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 utilized in contouring applications like a glue-dispensing nozzle for affixing a windshield to a car. Motion of the nozzle since it comes after the seam between a windshield and its 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 consistently achieve smooth movement where the sun gear is installed on the motor shaft. A good slight misalignment in the sun 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 whole system. This info is usually offered from the gearhead manufacturer.
Contouring applications generally involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding machines, water and flame cutters, laser welders and cutters, movement 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 a quantity 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 your controller tells the engine to go 110,000 encoder counts to get 1.0 in. of motion, thus compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent equipment teeth and its engaging tooth; lost movement is the total looseness or motion at a reducer’s servo motor gear reducers output shaft when the insight shaft is fixed. Dropped motion contains backlash, plus losses from bearing looseness, tolerances and suits, and shaft and gear tooth compliance.
Servo controllers can be programmed to compensate for backlash and dropped movement in planetary gearheads. This system compensates for backlash even where a credit card applicatoin requires accuracy much better than the minimal backlash of the gearhead.