Robotic hands with delicate fingers and thumbs have been developed over years of research, and every new generation of these comes with powerful features and accurate imitation of human hands. Inspired by nature and with aiming to give our robots human characteristics, all muscles, tendons, nerves, and bones were replaced with metal, plastic and electricity. Keeping the forms and functions of the human hands, in this article I made an overview of these marvels of tools used in robotics.
The arms and hands represent main working tools for a humanoid robot. If the arm has the role to allow rotational motion while linking the body of the robot with the hand, the hand has at least two main roles including the sense and object manipulation. A high flexibility of the hand is translated into various sizes and weights of the objects that can be manipulated. In addition, for a high flexibility of the hand each finger has to be independently controlled and to adopt an individual position depending on the task.
Motors and wires are used to replace muscles and tendons, while a wide range of sensors are used to sense. Materials occupy an important role in an efficient functioning of the hand. Using plastic and lightweight materials like aluminum, researchers designs robotic hands strong enough to grab objects, apply enough pressure for object manipulation, and sense the environment.
Shadow C6M
C6M is a wonderful robotic hand that mimics a human hand in movements and senses.
In the labs of Shadow company, one of the most advanced humanoid robot hand takes shape with the code-name C6M. The robotic hand was built from plastic and aluminum and the result is a wonderful dexterous hand integrated with ROS, while a high flexibility in work is provided by 20 degrees of freedom completed by 4 under-actuated movements that increase the number of joints to 24. Ever of the 24 joints has a movement range that imitates the movements of a human hand. The imitations of nature are found in the sensing capabilities of robotic hand. Each finger has integrated force sensors as well as position sensors. Depending on the environment where it is used, add-ons could be added for increased capabilities like protection for example when standard wearing gloves are used.
A wide range of sensors are located in the hand, a total number of 129 sensors that provide detailed information’s for an accurate control. Along force and position sensors, temperature and voltage sensors are also included.
Another important feature of C6M is the Smart motor concept, an advanced actuation system that includes in one unit all robotic parts needed to sense or produce motion.
ELU-2
Aimed to be used in advanced human-like robotic projects including research or medical fields, ELU-2 is a robotic hand able to imitate the speed and movements of a human hand.
Using lightweight materials, Elumotion company design and build a precision and powerful robotic arm with 9 degrees of freedom. ELU-2 is a combination between durability and reliability with accuracy in manipulation of objects with different shapes and sizes. Both fingers and the pad of the hand integrate tactile sensors, and with a design that imitates the design of a human hand, a wide range of tools and objects could be manipulated.
Sensing and positioning information for fingers are used to ensure safety in applications. With a flexible structure and advanced mechanical systems, the hand is aimed to be used in many more advanced humanoid robotic projects.
EH1
Open-source robotic hand with 12 degrees of freedom and a maximum payload of 5 kilograms.
Italy-based company Prensilia invests time and money and creates an open-source humanoid hand with features that can be used especially in research. EH1 has 12 degrees of freedom and a weight of 1.4 kilograms while the maximum payload is up to 5 kilograms.
Five fingers, five different options and control. Each finger is driven independently by electrical motors hosted in mechanical platform in case of portable systems, or in specific braces to ensure safety.
And because it is an open-source system, the hand is operated through a simple communication interface and the overall control is ensured by an embedded controller.
DART
A hand that can type up to 20 words while 23 degrees of freedom provide greater flexibility.
DART or Dexterous Anthropomorphic Robotic Typing is a robotic hand designed in the labs of Virginia Tech and is based on the idea to build a hand that writes dozens of words per minute. The idea took shape and the result is a performance human-like hand that can write at a computer keyboard up to 20 words per minute. While a human can type an average of 33 words per minute using both hands, a robot that uses both of these mechanical and electronic hands can type up to 40 words.
Up to 16 servo motors replace the muscles of fingers and other three motors are used for wrist motion. Tendons are also located in the forearm, but in the form of wires.
The control of the hand can be done in two ways including an input text using a keyboard or voice recognition software. At the other end, each finger receives commands and place the finger above the correct letter. After the letter is pressed, the control system checks the letter and in case that the key pressed is wrong, a command is released for twisting and wrist to navigate at the backspace key.
DLR Hand II
Four identical fingers and a high mobility. A perfect hand for grasping and manipulation.
Based on mobility, lightweight and flexible, engineers and researchers from Robotics and Mechatronics Center in Germany design the DLR Hand II. DLR hand is a perfect tool for mobile service applications including grasping and manipulate objects with different shapes and sizes.
While almost all human-like hands have five fingers, DLR II has four identical fingers. Each finger has four joints and three degrees of freedom. One degree of freedom is located in the palm for a high accuracy in grasping and manipulates objects.
DLR II has a completely integrated system allowing easy interfacing to different robots.
A wide range of sensors is integrated into the hand including force and position sensors.
ACT Hand
A robotic hand that imitates a human hand in detail including the mechanical and movement systems.
ACT hand or Anatomically Correct Testbed incorporate human-like anatomic features in order to imitate the neural commands using the power of electricity.
One of the important mechanisms that researchers and engineers imitate is the extensor mechanism with the role to provide independent control of the metacarpophalangeal joints as well as acts.
Bones were designed to mimic in detail the human bones including the mass and shapes. Also, the joints match in degrees of freedom and passive stiffness with mechanisms presented in a human hand.
This hand was designed to be used in three main capacities including telemanipulation, for experimental tests, or in medicine as a physical model of the human hand.
DEXMART
DEXMART is a robotic hand based on a new technology called twisted string actuator, a technology designed to provide flexibility and force.
Researchers from Saarland University in Saarbruecken, Germany works on a sensitive project, a five finger robotic hand that can hold an egg with only three fingers. Like all advanced human-like robotic hands, DEXMART imitate the structure of the human hand. Human tendons are replaced with small electrical motors, which in combination with twisted strings can perform delicate operations.
Each finger has three parts and is controlled with high accuracy using individual cables. A new technology developed in order to actuate the fingers of robotic hands and apply a higher force in operation. Up to 24 actuation units maintain the flexibility and force of the hand.
