6-axis robot arm orientations
The 6-axis robot can be operated in different arm orientations within a given work envelope as shown below:
| Righty hand orientation (Arm #1) | ||
|---|---|---|
| NoFlip wrist orientation | Flip wrist orientation | |
| Above elbow orientation |  |  |
| Below elbow orientation |  |  |
| Lefty hand orientation (Arm #1) | ||
|---|---|---|
| Above elbow orientation |  |  |
| Below elbow orientation |  |  |
Enlarged examples of right hand orientation are shown below.
| NoFlip wrist orientation | Flip wrist orientation | |
|---|---|---|
| Above elbow orientation |  |  |
| Below elbow orientation |  |  |
KEY POINTS
The simulator function allows you to check the robot's movements on your computer. See details below.
To specify the arm orientation of the 6-axis robot, add a forward slash (/) followed by:
- L (for Lefty hand orientation) or R (Righty hand orientation)
- A (Above elbow orientation) or B (Below elbow orientation)
- NF (NoFlip wrist orientation) or F (Flip wrist orientation)
There are eight available orientations as shown below, however, some combinations are not available depending on the point.
Available Orientation
- 1: /R /A /NF
- 2: /L /A /NF
- 3: /R /B /NF
- 4: /L /B /NF
- 5: /R /A /F
- 6: /L /A /F
- 7: /R /B /F
- 8: /L /B /F
At some points in the work envelope, the 6-axis robot can have the same position and orientation even if the fourth joint or the sixth joint is rotated 360 degrees. To distinguish these points, the J4Flag and J6Flag point attributes are provided.
To specify the J4Flag, add a forward slash (/) followed by:
- J4F0 (-180 < fourth joint angle <= 180), or
- J4F1 (fourth joint angle <= -180 or 180 < fourth joint angle)
To specify the J6Flag, add a forward slash (/) followed by:
- J6F0 (-180 < sixth joint angle <= 180), or
- J6F1 (-360 < sixth joint angle <= -180 or 180 < sixth joint angle <= 360), or
- J6Fn (-180*(n+1) < sixth joint angle <= -180*n or 180*n < sixth joint angle <= 180*(n+1))
Singularity
The orientation in the boundary where the arm orientation switches to the other.
Hand singularity: The boundary where Righty hand orientation and Lefty hand orientation switch
Elbow singularity: The boundary where Above elbow orientation and Below elbow orientation switch
Wrist singularity: The boundary where NoFlip wrist orientation and Flip wrist orientation switch
For the 6-axis robot, Hand / Wrist singularities exist also inside the motion range. When jogging near the singularity, follow the directions below.
PTP motion near the singularity
When jogging a robot from point P1 near the singularity to a point calculated by point operations such as P1+X(10), the robot may move to unintended direction because the arm orientation is not properly specified.
For example, when jogging from a point where the wrist is NoFlip to another point calculated by point operations, if the wrist keeps the NoFlip orientation while jogging, Joints #4 and #6 may rotate widely (by approx. 180 °). In this case, switch to the Flip wrist orientation to jog smoothly through the wrist singularity.
This phenomenon occurs not only with the point operations but also when creating points automatically with Pallet command or the result values that run from vision sequence.
Proper motion
Unintended motion (Joints #4 and #6 rotate 180 °)
However in the cases, it is difficult for users to specify the proper arm orientations by a program. For this LJM function is a useful command. LJM function switches the arm orientations to enable the least motion of the joints. For LJM function details, refer to the following manual:
"SPEL+ Language Reference"
Also, AutoLJM command can automatically apply LJM function to the motion commands which are included in a particular section of the program without using LJM function.
For details on the AutoLJM command, refer to the following manual:
"SPEL+ Language Reference"
In addition, you can set AutoLJM function to be enabled at the controller start up by setting preferences of the controller. However, if Auto LJM is enabled in preferences, this function automatically adjusts the posture of the manipulator to reduce the motion distance, even when you intend to move the joint widely. Therefore, it is recommended to build a program using AutoLJM command or LJM function to operate the manipulator as you desired.
If you specify all points by teaching, the arm orientations are also recorded. Therefore, the manipulator moves to the taught position without using LJM function or AutoLJM. Instead, the manipulator may move differently from the taught position by the use of LJM and AutoLJM.
LJM function for CP motion command
LJM function and AutoLJM command described above are also available for CP motion commands. However, since CP motion commands give priority to operate based on specified trajectories, the manipulator sometimes reach to the point Flag with a different posture from the specified one. At this time, if CP motion command is used with CP On, an error from 4274 to 4278 will occur according to the mismatched point flag. To avoid the error, operate the manipulator with CP Off, or match the point flag of a target point and the one after motion completion. If operated with CP Off, the error does not occur and the manipulator can continue operation from the point where the mismatch happened.
Also, you can set the controller's preference so that the mismatches of flags are not considered as an error at the controller startup. However, path motions which use CP On will be disabled.
CP motion near the singularity (singularity avoiding function in CP motion)
When executing Move or CP motion near the singularity, the joint speed may increase rapidly. The acceleration error will occur and the joints will move widely and interfere with peripherals. In particular, the position of Joint #1 near the hand singularity and Joints #2 - #6 near the wrist singularity change greatly.
Epson RC+ 8.0 has a singularity avoiding function to prevent acceleration errors during the execution of CP motion commands that pass the wrist singularity described above. With this function, the manipulator takes a detour to avoid an acceleration error by passing a different trajectory and returns to the original trajectory after passing the singularity.
Since it takes a different trajectory from the original one, it may reach an orientation that does not match the orientation specified for the target point. At this time, if CP motion command is used with CP On, an error from 4274 to 4278 will occur according to the mismatched point flag. To avoid the error, operate the manipulator with CP Off, or match the point flag of a target point and the one after motion completion. If operated with CP Off, the error does not occur and the manipulator can continue operation from the point where the mismatch happened.
For details on the singularity avoiding function, refer to the following manual:
"SPEL+ Language Reference - AvoidSingularity Statement"
Singularity avoiding function is enabled as default. If you want to avoid the error by reducing the motion speed in order to maintain the trajectory accuracy, you can enable the variable-speed CP motion function by setting the AvoidSingularity command to "3". With the variable-speed CP motion function, vertical 6-axis robots (including N-series) and RS-series robots that are approaching a singularity while performing CP motion can automatically suppress speed while maintaining trajectory to avoid acceleration and overspeed errors, and then return to normal speed instructions after leaving the singularity. Due to maintaining the trajectory and passing near the singularity, the first, second, fourth, and sixth joints may move significantly. If the AvoidSingularity command is set to "SING_VSD", the arm orientation does not change from before the motion.
If you cannot avoid errors even if you use the singularity avoiding function, use PTP motion to enable the least motion of the joints or arrange the manipulator installation position and hand offset volume to prevent the CP motion near the singularity.