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Techno Linear Motion Catalog 28 Technical Information Incremental encoders have only one track (or two) of segment patterns.  The resolution of the encoder is equal to the number of bands in the pattern segment.  Absolute positioning information cannot be provided since all of the signals are the same.  All incremental encoders rely on a counter to determine position and a stable clock to determine velocity.  Most incremental encoders provide a single mark on the disc called the Z channel, or indexer.  The pulse from this channel provides a reference once per revolution to detect errors within a given revolution. If a second band of patterns and a second light source were added to an incremental encoder, the result is a quadrature  encoder,  which  is  very  common  in machining  and  positioning  applications.    Channel  B (second  band  and  light  source)  is  spaced  one  half  a slot  width  apart  from  the  Channel A  light  source  and photo detection.  Electrically, the two signals are 90° out of phase from each other as shown. The quadrature multiplication results from the two square waves having four unique states at any given moment.  Notice that as the waves move in one direction ( the disk rotates in one direction), the four states cycle  in  a  specific  sequence.   As  the  disk  rotates  in  the  opposite  direction,  the  four  states  cycle  in  the reverse sequence.  Thus, the direction of rotation and the quad multiplying effect (which increases resolution fourfold) can be produced by the second channel. Sizing Stepper Motors Before the correct Stepper Motor can be chosen for a particular application, the following information must be determined: a.  operating speed in steps/sec e.  time to accelerate in milliseconds b.  torque in ounce •inches f.    time to decelerate in milliseconds c.  load inertia in lb •in2 g.  type of drive system to be used d.  required step angle h.  size and weight considerations Once this information is known, the best motor/drive combination can be determined using torque vs. speed curves and the formulas given on this and the following pages. Torque, T (oz•in) T = Fr where F = Force (in ounces) required to drive the load r  = Radius (in inches) Moment of Inertia, I (lb •in2)       Wr2 I = –––– for a disc        2 Incremental Encoder Absolute Encoder Closed Loop Quadrature Detect A Channel B Channel Quadrature Detect Z Channel "Marker" Slots The Encoder Disk Quadrature Encoder