Image forming apparatus using copy speed to control fixing temperature

An improved image forming apparatus of the type that includes thermal fixing means having a fixing roller and heating means for heating said fixing roller, temperature detecting means for detecting a temperature of said fixing roller, and temperature control means for controlling power supplied to said heating means and controlling the temperature of said fixing roller based on a signal from said temperature detecting means, wherein the improvement comprises:

• number of sheets storing means for storing the number of passing sheets upon a previous continuous-image-formation;
• counter means for counting a passing time from the end time of the previous continuous-image-formation;
• control means for, upon said continuous-image-formation, and based on the number of sheets stored by said number of sheets storing means and the time counted by said counter means, limiting the number of sheets image-formed at a first copying speed, at which the number of passing sheets per unit of time is large, to a predetermined number of sheets, and for, when the number of sheets is over the predetermined number of sheets, changing said first copying speed to a second copying speed at which the number of passing sheets per unit of time is small;
• and
• storing means for previously storing said predetermined number of sheets in a table format so that as the number of passing sheets stored by said number of sheets storing means is smaller, said predetermined number of sheets is larger and, as the passing time counted by said counter means is longer, said predetermined number of sheets is larger,
• wherein said control means refers to said predetermined number of sheets stored in the table format by said storing means and changes the copying speed from said first copying speed to said second copying speed, and
• wherein said temperature detecting means has a single temperature detector.

An image forming apparatus including thermal fixing means having a fixing roller and heating means for heating said fixing roller, temperature detecting means for detecting a temperature of said fixing roller, and temperature control means for controlling power supplied to said heating means and controlling the temperature of said fixing roller based on a signal from said temperature detecting means, the image forming apparatus comprising:

• number of sheets storing means for storing the number of passing sheets upon a previous continuous-image-formation;
• counter means for counting a passing time from the end time of the previous continuous-image-formation;
• control means for, upon continuous-image-formation, and based on the number of sheets stored by said number of sheets storing means and the time counted by said counter means, limiting the number of sheets image-formed at a first copying speed, at which the number of passing sheets per unit of time is large, to a predetermined number of sheets, for deciding said predetermined number of sheets so that as the number of passing sheets stored by said number of sheets storing means is smaller, said predetermined number of sheets is larger and, as the passing time counted by said is longer, said predetermined number of sheets is larger, and for, when the number of sheets is over said limited number of sheets, changing said first copying speed to a second copying speed at which the number of passing sheets per unit of time is small.