1. Affordable Prosthetic Hands


Motivated by the structure and functionality of human hand, the most versatile and dexterous end-effector known, we argue that anthropomorphism is an important feature in hand design, resulting in improved performance for a variety of every day life tasks. In our design, anthropomorphism is reflected in two specific design choices: 1) the use of an anthropomorphic kinematic model and 2) the use of a bio-inspired finger actuation and transmission system. In order to optimize anthropomorphism we use the index described in the anthropomorphism section of this website.

Bio-inspired Compliant Robot Fingers with Soft Fingertips

The finger actuation and transmission system follows a bio-inspired design that structurally reproduces the flexion (with tendons driven through low-friction tubes) and extension (using elastomer materials) movements of human fingers. The structure of the finger is constructed with Plexiglas (acrylic) and the flexure joints are implemented with silicone sheets.

For the robot fingers we use also the following materials: 1) sponge like tape that is easily deformable (to enlarge contact patches, reduce contact forces impact to the grasped object and enhance stability), 2) rubber tape (to increase friction and constrain the sponge like tape on the robot phalanges) and 3) anti-slip tape (to maximize friction during contact, enhansing stability of grasps).

Thumb Mechanism

A selectively lockable toothed mechanism that can implement 9 different opposition configurations, is proposed for the thumb. The proposed mechanism substitutes the three Degrees of Freedom (DoF) that implement the human thumb opposition with only one rotational DoF. The proposed mechanism is completely stiff when it is locked and is not affected by torsional forces inherent in dynamic / unstructured environments. A separate tendon routing system is used for the thumb and its tendon is terminated to a separate servo pulley.

Selectively Lockable Differential Mechanism (Whiffletree)

We propose a novel selectively lockable differential mechanism that can block the motion of each finger, using a button. The differential allows the user to select in an intuitive manner the desired finger combinations, implementing different grasping strategies with only 1 motor. The top two bars of our whiffletree have appropriately designed holes and the palm accommodates a series of buttons that upon pressing are elongated. The idea is that when the button is pressed the elongated part fills the appropriate finger hole and the motion of this particular finger is constrained.

A total of 16 different index, middle, ring and pinky combinations can be implemented using the differential mechanism and a single motor. These can be combined with the 9 discrete positions of the thumb, to produce a total of 144 different grasping postures.

Personalized Designs

Τhe use of parametric models derived from human hand anthropometry studies, allows for the development of personalized prosthesis. The only parameters that we need in order to derive the finger phalanges lengths and the personalized finger base frames positions and orientations, are the human hand length (HL) and the human hand breadth (HB).

The proposed hands can be fabricated using off-the-shelf, low-cost materials and rapid prototyping techniques (3D printing) or standard machinery tools. All required materials can be easily found in hardware stores around the world.

You can use the following link to order your personalized design (.CAD files):
Web Form for Personalized Designs

CAD Files

In this section we provide appropriate cad files (Solidworks .sldasm, .sldprt and .dwg, .dxf, .stl), for the replication of the proposed design.

Download the files here:
CAD Files (.zip) | CAD Files (.rar)

2. Robot Hands

Bioinspired Robot Fingers

Our design is based on a simple but yet effective idea: to use agonist and antagonist forces to implement flexion and extension of robot fingers, following a bioinspired approach where steady elastomer materials (silicone sheets) implement the human extensor tendons counterpart, while cables driven through low-friction tubes, implement the human flexor tendons analogous.

The structure of one robot finger is presented. The elastomer materials appear at the lower part of the image (white sheets), while the low-friction tubes that are used for tendon routing, appear at the upper part of the image (white tubes) together with the rigid phalanges. The finger base is also depicted at the right part of the figure.

Modular Fingers Basis with Multiple Slots

The robot hand has a modular fingers basis equipped with 5 slots, that can be used to “accommodate” a total of four fingers. More specifically robot hands with various geometries of finger base frames, can be developed. Line and 2D polytope geometries are easily created, while for 3D polytope geometries finger bases with different heights have to be used (to create vertical offsets). Those hands are very capable of grasping various everyday life objects and each one is specialized for different types of tasks.

The robot hands wrist module is depicted.

Disk Shaped Differential Mechanism

A disk-shaped differential mechanism has been developed, in order to connect all the independent finger cables with the actuator (servo motor). The differential mechanism, allows for independent finger flexions in case that one or multiple fingers have stopped moving, due to workspace constraints, or in case that they are already in contact with the object surface.

The disk-shaped differential mechanism used in our robot hands.

Replicating the Robot Hands Design

The robot hand consist of low-cost off-the-shelf materials:

[1] A combination of sponge-like material with low thickness rubber, that offers a high friction coefficient for fingertips.
[2] Dyneema fishing line which is used for the cables, offering zero elasticity and handling of high forces.
[3] Low friction tubes that are used for tendon routing.
[4] A series of v-groove sealed ball bearings (pulleys) that are used together with the low-friction tubes to minimize friction in tendon routing.
[5] Flexure joints that are made from silicone sheets of different thickness.
[6] Various fasteners.
[7] Rigid links which are built by 2mm acrylic material (plexiglas).

For the assembly of the robot fingers we use fishing line and needles in order to stitch the silicone sheets onto the rigid links (the links have appropriate holes by design).

CAD Files

In this section we provide appropriate cad files (Solidworks .sldasm, .sldprt and .dwg, .dxf, .stl), for the replication of the proposed design.

A new version of our design is under development and can be found in our GitHub repository:
OpenBionics GitHub Repository

Download the files here:
CAD Files (.zip)