Patent ID: 7294102

Claim:
A position control apparatus for controlling position along a depth or z axis, comprising: an extensible member that can be extended and contracted along said depth or z axis, comprising shape memory alloy configured and positioned to expand and contract linearly along said depth or z axis; a housing for said extensible member and for at least one optical element located forward of said extensible member, said housing constraining said optical element to move linearly along the depth or z axis and limiting buckling of at least a portion of said extensible member when said extensible member is being extended; a heater for controlling the temperature of said shape memory alloy; and a feedback mechanism for controlling said heater and responsive to variations in said position; wherein said position is controllable by said heater and said position can be stabilized by said feedback mechanism; and wherein said extensible member has a forward end coupled to said optical element and a rearward end coupled to said housing at a point rearward of said optical element so that extension and contraction of said extensible member causes said optical element to advance or retreat linearly within said housing along said depth or z axis.