US2747041A

US2747041A - Inertia operated shock load switch

Info

Publication number: US2747041A
Application number: US327254A
Authority: US
Inventors: Thomson Edward
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-12-22
Filing date: 1952-12-22
Publication date: 1956-05-22
Anticipated expiration: 1973-05-22

Description

May 22, 1956 E. THOMSON INERTIA OPERATED SHOCK LOAD SWITCH 2 Sheets-Sheet 1 Filed Dec. 22. 1952 y 1956 E. THOMSON INERTIA OPERATED SHOCK LQAD SWITCH 2 Sheets-Sheet 2 Filed Dec. 212, 1952 United States Patent INERTIA OPERATED SHOCK LOAD SWITCH Edward Thomson, Mount Vernon, Iii. Application December 22, 1952, Serial No. 327,254

13 Claims. (Cl. 200--61.46)

This invention relates to switches and is more particularly directed to an inertia actuated switch responsive to shock loads and which incorporates a magnetic element that assists in the operation of the switch.

One of the objects of the invention is to provide an inertia operated switch for a power circuit in which a magnetic over center actuator is employed.

Another object of the invention is to reduce the number of operating parts in a shock load release switch.

Another object of the invention is to provide an inertia actuated shock load release switch wherein a magnetic element is employed that assists in completing the relative motion of inertia element and the body of the switch after the relative movement of inertia element and body passes the mid or center point of its movement.

Another object of the invention is to provide a shock load release mechanism that can be placed in the drive motor circuit for opening the latter after the driven machine accelerates or decelerates greater than a prcdetermined rate.

A further object of the invention is to provide an inertia operated switch that can be quickly and sensitively adjusted for varying shock load conditions.

The invention consists in the provision of a shock load release switch wherein a make and break switch is actuated in response to the relative movement of an inertia device and the rotatable element with which it is asso ciated after said relative movement changes exceed a predetermined rate and wherein a magnetic element aids in completing said relative movement initiated by the inertia device.

in the drawings:

Fig. 1 is an end view of a device incorporating the invention,

Fig. 2 is an enlarged view taken substantially along the line 2-2 of Fig. i,

Fig. 3 is a view taken substantially along the line 3-3 of Fig. 2,

Fig. 4 is a view similar to Fig. 3 but showing the parts in different operative positions,

Fig. 5 is a sectional view similar to Fig. 2 of a modifled form of the invention,

Fig. 6 is a sectional view taken along the line 6-6 of Fig. 5 showing the switch in operative or closed position,

Fig. 7 is a view similar to Fig. 6 showing the switch in open position, and

Fig. 8 is an enlarged detailed structural view showing the method of assembly of the parts.

The invention is embodied in the several views of the drawings in which the numeral 1 designates the casing for the shock load release switch. This is an annular body in which a shaft 2 is rotatably mounted in a cylindrical bearing holder member 3 suitably secured to the casing i. The cylindrical member 3 is provided with suitable bushings 4 serving as bearings for the shaft. The shaft is normally equipped with a pulley or rigid coupling (not shown) and is placed between the load and r 2,747,041 Patented May 22,1956

ice

the motor that drives the machine on which the. release switch is installed. The invention is particularly useful for the driving of machine tools such as drill presses, tapping machines or similar devices. The machine drive is interconnected with the shaft 2 so that the shock load release switch is driven in unison therewith. The shaft 2 extends into the casing 1 and a cup-shaped inertia member 5, preferably being made of non-magnetic material, is supported on the shaft by suitable bushings 6. The inertia member is adapted to rotate with or relative to the shaft depending upon load conditions in the device.

The shaft 2 is provided with an armature 7 to which it is suitably secured and disposed between the ends of an annular magnet 8. This magnet is preferably formed from a paramagnetic material and the ends are spaced apart to form a gap in which the armature 7 is received. The preferred material is that sold under the trade name of Alnico or any suitable steel, and the use of an electromagnet is also contemplated in lieu of the permanent magnet shown. The magnet is suitably held within the cup-shaped inertia member and has an air gap between the ends thereof. During normal operation a bridging device 9 is secured to the armature 7 and is intended to bridge the gap between the ends of the magnet 8 to thus permit a freer and better flow of the magnetic lines of force. it is also used as a counterweight to produce more correct dynamic balance. I

The shaft 2 is provided with a cam 10 preferably made by milling off a portion of the shaft so as to form a flat surface thereon. The cam 10 moves the movable element 11 of a switch 12 so as to make and break a control circuit for the driving motor previously discussed, the element 11 being pivoted to the closure 24 for the inertia member 5. The movable element has a contact 13 secured thereto engageable with a fixed contact 13' suitably fastened to the base of the switch mounted on the closure for the inertia member 5. As the shaft 2 and the armature 7 move relative to the inertia member, the movable element of the switch will move with respect to the fixed element thus separating the

contacts

13 and 13 or bringing together depending upon the direction of motion of the armature 7 relative to the inertia device. The relative movement of armature and inertia device is based upon the change in the rate of the speed of the driven device or machine and when this rate exceeds a predetermined amount the inertia device will continue rotating in its normal speed and cause the switch contacts to separate thus interrupting the circuit to the drive motor, the separation or engagement being caused by the action of cam 1i) and follower 11.

The engagement of the armature 7 with one end of the magnet 8 causes the inertia element to be rotated with the shaft 2 and the armature 7 and the relative motion discussed above takes place upon the predetermined change in rate of rotation of the driven device. The amount of shock load at which the armature 7 is separated from the adjoining end of the magnet, as for instance shown in Fig. 3, will depend upon the air gap that is present between the armature and the end of the magnet. This gap is regulated by means of screws 14 and 1 also designated as stationary points threaded into the inertia device. These screws preferably are nonmagnetic so that they will not influence the adherence of the armature to the magnet. Thus by altering the size of the gap between the armature and the end of the magnet the amount of shock load required to produce an opening or a closing of the

switch contacts

13 and 13 will be readily determined. Enough clearance is left between cam surface 10 and the cam follower 11 to allow for the adjustment of armature 7 relative to the adjacent end of the magnet 8 to form an air gap when the contacts 13 and 13' are in closed position.

3 The casing is provided with a pair of conductors 15 and 16' suitably held in the removable cover 17' of the casing 1. Suitable insulating bushings and brush holders 18 are provided to receive. these conductors in the cover and each has a tubular extension 19 thereon that slidably holds brushes 2%). Springs 21 are provided between the brushes and the base of the tubular extensions to force the brushes into contact with collector rings 22 and '23 suitably secured to and insulated from the removable closure 24 for the cup-shaped inertia member 5.

Contacts

13 and 13 are electrically connected to

collector rings

22 and 23 respectively and as previously indicated are in the circuit of the driving motor. A manual switch 25 (Fig. 2) is connected across the

conductors

15 and 16 for initially starting the drive motor in the event the contacts 13 and 13' may not be in engagement with each other. The member 3 is provided with a grease fitting 26 for lubricating shaft 2.

During the operation of the device should the machine tool or other mechanism to which the shock load release switch is connected encounter in its operation a shock load that would tend to break a drill bit, tap, other tool, or cause machine breakage and which would not open the circuit breaker or blow fuses because of the extremely short period of time in which the obstruction to the operation of the machine occurs the instant device will open the drive motor circuit. Assuming that it is a drill bit that is jammed, the shaft 2 being driven by the drill bit spindle which, in turn, is driven by the motor that is connected to the

conductors

15 and 16, the

switch contacts

13 and 13 will be caused to open due to relative movement between the cam and the contacts by reason of the momentum of the inertia member causing the armature 7 to shift from the Fig. 4 to the Fig. 3 position. In other words when a momentary slow-down of shaft 2 occurs the armature 7 (Fig. 4) will also slow down while the inertia membercarrying the switch will continue rotating until the condition of Fig. 3 is attained. When the shift takes place the contacts 13 and 13' will be separated thus breaking the circuit to the drive motor.

When the device is to be started the switch 25 connected across the conductors and 16 will be closed thus permitting the motor to be started and since the mass of the inertia member is far greater than that of the shaft 2 and the armature 7 the latter will rotate relative to the inertia member so as to restore it to the Fig. 4 position. At this time the switch may be reopened and since the armature 7 now is in contact with one end of the magnet 8 or the adjusting screw 14' it will cause the inertia member to rotate with the armature. Motion will continue until the machine being driven encounters another sudden shock load whereupon the performance of the device will be repeated. It is thus apparent that a suitable and reliable device has been provided which breaks a circuit to a drive motor when a sudden load is applied to the machine which is of such a nature that will not open the circuit breaker or blow a fuse that may be connected in the power line leading to the motor. This device reduces tool breakage and damaged goods to such an extent that breakage is practically unknown and prevents burn-outs of the driving motor and permits restoration of the operation of the machine when the cause for the shock load has been removed. It is assumed that the direction of rotation of the inertia member and the shaft 2 is normally in the direction of the arrows shown in the figures of the drawing.

A modified form of the invention is shown in Figs. 5-S in which the numeral 30 designates a stationary casing in which a shaft 31 is rotably mounted. An inertia ring 32 is secured to

discs

33 and 34 rotatably supported on the shaft 31 by means of suitable bushings.

A nonmagnetic spacer is secured to the shaft 31 that has a length substantially equal to the width of the inertia ring 32. Secured to the spacer 35 is a magnet 36 made of paramagnetic material and is preferably made from each other.

4 a material sold under the brand name of Alnico. The armatures 37' and 37" for this magnet are extensions of the inertia ring 32, whose ends are turned radially inward to form the armatures.

Screws

38 and 39 are threaded into the armatures for controlling the size of the air gap and the amount of shock load required to cause the inertia ring and magnet to rotate relative to The screws are preferably formed from a suitable nonmagnetic material in order not to influence the action of armature and magnet.

A switch .8, constructed in the same way as switch 11, is securedto the disc 34. A cam 41 cut in shaft 31 cooperates with a follower 42 for opening and closing the points on the switch 4.0. Collector rings 43 and 44 are secured to and insulated from the disc 34 and serve the same purpose as the collector rings in the disciosure of Figs. 1-4.

The operation of this device is the same as that defined above. It is assumed that the brush structure and starting switch are provided as above.

In each of the above disclosures the switches 11 and 49 are equipped with springs 45 for normally holding

points

13 and 13 in engagement with each other. While

screws

38, 39 and 14, 14 have been defined as nonmagnetic it is not a strict necessity that they be limited thereto. Each screw adjusts the air gap but performs different functions. Gne screw determines the reduction in speed necessary to cause relative motion of armature and magnet while the other regulates the resetting of the armature for starting purposes when switch 25 is closed.

What I claim is:

l. A shock load release switch comprising a casing, a shaft rotatably mounted therein, an annular inertia device mounted on said shaft for rotation with or relative to said shaft, an annular magnet secured in said inertia device and having a gap therein, an armature secured to said shaft and located within said gap and in contact with one end of said magnet, a non-magnetic adjusting means located in each end of the magnet for adjusting the spacing between the armature and magnet, a switch mounted on said inertia device, and a cam in said shaft for actuating said switch upon relative rotational movement of said inertia device and shaft, said armature aiding in completing the relative movement as it moves through said gap into engagement with the other end of said magnet.

2. A shock load release switch comprising a casing, a shaft rotatably mounted therein, an annular inertia device mounted on said shaft for rotation with or relative to said shaft, an annular magnet secured in said inertia device and having a gap therein, an armature secured to said shaft and located within said gap and in contact with one end of said magnet, a member mounted on said armature for substantially bridging the gap in said magnet, a switch mounted on said inertia device, and a cam in said shaft for actuating said switch upon relative rotational movement of said inertia device and shaft, said armature aiding in completing the relative movement as it moves through said gap into engagement with the other end of said magnet.

3. A shock load release switch comprising a casing, a shaft rotatably mounted therein, an annular inertia device mounted on said shaft for rotation with and relative to said shaft, an annular magnet secured in said inertia device and having a gap therein, an armature secured to said shaft and located within said gap and in contact with one end of said magnet, a non-magnetic adjusting means located in each end of the magnet for adjusting the spacing between the armature and magnet, a member mounted on said armature for substantially bridging the gap in said magnet, a switch mounted on said inertia device, and a cam in said shaft for actuatingv said switch upon relative rotational movement of said inertia device and shaft, said member aiding in completing the relative rotational movement as it moves through said gap into engagement with the other end of said magnet.

4. A shock load release switch comprising a casing, a shaft rotatably mounted in said casing, an inertia element, means for supporting said inertia element upon said shaft for rotation with and relative to said shaft, a make and break switch mounted on said means, a cam on said shaft, means connecting said cam and switch to actuate same upon relative rotation of said shaft and inertia element; and a magnet carried by said shaft to assist in completing the relative movement, the inertia element forming an armature for said magnet.

5. A shock load release switch comprising a casing, a shaft rotatably mounted in said casing, an inertia element whose ends are projected radially inward to form a gap between the ends, means carried by said shaft for supporting said inertia element about said shaft for rotation therewith or relative thereto, a magnet mounted on said shaft, the inturned ends of said inertia element forming armatures for said magnet, a make and break switch mounted on said means; and a cam on said shaft for actuating said switch upon relative rotation of said inertia element and shaft, whereupon said magnet moves from a position adjacent one armature to a position adjacent the other.

6. A shock load release switch comprising a casing, a shaft rotatably mounted in said casing, an inertia element formed into a circle about said shaft and whose ends are directed radially inward to form armatures for a magnet, means carried by said shaft for supporting said inertia element, a make and break switch mounted on said means, cam means on said shaft for operating said make and break switch, a magnet mounted on said shaft adapted to swing between said armatures, upon relative rotation of said shaft and inertia element; and means for adjusting the air gap between said magnet and each armature.

7. A shock load release switch comprising a casing, a shaft rotatably mounted in said casing, an inertia element formed into a circle about said shaft and whose ends are directed radially inward to form armatures for a magnet, means for supporting said inertia element, a make and break switch mounted on said means, cam means on said shaft for operating said make and break switch, a magnet mounted on said shaft adapted to swing between said armatures, upon relative rotation of said shaft and inertia element; a screw extending through one of said armatures for engagement with said magnet for determining when said shaft and inertia device will rotate relative to each other to open said make and break switch; and a screw means in the other armature for determining when reverse relative rotation will occur for closing said make and break switch.

8. In an inertia actuated shock load responsive device, a casing for the device, a rotary shaft bearinged in said casing, a member fixed to said shaft so as to be movable with said rotary shaft and disposed within said casing, a second member disposed within said casing so as to be movable relative to said rotary shaft, said second member providing a gap to receive said fixed member and limit the extent of relative movement between such members, one of said last mentioned relatively movable members being formed from magnetic material and the other thereof acting as an armature for the magnetic member, said relatively movable members being magnetically coupled when in adjacence at one limit of the gap to rotate together with said shaft and said second member being freed from said magnetic coupling to rotate relative to said fixed member to the other limit of the gap upon a shock load reaction in said shaft, and circuit controlling switch means in said casing adapted to have a circuit make position in said first mentioned magnetically coupled position of said members and a circuit break position in said second mentioned relatively rotated position of said members, said switch being operated by said members.

9. in an inertia actuated shock load responsive device, a casing, a rotary shaft bearinged in said casing, 21 first member in said casing carried by said shaft to respond to shaft rotation, a second member in said casing bearinged upon said shaft to rotate relative to said shaft and providing a gap to receive said first member and allow limited relative movement between such members, one of said members being a magnet and the other an armature for the magnet member whereby such members have a magnetic coupling effect to retain them, adjacent one limit of relative movement allowed by the gap in said second member, adjustable means carried by said second member adjacent the gap to engage said first member and adjust the air gap spacing of said members for varying the strength of the magnetic coupling effect at said one limit of relative movement, said magnetic coupling effect at said one limit position being broken upon a shock load reaction in said shaft, and circuit controlling switch means between said relatively movable members normally in circuit make position with said members magnetically coupled together at said one limit and in circuit break position following a shock load reaction in said shaft breaking the magnetic coupling effect between said members, said switch being operated by and in response to relative movement of said members.

10. In an inertia actuated shock load responsive device, a casing, a rotary shaft bearinged in said casing, a first member carried by said shaft within said casing, a second member relatively movably carried by said shaft adjacent said first member, said second member having a gap therein to receive said first member and limit relative movement between said members, one of said members being magnetic and the other acting as an armature whereby said members are magnetically coupled at each limit of relative movement in the gap, adjustable means on one of said members in position to be engaged by the other member at the limit positions in the gap for determining the strength of the magnetic coupling efiect by adjusting the air gap space between said members, circuit controlling switch means carried by said second member adjacent said shaft, and cam means on said shaft to actuate said switch means toward circuit break position upon a shock load reaction in said shaft causing relative movement of said members to one limit of the gap, the opposite relative movement of said members causing cam actuation of said switch means to circuit make position.

11. The inertia actuated shock load responsive device set forth in claim 10, wherein said adjustable means is nonmagnetic.

12. The inertia actuated shock load responsive device set forth in claim 10, wherein said second member is formed of magnetic material and acts as the magnetic member.

13. The inertia actuated shock load responsive device set forth in claim 10, wherein said first member is formed of magnetic material and acts as the magnetic member.

References Cited in the file of this patent UNITED STATES PATENTS 1,638,718 Vroman Aug. 9, 1927 2,280,114 Athy Apr. 21, 1942 2,294,605 Newell Sept. 1, 1942 2,294,606 Newell Sept. 1, 1942 2,415,344 Eksergian Feb. 4, 1947