Page 44 - Kollmorgen PMX Series Stepper Motor Selection Guide
P. 44

Stepper Motor General Technical Guide

            Stepper Motor Basics
            A Kollmorgen stepper motor is a brushless motor consisting of a rotor and a stator assembly. The illustration shows the internal construction and
            tooth alignment of the motor. The fine teeth, evenly spaced around the entire diameter, provide the incremental angular rotation that results in
            mechanical motion.

            Kollmorgen Hybrid stepper motors have two windings (two phases)
            that are energized with DC current. When the current in one winding is
            reversed, the motor shaft moves one step, or 1.8° (options for 0.9° step   A
            angles are also available). By reversing the current in each winding,
            the position and speed of the motor is easily and precisely controlled,
            making these motors extremely useful for many different motion   B’                    B
            control applications.

            Holding Torque
                                                                    A’                                  A’
            “Holding torque” and the corresponding rated current are leading
            specifications for selection in the ratings tables for all motors. Holding
            torque is often used as a figure of merit when comparing motors. It
            specifies the maximum external torque that can be applied to a stopped
            motor with rated current applied without causing the motor to rotate
            continuously. When the motor begins to rotate the torque available is   B              B’
            often referred to as “pullout torque.” Pullout torque ratings correspond
            to values shown in performance speed/torque curves. At starting speeds    A
            the pullout torque is typically 20-30% lower than the motor’s rated
            holding torque.
                                                                         Stepper motor rotor & stator cross section
            Drive Selection and Motor Performance

            Stepper drives amplify and send DC current and voltage into the motor windings. Kollmorgen stepper motors are used with a variety of drives
            available from Kollmorgen and other manufacturers. These drives typically have a broad range of voltage and current ratings. A motor’s performance
            is highly dependent on the current and voltage supplied by a drive. For even finer resolution and smoother operation, micro-stepping drives divide
            each step into many increments by controlling the magnitude of the current in each winding.

                                     Power                                                        Step
                   AC Power          Supply      AC Power           Drive     Motor Current      Motor

            As applied voltage and/or current to the motor is changed, motor performance is altered. A performance speed/torque curve shows the pullout
            torque, which is directly dependent on the available current from the stepper drive. The torque values are shown along the motor’s entire speed
            range, which is dependent on the available voltage.

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