Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not affixed to the engine shaft, these gearheads can be used in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. Motion of the nozzle as it comes after 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 software.
Smooth motion, this means the absence 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 motor shaft. A good slight misalignment in sunlight gear (motor shaft runout or coupling inaccuracies) can cause rough procedure and noise.
Many servo controllers use servo gear reducer software compensation, and their success depends upon knowing the lost motion of the entire system. 
This information is usually obtainable from the gearhead manufacturer.
Contouring applications generally involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding devices, drinking water and flame cutters, laser beam welders and cutters, motion controlled 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 an amount equal to the system’s dropped movement, thereby bringing the load to the truly desired position. For instance, consider 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. dropped motion, then your controller tells the engine to go 110,000 encoder counts to get 1.0 in. of motion, thus compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent equipment teeth and its own engaging tooth; lost movement is the total looseness or motion at a reducer’s result shaft when the input shaft is fixed. Lost 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 technique compensates for backlash even where a credit card applicatoin requires accuracy much better than the minimal backlash of the gearhead.