JPH11157078A - Ink jet type image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent melting of a print head and an abnormal delivery of ink droplets by properly limiting the width of a pulse corresponding to the temperature of the print head. SOLUTION: A generated pulse signal 58 from a pulse generator 7 is sent via a pulse limiter 8 to a print head 1. The width of the signal 58 varies according to a head control setting 55 from an MPU 5; however, a high limit of the width of pulse is limited by the limiter 8. The limiter 8 limits a high limit value of the generated pulse 58 from the generator 7 corresponding to a pulse width limit value 57 given from a limit generator 9. The generator 9 generates the pulse width limit value 57 corresponding to an output of a temperature sensor 4 incorporated in the print head 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a plotter, and a copying machine, and more particularly, to an ink jet type image forming apparatus which forms an image on paper by discharging ink droplets by using heat. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art Such an ink jet type print head is provided with a plurality of nozzles for ejecting ink droplets, and a heater is provided for each of these nozzles. By passing current through this heater, the heater generates heat,
The ink droplets are ejected to the outside of the nozzles by utilizing the expanding force of the bubbles generated in the ink by the heat. The heater is normally driven by pulse driving. At this time, the pulse width is controlled by the print head temperature such that the pulse width becomes narrower when the temperature of the print head is high, and wider when the temperature of the print head is low. Not all the heat generated by the heater is consumed by the ejection of ink droplets, and some of the excess heat is stored in the print head. For this reason, if ink droplets are continuously ejected, the print head gradually rises in temperature around the heater portion, and there is a possibility that the print head will eventually melt from around the heater.

Therefore, a circuit for limiting the pulse width for driving the heater has been conventionally provided so that the print head is not melted and broken.

[0004]

However, the limit value of the conventional pulse width limit is a predetermined fixed value.

As described above, in order to allow a wide pulse width at a low temperature of the print head, it is appropriate to set this limit value in accordance with the pulse width at a low temperature. Driving the heater with a pulse width may melt the print head.

Conversely, if the limit value is set in accordance with the pulse width at a high temperature or at an intermediate temperature, the required pulse width cannot be generated at a low temperature and normal ink droplet ejection becomes impossible. There was a possibility.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and prevents the melting of the print head and the defective ejection of ink droplets by appropriately limiting the pulse width in accordance with the temperature of the print head. It is an object of the present invention to provide an image forming apparatus of an ink jet type capable of performing the above.

[0008]

An ink jet type image forming apparatus according to the present invention has a built-in heater, and uses a heat of the heater to eject ink droplets.
A temperature detecting means having a temperature sensor for detecting the temperature of the print head; and a pulse width corresponding to the temperature while detecting the temperature of the print head based on a signal from the temperature sensor separately from the temperature detecting means. Pulse generation control means for generating a pulse signal for driving a heater in the print head in accordance with the print data, and for limiting the pulse width of the pulse signal generated by the pulse generation control means to within a given pulse limit width. And a pulse limit generating means for generating the pulse limit width given to the pulse limit means in accordance with the temperature detected by the temperature detecting means.

The temperature sensor may be built in a print head.

As described above, the pulse limit width given to the pulse limit means is generated in accordance with the temperature detected by the temperature detecting means, so that the pulse limit width can be appropriately changed according to the temperature of the head. Becomes possible. That is, since the pulse width can be limited in accordance with the temperature of the print head, the pulse width required for ejecting ink droplets can be secured at any temperature, and the print head can be protected from melting.

There are various cases in which the frequency of updating the pulse limit width can be considered. One of them is, for each pulse for driving the heater of the print head, the print head at the time when the pulse is generated. The pulse width can be limited depending on the temperature.

Alternatively, the pulse for driving the heater is grouped by a plurality of predetermined consecutively generated pulses, and the pulse limit width is updated in accordance with the temperature detected by the temperature detecting means for each groove. It is also possible to do. This reduces the frequency of updates,
When an A / D converter or the like is used, a relatively low-speed one can be used.

In addition to the pulse width limitation for setting the same pulse limitation width to all the pulses in the group, the pulse in the group is determined by the order of the pulse in the group. The pulse width limitation may be performed at different pulse limitation widths depending on whether there is a pulse width limitation or not. This is so that the ink droplet is ejected by a second pulse (main pulse) which is preheated by a narrow first pulse (pre-pulse) and a second pulse (main pulse) is wide for adjusting the amount of ink to be ejected.
This is effective when applied to a case where ink droplets are ejected by a pulse.

Alternatively, when the plurality of heaters are divided into a plurality of blocks which are sequentially driven, the pulse limit width may be determined in accordance with the temperature detected by the temperature detecting means in each cycle of driving the plurality of blocks. May be updated. Updating the limit value of the pulse width in a short cycle may limit the pulse width more than necessary and cause density unevenness on the printed image. The adverse effect on the amount can be suppressed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic structural view of an image forming apparatus showing the features of the first embodiment according to the present invention. The print head 1 is controlled by the control unit 100.

The print head 1 includes a heater driving unit 2, a heater 3, and a temperature sensor 4, and forms an image by discharging ink droplets. The heater drive unit 2 controls energization of the plurality of heaters 3. In the present embodiment, the plurality of heaters 3 are divided into eight blocks, and the heaters 3 of the block selected by the block selection signal 54 are energized and driven according to the head drive pulse signal 53 and print data (not shown). Temperature sensor 4
Uses the temperature characteristic of the forward current of the diode, and is driven by the temperature signal buffer 10 at a constant current. The temperature signal buffer 10 outputs a temperature signal 52 to be input to the MPU 5 and the limit generator 9 in the control unit 100 by using a temperature sensor signal 51 generated by driving the temperature sensor 4 at a constant current as an input signal.

The MPU 5 in the control unit 100 controls the entire apparatus. Here, the temperature of the print head 1 is detected by the temperature signal 52, and the pulse width depending on the temperature is set in the pulse generator 7 by the head control setting 55. Further, a timing for driving the print head 1 is given to the head drive control unit 6 by the head drive trigger 56.
When receiving the head drive trigger 56 from the MPU 5, the head drive controller 6 outputs a block selection signal 54. The value of the block selection signal 54 changes at a cycle set by the head control setting 55 by the MPU 5. A pulse generation trigger 59 is output to the pulse generator 7 every time the block selection signal 54 changes. The pulse generator 7 outputs a generated pulse signal 58 each time a pulse generation trigger 59 is input according to the pulse width set by the MPU 5 in the head control setting 55.

The limit generator 9 detects the temperature of the print head 1 based on the temperature signal 52, and outputs a pulse width limit value 57 corresponding to the detected temperature to the pulse limiter 8. More specifically, the temperature signal 52 is converted into a signal 57 having an amplitude and a level suitable for input to the pulse limiter 8. The pulse limiter 8 limits the upper limit of the pulse width of the generated pulse signal 58. The pulse width of the generated pulse signal 58 from the pulse generator 7 is larger than the pulse width indicated by the pulse width limit value 57. If the pulse width is wider, the pulse width of the generated pulse signal 58 is adjusted to the pulse width limit value 57, and if the pulse width is less than the pulse width limit value 57, the head drive pulse 53 is output with the same pulse width.

FIG. 2 shows a timing chart of signals of respective parts of the configuration of FIG. The operation of the configuration of FIG. 1 will be described with reference to FIG.

When the head drive trigger 56 is generated from the MPU 5, the head drive controller 6 outputs a pulse generation trigger 59 which is a periodic pulse. The pulse generator 7 generates a generated pulse signal 58 of a single pulse signal using the pulse generation trigger 56 as a trigger. Since the heater 3 in the print head 1 is divided into eight blocks, the block selection signal 54 indicates eight states 0 to 7 sequentially. This is one cycle of head driving, during which all heaters of the print head 1 are to be driven (between time t1 and time t2). The state changes are in the order of 0 → 7 and 7 →
The order of 0 can be set selectively.

FIG. 4 is a block diagram showing the internal configuration of the pulse limiter 8. The generated pulse signal 58 enters the pulse width comparator 21. The pulse width comparator 21 includes an A / D converter (ADC) 22 and a counter 23.
A pulse regulation signal 71 is generated based on the generated pulse signal 58 and the pulse width limit value 57. A / D converter 22
Is operating in a through run, and always converts the pulse width limit value 57 into a digital value 72. Counter 23
Receives the digital value 72 as a data value, inputs the generated pulse signal 58 as an enable signal, captures the digital value 72 as data while the generated pulse signal 58 is “Low”, and generates the generated pulse signal 58.
Changes from "Low" to "High", the output signal is set to "High", and the countdown is performed with the digital value 72 as an initial value. The clock signal for this countdown is not shown, but its cycle is selected so that the time required for counting the number of clocks corresponding to the digital value 72 matches the pulse limit width represented by the digital value 72. When the count becomes 0, the output signal becomes “Low”. This output signal becomes the pulse regulation signal 71. In the last stage, the generated pulse signal 58 is gated by the AND circuit 25 by the pulse regulation signal 71.

Generated pulse signal 58 and head drive pulse 5
3, the operation of the pulse limiter 8 will be described with reference to FIG. FIG. 3 shows an operation related to a temperature signal 52 which is a signal corresponding to the temperature of the print head 1. The pulse regulation signal 71 based on the temperature signal 52 has a limit width (generated pulse signal 58) given by the pulse width limit value 57 output from the limit generator 9 according to the temperature signal 52.
(The allowable pulse width or the upper limit value).

When the temperature signal 52 indicates a low temperature, since the temperature of the print head 1 is low, the allowable pulse width of the pulse for driving the heater 3 becomes wide. Therefore, the pulse limit width by the temperature signal 52 is widened (see FIG. 3).
(A)). Conversely, when the temperature signal 52 indicates a high temperature, the allowable pulse width of the pulse for driving the heater 3 is narrowed, so that the pulse limit width by the temperature signal 52 is narrowed (FIG. 3C). Usually, when the temperature of the print head 1 is low, the temperature of the ink is also low, so that a large amount of energy is required to generate bubbles in the ink. Therefore, the MPU 5 controls the pulse width of the generated pulse signal 58 so as to increase the pulse width. Conversely, when the print head 1 is at a high temperature, energy may be smaller than at a low temperature. Therefore, the MPU 5 controls the pulse width of the generated pulse signal 58 so as to reduce the pulse width.

FIG. 3 assumes that all generated pulse signals 58 have the same pulse width in order to facilitate understanding of the pulse limitation. In the case of low temperature (a), the generated pulse signal 5
Since the pulse limit width by the temperature signal 52 is wider than that of 8, the pulse limit is not applied. However, at the time of high temperature (c), the generated pulse signal 58 is wider than the pulse limit width by the temperature signal 52, so that the head drive pulse 53 is limited to the pulse limit width by the temperature signal 52.

As described above, in the normal state, the generated pulse signal 58 is not limited by the pulse limit value.
When performing high-density printing or printing at a high printing rate, the generated pulse width 58 may become wider with respect to the temperature of the print head 1. Even in such a case, the pulse width allowed by the temperature of the print head 1 limits the pulse width of the head drive pulse 53 in individual pulse units as described above, so that ejection of ink droplets is normally secured. Then, destruction (melting) of the head 1 can be prevented.

(Second Embodiment) FIG. 5 is a schematic configuration diagram showing the features of the second embodiment of the present invention. This embodiment is different from the first embodiment in that the hold trigger signal 60 is output from the head drive signal 6 to the pulse limiter 11 (corresponding to the pulse limiter 8 in FIG. 1). The hold trigger signal 60 is a predetermined 1
This is a signal for sampling and holding the pulse width limit value 57 immediately before a group of pulses is generated. Thus, the pulse width limit is not updated for each pulse of the generated pulse signal 58, but the pulse width limit is updated for each group of pulses. The predetermined group of pulses can be determined by the number of pulses of the generated pulse signal 58 and the like. In this embodiment, two pulses of the generated pulse signal 58 form one group,
The hold trigger signal 60 is output for each pulse.

FIG. 6 shows a schematic configuration of the pulse limiter 11. The configuration of the pulse limiter 11 is almost the same as the configuration of the pulse limiter 8 shown in FIG. 4, but differs from the pulse limiter 8 in that the hold trigger signal 60 is input to the A / D converter 22. The A / D converter 22 determines the A / D conversion timing of the pulse width limit value 57 based on the hold trigger signal 60. Therefore, the digital value 72 does not change from the time when the hold trigger signal 60 is input at a certain point of time until the time when the next hold trigger signal 60 is input.

FIG. 7 shows the outline of the operation of this embodiment. Each time the block selection signal 54 changes, a two-pulse generation pulse signal 58 is generated. When the hold trigger signal 60 is generated when the block selection signal 54 is “0”, a pulse regulation signal 71 corresponding to the temperature signal 52 at the time point th1 is generated. The pulse width of the pulse control signal 71 does not change until the next hold trigger signal 60 is generated, that is, until two pulses of the generated pulse signal 58 appear. Therefore, the pulse limit widths for the two pulses during this period are both tw1. By performing printing, the temperature of the print head 1 rises, and the pulse width of the pulse regulation signal 71 becomes narrower. However, at the time point th2, the pulse limitation width tw2 of the pulse regulation signal 71 is still smaller than that of the head drive pulse 53. Wider than width. However, the pulse limit width tw3 at the time point th3 when the temperature signal 52 indicates that the temperature is higher, that is, when the block selection signal 54 is "3", becomes narrower than tw2, and the first pulse at this time is still smaller than tw2. The second pulse is not limited, but the pulse limit width t is larger than the generated pulse.
You can see that w3 is narrower and subject to restrictions.

When some pulses are generated at narrow intervals, the A / D converter 22 is used in the configuration of the first embodiment.
However, it is necessary to provide a specially high-speed A / D converter by grouping pulses in a limited range as in this embodiment and performing A / D conversion for each group. Without this, the pulse width can be limited according to the temperature of the print head.

(Third Embodiment) This embodiment is similar to the third embodiment.
In contrast to the second embodiment in which the same pulse limit width is applied to a group of generated pulses, a pulse limit width suitable for each pulse of the group of generated pulses is obtained. It was done. Its configuration is the same as that of the second embodiment shown in FIG.
Has a different internal configuration.

FIG. 8 shows the internal configuration of the pulse limiter 11 according to the third embodiment. This configuration is obtained by adding a switch 24 to the configuration of FIG. The switch 24 switches the value of the pulse limit width for each pulse of the generated pulse signal 58, is initialized by the hold trigger signal 60, and is switched every time the generated pulse signal 58 falls. The switch 24 shifts the digital value 72 down by one bit in the initialized state, that is, 1 /.
The value is set to 2 and output to the counter 23 as the counter initial value 73. When detecting the falling edge of the generated pulse signal 58, the switch 24 in the initial state changes its internal state, and changes the digital value 72 to the counter initial value 73 as it is.
Output as

FIG. 1 shows an example of the configuration of such a switch 24.
It is shown in FIG. The switching circuit 24 includes n combinational logic circuits 240 receiving an n-bit digital value 72 from the A / D converter 22 and one D flip-flop 2
41. Each combinational logic circuit 240
It comprises a pair of AND circuits 242 and 243 and an OR circuit 244 receiving these outputs. D flip-flop 2
41 is cleared by the hold trigger signal 60 and inverts its Q output at the fall of the generated pulse signal 58. This Q output is input to a pair of AND circuits 242 and 243 of each combinational logic circuit 240. However, since only one AND circuit 243 is input to the inverting input terminal,
The gates of the pair of AND circuits 242 and 243 are opened complementarily. To the other input terminal of each AND circuit 242, a bit 0 to bit n-1 signal of an n-bit digital value 72 is input, and each AND circuit 242 is input.
3 has an n-bit digital value 7 at the other input terminal.
Two bits 1 to n-1 and a logical "0" signal are input. Therefore, in the initial state in which the switch 24 is cleared by the hold trigger signal 60, the Q output of the D flip-flop 241 becomes "0", each AND circuit 243 is selected, and bits 0 to n-1 of the digital value 72 are selected. Is shifted down by one bit and output as the counter initial value 73. Next, when the generation pulse signal 58 is input, the Q output of the D flip-flop 241 is inverted to “1”, whereby each AND circuit 242 is selected. As a result, bits 0 to n-1 of the digital value 72 are output as the counter initial value 73 as they are.

FIG. 9 shows an outline of the operation of the third embodiment. This drawing is similar to FIG. 7 except that the pulse widths of two pulses of the pulse regulation signal 71 generated for each pulse of the hold trigger signal 60 are different from each other. That is, in this example, the pulse widths tw1 ', tw2', tw3 'of the first pulse of the pulse regulation signal 71 are half the pulse widths tw1, tw2, tw3 of the second pulse, respectively. For example, looking at the time point when the block selection signal 54 is "3", the first pulse not limited by the pulse width tw3 in the example of FIG. 7 is limited by the pulse width tw3 'in the example of FIG. You can see that it has become. In the ink jet method, the first narrower ink is used to adjust the amount of ejected ink.
In this method, the ink droplets are ejected in two pulses so that the ink droplets are ejected in a second pulse (main pulse) which is preheated by the second pulse (pre-pulse). Since the temperature rise of the print head 1 depends on the total energy generated by the applied pulse, it is preferable that the width of the pre-pulse is also limited by the temperature of the print head 1.

In this embodiment, by limiting the pulse width depending on the temperature of the print head 1 to the characteristic of the pulse to be limited as in this embodiment, the print head 1 can be effectively overheated even in the above case. Can protect from destruction.

(Fourth Embodiment) FIG. 10 is a schematic structural view of an image forming apparatus showing the features of a fourth embodiment according to the present invention. In this embodiment, the timing of detecting the temperature of the print head 1 for limiting the pulse width is performed by a head drive trigger 56. By using the head drive trigger 56 as the hold trigger signal 60 in the second and third embodiments, the temperature detection of the print head 1 serving as a reference for limiting the pulse width is performed for each cycle of the head drive, that is, for all heaters. The temperature is detected each time the block 3 is driven once. Although the temperature sensor 4 is incorporated in the print head 1, there is a slight difference in how the temperature sensor 4 is affected by heat generated due to the positional relationship with the heater 3 to be driven. As a result, if the limit value of the pulse width is updated in a short period such as every generated pulse signal 58 or every several pulses of the generated pulse signal 58, the pulse width is unnecessarily limited, and as a result, As this affects the ink ejection amount,
Density unevenness may occur on a printed image. Performing the temperature detection for each cycle of the head driving means that the drive control of all the heaters 3 is performed once at that time, so that the temperature signal 52 can be treated as the temperature of the entire heater portion of the print head 1. it can. Therefore, it is possible to suppress the influence of the ink ejection amount that causes the density unevenness as described above.

Although the preferred embodiment according to the present invention has been described above, various modifications and changes can be made without departing from the gist of the present invention. For example, in the second embodiment, one group is formed by two pulses of the generated pulse signal 58. However, one group may be formed by three or more pulses.

[0038]

As described above, the pulse width of the pulse applied to the print head is limited in accordance with the temperature of the print head. The head can be protected from melting.

[0039]

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a first embodiment of the present invention.

FIG. 2 is a timing chart according to the first embodiment of the present invention.

FIG. 3 is a schematic operation explanatory diagram according to the first embodiment of the present invention.

FIG. 4 is a block diagram of a pulse limiter according to the first embodiment of the present invention.

FIG. 5 is a functional block diagram according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a pulse limiter according to a second embodiment of the present invention.

FIG. 7 is a schematic operation explanatory view according to a second embodiment of the present invention.

FIG. 8 is a block diagram of a pulse limiter according to a third embodiment of the present invention.

FIG. 9 is a schematic operation explanatory diagram according to a third embodiment of the present invention.

FIG. 10 is a functional block diagram according to a fourth embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration example of a switch 24 illustrated in FIG. 8;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Print head, 2 ... Heater drive part, 3 ... Heater, 4 ...
Temperature sensor, 5: MPU, 6: Head drive control unit, 7:
Pulse generator 8, 11, 11 pulse limiter 9, 9 limit generator, 10 temperature buffer, 21 pulse width comparator, 22 A / D converter, 23 counter, 24
... Switcher, 25 ... AND circuit, 51 ... Temperature sensor signal, 52 ... Temperature signal, 53 ... Head drive pulse signal, 5
4: Block selection signal, 55: Head control setting, 56:
Head drive trigger, 57: pulse width limit value, 58: generated pulse signal, 59: pulse generation trigger, 60: hold trigger signal, 71: pulse control signal, 72: digital value, 73: counter initial value, 100: control unit , 240 ...
Combinational logic circuit, 242, 243 ... AND circuit, 244
... OR circuit.

Claims (6)

[Claims] 1. A print head which has a built-in heater and discharges ink droplets by utilizing the heat of the heater, temperature detecting means having a temperature sensor for detecting the temperature of the print head, and the temperature detecting means. Separately, while detecting the temperature of the print head based on a signal from the temperature sensor, pulse generation control means for generating a pulse signal for driving a heater in the print head according to print data with a pulse width corresponding to the temperature; Pulse limit means for limiting the pulse width of the pulse signal generated by the pulse generation control means to within a given pulse limit width; and said temperature limit means for providing said pulse limit width to said pulse limit means. And a pulse limit generating means for generating in accordance with the temperature detected by the inkjet method. Image forming device. 2. The method according to claim 1, wherein for each pulse for driving the heater of the print head, a pulse width limitation depending on the temperature of the print head at the time when the pulse is generated is performed. An inkjet type image forming apparatus. 3. A pulse group for driving the heater is grouped by a plurality of predetermined consecutively generated pulses, and the pulse limit width is updated in accordance with the temperature detected by the temperature detecting means for each of the grooves. 2. The image forming apparatus according to claim 1, wherein the image forming is performed. 4. The image forming apparatus according to claim 3, wherein a pulse width limit for setting the same pulse limit width is applied to all the pulses in the group. 5. The method according to claim 3, wherein the pulse width of the pulse in the group is limited by a different pulse limit width depending on the number of the pulse in the group. , An inkjet type image forming apparatus. 6. A plurality of heaters are divided into a plurality of sequentially driven blocks, and one of the plurality of blocks is driven.
2. The ink-jet type image forming apparatus according to claim 1, wherein the pulse limit width is updated in accordance with the temperature detected by the temperature detecting means in each cycle.