JP6222332B2 - Printing apparatus and printing method - Google Patents

Description

  The present invention relates to a printing apparatus and a printing method.

  2. Description of the Related Art Inkjet printing apparatuses that record images and documents by ejecting ink onto a print medium from a plurality of nozzles provided in a print head are widely used. In such a printing apparatus, for example, a piezoelectric element provided corresponding to each nozzle of the print head is driven according to a drive signal, whereby a predetermined amount of ink is ejected from the nozzle at a predetermined timing.

The drive signal is a pulse, for example, an analog reference drive signal pulse width modulation (Pulse Width Modulation, PWM) method or a pulse density modulation (Pulse Density Modulation, PDM) system, a pulse amplitude modulation (Pulse Amplitude Modulation, PAM) by such Modulation generates a digital modulation base drive signal, amplifies the modulation base drive signal to generate a modulation drive signal, smoothes the modulation drive signal, and converts it into an analog signal drive signal.

  2. Description of the Related Art Conventionally, there has been known a print head drive circuit that can reduce power consumption and suppress heat generation of a switching element by utilizing a capacitor (see, for example, Patent Document 1).

JP-A-11-170529

  In recent years, high-speed printing has been demanded for printing apparatuses, and the number of ejections per unit time tends to increase in order to increase the printing speed. In addition, high-quality, high-resolution printing is required for printing apparatuses, and the number of dots (number of pixels) per printed matter tends to increase. Therefore, the number of ejections per printed matter tends to increase. The user needs are high-speed and high-quality printing that combines these two requirements. The requirement is a requirement for an increase in the number of ejections per unit time as a direct requirement for the printing apparatus. When the increase in the number of ejections per unit time is realized, the power consumed by the print head increases in proportion to the number of ejections, which causes a problem of insufficient power. In addition to the problem of power consumption, heat generation resistance generated in each circuit and piezoelectric element is also a big problem in proportion to power consumption. The heat generation makes the operation of each circuit and the piezoelectric element unstable, and causes deterioration in print quality. As a result, there arises a problem that a printed matter that cannot satisfy the fundamental requirement “high image quality” is generated. In order to solve such a problem, a conventional amplifier using a switching element (so-called class D amplifier) has taken measures to reduce heat loss. However, as the demand for high-speed and high-quality images increases, the number of switching operations per unit time becomes excessive, and conventional measures may not be able to sufficiently cope with power consumption and heat generation problems.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms. The printing apparatus of the present invention is capable of printing at at least two printing speeds: a first printing speed and a second printing speed that is faster than the first printing speed. The printing apparatus amplifies the modulation base drive signal using a base drive signal generation unit that generates a base drive signal, a signal modulation unit that modulates the base drive signal to generate a modulation base drive signal, and a switching element A signal amplifying unit that generates a modulation driving signal, a signal conversion unit that converts the modulation driving signal into a driving signal, a piezoelectric element that is deformed by the driving signal, and a pressure chamber that expands or contracts due to deformation of the piezoelectric element In the first case of printing at the second printing speed and the nozzle opening communicating with the pressure chamber, the switching frequency of the switching element is limited to less than a predetermined value, and at the first printing speed. In the second case of printing, a frequency control unit that does not limit the switching frequency of the switching element to less than the predetermined value is provided.

(1) According to one aspect of the present invention, a printing apparatus is provided. The printing apparatus is capable of printing at at least two printing resolutions, ie, a first resolution and a second resolution higher than the first resolution, and a first printing speed and a first printing speed higher than the first printing speed. Printing is possible at at least two printing speeds, two printing speeds. The printing apparatus amplifies the modulation base drive signal using a base drive signal generation unit that generates a base drive signal, a signal modulation unit that modulates the base drive signal to generate a modulation base drive signal, and a switching element A signal amplifying unit that generates a modulation driving signal, a signal conversion unit that converts the modulation driving signal into a driving signal, a piezoelectric element that is deformed by the driving signal, and a pressure chamber that expands or contracts due to deformation of the piezoelectric element In the first case where the product of the nozzle opening communicating with the pressure chamber and the printing speed and the printing resolution is equal to or greater than a threshold value, the switching frequency of the switching element is limited to less than a predetermined value, In the second case where the product of the printing speed and the printing resolution is less than the threshold, a frequency control unit that does not limit the switching frequency of the switching element to less than the predetermined value; To characterized in that it comprises. According to the printing apparatus of this aspect, in the first case where the product of the printing speed and the printing resolution is equal to or higher than the threshold value, the switching frequency of the switching element is limited to a value less than the predetermined value, thereby suppressing the influence on the image quality. However, it is possible to avoid the occurrence of problems due to an increase in power consumption and heat generation. In the second case where the product of the printing speed and the printing resolution is less than the above threshold value, the switching frequency of the switching element is not limited to a value less than the predetermined value, so that high-quality printing by faithful waveform reproduction can be realized. .

(2) In the printing apparatus according to the above aspect, the signal modulation unit inputs the base drive signal and a comparison signal composed of a triangular wave or a sawtooth wave whose frequency changes according to the voltage of the base drive signal to a voltage comparator. In this case, the frequency control unit adds a clock signal having a frequency less than the predetermined value to the base drive signal before the modulation. In the second case, the clock signal may not be added and subtracted. According to the printing apparatus of this embodiment, the change width of the pulse duty ratio can be increased, and a modulation method that can ensure a wide output dynamic range is employed. Generation of defects due to heat generation can be avoided, and in the second case, high-quality printing by faithful waveform reproduction can be realized.

(3) In the printing apparatus of the above aspect, the signal modulation unit inputs the modulation base drive by inputting the base drive signal and a comparison signal composed of a triangular wave or a sawtooth wave that repeats a single waveform to a voltage comparator. Generating a signal, the frequency control unit sets the frequency of the comparison signal to be less than the predetermined value in the first case, and sets the frequency of the comparison signal to the predetermined value in the second case. It may be set as described above. According to the printing apparatus of this aspect, while adopting the modulation method that generates the modulation base drive signal by inputting the base drive signal and the comparison signal to the voltage comparator, in the first case, Generation of defects due to heat generation can be avoided, and in the second case, high-quality printing by faithful waveform reproduction can be realized.

(4) In the printing apparatus according to the above aspect, the signal modulation unit generates the modulation base drive signal by pulsing the amplitude of the base drive signal at a predetermined sampling frequency, and the frequency control unit In the case of 1, the sampling frequency may be set to be less than the predetermined value, and in the second case, the sampling frequency may be set to be not less than the predetermined value. According to the printing apparatus of this aspect, while adopting the modulation method that generates the modulation base drive signal by pulsing the amplitude of the base drive signal, in the first case, the occurrence of problems due to the increase in power consumption or heat generation In the second case, high-quality printing by faithful waveform reproduction can be realized.

  The present invention can be realized in various modes. For example, a printing method, a liquid ejection method, a liquid ejection apparatus, a printing apparatus or a control method for the liquid ejection apparatus, a printing apparatus or a drive circuit for the liquid ejection apparatus Or the like.

It is explanatory drawing which shows schematic structure of the printing apparatus 100 in embodiment of this invention. 4 is an explanatory diagram illustrating an example of various signals used in the print head 140. FIG. 4 is an explanatory diagram illustrating a configuration of a switching controller 160 of the print head 140. FIG. 4 is an explanatory diagram illustrating a configuration for generating a drive signal COM in the printing apparatus 100. FIG. 5 is an explanatory diagram showing an example of a configuration of a signal modulation circuit 82. FIG. 6 is an explanatory diagram showing an oscillation frequency in a modulation circuit 82. FIG. It is explanatory drawing which shows the switching aspect of a frequency restriction. It is explanatory drawing which shows an example of a structure of the signal modulation circuit 82a using pulse width modulation. It is explanatory drawing which shows an example of a structure of the signal modulation circuit 82b using pulse amplitude modulation.

A. Embodiment:
FIG. 1 is an explanatory diagram illustrating a schematic configuration of a printing apparatus 100 according to an embodiment of the present invention. The printing apparatus 100 according to the present embodiment forms a group of ink dots on a print medium by ejecting liquid ink, thereby including an image (characters, graphics, etc.) corresponding to image data supplied from the host computer 200. ).

  The printing apparatus 100 includes a print head 140 and a control unit 110 connected to the print head 140 via a flexible flat cable 139. The control unit 110 performs host computer (IF) 112 for inputting image data and the like from the host computer 200 and predetermined calculation processing for image printing based on the image data input via the host interface 112. The main control unit 120 to be executed, a paper feed motor driver 114 for driving and controlling the paper feed motor 172 for transporting the print medium, a head driver 116 for driving and controlling the print head 140, and the drivers 114 and 116 and the paper feed And a main interface (IF) 119 for connecting the motor 172 and the print head 140 to each other. The head driver 116 includes a main side drive circuit 80 and an oscillation circuit 40.

  The main control unit 120 includes a CPU 122 that executes various arithmetic processes, a RAM 124 that temporarily stores and expands programs and data, and a ROM 126 that stores programs executed by the CPU 122. Various functions of the main control unit 120 are realized by the CPU 122 reading out the program stored in the ROM 126 onto the RAM 124 and executing it. For example, the CPU 122 functions as a frequency limiting unit 128 described later. The main control unit 120 may include an electric circuit, and at least a part of the functions of the main control unit 120 may be realized by the electric circuit included in the main control unit 120 operating based on the circuit configuration. Good.

  When the main control unit 120 acquires image data from the host computer 200 via the host interface 112, the main control unit 120 performs printing such as image development processing, color conversion processing, ink color separation processing, and halftone processing based on the image data. By performing arithmetic processing, nozzle selection data (drive signal selection data) that defines which nozzle of the print head 140 is to eject ink or how much ink is to be ejected is generated and driven. A control signal is output to each of the drivers 114 and 116 based on the signal selection data and the like. It should be noted that the content of each calculation process for print execution executed by the main control unit 120 is a well-known matter in the technical field of the printing apparatus, and thus description thereof is omitted here. The drivers 114 and 116 output signals for controlling the operations of the paper feed motor 172 and the print head 140, respectively. For example, the head driver 116 supplies a reference clock signal SCK, a latch signal LAT, a drive signal selection signal SI & SP, and a channel signal CH, which will be described later, to the print head 140.

  The print head 140 is supplied with one or more colors of ink from one or more ink containers (not shown). The print head 140 includes a head interface (IF) 142, a head side drive circuit 90, a switching controller 160, and an ejection unit 150. The head side drive circuit 90 and the switching controller 160 operate based on various signals input from the control unit 110 via the head interface 142. The ejection unit 150 includes a plurality of nozzle openings 152 that eject ink, and a plurality of piezoelectric elements 156 provided corresponding to the plurality of nozzle openings 152. In the present embodiment, a piezoelectric element is used as the piezoelectric element 156. The nozzle opening 152 communicates with a pressure chamber 154 to which ink is supplied. The piezoelectric element 156 expands or contracts the pressure chamber 154 by being deformed according to a drive signal COM (described later) supplied via the head side drive circuit 90 and the switching controller 160. When the pressure chamber 154 expands or contracts and a pressure change occurs in the pressure chamber 154, ink is ejected from the corresponding nozzle opening 152 by the pressure change. By adjusting the peak value of the drive signal COM used to drive the piezoelectric element 156 and the voltage increase / decrease slope, the ink ejection amount (that is, the size of the dots to be formed) can be adjusted.

  The printing apparatus 100 according to the present embodiment can perform printing at at least two printing resolutions, that is, a first resolution and a second resolution higher than the first resolution. Further, the printing apparatus 100 can perform printing at at least two printing speeds, that is, a first printing speed and a second printing speed that is faster than the first printing speed. The selection of the print resolution and the print speed is performed on a user interface displayed by a printer driver operating on the host computer 200, for example. The user interface includes a portion for selecting any one of the at least two printing resolutions and a portion for selecting any one of the at least two printing speeds. When a print command including information indicating the print resolution and print speed selected on the user interface is sent from the host computer 200 to the printing apparatus 100, the main control unit 120 performs printing at the selected print resolution and print speed. Start. It should be noted that both the printing resolution and the printing speed may be selected at one selection portion on the user interface. For example, the user interface includes a part for selecting any one of a plurality of print modes (for example, “clean mode” and “fast mode”) having different combinations of print resolution and print speed, and the print mode is selected. Then, a combination of the print resolution and the print speed associated with the selected print mode may be selected. For example, when “clean mode” is selected, a relatively high printing resolution and a relatively slow printing speed are selected, and when “fast mode” is selected, a relatively low printing resolution and a relatively low printing speed are selected. A fast printing speed is selected. The user interface may be displayed on the printing apparatus 100. Further, the print resolution and the print speed may be automatically selected by the host computer 200 or the printing apparatus 100 instead of being selected on the user interface. For example, the host computer 200 or the printing apparatus 100 may determine the type of image to be printed and select a combination of print resolution and print speed associated with the determined image type.

  The printing apparatus 100 uses a so-called line printer (a line-type head having a plurality of nozzles arranged in a direction intersecting with the conveyance direction of the print medium, and is accompanied by relative movement of the head along the intersecting direction with respect to the print medium. In the case of a printing apparatus that performs printing, the printing medium is conveyed by the paper feed motor 172 and the ink is ejected from the nozzle opening 152 to the printing medium during printing. In this case, the paper feed motor 172 has a plurality of operation modes having different transport speeds. When the print speed and the print resolution are selected as described above, the paper feed motor driver 114 operates the paper feed motor 172 in an operation mode corresponding to the selected print speed and print resolution. For example, when a relatively high printing resolution or a relatively slow printing speed is selected, the paper feed motor 172 operates in a mode with a relatively slow conveyance speed, and a relatively low printing resolution or a relatively fast printing speed is selected. If it is, the paper feed motor 172 operates in a mode in which the transport speed is relatively fast. On the other hand, the printing apparatus 100 performs printing while performing so-called serial printer (print medium conveyance (sub-scan)) and relative movement of the head with respect to the print medium (main scan) along the direction intersecting the print medium conveyance direction. In the case of printing, the printing medium is conveyed by the paper feed motor 172 and the carriage (not shown) on which the head is mounted is reciprocated along the intersecting direction (main scanning direction). And ink discharge from the nozzle opening 152 to the print medium. In this case, the paper feed motor 172 has a plurality of operation modes with different conveyance speeds, and a carriage motor (not shown) for driving the carriage has a plurality of operation modes with different carriage movement speeds. When the print speed and the print resolution are selected as described above, the paper feed motor driver 114 operates the paper feed motor 172 in an operation mode according to the selected print speed and print resolution, and controls the carriage motor. A motor driver (not shown) operates the carriage motor in an operation mode corresponding to the selected printing speed and printing resolution. For example, when a relatively high printing resolution or a relatively slow printing speed is selected, the paper feed motor 172 operates in a mode in which the transport speed is relatively slow, and the carriage motor operates in a mode in which the carriage moving speed is relatively slow. To do. In addition, when a relatively low printing resolution or a relatively fast printing speed is selected, the paper feed motor 172 operates in a mode in which the transport speed is relatively fast, and the carriage motor operates in a mode in which the carriage moving speed is relatively fast. To do. Only one of the paper feed motor 172 and the carriage motor may have a plurality of operation modes, and the other one may have a single operation mode. In this case, the motor having the plurality of operation modes operates in an operation mode corresponding to the selected printing speed and printing resolution.

  FIG. 2 is an explanatory diagram illustrating an example of various signals used in the print head 140. FIG. 2A shows an example of the drive signal COM, the latch signal LAT, the channel signal CH, and the drive signal selection signal SI & SP. The drive signal COM is a signal for driving the piezoelectric element 156 provided in the ejection unit 150 of the print head 140. The drive signal COM is a signal in which drive pulses PCOM (drive pulses PCOM1 to PCOM4) as a minimum unit (unit drive signal) for driving the piezoelectric element 156 are continuous in time series. A set of four drive pulses PCOM of drive pulses PCOM1, PCOM2, PCOM3, and PCOM4 included in each cycle Tcom of the drive signal COM corresponds to one pixel (print pixel).

  FIG. 2B shows an enlarged example of the drive pulse PCOM2. The drive pulse PCOM2 includes an expansion element E1, an expansion holding element E2, a discharge element E3, a contraction holding element E4, and a vibration damping element E5. The same applies to the drive pulses PCOM3 and PCOM4. The expansion element E1 of each drive pulse PCOM increases the potential from the intermediate potential Vm corresponding to the steady state of the piezoelectric element 156 to the expansion potential (maximum voltage) Vh to deform the piezoelectric element 156, thereby increasing the volume of the pressure chamber 154. It is a part for expanding and drawing ink (which can be said to draw meniscus when considered from the ink discharge surface). The expansion holding element E2 is a part that maintains the expansion potential Vh by maintaining the expansion potential Vh. The ejection element E3 lowers the potential from the expansion potential Vh to the contraction potential (minimum voltage) Vl to deform the piezoelectric element 156, thereby contracting the volume of the pressure chamber 154 and pushing out ink (in terms of the ink ejection surface). It can be said that the meniscus is pushed out). The contraction holding element E4 is a part that maintains the contraction potential Vl and maintains the contracted state of the pressure chamber 154. The damping element E5 returns the volume of the pressure chamber 154 to the steady state by raising the potential from the contraction potential Vl to the intermediate potential Vm and returning the piezoelectric element 156 to the steady state (considering the meniscus in terms of the ink ejection surface). It can also be said to suppress vibration). The piezoelectric element 156 has a steady state, an expanded state that expands the volume of the pressure chamber 154, an expansion hold state that holds the volume of the expanded pressure chamber 154, and a volume of the pressure chamber 154 according to each element of each drive pulse PCOM. In order, the contraction hold state in which the volume of the contracted pressure chamber 154 is retained, and the vibration suppression state in which the volume of the pressure chamber 154 is returned to the steady state. By selecting one or a plurality of drive pulses PCOM from the drive pulses PCOM2, PCOM3, and PCOM4 and supplying them to the piezoelectric element 156, ink dots of various sizes can be formed. In the present embodiment, the drive signal COM includes a drive pulse PCOM1 called micro vibration. The drive pulse PCOM1 is used when only ink is drawn and no extrusion is performed, for example, when thickening of the nozzle opening 152 is suppressed. As will be described later, the drive signal COM is generated by amplifying the base drive signal WCOM, and the signal waveform of the base drive signal WCOM is the same as the waveform of the drive signal COM shown in FIG. is there.

  The drive signal selection signal SI & SP is a signal for selecting the nozzle opening 152 for ejecting ink and determining the timing for connecting the piezoelectric element 156 to the drive signal COM. The latch signal LAT and the channel signal CH are signals for connecting the drive signal COM and the piezoelectric element 156 of the print head 140 based on the drive signal selection signal SI & SP after the nozzle selection data for all the nozzle openings 152 are input. It is. As shown in FIG. 2A, the latch signal LAT and the channel signal CH are signals synchronized with the drive signal COM. That is, the latch signal LAT is a signal that becomes a high level corresponding to the start timing of the drive signal COM, and the channel signal CH is a high level that corresponds to the start timing of each drive pulse PCOM constituting the drive signal COM. Is a signal. Output of a series of drive signals COM is started according to the latch signal LAT, and each drive pulse PCOM is output according to the channel signal CH. The reference clock signal SCK is a signal for transmitting the drive signal selection signal SI & SP to the print head 140 as a serial signal. That is, the reference clock signal SCK is a signal used for determining the timing for ejecting ink from the nozzle openings 152 of the print head 140.

  FIG. 3 is an explanatory diagram showing the configuration of the switching controller 160 (FIG. 1) of the print head 140. The switching controller 160 selectively supplies the drive signal COM to the piezoelectric element 156. The switching controller 160 converts the level of the shift register 162 that stores the drive signal selection signal SI & SP, the latch circuit 164 that temporarily stores the data of the shift register 162, and the level of the output of the latch circuit 164 and supplies the output to the selection switch 168. A level shifter 166 and a selection switch 168 for connecting the drive signal COM to the piezoelectric element 156 are provided.

  The drive signal selection signal SI & SP is sequentially input to the shift register 162, and the area stored in accordance with the input pulse of the reference clock signal SCK is sequentially shifted to the subsequent stage. The latch circuit 164 latches the output signals of the shift register 162 according to the input latch signal LAT after the drive signal selection signals SI & SP for the number of nozzles are stored in the shift register 162. The signal stored in the latch circuit 164 is converted by the level shifter 166 to a voltage level at which the selection switch 168 in the next stage can be switched (ON / OFF). The piezoelectric element 156 corresponding to the selection switch 168 that is closed (becomes connected) by the output signal of the level shifter 166 is connected to the drive signal COM (drive pulse PCOM) at the connection timing of the drive signal selection signal SI & SP. As a result, the piezoelectric element 156 is deformed, and an amount of ink corresponding to the drive signal COM is ejected from the nozzle. Further, after the drive signal selection signal SI & SP input to the shift register 162 is latched by the latch circuit 164, the next drive signal selection signal SI & SP is input to the shift register 162, and the latch circuit 164 receives the ink discharge timing. Update stored data sequentially. According to the selection switch 168, even after the piezoelectric element 156 is disconnected from the drive signal COM (drive pulse PCOM), the input voltage of the piezoelectric element 156 is maintained at the voltage just before the disconnection. Note that the symbol HGND in FIG. 3 is the ground end of the piezoelectric element 156.

  FIG. 4 is an explanatory diagram illustrating a configuration for generating the drive signal COM in the printing apparatus 100. In FIG. 4, the configuration of the printing apparatus 100 that is not directly related to the generation of the drive signal COM is appropriately omitted. In the present embodiment, the drive signal COM is generated by the main side drive circuit 80 of the control unit 110 and the head side drive circuit 90 of the print head 140. The main drive circuit 80 includes a base drive signal generation circuit 81, a signal modulation circuit 82, and a signal amplification circuit 83. The head side drive circuit 90 includes a signal conversion circuit 91.

  The base drive signal generation circuit 81 is a circuit that generates a base drive signal WCOM that is an analog signal that is the basis of the drive signal COM described above. The base drive signal generation circuit 81 stores, for example, waveform forming data input from the main control unit 120 in a storage element corresponding to a predetermined address, as described in Japanese Patent Application Laid-Open No. 2011-207234. A memory, a first latch circuit for latching waveform forming data read from the waveform memory by a first clock signal, an output of the first latch circuit, and a waveform generation output from a second latch circuit described later An adder for adding the data W, a second latch circuit for latching the addition output of the adder by the second clock signal, and a waveform driving data output from the second latch circuit based on an analog signal And a D / A converter for converting the signal WCOM.

  The signal modulation circuit 82 is a circuit that receives the base drive signal WCOM from the base drive signal generation circuit 81, generates a modulation base drive signal MS that is a digital signal by performing pulse modulation on the base drive signal WCOM. The signal modulation circuit 82 will be described in detail later.

  The signal amplification circuit 83 is a circuit (so-called class D amplifier) that receives the modulation base drive signal MS from the signal modulation circuit 82 and amplifies the power of the modulation base drive signal MS to generate the modulation drive signal MAS. The signal amplifying circuit 83 includes a half-bridge output stage 85 including two switching elements (a high-side switching element Q1 and a low-side switching element Q2) for substantially amplifying power, and a modulation base from the signal modulation circuit 82. And a gate drive circuit 84 that adjusts the gate-source signals GH and GL of the switching elements Q1 and Q2 based on the drive signal MS. In the signal amplifying circuit 83, when the modulation base drive signal MS is at a high level, the high-side switching element Q1 is turned on because the gate-source signal GH is at a high level, and the low-side switching element Q2 is turned on at the gate-source. As a result, the output of the half-bridge output stage 85 becomes the supply voltage VDD. On the other hand, when the modulation base drive signal MS is at the low level, the high-side switching element Q1 is turned off with the gate-source signal GH being at the low level, and the low-side switching element Q2 is in the gate-source signal GL. As a result, the output of the half-bridge output stage 85 becomes zero. As described above, in the signal amplification circuit 83, power amplification is performed by the switching operation of the high-side switching element Q1 and the low-side switching element Q2 based on the modulation base drive signal MS, and the modulation drive signal MAS is generated. By the above operation, the switching frequency of each of the switching elements Q1 and Q2 becomes equal to the frequency of the modulation base drive signal MS input from the signal modulation circuit 82, that is, the oscillation frequency of the signal modulation circuit 82.

  The signal conversion circuit 91 is a circuit (so-called smoothing filter) that receives the modulation drive signal MAS from the signal amplification circuit 83 and smoothes the modulation drive signal MAS to generate a drive signal COM (drive pulse PCOM) that is an analog signal. In the present embodiment, a low-pass filter (low-pass filter) using a combination of a capacitor C and a coil L is used as the signal conversion circuit 91. The signal conversion circuit 91 attenuates the modulation frequency component generated by the signal modulation circuit 82 and outputs the drive signal COM having the waveform characteristics as described above. The drive signal COM generated by the signal conversion circuit 91 is supplied to the piezoelectric element 156 of the ejection unit 150 via the selection switch 168 of the switching controller 160.

  FIG. 5 is an explanatory diagram showing an example of a specific configuration of the drive circuit. In the present embodiment, self-excited pulse density modulation (PDM) is used as a modulation method in the signal modulation circuit 82. As shown in FIG. 5, the signal modulation circuit 82 inputs a base drive signal WCOM and a comparison signal composed of a triangular wave or a sawtooth wave whose frequency changes according to the voltage of the base drive signal WCOM to the voltage comparator. The modulation base drive signal MS is generated. In general, pulse density modulation compares an input signal with a predetermined value and outputs a signal that goes high when the input signal is greater than or equal to a predetermined value, and an error between the input signal and the output signal of the comparator. This is performed using a so-called ΔΣ modulation circuit that includes a subtractor that calculates the error, a delayer that delays the error, and an adder / subtracter that adds or subtracts the delayed error to or from the original signal. However, in the example shown in FIG. 5, the signal modulation circuit 82 using the pulse density modulation does not have a delay device. Since the low-pass filter configured as the signal conversion circuit 91 is a delay device if the expression is changed, an LC low-pass filter output (COM) is used as a delay signal instead of the delay device, as indicated by VFB in FIG. In the present embodiment, a circuit that emphasizes the high frequency component (high pass filter (HP-F) and high frequency boost (G)) and a circuit that feeds back the high frequency component (shown as “IFB”) are added. ing. That is, in this example, the signal modulation circuit 82 receives the modulation signal amplified by the signal amplification circuit 83 as a feedback signal and corrects the modulation base drive signal MS to be generated. The signal modulation circuit 82 may be configured using other circuits capable of performing pulse density modulation, including a circuit using a ΔΣ modulation circuit.

  The modulation method in the modulation circuit 82 of the present embodiment is a self-excited oscillation type pulse density modulation method, and the oscillation frequency varies according to the signal level (pulse duty ratio) of the input drive waveform signal WCOM. FIG. 6 is an explanatory diagram showing the oscillation frequency in the modulation circuit 82. As shown by the solid line in FIG. 6, the oscillation frequency in the pulse density modulation method is highest when the input signal level is the intermediate value L1 (becomes the maximum value f (t)), and the input signal level is the intermediate value L1. It becomes lower as it becomes larger or smaller. The pulse duty ratio in the vicinity of the intermediate value is approximately 50%, but the pulse duty ratio changes as the oscillation frequency decreases. The advantage of this method is that the change width of the pulse duty ratio can be increased as compared with the pulse width modulation method with a fixed modulation frequency, and a wide output dynamic range can be secured. That is, since the minimum positive pulse width and negative pulse width that can be handled by the entire modulation circuit are restricted by the circuit characteristics, a pulse signal less than that is lost on the way. For this reason, in the pulse width modulation method with a fixed frequency, it is possible to ensure only the pulse duty ratio change width within a predetermined range (for example, 10% to 90%). On the other hand, in the self-excited oscillation type pulse density modulation system of this embodiment, the oscillation frequency decreases as the input signal level increases or decreases from the intermediate value. Therefore, the pulse duty ratio is increased at a portion where the input signal level is very large. A larger signal can be handled, and a signal with a smaller pulse duty ratio can be handled in a very small part, so a wider range of pulse duty ratio change (for example, 5% to 95%) should be secured. Can do. Specific examples are shown below. For example, if the positive and negative minimum pulse widths that can be handled by the entire circuit are both 25 ns, when the modulation frequency is fixed at 4 MHz, the pulse duty ratio change width is determined by the ratio to the period, so that it is 10% to 90%. Only the pulse duty ratio change width can be secured. On the other hand, in the self-excited oscillation type pulse density modulation system of the present embodiment, the oscillation frequency changes according to the input signal level. For example, if the input signal is 2 MHz at both low and high levels, 5% to 95%. The pulse duty ratio change width can be ensured. Thereby, a wide output dynamic range can be ensured. Further, the self-excited oscillation type pulse density modulation method of the present embodiment does not require an external circuit for generating a high frequency signal as in the case of the separately-excited modulation method with a fixed frequency. There is an advantage in system configuration such as.

  Here, the frequency limiting unit 128 (FIG. 1) causes the oscillation circuit 40 to supply the frequency limiting clock signal LCK to the signal modulation circuit 82 in a predetermined case described later. When the frequency limiting clock signal LCK is input to the signal modulation circuit 82 (FIG. 4), in the modulation circuit 82, the frequency limiting clock signal LCK is input to the adder / subtractor AS (FIG. 5). The input frequency limiting clock signal LCK is added to or subtracted from the drive waveform signal WCOM by the adder / subtractor AS. In a state where the frequency limiting clock signal LCK is input to the signal modulation circuit 82, the oscillation frequency in the modulation circuit 82 is limited to the frequency of the frequency limiting clock signal LCK. That is, when the oscillation frequency of the signal modulation circuit 82 approaches the frequency limiting clock signal LCK, the oscillation frequency is drawn into the frequency limiting clock signal LCK and fixed to the frequency f (p) of the frequency limiting clock signal LCK ( (See broken line in FIG. 6). When the input signal level changes and the original oscillation frequency greatly deviates from the frequency f (p) of the frequency limiting clock signal LCK, the fixation to the frequency limiting clock signal LCK is released, and the oscillation frequency of the modulation circuit 82 is The normal oscillation frequency corresponding to the input signal level is restored. As described above, the frequency limiting unit 128 switches the oscillation frequency of the signal modulation circuit 82 from the oscillation circuit 40 to the signal modulation circuit 82 to thereby change the oscillation frequency of the signal modulation circuit 82 to the frequency limitation clock signal LCK. It is possible to switch between limiting to less than the frequency f (p). As described above, since the oscillation frequency of the signal modulation circuit 82 is equal to the switching frequency of the switching elements Q1 and Q2 of the signal amplification circuit 83, the frequency limiting unit 128 sets the switching frequency of the switching elements Q1 and Q2 to less than a predetermined value. It can also be expressed that it is possible to switch between restriction and non-restriction.

  FIG. 7 is an explanatory diagram showing a switching mode of frequency restriction. As illustrated in FIG. 7, the printing apparatus 100 according to the present embodiment can select one of three speeds (6, 12, 18 ipm (image per minute)) as the print speed, and can select six print resolutions. One of the resolutions (from 300 × 300 dpi (dot per inch) to 2400 × 2400 dpi) can be selected. The number on the right side of the print resolution indicates the ratio when the minimum resolution (300 × 300 dpi) is the reference value 1.

  In the present embodiment, the frequency limiting unit 128 includes each switching element in the first case where the product of the printing speed and the printing resolution (more specifically, the ratio value, and so on) is equal to or greater than a predetermined threshold value. In the second case where the product of the printing speed and the printing resolution is less than the threshold value, the switching frequency of each switching element Q1, Q2 is not restricted. The threshold is set to 100, for example. As shown in FIG. 7, when the printing speed is 6 ipm and the printing resolution is 1200 × 1200 dpi, the product is 96, so the frequency limiting unit 128 does not limit the switching frequency. On the other hand, when the printing speed is 6 ipm and the printing resolution is 1200 × 2400 dpi, the product is 192. Therefore, the frequency limiting unit 128 limits the switching frequency.

  If the printing speed is high or the printing resolution is high, the number of switchings per unit time of the switching elements Q1 and Q2 of the signal amplifier circuit 83 increases, so that power consumption increases and a problem due to heat generation may occur. In the printing apparatus 100 of the present embodiment, the frequency limiting unit 128 limits the switching frequency of each switching element Q1, Q2 in the first case where the product of the printing speed and the printing resolution is equal to or greater than a predetermined threshold. Therefore, it is possible to avoid the occurrence of problems due to increase in power consumption and heat generation. In this case, the waveform reproducibility is lowered and a slight influence on the image quality occurs. However, the frequency is limited only at the intermediate level of the pulse duty ratio (FIG. 6), and the influence on the image quality is reduced. Can be suppressed as much as possible. In the printing apparatus 100 of the present embodiment, the frequency limiting unit 128 limits the switching frequency of each switching element Q1, Q2 in the second case where the product of the printing speed and the printing resolution is less than the above threshold. Since this is not performed, high-quality printing can be realized by faithful waveform reproduction.

B. Variations:
In addition, this invention is not restricted to said embodiment, In the range which does not deviate from the summary, it can be implemented in a various aspect, For example, the following deformation | transformation is also possible.

B1. Modification 1:
The configuration of the printing apparatus 100 in the above embodiment is merely an example, and various modifications can be made. For example, although pulse density modulation (PDM) is used as the modulation method in the signal modulation circuit 82 in the above embodiment, pulse width modulation (PWM) may be used instead. FIG. 8 is an explanatory diagram showing an example of the configuration of the signal modulation circuit 82a using pulse width modulation. As shown in FIG. 8A, the signal modulation circuit 82a includes a comparison signal generation circuit 51 that outputs a comparison signal composed of a triangular wave (or sawtooth wave) that repeats a single waveform at a predetermined frequency, and a base drive signal WCOM. And a voltage comparator 52 for comparing the comparison signal with each other. FIG. 8B shows an example of the configuration of the comparison signal generation circuit 51. According to this signal modulation circuit 82a, a modulation base drive signal MS is generated that becomes Hi when the base drive signal WCOM is equal to or greater than the comparison signal and becomes Lo when the base drive signal WCOM is less than the comparison signal. That is, the frequency of the modulation base drive signal MS is equal to the frequency of the comparison signal. In this modification, the frequency limiting unit 128 (FIG. 1) can change the frequency of the modulation base drive signal MS (that is, the switching frequency of the switching elements Q1 and Q2) by changing the frequency of the comparison signal. . In the present modification, in the first case where the product of the printing speed and the printing resolution is equal to or greater than a predetermined threshold, the frequency limiting unit 128 sets the frequency of the comparison signal to be less than the predetermined value. Therefore, the switching frequency of each switching element Q1, Q2 is limited to less than the predetermined value, and it is possible to avoid the occurrence of problems due to increased power consumption and heat generation. Further, in the second case where the product of the printing speed and the printing resolution is less than the threshold value, the frequency limiting unit 128 sets the frequency of the comparison signal to be equal to or higher than the predetermined value. Therefore, the switching frequency of each of the switching elements Q1, Q2 is not limited to less than the predetermined value, and high-quality printing by faithful waveform reproduction can be realized.

  Further, pulse amplitude modulation (PAM) may be used as a modulation method in the signal modulation circuit 82. FIG. 9 is an explanatory diagram showing an example of the configuration of the signal modulation circuit 82b using pulse amplitude modulation. As shown in FIG. 9, the signal modulation circuit 82b generates the modulation base drive signal MS by pulsing the amplitude of the base drive signal WCOM at a predetermined sampling frequency. Specifically, the signal modulation circuit 82b shown in FIG. 9 is configured using a video amplifier IC1 (for example, “ADA4856-3” manufactured by Analog Devices, USA) having three operational amplifiers (A1, A2, A3). ing. Two resistors are connected to each of the operational amplifiers A1, A2, and A3. With the illustrated wiring, the operational amplifiers A1 and A3 function as a forward amplifier with a gain (amplification degree) of 1, and the operational amplifier A2 functions as an inverting amplifier with a gain of -1. IC2 is a BBM (Break-Before-Make) type high-speed multiplexer (for example, “ADG772” manufactured by Analog Devices, USA), and the connection destination to the input of the operational amplifier A3 is the output of the operational amplifier A1. And the output of the operational amplifier A2 are alternately switched. The control logic signal IN2 of IC2 is kept near 50% duty cycle. As a result, the average value of the output voltage of the operational amplifier A3 is approximately 0V. For example, when the modulation speed, that is, the frequency of the control logic signal is about 6 MHz, the DC component of the output voltage is only a low frequency offset voltage having an average of 4 mV or less. The switch contacts S2A and S2B are both temporarily turned off, typically with a 5 ns tBBM (Break-Before-Make Time Delay). When the control frequency is 60 MHz, each switch should be on for about 8.3 ns of its half cycle, but the actual on state period is 3.3 ns because tBBM exists. Further, if there is a difference between the turn-on times of the switch contacts S2A and S2B, it also appears in the result as a DC component. According to the circuit shown in FIG. 9, the absolute value of the amplitude of each pulse of the base drive signal WCOM input to the input terminal IN is equal to the instantaneous voltage level of the waveform of the base drive signal WCOM, and the sign is alternately positive and negative. It is possible to generate the modulation base drive signal MS as a changing pulse amplitude modulated wave. Since the average value of the generated waveform of the modulation base drive signal MS is approximately 0 V, the waveform can be easily transmitted in a state of being insulated by a transformer. Note that another multiplexer performing MBB (Make-Before-Break) type operation may be used as the multiplexer used in the circuit of FIG. With this type of multiplexer, the conduction period at a frequency of 60 MHz is more than tripled, and the effect of the difference in turn-on time between switches is reduced. When an MBB type multiplexer is used, it is necessary to prevent an overload due to a short circuit between the outputs of the operational amplifiers A1 and A2. Therefore, a surface mount resistor (for example, about 20Ω) is inserted into the outputs of the operational amplifiers A1 and A2. Is desirable. The signal modulation circuit 82b may be configured using another circuit capable of performing pulse amplitude modulation.

  In the modification shown in FIG. 9, the frequency of the modulation base drive signal MS is equal to the sampling frequency. In this modification, the frequency limiting unit 128 (FIG. 1) can change the frequency of the modulation base drive signal MS (that is, the switching frequency of the switching elements Q1 and Q2) by changing the sampling frequency. In this modification, the frequency limiting unit 128 sets the sampling frequency to be less than a predetermined value in the first case where the product of the printing speed and the printing resolution is equal to or greater than a predetermined threshold. Therefore, the switching frequency of each switching element Q1, Q2 is limited to less than the predetermined value, and it is possible to avoid the occurrence of problems due to increased power consumption and heat generation. Further, in the second case where the product of the printing speed and the printing resolution is less than the threshold value, the frequency limiting unit 128 sets the sampling frequency to be equal to or higher than the predetermined value. Therefore, the switching frequency of each of the switching elements Q1, Q2 is not limited to less than the predetermined value, and high-quality printing by faithful waveform reproduction can be realized.

B2. Modification 2:
The examples of printing speed and printing resolution options (FIG. 7) in the above embodiment are merely examples, and various modifications can be made. For example, the number of printing speed options may be two, or four or more. Similarly, the number of print resolution options may be 2, 3, 4, 5, 6, or 8 or more. Further, in the above-described embodiment, the case where the frequency limit is performed is determined depending on whether the product of the printing speed and the printing resolution is less than the threshold value, but the printing speed and the printing resolution when calculating this product are divided. The unit of can be arbitrarily changed. An appropriate threshold may be set according to the unit of the printing speed and the printing resolution. The threshold value may be selectable from a plurality of options.

B3. Modification 3:
The various signals exemplified in the above embodiment are merely examples, and various changes can be made. For example, in the above embodiment, the drive signal COM is a signal composed of a plurality of trapezoidal waveforms, but the drive signal COM may be a signal composed of a plurality of rectangular waveforms. The signal may include a curved waveform.

  In the above embodiment, the signal amplification circuit 83 is disposed in the main drive circuit 80 of the control unit 110. However, the signal amplification circuit 83 is disposed in the head drive circuit 90 of the print head 140. Also good. In the above embodiment, the signal conversion circuit 91 is arranged in the head side drive circuit 90 of the print head 140, but the signal conversion circuit 91 is mounted on the flexible flat cable 139 that connects the control unit 110 and the print head 140. It may be arranged in.

  In the above-described embodiment, the printing apparatus 100 receives image data from the host computer 200 and performs printing processing. Instead, the printing apparatus 100 uses, for example, image data acquired from a memory card, Printing processing may be performed based on image data acquired from a digital camera via a predetermined interface, image data acquired by a scanner, or the like. In the above embodiment, the main control unit 120 of the printing apparatus 100 that has received the image data performs arithmetic processing for printing such as image development processing, color conversion processing, ink color separation processing, and halftone processing. However, these arithmetic processes may be executed by the host computer 200. In this case, the printing apparatus 100 receives the print command generated by the calculation process by the host computer 200, and executes the print process according to the print command. The present invention can also be applied to a serial printer in which a carriage on which the print head 140 is mounted reciprocates during printing, and can also be applied to a line printer that does not involve such reciprocation. The present invention can also be applied to an on-carriage printer in which an ink container moves reciprocally with a carriage, and a holder for mounting the ink container is provided at a location different from the carriage so that the ink container is flexible. The present invention can also be applied to an off-carriage printer that supplies ink to the print head 140 via a tube or the like. The present invention is also applicable to a printing apparatus that forms an image on a printing medium using a liquid other than ink (including a liquid material in which particles of a functional material are dispersed and a fluid such as a gel).

  In the above embodiment, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware. Good. In addition, when part or all of the functions of the present invention are realized by software, the software (computer program) can be provided in a form stored in a computer-readable recording medium. In the present invention, the “computer-readable recording medium” is not limited to a portable recording medium such as a flexible disk or a CD-ROM, but an internal storage device in a computer such as various RAMs and ROMs, a hard disk, etc. It also includes an external storage device fixed to the computer.

DESCRIPTION OF SYMBOLS 40 ... Oscillator 51 ... Comparison signal generation circuit 52 ... Voltage comparator 80 ... Main side drive circuit 81 ... Base drive signal generation circuit 82 ... Signal modulation circuit 83 ... Signal amplification circuit 84 ... Gate drive circuit 85 ... Half bridge output stage 90 DESCRIPTION OF SYMBOLS ... Head side drive circuit 91 ... Signal conversion circuit 100 ... Printing apparatus 110 ... Control unit 112 ... Host interface 114 ... Paper feed motor driver 116 ... Head driver 120 ... Main control part 122 ... CPU
124 ... RAM
126 ... ROM
DESCRIPTION OF SYMBOLS 128 ... Frequency limitation part 139 ... Flexible flat cable 140 ... Print head 142 ... Head interface 150 ... Discharge part 152 ... Nozzle opening part 154 ... Pressure chamber 156 ... Piezoelectric element 160 ... Switching controller 162 ... Shift register 164 ... Latch circuit 166 ... Level Shifter 168 ... Selection switch 172 ... Paper feed motor 200 ... Host computer

Claims (5)

A printing apparatus capable of printing at at least two printing speeds, a first printing speed and a second printing speed that is faster than the first printing speed,
A base drive signal generator for generating a base drive signal;
A signal modulator that modulates the base drive signal to generate a modulated base drive signal;
A signal amplifier that amplifies the modulation base drive signal using a switching element to generate a modulation drive signal; and
A signal converter that converts the modulated drive signal into a drive signal;
A piezoelectric element deformed by the drive signal;
A pressure chamber that expands or contracts due to deformation of the piezoelectric element;
A nozzle opening communicating with the pressure chamber;
In the first case of printing at the second printing speed , the switching frequency of the switching element is limited to less than a predetermined value , and in the second case of printing at the first printing speed , the switching element A frequency controller that does not limit the switching frequency to less than the predetermined value; and
A printing apparatus comprising: The printing apparatus according to claim 1,
The signal modulation unit generates the modulation base drive signal by inputting the base drive signal and a comparison signal composed of a triangular wave or a sawtooth wave whose frequency changes according to the voltage of the base drive signal to a voltage comparator. And
In the first case, the frequency control unit adds or subtracts a clock signal having a frequency less than the predetermined value with respect to the base drive signal before the modulation, and in the second case, the frequency control unit A printing apparatus that does not add and subtract a clock signal. The printing apparatus according to claim 1,
The signal modulation unit generates the modulation base drive signal by inputting the base drive signal and a comparison signal composed of a triangular wave or a sawtooth wave repeating a single waveform to a voltage comparator,
The frequency control unit sets the frequency of the comparison signal to be less than the predetermined value in the first case, and sets the frequency of the comparison signal to be equal to or higher than the predetermined value in the second case. Characteristic printing device. The printing apparatus according to claim 1,
The signal modulation unit generates the modulation base drive signal by pulsing the amplitude of the base drive signal at a predetermined sampling frequency,
The frequency control unit sets the sampling frequency to be lower than the predetermined value in the first case, and sets the sampling frequency to be equal to or higher than the predetermined value in the second case. apparatus. A method of printing at one of at least two printing speeds, a first printing speed and a second printing speed that is faster than the first printing speed, comprising:
Generating a base drive signal;
Modulating the base drive signal to generate a modulated base drive signal;
Amplifying the modulation base drive signal using a switching element to generate a modulation drive signal;
Converting the modulated drive signal into a drive signal;
Ejecting ink from a nozzle opening communicating with a pressure chamber that expands or contracts by deformation of the piezoelectric element by deforming the piezoelectric element by the drive signal;
In the first case of printing at the second printing speed , the switching frequency of the switching element is limited to less than a predetermined value , and in the second case of printing at the first printing speed , the switching element Not switching the switching frequency below the predetermined value;
A printing method comprising:

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