Mesh Mounting Concept for a Mechanical Rock Excavation Machine

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Mesh Mounting Concept for a

Mechanical Rock Excavation Machine

Elin Skoog

Master of Science Thesis MMK 2017:91 MKN 206 KTH Industrial Engineering and Management

Machine Design SE-100 44 STOCKHOLM

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3 Examensarbete MMK 2017:91 MKN 206

Nätmonteringskoncept för en Mekanisk Bergavverkningsmaskin

Elin Skoog

Godkänt

2017-06-09

Examinator

Ulf Sellgren

Handledare

Ulf Sellgren

Uppdragsgivare

Svea Teknik AB

Kontaktperson

Jacob Wollberg

Sammanfattning

Denna rapport är resultatet av ett examensarbete som utförts på Institutionen för Maskinkonstruktion på KTH. Projektet gjordes med Svea Teknik AB i samarbete med Atlas Copco Rock Drills AB och deras avdelning för Gruv- och Bergbrytningsteknik i Örebro.

Atlas Copco håller för närvarande på att utveckla en ny TBM för mekanisk bergavverkning, som har fått namnet RVM (Remote Vein Miner). När bergavverkning sker så induceras spänningar och sprickor i berget som omger tunneln och det är därför nödvändigt att förstärka tunneln så att den inte rasar samman. I detta fall så sker denna förstärkning genom att borra hål i tunnelväggen och sätta in bergbultar, och samtidigt klä väggarna med ett skyddande nät. När operatörerna utför detta arbete så befinner de sig i en del av tunneln som inte är säkrad och de är således utsatta för säkerhetsrisker. Det är därför av intresse att göra denna nätmonteringsprocess automatiserad.

Syftet med detta projekt var att utveckla en konceptkonstruktion för näthanteringen- och monteringen för RVM-maskinen som innebär mindre manuellt arbete av operatörerna, alltså att ersätta den nuvarande semi-manuella näthanteringslösningen med en lösning som istället kan automatiseras och fjärrstyras.

Brainstormning användes för att ta fram 6 stycken olika koncept, 4 gällande näthanteringen och 2 för bulthanteringen. Dessa koncept utvärderades i två separata Pugh matriser. De två koncept som ansågs vara de mest lovande, bultkarusellen och en armkonstruktion för hantering av nätrullar, utvecklades vidare. CAD-modeller av de inkluderade komponenterna och systemen gjordes och användes för att verifiera armens räckvidd och att den uppfyllde att hålla sig inom maskinens platsbegränsningar. De hydrauliska cylindrarna dimensionerades utifrån krafter som erhölls från en ADAMS-simulering.

Den slutgiltiga konstruktionen uppfyllde alla specificerade krav, men ansågs vara väldigt komplex och det ansågs osäkert hur och om den skulle klara av den mycket tuffa miljön i tunnelgången.

Nyckelord: nätmontering, stängselnät, bergförstärkning, tunnelförstärkning

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5 Master of Science Thesis MMK 2017:91 MKN 206

Mesh Mounting Concept for a Mechanical Rock Excavation Machine

Elin Skoog

Approved

2017-06-09

Examiner

Ulf Sellgren

Supervisor

Ulf Sellgren

Commissioner

Svea Teknik AB

Contact person

Jacob Wollberg

Abstract

This report is the result of a Master’s Thesis done at the Machine Design Department at the Royal Institute of Technology. The project was carried out at Svea Teknik AB in cooperation with Atlas Copco Rock Drills AB and the Mining and Rock Excavation division in Örebro.

Atlas Copco is currently developing a new TBM for mechanical rock excavation, which have been named the RVM (Remote Vein Miner. When doing the excavation, stresses and cracks are induced in the tunnel walls and roof, why it is necessary to reinforce the tunnel so that is does not collapse. In this case this is done by drilling holes and inserting rock bolts into the tunnel walls, and at the same time clothe the walls with a chain link mesh. The operators that are doing this are working in an unsecured part of the tunnel and are hence exposed to a safety risk. It is therefore of interest to make this mesh mounting procedure automated.

The project’s purpose was to develop a design concept for the mesh handling and mounting for the RVM that require less manual hands-on work by the operators, i.e. replacing the existing semi-manual mesh handling to a solution that instead can be automatized and remote controlled.

Brainstorming was used to generate 6 different concepts, 4 for the mesh handling and 2 for the bolt handling, which were evaluated in two separate Pugh’s evaluation matrices. The two concepts that was deemed most promising, the bolt carrousel and an arm handling solution for mesh rolls, were further developed. CAD models of the included components and systems were made and used to verify the arm’s range and that it fulfilled all of the constraints related to the spatial limitations on the machine. The hydraulic cylinders were dimensioned with forces obtained from an ADAMS simulation.

The final conceptual design did fulfil the requirements, but was considered to be very complex and concerns were made regarding how it would handle the harsh environment in the tunnel.

Keywords: mesh mounting, chain link mesh, rock reinforcement, mine tunnel support

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FOREWORD

Firstly, I want to thank Svea Teknik for giving me the opportunity to take on this project with them and for their support and help during the semester. I would also like to thank Fredrik Saf and Jan Olsson at Atlas Copco in Örebro for their help in answering questions and providing me with all necessary information, and for taking time to show me around their production site. I really enjoyed that.

Lastly, I want to acknowledge my friends and fellow Master’s Thesis colleagues Oscar Hällfors and Jonas Torstensson, whom I have shared office with this last semester. Thanks for the brilliant company, many laughs and all the fun, passionate and interesting discussions we have had together.

Elin Skoog Stockholm, June 2017

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NOMENCLATURE

Abbreviations

KTH Kungliga Tekniska Högskolan/Royal Institute of Technology

TBM Tunnel Boring Machine

RVM Remote Vein Miner

CAD Computer Aided Design

CAE Computer Aided Engineering

WBS Work Breakdown Structure

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1 INTRODUCTION

This chapter presents background information to the subject and includes the project description with the purpose, as well as the limitations and methods used.

1.1 Background

Svea Teknik AB is a technical consultant company based in Stockholm. They have during several years been taking on development and design projects for Atlas Copco Rock Drills AB and the division for Underground Rock Excavation located in Örebro which is developing new Tunnel Boring Machines (TBMs) for mechanical underground rock excavation. Some of these projects have been offered as master’s thesis projects to machine design students at the Royal Institute of Technology. This report is the result of such a project.

Mechanical rock excavation is a continuous excavation method unlike the old traditional drill and blast method. Instead of drilling holes, insert explosives and blast, this excavation method does not use explosives but instead a machine with a circular cutterhead with cutting discs placed in front. The cutterhead rotates and is pressed against the tunnel face at enormous pressure, making the cutter discs roll on the rock surface and in that way inducing stresses in the surface which makes the rock break into small pieces.

This excavated material, called the muck, is then transported on a conveyor belt system through the body of the machine to the end where it can be collected for further transport.

[1]

An example of a TBM can be seen in figure 1, illustrating one of Atlas Copco’s more recent machines called the Reef Miner.

Figure 1. The Reef Miner [2]

Even though this mechanical excavation method is claimed to be kinder to the rock mass than the drill and blast-method, it still induces cracks in the rock and the tunnel is still in need of reinforcement to obtain a sufficient load-bearing capacity and prevent it from collapsing. This is especially important when the rock quality is bad, and it is of importance that as little as possible of the roof and the tunnel walls are unsupported during on-going excavation. The reinforcement can be done in different ways, one of which is to insert rock bolts in the tunnel walls and roof. Holes are drilled at certain places and then rock bolts are being inserted. The bolts distribute the stresses in the rock and make it self-supporting, comparable to an arch bridge.

When doing this, sometimes also the walls and the roof of the tunnel are being clad with a metal mesh (welded or chain link fence), which is fastened in between the tunnel face and

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the bolt bearing plate, as shown in figure 2. In addition to the reinforced support that the mesh provides, another strong motivation for doing this is to make the tunnel a safe working environment for the machine operators. The bolts secure larger rock blocks and the mesh protects the operators and the machine itself from smaller falling stones. [1]

Figure 2. Chain link mesh fastened on a tunnel wall [3]

On Atlas Copco’s newest TBM that is currently under development, the mounting of this mesh is today a semi-automatic process where the operators can control the procedures of drilling and bolting while standing under a protective roof or in a cabin. However, this current solution requires that the two operators need to do manual work about every half hour to refill bolts and locate the mesh segments. While doing this, the operators are working in an unsecured part of the tunnel and are exposed to a safety risk. It is therefore of great interest for the mining company to reduce the number of times that the operators need to do the manual tasks. [4]

This is also in agreement with the direction in which the development in the mining technology in general is heading. To improve the productivity, lower the labour costs and hence achieve higher economical profits for the mining companies together with the safety concerns for the mine workers are the driving factors for developing robotic/automatized systems. Automated systems would also mean improved precision and the outcome of the work would be more predictable, more exact and would lead to a safer mining process which gets increasingly important the deeper the mines go. The vision is to have fully automatized mine systems in the near future. [5]

So as a step in this development process towards full automatization, Atlas Copco is interested in reducing the time that the operators spend manually working on the machine from intervals of every half hour to once per working shift. [4]

1.2 Project description

This project’s purpose was to develop a design concept for the mesh handling and mounting for the RVM that require less manual hands-on work by the operator, i.e.

replacing the existing semi-manual mesh handling to a solution that instead can be automatized and remote controlled. The drilling and bolting process is also included in the mesh mounting procedure. The objective was to reduce the time that the machine operators need to be working in unsafe area and therefore reduce the risks that they are exposed to.

Only the mounting of the mesh on the tunnel walls was included in the task, since the mesh in the roof already will be in place because of the mining technique.

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1.3 Delimitations

Due to the project’s restricted time frame of 20 weeks (corresponding to about 800 work hours) and the initial knowledge of the author some limitations needed to be done.

 As stated previously in the project description, only the mounting of mesh on the tunnel walls had to be considered since the mesh in the roof already will be in place.

 The project is on a conceptual design stage, and no detailed design nor advanced FEA will be carried out.

 No physical prototype will be produced and no detailed drawings.

 The task does not include any design of control systems or software programming.

 No detailed selection of materials.

 To further limit the scope it was decided that changes to the existing drilling and bolting unit would be kept to a minimum, the same applies to other close by components and systems.

1.4 Method

The project consists of three main parts; the introduction, a background study with the concept development and the documentation. The project has been broken down in a Work Breakdown Structure (WBS), see figure 3. The WBS divides the project into the different activities (called work packages) that are needed to achieve the top deliverables which are the second level under the project name. [6]

Figure 3. Project’s Work Breakdown Structure

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The project planning and outline follows the Stage-Gate model, which is shown in figure 4, where the different stages of the project (in blue) are set and are followed by decision gates (in red). At these decision gates, the previous stage has to be approved before the project may proceed to the next stage. [7]

Figure 4. Stage-Gate Process

The requirements for the design were set in discussions with the customer. Brainstorming was used to generate different concepts with possible solutions, which were developed to a point where they could be fairly evaluated in a Pugh’s evaluation matrix. The concepts with the highest score and hence seemingly the most promising concepts were developed further to the final product. The development of the final concept was an iterative process where the design was being refined until all requirements were fulfilled.

The 3D computer-aided design models (CAD models) were made in the program ProEngineer Wildfire 4.0, since it is the software used by the customer. Matlab was used for calculations of static forces and ADAMS was used for verification and a dynamic simulation. The documentation has been done quite continuously during the project, but been more focused towards the last weeks.

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2 FRAME OF REFERENCE

This chapter presents the topics that were covered during the pre-study to provide some theoretical background information that are relevant in order to understand the project task. Also the result of the state of the art-search that was used in the concept generation and development phase is presented here.

2.1 Rock Reinforcement

The method of this continuous mechanical excavation with TBMs are generally said to be kinder to the rock mass than the method of drilling and blasting. However, mechanical excavation does have much higher advance rates that require much earlier load-bearing capacity than with the drill and blast method. [1] The stresses in the rock that existed prior to the excavation redistributes when boring a tunnel or mine. The vertical load before the excavation is carried out is equal to the weight of rock mass above, and thus is increasing the deeper into the ground the excavation proceeds. [8] Support systems are therefore needed in order to stabilize the tunnel and prevent it from shrinking or collapsing. This support of the tunnel can sometimes be carried out behind the machine, but in this case that would mean at least 20 meters behind the cutterhead and the tunnel face. That would leave much of the tunnel walls and roof to be unsupported during quite some time. That is the reason to instead place the drilling and bolting unit in the middle of the machine, as close to the cutterhead as possible, as shown in figure 6. [1], [8]

It exist two types of rock reinforcement possibilities, which are rock bolts and shotcrete.

[8] In this case with the new machine, it will use rock bolts of the type Split-Set which are a type of friction bolts that are described more in detail in section 2.3.2 below. [9] The main parameters in reinforcement design are size (the diameter) and length of the bolts and the spacing between them. The purpose of the rock bolts are to knit the rock mass together so that it becomes self-supporting. Movements and deformations that occur in the rock mass makes the bolt to elongate, which creates tension in the bolt. This tension transfers to the rock mass as compression stress and thus assists the rock mass to support itself by increasing the confinement. This means that rock bolts need to have good tensile capacity since they are normally under tension. [10]

In order to prevent so called fallout of smaller rock blocks and stones between the bolts, a chain link mesh may also be mounted as a skin support. [8]

2.2 The Mining Method

It exist many different methods for excavating ore in underground mines, which have been developed during the history of mining. This section briefly explains the specific method used at the location that the RVM is being made for, which is necessary in order to understand why the roof does not need to be clad with mesh as well as the walls, which is normally the case.

The method is called underhand cut and fill, and is illustrated in figure 5. The excavation is done in horizontal layers, starting from the top and going downwards. When one layer has been mined have about 20 cm of muck been left on the floor of the stope. In this muck are Dywidag reinforcement bolts with bearing plates installed vertically in a pre- determined pattern, and the bolts are kept in place with a thin steel wire attached between them and the walls. On top of the muck has a metal mesh been placed so that the bolts are

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inserted through it. When the layer has been finished are the mined-out stope being backfilled with a paste mixture of the muck from the excavation and cement. This fill is left to cure for about three days and when finished does it have excellent compressive strength properties. That makes it possible to excavate another layer underneath the previous one, and in that way keep excavating downwards. The mining are thus being carried out beneath the reinforced cemented backfill that will not fall in the case of a rock burst, which provides safety for the miners. The floor of that first layer becomes the roof of the next layer beneath. [12]

Figure 5. Cross section view of vein

The mining direction could also be carried out in the opposite direction, i.e. going upwards, and that is instead called overhand cut and fill. [12]

Many factors have to be taken into consideration when deciding what method should be the most suitable to use when excavating ore, which of the most important ones are the geometry of the ore body and the existing ground conditions and structure of the rock.

The cut and fill-method are especially suitable for when the ore body is steeply dipping vertically. [13]

Layer 1

Layer 2

Dywidag bolt with bearing plate Mesh

Muck Fill paste

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2.3 The RVM

This new machine from Atlas Copco is called the Remote Vein Miner (RVM), shown in figure 6 below, is still in the development phase. It is approximately 20 meters long and will weigh about 200 ton. [4]

2.3.1 General

In the front of the machine is the cutterhead with the cutting discs on the circumference that rotates and simultaneously is pressed with huge force against the tunnel face to execute the excavation. The head is moveable in both vertical direction, rotational to the sides and back and forth as indicated by the arrows in the figure 6. The crushed stone, called the muck, is then collected with help of the apron onto a conveyor belt system that goes in the bottom of the machine all the way through to the rear where it can be collected for further transport. The other two main parts of the machine are called the main body and the power module. The main body primarily contains the hydraulic systems that steers and pushes the cutterhead, and also holds the hydraulic system for the grippers and jacks that vertically extend from the top and bottom and fixates the machine against the tunnel floor and roof. This is so that the machine does not move backwards during excavation. The second part, the power module, contains components such as the hydraulic pumps, electric engines, drums for the electric cables and hydraulic hoses.

The drilling and bolting unit together with the mesh handling system will be placed in between these two main parts, which figure 6 does not show but the placement is indicated with the red arrow. The space is better illustrated further ahead in the report in figure 14 chapter 3.3.2 where the used CAD model is shown and explained. [4], [9]

Figure 6. The RVM with named parts

The excavation cycle for the RVM is similar to the cycle for most TBMs, and is carried out in the following steps.

The rotating cutterhead with the cutter discs are used to excavate the rock in front of the machine by being pressed very hard towards the face. To prevent the machine from moving backwards in the tunnel due to this huge pressing force are vertically mounted hydraulic cylinders, called stingers, and jacks being extended from the main body and

Placement of the mesh handling system

Apron Power module

Cutterhead

Main body

Stingers Conveyor belt

Rear tracks

Front tracks

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that clamps the machine between the tunnel roof and floor. When one full stroke and the desired tunnel profile has been finished by moving the cutter head, the machine retracts the stingers and jacks and moves forward by using the front and rear tracks. The working cycle is then repeated. As can be understood from this mode of procedure, this kind of gripper TBMs are only suitable for use in hard solid rock that can withstand the high forces from the stingers and jacks. [1]

This mechanical underground excavation machine is being designed to manage tunnel profiles ranging from 3.9-5.0 m in height and 3.2-4.5 m in width, see figure 7. The machine with its components itself should stay inside a rectangular cross-section shape of 2.0x3.6 m. [4]

Figure 7. Simplified cross-section view with max and min tunnel profile with dimensions and approximate bolt positions [mm]

2.3.2 Drilling and Bolting

The bolts have to be placed with a centre distance of maximum 1.2 meters both vertically and horizontally on the wall. Since the maximum stroke length for the machine is 0.6 meters, this means that the bolting in the horizontal direction only has to be done every second stroke on each side. The bolting can hence be done on alternating sides of the machine for each stroke, as shown in figure 8, which is how the existing drilling and bolting unit work. The one unit handles the bolting on both sides by being rotatable. [9]

The red arrow indicating the machine’s direction of travel.

Figure 8. Top view of the machine with bolt placement in the tunnel [mm]

5000 3900

2000

3200 4500 3600

1200

600 Max.

Min.

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21 This means that 3 bolts are required in the vertical direction when doing the minimum tunnel profile and 4 when doing the maximum profile, see figure 7. The bolts are installed more or less perpendicular to the to the tunnel wall, with the lower and upper bolt installed at an angle of 30°-45°. The mesh shall cover the tunnel walls starting from a maximum of 0.9 meters off the floor up to the corner of the profile, see figure 9. [9]

Figure 9. Placement of the mesh (blue) on the tunnel wall [mm]

The currently semi-automatic solution for the mesh handling and mounting procedure require the operators to do manual work once every stroke the machine does, to refill bolts in the magazine and locate the mesh. The time it takes for the machine to carry out one full cycle is 30 minutes, which hence also is the time for the manual task intervals. It is this interval that the customer wishes to be reduced to once per work shift of 8 hours (corresponding to 16 cycles). [4] This gives the total wall area to cover per shift 57.6 m²/78.7 m².

The bolts used are of friction type, and are called Split Set stabilizers and have a diameter of 39 mm and length 1800 mm. [9] Figure 10 shows the bolt, which basically is a slotted tube made of thin metal. As can be seen, one end of the tube is tapered for easier insertion into the drilled hole, and the other end have a welded ring flange to hold the bearing plate.

[14] The drilled hole is 37 mm, smaller than the bolt [9], meaning that when the bolt is forced into the hole the bolt diameter will be compressed slightly which is made possible because of the slotted design. This ensures a tight fit and forces exerted in the radial direction along the length of the bolt in contact with the rock provides friction that holds the rock together. [14]

The domed bearing plates, also shown in figure 10, have the dimensions 150x150x4 mm, and the hole is slightly larger than the diameter of the diameter of the bolt, which means that the plate can adapt to irregularities of the tunnel wall. The hanger on the plate can be used to support/attach loads for example cables, tubing and pipes. [14]

Figure 10. Split Set stabilizers SS-39 [14]

Max. 900

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2.3.3 The Mesh

The mesh used in this project is illustrated in figure 11 and is a regular metal chain link mesh where the holes have the dimensions 50x50 mm and the wire thickness is 3 mm. [9]

This type of mesh has very high load bearing capacity, however it is quite hard to handle during installation due to its flexibility. [11]

Figure 11. Metal chain link mesh [16]

The mounting of the mesh is carried out by an operator that manually places a section of mesh on a holder that keeps it in the correct place on the wall in order for the bolting unit to be able to place the bolts and secure it. The sections are placed vertically (seen from the side) from the upper corner and down. One section is 1500 mm wide because the chain link mesh must overlap the previous mesh sheet with at least 150 mm. It is in this seam the bolts are placed, as illustrated in figure 12, and in that way secures two mesh sides at the same time. The overlap is necessary due to safety concerns. [9]

The weight for the mesh has been estimated from data for a regular existing fence of the type “Gunnebostängsel”. A roll with the dimensions 1.5x4.1 meters weigh about 15 kg which corresponds to 2.4 kg/m² mesh. [9] To estimate the diameter for mesh rolls the circumference of a circle, equation 1, was used. Since the total required length of the mesh for different cases are known, could the required outer diameter be calculated by adding the circumference for several layers, see figure 13.

Ltot = ∑Di· π (1)

Di = d1 + d2 +…+ dn. The distance between the layer diameters was set to 16 mm and an inner rod to which the mesh is wrapped around to be 25 mm.

Figure 13. Illustration of cross-section of mesh roll [mm]

150

Figure 12. Placement of the rock bolt through two mesh sections, without the restraining plate [mm] mm

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23 This gave the dimensions that were used when doing the CAD models, and are presented in table 1.

Table 1. Calculated diameters for mesh roll

Required mesh length [min. profile/max. profile]

Calculated diameter for roll [min. profile/max. profile]

One single roll

(both sides) 48 m/65.6 m 0.70 m/0.83 m

Two half rolls

(one for each side) 24 m/32.8 m 0.50 m/0.60 m

16 rolls

(on roll per stroke) 3 m/4.1 m 0.20 m/0.20 m

Previous tests done by the customer have shown that one problem that occur when mounting the mesh is to stretch the mesh sections sufficiently in order to reduce the slack from the wall and also to position the mesh correctly. [9]

2.4 State of the art

A search for already existing automatic solutions for mesh mounting in the underground mining industry was carried out, both for inspirational purposes to the concept generation and also not to reinvent the wheel. The search resulted above all in numerous different patents in the area, which were briefly studied. Generally about the found patents can be said that it exists both separate more mobile stand-alone systems away from the mining machine itself which can be used together with different machines, as well as whole units attached to more specific machines. The patented solutions contain ways for not exposing the operators to direct risks while working with the mesh mounting, as they are working in the secured area of the tunnel. Most of the patents contains configurations of booms and/or arm systems that places reels of wire mesh in position for a bolting unit to bolt the mesh to the walls and/or roof. Two examples of more recently granted patents that are using different arm solutions are a patent from 2014 called “Method and apparatus for lining tunnel walls or tunnel ceilings with protective nets” [17] and another one called

“Mesh handling apparatus and related methods” from 2015. [18]

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3 CONCEPT DEVELOPMENT

This chapter describes the structured working process of the concept development phase, which started with defining the requirement specification and then progressed to the concept generation and evaluation.

3.1 Requirement specification

The previous explained and presented information from chapter 2.3 has been summarized in table 2 below and are the criteria that the design should meet to fulfil the purpose of the project. Where it is relevant it has been stated if the criteria was a demand or a wish from the customer. The available space is more clearly shown in figure 14.

Table 2. Requirement specification

Description Value Wish or

demand General

Operator’s manual interval 1 per shift á 8

hours D

Fit on the available space on the machine 2.0x2.6 m

(cross-section) D

Keep changes to other systems to a minimum W

Mesh mounted from max. 0.90 m up from

tunnel floor up to corner D

Tunnel profile (cross-section)

Minimum width 3.2 m D

Minimum height 3.9 m D

Maximum width 4.5 m D

Maximum height 5.0 m D

Machine data

Dimensions 2.0 m x 3.60 m

Distance between floor and tunnel ground

(space for muck handling system) 0.90 m

Available space on machine for the design, including space occupied by bolting unit (length x width)

- whereof space in front of bolting unit (frame not included)

- whereof space behind bolting unit (frame not included)

5.0 m x 2.0 m

1.7 m x 2.0 m 2.1 m x 2.0 m

D

Bolts and bearing plates

Number/stroke (min. profile) 3 D

Number/stroke (max. profile) 4 D

Total for one shift (min.) 48 D

Total for one shift (max.) 64 D

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3.2 Concept generation

When the project had been defined and the requirement specification had been formulated, the project continued with the concept generation phase. With the help of the state-of the-art-search, this phase started with brainstorming sessions and the making of a morphological matrix, see table 3 below.

3.2.1 Morphological Matrix

The task was first broken down to two separate main parts, which were the storage and handling of the bolts and the mesh respectively. Then different independent primary functions that were relevant in the design process were identified to be cutting mechanisms for the mesh, stretching mechanism for the mesh and mean to deliver the bolt to the drill and bolt unit. The matrix works by combining the solutions for each different sub-functions in different ways, several complete solutions can be obtained. [19]

Table 3. Morphological matrix

Solution Sub-

function

1 2 3 4 5 6

Storage of bolts

Standing Lying Groups Separate plate and

bolt

Handling of bolts

Hangar Carrousel Robot arm Perforated plate

Mesh storage

One big roll Vertical

One big roll Horizontal

Half rolls Vertical

Half rolls Horizontal

Single rolls Vertical

Single rolls Horizontal

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mounting

Arm Elevator

- moving whole roll

Elevator - Drag free

end

Cutting mechanism

Scissors/

Shears

Punch Knife Saw Drag/

pull

Laser

Stretch mesh section

Add arm with hook on existing bolting unit

External controlled

arm

Support internally inside mesh

roll

Frame Hooks on floor

Feed bolts to bolting

unit/

magazine

Replace whole magazine

Refill magazine

one at a time

Feed directly

from storage

3.3.2 Concept Feasibility

The CAD model of the RVM obtained from the customer was simplified in order to remove components and information not relevant to the task, as well for illustrational purposes to be able to clearly present the rendered concepts. The model was also important in order to get a good understanding of the geometrical constraints. The simplified CAD model is shown in figure 14.

Figure 14. 3D CAD-model of the RVM, skew side view and top view respectively

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The grey floor space does not represent an actual existing floor, but are showing the lower limit for the available space. The compartment underneath this grey “floor” is occupied by the conveyor belt system for the muck transport.

The board walks are retractable floor boards that will be used by the operators to reach the different compartments of the machine, for example when refilling mesh and bolts at the start of each shift, or when doing maintenance and reparation work.

The main restricting factor is the spatial limitations on the machine and the space given on the sides from the excavated tunnel. Bigger tunnel profile gives more room, however it does also require a larger amount of mesh and bolts that need to be carried on the machine during the working shift. The operator’s cabin was decided to be removed, since it will not be necessary when the processes are being remote controlled. That liberated space could instead provide room to storage of bolts, bearing plates and mesh rolls.

Using the morphological matrix, brainstorming sessions and sketching on paper resulted in numerous alternatives and possible combinations of placement and configurations of the handling of the mesh and bolts. However, many of them had to be dismissed early mostly due to one or a combination of the following factors:

 Spatial limitations

 The mesh sections should be mounted in front of the drilling and bolting unit, as shown by the red arrow in figure 15, which also limits the possibilities. The dashed arrow indicates the machine direction of travel.

Figure 15. Top view of machine, red arrow marking the mesh section to be bolted to the wall

If the mesh storage and handling system were to be placed behind the unit it would mean that there would be a long distance to get the mesh section in correct position for the bolting. Moving the drill and bolting unit would bring on significant changes to other systems, which was not desired from the project limitations.

 The alternative with storing the bolts in laying position were also disregarded, because of their length. The magazine of the bolt unit is loaded in upright position and there would be no space to turn the lying bolts up to get them in correct position for refilling.

Bolt/drill unit

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29 The following presented 6 different concepts; four for the mesh handling and two for the bolt handling, were the ones considered to have the most potential and hence worth to be developed further in order to be able to evaluate them fairly. In the figures 16, 18 and 20 have the bolting unit been hidden for clarity reasons.

3.2.3 Concept 1 – Vertically standing mesh rolls

This idea uses two vertically standing mesh rolls, one for the right and left tunnel wall respectively, that cover the whole length of the wall that should be clad with mesh, see figure 16. The right green roll shows the position for the minimum profile, and the left larger green roll shows the case for the maximum profile.

Figure 16. Illustrational model of concept 1 with vertical rolls, front view

The rolls each contain 10 m mesh which corresponds to the amount required for one working shift and by using equation 1 this results in a roll diameter of 40 cm. The steering mechanism consists of hydraulic cylinders placed on the frame supporting the bolting unit. There is one individual steering mechanism for each side, they are identical and only mirrored. To be adaptable to different tunnel profiles, the movement is steerable and extendable both vertically, in-out direction and rotationally around its own axis as indicated by the arrows in figure 16. To fit inside the dimensions of the machine and at the same time reach the walls when excavating the maximum tunnel profile, double- acting telescopic hydraulic cylinders would be used. The mesh rolls would each weigh maximum 95 kg, which is not an issue to handle and lift with a hydraulic system.

Figure 17. Illustrational model of concept 1 with vertical rolls, top view

Frame

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This solution mean that there would be no issue with holding and stretching out the previous mesh section to be able to drill and bolt in the mesh overlap. The mesh section in this case would be continuous during the shift and therefore there would not be necessary to cut in correct lengths. When the RVM is tramming (i.e. moving forward with the help of the tracks) the mesh unrolls with the movement. When the machine is tramming the rolls would be placed as in figure 17, retracted as indicated with the red arrows so they do not touch the tunnel wall and risk breaking.

To fit the vertically standing rolls within the required 2.6 m height of the machine, the rolls need to hang below the floor surface which is 0.9 m above the ground level. This would not disturb the conveyor belt system for the muck underneath because the rolls would hang outside of that system which is located in the middle. However when excavating the larger profile the roll needs to be 4.1 m, which would not meet the requirement to fit inside the height of 2.6 meters.

This concept as mentioned has got some advantages, but the main disadvantages besides that it does not fit within the required size, is mainly the inflexibility; it cannot handle changing profile heights during one shift without manual interaction from the operators that would need to change the roll to one with a different height. Also the handling of the large mesh rolls could be quite unmanageable, and also the bolts protruding from the roof might affect negatively and hinder the mesh from unrolling or similar.

3.2.4 Concept 2 – One horizontal laying roll

The second concept for the mesh handling has a link arm system placed on the frame of the drilling and bolting unit that holds only one single big mesh roll which is placed horizontally, see figure 18. The link arm system consists of two jointed arms, whereof the upper arm is extendable, and can be controlled by two hydraulic cylinders. The mesh roll then needs to be 1500 mm wide as previously explained in chapter 2.3.3 and it contains all the mesh required for both sides for one working shift (total of 65.6 m for the maximum profile) which according to table 1 corresponds to a roll diameter of 83 cm.

Figure 18. Illustrational model of concept 2 with one horizontal laying roll, front view

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31 A gripping claw mechanism on the end of the arm grips the mesh roll and lift it and keep it in place for the bolting unit. The platform on which the arm system is mounted, marked with the red arrow in figure 19, can rotate around its own axis to reach and locate the mesh on alternating sides. The blue arrow shows that the mesh roll needs to be able to move horizontally in order to reach to the bolting unit.

Figure 19. Illustrational model of concept 2 with one horizontal laying roll, top view

To be able to move the roll horizontally and position it outside of the bolting unit, a motorized linear motion slide guide is used which is marked in figure 19 with the red arrow.

To make this a fully functional concept, a cutting mechanism needs to be implemented, to get the correct lengths on the mesh sections. Also the issue with stretching of the mesh will need a solution. The need of this cutting and stretching solution adds complexity to the design.

This concept does fit inside the required 2.0x2.6 meters and is more flexible regarding adaption to different tunnel sizes, however it is disadvantageous because the mesh roll also in this case still is quite unmanageable due to its size. The roll will weigh about 240 kg and since the diameter is bigger than the width floor boards which are 60 cm would cause troubles when transporting the roll into position on the machine.

3.2.5 Concept 3 – Horizontal half roll

This concept is developed from the same idea as concept 2, using link arm system and hydraulic cylinders to position the mesh roll in place for the bolting unit. Instead of only one roll for all the required mesh it uses two half rolls mounted on two similar but separate arms. This would simplify the handling of the mesh rolls because of their more manageable size; the dimensions would be 1500 mm long, diameter 600 mm (from table 1) and weight about 120 kg each.

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This concept is shown below in figure 20, where the left roll shows the position for the minimum tunnel profile and the right roll shows the position for the maximum profile.

Figure 20. Illustrational model of concept 3 with two horizontal laying rolls, front view

The platform in this case will not need to be rotatable, however overall is this concept more complex since both arms for each side would need to have the cutting mechanism and solution for the stretching as in the previous concept.

This would also fit inside of the available space.

Figure 21. Illustrational model of concept 3 with two horizontal laying rolls, top view

3.2.6 Concept 4 – Small mesh rolls

This concept originated with the intention to avoid the additional complexity that the cutting and stretching adds to the two previous presented concepts. In this concept the mesh is pre-prepared in rolls with the correct dimensions before the start of the shift, and uses one roll for each stroke. The roll diameter would be 20 cm for each of the 16 rolls required during one whole shift. The storage placement of the rolls is shown in figure 22,

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33 in front of the bolting unit’s frame. The figure also shows the link arm position in the case of the maximum tunnel profile.

Figure 22. Illustrational model of concept 4 with small rolls, front view

Figure 23 shows the position for the minimum profile, with the mesh rolls in the storage area hidden.

Figure 23. Position of the arm for minimum profile, front view

As in the previous concepts also this consists of a link arm system placed on the frame and is steered with two hydraulic cylinders. The arm is as in concept 2 attached to a platform that is rotatable around its axis as the arrow indicates, meaning that it handles the positioning of the mesh for both sides.

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Also the motorized linear sliding guide as in previous concepts is needed to enable the movement horizontally, see figure 24.

Figure 24. Illustrational model of concept 4 with small rolls, top view

At the start of the shift are 15 rolls (5x3) placed in the storage and the 16^th and last roll is directly placed on the arm with the grippers.

Inside each of the rolls are a beam fastened to the edge of the mesh which when mounted on the tunnel wall will help stretch and hold out the mesh until the next section is placed.

3.2.7 Concept 5 - Bolt Conveyor Belt

Placing the mesh handling in front of the drilling and bolting unit gives the possibility to use all of the rear space to the storage and handling of bolts and bearing plates. This suits well with the placement of the existing bolt unit with the bolt magazine. Concept 5 and 6 are describing the two generated concepts for the bolt handling part.

This first idea is inspired by regular tool clips that are normally used for holding workshop tools, brooms or other object in place on a tool board or on a wall. Gripper clips like this exist in numerous different configurations and some examples are shown in figure 25.

Figure 25. Tool clips from Lesjöfors (a and b) [20], and gripper clip from Hardware World (right) [21]

a

b c

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35 If combining and integrating this gripping solution with a quite flexible rubber band, the resulting belt could be driven around a metal frame, as shown in figure 26. The 60 grippers (shown as indents in the black rubber band) would each hold one bolt with plate which would be kept in place with gripping force and friction.

Figure 26. Required dimensions for the frame to hold 60 bolts [mm]

To be able to hang the bolts as close together as possible to reduce the required space, the bolts will be hanging on slightly different heights as shown in figure 27.

Figure 27. Bolts hanging on altering heights

The belt can be controlled so that is rotates around the frame, carrying the bolts with it as it moves similar to the function of conveyor belt systems. One bolt at a time then rotates into a specific position where a device with grippers called the adapter is placed. The adapter is basically two claws that grips the bolt, turns and delivers it into the magazine of the drill and bolting unit. Since the bolts hang on varying heights the adapter would also need to be controllable vertically. The magazine has place for 4 bolts, sufficient for one stroke for the large tunnel profile. So at the start of each shift the operator places 4 bolts with bearing plates in the magazine directly, and 60 more in each of the holders in the band. After one stroke and the magazine is empty, the bolting unit is positioned in its original (vertical) start position, to be refilled. The operator steers the driving belt so that one bolt at a time reaches the position where it can be taken by the adaptor and placed in the magazine, and this is repeated four times until the magazine is full and ready for bolting the other side.

1500 1800

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Generally the tool clips are not dimensioned for such heavy objects as the bolt and plate which in this case would weigh about 4 kg, but by changing the dimensions of the hangar and/or material would be able to achieve sufficient load capacity without breaking.

This concept mean almost no modification to the drill and bolt unit, however it does require high precision both for the transport band and the adapter. The two individually controlled systems have to work together to obtain the complete working solution. To be able to hold the required amount of bolts it is not very space efficient, see figure 28, where the location of the frame on the machine is shown. Also, a quite thorough search for an already existing product with a combination of hook and rubber band like this has not given any results. This means that if this method would be used, it would require some time, engineering skills and money to develop this seemingly new product.

Figure 28. Top view of placement on the machine

3.2.8 Concept 6 - Bolt Carrousel

One negative aspect of the previous explained bolt handling concept was that it takes up almost all available area behind the drilling and bolting unit and it is also close to the sides of the machine which might hinder operators when refilling mesh and/or bolts, during reparations and maintenance work.

Another concept called the bolt carrousel is illustrated in figure 29 on the next page was developed specifically with the intension to provide a more space efficient solution. It consists of a middle large dividing plate that in turn has place for 10 smaller dividing plates that each are attached to arms (yellow in figure) which are mounted to a common centre. The arm and the large dividing plate are provided with bearings so that they can rotate around the centre. The bolts are placed in the cut-outs in the smaller dividing plates and supported from the below by a plate attached to each of the arms.

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Figure 29. The bolt carrousel and components

To be able to contain 60 bolts (4 bolts are directly placed in the bolt magazine by the operator at the start of the working shift as with the previous concept), the dimension of the large dividing plate is Ø1200 mm and the small Ø320 mm respectively. The restricting factor for the size are in this case the space that the bearing plates on the bolts take up, so also here the bolts could be placed at alternating heights in order to make the design somewhat more compact.

Figure 30 is showing the placement on the machine, as well as the placement of the adapter.

Figure 30. Placement on machine, top view

As mentioned, the yellow arm assembly has a mechanism that makes it rotatable around the centre and in that way place a bolt in position for an adapter to grip it and bring it into

Adapter

Bolt magazine

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the bolt magazine on the bolt unit. The same design for the adapter as in the previous concept can be used.

3.3 Concept evaluation

In the section the evaluation of the concepts are explained and discussed.

3.3.1 The Evaluation

The concepts in the previous chapter was being evaluated in a Pugh Evaluation Matrix, table 4. [22] Since the two parts could be considered independent of each other, one evaluation was made for the mesh concepts and another one for the bolt handling. The evaluation of the concepts criteria were decided together with the requirement specification as well as discussion with the customer.

For the mesh handling, concept number 1 was set as the datum reference to which the other three mesh concepts were compared. For each of the evaluation criteria stated in table 4 and 5 each concept were given the score +1 if considered to perform better than the reference, 0 if equal and -1 if the concept was considered worse.

Table 4. Pugh evaluation matrix for mesh handling concepts

Evaluation criteria Concept 1

Reference Concept 2 Concept 3 Concept 4 Work for both max. and min.

tunnel profile 0 +1 +1 +1

Adaption between profiles

- Flexibility 0 +1 +1 +1

Handling and change/refill of

mesh roll 0 0 +1 +1

Availability for operator 0 +1 +1 +1

Complexity 0 -1 -1 0

Robustness 0 0 -1 -1

Modifications of surrounding

systems and components 0 0 0 0

Number of parts/subsystems 0 -1 -1 -1

∑+ 0 3 4 4

∑- 0 2 3 2

Total score: 0 1 1 2

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39 For the bolt concepts the datum reference was decided to be concept 5.

Table 5. Pugh evaluation matrix for bolt handling concepts

Evaluation criteria Concept 5

Reference

Concept 6 Work for both max. and min. tunnel

profile 0 0

Adaption between profiles

– flexibility 0 0

Refill bolts 0 0

Availability for operator 0 +1

Required space/size 0 +1

Complexity 0 0

Robustness 0 -1

Modifications of surrounding systems

and components 0 0

Number of parts/subsystems 0 -1

∑+ 0 2

∑- 0 2

Total score: 0 0

3.3.2 Evaluation Discussion

Concerning the mesh handling it can be seen from the Pugh evaluation that concept number 4 scored the highest, even though the difference is small between the different concepts. However did concept 4 have more positives (equal as concept 3) but did have fewer negatives. It was thus decided that concept 4 did have the most potential and therefore was the concept to progress with and develop further.

The evaluation for the bolt handling turned out to be indecisive, as the two concepts both scored equal (0 points). The evaluation matrix showed that concept 6, the bolt carrousel, did score better than concept 5 in two aspects regarding the availability for operators and the space it takes up on the machine but worse in two other aspects regarding the robustness and number of parts. However, the two factors regarding the space were considered more important for the design and hence weigh more than the others. Also with concept 5 was taken into consideration the negatively contributing aspect of the extra added development required for the belt/clip combination. This lead to the decision to go further with concept 6, the bolt carrousel.

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4 DETAILED CONCEPT

This chapter presents the further development of the chosen concepts from the previous chapter, and the resulting final concept.

4.1 Overview of Final Concept

Figure 31 and 32 are showing the whole solution of the two combined concepts when positioned on the machine.

Figure 31. Overview of final concept and placement, side view

It can be seen that the components do fit inside the limited space, as was demanded from the requirement specification.

Figure 32. Overview of final concept and placement, zoomed in on mesh and bolt handling parts

In the following sections 4.2-4.4 are the included components described.

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4.2 The Mesh Mounting

As mentioned, 16 rolls are required during one working shift, 8 mounted on each side of the tunnel. At the start of each shift places the operator 15 rolls in the storage area shown in figure 32, and one roll is directly placed in the gripper arm that locates the mesh. Each of the rolls has been prepared on beforehand to have the right dimensions. The top edge of the mesh section is fastened to a metal rod that protrude about 10 cm on each side, shown in figure 33, and the mesh is rolled up around the rod.

Figure 33. The gripping arm

The protruding metal rods becomes handles that the claws grips to lift the roll to locate it on the tunnel wall, and the rod will also provide the stretching function by hindering the corner of the mesh to fall down as the red arrow in figure 34 is showing. Mesh section number 1 have been mounted first, and then when the machine has carried out two strokes are section 2 placed and bolted in place, overlapping the previous section. This continues as the excavation keeps progressing forward. The rod will hence be left on the tunnel wall as the machine excavates its way forward.

Figure 34. Mesh placement on the tunnel wall

The grippers are slightly bigger than the rod diameter so that the roll can rotate even though the grippers are closed. The mesh mounting on the wall starts with the lowest bolt, and when that one is fastened the mesh will unroll automatically as the arm moves upward to insert the next bolts. As mentioned in the frame of reference-chapter, the bolts are being placed in the overlap between the previous mesh section and the one currently mounted. When getting to the last and uppermost bolt, the rod is located just below or just above the previous rod, and the bolt is inserted so that the bearing plate cover both the rods to keep them in place. This is also shown in figure 34.

Rods Rod that make up the handles

1 2 3

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43 By using beam bending theory could the deflection at the free end of the rod be calculated. The rod was approximated to be a cantilevered beam with uniform load. The equation for the deflection y is

𝑦 = 𝑄𝑙³

8𝐸𝐼 (2)

where Q is the total load, l the length of the rod, E the modulus of elasticity for the material, and I is the moment of inertia. I for a circular cross section is defined as

𝐼 =𝜋𝑑⁴

64 (3)

where d is the rod diameter. [23] Setting the rod diameter to 25 mm, the length 1600 mm and the E-modulus to be 205 GPa [23], this resulted in a deflection of about 20 mm, which was considered acceptable.

4.3 CAD models

The development phase has been an iterative process, where the design has been changed and improved continuously when evaluations have shown necessary, until all requirements were fulfilled.

4.3.1 The Arm

Figure 35 is showing the 3D model for the arm that handles the mesh placement which was developed in ProE.

Figure 35. The arm configuration with named parts

The arm with the grippers must be able to reach all of the mesh rolls when placed in the storage, and also reach the top and bottom position on the wall for both the minimum and the maximum tunnel profile. At the same time it should not collide with the drilling and bolting unit or any of the other surrounding components. A geometrical investigation was done in order to verify that these demands were satisfied.

Cylinder 2 Cylinder 1

Platform Arm 2

Arm 1

Gripper Universal joint

Connector to linear sliding guide

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Figure 36. The two most difficult rolls to reach in the storage

Figure 22-23 in chapter 3.2.6 shows the positions for minimum and maximum tunnel profile. The lengths of respective parts were found by iterating the design until all the conditions were fulfilled, which was verified with the CAD model. The arm with the grippers must be able to reach every one of the mesh rolls which are placed in storage.

The lowest and uppermost roll closest to the arm turned out to be the positions that were the hardest to satisfy, but were achieved as shown in figure 36.

Arm 2 is a 2-part telescopic arm. To dimension the arms and the hydraulic cylinders (both to size and stroke lengths) a slightly simplified free body diagram was drawn, with corresponding derived equilibrium equations, see Appendix A. There are two equations for equilibrium in x and y-direction and one for torque equilibrium in the right direction around the point in the figure marked with a black dot for each body respectively. The platform gave no information about the system and was thus not included, which gave 12 unknowns and 12 equations and a fully determined system. The centre of mass for the parts was estimated to always be in the middle of each component.

The final lengths are listed in table 6.

Table 6. . Lengths of the arm parts

Dimension Length [mm]

Larm,1 985

Larm,2 min: 1740 max: 2730

Lcyl,1 min: 435 max: 695

Lcyl,2 min: 535 max: 850

X1 230

X2 15

X3 425

X4 678

X5 110

X6 105

X7 172

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45 The masses for the parts Arm1 and Arm2 are known from the CAD-model, material set to steel with density 𝜌 = 7800 kg m⁄ ³. The mass for the two cylinders have been estimated with data from existing hydraulic cylinders with approximated diameters and stroke lengths. The used masses are listed in table 7.

Table 7. Masses for the parts

Part Mass [kg]

Arm 1 30

Arm 2 55

Cylinder 1 7

Cylinder 2 6

Load 75

Platform 100

In the load mass are included one mesh roll with the inner rod, the sliding guide presented further on as well as the weight for the grippers and their actuators. With Newton’s second law,

𝐹 = 𝑚𝑎 (16)

and knowing the gravitational acceleration 𝑔 = 9.81 m s⁄ , can the forces be defined by ² the following equations

𝐹_{𝑎𝑟𝑚,1} = 𝑚_{𝑎𝑟𝑚1}∙ 𝑔 (17)

𝐹_{𝑎𝑟𝑚2}= 𝑚_{𝑎𝑟𝑚2}∙ 𝑔 (18)

𝐹_{𝑚𝑐,𝑐𝑦𝑙1}= 𝑚_{𝑐𝑦𝑙1}∙ 𝑔 (19)

𝐹_{𝑚𝑐,𝑐𝑦𝑙2}= 𝑚_{𝑐𝑦𝑙2}∙ 𝑔 (20)

𝐹_{𝑙𝑜𝑎𝑑} = 𝑚_{𝑙𝑜𝑎𝑑}∙ 𝑔 (21)

The magnitude of the force R1 was calculates with Pythagoras’ theorem

𝑅₁ = √𝑅_1𝑋² + 𝑅_1𝑌² (22)

and correspondingly for R2, R3, R4, R5 and R6. The equation system was solved in Matlab, see appendix A for the code.

When this analytical model had been set up was the arm modelled in ADAMS using the same lengths, see figure 35 and Appendix C.

Figure 37. ADAMS model to the left and CAD model to the right, in start position

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The analytical and the ADAMS models were compared in the low start position also shown in figure 35 above. The required angles and lengths to be able to execute the Matlab calculation were taken directly from the CAD model and presented in table 8. The length for Arm 2 was set to 2730 mm, meaning fully extended, since this gives the highest forces.

Table 8. Angles and cylinder lengths used in Matlab

α β γ θ Lcyl,1 Lcyl,2

56° 64° 66° 60° 679 mm 535 mm

The obtained forces from both models are presented and compared in table 9, and the difference of has been commented on later in the discussion chapter.

Table 9. Forces in the low position

Force Analytical model [kN]

ADAMS model [kN]

Difference [%]

R1X -3.61 3.57

R1Y -5.90 5.84

R1 6.92 6.84 1.2

R2X -3.61 -3.57

R2Y -7.60 -7.47

R2 8.41 8.28 1.5

R3X -3.61 -3.57

R3Y -7.54 -7.47

R3 8.36 8.28 0.9

R4X 3.32 3.26

R4Y 5.47 5.42

R4 6.40 6.32 1.3

R5X 3.32 -3.26

R5Y 6.81 -6.76

R5 7.60 7.50 1.3

R6X 3.32 3.26

R6Y 5.54 5.49

R6 6.46 6.38 1.3

The results coincide quite well, and were thus considered to be reliable.

The arm motion was simulated in order to obtain the maximum forces in the joints and the required forces from the cylinders, which were needed for the dimensioning. The simulation time was set to be 10 seconds, and the motion of the arm was defined so that only cylinder 1 was acting during the first 6.5 seconds, in order to raise Arm 2 to about horizontal position. Then cylinder 2 starts to move Arm 1 while the motion of cylinder 1/Arm 2 continues until both cylinders reaches their full stroke length and the arm stops in the high position shown. This simulation should represent a realistic motion and get the forces in the worst occurring case.

Mesh Mounting Concept for a Mechanical Rock Excavation Machine