Compensating for Dead Times

General

NOTE: To compensate for dead time, a constant velocity is required for the duration of the compensation time.

Dead time compensation can be explained best with a few examples.

Synchronous Run: Axis Follows Master Encoder

Example of synchronous run of an axis to a master encoder

Values of the delay parameters with a Sercos Cycle Time of 1 ms

Object	Parameter	Type	Value [ms]	Reasoning
LEnc2	Delay	EF	-Axis_Sync.ShaftRefDelay	Compensation of the "Sercos distance".
Axis_Sync2	ShaftDelay	AD	0.46994 ms⁽¹⁾	Dead time of the "Sercos distance" for the actual position.
Axis_Sync2	ShaftRefDelay	AD	-3.90506 ms⁽¹⁾	Dead time of the "Sercos distance" for the target position.
1. Example value

NOTE: The parameters ShaftDelay and ShaftRefDelay indicate the current dead time in the system. These, among other things, depend on the number of Sercos members and the cable length.

Touchprobe

PositionWithoutDelay is used to maintain the position of the master encoder shaft at a marker (TouchProbe event).

FC_TPEdge(TPld:=IM_0.LogAdr, DevId:=LEnc1.LogAdr, ParType:=6, (*PositionWithoutDelay*) PoaEdge:=TRUE, LowLimit:=IrLowLimit, HighLimit:=IrHighLimit);

ShaftMechPosition is used to maintain the position of the shaft of the "subsequent" axis at a marker (TouchProbe event).

FC_TPEdge(TPId:=IM_1.LogAdr, DevId:= Axis_Sync.LogAdr, ParType:= 4, (* ShaftMechPosition *) PosEdge:= TRUE, LowLimit:= lrLowLimit, HighLimit:= lrHighLimit);

Synchronous Run: Axis Follows Virtual Axis That Follows a Master Encoder

Example of a synchronous run of an axis to a virtual axis that follows a master encoder

Values of the delay parameters with a Sercos CycleTime of 1 ms

Object	Parameter	Type	Value [ms]	Reasoning
LEnc1	Delay	EFC	-Axis_Sync.ShaftRefDelay	Compensation of the "Sercos distance".
Axis_Sync	ShaftDelay	AD	0.46994 ms ⁽¹⁾	Dead time of the "Sercos distance" for the actual position.
Axis_Sync	ShaftRefDelay	AD	-3.90506 ms ⁽¹⁾	Dead time of the "Sercos distance" for the target values.
1. Example value

NOTE: The Parameters ShaftDelay and ShaftRefDelay indicate the current dead times in the system. These, among other things, depend on the number of Sercos members and the cable length.

Touchprobe

PositionWithoutDelay is used to maintain the position of the master encoder shaft at a marker (TouchProbe event).

FC_TPEdge(TPIId:=IM_=.LogADR,DevId:= Axis_Sync.LogAdr, ParType:=6, (*PositionWithoutDelay*) PosEdge:= TRUE, LowLimit:=IrLowLomit, HighLimit:= IrHighLimit)

ShaftMechPosition is used to maintain the position of the “subsequent” axis at a marker (TouchProbe event).

FC_TPEdge(TPId:=IM_1.LogAdr, DevId:= Axis_Sync.LogAdr, ParType:=4, (*ShaftMechPosition*) PosEdge:= TRUE, LowLimit:=IrLowLimit, HighLimit:= IrHighLimit);

Synchronous Run: Axis Follows Virtual Axis That Follows a Master Encoder

Example of a synchronous run of an axis to a virtual axis that follows a master encoder

Values of the delay parameters with a Sercos CycleTime of 1 ms

Object	Parameter	Type	Value [ms]	Reasoning
LEnc1	Delay	EFC	-Axis_Sync.ShaftRefDelay	Compensation of the "Sercos distance".
Axis_Sync	ShaftDelay	AD	0 ms	0,since axis is virtual.
Axis_Sync	ShaftRefDelay	AD	0 ms	0,since axis is virtual.
LEnc2	Delay	EFC	-Axis_Sync2.ShaftRefDelay	Compensation of the "Sercos distance".
AxisSync2	ShaftDelay	AD	0.46994 ms ⁽¹⁾	Dead time of the "Sercos distance" for the actual position.
Axis_Sync2	ShaftRefDelay	AD	-3.90506 ms⁽¹⁾	Dead time of the "Sercos distance" for the target values.
1. Example value

NOTE: The parameters ShaftDelay and ShaftRefDelay indicate the current dead times in the system. These, among other things, depend on the number of Sercos members in the cable length.

Synchronous Run: Axis Follows Axis That Follows a Master Encoder

Values of the delay parameters with a Sercos CycleTime of 1 ms

Object	Parameter	Type	Value [ms]	Reasoning
LEnc1	Delay	EFC	-Axis_Sync.ShaftRefDelay	Compensation of the "Sercos distance".
Axis_Sync	ShaftDelay	AD	0.41975 ms ⁽¹⁾	Dead time of the "Sercos distance" for the actual position.
Axis_Sync	ShaftRefDelay	AD	-3.230250 ms ⁽¹⁾	Dead time of the "Sercos distance" for the target values.
LEnc2	Delay	EFC		0, since "Sercos distance" is already compensated for in LEnc1 and Axis_Sync is a real axis.
Axis_Sync2	ShaftDelay	AD	0.41975 ms ⁽¹⁾	Dead time of the "Sercos distance" for the actual position.
Axis_Sync2	ShaftRefDelay	AD	-3.230250 ms ⁽¹⁾	Dead time of the "Sercos distance" for the target values.
1. Example value

NOTE: The parameters ShaftDelay and ShaftRefDelay indicate the current dead times in the system. These, among other things, depend on the number of Sercos members and the cable length.