Because the sun gear in a hybrid unit is pre-aligned within the gearhead rather than affixed to the electric motor shaft, these gearheads can be utilized in contouring applications like 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; otherwise a ripple in velocity alters the bead diameter and causes messy glue application.
Smooth motion, which means the absence of 
torque and velocity variations (ripple), is essential in contouring applications. But, it is difficult to regularly achieve smooth servo motor gear reducers motion where the sun gear is installed on the electric motor shaft. Even a slight misalignment in sunlight gear (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 movement of the entire system. This information is usually offered from the gearhead producer.
Contouring applications usually involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding devices, water and flame cutters, laser beam welders and cutters, motion controlled cameras, and CNC machine tools are good examples.
Software compensation is accomplished by commanding the engine to go beyond the apparently desired position by an amount add up 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 motor 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 extra space between two adjacent equipment teeth and its own engaging tooth; lost movement may be the total looseness or movement at a reducer’s output shaft when the insight shaft is fixed. Lost motion includes backlash, plus losses from bearing looseness, tolerances and suits, and shaft and equipment tooth compliance.
Servo controllers could be programmed to pay for backlash and dropped motion in planetary gearheads. This technique compensates for backlash actually where an application requires accuracy much better than the minimal backlash of the gearhead.