tcc.mov.trapSlew Namespace Reference

Classes
class	TrapSlewData
	Data returned by trapSlew. More...

Functions
def	trapSlew
	Compute a trapezoidal slew. More...

Variables
list	__all__ = ["trapSlew"]
float	Fudge = 1.05

Function Documentation

def tcc.mov.trapSlew.trapSlew	(		rBAi,
			vA,
			vB,
			dt2min,
			vMax,
			aMax
	)

Compute a trapezoidal slew.

You may specify a minimum duration for the constant-velocity segment, which is useful for "rounding the corners" of the slew to make it jerk-limited (see mov.fullSlew).

Parameters

[in]	rBAi	distance between "A" and "B" at time t = 0 (deg)
[in]	vA	velocity of "A" (deg/sec)
[in]	vB	velocity of "B" (deg/sec)
[in]	dt2min	minimum duration of segment 2 (constant velocity) (sec)
[in]	vMax	maximum allowed velocity (deg/sec)
[in]	aMax	maximum allowed acceleration (deg/sec^2)

Returns

a TrapSlewData

Exceptions

RuntimeError

if: dt2min < 0 vMax <= 0 aMax <= 0 |vB| > vMax / Fudge

Dies if vMax or aMax are so small as to cause under- or over-flow.

Details: The magic number "Fudge" is used to avoid borderline cases. It is set below, and should be a number a bit bigger than one.

How it works: The slew begins by tracking object A, and ends by tracking object B. Both objects are assumed to be moving at constant velocity.

A trapezoidal slew has three segments, two of constant acceleration separated by a constant velocity segment. It is called "trapezoidal" because that is the shape of the v vs. t curve.

Here are the initial velocity and constant acceleration for each segment, and the duration of that segment, in the notation of this subroutine:

segment v a duration 1 vA a1 dt1 2 vP 0 dt2 3 vP a2 dt3

The slew numbering and notation used in this subroutine are quite different than those used in the math notebook. Significant changes include: dt2 = delta-t3 in notebook slew type 0 is not mentioned in the notebook slew type 1 = notebook type 0 slew type 2 = notebook type 1 slew type 3, 4 = notebook type 3 note that the notebook type 2 slew (the only "reversed" slew) is NOT USED by this subroutine, because it is not needed, and it saves the bother of implementing the reversed slew equations; instead, a type 3 or 4 slew (this subr.) is used with reduced acceleration.

References: "Control of the Apache Point 3.5m Telescope: Slewing", R. Owen, 1990, unpub

TCC Math Notebook, section on slewing (warning: different notation)

History: 2013-12-06 ROwen Converted from mov_TrapSlew.for

Definition at line 48 of file trapSlew.py.

Variable Documentation

list tcc.mov.trapSlew.__all__ = ["trapSlew"]

Definition at line 8 of file trapSlew.py.

float tcc.mov.trapSlew.Fudge = 1.05

Definition at line 10 of file trapSlew.py.