Image forming apparatus which detects jam and jam detecting method for the same

An image forming apparatus, comprising:

• transportation means which transports a sheet-like recording medium along a predetermined transportation path;
• first detection means which outputs a predetermined first detection signal when said recording medium is located at a first detection position which is behind said transportation means in the transportation direction of transporting said recording medium;
• and
• jam judging means which measures the duration of said first detection signal, and based on a result of a comparison of the measurement result with a reference time which is set in accordance with the length of said recording medium along said transportation path, judges whether a jam of said recording medium has occurred;
• wherein said transportation means is a fixing unit which fixes an unfixed image on said recording medium.

A jam detecting method for use in an image forming apparatus comprising transportation means which is for transporting a sheet-like recording medium along a predetermined transportation path, said method comprising the steps of:

• setting a reference time in accordance with the length of said recording medium along said transportation path;
• measuring the duration of a first detection signal that first detection means, which is disposed at a first detection position which is behind said transportation means in the transportation direction of transporting said recording medium, outputs when said recording medium is located at said first detection position;
• detecting, by length detection means disposed ahead of said transportation means on said transportation path, the length of said recording medium along said transportation path;
• and
• comparing the measured duration with said reference time and judging whether a jam of said recording medium has occurred based on the comparison result;
• wherein said reference time is set based on a detection result obtained by said length detection means.

An image forming apparatus, comprising:

• transportation means which transports a sheet-like recording medium along a predetermined transportation path;
• first detection means which outputs a first detection signal when a recording medium moves past a first detection position which is ahead of said transportation means in the recording medium transportation direction;
• second detection means which outputs a second detection signal when a recording medium moves past a second detection position which is behind said transportation means in the recording medium transportation direction;
• third detection means which outputs a third detection signal when a recording medium moves past a third detection position which is behind said second detection position in the recording medium transportation direction;
• and
• jam judging means which judges that a jam of said recording medium has occurred, when at least one of a first condition and a second condition below is satisfied:
• the first condition being a condition that during a period in which outputting of said first detection signal has been continuing since the start of the outputting of said first detection signal, outputting of said second detection signal has started, and during the same period, the outputting of said second detection signal ends,
• the second condition being a condition that during a period in which outputting of said second detection signal has been continuing since the start of the outputting of said second detection signal, outputting of said third detection signal has started, and during the same period, the outputting of said third detection signal ends.

A jam detecting method for use in an image forming apparatus comprising transportation means which is for transporting a sheet-like recording medium along a predetermined transportation path, said method comprising the steps of:

• detecting whether said recording medium is present each at first through third detection positions, said first detection position being behind said transportation means in the recording medium transportation direction, said second detection position being behind said transportation means in the recording medium transportation direction, and said third detection position being behind said second detection position in the recording medium transportation direction;
• and
• judging that a jam of said recording medium has occurred when at least one of a first condition and a second condition below is satisfied:
• the first condition being a condition that during continuous detection of the presence of said recording medium at said first detection position, the detection result at said second detection position changes to one indicative the presence of said recording medium from one indicative the absence of said recording medium, and then changes to one indicative the absence of said recording medium again,
• the second condition being a condition that during continuous detection of the presence of said recording medium at said second detection position, the detection result at said third detection position changes to one indicative the presence of said recording medium from one indicative the absence of said recording medium, and then changes to one indicative the absence of said recording medium again.

An image forming apparatus, comprising:

• transportation means which transports a sheet-like recording medium along a predetermined transportation path;
• first detection means which outputs a first detection signal when a recording medium moves past a first detection position which is behind said transportation means in the recording medium transportation direction;
• second detection means which outputs a second detection signal when a recording medium moves past a second detection position which is behind said first detection position in the recording medium transportation direction;
• and
• jam judging means which judges whether a jam of said recording medium has occurred, based on output signals from said first and said second detection means;
• wherein the gap between said first and said second detection positions is shorter than the length of said recording medium in the recording medium transportation direction, and
• in the absence of said second detection signal during outputting of said first detection signal since the start of the outputting of said first detection signal, said jam judging means judges that a jam of said recording medium has occurred.

An image forming apparatus, comprising:

• transportation means which transports a sheet-like recording medium along a predetermined transportation path;
• first detection means which outputs a first detection signal when a recording medium moves past a first detection position which is behind said transportation means in the recording medium transportation direction;
• second detection means which outputs a second detection signal when a recording medium moves past a second detection position which is behind said first detection position in the recording medium transportation direction;
• and
• jam judging means which judges whether a jam of said recording medium has occurred, based on output signals from said first and said second detection means;
• wherein the gap between said first and said second detection positions is shorter than the length of said recording medium in the recording medium transportation direction, and
• when outputting of said second detection signal has started during a period in which outputting of said first detection signal has been continuing since the start of the outputting of said first detection signal and when the outputting of said second detection signal has ended during the same period, said jam judging means judges that a jam of said recording medium has occurred.

An image forming apparatus, comprising:

• transportation means which transports a sheet-like recording medium along a predetermined transportation path;
• first detection means which outputs a first detection signal when a recording medium moves past a first detection position which is behind said transportation means in the recording medium transportation direction;
• second detection means which outputs a second detection signal when a recording medium moves past a second detection position which is behind said first detection position in the recording medium transportation direction;
• and
• jam judging means which judges whether a jam of said recording medium has occurred, based on output signals from said first and said second detection means;
• wherein said transportation means is a fixing unit which fixes an unfixed image borne by said recording medium on said recording medium.

A jam detecting method for use in an image forming apparatus comprising transportation means which is for transporting a sheet-like recording medium along a predetermined transportation path, said method comprising the steps of:

• outputting, by a first detection means, a first detection signal when said recording medium moves past a first detection position which is behind said transportation means in the recording medium transportation direction;
• outputting, by a second detection means, a second detection signal when the recording medium moves past a second detection position which is behind said first detection position in the recording medium transportation direction;
• judging whether a jam of said recording medium has occurred, based on output signals from said first and second detection means;
• wherein the gap between the first and second detection means is shorter than the length of said recording medium in the recording medium transportation direction, and
• wherein a jam of said recording medium is judged to have occurred when outputting of said second detection signal has started during a period in which outputting of said first detection signal has been continuing since the start of the outputting of said first detection signal and when outputting of said second detection signal has ended during the same period.