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Techno Linear Motion Catalog 37 Technical Information Stepper Control (open loop):  Stepper motor controllers typically operate in one of three modes.  Full step mode provides the coarsest resolution, half step mode is next, and microstep mode offers the smallest resolution.  Most positioning and machining applications are well served by half step mode, but microstepping may be necessary.  Microstepping is when the control electronics divide each full motor step into many smaller steps by manipulating the current levels in the windings.  If  a servo system is not desired, applications involving very low speeds and much higher resolutions can utilize the advantages of microstepping. There are several key points to consider when analyzing a stepper motor control unit.  Circular interpolation is when two  stepper  motors  are  controlled  simultaneously  to achieve circular motion.  Due to the digital nature of stepper motors, all arcs have to be approximated by a series of very small line segments.  The deviation from a true circular path  is  determined  by  the  size  of  the  line  segment approximations.    Techno  stepper  motor  controllers execute circular interpolation true to within 1 step at all points along the arc. Since stepper motors have decreased torque output at increased  speeds  (see  Figure  1),  it  is  important  to understand how control electronics handle acceleration and   deceleration.      Machining   and   positioning applications  often  involve  direction  and  velocity changes.  The graphs indicate a velocity change, over time,  from  point A  to  point  B.    Two  common  types  of velocity  profiles,  parabolic  and  trapezoidal,  are illustrated.    Since  stepper  motors  can  stall  under dynamic shock, it is important to have a smooth velocity profile (see Figure 2).  The most effective way to achieve a smooth profile is to use parabolic ramping functions Micro Half Full Full  stepping  is  a  4-point  approximation  of  the  sine/cosine  waves.    Half  step  is  just  an  8-point approximation of the sine/cosine waves.  If more points are used to approximate the sine/cosine waves, this is called mini- or microstepping. Torque A B t t t t Acceleration Figure 1 Velocity Velocity Velocity Figure 3  Trapezoidal Figure 2  Parabolic Acceleration A B A B