Fanuc Spindle Feedback Types

Fanuc Spindle Feedback

There are currently six different feedback devices available for spindle applications. These are referred to in the documentation and have meanings as follows:

Term used in GE Fanuc
Serial Spindle O/I
1. Pulse Generator
(Detector column)
Motor mounted: This is the standard basic encoder. It has a low pulse count of 128 or 256 cycles per rev.
Application: This is standard unless one of the other units is specified. It is only satisfactory for velocity control.
2. Position Coder
(Remarks column)
Separate mounted: This is a 1024 cycles per rev encoder. It is normally mounted on the spindle.
Application: required for such functions as threadcutting, display, positioning, rigid tapping and synchronous operation. It is also used for multi-position orient.
3. Built-In Sensor
(Detector column)
Motor mounted: This sensor provides the pulse generator and position coder functions. It outputs a sine wave which must be converted to the 1024 cycles per rev encoder type signal and the pulse generator type velocity control signal by the signal conversion circuit A06B-6063-730 (replaces circuits A06B-6044-H603, 4 and 5).
Application: Can be used for the position coder functions when the motor and the spindle are coupled 1=1 (gear or timing belt).
4. High Resolution
Magnetic pulse coder
(with preamp)
Motor or separately mounted:This is a magnetic sensor with a preamplifier for signal conditioning. It requires an optional detector circuit board on the spindle servo unit to convert multiple sine waves per rev into:
– 360,000 pulse/rev (contouring)
– 1024 cycles/rev (positioning)
– 128/256 cycles/rev (velocity)
The spindle mounted version is available in three diameters. Circuit boards A06B-6063-J710 through J717 are required and mounted on the amplifier. They are size dependent (larger diameter sensors put out more sine waves per rev).
Application: required for contouring. If the spindle and motor are coupled 1:1, then the motor sensor only need be used, if not, then the separate sensor should be used on the spindle.
5. High Resolution
Magnetic pulse coder
(with preamp)
(velocity signal only)
Motor mounted: For velocity control, it is a single head version of the normal 2 head encoder item A4. It provides only the 1024 and 128/256 cycles per rev signals.
Application: required for contouring. Can be used when the separate encoder item A4 is provided, but it is also acceptable to have both separate and motor encoders item A4 type.
6. Magnetic Sensor Motor mounted: proximity switch and preamplifier requires an optional orientation board on the spindle servo unit. Application: fastest method for single position spindle orientation.

Terms used in this document have the following definitions:

Pulse In a Fanuc encoder with quadrature square wave output, “Pulse” is used to designate the “on” portion of each cycle.
Quadrature Refers to a 90 degree electrical phase relationship between two outputs (often designated A Quad B).
Cycles per revolution The number of quadrature square wave outputs per revolution of the encoder. Sometimes called pulses per rev but can cause confusion when output transition points (on/off,off/on) are counted to give four pulses per cycle.
Resolution The actual movement represented by one pulse. For example, a 2500 cycle per rev encoder provides 2500 x 4 (10000) pulses per rev for a 360/10000 (0.036) degree resolution.
Accuracy A general term referring to how close to commanded position a control can be depended on to deliver. It usually requires a qualifying term such as the following:
a. Incremental error Deviation from the norm between the leading edge of two adjacent pulses.
b. Absolute position error For a sensor’s deviation from the norm at any point within one revolution of the sensor.
c. Repeatability How much deviation may occur on repeated moves to the same position.
Pulse generator Not available – not critical.
Position coder Incremental error = + 1/5251 (degrees).
Built-in sensor Not available (for estimating purposes, consider as good as other magnetic units which are 1/70,000 incremental error).
High resolution Magnetic pulse coder
Absolute position error +0.005 degrees.
High resolution
Magnetic pulse coder
Incremental error + 1/18000 (+0.02 degrees).
Magnetic sensor Repeatability + 0.2 degree or less

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