In the context of robot arms, "witness marks" typically refer to marks or indicators that are used to verify or witness the alignment, position, or movement of components or parts within the robotic system. These marks can serve various purposes in robot arms and automation; but are usually used to master the robot.
Witness marks can be used during the calibration process to ensure that different components are properly aligned or positioned as per the specified configuration.
- Example of witness marks in Fanuc robot.
Parol6, Faze4, and CM6 robotic arms also have witness marks. These marks are indicated by holes in the mechanical parts, allowing the parts to be aligned by inserting a pin through those holes.
- Example of witness marks in PAROL6 robotic arm
Mastering the robot
Mastering the robotic arm is the process of bringing your robots joints to the witness mark of that joint and recording the position that robot is at that point.
When at the position of the witness mark robots position is know because of our knowledge of robots kinematics and CAD. it basically assigns robots encoder ticks / stepper ticks to the know joint angle
Lets take an example of J1 of our PAROL6 robotic arm.
- Image showing the standby position of the robotic arm. At this position, witness marks for all joints are aligned
At this exact position our robots joint is at 0 degrees. If everything was perfect you would place a pin at the witness marks and it would fit with no problems.
Homing the robotic arm
Homing is a process where a robot joint finds a known position in its rotation space, typically by hitting a limit switch or sensor.
The process for PAROL6 and FAZE4 robots is the same as that for 3D printers. After powering up, the robot doesn't know its position and needs to be homed. By hitting a limit switch, we determine the robot joint's position based on our knowledge of the limit switch's location, which we have from the CAD model. For example, when we hit a limit switch on Joint 1, we know that we need xxx steps to reach a witness mark or Joint 1's 0-degree position.
Now that we know our position after homing and the number of steps required from the limit switch to the witness mark, you might think we're done, right? Well, not quite. To be really precise, after hitting the limit switch, you should observe how many steps it actually takes from the limit switch to the witness mark. Each PAROL6 build may have slight differences due to various printers, tolerance variations, and parts.
The Parol6 control board comes preloaded with generic parameters that will work for anyone building the robot. However, if you want to fine-tune your robot, you now have the option to do so.