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Last Updated: March 31, 2007
Last Updated: March 31, 2007
Absolute rotary encoders are available in single and multiturn versions. Multiturn devices are primarily used with measuring screws.
Incremental rotary encoders are preferred when low cost is important, or when only relative position is needed. Rotary encoders typically produce output, which consists of two square waves, each corresponding to an increment of rotation. Incremental rotary encoders often have a third channel with a single segment slot or reference which is used to zero or home the device.
Single-channel rotary encoders, also called tachometers, are inherently less accurate than dual-channel versions and cannot register direction. Inaccurate readings from these rotary encoders often result when the code wheel stops on or near a slot's edge and vibrations move the code wheel back and forth. If the slot edge interrupts the light beam, the counter increments with each transition.
Other common rotary encoder versions include standard, modular, and kit. Standard rotary encoders are those that have their own shaft and bearing assembly. The rotary encoder shaft couples to the motor shaft with a belt, coupling, or gear train. Hollow shaft rotary encoders are similar, but the motor shaft fits into the rotary encoder shaft bore.
Some manufacturers claim there is a difference between modular and kit encoders, but others say they are the same. Some say that a modular rotary encoder is complete and ready to use, while kit rotary encoders require user assembly. Regardless of the amount of assembly, both fit directly on the motor shaft. A setscrew usually secures the code wheel to the shaft, but some designs have press-tight fittings.
Incremental rotary encoders are preferred when low cost is important, or when only relative position is needed. Rotary encoders typically produce output, which consists of two square waves, each corresponding to an increment of rotation. Incremental rotary encoders often have a third channel with a single segment slot or reference which is used to zero or home the device.
Single-channel rotary encoders, also called tachometers, are inherently less accurate than dual-channel versions and cannot register direction. Inaccurate readings from these rotary encoders often result when the code wheel stops on or near a slot's edge and vibrations move the code wheel back and forth. If the slot edge interrupts the light beam, the counter increments with each transition.
Other common rotary encoder versions include standard, modular, and kit. Standard rotary encoders are those that have their own shaft and bearing assembly. The rotary encoder shaft couples to the motor shaft with a belt, coupling, or gear train. Hollow shaft rotary encoders are similar, but the motor shaft fits into the rotary encoder shaft bore.
Some manufacturers claim there is a difference between modular and kit encoders, but others say they are the same. Some say that a modular rotary encoder is complete and ready to use, while kit rotary encoders require user assembly. Regardless of the amount of assembly, both fit directly on the motor shaft. A setscrew usually secures the code wheel to the shaft, but some designs have press-tight fittings.
Rotary encoders and linear optical encoders are common in position and motion sensing. Here, a disc or plate containing opaque and transparent segments passes between an LED and detector to interrupt a light beam. All rotary encoders consist of a light source, light detector, code wheel, and signal processor. There are two basic types of rotary encoders: absolute and incremental. Absolute rotary encoders contain multiple detectors and up to 20 tracks of segment patterns. For each rotary encoder position, there is a different binary output -- shaft position is absolutely determined.
Tracks on absolute rotary encoders often are arranged to produce a binary output called Gray code. The advantage of Gray code over straight binary is that only one bit changes at a time. Thus, the maximum error (if the rotary encoder stops halfway between transitions) is only 0.5 bit. In absolute rotary encoders, this information is available even if the rotary encoder is turned off and on. This suits them for low-speed applications, as in telescopes, or where rotary encoders may be temporarily shut down, as in highway bridges.
Tracks on absolute rotary encoders often are arranged to produce a binary output called Gray code. The advantage of Gray code over straight binary is that only one bit changes at a time. Thus, the maximum error (if the rotary encoder stops halfway between transitions) is only 0.5 bit. In absolute rotary encoders, this information is available even if the rotary encoder is turned off and on. This suits them for low-speed applications, as in telescopes, or where rotary encoders may be temporarily shut down, as in highway bridges.
