JP3235465B2 - Printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer equipped with a drive coil print head, such as a wire dot printer, and more particularly to the prevention of drive coil burnout, the control of print head temperature, and technology. It is.

[0002]

2. Description of the Related Art In a conventional print head temperature detecting means by a partial pressure method, as shown in FIG.
Constitutes the voltage dividing circuit 12,
Is activated and a large current flows through the drive coil 11,
The circuit configuration is such that a reverse current prevention diode 36 is inserted between the head information detection unit 30 and the drive coil so that current does not flow into the head information detection unit 30.

[0003]

However, since the temperature detecting means based on the resistance voltage dividing method described above detects a subtle voltage change at the voltage dividing point 13, the temperature change of the forward voltage of the diode 36 cannot be neglected. Accurate temperature detection was not possible due to instrument error due to the influence of temperature change.

It is an object of the present invention to provide a print head temperature detecting means which is not affected by the ambient temperature and is based on a resistance partial pressure method.

[0005]

In order to solve the above-mentioned problems, a printer according to the present invention comprises a print head on which a drive coil for driving a wire for dot printing is mounted, and a print head having a drive coil for changing the resistance of the drive coil. A head information detection unit for detecting a rise in internal temperature of the print head, wherein the head information detection unit is connected to the drive coil, supplies a current for detection to the drive coil, and A backflow prevention diode for preventing a backflow of the drive current of the drive coil, a detection resistor connected to the drive coil via the backflow prevention diode so that the detection current passes, and a power supply for supplying the detection current wherein disposed between the sense resistor, and a compensation diode having a temperature characteristic similar to the backflow prevention diode, before
The voltage is detected between the detection resistor and the backflow prevention diode.
It is characterized by putting out .

According to the above configuration of the present invention, when viewed from a point downstream of the detection resistor (hereinafter, referred to as a voltage dividing point) which is a detection point, the same temperature characteristics are present on both the detection resistor side and the drive coil side. , The change in the forward voltage of the diode with respect to the change in the ambient temperature is cancelled. Therefore, it is possible to detect almost only the change in the resistance value of the head drive coil at the voltage dividing point.

[0007]

FIG. 1 shows the configuration of a control unit of a printer according to an embodiment of the present invention.

This printer has a dot wire driven by a drive coil 11 of a print head 10, and is a dot printer that performs printing in a dot matrix format using the dot wire. Then, by detecting a change in the resistance value of any one of the head coils 11 forming the dot matrix, the temperature state inside the print head 10 is determined.

The control unit of the present embodiment includes a printer control circuit unit 40
A head control unit 20 that applies a driving voltage for printing to the print head 10 based on a command (negative pulse) from the printer, detects the resistance value of the head coil 11 as a voltage drop at the voltage dividing point 13, And a head information detection unit 30 that performs A / D conversion and outputs a digital value AD.

The head control section 20 has a drive switch 21 for applying 24 V for driving the head coil 11 as a main component, and turns on the drive switch 21 in response to a control signal (negative pulse) from a printer control circuit 40. 24
V is applied to the print coil 11, and a dot wire (not shown) is driven by an electromagnet configured from the coil to perform dot printing.

A head information detecting section 30 for detecting the resistance value of the head coil 11 as a voltage drop is provided with a measuring circuit 32 based on a timing signal from the printer control circuit section 40.
And the head coil 11 to connect the reference resistor 3
7 and a head coil 11 to constitute a voltage dividing circuit 12,
A constant voltage supply circuit 31 for applying a constant voltage from the measuring circuit 32 to the voltage dividing circuit 12; a measuring circuit 32 for detecting a change in the resistance value of the head coil 11 as a voltage drop from the voltage dividing point 13 of the voltage dividing circuit 12; It is constituted by a conversion circuit 33 for performing analog-to-digital (A / D) conversion of the obtained voltage drop.

The constant voltage supply circuit 31 includes a connection switch 34 composed of an NPN transistor for connecting the head coil 11 and the measurement circuit 32, and a PNP for driving the connection switch 34 based on a timing signal from the control circuit 40.
It comprises a switch 35 composed of a transistor and a diode 36 for preventing a reverse current. The measuring circuit 32 is connected in series with the head coil 11 having a resistance value RH via a connection switch 34, and has a reference resistor 37 having a resistance value R1 to which a constant voltage of 5 V is applied, and a temperature compensation added by the present apparatus. And a transmission resistor 39 for transmitting a voltage generated at the voltage dividing point 13 on the connection switch 34 side of the reference resistor 37. Then, the voltage transmitted from the measurement circuit 32 to the conversion circuit 33 is converted into an 8-bit digital value AD and input to the control circuit 40.

As described above, in the present apparatus, the connection switch 34 of the constant voltage supply circuit 31 is turned on at the timing when the drive voltage (24 V) is not supplied to the head coil 11.
As a result, the head information detector 30 applies a constant voltage V0 (5 V) to the head coil 11 via the reverse current prevention diode 36, the reference resistor 37, and the diode 38 for temperature compensation. Then, the potential of the voltage dividing point 13 is detected as a divided voltage of the reference resistor 37 and the head coil 11 by the measuring circuit 32, and the temperature of the head coil 11 is directly detected by the head coil 1.
1 is detected as a change in voltage from the change in resistance value.

The voltage dividing point 1 detected by the measuring circuit 32
The voltage V of No. 3 can be expressed by the following equation.

[0015]

(Equation 1)

Here, RH is a resistance value of the head coil 11 and varies with temperature. R1 is the resistance value of the reference resistor 37, V1 is the forward voltage of the reverse current prevention diode 36, V2 is the forward voltage of the temperature compensating diode 38, and is ignored because the voltage drop of the connection switch 34 is small. I have.

Here, as the reference resistor 37, a resistor whose resistance value R1 is close to the resistance value RH of the head coil resistor 11 is used.
Reverse current prevention diode 36 is connected to temperature compensation diode 38
A material having the same temperature characteristics as described above is used. Then, as can be seen from the equation, even if the ambient temperature changes, both diodes 3
Since the temperature characteristics of the diodes 8 and 36 are similar, the forward voltages V1 and V2 of both diodes also change similarly. Therefore, the change values of the second and third terms of the equation almost cancel each other, and the voltage V detected by the measurement circuit 32 is not affected by the ambient temperature. As a result, the temperature of the print head can be detected without being affected by the change in the ambient temperature.

[0018]

As described above, according to the present invention, since the temperature detection of the print head by the resistance partial pressure method is an accurate temperature detection which is not affected by the ambient temperature, the temperature control of the print head (for example, When the print head temperature reaches the destruction limit temperature, printing is stopped, etc.), so it is not necessary to set the temperature with a margin considering the ambient temperature change.
Printing speed can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a control unit of a printer according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a control unit of a printer for detecting a print head temperature by a resistance voltage dividing method according to the related art.

[Explanation of symbols]

 Reference Signs List 10 print head 11 head coil 12 voltage dividing circuit 20 head control unit 21 drive switch 30 head information detection unit 31 constant voltage supply circuit 32 .. Measurement circuit 33 ... Conversion circuit 34 ... Connection switch 35 ... Control switch 36 ... Reverse current prevention diode 37 ... Reference resistor 38 ... Temperature compensation diode 39 ... Transmission Resistance 40 ・ ・ ・ Printer control circuit

Claims (1)

(57) [Claims] 1. A print head on which a drive coil for driving a wire for dot printing is mounted, and a head information detection unit for detecting a rise in the internal temperature of the print head substantially due to a change in the resistance value of the drive coil. A backflow prevention diode connected to the drive coil, supplying a detection current to the drive coil and preventing a backflow of the drive current of the drive coil; A detection resistor connected to the drive coil via the backflow prevention diode so that a current for use passes therethrough; and a power supply that supplies the detection current and the detection resistor, and the same as the backflow prevention diode. Ri Na and a compensating diode having a temperature characteristic, the voltage between the sense resistor and the blocking diode
A printer characterized by detecting .