AEDR-8400 Series Reflective Surface Mount Optical Encoder Data Sheet Description Features Reflective technology The AEDR-8400 encoder is the smallest optical encod- er employing reflective technology for motion control Surface mount leadless package purposes. The encoder houses an LED light source and a Two channel quadrature digital outputs for direction photo-detecting circuitry in a single package. sensing TTL compatible The AEDR-8400 encoder offers two-channel quadrature digital outputs. Being TTL compatible, the outputs of the Single 2.8V supply AEDR-8400 encoder can be interfaced directly with most -20C to 85C absolute operating temperature of the signal processing circuitries. Hence the encoder Encoding resolution: provides great design-in flexibility and easy integration 254 (lines/inch) or 10 (lines/mm) into existing systems. 318 (lines/inch) or 12.5 (lines/mm) Applications Ideal for high volume applications: Printers Copiers Card readers Scanners Digital Still Cameras Camcorders Camera Phones Projectors Consumer Product Applications Note: Avago Technologies encoders are not recommended for use in safety critical applications such as. ABS braking systems, power steering, life support systems and critical care medical equipment. Please contact our sales represen- tative if clarification is needed.Theory of Operation The AEDR-8400 encoder combines an emitter and a de- State Width Error (S): The deviation of state width, in elec- tector in a single surface mount leadless package. When trical degree, from its ideal value of 90e. used with a codewheel or linear codestrip, the encoder Phase (): The number of electrical degrees between the translates rotary or linear motion into digital outputs. center of high state of Channel A and the center of high As seen in the block diagram, the AEDR-8400 consists state of Channel B. Nominally 90e. of three major components: a light emitting diode (LED) light source, a detector IC consisting photodiodes and Phase Error ( ): The deviation of phase, in electrical de- lens to focus light beam from the emitter as well as light gree, from its ideal value of 90e. falling on the detector. Pulse Width (P): The duration of high state of the output, in electrical degree, within one cycle. Nominally 180e Block Diagram of AEDR-8400 Encoder or half a cycle. V LED Pulse Width Error ( P): The deviation of pulse width, in elec- trical degree, from its ideal value of 180e. Gnd Count (N): The number of window and bar pair per revolu- V CC tion (CPR) of codewheel. For linear codestrip, defined as the number of window and bar pair per unit length (lines Signal Ch A per inch LPI or lines per mm LPmm ). Processing Ch B Circuitry One Cycle (C): 360 electrical degrees (e). Equivalent to one window and bar pair. Codestrip or Gnd Codewheel One Shaft Rotation: 360 mechanical degrees. Also equivalent Note: Drawing not to scale. to N counts (codewheel only). The operation of the encoder is based on the principle Line Density: The number of window and bar pair per unit of optics where the detector photodiodes sense the length, expressed in either lines per inch (LPI) or lines per absence and presence of light. In this case, the rotary/ mm (LPmm). linear motion of an object being monitored is converted Optical radius (Rop): The distance between the codewheel to equivalent light pattern via the use of codewheel/ center and the center of the encoder dome. codestrip. As shown in the above diagram, the reflective area (window) of the codewheel (or codestrip) reflects Gap (G): The distance from surface of the encoder to the light back to the photodetector IC, whereas no light is surface of codewheel or codestrip. reflected by the non-reflective area (bar). An alternating Radial and Tangential Misalignment Error (E , E ): For rotary mo- light and dark patterns corresponding to the window and R T tion, mechanical displacement in the radial and tangen- bar fall on the photodiodes as the codewheel rotates. The tial directions relative to the nominal alignment. moving light pattern is exploited by the detector circuitry to produce digital outputs representing the rotation of Angular Misalignment Error (E ): Angular displacement of the A the codewheel. When the codewheel is coupled to a mo- encoder relative to the tangential line. tor, the encoder outputs are then a direct representation of the motor rotation. The same concept applies to the Specular Reflectance (R ): The amount of incident light f use of a codestrip to detect linear motion. reflected by a surface. Quantified in terms of the per - centage of incident light. A spectrometer can be used to measure specular reefl ctance of a surface (contact factory Definitions for more information). State Width (S): The number of electrical degrees between a transition in Channel A and the neighboring transition in Channel B. There are 4 states per cycle, each nominally 90e. Angular (E ) A Radial (ER)) Tangential (E ) T Codestrip or Codewheel AEDR-8400 AEDR-8400 Gap Shaft Shaft Codewheel Codewheel Note: Drawing not to scale 2