JP2003291380A - Printer - Google Patents

Abstract

(57) Abstract: To detect a coil abnormality of a printer head wire drive solenoid by eliminating power loss of a drive circuit. SOLUTION: In a drive circuit for driving and controlling a printer head wire drive solenoid coil S1 by a transistor Q1, a coil short detection voltage A extracted from a preceding stage of a base current limiting resistor R1 of the transistor Q1 via a coil short detection resistor R2 is used. By clamping to the collector of the transistor Q1 with the clamp diode D1, the coil short detection voltage A in the abnormal state becomes higher than the normal state, and the state can be detected without wasting the power of the drive circuit. Become.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer capable of detecting an abnormal state due to a short circuit in a wire driving coil.

[0002]

2. Description of the Related Art Of a dot impact type printer head,
To detect an abnormal condition such as a coil short-circuit condition or a rare short-circuit condition caused by the burning of the wire drive solenoid coil, etc., generally insert a resistor R10 in the path of the drive current I10 shown in Fig. 3 and turn on the drive element Q10. And head drive power supply
A method is used in which a drive current I10 flowing from VDD to the solenoid coil S10 and the resistor R10 is monitored as a voltage value of the resistor R10, and an abnormal state is detected when a voltage exceeding a predetermined value is detected.

[0003]

However, the conventional method has a problem that the resistance inserted in the driving circuit causes a considerable loss of electric power. An object of the present invention is to solve the above problems and to provide an electronic circuit capable of detecting an abnormal state of a solenoid coil of a head without power loss.

[0004]

In order to solve the problems of the present invention, a drive means having a coil for driving a wire for dot formation, and a transistor for controlling the drive means according to an input control signal. In a printer comprising :, one end of a diode for clamping the voltage at the connection point is connected to a connection point between one end of the coil and one end of the transistor, and the other end of the diode is connected via a coil short detection resistor. Connect to the control signal line,
A voltage at a connection point where the other end of the diode is connected to the coil short detection resistor is detected as a coil short detection voltage, and an abnormality of the coil is detected based on the coil short detection voltage.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention is shown in FIG.
In FIG. 1, S1 is a coil of a wire driving solenoid, which functions as a driving unit for driving the dot forming wire. The coil S1 to which the drive voltage VDD is applied is on / off controlled by the transistor Q1 which is a solenoid coil drive element. The Head1 signal, which is a control signal, is low,
This is a high level binary signal. The line from the Head1 signal is connected to the base of the transistor Q1 via the current limiting resistor R1, and the coil short detection resistor R2 and one end of the diode at point B, which is the connection point between one end of the coil S1 and one end of the transistor Q1. It branches into a line that connects through.

The current limiting resistor R1 functions as a base current limiting resistor that limits the base current flowing in the transistor Q1, and the clamp diode D1 clamps the voltage at point B, which is the connection point between one end of the coil S1 and one end of the transistor Q1. Therefore, the voltage at the point A is set to a predetermined voltage as described later together with the voltage drop due to the coil short detection resistor R2. The positive input voltage of comparator CP1 is R
By dividing the resistance of 4 and R5, it is set to a value larger than the transistor Q1 collector saturation voltage Vce (sat) in the ON state and the forward voltage Vf of the clamp diode D1 when the solenoid coil is in the normal state (hereinafter, normal state). As an example, set the following values, VCC 5V, VDD 24V, Head1 low level 0V, high level 5V, clamp diode D1 forward voltage Vf 0.6V, transistor normal state collector saturation voltage Vce (sat) is 1.5V and the margin of the comparator is 0.5V.

In a normal state, when the Head1 signal is set to a high level (5V) and the transistor Q1 is turned on, the potential at the point B which is the collector voltage of the transistor Q1 becomes the collector saturation voltage Vce (sat) (1.5V). ing. The potential at the point A, which is the coil short-circuit detection voltage and is the negative input of the comparator CP1 in the subsequent stage, is clamped by the clamp diode D1 with the point B, and becomes the forward voltage Vf (2.1V) of the point B + the clamp diode D1. Don't The positive input potential, which is the threshold of the comparator CP1, is the voltage (2.6 V) set by the resistance division, and the negative input voltage (2.1
V) is lower than the threshold value, and the output of the comparator CP1 is inactive.

When the solenoid coil S1 becomes abnormal and the impedance becomes zero or close to zero, the potential at the point B rises to almost the same value as the drive circuit applied voltage VDD (24V). When the transistor Q1 is turned on in this state, the potential at the point B is so high that the potential at the point A is not clamped by the clamp diode D1 and becomes a voltage of Head1 high level (5V). Therefore, the negative side input voltage of comparator CP1 becomes Head1 high level (5V), and comparator C1
The Fault signal becomes active when the threshold of P1 is exceeded.

Next, another embodiment is shown in FIG. In FIG. 2, D11, D12, ... D1n are interference prevention diodes for coil short circuit detection voltage signals, and can collectively monitor coil short circuit detection signals of many head drive solenoid coils S1, S2 ,. This is what I did. In this case, the threshold voltage of the comparator CP1 made up of the dividing resistors R4 and R5 is set to a value obtained by subtracting the forward voltage Vf of the diodes D11, D12, ... D1n from the threshold voltage described in the above embodiment. To do. According to this embodiment, the coil short-circuit detection voltage output for each wire is connected to one signal line via the diode, and the coil abnormality is detected based on the signal detected from the one signal line. It can be detected.

[0010]

As described above, according to the present invention, the abnormality of the solenoid coil can be determined by monitoring the coil short-circuit detection voltage taken out from the portion other than the drive current path. It is possible to save power loss.

[Brief description of drawings]

FIG. 1 is an example of the present invention.

FIG. 2 is another embodiment of the present invention.

FIG. 3 is a conventional abnormality detection circuit.

[Explanation of symbols]

D1 Clamp diode Q1 Solenoid coil drive element R1 base current limiting resistor R2 coil short detection resistance S1 Wire drive solenoid coil

Claims (2)

[Claims] 1. A printer comprising: a drive unit having a coil for driving a dot forming wire; and a transistor for controlling the drive unit according to an input control signal, wherein one end of the coil and the transistor are provided. One end of a diode for clamping the voltage at the connection point is connected to a connection point with one end, the other end of the diode is connected to the control signal line through a coil short detection resistor, and the other end of the diode is connected. A printer that detects a voltage at a connection point where the coil short-circuit detection resistor is connected as a coil short-circuit detection voltage and detects a coil abnormality based on the coil short-circuit detection voltage. 2. The printer according to claim 1, wherein a plurality of coil short-circuit detection voltages output for each wire are
A printer characterized by being connected to one signal line via a diode and detecting an abnormality of a coil based on a signal detected from the one signal line.