Industrial Robot Development

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Master Diagram

Developers

• Paul Azevedo
• Yoonseo Kang
• Matthew Markudis

Progress Report and Task List

• Note that all development points are open to change, "completed" or not.

• Frame
  • Frame Concept (Completed)
  • Frame Specifications (Completed)

• Gearbox
  • Gearbox Concept (Completed)
  • Gearbox Specifications

• Stepper Mount
  • Stepper Mount Concept (Completed)
  • Stepper Mount Specifications (Completed)

• Shaft Encoder
  • Shaft Encoder Electrical Concept (Completed)
  • Shaft Encoder Electrical Specifications
  • Shaft Encoder Mechanical Concept (Completed)
  • Shaft Encoder Mechanical Specifications

• Hydraulics
  • Hydraulics Concept (Completed)
  • Hydraulics Specifications

• Electronics
  • Electronics Concept (Completed)
  • Electronics Specifications

• Programming
  • Microcontroller Programming

• Operation
  • Control 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:

Hydraulic Motor

Wikipedia on Hydraulic Motors

Damen Technical Agencies on Types of Hydraulic Motors

• Hydraulic motors turn the industrial robot at each of its 6 axes.

• Given an input flow pressure of X, the torque at the shaft of the hydraulic motor (in-lbs)
  • Hydraulic Motor 1:
  • Hydraulic Motor 2:
  • Hydraulic Motor 3:
  • Hydraulic Motor 4:
  • Hydraulic Motor 5:
  • Hydraulic Motor 6:

Gearbox

Presentation Slides on Gearbox Design

• The gearbox allows the industrial robot to make a tradeoff of speed for torque at each of its degrees of freedom.
• The encoder can be mounted onto the robot more easily near a gearbox.
• The gearbox permits a rigid connection between separate frame components.

• Gear reduction from input shaft to output shaft (revolutions of I to revolutions of O)
  • 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 and stop its end-effector at a certain location, shaft encoders determine where 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 of the shaft encoders significantly affects the repeatability of the robotic arm (the higher the resolution, the smaller the intervals); increasing the encoder resolution will improve repeatability.

Stepper Motor

Solarbotics on Stepper Motors

Wikipedia on Stepper Motors

• Stepper motors are brushless DC motors that rotate their shaft in "steps", each of which has consists of a minute angle. Hence, stepper motors can be accurately controlled even with open-loop control (no shaft encoder or such feedback devices).

• Stepper motors can be mounted onto one side of a metal angle then connected via a shaft coupling to a needle valve. This allows for flow control of the hydraulic system using electronically operated stepper motors.

• The torque of the stepper motors:

Kinematic Parameters

Wikipedia on Denavit-Hartenberg Parameters (video included)

Formal Lecture Notes on Denavit-Hartenberg

• The Denavit-Hartenberg parameters define the position relationships between 2 motors of the industrial robot. More specifically, the robot has 6 motors, hence one parameter would be between motor 1 and 2; another between motor 2 and 3, 3 and 4, 4 and 5, and 5 and 6.

• The Denavit-Hartenberg parameters are as follows, for joint(i): depth(i), normal length(i), z angle (i), x angle (i).

• • Joint(1): Depth(1)= , Normal Length(1)= , Z Angle(1)=90deg , X Angle(1)=*

• • Joint(2): Depth(2)= , Normal Length(2)= , Z Angle(2)=00deg , X Angle(2)=*

• • Joint(3): Depth(3)= , Normal Length(3)= , Z Angle(3)=90deg , X Angle(3)=*

• • Joint(4): Depth(4)= , Normal Length(4)= , Z Angle(4)=90deg , X Angle(4)=*

• • Joint(5): Depth(5)= , Normal Length(5)= , Z Angle(5)=90deg , X Angle(5)=*

• • where * is the joint variable

Force Analysis

• Format
  • Force is expressed in newtons (N)
  • Maximum absolute displacement is expressed in millimeters (mm)
  • Dimensions are expressed in inches (“)

• A36 Steel Specifications
  • Poisson Ratio = 0.285
  • Young's Modulus = 200GPa

Toolchain for Toolpaths

• CAD (FreeCAD) > export (stl, dxf, svg) > CAM (PyCAM) > export (gcode) > Machine Controller (EMC2) > export (logic signals) > Machine (CNC milling, various) > export (work)

• In FreeCAD, a 3d mesh drawing can be exported as an stl file; alternatively, a 2d drawing can be exported as a dxf or svg file. Any of these files can then be imported in PyCAM, in which toolpaths can be generated for those drawings. These toolpaths can then be exported from PyCAM as a gcode file. EMC2 can then import the gcode file and simulate the toolpath, plus send logic signals to an external electronic controller that moves a machine to correspond to the toolpath. This toolchain allows digital fabrication to be utilized for the construction of the industrial robot.

Design Resources

FANUC Maintenance Manual

Future 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.