Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not affixed to the engine shaft, these gearheads can be used in contouring applications like a glue-dispensing nozzle for affixing a windshield to an automobile. Movement of the nozzle since it comes after the seam servo gear reducer between a windshield and its own window frame must be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue app.
Smooth motion, which means the absence of torque and velocity variations (ripple), is essential in contouring applications. But, it really is difficult to regularly achieve smooth motion where the sun gear is mounted on the motor shaft. Even a slight misalignment in sunlight gear (electric 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 motion of the entire system. This info is usually available from the gearhead manufacturer.
Contouring applications usually involve end-effectors or tool-points that adhere to mathematically defined paths. Sealant and bonding machines, water and flame cutters, laser welders and cutters, movement controlled cameras, and CNC machine tools 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 dropped movement, thereby bringing the strain to the truly desired position. For instance, look at 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 machine has 0.1-in. dropped motion, then the controller tells the motor to go 110,000 encoder counts to obtain 1.0 in. of motion, therefore compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent gear teeth and its engaging tooth; lost motion is the total looseness or motion at a reducer’s output shaft when the input shaft is fixed. Dropped motion contains backlash, plus losses from bearing looseness, tolerances and fits, and shaft and gear tooth compliance.
Servo controllers can be programmed to pay for backlash and lost movement in planetary gearheads. This system compensates for backlash actually where an application requires accuracy better than the minimal backlash of the gearhead.