Because the sun equipment in a hybrid unit is pre-aligned within the gearhead rather than affixed to the engine shaft, these gearheads can be utilized in contouring applications such as a glue-dispensing nozzle for affixing a windshield to an automobile. Movement of the nozzle since it follows the seam between a windshield and its own window frame should be perfectly smooth; or else a ripple in velocity alters the bead diameter and causes messy glue application.
Smooth motion, this means the absence of torque and velocity variations (ripple), is essential in contouring applications. But, it is difficult to consistently achieve smooth servo gear reducer motion where the sun gear is installed on the electric motor shaft. Even a slight misalignment in the sun gear (engine 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 information is usually available from the gearhead manufacturer.
Contouring applications usually involve end-effectors or tool-points that stick to mathematically defined paths. Sealant and bonding devices, drinking water and flame cutters, laser welders and cutters, movement managed 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 motion, thereby bringing the load to the truly desired position. For example, look at 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. lost motion, then the controller tells the motor to go 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 own engaging tooth; lost motion may be the total looseness or motion at a reducer’s output shaft when the input shaft is fixed. Dropped motion includes backlash, plus losses from bearing looseness, tolerances and matches, and shaft and gear tooth compliance.
Servo controllers could be programmed to pay for backlash and dropped movement in planetary gearheads. This system compensates for backlash also where a credit card applicatoin requires accuracy better than the minimal backlash of the gearhead.