The CNC system of CNC machine tools includes CNC devices, feed drive (feed speed control unit and servo motor), spindle drive (spindle speed control unit and spindle motor) and detection components. The above content should be included when selecting a numerical control system. 1. Selection of CNC device (1) Type selection Select the corresponding CNC device according to the type of CNC machine tool. Generally speaking, CNC device has processing types suitable for car, drilling, boring, milling, grinding, stamping, electric spark cutting, etc., and should be selected in a targeted manner. ( 2) The choice of performance of different numerical control devices varies greatly. The number of input control axes is single-axis, 2-axis, 3-axis, 4-axis, 5-axis, or even more than 10 axes, more than 20 axes; the number of linkage axes is 2 or more than 3 axes, and the maximum feed speed is 10m/min, 15m/min, 24m/mi N,240m/min; the resolution is 0.01mm, 0.001mm, 0.0001mm. These indicators are different, and the price is also different. It should be based on the actual needs of the machine tool. For example, 2-axis or 4-axis (double tool holder) control is selected for general turning processing, and more than 3-axis linkage is selected for the processing of plane parts. Don’t pursue the latest and highest level, you should make a reasonable choice.
(3) Function selection The CNC system of CNC machine tools has many functions, including basic functions – essential functions of CNC devices; selection functions – functions for users to choose. Some of the functions are selected to solve different processing objects, some are to improve the quality of processing, some are to facilitate programming, and some are to improve operation and maintenance performance. Some selection functions are relevant, and you must choose another one to choose this one. Therefore, it is necessary to choose according to the design requirements of the machine tool, do not analyse, choose the function in too many steps, and omit the relevant functions, so as to reduce the function of the CNC machine tool and cause unnecessary losses. There are two kinds of programmable controllers in the selection function: built-in and independent. It is best to choose the built-in model, which has different models. First of all, it should be selected according to the number of input and output signals between the CNC device and the machine tool. The selected points should be slightly more practical points, and a cup may add and change the need for control performance. Secondly, it is necessary to estimate the scale of the sequential program and select the storage capacity. The scale of the program increases with the complexity of the machine tool, and the storage capacity increases. It should be reasonably selected according to the specific situation. There are also processing time, instruction function, timer, counter, internal relay and other technical specifications, and the quantity should also meet the design requirements.
( 4) The price of Xu Ze in different countries and manufacturers of CNC devices produces different specifications of products with great differences in price. On the basis of satisfying the control type, performance and function selection, we should comprehensively analyse the performance-price ratio and choose CNC devices with high performance-price ratio in order to reduce costs.(5) When choosing a numerical control device that meets the technical requirements, the selection of technical services should also take into account the manufacturer’s reputation, whether the product instructions and other documents are complete, and whether the user can train programming, operation and maintenance personnel. Is there a specialised technical service department to provide spare parts and timely maintenance services for a long time to realise the technical and economic benefits. 2. The choice of feed drive (1) AC servo motor is preferred, because compared with DC motor, the rotor inertia is small, the dynamic response is good, the output power is large, the rotation speed is high, the structure is simple, the cost is low, and the application environment is not limited. ( 2) Select the servo motor of the appropriate specification by correctly calculating the load conditions added to the motor shaft. ( 3) The feed drive manufacturer provides a series of complete sets of products for the feed speed control unit and servo motor, so after the servo motor is selected, the corresponding speed control unit is selected from the product manual. 3. The choice of spindle drive (1) The mainstream spindle motor is preferred, because it does not have the restrictions of commutation, high speed and large capacity like DC spindle motor. The constant power speed regulation range is large, the noise is low, and the price is cheap. At present, 85% of CNC machine tools are driven by AC spindles in the world. ( CNC machine tool)(2) Select the spindle motor according to the following principles: 1 The cutting power is calculated according to different machine tools, and the selected motor should meet this requirement; 2 According to the required spindle acceleration and deceleration time, it is calculated that the motor power should not exceed the maximum output power of the motor; 3 When the spindle is required to start frequently and brake, the level must be calculated. The value of the average power cannot exceed the continuous rated output power of the motor;④ In the case that the constant surface is required to be controlled, the sum of the cutting power required for constant surface speed control and the power required for acceleration shall be within the power range that the motor can provide. ( 3) The spindle drive manufacturer provides a series of complete sets of products for the spindle speed control unit and spindle motor, so after the spindle motor is selected, the corresponding spindle speed control unit is selected from the product manual. ( 4) When the spindle is needed for directional control, according to the actual situation of the machine tool, choose a position encoder or magnetic sensor to realise the spindle direction control. 4. Selection of detection elements (1) According to the position control scheme of the numerical control system, the linear displacement of the machine tool is directly or indirectly measured, and linear or rotary detection elements are selected. At present, semi-closed-loop control is widely used in CNC machine tools, and rotary angle measurement elements (rotary transformers, pulse encoders) are selected. ( 2) According to the requirements of CNC machine tools to detect accuracy or speed, choose position or speed detection elements (test generators, pulse encoders). Generally speaking, large machine tools mainly meet the speed requirements, and high-precision, small and medium-sized machine tools mainly meet the accuracy. The resolution of the selected detection element is generally an order of magnitude higher than the processing accuracy. ( 3) At present, the most commonly used detection element of CNC machine tools ( horizontal boring and milling machine ) is the photoelectric pulse encoder, which selects the pulse encoder of the corresponding specifications according to the ball screw pitch of the CNC machine tool, the minimum movement of the CNC system, the command magnification and the detection magnification. ( 4) When selecting the detection element, it should be taken into account that the numerical control device has a corresponding interface circuit.