US2986662A - Vibratory motor - Google Patents

Description

y 1961 J. F. WAHL 2,986,662

VIBRATORY MOTOR Filed Nov. 6, 1958 FIG. 1

IN V EN T OR.

BY John F Wa/zZ 4 M 5 n mm Hiiornciqs Patented May 30, 1961 VIBRATORY MOTOR John F. Wahl, Sterling,

Ill. assignor to Wahl Cli er Corporation, Sterling, pp

This invention relates to a vibratory motor and more particularly to a vibratory motor having an armature assembly which can be substantially undertuned without fluttering.

Present vibratory motors which operate on 60 cycle current (120 power strokes per second) have a natural tune frequency in the armature which is higher than 80% of the driving frequency, i.e. 80% of 120 cycles per second or higher than 96 cycles per second. Usually this tune frequency exceeds 100 cycles per second. This condition is undesirable in certain respects because vibratory motors will deliver more power and operate better generally when the armature assembly is undertuned to a greater extent. However, when the armature assembly is substantially undertuned, i.e. tuned slightly below 96 cycles per second, there is a tendency for the armature assembly to flutter, i.e. vibrate at a frequency of one half the driving frequency (60 cycle vibration in this case). This flutter is undesirable because the power output of the vibratory motor and the stroke length would be uncontrollable.

The reason that flutter occurs is that when the armature assembly is undertuned the predominant magnetic pull during normal operation occurs when the armature is in an out position, i.e. at its greatest distance from the pole faces of the core. This magnetic pull must overcome the inertia of the armature moving away from the pole faces, stop, and reverse its motion so that it is moving toward the pole faces. When there are no inertia forces on the armature moving away from the pole faces, as when the coil has been deenergized, the initial pull resulting from a high transient current upon energizing the coil will cause the armature to strike the pole faces solidly. If this happens the next pull will occur when the armature is out, and then again when the armature is in. The armature is thus operating at one half the desired frequency and will have a long stroke and hammer against the pole faces with destructive force.

It has been found that if the vibratory armature assembly is prevented from coming extremely close to the core of the motor or from contacting it, the above described condition leading to flutter can be avoided so that the vibratory motor can operate effectively when the armature assembly is tuned below 80% of the drive frequency.

What is needed therefore and comprises the principal object of this invention is an electromagnetic vibratory motor having substantially undertuned armature assembly which is provided with means for preventing armature flutter.

A further object of this invention is to provide an electromagnetic motor with an undertuned armature assembly which is provided with means for preventing the armature from contacting the core of the motor.

These and other objects of this invention will become more apparent when read in the light of the accompanying specification and drawing wherein:

Fig. 1 is a plan view of a hair cutter having an electric motor constructed according to the principles of this invention;

Fig. 2 is an enlarged view of a portion of the armature assembly and the core of the motor showing in dotted lines the motion of the armature assembly toward the core of the motor, and

Fig. 3 is a sectional view taken on the line 3--3 of Fig. l and looking in the direction indicated.

Referring now to Fig. 1 of the drawing, an electric clipper indicated generally by the reference numeral 10 comprises a support or casing 12 in which an electromagnetic vibratory motor 14 constructed according to the principles of this invention is mounted. The vibratory motor comprises a core 16 including an integrally attached centrally disposed elongated pole 18 with a pole face 20, see Fig. 2. Plastic molded and somewhat resilient rims 22 and 24 are secured to pole 18 in spaced parallel relationship to each other to form a spool 26 and an electromagnetic coil 28 is wound on this spool.

An armature assembly 30 including an armature 32 and parts (not shown) attached thereto for holding it on the clipper is secured to casing or support 12 for resilient vibratory movement. Armature 32 is disposed adjacent to pole face 20 in operative relationship therewith so that an alternating current applied to coil 28 will cause the armature to vibrate. Free end 34 of the armature is connected to a movable cutting blade 36 by any conventional means (not shown) so that the vibration of the armature will cause the movable cutting blade to oscillate relative to a fixed cutting blade 37 in a manner well known in the art. The armature assembly is designed so its natural tune frequency is less than the driving frequency of the motor. In practical terms, this means that the armature assembly must have a natural frequency which is less than 120 cycles per second because the usual household 60 cycle current causes an electromagnetic coil to supply two driving magnetic pulses per cycle.

In the conventional electric hair clipper, if the armature assembly was substantially undertuned, i.e. tuned to around 91 cycles per second, the initial magnetic pull caused by the high transient current of the coil 28 and 'core 16 would occur when armature assembly 30 is at rest in a neutral position. This magnetic pull combined with the lower natural vibratory frequency of the armature assembly causes the armature to be pulled solidly against the pole face 20. Since there is no air gap, the pulling force is extremely high. As the magnetic pulse decreases due to the alternation in the current in coil 28 the armature assembly will move away from the pole faces and will continue moving away from them for an abnormally long stroke until the next magnetic pulse begins to occur. The armature assembly of the conventional electric hair clipper tuned below will continue to have two magnetic pulses per cycle and will thus flutter. As stated above, flutter is objectionable because of the unpredictable power output, stroke, and the generally destructive nature of its operation.

To prevent the armature from fluttering, stroke limiting means may be disposed at or on any portion of the armature assembly or on the movable cutting blade. Such stroke limiting means may include placing any non-magnetic resilient material between the pole face and the armature assembly, or between any moving portion of the armature assembly 3% and the core 16 for limiting the magnitude of the stroke of the armature assembly as it moves in the direction of the core. It is noted, however, that the armature assembly will impinge against the stroke limiting means only on the initial strokes so as to prevent the armature from beginning its flutter stroke, and will have no affect on the stroke during continual normal operation.

In the illustrated device, the required stroke limiting means has been provided by giving the spool rim 22 an added function besides that of retaining the electromagnetic coil on pole 18. To do this, somewhat resilient bosses 38 are integrally formed or molded on plastic rim 22 and these bosses extend a small distance beyond the surface of pole face 20 toward armature portion 32, see Fig. 3. The magnitude of this distance is sufiicient to keep armature portion 32 from reaching the pole face 20 or from approaching close enough to it to permit the armature assembly to flutter and if portion 32 of the armature assembly encounters these bosses, as seen in Pig. 2, their resilience prevents damage to the armature and at the same time minimizes energy losses in the armature due to the encounter. In actual practice a distance of .006 to .008 inch has been found to work satisfactorily.

With this arrangement, the armature assembly can operate without flutter at a natural tune frequency which is as little as 75% of the driving frequency, i.e. 90 cycles per second When a 60 cycle current is supplied to the electromagnet. In fact good results have been obtained when the natural frequency of the armature is as low as 84 cycles/sec. The result is that the motor 14 will deliver more power per wattage input to the cutter and it will operate more smoothly. Also, since the armature tune is further from resonance, the detrimental effects of blade friction have less affect on the armature stroke length.

The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof as set forth in the claims and the present embodiment is therefore to be considered as illustrative and not restrictive and it is intended to include all changes which come within the scope and range of the claims.

I claim:

1. An electromagnetic vibratory unit comprising a support, a core having at least one pole mounted on said support, said pole having at least one pole face, resilient rims on said pole forming a spool, a coil wound on said spool and adapted to be connected to a source of alternating current, an armature assembly including an armature and means holding the armature in position on said support, the natural frequency of said armature assembly less than twice the frequency of the alternating current to be connected to said coil, said armature positioned in operative association with said pole face for vibratory movement, a portion of one rim extending beyond said pole face a distance less than the minimum distance of the armature from the pole face during steady operation so that the armature will contact said rim portion instead of the pole face only during an abnormally long initial stroke caused by transient currents in the electromagnetic coil when same is first energized whereby armature flutter is prevented.

2. An electromagnetic vibratory unit for 60 cycle current comprising a support, a core having at least one pole mounted on said support, said pole having at least one pole face, a spool on said pole, said spool having a rim with a surface adjacent said pole face, a coil on said spool, an armature assembly including an armature and means holding the armature in position on said support, said armature assembly having a natural frequency greater than 84 cycles per second but less than cycles per second, the armature mounted for vibratory movement and positioned in operative association with said pole face, and resilient bosses integrally formed with said rim on the surface thereof adjacent said pole face, said bosses extending beyond the pole face and toward the armature a distance less than the minimum distance of the armature from the pole face during steady operation so that the armature will contact said bosses instead of the pole face only during an abnormally long initial stroke caused by transient currents in the electromagnetic coil when same is first energized, whereby armature flutter is prevented.

References Cited in the file of this patent UNITED STATES PATENTS 1,684,260 Brown et al. Sept. 11, 1928 2,240,890 Kavle May 6, 1941 FOREIGN PATENTS 925,885 Germany Mar. 31, 1955

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