By Kal Kaur
Robotic Prosthetics - Structural Components
Research to Consider
A prosthetic limb is defined as a mechanical device that is
replace a missing human limb. The device is designed to help the user
coordinate better control of an amputated limp as a result of motor
control loss by a traumatic event, a congenital-related defect, or
dyvascular-related. According to statistics by
Ziegler-Graham, et al (2008), an estimated 1.6 million civilians were
living with the loss of a limb. This research also revealed that
approximately 38% of these people suffered an amputation of a limb as a
secondary consequence to a dyvascular disease. Shockingly, it has been
predicted that this statistic is likely to double to 3.6 million by the
Dyvascular disease is only one major contributing factor to amputation
of a limb; it is commonly known that war veterans often become wounded
in combat and considering the current affairs, it is estimated that the
number of veterans wounded in Afganistan is increasing. According to
the Department of Defence statistics, to-date more than 1,000 soldiers
have returned from Afganistan with the loss of a limb. With current
limb-loss statistics in perspective, there is a clear demand for the
use of prosthetics from healthcare angle.
- Structural Components
A robotic prosthetic limb is made up of the following components:
- Biosensors, required to detect neural transmission from the
human nervous and neuromuscular junctions (i.e., wires to track neural
activity near the surface of the skin). The video below by Bio Tac is a
great example of how biosensors are applied to study sensing modalities
if a robotic finger.
- A controller is the main connection between the
neuromuscular systems and the end device and so this receives the
information from the biosensors and feeds this information back to the
- The actuator is the end device which will receive
information from the controller and mimic the movement of a muscle.
The study of prosthetic limbs is vast and complex. For the
this article, attention will now focus on the prosthetic hand in more
detail. As mentioned, the main pathway involved in the function of a
prosthetic limb is based on three main components: a biosensor,
controller, and actuator. User preferences need to be considered before
designing a prosthetic limb and if focussing on a hand prosthesis, the
following preferences are important:
- Grasp function for a size range of objects
- Intricate finger movements should be possible for grasping
and pinching motion
- A prosthetic hand needs to be lightweight to allow for
better movement in continuous space
- Finger projections need to be designed with active joints
to allow for intricate movement
- Aesthetically, the prosthetic hand needs to appeal to the
patient and allow for comfort of use.
The use of biosensors is fundamental to initiating a pathway
result in movement of the actuator. To allow for control of a
prosthetic limb, the actuators are attached to the residual part of an
amputated area, which will provide feedback on tactile information
generated by the biosensors. The actuators are also connected to a
hardware interface system that acts as the controller which initiates
sensory feedback to the actuators.
The actuator is the key element to a fully functioning
and is what displays the end result (i.e., grasping an object). To
begin with, the actuator system to this prosthetic hand is made up of
micro-actuators which drive the metacarpo-phalangeal (MP) joints of the
thumb and the proximal interphalangeal (PI) joints. The distal
interphalangeal (DIP) joint is controlled by a link connected to the
Proximal interphalangeal (PIP) finger joint.
It is important to
considering the number of individual pieces of information that will
predict how a certain parameter will behave (degree of freedom [DOF]),
and so with this in mind, it is known that each finger to a hand has 4
DOF, the wrist has 3 DOF, which means that a prosthetic hand has to be
designed to function with 23 DOF. It is quite difficult to control the
movement of such a complex machine and so a basic two to three fingered
prostethic hand is usually designed for better control over the
monitoring of signal patterns. The thumb actuator works with two
degrees of freedom (DOF) which are comparative to the MP and IP joints.
The modeling of heavy actuators results in a lower DOF which can affect
the ability of the prosthetic hand to grasp objects effectively. The
following video is a good example of a patient adapting a myoelectric
prosthetic hand controller with signal activity being monitored.
To take this journey of prosthetic hand construction a little further
into detail, let’s consider application of the
sensor-controller-actuator system when measuring micro-electric
signals. An electromyography (EMG) signal is used to detect electrical
stimulus from the robotic hand as would have been the case if the real
limb was present. Electromyography involves the use of surface
electrodes to monitor muscle activity and, when considering bionic
signals, this method of signal control is ideal to monitor exactly how
the mechanical device is moving and responding to stimuli. The EMG is
particularly important as it provides functionality to amputees and the
basic principle to EMG signals is to pick up a signal based on movement
of a limb or robotic form. The video below demonstrates use of a
robotic hand with one degree of freedom to pick up an object and how
EMG is use to map the electrical signals during this movement.
Research to Consider
The present article has introduced a basic overview on the
modeling of a prosthetic hand, a study referred to as biomechatronic
design. Though the design of prosthetics is continuing to develop and
benefits many patients living with an amputated limb, there are still
challenges ahead in the design of a prosthetic limb that satisfies
intricate requirements, such as easy control of the prosthetic limb and
a to make this mechanical device cosmetically appealing. There is also
the challenge of understanding the issue of tissue reactions to
material used for the prosthetic limb and how an inflammatory response
to such a reaction may interfere with signal transmission of
- Ziegler-Graham K, MacKenzie EJ, et al. Estimating the
preference of limb loss in the United States: 2005 to 2050. Archives of
Physical Medicine and Rehabilitation. 2008: 89(3):422–9.
- Pitkin, M.R. (2006). Biomechanics of Lower Limb
Prosthetics. New York: Springer Science and Business Media.
- Chen, C. (2009). Hybrid Control Strategies for Smart
Prosthetic Hand. Arbor, Michigan: ISTE Publishing.
- Love, L.J. (2009). Mesofluidic Actuation for Articulated
Finger and Hand Prosthetics. The 2009 IEE/R S J International
Conference on Intelligent Robots and Systems. OCTOBER 11-15, 2009 St.
- Nasser, S., Rincon, D., Rodriguez, M. Design of an
Anthropomorphic Underactuated Hand Prosthesis with Passive-Adaptive
Grasping Capabilities. 2006 Florida Conference on Recent Advances in
Robotics, FCRAR 2006.
- Dr A.H.Bottomley and T.K. Cowell. An Artificial hand
controlled by the nerves. New Scientist. 1964 (No. 382).
- Carrozza, M.C., Micera, B., Micera, S., Zecca, M., Dario,
P. A “Wearable” Artificial Hand for Prosthetics and Humanoid Robotics
Applications. Proceedings of the 2001 IEEE-RAS International Conference
on Humanoid Robots.
- Lai, J.C.K., Schoen, M.P., Gracia, A.P, ET AL.
Prosthetic devices: challenges and implications of robotic
implants and biological interfaces. Journal of Engineering in Medicine.
2006: Vol.221 Part H.
- Antfolk, C.,
Balkenius, C., Lundborg, G., et al. Design and technical construction
tactile display for sensory feedback in a hand prosthesis system. BioMedical Engineering Online. 2010,