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 utilized 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 servo motor gear reducers should be perfectly smooth; otherwise a ripple in velocity alters the bead diameter and causes messy glue app.
Smooth motion, which means the lack of torque and velocity variations (ripple), is essential in contouring applications. But, it is difficult to consistently achieve smooth movement where the sun gear is mounted on the engine shaft. A good slight misalignment in the sun gear (engine 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 entire system. This details is usually offered from the gearhead manufacturer.
Contouring applications generally involve end-effectors or tool-points that follow mathematically defined paths. Sealant and bonding devices, water and flame cutters, laser beam welders and cutters, motion managed cameras, and CNC machine equipment are good examples.
Software compensation is accomplished by commanding the electric motor to move beyond the apparently desired position by a quantity equal to the system’s lost motion, thereby bringing the load 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 system has 0.1-in. dropped motion, then your 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 extra space between two adjacent gear teeth and its engaging tooth; lost motion is the total looseness or motion at a reducer’s result 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 even where an application requires accuracy much better than the minimal backlash of the gearhead.