US2967253A

US2967253A - Electromagnetic vibratory unit

Info

Publication number: US2967253A
Application number: US734605A
Authority: US
Inventors: John F Wahl
Original assignee: Wahl Clipper Corp
Current assignee: Wahl Clipper Corp
Priority date: 1958-05-12
Filing date: 1958-05-12
Publication date: 1961-01-03
Anticipated expiration: 1978-01-03

Description

Jan. 3, 1961 J. F. WAHL 2,967,253

ELECTROMAGNETIC VIBRATORY UNIT Filed May 12, 1958 INVENTOR.

John F Wa'hZ BY gfiz My 0146 m V Qiiarneys Patented Jan. 3, 1961 @fiiee ELECTROMAGNETKC VIBRATGRY UNIT John F. Wahl, Sterling, Ili., assignor to Wahl Clipper Corporation, Sterling, Ill., a corporation of lilinois Filed May 12, M58, Ser. No. 734,605

4 Claims. (Cl. 310-29) This invention relates to an electromagnetic vibratory unit, and more particularly to an armature assembly for an electromagnetic vibratory unit which operates so that its power consumption and its power output do not de crease appreciably with increase of load.

As increasing load is applied to a conventional alternating current electromagnetic vibratory unit, the stroke length of the magnetic armature will decrease. Since the power consumption, and consequently the power output of such vibratory units varies in accordance with magnetic armature stroke length, it has been found that when the load in the conventional vibratory unit is increased to where the magnetic armature is stopped completely, i.e. a stalling condition, then the power input to the motor drops by at least 25%. So if a conventional motor or vibrating unit draws 8 watts, for example, when operating under no load, then it will draw about 6 watts in a stalling condition, and as the vibratory unit ap proaches this stalling condition, its power output and the stroke length of the magnetic armature will decrease proportionately.

The foregoing means, for example, that if load conditions should require a power output of 8 watts, then a conventional vibratory unit would have to be selected which draws from 10 to 12 watts under no load conditions. This is a most inefficient arrangement both because the conventional vibratory units draw the greatest quantity of power when they least need it, i.e. under no load conditions, and because larger and more expen sive units are required for a given load than would otherwise be necessary if their power consumption did not armature assembly can be selected so that the stroke of the magnetic armature will not decrease substantially under load. As a matter of fact, if the spring constants of the armature system are chosen properly, the stroke of the magnetic armature may even remain constant or increase slightly as load is applied to the vibrating unit.

As seen in the drawings, the principles of this invention are embodied in a vibratory motor for a hair clipper, but it is evident that these principles could be applied to a large variety of different kinds of vibrating units. What is needed therefore, and comprises the principle object of this invention is an electromagnetic vibratory unit which is designed so its power consumption and power output will not decrease appreciably with load. Another object of this invention is to provide an electromagnetic vibratory unit in which the stroke length of the magnetic armature under any load condition is never less than one-third its stroke length under no load condition.

These and other objects of this invention will become apparent when read in the light of the accompanying drawings and specifications.

In the drawing:

Fig. 1 is a plan view of a hair clipper with a portion of the casing broken away to show an armature assembly embodying the principles of this invention.

Fig. 2 is a side view of the hair clipper of Fig. 1 with a portion of the casing broken away to show another view of the armature assembly.

Fig. 3 is an enlarged plan view of a portion of the armature assembly alone showing the shape of the magnetic armature and one form of resilient work arm which connects to a movable cutting blade.

Referring now to Fig. l of the drawing, a hair clipper embodying the novel features of this invention and indicated generally by the reference numeral 10 comprises casing 12 and a fixed cutter blade 14 which is secured to the casing by means such as bolt 15, see Fig. 2.

An electromagnetic coil 16 is rigidly secured to casing 12. An armature assembly 18, comprising a magnetic armature'2il and a vibratory resilient overtuned part is also secured to the casing at end portion 19. The resilient overtuned part comprises a resilient work arm 22, a mounting 24, and the work contacting portion or cutter blade 26. As seen in the drawings, the resilient work arm 22 is connected to the end of the magnetic armature 2d, and the mounting 24 and the movable cutter blade 26 are secured to the free end 23 of the resilient work arm 22. The resilient work arm 22 is connected at or near the free end of the magnetic armature to give it substantial travel. With this arrangement vibrations of the magnetic armature 2i) drive the movable cutter blade 26. The fixed and

movable cutter blades

14 and 26, as seen in Fig. 2 slide against each other in the usual manner. As will be understood, the magnetic armature 2t) vibrates in accordance with the varying magnetic field produced by the electromagnetic coil 16.

A conventional armature assembly, adjusting screw 28, shown in Fig. 1, is provided for adjusting the size of air gap 21 between a pole 25 of coil 16 and magnetic armature 2d.

The constructions thus far described, except for the resilient Work arm 22, are relatively conventional. Heretofore, in conventional clippers, the connection between the end of the magnetic armature and the movable cutter blade was comparatively rigid, insofar as relative movements between the end of the armature and the movable cutter blade in the plane of their vibratory movements was concerned. It is important to note, however, that even in conventional clippers a ditferent kind of resilient connection between the magnetic armature and the movable cutter blade usually is provided. This conventional resilient connection and the consequent relative movement is illustrated by the arcuate arrows in Fig. 2, and this resilience provides cutting bias between the blades and enables the blades to stay properly in cutting relation.

In this invention, however, resilience between the magnetic armature and the movable cutter blade refers only to a -esilience which permits relative movements between the magnetic armature and the movable cutter blade in the plane of their vibratory movements. This is illustrated by the straight arrows in Fig. 3. Without such a resilient connection, it can be seen that if movable cut ter blade 26 is slowed by heavy loads, then the stroke of magnetic armature 2 will decrease, resulting, as indicat ed above, in a decrease in the power output of the motor.

The limitations on resilient work arm 22 are very severe. It is apparent from an inspection of Fig. 3, that if the resilience of the work arm is too great, then any load can stop the movement of movable cutter blade 26 regardless of the movement of magnetic armature 26. It is also undesirable for the resilience to be such that the work arm is under-tuned because an objectionable phase shift between the movement of the cutter blade 26 and the armature 20 would be introduced. On the other hand, if the resilience in the work arm is too small, heavy loads on the vibratory unit could cause a substantial decrease in the stroke of the magnetic armature, and consequently cause the power output of the unit to drop. The unit in this case would operate much the same as conventional units.

Ideally it would be desirable for the resilient work arm to affect the armature assembly so that there either is no decrease in the stroke of the magnetic armature under load or else that the stroke will actually increase. Too large an increase in the stroke of the magnetic armature in the illustrated embodiment is, however. undesirable as the armature tends to strike against pole 25. Despite the ideal operating conditions described above, even if the magnetic armature stroke length decreased by as much as two-thirds under. loads heavy enough to stall the movable cutter blade, this improved vibratory unit would be superior to conventional vibratory units where the magnetic armature is substantially motionless at a stalling load.

In this device, advantage is taken of the behavior of the illustrated vibrating spring system when it encounters a load in the form of resistance to movement. The effect of such a load on the vibrating spring system acts to increase the spring constant of the armature assembly. This in turn causes the tune or natural frequency of the armature assembly to increase. If this increase in the natural frequency of the armature assembly is towards the frequency of the applied force, i.e. resonance, the amplitude of vibration of the armature assembly would tend to increase. and this is desirable. This means that the armature assembly must be undertuned.

For this to occur, it is evident that the tune of the armature assembly would have to be below 120 cycles per second since the frequency of the applied force when a 60 cycle current is applied to the electromagnetic coil is 120 cycles per second. With this arrangement if a load is applied to the armature assembly of such a vibrating unit, then the tune of the armature assembly increases toward resonance, and consequently the stroke of the magnetic armature will tend to increase.

In this vibratory unit the armature assembly is designed so it is undertuned under no load condition (at least 20% undertuned has been found most desirable, i.e. 95 to 105 cycles). Despite the fact that the annature assembly is undertuned, the resilient work arm and associated load device (blade) taken alone must be overtuned, i.e., having a natural frequency or tune of over 120 cycles per second. The extent of overtuning of the work arm-blade assembly is dependent upon the relationship between the momentnms of the armature arm and the work arm-blade assembly. A relatively light work arm-blade assembly connected to a heavy magnetic armature will cause a moderate rise in the natural tune of the armature assembly under load. Conversely, a. relatively heavy work arm-blade assembly having the same extent of overtuning connected to a light magnetic armature will cause a substantially greater rise in the natural tune of the armature assembly under load. It can be seen that by making suitable selections in the masses and lengths of portions of the armature assembly, the character of the increase in the tune of the armature assembly can be controlled.

At no load, since the work arm-blade assembly is overtuned its resilience will have no effect on the amplitude of the magnetic armature. As load is applied to the 4 vibrating unit, the tune of the entire armature assembly will increase towards resonance, and as long as such tune is less than over resonance when a blade stalling load is reached, the flexibility of resilient work arm 22 will cause the stroke length of the magnetic armature under any blade load to remain within at least one-third of its stroke length under no load conditions. In addition, depending upon the relative values of the spring constants of the magnetic armature and the resilient work arm, the stroke length of the magnetic armature could either be kept constant or even be permitted to increase slightly as load is applied to the unit. In this way, the above described decrease in the power output under load conditions of conventional vibratory units can be eliminated.

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 em bodiment 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.

From the above description it is thought that the construction and advantages of this invention will be readily apparent to those skilled in the art. Various changes in detail may be made without departing from the spirit or losing the advantages of the invention.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

1. A vibratory motor comprising a support, a coil energized by a current of fixed frequency mounted on said support, a magnetic circuit associated with said coil, a resilient armature assembly connected to said support and movable back and forth in said magnetic circuit in response to the frequency of the driving force caused by the varying magnetic field, said armature assembly including a magnetic armature and a vibratory resilient worn arm including a work contacting portion, said resilient work arm having a natural frequency higher than the frequency of the driving force connected to said magnetic armature, the resilience of said armature assembly selected so the natural frequency of the armature assembly is below the frequency of the driving force under no-load conditions while at stalling loads on said work contacting portion the natural frequency of the armature assembly is less than 50% above the frequency of the driving force whereby the resilience of the work arm will allow the length of the stroke of the magnetic armature at any load to be at least one-third the length of its stroke at no load.

2. The apparatus described in claim 1 wherein the natural frequency of the armature assembly is at least 20% below the frequency of the driving force under no load conditions, so that the power consumption of the motor will be low under no-load conditions.

3. The apparatus described in claim 1 wherein said resilient work arm is connected to the magnetic armature at a point having substantial travel.

4. The apparatus described in claim 3 wherein the length of the stroke of the armature increases under load so the power output of the motor is increased.

References Cited in the file of this patent UNITED STATES PATENTS