Because the sun gear in a hybrid unit is pre-aligned within the servo gear reducer 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. Motion 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 app.
Smooth motion, which means the lack of torque and velocity variations (ripple), is important in contouring applications. But, it really is difficult to consistently achieve smooth movement where the sun gear is mounted on the engine shaft. A good slight misalignment in the sun gear (electric 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 entire system. This details is usually obtainable from the gearhead manufacturer.
Contouring applications usually 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 equipment are good examples.
Software compensation is accomplished by commanding the motor to move beyond the apparently desired position by a quantity add up to the system’s dropped movement, thereby bringing the strain to the truly desired position. For instance, consider 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 your controller tells the electric 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 equipment teeth and its own engaging tooth; lost motion is the total looseness or motion at a reducer’s result shaft when the input shaft is fixed. Lost 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 motion in planetary gearheads. This technique compensates for backlash also where an application requires accuracy much better than the minimal backlash of the gearhead.