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The CDC series coupling-decoupling clutches are unidirectional devices that couple the output to the input when the input drives in the design direction. A reversal of the input direction, either momentary or continuous, causes the output to decouple. The output is fully decoupled after the input has displaced approximately 20º in the reverse direction. Additional reverse rotation of the input does not have any further effect on the decoupling action, in the decoupled state, the output is free to rotate in either direction.

The coupling-decoupling clutch consists of an input drum, an output drum, a spring for coupling the two, and a stationary member. For installation, the clutch is mounted on the output shaft as a stationary pin engages the slot to prevent rotation of the clutch structure. The clutch is capable of transmitting high torque loads.

Bidirectional tape transport driven by a single reversible motor

The schematic represents a bidirectional tape or ribbon drive using a single reversible motor and two directional coupling-decoupling clutches of the CDC series. When the motor rotates in the CW direction, the tape advances to the right since the CW clutch on the right couples and drives its spool in the take up direction. The CCW clutch on, the left decouples and thus allows its spool to be rotated in the supply direction at the speed demanded by the tape. When the motor is reversed, the two clutches by virtue of the change in the driving direction, reverse their functions automatically and the tape advances to the left.

The bidirectional driving functions described above cannot be accomplished through the use of overrunning clutches. While both the overrunning and the coupling-decoupling clutches drive unidirectionally , they differ in their decoupling modes. The overrunning clutch provides only unidirectional freedom for the output to overrun the input. The coupling-decoupling clutch once decoupled, provides bidirectional rotation freedom to the output.

The need for bidirectional decoupling is dictated by the relative speeds within the two spindles. On the take-up spindle, both the drive pulley and spool rotate at the same speed, irrespective of tape diameter. On the supply spindle, the drive pulley rotates at the same speed as the take-up pulley while the supply spool may rotate either faster or slower than the supply pulley. The change in the speed of the supply spool is caused by the continuous variation in the diameters of the tape on the two spools as the tape is being reeled from on to the other. When the take up spool diameter is smaller than the diameter of the supply, the supply spool is slower than its pulley. Conversely, when the diameter of the take up is larger than that of the supply, the supply spool is faster. The clutch on the supply spindle must therefore provide bidirectional freedom to the supply spool. Inasmuch as the overrunning clutch provides only unidirectional freedom it cannot meet the requirements of this drive. The (CDC series) coupling-decoupling clutch, because of its ability to supply bidirectional freedom to the decoupled output, is ideally suited for this type of application.