JPH0425342Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a print timing adjustment circuit that can correct print timing according to a drop in hammer voltage of a printer and can detect the minimum allowable voltage.

Conventionally, in impact printers that have been widely used, since the hammer voltage applied to the hammer drive coil drops due to power fluctuations and load fluctuations, a print timing adjustment circuit is provided to correct the print timing caused by this. FIG. 1 shows an example circuit. That is, the hammer voltage V is applied to the collector of the transistor 2 whose emitter is grounded through the resistor _R1 , and the print timing signal Q is applied to the NOT circuit 1.
In addition to the base, the collector outputs a hammer voltage corresponding to the printing timing. This hammer voltage is connected in series with a circuit in which a resistor _R3 and a diode D are shunted, and by passing it through a time constant circuit 3 which has a resistor _R2 and a capacitor C connected in parallel on both sides, the rise and fall of the hammer voltage is controlled. Repeat charging and discharging accordingly.

The waveform is shown by a chevron-shaped increase/decrease curve drawn in FIG. 3b for Q in FIG. 3a. This is input to the negative terminal of the comparator 4, and one positive terminal is set to a predetermined threshold level V _Z shown in FIG. 3b. Then, by passing the output of the comparator 4 through a constant voltage diode 5 and shaping the pulse with a transistor 6, a printing timing pulse delayed with respect to the printing timing of the input hammer voltage is obtained, as shown in FIG. 3c. This is input to the hammer drive circuit 7.

In this way, when the hammer voltage drops, printing is performed at a timing delayed according to the amount of drop, so that the optimum printing timing is always maintained regardless of the hammer voltage.

In this case, for example, the hammer voltage can be adjusted from 48V to 40V, but cannot be adjusted below that. For this reason, a separate circuit is provided as a hammer voltage drop detection circuit in which the lowest allowable voltage V _L is set on one side of the comparator, and when this detection circuit operates, the printer is stopped. The minimum allowable voltage V _L in this detection circuit
Although it is not directly related to the threshold level V _Z mentioned above,
It is possible to have these operating points at the same time.

The inventor of the present invention considered including the latter circuit in the former circuit by making the operating points of both the same.

An object of the present invention is to provide a print timing adjustment circuit that can correct the print timing according to a drop in hammer voltage of a printer and can detect the minimum allowable voltage.

In order to achieve the above object, the print timing adjustment circuit of the present invention generates a print timing pulse by inputting the printer's hammer voltage, passes the print timing pulse through a time constant circuit to obtain a charge/discharge waveform, and adjusts the print timing pulse to a predetermined threshold level. In the print timing adjustment circuit that corrects the print timing according to the drop in hammer voltage by slicing the input hammer voltage to form a delayed timing pulse, a predetermined threshold value is determined from the voltage division point between the resistor to which the input hammer voltage is applied and the constant voltage element. The present invention is characterized in that it includes a circuit for extracting a level, and the time constant voltage element becomes inoperable when the hammer voltage drops below the allowable minimum voltage.

The present invention will be described in detail below with reference to examples.

FIG. 2 is an explanatory diagram showing the configuration of an embodiment of the present invention. In the figure, the difference from Figure 1 is that the threshold level V _Z applied to the positive terminal of the comparator 4 is related to the hammer voltage V, and it is set so that it will not operate below the allowable minimum voltage V _L , and the hammer voltage This is because it has a descent detection function. That is, the hammer voltage V applied to the emitter of the transistor 2 is branched and grounded via a resistor 11 and a constant voltage diode (for example, a Zener diode) 12, and the threshold level is taken out from the upper end of this constant voltage diode. In this case, by appropriately setting the resistor 11, the time-regulating voltage diode 12 becomes inoperable when the hammer voltage falls below the allowable voltage, and is prevented from outputting from the comparator 4.

With this configuration, the hammer voltage can be adjusted within the print timing range, for example from 48V as mentioned above.
At 40V, the operation is the same as the conventional example shown in Figure 1.
As shown in Figures a to c. The hammer voltage is 40V or less, that is, the voltage V applied to the collector and emitter of transistor 2 through resistor _R1 is 40V.
If it becomes below, resistor 11 and Zener diode 12
The threshold voltage V _Z extracted from the series circuit becomes equal to V. This is a zener diode 12
This is because by setting the zener voltage to 40V, the zener current will no longer flow. This eliminates the voltage drop caused by the resistor 11. The voltage V _Z is then equal to the applied voltage V.

Below, the operation when the hammer voltage drops is shown in Figures 4 a to d.
As shown in Figure 3a and Figure 3b (same as Figure 3b), the voltage _VZ shown by the dotted line outputs the same _VZ as the Zener voltage from 48V to 40V.
If the voltage is below 40V, for example below 39V, Figure 4c
As shown in , the charge/discharge waveform no longer intersects with the charge/discharge waveform in b of the same figure. Therefore, the output from the comparator 4 shown in FIG. 2, that is, the print timing pulse, is fixed at a low level and cannot be changed. As a result, as shown in FIG. 4d, the transistor 6
is turned off and becomes 0V, and the operation of the hammer drive circuit 7 is stopped. Hammer voltage drop detection is performed in this manner.

In the hammer drive circuit 7, a drive operation is performed by selecting a case where the charging/discharging waveform of the hammer voltage intersects with the threshold voltage _VZ .

The operation of the Zener diode 12 described above will be explained in more detail using FIGS. 5a and 5b.

As shown in figure a, the voltage of Zener diode 12 is
V _Z means that the diode characteristics shown in b in the same figure, that is, the forward direction characteristic V _F −I _F and the reverse direction characteristic V _R
-I _R , when the voltage is increased in the direction of V _R , there is a point where almost no current flows, and a zener phenomenon (avalanche phenomenon) occurs at V _R = V _Z , where the current suddenly increases. Using this, ν is extracted as shown in a in the figure.

If V = 45 [V] and V _Z = 40 [V] in figure a, then
A voltage drop of 5 [V] occurs in the resistor 11, ν = 40
It becomes [V].

Further, when V=48 [V], a voltage drop of 8 [V] occurs across the resistor 11. Now, V=39 [V]
Then, V _R =39 [V], and the Zener phenomenon does not occur as shown in b in the same figure, and I _R hardly flows, so that no voltage drop across the resistor 11 occurs. Therefore ν
=V=39 [V].

In this case, as explained in FIGS. 4a to 4d, the hammer drive circuit 7 performs driving when V=40 to 48 [V], and stops driving when V=39 [V] or less.

As explained above, according to the present invention, the circuit that corrects the printing timing according to the drop in the hammer voltage of the printer also has a function to detect when the hammer voltage has dropped below the allowable minimum voltage. By sharing the comparator used in the conventional example, the configuration can be significantly simplified.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the conventional example, FIG. 2 is an explanatory diagram of the configuration of the embodiment of the present invention, FIGS. FIGS. 4a to 4d are explanatory diagrams of the operation when the hammer voltage drops, and FIGS. 5a and 5b are explanatory diagrams of the operation of the Zener diode. In the figure, 1 is a NOT circuit, 2 and 6 are transistors, 3 is a time constant circuit, 4 is a comparator,
5 and 12 are constant voltage diodes, 7 is a hammer drive circuit, and 11 is a resistor.

Claims (1)

[Scope of utility model registration request] The hammer voltage can be adjusted by inputting the printer's hammer voltage to generate a print timing pulse, passing the print timing pulse through a time constant circuit to obtain a charge/discharge waveform, and slicing it at a predetermined threshold level to form a delayed timing pulse. The print timing adjustment circuit corrects the print timing according to the drop in the input hammer voltage, and includes a circuit that extracts a predetermined threshold level from the voltage division point of the resistor and constant voltage element to which the input hammer voltage is applied, and that the hammer voltage is below the minimum allowable voltage. A printing timing adjustment circuit characterized in that a constant voltage element becomes inoperable when the voltage drops to .