Motion Planning of Ground Simulator for Space Instable Target Based on Energy Saving

In order to achieve the high-precision motion trajectory in ground experiment of space instable target (SIT) while reducing the energy consumption of the motion simulator, a robot motion planning method based on energy saving is proposed. Observable-based ground robot motion experiment system for SIT is designed and motion planning process is illustrated. Discrete optimization mathematical model of energy consumption of motion simulator is established. The general motion form of the robot joints in ground test is given. The optimal joint path of motion simulator based on energy consumption under discontinuous singularity configuration is solved by constructing the complete energy consumption directed path and Dijkstra algorithm. An improved method by adding the global optimization algorithm is used to decouple the coupled robot joints to obtain the minimum energy consumption path under the continuous singularity configuration of the motion simulator. Simulations are carried out to verify the proposed solution. The simulation data show that total energy saving of motion simulator joints adopting the proposed method under the condition of non-singularity configuration, joints coupled motion with continuous singularity configuration, and coexistence of non-singularity path and continuous singularity path are, respectively, 72.67%, 28.24%, and 62.23%, which proves that the proposed method can meet the requirements of ground motion simulation for SIT and effectively save energy.

A Design of Nonlinear Scaling and Nonlinear Optimal Motion Cueing Algorithm for Pilot's Station

Motion cueing algorithms (MCA) are often applied in the motion simulators. In this paper, a nonlinear optimal MCA, taking into account translational and rotational motions of a simulator within its physical limitation, is designed for the motion platform aiming to minimize human’s perception error in order to provide a high degree of fidelity. Indeed, the movement sensation center of most MCA is placed at the center of the upper platform, which may cause a certain error. Pilot’s station should be paid full attention to in the MCA. Apart from this, the scaling and limiting module plays an important role in optimizing the motion platform workspace and reducing false cues during motion reproduction. It should be used along within the washout filter to decrease the amplitude of the translational and rotational motion signals uniformly across all frequencies through the MCA. A nonlinear scaling method is designed to accurately duplicate motions with high realistic behavior and use the platform more efficiently without violating its physical limitations. The simulation experiment is verified in the longitudinal/pitch direction for motion simulator. The result implies that the proposed method can not only overcome the problem of the workspace limitations in the simulator motion reproduction and improve the realism of movement sensation, but also reduce the false cues to improve dynamic fidelity during the motion simulation process.

Analysis and compensation control of passive rotation on a 6-DOF electrically driven Stewart platform

With the development of motor control technology, the electrically driven Stewart platform (EDSP), equipped with a ball screw or lead screw, is being widely used as a motion simulator, end effector, and vibration isolator. The motor drives the lead screw on each driven branch chain to realize 6-DOF motion of the moving platform. The control loop of the EDSP adopts the rotor position as a feedback signal from the encoder or resolver on the motor. When the moving platform of the EDSP performs translational or rotational motion, the lead screw on each driven branch chain passively generates a relative rotation between its screw and nut in addition to its original sliding motion. This type of passive rotation (PR) of the lead screw does not disturb the motor; hence, it cannot be detected by the position sensor attached to the corresponding motor. Thus, the driven branch chains cause unexpected length changes because of PR. As a result, the PR generates posture errors on the moving platform during operation. In our research, the PR on the EDSP was modeled and analyzed according to the geometry configuration of EDSP. Then, a control method to compensate for the posture errors caused by the PR was proposed. Finally, the effectiveness of the analysis process and compensation control method were validated; the improvement in pose accuracy was confirmed both by simulation and experiments.

Effect of a Flexor Digitorum Superficialis Hemitenodesis on Reducing Volar Plate Strains for Swan Neck Deformities

Background Flexor digitorum superficialis (FDS) hemitenodesis is a common procedure to treat swan neck deformity (SND). We hypothesize that this surgical technique is a biomechanically effective way to reduce strain in the volar plate at the proximal interphalangeal joint (PIPJ). Methods Fifteen digits from 5 cadaveric specimens were tested using a novel in vitro active finger motion simulator under 4 finger conditions: intact, SND, FDS hemitenodesis, and FDS hemitenodesis with distal interphalangeal (DIP) joint fusion. Tensile loads in FDS and flexor digitorum profundus (FDP) and joint ranges of motion were measured by electromagnetic tracking. In addition, strain gauges were inserted under the volar plate to measure strain during PIPJ hyperextension. Results were analyzed using 1-way repeated-measures analysis of variance tests. Results The SND condition increased volar plate strain by 176% ± 25% ( P < .001) compared with the intact condition. The FDS hemitenodesis repair relieved more than 50% of the SND strain, restoring it to within no statistical difference from intact. The DIP fusion further reduced strain with no further statistical significance. At full flexion, FDS and FDP tendon loads diverged as a function of the test condition ( P < .001). With the FDS hemitenodesis, the FDP load increased by 2.1 ± 1.5 N from the SND condition ( P < .001), whereas the FDS load decreased by 1.3 ± 1.3 N ( P = .012). Conclusion The FDS hemitenodesis repair restored strains to within 3.0 milli-strain of the intact condition with no significant difference. Application of DIP fusion did not further protect the PIPJ from increased hyperextension and further exacerbated the imbalance of flexor tendon loads.

Analysis of neck muscle activity and comparison of head and body motion during rotational movement in a motion simulator

Most of the research relating to neck injuries performed to date has been tested in environments with linear motions. Disabled individuals tend to experience jerky neck rotations during falls, bed transfers, and while travelling in wheelchairs. This thesis, using various signal processing techniques, studied how healthy neck muscles, the head and body react to jerky rotational motion. Electromyogram (EMG) and motion data were gathered from 20 subjects as they were rotated 45 degrees in the forward and backward pitch plane, with and without visual input, in a motion simulator. Results showed that neck muscle behaviour was affected by the direction of motion and visual input. Maximum effective muscle power of 10.54% was reached, relative to maximum voluntary contractions (MVC). The factors found to influence neck muscle responses, such as head weight and visual input should be taken into consideration when designing headrests, neck braces and planning any rehabilitation programs.

Analysis of neck muscle activity and comparison of head and body motion during rotational movement in a motion simulator

Most of the research relating to neck injuries performed to date has been tested in environments with linear motions. Disabled individuals tend to experience jerky neck rotations during falls, bed transfers, and while travelling in wheelchairs. This thesis, using various signal processing techniques, studied how healthy neck muscles, the head and body react to jerky rotational motion. Electromyogram (EMG) and motion data were gathered from 20 subjects as they were rotated 45 degrees in the forward and backward pitch plane, with and without visual input, in a motion simulator. Results showed that neck muscle behaviour was affected by the direction of motion and visual input. Maximum effective muscle power of 10.54% was reached, relative to maximum voluntary contractions (MVC). The factors found to influence neck muscle responses, such as head weight and visual input should be taken into consideration when designing headrests, neck braces and planning any rehabilitation programs.