بحوث سكوبس — أ.م.د. حسن حمد علي

In this paper, a method of controlling a MR fluid brake by simultaneously altering both the input current to the electric coil, and the MR fluid thickness between the stationary and rotating part of a single-disk brake was presented. In the development of the nonlinear torque-model for the brake, nondimensional analysis was used to generalize the problem for any brake configuration with similar attributes, while providing design guidance for making the energized and non-energized brake components comparable in strength. In order to control the brake speed, two saturating proportional-integral (PI) controllers were used in parallel: one for adjusting the MR fluid thickness, and the other for adjusting the input current to the electric coil. It was shown in this paper that the controller always achieves a steady-state output with zero error; however, the combination of fluid thickness and current is non-unique and depends upon initial conditions and saturation events that occur during the transient response. In conclusion, the control method proposed in this paper is shown to extend the range of torque capacity for the brake without increasing the radial envelope for the brake itself. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2025.

Latterly, a variety of researches have been concentrated on developing and utilizing leg exoskeletons to serve and assure recuperation for people with mobility challenges. Commonly, both linear and nonlinear techniques are applied to adhere to the intended trajectory. Alternatively, this work has advocated a new analytical approach to guide and refine patient movement using Fourier series function. The hip and knee joint angles are described by a combination of sine and cosine functions, each joint is described by 8 coefficients, leading to a total of 16 coefficients. The coefficients are computed to ensure the boundary conditions at the start, midpoint, and end of the run time. Next, the hip and knee torques are obtained using the proposed Fourier series function to steer the leg’s movement, guaranteeing it tracks the predefined references trajectories. The leg’s dynamic model is tested using Monte Carlo method under broad set of operational conditions. The knee joint displayed a maximum velocity of (1.92 rad/s) and a frequency of about 1.86 Hz while the hip joint recorded a maximum velocity of (0.82 rad/s) and a frequency of about (0.93 Hz). In addition, the observed maximum torque at the hip joint was determined as (89 N·m) while at the knee joint it was (39 N·m). These results illustrated that the proposed approach effectively directs the patient readily, reliably, and with high stability despite a broad range of patients features. © (2025), (Perm National Research Polytechnic University). All rights reserved.

The prolonged sitting for disabled patients can cause several health problems such as muscle wasting, bedsores, and pain. The majority of these disabled people are paraplegic patients that the activities of their muscles can effectively increase due to knee position training. In this work, a new analytical methodology for controlling the human knee position is emphasized. The knee angle profile is parameterized using seven-term exponential function. These seven coefficients are computed by fulfilling the initial and final states for knee angle, knee velocity, and electrical torque. Then, the analytical pulse width will be used to simulate the nonlinear knee dynamic system achieving the steady-state knee position with fast settling time (0.48 sec) and small overshoot (3.22%). Eventually, the introduced algorithm is confirmed in the presence of initial knee angle dispersions using Monte-Carlo simulation method. As a result, the nonlinear analytical control is successfully able to steer the human knee angle from the initial state to the desired state shortly with maximum overshoot of about 6.8% while including a wide range of initial knee angle deviations. © 2024, Cefin Publishing House. All rights reserved.

A new motion control system for a hydraulic rotary actuator was designed in this work. The hydraulic fluid that goes to the actuator was used in a variable displacement pump to control the actuator movement. A mathematical model was conducted and the stability and performance of the open loop system were studied. Routh–Hurwitz stability criterion was implemented to assess the system stability which showed that the system is stable as long as realistic parameters are chosen for the design. Since the open loop system showed poor performance, PID and H-infinity controllers were considered to improve the system overall performance. Multiplicative uncertainty was considered in the H-infinity design process to ensure that the system responds well when uncertainties in the system parameters exist within a specified range. The leakage and friction coefficients are the parameters that were considered uncertain due to their expected change with time. The uncertainty was considered in the viscous friction and the leakage coefficients within a range of ±3%. The results showed that the open system has about 20% percent overshoot, 10% steady state error for a unit step input signal and a poor disturbance rejection. The system with both H-infinity and PID controller has no steady state error and a low settling time which is about 7 time constants (6.3 ms). The H-infinity controller provides the least percent overshoot in response to the unit step input signal, 4% compared to 10% for the PID controller. In addition, the H-infinity controller provides faster response and better disturbance rejection characteristics. Finally, only the H-infinity controller meets the robustness requirements. © 2024, Cefin Publishing House. All rights reserved.