AEDR-8320 Encoder Reflective Surface Mount Optical Encoder Data Sheet Description Features The AEDR-8320 encoder is an analog output encoder Reflective technology that employs optical reflective technology for rotary and Surface mount leadless package linear movement control. Two-channel analog voltage output With the introduction of reflective technology, encoder Lead free package packages can now be made smaller and weigh signifi - -40C to 85C operating temperature cantly lighter. This statement is better reflected in the Encoding resolution: ability of the AEDR-8320 encoder which can easily fit 180 (lines/inch) or 7.09 (lines/mm) into many space and weight constraint applications, e.g., CD or DVD writer laser heads linear movement. Applications The AEDR-8320 comes in a 180 LPI (Lines Per Inch) or 7.09 mm lines per mm. In addition its 2-channel analog Printers outputs can obtain higher resolution through interpola- Copiers tion of 2x, 4x, 8x or more. For example, with 8x interpola- CD/DVD writer tion, the final resolution of the encoder will yield 1,440 lines per inch, which is approximately 20 m accuracy. Card readers AEDR-8320 encoder enhances design flexibility and pro - vides an easy-to-assemble solution to a wide variety of applications, while continuously ensuring reliability in performance. Theory of Operation Block Diagram of AEDR-8320 The AEDR-8320 encoder combines an emitter and a de- Definitions tector in a single surface mount, leadless package. When State Width (S): The number of electrical degrees be- used with a codewheel or linear codestrip, the encoder tween a transition in Channel A and the neighboring translates rotary or linear motion into analog outputs. transition in Channel B. There are 4 states per cycle, each As shown in the block diagram below, the AEDR-8320 nominally 90e. encoder consists of three major components: a light emitting diode (LED) light source, a detector IC consist- State Width Error ( DS): The deviation of state width, in elec- ing photodiodes and lens to focus light beam from the trical degree, from its ideal value of 90e. emitter as well as light falling on the detector. Phase (f): The number of electrical degrees between the The operation of the encoder is based on the principle center of high state of Channel A and the center of high of optics where the detector photodiodes sense the state of Channel B. Nominally 90e. absence and presence of light. In this case, the rotary/ linear motion of an object being monitored is converted Phase Error ( Df): The deviation of phase, in electrical de- to equivalent light pattern via the use of codewheel/ gree, from its ideal value of 90e. codestrip. As shown in the above diagram, the reflective area (window) of the codewheel (or codestrip) reflects Pulse Width (P): The duration of high state of the output, in light back to the photodetector IC, whereas no light is electrical degree, within one cycle. Nominally 180e or reflected by the non-reflective area (bar). An alternating half a cycle. light and dark patterns corresponding to the window Pulse Width Error (DP): The deviation of pulse width, in elec- and bar fall on the photodiodes as the codewheel ro- trical degree, from its ideal value of 180e. tates. The moving light pattern is exploited by the detec- tor circuitry to produce analog outputs representing the Count (N): The number of window and bar pair per revolu- rotation of the codewheel. When the codewheel is cou- tion (CPR) of codewheel. For linear codestrip, defined as pled to a motor the encoder outputs are then a direct the number of window and bar pair per unit length (lines representation of the motor rotation. The same concept per inch LPI or lines per mm LPmm ). applies to the use of a codestrip to detect linear motion. One Cycle (C): 360 electrical degrees (e). Equivalent to one Block Diagram of AEDR-8320 window and bar pair. V LED One Shaft Rotation: 360 mechanical degrees. Also equiva- R CODEWHEEL lent to N counts (codewheel only). or GND CODESTRIP Line Density: The number of window and bar pair per unit V CC length, expressed in either lines per inch (LPI) or lines per CH A mm (LPmm). SIGNAL CH B PROCESSING Optical radius (Rop): The distance between the codewheel CIRCUITRY center and the centerline between the two domes of the encoder. GND Gap (G): The distance from surface of the encoder to the surface of codewheel or codestrip. RADIAL (E ) R ANGULAR (E ) A Radial and Tangential Misalignment Error (E , E ): For rotary mo- R T tion, mechanical displacement in the radial and tangen- TANGENTIAL (E ) T tial directions relative to the nominal alignment. AEDR-8320 AEDR-8320 Angular Misalignment Error (E ): Angular displacement of the A encoder relative to the tangential line. Specular Reflectance (R ): The amount of incident light re- f SHAFT SHAFT flected by a surface. Quantified in terms of the percent - CODEWHEEL CODEWHEEL age of incident light. A spectrometer can be used to measure specular reflectance of a surface (contact fac - NOTE: DRAWING NOT TO SCALE tory for more information). 2