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 used in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. Motion of the nozzle as it follows the seam between a windshield and its own window frame should be perfectly smooth; or else a ripple in velocity alters the bead diameter and causes messy glue program.
servo motor gear reducers smooth motion, which means the lack of torque and velocity variations (ripple), is essential in contouring applications. But, it really is difficult to consistently achieve smooth motion where the sun gear 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 on knowing the lost movement of the whole system. This information is usually offered from the gearhead producer.
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 controlled cameras, and CNC machine tools are good examples.
Software compensation is accomplished by commanding the motor to go beyond the apparently desired position by a quantity add up 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 electric motor to go 110,000 encoder counts to obtain 1.0 in. of motion, thus compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent equipment teeth and its engaging tooth; lost motion may be the total looseness or motion at a reducer’s result 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 pay for backlash and dropped motion in planetary gearheads. This system compensates for backlash even where an application requires accuracy better than the minimal backlash of the gearhead.