Q.When using the NX Series in torque control mode, how much error is there between the commanded torque value and the actual output torque?

It is within ±5 % of the rated torque.
For example, in the case of NX620AA, the rated torque value is 0.637 [N·m], so the error range is ±5 % of the rated torque, or ±0.032 [N·m].
Regardless of the commanded torque, an error of ±5 % will occur.
Please note that accuracy may be affected by operating conditions such as ambient temperature, motor temperature, regeneration operation, and motor speed.