Because the sun equipment 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 like 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 own 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 torque and velocity variations (ripple), is important in contouring applications. But, it is difficult to consistently achieve smooth movement where the sun gear is installed on the engine shaft. Even a slight misalignment in the sun 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 details is usually servo gear reducer obtainable from the gearhead producer.
Contouring applications usually 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 tools are good examples.
Software compensation is accomplished by commanding the engine to go beyond the apparently desired position by an amount add up to the system’s dropped movement, thereby bringing the strain to the truly desired position. For example, consider 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 engine to move 110,000 encoder counts to get 1.0 in. of motion, hence compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent equipment teeth and its own engaging tooth; lost motion may be the total looseness or movement at a reducer’s result shaft when the insight shaft is fixed. Lost motion includes backlash, plus losses from bearing looseness, tolerances and suits, and shaft and gear tooth compliance.
Servo controllers could be programmed to pay for backlash and lost motion in planetary gearheads. This system compensates for backlash even where an application requires accuracy better than the minimal backlash of the gearhead.