A positioning system adjusts a position of an optical element within an optical device, such as a variable-zoom lens system. A frame supports the optical element, and an elongated surface of each of one or more elongated support structures supports the frame. The frame also supports one or more piezoelectric actuators that, respectively, engage one of the elongated support structures. A controller supplies a control signal to activate each of the one or more actuator modules. Upon activation, a piezoelectric element of each of the activated actuator modules applies a combination of a first force and a second force to an elongated surface of the respective elongated support structures to position the frame along the elongated surface. The combination of forces applied by the piezoelectric element advances the piezoelectric actuator module along the elongated support structure.