JP2890600B2 - Wire dot printer drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A wire dot printer drive circuit that drives a print pin by a piezoelectric element. The object of the present invention is to detect abnormality of a piezoelectric element and a transistor that drives the piezoelectric element by simple means. A wire dot printer drive circuit for driving a print pin by a piezoelectric element, comprising: a reference voltage generator for generating reference pulse voltages of different levels; an output voltage of the reference voltage generator and a terminal voltage of the piezoelectric element. And a comparator for outputting a binary signal according to the magnitude, and detecting a fluctuation range of the terminal voltage of the piezoelectric element from the binary signal output of the comparator.

[Industrial applications]

The present invention relates to a wire dot printer drive circuit that controls a print pin by a piezoelectric element.

Various systems using a piezoelectric element as a driving element of a print pin of a wire dot printer are being studied. The piezoelectric element can operate at high speed and can be downsized. However, there is a problem in terms of reliability compared to a conventionally used magnet, and since a high driving voltage is required, the driving transistor for driving this is liable to be deteriorated. Alternatively, a problem such as smoking due to a short circuit of the element occurs, so that the target is necessary.

[Conventional technology]

FIG. 4 shows a drive circuit of a wire dot printer using a piezoelectric element. One of the output terminals of the print pin selector 1, S1, is connected to terminals A3, A4 of the drive transistors 2a, 2b through AND gates 1a, 1b. Further, a bias voltage V is applied to the drive transistors 2a and 2b through a series resistor R1. The control pulses input to the input terminals A1 and A2 of the AND gates 1a and 1b turn on / off the drive transistors 2a and 2b to drive the piezoelectric element 3. The print pin selector 1 has the number of dots,
.Times.n (n is an integer) are provided as many output terminals, and the above-described unit drive circuits are connected to the respective output terminals S2, S3. FIG. 5 shows a timing chart of the unit drive circuit, which is driven by a pulse sent from the output terminal S1. In the figure, when the terminal A3 is on and the terminal A4 is off, the voltage V is applied to the terminal A5.
Occurs, the piezoelectric element 3 is charged. When the terminal A3 is turned off and the terminal A4 is turned on, the voltage of the terminal A5 becomes 0 and the piezoelectric element 3 is discharged. As shown in the perspective view of FIG. 6, the piezoelectric element 3 is formed by bonding a piezoelectric plate 3a, and has the property of expanding and contracting when a voltage V is applied. The printing pin 3b is fixed to the piezoelectric element 3, and its movement is controlled by expansion and contraction of the piezoelectric element 3.

Since a high drive voltage of about 100 V is applied to the wire dot printer drive circuit that drives the print pins by the piezoelectric element, abnormalities such as short circuit or open due to deterioration of withstand voltage are applied to the piezoelectric element and the drive transistor that drives it. Tends to occur. However, the conventional circuit cannot properly cope with the occurrence of such an abnormality as described below.

[Problems to be solved by the invention]

In the conventional wire dot printer driving circuit shown in FIG. 4, when the piezoelectric element 3 is short-circuited, the output of the terminal A5 is always 0, so that the abnormality can be easily detected. However, when an abnormality such as short circuit or open circuit occurs in the drive transistors 2a and 2b, the terminal A5
It is difficult to identify which element has an abnormality by merely detecting the presence or absence of the output of the above. For example, when the transistor 2b is short-circuited, the output of the terminal A5 only drops from V to 1 / 2V and does not become 0. Therefore, in order to distinguish between the case where the piezoelectric element 3 is short-circuited and the case where the drive transistor 2b is short-circuited, not only the presence or absence of the output voltage at the terminal A5 but also the level of the output voltage is detected. There is a need. However, detecting such a voltage level for all of the unit drive circuits of the number equal to the number of print pins has a drawback that errors easily occur due to the influence of the variation of the elements constituting each unit drive circuit. .

Therefore, an object of the present invention is to detect an abnormality of a piezoelectric element and a transistor for driving the piezoelectric element by simple means.

[Means for solving the problem]

An object of the present invention is to provide a wire dot printer driving circuit for driving a print pin by a piezoelectric element, a reference voltage generator for generating different levels of reference voltages, an output voltage of the reference voltage generator, and A comparator that outputs a binary signal according to the magnitude of the terminal voltage of the element, and a function of detecting a fluctuation range of the terminal voltage of the piezoelectric element from the binary signal output of the comparator. And a wire dot printer driving circuit.

(Operation)

FIG. 1 is a diagram illustrating the principle of the present invention. The portion surrounded by a dotted line in the figure is the conventional wire dot printer driving circuit shown in FIG. 4, and as described above, the unit driving circuit composed of the piezoelectric element 3 and the transistors 2a and 2b for driving the same is a dot driving circuit. A number equal to the number 24 × n is incorporated.
Each of the unit driving circuits is sequentially driven by pulses transmitted from the output terminals S1, S2,... Of the print pin selector 1.

Therefore, in the configuration according to the present invention, the terminals of all the piezoelectric elements 3.
To the terminal C1 of the comparator 5. The output of a reference voltage generator 6 is connected to the other terminal C2 of the comparator 5, and the reference voltage generator 6 has a plurality of input terminals T1, T2,.
·have. A reference voltage of a different level is output to the terminal C2 of the comparator 5 according to the combination of the presence or absence of the control pulse to these input terminals T1, T2. The magnitude of the voltage input to the terminals C1 and C2 of the comparator 5 can be determined by the presence or absence of a voltage generated at the output terminal C3 of the comparator 5.

As described above, the piezoelectric element 3 and the driving transistor
Different levels of voltage are generated at the terminal C1 depending on which of the 2a and 2b has a short or open abnormality. Therefore, if the level of the reference voltage of various levels input from the reference voltage generator 6 to the terminal C2 and the magnitude of the voltage generated at the terminal C1 are detected based on the presence or absence of a pulse generated at the terminal C3 of the comparator 5, when an abnormality occurs, The range of the voltage level generated at the terminal C1 can be known. The level of the reference voltage can be known by a combination of control pulses to the input terminals T1, T2,. Therefore, it is possible to reliably detect which element has an abnormality.

The above-described abnormality detection is performed for the unit driving circuit connected to the output terminal S1 by a pulse transmitted from the output terminal S1 of the print pin selector 1. Similarly, the output terminals S2, S3 , It is possible to detect abnormality in other unit drive circuits. That is, abnormality can be detected for all the piezoelectric elements constituting the driving circuit of the wire dot printer and the driving transistors for driving the piezoelectric elements with a simple configuration including only one set of the reference voltage generator and the comparator.

〔Example〕

FIG. 2 is a circuit diagram showing an embodiment of a wire dot printer driving circuit according to the present invention, and the same components as those in FIG. 1 are denoted by the same reference numerals.

As shown in the figure, the terminal A5 of the piezoelectric element 3 is connected to the terminal C1 of the comparator 5 through the diode 4. As described above, there are sets of piezoelectric elements corresponding to the number of output terminals 24 × n of the print pin selector 1 and a set of transistors for driving the same, and all the terminals of these sets of piezoelectric elements are compared. To the terminal C1 of the container 5. In the figure, only one set is shown and the other is not shown.

On the other hand, the output of the reference voltage generator is connected to the other terminal C2 of the comparator 5. This reference voltage generator comprises transistors 6a and 6b connected in parallel, to which a bias voltage V is applied. The resistors R2, R3,
The magnitude of R4 is set so as to have the following relationship: R2> R3, R4 (1)

FIG. 3 is a timing chart of the circuit shown in FIG. The figure shows the terminals A3 and A4 of the driving transistors 2a and 2b and the terminals of the transistors 6a and 6b constituting the reference voltage generator 6.
FIG. 9 shows output pulses generated at a terminal C3 of the comparator 5 when a pulse is applied to T1 and T2. Regarding the output pulse of the terminal C3, the case where all of the drive transistors 2a and 2b and the piezoelectric element 3 are in a normal state is indicated by a solid line, and the case where any of the elements is abnormal is indicated by a dotted line.

Next, the presence or absence of the output pulse at terminal C3 is determined by the driving transistor.
With reference to FIG. 3, a description will be given of how the change is caused by the abnormality of the piezoelectric elements 3a and 2b.

In the phase I in the figure, both transistors 6a and 6b are on. Therefore, a voltage of V _C2 = V / (1 + R2 / R3 + R2 / R4) is generated at the terminal C2, and from the condition (1), V _C2 <V / 2. In the phase I, the driving transistor 2a is on and the driving transistor 2b is off. Therefore, the voltage V _C1 generated at the terminal C1 has the following value depending on the states of the driving transistors 2a and 2b and the piezoelectric element 3. Take.

1) When all of the drive transistors 2a and 2b and the piezoelectric element 3 are normal, V _C1 = V.

2) V _C1 = 0 when the piezoelectric element 3 is short-circuited or the drive transistor 2a is open.

3) When the driving transistor 2b is in a short state, V
_C1 = V / 2.

From the above, in the phase I, only in the case of the above 2), V _C1 <V _C2 and the pulse output of the terminal C3 becomes 0. That is, the pulse output of the terminal C3 becomes 0 only when the piezoelectric element 3 is in the short-circuit state or the drive transistor 2a is in the open state.
It can be seen that when the terminal 2b is in a short state, the pulse output of the terminal C3 does not become 0.

In the same manner in Phases II, III, and so on, as shown in FIG.
It can be narrowed to a specific range. Then, it becomes possible to specify which element has an abnormality from the presence or absence of the output pulse of the terminal C3 in each of these phases. The above result can be determined only by the presence or absence of the pulse generated at the terminal C3, and there is no need to know the level of this pulse voltage. Therefore, accurate and quick abnormality detection is possible.

The above-described abnormality detection can be performed for all the unit drive circuits by sequentially transmitting pulses from the output terminals S1, S2,... Of the print pin selector 1. Therefore, abnormality detection of a large number of elements constituting the wire dot printer driving circuit can be performed with only one set of the reference voltage generator and the comparator.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reliably and promptly determine which of a number of elements has an abnormality with a simple configuration. Therefore, it greatly contributes to the improvement of the reliability of the wire dot printer driving circuit.

[Brief description of the drawings]

 1 is a diagram illustrating the principle of the present invention, FIG. 2 is a circuit diagram showing an embodiment, FIG. 3 is a timing diagram in the embodiment, FIG. 4 is a circuit diagram showing a conventional example, and FIG. FIG. 6 is a perspective view of the piezoelectric element. In the figure, 1 is a print pin selector, 1a and 1b are AND gates, 2a and 2b are drive transistors, 3 is a piezoelectric element, 3a is a piezoelectric plate, 3b is a print pin, 4 is a diode, 5 is a comparator, and 6 is a reference. The voltage generators 6a and 6b are transistors.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/30 B41J 29/46

Claims (1)

(57) [Claims] 1. A wire dot printer driving circuit for driving a printing pin by a piezoelectric element (3), comprising: a reference voltage generator (6) for generating reference voltages of different levels; and a reference voltage generator (6). And a comparator (5) for outputting a binary signal according to the magnitude of the output voltage of (6) and the terminal voltage of the piezoelectric element (3), and the piezoelectric signal is output from the binary signal output of the comparator (5). A drive circuit for a wire dot printer, comprising a function of detecting a fluctuation range of a terminal voltage of the element (3).