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 utilized in contouring applications such as a glue-dispensing nozzle for affixing a windshield to a car. Movement of the nozzle since it follows the seam between a windshield and its window frame must be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue program.
Smooth motion, which means the lack of torque and velocity variations (ripple), is essential in contouring applications. But, it really is servo motor gear reducers difficult to regularly achieve smooth motion where the sun gear is installed on the motor shaft. Even a slight misalignment in sunlight gear (engine shaft runout or coupling inaccuracies) can cause rough operation and noise.
Many servo controllers use software compensation, and their success depends on knowing the lost movement of the whole system. This info is usually obtainable from the gearhead manufacturer.
Contouring applications usually involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding machines, drinking water and flame cutters, laser welders and cutters, movement managed cameras, and CNC machine tools are good examples.
Software compensation is achieved by commanding the electric motor to move beyond the apparently desired position by a quantity equal to the system’s dropped movement, thereby bringing the load to the truly desired position. For example, consider 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 obtain 1.0 in. of motion, hence compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent gear teeth and its own engaging tooth; lost motion is the total looseness or motion at a reducer’s result shaft when the input shaft is fixed. Dropped motion includes backlash, plus losses from bearing looseness, tolerances and matches, and shaft and equipment tooth compliance.
Servo controllers could be programmed to pay for backlash and lost motion in planetary gearheads. This system compensates for backlash actually where a credit card applicatoin requires accuracy better than the minimal backlash of the gearhead.