US3010089A

US3010089A - Contactless snap-action limit switch

Info

Publication number: US3010089A
Application number: US774672A
Authority: US
Inventors: Pierce Lawrence; Marshall P White
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1958-11-18
Filing date: 1958-11-18
Publication date: 1961-11-21
Anticipated expiration: 1978-11-21
Also published as: JPS361180B1; CA640670A

Description

Nov. 21, 1961 L PIERCE ET AL CONTACTLESS SNAP-ACTION LIMIT SWITCH Filed Nov. 18, 1958 Fig. I.

Fig.6.

INVENTORS Lawrence Pierce 8 Marshall R White. BY

WlTNESSES: @W RKG' ATTORNEY United States Patent This invention relates to limit switches and more particularly to limit switches utilizing contactless static magnetic elements.

There are many limit switches known in the prior art but such prior art switches include movable contacts that present a maintenance problem, since the reliability and useful life of movable contacts fall short of the standards of operationrequired in many industrial applications.

One object of this invention is the provisionof movable and stationary magnetic elements for producing a pulse of magnetization in a magnetic circuit which is effective to produce a switching action in a circuit.

It is a broader object of this inventionto providemagnetically actuated contactless limit switches.

The objects recited are merely illustrative. Other objects and advantages will become more apparent from a study of the following specification and drawings, in which: i

FIGURE 1 is a plan view, with the casing removed, of a limit switch embodying the invention;

FIG. 2 is a longitudinal sectional. view of the showing made in'FlG. 1;

FIGS. 3, 4 and 5 show some elements in detail; and- FIG. 6 is a diagrammatic view of a basic circuit for a switching system with which the mechanical elements of this invention are used.

FIGS. 1 and 2 together showthe complete limit switch.

A molded assembly 12 carries. an encapsulated saturable reactor. The assembly is rigidly bolted to. the base 6. In

FIG. 2 the cover 1 is shown in position. The cover has the conduit opening at the left through which the leads are passechfor connection to the terminals 7. and 7 for.

leakage between the

magnets

2 and 3, rigidly mounted on.

shaft B. The length of shaft B is slightly greater than the width of the pedestal P.

The magnet 2 is securely clamped to the left, end of the shaft B by means of the brass screw A. Magnet 3 is similarly clamped on the right end of; shaft B by means of" brass screw E.

The structure of screw E is, however, considerably different than screw A. Screw E is somewhat elongated and has a shoulder at itsmid region with theregion to the right of the shoulder-being an enlarged cylindrical portion to form a bearing stud between the head ofthe screw and the shoulder for the brass beveled pinion 5 and; the

magnet 4 secured to the pinion 5. A pair of brass spacing washers, one to fit over the threaded, end Cfscrew E and one to fit over the cylindrical portion, are disposed between the magnets 3. and 4. Whenthe screw ,E is tightened into the brass sleeve

shaft Bthe magnets

2 and 3 are rigidlyclamped on shaft B to rotate, as a unit, but the bevel gear 5 and. magnet 4, secured to gear 5. by bracket 21, are free to rotate on screw E between the 3,010,039 Patented Nov. 21, 1961 screw head and the right-hand spacing washers disposed between magnets 3 and 4.

end being disposed, as seenin FlG. 2, in front of the pin 15 projecting rigidly vertically from the base 6, and the other end. being disposed behind both

pins

14 and 15. The bracket 13 has the construction shown in FIG. 4 and thus. must rotate with shaft 19.

A lever-18 is adjustably secured to the lower end of the shaft 19. The outer end of-the lever carries a roller which engages a suitable dog on. a movable part of a machine requiring a limit switch.

The magnet 4 is secured to the bracket 21 as shown in FIG. 3 and the back of the bracket, in the assembled relation, is brazed to the beveled pinion 5.

A non-magnetic stop 22, constructed as shown in FIG. 5, is boltedby means of a non-magnetic bolt to the base 6, as shown inFIG. 1. This. stop prevents the

magnets

2 and 3 from rotating clockwisewhen viewed from, the left. When the lever 18 is not actuated, the springlti so biases the parts that the south pole of magnet 4, is, whenviewed from the-left, about 45 degrees in a counterclockwise direction from the vertical. Magnet 4 thus tends to rotate magnet 3 clockwise, but the stop 22 prevents such rotation.

Magnets

2 and 3 are thus normally in avertical position with their north polesat the top.

In the showings of both FIGS. 1 and 2, the lever 18 is shown as having been actuated by the dog on the machine from the normal position of the magnets hereinbefore mentioned to just prior to the triggering position, This movement was for lever 18 from above the paper into the paper, as seen in FIG. 2, or from some clockwise position to the counterclockwise position shown in FIG. 1. As this movement continues, the magnets first line up as shown in both FIGS. 1 and 2, and a moment later as the north pole of magnet 4 moves-out of the paper, the north poleof magnet? is repelled, and both

magnets

2 and 3 move counterclockwise, as seen fron the left in FIG. 2, with a snap action. The reactance value of the reactor is thus changed from an unsaturated condition to a saturated condition, and the switching operation is effected.

When the dog on the machine, not shown, releases the lever 18 the spring 16 rapidly restores the lever 18 to its full; clockwise position (below the position shown in FIG. 1). As the lever 18 makesthis movement, the magnet 4 moves counterclockwise, and as it moves past its horizontal position, the

magnets

2 and 3 snap back to the position shown.

When the Alnico magnet 2 is in a vertical position,

- as. shown, then the major portion of its flux is shunted actor impedance will thus be low. This change in reactor, i-inpedanceis here used to operate the limit switch circuit shown in FIG. 6. i

This limit switch circuit comprises four rectifying elements D1, D2, D3 and D4, two resistors R1 and R2, and a contactless saturable reactor type limit switch comprism ing the switch assembly shown in FIGS. 1 and 2. As

above described, the switch among other elements comprises aperrnanent magnet 2 which is actuated by a quick action, as explained hereinabove to vary the saturation of the reactor core.

When the core 9 of the reactor is saturated only a small part of the applied voltage is absorbed by the reactor and most of the voltage appears at the output terminals of the switching system. When the core is unsaturated, the inductance, and hence the impedance, is very high and most of the applied voltage is absorbed by the reactor, and substantially none appears at the output terminals of the switching system.

As shown in FIG. 6, an alternating-current voltage of one phase, or instant polarity is applied to input terminal 113. An alternating-current voltage of a different phase of opposite instantaneous polarity 6 is applied to input terminal 114. An output terminal 130 may be con nected to a magnetic logic element of a control board. This logic element is set to select only 6 phase voltages. An output terminal 14 may be connected to a magnetic logic element which is set to select only phase voltages. Both magnetic logic elements are connected to a common conductor C. The resistor R1 is connected to a DC. voltage and resistor R2 is connected to a D.C. qb voltage.

As previously explained, when the limit switch reactor core 9 is unsaturated, the reactor has a high impedance which causes the 0 and outputs to go to zero. When the p input voltage is considered as being current flows through the rectifier D3 to provide a output of 13. However, this output signal is of no importance since the logic element LE6 which it is feeding is set to select only 9 voltages. There will be no 5 output at 14 because most of the applied voltage is absorbed by the reactor. The reactor magnetizing current is passed by the D2, R2, D.C. combination to hold the output at 14 at zero. The positive side of DC. qb voltage is connected to the common conductor C. When the A.C. voltage is considered as being the A.C. 6 voltage is and current is prevented from flowing by the rectifier D4. Therefore, there is no 0 output signal at this time.

When the A.C. 6 voltage is considered as being there will be a 0 output signal at 14. This signal is of no importance since the logic element LE which it is feeding is set to select only s signals. There is no 0 output signal at 130 because the applied voltage is absorbed by the reactor. The magnetizing current for the reactor is passed by D1, R1, D.C. combination, thereby holding the output at 130 at zero. When the A.C. voltage is the A.C. voltage is and current is prevented from flowing by the rectifier D3.

It should be noted that the reactor core is reset every half cycle. This is done first by one of the alternatingcurrent sources and then by the other. if the reactor core is not reset, the impedance would be small and the limit switch would be ineffective.

As previously explained, when the reactor core 9 is saturated by the magnet 2, there is only a small voltage drop across the reactor. Therefore, the A.C. voltage will appear at the output terminal 14 and the A.C. voltage will appear at the output terminal 130. Thus, the switching system may be used to control magnetic logic elements and thus load units. With both 0 and 5 outputs, it is possible to drive or operate twice as many logic elements as was previously possible. Also, it is possible to separately operate the 0 and o logic elements.

Since changes may be made in the above-described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

'We claim is our invention:

1.. In a l mit switch actuator, in combination, a base,

bearing means on the base, a first shaft disposed for rotation in said bearing means, a second shaft, a crankarm. mechanically coupled to said second shaft, said crank-arm being biased to a given position on said base, a permanent magnet rigidly coupled to one end of the first shaft and having its poles disposed on opposite sides of the first shaft, a second permanent magnet operatively coupled to the second shaft and disposed for free rotation on an axis coincident with the axis of the first shaft and being disposed in close proximity to the first magnet and in facing relation thereto, stop means disposed on the base and positioned to limit the movement of the first magnet through an angle that is a fraction of one complete turn, said stop being so positioned that the repulsion force of the like poles of the magnets, when the lever is in its biased position, forces the first magnet with a snap-action to one position with respect to the stop, switching means having two positions, said switching means being caused to move to one position with a snap-action upon movement of the first magnet to one position and, when the lever is rotated through a given angle from its biased position, force the first magnet, with a snap-action as the lever is being moved, to a second position with respect to the stop, said switching means being caused to move to its second position with a snapaction upon movement of the first magnet to its second position.

2. In a limit switch actuator, in combination, a base, bearing means on the base, a shaft disposed for rotation in said bearing means, a crank-arm mechanically coupled to one end of said shaft, said crank-arm being biased to a given position on said base, a bevel gear connected to the other end of of said shaft, second bearing means on said base having a bearing axis normal to the axis of the shaft in the first mentioned bearing means, a shaft in the second bearing means, a bevel pinion disposed for rotation on one end of the second shaft and meshing with the bevel gear, a firs-t permanent magnet rigidly coupled to the bevel pinion and having its poles disposed on opposite sides of the second shaft, a second permanent magnet secured to the second shaft disposed for free rotation with the second shaft and being disposed in close proximity to the first permanent magnet and in facing relation thereto, stop means disposed on the base and positioned to limit the movement of the second magnet through an angle that is a fraction of one complete turn, said stop being so positioned that the repulsion force of the like poles of the magnets, when, the lever is in its biased position, forces the second magnet to one position with respect to the stop, and, a third magnet rigidly coupled to the second magnet but spaced from the second magnet to be substantially unaffected by leakage flux from the second magnet, and inductive contactless switching means caused to operate by the snap-action movement of the third magnet.

3. In a limit switch actuator, in combination, a base, bearing means on the base, a shaft disposed for rotation in said bearing means, a crank-arm mechanically coupled to one end of said shaft, said crank-arm being biased to a given position on said base, a bevel gear connected to the other end of said shaft, second bearing means on said base having a bearing axis normal to the axis of the shaft in the first mentioned bearing means,

a shaft in the second bearing means, a bevel pinion disposed for rotation on one end of the second shaft and meshing with the bevel gear, a permanent magnet rigidly coupled to the bevel pinion and having its poles disposed on opposite sides of the second shaft, a second permanent magnet secured to the second shaft and disposed for free rotation with the second shaft and being disposed in close proximity to the first magnet and in facing relation thereto, stop means disposed on the base and positioned to limit the movement of the second magnet through an angle that is a fraction of one complete turn, said stop being so positioned that the repulsion 5 6 force of the like poles of the magnets, when the lever position causing a rapid change oi flux in said core to is in its biased position, forces the second magnet to one effect a switching operation.

position with respect to the stop, and, a third magnet rigidly coupled to the second magnet but spaced from the Refetences Cited in the me of patent second magnet to be substantially unaffected by leakage 5 UNITED STATES PATENTS flux from the second magnet, a core composed of mag- 2,378,129 Chambers June 12, 1945 netic material, a coil disposed on the core, pole pieces at 2,414,688 Chambers Jan. 21, 1947 Opposite ends of the core, said third magnet when moved 2,471,947 Giannini May 31, 1949 by snap-action from its unactuated position to its actuated 2,856,591 White Oct. 14, 1958