There are three main types of CNC systems, which should be selected according to the specific situation when transforming.
1. Open loop system driven by stepper motor
The servo drive devices of the system are mainly stepper motors, power stepper motors, electro-hydraulic pulse motors, etc. The feeding command pulse sent by the numerical control system is controlled by the driving circuit and the power is amplified, so that the stepping motor rotates, and the execution part is driven by the gear pair and the ball screw pair. As long as the number, frequency and power-on sequence of command pulses are controlled, the displacement amount, speed and direction of movement of the execution part can be controlled. This kind of system does not need to feed back the measured actual position and speed to the input end, so it is called an open-loop system. Pitch accuracy, so the displacement accuracy of the system is low.
The system has simple structure, convenient debugging and maintenance, reliable operation, low cost and easy modification.
2. Asynchronous motor or DC motor driving, closed-loop numerical control system with grating measurement feedback
The difference between this system and the open-loop system is that the actual position feedback signal measured by the position detection device such as grating and induction synchronizer is compared with the given value at any time, and the difference between the two is amplified and transformed to drive the actuator. Move at a given speed in the direction of eliminating the deviation until the difference between the given position and the actual position fed back is equal to zero. The closed-loop feed system is more complex in structure than the open-loop feed system, the cost is also higher, and the ambient room temperature is strictly required. Both design and debugging are harder than open loop systems. However, higher precision, faster speed and greater drive power can be obtained than the open-loop feed system. It can be decided whether to adopt this system according to the technical requirements of the product.
3. Driven by AC/DC servo motor and semi-closed loop numerical control system with encoder feedback
The detection element of the semi-closed loop system is installed on the intermediate transmission part, and the position of the execution part is indirectly measured. It can only compensate the error of some components inside the system loop, so its accuracy is lower than that of the closed-loop system, but its structure and debugging are simpler than the closed-loop system. When the angular displacement detecting element is integrated with the speed detecting element and the servo motor, there is no need to consider the installation of the position detecting device.
At present, there are many companies producing CNC systems, such as famous foreign companies such as Germany's SIEMENS company and Japan's FANUC company; domestic companies such as China Everest Company, Beijing Aerospace Machine Tool CNC System Group Company, Huazhong CNC Company and Shenyang High-end CNC National Engineering Research Center .
When choosing the numerical control system, it is mainly based on the various precisions to be achieved by the machine tool after the numerical control transformation, the power of the driving motor and the requirements of the user.