An air-fuel ratio control system for an internal combustion engine has a perturbation control which oscillates the air-fuel ratio with a first frequency. A second slider mounting for the printer carriage includes a bushing incorporating a part-spherical portion and an arm which engage with corresponding parts of the carriage. A plurality of movable elements are provided wherein the movable elements and the stationary elements are substantially parallel, alternatingly arranged and a portion of the movable elements overlaps a portion of the stationary elements. The base portion can be provided with a reinforcement. The tri-layer conductor structure has minimized compressive stress after deposition of the three layers and an even lower compressive stress after annealing.