Synchronization between dual servomotor using

cross coupled sliding mode control

A Literature Review on

Guided By,Prof. M. C. Patel

Prepared By,Bharat R ValaEnroll: 130280703017

Overview:Servomotor:

• A servomotor is a rotary actuator that allows for precise control of angular position, velocity and acceleration.

• A servo system mainly consists of three basic components - a controlled device, a output sensor, a feedback system.

• This is an automatic closed loop control system.

• Controlling a device by applying variable input signal, the device is controlled by a feedback signal generated by comparing output signal and reference input signal.

DC Motor

Error detector amplifier

potentiometer

Servo mechanism for reduce shaft speed

Position cog

Output shaft

Reference input signal

Reference output signal

Servo motor block diagram

Applications of servo motor

• CNC machine• Robotics• Conveyors• Camera auto focus• Robotic vehicle• Solar tracking system• Other industrial application

Sliding mode control:

• sliding mode control, or SMC, is a nonlinear control method.

• Its application of a discontinuous control signal that forces the system to "slide" along a cross-section of the system's normal behaviour.

• This cross section is a sliding surface.

• Sliding mode control (SMC) is basically a high-speed switching feedback control.

• a sliding motion can be divided into two phases: a reaching phase and a sliding phase.

• The main advantage of sliding mode control to achieve order reduction, decoupling design procedure, disturbance rejection, insensitivity to parameter variations and simple implementation.

Paper 1: Shilong Wang ; Liang Huang ; Jie Zhou ; Ling Kang, "A Linear PI Cross-Coupled Control for Servo System of CNC Gear Hobbing Machine", IEEE International Conference on Information and Automation (ICIA), 2010, pp.987-991

• Cross-couple control with proportional-integral (PI) compensator proposed to reduce synchronization error.

• Recently one of the popular multi-axis control scheme as cross-coupled control, was proposed by Koren in 1980.

• Main two kind of synchronization control method proposed for CNC control system are, Set-point synchronization and feedback synchronization.

Set-point synchronization method

• In Set-point synchronization method, the speed command of following axis is given by the speed command of leading axis multiplied by a factor.

Feedback synchronization method

• In feedback synchronization method, the speed command of following axis is produced by the actual speed of leading axis multiplied by a factor.

• In this figure proposed a PI cross-coupled control scheme for dual servo system.

PI cross-coupled control

• the synchronization error is calculated and used as a input to proposed controller, whose output used as a compensation of both axis.

• P-I controller has some disadvantages such as: the high starting overshoot, sensitivity to controller gains and sluggish response due to sudden disturbance.

Limitations

Paper 2: O-Shin Kwon, Seung-Hoe Choe and Hoon Heo, "A study on the dual-servo system using improved cross-coupling control method ", 10th International Conference on Environment and Electrical Engineering (EEEIC), pp. 1-4, 2011

• In this paper cascade control and an improved cross-coupling control method proposed over Conventional synchronizing control.

• The improved cross-coupling control method performs in terms of angular position for high speed and accurate position control.

• The control goal is to achieve synchronous error between two servo motor and accurate position control to desire slide position.

• Two types of conventional control system widely used in servo control system, First one is series connection or Master-Slaved motion control and another one is parallel connection or Main-Main control.

• The conventional control system is shown in previous figure. It shown with feedback loop and synchronization loop.

• In these scheme the feedback loop is required for accurate position control and the cross coupling controller is used for the reduction of synchronous error between two servo motors.

Modified control system for Cross-coupling of angular position and velocity

• The proposed controller with cascade loop and an improved cross-coupling control method.

Limitations

• In this paper proposed controller is applied for series (Master-slave) servo system. Whenever we work with dual side motion tracking and position accuracy control in cross-coupled dual servo system to designing of PID controller is being very complicated to system.

Paper 3 : Alessandro Pisano, Alejandro Davila, Leonid Fridman and Elio Usai, "Cascade Control of PM DC Drives Via Second-Order Sliding-Mode Technique," IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 55, NO. 11, NOVEMBER 2008

• In this paper they discussed about a novel scheme for the speed/position control of permanent-magnet (PM) dc motor drive and suggested control algorithm is cascade-control scheme based on sliding mode control.

• They have also discussed about adaptive and H∞ control, VSC (variable structure control ) , features of VSC, but all controllers are not suitable to achieve precision, robustness, simplicity and finite time conversation. H

∞

• The implemented controller is cascade implementation of sliding mode controller. Its proved that cascade sliding mode control gives better performance over cascade PI controller. So its also applicable on dual servo synchronization technique.

• In this case sliding mode control achieve better output to optimization control scheme.

Paper 4: Variable-Gain Cross-Coupling Controller for Contouring

• Contouring is the most complex flexible and the most expensive type of machine tool control.

• In addition the distinguishing feature of the of contouring NC system is their capacity for simultaneously control of more than one axis.

• Milling and Turning are the common examples of  the use of contouring control.

The variable-gain cross-coupling controller.

The variable-gain cross-coupling controller.

Contour type Conventional controller(P-Controller)

Cross-Coupling Control

Linear 50.5 3.5

Circular 71.6 3.7

Parabolic 77.3 11.1

Maximum Control Error (in µm)

• A variable-gain cross-coupling controller that reduces the contour errors has been proposed.

• In this paper the method is based on building in real time the instantaneous contour error.

Objectives:

• In most of papers control algorithm is base on PI, Simple PID and Cross-Coupled Control scheme but my focus on Sliding Mode Control design for Dual-Servo system.

• Design a controller for Dual Loaded Servo System is difficult task in real time application formulation. So sliding mode control is really helpful to achieve optimization technique in Dual Servo synchronization accuracy.

• Using MATLAB tool, try to simulate as well as compare of all control algorithm in simulation and also implementation of sliding mode control in real time.

Paper Referred in Detailed:• Shilong Wang ; Liang Huang ; Jie Zhou ; Ling Kang, "A linear PI

cross-coupled control for servo system of CNC gear hobbing machine," IEEE International Conference on Information and Automation (ICIA), 2010, pp.987-991.

• Alessandro Pisano, Alejandro Davila, Leonid Fridman and Elio Usai, "Cascade Control of PM DC Drives Via Second-Order Sliding-Mode Technique," IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 55, NO. 11, NOVEMBER 2008

• O-Shin Kwon, Seung-Hoe Choe and Hoon Heo, "A study on the dual-servo system using improved cross-coupling control method " ,10th International Conference on Environment and Electrical Engineering (EEEIC), pp. 1-4, 2011

• Variable-Gain Cross-Coupling Controller for Contouring.

Thank You

• H∞ (H-infinity) methods are used in control theory to synthesize controllers achieving stabilization with guaranteed performance.

• To use H∞ methods, a control designer expresses the control problem as a mathematical optimization problem and then finds the controller that solves this optimization.

• H∞ techniques have the advantage over classical control techniques in that they are readily applicable to problems involving multivariate systems with cross-coupling between channels

• The phrase H∞ control comes from the name of the mathematical space over which the optimization takes place