Laser measurement system dedicated to the determination of rails deformation of a hybrid electromagnetic launcher

Abstract

The growing applications area of an electromagnetic launcher lead to numerous researches on new constructions and analyzes of existing and novel solutions of this type of device. The typical solutions with a coil or rail drive (named coil-gun and rail-gun) as well as a new hybrid construction which is a combination of these two types of drives are known. The paper presents the construction and mathematical model of the hybrid electromagnetic launcher (containing coil-gun and rail-gun module) with pneumatic assists, but the main purpose of this paper is to present measurement and simulation results of rails deformation for an electromagnetic launcher with rails (rail-gun module). The computer simulations were made using Inventor Professional software. In the measurement system the laser displacement sensor was used.

Keywords

Railgun electromagnetic launcher hybrid electromagnetic launcher coilgun electrodynamic force

1. Introduction

An electromagnetic launcher is a device that uses electromagnetic acceleration to launch missiles. The first of its kind had been developed at the beginning of the XX century. The workflow of the electromagnetic launcher is shown graphically below.

Fig. 1.

An electromagnetic launcher - graphically definition.

One of the two basic types of electromagnetic launchers is a launcher with coil-drive (named a coil-gun). The general concept of a coil-gun is shown in the picture below.

Fig. 2.

The general concept of a coil-gun.

There are many known solutions for this type of high-speed linear actuator, multi-stage solutions are the most popular [6,7]. But in addition to conventional solutions, the design with a stepped coil [9] or “E-shaped” design [8] are also known.

Conventional construction of an electromagnetic launcher with a rail drive module (rail-gun) consists of two parallel rails connected to the power supply [10,11].

Fig. 3.

The general concept of a rail-gun.

Intensive research on new solutions in recent years has contributed to the emergence of new constructions with a greater number of drive rails in various configurations. For example: stacked four rails railgun [12,13], parallel four rails railgun [13], hexagonal segmented solution [14].

The main reason for the dynamic development of electromagnetic launcher was the possibility of military applications [1,5]. Currently, many engineers and scientists are working on other applications of electromagnetic launchers (such as the dynamic test of puncture resistance of materials [2]) and a new type of supply module dedicated to electromagnetic launchers [15–17].

One of the important aspects of the design process of rail-gun is the analysis of drive deformation during launching. The highly dynamic electromagnetic forces generate stress waves thereby causing rail deformation that might contribute to loss of contact between the rails and the projectile or blockage the projectile.

Fig. 4.

The rail-gun schematic for rail deformation analysis.

The Autodesk Inventor Professional software used for the static stress analysis provided simulation results that are compared with the measurement results. The laser sensor was used to measure rail deformation.

This paper presents the following: construction of the hybrid electromagnetic launcher with pneumatic assists (Section 2), the computer simulation model oriented to determine rails deformation of the rail-gun module (Section 3), the laser measurement system (Section 4) and conclusions (Section 5).

2. The hybrid electromagnetic launcher

The hybrid electromagnetic launcher elaborated in the Mechatronics Department at the Silesian University of Technology in Gliwice (Poland) is a combination of two basic types of electromagnetic launchers: an electromagnetic launcher with the coil (coil-gun module) and an electromagnetic launcher with rail (rail-gun module). Additionally, both electromagnetic modules are pneumatically assisted. The idea of the 3-module construction, CAD model, and the real photo is shown in Fig. 5.

Fig. 5.

The idea, 3D CAD model, and the real photo of the hybrid electromagnetic launcher with pneumatic assists.

In this paper, stress analysis was performed for the rail-gun module. The mechanical structure of the rail-gun module (Fig. 6.) consists of drive rails made of copper with length 500 mm (denoted by number 1), structural elements made of a silicone–glass composite (denoted by number 2 and 5), structural elements made of stainless steel (denoted by number 3), spacers made of epoxy-glass composite (denoted by number 4).

Fig. 6.

The mechanical structure of the rail-gun module: (a) 3D CAD model, (b) main dimensions.

During the missile acceleration process on the rails, the high force acts in a cross direction. The determination of the effects of this force on the rail-guns structural construction is very important because this deformation could lead to breakage of the missile between the rails. The maximum value of force acting on rails calculated from the circuit-field model can reach a maximum value of up to 10 kN [3,4]. The rails deformation can be determined in two ways: with the help of computer simulations or with the help of a dedicated measurement system. Both methods are described in detail below.

3. The stress analysis of the rail-gun module

A field-circuit model [3] of the rail-gun module allows us to calculate e.g. the force acting on rails during the missile acceleration process. The idea of a field-circuit model of the rail-gun module is shown graphically below.

Fig. 7.

The idea of the field circuit-model (rail-gun module), where: U – voltage initial value for capacitor battery supplying rail-gun module, v - initial velocity value of the missile at the input of rail-gun module, i – discharging current of capacitor battery supplying rail-gun module, F – force acting on rails during acceleration process, v – missile velocity, x – missile displacement.

The simulations were performed for different values of voltage U (in the range of 1--2150 V) and missile velocity with an initial value of 30 m/s. Simulation results obtained show time curves of current, the force acting on the rails, missile velocity, and missile displacement. From researches on the deformation of rails, the time curves of current, the force acting on the rails, and missile displacement are important. The exemplary results for four different sets of supply data are shown in Fig. 8--Fig. 10.

Fig. 8.

Time curves of current for four different sets of supply data.

Fig. 9.

Time curves of force acting on the rails for four different sets of supply data.

Fig. 10.

Time curves of missile displacement for four different sets of supply data.

Based on the result of the simulations shown in Fig. 8--Fig. 10 mechanical calculations were performed with the help of Autodesk Inventor Professional software. The simulations were performed for the maximum value of force acting on the drive rails for four different sets of supply data – see Fig. 10. Each of these maximum values of force determined the missile position (the missile position relative to the beginning of drive rails with taking into account the short circuit part of the missile). These results are presented together in Table 1.

Table 1

Of force acting on the rails and missile position for four different sets of supply data

No	U [V]	F [N]	x [mm]
1	300	210	14
2	450	480
3	600	810
4	2150	10400

Fig. 11.

General view of the simulation model illustrating fixed parts and force acting on the rails.

The simulations performed for parameters of the materials are presented in Table 2.

Table 2

The materials parameters

Material	E [GPa]	Rm [MPa]	Re [MPa]
Copper	117,5	210	33
Stainless steel	206,7	861,25	689
Epoxy-glass composite	17	185	300
Silica-glass composite	18,6	175	X

The fixed boundary condition was used for the bases (see – Fig. 11) and separation contact type was used between contacting surfaces. The separation contact allows separation between parts but prohibits part penetration. The simulations were performed for the finish element mesh with more than 500 000 nodes. Simulation results were obtained for stress distribution, total displacement, and displacement in the x-axis (see - Fig. 12--Fig. 15) for each mechanical part of the rail-gun module. Exemplary result for voltage value was obtained at 600 V and for the initial value of missile, the velocity equal 30 m/s as shown in the pictures below.

Fig. 12.

Stress distribution of the rail-gun module structure.

Fig. 13.

The total displacement of the rail-gun module structure.

Fig. 14.

Displacement in the x-axis of the rail-gun module structure.

Fig. 15.

Displacement in the x-axis of the rails.

The simulation results of a numerical way are presented together in Table 3.

Table 3

Simulation results

No	U [V]	F [N]	σ [MPa]	d_t [μm]	d_x [μm]
1	300	210	1.8	0.12	0.07
2	450	480	4.2	0.27	0.16
3	600	810	7.1	0.46	0.24
4	2150	10400	87	4.5	3.1

4. The laser measurement system

The main properties of the measurement system are its high-speed, high-accuracy CCD laser displacement sensor (KEYENCE LK-G152) wchich is connected to an LK-Navigator software installed on a personal computer. The rail deformation measurement system is shown in Fig. 16.

Fig. 16.

The rail deformation measurement system.

Fig. 17.

Illustration of the point where maximum force value occurs.

The laser beam falls on the outer surface of the drive rail at the point where the maximum value of the force occurs and the measuring point can be freely selected by changing the position of the laser head. The measuring head is mechanically isolated from the laboratory stand with the hybrid launcher to eliminate transmission of vibrations to the measuring system. The location of this point is calculated with the help of the circuit-field model and depends on the power supply conditions and the value of initial missile velocity.

Exemplary measurement results for three different initial voltage values (U = 300 V, U = 450 V, and U = 600 V) of the capacitor battery supplying the rail-gun module and an initial missile velocity equalling 30 m/s are shown together in Fig. 18.

Fig. 18.

Exemplary results of the rail deformation for three different initial voltage values (300 V – blue line, 450 V – red line, 600 V- green line) and initial missile velocity equal 30 m/s.

The measurements result compared together with the simulations result in Table 4, where: d_xs – simulation maximum value of displacement in the x-axis of the rails, d_xm – measurement maximum value of displacement in the x-axis of the rails.

Table 4

Simulations result and measurements result

No	U [V]	d_xm [μm]	d_xs [μm]
1	300	0.33	0.07
2	450	0.35	0.16
3	600	0.46	0.24
4	2150	X	3.1

The difference between the results of the simulation and the measurement is due to simplifying assumptions: not taking into account the mechanical impact of the missile on the rails, possible movements of the ground on which the launcher is mounted and the measuring point of the laser head which was set based on the results of a mathematical model which realistically might have moved.

5. Conclusions

The paper contains general information about different types of electromagnetic launchers and in detail presents hybrid solutions for the type of electromechanical device elaborated in the Mechatronics Department of the Silesian University of Technology. The static stress analysis model developed using Autodesk Inventor Professional software for the rail-gun module of this hybrid launcher. The developed computer model allows the determination of deformation of drive rails under the influence of Lorenz’s force. The Lorenz force was calculated using a filed-current mathematical model of the rail-gun module. Simulations performed for the maximum value of the Lorenz force and simulation results obtained on stress distribution, total displacement, and displacement in the cross direction of the missile movement for each mechanical part of the rail-gun module. In Section 4, a proposed measurement system using the laser and the sensor measuring the rail deformation. The simulation results were compared with the measurement results. The difference between the results of the simulation and the measurement is due to simplifying assumptions: not taking into account the mechanical impact of the missile on the rails, possible movements of the ground on which the launcher is mounted and the measuring point of the laser head which was set based on the results of a mathematical model which realistically might have moved.

The performed computer simulations and measurements lead to the following conclusions:

the proposed solution of a rail deformation measurement system using a laser displacement sensor is suitable for measurement of rail deformation,

an increase in the initial value of capacitor’s battery voltage supplying the rail-gun module causes an increase in vibrations amplitude,

it is possible to measure the deformation of rails at different points by multiplying the number of heads,

the obtained results allow us to calculate the risk of missile blocked between the rails,

an increase in the initial value of capacitor’s battery voltage supplying the rail-gun module causes a decrease difference between the measurement and simulation results

Further work on developing a transient analysis and modification of the laser measurement system. Increasing the number of laser heads and using a missile position measurement module is purposeful.

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