Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not 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. Motion of the nozzle since it follows the seam between a windshield and its window frame should be perfectly smooth; or else a ripple in velocity alters the bead diameter and causes messy glue application.
Smooth motion, which means the lack of torque and velocity variations (ripple), is important in contouring applications. But, it is difficult to consistently achieve smooth movement where the sun equipment is mounted on the engine shaft. Even a slight misalignment in sunlight gear (electric 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 movement of the whole system. This info is usually offered from the gearhead manufacturer.
Contouring applications usually involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding devices, drinking water and flame cutters, laser beam welders and cutters, movement 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 add up to the system’s lost 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 movement and the system has 0.1-in. lost motion, then the controller tells the engine to move 110,000 encoder counts to get 1.0 in. of motion, therefore compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent equipment teeth and its engaging tooth; lost movement may be the total looseness or movement at a reducer’s servo gear reducer output shaft when the insight shaft is fixed. Dropped motion contains backlash, plus losses from bearing looseness, tolerances and fits, and shaft and equipment tooth compliance.
Servo controllers can 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 better than the minimal backlash of the gearhead.