Abstract:
A gripper device comprising at least two portions which are coupled together and which can be moved towards one another to effect a gripping action and away from one another to effect a release action. An electrical motor is arranged to effect such movement, and a battery is connected to supply electrical current to the motor. A capacitor device is also connected to be capable of supplying electrical current to the electrical motor. A control device is arranged to cause the capacitor device to supply electrical current to the electrical motor after supply of electrical current to the electrical motor by the battery, to increase the strength of the gripping action.

Description:
TECHNICAL FIELD 
   The present invention relates to a gripper device comprising at least two portions which are coupled together and which can be moved towards one another to effect a gripping action and away from one another to effect a release action, an electrical motor arranged to effect such movement, and a battery connected to supply electrical current to the motor. 
   BACKGROUND ART 
   Such a gripper device has been used in a band prosthesis which the user can operate to grasp objects. A disadvantage in such a construction is that, in order to increase the strength of the gripping action once the two portions come into contact with the article which is being grasped, it is necessary to use expensive and cumbersome gearing. 
   SUMMARY OF THE INVENTION 
   The present invention seeks to obviate this drawback. 
   Accordingly, the present invention is directed to a gripper device having the construction set out in the opening paragraph of the present specification, further comprising capacitor means also connected to be capable of supplying electrical current to the electrical motor, and control means arranged to cause the capacitor means to supply electrical current to the electrical motor after supply of electrical current to the electrical motor by the battery, to increase the strength of the gripping action. 
   Advantageously, the gripper device further comprises sensor means having an output and arranged to issue a sensor signal at its output when the two portions are exerting a force beyond a predetermined threshold during a gripping action whilst the battery is supplying electrical current to the electrical motor, the control means have an input connected to the output of the sensor means and are arranged to cause the capacitor means to supply electrical current to the electrical motor upon receipt of a sensor signal. This increases the efficiency of the device by ensuring that the capacitor means are used as soon as the said two portions come into contact with the article which is grasped. 
   Advantageously, the battery is connected to charge the capacitor. The sensor means may be such as to detect a rise in the electrical current supplied by the battery to the electrical motor. This provides a relatively simple means of determining when the two portions are exerting a force owing to contact between the said two portions and an article which is being gripped. 
   Alternatively, the sensor means may comprise one or more pressure sensors arranged to provide a sensor signal when the said two portions come into contact with an article which is to be gripped. 
   Desirably, the gripper device is provided with end-of-movement detector means to detect when the said two parts cease to move relative to one another owing to the gripping action being completed with the article which is being gripped resisting further relative movement of the said two portions towards one another. 
   To avoid unnecessary loss of energy and undesirable heating up of the component parts of the gripper, it is desirable for the control means to be connected to the end-of-movement detector means and to be so constructed and connected that the control means stop the supply of electrical current from both the battery and the capacitor upon receipt of a signal from the end-of-movement detector means. 
   Selector means may be available on the control means to select current reversal to effect a release action. input means may be provided as part of the control means to enable the user to control the gripper device. 
   Preferably, the gripper device forms part of a hand prosthesis. 
   The capacitor means may comprise a single capacitor or a bank of capacitors. The or each capacitor may comprise a double layer capacitor. The or each capacitor is preferably a supercapacitor. The or each capacitor is preferably an electrochemical capacitor. Desirably, the or each capacitor has a capacitance equal to or greater than 0.1 F. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An example of a gripper device made in accordance with the present invention will now be described with reference to the accompanying drawings, in which: 
       FIG. 1  shows diagrammatically a a gripper device embodying the present invention incorporated in a hand prosthesis; 
       FIG. 2  shows a block circuit diagram showing diagrammatically the circuitry of the device shown in  FIG. 1 ; and 
       FIG. 3  shows a flow chart of the operation of the gripper device shown in FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a hand prosthesis  10  in which is incorporated a gripper device  12 . The gripper device  12  comprises a mounting frame or plate  14  secured rigidly to one end of a shaft  16 . Two rotary bearings  18  and  20  are fixed to the frame  14  spaced apart along an axis which is co-linear with the shaft  16 . A screw threaded rod  22  extends between the bearings  18  and  20  so as to be rotatable about that axis. 
   A nut  24  is threaded on this screw  22 . Two L-shaped members  26  and  28  are pivotably connected at their corners to the frame  14  at pivots  30  and  32  respectively, such that respective limbs  34  and  36  are slidably secured to the nut  24  whilst the other limbs  38  and  40 , respectively, of the L-shaped members  26  and  28  extend generally parallel to one another away from the shaft  16 . 
   Slots  42  and  44  are formed in the L-shaped members  26  and  28  where they are slidably attached to the nut  24  to facilitate such sliding whilst inhibiting rotation of the nut. 
   A motor  46  is secured to the shaft  16  in such a fashion as to be able to rotatably drive the screw threaded rod  22  about its axis. 
   It will be seen from  FIG. 1  that the limb  38  of the L-shaped member  36  is embedded in the digits  50  of the hand prosthesis  10 , the limb  40  of the L-shaped member  28  is embedded in the thumb  52  of the hand prosthesis  10 , and the shaft  16  is embedded in the wrist  54  of the hand prosthesis  20 . 
   A battery  56 , a capacitor  58  and a microprocessor  60  constituting control means of the hand prosthesis  10  are also provided in the wrist  54  of the prosthesis. 
   The manner in which the different electrical parts of the circuitry of the prosthesis shown in  FIG. 1  are connected, as well as certain other auxiliary parts of this circuitry, is shown diagrammatically in FIG.  2 . 
   Thus, as can be seen from  FIG. 2 , the battery  56  is connected to charge the capacitor  58 . Both the battery  56  and the capacitor  58  are connected to the motor  46  via switches  62  and  64 , respectively, switchable by a microprocessor  60 . 
   A sensor  66  provided adjacent to the battery  56  detects when the current supplied by the battery  56  to the motor  46  exceeds a certain threshold level, wherever it issues a threshold signal at its output. A connection as illustrated in  FIG. 2  from the sensor  66  to the microprocessor  60  enables that signal to be delivered to the microprocessor  60 . 
   A detector  68  is arranged to detect when the current supplied by the capacitor  58  to the motor  46  is sufficiently large to indicate that the limbs  38  and  40  have ceased to move towards one another at the end of a gripping action. A signal indicative of this condition is fed from the detector  68  to the microprocessor  60  by way of a connection therebetween. 
   The microprocessor  60  is provided with inputs  70  and  72  to enable the user to operate the hand prosthesis, for example by means of vestigial muscles in the stump to which the hand prosthesis is attached operating switching (not shown) to those inputs. 
   The manner of operation of the apparatus is shown in FIG.  3 . 
   Thus, the initial state  72  is in place with the hand prosthesis attached to the user&#39;s stump and the battery  56  fitted within the wrist part  54  of the prosthesis  10 . The microprocessor  60  is powered-up at step  74 , and the capacitor  58  is charged by the battery unit  56 . 
   Step  76  represents the arrival, of a signal at the input  70 . This causes the microprocessor  60  to change the setting of the switch  62  at step  77 , whereby the gripper device  12  is operated by the switching of the battery  56  to supply electrical current to the motor  46  to effect a gripping action by the gripper device  12 . 
   This brings the gripper device to step  78  in  FIG. 3  in which the limbs  38  and  40  move towards one another at the start of a gripping action, with the motor  46  being powered by the battery  56 . At step  80 , the gripping device  12  starts to encounter resistance to further gripping action by the article that is being gripped. As a result, the current supplied by the battery unit  56  to the motor  46  rises until a signal is triggered by a sensor  66  to the microprocessor  60 . Upon receipt of such a signal, the microprocessor  60  causes the setting of the switch  64  to be changed at step  82 , whereby an electrical current is delivered from the capacitor  58  to the motor  46  via the switch  64 . 
   A point is reached at step  84  when the motor  46  can no longer drive the limbs  38  and  40  any closer together even with the additional current provided by the capacitor  58 . This is indicated by the end-of-movement detector  68 , which detects when the current supplied by the capacitor  58  to the motor  46  exceeds a given threshold value. The detector  68  provides the microprocessor  60  with a signal accordingly. As a result, the microprocessor  60  issues signals to change the settings of the switches  62  and  64 , to prevent further current being supplied to the motor  46  from either the battery  56  or the capacitor  58 . Because of the screw-threaded rod and nut construction of the gripper device  12 , the grip of the gripper device  12  is not released at this stage. 
   Such release does not occur until step  86  when the user sends a signal to the input  72  of the microprocessor  60 , whereupon the switch  62  is switched by the microprocessor  60  to connect the battery  56  to the motor  46  for reverse drive. This occurs at step  88  in FIG.  3 . Again, upon indication from the sensor  66  when the gripper device  12  is fully open, the microprocessor  60  opens the switch  62  to stop further supply of current from the battery  56  to the motor  46 . This occurs at step  90  in FIG.  3 . The procedure then reverts to step  74  in  FIG. 3  to commence a further grip and release cycle when the user is ready. 
   The capacitor  58  may be a type DYNACAP double layer capacitor of 1F, being Part No. DZ-2R5D105N manufactured by Elna of Japan. Alternatively, the capacitor may be a 5F type ULTRACAP double layer capacitor of the B49100 series, being Part No. B4900-A1503-Q000, manufactured by Epcos of Germany. 
   Numerous variations and modifications to the illustrated design of gripper device may be made without taking the resulting construction outside the scope of the present invention. For example, a contra-rotating gear construction could be used to move the limbs  38  and  40  towards and away from one another instead of the screw-threaded rod and nut assembly shown in FIG.  1 . 
   It will be appreciated that the invention is not restricted to hand prosthesis but may be used for robots or indeed any other application where a gripping action is required. 
   Means (not shown) may be provided to restrict the maximum current available from the capacitor  58 , and means (not shown) may also be provided to limit the duration for which the capacitor  58  is connected to drive the motor  46 , thus prolonging battery life and limiting thermal stresses to the motor  46 . Such time limiting means may be used instead of the end-of-movement detector  68 . 
   The battery  56 , the capacitor  58  and the microprocessor  60  may be located more remotely from the hand, for example in an arm prosthesis, if space is not available in the hand prosthesis, for example if it is a child&#39;s hand prosthesis. 
   The battery  56 , capacitor  58  and microprocessor  60  may also be provided in a single battery pack suitable for retro-fitting in existing prostheses. 
   Means (not shown) may be provided to limit the duration of operation of the supply of electrical current to the electrical motor  46  by the battery  56  before the capacitor  58  is used for that purpose, instead of using the sensor  66 .