mc1451a-e ETC-unknow, mc1451a-e Datasheet - Page 26

• Manufacturer Part Number: mc1451a-e
• Description: Advanced Brushless Motor Control Chipset
• Manufacturer: ETC-unknow

into the legal travel range before a positive over travel switch will
be recognized.
Motion Error Detection and Recovery
Under certain circumstances, the actual axis position may differ from
the target (desired) axis position by an excessive amount. Such an
excessive position error often indicates a potentially dangerous
condition such as motor or encoder failure, or excessive mechanical
friction.
To detect this condition, thereby increasing safety and equipment
longevity, the MC1231A includes a programmable maximum position
error.
The maximum position error is set using the command
SET_POS_ERR, and read back using the command GET_POS_ERR.
To determine whether a motion error has occurred the maximum
position error is continuously compared against the actual position
error. If the maximum position error value is exceeded, then the axis is
said to be in "motion error". When this occurs the motion error bit in the
axis status word is set, and the axis motor may be turned off,
depending on the state of the automatic motor shutdown mode (see
SET_AUTO_STOP_ON and SET_AUTO_STOP_OFF host command
descriptions).
At the moment motion error occurs several events occur
simultaneously. The following list describes these events:
If the automatic motor stop mode is not set than only the motion error
status bit is set.
Recovering From A Motion Error
To recover from a motion error which results in the motor being turned
off, the following sequence should be performed:
1)
2)
After the above sequence, the axis will be servoing correctly, and the
profile generator will be at rest, ready for another move.
-
-
-
Determine cause of motion error and correct problem (this may
require human intervention).
Turn motor on using MTR_ON command.
Motion Error bit of the axis status word is set
If automatic motor stop is enabled the motor is set off (set to
open loop control mode)
If the automatic stop is enabled the trajectory generator is
stopped
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Servo Loop Control & Timing
Each of the axes on the MC1231-series chipsets can be individually
enabled or disabled *. Each enabled axis receives a "time slice" of the
available computation power of the CP chip.
Disabled axes do not use any computing power; thus it is possible to
increase the servo loop rate when less than the supported number of
axes are used.
To set the servo loop rate to a value other than the default value, use
the command SET_SMPL_TIME. The value GET_SMPL_TIME can be
used to read this value back from the chipset.
The formula for determining the minimum loop time (maximum
sampling frequency) for a given number of enabled axis is 135 uSec for
each enabled axis.
The following table summarizes the minimum loop time for the
standard and -P parts.
# Axes
enabled
2
1
The loop time is specified to the chip set as an integer number from 1 to
32,767 with units of 135*** uSec For example to set the standard
MC1231A part for the minimum loop time with two axes enabled, a
value of 4 (4*135 = 540 uSec) would be sent to the chipset using the
SET_SMPL_TIME command.
Changing the loop time to increase servo loop rate when axes are
disabled is not required. It is available as an option if greater loop
speed is desired.
The servo loop rate should generally not be changed while axes
are in motion.
It is the responsibility of the host to insure that the servo loop rate
that is commanded can be supported for the # of axes enabled.
Failure to observe the maximums specified in the above table may
result in unexpected axis behavior.
* actual value = 542.72 uSec, 540 is an approximation
** actual value = 271.36 uSec, 270 is an approximation
*** actual value = 135.68 uSec, 135 is an approximation
* This is true even for the MC1131A, which has only one
axis, although generally disabling the only axis has no utility.
Minimum time
540*
270**