SDB (Safe Dynamic Brake)

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

Description

If the motor brake allows standstill braking only, dynamic braking is a method to slow down a servo system by dissipating the mechanical energy driven by the motor back EMF. When activated, the optional external Safe Dynamic Brake Contactor shortens the motor terminals. This forces all of the dynamic braking current to be stopping current. While the lines to the motor are shorted, the SDB status signal will be applied. When configured, SDB gets executed simultaneously along with STO.

Use this function when operating with high inertia loads.

Important Notes

No Brake Power at and near standstill!

Serious injury could result when the load is not properly blocked. This function does not ensure functional safety.

Add a safe mechanical blocking (for instance, a motor holding brake).
Configure (➜ # 1, SBC (Safe Brake Control)) to be used with SDB.

If SDB function is active, it is not possible to perform a controlled stop according to IEC 60204-1 category 1. If controlled stop category 1 is necessary, use the SS1 function.
A failure in the SDB-Contactor can only be detected when changing states. In order to detect a loss of the safety function, SDB (STO) needs to be activated regularly according to the SIL/PL of the safety function.
The SDB-Contactor is a safety related electromechanical component. The frequency of use contributes to its PFHd value and therefore to the whole safety chain.
Activating the SDB-Contactor (0V, closing contacts) will result in a short circuit on the output stage which could impair the drive when enabled. Therefore pay close attention to the parameterized timings especially during restart. Keep in mind the mechanical reaction time of the SDB-Contactor for activation and deactivation.
Brake power depends on the inertia and speed of the decelerated mass. Activating SDB when the motion contains high amounts of energy can result in a very fast stop or very high currents. The braking energy and therefore the braking speed can be limited by external resistors.
For assistance with determining stopping time and braking current when using the SBD function of the AKD2G refer to the online AKD2G Safe Dynamic Braking Tool or contact Kollmorgen technical support.

Function Input / Output Variables

Inputs

STO Active: refer to (➜ # 1, STO (Safe Torque Off))
SDB Readback: input for diagnosis signal returning from the SDB-Contactor

Outputs

SDB Activate: signal for activating the SDB-Contactor auxiliary contacts

Number of Instances

One instance per axis.

Activation

SDB can be configured to be activated during the STO process. The SDB-Contactor function must be supervised using the status path. AKD2G can supply a signal with OSSD pulses to the SDB-Contactor (set SOUTx to "ON") for diagnosis. This OSSD signal can also be provided by the safe PLC. The SDB-Contactor output status is evaluated by the drive. Use SDB.READBACKSOURCE for mapping the safe input to the SDB status signal.

The used SDB-Contactor must have a freewheeling diode in parallel to the coil. The braking energy can be limited using external resistors (Rext) limiting the back EMF current. Contact Kollmorgen Technical support for usable SDB-Contactors or component sizing.

Example: STO activated by safe inputs, SDB single channel, SIL2 PLd, SBC, SBT

Setting : SOUT1 = Activate SDB, SOUT2 = on, SIN3 = Readbacksource

Example: STO activated by safe inputs, SDB dual channel, SIL3 PLe, SBC, SBT

Setting : SOUT1 = Activate SDB channel 1, SOUT2 = Activate SDB channel 2,
SOUT3 = on, SIN3 = Readbacksource

Restart

Refer to STO for restart conditions (➜ # 1, Restart). When all conditions for a STO restart are fulfilled and SDB is configured, the SDB-Contactor will be deactivated and the readback diagnosis will be disabled. After the configured delay (same as during SDB activation) the STO will disable, allowing torque. The readback diagnosis will reengage after the configured time.

Timing

	SMM1
Timing	Max.	Remarks
t1 to t2	< 6 ms	STO response time
t1 to t3	configurable	tSDB: Delay before switching SDB-Contactor
t3 to t4	see datasheet	Mechanical delay SDB-Contactor
t3 to t5	configurable	t_D_SDB:Delay until readback diagnosis
t6 to t7	configurable	tSDB: Max. delay for SDB-Contactor to switch
t6 to t8	configurable	t_D_SDB: Delay until readback diagnosis

Related Parameters

SMM1
Name	Variables	Default	Parameter
Function Activation	-	0 (Never active)	AXIS#.SAFEPARAM.SDB.FUNCTIONACTIVATION
Readback	-	Not Used	AXIS#.SAFEPARAM.SDB.READBACKSOURCE
Delay Before Switching	tSDB	1 ms	AXIS#.SAFEPARAM.SDB.DELAYBEFORESWITCHING
Delay Before Diagnose	t_D_SDB	1 ms	AXIS#.SAFEPARAM.SDB.DELAYBEFOREDIAGNOSE

State Diagram

Setup in WorkBench

Select Safety Parameterization view see "WorkBench Safety Function Setup".

Choose the axis (1), category (2) and SDB function (3).

Fault Reaction / Failure Messages

The drive supervises the safe input(s) assigned as readback. An OSSD pulsed signal, either from a safe output or a safe PLC, is required. When the readback signal becomes static, an I/O error will be detected.

During the activation and deactivation of the SDB function, the readback diagnosis will be interrupted for the parameterized amount of time. When STO/SDB are active, a high signal (24V) is expected. When STO/SDB are not active, a low signal (0V) is expected. Deviating this expected behavior will additionally result in a SDB failure recognizable from the diagnostics view.

For detailed information on the signal states refer to Timing.

Safety State / Status Signals

The WorkBench view “Safety Diagnostics – Safe I/O” shows the current status off the safe inputs and outputs.

The target status can be read of the assigned output(s). The status of the SDB readback can be read from the assigned input(s). Which state is appropriate depends on the system state.

For detailed information on the signal states refer to Timing.

Safety Properties

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