Disk 4 of a circular eccentric cam carries two rectangular lugs 5 and has gear rack 6. Disk 3 has guides a along which lugs 5 slide. Shaft 1, with pinion 2 at its end, passes through hollow shaft 7. When shaft 1 is turned, pinion 2, meshing with rack 6 on disk 4 of the eccentric cam, moves the cam along guides a and thereby changes the eccentricity e.
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