Rencheng Wang

Kinematic and dynamic performance of prosthetic knee joint using six-bar mechanism

Six-bar linkages have been used in some prosthetic knees in the past years, but only a few publications have been written on the special functions of the mechanism as used in transfemoral prosthesis. This paper investigates the advantages of the mechanism as used in the prosthetic knee from the kinematic and dynamic points of view. Computer simulation and an experimental method were used in the investigation. The results show that the six-bar mechanism, as compared to the four-bar mechanism, can be designed to better achieve the expected trajectory of the ankle joint in swing phase. Moreover, a six-bar linkage can be designed to have more instant inactive joints than a four-bar linkage, hence making the prosthetic knee more stable in the standing phase. In the dynamic analysis, the location of the moment controller was determined for minimum value of the control moment. A testing prosthetic knee mechanism with optimum designed parameters was manufactured for experiments in the laboratory. The experimental results have verified the advantage revealed in the analyses.

Terrain identification for prosthetic knees based on electromyographic signal features

The features of electromyographic (EMG) signals were investigated while people walking on dif- ferent terrains, including up and down slopes, up and down stairs, and during level walking at different speeds. The features were used to develop a terrain identification method. The technology can be used to develop an intelligent transfemoral prosthetic limb with terrain identification capability. The EMG signals from 8 hip muscles of 13 healthy persons were recorded as they walked on the different terrains. The sig- nals from the sound side of a transfemoral amputee were also recorded. The features of these signals were obtained using data processing techniques with an identification process developed for the identification of the terrain type. The procedure was simplified by using only the signals from three muscles. The identifica- tion process worked well in an intelligent prosthetic knee in a laboratory setting.

Influence of Prosthetic Sagittal Alignment on Trans-Tibial Amputee Gait and Compensating Pattern: A Case Study

Abstract This study relates the gait asymmetry, residual limb comfort, and energy cost during walking and identifies a compensating pattern for the trans-tibial amputees when the prostheses are misaligned. One male subject with a trans-tibial amputation volunteered for the study. The knee joint moments at the prosthetic side, the phase symmetry index, and the interface pressures were discussed under three sagittal alignment settings. The results show that the subject changes the knee joint moment, gait symmetry, and interface pressure with a misaligned prosthesis to improve his comfort and movement during walking. A high-quality liner reduces the gait sensitivity to misalignment and enhances the amputees ability to compensate for misalignment. Since different people have different compensation patterns, more cases will be studied in future work.

An intelligent above-knee prosthesis with EMG-based terrain identification

Gait analyses show that knee moments are considerably different when walking on different terrain. To accommodate changing conditions, prostheses should provide a means for adjusting the knee moments by identifying conditions of the terrain. In this research, terrain identification is obtained by the use of electromyographic (EMG) signals that are used to control resistive moments of an above-knee prosthesis. Results from laboratory experiments demonstrate that the technique is effective for identification and adaptable to different terrain.

Effect of noise-enhanced on the balance control ability in older adults

Somatosensory function declines with age, and such changes have been associated with diminished motor performance. Noise input can enhance sensory and motor function. We tested the effects of the vibrating stimulation applied at the feet on balance control of 6 healthy elderly and 8 young volunteers. Balance performance was characterized using a FASTRAK System. We calculated four traditional measures of postural sway parameters and five stabilogram-diffusion analysis variables. Among the 14 participants, application of noise resulted in a reduction of seven of nine sway parameters in young participants and eight of nine sway variables in elderly participants. The results suggested that the imperceptible noise, when applied to the feet, could enhance the balance performance of healthy older adults. Therefore, using the noise-based devices may be an effective way to improve the balance control of elderly people.

Finite element analysis of a six-component force sensor for the trans-femoral prosthesis

It is significant to detect and analyze its mechanical property for the design of the artificial knee joint, especially for the design of an osseointegrated prosthetic limb. Since normal six-component force sensors are unsuitable for detecting the mechanical property of the lower limb prosthesis, a novel sensor is presented in this paper. It can be easily fixed between the artificial knee joint and the stump of the patient to detect the load condition during walking. The mathematic model of the sensor is analyzed, and strength check, stiffness design and the linearity of the sensor were studied with FEA. Finally, the Transmission Matrix is calculated. This kind of sensor can help us to get academic foundations for the designment and the evaluation of the limb prosthesis and its performance.

Simulation of the ligament forces affected by prosthetic alignment in a trans-tibial amputee case study

The aims of this study were to predict and explain the patterns of ligament forces in the stump of a left trans-tibial amputee during walking, and to study the effects of the prosthetic alignment. Musculoskeletal modeling and computer simulation were combined to calculate ligament forces. The prosthesis was aligned to be in optimal position for the subject and then changed by +/-6 degrees in the sagittal plane. The results showed most ligaments bearing the maximum tension forces around both heel-strike and toe-off. The PT force was the biggest in all of the ligaments which were studied. The load patterns of ACL and PCL were opposite in the gait cycle, but the load patterns of MCL and LCL appeared similar. The above results showed that the ligament forces increased at the incorrect alignment, because the incorrect alignment could break the relative translation of the femur and tibia, and that would generate the extra ligament strains. As a result, the ligament forces increased, and the long-duration fatigue occurred more easily. This finding suggests that the proper prosthetic alignment is very important for the normal activities of the stump ligaments.

DEVELOPMENT OF A TACTILE AND SLIP SENSOR CONTROLLED PROSTHETIC HAND SYSTEM

Supported by the latest sensor and microcontroller technologies, prosthetic hands have been widely used to reclaim the human functionaries. Among these, the most advanced prosthetic hand was controlled by the tactile and EMG singles. However, for a slippery object, attention has to be taken for the inexperienced users who need to control the shrinkage of the wrist flexor carefully. In this paper, the authors presented a prosthetic hand control system using PVDF film sensor to provide both tactile and slip force feedback signals to operate the hand. The PVDF film sensor used for this control system was specifically developed to detect both tactile and slip force between the prosthetic finger and object. The method of distinguishing two signals was described. A prototype system was constructed using a microcontroller to process the signal from the sensor and provide control signal to the motors operate the prosthetic hand. The test result of the prototype device shown that comparing with the one without sli...

Optimization of an unpowered energy-stored exoskeleton for patients with spinal cord injury

The paper describes a novel unpowered energy-stored exoskeleton (ES-EXO) for spinal cord injured patients in consideration of patients characteristics and injured levels. It proposed a method to optimize the energy-stored element to decrease the hip joint moment in walking. EMG patterns, ground reaction force and motion data from one participant with complete spinal cord injury at T10 were recorded. A combined human-ES-EXO model was built and the stored-energy element including locations and stiffness of springs were optimized in AnyBody Modeling System. Significant correlations between experimental and simulated muscle activations in without springs condition proved that the model was feasible. With optimized energy-stored elements, the hip flexion moment decreased by 37.2%, activations in abdominal muscles decreased and low back muscles slightly increased. The results suggest that ES-EXO could provide specific walking assistance for SCI patients through adjusting energy-stored elements according to patients characteristics.The paper describes a novel unpowered energy-stored exoskeleton (ES-EXO) for spinal cord injured patients in consideration of patients characteristics and injured levels. It proposed a method to optimize the energy-stored element to decrease the hip joint moment in walking. EMG patterns, ground reaction force and motion data from one participant with complete spinal cord injury at T10 were recorded. A combined human-ES-EXO model was built and the stored-energy element including locations and stiffness of springs were optimized in AnyBody Modeling System. Significant correlations between experimental and simulated muscle activations in without springs condition proved that the model was feasible. With optimized energy-stored elements, the hip flexion moment decreased by 37.2%, activations in abdominal muscles decreased and low back muscles slightly increased. The results suggest that ES-EXO could provide specific walking assistance for SCI patients through adjusting energy-stored elements according to patients characteristics.

The Investigation on sEMG of Lower Extremity When a Slip Occurs in Level Walking

The purpose of the present study was to determine the relationship between the surface electromyography (sEMG) variables and slip events using principal component analysis (PCA). Ten healthy young adults were required to walk on the oily surface on a self-selected comfortable pace. The sEMG signals of lower extremity muscles were recorded and analyzed, while kinematics data was recorded to assist slip definitions. When ten variables (seven in time domain and three in frequency domain) were considered in the PCA, the results indicated that 1) three most important principal components could explain more than 85% of the variation in the entire data set; 2) some variables should be especially noticed such as muscle power, the mean frequency, the median frequency and the amplitude amount exceeding the mean value