Tracking system for a video recorder using an auxiliary dc motor coupled to the capstan

Claim 1

A drive system for a magnetic recording and reproducing apparatus for video signals comprising magnetic tape drive means including a first rotary shaft and a capstan driven by said shaft, a rotary magnetic head device including a second rotary shaft and magnetic heads driven in rotation by said second shaft for selectively recording video signals on a magnetic tape driven by said capstan and reproducing the recorded video signals from said tape, and a control signal magnetic head for selectively recording a control frequency signal on said tape and reproducing the recorded control frequency signal from said tape; said drive system comprising a main motor coupled to said second shaft, an auxiliary DC motor coupled to said first shaft, pulleys on said first and second shafts, an elastic belt engaging around said pulleys so that said second shaft is rotated by said main motor and said first shaft is also rotated by said main motor by way of said pulleys and elastic belt and thereby tends to rotate at a speed in a predetermined ratio to the rotational speed of said one shaft, rotation detecting means associated with said second shaft and producing a frequency signal corresponding to the rotational speed and position of said second shaft and said magnetic heads driven thereby, phase comparator means to compare the phase of said frequency signal with the phase of said control frequency signal from said control signal head and provide a corresponding phase-comparison signal, and drive control circuit means actuated by said phase-comparison signal during reproducing of video signals from the tape to cause said auxiliary motor to rotate idly when said phase-comparison signal is at a predetermined level and to exert a braking torque and a driving torque, respectively, on said first shaft when said phasecomparison signal deviates from said predetermined level in opposite directions, and thereby ensure accurate tracking of said recorded video signals by said magnetic heads of the rotary magnetic head device, said drive control circuit means including a power source and first and second transistors, said auxiliary motor being connected with said power source through said first transistor and in parallel with said second transistor, said first and second transistors being both rendered nonconductive when said phase-comparison signal is at said predetermined level, said first and second transistors being rendered nonconductive and conductive, respectively, when said phase-comparison signal deviates from said predetermined level in one of said directions, and said first and second transistors being rendered conductive and nonconductive, respectively, when said phase-comparison signal deviates from said predetermined level in the other of said directions.