Because the sun gear in a hybrid unit is pre-aligned within the gearhead rather than affixed to the engine shaft, these gearheads can be utilized in contouring applications such as a glue-dispensing nozzle for affixing a windshield to a car. Movement of the nozzle since it follows the seam between a windshield and its window frame must be perfectly smooth; or else a ripple in servo motor gear reducers velocity alters the bead diameter and causes messy glue app.
Smooth motion, this means the absence of torque and velocity variations (ripple), is essential in contouring applications. But, it is difficult to regularly achieve smooth motion where the sun equipment is mounted on the engine shaft. A good slight misalignment in sunlight gear (engine shaft runout or coupling inaccuracies) can cause rough operation and noise.
Many servo controllers use software compensation, and their 
success depends upon knowing the lost motion of the entire system. This information is usually available from the gearhead manufacturer.
Contouring applications generally involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding machines, drinking water and flame cutters, laser welders and cutters, motion controlled cameras, and CNC machine tools are good examples.
Software compensation is accomplished by commanding the motor to move beyond the apparently desired position by a quantity equal to the system’s lost motion, thereby bringing the strain to the truly desired position. For instance, consider a servomotor, gearhead, and leadscrew mixture 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 obtain 1.0 in. of motion, therefore compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent gear teeth and its own engaging tooth; lost movement is the total looseness or movement at a reducer’s output shaft when the input shaft is fixed. Dropped motion includes backlash, plus losses from bearing looseness, tolerances and suits, and shaft and equipment tooth compliance.
Servo controllers can be programmed to pay for backlash and dropped movement in planetary gearheads. This technique compensates for backlash actually where an application requires accuracy better than the minimal backlash of the gearhead.