Because the sun equipment in a hybrid unit is pre-aligned within the gearhead rather than affixed to the electric 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 own window frame should be perfectly smooth; or else a ripple in velocity alters the bead diameter and causes messy glue program.
Smooth motion, this means the lack of torque and velocity variations (ripple), is important in contouring applications. But, it really is difficult to consistently achieve smooth motion where the sun equipment is installed on the motor shaft. A good slight misalignment in sunlight gear (electric motor shaft runout or coupling inaccuracies) can cause rough servo motor gear reducers procedure and noise.
Many servo controllers use software compensation, and their success depends on knowing the lost movement of the entire system. This information is usually available from the gearhead producer.
Contouring applications usually involve end-effectors or tool-points that stick to mathematically defined paths. Sealant and bonding devices, water and flame cutters, laser beam welders and cutters, motion managed cameras, and CNC machine tools are good examples.
Software compensation is achieved by commanding the motor to move beyond the apparently desired position by a quantity equal to the system’s dropped motion, thereby bringing the load to the truly desired position. For instance, consider a servomotor, gearhead, and leadscrew mixture in a pick-andplace robot. If 100,000 encoder counts equals 1.0 in. of linear movement and the machine has 0.1-in. dropped motion, then the controller tells the electric motor to move 110,000 encoder counts to get 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 motion may be the total looseness or movement at a reducer’s result shaft when the input shaft is fixed. Dropped motion includes 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 dropped movement in planetary gearheads. This technique compensates for backlash even where an application requires accuracy better than the minimal backlash of the gearhead.