L_MC4P_GroupTorquePreControl

With this FB, a torque feedforward control can be configured for an axes group. If the parameter setting is precise enough, the controller is relieved and the following error of the axes group is reduced considerably.

Torque feedforward control for reducing following errors

There are three sources for determining the required parameters:

Axes group parameters

Data sheet values, measured values

Specification with

L_MK4P_DynamicParDelta3_3dof (Use in axes group Delta3_3dof)

L_MK4P_DynamicParDelta3_4dof (Use in axes group Delta3_4dof)

L_MK4P_DynamicParScara_3dof (Use in axes group Scara_3dof)

L_MK4P_DynamicParScara_4dof (Use in axes group Scara_4dof)

Identified values from the L_MC4P_DynamicParIdent application FB

Note!

The calculated feedforward control values are NOT copied to the drive axes of the axes group in PLCopen states GroupDisabled and GroupErrorStop .

The feedforward control can only be calculated if the axes group has been referenced.

To prevent jumps in the feedforward control torque, switch-on and switch-off are performed via a ramp function within several PLC cycles.

Warning!

An incorrectly configured feedforward control can cause uncontrolled movements and machine damage.

Three different limitations and scalings can be specified for the torque:

Scaling factor for the calculated torque ( lrTorqueOverride ).

Limitation factor of the feedforward control torques with reference to the rated torques of the axes ( lrTorqueLimitFactor ).

Maximum change rate of the feedforward control torques in [Nm/s] with reference to the gearbox output ( alrTorqueRateLimit ).

The quality of the parameters selected for torque feedforward control is diagnosed during commissioning by comparing output signals alrActTorque (actual torque) and alrSetTorque-Out (calculated torque).

Checking results with a torque comparison

		L_MC4P_GroupTorquePreControl
AXES_GROUP_KIN	-	AxesGroup	xValid	-	BOOL
BOOL	-	xEnable	xBusy	-	BOOL
BOOL	-	xUseAxesGroupParam	xError	-	BOOL
BOOL	-	xWriteToParameter	eErrorID	-	L_IE1P_Error
LREAL	-	lrTorqueOverride
LREAL	-	lrTorqueLimitFactor
ARRAY[1..6] OF LREAL	-	alrTorqueRateLimit
LREAL	-	lrLoadMass	alrSetTorqueOut	-	ARRAY[1..6] OF LREAL
L_MC4P_DynamicPar	-	itfDynamicPar	alrActTorque	-	ARRAY[1..6] OF LREAL

Inputs

Name Data type	Information/possible settings
AxesGroup AXES_GROUP_KIN	axes group reference
xEnable BOOL	FALSE ä TRUE	Activate torque feedforward control. If there is a positive edge at this input, the feedforward control parameters are read in as specified in " xUseAxesGroupParam" .
xUseAxesGroupParam BOOL	TRUE	If there is a positive edge at " xEnable": Read the parameters for torque feedforward control from the parameter set of the axes group.
FALSE	If there is a positive edge at " xEnable": Read the parameters for torque feedforward control from "itfDynamicPar".
xWriteToParameter BOOL	FALSE ä TRUE	With a positive edge AND " xEnable" = TRUE: Copy values on the interface into the parameter set of the axes group. The "Save parameter set" device command must be executed for permanent saving of the parameters.
lrTorqueOverride LREAL	Scaling factor for the calculated torque. This input is evaluated cyclically. During commissioning, the torque feedforward control can be switched on step-by-step using this factor. We recommend setting the input to 0 first and, for typical axes group motions, comparing the calculated feedforward control torques ( alrSetTorqueOut ) with the actual axes torques ( alrActTorque ) using a trace. If the progressions are sufficiently similar, the feedforward control can be switched on step-by-step (e.g. in 10% steps) and the effectiveness can be checked using the following error. If the progressions are not similar or if they differ in terms of the value range, the system parameters applied to the FB must be checked. Here, special attention must be paid to ensuring that the units are correct and to the reference to the gearbox output. During operation, it is possible to adapt the calculated torques to the actual torques if the system parameters are not known with sufficient accuracy. Depending on the application case, it may be worth calculating the torques only partially with the feedforward control (e.g. 80%) to achieve a minimal following error.
0.00 ... 2.00	Transfer 0 ... 200% of the calculated torques to the axes.
lrTorqueLimitFactor LREAL	Limitation factor of the feedforward control torques with reference to the rated torque of the axes. This input is evaluated cyclically. With this input, the calculated feedforward control torques are symmetrically limited to a percentage value of the rated torque of the axis.
0.00 ... 5.00	0 ... 500% of the axis rated torques are pilot-controlled.
alrTorqueRateLimit ARRAY [1..6] OF LREAL	Maximum change rate of the feedforward control torques in [Nm/s] with reference to the gearbox output. This input is evaluated cyclically. This input limits the maximum change rate of the feedforward control torques so that no torque jumps are written to the drives of the axes group. Torque jumps in the calculated torque may occur, for example, in the event of erratic parameter changes at the block inputs during operation or if motions are executed without jerk limitation. It would probably make sense to have values somewhere in the magnitude of M _Rated for each PLC cycle.
0	Limitation is inactive
lrLoadMass LREAL	Mass of a load in [kg] optionally attached to the end effector. This input is evaluated cyclically. Caution: Erratic changes at this input typically cause erratic changes to the feedforward control torque as well. These changes can be limited via alrTorqueRateLimit .
itfDynamicPar L_MC4P_DynamicPar	Dynamic parameters of the axes group. This parameter interface provides axes group-specific parameters for calculating the torque feedforward control. The following FBs are currently supported: L_MK4P_DynamicParDelta3_4dof L_MK4P_DynamicParDelta3_4dof L_MK4P_DynamicParScara_3dof L_MK4P_DynamicParScara_4dof L_MC4P_DynamicParIdent

Name

Data type

Information/possible settings

AxesGroup

AXES_GROUP_KIN

axes group reference

xEnable

BOOL

FALSE ä TRUE

Activate torque feedforward control.

If there is a positive edge at this input, the feedforward control parameters are read in as specified in " xUseAxesGroupParam" .

xUseAxesGroupParam

BOOL

TRUE

If there is a positive edge at " xEnable": Read the parameters for torque feedforward control from the parameter set of the axes group.

FALSE

If there is a positive edge at " xEnable": Read the parameters for torque feedforward control from "itfDynamicPar".

xWriteToParameter

BOOL

FALSE ä TRUE

With a positive edge AND " xEnable" = TRUE:

Copy values on the interface into the parameter set of the axes group.

The "Save parameter set" device command must be executed for permanent saving of the parameters.

lrTorqueOverride

LREAL

Scaling factor for the calculated torque. This input is evaluated cyclically.

During commissioning, the torque feedforward control can be switched on step-by-step using this factor. We recommend setting the input to 0 first and, for typical axes group motions, comparing the calculated feedforward control torques ( alrSetTorqueOut ) with the actual axes torques ( alrActTorque ) using a trace. If the progressions are sufficiently similar, the feedforward control can be switched on step-by-step (e.g. in 10% steps) and the effectiveness can be checked using the following error. If the progressions are not similar or if they differ in terms of the value range, the system parameters applied to the FB must be checked. Here, special attention must be paid to ensuring that the units are correct and to the reference to the gearbox output.

During operation, it is possible to adapt the calculated torques to the actual torques if the system parameters are not known with sufficient accuracy. Depending on the application case, it may be worth calculating the torques only partially with the feedforward control (e.g. 80%) to achieve a minimal following error.

0.00 ... 2.00

Transfer 0 ... 200% of the calculated torques to the axes.

lrTorqueLimitFactor

LREAL

Limitation factor of the feedforward control torques with reference to the rated torque of the axes. This input is evaluated cyclically.

With this input, the calculated feedforward control torques are symmetrically limited to a percentage value of the rated torque of the axis.

0.00 ... 5.00

0 ... 500% of the axis rated torques are pilot-controlled.

alrTorqueRateLimit

ARRAY [1..6] OF LREAL

Maximum change rate of the feedforward control torques in [Nm/s] with reference to the gearbox output. This input is evaluated cyclically.

This input limits the maximum change rate of the feedforward control torques so that no torque jumps are written to the drives of the axes group.

Torque jumps in the calculated torque may occur, for example, in the event of erratic parameter changes at the block inputs during operation or if motions are executed without jerk limitation.

It would probably make sense to have values somewhere in the magnitude of M _Rated for each PLC cycle.

Limitation is inactive

lrLoadMass

LREAL

Mass of a load in [kg] optionally attached to the end effector. This input is evaluated cyclically.

Caution: Erratic changes at this input typically cause erratic changes to the feedforward control torque as well. These changes can be limited via alrTorqueRateLimit .

itfDynamicPar

L_MC4P_DynamicPar

Dynamic parameters of the axes group.

This parameter interface provides axes group-specific parameters for calculating the torque feedforward control.

The following FBs are currently supported:

L_MK4P_DynamicParDelta3_4dof

L_MK4P_DynamicParScara_3dof

L_MK4P_DynamicParScara_4dof

L_MC4P_DynamicParIdent

Outputs

Name Data type	Value/meaning
xValid BOOL	TRUE	Valid values are present at the outputs.
xBusy BOOL	TRUE	Processing is running.
xError BOOL	TRUE	An error has occurred. For details, see ErrorID .
eErrorID L_IE1P_Error	If Error = TRUE: Error number for the error that has occurred.
alrSetTorqueOut ARRAY [1..6] OF LREAL	Only for diagnostics purposes, e.g. during commissioning. Feedforward control torque calculated in the FB in [Nm] with reference to the gearbox output without considering inputs lrTorqueOverride , lrTorqueLimitFactor and lrTorqueRateLimit .
alrActTorque ARRAY [1..6] OF LREAL	Only for diagnostics purposes, e.g. during commissioning. Current torque of the axis in [Nm] with reference to the gearbox output.

Name

Data type

Value/meaning

xValid

BOOL

TRUE

Valid values are present at the outputs.

xBusy

BOOL

TRUE

Processing is running.

xError

BOOL

TRUE

An error has occurred. For details, see ErrorID .

eErrorID

L_IE1P_Error

If Error = TRUE: Error number for the error that has occurred.

alrSetTorqueOut

ARRAY [1..6] OF LREAL

Only for diagnostics purposes, e.g. during commissioning.

Feedforward control torque calculated in the FB in [Nm] with reference to the gearbox output without considering inputs lrTorqueOverride , lrTorqueLimitFactor and lrTorqueRateLimit .

alrActTorque

ARRAY [1..6] OF LREAL

Only for diagnostics purposes, e.g. during commissioning.

Current torque of the axis in [Nm] with reference to the gearbox output.