Incremental Linear Switched Reluctance Actuator

*Aymen Lachheb and Lilia El Amraoui*

## **Abstract**

Linear switched reluctance actuators are a focus of study for many applications because of their simple and robust electromagnetic structure, despite their lower thrust force density when compared with linear permanent magnet synchronous motors. This chapter deals with incremental linear actuator have switched reluctance structure. First, the different topologies of linear incremental actuators are mentioned. Furthermore, a special interest is focused on the switched reluctance linear actuator then the operating principal is explained. In addition, an analytical model of the proposed actuator is developed without taking account of the saturation in magnetic circuit. Finally, the control techniques that can be applied to the studied actuator are presented.

**Keywords:** linear actuator, switched reluctance, modeling, control, hybrid actuator, simulation

### **1. Introduction**

Nowadays, linear actuators are used more and more in various industrial fields. This type of actuator makes it possible to have a direct linear drive without recourse to an intermediate motion transmission system [1]. Indeed, unlike conventional approaches where linear movement is obtained by coupling a rotary actuator to a movement transmission system, the direct generation of linear movement makes it possible to reduce the number of mechanical parts and therefore the losses associated with them.

The absence of motion transformers improves the overall performance of the system. As a result, the linear actuator is essential when the speed and precision are required by the application (machining Tools, manipulator robots, etc.), for this type of actuator the thrust force generated is thus applied directly to the load, [2]. Linear displacement controls are often used in industrial devices. In most cases where rigidity is required, it is provided by the worm and worm wheel system or the straight rack. These solutions introduce problems of transforming rotary motion into linear motion: slip, drop in efficiency, and bulk [3].

In some cases, a linear actuator may offer a satisfactory alternative when its construction and cost issues are resolved [4].

Robotic systems offer vast opportunities for actuators and among these, those with switched reluctance structure, rotary or linear.

The purpose of this study is to reflect the principle of the operation, and control of a linear actuator with the study of the different topologies of linear actuators.

In the first part of this chapter the theory of switched reluctance machines well be explained. Then, the principle of operation as well as the analytical modeling of a linear actuator will be also studied. The last part of this chapter is devoted to the presentation of the control techniques dedicated for switched reluctance linear.

### **2. Classification of linear actuator**

There are mainly three types of incremental linear actuator which differentiate by the physical phenomenon which is at the origin of their movement.

These three types of actuators can have structures with a planar or tubular geometry [5, 6]. Contrarily to rotating machines where the rotor and stator are generally coaxial. Linear machines can be presented in flat form or cylindrical form. They consist of a moving part and a fixed stator whose positions can be reversed.

For flat structures, it is possible to realize actuators with single stator or with double stator. For cylindrical structures, it is possible to consider tubular actuators with internal or external moving part.

The single stator actuator is a simple variance which is easily integrated in current applications but which presents a significant force of attraction between the stator and the moving part [7]. The double stator structure makes it possible to obtain, on the one hand, higher thrust forces than for the single stator structure and on the other hand to lighten the mobile part, because if the latter is well centered the resultant of the forces attraction is then zero. This structure is particularly well suited to the case where the fixed stator.

The linear actuator can also have two symmetrical inductors in order to create a greater force compared to its single inductor counterpart. Nevertheless, it has a complex geometry for its manufacture.

They are composed of a fixed part (the stator) and a mobile part (the translator) whose displacement is governed by the tendency of the magnetic circuits to be in a position of maximum flux.

#### **2.1 Permanent magnet actuator**

The permanent magnet linear actuator consists of an armature comprising one or more permanent magnets and a stator comprising a number of coils. There are two configurations of this type of actuator. The first is with fixed coils and moving magnets. The second is with moving coils and fixed magnets, **Figure 1** [6].

The operation of this type of actuator is provided by the action of an electromagnetic field on the armature made up of permanent magnets. The magnetic field in the air gap created by the supply of the phase coils orients the magnets in one direction.

**61**

**Figure 3.**

**Figure 2.**

*Incremental Linear Switched Reluctance Actuator DOI: http://dx.doi.org/10.5772/intechopen.96584*

part rolled to form salient poles, **Figure 2**.

The switched reluctance actuator is among the simplest actuators. Regarding its construction, its basic structure consists of a coiled mobile part and an iron stator part which does not contain neither magnets or coils. The stator consists of an iron

The principle of operation of a switched reluctance actuator is based on the tendency of an electromagnetic system to achieve a stable equilibrium position, which minimizes reluctance of the magnetic circuit. The aligned position of a phase is defined as the situation where the teeth of the stator and the modulus teeth of the mobile of the phase are perfectly aligned with each other reaching a position where

**Figure 3** shows an incremental reluctant linear actuator with transverse flux configuration comprising three modules separated by a non-magnetic material, each phase of the actuator is composed of two windings in series. The feeding of a phase creates a force allowing the movement of the mobile towards a stable equilib-

For this type of actuator, if the poles of one module are aligned with the poles of the stator then the poles of the other module must be offset in order to create a propelling force. Indeed, magnetic separations between the modules are necessary

Hybrid stepping motors generally consist of a toothed mobile fitted with perma-

rium position, which it keeps as long as the power is maintained.

nent magnets. The **Figure 4** shows the structure of a hybrid motor, [9].

to impose a regular offset between the mobile modules.

*Switched reluctance actuator with longitudinal flux configuration.*

*Switched reluctance actuator with modular structure.*

**2.2 Switched reluctance actuator**

reluctance is minimal [8].

**2.3 Hybrid actuator**

**Figure 1.** *Permanent magnet linear actuator.*
