Robot payload includes the gripper, its attachments, the workpiece and sometimes process equipment. The load inventory describes that complete mass, its location and motion. Before selecting a model, check these data against the documentation for the exact arm variant.
Inventory the complete carried mass
Start with a bill of everything beyond the robot flange: gripper, fingers, tool changer, sensors, brackets and workpiece. Record documented, measured and still-estimated masses. Identify provisional values with their source and required validation. Late additions must trigger a review of this load inventory.
Distinguish actual operating states: empty tool, held part, grouped pick or different attachment. The Universal Robots payload manual reviewed supports multiple payload states. How they are declared depends on the controller. A function documented for that manufacturer is not an ESTUN configuration procedure.
Locate the centre of gravity in a defined frame
Total mass does not state how far from the flange it acts. Locate the centre of gravity of each carried assembly in a common frame, normally the one required by the robot manual. Retain units, axis directions and the drawing revision used. A coordinate without a frame can be entered correctly while describing the wrong location.
When component centres of gravity are known, the combined centre is calculated along each axis: sum mass × position products and divide by total mass. The tool centre point, or TCP, describes a working point. It does not replace the assembly’s centre of gravity.
Check mass distribution as well
Two tools with the same mass can load the wrist differently. A long workpiece or offset grip changes mass distribution. Inertia therefore needs checking in the axes and frame required by the manufacturer, including workpiece orientations during the cycle.
Universal Robots manuals distinguish mass, centre of gravity and inertia matrix. That does not justify transferring their fields or default values to another arm. For ESTUN, confirm the documentation and applicable moment and inertia limits for the selected model.
Read the correct variant and envelope
Compare the load inventory with the limits of the exact model, not a family capacity. Reach, wrist and generation variants are not interchangeable. A commercial name is not a measurement either: the ESTUN ER180-3100-PL-CE sheet states 3,060 mm reach despite “3100” appearing in its name.
Maximum reach alone does not establish access to a machine. Orientations, obstacles, singularities and tool-change movements need checking in the layout. The load inventory and working envelope must be assessed together.
Prepare a representative trial
Define cases that place the greatest demands on gripping: a part held far from the wrist, an unfavourable orientation, a grouped pick or a transfer involving turning. The protocol specifies configuration, paths and authorised trial conditions. It goes beyond observing that the robot moved one part once.
Record observed events, selected motion limits and gripping deviations. Throughput and process behaviour need their own measurements. A successful load trial does not validate finished quality or constitute acceptance of the entire cell.
Keep a reusable load record
The final file connects each tool and part with its complete mass, centre of gravity, inertia and robot reference. Keep assumptions, manufacturer documents and trials identified so a finger or product change can be reassessed.
Common questions
Points to clarify.
Is the TCP the centre of gravity?
No. The TCP describes the tool’s working point. The centre of gravity describes the carried mass distribution. They can be in different positions.
Should the assembled tool be weighed?
Documented or calculated mass can support the study. Weighing or another suitable check can resolve uncertainty before final configuration.
Is a kilogram margin sufficient?
It does not address moments, inertia or the work envelope by itself. Applicable limits are those of the selected variant under its operating conditions.
