JPS6015466B2 - Inkjet recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an inkjet recording device, more specifically, an electric field jet inkjet generating device that can be used as a recording head in a line recording device such as a ×1Y plotter used for automatic drawing, etc. Regarding recording devices.

2. Description of the Related Art Generally, a so-called contact type recording tool such as a hollow pen or a ballpoint pen is used as a recording head in an image recording apparatus such as an X-Y plotter.

However, these contact-type recording tools have poor durability and must be replaced frequently, making it difficult to perform high-speed recording and pongee line recording, and the density of recorded lines may be uneven.
It had many drawbacks, such as the tendency to generate noise. For this reason, in recent years, attempts have been made to apply so-called inkjet generators that eject ink in an ink tank from nozzles with a minute diameter to the recording heads of image recording apparatuses such as X-Y plotters.

Various devices have been proposed as this type of inkjet generating device, but when using the recording head of an image recording device, continuity of the image and ON/OFF of the jet flow are important.
Considering the responsiveness, etc., an electric field jet inkjet generator is most suitable. This Kameba injection type inkjet generator guides ink from an ink tank to a nozzle, and in a stationary state, applies a minute pressure to the ink to the extent that the ink forms a meniscus at the tip of the nozzle. By applying a high electric field between the nozzle and the accelerating electrode (ring-shaped counter electrode) installed in front, the ink is drawn out from the nozzle and ejected as a jet stream. By using this type of inkjet generator, many disadvantages of conventional contact recording devices are overcome, but the amount of ink ejected from the nozzle depends primarily on the applied voltage and the pressure acting on the ink. However, due to the influence of the physical properties of the ink used and the surrounding environment, there are the following significant disadvantages.

That is, when this type of inkjet generator is applied to an image recording device such as an XY printer, the relative moving speed between the recording head and the recording material (for example, paper, film, etc.) changes. If the amount of ejected ink is constant, the width and density of the image line will change depending on the recording speed, which is particularly inconvenient for automatic drafting. In addition, the amount of ink ejected is affected by the pressure acting on the nozzle inlet, that is, the sum of the pressure acting on the ink surface (e.g. air pressure) and the hydrostatic pressure of the ink from the ink surface to the nozzle inlet. When recording, the amount of ink ejected fluctuates due to the decrease in the amount of ink in the ink tank, and the jet ON characteristics deteriorate significantly. Therefore, all the ink in the ink tank cannot be used, and the amount of ink ejected is not affected. Since it can only be used for a limited amount of time, the recording time with one ink filling is short, which is a drawback. To this end, attempts have been made to detect the pressure acting on the inlet of the ink tank and the decrease in the amount of ink in the ink tank to drive a pulse motor, etc., and thereby operate an air compressor to apply pressure to the ink surface. However, when an air compressor is operated for a long time, the air pressure inside the cylinder changes due to friction on the cylinder wall and heat generated by the motor, etc., but there is no countermeasure against this, and there is no way to completely overcome the above drawbacks. do not have. The present invention aims to solve this problem.As a result of various studies, it has been found that when the applied voltage is constant, the pressure acting on the ink and the amount of ink jetted are in a proportional relationship. When the amount of ejected ink is changed by appropriately changing the applied pressure, if a diagram is drawn by taking the logarithm of the amount of ejected ink and the recording line width, the relationship between the two will be linear (Figure 1, (See Figure 2), and from this, if the physical properties of the ink, the shape of the nozzle, etc. are constant, the amount of injected ink, the pressure acting on the outside of the ink, the width of the recorded image line, and the recording speed are mutual. Since we can understand the relative relationship between , was completed based on this.

That is, a pressure control means is provided to control the pressure acting on the ink tank in accordance with the recording speed, and a pressure signal based on the air pressure controlled by the control means, an ink amount signal, and the temperature of the cylinder, etc. of the air pressure control means are provided. To provide an inkjet recording device that controls the operation of the air pressure control means with a signal so that the line width is always constant even when applied to an The purpose is to

Next, the present invention will be explained according to the accompanying drawings which are examples.

FIG. 3 shows an X-Y probetter 1 equipped with an inkjet recording device according to the present invention as a recording head. is cut out.

The x-movement girder 5, which extends over the pair of rails 3 and 4 and moves in the X direction, is mounted on support stands 6 and 7 that are slidable on the rails 3 and 4. An x-servo motor 8 is installed inside the support base 6, and drives a pinion gear (not shown) that engages with the rack of the rail 3 via an appropriate transmission mechanism to move in the x direction. . x A Y-direction rail 9 is installed parallel to the movable girder 5, and this
A rack is also cut into the one-way rail 9. A slider 10 is slidably provided on the Y one-way rail 9, a Y-servo motor 11 is installed inside the slider 10, and a pinion gear engages with the rack of the Y one-way rail 9 via an appropriate transmission mechanism. (not shown) to move in the Y-direction. The mover 101 has an inkjet generator 13 installed by the head main body 12, which moves integrally with the mover 10, jets ink by a control mechanism to be described later, and performs image recording by an X-Y servo mechanism. It is made to be done.

A flexible air pipe 18 that sends compressed air to the ink tank 14 and a high voltage cable 19 from a high voltage power source are connected to the inkjet generator 13. It is connected to a control unit, a compression pump, etc. inside the main body 2.

A drawing board 20 on the upper surface of the main body 2 is designed to support a recording material (paper, film, etc.) 21 while maintaining its flatness.

The X-Y plotter device having such a configuration is designed to plot by controlling the rotation angles of the x and Y servo motors 8 and 11 in response to a plotting pattern signal output from a computer or the like. There is.

In addition, as shown in FIG. 4, the inkjet generator 13 includes an ink tank 14 that stores ink 17, a nozzle 15 that is attached to the ink tank and that guides the ink to the outside, and a nozzle 15 that is adjacent to the nozzle. Installed counter electrode 1
It consists of 6.

FIG. 4 is a block diagram of the X-Y servo control mechanism.

Normally, in an x-Y plotter device, the position of the movable element 10 (recording head) needs to be controlled extremely accurately, and therefore a negative feedback method is used for position control.

Further, in the control mechanism shown in the figure, the target position signal is a digital signal such as the number of pulses, and this is an example of a case where an analog servo motor is used as the servo motor. The X-Y servo control is performed independently in each of the x and Y directions and is substantially the same, so the IX-control system will be described below. When a drawing signal is output as an output of a computer (not shown) and inputted to the interface 22 of the servo control mechanism, an ×1 target position signal is output as a digital signal, and a comparator 23 converts it into an X position signal. After being compared and converted into an analog signal by a digital-to-analog converter (D/A converter) 24, it is amplified by an X-servo amplifier 25, and the X-servo motor 8 is rotated by an angle corresponding to the output signal of the comparator 23. let

At this time, the output of the X-servo motor 8 is
6. The X-position is detected by the position detector 27, and the signal from the speed detector 26 is fed back to the previous stage of the X-servo amplifier 25 via the X-speed feedback amplifier 28. Further, the output of the position detector 27 is converted into a digital signal by an analog-to-digital converter (A/D converter) 29, and then input to a comparator 23, which controls the position while comparing it with the target position signal. It is now possible to do so. In this case, the rotational speed is detected by a speedometer such as a tachogenerator attached to the servo motor shaft, and the position is detected by a resolver or the like. In addition to such a servo control mechanism,
The present invention includes a pressure control mechanism for controlling the amount of ink ejected from the inkjet generator according to the recording speed.

It detects the rotation speeds of the X and Y servo motors 8 and 11 as outputs of the servo motors, outputs them as speed signals vx and vy, and uses these signals to control the pressure acting on the ink tank of the inkjet generator. A block diagram of this pressure control mechanism is shown in FIG. Pressure control mechanism interface 31
There is a recording speed signal v production circuit as shown in FIG. circuit 3
In step 4, vx2 + vy2 is taken, and the square root circuit 35 produces a recording speed signal v = vx2 + vy2.

This recording speed signal v is sent from the interface 31 to an analog comparator 36 consisting of a differential amplifier with a voltage gain of 1, etc., and the output (analog signal) of the pressure sensor 38 that detects the air pressure of the compression pump 37 is sent to the feedback amplifier 39. The amplified signal is compared with the amplified signal, and the comparison signal is inputted to four controllers. The controller 40 is composed of a window comparator, a pulse converter, etc., and only when the absolute value of the input error signal (comparison signal) is larger than the window width (VR), it outputs a clock pulse to the next stage pulse motor drive circuit 41. Set to send synchronized signals CW and CCW. Signal CW
is issued when the error signal is greater than 10 VR, and the air compression system 42 acts to increase the pressure, and the signal CCW is issued when the error signal is less than -VR, and the air compression system 42 acts to increase the pressure.
acts in the direction of lowering the pressure, and the conspiracy signal is VR and -VR
If the value is between, the controller 40 will not issue a signal. The pulse motor drive circuit 41 is a circuit for converting the signals CW and CCW into signals for driving the pulse motor 43 and amplifying the signals. When the input signal is CW, the pulse motor 43 is rotated in the normal direction to drive the compression pump. Increase the air pressure of 37,
In CCW, it is reversed.

The air pressure inside the compression pump 37 is detected by the pressure sensor 38, amplified by the feedback amplifier 36, and then sent to the comparator 3 as described above.
6, and pressure control is performed while being compared with the recording speed signal v.

For example, when the value of the recording speed signal v increases, the output of the pressure sensor 38 at that moment is smaller than the speed signal v, the comparator 36 outputs an error signal, and the controller 40 outputs a signal C.
W is released and acts to increase the pressure as described above.

In addition to the x1Y servo control signal, the drawing signal output from the computer etc. includes an inkjet ejection control signal Sd, which turns on the inkjet in synchronization with the x1Y servo control operation. It is sent directly to the interface 31 of the pressure control mechanism as an OFF signal.

This inkjet and ON-OFF signal is the "U" of the pen in the conventional X-Y plotter using contact type writing odor.
This corresponds to the p-Dowr signal, and is input to the high-voltage pulse generator 5 only when necessary, and applies a switching high voltage to the nozzle 15 of the inkjet generator 13 to eject a jet. Next, the above ×1 Y
The specific mechanism of the air compression system of the inkjet generator in the plotter device will be explained.

As shown in FIG. 7, the air compression system 42 includes a pulse motor 43 that operates in response to the output signal from the pulse motor drive circuit 41 described above, and converts the rotation angle of this pulse motor 43 into a corresponding linear displacement amount. A converter 46 includes a cam 44 fixed to the rotating shaft of the pulse motor and a piston 45 that follows the cam 44, and a piston 48 fixed to one end of the piston rod 45 and sliding inside a cylinder 47. , a diaphragm pneumatic pump 37 consisting of a diaphragm 49, etc., with one end fixed to the piston and the other end fixed inside the cylinder; and a pressure pump 37 that is attached to the cylinder 47 and detects the air pressure inside the cylinder 47 and converts it into an electric signal. It is composed of a sensor 38, a flexible air pipe 18 for sending compressed air in the cylinder to the ink tank 14 of the inkjet generator 13, and the like.

As described above, the air compression system 42 having the above configuration detects the air pressure in the cylinder by the pressure sensor 38 and converts it into voltage, which is amplified by the feedback amplifier 39, sends an air pressure signal to the analog comparator 36, and similarly This is a negative feedback method that compares the recorded speed signal with the converted recording speed signal. The air whose pressure has been controlled by the air pressure control device as described above is sent to the inkjet generator 13 shown in FIG. 1 through the flexible air piping 18.

In the XY block device equipped with the inkjet recording device of the present invention, the pressure applied to the ink is controlled in response to the speed signal as described above, but by changing the reference pressure level for this pressure control, It is also possible to configure a single nozzle to record in multiple image lines.

As mentioned above, the amount of ink jetted is affected by the pressure acting on the inlet of the nozzle, so when used for a long time, the hydrostatic pressure decreases, {a'' the amount of ink jetted is no longer proportional to the recording speed, and 'b} the jet There is a problem that the ON characteristics are extremely deteriorated.

Regarding {a}, the pressure acting on the ink surface is sufficiently larger than the hydrostatic pressure (ink hydrostatic pressure = several tens of Aq, pressure acting on the ink surface = several tens of Aq), so it is not a big problem, but 'b} Regarding this, the pressure acting on the ink surface when the jet key is turned on is always zero, that is, the pressure acting on the ink surface is the same as the pressure acting on the nozzle outlet (atmospheric pressure), so the hydrostatic pressure directly affects the pressure inside the tank. If the amount of ink is appropriate, as shown in Figure 8 a to a3, an appropriate meniscus is created before the switching voltage is applied (a, in the same figure), and the moment the switching voltage is applied, Ink jetting starts from (a2 in the same figure), and from 1 to
A steady state is reached after 3 seconds (a3 in the same figure), whereas when the amount of ink is small, an appropriate meniscus is not formed (0 in the same figure), as shown in figures 8q to 8, and the switching Even if a voltage is applied, the injection may not start immediately (see Q in the same figure), or the injection direction may deviate from the direction of the nozzle and curve. According to the present invention, a hydrostatic pressure correction means is provided to ensure that the pressure acting on the nozzle inlet remains constant even if the amount of ink in the ink tank decreases.

In order to operate this hydrostatic pressure correction means, it is necessary to detect the hydrostatic pressure of the ink within the ink tank, and this is achieved by detecting the rotation angle of the pass motor 43 in the pressure control mechanism. This is because even if the recording speed signal is constant, when the ink amount decreases (hydrostatic pressure decreases), the air volume in the ink tank increases, so in order to apply pressure proportional to the recording speed signal to the ink surface. This is based on the fact that it is necessary to increase the rotation angle of the pulse motor 43 in response to a decrease in hydrostatic pressure. In other words, the inkjet recording device of the present invention acts on the ink surface in a manner that corresponds to the recording speed so that an amount of ink corresponding to the recording speed can be ejected to always obtain recorded lines of a constant width. Since the pressure is controlled, the rotation angle of the pulse motor 43 in the pressure control mechanism is proportional to the amount of decrease in hydrostatic pressure. Note that as a method for detecting hydrostatic pressure, recording time may be measured and used.

However, in this case, it is desirable that the amount of ejected ink is always constant. As shown in FIG. 9, the hydrostatic pressure correction means includes a potentiometer 51 that is attached to the pulse motor 43 and detects its rotation angle;
Peak value hold circuit 52 detects and holds the peak value of 1
, an inverting amplifier 53 that inverts and amplifies the output thereof, and a level shift circuit 54 that operates with the output of the inverting amplifier 53, and the output thereof is applied to the analog comparator 36.

The level shift circuit 54 is a positive phase amplifier (voltage gain = 1)
The output voltage level is shifted by the output from the inverting amplifier 53. Since the rotation angle of the pulse motor 43 can be determined by detecting a value corresponding to a recording speed signal serving as a certain reference, the maximum recording speed signal at the maximum recording speed is used as a reference. This is because in an XY plotter, the maximum recording speed signal is usually constant. Also, for a long time,
When the air compressor 37 is operated, air pressure changes as seen in the temperature rise caused by friction between the air and the cylinder wall and heat generated from mechanical systems such as pulse motors being transferred to the air inside the cylinder by conduction. In order to guarantee the effect, an air compressor 37 is connected to the positive input side of the inverting amplifier 53.
A temperature sensor 55 (such as a thermistor) installed to measure the temperature of the air inside the cylinder, a signal converter 56 that converts the output into an electrical signal proportional to the temperature, and an inverting amplifier that inverts and amplifies the output. The multiplied output at 57 is connected.

Next, this operation will be explained. First, when the ink hydrostatic pressure and the air temperature in the cylinder are at specified values, the level shift circuit 54 passes the maximum recording speed signal Vmax as it is, rotates the pulse motor 43, and changes the output of the potentiometer 51 to a peak value. - The output of the inverting amplifier 53 is detected and held by the negative value hold circuit 52, and the output of the inverting amplifier 53 is input to the negative side of the level shift circuit .

At this time, the output potential of the potentiometer 51 and the output of the inverting amplifier 57 are set so that the output of the inverting amplifier 53 becomes zero (ground potential). Next, by record,
When the hydrostatic pressure decreases, as explained above, the rotation angle of the pulse motor 43 increases with respect to the maximum recording signal Vmax, the output of the potentiometer 51 increases, and the output of the peak value hold circuit 52 increases. and inverting amplifier 5
The output level of 3 moves to the negative side and is input to the level shift circuit 54. In response to this input, the level shift circuit 54 shifts its output to the positive side, and the pulse motor 4
3 acts in the direction of further increasing the output of the potentiometer 51. That is, positive feedback is generated, and the stopping position is determined by the relationship with the negative feedback loop (pressure sensor, feedback amplifier). The gains of the positive and negative feedback loops are determined experimentally. Furthermore, since the rate of decrease of the ink in the ink tank is extremely slow, it is preferable that the frequency characteristics of the positive feedback loop, that is, the cutoff frequency, be kept below IHZ. Next, if the temperature of the air in the cylinder fluctuates (generally increases for the reasons mentioned above), or if there is no temperature detection system including the inverting amplifier 57, for example, if the temperature of the air in the cylinder increases. , pulse motor 43
For the same rotation angle of
The output of the device is affected by temperature and does not operate properly. The temperature detection system including inverting amplifier 57 operates to ensure this. That is, when the temperature of the air inside the cylinder becomes higher than a specified value, the rotation angle of the pulse motor 43 decreases due to the action of the member feedback loop, which acts in the direction of increasing the output level of the inverting amplifier 53. , the output of the temperature detection system, that is, the inverting amplifier 57 decreases, and the output of the inverting amplifier 53 decreases.
The negative input side of the level shift circuit 54 is prevented from fluctuating due to temperature changes in the air pressure in the cylinder, and the ink in the ink tank is normally reduced. It acts to correct only the decrease in the amount of . Furthermore, in this embodiment, when the ink reaches the very edge of the nozzle entrance and it becomes impossible to continue recording, this state is detected by the rotation angle (maximum) of the pulse motor 43, which is also temperature-guaranteed, and the inverting amplifier 5
A warning device is provided which issues a warning signal Sa at the output of 3 and orders the operator to replenish ink. FIG. 10 shows another embodiment of the present invention, in which the feedback amplifier is replaced by a differential amplifier 5.
4a, the output of the pressure sensor 38 is input to the positive input side, and the peak value hold circuit 52 is input to the negative input side.
The output voltage obtained by amplifying the output with the positive phase amplifier 53a is inputted.

Further, the output of the inverting amplifier 57 is input to the negative input side of the positive phase amplifier 53a. In this case as well, when the ink hydrostatic pressure and the air temperature in the cylinder are at specified values, the output of the positive phase amplifier 53a is set to zero (ground potential), and the output of the pressure sensor 38 is directly output to the differential amplifier 54a. )
It is amplified and input to the negative side of the analog comparator 36, but
When the hydrostatic pressure decreases, the output of the peak value hold circuit 52 increases, the output level of the positive phase amplifier 53a shifts to the positive side, and becomes an inverted input to the fist motion amplifier 54a, thereby reducing the overall output level of the pressure sensor 38. is lowered, acting in the direction of increasing the output of the potentiometer 51 in the same way as in the previous embodiment, and producing the same effect as described above.

Furthermore, if there are temperature fluctuations in the air inside the cylinder,
As described above, the output of the inverting amplifier 57, which is inversely proportional to the detected temperature, is connected to the negative input side of the positive phase amplifier 53a, so that the temperature of the peak value hold circuit 52 is guaranteed, and the output of the positive phase amplifier 53a is
The output of 3a normally takes a value proportional to the decrease in the amount of ink in the ink tank, regardless of the temperature inside the cinder. Others are the same as those in FIG. 9, only the warning signal Sa
is generated by the output of the positive phase amplifier 53a. As is clear from the above description, the inkjet recording apparatus according to the present invention is provided with an air pressure control means for controlling the pressure acting on the ink surface in the ink tank in response to a control signal, and A means for detecting the amount of ink decrease and a means for detecting the temperature of the air pressure control means are provided, and these two detecting means shift the recording speed signal level or the negative feedback signal level to the correction side to detect the decrease or decrease in the amount of ink. The amount of ink ejected corresponding to the recording speed can be controlled extremely accurately without being affected by temperature changes in the air pressure control means.

Moreover, since the ink hydrostatic pressure against the nozzle does not change depending on the amount of ink, it can be used until the ink surface drops to the nozzle entrance and jet ejection becomes impossible, and long-time recording is possible with one ink replenishment. Incidentally, as an example, with one ink replenishment, it was possible to continuously record for about 3 hours and about 4 ship lengths in terms of print line length.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the pressure acting on the ink surface and the amount of ink ejected in an inkjet generator.
FIG. 2 is a graph showing the relationship between the amount of injected ink and the area in the recorded image, FIG. 3 is a perspective view of an Block diagram, Fig. 5 is a block diagram of the recording speed signal generation mechanism in the pressure control mechanism, Fig. 6 is a block diagram of the recording speed signal generation circuit, Fig. 7 shows the air compression system, a is its plan view, and b is the block diagram. Fig. 8 is a schematic diagram showing the influence of hydrostatic pressure on the jet ON characteristics;
1 and 10 are block diagrams showing essential parts of a pressure control mechanism provided with hydrostatic pressure correction means and pressure guarantee means. 12...Head body, 13...Inkjet generator, 14...Ink tank, 1
5... Nozzle, 16... Counter electrode, 18...
...Air piping, 21...Recorded object, 31...
...Interface, 23...Comparator,
24... D/A converter, 25... Servo amplifier, 26... Speed detector, 27... Position detector, 28... Feedback amplifier, 29・・・・・・A
/D converter, 36... Analog comparator, 37...
...Compressor, 38...Pressure sensor, 39...
... Feedback amplifier, 40 ... Controller, 41 ... Pulse motor drive circuit, 42 ... Air compression system, 43.
・．． ...Pulse motor, 44...Cam, 46
...Converter, 47...Cylinder, 48
... Piston, 50 ... High pressure pulse generator, 51 ... Potentiometer, 52 ...
... Peak value hold circuit, 53, 57 ... Inverting amplifier, 54 ... Level shift circuit, 55 ...
...Temperature sensor. Figure 1 Figure 2 Figure 3 Figure 6 Figure 8 Figure 4 Figure 7 Figure 5 Figure 9 Figure 10

Claims (1)

[Claims] 1. In an inkjet recording device that performs image recording by jetting ink from a nozzle provided at the bottom of an ink tank, there is a pneumatic control mechanism that controls the air pressure that acts on the ink surface in the ink tank, and an air pressure control mechanism that controls the air pressure that acts on the ink surface in the ink tank. The degree of decrease in the ink in the ink tank is detected by a detection means whose output changes according to the movement state of the movable member of the compression device, and thereby the above-mentioned method is used to compensate for the decrease in the hydrostatic pressure of the ink to the nozzle. means for inputting a control signal to the pneumatic control mechanism; and a correction signal for detecting the temperature of the pressure-controlled air and thereby correcting the operation of the pneumatic control mechanism that operates in response to the decrease in ink. An ink jet recording device comprising means for outputting.