US2297339A - Electromagnetically operated device - Google Patents

Description

a WWW m 7 m WMA n 2 m S V 4 ZMQ G. o. WILMS ET AL ELEOTROMAGNETICALLY OPERATED DEVICE Filed Jan 22 1940 Sept. 29, 1942.

Sept. 29, 1942. s. o. WILMS ET AL ELECTROMAGNETICALLY OPERATED DEVICE Fil d J 2 1940 4 Sheets-Sheet 2 f mm m W W 7 P 4 @4 Y B WaMdQW ATTORNEY.

Sept. 29, 1942.

G. O. WILMS ET AL ELECTROMAGNETICALLY OPERATED DEVICE Filed Jan. 22, 1940 4 Sheets-Sheet 5 INVENTORS GUS/34V O. M1443 41 SEPT d QAWE ATTORNEY.

Sept. 29, 1942. e. o. WILMS ETAL ELECTROMAGNETICALLY OPERATED DEVICE Jan. 22, 4 s t 4 INVENTORS 61/3741/ 0. Maps flux/er d .DAl Vf \AR QMQ CA ATTORNEY.

Patented Sept. 29, 1942 ELECTROMAGNETICALLY OPERATED DEVICE Gustav 0. Wilms and Albert J. Dawe, Milwaukee,

Wis., asslgnors to Allen-Bradley Company, Milwaukee, Wis., a corporation of Wisconsin Application January 22, 1940, Serial No. 315,040

4 Claims.

This invention relates in general to electromagnetically operated devices suitable for the opening and closing of electric switches and the like, and in particular to a novel device employing an armature and a fieldpiece which may be electrically magnetized and demagnetized to cause engagement and disengagement in such manner that a part or all of the field and armature assembly functions alternatively as an electromagnet and as a demagnetizable permanent magnet.

One advantage of the apparatus of this invention is that it requires electrical energy only to effect engagement and disengagement between the armature and fieldpiece and, therefore, is an efficient device in that no energy is expended to maintain engagement of armature and fieldpiece.

Another advantage of the apparatus of thisinvention is that it is silent in operation in any stationary position and causes sound only when motion of the device is effected.

A further advantage of the apparatus of this invention is that it may be embodied in a structure of practically the same dimensions and cost as a comparative electromagnetically operated and maintained device.

These and other advantages, which will be apparent from the following description, are not possessed by switch actuating apparatus heretofore known and used. In an effort to obtain the properties exhibited by the apparatus of this invention it has been customary in the art, prior to this invention, to employ a complicated, bulky and expensive system of locks and latches, none of which has been entirely satisfactory, or to employ permanent magnets in such a way that direct current only may be used to close the same.

To aid in the description of our invention reference is made to the accompanying drawings forming a part hereof wherein we have shown in Fig. 1 a front view of one form of electric switch embodying our invention, parts thereof being broken away and in section;

Fig. 2 is a wiring diagram of the electric switch shown in Fig. 1, with parts thereof in diagrammatic form;

Fig. 3 is a longitudinal view, partly in section, of Fig. 1 taken on the planes indicated by dotted line 3-3;

Fig. 4 is a detail view of the auxiliary lock-in switch indicated in general by numeral 3| in Fig. 3;

Fig. 5 is a detail view of the normally closed auxiliary switch indicated in general by numeral of Fig. 3;

Fig. 6 is a magnetic hysteresis curve; and

Fig. 7 is a magnetic hysteresis curve illustrative of the behavior of an electromagnet such as is employed with this invention correlated with a diagrammatic showing of the field strength and magnetic flux variations which are applied thereto to cause closing and opening of the switch in accordance with this invention.

Referring to the accompanying drawings, in which like numerals indicate like parts throughout the several views, the numeral l designates a flat sheet metal panel upon which the switch mechanism, designated generally as 2, and the electromagnetic actuating means, designated generally as 3, are mounted.

The switch mechanism 2, which may be of any form desired, is here shown as comprising two pairs of stationary contacts 4 adapted to be electrically bridged by the movable contact units 5, which are adapted for vertical movement in a manner similar to that shown in Patent Number 2,071,149 issued to Gustav O. Wilms et al., February 16, 1937. With a switch mechanism 2 of this form the stationary contacts 4 are secured to the top section 6 of the chamber 1, which chamber has a back section 8 and a front section 9. The back section 8 is secured to the metal panel I by two screws I0 and a mounting post II, the latter being riveted to panel I and projecting outwardly through a slot l2 in a partition l3, which partition depends medially from top section 6.

Back section 8 is slotted to receive the rear of top section 6 and front section 9 is slotted to receive the front of top section 6, the whole being secured in place by means of mounting post II, as shown.

The movable contacts 5 are mounted on posts II, which are carried by a cross bar I5 of insulation material. Intermediate cross bar [5 and contact 5 is a spring 52, shown in broken line, which biases the contact 5 upwardly toward a shoulder 53 on post H. The contact springs are each enclosed by a telescoping two part enclosure IS.

The electro-magnet designated in general by the numeral 3 comprises a U-shaped frame I! riveted as shown to sheet metal panel number I, a fieldpiece l8 secured to frame l1, an armature I9 of the form of an inverted T, and an energizing coil 20. The fieldpiece l8, which is of substantially inverted U-shape, is made up of laminations 21' and in this instance are of silicon steel.

The armature I9 is composed of laminations 22, which in this instance are of a hardened tungsten steel alloy and have the property of comparatively high retentivity and high coercive force. 1

All of the laminations 22 are of inverted T form and extend as shown toward the adjacent surface 23 of the top portion of fieldpiece IS. The middle lamination of non-magnetic material designated by 24, however, extends beyond the other laminations through an opening in the top portion of fieldpiece I B'and has mounted thereon cross bar l by means of screw 25.,

Middle lamination 24 is slotted as at 26 throu which opening a screw 21 passes, which screw holds in place coil clamp 28 and armature guide 29. Coil clamp 28 secures coil 20 in position and is of spring material having an inwardly projecting portion positioned between the top portion of fieldpiece l8 and the top surface of coil 20. The armature guide 29 is passed through an opening in the bottom of the fieldpiece structure l8 and through the coil 20, serving to hold the coil against sidewise movement and as a guide for armature IS. The armature guide 29 has projecting portions extending adjacent to the top portion of the fieldpiece l8 that are engaged by the screw 21.

The lock-in switch designated generally by numeral 3| is shown in detail in Fig. 4 and comprises stationary contacts 32 and a movable bridging contact 33, a mounting post 34 for the movable contact, a spring 35, and an actuating bar 36 which is mounted as shown on an extension 31 from cross bar IS.

The normally closed auxiliary switch designated generally as by numeral 45 is shown in detail in Fig. 5 and comprises stationary contact 46, movable contact 41, movable contact spring 5|, actuator assembly 48, biasing spring 49 and mounting block 50.

This type of auxiliary switch is described and claimed in the application of Lynn H. Matthias for Auxiliary Switches for Electromagnetically Operated Devices, filed February 10, 1940, Serial Number 318,292, and assigned to the assignee of this application, which is the Allen-Bradley Company.

It is to be noted that the magnetic switch is shown in the closed position in Figures 1, 2 and 3. In such position of the magnetic switch, the lock-in switch 3| has its contacts closed and auxiliary switch 45 has its contacts open.

Spring 49 biases the actuator assembly 48 in the clockwise direction. With the armature l9 in the up or closed position, the actuator will, therefore, press the movable contact 41 downwardly out of engagement with contact 46. With the armature in the down or ofi position, the weight of the armature is sufiicient to turn actuator 48 counterclockwise which allows contact magnetizing force) curve taken with continuously increasing values of H to the maximum, and then with continuously decreasing values of H to a negative maximum, and so on, will assume the shape shown in Fig. 6.

The ordinate 0C represents the retentivity, that is, the value of the residual magnetic flux density in the iron after the magnetizing force has been increased to its'maximum and then removed. The abscissa 0A represents the coercive force, that is,'-thevalue of the magnetizing force necessary to reduce the retentivity 0G to' zero.

Fig. 6 is a hysteresis curve plotted with magnetizing force H against flux density B and is representative of a piece of iron having a high retentivity and a high coercive force, whereas Fig. 7 shows a hysteresis curve plotted with magnetizing force H against total flux and is representative of the fieldpiece and armature, as used in this invention, in their closed position.

In the specific embodiment shown the alternating current flowing through the energizing coil 20 of the above described magnetic switch is proportional to the applied electromotive force. The energizing current, of course, lags the applied voltage or electro-motive force by an electrical angle depending upon the ratio of the coil's reactance to the coils efiective resistance.

The magnetizing force H is proportional to the magnetizing current, and any instantaneous value of H may be determined by projecting points of circle M onto the horizontal axis of Fig. 7. The circle M is described by a radius R proportional to the maximum value of the magnetizing current, and this radius or vector rotates with angular velocity equal to that of the magnetizing-current. Actually, however, the figure as traced by the radius R is not a true circle, but rather an ellipse as R is slightly modified by the non-linearity of the magnetizing force vs. flux density relationship of the magnetic circuit. For purposes of simplification this is to be considered as a linear relationship in the following description.

In Fig. 7, 5 is the total flux in the armature and fieldpiece when in the closed position.

The instantaneous values of are determined by projecting the instantaneous value of H onto the proper portion of the hysteresis curve.

It is to be noted that the instantaneous values of and of H are designated by the adding of sub numerals.

The convention is followed in Fig. 7 in that values of H to the left of the vertical axis are negative values, and that values of below the horizontal axis are negative values.

As the time increases 'from the instant corresponding to vector R at point J, moving counterclockwise to point K, the instantaneous values change from H2=0 to H4 54. After point L on the hysteresis curve has been reached and as the time increases, the instantaneous values of are determined by following the top of the loop as indicated by'the arrow.

If, when H is a maximum, or at the instantaneous valueof Hi the magnetizing force is suddenly removed, the residual flux will have the particular value 2 as indicated on the hysteresis curve.

It is to be further understood that if the magnetizing force is removed at any instant from Hi to H=0, after having reached the maximum value Hi, the residual flux will always be equal to 4m. This condition will also exist on the negative portion of the cycle, except that the residual flux will be a as indicated.

The magnetic switch as shown in Figures 1 and 3 requires a particular force to hold the contacts and other parts in the closed position. The flux corresponding to such a particular value is indicated in Figure 7 by the line (I for a flux value of positive sign and line d for a flux value oi negative sign.

The lines d and d thus define the minimum values of flux necessary for the armature and fieldpiece to remain in the closed position against the action of the opening bias which in the specific example disclosed is the weight of the armature and other associated parts plus the action of the various springs associated therewith. These lines also determine, as described below, the limits in electrical angle in which the armature and fieldpiece will not remain closed if H is removed. a

The particular value H1 is the value of H that is just suflicient to reduce the residual flux 2 t0 a value 1 defined by the line d. The particular value H3 is the value of H that is just suflicient to yield after de-energization a residual flux 1 defined by the line d. There are thus established two values of H, H1 and -H3 that correspond to the set limits of switch closure d and d respectively, in which the switch will not remain closed, upon de-energization of H, during one-half of the hysteresis cycle.

It is evident that twice the angle: in electrical degrees divided by 360 is equal to the fraction of a cycle during which, if the coil circuit is interrupted, the switch will not remain closed. In one particular device built in accordance with this invention, the possible period during which the switch will not remain closed constitutes 20% of a cycle. Such possible failure of the switch to remain closed, however, will be precluded as explained later on.

In order to open the switch, a sufficient alternating magnetizing force must be present to reduce the residual magnetism to some value less than 1 or 1. It is assumed in the particular example as shown in Fig. 7 that 2 or -2 is the maximum residual magnetism possible, and in this case, a slightly greater magnetizing force than H1 or H1 will be sufilcient to accomplish the opening. In order to assure the reduction of the maximum possible value of residual flux 452 or 2, it is then necessary that the H relationship during energization of the drop out coil 20 have such values as shown by the small H curve in dotted line in Fig. 7.

Referring to Fig. 2, which is a wiring diagram of the electric switch with parts thereof in diagrammatic form, it is to be noted that the same is in the closed position. Conductors 60 and GI are power feeder wires, each of which is connected to a stationary contact 4, and the movable contact units 5 being in closed position the circuit is completed through the other set of stationary contacts 4 to the conductors 62 and 63 leading to the load.

With the magnetic switch in the open position, auxiliary switch 3| open and auxiliary switch 45 closed, and the pilot start switch closed, a circuit is completed from conductor 6|, conductor 64, contacts of the start switch 10, conductor 65 through the contacts 46 and 41 of normally closed auxiliary switch 45, through the conductor 55 through a portion of energizing coil and fix the angle 0: (alpha) 20, through conductor 61 to power line 60. Thus coil 20 is energized to cause the armature I! to moveto the closed position. At substantially the closed position the magnetizing force H is a vector quantity, varying with the time and having a maximum value equal to H4 as shown in Figure '7 and described above.

As the magnetic switch closes, it will be noted that contacts of the auxiliary switch 45 open, thereby breaking the closing energizing circuit and the switch will remain in the closed position providing the residual magnetism exceeds the opening bias. However, if the residual magnetism is insuflicient and the switch does start to open the auxiliary contact closes again reapplying the closing magnetizing force to the switch and if the residual magnetism is then sufilcient when the closing energizing circuit is open, the

switch will remain in the closed position. The probability of the resulting residual magnetism being large enough is great since the ratio of the electrical angle over which the switch will not remain closed to that over which it will remain closed is small, and the necessity for several tries is remote.

The magnetic switch is so constructed that the closed position of the main switch contacts 4 and 5 overlap the operating position of the auxiliary switch 45 to such a degree that they do not open the main circuit in the event that the magnet makes several ftries" for a successful operation.

To open the magnetic switch, the pilot stop switch H 'is closed, whereby a circuit is completed from power conductor 6| through conductor 64, through contacts of stop switch ll, through conductor 68, through the contacts 32 and 33 of. lock-in switch 3|, throughconductor 69, through all of coil 20, through conductor 61 and then to power conductor 60. The energizing coil 20 being so designed that with the utilization of the complete coil, the magnetic force H which is a vector quantity varying with time and having in this instance a maximum value slightly greater than H1 reduces the residual magnetism to such a value that the'switch opens. This is accomplished by increasing the number of turns of the opening coil as shown in Figure 2.

As described above, the closing circuit utilizes a portion of the coil and the opening circuit uses the complete coil.

In order to preclude the possibility of closing both the start and stop contacts simultaneously, which would cause the switch to chatter, a mechanical interlock or other device should be included in the start and stop contact device to eliminate this possible condition.

In the description of the example of carrying.

our invention into practice, an electro-magnet of a straight line actuating motion is shown, however, other types of electromagnets may be employed such as the type that incorporates the pivotally mounted armature.

Our invention may be practiced with the same structure where direct current is used for securing magnetization i. e., to cause engagement of the fieldpiece and armature and to maintain the switch in the closed position by virtue of the residual magnetism derived from the closing energization. The opening of the switch can then be obtained by using A. C. as described above or by means of D. C. magnetizing force of opposite polarity from the residual magnetism and of such magnitude that the switch opens.

.- Further, our invention may be also used where alternating current is used for magnetization and direct current of proper polarity is used to reduce the residual magnetism.

In every case, including the specific example as given in this specification, it should-be understood that the reduction of the residual magnetism which causes the disengagement of the armature from the fieldpiece, is caused by a magnetizing force produced in the opposite direction to that of the residual magnetism. The magnitude of the magnetizing force which reduces the residual magnetism is determined by the method as shown in our disclosure, wherein the residual magnetism must be reduced to some value less than d or d' which is the value necessary to hold the parts in engagement.

The spec c example herein disclosed may be considered a magnetic device wherein the armature l9 becomes a magnet on a temporary energization of the fieldpiece I! by the coil 20, and wherein the fieldpiece after energization becomes a keeper; and on second temporary energization of the keeper or fieldpiece, the armature'or. magnet has its magnetism reduced to aw value to permit disengagement of fieldpiece and armature. It is to be understood that armature or keeper is biased to the disengaged position.

In practicing the invention, that the magnetic circuit have such characteristics that the magnetizing force can create a residual flux that is greater than that necessary to keep the fieldpiece and armature engaged and that the demagnetizing force be sufficient to reduce the total magnetic flux to a value less than that necessary to keep the parts engaged.

While in accordance with the patent statutes we have disclosed the foregoing details of a specific embodiment of our invention, and whilecertain of the claims are directed to the details of this preferred embodiment, it is to be understood that the principles disclosed are capable of much wider adaptation to the art of magnetic devices generally. We desire, therefore, that the language of our claims shall be accorded the broadest reasonable construction, and that our invention shall be limited only by what is expressly stated therein andyby the prior art.

We claim as our invention:

it is only required peatthe closing of said finding switch until said holding force is obtained greater than said bias.

2. An electro-magnet device operable by alternating current, comprising a magnetic circuit including a fieldpiece and an armature, an energizing winding for said fieldpiece, a finding switch in series with said energizing winding and a control switch in series with the finding switch and energizing winding for connecting the circuit of sad energizing winding and said finding switch to a source of alternating current; said armature being biased from its closed position with the fieldpiece; said magnetic circuit, with armature and fieldpiece closed, having suflicient coercive force and retentivity, whereby, a holding force greater than said bias is obtained from an alternating current magnetizing force upon deenergization at such a point on the alternating current cycle that the residual magnetism is sufllcient to develop said holding force; said finding switch being under the control of said armature so as to be closed when the armature is in open position and to be open when the armature is in closed position; whereby, said winding and said finding switch .on being connected by said control'switch to a proper source of alteropen to closed position and if not retained in nating current causes the armature to move from closed position-then to move to open position and 1. An electro-magnet device operable by alternating current comprising a magnetic circuit including a fieldpiece and an armature, an energizing winding for said fieldpiece, a finding switch in series with said energizing winding and a control switch in series with the finding switch and energizing winding for connecting the circuit of said energizing winding and said finding switch to a source of alternating current; said armature being biased from its closed position with the fieldpiece; said magnetic circuit, with armature andfieldpiece closed, capable of residual magnetism derived from energization of said winding by alternating current to provide a holding force suflicient to maintain said armature closed against said bias; said finding switch being under the control of said armature so as to be closed when the armature is in open position and to be open when the armature is in the closed position; whereby, said winding and said finding switch on being connected by said control switch to a proper source of alternating current causes the armature to move from open repeat the closing of saidfinding switchuntil said holding force is obtained greater than said bias.

'3. An electro-magnet device operable by alternating current, comprising a magnetic circuit including a fieldpiece and an armature, an energizing winding for said fieldpiece, a finding switch in series with said energizng winding and a control switch in series with the finding switch and energizing winding for connecting the circuit of said energizing winding and said finding switch to a source of alternating current; said armature being biased from its closed position with the fieldpiece; said armature having high coercive force and high retentivity compared to said fieldpiece and said magnetic circuit, with armature and fieldpiece closed, capable of residual magnetism derived from energization of said winding by alternating current to provide a holding force suflicient to maintain said armature closed against said bias; said finding switch being under the control of said armature so as to be closed when the armature is in open position and to be open when the armature is in closed position; whereby, said winding and said finding switch on being connected by said control switch to a proper source of alternating current causes the armature to move from open to closed position and if not retained in closed position then to move to open position and repeat the closing of said finding switch until said holding force is obtained greater than said bias,

4. An electro-magnet device'operable by alternating current comprising a magnetic circuit including a fieldpiece and an armature, an energizing winding for said fieldpiece, a finding switch in series with said energizing winding, a

control switch in series with the finding switch and energizing winding for connecting the circuit of said energizing winding and said finding switch to a source of alternating current, a deenergizing winding for said fieldpiece and a second control switch to connect the circuit of said de-energizing winding to a source of altemating current; said armature being biased from its proper source of alternating current causes the armature to move from open to closed position and if not retained in closed position then to move to open position and repeat the closing of said finding switch until said holding force is greater than said bias and said second control switch on being closed causes said de-energizing winding to reduce the holding force to less than the said holding force to cause the armature to 10 move to open position.

GUSTAV O.- WILMS. ALBERT J. DAWE.

Images