Vibration motor with stroke control

Abstract

A hair trimmer 10 has a stationary blade 12, a reciprocating blade 14 and a vibrating motor 16. The vibrating motor 16 has a reciprocating armature 18 operatively connected to the reciprocating blade 14, and an electromagnet 20 and a spring 22. The armature 18 and the electromagnet 20 are separated by an air gap 23. The armature 18 moves during operation, which causes the air gap 23 to vary as the armature 18 reciprocates. The electromagnet 20 has a wire 26 wound around a metal core 24 to form a plurality of windings. The electromagnet 20 has an inductance that varies as the armature 18 reciprocates and the air gap 23 varies. A first end 28 of the wire 26 is electrically connected to an AC power source 30, and a second end 36 of the wire 26 is electrically connected to a first lead 38 of the capacitor 40. The capacitor 40 has a second lead 42 electrically connected to the AC power source 30.

Description

[0001] This Patent Cooperation Treaty (PCT) international application claims the benefit of U.S. Provisional Application Serial No. 63 / 366,801, filed on June 22, 2022, under 35US119(e), the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to a vibration motor, and more particularly, to a vibration motor for a hair trimmer. Background Art

[0003] The hair trimmer has a fixed blade and a reciprocating blade. The blades have cutting teeth that cooperate to cut the hair strands that come between the teeth as the reciprocating blade teeth move back and forth relative to the fixed blade teeth. The reciprocating blade in many hair trimmers is driven by a vibrating motor.

[0004] A vibrating motor uses an electromagnet and a spring-loaded armature to move the moving blade back and forth past the stationary blade. The relative displacement of the two blades relative to each other is called the stroke. The stroke of a hair trimmer must maintain a minimum value to cut hairs without pulling or snagging them. The minimum stroke is set by the geometry of the blade pair, but every blade pair has a minimum possible stroke. It is therefore important that the hair trimmer can maintain the stroke under load (i.e. when cutting hairs), otherwise it may fall below its minimum possible stroke and start pulling the hairs to be cut.

[0005] Because there is no mechanical coupling between the two blades, the construction of the vibratory motor is susceptible to stroke loss under load. The stroke is determined by the strength of the magnets and the vibration dynamics of the system (e.g., natural frequency, damping, load, etc.). The strength of the vibratory motor is also limited by thermal constraints, because the ohmic losses in the electromagnets generate a lot of heat, which limits the amount of magnetomotive force that can be generated. Therefore, a more efficient vibratory motor is needed.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide new and improved vibratory motors.

[0007] Another object is to provide a new and improved vibrating motor for a hair trimmer. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above and other features of the present invention and the manner in which these features are obtained will become more apparent, and the present invention itself will be better understood, by referring to the following description of the embodiments of the present invention in conjunction with the accompanying drawings, in which:

[0009] Fig. 1 is a plan view of a hair trimmer having a vibrating motor;

[0010] Figure 2 is a schematic diagram of a vibration motor according to the present invention;

[0011] Figure 3 It is for Figure 2 A graph showing the relationship between a fixed power supply voltage, a current amplitude, and an inductance and a capacitance in a vibration motor;

[0012] Figure 4 is a graph of tests comparing the strokes of (a) a vibration motor manufactured according to the present invention and (b) a conventional vibration motor under different loads;

[0013] Figure 5 This is a graph of the inductance of the vibration motor at different air gaps;

[0014] Fig. 6A is a contour plot of the relationship between free travel and the system spring constant and system capacitance;

[0015] Figure 6B is a contour plot of the relationship between stroke ratio and system spring constant and system capacitance;

[0016] Figure 6C is a contour plot of the power versus the system spring constant and the system capacitance;

[0017] Fig.6D is a contour plot of the relationship between the voltage on the capacitor and the system spring constant and the system capacitance;

[0018] Fig. 6E is another contour plot of the voltage on the capacitor versus the system spring constant and the system capacitance. DETAILED DESCRIPTION

[0019] As shown in Figure 1 and Figure 2 As shown, the hair trimmer 10 has a fixed blade 12, a reciprocating blade 14 and a vibrating motor 16. The reciprocating blade 14 and the fixed blade 12 have teeth 18, and when the reciprocating blade 14 moves back and forth in the direction of the arrow 19, the teeth will cut the hair entering the space between the teeth. The overall construction of the hair trimmer is described in more detail in U.S. Patent No. 8,276,279, which is incorporated herein by reference in its entirety. Although described in the context of a hair trimmer, it will be appreciated by those skilled in the art that the present invention is not limited to hair trimmer applications. In fact, the applicant has found that the present invention can be easily applied to any electromagnetic motor having the components described herein.

[0020] The motor 16 has an armature 18 operatively connected to the reciprocating blade 14, as well as an electromagnet 20 and a spring 22. An air gap 23 between the electromagnet 20 and the armature 18 allows the armature 18 to reciprocate. As the armature 18 moves back and forth under the operation of the electromagnetic motor 20, the air gap 23 changes.

[0021] The electromagnet 20 has a metal core 24 and a wire 26 ( Figure 2 ) to form a plurality of windings around the metal core 24. The wire 26 has an inherent resistance. The first end 28 is connected to an AC power source 30 through a resistor 32 (not shown in FIG. 1 ), and the second end 36 is connected to a first lead 38 of a capacitor 40 (not shown in FIG. 1 ). The capacitor 40 has a second lead 42, which is connected to the AC power source 30.

[0022] By adding capacitor 40, a circuit capable of electrical resonance is formed. Electrical resonance, like mechanical resonance, maximizes the amplitude of oscillation for a given input. The resistance of the wire is a parameter that controls the bandwidth of the resonance peak. Resistor 32 (if present) is another parameter that controls the bandwidth of the resonance peak.

[0023] As described above, the embodiments described above present a circuit capable of resonance. Depending on the selection of the capacitance value of capacitor 40, the system can be designed to be close to electrical resonance. When the system is designed to be close to electrical resonance, applying a load to the system brings the system closer to electrical resonance and effectively increases the strength of the electromagnet. Since the stroke increases as the strength of the electromagnet increases, the trimmer is better able to maintain its stroke under load. The addition of a capacitor can also produce a more efficient motor. By adding a capacitor, more turns can be added to the inductor without inducing inductive impedance losses because the inductive impedance can be offset by the capacitor, thereby reducing the ohmic losses in the motor windings and reducing the heat generated in the motor.

[0024] The dynamics of the system are determined by the electrical and mechanical coupling within the system. Therefore, adding a capacitor 40 of appropriate size takes advantage of the interaction between the two parts of the system to produce a vibrating motor that can maintain stroke under load, while also producing a motor that runs more efficiently and cooler. Maintaining stroke under load is very important for the hair trimmer scenario. Traditional hair trimmers lose stroke as the load increases. Loss of stroke can cause hair pulling and snagging as described above. A motor that runs cooler also has the advantage that the hair trimmer does not transfer as much heat to the blade as a traditional hair trimmer transfers, making the hair trimmer feel cooler when it contacts the skin.

[0025] The above described embodiments of the circuit according to the invention are capable of resonating when driven at the correct frequency. In this scenario, resonance means that the RMS current flowing at a given supply voltage reaches a maximum value, due to the inductive and capacitive impedances canceling out. The natural frequency ωn (the frequency around which the circuit will resonate) depends on the inductance L and capacitance C of the circuit and is Figure 3A diagram showing the relationship between the magnitude of the current and the inductance and capacitance for a fixed supply voltage is shown.The natural frequency of the hair trimmer circuit can be adjusted to the mains (wall / socket) voltage frequency (eg 50 Hz or 60 Hz) ω so that it is close to resonance.

[0026] The inductance L depends on the gap 23 between the electromagnet 20 and the armature ( Figure 2 ). When the value of capacitor 40 is correctly chosen, the act of loading the trimmer causes the inductance L to change so as to bring the electrical system closer to resonance. This means that when a load is applied, the circuit responds by sending more current through the electromagnet, enabling the motor to maintain travel under load better than contemporary designs.

[0027] Another benefit of adding a capacitor to the circuit is improved motor efficiency. The strength of an electromagnet or its magnetomotive force (MMF) is defined as the product of the number of turns N and the current I. The energy dissipated by the motor and the heat generated thereby is equal to the product of the resistance R and the square of the current I. In a vibration motor without a capacitor (such as that present in existing designs), the current is proportional to 1 / N^2, so the MMF of the motor is proportional to 1 / N. Therefore, in order to make the motor stronger, the number of turns must be removed, resulting in greater current and more heat generation. However, in the present invention as described in the embodiments herein, the circuit including the capacitor 40 operates near resonance, and the current is independent of the number of turns on the coil, so the turns / current ratio can be adjusted while keeping the MMF the same (i.e., doubling the number of turns and halving the current will keep the MMF the same). By reducing the current, ohmic losses are reduced, efficiency is improved, and heat generation is reduced while maintaining motor strength.

[0028] In experiments conducted by the applicant, a hair trimmer was created that allows the addition and removal of capacitors. The hair trimmer was then tested in a device capable of measuring the load applied to the blade (in the form of friction) while also measuring the stroke. The power consumption of the trimmer without capacitor 40 was about 10 watts. The power consumption of the trimmer with capacitor 40 in the circuit was about 4 watts.

[0029] Reference now Figure 4, where the two lines shown are for the same trimmer, but in line 50, there is a capacitor 40 in series with the motor 16, while in line 52 it is not. Testing with the capacitor installed showed that the trimmer was able to maintain stroke better than when the trimmer unit was operated without the capacitor. The test equipment uses a load sensor to measure the clamping force between the blades, which simulates the load on the motor as the friction between the blades increases. The motor is tested with a nominal voltage of 220V at 60hz applied to the electromagnet. For the trimmer construction used in the tests, the capacitance was .88uF, the resistance was 260 ohms, and the inductance (depending on the armature position) varied between 4 and 25 Henry (H), as shown. Figure 5 shown.

[0030] The air gap typically varies between about 1 mm and about 4 mm, with a nominal value of 3 mm. Figure 5 In the example, when the air gap is 1mm, the inductance is about 7H, when the air gap is 3mm, the inductance is about 5H, and when the air gap is 4mm, the inductance is about 4H.

[0031] The possible values ​​of the capacitor depend on the configuration and operating point of the specific motor, e.g., the shape and size of the inductance vs. air gap curve, the supply frequency, the natural frequency of the mechanical system, etc. Depending on the motor inductance and the drive frequency, the value can be from 1 pF to 1 F.

[0032] The values ​​of the components can be determined using contour plots, e.g. Figures 6A-6E As shown. Fig. 6A In the figure, the left ordinate represents the system spring constant, and the right ordinate represents the free stroke. The horizontal axis represents the system capacitance. Figure 6B In the figure, the left ordinate represents the system spring constant, and the right ordinate represents the stroke ratio. The abscissa represents the system capacitance. Figure 6C In the figure, the left ordinate represents the system spring constant, and the right ordinate represents the power. The horizontal axis represents the system capacitance. Fig.6D In the figure, the left ordinate represents the system spring constant, and the right ordinate represents the voltage on the capacitor. The abscissa represents the system capacitance. Fig. 6E In the figure, the left ordinate represents the system spring constant, the right ordinate represents the voltage on the inductor, and the abscissa represents the system capacitance.

[0033] The design process starts with the target free travel. Fig. 6A In the example shown, the target is a travel of 30 to 60 thousandths of an inch. The circled points represent the operating points that meet this travel condition.

[0034] The next consideration is the stroke ratio, Figure 6BThis is the load / free travel ratio, a measure of how well the motor can maintain its travel under load. For example, for a minimum travel ratio of 0.70, the travel will be reduced by no more than 30%.

[0035] Figure 6C All points in the circle to minimize power consumption have been studied so far. Figure 6C The circle in satisfies all other previous requirements and minimizes power consumption.

[0036] Free capacitor voltage ( Fig.6D ) is another variable that can be used to specify the capacitor rating, and the motor voltage measurement ( Fig. 6E ) can be used to specify the electrical shielding required on the wires.

[0037] The advantages of the present invention are now apparent. A more efficient, cooler running vibrating motor is produced.

Claims

1. A hair trimmer 10, characterized in that: It includes a fixed blade 12, a reciprocating blade 14 and a vibration motor 16, The vibration motor 16 has a reciprocating armature 18 operatively connected to the reciprocating blade 14, and an electromagnet 20 and a spring 22, the armature 18 and the electromagnet 20 being separated by an air gap 23, wherein the armature 18 moves during operation, which causes the air gap 23 to change as the armature 18 reciprocates; The electromagnet 20 has a metal core 24 and a wire 26 wound around the metal core 24 to form a plurality of windings around the metal core 24. The electromagnet 20 has an inductance that changes as the armature 18 reciprocates and the air gap 23 changes. The wire 26 has a resistance. The first end 28 of the wire 26 is electrically connected to an AC power source 30 , and the second end 36 of the wire 26 is electrically connected to a first lead 38 of a capacitor 40 . The capacitor 40 has a second lead 42 electrically connected to the AC power source 30 .

2. The hair trimmer 10 according to claim 1, characterized in that: A resistor 32 is included that is connected in series with the first lead 38 or the second lead 42 of the capacitor 40 .

3. A vibration motor 16, characterized in that: include: a reciprocating armature 18 operatively connected to a load; as well as The armature 18 and the electromagnet 20 are separated by an air gap 23, wherein the armature 18 moves during operation, which causes the air gap 23 to change as the armature 18 reciprocates. The electromagnet 20 has a metal core 24 and a wire 26 wound around the metal core 24 to form a plurality of windings around the metal core 24. The electromagnet 20 has an inductance that changes as the armature 18 reciprocates and the air gap 23 changes. The wire 26 has a resistance. The first end 28 of the wire 26 is electrically connected to an AC power source 30 , and the second end 36 of the wire 26 is electrically connected to a first lead 38 of a capacitor 40 . The capacitor 40 has a second lead 42 electrically connected to the AC power source 30 .

4. The vibration motor according to claim 3, characterized in that: A resistor 32 is included that is connected in series with the first lead 38 or the second lead 42 of the capacitor 40 .

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