Industrial Robot Mechanical Design

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.

Mechanical Concept

Motors

Brushed motors wear out relatively rapidly. Yet, the industrial robot must be designed for lifetime use. Therefore, AC brushless or DC brushless motors seem like the better design choice for electric drive.

For hydraulic drive, epicyclic (gerotor) motors seem to be the optimal choice for their low leakage, low speed, and high torque. Other types include vane motors and axial/radial piston motor

Gear Reduction

Presentation Slides on Gearbox Design

By virtue of using hydraulic drive, the motor shaft output speeds are low enough that we might be able to use a compact spur gearbox at each joint instead of a more complicated configuration such as harmonic drive.

One possibility is a single stage spur gearbox where the "input shaft to output shaft offset" equals the sum of radius one and radius two, where radius one is that of the first (input) spur gear and radius two is that of the second (output) spur gear. Both shafts would be immobile in all directions except for rotation; this can be accomplished by mounting the motor and gearbox on a common frame for the input shaft; by welding a small disc for the output shaft.

Kinematic Parameters

Wikipedia on Denavit-Hartenberg Parameters (video included)

Formal Lecture Notes on Denavit-Hartenberg

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)=0.2m , Normal Length(1)=0.2m , Z Angle(1)=90deg , X Angle(1)=*

Joint(2): Depth(2)=0.0m , Normal Length(2)=1.0m , Z Angle(2)=00deg , X Angle(2)=*

Joint(3): Depth(3)=0.0m , Normal Length(3)=0.1m , Z Angle(3)=90deg , X Angle(3)=*

Joint(4): Depth(4)=0.0m , Normal Length(4)=0.0m , Z Angle(4)=90deg , X Angle(4)=*

Joint(5): Depth(5)=0.2m , Normal Length(5)=0.0m , Z Angle(5)=90deg , X Angle(5)=*

where * is the joint variable

Mass

Given density of A36 steel as 0.28 pounds per cubic inch, or 7750 kilograms per cubic metre, and using numbers from the current design:

Foundation Underplate: 15.75 pounds, or 7.144 kilograms

Foundation Pillar: 11.2 pounds, or 5.08 kilograms

Foundation Pillar Angle: 0.525 pounds, or 0.238 kilograms

Foundation Overplate: 8.47 pounds, or 3.84 kilograms

Base Angle: 33.6 pounds, or 15.2 kilograms

Main Arm: 161.28 pounds, or 73.155 kilograms

Forearm: 60.48 pounds, or 27.43 kilograms

Forearm Angle: 33.6 pounds, or 15.2 kilograms

Wrist Angle: 33.6 pounds, or 15.2 kilograms

Wrist Plate: 60.48 pounds, or 27.43 kilograms

Endeffector Angle: 33.6 pounds, or 15.2 kilograms

Sum 1:The mass of the steel frame pieces of the foundation is 71.12 pounds, or 32.26 kilograms.

Sum 2: The mass of all steel frame pieces excluding the foundation is 416.64 pounds, or 188.98 kilograms.