Stopping and Braking Attributes

These are the active stopping and braking related attributes associated with a Motion Control Axis.

AC Injection Brake Frequency Threshold

Value that sets the frequency that initiates the transition from AC injection braking to DC injection braking when executing an “AC Injection Brake” Stopping Action. When the output frequency drops below this threshold during the braking operation, the transition from AC injection braking to DC injection braking occurs.

AC Injection Brake Power Threshold

Value that adjusts the drive’s internally defined power threshold that initiates the transition from AC injection braking to DC injection braking when executing an “AC Injection Brake” Stopping Action. When the output power level drops below this threshold during the braking operation, the transition from AC injection braking to DC injection braking occurs. A value of 100% results in the drive using 100% of its internally defined power threshold when checking for this transition condition.

AC Injection Brake Regulator Ki

Value that sets the proportional gain of the regulator that controls the output frequency applied to the motor based on the DC bus voltage when executing an “AC Injection Brake” Stopping Action.

AC Injection Brake Regulator Kn

Value that sets the proportional gain of the regulator that controls the output frequency applied to the motor based on the DC bus voltage when executing an “AC Injection Brake” Stopping Action.

AC Injection Brake Regulator Kp

Value that sets the proportional gain of the regulator that controls the output frequency applied to the motor based on the DC bus voltage when executing an “AC Injection Brake” Stopping Action.

Stopping Action

When disabling or aborting an axis, through a Disable Request or an Abort Request this value determines the stopping method to apply to the motor. Each supported Stopping Action initiates one of three Stopping Sequences (IEC60204-1 Category Stops 0, 1, and 2).

In either final state the device's inverter power structure will either be Disabled (Disable selection) and free of torque or actively held (Hold selection) in a static condition. This attribute has no impact or relationship to the planner generated acceleration and deceleration profiles. This attribute does not, in any way, determine the stopping actions applied in response to fault conditions.

Connection Loss Stopping Action

When a CIP Motion connection loss is detected, this value determines the stopping method to apply to the motor. Each supported Stopping Action initiates the associated Stopping Sequence (IEC60204-1 Category Stops 0, 1, and 2). If the connection is closed intentionally using a Forward Close service, the selected stopping method is applied while in the Stopping state and the final state after the stopping method completes is the Initializing state. If the connection is unintentionally lost and the resulting Node Fault generated (Node Fault Codes 1 or 6), the selected stopping method is applied while in the Aborting state and the final state after the stopping method completes is the Major Faulted state. In either final state the device’s inverter power structure will either be Disabled (Disable selection) and free of torque or actively held (Hold selection) in a static condition.

Stopping Action Enumeration Definitions

Stopping Torque

When disabling or aborting an axis, this value determines the maximum amount of torque producing current available to stop the motor when the Stopping Action is set to Current Decel. If this attribute is not supported, the drive device will use the configured Positive and Negative Peak Current Limits.

Stopping Time Limit

When disabling or aborting an axis, this parameter determines the maximum amount of time the drive allows to reach zero speed as part of the Category 1 or Category 2 Stop sequence. Action taken by the drive once the time limit is reached depends on the Stop Category. For a Category 1 Stop, the drive continues to apply Stopping Torque while engaging the brake. For a Category 2 Stop the drive continues to apply Stopping Torque but does not engage the brake. If Stopping Time Limit is not supported a factory set timeout may be applied.

Coasting Time Limit

When disabling or aborting an axis, this parameter determines the maximum amount of time the drive allows to reach zero speed as part of the Category 0 "Disable and Coast" Stop sequence. Action taken by the drive if the time limit is reached is to engage the brake and advance to the Stopped state. If this attribute is not supported, the Coasting Time Limit applies the Stopping Time Limit value. If Stopping Time Limit is not supported a factory set timeout may be applied.

Resistive Brake Contact Delay

When an external resistive brake is used, an external contactor switches the UVW motor leads from the inverter power structure to an energy dissipating resistor to stop the motor. This switching does not occur instantaneously and enabling the power structure too early can cause electrical arcing across the contactor. To prevent this condition, the Resistive Brake Contact Delay can be set to the maximum time that it takes to fully close the contactor across the UVW motor lines so when the axis is enabled, the inverter power structure is not enabled until after the Resistive Brake Contact Delay Time has expired. Resistive Brake operation is only applicable to PM Motor types.

The following sequence further defines how the Resistive Brake Contact Delay factors into the overall Enable Sequence that may also include the operation of a Mechanical Brake. Note that the Resistive Brake Contact Delay and the Mechanics Brake Release Delay attributes apply even if there is no external contactor or mechanical brake connected to the drive.

Enable Sequence:

Mechanical Brake Control

The Mechanical Brake Control attribute governs the operation of the Mechanical Brake Output of the drive. The Mechanical Brake Output controls the mechanical brake mechanism. When set to Automatic, the Mechanical Brake is under the control of the axis state machine. The Mechanical Brake Engage Delay and Mechanical Brake Release Delay attributes describe the sequencing for the brake. To release the brake, set the brake to Brake Release. The axis state machine releases control of the brake.

Mechanical Brake Release Delay

When enabling the axis with an engaged mechanical brake, the Mechanical Brake Release Delay value determines the amount of time the drive shall delay transition from the Starting state to the Running or Testing states. This delay prevents any commanded motion until the external mechanical brake has had enough time to disengage. If supported, a Torque Proving operation is included in this sequence prior to releasing the brake. Note that the Resistive Brake Contact Delay and the Mechanical Brake Release Delay attributes apply even if there is no external contactor or mechanical brake connected to the drive.

Enable Sequence:

Mechanical Brake Engage Delay

When disabling the motion axis using a Category 1 Stopping Action, the Mechanical Brake Engage Delay value determines the amount of time the device power structure will remain enabled after the axis has decelerated to standstill. This attribute allows time for an external mechanical brake to engage. The configured Stopping Action determines the type of stopping sequence applied. If supported, a Brake Proving operation is included in the Category 1 stopping sequence prior to disabling the power structure. Note that the Mechanical Brake Release Delay attribute applies even if there is mechanical brake connected to the drive.

Zero Speed

This attribute sets the speed threshold associated with the zero speed criteria of the stop sequence. Zero Speed is specified as a percent of motor rated speed. When Zero Speed Time attribute is supported, this attribute sets the speed threshold where the zero speed timer starts. When the axis speed has been below the Zero Speed threshold for Zero Speed Time the axis has satisfied the zero speed criteria. In all but Category 2 stops, this results in action to engage the mechanical brake. If this attribute is not supported, the zero speed threshold is left to the vendor’s discretion and typically set to 1% of motor rated speed. Axis speed in the above description is based on the Velocity Feedback signal, or in the case of a Frequency Control drive, axis speed is based on Velocity Reference signal.

When supporting a Load Observer, the zero speed criteria is not based on the Velocity Estimate since that signal can differ considerably from the actual speed of the motor. When the Load Observer is configured to apply the Velocity Estimate to the velocity loop summing junction as Velocity Feedback, the zero speed criteria must be based on the velocity feedback signal input to the Load Observer.

Zero Speed Time

This attribute sets the amount of time that the axis speed must be below the zero speed threshold, set by the Zero Speed attribute or established by the drive vendor, before satisfying the zero speed criteria. In all but Category 2 stops, when this attribute is set it results in action to engage the mechanical brake. If this attribute is not supported, the amount of time needed to satisfy the zero speed criteria is left to the vendor’s discretion and typically is immediate (0). Axis speed in the above description is based on the Velocity Feedback signal, or in the case of a Frequency Control drive, axis speed is based on Velocity Reference signal.

When supporting a Load Observer, the zero speed criteria is not based on the Velocity Estimate since that signal can differ considerably from the actual speed of the motor. When the Load Observer is configured to apply the Velocity Estimate to the velocity loop summing junction as Velocity Feedback, the zero speed criteria must be based on the velocity feedback signal input to the Load Observer.

Vertical Load Control

This enumerated value allows the drive to tailor motor control behavior for vertical load applications. When the Enabled enumeration is selected, the drive attempts, whenever possible, to avoid applying Category 0 stop actions in response to Major Fault conditions. The drive may tailor other aspects of its behavior to best handle vertical loads.

Proving Configuration

This attribute enables the operation of the drive's Torque Proving and Brake Proving functions that work in conjunction with mechanical brake control. When 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 slip, a Brake Slip exception is generated along with a Brake Malfunction start inhibit.

The sequencing of the torque and brake "prove" tests are described in detail by the Mechanical Brake Engage Delay and Mechanical Brake Release Delay attributes.

The Proving feature includes a number of optional Sub-Features, many of which depend on support of other Proving feature attributes. The following table defines these attribute dependencies.

Proving tests are performed when enabling or disabling the drive axis. During these state transitions a series of operations are performed by the drive to ensure the proper function of the motor (Torque Proving) and the brake (Brake Proving).

Torque Prove Current

This attribute sets the percent of motor rated torque applied to the motor by the Torque Prove test as part of the Torque Proving function executed in the Starting state. The Torque Prove test applies current to the motor to "prove" that current is properly flowing through each of the motor phases before releasing the brake.

Brake Test Torque

This attribute sets the percent of motor rated torque applied to the motor by the Brake Test as part of the Torque Proving function executed in the Starting state. This Brake Test proactively tests the ability of the mechanical brake to hold the maximum anticipated load before releasing the brake and allowing operation. Should the Brake Test detect brake slip, a Brake Slip exception is generated.

If the Brake Test Torque attribute value is 0 the Brake Test is not performed in the Starting state.

Brake Prove Ramp Time

This attribute determines the amount of time the drive will take to ramp the applied torque of the motor down to zero during the Brake Proving test in the Stopping or Aborting state. The Brake Prove Ramp Time determines the ramp down rate of the applied torque output by dividing the Torque Limit by the Brake Prove Ramp Time. The Torque Limit in this case is the maximum of the configured Torque Limit Positive and Torque Limit Negative values. The Brake Prove test is performed to check for brake slip before the power structure is disabled.

Brake Slip Tolerance

This attribute determines the amount of brake slip allowed after the brake is engaged. If this tolerance is exceeded while the brake is engaged, a Brake Slip exception is generated. Brake slip can therefore be monitored in any axis state where the brake is engaged.

DC Injection Brake Current

The DC Injection Brake Current attribute defines the brake current level injected into an induction motor stator when DC Injection Brake is selected as the Stopping Action. This attribute is specified as a percent of motor rated speed.

DC Injection Brake Time

The DC Injection Brake Time attribute defines the amount of time that the DC brake current is injected into an induction motor stator when DC Injection Brake is selected as the Stopping Action. This attribute is specified in seconds.

Flux Braking Enable

The Flux Braking Enable attribute value determines if the drive device is to apply additional flux current to the induction motor in an effort to increase motor losses and reduce the deceleration time while in the Stopping state. This feature is useful when there is no Shunt Regulator or Regenerative Brake available.

Auto Sag Configuration

This attribute is used to enable the optional Auto Sag feature that, in the event of detected a brake slip condition, safely lowers the load to the floor in a series of controlled Auto Sag Slip Increments. When a brake slip condition is detected and Auto Sag is enabled, the drive not only sets the standard Brake Slip exception, but the drive also sets the Brake Malfunction start inhibit. This prevents the drive from restarting after the load has been safely lowered to the floor.

Auto Sag Slip Increment

This attribute sets the incremental amount of brake slip allowed by the drive's optional Auto Sag function before restoring holding torque. When brake slip occurs, the drive allows this amount of displacement and then automatically enables the power structure and applies holding torque to arrest the slip. The drive then ramps the motor torque to zero based on the Brake Prove Ramp Time while checking for slip. Should brake slip continue, the cycle repeats. In crane and lift applications, this repeating "Auto Sag" cycle is designed to lower the load in a controlled series of Auto Sag Slip Increments until the load reaches the ground.

Auto Sag Time Limit

This attribute sets the time limit over which the drive checks for brake slip as performed by the Auto Sag function before restoring holding torque. When brake slip occurs, the drive allows this amount of time before automatically enabling the power structure and applying holding torque. The drive then ramps the motor torque to zero based on the Brake Prove Ramp Time while checking for slip. Generally, in a brake slip situation, the Auto Sag Slip Time Limit expires when the load reaches the ground after one or more Auto Sag Slip Increment cycles. With no further slip occurring while the motor torque is ramping to zero, the Auto Sag feature transitions the axis to the Major Faulted state and the drive power structure is disabled.

The optional Auto Sag Slip Time Limit attribute is not required by the Auto Sag feature. If not supported, a vendor specific value for the Auto Sag Slip Time is applied, typically 0.25 seconds.

Auto Sag Start

When the Auto Sag Configuration attribute is set to Enabled, this attribute is used to enable the Auto Sag function in the Stopped or Faulted state. When Auto Sag Start is enabled, the drive monitors the load for possible brake slip and should the amount of brake slip exceed the Brake Slip Tolerance a Brake Slip exception is generated, along with a Brake Malfunction start inhibit. When this occurs, the drive power structure is enabled (Started) without holding torque and the axis transitions to the Aborting State. The drive continues to monitor brake slip and when the amount of slip exceeds the Auto Sag Slip Increment holding torque is applied to the motor to arrest the brake slip. The drive then ramps the motor torque to zero based on the Brake Prove Ramp Time while again checking for slip. Should brake slip continue and exceed the Auto Sag Slip Increment, holding torque is applied and the cycle repeats. In crane and lift applications, this repeating "Auto Sag" cycle is designed to lower the load in a controlled series of Auto Sag Slip Increments until the load reaches the ground.