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 Archiwum Process Control Club 2003, poz.22

 
 


Facility for Induction Motor Velocity Control 
with a Magnetorheological Brake

 

Sławomir Bydoń
Department of Process Control
University of Mining and Metallurgy, Cracow, Poland
 

Abstract. The paper presents the facility which was developed for testing velocity control system with induction motor and magnetorheological (MR) brake. The induction motor was equipped with frequency inverter. An incremental encoder was used to measure rotation velocity. The control system consisted of PC with multi I/O board of RT-DAC type, operating in Matlab/Simulink environment. The paper describes parameters and characteristics of MR brake, construction and operation of the experimental setup and exemplary results of control system tests.

Keywords: MR brake, velocity control, facility, induction motor


TABLE OF CONTENTS

1. Introduction
2. Structure and operation of MR brake
3. Experimental setup
     3.1. Mechanical subsystem
     3.2. Electrical subsystem of experimental setup
     3.3. Software
4. Control system
5. Exemplary results of experimental tests
6. Conclusions
References


1. Introduction

       Investigations under MR devices like brakes and linear dampers, tests of usage them as an auxiliary part of control systems [1, 2, 3] and in mechanical vibration damping systems [5] shows, that these devices, in spite of nonlinear characteristics and expensiveness, can be successfully applied in automatic control systems. Experiments are also conducted in Department of Process Control* in the field of mathematical modeling, structure and control [4, 5, 6]. Advantages of MR brakes, clutches and dampers are: fast acting, reflexivity of MR fluid transformation, low static friction coefficient, low power consumption and fluent torque or force control [12].
       Viscosity of MR fluid depends on magnetic field strength. Moving parts of MR devices (rotor and stator in brake or piston and cylinder in linear damper) are mechanically connected with each other with the help of MR fluid. Resistance caused by fluid depends on it's viscosity. Viscosity changes with the current flowing through the coil.
       The paper presents facility for testing possibility of usage MR brake in rotation velocity control and positioning system of induction motor shaft. Because of high inertia of rotor (for example in comparison to DC motor of same power), braking and acceleration time of induction motor is longer that for other kind of drives. Due to this dynamic properties of drives that uses induction motors are impaired. On the other hand, usage of induction motor is explained by low price and long durability.
       Induction motor coupled with MR brake allow to control rotation velocity not only by use of frequency inverter but also by change of resistance torque. The main goal of facility creation is to test control algorithms obtained in simulation tests.
       During the design of experimental setup two assumptions were made: motor torque must be lower than MR brake torque and rotation speed of motor can be changed from zero to maximum rotation speed of brake (1000 rpm).

*Department of Process Control, University of Mining and Metallurgy, al. Mickiewicza 30, 30-059 Cracow, Poland


2. Structure and operation of MR brake

Fig. 1
Fig. 1. Structure of MR rotary brake.

Fig. 2
Fig. 2. Behaviour of MR fluid a) H = 0 and
b) H 0 

Fig. 3
Fig. 3. Direct-sheer mode of MR fluid.

 

Fig. 4
Fig. 4. Current I in the coil vs. torque M.

 

       Structure of MR rotary brake was shown in Fig.1. Structure of brake with MR fluid (8) and construction of coil (2) enables the gap (7) to be in magnetic field H. Rotor (3) is fixed to the shaft (6), which is placed in bearings (5) and can rotate in relation to housing (4). Wires (1) allow supplying electric current to the coil.

       MR fluid is suspension of magnetic particles in the carrier liquid (water, oil or some other kind of liquid). Magnetic particles are dissipated in the liquid when field strength is equal to zero (H = 0) (Fig. 2.) but when the field strength is greater than zero (H 0) then particles are magnetized, gather in chains and make liquid flow through them to be more difficult. Chains direction is parallel to magnetic field lines.

       Operation of MR brake is based on so called 'MR effect' [2, 3]. MR fluid being in the gap changes viscosity very fast when magnetic field is applied. Fig. 3. shows MR fluid in the gap during working in clutch (direct-sheer) mode, when there is magnetic field applied (H 0). Fluid is between two surfaces moving in the different directions. In the brake these are surfaces of housing and rotor. Current in the coil creates magnetic field in the gap. Value of the current can be set from 0 to 1 A. Fluid viscosity depend on the current in the coil. Viscosity of the fluid influence torque that brakes the rotor.

       Fig. 4. shows the ideal static characteristic (dependence between torque M and current I) of MR brake. When the current in the coil is equal to zero, then there is no magnetic field (I = 0 H = 0) and torque is equal to minimum Mmin. This value is equal to the torque caused by bearings, seals and viscosity of carrier liquid. When current I = 1 A then H   0 and brake has highest possible value of the torque (Mmax 5,65 Nm), that is limited by maximum current in the coil Imax and construction of brake. Maximum power consumption is 12W. Maximum power dissipation ( =1000 rpm, Mh = 5.65 Nm) is 600W.


3. Experimental setup

       The experimental setup is shown schematically in Fig. 5. and 7. It consists of hardware (mechanical and electrical subsystems) and software. Photo of mechanical subsystem was shown in Fig. 6.

 
Fig. 5. Block diagram of experimental setup.

3.1. Mechanical subsystem

       Induction motor (5) (rated torque: Mn=1.7Nm, power: P=0,12kW) was chosen as an actuator. Motor's shaft is coupled with brake's (3) shaft with the help of rigid or elastic coupling (4). Additional inertia load (1) is connected to the shaft of brake. Incremental encoder (6) with 360 pulses per rotation is position measuring device. Motor and brake are fixed to aluminium housing (2).

Fig. 6
Fig. 6. Mechanical part of experimental setup. 1 - inertia load, 2 - housing, 3 - MR brake, 4 - coupling, 5 - motor, 6 - encoder.

3.2. Electrical subsystem of experimental setup

       The control system is based on PC equipped in multi I/O board of RT-DAC-2 type. Board being an interface, that connects plant with PC is universal type, that is why it was necessary to design electronic device, that counts pulses from encoder and passes number of them as 16-bit value to board though digital inputs. To obtain possibility of induction motor velocity control frequency inverter (MITSUBISHI, FR-E520S-0,75K) was used. The board is equipped in two 12-bits analog outputs. One of them is used to control frequency of electric current, that supplies motor. Second analog output is connected with current amplifier ((05) V(01) A), that supplies coil of MR brake.

3.3. Software

       Control system designed in MATLAB/Simulink [9] environment with Real-Time Workshop (RTW), that enables to run application in real time [8] and makes possible to store measurement data.


4. Control system

       The facility configuration made possible to test different kind of rotation velocity control algorithms. Diagram of control system and connection of it with plant is shown in Fig. 7.

Fig. 7
Fig. 7. Induction motor velocity control system with MR brake.

       Velocity signal in calculated as a slope of a straight line, that is linear regression (calculated in real time) of four samples of position signal from encoder.


5. Exemplary results of experimental tests

       Experimental tests conducted with the help of facility allowed to verify the mathematical model of induction motor [11]. Synthesis and simulation of control system was done. Results of simulation test was verified with the help of facility. 
       The comparison of two control systems (without and with MR brake) was done. Time responses of two control systems to step and sin wave were shown in Fig. 8. and 9.

Fig. 8
Fig. 8. Step response of velocity control systems a) without MR brake , b) with MR brake MR
zad - velocity set value, Mh - braking torque.

Fig. 9
Fig. 9. Time patterns of velocity for sine excitation zad with frequency 1 Hz for control systems a) without MR brake , b) with MR brake MR. Mh - braking torque.


6. Conclusions

       Experimental tests show, that preliminary assumptions taken during design process were satisfied. Facility enables to make studies over control system and is also usable for didactics.
       MR brake connected to induction motor reduces setting time during rotation velocity decreasing as it is shown in Fig. 8. and 9. 
       Improvement of control algorithm and determining of accurate static and dynamic characteristics of brake are being planed.


References

[1] B. SAPIŃSKI, S. BYDOŃ: Zastosowanie hamulca magnetoreologicznego do regulacji prędkości obrotowej siłownika pneumatycznego, Pneumatyka 3(34), maj - czerwiec 2002, str. 27-29.
[2] S. BYDOŃ: Construction and Operation of Magnetorheological Rotary Brake, Proceedings of STOC'2002, Ostrava, 2001, April 26-27
[3] M. R. JOLLY: Pneumatic Motion Control Using Magnetorheological Fluid Technology, 27th International Symposium on Smart Actuators and Transducers (ICAT), State College, PA, 1999, April 22-23.

[4]

B. SAPIŃSKI: Parametric Identification of MR Linear Automotive Size Damper, Journal of Theoretical and Applied Mechanics, 2, 40, 2002, p. 703-722.

[5]

B. SAPIŃSKI: Badania semiaktywnego układu wibroizolacji fotela operatora maszyny roboczej z liniowym tłumikiem magnetoreologicznym, Mechanika, Tom 21, Zeszyt 4, 2002
[6] B. SAPIŃSKI: Autonomic Microcontroller with Fuzzy Capabilities for MR Seat Damper Control, proceedings of MARDiH, maj 7-9, 2003
[7] D. CARLSON, D. M. CATANZARITE, K. CLAIR: Commercial Magnetorheological Fluid Devices, Lord Corporation.
[8] W. GREGA: Sterowanie cyfrowe w czasie rzeczywistym, wydawnictwo Wydziału Elektroniki AGH, Kraków 1999.
[9] A. ZALEWSKI, R. CEGIEŁA: Matlab - obliczenia numeryczne i ich zastosowanie, Wydawnictwo Nakom, Poznań 1998.
[10] W. I. KORDOŃSKI: Elements and Devices Based on Magnetorheological Effect, Journal of Intelligent Systems and Structures, vol.4, Styczeń, 1993, str. 65-69.
[11] L. SZKLARSKI, K. JARACZ: Wybrane zagadnienia z dynamiki napędów elektrycznych, PWN, Warszawa 1986.
[12] J. D. CARLSON, J. L. SPRONSTON: Controllable Fluid in 2000 Status of ER and MR Fluid Technology, "Actuator 2000"- 7th International Conference on New Actuators, June 19-2, 2000

This work was supported by University of Mining and Metallurgy under research no. 10.10.130.339/2002.