Abstract:
A hair cutting apparatus comprising a structure ( 126 ), a portion ( 1216 ) of which being adapted for placement against a skin surface where hair is to be cut, a heat generator comprising one or more heat elements ( 1214 ) positioned to touch said hair and heated to a temperature sufficient to cut hair, at least one of said heat elements being juxtaposed with said portion and a controller that controls the power source to provide pulsed heating of said one or more heat elements.

Description:
RELATED APPLICATIONS 
     The present application is a U.S. national application of PCT/IL02/00603, filed on Jul. 21, 2002. The present application claims the benefit under §119(e) of U.S. provisional application No. 60/306,892 filed on Jul. 23, 2001, and U.S. provisional application No. 60/354,019 filed on Feb. 5, 2002, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to removing hair with periodically applied heat without damaging the skin. 
     BACKGROUND OF THE INVENTION 
     The removal of unwanted hair from the body can be accomplished with non-mechanized means, for example razors, tweezers or wax, all of which are uncomfortable to use, irritate the skin and/or cause damage to the skin. 
     Mechanized cutting means for cutting hair, for example dry shavers, in addition to being uncomfortable to use, are limited to cutting hair of a specific length. Beard trimmers, for example, cut facial hair stubble, but cannot cut longer hairs on the scalp. 
     Alternate devices that use an electrical or electromagnetic source, for example electrolysis and photothermolysis, are effective but usually require an experienced operator to ensure proper administration without untoward side effects. 
     The use of heated wires or other structures to cut hair from a skin surface has been proposed. However, a heat generator that generates heat of a sufficient magnitude to cut hair and that cuts the hair close to the skin, often damages the skin. Alternatively, since the heat generator is offset from the skin to prevent skin damage, unwanted stubble is left behind. 
     In Peterson, U.S. Pat. No. 3,934,115, parallel metal strips on the upper side of a ceramic facing that contacts the skin, are used to cut hair. Hills, in U.S. Pat. No. 2,727,132 and P. Massimo in IT 1201364, use a continuously heated element to burn hair. P. M. Bell in U.S. Pat. No. 558,465, D. Seide in U.S. Pat. No. 589,445, G. S. Hills in U.S. Pat. No. 2,727,132, G. L. Johnson in U.S. Pat. No. 3,093,724, Hashimoto in U.S. Pat. Nos. 5,064,993 and 6,307,181 B1, F. Solvinto in FR 2531655 and EP 0102289, and E. Michit in FR 2612381, use a continuously heated wire to burn hair. J. F. Carter in U.S. Pat. No. 3,474,224, provides a circular comb device for burning nose hairs. Aside from physically separating the skin from the heated element, these references do not appear to provide other protection against burning of the skin. 
     Vrtaric in U.S. Pat. No. 4,254,324, provides a heat hair cutting system that is applied only to the tips of the hair to remove the split ends. 
     A prior art system for depilation, based upon photothermolysis is shown in U.S. Pat. No. 6,187,001, the disclosure of which is incorporated by reference. In this method, radiant energy is used to heat the air surrounding the skin to remove hair. EP publications EP 0 736 308 and EP 0 788 814, the disclosures of which are incorporated herein by reference, utilize radiant energy to selectively heat the hair, destroying it. 
     SUMMARY OF THE INVENTION 
     According to an aspect of some embodiments of the present invention, pulsed heat is applied through a heat generator containing one or more heat elements that contact the skin at least intermittently. In an exemplary embodiment, a pulsed heat generator provides pulsed heat at the heat elements wherein the pulses of heat are short enough so that although the temperature is high, the amount of heat transferred to the skin does not damage the skin. On the other hand, hair that contacts the heat element is destroyed, due to the lower heat capacity of the hair. Such a device may contact the skin substantially continuously. 
     According to an aspect of some embodiments of the present invention, a device comprises a heat generator that generates continuous heat of sufficient temperature to cut hair while contacting the skin. However, during the process of cutting hair, the heat generator is prevented from damaging the skin by controlling the period of time during which heat continuously contacts a given area of skin. In some embodiments of the present invention, a heat generator continually contacts the skin and the period of its heat generation is limited to prevent skin damage. In some embodiments of the present invention, the generator remains hot throughout its duty cycle and is removed from contacting a section of skin to limit the period of time in which heat is applied, thereby preventing skin damage. 
     As used herein, a heat generator is defined as a unit containing one or more heat elements heated to a temperature sufficient to cut hair during a given period of time in which it is in contact with the hair. It should be understood that current applied to the heat element at the line frequency (50–60 Hz) is to be considered continuous current, since it provides substantially constant heat. 
     Unless specified, further embodiments apply to both pulsed heating aspects and non-pulsed heating aspects of the present invention. Furthermore, while either pulsed or continuous heating may be described in reference to an embodiment of the invention, pulsed heating is generally usable in all the embodiments that are described with continuous heating. Additionally, embodiments that are described as using pulsed heating can use continuous heating if means for avoiding overheating of the skin as described herein are provided. 
     The cutting of a hair is dependent upon the magnitude of heat absorbed by the hair, whether a low temperature over a long period of time or a high temperature over a short period of time, whether pulsed or non-pulsed heat. Hence, the heat generator may generate heat at a lower temperature for a longer period of time or at a higher temperature for a shorter period of time in order to cut hair. 
     Heat builds in a specific area of a given hair and reaches a sufficient magnitude to cut the hair substantially independent of the hair length. In an exemplary embodiment of the present invention, a single apparatus cuts hair of a variety of lengths, from facial stubble to long hair on the scalp, in a variety of persons. Additionally or alternatively, the present invention allows a single apparatus to cut hair of a variety of lengths without exchanging, for example, cutter accessories. Further, the heat element used to cut hair, provides a sterile cutting environment, preventing the transmittal, for example, of scalp bacteria from one user to the next. 
     In some embodiments of the present invention, a heat generator provides heat of sufficient temperature to cause cessation of hair regrowth through destroying a hair growth regulatory mechanism as identified by R. L. Rusting in “Hair—Why it grows, Why it stops”,  Scientific American  248:6 June 2001, pp. 56–63. Alternatively, a heat generator provides heat at a lower magnitude to cause delay of hair regrowth through partial destruction of the hair growth regulatory mechanism. 
     In an exemplary embodiment of the invention, the heat generator contains one or more heat elements, for example a heated wire and/or heated strip that contacts the hair and, optionally, the skin. Additionally or alternatively, the one or more heat elements consist of one or more of a wire, a ribbon, or a conductive coating on a non-conductive surface, for example a ceramic material in the form of a bar. Optionally, the one or more heat elements contain, at least in part, a metal. Alternatively, they do not contain any metal. 
     In other embodiments of the invention, the heat generator comprises two or more heat elements. The hair is cut, for example, with absorption of an appropriate amount of cumulative heat by each hair. Two or more heat elements promote faster transfer of the necessary cumulative heat than, for example one heat element, allowing faster movement of the unit while cutting the hair. 
     Additionally or alternatively, two or more heat elements allow each heat element in the heat generator to maintain a lower temperature while cutting hair as compared to a heat generator with a single heat element at a higher temperature. 
     Additionally or alternatively, the pulsed current is pulsed at different times through the two or more heat elements and is, for example, synchronized so that one heat element generates heat while another heat element does not generate heat or, optionally, generates heat at a lower temperature. 
     Optionally, the heat generator comprises one or more walls that are perpendicular to the skin comprising, for example, a slot through which hair passes. In an exemplary embodiment, the one or more heat elements are moved by the device in relationship to the slot during use to prevent damage from heat buildup in a given area of skin. For example, in some embodiments of the invention, the heat generator, or a portion of the heat generator, is mechanized to be periodically removed from an area of skin. The heat generator, for example lifts the one or more heat elements from the skin in a regular cycle or by moving them along the surface of the skin. When a mechanized heat generator contains two or more heat elements, the heat elements, for example, have an axis parallel to the skin and rotate around the axis that is parallel to the skin. 
     In an alternative mechanical embodiment, the mechanization provides for rotation of the heat elements about an axis perpendicular to the skin, such that the heat element moves along the surface of the skin. This provides for contact times with the skin that do not cause skin burns while providing for continuous cutting action, since all of the heat elements are adjacent to the skin with a high duty factor. 
     In some embodiments of the present invention, two or more heat elements are situated on a vertical plane in relationship to the skin surface, so that the hairs are cut successively closer to the skin as the heat elements sequentially pass an area of skin. Alternatively or additionally, the heat generator comprises two or more heat elements situated on a horizontal plane to the skin so that cumulative heat appropriate for cutting a hair may be provided sequentially as the multiple heat elements pass the same site. 
     In an exemplary embodiment, the heat generator comprises two or more heat elements of different cross sectional sizes, with the heat element of greater cross section providing greater transfer of heat to cut hair while at the same temperature as the heat element of lesser cross section. Optionally, heat elements of different cross sectional sizes are located in a cylinder about an axis that moves perpendicular to the skin. Additionally or alternatively, the heat elements of different cross sectional sizes are situated in a non-vertical plane in relationship to the skin with one heat element at a different height from the skin than another heat element. For example the thicker heat element is located further from the skin to provide faster coarse cutting of the hair. Additionally or alternatively, the heat elements of different cross sectional sizes are situated on a horizontal plane in relation to the skin with one behind the other. For example, the thicker heat element is located in front of the thinner heat element, so the thinner heat element is used to cut the relatively fewer hairs that may have been left uncut the larger first heat element. 
     Similarly, heat elements of different cross sectional sizes that are arranged in a cylinder or on a horizontal or non-horizontal plane, allow the thicker heat element to cut the bulk of the hairs in its path while the thinner heat element cuts the relatively few hairs missed by the first heat element. 
     In an exemplary embodiment, the heat generator cuts hair in conjunction with a cooling apparatus, for example a fan, to provide cooling to the skin during the cutting process. In addition, when pulsed heating is used, the fan helps to remove heat from the heat element during the “off” time, so that a higher repetition rate for the heat pulses and a higher duty cycle can be used. 
     In an exemplary embodiment, the hair cutting apparatus includes a grasping structure designed to be grasped by an operator to which the heat generator is attached. The heat generator is held by the grasping structure at a specific angle to the skin, for example, perpendicular to the skin. Optionally, the heat generator is held at a non-perpendicular angle to the skin. The angle of heat generator, whether perpendicular or non-perpendicular is varied, for example, according to the design of the grasper. 
     In an exemplary embodiment, one or more posts provide the connection between the grasping structure and the heat generator. These posts are, for example, flexible or spring loaded so that as the heat generator moves across the contour of the skin, the heat generator moves up and down and/or swivels on the flexible posts in relation to the grasper. This movement prevents, for example, the heat element from pressing with undue force into the skin surface, causing skin damage. 
     In an exemplary embodiment of the present invention, heat is applied through a heat element that contacts the skin while two or more skin depressors located in proximity to the heat elements hold the skin flat. The two or more skin depressors prevent the heat element from sinking into the skin and causing skin damage due to increased contact area between the skin and the heat element. Optionally, one or more rows of skin depressors touch the skin and the one or more heat elements are parallel to the one or more rows of skin depressors. Additionally or alternatively, two rows of skin depressors are provided and the one or more heat elements are located between the two rows of skin depressors, optionally parallel to the two rows of skin depressors. Optionally, the one or more heat elements are not parallel to the two rows of skin depressors. 
     In an exemplary embodiment, the one or more heat elements of the heat generator are held at one or both ends by a tension generator. The one or more tension generators comprise, for example, a spring-loaded mechanism, to tighten the one or more heat elements of the heat generator during longitudinal expansion that may occur during heat generation. Additionally or alternatively, said one or more tension generators tighten the one or more heat elements to prevent substantial deformation while pressing against hair during hair cutting. 
     In an exemplary embodiment of the present invention, the one or more skin depressors are designed so that the one or more tension generators do not cause skin damage during cutting. For example, the one or more skin depressors located near the tension generator protrude beyond the tension generator so the skin does not contact the tension generator, thereby preventing buildup of heat and resultant skin damage. 
     Additionally or alternatively, the one or more rows of skin depressors provide a cooling mechanism for the heat elements. As the pressure on the heat elements of the heat generator, caused by the hairs in its path, increases, the heat elements of the heat generator displace and touch one or more of the skin depressors and cool. This cooling of the heat elements of the heat generator prevents heat buildup that can cause damage to the skin. A second pass cuts the hairs in the path of the cooled heat generator that were not cut during a first pass. 
     Optionally, the one or more rows of skin depressors provide current to the one or more heat elements of the heat generator only when the heat generator is in motion. In an exemplary embodiment the heat elements contain, for example, a positive charge potential and the two or more rows of skin depressors are connected to an electrical ground. As the heat generator is moved along the skin and comes against hairs in its path, the cool heat elements remain stationary against the hairs. As the heat generator continues motion, the heat elements bend and touch a row of skin depressors, thereby completing the circuit so electricity flows through the heat elements to the grounded skin depressors and the elements heat up. Upon cessation of motion, the heat elements no longer press against hairs in their path and become straight, for example with the assistance of the tension generated by the tension generator, so they no longer touch a row of skin depressors. The current through the heat elements is thereby disrupted and the heat elements cool. 
     In an exemplary embodiment, heat is applied through a heat element controlled by a motion detector so the heat element provides heat only while the heat element moves in relation to the skin. Upon slowing of the heat generator&#39;s motion below a specific rate, or its cessation of motion, the motion detector stops the production of heat by the heat element. Additionally or alternatively, in response to reduction or cessation of motion, the temperature of heat, produced by the heat generator, is reduced. 
     In an exemplary embodiment, the temperature and (when a pulsed heat source is used) pulse rate, and/or pulse width in a single heat element is controlled by a velocity detector. One or more of these factors is raised or lowered responsive to the velocity of the heat generator. This control, for example, prevents damage to the skin by excessive heat at a lower velocity. Additionally or alternatively, a velocity detector controls one or more factors of temperature, pulse rate and/or pulse width in each heat element individually when there are, for example, two or more heat elements. 
     In an embodiment of the pulsed aspect of the present invention, the pulsed heat generator applies continuous current as it moves at a higher speed in relation to the skin and applies pulsed current optionally at a rate that is reduced as the heat generator moves at a lower speed. 
     There is thus provided a hair cutting apparatus comprising a structure, a portion of which being adapted for placement against a skin surface where hair is to be cut a heat generator comprising one or more heat elements positioned to touch said hair and heated to a temperature sufficient to cut hair, at least one of said heat elements being juxtaposed with said portion and a controller that controls the power source to provide pulsed heating of said one or more heat elements. Optionally, the one or more heat elements are heated for a period of between 10 and 100 msec for each on-off cycle. Optionally, the heating of the heat element is repeated at a pulse repetition rate of 1–100 Hz. 
     In an exemplary embodiment, said controller comprises a velocity detector. Optionally, the velocity detector causes said heat generator to increase its rate of repeated pulsing when the velocity of said apparatus increases in relation to said skin and to decrease its rate of repeated pulsing when the velocity of said apparatus decreases in relation to said skin. 
     Optionally, the velocity detector causes said heat generator to increase the width of each pulsation during said repeated pulsing when the velocity of said apparatus increases in relation to said skin and to decrease the width of each pulsation during said repeated pulsing when the velocity of said apparatus decreases in relation to said skin. In an exemplary embodiment, said pulsation changes to continuous heating when the velocity increases above a specific rate, as sensed by said velocity detector. 
     Optionally, the velocity detector causes said heat generator to increase the temperature of said heat element when the velocity of said apparatus increases in relation to said skin and to decrease the temperature of said heat element when the velocity of said apparatus decreases in relation to said skin. Optionally, said velocity detector comprises an optical velocity detector. In an exemplary embodiment, said velocity detector comprises a mechanical velocity detector. 
     In an exemplary embodiment, the heat generator includes an interruptible power supply that energizes said heat element, said controller controls the interruptible power supply to periodically heat said heat generator to a temperature at which it is hot enough to cut hair and then causes it to cool to a lower temperature at which said skin surface is not damaged. 
     Optionally, said controller comprises a motion detector. Optionally, the motion detector controls said heat generator, switching said heat generator on when said heat generator is in motion in relation to said skin and switching said heat generator off when said heat generator is not in motion in relation to said skin. Alternatively, said motion detector comprises an optical motion detector. Optionally, said motion detector comprises a mechanical motion detector. 
     In an exemplary embodiment, the one or more heat elements comprise ribbon-shaped and a wide side of said ribbon-shaped heat elements are substantially perpendicular to said skin. Optionally, the one or more heat elements comprise a wire substantially parallel to said skin. Optionally, the one or more heat elements comprise two or more heat elements. Additionally or alternatively, a plane formed by the two or more heat elements is parallel to said skin. Optionally, the plane formed by the two or more heat elements is perpendicular to said skin. Optionally, the plane formed by the two or more heat elements is neither parallel nor perpendicular to said skin. 
     In an exemplary embodiment, the two or more heat elements have different cross-sectional areas. Optionally, the two or more heat elements have different cross-sectional configurations. Optionally, the heat applied by at least two of the two or more heat elements is applied at a different pulse rate. Optionally, the heat applied by at least two of the two or more heat elements is applied at a different pulse width or the temperature in at least two of the two or more heat elements is different. 
     In an exemplary embodiment of the present invention, at least one end of one heat element is attached to a tension generator. Optionally, the tension generator comprises a spring. Optionally, the tension generator comprises a spring-loaded wire. Additionally or alternatively, said portion that is adapted for placement against the skin comprises two or more skin depressors that contact said skin surface. Optionally said two or more skin depressors are perpendicular to said skin. 
     Optionally, said two or more skin depressors comprise one or more rows of skin depressing elements. 
     In an exemplary embodiment, said two or more skin depressors comprise at least two rows of skin depressing elements. Optionally, said two or more skin depressors comprise two parallel rows of skin depressing elements. Optionally, said one or more heat elements are located between said two rows of skin depressing elements. 
     Additionally or alternatively, at least one heat element is parallel to one or more rows of skin depressing elements. Optionally, said at least one heat element is not parallel to one or more rows of skin depressing elements. Alternatively, said at least one heat element is not parallel to said two or more rows of skin depressing elements. Optionally, at least one end of one heat element is connected to a tension generator and one or more of said skin depressing elements protrude beyond said tension generator. 
     In an exemplary embodiment, when the at least one heat element is so constructed that when it contacts one or more hairs during motion, it displaces opposite its direction of motion in relation to the skin. Optionally, when said heat element displaces in an amount sufficient to contact one of said skin depressors, it cools as it contacts the skin depressors. Optionally, when said heat element displaces in an amount sufficient to contact one of said skin depressors, it heats as it contacts the skin depressors. 
     In an exemplary embodiment, said portion adapted for placement against a skin surface is separate from said structure and said portion is mounted with one or more mountings on said structure. Optionally, said mounting comprises flexible posts. Additionally or alternatively, said mounting comprises spring-loaded mountings. Additionally or alternatively, said mountings are electrically connected to said heat elements. 
     In an exemplary embodiment, the controller comprises a motor that moves the heat elements along the skin, so that the temperature of the skin does not rise to a level, that causes it to burn. Optionally, the heat elements are elongate heat elements arranged to form a discontinuous cylindrical surface having a rotation axis. Additionally or alternatively the heat elements rotate about the axis they are periodically brought into contact with and removed from contacting said skin surface. Optionally, the axes of the heat elements radiate from an axis, said axis being perpendicular to the axes of the heat elements. Optionally, the controller rotates the elongate heat elements about the axis. 
     In an exemplary embodiment, said apparatus includes a fan that provides cooling for at least one heat element. 
     There is thus further provided a method of cutting hair comprising providing a pulsatingly heat element touching the skin, said heat element being heated to a peak temperature high enough to cause the cutting of hair without burning of skin at said position, wherein said pulsation allows the heat element to cool between pulses to an extent that it does not burn the skin while still cutting hair. 
     Optionally, said reducing comprises reducing the pulsation rate of pulsated heat to the heat element. Optionally, reducing comprises reducing the width of each pulsation of pulsated heat to the heat element. Additionally or alternatively, reducing comprises reducing the temperature of each pulsation of pulsated heat to the heat element. Alternatively, reducing is accomplished by a velocity detector when it detects a reduction in velocity of said heat element in relation to said skin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary non-limiting embodiments of the invention are described in the following description, read with reference to the figures attached hereto. In the figures, identical and similar structures, heat elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features shown in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. The attached figures are: 
         FIG. 1  is a simplified schematic diagram of a wire cutting a hair, in accordance with an exemplary embodiment of the invention; 
         FIG. 2  is a simplified electrical schematic diagram of strip cutting a hair, in accordance with an exemplary embodiment of the invention; 
         FIG. 3  is a simplified schematic diagram, in accordance with an exemplary embodiment of the invention; 
         FIGS. 4A and 5  are respective orthogonal cross-sectional views of a hair cutting apparatus, in accordance with an exemplary embodiment of the invention; 
         FIG. 4B  is a cross sectional view of an alternative hair cutting apparatus, in accordance with an exemplary embodiment of the invention; 
         FIGS. 6 and 7  are cross-sectional and top perspective views, respectively, of an embodiment of a hair cutting device, in accordance with an exemplary embodiment of the invention; 
         FIG. 8  is a bottom perspective view of the device of  FIGS. 6 and 7 , in accordance with an exemplary embodiment of the invention; 
         FIGS. 9A–C  is respective partial side, end and perspective views of an alternative motorized example of a hair cutting apparatus, in accordance with an exemplary embodiment of the invention; 
         FIG. 10A  is a heat generator with an optical velocity detector, in accordance with an exemplary embodiment of the invention; 
         FIG. 10B  is a heat generator with a servo-velocity detector, in accordance with an exemplary embodiment of the invention; 
         FIG. 11A  is a hair cutting apparatus with a heat element situated between two parallel lines of skin depressors, in accordance with an exemplary embodiment of the invention; 
         FIG. 11B  is a side view schematic diagram of a hair cutting apparatus shown in  FIG. 11A  on a skin surface, in accordance with an exemplary embodiment of the invention; 
         FIG. 11C  is a schematic diagram of a heat element on a skin surface; 
         FIG. 11D  is a portion of a hair cutting apparatus of  FIG. 11A  taken along lines A—A, in accordance with an exemplary embodiment of the invention; 
         FIG. 11E  is a portion of a hair cutting apparatus of  FIG. 11A  taken along lines A—A, in accordance with an exemplary embodiment of the invention at a different time; 
         FIG. 12  is a partially exploded view of a hair cutting unit, in accordance with an exemplary embodiment of the invention; 
         FIG. 13  is an assembled hair cutting unit corresponding to the exploded view of  FIG. 12 , in accordance with an exemplary embodiment of the invention; 
         FIG. 14  is an electrical functional block diagram of a section of a hair cutting apparatus, in accordance with an exemplary embodiment of the invention; 
         FIG. 15  is an electrical schematic diagram of pulses from an optical mouse velocity detector on a hair cutting apparatus, in accordance with an exemplary embodiment of the invention; 
         FIG. 16  is an electrical schematic diagram of pulses from an electronic circuit on a hair cutting apparatus, in accordance with an exemplary embodiment of the invention; and 
         FIG. 17  is an electrical schematic diagram of voltage in response to a motion detector on a hair cutting apparatus, in accordance with an exemplary embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is a schematic cross-sectional diagram of an embodiment of a wire  100  cutting a hair  102 , while optionally touching a portion of skin  104 , in accordance with an exemplary embodiment of the invention. 
     In a pulsed embodiment of the invention, the current through wire  100  is pulsed on for between 10 and 100 milliseconds. The length of current pulse, for example, is based upon the peak temperature of wire  100 , for example, or other factors such as the speed at which wire  100  passes over skin  104 . During this short period of time, wire  100  heats to the desired temperature. However, in the short time that the current is on, the amount of heat generated is not sufficient to heat skin  104  to a temperature at which it is damaged. Because the heat dissipates in skin  104  faster than in a hair, wire  100  does not have sufficient time to damage skin  104 , but cuts hair  102 . Generally, wire  100  moves in a direction  108  along a portion of skin  104  and if the movement is halted, absent the pulsing of the heat, wire  100  will burn skin  104   
     In non-pulsed embodiments of the present invention, for example, wire  100  is periodically removed from skin  104  to prevent skin damage. Additionally or alternatively, wire  100  remains in constant contact with skin  104  and the current through wire  100  is turned off to prevent skin damage when wire  100  is stationary with respect to skin  104 . Mechanisms, for example, that turn the current to wire  100  on or off while in contact with skin  104  or periodically remove wire  100  from skin  104 , will be explained below. 
     In an exemplary embodiment, the current through wire  100  is 0.5 A, though it may vary, depending on the dimensions and/or materials of wire  100 . In order to cut efficiently, wire  100 , for example, reaches a peak temperature of between 700 and 800° C., when wire  100  is held against hair  102  for 10–50 milliseconds. Lower temperatures, for example 500° C., can be used to cut hair  108  when wire  100  is held against hair for longer periods of times, for example, 50–100 milliseconds. Higher temperatures, for example 1000° C., can be used to cut hair  108  when wire  100  is held against hair  108  for shorter periods of time, for example, 5–10 milliseconds. 
     Optionally, a fan  106  is provided that cools skin  104  and wire  100  to avoid overheating skin  104 . The operating temperature of the device and/or the duration of heat application to a given area of skin  104  will likely change based upon whether or not a fan is used in conjunction with wire  100 . For example, temperatures of 1000° C. for a duration of more than 10 milliseconds are contemplated for cutting hair  108  in conjunction with fan  106 . 
     Additionally or alternatively, the color of wire  100  as it attains different temperatures, may be used as a determinate of hair cutting ability. For example, the power supply may be set to a level that causes wire  100  to become red hot at which it will cut hair  108  rapidly. Additionally or alternatively, the power supply may be set to a level that causes wire  100  to become yellow to yellow-red hot or a color indicating a temperature at which, for example, it will cut hair  108  less rapidly. Optionally, an operator can be apprised of these temperature-associated colors. By increasing and/or decreasing a current control to wire  100 , for example, the operator can cause wire  100  to glow at a specific color, indicating that an optimal temperature of wire  100  has been reached. 
     In an exemplary embodiment, wire  100  has a diameter of 0.070 millimeters, 0.01 millimeters or less, for example, when manufactured of a flexible material. A flexible material, for example, comprises, for example, a wire  100  manufactured from Kantaal D, (an alloy of nickel chromium and other metals manufactured by Kantaal Group). Alternative materials for wire  100  include Nichrome or other wire resistance materials. Alternatively, wire  100  could have a diameter of between 0.08 and 0.5 millimeters, when a less flexible material is used for its manufacture. 
     In an exemplary embodiment, wire  100  has a length, for example, of 10 millimeters, so that it cuts only a 10-millimeter swath of hair on each pass. Optionally, wire  100  has a longer length, for example 30 millimeters or more, providing a larger swath of hair cut with each pass. 
     An advantage of the present invention over prior art dry shavers, for example, is that heated wire  100  sterilizes skin surface  104 , or provides an aseptic environment, during cutting hair  108 . Additionally or alternatively, the heat of wire  100  suppresses and/or does not promote the spread of bacteria or other unwanted organisms during the cutting process. In contrast, for example, a dry shaver neither provides an aseptic environment nor suppresses the spread of bacteria during the cutting process. Hence, bacteria is often spread on skin  104  during cutting with a dry shaver, with a resultant infection, for example, when skin surface  104  is breached. 
       FIG. 2  is a schematic diagram of an alternative embodiment of a hair cutting device utilizing a ribbon  200 , shown in cross section (optionally touching the skin), cutting a hair  202  while moving in a direction  208  along a skin surface  204 , in accordance with an exemplary embodiment of the invention. A follicle  232 , the remains of a cut hair  230 , is, for example, cut below skin surface  204 . 
     R. L. Rusting in “Hair—Why it grows, Why it stops” by,  Scientific American  248:6 June 2001, pages 56–63, identifies the existence of stem cells within a bulge  234  that are part of the hair regulatory mechanism. In an exemplary embodiment, the heat of ribbon  200  radiates from skin surface  204  through hair follicle  232  to affect the cells of bulge  234 , thus providing a cessation of hair regrowth for a period of time, for example, a few days, a few weeks, a few months or even permanently. 
     In an exemplary embodiment of the present invention, a curved end  244  forms on a hair bulb  242  that has been cut with a heat element, for example ribbon  200 , that is more comfortable to shaved skin  204 . This is a distinct advantage over, for example most razors and electric shavers, that often leave a hair bulb  250  with a sharp point  252  that is uncomfortable to shaved skin  204 . 
     Ribbon  200 , for example, has a width, dimension a, of 0.05 millimeters or less, when manufactured from strong materials and/or the peak temperature is low. Alternatively, ribbon  200  could have a higher width dimension a, for example 0.2 millimeters or more, when manufactured from weaker materials and/or a higher peak temperature is maintained. Height, a dimension b, is not critical, except that excessive height results in high power consumption. 
     Ribbon  200  with a greater height dimension b, however, allows a large heated area to contact hair  202 , providing faster buildup of heat in hair  202  and faster rate of cutting. A narrow width dimension a, provides less heat transfer to skin  204  when using a ribbon  200  with a greater height b for rapid cutting. Other useful shapes, for example a sharp edge on the lower portion of ribbon  200  or an oval shape to ribbon  200 , provide other associated advantages as will be clear to persons of skill in the art. 
     In general the dimensions of ribbon  200  can be based on the amount of power available (whether the device run from batteries or from mains), and factors including whether the heat is pulsed or continuous, whether movement of ribbon  200  is mechanical or manual, whether fan cooling is provided and limitations on the heat capacity of the ribbon  200  so that skin damage is avoided. The values given above are typical for the particular material and are not to be considered as limiting. 
       FIG. 3  is a simplified schematic representation of an embodiment of a device  300 , in accordance with an exemplary embodiment of the invention. A power supply  310 , for example, produces between 3 and 30 volts and between 0.030 and 5 amperes, depending on the dimensions of a heat element  324 . Power from power supply  310  causes heat element  324  to heat to a temperature that is sufficient to cut hair, for example, between 700–800° C. when contact with a hair is between 10 and 50 milliseconds. An optional pulsar  320  (which can be part of power supply  310 ) regulates the current produced by power supply  310  so that it, for example, produces pulsed heat for a period of 10–200 milliseconds such as 50 ms. The time between pulses is regulated, depending on the rest of the construction, to allow heat element  324  to cool sufficiently and to be off for a sufficient period to avoid burning of the skin and build-up of heat, even if heat element  324  is not moved. Generally, the pulse rate is between 1 and 100 Hz. However, as described below, if mechanical motion is provided to heat element  324  so that it does not continuously contact the skin, high duty cycles and even continuous heating may be provided. 
     Heat element  324  is optionally attached to a post  340  by a spring  332  and to a post  342  by a spring  330 . These springs maintain tension on heat element  324  even as it expands during the heating phase so that it remains taut against a hair  312 , shown in cross section. 
       FIGS. 4A and 5  are respective orthogonal cross-sectional views of a hair cutting apparatus  500 , with  FIG. 5  taken along lines V—V of  FIG. 4A , in accordance with an exemplary embodiment of the invention. Apparatus  500  comprises one or more heat elements  514 ,  516  and  518  stretched across a slot  504  in a housing  506 . Slot  504  is, for example, 1.0 centimeter wide to allow a small swath of hair to enter slot  504  for cutting. Alternatively, slot  504  may have a width of 0.5 centimeters or less, to cut an even smaller swath of hair or a width of 2.0 centimeters of more in order to cut a larger swath of hair on each pass. 
     Heat elements  514 ,  516  and  518 , as shown in  FIG. 4A , are on the same horizontal plane so that they are all, for example, in continuous contact with a portion of skin  524 . Additionally or alternatively, the heights of heat elements  514 ,  516  and  518  can be set so that, for example, they are not in contact with skin  524  and cut hairs to a specific length. Alternatively or additionally, heat elements  514 ,  516  and/or  518  can have different duty cycles, limiting, for example, the number of heat elements  514 ,  516  and/or  518  providing heat at any given time. 
     A spring  544  ( FIG. 5 ) is attached to each heat element  518  (only  518  is shown in  FIG. 5 ) to keep it taut even as it expands during heating. Heat element  518  is attached to a power supply  510 , shown schematically. One way of placing heat element  518  so it contacts skin  524  is to provide rods  502 , mounted in walls  506  that are attached to heat element  518  and bring heat element  518  close to skin surface  524 . When heat element  518  is formed in a ribbon, for example, slots may be placed in rods  502  to position and orient ribbon heat element  518 . 
       FIG. 4B  shows an alternative exemplary embodiment of hair cutting apparatus  500 ′ comprising heat elements  514 ′,  516 ′ and  518 ′ that are of different heights in respect a skin surface  524  direction beneath slot  504 ′ in housing  506 ′. Heat elements  514 ′,  516 ′ and  518 ′ are positioned so that as apparatus  500 ′ moves in direction  508 , they sequentially cut a hair  522 ′ at different levels in relation to skin surface  524 . 
     Heat element  518 ′, for example, cuts hair  522 ′ at two millimeters above skin surface  524 , though it could be positioned to cut hair  518 ′ at one millimeter or less or 10 millimeters or more above skin  524 . 
     Following heat element  518 ′, heat element  516 ′, for example, cuts hair  522  to a lower level in relation to skin surface  524 , for example one millimeter, though it could be positioned to cut hair  528  at as little as 0.5 millimeters or less as long as 5 millimeters or more. 
     Following heat element  516 ′, heat element  514 ′ cuts hair  522 , for example, so it is flush with skin surface  524 , though heat element  514 ′ could be set to cut hair  522  at 0.5 millimeters or greater. Alternatively or additionally, when heat element  516 ′ is positioned flush with skin surface  524 , it is capable of cutting hair  522  below skin surface  524  due to the fact that heat from heat element  514 ′ spreads along shaft of hair  522 , below skin surface  524 ′. 
     For example, heat element  514 ′ could cut hair  522  to 0.5 millimeters below skin surface  524  or even one millimeter or more below skin surface  524 , depending, for example, on the magnitude of heat generated and/or duration of contact between heat element  514 ′ and skin surface  524 . Other factors affecting the depth to which hair  522  is cut below skin surface  524  include, for example, hair  522  shaft thickness and/or number of hairs  522  contacting heat element  514 ′ simultaneously, thereby dissipating the peak heat from heat element  514 ′ and diminishing its cutting power. 
     In an alternative embodiment of the present invention, heat elements  514 ′,  516 ′ and  518 ′ (and/or elements  514 ,  516 ,  518 ) provide pulsed heat. The pulsing of the heat can be simultaneous for heat elements  514 ′  516 ′ and/or  518 ′. Alternatively or additionally, the pulsing of heat from heat elements  514 ′,  516 ′ and  518 ′ may not be simultaneous, allowing lower peak power requirements for apparatus  500 ′ during operation. 
     A bottom  512  ( FIG. 4A ) of housing  506  can be of a variety of shapes that provide, for instance, comfort to skin  524  and/or ease of use. For instance, bottom  512  could be curved with a single curve or with multiple curves. 
       FIGS. 6 and 7  are cross-sectional and top perspective views of an embodiment of a hair cutting device  600 , cutting a hair  602 , according to an embodiment of the present invention. A plurality of heat elements  604  (shown as round wires) are shown on a cylinder  606 . Heat elements  604  are attached to two end plates  608 , which are urged apart by a spring  610 , keeping heat elements  604  taught in spite of expansion during heating. 
     A motor (not shown) mechanically rotates a cylinder  606  that supports heat elements  604  in a direction  612  during the hair cutting process. Hair cutting device  600  preferably includes a housing  614  shown in cross-section in  FIG. 6 . A surface  616  of housing  614  contacts the skin. Hair  602 , for example enters housing  614  through a slot  618 , contacts heat elements  604  and are cut. 
     Slot  618 , for example, is between a few millimeters to 1 cm or more wide, depending on the amount of hair  602  desired to be cut on each pass. It should be noted that heat elements  604  may be in contact with the skin while cutting hair  602 . However, since heat elements  604  move along the skin surface as cylinder  608  rotates, heat elements  604  are not in any one place for a long enough time to cause damage to the skin. Pulsed or continuous heat may be generated from heat elements  602  in this embodiment. 
     For simplicity, in this and the other embodiments, the location of the power supply and any commutation required to transfer electricity to heat elements  604  is not shown. However, a simple commutator arrangement may be used to electrify end plates  608  and continuously electrify heat elements  604 . Alternatively, end plates  608  are non-conducting and heat elements  604  have their ends connected to a common rotating connection. Alternatively, heat elements  604  are heated only just before they reach slot  618  and the electricity is disconnected from them after they leave the vicinity of slot  618 . 
     While slot  618  is shown as being open, in some embodiments of the invention, a thin screen is provided over slot  618  through which hairs pass. A screen, for example that is non-heat conducting, comprises a series of slits or a mesh. Even with such a screen, heat elements  604  may be kept in effective contact with the skin surface. 
     Optionally, in addition to one or more heat elements  604  of one cross sectional size or thickness, an embodiment of hair cutting device  600  includes heat elements  624  of more than one cross-sectional size or thickness. 
     In an exemplary embodiment, heat elements  604  of different cross sectional sizes are situated on different portions of cylinder  606  so that thicker heat element  624  cuts hair  602  that, for example, is resistant to cutting by heat element  604 . 
       FIG. 8  shows a bottom perspective view of device  600  in  FIGS. 6 and 7 , in accordance with an exemplary embodiment of the invention. 
       FIGS. 9A–C  show respective cross-sectional partial side, cross-sectional end and perspective views of an alternative motorized example of a hair cutting apparatus  900 , in accordance with an exemplary embodiment of the present invention. In this embodiment, a plurality of heat elements  904  are mounted between a hub  920  and an outer ring  906 . Hub  920  is formed with a shaft  908 , which is rotated during operation by a motor  912 , which also turns an optional fan,  914 . Alternatively, two motors are provided, one that rotates hub  920  and a second motor that turn fan  914 . 
     As motor  912  turns, heat elements  904  pass across slots or holes in a faceplate  916 , through which hairs enter the device. The faceplate may be formed with radial or circumferential slots or with openings of round or square shape. The same variations in heating cycles, and electric power described with respect to  FIGS. 6–8  are available for this embodiment.  FIG. 9C  is a possible external view of a hair cutting apparatus embodiment, in accordance with an exemplary embodiment of the invention. 
       FIGS. 10A and 10B  are schematic representations of hair cutting apparati  1000  and  1002 , equipped with detectors  1070  and  1062  respectively that measure motion and/or velocity, in accordance with an exemplary embodiment of the invention. In apparatus  1000 , optical motion/velocity detector  1070  is shown while in apparatus  10 B, mechanical motion/velocity detector  1062  is shown. Both units  1000  and  1002  provide either pulsed or continuous current that is changed in relation to the motion and/or velocity. 
       FIG. 10A  shows hair cutting apparatus  1000  with a cross section of a wire heat element  1010  that heats with either pulsed or non-pulsed heat, in accordance with an exemplary embodiment of the invention. A base  1012  regulates the power from a power supply (not shown) to heat element  1010  according to information provided by detector  1070 . 
     A distance  1042  between wire heat element  1010  and base  1012 , for example, is 30 microns. Additionally or alternatively, distance  1042  is generally 10 microns or less or 40 microns to 0.1 millimeters or more, dependent, for example, upon the flexibility of wire  1010 . For example, when heat element  1010  comprises a flexible material, distance  1042  can be greater than, for example, when heat element  1010  comprises a hard material that does not bend as much. 
     In an exemplary embodiment, when detector  1070  is configured as a velocity detector, velocity is detected through an optical wave  1020  that reflects from skin  1018  or, for example, a hair  1024 . Velocity detector  1070  can use a variety of methods for determining velocity along a portion of skin  1018 . For instance, an optical wave  1020  can be used to register Doppler shift to determine velocity of unit  1000 . When unit  1000  ceases movement, or moves below a minimal velocity, current to wire heat element  1010  is shut off. Additionally or alternatively, unit  1000  contains a manual switch that can be operated by a user. 
     Alternatively, detector  1070  can be configured as a motion detector that switches on current to wire heat element  1010  so that it heats only when there is a minimal movement of hair cutting apparatus  1000  in relation to skin surface  1016 . 
     Optionally, heat element  1010 , for example, produces a continuous current and the level of current is varied in relationship to velocity as detected by detector  1070 . When heat element  1010  moves at a lower speed, for example 20–30 millimeters per second, current is provided to heat element  1010 , for example at 0.5 to one ampere. When the speed of heat element  1010  increases to 30–40 millimeters per second, current is provided to heat element  1010 , for example, from 1 to 1.3 amperes. Above 40 millimeters per second, the level of 1 to 1.3 amperes, for example, is maintained. These figures relating to peak current and/or duty cycle are used, for example, when heat element  1010  is made nickel chromium with a length of 20 millimeters and a diameter of 70 microns and can vary based upon changes in diameter, length and/or material. 
       FIG. 10B  shows a hair cutting apparatus  1002  with cross sections of heat elements  1030  and  1032  (supported by a base  1050 ) that provide heat to cut hair  1024 , in accordance with an exemplary embodiment of the invention. Unit has a mechanical velocity detector  1062  that uses a mechanical wheel  1064  to determine velocity or motion in relation to skin surface  1018 . 
     Alternatively, a mechanical ball can be used in place of mechanical wheel  1064 , similar to those used in a computer mouse that rolls on skin surface  1018 . As in detector  1070  of unit  1000 , detector  1062  of unit  1002  functions to detect motion whereby current to heat elements  1030  and  1032  ceases below a specific amount of motion. Additionally or alternatively, detector  1062  functions to detect variations in velocity, thereby varying temperature, pulsation rate and/or width in heat elements  1030  and/or  1032 . 
     Optionally, both heat elements  1030  and  1032  have the same cross section and one or more of the temperature, pulse width and or pulse repetition is changed to both heat elements  1030  and  1032  in response to changes in speed of unit  1002 . 
     Additionally or alternatively, heat element  1030  is heated to full capacity while heat element  1032  is not heated or, optionally, heated below its maximal heat capacity. When velocity of unit  1002  is slowed, for example, velocity detector  1062  detects the change in speed and signals base  1050 . Base  1050  decreases the temperature of heat element  1030  and/or increases the temperature of heat element  1032 . As heat element  1032  is of a greater offset from skin  1018 , it cuts hair  1024  without causing damage to skin  1018 . 
     Additionally or alternatively, base  1050  increases the pulse width or the pulse repetition of heat element  1032  to cut hair  1024  at a lower velocity along skin  1018 . 
     Either motion detector and/or velocity detector  1070  can be configured with units  1000  and/or  1002 , including any of the various embodiments of either unit noted above. To understand the workings of motion detector and/or velocity detector  1070 , reference is now made to  FIGS. 14–18 . 
       FIG. 14  is an electrical functional block diagram of a section  1000 A of optical hair cutting apparatus  1000  including detector  1070 , power regulating base  1012  and its associated power, in accordance with an exemplary embodiment of the invention. Optical mouse sensor  1070  detects velocity of unit  1000  and signals a regulator  1052 A to regulate power from a power supply  1072 . Alternatively, a mechanical mouse sensor  1062  is utilized in place of optical sensor  1070 . 
       FIG. 15  is an electrical schematic diagram  1072  (not shown to scale) of pulses from power supply as a result of regulation by regulator  1052 A, in accordance with an exemplary embodiment of the invention. As the velocity of apparatus  1000  or  1002  is at a given level, pulsing from power supply  1072  appears in an area  1502 . Alternatively, as the velocity of apparatus  1000  or  1002  increases, pulsing from power supply  1072  appears in an area  1504 . More frequent pulses with the same pulse width, for example, result in a higher peak temperature. 
       FIG. 16  is a diagram of pulses from regulator  1052 A on hair cutting apparatus  1000  equipped with velocity detector  1070  or hair cutting apparatus equipped with velocity detector  1062 , in accordance with an embodiment of the present invention. A high repetition rate of pulses  1602  occurs when apparatus  1000  or  1002  moves rapidly in relation to a hair  1024  ( FIG. 10A ). A low repetition rate of pulses  1604  occur when apparatus  1000  or  1002  moves slowly in relation to hair  1024 . Both pulses  1604  and  1602  have the same duty cycle. 
     Additionally or alternatively, detectors  1070  and  1062  of units  1000  and  1002  respectively, may function as motion detectors, providing heat only when a specific minimum speed is reached. Illustrations of detectors  1070  and  1062  in embodiments as motion detectors are provided in  FIGS. 17 and 18 . 
       FIG. 17  is an electrical schematic diagram of a DC voltage  1706 ′ in response to a speed of motion  1706 , in accordance with an exemplary embodiment of the invention. Speed of motion  1706 , for example is sensed by motion detector  1070  ( FIG. 10A ) while DC voltage  1706 ′ is controlled by regulator  1052 A on hair cutting apparatus  1000 . 
     A falling speed of motion  1702  (as sensed by sensor  1070 ) that falls below a base level  1704 , causes DC voltage  1706 ′ to fall shut off a voltage level  1704 ′. 
       FIG. 11A  is a hair cutting apparatus  1100  with a heat element  1114  situated between a first line of skin depressors  1112  parallel to a second line of skin depressors  1116  that are attached to a base  1110 , in accordance with an exemplary embodiment of the invention. Base  1110  can be made of clear material, for example a clear plastic that maintains the passage of an optical sensor signal through base  1110 . Additionally or alternatively, base  1110  is made of one or more materials, including opaque materials, for example a ceramic or opaque plastic, and the path of an optical sensor signal is set to bypass the opaque areas. Additionally or alternatively, there is no optical sensor signal and heat element  1114  provides pulsed heat that, for example, does not require optical sensing. 
     When base  1110  is made of a clear plastic or an alternative optical path is provided, an optical velocity detector  1160  mounted above it sends optical signals to skin surface  1018  that return to velocity detector  1160  that registers velocity and maintains heat element  1114  in a heated state. In an embodiment shown in  FIG. 11E , as explained below, for example, neither velocity detector  1160  or pulsed current are required to prevent damage to skin  1018  while being touched by heat element  1114 . 
     When optical signals traveling through base  1110  register that hair cutting apparatus  1100  is not in motion in relation to a skin surface  1018 , velocity detector  1160  switches off the current to heat element  1114  so that heat element  1114  cools, preventing damage to skin surface  1018 . A delay in motion for 100 ms, for example, signals base  1110  to make necessary changes in temperature. Alternative periods of motion delay can be used, for example, with different peak temperatures and/or pulse rates in heat element  1114 . 
     Heat element  1114 , for example, is attached to a tension generator  1140  at one end and/or a tension generator  1142  at its opposite end. Tension generators  1140  and/or  1142  serve to keep heat element  1114  taught during motion across skin surface  1118 . Though tension generators  1140  and  1142  are, for example, flexible strips that serve to provide tension on heat element  1114 , they could have a variety of other configurations. For example, tension generators  1140  and  1142  could comprise two coiled springs that provide tension on heat element  1114 . 
     Heat element  1114  optionally has a diameter of 0.070 millimeters, though it could have a diameter of 0.02 or less or 0.5 millimeters or more based upon a variety of factors such as materials, temperature and/or pulsation rate. Skin depressors  1112  and  1116 , for example, have a diameter of 3 millimeters though they could be 5 millimeters or thicker or 1 millimeter or thinner, depending, for example on the desired strength of depressors  1112  and/or  1116  and/or the ease with which they are to travel along skin  1118 . 
     Skin depressors  1112  and  1116  are shown as being straight comb-like pieces though their shape could vary. For instance, skin depressors  1112  and  1116  could be curved along their length. Alternatively or additionally, the tips of skin depressors  1112  and  1116  that contact skin surface  1118  could be any shape, for example ending in round balls to provide smooth movement along skin  1118 . Alternatively or additionally, depressors  1112  and/or  1116  can be coated, for example with a ceramic or Teflon coating, to aid in smoother movement along skin  1118 . 
     A distance  1126  of heat element  1114 , for example, to row of skin depressors  1112  usually equal to a distance  1128  to row of skin depressors  1116 . Distances  1126  and  1128 , for example, are one millimeter though they could be 1.5–5 millimeters or more or 0.8–0.2 millimeters or less, depending on the diameter, peak temperature and/or duty cycle of heat element  1114 . 
     In  FIG. 11B , skin depressors  1112  and  1116  maintain skin surface  1118  flat so that heating heat element  1114  does not sink into skin surface  1118 , thereby providing greater surface contact and associated heat buildup that can damage skin surface  1118 , in accordance with an exemplary embodiment of the invention. Heat element  1114  is shown in  FIG. 11C  on skin surface  1118  without skin depressors  1112  and  1116 , demonstrating that it sinks into skin surface  1118 , potentially causing skin damage due to the increased contact area with skin surface  1118 . 
     The length of skin depressors  1112  and  1116 , for example, is 2 millimeters, though they could be 1–0.5 millimeters or shorter or 3–8 millimeters or longer, based for example, on the distance heat element  1114  is spaced from an edge  1130  that is, for example, parallel to a skin surface  1118 . 
     In an alternative embodiment, skin depressors  1116  are of a first length and skin depressors  1112  are of a second, different, length that puts base  1110  at an angle to skin surface  1118 , for example between 30 and 60 degrees. The variation in angle of base  1110 , for example, may be determined by the most frequent use for which unit  1100  is built, such as home or professional use. A profession using unit  1100  on others may prefer a different angle than, for example, a home user cutting his or her own hair. 
     Optionally, skin depressors  1112  are parallel to skin depressors  1116  and heat element  1114  is parallel to skin depressors  1112 . Additionally or alternatively, skin depressors  1112  are parallel to skin depressors  1116  and heat element  1114  is not parallel to skin depressors  1112 . 
     Additionally or alternatively, skin depressors  1112  are not parallel to skin depressors  1116  and heat element  1114  is parallel to skin depressors  1112  or skin depressors  1116 . Alternatively, skin depressors  1112  are not parallel to skin depressors  1116  and heat element  1114  is not parallel to skin depressors  1112  or skin depressors  1116 . 
     Alternatively or additionally, skin depressors  1112  and  1116  are removable from hair cutting apparatus  1100  and supplied in multiple lengths, widths or shapes based upon texture, plushness or length of hair  1024  ( FIG. 10B ) to be cut. 
     In an embodiment of the present invention, apparatus  1100  contains springs  1182  and a handle  1180  (shown schematically) that an operator can grasp during use of unit  1100 . Springs  1182  provide shock absorption between heat element  1114  and skin  1118 . Additionally or alternatively, springs  1182  allow unit  1100  to follow contours in skin surface  1118  during movement along skin  1118  by an operator. While springs  1182  are shown in each corner of handle  1180 , as few as one spring, for example, in the middle of handle  1180  or many more springs  1182 , for example  10  or more, can be located on apparatus  1100 . A greater amount of springs  1182  may be built into units that are, for example, for use with sensitive skin. Fewer springs  1182  may be built into units that are for example, for use with more robust skin. 
       FIG. 11D  shows a portion of a hair cutting apparatus  1100  taken along a line A—A with heat element  1114  situated between skin depressors  1112  that are parallel to skin depressors  1116 , in accordance with an exemplary embodiment of the invention. Hair cutting apparatus  1100  moves in a direction  1148  and hairs  1134 , shown in cross section, are cut by heat element  1114 . 
       FIG. 11E  shows a portion of a hair cutting apparatus  1100  taken along lines A—A with a portion of heat element  1114  displaced by the pressure of hairs  1134 , shown in cross section, as unit  1100  is moved in a direction  1148 , in accordance with an exemplary embodiment of the invention. Heat element  1114  is flexible, as noted earlier, by virtue of being attached to tension generators  1140  and  1142  (shown in  FIG. 11A ). Heat element  1114  cools as it touches skin depressors  1116 , preventing heat buildup in heat element  1114  that can damage skin surface  1118 . As heat element  1114  cools, it passes over some of hairs  1134  without cutting them. 
     Hair cutting apparatus  1100  is passed again, in direction  1148  for example, to cut the balance of hairs  1134  that were not cut during the first pass. In each pass over hairs  1134 , some of hairs  1134  are cut. When pressure on heat element  1114  builds, heat element  1114  bends and touches skin depressors  1112  or  1116  and cools. With heat element  1114  cooled, it passes over the balance of hairs  1134  without cutting them. Another pass with hair cutting apparatus  1100  is then made in order to cut the remainder of hairs  1134 . 
     Alternatively, apparatus  1100  comprises a safety feature that prevents heat element  1114  from heating when apparatus  1100  is not in motion in relation to hairs  1134 . In and exemplary embodiment, heat element  1114  is charged with a potential electric current while skin depressors  1112  and/or  1116  are connected to an electrical ground. When apparatus is not being moved in relation to hairs  1134 , heat element  1114  does not touch skin depressors  1112  and/or  1116  and therefore current does not pass through heat element  1114  ( FIG. 11D ). When not in motion, heat element  1114 , for example, remains cool. 
     As apparatus  1100  is moved in direction  1148 , heat element  1114  touches hair  1134 , causing it to bend and touch skin depressors  1116  ( FIG. 11E ). With heat element  1114  touching skin depressors  1116 , current flows from electrically charge heat element  1114  through electrically grounded skin depressors  1116 . Grounded heat element  1114  heats up and cuts hairs  1134 . Upon cessation of motions, heat element  1114  no longer touches skin depressors  1112  and/or  1116  ( FIG. 11D ) and heat element  1114  cools once again. 
     In an alternative embodiment, skin depressors  1112  and/or  1116  are charged with a potential electric current while heat element  1114  is connected to an electrical ground. Movement of apparatus  1100  in relation to hairs  1134  in direction  1148 , causes heat element  1114  to touch skin depressors  1116 , thereby completing an electrical circuit, causing heat element  1114  to heat up. Alternatively or additionally, apparatus  1000  is moved in the opposite direction and heat element touches skin depressors  1112  and heats up. 
       FIGS. 12 and 13  show a hair cutting apparatus  1200  with a grasper  1232  that is suitable for grasping by the hand of an operator, in accordance with an exemplary embodiment of the invention. A frame  1260 , including a heat element  1214 , is shown removed from grasper  1232  in  FIG. 12 . In some embodiments of the present invention, frame  1260  includes one or more tension generators  1240  attached to one or more heat elements  1214  to tighten them as they deform upon pressing against hair during hair cutting or expand due to heat application. 
     Frame  1260 , for example, is attached to grasper  1232  so that frame  1260  is held at a specific angle to skin  1218 , for example perpendicular to skin  1218 . The connection of frame  1260  to grasper  1232 , for example is by one or more posts  1206  that may be, for example, flexible or spring loaded and fit into post connection  1204 . As frame  1260  moves across the contour of skin  1218 , it moves up and down and/or swivels on flexible posts  1206  in relation to grasper  1232 . Additionally or alternatively, one or more flexible posts  1206  between frame  1260  and grasper  1232  absorb shock caused by tremors and shakes as grasper  1232  is held in an operator&#39;s hand. The flexibility of posts  1206  prevents heat element  1214  from pressing with undue force into a skin surface  1218 , causing skin damage. 
     In an exemplary embodiment, posts  1206  are comprised of a metal contact area  1264  that provides electric current to contact area  1262  of tension generator  1240 . Contact area  1262  contacts a metal contact  1262  when it is pushed through a posthole  1204  as frame  1260  snaps onto posts  1206 . Contact area  1262  is, for example, springy and set in a contact gutter  1266  that is wide to allow movement of contact area  1262  as contact area  1262  snaps into place. 
     Additionally or alternatively, contact area  1262  is springy to allow movement of frame  1260  on posts  1206  in post holes  1204  while frame  1260  moves in relation to grasper  1232  without disrupting power between posts  1206  and contact area  1262 . For example, area  1264  is wider than contact area  1262 , allowing movement between frame  1260  and grasper  1232 . Additionally or alternatively, posts  1206  swivel to provide flexibility to frame  1260 . 
     Optionally, frame  1260  comprises two rows of skin depressors  1216  that are perpendicular to an area of skin  1218  ( FIG. 13 ) and, for example, parallel to one or more heat elements  1214 . When frame  1260  comprises two rows of skin depressors  1216 , one or more heat elements  1214  are optionally between them, as shown. 
     Optionally, skin depressors  1216  include a mechanism for preventing skin damage due to the protrusion of a tension generator end  1220 . For example, a skin depressor  1222  located near tension generator end  1220  is longer than tension generator end  1220  preventing its contact and resultant heat damage to skin  1218 . In an alternative embodiment, skin depressors  1222  do not protrude beyond tension generator end  1220 , and tension generator end  1220  is coated with a material that insulates it so that build-up of heat is below a level that causes skin damage. 
     A velocity detector beam  1270  is shown in relation to an optical velocity detector  1272  that senses the speed of unit  1200  along skin  1218  and thereby varies the electric pulse width, repetition rate and/or temperature of heat element  1214  to prevent skin damage. 
       FIG. 13  is an assembled unit  1200 , with a perspective showing an operator controlled on-off switch  1290 , in accordance with an exemplary embodiment of the invention. 
     While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. For example, while either pulsed or continuous heating has been described in reference to an embodiment of the invention, pulsed heating is generally usable in all the embodiments that were described with continuous heating. Further, embodiments that were described as using pulsed heating can use continuous heating if means for avoiding overheating of the skin as described herein are provided. 
     Also, combination of heat elements from variations may be combined and single heat elements may be used. As an example, one or more heat elements that displace and, in one embodiment, cool as they touch skin depressors, may be utilized in an embodiment utilizing a cylindrical arrangement of heat elements. Such variations and modifications, as well as others that may become apparent to those skilled in the art are intended to be included within the scope of the invention, as defined by the appended claims. 
     A variety of values have been utilized to describe the heat elements comprising the invention including, diameters, lengths and materials of heat elements, pulse rates, pulse widths, current levels and peak temperatures through heat elements. Additionally, a variety of values have been utilized to describe structures besides heat elements, including length, diameter and position of skin depressors in relation to heat elements and the minimum velocity or motion at which a controller signal a heat element to provide heat. Although a variety of values for these, and other, structures have been provided, it should be understood that these values could vary even further based upon a variety of engineering principles, materials, intended use and designs incorporated into the invention. 
     The terms “include”, “comprise” and “have” and their conjugates as used herein mean “including but not necessarily limited to.” 
     It will be appreciated by a person skilled in the art that the present invention is not limited by what has thus far been described. Rather, the scope of the present invention is limited only by the following claims.