Electric Light System For A Motor-driven Appliance

Abstract

A compact light-weight electric shaver includes a DC motor, a bridge rectifier for converting the AC line current to DC line current, and a low-voltage electric lamp for illuminating the work area adjacent the shaver. The lamp is connected in series between the bridge rectifier and the motor to obviate the need for a low-voltage power supply, and a zener diode is connected across the lamp to provide a constant illumination level and to prevent the current through the lamp from exceeding the rating of the lamp when the motor is starting or operating under heavy load.

Description

BACKGROUND OF THE INVENTION

The present invention relates to electric light circuits, and more particularly to an electric light circuit for a motor-driven electric appliance.

Small hand-held motor-driven line-operated appliances, such as electric shavers and electric drills, are often used in areas having poor illumination, making it difficult or impossible to operate the appliances without additional illumination. Accordingly, it is highly desirable that such appliances include an integral source of illumination for their adjacent work area.

The wide disparity between the relatively high operating voltage of the 120-volt motors generally employed in such appliances, and the relatively low operating voltage of available lamps which combine sufficient light output with the necessary degree of miniaturization, make it impractical to power a lamp in such appliances directly from the AC line. Thus, in the case of appliances with AC motors it has become standard practice to provide a tap or an additional winding on the motor to obtain the necessary low-voltage current. However, many hand-held appliances use permanent-magnet DC motors because of the substantial savings in cost, size, and weight these motors provide over comparable AC motors, and in these appliances a tapped motor winding is not available as a low-voltage current source. Instead, in these appliances it has become standard practice to utilize one or more series-connected voltage-dropping elements between the AC line and the low-voltage lamp. While these elements can be resistors, the large power dissipation required of resistors and the attendant problems of cooling and insulating them have made it more desirable to incorporate a series reactance instead. Thus, it has become standard practice to provide a capacitor in series between the AC line and the low-voltage lamp in many DC motor-powered appliances.

Unfortunately, mylar and other AC-type capacitors suitable for this purpose occupy a relatively large volume within an appliance, where space is often at a premium. This is especially true in such small hand-held appliances as ladies electric shavers, where the need for illumination is more pronounced because the appliance is normally not used in front of an illuminated mirror, and where weight and size factors contribute heavily to customer acceptance. Furthermore, mylar capacitors are relatively expensive components and, therefore, present an undesirable additional cost burden in the highly competitive electric shaver industry.

Accordingly, it is a general object of the present invention to provide a new and improved work area illumination circuit for a motor-driven appliance.

It is a more specific object of the present invention to provide a more economical and compact illumination circuit for a motor-driven appliance.

Accordingly, the invention is directed to a system for illuminating the work area of a motor-driven appliance. The system comprises a motor having a running current requirement and a greater peak starting current requirement, a source of current capable of supplying the operating requirements of the motor, and an electric lamp having a predetermined maximum allowable current rating for illuminating the work area. Circuit means coupled between the current source and the motor and serially including the electric lamp are also included for supplying the required current to the motor, the supplied current exceeding the predetermined maximum allowable current rating of the lamp. Means coupled to the electric lamp are also provided for limiting the current therethrough to a level less than the predetermined maximum allowable level.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 is a perspective view of a ladies electric shaver incorporating an electric light circuit constructed in accordance with the invention; FIG. 2 is a top view, partially fragmentary, of the electric shaver taken along lines 2--2 of FIG. 1.

FIG. 3 is a cross-sectional side view of the electric shaver of FIG. 1 taken along lines 3--3 of FIG. 2;

FIG. 4 is a schematic circuit diagram of the electric shaver of FIG. 1.

Referring now to FIG. 1, the invention is shown as incorporated into a compact, light-weight, ladies electric shaver 10. The shaver is seen to have a housing formed by two complimentary half sections 11 and 12 formed of a high impact plastic or similar nonconductive material. The lower end of the housing forms a handle for the shaver and the upper end is widened to accommodate a shaving head. The lower portion of the shaving head comprises a three tier stationary comb blade 13 mounted on a carriage block 14. Comb blade 13, carriage block 14, and the underlying cutting blade together form a novel unitary cartridge assembly which can be removed at will. The cartridge assembly may be frictionally held in position between the extended half sections of the housing which define the shaver head, or may be secured by means of a spring clip or machine screw. Removal of the cartridge is facilitated by an ejection control 15, which is slidably mounted in opposed recesses in the handle portions of the housing sections and is disposed to push up on the cartridge when actuated. A single-pole single-throw switch 17 is carried near the bottom end of the housing to enable the shaver to be turned on and off at will.

The upper portion of the shaving head comprises a transparent plastic lens 16 for illuminating the work area adjacent the shaver head. This lens is preferably formed to extend around the top edge of the shaver head and may have one or more of its surfaces scored or otherwise treated to better diffuse light passing through from an underlying source of illumination. In FIG. 2 the lens is seen to overlie an electric lamp 18, and to have its undersurface scored adjacent the lamp with a large number of parallel lines 19 to diffuse the light from the lamp. It will be appreciated that for certain purposes it may be desirable to focus this light on a particular point, and that for other purposes it may be desirable to widely diffuse the light, and that in either case this can be accomplished by appropriate modification of lens 14.

Referring now to FIG. 3, the shaver in cross section is seen to include an electric motor 20, which, for the previously mentioned reasons of size, weight, and economy, may be a conventional permanent magnet type designed to operate from DC current. It will be appreciated that, while a permanent magnet DC motor is shown, other types of motors and other types of electromechanical transducers, such as solenoid-driven vibrators, could be used in appropriate instances in conjunction with the invention. An eccentric drive member 21 is mounted on the output shaft 22 of the motor. This member includes an off-center pin 23 which engages a slot-shaped recess in one end of a connecting arm 24. As the motor turns, drive member 21 rotates and imparts a reciprocating motion to connecting arm 24. The other end of arm 24 is operatively engaged with a cutting blade 25, which is slidably mounted on carriage clock 14 immediately beneath stationary comb 13. As blade 25 is caused to reciprocate under comb 13 by connecting arm 24, it coacts with comb 13 to achieve the desired shaver cutting action.

Power for shaver 10 is obtained by means of a line cord (not shown) which plugs into a standard two-prong male socket 26 on the bottom of the shaver handle. Lamp 18, which may have either pigtail-type connecting leads or a standard bayonet or screw-type base, is held in position by means of an appropriate socket 27.

Referring now to the schematic diagram of FIG. 4, one terminal of socket 26 is connected by a current-limiting resistor 28 to one input terminal of a bridge rectifier 29. The remaining terminal of socket 26 is connected through switch 17 to the remaining input terminal of the bridge rectifier. Bridge rectifier 29 comprises four diodes 30-33 connected in a standard bridge configuration. Specifically, the cathode of diode 30 and the anode of diode 31 are connected to resistor 28 and the cathode of diode 32 and the anode of diode 33 are connected to switch 17. The anode of diodes 30 and 32 are connected together to form a negative output terminal 34 for the bridge rectifier, and the cathodes of diodes 31 and 33 are connected together to form a positive output terminal 35. Negative output terminal 34 is connected directly to the negative input terminal of the motor, and positive output terminal 35 is connected to the remaining motor input terminal through lamp 18.

In accordance with the invention, a current limiting means in the form of a zener diode 36 is connected across lamp 18 to prolong lamp life and provide a more uniform illumination level during variations in motor loading. Specifically, the anode of zener diode 36 is connected to terminal 35 and the cathode is connected to motor 20 so that the diode, in effect, forms a shunt path for current around lamp 18. While a zener diode is shown in the present embodiment it will be appreciated that other types of elements having an avalanche characteristic, i.e. having a predetermined conduction threshold voltage at which they begin to conduct, or their circuit equivalents, could be used as well.

In operation, and assuming switch 17 is closed, AC power is applied through resistor 28 to bridge rectifier 29. As a result, a DC current is developed across terminals 34 and 35, and motor 20, which is effectively connected across these terminals, begins to operate. Resistor 28 serves as a current limiting device at this point to inhibit arcing between commutator segments as current is first applied to the motor.

Initially, motor 20 may draw a starting current of three to five times its full load current. Absent zener diode 36, this starting current would flow through lamp 18, resulting in an overrated condition and an annoying high intensity flash each time the motor is started. The repeated overrated condition would eventually result in premature lamp failure. Zener diode 36 eliminates this condition by limiting the voltage across the lamp to the conduction threshold voltage of the diode.

When the motor is running under normal load, the circuit parameters are selected so that lamp 18 produces its full rated light output. This is accomplished by selecting lamp 18 to have a rated current approximately equal to or less than that of motor 20, and by selecting the conduction threshold of zener diode 36 to be approximately equal to the rated voltage of the lamp. Now, should the motor current increase, as during starting, zener diode 36 conducts more heavily and shunts current away from lamp 18. This maintains the voltage drop across lamp 18 at the threshold voltage level of the diode, which corresponds to the rating of lamp 18. Thus, the lamp is protected from having an applied voltage, and, hence, an applied current, in excess of its ratings. Furthermore, the lamp is caused to operate without the annoying flash which would otherwise accompany each start.

In one embodiment of a ladies electric shaver incorporating the invention, a DC motor is used which has a running current of 60 milliamperes. The lamp selected has a rating of 28 volts at 40 milliamperes, the zener diode has a conduction threshold of 28 volts, and the motor is designed to operate at 92 volts. Although the motor current may increase to 120-220 milliamperes while starting, the current through the lamp is effectively limited to 40 milliamperes by reason of voltage across the lamp being limited to 28 volts.

In some instances it may be desirable to select a zener diode having a higher or lower conduction threshold than the voltage rating of the lamp. For example, if the motor in the above example had had a running current at or slightly below the rating of the lamp, say 40 milliamperes instead of 60 milliamperes, or if the zener diode had had a wide conduction threshold tolerance, it might have been desirable to select a zener diode having a threshold voltage above the rated voltage of the lamp, say 30 volts instead of 28 volts, to insure full illumination of the lamp. Another example is where the zener diode is selected to have a threshold voltage below the rated voltage of the lamp to prolong the life of the lamp. The disadvantage with this is that full illumination is not obtained from the lamp and the resulting light may have an undesirable yellow cast.

It will be appreciated that the illustrated electric shaver will operate from direct current as well as alternating current, the bridge rectifier network functioning during DC operation to establish the DC current at the proper polarity on terminals 34 and 35. Furthermore, it is possible to utilize the invention in connection with AC lines of different voltages and frequencies, or in connection with a dual voltage, e.g. 120-220 volt shaver by selecting appropriate components for the circuit. It is also contemplated that the invention could be practiced in connection with an AC motor by connecting two zener diodes having an appropriate threshold in opposed polarization across the lamp.

Thus, a novel lighting circuit has been shown for electric shavers and other small motor-driven appliances. The circuit provides constant light output, regardless of the load imposed on the motor, and extends lamp life by protecting the lamp from operation beyond its ratings. The circuit is compact and inexpensive, making it particularly attractive for incorporation in small electric shavers where size, weight, and cost are major factors in product acceptance. Furthermore, it can be readily adapted to a wide variety of appliances because of its lack of resistors and other power dissipating components.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

We claim:

1. A system for illuminating the work area of a motor-driven appliance comprising:

a motor having a running current requirement and a greater peak current requirement;

a source of current capable of supplying the operating requirements of said motor;

an electric lamp having a predetermined maximum allowable current level for illuminating said work area;

means for establishing an electrical circuit serially including said electric lamp between said current source and said motor to supply said running and peak current requirements of said motor, said supplied current on occasions exceeding said predetermined maximum allowable current of said lamp; and

means coupled to said electric lamp for limiting the current therethrough to a level less than said predetermined maximum allowable level.

2. A system for illuminating the work area of a motor-driven appliance as defined in claim 1 wherein said motor is a DC motor and said current source is unidirectional.

3. A system for illuminating the work area of a motor-driven appliance as defined in claim 2 wherein said motor-driven appliance is operable from an AC line and said source of unidirectional current comprises a rectifier-type power supply.

4. A system for illuminating the work area of a motor-driven appliance as defined in claim 1 wherein said current limiting means comprise a zener diode.

5. A system for illuminating the work area of a motor-driven appliance as defined in claim 4 wherein said zener diode is connected across said electric lamp.

6. A system for illuminating the work area of a motor-driven appliance as defined in claim 1 wherein said predetermined maximum allowable current level is substantially equal to said running current requirement of said motor.

7. A system for illuminating the work area of a motor-driven appliance as defined in claim 1 wherein said electric lamp comprises an incandescent lamp having a rated current level substantially corresponding to said predetermined maximum allowable current level.

8. A system for illuminating the work area of a motor-driven appliance operable from an AC line comprising:

a DC motor having a running current requirement and a greater peak starting current requirement;

means comprising a rectifier circuit for converting said AC line current to a unidirectional current capable of supplying said operating requirements of said motor;

an incandescent electric lamp having a predetermined current rating for illuminating said work area;

means for establishing an electrical circuit between said rectifier circuit and said motor which serially includes said incandescent lamp for supplying said required current to said motor, said supplied current on occasions exceeding said current rating of said incandescent lamp; and

means comprising a zener diode connected across said incandescent lamp for limiting the current therethrough to a level not exceeding said rated level.

9. A system for illuminating the work area of a motor-driven appliance as defined in claim 8 wherein said current rating of said incandescent lamp corresponds substantially to said running current requirement of said DC motor.