Operation
54
Atlas
®
Digital Amplifier Complete Technical Reference
4
To set the PWM limit value the command
SetDrivePWM
is used. To read this value back the command
GetDrivePWM
is used.
4.6.2
Disabling the Power Stage
During normal operation the Atlas unit’s primary function is to drive the motor at the torque or voltage requested by
the external controller. However there are a number of circumstances where it may be desirable to disable the power
stage. In particular, the power stage may be disabled if certain safety-related conditions occur, or for system calibration.
See
Section 4.8, “Safety Processing Functions”
for more information on Atlas safety processing.
If the power stage module is disabled, all external controller-provided voltage or torque commands are ignored, and
all bridge FETs are turned off. This has the effect of “free-wheeling” the motor, which means the motor may stop,
coast, or even accelerate (if a constant external force exists such as a gravitational load) depending on the load, inertia,
and configuration of the axis mechanics.
To disable the power stage module the command
SetOperatingMode
is used. The value set using this command can
be read using
GetOperatingMode
.
The default condition of the power stage is disabled. Therefore to begin drive operations, a
SetOperatingMode
command must be sent to enable the drive stage module.
4.6.3
Enabling the Power Stage
A previously disabled power stage module may be re-enabled in a number of ways. If output was disabled using the
SetOperatingMode
command, then another
SetOperatingMode
command may be issued. If this module was
disabled as part of an automatic safety event-related action (see
Section 4.8.9.3, “Current Foldback Event Processing”
for more information), then the command
RestoreOperatingMode
is used.
To read the instantaneous actual state of the operating mode the command
GetActiveOperatingMode
is used.
Regardless of how the module is re-enabled, at the time that the re-enable operation is requested, the power stage
module will begin normal operations within approximately 1.0 milliseconds. Care should therefore be taken to re-
enable the power stage when the motor axis is in a stable condition such that no abrupt motion occurs.
The programmed drive limit value affects the PWM duty cycle only. It does not limit the effective current that is
delivered to the motor. To explicitly limit the current, the current foldback mechanism can be used. See
for more information.
If Atlas is in a condition where the current loop module also needs to be re-enabled, both the power stage and
the current loop module should be enabled at the same time. This is normally the case when recovering from all
safety processing conditions. See
Section 4.8, “Safety Processing Functions”
for more information.
It is the responsibility of the user to manage the operation of the power stage so that appropriate safety conditions
are maintained at all times.