What it is: Fixturing means creating a constrained workspace so that objects with which the Forge/Station interacts can be presented and manipulated repeatably.
Fully constrained workspace
- The precision of the Forge/Station arm is irrelevant if objects in its workspace are not constrained to a similar level of precision.
- Machine tools are usually heavy enough to not require extra clamping or pinning.
- Tables on which the system is working should either be heavy enough that they can't easily be moved, or pinned to the floor.
- Objects on the table should be firmly clamped or bolted to the table so that they cannot move or rotate. Even heavy objects may slowly start to 'walk' away over time if they are repeatedly interacted with or if objects in the operational environment cause the table to vibrate.
- If objects on a table are rigidly attached to the table, a single alignment socket on the table can apply to all waypoints for those objects.
- Any tools that the Forge/Station picks up should have a rigid resting point for the tool to return to.
- An ideal resting spot for a tool is a gravity alignment tray that locates the tool in a corner or against a fence so that no matter how it's dropped off, it rests at the same location. For more information on gravity alignment trays, see the section below.
- The 3-2-1 principle is the method by which you can restrict all degrees of freedom of an object with external fixturing.
Gravity alignment tray
- Some parts cannot be easily stacked in a repeatable parts presentation fixture.
- If there's a possibility that parts will be picked up in different orientations or from different positions, a gravity alignment tray can add repeat-ability.
- Much like the '3-2-1' concept, an alignment tray is a flat surface with two fences that form a corner into which a part can be dropped.
- The part slides into the corner created by the fences and then is re-gripped, now in a repeatable position.
- Parts presentation methods can also be built to serve as gravity alignment trays, for example a part stack that's titled back so parts always sit in a corner, or a laser cut grid that precisely fits the parts it's holding.
Using the Forge/Station tabletop
- Because the robot arm is mounted directly to the tabletop, any items fixtured on the tabletop will always remain at the same location relative to the arm.
- Any processes within a task that are performed on the tabletop will not need realignment sockets or landmarks if the Forge/Station is moved.
- If it's not possible to constrain a part in a fixture, you can program a force move or series of force moves that bottom out the part against a fence or other stationary object.
- For example, tie rods presented on a sloped surface may not roll straight to the bottom. Affix a fence to the side of the slope and use a force move to push the next tie rod against the fence before grabbing it.