Fig 1.
An ideal case of overcompensation of the glove characteristic.
The operation of the resultant characteristic is reversed and turns an otherwise voluntary opening device into a voluntary closing device.
Fig 2.
Conceptual design of the Rolling Stiffness Compensation Mechanism (RSCM).
(a) Its overall shape and how the parts connect through cross-weaved stabilization bands, indicating the visible fixation points, and (b) its working principle in combination with the WILMER WHD-4 mechanism.
Fig 3.
Geometry and force analysis of the mechanism.
(a) The used rolling link mechanism and used geometric annotations. In (b), the free body diagram is shown of the roller inside the encircled area, together with the accompanying force triangle in which the forces are in balance. The vertical component of force FR directly contributes to the total compensation force Fcomp.
Fig 4.
Stiffness characteristics of a prosthesis fitted with different gloves.
Showing the average fit (black) compared to the range of different fits (grey) for all types of glove material, as well as for the ungloved prosthesis. The area beneath the loading curve is equal to required input energy (Ein), area enclosed by both curves is equal to the hysteresis (Ehyst). Average energy values are for PVC (Otto Bock): Ein = 833 Nmm, Ehyst = 259 Nmm, for silicone (Otto Bock): Ein = 277 Nmm, Ehyst = 105 Nmm, for coated silicone (Regal): Ein = 388 Nmm, Ehyst = 133 Nmm.
Fig 5.
The manufactured RSCM prototype.
Displayed alongside a Euro coin [Ø 23.25mm] for scale.
Fig 6.
Absolute compensation force of the prototype.
Showing the averaged measured force (solid) with standard deviation (grey) and as predicted by the model (dashed). Input energy and hysteresis are also shown for measured values. Both spring stiffness (k) and stabilization band thickness (t) were varied. Arrows indicate the direction of the curves, distinguishing loading and unloading curves.
Fig 7.
The compensated hand prosthesis.
A photo and corresponding illustration of the RSCM in combination with a gloved hand prosthesis. The RSCM was fixed into a wrist unit and pushed against the gloved prosthesis using a pushrod.
Fig 8.
Resultant force of the compensated gloved prosthesis.
Showing the averaged measured force (solid) with standard deviation (grey) and compared to the original gloved prosthesis (dotted). Input energy and hysteresis are also shown for the compensated prosthesis. Both spring stiffness (k) and stabilization band thickness (t) were varied. Arrows indicate the direction of the curves, distinguishing loading and unloading curves. Notice how the direction of the curves have been reversed, creating a voluntary closing prosthesis.
Fig 9.
Resultant force of the compensated gloved prosthesis at different cycles.
Showing the averaged measured force with standard deviation of the gloved prosthesis with compensation mechanism, undergoing different sized cycles at one-third, two-third and 100% of the total opening width. The left figure starts with an open hand (resting position), closing the hand at the different widths. The right figure starts with a closed hand, opening the hand at the different widths.