Information retrieval system

Claim 1

An information retrieval system to selectively retrieve the desired recorded frame from a long recorded band, said system comprising; a group-retrieval mark allocated to at least one of a series of related frame groups on the recorded band having a series of information-recorded frames; a frame retrieval mark allocated to each frame except those to which is allocated said group retrieval mark, said group mark and frame mark being allocated to the same side on the recorded band and having different shapes; a light-source means to irradiate each mark on the recorded band; a pair of photoelectric conversion elements to receive optical signals from each mark when the recorded band has traveled, said pair of photoelectric conversion elements being so designed as to produce intermittently a first detection signal when a frame mark is received and produce second detection signals simultaneously when a group mark is received; a gate means which receives individual detection signals produced by said pair of photoelectric conversion elements, in order that either one of the detection signals may be passed through selectively; a counter means connected to said gate means, in order to count the detection signals which have passed through the gate means and to produce a control signal when the counted value has reached a predetermined value; a control means connected to said counter means, which responsive to the counted value of the counter means controls the opening and closure of the gate means, in order to pass through particular detection signals; and a recorded band feeding means which is connected to said counter means and receives control signals, said feeding means being so designed as to reduce the feeding speed of the recorded band and allow the recorded bandn to overrun when the counter means has counted a number of group marks equal to the number of the predetermined recorded frame, and feeds the recorded band in the reverse direction when said counter means has counted the predetermined number of frames which have overrun by way of frame marks and group marks, and then halts the recorded band when the counter means has counted the number of frames which have overrun.