ScrewTighten Object

The ScrewTighten object is a force guide object used to tighten screws while moving the robot by pressing in a specified direction with a specified amount of force.

The diagram above provides a visual representation of a ScrewTighten object. Executed from a non-contact state, this object moves the robot in the screw tightening direction depicted by the white arrow. From the point of contact, the robot tightens screws with a set amount of force in the screw tightening direction shown by the yellow arrow.

The ScrewTighten object can apply end conditions related to the screw tightening completion signal given by driver, and force and position. Each end condition is always applied.

When all the success conditions for each end condition are met: The ScrewTighten object execution ends. The execution is determined as succeeded and proceed to the next force guide object. When the screw retightening operation is enabled, skip the ScrewRetighten object and proceed to the next object.

When at least one of the failure conditions for each end condition is met: The ScrewTighten object execution ends. The execution is determined as failed and abort the force guide sequence. When the screw retightening operation is enabled, when the screw tightening completion signal given by driver is received and the failure condition of the position end condition is satisfied, it is determined that the execution of the ScrewTighten object is finished and the screw is jammed, then proceed to the ScrewRetighten object.

End condition	Success condition
End conditions related to the screw tightening completion signal	The screw tightening completion signal given by driver is received.
End conditions related to position	The moving distance from the force guide object start point in the axial direction specified in PressOrient is within the range of ApproachDist + ScrewLength - DistCheckTol to ApproachDist + ScrewLength + DistCheckTol

End condition	Failure condition
End conditions related to the screw tightening completion signal	Moved from the force guide object start point by the amount specified by ApproachDist and InsertDepth, but did not receive the screw tightening completion signal from the driver.
End conditions related to position	Before receiving the screw tightening completion signal, the following is satisfied: Before receiving the screw tightening completion signal, the following is satisfied: The moving distance from the force guide object start point in the axial direction specified by PressOrient exceeds ApproachDist + InsertDepth + DistCheckTol. Alternatively, after receiving the screw tightening completion signal, the following is satisfied: The moving distance from the force guide object start point in the axial direction specified by PressOrient does not reach ApproachDist + InsertDepth - DistCheckTol.
End conditions related to force	The pressing force in the axial direction specified by PressOrient exceeds the value set by CollisionForceThresh.

End condition

Failure condition

End conditions related to the screw tightening completion signal

Moved from the force guide object start point by the amount specified by ApproachDist and InsertDepth, but did not receive the screw tightening completion signal from the driver.

End conditions related to position

Before receiving the screw tightening completion signal, the following is satisfied:

The moving distance from the force guide object start point in the axial direction specified by PressOrient exceeds ApproachDist + InsertDepth + DistCheckTol.

Alternatively, after receiving the screw tightening completion signal, the following is satisfied:

The moving distance from the force guide object start point in the axial direction specified by PressOrient does not reach ApproachDist + InsertDepth - DistCheckTol.

End conditions related to force

The pressing force in the axial direction specified by PressOrient exceeds the value set by CollisionForceThresh.

Property guideline for ScrewTighten object

Step 1. Set basic information
Set properties (Name, Description, StepID, AbortSeqOnFail) related to the basic information.

Properties	Description, setting guide
Name	This property sets names of force guide objects. Set a particular name.
Description	This property sets descriptions about force guide objects. Describe the operations. Set a character string.
StepID	StepID during the force guide object execution. Set an ID. StepID is an ID which is recorded in the log data. It helps you to understand which log data support a process. It is applied when AutoStepID of the force guide sequence is False.
AbortSeqOnFail	Set whether to abort or continue the force guide sequence when the force guide object fails.
	True : Normal End a force guide sequence.
	False : Cases where the force guide sequence contains recovery operations in case of failure; cases where the sequence will be able to continue even in the event of a failure.

Step 2. Set a movement motion
Set properties (AccelS, SpeedS) related to movements.

Properties	Description, setting guide
AccelS	Set the translational acceleration of the movement. It is automatically set from the driver rotation speed and screw lead length set in the sequence wizard. When having trouble tightening the screws, you can change the value. Actual acceleration is adjusted by the force control functions.
SpeedS	Set the translational velocity of the movement. It is automatically set from the driver rotation speed and screw lead length set in the sequence wizard. When having trouble tightening the screws, you can change the value. Actual speed is adjusted by the force control functions.

Properties

Description, setting guide

AccelS

Set the translational acceleration of the movement.

It is automatically set from the driver rotation speed and screw lead length set in the sequence wizard. When having trouble tightening the screws, you can change the value.

Actual acceleration is adjusted by the force control functions.

SpeedS

Set the translational velocity of the movement.

It is automatically set from the driver rotation speed and screw lead length set in the sequence wizard. When having trouble tightening the screws, you can change the value.

Actual speed is adjusted by the force control functions.

Step 3. Set a destination point
Set properties (ApproachDist, ScrewLength) related to trajectories to move.

Properties	Description, setting guide
ApproachDist	Set an approach distance from the start point of the force guide object to the opening of the screw hole. The approach distance is distance 1 depicted in the diagram below, which is the distance between the screw end point of the gripped workpiece at the start point of the force guide object indicated by the green dot, and the opening of screw hole. Teach the robot a start point of the motion that shortens the approach distance as much as possible. As the force control function is slower than position control, longer approach distances will result in longer cycle times.
ScrewLength	Set the length of the screw. As shown in the ApproachDist diagram, ScrewLength is a length of 2.

Properties

Description, setting guide

ApproachDist

Set an approach distance from the start point of the force guide object to the opening of the screw hole.

The approach distance is distance 1 depicted in the diagram below, which is the distance between the screw end point of the gripped workpiece at the start point of the force guide object indicated by the green dot, and the opening of screw hole.

Teach the robot a start point of the motion that shortens the approach distance as much as possible. As the force control function is slower than position control, longer approach distances will result in longer cycle times.

ScrewLength

Set the length of the screw.

As shown in the ApproachDist diagram, ScrewLength is a length of 2.

Step 4. Set force control functions
Set properties (PressOrient, PressForce, PressFirmnessF, FollowOrient, FollowFirmnessF) related to the force control functions.

Properties	Description, setting guide
PressOrient	Set a direction to tighten screw. The robot moves to the specified direction.
PressForce	Set a pressing force to apply in the direction of screw tightening. When PressOrient is positive direction: Enter a negative value. When PressOrient is negative direction: Enter a positive value.
PressFirmnessF	Set a firmness of the force control functions in screw tightening direction.
	When setting a large value: The Force Control functions become stronger, but response to changes in force is slow.
	When setting a small value: The Force Control function will become weaker. Response to changes in force is fast; however, vibrations can easily occur.
FollowOrient	In addition to the PressOrient direction, it is the direction to move while following. It is changed automatically according to PressOrient. Read only. It cannot be edited.
FollowFirmnesF	Set a firmness of the force control functions in translational direction except for screw tightening direction.
	When setting a large value: The Force Control functions become stronger, but response to changes in force is slow.
	When setting a small value: The Force Control function will become weaker. Response to changes in force is fast; however, vibrations can easily occur.

Step 5. Set end conditions related to force
Set properties (CollisionForceThresh) related to the end conditions of force.

Properties	Description, setting guide
CollisionForceThresh	This property sets a force to detect that a screw collides with a hole other than the screw hole during screw tightening operation. It fails when the pressing force exceeds the set value. The pressing force may be larger than the PressForce value due to the frictional force generated between the screw and the screw hole. Set it to a value sufficiently larger than the force set by PressForce.

Properties

Description, setting guide

CollisionForceThresh

This property sets a force to detect that a screw collides with a hole other than the screw hole during screw tightening operation.

It fails when the pressing force exceeds the set value.

The pressing force may be larger than the PressForce value due to the frictional force generated between the screw and the screw hole. Set it to a value sufficiently larger than the force set by PressForce.

Step 6. Set end conditions about position
Set property (DistCheckTol) related to the end conditions of the positions.

Properties	Description, setting guide
DistCheckTol	This property sets the screw tightening direction range of the end conditions related to position. It monitors that the moving distance from the operation start point to the destination point in the direction specified by PressOrient is within the range of ApproachDist + ScrewLength - DistCheckTol to ApproachDist + ScrewLength + DistCheckTol The following is an image of DistCheckTol.

Properties

Description, setting guide

DistCheckTol

This property sets the screw tightening direction range of the end conditions related to position.

It monitors that the moving distance from the operation start point to the destination point in the direction specified by PressOrient is within the range of ApproachDist + ScrewLength - DistCheckTol to ApproachDist + ScrewLength + DistCheckTol

The following is an image of DistCheckTol.

Details on the properties of the ScrewTighten object

Name Property
This property sets a particular name that is assigned to force guide object.
When creating the ScrewTighten sequence, name is assigned automatically. Automatically assigned name is added a number after ScrewTighten (e.g. ScrewTighten01).
You can change the name. Set up 16 characters at the maximum. Please use alphanumeric characters and underscores [_]. Note: The initial character cannot be a numeric character.

Description Property
This property sets descriptions about force guide objects. You can set the character string up to 255 characters.

StepID Property
This property sets StepID during the execution of the force guide objects. It is only used when AutoStepID is False.

Value

Minimum Value 0

Maximum value 32767
Default: Automatically set according to the numbers of the force guide sequence and the force guide object.

	Value
Minimum Value	0
Maximum value	32767

AbortSeqOnFail Property
This property sets operations when force guide object fails.
When True is specified: If the force guide object fails, the program ends the force guide sequence and proceeds to the next SPEL statement.
When specifying False: If force guide object fails, the program proceeds to the next force guide object without ending the force guide sequence.
Use this property when you want to continue the force guide sequence (e.g. the recovery processes are included in the force guide sequence when the force guide object fails.)
Value

Description

True Abort the force guide sequence when the force guide object fails.

False Start the next force guide sequence when the force guide object fails.
Default: True

Value	Description
True	Abort the force guide sequence when the force guide object fails.
False	Start the next force guide sequence when the force guide object fails.

SpeedS Property
This property sets speed of force guide objects during the execution.
When you create a ScrewTighten sequence, it is automatically set from the driver rotation speed and screw lead length set in the sequence wizard.
However, this set value is the speed for the set trajectory. The actual speed is adjusted by the force control functions.

Value (unit: [mm/sec])

Minimum Value 0.1

Maximum value 200
Default: 5

	Value (unit: [mm/sec])
Minimum Value	0.1
Maximum value	200

AccelS Property
This property sets acceleration of force guide objects.
When you create a ScrewTighten sequence, it is automatically set from the driver rotation speed and screw lead length set in the sequence wizard.
However, this set value is the acceleration for the set trajectory. The actual acceleration is adjusted by the force control functions.

Value (unit: [mm/sec²])

Minimum Value 1

Maximum value 2000
Default: 50

	Value (unit: [mm/sec²])
Minimum Value	1
Maximum value	2000

ApproachDist Property
This property sets the moving distance from the start point of the force guide object to the start point of the insert operation.
Teach the robot a start point of the motion that shortens the moving distance as much as possible. As the force control function is slower than position control, longer moving distances will result in longer cycle times.

Value (Unit: [mm])

Minimum Value 0

Maximum value 50
Default: 10

	Value (Unit: [mm])
Minimum Value	0
Maximum value	50

ScrewLength Property
This property sets the screw length.

Value (Unit: [mm])

Minimum Value 1

Maximum value 100
Default: 10

	Value (Unit: [mm])
Minimum Value	1
Maximum value	100

PressOrient Property
This property sets the direction of motion for screw tightening operations in the coordinate system specified by the ForceOrient property for the force guide sequence.

Value	Description
+Fx	Sets the direction of motion to the +Fx direction in the specified coordinate system.
-Fx	Sets the direction of motion to the -Fx direction in the specified coordinate system.
+Fy	Sets the direction of motion to the +Fy direction in the specified coordinate system.
-Fy	Sets the direction of motion to the -Fy direction in the specified coordinate system.
+Fz	Sets the direction of motion to the +Fz direction in the specified coordinate system.
-Fz	Sets the direction of motion to the -Fz direction in the specified coordinate system.

Default: +Fz

PressForce Property
This property sets the pressing force in the direction of motion specified by the PressOrient property for the force guide object during the execution of the force guide object.
- If PressOrient is +Fx, +Fy, +Fz:
  
  Value (unit: [N])
  
  Minimum Value -50
  
  Maximum value 0
  
  Default: -4
- If the PressOrient is -Fx, -Fy, or -Fz:
  
  Value (unit: [N])
  
  Minimum Value 0
  
  Maximum value 50
  
  Default: 4

	Value (unit: [N])
Minimum Value	-50
Maximum value	0

	Value (unit: [N])
Minimum Value	0
Maximum value	50

PressFirmnessF Property
This property sets the firmness in relation to the force control function in the direction of motion specified by the PressOrient property for the force guide object during the execution of the force guide object.
The larger the PressFirmnessF value, the stronger the force control function becomes in the direction of motion. This slows response to changes in force, but reduces vibration.
The smaller the PressFirmnessF value, the weaker the force control function becomes in the direction of motion. This speeds up response to changes in force, but increases vibration.

Value

Minimum Value 0.1

Maximum value 10
Default: 2

	Value
Minimum Value	0.1
Maximum value	10

FollowOrient Property
This property sets the translational following orientation set for screw tightening operations.
This property is set automatically based on the direction of motion set by the PressOrient property for the force guide object. It cannot be edited.
Value

Description

FyFz Motion following in the FyFz direction.

FxFz Motion following in the FxFz direction.

FxFy Motion following in the FxFy direction.
Default: FxFy

Value	Description
FyFz	Motion following in the FyFz direction.
FxFz	Motion following in the FxFz direction.
FxFy	Motion following in the FxFy direction.

FollowFirmnessF Property
This property sets the firmness in relation to the force control function for force in the following direction during the execution of the force guide object.
The larger the FollowFirmnessF value, the stronger the force control function becomes in the following direction. This slows response to changes in force, but reduces vibration.
The smaller the FollowFirmnessF value, the weaker the force control function becomes in the following direction. This speeds up response to changes in force, but increases vibration.

Value

Minimum Value 0.1

Maximum value 10
Default: 1

	Value
Minimum Value	0.1
Maximum value	10

CollisionForceThresh Property
This property sets a force to detect that a screw collides with a hole other than the screw hole during screw tightening operation.
Set it to a value sufficiently larger than the force set by PressForce.
- If PressOrient is +Fx, +Fy, +Fz:
  
  Value (unit: [N])
  
  Minimum Value -100
  
  Maximum value -10
  
  Default: -30
- If the PressOrient is -Fx, -Fy, or -Fz:
  
  Value (unit: [N])
  
  Minimum Value 10
  
  Maximum value 100
  
  Default: 30

	Value (unit: [N])
Minimum Value	-100
Maximum value	-10

	Value (unit: [N])
Minimum Value	10
Maximum value	100

DistCheckTol Property
Specify the range that is the success condition (when the operation is finished) of the distance moved from the operation start position.
This sets the ApproachDist + ScrewLength ± DistCheckTol range as the success condition.

Value

Minimum Value 0.01

Maximum value 10
Default: 1

	Value
Minimum Value	0.01
Maximum value	10

Details on results of ScrewTighten object

EndStatus Result
It is a result of the execution.
It succeeds when the "success conditions" described in 4.2.2.2 Relax Object are satisfied.
ScrewTighten Object

Value	Description
Passed	Force guide object is succeeded.
Failed	Force guide object is failed.
NoExec	Force guide object is not executed.
Aborted	Aborted during the execution of force guide object.
FailedCont	Force guide object is failed, but the next force guide object is executed.

Time Result
This is the time required for execution.
Unit: [sec]

EndForces Result
It is force and torque when force guide object ends. Acquire values of Fx, Fy, Fz, Tx, Ty, and Tz.
Unit: Fx, Fy, Fz [N] / Tx, Ty, Tz [N・mm]

EndPos Result
Positions when the force guide object ends. Acquire values of X, Y, Z, U, V, and W.
Unit: X, Y, Z [mm] / U, V, W [deg]

AvgForces Result
Average values of force and torque during the force guide object execution. Acquire values of Fx, Fy, Fz, Tx, Ty, and Tz.
Unit: Fx, Fy, Fz [N] / Tx, Ty, Tz [N・mm]

PeakForces Result
Peak values of force and torque during the force guide object execution. The peak value is a value which absolute value is the largest. Acquire values of Fx, Fy, Fz, Tx, Ty, and Tz.
Unit: Fx, Fy, Fz [N] / Tx, Ty, Tz [N・mm]

TriggeredForces Result
It is the force and torque when satisfying the end conditions related to force. Acquire values of Fx, Fy, Fz, Tx, Ty, and Tz.
Unit: Fx, Fy, Fz [N] / Tx, Ty, Tz [N・mm]

TriggeredPos Result
Positions when satisfying the end conditions related to force. Acquire values of X, Y, Z, U, V, and W.
Unit: X, Y, Z [mm] / U, V, W [deg]

PosCondOK Result
Shows whether the end conditions related to position were satisfied.
Value

Description

True Satisfy the end conditions related to position.

False The end conditions related to position are not satisfied.

Value	Description
True	Satisfy the end conditions related to position.
False	The end conditions related to position are not satisfied.

IOCondOK Result
Shows whether the end conditions related to I/O were satisfied.
Value

Description

True Satisfy the end conditions related to I/O.

False The end conditions related to I/O are not satisfied.

Value	Description
True	Satisfy the end conditions related to I/O.
False	The end conditions related to I/O are not satisfied.

PosLimited Result
Shows whether the limit range related to position was exceeded.
Value

Description

True Exceed the limit range related to position.

False The limit range related to position is not exceeded.

Value	Description
True	Exceed the limit range related to position.
False	The limit range related to position is not exceeded.

ForceLimited Result
Shows whether the limiting range related to force was exceeded.
Value

Description

True Exceed the limit range related to force.

False The limit range related to force is not exceeded.

Value	Description
True	Exceed the limit range related to force.
False	The limit range related to force is not exceeded.

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