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 a car. Movement of the nozzle as it comes after 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 software.
Smooth motion, which means 
the lack of torque and velocity variations (ripple), is essential in contouring applications. But, it really is difficult to regularly achieve smooth movement where the sun equipment is installed on the electric motor shaft. Even a slight misalignment in sunlight gear (electric motor shaft runout or coupling inaccuracies) can cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost servo motor gear reducers 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 machines, 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 load to the truly desired position. For example, 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 own engaging tooth; lost movement may be the total looseness or motion 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 gear tooth compliance.
Servo controllers could be programmed to compensate for backlash and dropped motion in planetary gearheads. This technique compensates for backlash also where an application requires accuracy much better than the minimal backlash of the gearhead.