Design and Optimization of Mechanical Components of a Treadmill for - - PowerPoint PPT Presentation

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Design and Optimization of Mechanical Components of a Treadmill for - - PowerPoint PPT Presentation

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Design and Optimization of Mechanical Components of a Treadmill for Use in Space Majid Abdulameer & Joost Vanreusel QinetiQ space Masters Thesis 1 Design and Optimization of Mechanical Components of a Treadmill for Use in Space

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Design and Optimization of Mechanical Components

  • f a Treadmill for Use in Space

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Majid Abdulameer & Joost Vanreusel Master’s Thesis

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Majid Abdulameer & Joost Vanreusel Master’s Thesis

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Design and Optimization of Mechanical Components

  • f a Treadmill for Use in Space
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Majid Abdulameer & Joost Vanreusel Master’s Thesis

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Design and Optimization of Mechanical Components

  • f a Treadmill for Use in Space
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PURPOSE:

  • Exercising in space is necessary to keep astronauts

healthy and functional. On Earth, gravity works against our muscles and bones every time we move so our bodies maintain enough muscle and bone mass to be able to support our weight. In the weightless environment of space, where the relative force of gravity is minute, astronauts lose muscle and bone mass since it is not required to support their weight. The longer an astronaut is in microgravity, the greater the loss. Exercising in space is the most effective way to date to compensate for the relative lack of gravity.

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Although astronauts gradually recover their muscle tissue and bone when they return to

  • Earth. It is important that they are strong

enough to perform emergency procedures during landing. Completing a regular exercise routine in space prepares the astronaut for these situations and also facilitates a shorter period of rehabilitation to recover their muscle and bone. One of the important exercise equipment is treadmill .

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1. Overall principle

  • f SLS system

subject loading system

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1. Overall principle

  • f SLS system

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The system constantly provideds a pull down force to the subject running on the treadmill in such way that the person is pulled towards the treadmill with a force of 1g the earth’s gravity.

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CONSTRAINTS

1. PARKING MECHANISM

  • Mass
  • Dimensions
  • Reliability
  • Boundary conditions
  • Lifetime
  • Material requirements

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CONTENT

1. PARKING MECHANISM 2. EXIT PULLEY

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  • 1. PARKING MECHANISM

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PURPOSE

1. PARKING MECHANISM

  • Avoid slack of rope inside the mechanism in case
  • f pressure loss of the activators.
  • Ensure that the rope remains on the pulleys

internally to SLS at all times.

  • Parking mechanism starts working when there is

less than 0.3 bar into the low pressure system.

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1. PARKING MECHANISM

PURPOSE

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PROBLEMS & ALTERNATIVES

1. PARKING MECHANISM

  • Spring
  • Rotation of cylinder
  • Cam system
  • Translating movement

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PROBLEM 1

1. PARKING MECHANISM

Spring seizes compressed/uncompressed

From Block level FMECA At item Block 1.11.3 Cause: Environmental conditions

Effect: parking mechanism will not operate and rope may become dislocated from pulleys. Can we remove the spring from the cylinder?

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ALTERNATIVE 1

1. PARKING MECHANISM

  • 3/2-valve to make the parking cylinder bistable

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ALTERNATIVE 1

1. PARKING MECHANISM

  • Parked piston

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ALTERNATIVE 1

1. PARKING MECHANISM

  • Free piston

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PROBLEM 2

1. PARKING MECHANISM

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What do we mean by environmental conditions? (FMECA, QinetiQ, 2009, pp. 28-29)

  • It can be due to 2 DOF
  • Less movement means less vibration and longer

lifetime

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PROBLEM 2

1. PARKING MECHANISM

  • “The spring of the cylinder retracts the piston that

begins with moving upward.” (Mechanical & Pneumatical Design Report, QinetiQ, 2009)

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1. PARKING MECHANISM

PROBLEM 2

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The hook has 2 degrees of freedom: a transitional movement

  • f 40 mm

and Upward/downward movement (+- 10 mm)

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Proposal: we can use a kind of Cam shape. In this case the rod of the piston moves just in one direction (1 DOF).

1. PARKING MECHANISM

ALTERNATIVE 2

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ALTERNATIVE 3

1. PARKING MECHANISM

The more moving parts, the more possible problems (hinge joint, needle bearings) => Can we make a system which only translates?

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ALTERNATIVE 3

1. PARKING MECHANISM

Problem: Need for a piston with a stroke of more than 150 mm (= stroke main cylinder) Norgren?

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  • 2. EXIT PULLEY

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PURPOSE

1. PARKING MECHANISM 2. EXIT PULLEY

  • Ensure the rope follows the movement of the

astronaut on the treadmill.

  • Transfer the vertical – horizontal displacement into

a vertical displacement.

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CONTENT

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dynamics calculation 2.5 Excentricity calculations 2.6 Alternative

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2.1 Problem

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem

BEARINGS: lifetime GREASE: Lubrication – Type EXIT PULLEY: excentricity

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2.2 Bearings.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings

Two types of bearings:

  • FAG-71806-B-TVH

– Single row angular contact ball bearing

  • FAG-30-6-B-2Z-TVH.

– Double row angular contact ball bearing – Cages: glass fibre reinforced polyamide

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2.2 Bearings.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings

Lifetime calculation:

  • Static load rating

– Properties which bearing must have to withstand loads during standstill.

  • Dynamic load rating

– Describes during a certain number of revolutions certain mechanical loads under certain conditions.

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2.2 Bearings.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings

Lifetime calculation:

  • Lifetime comparison according to NEN-ISO-281

Problem:

  • Radial and axial force on the bearing unknown

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2.3 Grease.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease

  • Lithium based grease

– Separated in vacuum

  • Silicon based grease

– Higher evaporation value

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2.3 Grease.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease

Krytox 240AC

  • A high vacuum grease (up to 10-16 bar).
  • Functionates in both extremely high and low

temperatures (-15°C - 300°C) and in hostile environments.

  • Oxidation resistant.
  • Chemically inert
  • Offers needed lubrication properties

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2.3 Grease.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease

LGET2

  • A premium quality
  • A high vacuum grease (up to 10-16 bar).
  • Functionates in both extremely high and low

temperatures (-40°C - 260°C)

  • Excellent oxidation resistant.
  • synthetic ( fluorinated polyether ).
  • Very expensive.

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2.4 Dynamic calculation.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dynamic calculation

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  • Purpose

The pulley has to follow the oscillating movement of the rope without slipping. If the inertia is too high there will be too much slip (heat generation) and extra wear of the rope so the life time is limited.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dynamic calculation

2.4 Dynamic calculation.

  • Forces on exit pulley

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SLIDE 36

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dynamic calculation

2.4 Dynamic calculation.

  • Data

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  • Minimum tension in the rope 89 N.
  • The driving frequency 3Hz.
  • Hip movement of the running object.
  • Forward, backward ±30°
  • Upward, downward inclined maximum 10°.
  • Friction coefficient between rope and pulley =0,35
  • Friction coefficient for the bearings = 0.002
  • Preload 3N for pulley, 10N for swivel
  • Density of aluminum 2700 kg/m3
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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dynamic calculation

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  • Data
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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Approximation of sine wave

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10 20 30 40 50 60 70 80 90 100 0,1 0,2 0,3 0,4 0,5 0,6

time (s) X 10-3 Tension in the rope (N)

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Equation of motion

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Exit pulley

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  • 0,04
  • 0,03
  • 0,02
  • 0,01

0,01 0,02 0,03 0,04 0,1 0,2 0,3 0,4 0,5

time (s) vertical displacement (m)

By taking the derivative The second derivative The amplitude of the angular acceleration can be calculated.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Mass moment of inertia

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Friction force

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As a matter of fact the type of material of the rope and the type of coating has a significant effect on the value of the coefficient of friction. In case of the

  • treadmill. the pulley is coated with a certain

material ( surlon) to decrease the coefficient of friction in order to increase the life time of the rope, and to do our calculation we assumed that the value of friction coefficient is ranged between 0,35 as a worst case and 0,25 as a perfect case. We consider the worst case in our calculation.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Friction force

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  • The moment due to friction force can be

calculated.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Preload force

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The preload is equal the mass of the pulley multiplied by the acceleration during lunch.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Total moment exerted on pulley.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Mass of swivel part.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • The amplitude of angular acc.

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By taking the derivative The second derivative The amplitude of the angular acceleration can be calculated.

  • 0,025
  • 0,02
  • 0,015
  • 0,01
  • 0,005

0,005 0,01 0,015 0,02 0,025 0,1 0,2 0,3 0,4 0,5

time (s) fore-aft displacement (m)

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Mass moment of inertia.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • The moment due to inertia force.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

  • Preload force

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The preload is equal the mass of the pulley multiplied by the acceleration during lunch.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Dyanmic calculation

2.4 Dynamic calculation.

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  • Total moment exerted on swivel.
  • The dynamic eccentricity .
  • With worst case, the angle is 30° degree. With

this angle the eccentricity is determined as follows

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2.5 Excentricity calculations.

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Coefficient of friction 2.5 Excentricity

Problem: The astronaut moves backward, forward, left and right. This way the rope doesn’t always stay on the pulleys. So the pulleys have to be placed excentric from the center line of the rope coming up.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Coefficient of friction 2.5 Excentricity

2.5 Excentricity calculations.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Coefficient of friction 2.5 Excentricity

  • Forward, backward ±30°
  • Upward, downward maximum

10°.

  • Friction coefficient between

rope and pulley = 1.4

  • Friction coefficient for the

bearings = 0.002

  • Preload = 3N
  • Tension in the rope = 500N

2.5 Excentricity calculations.

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1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Coefficient of friction 2.5 Excentricity

Ѳ Excentricity (mm) 30 2.28 20 3.33 10 6.56

2.5 Excentricity calculations.

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2.6 Alternative

1. PARKING MECHANISM 2. EXIT PULLEY

2.1 Problem 2.2 Bearings 2.3 Grease 2.4 Coefficient of friction 2.5 Excentricity 2.6 Alternative

Advantages:

  • 360° rotation
  • Force on the rope absorbed by the bearing
  • Easy replacement

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