HCTL-1100 Datasheet, PDF (33/40 Pages) Agilent(Hewlett-Packard) – General Purpose Motion Control ICs

The conversion from rpm to
quadrature counts/sample time is
shown in equation 9. The
Command Velocity register
(R3CH) contains only integer data
and has no fractional component.
While the overall range of the
velocity command is 8 bits, two’s-
complement, the difference
between any two sequential
commands cannot be greater than
7 bits in magnitude (i.e., 127
decimal). For example, when the
HCTL-1100 is executing a
command velocity of 40H
(+64D), the next velocity com-
mand must fall in the range of
7FH (+127D), the maximum
command range, C1H (-63D), the
largest allowed difference.
The command acceleration is a
16-bit scalar word stored in R27H
and R26H. The upper byte
(R27H) is the integer part and the
lower byte (R26H) is the
fractional part provided for
resolution. The integer part has a
range of 00H to 7FH. The
contents of R26H are internally
divided by 256 to produce the
fractional resolution.
Ar = Acceleration in rpm/sec
N = 4 times the number of slots
in the codewheel (i.e.,
quadrature counts)
t = The HCTL-1100 sample time
in seconds. (See the section on
the HCTL-1100’s Sample Timer
register).
Because the Command Accelera-
tion registers (R27H and R26H)
are internally interpreted by the
HCTL-1100 as 8 bits of integer
and 8 bits of fraction, the host
processor must multiply the
desired command acceleration (in
quadrature counts/[sample time]²)
by 256 before programming it
into the HCTL-1100’s Command
Acceleration registers.
Internally, the controller performs
velocity profiling through position
control.
Each sample time, the internal
profile generator uses the
information which the user has
programmed into the Command
Velocity register (R3CH) and the
Command Acceleration registers
(R27H and R26H) to determine
the value which will be automat-
ically loaded into the Command
Position registers (R0CH, R0DH,
and R0EH). After the new
command position has been
generated, the difference between
the value in the Actual Position
registers (R12-R13H, and R14H)
and the new value in the
Command Position registers is
calculated as the new position
error. This new position error is
used by the full digital compensa-
tion filter to compute a new motor
command output by this sample
time. The register block in Figure
3 further shows how the internal
profile generator works in
Integral Velocity mode. In control
theory terms, integral compensa-
tion has been added and there-
fore, this system has zero steady-
state error.
Although Integral Velocity Control
mode has the advantage over
Proportional Velocity mode of
zero steady state velocity error,
its disadvantage is that the closed
R27H
R26H
0IIIIIII FFFFFFFF/256
Command Acceleration Format
The units of acceleration are
quadrature counts/sample time
squared.
To convert from rpm/sec to
quadrature counts/[sample time]²,
use the formula shown below:
Aq = (Ar)(N)(t²)(0.01667/rpm-
sec)
[10]
Where:
Aq = Acceleration in quadrature
counts/[sample time]²
Figure 13. Integral Velocity Modes.
33