessary to repeat the process of causing a specific LED element to emit light for correction a plurality of times, so that the printing speed can be increased and the control speed can be improved. Since the circuit and the like can be simplified, the manufacturing cost can be reduced. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.
This will be specifically described with reference to the drawings. FIG. 1 is a schematic overall configuration diagram of a light quantity adjustment data determination device used for carrying out a light quantity adjustment data determination method for an LED print head according to the present invention, and shows a plurality of LED elements formed on an LED array chip 1. Are each FE
It is connected to a DC power supply Vdd of a predetermined voltage via T2. The gate of each FET 2 is connected to the output terminal of the D / A converter 3, and the LED array chip 1 includes a plurality of phototransistors and the like.
The light amount measuring means 4 for individually measuring the amount of light emitted from each LED element and outputting a signal corresponding to the measurement result is disposed close to and opposed to each other. An output terminal of the light quantity measuring unit 4 and an input terminal of the D / A converter 3 are connected to a control unit 5 including a microcomputer or the like. The control means 5 includes a pattern determination means 6, a correction element determination means 7, a coincidence determination means 8, a current value signal output means 9, and a RAM 10. Pattern determining means 6 and correction element determining means 7
And the coincidence determining means 8 and the current value signal output means 9 are realized by a microcomputer constituting the control means 5. The pattern discriminating means 6 detects the adjacent LED of the LED array chip 1 based on the signal from the light quantity measuring means 4.
A deviation of the light amount between the elements is obtained, and a variation pattern of the light amount is determined from the result. The correction element determination means 7 is an LED for correcting the light amount based on a predetermined determination condition according to the pattern determined by the pattern determination means 6.
The LED element of the array chip 1 is determined. The coincidence determining means 8 calculates the virtual average energy of the light quantity of the entire LED array chip 1 when the light quantity of the LED element of the LED array chip 1 determined by the correction element determining means 7 is corrected under a predetermined correction condition. An arithmetic operation is performed to determine whether the calculated average energy matches a predetermined target average energy.
The current value signal output means 9 is connected to the LE of the LED array chip 1.
A digital current value signal corresponding to the current to be passed to the D element is output. The RAM 10 stores the data of the LED element determined by the correction element determination means 7 and the data of the current value output by the current value signal output means 9 when the coincidence determination means 8 determines that they match. Remember. Next, an example of a procedure of a method for determining light amount adjustment data of the LED print head according to the present invention will be described with reference to a flowchart shown in FIG. First, the control means 5 sets N to n (step S1). This n is the number of LED array chips 1 incorporated in the LED print head. Next, the current value signal output means 9 outputs a current value signal consisting of digital data corresponding to the initial current value to D
Output to the A / A converter 3 for a predetermined time (step S
2). This current value signal is output from the LE of the LED array chip 1
The current flowing through the D element is determined. For example, when the current value can be adjusted in 256 steps from 0 to 255, 127 at the center of the adjustment range is output as the initial current value. As a result, the D / A converter 3 converts the current value signal from the current value signal output means 9 into an analog voltage and applies the analog voltage to the gate of each FET 2. This gives F
The ET 2 supplies a current corresponding to the gate voltage from the D / A converter 3 to the LED elements of the LED array chip 1. As a result, the LED elements of the LED array chip 1 emit light for a predetermined time, the light quantity measuring means 4 measures the light quantity of each LED element, and outputs digital data corresponding to the measured value to the pattern discriminating means 6 (step S3). Next, a pattern discriminating means 6 calculates a deviation of the light quantity between adjacent LED elements of the LED array chip 1 based on the data from the light quantity measuring means 4, and discriminates a variation pattern of the light quantity from the calculation result. (Step S
4). That is, for example, a pattern as shown in FIG. 3 can be considered as the variation in the light amount between the adjacent LED elements of the LED array chip 1. Therefore, it is determined which pattern corresponds to the variation in the light amount between the adjacent LED elements. I do. FIG. 3A shows a pattern in which the light amount is relatively uniform, FIG. 3B shows a pattern in which the light amount of some LED elements protrudes and is large, and FIG. FIG. 3D shows a pattern that is prominently small and divided into a large light amount and a small light amount. Next, the correction element determining means 7 determines an LED element whose light quantity is to be corrected based on a determination condition predetermined according to the pattern determined by the pattern determination means 6 (step S5). That is, when the print quality of the LED print head is comprehensively considered, the conditions for determining the LED element to be corrected are different depending on which of the patterns (A), (B), (C), and (D) in FIG. Therefore, a determination condition is set for each pattern. However, here, in order to make the description easy to understand, a case where the pattern is divided into two patterns as shown in FIG. 4 will be specifically described. First, in step S4, the measurement result of the light amount of each LED element is normalized so that the maximum light amount becomes 100. Then, it is determined whether or not the minimum light amount thus normalized is 70 or more,
If the minimum light amount is 70 or more, it is determined that the pattern is the pattern shown in FIG. 4A, and in step S5, the LED whose normalized light amount is 81.41 or less is corrected as indicated by oblique lines. Determined as an element. In step S4, if the minimum light quantity is less than 70, it is determined that the pattern is the pattern shown in FIG. 4B, and the average light quantity of the LED elements of the LED array chip 1 is calculated. Normalization is again performed so that the additional light amount becomes 100, and in step S5, the LED elements whose normalized light amounts are 81.41 or less and 70 or more are determined as the LED elements to be corrected as indicated by the cross line. I do.
It should be noted that LED elements whose normalized light quantity is larger than 100 or smaller than 70 as shown by oblique lines are excluded from the correction target because they are peculiar LED elements. The pattern of FIG. 4A substantially corresponds to the patterns of FIGS. 3A and 3D, and the pattern of FIG. 4B corresponds to the patterns of FIGS. 3B and 3C. Almost compatible. Next, the coincidence judging means 8 calculates the virtual average energy of the light quantity of the entire LED array chip when the light quantity of the LED element determined by the correction element decision means 7 is corrected under predetermined correction conditions. (Step S6),
It is determined whether or not it matches a predetermined target average energy (step S7). That is, in the case of the pattern of FIG. 4A, the normalized light amount is 81.41.
A virtual average energy is calculated by uniformly multiplying the following by 1.163 and averaging the whole. FIG. 4
In the case of the pattern (B) of FIG.
A virtual average energy is calculated by uniformly multiplying 1.43 or less by 1.163 and averaging the whole.
Such a calculation method is obtained as a result of an experiment. If the virtual average energy does not coincide with the target average energy within a predetermined error range, the current flowing through the LED elements of the LED array chip 1 is changed to change the current value to determine the LED element to be corrected. Value signal output means 9
Changes the current value signal and outputs it to the D / A converter 3 (step S8). Thereby, the operation after step S3 is repeated. The change of the current value signal is set to 191 at the center of 128 to 255 when the virtual average energy is smaller than the target average energy, and is set to 0 when the virtual average energy is larger than the target average energy.
It is set to 63 at the center of ~ 127. In this way, every time the current value signal is changed, if the range is narrowed down to half according to the magnitude relationship between the virtual average energy and the target average energy, the virtual average energy can be easily shifted from the target average energy by a predetermined error. To reach a current value signal that matches within the range. If the virtual average energy coincides with the target average energy within a predetermined error range, the data of the current value signal output from the current value signal output means 9 and the correction element determination means 7 are finally determined. LED to be corrected
The data of the element is stored in the RAM 10 and the control means 5
However, 1 is subtracted from N (step S9), and it is determined whether or not N is 0 (step S10). If not, the process returns to step S2. That is, since the processing for one LED array chip 1 has been completed, 1 is subtracted from N, and
Since N is not 0, that is, the processing of all the LED array chips 1 is not completed, the process returns to step S2 and the processing of the next LED array chip 1 is started. When the processing is completed for all the LED array chips 1, N becomes 0, so that the current value information to be passed to the LED elements and the information about the LED elements to be corrected for all the LED array chips 1 And the RAM
From step 10, the data is stored in a nonvolatile memory such as a RAM provided in the LED print head (step S11), and the routine ends. That is, at this point, all the LEs
Since the current value information to be passed to the LED elements and the information about the LED elements to be corrected for the D array chip 1 are stored in the RAM 10, in order to use those data when using the LED print head, RAM
From 10 is stored in the ROM or the like of the LED print head. In the above-described embodiment, an example has been described in which the LED array chips are set one by one in the light quantity adjustment data determination device to determine the light quantity adjustment data.
The ED array chip may be set in the light amount adjustment data determination device to determine the light amount adjustment data sequentially or simultaneously. FIG. 5 is a circuit diagram of a main part of the LED print head, in which each LE of a predetermined number of LED array chips 1 is provided.
The D element is a DC power supply Vd of a predetermined voltage via the FET 11
d. The gate of each FET 11 is connected to the output terminal of the D / A converter 13 via the switching element 12, and the control terminal of each switching element 12 is connected to the output terminal of the AND circuit 14. D / A
The converter 13 is provided separately for each LED array chip 1, and can supply a different current value to each LED element for each LED array chip 1. One input terminal of each AND circuit 14 is connected to an output terminal of a data control circuit 15, and an input terminal of the data control circuit 15 is connected to a print data latch circuit 16 for latching print data.
And an output terminal of a correction data latch circuit 17 for latching correction data. An input terminal of the print data latch circuit 16 is connected to an output terminal of the shift register 18 having a predetermined number of bits.
, A control end of the data control circuit 15, a timing control end of the print data latch circuit 16, an input end and a timing control end of the correction data latch circuit 17, an input end and a clock input end of the shift register 18, and the like. Is connected to the control means 19 comprising The control means 19 is also connected to a ROM 20 which stores data obtained by the light amount adjustment data determination device. The control means 19 and the correction data latch circuit 17
Are connected to the input terminal and the timing control terminal of the shift register 18 and the input terminal and the clock input terminal of the shift register 18 by one line for easy understanding of the drawing. Next, the operation will be described. First, at the time of initial setting such as when the power is turned on, the control unit 19 reads out the data on the LED element to be corrected stored in the ROM 20 from the ROM 20 and stores it in the correction data latch circuit 17 in advance. Further, the control means 19 uses the data of the current value stored in the ROM 20 as a current value signal for each D / A
Output to converter 13. Thereby, each D / A converter 13 converts the current value signal from the control means 19 into an analog voltage and supplies the analog voltage to the switching element 12. When a print command is input to the control means 19, the control means 19 serially inputs print data to the shift register 18 in synchronization with the clock signal. Next, the control means 19 outputs a latch signal to the timing control terminal of the print data latch circuit 16. As a result, print data is input in parallel from the shift register 18 to the print data latch circuit 16. And control means 19
Outputs a signal instructing the control end of the data control circuit 15 to output correction data. As a result, the data control circuit 15 calculates, for each bit, the logical product of the correction data latched by the correction data latch circuit 17 and the print data latched by the print data latch circuit 16, and calculates the logical product of the logical product circuit 14. Output to one input terminal. Then, the control means 19 generates a correction pulse STR1 from the strobe signal as shown in FIG.
A parallel output is provided to the other input terminal of each AND circuit 14.
As a result, the AND data of the print data and the correction data is output from the output terminal of the AND circuit 14 to the control terminal of the switching element 12, and the switching element 12 is turned on only for the bit whose AND data is at a high level, and the FE
The output voltage of the D / A converter 13 is applied to the gate of T11. As a result, the DC power supply Vdd is
A current corresponding to the current value signal flows through the LED elements of the LED array chip 1 through the LED, and the LED elements emit light and irradiate the photoconductor. Here, the reason why the AND data of the print data and the correction data is created is to prevent the LED elements corresponding to the dots that do not need to be printed from emitting light. Further, the control means 19 outputs the printing pulse STR2 of the strobe signal as shown in FIG.
A parallel output is provided to the other input terminal of each AND circuit 14.
As a result, the print data is output to the control terminal of the switching element 12, and the switching element 12 is turned on only for the high-level bits of the print data, and the FET 11
The output voltage of the D / A converter 13 is applied to the gate of. As a result, a current corresponding to the current value signal flows from the DC power supply Vdd to the LED element of the LED array chip 1 through the FET 11, and the LED element emits light and irradiates the photoconductor. Here, the ratio of the on-period of the correction pulse STR1 to the on-period of the printing pulse STR2 is, for example, 1:10.
For the dots corresponding to the elements, the amount of light applied to the photoconductor increases by 10%. The on-period of the correction pulse STR1 and the on-period of the printing pulse STR2 are temporally close to each other because the irradiation position for correction and the irradiation position for printing can be set in the sub-scanning direction of the photoconductor. This is to keep the same position as much as possible. The voltage supplied from the D / A converter 13 to the gate of the FET 11 via the switching element 12 is the current supplied from the DC power supply Vdd to the LED element of the LED array chip 1 via the FET 11 according to the light amount adjustment data. The current value is set so as to be determined for each LED array chip 1 by the determining device. Therefore, for the LED element having a small light amount, the shortage of the LED element is determined by LE in the ON period of the correction pulse STR1 different from the ON period of the printing pulse STR2.
The light emission of the D element increases the amount of light irradiated on the photoconductor as a result. Moreover, since the virtual average energy of the corrected LED array chip 1 is made to coincide with the target average energy, there is no variation in the average light amount between the LED array chips 1 and only one irradiation for correction is required. it can. As a result, irradiation time, data transfer time, and the like can be reduced, and high-speed printing can be realized. Further, since only one correction data latch circuit 17 is required, downsizing of hardware and cost reduction can be realized. FIG. 7 is a circuit diagram of a main part of another example of the LED print head. The difference from the circuit of FIG. 5 is that the data control circuit 15 and the correction data latch circuit 17 are omitted. . That is, in this example, the control unit 19 realizes functions equivalent to those of the data control circuit 15 and the correction data latch circuit 17 by software. Next, the operation will be described. First, the control unit 19
Is synchronized with the clock signal shown in FIG.
(B), the logical product data Da of the correction data and the print data is serially input to the shift register 18;
The latch signal shown in FIG. 8C is supplied to the timing control terminal of the print data latch circuit 16, and then the latch signal shown in FIG.
Is output to the other input terminal of the AND circuit 14 as a strobe signal. As a result, the logical product data D is generated only during the ON period of the pulse STR1.
The LED element corresponding to the ON bit of a emits light, and the photoconductor is exposed. This completes the exposure for correction. Thereafter, the control unit 19 serially inputs the print data Db shown in FIG. 8B to the shift register 18 in synchronization with the clock signal shown in FIG. c)
Is supplied to the timing control terminal of the print data latch circuit 16, and then the printing pulse STR2 shown in FIG.
4 to the other input terminal. Thereby, the pulse ST
Only during the ON period of R2, the LED element corresponding to the ON bit of the print data Db emits light, and the photoconductor is exposed. This completes the exposure for printing. That is, for the LED elements that need to be corrected, the pulse S
Since the exposure time is lengthened by the ON period of TR1, the same result as when the light emission amount is increased is obtained, and the light amount correction is realized. Hereinafter, the same operation is repeated.
In this example, the same effect as in the previous example shown in FIG. 5 can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic overall configuration diagram of a light quantity adjustment data determination device used for performing a light quantity adjustment data determination method for an LED print head according to the present invention. FIG. 2 is a flowchart illustrating an operation of a light quantity adjustment data determination device used for implementing a light quantity adjustment data determination method for an LED print head according to the present invention. FIG. 3 is an explanatory diagram of a light intensity variation pattern of each LED element of an LED array chip. FIG. 4 is an explanatory diagram of a method of determining an LED element to be corrected. FIG. 5 is a circuit diagram of a main part of an example of an LED print head. FIG. 6 is a waveform diagram of a strobe signal. FIG. 7 is a circuit diagram of a main part of another example of the LED print head. FIG. 8 is a signal waveform diagram of each part in a circuit of another example of the LED print head. [Description of Signs] 1 LED array chip 4 Light quantity measuring means 6 Pattern discriminating means 7 Correction element determining means 8 Matching judging means 9 Current value signal output means

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Claims (1)

(57) [Claim 1] A method for determining light amount adjustment data of an LED print head for correcting variation in light amount of each LED element by light emission time, wherein each LED element of an LED array chip is light quantity measurement step and the light amount variation of seeking quantity deviations between adjacent LED elements from a measured amount of light in the light amount measurement step is pre of measuring the light intensity of each LED element by flowing a predetermined time constant current to
Any of the multiple patterns set
A pattern determining step of determining whether or not the LED element to correct the light amount based on a predetermined determination condition according to the pattern determined in the pattern determining step; L when the light amount of the LED element determined in the element determination step is corrected under a predetermined correction condition.
Calculating a virtual average energy of the light amount of the entire ED array chip, and determining whether or not it matches a predetermined target average energy. If it is determined that there is the same, the above-described series of steps are similarly performed for the next LED array chip. the by repeating, for each LED array chip, the data value of the current flowing to the LED element, and determines the data of the LED elements to be corrected, this
These data are mounted on the LED print head
A method for determining light amount adjustment data for an LED print head, which is stored in a nonvolatile memory .