Trigger switch for speed control of hand tool - requiring transiently higher pressure to move from low to higher speed operation

摘要

The application is typically to a hand held electric drill. The trigger switch (1,2) comprises an operating shaft (1') with a cut out section (8) ending in two sloping flanks (10,14). Attached to the shaft is the slider (5) of a potentiometer (4) with linear motion, and a return spring (7). The notched section (8) engages at the front end (10) with an on-off switch (11,13). In the notch runs a plunger (3) with a rounded end (3') which moves normal to the shaft axis against a spring (15) in a housing. Initial pressure on the trigger closes the on-off switch and sets the potentiometer to give the slowest speed. This speed can be gradually increased by a small value until the rear flank (14) engages with the plunger (3). To obtain a higher speed, considerable pressure must be applied to make the plunger rise up the flank. After that the pressure required for speed adjustment is again modest. The mechanism makes for easier control at very low speeds.