# Joint limits and directions

## Joint numbering and positive directions

Joints are numbered from the base up. Joints 1, 2 and 3 are also called the base, shoulder and elbow joints, and
joints 4, 5 and 6 wrist 1, wrist 2 and wrist 3, the names the robot model and ROS use. Each picture shows one joint
turned 30° in its positive direction, in colour, over the pose in grey. The arrow at the joint points the same
way, and the commander software's left arrows jog in that direction.

![Each joint turned 30 degrees in its positive direction, in colour, over the pose in grey](https://docs.source-robotics.com/PAROL-docs/1.1/assets/kinematics/parol6_joint_directions.webp){ width="900" }
![Each joint turned 30 degrees in its positive direction, in colour, over the pose in grey](https://docs.source-robotics.com/PAROL-docs/1.1/assets/kinematics/parol6_joint_directions_dark.webp){ width="900" }

| Joint | Also called | Positive direction |
|---|---|---|
| J1 | base | counter-clockwise, seen from above |
| J2 | shoulder | leans the upper arm forward, the way the forearm points in the standby pose |
| J3 | elbow | raises the forearm |
| J4 | wrist 1 | clockwise, seen from the tool |
| J5 | wrist 2 | tips the tool up, in the standby pose |
| J6 | wrist 3 | clockwise, seen from the tool |

## Standby and after homing

The **standby pose** is the pose of the Denavit-Hartenberg table and the kinematics sheets, and the reference
for the limits below: the upper arm vertical, the forearm horizontal, the arm pointing away from the
electronics case at the back of the base. **After homing** the robot stands in the same pose turned 90° about joint 1, counter-clockwise
seen from above: the firmware sets joint 1 to +90° when it finishes homing.

| Pose | Joint 1 | Joint 2 | Joint 3 | Joint 4 | Joint 5 | Joint 6 |
|---|---|---|---|---|---|---|
| Standby | 0° | −90° | 180° | 0° | 0° | 180° |
| After homing | 90° | −90° | 180° | 0° | 0° | 180° |

The Python API calls the after-homing pose its standby (`STANDBY_ANGLES_DEG`), and a later `home()` moves
there; the commander software's standby is the standby pose above.

![The standby pose, from the front and from the side, with the joints marked](https://docs.source-robotics.com/PAROL-docs/1.1/assets/figures/parol6_standby.webp){ width="900" }
![The standby pose, from the front and from the side, with the joints marked](https://docs.source-robotics.com/PAROL-docs/1.1/assets/figures/parol6_standby_dark.webp){ width="900" }

## Limits

The joint limits of PAROL6's model in [robot_descriptions](https://github.com/Source-Robotics/robot_descriptions)
(version 2.15.1), in degrees, in the angles the software shows (the standby pose above).

| Joint | Negative limit | Standby | Positive limit | Range |
|---|---|---|---|---|
| J1 | −97.40° | 0° | +97.40° | 194.8° |
| J2 | −146.15° | −90° | −32.70° | 113.4° |
| J3 | 105.52° | 180° | 294.59° | 189.1° |
| J4 | −114.59° | 0° | +114.59° | 229.2° |
| J5 | −120.32° | 0° | +120.32° | 240.6° |
| J6 | none | 180° | none | no limit with the bare flange; with a tool, its cables and tubes set it |

![Each joint at both its limits, in its colour, over the standby pose in grey; the arc spans the range, in the angles the software shows. Joint 1 is seen from above, with the after-homing position marked; joint 4 is seen from the tool, with joint 5 at 90 degrees so that the tool's swing shows; joint 6 has no limit](https://docs.source-robotics.com/PAROL-docs/1.1/assets/figures/parol6_joint_ranges.webp){ width="860" }
![Each joint at both its limits, in its colour, over the standby pose in grey; the arc spans the range, in the angles the software shows. Joint 1 is seen from above, with the after-homing position marked; joint 4 is seen from the tool, with joint 5 at 90 degrees so that the tool's swing shows; joint 6 has no limit](https://docs.source-robotics.com/PAROL-docs/1.1/assets/figures/parol6_joint_ranges_dark.webp){ width="860" }

!!! note "The firmware and the software still use the earlier limits"
    Firmware 1, the commander software and the Python API (0.9.1) enforce the
    limits of the earlier model until they are updated: J1 ±123.05°, J2 −145.01° to −3.38°, J3 107.87° to
    287.87°, J4 ±105.47°, J5 ±90°, J6 0° to 360°. A target between the two is accepted by them; keep to the table
    above. Before homing they apply these limits to a position count that starts at 0 at power-up, so joint 2
    cannot be jogged in its positive direction, nor joints 3 and 6 in their negative one, until the robot is
    homed ([Jogging](https://docs.source-robotics.com/PAROL-docs/1.1/05-operation/jogging/#jogging-a-robot-that-is-not-homed)).

Joints 1 to 5 are stopped at both ends by printed blocker parts, the mechanical stops a little past the limits
above. The limit switch or sensor that homes a joint sits near its blocker, so that it triggers just before the
joint reaches it. Joint 6 has no blocker: with the bare flange nothing stops it, and with a tool only the tool's
cables and tubes do.

!!! warning "Grippers and bases change the limits"
    A gripper changes where joint 5 can go without colliding with the forearm, and a riser under the base changes
    what joint 2 can reach. The software limits do not know about either: check the real clearances with a slow
    jog before you run a program near a limit.

!!! warning "The limits are not a safety function"
    The limits only stop the software from commanding a joint further. Inside them the arm can still hit a
    person, the table or itself, no safety-rated part checks them, and a wrong homing shifts them with it. They
    protect the robot's cables and parts, not the people near it ([Safety](https://docs.source-robotics.com/PAROL-docs/1.1/02-safety/)).

!!! danger "Never more than one turn, except joint 6"
    **No joint may ever be turned more than one full turn**, by hand or by software: the cables and pneumatic
    tubes that pass through the joints wrap and tear. The one exception is **joint 6**: with the bare flange it
    can turn without limit; with a gripper or a tool, the tool's cables and tubes wrap as it turns, and they set
    how far it may go ([Moving the robot by hand](https://docs.source-robotics.com/PAROL-docs/1.1/02-safety/moving-by-hand/)).