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
4 Comments
Wadhah Mari
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.
Wadhah Mari
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.
Wadhah Mari
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
remotely.
Wadhah Mari