Friday, July 23, 2010

Lever Mechanism

The gear – lever mechanism is based on the slot - crank motion (like Geneva wheels) configuration. When oscillated motion is applied at the input gear (by an oscillated lever about fixed axis A -not shown), which meshes with the second gear, it forces it to oscillate in opposite direction. On the second gear is mounted rigidly a crank whose pin slides along slot of output lever which turns freely about axis A. Output lever transmits reciprocating motion to an intermediate link (not shown) which is connected to the driven part of the mechanism. Thus oscillation of input gear (and lever) is converted into different oscillation of output lever.

When the crank’s (rigidly attached at the second gear) symmetry plane coincides with the output lever’s symmetry plane in the neutral position, then the output oscillation angle is smaller than the input one. If we rotate the second gear counterclockwise (like a planet) around the input gear and maintain the same neutral position of the output lever, then the oscillation characteristics will be modified. Under a suitable selection of the crank length and the position of the second gear, the output lever will perform a double oscillation (attention, two complete oscillations of smaller angle during the input one).

The advantages of the gear - lever mechanism against the cam actuated is the lower cost of gear trains, and the adaptability to different positions of the input lever (remember that a lever oscillates the input gear) or the input shaft. It can be used reversely (but not in many positions) in order to produce a larger oscillation angle. At the configuration shown at the figures there is a formula for calculation of the angular displacement of the output lever b corresponding to crank angle a, which is equal (if the gear train ratio is one) to input gear angle.

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