Because the sun equipment 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 servo gear reducer should be perfectly smooth; or else 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 movement where the sun equipment is installed on the engine shaft. Even a slight misalignment in the sun 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 motion of the entire system. This information is usually available from the gearhead producer.
Contouring applications usually involve end-effectors or tool-points that stick to mathematically defined paths. Sealant and bonding devices, 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 electric motor to move beyond the apparently desired position by an amount equal to the system’s dropped motion, thereby bringing the strain 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. lost motion, then your controller tells the engine to move 110,000 encoder counts to get 1.0 in. of motion, therefore compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent equipment teeth and its engaging tooth; lost motion is the total looseness or movement 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 equipment tooth compliance.
Servo controllers could be programmed to compensate for backlash and dropped movement in planetary gearheads. This system compensates for backlash also where an application requires accuracy better than the minimal backlash of the gearhead.