  Synergistic prostheses enable the coordinated movement of the
human-prosthetic arm, as required by activities of daily living. This is
achieved by coupling the motion of the prosthesis to the human command, such as
the residual limb movement in motion-based interfaces. Previous studies
demonstrated that developing human-prosthetic synergies in joint-space must
consider individual motor behaviour and the intended task to be performed,
requiring personalisation and task calibration. In this work, an alternative
synergy-based strategy, utilising a synergistic relationship expressed in
task-space, is proposed. This task-space synergy has the potential to replace
the need for personalisation and task calibration with a model-based approach
requiring knowledge of the individual user's arm kinematics, the anticipated
hand motion during the task and voluntary information from the prosthetic user.
The proposed method is compared with surface electromyography-based and
joint-space synergy-based prosthetic interfaces in a study of motor behaviour
and task performance on able-bodied subjects using a VR-based transhumeral
prosthesis. Experimental results showed that for a set of forward reaching
tasks the proposed task-space synergy achieves comparable performance to
joint-space synergies without the need to rely on time-consuming calibration
processes or human motor learning. Case study results with an amputee subject
motivate the further development of the proposed task-space synergy method.
