經(jīng)濟(jì)型數(shù)控車床進(jìn)給伺服系統(tǒng)設(shè)計(jì)
經(jīng)濟(jì)型數(shù)控車床進(jìn)給伺服系統(tǒng)設(shè)計(jì),經(jīng)濟(jì)型,數(shù)控車床,進(jìn)給,伺服系統(tǒng),設(shè)計(jì)
NC machine
NC machine tool was developed as a new automation tool in the 50s of the 20th century, which use NC technique to solve mechanical cutting process. Following the advanced developing of the modern manufacture, NC machine tool was one of the most important basic equipments as FMC, FMS and CIMS. As the key technology of NC machine tool, NC technology is one of the professional technologies engineering college students should master.
One The number of tool machine controls a technique to include tool machine and count to control system and outer circle technique，It constitutes to see form：
Number's controlling tool machine is generally lain quality by control, the number control device, servo system and measure feedback device and tool machine host to constitute. Now to each constitute parts of brief introductions as follows:.
1st, control medium
When the numerical control engine bed processes, needs each kind of control information must depend on some kind of middle carrier carry home and the transmission，This kind of carrier being called as control medium, The control medium is saves acts completely and the cutting tool which the numerical control processing needs is opposite in the work piece positional information intermedium, it is recording the components processing procedure.
The control medium has many kinds of, like punched tape, punch card, magnetic tape and floppy disk and so on, also may need each kind of information through the correspondence connection direct input, uses what kind of control medium to be decided by the numerical control installment type.
2nd, numerical control installment
The numerical control installment is the numerical control engine bed core, is the high-tech intensity product. It integrated the microelectronic technology, the information technology, the automatic control technology, the actuation technology, the monitoring examination technology, the software engineering technology and the machine-finishing craft knowledge.
The numerical control engine bed is precisely under its control, according to the procedure, which assigns automatically to the machine parts carries on the processing. From 50's in 20 centuries the number controlled tool machine to publish, number's controlling device is already developed CNC by NC.
Especially microprocessor and microcomputer make the calculator number control function and credibility of device to raise continuously after counting to control to equip up the successful application, the cost descends continuously, and its high performance price ratio promoted number control the quick development of tool machine.
The installment is composed by the hardware and the software. The CNC hardware is a special purpose computer, realizes partial or the complete numerical control function by the software, Through changes the software to be very easy to change or to expand its function.
The installment basic skills work includes: Input, decoding, cutting tool compensation, feed rate processing, interpolation, position control, processing, demonstration and diagnosis and so on, It has the main function is as follows:
(1) Multi-coordinates control (Multiple spindle linkage);
(2)Realizes many kinds of function interpolation;
(3) Many kinds of procedure input (Man-machine conversation, manual data feeds, by higher authority computer and other computer equipment excuse input), As well as edition and revision
(4) Information transformation;
(5)Compensation (Cutting tool radius compensation, cutting tool length compensation, transmission gap compensation, pitch error compensation and so on);
(6) multi-processing Options;
(7)The breakdown from examines the demonstration
(8) Communications and networking.
3rd, The servo system
The tool machine servo system is the conjunction link that the number controls device and tool machine, It is based on mobile components of the machine location and speed as the control of automatic control systems, NC device used to accept (or computing) interpolation generation of feed or feed pulse displacement, Driving Machine executive body movement. It includes spindle drive modules (mainly speed control), feed-driven modules, the spindle motor and feed motor, etc.. In general, CNC servo system requirements of a good rapid corresponding performance, feed rate scope, sensitive and accurate tracking and command functions and speed, in the larger context of a good job stability. What to use is the direct current servo system and communicates now servo system, and communicate the servo system is replacing the direct current servo system.
4th, the diagraph feedback equip.
The device can be included in the servo system. It consists of measuring element and the corresponding circuit, whose main role is to detect the speed and displacement, Information and feedback control system to form closed loop control. No feedback device measurement systems become open-loop system. The common element is measured pulse encoder, resolve, lnductosyn, grating, and the magnetic-foot Laser Displacement Monitoring System.
5th, The host machine
Host NC machine is the mainstay, including bed, box, rail, spindle, feed institutions mechanical parts. The numerical control engine bed structure has following several characteristics:
As a result of the high-performance spindle feed servo drives, simplifying the CNC machine mechanical transmission structure, Drive a short chain.
CNC machine tools with high mechanical structure of the dynamic characteristics of dynamic stiffness, damping precision, wear resistance and thermal deformation properties, continuous adaptation processing automation;
More efficient use of transmission pieces, such as ball screws, linear motion guide, such as hydrostatic guideway.
Three, NC Machine features
1st, the characteristics of CNC machine tools
Modification of processing objects adaptability, As the NC processing machine parts change, only the need to re-establishment procedures, replacement of a new perforated paper tape or manually input we will be able to realize the processing of parts. It is different from traditional machines, not manufacture, replacement of a large number of tools, fixtures and equipment, no more re-adjustment machine. Therefore NC machine tools can quickly from a processing components into a processing components, which has single pieces, Trial Production small batch of new products and provide great convenience. It reduces the preparation cycle, and save a lot of equipment. For the use of point-to-point control system porous parts processing, when necessary design modifications, change some of the hole locations and size, only partial changes to delete the corresponding porosity zones, spent a very short time on the product can be modified to create new products, and Results for the products constantly attacking provide favorable conditions.
2nd, the high precision machining
CNC machine tools are based on figures given in the form of instructions for processing. Since the NC device pulse equivalent up to 0.001mm， and feed chain drive space and reverse screw pitch error NC devices, etc. can be compensated, therefore, NC machine tools can achieve higher precision. For small and medium-sized CNC machine tools, positioning accuracy can be achieved 0.03mm general, repetitive positioning accuracy of 0.01mm. Because the transmission system with CNC machine tools and the structure has reached a very high stiffness and thermal stability, and improved its manufacturing precision, CNC machine tools, especially the automatic processing methods to avoid the producer human operational error, with a number of machined dimensional consistency, and the rate of qualified products, processing quality is quite stable.
The introduction of point-to-point control of the drilling system, eliminating the need for the use of drilling template and the drilling package Drilling Template Error coordinates the impact would cease to exist。Also excluded due to the processing of cutting conditions can be improved and can be effective cooling, be processed with precision and surface quality has been enhanced. For complex parts of the contours of processing, the preparation process is taking into account the feed rate control，Can be done in curvature change, the tool cut along the contour to the feed rate is essentially the same, Surface processing can be obtained high precision and surface quality.
3th, processing productivity
Time that spare parts need when processing includes mobile time and assistance
time two parts. Number's controlling tool machine can reduce these two part of times effectively and therefore processing machine than the average productivity is much higher. CNC machine tool spindle speed and feed rate range than the scope of general machine tools, Every process can choose the most advantageous cutting capacity good structural rigidity to allow CNC Cutting Machine large amount of heavy cutting, effective mobile savings time. NC machine moving parts fast-moving and positioning adopted a deceleration and acceleration measures thus choice of a high velocity air journeys, consumed by the fast progress quick retreat and positioning of the machine than the average much less.
CNC machine tools are processing the replacement parts is almost no need for re-adjustment machine, and the parts that were installed in simple positioning device to intensify, stands for parts for installation adjustments could save a lot of time.
With a knife in the use of the devices and automatic tool change CNC Machining Center Machine, in a machine to achieve multiple processes of continuous processing reduced the turnaround time for semi finishes products, the enhancement of production efficiency even more apparent.
4th, Reduces operator's labor intensity
CNC machine tool is according to the procedure which beforehand composes automatically completes to the components processing, the operator besides places the punched tape 'or’ operation keyboard, the loading and unloading components, the essential working procedure middle survey as well as observes the engine bed the movement, Does not need to carry on the arduous duplicated manual operation, the labor intensity and the tense degree may greatly for reduce, the work condition also has the corresponding improvement. For example in electronics industry printed wiring board drill hole，If drilling on the desktop manually processing, monotonous frequent manual workers is likely to result in extreme visual fatigue, so a lot of mistakes. It is often very difficult for one or more hours of continuous operation. When using high speed CNC drilling, will be able to fundamentally improve the operator's working conditions.
5th, Good economic returns
When using the number controlled tool machine to process spare parts, the equipments expenses which share in each spare part was more expensive. But can save many other expenses under the situation that the single piece, small batch quantity produce, so can acquire a good economic performance.
Using the number controls tool machine, saving lineation man-hour before processing, can reduce adjustment and process after the spare parts install to top in the tool machine with examination time, reduce direct factor cost. The other hand, as the CNC machine tool parts not hand model, Cam, drilling template and the other fixture. Saving technology equipment. The other hand, as the CNC machine tool parts not hand model, Cam, drilling template and the other fixture. Saving technology equipment.
6th、it is advantageous to a production control.
Control tool machine to process spare parts with the number, the ability accurate calculation spare parts processes man-hour, and simplified an examination and work tongs, semi-processed goods effectively of management work. These characteristics are advantageous to make production control modern.
CNC machine tools to use digital information with the standard code input, the most suitable place for contacts with the digital computer, the foundation had become the design, manufacturing and management of the calculator assistance integral whole to turn currently.
Four, CNC machine’s applications
The number controls many advantages that the tool machine really exists general tool machine not to have, but these advantages take certain condition as antecedent of. CNC machine tools on the application is continuing to expand, but it can not completely replace other types of machine tools, not in the most economical solution to the machining of all the problems. CNC machine tools are usually the most appropriate processing is characterized by the following components:
1st, Multi- varieties small volume production
Components
Diagram 1 meant three types of spare parties of tool
machines to process an amount relationship with
comprehensive expenses. Figure seen parts of the
batch processing for increased election CNC machine
disadvantage. The reason lies in a number to control
a tool machine oolsequipments expensive,
measure appropriation tool complexity machine of producing the adoption with large quantity to compare, count to control a tool machine efficiency return not enough high.
2nd, The structure more complicated spare parts
Diagram 2 meant three types of tool machines of are processed the spare parts complicated degree and spare parts the relation of batch quantity size. CNC machine tools are usually suitable for processing structure more complex than a few, CNC machine tools in the processing is the need for expensive processing equipment (tools, clamps and mold) parts.
3th、Frequent modifications to the parts
In the national defense and the state-of-art industry sector, the components frequent modification necessity is well known. Introduced the competitive system in the consumer industry department, the product which in the market sold has also had unceasingly tore new, this has provided the user for the CNC machine tools. It saves a lot of technique and equipment costs, overall expenses declined.
4th, High value, and no scrap key parts
5th, The production cycle takes at least an urgent part
CNC machine tools widely promoted are the biggest obstacle to the initial equipment investment, as the complexity of the system itself, increased maintenance costs. It will affect the machine utilization in some extent If satisfactory after-sales service, often fail to remove equipment failures. These factors can increase the synthesis production cost.
The position-control system is number controls tool machine’s important partial, now introduces its control the concrete principle
The position-control servo-mechanism which must reproduce at some remote point the motion applied to a handwheel located at a local command station .the output motion might be used to drive a heavy object (such as a missile launcher) into a required position; power amplification of the command and accurate reproduction are thus necessary.
The signals can be transmitted by direct mechanical linkage or by hydraulic, pneumatic, or electric conduit. Apart from mechanical linkage the most rapid transmission may be achieved with electrical connection and this is often but not always used. Where it is used, the mechanical input and output signals are first converted into proportional electrical signals and then transmitted through wires to a subtracting device, which produces a signal proportional to the error. a typical arrangement is shown in fig.1.
The low-power error signal is used to drive an amplifier, which also receives power from an external source and delivers controlled power to the motor.
The combination of transducers and subtracting element from the error detector, the amplifier is the controller and the motor together with its gearbox from the output element.
The amplifier may be purely electrical if the motor is electrical but must be either electro-hydraulic or electro-pneumatic if the motor is either hydraulic or pneumatic.
It is emphasized that the object of the system is to make the relatable mass copy as nearly as possible the motion of the handwheel . Let us consider what will happen if the position of the handwheel is turned very rapidly through an angle , the mass being initially at rest. Initially the mass has no velocity and the output position θ0 is zero , thus a signal instantaneously appears at the terminals of the amplifier ;Power from the source is allowed to reach the motor, which then begins to drive the mass so
as to reduce the error. As θ0 approaches the error gets smaller and thus less power is allowed to reach the motor, systems are usually designed so that the mass just overshoots the required position; Since is then greater than , the error becomes negative and the motor forces the mass to stop and reverse direction. Some undershoots and further overshoots will then probably take place before the mass finally settles at the required position ( equals to ). Only when exact coincidence occurs does the amplifier receive zero signal and thus the motor is forced to move either one way or the other until all motion dies away. The motor can therefore only come to rest when the signal entering the amplifier is zero.
It becomes evident from the above discussion that unless very great care is taken in the design, it is quite possible that the oscillations about the desired position will build up instead of dying away quickly. a system in which oscillations build up is said to be unstable and much of the design work in control engineering is associated with producing a stable system . Adequate stability is, of course only one of several requirements, another requirement is faithful reproduction of a variety of input signals, and it has already been seen that the system of fig.1.is unlikely to reproduce a sudden change in input position with any degree of fidelity. Another type of input command might consist of handwheel motion of constant velocity .The system would then respond with an oscillatory transient and the mass would finally settle flown with a velocity equal to the command bur with a position lagging the command by a small angle .The slight difference between input and output positions would be of such magnitude as to produce an output torque from the motor sufficient to drive the mass at the required velocity against frictional torques .The error could not be zero otherwise the motor would stop and the error would the build up .
It is thus apparent that whilst the output will automatically align itself with the command under static conditions, under dynamic conditions the output motion only approximates to that of the command. The closeness of the approximation can however usually be made as good as is necessary to overcome most physical; for example, in certain types of automatically controlled profile milling machines a tracking accuracy to 0.0001inch has been achieved.
Another object of the position control system is that it must be capable of holding the output position equal to the presence of severe of severe load disturbances .for example, a launcher must remain pointing in the desired regardless of random guests of wind .the position control system of fig .1. If correctly designed, would be able to achieve quite good regulation against load disturbances of this kind but a steady load disturbances of this kind but a steady load disturbance would inevitably produce a small misalignment between output and command .In systems where such a misalignment would be intolerable, a more sophisticated type of controller must be used.
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