Selectric Resources

SHIFT SENSING MECHANISM OPERATIONAL THEORY

The purpose of the shift sensing mechanism is to move the low velocity vane to the left when the machine is in the upper case mode. This allows certain keyboard positions, that are low velocity in lower case, to be high velocity in upper case. This is used on keyboards with the ten-key number inset such as the 056 and 065 OCR keyboards where the numbers 8 and 9 are above the comma and period (Figure 1).

With the machine in lower case, the low velocity vane is held to the right by a flat spring. The vane actuating bellcrank is mounted to the rear of the vane and held against its spring tension in a counterclockwise position by the shift sensing cable. The other end of the cable is mounted to a plate on the rear of the shift arm. When the machine is shifted to uppercase, tension on the sensing cable is released and the bellcrank spring rotates the bellcrank clockwise. As the bellcrank rotates, it pushes the low velocity vane to the left. This allows certain interposers which have low velocity in lower case to now have high velocity in upper case because the lugs on the low velocity vane are not in front of the interposers.

Figure 1 — Shift Sensing Mechanism