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12 : Mechanical and Machine Design<


Learning Outcomes<

What did I learn this week ?

  • Machine Design :
    • Machine architecture
    • Different parts and steps of machine designing
  • Building :
    • Using Timing Belts
    • Building Core XY structure
  • Video Editting
    • Using KdenLive for video cutting


Assignments<

This twelfth week's asignments are :

  • Group :
    • Design a machine that includes mechanism + actuation + automation + application
    • Build the mechanical parts and operate it manually
    • Document the group project
  • Individual :
    • Document your individual contribution

1. Theory<

1.1. Machine Definition<

Wikipedia defines a machine as :

a thermodynamic system that uses power to apply forces and control movement to perform an action.

Here, we will restrict this definition by considering a machine as :

a device that moves an end-tool using mechanisms, drivers and control systems.

1.2. Machine Architecture<

A machine architecture can be divided in two stacks :

Mechanical Stack
Actuation : Injects energy into the system
Transmission : Converts rotation into linear motion
Guides : Dictates the exact path of the force
Structure : Absorbs the reaction and maintains geometry

Control Stack :

  • Planning and UI : Generates toolpaths and UI for interaction
  • Coordination and Communication : Synchronizes mutliple axes and communicate with UI
  • Motion Control : Executes precise movement and interpolation
  • Power electronics : High-power interface that drives actuators
  • Actuators

1.3. Machine Design<

Tool Head :<

  • What does it do ? (Cut, Mill, Extrude, Burn, Dispense Candies, ...)

  • What constraint does the tool head require ? (Slow motion, Lot of force, Precision, Superfast, ...)

Mechanical System :<

  • What motion mechanism ? (Lead and screw, Rack and pinion, Timing belt)

  • What motion restriction ? (Shaft, Rails, ...)

  • Parallel Kinematics ? (One motion requires multiple motors)

  • Makes everything hold (Frame)

  • Machine enveloppe : either defined by the required workplace or by an exterior constraint

Sensors and actuators :<

  • How do you actuate your machine ? (Sensors, Controllers, ...)

  • How do you control the machine ? (Interface, Software, Application, ...)

1.3. Mechanical Parts<

Fasteners Picture
Buttonhead screws
Flathead screws
Shoulders screws
Heat-set inserts
Dowel pins
Small L-brackets
Push-in plastic rivets
Mechanisms Picture
Revolute Joints
Prismatic Joints
Ball-and-Socket Joints
Universal Joints
Cams
Linkages
Gears
Bearings
Compliant Mechanisms

1.5. Control<

Open-loop and Close-loop<

Open-loop system : Predictable machine system, no need to control the output

Close-loop system : Unpredictable system, requires to reconsider the actuation depending on the output

Control methods<

Bang-bang control (two thresholds)

PID control

A lot of different control methods exist

Control architecture<

Centralized : Everything is controlled by one controller

Extended : Centralized + one smarter tool head

Distributed/BUS : Each axis has its own local controller

Daisy Chain : Controllers connected one after another in a chain

Hybrid : Combination of bus + tree + star

Virtual Machine Control : Control a virtual machine instead of a real one

Dataflow : ?

Communication<

2. Group Project Management Meeting<

Project Description<

We first discussed about potential machine ideas and Michel suggested a machine which draws on the sand : it is composed of a magnetic marble in a sandbox moved from below by a magnet whose position is controlled by motors. You may find all the inspirations on the group page.

Below you may find the raw notes of our meeting.

Meeting Notes<

Workspace<

Motion in a plane :

  • circular work zone -> polar coordinate :
    • an axis fixed at the center that can rotate
    • a cart that rolls axis that makes the radial motion
  • rectangular work zone -> cartesian coordinate :
    • an axis fixed on the side that can move along one axis
    • a cart that rolls on the axis makes the other axis motion
Machine Design<

Constraint : slow motion, precision

Motion mechanism : strongly depends on the work space shape, we have to decide :

  • rectangular core xy
  • timing belt + 2 steppers motors (for precision)

System Diagram :

  • TOOL : magnet + magnetic marble
  • CONSTRAINT STRUCTURE : rails
  • KINEMATIC STRUCTURE : belts
  • MOTORS : stepper motors
  • CONTROL : centralized, RP2040, feedback = stop buttons
Prototyping steps<

  1. CONCEPT TESTING :

    • rectangular sand box
    • sand
    • magnet
    • magnetic marble

  2. MANUAL TESTING :

    • cart
    • rails
    • belts system
    • fasteners

  3. AUTOMATION TESTING : CONTROL

Required materials<

MATERIALS for ~50cm square work space :

  • 5 x 50cm rails
  • 2 x 2,5 m belt
  • 8 x pulleys with teeth
  • 2 x pulleys (with or without teeth)
  • 9 x wheels
  • fasteners
Tasks distribution<
  • Elodie : Feet + Sliders
  • Jonas : Cart (Wheels + Holding Magnet + Pulleys)
  • Michel : Control
  • Fabio : Sandbox

3. My contribution summarized<

Cart Design and Build<

Part of Structure Building<

Video Editting<

4. Logbook<

Wheels<

Cart Prototype 1<

Cart Prototype 2<

Cart Prototype 3<

Structure Building 1<

Feet 1<

Concept Testing<

Feet 2 and Sliders 1<

Structure Building 2<

Manual Testing Fail<

Sliders 2<

Structure Building 3<

Feet and Sliders 3<

Structure Building 4<

Manual Testing Success But ...<

Belt Tension Adjustment<

Manual Testing Success !!!<

Sand Installation<

Manual Testing in Sand<

Automated Testing in Sand<

Presentation Video Editting<