The WILMER appealing prehensor is a body-powered (BP) prosthesis for people with a trans-radial upper limb deficiency, which is highly appreciated because of its outward appearance and functionality. Currently, prehension of the WILMER appealing prehensor is voluntary opening (VO). Voluntary closing (VC) prehension could offer the prosthetic user some clear advantages, especially equipped with a locking mechanism. A VC controlling mechanism is designed and evaluated in order to provide prosthetic users a VC version of the WILMER appealing prehensor. Furthermore, an adequate locking mechanism is searched for. A final prototype of the VC WILMER appealing prehensor is evaluated. By preserving the outline of its VO equivalent, a high appreciation for its outward appearance is secured. With a mass of only 99 gr, the VC WILMER appealing prehensor is comfortable to wear. The terminal device has an adequate opening width of 53.5mm, enabling its prosthetic users to grasp a wide variety of objects. The hysteresis of one cycle of the VC WILMER appealing prehensor is very low, indicating that the terminal device is very efficient. Preliminary
results show that there is room for improvement regarding the cable operating force and locking mechanism. At larger apertures the cable operating force necessary to get an adequate grip force slightly exceeds comfortable limits. The VC WILMER appealing prehensor is equipped with the vertical mount Sure-Lok.
Although the vertical mount Sure-Lock is a more effective locking mechanism than locking mechanisms tested in literature, the drop in grip force induced after activation is still quite large.