JPH06166189A - Drive circuit for impact printer - Google Patents

Abstract

PURPOSE:To provide a drive circuit for an impact printer for assuredly protecting a circuit from abnormal heating. CONSTITUTION:In standby of a printing element, a control means controls a coil driver 1, turns on a transistor Tr, supplies auxiliary power source of 5V to a common power source line L of coils C1-C9 through a resistance R and an inverter i, turns on transistors Tr1-Tr9 in sequence, and supplies current to the coils C1-C9 in sequence. Synchronizing with the sequential supply, A/D conversion of potential of a terminal AD is carried out by an A/D converter 2 so as to output to a control circuit 3. The control circuit checks temperature of each coil. When the temperature of the coil reaches a heat resisting limit temperature, driving of the coils C1-C9 is controlled accordingly so as to protect the circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an impact printer.

[0002]

2. Description of the Related Art In recent years, in dot matrix impact printers, the amount of heat generated by the print head has increased with the increased response speed and higher density of print elements. If it is driven excessively, the print head may be damaged due to a coil short circuit or the like, and in the worst case, ignition may occur. Currently, as a countermeasure, a thermistor is provided in a part of the print head to detect the temperature of the print head. When the detected temperature exceeds a predetermined temperature range, the printing operation is stopped and the print head is protected. is there.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
A thermistor provided in a part of the print head detects the average temperature of the entire print head regardless of the temperature of each coil. On the other hand, the heat generation amount of each coil varies depending on the operation frequency of each coil, and therefore some coils may generate abnormal heat. In this case, some abnormal heat generation cannot be detected, so it is judged to be safe, the protective function does not work, the coil shorts, etc., causing the print head to malfunction, and in the worst case, it causes ignition, which is still a safety issue. Cause Further, there is a time lag between the temperature of the thermistor and that of the coil, and it is difficult to detect the heat generation of the coil in a short time.

It is an object of the present invention to provide a drive circuit for an impact printer that ensures circuit protection against abnormal heat generation.

[0005]

When the printing element is on standby, the detection means detects and outputs the temperature of the printing element driving coil. The control circuit receiving this output controls the driving of the coil. At this time, when the detection means detects an abnormal temperature outside the predetermined temperature range, the control means suspends the driving of the coil until the temperature falls within the predetermined range, thereby achieving the above object.

Here, it is preferable that the detecting means detects the temperature by measuring the resistance value of the coil.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drive circuit for an impact printer according to an embodiment of the present invention will be described with reference to the drawings. This example is a dot matrix serial impact printer including a print head having nine print elements, and FIG. 1 is a block diagram showing the configuration of this example. In FIG.
C9 is a coil for driving a printing element (not shown) such as a printing wire. The coils C1 to C9 are coil drivers 1
Is driven selectively to drive the printing element. These printing elements are arranged side by side in the column direction and are scanned in the row direction to perform printing.

FIG. 2 shows the temperature characteristics of the resistance values of the coils C1 to C9. The coils C1 to C9 used in this example have a length of 4.
It is made by winding a copper wire with a length of 96 m and a diameter of 0.11 mm at 225 turns.
18 ° C, which is the heat-resistant limit temperature of the coils C1 to C9
Resistance value up to 0 ° C shows almost linear change,
It is 9.7Ω at room temperature (20 ° C) and 16.3Ω at 180 ° C. In this example, by measuring the potential of the terminal AD based on the temperature-resistance characteristic of this coil,
Detect the coil temperature.

Reference numeral 2 denotes an A / D converter as a detecting means, which is in non-printing (standby) of the printing element in the process of processing the print data of the next line during standby, that is, while printing of one line is completed and printing of the next line is started. In the state, the coil C1 by the coil driver 1 according to the control signal of the control circuit described later.
The potential of the terminal AD is detected in synchronization with the sequential driving of
After D / D conversion, it outputs to the control means.

Reference numeral 3 is a control circuit as control means, which is C
It consists of PU, RAM and ROM. A host 4 is a personal computer, a workstation, or the like. The control circuit 3 receives print data such as a print text and a format from the host 4, processes the print data, and processes the LF (line feed) motor and CR (carriage) motor (not shown).
Also, control data for controlling the coils C1 to C9 is obtained, and these are controlled to perform the printing operation. In the standby mode, the coil driver 1 and the A / D converter 2 are controlled to check the individual temperatures of the coils C1 to C9.

Next, the operation of the present invention will be described with reference to FIGS.
This will be described with reference to the flowchart of FIG.

The control circuit 3 receives print data such as print text and format from the host 4 and starts control operation (STAR).
T). Print data such as print text and format can be read in the control circuit.
According to the control program read from the OM, it is processed as control data for the LF motor, the CR motor, the coils C1 to C9, etc. (step a). Following this data processing, the coil Cn (C1 to C9) and the transistor Trn
Of (Tr1 to Tr9), the coil 1 and the transistor 1 are designated (step b), and the temperature detection operation of the coil C1 is started (step d). That is, during this standby, the control circuit 3 outputs a control signal to the coil driver 1. The coil driver 1 receiving this receives the transistor T
r is turned on to supply a 5V sub power supply to the common power supply line L of the coils C1 to C9 via the resistor R and the inverter i, and Tr1 is turned on to supply power from the power supply line L to the coil C1. And drive this. This drive is such that printing is not performed. In synchronization with this driving, the A / D converter 2 detects the potential of the terminal AD, A / D converts it, and outputs it to the control circuit.

Here, the potential of AD is determined by the resistance of the coil C1, and the resistance of the coil C1 exhibits the above temperature characteristics. For example, at room temperature (20 °
C) is 9.7Ω, which is the heat-resistant limit temperature (180 ° C)
Shows 16.3Ω. In this way, detecting the potential of the terminal AD means detecting the temperature of the coil.

The control circuit which receives the output of the A / D converter 2 judges from the output value whether the temperature of the coil C1 exceeds the heat resistance limit temperature (step e).

If it is determined that the temperature is higher than the heat-resistant limit temperature, the operation up to this point is repeated from (step b), and the process waits until the coil temperature falls below the heat-resistant limit temperature.

If the coil temperature is below the heat-resistant limit temperature,
1 is added to n (step f), and n is obtained in (step c).
Is 9 or less, that is, it is confirmed that all the coils have not been checked, the coil driver 1 is controlled, the transistors Tr and Tr2 are turned on, power is supplied to the coil C2, and the terminal AD The electric potential is A / D converted by the A / D converter 2 (step d), and the temperature of the coil C2 is judged by the control circuit (step e). Repeat the operation.

In this way, by individually checking the coil temperatures of the coils C1 to C9, if any one of the coils has an abnormal temperature, the coil can be protected by waiting until the temperature drops to the normal temperature. It is possible.

When the coil temperatures of all the coils C1 to C9 are individually checked (step c), the LF motor, the CR motor, and the coils C1 to C9 are controlled according to the data processed in the above (step a) to perform the printing operation. Is started (step g). That is, the control circuit 3 outputs a signal for controlling printing to the coil driver 1. Upon receiving this, the coil driver 1 always operates the transistor T during the printing operation.
While turning on r0, the main power of 24 V is supplied to the common power supply line L of the coils C1 to C9, and the transistors Tr1 to Tr9 are selectively turned on to selectively drive the coils C1 to C9 from the power supply line L. Are supplied, and these are selectively driven to perform printing.

When the printing of one line as described above is completed and there is print data to be printed on the next line (step h), the operation of (step a) is performed again, even in this standby state (step b) The following operation is repeated to control the coil driver 1 to sequentially supply the coils C1 to C9 with the sub power of 5V through the resistor R and the inverter i.
In synchronization with this, the potential of the terminal AD is sequentially A / D converted, the temperature of each coil is checked by the control circuit, it is judged whether the coil temperature has reached the heat-resistant limit temperature, and if it is the heat-resistant limit temperature, standby The state is maintained, the next printing operation (step g) is suspended, the coil is cooled, and the coil is protected.

As described above, the control circuit 3 controls the coil driver 1 and the A / D converter 2 to check the temperature of each coil during standby during the printing operation of each line. It is possible to reliably detect heat generation, and it is possible to immediately protect the circuit according to heat generation of the coil.

In the above embodiment, the transistor Tr is turned on during standby, and the common power line L for the coils C1 to C9 is connected to the resistor R and the inverter i at 5V.
However, the same effect can be obtained even if the transistor Tr is not provided and the auxiliary power is always supplied to the power supply line L.

In the above embodiment, the number of printing elements is 9
However, the number is not limited to this, and the number may be further increased to increase the density.

In addition, according to the present invention, since the resistance value of each coil is judged by the control circuit, it is possible to detect a coil short circuit or the like by this potential, and the position of the coil is stored in the RAM in the control circuit. It may be stored and the coil may be cut off by the power supply.

According to the present invention, since the present apparatus is always operated below the heat-resistant limit temperature of the coil, the service life of the apparatus can be extended.

[0025]

According to the present invention, the detection means for detecting the temperature of the coil for driving the printing element is provided in the standby state, and the control means controls the drive of the coil according to the detection of the temperature of the coil. Even if some of the coils are abnormally heated, this can be reliably detected immediately and the print head can be protected. In addition, the coil drive can be controlled so as to be stopped until abnormal heat generation is no longer detected, and it is possible to reliably protect from heat generation.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a drive circuit of an impact printer according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing resistance-temperature characteristics of a printing element driving coil.

FIG. 3 is a flowchart for explaining the operation of FIG.

[Explanation of symbols]

 C1 to C9 Coil 2 Detection means 3 Control means

Claims (3)

[Claims] 1. An impact comprising a printing element drive coil, a detection means for detecting the temperature of the coil when the printing element is in a standby state, and a control means for receiving the output of the detection means and controlling the driving of the coil. Printer drive circuit. 2. The drive circuit for an impact printer according to claim 1, wherein the detection means detects the temperature of the coil from the resistance value of the coil. 3. The control means, when the detecting means detects an abnormal temperature exceeding a predetermined temperature range, drives the coil until the temperature detected by the detecting means falls within the predetermined temperature range. The apparatus according to claim 1, wherein the apparatus is stopped.
Drive circuit of the impact printer described.