Abstract: A shuttle assembly comprises a first mass, including printheads, connected by springs to a second mass. Both masses are suspended for low friction long-stroke linear oscillation on bearing rollers. A small electromagnetic drive force from a frame-mounted voice coil is coupled to the first mass so that it will ultimately assume, and thereafter maintain, linear oscillation at a natural resonant frequency. The second mass is symmetrically connected, thereby inducing but an extremely minor net moment of force about the shuttle center of mass. The shuttle assembly is internally force-balanced and couples, through the small drive forces, but very small forces to the machine frame. A control circuit maintains resonant sinusoidal oscillation in a manner insensitive to printing impacts or outside disturbances by sensing shuttle velocity and position in a phase-locked loop.