Semi-closed loop servo system and full closed-loop servo system

　　semi-closed loop servo system , is the original feedback is added to the motor shaft, commonly used is the encoder, only to ensure the accuracy of the motor, can not compensate for the mechanical error.

This type of servo system position detection point is from the drive motor (commonly used AC/DC servo motor) or lead screw end, through the detection of motor and screw rotation angle to indirectly detect the displacement of the table, rather than directly detect the actual position of the workbench. Because the semi-closed loop does not include or only a small number of mechanical transmission links, so that stable control performance, the stability of the system is not as good as the open-loop system, but better than closed-loop.

In addition, due to the error of the components in the position ring can be corrected to some extent, and the position ring outside the various links such as screw pitch error, gear gap caused by the motion error is difficult to eliminate. Therefore, the accuracy is better than the open loop, which is worse than the closed loop. However, this kind of error can be compensated so that satisfactory accuracy can still be obtained. The semi-closed-loop NC system has been widely used in modern CNC machine tools because of its simple structure, convenient debugging and high precision.

　　full closed-loop servo system , is the feedback original is added to the workbench, can maximize the error caused by machinery.

Full closed-loop servo system will position detection device directly installed on the workbench, so as to obtain accurate information of the actual position of the table, positioning accuracy can reach the sub-micron level, theoretically speaking, its accuracy depends mainly on the error of the detection of feedback components, and the amplifier, transmission device has no direct contact, is an ideal control scheme for high-precision position control. But it is difficult to achieve, the mechanical transmission chain of inertia, clearance, friction, rigidity and other non-linear factors will affect the servo system, so that the control and commissioning of the system becomes very complex, manufacturing costs will rise rapidly. Therefore, the full closed-loop servo system is mainly used for high-precision and large-scale electromechanical integration equipment.

Semi-closed loop servo system and full closed-loop servo system