referring now to the drawings wherein like reference numerals designate corresponding parts throughout the several views , fig1 - 9 illustrate components of the externally - powered hand prosthesis 100 according to the present invention , hereinafter generally referred to as “ prosthesis mechanism 100 .” as shown in fig1 - 9 , the present invention provides a highly compact externally powered hand prosthesis mechanism 100 for use by persons with amputations at or proximal to the level of the metacarpophalangeal joint ( i . e . persons who have lost one or all digits ( thumb and fingers ) but still retain a palmar surface of the hand , and persons with high - level ( i . e . above - elbow ) amputations where weight considerations are of paramount importance . as discussed above , generally a prosthesis is only recommended for cases where all digits ( thumb and all four fingers ) have been lost at a level equal or proximal to the metacarpophalangeal joint . the majority of mechanical hands that are currently available for persons with trans - radial ( below - elbow ) and trans - humeral ( above - elbow ) amputations are not suitable for persons with wrist disarticulations or partial - hand amputations because the resulting prostheses are too long . a powered - partial hand prosthesis is needed because , although a wide range of devices have been fabricated for partial hand amputees , there are no partial - hand prostheses that provide prehension and are cosmetically feasible for persons with trans - metacarpal amputations . as shown in fig1 and 6 , prosthesis mechanism 100 , which overcomes the aforementioned exemplary drawbacks and deficiencies of existing prosthesis mechanisms , may generally include drive system 102 for operating fingers 142 and thumb 166 of grasping mechanism 105 , with system 102 and mechanism 105 being described in detail below . referring to fig1 - 7 and 9 , drive system 102 may include motor 104 , which in the embodiment of fig1 may be a micromo mm1724 3 volt motor that is overvoltaged to boost its performance . since the overall width of prosthesis mechanism 100 is designed to be less than the width of a typical user &# 39 ; s hand , as compared to standard component lengths for a micromo mm1724 motor , motor 104 may include a reduced length output shaft 106 and likewise a reduced length output pinion 108 . a motor gearhead spacer 110 may be mounted to motor 104 by means of screws 113 threaded through guide apertures 111 , and may be provided to ensure the proper mating of motor output pinion 108 with the input stage of planetary geartrain 112 . the present invention employs a planetary geartrain because of its self - centering capability and because of the equal distribution of torque on the planet gears , thus enabling higher efficiency multistage geartrains . moreover , the use of a planetary geartrain for the present invention allows for an efficient high gear ratio drive train capable of handling the high torques required to generate acceptable grip forces for grasping mechanism 105 . in the embodiment shown , planetary geartrain 112 may be similar in structure to a micromo 16 / 7 66 : 1 planetary geartrain . planetary geartrain 112 may include three input planetary gear stages , which respectively include first , second and third gear stages 114 , 116 and 118 . each planetary gear stage may consist of three planet gears 122 . in the embodiment of fig1 - 9 , although three planet gears 122 are shown , the number of gears may be increased or decreased as needed to adjust the grip force of fingers 142 and thumb 166 . first planetary gear stage 114 may further include a carrier 124 including an output pinion 131 thereon , and a washer 126 . second planetary gear stage 116 may further include a carrier 125 including an output pinion 133 thereon , and a washer 127 . third planetary gear stage 118 may further include a carrier 132 and a ball bearing 129 . planetary gear stages 114 , 116 and 118 may be operatively disposed within gear housing or annulus 128 , which may be disposed within drive housing 130 which also doubles as an axle for prosthesis fingers 142 . carrier 132 of third planetary gear stage 118 may be designed to accommodate a backlock input pinion 140 so that stage 118 mates with the drive stage including backlock assembly 134 . for assembly , planetary gear stages 114 , 116 and 118 may be disposed inside annulus 128 and thereafter inserted within drive housing 130 . thereafter , motor gearhead spacer 110 may be disposed in drive housing 130 , followed by pinion 108 and motor 104 . thus , as illustrated in fig9 motor 104 , pinion 108 , spacer 110 and planetary gear stages 114 , 116 and 118 , all generally referred to as the motor and geartrain assembly 136 , may be operatively disposed inside drive housing 130 . as shown in fig8 and 9 , a teflon impregnated delrin finger bearing 138 may be slid over axle portion 141 of drive housing 130 so as to enable free movement of fingers 142 about portion 141 . with motor and geartrain assembly 136 disposed inside drive housing 130 , backlock assembly 134 may next be attached to the drive train . backlock assembly 134 , which performs the function of a brake , one - way clutch , or an overrunning clutch , is used to prevent external forces applied at the tips of fingers 142 from opening mechanism 100 when power is discontinued . in this manner , an object may remain grasped even if power to motor 104 is discontinued . backlock assembly 134 may include casing 144 , carrier 146 disposed within casing 144 , and output pinion 148 attached to backlock locking cam 150 , to provide output from assembly 134 to output planetary gear stage 164 . when rotated in a counter - clockwise direction in the illustration of fig8 cam 150 may be operative to drive / wedge rollers 152 up against the interior wall of casing 144 for preventing further rotation thereof . backlock assembly 134 may be pinned at four points ( not shown ) in casing 144 , and have a gear ratio of 5 . 3 : 1 for the embodiment shown . a pair of thrust washers 153 may be disposed over backlock output pinion 148 to promote free movement of fingers 142 when placed on bearing 138 . fingers 142 of grasping mechanism 105 may be formed as a single piece of metal and the like , and include integrally formed sleeve 154 that fits over bearing 138 disposed over axle portion 141 of drive housing 130 . in the illustrations of fig1 - 6 , 8 and 9 , fingers 142 may include a pair of tines 156 , 158 that respectively make up the index and middle fingers , and may include additional tines , as would apparent to those skilled in the art . sleeve 154 may carry planet gears 162 of final planetary gear stage 164 for mechanism 100 . fingers 142 may be kinematically linked to thumb 166 by means of link 168 having axle 170 disposed within aperture 171 in fingers 142 and axle 172 disposed in apertures 173 in thumb 166 , with each of the axles 170 and 172 further disposed within apertures 175 in link 168 . in this manner , opening / closing of fingers 142 acts to simultaneously drive thumb 166 to open / close , thus generating a wider opening width for grasping mechanism 105 . planetary gear stage 164 for driving prosthesis mechanism 100 may use six ( 6 ) planet gears 162 mounted on pins at locations 165 in the side of sleeve 154 . the use of six ( 6 ) planet gears 162 acts to distribute the load that must be handled by each gear , and thus allows mechanism 100 to withstand the high torques necessary to generate a high grip force . planet gears 162 may exert torque on internal gear 174 , which is fixed to frame 176 . in the embodiment shown , the gear ratio for planetary gear stage 164 stage may be 2 : 1 . moreover , in the embodiment of fig1 - 6 , 8 and 9 , although six planet gears 162 are shown , the number of gears may be increased or decreased as needed to adjust the grip force of fingers 142 and thumb 166 . drive housing 130 with sleeve 154 of fingers 142 disposed on bearing 138 may be attached to frame 176 by screws and the like through apertures 178 screwed into threaded apertures ( not shown ) on the back face of housing 130 . internal gear 174 of the final planetary gear stage 164 may be attached to frame 176 by screws and the like through apertures 182 screwed into threaded apertures ( not shown ) on the back face of gear 174 . thumb 166 may be attached to extension 177 of frame 176 by an axle 184 disposed into apertures 179 of extension 177 and corresponding aperture 181 of thumb 166 . spring clips 198 may be used to retain axle 184 within aperture 181 , as shown in fig3 . lastly , side plate 186 may be attached to the side of frame 176 to close off planetary gear stage 164 by screws and the like through apertures 190 screwed into threaded apertures 192 of frame 176 . it should be noted that the shaft of output pinion 148 of the backlock assembly 134 fits in aperture 188 in side plate 186 , as illustrated in fig8 . in the particular embodiment shown , prosthesis mechanism 100 may have a width of 2¼ ″ and the capability of providing a pinch force for 3 ″ fingers in excess of 10 ibs f at speeds of approximately 2 rads / sec , with the overall opening width of fingers 142 and thumb 166 being at least 3½ ″. those skilled in the art would appreciate in view of this disclosure that due to the compact nature of the resulting drive for mechanism 100 , the components that make up the drive train , such as motor and geartrain assembly 136 disposed inside drive housing 130 , bearing 138 with backlock assembly 134 attached to drive housing 130 and planetary gear stage 164 , have application , when used with frame 176 , fingers 142 and thumb 166 , as drive trains for other prosthetic components such as wrist rotators , wrist flexion units , or as drive units for multifunctional prosthesis devices . the operation and control of prosthesis mechanism 100 will now be described in detail . in normal operation , prosthesis mechanism 100 may be mounted on a prosthetic socket ( not shown ), in a conventional manner , that has been custom fabricated to fit the residual limb of a person with an amputation of the hand . a cosmetic glove and liner ( not shown ) may be pulled over mechanism 100 to give it a hand like appearance . as discussed in greater detail below , generally , power supplied to motor 104 at a first polarity causes fingers 142 and thumb 166 of mechanism 100 to open . power supplied to motor 104 in a reverse polarity causes fingers 142 and thumb 166 of mechanism 100 to close . the opening / closing speed of grasping mechanism 105 and the amount of gripping force may be proportional to the amount of voltage supplied to terminals 194 of motor 104 . in order to connect prosthesis mechanism 100 to a patient &# 39 ; s hand , as discussed above , a standard prosthetic interface ( not shown ) including a self - suspending silicone sleeve - socket may be used to attach mechanism 100 thereon . fingers 142 and thumb 166 may be incorporated into a silicone sleeve ( not shown ) made of nylon impregnated with laminating silicone so as to provide resistance to tear and enable various electrodes 196 connected to motor 104 to be pushed through the silicone sleeve and remain in place without tearing the silicone . electrodes 196 may then be screwed into their electronics , which may be located on the outside of the sleeve . the associated electrode electronics , wires , myocontroller , and synergetic controller may be fitted onto the dorsal surface of mechanism 100 for protection . as discussed above , an outer cosmetic glove may be rolled over this inner silicone sleeve socket . the silicone sleeve socket and cosmetic glove may then be rolled on and off together in a fashion similar that used to donning and doffing trans - tibial silicone suspension sleeves . the control system ( not shown ) for mechanism 100 may include proportional myoelectric control using electromyographic ( emg ) sites on a person , as is known in the art . preferably , mechanism 100 may utilize two emg sites which use the intrinsic muscles of the hand for control of mechanism 100 . for example , the opening of mechanism 100 may be controlled by an electrode over the lateral aspect of the hypo - thenar eminence , and closing could be provided by an electrode over the thenar eminence . thus , thinking about flexing / adducting the thumb would cause mechanism 100 to close while adducting the little finger would cause mechanism 100 to open . this kind of control might not always be possible , but even if only a single emg site is available , three - state control may be used . the power source for motor 104 may be a rechargeable 9v transistor battery so as to enable mechanism 100 to be recharged overnight . in employing transversely oriented drive system 102 discussed above , the present invention achieves the driving and space requirements for a partial hand mechanism , for which typically a minimal amount of space is available if an aesthetic result is to be achieved , with the drive system having a knuckle depth of only ¾ ″ and with a hand width of only 2¼ ″, for the particular embodiment illustrated . the use of a single motor 104 for mechanism 100 of the present invention provides simplicity over prosthesis devices that use two or more motors , with regard to the size , weight and the electronics necessary to coordinate the control of multiple motors . thus to summarize , prosthesis mechanism 100 of the present invention may be used with persons with amputations at or proximal to the level of the metacarpophalangeal joint ( i . e . persons who have lost one or all digits ( thumb and fingers ) but still retain a palmar surface of the hand , and persons with high - level ( i . e . above - elbow ) amputations where weight considerations are of paramount importance ). prosthesis mechanism 100 of the present invention is applicable in the prosthetic restoration of prehension in trans - metacarpal partial hand , and wrist disarticulation amputations , as well as trans - radial and trans - humeral amputations . although particular embodiments of the invention have been described in detail herein with reference to the accompanying drawings , it is to be understood that the invention is not limited to those particular embodiments , and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims .
an externally - powered prosthesis mechanism usable with persons with amputations at or proximal to the level of the metacarpophalangeal joint , as well as persons with high - level amputations . the prosthesis mechanism includes a grasping mechanism including a mechanically operable finger member and a mechanically operable thumb member kinematically linked to the finger member such that the grasping mechanism is disposed in respective opened and closed configurations when the finger member is respectively moved away from and toward the thumb member . the prosthesis mechanism further includes a drive system extending tangentially with respect to the grasping mechanism and including a motor operatively connected to drive at least one planetary gear stage , which is operatively connected to drive the grasping mechanism to the opened configuration when the motor is driven in a first direction and further drive the grasping mechanism to the closed configuration when the motor is driven in a second opposite direction .