Executive Summary

University of California, San Diego

Mechanical and Aerospace Engineering 

MAE 156A/B: Senior Design Project (Winter 2024 - Spring 2024)

PROJECT OVERVIEW

BACKGROUND

Mass casualty events such as earthquakes, fires and combat produce dangerous conditions for search and rescue particularly for emergency responders. Current research in rescue robotics focuses on navigation and mapping. However, UCSD's ARCLab has chosen to pursue research on the ability of general manipulators to execute search and rescue protocols for casualty extraction specifically solving the problem of pHRI. Part of this research involves understanding biomechanical models and physically interacting with humans. Our tasks will be to enable this research without the need for large user studies in which robots could injure humans by replacing the subject with a robotic limb.

PREVIOUS WORK BY SPONSOR

PROJECT OBJECTIVES

To address this task, our team developed a physical system capable of replicating one of the maneuvers often necessary to reposition human casualties into a feasible configuration for extraction. This maneuver is referred to as Upper Arm Repositioning (UAR). 

For example, if a casualty is encountered in a prone position, i.e. facing down, they first need to be reoriented to then be safely extracted from the disaster site. Reorientation in this case would consist of three steps:

1. Limb repositioning, which often includes Upper Arm Repositioning (video on the left)

2. Logrolling (video on the right)

3. Repeat limb repositioning as needed

4. Extraction

THE SHULDRD 

The Shoulder Haptic Universal Limb Dynamic Repositioning Device

We developed the Shoulder Haptic Universal Limb Dynamic Repositioning Device (SHULDRD), which is able to measure and simulate the motion and resistive forces of a human shoulder when performing upper arm repositioning. This system will be used to train a general robotic manipulator to safely maneuver a human shoulder while performing upper arm repositioning. The functional requirements for our physical system, from highest to low priority, are:

• • Accurately simulate and track human shoulder motion in 3 degrees of freedom (DOF)

  • Capability to obtain an accurate measurement of the load being applied on the shoulder

  • Capability to apply resistive forces to simulate limitations in the motion of a real shoulder

  • Accurately replicate human shoulder movement by having a singular center of rotation (COR)

Sensing + Torque Feedback

The code implemented on the haptic shoulder project is built using C++ for its ease of implementation with the Arduino IDE framework and its ability to do object-oriented programming. Each motor is initialized with a motor identity, encoder pins, motor pins, range-of-motion limits, and dynamic parameters (stiffness constant and damper ratio). The scripts are stored at this repository.

To simulate the resistive forces of a shoulder, a virtual spring and damper were modeled in software based on the position of the upper arm.

DEMONSTRATION VIDEO

PARTS GALLERY

DESIGN PROCESS

Mechanical Design

The mechanical design process of the project was guided by two main constraints: replicating accurate human shoulder movement by achieving the full range of motion (ROM) necessary to perform upper arm repositioning (UAR) and ensuring anatomically precise shoulder movements. Specifically, having a singular center of rotation (COR) and reaching the full ROM of a human shoulder were difficult features to find in the same design.

Initially, a Pugh chart was created to evaluate various shoulder joint design ideas based on criteria such as cost, familiarity, mass, range of motion, and others. This evaluation led to the selection of two designs for prototyping. Initial prototyping information can be seen at the bottom of this page in greater detail.

Both prototypes were developed and tested, and the final design emerged as a combination of the best elements from each. This hybrid and novel design, however, still required important modifications to optimize its functionality. These refinements were crucial in ensuring that the final design not only met the project's original constraints but also provided a robust and accurate replication of human shoulder motion. The iterative process of prototyping and refining enabled us to achieve a high-performing mechanical component for advanced physical human robot interaction applications.

Software and Electronics

The software component of the project can be broken down into two separate functions: sensing position and applying torque feedback. 

FEATURES

• Timestamped position logging to a CSV file

• Variable stiffness and dampening

• Variable free range of motion (ROM)

• Customizable coupling ROM between joints

PERFORMANCE RESULTS

Range of Motion (ROM) Analysis

The only movement for which the SHULDRD does not access the same ROM as the human shoulder is flexion. To perform UAR, however, flexion is not executed while the extension motion is. Therefore, a trade-off between losing flexion ROM and gaining extension ROM was necessary to fulfill the project's objective.