Festo CMMT-AS Series User manual

CMMT-AS-...-S1
Servo drive
Manual | Safety
sub-function | STO,
SBC, SS1
8153822
2021-04d
[8153824]

Translation of the original instructions
ET 200SP®, PNOZ®, Pilz®, SIEMENS® are registered trademarks of the respective trademark owners in
certain countries.

Festo — CMMT-AS-...-S1 — 2021-04d
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Table of contents
1 About this document. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Target group. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Applicable documents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Product version. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Product labelling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.5 Specified standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Safety instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Intended use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Application areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Permissible components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Foreseeable misuse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Training of qualified personnel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.5 CE marking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.6 Safety engineering approval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3Additional information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4 Product overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1 Safety sub-functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.1 Function and application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.2 Safety sub-function STO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.3 Safety sub-function SBC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1.4 Safety sub-function SS1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1.5 Cross wiring of several servo drives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.1.6 Fault exclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.1.7 Safety relay unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.1.8 Interfaces of the PDS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5 Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.1 Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2 STO installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.3 SBC installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.4 SS1 installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.5 Installation for operation without safety sub-function. . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6 Commissioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1 Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.2 Check lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8 Malfunctions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1 Diagnostics via LEDs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.2 Repair. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9 Technical data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.1 Technical data, safety engineering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.2 General technical data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

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9.3 Technical data, electrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.3.1 Motor auxiliary connection [X6B]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.3.2 Inputs, outputs, ready contact at [X1A]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
9.3.3 Inputs and outputs for the axis [X1C]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

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Safety
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1 About this document
1.1 Target group
The document is targeted towards individuals who mount and operate the product. It is additionally
targeted towards individuals who are entrusted with the planning and application of the product in a
safety-oriented system.
1.2 Applicable documents
This document describes the use of the safety sub-functions safe torque off (STO/Safe torque off) and
safe brake control (SBC/Safe brake control) in accordance with EN 61800-5-2.
It is possible to implement the sub-function safe stop 1 (SS1/Safe stop 1) with a suitable external
safety relay unit and appropriate wiring of the servo drive.
•Observe the safety instructions in the documentation è Operating instructions Assembly Installa-
tion Safety sub-function.
All available documents for the product è www.festo.com/sp.
1.3 Product version
This documentation refers to the following version of the device:
–Servo drive CMMT-AS-...-S1, revision R01 and higher, see product labelling
1.4 Product labelling
Product labelling è Manual Assembly, Installation.
1.5 Specified standards
Version
IEC 61800-5-1:2016 EN 61800-2:2015
EN ISO 13849-1:2015 EN 61800-3:2004+A1:2012
EN 60204-1:2006+A1:2009+AC2010 EN 61800-5-2:2017
EN 61131-2:2007 EN 62061:2005+AC:2010+A1:2013+A2:2015
EN 61508 Parts 1-7:2010 –
Tab. 1: Standards specified in the document
2Safety
2.1 Safety instructions
It is only possible to determine whether the product is suitable for specific applications by also
assessing further components of the subsystem.
Analyse and validate the safety function of the entire system.

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Safety
Check the safety functions at adequate intervals for proper functioning. It is the responsibility of the
operator to choose the type and frequency of the checks within the specified time period. The manner
in which the test is conducted must make it possible to verify that the safety device is functioning
perfectly in interaction with all components. Time period for cyclical test è 9.1 Technical data, safety
engineering.
Prior to initial commissioning, wire the control inputs of the safety sub-functions STO and SBC. The
safety sub-functions STO and SBC are available on the CMMT-AS on delivery without the need for any
additional parameterisation.
Keep the documentation somewhere safe throughout the entire product lifecycle.
2.2 Intended use
The CMMT-AS-...-S1 supports the following safety sub-functions in accordance with EN 61800-5-2:
–Safe torque off (STO/Safe torque off)
–Safe brake control (SBC/Safe brake control)
–Safe stop 1 (SS1/Safe stop 1), achievable with suitable safety relay unit and appropriate circuitry of
the servo drive
The safety sub-function STO is intended to switch off the torque of the connected motor, thereby
preventing an unexpected restart of the motor.
The safety sub-function SBC is intended to safely hold the motor and axis in position at standstill.
The safety sub-function SS1 is intended for performing a rapid stop with subsequent torque switch-
off.
2.2.1 Application areas
Safety sub-functions may only be used for applications for which the stated safety reference values
are sufficient è 9.1 Technical data, safety engineering.
2.2.2 Permissible components
The logic power supply must meet the requirements of EN 60204-1 (protective extra-low voltage,
PELV).
If holding brakes and clamping units without certification are used, a risk assessment is required to
assess their suitability for the related safety-oriented application.
In addition to the requirements of EN 60204-1, the following requirements apply to other components
of the drive system from EN 61800-5-2:
–Annex D.3.5 and D.3.6 for motors
–Annex D.3.1 for motor and brake cables
–Annex D.3.4 for mating plugs
Components approved by Festo for the CMMT-AS fulfil these requirements.
2.3 Foreseeable misuse
Foreseeable misuse, general
–Use outside the limits of the product defined in the technical data.
–Cross-wiring of the I/O signals of more than 10 servo drives CMMT-AS.
–Use in IT networks without insulation monitors for detection of earth faults.

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Additional information
7
If the device is operated in IT networks, the potential conditions will change in the event of a fault
(earth fault on the feeding mains supply). As a result, the rated voltage of 300 V to PE – which has
important implications for the design of insulation and network disconnection – will be exceeded.
This error must be detected.
–Use of a diagnostic output for connection of a safety function.
The diagnostic outputs STA and SBA are not part of the safety circuit. The diagnostic outputs are
used to improve diagnostic coverage of the related safety sub-function. The diagnostic outputs
may only be used in combination with the related safe control signals (AND operation) plus a
reliable time monitoring function in the safety relay unit for the purpose of switching additional
safety-critical functions.
Foreseeable misuse of the safety sub-function STO
–Use of the STO function without external measures for drive axis influenced by external torques.
If external torques influence the drive axis, use of the safety sub-function STO on its own is
not suitable for stopping the axis safely. Additional measures are required to prevent dangerous
movements of the drive axis, such as use of a mechanical brake in combination with the safety
sub-function SBC.
–Disconnection of the motor from the power supply.
The safety sub-function STO does not disconnect the drive from the power supply as defined by
electrical safety.
Foreseeable misuse of the safety sub-function SBC
–Use of an unsuitable holding brake or clamping unit, also in view of:
–Holding or brake torque and emergency brake characteristics, if required.
–Frequency of actuation
–Use of an unsuitable logic voltage supply
2.4 Training of qualified personnel
The product may be installed and placed in operation only by a qualified electro technician, who is
familiar with the topics:
–installation and operation of electrical control systems
–applicable regulations for operating safety-engineering systems
Work on safety-related systems may only be carried out by qualified personnel trained in safety
engineering.
2.5 CE marking
The product has the CE marking.
The product-related EC/EU directives and standards are listed in the declaration of conformity
è www.festo.com/sp.
2.6 Safety engineering approval
The product is a safety device in accordance with the Machinery Directive. For details of the safety-ori-
ented standards and test values that the product complies with and fulfils, see è 9.1 Technical data,
safety engineering.
3 Additional information
–Contact the regional Festo contact if you have technical problems è www.festo.com.

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Product overview
4 Product overview
4.1 Safety sub-functions
4.1.1 Function and application
The servo drive CMMT-AS-...-S1 has the following safety-related performance features:
–Safe torque off (STO)
–Safe brake control (SBC)
–Safe stop 1 (SS1) with use of a suitable external safety relay unit and appropriate wiring of the
servo drive
–Diagnostic outputs STA and SBA for feedback of the active safety sub-function
4.1.2 Safety sub-function STO
Fig. 1: Symbol for STO
The function described here implements the safety sub-function STO according to EN 61800-5-2
(corresponds to stop category 0 from EN 60204-1).
The safety sub-function STO is used when the power supply to the motor needs to be switched off
safely in the application but there are no further requirements for a targeted standstill of the drive
(such as stop category 1 from EN 60204-1 è Safety sub-function SS1-t).
Function and application of STO
The safety sub-function STO switches off the driver supply for the power semiconductor, thus pre-
venting the power output stage from supplying the energy required by the motor. The power supply
to the drive is safely disconnected when the safety sub-function STO is active. The drive cannot
generate torque and so cannot perform any dangerous movements. With suspended loads or other
external forces, additional measures must be put in place to prevent movements being performed
(e.g. mechanical clamping units). In the STO state, the standstill position is not monitored.
The machines must be stopped and locked in a safe manner. This especially applies to vertical axes
without automatic locking mechanisms, clamping units or counterbalancing.
NOTICE
If there are multiple errors in the servo drive, there is a danger that the drive will move. Failure of the
servo drive output stage during the STO status (simultaneous short circuit of 2 power semiconductors
in different phases) may result in a limited detent movement of the rotor. The rotation angle/travel
corresponds to a pole pitch. Examples:
• Rotating motor, synchronous machine, 8-pin è Movement < 45° at the motor shaft
• Linear motor, pole pitch 20 mm è Movement < 20 mm at the moving part

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Product overview
9
Functional principle of STO
Fig. 2: Functional principle of STO
1
2
3
Fig. 3: Power stage with power transistors
1High-side power stage
2Low-side power stage
3DC link voltage
STO request
The safety sub-function STO is requested on 2 channels by simultaneously switching off the control
voltage at both control inputs #STO-A and #STO-B.

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Product overview
The drive behaves as follows when the safety sub-function STO is requested:
–Behaviour of the drive with a running motor: the movement of the drive is not decelerated via a
braking ramp. The drive continues to move uncontrolled due to inertia or external forces until it
comes to a standstill by itself.
–Behaviour of the drive with a stopped motor: the drive is uncontrolled and can be moved by external
forces.
STO feedback via STA diagnostic contact
The status of the safety sub-function STO can be reported to the safety relay unit via the STA
diagnostic output.
The STA diagnostic output indicates whether the safe status has been reached for the safety sub-func-
tion STO. The STA diagnostic output switches to high level only when STO is active on 2 channels via
the control inputs #STO-A and #STO-B.
#STO-A #STO-B STA
Low level Low level High level
Low level High level Low level
High level Low level Low level
High level High level Low level
Tab. 2: Level of STA
If protective functions are triggered on both channels (STO-A and STO-B), e.g. if the voltage at STO-A
and STO-B is too high, the internal protective functions switch off and STA also delivers a high level
signal.
Recommendation: the safety relay unit should check the status of the diagnostic output whenever
there is a STO request. The level of STA must change according to the logic table. The safety relay unit
can cyclically test the signals #STO-A and #STO-B for high level with low test pulses and for low level
with high test pulses.

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Product overview
11
STO timing
Fig. 4: STO timing diagram
Legend for STO timing
Term/abbreviation Explanation
#STO-A/#STO-B 2-channel input for STO request
#STO-HS/#STO-LS Internal triggering, pulse-width modulation driver high side/low side
tSTO,TP Length, low test pulses1) at #STO-A/B
tSTO,In Max. delay until STO switches off (≤ permissible reaction time when a safety
sub-function is requested1))
STA Feedback, STO active

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Product overview
Term/abbreviation Explanation
tSTA,Out Max. delay for diagnostic feedback (≤ permissible reaction time when a
safety sub-function is requested1) + 10 ms)
n Rotational speed
1) See Technical data, safety reference data for STO
Tab. 3: Legend for STO timing
4.1.3 Safety sub-function SBC
Fig. 5: Symbol for SBC
The function described here implements the safety sub-function SBC according to EN 61800-5-2.
The safety sub-function SBC is used for controlling a holding brake in the motor and a clamping unit or
brake on the axis to slow an axis down mechanically or stop it safely.
Function and application of SBC
The safety sub-function SBC provides safe output signals for the control of brakes (holding brakes or
clamping units). The brakes are controlled on 2 channels by switching off the voltage at the following
outputs:
–Safe output BR+/BR– [X6B] for the holding brake of the motor
–Safe output BR-EXT/GND [X1C] for the external brake/clamping unit
The holding brake and/or clamping unit engage and slow the motor or axis. The purpose of this is
to slow down dangerous movements by mechanical means. The braking time is dependent on how
quickly the brake engages and how high the energy level is in the system.
The use of just one brake is only possible when performance requirements are low è Tab. 17 Safety
reference data for the safety sub-function SBC. To do this, connect the brake either to BR+/BR– or to
BR-EXT.
NOTICE
If there are suspended loads, they usually drop if SBC is requested simultaneously with STO. This
can be traced back to the mechanical inertia of the holding brake or clamping unit and is thus
unavoidable. Check whether safety sub-function SS1 is better suited to your application.
SBC may only be used for holding brakes or clamping units which engage in the de-energised state.
Ensure the lines are protected when installed.

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Product overview
13
Functional principle of SBC
Fig. 6: Functional principle of SBC
SBC request
The safety sub-function SBC is requested on 2 channels by simultaneously switching off the control
voltage at both control inputs #SBC-A and #SBC-B:
–The #SBC-A request switches off the power to the signals BR+/BR-.
–The #SBC-B request switches off the power to the signal BR-EXT.
In the event of a power failure in the logic voltage supply of the servo drive, power is also cut off to the
brake outputs.
If SBC is requested and subsequently cancelled, the safe brake control is only re-energised when the
functional micro controller enables the holding brake. This ensures that Z-axes with a suspended load
can be restarted without the load dropping.
SBC feedback via SBA diagnostic contact
The 2-channel switching of the brake is indicated via the SBA output. SBA is used to report the status
of the safety sub-function SBC for diagnostic purposes, e.g. by reporting it to an external safety relay
unit.
The SBA diagnostic output indicates whether the safe status has been reached for the safety sub-func-
tion SBC. It is set if the following two conditions are fulfilled:
–Switching off of both brake outputs is requested (#SBC-A = #SBC-B = low level)
–The internal diagnostic functions have determined that there is no internal error and both brake
outputs are de-energised (switched off).
Test pulses that occur simultaneously at SBC-A and SBC-B are not filtered. For this reason, the SBA
diagnostic output delivers a high level signal for the duration of these low test pulses.

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Product overview
Testing the safety sub-function SBC
Test inputs #SBC-A and #SBC-B separately from each other and together. The diagnostic feedback may
only be set to high level when inputs #SBC-A and #SBC-B are both requested. If the signal behaviour
does not correspond to expectations, the system must be set to a safe condition within the reaction
time. It is essential that time monitoring be provided in the safety relay unit.
The safety sub-function SBC with feedback via SBA must be tested at least 1x within the space of 24 h.
• Test SBA feedback based on the SBC-A and SBC-B level according to the following table.
#SBC-A (BR+) #SBC-B (BR-Ext) SBA
Low level Low level High level
Low level High level Low level
High level Low level Low level
High level High level Low level
Tab. 4: Testing all SBC levels
While you are testing the safety sub-function SBC, discrepancy error detection may be activated in the
CMMT-AS if the test lasts longer than 200 ms. If a corresponding error message is output by the basic
unit, you will need to acknowledge it.
Evaluation of SBA
Recommendation: evaluation with every actuation.
•Check SBA feedback whenever there is a request.
#SBC-A (BR+) #SBC-B (BR-Ext) SBA
Low level Low level High level
High level High level Low level
Tab. 5: Evaluation of SBC level

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Product overview
15
Timing of SBC
Fig. 7: SBC timing diagram
Legend for SBC timing
Term/abbreviation Explanation
tBrake Mechanical delay of the brake
#SBC-A/#SBC-B 2-channel input for SBC request
tSBC,TP Length of low test pulses1) at #SBC-A/B
tSBC,In Max. delay until the related brake output is switched off (≤ permissible
reaction time when a safety sub-function is requested1))
SBA Feedback, SBC active

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Product overview
Term/abbreviation Explanation
tSBA,Out Max. delay for diagnostic feedback (≤ permissible reaction time when a
safety sub-function is requested1) + 10 ms)
n Rotational speed
1) see Technical data, safety reference data SBC
Tab. 6: Legend for SBC timing
Requirements for the brakes
• Check the brakes used for suitability for the application.
As a rule, the brakes used are holding brakes. This means the brakes are well suited to keeping the
motor at a standstill.
The internal holding brake of the motor is also used for the safety sub-function SBC. Please be aware
of the following constraints:
–The holding brake must be designed for the load torque that is to be stopped.
–The specifications for the holding brakes permit a certain amount of movement until the full
holding torque is reached. This must be taken into account in the design of the vertical axes and
configuration of the safety sub-function SBC.
–“Reserves” should be factored in when selecting the motor plus holding brake, e.g. operation at no
more than 2/3 of the nominal torque. The holding brakes in the motors are usually designed so that
the motor shaft will come to a standstill without coasting at loads below 70% of the nominal torque.
–Depending on the hazard situation, the holding brake must be designed with a correspondingly
higher nominal torque.
–When designing the holding brake, the additional load torque for the brake test must be consid-
ered.
The number of clamping and braking applications for the clamping unit is limited by its wear.
1. Observe the corresponding specifications in the data sheet.
2. Replace clamping unit before the maximum number of clamping applications is reached.
3. Replace clamping unit if the emergency brake features of the clamping unit have to be used. Note
the permissible number of emergency braking applications.
Brake test
•Check whether a brake test is required. The DGUV information sheet “Gravity-loaded axis” pro-
vides information on this.
4.1.4 Safety sub-function SS1
Fig. 8: Symbol for SS1
The function described here implements the safety sub-function SS1-t according to EN 61800-5-2.

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The safety sub-function SS1 is used when the motor needs to be braked and the power supply to the
motor then has to be safely switched off in the application but there are no further requirements for a
targeted standstill of the drive (controlled stop, stop category 1 according to EN 60204-1).
Together with a suitable safety relay unit, the following can be achieved:
–Safe stop 1 time controlled (SS1-t/Safe stop 1 time controlled); triggering of motor deceleration
and, after an application-specific time delay, triggering of the safety subfunction STO
Requirements of SS1
–For details of wiring the safety sub-function STO, see è Fig. 13.
–Execute emergency stop command with the safety relay unit (either directly by wiring CTRL-EN
accordingly or indirectly via a further functional controller).
–The time for executing an emergency stop is known.
–The safety relay unit supports programmable timers and simple logic elements.
Function and application of SS1
The procedure for triggering SS1-t comprises the following steps:
1. Functional emergency stop requested (e.g. set input CTRL-EN to low level).
This causes the servo drive to trigger a braking ramp function and – if present – allows the brake
function to engage at the end of the braking ramp. On completion of the braking ramp and once
the parameterisable delay time for brake closing has elapsed, the power stage is functionally
switched off.
2. Start of a time-delay element for actuation of STO.
Select a delay time that ensures the functional braking ramp is completed in normal operation, the
holding brake function is engaged and the power stage is functionally switched off. Otherwise, the
axis may drop if STO is triggered concurrently with the brake engagement time that is required for
mechanical reasons. If the brake is engaged while the axis is still in motion, increased wear will
occur on the holding brake (only permitted for emergency braking).
3. Safety sub-function STO requested plus – if required – SBC once the delay time has elapsed.
The figure below shows the necessary logic circuits for the safety relay unit:
Logic in the safety relay unit for SS1

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Fig. 9: Logic in the safety relay unit for SS1
The delay times are directly included in the reaction time of the system.
SS1 feedback
The STA signal can be used as feedback for the safety sub-function SS1.

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Timing of SS1
Fig. 10: Timing diagram SS1
Legend for SS1 timing
Term/abbreviation Explanation
Timer Delay element in safety relay unit
CTRL-EN Enable signal
tDelay Delay time until STO and SBC are requested (drive has safely come to a
standstill and brake is closed)
#STO-A/B 2-channel input for STO request
#SBC-A/B 2-channel input for SBC request
STA Feedback, STO active
SBA Feedback, SBC active
t1Braking ramp followed, rotational speed = 0 (functionally)
t2Brake closed and power stage switched off (functionally)
n Rotational speed
Tab. 7: Legend for SS1 timing

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Festo — CMMT-AS-...-S1 — 2021-04d
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SBC request
If there are suspended loads, they usually drop if STO and SBC are requested directly before the
braking ramp is completed because the engagement time of the holding brakes must be considered.
For details of how to wire up safety sub-function STO with SBC, see è Fig. 14.
•When selecting the delay time tDelay, make sure it is long enough to account for the maximum
braking ramp time and brake engagement time.
4.1.5 Cross wiring of several servo drives
For cross wiring, wire the diagnostic outputs as a ring. Route both ends of the ring to a 2-channel input
of the safety relay unit. The safety relay unit monitors for discrepancies. A maximum of 10 servo drives
can be wired in parallel.
Cross-wiring, example STA
Fig. 11: Cross-wiring, example STA
For cross-wired diagnostic outputs, the condensed state results from a logical AND link. An output of a
CMMT-AS is capable of pulling all other outputs to low signal. A high signal is present at the two inputs
of the safety relay unit only if all diagnostic outputs deliver high signals. The ring-shaped cross wiring
of the diagnostic outputs with sensing at the beginning and end of the signal chain makes it possible
to detect cable breaks in the cross wiring.
At this point, the diagnostic outputs deviate from the closed current principle. Cyclical automatic
testing of the diagnostic output by the safety relay unit is therefore highly recommended è STO
feedback via STA diagnostic contact and è SBC feedback via SBA diagnostic contact.
4.1.6 Fault exclusion
Put suitable measures in place to prevent faulty wiring: