Safe Stop 1 (SS1)

The Safe Stop 1 (SS1) instruction initiates and monitors the motor deceleration within set limits to ensure the motor stops in a controlled manner.

Available Languages

Ladder Diagram

Function Block

This instruction is not available in function block.

Structured Text

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Safe Stop 1 Application

Safe Stop 1 is used with a CIP safety drive that supplies speed and position of an axis or motor, and a Safety Feedback Interface (SFX) instruction to scale the feedback. During operation the SS1 instruction signals when the motor speed is at or below the Standstill Speed. The output is then used to initiate Safe Torque Off (STO) in the drive.

Operands

The following table provides the operands used for configuring the instruction.

The following table explains the instruction inputs.

1

ISO 13849-1 stipulates instruction reset function must occur on falling edge signals. To comply with ISO 13849-1 requirements, add the logic immediately before this instruction. Rename the Reset_Signal tag in this example to the reset signal tag name. Then use the OSF instruction Output Bit tag as the instruction’s reset source.

This table explains the instruction outputs. The outputs are external tags (safety output modules) or internal tags used in other logic routines.

This table explains instruction outputs that are written to the user-specified tag.

Affects Math Status Flags

No

Major/Minor Faults

None specific to this instruction. See Index Through Arrays for array-indexing faults.

Execution

Operation

Normal Operation

The SS1 function begins if it has been previously reset and the Request input is asserted ON(1). At this point the Stop Monitor Delay Timer will begin. When the Stop Monitor Delay Timer expires the current axis speed is captured and the Stop Delay timer begins. As the Stop Delay Timer runs, the speed of the axis is monitored in real time according to the Speed Limit function, S(t), starting with Stop Delay Timer:

Speed Limit Function

S(t) = S0 + St - (Sr/ Ts)(t)

Where:

S(t) = Speed Limit

S0 = Speed captured at the end of Stop Monitor Delay

St= Decel Speed Tolerance

Sr = Decel Ref Speed

Ts = Stop Delay

t = the Stop Delay Timer value

When the Standstill Speed is reached the output O1 is cleared to OFF(0). Standstill speed is reached before the Stop Delay timer expires in normal operation.

All speed values in the Speed Limit Function are expressed in Position Units / Time Unit. A position unit is user defined according to the particular application and is configured in the SFX instruction. Time units are also configured in the SFX instruction and may be selected as seconds or minutes.

Pass-Through Tags

A Safe Motion Monitoring Drive has one or more motion axes that are controlled by a motion task. The Safe Motion Monitoring Drive also has one or more motion safety instances that support safety functions used in a safety task of a safety controller. Some of the tags associated with a drives motion safety instance are pass-through tags. The following table shows the pass-through tags and the corresponding axis tags for the SS1 function:

1

module is the name for the drive module in Logix Designer I/O Configuration tree

2

instance is 1 or 2 for dual axis drives otherwise null

3

axis is the axis name in the Logix Designer Motion Group and is associated with module

When assigning the SS1 Active and SS1 Fault instruction outputs to the motion safety instance pass-through tags, the corresponding Axis Safety Status and Axis Safety Faults tags automatically update in the motion controller. The motion control task of motion controller reads the Axis Safety Status and the Axis Safety Faults tags to coordinate operation between the safety task and motion task. The following is a typical sequence of events:

Normal Operation, Automatic Restart

The following diagram shows a timing diagram for normal operation. In the diagram, the Speed Limit function is shown as a solid red line ramping towards zero speed. The speed must stay below the Speed Limit function to maintain normal operation. For automatic restart operation, the SS1 function will be reset when the Request is removed OFF(0) provided no SS1 faults have occurred. When the SS1 function is reset, the output O1 will be set to ON(1) indicating the function is ready to operate.

Normal Operation, Manual Restart

When manual restart is enabled then the SSI operation requires an OFF(0) to ON(1) transition of the Reset input to reset the instruction before subsequent operation. The Reset Required output indicates that the Reset input must make an OFF(0) to ON(1) transition to reset the instruction. The following diagram shows normal operation with Manual Restart. The Speed Limit Function is calculated according to the Speed Limit Equation.

Faulted Operation, Deceleration Fault

The following figure, a timing diagram of SS1 where a Deceleration Fault occurs, is shown. In the figure the axis speed being monitored exceeded the Speed Limit Function, resulting in a Deceleration Fault.

Faulted Operation, Maximum Time Fault

A timing diagram of SS1 where a Maximum Time Fault occurs is shown in the following figure. As shown, the axis speed being monitored did not reach the zero speed limit before the Stop Delay Timer expired and a Maximum Time Fault occurred.

Fault Codes and Corrective Actions

Diagnostic Codes and Corrective Actions

Example