Payload Calculations

You do not need to calculate the maximum payload a robot can carry. This will always be stated in the technical data ie. A robot with a payload capacity of 100kg can carry 100kg. Whilst this is quite true it is not the whole picture.

A 6 axis robot does not just lift like a crane. It manipulates and this requires that all the joints are capable of handling the load in all orientations.

The Critical joint is Joint 4 or wrist bend. You must look for the torque limitation on this joint which will be expressed in kg/M. A typical example would be say a 150kg capacity robot with a wrist torque of 100kg/M. The Metre is expressed from the centre of the wrist joint. Part of the robot occupies another 300mm from centre of wrist to mounting flange face. The gripper is mounted on the flange face which occupies perhaps another 200mm. You now have only half a metre to work with so the centre of mass must be very close to the gripper to stay within the wrist torque limitations.

It depends entirely on the attitude of the wrist. If the robot programme is executed with wrist bend down at all times, then none of the above considerations apply and the robot os truly capable of handling 150kg.