SINAMICS Drives - Safety Integrated Functions

Safe Torque Off (STO)

Safety diagram - STO

The STO function is the most common and basic drive-integrated safety function. It ensures that no torque-generating energy can continue to affect a motor and prevents unintentional start-ups. This function is a mechanism that prevents the drive from restarting unexpectedly, in accordance with EN 60204-1, Section 5.4.

Effect
 The Safe Torque Off function clears the pulses of the drive, making it reliably torque-free. This state is monitored internally in the drive.

Applications
STO has the immediate effect that the drive cannot supply any torque-generating energy. STO can be used wherever the drive will reach a standstill in a sufficiently short time based on the load or friction or when the coasting down of the drive will not have any relevance for safety.

Benefits
The advantage of the integrated STO safety function compared to standard safety technology using electromechanical switchgear is the elimination of separate components and the effort that would be required to wire and service them. Because of the rapid electronic switching times, the function has a shorter switching time than the electromechanical components in a conventional solution.

Safe Stop 1 (SS1)

Safety diagram - SS1

The SS1 function causes a motor to stop rapidly and safely and switches the motor to torque-free mode after the standstill, i.e. STO is activated. The Safe Stop 1 function can safely stop the drive in accordance with EN 60204-1, Stop Category 1.

Effect
When the SS1 function is selected, the drive brakes along a quick stop ramp autonomously and automatically activates the Safe Torque Off and Safe Brake Control functions (if enabled) when the parameterized safety delay timer expires.

Applications
The SS1 function is used when in the event of a safety-relevant incident the drive must stop as quickly as possible with a subsequent transition into the STO state. It is thus used to bring large centrifugal masses to a stop as quickly as possible for the safety of operating personnel, or to brake motors at high speeds as quickly as possible. Typical application examples include saws, grinding machine spindles, centrifuges, stacker cranes.

Benefits
The targeted stopping of a drive by means of SS1 reduces the risk of danger, increases the productivity of a machine, and allows safety clearances in a machine to be reduced. The reason is the active stopping of the drive compared to the use of the STO function alone.

Safe Operating Stop (SOS)

Safety diagram - SOS

With the SOS function, the stopped motor is kept in its position and monitored by a drive control.

Effect
The Safe Operating Stop function represents safe standstill monitoring. The drive control remains in operation. The motor can therefore deliver the full torque to hold the current position. The actual position is reliably monitored. In contrast to safety functions SS1 and SS2, the speed setpoint is not influenced automatically. After SOS has been activated, the higher level control must bring the drive to a standstill within a parameterized time and then hold the position setpoint.

Applications
SOS is an ideal solution for applications in which the machine or parts of the machine must be at a safe standstill in certain steps, but the drive must also supply a holding torque. It is ensured that despite counter torque the drive remains in its current position. In contrast to SS1 and SS2, the drive does not brake autarchically in this case. It expects the higher-level controller to shut down the relevant axes as a coordinated group within an adjustable delay time. This can be used to prevent any damage to the machine or product.

Benefits
No mechanical components are necessary to keep the axis in position despite any counterforce that might appear. Due to the short switching times and the fact that the position control always remains active, setup and downtimes are reduced. Recalibration of the axis after exiting the SOS function is not necessary. The axis can immediately be moved again after deactivation of the SOS function.

Safe Stop 2 (SS2)

Safety diagram - SS2

The SS2 function shuts down a motor quickly and safely and then monitors the standstill positions, in accordance with EN 60204-1, Stop Category 2.

Effect
When the SS2 function is selected, the drive brakes autonomously along a quickstop ramp. In contrast to SS1, the automatic speed control remains operational afterwards, i.e. the motor can supply the full torque required to maintain zero speed. Standstill is safely monitored (Safe Operating Stop function).

Applications
As with SS1, the SS2 function ensures the quickest possible deceleration of the motor. However, the motor power is not switched off, but prevented by a control system from leaving the standstill position even if affected by external forces.

Benefits
The SS2 function ensures a rapid axis stop. Because the control remains active, after the safety function is deselected, productive operation can continue without referencing. This ensures short setup and standstill times and high productivity.

Safe Brake Control (SBC)

Safety diagram - SBC

The SBC function permits the safe control of a holding brake -  always activated in parallel with STO.

Effect
A holding brake which is active in a de-energized state is controlled and monitored using safe two-channel technology. Due to this level of control, the brake may still be activated in the event of an insulation fault in the control cable. Errors of this kind are detected early by means of test pulses.

Applications
The SBC function is used in conjunction with the functions STO or SS1 to prevent the movement of an axis in the torque-free state, e.g. because of gravity.

Benefits
Again, the function saves the use of external hardware and the associated wiring.

Safely-Limited Speed (SLS)

Safety diagram - SLS

The SLS function ensures that the drive does not exceed a preset speed limit.

Effect
The drive reliably monitors the speed and activates a fault response defined by the configuration if the set speed / rpm limit is exceeded.

Applications
The SLS function is used if people are in the danger zone of a machine and their safety can only be guaranteed by reduced speed. First, therefore, the speed is reduced, then safe monitoring is activated using the SLS function so that accidental exceeding of the set speed limit is prevented. Typical examples are cases in which an operator must enter the danger zone of the machine for maintenance or setup. A typical use of SLS is a winder, in which the material is manually threaded by the operator. To prevent injury to the operator, the roller may only spin at a safe reduced speed. SLS is often also used as part of a two-stage safety concept. While a person is in a less critical zone, the SLS function is activated, and the drives are only stopped in a smaller area with higher potential risk. SLS can be used not only for operator protection, but also for machinery protection, e.g. if a maximum speed must not be exceeded.

Benefits
The SLS function can contribute to a significant reduction in downtime, or greatly simplify or even accelerate setup. The overall effect achieved is a higher availability of a facility. Moreover, external components such as speed monitors can be omitted.

Safe Speed Monitor (SSM)

Safety diagram - SSM

The SSM function warns when a drive is working below a specified speed / feed speed. As long as it remains below the threshold, the function issues a safety signal.

Effect
If a speed value drops below a parameterized level, a safety signal is generated. This can be processed, for example, in a safety controller to respond to the event by programming, depending on the situation.

Applications
With the SSM function, in the simplest case, a safety door can be unlocked if the speed drops below a non-critical level.

Benefits
Unlike SLS, there is no drive-independent fault reaction when the speed limit is exceeded.
The safe feedback can be evaluated in a safety control unit, allowing the user to respond appropriately to the situation.

Safe Direction (SDI)

Safety diagram - SD1

The SDI function ensures that the drive can only rotate in the selected direction.

Effect
A deviation from the currently monitored direction of motion / rotation is reliably detected and the configured autonomous fault response of the drive is initiated. It is possible to monitor both directions of motion optionally.

Applications
The SDI function is used if the drive must only move in one direction. A typical application is to make a danger zone accessible to the operator, provided the machine is moving in the safe direction, i.e. away from the operator. In this status, the operator can safely feed material into or remove it from the work area.

Benefits
The function does away with the use of external components such as speed monitors and the associated wiring expense. The release of a danger zone while the machine is moving away from the operator also raises productivity. Without the SDI function, the machine would have to be stopped safely while material was fed in or removed.

Safe Brake Test (SBT)

Safety diagram - SBT

Performs a test of the brake function at cyclical intervals.

Effect
The intended function of wear-prone brakes is safely tested by increasing torque against the closed brake. Two brakes can be tested with different test torques on each drive, e.g. motor brake and external brake.

Applications
This function is suitable for implementing a safe brake combined with the SBC function

Benefits
The function identifies faults or wear in the brake mechanics. Automatically testing the effectiveness of brakes reduces maintenance costs and increases the safety and availability of plants / machines. Goes beyond the safety functions named in IEC 61800-5-2d.

Safely-Limited Position (SLP)

Safety diagram - SLP

This function monitors the axis to ensure that it remains within the permissible traversing range.

Effect
The traversing range limited by the configured software limit switch is safely monitored. If the permitted traversing range is exited, a configurable fault response is initiated. It is possible to toggle between two traversing ranges, even during operation.

Applications
SLP is used for applications in which machine operators have to enter a protection area, e.g. for feeding in and removing material. Safe monitoring of the axis position ensures that the axis cannot move into the protection area released for operators, placing them in danger, e.g. for stacker cranes, gantry cranes, production centers.

Benefits
SLP can be used for highly-effective protection area monitoring, eliminating the use of external components such as hardware limit switches and the associated wiring complexity. Because the response time following a limit overshoot is short, safety clearances can be reduced.

Safely Position (SP)

Safety diagram - SP

Transfers the safely determined actual position values in the drive to a safety controller via safe PROFIsafe communication.

Effect
Unlike the SLP function, which monitors the current actual position value against a limit within the drive and initiates an autonomous fault response by the drive to an overshoot, SP communicates the current actual position values to the safety control. This allows Monitoring functions to be implemented more flexibly..

Applications
Tailored safety concepts can be developed with the SP function. The function is particularly suitable for machines where flexible safety functions are required. It can be used in a wide range of applications, e.g. to implement safe, axis-specific range recognition via safe cams (SCA). The function can also be used to design cross-axis safety concepts, multi dimensional protection areas and zone concepts.

Benefits
Additional sensors or external safe encoders, their installation and evaluation are not necessary to monitor protection areas. The function goes beyond the safety functions stated in IEC 61800-5-2.