Dielectric heating device and printing system

Abstract

To provide a technique in which in a dielectric heating device, the amount of heating of an object to be heated is adjusted according to the degree of dryness of the object to be heated without the use of a sensor for measuring a water content.SOLUTION: A dielectric heating device comprises: an electrode unit that has a first electrode and a second electrode facing an object to be heated and heats the object to be heated; a voltage application unit that applies AC voltage to the first electrode and the second electrode; a current value detection unit that detects the current value of AC current flowing in the electrode unit; a phase difference detection unit that detects the phase difference between the AC voltage and the AC 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 voltage application unit based on the impedance to control output of AC power output to the electrode unit.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Regarding a dielectric heating device, Patent Document 1 discloses that the output of a high-frequency heating means having a magnetron is feedback-controlled based on the moisture content of the recording medium measured by a moisture content sensor. This allows the amount of heat applied to the recording medium to be adjusted according to the dryness of the recording medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-301131 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology of Patent Document 1 requires that a sensor for measuring the moisture content of the recording medium be provided at a position corresponding to the recording medium. For example, if the sensor is a capacitance moisture meter, the sensor must be provided at a position where it can come into contact with the recording medium, and if the sensor is an optical or high-frequency moisture meter, the sensor must be provided at a position where it can face the recording medium. [Means for solving the problem]

[0005] According to a first aspect of the present disclosure, there is provided a dielectric heating device comprising: an electrode unit having first and second electrodes facing an object to be heated and for heating the object, a voltage application unit applying an AC voltage to the first and second electrodes, a current value detection unit detecting the current value of an AC current flowing through the electrode unit, a phase difference detection unit detecting the phase difference between the AC voltage and the AC current, an impedance detection unit detecting the impedance of the electrode unit based on the current value and the phase difference, and a control unit controlling the voltage application unit based on the impedance to control the output of AC power output to the electrode unit.

[0006] According to a second aspect of the present disclosure, there is provided a printing system including the dielectric heating device of the above aspect and a discharge unit that discharges and deposits a liquid onto a printing medium. The electrode unit heats the printing medium with the liquid deposited thereon as the object to be heated. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view showing a schematic configuration of a dielectric heating device. [Figure 2] FIG. 1 is a block diagram showing a schematic configuration of a dielectric heating device. [Figure 3] FIG. 2 is a perspective view showing a schematic configuration of an electrode unit. [Figure 4] FIG. 3 is a schematic diagram illustrating a circuit formed by an electrode unit and an object to be heated. [Figure 5] Equivalent circuit diagram of a dielectric heating device. [Figure 6] FIG. 10 is a diagram illustrating a change in impedance in an equivalent circuit. [Figure 7] FIG. 4 is a diagram illustrating an example of output control of a first AC voltage by a control unit. [Figure 8] FIG. 1 is a diagram showing a schematic configuration of a printing system. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. First embodiment: FIG. 1 is a perspective view showing the schematic configuration of a dielectric heating device 100 according to the first embodiment. Arrows indicating mutually orthogonal X, Y, and Z directions are shown in FIG. 1. The X and Y directions are parallel to a horizontal plane, and the Z direction is a vertically upward direction. The arrows indicating the X, Y, and Z directions are also shown in other figures as appropriate so that the illustrated directions correspond to those in FIG. 1. In the following description, when specifying the direction, positive and negative signs are used in combination to indicate the direction indicated by the arrow in each figure, with "+" indicating the direction indicated by the arrow and "-" indicating the opposite direction. Hereinafter, the +Z direction will also be referred to as "up" and the -Z direction as "down." Furthermore, in this specification, "orthogonal" includes a range of 90°±10°.

[0009] The dielectric heating device 100 includes an electrode unit 20 for heating the object to be heated OH, a transport section 200 for transporting the object to be heated OH, a voltage application section 80 for applying an AC voltage to the electrode unit 20, and a control section 500.

[0010] The dielectric heating device 100 of this embodiment heats the object OH using an electric field generated by the electrode unit 20 while transporting the object OH using the transport unit 200. In this embodiment, the dielectric heating device 100 dries the object OH by heating a sheet-like print medium, which serves as the object OH and has a liquid applied to it. Examples of print media that can be used include paper, cloth, and film. The liquid applied to the print medium can be, for example, various inks whose main component is water or an organic solvent. In this embodiment, an aqueous ink whose main component is water is used as the liquid. Note that, in this specification, the main component of the liquid refers to a substance contained in the liquid whose mass fraction is 50% or more. The liquid is applied to the print medium using a liquid ejection device such as an inkjet printer.

[0011] The control unit 500 is configured by a computer including a CPU 510, a storage unit 520, and an input / output interface for inputting and outputting signals from and to the outside. The control unit 500 controls each unit, such as the transport unit 200 and the voltage application unit 80, described above, to heat the object OH in the dielectric heating device 100. In other embodiments, the control unit 500 may be configured by, for example, a combination of multiple circuits.

[0012] The conveying unit 200 in this embodiment has two roller units 205 and a drive unit (not shown) configured by a motor or the like that drives the roller units 205. The conveying unit 200 conveys the sheet-like object to be heated OH by driving the roller units 205. In other embodiments, the conveying unit 200 may be configured by, for example, a belt for supporting and conveying the object to be heated OH, and a drive unit for driving the belt.

[0013] The dielectric heating device 100 in this embodiment includes a first electrode unit 30 and a second electrode unit 40 as electrode units 20. The first electrode unit 30 has a first electrode 31 and a second electrode 32 that face the object to be heated OH. The second electrode unit 40 has a third electrode 41 and a fourth electrode 42 that face the object to be heated OH. As shown in FIG. 1 , in this embodiment, the second electrode unit 40 is disposed in the −X direction of the first electrode unit 30. In this embodiment, the first electrode unit 30 and the second electrode unit 40 have the same configuration. Hereinafter, when there is no need to distinguish between the first electrode unit 30 and the second electrode unit 40, they may both be simply referred to as electrode units 20.

[0014] The dielectric heating device 100 in this embodiment includes a first voltage application unit 81 and a second voltage application unit 82 as the voltage application unit 80. The first voltage application unit 81 is electrically connected to the first electrode unit 30 and applies an AC voltage to the first electrode 31 and the second electrode 32. The second voltage application unit 82 is electrically connected to the second electrode unit 40 and applies an AC voltage to the third electrode 41 and the fourth electrode 42. One of the potentials applied to the first electrode 31 or the second electrode 32 and one of the potentials applied to the third electrode 41 or the fourth electrode 42 may be a reference potential. The reference potential is a constant potential that serves as a reference for the high-frequency voltage, such as a ground potential. Hereinafter, the AC voltage applied to the first electrode unit 30 by the first voltage application unit 81 will also be referred to as a first AC voltage. The AC voltage applied to the second electrode unit 40 by the second voltage application unit 82 will also be referred to as a second AC voltage.

[0015] In this embodiment, the first voltage application section 81 and the second voltage application section 82 have the same configuration. Hereinafter, when there is no need to distinguish between the first voltage application section 81 and the second voltage application section 82, they may both be simply referred to as voltage application section 80. In this embodiment, each voltage application section 80 applies a high-frequency voltage to each electrode of each electrode unit 20. In this specification, "high frequency" refers to a frequency of 1 MHz or higher.

[0016] Fig. 2 is a block diagram showing a schematic configuration of a dielectric heating device 100 in this embodiment. As shown in Fig. 2, the first voltage application unit 81 in this embodiment has an inverter 83, a current detection unit 84, a phase difference detection unit 85, an amplifier 86, and a rectification unit 87. The first voltage application unit 81 is electrically connected to a DC power supply 150. Although not shown, the second voltage application unit 82 also has the above-mentioned inverter 83 and the like, and is electrically connected to the DC power supply 150.

[0017] The inverter 83 provided in each voltage application section 80 is electrically connected to the DC power supply 150 and each electrode unit 20. The inverter 83 converts the DC voltage input to the inverter 83 from the DC power supply 150 into an AC voltage and outputs it to the electrode unit 20. More specifically, the inverter 83 has a switching transistor, and by operation of this transistor, the inverter 83 converts the DC voltage input to the inverter 83 into an AC voltage having a rectangular waveform with a frequency f1 and outputs it to the electrode unit 20.

[0018] The current detection unit 84 provided in each voltage application unit 80 is configured as a resistor for detecting the AC current flowing through each electrode unit 20. When an AC voltage is applied to the electrode unit 20, an AC current having a sinusoidal waveform flows through the electrode unit 20, and the current detection unit 84 detects this AC current having a sinusoidal waveform. The current detection unit 84 outputs the detected AC current to the amplifier 86. The amplifier 86 amplifies the current input from the current detection unit 84 and outputs the amplified current to the phase difference detection unit 85 and rectification unit 87.

[0019] The phase difference detection unit 85 provided in the first voltage application unit 81 detects the phase difference between the phase of the AC voltage applied to the first electrode 31 and the second electrode 32 and the phase of the AC current flowing through the first electrode unit 30. Similarly, the phase difference detection unit 85 provided in the second voltage application unit 82 detects the phase difference between the phase of the AC voltage applied to the third electrode 41 and the fourth electrode 42 and the phase of the AC current flowing through the second electrode unit 40. The phase difference detection unit 85 transmits the detected phase difference to the control unit 500.

[0020] Rectifier 87 is configured with diodes, rectifies the AC current input from amplifier 86, converts it into DC current, and outputs the DC current to control unit 500. The voltage value of the DC current output from each rectifier 87 to control unit 500 is proportional to the amplitude of the AC current flowing through each electrode unit 20.

[0021] 1 and 2, the dielectric heating device 100 includes a current value detection unit 511 and an impedance detection unit 512. The current value detection unit 511 detects a unit current value that indicates the current value of the AC current flowing through each electrode unit 20. The impedance detection unit 512 detects the impedance Z of each electrode unit 20 based on each unit current value detected by the current value detection unit 511 and each phase difference detected by each phase difference detection unit 85. In this embodiment, the current value detection unit 511 and the impedance detection unit 512 are functional units that are realized when the CPU 510 of the control unit 500 executes a program stored in the storage unit 520.

[0022] In this embodiment, the control unit 500, functioning as the current value detection unit 511, detects the effective value of the current flowing through the electrode unit 20 as the unit current value based on the voltage value of the DC voltage input from the rectifier 87. The impedance detection unit 512 detects the impedance Zr of the electrode unit 20 based on the unit current value, the phase difference detected by the phase difference detection unit 85, and the voltage value of the AC voltage applied to each electrode of each electrode unit 20. For example, the impedance detection unit 512 detects the impedance Zr of the first electrode unit 30 based on the unit current value of the first electrode unit 30, the phase difference detected by the phase difference detection unit 85 provided in the first voltage application unit 81, and the voltage value of the AC voltage applied to the first electrode 31 and the second electrode 32. As will be 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 will also be referred to as the first impedance Zr1. The impedance Zr of the second electrode unit 40 is also referred to as the second impedance Zr2.

[0023] FIG. 3 is a perspective view showing a schematic configuration of the first electrode unit 30 in this embodiment. As described above, the first electrode unit 30 has a first electrode 31 and a second electrode 32. Furthermore, the first electrode unit 30 in this embodiment has a first coil 34. Although not shown in the drawings, in this embodiment, the third electrode 41 and the fourth electrode 42 of the second electrode unit 40 described above have the same configurations as the first electrode 31 and the second electrode 32, respectively. Furthermore, the second electrode unit 40 has a second coil (not shown) that has the same configuration as the first coil 34. Hereinafter, when there is no need to distinguish between the first coil 34 and the second coil, both may be simply referred to as coils.

[0024] The first electrode 31 and the second electrode 32 are conductors and are formed of, for example, a metal, an alloy, a conductive oxide, or the like. The first electrode 31 and the second electrode 32 may be formed of the same material or different materials. For example, in order to maintain their posture and ensure their strength, the first electrode 31 and the second electrode 32 may be placed on a substrate or the like formed of a material with low dielectric tangent or conductivity, or may be supported by another member.

[0025] The first electrode 31 and the second electrode 32 are arranged so that the shortest distance between them is one-tenth or less of the wavelength of the electromagnetic field output from the first electrode unit 30. In this embodiment, the first electrode 31 has a boat-like shape with the Y direction as the longitudinal direction and the X direction as the transverse direction. The lower surface of the first electrode 31 has a curved shape that is convex in the -Z direction. When viewed along the Z direction, the first electrode 31 has an oval shape that is long in the Y direction. The second electrode 32 is flat in the X and Y directions and has an oval ring shape that is long in the Y direction. When viewed along the Z direction, the second electrode 32 is arranged to surround the periphery of the first electrode 31.

[0026] 1, the first electrode 31 and the second electrode 32 are both disposed on a substrate 110 that is disposed parallel to the X and Y directions. More specifically, the first electrode 31 is disposed so that the central portions of the lower surface of the first electrode 31 in the X and Y directions are in contact with the upper surface of the substrate 110. The second electrode 32 is disposed so that the lower surface of the second electrode 32 is in contact with 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. Note that in this embodiment, the substrate 110 is provided in common to the first electrode unit 30 and the second electrode unit 40.

[0027] The first electrode 31 and the second electrode 32 are both arranged to face in the Z direction relative to the object to be heated OH, which is transported in the -Y direction by the transport unit 200. In this embodiment, the first electrode 31 and the second electrode 32 are arranged above the object to be heated OH. That is, in this embodiment, the lower surfaces of the first electrode 31 and the second electrode 32 face the upper surface of the object to be heated OH. In addition, the above-mentioned substrate 110 is arranged between the object to be heated OH and the first electrode 31 and the second electrode 32.

[0028] In this embodiment, the substrate 110 is made of glass. The substrate 110 prevents a liquid such as ink applied to the object to be heated OH from adhering to the first electrode 31 and the second electrode 32, and prevents fluff from the object to be heated OH from adhering to the first electrode 31 and the second electrode 32 if the object to be heated OH is a cloth. In this embodiment, the substrate 110 also prevents the liquid and fluff from adhering to the third electrode 41 and the fourth electrode 42 of the second electrode unit 40, as described above. In other embodiments, the substrate 110 may be made of, for example, alumina.

[0029] Returning to Fig. 3, in this embodiment, the 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. The second electrode 32 is electrically connected to the first voltage application unit 81 via a connection member 33 disposed above the second electrode 32, an outer conductor of the coaxial cable (not shown), etc.

[0030] When an AC voltage is applied to the first electrode 31 and the second electrode 32, an electromagnetic field having a wavelength λ1 corresponding to the frequency f1 of the applied AC voltage is generated from the first electrode 31 and the second electrode 32. The intensity of this electromagnetic field is very strong near the first electrode 31 and the second electrode 32 and very weak farther away. In this specification, the electromagnetic field generated near the first electrode 31 and the second electrode 32 by the application of an AC voltage is also referred to as the "near electromagnetic field." The "near" of the first electrode 31 and the second electrode 32 refers to a range where the distance from the first electrode 31 and the second electrode 32 is ½π or less of the wavelength of the generated electromagnetic field. A range farther away than the "near" is also referred to as the "far" range. In this specification, the electromagnetic field generated far from the first electrode 31 and the second electrode 32 by the application of an AC voltage is also referred to as the "far electromagnetic field." The far electromagnetic field corresponds to the electromagnetic field used in communication using a general communication antenna, etc.

[0031] As described above, the first electrode 31 and the second electrode 32 are arranged so that the shortest distance between them is equal to or less than one-tenth the wavelength of the electromagnetic field. This allows the electric field density of the electromagnetic field generated from the first electrode 31 and the second electrode 32 to be attenuated in the vicinity of the first electrode 31 and the second electrode 32. Therefore, by maintaining an appropriate distance between the object to be heated OH and the first electrode 31 and the second electrode 32, the liquid adhering to the object to be heated OH can be efficiently heated by the electric field generated in the vicinity of the first electrode 31 and the second electrode 32, while suppressing radiation of the far electromagnetic field from the first electrode 31 and the second electrode 32. In particular, in this embodiment, the second electrode 32 is arranged to surround the first electrode 31 when viewed along the Z direction, which further suppresses radiation of the far electromagnetic field from the first electrode 31 and the second electrode 32.

[0032] 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 in series to the first voltage application unit 81 shown in FIGS. 1 and 2 . In this embodiment, the first coil 34 is configured as a solenoid coil and is disposed so that its length direction is along the Z direction. The shape, length, cross-sectional area, number of turns, material, etc. of the first coil 34 are selected, for example, so as to form a resonant circuit that resonates with the first electrode 31 and the second electrode 32 at frequency f1 and to achieve impedance matching between the first electrode unit 30 and the first voltage application unit 81. Note that, although not shown, in this embodiment, one end of the second coil is electrically connected to the third electrode 41 via the second electric wire, and the other end is electrically connected in series to the second voltage application unit 82. In other embodiments, one end of the first coil 34 may be connected in series to the second electrode 32 instead of the first electrode 31. Similarly, one end of the second coil may be connected in series to the fourth electrode 42 instead of the third electrode 41.

[0033] When the first voltage application unit 81 applies an AC voltage to the first electrode unit 30, a high voltage is generated at one end of the first coil 34. This increases the strength of the electric field generated by the first electrode 31 and the second electrode 32. The first coil 34 is preferably positioned so 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 generate an electric field between the first coil 34 and the first electrode 31 or between the first electric wire 35 and the second electrode 32 that does not contribute to heating the object OH, thereby reducing the effect of increasing the strength of the electric field generated by the first electrode 31 and the second electrode 32. By reducing the distance between the one end of the first coil 34 and the first electrode 31, the generation of such an electric field that does not contribute to heating the object OH can be suppressed, thereby effectively increasing the strength of the electric field generated by 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. Note that in other embodiments, the first electrode unit 30 and the second electrode unit 40 may not have a coil, and for example, the first electrode 31 and the third electrode 41 may be formed in a meander shape so that the first electrode 31 and the third electrode 41 can function similarly to a coil.

[0034] Fig. 4 is a schematic diagram illustrating a circuit formed by the first electrode unit 30 and the object to be heated OH to which the liquid Lq is attached in this embodiment. Fig. 5 is an equivalent circuit diagram of the dielectric heating device 100 in this embodiment. In the circuits shown in Figs. 4 and 5, the first electrode 31 and the second electrode 32 of the first electrode unit 30 can each be considered as electrode plates that constitute a single capacitor. Although not shown, a circuit similar to the circuits shown in Figs. 4 and 5 is also formed by the second electrode unit 40 and the object to be heated OH.

[0035] R shown in Figs. a represents the resistance of the first electrode unit 30. L shown in FIG. arepresents the inductance of the first electrode unit 30. In this embodiment, the inductance L a In this case, the inductance L of the first coil 34 shown in FIG. c and the parasitic inductance of each electrode of each electrode unit 20. a represents the capacitance of the first electrode unit 30. In this embodiment, the capacitance C a includes the parasitic capacitance of the first coil 34 and the capacitance between the electrodes of each electrode unit 20. b represents the electrical resistance of the liquid Lq, such as ink, attached to the heated object OH. b1 represents the parasitic capacitance between the first electrode 31 and the liquid Lq. b2 represents the parasitic capacitance between the second electrode 32 of each electrode unit 20 and the liquid Lq. b is the parasitic capacitance C b1 and C b2 It is expressed as the sum of

[0036] As the liquid Lq on the object to be heated OH is heated and dried, the capacitance C a and the resistance R of the liquid Lq b In more detail, as the liquid Lq dries, the thickness of the liquid Lq on the object to be heated OH decreases, and the capacitance of the capacitor formed by the first electrode 31 and the second electrode 32 decreases. a decreases. This is because the dielectric constant of the liquid Lq is higher than the dielectric constant of a vacuum. In addition, for example, if the liquid Lq is a liquid containing water, such as water-based ink, the water content of the liquid Lq decreases as it dries, which reduces the conductivity of the liquid Lq, and the resistance R b The "water content of liquid Lq" refers to the mass fraction of water in liquid Lq. Note that the capacitance C b also decreases, but the decrease is a The decrease in resistance R bThis can be ignored because it is small compared to the increase in

[0037] The impedance Z in the equivalent circuit shown in FIG. 5 is expressed by the following formula (1).

[0038]

number

[0039] In the above formula (1), ω represents the angular frequency of the AC voltage applied to the first electrode 31 and the second electrode 32.

[0040] FIG. 6 is a diagram illustrating the change in impedance Z due to the progress of drying of the liquid Lq in the equivalent circuit shown in FIG. 5. More specifically, FIG. 6 is a graph in which the vertical axis represents the real part of the impedance Z and the horizontal axis represents the progress of drying of the liquid Lq when a cotton cloth is used as the object to be heated OH and yellow water-based ink is used as the liquid Lq. The "progress of drying" shown in FIG. 6 represents the reciprocal of the moisture content of the liquid Lq. The graph in FIG. 6 shows the relationship between the moisture content of the liquid Lq and the capacitance C a and resistor R b The relationship between the capacitance and the capacitance C a and resistor R b The real part of the impedance Z calculated by substituting the value of (1) into the above equation was plotted against the reciprocal of the moisture content. Figure 6 shows that the real part of the impedance Z decreases as the drying of the liquid Lq on the object OH progresses, that is, as the moisture content of the liquid Lq decreases. In this way, there is a correlation between the impedance Z and the degree of dryness of the object OH.

[0041] The control unit 500 shown in FIGS. 1 and 2 controls the first voltage application unit 81 based on the first impedance Zr1 detected by the impedance detection unit 512, thereby controlling the output of AC power to the first electrode unit 30. Hereinafter, the AC power output to the first electrode unit 30 will also be referred to as the “first AC power.” The impedance Zr corresponds to the measured impedance value in the circuit formed by the electrode unit 20 and the object OH. Therefore, similar to the impedance Z in the equivalent circuit described above, the impedance Zr correlates with the dryness of the object OH. Therefore, by controlling the output of the first AC power based on the first impedance Zr1, the amount of heat applied to the object OH is adjusted according to the dryness of the object OH. Similarly, in this embodiment, the control unit 500 controls the output of AC power to the second electrode unit 40 by controlling the second voltage application unit 82 based on the second impedance Zr2. Hereinafter, the AC power output to the second electrode unit 40 will also be referred to as the “second AC power.”

[0042] In this embodiment, the control unit 500 controls the output of the first AC power based on the value of the real part of the first impedance Zr1. More specifically, the control unit 500 first estimates the amount of liquid contained in the object to be heated OH based on the value of the real part of the first impedance Zr1, thereby estimating the dryness level of the object to be heated OH. The control unit 500 then stores the estimated dryness level in the memory unit 520 and controls the output of AC power based on the stored dryness level. The amount of liquid estimated in this manner corresponds to the amount of liquid adhering to the object to be heated OH that is located near the first electrode 31 and the second electrode 32. The amount of liquid contained in the object to be heated OH may be estimated, for example, as the weight, volume, or thickness of the liquid, or as a ratio to a predetermined reference value such as weight.

[0043] More specifically, in this embodiment, the control unit 500 estimates the dryness of the object to be heated OH by estimating the amount of moisture in the liquid applied to the object to be heated OH as the amount of liquid contained in the object to be heated OH based on the value of the real part of the first impedance Zr1. The control unit 500 estimates the moisture content of the liquid by, for example, referring to a relationship between the value of the real part of the impedance and the moisture content of the liquid, which is determined in advance based on experiments, based on the value of the real part of the first impedance Zr1. In this case, the relationship between the value of the real part of the impedance and the moisture content of the liquid may be determined for each material and thickness of the object to be heated OH and each type of liquid, for example.

[0044] In this embodiment, the control unit 500 controls the output of the second AC power based on the value of the real part of the second impedance Zr2, just as it controls the output of the first AC power based on the value of the real part of the first impedance Zr1. The liquid content estimated based on the second impedance Zr2 corresponds to the amount of liquid adhering to the object to be heated OH that is located near the third electrode 41 and the fourth electrode 42.

[0045] FIG. 7 is a diagram illustrating an example of output control of the first AC voltage by the control unit 500 in this embodiment. FIG. 7 shows waveforms Wf1, Wf2, and Wf3 as examples of the waveform of the first AC voltage. As shown in FIG. 7, the control unit 500 outputs to the first electrode unit 30 an AC voltage of waveform Wf1 when the dryness level is D1, an AC voltage of waveform Wf2 when the dryness level is D2, and an AC voltage of waveform Wf3 when the dryness level is D3. The dryness levels increase in the order D1, D2, and D3. FIG. 7 also shows the period T1 of the AC voltage. The period T1 is the reciprocal of the frequency f1 and is proportional to the wavelength λ1.

[0046] In this embodiment, the control unit 500 controls the output of the first AC power by intermittently operating the inverter 83 of the first voltage application unit 81 based on the first impedance Zr1. More specifically, in this embodiment, the control unit 500 changes, based on the degree of dryness estimated based on the first impedance Zr1, the proportion of time during which the inverter 83 is continuously operated to output an AC voltage of frequency f1 to the first electrode unit 30, and the proportion of time during which the inverter 83 is not operated and the output of voltage to the first electrode unit 30 is stopped, within a predetermined time period. More specifically, when the degree of dryness is higher, the control unit 500 reduces the proportion of time during which the AC voltage is output to the first electrode unit 30 and increases the proportion of time during which the output of voltage to the first electrode unit 30 is stopped. Conversely, when the degree of dryness is lower, the control unit 500 increases the proportion of time during which the AC voltage is output to the first electrode unit 30 and decreases the proportion of time during which the output of voltage to the first electrode unit 30 is stopped. For example, since the dryness level D2 is higher than the dryness level D1, the proportion of time during which AC voltage is output to the first electrode unit 30 is smaller in the waveform Wf2 than in the waveform Wf1, and the proportion of time during which no voltage is output to the first electrode unit 30 is larger. In this manner, the output of the first AC power is controlled. Note that, although not shown in the figures, in this embodiment, the control unit 500 similarly controls the output of the second AC power by controlling the inverter 83 of the second voltage application unit 82 based on the second impedance Zr2.

[0047] In this embodiment, the control unit 500 sets the output of the first AC power to 0 when the dryness level estimated based on the first impedance Zr1 is equal to or greater than a predetermined level. More specifically, the control unit 500 sets the output of the first AC power to 0 when the dryness level is equal to or greater than a reference dryness level Ds. The reference dryness level Ds is defined as a dryness level indicating that the heated object OH has been sufficiently dried, for example. In the example of FIG. 7 , the dryness levels D1 and D2 are less than the reference dryness level Ds, and the dryness level D3 is equal to or greater than the reference dryness level Ds. Therefore, in this embodiment, when the dryness level is D3, the control unit 500 controls the inverter 83 to set the proportion of the time during which AC voltage is output to the first electrode unit 30 to 0 in a predetermined period of time, thereby setting the output of the first AC power to 0. Note that, for example, after the output of the first AC power is temporarily set to 0, if the object to be heated OH is transported and a portion of the object to be heated OH with a relatively large amount of liquid adhering thereto is positioned near the first electrode unit 30, the dryness level estimated based on the impedance Zr may again become less than the reference dryness level Ds. In this case, the control unit 500 again increases the output of the first AC power above 0. Similarly, in this embodiment, the control unit 500 sets the output of the second AC power to 0 when the dryness level estimated based on the second impedance Zr2 is equal to or greater than the reference dryness level Ds.

[0048] Furthermore, in this embodiment, the control unit 500 estimates the temperature of the object to be heated OH based on the detected impedance Zr. The control unit 500 can estimate the temperature of the object to be heated OH based on, for example, the integrated value of the calorific value estimated based on the impedance Zr. More specifically, the control unit 500 estimates the calorific value at a certain time by referring to the relationship between the impedance determined in advance through experiments and the calorific value of the liquid attached to the object to be heated OH based on the impedance Zr at that time. Then, the control unit 500 can estimate the integrated value of the calorific value by calculating the time integral of the calorific value from the start of heating to the present based on the estimated calorific value. As a result, the control unit 500 can estimate the temperature of the object to be heated OH by estimating the temperature of the liquid based on the specific heat of the liquid and the integrated value of the estimated calorific value.

[0049] In addition, in this embodiment, when the dryness of the object OH near the first electrode unit 30 is lower than the dryness of the object OH near the second electrode unit 40, the control unit 500 increases the output of the first AC power greater than the output of the second AC power. Conversely, when the dryness of the object OH near the first electrode unit 30 is higher than the dryness of the object OH near the second electrode unit 40, the control unit 500 decreases the output of the first AC power greater than the output of the second AC power. This increases the amount of heat to be applied to the less dry portion of the object OH and decreases the amount of heat to be applied to the more dry portion. Therefore, even if the amount of liquid adhering to the object OH varies, the object OH is more likely to be heated uniformly. In this embodiment, the first voltage application unit 81 and the second voltage application unit 82 are individually controlled based on the dryness as described with reference to FIG. 7, thereby achieving the magnitude relationship between the output of the first AC power and the output of the second AC power. In other embodiments, the control unit 500 may, for example, compare the degree of dryness in the vicinity of the first electrode unit 30 with the degree of dryness in the vicinity of the second electrode unit 40, and change the magnitude relationship between the output of the first AC power and the output of the second AC power based on the comparison result.

[0050] According to the dielectric heating device 100 of the first embodiment described above, the control unit 500 controls the output of the first AC power by controlling the first voltage application unit 81 based on the impedance Zr of the first electrode unit 30 having the first electrode 31 and second electrode 32 facing the object to be heated OH. According to this embodiment, the output of the first AC power is controlled based on the impedance Zr, which correlates with the dryness of the object to be heated OH, and therefore the output of the first AC power is adjusted according to the dryness. Therefore, even if a sensor for measuring the moisture content of the object to be heated OH is not provided at a position corresponding to the object to be heated OH, the amount of heat of the object to be heated OH can be adjusted according to the dryness of the object to be heated OH.

[0051] Furthermore, according to this embodiment, the control unit 500 estimates the dryness level of the object to be heated OH based on the impedance of the first electrode unit 30, and stores the estimated dryness level in the memory unit 520. This makes it possible to display the dryness level stored in the memory unit 520 on a display unit (not shown), and to control the output of the first AC power based on the dryness level stored in the memory unit 520.

[0052] Furthermore, according to this embodiment, when the dryness of the object to be heated OH is equal to or greater than a predetermined level, the control unit 500 sets the output of the first AC power to 0. This makes it possible to prevent discoloration and burning of the object to be heated OH, which may occur when the object to be heated OH is heated in a sufficiently dry state.

[0053] Furthermore, according to this embodiment, the control unit 500 estimates the temperature of the object OH based on the first impedance Zr1. Therefore, the temperature of the object OH can be acquired without providing a temperature sensor for measuring the temperature of the object OH. As a result, for example, if the ink attached to the object OH contains a resin component that fixes components such as pigment contained in the ink to the object OH, the degree of melting of the resin component can be estimated based on the estimated temperature of the object OH.

[0054] Furthermore, according to this embodiment, the first electrode unit 30 has a first coil 34 electrically connected in series with either the first electrode 31 or the second electrode 32. This allows the first coil 34 to increase the strength of the electric field generated from the first electrode 31 and the second electrode 32 when a voltage is applied. This allows the object to be heated OH to be heated more efficiently.

[0055] Furthermore, according to the present embodiment, the first voltage application section 81 has an inverter 83 that converts the DC voltage output from the DC power supply 150 into an AC voltage and outputs it to the first electrode unit 30. This increases the possibility of realizing a smaller size and improved power efficiency of the first voltage application section 81 compared to when the first voltage application section 81 is configured by, for example, a high-frequency power supply circuit having an analog amplifier and a transformer.

[0056] Furthermore, according to the present embodiment, the control unit 500 controls the output of the first AC power by intermittently operating the inverter 83 based on the impedance of the first electrode unit 30. This makes it possible to easily control the output of the first AC power.

[0057] B. Second embodiment: 8 is a diagram showing a schematic configuration of a printing system 600 according to the second embodiment. The printing system 600 includes the dielectric heating device 100 described in the first embodiment and a liquid ejection device 610.

[0058] The liquid ejection device 610 of this embodiment is configured as an inkjet printer and includes an ejection unit 620 that ejects liquid onto a print medium, a medium transport unit 630 that transports the print medium, and an ejection control unit 640 that controls the ejection unit 620 and the medium transport unit 630. The ejection unit 620 is configured, for example, by a piezoelectric or thermal liquid ejection head. The medium transport unit 630 is configured, for example, by a roller, similar to the transport unit 200. The ejection control unit 640 is configured, for example, by a computer, similar to the control unit 500 of the dielectric heating device 100. The ejection control unit 640 controls the ejection unit 620 and the medium transport unit 630 to eject and adhere liquid onto the print medium while transporting the print medium.

[0059] As described in the first embodiment, the dielectric heating device 100 heats the print medium to which the liquid discharged by the discharge unit 620 is attached as the object to be heated OH. That is, the first electrode unit 30 and the second electrode unit 40 heat the print medium to which the liquid is attached as the object to be heated OH. As shown in FIG. 8 , the object to be heated OH may be continuously transported from the liquid discharge device 610 to the dielectric heating device 100. In this case, for example, the transport unit 200 of the dielectric heating device 100 may function as the medium transport unit 630. Furthermore, the object to be heated OH does not have to be continuously transported from the liquid discharge device 610 to the dielectric heating device 100. For example, the print medium to which the liquid discharged by the liquid discharge device 610 is attached may be wound into a roll, and then the wound print medium may be moved to the dielectric heating device 100 by a robot or the like. In this case, the rolled print medium is unwound while being transported as the object to be heated OH by the transport unit 200, thereby allowing the object to be heated OH to be heated in the dielectric heating device 100.

[0060] According to the second embodiment described above, the amount of heat applied to the object OH can be adjusted according to the degree of dryness of the object OH, even if a sensor for measuring the moisture content of the object OH is not placed in a position corresponding to the object OH.

[0061] C. Other Embodiments: (C-1) In the above embodiment, the control unit 500 estimates the dryness level of the object to be heated OH based on the detected impedance Zr, but it is not necessary to estimate the dryness level of the object to be heated OH.

[0062] (C-2) In the above embodiment, the control unit 500 estimates the dryness level by estimating the amount of liquid contained in the object to be heated OH based on the detected impedance Zr. In contrast, the control unit 500 may estimate the dryness level without estimating the amount of liquid contained in the object to be heated OH.

[0063] (C-3) In the above embodiment, the control unit 500 sets the output of the first AC power to 0 when the dryness level estimated based on the first impedance Zr1 is equal to or greater than the reference dryness level Ds. In contrast, the control unit 500 does not have to set the output of the first AC power to 0 when the dryness level estimated based on the first impedance Zr1 is equal to or greater than the reference dryness level Ds. Similarly, the control unit 500 does not have to set the output of the second AC power to 0 when the dryness level estimated based on the second impedance Zr2 is equal to or greater than the reference dryness level Ds.

[0064] (C-4) In the above embodiment, the control unit 500 estimates the temperature of the object to be heated OH based on the impedance Zr. However, the control unit 500 does not have to estimate the temperature of the object to be heated OH based on the impedance Zr.

[0065] (C-5) In the above embodiment, the first voltage application unit 81 has an inverter 83. In contrast, the first voltage application unit 81 does not have to have the inverter 83, and may be configured as a high-frequency power supply circuit having, for example, an analog amplifier and a transformer. Similarly, the second voltage application unit 82 does not have to have the inverter 83.

[0066] (C-6) In the above embodiment, the control unit 500 controls the output of the first AC power by intermittently operating the inverter 83 based on the first impedance Zr1. In contrast, the control unit 500 does not have to control the output of the first AC power by intermittently operating the inverter 83. For example, the control unit 500 may control the output of the first AC power by changing the amplitude of the AC voltage applied to the first electrode unit 30 based on the first impedance Zr1. Similarly, the control unit 500 does not have to control the output of the second AC power by intermittently operating the inverter 83 based on the second impedance Zr2.

[0067] (C-7) In the above embodiment, the electrode unit 20 includes a first electrode unit 30 and a second electrode unit 40, and the voltage application section 80 includes a first voltage application section 81 and a second voltage application section 82. In addition to these, one or more other electrode units 20 may be provided as the electrode unit 20, and one or more other voltage application sections 80 that apply AC voltages to each electrode unit 20 may be provided as the voltage application section 80. Alternatively, only the first electrode unit 30 may be provided as the electrode unit 20, and only the first voltage application section 81 may be provided as the voltage application section 80.

[0068] (C-8) In the above embodiment, when a print medium with a liquid attached thereto is heated as the object to be heated OH, the control unit 500 may control the output of the AC power output to the electrode unit 20 by controlling the voltage application unit 80 based on the print information of the print medium. In this case, the print information may include, for example, information on the type of liquid attached to the object to be heated OH, adhesion amount information on the amount of liquid attached, or pattern information on the print pattern. This allows the output of the AC power adjusted based on the impedance Zr to be further adjusted based on the print information, thereby further increasing the possibility of uniformly drying the object to be heated OH. The print information may be, for example, stored in advance in the memory unit 520 or obtained from the liquid ejection device 610.

[0069] (C-9) In the above embodiment, the second electrode 32 is arranged to surround the first electrode 31 when viewed along the Z direction. In contrast, for example, the first electrode 31 and the second electrode 32 may be arranged to be adjacent to each other when viewed along the Z direction, or may be arranged so that the first electrode 31 and the second electrode 32 sandwich the object to be heated OH in the Z direction. In this case, the shapes of the first electrode 31 and the second electrode 32 may be any shape, such as a circle, an oval, a rectangle, or a polygon. Furthermore, the areas of the first electrode 31 and the second electrode 32 when viewed along the Z direction may be the same or different from each other. It is preferable that the first electrode 31 and the second electrode 32 are arranged so as not to overlap each other when viewed along the Z direction. Similarly, the third electrode 41 and the fourth electrode 42 may be arranged, for example, so as to be adjacent to each other when viewed along the Z direction, or so as to sandwich the object to be heated OH between the third electrode 41 and the fourth electrode 42 in the Z direction.

[0070] (C-10) In the above embodiment, the electrode unit 20 may be configured to be reciprocally movable in a direction intersecting the direction in which the object to be heated OH is transported. For example, the electrode unit 20 may be supported by a drive unit (not shown) configured by a belt mechanism or a ball screw mechanism, and may be reciprocally movable in the X direction.

[0071] (C-11) In the above embodiment, the control unit 500 controls the output of AC power output to the electrode unit 20 based on the value of the real part of the impedance Zr. Alternatively, the control unit 500 may control the output of AC power based on, for example, the value of the imaginary part of the impedance Zr or the absolute value of the impedance Zr, which is expressed as the vector sum of the real and imaginary parts on a complex plane, in addition to or instead of the value of the real part of the impedance Zr. This allows the output of AC power output to the electrode unit 20 to be appropriately controlled even when the degree of dryness cannot be uniquely determined based on the value of the real part of the impedance Zr alone, for example, depending on the type of liquid adhering to the object to be heated OH. This is because the value of the imaginary part of the impedance Zr changes periodically, more specifically, in a counterclockwise direction on the Smith chart, as the liquid on the object to be heated OH dries. In this case, for example, first, candidates for the dryness level may be extracted based on the value of the real part of the impedance Zr, and then one dryness level may be estimated from the extracted candidates based on the value of the imaginary part of the impedance Zr.

[0072] (C-12) In the above embodiment, a high-frequency voltage is applied to the electrode unit 20. In contrast, the frequency of the AC voltage applied to the electrode unit 20 does not have to be high-frequency as long as it is a frequency that can heat the object to be heated OH. In this case, the frequency of the AC voltage is preferably, for example, not less than 100 kHz and less than 1 MHz.

[0073] D. Other forms: The present disclosure is not limited to the above-described embodiments and can be realized in various forms without departing from the spirit thereof. For example, the present disclosure can also be realized in the following forms. The technical features in the above embodiments corresponding to the technical features in each form described below can be appropriately replaced or combined to solve some or all of the problems of the present disclosure or to achieve some or all of the effects of the present disclosure. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0074] (1) According to a first aspect of the present disclosure, there is provided a dielectric heating device comprising: an electrode unit having first and second electrodes facing an object to be heated and configured to heat the object, a voltage application unit applying an AC voltage to the first and second electrodes, a current value detection unit detecting a current value of an AC current flowing through the electrode unit, a phase difference detection unit detecting a phase difference between the AC voltage and the AC 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 the voltage application unit based on the impedance to control an output of AC power output to the electrode unit. According to this configuration, the output of AC power output to the electrode unit is controlled based on the impedance of the electrode unit, which correlates with the dryness level, so that the output of AC power output to the electrode unit is controlled according to the dryness level. Therefore, even if a sensor for measuring the moisture content of the object is not provided at a position corresponding to the object, the amount of heat applied to the object can be adjusted according to the dryness level of the object.

[0075] (2) In the above embodiment, a storage unit may be provided, and the control unit may estimate the dryness level of the object to be heated based on the impedance and store the estimated dryness level in the storage unit. According to this embodiment, the dryness level stored in the storage unit can be displayed on the display unit, and the output of AC power applied to the electrode unit can be controlled based on the dryness level stored in the storage unit.

[0076] (3) In the above aspect, the control unit may estimate the dryness level by estimating an amount of liquid contained in the object to be heated based on the impedance.

[0077] (4) In the above embodiment, when the degree of dryness is equal to or greater than a predetermined level, the control unit may set the output of the AC power to 0. According to this embodiment, it is possible to prevent discoloration or burning of the object to be heated, which may occur when the object is heated in a sufficiently dry state.

[0078] (5) In the above embodiment, the control unit may estimate the temperature of the object based on the impedance. According to this embodiment, the temperature of the object can be obtained without providing a temperature sensor for measuring the temperature of the object.

[0079] (6) In the above embodiment, the electrode unit may have a coil electrically connected in series with either the first electrode or the second electrode. According to this embodiment, the coil can increase the strength of the electric field generated from the first electrode and the second electrode when a voltage is applied. This allows the object to be heated more efficiently.

[0080] (7) In the above embodiment, the voltage application unit may have an inverter that converts a DC voltage input from a DC power supply into an AC voltage and outputs the AC voltage to the electrode unit. This embodiment increases the possibility of realizing a smaller voltage application unit and improved power efficiency.

[0081] (8) In the above aspect, the control unit may control the output of the AC power by intermittently operating the inverter based on the impedance. According to this aspect, the output of the AC power output to the electrode unit can be easily controlled.

[0082] (9) According to a second aspect of the present disclosure, there is provided a printing system including the dielectric heating device of the above aspect and a discharge unit that discharges and deposits a liquid onto a printing medium. The electrode unit heats the printing medium with the liquid deposited thereon as the object to be heated. [Explanation of symbols]

[0083] 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 unit, 81...first voltage application unit, 82...second voltage application unit, 83...inverter, 84...current detection unit, 85...phase difference detection unit, 86...amplifier, 87...rectification unit, 100...dielectric heating device, 110...substrate, 150...DC power supply, 200...conveyance unit, 205...roller unit, 500...control unit, 510...CPU, 511...current value detection unit, 512...impedance detection unit, 520...storage unit, 600...printing system, 610...liquid ejection device, 620...ejection unit, 630...medium conveyance unit, 640...ejection control unit

Claims

1. An electrode unit for heating the heated object, the electrode unit having a first electrode unit including a first electrode and a second electrode facing in a direction opposite to the heated object being transported in a transport direction, and a second electrode unit including a third electrode and a fourth electrode facing the heated object, arranged side by side with the first electrode unit in a direction intersecting the transport direction and perpendicular to the facing direction; a voltage application unit including a first voltage application unit that applies a first AC voltage to the first electrode and the second electrode, and a second voltage application unit that applies a second AC voltage to the third electrode and the fourth electrode; a current value detection unit that detects a first current value that is a current value of a first AC current that is an AC current flowing through the first electrode unit, and a second current value that is a current value of a second AC current that is an AC current flowing through the second electrode unit; a phase difference detection unit that detects a first phase difference that is a phase difference between the first AC voltage and the first AC current, and a second phase difference that is a phase difference between the second AC voltage and the second AC current; an impedance detection unit that detects a first impedance that is the impedance of the first electrode unit based on the first current value and the first phase difference, and detects a second impedance that is the impedance of the second electrode unit based on the second current value and the second phase difference; a control unit that controls the first voltage application unit based on the first impedance to control an output of first AC power, which is AC power output to the first electrode unit, and that controls the second voltage application unit based on the second impedance to control an output of second AC power, which is AC power output to the second electrode unit, The control unit Estimating a first dryness degree, which is a dryness degree of the object to be heated based on the first impedance, and a second dryness degree, which is a dryness degree of the object to be heated based on the second impedance; When the first dryness degree is lower than the second dryness degree, the output of the first AC power is made larger than the output of the second AC power; When the first dryness degree is higher than the second dryness degree, the output of the first AC power is made smaller than the output of the second AC power. Dielectric heating device.

2. 2. The dielectric heating device according to claim 1, A storage unit is provided, The control unit stores the estimated first dryness degree in the memory unit.

3. The dielectric heating device according to claim 1 or 2, The control unit estimates the first dryness degree by estimating the amount of liquid contained in the object to be heated based on the first impedance.

4. The dielectric heating device according to any one of claims 1 to 3, The control unit sets the output of the first AC power to 0 when the first dryness degree is equal to or greater than a predetermined level.

5. The dielectric heating device according to any one of claims 1 to 4, The control unit estimates the temperature of the object to be heated based on the first impedance.

6. 6. The dielectric heating device according to claim 1, The electrode unit includes a coil electrically connected in series with either the first electrode or the second electrode.

7. 7. The dielectric heating device according to claim 1, The voltage application unit is a dielectric heating device having an inverter that converts a DC voltage input from a DC power supply into an AC voltage and outputs the AC voltage to the electrode unit.

8. The dielectric heating device according to claim 7, The control unit controls the output of the first AC power by intermittently operating the inverter based on the first impedance.

9. The dielectric heating device according to any one of claims 1 to 8, a discharge unit that discharges and deposits liquid onto the print medium, The electrode unit heats the printing medium having a liquid attached thereto as the object to be heated.

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