TMC 188/40 Motion Control Module
Appendix D: Application Notes
Delta Computer Systems, Inc. 360/254-8688
101
Acceleration and Deceleration Modes
The Motion Control Module defaults to expressing acceleration and deceleration in ramping distance.
A value of 2000 in the acceleration field represents a ramp length of 2 inches. By setting bit 16 of the
Mode word to 1, acceleration can be expressed in inches/sec
2
. Generally, expressing acceleration
as a ramp distance is easier if two or more axes must move together in coordination but not at the
same speed or distance. Otherwise, expressing the acceleration in inches/sec
2
is easier. The
drawback to using the distance method is that the acceleration and deceleration distance must
change every time the speed changes, if the rate is to be constant. The relationship between the rate
and the distance is:
Rate = ( Speed x Speed ) / ( 2000 x Distance )
or
Distance = ( Speed x Speed ) / ( 2000 x Rate )
These calculations are not difficult, but by expressing the acceleration and deceleration as a rate the
Motion Control Module will calculate the ramp distances. The distance mode is for applications such
as headrigs or x-y positioning devices, where you want two different axes to move to new positions
and arrive at the same time even though they must move different distances. For example, assume
an x-y plotter at position 0,0. Now assume you want to move straight to position 4,3. To do this set
the x axis' speed, acceleration, and deceleration distance. Now use 3/4 of the x speed for the y
speed and do likewise for the y ramps. The parameters might look like this:
X Y
------ -----
ACCEL 2000 1500
DECEL 2000 1500
SPEED 12000 9000
REQ POS 4000 3000
The two axes will draw a straight line between 0,0 and 4,3.
