Galil Motion Control DMC-42 0 Series, User Manual

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The “t” value is entered in samples, which will depend on the TM setting. With the default TM of 1000, one sample
is 976us. This means that a “t” value of 1024 will yield one second of motion. The velocity value, “v” will always be
in units of counts per second, regardless of the TM setting. PVT mode is not available in the “-FAST” version of the
firmware. If this is required please consult Galil.
Command Summary – PVT
COMMAND DESCRIPTION
PVa = p,v,t Specifies the segment of axis 'a' for a incremental PVT segment of 'p' counts, an end speed
of 'v' counts/sec in a total time of 't' samples.
_PVa Contains the number of PV segments available in the PV buffer for a specified axes.
BT Begin PVT mode
_BTa Contains the number PV segments that have executed
PVT Examples
Parabolic Velocity Profile
In this example we will assume that the user wants to start from zero velocity, accelerate to a maximum velocity of
1000 counts/second in 1 second and then back down to 0 counts/second within an additional second. The velocity
profile would be described by the following equation and shown in Figure 6.15.
To accomplish this we need to calculate the desired velocities and change in positions. In this example we will
assume a delta time of ¼ of a second, which is 256 samples (1024 samples = 1 second with the default TM of 1000).
Velocity(counts/second) Position(counts)
1000 ) 1 ( 1000 ) (
2
   
t t v
dt t t p ) 1000 ) 1 ( 1000 ( ) (
2
   


) 25 (. v
437.5
p (0 to .25) = 57

) 5 (. v
750
p (.25 to .5) = 151

) 75 (. v
937.5
p (.5 to .75) = 214

) 1 ( v
1000
p (.75 to 1) = 245

) 25 . 1 ( v
937.5
p (1 to 1.25) = 245

) 5 . 1 ( v
750
p (1.25 to 1.5) = 214

) 75 . 1 ( v
437.5
p (1.5 to 1.75) = 151

) 2 ( v
0
p (1.75 to 2) =57
Chapter 6 Programming Motion ▫ 83 DMC-42x0 User Manual
Figure 6.15: Parabolic Velocity Profile
1000 ) 1 ( 1000 ) (
2
   
t t v
Desired Velocity Profile
0
200
400
600
800
1000
1200
0
0.
25
0.
5
0.
75
1
1.
25
1.
5
1.
75
2
Time(Seconds)
V
e
lo
ci
ty
(c
o
u
n
ts
/s
ec
o
n
d
)
Velocity