Browsing by Author "Weir, Richard F."
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Item Open Access A MYOELECTRICALLY CONTROLLED PROSTHETIC HAND FOR TRANSMETACARPAL AMPUTATIONS.(2002) Weir, Richard F.; Grahn, Edward C.We have developed a new externally-powered, myoelectrically controlled partial hand prosthesis that is suitable for fitting those persons with amputations at or more proximal to the level of the metacarpophalangeal (MCP) joint. This hand mechanism is capable of reasonable pinch forces (12 lbsf) and fast opening and closing (2 rads/sec). In a partial hand mechanism there is very little space available for the drive mechanism if an aesthetic result is to be achieved and any residual motion of the wrist is to be preserved. The challenge is to be able to fit all the requisite mechanisms and electronics in the highly confined volume that remains after accommodating the residual limb and still have reasonable performance.Item Open Access ANALYSIS WINDOW INDUCED CONTROLLER DELAY FOR MULTIFUNCTIONAL PROSTHESES(2008) Farrell, Todd; Weir, Richard F.Many upper-limb, multifunctional prosthesis controllers analyze fixed segments of EMG data collected from the residual musculature in an attempt to discern the intended movement of the user. However, many researchers have designed controllers with little or no regard for the delay the controller will introduce when operated in real-time. If the delay is too large the prosthesis will feel sluggish and performance will suffer. Several attributes of the classifier affect the delay it will create. State-based pattern recognition classifiers typically collect EMG data in ‘analysis windows’ whose length will be defined as Ta. Class decisions based upon these collected data cannot be generated instantaneously because time is required to both record and then process the EMG. The processing time ( ) is the time from the completion of data collection until a class decision is made. The length of the window being analyzed (Ta), the microprocessor used to perform the calculations, as well as the number of channels and the number and type of features being extracted will determine . Thus must be determined empirically for each classifier. Both overlapped and disjoint analysis windows have been employed in experimental prosthesis controllers. Windows can be overlapped if the analysis windows are incremented by some amount of time (Tnew) that is greater than the processing time ( ). Overlapping the windows increases the density of class decisions which will allow majority voting. Majority voting is a post-processing strategy that has been shown to increase classifier accuracy [1-2] by analyzing the current class decision along with the n-1 previous class decisions and selecting the class that occurs most frequently in those n decisions as the controller output. The authors recently completed a study which found that 100 ms was the maximum amount of time that could be used to collect and analyze EMG signals (to maximize the classification accuracy) without substantially degrading the performance of the prosthesis [3]. This finding implies that the values of Ta, Tnew, n and should be set to ensure that the amount of time from the user’s intended change in class until the change in the output of the controller (i.e., the controller delay or ‘D’) is less than 100 ms. The goal of this work is to quantitatively define how each parameter (Ta, Tnew, n and ) affects the maximum delay as well as the range of delays introduced by the controller. Four controller configurations were examined including those that use overlapped or disjoint windows as well as those that did or did not use majority voting. Note: the data are collected with a sampling period of Ts and a frequency of 1/Ts Hz.Item Open Access DESIGN OF A CLINICALLY VIABLE MULTIFUNCTIONAL PROSTHETIC HAND.(2002) Weir, Richard F.We are in the process developing a new multifunctional hand mechanism in the hopes of providing a new mechanism that will have superior function over today’s single degree-offreedom (DOF) mechanisms and yet be clinically viable. However, this is no easy task. There have been a multitude of multifunctional hands built, all of which have failed to find clinical application as an artificial hand replacement. During the 60s and 70s much time, effort, and money was invested in the development of externally-powered multi-functional hand-arm systems. Prime among these being the Edinburgh Arm [1], the Boston Arm [2,3], the Philadelphia Arm [4,5], the Belgrade hand [6,7], the Sven Hand [8], the Utah Arm [9]. However while many of today’s commercially available externally-powered elbow systems (Boston Elbow – Liberating Technology Inc [10], NYU Elbow – Hosmer-Dorrance, and Utah Elbow – Motion Control [11]) owe their origins to this era of upper-limb research no multifunctional hand mechanisms made the transition from the Laboratory into clinical practice.Item Open Access Design Of A Myoelectric Controller For A Multi-Dof Prosthetic Hand Based On Principal Component Analysis(2011) Segil, Jacob; Weir, Richard F.; Reamon, DerekThe goal of this investigation is to develop a multi-degree of freedom (DOF) prosthesis controller that uses myoelectric signals as control inputs and which has been dimensionally optimized using Principal Component Analysis (PCA). Currently available multi-DOF hand prostheses cannot be fully utilized because there are fewer control inputs than the number of degrees of freedom (i.e. – joints) that need to be controlled. Based on work from the field of neuroscience it has been shown that grasping is a ‘low dimensional’ task. Santello et al. used PCA to quantify the principal components (patterns of joint movements) involved in grasping. It was found that grasping tasks involving a number of everyday items could be described by only two principal components. This implies that multi-DOF hand postures can be controlled using only two degrees of control. Therefore, a PCA-based myoelectric prosthetic hand controller can drive grasping postures with only two independent control sites. This is an encouraging finding since current clinical practice indicates two, or three, independent control sites can be located on the residual limb of a typical person with a transradial amputation. The following paper discusses the design and development of a PCA-based myoelectric prosthetic hand controller. Also, the results of a validation experiment are shared.Item Open Access DEVELOPMENT OF A CLINICALLY VIABLE MULTIFUNCTIONAL HAND PROSTHESIS(2008) Mitchell, Michael; Weir, Richard F.We have developed a new multifunctional hand mechanism in the hopes of providing a new mechanism that will have superior function over today’s single degree-of-freedom (DOF) mechanisms and yet be robust enough to be clinically viable. There have been a multitude of multifunctional hands built, all of which have failed to find clinical application as an artificial hand replacement. Bolstered by advancements in motor and robotic technology, the past two decades has seen significant effort, and money invested in the development of externally-powered multi-functional hand systems [4, 7,8,9,10,11]. However while many of today’s commercially available externally-powered systems owe their origins to modern upper-limb research, save for the Touch Bionics hand [14], no multifunctional hand mechanisms have made the transition from the Laboratory into clinical practice.Item Open Access Development of a Clinically Viable Multifunctional Underactuated Hand Prosthesis Using Differential Transmissions(2008) Clark, Stephen; Weir, Richard F.We are now in the process of developing a multifunctional prosthetic hand that uses six commercially available DC electric motors and transmissions in an under-actuated system to drive 16 degrees of motion. Providing greater finger dexterity as well as a wide range of major prehension patterns may require many degrees of freedom. It has been shown that increasing the number of actuators to increase the degrees of freedom can result in a complicated system with many parts which can be heavy, unreliable and costly, and therefore clinically unviable. This paper presents a design that limits the number of motors needed in the device by utilizing differentials transmissions. By limiting the number of actuators and other mechanical components, complexity is reduced and reliability is increased while still achieving a high degree of motion. The function of the differential allows for adaptive grasping through the mechanical self-adaptability of the actuators. Each digit is independently driven by one motor and transmission with the power being distributed to each of the three joints by way of a differential transmission and kinematic linkages, with an additional degree of freedom added to the thumb for palmer rotation. We believe that this will produce a highly functional prosthetic device that will be able to achieve all major prehension patterns as well as having a degree of individual finger dexterity.Item Open Access EVALUATION OF A PROTOTYPE ELECTRIC-POWERED PARTIAL-HAND PROSTHESIS(2005) Heckathorne, Craig W.; Weir, Richard F.A prototype partial hand mechanism has been developed for fittings at the trans-metacarpal level. Subjects selected for evaluation of the prototype device have absence of all fingers of the affected hand, all or some portion of the metacarpals present, at least one active intrinsic hand muscle, and relatively unimpaired wrist movement. The presence of one or two intrinsic hand muscles allows for proportional myoelectric control without resorting to forearm muscles that would be recruited during wrist positioning. The mechanism is suspended from the hand structure with a custom silicone socket. The socket extends no more proximal than the styloids so that the physiological wrist motion is unencumbered, allowing for orientation of the hand in a near physiological manner.Item Open Access Implantable Myoelectric Sensors (IMES)(2005) Weir, Richard F.; Troyk, P.R.; DeMichele, G.; Lowery, M.; Kuiken, T.We are developing a multi-channel/multifunction prosthetic hand/arm controller system capable of receiving and processing signals from up to sixteen Implanted MyoElectric Sensors (IMES). The appeal of implanted sensors for myoelectric control is that EMG signals can be measured at their source providing relatively cross-talk free signals that can be treated as independent control sites. Therefore the number of degrees-of-freedom that can be simultaneously controlled and coordinated in an externally-powered prosthesis will be greater than with surface EMG or mechanical control sites. To explore the issue of intra-muscular signal independence and the ability to control them, human subject experiments have been performed in which intra-muscular EMGs were obtained. Choice of muscles was based on a desire to be able to independently control a two degree-of-freedom (DOF) wrist, and 3 DOF prosthetic hand. This paper provide our result so far.Item Open Access MULTIFUNCTION PROSTHESIS CONTROL USING IMPLANTED MYOELECTRIC SENSORS (IMES)(2008) Schorsch, Jack F.; Maas, Huub; Troyk, Phil R.; DeMichele, Glen A.; Kerns, Douglas A.; Weir, Richard F.Persons with recent hand amputations expect modern hand prostheses to function like intact hands. Current stateof- the-art electric prosthetic hands are generally single degree-of-freedom (opening and closing) devices that are controlled using only two muscle signals. As a result, most state-of-the-art devices fail to meet user’s expectations and tend to be under-utilized or rejected. [2]. In this paper we describe the development of implantable myoelectric sensors (IMES) that will allow us to record myoelectric signals from up to 32 muscle sites. Most of the eighteen extrinsic muscles of the hand remain intact following hand amputation. The goal of this work is to develop the means to control for a multi-degree-of-freedom prosthetic hand that is capable of true dexterous manipulation. The development of IMES allows us to create many more control sources than has been possible in the past, greatly increasing the number of degrees-of-freedom we can control in a prosthetic system.Item Open Access Neurofuzzy Logic as a Control Algorithm for an Externally Powered Multifunctional Hand Prosthesis(2002) Ajiboye, Abidemi Bolu; Weir, Richard F.; Heckathorne, Craig W.; Childress, Dudley S.We propose an algorithm based upon neurofuzzy technology. We believe that because of the inherent “fuzziness” of human activity, a control algorithm based on fuzzy logic may have advantages for multifunctional prosthesis control. We seek an acceptable compromise between the number of electrode sites used and processing complexity, and thereby desire not more than three to four control sites to control three to four DOF. This approach delivers more information to the system and, by using fuzzy logic, reduces the complexity of the processing.Item Open Access NON-BACKDRIVABLE SERIES ELASTIC ACTUATOR FOR USE IN A PROSTHETIC ELBOW(2005) Sensinger, Jonathon W.; Weir, Richard F.Commercially available prosthetic elbows have stiff actuators (motors) that are only capable of motion (position or velocity) control. In an attempt to mimic human physiology while accommodating prosthetic demands, a non-backdrivable motor has been created that is less stiff and capable of impedance control. Impedance control responds well to different environments and the presence of perturbations. Results have shown that this motor, though non-backdrivable to ensure sufficient battery supply, is still capable of exerting sufficient torque, speed, and frequency bandwidth to be useful in prosthetics. In the future, patients will be fit with this type of motor to examine if they objectively and subjectively perform better using this more physiologically appropriate prosthesis.Item Open Access PHANTOM LIMB SENSORY FEEDBACK THROUGH NERVE TRANSFER SURGERY(2005) Sensinger, Jonathon W.; Kuiken, Todd; Farrell, Todd R.; Weir, Richard F.Commercially used prostheses are essentially open-loop devices and provide little or no feedback to the amputee as to how much force they exerting with the terminal device, despite numerous attempts to provide closed loop control in prosthetics [1]. Providing pressure feedback clearly has great value for function of the prosthesis—the goal is for the amputee to ‘feel’ what they are holding. Indirect pressure feedback has been attempted by methods including vibration [2] and functional electrical stimulation [3, 4]. The information contained in these forms of feedback is not in the same modality as that which they sense. As a result, while providing information to the user, it is likely that it comes at the cost of increased mental load and low level of information transfer [5]. Patterson and Katz [6] have obtained better qualitative feedback with pressure to pressure feedback than with pressure to vibratory or electrical stimulation feedback, offering support for this suggestion. An adaptive process is still involved since the subject must learn to associate pressure in one area with pressure in another area. Ideally, the sensory nerve endings of the amputated area need to be stimulated in direct correlation to the function of the prosthesis. The recent work of Kuiken [7] has made this concept feasible by the use of targeted reinnervation. The potential thus exists for the subject to feel as if touch, pressure and even hot or cold temperatures are being exerted on their hand. This study will examine the potential of intuitive pressure feedback.Item Open Access Powered Humeral Rotator for Persons with Shoulder Disarticulation Amputations(2005) Weir, Richard F.; Grahn, Edward G.There are no commercially available externally-powered humeral rotators. This paper describes the development of a new powered-humeral rotator based on an LTI Boston Elbow II drive train suitable for use on persons with short transhumeral amputations or shoulder disarticulation amputations. An initial fitting of the device as part of a six motor arm demonstrated the efficacy of the device and anecdotal evidence suggested the patient found the device to be of benefit.Item Open Access REAL-TIME COMPUTER MODELING OF A PROSTHESIS CONTROLLER BASED ON EXTENDED PHYSIOLOGICAL PROPRIOCEPTION (EPP)(2002) Farrell, Todd; Weir, Richard F.; Heckathorne, Craig W.; Childress, Dudley S.Proprioception utilizes the physiological components of the nervous and musculoskeletal systems to allow an individual to sense the position of their limbs subconsciously. By providing a rigid connection to an object this proprioceptive ability can be extended to the object and allow the user to sense the spatial location and orientation of these objects with respect to his or her body. This concept explains how a person can use a tennis racquet to hit a tennis ball without having to observe the position of the racquet during their swing or the way a blind person uses a long cane to ‘feel’ the location of objects in their surroundings. Body-powered prostheses take advantage of this proprioceptive ability by relating the motion and position of the prosthesis to the motion and position of an intact joint of the amputee via the control cable. However, most externally powered prostheses do not have any mechanism with which to provide feedback regarding the state of the prosthesis to the proprioceptive system of the amputee. In these cases the amputee must rely on vision and other incidental sources of feedback such as motor whine and socket pressure to control their prostheses and this may place a significant cognitive load on the user.Item Open Access Removal of ECG Artifacts from Myoelectric Prosthesis Control Signals(2005) Zhou, Ping; Lowery, Madeleine M.; Weir, Richard F.; Kuiken, Todd A.We investigated removal of electrocardiogram (ECG) artifacts from the myoelectric prosthesis control signals, taken from the reinnervated pectoralis muscles of a patient with bilateral amputations at shoulder disarticulation level. The performance of various ECG artifact removal methods including high pass filtering, spike clipping, template subtracting, wavelet thresholding and adaptive filtering was presented. In particular, considering the clinical requirements and memory limitation of commercial prosthesis controllers, we further explored suitable means of ECG artifact removal for clinical application.Item Open Access SURFACE VS. IMPLANTED EMG FOR MULTIFUNCTIONAL PROSTHESIS CONTROL: PILOT RESULTS(2005) Farrell, Todd R.; Weir, Richard F.It has been hypothesized that, due to the potential to both provide a larger number of independent control sites and selectively record from forearm muscles (in particular the deep muscles), intramuscular EMG should be advantageous for multifunctional prosthesis control [1]. The use of surface electromyograms (EMG) to control a multiple degree-of-freedom prosthesis has been investigated for several decades. A variety of approaches have been employed with groups using different numbers of input channels [2-3], feature extraction methods [3-6] and pattern recognition algorithms [3,7-8]. While much work has been done, all of these efforts have used surface EMG as the control signal. Only a single preliminary study was found that acquired intramuscular EMG for prosthesis control [9]. Admittedly, the technology has not existed for chronic intramuscular recordings to be clinically feasible for prosthetic use. The Implantable Myoelectric Sensor (IMES) that is being developed at the Northwestern University Prosthetic Research Laboratory will make chronic intramuscular recordings clinically feasible [10]. We hypothesize and hope to demonstrate that by utilizing intramuscular EMG it will be possible to substantially increase classification accuracies of multifunctional prosthesis controllers (i.e., increase the percentage of the time that the controller can correctly predict the intended movement of the user). If a substantial increase in classification accuracy is demonstrated, this will justify the invasiveness of using these devices. However, if similar accuracies can be obtained from surface recordings then there will be little justification for pursuing these devices for transradial prosthesis control purposes.Item Open Access THE EFFECT OF CONTROLLER DELAY ON BOX AND BLOCK TEST PERFORMANCE(2005) Farrell, Todd R.; Weir, Richard F.; Heckathorne, Craig W.Multifunctional prosthesis controllers have shown higher classification accuracies when EMG feature extraction and pattern recognition are performed on time windows of longer duration [1] (see figure 1). However, there is a limit to the time over which EMG data can be collected and analyzed before the delay causes the control of the prosthesis to become cumbersome. While no one has objectively examined the impact of controller delays on performance, the controller delay that can be present before prosthesis control degrades has been debated. Childress and Weir [2] believe that controller delays should be kept below 50 ms to ensure that these delays are imperceptible to the user. However, another group has stated that delays as large as 300 ms are not perceivable by the user [3-4] and, while they have not commented on the effect of these delays on performance, they have stated that a 300 ms delay is acceptable for control of a prosthesis. The desired controller delay may affect the choice of signal processing and pattern recognition algorithms that can be utilized. Thus it would be beneficial to establish this value for future investigations. Experiments were designed to find the longest period of delay that does not significantly degrade prosthesis performance and can thus be dedicated to EMG collection and processing.Item Open Access THE EFFECTS OF ELECTRODE IMPLANTATION AND TARGETING ON PATTERN CLASSIFICATION ACCURACY FOR PROSTHESIS CONTROL(2008) Farrell, Todd; Weir, Richard F.Many researchers have attempted to recognize patterns of muscle activity associated with different movements of the phantom limb and link these patterns to movements of the prosthesis. Researchers have examined a variety of different classifiers and extracted complex features from the electromyographic (EMG) signals to maximize classification accuracy. However, nearly all of these efforts used surface electrodes. Surface electrodes are advantageous because they are cheap, non-invasive and have a large pickup area. Extracting features from these recordings can allow the classifier to parse out the activity from the different muscles that sum together to produce the myoelectric signal and may increase the information available to the classifier. Alternatively, intramuscular electrodes may be advantageous for multifunctional prosthesis control because they record focally from deep muscles, provide consistent recording sites as the user changes arm orientation or dons and doffs the prosthesis and reduce crosstalk. However, only two groups have investigated intramuscular EMG for pattern recognition based control [1- 4] and only Hargrove, et al. [1] compared surface and intramuscular electrodes, recording from sixteen untargeted surface and six targeted intramuscular channels. As well as almost solely utilizing surface electrodes, previous studies in pattern recognitionbased multifunctional prosthesis control have either targeted the electrodes to specific muscles or used untargeted electrode arrays. However, no previous work has attempted to determine which approach is superior by directly comparing targeted and untargeted electrodes. Untargeted electrodes are simpler to implement and are preferable for both intramuscular and surface recordings. Socket fabrication can be simplified if the surface electrodes only need to be arranged in an array instead of targeted to specific muscles. Additionally, targeting implantable sensors (such as the IMES [5]) to specific muscles is not a trivial task and would likely require approaches such as ultrasound guidance to properly orient the implants in specific muscle bellies. Given that the effect of either electrode targeting or electrode implantation has rarely been examined, the goals of this work were to compare the classification accuracies of multifunctional prosthesis classifiers that use either surface or intramuscular EMG as well as those that use either targeted and untargeted electrodes. Further details are available in Farrell and Weir [6].