Image forming apparatus featuring first and second peak-to-peak charging voltages, respectively, corresponding to first and second image bearing member speeds and voltage frequencies

An image forming apparatus comprising:

• an image bearing member;
• a charging member, which is provided in proximity or in contact to said image bearing member and to which an oscillating voltage is applied to charge said image bearing member;
• and
• determining means for determining a peak-to-peak voltage of the oscillating voltage applied to said charging member, based on a first alternating current flowing in said charging member under application of at least a first peak-to-peak voltage less than 2 Vth to said charging member and based on second and third alternating currents flowing in said charging member under application of first and second peak-to-peak voltages not less than 2 Vth to said charging member, where Vth represents a discharge start voltage between said charging member and said image bearing member,
• wherein when a peripheral speed of said image bearing member is a first peripheral speed, a frequency of the oscillating voltage is a first frequency,
• wherein when the peripheral speed of said image bearing member is a second peripheral speed, the frequency of the oscillating voltage is a second frequency, and
• wherein said determining means determines a first peak-to-peak voltage of the oscillating voltage corresponding to the first peripheral speed and the first frequency and a second peak-to-peak voltage of the oscillating voltage corresponding to the second peripheral speed and the second frequency, based on the first, second and third alternating currents in use of the first peripheral speed and the first frequency.