Because the sun gear in a hybrid unit is pre-aligned within the gearhead rather than affixed to the motor shaft, these gearheads can be used in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. 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 velocity alters the bead diameter and causes messy glue program.
Smooth motion, this means the lack of torque and velocity variations (ripple), is important in contouring applications. But, it is difficult to regularly achieve smooth motion where the sun gear is mounted on the motor shaft. A good slight misalignment in the sun gear (motor shaft runout or coupling inaccuracies) can cause rough operation and noise.
Many servo controllers use software compensation, and their success depends on knowing the lost motion of the entire system. This details is usually offered from the gearhead manufacturer.
Contouring applications usually involve end-effectors or tool-points that stick to mathematically defined paths. Sealant and bonding devices, water and flame servo motor gear reducers cutters, laser welders and cutters, motion managed cameras, and CNC machine tools 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 motion, thereby bringing the strain to the truly desired position. For example, look at 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 the controller tells the motor 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 motion may be 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 could be programmed to compensate for backlash and dropped motion 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.