JPH0126459Y2 - - Google Patents

Description

[Detailed Description of the Invention] (A) Technical Field of the Invention The present invention relates to a printing device drive circuit used in impact-type line printers and the like.

(B) Conventional technology and problems For example, in an impact-type line printer using a printing belt, the normal
It is equipped with 136 printing hammers, which are selected and activated at appropriate times to collide with a type belt that runs endlessly in the direction of the print line, via the recording medium, thereby printing. The printing hammer is electromagnetically actuated by current flowing through the coils, but the time period during which the current is passed through each coil is very short and precisely controlled.

In such devices, in order to prevent malfunctions in the printing device, such as current flowing through the coil for a long period of time exceeding a predetermined time and damaging the coil, the malfunction of the printing device is detected and the coil is A switch is provided to cut off the flowing current.

Such a switch is equipped with a spark extinguisher to prevent the generation of sparks when the current is cut off. However, the spark quencher is quite large in size, which is one of the obstacles to downsizing the printing device.

(C) Purpose of the invention The purpose of the invention is to obtain a printing device that does not require the spark quencher in the conventional example.

(D) Structure of the invention The printing device drive circuit according to the invention includes a switch that detects a malfunction of the printing device and cuts off the power supply to the coil described below, a coil that operates the printing hammer by electromagnetic action, and a coil that operates the printing hammer by electromagnetic action. A drive transistor that turns on/off the current flowing through the coil in accordance with the print signal, and a drive transistor protection that prevents the drive transistor from malfunctioning or being damaged due to transient power fluctuations when the printing device is turned on or off. and a switch protection circuit for activating the drive transistor protection circuit prior to shutting off the switch.

(E) Embodiments of the invention Next, the gist of the invention will be specifically explained with reference to illustrated embodiments.

The figure is a configuration diagram of one embodiment of the present invention, in which 1 is a switch that detects a malfunction of the printing device and cuts off the power supply A to the coil described later, 2 is a coil that operates a printing hammer by electromagnetic action, and 3 4 is a driving transistor that turns on/off the current flowing through the coil 2 in accordance with a control signal supplied from a printing control circuit described later, and 4 is a driving transistor that applies a control signal to the base of the driving transistor 3 in response to a printing signal B to control printing. 5 is a diode for preventing mutual interference; 6 is a printing control circuit that supplies current to the coil 2 when the base voltage of the driving transistor 3 is unstable due to transient power fluctuations when the printing device is turned on or off; 61 is a protection transistor, 62 is a protection transistor drive circuit, and 7 is a switch 1 cutoff circuit. 71 is an OR circuit, and 72 is a delay circuit. Further, C indicates a malfunction detection signal for detecting a malfunction of the printing apparatus, and D indicates a clear signal for activating the drive transistor protection circuit 6. In addition, the coil 2, the driving transistor 3, the printing control circuit 4
and diode 5 for example 136 per printing hammer.
A set is provided.

With the above configuration, when the printing device is powered on and off, the clear signal D is applied to the protection transistor drive circuit 62 via the OR circuit 71, the protection transistor 61 is activated, and the drive transistor 3 is activated. The base current of the coil 2 is cut off, and the current flowing through the coil 2 is turned off.

Furthermore, when a malfunction occurs in the printing device, the protection transistor 61 is activated in the same way as described above, and the current flowing through the coil 2 is turned off, and the malfunction detection signal C is supplied to the switch 1 via the delay circuit 72. The switch 1 is disconnected a predetermined time after the malfunction detection signal C is issued. At this time, the current flowing through the normally operating coil 2 is already turned off, so that almost no spark is generated in the switch 1 even if a spark quencher is not provided.

(F) Effects of the invention As explained above, according to the invention, the contacts of the switch can be protected without using a spark quencher.

[Brief explanation of drawings]

The figure shows a configuration diagram of an embodiment of the present invention, where 1 is a switch, 2 is a coil, 3 is a driving transistor, and 6 is a block diagram of an embodiment of the present invention.
7 is a drive transistor protection circuit, and 7 is a switch protection circuit.

Claims (1)

[Scope of utility model registration request] A switch that detects a malfunction in the printing device and cuts off the power supply to the coil described below, a coil that operates the printing hammer by electromagnetic action, and a drive that turns on/off the current flowing through the coil according to the printing signal. a transistor, a driving transistor protection circuit that prevents the driving transistor from malfunctioning and damage due to transient power fluctuations when the power of the printing device is turned on or off, and a driving transistor protection circuit that prevents the driving transistor from malfunctioning or being damaged prior to turning off the switch. A printing device drive circuit comprising: a switch protection circuit that operates a switch protection circuit.