Patent ID: 7199332

Claim:
A heating device comprising: a cylindrical heating member configured to heat and fix a toner image carried on a recording sheet brought into contact with a periphery of the heating member by rotation; a first heating unit disposed within the heating member and having a first heat generating section including a heating generating portion facing a central portion of the recording sheet, and a first no-heat generating section continuous with the first heat generating section; and a second heating unit disposed within the heating member and having a second no-heat generating section opposed to the first heat generating section, and a second heat generating section opposed to the first no-heat generating section, wherein MRnh, SRnh and ΣRnh satisfy the formula (1): Σ Rnh≧ 30.5 ·Ln ( Ht )+382 formula (1), where MRnh is a mean value of heat distribution in the first no-heat generating section of the first heating unit; SRnh is a mean value of heat distribution in the second no-heat generating section of the second heating unit; ΣRnh(=MRnh+SRnh) is the sum total of the mean value of heat distribution in the first no-heat generation section and the mean value of heat distribution in the second no-heat generating section; and Ht=vp/(Mh·λ) where vp is a fixing speed (m/s), Mh a heat capacity per unit length of the heating member (J/(° C.·m)) and λ a heat conductivity of a material forming the heating member (W/(m·° C.)).