About Spindle Encoder

Dear All,

I am New to Linuxcnc.I have 4 axis milling machine. I want to use spindle in synchronize mode with all other axis feedrate. Is it possible in linuxcnc. What type of Encoder needed for spindle. Dual Phase singal channel (A phase and B Phase). or Differential Type ( A+, A- and B+, B-) . which encoder is supported by linuxcnc.
need your help.
Regards
Pradeep jadhav

I am no expert on Linuxcnc, but the answer for your question I think is both, depending to what hardware you will connect the encoder.
If possible use the differential as it will be less sensitive to noise.

Pradeep.Jadhav wrote:

Dear All,

I am New to Linuxcnc.I have 4 axis milling machine. I want to use spindle in synchronize mode with all other axis feedrate. Is it possible in linuxcnc. What type of Encoder needed for spindle. Dual Phase singal channel (A phase and B Phase). or Differential Type ( A+, A- and B+, B-) . which encoder is supported by linuxcnc.
need your help.
Regards
Pradeep jadhav

just about any encoder will do for spindle sync , you need at minimum 120 counts and single channel + an index pulse , around a 500 count is ideal
the index pulse is important . these are usualy shown as A+B+I

Just to fill in some of the details, LinuxCNC is most compatible with quadrature digital rotary or linear encoders and analog resolvers.
en.wikipedia.org/wiki/Quadrature_encoder...-track_Gray_encoding
en.wikipedia.org/wiki/Linear_encoder

LinuxCNC is generally limited to only simple digital inputs, unless one uses an interface card of some kind. Analog resolvers will need an interface card from Mesa or Pico Systems
en.wikipedia.org/wiki/Resolver_%28electrical%29

Digital sensors use a digital input to LinuxCNC which generally are 0 or 5 Volts ____|TTTTT|____ which uses a wire for the 0/5 Volt signal and another wire as a ground reference. For better noise immunity a differential converter may be used on each end of the cable and is usually of the RS-422 or RS-485 type. Two wires are used, but they are referenced to each other.
en.wikipedia.org/wiki/Differential_signaling
en.wikipedia.org/wiki/RS-422

There are incremental and absolute encoders that use proprietary encoding which generally are not usable with LinuxCNC.

For spindle encoders, the resolution needed depends on what the encoder will be used for. For simple velocity feedback, just a single channel (A) 1 pulse per rev can work, but more pulses are better. These pulses can go into a parallel port input, but only up to 10 to 40 kHz. This may limit your maximum RPM or encoder resolution. I would consider a good single channel velocity encoder count of 10 to 100 pulses per rev. If one needs to get direction from the encoder, two channels are needed (A, B ) of the same count range. For rigid tapping and threading, an index pulse is needed (A, B, I index or A, B, Z zero). Higher counts are needed and I would calculate the pulse rate from the maximum spindle speed and the maximum pulse rate of the input to get the encoder resolution. Often a hardware pulse counter (FPGA card) is needed for decent pulse rates.

VFDs and motor drivers can give off a lot of electrical noise. Differential signalling can help with that, but I would first add a filter to your VFD AC input and shielded cabling for motor and signal cables. Differential signalling can be added if needed, or for more insurance. Also don't overlook proper cable termination.
en.wikipedia.org/wiki/Electrical_termination

Each cable and signalling type (power circuits included) need a matching termination technique (resistors, capacitors, grounds, reference signals).
--
Kirk Wallace
www.wallacecompany.com/machine_shop/