title: A mechanism to compensate undesired stiffness in joints of prosthetic hands.
abstract: BACKGROUND
  Cosmetic gloves that cover a prosthetic hand have a parasitic positive stiffness that counteracts the flexion of a finger joint.
  
  
  OBJECTIVE
  Reducing the required input torque to move a finger of a prosthetic hand by compensating the parasitic stiffness of the cosmetic glove.
  
  
  METHODS
  Experimental, test bench.
  
  
  METHODS
  The parasitic positive stiffness and the required input torques of a polyvinyl chloride glove and a silicone glove were measured when flexing a metacarpophalangeal finger joint for 90°. To compensate this positive stiffness, an adjustable compensation mechanism with a negative stiffness was designed and built. A MATLAB model was created to predict the optimal settings of the mechanism, based on the measured stiffness, in order to minimize the required input torque of the total system. The mechanism was tested in its optimal setting with an applied glove.
  
  
  RESULTS
  The mechanism reduced the required input torque by 58% for the polyvinyl chloride glove and by 52% for the silicone glove. The total energy dissipation of the joint did not change significantly.
  
  
  CONCLUSIONS
  This study shows that the undesired positive stiffness in the joint can be compensated with a relatively simple negative stiffness mechanism, which fits inside a finger of a standard cosmetic glove. Clinical relevance This study presents a mechanism that compensates the undesired stiffness of cosmetic gloves on prosthetic hands. As a result, it requires less input force, torque and energy to move the fingers. Application of this mechanism in body-powered hands will reduce the control effort of the user.
authors.affiliation: Department of Biomechanical Engineering, Delft University of Technology, Delft, The Netherlands.
authors.forename: Gerwin
authors.initials: G
authors.lastname: Smit
authors.forename: Dick
authors.initials: D
authors.lastname: Plettenburg
authors.forename: Frans
authors.initials: F
authors.lastname: Van der Helm
mesh_terms: D001696:Biomechanical Phenomena; D003358:Cosmetics; D017575:Gloves, Protective; D006225:Hand; D050823:Hand Joints; D006801:Humans; D011143:Polyvinyl Chloride; D019736:Prostheses and Implants; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012828:Silicones; D019415:Torque
chemical_list: D003358:Cosmetics; D012828:Silicones; D011143:Polyvinyl Chloride
keywords: Upper limb prosthetics; compensation mechanism; cosmetic glove; prosthetic design