Chapter 4
CIP Axis Attributes
440
Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018
Proving is enabled, the mechanical brake must be set as soon as the drive is
disabled. When the brake is under the control of the axis state machine this is
automatic. But when controlled externally, failure to set the brake when the drive
is disabled can cause a free fall condition on a vertical application.
When enabled, the drive performs a Torque Prove test of the motor current while
in the Starting state to "prove" that current is properly flowing through each of the
motor phases before releasing the brake. Should the Torque Prove test fail, a
Motor Phase Loss exception is generated.
While Torque Proving functionality is applicable to drive Control Modes that are
not capable of generating reliable holding torque based on a feedback device, such
as Frequency Control and Sensorless Velocity Control, Torque Proving should
not be used in these modes for applications where holding torque is critical to safe
operation, such as in a typical lift or crane application.
If the optional Brake Test Torque attribute is supported, the Torque Prove test
also includes a proactive Brake Test to ensure the mechanical brake is functioning
properly. Should the Brake Test detect brake slip, a Brake Slip exception is
generated.
When Proving is enabled, the drive also performs a Brake Prove test while in the
Stopping or Aborting states to "prove" proper mechanical brake function before
the drive power structure is disabled. Should the Brake Prove test detect brake slip
a Brake Slip exception is generated.
Unless another vendor specific method is used to address a Brake Slip condition in
the Stopping or Aborting state, the appropriate Fault Action for the Brake Slip
exception is Torque Limited Stop and Hold. This Fault Action applies holding
torque to arrest the brake slip and transitions the axis to the Major Faulted state.
In general, Brake Proving functionality is only applicable to drive Control Modes
that are capable of generating holding torque based on a feedback device. Brake
Proving is therefore not applicable to Frequency Control or Sensorless Velocity
Control modes.
When Proving is enabled, and the Auto-Sag feature is supported, upon detection
of a brake slip condition, the drive has the capability of safely lowering the load to
the ground in a controlled series of increments. The Auto Sag Configuration
attribute is used to enable this feature. In addition to Brake Slip initiating a Brake
Slip exception, the drive also generates a Brake Malfunction start inhibit when the
Auto Sag feature is enabled.
When Proving, Auto Sag, and Auto Sag Start are all enabled, the drive also
monitors for brake slip in the Stopped or Faulted states. If brake slip is detected,
the drive power structure is automatically started to arrest the slip allowing the
Auto Sag function to safely lower the load to the ground. Upon detection of brake