Control of Servo System of CNC Machine using PID

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1 International Jornal of Engineering, Applied and Management Sciences Paradigms, Vol. 42, Isse 0 Pblishing Month: December 206 Control of Servo System of CNC Machine sing PID Ahmed Msa Ahmed Mohamed and Dr. Eltahir Mohamed Hssein 2 Control Engineering, Al- Neelain University, Khartom, Sdan ahmedmosa892009@gmail.com 2 Biomedical Engineering Department, Sdan University of Science and Technology (SUST) and Faclty of Engineering, Al-Neelain University, Khartom, Sdan altahir_33@yahoo.com Pblishing Date: December 2, 206 Abstract This research concentrates on compter nmerical control (CNC) as one of the modern control system which has a great benefits and Redced the problems and errors of the traditional machines that depend on operators the main problems of traditional machines are waste of time and effort beside that CNC machines have the capability of prodcing the complicate pieces in a mass prodction form in a very limited time as any other machines the CNC machine faces some problem sch as technical errors de to high temperatre the actator deviation and finally the error prodced by the motor sed as motion sorce one of the CNC error is tracking error from the servo motor sing PID controller for position and speed control minimizes this error hence improving the motor performance and increased the qality of the prodct as desire by the designers. Keywords: PID Controller, DC Servo Motor, CNC Machines and Matlab Program.. Introdction Mechatronics are the synergistic integration of sensors, actators, signal conditioning, power electronics, decision and control algorithms, and compter hardware and software to manage complexity, ncertainty, and commnication in engineered systems[2]. Mechatronics are inclding 40% electricity, 30% mechanics, 20% electronics and 0% programming so CNC machines are department for applications of mechatronics engineering. The present day compter can be considered as a direct conseqence of the progress in the field of nmerical control of machine tools. A real break-throgh was achieved arond 965 when nmerical control machines were fitted with minicompters which introdced the name Compter Nmerical Control. The first step in the process of implementing atomation in any indstry is to manfactre parts or components throgh atomation sing machines and machine tools with little hman intervention. In order to meet the increasing demand to manfactre complicated components of high accracy in large qantities, sophisticated technological eqipment and machinery have been developed. Prodction of these components calls for machine tools which can be set p fairly rapidly withot mch attention [3]. The design and constrction of Compter Nmerically Controlled (CNC) machines differs greatly from that of conventional machine tools. This difference arises from the reqirements of higher performance levels. The CNC machines can be operated atomatically sing compters. A CNC is specifically defined as The nmerical control system where a dedicated, stored program compter is sed to perform some or all of the basic nmerical control fnctions in accordance with control programs stored in read & write memory of the compter by Electronic Indstries Association (EIA) [4]. CNC is a microprocessor based control system that accepts a set of program instrctions, processes and sends otpt control information to a machine tool, accepts feedback information acqired from a transdcer placed on the machine tool and based on the instrctions and feedback, assres that proper motion, speed and operation occr. Some of the important parts of CNC machines are Machine strctre, gide ways, feed drives, spindle and Spindle bearings, measring systems, controls, software and operator interface, gaging, tool monitoring.the information stored in the compter can be read by atomatic means and converted into electrical signals, which operate the electrically controlled servo systems. Electrically controlled servo systems permits the slides of a machine tool to be driven simltaneosly and at the appropriate feeds and direction so that complex shapes can be ct, often with a single operation and withot the need to reorient the work piece. Compter Nmerically Control can be applied to milling machines, Lathe machines, Grinding machines, Boring machines, Flame ctters, Drilling machines etc.pid ( Proportional (P), the integral 9

2 Amplitde International Jornal of Engineering, Applied and Management Sciences Paradigms, Vol. 42, Isse 0 Pblishing Month: December 206 (I), and the derivative (D)) controllers are everywhere de to its simplicity, robstness, and excellent if not Optimal performance in many applications, PID controllers are sed in More than 95% of closed-loop indstrial processes [5].. The Proposed System: This signal () will be sent to the plant, and the new otpt (Y) will be obtained. The new otpt (Y) will be sent back to the sensor again to find the new error signal (e). The controller takes this new error signal and comptes its derivative and it s integral again. This process goes on and on. Figre : The Block Diagram of the Proposed System.2 Steps for Design PID Controller: - Determine what characteristics of the system need to be improved. 2 - Use K p to decrease the rise time. 3 - Use K d to redce the overshoot and settling time. 4 - Use K i to eliminate the steady- state error..3 Open loop step response in dc servo motor modeling in eqation: g Step Response Rise Time: N/A Peak amplitde >= 75 Overshoot (%): NaN At time (sec) >.5e Time (sec) Figre 2: Step Response for Open Loop of dc Servo Motor Normally PID controllers are sed to improve the transient response of DC servo motors..4 DC servo motor by sing PID controller: Servomotors se feedback controller to control the position or the speed, or both. The basic continos feedback controller is PID controller which possesses good performance. 92

5 Position Control: Figre 3: Using PID controller to control the position of dc servo motor.

S) = K*[Kd S^2 + Kp S + Ki] / J S^3 + ( Kd + B ) S^2 + Kp S + Ki Using matlab program :.4.2 0.8 Peak amplitde:.0 Overshoot (%):.

3 Amplitde International Jornal of Engineering, Applied and Management Sciences Paradigms, Vol. 42, Isse 0 Pblishing Month: December Position Control: Figre 3: Using PID controller to control the position of dc servo motor.6 PID Controller: For the general PID controller transfer fnction of the closed loop system dc servo motor its written as : G ( S) = K*[Kd S^2 + Kp S + Ki] / J S^3 + ( Kd + B ) S^2 + Kp S + Ki Using matlab program : Peak amplitde:.0 Overshoot (%):.34 At time (sec): 0.47 Rise Time (sec): 0.38 Settling Time (sec): Step Response g Final Vale: Time (sec) Figre 4: Step response for PID controller.7 Velocity control: Speed Figre 5: Using PID controller to control the velocity of dc servo motor 93

International Jornal of Engineering, Applied and Management Sciences Paradigms, Vol. 42, Isse 0 Pblishing Month: December 206 2.

4 International Jornal of Engineering, Applied and Management Sciences Paradigms, Vol. 42, Isse 0 Pblishing Month: December Matlab Simlink Technology We are sed Matlab simlink technology becase it considers the best method to modeling and represent systems the sefl from this system research and ser perform to tests needed to bild a model or take older model and applied tests or additions. Scope e y Step PID Controller Plant 450 Proportional e 00 Integral s Integrator Sm 00 d/dt Derivative Derivative (a) 0s 2+20s Identified Plant Model y (b) Figre 6: Simlink Techniqe in Matlab Program (a) PID controller (b) Transfer Fnction of dc servo motor. 94

5 International Jornal of Engineering, Applied and Management Sciences Paradigms, Vol. 42, Isse 0 Pblishing Month: December Reslts Geometric errors of machine components and strctres and Errors indced by the distortions and Deflection errors cased by ctting forces in this set of error sorces can be redced by improving the mechanical hardware or tilizing compensation techniqes, bt cannot be redced by the control techniqes discssed in this search. 3. Reslts of Simlation Table : Reslts of PID Controller Parameters Close Loop Response Rise Time (sec) Settling Time (sec) Overshoot (%) Peak Amplitde Steady State P controller PD controller PI controller PID controller P Controller In this control method redcing the rise time bt never eliminates the steady state error and present overshoot PD Controller In this method control of dc servo motor redce rise time and eliminate the steady state error 3..3 PI Controller In this method control of dc servo motor increasing the stability of the system becase redce rise time and redce the overshoot 3..4 PID Controller Enhancement stability of Dc servo motor in CNC machines system sing this method control becase redce rise time and redce the overshoot and eliminate the steady state error so that redce the tracing error cased by point - to - point path position system.the position error (X-axis and Y- axis) is the linear distance between the actal tool position and the reference point.the prpose of tracking control (point - to point path system) is to minimize the position errors of each axis.pid controller decrease the position errors of each axis so that more accracy for machine tool in CNC machine and enhancement for tracking control method by dc servo motor which is decrease the error in final prodct by CNC machines P-PI Controller In this method sing to control the velocity of dc servo motor so that increasing the stability of the system becase redce rise time and redce the overshoot. 4. Conclsion Finally in this research and according to the simlations and experimental reslts, a comparison of these servo controllers is smmarized in Table 3.Based on the comparison, the selection of servocontrollers for different machine tool contoring applications and ctting conditions is sggested in the following: The P controller works well only when ctting a contor on a machine with small friction, small ctting loads, small mismatch in axial parameters, and conventional feed rates (e.g., 0.25 m/min ~ 0 I p m).the PID controller has a good distrbance rejection ability and is more robst to mismatched axial parameters. Its drawbacks are poor tracking ability of nonlinear contors and sharp corners, and in addition, it may reslt in an overshoot at stopping. Therefore, the PID controller is preferred on low-speed machines. Usally, a deceleration is needed at the end of every contor segment in order to avoid the overshooting problem.however, these increases the total ctting time. A special algorithm can be tilized to perform corner tracking: the I component of the PID controller can be trned off before the corner. This, however, can case 95

6 International Jornal of Engineering, Applied and Management Sciences Paradigms, Vol. 42, Isse 0 Pblishing Month: December 206 nderct and contor errors becase of the friction and other distrbances. References [] /Accessed on 5/6/203. [2] Indstrial centre, compter nmerical control (CNC), IC Professional training series, the Hong Kong polytechnic niversity, Agst [3] Accessed on 2/7/203. [4] Sk-Hwan Sh, Seong-Kyoon Kang, Dae- Hyk Chng, Ian Strod, Theory and design of CNC systems, British Library, March [5] Jingha Zhong, PID Controller Tning: A Short Ttorial, Mechanical Engineering, Prde University, spring, [6] Parker Hannifin Electromechanical Atomation Div. / [7] Ban Akar, Neşe Kaynak, Dyg Gökçe, Meltem Erdi, Compter Nmerical Control(CNC), Hacettepe University Chemical Engineering Department,

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