Because the sun gear in a hybrid unit is pre-aligned within the gearhead rather than affixed to the electric 
motor shaft, these gearheads can be used in contouring applications like a glue-dispensing nozzle for servo motor gear reducers affixing a windshield to an automobile. Movement of the nozzle since it follows the seam between a windshield and its window frame should be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue app.
Smooth motion, this means the lack of torque and velocity variations (ripple), is important in contouring applications. But, it really is difficult to consistently achieve smooth motion where the sun gear is installed on the electric motor shaft. Even a slight misalignment in the sun gear (motor shaft runout or coupling inaccuracies) could cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost motion of the entire system. This info is usually obtainable from the gearhead manufacturer.
Contouring applications usually involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding machines, drinking water and flame cutters, laser welders and cutters, motion controlled cameras, and CNC machine tools are good examples.
Software compensation is achieved by commanding the engine to go beyond the apparently desired position by an amount equal to the system’s lost movement, thereby bringing the strain to the truly desired position. For instance, look at a servomotor, gearhead, and leadscrew combination in a pick-andplace robot. If 100,000 encoder counts equals 1.0 in. of linear motion and the system has 0.1-in. dropped motion, then your controller tells the electric motor to move 110,000 encoder counts to obtain 1.0 in. of motion, hence compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent equipment teeth and its own engaging tooth; lost movement may be the total looseness or motion at a reducer’s result shaft when the input shaft is fixed. Lost motion contains backlash, plus losses from bearing looseness, tolerances and matches, and shaft and gear tooth compliance.
Servo controllers could be programmed to pay for backlash and lost movement in planetary gearheads. This system compensates for backlash also where an application requires accuracy better than the minimal backlash of the gearhead.