Liquid ejecting apparatus and liquid ejecting head unit

A liquid ejecting apparatus includes an ejecting section configured to eject liquid to a print medium, a movement mechanism configured to change the relative positional relationship between the print medium and the ejecting section, an encoder configured to include a scale, a light emitting element emitting light, and a light receiving element receiving light reflected by the scale or light transmitted through the scale in the emitted light and configured to output information changed in accordance with a change in the positional relationship, a signal generation section configured to generate a pulse signal including a pulse prescribing a timing when the ejecting section ejects liquid based on the information, a measurement section configured to measure a time length between pulses included in the pulse signal, and an ejection restriction section configured to restrict ejection of liquid from the ejecting section when the time length is larger than a threshold value.

The present application is based on, and claims priority from JP Application Serial Number 2019-207673, filed Nov. 18, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure related to a liquid ejecting apparatus and a liquid ejecting head unit.

2. Related Art

In general, liquid ejecting apparatuses ejecting liquid, such as ink, have been used as represented by ink jet printers. This type of apparatus, as disclosed in JP-A-2002-356033, ejects liquid to be landed on a print medium from a liquid ejecting head unit while the relative positional relationship between the liquid ejecting head unit ejecting liquid and the print medium is changed, for example.

The apparatus disclosed in JP-A-2002-356033 changes the relative positional relationship between a head and a print sheet by causing a carriage in which a head ejecting ink is fixed to reciprocate in a vertical direction relative to a sheet feeding direction. Here, ejection of ink from the head is controlled based on an output of an encoder for detecting a position of the carriage. The encoder has a scale, a light emitting element emitting light to the scale, and a light receiving element receiving light transmitted through the scale in the light emitted from the light emitting element.

In general, mist of liquid droplets floating in a housing of a liquid ejecting apparatus without being attached to a print medium is secondarily generated in addition to liquid droplets attached to the print medium when a liquid ejecting head unit ejects liquid to the print medium as liquid droplets. Such mist of liquid droplets causes a detection error of an encoder when being attached to a scale of the encoder.

In the apparatus disclosed in JP-A-2002-356033, even when an error occurs in detection performed by the encoder, a timing when liquid is to be ejected is controlled based on an output of the encoder of the erroneous detection without change. Therefore, there arises a problem in the apparatus disclosed in JP-A-2002-356033 in that printing is performed in a state in which image quality is degraded.

SUMMARY

According to an aspect of the present disclosure, a liquid ejecting apparatus includes an ejecting section configured to eject liquid to a print medium, a movement mechanism configured to change the relative positional relationship between the print medium and the ejecting section, an encoder configured to include a scale, a light emitting element emitting light to the scale, and a light receiving element receiving light reflected by the scale or light transmitted through the scale in the emitted light and configured to output information changed in accordance with a change in the positional relationship, a signal generation section configured to generate a pulse signal including a pulse prescribing a timing when the ejecting section ejects liquid based on the information, a measurement section configured to measure a time length between pulses included in the pulse signal, and an ejection restriction section configured to restrict ejection of liquid from the ejecting section when the time length is larger than a threshold value.

According to another aspect of the present disclosure, a liquid ejecting head unit mounted on a liquid ejecting apparatus including an ejecting section configured to eject liquid to a print medium, a movement mechanism configured to change the relative positional relationship between the print medium and the ejecting section, and an encoder configured to include a scale, a light emitting element emitting light to the scale, and a light receiving element receiving light reflected by the scale or light transmitted through the scale in the emitted light and configured to output information changed in accordance with a change in the positional relationship, includes the ejecting section, a signal generation section configured to generate a pulse signal including a pulse prescribing a timing when the ejecting section ejects liquid based on the information, a measurement section configured to measure a time length between pulses included in the pulse signal, and an ejection restriction section configured to restrict ejection of liquid from the ejecting section when the time length is larger than a threshold value.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Note that, in the drawings, sizes and scales of the sections are different from actual sections where appropriate. Note that, although technically preferred restrictions are assigned to the embodiments described below since the embodiments are preferred concrete examples of the present disclosure, the scope of the present disclosure is not limited to the embodiments unless a description indicating that the present disclosure is restricted is made.

A1. First Embodiment

A1-1. Brief Description of Liquid Ejecting Apparatus1

FIG. 1is a perspective view schematically illustrating a configuration of a liquid ejecting apparatus1according to a first embodiment. The liquid ejecting apparatus1is an ink jet printer performing printing by ejecting ink which is an example of liquid to a print medium P as liquid droplets. Typical examples of the print medium P include a print sheet. Note that the print medium P is not limited to a print sheet and may be a print target of arbitrary material, such as a resin film or fabric.

In the example ofFIG. 1, the liquid ejecting apparatus1is a serial printer. Specifically, the liquid ejecting apparatus1includes a housing10, a carriage20, a movement mechanism30, a transport mechanism40, encoders50and60, and a control module70.

In the liquid ejecting apparatus1, print data is supplied to the control module70from a host computer which is an external apparatus, such as a personal computer or a digital still camera, not illustrated. Thereafter, under control of the control module70, the transport mechanism40transports the print medium P in a sub-scanning direction, and in addition, a head unit HU mounted on the carriage20ejects ink toward the print medium P while the movement mechanism30causes the carriage20to reciprocate in a main scanning direction. Here, an image corresponding to the print data is printed on the print medium P when the control module70controls an operation of the head unit HU based on the print data. Furthermore, the encoder50detects an operation state of the movement mechanism30, and in addition, the encoder60detects an operation state of the transport mechanism40, so that the control module70controls the various sections included in the liquid ejecting apparatus1appropriately using results of the detections.

Hereinafter, first, configurations of the sections included in the liquid ejecting apparatus1are briefly described with reference toFIG. 1. Note that, for simplicity of description, X, Y, and Z axes which orthogonally intersect with one another are appropriately used in the description hereinafter. Furthermore, a direction along the X axis is referred to as an X1direction and a direction opposite to the X1direction is referred to as an X2direction. Similarly, a direction along the Y axis is referred to as a Y1direction and a direction opposite to the Y1direction is referred to as a Y2direction. A direction along the Z axis is referred to as a Z1direction and a direction opposite to the Z1direction is referred to as a Z2direction. In this embodiment, at least one of the Y1direction and the Y2direction is the main scanning direction described above and the X1direction is the sub-scanning direction described above. Note that it is not necessarily the case that the X, Y, and Z axes orthogonally intersect with one another but the X, Y, and Z axes at least intersect with one another within a range in which the operation of the liquid ejecting apparatus1is not adversely affected.

The housing10is a structure supporting the movement mechanism30and the transport mechanism40. The housing10of this embodiment has a box shape accommodating the carriage20, the movement mechanism30, and the transport mechanism40. Note that, inFIG. 1, a portion of the housing10is omitted for simplicity of the description. The housing10has a member covering the movement mechanism30and the transport mechanism40, such as a lid, in practice, for example.

The movement mechanism30causes the carriage20to reciprocate in the Y1direction and the Y2direction relative to the housing10. Accordingly, the movement mechanism30changes the relative positional relationship between the print medium P and ejecting sections D described below along the Y axis. Specifically, the movement mechanism30includes a guide shaft31, a pair of pulleys32and33, a timing belt34, and a motor35.

The guide shaft31is fixed on the housing10, has a bar shape extending along the Y axis, and supports the carriage20so that the carriage20is movable along the Y axis. The pulley32is driven in a rotatable manner by the motor35. The pulley33is rotated in accordance with driving force transmitted from the pulley32through the timing belt34. The timing belt34having an endless shape extends along the guide shaft31and is hung on the pair of pulleys32and33. The carriage20is fixed in a portion of the timing belt34in a circumferential direction.

In the movement mechanism30described above, when the rotation of the motor35is alternately switched between a normal direction and an opposite direction, the carriage20reciprocates in the Y1and Y2directions along the guide shaft31by the driving force transmitted from the motor35through the timing belt34to the carriage20.

The transport mechanism40transports the print medium P in the X1direction relative to the housing10. Specifically, the transport mechanism40includes a platen41, a transport roller42, and a motor43. The platen41is a board of a plate shape supporting the print medium P to which ink is applied from the head unit HU. The print medium P is supplied onto the platen41one by one by a sheet supply roller not illustrated. The transport roller42is driven by the motor43in a rotatable manner and transports the print medium P on the platen41in the X1direction.

A position of the carriage20relative to the print medium P is changed in the direction along the X axis and the direction along the Y axis by the operation of the movement mechanism30and the transport mechanism40in combination described above. The head unit HU and a plurality of ink cartridges C are mounted on the carriage20.

The encoder50is a transmission type linear encoder detecting a position of the carriage20in the Y1direction or the Y2direction. The encoder50includes a scale51and an optical sensor52. The scale51and the optical sensor52will be described in detail hereinafter. However, when the scale51and the optical sensor52are briefly described here, the scale51is a member of a band shape disposed along the Y axis and is fixed on the housing10. Although not illustrated inFIG. 1, the scale51has a base member having light transparency and a pattern of a light shielding property disposed on the base member by printing or the like. The pattern includes a plurality of light shielding sections arranged with a predetermined gap in a longitudinal direction of the scale51. The optical sensor52is fixed on the carriage20and outputs a signal in accordance with a change in a position relative to the scale51. Although not illustrated inFIG. 1, the optical sensor52includes a light emitting section including a light emitting element emitting light to the scale51and a light receiving section including a light receiving element receiving light transmitted through the scale51in the light emitted from the light emitting section. Note that the encoder50is not limited to the configuration illustrated inFIG. 1as long as a position of the carriage20in the Y1direction or the Y2direction is detected, and may be a reflection type linear encoder, for example.

The encoder60is a transmission-type rotary encoder detecting a rotation angle of the transport roller42. The encoder60includes a scale61and an optical sensor62. The scale61is a circular disc member or a circular ring member fixed on the transport roller42and disposed in the same axis as the transport roller42. Although not illustrated inFIG. 1, the scale61has a base member having light transparency and a pattern having a light shielding property disposed on the base member by printing or the like. The pattern includes a plurality of light shielding sections arranged with a predetermined gap in a circumferential direction of the scale61. The optical sensor62is fixed on the housing10and outputs a signal in accordance with a change in a rotation angle of the scale61. Although not illustrated inFIG. 1, the optical sensor62has the same configuration as the optical sensor52of the encoder50described above. Note that the encoder60is not limited to the configuration illustrated inFIG. 1as long as a rotation angle of the transport roller42is detected and may be a reflection type rotary encoder, for example.

Each of the plurality of ink cartridges C accommodate ink to be supplied to the head unit HU. Different types of ink are accommodated in the different ink cartridges C. In the example ofFIG. 1, the number of ink cartridges C is four, and different colors of ink are accommodated in the four different ink cartridges C. Examples of the colors of ink accommodated in the four ink cartridges C include four colors of cyan, magenta, yellow, and black. Furthermore, composition of the ink is not particularly limited, and water-based ink or solvent-based ink, for example, may be used. Note that the plurality of ink cartridges C may not be mounted on the carriage20but mounted on the housing10. In this case, the ink may be supplied from the plurality of ink cartridges C through tubes to the head unit HU, for example. Furthermore, the number of ink cartridges C included in the head unit HU may be three or less or five or more.

The head unit HU ejects the ink from the plurality of ink cartridges C as liquid droplets to the print medium P. In the example illustrated inFIG. 1, the head unit HU ejects the four colors of ink after receiving supply of the four colors of ink from the four ink cartridges C described above.

The carriage20described above is electrically coupled to the control module70through a cable80. In the example illustrated inFIG. 1, the cable80is a flexible flat cable. Note that the cable80is not limited to the flexible flat cable and may be a flexible wiring substrate, for example.

A1-2. Electrical Configuration of Liquid Ejecting Apparatus1

FIG. 2is a block diagram illustrating an electrical configuration of the liquid ejecting apparatus1according to the first embodiment. As illustrated inFIG. 2, the movement mechanism30includes, in addition to the components described above, a motor driver36driving the motor35described above. The transport mechanism40includes, in addition to the components described above, a motor driver44driving the motor43described above. Note that a portion of or all the motor driver36or the motor driver44may be included in the control module70.

The head unit HU includes a recording head HD, a supply circuit90, and a restriction circuit100. The recording head HD includes the plurality of ejecting sections D ejecting ink to the print medium P. The supply circuit90supplies a supply driving signal Vin driving the ejecting sections D to at least selected one of the ejecting sections D. The restriction circuit100restricts ejection of ink from the recording head HD when a detection error of the encoder50is detected. The recording head HD, the cable80, the supply circuit90, and the restriction circuit100described above will be described in detail hereinafter.

Note that, although the number of recording heads HD included in the head unit HU is one in the example illustrated inFIG. 2, the number is not limited to this and the number of recording heads HD included in the head unit HU may be two or more. Furthermore, the number of ejecting sections D included in the recording head HD may be one. Hereinafter, assuming that the number of ejecting sections D included in the recording head HD is M, the ejecting sections D are referred to as ejecting sections D[m] using a subscript[m] where appropriate so that the M ejecting sections D are individually distinguished from one another. Note that M is a natural number equal to or larger than 1. Furthermore, the M other components or M signals of the liquid ejecting apparatus1have the correspondence relationship with the ejecting sections D[m] using the subscript [m] where appropriate.

The control module70individually controls driving of the movement mechanism30, the transport mechanism40, and the head unit HU described above. Specifically, the control module70includes a control circuit71, a storage circuit72, a power source circuit73, and a driving signal generation circuit74.

The control circuit71has a function of controlling operations of the various sections included in the liquid ejecting apparatus1and a function of processing various data. The control circuit71includes at least one processor, such as central processing unit (CPU). Note that the control circuit71may include a programmable logic device, such as a field-programmable gate array (FPGA) instead of the CPU or in addition to the CPU.

The storage circuit72stores various programs to be executed by the control circuit71and various data, such as print data Img, to be processed by the control circuit71. The storage circuit72includes at least one of a semiconductor memory of a volatile memory, such as a random access memory (RAM), and a semiconductor memory of a nonvolatile memory, such as a read only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), or a programmable ROM (PROM). The print data Img is supplied from a host computer which is an external apparatus, such as a personal computer or a digital still camera, not illustrated.

The power source circuit73generates various predetermined potentials when receiving electric power supplied from a commercial power supply not illustrated. Specifically, the power source circuit73generates a power source potential VHV on a high potential side, a power source potential VDD on a low potential side, and an offset potential VBS. As setting values of these potentials, the offset potential VBS is approximately 6 V, the power source potential VHV is approximately 42 V, the power source potential VDD is approximately 3.3 V, and the offset potential VBS is approximately 6 V. These potentials are supplied to the head unit HU through the cable80. Furthermore, the power source potential VHV is also supplied to the driving signal generation circuit74. Note that, although not illustrated, a reference potential of 0 V which is a reference of the potentials described above is also supplied to the head unit HU through the cable80.

The driving signal generation circuit74generates a driving signal Com used to drive the ejecting sections D. Specifically, the driving signal generation circuit74includes a DA conversion circuit and an amplification circuit, for example. In the driving signal generation circuit74, the DA conversion circuit converts a digital waveform specifying signal dCom supplied from the control circuit71into an analog waveform specifying signal dCom and the amplification circuit amplifies the analog signal using the power source potential VHV supplied from the power source circuit73so that the driving signal Com is generated. Here, a signal having a waveform actually supplied to the ejecting sections D in waveforms included in the driving signal Com is the supply driving signal Vin described above. The waveform specifying signal dCom is a digital signal prescribing a waveform of the driving signal Com.

The control circuit71has a function of controlling the operations of the sections included in the liquid ejecting apparatus1by executing the programs stored in the storage circuit72. Specifically, the control circuit71generates control signals CNT1and CNT2, a print signal SI, the waveform specifying signal dCom, a clock signal CLK, a latch signal LAT, and a change signal CNG as signals for controlling operations of the sections included in the liquid ejecting apparatus1by executing the programs.

The control signal CNT1controls driving of the movement mechanism30. The control signal CNT1is supplied to the motor driver36of the movement mechanism30. The motor driver36drives the motor35in accordance with the control signal CNT1.

The control signal CNT2controls driving of the transport mechanism40. The control signal CNT2is supplied to the motor driver44of the transport mechanism40. The motor driver44drives the motor43in response to the control signal CNT2.

The print signal SI is a digital signal specifying a type of an operation of the ejecting sections D. Specifically, the print signal SI specifies whether the driving signal Com is to be supplied to the ejecting sections D so as to specify a type of operation of the ejecting sections D. Here, “to specify a type of operation of the ejecting sections D” means to specify whether the ejecting sections D are to be driven, to specify whether ink is to be ejected from the ejecting sections D when the ejecting sections D are driven, or to specify an amount of ink to be ejected from the ejecting sections D when the ejecting sections D are driven.

The latch signal LAT and the change signal CNG are used with the print signal SI and prescribe a timing when the ink is ejected from the ejecting sections D. Timings of pulses included in the signals are set as a timing synchronized with an operation of the carriage20based on an output of the encoder50described above, for example. Accordingly, the control circuit71is a signal generation section generating a pulse signal including a pulse prescribing the timing when ink is ejected from the ejecting sections D based on information supplied from the encoder50. Note that the relationship between an output of the encoder50and the latch signal LAT will be described in detail hereinafter.

A1-3. Detailed Description of Encoder50

FIG. 3is a diagram illustrating the encoder50viewed in the Y2direction. As described above, the encoder50includes the scale51and the optical sensor52. As described above, while the scale51is fixed on the housing10, the optical sensor52is fixed on the carriage20. A support section21supporting the optical sensor52is disposed on the carriage20of this embodiment as illustrated inFIG. 3. For example, the support section21is formed with the carriage20in an integrated manner. A slit21ato which the scale51is inserted is formed in the support section21. The slit21ais opened in opposite directions, that is, the Y1and Y2directions. Therefore, the scale51may be inserted in the slit21a. Furthermore, the slit21ais opened in the Z2direction. Therefore, the scale51may be more easily inserted in the slit21awhen compared with a state in which the slit21ais opened only in the Y1and Y2directions. Note that a configuration of the support section21, such as a position or a configuration, in the carriage20is determined in accordance with a position where the encoder50is installed or the like, and is arbitrarily determined without being limited to the configuration illustrated inFIG. 3.

The scale51includes a long base member51ahaving light transparency and a pattern51bwhich is configured by a plurality of light shielding sections arranged with a predetermined gap in a longitudinal direction of the base member51aand which has a light shielding property. The base member51ais configured by resin material, such as polyethylene terephthalate (PET), for example. The pattern51bis disposed on the base member51aby printing or the like and is formed by ink having a light shielding property. The gap among the plurality of light shielding sections forming the pattern51bis not limited and is appropriately determined in accordance with resolution or the like required for the liquid ejecting apparatus1.

The optical sensor52includes a light emitting section52aemitting light to the scale51and a light receiving section52breceiving light emitted from the light emitting section52aand transmitted through the scale51. The scale51is interposed between the light emitting section52aand the light receiving section52b. In the example ofFIG. 3, the light emitting section52ais disposed in the X1direction and the light receiving section52bis disposed in the X2direction relative to the scale51. Note that the light emitting section52amay be disposed in the X2direction and the light receiving section52bmay be disposed in the X1direction relative to the scale51.

FIG. 4is a diagram schematically illustrating a configuration of the encoder50. The light emitting section52aincludes a light emitting element53and a lens54. The light emitting element53is a light emitting diode, for example. The lens54is a collimated lens, for example, used to change light from the light emitting element53to parallel light. Light from the light emitting element53is incident on the scale51through the lens54.

The light receiving section52bincludes light receiving elements55a,55b,56a, and56b, an amplification circuit57, and comparators58and59. Each of the light receiving elements55a,55b,56a, and56bis a photo transistor, a photo diode, or a photo integrated circuit (IC), for example. The light receiving elements55aand55bare arranged in parallel along the Y axis with a center-to-center distance of half a pitch of the pattern51bdescribed above interposed therebetween. Similarly, the light receiving elements56aand56bare arranged in parallel along the Y axis with a center-to-center distance of half the pitch of the pattern51bdescribed above interposed therebetween. Note that the light receiving elements56aand56bare disposed with a distance sift corresponding to a quarter of the pitch of the pattern51bdescribed above along the Y axis relative to the light receiving elements55aand55b. Note that, inFIG. 4, the light receiving elements55a,55b,56a, and56bare arranged in an equal interval for simplicity of description.

The amplification circuit57amplifies analog signals supplied from the light receiving elements55a,55b,56a, and56b. The analog signals are supplied from the light receiving elements55aand55bto the comparator58through the amplification circuit57. The comparator58compares magnitudes of the analog signals and outputs a signal ENC_A of a high level or a low level in accordance with a result of the comparison. Similarly, the analog signals are supplied from the light receiving elements56aand56bto the comparator59through the amplification circuit57. The comparator59compares magnitudes of the analog signals and outputs a signal ENC_B of a high level or a low level in accordance with a result of the comparison.

FIG. 5is a diagram illustrating the signals ENC_A and ENC_B output from the encoder50. As illustrated inFIG. 5, a pulse time interval Td is common to the signal ENC_A and the signal ENC_B. However, a phase of the signal ENC_A and a phase of the signal ENC_B is shifted by 90 degrees as a shift amount ΔT. Here, a direction of the shift between the phases of the signals ENC_A and ENC_B varies depending on a movement direction of the optical sensor52relative to the scale51. Therefore, a movement direction of the optical sensor52relative to the scale51may be identified based on the direction.

As described above, the encoder50includes the scale51, the light emitting element53, and the light receiving elements55a,55b,56a, and56b. Here, the light emitting element53emits light to the scale51. The light receiving elements55a,55b,56a, and56breceive light transmitted through the scale51in the emitted light. Consequently, the light receiving elements55a,55b,56a, and56boutput the signals ENC_A and ENC_B as information changed in accordance with a change in the relative positional relationship between the print medium P and the ejecting sections D described below in the Y1direction or the Y2direction. Note that, when the encoder50is a reflection type encoder, the light receiving elements55a,55b,56a, and56breceive light reflected by the scale51in the light emitted by the light emitting element53.

A1-4. Schematic Configuration of Ejecting Sections D

FIG. 6is a cross-sectional view schematically illustrating a configuration of the recording head HD including the ejecting sections D. As illustrated inFIG. 6, the recording head HD includes a nozzle plate91, a flow path substrate92, a vibration plate93, and a plurality of piezoelectric elements PZ. The nozzle plate91, the flow path substrate92, the vibration plate93, and the plurality of piezoelectric elements PZ are laminated in this order.

A plurality of nozzles N arranged in a predetermined direction are formed on the nozzle plate91. Each of the nozzles N is a through hole through which the ink passes. A plurality of cavities SC, a reservoir SRV, a plurality of ink supply paths SS, and an ink inlet OI are formed in the flow path substrate92. The cavities SC are disposed for individual nozzles N and are spaces communicated with the nozzles N. The reservoir SRV is disposed in common to the plurality of nozzles N and extends in a direction in which the plurality of nozzles N are arranged. The plurality of ink supply paths SS are disposed for individual nozzles N and are spaces causing the plurality of cavities SC and the reservoir SRV to communicate with each other. The ink inlet OI is an opening used to guide the ink from the ink cartridges C to the reservoir SRV. The vibration plate93constitutes portions of wall surfaces of the plurality of cavities SC and is a plate-like member which may be elastically deformed in a direction in which volume of the cavities SC is changed for individual cavities SC.

In the example illustrated inFIG. 6, each of the plurality of piezoelectric elements PZ is a unimorph (monomorph) type piezoelectric element. Specifically, each of the plurality of piezoelectric elements PZ includes an upper electrode Zu, a piezoelectric body Zm, and a lower electrode Zd. These are laminated in this order from the top. An offset potential VBS is supplied from the power source circuit73described above to the lower electrode Zd. A supply driving signal Vin including a portion of or all the waveform of the driving signal Com supplied from the driving signal generation circuit74described above is supplied to the upper electrode Zu. When a voltage based on a potential difference between the offset potential VBS and the supply driving signal Vin is applied to a portion between the upper electrode Zu and the lower electrode Zd, the piezoelectric elements PZ vibrates the vibration plate93in the Z1direction or the Z2direction by an inverse piezoelectric effect of the piezoelectric body Zm. The ink is ejected from the nozzles N when pressure of the cavities SC is changed along with a change in the volume of the cavities SC by the vibration. Note that the configuration of the piezoelectric elements PZ is not limited to a unimorph type described above and may be a bimorph type or a laminated type, for example.

In the components of the recording head HD described above, an aggregate of the components disposed for each nozzle N is the ejecting section D. Here, the ejecting section D includes the cavity SC, the piezoelectric element PZ, and the nozzle N.

A1-5. Electrical Configuration of Head Unit HU

FIG. 7is a diagram illustrating an electrical configuration of the head unit HU. Although described above, as illustrated inFIG. 7, the head unit HU is coupled to the cable80, and the head unit HU includes the recording head HD, the supply circuit90, and the restriction circuit100.

The cable80includes a plurality of lines81to88. The line81is a power supply line on a high potential side supplying the power source potential VHV which is a fixed potential. The power source potential VHV is used to drive the ejecting sections D. The line82is a signal line transmitting a LAT signal which is an example of a pulse signal prescribing a timing when the ink is ejected from the ejecting sections D. The line83is a signal line transmitting a driving signal Com. The line84is a signal line transmitting a print signal SI. The line85is a signal line transmitting a clock signal CLK. The line86is a signal line transmitting a change signal CNG. The line87is a power supply line supplying the offset potential VBS. The line88is a power supply line on a low potential side supplying the power source potential VDD. The power source potential VDD is used to drive various logic circuits included in the head unit HU. Although not illustrated, in addition to the lines described above, a line of a ground potential of 0 V used as a reference potential is included in the cable80.

The supply circuit90includes M switches SW (SW[1] to SW[M]) and a connection state specifying circuit90aspecifying connection states of the switches SW. InFIG. 7, M is 3 for simplicity of description.

A switch SW[m] performs switching between a conductive (ON) state and a non-conductive (OFF) state in a portion between the line83and a piezoelectric element PZ[m] in a transmission path of the driving signal Com from the driving signal generation circuit74to the piezoelectric element PZ[m]. Each of the switches SW is a transmission gate, for example.

The connection state specifying circuit90agenerates connection state specifying signals SL[1] to SL[M] specifying an ON or OFF state of the switches SW[1] to SW[M] based on the clock signal CLK, the print signal SI, the latch signal LAT, and the change signal CNG supplied from the control circuit71.

Specifically, the connection state specifying circuit90aincludes transfer circuits SR[1] to SR[M], latch circuits LT[1] to LT[M], and decoders DC[1] to DC[M] which correspond to the ejecting sections D[1] to D[M], respectively. Among these, the print signal SI is supplied to a transfer circuit SR[m] through the line84. Here, the print signal SI includes a discrete specifying signal Sd[m] described below. In the example ofFIG. 7, the discrete specifying signals Sd[1] to Sd[M] are serially supplied, and for example, the discrete specifying signals Sd[m] are successively transferred to the transfer circuits SR[1] to SR[M] in synchronization with the clock signal CLK supplied from the line85. Furthermore, a latch circuit LT[m] latches the discrete specifying signal Sd[m] supplied to the transfer circuit SR[m] at a timing when a pulse PlsL of the latch signal LAT supplied from the line82is brought into a high level. Furthermore, the decoder DC[m] generates a connection state specifying signal SL[m] based on the discrete specifying signal Sd[m], the latch signal LAT, and the change signal CNG. Here, when the decoder DC[m] generates the connection state specifying signal SL[m], the power source potential VHV is also used.

The ON state or the OFF state of the switch SW[m] is switched in accordance with the connection state specifying signal SL[m] generated as described above. For example, the switch SW[m] is turned on when the connection state specifying signal SL[m] is in a high level and turned off when the connection state specifying signal SL[m] is in a low level. As described above, the supply circuit90supplies a portion of or all the waveform included in the driving signal Com to at least selected one of the ejecting sections D as a supply driving signal Vin.

The restriction circuit100restricts ejection of the ink in the recording head HD when a detection error occurs in the encoder50. Specifically, the restriction circuit100includes a measurement section110, an ejection restriction section120, and a storage circuit130.

The measurement section110is a circuit measuring a time length t between pulses in the latch signal LAT. Specifically, the measurement section110includes a counter111and an oscillation circuit112. The counter111counts the number of pulses of a clock signal supplied from the oscillation circuit112for each period between pulses of the latch signal LAT. For example, the counter111repeatedly performs an operation of starting counting of a clock signal supplied from the oscillation circuit112when a pulse of the latch signal LAT falls and stopping the count when a next pulse of the latch signal LAT rises. Here, the counter111outputs a count value as information corresponding to the time length t between pulses of the latch signal LAT every time the counter is stopped. The oscillation circuit112outputs a clock signal using a crystal oscillator, for example. A clock frequency of the clock signal is not particularly limited and is arbitrarily determined as long as the time length t between pulses of the latch signal LAT is measured.

Note that the counter111may start the counting when a pulse of the latch signal LAT rises or stop the counting when a pulse of the latch signal LAT falls. Furthermore, the counter111may reset a count value every time the counting is started.

The ejection restriction section120restricts ejection of the ink from the ejecting sections D when the time length t which is a result of the measurement performed by the measurement section110is longer than a threshold value Tth. Specifically, the ejection restriction section120includes a comparator121comparing the time length t with the threshold value Tth. The ejection restriction section120restricts an operation of ejecting ink performed by the ejecting sections D based on a result of the comparison performed by the comparator121. For example, the ejection restriction section120stops an operation of the connection state specifying circuit90adescribed above so that the switch SW[m] is maintained in the OFF state when the time length t is larger than the threshold value Tth. Note that the ejection restriction section120may include a programmable logic device, such as a FPGA.

When ejection of ink from the ejecting sections D is to be restricted, the ejection restriction section120outputs information E associated with the ejection to an outside. The information E is input to the control circuit71, for example. The control circuit71notifies a user of the information associated with the restriction using a display device or a sound generation device, not illustrated, for example, based on the information E.

The storage circuit130stores information required for operations of the ejection restriction section120. The storage circuit130includes a semiconductor memory, for example. The storage circuit130of this embodiment stores threshold value information D1. The threshold value information D1is associated with the threshold value Tth which is a reference for determining whether a detection error has occurred in the encoder50. The threshold value Tth is set as a value within a range from a normal value of a length of a unit period Tu described below to a value smaller than twice the normal value, for example. Note that a portion of or all the storage circuit130may be included in the ejection restriction section120.

A1-6. Operation of Head Unit HU

FIG. 8is a timing chart of an example of an operation of the head unit HU. As illustrated inFIG. 8, the latch signal LAT includes a pulse PlsL for prescribing the unit period Tu. The unit period Tu is prescribed as a period from when a pulse PlsL rises to when a next pulse PlsL rises, for example. Furthermore, the change signal CNG includes a pulse PlsC for dividing the unit period Tu into a control period Tu1and a control period Tu2. The control period Tu1is a period from when the pulse PlsL rises to when the pulse PlsC rises. The control period Tu2is a period from when the pulse PlsC rises to when the pulse PlsL rises.

Furthermore, the print signal SI includes discrete specifying signals Sd[1] to Sd[M] specifying types of operation of the ejecting sections D[1] to D[M] for each unit period Tu. The discrete specifying signals Sd[1] to Sd[M] are supplied to the connection state specifying circuit90ain synchronization with the clock signal CLK as described above before the unit period Tu. The connection state specifying circuit90agenerates a connection state specifying signal SL[m] based on the discrete specifying signal Sd[m] in the unit period Tu.

As illustrated inFIG. 8, the driving signal Com has a waveform PX formed in the control period Tu1and a waveform PY formed in the control period Tu2. In the example ofFIG. 8, a potential difference between a highest potential VHx and a lowest potential VLx in the waveform PX is larger than a potential difference between a highest potential VHy and a lowest potential VLy in the waveform PY.

When the discrete specifying signal Sd[m] is a value specifying formation of a middle dot, the connection state specifying signal SL[m] is brought into a high level in the control period Tu1and a low level in the control period Tu2. Therefore, only the waveform PX in the driving signal Com is supplied to the ejecting sections D as a supply driving signal Vin. Consequently, an amount of ink corresponding to the middle dot is ejected from the ejecting sections D.

When the discrete specifying signal Sd[m] has a value specifying formation of a small dot, the connection state specifying signal SL[m] is brought into a low level in the control period Tu1and a high level in the control period Tu2. Therefore, only the waveform PY in the driving signal Com is supplied to the ejecting sections D as a supply driving signal Vin. Consequently, an amount of ink corresponding to the small dot is ejected from the ejecting sections D.

When the discrete specifying signal Sd[m] has a value specifying formation of a large dot, the connection state specifying signal SL[m] is brought into a high level in both the control periods Tu1and Tu2. Therefore, the waveforms PX and PY in the driving signal Com are supplied to the ejecting sections D as a supply driving signal Vin. Consequently, an amount of ink corresponding to the large dot is ejected from the ejecting sections D.

When the discrete specifying signal Sd[m] has a value specifying non-ejection of ink, the connection state specifying signal SL[m] is brought into a low level in the control periods Tu1and Tu2. Therefore, the waveforms PX and PY in the driving signal Com are not supplied to the ejecting sections D. Consequently, ink is not ejected from the ejecting sections D.

A1-7. Operation of Ejection Restriction Section120

FIG. 9is a diagram illustrating a time length t between pulses of the latch signal LAT obtained when detection performed by the encoder50is normal. In this case, the time length t is equal to or smaller than the threshold value Tth and is within a normal range of a length of the unit period Tu described above. Here, the time length t is prescribed based on information from the encoder50described above. Specifically, the control circuit71described above calculates the time length t in accordance with a pulse time interval Td of the signal ENC_A supplied from the encoder50. Then the control circuit71generates the latch signal LAT including the pulse PlsL generated every time length t.

InFIG. 9, n pulses PlsL are included in the pulse time interval Td of the signal ENC_A supplied from the encoder50, for example. Note that n is a natural number equal to or larger than 1. In the example ofFIG. 9, n is 7. InFIG. 9, n pulses PlsL are indicated by pulses PlsL_1to PlsL_n. Note that n is not limited to the example ofFIG. 9, and is preferably within a range equal to or larger than 1 and equal to or smaller than 20. More preferably, n is within a range equal to or larger than 5 to equal to or smaller than 10.

As described above, the signal ENC_A is generated based on a result of reception of light transmitted through the scale51in the light emitted from the light emitting element53using the light receiving elements55a,55b,56a, and56b. On the other hand, in the liquid ejecting apparatus1, mist of ink floating in the housing10of the liquid ejecting apparatus1without being attached to the print medium P is secondarily generated in addition to ink attached to the print medium P when the ejecting sections D eject ink. Such mist of ink attached to the scale51causes a detection error of the encoder50. When a detection error occurs in the encoder50, the time length t described above is changed.

FIG. 10is a diagram illustrating a time length t between pulses of the latch signal LAT obtained when an error occurs in detection performed by the encoder50. In this case, the time length t is longer than the threshold value Tth and is out of a normal range of the length of the unit period Tu described above. When the time length t is changed in this way, image quality may be deteriorated. Then the ejection restriction section120restricts ejection of ink from the ejecting sections D when the time length t is larger than the threshold value Tth.

Note that a detection error in the encoder50may be detected by determining whether a pulse time interval Td of the signal ENCA supplied from the encoder50is larger than a predetermined threshold value. However, in this case, when the determination is performed by the head unit HU, a line used to transmit the signal ENC_A is required to be disposed in the cable80. On the other hand, in the configuration of this embodiment in which a detection error of the encoder50is detected based on the time length t between pulses in the latch signal LAT, it is advantageous in that the line is not required to be disposed.

FIG. 11is a flowchart of an operation performed by the ejection restriction section120. As illustrated inFIG. 11, first, in step S100, the ejection restriction section120determines whether the time length t is larger than the threshold value Tth. The process in step S100is repeatedly performed until the time length t becomes larger than the threshold value Tth.

When the time length t is larger than the threshold value Tth, the ejection restriction section120restricts the ink ejection operation performed by the ejecting sections D in step S110.

The liquid ejecting apparatus1described above includes the ejecting sections D, the movement mechanism30, the encoder50, the control circuit71which is an example of a signal generation section, the measurement section110, and the ejection restriction section120as described above. Here, the liquid ejecting apparatus1has the head unit HU which is an example of a liquid ejecting head unit mounted on the liquid ejecting apparatus1. The head unit HU includes the ejecting sections D, the control circuit71, the measurement section110, and the ejection restriction section120.

The ejecting sections D eject ink which is an example of liquid to the print medium P. The movement mechanism30changes the relative positional relationship between the print medium P and the ejecting sections D. The encoder50includes the scale51, the light emitting element53, and the light receiving elements55aand55b. The light emitting element53emits light to the scale51. The light receiving elements55aand55breceive light transmitted through the scale51in the emitted light and outputs the signal ENC_A as information changed in accordance with a change in the positional relationship. The control circuit71generates the latch signal LAT which is a pulse signal including the pulse PlsL prescribing the timing when the ejecting sections D eject ink based on the signal ENC_A. The measurement section110measures the time length t between pulses of the latch signal LAT. The ejection restriction section120restricts ejection of ink from the ejecting sections D when the time length t is larger than the threshold value Tth.

Here, when an amount of contamination of the mist of ink or the like attached to the scale51of the encoder50exceeds a certain amount, detection accuracy of the encoder50is considerably degraded, and therefore, the time length t between pulses in the latch signal LAT is considerably increased. Accordingly, when the time length t is larger than the threshold value Tth, it may be estimated that image quality is deteriorated when the timing of ejection of ink from the ejecting sections D is largely shifted from a regular timing. Therefore, print in degraded image quality may be suppressed by restricting ejection of ink from the ejecting sections D when the time length t is larger than the threshold value Tth.

In particular, when the ink ejected from the ejecting sections D has liquid droplets of a diameter within a range from 2 μm to 10 μm, mist of liquid droplets is likely to float without being attached to the print medium P. Accordingly, in this case, the restriction of ejection of ink from the ejecting sections D by the ejection restriction section120is particularly effective to suppress printing in low image quality.

Furthermore, the liquid ejecting apparatus1further includes the housing10accommodating the ejecting sections D and the encoder50as described above. With the configuration including the housing10, mist of ink secondarily generated in accordance with the ejection of the ink from the ejecting sections D floats in the housing10. Therefore, the mist of ink is likely to be attached to the scale51of the encoder50. Accordingly, when the liquid ejecting apparatus1includes the housing10, the restriction of ejection of ink from the ejection restriction section120as described above is particularly effective to suppress printing in low image quality.

Furthermore, the scale51includes resin material as described above. Here, when solvent ink including solvent of dissolubility for the resin material is used, it is difficult to remove the ink attached to the scale51by wiping or the like. Therefore, when the scale51and such ink are used in combination, the restriction of ejection of the ink from the ejecting sections D by the ejection restriction section120described above is particularly effective to suppress printing in low image quality.

Note that solvent used in the solvent ink is not particularly limited, and examples of the solvent include glycol ether series solvent and alcohol series solvent. Furthermore, the solvent ink includes, in addition to solvent, color material, resin, or the like resolved or dispersed in the solvent.

The liquid ejecting apparatus1further includes, as described above, the carriage20having the ejecting sections D, the light emitting element53, and the light receiving elements55aand55bmounted thereon. Here, the movement mechanism30has a mechanism for moving the carriage20. Furthermore, the encoder50is a linear encoder detecting a position of the carriage20. The scale51of the linear encoder is long along a movement direction of the carriage20as described above. Therefore, it is difficult to dispose a structure for suppressing attachment of mist of ink to the scale51. Since the mist of ink is dispersed due to air current caused by a movement of the carriage20, the mist of ink is likely to be attached to the scale51in this regard. Accordingly, with the configuration including the carriage20, the restriction of ejection of ink from the ejecting sections D by the ejection restriction section120is particularly effective to suppress printing in low image quality.

The measurement section110of this embodiment includes the oscillation circuit112generating a clock signal and measures the time length t using the clock signal. Therefore, measurement accuracy of the measurement section110may be enhanced when compared with a configuration in which the clock signal is supplied from an outside of the measurement section110. In particular, since the oscillation circuit112is mounted on the head unit HU, a transmission path of the clock signal may be reduced when compared with a state in which the oscillation circuit112is mounted on the control module70or the like. Therefore, the measurement accuracy of the measurement section110may be appropriately enhanced.

A2. Second Embodiment

FIG. 12is a block diagram illustrating an electrical configuration of a liquid ejecting apparatus1A according to a second embodiment. The liquid ejecting apparatus1A uses ultraviolet curable ink. The ink includes ultraviolet curable resin or the like. The liquid ejecting apparatus1A includes, in addition to the components of the liquid ejecting apparatus1described above, an ultraviolet emission machine200.

The ultraviolet emission machine200emits ultraviolet rays to ink landed on the print medium P. Specifically, the ultraviolet emission machine200includes a light emitting element, such as a light emitting diode, not illustrated, emitting light in an ultraviolet part. InFIG. 12, the ultraviolet emission machine200is mounted on a head unit HU, for example. Although not illustrated, the ultraviolet emission machine200is arranged in a position which is parallel to ejecting sections D in a Y1direction or a Y2direction, for example. Note that the ultraviolet emission machine200may be fixed on a housing10. In this case, the ultraviolet emission machine200is disposed in a position in an X1direction relative to a movement range of a carriage20, for example.

As described above, the ink has a ultraviolet curable property, and the liquid ejecting apparatus1A of this embodiment further includes the ultraviolet emission machine200emitting ultraviolet rays to the print medium P. With this configuration, it is difficult to remove the ink attached to a scale51by wiping or the like. Therefore, when the scale51and the ink are used, the restriction of ejection of the ink from the ejecting sections D by an ejection restriction section120described above is particularly effective to suppress printing in low image quality.

The embodiments described above are variously modified. Modifications are illustrated hereinafter in detail. Two or more embodiments arbitrarily selected from examples below may be appropriately combined as long as the embodiments are consistent with each other. Note that components having the same operations and the same functions as the embodiments in the modifications described below are denoted by reference numerals used in the foregoing description and detailed descriptions thereof are appropriately omitted.

B1. First Modification

Although the encoder50detecting an operation state of the movement mechanism30is a linear encoder in the foregoing embodiments, the encoder50may be a rotary encoder. In this case, the encoder50detects a rotation angle of the motor35and the control circuit71calculates a position of the carriage20based on a result of the detection performed by the encoder50.

B2. Second Modification

Although it is assumed that the liquid ejecting apparatus is a serial printer in the foregoing embodiments and the modifications, the present disclosure is not limited to such modes, and the liquid ejecting apparatus may be a so-called line printer including a plurality of nozzles N, in the recording head HD, disposed in a range wider than a width of the print medium P.

FIG. 13is a block diagram illustrating an electrical configuration of a liquid ejecting apparatus1B according to a second modification. The liquid ejecting apparatus1B is a line printer. The liquid ejecting apparatus1B has the same configuration as the liquid ejecting apparatus1of the first embodiment described above except that the movement mechanism30is omitted. Note that a restriction circuit100restricts ejection of ink in a recording head HD when a detection error of an encoder60is detected. Furthermore, in a head unit HU, a plurality of nozzles N are disposed in a range wider than the width of the print medium P. A transport mechanism40in the second modification is a movement mechanism changing the relative positional relationship between the print medium P and ejecting sections D. Note that, although the transport mechanism40intermittently transports the print medium P in the foregoing embodiments, the transport mechanism40may consecutively transport the print medium P in the second modification.

Here, the encoder60is a rotary encoder as described above. When a scale of the encoder60is disposed in a space communicated with a space through which ink ejected by the ejecting sections D passes, mist of ink is likely to be attached to the scale. Therefore, a problem the same as that arises in the linear encoder in the forgoing embodiment arises. Accordingly, printing in deteriorated print quality may be suppressed by restricting ejection of ink by the recording head HD when a detection error is detected in the encoder60.

B3. Third Modification

Although a configuration in which the control circuit71is a signal generation section is illustrated in the foregoing embodiments and the modifications, a configuration is not limited to this and a signal generation section may be configured by a circuit different from the control circuit71. In this case, the signal generation section may be configured separately from a control module70or mounted on a carriage20.

FIG. 14is a block diagram illustrating an electrical configuration of a liquid ejecting apparatus1C according to a third modification. The liquid ejecting apparatus1C has the same configuration as the liquid ejecting apparatus1of the first embodiment described above except that a signal generation section300is mounted on the carriage20. The signal generation section300generates a latch signal LAT and a change signal CNG as pulse signals including pulses prescribing a timing when ejecting sections D eject ink. In an example ofFIG. 14, the latch signal LAT and the change signal CNG generated by the signal generation section300are supplied to a head unit HU through a control circuit71. Note that the latch signal LAT and the change signal CNG generated by the signal generation section300may be directly supplied to the head unit HU.

B4. Fourth Modification

Although the configuration in which the measurement section110measures the time length t between pulses of the latch signal LAT is illustrated in the foregoing embodiments, a pulse signal which is a target for measurement of a time length between pulses performed by a measurement section110is not limited to the latch signal LAT as long as the pulse signal includes a pulse prescribing the timing when ejecting sections D eject ink based on an output of an encoder50, and the change signal CNG or other signals may be employed.