Because the sun gear in a hybrid unit is pre-aligned within the gearhead rather than affixed to the motor shaft, these gearheads can be utilized in contouring applications like a glue-dispensing nozzle for affixing a windshield to an automobile. Movement of the nozzle as it comes after the seam between a windshield and its window frame must be perfectly smooth; or else 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 servo motor gear reducers important in contouring applications. But, it is difficult to consistently achieve smooth movement where the sun equipment is mounted on the engine shaft. Even a slight misalignment in sunlight gear (motor shaft runout or coupling inaccuracies) could cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends on knowing the lost motion of the whole system. This details is usually obtainable from the gearhead producer.
Contouring applications usually involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding devices, 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 electric motor 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 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. lost motion, then the controller tells the engine to go 110,000 encoder counts to get 1.0 in. of motion, hence compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent equipment teeth and its engaging tooth; lost motion may be the total looseness or movement at a reducer’s output shaft when the insight shaft is fixed. Dropped motion contains backlash, plus losses from bearing looseness, tolerances and matches, and shaft and equipment tooth compliance.
Servo controllers could be programmed to compensate for backlash and dropped motion in planetary gearheads. This technique compensates for backlash also where a credit card applicatoin requires accuracy better than the minimal backlash of the gearhead.