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RDL VL 11 Mechanical Design

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up:: RDL MOC
lecture11-mechanical-design-0.pdf

What is Mechanical Design?

The design process of mechanical components and systems
(natural and artificial)

also see: Robots at the DFKI

Three steps involved in mechanical design

Specifications

Principles

Design

Machine Elements

Screws

Bearings:

  • Balsl for high revelotions
  • Zylinder or Neelde for high Forces

Sealings (O-Rings)


Springs

Hooks Law


Spring force [N] = spring rate [N/mm] x spring travel [mm]

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Motors

Motor

Example

Direct current motors (DC-motors)

  • Up to 98% efficiency
  • Power cord or battery

Brush motor:

  • cheap
  • Mature technology
  • Sparking / high-frequency interferences
  • Life limit – carbon brushes

Brushless motor:

  • More efficient / less heat
  • Less wear
  • More power per weight
  • Requires a controller

Stepper Motors

  • Revolutions will be made in an amount of steps (degree), not as a constant movement, exact positions can be achieved

  • Bipolar: 2 coils 4 connections (more power per motor-volume)

  • Unipolar: at least 5 connections, simpler control

  • Reluctance motor

    • toothed soft iron structured rotor
    • No permanent magnets
    • Free magnetic flow, no magnetic field after switched off

  • Permanentmagnet motor

    • Permanentmagnet on the shaft / Stator made of soft iron
    • Moment of rest
    • Lower resolution in comparison to ther reluktance motor

  • Hybridmotor

    • Permanentmagnet and toothed soft iron core on the shaft

Servos

  • Analog servos
    • Low power consumption
    • Low price
  • Digital servos
    • Faster positioning time
    • Higher resolution
    • Partly programmable
  • PWM-control

    • Common for hobby servos

    • Servo elektronics regulate the actor (potentiometer) against the motor position

    • The pulse width of the control signal regulates the target position

    • Various variations on pulse widths and travel ranges

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Desing

qualitative design

(norms, shapes etc.)
⇒ Knowlage about desing

quantitative design

(material, strength, stiffness, other desired parameters.)
⇒ Desinging something in a way it can’t fail

  • if you have to calculate, the construction is not good.” → Observe proportions.
  • Roughing calculations – survey orders of magnitude

Loads

Elastic range

components behave like a „spring“
tension [N/mm2 ] = force [N] / cross-sectional area [mm2 ]

Plastic range

components deform permanently
elongation = change in length [mm] / initial length [mm]

E-modulus

The relationship between tension and elongation is called the elasticity modulus
Modulus of elasticity [N/mm2 ] = tension [N/mm2 ] / elongation

Additive and subtractive manufacturing processes

Additive

Subtractive

  • Sheet cutting

    • Laser cutting
    • Plasma cutting
    • Water-jet cutting

  • Milling

Biomimetics

Bottom-up-Prozess

Top-down-Prozess

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Good Books

  • Warum alles Kaputt geht
  • Tabellenbuch Metall

next: RDL VL 12 Actuators

Graph View

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