MC33991DW View Datasheet(PDF) - Freescale Semiconductor
Part Name
Description
Manufacturer
MC33991DW Datasheet PDF : 36 Pages
| |||
TIMING DESCRIPTIONS AND DIAGRAMS
DEVICE FUNCTIONAL DESCRIPTION
Table 16. Coil Step Value
20
300
-0.866
-
222
21
315
-0.707
-
181
22
330
-0.5
-
128
23
345
-0.259
-
66
Notes * Denotes Normalized Values.
The motor is stepped by providing index commands at
intervals. The time between steps defines the motor velocity,
and the changing time defines the motor acceleration.
The state machine uses a table defining the allowed time
steps, including the maximum velocity. A useful side effect of
the table is, it also allows the direct determination of the
position the velocity should reduce to allow the motor to stop
at the desired position.
The motor equations of motion are generated as follows:
The units of position are steps, and velocity and
acceleration are in steps/second, and steps/second²
From an initial position of 0, with an initial velocity u, the
motor position, s at a time t is
s
=
ut
+
1
2
at
2
For unit steps, the time between steps is:
⇒ t = − u + u 2 + 2a
a
This defines the time increment between steps when the
motor is initially travelling at a velocity µ. In the ROM, this time
is quantized to multiples of the system clock by rounding
upwards, ensuring acceleration never exceeds the allowed
value. The actual velocity and acceleration is calculated from
the time step actually used.
Using
DE
0.5
+
B5
0.707
+
80
0.866
+
42
0.966
+
128
80
181
B5
222
DE
247
F7
v 2 = u 2 + 2as
and
v = u + at
and solving for v in terms of u, s and t gives:
v
=
2
t
−u
The correct value of t to use in this equation is the
quantized value obtained above.
From these equations, a set of recursive equations can be
generated to give the allowed time step between motor
indexes when the motor is accelerating from a stop to its
maximum velocity.
Starting from a position p of 0, and a velocity v of 0, these
equations define the time interval between steps at each
position. To drive the motor at maximum performance, index
commands are given to the motor at these intervals. A table
is generated giving the time step ∆t at an index position n.
p0 = 0
∆t n
=
⎡
⎢
−
v n−1
+
⎢
⎢
v
2
n −1
v+02a=
⎥⎤0
a
⎥
⎥ , where
⎡
⎤
indicates
rounding up.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33991
21
Share Link: 