Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not servo motor gear reducers affixed to the motor shaft, these gearheads can be utilized in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. Movement of the nozzle as 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 application.
Smooth motion, this means the absence of torque and velocity variations (ripple), is essential in contouring applications. But, it is difficult to consistently achieve smooth movement where the sun equipment is mounted on the electric motor shaft. A good slight misalignment in the sun gear (electric motor shaft runout or coupling inaccuracies) could cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends on knowing the lost motion of the whole 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 machines, water and flame cutters, laser beam welders and cutters, movement managed cameras, and CNC machine equipment 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 lost 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 motion and the machine has 0.1-in. lost motion, then your controller tells the engine 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 excess space between two adjacent equipment teeth and its engaging tooth; lost motion is the total looseness or motion at a reducer’s output shaft when the input shaft is fixed. Lost motion contains 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 also where a credit card applicatoin requires accuracy much better than the minimal backlash of the gearhead.