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Wearable mechatronic devices for upper-limb amputees  211


              wearer’s body to move in an excessive range of motion (Heo and Kim, 2014).
              Designing a comfortable mechanical interface between the device and its
              wearer is a critical yet underrated issue in wearable robots (Xiloyannis
              et al., 2019). Wearable robots provide a physical interface between their
              human wearers and the wearers’ environment, enhancing the wearers’ inter-
              action with the world. This is beneficial because these devices can assist in
              rehabilitation, improve the independence of disabled people, and even pro-
              vide ergonomic and safe support of industrial workers. Currently, great efforts
              are being made to create actuators and sensors with inherent physical softness
              for ergonomic and safe interaction (Veale et al., 2018).




              4 Upper-limb prosthetic technologies
              4.1 Overview
              Losing an upper limb is a major cause of decreased bodily function because
              the hand is an integral component of the human body that performs a wide
              range of tasks, including grasping and manipulating the environment as well
              as communicating nonverbally. Thus, upper-limb loss is a shocking experi-
              ence that needs psychological and physical treatment. To mitigate the effects
              of limb loss, artificial WDs (prostheses) were developed that could help peo-
              ple gain and recover functionalities in the amputated regions. Upper-limb
              prostheses (Cordella et al., 2016) can be classified into two main categories
              based on their function: passive prostheses (which in turn are divided into
              cosmetic and functional) and active prostheses (which include body-
              powered and externally powered devices). The first mechanisms were
              denominated passive devices because no moving parts were included in
              the prostheses in order to move them; external and direct force interaction
              was needed to move and operate them. One of the first documented pros-
              thetic works is described in 77CE in Naturalis Historia (Zuo and Olson,
              2014), where in the Second Punic War (218–201BCE) a Roman general
              received a prosthesis that enabled him to successfully return to battle. The
              concept of an “automatic” body-powered upper-limb prosthesis was pio-
              neered by the German dentist Peter Baliff in 1818 (Childress, 1985; Meier,
              2004). Using transmission of tension through leather straps, Baliff’s device
              enabled the intact muscles of the trunk and shoulder girdle to elicit motion
              in a terminal device attached to the amputated stump. In 1948, the Bowden
              cable body-powered prosthesis was introduced replacing bulky straps with a
              sleek, sturdy cable. Despite new materials and improved craftsmanship,
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