JPH0839860A - Led printing head adjusted in exposure energy and adjustment of exposure energy thereof - Google Patents

Abstract

PURPOSE:To uniformize exposure energy between respective LEDs while equalizing average exposure energy between respective printing heads by always estimating such a state that a time correction bit is allotted when the drive currents in respective chips are adjusted to operate exposure energy. CONSTITUTION:A prelimlnarily arbitrarily initialized drive current is applied to the respective LEDs 12(12-1-12-64) of a chip to be adjusted to simultaneously drive the respective LEDs 12 to measure the emission quantities of the LEDs 12. Next, a time correction bit is virtually allotted at every LEDs 12 on the basis of the measured emission quantities of the respective LEDs 12. Next, the exposure energies of the respective LEDs 12 are operated on the basis of the virtually allotted time correction bit and the applied drive current and the average exposure energy of the chips 10-1-10-3 is virtually operated on the basis of the operation result. The imaginary average exposure energy is compared with an objective value and a drive current is altered on the basis of the comparison result and the respective LEDs 12 are driven by the drive current after alteration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure energy adjusting method for making an exposure energy of an LED print head mounted on a printer or a facsimile uniform to a target value, and more particularly, to a plurality of chips in which a plurality of LEDs are aligned and arranged. With respect to the aligned LED print heads, the amount of light emission between the chips is corrected by adjusting the LED drive current, and the exposure energy of the LEDs in the chips is adjusted by adjusting the drive current supply time. Regarding the method. The present invention also relates to an LED print head whose exposure energy is adjusted by the adjusting method described above.

[0002]

2. Description of the Related Art An LED print head is an LED that corresponds to a print dot with respect to an LED that is arranged along a print line.
A drive current is selectively supplied to the LEDs to cause the LEDs to emit light, and line printing is performed line by line. In this type of print head, the exposure energy of each aligned LED must be pre-uniformly adjusted to obtain uniform print quality in each row.

As is well known, the exposure energy of an LED depends on the magnitude of the drive current and its supply time. Usually L
It is preferable to form as many LEDs as possible on the same chip in order to suppress variations in light emission efficiency between ED elements. However, in order to obtain a required print width, a plurality of LEDs are required to print one line. It will be necessary to assemble the chips. Therefore, such an L
In the ED print head, the amount of light emission between chips is generally adjusted by adjusting the drive current applied to each chip. Then, regarding the variation in the luminous efficiency of the LEDs in each chip, the drive current supply time for each LED is adjusted by the allocation of the time correction bit. That is, the LED drive current is supplied at each LE
It is controlled by the main drive current pulse set equal to D and the time correction bit pulse connected to the main drive current pulse, and the number or length of the time correction bit pulse is individually adjusted according to the quality variation of the LED element. To be done.

FIG. 4 shows a conventional exposure energy adjusting method for a print head. In FIG.
In the conventional adjustment method, first the drive current is adjusted so that the average light intensity reaches the target value for each chip, and then the time correction bits are assigned to the entire printhead that combines multiple chips to expose the entire exposure. Energy is made uniform.

That is, conventionally, an arbitrary initial drive current is supplied to the LED chip to be adjusted (S
1) Then, the light emission amount at this time is measured for each LED (S2). At this time, the drive current supplied to each LED is only the main pulse, and the pulse of the time correction bit is not considered.

The average light amount L _A is calculated from the light emission amount of each LED (S3), and then the average light amount L _A and the target value L ₀ are compared (S4). For comparison in step S4, the target value L ₀ is given a predetermined allowable value α. If the average light amount L _A matches the target value in the comparison in step S4, the adjustment of the drive current is completed, but if they do not match, the initially set drive current is changed (S
5) and steps S1 to S4 are repeated again.

After some repetition, step S4
When the average light amount L _A reaches the target value L _{0 in} , the adjustment of the drive current is completed, and the time correction bit for each LED is assigned to all the chips incorporated in the print head next (S6). ). This allocation is
The drive currents adjusted as described above are supplied to the corresponding chips, and the light emission amount of each LED at this time is measured. Normally, the exposure energy is determined only by applying the main pulse without adding the time correction bit to the LED with the largest light emission amount. Therefore, the time correction bit is set to other LEDs so as to be equal to this exposure energy. give.

As described above, conventionally, the exposure energy of the print head is adjusted by the two-step adjustment of determining the drive current for each chip and allocating the time correction bit to the entire LED.

[0009]

However, according to such a conventional adjustment method, the final adjustment of the exposure energy of all the LEDs included in the plurality of chips must be performed when the time correction bits are allocated. Therefore, there is a problem that the load of the time correction bits becomes large, and that the number of correction bits actually prepared in advance must be large enough to handle such a large adjustment.

This has a drawback that the light emission time itself in the time correction bit becomes long at the time of actual printing, and the printing time and printing quality of the print head are restricted.

Further, in the conventional method, since the time correction bit is not considered at all when the drive current is determined, even when the light amount target value L ₀ is made constant, the final value is determined according to the variation of the LED elements in each print head. There is a problem that the average exposure energy greatly varies from printhead to printhead, which has been a factor of deteriorating printhead quality.

The present invention has been made in view of the above conventional problems, and an object thereof is to make the exposure energy of each LED extremely uniform and to make the average exposure energy evenly uniform among the print heads. An object of the present invention is to provide an improved exposure energy adjusting method.
Another object of the present invention is to easily provide an LED print head adjusted by such an exposure energy adjusting method.

[0013]

In order to achieve the above object, the present invention is to make the exposure energy of an LED print head in which a plurality of chips in which a plurality of LEDs are aligned are aligned to a target value. In addition, the amount of light emission between the chips is corrected by adjusting the LED drive current, and the light emission time of the LEDs in the chip is corrected by adjusting the supply time of the drive current.
In a method of correcting the exposure energy of an LED print head, a step of driving an LED with a predetermined drive current and each LE
A step of measuring a light emission amount of D, a step of temporarily assigning a time correction bit to each LED, and a step of calculating an exposure energy of each LED based on the drive current and the temporarily assigned time correction bit. A step of calculating a virtual average exposure energy from the exposure energy of each LED, a step of comparing the virtual average exposure energy with a target value, and a step of changing a drive current based on the comparison result,
Each of the above steps is repeated until the virtual average exposure energy reaches a desired target value.

The present invention also features an LED print head whose exposure energy is adjusted by the above adjusting method.

[0015]

According to the above method, the exposure energy can be calculated assuming that the time correction bit is always assigned when the drive current in each chip is adjusted, whereby the drive current and the time correction bit can be calculated. Both adjustments can be performed at the same time.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a flow chart showing an embodiment of an exposure energy adjusting method suitable for the present invention.

A drive current that has been arbitrarily initialized in advance is given to each LED of the chip to be adjusted, and each LED is simultaneously driven (S11). Then, the light emission amount of each LED is measured (S12).

A feature of the present invention is that the time correction bits are allocated at the same time when the drive current is adjusted. That is, each of the measured LEDs
A time correction bit is virtually assigned to each LED based on the light emission amount of (S13). This tentative allocation is usually performed based on the light emission amount of each LED. For example, for the LED with the largest light emission amount, there is no time correction bit allocation, and for LEDs lower than this, the insufficient light emission amount is determined. The time correction bits are allocated accordingly. After the virtual time correction bits are allocated in this way, the exposure energy of each LED is calculated from the temporarily allocated time correction bits and the applied drive current (S14). Next, the average exposure energy E _A of the chip is virtually calculated based on the exposure energy of each LED (S15).

Next, the virtual average exposure energy E _A is compared with the target value E ₀ (S16). Of course, step S
In 16, the average exposure energy target value E ₀ is given a predetermined allowable value α.

In the usual case, in the initial comparison performed in this way, the virtual average exposure energy E _A does not match the target value E _0, and the drive current is changed according to the comparison result (S17). ). Then, each LED is driven again by this newly set drive current, and such steps S11 to 16 are repeated, and adjustment is performed in a state where the virtual average exposure energy E _A matches the target value E ₀ in step S16. Complete.

Therefore, according to the present invention, each time the drive current is changed, provisional allocation of the time correction bits under this new drive current is performed, and adjustment is performed while obtaining the exposure energy of the chip for each adjustment cycle. Is done.

Therefore, according to the present invention, both the adjustment of the drive current and the adjustment of the time correction bit can be performed at the same time.

Further, even if the adjustment is performed for each chip in this manner, the adjustment is performed so that the virtual average exposure energy E _{A of the} chip always matches the target value E ₀ , so that each chip is adjusted. It is possible to make the final average exposure energies of all the chips incorporated into the printhead very uniform, with only a separate adjustment to the.

Further, since the time correction bit is always taken into consideration when adjusting the drive current, there is a tendency that the final average exposure energy tends to vary from chip to chip or settle to a relatively high value as in the conventional case. It can be reliably removed.

As is apparent from FIG. 1, the time correction bits are newly provisionally allocated each time in each adjustment cycle. This is because each LED is changed each time the drive current is changed.
This is because the optimum value of the time correction bit of is different. As is well known, LEDs have a non-linear light emission characteristic with respect to a drive current, and as the drive current given to the chip normally decreases, the variation in light emission of the LEDs in the chip tends to increase. Due to such characteristics, it is effective to newly provisionally allocate the time correction bit every time the drive current is changed. In the embodiment, the time correction bit is composed of 3 bits, and the temporary allocation of 3 bits is stored in a memory (not shown) in each adjustment cycle, and is overwritten and updated every cycle. Therefore, in step S16, the time correction bit when the virtual average exposure energy E _A matches the target value E ₀ can be directly used as the final adjustment value.

FIG. 2 shows a slightly different embodiment of the present invention. In this embodiment, the drive current is set by the bit setting of a DAC (digital-analog converter).

In the print head, the drive current for each chip is controlled by the DAC, the adjustment value digitally stored in the memory (not shown) is read from the DAC as an analog value, and this analog control signal will be described later in detail. As described above, a MOS-F that supplies a drive current to each chip
It is given as a control signal to the ET gate control element.
Such a DAC has a capacity of 10 bits, for example, and can perform extremely fine drive current adjustment.

FIG. 2 shows an embodiment in the case of controlling the drive current using such a DAC.

In step S21, the number of DAC bits n is set, and in the embodiment, n = 10 is set.

In step S22, the initial drive current is set, and in the embodiment, the nth or 10th bit of the DAC is set to "1" and the rest are all "0".
Set to. In the DAC shown in the embodiment, each bit is driven at "0". Therefore, step S22 sets a drive current such that only the most significant bit is in the non-driven state and all other bits are in the driven state. To do.

The DAC output is supplied to the chip by this drive current, and the drive current is supplied to each LED (S2).
3). Then, the light emission amount of each LED at this time is measured (S24), and in this state, temporary allocation of the time correction bit, which is a characteristic of the present invention, is performed (S25). Also in this embodiment, the time correction bit is made up of 3 bits, the time correction bit is not given to the LED having the largest light emission amount in accordance with the light emission amount of each LED, and the other LEDs are provided with the insufficient light emission amount. The time correction bits are virtually assigned.

Next, the exposure energy thus allocated is calculated for each LED (S26), and the virtual average exposure energy E _{A of the} chip is calculated based on the exposure energy of each LED (S26). S27).

Then, the virtual average exposure energy E _A is compared with the target value E ₀ (S28).

In this embodiment, in step S28, it is determined whether the virtual average exposure energy E _A is larger than the target value E _0. If it is smaller than the target value, the initially set n-th bit is set. Change to "0" (S2
9). That is, the change is made to increase the drive current. On the other hand, when the comparison result is opposite, that is, when the average exposure energy E _A exceeds the target value, the n-th bit is held as it is, that is, “1”. In this way, the most significant bit is fixed.

In step S30, it is determined whether or not all the bits have been determined. If n is not 0, the initial value n is subtracted one by one in step S31.

As described above, steps S22 to S29 are sequentially repeated from the most significant bit to the least significant bit to fix each bit value of the DAC.

As is apparent from the embodiment, in the determination of each bit value, the time correction bit is provisionally allocated each time, and the predetermined adjustment is made while the exposure energy is calculated from both the drive current and the time correction bit. Done.

Therefore, allocation of the time correction bits is completed at the same time with all bits of the DAC fixed.

FIG. 3 shows the entire driving circuit of the LED print head in which the driving current is controlled by the DAC shown in FIG.

The print head comprises a plurality of chips 10-1,
10-2, 10-3, ... Are arranged in a line, and a plurality of LEDs 12-1 to 12-64 are lined up in each chip 10. Driving circuits 14-1, 14-2, 14-3 are provided for the respective chips 10, and the respective driving currents are DAC 16-1, 16-2,
16-3.

The inside of the drive circuit 14 has the same circuit configuration, and only the circuit 14-1 is shown in detail in FIG.

A driving MOS-F for each LED 12
An ET 18 is provided and a drive current is supplied to the selected LED 12. The switching element 20 is connected to the gate of the FET 18, and the desired FET 18 is controlled to be turned on and off by the output signal from the AND gate 22, and the drive current adjusted by the present invention is supplied from the FET 18 to each LED 12 as described above. You can

The strobe signal STR is supplied to one input of the AND gate 22, and the print control signal from the data control circuit 24 is supplied to the other input.

In the present invention, as described above, both the application of the correction pulse by the time correction bit and the application of the main pulse for main printing are controlled in order to adjust the light emission variation of each LED in the chip, and The data control circuit 24 switches between the correction data and the main data. Once the time correction bits have been defined by the invention described above, the correction data is provided to the latch 26 and stored as a numeric value specific to the chip 10 in question.

On the other hand, the print data is supplied to the shift register 28, which is temporarily stored as a parallel signal by the latch 30.

As described above, both the latches 26 and 30 store both the correction data and the main data, and the correction data 26 is actually output to the LEDs which need to be printed by the print signal DIN supplied to the shift register 28. Only temporarily latched. The data control circuit 24 switches the outputs of both latches 26 and 30 in a predetermined order, and
The D signal is supplied to the D gate 22 and is AN with the strobe signal STR.
By the D control, the switching element 20 is opened, and at this time, the drive current determined by the DAC 16 is supplied to the selected LED 12, and light emission with desired exposure energy adjustment is performed.

As described above, according to the present invention, each L
It is possible to correct the drive time of the ED and adjust the drive current for each chip in an optimum state for actual printing work.

[0049]

As described above, according to the present invention, since the LED print head is adjusted based on the actual exposure energy which is determined by both the drive current and the drive time, an extremely uniform exposure energy is obtained. The print quality of the print head can be significantly improved.

Further, according to the present invention, since the final exposure energy target value is used as a reference, the variation in the printing quality among the respective chips is remarkably reduced, and it is extremely uniform even when a plurality of chips are incorporated as a print head. It is possible to obtain a reduced exposure energy, and it is possible to obtain a head in which the variation of the exposure energy is small among the print heads.

Furthermore, since the exposure energy can be adjusted on a chip basis, the burden of the time correction bits can be reduced, and the number of time correction bits can be reduced as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a flowchart showing a preferred embodiment of an adjusting method according to the present invention.

FIG. 2 is a flow chart showing another preferred embodiment of the adjusting method according to the present invention, which is a preferred embodiment of the method for adjusting the drive current by the DAC.

FIG. 3 is an overall configuration diagram of a print head driving system suitable for the present invention.

FIG. 4 is a flowchart showing a conventional adjusting method.

[Explanation of symbols]

 S11, S23 LED drive S12, S24 Light emission amount measurement S13, S25 Temporary allocation of time correction bits S14, S26 Calculation of exposure energy after allocation S15, S27 Calculation of virtual average exposure energy S16, S28 Comparison S17, S29 Driving current Change

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04N 1/036 A 1/40

Claims (2)

[Claims] 1. In order to equalize the exposure energy of an LED print head in which a plurality of chips in which a plurality of LEDs are aligned are aligned to a target value, the light emission amount between the chips is adjusted by adjusting an LED drive current. The light emission time of the LED in the chip is corrected by adjusting the drive current supply time.
In the method of adjusting the exposure energy of an LED print head, a step of driving an LED with a predetermined drive current, a step of measuring a light emission amount of each LED, a step of temporarily assigning a time correction bit to each LED, The step of calculating the exposure energy of each LED based on the drive current and the temporarily allocated time correction bit; the step of calculating the virtual average exposure energy from the exposure energy of each LED; and the virtual average exposure energy and the target value. Exposure energy of an LED print head, comprising: a step of comparing and a step of changing a drive current based on the comparison result, and repeating the steps until the virtual average exposure energy reaches a desired target value. Adjustment method. 2. An LED print head adjusted by the exposure energy adjusting method according to claim 1.