JP2022124601A - Printing device - Google Patents

Abstract

To improve measurement accuracy of an acoustic wave sensor.SOLUTION: A printing device comprises a platen, a printing head, an acoustic wave sensor, a reflection plane, a carriage, a moving mechanism and a control part. The control part drives the moving mechanism, and moves the acoustic wave sensor to a first position with respect to the reflection plane; obtains first transmission/reception times in the first position and in the reflection plane; drives the moving mechanism and moves the acoustic wave sensor to a second position with respect to the reflection plane; obtains second transmission/reception times in the second position and in the reflection plane; and calculates a sound speed from a relation between the positions and the transmission/reception times in the positions.SELECTED DRAWING: Figure 4

Description

The present invention relates to printing devices.

Conventionally, as shown in Patent Document 1, a carriage on which a print head and an acoustic wave sensor are mounted, and a platen portion including a flat portion having a plurality of flat surfaces arranged at different distances from the acoustic wave sensor. is known.
In the printing apparatus, a relational expression is derived from the distance difference between the planes of the flat portion and the transmission and reception time between the planes obtained based on the measurement by the sound wave sensor, and based on the relational expression, the print head and the distance from the medium supported by the platen.

Japanese Patent Application Laid-Open No. 2020-124830

However, since the flat portion of the printing apparatus has a stepped shape, foreign matter such as paper dust tends to accumulate on each flat surface, and when the sound waves transmitted from the sound wave sensor are reflected by the foreign matter, the measurement accuracy of the sound wave sensor decreases. There is a problem of doing so.

A printing apparatus includes a platen having a platen surface on which a medium is supported, a print head arranged to face the platen and ejecting liquid onto the medium, and a print head arranged to face the platen to transmit sound waves. a sound wave sensor capable of receiving the reflected sound wave; a reflective surface disposed facing the sound wave sensor for reflecting the sound wave transmitted from the sound wave sensor; and the print head and the sound wave sensor. A carriage, a moving mechanism capable of moving the carriage in a height direction with respect to the platen, and a control unit, wherein the control unit drives the moving mechanism to move the sound wave sensor with respect to the reflecting surface. is moved to a first position, a first transmission/reception time of the sound wave at the first position and the reflecting surface is obtained, the moving mechanism is driven, and the sound wave sensor is moved to a second position with respect to the reflecting surface It is moved, the second transmission/reception time of the sound wave at the second position and the reflecting surface is acquired, and the speed of sound is calculated from the relationship between each of the positions and the transmission/reception time at each of the positions.

Schematic diagram showing the configuration of a printing apparatus. FIG. 2 is a partially enlarged view showing the configuration of the printing apparatus; 4 is a block diagram showing the configuration of a control unit in the printing apparatus; FIG. The schematic diagram which shows the calculation method of sound velocity. The graph which shows an example of the relational expression of each transmission-and-reception time in each position and each position.

First, the configuration of the printer 1 will be described. The printing device 1 is a printer that prints an image or the like on a medium P such as paper, for example.

As shown in FIGS. 1 and 2, the printing apparatus 1 includes a platen 10 on which a medium P is supported, a printing unit 20 for printing an image or the like by ejecting liquid onto the medium P supported by the platen 10, a medium and a transport unit 30 that transports P.

The conveying section 30 includes a sending section 31 and a winding section 32 . The medium P is conveyed from a feeding unit 31 that feeds the medium P to a winding unit 32 that winds the medium P through the platen 10 . That is, the transport path of the medium P in the printing apparatus 1 is from the delivery unit 31 to the winding unit 32, and the platen 10 is a support unit for the medium P provided in the transport path.
The platen 10 includes a first platen 10a, a second platen 10b, and a third platen 10c. placed. In addition, the platen 10 may be configured to incorporate a heater.
The transport section 30 further includes a transport roller pair 33 . The transport roller pair 33 is arranged between the first platen 10a and the second platen 10b in the transport path. The transport roller pair 33 has a driving roller 33a and a driven roller 33b, and transports the medium P while sandwiching the medium P between the driving roller 33a and the driven roller 33b.

In this embodiment, the configuration is such that printing can be performed on a roll-shaped medium P, but the configuration is not limited to this configuration, and a configuration in which printing is performed on a cut-sheet medium P may be employed. In the case of a configuration in which recording is performed on a cut-sheet medium P, a so-called paper feed tray, paper feed cassette, or the like is used as the feeding section 31 for the medium P, for example. In addition, as a collection unit for the medium P, other than the winding unit 32, for example, a receiving unit for discharge, a paper discharge tray, a paper discharge cassette, and the like are used.

Here, in FIG. 1, the X-axis and the Y-axis are horizontal directions perpendicular to each other, and the Z-axis is a vertical direction. In the printing apparatus 1 of this embodiment, the platen surface 11 of the second platen 10b on which the medium P is supported is the XY plane (horizontal plane).

A printing unit 20 is arranged to face the platen 10 (second platen 10b). The printing section 20 includes a carriage 21 and a print head 22 .
The print head 22 is arranged to face the second platen 10 b and ejects liquid (for example, ink) as droplets onto the medium P supported on the platen surface 11 .
The print head 22 is mounted on the carriage 21 . The carriage 21 is supported by guides extending in the direction along the X-axis. The carriage 21 is configured to be reciprocatable along the guide shaft by being driven by a drive motor. The print head 22 performs printing (recording) on the medium P by ejecting liquid while reciprocating together with the carriage 21 .

The printing apparatus 1 also includes a moving mechanism 23 capable of moving the carriage 21 in the height direction with respect to the platen 10 (second platen 10b). In this embodiment, the carriage 21 is provided with a cam mechanism as the moving mechanism 23 . Thereby, the carriage 21 can move in the direction along the Z-axis with respect to the platen surface 11 to adjust the distance (platen gap) between the print head 22 and the platen surface 11 . Note that the moving mechanism 23 may have a configuration such as a ball screw.

A sound wave sensor 40 is arranged facing the platen 10 (second platen 10b). The sound wave sensor 40 of this embodiment is mounted on the carriage 21 . Acoustic sensors 40 are positioned in the +X and -X directions of printhead 22 (FIG. 2). The sound wave sensor 40 reciprocates as the carriage 21 moves.
The sound wave sensor 40 is a sensor capable of transmitting sound waves and receiving reflected sound waves. The sound wave sensor 40 measures a transmission/reception time from transmitting a sound wave to receiving a sound wave reflected from an object. Then, the distance DP between the sound wave sensor 40 and the object can be measured from the detected transmission/reception time. As a result, for example, by transmitting a sound wave to the medium P conveyed to the platen surface 11 and receiving the sound wave reflected by the medium P, when wrinkles are generated in the medium P, transmission and reception of the sound wave can be performed. Since the time is shortened and the distance between the print head 22 and the medium P is shortened, contact between the print head 22 and the medium P can be avoided, and contamination of the print head 22 and deterioration of the image quality of the medium P can be suppressed. can.
By arranging the sound wave sensor 40 ahead of the print head 22 in the moving direction, the distance can be detected before the print head 22 reaches the wrinkles of the medium P regardless of the direction in which the carriage 21 moves. can be measured.

Measurement by the sound wave sensor 40 is performed by a so-called pulse echo method. Specifically, based on instructions from the control unit 100 (FIG. 3), the sound wave is reflected from the object from the time the sound wave is transmitted from the piezoelectric vibrator arranged at the tip of the sound wave sensor 40, and the piezoelectric vibrator Measure the time it takes to be received. That is, the transmission/reception time measured by the sound wave sensor 40 includes the time for the sound wave to travel back and forth with respect to the object.

The sound wave is transmitted from the piezoelectric vibrator by, for example, applying an alternating voltage to the piezoelectric vibrator to deform the piezoelectric vibrator, thereby vibrating the piezoelectric vibrator. Here, the piezoelectric vibrator may deform in the thickness direction. Further, reception of sound waves by the piezoelectric vibrator is performed by vibrating and deforming the piezoelectric vibrator due to the sound waves. This is done by converting the amount of electric charge generated by polarization into a voltage value by means of a charge amplifier.

The output from the sound wave sensor 40 is the transmission/reception time obtained from the change in voltage value obtained by converting the amount of charge generated by the piezoelectric vibrator into a voltage value with a charge amplifier.

FIG. 3 is a block diagram showing the configuration of the control section 100 of the printing apparatus 1. As shown in FIG.
As shown in FIG. 3 , the printing device 1 includes a control unit 100 that controls various operations performed by the printing device 1 . The control unit 100 has a CPU 101 , a memory 102 , a control circuit 103 and an I/F (interface) 104 . A CPU 101 is an arithmetic processing unit. The memory 102 is a storage device that secures an area for storing programs of the CPU 101 or a work area, and has storage elements such as RAM and EEPROM. When recording data or the like is acquired from an external device such as an information processing terminal via the I/F 104, the CPU 101 controls the print head 22, the carriage 21 (driving motor), the transport unit 30, the moving mechanism 23, the sound wave It controls each drive unit such as the sensor 40 .

Here, the measurement of the distance by the sound wave sensor 40 is generally calculated by multiplying the above-mentioned transmission/reception time by half by the sound wave propagation speed. However, although sound waves cause a change in the density of air, which is a medium, to propagate, the propagation speed c of sound waves is defined by c = √ (specific heat ratio/atmospheric pressure/medium density). Thus, the propagation speed c of the sound wave changes depending on the atmospheric pressure and the density of the air. That is, since the air pressure and the density of the air are greatly changed by the temperature and humidity, the propagation speed c of the sound wave is greatly changed by the temperature and humidity.
Also, the propagation speed c of sound waves in dry air is simply given by c≈331.5×((273+θ)/273). where θ is the temperature (°C). That is, even in dry air, the propagation speed of sound waves varies depending on the air temperature. As a result, in an environment including the print head 22, the platen 10, and the like, heat is generated by the driving of each driving unit, which may cause a measurement error.
Therefore, in the present embodiment, in order to eliminate the measurement error caused by the sound wave sensor 40 described above, the distance is calculated using a relational expression from the transmission/reception time without using the propagation speed of the sound wave, which is simply used. Specifically, the transmission/reception time is measured based on the known distance, the relational expression between the transmission/reception time and the distance is derived, and the transmission/reception time obtained by measuring the object is used to calculate the relational expression. Calculate the distance. That is, the speed of sound is calculated from the above relational expression.

A method of calculating the relational expression (a method of calculating the speed of sound) will be described below.
As shown in FIG. 4, the control unit 100 drives the moving mechanism 23 to move the positions (reference position Pt0, first position Pt1, second position Pt2) at different distances between the platen surface 11 as a reflecting surface and the sound wave sensor 40. , to the third position Pt3). In the example of FIG. 4, the reference position Pt0, the first position Pt1, the second position Pt2, and the third position Pt3 increase in order from the platen surface 11 in the +Z direction.

Then, the sound wave sensor 40 is driven at each position to acquire the transmission/reception time at each position.
Here, the distance between the platen surface 11 and the sensor surface 40a of the sound wave sensor 40 at the reference position Pt0 is D0. The distance between the platen surface 11 and the sensor surface 40a at the first position Pt1 is D1. The distance between the platen surface 11 and the sensor surface 40a at the second position Pt2 is D2. The distance between the platen surface 11 and the sensor surface 40a at the third position Pt3 is D3.
The distance difference between the reference position Pt0 and the first position Pt1 is (D1-D0), the distance difference between the first position Pt1 and the second position Pt2 is (D2-D1), and the second position Pt2 and The distance difference from the third position Pt3 is (D3-D2). These distance differences may or may not have the same dimensions.
The sensor surface 40a of the sound wave sensor 40 is arranged at the same height as the head surface 22a of the print head 22 from which the liquid is ejected.

Further, the inter-surface distance difference dDi, which is the difference between the distance D0 from the sensor surface 40a to the platen surface 11 at the reference position Pt0 and the distances from the sensor surfaces 40a at the first to third positions Pt1, Pt2, and Pt3, is dD1 at the first position Pt1, dD2 at the second position Pt2, and dD3 at the third position Pt3. That is, with the sensor surface 40a at the reference position Pt0 as a reference surface, the distance differences dD1, dD2, and dD3 from the sensor surface 40a at the other positions Pt1, Pt2, and Pt3 are dD1<dD2<dD3.
Each position Pt0, Pt1, Pt2, Pt3 is a position to move relative to the same position on the platen surface 11. FIG. That is, each of the positions Pt0, Pt1, Pt2, and Pt3 causes the carriage 21 to move with respect to the platen surface 11 only in the direction along the Z-axis.

Note that at least two points (eg, first position Pt1 and second position Pt2) may be used to move the sound wave sensor 40 to positions different from the reference position Pt0. In this embodiment, three different positions (first position Pt1, second position Pt2, and third position Pt3) are provided with respect to the reference position Pt0. A more accurate relational expression can be obtained by increasing the number of measurement positions. Further, four or more measurement positions may be set.

The distance differences (D1-D0), (D2-D1), and (D3-D2) should be sufficiently larger than the resolution of the sound wave sensor 40 and the processing accuracy of the moving mechanism 23, and are particularly limited. is not. The distance differences (D1-D0), (D2-D1), and (D3-D2) are, for example, 0.5 mm or 1.0 mm.

Distance differences dD1, dD2, and dD3 from the reference position Pt0 to the sensor surface 40a are, for example, 0.5 mm, 1.0 mm, and 1.5 mm. Further, distances D0, D1, D2, and D3 from the platen surface 11 at the reference position Pt0 and the first to third positions Pt1, Pt2, and Pt3 are given to the controller 100 in advance as known data. That is, the shape of the cam that constitutes the moving mechanism 23 is precisely measured in advance by a laser length measuring device or the like, and each distance D0, D1, D2, D3 is associated with the position of the cam. As a result, the distance differences dD1, dD2, and dD3 are also given to the controller 100 as known data.

Each transmission/reception time Ti measured by the sound wave sensor 40 at the reference position Pt0 and the first to third positions Pt1, Pt2, and Pt3 is the reference transmission/reception time T0 at the reference position Pt0, and the first transmission/reception time T1 at the first position Pt1. , a second transmission/reception time T2 at the second position Pt2, and a third transmission/reception time T3 at the third position Pt3.
Further, the transmission/reception time difference dTi, which is the difference between each transmission/reception time T1, T2, and T3 measured at each of the first to third positions Pt1, Pt2, and Pt3 and the transmission/reception time T0 measured at the reference position Pt0, is dT1 at the first position Pt1, dT2 at the second position Pt2, and dT3 at the third position Pt3. Here, dT1=T1-T0, dT2=T2-T0, and dT3=T3-T0.

The relational expression expresses the relationship between the distance difference dDi and the transmission/reception time difference dTi. The relational expressions are derived from 1/2 of the transmission/reception time differences dT1, dT2, and dT3 at the first to third positions Pt1, Pt2, and Pt3 and the known distance differences dD1, dD2, and dD3.

Assuming that the transmission/reception time T is an independent variable and the distance D is an explanatory variable, it can be inferred that the distance D has a linear relationship with the transmission/reception time T. can be expressed as where α represents the slope of D with respect to T, and β represents the intercept with the D axis.
D=α・T+β (1)

The method of deriving the relational expression is not particularly limited as long as it is a generally used method. The relational expression may be derived by linear fitting to the known distance differences dD1, dD2, dD3 and the measured transmission/reception time differences dT1, dT2, dT3 halved. The relational expression may be derived, for example, by the method of least squares. The relational expression may be obtained simply by dividing each known distance difference dD1, dD2, dD3 by 1/2 of the measured transmission/reception time difference dT1, dT2, dT3.

FIG. 5 shows a scatter diagram of known face-to-face distance differences dDi (dD1, dD2, dD3) and measured transmission/reception time differences dTi (dT1, dT2, dT3). A straight line 200 shown in FIG. 5 represents a relational expression for estimating the distance D with respect to the transmission/reception time T derived from the known inter-surface distance difference dDi and the measured transmission/reception time difference dTi.
Then, the slope α is calculated as the speed of sound.
In addition, the correlation coefficient between the actually measured transmission/reception time difference dTi and the inter-surface distance difference dDi and the relational expression obtained by the relational expression is calculated. It may be configured to measure the transmission/reception time difference dTi.
Such control is performed periodically. For example, it is performed in accordance with the timing of adjusting the platen gap before printing. Also, a plurality of platen gaps already prepared may correspond to each position (reference position Pt0, first position Pt1, second position Pt2, third position Pt3). By doing so, the measurement time can be shortened.

As control for preventing contact between the print head 22 and the medium P during printing, the control unit 100 obtains the distance DP from the sensor surface 40a (head surface 22a) to the medium P from a relational expression.
The distance DP to the medium P is calculated by substituting 1/2 of the transmission/reception time TPi obtained by measuring the medium P with the sound wave sensor 40 into the derived relational expression (1). be.
That is, when the transmission/reception time TPi to the medium P at the measurement position Pti measured by the sound wave sensor 40 is halved and substituted into the relational expression (1), the distance DPi to the medium P at the measurement position Pti is DPi=α・TPi/2+β.

For example, when the control unit 100 determines that the print head 22 will come into contact with the medium P based on the calculated distance DPi, the control unit 100 stops driving the carriage 21 . As a result, contamination of the print head 22 and degradation of image quality on the medium P can be suppressed.

As described above, according to the present embodiment, by using the flat platen surface 11 as the reflecting surface, the influence of foreign matter such as paper dust is reduced, the distance between the sound wave sensor 40 and the platen surface 11 becomes more accurate, and the sound wave sensor 40 measurement accuracy can be improved.
Further, by using the flat platen surface 11 as the reflective surface, the configuration of the platen 10 can be simplified compared to, for example, a configuration in which the platen is formed with a reflective surface having a plurality of stepped surfaces. It can be made small.
Moreover, even if the platen 10 is provided with a heating unit such as a heater, the influence of thermal expansion is small, and the distance between the sound wave sensor 40 and the platen surface 11 can be accurately measured.
Moreover, even in a configuration without a temperature/humidity sensor, an accurate sound velocity can be calculated.

In the present embodiment, the transmission/reception time Ti is measured sequentially from the first position Pt1 toward the third position Pt3, but the transmission/reception time Ti is not limited to this, and the transmission/reception time Ti is measured sequentially from the third position Pt3 toward the first position Pt1. may be measured.

Reference Signs List 1 printing device 10 platen 10a first platen 10b second platen 10c third platen 11 platen surface 20 printing unit 21 carriage 22 print head 23 movement mechanism , 30... Conveying section, 31... Sending section, 32... Winding section, 33... Conveying roller pair, 40... Sound wave sensor, 40a... Sensor surface, 100... Control section, 200... Straight line, Pt0... Reference position, Pt1... Third 1 position, Pt2... 2nd position, Pt3... 3rd position, P... Medium.

Claims (3)

a platen having a platen surface on which media is supported;
a print head disposed facing the platen for ejecting liquid onto the medium;
a sound wave sensor disposed facing the platen and capable of transmitting sound waves and receiving the reflected sound waves;
a reflective surface arranged to face the sound wave sensor and reflecting the sound wave transmitted from the sound wave sensor;
a carriage on which the print head and the sound wave sensor are mounted;
a moving mechanism capable of moving the carriage in a height direction with respect to the platen;
a control unit;
The control unit
driving the moving mechanism, moving the sound wave sensor to a first position with respect to the reflecting surface, acquiring a first transmission/reception time of the sound wave between the first position and the reflecting surface;
driving the moving mechanism, moving the sound wave sensor to a second position with respect to the reflecting surface, obtaining a second transmission/reception time of the sound wave between the second position and the reflecting surface;
A printing apparatus that calculates a speed of sound from a relationship between each position and each transmission/reception time at each position. The printing device according to claim 1, wherein
The control unit
Further, the printing apparatus moves the sound wave sensor to a third position with respect to the reflecting surface, obtains a third transmission/reception time of the sound wave between the third position and the reflecting surface, and calculates the speed of sound. The printing apparatus according to claim 1 or claim 2,
A printing apparatus, wherein the reflective surface is the platen surface.

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