JPH066376B2 - Ink jet printer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer, and more particularly to changing a dot pitch of the ink jet printer.

[Prior Art] In general, an ink jet printer includes a rotating print drum and an ink jet nozzle that faces the print drum and that moves a predetermined distance in the rotation axis direction of the print drum at every predetermined rotation of the print drum. By printing a printing paper on the peripheral surface of the printing drum and selectively adhering the ink ejected from the ink jet nozzles to the printing paper while rotating the printing drum, one ink dot row is printed. When the print drum makes one rotation, the direction of the ink ejected from the ink jet nozzle is slightly changed in the direction of the rotation axis of the print drum. As a result, at the time of the next one rotation of the print drum, the line next to the one ink dot line previously formed is printed. In this way, one character line is printed by a plurality of ink dot lines. As described above, in the ink jet printer, the circumferential direction of the print drum is the main scanning direction and the sub-scanning direction of the rotation axis direction.

Here, the dot pitch in the sub-scanning direction can be freely set according to the angle at which the ink jet direction of the ink jet nozzle is deflected. However, the dot pitch in the main scanning direction must be determined according to the rotation speed of the print drum. Therefore, usually, a rotary encoder is connected to the rotary shaft of the print drum, and it is determined according to the output pulse from this rotary encoder. Generally, the number of output pulses per rotation of a commercially available rotary encoder is fixed in advance such as 1024 pulses and 2048 pulses, and there is no one that can output an arbitrary number of pulses. Therefore, the dot pitch in the main scanning direction is determined according to the number of pulses of the rotary encoder and the diameter of the print drum.

[Problems to be Solved by the Invention] In such a conventional ink jet printer, in order to change the dot pitch in the main scanning direction, the diameter of the print drum is changed or the rotary encoder is assumed to have a different number of pulses. Had to replace or do both of these. Here, it is difficult to change the diameter of the print drum. Even if you replace the rotary encoder,
There is a drawback that the dot pitch that can be set is less flexible.

The present invention has been made to address the above-mentioned circumstances,
It is an object of the present invention to provide an ink jet printer having a simple structure in which the dot pitch can be changed arbitrarily.

[Means for Solving Problems] The ink jet printer according to the present invention includes a phase-locked loop circuit 16 for frequency-multiplying the output pulse of the rotary encoder 14, and a frequency divider 18 for dividing the output of the phase-locked loop circuit 16. A print control circuit 20 for controlling the dot pitch according to the output pulse of the frequency divider 18 is provided.

[Operation] According to the present invention, the dot pitch can be arbitrarily changed by appropriately setting the frequency multiplication ratio by the phase locked loop circuit and the frequency division ratio of the frequency divider.

Embodiment An embodiment of the ink jet printer according to the present invention will be described below with reference to the drawings. The print drum 10 is rotated at a predetermined speed by the drive motor 12. A rotary encoder 14 is connected to the rotary shaft of the print drum 10, and a predetermined number of pulses are output from the rotary encoder 14 per one rotation of the print drum 10. The output pulse of the rotary encoder 14 is passed through a phase lock loop (PLL) circuit 16 and a frequency divider 18 as pitch data to the print control circuit 2
Supplied to zero. Print data is also supplied to the print control circuit 20. The print control circuit 20 divides the print data by the frequency divider 18
And is supplied to the ink jet nozzle 22 as a print signal in synchronization with the output pitch data of. The ink jet nozzle 22 controls the ejection of ink according to the print signal. As a result, ink dot rows are formed on the print paper 24 on the print drum 10 at a dot pitch according to the pitch data.

The PLL circuit 16 includes a phase comparator 30, a voltage controlled oscillator (V
CO) 32 and frequency divider 34. The output pulse of the rotary encoder 14 is compared with the output of the frequency divider 34 by the phase comparator 30. The output of the phase comparator 30 (a signal corresponding to the phase difference between the two input signals) is supplied to the VCO 32 as a control signal, whereby the oscillation frequency of the VCO 32 is controlled. The output of the VCO 32 is supplied to the phase comparator 30 via the frequency divider 34. The output of the VCO 32 is also supplied to the frequency divider 18 as the output of the PLL circuit 16.

Although not shown, the ink jet nozzle 22 is moved in the rotation axis direction as the print drum 10 rotates.

Next, the dot pitch control operation in the main scanning direction according to this embodiment will be described. Rotary encoder 1
4 outputs 4096 pulses for one rotation of the print drum 10. The diameter of the printing drum 10 is 130.4 mm
If the circumference is 409.6 mm, the PLL circuit 16,
If there is no frequency divider 18, the dot pitch (main scanning direction) is 1.
It becomes 00 μm.

Here, in order to change the dot pitch to 90 μm, the rotary encoder 14 is replaced with one having an output pulse number of about 4551, or the diameter of the print drum 10 is 117.4 mm.
(The circumference is 368.5 mm) and must be replaced.
The former method is not feasible to implement easily and is very expensive to implement. The latter requires not only the replacement of the drum itself but also the replacement of the peripheral mechanism, which also results in higher prices.

In this embodiment, since the PLL circuit 16 and the frequency divider 18 are connected between the rotary encoder 14 and the print control circuit 20, the frequency division ratio of the frequency divider 34 of the PLL circuit 16 and the frequency division of the frequency divider 18 are divided. By changing the circumference ratio, the number of output pulses of the rotary encoder 14 can be substantially changed.
When the output pulse number of the rotary encoder 14 is Pin and the frequency division ratio of the frequency divider 34 is N, the output pulse number of the PLL circuit 16 is multiplied by N times Pin × N. That is, the PLL circuit 16 functions as a frequency multiplication circuit. Therefore, assuming that the frequency division ratio of the frequency divider 18 is M, the pulse number Pout of the pitch data input to the print control circuit 20 is Pin × N / M.
(Per rotation of the print drum 10). From this, it can be seen that N = 10 and M = 9 are sufficient to set the dot pitch to 90 μm as described above. That is, Pout is as follows.

Thus, by freely changing M and N, it is possible to generate pitch data of the number of pulses according to a desired dot pitch. Here, a value up to the 100th place can be set as N and any value can be set as M. Therefore, the degree of freedom in setting the dot pitch is very large. However, if the ratio of N and M is the same, the smaller the value of M, the better the responsiveness. In addition, when it is not possible to achieve the adjustment only by changing the ratio of N and M, fine adjustment may be performed by the drum diameter. Or PL
The L circuit and the frequency divider may be further connected in series to adjust the number of pulses as (N / M) ² .

The dot pitch in the sub-scanning direction can be determined by the deflection angle of the ink jet as in the conventional case, and is set to the same value as the dot pitch in the main scanning direction.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified.

[Effects of the Invention] As described above, according to the present invention, the output pulse of the rotary encoder is changed in the number of pulses / one rotation (frequency) of the printing drum by using the PLL circuit and the frequency divider. Since the pitch data is supplied to the print control circuit, the dot pitch can be changed to an arbitrary value by changing the frequency multiplication number and the frequency division ratio of the frequency divider by the PLL circuit. Therefore, the costly work such as the replacement of the rotary encoder and the replacement of the printing drum, which are conventionally required, becomes unnecessary, and the ink jet printer having a simple structure and capable of arbitrarily changing the dot pitch is provided at a low cost. It

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of an ink jet printer according to the present invention. 10 ... Printing drum, 14 ... Rotary encoder, 16 ...
PLL circuit, 18 ... Frequency divider, 20 ... Print control circuit, 22
… Ink jet nozzle.

Claims (1)

[Claims] 1. A rotary encoder for generating a pulse according to the rotation of a print drum, a means for multiplying the frequency of the pulse, a means for dividing the output of the multiplying means, and an output pulse of the dividing means. An ink jet printer comprising a dot pitch control means for controlling an operation cycle of an ink jet nozzle in accordance therewith, and realizing an arbitrary dot pitch by controlling a multiplication ratio of the multiplication means and a division ratio of the frequency division means.