Roll Axis Research Articles

A consistent method to design and evaluate the performance of Anti-Roll Tanks for ships

ABSTRACT This article presents practical methods to design an Anti-Roll tank (ART) for a ship and to predict the performance of the system ship + ART in a sea state. The methods presented are extensions of existing mathematical models. The prediction of the moment exerted by the tanks has been improved and new models for the lateral force have been derived. Instead of using only the roll angle, a combination of the roll angle and the local lateral acceleration is used as excitation of the motion of the tank. The main advantage of this combined parameter is that it accounts for the distance of the tank bottom to the roll axis and the effect of sway. Experimental and CFD methods have been reviewed and results are shown. Limits of the use of the U and FS-type of ART are separately discussed and quantified. The procedure is demonstrated by a design example.

Comparative Biomechanics of Canine Agility

Agility is a sport in which dogs compete on an obstacle course for both accuracy and time. Dogs that participate in competitions must negotiate a complex course of approximately 20 obstacles. We describe a literature review of the biomechanics of canine agility and our preliminary results. The number of articles that have reported biomechanics of canine agility has gradually increased since 2010. Most previous studies have focused on the bar jump, which is a basic obstacle to agility. In our preliminary study, we investigated the roll motion of the head and trunk using inertial sensors for Border Collies that completed weave poles (obstacles in which dogs weave through approximately 10 poles placed 0.6 m apart in a straight line). The roll angles of the head and trunk were measured based on the angular velocity and linear acceleration data using a sensor fusion algorithm. The head and trunk rotated about the roll axis nearly in unison. The roll amplitude of the head was lower than that of the trunk. We discuss the importance of biomechanical studies on canine agility to gain a deeper understanding of mammalian quadrupedal locomotion.

Investigation of Lateral and Vertical Direction Dynamic Responses of a Full Car Model Exposed to Sine Road Input

In this study, the full car model, which is exposed to a sinusoidal road input, has been examined to ensure the driving safety of the vehicles and the comfort of the passengers. In this context, the full car, including lateral and vertical movements, is modeled with fourteen degrees of freedom. The second-order equations of motion of the modeled vehicle were obtained using the Lagrangian method and reduced to first-order equations of motion using the state-space form. Then, these equations of motion were solved precisely in the time domain using the Euler method in the Matlab environment. To examine the lateral movements and the rotations of the vehicle in the pitch and roll axis, a sine wave with a wavelength of 5 m and an amplitude of 0.1 m was applied to the wheels of the vehicle. In the analysis, the right front wheel is exposed to a sinusoidal road input at t=0 s, while the left front wheel is exposed to a sinusoidal road input after the vehicle moves 2.5 m. Thus, both the pitch and roll motion of the vehicle will be examined in detail. In the study, four different vehicle masses 500 kg, 1000 kg, 2000 kg, and 3000 kg were taken into consideration and the effect of different vehicle masses on passenger and vehicle dynamic behaviors was investigated. In addition, the situation of passing vehicles at variable speeds from the given disruptive road input has also been examined. The maximum dynamic responses of the passenger and the vehicle were examined when the vehicle speed changed from 3 m/s to 50 m/s by 0.1 m/s. In the study, it has been observed that the vehicle mass and certain vehicle speed have effects on the vertical and lateral displacements and accelerations of the passenger and the vehicle

An optimization of target classification tracking and mathematical modelling for control of autopilot

ABSTRACT This paper describes the optimization of target categorization tracking and mathematical modelling to control the autopilot in the missile guidance system, which can recognize any type of target using intelligent devices and image processing. A typical inaccuracy in a reliable connection to the flight path can be reduced by using imaging techniques and new cell communication-based fruit fly swarm optimization within the object recognition processes. The suggested approach is able to locate a target among a batch of visual images captured from a camera, despite the inclusion of two targeting artefacts and their nearly similar layout. Furthermore, it has been proposed to not only evaluate movement objects but also track artefacts with consistent rotation speeds and steady speeds. Aside from adjusting the yaw, pitch, and roll axes, a simulation result for auto-pilot regulation has now been used to control a flight path. Using MATLAB and Simulink software, a simulated missile model was created that moves at 328 m/s toward the target and hits it in 3.25 seconds.

Spin revolution breaks time reversal symmetry of rolling magnets

The classical laws of physics are usually invariant under time reversal. Here, we reveal a novel class of magnetomechanical effects rigorously breaking time-reversal symmetry. These effects are based on the mechanical rotation of a hard magnet around its magnetization axis in the presence of friction and an external magnetic field, which we call spin revolution. The spin revolution leads to a variety of symmetry breaking phenomena including upward propulsion on vertical surfaces defying gravity as well as magnetic gyroscopic motion that is perpendicular to the applied force. The angular momentum of spin revolution differs from those of the magnetic field, the magnetic torque, the rolling axis, and the net torque about the rolling axis. The spin revolution emerges spontaneously, without external rotations, and offers various applications in areas such as magnetism, robotics and energy harvesting.

QUANTIFICATION OF 6D INTER-FRACTION TUMOUR LOCALISATION ERRORS IN TONGUE AND PROSTATE CANCER USING DAILY KV-CBCT FOR 1000 IMRT AND VMAT TREATMENT FRACTIONS.

This study aimed to evaluate the 6D inter-fraction tumour localisation errors in 20 tongue and 20 prostate cancer patients treated with intensity-modulated radiation therapy and volumetric-modulated arc therapy. The patient tumour localisation errors in lateral, longitudinal and vertical translation axes and pitch, roll and yaw rotational axes were analysed by automatic image registration of daily pretreatment kilovoltage cone-beam computed tomography (kV-CBCT) with planning CT in 1000 fractions. The overall mean error (M), systematic error (Σ), random error (σ) and planning target volume (PTV) margins were evaluated. The frequency distributions of setup errors were normally distributed about the mean except for pitch in the tongue and prostate. The overall 3D vector length≥5mm was 14.2 and 49.8% in the ca-tongue and ca-prostate, respectively. The frequency of rotational errors ≥1 degree was a maximum of 37 and 59.5%, respectively, in ca-tongue and ca-prostate. The M, Σ and σ for all translational and rotational axes decreased with increasing frequency of verification correction in ca-tongue and ca-prostate patients. Similarly, the PTV margin was reduced with no correction to alternate day correction from a maximum of 4.7 to 2.5mm in ca-tongue and from a maximum of 8.6 to 4.7mm in ca-prostate. The results emphasised the vital role of the higher frequency of kV-CBCT based setup correction in reducing M, Σ, σ and PTV margins in ca-tongue and ca-prostate patients.

A Preliminary Study of a Novel Reference Plane of the Head: Comparing With the True Horizontal Plane.

A new reference plane of the head, based on soft tissue landmarks and suitable for clinical analysis and soft tissue measurements, is needed. We recently discovered a novel reference plane, that is, the COs plane, which was formed by bilateral Lateral Canthus and bilateral Otobasion Superius and might be horizontal at the natural head position (NHP). In this study, we investigated the angles between the COs plane and the true horizontal (TrH) plane while sitting and standing, aiming to explore whether the new plane could be used as a substitution for the reference plane in clinical practice. Briefly, 26 volunteers were enrolled. Their sitting and standing NHP were recorded using the 3dMDface system. In the pitch axis, the mean angle of COs/TrH was 0.29 degrees and 0.41 degrees for sitting and standing positions, respectively, showing no statistical difference ( P >0.05). However, in the roll axis, the mean angle of COs/TrH for sitting position and standing positions was 1.08 and 1.33 degrees ( P <0.05), which was considered to be the result of habitual canting of the head. Moreover, there were no significant differences between the sitting and standing NHP, considering the COs/TrH angles ( P >0.05). To sum up, we concluded that the COs plane could be used as a reliable reference plane in certain soft tissue analysis and clinical applications.

Flight Dynamics and Control of an eVTOL Concept Aircraft with a Propeller-Driven Rotor

The objective of this investigation is threefold. First, to assess the flight dynamics of an electric vertical take-off and landing (eVTOL) concept aircraft with a propeller-driven rotor. Second, to develop an automatic flight control system (AFCS) for this concept aircraft. Third, to verify the potential safety benefits of the concept aircraft by analyzing the autorotation performance following a total loss of power. The paper begins with an overview of the design of the aircraft and description of the simulation model, including a detailed discussion on the inflow model of the propellers that drive the main rotor. Next, the flight dynamics are assessed at hover and in forward flight. An AFCS based on dynamic inversion is developed to provide stability and desired response characteristics about the roll, pitch, yaw, and heave axes for speeds ranging from hover to 80 kt. Additionally, an RPM governor is implemented to hold the main rotor angular speed constant at its nominal value. Finally, simulations that make use of the AFCS are performed to analyze the autorotation performance following total loss of power.

TO SPECIFICATION OF THE FORCE OF A VIBRATORY ROLLER ON THE SOIL

As a result of the analysis of tillage rollers, it was revealed that the main design feature is to ensure the required specific pressure on the soil, consequently, it is necessary to increase the roller mass per 1 m of the working width, whereas it leads to metal consumption increase of the tool. Based on the obtained data, we developed a fundamentally new design of the vibratory roller, its application will ensure the fulfillment of agrotechnical requirements for soil density with a minimum metal consumption of 70 kg/m. High-quality tillage with a vibratory roller is ensured by a passive drive of unbalancers installed on the axis of a hollow cylinder. To determine the center of mass of the unbalancers, the KOMPAS 3D v 20 program was used, which allows to obtain the desired result with an accuracy of 0.000001 mm. It was revealed in the course of the theoretical study that the unbalancers create vibrations with an amplitude of 0.00008 ... 0.0011 m at a rotation frequency of 800 min-1 due to their displacement in relation to the axis of the vibratory roller. Also, it was revealed that when the unbalancers are displaced in relation to the roller axis, the position of their center of gravity changes by approximately the same value. Concurrently, the specific pressure of the vibratory roller on the soil changes from 732.81 N/m to 1275.28 N/m, increasing by 74% in case of displacement of the unbalancers in relation to the axis of the vibratory roller up to the maximum value of a = 20 mm. Field studies of the proposed roller showed that the quality of soil compaction by the proposed vibratory roller with improved parameters and modes of operation is better than that of the most common rollers, namely, ZKVG-1.4 and ZKKSH-6.

Optimal Rotational Angular Velocity Determination Method Based on Compound Rotary Semi-Strapdown Inertial Navigation System.

Single-axis rotation modulation (SRM) still accumulates errors in the roll axis direction, which leads to the navigation accuracy not meeting the requirements of guided missiles. Compound rotation modulation (CRM) superimposes one-dimensional rotation on the basis of SRM, so that the error of the projectile in the direction of the roll axis is also modulated. However, the error suppression effect of CRM is not only affected by the error of the IMU itself, but also related to the modulation angular velocity. In order to improve the accuracy of rotary semi-strapdown inertial navigation system (RSSINS), this paper proposes an optimal rotation angular velocity determination method. Firstly, the residual error in CRM scheme is analyzed; then, the relationship between the incomplete modulation error and the modulation angular velocity in CRM is discussed; finally, a method for determining the optimal modulation angular velocity is proposed (K-value method). The analysis of the results shows that the navigation accuracy of the guided projectile is effectively improved with the rotation scheme set at the modulation angular velocity determined by the K-value method.

Optimization and Test of Structural Parameters of Flat Hob Chopper

In order to reduce the chopping power consumption of a flat hob chopper (referred to herein as chopper) on the premise of ensuring the chopping effect of the chopper, the mathematical model of optimal design of chopper is established in this paper with the minimum chopping power as the objective. With the help of MATLAB software, the mathematical model is solved. The chopping power curves of each point on the chopper blade edge line before and after the optimization of structural parameters are generated. The results indicate that when the coordinate value of point A on the blade edge line on the Z axis is 0.7 m; the included angle between the bottom surface of the blade and the axis of the cutter roll is 6°. When the radius of the chopper is 0.11 m, the chopper can obtain the theoretical minimum chopping power. The analysis result of chopping power curve is the chopping power after structural parameter optimization is reduced by about 25.50% compared with that before optimization. The choppers before and after the optimization of structural parameters was trial manufactured and sequentially mounted on the performance test bench of the chopping system of the forage ramie harvester. The test results show the standard-length rate of ramie stalk chopped by the choppers before and after the optimization of structural parameters were 92.96% and 92.84%, respectively, which were extremely close to each other, indicating that the optimization of structural parameters has no influence on the chopping effect of the chopper. The chopping power of the chopper is reduced by 22.25% after optimization, which is close to the software analysis value (25.50%), indicating that the optimization result is accurate and reliable. This study can provide parameter foundation and an optimization method for lowering chopping power consumption of the chopper.

Intuitive endoscopic robot master device with image orientation correction.

The camera of an endoscope is fixed to the device, and the image rotates together with the endoscope. This can lead to visual confusion for the user and incorrect image reading. The problem also occurs with endoscopic robots. Using a master device with the same degrees of freedom as the endoscope to control an endoscopic robot causes visual-motor misorientation, making intuitive control difficult. The roll misorientation between the image and master device handle was removed by measuring and correcting for the roll axis displacement of the master device. This enabled intuitive manipulation of the master device. The work speed and number of mistakes were experimentally measured with and without image correction. The tasks were completed significantly faster and more accurately with image orientation correction than without. The proposed method enables intuitive manipulation of the master device by correcting the image orientation in endoscopic robot control.

Real-Time Camera Localization during Robot-Assisted Telecystoscopy for Bladder Cancer Surveillance

Telecystoscopy can lower the barrier to access critical urologic diagnostics for patients around the world. A major challenge for robotic control of flexible cystoscopes and intuitive teleoperation is the pose estimation of the scope tip. We propose a novel real-time camera localization method using video recordings from a prior cystoscopy and 3D bladder reconstruction to estimate cystoscope pose within the bladder during follow-up telecystoscopy. We map prior video frames into a low-dimensional space as a dictionary so that a new image can be likewise mapped to efficiently retrieve its nearest neighbor among the dictionary images. The cystoscope pose is then estimated by the correspondence among the new image, its nearest dictionary image, and the prior model from 3D reconstruction. We demonstrate performance of our methods using bladder phantoms with varying fidelity and a servo-controlled cystoscope to simulate the use case of bladder surveillance through telecystoscopy. The servo-controlled cystoscope with 3 degrees of freedom (angulation, roll, and insertion axes) was developed for collecting cystoscope videos from bladder phantoms. Cystoscope videos were acquired in a 2.5D bladder phantom (bladder-shape cross-section plus height) with a panorama of a urothelium attached to the inner surface. Scans of the 2.5D phantom were performed in separate arc trajectories each of which is generated by actuation on the angulation with a fixed roll and insertion length. We further included variance in moving speed, imaging distance and existence of bladder tumors. Cystoscope videos were also acquired in a water-filled 3D silicone bladder phantom with hand-painted vasculature. Scans of the 3D phantom were performed in separate circle trajectories each of which is generated by actuation on the roll axis under a fixed angulation and insertion length. These videos were used to create 3D reconstructions, dictionary sets, and test data sets for evaluating the computational efficiency and accuracy of our proposed method in comparison with a method based on global Scale-Invariant Feature Transform (SIFT) features, named SIFT-only. Our method can retrieve the nearest dictionary image for 94–100% of test frames in under 55[Formula: see text]ms per image, whereas the SIFT-only method can only find the image match for 56–100% of test frames in 6000–40000[Formula: see text]ms per image depending on size of the dictionary set and richness of SIFT features in the images. Our method, with a speed of around 20 Hz for the retrieval stage, is a promising tool for real-time image-based scope localization in robotic cystoscopy when prior cystoscopy images are available.

Experimental study on thermal hydraulic characteristics of natural circulation loop under motion condition

• Comparatively studied thermal hydraulic characteristics of natural circulation loop under various motion conditions. • Obtained the periodic average frictional resistance coefficient and Nu. • Obtained the empirical relation of frictional resistance coefficient in turbulent region. • Under large flow rate conditions, rolling motion affects heat transfer characteristics mainly by affecting flow rate. • Some suggestions on the layout of marine natural circulation loop were given. In this present paper, an experimental research was carried out to investigate the influence of various motion conditions on the flow and heat transfer characteristics in natural circulation loops. A natural circulation loop was built on the six-degree-of-freedom motion experiment platform at Xi’an Jiaotong University (XJTU). First, it was found that the small acceleration heaving would not cause significant changes on flow rate of the natural circulation loop. Then, the influence mechanism of rolling motion on the natural circulation loop is different as the central axis of rolling is changed. The increase of additional inertial force along the coolant flow direction causes larger flow fluctuation. The periodic average frictional resistance coefficient under different working conditions is obtained, which is divided into flow fluctuation region ( Re < 5000) and turbulence region (5000 < Re < 35000). Last, according to the experimental data, a mathematical model to predict the periodic average frictional resistance coefficient which is suitable for the turbulent region is obtained, and the deviation between the predicted value and the experimental data is less than 20%. Beyond that, the period average Nu under different working conditions is also achieved. It shows that the rolling motion promotes the heat transfer with the small flow rate, while the rolling motion affects the heat transfer characteristics mainly by affecting the flow rate under the large flow rate conditions. Based on our research, some suggestions on the layout of marine natural circulation loop were given.

Generating Flight Illusions Using Galvanic Vestibular Stimulation in Virtual Reality Flight Simulations.

Vestibular flight illusions remain a significant source of concern for aviation training. Most fixed-based simulation training environments, including new virtual reality (VR) technology, lack the ability to recreate vestibular flight illusions as vestibular cues cannot be provided without stimulating the vestibular end organs. Galvanic vestibular stimulation (GVS) has long been used to create vestibular perception. The purpose of this study is to evaluate the ability of GVS to simulate common flight illusions by intentionally providing mismatched GVS during flight simulation scenarios in VR. Nineteen participants performed two flight simulation tasks-take off and sustained turn-during two separate VR flight simulation sessions, with and without GVS (control). In the GVS session, specific multi-axis GVS stimulation (i.e., electric currents) was provided to induce approximate somatogravic and Coriolis illusions during the take-off and sustained turn tasks, respectively. The participants used the joystick to self-report their subjective motion perception. The angular joystick movement along the roll, yaw, and pitch axes was used to measure cumulative angular distance and peak angular velocity as continuous variables of motion perception across corresponding axes. Presence and Simulator Sickness Questionnaires were administered at the end of each session. The magnitude and variability of perceived somatogravic illusion during take-off task in the form of cumulative angular distance (p < 0.001) and peak velocity (p < 0.001) along the pitch-up axis among participants were significantly larger in the GVS session than in the NO GVS session. Similarly, during the sustained turn task, perceived Coriolis illusion in the form of cumulative angular distances (roll: p = 0.005, yaw: p = 0.015, pitch: p = 0.007) and peak velocities (roll: p = 0.003, yaw: p = 0.01, pitch: p = 0.007) across all three axes were significantly larger in the GVS session than in the NO GVS session. Subjective nausea was low overall, but significantly higher in the GVS session than in the NO GVS session (p = 0.026). Our findings demonstrated that intentionally mismatched GVS can significantly affect motion perception and create flight illusion perceptions during fixed-based VR flight simulation. This has the potential to enhance future training paradigms, providing pilots the ability to safely experience, identify, and learn to appropriately respond to flight illusions during ground training.

DEVELOPMENT OF UNIVERSAL MATHEMATICAL MODEL FOR CALCULATION OF THE GEOMETRICAL PARAMETERS OF DEFORMATION ZONE DURING TUBE ROLLING USING PIERCING MILLS WITH CUP-SHAPED, BARREL TYPE AND CONICAL ROLLERS

The piercing mill parameters directly influence on the quality of pipes. In piercing mills, the process or setting parameters are the distance between rolls, rulers or guiding tools, mandrel extension, feed angle, rolling angle, etc. The geometrical parameters of deformation zone depend on the parameters of piercing mill. Non-optimal setting param-eters of the piercing mill result in defects such as external and internal slabs. The accurate technological parameters of piercing process are needed to define the setting parameters of the piercing mill. There are numerous numbers of math models and methods to calculate the technological parameters, but all of them were developed for one specific type of piercing mill rollers. Taking into consideration all of the disadvantages of the existing math models, the new mathematical model has been developed to define technological parameters of piercing process. The main purpose of the math model is to calculate the technological parameters of piercing mill with barrel type, conical and cup-shaped rollers. The ad-vantages of the math model comparison to the existing models are flexibility, a capability to define the parameters of all &#x0D; three types of the rollers and high accuracy. The model shows high accuracy even with high angle of rotation and the incline of the rollers up to 45°. The main idea of the model is to define the shortest distance between the rolling axes and the surface of rollers. The results have been evaluated using the CAD software program KOMPAS 3D for all three types of rollers of piercing mill. According to the results of comparison, the identities are equal to 100% for all three types of rollers.

Wake Vortex Effects due to Horizontal Crossing at Any Angle

The effects of wake crossing at any horizontal angle, airspeed, and altitude are considered, focusing on crossing at cruise speeds at altitudes close to the tropopause. The roll effect is considered in two cases: 1) specification of the aileron deflection as a function of time that exactly compensates for the rolling moment induced on the crossing aircraft by the wake of the leading aircraft so that the crossing aircraft is undisturbed; and 2) in the case when the available roll control power is not sufficient to compensate completely for the wake induced rolling moment, the resulting roll rate and bank angle of the crossing aircraft are calculated as a function of time. The distinction between the two cases is made by a safe separating distance or safe separating time: beyond which, roll compensation 1) is possible; and below which, rolling motion 2) is unavoidable. Besides the roll acceleration, roll rate, and bank angle for the roll axis, the effects of wake crossing are also considered for the vertical axis, including the load factor, vertical velocity, and altitude change. The theory applies to any pair of aircraft and indicates the dependence on aircraft parameters, flight, and atmospheric conditions.

Modernization of screw rolling technology in a multi-roll mill

Analysis of the screw rolling process showed that change in axial speed of the roll along the length of the roll groove of cross rolling mill does not correspond to the required character of change in the speed of deformed billet. The process proceeds under intense axial compression, as a result of which a significant part of the metal crimped in the contact zone is displaced into the inter-roll area. It is shown that direction of the axial force in the corresponding zone of the roll groove depends on the value of inclination angle of the considered roll section generatrix to the rolling axis. The proposed modernization of screw rolling technology makes it possible to carry out deformation of the billet under the influence of intra-focal axial tension. The task is accomplished by rolls calibration when at the beginning there is a ridge section of the roll on which the axial force is directed against rolling direction; and behind it, a pulling one, on which the direction of the axial force coincides with rolling direction. Such a scheme of the axial forces action in the zone of intensive billet reduction creates the most favorable conditions for the metal flow in axial direction. A technical solution is proposed for the implementation of the stage of the billet gripping by rolls, and description of this stage and the process stationary phase is given. The cardinal change in the billet deformation condition after modernization makes it possible to reduce the power load on the work rolls, increase their efficiency and reduce energy costs during rolling. This will ensure the rolling of a solid billet in a roughing mill with a higher stretch, create the preconditions for expanding the size and grade assortment when obtaining rods in radial-displacement rolling mills and at production of pipes in rolling lines with the Assel mill. The range of finished products can be significantly expanded due to the production of thin-walled highprecision pipes.

Experimental study on heat transfer characteristics of sub-cooled flow boiling in tube bundle channel under rolling motion

Rolling motion usually shows great influence on the dynamic and heat transfer characteristics in some marine nuclear power plants compared with land-based ones. The existence of two-phase fluid will aggravate the effect of rolling motion, indicating significant difference on the heat transfer mechanism. In present study, sub-cooled flow boiling in a vertically arranged tube bundle channels is experimentally investigated under various rolling motions. Results show that, when the rolling motion illustrates negligible effect on the mass flow rate, the influence of rolling motion can be attributed to the periodic change of the interface between hot and cold fluids as well as the circumferential transverse flow. A delay may occur on the fluid temperature since the rolling motion starts, while the delay of wall temperature variation is negligible. In addition, the farther away the flow channel is from the rolling axis, the more obvious the effect of the rolling motion is. Various rolling parameters including period and amplitude are considered. Note that the period of relevant parameters increases with after rising the rolling period, and the amplitude of fluid temperature increases with the increase of rolling frequency and amplitude. In comparison to the parameter of rolling amplitude, the rolling period displays a more critical role on the changes of wall temperature.

Evaluation of natural head position over five minutes: A comparison between an instantaneous and a five-minute analysis with an inertial measurement unit.

BackgroundHead posture is a balance of several positions and therefore shows inherent variation. Most methods available to quantify this are however instantaneous, not providing information about its variation over time. A dynamic recording of head posture would thus be beneficial.ObjectivesThe purpose of this study was to evaluate the variation in natural head position (NHP) over 5 min using an inertial measurement unit (IMU).MethodsFifteen healthy young volunteers were asked to sit on a chair and keep their head in the self‐balanced position for 5 min. A mirror was then revealed in front of them, and they were asked to look at their eyes for 20 s. This procedure was undertaken on two separate occasions with a one‐week interval. This was compared to an instantaneous measurement of head position at a specific time point corresponding to the 15th second of the recording.ResultsDuring the 5 min of recording, the participants tended to elevate their head progressively by a mean of 1.5°, which is then corrected by looking at oneself in the mirror. Most participants tended to rotate their head to the left and continued that progressive rotation despite looking in the mirror. The roll axis had no systematic changes observed between the self‐balanced position and the mirror‐guided position and was the most reproducible axis. Moderate to good correlations were found comparing both sessions for each axis.ConclusionThe comparison between the five‐minute analysis and the instantaneous measurement showed a systematic difference on the pitch axis but no differences for the yaw and roll. These results suggest that the variation in the NHP during a period of 5 min is generally specific to each participant with a head elevation and rotation to the left in most cases.