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 utilized in contouring applications such as a glue-dispensing nozzle for affixing a windshield to a car. servo gear reducer movement of the nozzle as it comes after 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 software.
Smooth motion, this means the absence of torque and velocity variations (ripple), is essential in contouring applications. But, it is difficult to regularly 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) 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 available from the gearhead producer.
Contouring applications generally involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding devices, water and flame cutters, laser beam welders and cutters, movement managed cameras, and CNC machine equipment are good examples.
Software compensation is accomplished by commanding the electric 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 example, consider 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 system has 0.1-in. dropped motion, then the controller tells the motor to move 110,000 encoder counts to get 1.0 in. of motion, thus compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent gear teeth and its engaging tooth; lost motion may be the total looseness or motion at a reducer’s output shaft when the input shaft is fixed. Dropped motion includes backlash, plus losses from bearing looseness, tolerances and fits, and shaft and gear tooth compliance.
Servo controllers could be programmed to compensate for backlash and dropped movement in planetary gearheads. This technique compensates for backlash also where an application requires accuracy much better than the minimal backlash of the gearhead.