SDIneg and SDIpos - Safe Direction Negative/Positive Function

General Function Description

The Safe DIrection (SDI) safety-related function ensures that rotation/movement is only possible in the permitted (parameterized) direction.

The function block distinguishes two rotation/movement directions by providing separate inputs for requesting the SDI Negative or SDI Positive monitoring function: SDIneg and SDIpos. Both SDI monitoring functions are configured using the same parameters but can be requested independently.

NOTE: In which physical rotation/movement direction SDIpos or SDIneg actually results, depends on your application.
NOTE: If SDIpos and SDIneg are requested at the same time, the SS1 function is automatically executed as the defined fallback function.

The SDIneg/SDIpos function helps prevent the motor from rotating more than a defined amount into the incorrect direction (device parameter SDI_PositionTolerance[sTol], see below).

Monitoring by the Safety-Related FB/Safety Logic

The request of the safety-related function occurs at the beginning of the t1 time interval (S_SDI*_Request signal in the diagram on the left). t1 is set with the device parameter SDI_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 direction is monitored by capturing the position. Moving/rotating a certain distance against the allowed direction is permitted if it does not exceed the defined position tolerance STol.

If the SDI function is executed successfully, the function block switches S_SDI*_SafetyActive = SAFETRUE (see diagram).

If the SS1 fallback function has been activated due to an error detected of the position tolerance as described below, this is indicated by S_SS1_SafetyActive = SAFETRUE.

Fallback Function

If the absolute value of the position exceeds the position tolerance (parameter SDI_PositionTolerance[sTol]) after t1 has elapsed, the SS1 function is automatically executed as the fallback function.

Application

The SDI function is used to help ensure that rotation or movement is not possible towards a prohibited direction, for example, when personnel access the zone of operation of a machine.