US1602976A - Limit switch - Google Patents

Description

Oct. 12 41926.

C. H. HODGKINS ET AL LIMIT SWITCH 4 Sheets-Sheet I XWITNESSES;

maries/ od l'nsc @Sed/72 Pag/f6 ATTRNEY oct. 12 192e. 1,602,976 V C. H. HODGKINS ET AL LIMIT SWITCH Filed June 25, 1920 4 Shee'cSSheet 2 WITNESSES:

B #Mp4/2 f Oct.A 12, 192s. 1,602,976

l C. H. HODGKINS ET AL LIMIT SWITCH Filed' June 25, 1920 4 sheets-sheet 5 WITNESSES:

J 7U ATTORNEY Oct. 12 1926. 1,602,976

.c.` H. HoDGKlNs ET AL LIMIT SWITCH Filed June 25, 1920 4 SheQSvShGe, 4

ATTORNEY Patented Oct. 12, 1926.

UNITE-D STATES 1,602,976 PATENT OFFICE.

CHARLES H. HODGKINS, OF PITTSBRGH, .AND FRED M. PRKS, OF MUBBYSVILLB,

PENNSYLVANIA, ASSIGNORS-TO WESTINGHOUSE ELECTRIC AND MANUFACTUR- ING COMPANY, .A CORPORATION 0F PENNSYLVANIA.

LIMIT SWITCH.

Our invention nelates to switches, and particularly to limit switches such as are employed in combination with controllers 4for motors used in operating crane machinery.

An object of our invention is to provide a switch mechanism that will automatically interrupt the circuit through the operating motor when the apparatus driven thereby has reached a limit of movement.

Another object is to provide a switch mechanism having the above characteristics 'wherein the movable switch member is moved. into and out of engagement with the contact members with a snap, thereby avoiding destructive arcing.

Another obiect is to provide a switch mechanism wherein the switch is positiveiy retained in engagement with a contact member or held out of engagementy therewith, until the switoh-member-actuating means has moved a determined distance, and

` wherein the switch member is actuated with a snap.

Another object is to provide a switch mechanism of the double-throw type wherein the switch member separately engages the Contact members and is positively held in engagement with the contact members until the switch-member-actuating means has moved a determined distance and wherein the switch member is withdrawn from one contact member and moved into engagement with the other contact member with a snap after said determined movement of the switch-actuating means.

Another object is to provide a switch mechanism of the double-throw type wherein the switch member is moved into contact with one member by a gravity-actuated member and into engagement with the other contact member b a yielding means, the tension of which 1s normally overcome by the gravity-actuated .member and whereby the switch member is made responsive to the variations of the load upon the gravityactuated member. e

These and other objects are attained by means of apparatus embodying the features herein described and illustrated in the accompanying drawin Referring to the drawings illustrating one embodiment of our invention, Fig. 1 is a transverse section through the switch mechanism taken on the line I--I of Fig. 2.

the re ive positions occupied by the ele- .uring various stages oi" their operations.

-l`.i.g. i an elevational. 'View similar to that ori iiig o, showing the reiative positions of certain elements "i the switch "s lthe switch r has been i original pf M...ion and into ngagei the opposite contact members Fig. d is o. diagram illustrating the conn nections the iimit switch with the controller and motor circuit.

Reierringto the drawings, the apparatus includes a bcn com rising a cover 8 and end walls Si and It@ which .are preferably cast integral with the bottom 1l oi the box. The cover is preferably made or' sheet metal which is vso 'formed that it tits snugly between'the end and is supported upon the inwardly projecting flanges 12 bordering the periphery thereof. The switch mechanismincludes a pair of separate insulated contact supporting bars 13 and 14 extending longitudinally of the box and arranged in parallel relation. 'The bars are supported upon the end plates or walls 9 and 10 and carry the contact units 15 and 16, respectively. Any desired number of contact units may be arranged in spaced relation upon the-'bars 13 and 14 and, in the present embodiment of the invention, two units of a well known type are mounted in spaced reiation upon each Each contact unit includes the usua blowout coil i?, contact termina-l 1S, and a stationary contact member which is disposed between the arc shields For the purpose of illustration, the contact members of the units 15 and 16 are designated by the numerals 20 and 21, respectively, and, as illustrated in Fig. 1, occupy positions on opposite sides of the axis of the switch shaft 22 which extends longitudinally of the box 8. The shaft 22 is rotatably journaled Aat one end to the endv switch shaft are axially aligned and may be relatively rotated.

Referring to Figs. 3 and 4, the switch unit of the apparatus includes the shaft 22 and a pair of switch members 23a mounted upon the shaft in spaced relation. The switch members are so positioned that they rotate in the transverse planes of the contact members and may be oscillated between them. Each switch member includes a clamping member 27 secured to the shaft 22 and which is provided lwith a clevis at its upper end, in which a pair of contact supports 28 are pivotally mounted for rotation about the pins 29. The upper ends of the supports 28 carry the switch contacts 30 and 31 and the lower ends are rovided with inwardly directed webs 32 w ich are adapted to engage the edges of the clamp member 27. rEhe contact supports 28 are yieldingly held in a predetermined position with respect to the clamp member by means of a compression spring 33 which is mounted between the supports 28 and which tends to separate the contact members 3@ and 31. The outward movement of the supports 28 is limited b the webs 32 which abut against the edges o the clamp member 27 when the spring 33 is distended. rl`he clamp 27l is i rigidly secured to the shaft 22 by means of the bolts 34. The contact members 30 and 31 are connected to the bolts 34 by flexible conductive strips 35 and eachY bolt 34 is connected to a se arate terminal 36 by means of a flexible con uctor 37. (See Fig. 1.)

From the foregoing it will be seen that the switch contact 30 will engage the contact member 20 when the switch member 23a is moved to ,the right and that the switch contact 31 will enga e the contact member 21 when the swltc member is moved to the left.

In order to reduce the destructive arcing to a minimum, it is well known that the contact members should be. instantl separated in the operation of the switc In the particular application for which this mechanism is intended, it is necessary to connect one terminal with another with the greatest rapidity inl order that the sequence of o eration of the apparatus controlled there y shall not be detrimentally affected. It is an object of this invention, therefore, to withdraw the switch member from a lcontact member and move it into engagement with the opposite contact member with a quick snap. To accomplish this function, the operating shaft 25 is connected to the switch shaft 22 by a flexible connection which will permit relative movement of the shafts. gagement Vwith the contact member by 'a latch adapted to be released by engagement with the member carried by the operating shaft when the latter has moved a predetermined distance. The principle of operation is, therefore, that rotary movement of the operating shaft first exerts a tension upon the switch member tending to withdraw it from engagement with the Contact member. The sprlng is stretched as the ope'ratinor shaft is rotated until the latch is tripped and the switch member is released. The latter then snaps into en agement with the contact member in an e ort to resume its original position with respect to the operating lever.

The mechanism for accomplishing this operation includes a switch shaft crank 38 whichv is so mounted upon the square end 3b (Figs. 2 and 3) of the switch shaft 22 that movement of the crank imparts rotative movement to the switch shaft and to The switch member is held in enthe switch member 23a mounted on thev are provided with crank ins 42 and 43, re-

spectively, which, when t e operating shaft and the switch shaft are in normal o rative relation, overlap one another an occupy the same radial plane, the in 43 being closer to the axis of the s aft than the pin 42.

The cranks 38 and '40 are flexibly connected by means of a pair of be1l-crank levers 44 and 45 which are pivoted for rotation on the shaft 25 and arranged relatively in closed relation in the manner of pivoted tongs, the u per extensions 46 and 47, respectively, t ereof occupying positions on opposite sides of the crank ins 42 and 43. The lower extensions 48 an 49 of the bellcrank levers 44 and 45, respectively, are located on o posite sides of a lane traversing the ax o the shaft 25 and t e crank ins 42 and 43. The upper extension of each ever is positioned at the side of said plane opposite to that occupied by the lower extension thereof, and the levers are connected b imeans of a tension spring 50 which ten lto draw the upperandlower extensions of and the movable contact members 30 and 31 that are supported thereb will normally occupy a predetermined relation with respect to the operating lever 26 and it will be seen that, if the shaft 25 and the operating crank which is attached thereto are moved counter-clockwise, the crank pin 43 carried tlereb will positively engage the extension 4 an the bell-crank lever 45, which, in turn, will cause turning of the bell-crank lever 44 through the medium of the spring 50. The switch-shaft crank 38 is turned similarly by reason of the engagement of the extension.

46 with the pin 42 that is carried by the switch-shaft crank 38. Further, by reason of the above arrangement, turning of the operating shaft in a counter-clockwise direction is possible even though the move ment of the switch-shaft crank 38 be prevented. In this event, the bell-cranklever 44 remains stationar while the bell-crank lever turns with t e operating crank 40. Thisoperation causes the spring to be stretched but the tension tending to turn the bell-crank' lever 44 in a clockwise direction is not' increased, for the reason that, as the arm 49 turns about the shaft 25, the line of stress or the centerline of the spring is moved toward the shaft and, consequently, the leverage is sufficiently reduced to com pensate for the increased tension of the spring. It will be apparent, therefore, that .the pressure exerted by the upper lever 46 upon the pin 42 to withdraw the switch contact 30 from engagement with the contact 20, is maintained substantially uniform throughout the movement of the bell-crank lever 45. If the increased tension of the spring were not thus compensated, the switch contacts might be actuated with such force that the impact with the stationary contact members would bel destructive. shaft crank is released while the lower extremities of the bell-crank levers aril separated, as above indicated, the bell-cra lever 44 instantly snaps into its original relativo position with the crank pin 43. All that remains,therefore, to complete the switchv lmechanism is the latching means for holding the switch member in operative engagement with either contact, and the means actuated by the operating shaft for tripping the latch after the operating lever has moved to place the spring 50 under tension.

The latch mechanism includes a latch member 5 1 (Figs. 1 land 7) having an upwardly directed tripping arm 52 and a pair of pawl extensions 53 and 54. -The-latch lprovided with an integral lug 57 cause counter-clockwise turning of` Vhen the switch-v member is pivoted to the end plate 10 (Fig. 2) upon a stud shaft 55 which is riveted at one lend to the` end late 10 and which carries the latch mem er 51 at its inner extremity. The latch is retained in position on the shaft by means of a screw 56. The upper end of the switch-shaft crank 38 is l see Fig. which is adapted to be engage on its respective sides, by the pawl members 53 and 54 of the latchl. As shown in Figs. 1 and 6, the pawl is in engagement with the left side of the lug and serves to prevent separation of the switch contact 30 from engagement with the contact member 2Q. Fig. 7 shows the position of the elements when the switch Contact 31 is moved into operative engagement with the contact member 21. When the switch member occupies the position indicated in this figure, the pawl 54 engages the right side of the lug 57 andV prevents separation of the said contact members. The latch is retained in either extreme position thereofby means of a helical spring 58 which is pivoted, at its upper end, to a pin 59 carried by the latch member 51, and, at its lower end, to a pin 60 carried by the switch-shaft crank 38.

Referring to Figs. 1 and 7 showing eX- treme positions lof the switch member 23, it will be seen that the spring 58 functions as an olif-center spring and lies on different sides of the vertical plane cutting the axis of the stud shaft 55, when in `different extreme operative positions. Therefore, during the throwing movement of the switchshaft crank 38, for instance, when the switch member 23a is being moved toward the left from the'position indicated in Fig. l, the spring 58 will exert a stress upon the latch 51, tending to turn it counter-clockwise the instant the pin 60 moves to the left of the line traversing the axes of the stud shaft 55 and the pin 59 carried by the latch 51. This spring, therefore, so functions to tilt the latch ltromone extreme position to the other that it is always in position to oppose the return of the switch member or switchshaft crank 38 until the latch pawls 53 and 54 have been positively tripped out of engagement with the lug 57.

The latch is tripped by means of a pair of tripping arms 61 and 62 which are secured to the operating crank 40. Fig'. .6 shows two intermediate stages of the operation of moving the switch member 23 from the position indicated in Fig. 1 to the position indicated in Fig. 7, and, by reference thereto, it will be seen that the full lines indicate'the relative position of the operating crank 40, the switch crank 38 and the latch 51 when the tripping arm 61 engages the latch arm 52. In this position, movement of the switch-shaft crank 38 and, consequently, the switch, is prevented by the pawl 53. The broken lines indicate the position of the above-referred-to elements at the time when further movement of the operating crank has so moved the latch that the pawl 53 has just cleared the lug 57 on the switch-shaft crank 38. The operating crank 40, at this time, occupies nearly its extreme position to the let and is in position to draw the switch member to the position indicated in Fig. 7, wherein the switch contact 31 is in complete operative engagement;v

. is suspended, by means of a cable 63, a counterweight64 which tends to hold the switch elements in the position indicated in Fig. 1. A coil spring 65 surrounds the outer end of the operating shaft 25, and the ends 66 and 67 thereof respectively Vengage lugs 68 and 69 carried, respectively, by the end plate 10 and the lever 26. The spring is' so coiled that it tends to turn the operatin shaft in a counter-clockwise direction, as in icated by the arrow. The counter-weight, however, is of suiicient weight to overcome the tension of the spring and to hold the lever in the position'indicated in Fig. 5, wherein they switch elements 'occupy the positions indi cated in Fig. 1.

The switch member is moved to the left by reason of the action of the spring 65 when a lifting member 70, carried by some part. of the hoisting apparatus, raises the counter-weight, in accordance with a familiar practice. The movement of the lever 26 is limited between the stops 71 and 72, the former limiting the movement of the operating shaft in a clockwise direction and the latter limiting the movement of thesaid shaft in the opposite direction.

It has previously been stated that, in the present embodiment of the invention, there are two separate switch elements mounted on the switch shaft 22, each of which is provided with contacty members 30 and31 and that there are two separate stationary con. tact members 20 mounted on the supporting baril?) and two separate stationary contact members 21 mounted upon the supporting bar 14 and so dis osed that they will. be sep arately engaged oy the contact members 30 and 31 of the switch members, respectively.

Referring to Figs. 1 and 2 for the p se of illustration, the conductors connec to the contact members 20 are indicated by the numerals 7 3 and 74; the conductors connected to the contact members 21 are indicated by numerals and 76, and the conductors connected to the Switch contact members 3b and 31 are indicated by numerals 77 and 78.

The manner in which the switch contact` During the operation, current flows throu h v the conductors 79 and 80, the switch A., t e conductor 73, the contact member 20, the Contact member 30, the conductor 77, the motor armature 81, the conductor 78, the contact members 30 and 20, the conductor 74, the switch B, the conductor 82, the series vfield winding 83 of a hoisting motor, a

magnetic brake coil 84, a series resistor 85 Y and a main switch 86. When the operating member 70 carried by the hoist lifts the counterweight 64, the spring 65, being norlmally under tension turns the operating shaft 25 counter-clockwise and withdraws the contact members 30 from engagement with the contact members 2O and moves the contact members 31 into engagement with the contact members 21, as previously described. The separation of the contact members 2O and 30 breaks the circuit through the conductor 73 and the closure .of contact members 21 and 31 establishes a closed circuit through the -armature 81 and the series field winding 83 (see Fig. 8), which creates a dynamic-braking effect, tending to resist further rotation of the armature, in accordance with a familiar practice. The magnetic-brakin action is augmented by the dynamic-bra 'ng action set u in the motor the instant the switch has n operated. The motor is thus brought to rest within the safety limits. The limit-switch contact members )ust enumerated are, at this time, in a position that will not interfere with the reversal of the current through the armature when the controller switches A land B are opened and the switches C and D are closed to produce the reverse movement of the hoist, -as will be evident from an inspection of Fig. 8.

The instant the; operating member -70 (see Fig. 5) recedes from its position in supporting engagement with the counterweight member 64, the limit switch is returned to its originalA position, in accordlao ance with the previousl described normal eflect of the counterweig t. It will be seen :from an inspection of Fig. 8 that the current through the armature at this time, by reason 0f the above-noted closure of switches C and D flows in a direction tending to operate the motor in a direction opposite to the original direction of rotation of the motor during the hoisting operation. From the foregoing, it ywill be evident that our limit switch in no way interferes with the normal :functions of the controller switches and only comes into operation in the event that the hoist is raised above a safe or determined limit.

While we have described and illustrated but one embodiment of our invention, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made in the apparatus i described without departing from the spirit and scope of the invention, as set forth by the appended claims.

We claim as our invention:

1. A circuit interrupter comprising a terminal contact member, a switch member adapted to be moved into and out of cngagement with the said contact member with a rolling motion, yielding means for moving the Switch member out of operative relation with the contact member, and means for latching the switch member in operative relation with the contact member under substantially constant contact pressure and adapted to be released by the said switchmember-moving means to permit sudden movement of the switch member 'when the said moving means has moved a determined distance.

2. A circuit intcrrupter comprising a. terminal contact member, a switch member adapted to be moved into and out of enn gagement with the said contact member, means for normally holding the said switch member in operative relation with the said contactr member under substantially constant contact pressure, an operating means for the switch member adapted to exert tension upon the switch member tending to disenga e the said member from the Contact mem er without relieving the contact pressure when the o eratin-g means is 4moved and to trip the said holding means when the operating means has traveled a determined distance to permit the switch member to move quickly in response to the tension applied by said operating means.

3. A limit switch comprising a. terminal contact member, a contactor type switch member adapted to be moved into and out of' enga ement-with the said Contact member, a latc i member adapted to move into engagement with the switch member when the latter is moved into engagement with the contact member for preventing separation of the switch from the contact member means for moving the switch member out of operative relation with the contact member and adapted to release the said latch member when moved a determined distance in a direction tending to withdraw the switch member from the contact member vand means for automatically restoring said switch mem'- bers. 4. A contactor switch mechanism compris- Inga pair of separate terminal contact members, a terminal, a switch memberfor separately engaging the said contact members and for connecting the said terminal separately with the contact members, an operating means for the switch member having a spring connection thereto and adapted to stress the said switch member into engagement with the said contact members, latching means for preventing the separation of the switch member from a contact member until the operating means has stressed said spring and means for insuring the restoration of saidl switch member.

5. A switch mechanism com rising a' pair of separate switch contact mem ers, a switch member adapted to be moved into 'separate engagement with the said contact members, latching means engaging the switch mernber for normally holding it in engagement with either contact member, a pair of switch operating members one ot which is adapted to move the switch into engagement with one Contact member and the other of which is adapted to move the switch member into engagement with the other contact member, tension means normally holding the said operating members in a redetermined relation with respect to t e switch member, means for moving one operating member independently of the other in opposition to said tension means and adapted to release the said latching means when moved a determined distance and thereby other operating member to witl draw the switch member from engagement with the contact member in response to the action of the said tension means.

6. A switch mechanism comprising a pair of se arate switch contact members, aswitch member adapted to be moved into separate enga-gement with the said Contact members, latching means engaging the switch member for normally holding it in engagement with either contact member, a pair of switchoperating members one of which is adapted to move the switch into engagement with one contact member and the other of which is adapted to move the switch member into engagement with the other contact member, tension means normally holding the said operating members in a predetermined relation with respect to the switch member, means'for moving one operating member independently of the other ini opposition to rmit the liti said tension means and adapted to release the said latching means when moved a determined distance and thereby permit the other operating member to move the switch member out of engagement with one contact member and into engagement with the other `With either contact member and to normally prevent withdrawal of the switch member from the contact member with which it is engaged, a pair of yieldingly connected switch-operating members, each responsive to movement of the other, and means for releasing the said-latching means rom engagement with the switch member when one of the operating members has moved a predetermined distance.

8. A switch mechanism comprising a Switch contact member, a switch member adapted to be moved into and out of engagement with the contact member, a switchoperating member adapted to move the switch member into engagement with the contact member, a switch-operating member adapted to move the switch member out of engagement with the contact member, yielding means connecting the said operating members Awhereby the said members are made responsive tomovements of one another, and means for preventing the movement of one member until the other has moved a predetermined distance.

9. A limit-switch mechanism comprising a contact member, a switch member adapted to be moved into and out of engagement 'with the contact membena spring-actuated means for moving the switch member in one direction, a gravity-actuated means for actuating the switch member in the opposite direction, and latching means for holding the switch member in an operative position and responsive to a determined movement of the said switch-member-actua-ting means and meansvcomprising said gravity actuated means for restoring said switch member.

10. A switch mechanism comprising a pair of separate contact members, a switch member adapted to separately engage the said contact members, a pair of yieldinglyconnected operating members for the switch member having a lost-motion connection therewith, means for separately actuating the said operating members to impart movement to the switch member, and means for arresting movement of the switch member until the operating members have been relatively displaced a predetermined distance.

11. A switch comprising two separate contact members, a switch member adapted to separately engage the contact members, a. oscillatable latch adapted to engage the switch member and normally retain it in operative engagement with either contact member, an operating member, a pair of tripping arms carried thereby for selectively engaging the latch andreleasing the .a

switch member when the said operating member is moved a predetermined distance toward an extreme operating position thereof, and a yielding connection between said v operating member and the switch member adapted to withdrawv the switch member from contact with a snap action when the latch is moved to releasing position by the operating member.

In testimony whereof, we have hereunto dslv'gcribed our names this 21st day of June,

CHARLES H. HoDGKINs. FRED M. PARKS. Y

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