Abstract:
A hybrid prosthetic hand is detailed which is controlled via input from both sEMG signals, as well as mechanical control from the elbow and shoulder of an amputee. The device is equipped with mechanical fingers, which are driven by electrical motors, and controlled via microcontrollers. The mechanical fingers are designed to form a variety of shapes and provide variable force in accordance with the contextual desires of the amputee, which are conveyed to the device primarily through the movement of the shoulder and/or elbow of the amputee. The instructions sent to the mechanical fingers of the device by the shoulder or elbow is augmented by instructions provided via sEMG signals.

Description:
[0001]    This application is a non-provisional application of provisional patent application No. 61/717,630 filed on Oct. 23, 2012, and priority is claimed thereto. 
     
    
     FIELD OF THE PRESENT INVENTION 
       [0002]    The present invention is in the technical field of prosthetic devices. More particularly, the present invention is in the technical field of hand prosthetic devices using shoulder harness and electromyographic (EMG) based activation and control. 
       BACKGROUND OF THE PRESENT INVENTION 
       [0003]    Current statistics about trans-radial amputation indicates upper limb prosthetics is in high demands. A lot of effort has been placed on research dealing with advanced prosthetic devices. However, up to date there are no prosthetic devices available that mimic the full functionality of a human hand. There are multiple types of hand prostheses. In most cases these devices are controlled using a shoulder harness that allows the operator to capture shoulder or elbow movements and translate these into a mechanical opening and closing of a hook or clamp that is used to give some ability back to the amputee. Another type of prosthetic hand device is based on measuring surface Electromyographic (sEMG) signals to initiate the actuation of the prosthetic device. Since sEMG signals are spatially distributed, the sEMG probes pick up signals from other motor units stemming from different muscle groups. This phenomenon is called crosstalk, which is a major cause for the difficulty in interpreting the intended hand/finger motion. EMG signals are generated by the simultaneous firing of several motor units during muscle contraction. Before reaching the skin surface, the EMG signal passes through numerous layers of tissues, which leads to noise and interference in the signal acquisition. The random nature of the sEMG signal represents an added complexity in studying it. All of these issues make it rather complex to distinguish the content of the sEMG signal against noise and interference. 
         [0004]    Prosthetic devices have been developed with the aim of matching the human hand in terms of dexterity and adaptation capabilities. Prosthetic hands are often designed to equip a dexterous manipulator for pick-and-place tasks or full mechanical designs that use other motion of the body—typically shoulder or elbow motion—to create a gripping motion in prosthetic devices. Both types of devices have been shown to give some functionality back to an amputee. In manipulator pick-and-place devices, the prosthetic device looks and feels like the human hand and can create human hand like function. However, training and fitting of these devices is cumbersome and often times the amputee will part from using the device in as little as two years. Full mechanical design prosthetics provide robust designs that simplify the human hand function down to the simplicity of a simple hook that has the ability to pinch an object. These designs have become the fall back choice for most amputees. 
         [0005]    The devise that is described in this application is a hybrid version of the systems described above. It has both mechanical actuation functions, such as typical mechanical prosthetic devices possess with the dexterous manipulator, and actuation function controlled by the use of sEMG signals. The present invention has the ability to control hand motion by both types of actuation. This allows the amputee to us the mechanical controls/actuation to help train mussels when actuating the prosthetic with sEMG signals. It also allows the amputee to choose what type of actuation (sEMG, mechanical, or both at the same time) he or she desires for a particular task, making the system adaptive to the user. 
       SUMMARY OF THE PRESENT INVENTION 
       [0006]    The present invention is a hybrid prosthetic hand capable of controlling the motion set of a prosthetic device through sEMG signals as well as through the motion of the respective shoulder and elbow of the prosthetic hand user. 
         [0007]    The mechanical functions of the present invention are controlled by either a shrugging shoulder motion, elbow straitening or collapsing motion, or both. The forces provided by these motions are transferred to hand using a Bowden cable design. The operator can then chose what this motion will do in the hand function, allowing the system to adapt to the amputee&#39;s personal ability and desired task. 
         [0008]    The second type for controlling the prosthetic device is given by using the sEMG signals. In this mode, the present invention utilizes a hierarchical control structure, where classification of sEMG signals are used to infer the general motion set, and sEMG signals-motion as well as sEMG signal-force models are used to control the intricate motion of individual joints of the prosthetic device. 
         [0009]    A third option of controlling the prosthetic device is given by evoking both approaches described above at the same time as a hybrid mode, i.e. using the shoulder harness or elbow harness, in addition to the sEMG signal as control input for the prosthetic device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a depiction of the hierarchical control structure. 
           [0011]      FIG. 2  is a view of the upper level control of the hierarchical controller. 
           [0012]      FIG. 3  is a depiction of the lower level control of the hierarchical controller. 
           [0013]      FIG. 4  is a depiction of the mechanical input and function of the invention. 
           [0014]      FIG. 5  is a view of some of the advanced capabilities of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    The sEMG based control system uses a hierarchical architecture that utilizes two approaches to infer the intended motion for the prosthetic device. The “upper” level control is based on a classification scheme, where a set of sEMG sensor signals allow for categorizing what type of motion is intended by the user. With this information, the set of joints and links that are being controlled are identified. The second layer is the joint motion control layer. The control structure for this layer is such that individual joint positions and motions are directly controlled through a set of dynamic models representing the relationship between the sEMG signal and the joint motion. A second set of models is used to relate the intended finger tip forces with the measured sEMG signals. 
         [0016]    Referring to the invention given in  FIG. 1  the components of the hierarchical control architecture are depicted  1 . The system has a surface EMG sensor array  2 , amplification and filtering section  3 , the upper layer control system  4 , the lower level control system  5 , the activation block  6 , and the prosthetic hand device  7 . 
         [0017]    Referring now to the invention in more detail, in  FIG. 1  there is shown a hierarchical controller  1  having five sections, namely the surface EMG sensor array  2 , the amplification and filtering section  3 , the upper layer control system  4 , the lower level control system  5 , the activation block  6 , and the prosthetic hand mechanism  7 . The surface EMG sensor array  2  collects the skin surface electrical potential resulting from the human muscle activation. The sensors combine the signals based on the spatial location where the individual is located with respect to a muscle. The amplification and filtering  3  is performed by using a notch filter removing low and high frequency components from the acquired signal. In addition, in this stage  3 , amplification and rectification of the sEMG signal is performed. The upper layer control system  4  is responsible for additional signal processing to format the filtered sEMG signal to a normalized size, which is used to identify what type of motion the prosthetic hand user intends to perform. The lower level control system  5  defines the actual movement of the individual joints of the prosthetic. In addition, the lower level control system  5  is responsible of determining the intended finger forces to be generated by the prosthetic hand device  7 . The activation block  6  implements the joint motion and finger force commands by activating motors which drive the joints and generate torques and the resulting finger forces. 
         [0018]    In further detail, still referring to the invention of  FIG. 1 , the surface EMG sensor array  2  is designed by having a measure of an electrical potential between two points on the skin, with respect to a reference point, commonly placed at the outer part of the elbow. The two point measure is on the skin surface in the vicinity of the respective skeletal muscle responsible for a particular motion of a finger or set of fingers. The amplification and filtering  3  is designed by using amplifier circuitry and filtering circuitry. The rectification is performed as well using an amplification circuitry. The upper layer control system  4  and lower level control system  5  are embedded into a microcontroller. The activation block  6  is constructed by using electric motors with cabling to the individual joints of the prosthetic hand device  7 . 
         [0019]    Referring now to  FIG. 2 , the upper level control  4  is structured by a set of sequential processes. The sEMG signal obtained from the filtering unit  3  is processed by the signal processing stage  8 , and mapped by the signal mapping stage  9 . The mapped signal is submitted to the compare stage  11  that utilizes a classification table  10 . This is then used in the motion set determination  12  stage. 
         [0020]    In more detail, still referring to the invention in  FIG. 2 , the signal processing stage  8  utilizes a number of mathematical operations to break down the filtered, rectified and amplified sEMG signal. The outcome of this process is than normalized in amplitude. The normalized signal is then mapped by the mapping stage  9  to classes of hand and finger motions. The outcome of the signal mapping stage  9  is compared in the compare stage  11  with the classification table  10 . Based on the comparison  11 , a motion set determination  12  is made. 
         [0021]    In further detail, still referring to the invention of  FIG. 2 , the upper level control  4  is implemented by using a microcontroller. The stages of signal processing  8 , mapping  9 , compare  11 , and motion set determination  12  is programmed in equation form. The classification table  10  is stored in the microcontroller memory in tabular format. 
         [0022]    Referring now to  FIG. 3 , the lower level control  5  is composed of three stages, namely a motion intend stage  14 , a model mapping stage  13 , and a motion control  15  as well as a force control stage  16 . 
         [0023]    In more detail, still referring to the invention of  FIG. 3 , the lower level control system  5  utilizes the information obtained from the upper level control  4  and the resulting motion determination set  12  to determine the motion intend stage  14 . This stage  14  determines which joints and which fingers are being controlled. This information is then used in the mapping stage  13  of the lower level control system  5  to map the motions and forces to individual equations. These equations relate the dynamic relationship between the measured and processed 8 sEMG signal and the actual finger motion and finger forces. The finger/joint motions are determined by the motion control stage  15 , while the finger forces are determined by the force control stage  16 . The motion control stage  15  and the force control stage  16  drive the electric motors of the activation block  6 . 
         [0024]    In further detail, still referring to the invention of  FIG. 3 , the lower level control  5  is implemented by using a microcontroller. The stages of motion intend stage  14 , the model mapping stage  13 , the motion control stage  15  and force control stage  16 , are programmed in equation form. 
         [0025]    Referring to the invention given in  FIG. 4 , the primary control input for the mechanical control  21  of the prosthetic hand device  7  are shoulder motions  25  and elbow motions  17 . Some of the shoulder motions that are incorporate in the mechanical control are based on protraction  18 , and retraction  19 , where the shoulder blades  20  move in opposite directions. Some of the resulting prosthetic hand  7  motions are open hand  22 , closed hand with thumb up  23 , and grip with thumb outside  24 .  FIG. 4  details the depiction of one of the mechanical fingers  28  of the present invention  7 , which contains tension  26  and loosening cables  27 . 
         [0026]    In more detail, still referring to the invention of  FIG. 4 , the mechanical control  21  of the prosthetic hand device  7 , is based on the motion created when the elbow  17  is rotated. This motion is transferred to the prosthetic hand device  7  via dual cables  26  and  27 . These cables create a pull-pull affect that allows one of the cables  26  and  27  to be tensioned independent of the rotation of the elbow  17 . When the elbow  17  is rotated in one direction cable  26  is tensioned and cable  27  is loosened. When the elbow  17  is rotated in the opposite direction, cable  27  is tensioned and cable  26  is loosened. Similar control of a different motion set of the invention  7  can be achieved using the shoulder motion  25 . As the amputee moves their shoulders  20 , the motion is captured with a harness  29  and converted into tension in the Bowden cables  26 ,  27 . The resulting force is then transferred into the designed motion in the prosthetic hand device  7  based on operator input. For example, the operator can go from an open hand  22  to a closed hand with thumb up  23  by moving their shoulders. All simple motions of the prosthetic hand device can be created by the combination of the three input methods, shoulder motion, elbow rotation, and sEMG signal. 
         [0027]    Referring now to  FIG. 5 , two particular motions of the prosthetic hand device  7  are depicted. The lateral motion  30  and the light tool motion  31  are depicted. The example object for the tool motion is a small cylinder  32 . 
         [0028]    In more detail, still referring to the invention of  FIG. 5 , the first motion, lateral  30  is achieved using the hybrid control composed of the hierarchical controller  1  and mechanical controller  21 . In the same fashion, the light tool motion  31  can be achieved, i.e. using the hierarchical controller  1  and mechanical controller  21 . 
         [0029]    While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention as claimed.