Hair roller heater

Abstract

For controlling the heating of heating posts in a hair roller heater in which each heating post includes a respective resistive heating element, an emulator or physical model has a thermal time constant that is about equal to the time constant of each post assembly to emulate the thermal behaviour of the heating posts during both heating and cooling. Direct temperature feedback from the emulator to a thermostatic switch is used for controlling the current delivered to the heating elements. The emulator includes a pair of insulators between which a heating element is provided, one of the insulators being thermally coupled to a conductive mounting to which the posts are directly connected

1 . An electrical resistance heater for a set of hair rollers, comprising:
 a housing having a floor, at least one upper opening, and a closure for closing each upper opening, wherein the housing is an insulating material or is thermally insulated;   a mounting member having an inner side facing the floor and an opposing outer side;   a plurality of posts disposed on the mounting member and projecting from the outer side, each post having an outer surface with a shape complementary to an inner surface of a hair roller, each post including a post heating element for heating each post, and each post having a thermal time constant in heating and cooling;   an emulator body mounted to the inner side of the mounting member;   an emulator heating element thermally coupled to the emulator body, the emulator body having a time constant that is substantially equal to the thermal time constant of each post;   a circuit connecting the post heating elements and emulator heating element for receiving power from a power supply; and   a thermostatic switch thermally coupled to the emulator body, the thermostatic switch being connected in series between the power supply and the post heating elements.   
   
   
       2 . The heater of  claim 1  wherein
 each post comprises a hollow cylindrical metal skin with a closed end and an opposing open end,   the open end is mechanically fixed to, or integral with, the mounting member, and   each post heating element is generally cylindrical and helically wound and is received coaxially within the posts and including a cylindrical dielectric liner extending about an inner side of each post, separating the post from this post heating element.   
   
   
       3 . The heater of  claim 1  wherein
 the emulator body comprises first, seconds and third sheets of insulating material,   the emulator heating element is wound around the second sheet,   the second sheet is received between the first and third sheets, and   the first sheet is secured to the inner side of the mounting member.   
   
   
       4 . The heater of  claim 3  wherein
 the first and second sheets are mica sheets, and the post heating elements and the emulator heating element are electrically connected in series with the thermostatic switch.   
   
   
       5 . An electrical resistance heater for a set of hair rollers comprising:
 a plurality of post heating elements electrically connected in series;   a circuit connecting the post heating elements for receiving power from a power supply;   a plurality of post assemblies, each post assembly having an outer surface with a shape complementary to an inner surface of a hair roller, each post assembly enclosing one of the post heating elements, and each post assembly having a thermal time constant in heating and cooling;   an emulator heating element connected in the circuit in series with the post heating elements;   an emulator body thermally coupled to the emulator heating element for emulating thermal response of each post assembly,; and   a thermostatic switch co-located with and thermally coupled to the emulator body, the thermostatic switch being connected in series with the post heating elements.   
   
   
       6 . A process for controlling heating of heating posts in a hair roller heater in which each heating post includes a respective resistive heating element, comprising:
 emulating thermal behaviour of the heating posts during both heating and cooling, and,   using temperature feedback from the emulation, controlling the current delivered to the heating elements.   
   
   
       7 . The process of  claim 6  wherein
 the heating elements are electrically connected to a power supply in series with a thermostatic switch for controlling the heating of the heating posts,   the emulating is performed using a physical model of the heating post and providing a temperature that is proportional to heating post temperature when the heating post receives a hair roller, and   the temperature feedback is provided by thermally coupling the model and the thermostatic switch.