Is there any tool or plugins to turn arc or curve to line segments?
It seems my CAM tool can only feed line segments.

I don't know of a tool that can perform the process on a whole drawing at once, but if you've only got a small number to deal with, there is a simple manual approach:

1) Select the arc or curve
2) Convert to path (not required if you've already got a path, but needed for arcs, ellipses, circles, etc.)
3) Switch to node tool
4) CTRL-A to select all the nodes
5) Repeatedly press the INSERT key on your keyboard to add new nodes until you think there are enough of them to do a good job of representing the line
6) All the nodes should still be selected. Click the "Make segments lines" button in the tool control bar

See 'Extensions > Modify Path > Flatten bezier'.

Inkscape's 'HPGL' output file format also can flatten curves (the manual documents 0.48; the output extension has slightly changed (enhanced) in 0.91).

thanks all!!
problem solved!