Abstract: In view of the current technical status of domestic economical numerical control system, the performance of economical numerical control system is analyzed from three aspects: the convenience of system use, the advancement of technology and the reliability of the system, in order to study the work of this aspect. , production and use personnel to provide a reference.
In view of the current technical status of domestic economical numerical control system, this paper analyzes the performance of economical numerical control system from three aspects: the convenience of system use, the advancement of technology and the reliability, in order to study and produce in this aspect. The user provides a reference.
The scope of this paper is the single-chip numerical control system, with the industrial PC as the platform, and the CRT display belongs to another category. However, the content discussed in the article is suitable for them in principle, but the performance indicators of the two should be different due to different microprocessors.

1 System ease of use

The ease of use of the system is mainly reflected in the editing part of the system. The editing part is the part where people and the system directly deal with each other, the so-called human-machine interface. The human-machine interface should be user-friendly, that is, the editing part should provide users with convenience, speed and comfort. As a good system, you should have the following performance.

1. A modal command modal command, also known as a continuation command, means that an instruction not only functions inside the program segment, but also remains in the subsequent program segment, and can be omitted until it is replaced or aborted by an appropriate instruction. . Obviously, the use of modal characteristics can save the programming workload, so the modality is the basic function that a CNC system should have.
2. Multi-instruction common segment Multiple instruction common segment refers to a plurality of instruction words that can be included in one program segment. It is inconvenient that multiple instructions cannot be shared, which is bound to increase the number of instructions.
3. Input, Retrieval, and Modification Integration Many domestic systems divide input and retrieval into two different operation methods during editing, which makes the input process unable to check the program. The retrieval process cannot automatically generate the block number, which is very inconvenient. A good system should realize the integration of input, retrieval and modification, that is, it can be retrieved and modified when inputting, and can be modified and input when searching, and the program segment number is automatically output.
4. Hanhua Button At present, foreign CNC systems want to enter the Chinese market, and try to adopt the Chinese human-machine interface. The economical CNC system we produce ourselves should use the Chinese button to facilitate the user.
5. Automatically sorting letters When entering a program, it is difficult for users to enter in alphabetical order, and when searching, they want to search in alphabetical order. For the convenience of users, the CNC system should have the function of automatically sorting letters.
6. Quick Retrieval Users want to be able to quickly find the desired program segment when they retrieve the program. Therefore, the system should have the ability to quickly flip through the file, immediately find the end of the program, start the program, and any part of the program.
7. Strong command function The powerful command function greatly simplifies user programming. For example, a five-head left-handed worm is machined with a worm length of 100 mm, a tooth depth of 3 mm, a modulus of 0.8, and 15 thread cycles per head. For the processing of such a part, many domestic systems require the user to write 75 cycle blocks, plus a multi-head thread indexing to stagger a pitch command. In addition, you must arrange an X-direction walk instruction before the instruction is executed to determine the direction of the exit, otherwise the program will be wrong. In this way, the processing of the above parts is a few pages after being programmed. Some systems can automatically achieve 75 cycles with only one instruction, namely G31 W100 I-3 K5 F0.8 L15. This is obviously more convenient.
8. Variety of instructions For arc machining, the center coordinates can be programmed with I or K or with radius R. Programming with radius R is convenient, but it does not describe the entire circle. Programming with I and K is a bit inconvenient, but it can describe the whole circle. A good solution is to have both features.
   For threading, threads with undercuts are expected to be straight-ended to reduce the length of the tail. In thread turning of pipe threads, bolts, etc., the length of the tail is secondary, and it is important to require the pitch to be retracted to ensure a good seal when threaded. However, the length of the retreat of the pitch is too long. A good solution is to have both features to meet user requirements.
   

2 Advanced technology

1. Interpolation speed Interpolation refers to the slash and arc. The circular interpolation speed of a system can reflect the level of the system. The circular interpolation speed of the domestic economical numerical control system is generally less than 600mm/min, but some have reached 1200mm/min.
2. Thread function The thread function best reflects the level of a system. Looking at the thread function of a system usually comes from four aspects: one is the degree of automation, the other is the high-speed machining capability, the third is the large lead processing capability, and the fourth is the function of the pitch retreat.
   Degree of automation: The threading software should be able to automatically determine whether the zero signal of the spindle encoder is active high or low, without changing the hardware; it can automatically calculate the spindle speed without inputting the spindle speed S command in the program. It can avoid the error caused by the spindle speed input error; it can automatically index the multi-start thread and divide it in the circumferential direction to avoid the tool that hits the tip or the shoulder of the workpiece when the axis is indexed; The sign of the sign automatically determines the direction of the retreat; it can realize the automatic cycle of multiple cuts.
   High-speed machining capability: The high-speed machining capability of the thread is mainly reflected in the feed rate of the thread. Thread feed speed = spindle speed x lead. The thread feed rate should be above 2m/min.
   Large lead processing capability: Many domestic systems provide a formula for this in the specification. N≤(1200/T)-80 Where n - spindle speed, r / min
   T——lead, mm
   For large lead T = 12mm, this system can only be processed under the condition that the spindle speed is less than 20r/min, which is difficult to meet the user's requirements. The economical CNC system can increase the spindle speed to 125r/min without losing steps when machining 12mm lead threads.
   Equal pitch retracting function: In the thread turning of pipe threads, bolts, etc., it is required to retreat the pitch to ensure good sealing when threaded. The system does not have the same pitch retreat function and cannot be guaranteed.
3. Speed ​​connection technology Stepping motor needs to be lifted and lowered during operation. Therefore, from one block to another, the stepper motor is first down-converted, stopped, and then up-converted. This problem is not trivial when the two contour curves intersect, but when the two contour curves are tangent, this characteristic of the stepper motor will result in a machining tool mark or platform. The speed connection technology enables the system to achieve a smooth connection between the two programs during the machining process, which not only ensures the processing quality but also improves the productivity.
4. Manual setting and chamfering Only one cylindrical surface or chamfer is machined. If manual setting and chamfering are available, no programming is required.
5. Speed ​​control and coordinate dynamic display during machining This technology reflects the technical level of the software. Some systems do not handle this problem well, so the speed cannot be adjusted during the machining process, and the dynamic display cannot be performed when the speed is greater than 2 m/min, which causes inconvenience to the user.
6. Power-down protection movement position and breakpoint operation If the machine suddenly powers off during the machining process, the user always wants the system to record the current position and continue to run from there when the call is received, thus avoiding the scrapping of the workpiece. The power-down protection motion position and breakpoint operation function can solve the above problems.
7. Electric Tool Holder Controller The electric tool holder controller is a part of the high failure rate of CNC lathes. The general tool holder controller uses the relay logic control circuit to realize the automatic tool change control of the electric tool holder. The number of components used in this kind of logic control circuit is large, especially the use of nearly 10 relays with mechanical contacts, the reliability is very poor. Some CNC systems use software to control tool change, using only two contactors, so that the reliability of the electric tool holder control is greatly improved.
8. Automatic tool setting An electric tool holder is often provided on a CNC lathe. The relative position of several tools on the electric tool holder must be known before processing. If manual cutting is used, it will take time, effort and cost. With automatic tool setting technology, the tool is simple, quick and accurate, and it takes only a few minutes for 4 knives.
9. Closed-loop control Closed-loop control technology automatically compensates for deformation, clearance, and transmission errors of mechanical transmission components to ensure machine tool machining accuracy.
10. Subdivision Technology Subdivision control technology is an important technology in current economical CNC systems. Its advantages: First, it effectively solves the low-frequency oscillation problem of the stepping motor, so that the stepping motor runs smoothly at low speed and no longer loses step. The second is to make the pulse equivalent of the CNC machine tool refined, for example, the ten subdivision makes the original pulse equivalent of 0.01mm become 0.001mm, thereby improving the control precision. Third, the subdivision control technology can also increase the output torque of the stepper motor by about 30% at low speed.
11. PLC functions Some machine tools not only require a numerical control system to achieve precise positioning or trajectory control, but also the system has the function of a programmable logic controller (PLC) to realize the logic control of the switching quantity. Of course, the above requirements can be achieved with the CNC system + PLC controller, but after all, it is expensive and troublesome. If the CNC system itself has a PLC function, and the PLC part of the programming uses the ladder programming that everyone is used to, it will be welcomed by users.
12. VMOS Drive Technology An important factor affecting system reliability is the stepper motor drive power supply. The driving power supply line using the power transistor is complicated and consumes a large amount of power, especially due to the secondary breakdown of the transistor, resulting in poor reliability of the driving power source of the high power transistor. The VMOS tube has no secondary breakdown problem, the circuit is simple, the power consumption is small, the switching speed is high, and the reliability is greatly improved. So a good system should have VMOS drive technology.

3 system reliability

Looking at the reliability of a system, you should pay attention to the following five aspects.

1. System Design As an industrial control microcomputer, the system design should take a series of measures in terms of hardware anti-interference and software anti-interference to ensure high reliability.
2. Production conditions System production specifications, with strict component screening, aging, inspection, testing capabilities. The whole machine must run continuously for 48 hours at 45 °C before leaving the factory, so that the system can be reliable.
3. Drive Technology Advanced VMOS drive technology is much more reliable than high power transistor drive.
4. Tool Holder Controller The electric tool holder controller is software controlled and much more reliable than the relay switch logic control with contacts.
5. Structural Design Domestic systems usually have two vents, one for the air, one for the wind, and the wind for the wind to pass through the system. This structure allows the system to bring dust, soot, chips and the like to the inside of the system while it is air-cooled. Such a system has been used for a long time, and it is difficult to make a mistake. A well-designed system should have a positive air pressure inside the system cabinet or allow cooling air to pass through the outside of the system, using so-called external cooling.

4 How to choose an economical CNC system

1. The system should be reliable . The reliability determination method described above can be used to judge or inquire about the use situation from the old user of the manufacturer.
2. The system performance should meet the demand. The system interpolation speed is low, and the productivity is not good. The system thread technology is not closed, which will cause the tool to hit the tail thimble or the workpiece shoulder when the multi-thread turning is indexed. The spindle speed will not go up during high-speed turning. Large lead thread can not be used, no thread retracting function can not be used for car thread; if you want to process two-section tangential workpiece, there is no speed connection technology, which may form machining marks and reduce productivity; if stepper motor is needed In the low frequency range (about 200Hz for 0.01mm pulse equivalent, 200Hz frequency is equivalent to 120mm/min speed), the work is not lost, subdivision technology is the best choice; without automatic tool setting technology, many tools are very troublesome when turning There is no closed-loop technology, precision can not be guaranteed during precision machining; there is no PLC function, logic control can not be realized, etc., which are all according to the needs of users.
3. The technical service capability of the sales unit The CNC system is an industrial control microcomputer, which works in a relatively harsh environment and is difficult to guarantee. In addition, it is a technology-intensive product, and users have a familiar process before using it. Therefore, the quality of technical services is very important for the normal use of CNC systems.
4. The technical development capability of the production unit The CNC system is constantly developing and perfecting in terms of hardware or software. Without technical development capabilities, the system cannot be upgraded in the future and cannot meet the further requirements of users.
5. Performance price ratio After considering the above four aspects, it is more comprehensive to consider the price issue. This is the so-called performance price ratio problem. Simply looking at the price, not looking at performance, not looking at reliability, not looking at technical services and technology development capabilities, the results may be counterproductive.

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