US2832874A - Lever-retarding accessory for dental engine - Google Patents

Description

J.M.CLAUSER ETAL LEVER-RETARDING ACCESSORY FOR DENTAL ENGINE Filed May 10. 1954 '/Z5 I 5 1 2/ 7L J; l

INVENTORQ United States PatentO LEVER-RETARDING ACCESSORY FOR DENTAL 2 ENGINE John M. Clauser and Frederick K. Clauser, St. Louis, Mo., assignors to Midvale Dental Supply Company, St. Louis, M0., a corporation ofMissouri Application May 10, 1954, Serial No. 428,458 g 6 Claims. 01. 201-48 This invention relates in general to controllers for dental engines and, more particularly, to a lever-retarding accessory therefor. The invention is particularly adapted for engines operated atthe relatively high speeds of 12,000 R. P. M. which is a recent development in dental practice.

Dental engines for operating discs and burrs are usually driven by electric motors which have associated therewith a speed controller normally located on the floor and including a horizontally movable lever having a pedal portion at each of its ends for operation by the users foot. Connected to the lever is a control arm for progressive movement across a series or shunt resistance, fixed contacts arranged concentrically of the controller for increasing or decreasing the engine speed. Contacts on one side of the median line of the controller cause rotation of themotor in one direction-while the contacts on the other side of said line will effect rotation in the opposite or reverse direction. The lever is biased into off position by return springs, so that upon release of the lever from any one of its circuit-closing positions, the same will be automatically swung to move the control arm to circuit-open position.

On release of the lever from high speed position, wherein the shunt resistance is open, it will rapidly accelerate under influence of the springs with the interval of travel from such position to off position being relatively short. Ithas been noted that during such interval, a well-developed sparking takes place between the commutator and brushes. Such sparking is intense enough to cause pitting of the commutator and a burning of the brusheswhich materially decrease engine effectiveness, requiring periodic replacement of parts. If the movement of the lever from high speed to off position be retarded sufficiently, sparking between the commutator and brushes is reduced to non-damaging proportions.

Assumedly, the destructive sparking is due to selfinductive flow of current which occurs across the brushes; also,'the short-circuiting action of the brushes on the coils brought out to the commutator segments; also, the electro-motive force generated by the armature under its own momentum after the circuit is opened.

It the control lever moves slowly enough towards off position, the effects noted above are decreased to an extent that the destructive sparking is avoided.

The main object of the present invention is to slow the return of the control lever upon the operators release of the pedal and avoid the rapid action otherwise resulting from the force of the return springs.

Another object is to provide an accessory for ready application to a common form of pedal and lever of a dental engine controller for slowing down the action of the lever-return-spring and activated by the speed of the lever.

Another object is to utilize the inertia of a weight applied to the control lever to obtain the slowing down effect.

Another object is to provide an accessory for application to a controller leverand pedal which will provide frictional resistance to the action of the lever-returnspring in order that the lever may move more slowly from high speed to off position.

Another object is to provide an accessory of the character stated which can be cheaply manufactured; which may be installed upon the lever by unskilled individuals;

which may be adapted for use with various types of lever mounting and an associated foot-actuated controller to which the invention may be applied. 1

Figure 2 is a fragmentary side view of the controller provided with a lever retarding accessory embodying the present invention.

Figure 3 is a fragmentary top plan view of the accessory shown in Figure 2; and related controller mechanism.

Figure 4 is a perspective view of another form of leverretarding accessory constructed in accordance with the present invention.

Figure 5 is a fragmentary side view of a controller lever and pedal provided with an accessory of the form shown in Figure 4.

The dental engine 1 is mounted on a supporting yoke conventional type foot controller having a cylindrical casing 5 with a'rcuate openings 6 in the sides thereof through which extends a. horizontally movable lever 7 pivoted at P and enlarged at its ends to form pedals 8. Movement of the lever by either pedal in clockwise or anti-clockwise direction shifts a well-known rheostat device to start and accelerate the motor step by step according to the positions determined by the operator. Such movement elongates one of springs S and when the pedal is moved to return the lever to normal off position, the spring ordinarily would accelerate the lever movement to such extent as to result in undesirable sparking.

To avoid this result, there is mounted upon each pedal 8 a lever-retarding accessory comprising a pair of parallel side plates 9, 10 atopposite sides of pedal 8 and spaced apart by rivets 11 and sleeves 12 above and below the pedal. Plate 9 has an extension 13 projecting across and above lever 7 with its lower edge resting on the upper face of the lever, spaced from the inner end of pedal 8. Extension 13 terminates in a flange 14 turned inwardly toward controller casing 5, parallel to plates 9, 10. Mounted upon flange 14 by pivot pin 15 is a normally vertically disposed rocker arm 16 projecting in its lower portion downwardly beyond lever 7 and having its lower end weighted, as at 17. The upper portion of rocker arm 16 forms a clevis 18 opening toward controller casing 5 for supporting a rotatable pin 19 which mounts a friction wheel 20 of rubber or similar material. Friction wheel 20 will normally be in immediate proximity, but out of contact with, controller casing 5.

When the operator releases foot pressure on pedal 8 and lever 7 and a spring S rotates the lever from high speed position to off position, the lower weighted end of rocker arm 16 will swing outwardly through centrifugal force as the lever is accelerated, causing wheel 20 to frictionally engage controller casing 5, as indicated in dotted lines in Figure 2. The braking action so produced partially counteracts the force of the return spring, whereon Patented Apr. 29, 1958 body, having a weight of about one pound, and prefen,

ably having parallel side walls 21, 22, and arcuate ,top wall 23, and being-cut away in its lower portion at its normally inner end to provide a shoulder24. Walls 21, 22 are spaced apart a distance substantially equal to the thickness of pedal 8 and may 'bepress'ed :towards each other to be secured to the lever. Shoulder. 24 will overlie lever 7, which is of greater width than the thickness of lever 8, as shown at 7' in Figure "3.

Upon release of lever .7 .from .footpressure, the inertia or weight will resist the force of the lever-return springs so that lever 7 will be slowly returned to off position, as the spring overcomes 'thei'inertia of the weighted pedal. With this type of retarding or snubbing device, the control arm on lever 7 will move more slowly as the lever returns to off position, whereby sparking is effectively reduced or eliminated between the commutator and brushes. vAn additional advantage is that-the deceleration of the motor avoids the likelihood of the motor belt jumpingfrom its pulleys to the annoyance and interruption of the operator.

The lever-retarding accessory of the present invention can be readily applied to the pedal ofany type of controller, irrespective of design of such pedal. No modification or alteration of the pedal is required to properly apply the accessory thereto and it is apparent that the same may be mounted without the exercise of skill on the part of the user. The accessory is so constructed as to be securely engaged upon the lever pedal so that inadvertent displacement is avoided.

The details of construction may be varied otherwise than as indicated without departing from the spirit of the invention and the exclusive use of those modifications coming within the scope of the claims is contemplated.

What is claimed is:

1. In combination with a dental engine motor controller, including a housing having a side wall provided with an elongated slot, there being a rheostat lever projecting through said slot and terminating in a pedal for engagement by an operator and provided with a spring for moving the lever to a normal off position, a weight device readily applicable to said pedal and movable therewith and operated automatically upon release of the operators thrust on said pedal to retard, by its inertia, the speed of the return movement of said'lever and controller throughout the extent of the return movement.

2. For use with a dental engine controller having a spring-biased operating lever with a pedal formed at its end, an accessory for said pedal to resist the force of the lever spring comprising a body for application upon the pedal, and a friction element rockably carried on said body for movement towardsaid controller through centrifugal force on spring-actuated swinging of said lever to engage said controller for retarding swinging of said lever.

3. For use with a dental engine controller having a spring-biased operating, lever with a pedal formed at its end, an accessory for said pedal to resist the force of the a lever spring comprising a body for application .upon the pedal, and an arm rockably carried on said body at the inner end thereof, said arm being of increased weight at its lower end, and a friction element carried at the upper end of said arm for engagement withthe controller on rocking of the arm through centrifugal force.

4. For 'use'with aderrtal engine controller having a spring-biasedoperating lever with a pedal formed at its end, an accessory for said pedal to, resist the force of thelever spring comprising a body for application upon the pedal, and an arm rockably carried on said body at the inner end thereof, said arm being Weighted a predetermined amount at its lower 'end, a yieldable friction element carried at the upper end of said 'arm in confronting relation to said'controller for engagement therewith on rocking of the arm through centrifugal force.

' 5. In combination with a dental engine having a motor anda rheostat type control including a horizontally disposed radial levcr pivoted near one end and movable under thrust-by an operator, applied to its other end, from an off position to successively higher-speed operative positions, there being a spring returning said lever to off position when released trom'said thrust, a weight detachably mounted on said lever near its outer end and forming an inertia device resisting acceleration in the return movement ofthe released lever 10 0E position by said spring.

6. In combination with a dental engine motor controller, including a housing having a side wall provided with an elongated slot, there being a'rheostat lever projecting through said slot'and terminating in a horizontally movable pedal for lateral thrust by an operator and provided with a spring for 'returningthe lever to a normal or? position, a separately formedweight device readily applicable to-said pedal and movable'therewithand acting automatically, by'its inertia,'upon release of'the operators thrust on said pedal to retard the spring-induced return movement of said lever until the lever reaches its normal off position.

References Cited in the file of this patent v UNITED' STATES PATENTS

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