How-to & Troubleshooting - twinControls Forum

Inquiry: Actual Position Leading Target Position in TwinCAT MoveAbsolute

dxt123 — Thu, 15 Oct 2026 02:02:14 +0000

I am writing to inquire about an unusual issue we have encountered while controlling a servo motor using the TwinCAT system.

Currently, we are operating the motor by inputting the target position and velocity into the MoveAbsolute function block. While monitoring the servo motor's actual position (GVL.Axis1.NcToPlc.ModuloActPos) using the Scope function, we noticed a strange behavior: during the initial phase of the movement, the actual position lags behind the target position. However, after a certain point, the actual position starts to lead the target position by approximately 1 degree.

Unlike a standard following error (lagging), it is difficult for us to pinpoint why the motor would move ahead of the target position. Therefore, we are reaching out for your assistance.

To help with your investigation, I have attached the relevant test files. In the attached test_profile.csv file, 'F' represents the velocity and 'U' represents the target position.

We would greatly appreciate your insights into the potential causes of this issue and any recommendations on additional parameters or settings we should inspect.

Additionally, I have provided the PLC code below.

Thank you for your support.

PROGRAM MAIN

VAR

Robot1: FB_FANUC_Basic;

bReset: BOOL;

RobotEnable, RobotFault: BOOL;

// Buffer

send_single_buffer_v2 : ARRAY OF REAL;

goto_buffer : ARRAY OF REAL; // Buffer to move robot for manual

send_buffer1_1_v2, send_buffer1_2_v2, send_buffer1_3_v2,

send_buffer2_1_v2, send_buffer2_2_v2, send_buffer2_3_v2: ARRAY OF REAL;

// Function Block

fb_custom_service : FB_CUSTOM_SERVICE; // Send a Sequence Data to Robot

fbMove1, fbMove2, fbHome : MC_MoveModulo; // Turn Table Motor Move, Only Turn Table Motor Move, Turn Table Motor Homing

fbMove : MC_MoveAbsolute;

fbMove_rev1, fbMove_rev2, fbMove_rot1, fbMove_rot2 : MC_MoveVelocity; // Revolution & Rotation Motor Move

fbReset : MC_Reset; // Motor Reset

fbPower, fbPower_rev, fbPower_rot : MC_Power; // Motor Power On

mc_readactpos : MC_ReadActualPosition; // Read Position of Turn Table Motor

mc_readactvel_rev, mc_readactvel_rot : MC_ReadActualVelocity; // Read Velocity of Revolution & Rotation Motor

mc_stop, mc_stop_rev, mc_stop_rot : MC_Stop; // Motor Stop

mc_setpos: MC_SetPosition;

bSetDone: BOOL;

fbTimer_SetPos: TON;

bTimer: BOOL;

REdge_setdone: R_TRIG;

// Variables

// Bool

bExecute : BOOL; // fb_custom_service.Execute

motor_trig1, motor_trig2 : BOOL; // Signal for cross-action of Motors

bStopDone, bStopDone_rev, bStopDone_rot : BOOL; // Stopped Rising Edge Signal

bHomeDone : BOOL; // Hoiming Done Signal

// LREAL

nPos, nVel : LREAL; // Input Data of Turn Table Motor

fServoCurrPos, fServoCurrVel_rev, fServoCurrVel_rot : LREAL; // Output Data of the Motors

// INT

nState : INT:= 0;

nPointIdx : INT:= 1;

trig_status : INT:= 0;

// fb_custom_service variables

nServiceCode : BYTE;

nClass, nInstance, nAttribute : WORD;

nNumberofData : DINT;

nBufferID : INT;

pCurrentAddr : PVOID;

nCurrentSize : WORD;

nErrId : UDINT;

error : STRING;

// Rising Edge Trigger

REdge_first : R_TRIG;

REdge_StopDone : R_TRIG;

REdge_StopDone_rev : R_TRIG;

REdge_StopDone_rot : R_TRIG;

REdge_Restart : R_TRIG;

REdge_HomeDone : R_TRIG;

REdge_DO48 : R_TRIG;

bWaitCheckPoint: BOOL;

nNextState: INT;

bRobotAck: BOOL;

bInit : BOOL:= TRUE;

bFirstStart : BOOL:= TRUE;

bNextStepReq : BOOL;

nCntIdx : INT;

fbScanTimer : TON;

fbSetOverride : MC_SetOverride;

fRobotFirstPos: LREAL;

fRobotStartPos, fRobotTargetPos, fRobotActualPos,

fRobotTotalDist, fRobotRemainRatio,

fMotorStartPos, fMotorTargetPos, fMotorActualPos,

fMotorTotalDist, fMotorVirtualTarget : LREAL;

fSampledTargetPos, fSampledActualPos : LREAL;

fOutput : LREAL;

fCalculatedOverride : LREAL:= 0.0;

nPos_X: UDINT:= 0;

nPos_Y: UDINT:= 0;

fBackupValue: LREAL;

fRelativePos: LREAL;

REdge_bStart: R_TRIG;

fScaled_Kp: LREAL;

fDrivePosLoopGain: LREAL:= 32.0;

fPositionError: LREAL;

bSequenceMode: BOOL:= FALSE;

nXorY: INT;

nRobotIdx: UDINT:=0;

nRobotIdx_int: INT;

frobot: LREAL;

nTrackingIdx: INT:= 1;

nTotalProcessCnt: DINT:= 1;

END_VAR

Robot1.Update();

RobotEnable:= Robot1.qEnable;

RobotFault:= Robot1.qFault;

CASE nBufferID OF

pCurrentAddr:= ADR(send_single_buffer_v2);

nCurrentSize:= SIZEOF(send_single_buffer_v2);

pCurrentAddr:= ADR(goto_buffer);

nCurrentSize:= SIZEOF(goto_buffer);

11:

pCurrentAddr:= ADR(send_buffer1_1_v2);

nCurrentSize:= SIZEOF(send_buffer1_1_v2);

12:

pCurrentAddr:= ADR(send_buffer1_2_v2);

nCurrentSize:= SIZEOF(send_buffer1_2_v2);

13:

pCurrentAddr:= ADR(send_buffer1_3_v2);

nCurrentSize:= SIZEOF(send_buffer1_3_v2);

21:

pCurrentAddr:= ADR(send_buffer2_1_v2);

nCurrentSize:= SIZEOF(send_buffer2_1_v2);

22:

pCurrentAddr:= ADR(send_buffer2_2_v2);

nCurrentSize:= SIZEOF(send_buffer2_2_v2);

23:

pCurrentAddr:= ADR(send_buffer2_3_v2);

nCurrentSize:= SIZEOF(send_buffer2_3_v2);

99:

pCurrentAddr:= ADR(nNumberofData);

nCurrentSize:= SIZEOF(nNumberofData);

END_CASE

fb_custom_service(

sNetId:= '192.168.0.196.3.1',

sIPv4Addr:= '100.100.100.1',

bExecute:= bExecute,

nServiceCode:= nServiceCode,

nClass:= nClass,

nInstance:= nInstance,

nAttribute:= nAttribute,

pSrc:= pCurrentAddr,

nSrcDataLen:= nCurrentSize,

);

error:= F_GET_ETHERNETIP_ERROR_TEXT(nErrorId:= nErrId);

fbPower(Axis:= GVL.Axis1, Enable:= TRUE, Enable_Positive:= TRUE, Enable_Negative:= TRUE, Override:= 100.0);

fbPower_rev(Axis:= GVL.Axis2, Enable:= TRUE, Enable_Positive:= TRUE, Enable_Negative:= TRUE, Override:= 100.0);

fbPower_rot(Axis:= GVL.Axis3, Enable:= TRUE, Enable_Positive:= TRUE, Enable_Negative:= TRUE, Override:= 100.0);

fbReset(Axis:= GVL.Axis1, Execute:= GVL.bReset);

IF GVL.bReset THEN

nState:= 0;

GVL.bStart:= FALSE;

GVL.bReqUpdateLower:= FALSE;

GVL.bReqUpdateUpper:= FALSE;

END_IF

CASE nState OF

IF GVL.bStart THEN

nPointIdx:= 1;

nState:= 10;

END_IF

10:

fbMove1.Position:= GVL.aPathData.fPosition;

fbMove1.Velocity:= GVL.aPathData.fVelocity;

fbMove1.BufferMode:= MC_BufferMode.MC_Aborting;

fbMove1.Direction:= MC_Positive_Direction;

fbMove1.Execute:= TRUE;

fbMove_rev1.Velocity:= GVL.aPathData.fVelocity2;

fbMove_rev1.BufferMode:= MC_BufferMode.MC_Aborting;

fbMove_rev1.Execute:= TRUE;

fbMove_rot1.Velocity:= GVL.aPathData.fVelocity3;

fbMove_rot1.BufferMode:= MC_BufferMode.MC_Aborting;

fbMove_rot1.Execute:= TRUE;

IF fbMove1.Active AND fbMove_rev1.Active AND fbMove_rot1.Active THEN

fbMove1.Execute:= FALSE;

fbMove_rev1.Execute:= FALSE;

fbMove_rot1.Execute:= FALSE;

nPointIdx:= nPointIdx + 1;

motor_trig1:= TRUE;

nState:= 20;

END_IF

20:

fbMove2.Position:= GVL.aPathData.fPosition;

fbMove2.Velocity:= GVL.aPathData.fVelocity;

fbMove2.BufferMode:= MC_BufferMode.MC_BlendingPrevious;

fbMove2.Direction:= MC_Positive_Direction;

fbMove_rev2.Velocity:= GVL.aPathData.fVelocity2;

fbMove_rev2.BufferMode:= MC_BufferMode.MC_BlendingPrevious;

fbMove_rot2.Velocity:= GVL.aPathData.fVelocity3;

fbMove_rot2.BufferMode:= MC_BufferMode.MC_BlendingPrevious;

IF motor_trig1 THEN

IF GVL.aPathData.fVelocity > 0.0 THEN

fbMove2.Execute:= TRUE;

fbMove_rev2.Execute:= TRUE;

fbMove_rot2.Execute:= TRUE;

ELSE

motor_trig1:= FALSE;

nState:= 99;

END_IF

IF fbMove2.Active AND fbMove_rev2.Active AND fbMove_rot2.Active THEN

fbMove2.Execute:= FALSE;

fbMove_rev2.Execute:= FALSE;

fbMove_rot2.Execute:= FALSE;

motor_trig1:= FALSE;

nPointIdx:= nPointIdx + 1;

nTotalProcessCnt:= nTotalProcessCnt + 1;

IF (nTotalProcessCnt > 1) AND (((nTotalProcessCnt - 1) MOD 63) = 0) THEN

bWaitCheckPoint:= TRUE;

END_IF

IF nPointIdx = 501 THEN

GVL.bReqUpdateLower:= TRUE;

ELSIF nPointIdx > GVL.nMaxPoints THEN

nPointIdx:= 1;

IF NOT GVL.bAllDataFinished THEN

GVL.bReqUpdateUpper:= TRUE;

END_IF

IF nState <> 99 THEN

IF bWaitCheckPoint THEN

nNextState:= 30;

nState:= 40;

ELSE

motor_trig2:= TRUE;

nState:= 30;

END_IF

ELSIF fbMove2.Error THEN

nState:= 900;

END_IF

30:

fbMove1.Position:= GVL.aPathData.fPosition;

fbMove1.Velocity:= GVL.aPathData.fVelocity;

fbMove1.BufferMode:= MC_BufferMode.MC_BlendingPrevious;

fbMove1.Direction:= MC_Positive_Direction;

fbMove_rev1.Velocity:= GVL.aPathData.fVelocity2;

fbMove_rev1.BufferMode:= MC_BufferMode.MC_BlendingPrevious;

fbMove_rot1.Velocity:= GVL.aPathData.fVelocity3;

fbMove_rot1.BufferMode:= MC_BufferMode.MC_BlendingPrevious;

IF motor_trig2 THEN

IF GVL.aPathData.fVelocity > 0.0 THEN

fbMove1.Execute:= TRUE;

fbMove_rev1.Execute:= TRUE;

fbMove_rot1.Execute:= TRUE;

ELSE

motor_trig2:= FALSE;

nState:= 99;

END_IF

IF fbMove1.Active AND fbMove_rev1.Active AND fbMove_rot1.Active THEN

fbMove1.Execute:= FALSE;

fbMove_rev1.Execute:= FALSE;

fbMove_rot1.Execute:= FALSE;

motor_trig2:= FALSE;

nPointIdx:= nPointIdx + 1;

nTotalProcessCnt:= nTotalProcessCnt + 1;

IF (nTotalProcessCnt > 1) AND (((nTotalProcessCnt - 1) MOD 63) = 0) THEN

bWaitCheckPoint:= TRUE;

END_IF

IF nPointIdx = 501 THEN

GVL.bReqUpdateLower:= TRUE;

ELSIF nPointIdx > GVL.nMaxPoints THEN

nPointIdx:= 1;

IF NOT GVL.bAllDataFinished THEN

GVL.bReqUpdateUpper:= TRUE;

END_IF

IF nState <> 99 THEN

IF bWaitCheckPoint THEN

nNextState:= 20;

nState:= 40;

ELSE

motor_trig1:= TRUE;

nState:= 20;

END_IF

ELSIF fbMove1.Error THEN

nState:= 900;

END_IF

40:

IF Robot1._UO1.DO237 THEN

Robot1._UI1.DI44:= TRUE;

bRobotAck:= TRUE;

END_IF

IF bRobotAck AND NOT Robot1._UO1.DO237 THEN

Robot1._UI1.DI44:= FALSE;

bRobotAck:= FALSE;

bWaitCheckPoint:= FALSE;

IF nNextState = 20 THEN

motor_trig1 := TRUE;

ELSIF nNextState = 30 THEN

motor_trig2 := TRUE;

END_IF

nState := nNextState;

END_IF

99:

IF NOT fbMove1.Busy AND NOT fbMove2.Busy THEN

IF Robot1._UO1.DO237 THEN

Robot1._UI1.DI44:= TRUE;

ELSE

Robot1._UI1.DI44:= FALSE;

nState:= 0;

nPointIdx:= 1;

nTrackingIdx:= 1;

motor_trig1:= FALSE;

motor_trig2:= FALSE;

bWaitCheckPoint:= FALSE;

bRobotAck:= FALSE;

nNextState:= 0;

fbMove1.Execute:= FALSE;

fbMove2.Execute:= FALSE;

fbMove_rev1.Execute:= FALSE;

fbMove_rev2.Execute:= FALSE;

fbMove_rot1.Execute:= FALSE;

fbMove_rot2.Execute:= FALSE;

GVL.bStart:= FALSE;

IF NOT GVL.bStop_rev THEN

GVL.bStop_rev:= TRUE;

END_IF

IF NOT GVL.bStop_rot THEN

GVL.bStop_rot:= TRUE;

END_IF

bSequenceMode:= FALSE;

END_IF

900:

IF NOT fbMove1.Busy AND NOT fbMove2.Busy THEN

GVL.bStart:= FALSE;

nState:= 0;

nPointIdx:= 1;

nCntIdx:= 0;

bSequenceMode:= FALSE;

END_IF

END_CASE

fbMove1(Axis:= GVL.Axis1);

fbMove2(Axis:= GVL.Axis1);

fbMove_rev1(Axis:= GVL.Axis2);

fbMove_rev2(Axis:= GVL.Axis2);

fbMove_rot1(Axis:= GVL.Axis3);

fbMove_rot2(Axis:= GVL.Axis3);

IF GVL.bReqUpdateLower AND GVL.bUpdateDone THEN

GVL.bReqUpdateLower:= FALSE;

END_IF

IF GVL.bReqUpdateUpper AND GVL.bUpdateDone THEN

GVL.bReqUpdateUpper:= FALSE;

END_IF

REdge_first(CLK:= MAIN.Robot1._UO1.DO45);

IF REdge_first.Q THEN

GVL.bStart:= TRUE;

END_IF

fbMove(

Axis:= GVL.Axis1,

Execute:= GVL.bStart2,

Position:= nPos,

Velocity:= nVel

);

fbHome(

Axis:= GVL.Axis1,

Execute:= GVL.bHome,

Position:= 0.0,

Velocity:= 10,

Direction:= MC_Direction.MC_Shortest_Way,

Done=> bHomeDone,

);

mc_readactpos(

Axis:= GVL.Axis1,

Enable:= TRUE,

Position=> fServoCurrPos

);

mc_readactvel_rev(

Axis:= GVL.Axis2,

Enable:= TRUE,

ActualVelocity=> fServoCurrVel_rev

);

mc_readactvel_rot(

Axis:= GVL.Axis3,

Enable:= TRUE,

ActualVelocity=> fServoCurrVel_rot

);

mc_stop(

Axis:= GVL.Axis1,

Execute:= GVL.bStop,

Done=> bStopDone,

);

mc_stop_rev(

Axis:= GVL.Axis2,

Execute:= GVL.bStop_rev,

Done=> bStopDone_rev,

);

mc_stop_rot(

Axis:= GVL.Axis3,

Execute:= GVL.bStop_rot,

Done=> bStopDone_rot,

);

mc_setpos(

Axis:= GVL.Axis1,

Position:= 0.0,

Done=> bSetDone

);

REdge_HomeDone(CLK:= bHomeDone);

IF REdge_HomeDone.Q THEN

GVL.bHome:= FALSE;

bTimer:= TRUE;

END_IF

fbTimer_SetPos(IN:= bTimer, PT:= T#1S);

IF fbTimer_SetPos.Q THEN

mc_setpos.Execute:= TRUE;

END_IF

REdge_setdone(CLK:= bSetDone);

IF REdge_setdone.Q THEN

mc_setpos.Execute:= FALSE;

bTimer:= FALSE;

END_IF

REdge_StopDone(CLK:= bStopDone);

IF REdge_StopDone.Q THEN

GVL.bStart := FALSE;

GVL.bStart2 := FALSE;

IF motor_trig1 THEN

trig_status:= 1;

motor_trig1:= FALSE;

fbMove2.Execute:= FALSE;

fbMove_rev2.Execute:= FALSE;

fbMove_rot2.Execute:= FALSE;

ELSIF motor_trig2 THEN

trig_status:= 2;

motor_trig2:= FALSE;

fbMove1.Execute:= FALSE;

fbMove_rev1.Execute:= FALSE;

fbMove_rot1.Execute:= FALSE;

END_IF

GVL.bStop:= FALSE;

END_IF

REdge_StopDone_rev(CLK:= bStopDone_rev);

IF REdge_StopDone_rev.Q THEN

GVL.bStop_rev:= FALSE;

END_IF

REdge_StopDone_rot(CLK:= bStopDone_rot);

IF REdge_StopDone_rot.Q THEN

GVL.bStop_rot:= FALSE;

END_IF

REdge_Restart(CLK:= GVL.bRestart);

IF REdge_Restart.Q THEN

GVL.bStart:= TRUE;

IF trig_status = 1 THEN

motor_trig1:= TRUE;

ELSIF trig_status = 2 THEN

motor_trig2:= TRUE;

END_IF

GVL.bRestart:= FALSE;

END_IF

nPos_X.0:= Robot1._UO1.Xl0;

nPos_X.1:= Robot1._UO1.Xl1;

nPos_X.2:= Robot1._UO1.Xl2;

nPos_X.3:= Robot1._UO1.Xl3;

nPos_X.4:= Robot1._UO1.Xl4;

nPos_X.5:= Robot1._UO1.Xl5;

nPos_X.6:= Robot1._UO1.Xl6;

nPos_X.7:= Robot1._UO1.Xl7;

nPos_X.8:= Robot1._UO1.Xl8;

nPos_X.9:= Robot1._UO1.Xl9;

nPos_X.10:= Robot1._UO1.Xl10;

nPos_X.11:= Robot1._UO1.Xl11;

nPos_X.12:= Robot1._UO1.Xl12;

nPos_X.13:= Robot1._UO1.Xl13;

nPos_X.14:= Robot1._UO1.Xl14;

nPos_X.15:= Robot1._UO1.Xl15;

nPos_X.16:= Robot1._UO1.Xh0;

nPos_X.17:= Robot1._UO1.Xh1;

nPos_X.18:= Robot1._UO1.Xh2;

nPos_X.19:= Robot1._UO1.Xh3;

nPos_X.20:= Robot1._UO1.Xh4;

nPos_X.21:= Robot1._UO1.Xh5;

nPos_X.22:= Robot1._UO1.Xh6;

nPos_X.23:= Robot1._UO1.Xh7;

nPos_Y.0:= Robot1._UO1.Yl0;

nPos_Y.1:= Robot1._UO1.Yl1;

nPos_Y.2:= Robot1._UO1.Yl2;

nPos_Y.3:= Robot1._UO1.Yl3;

nPos_Y.4:= Robot1._UO1.Yl4;

nPos_Y.5:= Robot1._UO1.Yl5;

nPos_Y.6:= Robot1._UO1.Yl6;

nPos_Y.7:= Robot1._UO1.Yl7;

nPos_Y.8:= Robot1._UO1.Yl8;

nPos_Y.9:= Robot1._UO1.Yl9;

nPos_Y.10:= Robot1._UO1.Yl10;

nPos_Y.11:= Robot1._UO1.Yl11;

nPos_Y.12:= Robot1._UO1.Yl12;

nPos_Y.13:= Robot1._UO1.Yl13;

nPos_Y.14:= Robot1._UO1.Yl14;

nPos_Y.15:= Robot1._UO1.Yl15;

nPos_Y.16:= Robot1._UO1.Yh0;

nPos_Y.17:= Robot1._UO1.Yh1;

nPos_Y.18:= Robot1._UO1.Yh2;

nPos_Y.19:= Robot1._UO1.Yh3;

nPos_Y.20:= Robot1._UO1.Yh4;

nPos_Y.21:= Robot1._UO1.Yh5;

nPos_Y.22:= Robot1._UO1.Yh6;

nPos_Y.23:= Robot1._UO1.Yh7;

IF nXorY = 0 THEN

fRobotActualPos:= UDINT_TO_LREAL(nPos_X) / 1000.0;

IF Robot1._UO1.X_Check THEN

fRobotActualPos:= fRobotActualPos * (-1);

END_IF

ELSIF nXorY = 1 THEN

fRobotActualPos:= UDINT_TO_LREAL(nPos_Y) / 1000.0;

IF Robot1._UO1.Y_Check THEN

fRobotActualPos:= fRobotActualPos * (-1);

END_IF

REdge_bStart(CLK:= Robot1._UI1.UI09_RSR1);

IF REdge_bStart.Q THEN

fBackupValue:= fRobotActualPos;

bSequenceMode:= TRUE;

(*fRobotTargetPos := fRobotFirstPos;

fRobotStartPos := fRobotFirstPos;

fMotorTargetPos := 0.0;

fMotorStartPos := 0.0;*)

nTotalProcessCnt:= 1;

nTrackingIdx:= 1;

fRobotTargetPos:= GVL.aPathData.fRobot_Pos;

fRobotStartPos:= fRobotFirstPos;

fMotorTargetPos:= GVL.aPathData.fPosition;

fMotorStartPos:= 0.0;

fRobotTotalDist := 0.0;

fRobotRemainRatio := 0.0;

fSampledTargetPos := GVL.Axis1.NcToPlc.ModuloActPos;

fPositionError := 0.0;

fOutput := 0.0;

fCalculatedOverride := 0.8;

END_IF

fRelativePos:= fRobotActualPos - fBackupValue;

IF bSequenceMode THEN

IF ABS(fRelativePos) >= ABS(fRobotTargetPos) THEN

nTrackingIdx:= nTrackingIdx + 1;

IF nTrackingIdx > GVL.nMaxPoints THEN

nTrackingIdx:= 1;

fRobotTargetPos:= GVL.aPathData.fRobot_Pos;

fRobotStartPos:= GVL.aPathData.fRobot_Pos;

fMotorTargetPos:= GVL.aPathData.fPosition;

fMotorStartPos:= GVL.aPathData.fPosition;

ELSE

fRobotTargetPos:= GVL.aPathData.fRobot_Pos;

fRobotStartPos:= GVL.aPathData.fRobot_Pos;

fMotorTargetPos:= GVL.aPathData.fPosition;

fMotorStartPos:= GVL.aPathData.fPosition;

END_IF

fbScanTimer(IN:= NOT fbScanTimer.Q, PT:= T#10MS);

IF fbScanTimer.Q THEN

fRobotTotalDist:= fRobotTargetPos - fRobotStartPos;

IF fRobotTotalDist <> 0 THEN

fRobotRemainRatio:= (fRobotTargetPos - fRelativePos) / fRobotTotalDist;

ELSE

fRobotRemainRatio:= 0.0;

END_IF

IF fMotorTargetPos = 0 THEN

fMotorTargetPos:= 360;

END_IF

fMotorTotalDist:= fMotorTargetPos - fMotorStartPos;

fMotorVirtualTarget:= fMotorTargetPos - (fMotorTotalDist * fRobotRemainRatio);

fSampledTargetPos:= fMotorVirtualTarget;

fSampledActualPos:= GVL.Axis1.NcToPlc.ModuloActPos;

END_IF

fScaled_Kp:= fDrivePosLoopGain / 500.0;

fPositionError:= fSampledTargetPos - fSampledActualPos;

fOutput:= fPositionError * fScaled_Kp;

fCalculatedOverride:= LIMIT(0.5, (0.8 + fOutput), 1.0);

nRobotIdx.0:= Robot1._UO1.DO221;

nRobotIdx.1:= Robot1._UO1.DO222;

nRobotIdx.2:= Robot1._UO1.DO223;

nRobotIdx.3:= Robot1._UO1.DO224;

nRobotIdx.4:= Robot1._UO1.DO225;

nRobotIdx.5:= Robot1._UO1.DO226;

nRobotIdx.6:= Robot1._UO1.DO227;

nRobotIdx.7:= Robot1._UO1.DO228;

nRobotIdx.8:= Robot1._UO1.DO229;

nRobotIdx.9:= Robot1._UO1.DO230;

nRobotIdx.10:= Robot1._UO1.DO231;

nRobotIdx.11:= Robot1._UO1.DO232;

nRobotIdx.12:= Robot1._UO1.DO233;

nRobotIdx.13:= Robot1._UO1.DO234;

nRobotIdx.14:= Robot1._UO1.DO235;

nRobotIdx.15:= Robot1._UO1.DO236;

nRobotIdx_int:= UDINT_TO_INT(nRobotIdx);

IF nRobotIdx_int >= 1 AND nRobotIdx_int <= GVL.nMaxPoints THEN

frobot := GVL.aPathData.fRobot_Pos;

ELSE

frobot := 0.0;

END_IF

MC_CamIn - velocity of master axis not reaching maximal values

stavi — Fri, 24 Apr 2026 10:11:03 +0000

Hello,

We have a machine with spindle and a 'support' axis. It was programmed to move coupled using MC_CamIn for the main automatic cycle and normal absolute movements for positioning and auxilary movements.

When we position the spindle and/or the support X axis using the normal movements both reach our set/desired velocities i.e. 3000mm/s.

However when we run the 'main' automatic cycle using MC_CamIn where spindle is the master axis and X is our slave axis (using a table for positions for both) the spindle only reaches 719.36mm/s (always, if the movement is long enough it reaches it fast and caps at this specific value).

We cannot find how the MC_CamIn is calculating the velocity? From which settings does it get it?

The distance for Spindle is long enough it reaches the velocity in about 2 revolutions, and than runs 8 more revolutions with this specific yet low velocity. Our support axis X only makes small jumps of 1-2mm.

We tried different sets of maximum velocity/ reference velocity / acceleration /deceleration and jerk for both the spindle and x axis from the drive parameters. Even set it up 10x times higher, however the effect is always the same Spindle runs at 719.36 max.

This only occurs with MC_CamIn the normal motion works fine and spindle as well as X axis reach our set velocity i.e. 3000mm/s

Can anyone help with some insider info from where or how does the MC_CamIn calculate its movement velocity? We cannot find any place it would be declared or set. We have our position table for master and slave, the maximal velocity etc from drive parameters, so how can we increase master axis velocity?

Thanks in advance!

TwinCAT 3.1 (Build 4026) & Git – Online Change fails after cloning project (mapping mismatch)

funka84 — Thu, 06 Nov 2025 21:02:29 +0000

Hi everyone,

we’re currently running a TwinCAT 3.1 project (version 4026) with Git as our version control system, and we’ve run into a workflow issue that we can’t seem to solve.

Setup:

3 developers working in parallel
Multi-PLC project (separate PLC task for each developer)
One “main” development PC where the hardware configuration is activated
Each colleague clones the project from Git and works on their PLC
The goal is that all of us can be logged into our own PLC at the same time and perform Online Changes

The problem:

After the hardware config is activated on the main PC and we all pull the project from Git, TwinCAT refuses Online Change on the other machines.
We get an error saying that the mapping does not match or is invalid, even though nothing has been changed in the I/O configuration.

It seems like TwinCAT thinks the project is different from what’s running on the target, although everything (in theory) is identical – same commit, same configuration, same PLC code.

What we tried:

Full rebuild on every workstation → no effect
Deleting the .compileinfo, .tmc, and generated build folders before building → no effect
Re-activating hardware locally on every PC → works, but then every developer ends up committing different hardware GUIDs to Git → merge chaos
Using “PLC only” activation → same mapping error when trying Online Change

What we think is happening:

TwinCAT stores some hardware-related GUIDs / internal hashes locally, and after cloning the project, they don't match the target runtime, even if the code is identical.
As soon as one person re-activates the solution, the others can no longer do Online Change.

Question:

Has anyone found a clean workflow for multi-developer TwinCAT projects with Git, where multiple people can:

clone the repo
go online with their PLC
do Online Change
without everyone having to re-activate the I/O tree individually?

Is there a recommended “.gitignore” setup to avoid committing machine-specific files?
Or is TwinCAT simply not made for true parallel development with shared hardware config?

Any best practices, workarounds, or real-world experiences are highly appreciated!

Thanks in advance!

Note: English is not my native language, so I used ChatGPT to help write this post. Hopefully everything is understandable – feel free to correct me if something sounds unclear.

Visual Studio Task List (Comment Tokens like TODO:) not showing in TwinCAT 3 XAE

Jonas_R — Thu, 23 Oct 2025 07:54:30 +0000

Hi everyone,

I'm currently working with TwinCAT 3 XAE (2017) and I'm trying to use the standard Visual Studio Task List feature to track comments like TODO:.

I've confirmed that "TODO" is listed under Tools -> Options -> Environment -> Task List, and I can even add custom tokens there.

However, when I add comments in my code like:

// TODO: Refactor this section

(* TODO: Check calculation logic *)

These comments do not appear in the Task List window (View -> Task List).
I understand that "Tasks" in TwinCAT usually refer to real-time execution tasks, which makes searching for this specific issue a bit difficult.

I'm explicitly asking about the Visual Studio feature that parses code comments for predefined tokens.

Is this Task List comment functionality expected to work within the TwinCAT 3 XAE environment for PLC code? Are there any specific TwinCAT project settings or known limitations that might prevent it from working? Or perhaps a different syntax is required within PLC comments?

Has anyone else encountered this and found a way to get comment tokens to show up in the Task List?

Thanks in advance for any insights!

NC Camming - In desperate need of help

mguido — Sun, 21 Sep 2025 18:12:33 +0000

I have a multi-axis NC Camming application. Kind of struggling to gain traction. I've watched the Beckhoff webinar on the topic (Vimeo). The Infosys documentation is pretty lacking in terms of application example. Went through a few plcOpen tutorials (thinking they might help things click), considering watching through Yaskawa's youtube videos on plcOpen to see if I can glean any additional insights (even though its demo'd in their software).

Read through the one post I could find on the topic here, and since it was more helpful than anything else I've found in the past several weeks, I figured I'd post looking for help. If anyone has some good resources for learning, or wouldn't mind downloading their knowledge/understanding into an example and post it as a reply to this thread, I'd be incredibly grateful.

API to Interact with PLC/IDE?

henjoh — Thu, 04 Sep 2025 07:14:07 +0000

I would like to write an application (preferably using .NET) that can trigger and save backup/restore of both source project files and binaries(?) published to hardware, e.g. a C9900-I627.

Is this possible? If so, any pointers and references would be greatly appreciated!

Running TwibCAT on a Virtual Box win10 Virtual Machine

Simone71 — Wed, 27 Aug 2025 12:07:18 +0000

Hello everybody, I'm new member of twinControls and this my first Topic. I hope to be clear and using the right spirt of this Forum.

I'm trying to use TwinCAT on a Virtual Machine created with Virtual Box, but when I try to put TC in Run mode I get the following errors:

935 936

The first with the Previrtualization Interface set to "Hyper-V" and the second error when it is set to "None" (in the Virtual Box Settings --> System).
I tried already many suggestion is possible to find on the Network, like: deactivation of Hyper-V, Virtual Machine Platform and Windows Hypervision Platform on the Host system, setting of shared CPUs leaving one Insulated and putting it as Default, running as administrator win8settick, etc...

From the second Error, I though that the Guest machine is not able to find an active virtualization (Intel VT-x) by nested virtualization.

Indeed in the Setting of VM (in System --> Processor) the setting of "Nested VT-x/AMD-V is not selectable, and I was not able to make the selection active.

937

Here my system parameters:

Host machine:

HP ZBook Power with processor Intel Ultra 9 185H

OS Win11 Pro

Virtualization Technology and Intel VT-x in the BIOS are active

Virtual Box version 7.2.0 r170228

Guest machine:

OS Win 10 Pro

TwinCAT 3.1 build 4024.67

In the following screenshot all the setting of the Virtual Machine:

938

I decided to use a virtual machine, thinking was a good idea to start using TwinCAT and perform testing and prototyping in a saparated part of my PC. I wanted in the end install TwinCAT directly in the win11 real machine , but I'm very worry these problem could happen also there.

I'm really close to be disparate, and I hope someone could know a solution for this issue.
I thank you in advance for every help and apologize if my post is not orthodox.

With best regards,

Simone

Pull External OPC UA nested data structure into TC3 project

mguido — Tue, 26 Aug 2025 21:42:40 +0000

Wondering if anyone knows of a way to pull an existing external nested data structure into a TC3 project via OPC UA? For reference, UDT was set up in Rockwell's Studio 5000 and migrated to FactoryTalk Optix (which is heavily OPC UA based).

I have the object model for the UDT in FT Optix, and we pivoted to a Beckhoff platform for everything but the HMI (given it's a rather complex HMI project that wouldn't be realistic to redo given our project timeline for runoff). Given the size and scope of the existing UDT structure, I would love to avoid having to redo it from scratch. Every other PLC brand exports these in standard PLCOpen formats, except Rockwell. Was told from a Beckhoff AE that it might be possible to pull the structure in via OPC UA and generate the analogous Struct in TC3.

Anyone out there done this? If so, any pointers or instructions you've found that kind of spell this out?

twincat installation

kirsti — Thu, 14 Aug 2025 08:02:18 +0000

During twincat standard instalation this occure

933

Change the default port of OPC UA in Twincat3

Weronika — Fri, 08 Aug 2025 11:47:58 +0000

Hi,

I’m working on a project where I want to connect two simulated PLCs (TwinCAT 3 and CODESYS) to a SCADA system (Ignition) via OPC UA. I already have a connection between Ignition and CODESYS, and now I want to add a connection between TwinCAT 3 and Ignition.

In CODESYS, I’m using the default port 4840. I think using the same port in TwinCAT as in CODESYS could cause problems. Is it possible to change the default port in TwinCAT 3?