US3316475A

US3316475A - Portable high-voltage generator device

Info

Publication number: US3316475A
Application number: US328079A
Authority: US
Inventors: Hayama Kaname; Sato Ichijiro
Original assignee: Asahi Chemical Industry Co Ltd
Current assignee: Asahi Kasei Corp; Asahi Chemical Industry Co Ltd
Priority date: 1963-07-03
Filing date: 1963-12-04
Publication date: 1967-04-25
Anticipated expiration: 1984-04-25
Also published as: GB1026789A

Description

P" 1967 KANAME HAYAMA ETAL 3,316,475

PORTABLE HIGH-VOLTAGE GENERATOR DEVICE Filed Dec.

United States Patent Ofifice 3,3 16,4 75 Patented Apr. 25, 1967 3,316,475 PORTABLE HIGH-VOLTAGE GENERATOR DEVICE Kaname Hayama, Fuji-shi, and Ichijiro Sato, Yokohama, Japan, assignors to Asahi Kasei Kogyo Kabus'hiki Kaisha, Usaka, Japan, a corporation of Japan Filed Dec. 4, 1963, Ser. No. 328,079 Claims priority, application Japan, July 3, 1963, 38/455,891 1 Claim. (Cl. 321-45) This invention relates to electric power units for use in the electro-flocking of fibrous material such as flock or granular material such as pulverized granite, vermiculite, marble, perlite or the like on the surface of building structures including walls, ceilings or of various boards, moldings and other objects and is concerned particularly with high-voltage generator devices of the portable type which are compact, lightweight and handy for use in the field.

In this field of industry, power units originally intended to serve electrostatic coating purposes have largely been employed but without any modification. Particularly in the field of electrostatic flocking, use has been made mostly of units which are bulky or of the stationary type.

The present invention includes the following improvements over units previously used.

l) The present unit is made compact, lightweight and portable with the interior structure designed to have an increased durability and protection against vibration by employing semiconductor type rectifiers such as selenium and silicon rectifiers.

(2) To obtain satisfactory results in the electrofiocking of fibrous or granular material, the voltage impressed can be varied with the type of material. For example, the jumping distance of granular material under a certain voltage depends upon the specific gravity of the material. Thus, the jump of particles of vermiculite, which has only a limited specific weight, will be larger than that of pulverized granite, marble or other stone higher in specific gravity under the same voltage. If the power unit providing an optimum voltage for pulverized stone having a higher specific gravity be employed without voltage reguation, for example, in the electro-fiocking of flock, the unit must be adjusted for the jumping distance each time the material is changed. In the case where the material to be electro-flocked is placed on a specially devised electrode, which is held by hand for operation, the jumping distance must be controlled manually. This requires skilled labor and involves scattering of the material and hence increased spillage thereof.

Some previous units have been equipped with a complicated device for voltage control employing vacuum tubes or a tapped transformer for stepwise voltage control. According to the present invention, the working voltage can be controlled in a continuous fashion and with ease between a maximum and a minimum value by means of a simple voltage regulator which enables the user to select a voltage suitable for the particular material and working procedure.

(3) With previous units, the ground capacity of the high-voltage generator circuit has generally been substantial so that even after the power source had been switched off, some electric charge has remained in the high voltage generator circuit or on the electrodes of the unit and had to be discharged through a separate grounding conductor to eliminate the danger to the operator of electric shock or spark discharge, the material being electro-flocked is replenished in the electrode, it has been necessary to disconnect the power source and to dissipate the remaining charge through the grounding conductor. To overcome this difiiculty, the present invention proposes to reduce the ground capacity of the highvoltage generator circuit by arranging high resistances in the rectifier circuit in parallel with the respective rectifiers, for example, of the silicon type. By this means, the ground capacity of the high-voltage generator circuit can be satisfactorily reduced without impairing the rectifying function of the rectifiers and without loss of output. In other words, according to the present invention, the replenishment of material can be performed immediately after the switch on the high-voltage output is opened or the voltage regulator is operated to reduce the output voltage to zero since the charge remaining in the highvoltage generator circuit or on the electrode is instantly dissipated. Thus, the present device can be operated with increased safety while saving labor and time.

(4) The high-voltage generator circuit used serves to rectify the high-frequency output, e.g. 10 to 20 kilocycles to obtain a direct-current high voltage, e.g. 10 to 60 kilovolts. The rectifier circuit for this purpose, includes a capacitor having a suitable capacitance of the order of 1,000 to 1,500 picofarads to form a desired magnitude of high-frequency ripple in the direct-current high voltage obtained. With this arrangement, the elec tro-flocking current can be conducted by virtue of the resistance to surface leakage and the stray capacitance of the object onto the surface of which the fibrous or granular material are being flocked even Where the object is made of cloth, wood, paper or other material having a substantial insulating strength. Therefore, according to the present invention, the previous inconvenience of employing a grounded electrode is completely eliminated making it easy to work, for example, walls, ceilings and other building surfaces. In addition, because of the high direct-current voltage output of the unit, even pulverized stone having a relatively high specific gravity, say, of 2.3 to 2.5 and a larger particle size, say, of 0.2 to 0.9 mm. can be easily caused to jump to be electr-o-flocked. As far as fibers and other materials having specific weights of 1 or less are concerned, high-frequency high-voltage generator devices or the like previously used have worked with substantial success. However, materials having higher specific weights of 1.0 to 2.6 have been electro-flocked exclusively on a direct-current high-voltage generator unit. The device of the present invention combines the features of the two forms of high-voltage generator units by including in the high-voltage output a high-frequency ripple in addition to the direct-current component thereof and thus can deal with a wide variety of materials irrespective of the specific weight thereof.

The present invention will now be described in further deail with reference to the accompanying drawing, in which:

FIG. 1 is a schematic illustration of an output voltage controlling circuit A and power supply rectifier circuit of one preferred embodiment of the invention; and

FIG. 2 schematically illustrates the high-frequency oscillation booster circuit B and a voltage doubling rectifier circuit C of the embodiment.

Referring to the drawing and particularly to FIG. 1, reference numeral 1 indicates a power source, and 2 a power source connecting and disconnecting switch. When the switch is closed, the full source voltage is impressed through a fuse 3 upon a transformer 7 producing a secondary voltage of a value as low as 6.3 v. The secondary voltage is impressed upon a pilot lamp 1-6 and a resistance 17 and also upon a circuit 18 to heat the filaments of oscillator tubes 21 and 21' arranged therein (FIG. 2). Another transformer 6 in the output voltage controlling circuit A is fed with a voltage adjusted through a voltage regulator 5 so that the secondary voltage of the transformer 6 can be freely adjusted by the regulator 5, for example, within a range of from zero to 450 v. This adjusted voltage is rectified by rectifiers 12 to form a direct-current voltage as indicated at 20 in FIGS. 1 and 2.

The output volt-age controlling circuit A is also provided with a switch 8 for changeover between the direct and the remote control of the unit. Reference numeral 9 indicates a switch for firect control and 11 a remote control switch connected with a plug to be received in a cooperating socket 10. A relay 13 is provided for operating switches 14 and 15 to open and close the directcurrent rectifier circuit and the pilot lamp circuit. a An ammeter 19 indicates the rectified current. Capacitors 4 are provided for noise prevention. The direct-current voltage 20 controlled by the circuit of FIG. 1 is applied to the respective screen grids of the vacuum tube oscillators 21 and 21 (FIG. 2) and to the respective anodes thereof through respective primary windings of two oscillator and booster transformers 22 and 23, each including a metallic oxide core.

The control grids of the oscillatoir tubes 21 and 21' start oscillation when their control grids are fed with an oscillation voltage from the winding 26 of the oscillator and booster transformer 23 and a bias voltage from a circuit including a resistor 25 and a capacitor 24. The oscillation voltage is raised by the oscillator and booster transformers 22 and 23 to produce a high-frequency high voltage, e.g. 10 to 20 kilocycles and 10 to 15 kilovolts. The output voltages of the oscillator and booster transformers 22 and 23 are directed to respective voltagedoubling rectifier circuits each including at least two rectifiers 27, for example, of the silicon type. The rectifier circuits are connected in series, as illustrated. One end of the series connection forms a grounding electrode, and the other end an output terminal of the voltagedoubling rectifier circuit C giving a high direct-current voltage, e.g. of 60 kilovolts. In this case, the direct-current voltage'fed to the anodes of the vacuum tube oscillators 21 and 21' through the oscillator and booster transformers 22 and 23 can be adjusted as desired by means of the voltage regulator 5 shown in FIG. 1. Thus, also adjustable are the high-frequency voltage as raised by the oscillator and booster transformers 22 and 23 and the high direct-current voltage, obtained at the output end 30. However, if the direct-current voltage fed to the anodes of the oscillator tubes 21 and 21' is excessively low, the oscillator tubes often tend to cease oscillation. In this way, the output voltage can be smoothly adjusted in a range upwards of 8 to 10 kilovolts. In this connection, the device of the present invention'aifords no problems, since in the practice of electrofiocking, a voltage of 10 kilovolts or over is generally employed.

A circuit heretofore frequently employed included a separately provided oscillator tube, an amplifier tube for amplifying the oscillating voltage output of the oscillator tube, and a booster wave transformer for raising the amplifier output. With this form of circuit, however, smooth and satisfactory oscillation is not obtained if the power supply voltage is reduced to approximately 85% or less of its normal value. Therefore, it is impossible to control the output voltage over any wide range by adjustment of the supply voltage.

According to the present invention, a stable high-voltage output can be obtained within a wide range even where the power supply voltage is adjusted by virtue of the fact that the voltage input to the control grid circuits of oscillator tubes 21 and 21' is directed from the oscillator coil 26 in the oscillator and booster transformer 23. Also, the filament circuits of the oscillator tubes 21 and 21' are energized with a predetermined supply voltage, independently from the control of the supply voltage to enable the oscillator tubes 21, 21' to maintain their function to oscillate in a stable manner.

As seen in FIG. 2, high value resistances 28, e.g. 100 to 200 megohms are connected in parallel with the respective rectifiers 27, provided for rectification of the high-frequency voltage. The rectifiers 27 can function satisfactorily when a current is fed thereto in the forward 7 direction since the resistance of the rectificrs to such current is extremely small compared with the resistance 28. In the use of this device, when the power supply is interrupted by means of switch 2, 9 or 11 in FIG. 1 or the voltage regulator 5 is set to zero to turn off the highvoltage output, some electric charge might be expected to remain on the output treminal 30 and the electrode connected therewith on account of the charges stored in the capacitors 29 of the high-voltage rectifier circuit of FIG. 2 and in the high-voltage cables and, electrodes connected to the terminal 30. In fact, however, such remaining charge is immediately grounded through the high resistances 28 when the power supply is interrupted.

When rectifiers 27 connected in parallel with high resistances 28, each take the form of a semiconductor rectifier, for example, a silicon rectifier, which has a considerably but not infinitely high resistance to the current in the reverse direction, this resistance and the associatedhigh resistance 28 produce only a reduced resultant resistance because of their parallel connection, allowing any remaining charge to be dissipated still more quickly.

Heretofore, electric shock and other unexpected troubles have' been accounted for largely by the carelessness of the operator, who forgets the remaining charge on the unit after he has once opened the power switch upon completion of the electro-flocking operation.

In this connection, it will be apparent that the present device is operable with increased safety since any remaining charge is completely and quickly discharged, as described hereinabove. Also, where a high resistance 31, e.g. 50 to 200 megohms is connected at the output end 30 for the purpose of further ensuring the safety during charging operation, onlya slight spark discharge will take place even if the electrode connected to the terminal 30 is inadvertently grounded during charging. This is partly accounted for by the reduced ground capacity of the high-voltage rectifier circuit.

The capacitors 29 in the high-voltage rectifier circuit in FIG. 2 have a capacitance of from 1,000 to 1,500 picofarads to impart ahigh-frequency ripple to the rectified direct-current voltage for the purpose of combining the features of the eletcro-flocking process employing a pure direct-current voltage and one employing a high-frequency high voltage thereby to extend the range of application of the unit. Also, as described hereinbefore, the high-voltage rectifier circuit used in the present device is of the full-wave voltage-doubling rectification type, which has an ample output, for the purpose of facilitating the electro-flocking of pulverized stone or other granular material having a comparatively high specific gravity.

What is claimed is;

A portable high voltage generator device suitable for use in combination with an electro-flocking device for electro-flocking a fibrous or granular material onto the surface of an object, said generator comprising a output voltage controlling circuit including a transformer, a power source, a voltage regulator connected between said power source and the primary winding of said transformer, and rectifiers connected between the secondary winding of said transformer and the output of the said circuit to provide a rectified output voltage of adjustable magnitude, and means for switching said output voltage on and off; a high frequency oscillator and booster circuit including at least two oscillator tubes, at least two oscillator and booster transformers each having a metallic oxide magnetic core, a resistor and capacitor connected in parallel and to ground, an oscillator coil coupled to one of the latter transformers and having one end connected to the control grids of the oscillator tubes and the other end grounded through said resistor'and capacitor, the output of the output voltage controlling circuit being connected to the screen grids of the oscillator tubes and to the anodes thereof through the primary windings of the respective oscillator and booster transformers whereby the second- 5 ary windings of these transformers provide high frequency References Cited by the Examiner oscillating voltages of a magnitude dependent upon the UNITED STATES PATENTS output voltage of the output voltage controlling clrcutt; and a voltage doubling circuit connected to the last-men- 3,118,103 1/1964 Mandoh et 321 15 tioned secondary windings and including at least two semi- 5 312431683 3/1966 Ackley 321 15 conductor rectifiers through which any residual charges at the high voltage output of the device are dissipated JOHN COUCH Pnmary Exammer' upon switching 01f the output voltage controlling circuit. M. L. WACHTELL, Assistant Examiner.