Because the sun gear in a hybrid unit is pre-aligned within the gearhead rather than affixed to the motor shaft, these gearheads can be used in contouring applications such as a glue-dispensing nozzle for affixing a windshield to a car. Motion of the nozzle since it follows the seam between a windshield and its own window frame should be perfectly smooth; or else a ripple in velocity alters the bead diameter and causes messy glue app.
Smooth motion, this means the absence of torque and velocity variations (ripple), is important in contouring applications. But, it really is difficult to regularly achieve smooth movement where the sun gear is installed on the motor shaft. A good slight misalignment in the sun gear (electric motor shaft runout or coupling inaccuracies) could cause rough operation and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost movement of the entire system. This information is usually offered from the gearhead producer.
Contouring applications generally involve end-effectors or tool-points that stick to mathematically defined paths. Sealant and bonding devices, drinking water and flame cutters, laser beam welders and cutters, motion managed cameras, and CNC machine tools are good 
examples.
Software servo motor gear reducers compensation is accomplished by commanding the motor to move beyond the apparently desired position by an amount add up to the system’s dropped movement, thereby bringing the load 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 the controller tells the electric motor to go 110,000 encoder counts to get 1.0 in. of motion, hence compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent equipment teeth and its engaging tooth; lost movement may be the total looseness or motion at a reducer’s result shaft when the insight shaft is fixed. Dropped motion includes backlash, plus losses from bearing looseness, tolerances and matches, and shaft and gear tooth compliance.
Servo controllers can be programmed to compensate for backlash and dropped motion in planetary gearheads. This technique compensates for backlash also where an application requires accuracy better than the minimal backlash of the gearhead.