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 utilized in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. Motion 
of the nozzle since it comes after the seam between a windshield and its window frame must 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 is servo gear reducer difficult to consistently achieve smooth movement where the sun gear is mounted on the engine shaft. A good slight misalignment in sunlight gear (engine shaft runout or coupling inaccuracies) could cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost movement of the whole system. This information is usually obtainable from the gearhead producer.
Contouring applications usually involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding devices, water and flame cutters, laser welders and cutters, movement controlled cameras, and CNC machine equipment are good examples.
Software compensation is achieved by commanding the motor to go beyond the apparently desired position by an amount equal to the system’s lost movement, thereby bringing the load to the truly desired position. For instance, look at a servomotor, gearhead, and leadscrew mixture in a pick-andplace robot. If 100,000 encoder counts equals 1.0 in. of linear movement and the machine has 0.1-in. dropped motion, then the 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 gear teeth and its engaging tooth; lost movement may be the total looseness or motion at a reducer’s output shaft when the input shaft is fixed. Dropped motion contains backlash, plus losses from bearing looseness, tolerances and suits, and shaft and equipment tooth compliance.
Servo controllers can be programmed to compensate for backlash and lost movement in planetary gearheads. This system compensates for backlash actually where a credit card applicatoin requires accuracy much better than the minimal backlash of the gearhead.
