Contributions to the Two Degrees of Freedom Modular Variable Reluctance Motors Used in Advanced Manufacturing Systems

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Contributions to the Two Degrees of Freedom Modular Variable Reluctance Motors Used in Advanced Manufacturing Systems Loránd Szabó Ioana Benţia Dan-Cristian Popa Mircea Ruba Technical University of

1 Contributions to the Two Degrees of Freedom Modular Variable Reluctance Motors Used in Advanced Manufacturing Systems Loránd Szabó Ioana Benţia Dan-Cristian Popa Mircea Ruba Technical University of Cluj-Napoca Department of Electrical Machines and Drives Cluj-Napoca, Romania Abstract In advanced manufacturing systems complex movements are frequently needed. These can be performed by motion systems able to execute motion of several degrees of freedom. Usually each type of movement is performed by one independent electrical machine. In a more developed approach electrical machines able to perform more degrees of freedom motion are widely required. In the paper some contributions to two degrees of freedom modular variable reluctance motors are presented. Two typical machines able to perform such motion are discussed: a planar motor and a rotary-linear one. Keywords-variable reluctance electrical machine, two degrees of freedom movement, planar motor, rotary-linear motor. I. INTRODUCTION Sophisticated motions are frequently required in robots, machine tools or pick-and-place systems used in advanced manufacturing. The complex motion trajectories are often involving several mechanical degrees of freedom (DoF). Presently in such applications often single DoF electrical machines are used, each one managing a single mechanical DoF of the motion system. The elementary motions developed are then combined by means of suitable mechanical devices. Since the performances, volume, weight, cost and maintenance requirements of similar systems are relevant, appreciable benefits might be obtained by using electrical machines able to perform multiple DoF movements [1]. The variable reluctance machines are widely used in advanced manufacturing systems due to their simplicity and high reliability [2]. In some cases for easy manufacturing and repairing purposes these are built up modularly [3], [4] In the paper the main contributions of the researchers from Technical University of Cluj-Napoca to two DoF modular variable reluctance motors are presented. Two typical machines able to perform such movements are detailed: i.) the modular surface motor ii.) the rotary-linear switcher reluctance motor (SRM). For both machines their constructions are presented. Their performances are analyzed by means of finite elements method (FEM) based numeric field computations. II. THE MODULAR SURFACE MOTOR Surface (planar) motors can be used in those applications (mainly in the advanced manufacturing field) which require movement on a plane in two directions (x-y axes). The use of an appropriate control system together with accurate position detectors allows very precise planar positioning [5]. The proposed permanent magnet modular surface motor (PMMSM) has the advantages of direct driving, low friction, no backlash, high accuracy, etc. It was designed on the basis of the three-phase modular double salient linear motor (DSLM) also developed by the researchers from Technical University of Cluj-Napoca [6], [7]. The PMMSM combines the advantages of variable reluctance motors with those of the synchronous permanent magnet (PM) motors (simplicity, high power density, significant positioning accuracy, etc.) [8], [9]. A. Construction The construction of the PMMSM is simple (see Fig. 1). Figure 1. The basic structure of the PMMSM It has of two basic parts: the platen and the mover. Due to the air bearing between them the movement is practically frictionless. Therefore the PMMSM moves very smoothly and its velocity speed can be precisely controlled. As the load can be placed directly on the mover the PMMSM is a direct-driven motor /12/$ IEEE AQTR 212

The passive platen made of steel has slots filled with epoxy resin on both orthogonal directions. Practically the platen can have any sizes function of the requirements of its application.

A module of the PMMSM The working principle of the PMMSM is based on the variable reluctance principle [2].

If the coil is fed its magnetic flux forces the flux generated by the PM through the air-gap. In this case significant force is generated.

Each of them is producing motion on one of the perpendicular axis, as shown in Fig. 3. B.

2 The passive platen made of steel has slots filled with epoxy resin on both orthogonal directions. Practically the platen can have any sizes function of the requirements of its application. The mover of the PMMSM is built up of magnetically independent modules (see Fig. 2) having a PM, two salient poles with teeth and a coil. Figure 4. The mover of the three-phase PMMSM Figure 2. A module of the PMMSM The working principle of the PMMSM is based on the variable reluctance principle [2]. When the coil is not fed the flux of the PM is crossing the core segment under the PM due to its smaller magnetic resistance. In this case no force is generated. If the coil is fed its magnetic flux forces the flux generated by the PM through the air-gap. In this case significant force is generated. Due to the tangential component of the force the module moves a step in order to minimize the magnetic energy stored in the air-gap [9]. Practically the mover of the PMMSM is a compound of two DSLMs. Each of them is producing motion on one of the perpendicular axis, as shown in Fig. 3. B. Simulation The above presented three-phased PMMSM was analyzed via three-dimensional (3D) FEM based numerical magnetic field computation by means of the ANSYS Maxwell electromagnetic field simulation software. The computations were performed for only a single mover module and the portion of the platen under it, as shown in Fig. 5 [9]. Figure 3. The force development principle of the PMMSM The PMMSM can be built up for diverse traction forces and step length upon the requirement of the application. By means of appropriate command system the positioning accuracy pf the PMMSM be increased considerably [9]. The simplest PMMSM has at minimum three phases. It is built up of 6 modules, 3-3 for both perpendicular directions. A three dimensional picture of such a PMMSM can be seen in Fig. 4. Figure 5. The solid model of the analyzed PMMSM In the paper from the several simulation results only two significant ones are given. Firstly the magnetic field density distributions in the two basic cases in study are given. If the teeth on the two armatures are perfectly aligned and the coil is not energized almost no magnetic flux is passing through the air-gap (see Fig. 6a). When the mover is at a third part of the teeth pitch on the y-axis direction (the relative positions on the orthogonal axis are x = mm and y =.66) and the coil is fed by the rated current (I c =.7 A) the magnetic flux of the PM is forced to pass through the air-gap, as it is shown in Fig. 6b). In this case N tangential force is generated.

By performing several simulations for different positions of the mover and diverse values of the current the static characteristics of the total tangential force given in

The static characteristics obtained via simulations b) active module (coil energized) Figure 6. The flux density distribution obtained via 3D FEM analysis In Fig.

THE ROTARY-LINEAR SWITCHED RELUCTANCE MOTOR In modern industrial applications both rotary and linear movements are widely required.

For such application the rotary-linear switched reluctance motor (RLSRM) is a quite good solutions. This is also a direct-driven machine.

Other advantages of such motors are their fast response, high flexibility and their drive and control system may be relatively simple [11]. A.

3 By performing several simulations for different positions of the mover and diverse values of the current the static characteristics of the total tangential force given in Fig. 8 was plotted Static characteristics obtained via simulations,7 A,8 A,9 A 1, A 1,1 A 1,2 A 12 F t [N] a) passive module (coil unfed) x [mm] Figure 8. The static characteristics obtained via simulations b) active module (coil energized) Figure 6. The flux density distribution obtained via 3D FEM analysis In Fig. 7 for a better view a zoom on the air-gap area of the flux density distribution color maps shown in Fig. 6 are given. III. THE ROTARY-LINEAR SWITCHED RELUCTANCE MOTOR In modern industrial applications both rotary and linear movements are widely required. But in many cases, mainly due to space limitations, it is difficult to place two motors to ensure the two types of motion [1]. For such application the rotary-linear switched reluctance motor (RLSRM) is a quite good solutions. This is also a direct-driven machine. Basically being a SRM it has low manufacturing and maintenance costs at high reliability. Other advantages of such motors are their fast response, high flexibility and their drive and control system may be relatively simple [11]. A. Construction The iron core structure of a three-phase RLSRM is given in Fig. 9. a) passive module b) active module Figure 7. Zoomed view on the flux density color maps Figure 9. The basic structure of the RLSRM Also this machine has a modular construction. It is compound of three classical 8 poles SRM stators. The rotor is constructed of several common 6 poles SRM rotor stacks. The number of the rotor stacks depends on the required stroke on

If the machine has to perform a linear movement it will work similarly to a linear SRM [12].

4 the axial direction. The proposed RLSRM can rotate round its shaft and it can also move the axial direction. When rotation is required two coils on each stator stack are fed function of the rotor position and the imposed current pulses sequence. If the machine has to perform a linear movement it will work similarly to a linear SRM [12]. In the case of rotation the stator which has its poles aligned in the axial direction with the rotor poles will develop most of the torque. The other two stator stacks will also contribute to the rotational movement. As they are symmetrically unaligned on the axial direction the axial forces developed by them will be equal but of opposite direction, hence their sum will be nil and no linear movement will be produced. When linear displacement is imposed several phases of one module will be fed. The rotor stack will be aligned upon the variable reluctance principle with the energized coils stator's poles. The diverse complex command possibilities of the rotarylinear SRM are detailed in [13]. Each of the totally 12 phases are connected to a half H-bridge power converter. The phase currents are controlled by means of pulse-width modulation (PWM) techniques [14]. B. Simulation Due to the complex structure of the proposed rotary-linear SRM and its three-dimensional magnetic flux paths its analysis was possible only by means of 3D FEM computations. To simplify the computations only a single stator stack was considered together with a single rotor stack. Due to the periodicity of this structure it was enough to study a half of it. The 3D model of the machine was built up in Flux 3D software. Its structure without the coils is given in Fig. 1 Figure 11. The color map of the flux density By performing the field computations for diverse angular and linear positions at various phase currents between 1 6 A the static characteristics of the RLSRM in study were plotted (see Fig. 11). These static characteristics are very useful in both the dynamic simulations of the RLSRM and in the development of its control strategy. Torque [N m] Angular displacement [electrical degree] 2 a) rotational movement Tangential force [N] Figure 1. The 3D model of the analyzed RLSRM From the numerous simulations here only a single result is given. In Fig. 11 the color map of the flux density was computed for the position where the stator pole is perfectly aligned on both directions with a rotor pole. Upon the analysis of the color map it can be stated that the flux density levels are in accordance with the designed values Linear displacement [mm] b) axial movement Figure 12. The static characteristics computed via 3D numeric field analysis

5 IV. CONCLUSIONS Both the analyzed 2 DoF modular variable reluctance motors are good choices to be used in advanced manufacturing systems due to their robust constructions and easy controllability. By appropriate control strategies they are able to assure smooth planar, respectively combined rotary-linear motions. ACKNOWLEDGMENT This paper was partially supported by the projects "Doctoral studies in engineering sciences for developing the knowledge based society SIDOC" contract no. POSDRU88/1.5/S/678, respectively "Develop and support multidisciplinary postdoctoral programs in primordial technical areas of national strategy of the researchdevelopment-innovation 4D-POSTDOC, contract no. POSDRU/89/1.5/S/5263, both co-funded from European Social Fund through Sectorial Operational Program Human Resources REFERENCES [1] P. Bolognesi, et al., "Electromagnetic actuators featuring multiple degrees of freedom: a survey," in Proceedings of the Proceedings of the 16th International Conference on Electrical Machines (ICEM '24) Krakow (Poland), 24. [2] G. Henneberger and I.A. Viorel, Variable Reluctance Electrical Machines. Aachen (Germany): Shaker Verlag, 21. [3] I. Benţia, et al., "Modular electrical machines A survey," in Proceedings of the International Scientific Conference MicroCAD '21, Miskolc (Hungary), 21, pp [4] M. Ruba, et al., "Novel modular fault tolerant switched reluctance machine for reliable factory automation systems," in Proceedings of the 21 IEEE International Conference on Automation, Quality and Testing, Robotics (AQTR '21) THETA 17, Cluj (Romania), 21, pp [5] J. Pan, et al., "High-precision position control of a novel planar switched reluctance motor," IEEE Transactions on Industrial Electronics, vol. 52, pp , 25. [6] I.A. Viorel and L. Szabó, "On a three-phase modular double salient linear motor's optimal control," in Proceedings of the 9th European Conference on Power Electronics and Applications (EPE '21), Graz (Austria), 21, p. PP237.pdf. [7] L. Szabó, et al., "A novel double salient permanent magnet linear motor," in Proceedings of the International Conference on Power Electronics, Drives and Motion (PCIM '99). Nürnberg (Germany), 1999, pp [8] J. Cao, et al., "A novel synchronous permanent magnet planar motor and its model for control applications," IEEE Transactions on Magnetics, vol. 41, pp , 25. [9] L. Szabó, et al., "On the Usefulness of Simulation in Designing a Permanent Magnet Modular Surface Motor for Advanced Mechatronic Systems," in Proceedings of the 26 IEEE International Conference on Mechatronics (ICM '26), Budapest (Hungary), 26, pp [1] I. Benţia and L. Szabó, "Rotary-linear machines - A survey," Journal of Computer Science and Control Systems, vol. 3, pp , 21. [11] R. Krishnan, Switched reluctance motor drives: modeling, simulation, analysis, design, and applications. Boca Raton (USA): CRC, 21. [12] I.A. Viorel, et al., "Speed-thrust control of a double sided linear switched reluctance motor (DSL-SRM)," in 18th International Conference on Electrical Machines (ICEM '28), Vilamoura (Portugal), 28. [13] I. Benţia, et al., "On the control of a rotary-linear switched reluctance motor," in Proceedings of the 5th International Symposium on Computational Intelligence and Intelligent Informatics (ISCIII '211), Floriana (Malta), 211, pp [14] T.J.E. Miller, Electronic Control of Switched Reluctance Machines. Oxford (U.K.): Newnes, 21.

MULTI-LEVEL MODELLING OF A MODULAR DOUBLE SALIENT LINEAR MOTOR

MULTI-LEVEL MODELLING OF A MODULAR DOUBLE SALIENT LINEAR MOTOR L. Szabó, I.A. Viorel and J.B. Dobai, TU Cluj, Romania Corresponding Author: L. Szabó Technical University of Cluj, Department of Electrical