US2019093A - Electric switch - Google Patents

Description

Oct. 29, 1935. c. A. RASMUSSEN ELECTRIC SWITCH Filed March 19, 1934 2 Sheets-Sheet l octQ 29, 1935 Q RASMUSSEN 2,019,093

- ELECTRIC SWITCH Filed March 19, 1934 2 Sheets-Sheet 2 Patented Oct. 29, 1935 UNITED STATES PATENT OFFICE ELECTRIC SWITCH Christian A. Rasmussen, Cleveland, Ohio Application March 19, 1934, Serial blo. 716,370

3 Claims.

This invention relates in general to electric switches and more particularly to plugging switches for electric motors which embody current reversing switching means adapted to be automatically actuated when the switch is cut off for quickly braking the motor by reverse current. However the current reversing switching means of conventional plugging switches are mechanically controlled by the rotary movement of the motor so that the motor must reverse its direction of rotation before the braking reverse current can be cut off. Consequently these plugging switches are unsuitable where reverse rotation of the motor is objectionable, as for example in electrically driven tools, in which the motor is directly coupled with a tool, the rotation of which cannot readily be reversed without danger of damage.

It is the general object of the present invention I to provide a switch of the type referred to above with independent mechanical means adapted to cut off the braking current reversing means just before the motor completes its normal or desired rotation and comes to a complete stop under the i braking action of the reverse current. The ob- Jectionable reverse movement of the motor is thus avoided.

Another object of the invention is to provide a switch of the type referred to above with auto- 1 matically actuating shiftable switching means for controlling the braking current in the manner described above.

A further object of the invention is to provide a. plugging switch with driven, rotatable and axially shiftable means for actuating the shiftable controlling means for the braking circuit for automatically cutting out the braking current just before the motor stops rotating.

Still another object of the invention is to provide a simple, inexpensive and durable plugging switch of the type referred to above, of economic construction which may be readily assembled, and as easily disassembled for repairs and re- 5 placement.

' With the above and other objects in view which will appear as the description proceeds, my invention resides in the novel construction, combination and arrangement of parts substantially as m hereinafter described, and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claims.

to A physical embodiment of the invention is illustrated in the accompanying drawings in which:

vFigure 1 is a top plan view of the plugging switch, the cover and end walls being broken away to more clearly illustrate details of con- 5 struction;

Figure 2 is a transverse sectional view of the switch shown in Figure 1, the section being taken on line 2-2 of that figure;

Figure 3 is a longitudinal sectional view through the plugging switch the section being taken on line 33 of Figure 1;

Figure 4 is a transverse sectional view of the switch, the section being taken on line 4-4 01' Figure 3;

Figure 5 is an electrical diagram of a hook up of the plugging switch with a motor showing a push button control for the switch; and

Figure 6 is an electrical diagram of a hook up of the plugging switch with a reversible motor controlled by a master switch.

The improved plugging switch which is applicable for plugging operations in either direction of rotation of a motor, comprises a cast U-shaped housing member A, embodying a bottom wall 2 and oppositely arranged spaced end walls 3, which are preferably integrally formed with said bottom wall. A depending web portion or flange 4 also integrally formed with bottom wall 2, and having perforations 5 for the reception of bolts or the like, not shown, serves as a convenient means for supporting the housing. A screw shaft 6 rotatably supported in thrust ball bearings 8, is held in place against longitudinal movement by means of collars 9. The shaft 6 is geared or other- 36 wise suitably connected to the drive shaft (not shown) of a motor 50, to be controlled. As shown the thrust ball bearings are mounted in recesses III of plates II, which are seated in oppositely arranged flanged openings I! in the side walls 40 and secured thereto by bolts I4, but it should be understood that this arrangement is chosen merely to facilitate assembly and that the bearings 8 may be supported directly in the side walls. Mounted upon the threaded portion 1 of shaft 6 is a very heavy hubbed nut member 15, adapted for longitudinal or axial movement with respect thereto when the screw shaft 6 begins to rotate or when the screw shaft changes its speed of rotation. This nut member actuates and supports 5 a slidable switching mechanism S, for controlling the braking circuit of th plugging switch. as will be described later. Thus nut member [5 carries at its hubbed end 16 a thrust ball bearing l1 clamped thereto by a nut Hi. This :ba-ll bear- 66 ing is mounted in a cage l9 provided at its upper portion with a vertically disposed support or' arm 26, which is connected at its upper end to a base plate 31 of the switching mechanism S. The cage l9 carries or is integrally formed with oppositely extending bifurcated guide members or arms 2|, arranged at right angles to supporting arm 26, the bifurcations 22 of arms 2| being adapted to snugly accommodate threaded guide rods 23. These rods extend between the side walls 3 of housing A, parallel to and at opposite sides of screw shaft 6 and are rigidly held in place by nuts 24, threadedly engaged with the opposite ends of said guide rods. Rotation of the hubbed member I5 together with or independently of screw shaft 6 is thus possible, whereas tilting of cage l9, stem 26 and the switching mechanism S is prevented.

The switching mechanism S includes a pivotally supported contact member C which slidably contacts with contact strips 25, 25 and 26, 26' when said mechanism is in predetermined positions, the contact strips being mounted upon an insulating bridge 21, resting upon and secured to ledges 28 on end plates 3,'screws 29 being employed to secure the member 21 in place.' This contact member C comprises a body portion 30, having two downwardly extending end flanges 3| and two up wardly extending apertured side flanges 33. A pair of contact rollers 32 are supported between the end flanges 3| for rolling contact with the contact strips, whereas the apertured flanges 33 are connected to flanged end 35 of a lever 36, in turn hingedly connected to the base 31 of switching mechanism S. Thus lever 35 is formed at its hinged end with a narrow finger portion 38-, extended into and through a perforation 39 in the flange 40, of the supporting base or plate 31, which as previously explained is rigidly secured to the arm 20, the latter extending through an elongated slot 4|, in bridge 21, to permit of the switching mechanism S being moved to and fro with respect to contact strips 25, 25' and 26, 26. While lever 36 may freely turn or pivot on its hinge connection with supporting base 31, the hinge connection is such as to prevent the lever from becoming displaced or disconnected, as will be presently understood. A post 42 projecting loosely through an opening 43 formed in lever 36 prevents displacement of the latter and also serves as a mounting for a short helically coiled compression spring 44, which seats upon lever 36 and encircles post 42. The post 42 is securely screwed at its lower end into supporting base 31 and at its other end is screw threaded to receive an adjusting nut 45, employed to adjust the tension of compression spring 44. As the degree to which contact member C is pressed into engagement with the contact strips depends upon the tension of the spring 44, it follows that the extent of axial travel or movement of the nut l5 during stopping operations can be controlled to any desired extent. The switch mechanism is enclosed by a hood shaped cover member 46 which is supported upon a rim shaped flange 41 and secured to said flange by means of screws 48.

The operation of the plugging switch will best be understood from the electrical diagrams shown in Figures 5 and 6. In Figure 5 the three phase squirrel cage motor 56, previously referred to, is connected to the three wires 5 I, 52, 53 of a main line over two magnetically operated double pole contactors 54, 55. The contactor 54 controls the rotation of the motor in a forward direction or in the direction indicated by the arrow 68 in Figure 5, and the contactor 55 controls the rotation of the motor in a reverse direction. A double pole switch 56 of contactor 54 is automatically actuated by a coil 51, which is electrically connected to wires 5| and 53 of the main line by wires 58 and 59 and controlled by a push button switch 60. A double pole switch 6| of contactor 55 is automatically actuated by a coil 62, which is electrically connected to wires 5| and 53 by wires 63 and 64. Wire 64 is interrupted by two switches 65 and 66. The switch 65 is actuated by the X3011 51 in such a way that switch 65 is closed when coil 51 is not under current. The opening and closing of switch 66 depends upon the position of the hubbed nut member I5 on screw shaft 6, which nut actuates the switching mechanism S. Starting of the motor 5|] is effected by pressing button 61 of switch 60. This operation closes the circuit for coil 51, which then actuates the double pole switch 56. thus connecting the motor with the line. While switch 56 closes, switch 65 automatically opens and therefore prevents the flow of current through coil 62, which actuates the double pole switch 6|, thus connecting the motor with the main line for reverse rotation. When the motor 50 starts its forward rotation as indicated by arrow 68 the inertia of the heavy hubbed nut member 15 retards rotation of the latter member with respect to screw shaft 6. Consequently the nut member |5 travels axially on shaft 6, as indicated by arrow 69, and contact rollers 32 of contact member C will engage the contact pieces 25, 25' of switch 66 arranged in the circuit for coil 62. This relative longitudinal movement of nut IS with respect to screw shaft 6 is limited by stop members 1|) on threaded guide rods 23. After the nut |5 engages the stop members 10 the nut |5 rotates with the speed of screw shaft 6, and of course switch 66 remains in closed position.

When the motor 56 is to be stopped, the button 1| of switch 6|! is actuated to interrupt the circuit forcoil 51 to permit of the double pole switch 56 being opened by means of spring 12 or by gravity. In its open position double pole switch 56 closes the switch 65 by means of a bridge portion 13 and thus closes the circuit for coil 62, which now closes the double pole switch 6|, thus connecting the motor with the main line for reverse rotation. The reverse current brakes the motor so that the rotary speed of screw shaft 6 is quickly retarded, however, the rotation of relatively heavy nut member I5 is not so readily retarded as the rotation of screw shaft 6, and consequently nut member I5 will travel axially upon shaft 6, until the rollers 32 of contact member C ride out of engagement with the contact pieces 25, 25 and thus open switch 66 which controls the coil circuit for coil 62, so that spring 14 can readily open the double pole switch 6| and cut out the reverse current to the motor. 6

My improved plugging switch can be used for checking forward and reverse rotation of a motor, and can also be applied to motors, the speed of which is controlled by a master switch. An electrical diagram of a hook up for a master switch controlled motor is disclosed in Figure 6. In this diagram the hook up of the coils 51 and 62, for operation of the double pole switches 56 and 6|, is practically the same as that of the Figure 5 hook up, with the exception that the switch 65 of Figure 5 is placed into the master switch 15. The running position for the motor 50 in the Figure 6 diagram is designated II and the plugging position I.

As the motor 5|! can be run in forward or re-n Ierse the contact pieces 25, 25' and 26, 26' of the plugging switch are both connected to their respective circuits, that is to the circuits of coils 51 and 52. The travel of hubbed nut member IS in either a forward or reverse direction must of course be limited by stop members 10, but otherwise the operation of the device is identical with that disclosed in the Figure 5 diagram.

Preferably the spaces between contact pieces 25 and 26 and 25 and 26' are separated by recessed insulating pieces 16, the recesses 11 of which serve to arrest the movement of,;,the nut member l5, when switch mechanism S is in neutral position. The described switch embodying the independent mechanical means for cutting out any undesired circuit may also be used for directional switches or phase reversing protectional switches, which permit rotation of a motor in a single predetermined direction but prohibit rotation of the motor in reverse direction. Further slight modifications and changes in construction of the plugging switch may be made without departing from the spirit of the invention all as concisely pointed out in the following claims.

Having thus described my invention what I claim is:

1. In a plugging switch adapted to control the braking of the rotary speed of an electric motor,

a stationary switching member, a shiftable switching member having a downwardly extending arm, rotatable axially shiftable mechanical means for free rotation with respect thereto, a rotatably mounted screw shaft threadedly engaged with said rotatable means for shifting same laterally, when the said shaft is rotated by the motor to be controlled, forked means on the arm of said shiftable switching member for guiding same, guide rods for said forked means, and adjustable means on said guide rods for limiting the shifting of said forked means and therewith the shifting of said shiftable switch member and said rotatable, axially shiftable mechanical means.

2. In a plugging switch adapted to control the braking of the rotary speed of an electric motor,

a stationary switching member, a shiftable switching member having a downwardly extending arm supporting the outer race of a roller bearing, rotatable axially shiftable mechanical means supporting the inner race of said roller bearing whereby said rotatable mechanical means is coupled by means of said arm with said shiftable switching means for free rotation with respect thereto, a rotatably mounted screw shaft, threadedly engaged with said rotatable means for shifting same laterally, when the said shaft is rotated by the motor to be controlled, means on the arm of said shiftable switching member for guiding same, and means cooperating with said arm in limiting the shifting of said shiftable switch member and said rotatable, axially shiftable mechanical means.

3. In a plugging switch adapted to control the braking of the rotary speed of .a reversible electric motor, a stationary switching member em bodying two sets of contacts separated from each other by insulated material, a shiftable switching member adapted to bridge the contacts of each of said sets and to rest between the contacts of said sets, rotatable axially shiftable mechanical means coupled with said shiftable switching means for free rotation with respect thereto, and a rotatably mounted screw shaft threadedly engaged with said rotatable means for shifting same laterally when the said shaft is rotated by the motor to be controlled.

CHRISTIAN \A. RASMUSSEN.

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