The spindle system and feed system of CNC machine tools are very different
According to the working characteristics of the main drive of CNC machine tools, the early CNC machine tool spindle drive adopts the structure of three-phase asynchronous motor plus multi-stage gearbox. With the continuous development of technology, the machine tool structure has been greatly improved, which puts new requirements on the spindle system and varies depending on the application. In CNC machine tools, CNC lathes account for 42%, CNC drill boring and milling machines account for 33%, CNC grinding machines and punch presses account for 23%, and others only account for 2%. In order to meet the needs of the first two types of CNC machine tools with a large amount of coverage, the following requirements are imposed on the spindle drive: the main drive motor should have a power range of 2.2 to 250 kW; if there is a large stepless speed regulation range, if it can be 1 : Constant torque speed regulation and 1:10 constant power speed regulation in the range of 100~1000; the main drive has four-quadrant drive capability; in order to meet the thread turning, the spindle can be synchronously controlled with the feed; In order to automatically change the tool, the spindle is required to perform high-precision directional stop control, and even the spindle has an angular indexing control function.
The spindle drive and the feed drive have experienced the transmission from the ordinary three-phase asynchronous motor to the DC spindle drive. With the advancement of microprocessor technology and high-power transistor technology, it has now entered the era of the AC spindle servo system. It is rare to see that a DC spindle servo system is used on a CNC machine. However, the products of the domestically produced AC spindle servo system are still rare, and most of them are imported products.
The AC servo motor has two types of structures: a permanent magnet synchronous motor and a cage asynchronous motor, and most of them adopt the structure of a permanent magnet synchronous motor. The case of the AC spindle motor is different. The AC spindle motor adopts the structure of the asynchronous motor. This is because, on the one hand, it is limited by the permanent magnet. When the motor capacity is made large, the motor cost will be high. On the other hand, the spindle drive system of CNC machine tools does not need such high performance as the feed servo system. The low-cost asynchronous motor is used for vector closed-loop control, which can fully meet the requirements of CNC machine tool spindles. However, the performance requirements of the AC main shaft motor are different from those of the ordinary asynchronous motor. The output characteristic curve (output power and speed) of the AC main shaft motor is required to be a constant torque region below the basic speed, and constant power above the basic speed. region.
The spindle drive system used in CNC machine tools can be divided into two major categories: DC spindle drive system and AC spindle drive system. The spindle drive system is selected based on the characteristics of the two major types of spindle drive systems.