Safe stop 2 (SS2)

Properties

Safety function according to DIN EN 61800-5-2:2008-04
Controlled stop according to EN 60204-1, stop category 2
Safe standstill control with drift recognition
(2-channel monitoring of the actual speed and position values)

Description

The safety function is started by the corresponding bit in the control data.
The acknowledgement is fed back by status data.

The initialised SS2 safety function monitors the deceleration process of the drive and subsequently the safe standstill in regular operations. The deceleration procedure must be initiated by the user controller.

GEFAHR

Danger to life due to unexpected movements!

The normal operating function 'Safe encoder monitoring (SEM)' is active at any time.
It will switch the drive from 'Safe operating stop (SOS)' to 'Safe stop 1 (SS1)' and subsequently to 'Safe torque off (STO)' if the monitored encoder stays in standstill for a longer time than parameterised in 'Safe encoder monitoring (SEM)'.

In the status 'Safe torque off (STO)', in case of mains failure or defective drive controller, the drive will be torque-free.

External force applied to the drive axis can cause life-threatening movements, e.g. hanging axes can fall down.

Steps to prevent:

Install an external, mechanical brake that prevents a movement.
Install a counterweight in order to maintain the axis in balance.
Adapt the parameters of 'Safe encoder monitoring (SEM)' to your application.

Example 1: Drive movement in the permissible range of movement

Time t	Explanation
t = t₀	The safety function is started by a 1-0 edge and cannot be interrupted.
t₀ < t < t₁	During the transition period, the actual speed value of the drive must be adjusted to the parameterised limits of the started safety function. The parameterised limits are not monitored yet.
t₁ ≤ t < t₂	The safety function monitors the parameterised ramp and checks whether the actual speed value meets the permissible range of movement.
t ≥ t₂	The safety function switches the drive into the SOS state and sets the SOS acknowledgement bit. In the SOS state, the safety function monitors whether the actual speed value meets the safe speed standstill window and the actual position value meets the safe position standstill window.
t = t₃	SOS acknowledgement at maximum speed

Reaction in case of an error

As soon as the safety function detects a deviation from the limits of the monitored values, the drive is set to the safe state 'Safe torque off (STO)' (example 2) and (example 3).

DANGER

Danger to life due to unexpected movements!

The drive will be torque-free in the status 'Safe torque off (STO)', in case of mains failure or in case of faulty drive controller. External application of force on the drive axis may result in life-threatening movements (e.g. hanging axes can fall down).

Steps to prevent:

Install an external, mechanical brake that prevents a movement.
Install a counterweight in order to maintain the axis in balance.

Example 2: Drive movement deviates from the parameterised deceleration ramp

Time t	Explanation
t = t₀	The safety function is started by a 1-0 edge and cannot be interrupted.
t₀ < t < t₁	During the transition period, the actual speed value of the drive must be adjusted to the parameterised limits of the started safety function. The parameterised limits are not monitored yet.
t₁ ≤ t < t₂	The safety function monitors the parameterised ramp and checks whether the actual speed value meets the permissible range of movement.
t = t₂	The safety function detects an error, switches the drive into the STO state and sets the error bit.
t ≥ t₂	In the STO state, drive movements are no longer monitored since no further error reaction is possible.

Example 3: Drive movement deviates from the safe speed standstill window in the SOS state

Time t	Explanation
t = t₀	The safety function is started by a 1-0 edge and cannot be interrupted.
t₀ < t < t₁	During the transition period, the actual speed value of the drive must be adjusted to the parameterised limits of the started safety function. The parameterised limits are not monitored yet.
t₁ ≤ t < t₂	The safety function monitors the parameterised ramp and checks whether the actual speed value meets the permissible range of movement.
t = t₂	The safety function switches the drive into the SOS state and sets the SOS acknowledgement bit.
t₂ ≤ t < t₃	In the SOS state, the safety function monitors whether the actual speed value is in the safe speed standstill window and the actual position value complies with the safe position standstill window.
t = t₃	The safety function detects an error, switches the drive into the STO state and sets the error bit. The SOS acknowledgement bit is reset.
t ≥ t₃	In the STO state, drive movements are no longer monitored since no further error reaction is possible.

Acknowledge an error with "Clear error"

As soon as an active safety function detects a deviation from the limits of the monitored values, the drive is set to the intended stop function. The error bit (FSoE status bit 7) is set and the acknowledgment of the safe status is withdrawn.

With the 'Clear error' signal (FSoE control bit 7 or the 'Clear error' command in the drive controller) the

error status ist acknowledged (deleted). If during and after the 'Clear error' the start signal from a previous safety function is still active and no other changes to the settings of the safety function have been made, the safety function restarts and also transition times (if available) work again.

Parameters

Safe parameters

Parameter

Name

Code

Unit

Min

Max

Prm23

'SS2 transition period'

T(d,SS2)

65535