US3689904A

US3689904A - Demagnetizing circuit

Info

Publication number: US3689904A
Application number: US876637A
Authority: US
Inventors: Frank H Blitchington Jr
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1969-11-10
Filing date: 1969-11-10
Publication date: 1972-09-05
Anticipated expiration: 1989-09-05
Also published as: CA929661A

Abstract

A circuit for selectively producing magnetized areas on a sheetlike magnetizable material utilizing a plurality of magnetic heads adjacent to the magnetizable material. A DC current is first passed through the coils in the heads and then a decreasing AC current is passed through selected coils. The decreasing AC current is produced by a radiant energy controlled resistance in series with the selected coils. A lamp controlled by an RC circuit illuminates the radiant energy controlled resistance to produce the decreasing AC current.

Description

United States Patent Blitchington, Jr.

1451 Sept. 5, 1972 541 DEMAGNETIZING CIRCUIT 72 Inventor: Frank 11. Blitchington, Jr., Greensboro, NC.

[73] Assignee: Western Electric Company, Incorporated, New York, NY.

[22] Filed: Nov. 10, 1969 [21] Appl. No.: 876,637

[52] US. Cl. ..340/l74.l R, 179/1002 D, 315/8, 335/284 [51] Int. Cl ..H0lj 29/06 [58] Field of Search ..307/3l1, 312; 179/1002 D; 340/174.1 D, 174.1 G; 317/1575; 335/284;

[56] References Cited UNITED STATES PATENTS 3,218,396 11/1965 Mllllin; ..179/1o0.2 K 3,218,620 11/1965 Clunis ..340/ 1.74.1 D

3,346,703 10/1967 Mullil'l er a1 ..179/1oo.2 K 3,450,933 6/1969 Hayden et a1 ..315/s 2,743,492 5/1956 Easton ..335/2s4 Primary Examiner-Maynard R. Wilbur Assistant Examiner-Jeremiah Glassman AttorneyW. M. Kain, R. P. Miller and B. l. Levine [57] ABSTRACT v A circuit for selectively producing magnetized areas on a sheet-like magnetizable material utilizing a plurality of magnetic heads adjacent to the magnetizable material. A DC current is first passed through the coils in the heads and then a decreasing AC current is passed through selected coils. The decreasing AC current is produced by a radiant energy controlled resistance in series with the selected coils. A lamp controlled by an RC circuit illuminates the radiant energy controlled resistance to produce the decreasing AC current.

6 Claims, 5 Drawing Figures PATENTEDsEP 5:912

SHEET 2 BF 3 r w 5 M PATENTEDSEP m? 3.689.904

SHEEI 3 OF 3 1 DEMAGNETIZING cmcurr BACKGROUND OF THE INVENTION There are many prior art circuits for changing the magnetic state 'of a permanent magnetic object or material. Generally, 'a DC current applied through a coil in close proximity to the object creates a magnetic field which magnetizes the object in a selected direction An object is'dema'gnetized by applying a decreasing alternating magnetic field to the object. The decreasing magnetic field in the prior art has been produced by supplying a decreasing current to a coil by means of a manual or motor driven potentiometer or variable transformer. Such mechanical devices are unduly cumbersome and slow in operation.

SUMMARYIOF THE INVENTION magnetic object which produces a decreasing magneticfield to demagnetize the object. A radiant energy emission device which is energized by a decreasing current controlsrthe radiant energy controlled resistance to produce a decreasing alternating current iii the coil to demagnetize the magnetic object.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.- 1 shows a magnetic card whichv is to be selectively magnetized in certain areas;

FIG. 2 shows a punched card placed on a reading device which controls the selective magnetization of the magnetic card shown in FIG. 1;

FIGS. 3 and 4 compose a diagram of a circuit embodying the principlesof the present invention. FIG. 3 contains the left-hand side of the circuit, while FIG. 4 contains the right-hand side of the circuit. The total circuit may be reconstructed by placing FIGS. 3 and 4 side memory device side; and t FIG. 5 shows the operating times of various parts of the circuit shown in FIGS. 3 and 4.

DETAILED DESCRIPTION Referring first to FIG. 1, there is shown a magnetic card, 10 made of a sheet of aluminum'with a plurality of permanent magnetic objectsor elements 11-11, such as or 65 VICALLOY, embedded therein. The magnetic cards 10 are used in a magnetic device, such as is described in U.S. Pat. No. 3,163,855, issued on Dec. 29, 1964 to A. H. Bobeck. The magnetic objects l1- 11 are selectively magnetized or demagnetized to store or represent permanent information in the magnetic memoryto control the operation of an electronic telephone system. A plurality of writing or erasing heads 12-12 mounted on a suitable indexing carriage (not shown) over the card 10 are utilized to magnetize and selectively demagnetize the objects 11-11. It has been found that magnetizing allthe objects ll-l1 in a i preferred direction and selectively demagnetizing produces fewer errors than demagnetizing all the elements 11-11 and selectively magnetizing. The AC magnetic field used to selectively demagnetize affects adjacent objectsl'ess than the DC magnetic field.

' Referring now to'FIGS. 3 and 4, there isshow'n an electrical circuit for selectively energizing the heads 12-12 to produce the desired magnetization'on the card 10. FIG. 5 shows the operating times of various components Of FIGS. 3 and 4 during one cycle of operation. One cycle of operation is divided into two halves, the first half labeled magnetize and the second half labeled demagnetize.

Referring back to FIGS. 3 and 4, there is shown a I plurality of coils 31-38 each of which is associated with one of the heads 12-- 12 of the magnetic recording device. Contact arms 39-39 of a relay 40 engage normally open contacts 27-27 to connect a first group of coils 31-34 all in series with resistors 28-28 when the relay 40 is not actuated. When the relay 40 is actuated, the contact 'arms 39-39 engage normally open contacts 29--29 to connect the second group of coils 3538 in series with the resistors 28-28. Referring now to FIG. 5, the first half or magnetizing portion of one cycle'is divided into a first portion or one-fourth cycle labeled 31-34 and asecond portion or second one-fourth cycle labeled 35-38. Also the second half or demagnetize portion is divided into a third one-fourth cycle labeled 31-34 and a fourth one-fourth cycle labeled 35-38. Dividing the coils 31-38 into two groups and switching between the two groups reduces the amount of circuitry. I

Alternating current is applied through a power plug 13 to.a transformer 14 and a full wave rectifier 16. The output of the full wave rectifier 16 on lines 17 and 18 is controlled by a voltage regulator 19 to produce a +30 volt potential on line 17 and a l5 volt potential on line 18. Lines 17and 18 are connected to relays 21-26 which control the sequence of operation of the circuit.

Referring to FIG. 2, there is shown a punched card 111 in a reading device 112. The presence of a properly oriented card 111 must be sensed by two photocells 107 and '109 to actuate a relay (FIG. 3) before a cycle of operation may be initiated. A transistor 108 in series with the winding of relay75 connected by a resistor to line 17 must be operated by the photocell 109 located beneath the cutoff comer of the card 111. Also, a transistor 106 in parallel with the winding of the relay 75 must remain unoperated by the photocell 107 beneath a non-cutoff corner of the card 111. A pair of lamps and 131 connected between lines 17 and 18 provide illumination for the

photocells

107 and 109. Operation of relay 75 closes normally open contacts 74. If the card 111 is not oriented as shown in FIG. 2, the relay will not be actuated.

After the plug 13 is connected to a power source and before a cycle of operation has been initiated, a lamp 101 is illuminated by current through a contact arm 102, a normally closed contact 103 of the relay 21 and a normally closed contact 104 and a contact arm 73 of with a normally closed contact 94, acontact arm 93,

the winding'of relay 26 and contacts 74 to line 17. Actuation of the relay 26 connects the contact arm 93 to a normally open contact 95 which is connected to ground throughout most of the cycle of operation by a normally closed contact, 96 and a contact arm 97 of the relay 25, a normally closed contact 98 and a contact arm 99 of.relay 21, or a normally closed contact 100 and a contact arm 66 of relay 23. One of the

relays

21, 23 or 25 is unactuated during the cycle to maintain the relay 26 actuated until the end of the cycle at which time the

relays

21, 23 and 25 are all actuated to deactuate the relay 26, as shown in FIG. 5.

- Actuation of the relay 26 engages the contact arm 73 with the contact 72 to connect contact 72 to line 17 through the contacts 74. Much'of the circuitry is connected to contact 72 and it should be remembered that contact 72 supplies a voltage of +30 volts until near the end of the cycle of operation. I

A primary winding of a transformer 51 is connected in series with a pairof parallel connected radiant energy

sensitive resistors

52 and 53 across the power plug 13. A suitable type of radiant energy sensitive resistor is LDR-25 power photocells sold by Delco Radio, Box 1018, Chestnut Station, Union, N.J., or type SLD4L photoconduc tive cells sold by Clairex Corporation, 1239 Broadway, New York, N.Y. A secondary winding of the transformer 51 is connected through normally open contacts 54 of a relay 55 to a first of the contact arms 39-39. The radiant energy

sensitive resistors

52 and 53 are energized by alamp 77 in a light-tight enclosure 90 which is controlled by -a transistor 78 which has its emitter and collector connected betweenthe lamp 77 and the contact 72. A capacitor 80 and resistor 81 are connected in parallel from the base of the transistor 78 to ground. Current is applied to the base of the through resistor 82 and 'diode 83. The capacitor 80 then discharges through the resistor 81 and the based the transistor 78. The parameters of the lamp 77, the

transistor 78, the capacitor 80, the resistor 81 and the resistor 82 are selected to cause the lamp to become slowly illuminated during the unactuated time of the relay 21 and to become slowly dark during the actuated time of the relafll. Thus, as shown in FIG. 5, the current

throughthe radiation'sensitive resistors

52 and 53 slowly increases during each unactuated time of. relay 21 while the current through the radiation

sensitive resistors

52 and 53 slowly decreases during each actuated time of relay 21. The parameters of the

resistors

81 and 82, the capacitor 80 and the transistor 78 may be selected to give any desired change in currentthrough the radiation

sensitive resistors

52 and 53. For example, the current may be varied linearly, as shown in FIG. 5, or it may be varied exponentially.

The card reader 112 contains a plurality of photocells 114-123 for, reading the information punched in the 'card 111. A suitable typeof photocell for use with the

photocells

107, 109 and 114-123 is silicon readout cell SSR sold by Solar Systems Inc. of

8241 Kimball Avenue, Skokie, Ill. The magnetic card writer herein described is utilized to change magnetic information already stored in the magnetic card 10. It

may be that only information stored in objects 11-11 beneath heads 12-12 associated with the first group of coils31-34 is to be changed while nochange is to be 'made in the objects '11-11 beneath the heads 12-12 associated with the second group of coils -38. The

'

photocells

114 and 119 sense holes in the card 111 which-indicates that changes are to be made in the objects associated with the respective first group of coils 31-34 and second group of coils 35-38. The

photocells

114 and 119 operate a transistor 129 in series with the relay 55 which closes thenormally open contacts 54.

. The relay 55 is actuated only when there are changes transistor 78 through a resistor 82, a diode 83, a norclosed contact 87 to ground. A capacitor 89 is connected in parallel in the winding of the relay 21 to cause the relay 21 to operate as an oscillator bypassing current through normally closed contact 87 to build up charge on the capacitor 89 until the relay 21 is actuated at which time current is discharged from the capacitor 89 through the winding of relay 21 until-the charge is insufficient to maintain relay 21 actuated. As shown in FIG. 5, the relay 21 is actuated and deactuated four times during one cycle of operation. Referring back to FIGS. 3 and 4, a normally open contact 91 connects the contact arm 88 through a contact arm 166 and a normally open contact 167 of the relay 25 to the start switch 92. If an operator holds the switch 92 closed, the cycling of the circuit will be held up after the relay 25 is actuated until the switch 92 is released.

When the relay 21 is actuated the contact arm 85 disengages the contact 84 to interrupt the current flow being made in the respective first and second group of coils.

As shown in FIG. 5, the

relays

24, 22, 25and 23 are actuated in a stepping order. The relay 24 is actuated by current through a contact arm 139, a normally closed contact 140, a normally open contact 141 and contact arm of the relay 21 connected to the contact 72 when the relay 21 is first actuated. Relay 24 is maintained in actuated condition by current through the contact arm 139, a normally open contact 142-, a contact arm 143 and either the normally closed contact 144 or the normally open contact 145 of the relay 23 connected tothe contact 72. When the relay 23 is actuated, the contact arm 143' disengages the normally closed contact 144 and engages the normally open contact 145. The time interval between the disengagement of the contact 144 and the engagement of the contact 145 is sufficient to cause deactuation of the relay 24.

The relay22 is actuated by current through a contact arm 147, a normally closed contact 148, a normally open contact 149 of therelay 24, a contact arm 150, the contact 84 and the contact arm 85 of the relay 21 connected to the contact 72 when the relay 21 deactuates after the relay 24 is actuated. Relay 22 is maintained actuated by current through the contact arm 147, a normally open contact 158, a normally open contact 156 and acontact arm 157 of the relay 24 connected to the contact 72.

The relay 25 is actuated by current passing through a contact arm 15 1, anormally closed contact 152, a normally open contact 1530f the relay 22, a contact arm 154, the normally open contact 141 and the contact arm 85 of the relay 21 connected to contact 72 of relay 26 when the relay 21 isactuated after the relay 22 is actuated; Relay 25 is maintained in an actuatedcondition by current through the contact arm 151, a normally open contact 155, the normally open contact 156 and the contact arm 157 of the relay 24 connected to 'contact 72 of-relay 26.

' The relay 23 is actuated by current through a contact arm 160, a normally closed contact 161, a normally open contact 162 of the relay 25,'a contact arm 163, the normally closed contact 84 and the contact arm 85 of the relay 21 connected to the contact 72 when the relay 21 is deactuated after the relay 25 is actuated. The relay 23 is maintained in actuated position by current through the contact arm '160-and a normally open contact 164 connected to the 'contact72.

The

relays

22 and 25 are deactuated when the relay 24 is deactuated by actuation of the relay 23. As shown in FIG. 5, the actuation of relay 23 and the deactuation of the

relays

24, 22 and 25 occurs at the beginning of the second half or demagnetization portion of the cycle of operation. The

relays

24, 22 and 25 are again actuated in a step wise fashion. Near the end of the complete cycle of operation, relays 21, .25 and 23 become all actuated to deactuate the relay 26 to disengage thecontact arm-73 from the contact 72. Power from the line 17 through the contact 74 is maintained on the contact 72 by a normally open contact 168 engaged by a contact arm 169 of relay 21.- When the relay 21 subsequently deactuates, .the line 17 is disconnected from the contact 72 to deactuate the

relays

24, 22, 25 and 23 as well as to remove the power from the other parts of the circuit connected to the contact 72.

During the magnetization portion of the cycle, the series circuit of the secondary of the transformer 51', the contacts 54, the contact arms 39, the contacts 27, the coils 31-34 and the resistors 28 or the series circuit of the secondary of the transformer 51, the contacts 54, the contact arms 39, the contacts 29, the coils 35-38 and the resistors 28 are respectively connected to ground either through a diode 57 or a diode 58. Referring now to FIG. 1, there is shown a notch 59 in the card 10 which is placed'over the normally open switch 63 FIG. 3) to control the direction of magnetization of the objects ll-l 1. The switch 61 beneath the card at 62 is closed to connect the diode 57 to the circuit to rectify the current through the coils 3l-34'or the coils 35-39 to produce a DC- current which magnetizes the objects 11-11 beneath the coils 31-34 or the coils 35-39 in a selected direction during the magnetization portion of the cycle. Alternately the notch could be located in the position 62 shown inphantom in FIG. 1,

the cycle, the relay 23 is actuated to connect ground through a contact arm 66 and a normally open contact 67 to the coils 31-34 or the coils 35 -3 8 to shunt the

switches

61 and 63 and diodes 57'and 58. Operation of the relay 23 also .connects power to relays 46-49 through a normally open contact 68, a contact arm 69, the normally-closed contact 70 or the normally open contact 76 and the contact arm 71 to the contact 72.

The relays '46-49 control respective normally open 1 through the selected coils caused by contact resistance 7 of the respective contacts41-44.

A relay 125 in parallel with the relay 40 connected by a normally open contact 176 and a contact arm 177 of the relay22 between thelines 17 and 18 is deactuated during the first one-fourth of the cycle and the third one-fourth of the cycle -to connect a contact arm 126 to a normally closed contact 127 connected to the photocells 114-118 to read a first half. of the holes punched in the card'lll. Similarly, during the second one-fourth and the fourth one-fourth portion of the cycle of operation, the relay 125 is actuated toconnect the contact arm 126 to a normally open contact 128 connected to the photocells 119-123 to read the second half of 'the card 111. Also, a lamp 132 connected througha normally closed contact 134 of the relay 22, acontact arm 135, a normally open contact 136 of the relay 23 and a contact arm 137- across the secondary of the transfonner 14 is illuminated during the third one-fourth portion of the-cycle to illuminate only the first half of the card 111. Similarly, a lamp 133 connected through a normally open contact 138 of the relay 22, the contact arm 135, the contact 136 of the relay 23 and the contact arm 137 across the secondary of the transformer 14 to illuminate the second half of the card 111 during the fourth one-fourth portion of the cycle.

OPERATION Referring to FIGS. 3 and 4, initially the plug 13 is connected to an AC power source. The magnetic card 10 is placed in a writing mechanism not shown) containing the heads 12-12 (FIG. 1) which have respective coils 31-38. A switch 61 is closed beneath the area 62 while a switch 63 is left open by the notch 59 to connect the first group of coils 31-34 in series with the diode 57, the contacts 54 and the secondary of the transformer 51.

The punched card 111 FIG. 2) is properly inserted into' the card reader l12 .where the photocell 109' beneath the cutoff corner of the card 111 is operated and the photocell 107 remains unoperated to actuate the relay and close the contacts 74 to illuminate the lamp 101. The photocell 114 senses a hole in the card 111 indicating that the first half of the objects 11-11 beneath the heads l2-12 are to be changed. The

photocell 114 operates the transistor 129 which actuates relay 55 to close contacts 54.

The operator presses and releases the switch 92 to actuate the relay 26 to initiate the cycle of operation. The capacitor slowly charges to operate the transistor 78 and slowly increases the radiation emitted by the lamp The radiation

sensitive resistors

52 and 53 slowly decreases in resistance to gradually increase ate relay 21.

When the relay 21 deactuates at .the end of the first one-fourth portion of the cycle, the relay 22 is actuated to actuate the relays 40 and125. The contact arms 39 of the relay 40 disengage contacts 27 andengage conthe diode S7. The contact arm 126 disengages contact 127 and engages contact 128 to supply power to photocell 119. The photocell 119 senses a hole in the card 111 indicating that the second half of'the objects 11-11 beneath the he'ads 12-12 areto be changed. The photocell operates the transistor 129 to actuate the relay 55 to close the contacts 54.

During the second one-fourthportion of the cycle, the capacitor 80 is again slowly charged and discharged to produce a slow increase and decrease of rectified current through the coils 35-38 to magnetize second half of the objects 11-11 in the selected direction. Also, the capacitor 89 charges and discharges to actuate and deactuate the relay 21.

At-the beginning of the third one-fourth portion of the cycle, the relay 23 is actuated to short out the diode 57 toground. Power is applied by the relay 23 to the relays 46-49 and the transistor pairs 171-174. Also,- the relay 22' is deactuated to deactuate the relays 40 and 125 to connect the coils 3l-34and the photocells 114-118 back into the circuit. The photocells 115-118 in response to the presence of holes in the first half of the card 111 which is illuminated by the lamp 132,

selectively operate the transistor pairs 171-174 to actuate the relays 46-49 and close contacts 41-44. Thus, in

accordance with the information punched in the card 1 1 1 selected coils 31-34 are shunted.

During the third one-fourth portion of the cycle, the current through radiation

sensitive resistors

52 and 53 is slowly increased and decreased. Since the diode 57 is shunted, the current is AC current which demagnetizes the objects 11-11 beneath the heads 12'-12 having the coils 31-34 which are not shunted by the contacts It is to be understood that the above-described embodiments are simply illustrative of the principles of the invention and that many embodiments may be derived without departing from the scope and spirit of the invention. For example, another arrangement other than the transistor 78, capacitor 80 and

resistors

81 and 82 may be used to vary the illumination of the lamp 77.

What is claimed is:

1. A circuit for demagnetizing magnetic objects having remanent magnetic states comprising:

a coil to which the magnetic object may be placed in close proximity; a radiantenergy controlled resistance in series with the coil;

i I means for connecting the radiant energy sensitive resistance and coil inseries with an alternating current source; 1 v

a radiant energy emission device in close proximity to the radiant energy controlled resistance; and means for energizing "the radiant energy emission device to produce a decreasing alternating current in the coil to demagnetize the magnetic object.

2. A demagnetizing circuit as defined in claim 1, wherein the radiant energy controlled resistance is sensitive to radiation in the visual light range and the radiant energy emission device is a lamp and a light-tight enclosure contains both the radiant energy controlled resistance and the radiant energy emission device.

3. A demagnetizing circuit as defined in claim 1, wherein the energizing means includes a resistor and a capacitor and the discharge time of the capacitor through the resistor controls the excitation of the radiant energy emission device.

4. A circuit for demagnetizing magnetic objects comprising:

. a coil to which a magnetic object may be closely the coil, said resistance being responsive to radia- I a tion in the infrared and visual light spectrum; a lamp; v I l an enclosure impervious to infrared andvisual radiation for containing'the radiant energy controlled 5 resistance and lamp; means for connecting the lamp to an energy source; a semiconductor device having its power electrodes connected in series with the energy source and the p; I a capacitor connected to the control electrode of the semiconductor device; and r a resistor connected to the capacitor to discharge the capacitor such that the semiconductor device becomes slowly nonconduetive to cause the demagnetizing of the magnetic object. 5. A circuit for selectively storing bits of information on a magnetizable sheet-like material comprising ated to end the cycle and prepare the circuit for another cycle of operation.

a plurality of magnetic beads each having a coil arranged to extend across the magnetizable material;

means for connecting the coils of the heads in series with a source of alternating current; means for connecting a diode in series with the heads during the first portion of a cycle of operation such that direct current .passes through the coils of the heads to magnetize the material adjacent to each resistance to slowly demagnetize selected areas adhead; a jacent to the magnetic heads. means for selectively shunting certain of the mag 6. A circuit as defined in'claim wherein the means netic heads; for producing a slowly decreasing quantity of energy ina radiant energy controlled resistance in series with 5 dudes lamp, a capacitor a resistor and the h lg i current source; d discharge time of the capacitor through the resistor means for producing a slowly decreasing quantity of controls the excltauon ofth? lamp energy to impinge on the radiant energycontrolled

Claims

1. A circuit for demagnetizing magnetic objects having remanent magnetic states comprising: a coil to which the magnetic object may be placed in close proximity; a radiant energy controlled resistance in series with the coil; means for connecting the radiant energy sensitive resistance and coil in series with an alternating current source; a radiant energy emission device in close proximity to the radiant energy controlled resistance; and means for energizing the radiant energy emission device to produce a decreasing alternating current in the coil to demagnetize the magnetic object.

4. A circuit for demagnetizing magnetic objects comprising: a coil to which a magnetic object may be closely placed; means for connecting the coil to a source of alternating current; a radiant energy controlled resistance in series with the coil, said resistance being responsive to radiation in the infrared and visual light spectrum; a lamp; an enclosure impervious to infrared and visual radiation for containing the radiant energy controlled resistance and lamp; means for connecting the lamp to an energy source; a semiconductor device having its power electrodes connected in series with the energy source and the lamp; a capacitor connected to the control electrode of the semiconductor device; and a resistor connected to the capacitor to discharge the capacitor such that the semiconductor device becomes slowly nonconductive to cause the demagnetizing of the magnetic object.

5. A circuit for selectively storing bits of information on a magnetizable sheet-like material comprising: a plurality of magnetic heads each having a coil arranged to extend across the magnetizable material; means for connecting the coils of the heads in series with a source of alternating current; means for connecting a diode in series with the heads during the first portion of a cycle of operation such that direct current passeS through the coils of the heads to magnetize the material adjacent to each head; means for selectively shunting certain of the magnetic heads; a radiant energy controlled resistance in series with the alternating current source; and means for producing a slowly decreasing quantity of energy to impinge on the radiant energy controlled resistance to slowly demagnetize selected areas adjacent to the magnetic heads.

6. A circuit as defined in claim 5, wherein the means for producing a slowly decreasing quantity of energy includes a lamp, a capacitor and resistor and the discharge time of the capacitor through the resistor controls the excitation of the lamp.