JP2009083401A - Recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To record a high-quality image while achieving reduction of cost. <P>SOLUTION: An inkjet printer includes a conveying mechanism to convey paper by rotating a conveying roller by a conveying motor, an encoder to output a pulse signal with the rotation of the conveying roller, and an inkjet head to eject an ink droplet to the conveyed paper. A conveying motor control part controls drive of the conveying motor 19 based on a pulse signal of the encoder passing through an LPF having frequency characteristic of cutoff frequency f1. A head control part controls the ejection timing of the ink droplet of the inkjet head based on the pulse signal of the encoder passing through the LPF having frequency characteristic of cutoff frequency f2 higher than the cutoff frequency f1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a recording apparatus that forms an image on a recording medium.

  As an ink jet printer that prints an image on a recording medium such as recording paper, an endless conveying belt that conveys the recording medium is stretched over two rollers, and the conveying belt is rotated on the conveying belt by rotating the conveying belt through the rollers. There is known one having a transport mechanism for transporting a recording medium placed on the recording medium and an ink jet head for ejecting ink droplets onto the recording medium transported by the transport mechanism (see Patent Document 1).

Japanese Patent Laying-Open No. 2006-131353 (FIG. 1)

  In such an ink jet printer, high quality printing is possible by synchronizing the ink droplet ejection period of the ink jet head and the driving speed of the transport belt. For this reason, an encoder that outputs a pulse signal as the conveyor belt is driven is provided, and the ink ejection timing of the ink head is controlled so as to synchronize with the period of the pulse signal output from the encoder. . At this time, in order to perform higher quality printing, it is preferable to stabilize the driving speed of the conveyor belt. Thus, it is conceivable to feedback control the driving speed of the conveyor belt using the pulse signal output from the encoder. However, the transport mechanism has a mechanical structure such as a roller or a transport belt that has a slow response to commands, and requires feedback control with a large time constant. On the other hand, the ink ejection control system has an electrical configuration with a quick response like a pulse generation electronic circuit, and can perform feedback control with a small time constant. For this reason, it is preferable to use encoders having different output characteristics between the control system of the ink jet head and the control system of the transport mechanism, but the structure of the ink jet printer is complicated and the cost is increased.

  On the other hand, it is conceivable to use a common feedback control system from the viewpoint of simplification of structure and cost reduction. For example, if the characteristics of the control system are matched to the transport mechanism, the high-speed response of the discharge system cannot be utilized. In feedback control with a long time constant, instantaneous conveyance unevenness (belt wobbling, slippage of the conveyance roller, backlash of the motor rotation shaft, etc., and instantaneous speed fluctuation due to the combination) that occurs in the conveyance mechanism is fed back. hard. Since the ejection system does not cope with this conveyance unevenness, printing unevenness occurs. On the other hand, feedback control with a short time constant may deviate from the frequency band where stable feedback control is possible for the transport mechanism. This leads to an uncontrollable state due to the oscillation phenomenon of the control system.

  SUMMARY An advantage of some aspects of the invention is that it provides a recording apparatus capable of recording a high-quality image while reducing costs.

  The recording apparatus of the present invention has a plurality of rollers including a conveyance roller and a conveyance motor for rotating the conveyance roller, and includes a conveyance mechanism that conveys a recording medium on which an image is recorded in the conveyance direction, and the conveyance A recording head that records an image on the recording medium conveyed by a mechanism, an encoder that outputs a pulse signal associated with the rotation, and the conveyance motor and the recording head as the conveyance roller rotates. And a control device. The control device receives the pulse signal output from the encoder, the first filter that passes a pulse signal having a frequency equal to or lower than the first frequency, and the pulse signal output from the encoder. A second filter that passes a pulse signal of a second frequency that is higher than the first frequency and lower than the first frequency; a motor control unit that controls driving of the transport motor based on the pulse signal that has passed through the first filter; and the second filter Head control means for controlling the dot recording timing of the recording head based on the pulse signal that has passed through.

  According to the present invention, the first filter having a low cut-off frequency (first frequency) is used in the control system of the transport mechanism having low control responsiveness, and the print head has high control responsiveness compared to the transport mechanism. Since a second filter having a high cutoff frequency (second frequency) is used in the control system, the pulse signal from the encoder can be filtered with an optimum frequency characteristic in each control system. For this reason, it is possible to stably convey the recording medium with good followability to the speed command by the feedback control of the conveying motor, and to improve the recording accuracy by the recording head. Thereby, a high-quality image can be recorded on the recording medium. Further, since the encoder can be shared by the control system of the transport motor and the control system of the recording head, the cost can be reduced.

  In the present invention, at least one of the first filter and the second filter may output a moving average of the frequency related to the input pulse signal. According to this, a filter having an optimal frequency characteristic can be easily configured.

  In the present invention, the head control means sets the distance between dots in the transport direction in the image recorded on the recording medium to the recording paper during one cycle of the pulse signal that has passed through the second filter. A correction coefficient calculating means for calculating a correction coefficient divided by the distance transported, and a pulse signal obtained by correcting the pulse signal that has passed through the second filter with the correction coefficient calculated by the correction coefficient calculating means. Thus, it is preferable to determine the dot recording timing of the recording head. This facilitates control of dot recording timing.

  Furthermore, in the present invention, it is more preferable that the first frequency is lower than the natural frequency of the transport mechanism. According to this, since the influence of the mechanical vibration of the transport mechanism is suppressed, the transport motor can be controlled efficiently.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic side view showing an overall configuration of an ink jet printer which is a preferred embodiment of the present invention. As shown in FIG. 1, an inkjet printer (recording apparatus) 101 is a color inkjet printer having four inkjet heads (recording heads) 1. The inkjet printer 101 includes a control device 16 that controls the entire inkjet printer 101. The ink jet printer 101 includes a paper feeding unit 11 on the left side in the drawing and a paper discharge unit 12 on the right side in the drawing.

  Inside the ink jet printer 101, a paper conveyance path through which a paper (recording medium) P is conveyed from the paper supply unit 11 toward the paper discharge unit 12 is formed. The paper feed unit 11 includes a paper stocker 11a and a pickup roller 11c. The sheet stocker 11a accommodates a large number of sheets P stacked therein, and is arranged so that the upper opening is inclined toward the right side (downstream side) in the drawing. A support plate 11b urged from the bottom of the paper stocker 11a toward the upper opening is disposed in the paper stocker 11a, and a large number of sheets P are stacked on the support plate 11b. The pickup roller 11c is driven by a placement motor (not shown) to pick up the sheets P stacked in the sheet stocker 11a one by one from the top and to send the picked up sheets P downstream. The paper P sent out from the paper stocker 11 a by the pickup roller 11 c is placed on the outer peripheral surface 8 a of the transport belt 8.

  A transport mechanism 13 is provided at an intermediate portion of the paper transport path. The transport mechanism 13 includes two belt rollers 6, 7, an endless transport belt 8 wound around the rollers 6, 7, and a transport that rotates the belt roller (transport roller) 6. A motor 19 and a platen 15 arranged in a region surrounded by the conveyor belt 8 are included. The platen 15 supports the conveyance belt 8 so that the conveyance belt 8 does not bend downward at a position facing the inkjet head 1. A nip roller 4 is disposed at a position facing the belt roller 7. The nip roller 4 presses the paper P against the outer peripheral surface 8a when the paper P is placed on the outer peripheral surface 8a of the transport belt 8 by the pickup roller 11c of the paper feeding unit 11. An encoder 59 is disposed on the downstream side of the nip roller 4 and immediately upstream of the inkjet head 1. The encoder 59 outputs a pulse signal as the outer peripheral surface 8a moves, in other words, as the belt roller 6 driven by the transport motor 19 rotates, and is a roller attached to the input shaft of the encoder 59. The outer peripheral surface of the conveyor belt 8 and the outer peripheral surface 8a of the conveyor belt 8 are fixed in contact with each other. Therefore, the driving speed of the conveyor belt 8 can be detected by analyzing the cycle of the pulse signal output from the encoder 59. When the transport motor 19 rotates the belt roller 6, the transport belt 8 travels (rotates). Thereby, the conveyance belt 8 conveys the paper P pressed against the outer peripheral surface 8 a by the nip roller 4 toward the paper discharge unit 12 while being adhesively held. A weak adhesive silicon resin layer is formed on the surface of the conveyor belt 8.

  A peeling mechanism 14 is provided immediately downstream of the conveying belt 8. The peeling mechanism 14 is configured to peel the paper P adhered to the outer peripheral surface 8a of the transport belt 8 from the outer peripheral surface 8a and guide it toward the paper discharge unit 12 on the right side in the drawing.

  The four inkjet heads 1 are provided side by side along the transport direction corresponding to four colors of ink (magenta, yellow, cyan, and black). That is, the ink jet printer 101 is a line printer. Each of the four inkjet heads 1 has a head body 2 at the lower end thereof. The head main body 2 has an elongated rectangular parallelepiped shape that is long in a direction orthogonal to the transport direction. Further, the bottom surface of the head main body 2 is an ink ejection surface 2a that faces the outer peripheral surface 8a. When the paper P transported by the transport belt 8 sequentially passes immediately below the four head bodies 2, ink droplets of each color are ejected from the ink ejection surface 2a toward the upper surface of the paper P, that is, the printing surface. Thus, a desired color image can be printed on the printing surface of the paper P.

  Next, the head main body 2 will be described with reference to FIGS. FIG. 2 is a plan view of the head body 2. FIG. 3 is an enlarged view of a region surrounded by a one-dot chain line in FIG. In FIG. 3, for convenience of explanation, the pressure chamber 110, the aperture 112, and the nozzle 108 that are to be drawn with broken lines below the actuator unit 21 are drawn with solid lines. FIG. 4 is a partial cross-sectional view taken along the line IV-IV shown in FIG. FIG. 5 is a partial cross-sectional view of the actuator unit 21.

  The head body 2 constitutes the inkjet head 1 by assembling a reservoir unit (not shown) for supplying ink and a driver IC (not shown) for generating a drive signal for driving the actuator unit 21.

  As shown in FIG. 2, the head main body 2 includes a flow path unit 9 and four actuator units 21 fixed to the upper surface 9 a of the flow path unit 9. As shown in FIG. 3, the flow path unit 9 has an ink flow path including a pressure chamber 110 and the like formed therein. The actuator unit 21 includes a plurality of actuators corresponding to the pressure chambers 110, and has a function of selectively giving ejection energy to the ink in the pressure chambers 110 when driven.

  The flow path unit 9 has a rectangular parallelepiped shape. A total of ten ink supply ports 105b are opened on the upper surface 9a of the flow path unit 9 corresponding to the ink outflow flow path (not shown) of the reservoir unit. As shown in FIGS. 2 and 3, a manifold channel 105 communicating with the ink supply port 105 b and a sub manifold channel 105 a branched from the manifold channel 105 are formed inside the channel unit 9. On the lower surface of the flow path unit 9, there is formed an ink ejection surface 2a in which a large number of nozzles 108 are arranged in a matrix. A large number of pressure chambers 110 are also arranged in a matrix like the nozzles 108 on the fixed surface of the actuator unit 21 in the flow path unit 9.

  In the present embodiment, 16 rows of pressure chambers 110 arranged at equal intervals in the longitudinal direction of the flow path unit 9 are arranged in parallel to each other in the short direction. The number of pressure chambers 110 included in each pressure chamber row is arranged so as to gradually decrease from the long side toward the short side corresponding to the outer shape (trapezoidal shape) of the actuator unit 21 described later. Yes. The nozzle 108 is also arranged in the same manner.

  As shown in FIG. 4, the flow path unit 9 includes a cavity plate 122, a base plate 123, an aperture plate 124, a supply plate 125, manifold plates 126, 127, and 128, a cover plate 129, and a nozzle plate 130 in order from the top. It consists of nine metal plates such as stainless steel. These plates 122 to 130 have a rectangular plane elongated in the main scanning direction.

  By laminating these plates 122 to 130 while aligning each other, the through holes formed in the plates 122 to 130 are connected, and the manifold unit 105 to the sub-manifold channel 105 a and the sub-channels are connected to the channel unit 9. A large number of individual ink flow paths 132 are formed from the outlet of the manifold flow path 105a through the pressure chamber 110 to the nozzle 108.

  Next, the ink flow in the flow path unit 9 will be described. The ink supplied from the reservoir unit into the flow path unit 9 via the ink supply port 105b is branched from the manifold flow path 105 to the sub-manifold flow path 105a. The ink in the sub-manifold channel 105a flows into each individual ink channel 132 and reaches the nozzle 108 through the aperture 112 and the pressure chamber 110 functioning as a throttle.

  The actuator unit 21 will be described. As shown in FIG. 2, each actuator unit 21 has a trapezoidal planar shape. As shown in FIG. 5, the actuator unit 21 includes three piezoelectric sheets (piezoelectric layers) 141 to 143 made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity. . An individual electrode 135 is formed at a position facing the pressure chamber 110 on the uppermost piezoelectric sheet 141. The individual electrode 135 has an electrode portion arranged to face the pressure chamber 110 and an extending portion drawn out to a region facing the pressure chamber 110, and a land 136 is formed on the extending portion. Is formed. A common electrode 134 formed on the entire surface of the sheet is interposed between the uppermost piezoelectric sheet 141 and the lower piezoelectric sheet 142.

  The common electrode 134 is equally grounded in the region corresponding to all the pressure chambers 110. On the other hand, the individual electrode 135 is electrically connected to a driver IC (not shown), and a drive signal from the driver IC is selectively input. That is, in the actuator unit 21, a portion sandwiched between the individual electrode 135 and the pressure chamber 110 functions as an individual actuator, and a plurality of actuators corresponding to the number of pressure chambers 110 are formed.

  Here, a driving method of the actuator unit 21 will be described. The piezoelectric sheet 141 is polarized in the thickness direction, and a portion corresponding to the individual electrode 135 functions as an active portion that is bent by the piezoelectric effect. When the individual electrode 135 has a potential different from that of the common electrode 134, an electric field is applied to this portion in the polarization direction. The active portion expands in the thickness direction and contracts in the plane direction when the electric field and the polarization direction are the same. In addition, the amount of displacement at this time is larger in the surface direction than in the thickness direction. That is, the actuator unit 21 uses the upper one piezoelectric sheet 141 away from the pressure chamber 110 as a layer including an active portion and the lower two piezoelectric sheets 142 and 143 close to the pressure chamber 110 as inactive layers. The so-called unimorph type. The piezoelectric sheets 141 to 143 are fixed to the upper surface of the cavity plate 122 that partitions the pressure chamber 110. Here, when there is a difference in distortion in the plane direction between the electric field application portion of the piezoelectric sheet 141 and the piezoelectric sheets 142 and 143 below the electric field applying portion, the entire piezoelectric sheets 141 to 143 become convex toward the inside of the pressure chamber 110. (Unimorph deformation). As a result, pressure (discharge energy) is applied to the ink in the pressure chamber 110, and a pressure wave is generated in the pressure chamber 110. Then, the generated pressure wave propagates from the pressure chamber 110 to the nozzle 108, whereby an ink droplet is ejected from the nozzle 108.

  In this embodiment, a predetermined potential is applied to the individual electrode 135 in advance, and a ground potential is once applied to the individual electrode 135 every time there is a discharge request, and then the predetermined potential is applied again at a predetermined timing. A drive signal to be applied to the individual electrode 135 is output from the driver IC. In this case, at the timing when the individual electrode 135 becomes the ground potential, the pressure of the ink in the pressure chamber 110 drops and the ink is sucked from the sub manifold channel 105 a into the individual ink channel 132. Thereafter, the ink pressure in the pressure chamber 110 rises at the timing when the individual electrode 135 is set to a predetermined potential again, and ink droplets are ejected from the nozzles 108. That is, a rectangular wave pulse is applied to the individual electrode 135. This pulse width is AL (Acoustic Length), which is the length of time during which the pressure wave propagates from the outlet of the sub-manifold channel 105a to the tip of the nozzle 108 in the pressure chamber 110, and the ink in the pressure chamber 110 is negative pressure. Since both pressures are combined when the state is reversed from the positive pressure state, the ink droplets can be ejected from the nozzles 108 with a strong pressure.

  Next, the control device 16 will be described in detail with reference to FIG. FIG. 6 is a functional block diagram of the control device 16. In FIG. 6, only one of the four inkjet heads 1 is schematically shown. As shown in FIG. 6, the control device 16 includes a print data storage unit 63, a head control unit 64, and a transport motor control unit 68. The pulse signal output from the encoder 59 of the transport mechanism 13 is input to the head controller 64 and the transport motor controller 68, respectively. The print data storage unit 63 stores print data transferred from a host computer (not shown). The print data includes image data relating to an image to be formed on the paper P.

  The conveyance motor control unit 68 controls the conveyance motor 19 so that the conveyance belt 8 travels in a predetermined speed pattern (including an acceleration pattern, a constant speed pattern, and a deceleration pattern).

  The control contents of the transport motor control unit 68 will be described with reference to FIG. FIG. 7 is a block diagram showing a control system of the transport motor control unit 68. The block diagram shows a signal transmission state in the control system, and FIG. 7 shows a signal transmission state related to the frequency response.

  As shown in FIG. 7, the control system has a configuration that compares the rotational angular velocity command ωref with the rotational angular velocity ωest of the transport mechanism 13 (conveyance motor 19), and the rotational angular velocity ωest is the rotational angular velocity ω of the transport motor 19. Estimated as a moving average. This comparison / estimation operation is performed discretely on a predetermined cycle, that is, on the time axis. In the control system, the conveyance motor control unit 68 obtains a difference between the set rotational angular velocity command ωref and the estimated rotational angular velocity ωest. The rotational angular velocity ωest is estimated from the rotational angular velocity (output) ω related to the transport motor 15 by an encoder pulse frequency calculation unit 76 and an LPF (Low Pass Filter: first filter) 77. Further, the control system outputs this difference to the transport motor 19 through the PID (proportional integral derivative) control unit 71.

  As shown in FIG. 7, the transport motor control unit 68 generates a rotational speed command for the transport motor 19 in each control cycle as a rotational angular speed command ωref in accordance with a predetermined speed pattern. The rotational angular velocity command ωref is a voltage signal. In the PID control unit 71, the values of the position gain (Kp), integral gain (Ki / s), and differential gain (s * Kd) determined in advance are individually added to the generated rotational angular velocity command ωref. The multiplied items are added together. That is, this control system performs feedback control by PID control. The position gain is a coefficient that changes the input value in proportion to the deviation between the input value (rotational angular velocity command ωref) and the output value (rotational angular velocity ω of the transport motor 19), and the integral gain is the input value and the output. The differential gain is a coefficient that changes the input value in proportion to the differential of the deviation between the input value and the output value. The symbol s in the integral gain and the differential gain is a Laplace operator.

  Thereafter, the voltage signal output from the conveyance motor control unit 68 is converted into a current signal by the voltage-current conversion unit 72. Specifically, the voltage-current conversion unit 72 adds the reciprocal of the impedance (1 / (Ra + s * La), where Ra: resistance, La: inductance) in the electric circuit that implements the transport motor control unit 68 to the voltage signal. Multiply and convert to current signal.

  The current signal converted by the voltage / current converter 72 is multiplied by a torque constant Kt by the torque command converter 73 and converted into a torque signal. The transport motor 19 is affected by disturbance torque generated by mechanical vibration (for example, vibration of the transport belt 8). Therefore, a signal corresponding to the disturbance torque is added to the torque signal converted by the torque command conversion unit 73 and input to the rotation angular velocity conversion unit 74. The rotation angular velocity conversion unit 74 outputs the rotation angular velocity ω related to the transport motor 19. This output is an output from the encoder 59. At this time, the rotational angular velocity ω corresponds to a value obtained by multiplying the torque command by the reciprocal of the inertia of the transport motor 19 (1 / (J * s + D), where J: inertia, D: damper).

  On the other hand, when the transport motor 19 rotates, a counter electromotive voltage is generated. Therefore, the counter electromotive voltage calculation unit 75 calculates the counter electromotive voltage by multiplying the rotational angular velocity ω by the counter electromotive voltage constant Ke related to the transport motor 19 and subtracts the counter electromotive voltage from the voltage signal output by the PID control unit 71. .

  In the above description of the conveyance motor control unit 68, the voltage / current conversion unit 72, the torque command conversion unit 73, the rotation angular velocity conversion unit 74, and the counter electromotive voltage calculation unit 75 are configured by the conveyance motor 19 and the encoder 59. Further, the configuration in which disturbance torque is added to this configuration represents the conveyance mechanism 13 in which the conveyance belt 8 and the conveyance roller 6 are added. That is, the transport motor control unit 68 includes a PID control unit 71, an encoder pulse frequency calculation unit 76, and an LPF 77.

  Here, the rotational angular velocity ω of the transport motor 9 is acquired as a pulse signal from the encoder 59. Then, the encoder pulse frequency calculation unit 76 calculates the frequency f of the pulse signal from the pulse signal from the encoder 59 (corresponding to the rotational angular velocity ω in FIG. 7). Specifically, the encoder pulse frequency calculation unit 76 calculates the period T by measuring the pulse interval of the pulse signal from the encoder 59 by the number of clocks of the reference clock, and further sets the inverse of the calculated period T as the frequency f. . The frequency f calculated by the encoder pulse frequency calculator 76 is filtered by an LPF (Low Pass filter) 77 that is a digital filter that outputs a moving average of the input frequency f.

  In the LPF 77, the frequency f for a plurality of times is a moving average (described later). By this averaging process (filtering), the rotational angular velocity of the transport motor 19 is estimated, and the noise component (high frequency component) included in each frequency f is leveled. As a result, the influence of the noise component on the output value (estimated rotational angular velocity ωest) is reduced. That is, high frequency components are effectively removed.

  The LPF 77 will be described with reference to FIG. FIG. 8 is a functional block diagram of the LPF 77. As shown in FIG. 8, the LPF 77 has a plurality of buffers 77a to 77c and a divider 77d. 8 shows a case where the LPF 77 has three buffers 77a to 77c and the divider 77d divides by 4. Further, the frequency f calculated by the encoder pulse frequency calculation unit 76 at the current time is defined as a frequency f [n]. The buffer 77a stores the frequency f [n-1] sampled at the time immediately before the current time, and the buffer 77b stores the frequency f [n-2] sampled at the time two times before the current time. The buffer 77c is configured to store the frequency f [n-3] sampled at the time three times before the current time. Then, the LPF 77 has the frequency f [n] at the current time and the frequencies f [n−1], f [n−2], and f [n−3] stored in the buffers 77a to 77c, that is, The result obtained by dividing the sum of the four sampled frequencies f by 4 by the divider 77d is output.

  Thus, the LPF 77 is a low-pass filter that outputs a moving average of the input frequency f. FIG. 8 shows a configuration in which a moving average of four sampled frequencies f is output. Depending on the frequency characteristics required for the LPF 77, that is, the cutoff frequency (first frequency) f1 (see FIG. 10). The number of frequencies f to be sampled is determined. As the number of frequencies f to be sampled increases, the cut-off frequency f1 can be lowered. This cutoff frequency f1 is appropriately selected depending on the responsiveness related to the control of the transport mechanism 13, and is equal to or lower than the natural frequency of the transport mechanism 13. Thereby, the influence of the mechanical vibration of the conveyance mechanism 13 can be suppressed. In the present embodiment, the sampling number of the frequency f is any one of 150 to 200.

  The frequency f filtered by the LPF 77 is the rotational speed of the transport belt 8 (belt roller 6), that is, the rotational angular speed of the transport motor 19. Then, the frequency f (rotational angular velocity value) is subtracted from the rotational angular velocity command ωref. As described above, the transport motor control unit 68 performs feedback control based on the pulse signal input from the encoder 59. Thereby, the followability of the driving speed of the conveying belt 8 with respect to the speed command of the conveying motor control unit 68 is enhanced, and the conveying speed of the paper P is stabilized.

  Returning to FIG. 6, the head controller 64 forms an image to be printed on the transported paper P in synchronization with the transport belt 8 rotating at the rotational speed controlled by the transport motor controller 68. In this manner, the ejection timing (dot recording timing) of the ink droplets from the head body 2 is controlled. The head control unit 64 of the present embodiment does not perform feedback control as described later, but is not limited to this.

  The control content of the head controller 64 will be described with reference to FIGS. 9 and 10. FIG. 9 is a functional block diagram of the head controller 64. FIG. 10 is a graph showing the frequency characteristics of the LPFs 77 and 81. As shown in FIG. 9, the head controller 64 includes an LPF (second filter) 81, a period correction coefficient calculator (period correction coefficient calculator) 82, a discharge timing generation circuit 83, and a discharge waveform generation circuit 84. have.

  The LPF 81 filters the pulse signal (encoder pulse) output from the encoder 59 and, like the LPF 77, is configured to output a moving average of the frequency related to the input pulse signal. The LPF 81 has a frequency characteristic of a cutoff frequency (second frequency) f2. This cutoff frequency f2 is appropriately selected depending on the responsiveness related to the control of the head body 2 (actuator unit 21). Since the head main body 2 has higher control responsiveness than the transport mechanism 13, the cut-off frequency f2 is higher than the cut-off frequency f1, as shown in FIG. In the present embodiment, the number of samplings of the frequency f is set to about one digit less than that of the LPF 77, and is set to any one of 15 to 20.

  The period correction coefficient calculation unit 82 calculates the distance between dots in the paper transport direction in the image printed on the paper P (corresponding to the resolution in the paper transport direction), and the paper P is in one period regarding the pulse signal that has passed through the LPF 81. The correction coefficient divided by the transported distance is calculated. Then, the pulse signal is corrected by multiplying the calculated correction coefficient by the pulse signal that has passed through the LPF 81. As a result, the distance that the paper P is transported during one period related to the corrected pulse signal matches the distance between dots in the paper transport direction.

  The ejection timing generation circuit 83 generates a timing pulse that determines the ejection timing of the ink droplet so as to be synchronized with the corrected pulse signal. At this time, as described above, the distance at which the paper P is transported during one cycle related to the corrected pulse signal matches the distance between dots in the paper transport direction. A simple circuit can be used.

  Further, the discharge waveform generation circuit 84 generates a discharge waveform that drives the actuator unit 21 so that ink droplets are discharged from the nozzles 108 in synchronization with the timing pulse generated by the discharge timing generation circuit 83. The ejection waveform generated by the ejection waveform generation circuit 84 is output to the driver IC of the inkjet head 1. The driver IC drives the actuator unit 21 according to this ejection waveform, and ejects ink droplets from the nozzles 108. Thereby, the rotation speed of the conveyance belt 8, that is, the conveyance speed of the paper P and the ejection timing of the ink droplets from the nozzles 108 can be completely matched.

  As described above, according to the present embodiment described above, the LPF 77 having the low cutoff frequency f1 is used for the control system of the transport mechanism 13 having low control-related responsiveness, and the inkjet head has higher control-related responsiveness than the transport mechanism 13. Since the LPF 81 having a high cutoff frequency f2 is used for the control system 1, the pulse signal from the encoder 59 can be filtered with the optimum frequency characteristics in each control system. For this reason, the feed control of the carry motor 19 can stably carry the paper P with good followability to the speed command, and the ink jet head at the optimum ink droplet discharge timing synchronized with the paper P carry speed. 1 can be controlled. Thereby, a high quality image can be printed on the paper P. In addition, since the encoder 59 can be shared by the control system of the transport mechanism 13 and the control system of the inkjet head 1, the cost can be reduced.

  Further, since the LPFs 77 and 81 are configured to output a moving average of the frequency f related to the input pulse signal, a filter having an optimal frequency characteristic can be easily configured.

  Further, the pulse signal that has passed through the LPF 81 is corrected with the correction coefficient calculated by the period correction coefficient calculation unit 82, so that the distance that the sheet P is transported during one period related to the corrected pulse signal, and the sheet transport The distance between dots in the direction matches. This facilitates control of ink droplet ejection timing.

  In addition, since the cutoff frequency f1 of the LPF 77 is equal to or lower than the natural frequency of the transport mechanism 13, the influence of mechanical vibration of the transport mechanism 13 can be suppressed.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. For example, in the above-described embodiment, the LPFs 77 and 81 are configured to output a moving average of the frequency f related to the input pulse signal. However, the LPFs 77 and 81 are configured to have a low-pass filter with other configurations. It may be.

  Further, in the above-described embodiment, the pulse signal that has passed through the LPF 81 is corrected with the correction coefficient calculated by the period correction coefficient calculation unit 82, so that the paper P is conveyed during one period related to the corrected pulse signal. However, such a correction may not be performed.

  Furthermore, in the above-described embodiment, the cutoff frequency f1 of the LPF 77 is equal to or lower than the natural frequency of the transport mechanism 13, but the cutoff frequency f1 may coincide with the natural frequency of the transport mechanism 13. It may be greater than or equal to the natural frequency.

  In the above-described embodiment, the example in which the present invention is applied to the inkjet printer 101 including the inkjet head 1 that ejects ink droplets onto the paper P has been described. However, the thermal head that thermally transfers the ink to the paper P is provided. The present invention can also be applied to other types of recording devices such as printers.

  In the above-described embodiment, the inkjet printer 101 has a belt conveyance mechanism as a feedback control target. However, the inkjet printer 101 moves like a roller conveyance mechanism or a flat bed that conveys a combination of rollers instead of a belt. You may have the platen conveyance mechanism conveyed with the flat plate to do. Alternatively, the ink jet printer may be a carriage drive type printer that scans the recording head itself.

1 is an external side view of an inkjet printer according to a first embodiment of the present invention. FIG. 3 is a plan view of the head main body shown in FIG. 2. It is an enlarged view of the area | region enclosed with the dashed-dotted line shown in FIG. It is the IV-IV sectional view taken on the line shown in FIG. It is sectional drawing of the actuator unit shown in FIG. It is a functional block diagram of the control apparatus shown in FIG. It is a block diagram which shows the control system of the conveyance motor control part shown in FIG. It is a functional block diagram of LPF shown in FIG. FIG. 7 is a functional block diagram of the head controller shown in FIG. 6. 10 is a graph showing frequency characteristics of the LPFs shown in FIGS. 7 and 9.

Explanation of symbols

1 Inkjet head (recording head)
6 Belt roller (conveyance roller)
13 Transport Mechanism 16 Control Device 19 Transport Motor 21 Actuator Unit 59 Encoder 63 Print Data Storage Unit 64 Head Control Unit (Head Control Unit)
68 Conveyance motor control unit (conveyance motor control means)
71 PID control unit 72 Voltage current conversion unit 73 Torque command conversion unit 74 Rotational angular velocity conversion unit 75 Back electromotive voltage calculation unit 76 Encoder pulse frequency calculation unit 77 LPF (first filter)
77a to 77c Buffer 77d Divider 81 LPF (second filter)
82 period correction coefficient calculation unit (period correction coefficient calculation means)
83 Ejection Timing Generation Circuit 84 Ejection Waveform Generation Circuit 101 Inkjet Printer (Recording Device)

Claims (4)

A conveyance mechanism that includes a plurality of rollers including a conveyance roller and a conveyance motor for rotating the conveyance roller, and conveys a recording medium on which an image is recorded in a conveyance direction;
A recording head for recording an image on the recording medium conveyed by the conveyance mechanism;
An encoder that outputs a pulse signal associated with the rotation in accordance with the rotation of the transport roller;
A controller for controlling the transport motor and the recording head,
The control device is
A first filter that receives the pulse signal output from the encoder and passes a pulse signal having a frequency equal to or lower than the first frequency;
A second filter that receives a pulse signal output from the encoder and passes a pulse signal that is higher than the first frequency and lower than a second frequency; and
Motor control means for controlling the drive of the transport motor based on the pulse signal that has passed through the first filter;
A recording apparatus comprising: a head control unit that controls dot recording timing of the recording head based on a pulse signal that has passed through the second filter.   The recording apparatus according to claim 1, wherein at least one of the first filter and the second filter outputs a moving average of a frequency related to an input pulse signal. The head control means;
A correction coefficient is calculated by dividing the distance between dots in the transport direction in the image recorded on the recording medium by the distance by which the recording paper is transported during one period of the pulse signal that has passed through the second filter. Having correction coefficient calculation means,
2. The dot recording timing of the recording head is determined by a pulse signal obtained by correcting the pulse signal that has passed through the second filter with the correction coefficient calculated by the correction coefficient calculating means. 2. The recording apparatus according to 2.   The recording apparatus according to claim 1, wherein the first frequency is lower than a natural frequency of the transport mechanism.

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