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Lightweight, multiarticulated robotic wrist

Basic Information

Project ID: AEE-2020-32

Students: Reinis Geizans, Sanna Halmkrona, Kasperi Hannula, Wadhah Mari, Erno Valtavirta

Project manager: Sanna Halmkrona

Instructor: Ivan Vujaklija

Other advisors: -

Starting date: 16.1.2020

Completion date: 29.5.2020


  1. Abstract

    In the prosthetics market, demand for lightweight and inexpensive solutions is rising. Performing
    daily activities is a lot more comfortable when the weight of the prosthesis is close to the natural
    weight of the human arm. The dexterity of robotic grippers is dependent on the available DOFs of the
    consecutive joints. Using a lightweight wrist joint will help with the dexterity of the whole limb
    solution while reducing its weight. These two fields, mostly prosthetics, are what the project is
    focusing on.
    The goal of our project was to develop and test a lightweight wrist-like joint with two degrees of
    freedom (DOFs), full actuation, and embedded standalone control. The DOFs are pitch and roll, or
    flexion/extension and pronation/supination in wrist joint movement terminology. The range of motion
    of the flexion/extension axis is 180 degrees and rotation axis 350 degrees. A servo is used to achieve
    flexion/extension and geared motor drives for rotation. The system is controlled by a microcontroller
    and we also developed a graphical user interface.
    The wrist prototype is a table-top model driven by synthetic signals. The assembly consists of three
    subassemblies: electronics, control unit and wrist unit assembly. Assembled wrist unit weighs 197
    grams and it was tested that it can safely sustain a load of 300 grams.

  2. Objective

    The objective of our project was to develop and test a compact, lightweight, articulated “wrist-like”
    joint with full actuation and an embedded standalone control. The robotic wrist should be capable of
    moving with at least two DOFs (roll and pitch). Initially we preferred that it would have three DOFs
    (roll, pitch and yaw). Rotation wrist unit should provide 360 degrees of operation and
    flexion/extension unit the full range of motion of a human wrist (78 degrees).
    The system was planned to be a table-top model with synthetic control signals. This meant that the
    wrist would be tested in “ideal” conditions and implementation would not become too complex. Both
    wrist units were to be tested to ensure precise control and to be characterized in terms of joint angle
    accuracy. The two units were to be merged into a single design with a single control interface
    including a test software. The control interface was to be incorporated into a single user-friendly
    control framework. We planned to operate the joint with e.g. joystick or synthetic signals generated
    by GUI buttons, so that even someone with no previous experience could understand easily how the
    joint is operated. Prosthetic hand was meant to be used as a reference end-effector.
    Expected performance was that the wrist joint could sustain a small load (~150 grams) and move at
    reasonable speed (~7 - 9 rpm). These numbers seemed to be safe to aim for in the beginning, when
    we had not yet done much research on the matter. To be able to prove that the wrist joint would have
    e.g. the ranges of motion as it was supposed to and to measure speeds and angles, an evaluation
    protocol was composed, and test setup planned.

  3. Conclusions

    Even though COVID-19 situation also affected the project work course, we managed to achieve what
    we had planned. As has been described in this report, we accomplished to design and build a
    lightweight wrist prototype. Detailed explanations about the mechanical and electrical systems are
    given, so the joint could be fairly easily replicated based on this report.
    Besides the new technical skills we obtained during the project, due to the unexpected pandemic
    situation we needed to rely on utilizing remote meeting platforms and other online collaboration tools.
    In addition to that, we believe we had a great opportunity to learn more about “real life” working
    environments where not everything happens as planned. Pandemic has caused many disruptions in
    daily life, such as increased delivery times when ordering parts from shops. In some cases, delivery
    was long after planned dates and certain items are still pending. Not only that but also labs were
    closed, and so these resources were not available anymore. Despite all the negative aspects of the
    pandemic situation, we think there is a good opportunity to learn new skills, such as self-organization,
    better task distribution and staying in touch with each other, that in a “normal” working environment
    often are not noticeable, when we interact with each other daily face to face. We needed to quickly
    find solutions to previously mentioned issues: find new or different components and suppliers, and
    find solutions to closed school facilities. Fortunately, many group members had some fabrication
    capabilities in their home. By quickly reorganizing our work habits, we were able to adapt and
    overcome the above-mentioned problems.
    We believe that this has given us new and strong skills in dealing with unforeseen circumstances,
    strong self-organizing skills, support each other, and prepared us for work in multinational companies
    and organizations. In the future, the skills can be very crucial as some companies and organizations
    have already started to explore hybrid working models where some or majority of employees work

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  File Modified
Multimedia File 3-2_video.mp4 May 12, 2020 by Sanna Halmkrona
PDF File Final_report_2020_3-2.pdf May 29, 2020 by Wadhah Mari
PNG File final product.png May 29, 2020 by Wadhah Mari