US3281551A - Mechanical oscillatory switch - Google Patents

Description

R m m 0mm 11 m e O a, m c Wm M Q B 1 3 M 52 w W MW w \J a+a2 1 M J. t :2 Wm M P w L. BECKE MECHANICAL OSCILLATORY SWITCH 30? J9 l E 302 Filed Feb. 25. 1964 Get. 25, 1966 United States Patent 3,28 MECHANHCAL OSQILLATORY SWETCH Ludwig Becke, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, witzerland,

a joint-stock company Filed Feb. 25, 1964, Ser. No. 347,188 Claims priority, applicaztigggswitzerland, Mar. 1, 1963, 63 5 Claims. (Cl. Nil-61.45)

The present invention relates to electrical switch construction and more particularly to an improved construction for a safety switch whose contacts are actuated in response to creation of abnormal vibratory forces. The general construction as to which the present invention constitutes an improvement is comprised of a springloaded mass which is normally attracted to and held by a magnet, but wherein this mass will 'be caused by acceleration forces incident to mechanical vibratory forces of a predetermined magnitude, to break away from the magnet and actuate the switch contacts.

Safety switches of this type are in common use on machinery to protect the latter against strong vibrations. For example, they are used on rotating machinery such as turbines, generators, etc. to protect the same in the event any strong vibrations are produced which could cause damage to the foundation for the machine or its bearings. Such machines are normally mounted and so balanced that normal vibrations incident to normal running are very small and cause no damage. However, should damage occur within the rotor element of the machine such as failure of one or more blades of a gas or steam turbine, the unbalance which results creates very strong virbations which'may have dangerous consequences for the machine and in particular its bearing suspensions. To provide the necessary protection for the machinery, vibration-responsive switches of the general type mentioned are mounted on the machine in any suitable position such as on the bearing housing and in the event strong vibrations arise, the switch contacts are closed and either give a warning signal or cause the'machine to be stopped.

Vibration-responsive switches which have so far been developed have the disadvantage that they respond to only very strong vibrations and are not sufficiently sensitive. The mass member attractable to the magnet is loaded in the direction away from the magnet by compression of a helical spring, and in addition the mass is fastened through a flexible joint to the base plate. In the event of a strong vibration or impact, the mass is broken away from the magnet as the acceleration forces exceed the magnetic attractive forces and strikes against a pin which in turn actuates the electrical switch contacts to a closed position. A screw is usually provided to effect an adjustment of the loading force exerted by the spring and hence makes it possible to set the response point at which the mass breaks away from the magnet. The disadvantage of this arrangement is that a very slight adjustment brings about a very wide range of variation for the break-away response point of the mass. In the case of automatic systems which are not supervised by personnel, however, it is necessary to bring about a warning signal or a disconnecting operation for the machine even at relatively smaller vibration amplitudes. For this rea son the known constructions are not adequate.

The improved construction in accordance with the present invention eliminates many of the disadvantages inherent in the prior known arrangements and is characterized by an improved mounting arrangement for the mass and the magnet. More particularly, the mass is mounted on a cantilever type spring and the magnet is mounted on an adjustable double reduction dual lever system. With 3,281,551 Patented Oct. 25, 1966 this construction, adjustment of the response point for the mass is made, not on the spring, but rather on the double lever system.

The foregoing as well as other advantages inherent in the invention will become more apparent from the following detailed description of one suitable embodiment of the vibration-responsive switch and from the accompanying drawings which illustrate the same. In these drawings:

FIG. 1 is a view in side elevation of the switch with certain parts shown in section;

FIG. 2 is an electrical schematic view of one suitable circuit arrangement incorporating the switch and which enables the protective system to distinguish between sustained vibration forces which characterize actual imbalance conditions within the machine and occasional vibrations or impacts which have a rather long interval therebetween and hence indicate occasional extraneous forces not harmful to the machine; and

FIG. 3 is also an electrical schematic view of another circuit arrangement similar to FIG. 2 in that it is enabled to discriminate between harmful and non-harmful forces.

With reference now to the drawings and to FIG. 1 in particular, the improved switch construction includes a base plate 1 which is adapted to be mounted on 'a suitable surface of the machine for which it is to protect against severe vibrational forces. For example, it can be mounted in a force-transmitting relation to the bearing housing whose vibration is to be monitored. Upstanding at one end of plate 1 is a block 2 in which is anchored, by insertion, one end of a cantilever spring leaf 3. A mass 4 of magnetic material is mounted at the opposite, free end of spring 3 and this mass normally rests upon a spacer ring 5 which in turn is supported on the base plate 1. Within the opening in spacer ring 5 is located a magnet 6, preferably of the permanent type, which is arranged for vertical adjustment to an extremely fine degree by means of a double reduction effect established by a dual lever system. For this purpose magnet 6 is supported on the flat upper face of a first lever 7 that is provided with depending feet at the front and rear ends thereof and which terminate in knife edges 7a and 7b, respectively. The rear knife edge 7b rests upon the flat upper face of base plate 1, and since lever 7 is located above a second lever 8, the contact between knife edge 7b and the upper face of base plate 1 is established in any suitable manner such as by passing the rear foot of lever 7 through a slot 8b in the lower lever 8. The front knife edge 7a rests upon the flat upper face of the second lever 8. The front end of lever 8 is provided with a depending foot which terminates in a knife edge 8a that rests upon the upper face of the base plate 1 and the rear end portion of lever 8 is provided with a vertical threaded hole 9 which receives a vertically disposed adjusting screw 10, the lower end of which also engages the upper face of base plate 1. By turning adjustment screw 10 in one direction or the other, one is able to make a corresponding adjustment in the height of the magnet 6 and hence effect a similar adjustment in the spacing and hence the degree of magnetic attraction maintained between the upper face of magnet 6 and the lower face of the mass 4. It is preferred to always maintain a certain spacing as between mass 4 and magnet 6 to prevent the mass from sticking to the magnet which, if it occurred, would result in faulty operation of the safety switch.

The adjustment in magnetic attraction as between mass 4 and magnet 6 is extremely sensitive due to the use of the novel double-lever transmissions 7-8 interposed between screw 10 and magnet 6 as is readily apparent from FIG. 1. Thus, when screw 10 is turned in one direction or the other, lever 8 will rise, or fall, about a fulcrum established at knife edge 8a at the opposite end of this lever. This in turn will cause knife edge 7a of tlever 7 to also rise, or fall, but the amplitude of displacement of knife edge 7a will be only a small fraction of the displacement of screw since knife edge 7a is located close to that end of lever 8 at which knife edge 81: is llocated. Similarly, the rise, or fall, of knife edge 7a results in a rise, or fall, of lever 7 about a fulcrum established at knife edge 7b at the opposite end of lever 7 where magnet 6 is located, and hence causes a rise, or fall, of this magnet. However, the amplitude of displacement of magnet 6 will be only a small fraction of the displacement of knife edge 7a. Thus, it will be evident that the displacement of screw 10 is reduced once at knife edge 7a by a factor which varies with the length of lever 8, and is then reduced 21 second time at magnet 6 by a factor which varies with the length of lever 7. This double reduction effected by the dual lever system 78 thus provides an extremely fine control so that even a complete revolution of adjustment screw 10 will result in only a very small displacement of magnet 6. Also, the magnetic attraction established between mass 4 and magnet 6 which overcomes the counter-loading force of spring 3 will be so adjusted that there is no movement of the mass 4 in the direction away from magnet 6 under vibrational or impact conditions having magnitudes less than what has been selected as critical. However, in the event this critical value is exceeded, mass 4 will pull away from the magnet due to the related acceleration forces in combination with the constant force in such direction as represented by the loading of spring 3. This causes the upper face of mass 4 to strike against pin 11 which in turn causes the contacts, not shown in this view, of switch 12 to be actuated and raise the desired alarm or bring the machine to a stop before any damage can be caused. For resetting the mass 4 so that the latter again comes under the influence of the attractive magnetic field of magnet 6 after normal conditions are restored, a reset plunger 16a is provided. This reset plunger can be actuated manually by pressing downwardly on the head part or it can be actuated electromagnetically by having it function as the core element of a solenoid 16. Solenoid 16 will be energized at the proper time to reset the mass 4 in accordance with the alternative circuit arrangernents shown in FIGS. 2 and 3.

Coming now to the circuits in which the safety switch 12 is connected, two such alternatively usable circuits being shown in FIGS. 2 and 3, respectively, it should be noted that it is quite necessary for the alarm or machine shut-down systems to remain passive, i.e. non-responsive, to isolated, or infrequent, spurious shocks on the machine not related to such sustained large vibrations or shocks which come about as a result of some damage within the machine itself which is reflected by rotational imbalance. Both circuits illustrated will provide the necessary discrimination.

FIG. 2 shows a circuit which includes a step-switch mechanism. In this circuit the spring 3, mass 4, switch 12 and reset solenoid 16 from FIG. 1 are depicted somewhat schematically. It will be noted that the contacts of switch 12 serve, when closed, to close a circuit for energizing electromagnet 13 and also relay 14. Magnet 13 then attracts its pivotally mounted armature and causes the toe of the latter to advance, by one step, the step wheel 151. Relay 14 attracts its contact 143 which establishes a holding circuit for the relay coil. Relay contact 141 of this relay also closes after a time delay 1 to energize magnet 18. A further relay contact 142 of this relay also closes after a time delay t The time delay t should be less than t Closure of relay contact 142 serves to complete a circuit for energizing the reset solenoid 16, which as previously explained, serves to reset mass 4 to its initial position on spacer ring 5.

The system of FIG. 2 operates such that step wheel 151 is advanced one step each time the contacts of switch 12 are closed. After time has expired, mass 4 will be reset by energization of reset solenoid 16. If a second mass-moving impact occurs immediately following the first one, wheel 151 will be advanced another step and this will be sutficient to bring the spring-mounted arm 152 rotated by step wheel 151 into such position as to actuate the contacts of switch 17 to a closed position and thereby energize the circuit A which actuates the alarm signal or shuts down the machine. The details of the actuating circuit A have not been included since they are not considered to be essential to the present invention and moreover can take a wide variety of forms already known.

In the event the impacts act upon mass 4 at very infrequent intervals, the time delay mechanism represented by relay 14 runs out after expiration of time t and effects closure of relay contacts 141. This effects energization of magnet 18 and the resulting movement of its armture 180, which also engages the steps on step wheel 151, serves to rotate the wheel 151 one step backward to its initial position. Thus, the system remains passive and no alarm or machine shut-down takes place. The system of FIG. 2 is thus able to discriminate as between actual faults arising within the machine which bring about a sustained vibration effect, and infrequent vibrations or shocks which may occur and which have no relation to the operating condition of the machine itself.

The circuit arrangement illustrated in FIG. 3 is similar in final function to that shown in FIG. 2 but operates with electrical relays only. As with the FIG. 2 circuit, the spring 3, mass 4, switch contacts 12 and reset solenoid 16 are shown schematically. In this particular arrangement, closure of switch contacts 12 serves to energize relay 19 having two sets of contacts 191 and 192 which are closed without any time delay.

Closure of contacts 191 serves to energize relay 20 which has two sets of contacts 201 and 202. Contacts 201 close immediately and contacts 202 close after expiration of a time delay period t Contacts 201 serve as hold-in contacts for the relay coil to keep the latter energized even after relay contacts 191 re-open.

Closure of contacts 192 serves to energize relay 21 which is a timing relay with a delay release characteristic. That is to say, this relay releases its contacts 211 after expiration of time period but pulls in without any deliberately introduced delay. Closure of relay contacts 192 also serves to energize relay 22 which closes its contacts 221 after expiration of time delay period t The circuit of FIG. 3 operates in the following manner. As in the previous case, any impact force exceeding the critical value set on the safety switch will cause mass 4 to pull away and close the switch contacts 12. This serves to energize the auxiliary relay 19 to close its two sets of contacts 191, 192. Closure of contacts 192 energizes relay 21 which in turn immediately closes its contacts 211. Closure of relay contacts 191 will now supply voltage to relay 20 which, since contacts 211 are already closed, immediately close its contacts 201 and thereby hold itself in. Contacts 202 will close only after time Closure of relay contacts 192 also serves to energize relay 22 but which does not yet effect closure of its contacts 221, the latter being closed only after expiration of time delay 1 which, incidentally must be shorter than 1;; and t and this serves to energize the reset solenoid 16 to thereby reset mass 4. If another shock follows immediately on the heels of the first one, relay 19 is thereby immediately energized again and relay 20 continues to run, so to speak, without having been released, as the circuit has remained closed through the relay contacts 211. If there occurs still another re-setting operation through relay 22 and if thereupon another shock occurs, relay 20 runs down with the time t closing its contacts 202 and thereby energizing the alarm or machine shut-down circuit A.

If the shocks do not immediately succeed one another relay 21, which is de-energized after contacts 192 have been re-opened, releases after expiration of time period i and thereby de-energizes also the timing relay 20. Thus, the entire arrangement is then brought into the rest position once again. Thus, the circuit of FIG. 3 will also discriminate properly as between a sustained vibration or shock effect incident to actual machine damage and occasional shocks which reflect no damage whatsoever.

In conclusion, the improved safety switch construction which has been described operates in the prescribed discriminatory manner and also functions with a very fine degree of sensitivity as a result of the very fine adjustment obtainable through use of the double-lever magnet support mechanism and the leaf spring support for the mass which produces a rapid and definite switching.

I claim:

1. In a vibration responsive safety switch, the combination comprising a base plate adapted to be secured to a machine part whose vibration is to be monitored, a leaf spring mounted on said base plate, a mass of magnetic material mounted on said leaf spring, an adjustable double reduction dual lever system mounted on said base plate, said dual lever system comprising a first lever including a point of rest at the forward end thereof bearing on said base plate and an adjustable screw at the rear end thereof bearing against said base plate, and a second lever including a point of rest at its forward end bearing on the forward end of said first lever and another point of rest at its rear end bearing on said base plate, a magnet mounted on the rear end of said second lever, said rnagnet serving to attract and hold said mass against a counter biasing force exerted by said leaf spring only for vibration forces which do not exceed a critical magnitu-de selectable by the adjustment made on said double lever system to effect a corresponding variation in the spacing between said mass and magnet, and switch means including contacts actuated in response to a break-a-way of said mass from said magnet.

2. A safety switch as defined in claim 1 wherein said leaf spring is of the cantilever type.

3. A safety switch as defined in claim 1 and which further includes spacer means interposed betwen said mass and magnet to prevent said mass from touching said magnet.

4. A safety switch as defined in claim 1 and which further includes means for resetting said mass and spring to their initial positions.

'5. A safety switch as defined in claim 4 wherein said resetting means for said spring and mass is constituted by an electromagnet.

References Cited by the Examiner UNITED STATES PATENTS 1,529,650 3 1925 Darlington. 1,765,479 6/ 1930 Benson. 2,007,371 7/1935 Hopkins et a1. 340-261 2,03 0,237 2/ 1936 Brittain et a1.

FOREIGN PATENTS 623,733 7/ 1961 Canada. 893,170 4/ 1962 Great Britain.

MILTON O. HIRSHFIELD, Primary Examiner.

SAMUEL BERNSTEIN, STEPHEN W. CAPELLI,

Examiners.

I. A. SILVERMAN, Assistant Examiner. r

Claims (1)

1. IN A VIBRATION RESPONSIVE SAFETY SWITCH, THE COMBINATION COMPRISING A BASE PLATE ADAPTED TO BE SECURED TO A MACHINE PART WHOSE VIBRATION IS TO BE MONITORED, A LEAF SPRING MOUNTED ON SAID BASE PLATE, A MASS OF MAGNETIC MATERIAL MOUNTED ON SAID LEAF SPRING, AN ADJUSTABLE DOUBLE REDUCTION DUAL LEVER SYSTEM MOUNTED ON SAID BASE PLATE, SAID DUAL LEVER SYSTEM COMPRISING A FIRST LEVER INCLUDING A POINT OF REST AT THE FORWARD END THEREOF BEARING ON SAID BASE PLATE AND AN ADJUSTABLE SCREW AT THE REAR END THEREOF BEARING AGAINST SAID BASE PLATE, AND A SECOND LEVER INCLUDING A POINT OF REST AT ITS FORWARD END BEARING ON THE FORWARD END OF SAID FIRST LEVER AND ANOTHER POINT OF REST AT ITS REAR END BEARING ON SAID BASE PLATE, A MAGNET MOUNTED ON THE REAR END OF SAID SECOND LEVER,

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