Prosthetics is an obviously emotive issue, as the absence of a limb, either by amputation or by congenital defect is a highly visible âdisabilityâ. Despite this prejudice, many of those with congenital defects do not consider themselves disabled, or in need of a prosthesis, due to their existing ability to adapt to the surrounding environment or task. Others, including the majority of amputees, often wish to regain some of the functionality (or at least, the appearance) lost with the limb, by the use of a prosthesis. However, the potential use of functional prostheses, or cybernetic systems, involving an interface between man and machine, is also sometimes viewed as unnatural or unappealing. Consequently issues such as anthropomorphism become as critical in prosthesis design as the size, weight, and power consumption of the device.
The Southampton Philosophy
The Southampton Artificial Hand has been in existence for several decades, and is based upon the original hypothesis for the development of a hierarchically controlled, myoelectric prosthetic hand. Although the mechanics of the Southampton hand has undergone several evolutionary stages, it is the main control hypothesis that forms the foundation of the Southampton Hand.
In order to grip an object with a natural hand, the brain utilises vast quantities of information from sites all over the hand and fingertips, to provide muscular reflexes that adjust the grip to ensure that the object doesnât slip. Conventional myo-devices require the user to decide how much force to exert on an object by control of the EMG signals in the forearm. The main difficulty is that there is no feedback (other than visual), hence it becomes very difficult for the user to maintain any form of minimal grip without the object slipping.
The Southampton philosophy concentrates on devolving the responsibility of grip adjustment from the user to the hand itself. The âintelligentâ hand uses sensors, electronics and microprocessor technology to allow this adaptive device to maintain optimum grip (thereby ensuring that objects do not slip from the hand) under the jurisdiction of a state driven control system (which allows easy control of the prosthesis).Continuing Research
At present a multiple degree of freedom device is under development, utilising lightweight materials to produce a highly functional, adaptive prosthesis. Funding from Remedi (Rehabilitation and Medical Research Trust) has enabled the realisation of prototype systems, which will undergo further development and evaluation.
Funding from the Engineering and Physical Sciences Research Council (EPSRC) allowed us to investigate the use of thick-film technology to design and construct sensors to improve the functionality of the hand. The approach adopted has been to instrument the fingertips with sensors to measure grip force and object temperature and to develop sensors to detect the onset of object slip as part of an autonomous control system with the aim of automatically adjusting hand grip strength or posture to prevent slip occurring. As part of this project, a new generation of hand has been produced.
Future work will concentrate on developing the âintelligentâ finger: a self-contained modular unit that combines both sensors and associated instrumentation circuits and that communicates with a central control system (potentially located on the palm or the wrist socket) through an RF wireless link.
Research Areas Involved
This project spans a wide range of disciplines which is often the case in biomedical engineering. The diversity of these knowledge requirements is frequently overlooked, yet the very essence of the Southampton Hand lies in the control of motor-drive systems. Although the overall research continues at postgraduate level, undergraduates are actively involved in specific areas of the work, which forms the basis of final year projects, or group projects. Examples of student projects include the modelling of the mechanical design, development of force/slip sensors, and associated work such as the design of a rehabilitation gripper for fitment to a wheelchair.
A computer animation of the latest version of the Southampton Hand showing the thumb moving across the palm to oppose the index finger can be found here.
Thick-film force, slip and temperature sensors for a prosthetic hand
Contact force sensor for artificial hands with a digital interface for a controller
Intelligent multifunction myoelectric control of hand prosthesis
The design of anthropomorphic prosthetic hands: A study of the Southampton Hand
Development of a lightweight and adaptable multiple-axis hand prosthesis