Patent ID: 7340200

Claim:
A charging unit configured to charge an image bearing member in a non-contact arrangement, comprising: a charging member, wherein a fluctuation margin of a charging gap as a distance between said image bearing member and said charging member caused by a change in an environmental condition is controlled in terms of fluctuation characteristics of said charging member by setting a materials condition of said charging member beforehand within a predetermined range, wherein (a) the environmental condition is taken as an ambient temperature, (b) a midpoint is obtained as a standard for a change in the ambient temperature, (c) higher side and lower side ambient temperatures are determined as the temperatures higher and lower by a predetermined temperature ftom the midpoint, respectively; and (d) an average of the charging gap at the higher side ambient temperature is obtained as a first average and a further average of the charging gap at the lower side ambient temperature is obtained as a second average, and wherein further said materials condition of said charging member is set such that an absolute value of the difference between the first and second averages multiplied by an integer is equal to, or smaller than an average of the charging gap at the midpoint.