US2490320A - Method for adjusting spring mechanisms - Google Patents

Description

Dec. 6, 1949 R. w. PASHBY 2,490,320

METHOD FOR ADJUSTING SPRING MECHANISMS @j gef/W? Jigs.

Dec. 6, 1949 R. w. PAsHBY 2,490,320

METHOD FOR ADJUSTING SPRING MECHANISMS Filed Sept. 25, 1946 3 Sheets-Sheet 2 STEP ONE (2l/f6# EVER 59 42 STEP TWO Fig. 7

DGC- 6 1949 R. w. PAsHBY 2,490,320

METHOD FOR AnJusTING SPRING MEcHANrsMs Filed sept. 25, 194e 3 sheets-sheet s hob'. c?

Patented Dec. 6, '1949 METHOD FOB ADJUSTING SPRING MECHANI Robert w. Pashby, Perk mage, nl., signor to First Industrial Corporation, W

ilmington, Del.,

a corporation of Delaware Application September 25, 1946, Serial No. 099,315

1o claims. 1

The present invention relates to a method for the adjustment of spring mechanisms, particularly to those types of snap acting spring mechanisms employed in certain electric switches. It is especially adapted to the adjustment of overcenter snap acting spring mechanism such as employed in compactprecision type electric switches illustrated by the McGall Patent 1,960,020. Apparatus for eiecting adjustment in accordance with this method is disclosed and claimed in copending application, Serial No. 699,314, filed September 25, 1946.

Hand adjustment of small compact snap acting switches has long been a bottleneck in their manufacture. The production of individual parts oi' the switches as well as their assembly has long been completely mechanized so that one worker could produce thousandsl of individual parts or assemble thousands of switches per day; but adjustment for the desired operating and release forces have been carried out only by painstakingly slow hand methods requiring a high degree of skill and entailing much trial and error.

The object of the present invention lies in the provision of a method which eliminates this long existing production bottleneck by enabling the switch adjusting operation to be made completely automatic so that all the operator has to do is feed in the switches to be adjusted. For example. in the case of one specific type of switch that the present method has been appliedto,

'one workman can adjust approximately 3200 switches in a day as contrasted with approximately 400 by the old hand method. Furthermore, the adjustment made by the present method is far more competent and accurate than present with the hand method.

A primary object of the present invention is to provide a method of adjusting a self-returning spring mechanism by initially positioning the spring support to one side of a preferred position and deforming or moving the spring support toward its preferred position While at the same time applying a predetermined release load to the spring system and terminating the deformation or movement of the support when the spring system snaps to released position.

Another object of the present invention lies in the provision of a method of adjusting a compact precision type switch having a casing with an overcenter snap spring system mounted. on a support and carrying a movable contact between normal and abnormal positions, one modication of the method comprising the steps as follows: initially assembling the spring system and support within the casing in sucha manner that the support is positioned one side of the posi'- tion it must assume for propenope'ration of the switch, and with the lspring system in normal position; moving the spring system to abnormal position by a load exceeding a predetermined maxi- `mum operating force for the switch, this load `being applied to the spring system at the 'point normally engaged by the operating plunger in the assembled switch; changing "the loading on the spring system operating point to a value determined by the desired release force for the switch and applying a force to the support to deform or move it toward a position to cause the spring system to snap from abnormal to normal position; and terminating the movement or deformation oi the support at the time the spring system moves to normal position.

Other objects and advantages will become apparent from the following description in connection with the drawings in which- Figure l is a longitudinal sectional view of' one form of compact precision type snap acting switch which is presented to illustrate how the method of the present invention may be applied to the adjustment of an overcenter spring system;

Fig. 2 is a sectional view of Figure 1 on the line 2 2;

Fig. 3 is a perspective view of the spring system shown in Figure 1;

Fig. 4 is a perspective view of the spring supporting member shown in Figure 1;

Fig.- 5 is a diagram showing a representative set of forces required to maintain'the plunger of the Figure 1 switch in various operative positions;

Fig. 6 is a diagrammatic view of one form of apparatus illustrating the rst step in adjusting an electric switch by the method of the present invention;

Figs. 7, 8 and 9 are diagrammatic views similar to Fig. 6 illustrating second, third and fourth steps involved in the method of the present invention.

As will be seen, the method of the present invention is applicable to the adjustment particularly during manufacture of self-returning snap acting mechanisms generally, as well as speciiically to the adjustment of electric switches employing snap acting mechanisms.

Referring first to Figures 1-5, inclusive, for a preliminary description of the construction and operation of the switch shown, it includes an insulating case having a base I0 and a cover Il; upper and lower stationary contacts I3 and Il,

respectively, having terminal tabs |8 and I8; and a movable double faced contact I8 carried by an overcenter snap spring member 2| which is connected at the opposite end to the terminal tab 23.

The snap spring system 2| comprises a thin leaf tension element 24 which is connected in cantilever fashion to terminal tab 23 by means of screws 22 and 28, and bushing 28. A pair of thin leaf compression elements 3| are joined to the tension element 24 at the movable contact |8 and pivotally supported intermediate the ends of the tension element 24 where they bear against an anchor or support member 32 (see Fig. 4). This support member 82 is cut out in the center so as to clear the tension member 24 and has a pair of notches 33 for receiving and pivotally supporting the compression elements 3|. The spring is such that when the plunger 34 is depressed with a force slightly in excess of 25 ounces, in the case of the particular switch illustrated, as shown in Fig. 5, it will move the tension element 24 downward through a position of maximum stress in line with the pivot grooves 33.

This will cause the spring system 2| to move downwardly to its abnormal position where the movable contact I8 is maintained in engagement with the lower stationary contact I4 as long as the operating plunger is maintained depressed. As shown in Fig. 5, as soon as the operating positionis passed, the force required to maintain the operating plunger depressed will be much diminished and a force of ten ounces will be suillcient to maintain it beneath the operating position. To release the switch, the force on the operating plunger will be released and it will move upward to the release position which in the case of the switch illustrated is approximately .0035 inch above the operating position. At the release point, the force of the plunger will have dropped to six ounces and at this time the tension element 24 will have been allowed to move upwardly to a position once more in line with the anchor pivots 33. Thus, in the present instance, the release force will be six ounces and when the downward force on the operating plunger is diminished below that the spring system 2| will snap upwardly beyond the position of maximum stress to its normal position where the movable contact I9 will once more engage the upper stationary contact I3.

The apparatus shown diagrammatically in Figures 6-9, inclusive, to illustrate the progressive operative steps in the method of the present invention is the same as disclosed in the aforesaid copending application.

The -switch already described in connection with Figs. 1-5 inclusive, is fragmentarily shown much enlarged with respect to the scale of the rest of the apparatus in these diagrammatic views. Upper and lower loading arms 88 and 81 are pivotally mounted on pins 81 attached to the stationary fulcrum member 88. The pointed extension of the lower arm 81 is engageable with the spring tension element 24 at 20 (see Fig. 3) where the switch plunger 34 normally engages the spring system when the switch is assembled.

Upper arm 88 is adapted to apply its weight to the lower arm through roller |06. A vertically movable rack 38 is engaged with a pinion 25, the latter being mounted on a rotatable shaft 31. An electromagnetic clutch coil 42 is mounted on a clutch lever arm 38 which in turn is keyed to the shaft 31. An operating lever 8| shown only partially in the diagrammatic views of Figs. 69, is

` rotatably journaled about the shaft 31 independently thereof, and can be swung independently of the clutch lever when the coil 42 is deenergized. An armature 82 is mounted on the operating lever 8| and is adapted to be attracted to the clutch coil 42 when the latter is energized. An operating handle 83 is mounted on o ne end of the lever 8| and the opposite end of the lever is elongated and adapted to open a normally closed switch |48 which is referred to herein as the preloading switch." Movement of the loading arms 81 and 88 through a series of positions to apply preselected loads to the spring system 2| in predetermined sequence as the rack 38 is lowered is controlled by the lifting bar |83 and lower a'rm pin |82 which coact to lift the weight of both arms from the spring system when the rack is raised and also by the lifting lever which is mounted on the stationary post ||3, the lifting lever being engageabie by pins 82 and ||2 onthe rack and upper arm, respectively, to liftthe upper arm from the lower arm when the rack is moved downwardly. The preloading switch |48 and clutch coil 42 are connected in series with the current source |48 by means of conductors |8|, |82 and |83; and in this instance the spring system 2| of the switch being adjusted and the clutch coil 42 are connected in series with the current source 48 through conductors |8|. |84, |88, |82 and'|83. |48 may be either an alternating current or direct current source but direct current is preferable since in many instances a cheaper clutch can be used.

Operation Considering now the application of the present invention employing the apparatus shown diagrammatically in Fig. 6 to adjust a self-returning switch such as shown in Figure l. the adjustment will be carried out with the cover plate and operating plunger 34 removed so that the lower loading arm extension |8| and rack 38 may extend through the open top of the casing |8. .Step 1 in the adjustment consists, therefore. of mounting the casing portion of the switch within a suitable mounting means beneath the loading arms and rack.

The clutch lever 38 will have a suitable counterweight (not shown) attached to it so as to urge the clutch lever counterclockwise to the position shown in Figure 6 where it will be at the beginning of the adjusting operation. The lifting bar |03 on the rack 38 will normally maintain both loadingarms 81 and 88 in raised position as also shown in Fig. 6. The end of the operating lever 8| opposite the handle 83 will be heavy enough to act as a counterweight and maintain the handle 83 in a raised position substantially as shown in Fig. 6 with the armature 82 proximate to the clutch coil 42. In the Fig. 6 position the clutch coil 42 will be energized through the preloading switch |48 by current source |48 so that the clutch coil and armature will be magnetically connected and downward movement of the handle 53 will cause the clutch lever 38 to follow it as long as the coil is energized.

Fig. 7 illustrates step 2 where the handle 83 has been moved downward to lower the rack bar |03 suillciently to permit the weight of both loading arms 81 and 88 to be applied to the tension element 24 of the spring system 2|. The combined weight of arms 81 and 88 will .be suilicient to apply a load to the spring system in excess of the operating force for the switch being adjusted, in this case -25 ounces (see Fig. 5). This will "operate" the spring system 2|, that andere is, move the carried contact I9 from its upper or normall position to its lower or abnormal position in engagement with the stationary contact I4. Clutch coil 42 is now energized by the current source |49 through both the preloading switch |48 and the springr system 2| which is being adjusted. Fig. 8 illustrates step 3 where the handle 53 has been moved to lower the rack 38 further an amount suicient to move the pin 82 down upon lever which in turn is effective' to lift the upper arm from the lower arm by engagement with the pinv ||2. The weight a'pplied by the lower` arm 81 upon the tension element 24 is now anproxmately the desired release force for the spring system, in this case (see Fig. 5) being approximately six ounces. Theoretically, if the anchor 32 were made of comerable, for example, in a switch of the type in whichthe plunger extends through the base inf stead of through the cover and the anchor or pletely non-resilient material which would not spring back after deformation. the loading applied by the lower arm 81 would be exactly the release loadv desired, in this case, exactly six ounces. Actually, to compensate for this springback, the load applied by the lower arm 81 will be somewhat in excess of the theoretical six ounces, the exact load being best determined by experiment for a particular size and shape of support 32.

Between the second step (Fig. 7) already described and the fourth step (Fig. 9) to be described, the operating lever 5| will be moved to the position shown in Fig. 8 where it will open the preloading switch |48, thereby causing the clutch coil 42 to be energized by current source |49 only through the spring system 2| which is being adjusted.

Fig. 9 illustrates the fourth and last step, when the handle 53 moves the rack 38 clown upon the ends of the anchor legs '|1, while the release load is applied to the spring tension element 2d, and by a load transmitted through the magnetic clutch, deforms the anchor leg 'i1 downward until the pivot grooves 33 are moved past the plane of the tension element 24 at which time the spring system snaps to its upper or normal position, deenergizes the clutch coil i2 and releases the operating lever 5| from the clutch so as to prevent further deformation of the support 32.

Thus, a basic feature of the method of adjusting spring systems by the present invention com-v prises applying a preselected release load to the spring system, moving or deforming the spring support until the spring system moves from one position to another, and terminating the movement or deformation of the support at the time the spring system moves.

While the method of the present invention hasbeen described in connection with a selfreturning snap acting switch it will obviously be applicable to self-returning snap acting systems generally. Furthermore, while the invention has been described as applied to the adjustment of a double throw switch it is likewise applicable to normally open or normally closed types.

The difference between the operating and release forces, which is known as the force diilierentia-l and in the present instance indicated as i9 ounces in Fig. 5, is substantially consistent for a given distance between the stationary contacts when substantially identical parts are used. For this reason, adjustment of either the operating or the release force to a particular value will automatically adjust the other to a particular value determined by the stationary contact spacing. To adjust the switch in this spring support is so positioned `that the movable contact .would normally engage the lower stationary contact instead of the upper stationary contact. -Thus, the method of the present in vention also contemplates broadly applying a preselected load, not necessarily a release load, to the spring system and concurrently applying a force to permanently move a support for the spring system to effect the movement of the l latter from one position to another.

It will be obvious that the present invention may be appliedby a number of minor changes that will readily suggest themselves to others skilled in the art without departing from the spirit and scope of'the present invention.

Having thus described the invention, what is claimed as new is:

l. The method of adjusting an assembled spring mechanism having a spring system movable between two positions and a separate support member for said spring comprising the steps of applying a preselected load to the spring system and permanently moving the support in one direction sucient to cause movement of the spring from one to the other of said two positions.

2. The method of adjusting an assembled mechanism having an overcenter snap spring system movable between two positions and a separate support member for a portion of said spring system comprising the steps of applying a preselected load to the spring system, permanently moving the support member through an axis of maximum stress to cause said spring system to move from one to the other of said two positions, and terminating the permanent movement of said support member at that time.

3. The method of adjusting a self-returning type of snap acting spring mechanism having an overcenter snap spring system movable between normal and abnormal positions and a support for said spring system comprising the steps of moving said spring system to abnormal position, applying to said spring system while in abnormal position a load determined in accordance with a preselected release load, permanently deforming said support to initiate movement of said spring system from abnormal to normal position, and terminating the permanent deformation of said support at the time of saidv movement of said spring system to normal position.

4. The method of adjusting an assembled spring mechanism having a spring movable between two positions anda separate support for said spring, comprising the steps of forming the spring support so that when assembled with the spring a portion of the support supporting the .spring is out of a preferred conguration in a preselected release force for the assembled mechanism, and permanently moving the support in the direction of said preferred configuration until the spring moves to its other position.

5. The method of adjusting an assembled snap acting spring mechanism having an overcenter snap spring movable between normal and abnormal positions and a deformable support for said spring, comprising the steps of initially forming the spring support so that when assembled a portion of the support supporting the spring will be spaced from a preferred position, loading the spring to move it from normal to abnormal position, thereafter loading the spring to an extent determined by a preselected release force for the assembled mechanism, and deforming the support in the direction' of the preferred configuration until the spring moves from abnormal to normal position.

6. The method of adjusting an assembled mechanism having an overcenter snap spring system movable between two positions, a support for a portionl of said spring system, and mounting means for said spring system and support, comprising the steps of: forming the support rinitially so that when assembled upon the mounting means a portion thereof supporting the spring will -be spaced from a preferred location; applying to the spring system in one of said positions, a predetermined force corresponding to a preselected release force; applying a force to the support to permanently bend the support toward its preferred position while said predetermined force is effective on the spring system; and terminating the bending of said support when the movement thereof is suiliclent to cause said spring system to snap from said one position to the other position.

'7. The method of adjusting an assembled snap acting mechanism having an overcenter snap spring system movable between two stable positions, an operating plunger engageable with a portion of said spring system, and a support for a portion of said spring system, comprising: a step of loading the spring system at said position while the spring system is in one of said positions by a force dependent on a predetermined release force for the mechanism; and a succeeding step of movin a portion of the support carrying the spring system toward its said preferred position while said spring system is subject to said force in said one position until said spring system is caused to snap to the other of said positions.

8. The method of adjusting an assembled snap acting mechanism having an overcenter snap spring system therewithin movable between normal and abnormal positions, an operating plunger engageable with a portion of said spring system and a support for a portion of said spring system, comprising: a step of loading the spring sy;tem at the portion normally engaged by the plunger when the mechanism is fully assembled with a force exceeding a predetermined maximum cperatz'ng force for the mechanism to cause the spring system to move to abnormal position; a succeeding step of loading the spring system, at said portion normally engaged by the plunger, while the spring system is in the abnormal position, with a force determined by a release force for the mechanism; and a succeeding step o! moving a portion of the support carrying the spring system towards its said preferred position while said spring system is subject to the last mentioned force until said spring system is caused to move to normal position, and terminating the movement of said support at that time.

9. The method of adjusting an assembled electric switch having mounting means, an overcenter snap spring system canying a contact movable between two contact positions and a support for a portion of said spring system cornprising the steps of forming the support initially so that when assembled upon said mounting means a portion thereof supporting the spring will be spaced from an axis of maximum stress: applying to the spring system a predetermined force tending to hold it in one of said two positions; passing an electric current through said contact atsaid one contact position; applying an adjusting force to the support to move the support toward said axis of maximum stress while said predetermined force is eilective on said spring system in said one position; and terminating the application of adjusting force in response to the interruption of the current upon movement of the spring system to the other of said positions. 10. The method of adjusting a switch having when assembled a casing with an overcenter snap spring system therewithin movable between normal and abnormal positions, an operating plunger engageable with a portion of said spring system and a bendable support for a portion of said spring system, comprising: a step of initially assembling the support and spring system within the casing so that said support is located to one side of a preferred position and said spring system is in its normal position; a succeeding step of loading the spring-system at the position normally engaged by the plunger when the switch is fully assembled by a force exceeding a predetermined maximum operating force for the switch to cause the spring system to move to abnormal position; a succeeding step of loading the spring system, at said position normally engaged by the plunger, while the spring system is in the abnormal position, by a force exceeding a predetermined minimum release force for the switch; and a succeeding step of bending the support toward said preferred position, while said spring system is in abnormal position, until said spring system is caused to move to normal position, and terminating the bending of said support at that time.

ROBERT W. PASHZBY.

REFERENCES CITED The following references are of record in the

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