Paper jam detecting device for use in an electrophotographic copying machine

In an electrophotographic copying machine the combination comprising:

• paper detecting means for detecting the presence or absence of the copy paper at at least one predetermined position in a path along which the copy paper moves,
• means for starting the copy process,
• means for detecting the size of copy paper used in the copy process,
• feeding means for feeding the copy paper from a supply of copy paper to said path,
• means connected to said feeding means for driving said feeding means in response to the operation of the copy process starting means,
• control means for controlling the operation of the copying machine sequentially in accordance with a control program stored therein and to which said paper size detecting means is connected,
• pulse generating means connected to said control means for generating a pulse train used as standard pulses for operating the control means,
• first and second digital timer means connected to said control means for counting periods of time to generate signals showing that the periods of time have elapsed by counting the number of said standard pulses,
• means connected to said first and second digital timer means for synchronizing the starting of the operation of the first and second digital timer means with the motion of the copying machine, said first digital timer means being set with digital data corresponding to the period of time it takes the leading edge of the copy paper transported in accordance with the operation of the copy process to reach the position of the paper detecting means,
• converting means provided in the control means for converting the paper size detected by said paper size detecting means into digital data for a number of pulses corresponding to the time it takes the trailing edge of the detected paper size to reach the position of the paper detecting means and setting the pulses in the second digital timer means, and
• means connected to said paper detecting means and said first and second digital timer means for sensing the state of the output of the paper detecting means in response to the instructions provided by the first digital timer means or the second digital timer means so as to generate signals indicative of a paper jam if no paper is detected when the first digital timer means has completed counting of the period of time set in the first timer means and if paper is detected when the second digital timer means has completed counting of the period of time set in the second timer means.