What is axis and a half

Can someone please give me a technical explanation of what is meant by "axis-and-a-half" control or direct me to a technical document. I've seen this on the web in the following form: "We offer single-axis, axis-and-a-half, and multi-axis control." Thank you.

An axis an a half is a normal axis and an input that the axis can be geared to. This is typical of system is a flying cutoff or fly shear system where the feed line provides it speed or postion using the half axis and the flying shear is moves and synhronizes it self to the half axis and then triggers a knife or shear.

I should demure to Peter Nach. as he is the motion guru in here, but cos I can't resist getting in first ;

1. Single axis is fairly self expalantory. One motion planner, one encoder feedback, and one motor being controlled to postion. These three things combined are called an "axis".

2. Axis and half. Same as above but now there are two encoder feedback channels. The extra one is used solely for either display purposes, or more commonly as a "master axis" that is then ratio'ed or geared, or cammed to the other "slave axis".

3. Multi-axis. Simply extends the single axis concept to as many "axis'" as the system supports....typically 8,16 or 32. In this case the system usually supports complex gearing motions between mulitple axis, allowing interpolated, circular, and helical motions to be generated. Usually any axis may be configured a Master or Slave.

Some systems support an axis type called "Imaginary" that have a motion planner only, ie no feedback or motor output. These are useful for complex gearing systems.

axis and a half = electronic gearing ?

Thank you for your responses, Gentlemen. SO if I understand correctly, for every [insert ratio here] tick of the master encoder (half-axis), the slave axis will follow by one tick. It's the electronic equivalent of mechanical gears. Hence, electronic gearing! Is this correct?

Yup you are on to it.

Although there is one fascinating difference between mechanical gearing and electronic gearing, and it becomes very obvious when you set up a trial system.

Whereas a mechanical system will transfer torque in both directions, ie Shaft A drives Shaft B and vice versa, and electronic system is uni-directional..ie Shaft A will drive Shaft B, but NOT vice versa.

The ratio between the master half axis and the slave full axis can be what ever ratio you want. Not just one to one.
This is often necessary because the master axis is normally a quadrature encoder but the slave full axis can be almost anything. Many of our customers gear to a feed chain and the slaves are hydraulic cylinders that are slaves to the feed chain encoder.

It is also possible to have the gear ratio change on-the-fly. This must be done smoothly or the slaves will jerk when the gear ratios change.

Some controllers will allow you to program a table and make an elecronic cam with the same setup.