US2391086A

US2391086A - Radio frequency motor control

Info

Publication number: US2391086A
Application number: US512911A
Authority: US
Inventors: Ervin L Crandell
Original assignee: Compo Shoe Machinery Corp
Current assignee: Compo Shoe Machinery Corp
Priority date: 1943-12-04
Filing date: 1943-12-04
Publication date: 1945-12-18
Anticipated expiration: 1962-12-18

Description

Dec. 18, 1945. E. L. CRANDELL 2,391,086

RADIO FREQUENCY MOTOR CONTROL Filed Dec. 4, 1945 SDLENDID @oteuted Bee. 18 i945 tits Comps Shoe Machinery tjorporatiou, Boston, Mass, a corporation of Delaware Application llecemher l, 1933, Serial No. 512ml ((7 1. El t e?) 2 Claims.

invention relates to apparatus utilizing high frequency electrostatic energy for generat= irig heat in materials advanced therethrough and relates more particularly to controls for regulat= ing the speed at which materials are advanced through such apparatus.

My U. 5. Patent No. 2,32%,668 which issued July 13, 1943, discloses bonding apparatus utilizing cctrostatic energy from a vacuum tube oscillator for the generation or" heat for hondiug piles of material together. In such apparatus, t" e amount of heat generated in the material heiug heated is directly proportional to the dielectric loss of the material. Changes in the dielectric loss in the material being heated may ice caused by changes in the density, moisture content, thickness or other physical or chemical characistics of the material and these changes may resuit in some portions of the material being over-- heated and other portions being uoderheatecl if the material is advanced at a constant rate through the electrostatic field.

This invention compensates for changes in the dielectric loss oi material being advanced through an electrostatic field by varying the speed of ao'ivauce of the material through the field in accordance with chan es in the dielectric loss of the material, whereby material having higher trio losses is exposed for a smaller t he to the electrostatic field and. material having lower iiielectric losses has longer exposure.

An object of the invention is to improve the quality the bond or" material receiving in an electrostatic field by varying the time of exposure of the material to the field in accordance with the dielectric loss of the material.

The invention will now he described with reference to the drawing, of which:

Fig. 1 illustrates diagrammatically the electric circuit connections to the driving motor and electrodes of a roller type bonding press embodying this invention, and

Fig. 2 is a diagrammatic view of another embodiment of a control circuit which may be used with the bonding press of Fig. 1.

With reference first to Fig. l, the base 5 of the press has mounted thereon the four upright supports 6. The metal bars l are attached to the lower ends or the supports t, and have joumalled therein the bearings 8 which support the cylin drical, metal roller 9.

The Years it of electric insulating material are slidably positioned along the supports '5. The springs H have their upper ends attached by the clamps I? to the upper ends of the supports 6 and are attached at their lower ends to t e insulating bare it and serve to support the bars it on the supports t while at the same time, they bias the bars it towards the lower "cars l.

The bearings i of the cylindrical, metal -oller it are jourualled in the bar iii. The springs ll thus act to force the rollers and 1163 together for exerting pressure on the work to he oouded as will be described.

The lower roller is rotated through the pulley and belt by the pulley 2 9 of the electric motor and acts to move work piece therethrough.

Th wori: piece illustrated comprises tw leather with an adhesive thei'ebet ecu.

plies The roller is connected through its bearing i3 and shaft to the electric couciuc'or is connected to the tool: coil o thvacuum tube oscillator The metal her i is connected by the electri conductor it to the center of the tank coil and to ground.

The tank coil is connected at oueehd through the coupling condenser 25 to the anode 26 of the tube 2t and through the radio fro cueucy choke it to the positive side of a suitable high voltage direct cu 'eht supply. The other end of the coil 23 is connected through the grid leak shunted by condenser to the grid of the tube 25. The midpoint Of the coil is connected to the cathode of the. tube and to the negative side of the direct cu; a source.

The oscillator circuit described th going is a conventional one and may t as is Well known those skilled ill the art to a high. frequency which may, for example, he megacycles, for establishing an electrostatic field between therollers 9 and M which act as electrodes.

The electric motor it which advances the work piece through the electrostatic field, is energized by direct current from the vacuum tube rectifier lhe anode of the rectifier is connected to one end or" the secondary 3:3 of the transformer The other end of the secondary 3 1 is con-- nected by the conductor 2% to one supply terminal oi the electric motor 2i, and to ground.

The primary 3t of the transformer is connested by the conductors 3t and lit to a suitable source of alternating current which may be vol 60 cycle.

The primary fit of the filament transformer ti is connected in parallel with the primary 3? of the transformer 35. The secondary 42 of the 61 bypasses radio frequency currents around the 4 motor 2|. The motor thus receives direct current from the rectifier 32.

The grid 46 of the rectifier is connected by the conductor 48 and the coupling condenser 49 to the tank coil 23 and receives high frequency alternating current therefrom.

In operation, as the motor 2| advances the work piece 22 through the electrostatic field between the roller electrodes 9 and Id, changes in the dielectric loss in the work piece cause changes in the high frequency voltage at the tank coil 23. Increases'in the dielectric lossin the work piece will cause reduced high frequency voltages and decreases in the dielectric loss will cause increases in the high frequency voltages.

The high frequency alternating currents applied through the conductor 48 and coupling condenser 49 to the grid 48 of the rectifier 32 are rectified and provide voltage drops in the radio frequency choke 45 and the resistor 46 which vary with changes in the voltage of the high frequency current. These voltage drops bias the grid 46 of the rectifier 32 negative. Increases in the grid bia of the rectifier 32 cause corresponding decreases in the direct current voltage delivered by it to the motor 2| and decreases in the grid bias cause correspondin increases in the direct current voltage delivered to the motor 2|.

The speed of the motor 2| varies in accordance with the voltage of the current delivered to it by the rectifier 32 so that when the dielectric loss in the Work piece 22 increases, the motor 2| automatically speeds up so that the work piece has a shorter exposure to the electrostatic field, and when the dielectric loss decreases, the motor 2| automatically slow down so that the work piece is exposed a longer time to the electrostatic field. Thus regardless of changes in the dielectric loss of the material being bonded, the heat produced therein is that which is desired.

With reference to Fig. 2, the rectifier 32 instead of supplying the energizing current to the tact arm 53 and the armature The contact arm 53 is attached to one end of the plunger 56 of the solenoid 55. The plunger 56 has mounted thereon the bias spring 55 which tends to restore the armature 5%, when retracted, to unretracted position.

asonose The energizing winding of the solenoid 55 receives through the conductors 36 and 51, energizing current from the rectifier 32, which is connected and operated as described in the foregoing except that its output current is supplied to the solenoid 55 instead of the motor 2|.

An increase in the voltage of the current supplied by the rectifier 32 to the solenoid 55 and caused as described, by a decrease in the dielectric loss in thework being bonded, causes the solenoid 55 to retract further its plunger 54.

This causes the contact arm 53 to move along the resistor 52 and to decrease the resistance in series with the motor field winding 5| and causes the motor 2| to slow down. A decrease in the voltage of the current supplied by the rectifier to the solenoid, caused by an increase in the dielectric loss in the work being bonded, causes the field strength of the solenoid to be less so that the spring 56 moves the plunger 54 towards unretracted position, which in turn moves the contact arm 53 to place more resistance in series with the motor field winding 5| causing the motor to speed up.

While the work piece being bonded has been illustrated as a continuous ply of leather with adhesive therebetween, the material being bonded may be plastics not requiring adhesives and may be advanced as separate items as on a conveyor.

While embodiments of the invention have been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangements of apparatus illustrated as modifications thereof may be suggested by those skilled in the art without departure from the essence of the invention.

What is claimed is:

1. Heating apparatus COmPIlSlI'Ig means including a vacuum tube oscillator for generating alternating current, means including said oscillator for establishing an electrostatic field, means for advancin material to be heated through said field, a rectifier, means for supplying alternating current from said oscillator to said rectifier for rectification, and means including means utilizing rectified current from said rectifier for adjusting the rate of advance of said advancing means.

2. Heating apparatus comprising means including a vacuum tube oscillator for generating alternating currents, means including said oscillator for establishing an electrostatic field, means including an electric motor for advancing material to be heated through said field, a vacuum tube rectifier, means including said rectifier for supplyin rectified alternating current to said motor for energizing same, and means responsive to variations in the alternating current voltage from said oscillator for varying .the impedance of said rectifier for varying the voltage of the current delivered thereby to said motor.

ERVIN L. CRANDELL.