Encoders
STEGMANN
SICK|STEGMANN products are designed and developed using the most modern methods to ensure performance targets are met. Before and during manufacturing, they are subjected to the most stringent quality controls, using state-ofthe- art techniques, and high-precision measuring equipment. SICK|STEGMANN manufacturing plants are ISO 9001:2000 certified, ensuring that customer expectations are met in quotation, order entry, engineering, manufacturing, and after-sale service.
STEGMANN Absolute Encoders
Use absolute encoders when position data must be retained after loss of power. Examples include robotics, lead/ball screws, overhead cranes, and rack and pinion applications.
Basic Operation of Optical Rotary Absolute Encoders
As with incremental encoders, absolute optical rotary encoders use a rotating disk to interrupt the light path to a photodetector, which produces an output signal. However, absolute encoders read uniquely coded tracks to generate position information. No two adjacent positions are alike. Therefore, absolute encoders do not lose position data when power is lost. True position is available as soon as power is restored.
Conventional Optical Absolute Encoder Disks A conventional absolute encoder disk features a series of concentric tracks, each consisting of a pattern of transparent and opaque segments. These independent tracks provide a unique combination of absolute values for each resolvable position. One track is needed for each “bit” of position information that is
output as either a serial or parallel data “word.” The preferred code format is Gray Code, in which only one bit of information changes between adjacent positions on the disk. This limits the position error from the track sensors to plus or minus one count. Other available codes, such as Natural Binary or Binary Coded Decimal (BCD), may have several bits change between adjacent positions.
Magnetic Absolute Encoders Many applications require resistance to extremely high shock and vibration, wide temperature variations, or high humidity with condensation. SICK|STEGMANN magnetic absolute encoders meet these unique challenges.
Magnetic field strength of a proprietary 32-pole magnetic ring is measured using two strategically spaced magneto-resistors that pick up variation of the magnetic field intensity along the circumference of the ring. The resulting 32 sine/cosine signals per turn (5-bit) are then enhanced by 8-bit interpolation. A single north
south pole magnet, read by a Hall effect sensor, is used to assign absolute values to individual sine/cosine cycles. Thus, the 32-pole magnetic ring is calibrated for a 13-bit single-turn absolute position feedback. Additional software is used to compensate for temperature variation and resulting differential thermal expansion to insure data integrity.
Electronic Zero Position Teach With all SICK|STEGMANN absolute encoders, the zero position is electronically assigned by the user to the current mechanical position by activation of a pushbutton or set line. No mechanical detachment or rotation of the encoder is necessary.
