tcc.mov.fullSlew Namespace Reference

Functions
def	fullSlew
	Compute a jerk-limited trapezoidal slew. More...

Function Documentation

def tcc.mov.fullSlew.fullSlew	(		pA,
			vA,
			pB,
			vB,
			tJerk,
			vMax,
			aMax
	)

Compute a jerk-limited trapezoidal slew.

Inputs:

Parameters

[in]	pA	dp position of starting point at time t = 0 (deg)
[in]	vA	dp velocity of starting point at time t = 0 (deg/sec)
[in]	pB	dp position of ending point at time t = 0 (deg)
[in]	vB	dp velocity of ending point at time t = 0 (deg/sec)
[in]	tJerk	dp sets maximum allowed jerk and minimum slew duration (deg/sec^3) (see Details for more information)
[in]	vMax	dp maximum allowed |velocity| (deg/sec)
[in]	aMax	dp maximum allowed |acceleration| (deg/sec^2)

Returns

pvtList: a list of approximately 8 PVTs; the time of the first one is 0

Exceptions

RuntimeError

if cannot compute a slew

Warning

: |vA| must be <= vMax, |vB| must be some margin less than vMax. See tcc.mov.trapSlew for details.

Details: tJerk sets the maximum jerk and minimum duration of slew as follows:

• jmax = tJerk/aMax
• minimum duration of slew = tJerk

Here is how the subroutine works:

First a trapezoidal slew is computed, with several special characterstics:

• it begins a short time ("tJerk / 2") after 0
• the duration of its constant-velocity segment is at least "tJerk"
• the maximum possible acceleration ("aMax") is used for both constant acceleration segments.

The resulting trapezoidal slew is then "rounded" to give jerk limiting, as follows:

• Rounding extends for a time (tJerk / 2) (or less if required) symmetrically to both sides of each trapezoidal slew node.
• The rounded segments are paths of constant jerk. This process does not affect the total area under the v vs. t curve, hence the total distance travelled remains unchanged.

Trapezoidal slews, and possibly jerk-limiting, are discussed further in my orange notebook.

Note: most of the equations used below are less algebraically straightforward than is possible. They have been processed to reduce accumulated error and limit the number of intermediate variables. For example, expressions such as j = a / dt are used to eliminate explicit reference to jerk.

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

Definition at line 9 of file fullSlew.py.