Electric connection for exciting the spraying nozzle magnetic coils

(54) Electrical connections for driving the magnetic coils of the spray nozzles

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an electrical circuit for driving magnetic coils of spray nozzles of a machine for applying paint to a flat material, in particular a sheet material.

The prerequisite for successful printing of flat material without the use of a template is the necessity to bring the spray nozzle as close as possible to the material and to control the spray nozzles quickly and accurately.

There are known nozzles that meet the requirements for printing material without templates, for example from Czechoslovakia. No. 212,210, the actuating needle of which is mounted on an annular coil located in the magnetic field of the permanent magnet and excited by suitable current signals that cause the coil to move with the needle and thereby open and close the nozzle. Various electrical connections are known for actuating coils in the field of permanent magnets or electromagnets, but which have a number of electrical and mechanical drawbacks, and do not allow the operation of spray nozzles with a repetition rate of 2,000 to 3,000 Hz which is necessary for sharp printing without material templates and for creating halftones. The mechanical aspect of these problems was solved by the construction of the spray nozzle of the material printing machine according to US. No. 212,210. The proper functioning of these spray nozzles, however, requires electrical wiring to rapidly drive the magnetic coils of the spray nozzles at the repetition rate.

These drawbacks of the known spray nozzles and their electrical connections are eliminated by the electrical connection for driving the magnetic coils of the spray nozzles of the ink jet coating machine, in particular the sheet material according to the invention, characterized in that the first magnetic coil outlet is connected via a first power transistor. to a first voltage source and through a first diode to a second voltage source, wherein the second magnetic coil terminal is upstream of the second power, the transistor is coupled to ground, and the base of the power transistors are connected to the pulse source via switching transistors.

Preferably, the emitter of the second power transistor is coupled to ground through a first resistor and the magnetic coil and the first power transistor are bridged by a series combination of a second resistor and a second diode connected in an impermeable direction.

The power transistor bases are connected to the collectors of the switching transistors whose emitters are grounded and whose bases are connected to a pulse source.

The pulse source comprises a monostable flip-flop to which a delay capacitor and an adjusting resistor are connected, the base of the first switching transistor being connected to the output of the monostable flip-flop and the base of the second switching transistor connected to the output of the first Schmitt flip-flop Schmitt's flip-flop is connected to the monostable flip-flop input.

Also advantageous is an embodiment in which an inverting input of an operational amplifier is connected between the emitter of the raw power transistor and the first resistor, the output of which is connected to the base of the first switching transistor via a separating diode.

A novel and superior effect of the invention is that it allows opening and closing of the nozzles for material printing without the use of a template at a repetition rate of 2,000 to 3,000 Hz, which makes it possible to produce complex yet sharp color patterns on the printed material.

The invention will now be described by way of example with reference to the drawing, in which: FIG.

The magnetic coil 201 is connected between the two power transistors 202. 203. The first power transistor 202 supplies voltage to the magnetic coil 201 for a short time, for example 70 V from the first voltage source 230. The second power transistor 203, whose emitter is coupled to ground through a first low resistance resistor 204, must also be in a conductive state.

The first power transistor 202 needs to be in a conductive state for only a short time, for example about 0.5 ms, during which current flowing through the magnetic coil 201 rapidly increases.

After closing the first power transistor 202, the magnetic coil 201 is then connected via a first diode 205 to a voltage +87 from a second voltage source 231. This voltage is sufficient for the holding current to pass through the magnetic coil 201 when the second power transistor 203 is in a conductive state. Once the second power transistor 203 is closed, the current flowing through the magnetic coil 201 should cease as fast as possible.

Therefore, the magnetic coil terminal 201 connected to the collector of the second power transistor 203 is connected to the first voltage source 230 before the second resistor 206 and the second diode 207.

This achieves that the energy stored in the magnetic coil 201 returns to the first voltage source 230 so that the energy stored in the magnetic coil 201 is not converted to heat, which would represent a significant thermal load on the switching circuits, but is returned to the first Power supply 23ft The control of both power transistors 203, 202 is performed as follows:

The rectangular signal after which the magnetic coil 201 is to be energized is applied to the wiring terminal 208. This signal, passing through the third resistor 209, excites the emission diode 210 of the optic-electric relay 211. The phototransistor 212 of the optic-electric relay 211 shorts the input 213 of the Schmitt flip-flop 214 to ground for the duration of the pulse. At this time, the output 215 of the Schmitt flip-flop 21.4 is a signal that roughly corresponds to the ground potential. This signal is transmitted to two different lines. The signal is supplied on the basis of 216 of the second switching transistor 217, which consequently closes, so that the voltage on its collector rises and the connected second power transistor 203 opens.

The signal from the output 215 of the Schmitt flip-flop 214 is simultaneously fed to the second Schmitt flip-flop 218. whose output signal is inverted at output 228 and fed to the monostable flip-flop 220 input 221 of the monostable flip-flop 220 output. The first switching transistor 224 is opened for the duration of the needle pulse duration. which opens the first power transistor 202 so that the magnetic coil 201 connects to the first voltage source 230. At the end of the needle pulse, the first abutment power transistor 202 is closed, so that the magnetic coil 201 again has a voltage of 8 V via the first diode 205.

In order to prevent the monostable flip-flop eventually from starting multiple times and thus from dirty circuits, current through the magnetic coil 201 is measured and limited. When the monostable flip-flop 220 is started multiple times, the first power transistor 202 may be opened for an unacceptably long time. means that the flow through the magnetic coil 201 and naturally also through the power transistors 202, 203 increases steadily.

For this reason, the voltage drop across the first low resistance resistor 204 is measured, for example

14,2 nOhm. Voltage is applied to the inverting input of an operational amplifier 225 connected as a Schmitt flip-flop that closes the first power transistor 202 when the power transistor 202 is opened too long. If at the first resistor 204 the voltage exceeds the allowable limit, the voltage at the output 226 of the operational amplifier 225 drops to a low value. This voltage is applied via the decoupling diode 227 on the basis of the first switching transistor 224 which is closed, thereby causing the first power transistor 202 to close.