US2727108A - Snap action make-and-break electric switch - Google Patents

Description

Dec. 13, 1955 E. CHlSHOLM SNAP ACTION MAKE-AND-BREAK ELECTRIC SWITCH 2 Sheets-Sheet 1 Filed May 19, 1951 /2 [B K xii INVENTDR ALLEN E. EHISHDLM ig 7W 25 wy l ATTDRNEY Dec. 13, 1955 A. E. CHISHOLM 2,727,103

SNAP ACTION MAKE-AND-BREAK ELECTRIC SWITCH Filed May 19, 1951 2 Sheets-Sheet 2 INVENTUR 2 5 ALLEN E.|3HISHULM AHHRNEY United States Patent SNAP ACTION MAKE-AND-BREAK ELECTRIC SWITCH Allen E. Chisholm, Portland, ()reg.

Application May 19, 1951, Serial No. 227,151

Claims. (Cl. 2410-67) This invention relates to a snap action malte-and-break electric switch, and is an improvement over the magnetic switch disclosed in my pending application Ser. No.

32,470, filed June 11, 1948, and which issued as Patent.

No. 2,555,571 on June 5, 1951.

in the usual switch of this type snap action is accomplished by positioning an elastic means, such as a spring, so that the thrust thereof will tend to hold the switch blade in one position, then by external force concurrently alter such position and increase the thrust of the spring to a point where the switch blade will tend to move to an opposite position, at which point the potential energy stored in the spring by the external force is released as kinetic energy to cause snap action of the blade to opposite position. Thus, the pressure between the make and-break contacts is maximum at instant of break and minimum at the instant of make," and the external force required to operate the switch is considerably greater than the force required to hold the switch in either normal position.

The primary object of this invention is to provide a snap action switch operable by a minimum external force in which such force need be no greater than the force normally required to maintain good electric conductivity between the make-and-break contacts.

Another object is to provide in a switch of this type magnetic means instead of spring means to promote snap action, whereby the phenomenon of cumulative gain in force by the magnetic means is utilized to cause the switch blade to gain speed when reversing position, whereas the characteristic of cumulative loss in power by spring expansion causes an undesirable diminishing of speed of the switch blade when reversing position.

A further object is to provide in a magnetic actuated switch as described infra, auxiliary non-magnetic means to separate the make-and-break contacts in case of sticking r under abnormal conditions.

Other objects will be apparent to the skilled electrical designer from the text infra and are particularly pointed out in the claims.

It will also be remembered that the attractive force of a magnet for an armature varies inversely as the square of the distance separating the armature from the magnet and the overall result of the invention is to utilize a small movement of a small powered apparatus to move one magnet away from the armature while its confronting magnet, usually with identical magnetic flux characteristics, moves towards the armature from the opposite side. It will be at once seen that the efiect derived from an exceedingly small initial motion of the actuating device is translated into a ditierence in magnetic force that is twice the square of the small initial motion just mentioned, provided that the travel of the magnets and the mover is the same.

Drawings illustrating devices at present preferred as means for achieving the objectives stated and others that are to be fully explained in the disclosure, accompany and form a part hereof, in which:

Fig. l is a plan view of the switch alone as at present preferred, with a part cut away, as will be described;

Fig. 2 is an elevation of the structure of Fig. 1 in orthographic projection from that figure;

Fig. 3 is a sectional view of Fig. 1, taken on the plane 33, Fig. 1;

Fig. 4 is a plan of a modified form of the invention; and

Fig 5 is a plan view of a switch, as shown in Fig. 1, modified as will be described, with a diagram of a splitphase alternating current motor, associated with the modified switch.

Describing the drawings in greater detail, a base 1, preferably of insulating material, serves as a mounting for binding posts 14' and 14" and, to provide means for attaching electrical conductors to a reed bracket 9, upon which is mounted a reed 10, having a free end 11 enlarged by buttons shown to be in electrical contact with a rigid button 11a electrically connected to the post 14" by the plate 13, thus constituting a single pole, double throw switch.

Mounting stud 14 serves as a binding post for another line, if desirable, through the plate 13a and the button contact 11b. Contact buttons 11a and 11b also provide means for limiting movement of the free end of reed 10. A magnet carrier 4 is swingably mounted on the pivot 5, mounted on the plate 2 at one end of the plate, the other end of the plate 2 being turned up to provide a holder 3 for the spring 3. The magnet carrier is formed with two main slotted limbs 4a and 412, within which are mounted the magnets 7 and 7a in confronting position, with the reed l0 and its ferrous armature 12 between the pole pieces of the magnets 7 and 7a. These magnets are of the best modern permanent type in the embodiment of Figs.

'1, 2 and 3. The magnets 7 and 7a are rigidly held by the magnet carrier 4.

The magnet carrier 4 is also formed with an integral ramp portion 6 against which swinging force may be applied as from a condition sensitive apparatus or from any other source of switch actuating power in the direction indicated by the arrow 6. A plate 8 is formed with integral abutments 8a and 8b and constitutes a limiting means for motion of the magnet carrier 4 as will be explained infra.

The mode of operation of the invention illustrated in Figs. 1 to 3 inclusive is now to be explained. External force is being applied to ramp 6 as indicated by arrow 6', causing the magnet carrier to rotate on the pivot 5 to bring the magnet 7 close to armature 12, causing snap movement thereof by unbalanced magnetic flux, moving the contact button 11 against button 110 which is immovable. The rotation of the magnet carrier 4 is limited by contact against abutment 8a and in the opposite direction by abutment 8b. This part of the switch movement is for convenience named cycle A.

The abutment 8a limits the travel of the magnet 7 towards armature 12 and provide a fixed minimum air gap between magnet and armature with maximum contact pressure between circuit closing contacts 11 and 11a. When magnet carrier 4 is rotated in opposite direction, a similar relationship prevails between abutment 8b and magnet 7a in respect to armature 12, with maximum contact pressure between contacts 11 and 11b.

The spring 3 has been yieldingly overcome, partially by the magnetic force that has resulted in the firm contact of contact elements 11 and 11a and in major part by the force represented by arrow 6. Limb 4a of magnet carrier 4 bears against limb 15a of the follower 15 causing the upper boundary of the slot 18 to follow but not into actual contact with the armature 12. The follower 15 is made with an upturned end 17, with a slot 18 that is wider than the combined thickness of the reed with its two-part armature. Upon force sufficient its pivot 16 so that the slotted portion 17 moves the slot to permit contact beween the buttons 11 and 11a without actual contact of the armature with slot boundaries under normal conditions. The plate member is pivoted to the base lby the pivot mounting 16.

- Contra, when force represented by arrow 6 diminishes, the spring 3 tends to cause the magnet 7 to recede from armature 12, the magnet 7a of course approaching by an equal amount until the force exerted by the confronting magnets on the armature 12 is equal; whereupon the slightest additional movement of the magnet carrier 4 will cause approaching magnet 7a to overcome magnet 7 and magnet 7 yields control; the force tending to break the circuit gains as the square of the gained distance to cause an extremely fast break, moving the contact button '11 into firm contact with the fixed button 11b, with :1 pressure above mere contact.

As stated, slot 18 is of sufficient length to permit the plate 15 to follow the armature 12 out of contact therewith. However, if the electrical contacts 11 and 11a become stuck together as sometimes will occur when carrying heavy current, to such a degree that the maXinetic center of the flux between the magnets whereupon one of the magnets will be in position to take over and *complete the throw of the switch. In the setup described,

the contact 11 closes a circuit-between binding posts 14 and 14". The pressure between buttons 11a or 111) and button 11 of the reed, may be increased or decreased by changing the width of the air-gap between armature and magnet which remains after contact is established. The reason this may be desirable is to lessen the power required from the spring 3 when conditions require, or to vary the external power required when said spring is omitted as in Figs. 4 and 5.

The foregoing is regarded as the complete disclosure of the structures illustrated in the first three figures of the drawing and the remainder of the disclosure will refer to the modified construction, based on the invention illustrated hereinbefore, withthe same parts used in the first three figures identified by the same numerals and the modified or additional parts being distinctly identified over them. I will now describe the modified constructions of Figs. 4 and 5. t

Fig. 4 shows the basic invention of the first three figures,

but is changed structurally to constitute a double snap action switch-biased to circuit closing position by magnetic means in either one of two positions. In thismodification the binding post 14' will serve as a part of an extra circuit through which energy may flow from 14, through the switch reed 10, the contact 11b, plate 13a 7 and to an apparatus for carrying out a desired purpose. -The assumed conductor attached to 14 will ordinarily be the hot leg of an electric circuit. The chief difference from the first illustrated and described switchis in the operating means. Said operating meansv is shown as a disc 19, revoluble on its pivot mounting under influence of forces responsive to conditions requiring that the switch be operated, i. e. that the circuits be energized or deenergized as conditions require.

Replacing the ramp e of Fig. 1 is an upwardly projecting cam 6a made rigid with the cover of the magnet carrier 4. It is shown in dotted outline, being normally concealed by the disc 19. The disc also carries cam operators 21 and 21a on its underside,which for convenience have been shown to be brought through the material of the disc 19 in unchanged shape. The cam operators 21 and 21a serve upon contact with the cam 6a to move the magnet carrier 4 in one direction and the cam operators 22 and 22a being similar and also on the reverse side of the disc, serve to throw the magnet carrier 4 in the oppositedirection.

The spring 3 has been omitted and a balancing device that includes the threaded stafi 23 and the movable weight 24 threaded thereon, serve to balance the magnet carrier 4. If the switch assembly is vertical with the magnet carrier suspended as a pendulum from pivot 5, the weight and its adjusting means may be omitted.

As illustrated in Fig. 4, the cam operator 21 has been moved to operate the cam 6a, giving magnet 7 (shown dotted in this figure) the advantage of a shorter air gap over magnet 7a, the switch reed has closed the upper cf the two circuit legs shown and further revolution of the disc 19 will bring cam operator 22 into operative contact with cam 6a starting a contra cycle of energizing the circuit legs.

It will be noted here that cam operator 21. is so placed that if the electrical contacts are stuck together beyond the capacity of the magnetic difference in flux, which will not be great, to separate them, mechanical force will supplement the magnetic force; yet if the switch operates normally, the mechanical force is nullified by the fact that the switch contacts will be open before the magnet carrier has moved the parts 17 into contact with the armature 12.

Spaced additional cam operators for carrying out operations, as in timed sequence, may be provided for as illustrated by additional cam operators such as 21a and 22a, in any preferred spacing, timing or other difference.

I will now describe Fig. 5 which is shown to illustrate the versatility of the invention and its adaptability to controls not heretofore adequately taken care of.

The chief structural differences in Fig. 5 over the fundamental structural setup illustrated in previousiy described examples is that electromagnets are substituted for the original permanent magnets, there are adjustment screws on the abutments 8a and 8b, likewise an adjustment screw 27, not live, has been substituted for the button 11b of Fig. l and the balancing device of Fig. 4 has been continued.

The snap action in this variety of the main invention acts due, principally, to a variation of flux values for magnets 7 and 7a due to the heavy starting current in transformer CT wh'ich sharply increases the flux value of electromagnet 7. Since electromagnets and permanent magnets are recognized as equivalents. differential excita tion of the electromagnets is equivalent to mechanical difference in spacing of the air gaps between magnets such as 7 and 7a and the armature 12 of Fig. l.

The component parts of the switch are similar to their counterparts in Figs. 1 to 4, plus means for arying the air gaps as mentioned, supra. Binding posts P1, P2, P3, and P4 serve to hold conductors W3, W4, W5 and W6 and the switch in this instance is a single pole single throw. For illustrative purposes the electrical hookup includes a diagram of a conventional splitphase motor having a normal running winding R and a starting winding S. CT represents a current transformer in series with winding R as to its primary winding and a secondary windnet type. "ductors W5 and W6 which are a shunt across the main electrical circuit elements L1 and ing that is connected as shown to binding posts P1 and F2, to energize the magnet 7, which, as noted supra, is electro magnetic instead of the original permanent mag- The electromagnet 7a is energized by COilexternal force need be no Electromagnet 7 is operated by the secondary winding of transformer CT and is suitably wound to provide a variable force in said magnet sufficient under heavy current conditions to overcome the constant force exerted by magnet 7a on the armature 12, instantly causing the movement of the reed 10 by the armature 12 ant closing contacts 11 and 11a as shown in Fig. 5.

One end of the motor starting winding S is connected to L2 directly, the opposite end thereof being connected by conductor W2 to binding post 14" through plate 13, contacts 11 and 11a to the reed 10, member post 1-? and conductor W1 to L1 to complete the circuit, openable by separation of the contacts 11 and 11a. It is well known that locked rotor or starting current in a motor of the type mentioned is several times greater than normal full load value, hence when L1 and L2 are energized, transformer CT feeds a ratio of current to eiectromagnet 7 causing a flux value for the instant overpowering of magnet 7a to close the contacts 11 and 11a, thus energizing the starting winding S and causing quick acceleration of the motor to full speed, meanwhile decreasing the flux value of magnet 7 proportionately until at full load speed the magnet 7 is weaker than the fixed flux value of magnet 7a, causing a response of armature 12 to instantly separate contacts 11 and 11a and open the circuit of starting winding S.

The fundamental invention in the disclosure supra is a switch blade reversely movable by magnets to control one or a plurality of circuits. The basic structure is a reed type switch blade (or its equivalent), an armature made rigid with the said blade, magnets mounted on a magnet carrier in such manner that the pole pieces tend to oppositely attract the armature and thus cause a movement of the blade if one magnet has ever so slight an advantage in its air space relations with the armature.

It is a well known law of magnetic action that the pull of a magnet is inversely proportionate to the square of its spacing from an armature, or what serves as one, hence if the armature is exactly spaced between two equal magnets, the very equality will prevent movement in either direction. WVhile this is theoretically possible, it is believed impractical to carry out. The magnets will in all cases, according to the invention, be made rigid with a magnet carrier and the pole pieces of the magnets so spaced from the armature therebetween that actual contact is not possible; and for that matter the air gap must never be so short that the opposed magnet cannot approach the opposite side with a shorter gap.

Under normal conditions the external force required to overpower the magnetic bias of the switch blade, as

ternally initiated movement of the magnet carrier progresses to position the magnets in equilibrium status with the armature, the slightest further movement of the carrier dequilibrates such status to reverse the bias on the armature and cause same to snap the blade to opposite position, wherefore the blade becomes an immovable magnetic anchor, and in such position mutually attracts the onward moving magnet which now has the shorter air gap, whereby the carrier is now magnetically biased to complete its movement to engage its limiting stop without further aid by said external force, thus magnetically biasing both blade and magnet carrier to their respective limited positions without other bias. Such greater than that required to overcome said magnetic bias.

It will be at once seen that the actual movement required to start a switch throw is less than one-half of the minimum distance required of any other means for applying bias to the switch blade, because when either .magnet has its air gap shortened, by ever so small an increment, the opposite magnet has its gap broadened by 8 exactly the same amount and the variation in magnetic pull will vary as twice the square of the magnitude of the movement, resulting in a sensitivity not believed to be approachable by any other means of switch throwing.

The claimed invention, therefore, is for structure capable of applying the principle. It will also be seen that unless there is always an air gap between the pole pieces of a magnet and the armature, an opposed magnet cannot prevail over the first, which it must likewise do without wiping out the air gap on its side of the armature.

it is thought that the external position of the switch and its comparative simplicity when compared with the best of the centrifugal type circuit breakers will be apparent at a glance to motor designers in the fractional and small horsepower field, though the application is only one of a very large number of uses in which the variable flux values in the electro-magnets will contribute to snap action of the switch and electrical engineers will appreciate the value of the air gap adjusting means and understand their application.

The word reed as applied to a switch part is used to include one that is flexible or not flexible. While three different applications of my underlying principles of operation have been shown, it will be understood that there are many others that wili suggest themselves to the skilled designer without leaving the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent, is:

l. A sensitive switch for an electric circuit, comprising a base member, switch contact members mounted thereon, a switch blade member mounted to swing between said members, an electric circuit of which said biade member and said contact members are part, a freely swinging magnet carrier pivotally mounted on said base, actuating means for swinging said carrier in an arcuate path around its pivot mounting, a pair of opposed U shaped magnets mounted on said carrier, an armature associated with said switch blade, said magnets in opposite spaced position with their pole pieces confronting each other with said armature normally bisecting a predetermined air gap between said magnets, and stops to limit the swing of said magnet carrier effective to prevent actual contact of a magnet pole with said armature.

2. A sensitive switch comprising a base, a magnet carrier swingably mounted on said base, a mounting pivot therefor, said carrier connected to a condition sensitive device to swing on its pivot, a pair of opposed U-shaped magnets mounted on said carrier in spaced confronting position, to swing therewith, a switch blade, electric terminals therefor, an armature folded around the median portion of said blade, said armature positioned between said opposed magnets and responsive to magnetic flux from both poles of the nearest magnet to move the switch blade by magnetic force applied to said armature when the magnets move with said carrier, and restraining means to prevent engagement between said armature and said magnets.

3. The combination as claimed in claim 1 and including a movable follower for the switch blade, normally out of contact therewith, said follower including primary abutment effective to engage and move said blade when and if same sticks under abnormal conditions, and secondary abutments effective to engage said magnet carrier, said follower responsive to movement of said magnet carrier and the motive forces applied thereto.

4. In a snap action magnetic switch characterized by a swingable switch blade to open and close electric circuits, said blade actuated by an armature responsive to magnetic bias, said bias created by magnetic means on each side of the armature, said means attached to and actuated by a swingable magnet carrier which carrier is actuated in part by external forces, substantially as described, the combination therewith of means to insure opening of the electric contacts under overload conditions in which the normal magnetic bias would be insufficient blade to contra position, said means including movable follower for the switch blade, normally out of contact therewith, said follower including primary abutment means effective to engage and move said blade when and if same sticks under abnormal conditions, andsecondary abutments elfective to engage said magnet carrier, said follower responsive to movement of said magnet carrie and the motive forces applied thereto.

5. An electrical switch of the fast, snap-over type comprising an elongated switch blade movably connected by one end to an electrical circuit part, with a switch closing contact on its opposite end, an armature made rigid with the median portion of said blade, a swingable magnet carrler mounted near said switch blade, a pair of confronting U shaped magnets mounted on said carrier and movable therewith, said magnets in spaced position on opposite sides of said armature to oppositely tend to move said switch blade by magnetic influence on both sides of said armature and means for limiting the movement of said carrier, efieetive to prevent the magnet poles from touching said armature, the throw of the switch blade being likewise limited by contact buttons to prevent the same contact.

6. In a magnetically biased electric switch, in com bination a base, electrical circuit components mounted thereon including a switch blade cooperative therewith to open or close said electrical circuit, said blade swingably mounted with its free end confined to swing withina predetermined are by limiting abutments, a ferrous armature median mounted on said blade, :1 carrier member pivotally mounted on said base, said member transversely swingable in relationship with the longitudinal axis of said blade, limiting stops to limit the swing of said member in relationship to the swing of said switch blade, a pair of magnets mounted on said carrier member in opposed confronting polar relationship with a predetermined air gap therebetween, said armature positioned within said air gap and responsive to the pull of said magnets, said pull of equal value on each side of said armature at exact mag netic equilibrium, the normal position of said armature being nearest to one of said magnets with a minimum air gap therebetween and a maximum air gap between said armature and the opposite magnet, the normal position of said carrier member in engagement with one of its limitingstops, the normal position of said switch blade in engagement with one of its limiting abutments, said normal positions etfectuated by magnetic bias between one magnet and said armature, and means responsive to external forces coacting with said carrier member to swing said member from said limiting stop to a position past dead center of the maximum swing of said member thereby to lengthen said minimum air gap and shorten the opposite air gap, whereby said magnetic bias reverses to the opposite magnet and said armature, thereby completing the swing of said member and said switch blade to contra position, said external force being no greater in value than the force required to overcome the first mentioned magnetic bias.

7. The combination claimed in claim 6 wherein the magnets are wound electromagnets having independent variable in wattage by external conditions, the wattage in one winding of constant value to bias the switch blade and the magnet carrier to their normal positions as set forth in said claim 6, the wattage in the .opposite winding "variable by saidexternal conditions, thereby to reverse the magnetic relationshipbetween said air gaps, said magnets and said armature, whereby the pull of the stronger magnet snaps the switch blade to its reverse position and consecntively causes snap action movement of said magnet carrier to contraposition, inwhichcyclethe reversed position of the armaturecarrying switch blade provides a magnetic anchor for the latter movement of said-magnet carrier, said cycle reversible when the variable-wattage in its winding becomes less than the constant wattage in the opposite winding.

8. A sensitive snap action switch for. electric-circuits comprising a base member, switch contact elements mounted thereon, a switch blade mounted to swingably engage said elements, means to limit the swing of said blade, an armature associated with said blade to swing therewith, an electric circuit of which said blade and said elements are a part, a freely swinging magnet carrier associated with said base, actuating means toswing said carrier to operate said switch, two U shaped magnets mounted on said carrier to swing therewith, said magnets in opposed predetermined spaced apart position with their pole faces confronting each other with an air gap therebetween, said armature positioned to bisect said air gap between the faces of said magnets, in which position'said armature is responsive to simultaneous equal contra pull by each magnet without bias toward either magnet, said pull sufficient to bias the armature toward one magnet when said bisected air gap is differentiated, and stops to limit the swing of said magnet carrier in relation to the swing of said switch blade to prevent engagement of a magnet with said armature and to eifectuate a minimum air gap between said armature and each magnet which is non extinguishable, said blade freely swingable in response to unequal pull between said armature and said magnets, said bisected air gap differentiated instantaneously into major and minor air gaps by the swing of said carrier to bias said armature and blade with snap action toward that magnet separated from said armature by the lesser air gap.

9. in a sensitive switch for electric circuits comprising a supporting member with switch elements mounted thereon including a swingable switch blade the free end thereof engaging said elements, limiting abutments to limit the swing of said blade in a predetermined are, an armature associated with said blade to swing therewith, two magnets positioned one on each side of said armature with normally equal air gaps between said armature and each magnet, a magnet carrier swingably mounted on said member, said magnets afiixed to said carrier in confronting spaced apart relation and swingable with said carrier in an arcuate path transverse to the swing of said armature, said magnets concurrently exerting equal contra pull on each side of said armature at magnetic equilibrium, means to limit the swing of said carrier in its arcuate path to prevent engagement between said armature and the magnets, and actuating means coacting with said carrier to initially swing said magnets to differentiate-said equal air gaps simultaneously into major and minor air gaps between said armature and said magnets, to magnetically bias said armature thru the minor air gap toward that magnet nearest said armature, to swing said armature and switch blade in said arcuate path to engage one of said abutments, together with sequential magnetic bias between the armature and said magnet etfective to complete the swing of said carrier to one'of its limiting means, said major and minor air gaps reversible to swing-said blade and said carrier to contra engagement with theirrespective limiting components by reverse swing of said carrier by said actuating means.

10. in a sensitive snap action magnetic'switch for electric circuits including a supporting structure for the elements of said switch, a swingable switch blade to control said electric circuits, armature means associated with said blade to swing the blade by magnetic force, said means concurrently swingable with said blade, limiting means to limit the swing of said blade in an arcuate path, a swingable magnet carrier associated with said switch, said carrier swingably positioned in predetermined relationship with the swing of said blade, a pair of U-shaped magnets atfixed to said carrier in spaced apart relationship and swingable therewith, an air gap between the armature means and each magnet the gaps concurrently variable yet non-extinguishable said magnets positioned to exert simultaneous contra pull on said blade by their concurrent magnetic pull on said armature means when equal air gaps prevail between each magnet and said armature means, means to limit the swing of said carrier and its supported magnets in relation to the swing of said blade and armature means to prevent extinguishment of said air gaps, and actuating means cooperative with said carrier to initially swing the magnets simultaneously to differentiate said equal air gaps into major and minor air gaps the sum of their distance equivalent to sum of the distance of the equal air gaps, whereby said blade is magnetically biased toward that magnet separated from said armature means by the minor air gap, together with sequential magnetic bias between said armature means and said magnet to complete the swing of said carrier to engage one of its limiting means, said differentiated air gaps reversible to reversely swing the blade and carrier, by movement of said carrier by said actuating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,933,083 Ackerman Oct. 31, 1933 1,976,953 Mantz Oct. 16, 1934 1,976,954 Mantz Oct. 16, 1934 2,125,150 Bruns July 26, 1938 2,188,438 Judson et a1 Jan. 30, 1940 2,302,250 Penn Nov. 17, 1942 2,436,224 Ogle Feb. 17, 1948 2,490,877 Lindfors Dec. 13, 1949 2,518,480 Lilja Aug. 15, 1950 2,641,664 Knutson June 9, 1953

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