Kebin Yuan

Fuzzy-Logic-Based Terrain Identification with Multisensor Fusion for Transtibial Amputees

Terrain identification is essential for the control of robotic transtibial prostheses to realize smooth locomotion transitions. In this paper, we present a real-time fuzzy-logic-based terrain identification method with multisensor fusion. Five locomotion features, including the foot inclination angle at the first strike, the shank inclination angle at the first strike, foot strike sequence, the foot inclination angle at mid-stance, and the shank inclination angle at toe-off, are used to identify different terrains and terrain transitions. These features are measured by the fusion of two triaxis gyroscopes, two triaxis accelerometers, two force sensitive resistors, and a timer, which can be embedded into the prosthesis. Based on these features, a fuzzy-logic-based identification method is proposed to identify five terrains: level ground, stair ascent, stair descent, ramp ascent, and ramp descent. Moreover, a transition constraint function is developed to improve the identification performance. The execution time of the identification method is 0.79 ms ± 0.02 ms (mean ± standard error of mean) and continuous terrain identification results show that the method can be operated online in real time. The average identification accuracy of 98.74% ± 0.32% is obtained from experiments with six able-bodied and three amputee subjects during steady locomotion periods (no terrain transition). In locomotion transition periods, all the eight transitions we studied are correctly identified and the average identification delay is 9.06% ± 3.46% of one gait cycle.

Finite-State Control of Powered Below-Knee Prosthesis with Ankle and Toe

Abstract Current finite-state control strategies for powered below-knee prosthesis, though effective to the normal gait, can not eliminate the disturbance of abnormal gaits such as slip and stamp. In addition, toe joint is not taken into consideration. This paper presents a finite-state control strategy for a powered below-knee prosthesis with ankle and toe. We first introduce the concerned prosthesis prototype in detail. By dividing the walking gait with toe and joint into more states and setting stricter transition conditions, the gait identification becomes more accurate and gait disturbance such as slip and stamp can be eliminated. Experimental results show that the proposed method improves the accuracy of gait identification. It makes the motion of the prosthesis more natural and provides better bases for control.

Walk the Walk: A Lightweight Active Transtibial Prosthesis

Active transtibial prostheses that can overcome the deficiencies of passive prostheses are gaining popularity in the research field. In addition to the advantages in joint torque and gait symmetry, terrain adaptation and total weight are other benefits that can help push active prostheses into the commercial market. In this article, we present a lightweight robotic transtibial prosthesis with damping behaviors for terrain adaptation. The proposed prosthesis, which mainly consists of a low-power motor, weighs only 1.3 kg, excluding the battery. It focuses on terrain adaptation instead of providing positive work at the stance phase. A damping control strategy is proposed to enable the prosthesis to manipulate the ankle impedance during stance with little power consumption. Experiments with three amputee subjects using the robotic prosthesis on different terrains show similar angle trajectories to the intact limb during the controlled flexion (CF) period as well as improved gait symmetry and walking stability compared with the robotic prosthesis in the maximal damping mode. The average power consumption of the prosthesis during one gait cycle is around 3.5 W, and a 0.28-kg rechargeable lithium-ion (Li-ion) battery can sustain a usage duration of more than 12 h or 20,000 steps.

Finite-state control of a robotic transtibial prosthesis with motor-driven nonlinear damping behaviors for level ground walking

This paper presents a finite-state control strategy for a robotic transtibial prosthesis to realize level ground walking with controlled damping behaviors in the ankle joint. We use a motor-driven method to generate braking torque to realize nonlinear damping behaviors. The controller performs damper control for the stance phase and angle control for the swing phase. We design and construct a robotic transtibial prosthesis prototype to evaluate the effectiveness of the proposed control strategy. One transtibial amputee subject participated in the experiments. By using the proposed finite-state control method, the robotic prosthesis can successfully mimick the behaviors of normal limb. The damping control strategy enabled the ankle to dorsiflex smoothly.

A fuzzy logic based terrain identification approach to prosthesis control using multi-sensor fusion

This paper presents a fuzzy logic based terrain identification method using multi-sensor fusion for powered prosthesis control. Five locomotion features including rising time of ground reaction force, sequence of foot strike on ground, foot inclination angle during stance, shank inclination angle at toe-off and maximal shank inclination angle during swing are selected to identify different terrains. These features are measured by fusion of two gyroscopes, two accelerometers, two force sensitive resistors and a timer. Based on the features, a fuzzy logic identification method is developed to identify level-ground, stair ascent, stair descent, upslope and downslope online in real time. Average identification accuracy higher than 97.5% is obtained in experiments of five able-bodied subjects and a transtibial amputee. Continuous identification results show the prospect of using the proposed method to realize real-time terrain identification of powered prostheses.

A realtime locomotion mode recognition method for an active pelvis orthosis

This paper presents a realtime locomotion mode recognition method for an active pelvis orthosis. Five locomotion modes, including sitting, standing still, level-ground walking, ascending stairs, and descending stairs, are taken into consideration. The recognition is performed with locomotion information measured by the onboard hip angle sensors and the pressure insoles. These five modes are firstly divided into static modes and dynamic modes, and the two kinds are classified by monitoring the variation of the relative hip angles of the two legs within a pre-defined period. Static states are further classified into sitting and standing still based on the absolute hip angle. As for dynamic modes, a fuzzy-logic based method is proposed for the recognition. Two event-based locomotion features, including the hip joint angle at the first foot-strike and the center of foot pressure at the first foot-strike are used to calculate the membership of different modes based on the membership function, and the mode with the maximal membership is selected as the target mode. Experimental results with three subjects achieve an average recognition accuracy of 99.87% and average recognition delay of 18.12% of one gait cycle.

Fuzzy-logic-based hybrid locomotion mode classification for an active pelvis orthosis: Preliminary results

In this paper, we present a fuzzy-logic-based hybrid locomotion mode classification method for an active pelvis orthosis. Locomotion information measured by the onboard hip joint angle sensors and the pressure insoles is used to classify five locomotion modes, including two static modes (sitting, standing still), and three dynamic modes (level-ground walking, ascending stairs, and descending stairs). The proposed method classifies these two kinds of modes first by monitoring the variation of the relative hip joint angle between the two legs within a specific period. Static states are then classified by the time-based absolute hip joint angle. As for dynamic modes, a fuzzy-logic based method is proposed for the classification. Preliminary experimental results with three able-bodied subjects achieve an off-line classification accuracy higher than 99.49%.

Segmented Foot with Compliant Actuators and Its Applications to Lower-Limb Prostheses and Exoskeletons

In recent years, there has been an increasing interest in the functionality of the foot in human normal walking. Different from the existing methods that represent the foot as a single rigid bar, several multi-segmented foot models have been studied to evaluate the effects of the segmented foot structures on human walking for clinical applications [1], adolescent gaits [2] and pediatric gaits [3]. The results show that the segmented foot with a toe joint has several advantages compared to the rigid foot in: walking step, walking speed, range of joint angle, change in angular velocity and joint energy-output. In addition, biomechanical studies conducted on ten donated limbs [4] indicate that the human foot can not be considered as a single rigid body with no intrinsic motion.

An energy-efficient torque controller based on passive dynamics of human locomotion for a robotic transtibial prosthesis

During early and middle stance of level-ground walking, the ankle joint usually rotates passively due to the locomotion of human body. Based on this passive dynamics of human locomotion, we develop an energy-efficient torque controller with hierarchical structure for a robotic prosthesis. The low-level controller generates motor current from the human locomotion and controls the motor current/torque according to the high-level command. The high-level controller consists of a forward estimator and a feedback compensator. The forward estimator estimates the motor torque according to the desired ankle torque based on the prosthesis model that represents the transmission gain between the motor torque and the ankle torque. The feedback compensator compensates for the model and low-level control errors based on the torque measurements. Step response and frequency response show that the low-level controller could reach the desired value within 0.3 seconds and had a bandwidth of 4.2 Hz. Experiments of constant and linear torque tracking achieve small RMS tracking errors, which confirm the effectiveness of the proposed high-level controller.

Motion control of a robotic transtibial prosthesis during transitions between level ground and stairs

This paper presents a hierarchical control strategy for a robotic transtibial prosthesis to realize smooth locomotion transitions between level ground and stairs. The high level controller identifies current terrain with a fuzzy logic based method and decides the corresponding parameters for lower level controllers. The middle level controller detects different gait phases of one gait cycle on a specific terrain and decides which control method to be used for the current phase. Based on the recognized terrain and gait phase, the low level controller performs damper control for the stance phase and angle control for the swing phase. To evaluate the effectiveness of the proposed control method, we design and construct a robotic transtibial prosthesis prototype. Experimental results of a transtibial amputee subject show improved gait symmetry on level ground and stairs with the proposed control strategy. A 12-s long trial that includes different terrains and terrain transitions indicates that the proposed method can realize smooth locomotion transitions between level ground and stairs.