Patent Grant
10780693
Embodiments described herein relate generally to an inkjet head.
In an inkjet head that can discharge multiple droplets from a single nozzle, the number of droplets discharged is adjusted when gradation-type printing is being performed. In the multi-drop printing method in the related art, a drive waveform for discharging a single ink droplet from the nozzle is repeated as many times as necessary to provide the desired total number of droplets. Therefore, as the number of ink droplets is increased, the number of operations of an actuator is also increased, and, as a result, power consumption is increased. In addition, in general, since an operating time increases in direct proportion to the number of ink droplets that are discharged, there is a problem in that it is difficult to increase a drive frequency.
For this reason, there is a demand for an inkjet head providing reduced power consumption when discharging multiple ink droplets from a nozzle in a multi-drop printing method, while still being capable of providing high-speed operation.
In general, according to one embodiment, an inkjet head includes a pressure chamber connected to a nozzle, an actuator corresponding to the pressure chamber and configured to change a volume of the pressure chamber, and a drive circuit configured to drive the actuator causing two or more ink droplets to be consecutively discharged from the nozzle. The drive circuit applies in sequence a first drive waveform for expanding the pressure chamber, a second drive waveform having a first pulse width, a third drive waveform for releasing the pressure chamber from an expanded state, a fourth drive waveform having a second pulse width, and a fifth drive waveform for contracting the pressure chamber.
Hereinafter, embodiments of inkjet head that can reduce power consumption and increase an operation speed by discharging multiple ink droplets will be described with reference to the drawings.
First, the configuration of an inkjet head 1 will be described with reference to
The inkjet head 1 has a substrate 100, a frame 200, a nozzle plate 300, and a casing 400. Further, the inkjet head has upstream and downstream side ink manifolds (not specifically illustrated), a drive circuit 40, and the like in the casing 400. The drive circuit 40 operates the inkjet head 1. The upstream and downstream side ink manifolds are connected to upstream and downstream side ink tanks (not specifically illustrated) outside the head 1.
The substrate 100 is a rectangular shaped plate, and one surface of the substrate 100 is a mounting surface 121. The inkjet head 1 has two lines of piezoelectric members 118, which extend in the longitudinal direction of the substrate 100 and are arranged in two rows in a central portion of the mounting surface 121. Each of the piezoelectric members 118 has a trapezoidal cross section in a transverse direction, and the piezoelectric members 118 are disposed in parallel and spaced apart from each other. The substrate 100 includes a multiple supply ports 125 and multiple discharge ports 126 arranged in the longitudinal direction of the piezoelectric members 118.
The supply ports 125 are arranged between the two piezoelectric members 118 in the longitudinal direction of the substrate 100 along the central portion of the substrate 100. Each of the supply ports 125 penetrates the substrate 100 and is in fluid communication with an upstream side ink manifold, and an end of the supply port 125 is connected to the upstream side ink tank. In other words, the ink, which is supplied to the inkjet head 1 from the upstream side ink tank through the upstream side ink manifold and the supply ports 125, flows into an ink chamber 116 (see
The nozzle plate 300 is a rectangular plate shape, and has multiple nozzles 301 for discharging ink droplets. The nozzles 301 penetrate the nozzle plate 300 and are arranged in two rows in the longitudinal direction of the nozzle plate 300. An ink repellent film is formed on a surface 302 of the nozzle plate 300 on a side from which the ink droplets are discharged from the nozzles 301. For example, the ink repellent film is made of a silicon-based liquid repellent material or a fluorine-containing organic material that has liquid repellency.
The nozzle plate 300 is disposed to face the mounting surface 121 of the substrate 100 via the frame 200. With this arrangement, the inkjet head 1 forms the ink chamber 116 surrounded by the substrate 100, the frame 200, and the nozzle plate 300.
The frame 200 is disposed between the mounting surface 121 of the substrate 100 and the nozzle plate 300. The frame 200 has a size that surrounds the two piezoelectric members 118 and surrounds all of the nozzles 301.
The piezoelectric members 118 are formed of lead zirconate titanate (PZT). The piezoelectric members 118 are formed by sticking two plate-shaped piezoelectric bodies together such that polarization directions thereof are opposite to each other. In the example embodiment described herein, the piezoelectric members 118 are bar-shaped extending in the longitudinal direction. Further, the piezoelectric material is not limited to lead zirconate titanate (PZT), and for example, various types of piezoelectric materials such as PTO (PbTiO3: lead titanate), PMNT (Pb(Mg1/3Nb2/3)O3—PbTiO3), PZNT (Pb(Zn1/3Nb2/3)O3—PbTiO3), ZnO, and AlN may be used.
The piezoelectric members 118 are attached to the mounting surface 121 of the substrate 100. For example, a thermosetting epoxy-based adhesive is used as an adhesive.
The piezoelectric member 118 has an upper surface 118c and two inclined surfaces 118b. The upper surface 118c extends in the transverse direction of the substrate 100 in parallel with the mounting surface 121 of the substrate 100. The two inclined surfaces 118b extend toward the mounting surface 121 from either end sides of the upper surface 118c. Multiple first grooves 131 (hereinafter, also referred to as pressure chambers 131) and multiple second grooves 132 (hereinafter, also referred to as dummy chambers 132), which extend in the transverse direction of the substrate 100, are alternately provided on a surface 118a of the piezoelectric member 118. That is, the piezoelectric member 118 has partition walls 133 which separate the first grooves 131 and the second grooves 132. In other words, each partition wall 133 is a protrusion portion between adjacent first and second grooves 131 and 132. The opposite ends of the first grooves 131 and the opposite ends of the second grooves 132 are connected to the inclined surfaces 118b. In the example embodiment described herein, the first grooves 131 and the second grooves 132 are formed in the same shape. However, the shapes of the first grooves 131 and the second grooves 132 may be different from each other in other examples.
Wall materials 117 are provided at the both end portions of the second grooves 132, respectively. The wall materials 117 seal the opposite ends of the second grooves 132. Each of the wall materials 117 has an upper surface 117a provided to be flush with the upper surface 118c of the piezoelectric member 118. The upper surface 118c of the piezoelectric member 118 and the upper surfaces 117a of the wall materials 117 are attached to the nozzle plate 300. Therefore, the ink in the ink chamber 116, is prevented from penetrating into the second grooves 132.
First, as illustrated in
As illustrated in
The ink is supplied to the first ink chamber 116a via the upstream side ink manifold from the upstream side ink tank outside the head 1. The ink chamber 116 is slowly filled with the supplied ink. Specifically, the ink flowing into the first ink chamber 116a flows toward the two second ink chambers 116b outside the first ink chamber 116a via the first grooves 131 of the piezoelectric members 118 on the both sides of the first ink chamber 116a. Therefore, the entire ink chamber 116 surrounded by the frame 200 is filled with the ink. Further, the ink flowing into the second ink chamber 116b flows toward the downstream side ink tank in the outside of the head 1 via the downstream side ink manifold through the discharge ports 126.
The both ends of the second grooves 132, which is alternately disposed between the first grooves 131, are closed by the wall materials 117, as illustrated in
Next, electrodes and wires on the substrate 100 and the piezoelectric members 118 will be described.
As illustrated in
As illustrated in
For example, the first and second electrodes 134 and 135 provided in the first and second grooves 131 and 132 are formed of a nickel thin film. The material of the first and second electrodes 134 and 135 is not limited thereto, and for example, the first and second electrodes 134 and 135 may be formed of a thin film made of Pt (platinum), Al (aluminum), or Ti (titanium). Further, other materials such as Cu (copper), Al (aluminum), Ag (silver), Ti (titanium), W (tungsten), Mo (molybdenum), and Au (gold) may be used as the material of the first and second electrodes 134 and 135.
With the aforementioned configuration, each piezoelectric member 118 may be deformed by a potential difference between the first electrode 134 and the second electrode 135 that faces the first electrode 134 with the piezoelectric member 118 interposed therebetween. That is, an actuator for varying the volume of the first groove 131 is configured with the piezoelectric member 118 and the first and second electrodes 134 and 135 with the piezoelectric member 118 interposed therebetween. Further, one channel for discharging the ink includes the actuator, the first groove 131 filled with the ink, and the nozzle 301 corresponding to the first groove 131.
In the following descriptions, the first groove 131 will be referred to as a pressure chamber 131, and the second groove 132 will be referred to as a dummy chamber 132. The drive circuit 40 of the inkjet head 1 will be described with reference to
The drive circuit 40 is a circuit for applying a driving signal of the actuator to the first and second electrodes 134 and 135. The drive circuit 40 includes a corresponding waveform generating unit 41, an adjacent waveform generating unit 42, a printing data setting unit 43, a waveform selecting unit 44, a driver unit 45, and a waveform connection control unit 46.
The waveform generating unit 41 generates a signal S1 to be applied to the first electrode 134. The waveform generating unit 42 generates a signal S2 to be applied to the second electrodes 135 in the two dummy chambers 132 adjacent to the pressure chamber 131.
The printing data setting unit 43 sets external printing data provided from the outside. The waveform selecting unit 44 outputs an ON/OFF selecting signal SL based on the printing data set by the printing data setting unit 43. An ON time of the selecting signal SL varies depending on a gradation value of the printing data (see
The driver unit 45 has a first driver 451 connected to the first electrode 134, and second drivers 452 connected to the second electrodes 135. The first driver 451 is interposed between the waveform generating unit 41 and the first electrode 134. The first driver 451 applies the signal S1, which is generated by the waveform generating unit 41, to the first electrode 134. Each of the second drivers 452 is interposed between the waveform generating unit 42 and the second electrodes 135. Each of the second drivers 452 has a floating (high impedance) control input terminal, and the selecting signal SL is input to the floating control input terminal. When the selecting signal SL is ON, the second drivers 452 apply the signal S2, which is generated by the waveform generating unit 42, to the second electrodes 135. When the selecting signal SL is OFF, the second drivers 452 bring the output into the OFF state, and do not apply the signal S2, which is generated by the waveform generating unit 42, to the second electrodes 135.
The waveform generating unit 41 and the waveform generating unit 42 have a 1-drop waveform setting unit 411 and 421, a 2-drop waveform setting unit 412 and 422, a 3-drop waveform setting unit 413 and 423, and a drive waveform generating unit 414 and 424, respectively.
In the waveform generating unit 41, the 1-drop waveform setting unit 411 sets drive waveform data for the first electrode 134 for discharging one ink droplet from the nozzle 301. The 2-drop waveform setting unit 412 sets drive waveform data for the first electrode 134 for continuously discharging two ink droplets from the nozzle 301. The 3-drop waveform setting unit 413 sets drive waveform data for the first electrode 134 for continuously discharging three ink droplets from the nozzle 301.
In the waveform generating unit 42, the 1-drop waveform setting unit 421 sets drive waveform data for the second electrodes 135 for discharging one ink droplet from the nozzle 301. The 2-drop waveform setting unit 422 sets drive waveform data for the second electrodes 135 for continuously discharging two ink droplets from the nozzle 301. The 3-drop waveform setting unit 423 sets drive waveform data for the second electrodes 135 for continuously discharging three ink droplets from the nozzle 301.
Hereinafter, the drive waveform data set by the respective waveform setting units 411, 421, 412, 422, 413, and 423 will be referred to as drive waveform units.
In the waveform generating unit 41, the drive waveform generating unit 414 selects and connects, in the predetermined order, the drive waveform units set by the respective waveform setting units 411, 412, and 413. Further, the drive waveform generating unit 414 outputs the drive waveform signal S1 for the first electrode 134, to which the drive waveform units are connected, to the first driver 451 of the driver unit 45.
In the waveform generating unit 42, the drive waveform generating unit 424 selects and connects, in the predetermined order, the drive waveform units set by the respective waveform setting units 421, 422, and 423. Further, the drive waveform generating unit 424 outputs the drive waveform signal S2 for the second electrode 135, to which the drive waveform units are connected, to the second driver 452 of the driver unit 45.
The order in which the drive waveform generating units 414 and 424 select the drive waveform units is controlled by the waveform connection control unit 46. That is, the waveform connection control unit 46 sets the order for connecting the waveform setting units 411, 421, 412, 422, 413, and 423, and controls the drive waveform generating units 414 and 424 such that waveform units are connected based on the setting.
Here, the drive waveform unit selected by the drive waveform generating unit 414 corresponds to the drive waveform unit simultaneously selected by the drive waveform generating unit 424. That is, when the drive waveform generating unit 414 selects the drive waveform unit for the 1-drop waveform setting unit 411, the drive waveform generating unit 424 also selects the drive waveform unit for the 1-drop waveform setting unit 421. When the drive waveform generating unit 414 selects the drive waveform unit for the 2-drop waveform setting unit 412, the drive waveform generating unit 424 also selects the drive waveform unit for the 2-drop waveform setting unit 422. When the drive waveform generating unit 414 selects the drive waveform unit for the 3-drop waveform setting unit 413, the drive waveform generating unit 424 also selects the drive waveform unit for the 3-drop waveform setting unit 423. The connection order may be programmable.
As described above, while the selecting signal SL is ON, the drive waveform signal S1 is applied to the first electrode 134, and the drive waveform signal S2 is applied to the second electrodes 135. As such, the actuator is operated by differential voltage between the drive waveform signal S1 and the drive waveform signal S2. While the selecting signal SL is OFF, the drive waveform signal S1 is applied to the first electrode 134, but the drive waveform signal S2 is not applied to the second electrodes 135, and the second electrodes 135 are brought into a floating state. Therefore, electric potential of the second electrodes 135 follows the electric potential of the first electrode 134 which is induced as the capacitance of the actuator. As a result, no potential difference occurs between the first electrode 134 and the second electrodes 135 such that the actuator is not operated.
Next, the drive waveform units providing a 1-drop waveform, a 2-drop waveform, and a 3-drop waveform will be described with reference to
As illustrated in
A combination of the first waveform element e11, the second waveform element e12, and the third waveform element e13 forms an expansion pulse P11 that returns the volume of the pressure chamber 131 to the original state after expanding the volume of the pressure chamber 131. That is, the first waveform element e11 corresponds to a leading edge of the expansion pulse P11, the second waveform element e12 corresponds to a pulse width of the expansion pulse P11, and the third waveform element e13 corresponds to a trailing edge of the expansion pulse P11. A combination of the fifth waveform element e15, the sixth waveform element e16, and the seventh waveform element e17 forms a contraction pulse P12 that returns the volume of the pressure chamber 131 to the original state after contracting the volume of the pressure chamber 131. That is, the fifth waveform element e15 corresponds to a leading edge of the contraction pulse P12, the sixth waveform element e16 corresponds to a pulse width of the contraction pulse P12, and the seventh waveform element e17 corresponds to a trailing edge of the contraction pulse P12.
At time t11 when the waveform element e11 is applied, that is at the leading edge of the expansion pulse P11, the partition walls 133 on the both sides are displaced to expand the volume of the pressure chamber 131. With this displacement, negative pressure is instantaneously applied to the ink in the pressure chamber 131, as illustrated in
Thereafter, the ink pressure is changed from negative to positive in accordance with natural pressure vibration of the ink in the pressure chamber. Further, when the first standby time, during which the waveform element e12 is applied, has elapsed at time t12, that is at the trailing edge of the expansion pulse P11 when the waveform element e13 is applied, the volume of the pressure chamber 131 returns to the original state. As illustrated in
Thereafter, the ink pressure is changed from positive to negative in accordance with natural pressure vibration of the ink in the pressure chamber. When the ink pressure is changed to negative, the meniscus is retracted following the ink pressure change. Further, when the second standby time, during which the waveform element e14 is applied, has elapsed at time t13, that is at the leading edge of the contraction pulse P12 when the waveform element e15 is applied, the partition walls 133 on the both sides are displaced to contract the volume of the pressure chamber 131. With this displacement, positive pressure is instantaneously applied to the ink. However, no ink droplet is discharged from the nozzle 301 because the ink pressure is negative at time t13 at which positive pressure is applied.
In a state in which the volume of the pressure chamber 131 is contracted, when the third standby time, during which the waveform element e16 is applied, has elapsed at time t14, that is at the trailing edge of the contraction pulse P12 when the waveform element e17 is applied, the volume of the pressure chamber 131 returns to the original state. At this time t14, a magnitude of amplitude of pressure vibration of the ink is equal to negative pressure instantaneously applied to the ink at the trailing edge of the contraction pulse P12, and the ink flow velocity is zero. Therefore, residual vibration in the pressure chamber 131 is cancelled thereafter. That is, the second standby time and the third standby time are timed such that the residual vibration in the pressure chamber 131 is cancelled at the trailing edge of the contraction pulse P12.
As described above, as the drive voltage of the 1-drop waveform illustrated in
As illustrated in
A combination of the first waveform element e21, the second waveform element e22, and the third waveform element e23 forms an expansion pulse P21 that returns the volume of the pressure chamber 131 to the original state after expanding the volume of the pressure chamber 131. That is, the first waveform element e21 corresponds to a leading edge of the expansion pulse P21, the second waveform element e22 corresponds to a pulse width of the expansion pulse P21, and the third waveform element e23 is a trailing edge of the expansion pulse P21. A combination of the fifth waveform element e25, the sixth waveform element e26, and the seventh waveform element e27 forms a contraction pulse P22 that partially returns the volume of the pressure chamber 131 after the contracting of the volume of the pressure chamber 131, thereby bringing the pressure chamber 131 into a weak contraction state in which the pressure chamber 131 is contracted less than in the contraction state maintained by the sixth waveform element e26. That is, the fifth waveform element e25 corresponds to a leading edge of the contraction pulse P22, the sixth waveform element e26 corresponds to a pulse width of the contraction pulse P22, and the seventh waveform element e27 corresponds to a trailing edge of the contraction pulse P22. A combination of the eighth waveform element e28 and the ninth waveform element e29 forms a weak contraction pulse P23 that returns the pressure chamber 131 to the original state after maintaining the weak contraction state for a predetermined time. That is, the eighth waveform element e28 corresponds to a pulse width of the weak contraction pulse P23, and the ninth waveform element e29 corresponds to a trailing edge of the weak contraction pulse P23.
At time t21 when the waveform element e21 is applied, that is at the leading edge of the expansion pulse P21, the partition walls 133 on the both sides are displaced to expand the volume of the pressure chamber 131. With this displacement, negative pressure is applied to the ink in the pressure chamber 131, as illustrated in
Thereafter, the ink pressure is changed from negative to positive in accordance with natural pressure vibration of the ink in the pressure chamber. Further, when the first standby time, during which the waveform element e22 is applied, has elapsed at time t22, that is at the trailing edge of the expansion pulse P21 when the waveform element e23 is applied, the volume of the pressure chamber 131 returns to the original state. As illustrated in
Thereafter, the ink pressure is changed from positive to negative in accordance with natural pressure vibration of the ink in the pressure chamber. When the ink pressure is changed to negative, the meniscus is retracted following the ink pressure change. Thereafter, the ink pressure is changed back to positive pressure. Further, when the second standby time, during which the waveform element e24 is applied, has elapsed at time t23, that is at the leading edge of the contraction pulse P22 when the waveform element e25 is applied, the partition walls 133 on the both sides are displaced to contract the volume of the pressure chamber 131. With this displacement, positive pressure is instantaneously applied to the ink. Here, time t23 is a time at which the ink pressure becomes substantially the same value as that at time t22. Therefore, as positive pressure is instantaneously applied to the ink by a pulse change in a state in which the ink pressure is positive pressure equal to or higher than a threshold value, the meniscus begins to be advanced and a second ink droplet is discharged from the nozzle 301. That is, the second standby time is a time for waiting until the ink pressure increases to a pressure at which the second ink droplet can be discharged by the instantaneous application of positive pressure to the ink at the leading edge of the contraction pulse P22.
In a state in which the volume of the pressure chamber 131 is contracted, when the third standby time, during which the waveform element e26 is applied, has elapsed time t24, that is at the trailing edge of the contraction pulse P22 when waveform element e27 is applied, the partition walls 133 on the both sides are displaced so that the volume of the pressure chamber 131 returns slightly. With this displacement, the pressure chamber 131 is brought into a weak contraction state weaker than the contraction state. The weak contraction state is maintained until the fourth standby time, during which the waveform element e28 is applied, has elapsed. Further, at time t25 of the trailing edge of the weak contraction pulse P23 when the waveform element e29 is applied, the volume of the pressure chamber 131 returns to the original state. At time t25, a magnitude of amplitude of vibration of the ink pressure is equal to negative pressure applied to the ink by the trailing edge of the weak contraction pulse P23, and the ink flow velocity is zero. Therefore, residual vibration in the pressure chamber 131 is cancelled thereafter. That is, the third standby time and the fourth standby time are timed such that the residual vibration in the pressure chamber 131 is cancelled by the trailing edge of the weak contraction pulse P23.
As described above, as the drive voltage of the 2-drop waveform illustrated in
As illustrated in
Here, the first waveform element e31, the second waveform element e32, and the third waveform element e33 form an expansion pulse P31 that returns the volume of the pressure chamber 131 to the original state after expanding the volume of the pressure chamber 131. That is, the first waveform element e31 is a leading edge of the expansion pulse P31, the second waveform element e32 has a pulse width of the expansion pulse P31, and the third waveform element e33 is a trailing edge of the expansion pulse P31. A combination of the fifth waveform element e35, the sixth waveform element e36, and the seventh waveform element e37 forms a first contraction pulse P32 that slightly returns the volume of the pressure chamber 131 after contracting the volume of the pressure chamber 131 so as to bring the pressure chamber 131 into a contraction state (weak contraction state) weaker than the contraction state maintained by the sixth waveform element e36. That is, the fifth waveform element e35 is a leading edge of the first contraction pulse P32, the sixth waveform element e36 is a pulse width of the first contraction pulse P32, and the seventh waveform element e37 is a trailing edge of the first contraction pulse P32. The eighth waveform element e38 forms a first weak contraction pulse P33 for maintaining the weak contraction state of the pressure chamber 131 formed by the first contraction pulse P32 for a predetermined time. That is, the eighth waveform element e38 is a pulse width of the first weak contraction pulse P33. A combination of the ninth waveform element e39, the tenth waveform element e40, and the eleventh waveform element e41 forms a second contraction pulse P34 that slightly returns the volume of the pressure chamber 131 after contracting the volume of the pressure chamber 131 so as to bring the pressure chamber 131 into the weak contraction state. That is, the ninth waveform element e39 is a leading edge of the second contraction pulse P34, the tenth waveform element e40 is a pulse width of the second contraction pulse P34, and the eleventh waveform element e41 is a trailing edge of the second contraction pulse P34. A combination of the twelfth waveform element e42 and the thirteenth waveform element e43 forms a second weak contraction pulse P35 that returns the weak contraction state of the pressure chamber 131 to an original state after maintaining the weak contraction state of the pressure chamber 131 for a predetermined time. That is, the twelfth waveform element e42 is a pulse width of the second weak contraction pulse P35, and the thirteenth waveform element e43 is a trailing edge of the second weak contraction pulse P35.
At time t31 when the waveform element e31 is applied, that is at the leading edge of the expansion pulse P31, the partition walls 133 on the both sides are displaced to expand the volume of the pressure chamber 131. With this displacement, negative pressure is instantaneously applied to the ink in the pressure chamber 131, as illustrated in
Thereafter, the ink pressure is changed from negative pressure to positive pressure in accordance with a natural pressure vibration period of the ink in the pressure chamber. Further, when the first standby time, during which the waveform element e32 is applied, has elapsed at time t32, that is at the trailing edge of the first expansion pulse P31 when the waveform element e33 is applied, the volume of the pressure chamber 131 returns to the original state. As illustrated in
Thereafter, the ink pressure is changed from positive pressure to negative pressure in accordance with natural pressure vibration of the ink in the pressure chamber. Further, in the state in which the ink pressure is positive, when the second standby time, during which the waveform element e34 is applied, has elapsed at time t33, that is at the leading edge of the first contraction pulse P32 when the waveform element e35 is applied, the partition walls 133 on the both sides are displaced to contract the volume of the pressure chamber 131. With this displacement, positive pressure is instantaneously applied to the ink. Here, time t33 is a time at which the ink pressure becomes substantially the same value as that at time t32. Therefore, as positive pressure is instantaneously applied to the ink by a pulse change in the state in which the ink pressure is positive pressure equal to or higher than a threshold value, the meniscus begins to be advanced and a second ink droplet is discharged from the nozzle 301. That is, the second standby time is a time for waiting until the ink pressure increases to a pressure at which the second ink droplet can be discharged by the instantaneous application of positive pressure to the ink at the leading edge of the first contraction pulse P32.
The ink pressure is changed to negative pressure after the volume of the pressure chamber 131 is contracted. Further, when the third standby time, during which the waveform element e36 is applied, has elapsed at time t34, that is at the trailing edge of the contraction pulse P32 when the waveform element e37 is applied, the partition walls 133 on the both sides are displaced to return the volume of the pressure chamber 131 slightly. With this displacement, the pressure chamber 131 is brought into the weak contraction state weaker than the contraction state, so that the meniscus is retracted. Here, time t34 is included in a time period in which the ink pressure is being negative pressure and is a time at which negative ink pressure is maximized in the example illustrated in
The weak contraction state is maintained until the fourth standby time, during which the waveform element e38 is applied and the ink pressure is changed to the positive pressure, has elapsed. Further, at time t35, that is at the trailing edge of the weak contraction pulse P33 when the waveform element e39 is applied, the partition walls 133 on the both sides are displaced to contract the volume of the pressure chamber 131 again. With this displacement, positive pressure is instantaneously applied to the ink. Further, the meniscus is advanced again. Here, time t35 is set to be later than a time at which the ink pressure is substantially the same as that at the times t32 and t33. A magnitude of the waveform element e39, which provides positive pressure to discharge a third ink droplet, is only a half of a magnitude of the waveform element e33 for discharging a first ink droplet and a magnitude of the waveform element e35 for discharging a second ink droplet. Therefore, since it is necessary to wait until the ink pressure becomes higher than those in the case of discharging the first ink droplet and the second ink droplet, the timing of the waveform element 39 is delayed. Further, the ink pressure after performing the operation with the waveform element e39 at time t35 is substantially the same value as the ink pressure immediately after times t32 and t33. Therefore, since positive pressure is instantaneously applied to the ink by a pulse change in the state in which the ink pressure is positive pressure equal to or higher than a threshold value, a third ink droplet is discharged from the nozzle 301. That is, the fourth standby time is a time for waiting until the ink pressure increases to a pressure at which the third ink droplet can be discharged by the instantaneous application of positive pressure to the ink at the leading edge of the second contraction pulse P34.
In the state in which the volume of the pressure chamber 131 is contracted, when the fifth standby time, during which the waveform element e40 is applied, has elapsed at time t36, that is at the trailing edge of the second contraction pulse P34 when the waveform element e41 is applied, the partition walls 133 on the both sides are displaced such that the volume of the pressure chamber 131 returns slightly. With this displacement, the pressure chamber 131 is brought into a weak contraction state weaker than the contraction state. The weak contraction state is maintained until the sixth standby time, during which the waveform element e42 is applied, has elapsed. Further, at time t37, that is at the trailing edge of the second weak contraction pulse P35 when the waveform element e43 is applied, the volume of the pressure chamber 131 returns to the original state. At time t37, a magnitude of amplitude of vibration of the ink pressure is equal to negative pressure instantaneously applied to the ink by the trailing edge of the second weak contraction pulse P35, and the ink flow velocity is zero. Therefore, residual vibration in the pressure chamber 131 is cancelled thereafter. That is, the fifth standby time and the sixth standby time are timed such that the residual vibration in the pressure chamber 131 is cancelled by the trailing edge of the second weak contraction pulse P35.
As described above, when the drive voltage of the 3-drop waveform illustrated in
By the way, in the aforementioned 2-drop waveform, the weak contraction pulse P23 is formed at the trailing edge of the contraction pulse P22, such that residual vibration is cancelled at the trailing edge of the weak contraction pulse P23. The same applies to the case of the 3-drop waveform. However, in a case in which damping of pressure vibration of the ink in the pressure chamber 131 is comparatively low, residual vibration may be cancelled at the trailing edge of the contraction pulse P22 in the 2-drop waveform or the 3-drop waveform, similar to the 1-drop waveform.
In the following, another 2-drop waveform, which cancels residual vibration at the trailing edge of the contraction pulse P22, will be described with reference to
As illustrated in
A combination of the first waveform element e41, the second waveform element e42, and the third waveform element e43 forms an expansion pulse P41 that returns the volume of the pressure chamber 131 to the original state after expanding the volume of the pressure chamber 131. That is, the first waveform element e41 is a leading edge of the expansion pulse P41, the second waveform element e42 is a pulse width of the expansion pulse P41, and the third waveform element e43 is a trailing edge of the expansion pulse P41. A combination of the fifth waveform element e45, the sixth waveforms element e46, and the seventh waveform element e47 forms a contraction pulse P42 that returns the volume of the pressure chamber 131 to the original state after contracting the volume of the pressure chamber 131. That is, the fifth waveform element e45 is a leading edge of the contraction pulse P42, the sixth waveform element e46 is a pulse width of the contraction pulse P42, and the seventh waveform element e47 is a trailing edge of the contraction pulse P42.
At time t41, that is at the leading edge of the expansion pulse P41 when the waveform element e41 is applied, the partition walls 133 on the both sides are displaced to expand the volume of the pressure chamber 131. With this displacement, negative pressure is instantaneously applied to the ink in the pressure chamber 131, as illustrated in
Thereafter, the ink pressure is changed from negative pressure to positive pressure in accordance with a natural pressure vibration period of the ink in the pressure chamber. Further, when the first standby time, during which the waveform element e42 is applied, has elapsed at time t42, that is at the trailing edge of the expansion pulse P41 when the waveform element e43 is applied, the volume of the pressure chamber 131 returns to the original state. In this case, as illustrated in
Thereafter, the ink pressure is changed from positive pressure to negative pressure in accordance with natural pressure vibration of the ink in the pressure chamber. When the ink pressure is changed to negative pressure, the meniscus is retracted late. Thereafter, the ink pressure is changed back to positive pressure. Further, when the second standby time, during which the waveform element e44 has elapsed at time t43, that is at the leading edge of the contraction pulse P42 when the waveform element e45 is applied, the partition walls 133 on the both sides are displaced to contract the volume of the pressure chamber 131. With this displacement, positive pressure is instantaneously applied to the ink. Here, time t43 is a time at which the ink pressure becomes substantially the same value as that at time t42. Therefore, as positive pressure is instantaneously applied to the ink by a pulse change in the state in which the ink pressure is positive pressure equal to or higher than a threshold value, the meniscus begins to be advanced and a second ink droplet is discharged from the nozzle 301. That is, the second standby time is a time for waiting until the ink pressure increases to a pressure at which the second ink droplet can be discharged by the instantaneous application of positive pressure to the ink at the leading edge of the contraction pulse P42.
In the state in which the volume of the pressure chamber 131 is contracted, when the third standby time, during which the waveform element e46 is applied, has elapsed at time t44, that is at the trailing edge of the contraction pulse P42 when the waveform element e47 is applied, the volume of the pressure chamber 131 returns to the original state. At time t44, a magnitude of amplitude of vibration of the ink pressure is equal to negative pressure instantaneously applied to the ink by the trailing edge of the contraction pulse P42, and the ink flow velocity is zero. Therefore, residual vibration in the pressure chamber 131 is cancelled thereafter. That is, the third standby time is timed such that the residual vibration in the pressure chamber 131 is cancelled by the trailing edge of the contraction pulse P42.
As described above, as the drive voltage of the modified 2-drop waveform illustrated in
In the modified 2-drop waveform illustrated in
During an application of the 2-drop waveform or the 3-drop waveform illustrated in
As illustrated in
The simulation may be performed using an equivalent circuit illustrated in
A loss of the pressure chamber 131 is represented by the value of the resistor R of the equivalent circuit. If a loss of the pressure chamber 131 is higher, that is, the value of the resistor R is larger, pressure amplitude of the residual vibration is smaller. In this case, time t24 at which the contraction state transitions to the weak contraction state should be shifted earlier. In this way, it is possible adjust the pressure amplitude of the residual vibration at when the ink flow velocity is zero, up to the pressure amplitude generated by the change of the state of the pressure chamber 131 from the weak contraction state to the initial state. Then, the time ink flow velocity is zero is set as time t25 at which the weak contraction state is ended.
For example, when the appropriate times t24 and t25 are selected by increasing the resistor R to 0.38Ω and performing the simulation, the drive voltage waveform, the ink pressure waveform, and the ink flow velocity waveform are made as illustrated in
On the contrary, when a loss of the pressure chamber 131 is lower, that is, the value of the resistor R is smaller, residual vibration is larger. In this case, time t24 at which the contraction state transitions to the weak contraction state should be shifted later. In this way, it is possible adjust the pressure amplitude of the residual vibration at when the ink flow velocity is zero, down to the pressure amplitude generated by the change of the state of the pressure chamber 131 from the weak contraction state to the initial state. Then, the time ink flow velocity is zero is set as time t25 at which the weak contraction state is ended.
For example, when appropriate times t24 and t25 are selected by decreasing the resistor R to 0.28Ω and performing the simulation, the drive voltage waveform, the ink pressure waveform, and the ink flow velocity waveform are made as illustrated in
Since the step of bringing the pressure chamber into the weak contraction state is provided at the trailing edge of the contraction pulse as described above, it is possible to adjust the waveform element e29 or the waveform element e43 for cancellation in accordance with a magnitude of damping of residual vibration of the ink, and as a result, the degree of freedom is widened at the time of cancellation.
Next, an operation of the drive circuit 40 will be described with reference to
In the first example illustrated in
The waveform selecting unit 44 outputs a selecting signal that validates a period of the first unit U1 when a gradation value of printing data is 1. When the gradation value is 2, the waveform selecting unit 44 outputs a selecting signal that validates a period of the first unit U1 and a period of the second unit U2. When the gradation value is 3, the waveform selecting unit 44 outputs a selecting signal that validates periods of the 2nd and 3rd units U2, U3. When the gradation value is 4, the waveform selecting unit 44 outputs a selecting signal that validates periods of the first to third units U1 to U3. When the gradation value is 5, the waveform selecting unit 44 outputs a selecting signal that validates periods of the 2nd to 4th units U2, U3, U4. When the gradation value is 6, the waveform selecting unit 44 outputs a selecting signal that validates periods of the first to fourth units U1 to U4.
Although not illustrated, when the waveform selecting unit 44 outputs the selecting signal SL that validates the period of the first unit U1 and the period of the second unit U2, two ink droplets are continuously discharged in one printing cycle.
Therefore, the ink droplets are selectively discharged by one ink droplet, two ink droplets, four ink droplets, or six ink droplets in accordance with printing data, thereby realizing a multi-drop method of performing gradation printing.
Although not illustrated, when the waveform selecting unit 44 outputs the selecting signal SL that validates the period of the second unit U2 and the period of the third unit U3, three ink droplets are continuously discharged in one printing cycle.
Although not illustrated, when the waveform selecting unit 44 outputs the selecting signal SL that validates the period of the second unit U2 and the periods of the third and fourth units U3 and U4, five ink droplets are continuously discharged in one printing cycle.
When it is programmable which period the waveform selecting unit 44 validates in relation to a predetermined gradation value, zero to six ink droplets may be discharged with any combination of the units U1 to U4 in relation to the gradation value.
In an example illustrated in
The waveform selecting unit 44 outputs a selecting signal that validates a period of the first unit U1 when a gradation value of printing data is 1. When the gradation value is 2, the waveform selecting unit 44 outputs a selecting signal that validates a period of the first unit U1 and a period of the second unit U2. When the gradation value is 3, the waveform selecting unit 44 outputs a selecting signal that validates periods of the 2nd and 3rd units U2, U3. When the gradation value is 4, the waveform selecting unit 44 outputs a selecting signal that validates periods of the first to third units U1 to U3. When the gradation value is 5, the waveform selecting unit 44 outputs a selecting signal that validates periods of the 3rd and 4th units U3, U4. When the gradation value is 6, the waveform selecting unit 44 outputs a selecting signal that validates periods of the 2nd to 4th units U2, U3, U4. When the gradation value is 7, the waveform selecting unit 44 outputs a selecting signal that validates periods of the first to fourth units U1 to U4.
Although not illustrated, when the waveform selecting unit 44 outputs the selecting signal SL that validates the period of the first unit U1 and the period of the second unit U2, two ink droplets are consecutively discharged in one printing cycle.
Therefore, the ink droplets are selectively discharged as one ink droplet, two ink droplets, four ink droplets, or seven ink droplets in accordance with printing data, thereby realizing a multi-drop method of performing gradation printing.
Although not illustrated, when the waveform selecting unit 44 outputs the selecting signal SL that validates the period of the second unit U2 and the period of the third unit U3, three ink droplets are consecutively discharged in one printing cycle.
Although not illustrated, when the waveform selecting unit 44 outputs the selecting signal SL that validates the periods of the third and fourth units U3 and U4, five ink droplets are consecutively discharged in one printing cycle.
Although not illustrated, when the waveform selecting unit 44 outputs the selecting signal SL that validates the periods of the 2nd to 4th units U2, U3, and U4, six ink droplets are consecutively discharged in one printing cycle.
When it is programmable which period the waveform selecting unit 44 validates in relation to a predetermined gradation value, zero to seven droplets may be effectively discharged by validating any combination of the periods of the units U1 to U4 in relation to the gradation value.
There are multiple combinations of the periods of the units U1 to U4 for discharging a predetermined number of ink droplets in one printing cycle. For example, to discharge two ink droplets in one printing cycle, the period of the unit U3 may be used, or the periods of the units U1 and U2 may be used. To discharge three ink droplets in one printing cycle, the periods of the units U1 and U3 may be combined, the period of the unit U4 may be used, or the periods of the units U2 and U3 may be used. To discharge five ink droplets in one printing cycle, the periods of the units U1, U2, and U4 may be combined, or the periods of the units U3 and U4 may be combined. Because timing for discharging ink droplets varies depending on such combinations even for discharging a same number of ink droplets, there may be a difference in printing characteristics. A combination for discharging a predetermined number of ink droplets in one printing cycle may be selected in accordance with desired printing characteristics.
The inkjet head 1 according to the example embodiments described above can discharge two ink droplets from the nozzle 301 by using the 2-drop waveform illustrated in
The degree of freedom when cancelling residual vibration is higher in the case in which the 2-drop waveform illustrated in
The inkjet head 1 according to the example embodiments described above can discharge three ink droplets from the nozzle 301 by using the 3-drop waveform illustrated in
Hereinafter, modified examples of the present example embodiments described above will be described.
In the example embodiments described above, as illustrated in
In this example, while a time at which the normalized ink pressure is 0.75 is set as time t22 of the trailing edge of the expansion pulse P21, a time at which the normalized ink pressure is 0.5 is set as time t23 of the leading edge of the contraction pulse P22. In this waveform, the discharge velocity of the second ink droplet is lower than that of the first ink droplet, but even with this 2-drop waveform, it is possible to discharge two ink droplets from the nozzle 301.
In this example, while a time at which the normalized ink pressure is 0.75 is set as time t22 of the trailing edge of the expansion pulse P21, a time at which the normalized ink pressure is changed to positive pressure is set as time t23 of the leading edge of the contraction pulse P22. In this waveform, the discharge velocity of the second ink droplet becomes further lower than that of the first ink droplet, but even with this 2-drop waveform, it is possible to continuously discharge two ink droplets from the nozzle 301.
In this example, while a time at which the normalized ink pressure is 0.75, which is equal to that in
In the example embodiments described herein, as illustrated in
The configuration of the inkjet head 1 is not limited to the configuration described with reference to
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-058661 | Mar 2017 | JP | national |
| 2017-058662 | Mar 2017 | JP | national |
This application is a division of U.S. patent application Ser. No. 15/928,816, filed Mar. 22, 2018, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-058661, filed on Mar. 24, 2017 and Japanese Patent Application No. 2017-058662, filed on Mar. 24, 2017, the entire contents of each of which are incorporated herein by reference.
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| Number | Date | Country | |
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| 20190184700 A1 | Jun 2019 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15928816 | Mar 2018 | US |
| Child | 16273766 | US |
