Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not affixed to the engine shaft, these gearheads can be utilized in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. Movement of the nozzle since it comes after the seam between a windshield and its window frame must be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue application.
Smooth motion, which means the absence of servo motor gear reducers torque and velocity variations (ripple), is important in contouring applications. But, it is difficult to regularly achieve smooth motion where the sun equipment is mounted on the electric motor shaft. Even a slight misalignment in the sun gear (motor shaft runout or coupling inaccuracies) can cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends on knowing the lost movement of the entire system. This details is usually obtainable from the gearhead manufacturer.
Contouring applications generally involve end-effectors or tool-points that stick to mathematically defined paths. Sealant and bonding machines, drinking water and flame cutters, laser welders and cutters, motion controlled cameras, and CNC machine equipment 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 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 engine to move 110,000 encoder counts to obtain 1.0 in. of motion, hence compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent gear teeth and its own engaging tooth; lost movement may be 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 pay for backlash and dropped movement 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.