Eccentric drive

In an eccentric drive system including a rotatably mounted driven shaft, at least one primary eccentric mass fixed to the driven shaft for rotation therewith, an additional eccentric mass mounted for rotation with the shaft in a manner to permit adjustment of the angular position of the additional mass relative to that of the primary mass, the improvement wherein:

• said shaft is provided with a shaft portion presenting an outer periphery which is arranged eccentrically to the axis of rotation of said shaft;
• said additional mass is mounted on said portion to be angularly movable relative to said portion;
• and said system comprises spring means connected between said additional mass and said shaft for producing a force about the axis of said shaft urging said additional mass into an initial angular position relative to said shaft, and fastening means disposed between said shaft and said additional mass and actuatable between a released position in which it permits said additional mass to undergo such angular movement relative to said shaft portion and a locking position in which it prevents such movement, said fastening means including actuating means operable during rotation of said shaft for effecting actuation of said fastening means between its said positions.