JP2005125763A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance ink ejection efficiency without requiring a restriction member by preventing up/down movement of a pressure chamber at the time of ejecting ink. <P>SOLUTION: The image forming apparatus is arranged to generate a rotational moment between the piezoelectric element 50a of an ejection nozzle 56a and the piezoelectric element 50b of a non-ejection nozzle 56b by applying a voltage Vapush to the piezoelectric element 50a of the ejection nozzle 56a and applying a voltage Vbpull including a waveform component for driving reversely to the piezoelectric element 50a of the ejection nozzle 56a to the piezoelectric element 50b of the non-ejection nozzle 56b located in the vicinity thereof (e.g. adjacently thereto). Consequently, up/down movement of the pressure chamber 54a of the ejection nozzle 56a is prevented and ink ejection efficiency of the pressure chamber 54a can be enhanced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as an ink jet printer that discharges ink onto a recording medium to form an image on the recording medium.

  An ink jet printer drives a recording head in accordance with image formation data, and ejects ink from nozzles of the recording head to form an image on recording paper. As the ink ejection means of the recording head, there is a piezo actuator type, which deforms the diaphragm of the pressure chamber by a piezoelectric element (piezo element) to apply pressure to the pressure chamber, and ejects ink from the nozzle of the pressure chamber.

  In an inkjet printer using a stacked piezoelectric element, when a voltage is applied to the piezoelectric element during ink ejection, the piezoelectric element extends in the stacking direction. This movement not only increases or decreases the pressure chamber volume, but also the entire pressure chamber. If the latter is dominant, there is a risk that the ink ejection capability may not be sufficiently obtained. In order to prevent this, the side opposite to the pressure side of the diaphragm of the piezoelectric element and the side wall of the pressure chamber are fixed by a restraining member, and the pressure chamber is efficiently expanded and contracted. However, if the restraining member is not accurately positioned, the discharge capacity is not stable, and there is a problem that manufacturing cost is required to do this.

On the other hand, when driving energy is applied to the piezoelectric element of the nozzle that discharges ink, driving energy that does not discharge ink is applied to the piezoelectric element of the nozzle that does not discharge ink. A technique for preventing entry is known (see Patent Document 1).
Japanese Patent Application Laid-Open No. 11-157076

  However, even if the ink jet printer of Patent Document 1 can prevent bubbles from entering a pressure chamber that does not eject ink, the necessity of the restraining member is not eliminated.

  The present invention has been made in view of such circumstances, and provides an image forming apparatus capable of improving ink ejection efficiency by preventing unnecessary vertical movement of a pressure chamber during ink ejection without using a restraining member. Objective.

  In order to achieve the above object, the present invention applies the pressure signal by applying nozzles arranged in a line or two-dimensionally, pressure chambers arranged corresponding to the nozzles, and a drive signal. In an image forming apparatus comprising a piezoelectric element that applies pressure to the chamber and discharges ink from the nozzle, during ink discharge, the piezoelectric element of the non-discharge nozzle near the ink discharge nozzle is opposite to the piezoelectric element of the discharge nozzle. A drive signal including a drive component that drives in a direction is given.

  According to the present invention, since the drive signal for driving in the direction opposite to the piezoelectric element of the ejection nozzle is given to the piezoelectric element of the non-ejection nozzle in the vicinity of the ink ejection nozzle, the upper and lower sides of the pressure chamber during ink ejection are not used. It is possible to prevent movement, and to efficiently extend and contract the pressure chamber.

  According to the second aspect of the present invention, the drive waveform of the drive signal applied to the piezoelectric element of the non-ejection nozzle is at least partially in phase with the drive waveform of the drive signal of the piezoelectric element of the ejection nozzle, and the ink The pressure chamber can be prevented from vertically moving during discharge, and the pressure chamber can be efficiently expanded and contracted.

  According to the third aspect of the present invention, the magnitude of the drive signal given to the piezoelectric element of the non-ejection nozzle is determined according to the distance from the ejection nozzle. It is possible to prevent movement, and to efficiently extend and contract the pressure chamber.

  According to the present invention described in claim 4, since the dummy piezoelectric element that does not contribute to image formation is provided outside the outermost nozzle, the vertical movement of the pressure chamber of the outermost nozzle can be prevented, The pressure chamber can be expanded and contracted efficiently.

  The “discharge efficiency” of the pressure chamber indicates the ratio of “volume of droplet discharge” to “volume change of the pressure chamber during pressurization of the pressure chamber”. The droplet discharge volume approaches the volume change amount of the pressure chamber.

  Further, in this specification, “recording” represents the concept of forming an image in a broad sense including characters. A “recording medium” is a medium on which an image is formed by a head (an image forming medium, a recording medium, an image receiving medium, a recording paper, etc.), such as continuous paper, cut paper, sticker paper, OHP sheet, etc. Regardless of the resin sheet, film, cloth, and other materials and shapes, various media are included.

  According to the present invention, a drive signal for driving the piezoelectric element of the non-ejection nozzle near the ejection nozzle in the opposite direction to the piezoelectric element of the ejection nozzle is provided, so that the vertical movement of the pressure chamber in a direction different from the pressurizing direction is prevented during ink ejection The pressure chamber can be efficiently expanded and contracted without using a restraining member.

  Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a side view schematically showing a configuration of an image forming apparatus 10 to which the image forming apparatus is applied.

  The image forming apparatus 10 supplies a recording head 12, a belt conveyance unit 18 that is disposed to face the recording head 12, conveys the recording paper 16 while maintaining the flatness of the recording paper 16, and the recording paper 16. A paper feed unit 20 and a paper discharge unit 22 for discharging the recording paper on which an image has been formed to the outside are provided.

  The recording head 12 is a so-called full-line head in which a line-type head having a length corresponding to the paper width of the recording paper 16 is fixedly arranged in a direction orthogonal to the paper feeding direction. Recording heads 12K, 12C, 12M corresponding to the respective color inks in the order of black (K), cyan (C), magenta (M), yellow (Y) from the upstream side along the conveyance direction (arrow A) of the recording paper 16. 12Y is arranged. Underneath these recording heads, a plurality of nozzles arranged in a staggered matrix in a direction orthogonal to the transport direction are provided, and each color ink is ejected from the nozzles onto the recording paper 16 while transporting the recording paper 16. As a result, a color image or the like is formed on the recording paper 16.

  A roll paper 26 is detachably set in the paper supply unit 20. In the vicinity of the paper feeding unit 20, drawer rollers 21 and 21 for pulling out the recording paper 16 from the roll paper 26 are provided. The power of the motor 114 (see FIG. 3) is transmitted to at least one of the drawing rollers 21, and the drawn recording paper 16 is conveyed from right to left in FIG. Reference numeral 24 denotes a cutting cutter installed between the rollers 21 and 21, and the recording paper 16 drawn from the roll paper 26 by the cutter 24 is cut into a desired size.

  The belt conveyance unit 18 has a structure in which an endless belt 38 is wound between rollers 30, 32, 34, and 36, and is configured such that at least a portion facing the recording head 12 forms a flat surface. The belt 38 has a width that is wider than the width of the recording paper 16 and conveys the recording paper 16. The power of the motor 116 (see FIG. 3) is transmitted to at least one of the rollers 30, 32, 34, and 36 around which the belt 38 is wound, and the belt 38 is driven counterclockwise in FIG. The recording paper 16 adsorbed on the belt 38 is conveyed from right to left in FIG.

  Reference numeral 82 is a recording paper detection section for reading the position and size of the recording paper, reference numeral 84 is a recording position detection section for determining ink ejection timing to the recording paper 16, and reference numeral 88 is a paper jam of the recording paper 16 or the next paper. It is a recording paper end detection unit for determining supply timing. Further, the image forming apparatus 10 is provided with a system controller, which will be described later, for controlling the image forming apparatus 10 based on the detection results of these detection units. This system controller is composed of a central processing unit (CPU) and its peripheral circuits, and generates, for example, drive signals and control signals for each motor for conveying the recording paper 16 and image forming signals for the recording head 12.

  As shown in FIG. 2, the recording head 12 includes a nozzle plate 42, a partition wall 43, a diaphragm 44, a laminated piezoelectric element 50, and the like. A pressure chamber 54 is formed by a space surrounded by the nozzle plate 42, the partition wall 43, and the vibration plate 44. A nozzle 56 that penetrates is formed in the nozzle plate 42 corresponding to the bottom of the pressure chamber 54. The diaphragm 44 is attached so as to close the upper surface of the pressure chamber 54, and the piezoelectric element 50 is disposed on the upper surface.

  The piezoelectric element 50 is a laminated piezoelectric element having a structure in which piezoelectric thin plates and internal electrodes are alternately stacked and joined.

  In addition, a flexible substrate (not shown) is connected to an end portion (upper end in FIG. 2) on the free end side of the piezoelectric element 50. A wiring pattern corresponding to the individual electrode of the piezoelectric element 50 is formed on the flexible substrate, and wiring is collectively performed to the outside through the flexible substrate. The flexible substrate is made of a flexible resin material, and is stretched over and connected to the plurality of piezoelectric elements 50.

  The diaphragm 44 of this example also serves as a common electrode of the piezoelectric element 50. The common electrode (common electrode) is electrically connected to the metallic diaphragm 44 through an adhesive. In addition, conduction | electrical_connection by an adhesive agent may be conducted by the effect of surface roughness, and a conductive adhesive agent may be used.

  When a voltage is applied to the individual electrodes of the piezoelectric element 50, a potential difference is generated in the piezoelectric thin plate inside the piezoelectric element 50, and the piezoelectric element 50 is deformed in the stacking direction (vertical direction in FIG. 2). As the piezoelectric element 50 is deformed, the vibration plate 44 bends downward and contracts the pressure chamber 54, whereby ink is ejected from the nozzle 56.

  FIG. 3 is a principal block diagram showing the system configuration of the image forming apparatus 10. The image forming apparatus 10 includes a communication interface 100, a system controller 102, a print control unit 104, a head driver 106, and the like.

  The communication interface 100 is an interface unit that receives image data sent from the host computer 120. For the communication interface 100, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, and a parallel interface such as Centronics can be applied. Image data sent from the host computer 120 is taken into the image forming apparatus 10 via the communication interface 100 and temporarily stored in the image memory 110. The image memory 110 is a storage unit that temporarily stores input image data. The image data is read and written through the system controller 102.

  The system controller 102 is a control unit that controls the communication interface 100, the image memory 110, the motor driver 112, and the like. That is, the system controller 102 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 120, read / write control of the image memory 110, and recording by the motors 114 and 116. A control signal for controlling the conveyance of the paper 12 is generated.

  The motor driver 112 is a driver that drives the motors 114 and 116 in accordance with instructions from the system controller 102.

  The print control unit 104 is a control unit that controls each unit such as the head driver 106 and the cutter 24 based on the detection result from the sensor unit 108. The print control unit 104 performs processing such as various processes for generating a recording control signal from the image data in the image memory 110 according to the control of the system controller 102, and uses the generated recording control signal (recording data) as a head. Supplied to the driver 106. The head driver 106 drives the recording head of each color (K, C, M, Y) of the recording head 12 based on the recording data given from the print control unit 104.

  Further, as shown in FIG. 4 described later, the print control unit 104 gives a drive signal to the head driver 106 to be given to the piezoelectric element 50b of the nozzle 56b adjacent to the ejection nozzle 56a.

  The sensor unit 108 provided in the print control unit 104 is a block including the recording paper detection unit 82, the recording position detection unit 84, and the recording paper end detection unit 88 described above, and the detection results detected by these detection units are as follows. Provided to the print controller 104. The print control unit 104 performs predetermined arithmetic processing based on the detection results detected by each detection unit, and provides the processing results to the system controller 102. That is, the cutting timing of the recording paper 12 by the cutter 24 is determined based on the detection result in the recording paper detection unit 82.

  Next, the ink ejection operation of the recording head 12 configured as described above will be described.

  In FIG. 4, the central nozzle is the discharge nozzle 56a, the nozzles adjacent to the discharge nozzle 56a on both the front, rear, left, and right sides are non-discharge nozzles 56b. The plates are denoted by reference numerals 44a and 44b. The drive voltage is applied as a drive voltage pulse having a drive waveform based on the image forming pattern.

  In order to form an image based on the image formation pattern, a drive voltage is applied to the piezoelectric element 50a by the system controller. As shown in FIG. 5, the voltage waveform Va is a drive voltage applied to the piezoelectric element 50a of the nozzle 56a that ejects ink, and the voltage waveform Vb is applied to the piezoelectric element 50b of the non-ejection nozzle 56b that does not eject ink. Drive voltage.

  In FIG. 4, when a driving voltage is applied to the piezoelectric element 50a of the discharge nozzle 56a, the piezoelectric element 50a extends and deforms in the vertical direction in FIG. 4, the vibration plate 44a bends downward, and the pressure chamber 54a of the discharge nozzle 56a contracts. The ink is ejected. When the voltage Vbpull is applied to the piezoelectric element 50b of the adjacent non-ejection nozzle 56b almost simultaneously with the application of the voltage Vapush, the piezoelectric element 50b is contracted and deformed in the vertical direction in FIG. 4 and the diaphragm 44b is bent upward. A rotational moment M is applied to both boundary portions of the diaphragms 44a and 44b located between the discharge nozzle 56a and the non-discharge nozzle 56b, thereby preventing the pressure chamber 54a from moving up and down.

  Here, the voltage waveform Vb shown in FIG. 5 may be a phase that generates a rotational moment in the diaphragm 44a by using a part of the drive waveform, and may not be a completely opposite phase.

  Further, the voltage waveform Vb may include a part of a component opposite to the driving method of the voltage waveform Va.

  Note that the maximum voltage of the voltage waveform Vb applied to the piezoelectric element 50b of the non-ejection nozzle 56b is set to a driving voltage that does not allow bubbles to enter the pressure chamber 54 or eject ink. As shown in FIG. 6A, when the ink protrudes from the nozzle 56b to the outside by the amount of approximately a hemisphere with respect to the nozzle plate 42b, or from the nozzle plate 42b to the inside of the pressure chamber 54b as shown in FIG. 6B. If the bubbles exceed the protruding case, an accidental drop or bubbles are mixed into the pressure chamber 54. If the pressure difference between the inner side and the outer side of the nozzle 56 at this time is ΔP (ΔP = 2 T / r where T is the surface tension of the ink and r is the nozzle radius), ink leakage occurs when the internal pressure-external pressure ≧ ΔP. Then, bubbles are mixed into the pressure chamber 54 when external pressure-internal pressure ≧ ΔP. Actually, since an influence such as a contact angle between the ink and the nozzle and a nozzle shape occurs, a driving voltage is applied so that at least the pressure difference ΔP falls within about 2T / r.

  According to the image forming apparatus of the present embodiment, a rotational moment is applied to the vibration plate 44 positioned between the discharge nozzle and the non-discharge nozzle to prevent the pressure chamber 54a from moving up and down, thereby improving the ink discharge efficiency. . As a result, ink with higher viscosity can be used, and the head density can be increased.

  The piezoelectric element is not limited to a form in which the laminated piezoelectric body is mechanically separated for each pressure chamber, and may be a form in which each laminated pressure body is individually driven by an electrode pattern of the laminated piezoelectric body or a unimorph structure (single plate piezoelectric element). .

  Further, the reverse drive voltage may be applied to the non-ejection nozzles that are separated from the ejection nozzle by one or more in the front-rear and left-right directions.

  That is, in the description using FIG. 4, the example in which the piezoelectric element 50b of the non-discharge nozzle 56b adjacent to the discharge nozzle 56a is driven in the opposite direction with respect to the piezoelectric element 50a of the discharge nozzle 56a has been described. A mode is also possible in which a piezoelectric element (not shown in FIG. 4) of a non-discharge nozzle that is in the vicinity and is not adjacent to the discharge nozzle 56a is driven in the opposite direction with respect to the piezoelectric element 50a of the discharge nozzle 56a.

  As shown in FIG. 7, a push waveform of the voltage waveform Va (driving waveform) described in FIG. 5 is added to the piezoelectric element 50a provided corresponding to the pressure chamber 54a (center of the drawing) of the discharge nozzle 56a. When the downward force F0 is generated, the piezoelectric elements 50b corresponding to the left and right non-discharge nozzles 56b adjacent to the discharge nozzle 56a generate forces F2 and F3 opposite to F0 (upward), respectively. Therefore, adding the pull waveform of the voltage waveform Vb (see FIG. 5) has been described with reference to FIG.

  At this time, it is important for high-precision ejection to balance the moment of force applied to the recording head 12 so that the recording head 12 is not subjected to bending stress. As shown in FIG. 7, when driving the piezoelectric element 56b of the non-ejection nozzle 56b adjacent to the ejection nozzle 56a, if the distance between the adjacent nozzles is set to L2 and L3 (L2 = L3 = nozzle pitch), F2 × L2 = F3 × L3 is desirable.

  Similarly, when driving non-adjacent piezoelectric elements, it is desirable to set the force so that the moments are balanced according to the distance. For example, in FIG. 8, the piezoelectric element 50b-1 corresponding to the non-ejection nozzle 56b-1 at a distance L1 not adjacent to the ejection nozzle 56a and the piezoelectric element 50b corresponding to the non-ejection nozzle 56b at a distance L3 adjacent. Are driven to generate forces F1 and F3 opposite to F0, it is desirable to set the force so that F1 * L1 = F3 * L3. Here, if L1 = 2 × L3 holds, F1 = F3 / 2.

  From the above relationship, the relationship between the distance from the discharge nozzle and the magnitude (voltage value) of the drive signal to the piezoelectric element is almost inversely proportional (L × F = constant) as shown in FIG.

  In addition, when a plurality of nozzles are arranged in a two-dimensional pattern in a staggered manner, a reverse drive voltage may be applied to the piezoelectric elements of the nozzles adjacent to each other in an oblique direction, not limited to the front, rear, left and right of the discharge nozzle. Furthermore, the magnitude of the driving voltage of the piezoelectric element 50b may be changed according to the distance from the discharge nozzle 56a (see FIG. 9).

  In order to give a rotational moment to the diaphragm of the nozzle located on the outermost side, a dummy piezoelectric element that does not contribute to image formation may be provided outside the nozzle located on the outermost side. An example is shown in FIG.

  FIG. 10 is a schematic plan view of a recording head in which pressure chambers are arranged in a two-dimensional matrix. A range 130 surrounded by an alternate long and short dash line is an area where the piezoelectric element 50-va corresponding to the pressure chamber of a nozzle (nozzle that contributes to image formation) used for ink ejection for printing (hereinafter referred to as an area) is arranged. "Effective nozzle range"). A dummy piezoelectric element 50-dm that does not contribute to image formation is disposed outside the effective nozzle range 130 (outer peripheral range 140 surrounded by a dotted line in the figure).

  It is apparent from the above description that the moments can be balanced by driving the dummy piezoelectric element 50-dm during ejection from the nozzle located at the outermost side in the effective nozzle range 130.

1 is a side view showing an image forming apparatus according to an embodiment of the present invention. Sectional drawing which shows the recording head as an image forming apparatus which concerns on embodiment of this invention Control block diagram of image forming apparatus according to an embodiment of the present invention Sectional drawing which shows the effect | action of the image forming apparatus which concerns on embodiment of this invention Explanatory drawing which shows the drive voltage applied to the piezoelectric element of the image forming apparatus which concerns on embodiment of this invention Explanatory drawing showing nozzle discharge limit and bubble mixing limit Explanatory drawing which shows an effect | action at the time of driving the non-discharge nozzle adjacent to a discharge nozzle Explanatory drawing which shows the effect | action when driving the non-discharge nozzle which is not adjacent to the discharge nozzle Graph showing the relationship between the distance from the discharge nozzle and the magnitude of the drive signal to the piezoelectric element Plane schematic diagram showing an example of the arrangement of dummy piezoelectric elements

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 12 ... Recording head, 16 ... Recording paper, 44a, 44b ... Diaphragm, 50, 50a, 50b ... Piezoelectric element, 50-dm ... Dummy piezoelectric element, 54, 54a, 54b ... Pressure chamber, 56, 56a, 56b ... nozzle,

Claims (4)

Nozzles arranged in a line or two-dimensional shape;
A pressure chamber disposed corresponding to each nozzle;
In an image forming apparatus comprising: a piezoelectric element that applies a drive signal to apply pressure in the pressure chamber to discharge ink from the nozzle;
An image forming apparatus, wherein a drive signal including a drive component for driving in a direction opposite to the piezoelectric element of the discharge nozzle is given to the piezoelectric element of the non-discharge nozzle in the vicinity of the ink discharge nozzle during ink discharge.   2. The image formation according to claim 1, wherein the drive waveform of the drive signal applied to the piezoelectric element of the non-ejection nozzle is at least partially in phase with the drive waveform of the drive signal of the ejection nozzle piezoelectric element. apparatus.   3. The image forming apparatus according to claim 1, wherein the magnitude of the drive signal given to the piezoelectric element of the non-ejection nozzle is determined according to a distance from the ejection nozzle. 4. 4. The image forming apparatus according to claim 1, wherein a dummy piezoelectric element that does not contribute to image formation is provided outside the outermost nozzle.

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