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 a car. Motion of the nozzle as it follows the seam between a windshield and its window frame must be perfectly smooth; or else a ripple in velocity alters the bead diameter and servo gear reducer 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 consistently achieve smooth motion where the sun equipment is installed on the electric motor shaft. Even a slight misalignment in the sun gear (engine shaft runout or coupling inaccuracies) could cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost movement of the entire system. This info 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, water and flame cutters, laser beam welders and cutters, motion controlled cameras, and CNC machine tools 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 dropped 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 motion 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, therefore compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent equipment teeth and its own engaging tooth; lost motion is the total looseness or movement at a reducer’s output shaft when the input shaft is fixed. Dropped motion includes backlash, plus losses from bearing looseness, tolerances and suits, and shaft and gear tooth compliance.
Servo controllers can be programmed to pay for backlash and dropped movement in planetary gearheads. This technique compensates for backlash also where a credit card applicatoin requires accuracy better than the minimal backlash of the gearhead.