This article might be helpful for you:

http://findarticles.com/p/articles/mi_m3101/is_n10_v67/ai_16...

Here's the relevant part on w axis, but you'll probably have to read the whole article:

"Figure 1 illustrates a horizontal spindle version of a 5-axis machine where an A-axis rotary table is mounted on top of a B-axis rotary table. The 5 axes are identified as X,Y,Z,A and B, where A and B move the part in the rotational axes and X,Y and Z move the cutter in the linear axes. In this arrangement of axes, the tool's center line relationship to the X and Y axes does not change relative to the position of the A and B axes.
...
Figure 5 represents a machine where the Z axis (typically a quill) is pivoted with the A and B axes. This allows the Z-axis movement to follow the tools' center line greatly simplifying the Z-axis feed functions. In this case a tool center line move is programmed as a simple Z-axis move regardless of the A and B axes position. This configuration is popular with users who drill a lot of holes at compound angles in the workpiece. ***On machines equipped with a spindle quill axis plus a Z axis, the quill axis is usually designated the W axis.***"

And 全軸リニアスケールフィードバック will be linear scale feedback on all axis, just like here:

"Heckert has Renishaw probes (part probe and tool probes), lift-up chip conveyor, a full fourth-axis and ***linear scale feedback on all axis***-so many features and benefits that it cannot be contained in this article."

http://www.ipnews.com/archives/general_editorials/dec04/SE_C...

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Note added at 2 hrs (2007-12-18 03:19:33 GMT)
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"The Cincinnati FTV Series

X Axis 1220-3700 mm
Y Axis 635-1000 mm
Z Axis 670-800 mm
Fifth axis capability.

Rapid XYZ 40 m/min
Spindle Power 18.5-42 kw
Spindle Speed 5000-12500 rpm
***Linear scale feedback standard on all axis.***

http://www.blsystems.com.au/alltimecnc/cincinnati_machine.ht...


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Note added at 2 hrs (2007-12-18 03:30:07 GMT)
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One more note and correction:

the plural of "axis" is "axes", so it should be "linear scale feedback on all axes", as it is here and on several other sites (google it):

"Linear scale feedback on all axes giving accuracy on all axes of 0.020mm and 0.015mm repeatability"

http://www.asquithbutler.com/horizontal-milling-machine-tool...

Sorry for the mistake.