Optical scanning carriage

Claim 1

An optical scanning carriage, including drive means to move said carriage in a scanning direction and means to rapidly move said carriage in a rescan direction back to the start of scan position, dashpot means to decelerate the rate of return of the scanning carriage to the start of scan position, said dashpot comprising a cylinder having an end plate at one end, said end plate having a fixed size orifice therein, a piston slidably movable within the cylinder from a start of scan position adjacent the end plate to an end of scan position away from the end plate, the piston having a tapered metering pin mounted on its end, said metering pin being engagable with the orifice in the cylinder end plate, the end of said metering pin being spaced from the cylinder end plate when said carriage is in the end of scan position and being inserted in the orifice of said end plate when said carriage is in the start of scan position, said metering pin having a first portion of constant cross sectional shape and area and a second portion tapering from said constant cross sectional shape and area to a point at its end, said orifice having a shape and area slightly larger than the shape and area of said first portion of said metering pin whereby when said piston moves in the rescan direction said dashpot provides a triple mode of operation comprising a first maximum flyback velocity by the action of the piston and the orifice only, a second deceleration profile as the tapered metering pin enters the orifice in the end plate and a third minimum constant velocity when the constant shape and area portion of the metering pin enters the orifice in the end plate.