JPS61242855A - Printing head driving device - Google Patents

Abstract

PURPOSE:To enable the constant printing force of a head to be always maintained and the improvement of system performance and cost reduction to be realized by controlling a head current in accordance with the length of a printing cycle in a printing head driving device used for an impact printer. CONSTITUTION:A head assisting means 20 which gives an energization starting command each time a printing command is generated, a time detection means 21 which starts by following the previous printing action, detects a time upto the present and generates an output corresponding to said time, an energizing time setting means 22 which sets an energizing time according to an output from the time detection means 21 each time a printing command is issued, and a head de-energizing means 23 which issues an energization stop command to the head 16 after detection of the termination of an energizing time are provided. Whenever a printing command is issued, a time which has passed from the previous printing command to the present printing command is detected, and if this time is short, an energizing time for the present printing needs to be shortened so that any excess printing force after the second printing may not be generated and subsequently, a constant printing force be always available.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printing head drive device used in an impact printer.

(Prior Art) In general, the head of an impact printer is configured as shown in Fig. 4. That is, 11 is a PNP type transistor which serves as a driver, and 12 is an NPN type transistor which also serves as a driver. A head drive coil 13 is connected between the collectors, and the emitter of one transistor 11 is connected to a head N source that generates voltage VCC, and the emitter of the other transistor 12 is connected to ground. coil 13
A flywheel diode 14 is connected between the lower end and the emitter of the transistor 11 and between the upper end of the head drive coil 13 and the emitter of the transistor 12, respectively. Further, a pulse T2 is applied to the base of one transistor 11 via an inverter gate 15, and a pulse T1 is applied to the base of the other transistor 12.

Here, pulse T1. The rising timings of T2 are equal to each other as shown in FIG. 5, but the time width until the falling edge of pulse T1 is shorter. When such pulses T1 and T2 are applied to the driver transistors 12 and 11, the waveform of the head current flowing through the head drive coil 13 becomes as shown in FIG.

[Problem that the invention seeks to solve]

Although the head is driven according to the above-mentioned timing, when continuous impact is performed, there is a problem that the impact force varies depending on the characteristics of the head even when the same current is applied. That is, as shown in FIG. 6, in the case of consecutive impacts, the first impact force is weaker than the subsequent impact forces. This is due to the leaf spring characteristics of the head, and the difference in impact force increases as the impact period becomes shorter.

In order to compensate for this first lack of impact power (printing power),
Currently, the pulse T1 that determines the drive timing is lengthened to increase the head current. However, if the head current is increased in this way, the impact force after the second impact will be too large. Additionally, the response frequency of the head decreases. Furthermore, since a large current always flows as head current, a large power supply is required.
There are also problems when installing the head, such as the set dimensions becoming strict.

The purpose of the present invention is to be able to keep the printing force of the head constant at all times, without lowering the response frequency of the head or increasing the size of the power supply for the head, and making it easy to assemble the head. It is an object of the present invention to provide a printing head drive device that makes it possible to improve system performance and reduce costs.

[Means for solving problems]

As shown in FIG. 1, the printing head driving device according to the present invention includes a head energizing means 20 that gives a command to start energizing the printing head 17 every time a printing command is generated, and a head energizing means 20 that gives a command to start energizing the printing head 17 every time a printing command occurs, and a time detection means 21 which detects the time up to the present time and produces an output according to this time; and an energization time setting means 22 which sets the energization time according to the output of the time detection means 21 every time the printing command is generated. , head deenergizing means 23 detecting that the energization time has expired and issuing a command to stop energization to the head 17.

[Effect]

The present invention solves the conventional problem by detecting the time from the previous printing command to the current printing command every time a printing command occurs, and if this time is short, setting the current energization time for the current printing to be short. This prevents the printing force from becoming too large from the second time onwards, thereby ensuring that a constant printing force is always obtained.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, the printing head 17 has the same configuration as that shown in FIG. 4, and corresponding parts are designated by the same reference numerals.
The explanation will be omitted. The head biasing means 20 has an input/output port 25 for a central processing unit (hereinafter referred to as CPU), which is not shown. This input/output boat 25 outputs the rHJ level pulse T2 shown in FIG. 5 and bin data based on a print command from the CPU. The above pulse T2
turns on the driver 11 via the inverter gate 15. Further, this pulse T2 operates the pulse T1 timing circuit 26 to generate the pulse T1 at the rHJ level shown in FIG. Note that the width of this pulse T1 changes depending on the voltage supplied from the head power source 27.

The pulse T1 is sent to the AND gate 28 along with the bin data.
This is the input condition. Another input condition for this AND gate 28 is the addition of the output signal from the head deenergizing means 23. This head deenergizing means 23 consists of a Nandt gate 29, which produces an output "1" in the non-operating state. Therefore, the AND gate 28 conducts the pulse T1 and turns on the driver 12 because the head deenergizing means 23 is in an inactive state and is selected by the bin data.

The time detection means 21 consists of a time detection capacitor C1, its charging resistor R1, and a differentiation circuit 30 for discharging the capacitor C1. This differentiating circuit 30 inputs the pulse T1 and differentiates its fall, and capacitor C1
This instantly discharges the electrical charge that was previously stored in the battery.

The energization time setting means 22 includes a timing circuit 31 for pulse T1'. This timing circuit 31 uses the head power supply 27 as a power source, and each time the pulse T2 rises, that is, each time a printing command occurs, an output corresponding to the detection time by the time detection means 21, that is, corresponds to the charging time of the capacitor C1. The potential at point A is input, and a pulse T1' of the rLJ level with a time width corresponding to that potential is generated. The time width of this pulse T1' becomes the time during which the head 17 is energized.

The pulse Tt' is inputted to one input terminal of the Nant gate 29 constituting the head deenergizing means 23. Further, the previous bin data latched by the latch circuit 32 is input to the other input terminal of the Nant gate 29. The latch circuit 32 receives the bin data output from the input/output port 25 and latches the bin data at the falling edge of the pulse T1.

Next, the operation will be explained with reference to the time chart shown in FIG. First, it is assumed that printing is being performed for the first time. In response to a print command from a CPU (not shown), the input/output boat 25 outputs bin data indicating the print location of the pulse T2. In synchronization with the rise of this pulse T2, a pulse T1 rises and is output from the timing circuit 26. The rHJ level of the pulse T2 is inverted by the inverter gate 15 to become the rLJ level, turning on the driver 11.

Further, the rHJ level of the pulse T1 passes through the AND gate 28 according to the bin data and the output rHJ of the head deenergizing means 23 when the head is not in motion, and turns on the driver 12.

The head coil 13 is energized by the ON operation of both drivers 11 and 12.

Further, the timing circuit 31 is activated by the rising edge of the pulse T2, and generates a pulse T1' at the rLJ level with a time width corresponding to the potential at point A of the capacitor C1. In this case, there is no previous printing operation, so no discharge is occurring, and
The potential at point A is high enough to generate a pulse T with the maximum time width.
+' occurs.

The output of the latch circuit 32, which is one input of the head deenergizing means 23, always remains at the rLJ level because there is no previous printing. Therefore, even if the pulse T1' rises to the rHJ level after a predetermined time width has elapsed, the Nant gate 2
The output of No. 9 remains at the rHJ level. That is, when there is no previous printing, the head deenergizing means 23 remains inactive and maintains the output at the rHJ level. therefore,
The AND gate 28 is activated by the output from the head deenergizing means 23.
does not turn off, and the drivers 11 and 12 remain in the on state until the time width of pulse T1 has elapsed.
A sufficiently large head current is applied to solve the first problem of lack of impact force (printing force) in the past.

When the time width of the pulse T1 passes and the voltage falls to the rLJ level, the output side of the AND gate 28 becomes the rLJ level. Therefore, the head current decreases as in the conventional case. Furthermore, the bin data input to the latch circuit 32 is latched by the fall of the pulse T1, and thereafter the output side of the latch circuit 32 becomes rHJ level. Further, with the fall of the pulse T1, the differentiating circuit 30 is activated, and its output terminal is temporarily brought to the rLJ level, and the charge stored in the capacitor C1 is instantly discharged. Therefore, the potential at point A also drops rapidly. Thereafter, the output terminal of the differentiating circuit 30 immediately reaches the rHJ level, so the capacitor C1 is charged with a time constant determined by the charging resistor R1, and the potential at point A gradually rises.

After that, as the pulse T2 falls to the rLJ level, the output side of the inverter gate 15 becomes the rHJ level.
The head current is further reduced and the head current is turned off.

Next, a print command is generated from the CPU in a relatively short period after the above printing, and when the pulse T2 and the bin data are output from the input/output board 25, the pulse T1 rises in the same way as described above, and the driver 11.12 is turned on. Then, the head coil 13 is energized. Further, the timing circuit 31 also operates in synchronization with the rising edge of the pulse T2, and inputs an output corresponding to the charging time of the capacitor C1, that is, the potential at point A, and receives a pulse at the "off" level with a time width corresponding to the potential. T1' occurs.

Here, as mentioned above, since the next printing command is generated in a relatively short period from the previous printing, the potential at point A is not very high, and therefore the lI@ width of pulse T1' is also short.
Immediately returns to rHJ level. That is, the head current supply time is set short. When the pulse T1' returns to the rHJ level, that is, when the set energization time has expired, the two-way power of the Nantes gate 29 goes to the rHJ level, so the output side goes to the rLJ level. For this reason, and gate 28
is locked, its output terminal becomes rLJ level, and the head current decreases.

That is, although the pulse T1 still maintains the rHJ level, the AND gate 2
B is locked and the head 17 is deenergized.

Therefore, the through Wi'In flow of the head 11 is suppressed to a low level,
There is no problem that the impact force of the 21st stitch is too strong when the printing cycle is short as in the conventional case.

The subsequent operations are the same as those described above, and their explanation will be omitted.

When a printing command occurs in a relatively long period after the previous printing, such as the fourth printing command in Fig. 2, the capacitor C1 of the time detection means 21 is sufficiently charged, and the potential at point A is also compared. The target is high, and the time width of pulse 1' is also long. Therefore, the head current becomes large, and sufficient printing can be performed by compensating for the decrease in impact force caused by the printing cycle.

Here, the circuit in FIG. 1 is expressed in terms of hardware to make the explanation easier to understand, but in reality, all operations can be controlled by CPU processing. In this case, the voltage value of the head power supply 21 is input to the CPU by an A/D converter. Further, the printing cycle detection function using the resistor R1 and the capacitor C1 can be achieved by using a timer in the microcomputer system.

The processing contents when all the steps are performed by the CPU as described above will be explained with reference to the flowchart of FIG.

First, the voltage value of the head N source 27 shown in FIG.
The voltage value is inputted via the A/D converter to inform U (step S1). Next, the time width of the pulse T1 corresponding to the input voltage value is set using a table in which the value of the pulse T1 corresponding to the voltage value is set in advance (
Step 82).

Next, it is determined whether it is the printing position (step Sa), and if YES, the bin data is output (step S4). At this time,
The pulse T1. T2 rises together, energizing the head 17 as described above. In addition, the time detection means 2 in FIG.
A timer A replacing the capacitor C1 of No. 1 starts (step Ss). After that, the time of pulse T1 ends (step S6), the bin data is turned off (step S7),
When the time of pulse T2 ends (step S8), pulse T2
is turned off (step 89), and the first printing operation is completed. Then, it is determined whether all printing has been completed (Step 510), and if not, it is determined whether the printing position is in order to perform the next printing (if it is at the middle position of Stellaf 11, the above-mentioned timer A is stopped (Step 512)).
. Then, the time widths of pulses T1 and Tt' are set based on the value of timer A and the input voltage value at this time (
Step S ta ).

Then start timer A again in step 51.
4) and output the bin data (step 515).
, energize the head. When the time of pulse T1' ends (step 81B), the previous bin data is inverted and outputted (step 517), and the head is deenergized. After that, the process returns to step S8 and the same process is repeated thereafter.

That is, the flowchart in FIG. 3 shows that each function expressed as a means in FIG. 1 is all executed by processing within the CPU.

In the above description, the head energization control is performed using two pulses T1. Although this is done at pulse T2, this is to efficiently utilize the energy of the head coil (inductance), and the head coil may be driven only by pulse T1.

Further, the latch circuit 32 and its output terminal in FIG. 1 may be omitted, and the head deenergization circuit 23 may be configured by an inverter gate.

〔Effect of the invention〕

As described above, according to the present invention, since the head current is controlled according to the length of the printing cycle, it is possible to control the head current according to the length of the printing cycle.
The impact force of the second impact force is never insufficient, or the impact force of the second impact force is never too strong, and the impact force of the head is always constant, so there is no unevenness in print density. Furthermore, there is no need to constantly supply a large head current, which increases the response frequency of the head and improves product performance. Furthermore, the power supply for the head can be downsized, and the head can be easily assembled.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing one embodiment of a printing head driving device according to the present invention, FIG. 2 is a time chart for explaining the operation of the device shown in FIG. 1, and FIG. 3 is a diagram similar to that shown in FIG. 1. Flowchart showing the flow of processing when the density achieved by the circuit is performed by CPU processing, Fig. 4 is a circuit diagram showing the configuration of a general head, and Fig. 5 shows the pulses and head current applied to the circuit of Fig. 4. FIG. 6 is a waveform diagram showing the conventional problem. 11. Printing head, 20. Head biasing means, 21
...Time detection means, 22.. Energization time setting means, 23.
・Head deenergization means. April 22, 1985

Claims (1)

[Claims] (1) A head energizing means that gives a command to start energizing the printing head every time a printing command occurs, and a time that starts with the previous printing operation and detects the time up to the present time and generates an output according to this time. a detection means; an energization time setting means for setting an energization time according to the output of the time detection means each time the printing command is generated; and a head that detects that the energization time has expired and issues an energization stop command to the head. A printing head drive device comprising: a deenergizing means.