Industrial Robot Development

---

Master Diagram

Developers

Paul Azevedo

Yoonseo Kang

Wonjohn Choi

Joshua Lee

Roberto Bortolussi

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

Continue design optimization and understanding through research and collaboration

Complete analysis (deflection)

Complete calculations (required torque)

Complete all CAD files

Complete all CAM files

Complete detailed bill of materials

Complete build instructions

Complete user's manual

Design Rationale

• Using hydraulic drive over electric drive: electric drive requires complicated electronic circuits, requires a high reduction gearbox (such as harmonic drive, which is complicated to design and fabricate), and is not as scalable as hydraulic drive (for very high loads).

• Needle valves and solenoid valves over proportional servovalves: proportional servovalves experience coil heat buildup that changes the resistance of the solenoid hence diminishes its accuracy of control; proportional servovalves also are more complicated to design and fabricate.

• Stepper motors to allow the electronic control of needle valves: eliminates need to have closed-loop system for needle valve control while maintaining high accuracy through stepping.

• Two plate, four pillar design for foundation: simple to design, fabricate, and assemble, does not require casting with molds while maintaining high degree of stability.

• Angles and bars frame design: simple to design, fabricate, and assemble, does not require casting with molds while maintaining high degree of stability akin to the designs of existing commercial industrial robots.

• Spur gearbox: High efficiency, minimal axial force transmitted onto shaft; simple to design, fabricate, and assemble relative to other gearbox types (such as planetary or harmonic).

• Incremental Encoder: simpler design, higher resolution, more economical relative to absolute encoders. Achieves absolute positioning capability through homing.

Repeatability

The precision of the industrial robot is determined by the following factors (assuming sufficient control over hydraulic motors where the minimum non-zero movement interval causes a degree of movement that is less than the arc length of one encoder wheel sector):

• Deflection of frame components
• Resolution of shaft encoders

Repeatability then can be improved by the following methods:

• By bolstering the structural rigidity of the industrial robot, minimizing the deflection factor
• By augmenting the resolution of the shaft encoder, minimizing the resolution factor

Methods of improving the factors affecting repeatability include various considerations:

• Greater frame component volumes are more rigid but more heavy as to cause more and less deflection in certain regions (deflection-deflection tradeoff)
• In a gear reducer, the closer the stage to which the encoder wheel is connected, the lower the effective resolution (deflection-resolution tradeoff)
• In a gear reducer, larger encoder wheels necessitate larger and potentially less rigid container walls (resolution-deflection tradeoff
• In a gear reducer, perpetual contact between gears must be maintained for accuracy of the microcontroller's observation for the relationship between the mechanical state and the encoder's electronic output

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.