Dielectric heating device and printing system

Abstract

Provided is a dielectric heating device and a printing system, which provide a technique for adjusting the amount of heating of a heated object based on the dryness of the heated object without using a sensor for measuring the moisture content in the dielectric heating device. The dielectric heating device includes: an electrode unit having a first electrode and a second electrode that oppose a heated object, for heating the heated object; a voltage application unit that applies an alternating-current voltage to the first electrode and the second electrode; a current value detection unit that detects a current value of an alternating-current current flowing through the electrode unit; a phase difference detection unit that detects a phase difference between the alternating-current voltage and the alternating-current current; an impedance detection unit that detects the impedance of the electrode unit based on the current value and the phase difference; and a control unit that controls the output of the alternating-current voltage output to the electrode unit based on the impedance.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a dielectric heating device and a printing system. BACKGROUND

[0002] Regarding the dielectric heating device, in Patent Literature 1, an output of a high-frequency heating unit having a magnetron is feedback controlled based on a moisture content of a recording medium measured by a moisture content sensor. Thereby, it is possible to adjust a heating amount of the recording medium according to a dryness of the recording medium.

[0003] Patent Literature 1: Japanese Patent Application Laid-Open No. 2001-301131

[0004] However, in the technology of Patent Literature 1, it is necessary to provide the sensor for measuring the moisture content of the recording medium at a position corresponding to the recording medium. For example, in a case where the sensor is constituted by a capacitance type moisture meter, it is necessary to provide the sensor at a position capable of contacting the recording medium, in a case where the sensor is constituted by an optical type or a high-frequency type moisture meter, it is necessary to provide the sensor at a position capable of opposing the recording medium, and the like. SUMMARY

[0005] According to a first aspect of the present disclosure, there is provided a dielectric heating device. The dielectric heating device includes: an electrode unit having a first electrode and a second electrode opposing a heated object, for heating the heated object; a voltage application unit applying an alternating-current voltage to the first electrode and the second electrode; a current value detection unit detecting a current value of an alternating-current flowing through the electrode unit; a phase difference detection unit detecting a phase difference between the alternating-current voltage and the alternating-current; an impedance detection unit detecting an impedance of the electrode unit based on the current value and the phase difference; and a control unit controlling an output of the alternating-current applied to the electrode unit by controlling the voltage application unit based on the impedance.

[0006] According to a second aspect of the present disclosure, there is provided a printing system. The printing system includes: the dielectric heating device according to the above aspect, and an ejection unit ejecting a liquid to a printing medium and causing the liquid to adhere to the printing medium. The electrode unit heats the printing medium to which the liquid adheres as the heated object. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a perspective view showing a schematic configuration of a dielectric heating device.

[0008] Figure 2 is a block diagram showing a schematic configuration of a dielectric heating device.

[0009] Figure 3 is a perspective view showing a schematic configuration of an electrode unit.

[0010] Figure 4 is a schematic view illustrating a circuit formed by the electrode unit and the heated object.

[0011] Figure 5 is an equivalent circuit diagram of the dielectric heating device.

[0012] Figure 6 is a graph illustrating a change in impedance in the equivalent circuit.

[0013] Figure 7 is a graph illustrating an example of output control of the first alternating voltage by the control section.

[0014] Figure 8 is a graph illustrating a schematic configuration of the printing system.

[0015] Explanation of Reference Numerals

[0016] 20... electrode unit; 30... first electrode unit; 31... first electrode; 32... second electrode; 33... connecting member; 34... first coil; 35... first electric wire; 40... second electrode unit; 41... third electrode; 42... fourth electrode; 80... voltage application section; 81... first voltage application section; 82... second voltage application section; 83... inverter; 84... current detection section; 85... phase difference detection section; 86... amplifier; 87... rectifier section; 100... dielectric heating device; 110... substrate; 150... direct current power supply; 200... conveyance section; 205... roller section; 500... control section; 510... CPU; 511... current value detection section; 512... impedance detection section; 520... storage section; 600... printing system; 610... liquid ejection device; 620... ejection section; 630... medium conveyance section; 640... ejection control section. DETAILED DESCRIPTION

[0017] A. First Embodiment:

[0018] Figure 1 is a perspective view illustrating a schematic configuration of the dielectric heating device 100 in the first embodiment. In Figure 1 , arrows indicating X, Y, Z directions orthogonal to each other are shown. The X direction and the Y direction are directions parallel to a horizontal plane, and the Z direction is a direction along the vertical upward direction. The arrows indicating the X, Y, Z directions are also appropriately illustrated in the directions shown in other drawings Figure 1 corresponding to the first embodiment. In the following description, in the case where the direction is determined, the direction indicated by the arrow in each drawing is set to "+" and the opposite direction thereof is set to "-", and the positive and negative signs are used in the direction marks. Hereinafter, the +Z direction can be also referred to as "up" and the -Z direction can be also referred to as "down". In addition, in the present specification, the orthogonal includes a range of 90° ± 10°.

[0019] The dielectric heating device 100 includes an electrode unit 20 for heating an object to be heated OH, a conveyance unit 200 for conveying the object to be heated OH, a voltage application unit 80 for applying an alternating voltage to the electrode unit 20, and a control unit 500.

[0020] The dielectric heating device 100 of the present embodiment conveys the object to be heated OH by the conveyance unit 200 while heating the object to be heated OH by the electric field generated from the electrode unit 20. In the present embodiment, the dielectric heating device 100 dries the object to be heated OH by heating a sheet-shaped printing medium coated with a liquid as the object to be heated OH. As the printing medium, for example, paper, cloth, film, or the like is used. As the liquid coated to the printing medium, for example, various inks having water or an organic solvent as a main component are used. In the present embodiment, an aqueous ink having water as a main component is used as the liquid. Note that in the present specification, the main component of the liquid means a substance having a mass fraction of 50% or more among substances contained in the liquid. The liquid is coated to the printing medium by a liquid ejection device such as an inkjet printer, for example.

[0021] The control unit 500 is constituted by a computer including a CPU 510, a storage unit 520, and an input / output interface for inputting and outputting an external signal. The control unit 500 performs heating of the object to be heated OH in the dielectric heating device 100 by controlling each unit such as the conveyance unit 200 or the voltage application unit 80. In other embodiments, the control unit 500 can also be constituted by a combination of a plurality of circuits, for example.

[0022] The conveyance unit 200 in the present embodiment has two roller units 205 and a not-shown drive unit constituted by a motor or the like that drives the roller units 205. The conveyance unit 200 conveys the sheet-shaped object to be heated OH by driving the roller units 205. In other embodiments, the conveyance unit 200 can also be constituted by a belt for conveying while supporting the object to be heated OH and a drive unit that drives the belt, for example.

[0023] The dielectric heating device 100 in the present embodiment includes a first electrode unit 30 and a second electrode unit 40 as the electrode unit 20. The first electrode unit 30 has a first electrode 31 and a second electrode 32 that oppose the object to be heated OH. The second electrode unit 40 has a third electrode 41 and a fourth electrode 42 that oppose the object to be heated OH. As shown in FIG. 1, in the present embodiment, the second electrode unit 40 is disposed at a position in the -X direction of the first electrode unit 30. In the present embodiment, the first electrode unit 30 and the second electrode unit 40 each have the same configuration. Hereinafter, in the case where the first electrode unit 30 and the second electrode unit 40 are not distinguished, the two can also be simply referred to as the electrode unit 20. Figure 1

[0024] ​The dielectric heating device 100 in the present embodiment has the first voltage application section 81 and the second voltage application section 82 as the voltage application sections 80. The first voltage application section 81 is electrically connected to the first electrode unit 30, and applies an alternating voltage to the first electrode 31 and the second electrode 32. The second voltage application section 82 is electrically connected to the second electrode unit 40, and applies an alternating voltage to the third electrode 41 and the fourth electrode 42. One of the first electrode 31 or the second electrode 32 to which a potential is applied and the other of the third electrode 41 or the fourth electrode 42 to which a potential is applied can also be a reference potential. The reference potential is a constant potential that becomes a reference of a high-frequency voltage, and is, for example, a ground potential. Hereinafter, the alternating voltage applied to the first electrode unit 30 by the first voltage application section 81 is also referred to as a first alternating voltage. In addition, the alternating voltage applied to the second electrode unit 40 by the second voltage application section 82 is also referred to as a second alternating voltage.

[0025] In the present embodiment, the first voltage application section 81 and the second voltage application section 82 each have the same configuration. Hereinafter, in the case where the first voltage application section 81 and the second voltage application section 82 are not distinguished, both can also be simply referred to as the voltage application sections 80. In the present embodiment, each voltage application section 80 applies a high-frequency voltage to each electrode of each electrode unit 20. Note that, in the present specification, "high frequency" refers to a frequency of 1 MHz or more.

[0026] Figure 2 is a block diagram showing a schematic configuration of the dielectric heating device 100 in the present embodiment. As shown in Figure 2 The first voltage application section 81 in the present embodiment has an inverter 83, a current detection section 84, a phase difference detection section 85, an amplifier 86, and a rectification section 87. The first voltage application section 81 is electrically connected to the direct-current power supply 150. Note that, although illustration is omitted, the second voltage application section 82 also has the inverter 83 and the like described above, and is electrically connected to the direct-current power supply 150.

[0027] The inverter 83 provided in each voltage application section 80 is electrically connected to the direct-current power supply 150 and each electrode unit 20. The inverter 83 changes the voltage of the direct current input to the inverter 83 from the direct-current power supply 150 to an alternating voltage and outputs to the electrode unit 20. In more detail, the inverter 83 has a transistor for conversion, and by the action of the transistor, changes the voltage of the direct current input to the inverter 83 to an alternating voltage having a waveform of a rectangular wave shape with a frequency f1 and outputs to the electrode unit 20.

[0028] The current detection section 84 provided in each voltage application section 80 is configured as a resistor for detecting the alternating current flowing through each electrode unit 20. By applying an alternating voltage to the electrode unit 20, an alternating current having a waveform in a sinusoidal shape flows through the electrode unit 20, and thus the alternating current having the waveform in the sinusoidal shape is detected in the current detection section 84. The current detection section 84 outputs the detected alternating current to the amplifier 86. The amplifier 86 amplifies the current input from the current detection section 84 and outputs to the phase difference detection section 85 and the rectification section 87.

[0029] The phase difference detection section 85 provided in the first voltage application section 81 detects a phase difference between the phase of the alternating voltage applied to the first electrode 31 and the second electrode 32 and the phase of the alternating current flowing through the first electrode unit 30. Similarly, the phase difference detection section 85 provided in the second voltage application section 82 detects a phase difference between the phase of the alternating voltage applied to the third electrode 41 and the fourth electrode 42 and the phase of the alternating current flowing through the second electrode unit 40. The phase difference detection section 85 transmits the detected phase difference to the control section 500.

[0030] The rectification section 87 is configured by a diode, rectifies the alternating current input from the amplifier 86 and converts it into a direct current, and outputs the direct current to the control section 500. The voltage value of the direct current output from each rectification section 87 to the control section 500 is proportional to the amplitude of the alternating current flowing through each electrode unit 20.

[0031] As shown in FIGS. 1, 2, and 3, the dielectric heating device 100 includes a plurality of electrode units 20, a plurality of voltage application sections 80, a plurality of current detection sections 84, a plurality of phase difference detection sections 85, a plurality of rectification sections 87, a control section 500, and a display section 600. Figure 1 and Figure 2 As shown in FIGS. 1, 2, and 3, the dielectric heating device 100 includes a plurality of electrode units 20, a plurality of voltage application sections 80, a plurality of current detection sections 84, a plurality of phase difference detection sections 85, a plurality of rectification sections 87, a control section 500, and a display section 600.

[0032] In the present embodiment, the control section 500 functioning as the current value detection section 511 detects the effective value of the current flowing through the electrode unit 20 as the cell current value, based on the voltage value of the direct current voltage input from the rectifying section 87. The impedance detection section 512 detects the impedance Zr of the electrode unit 20, based on the cell current value, the phase difference detected by the phase difference detection section 85, and the voltage value of the alternating current voltage applied to each electrode of each electrode unit 20. For example, the impedance detection section 512 detects the impedance Zr of the first electrode unit 30, based on the cell current value of the first electrode unit 30, the phase difference detected by the phase difference detection section 85 provided in the first voltage application section 81, and the voltage value of the alternating current voltage applied to the first electrode 31 and the second electrode 32. As described later, the impedance Zr corresponds to the impedance of the circuit formed by the electrode unit 20 and the object to be heated OH. Hereinafter, the impedance Zr of the first electrode unit 30 can also be referred to as the first impedance Zrl. In addition, the impedance Zr of the second electrode unit 40 can also be referred to as the second impedance Zr2.

[0033] Figure 3 Fig. 1 is a perspective view showing the outline configuration of the first electrode unit 30 in the present embodiment. As described above, the first electrode unit 30 has the first electrode 31 and the second electrode 32. In addition, the first electrode unit 30 in the present embodiment has the first coil 34. Note that although not shown, in the present embodiment, the third electrode 41 and the fourth electrode 42 of the above-described second electrode unit 40 each have the same configuration as the first electrode 31 and the second electrode 32. In addition, the second electrode unit 40 has a second coil, not shown, which has the same configuration as the first coil 34. Hereinafter, in the case where the first coil 34 and the second coil are not distinguished from each other, both can be simply referred to as a coil.

[0034] The first electrode 31 and the second electrode 32 are conductive bodies, for example, formed of a metal, an alloy, a conductive oxide, or the like. The first electrode 31 and the second electrode 32 can be formed of the same material as each other, or can be formed of different materials. The first electrode 31 and the second electrode 32 can be disposed on a substrate or the like formed of a material having a dielectric property or a low conductivity, or can be supported by other members, for the purpose of securing the posture maintenance or strength thereof.

[0035] The first electrode 31 and the second electrode 32 are arranged such that the shortest distance between them is less than or equal to one-tenth of the wavelength of the electromagnetic field output from the first electrode unit 30. In this embodiment, the first electrode 31 has a boat-shaped form with the Y direction as its longer side and the X direction as its shorter side. The lower surface of the first electrode 31 has a curved shape convex in the -Z direction. When viewed along the Z direction, the first electrode 31 has an elongated elliptical shape in the Y direction. The second electrode 32 is flat in both the X and Y directions and has an elongated elliptical ring shape in the Y direction. When viewed along the Z direction, the second electrode 32 is arranged to surround the first electrode 31.

[0036] like Figure 1 As shown, both the first electrode 31 and the second electrode 32 are disposed on a substrate 110 arranged parallel to the X and Y directions. More specifically, the first electrode 31 is disposed such that the central portion of the lower surface of the first electrode 31 in the X and Y directions contacts the upper surface of the substrate 110. The second electrode 32 is disposed such that the lower surface of the second electrode 32 contacts the upper surface of the substrate 110. Therefore, in this embodiment, the central portion of the lower surface of the first electrode 31 and the lower surface of the second electrode 32 are disposed on the same plane. It should be noted that in this embodiment, the substrate 110 is jointly disposed on the first electrode unit 30 and the second electrode unit 40.

[0037] The first electrode 31 and the second electrode 32 are both arranged opposite each other in the Z direction relative to the heated material OH conveyed by the conveying unit 200 in the -Y direction. In this embodiment, both the first electrode 31 and the second electrode 32 are disposed above the heated material OH. That is, in this embodiment, the lower surfaces of the first electrode 31 and the second electrode 32 are opposite to the upper surface of the heated material OH. In addition, the aforementioned substrate 110 is disposed between the heated material OH and the first electrode 31 and the second electrode 32.

[0038] In this embodiment, the substrate 110 is formed of glass. The substrate 110 prevents liquids such as ink applied to the heated material OH from adhering to the first electrode 31 and the second electrode 32, or, in the case where the heated material OH is cloth, prevents fuzz from adhering to the first electrode 31 and the second electrode 32. Similarly, in this embodiment, the substrate 110 also prevents the adhesion of liquids or fuzz to the third electrode 41 and the fourth electrode 42 of the second electrode unit 40. In other embodiments, the substrate 110 may, for example, be formed of alumina.

[0039] Back Figure 3The first electrode 31 is electrically connected to the first voltage application unit 81 via the first electric wire 35, the first coil 34, and the inner conductor IC1 of the coaxial cable in this embodiment. The second electrode 32 is electrically connected to the first voltage application unit 81 via the connecting member 33 disposed at the upper portion of the second electrode 32, the outer conductor of the coaxial cable, and the like, which are not shown.

[0040] An electromagnetic field having a wavelength λ1 is generated from the first electrode 31 and the second electrode 32 in accordance with the frequency fl of the applied alternating voltage. The intensity of the electromagnetic field is very strong in the vicinity of the first electrode 31 and the second electrode 32, and becomes very weak at a distance. In this specification, the electromagnetic field generated in the vicinity of the first electrode 31 and the second electrode 32 by the application of the alternating voltage is also referred to as a "near-field". The "vicinity" of the first electrode 31 and the second electrode 32 refers to a range in which the distance from the first electrode 31 and the second electrode 32 is less than or equal to 1 / 2π of the wavelength of the generated electromagnetic field. A range farther than the "vicinity" is also referred to as a "distance". In this specification, the electromagnetic field generated at a distance from the first electrode 31 and the second electrode 32 by the application of the alternating voltage is also referred to as a "far-field". The far-field corresponds to an electromagnetic field used for communication by a general communication antenna or the like.

[0041] As described above, the first electrode 31 and the second electrode 32 are disposed in such a manner that the shortest distance therebetween is less than or equal to one-tenth of the wavelength of the electromagnetic field. Thereby, the electric field density of the electromagnetic field generated from the first electrode 31 and the second electrode 32 can be attenuated in the vicinity of the first electrode 31 and the second electrode 32. Therefore, by securing an appropriate distance between the heated object OH and the first electrode 31 and the second electrode 32, the liquid adhering to the heated object OH can be effectively heated by the electric field generated in the vicinity of the first electrode 31 and the second electrode 32, while the radiation of the far-field from the first electrode 31 and the second electrode 32 is suppressed. In particular, in this embodiment, the second electrode 32 is disposed in such a manner as to surround the first electrode 31 when viewed in the Z direction, and thus the radiation of the far-field from the first electrode 31 and the second electrode 32 can be further suppressed.

[0042] In this embodiment, one end of the first coil 34 is electrically connected in series to the first electrode 31 via the first electric wire 35, and the other end is electrically connected to the first voltage application unit 81 via the inner conductor IC1 of the coaxial cable. Figure 1 and Figure 2The first voltage application unit 81 shown is connected in series. In this embodiment, the first coil 34 is composed of a solenoid coil, and its length direction is arranged along the Z direction. The shape, length, cross-sectional area, number of turns, material, etc. of the first coil 34 are selected, for example, to form a resonant circuit with the first electrode 31 and the second electrode 32 resonating at a frequency f1, and to achieve impedance matching between the first electrode unit 30 and the first voltage application unit 81. It should be noted that, although the figure is omitted, in this embodiment, one end of the second coil is electrically connected to the third electrode 41 via a second wire, and the other end is connected in series with the second voltage application unit 82. In other embodiments, one end of the first coil 34 may be connected in series with the second electrode 32 instead of the first electrode 31. Similarly, one end of the second coil may be connected in series with the fourth electrode 42 instead of the third electrode 41.

[0043] An alternating voltage is applied to the first electrode unit 30 by the first voltage application unit 81, generating a high voltage at one end of the first coil 34. This increases the strength of the electric field generated from the first electrode 31 and the second electrode 32. It should be noted that the first coil 34 is preferably configured such that the distance between one end of the first coil 34 and the first electrode 31 is as small as possible. If the distance between one end of the first coil 34 and the first electrode 31 is large, the high voltage generated at one end of the first coil 34 may create an electric field between the first coil 34 and the first electrode 31, or between the first wire 35 and the second electrode 32, that does not contribute to the heating of the heated object OH, potentially reducing the effectiveness of increasing the strength of the electric field generated from the first electrode 31 and the second electrode 32. Conversely, by bringing the distance between one end of the first coil 34 and the first electrode 31 closer, the generation of such an electric field that does not contribute to the heating of the heated object OH can be suppressed, thus effectively increasing the strength of the electric field generated from the first electrode 31 and the second electrode 32. Similarly, the second coil can increase the strength of the electric field generated from the third electrode 41 and the fourth electrode 42. It should be noted that in other embodiments, the first electrode unit 30 or the second electrode unit 40 may not have a coil. For example, the first electrode 31 or the third electrode 41 may be formed into a curved shape, so that the first electrode 31 or the third electrode 41 can perform the same function as a coil.

[0044] Figure 4 This is a schematic diagram illustrating the circuit formed by the first electrode unit 30 and the heated substance OH attached to the liquid Lq in this embodiment. Figure 5 This is an equivalent circuit diagram of the dielectric heating device 100 in this embodiment. Figure 4 and Figure 5In the circuit shown, the first electrode 31 and the second electrode 32 of the first electrode unit 30 can be regarded as electrode plates that constitute a capacitor, respectively. Note that although not illustrated, even through the second electrode unit 40 and the object to be heated OH, a circuit identical to that shown in FIG. 1 is formed. Figure 4 and Figure 5 a circuit identical to that shown in FIG. 1.

[0045] Figure 4 and Figure 5 R a represents the resistance of the first electrode unit 30. Figure 5 L a represents the inductance of the first electrode unit 30. In the present embodiment, the inductance L a includes the inductance L Figure 4 of the first coil 34 and the parasitic inductance of each electrode of each electrode unit 20. c and the parasitic inductance of each electrode of each electrode unit 20. Figure 4 and Figure 5 C a represents the capacitance of the first electrode unit 30. In the present embodiment, the capacitance C a includes the parasitic capacitance of the first coil 34 and the capacitance between each electrode of each electrode unit 20. Figure 4 and Figure 5 R b represents the electrical resistance of the liquid Lq such as ink attached to the object to be heated OH. Figure 4 C b1 represents the parasitic capacitance between the first electrode 31 and the liquid Lq. Figure 4 C b2 represents the parasitic capacitance between the second electrode 32 of each electrode unit 20 and the liquid Lq. Figure 5 C b represents the sum of the parasitic capacitance C b1 and C b2 .

[0046] By heating and drying the liquid Lq on the object to be heated OH, the capacitance C a of each electrode unit 20 and the resistance R b of the liquid Lq change. In more detail, since the thickness of the liquid Lq on the object to be heated OH decreases as the liquid Lq dries, the capacitance of the capacitor constituted by the first electrode 31 and the second electrode 32 decreases, so the capacitance C a decreases. The reason for this is that the dielectric constant of the liquid Lq is higher than the dielectric constant of a vacuum. In addition, for example, in the case where the liquid Lq is a liquid containing water-based ink or the like, since the water content of the liquid Lq decreases by drying, the conductivity of the liquid Lq decreases, so the resistance R bIncrease. "Water content of liquid Lq" refers to the mass fraction of water in liquid Lq. It should be noted that the drying capacitance C of liquid Lq... b It also decreases, but the magnitude of this decrease is related to the capacitance C. a The reduction in amplitude and resistance R b The increase is relatively small and can therefore be ignored.

[0047] Figure 5 The impedance Z in the equivalent circuit shown is represented by the following mathematical formula (1).

[0048]

Mathematical Formula 1

[0049] [Math.1]

[0050]

[0051] In the above mathematical formula (1), ω represents the angular frequency of the AC voltage applied to the first electrode 31 and the second electrode 32.

[0052] Figure 6 This means that in Figure 5 The diagram shows the change in impedance Z in the equivalent circuit due to the drying of liquid Lq. More specifically, in the case where cotton cloth is used as the heated material OH and yellow water-based ink is used as the liquid Lq, Figure 6 The graph shows the real part of the impedance Z on the vertical axis and the degree of drying of the liquid Lq on the horizontal axis. Figure 6 The “degree of drying progress” shown represents the reciprocal of the water content of liquid Lq. Figure 6 The curve is calculated by simulation based on the water content of liquid Lq and capacitance C. a and resistance R b The relationship will be used to calculate the capacitance C. a and resistance R b Substitute the value into the above mathematical formula (1) and plot the real part of the calculated impedance Z relative to the reciprocal of the water content. Figure 6 As the liquid Lq on the heated material OH dries, i.e., as the water content of the liquid Lq decreases, the real part of the impedance Z decreases. Therefore, the impedance Z is related to the degree of dryness of the heated material OH.

[0053] The above Figure 1 and Figure 2The control section 500 controls the output of the alternating current to the first electrode unit 30 by controlling the first voltage application section 81 based on the first impedance Zr1 detected by the impedance detection section 512 as described above. Hereinafter, the alternating current output to the first electrode unit 30 is also referred to as the first alternating current. The impedance Zr corresponds to the measured value of the impedance in the circuit formed by the electrode unit 20 and the heated object OH, and is related to the dryness of the heated object OH as with the impedance Z in the equivalent circuit described above. Therefore, by controlling the output of the first alternating current based on the first impedance Zr1, the amount of heating of the heated object OH is adjusted according to the dryness of the heated object OH. Similarly, in the present embodiment, the control section 500 controls the output of the alternating current to the second electrode unit 40 by controlling the second voltage application section 82 based on the second impedance Zr2. Hereinafter, the alternating current output to the second electrode unit 40 is also referred to as the second alternating current.

[0054] In the present embodiment, the control section 500 controls the output of the first alternating current based on the value of the real part of the first impedance Zr1. More specifically, the control section 500 first estimates the amount of liquid contained in the heated object OH based on the value of the real part of the first impedance Zr1, and estimates the dryness of the heated object OH. Then, the control section 500 stores the estimated dryness in the storage section 520, and controls the output of the alternating current based on the stored dryness. The estimated amount of liquid corresponds to the amount of liquid in the vicinity of the first electrode 31 and the second electrode 32 among the liquid adhering to the heated object OH. The amount of liquid contained in the heated object OH can be estimated as the weight, volume, thickness of the liquid, for example, or as a ratio with respect to a predetermined reference value such as weight.

[0055] More specifically, in the present embodiment, the control section 500 estimates the dryness of the heated object OH by estimating the amount of moisture of the liquid applied to the heated object OH as the amount of liquid contained in the heated object OH based on the value of the real part of the first impedance Zr1. The control section 500 estimates the amount of moisture of the liquid, for example, by referring to a relationship between the value of the real part of the impedance and the amount of moisture of the liquid based on an experimentally predetermined value of the real part of the impedance based on the value of the detected real part of the first impedance Zr1. In this case, the relationship between the value of the real part of the impedance and the amount of moisture of the liquid can be determined, for example, according to the material or thickness of the heated object OH or the type of the liquid.

[0056] In the present embodiment, the control section 500 controls the output of the second alternating current based on the value of the real part of the second impedance Zr2 as with the control of the output of the first alternating current based on the value of the real part of the first impedance Zr1. The estimated amount of liquid contained based on the second impedance Zr2 corresponds to the amount of liquid in the vicinity of the third electrode 41 and the fourth electrode 42 among the liquid adhering to the heated object OH.

[0057] Figure 7 is a graph illustrating an example of output control of the first alternating voltage by the control section 500 in the present embodiment. In Figure 7 , as examples of waveforms of the first alternating voltage, there are shown a waveform Wf1, a waveform Wf2, and a waveform Wf3. As Figure 7 indicated, the control section 500 outputs the alternating voltage of the waveform Wf1 at the dryness D1, the alternating voltage of the waveform Wf2 at the dryness D2, and the alternating voltage of the waveform Wf3 at the dryness D3 to the first electrode unit 30. The dryness becomes higher in the order of D1, D2, D3. Note that, Figure 7 the period T1 of the alternating voltage is shown in. The period T1 is the inverse of the frequency fl and is proportional to the wavelength λ1.

[0058] The control section 500 in the present embodiment controls the output of the first alternating current based on the first impedance Zr1 by causing the inverter 83 of the first voltage application section 81 to intermittently operate. In more detail, in the present embodiment, the control section 500 changes the ratio of the time during which the inverter 83 is caused to continuously operate and outputs the alternating voltage of the frequency fl to the first electrode unit 30 and the ratio of the time during which the inverter 83 is caused to stop operating and the output of the voltage to the first electrode unit 30 is stopped, in accordance with the dryness estimated based on the first impedance Zr1, within a prescribed time. More specifically, the control section 500 decreases the ratio of the time during which the alternating voltage is output to the first electrode unit 30 and increases the ratio of the time during which the output of the voltage to the first electrode unit 30 is stopped, in the case where the dryness is high. Conversely, the control section 500 increases the ratio of the time during which the alternating voltage is output to the first electrode unit 30 and decreases the ratio of the time during which the output of the voltage to the first electrode unit 30 is stopped, in the case where the dryness is low. For example, the dryness D2 is higher than the dryness D1, and therefore the waveform Wf2 has a smaller ratio of the time during which the alternating voltage is output to the first electrode unit 30 and a larger ratio of the time during which the voltage is not output to the first electrode unit 30, as compared with the waveform Wf1. Thus, the output of the first alternating current is controlled. Note that, although illustration is omitted, in the present embodiment, the control section 500 likewise controls the output of the second alternating current by controlling the inverter 83 of the second voltage application section 82 based on the second impedance Zr2.

[0059] In the present embodiment, the output of the first alternating current is 0 in the case where the dryness estimated based on the first impedance Zr1 is equal to or higher than a predetermined degree. In more detail, the control section 500 causes the output of the first alternating current to be 0 in the case where the dryness is equal to or higher than a reference dryness Ds. The reference dryness Ds is, for example, set to a dryness indicating that the heated object OH is sufficiently dried. In Figure 7In the example of FIG. 9, the dryness Dl and D2 are below the reference dryness Ds, and the dryness D3 is above the reference dryness Ds. Therefore, in the present embodiment, the control section 500 controls the inverter 83 so that the output of the first alternating current is 0 for a predetermined time by setting the ratio of the time during which the alternating voltage is output to the first electrode unit 30 to 0, in the case where the dryness is D3. Note that, for example, in a case where the dryness estimated on the basis of the impedance Zr becomes below the reference dryness Ds again after the output of the first alternating current is temporarily 0 by the conveyance of the heated object OH in a case where the portion where the amount of liquid adhering to the heated object OH is relatively large is positioned near the first electrode unit 30, the control section 500 causes the output of the first alternating current to be greater than 0 again. In the present embodiment, similarly, the control section 500 causes the output of the second alternating current to be 0 in a case where the dryness estimated on the basis of the second impedance Zr2 is above the reference dryness Ds.

[0060] In the present embodiment, the control section 500 estimates the temperature of the heated object OH on the basis of the detected impedance Zr. The control section 500 can estimate the temperature of the heated object OH, for example, from the cumulative value of the heat generation amount estimated on the basis of the impedance Zr. In more detail, the control section 500 estimates the heat generation amount at a certain time by referring to the relationship between the impedance and the heat generation amount in the liquid adhering to the heated object OH, which is predetermined by experiment, on the basis of the impedance Zr at the time. Then, the control section 500 can estimate the cumulative value of the heat generation amount described above by calculating the time integral value of the heat generation amount from the start of heating to the present time on the basis of the estimated heat generation amount. Thus, the control section 500 can estimate the temperature of the liquid, and thereby the temperature of the heated object OH, on the basis of the specific heat of the liquid and the cumulative value of the heat generation amount estimated.

[0061] In the present embodiment, the control section 500 causes the output of the first alternating current to be greater than the output of the second alternating current in a case where the dryness of the heated object OH in the vicinity of the first electrode unit 30 is lower than the dryness of the heated object OH in the vicinity of the second electrode unit 40. Conversely, the control section 500 causes the output of the first alternating current to be smaller than the output of the second alternating current in a case where the dryness in the vicinity of the first electrode unit 30 is higher than the dryness in the vicinity of the second electrode unit 40. Thus, in the heated object OH, it is possible to increase the amount of heating of the portion where the dryness is low and to decrease the amount of heating of the portion where the dryness is high. Therefore, even in a case where the amount of liquid adhering to the heated object OH is deviated, it is possible to increase the likelihood of uniformly heating the heated object OH. In the present embodiment, as used in the above description, the "dryness" refers to the ratio of the volume of the heated object OH to the volume of the heated object OH in a case where the heated object OH is completely dried. Figure 7As described above, the first voltage application section 81 and the second voltage application section 82 are individually controlled based on the dryness, whereby the magnitude relationship of the output of the first alternating current and the output of the second alternating current is realized. In other embodiments, the control section 500 can also, for example, compare the dryness in the vicinity of the first electrode unit 30 with the dryness in the vicinity of the second electrode unit 40, and based on the comparison result, change the magnitude relationship of the output of the first alternating current and the output of the second alternating current.

[0062] According to the dielectric heating device 100 in the first embodiment described above, the control section 500 controls the output of the first alternating current by controlling the first voltage application section 81 based on the impedance Zr of the first electrode unit 30 having the first electrode 31 and the second electrode 32 opposed to the heated object OH. According to such a manner, the output of the first alternating current is controlled based on the impedance Zr related to the dryness of the heated object OH, and thus the output of the first alternating current is adjusted according to the dryness. Therefore, even if a sensor that measures the water content of the heated object OH is not provided at a position corresponding to the heated object OH, it is possible to adjust the amount of heating of the heated object OH according to the dryness of the heated object OH.

[0063] In addition, according to the present embodiment, the control section 500 estimates the dryness of the heated object OH based on the impedance of the first electrode unit 30, and stores the estimated dryness in the storage section 520. Thereby, it is possible to display the dryness stored in the storage section 520 on a display section not shown, and control the output of the first alternating current based on the dryness stored in the storage section 520.

[0064] In addition, according to the present embodiment, the control section 500 sets the output of the first alternating current to 0 in a case where the dryness of the heated object OH is equal to or greater than a predetermined degree. Thereby, it is possible to suppress discoloration or scorching of the heated object OH due to the heated object OH being heated in a sufficiently dry state.

[0065] In addition, according to the present embodiment, the control section 500 estimates the temperature of the heated object OH based on the first impedance Zr1. Therefore, it is possible to acquire the temperature of the heated object OH without providing a temperature sensor for measuring the temperature of the heated object OH. Thereby, for example, in a case where a resin component is included in ink adhering to the heated object OH, it is possible to estimate the degree of melting of the resin component based on the estimated temperature of the heated object OH in a case where the pigment or the like component included in the ink is fixed to the heated object OH.

[0066] In addition, according to the present embodiment, the first electrode unit 30 has the first coil 34 electrically connected in series with either one of the first electrode 31 or the second electrode 32. Thereby, the strength of the electric field generated from the first electrode 31 and the second electrode 32 at the time of voltage application can be increased by the first coil 34. Thus, the heating of the heated object OH can be performed more efficiently.

[0067] In addition, according to the present embodiment, the first voltage application section 81 has the inverter 83 that converts the direct current voltage output from the direct current power supply 150 into an alternating current voltage and outputs to the first electrode unit 30. Thereby, the first voltage application section 81 can achieve the possibility of the miniaturization or the improvement of the power efficiency of the first voltage application section 81, for example, compared to the case where it is constituted by a high frequency power supply circuit having an analog amplifier and a transformer.

[0068] In addition, according to the present embodiment, the control section 500 controls the output of the first alternating current by causing the inverter 83 to operate intermittently based on the impedance of the first electrode unit 30. Thus, the output of the first alternating current can be controlled simply.

[0069] B. Second Embodiment:

[0070] Figure 8 is a diagram showing an outline configuration of a printing system 600 as a second embodiment. The printing system 600 has the dielectric heating device 100 explained in the first embodiment and a liquid ejection device 610.

[0071] The liquid ejection device 610 in the present embodiment is constituted as an inkjet printer and has an ejection section 620 that ejects a liquid to a print medium, a medium conveying section 630 that conveys the print medium, and an ejection control section 640 that controls the ejection section 620 and the medium conveying section 630. The ejection section 620 is constituted by a liquid ejection head of a piezoelectric method or a thermal method, for example. The medium conveying section 630 is constituted by a roller or the like, similarly to the conveying section 200, for example. The ejection control section 640 is constituted by a computer or the like, similarly to the control section 500 of the dielectric heating device 100, for example. The ejection control section 640 conveys the print medium while ejecting and adhering the liquid to the print medium by controlling the ejection section 620 and the medium conveying section 630.

[0072] The dielectric heating device 100 heats the print medium to which the liquid ejected by the ejection section 620 is adhered as the heated object OH as explained in the first embodiment. That is, the first electrode unit 30 or the second electrode unit 40 heats the print medium to which the liquid is adhered as the heated object OH. Note that, as Figure 8The heated object OH can also be continuously transported from the liquid ejection device 610 to the dielectric heating device 100. In this case, for example, the transport section 200 of the dielectric heating device 100 can also function as a medium transport section 630. Alternatively, the heated object OH can not be continuously transported from the liquid ejection device 610 to the dielectric heating device 100. For example, after the print medium to which the liquid ejected by the liquid ejection device 610 is attached is temporarily wound in a roll shape, the wound print medium can be moved to the dielectric heating device 100 by a robot or the like. In this case, the wound print medium is unwound while being transported as the heated object OH by the transport section 200, whereby the heated object OH in the dielectric heating device 100 can be heated.

[0073] According to the second embodiment described above, even if the sensor that measures the moisture content of the heated object OH is not provided at a position corresponding to the heated object OH, the amount of heating of the heated object OH can be adjusted in accordance with the dryness of the heated object OH.

[0074] C. Other Embodiments

[0075] (C-1) In the above-described embodiments, the control section 500 can not estimate the dryness of the heated object OH based on the detected impedance Z.

[0076] (C-2) In the above-described embodiments, the control section 500 estimates the dryness by estimating the amount of liquid contained in the heated object OH based on the detected impedance Zr. In contrast, the control section 500 can not estimate the dryness by estimating the amount of liquid contained in the heated object OH.

[0077] (C-3) In the above-described embodiments, the output of the first alternating current is 0 when the dryness estimated based on the first impedance Zr1 is equal to or higher than the reference dryness Ds. In contrast, the output of the first alternating current can not be 0 when the dryness estimated based on the first impedance Zr1 is equal to or higher than the reference dryness Ds. Similarly, the output of the second alternating current can not be 0 when the dryness estimated based on the second impedance Zr2 is equal to or higher than the reference dryness Ds.

[0078] (C-4) In the above-described embodiments, the control section 500 estimates the temperature of the heated object OH based on the impedance Zr. In contrast, the control section 500 can not estimate the temperature of the heated object OH based on the impedance Zr.

[0079] (C-5) In the above-described embodiment, the first voltage application section 81 has the inverter 83. In contrast, the first voltage application section 81 can not have the inverter 83, and can be configured as a high-frequency power supply circuit having an analog amplifier and a transformer, for example. Similarly, the second voltage application section 82 can not have the inverter 83.

[0080] (C-6) In the above-described embodiment, the control section 500 controls the output of the first alternating current by causing the inverter 83 to intermittently operate based on the first impedance Zr1. In contrast, the control section 500 can control the output of the first alternating current without causing the inverter 83 to intermittently operate. For example, the control section 500 can control the output of the first alternating current by causing the amplitude of the alternating voltage applied to the first electrode unit 30 to vary based on the first impedance Zr1. Similarly, the control section 500 can control the output of the second alternating current without causing the inverter 83 to intermittently operate based on the second impedance Zr2.

[0081] (C-7) In the above-described embodiment, the first electrode unit 30 and the second electrode unit 40 are provided as the electrode unit 20, and the first voltage application section 81 and the second voltage application section 82 are provided as the voltage application section 80. In addition to this, one or more other electrode units 20 can be provided as the electrode unit 20, and one or more other voltage application sections 80 that apply an alternating voltage to each electrode unit 20 can be provided as the voltage application section 80. In addition, only the first electrode unit 30 can be provided as the electrode unit 20, and only the first voltage application section 81 can be provided as the voltage application section 80.

[0082] (C-8) In the above-described embodiment, the control section 500 can control the output of the alternating current output to the electrode unit 20 by controlling the voltage application section 80 based on print information of the print medium in a case where the print medium to which the liquid is attached is heated as the heated object OH. In this case, the print information can include, for example, any one of information related to the kind of the liquid attached to the heated object OH, attachment amount information related to the attachment amount of the liquid, and pattern information related to a print pattern. Thus, since the output of the alternating current adjusted based on the impedance Zr can be further adjusted based on the print information, the possibility of uniformly drying the heated object OH increases. The print information can be stored in the storage section 520 in advance, or can be acquired from the liquid ejection device 610, for example.

[0083] (C-9) In the above-described embodiment, the second electrode 32 is arranged so as to surround the first electrode 31 as viewed in the Z direction. In contrast, for example, the first electrode 31 and the second electrode 32 can also be arranged so as to abut each other as viewed in the Z direction, or can be arranged so as to sandwich the object to be heated OH in the Z direction by the first electrode 31 and the second electrode 32. In this case, the shapes of the first electrode 31 and the second electrode 32 can be arbitrary, and can be a circular shape, an elliptical shape, a rectangular shape, a polygonal shape, or the like. Further, the areas of the first electrode 31 and the second electrode 32 can be the same as or different from each other as viewed in the Z direction. The first electrode 31 and the second electrode 32 are preferably arranged so as not to overlap each other as viewed in the Z direction. Likewise, the third electrode 41 and the fourth electrode 42 can also be arranged so as to abut each other as viewed in the Z direction, or can be arranged so as to sandwich the object to be heated OH in the Z direction by the third electrode 41 and the fourth electrode 42, for example.

[0084] (C-10) In the above-described embodiment, the electrode unit 20 can also be configured to be able to reciprocate in a direction intersecting the direction in which the object to be heated OH is transported. For example, the electrode unit 20 can be supported by a not-illustrated drive section configured of a belt mechanism or a ball screw mechanism, and can reciprocate in the X direction.

[0085] (C-11) In the above-described embodiment, the control section 500 controls the output of the alternating current to the electrode unit 20 based on the value of the real part of the impedance Zr. In contrast, the control section 500 can also control the output of the alternating current based on the value of the imaginary part of the impedance Zr, or, instead, based on the absolute value of the impedance Zr represented as the vector sum of the real part and the imaginary part on the complex plane, in addition to the value of the real part of the impedance Zr, for example. Thereby, for example, even in a case where the degree of drying cannot be uniformly determined based on only the value of the real part of the impedance Zr, depending on the kind of the liquid attached to the object to be heated OH or the like, it is possible to appropriately control the output of the alternating current to the electrode unit 20. The reason for this is that the value of the imaginary part of the impedance Zr changes periodically in accordance with the drying of the liquid on the object to be heated OH, more specifically, in the direction of rotation to the left in the Smith chart. In this case, for example, it is possible to first extract candidates for the degree of drying based on the value of the real part of the impedance Zr, and then estimate the degree of drying of one of the extracted candidates based on the value of the imaginary part of the impedance Zr.

[0086] (C-12) In the above-described embodiment, a high-frequency voltage is applied to the electrode unit 20. In contrast, the frequency of the alternating voltage applied to the electrode unit 20 can also be other than high frequency, as long as the object to be heated OH can be heated. The frequency of the alternating voltage in this case is preferably, for example, 100 kHz or higher and less than 1 MHz.

[0087] D. Other modes:

[0088] The present disclosure is not limited to the above-described embodiments and can be implemented in various ways without departing from the scope of the gist thereof. For example, the present disclosure can be implemented in the following manner. The technical features in the above-described embodiments corresponding to the technical features in each of the following modes can be appropriately replaced or combined in order to solve part or all of the technical problems of the present disclosure or in order to achieve part or all of the effects of the present disclosure. In addition, the technical features can be appropriately deleted from the present specification when not described as essential.

[0089] (1) According to a first mode of the present disclosure, a dielectric heating device is provided. The dielectric heating device includes an electrode unit having a first electrode and a second electrode opposed to a heated object, for heating the heated object; a voltage application unit that applies an alternating-current voltage to the first electrode and the second electrode; a current value detection unit that detects a current value of an alternating-current flowing through the electrode unit; a phase difference detection unit that detects a phase difference between the alternating-current voltage and the alternating-current; an impedance detection unit that detects an impedance of the electrode unit based on the current value and the phase difference; and a control unit that controls an output of the alternating-current to the electrode unit by controlling the voltage application unit based on the impedance.

[0090] According to such a mode, the output of the alternating-current to the electrode unit is controlled based on the impedance of the electrode unit related to the dryness, and thus the output of the alternating-current to the electrode unit is controlled according to the dryness. Therefore, even if a sensor that measures the water content of the heated object is not provided at a position corresponding to the heated object, it is possible to adjust the amount of heating of the heated object according to the dryness of the heated object.

[0091] (2) In the above-described mode, a storage unit can be provided, and the control unit can estimate the dryness of the heated object based on the impedance, and store the estimated dryness in the storage unit. According to such a mode, it is possible to display the dryness stored in the storage unit on a display unit, and control the output of the alternating-current applied to the electrode unit based on the dryness stored in the storage unit.

[0092] (3) In the above-described mode, the control unit can estimate the dryness by estimating the amount of liquid contained in the heated object based on the impedance.

[0093] (4) In the above-described mode, the control unit can set the output of the alternating-current to 0 when the dryness is equal to or greater than a predetermined degree. According to such a mode, it is possible to suppress discoloration or scorching of the heated object OH due to heating of the heated object OH in a sufficiently dry state.

[0094] (5) In the above-described aspect, the control section can estimate the temperature of the heated object based on the impedance. According to this aspect, it is possible to obtain the temperature of the heated object without providing a temperature sensor that measures the temperature of the heated object.

[0095] (6) In the above-described aspect, the electrode unit can have a coil electrically connected in series with either the first electrode or the second electrode. According to this aspect, the strength of the electric field generated by the first electrode and the second electrode at the time of voltage application can be increased by the coil. Thus, the heated object can be heated more efficiently.

[0096] (7) In the above-described aspect, the voltage application section can have an inverter that converts the voltage of direct current input from a direct current power supply into alternating current and outputs the voltage to the electrode unit. According to this aspect, the possibility of achieving the miniaturization of the voltage application section and the improvement of power efficiency is increased.

[0097] (8) In the above-described aspect, the control section can control the output of the alternating current by causing the inverter to intermittently operate based on the impedance. According to this aspect, the output of the alternating current output to the electrode unit can be easily controlled.

[0098] (9) According to a second aspect of the present disclosure, a printing system is provided. The printing system includes the dielectric heating device of the above-described aspect and an ejection section that ejects a liquid to a print medium and causes the liquid to adhere to the print medium. The electrode unit heats the print medium to which the liquid adheres as the heated object.

Claims

1. A dielectric heating device, characterized by, Possessing: an electrode unit having a first electrode and a second electrode opposed to a heated object, for heating the heated object; a voltage application section that applies an alternating voltage to the first electrode and the second electrode; a current value detection section that detects a current value of an alternating current flowing through the electrode unit; a phase difference detection section that detects a phase difference between the alternating voltage and the alternating current; an impedance detection section that detects an impedance of the electrode unit based on the current value and the phase difference; and a control section that controls an output of the alternating current output to the electrode unit by controlling the voltage application section based on the impedance, the electrode unit has a coil electrically connected in series with either the first electrode or the second electrode.

2. The dielectric heating device according to claim 1, wherein the dielectric heating device possesses a storage section, the control section estimates a dryness of the heated object based on the impedance, and stores the estimated dryness in the storage section.

3. The dielectric heating device according to claim 2, wherein the control section estimates the dryness by estimating an amount of liquid contained in the heated object based on the impedance.

4. The dielectric heating device according to claim 2 or 3, wherein the control section sets the output of the alternating current to 0 in a case where the dryness is above a predetermined degree.

5. The dielectric heating device according to claim 1, wherein the control section estimates a temperature of the heated object based on the impedance.

6. The dielectric heating device according to claim 1, wherein the voltage application section has an inverter that converts a voltage of direct current input from a direct current power supply into alternating current and outputs to the electrode unit.

7. The dielectric heating device according to claim 6, wherein the control section controls the output of the alternating current by causing the inverter to intermittently operate based on the impedance.

8. A printing system characterized by, Possessing: the dielectric heating device according to any one of claims 1 to 7; and an ejection section that ejects a liquid to a print medium and causes the liquid to adhere to the print medium, the electrode unit heats the print medium to which the liquid adheres as the heated object.

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