Fanuc Spindle Feedback
General
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 |
Description/Application |
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| 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. |
Definitions
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. |
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| Quadrature | Refers to a 90 degree electrical phase relationship between two outputs (often designated A Quad B). |
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| 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. |
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| 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. |
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| 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: |
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| a. | Incremental error | Deviation from the norm between the leading edge of two adjacent pulses. |
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| b. | Absolute position error | For a sensor’s deviation from the norm at any point within one revolution of the sensor. |
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| c. | Repeatability | How much deviation may occur on repeated moves to the same position. | |
| Accuracy |
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| Pulse generator | Not available – not critical. |
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| Position coder | Incremental error = + 1/5251 (degrees). |
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| Built-in sensor | Not available (for estimating purposes, consider as good as other magnetic units which are 1/70,000 incremental error). |
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| 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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