SS1 - Safe Stop 1 Function

General Function Description

The Safe Stop 1 function causes a rapid and controlled stopping of a drive. It controls the drive to decelerate autonomously and finally activates the drive-internal Safe Torque Off (STO) safety-related function. As a result, the drive remains torque-free and the motor is no longer supplied with power.

The active STO function results in a subsequent start-up/restart inhibit (see section below).

SS1 realizes a functional safety-related stop in accordance with stop category 1 according to EN 60204-1.

SS1 is the defined fallback function of the safety-related functions SLS1 to SLS4, SMS, SDIneg, and SDIpos.

Monitoring by the Safety-Related FB/Safety Logic

The monitoring behavior by the function block depends on the parameterization of the Safety Logic:

  • If ramp monitoring is deactivated, monitoring is passive until the t2 time interval has elapsed (see figure and description below).

  • If ramp monitoring is activated, the Safety Logic monitors the motor deceleration rate specified by the deceleration ramp.

In both cases, the SS1 function monitors the motor and then initiates the STO function to set the drive torque-free. Note that the safety-related function only monitors the movement. Controlling the axis is done by the Safety Logic autonomously and independent of the function block.

The request of the safety-related function occurs at the beginning of the t1 time interval (S_SS1_Request signal in the diagram on the left). t1 is set with the device parameter SS1_StartDelayTime[t1].

Within the t1 time interval, the standard (non-safety-related) controller also receives the request from the connected process and initiates the motion control function according to the logic and drive parameterization defined in the standard (non-safety-related) application.

After t1 has elapsed, the deceleration of the drive is executed. The maximum allowed duration t2 of this ramp-down phase is defined by the device parameter SS1_RampMonitoringTime[t2]. At the end of t2, STO is activated.

During t2, the deceleration can be monitored by setting the device parameter SS1_RampMonitoring = Activated.

If ramp monitoring is deactivated, the deceleration curve is not monitored. Even acceleration is allowed during the t2 interval. Standstill is enforced when t2 elapses by engaging the STO function.

If ramp monitoring is activated, the deceleration curve is monitored and must follow the parameterized ramp (as shown in the figure). Otherwise, STO is activated as the defined fallback function.

If zero speed has been achieved while t2 has not yet elapsed, a defined velocity tolerance (parameter SS1_MinRampVelocity[v2]) of the axis is allowed and monitored in respect with v2.

If the torque-free status of the drive has been achieved by the correct execution of the SS1 function, the function block switches S_SS1_SafetyActive = SAFETRUE (see diagram). Otherwise, if the STO fallback function has been activated due to an error detected as described above, this is indicated by S_STO_SafetyActive = SAFETRUE.

Fallback Function

If the parameterized SS1_RampMonitoringTime[t2] value is exceeded, or (in case of activated ramp monitoring) if the parameterized deceleration ramp is not respected as defined, or if the velocity tolerance (v2 in the figure) is exceeded, the STO function is automatically executed as the fallback function.

Application

The SS1 function is used if a controlled deceleration of the drive with a following torque-free standstill state is required, for example, after a safety-relevant event.

SS1 is suitable to bring a large flywheel mass as quickly as possible to a halt or to slow down and come to a standstill from high drive speeds as fast as possible. Typical examples are grinding spindles, centrifuges, storage, and retrieval devices.