Industrial Robot Development

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Master Diagram

Developers

Paul Azevedo

Yoonseo Kang

Matthew Markudis

Progress Report

General Developmental Bill of Materials Completed

Mechanical Design Illustrated

Denavit-Hartenberg Kinematic Parameters Completed for Sample Design

Electrical Design Illustrated

Hydraulic Design Illustrated

Stepper Motor - Needle Valve Bracket Design Illustrated

Systems Engineering Diagrams Added

Task List

• Complete working concept pictures in build instructions

• Complete addition of specific dimensions in build instructions

• Complete CAD images in build instructions

• Complete addition of CAD files to repository

• Complete addition of CAM files to repository

• Complete programming instructions in build instructions

• Complete shaft encoder circuit diagram and add printed circuit board CAM file to repository

• Continue analysis (eg. FEA) and calculations (eg. required torque)

• Continue editing bill of materials to parallel development and build instructions

Design Rationale

• Hydraulic Drive
  • Scales to very high payloads
  • Requires low gear reduction

• Needle Valves and Solenoid Valves
  • Simplifies design and fabrication

• Basic Frame
  • Simplifies design and fabrication

• Spur gearbox
  • Achieves high efficiency
  • Incurs no axial force onto shaft
  • Simplifies design and fabrication

• Incremental Encoder
  • Simplifies design and fabrication
  • Achieves high resolution
  • Achieves absolute position encoding through homing

Mass

Given density of A36 steel as 0.28 pounds per cubic inch (numbers are in pounds):

• Frame
  • Foundation Underplate: 81
  • Foundation Pillar: 14
  • Foundation Overplate: 36
  • Base Angle: 84
  • Main Arm: 16.8
  • Forearm Angle: 42
  • Forearm Plate A: 5
  • Wrist Angle: 42

• Hydraulic Motors
  • Hydraulic Motor 1: 20
  • Hydraulic Motor 2: 20
  • Hydraulic Motor 3: 20
  • Hydraulic Motor 4: 20
  • Hydraulic Motor 5: 20
  • Hydraulic Motor 6: 20

• Gearboxes
  • Gearbox 1:
  • Gearbox 2:
  • Gearbox 3:
  • Gearbox 4:
  • Gearbox 5:
  • Gearbox 6:

Repeatability

• Explaining Repeatability
  • When a robotic arm is commanded to move its end-effector to a particular point in space, the end-effector may arrive a location close to the desired point but not quite. Through testing, the maximum possible inaccuracy (the distance from the desired point) can be observed and recorded. The value of this measurement is called the repeatability of the robotic arm; hence, if a robotic arm is said to have a repeatability of 1mm, then the robot's greatest margin of error when moving its end-effector to a desired point is 1mm.
  • Visually, the repeatability of the robotic arm can be represented by a sphere centered at the desired point of movement with a radius equal to the repeatability; when moving to that desired point, the robotic arm will always finish at a point within the sphere.
  • Note that the repeatability of a robotic arm is determined by a repetition test where the arm moves to and from a desired point a given number of times while measuring the inaccuracy each time it stops; it follows that the observed value of repeatability is imperfect, though a high number of trials can reduce the uncertainty.

• Improving Repeatability
  • Repeatability can be improved by lowering the deflection that occurs when the frame of the robotic arm is placed under stress. Deflection minimization can be achieved by increasing the rigidity of all components placed under stress.
  • When a robotic arm is commanded to move its end-effector to a certain location, shaft encoders determine when the robot stops moving. Shaft encoders measure the angular position of the shaft (ex. 45.6 degrees) but must do so in intervals (ex. between 1 and 4 degrees, between 4 and 7 degrees, ...). Therefore, the resolution (higher the resolution, the smaller the intervals) of the shaft encoders significantly affects the repeatability of the robotic arm; increasing the encoder resolution will improve repeatability.

Frame and Gear Reducer Integration

• Through design that integrates each gear reducer with corresponding frame components, material requirements are decreased while ease of fabrication, maximum payload, and structural rigidity all potentially increase.
• This integration does not allow gear reducers and frame pieces to be modules independently of each other; the extent to which the robot's components are modular is increased by one system level (instead of separate frame pieces and gearboxes, integrated frame-gearbox components)
• The extent of modularity does not change, however, for the following 2 critical frame components, still allowing the robotic arm to be versatile with regard to usage (different lengths and working envelopes are possible):
  • Main arm
  • Forearm
• Also, the end-effector remains modular as frame-gearbox integration does not affect such external components.

Prototype Development

• As various components of the industrial robot shift from commercial purchase to open source fabrication, design flexibility will increase, improving performance while reducing input resource usage.