GB2083745A - Controlled temperature hair dryer - Google Patents

Abstract

A hair dryer is provided wherein the temperature of the air stream is automatically controlled by the temperature of the hair being dried. The dryer includes a primary air inlet 16, a fan 17 for blowing inlet air out of the dryer, and a heater 20 by which the blown air is heated before it is directed against a user's hair. The dryer also includes a feedback air duct 25 and a thermistor 26 positioned in the duct to sense the temperature of the air being reflected off the user's hair as it is dried. The thermistor changes resistance in accordance with the temperature of the reflected air. The change in resistance is sensed by an integrated circuit zero crossing switch that electronically signals a thyristor causing the thyristor either to switch off or proportionally reduce the power to the heater, thereby reducing the amount of heat energy input in the blown air. Consequently, the temperature of the air being blown against the user's hair is continuously monitored as the hair dries to avoid overheating of the hair and scalp. <IMAGE>

Description

SPECIFICATION Controlled temperature hair dryer This invention relates to a hair dryer. More specifically, it relates to a hair dryer having means for sensing the temperature of hair being dried so that the temperature of the drying air is automatically reduced in accordance with the sensed temperature.

Hair drying is the removal of water from hair, for exaniple, after the hair has been washed. Some of the water in the hair is loose, bridging the hairs, and some is absorbed in each hair. Loose water, for the most part, can be removed by mechanical means, such as towel drying, combing or brushing.

Absorbed water is best removed by evaporation.

The rate of evaporation is a function of the heat energy delivered to the hair. Heat energy first raises the temperature to break the bond of the water with the hair (heat of sorption) and then converts the water into vapor.

If an air stream of constant temperature is directed against wet hair, most of the heat energy of the air stream will be absorbed by the hair causing the temperature of the air reflected off the hair to be considerably lower than that of the drying air stream. As evaporation proceeds and the hair dries, less of the heat energy of the drying air stream will be absorbed by the hair resulting in a higher reflected air temperature until finally, when most of the water is evaporated, the temperature of the reflected air will approach the temperature of the drying air stream. By continuously sampling the temperature of the reflected air and controlling power to the heater, the dryer of this invention protects the hair and scalp from being overheated. In addition, the temperature of the reflected air at a given distance may serve as a measure of the dryness of the hair.

Because the flexibility of hair decreases with its dryness, excessive drying can contribute to its damage. Further, while hair can withstand high temperatures (1600C to 180"C), the scalp exhibits pain sensations at air temperatures above 50"C.

When the heat is wet, the heat of the drying air stream is absorbed by the water in and on the hair, so that no pain is felt by the user. However, when the hair is dry, it is heated faster and the air stream reaches the scalp, thereby increasing the possibility of pain sensations.

U.S. Pat. No. 3,426,441, issued to Broski, describes a hair dryer that utilizes a thermistor for measuring the temperature of ambient air. U.S. Pat. No.

3,082,540, issued to Hiltenbrand, describes a hair dryer that measures the humidity of air that has already passed through hair being dried. Neither of these dryers, nor any other dryer of the prior art, is known to measure the temperature of air reflected of hair being dried, as does the dryer of the present invention. In response to such temperature measurement, the dryer of the present invention is capable of automatically controlling the temperature of the hair and scalp during the drying operation, with the added advantage of limiting the level of dryness of the hair.

According to the present invention, a hair dryer is provided which comprises a fan for blowing air out of the dryer and a heater for heating the air before it is blown out of the dryer. The invention further comprises means for sensing the temperature of the air reflected off the hair as it is being dried. The device further comprises means operatively connected to the sensing means for regulating the heat output of the heater in accordance with the temperature of the reflected air. Thus, as the hair is dried, the temperature of the air being blown out of the dryer is reduced to prevent excessive heating of the hair and scalp and to limit the level of dryness of the hair.

A more detailed description of the present invention will be facilitated by reference to the following drawings: Figure 1 is a partially broken-away, side view of a hair dryer of the present invention.

Figure 2 is a front view of the dryer of Figure 1.

Figure 3 is a rear view of the dryer of Figure 1.

Figure 4 is a schematic view of the electronic circuitry of the dryer of Figure 1.

The hair dryer 10 of this invention is shown in Figure 1. The dryer has a housing 11, which defines a handle 12, air inlets and an air outlet. As best shown in Figure 2, an air outlet 13 is defined in the front portion of the dryer. Disposed in outlet 13 is an exhaust grill 14. As best shown in Figure 3, several primary air inlets 16 are defined in the rear portion of the dryer through which air is drawn into the dryer by a fan 17. The fan is powered by a fan motor 18 that receives electrical current through a conventional electrical cord when the cord is plugged into a power source. A dual-switched 19 is provided in handle 12. Switch 19 conventionally controls fan speed and power to the heater. Forward of fan 17 near air outlet 13 is a heater assembly, generally indicated at 20. The heater assembly includes several heater coils 21 supported on a heater support board 22.Also supported on the board and electrically connected to coils 21 are a thermostat 23 and a fuse 24, which additionally insure that the heater assembly does not overheat.

Housing 11 further defines a feedback air duct 25.

Positioned in the duct adjacent air outlet 13 is a thermistor 26, which is part of a temperature sensing circuit, generally indicated at 27. In the rear portion of duct 25 adjacent primary air inlets 16 is a secondary air inlet 16a.

Feedback air duct 25, thermistor 26, and temperature sensing circuit 27 provide a means for determining the temperature of air being reflected off the user's hair as it is dried.

As indicated by arrows in Figure 1, air entering inlets 16 is drawn into fan 17 and blown by the fan past heating coils 21. The air thus heated by the coils is blown out through outlet 13 against first the user's hair and then the scalp. Some of the drying air is reflected back into the dryer through duct 25, particularly because of the suction effect created by fan 17. The reflected air in duct 25 is eventually circulated into the dryer through secondary air inlet 16a, but may also be exhausted without entering the dryer if that is desired.

Thermistor 26 and temperature sensing circuit 27 are shown schematically in Figure 4. Thermistor 26 is preferably a negative temperature coefficient resistor, but may also be a positive temperature coefficient resistor. Such a thermistor is available from the Fenwall Electronics Corp., Waltham, MA, under the name "Model GA51 L2." Proceeding right to left with reference to Figure 4, thermistor 26 senses the temperature of the air being reflected off the user's hair. In response to a change in the reflected air temperature, the resistance of the thermistor changes. This change is detected by an integrated circuit zero crossing switch 28, which is composed of a comparator and a differential amplifier.Such a useful sensing circuit is available from the RCA Corporation, Sommerville, NJ, underthe name "CA-3079." Switch 28 electrically provides a controlling signal to the thyristor 29, which cuts off or reduces the power to heater coils 21, thereby cutting off or reducing heat input into the air stream from the dryer. Such a thyristor is available from the RCA Corporation underthe name of"TriacT- 20800b." By varying the power to the heater, the temperature of the air being blown against the user's hair is reduced as the hair dries. Consequently, even though the user may operate switch 19 to select a high fan speed and a high level of heat of the air being blown out of the dryer, the dryer automatically reduces the temperature of the air stream in accord ante with the reflected air temperature from the hair to prevent the hair and scalp from being overheated.

Additionally, a neon lamp 30 is provided for indicating to the user when the heater is on or off and a potentiometer 31 is provided by which the sensitivity to temperature changes of thermistor 26 can be adjusted. Further, an opening 32 may be provided as shown in Figure 1 between the heater area and duct 25 to allow thermistor 26 to sense the temperature of air deflected from the heater area and duct 25 to allow thermistor 26 to sense the temperature of air deflected from the heater area and into the duct, if outlet 13 is blocked.

Claims (3)

1. A hand held hair dryer comprising a housing, said housing defining an air inlet, an air outlet and a handle; a fan disposed in the housing for drawing air through the air inlet into the housing and blowing it out the air outlet; a heater for heating the air before it is blown out of the dryer said heater disposed in the housing between the fan and the air outlet; a feedback air duct, adjacent the air outlet, having a thermistor positioned therein for sensing the temperature of air reflected off the hair and drawn into the feedback air duct at the front of the hair dryer as the hair is being dried; and means operatively connected to the thermistor for regulating the heat output of the heater by gradually reducing its power output in accordance with the temperature of the reflected air, whereby as the hair is dried the temperature of the air being blown out of the hair dryer is reduced to prevent the hair from being overheated.

2. The dryer of Claim 5 wherein the heat output regulating means comprises an integrated circuit zero crossing switch which measures the resistance of the thermistor, and a thyristor, which cuts off or gradually reduces the power output of the heater, the switch directing the thyristor to cut off or gradually reduce the power output of the heater in accordance with the resistance of the thermistor.

3. A hand held hair dryer substantially as hereinbefore described with reference to the accompanying Drawings.