Basics of rotary encoders.12/29/2017Encoders are sensors for monitoring position and speed. Rotary encoders are the type of encoders used on permanent magnet AC servo motors. These encoders are divided into the two sub-categories of absolute encoders and incremental encoders.Absolute encoders produce a unique binary value for a given shaft position. As an example, an absolute encoder that uses a 4-bit binary value to resolve or divide one revolution into 16 positions. The number of bits and resulting positions determines the encoder disk’s resolution. The resolution of an encoder doubles with each additional bit used. Each position of the disk is separated into tracks equal to the number of bits used by the encoder. A 4-bit or 4-track encoder has sections that are either open or filled in. The open and filled-in sections are converted into binary signals by the encoder’s lamp and sensor boards. A binary value of 1 is produced by the open sections because the light is allowed to pass to the sensor board. A binary value of 0 is produced by the filled-in sections because the light is blocked from the sensor board. The most common use of absolute encoders is for position feedback.Incremental encoders generate one or two pulse strings, depending on whether it is a one or two channel encoder. Incremental encoders are very versatile because they can indicate position, velocity, and direction. As an example, a simple 2-channel encoder for forward rotation will have channel A and channel B 90 degrees out of phase. The direction of rotation is determined by which channel is leading. The number of pulses per set monitoring cycle determines the velocity or rate. To aid in determining position, many encoders will include a marker pulse. The marker pulse will occur once per revolution. The number of pulse edges along with the marker pulse determines position. The pulse edges may be multiplied before they are fed to the controller to improve the resolution, especially for positioning. Doing this requires additional circuitry to perform the multiplication. The fact that incremental encoders can provide both direction and speed feedback in a digital form, makes them an excellent choice to provide feedback to many controllers because no analog to digital conversion is necessary. Yaskawa servo motors use both absolute and incremental encoders that can be specified with either type depending on the application and servo drive used to control it. The servo motor experts at PES have the experience to repair and test both types of rotary encoders. Call on us today at 800-732-4695. Back To Blog
Basics of rotary encoders.12/29/2017Encoders are sensors for monitoring position and speed. Rotary encoders are the type of encoders used on permanent magnet AC servo motors. These encoders are divided into the two sub-categories of absolute encoders and incremental encoders.Absolute encoders produce a unique binary value for a given shaft position. As an example, an absolute encoder that uses a 4-bit binary value to resolve or divide one revolution into 16 positions. The number of bits and resulting positions determines the encoder disk’s resolution. The resolution of an encoder doubles with each additional bit used. Each position of the disk is separated into tracks equal to the number of bits used by the encoder. A 4-bit or 4-track encoder has sections that are either open or filled in. The open and filled-in sections are converted into binary signals by the encoder’s lamp and sensor boards. A binary value of 1 is produced by the open sections because the light is allowed to pass to the sensor board. A binary value of 0 is produced by the filled-in sections because the light is blocked from the sensor board. The most common use of absolute encoders is for position feedback.Incremental encoders generate one or two pulse strings, depending on whether it is a one or two channel encoder. Incremental encoders are very versatile because they can indicate position, velocity, and direction. As an example, a simple 2-channel encoder for forward rotation will have channel A and channel B 90 degrees out of phase. The direction of rotation is determined by which channel is leading. The number of pulses per set monitoring cycle determines the velocity or rate. To aid in determining position, many encoders will include a marker pulse. The marker pulse will occur once per revolution. The number of pulse edges along with the marker pulse determines position. The pulse edges may be multiplied before they are fed to the controller to improve the resolution, especially for positioning. Doing this requires additional circuitry to perform the multiplication. The fact that incremental encoders can provide both direction and speed feedback in a digital form, makes them an excellent choice to provide feedback to many controllers because no analog to digital conversion is necessary. Yaskawa servo motors use both absolute and incremental encoders that can be specified with either type depending on the application and servo drive used to control it. The servo motor experts at PES have the experience to repair and test both types of rotary encoders. Call on us today at 800-732-4695.