A tramming concept for a mechanical rock excavation...

A tramming concept for a mechanical rock excavation machine

SARA BLOMQVIST

Master of Science Thesis

Stockholm, Sweden 2015


Sara Blomqvist

Master of Science Thesis MMK 2015:52 MKN 139

KTH Industrial Engineering and Management

Machine Design

SE-100 44 STOCKHOLM

Examensarbete MMK 2015:52 MKN 139

Ett trammningskoncept för en mekanisk bergavverkningsmaskin

Sara Blomqvist

Godkänt

2015-06-09

Examinator

Ulf Sellgren

Handledare

Ulf Sellgren

Uppdragsgivare

Svea Teknik AB

Kontaktperson

Jacob Wollberg

Sammanfattning Denna rapport är resultatet av ett examensarbete på KTH i samarbete med Svea Teknik AB och

Atlas Copco Mining and Rock Excavation.

Atlas Copco utvecklar för närvarande en familj av maskiner för mekanisk bergsbrytning.

Samtliga maskiner i familjen har två framdrivningsmetoder. Målet med detta projekt har varit att

reducera antalet framdrivningsmetoder till en i en av dessa maskiner, Mobile minern.

Projektet har varit uppdelat i tre huvudfaser; bakgrundsstudier, konceptutveckling och

dokumentation. Konceptutvecklingen har i sin tur varit uppdelad i fyra delar; generering,

bedömning, utveckling och validering.

I projektet har inga fysiska prototyper, ritningar, komponentval, mjukvaruprogrammering,

beräkningar av friktionsförluster eller detaljerade FEM-analyser gjorts.

Nio koncept togs fram. Dessa bedömdes med avseende på en produktspecifikation med hjälp av

en viktad PUGH-matris. Det koncept som fick högst rankning i PUGH-matrisen var sex armar

som används för att dra maskinen framåt. Konceptet utvecklades med avseende på

applicerbarhet, hållbarhet och utmattning och slutade som ett koncept med fyra armar liknande

saxlyftbord som lagts horisontellt. Funktionen har verifierats genom CAD-modeller, beräkning

av säkerhetsfaktorer mot utmattning och FEM-modeller.

Den enda produktspecifikationen som inte uppnåddes var farten.

Nyckelord: Tramming, Propellering, Mekanisk bergavverkning

Master of Science Thesis MMK 2015:52 MKN 139


Sara Blomqvist

Approved

2015-06-09

Examiner

Ulf Sellgren

Supervisor

Ulf Sellgren

Commissioner

Svea Teknik AB

Contact person

Jacob Wollberg

Abstract This report is the result of a thesis project at KTH in cooperation with Svea Teknik AB and Atlas

Copco Mining and Rock Excavation.

Atlas Copco is currently developing a family of machines for mechanical rock excavation. All

machines in the family have two propulsion methods. The goal of this project has been to reduce

the number of propulsion methods down to one, in one of these machines, the Mobile miner.

The project has been divided into three main phases; background studies, concept development

and documentation.

The concept development phase has in turn been divided into four parts; generation, evaluation,

development and validation.

During the project no physical prototypes, drawings, component selections, software

programming, calculations of friction losses or detailed FEM analysis were made.

Nine concepts were developed. These were assessed with respect to a product specification using

a weighted PUGH-matrix. The concept that received the highest ranking in the PUGH-matrix

was six arms that are used to pull the machine forward. The concept was developed with respect

to applicability, durability and fatigue. This resulted in a concept with four arms similar to

scissor lift tables placed horizontally. The function has been verified using CAD-models, calculation of safety factors against fatigue and FEM-models.

The only specification that was not achieved was the speed.

Keywords: Tramming, Propelling, Mechanical rock excavation

FOREWORD

I would like to thank my supervisors Ulf Sellgren and Jacob Wollberg for giving me the

opportunity to undertake this project and for their support throughout these past few months. I

would also like to thank the staff at Svea Teknik AB and Mikael Ramström for always being

available and for answering all kinds of questions. Lastly I would like to give many thanks to

David Viberg for brilliant company, lots of laughs and for being a great person to bounce ideas

off of.

Sara Blomqvist

Stockholm, May 2015

Nomenclature

This chapter presents the notations and abbreviations used in the report.

Notations

Symbol Description

vcs Stroke speed, for comparison of generated concepts [m/s]

sch Horizontal stroke, for comparison of generated concepts [m]

scv Vertical stroke, for comparison of generated concepts [m]

tc1 − tc8 Time for one movement sequence for concept 1 to 9 [s]

vc1 − vc8 Speed of Concept 1 to 9 [km/h]

vpc3 Vertical play, Concept 3 [m]

l f p Total length of the Mobile miner [mm]

dh Diameter of cutter head, Mobile miner [mm]

cm Distance from COGm to the centre of cutter head, Mobile miner [mm]

COGm Centre of gravity for the Main body and Head, Mobile miner

COGb Centre of gravity for the Backup, Mobile miner

cb Distance from COGb to the centre of cutter head, Mobile miner [mm]

ct Distance from GOGt to the centre of cutter head Mobile miner [mm]

COGt Centre of gravity in the Mobile miner

mm Weight of the Main body, Mobile miner [ton]

mb Weight of the Backup, Mobile miner [ton]

Fa Total force from the weight of the Mobile miner on each arm [N]

m Total weight of the Mobile miner [ton]

Fg Gravitation force for the Mobile miner [N]

g Gravitation [m/s2]

Farm Force on each arm from the weight of the machine [N]

sa Stroke length of the arms [mm]

n Number of steps needed to walk the length of a plunge [ ]

Rb Reaction force on caterpillar tracks in the Backup [N]

Fa1−a4 Reaction forces on arm 1-4 [N]

la1 Distance from support 1 in arm 1 and 2 to GOGt [mm]

la2 Distance from support 1 in arm 3 and 4 to GOGt [mm]

Fa Acting reaction force on arms [N]

l3 Distance from joint 1 to upper attachment point of machine [mm]

l4 Distance from joint 3 to joint 1 [mm]

l5 Distance from upper attachment point of machine to the ground [mm]

l6 Distance from upper attachment point of machine to the lower [mm]

ll Length of links [mm]

R1 Force in upper attachment point of machine [N]

R2 Force in lower attachment point of machine [N]

J1x Force in joint 1, x-direction [N]

J1y Force in joint 1, y-direction [N]


C Force in cylinder in support 1 [N]



J5 Force in joint 5 [N]



α Angle between the upper link and the x-axis [rad]

l7 Distance between joint 1 and 5, x-direction [mm]

l8 Distance between joint 1 and 5, y-direction [mm]

µr Rolling resistance in the caterpillar tracks on the Backup [ ]

Fr Force from the rolling resistance in the caterpillar tracks on the Backup [N]

vcm Maximal speed of cylinder in support 1 [m/s]

s Safety factor against fatigue [ ]

λ Factor for technological volumetric dependence [ ]

δ Factor for geometrical volumetric dependence [ ]

κ Surface factor [ ]

σD Fatigue limit [ ]

φ Coefficient of restitution [ ]

q Fillet sensitivity factor [ ]

Kt Shape factor [ ]

σnom Nominal stress[ ]

Db Diameter of bearing [mm]

Fb Force on bearing [N]

Pb Maximum allowed pressure on bearing [MPa]

lb Length of bearing [mm]

I Moment of inertia, Mobile miner [kgm2]

T Torque needed to turn in a 5◦slope [Nm]

ns Number of screws, shaft for joint 1 [ ]

Fpl Maximum preload of screws, shaft for joint 1 [N]

µss Coefficient of friction steel against steel [ ]

J6ymax Maximum force in joint 6 [N]

Abbreviations & Expressions

KTH Royal Institute of Technology (Kungliga Tekniska Hogskolan in

swedish)

Mobile miner Mechanical rock excavation machine from Atlas Copco

Tramming Method of propelling, similar to walking

CAD Computer-Aided Design

FEM Finite Element Method

Heading Excavation of rock, support of the cavity and mucking

Head Anterior part of the mechanical rock excavation machines

Cutter head Circular block which carries the indenters

Cutter Indenter

Slewing mechanism Mechanism for slewing the cutter head

Apron Devise used for mucking

Muck Excavated earth or rock

Mucking Removal of excavated earth or rock

Main body The middle part of the mechanical rock excavation machines

Gripper Hydraulic cylinder used to hold the mechanical rock

excavation machines

Backup The posterior part of the mechanical rock excavation machines

TBS Tunnel Bore System

Plunging Pushing the cutter head into the rock

COG Centre of gravity

Table of contents

1 Introduction 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Purpose and delimitations . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Methodological choices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Frame of reference 32.1 Mechanical rock excavation . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 The Mobile miner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 The Reef miner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4 The Tunnel Bore System (TBS) . . . . . . . . . . . . . . . . . . . . . . . . . 72.5 Excavation and tramming . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Methodology and Results 93.1 Product specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 Generated concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2.1 Concept 1 - Earth worm movement, 3 body parts . . . . . . . . . 103.2.2 Concept 2 - Earth worm movement, 2 body parts . . . . . . . . . 113.2.3 Concept 3 - Feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2.4 Concept 4 - Feet with no slewing mechanism . . . . . . . . . . . . . 133.2.5 Concept 5 - Arms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.2.6 Concept 6 - Arms with no slewing mechanism . . . . . . . . . . . . 153.2.7 Concept 7 - Walking with 3 arms . . . . . . . . . . . . . . . . . . . 153.2.8 Concept 8 - Walking with 3 arms with no slewing mechanism . . . 163.2.9 Concept 9 - Omnidirectional wheels . . . . . . . . . . . . . . . . . 16

3.3 Concept evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.4 Concept development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.4.1 Centre of gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.4.2 Linear motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.4.3 Arm placement and load . . . . . . . . . . . . . . . . . . . . . . . 213.4.4 Dimensioning of the arms . . . . . . . . . . . . . . . . . . . . . . . 243.4.5 The final CAD-model . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.5 Concept verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.5.1 Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.5.2 Movement and size . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4 Discussion and conclusions 454.1 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.2 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5 Future work 49

6 References 51Appendix A – Ansys setupAppendix B – Haigh-diagrams

1 Introduction

This chapter describes the background to and the purpose of this report.

1.1 BackgroundThis report is a master thesis written as a result of a project conducted at Svea Teknik ABby a student of the master program Machine Design at the Royal Institute of Technology,KTH.

Svea Teknik AB is a technical consulting firm with a focus on product development.They are developing parts for mechanical rock excavation machines at the request ofAtlas Copco Mining and Rock Excavation [1]. An example of such a machine, the Mobileminer, is presented in Figure 1.

Figure 1: The Mobile miner [2]

Atlas Copco is currently developing a family of machines for mechanical rock exca-vation. These should be able to form the subsurface infrastructure and excavate ore ata performance level twice that of traditional methods, with the highest possible safetystandard. Four machines are currently in the product family. One is ready for testing,two are being built and the fourth, the Mobile miner, is in an early concept stage. Thisproject focuses on the fourth machine, the Mobile miner [1].

All machines in the product family are propelled by caterpillar tracks whilst out-side a tunnel and for turning within a tunnel. For straight movement within a tunnelthe machine is pulled forward using hydraulic cylinders. The caterpillar tracks areheavy and expensive. There was therefore a desire to reduce the number of propellingmethods down to one [3].

1

1.2 Purpose and delimitationsThe purpose of this project was to generate a functional concept of tramming, i.e. pro-pelling, for the Mobile miner that can be further developed and potentially applied.

Different concepts of tramming was investigated during the project. The conceptsonly applies to one machine, the Mobile miner. The concept deemed most suitable wasfurther investigated in terms of applicability, durability and fatigue. Time was thecontrolling factor in this project and was limited to 20 weeks, or 800 hours [4]. Theproject does not include the following:

• Physical prototypes

• Production preparation, tolerancing or detailed drawings

• Component selection

• Software programing for the hydraulic system

• Calculations of friction losses or their contribution to the loads

• Advanced FEM-analysis

1.3 Methodological choicesThe project has been divided into three main parts; background study, concept devel-opment and documentation. The concept development phase was in turn divided intofour sub-phases; generation, evaluation, development and verification.

All information necessary to solve the problem was gathered during the back-ground study as well as inspiration for the concepts.

The concept generation was performed by combining already existing solutions,found during the background study, with self-created ideas. The self-created ideaswere generated through brainstorming etc. The generated concepts were then furtherdeveloped till the extent that they could be evaluated in a PUGH-matrix. The PUGH-matrix method was chosen due to its simplicity and recognition. The highest scoringconcept was further developed and investigated in terms of applicability, durabilityand fatigue. This was done as computer-aided design models, CAD-models, in ProEngineer, calculations of static behaviour in MATLAB, modelling of static and dynamicbehaviour in Adams and with finite element method, FEM, calculations, in Ansys. Thesoftwares were selected since they were provided by Svea Teknik AB or by KTH. Somecalculations were performed using Mathcad and Excel.

All components were dimensioned for infinite life using Haigh-diagrams [5].The documentation of the project has been done continuously throughout the project

but with an emphasis on the end.

2

2 Frame of reference

This chapter describes the theory of mechanical rock excavation, three of Atlas Copco’s me-chanical rock excavation machines, the excavation methods of these machines and the currenttramming method.

2.1 Mechanical rock excavationMechanical rock excavation is an alternative method to the drill-and-blast methodwhere a machine drills holes into the rock and fills them with a kind of plastic explo-sive. The explosive is then ignited in intervals. The drill-and-blast method is a cyclicheading whereas mechanical excavation is considered to be continuous, even though ittoo involves several steps [6].

In mechanical rock excavation the rock is harvested by inducing stresses exceedingthe rocks strength which fractures the rock. There are two main methods for inducingthese stresses; penetrating the surface with a drag bit and moving it across the surface,see Figure 2, or by pressing an indenter into the rock and, in some cases, letting it rollover the rock surface, see Figure 3 [7].

Figure 2: Drag bits. To the left: sharp drag bit, to the right: blunt drag bit [7]

3

Figure 3: Indenter [7]

As long as the drag bit is sharp, the main part of the force acting on it has the samedirection as the motion, see Figure 2. As the drag bit becomes blunted from wear theimpact from the normal force increases rapidly [7].

When an indenter is pressed into the rock’s surface it fractures the rock beneath,see Figure 3. This leads to tensile cracks that expands and, ultimately, propagates thesurface [7].

Drag bits needs less force to break the rock compared to indenters. However, sincedrag bits are vulnerable to wear they are generally applied exclusively in weak, non-abrasive rock [7].

Using indenters, there are two methods for cutting the rock, conventional cuttingand undercutting, see Figure 4 [6].

Figure 4: Conventional cutting, to the left, and undercutting, to the right [7]

4

In the conventional method the indenter is simply rolled over the surface. In theundercut method the process starts from a pre drilled edge and cuts the rock fromthe side [6]. The advantage of the undercutting method is that it generates the tensiletension, required to fracture the rock, with less applied force than the conventionalmethod [7].However, there is no appropriate method to control the size of the har-vested rocks, which complicates the mucking, i.e. the removal of excavated material[3].

2.2 The Mobile minerThe Mobile miner is a mechanical excavation machine from Atlas Copco, still in a con-ceptual phase [3]. It is comprised of three main parts, see Figure 5.


The anterior part, called the Head, consists of the cutter head, which carries the in-denters, or cutters, and an apparatus for changing the direction of the cutter head, theslewing mechanism. It also has an apron used for gathering excavated rock, muck [8].

The middle part, called the Main body, has vertically mounted hydraulic cylinders,called grippers, for fixating the machine in the tunnel and horizontal cylinders that canpush the Head forward [8].

The posterior part of the machine, called the Backup, contains engines, hydraulicpumps etc. The Backup is propelled by caterpillar tracks [8].

The Mobile miner uses a conventional cutting application, with cutters that can ro-tate in relation to the cutter head which, in turn, rotates in relation to the machine [3].

The vertical position of the Head can be altered with hydraulic cylinders, see Figure5. The Head and the cylinders are attached to a circular plate. By sliding along this platethe cutter head is slewed [3].

Some requirements for the Mobile miner are listed in Table 2.

5

Table 2: Requirements for the Mobile miner [8]

Machine specification Value Unit

Geotechnical

Friction coeff. Grippers/tunnel walls 0.33

Cutter head

Diameter 4 m

Width 1.5 m

Main dimensions

Weight excl. Backup 270 ton

Weight incl. Backup 310 ton

Cutter head boom

Extension stroke 1.5 m

Undercarriage

Traction speed [3] 1 km/h

2.3 The Reef minerThe Reef miner, see Figure 6, is a mechanical rock excavation machine similar to theMobile miner, see Chapter 2.2. The main difference is that the cutter head is horizontaland that it is equipped with bolting devices and cabins. The bolting devices, see Figure6, inserts bolts into the tunnel roof to ensure that it does not collapse [3].

Figure 6: Reef Miner [10]

6

2.4 The Tunnel Bore System (TBS)The TBS is the largest machine in the family. The Head is very similar to the Mobileminer. The rest of the machine contains roof support equipment, safety chamber etc.,see Figure 7 [3].

Figure 7: The TBS [11]

2.5 Excavation and trammingThe excavation method is fairly similar for all of the machines. The procedure is asfollows: [3]

1. The machine is fixated by pressing the grippers on the Main body onto the floorand roof of the tunnel.

2. The cutter head is pressed into the rock using cylinders between the Main bodyand the Head. The head, for some of the machines, rests on cylinders connectedto skids. This is called plunging.

3. The cutter head is pulled back and repositioned to the side and/or height wise.

4. Step 2 and 3 is repeated until the desired tunnel profile is achieved. When thelast cut has been made the cutter head is left in the plunged position.

5. The grippers on the Head are pushed onto the floor and roof of the tunnel.

6. The grippers on the Main body is loosened.

7. The cylinders, previously used for plunging, now pulls the Main body and theBackup forward. As the machine moves, the muck is scoped up by the apronand transported under the machine using a conveyor. The muck is transportedbehind the machine where it is taken away.

8. The sequence is repeated.

7

The machines have two different tramming methods. The first is described in step5 - 7 above. Using this method, the machine cannot turn and it needs to be in a tunnelfor roof support. The second tramming method is crawling using caterpillar tracksattached beneath the Main body [3].

8

3 Methodology and Results

This chapter explains the methods used during this project and the results.

3.1 Product specificationThe generated concepts had certain criteria that should be met. These criteria are listedin Table 3. In the right hand column it is stated whether the criteria is a wish or ademand. This refers to if the specification value was demanded by Atlas Copco andSvea Teknik AB or if it was simply a wish.

Table 3: Product specification [8]

Specification Value Unit Wish or demand

Contact between machine and tunnel

Max. applied ground force contact pressure 3 MPa D

Tunnel shape

Minimum inner curve radius 18 m W

Minimum outer curve radius 24 m W

Height centre 4.5 m D

Width 3.5 m D

Width half way up 4.5 m D

Machine movement

Extension stroke 1.5 m W

Max incline 5 deg W

Max decline 5 deg W

Forces

Total force applied, all grippers pressurized 13.5 MN D

Corresponding force holding capacity 4 MN D

Speed

Traction speed [3] 1 km/h W

9

3.2 Generated conceptsSeveral concepts were derived for the specifications listed in Chapter 3.1. The preemi-nent concepts are presented in this chapter.

All hydraulic cylinders are assumed to have a maximum stroke speed, vcs, of 0.2m/s [9], to allow for comparison between the concepts. The stroke of the horizontalcylinders, sch, are all 1500 mm so that the machine can travel between faces in onemovement sequence. The stroke of the vertical cylinders, scv, are assumed to be 50mm.

3.2.1 Concept 1 - Earth worm movement, 3 body parts

The first concept, see Figure 8, is based on the same tramming principle as the existingsolution, see Chapter 2.5.

Figure 8: Concept 1

Only one of the three main parts of the machine would be moved at a time, thiswhilst kept above ground. With the part numbers referring to the arrows in Figure 8,the sequence for moving would be:

1. Pull up vertical cylinders, part 1, on the Head

2. Push the Head forward with the horizontal cylinders, part 2

3. Lower the vertical cylinders, part 1, on the Head to the ground

4. Pull up vertical cylinders, part 3, on the Main body

5. Push/pull the Main body forward with the horizontal cylinders, part 2 and 4

6. Lower the vertical cylinders, part 3, on the Main body to the ground

10

7. Pull up vertical cylinders, part 5, on the Backup

8. Pull the Backup forward with the horizontal cylinders, part 4

9. Lower the vertical cylinders, part 5, on the Backup to the ground

10. Repeat sequence

The time for one movement sequence, tc1, and the machine’s speed, vc1, is calcu-lated in equation 1 and 2.

tc1 =scv

vcs+

schvcs

+2 · scv

vcs+

schvcs

+2 · scv

vcs+

schvcs

+scv

vcs= 24 s (1)

vc1 =schtc1

= 0.225 km/h (2)

The horizontal cylinders, part 2 and 4 in Figure 8, are connected to controllablerotational joints so that the machine can turn whilst moving by pushing the Head in anappropriate angle.

For reversing the anterior and posterior part numbers are interchanged in the move-ment sequence described above.

If the strain on the horizontal cylinders is too great the machine parts can be sup-ported by keeping the vertical cylinders, part 1, 3 and 5, on the ground whilst mov-ing. The machine would then slide over the floor just like in the existing solution, seeChapter 2.5. Another solution could be to support the horizontal cylinders, part 2 and4, with some sort of a link system.

3.2.2 Concept 2 - Earth worm movement, 2 body parts

The second concept has the same general principle as the first but with only two, ofthe machine’s three, main parts involved in the movement. The moving part of themachine could no longer be held up over the ground but the speed of the trammingwould be enhanced.


tc2 =scv

vcs+

schvcs

+2 · scv

vcs+

schvcs

+scv

vcs= 16 s (3)

vc2 =schtc2

= 0.338 km/h (4)

11

3.2.3 Concept 3 - Feet

The third concept is inspired by a product from Columbia Industries, used for movingvarious heavy objects [12]. The concept is presented in Figure 9 below.

In this concept, and all following concepts, only the movement of the Main bodyand Head is considered. The caterpillar tracks on the Backup are preserved.

Figure 9: Concept 3

The Main body is connected to feet via vertical cylinders, part 1 in Figure 9. The feetconsist of a horizontal cylinder, part 2, and a liner guiding, part 3.

With the part numbers referring to the arrows in Figure 9, the sequence for movingwould be:

1. Lift the Main body using the vertical cylinders, part 1

2. Push the machine forward with the horizontal cylinders, part 2, letting themslide over the linear guiding

3. Put the Main body back on the ground

4. Pull the horizontal cylinders, part 2, back

5. Repeat sequence


tc3 =scv

vcs+

schvcs

+scv

vcs+

schvcs

= 15.5 s (5)

vc3 =schtc3

= 0.348 km/h (6)

12

The vertical cylinders, part 1, can be rotated so that the machine can turn. Fordoing so, these cylinders also need to be connected to a linear guiding so as to enablethe machine to move in an arc, see Figure 10.

Figure 10: Vertical play, Concept 3

Assuming the feet are mounted as in Figure 10 the required vertical play, vpc3, iscalculated as in Equation 7.

vpc3 = 2174 −√

21742 −( sch

2

)2= 133 mm (7)

3.2.4 Concept 4 - Feet with no slewing mechanism

The fourth concept has the same tramming solution as Concept 3 but the separate steer-ing for the Head, the slewing mechanism described in Chapter 2.2, has been eliminated.The idea is that the entire machine would be repositioned between plunges. The plung-ing movement could also be performed by the feet.

The time for one movement sequence, tc4, and the speed, vc4, would be the sameas for Concept 3.

13

3.2.5 Concept 5 - Arms

The fifth concept consists of six arms mounted on the side of the Main body, see Fig-ure 11. The arms are two hydraulic cylinders mounted horizontally with a cylindermounted vertically in one end and a rotary actuator in the other.

Figure 11: Concept 5

With the part numbers referring to the arrows in Figure 11 the sequence for movingwould be:

1. Pull up three of the vertical cylinders, parts number 1

2. Extend the corresponding horizontal cylinders, parts number 2

3. Lower the vertical cylinders, parts number 1, to the ground

4. Pull up the other three vertical cylinders, parts number 3

5. Pull the corresponding horizontal cylinders, parts number 4, forward.

6. Lower the vertical cylinders, parts number 3, to the ground

7. Drag/push the machine forward using the horizontal cylinders, parts number 2and 4

8. Repeat sequence

14


tc5 =( scv

vcs+

schvcs

+scv

vcs

)· 2 +

schvcs

= 23.5 s (8)

vc5 =schtc5

= 0.23 km/h (9)

This concept would most likely require the same gripper cylinders as the originaldesign, see Chapter 2.5, so as to not subject the horizontal cylinders to too high sideforces.

3.2.6 Concept 6 - Arms with no slewing mechanism

The fifth concept could be modified so as to eliminate the slewing mechanism. Just asfor Concept 4, the entire machine could be repositioned between plunges. The plungingmovement of the Head would most likely have to be done separately.


3.2.7 Concept 7 - Walking with 3 arms

The seventh concept, see Figure 12, has the same basic principle as the fifth but onlythree arms are in contact with the ground whilst the machine is moving.

Figure 12: Concept 7

15

With the part numbers referring to the arrows in Figure 12 the sequence for movingwould be:

1. With three of the horizontal cylinders, parts number 2, and the correspondingvertical cylinders, parts number 1, extended, pull up the other three verticalcylinders, parts number 3.

2. Pull the Main body forward using the horizontal cylinders, parts number 2. Atthe same time, extend the other three horizontal cylinders, parts number 4.

3. Lower the vertical cylinders, parts number 3, to the ground.

4. Repeat sequence but start with parts number 4 as extended.

The movement is hence more fluent and much faster than the other concepts as canbe seen in equation 10 and 11 where the time for one movement sequence, tc7, and thespeed, vc7, is calculated.

tc7 =scv

vcs+

schvcs

+scv

vcs= 8 s (10)

vc7 =schtc7

= 0.675 km/h (11)

3.2.8 Concept 8 - Walking with 3 arms with no slewing mechanism

Concept 7 could also be modified so as to eliminate the slewing mechanism. Just as forConcept 4 and 6, the entire machine could be repositioned between plunges.


3.2.9 Concept 9 - Omnidirectional wheels

In the ninth concept the machine would be fitted with omnidirectional wheels [13]such as the one presented in Figure 13.

Figure 13: Omnidirectional wheel [14]

16

If conventional wheels were applied the corresponding shafts would have to berotated in order to turn the machine. Since the load from the machine weight is sogreat this would result in the need for large components and most probably, largewear. Omnidirectional wheels enable movement in all directions, including turning,without having to change the direction of the wheels.

The movement would be fluent. The speed would be dependent on the capacity ofthe wheel and the engine.

With this concept the machine would need to be fitted with the same kind of grip-pers as the existing solution, see Chapter 2.5.

3.3 Concept evaluationThe concepts described in Chapter 3.2 have been evaluated with respect to the featuresdescribed in Table 4.

Table 4: Concept evaluation criteria’s

Feature Assessment criteria

Forward movement Ability, speed

Backwards movement Ability, speed

Turning Radius, speed

Turning whilst moving Radius, speed

Parallel movement Ability

Elimination of slewing mechanism Ability

Moving in incline/decline Ability, speed

Turning in incline/decline Ability

Lifting the machine Ability, Speed

Serviceability Accessibility, required time, time between

services etc.

Price Manufacturing method, mass and material price,

component price etc.

Reliability Use of standard components, simple design etc.

Weight Mass

Manoeuvrability Operability, ability to steer to a specific point

Redundancy Alternative propulsion possibilities

17

The features presented in Table 4, form the basis for a PUGH-matrix, see Table 5.Weights, from 1 to 5, have been added in agreement with Atlas Copco and Svea TeknikAB, the more important the feature the higher the weight. The weights are multipliedto each concept’s rating for the corresponding feature to create the score. The concept’srating are -1 for worse than the benchmark concept, 0 for as good as and 1 for better.All scores are then added into a final sum. The benchmark concept is the Mobile mineras it is originally designed, see Chapter 2.2 and 3.1.

Table 5: PUGH-matrix

Criteria Wei

ght

Ben

chm

ark

Con

cept

1

Con

cept

2

Con

cept

3

Con

cept

4

Con

cept

5

Con

cept

6

Con

cept

7

Con

cept

8

Con

cept

9

Forward movement 5 0 -1 -1 -1 -1 -1 -1 -1 -1 0

Backwards movement 5 0 -1 -1 -1 -1 -1 -1 -1 -1 0

Turning 4 0 -1 -1 1 1 1 1 1 1 1

Turning whilst moving 2 0 1 1 1 1 1 1 1 1 1

Parallel movement 1 0 0 0 1 1 1 1 1 1 1

Elimination of slewing mech-anism

3 0 0 0 0 1 0 1 0 1 0

Moving in incline/decline 3 0 0 -1 1 1 1 1 1 1 1

Turning in incline/decline 1 0 0 -1 0 0 1 1 1 1 1

Lifting the machine 2 0 0 0 0 0 1 1 1 1 0

Serviceability 4 0 1 -1 -1 -1 1 1 1 1 -1

Price 3 0 1 1 0 0 0 0 0 0 0

Reliability 5 0 1 1 1 1 1 1 1 1 -1

Weight 2 0 1 1 0 0 1 1 1 1 1

Manoeuvrability 4 0 -1 -1 1 1 1 1 1 1 1

Redundancy 2 0 -1 -1 1 1 1 1 1 1 0

Sum: 46 0 -4 -16 7 10 20 23 30 33 8

After discussions of the PUGH-matrix with Atlas Copco and Svea Teknik AB, Con-cept 8, with some modifications, was considered most suitable and was hence furtherdeveloped [9].

18

3.4 Concept developmentAfter rendering Concept 8 the most suitable, see Chapter 3.3, it was further developed.That process is described in this chapter.

After discussions with Atlas Copco it was concluded that the machine can be sup-ported by the caterpillar tracks on the Backup, see Figure 14 [9]. The machine thereforeonly needs two arms, not three as described in Chapter 3.2.7, to stand on at a time.Thus, the total of only four, not six, arms are needed.


3.4.1 Centre of gravity

To derive the forces acting on the movement mechanism the location of the centre ofgravity, COG, for the machine parts had to be established.

The Main body of the Mobile miner is assumed to be so similar to the Main body ofthe TBS that the geometry of the TBS can be used to identify the COG in the Mobileminer. The TBS is scaled down with the ratio between the cutter head’s diameters asthe dimensioning value. Furthermore, the Backup on the Mobile miner’s drawings issmaller than the Backup on the smaller machine, the Reef miner. The Reef miner hascabins which the Mobile miner does not, but the Mobile miner is assumed to requirelarger, or more, pumps etc. The Backup on the Mobile miner is hence assumed to be ofthe same size as the Reef miner’s. The total length of the machine, l f p, with the Headretracted, is then 17930 mm [15].

When the cutter head in the TBS is fully retracted the COG for the Main body andHead is located 4710 mm from the centre of the cutter head [16]. The TBS’ cutter headhas a diameter of 4500 mm [16] and the Mobile miner’s cutter head has a diameter, dh, of4000 mm [8].

19

The location, cm, of the COG for the Main body and Head, COGm, in the Mobile minerin relation to the centre of the cutter head is calculated in equation 12.

cm =4710 · 4000

4500= 4186.7 mm (12)

The COG in the Backup, COGb, is located in its volumetric centre, 14170 mm fromthe centre of the cutter head, cb [15].

The location, ct, of the COG for both the Backup and the Main body, COGt, in relationto the centre of the cutter head is calculated in equation 13.

ct =cm · mm + cb · mb

mm + mb= 5784 mm (13)

, where mm is the weight of the Main body and Head and mb is the weight of the Backup,see Chapter 2.2.

A schematic drawing of the Mobile miner with COGm, COGb and COGt marked ispresented in Figure 15.

Figure 15: Schematic drawing of Mobile miner

3.4.2 Linear motion

The linear motion in Concept 8 is performed by hydraulic cylinders, see Chapter 3.2.7.Hydraulic cylinders can withstand a relatively small force in the direction perpen-dicular to the motion it actuates [9]. Since the horizontal cylinders in Concept 8 areperpendicular to the gravitation force from the machine, they will need to be unnec-essarily large in relation to what would have been needed to only pull the machineforward. To avoid this, a different solution for the linear motion was generated, seeFigure 16.

20

Figure 16: Concept for linear motion

The concept works as a scissor lifting table placed horizontally. The machine willbe attached to support 1 and the foot will be placed on the ground. As the piston ispressed out of the cylinder support 1, i.e. the machine, will move to the right in Figure16 and vice versa when the piston is pressed in to the cylinder. Joint number 2 and 5are connected to linear bearings in support 1 and 2 respectively.

3.4.3 Arm placement and load

Assuming that a pair of arms should be able to carry the entire weight of the machineeach arm would be required to carry half of that. The force from the weight of themachine, Fg, and the total force on each arm, Farm, is calculated in equations 14 and 15.

Fg = m · g (14)

, where m is the total weight of the machine and g is the gravitation, 9.81 m/s2.

Farm =Fg

2= 1520550 N (15)

21

Assuming that the same kind of hydraulic cylinders are needed for the arms as forother purposes in the machine, the minimum piston diameter needed is calculated inequation 16 [8]. √

Farm

16 MPa · π· 2 ≈ 0.35 m = 350 mm (16)

If the machine is to be fitted with only four arms, and therefore also only stand ontwo at a time, they have to be attached in front of COGt to ensure that the machinedoes not tip over. Since the radius of the cutter head is 2000 mm[8], the distance fromthe COGt to the edge of the cutter head is 3784 mm, see Figure 15 in Chapter 3.4.1. If astroke of 1500 mm is desired this leaves 784 mm for material in and space between thearms. Since the minimum piston diameter is 350 mm, see equation 16, 784 mm couldnot possibly be enough space. Consequently the stroke length has to be reduced. Sincethis concept allows for an almost continuous propulsion this does not greatly affectthe speed. It will, however, significantly enhance the mobility of the machine since theshortening of the arms will make the machine fit easier in the tunnel.

Each plunge into the rock is 1500 mm deep. Even though this distance no longercan be reached with one step it would still be preferable to do so in a whole number ofsteps so as to simplify the control and utilize the entire stroke i.e. the stroke, sa, mustsatisfy equation 17.

sa =1500

n(17)

, where the number of steps, n, is a natural number.Assuming that the width of each support in the arms must be 500 mm, to fit the

cylinders and to manage the load, and that the feet always must be at least 300 mmfrom the edge of the cutter head, in order to fit the apron etc., the maximum strokelength is calculated as in equation 18.

3784 − 500 · 2 − 3002

= 743.35 mm (18)

Thus the maximum stroke length must satisfy equation 19.

743.35 >1500

n(19)

From which follows that the stroke length, sa, must be 500 mm.From Figures 17 and 18 below, the reaction forces from the caterpillar tracks on the

Backup, Rb, and the arms, Ra1 − Ra4, can be calculated, see equations 14 to 22.

22

Figure 17: Free body diagram of the entire machine, arm 1 and 2 is in contact with theground

Figure 18: Free body diagram of the entire machine, arm 3 and 4 is in contact with theground

Fa1 = Fa2 =Fg · (cb − ct)

2 · (cb − ct + la1)(20)

, where la1 is the distance from COGt to the centre of Support 2, see Figure 17.

Fa3 = Fa4 =Fg · (cb − ct)

2 · (cb − ct + la2)(21)

, where la2 is the distance from COGt to the centre of Support 2, see Figure 18.

Rb = Fg − 2 · Fa (22)

, where Fa is the reaction force currently acting on the arms.From equations 20 and 21, it is clear that the shorter the distances la1 and la2, the

higher the loads Fa1, Fa2, Fa3, Fa4. Thus the rear arms, arm 1 and 2, will be subjectedto the highest loads, yet always less than half that of the total weight of the machine.Since the machine is fitted with an apron just behind the Head, it would be preferableto keep the arms as far away from the Head as possible yet in front of COGt. The centreof Support 1 in the hind arms are therefore placed in line with COGt.

23

3.4.4 Dimensioning of the arms

To dimension the arms the forces acting on each part of them had to be derived. Inorder to do so, a free body diagram was drawn, see Figure 19.

Figure 19: Free body diagram of arm

With l7 and l8 as displayed in equations 23 and 24, the forces in Figure 19 can bedescribed as in equations 25 to 35, assuming all parts are weightless.

l7 = ll · cos(α) (23)

l8 = ll · sin(α) (24)

J5 = 0 (25)

J6x = J5 (26)

J6y = Fa1 (27)

J1y =J6y · l7 − J6x · l8 + J5 · l8

l7(28)

J1x =J1y · l7 − J5 · l8

l8(29)

24

J2x = J1x − J5 + J6x (30)

J4x = J2x − J6x (31)

R2 =J2x · (l8 + l3)− J1x · l3

l6(32)

R1 = R2 + J1x − J2x (33)

C = Fa1 − J1y (34)

J4y = J1y (35)

The caterpillar tracks on the Backup has separate drive but the arms should be ableto pull the Backup if this system fails or if the caterpillar tracks gets stuck etc. Afterdiscussions with engineers at Svea Teknik AB, the rolling resistance in the caterpillartracks, µr, was estimated to 0.35. The force from the rolling resistance, Fr, is calculatedin equation 36 [17].

Fr = Rb · µr (36)

This force will be horizontal and always in the opposite direction of the motion.The free body diagram is now altered as displayed in Figure 20.

Figure 20: Free body diagram of arm with rolling resistance from caterpillar tracks

25

The only alternations to the system of equations will be to equations 25 and 26, seeequations 37 and 38.

J5 = −Frl5l8

(37)

J6x = J5 + Fr (38)

The forces were calculated for all positions of the arm using some suitable assump-tions for the lengths of the components. The results are presented in Figures 21 and22.

Figure 21: Calculated forces, no rolling resistance

Figure 22: Calculated forces, rolling resistance

26

Using the same lengths, the arm was modelled in Adams, see Figures 23 and 24.

Figure 23: Adams setup, zoomed

As can be seen in Figure 23, revolute joints are placed between support 1 and theupper link, the sliding block in support 1 and the lower link, support 1 and the cylin-der in support 1, the upper link and the lower link, the sliding block in support 2 andthe upper link and between support 2 and the lower link. A spherical joint is placedbetween the piston in support 2 and the ground. Translational joints are placed be-tween the sliding block in support 1 and support 1, the piston and cylinder in support1, the sliding block in support 2 and support 2 and the piston and cylinder in support2. A fixed joint has been placed between support 2 and the cylinder in support 2.

Figure 24: Adams setup

27

As can be seen from Figure 24, the Backup and caterpillar tracks are represented bylinks. Revolute joints are placed between the Backup and the upper and lower edge ofsupport 1 and between the Backup and caterpillar track. A translational joint is placedbetween the caterpillar track and the ground. A fixed joint is placed between two partsof the Backup.

The motion was first modelled very slowly so as to simulate static conditions likethe ones calculated. The results are presented in Figures 25 and 26.

Figure 25: Simulated forces, no rolling resistance, static conditions

Figure 26: Simulated forces, rolling resistance, static conditions

28

The maximum and minimum for each force is presented in Table 6 and 7, to visu-alize the differences between the calculated and the simulated forces.

Table 6: Maximum and minimum forces, no rolling resistance

ForceMax calc Max sim Diff Min calc Min sim Diff

[MN] [MN] [MN] [MN]

J1x 1.0699 1.0698 0.009% 0.38045 0.38045 0.000%

J1y 1.4596 1.4596 0.000% 1.3806 1.3806 0.000%

J2x 1.0699 1.0698 0.009% 0.38045 0.38045 0.000%

J4x 1.0699 1.0698 0.009% 0.38045 0.38045 0.000%

J4y 1.4596 1.4596 0.000% 1.3806 1.3806 0.000%

J5 0 0 0.000% 0 0 0.000%

J6x 0 0 0.000% 0 0 0.000%

J6y 1.4596 1.4596 0.000% 1.3806 1.3806 0.000%

R1 0.87394 0.87389 0.006% 0.38045 0.38045 0.000%

R2 0.87394 0.87389 0.006% 0.38045 0.38045 0.000%

C 0 0 0.000% 0 0 0.000%

Table 7: Maximum and minimum forces, rolling resistance

ForceMax calc Max sim Diff Min calc Min sim Diff

[MN] [MN] [MN] [MN]

J1x 1.181 1.1809 0.008% 0.30564 0.30564 0.000%

J1y 1.7945 1.7945 0.000% 1.1248 1.1248 0.000%

J2x 1.2683 1.2682 0.008% 0.21837 0.21837 0.000%

J4x 1.3795 1.3793 0.015% 0.14356 0.14356 0.000%

J4y 1.7945 1.7945 0.000% 1.1248 1.1248 0.000%

J5 0.19843 0.19842 0.005% -0.19843 -0.19842 0.005%

J6x 0.11115 0.11115 0.000% -0.11115 -0.11114 0.009%

J6y 1.4596 1.4596 0.000% 1.3806 1.3806 0.000%

R1 0.94875 0.94869 0.006% 0.30564 0.30564 0.000%

R2 1.036 1.036 0.000% 0.21837 0.21837 0.000%

C 0.33484 0.33484 0.000% -0.33484 -0.33484 0.000%

29

As can be seen from Table 6 and 7 the results from the calculations and the modelcoincide well. Both the model and the calculations are therefore deemed reliable.

The arm was modelled with a cylinder speed more closely corresponding to whatwas assumed possible in reality. The cylinders maximum speed, vcm, is 0.2 m/s [9].The position of the piston, in relation to the cylinder, over time was modelled as asinus curve, see Figure 27.

Figure 27: Piston position and speed

As can be seen in Figure 27 the speed of the piston peaks at 0.2 m/s .The loads were also altered so as to simulate a five degree slope, the maximum

allowed according to the specifications see Chapter 3.1. The gravitation force from themachine was split into an x- and a y-component equal to 0.13252 MN and 1.5148 MNrespectively. This set-up constitutes the worst case scenario and the forces subjectedto the different joints are presented in Figure 28.

Figure 28: Dynamically simulated forces

30

The maximum and minimum for all forces are presented in Table 8.

Table 8: Maximum and minimum forces

ForceMax Min

[MN] [MN]

J1x 1.3485 0.41185

J1y 1.3174 0.63968

J2x 1.5705 0.45066

J4x 1.8538 0.48263

J4y 1.3174 0.63972

J5 0.50539 0.070629

J6x 0.28309 0.032598

J6y 1.4556 1.3748

R1 1.0613 0.41043

R2 1.2825 0.4517

C 0.81582 0.06168

To give a sense of the necessary dimensions of the components some preliminaryfatigue calculations were performed using the results displayed in Table 8. This wasdone with a safety factor, s, that was set to 1.5, see equation 39 [18].

s =λ · δ · κ · σD

φ(1 + q · σnom(Kt − 1))(39)

, where λ is the factor for technological volumetric dependence as a function of thedimensions, δ is the factor for geometrical volumetric dependence as a function of thediameter and the tensile strength of the material, κ is the surface factor as a functionof the tensile strength and the surface roughness, σD is the fatigue limit, φ is the coeffi-cient of restitution, q is the fillet sensitivity factor as a function of the fillet radius andthe tensile strength, Kt is the shape factor and σnom is the nominal stress.

Two kinds of steel have been chosen, SS2225-05 for the casted parts and SS2541-04for the shafts, see Table 9. The materials have been selected since they are used in othersimilar components of the machine.

31

Table 9: MaterialsMaterial σD bending, σD bending, Rm ReL

Rs = 0, [MPa] Rs = −1, [MPa] [MPa] [MPa]

SS2225-05 830 [18] ± 480 [18] 1000 [18] 700 [19]

SS2541-04 1040 [18] ± 600 [18] 1200 [18] 800 [20]

For the components in need of bearings, equation 40 was used to realize the neces-sary diameters. A journal bearing material called JM7-15 [21] was selected, see Table10, since it can withstand large loads and it has the same supplier as other bearingmaterials used in the machine.

Db =

FbPb

Lb(40)

, where Db is some bearing diameter available from the supplier [21], Fb is the totalload on the bearing, see Table 8, Pb is the maximum allowed pressure, see Table 10,and Lb is some bearing length available from the supplier [21].

Table 10: JM7-15 [21]

Feature Value Unit

Max speed 0.3 m/s

Max pressure 90 MPa

When dimensioning the linear bearings in the supports, equation 40 was also usedbut with the diameter as the width.

After discussions with engineers at Svea Teknik AB and some investigations of othercylinders the length of the cylinder in support 1 was assumed to be 270 mm longer thanthe stroke length needed.

A suitable slew drive that can achieve the rotation of the arms was found [22].Assuming that the distance from the front arms to the COGt, i.e. the longest distancefrom an arm’s attachment point to the COGt, is 2.2 m the moment of inertia for themachine, I, is approximately 6.7 · 105 kgm2. The torque needed to turn whilst in a5◦slope, , T, is calculated as in equation 41.

T = sin(5◦) · Fg = 1.1503 · 105 Nm (41)

These needs would be filled with the model WD-H 0645/3-00001 [22] and still givean acceptable acceleration, see equation 42.

TI= 3.2 ◦/s2 (42)

32

3.4.5 The final CAD-model

The process of deriving the final CAD-model was iterative. The result is presented inFigures 29 and 30. No bearings are included in the model.

Figure 29: Final CAD-model, size

Figure 30: Final CAD-model

33

Support 1 consists of two, almost identical, halves, see Figure 31. The only differ-ence is the holes in the side that should be cut out for tubes for the hydraulic cylinder.The two halves can be casted in the same mould and the holes can be drilled after as-sembly. The two halves are assembled with screws and nuts. The walls of the squareholes are lined with plates of bearing material JM7-15[21], not shown in the figure.The top of the support halves are fixed with two plates, shaped as partial circles, andfour screws. These plates will be casted. The top of the support is screwed on to ashaft connected to the slew drive. The slew drive is connected to the machine. On thebottom of the support the male part of a journal bearing, connecting the arm to themachine, is mounted. Both the slew drive shaft and the male of the journal bearingwill be lathed. The screws have not been dimensioned.

Figure 31: Support 1

34

The hydraulic cylinder is placed inside support 1, see Figure 32. It is connectedto the support by a shaft which is fastened with screws and lids on both sides. Thescrews in the figure is M6 but has not been dimensioned. The cavity in the supportis slightly larger than the cylinder so that it is free to move and will hence only besubjected to loads in the axial direction of the piston. The piston is attached to thesliding block either by welding or by screws. The sliding block has two extrusionsthat fit into a track in the support to hold the sliding block in place. The sliding blockwill be manufactured by milling and lathing.

Figure 32: Support 1, contents

35

Support 2, see Figure 33, is going to be casted. Just as for support 1 the squarehole is lined with plates of the bearing material JM7-15 [21]. The sliding block, likethe one in support 1 but without the extrusion, will be placed in the square hole. Ahydraulic cylinder is connected to the bottom of the support using screws. The pistonis connected to a plate through a spherical bearing, not included in the model.

Figure 33: Support 2

36

The upper and lower links are almost identical with the exception of screw holes inthe lower links, see Figure 34. All four links can hence be casted in the same mould andthe holes drilled after. The links are connected to the sliding blocks through bearings,not included in the figure. They are fixed using lids and screws. The upper and lowerlinks are connected via a shaft that is fastened to the lower link trough a lid and screws.The links are connected to the supports through shafts and kept in place using lids.The lids and shafts will be lathed.

Figure 34: Links

Since there is limited room for screw heads on the shafts connecting the links to themachine the necessary number of screws, ns, were calculated, see equation 43.

ns =

√J21x + J2

1y

Fpl · µss(43)

, where Fpl is the maximum preload for screws of grade 12.9 [23] and µss is the coeffi-cient of friction between steel and steel, equal to 0.78 [24]. The forces acting in joint 1,J1x and J1y are taken from Table 11 see Chapter 3.5.1.

The largest diameter of the screws that will fit, with regards to the socket wrenchdiameter for hexagonal screw heads [25], is M12.

The number of screws needed, ns, was hence calculated to 10.4. Since the maximumforces only occur very shortly, the number was rounded down to 10.

37

All parts are presented in Figure 35.

Figure 35: Final CAD-model, exploded

Regards have been taken to the diameter of socket wrenches [25] for all counterbores in the model.

38

3.5 Concept verificationTo verify the function of the concept it has been tested in regards to fatigue life, move-ment and size.

3.5.1 Fatigue

The movement of the final CAD-model was simulated in Adams, in the same setup asthe previous models, see Chapter 3.4.3. The results are presented in Figure 36.

Figure 36: Forces in final CAD-model

To realize the stresses in the different components simplified versions of the CAD-models were put in to Ansys and subjected to the loads presented in Table 11. Theseare not the largest forces since not all maximum forces occur at the same time, seeFigure 36.

39

Table 11: Loads, worst case scenarioForce Value [MN]

J1x 0.94898

J1y 0.75649

J2x 1.1121

J4x 1.228

J4y 0.85783

J5 0.27907

J6x 0.1159

J6y 0.82538

R1 0.69583

R2 0.9157

C 0.57371

As can be seen from Table 11, only the forces in the x- and y-plane are considered.This is to simplify the modelling and the calculations and because the loads in the z-plane are comparatively small. Only the worst case scenario was modelled and onlyone model for each kind of part was produced. For example only one link was mod-elled, the lower link, since it would be subjected to larger loads than the upper link.Images of the arrangements and the results are attached in Appendix A. The maximalequivalent stresses and the components materials are presented in Table 12.

Table 12: Maximal stresses and component material

Component Max stress [MPa] Material

Support 1 349 SS2225-05

Link 385 SS2225-05

Shaft for joint 1 312 SS2541-04

Shaft for joint 4 657 SS2541-04

Shaft to machine 320 SS2541-04

Sliding block 1 859 SS2541-04

Shaft for cylinder in support 1 206 SS2541-04

Support 2 78.8 SS2225-05

40

To verify that the components will not fail due to fatigue a Haigh-diagram wasmade for each part subjected to stresses above 250 MPa. In all reductions the shapefactor, Kt, was set to 1 since the highest stress in the part was known. The minimumstress was always set to 0 since the arm will be raised above the ground betweensteps and will then essentially be unloaded. In the CAD-models used in the Ansysmodels all rounds and small holes have been excluded since the number of nodes inthe student license is limited. There are hence some extreme stress concentrations. Inthe Haigh-diagrams, the stresses presented two steps away from such a concentration,in the yellow zone, were used, see Appendix A and Table 12. The Haigh-diagrams areattached in Appendix B. The safety factors against fatigue, s, corresponding to thesediagrams are presented in Table 13. The safety factors have been calculated accordingto equation 44 [5].

s =OBOA

(44)

, where OB is the vector from origo to the intersection between R and the reducedHaigh-diagram and OA is the vector from origo to the stress, see Appendix B.

Table 13: Safety factor

Component s

Support 1 1.68

Link 1.69

Shaft for joint 1 3.18

Shaft for joint 4 1.51

Shaft to machine 3.10

Sliding block 1 1.29

3.5.2 Movement and size

To ensure that the machine can fit in the tunnel and move as required, a CAD-model ofthe Main body and Head was created. Firstly the arms should fit on the machine. Sincethe size of the other components on the machine, such as the apron, grippers and cylin-ders for plunging, is not yet decided this cannot be completely determined. However,as can be seen in Figures 37 and 38 there is potential room for such components.

41

Figure 37: Machine seen from the side

Figure 38: Machine seen from above

Secondly, the machine should fit in the tunnel. As can be seen from Figure 38, itdoes since the tunnel is 4500 mm wide half way up from the floor to the roof [8].

The machine can be moved in a circle with its centre in almost any point depend-ing on how the movement is programmed. The minimal inner curve radius is henceentirely dependent on the length of the Main body and Head. In Figure 39 the arms areplaced in a 45◦angle to the Main body and the machine still fits in the tunnel.

42

Figure 39: Machine seen from above, 45◦

The machine could also be moved parallel however not with an entire stroke lengthof the arms, see Figure 40.

Figure 40: Machine seen from above, parallel

The final stroke length of the hydraulic cylinder in support 1 is 370 mm and thestroke length of the arm is 500 mm. Assuming that the cylinders speed is 0.2 m/s [9],the speed of the machine would be as calculated in equation 45 excluding the timeneeded to place the foot on the ground.

0.50.370.2

= 0.27 m/s (45)

However, the average speed when running simulations in Adams was 0.17 m/ssince the cylinder was accelerating and decelerating.

43

The maximum allowed ground pressure is 3 MPa, see Chapter 3.1. The diameterof the feet are 500 mm. The ground pressure is calculated in equation 46.

J6ymax

π0.52 ≈ 1 MPa (46)

, where J6ymax is the maximal value of J6y, see Table 11, which is equal to the normalforce acting on the foot see equation 27 in Chapter 3.4.4.

The mass of each arm, excluding the shaft to the slew drive and the slew drive, is5670 kg. This has been asessed using Pro Engineer.

44

4 Discussion and conclusions

In this chapter the methods and results of this project are discussed and the conclusion pre-sented.

4.1 DiscussionThe concept meets all product specifications, see Chapter 3.1, except the trammingspeed. It is however possible that the piston in the hydraulic cylinder in support 1could be moved faster than 0.2 m/s but that would increase the loads. Another wayof increasing the speed would be to elongate the arms thus making the stroke lengthof the hydraulic cylinder in support 1, shorter. This would however have a negativeeffect on the mobility of the machine and make the placement of the arms, and sur-rounding components, more difficult. The attachment points of the cylinder in sup-port 1 could also be moved to some entirely different location so that the cylinder, forexample, acts more closely to joint 4. This could make the stroke length of cylindershorter and hence increase the speed of the arms. This would however increase theload on the cylinder and, most likely, the length of the arm.

The mobility of the machine would be enhanced with arms instead of the originaltramming mechanism, see Chapters 2.5 and 3.5.2. The software needed to steer themachine would, however, most likely be complicated.

The assumed length of the cylinder in support 1 might be a bit too short, see Chap-ter 3.4.5. Since the stresses in support 1 are low in regards to fatigue life, see Table 13in Chapter 3.5.1, the mounting could be raised and placed on the inside of the shaftfor joint 1, see Figure 41.

Figure 41: Placement of cylinder, support 1

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Consequently even if the assumed length of the cylinder is too short, there is roomfor it to be longer.

The arms could have been 50 mm shorter if the flange for the screws in the connec-tion between the two halves of support 1, see Figure 31 in Chapter 3.4.5, were movedtangentially. This was not done in this project due to two reasons, the first that theforces in support 1 would have been harder to model and to estimate and the secondwas the project’s time limitation.

The linear bearings in the supports needs to be covered so as to avoid contamina-tion. This could, for example, be done with a rubber mat of some sort.

The arm’s weight is high, see Chapter 3.5.2, but there are many factors that couldreduce the mass. Since the stress in support 2 is so low, see Chapter 3.5.1, its mass,along with some other components, could most likely be reduced. The geometry of thearms could be optimized. No consideration of the reduction to the machine’s weight,due to for example the elimination of the slewing mechanism, has been taken. If it had,the gravity force might have been reduced and consequently the loads on the differentparts. This too could have made a reduction of the arm’s weight possible.

The shaft connecting support 1 to the slew drive is modelled as solid. Since it is sothick it most likely does not have to be solid but no calculations have been done onthis part.

The slew drive chosen for the arms is large. A smaller model could be used as-suming that the weight of the machine is reduced due to for example the eliminationof the slewing mechanism, described in Chapter 2.2. Another option is to have two,significantly smaller, slew drives connected to each arm, one in the upper connectionwith the machine, where the slew drive is placed in the CAD-model, and one in thelower connection, where a journal bearing is placed in the CAD-model, see Figure 31in Chapter 3.4.5.

Originally the cost of the generated concepts should have been estimated. This washowever quite difficult and was excluded from the project due to the time limitation.

An alternative solution to the original problem could be to use the arms as grippersas well as a mean of propulsion. The alternative design is presented in Figure 42.

Figure 42: Concept with arms as grippers

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As can be seen in Figure 42, another hydraulic cylinder is placed on top of support2 in the opposite direction of the cylinder in the original CAD-model. The plung-ing movement would be done with the arms and the loads on all components wouldtherefore be significantly higher. Since the arm’s stroke length is 500 mm, the depthof the plunge would be decreased. The number of components in the machine would,however, be reduced and perhaps also the weight. However, if the plunge depth wouldbe decreased to a third of the original, there would be no reason to keep the size of thecutter head as in the original machine. This would significantly reduce the weight ofthe machine and, in turn, the load on the arms.

4.2 ConclusionThe concept developed during this project could most likely be applied in reality. Thiswould however need extensive engineering work and testing.

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5 Future work

In this chapter the recommended next step for the developed concept is presented.

In order to apply the concept developed in this project there are many things thatneeds doing, some examples are listed below:

• The geometry of the parts in the model needs to be revised to make the armsmore size efficient.

• Much more extensive calculations than the ones performed on forces and stressesduring this project, needs to be done for both the arms and the machine

• A structure on the Main body so that it can be connected to the arms needs to bedesigned

• The space necessary for components, other than the arms, needs to be estimated

• After dimensioning the arms and the Main body, the software for steering needsto be programmed, etc.

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6 References

[1] Svea Teknik AB, Atlas Copco, Master thesis proposal, available at Svea Teknik AB, 2014

[2] Atlas Copco, Image of the Mobile miner, available at Atlas Copco, 2012

[3] Atlas Copco, Meeting regarding the master thesis, [interview], 150107.

[4] Department of Machine Design, ”Master Thesis Projects at the Department of Ma-chine Design”, Stockholm, 2012, pp 1

[5] Lundh, H., ”Grundlaggande hallfasthetslara”, KTH Hallfasthetslara, Stockholm,2000, pp 246-256

[6] Kolymbas D., ”Tunnelling and Tunnel Mechanics – A Rational Approach to Tun-nelling”, Springer-Verlag, Berlin, 2008, pp 75, 87, 123-125.

[7] Ramezanzadeh A. and Hood M., ”A state-of-the-art review of mechanical rock excava-tion technologies”, International Journal of Mining and Environmental Issues, Vol.1, No. 1, 2010, pp 29-39.

[8] Atlas Copco, ”Mobile Miner Pre-feasibility Study”, R&D Memorandum of Under-standing, [Internal document Atlas Copco], 2012

[9] Atlas Copco, Meeting regarding the generated concepts, [interview], 150306.

[10] Leonida, C., ”MM’s Top 10 technologies: 1”, http://www.miningmagazine.com/equipment/mine-development/mms-top-10-technologies-1/, 2015, [online],150525

[11] World Market Intelligence, ”Atlas Copco Mobile Miner”, http://www.tunnelsonline.info/features/inroads-below-4140534/image/inroads-below-4140534-4.html, [online], 150525

[12] Columbia Industries, ”Rig Walking Systems, http://www.columbiacorp.com/walkingsystems.php, [online], 150518.

[13] Diegel O., Badve A., Brigth G., Potgieter J. and Tlale S.,”Improved Mecanum Wheel Design for Omni-directional Robots”,Australasian Conference on Robotics and Automation, 2002, pp 117-121.

[14] Wikipedia, ”Mecanum-Rad”, http://de.wikipedia.org/wiki/Mecanum-Rad,2015, [Online], 150527

[15] Back, J. at Svea Teknik AB, Meeting regarding the geometry of the Mobile miner, [inter-view], 150310.

[16] Eriksson, P., Kristersson, M., ”TBS 3B new SH load spec 0621”, [Internal documentAtlas Copco], 2011

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[17] van Beek, A., ”Advanced engineering design, Lifetime performance and reliability”, TUDelft, 2009, pp 109

[18] Bjork, K. Formler och tabeller for mekanisk konstruktion, Sjatte upplagan, Karl BjorksForlag HB, 2011, pp 36-38, 42-43

[19] Khilbergs Stal AB, SS 2225/25CrMo4/25CrMoS4 - Svetsbart seghardningsstal, http://www.kihlsteel.se/ss2225.html, [Online], 150523

[20] Khilbergs Stal AB, SS 2541/34CrNiMo6/34CrNiMoS6, http://www.kihlsteel.se/ss2541.html, [Online], 150523

[21] Johnson metall AB, Materialguide, http://www.johnson-metall.com/wp-content/uploads/2014/04/JM-Guide-utg.13-2014-SV.pdf, [Online], 150523, pp24, 29

[22] Bengtssons-maskin, Slew drive Product catalogue, http://www.bengtssons-maskin.se/uploads/extrafiles file 1.pdf, [Online], 150523, pp 68

[23] Lindstrom, B., Rundqvist, B., Crafoord, R., Hageryd, L., ”Karlebo Handbok”, edi-tion 15, Liber AB, 2000, pp 249

[24] EngineersHandbook, ”Reference Tables – Coefficient of Friction”,http://www.engineershandbook.com/Tables/frictioncoefficients.htm, [On-line], 150527

[25] Institutionen for maskinkonstruktion, ”Maskinelement Handbok”, Institutionen formaskinkonstruktion KTH, 2008, pp 77

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Appendix A – Ansys setup

Support 1

Figure 43: Support 1, setup

Figure 44: Support 1, equivalent stress

Figure 45: Support 1, deformation

Support 2

Figure 46: Support 2, setup

Figure 47: Support 2, equivalent stress

Figure 48: Support 2, deformation

Link

Figure 49: Link, setup

Figure 50: Link, equivalent stress

Figure 51: Link, deformation

Sliding block

Figure 52: Sliding block, setup

Figure 53: Sliding block, equivalent stress

Figure 54: Sliding block, deformation

Shaft for cylinder in support 1

Figure 55: Shaft for cylinder in support 1, setup

Figure 56: Shaft for cylinder in support 1, equivalent stress

Figure 57: Shaft for cylinder in support 1, deformation

Shaft for joint 1 and 6

Figure 58: Shaft for joint 1 and 6, setup

Figure 59: Shaft for joint 1 and 6, equivalent stress

Figure 60: Shaft for joint 1 and 6, deformation

Shaft for joint 4

Figure 61: Shaft for joint 4, setup

Figure 62: Shaft for joint 4, equivalent stress

Figure 63: Shaft for joint 4, deformation

Male part of journal bearing connecting the arms to the ma-chine

Figure 64: Male part of journal bearing, setup

Figure 65: Male part of journal bearing, equivalent stress

Figure 66: Male part of journal bearing, deformation

Appendix B – Haigh-diagrams

Figure 67: Support 1, [Pa]

Figure 68: Link, [Pa]

Figure 69: Sliding block, [Pa]

Figure 70: Shaft for joint 1 and 6, [Pa]

Figure 71: Shaft for joint 4, [Pa]

Figure 72: Male part of journal bearing, [Pa]

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