JPH0880655A - Serial printer - Google Patents

Abstract

PURPOSE: To provide a serial printer capable of performing printing stable in quality hardly affected by the surface shape of a printing medium by always keeping the interval between a printing head and the surface of the printing medium constant even when there is unevenness or inclination on the surface of the printing medium. CONSTITUTION: A distance sensor 20 is provided in front of the main scanning direction in the vicinity of a printing head 15 and measures the distance up to the surface of a printing medium 17 during main scanning. The position in the Z-direction of the printing head 1 at a next dot forming position is regulated to control the distance between the leading end surface of the printing head 15 and the surface of the printing medium 17 to an ideal distance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a serial printer suitable for printing characters, images, etc. on a print medium having an uneven surface or an inclined surface. In this specification, an ink jet type serial printer (hereinafter, referred to as “ink jet printer”) will be described as an example.

[0002]

2. Description of the Related Art The printing elements of ink jet printers are
Generally, as shown in FIG. 1, by applying a mechanical pressure to the ink by a piezo element 51 or the like, or by utilizing the pressure at which the ink becomes bubbles 53 by heating the thermistor 52, a fixed amount of ink is applied to the nozzle. By ejecting from the nozzle, a dot array having a constant density is formed on the print recording medium and printing is performed.
Normally, one line is printed by moving the print head in which the print elements are arranged in the Y direction (vertical direction) at a constant density in the X direction (horizontal direction), and then the print medium is arranged in the print element array. Send in the Y direction a distance equivalent to the length of a minute,
By repeating the above operation, printing of one page of the print medium is performed.

[0003]

By the way, since each printing element ejects a certain amount of ink, when the distance between the print head and the print medium changes, each print dot varies and the print quality is stable. The specified print cannot be performed. So, in the conventional inkjet printer,
A mechanism for fixing the print medium is provided in order to keep the distance between the print head and the print medium constant. However, the distance can be kept constant by the fixing mechanism only for printing media with a thin and smooth surface, and for media with uneven surfaces or media with a sloping surface because the thickness varies depending on the location, the above distance Cannot be kept constant.

Further, in order to improve printing accuracy, the print head is fixed in the Z direction, which is the distance direction to the print medium, during the main scanning in which the print head is moving. In addition, there is a device provided with an adjusting mechanism for the head position in the Z direction in order to enable printing on a thick print medium, but the head position is adjusted before starting printing, and during printing, the head position is adjusted in the Z direction. The head position is fixed. Therefore, it is difficult to perform high-quality printing on a print medium having an uneven surface or an inclined surface.

Therefore, an object of the present invention is to ensure that the distance between the print head and the print medium is always kept constant even if the surface of the print medium has irregularities or slopes, so that the surface shape of the print medium is not affected. To provide a serial printer capable of stable printing.

[0006]

In order to achieve the above object, the serial printer of the present invention includes a print head moving means for moving the print head in a direction to move toward and away from the print medium, a print head and a print medium. Distance measuring means that outputs a signal that changes depending on the distance between the distance measuring means and the distance measuring means in order to match the distance between the print head and the print medium with a predetermined ideal distance during scanning of the print head. And a distance adjusting means for controlling the print head moving means on the basis of the output signal.

[0007]

According to the above construction, a signal corresponding to the distance between the print head and the print medium is detected during scanning, and the distance position of the print head with respect to the print medium is adjusted based on this signal. As a result, the position of the print head is adjusted according to the surface shape of the print medium, and the distance between the print head and the print medium is kept substantially at the ideal position.

In a preferred embodiment, a distance sensor that moves with the print head to measure the distance to the print medium at a predetermined position ahead of the print head in the scanning direction is provided as the distance measuring means. If the signal from this distance sensor is used, the distance between the print head and the print medium at the future arrival position of the print head can be easily predicted. It is possible to control the distance to the print medium to the ideal distance before reaching. Further, the distance sensor may be provided not only on the front side in the scanning direction of the print head but also on the rear side in the scanning direction. By doing so, the above-mentioned control can be performed even if the above-described distance prediction calculation can be performed more accurately, and the printing scanning direction changes.

Further, in a preferred embodiment, the distance adjusting means alternately repeats the movement of the print head by the print head moving means and the acquisition of the output signal from the distance measuring means while the print head is scanning. . At that time, the signal is taken in from the distance measuring means after a predetermined stable time has elapsed after the completion of the movement of the print head. As a result, the accurate distance can be measured without being affected by the vibration of the print head due to the movement of the print head.

Further, in this preferred embodiment, when the change in the output signal from the distance measuring means exceeds a predetermined threshold value, the scanning of the print head is stopped. Accordingly, when the unevenness of the surface of the print medium is too large to collide with the print head, it is possible to prevent the collision and protect the print head.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 3 shows a structure of a print head driving portion of a serial printer according to an embodiment of the present invention.

In FIG. 3, the print medium 17 is a base frame 11.
It is designed to be fixed in a fixed position with respect to. Here, the horizontal direction, the vertical direction, and the thickness direction of the print medium 17 are referred to as the X direction, the Y direction, and the Z direction, respectively, as indicated by arrows. Since the print medium 17 shown in the drawing has different thicknesses in the X direction, the surface thereof is inclined with respect to the XY plane.

A guide rail 12 extending in the X direction is attached to the base frame 11 so as to be reciprocally movable in the Y direction (sub-scanning direction) by a motor (not shown). A main scanning member 14 is attached to the guide rail 12 so as to be reciprocally movable in the X direction (main scanning direction) along the guide rail 12 by a motor (not shown).
Further, a carriage 13 is attached to the main scanning member 14 via a Z-direction moving mechanism 16, and a print head 15 is attached to the carriage 13.

The Z-direction moving mechanism 16 moves the carriage 13 in the Z direction in order to keep the distance between the print head 15 and the surface of the print medium 17 constant, and is driven by, for example, a pulse motor (not shown). It A linear actuator such as a linear motor or a solenoid may be used for the Z-direction moving mechanism 16.

In such a structure, the main scanning member 14
Main scanning is performed by moving the carriage 13 along the guide rails 12 and sub-scanning is performed by moving the guide rails 12 in the Y direction. Printing is performed during main scanning while repeating main scanning and sub-scanning. Printing on the surface of the print medium 17 is performed by driving the head 15. During this printing, the Z-direction movement mechanism 16 adjusts the Z-direction position of the carriage 13,
The distance between the print head 15 and the surface of the print medium 17 is kept constant.

4 and 5 show a detailed structure of the carriage 13 and the print head 15 shown in FIG. 3, and FIG. 4 is a side view of this portion taken along the Y direction. Shows side views of this portion viewed along the X direction.

As shown, a distance sensor 20 is provided in the vicinity of the print head 15 in order to measure the distance between the print head 15 and the surface of the print recording medium 17 during the main scanning and the sub scanning. ing.

As shown in a partial cross section in FIG. 4, the distance sensor 20 is a micrometer mounted on the carriage 13 and utilizing a differential transformer, and its tip is always in contact with the surface of the print recording medium 17. From a contactor 21 in contact with the Z-direction, an iron core 22 attached to the base end of the contactor 21, and a differential coil 23 that generates a differential voltage according to the Z-direction position of the iron core 22. Composed. The differential coil 23 includes an exciting coil (primary coil) 24 and two secondary coils 25 and 26 that generate an induced voltage. The differential voltage generated between the secondary coils 25 and 26 determines the print medium 17. A small displacement in the Z direction of the surface of can be recognized.

As shown in FIG. 4, the distance sensor 20 is separated from the print head 15 by a small distance in the X direction, and as shown in FIG. It is arranged at the same position as the middle print element in the element array (not shown).

Further, the distance sensor 20 is arranged so as to always come forward in the moving direction of the print head 15 in order to measure the distance ahead of the print head 15 during the main scanning. In FIG. 4, the distance sensor 20 is located on the right side of the print head 15, but this is the position when main scanning is performed in the right direction in the figure.

FIG. 6 is a functional block diagram of the control device provided in the printer of this embodiment.

As shown in the figure, this control device has a CPU.
1, a ROM 2, a RAM 3, a host interface 4, an input interface 5, an X-direction motor drive circuit 6, a Y-direction motor drive circuit 7, a head drive circuit 8 and a Z-direction motor drive circuit 9.

The host interface 4 is an interface for receiving print data from an external host device. The input interface 5 is an interface for inputting signals from various sensors (not shown) in the printer including the distance sensor 20 shown in FIG. 5 and signals from an operation panel (not shown) of the printer. is there.

The CPU 1 processes the print data from the host device, controls the printing operation through the X-direction and Y-direction motor drive circuits 6 and 7 and the head drive circuit 8, and processes the signal from the distance sensor 20. Then, arithmetic processing for adjusting the Z-direction position of the carriage 13 through the Z-direction drive circuit 9 is performed.

The ROM 2 includes a print processing program for the CPU 1 to control the printing operation described above, character font data, a position control program for the CPU 1 to adjust the position of the carriage 13 in the Z direction, and the like. It is stored. The position control program incorporates allowable value data for the unevenness of the surface of the print recording medium 17, distance data in the X direction between the print element array of the print head 15 and the distance sensor 20, and the like. The above tolerance data is
In order to prevent the print head 15 from being damaged,
It shows the maximum value of the allowable unevenness change. Also,
The above-mentioned interval data represents the X-direction distance between the print element array and the position of the distance sensor 20 in terms of a multiple of the print dot pitch.

A reception buffer, a print buffer, a status area, a work area, etc. are set in the RAM 3.

The X-direction motor drive circuit 6 drives an X-direction motor (not shown) based on a control signal from the CPU 1 so that the main scanning member 14 shown in FIG. Scanning is performed.

The Y-direction motor drive circuit 7 drives the Y-direction moving motor (not shown) based on the control signal from the CPU 1 so that the guide rail 12 shown in FIG.
The sub-scanning is performed by moving in the direction.

The head drive circuit 8 receives the bitmap data developed on the print buffer by the CPU 1 processing the print data, and the print head 15 shown in FIG.
The printing element is driven to form dots.

The Z-direction motor drive circuit 9 is based on a control signal from the CPU 1 and is provided with a Z-direction movement motor 16 (not shown).
Driving the Z-direction moving mechanism 1 shown in FIG.
6 is for adjusting the distance between the front end surface of the print head 15 and the surface of the print recording medium 17 to be constant.

FIG. 7 is a functional block diagram of a portion for adjusting the position of the print head 15 in the Z direction in the configuration described above.

The differential voltage output from the distance sensor 20 is
It is amplified by the amplifier 29 in the interface 5 and converted into digital data by the A / D converter 30. The digitalized differential voltage data is input to the head movement amount calculation unit 31 by the CPU 1, and the head movement amount calculation unit 31
The amount of movement of the print head 15 in the Z direction is calculated. This movement amount is output to the Z-direction movement motor drive circuit 9. As a result, the Z-direction moving mechanism 16 moves the carriage 13 in the Z direction by a distance corresponding to the amount of movement, so that the distance between the front end surface of the print head 15 and the surface of the print medium 17 is always adjusted to a constant value.

The calculation of the movement amount of the print head 15 will be described in detail below.

The distance sensor 20, the amplifier 29 and the A / D converter 30 are connected to the front end surface of the print head 15 and the print medium 1.
The difference voltage data "0" is generated when the distance to the surface of 7 is a predetermined ideal distance, and when the distance deviates from the ideal distance, difference voltage data having a value corresponding to the difference is generated. , Adjusted and initialized in advance. That is, the difference voltage data represents the difference distance of the above distance from the ideal distance.

The head movement amount calculator 31 which has received the difference voltage data first divides the difference voltage data by the distance in the X direction between the print element array stored in the ROM 2 and the distance sensor 20. Here, as described above, the distance in the X direction is a value converted into a multiple of the dot pitch of printing, for example, N dot pitch. Therefore, the division is to divide the measured difference distance N dots ahead by N, which is the dot formation position next to the current dot formation position (that is, 1 dot pitch from the current position of the print head). This means that the difference distance from the ideal distance between the front end face of the head and the surface of the print recording medium 17 at the position (forward position) is obtained by linear interpolation from the measured difference distance N dots pitch ahead. In order for this linear interpolation to be effective, N
The inclination of the surface of the print medium 17 between the dot pitches needs to be substantially linear, but this condition is similar to the case where a medium having a rough surface is used if the N dot pitch is sufficiently short. With the exception of

When the difference distance at the next dot formation position is obtained in this way, the value is given to the Z direction motor drive circuit 9. As a result, the position of the print head 15 is corrected by the difference distance at the next dot formation position, and as a result, when the print head 15 comes to the next dot formation position, the head tip surface and the print medium surface are separated. The distance will match the ideal distance.

In the above process, if the difference distance measured by the distance sensor 20 exceeds the allowable value stored in the ROM, the unevenness of the surface of the print medium 17 is too large and the print head 15 and the print medium 17 are too large. Immediately stop the main scan because it is determined that there is a possibility of collision.

Next, the timing of performing the above control operation will be described with reference to FIG.

In the standby state immediately before the start of main scanning, initialization is performed so that the distance between the head surface and the surface of the print medium matches the ideal distance. After that, the print head 15 is moved in the X direction to start main scanning. As described above, the distance sensor 20 measures the distance between the front end surface of the head and the surface of the print medium at a position displaced from the print head 15 forward in the main scanning direction by a certain distance.

In FIG. 8, it is assumed that the adjustment of the position of the print head 15 in the Z direction is completed at time t1. After that, at time t2 (hereinafter, the time from t1 to t2 is referred to as a stabilization time) when the vibration of the print head 15 in the Z direction caused by this adjustment disappears completely and the print head 15 stops in the Z direction. Then, the printing operation by the head 15 (timing a) and the distance measurement at the N dot pitch forward position by the distance sensor 20 (timing b) are performed in parallel. When the printing operation is completed at time t3 and then the distance measurement is completed at time t4, the above-described movement amount calculation is performed based on the measured distance (timing c).

When the calculation of the movement amount is completed at time t5, the print head 15 is subsequently moved in the Z direction based on this movement amount (timing d). This movement in the Z direction is completed at time t6, but this completion time t6 is earlier than the time t7 when the print head 15 arrives at the next dot forming position by the stable time of the head.

By repeating the above, the distance between the head end surface and the print medium surface is maintained at the ideal distance during the main scanning.

When the main scanning of one row is completed and the carriage 13 is stopped in this way, the contact 21 of the distance sensor 20 is temporarily pulled into the carriage 13. Subsequently, the guide rail 12 moves to the position of the next row, the carriage 13 returns to the main scanning start position, and the contact 21 is again pushed out of the carriage 13 and comes into contact with the medium surface. From this state, the main scan of the next line starts in the same direction as the previous line,
The head position is adjusted during the main scanning in the same manner as described above. The above operation is repeated.

As described above, according to this embodiment,
It is possible to print characters / images with stable print quality that are not easily influenced by the surface shape of the print medium 17.

The contents described above relate to only one embodiment of the present invention, and the present invention is not limited to the above contents, but can be implemented in various other modes.

For example, a distance sensor to which an optical device such as a photo coupler is applied can be used as the distance sensor. In this case, even if the distance sensor cannot be mounted very close to the print head, by directing the direction of the light beam to the next dot formation position, the interpolation calculation as in the above embodiment is not performed directly. The distance between the head and the medium surface at the next dot formation position can be measured.

When the distance sensor measures the difference distance N dots pitch ahead of the print head as in the above embodiment,
The measured differential distance is N
It may be used for calculation of the head movement amount at the dot formation position ahead of the dot pitch.

Further, a distance sensor may be provided before and after the print head, and the head movement amount may be calculated by linearly interpolating the measured distances of the two distance sensors. By doing so, more accurate control can be performed than in the above embodiment. In that case, if a distance sensor is provided in front of and behind the print head, the series of control becomes possible not only when the main scanning is performed in the right direction but also when the main scanning is performed in the left direction. Also, FIG.
If the distance sensor 20 is rotated about the axis P of and is positioned in front of the print head in the scanning direction,
Similar control is possible.

Further, in the above-mentioned embodiment, the number of adjustments of the head position per dot pitch is set to one, but the number of times that can be allowed from the above-mentioned stable time of the print head 15 and the interval of the print timing is allowable. However, if the number of head position adjustments per dot pitch is increased, it is possible to improve the followability of the print head to the inclination even if the inclination of the surface of the print medium is steep.

Further, if the print head is not only movable in the Z direction but also swingable on the X-Z plane about the Y direction axis, it can be moved in the main scanning direction as shown in FIG. Since the front end surface of the head can be kept parallel to the medium surface inclined along the same, higher print quality can be obtained.

In the above embodiment, the distance sensor does not work during the sub-scan, but the distance sensor may work during the sub-scan to adjust the Z-direction position of the print head.

Further, although the head position is adjusted by the digital arithmetic processing in the above embodiment, if the output of the distance sensor 20 is adjusted to be exactly 0 or a constant value at the ideal distance, DC servo motor technology or the like will be used. It is also possible to adjust the head position with high accuracy by using an analog control system using the.

Although the carriage is moved in both the main scanning and the sub scanning in the above embodiment, the present invention can be applied to a general printer which performs the sub scanning by moving the print medium.

[0055]

As described above, according to the present invention,
Since the position of the print head is adjusted by measuring the distance between the print head and the print medium in parallel with printing, the distance between the print head and the print medium is substantially adjusted according to the surface shape of the print medium. It can be kept constant, and stable printing of a quality that is unlikely to be influenced by the surface shape of the print medium can be performed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the principle of a printing element of an inkjet printer.

FIG. 2 is a schematic sectional view showing the principle of another printing element of the inkjet printer.

FIG. 3 is a perspective view showing a structure of a head drive mechanism portion of an inkjet printer according to an embodiment of the present invention.

FIG. 4 is a side view showing the structure of the carriage and the head portion of the embodiment as seen along the sub-scanning direction.

FIG. 5 is a side view showing the structure of the carriage and the head portion of the embodiment as seen along the main scanning direction.

FIG. 6 is a block diagram showing a hardware configuration of a control device of the embodiment.

7 is a block diagram showing a function of a portion for moving a print head in the Z direction in the control device of FIG.

FIG. 8 is a timing chart showing a temporal relationship between control for moving the print head in the Z direction and printing in the embodiment.

[Explanation of symbols]

 1 CPU 2 ROM 3 RAM 4 Host interface 5 Input interface 6 X direction motor drive circuit 7 Y direction motor drive circuit 8 Head drive circuit 9 Z direction motor drive circuit 12 Guide rail 13 Carriage 14 Main scanning member 15 Print head 16 Z direction movement Mechanism 17 Print medium 20 Distance sensor 29 Amplifier 30 A / D converter 31 Head movement amount calculation unit

Claims (6)

[Claims] 1. A serial printer for performing printing while scanning the surface of a print medium with a print head, a print head moving means for moving the print head in a direction of moving toward and away from the print medium, the print head and the print head. A distance measuring unit that outputs a signal that changes depending on the distance to the print medium, and to match the distance between the print head and the print medium with a predetermined ideal distance during scanning of the print head. To
A serial printer comprising: a distance adjusting unit that controls the print head moving unit based on an output signal from the distance measuring unit. 2. The serial printer according to claim 1, wherein the distance measuring unit moves together with the print head,
A serial printer having a distance sensor that measures a distance to the print medium at a predetermined position ahead of the print head in the scanning direction. 3. The serial printer according to claim 1, wherein the distance measuring unit moves together with the print head,
A serial printer comprising two distance sensors provided so as to measure a distance to the print medium at a predetermined position ahead of and behind the print head in the scanning direction. 4. The serial printer according to claim 1, wherein the distance adjusting unit determines a distance between the print head and the print medium at a future dot forming position based on an output signal of the distance measuring unit. Calculating a movement amount of the print head required to match the ideal distance, and controlling the print head moving means according to the movement amount before the print head reaches the future dot formation position. A serial printer characterized by. 5. The serial printer according to claim 1, wherein the distance adjusting unit moves the print head by the print head moving unit during scanning of the print head and outputs an output signal from the distance measuring unit. The serial printer is characterized in that the loading and the loading are alternately repeated, and the loading of the output signal is performed after a predetermined stabilization time has elapsed after the movement of the print head is completed. 6. The serial printer according to claim 1, wherein scanning of the print head is stopped when a change in an output signal from the distance measuring unit exceeds a predetermined threshold value. A serial printer further comprising stop means.