Because the sun equipment in a hybrid unit is pre-aligned within the gearhead and not affixed to the electric motor shaft, these gearheads can be utilized in contouring applications like 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 own window frame should be perfectly smooth; servo motor gear reducers otherwise 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 essential in contouring applications. But, it is difficult to regularly achieve smooth movement where the sun gear is mounted on the electric motor shaft. Even a slight misalignment in sunlight gear (engine 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 motion of the entire system. This details is usually available from the gearhead producer.
Contouring applications usually involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding devices, 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 electric motor to move beyond the apparently desired position by an amount equal to the system’s lost movement, 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 machine has 0.1-in. dropped motion, then your controller tells the motor to move 110,000 encoder counts to obtain 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 motion is the total looseness or movement at a reducer’s output shaft when the input shaft is fixed. Lost motion contains backlash, plus losses from bearing looseness, tolerances and suits, and shaft and equipment 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.