Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not affixed to the motor shaft, these gearheads can be used in contouring applications like a glue-dispensing nozzle for affixing a windshield to a car. Motion of the nozzle as it follows the seam between a windshield and its own window frame should be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue application.
Smooth motion, which means the absence of torque and velocity variations (ripple), is important in contouring applications. But, it is difficult to regularly achieve smooth motion where the sun gear is installed on the motor shaft. Even a slight servo gear reducer misalignment in the sun gear (motor shaft runout or coupling inaccuracies) can cause rough operation and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost motion of the entire system. This details is usually available from the gearhead manufacturer.
Contouring applications usually involve end-effectors or tool-points 
that follow mathematically defined paths. Sealant and bonding devices, drinking water and flame cutters, laser welders and cutters, movement managed cameras, and CNC machine tools are good examples.
Software compensation is accomplished by commanding the electric motor to move beyond the apparently desired position by an amount add up to the system’s dropped 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 movement and the system has 0.1-in. lost motion, then the controller tells the motor to go 110,000 encoder counts to obtain 1.0 in. of motion, thus compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent gear teeth and its engaging tooth; lost movement may be the total looseness or motion at a reducer’s output shaft when the input shaft is fixed. Dropped motion contains backlash, plus losses from bearing looseness, tolerances and fits, and shaft and gear tooth compliance.
Servo controllers could be programmed to pay for backlash and lost motion in planetary gearheads. This technique compensates for backlash also where a credit card applicatoin requires accuracy much better than the minimal backlash of the gearhead.