Look-ahead

Gentlemen:
I'm sure some of you have experience in the design of CNC controllers
so I wonder if you could elaborate on just what "look-ahead" means
and what its benefits are.

I am making a 3 axis CNC controller, DOS based, for my own amusement
and would like to have smoother operation at high speeds with some of
these programs which consist exclusively of short, straight line
approximations. High speeds are defined as 100 IPM and above, with
the smallest increment of motion being .001". My accel and decel
cause slowdown between blocks since my cornerspeed is set at about 30
IPM.

As I see it, the factors effecting the slowdown speed between blocks
are: 1) the angle between adjacent line segments, 2) the length of
successive line segments, 3)radius of an arc which follows a str line,
4)the length of the arc, and no doubt there are more factors.

As to how to handle the setting of speed between segments, it seems
to me that one can either 1) pre-process the data setting in the
calculated minimum speed or 2) do the calculations between reading
the blocks. The second alternative would seem to slow down things
too much!

I would appreciate hearing from all of you who have experience and
ideas along this line. Thank you

Jack C. Cain jccinc@...