A linkage design for the `machine-to-patient´ interface of a servo-controlled motorised hand therapy machine

The authors have developed a continuous passive motion (CPM) machine for the therapeutic treatment of finger disorders. The machine operates under position feedback control using Visual Basic software operating on a laptop computer. It has proved to be extremely difficult to provide adequate fixation of the machine´s actuating rod onto a patient´s finger because of the latter´s cylindrical shape and the small sizes of the phalanges. The authors identified an urgent need to develop a linkage assembly which could be applied to a finger and which fulfilled three functions, namely; it securely attached an actuating rod to a finger, it moved the finger in an arcuate fashion, and it provided the facility for individual goniometer attachment to all three finger joints. The authors have used DE/Mec mechanism software to design two linkages, with one and two degrees of freedom, which behave as ´kinematic chains´. The two degree of freedom linkage has been manufactured and it can be used either in a passive mode (i.e. driven by a machine) or an active mode (i.e. driven by a patient)