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 such as a glue-dispensing nozzle for affixing a windshield to a car. Motion of the nozzle as it follows the seam between a windshield and its window frame should be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue app.
Smooth motion, this means the absence of torque and velocity variations (ripple), is important in contouring applications. But, it is difficult to consistently achieve smooth movement where the sun equipment is mounted 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 motion of the entire system. This details is usually offered from the gearhead manufacturer.
Contouring applications generally involve end-effectors or tool-points that stick to mathematically defined paths. Sealant and bonding machines, drinking water and flame cutters, laser welders and cutters, movement controlled cameras, and CNC machine equipment are good examples.
Software compensation is achieved by commanding the motor to go beyond the apparently desired position by an amount add up to the system’s lost 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 movement and the machine has 0.1-in. lost motion, then your controller tells the electric motor to move 110,000 encoder counts to obtain 1.0 in. of motion, thus compensating for the 0.1-in. lost motion.
servo motor gear reducers backlash is the excess space between two adjacent gear teeth and its own engaging tooth; lost movement may be the total looseness or motion at a reducer’s result shaft when the insight shaft is fixed. Lost motion contains backlash, plus losses from bearing looseness, tolerances and fits, and shaft and gear tooth compliance.
Servo controllers can be programmed to compensate for backlash and lost movement in planetary gearheads. This technique compensates for backlash even where an application requires accuracy better than the minimal backlash of the gearhead.