Patent Application
20080049056
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
An embodiment of the invention will now be described with reference to the accompanying drawings. Note that, in the following, an ink jet printer (hereinafter, simply referred to as a printer) shown in
The control portion 6 not only controls portions of the printer but also converts print data received from the external device through the external I/F 3 to discharge data corresponding to a dot pattern and outputs the discharge data toward the recording head 10 through the internal I/F 9. In addition, the control portion 6 supplies a latch signal, a channel signal, or the like, to the recording head 10 on the basis of the clock signal from the oscillator circuit 7. Latch pulses and channel pulses included in these latch signal and channel signal specify timing for supplying pulses that form a driving signal, which will be described later.
The driving signal generating circuit 8 is controlled by the control portion 6 and generates a driving signal for driving a piezoelectric vibrator 20 (see
The configuration of the side of the print engine 2 will now be described. The print engine 2 includes the recording head 10, a carriage moving mechanism 12, a paper feeder 13, and a linear encoder 14. The recording head 10 includes a shift register (SR) 15, a latch 16, a decoder 17, a level shifter 18, a switch 19, and the piezoelectric vibrator 20. A discharge data (SI) from the printer controller 1 is synchronized with a clock signal (CK) from the oscillator circuit 7 and serially transmitted to the shift register 15. The discharge data is a 2-bit data and, for example, formed of gray scale level information that represents four recording gray scale levels (discharge gray scale levels) consisting of non-record (microvibration) small dot, intermediate dot, large dot. Specifically, the non-record is represented by the gray scale level information “00”, the small dot is represented by the gray scale level information “01”, the intermediate dot is represented by the gray scale level information “10”, and the large dot is represented by the gray scale level information “11”.
The latch 16 is electrically connected to the shift register 15. When a latch signal (LAT) from the printer controller 1 is input to the latch 16, a discharge data in the shift register 15 is latched. The discharge data latched by the latch 16 is input to the decoder 17. The decoder 17 translates 2-bit discharge data to generate pulse selection data. The pulse selection data is configured so that each bit is made correspondence with each of pulses forming the driving signal COM. Then, in accordance with the content of each bit, for example, “0”, “1”, supplying or not supplying a discharge pulse to the piezoelectric vibrator 20 is selected.
Then, the decoder 17, when receiving a latch signal (LAT) or a channel signal (CH), outputs pulse selection data to a level shifter 18. In this case, the pulse selection data is sequentially input to the level shifter 18 initially from the higher-order bits. The level shifter 18 serves as a voltage amplifier and, when the pulse selection data is “1”, outputs an electrical signal that is boosted to a voltage, with which a switch 19 can be driven, that is, for example, a voltage of about tens of volts. The pulse selection data “1” that has been boosted by the level shifter 18 is supplied to the switch 19. The input side of the switch 19 is supplied with a driving signal COM from the driving signal generating circuit 8, and the output side of the switch 19 is connected to the piezoelectric vibrator 20.
Then, the pulse selection data is used to control operation of the switch 19, that is, supply of a driving pulse included in a driving signal to the piezoelectric vibrator 20. For example, during a period when the pulse selection data input to the switch 19 is “1”, the switch 19 enters a connected state, a corresponding discharge pulse is then supplied to the piezoelectric vibrator 20. The potential level of the piezoelectric vibrator 20 varies in response to the waveform of the discharge pulse. On the other hand, during a period when the pulse selection data is “0”, the level shifter 18 does not output an electrical signal for activating the switch 19. Therefore, the switch 19 enters a disconnected state and, as a result, no discharge pulse is supplied to the piezoelectric vibrator 20.
The decoder 17, the level shifter 18, the switch 19, and the control portion 6, which operate as described above, serve as a pulse selection supply unit, and, on the basis of discharge data, select a required discharge pulse from a driving signal and then apply (supply) the discharge pulse to the piezoelectric vibrator 20. As a result, an ink droplet of an amount corresponding to a gray scale level that forms a discharge data is discharged from the nozzle opening. In addition, when the gray scale level information is non-record, for example, a microvibration pulse is supplied to the piezoelectric vibrator 20 and the meniscus is then slightly vibrated.
The flow passage unit 25 is configured so that a nozzle plate 31 is connected to one of the faces of a flow passage formation substrate 30 and a vibration plate 32 is connected to the other face of the flow passage formation substrate 30. The flow passage unit 25 has a reservoir 33 (common liquid chamber), ink supply ports 34, pressure chambers 35, nozzle communication ports 36, nozzle openings 37. Then, lines of ink flow passages that extend from the ink supply ports 34 through the pressure chambers 35 and the nozzle communication ports 36 to the nozzle openings 37 are formed in correspondence with the nozzle openings 37.
The nozzle plate 31 is a thin plate made of metal such as stainless, in which the plurality of nozzle openings 37 are formed in columns at a pitch corresponding to a dot formation density (for example, 360 dpi). The nozzle plate 31 is provided with a plurality of columns of nozzles (groups of nozzles) by forming the nozzle openings 37 in columns. Each of the nozzle columns is, for example, formed of 360 nozzle openings 37.
The vibration plate 32 has a double layer structure in which an elastic body film 39 is laminated on the surface of the support plate 38. In the present embodiment, the vibration plate 32 is formed of a composite plate material which is formed so that a stainless plate, which is one of metal plates, is used as the support plate 38 and a resin film is laminated on the surface of the support plate 38 as the elastic body film 39. The vibration plate 32 is provided with a diaphragm portion 40 that changes volumes in the pressure chambers 35. In addition, the vibration plate 32 is provided with a compliance portion 41 that seals a portion of the reservoir 33.
The diaphragm portion 40 is formed by removing portion of the support plate 38 through etching process, or the like. In other words, the diaphragm portion 40 includes an island portion 42, to which the distal end face of the free end portion of the corresponding piezoelectric vibrator 20 is connected, and a thin elastic portion 43 that surrounds the island portion 42. The compliance portion 41 is formed by removing a portion of the support plate 38, opposite an opening face of the reservoir 33, through etching process, or the like, as in the case of the diaphragm portion 40. The compliance portion 41 serves as a damper that absorbs pressure fluctuation in liquid present in the reservoir 33. Note that, in the present embodiment, an example of configuration in which the vibration plate 32 is formed of two members, that is, the support plate 38 and the elastic body film 39 is illustrated, but the vibration plate 32 is not limited to this configuration. For example, a configuration may be applied, in which the vibration plate 32 is formed of a single member, and a portion corresponding to the thin elastic portion 43 of the diaphragm portion 40 and/or a portion corresponding to the compliance portion 42 are made thin.
Then, because the distal end face of the piezoelectric vibrator 20 is connected to the island portion 42, the volume in the corresponding pressure chamber 35 may be changed by expanding or contracting the free end portion of the piezoelectric vibrator 20. In response to this volume change, pressure fluctuation occurs in the ink present in the pressure chamber 35. Then, the recording head 10 is configured to discharge ink droplets from the corresponding nozzle opening 37 using the pressure fluctuation.
The driving signal generating circuit 8 will now be described.
The waveform generating circuit 45 includes a waveform memory 51, a first waveform latch circuit (latch 1) 52, a second waveform latch circuit (latch 2) 53, an adder 54, a digital analog converter (D/A converter) 55, and a voltage amplifier 56. The waveform memory 51 serves as a variation data storage unit that separately stores a plurality of voltage variation data. The first waveform latch circuit 52 is configured to hold a voltage variation data stored at a predetermined address in the waveform memory 51 in synchronization with the first timing signal. The adder 54 is connected to the first waveform latch circuit 52 and the second waveform latch circuit 53, and the output of the first waveform latch circuit 52 and the output of the second waveform latch circuit 53 are input to the adder 54. Then, the adder 54 serves as a variation data adding unit, and adds the output signal of the latch circuit 52 and the output signal of the latch circuit 53 and then outputs the result.
The second waveform latch circuit 53 is an output data holding unit that holds a data (voltage information) output from the adder 54 in synchronization with the second timing signal. The D/A converter 55 is connected to the subsequent stage of the second waveform latch circuit 53. The D/A converter 55 converts a digital output signal that is held by the second waveform latch circuit 53 to an analog signal. The voltage amplifier 56 is connected to the output side of the D/A converter 55 and amplifies the analog signal that has been converted by the D/A converter 55 to a voltage of the driving signal.
The current amplifier 50 is connected to the output side of the voltage amplifier 56, that is, the subsequent stage of the waveform generating circuit 45. The current amplifier 50 amplifies electric current of a signal of which a voltage is amplified by the voltage amplifier 56 and outputs a driving signal COM.
In the driving signal generating circuit 8 having the above described configuration, in advance of generation of a driving signal, a plurality of variation data that indicate voltage variation are separately stored in a storage region of the waveform memory 51. For example, the control portion 6 outputs a variation data and an address data corresponding to the variation data to the waveform memory 51. Then, the waveform memory 51 stores the variation data in a storage region specified by the address data. Note that, in the present embodiment, the variation data is formed of a data that includes positive or negative information (increase or decrease information), and the address data is formed of a 4-bit address signal.
In this manner, when multiple types of variation data are stored in the waveform memory 51, generation of a driving signal is enabled. The generation of a driving signal is performed so that variation data is set to the first waveform latch circuit 52 and, at predetermined update intervals, the variation data set in the first waveform latch circuit 52 is added to an output voltage from the second waveform latch circuit 53.
In the present embodiment, setting of the variation data to the first waveform latch circuit 52 is performed using a 4-bit address signal input in the waveform memory 51 and the first timing signal input to the first waveform latch circuit 52. That is, the waveform memory 51 selects a variation data that is targeted on the basis of the address signal. Then, when the first timing signal is input, the first waveform latch circuit 52 reads out the selected variation data from the waveform memory 51 and holds the data.
The variation data held in the first waveform latch circuit 52 is input to the adder 54. An output voltage held in the second waveform latch circuit 53 is also input to the adder 54, so that the output data from the adder 54 takes a voltage value that results from adding the variation data held in the first waveform latch circuit 52 and the output voltage held in the second waveform latch circuit 53. Here, the variation data includes positive or negative information. When the variation data is a positive value, the output data from the adder 54 takes a voltage value higher than the output voltage (that is, the voltage value increases). On the other hand, when the variation data is a negative value, the output data from the adder 54 takes a voltage value lower than the output voltage (that is, the voltage value decreases). Note that, when the variation data takes a value “0”, the output data from the adder 54 is the same voltage value as the output voltage. Then, the output data from the adder 54, in synchronization with the second timing signal, is taken into the second waveform latch circuit 53 and held therein. That is, the output voltage from the second waveform latch circuit 53 is updated in synchronization with the second timing signal. The output voltage from the second waveform latch circuit 53 is converted from a digital signal to an analog signal by the D/A converter 55 and then output as the driving signal COM through the voltage amplifier 56 and the current amplifier 50.
When the discharge pulse DP is supplied to the piezoelectric vibrator 20, the following operation will occur. When the first electric charge element PE1 is supplied and the piezoelectric vibrator 20 contracts, the pressure chamber 35 expands from a reference volume corresponding to the reference potential VB to a maximum volume specified by the maximum potential VH. This expansion state of the pressure chamber 35 is maintained over a period during which the first hold element PE2 is being supplied. After that, the piezoelectric vibrator 20 sharply expands due to the supply of the first electric discharge element PE3, so that the volume in the pressure chamber 35 contracts. In this manner, ink present in the pressure chamber 35 is pressurized and a few picoliter (pl) ink droplet is then discharged from the nozzle opening 37. This contraction state of the pressure chamber 35 is maintained over a period during which the second hold element PE4 is being supplied. In the meantime, meniscus that projects in the discharge direction due to the discharge of the ink droplet is drawn toward the pressure chamber side again. In association with this timing, the second electric discharge element PE5 is supplied to the piezoelectric vibrator 20. Thus, the piezoelectric vibrator 20 further expands, so that the volume in the pressure chamber 35 contracts. By so doing, residual vibration of meniscus due to the discharge of the ink droplet is suppressed. Thereafter, the third hold element PE6 and the second electric charge element PE7 are sequentially supplied to the piezoelectric vibrator 20, so that the volume of the pressure chamber 35 is restored to the reference volume.
Suppression of residual vibration that would occur in association with discharge of an ink droplet will now be described. As described above, when an ink droplet is discharged, pressure vibration of the characteristic vibration period Tc in which the inside of the pressure chamber acts as an acoustic tube is excited over ink present in the pressure chamber 35. If the subsequent ink droplet is discharged under a situation where the meniscus is unstable due to the residual vibration, there may be a decrease in flying speed of an ink droplet or a decrease in discharge characteristics, such as curve of flying. Therefore, the second electric discharge element PE5 as a vibration damping element is included in the discharge pulse DP, and the second electric discharge element PE5 is supplied to the piezoelectric vibrator 20, so that residual vibration is suppressed.
Meanwhile, the piezoelectric vibrator 20, which is the pressure generating unit, also has a characteristic vibration form that is determined on the basis of the shape, material, and the like.
In the above discharge pulse DP, in order to rapidly discharge fine ink droplets, a period during which the first electric discharge element PE3 is supplied to the piezoelectric vibrator 20 is set shorter than the characteristic vibration period Ta. Thus, when an ink droplet is discharged by supplying the first electric discharge element PE3 to the piezoelectric vibrator 20, vibration of the characteristic vibration period Ta is excited in the piezoelectric vibrator 20. This residual vibration of the piezoelectric vibrator 20 may adversely affect the discharge characteristics of ink droplets. Specifically, because the residual vibration of the piezoelectric vibrator 20 is transmitted to another piezoelectric vibrator 20 in the same vibrator unit 24, when an ink droplet is discharged by driving the another piezoelectric vibrator 20, there may be fluctuation in amount of ink droplet, fluctuation in flying speed, curve of flying, or the like.
Therefore, in the above printer, the timing at which vibration damping is performed after an ink droplet is discharged is optimized to considerably suppress residual vibration of the piezoelectric vibrator 20. Specifically, as shown in
Furthermore, the driving signal generating circuit 8 optimizes the period of time (Pw1) from the trailing edge of the first electric discharge element PE3 to the leading edge of the second electric discharge element PE5 in order to suppress the residual vibration of meniscus after the ink droplet is discharged as described above. That is, the period of time is set in a range of ⅓ to ⅔ of the characteristic vibration period Ta of the piezoelectric vibrator 20 and equal to or below ⅓ of a characteristic vibration period Tc of ink present in the pressure chamber 35. When the period of time from the trailing edge of the first electric discharge element PE3 to the leading edge of the second electric discharge element PE5 is set equal to or below ⅓ of the characteristic vibration period Tc, the second electric discharge element PE5 is applied to the piezoelectric vibrator 20 at the timing when the vibration of meniscus after the ink droplet is discharged is moving in a direction opposite to the direction in which the ink droplet is discharged (in a direction in which ink is drawn toward the pressure chamber 35). Thus, it is possible to considerably suppress residual vibration of meniscus after an ink droplet is discharged at an early stage. As a result, when ink droplets are successively discharged from the same nozzle opening 37 at short intervals as well, it is possible to prevent the residual vibration of meniscus due to the previous discharge action from adversely affecting the next discharge action. As a result, it is possible to drive the recording head 10 in high frequency.
Furthermore, in the present embodiment, the period of time from the leading edge of the second electric discharge element PE5 to the trailing edge of the second electric discharge element PE5, that is, a period of time during which the second electric discharge element PE5 is generated (Pw2), is set equal to or above the characteristic vibration period Ta of the piezoelectric vibrator 20. In this manner, it is possible to not oscillate vibration of the characteristic vibration period Ta even when the piezoelectric vibrator 20 is driven by the second electric discharge element PE5. Thus, it is possible to reliably prevent an adverse effect on the next discharge action.
In addition, when the period of time Pw1 from the trailing edge of the first electric discharge element PE3 to the leading edge of the second electric discharge element PE5 is set equal to or below ⅓ of the characteristic vibration period Tc and outside the range of ⅓ to ⅔ of the characteristic vibration period Ta of the piezoelectric vibrator 20, residual vibration of the characteristic vibration period Ta of the piezoelectric vibrator, which is shorter than that of the vibration of Tc is generated so as to overlap the residual vibration of the characteristic vibration period Tc. Therefore, the amplitude of the residual vibration of Ta may possibly project upward from the level indicated by “0” in
Meanwhile, the invention is not limited to the embodiment described above, but it may be modified into various alternative embodiments within the scope of the claims. For example, in the above embodiment, the discharge pulse DP shown in
In addition, in the above embodiment, a so-called longitudinal vibration mode piezoelectric vibrator 20 is employed as an example of a pressure generating unit according to the aspect of the invention, but it is not limited to it. As long as a pressure generating unit that has a problem of residual vibration after an ink droplet (liquid droplet) is discharged, any pressure generating unit may apply the aspect of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-228233 | Aug 2006 | JP | national |
