Man-machine interaction-based motion control of a robotic walker.

BACKGROUND: The aging population brings the problem of healthcare and dyskinesia. The lack of mobility extremely affects stroke patient's activities of daily living (ADL) and decreases their quality of life. To assist these mobility-limited people, a robotic walker is designed to facilitate gait rehabilitation training. OBJECTIVE: The aim of this paper is to present the implementation of a novel motion control method to assist disabled people based on their motion intention. METHODS: The kinematic framework of the robotic walker is outlined. We propose an intention recognition algorithm based on the interactive force signal. A novel motion control method combined with T-S fuzzy controller and PD controller is proposed. The motion controller can recognize the intention of the user through the interactive force, which allows the user to move or turn around as usual, instead of using their hands to control the walker. RESULTS: Preliminary experiments with healthy individuals and simulated patients are carried out to verify the effectiveness of the algorithm. The results show that the proposed motion control approach can recognize the user's intention, is easy to control and has a higher precision than the traditional proportional-integral-derivative controller. CONCLUSION: The results show that users could achieve the task with acceptable error, which indicates the potential of the proposed control method for gait training.

Analysis and modeling of human seat interaction with a focus on the upper body and backrest using biomechanics and contact mechanics.

BACKGROUND: This paper outlines a method to study the interaction between the human body and the aircraft seat concerning the seat comfort. METHOD: Firstly, the human body is modeled based on biomechanics and divided into a number of body segments connected by joints according to human anatomy. The angles between the body segments are obtained by curve fitting of the existing biomechanical research data. The contact forces between the human body and the seat are modeled using pairs of bi-lateral point forces. These forces are calculated and located through the analysis of the center of gravity of each body segment and average muscular structure of the human body. The geometry of the human and the seat is obtained from a 3D scan model or a CAD model. Secondly, the pressure distribution between the human body and the seat is modeled and calculated using the contact stress theory. The results of the two parts are combined to analyze the comfortability in relation to different postures, backrest recline angles and changing in shape and material. RESULTS: Simulations were performed and they are compared with experimental measurement and various FEM studies for validation. It is found that accuracy of this method is comparable with most FEM calculation. CONCLUSION: This method provides a new direction in cushion conform research. It is faster and convenient to use comparing to the FEM, and the result is reliable.

Tip-Over Stability Analysis of a Pelvic Support Walking Robot.

Discussed in this paper is the tip-over stability analysis of a pelvic support walking robot. To improve the activities of daily living (ADL) in hemiplegic patients, a pelvic support walking robot is proposed to help patients facilitating their rehabilitation. During the gait training with the robot, the abnormal man-machine interaction forces may lead to the tip-over of the robot, which is not beneficial to the rehabilitation process. A new method is proposed to predict the possibility of tipping over and evaluate the stability of the robot based on statics model, dynamics model, and zero-moment point (ZMP) theory. Through the interaction forces and moments analysis with static case, the safe point (ZMP) is studied, and the influence factors of force/moment are analyzed by dynamics case. An optimization algorithm based on the genetic algorithm (GA) is proposed to reduce the risk of tipping over. The simulation results show that the optimization algorithm can keep the robot from tipping over when the interaction forces exceed the safety threshold.

Pressure sensing of an aircraft passenger seat with lumbar control.

Musculoskeletal sitting discomfort, specifically caused by long-term sitting, is primarily triggered by physiological fatigue on the human body due to its own weight. Passive seat designs can produce inadequate surface pressure zones on the body resulting in high musculoskeletal stress leading to physical discomfort. However, as proposed in this work, this can be alleviated by decentralizing the occupant's weight with an automatic morphing lumbar seat design. The morphing seat design presented in this paper adjusts in real-time, the seat's surface curvature to decentralize the pressure distribution. The seat system consists of a custom-made pressure sensor mat embedded within the backrest cushion and two pneumatic actuators located in the lumbar area. The purpose of this seat design is to produce a change in the backrest surface curvature so that such change creates a pressure distribution closely resembling a reference distribution. Said reference distribution is derived in this work based on the concept of the Ideal Pressure Distribution. The effectiveness of the discomfort reduction due to the decentralization of the backrest load is evaluated using an objective discomfort metric known as Seat Pan Distribution percentage applied only to the backrest, peak pressure areas and contact area. Preliminary performance tests of the seat system demonstrate the successful decentralization of the passenger's pressure distribution. The evaluation of the discomfort reduction is observed via the lowering in the objective discomfort metric and peak pressure areas while simultaneously increasing the contact area between the passenger and seat.

Force Analysis and Evaluation of a Pelvic Support Walking Robot with Joint Compliance.

The force analysis of a pelvic support walking robot with joint compliance is discussed in this paper. During gait training, pelvic motions of hemiplegic patients may be excessively large or out of control; however, restriction of pelvic motions is not likely to facilitate successful rehabilitation. A robot-assisted pelvic balance trainer (RAPBT) is proposed to help patients control the range of motion via force field, and force analysis is necessary for the control of the compliant joints. Thus, kinematic model and static model are developed to derive the Jacobian and the relation between the interaction forces and the pelvic movements, respectively. Since the joint compliance is realized through a nontorsional spring, a conventional (linear) Jacobian method and a piecewise linear method are derived to relate the interaction forces with the pelvis movements. Three preliminary experiments are carried out to evaluate the effectiveness of the proposed methods and the feasibility of the RAPBT. The experiment results indicate that the piecewise linear method is effective in the calculation of the interaction forces. Gait with pelvic brace strongly resembles free overground walking and partly decreases motion range via force field. The findings of this research demonstrate that the pelvic brace with joint compliance may provide effective interventions.

Design and analysis of a novel fall prevention device for lower limbs rehabilitation robot.

BACKGROUND: Most stroke survivors are suffering from physical motor impairments and confronting with the risk of falls, and well trunk stability is essential for balance during daily functional activities. OBJECTIVES: Current fall prevention devices have various limits to the efficient recovery of balance function of the trunk. To provide hemiplegic patients after stroke with the retraining of trunk position sense and a safety environment, a novel fall prevention device is proposed. METHODS: Firstly, the structure of the device is introduced and this work is a first effort towards restoring trunk balance function through retraining of trunk position sense. Secondly, the kinematic and static model of the device are developed. Lastly, kinematic and static analysis are carried out to study the motion characteristics, and a contrast experiment was derived to show the effectiveness of robot. RESULTS: No obvious difference in balance ability between two groups prior treatment (P> 0.05). Fugl-Meyer assessment in all the cases were improved in different extent (P< 0.05). The robot group had significantly higher Fugl-Meyer scores after treatment than the control group (P< 0.05). CONCLUSIONS: The results show that the fall prevention device has good kinematic dexterity within the prescribed workspace and markedly improves balance function.