User`s manual

7-38 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual – January 2001 GFK-1742A
7
t
v
Actual
Profile
Desired
Profile
Other Programmed Motion Considerations
The following examples are not complete programs. For example, in many cases the
PROGRAM
and ENDPROG
statements are not shown. These statements (in correct context) would need to be
added to make the program compile successfully.
Maximum Acceleration Time
The maximum time for a programmed acceleration or deceleration is 131 seconds. If the time to
accelerate or decelerate is computed to be longer than this time, the DSM314 will compute an
acceleration to be used based on 131 seconds. To obtain longer acceleration times, multiple
CMOVEs with increasing or decreasing velocities must be used.
Example 15: Maximum Acceleration Time
The following two program examples are only valid for a DSM314 using a 2ms position loop
update time. They show a hypothetical problem with a very long acceleration time in Example1,
and a possible solution in Example 2. In Example 1 below, 240 seconds is required to reach the
programmed velocity of 24,000 at an acceleration rate of 100 (24000
÷
100 = 240). Since this is
greater than the DSM’s limit of 131 seconds per acceleration or deceleration, the DSM will
calculate a value within its limit. In this case, the DSM calculates that to reach a velocity of
24,000 in 131 seconds, an acceleration of 183 would be required. The Example 1 solid line
velocity profile shows the higher (183) acceleration rate used by the DSM. The dashed line
profile in that drawing indicates the desired (programmed) acceleration rate and velocity profile
that could not be attained.
ACCEL 100
VELOC 24000
PMOVE 8000000, INCR, LINEAR
Figure 7-18. Maximum Acceleration Time Example 1
One solution (which requires some extra calculations) for obtaining a low acceleration for a long
period of time breaks a move up into separate continuous moves (using CMOVE commands), with
each move’s acceleration time being less than 131 seconds. In the problem introduced in
Example 1, the programmed move would require 240 seconds each for acceleration and
deceleration. We can easily see that if we divide this time in half, by using two moves whose
acceleration or deceleration times are each 120 seconds, we would be within the DSM’s limit of
131 seconds. This scheme is used in the following example.