Renovation of Ordinary Lathe by Numerical Control

1 Overview CNC transformation generally refers to some parts of the general machine tool to do some transformation, coupled with the numerical control device, so that the machine has the ability of CNC machining. China’s existing ordinary machine 3 million or so of these equipment CNC transformation has become an important national technical policy in production in the implementation. Using MCS-51 series 8031 ​​single-chip microcomputer, CNC machine tool C620 lathe is reformed numerically. The micro-computer is used to open and control the longitudinal and transverse feeding system. The stepping motor is used as the driving element and the ball screw is used in the drive system. The system block diagram such as.
2 machine repair before the repair and treatment As a result of computer transformation of the machine can only improve the quality of parts processing consistency, precision machining parts by the precision of the machine itself and the stepper motor step precision to ensure accuracy. So the machine must be modified before the machine repair.
(1 on the actual service age of 5 years in the following machine tools, parts of the parts are still in good accuracy has not decreased, the rail scratches in the basic visible state, can not be overhauled on this type of machine can have both computer control and manual operation In order to ensure that individual parts of small batch processing, in the absence of the need for CNC cutting, can still be used manual operation, give full play to the potential of machine tools to improve machine utilization.
(5: 10 years of service in the basic parts of the machine is still good, just some of the parts for repair and replacement, and in accordance with the standard overhaul of the lathe can be qualified to check the transformation.
3 conversion process 3.1 transformation of the lathe transmission system for the general lathe main drive system and feed system are from the spindle motor, and the transformation of the CNC lathe, the main drive system and the feed system separated into two unrelated systems .
Three-phase motor – Pulley – Spindle gearbox – Spindle (feed system vertical and horizontal respectively to!) Said the transmission path plate box tool post) transformation of the incentive control of the lathe transmission schematic see.
3.2 stepper motor and ball screw connection Stepper motor and ball screw connection is an important problem in the conversion machine, requiring reliable connections.
In order to facilitate programming, to ensure processing accuracy, the general requirements of vertical lathe! To the pulse equivalent to 0.01mm lateral “to) pulse equivalent to 0.05mm so that the diameter value of 0.01mm. As the rotary workpiece drawing size are expressed in diameter values, so the horizontal” experience exchange “machine I work I The pulse equivalent of 0 is not only intuitive, but also can improve the repeat positioning accuracy.
The stepper motor and the ball screw connection is not necessarily just 11 relationship, this time, you must use the two gears, “1,” 2 “stepper motor pulse angle equivalent” and the ball screw pitch! The gear ratio of “1” and “2” is: Number of teeth A-Feed screw Basic lead, one pulse equivalent!
= 0.75mm, = 0.01mm, then) = 5/3 = screw gear teeth / stepper motor gear teeth) = 25/3 = the ball screw pitch = 8mm, using 110BF stepper motor step angle = 12 = screw gear teeth / stepper motor gear teeth To achieve the transmission ratio to ensure that pulse equivalent, CNC lathe ball screw and stepper motor connections are used gear connection type.For example, the transformation of the C620 110BF003 type stepper motor , Then other lathes can be modified according to the above formula, according to the structure size to determine the design parameters of the gear.
3.3 stepper motor and machine tool connection using the form of transmission-type connection. The stepper motor shaft and the screw shaft with a box connection, the center of the hole can be more accurate to ensure that the meshing gears, smooth transmission of low noise and easy to dust. Suitable for precision lathe modification to maintain good.
3.4 Measures to eliminate the gear gap Since the stepper motor and the ball screw between the use of a pair of gear drive, the introduction of the transmission gap, stepper motor rotation step angle can not make a synchronous rotation of the ball screw a corresponding angle, thus Reduce machining accuracy. Such as the transmission gap can not be compensated for the accumulation of parts processing error is growing, resulting in dead and return error.
Eliminate the gear gap measures, on the one hand the use of computer software to modify the other hand, the use of non-slotted gear drive.
The system uses two-tooth wrong tooth-shaped anti-gap structure) 2, the same number of teeth of the two films at the same time with another wide gear meshing between two lamellar gears rely on spring force to open a certain angle, so that the two gears left and right gear tooth contact The right and left flanks of the wide gear eliminate backlash. See the structure.
3.5 hardware circuit the overall program After the transformation of CNC lathe control system hardware circuit synopsis by the following four parts: the main controller, memory, bus and interface. The reliability of the hardware circuit directly affects the performance index of the numerical control system, in which the CPU is the heart of the numerical control system. See the hardware block diagram.
As the 9 /: – 51 series CNC machine tools in China in the application of its more common inexpensive chip, the performance of the United States to meet the requirements of economic CNC machine tools, so the 8031 ​​as the central processing unit CNC system.
6) memory expansion As the master CPU 8031,031 MCU only 128 bytes of RAM, no ROM, and CNC machine tools need to program memory and data memory capacity are larger external memory (EPRO9 Xiang data Memory RAM) chips. So choose a piece of 2764 as a program memory, a piece of 6264 as data storage. In order to 8031P0 interface address information separated out to provide external memory with low 8-bit address information The system also uses 74L373 as the address latch. As the main chip connection diagram.
System expansion, the completion of the keyboard / monitor input and output.
NC device sent a series of continuous pulse must be distributed through the ring, according to a certain order assigned to the phase of the stepper motor winding, the winding in accordance with the pre-specified control power or power. The system design uses YB013 ring distributor. At the same time stepping motor drive circuit should also consider the power amplifier circuit, optical isolation circuit.
3.6 software design The SCM numerical control system software using modular design method, which is the main block package, subroutine module and interrupt handling module. Main module functions: 155I / O initialization, single-chip T0, T1 timer / counter initialization, the keyboard data area, display buffer initialization software logo initialization and so on. The main module of the monitoring is to determine whether there is a function key to press if there is, then turn the corresponding function subroutine module.
The subprogram module is designed according to the function keys.
In the interrupt processing, three modules are included in the system. According to the priorities of the different events in the computer numerical control system, they are: emergency repair processing and limit switch; the real-time modification of the display buffer data module is shown in Fig. Scan management module.
3.7 mechanical and electrical installation after the test machine e off power amplifier experimental setup procedures. E) manual operation of the stepper motor must be consistent with the direction of the provisions of the direction of the motor should be replaced; e into the processing procedures for no-load operation; e) E) processing of a group of parts to check the accuracy of repeated processing, if the dispersion of the size distribution of parts to be a specific analysis of the reasons for the error of the reasons for the error of the size of the part of the processing; And then make improvements until the desired purpose is achieved.
4 with the development of microelectronics technology in China’s machine tool NC in the last decade has been great development, and the transformation of ordinary CNC machine tools to meet the same processing tasks in the premise, can greatly reduce the technological transformation Of the investment funds, in practice has been widely used.

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