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 used 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 own 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 lack of torque and velocity variations (ripple), is essential in contouring applications. But, it really is servo motor gear reducers difficult to regularly achieve smooth motion where the sun equipment is installed on the electric motor shaft. A good slight misalignment in the sun 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 movement of the whole system. This info 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 devices, 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 engine to move beyond the apparently desired position by an amount equal to the system’s lost motion, thereby bringing the load to the truly desired position. For example, consider a servomotor, gearhead, and leadscrew mixture in a pick-andplace robot. If 100,000 encoder counts equals 1.0 in. of linear motion and the system has 0.1-in. lost motion, then the controller tells the engine to move 110,000 encoder counts to obtain 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 engaging tooth; lost motion is the total looseness or movement at a reducer’s output 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 could be programmed to compensate for backlash and dropped movement in planetary gearheads. This technique compensates for backlash actually where a credit card applicatoin requires accuracy better than the minimal backlash of the gearhead.