Denford Software & Machines

can any of the tech guys give a simplified explanation of the linear and rotary transducers used in CNC machines for help with some BTEC coursework.
Are they the magnetic induction type? etc
thanks
Paul

I will try and explain what the difference is.

The linear unit is normally attached directly to the moving slide. as the slide moves along the reading head travels along the body of the unit. This will give a very acurate position feedback as there is no gearing involved. The down side is that they are generally in the working area and get coolant etc over them which can cause them to fail.

A rotary device will be mounted on the end of the motor shaft or the end of the ballscrew. The position is calculated by working out the ratio of the encoder rotation through the gear ratio to actual motion. If there is backlash or there are ballscrew inacuracys the rotary system will not be able to take these into account.

Magnetic induction systems (or Inductosyn) are quite old linear positioning devices and use the same principles as a linear induction motor - ie monitoring electro magnetic fields being cut to determine how far the reading head has moved.

I think Renishaw still make an inductive sensor which can be glued onto long axes or around tables

Most CNC nowadays use optical encoders - either linear or rotary - basically shining light onto a fine grid, and reading the interference pattern back to judge change in position.
If I remember correctly, the basic principle only reads a change in position to give a pulse (or two) and a direction - absolute encoders (linear or rotary) are different in that they have reference marks which allow the electronics to count from a known position an keep a track of where the axis is - then its stored on flash or battery backed memory inside the encoder so machine can power up knowing where it is.

Check out https://www.heidenhain.com/ as well