In order to meet the requirements of machining main drive of CNC lathe, the stepless speed regulation system of electric motor is often selected for CNC lathe. In order to expand the speed regulation boundary and meet the requirements of low speed and large torque, the stepless speed regulation of gear and motor is also commonly used to complete the spindle speed regulation.
1. Mechanical gear shifting
In the main drive system of CNC lathe machining, the traditional spindle box structure is greatly simplified due to the use of stepless speed regulation of electric thoughts. However, due to the limitation of the spindle motor and driving power, the constant torque transmission is often used in its low speed section. In order to make the main shaft provide the high transmission power of the main electric idea within the full speed limit as far as possible, and meet the demand of low-speed powerful cutting of CNC machine tools, it is often selected to use the combination of 1-4 gear speed change and stepless speed change, that is, the so-called stepless speed change in sections. The selection of mechanical gear slows down, which not only enlarges the transmission power, but also enlarges the speed regulating boundary.
When the CNC lathe is cutting, the spindle operates automatically according to the rotation speed specified by the s command in the part processing program. Therefore, there must be two kinds of spindle speed command information in the numerical control system, that is, to control the drive and speed regulating circuit of spindle motor by using analog or digital information (s code), and to control the implementation and organization of automatic gear shifting by using switch information (M code). Automatic shift organization is a kind of electric mechanical conversion device, commonly used are hydraulic fork and electromagnetic clutch.
2. Electric drive
There are two main types of speed regulating electric thoughts used in NC lathe machining spindle drive: DC and AC.
(1) DC motor speed regulation? The speed regulation boundary of ordinary CNC machine tools is relatively large. For DC motor speed regulation, two methods of voltage regulation and magnetic regulation are used simultaneously. The typical characteristic curve of DC spindle electric? Machine is shown in Figure 6-1. From its characteristic curve, it can be known that the electric idea is a constant torque speed regulation under the speed N0, that is to say, the armature voltage is selected to be changed to complete; the speed above N0 is a constant power speed regulation, which is completed by changing the excitation current.
The more commonly used “FANUC DC separately excited spindle electric machine” is a three-phase fully controlled thyristor non circulation reversible speed regulation system, which can complete the speed regulation of voltage regulation and magnetic regulation, and the speed regulation boundary is 35? ～ 3500r / min.
(2) AC motor speed regulation
At present, the cage type induction motor is used in the AC spindle drive of CNC machine tools, and the vector control variable frequency speed control method is commonly used.
With the improvement of the new DC and AC spindle speed control electric ideas, electric ideas speed control will be used in the ordinary, but in order to reduce the cost of economic CNC machine tools, mechanical gear shifting is often used to change the spindle speed.
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