SBC (Safe Brake Control)

Safe Brake Control description for drive option Functional Safety 2 or 3.

Description

The safety function SBC (Safe Brake Control) is used for controlling the brakes wired to X1, X2 or X4 of the AKD2G. The connected brake is engaged and released by switching both lines (BR+ and BR-).

  • The safety function SBC makes a motor with a motor brake suitable for the usage scenarios A1, A2, E1, E2, E3 according to DGUV.
  • The safety function SBC makes a motor with a motor brake and a second brake on the same axis suitable for the usage scenarios A1, A2, A3, E1, E2, E3 according to DGUV.
  • The brake can be configured with or without (➜ # 1, SDB (Safe Dynamic Brake)).
  • For requirements to the motor brakes refer to (➜ # 1, Motor Brake Requirements ).

Association of brake outputs to drive axes

Drive Type Brake 1 Brake 2 max. SBC Safety Level

Single Axis

Axis 1 (X1)

Axis 1 (X4)

Axis 1 : SIL3 / PLe

Single Axis

Axis 1 (X1)

Not used

Axis 1 : SIL2 / PLd

Single Axis

Not used

Axis 1 (X1)

Axis 1 : SIL2 / PLd

Dual Axes

Axis 1 (X1)

Axis 2 (X2)

Axis 1 : SIL2 / PLd
Axis 2: SIL2 / PLd

Dual Axes

Axis 1 (X1)

Axis 1 (X2)

Axis 1 : SIL3 / PLe
Axis 2 : no brake

To achieve SIL 3 / PLe for SBC,

  • two brakes per axis must be used. With one brake the axis can reach SIL 2 / PLd only.
  • the brake function must be tested periodically with SBT see "SBT (Safe Brake Test)"

Important Notes

Hoist and crane support: The drive will safely ensure a holding position, as long as SBC (braking ramp, delay time) is configured correctly.

  • Any brake must be connected to one of the SBC interfaces (X1, X2, X4).
  • The user is responsible for the execution of the safe brake test SBT SBT (Safe Brake Test).

For requirements to the motor brakes refer to Motor Brake Requirements .

Function Input / Output Variables

Inputs

  • SBC Delay: brake delay tSBC
  • SBC Muting:
  • can be used for enabling manual override of the brakes while STO is active.
  • muting can be activated by FSoE or safe digital inputs (must be mapped).
  • SBC Activate:
  • can be triggered by STO only without delay.
  • the trigger with delay depends on the configuration, with/without SDB.

Outputs

  • SBC Active: logical status of the SBC function
  • Safe Brake State: state of the brake outputs (24V or 0V)

Number of Instances

One instance per axis.

Test Pulses

Test pulses are applied to the Brake+ and Brake- outputs (X1, X2, X4) alternately to ensure valid feedback. The test pulses are 1ms at the bottom but are 3ms long due to their slow edges.

 

Activation

SBC for one or two brakes can be configured to be activated during STO process.

The controlled brake(s) can be configured to be engaged while motor torque is available (STO not active yet) or with STO became active (no motor torque).

The safety function can be configured with WorkBench or via FSoE.

Example:
STO activated by safe digital inputs, one axis, SIL3 PLe, SBC with two brakes, SBT, without SDB

Restart

The brakes controlled by SBC will disengage simultaneously with the deactivation of STO if AXIS#.SAFE.STO.REPORTFAULT is set to 0.

If AXIS#.SAFE.STO.REPORTFAULT is set to 1, the brake will release when the axis is enabled again. See STO Timing.

SBC Muting Function

SBC muting is critical with regards to safety and has important influence on the safety level of an application. It has to be ensured that the use of SBC muting has no negative impact on the required safety level within the complete operational range of the application. The reliability has to be independent from the application.
Consult your notified body for further information and approval.

For servicing purposes, manual control of the brakes may be necessary.

When SBC muting is active, the brakes can be overwritten even if STO/SBC is active. The SBC active signal will be suppressed and manual control via WorkBench, digital input or EtherCAT is possible.

Manual control of the brakes is prohibited when SBC muting is not active and STO/SBC is active at the same time.

 

Overwriting the brake(s) behavior may create unsafe situations and/or damage.

If the axis is used for a vertical load, forcing the brake(s) to release may damage the load.

  • Only use this function when safety is ensured by other measures.
  • Deactivate SBC Muting before reentering normal operation.

If SBC Muting is active during STO activation and brake control is set to "automatic", brake behavior is determined by standard brake parameters.

Safety parameters

Name Variables

Default

Parameter

SBC Brake 1

-

0

AXIS#.SAFEPARAM.SBC​.BRAKE#ATTACHED

SBC Brake 2

-

0

AXIS#.SAFEPARAM.SBC​.BRAKE#ATTACHED

Brake Delay

tSBC

100 ms

AXIS#.SAFEPARAM.SBC​.BRAKETIMEDELAY

SBC Muting

-

0

AXIS#.SAFEPARAM.SBC​.MUTINGSOURCE

Diagnostic parameters

Name

Variables

Default

Parameter

Function Active Status

-

-

see "AXIS#.SAFE.SBC.ACTIVE"

Safe Brake State

-

-

AXIS#.SAFE.BRAKE#.STATE

Device parameters

Name

 

    

BRAKEx.AXIS

For device parameters refer to WorkBench online help.

AXISx.MOTOR.BRAKE

Timing: SS1 followed by SBC without SDB

Process:

  • STO is requested.
  • The brake output is deactivated.
  • The system activates STO after the configured brake delay elapsed.

Timing

Max.

Remarks

t1

 

SS1 activate

t1 to t2

configurable

t_SS1: Time window for deceleration

t2

 

SBC activate. brake output 0V

t2 to t3

see brake datasheet

Brake engaging

t3

 

Brake is applied

t2 to t4

configurable

tSBC: Brake time delay

t4

 

STO activate

t5

 

STO, SBC deactivate, Brake output 24V

t5 to t6

see brake datasheet

Brake disengaging

t6

 

Brake is released

Timing: SS1 followed by SBC with SDB

Process:

  • STO is requested.
  • The brake output and the output power stage are deactivated simultaneously.

 

  SMM1

Timing

Max.

Remarks

t1

 

SS1 activate

t1 to t2

configurable

t_SS1: Time window for deceleration

t2

 

SBC activate. Brake output 0V

t2 to t3

see brake datasheet

Brake engaging

t3

 

Brake is applied

t2 to t4

configurable

tSDB: Delay before switching

t5

 

SDB active. SOUTx active

t5 to t6

configurable

tSDB: Delay before switching

t6

 

STO and SBC deactivates

t6 to t7

see brake datasheet

Brake disengaging

t7

 

Brake is released

Note: tSBC is not used in case SDB is configured.

Setup in WorkBench

Select Safety Parameterization view see "WorkBench Safety Function Setup". Choose the axis (1), category (2) and SBC function (3). The instance number (4) is not applicable for SBC.

Each brake needs to be assigned to its controlling axis with the device related parameters:

Assigne the axis for Brake1 (5), assigne the axis for Brake2 (6).
(7) indicates whether the drive has detected a brake for the corresponding axis.

The device related parameter settings are not safe. Changing the configuration in this view will affect the device related parameters.

If the configuration collides with the safe settings, warning 9007 will be issued when the axis is disabled. Enabling the affected axis will be prohibited in this case.

On single axis drives, axis 1 can be configured to control brake 1 and 2 with SBC. For dual axis drives, the brake configuration must be considered:

Assignment

Axis#

Brake1

Brake2

Comment

Example 1

Axis1

SBC

SBC

If both brakes are assigned to axis1, axis2 cannot control any of those two brakes.

Axis2

-

-

Example 2

Axis1

SBC

-

If axis1 controls brake1 with SBC, axis2 can control brake2 with SBC.

Axis2

-

SBC

Example 3

Axis1

-

-

If both brakes are assigned to axis2, only brake2 can be controlled with SBC. Brake1 will be controlled, but not safe (no SBC).

Axis2

no SBC

SBC

Fault Reaction / Failure Messages

It is not possible to detect a malfunctioning brake through SBC. Therefore diagnosis with SBT is necessary in regular time intervals (see (➜ # 1, SBT (Safe Brake Test))).

A disconnected brake or an open circuit on the brake connectors (X1, X2 or X4) will result in an I/O failure causing SS1_1 (fault reaction) to be triggered followed by STO.

An I/O failure warning is issued when the AKD2G is disabled.

A fault will be issued when the AKD2G is enabled and AXIS#.SAFE.STO.REPORTFAULT is set to 1.

Safety State / Status Signals

See Fault reaction/Failure messages in chapter (➜ # 1, SBT (Safe Brake Test))

Safety Properties

Refer to (➜ # 1, Safety Properties Overview).