Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not affixed to the electric motor shaft, these gearheads can be used in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. Movement of the nozzle as it follows the seam between a windshield and its window frame should be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue software.
Smooth motion, which means the absence of torque and velocity variations (ripple), is essential in contouring applications. But, it really is difficult to consistently achieve smooth movement where the sun equipment is installed on the electric motor shaft. Even a slight misalignment in sunlight gear (motor shaft runout or coupling inaccuracies) could cause rough operation and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost motion of the entire system. This information is usually available from the gearhead producer.
Contouring applications generally involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding devices, drinking water and flame cutters, laser welders and cutters, movement controlled cameras, and CNC machine equipment are good examples.
Software compensation is achieved by commanding the engine to move beyond the apparently desired position by an amount 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 movement and the machine has 0.1-in. dropped motion, then the controller tells the engine 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 extra space between two adjacent equipment teeth and its engaging tooth; lost motion is the total looseness or movement at a reducer’s servo gear reducer result shaft when the input shaft is fixed. Lost motion contains backlash, plus losses from bearing looseness, tolerances and fits, and shaft and gear tooth compliance.
Servo controllers can be programmed to compensate for backlash and dropped motion in planetary gearheads. This technique compensates for backlash also where an application requires accuracy much better than the minimal backlash of the gearhead.