Platform Tilt Research Articles

Stable Platform Based on Workbench Vehicle Structure Analysis

This paper has conducted a structural analysis by workbench after establishing a stable platform for automotive three-dimensional model, primarily concerning whether the platform can provide a benchmark to meet the requirements of equipment, including the numerical analysis of whether the platform tilt angle under load can achieve the requirements as well as the scheme of improvement direction of the structure.

A control algorithm for the deepwind floating vertical-axis wind turbine

A generator torque control system was developed for the Deepwind floating vertical-axis wind turbine. Deepwind is a spar platform of a unique design. The generator is mounted underwater at the base of the spar, which functions as the main driveshaft. Despite the novel configuration, it is shown that a simple proportional-integral (PI) control system is able to successfully regulate the generator torque, over the full operating range of the turbine. Moreover, a simple linearized model, including only yaw degrees-of-freedom of the rotor/spar and stator, captures the most important dynamics for purposes of designing and tuning the control system. Two torque-speed operating schedules are compared, one with a conservative constant rotational-speed cutoff, and the other with a higher maximum speed. The latter increases energy capture, in exchange for more severe fluctuations in generator torque and mooring system yaw. The control system has little influence over the platform tilt angle.

Foot Structure and Muscle Reaction Time to a Simulated Ankle Sprain

Foot structure has been shown to affect aspects of neuromuscular control, including postural stability and proprioception. However, despite an association between pronated and supinated foot structures and the incidence of lateral ankle sprains, no one to our knowledge has measured muscle reaction time to a simulated ankle-sprain mechanism in participants with different foot structures. To determine whether pronated or supinated foot structures contribute to neuromuscular deficits as measured by muscle reaction time to a simulated ankle-sprain mechanism. Cross-sectional study. University biomechanics laboratory. Thirty volunteers were categorized into 3 groups according to navicular-drop-height measures. Ten participants (4 men, 6 women) had neutral feet (navicular-drop height = 5-9 mm), 10 participants (4 men, 6 women) had pronated feet (navicular-drop height ≥ 10 mm), and 10 participants (4 men, 6 women) had supinated feet (navicular-drop height ≤ 4 mm). Three perturbations on a standing tilt platform simulating the mechanics of an inversion and plantar-flexion ankle sprain. Muscle reaction time in milliseconds of the peroneus longus, tibialis anterior, and gluteus medius to the tilt-platform perturbation. Participants with pronated or supinated foot structures had slower peroneus longus reaction times than participants with neutral feet (P = .01 and P = .04, respectively). We found no differences for the tibialis anterior or gluteus medius. Foot structure influenced peroneus longus reaction time. Further research is required to establish the consequences of slower peroneal reaction times in pronated and supinated foot structures. Researchers investigating lower limb muscle reaction time should control for foot structure because it may influence results.

A study on the application of electromagnetic-field-assisted magnetic soft mold photocuring imprinting technology in micro-structure gradient replication molding

This study proposed a new imprinting process using electromagnetic-field- assisted imprinting technology, a composite PDMS magnetic soft mold, and UV-LED arrays photocuring equipment to change an even microlens mold by imprinting the replication into a gradient microlens structure. This function is similar to the continuous gray scale technology of the semi-conductor industry. However, the structural appearance, as defined by the gray scale photo mask process, is smoother and continuous. As the method only requires one time of imprinting, the process is simple, with lower cost and higher competitiveness, thus providing a more effective alternative for imprinting technology and applications. This study used pressure-sensitive film to explore the imprinting pressure distribution of gradient magnetic soft molding. The imprinting results showed that, magnetic powder is distributed in a linear tilting pattern that is consistent with pressure measurement distribution. Hence, the magnetic powder casting angle control of a precision tilt platform can achieve gradient control of imprinting pressure. Finally, the observations and analysis by instruments, including SEM, a surface profiler, and a Laser Scanning Confocal Microscope, confirmed that the gradient magnetic PDMS film made using a precision tilt platform to control the magnetic powder casting angle, coupled with electromagnetic-field-assisted imprinting and UV-LED arrays light curing technology, can replicate the gradient microlens arrays structure of the same tilt angle through one imprinting.

An efficient two-step solution for vision-based pose determination of a parallel manipulator

A vision sensor for the direct pose determination of a parallel manipulator can extend the manipulators capabilities in many aspects. The existing approaches to a solution to the pose problem fall into two distinct categories: analytical solutions and iterative solutions. In this paper, we present an efficient two-step solution for the pose determination of a parallel manipulator by combining the advantages of the above two methods. Four points in an image, vertices of a parallelogram in object space, and the correspondences among these four coplanar points are utilized in the proposed method. In the first step, four coplanar vertices of a parallelogram, which locate the parallel manipulator's surface, are detected, Subsequently, the pose of the parallel manipulator can be determined with two affine invariants. In the second step, an iterative method is introduced, and the results of the first step are passed to the current step being used as initial values of the iterative process. Also, an error matrix is established through seven error functions, that are produced by the depth estimation and the co-planarity of the four vertices. The proposed method has been experimentally validated by a calibration board and the Pan and Tilt platform, which is a parallel manipulator developed by Googol Technology Ltd. The proposed method is then compared with three other existing methods. Experimental results demonstrate that the proposed method has the advantage of lower computational cost. The accuracy and stability, which are the main concerns during the real-time applications, are also improved.

Platform Tilt Perturbation as an Intervention for People With Chronic Vestibular Dysfunction

Training to improve responses to perturbations may be beneficial for individuals with unilateral vestibular dysfunction. We evaluated the effects of an incrementally increasing surface tilt perturbation intervention for individuals with chronic vestibular pathology on gait, activities of daily living, and dizziness. Participants (n = 29) were randomly assigned to 1 of 3 groups. The first group received random surface tilt perturbations of increasing angles and speed, half of the trials with vision-occluding goggles, 3 times weekly for 3 weeks (P group). The second group received tilt perturbation intervention (as above) plus a home program of vestibular rehabilitation exercises (P+EX group). The third group performed only the vestibular rehabilitation exercises (EX group). Outcome measures included temporospatial gait measures, Dynamic Gait Index (DGI), Dizziness Handicap Inventory (DHI), Patient Specific Functional Scale (PSFS), and a Perceived Outcomes Scale (POS). The P and P+EX groups showed greater improvement on the PSFS and the POS compared to the EX group. DGI scores indicated decreased fall risk in 8 of 9 individuals who participated in P or P+EX training and who initially scored below the 19-point cutoff score. Both the P and P+EX groups showed significant within-group changes on some gait characteristics, DGI, DHI, PSFS, and POS measures. The EX group showed within-group change only on the DHI. Surface tilt perturbation training appears to be more effective for improving abilities at the activities and participation levels than vestibular exercises alone. In addition, tilt perturbation training reduced fall risk as measured by the DGI.

Effect of Respiration on the Static Rear Stability of Wheelchairs

Kirby RL, Heimrath O, Stewart A, Smith C, MacLeod DA. Effect of respiration on the static rear stability of wheelchairs. Objective To test the hypothesis that the static rear stability of an occupied wheelchair is greater during full inspiration than expiration. Design Within-subject comparisons. Setting Rehabilitation center. Participants Able-bodied participants (N=10). Intervention None. Main Outcome Measures We measured the static rear stability (brakes unlocked) of an occupied wheelchair on a test platform according to International Organization for Standardization standards. We also used the Exhalation Threshold Test. The Exhalation Threshold Test was positive if, having been positioned at the maximum degree of platform tilt needed to maintain stability during full inspiration, the wheelchair tipped backward when the participant exhaled. Results The mean static rear stability values at full inspiration and expiration ± SD were 16.5°±2.3° and 16.1°±2.4°, with a mean difference of .46°±.24° (3%; P=.002). The Exhalation Threshold Test was positive in 19 (95%) of 20 trials. Conclusions Respiration has a slight but statistically significant effect on the rear stability of occupied wheelchairs, with greater stability at full inspiration. This has potential clinical implications for stability testing and the training of wheelchair skills, but further study is needed.

Modelling and motion control of a mechatronic system using BGM with intelligent controllers

In this research paper, a mechatronics system such as a pan tilt platform (PTP) has been considered for motion control under intelligent controllers. A proportional-derivative (PD) controller is considered for comparison of results obtained from fuzzy and hybrid controllers. The trajectory following performance of the mechatronics system is found against these controllers. The results of simulations show that hybrid fuzzy controller reduce the tracking error effectively in lesser settling time. The intelligent controllers require knowledge base of error and derivative of error to compensate the PTP dynamics. The intelligent controllers have similar trends as the PD controllers and compensated both electrical and mechanical dynamics. The PD controller requires position measurement. The intelligent controllers have knowledge base consisting of position and velocity data. Thus intelligent controllers have position measurement along with knowledge base for position control system. The best results were achieved with hybrid fuzzy controllers. They meet the desired specifications.

Unmanned aerial vehicles UAVs attitude, height, motion estimation and control using visual systems

This paper presents an implementation of an aircraft pose and motion estimator using visual systems as the principal sensor for controlling an Unmanned Aerial Vehicle (UAV) or as a redundant system for an Inertial Measure Unit (IMU) and gyros sensors. First, we explore the applications of the unified theory for central catadioptric cameras for attitude and heading estimation, explaining how the skyline is projected on the catadioptric image and how it is segmented and used to calculate the UAV’s attitude. Then we use appearance images to obtain a visual compass, and we calculate the relative rotation and heading of the aerial vehicle. Additionally, we show the use of a stereo system to calculate the aircraft height and to measure the UAV’s motion. Finally, we present a visual tracking system based on Fuzzy controllers working in both a UAV and a camera pan and tilt platform. Every part is tested using the UAV COLIBRI platform to validate the different approaches, which include comparison of the estimated data with the inertial values measured onboard the helicopter platform and the validation of the tracking schemes on real flights.

Simulating believable forward accelerations on a stewart motion platform

It is still an unsolved problem how to optimally simulate self-motion using motion simulators. We investigated how a forward acceleration can be simulated as believably as possible on a hexapod motion platform equipped with a projection screen. Human participants rated the believability of brief forward accelerations. These were simulated as visual forward accelerations over a ground plane with people as size cues, presented together with brief forward surge translations and backward pitches of the platform, and synchronous random up--down movements of the camera in the visual scene and the platform. The magnitudes of all of the parameters were varied independently across trials. Even though variability between participants was high, the most believable simulation occurred when visual accelerations were combined with backward pitches of the platform, which changed the gravitoinertial vector direction approximately consistent with the visual acceleration. However, a wide range of platform pitches was accepted as believable. With high visual acceleration cues most participants reported trials as realistic even when the platform tilt rate was above vestibular canal thresholds reported in other works. Other manipulated parameters had only a mild influence on the responses. These results can be used to optimize motion-cueing algorithms for simulating linear accelerations in motion simulators.

Real-time Target Tracking Using a Pan and Tilt Platform

Real-time Target Tracking Using a Pan and Tilt Platform

Modeling, analysis and motion control of a pan tilt platform based on linear and nonlinear systems

This paper deals with the modeling, analysis and controlled motion control of a two degree of freedom pan tilt platform (PTP) for positioning or aiming a device. The PTP has two revolute joints. The PTP is a device that makes it possible for the camera to point in a desired direction when mounted under a carrier such as an aircraft. The objective of this research work is to derive a linear and nonlinear control system of the PTP to point in a desired direction within allowable specifications. To perform the analysis and simulation, all the parameters involved in the system dynamics were identified. To achieve the motion control a feedback control system with PD controllers was simulated and tested for the position control of pan and tilt mechanism. These PD controllers were derived from linear system model were used in nonlinear control system simulation and tested with real system. The nonlinear control system developed in this paper is nearest to the physical system. The motion controller results matched closely with the simulation results.

Development of Light Powered Sensor Networks for Thermal Comfort Measurement.

Recent technological advances in wireless communications have enabled easy installation of sensor networks with air conditioning equipment control applications. However, the sensor node power supply, through either power lines or battery power, still presents obstacles to the distribution of the sensing systems. In this study, a novel sensor network, powered by the artificial light, was constructed to achieve wireless power transfer and wireless data communications for thermal comfort measurements. The sensing node integrates an IC-based temperature sensor, a radiation thermometer, a relative humidity sensor, a micro machined flow sensor and a microprocessor for predicting mean vote (PMV) calculation. The 935 MHz band RF module was employed for the wireless data communication with a specific protocol based on a special energy beacon enabled mode capable of achieving zero power consumption during the inactive periods of the nodes. A 5W spotlight, with a dual axis tilt platform, can power the distributed nodes over a distance of up to 5 meters. A special algorithm, the maximum entropy method, was developed to estimate the sensing quantity of climate parameters if the communication module did not receive any response from the distributed nodes within a certain time limit. The light-powered sensor networks were able to gather indoor comfort-sensing index levels in good agreement with the comfort-sensing vote (CSV) preferred by a human being and the experimental results within the environment suggested that the sensing system could be used in air conditioning systems to implement a comfort-optimal control strategy.

Human stance control beyond steady state response and inverted pendulum simplification

Systems theory analyses have suggested that human upright stance can be modelled in terms of continuous multi-sensory feedback control. So far, these analyses have considered mainly steady-state responses to periodic stimuli and relied on a simplifying model of the body's mechanics in the form of an inverted pendulum. Therefore, they may have ignored relevant aspects of the postural behaviour. To prove a more general validity of a stance control model that we previously derived from such analyses, we now presented subjects with static-dynamic stimulus combinations and assessed response transients, anterior-posterior (a-p) response asymmetries, and possible deviations from the 'inverted pendulum' simplification (by measuring hip and knee bending). We presented normal subjects (Ns) and vestibular loss patients (Ps) with a-p support surface tilt on a motion platform under the instruction to maintain, with eyes closed, the body upright in space. In addition, subjects were to indicate perceived platform tilt with the help of pointers. We combined a fixed-amplitude sinusoidal tilt (0.1 Hz) with static tilts that were varied in amplitude and direction. We recorded upper body (shoulder) and lower body (hip) excursions in space and centre of pressure (COP) shift, and calculated the centre of mass (COM) angular excursion. We found that: (1) Immediately prior to stimulus onset (which was highly predictable), subjects showed a small anticipatory forward lean. (2) The subsequent transient response consisted of two parts. First, the body was moved along with the platform tilt and then, in the second part, the body excursion was braked by starting tilt compensation. Upon increasing tilt amplitude, the braking point showed a pronounced saturation with for-aft asymmetry. (3) During the following prolonged tilt, the tonic body excursions saturated with increasing static tilt amplitude. This saturation also showed a for-aft asymmetry (backwards saturation more pronounced). In contrast, the dynamic body excursions did not depend on the static tilt stimulus. (4) Tilt compensation occurred mainly in the ankle joints, but also involved small synergistic bendings in hips and knees in fixed register to the ankle rotation. (5) After the end of the stimulus, the body returned towards primary position, followed by a pronounced and slowly decaying tonic overshoot which was mainly related to tilt amplitude and initial tonic body excursion. (6) The responses of Ps qualitatively resembled those of Ns, apart from larger body excursions, less pronounced saturations, and less for-aft asymmetries. (7) Perceived platform tilt of Ns and Ps was correlated with their postural tilt compensations, but unlike the postural responses the perceptual responses overestimated actual static and dynamic tilt by a factor of 3-4. Our findings suggest two, so far undescribed and highly nonlinear mechanisms in human stance control. (a) The braking during the transient response appears to reflect a 'sensory reweighting switch' by which subjects change from a control that is referenced to the support to one that is referenced to space. (b) The saturation of the tonic body excursion also reflects a sensory reweighting mechanism; by this, subjects keep their balancing within a certain excursion limit. The two mechanisms were originally not predicted by our stance control model, but do not invalidate it, because they can simply be added to it. Also the observed for-aft asymmetries can be accounted for (by making thresholds in the two mechanisms asymmetric). In its extended form, the model mimics the previous and the new findings. We also conclude that the 'inverted pendulum' simplification is a legitimate simplification. We demonstrate the utility of the model by implementing it into a humanoid robot that then mimics closely the human experimental data. Finally, we present a hypothetical concept on sensory reweighting mechanisms in human stance control, which is meant to serve as a framework for future research.

Low-frequency vibration control of a pan/tilt platform with vision feedback

This paper aims to develop active control techniques with vision feedback for suppressing low-frequency vibration of a device mounted on a pan/tilt platform due to its base disturbances. Pan/tilt platforms are commonly seen in the head of a waking robot, in an antenna, in a vision surveillance equipment, in a cannon platform, etc., for yaw and pitch direction control. However, due to its inevitable low-frequency base vibration possibly from road or sea wave disturbance in a mobile situation, orientation control of the device mounted on the top tilt platform can be seriously affected. In this paper, an adaptive sliding control (ASC) scheme is first derived and employed for vibration attenuation. Function approximation technique is used to represent the unknown disturbance in some finite linear combination of the orthogonal basis. The dynamics of pan/tilt system can thus be proved to be a stable first-order filter driven by function approximation errors. Moreover, the adaptive update law can be obtained by using the Lyapunov stability theory. Secondly, the frequently used feedback active vibration control (AVC) with filtered- x LMS algorithm is to be used and compared with the adaptive sliding control for vibration suppression performance. Experimental tests of the control algorithms show that for independent single axis excitation, about 25.14 and 23 dB attenuations in average for single-frequency disturbance have been obtained by using the ASC and feedback AVC, respectively. For dual-frequency excitation, the vibration attenuations are about 20.77 and 12.73 dB by the two methods, respectively. As for simultaneous two axes excitations, ASC and feedback AVC have respective 17.57 and 15.18 dB vibration reductions under single-frequency disturbances. Thus, validity and effectiveness of the two active control methods with vision feedback for suppressing low-frequency vibration of the device on the pan/tilt platform is verified.

Vision-based interception of a moving target with a nonholonomic mobile robot

A novel vision-based scheme is presented for driving a nonholonomic mobile robot to intercept a moving target. The proposed method has a two-level structure. On the lower level, the pan–tilt platform carrying the on-board camera is controlled so as to keep the target as close as possible to the center of the image plane. On the higher level, the relative position of the target is retrieved from its image coordinates and the camera pan–tilt angles through simple geometry, and used to compute a control law which drives the robot to the target. Various possible choices are discussed for the high-level robot controller, and the associated stability properties are rigorously analysed. The proposed visual interception method is validated through simulations as well as experiments on the mobile robot MagellanPro.

Analysis of a combined tip-tilt and deformable mirror

A deformable mirror mounted on a two-axis tilt platform can provide wavefront compensation at a single location in an adaptive optics system, resulting in a significant reduction in the number of optical components in the system and in a simplification of the alignment. However, the moment of inertia of a deformable mirror is significantly different from that of the monolithic mirror commonly mounted on a tilt platform. We report on what are to our knowledge the first experimental results of mounting a microelectromechanical deformable mirror onto a fast steering platform and the first observation that at low operating frequencies high-order deformation of the deformable mirror membrane was not recorded.

A cognitive intersensory interaction mechanism in human postural control

Human control of upright body posture involves inputs from several senses (visual, vestibular, proprioceptive, somatosensory) and their central interactions. We recently studied visual effects on posture control and their intersensory interactions and found evidence for the existence of an indirect and presumably cognitive mode of interaction, in addition to a direct interaction (we found, e.g., that a 'virtual reality' visual stimulus has a weaker postural effect than a 'real world' scene, because of its illusory character). Here we focus on the presumed cognitive interaction mechanism. We report experiments in healthy subjects and vestibular loss patients. We investigated to what extent a postural response to lateral platform tilt is modulated by tilt of a visual scene in an orthogonal rotational plane (anterior-posterior, a-p, direction). The a-p visual stimulus did not evoke a lateral postural response on its own. But it enhanced the response to the lateral platform tilt (i.e., it increased the evoked body excursion). The effect was related to the velocity of the visual stimulus, showed a threshold at 0.31 degrees /s, and increased monotonically with increasing velocity. These characteristics were similar in normals and patients, but body excursions were larger in patients. In conclusion, the orthogonal stimulus arrangement in our experiments allowed us to selectively assess a cognitive intersensory interaction that upon co-planar stimulation tends to be merged with direct interaction. The observed threshold corresponds to the conscious perceptual detection threshold of the visual motion, which is clearly higher than the visual postural response threshold. This finding is in line with our notion of a cognitive phenomenon. We postulate that the cognitive mechanism in normals interferes with a central visual-vestibular interaction mechanism. This appears to be similar in vestibular loss patients, but patients use less effective somatosensory instead of vestibular anti-gravity mechanisms.

Multisensory control of human upright stance

The interaction of different orientation senses contributing to posture control is not well understood. We therefore performed experiments in which we measured the postural responses of normal subjects and vestibular loss patients during perturbation of their stance. Subjects stood on a motion platform with their eyes closed and auditory cues masked. The perturbing stimuli consisted of either platform tilts or external torque produced by force-controlled pull of the subjects' body on a stationary platform. Furthermore, we presented trials in which these two stimuli were applied when the platform was body-sway referenced (i.e., coupled 1:1 to body position, by which ankle joint proprioceptive feedback is essentially removed). We analyzed subjects' postural responses, i.e., the excursions of their center of mass (COM) and center of pressure (COP), using a systems analysis approach. We found gain and phase of the responses to vary as a function of stimulus frequency and in relation to the absence versus presence of vestibular and proprioceptive cues. In addition, gain depended on stimulus amplitude, reflecting a non-linearity in the control. The experimental results were compared to simulation results obtained from an 'inverted pendulum' model of posture control. In the model, sensor fusion mechanisms yield internal estimates of the external stimuli, i.e., of the external torque (pull), the platform tilt and gravity. These estimates are derived from three sensor systems: ankle proprioceptors, vestibular sensors and plantar pressure sensors (somatosensory graviceptors). They are fed as global set point signals into a local control loop of the ankle joints, which is based on proprioceptive negative feedback. This local loop stabilizes the body-on-foot support, while the set point signals upgrade the loop into a body-in-space control. Amplitude non-linearity was implemented in the model in the form of central threshold mechanisms. In model simulations that combined sensor fusion and thresholds, an automatic context-specific sensory re-weighting across stimulus conditions occurred. Model parameters were identified using an optimization procedure. Results suggested that in the sway-referenced condition normal subjects altered their postural strategy by strongly weighting feedback from plantar somatosensory force sensors. Taking this strategy change into account, the model's simulation results well paralleled all experimental results across all conditions tested.

Pronounced overestimation of support surface tilt during stance

A veridical internal notion of the kinematic state of the foot support is essential for postural control. The means by which this is obtained is still a matter of debate. We therefore measured the conscious perception of support tilt during transient anterior-posterior rotations of a motion platform in six healthy subjects, using a psychophysical matching procedure. Furthermore, we evaluated subjects' postural responses (in terms of displacement of subjects' center of mass, COM, and their ankle torque, as represented by the center of foot pressure, COP). The platform tilts were applied in absence of visual and auditory orientation cues. The platform rotations consisted of smoothed position ramps with different dominant frequencies (0.025, 0.05, 0.1, 0.2, 0.4, and 0.8 Hz) and different amplitudes (0.125 degrees, 0.25 degrees, 0.5 degrees, 1 degree, 2 degrees, 4 degrees, and 8 degrees) for the forward and backward directions, which yielded a 6x14 stimulus matrix. The stimuli were repeated five times in a random order. For the matching procedure, subjects tried to maintain an upright body orientation, while trying to orient a light-weight rod, which was attached to a belt around their waists, parallel to the perceived platform surface. We measured the stimulus-evoked angular excursions of the rod and of the subjects' COM as well as the COP shift. We found that the subjects' rod indications overestimated the platform tilts, particularly with small stimulus amplitudes. To characterize the overestimation, we compared the rod indications obtained while subjects stood on the tilting platform, to rod indications in a situation in which they stood next to the platform and tried to match the rod angle to the now visually perceived platform angle. From this comparison, we inferred that the subjects' kinesthetically derived notion of platform tilt overestimates the actual tilt by a factor of approximately 4. The estimates were linearly related to the angle between body (COM) and platform, i.e., to approximately the angle of the ankle joint, a finding which suggests a proprioceptive source of the overestimation. Further analyses supported this view; they showed that the onset latencies of the rod indications could be approximated by a theoretical indication mechanism with a reaction time of about 0.31 s, a velocity threshold of 0.099 degrees/s, and a displacement threshold of 0.12 degrees. These threshold values are well in line with previous work on the leg proprioceptive detection threshold of conscious perception of body sway. We therefore assume that the phenomenon of support tilt overestimation reflects a still unknown mechanism of leg proprioception in postural control.