Because the sun gear in a hybrid unit is pre-aligned within the gearhead and not affixed to the motor shaft, these gearheads can be used in contouring applications such as a glue-dispensing nozzle for affixing a windshield to a car. Motion of the nozzle since it follows the seam 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 software.
Smooth motion, this means the lack of torque and velocity variations (ripple), is essential in contouring applications. But, it is difficult to consistently achieve smooth motion where the sun equipment is installed on the engine shaft. A good slight misalignment in sunlight gear (engine shaft runout or coupling inaccuracies) could cause rough operation and noise.
Many servo controllers use software compensation, and their success depends upon knowing the lost motion of the entire system. This details is usually available from the gearhead producer.
Contouring applications generally involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding machines, water and flame servo motor gear reducers cutters, laser beam welders and cutters, motion managed cameras, and CNC machine tools are good examples.
Software compensation is achieved by commanding the engine to go beyond the apparently desired position by a quantity equal to the system’s dropped motion, thereby bringing the strain to the truly desired position. For example, 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 machine 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, hence compensating for the 0.1-in. lost motion.
Backlash is the extra space between two adjacent gear teeth and its own engaging tooth; lost movement is the total looseness or motion at a reducer’s output shaft when the insight shaft is fixed. Lost 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 even where a credit card applicatoin requires accuracy much better than the minimal backlash of the gearhead.