Anthropomimetic approach to the design of a prosthetic robot hand

A loss of a limb is a common phenomenon among both humans and animals. Where animals have to cope with such a loss, humans have pushed attempts towards limb replacements for quite a long time. It has only been relatively recently that such devices, in addition to providing a cosmetic replacement can also be sophisticated enough to account for some of the functions of the lost limb. Upper-limb replacements in particular are inherently difficult to realize as the human hand is the most complex and important tool man possesses. The prosthetics and robotics research fields have marked increasing progress towards functional hand replacements. By satisfying requirements such as (1) numerous sensory modalities, (2) high processing capabilities, and (3) high output torque, current robotic/prosthetic prototypes are close to attaining functionalities similar to those of the human hand (Balasubramanian et al., 2008). In the prosthetics industry however, such advancements are usually not realized. Upper limb prostheses used in the real world pose additional, inherent requirements which are usually not taken into consideration by robot designers. Such requirements, vital to the adoption of the prosthetic device by its user (Carrozza et al., 2006), are: (1) reduced power consumption, (2) low device weight, (3) high dexterity, and (4) ease of use. In contrast, prosthetics research is carried out using robotic hand prototypes that only partially fulfill the above requirements. Even so, most prosthetic – and arguably robotic – hand prototypes cannot be considered optimal. Size and weight considerations are rarely taken into account, and power consumption issues are usually not dealt with; when they are, usual approaches involve either smaller or fewer motors, disregarding any dexterity requirements. Clearly, for upper-limb amputees to directly benefit from prosthetics research, the devices being used to conduct this research should themselves adhere to these real world requirements. Had the biomechanics of the human hand been taken into consideration, could such requirements be met in a better fashion than traditional engineering approaches? We argue that by studying the morphology of the human hand, we can identify and exploit principles that underlie its functions, creating a device that can be of use to patients in real world circumstances. Towards identifying the underlying functional principles of the human hand, we focus our attention on two important properties: (1) the phalangeal curvature and (2) the friction between tendons and their sheathing under high loads. Even though both properties have been well documented …