Because the sun equipment in a hybrid unit is pre-aligned within the gearhead rather than affixed to the electric 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 follows the seam between a windshield and its own window frame should 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 is difficult to consistently achieve smooth motion where the sun gear is installed on the electric motor shaft. Even a slight misalignment in the sun gear (electric motor shaft runout or coupling inaccuracies) can cause rough procedure and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost motion of the whole system. This information is usually offered from the gearhead producer.
Contouring applications usually involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding machines, drinking water and flame cutters, laser welders and cutters, motion managed cameras, and CNC machine tools are good examples.
Software compensation is achieved by commanding the motor to move beyond the apparently desired position by an amount add up to the system’s dropped motion, thereby bringing the strain to the truly desired position. For instance, look at a servomotor, gearhead, and leadscrew mixture 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 electric motor to go 110,000 encoder counts to get 1.0 in. of motion, thus compensating for the 0.1-in. lost motion.
Backlash is the excess space between two adjacent equipment teeth and its own engaging tooth; lost movement may be the total looseness or movement at a reducer’s output shaft when the input shaft is fixed. Dropped motion contains backlash, plus losses from bearing looseness, tolerances and matches, and shaft and gear tooth compliance.
Servo controllers can be programmed to compensate for backlash and dropped movement in planetary gearheads. This system compensates for backlash also where an application servo motor gear reducers requires accuracy better than the minimal backlash of the gearhead.