Static friction, backlash, and saturation are all non-linearities that can affect the performance of a servomotor. However, the non-linearity caused by a servomotor is primarily due to saturation.

Saturation is a phenomenon that occurs when the magnetic flux in the motor's core reaches its maximum value. At this point, further increases in the current through the motor windings do not result in a proportional increase in the magnetic flux. This limits the maximum torque that the motor can produce.

Explanation:

Static Friction:
Static friction refers to the resistance encountered when trying to initiate motion between two surfaces that are in contact but not moving relative to each other. While static friction can introduce non-linearity in the system, it is not specifically caused by the servomotor itself. It is a characteristic of the mechanical components and load connected to the motor.

Backlash:
Backlash is the play or clearance between mating mechanical components, such as gears or leadscrews. It can introduce non-linearity in a servomotor system because any change in direction of the motor will first have to overcome the backlash before any actual movement occurs. However, backlash is again not caused by the servomotor itself but rather by the mechanical components.

Saturation:
Saturation is a non-linearity caused by the magnetic properties of the motor. When the motor is driven with a high current, the magnetic field in the motor's core can reach a saturation point where the flux density no longer increases linearly with the current. As a result, the torque produced by the motor will not increase linearly with the current, leading to non-linearity in the system.

Conclusion:
While static friction and backlash can introduce non-linearity in a servomotor system, the primary non-linearity caused by the motor itself is saturation. Saturation occurs when the magnetic flux in the motor's core reaches its maximum value, limiting the maximum torque that can be produced. It is important to consider these non-linearities and compensate for them in the control algorithm to achieve accurate and reliable performance from the servomotor system.