JP2003112441A - Device for focusing printing head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for focusing a printing head which can make an adjusting time short and can reduce variations of an adjusting accuracy without requiring a sophisticated adjusting technique by particularly comparing an image formation state and making the center of a distance where the state matches a true focal point position in relation to a focusing device for the printing head. SOLUTION: A focal point shaft rotation unit 8 is set from above to a printer 1 whose printing head is to be focused, and is fitted in head focal point shafts 22a and 22b for adjusting a printing head unit 2 in an up-down direction. The printing head is focused by rotating stepping motors 11a and 11b. In this case, light is emitted from the printing head on the basis of focusing pattern data to a photoreceptor drum 3, whereby a focusing pattern is printed to a paper transfer belt 5. The density of the printing data is read by a printing state read unit 9 and supplied to a focal point jig controller 26. The printing head is brought in focus in this manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, and more particularly to a focus adjusting device for adjusting the focus of a print head.

[0002]

2. Description of the Related Art In an image forming apparatus such as a printer,
A print head using an ED element or the like is used. The print head emits light according to print data to the photosensitive drum, and many LED elements are arranged in a line to emit light to the photosensitive drum. This light is emitted from each LED
This is performed through an imaging lens array in which a lens is formed for each element, and an electrostatic latent image is formed on the photosensitive surface of the photosensitive drum.

In this case, it is necessary that the focal points of the light emitted from the LED elements are aligned on the photosensitive surface. For this reason,
Conventionally, focus adjustment is performed to adjust the relative position between the print head and the photosensitive drum. For example, the print density formed on the recording paper or the paper transport belt is detected by optical means, photoelectric conversion is performed, and the position of the print head is adjusted manually or automatically.

[0004]

However, the conventional focus adjustment of the print head is to detect the peak value of the print density formed on the recording paper or the paper transport belt.
Therefore, the conventional device requires a high degree of adjustment operation.

That is, the elements formed in the print head are highly densified in accordance with today's demand for high resolution image precision, and accurate focus adjustment leads to the requirement of advanced adjustment technology, and the adjustment time is long. It becomes necessary and also causes a variation in the adjustment accuracy by the operator.

Further, the focus adjusting jig is also required to have high performance, which causes an increase in the cost of the adjusting jig. Therefore, the present invention requires advanced adjustment technology by comparing image forming states at positions that are intentionally symmetrically shifted with respect to the focus, and setting the center of the distance where the states match as the true focus position. Adjustment time can be shortened without
Provided is a focus adjusting device for a print head which can reduce variations in adjustment accuracy.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 is to move a position of a print head having a print element up and down, and to rotate the head focus shaft. Is provided with a motor for adjusting the axis of the motor to the head focus shaft and set in the apparatus main body, and the motor is rotated based on a focus position adjustment signal to move the head focus shaft. A focus position adjusting means for rotating the print head to adjust the position of the print head, and based on focus adjustment pattern data, the print head emits light to generate a focus adjustment pattern on a recording paper or a paper transport belt. A print density reading jig that detects the density of the generated pattern, and the focus position adjustment signal is created based on the density data read by the print density reading jig. It can be achieved by providing a focus adjustment device of the print head and a focus position adjusting signal generating means for transmitting to the cement position adjusting means.

Here, a large number of printing elements are formed on the print head, and the print head on which the print head is formed can be moved up and down by a head focus axis, and a focus adjustment jig for driving the head focus axis. The tool is provided with a motor for rotating the head focus shaft, and by driving the motor, the head focus shaft is rotated to vertically adjust the print head.

Further, the focus adjustment pattern data is printed from the print head (print element) on the photosensitive surface of the photosensitive drum, and the print density is read by a print density reading jig,
A focus position adjustment signal is created and sent to the focus position adjustment means.

With this configuration, the position of the print head is adjusted in accordance with the focus position adjustment signal, and the focus position is adjusted accurately by repeating this process.

According to a second aspect of the present invention, in the first aspect of the present invention, the focus position adjustment signal creating means compares the print densities at a focus position different from the focus, and the center position of the distance where the print densities match. Is a true focus position, and the focus position adjustment signal is created.

With this configuration, the fact that the measurement result of the print density is subject to the focus as the center is used to output a focus position adjustment signal with the center position of the front and rear measurement positions as the true focus. The focus position is adjusted more easily, the focus of the print head is adjusted accurately in a short time without requiring a high degree of skill.

According to a third aspect of the present invention, in the invention of the first aspect, the focus position adjustment signal creating means measures print densities at a plurality of focus positions, and an inclined line created based on the measurement result is measured. In this configuration, the focus position adjustment signal is created with the intersection point as the true focus position.

This example is an example in which the measurement result of the print density is not focused around the focus. In this case, the intersection (vertex) of the two slope lines created by plotting from the measurement results of the plurality of print densities. ) Is the true focus, the focus position is adjusted to this position.

With such a structure, the focus position can be adjusted more easily, the focus of the print head can be adjusted accurately in a short time without requiring a high degree of skill. According to a fourth aspect of the present invention, in the first, second or third aspect, the print density reading jig is moved on a rail provided inside the apparatus main body and set at a print position of the focus adjustment pattern. It is a configuration that is done.

Further, the description of claim 5 relates to claims 1, 2 and
In the description of 3 or 4, the motor is, for example, a stepping motor.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 shows the entire system of a focus adjusting device for a print head according to the present embodiment. In the figure,
Reference numeral 1 denotes a printer, which is provided with a print head 2 '(print head unit 2) which is a focus adjustment target. Further, in the printer device 1, an image forming lens array 4 for forming an image of light emitted from the LED elements formed on the print head 2 ′ on the peripheral surface of the photosensitive drum 3, a sheet conveying belt 5 for conveying recording paper, An engine controller 6 that controls the engine unit such as the body drum 3 and the developing roll, a main motor unit 7 that drives a main motor, and the like are provided.

Head focus shaft fitting portions 20a and 20b are provided on both sides of the print head unit 2. Head focus shaft fitting portions 20a and 20b are provided with head focus shaft fitting portions 20a and 20b, respectively, and screw holes 20a 'are provided inside the head focus shaft fitting portions 20a and 20b, respectively. Head focus axis 2 on 20b '
2a and 22b are screwed together. That is, the screwing hole 20a ',
20b 'is formed with spiral grooves having a predetermined pitch in a spiral shape,
The spiral projections on the surfaces of the head focus shafts 22a and 22b are screwed into the grooves.

The lower ends of the head focus shafts 22a and 22b are rotatably held by holding portions 23a and 23b, respectively. Also, the head pressing spring 25
A and 25b apply a biasing force to the print head unit 2 and hold the print head unit 2 downward.

The focus shaft rotating unit 8 and the print density reading unit 9 are set in the system having the above construction. 2A and 2B are perspective views of the units 8 and 9. First, FIG. 2A shows a focus shaft rotating unit (focus adjusting jig) 8, in which a base 10 is provided with stepping motors 11a and 11b. The tip of the rotary shaft 12a of the stepping motor 11a is provided with an adjusting convex pin 13a for vertically adjusting the head focus shaft 22a. Similarly, the tip of the rotary shaft 12b of the stepping motor 11b is also provided with an adjustment convex pin 13b for vertically adjusting the head focus shaft 22b.

The adjusting convex pins 13a and 13b are plate-shaped and have a structure to be fitted in a groove (concave portion) formed in the head focus shaft. That is, the handle 14 provided on the base 10
The head focus shaft 22 from above the printer device 1.
The focus shaft rotating unit 8 is set on the printer device 1 by aligning with the grooves (recesses) of a and 22b and fitting the adjusting convex pins 13a and 13b.

The rotation control signal to the stepping motors 11a and 11b is supplied through the harness 15. The print density reading unit 9 shown in FIG. 2B is configured by disposing two substrates 17a and 17b on the base 16. A CCD sensor 18a is formed on the substrate 17a, and the density of the focus adjustment pattern created by the process described later is measured. Similarly, the substrate 17b also has a CCD
The sensor 18b is formed, and the density of the focus adjustment pattern to be created at another position is measured by the process described later.
The information read by the CCD sensors 18a and 18b is sent to a focusing jig controller described later via the harness 19.

The print density reading unit 9 is set in the printer 1 by using the rail 21 provided in the printer 1 as a guide. That is, the rollers 16a and 16b provided in the print density reading unit 9 are used,
The rail 21 is slid and set in the printer device 1.

On the other hand, in FIG. 1, the signal line (harness) wired from the focus shaft rotation unit 8 and the print density reading unit 9 is connected to the focus jig controller 26, and the main motor unit 7 is connected to the engine controller 6 from the engine controller 6. The signal line is connected. A signal line from the video printing jig 27 is connected to the engine controller 6, and the video printing jig 27 and the focusing jig controller 26 are connected.
Signal lines are also connected between the two.

FIG. 3 is a block diagram of the above control units.
The focusing jig controller 26 includes a CPU 30 and a RAM 3
1, program storage memory 32, pulse drive circuit 33,
Analog / digital conversion circuit 34, density comparison circuit 35,
And a start switch 36 and a reset circuit 37. A power supply unit 38 is also provided in the focusing jig controller 26 to supply driving power to each part.

The CPU 30 performs processing according to a program stored in the program storage memory 32, uses the RAM 31 as a work area, outputs a pulse signal to the pulse drive circuit 33, and outputs comparative density data to the density comparison circuit 35. Further, density data is input to the analog / digital conversion circuit 34 from the focus pattern density sensors 18a and 18b. Further, a processing start signal is supplied from the start switch 36, and the reset signal is input from the reset circuit 37.

The focus shaft rotating unit 8 is, as described above,
It is a unit for rotationally driving the head focus shafts 22a and 22b, and drives the stepping motors 11a and 11b in accordance with the pulse signal supplied from the pulse drive circuit 33.

Further, the print density reading unit 9 is formed with the focus pattern density sensors 18a and 18b as described above, and the density information of the patterns detected by the focus pattern density sensors 18a and 18b is converted into the analog / digital conversion circuit 34. Converted into digital data by the CPU3
Supplied to zero.

The video printing jig 27 stores focus adjustment pattern data, which will be described later, and outputs it to the printer device 1 according to an instruction from the CPU 30. The printer device 1 includes the above-described engine controller 6, head controller 39,
The print head 2'has circuits such as a print head 2 ', and light is emitted from the print head 2'based on the focus adjustment pattern data supplied from the video printing jig 27. The print head 2'is composed of a plurality of LED chips (for example, 56 LED chips), and each LED chip has many LED elements (for example, 56 LED chips).
128 LED elements) are formed. In the focus adjusting device for a print head having the above configuration, the adjusting process will be described below. When the focus adjustment of the print head of this example is performed, it is assumed that the focus shaft rotation unit 8 and the print state reading unit 9 have already been set in the target printer device 1.

FIG. 4 is a flow chart for explaining the adjustment processing of this example. In the figure, first, an operator starts the start switch 36 provided on the focus jig controller 26.
(Step (hereinafter referred to as ST). By this operation, a start signal is input to the CPU 30 and the CPU 3
0 takes in the reset signal from the reset circuit 37,
The rotation angles of the stepping motors 11a and 11b are initialized (ST2). Further, the focus density level data is initialized (ST3).

Next, the focus adjustment pattern data is read from the reset circuit 37, and the print head 2'is caused to emit light via the engine controller 6 and the head controller 39 (ST4). Due to this light emission, an electrostatic latent image of the focus adjustment pattern data is formed on the photoconductor drum, further development processing is performed, and the toner image is transferred to the paper transport belt 5. FIG. 5 is a schematic diagram including this process and subsequent processes. That is, the electrostatic latent image formed on the photoconductor drum 3 is developed by the developing roll 41 and transferred to the paper transport belt 5 by the transfer device 42. still,
Reference numeral 40 is a charger for applying an initial charging voltage to the photosensitive drum 3 in advance.

The focus adjustment pattern transferred to the paper transport belt 5 by the above processing is sent to just above the focus pattern density sensors 18a and 18b by the rotation of the transport roller 43. The CPU 30 reads the density information of the focus adjustment pattern at this timing (ST5). This information is sent to the analog / digital conversion circuit 34 of the focusing jig controller 26 via the harness as described above, converted into digital data, and input to the CPU 30. CPU
30 stores this data in the RAM 31, for example (S
T6).

Next, this data is output to the density comparison circuit 35, and it is determined whether the density is solid black (ST7). Here, when the solid black density is obtained (YES in ST7), the CPU
30 sends a drive signal to the pulse drive circuit 33 to drive the stepping motors 11a and 11b (ST
8).

FIG. 6 is a diagram for explaining changes in the image image with respect to the image forming position on the photosensitive surface. Shown in the figure is 1
An image image of dots is shown, and is a density image of the entire focus adjustment pattern. Further, is a density image of the entire focus adjustment pattern when the resolution is increased. From these figures, the darkest part (solid black density) is located at a position shifted Zo (Zo ') from the focus position of the image, and the middle density part is located at the focus position, for example Z1.
It can be seen that (Z1 ') is located at a shifted position. Therefore, in this example, a position inside, for example, Z1 displaced from the position displaced from Zo from the focus position is set as a reference value (first focus position) (ST2 to ST7). By this processing, the first focus position is set.

Next, in order to find the second focus position, the focus adjustment pattern data is output again from the video printing jig 27 and the focus adjustment pattern is transferred to the paper carrying belt 5 (ST8, ST9). Then, the density information is read by the focus pattern density sensors 18a and 18b (ST1
0). This data is stored in the RAM 31, and the density comparison circuit 35 compares it with the density data at the previous first focus position (ST11 to ST13).

If the two data do not match (NO in ST13), the CPU 30 outputs the control signal to the pulse drive circuit 33 again, and the stepping motor 11a,
11b is driven. By this drive, the head focus axis 2
2a and 22b rotate to move the print head 2 '(print head unit 2) (ST14). Then, similarly to the above, the focus adjustment pattern data is output, the focus adjustment pattern is transferred to the sheet conveying belt 5, and the density information is read by the focus pattern density sensors 18a and 18b (S
(T9 to 10), and the density comparison circuit 35 further compares the density data at the previous first focus position (ST11 to ST1).
3).

When the first focus position and the second focus position match (YES in ST13) by repeating the above process, the target adjustment position is obtained from the information of the first focus position and the second focus position. That is, the first focus position and the second focus position
A half position (center position) between the focus positions is set as a target adjustment position, and the target position is adjusted (ST14, ST15).
Specifically, the stepping motors 11a and 11b are driven to adjust the print head 2 '(print head unit 2) to a target position.

FIG. 7 is a graph showing the above processing.
The third focus position shown in the figure is the target adjustment position.
The MTF (modulation transfer function) shown in the figure is the ratio of the minimum light amount between the target light emitting element and the adjacent light emitting element, and the larger this ratio is, the more the light emission is concentrated. means.

FIG. 8 is a diagram showing the positional relationship between the print head 2 '(print head unit 2) and the photosensitive drum 3 as the first focus position to the third focus position. By performing the adjustment as described above, the focus position can be adjusted more easily, the focus of the print head can be accurately adjusted without requiring a high degree of skill. For example, as shown in FIG. 9, the true focus position (third focus position) is flat on both sides, and it is difficult to adjust the true focus position with such characteristics. In this respect, according to the present example, by searching for the 1st focus position and the 2nd focus position where the print density is the same, the center position is the true focus, and it can be easily adjusted.

Incidentally, FIG. 10 shows a stepping motor 11a,
11 is a diagram showing the relationship between the rotation angle of 11b, the rotation direction, the moving distance between the photosensitive drum 3 and the photosensitive drum 3, and the imaging lens array 4. FIG. Further, in FIG. 11, the above Zo is 3.
FIG. 5 is a diagram in which the distance between the photosensitive drum 3 and the imaging lens array 4 when the distance is 5 mm is divided according to the focus position, C indicates a range of ± 0.5 mm with respect to the focus position, and B indicates the above C. A range of 2 mm from the photosensitive drum 3, a range of 2 mm from D of the imaging lens array 4 from the above C, a range of 1 mm from the photosensitive surface by E, and an area of E from the imaging lens array 4 of E. The range of 1 mm is shown. Each of the above positions corresponds to the display of A to E shown in FIG. <Second Embodiment> Next, a second embodiment of the present invention will be described.

The MTF characteristic is measured in the state of the head unit using a special optical measuring device. However, in this example, the MTF characteristic can be measured with the printer device 1 assembled.

For example, an example of a print head having the MTF characteristic shown in FIG. 12 will be described. In this case, an arbitrary focus position is set as the reference value P0, and the print density level at this time is recorded. Next, the density level and the focus movement distance at the positions P1, P0 'and P1' are recorded. Here, the focus movement distance is the movement distance from the reference value P0.

Next, based on the above data, the slope lines C'and C "of the MTF characteristic are obtained. The slope lines C'and C" are as shown in FIG. Therefore, the characteristic created in this way becomes an MTF characteristic curve with the intersection of the slope lines C ′ and C ″ as the apex. That is, the intersection (apex) at this time is the focus position and the desired focus adjustment position. Becomes

Therefore, in this case, the focus position is adjusted with the intersection (vertex) of the tilt lines C'and C "as the true focus. In this case as well, the adjustment signal is focused according to the data detected by the print density reading jig 9. The print head is sent to the jig controller 26 and the stepping motors 11a and 11b are driven to adjust the position of the print head at the intersection (vertex).

With this arrangement, it is possible to more easily adjust the focus of the print head without requiring skill to adjust the focus.

[0046]

As described above, according to the present invention,
The true focus position is intentionally shifted, and the focus is at the center position of the distance obtained by comparing the printing states, so accurate focus adjustment can be performed in a short time without requiring advanced adjustment technology. You can

[Brief description of drawings]

FIG. 1 shows an overall system of a focus adjusting device for a print head according to the present embodiment.

2A and 2B are perspective views of a unit.

FIG. 3 is a circuit block diagram of the system.

FIG. 4 is a flowchart illustrating an adjustment process.

FIG. 5 is a schematic explanatory diagram of this example.

FIG. 6 is a diagram illustrating an adjustment process of this example.

FIG. 7 is a diagram illustrating the principle of the present example based on MTF characteristics.

FIG. 8 is a diagram illustrating a positional relationship between a photosensitive drum and an imaging lens array.

FIG. 9 is a diagram illustrating the principle of the present example based on MTF characteristics.

FIG. 10 is a diagram showing a rotation angle of the stepping motor, a rotation direction, a moving distance between the stepping motor, and a relationship between the photoconductor drum and the imaging lens array.

FIG. 11 is a diagram in which the distance between the photosensitive drum and the imaging lens array when Zo is set to 3.5 mm is divided according to the focal position.

FIG. 12 is a diagram illustrating a second embodiment.

[Explanation of symbols]

1 Printer device 2 Print head unit 3 photoconductor drum 4 Imaging lens array 5 Paper transport belt 6 engine controller 7 Main motor unit 8 focus axis rotation unit 9 Print status reading unit 10 bases 11a, 11b Stepping motor 12a, 12b rotating shaft 13a, 13b Adjusting convex pin 14 Toride 15, 19 harness 16a, 16b roller 17a, 17b substrate 18a, 18b Focus pattern density sensor 18a, 18b Head focus shaft fitting part 20a, 20b Head focus shaft fitting part 21 rails 22a, 22b Head focus axis 23a, 23b holding part 25a, 25b Head holding spring 26 focus jig controller 27 Video printing jig 30 CPU 31 RAM 32 program storage memory 33 pulse drive circuit 34 Analog / digital conversion circuit 35 Density comparison circuit 36 Start switch 37 Reset circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 27/18 G02B 7/11 N 5C074 G03B 13/36 G03B 3/00 A H04N 1/036 B41J 25/30 G 1/23 103 (72) Inventor Kazutaka Otsuka 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Co., Ltd. Tokyo Business Office F-term (reference) 2C064 CC05 CC13 DD01 DD05 DD09 DD14 2C162 AE28 AE47 AE55 AF83 FA04 FA17 FA44 FA54 FA59 FA67 FA70 2H011 AA06 BA51 2H051 AA00 BB31 5C051 AA02 CA08 DA03 DB02 DB22 DB29 DE22 DE33 5C074 AA07 BB04 BB26 CC26 DD05 EE20 GG01 GG14

Claims (5)

[Claims] 1. A head focus shaft that moves up and down the position of a print head on which a printing element is formed, and a motor that rotates the head focus shaft are provided, and the shaft of the motor is fitted to the head focus shaft. Then, the motor is rotated based on the focus adjustment jig that is set in the main body of the device and the focus position adjustment signal,
Focus position adjusting means for rotating the head focus shaft to adjust the position of the print head, and light emission from the print head based on the focus adjustment pattern data, and the focus adjustment pattern on the recording paper or the paper conveyance belt. And a print density reading jig for detecting the density of the generated pattern, and the focus position adjustment signal is created based on the density data read by the print density reading jig and transmitted to the focus position adjusting means. A focus adjusting device for a print head, comprising: focus position adjusting signal generating means. 2. The focus position adjustment signal creating means compares the print densities at a focus position different from the focus, and creates the focus position adjustment signal with the center position of the distance where the print densities match as the true focus position. The focus adjusting device for a print head according to claim 1, wherein: 3. The focus position adjustment signal creating means measures the print densities at a plurality of focus positions, and determines the focus position adjustment signal with the intersection of the inclined lines created based on the measurement result as the true focus position. The focus adjusting device for a print head according to claim 1, which is produced. 4. The print density reading jig moves on a rail provided in the apparatus main body and is set at a print position of the focus adjustment pattern. Focus adjustment device for the print head described. 5. The print head focus adjusting device according to claim 1, wherein the motor is a stepping motor.