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Researchers have studied Stewart-Gough platforms, also known as Gough-Stewart platforms or hexapod platforms extensively for their inherent fine control characteristics. Their studies led to the potential deployment opportunities of Stewart-Gough platforms in many critical applications such as medical field, engineering machines, space research, electronic chip manufacturing, automobile manufacturing, etc. Some of these applications need micro- and nano-level movement control in 3D space for the motions to be precise, complicated, and repeatable; a Stewart-Gough platform fulfills these challenges smartly. For this, the platform must be more accurate than the specified application accuracy level and thus proper calibration for a parallel robot is crucial. Forward kinematics-based calibration for these hexapod machines becomes unnecessarily complex and inverse kinematics complete this task with much ease. To experiment with different calibration techniques, various calibration approaches were implemented by using external instruments, constraining one or more motions of the system, and using extra sensors for auto or self-calibration. This survey paid attention to those key methodologies, their outcome, and important details related to inverse kinematic-based parallel robot calibrations. It was observed during this study that the researchers focused on improving the accuracy of the platform position and orientation considering the errors contributed by one source or multiple sources. The error sources considered are mainly kinematic and structural, in some cases, environmental factors also are reviewed; however, those calibrations are done under no-load conditions. This study aims to review the present state of the art in this field and highlight the processes and errors considered for the calibration of Stewart-Gough platforms. [ABSTRACT FROM AUTHOR]

Path planning is one of the most fundamental problems that must be solved before a robot can navigate and explore autonomously. Path planning needs to be integrated with path tracking to be applied to autonomous robots. This makes path tracking also important for autonomous robot navigation which cannot be separated from path planning. There are two path planning methods, the first is search-based method, the second is sampling-based method. Both have their own advantages, but the popular and commonly used sampling-based algorithm due to its fast convergence is preferred in path planning. The RRT* algorithm was developed. This improvement initiated a major civilization in sampling-based algorithms, namely parent node selection and rewiring in RRT. Although there has been an improvement in optimality, RRT* still doesn't provide the distance optimality value as expected, due to its character that is still adopted from RRT. The resulting path is still suboptimal and not smooth (jagged). On the other side, Path tracking has several methods, however, these path tracking methods are difficult to apply to autonomous robots and need to be adapted to the robot used. Based on the description above, there are still problems with path planning, namely paths that are still less than optimal and convergence that is still slow. This research will add a way to shorten the distance in the RRT* algorithm with the triangular inequality method. Meanwhile, for path tracking, we will apply the pose-to-pose method, which follows the waypoint that has been made by path planning.

In recent years, many microrobots have been developed for search applications using swarms in places where humans cannot enter, such as disaster sites. Hexapod robots are suitable for moving over uneven terrain. In order to use micro-hexapod robots for swarm exploration, it is necessary to reduce the robot's size while maintaining its rigidity. Herein, we propose a micro-hexapod with an SU-8 rigid frame that can be assembled from a single sheet. By applying the SU-8 coating as a structure to the hexapod and increasing the rigidity, the substrate size can be reduced to within 40 mm × 40 mm and the total length when assembled to approximately 30 mm. This enables the integration of the micro electromechanical systems (MEMS) process into small and inexpensive hexapod robots. In this study, we assembled the hexapod with a rigid frame from a sheet created using the MEMS process and evaluated the leg motion. [ABSTRACT FROM AUTHOR]

[Display omitted] Synthesis of advanced structure and multiple heteroatom-doped carbon based heterostructure materials are the key to the preparation of high-performance energy storage electrode materials. Herein, the hexapod-shaped Co 1-x S@NPSC has been triumphantly prepared using hexapod ZIF-67 as the sacrificial template to prepare Co 1-x S inner core and N, P, and S tri-doped carbon (NPSC) as the shell through the carbonization of the organic polymer precursor. When applied as anode for Na+ batteries (SIBs) and K+ batteries (PIBs), Co 1-x S@NPSC presents the high reversible specific capability of 747.4 mAh/g at 1.0 A/g after 235 cycles and 387.8 mAh/g at 5.0 A/g after 760 cycles for SIBs, as well as 326.7 mAh/g at 1.0 A/g after 180 cycles for PIBs. The excellent storage capacity and rate capability of Co 1-x S@NPSC is ascribed to hexapod structure of ZIF-67 unlike the common dodecahedron, which is constructed with interior porous and exterior framework repository, donating supplemental active sites, and doping of multiple heteroatoms forming organic polymer coating inhibiting the volume expansion and restrains the agglomeration of Co 1-x S nanoparticles. This approach has paved a bright avenue to exploit promising anode materials with novel structure and hetero-atom doping for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

The adaptability of hexapods for various locomotion tasks, especially in rescue and exploration missions, drives their application. Unlike controlled environments, these robots need to navigate ever-changing terrains, where ground irregularities impact foothold positions and origin shifts in contact forces. This dynamic interaction leads to varying hexapod postures, affecting overall system stability. This study introduces a posture control approach that adjusts the hexapod's main body orientation and height based on terrain topology. The strategy estimates ground slope using limb positions, thereby calculating novel limb trajectories to modify the hexapod's angular position. Adjusting the hexapod's height, based on the calculated slope, further enhances main body stability. The proposed methodology is implemented and evaluated on the ATHENA hexapod (All-Terrain Hexapod for Environment Adaptability). Control feasibility is assessed through dynamic analysis of the hexapod's multibody model on irregular surfaces, using computational simulations in Gazebo software. Environmental complexity's impact on hexapod stability is tested on both a ramp and uneven terrain. Independent analyses for each scenario evaluate the controller's effect on roll and pitch angular velocities, as well as height variations. Results demonstrate the strategy's suitability for both environments, significantly enhancing posture stability. [ABSTRACT FROM AUTHOR]

En-bloc retraction is a common procedure in orthodontic therapy. The application of palatal root torque moments is required to control incisor inclination during retraction, yet studies comparing forces and moments with respect to different mechanics are lacking. This study aimed to investigate the forces and moments during orthodontic en-bloc retraction using a robotic biomechanical simulation system, comparing two distinct approaches: (I) compound technique [stainless steel (SS) combined with nickel-titanium (NiTi)] using industrially pretorqued retraction-torque-archwires (RTA) in combination with NiTi closed coil springs; (II) conventional sliding mechanics using SS archwires with manually applied anterior twist bends in combination with elastic chains. Two dimensions (0.017" × 0.025" and 0.018" × 0.025") and ten archwires per group were investigated using 0.022" slot self-ligating brackets. Kruskal–Wallis tests with a significance level of α = 0.05 were conducted. The biomechanical simulation showed that en-bloc retraction was characterized by a series of tipping and uprighting movements, differing significantly regarding the examined mechanics. Collateral forces and moments occurred in all groups. Notably, RTA exhibited fewer extrusive forces. The most bodily movement was achieved with the compound technique and the 0.018" × 0.025" RTA. Sliding mechanics exhibited maximum palatal root torque moments of more than 20 Nmm, exceeding recommended values. [ABSTRACT FROM AUTHOR]

Background: The management of failed tibial fracture fixation remains a challenge for orthopaedic surgeons. This study investigate the utility and outcomes of circular external fixation in the management of failed internal fixation of tibial fractures. Methods: Retrospective review of a prospectively collected database of a complex limb reconstruction unit at a major trauma centre was done during December 2022. Patients with failed internal fixation of tibial fracture who underwent revision surgery with circular external fixation frame were included. Results: 20 patients with a mean age of 47.8 ± 16.5 years (range: 15–69) were included. Fourteen (70.0%) patients had failed plate and screws fixations, and the remaining six (30.0%) failed intramedullary nail fixation. The most common indication for revision surgery was development of early postoperative surgical site infection (5 patients; 25.0%). The mean duration of frame treatment was 199.5 ± 80.1 days (range = 49–364), while the mean follow-up duration following frame removal was 3.2 ± 1.8 years (range = 2–8). The overall union rate in this series was 100%; and all infected cases had complete resolution from infection. The total number of complications was 11, however, only two complications required surgical intervention. The most common complications reported were pin site infection (6; 30.0%) and limb length discrepancy of 2 cm (2; 10.0%). Conclusions: Circular external fixation is a reliable surgical option in the treatment of failed internal fixation of tibia fractures. This technique can provide limb salvage in complex infected and noninfected cases with a high union rate and minimal major complications. [ABSTRACT FROM AUTHOR]

The article considers the issues of developing optimum reef module design. It is a small man-made feature which increases the underwater landscape heterogeneity by means of the flow-through development of the bottom relief into the water column. When creating a reef module, the study proves the feasibility of using as its base part an L-shaped beam, a primitive "bend of a flat interface between the solid and liquid habitats of aquatic organisms (hydrobionts)." [ABSTRACT FROM AUTHOR]

A six-legged spider robot is a complex object from the point of view of the problem of synthesizing a system for controlling its movement. To synthesize an advanced control system for such a robot, which must solve non-trivial problems of overcoming obstacles, functioning under conditions of external disturbances, etc., we first solve the problem of synthesizing an information model of the object, on the basis of which its control system will subsequently be built. The paper compares two methods for synthesizing the information model of a six-legged spider-robot. In the first method, an information model is automatically synthesized from a CAD model of a spider-robot in a MATLAB-based graphical programming environment Simulink. In the second method, the information model is synthesized in the environment of dynamic modeling of technical systems SimInTech on the basis of a system of differential equations in the Cauchy form. Control loops and external influences are added to the information models synthesized in each of the modeling environments. The study showed that each of the resulting models has both its own individual advantages and disadvantages. They are mainly related to taking into account the mutual influence of various blocks of models on each other. It is shown that, in the end, the two models complement each other and make it possible to obtain an advanced basis for further synthesis of the motion control system. The results obtained in this work make it possible to use information models as a basis for the development of a control system for a physical model of a sixlegged spider-robot, printed on a 3D printer and assembled on the basis of the Arduino hardware platform. [ABSTRACT FROM AUTHOR]

By observing the movement characteristics of each foot when hexapod crawls in reality, according to this feature, an innovative three segment spatial crankshaft is designed. Connect the three sections of the crankshaft in this space with the front, middle and rear feet in turn. The connecting parts with each foot are designed into different spatial linkage mechanisms. In order to ensure the motion coordination of each foot when crawling, the kinematic parameters of the spatial crankshaft and its connected mechanisms are analyzed. Based on the coordinated motion parameters, the hexapod structure is modeled, and the walking coordination is simulated by Catia. At last, real objects are produced for motion test. Therefore, the feasibility of spatial crankshaft transmission structure is verified.

The article considers the control system of a parallel structure mechatronic device for space application such as a hexapod (Stewart platform). The solution of the inverse problem of kinematics is described and the necessity of solving the direct problem of kinematics by numerical methods is substantiated. During the research, it was revealed that the main source of positioning errors of the hexapod without the main feedback is its linear drives, which have systematic errors in the mechanical part of the linear transmission, gearbox, in the location of the motor windings; temperature errors due to changes in the dimensions of parts due to heating or cooling; errors caused by elastic deformations under load. To improve the static accuracy of the hexapod, a number of both design and software solutions are proposed: mechanical transmission preload, individual calibration of each drive, compensation for thermal expansion, etc. To improve the dynamic accuracy, it is proposed to use the method of controlling linear drives in the servo mode along with ensuring the trajectory of the platform with the limitation of the speed of its movement and derivatives of the speed. The use of these methods makes it possible to significantly improve the accuracy of the operation of the mechanisms of a parallel structure and, thereby, to approach the achievement of the limiting qualitative properties of onboard optical-electronic and information systems of spacecraft and stations.

This study aimed to investigate the dynamic behavior of different torque archwires for fixed orthodontic treatment using an automated, force-controlled biomechanical simulation system. A novel biomechanical simulation system (HOSEA) was used to simulate dynamic tooth movements and measure torque expression of four different archwire groups: 0.017″ x 0.025″ torque segmented archwires (TSA) with 30° torque bending, 0.018″ x 0.025″ TSA with 45° torque bending, 0.017″ x 0.025″ stainless steel (SS) archwires with 30° torque bending and 0.018″ x 0.025″ SS with 30° torque bending (n = 10/group) used with 0.022″ self-ligating brackets. The Kruskal–Wallis test was used for statistical analysis (p < 0.050). The 0.018″ x 0.025″ SS archwires produced the highest initial rotational torque moment (My) of −9.835 Nmm. The reduction in rotational moment per degree (My/Ry) was significantly lower for TSA compared to SS archwires (p < 0.001). TSA 0.018″ x 0.025″ was the only group in which all archwires induced a min. 10° rotation in the simulation. Collateral forces and moments, especially Fx, Fz and Mx, occurred during torque application. The measured forces and moments were within a suitable range for the application of palatal root torque to incisors for the 0.018″ x 0.025″ archwires. The 0.018″ x 0.025″ TSA reliably achieved at least 10° incisal rotation without reactivation. [ABSTRACT FROM AUTHOR]

Fibrous dysplasia (FD) is a congenital skeletal disorder characterized by the replacement of the bone marrow with fibrous tissue. FD may occur in isolation or association with endocrinopathies, and in that case, labeled McCune–Albright syndrome (MAS). FD can cause bone deformities or/and limb length discrepancies. The surgical intervention aims to correct limb deformities and length discrepancies while improving regional aesthetics. We report a case of a 14-year-old girl with FD that had affected her upper limbs. More characteristic had been the shortening of the right humerus (10 cm discrepancy from the left humerus) and the gun-stock deformity of the elbow. On the X-ray, a prominent feature was the shortening of the humerus and the valgus deformity of its distal end. The lengthening and correction of the deformity of the right humerus had been performed using the Taylor spatial frame (TSF) system. The software program had provided us with the estimated minimum correction time of 143 days for 7 cm humeral lengthening. A total of 157 days had been needed to lengthen and correct the deformity. The TSF system allows the simultaneous lengthening and correction of all the components of a multiplanar malformation of a limb and minimizes the required time. [ABSTRACT FROM AUTHOR]

The paper deduces a mathematical model of a spider-robot with six three-link limbs. Many limbs with a multilink structure greatly complicate the process of synthesizing a model, since in total the robot has twenty-four degrees of freedom, i.e., three coordinates of the center of mass of the body in space, three angles of rotation of the body relative to its center of mass and three degrees of freedom for each limb, to describe the position of the links. The derived mathematical model is based on the Lagrange equations with a further transformation of the equations to the Cauchy normal form in a matrix form. To test the resulting model in a SimInTech environment, an information model is synthesized and two simple experiments ar carried out to simulate the behavior of real spiders: moving forward in a straight line and turning in place at a given angle. The experimental results demonstrate that the synthesized information model can well cope with the tasks and the mathematical model underlying it can be used for further research. [ABSTRACT FROM AUTHOR]

En-bloc retraction is a common procedure in orthodontic therapy. The application of palatal root torque moments is required to control incisor inclination during retraction, yet studies comparing forces and moments with respect to different mechanics are lacking. This study aimed to investigate the forces and moments during orthodontic en-bloc retraction using a robotic biomechanical simulation system, comparing two distinct approaches: (I) compound technique [stainless steel (SS) combined with nickel-titanium (NiTi)] using industrially pretorqued retraction-torque-archwires (RTA) in combination with NiTi closed coil springs; (II) conventional sliding mechanics using SS archwires with manually applied anterior twist bends in combination with elastic chains. Two dimensions (0.017” × 0.025” and 0.018” × 0.025”) and ten archwires per group were investigated using 0.022” slot self-ligating brackets. Kruskal–Wallis tests with a significance level of α = 0.05 were conducted. The biomechanical simulation showed that en-bloc retraction was characterized by a series of tipping and uprighting movements, differing significantly regarding the examined mechanics. Collateral forces and moments occurred in all groups. Notably, RTA exhibited fewer extrusive forces. The most bodily movement was achieved with the compound technique and the 0.018” × 0.025” RTA. Sliding mechanics exhibited maximum palatal root torque moments of more than 20 Nmm, exceeding recommended values.

Terrain adaptation research can significantly improve the motion performance of hexapod robots. In this paper, we propose a method that combines reinforcement learning with a central pattern generator (CPG) to enhance the terrain adaptation of hexapod robots in terms of gait planning. The hexapod robot's complex task presents a high-dimensional observation and action space, which makes it challenging to directly apply reinforcement learning to robot control. Therefore, we utilize the CPG algorithm to generate the rhythmic gait while compressing the action space dimension of the agent. Additionally, the proposed method requires less internal sensor information, which exhibits strong applicability. Finally, we conduct experiments and deploy the proposed framework in the simulation environment. The results show that the terrain adaptation policy trained in our framework enables the hexapod robot to move more smoothly and efficiently on rugged terrain compared to the traditional CPG method. [ABSTRACT FROM AUTHOR]

The paper investigates the proposed concept of a force-measuring device for ground testing of propulsion system demonstrators and its mathematical model as well as the effect of scaling the large flange of the device on the displayed data at a constant load. [ABSTRACT FROM AUTHOR]

Tibial non-union with deformity in abnormal bone is rarely reported in literature. We report a case of a 65 years old male with a history of achondroplasia. The patient presented after a mechanical fall with an undisplaced right midshaft tibia fracture associated with pre-existing varus and procurvatum tibial deformities, which was initially managed non- operatively. However, after nine months he developed a painful non-union. Because of the symptomatic non-union as well as the pre-existing deformities, osteotomy of the tibia and fibula was performed with the application of a Truelok- Hexapod (TL-Hex, Orthofix) frame. We were able to achieve compression at the fracture site, and the software guided TL- Hex frame enabled gradual three-dimensional correction of the deformity. At six months, bony union and simultaneous correction of the tibia deformity were achieved. At two years, the patient was able to ambulate well without pain and perform his activities of daily living. We present a case of tibial non-union with pre-existing deformity in an achondroplasia patient successfully treated with a circular frame application.

Traditional Ilizarov and hexapod frames have different biomechanical properties and there is limited literature regarding their effect on time to fracture union or time to frame removal. Tibial fractures managed with a circular frame at a tertiary limb reconstruction referral centre between 2011 and 2018 were retrospectively identified from a prospectively maintained database. They were classified into three treatment groups; Ilizarov style, Taylor Spatial Frame (TSF) and TrueLok Hex (TL-Hex). Data were extracted from electronic patient records and digital radiographs. The primary outcome was time to frame removal, which was seen as an indicator of clinical and radiological fracture union. Odds ratios were calculated with the clinical significance set at 30 days. 274 patients (median age 49 years, 36% female) were included in the analysis. 8.4% Ilizarov, 10.5% TSF and 13.5% TL-Hex frames required further surgery to aid fracture healing (p = 0.38). 30% of patients had open fractures. Median time to removal for Ilizarov, TSF & TL Hex frames was 167, 198 and 185 days respectively. There was a significant difference between Ilizarov and hexapod frames. Both TSF (OR 2.2, p <0.003) and TL-Hex (OR 1.8, p <0.04) had a significantly increased time to removal of 30 days or more compared with Ilizarov frames.The time to frame removal in metaphyseal fractures was significantly shorter for Ilizarov frame fixation than hexapod frames (p = 0.04). Open fractures were significantly more likely to require at least 30 days extra time to removal than closed fractures (OR 3.3, p <0.001). There was no significant difference in the time to frame removal between fracture location, age or sex. Ilizarov frames have demonstrated a reduced time to frame removal in the management of tibial fractures than hexapod frames. Differences in the time to frame removal, an indicator of time to fracture union, may be due to the different mechanical properties of the frame, or early disruption of the fracture haematoma through secondary frame manipulation and fracture reduction, increased proportion of metaphyseal fractures treated with Ilizarov, or patient selection. The healing time was comparable across the tibia. Pooled meta-analyses may be able to further quantify these associations. [ABSTRACT FROM AUTHOR]

Aims: The timing of when to remove a circular frame is crucial; early removal results in refracture or deformity, while late removal increases the patient morbidity and delay in return to work. This study was designed to assess the effectiveness of a staged reloading protocol. We report the incidence of mechanical failure following both single-stage and two stage reloading protocols and analyze the associated risk factors. Methods: We identified consecutive patients from our departmental database. Both trauma and elective cases were included, of all ages, frame types, and pathologies who underwent circular frame treatment. Our protocol is either a single-stage or two-stage process implemented by defunctioning the frame, in order to progressively increase the weightbearing load through the bone, and promote full loading prior to frame removal. Before progression, through the process we monitor patients for any increase in pain and assess radiographs for deformity or refracture. Results: There were 244 frames (230 patients) included in the analyses, of which 90 were Ilizarov type frames and 154 were hexapods. There were 149 frames which underwent single-stage reloading and 95 frames which underwent a two-stage reloading protocol. Mechanical failure occurred after frame removal in 13 frames (5%), which suffered refracture. There were no cases of change in alignment. There was no difference between refracture patients who underwent single-stage or two-stage reloading protocols (p = 0.772). In all, 14 patients had failure prevented through identification with the reloading protocol. Conclusion: Our reloading protocol is a simple and effective way to confirm the timing of frame removal and minimize the rate of mechanical failure. Similar failure rates occurred between patients undergoing single-stage and two-stage reloading protocols. If the surgeon is confident with clinical and radiological assessment, it may be possible to progress directly to stage two and decrease frame time and patient morbidity. Cite this article: Bone Jt Open 2022;3(5):359–366.

Introduction: Acute tibial fracture-related infection (FRI) is one of the most feared and challenging complications after a tibial fracture. The most appropriate treatment in this scenario is far from a resolved topic. Circular external fixators (CEFs) offer multiplanar control and minimize soft tissue injury using temporary implants far from the infected area. This study aimed to investigate the outcomes of two different types of CEFs (Ilizarov and hexapod) in the treatment of a series of acute tibial FRIs.Material and Methods: A retrospective study at two specialized limb reconstruction centres identified all patients with an acute tibial FRI (≤4 weeks after index procedure) definitively treated with a CEF from January 2015 to December 2020.Primary Outcomes: fracture healing and infection eradication rate with a minimum FU of 12 months after frame removal.Secondary Outcomes: to investigate the differences between the two types of circular frames regarding final post-treatment deformity magnitude.Results: We included 31 patients with acute tibial FRIs: 18 treated with hexapod-type and 13 with Ilizarov-type CEFs. Average age was 45.5±16.56 years. Fracture healing and infection eradication were achieved in all patients (31/31) after a mean follow-up of 24.7 months (range 12.1-55.3). Patients treated with an Ilizarov-type fixator presented shorter time to fracture union (5.5±2.2 months vs. 9.2±6.0 months; p-value 0.021) and shorter duration of external fixation (p-value 0.001). Regarding residual post-treatment deformity, the hexapod system presented significantly less residual coronal translation deformity (p-value 0.034) and better callus quality. Fixator-related complications were similar when comparing the two groups. No significant differences were seen in pain (p-value 0.25), RTW rate (35% vs. 45%; p-value 0.7) or functionality (p-value 0.4).Conclusions: Definitive circular external fixation is an excellent treatment for acute tibial FRI. Both Ilizarov and hexapod systems offer a very high rate of fracture healing and infection eradication. Although both presented very low radiological post-operative residual deformity, the hexapod system showed less residual coronal translation deformity and better callus quality. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the dynamic behavior of different torque archwires for fixed orthodontic treatment using an automated, force-controlled biomechanical simulation system. A novel biomechanical simulation system (HOSEA) was used to simulate dynamic tooth movements and measure torque expression of four different archwire groups: 0.017″ x 0.025″ torque segmented archwires (TSA) with 30° torque bending, 0.018″ x 0.025″ TSA with 45° torque bending, 0.017″ x 0.025″ stainless steel (SS) archwires with 30° torque bending and 0.018″ x 0.025″ SS with 30° torque bending (n = 10/group) used with 0.022″ self-ligating brackets. The Kruskal–Wallis test was used for statistical analysis (p < 0.050). The 0.018″ x 0.025″ SS archwires produced the highest initial rotational torque moment (My) of −9.835 Nmm. The reduction in rotational moment per degree (My/Ry) was significantly lower for TSA compared to SS archwires (p < 0.001). TSA 0.018″ x 0.025″ was the only group in which all archwires induced a min. 10° rotation in the simulation. Collateral forces and moments, especially Fx, Fz and Mx, occurred during torque application. The measured forces and moments were within a suitable range for the application of palatal root torque to incisors for the 0.018″ x 0.025″ archwires. The 0.018″ x 0.025″ TSA reliably achieved at least 10° incisal rotation without reactivation.

As recently demonstrated, a passive Gough-Stewart platform (a.k.a. hexapod) can be used to create a personalized surgical template to achieve minimally invasive access to the cochlea. The legs of the hexapod are manually adjusted to the desired length, which must be read off an analog scale. Previous experiments have shown that manual length setting of the hexapod’s legs is error-prone because of the imprecise readability of the analog scale. The objective of this study is to determine if integration of a linear encoder and digitally displaying the measured length help reduce the length setting error. Two experiments were conducted where users set the leg length manually. In both experiments, the users were asked to set the leg length to 20 nominal values using the whole setting range from 0 mm to 10 mm. In the first experiment, users had to rely only on the analog scale; in the second experiment, the electronic display additionally showed the user the actual leg length. Results show that the mean length setting error without using the digital display and only relying on the analog scale was (0.036 ± 0.020) mm (max: 0.107 mm) in contrast to (0.001 ± 0.000) mm (max: 0.002 mm) for the experiment with the integrated digital measurement system. The results support integration of digital length measurement systems as a promising tool to increase the accuracy of surgical template fabrication and thereby patients’ safety. Future studies must be conducted to evaluate if integration of a linear encoder in each of the six legs is feasible.

The present paper considers workspace and performance analysis of a six degree-of-freedom hexapod-type parallel manipulator with a circular guide. Compared to other similar manipulators, the design of this one allows locating all the drives fixed on the base and avoiding collisions between the carriages. The first half of the paper focuses on a procedure to determine the constant orientation (translation) workspace. The study first considers all the constraints that can affect the working area: constraints in active and passive joints, leg interference, and singularities. Next, the paper discusses the numerical procedure to construct the workspace. The proposed innovative approach combines the features of conventional geometrical and discretization methods. The suggested techniques are implemented in a MATLAB package and verified by examples with various orientations of the mechanism output link. The paper also discusses the accuracy of developed methods and mentions the required computational efforts. The second half of the work analyzes manipulator performance by calculating the conditioning index over the workspaces obtained earlier. The paper evaluates the conditioning index for an ordinary Jacobian matrix and a normalized one. In the latter case, two normalization approaches are considered: using a characteristic length and using linear velocities of three points selected on the mechanism output link. [ABSTRACT FROM AUTHOR]

Here we introduce a new 6-axes positioner, called a hexblade positioner, that achieves high speeds over large ranges with high precision. The positioner achieves these capabilities due to its bent-blade-flexure topology, which decouples its 6 actuators. A matrix-based analytical approach is used to model the stiffness and inertia of the positioner's topology and its performance capabilities are subsequently calculated and plotted for each version of the design over a comprehensive sweep of its geometric parameters. The approach is verified by comparing its modal analysis results with finite-element-analysis results performed on the same designs sampled from the parameter sweep. An optimal version of the design is fabricated and frequency-sweep data is provided to (i) demonstrate the design's open-loop dynamic performance capabilities in all 6° of freedom and (ii) experimentally validate the analytical approach. The fabricated design's lowest eigenfrequency is measured when its stage is driven to extreme displacements in all 6 directions to demonstrate that the system's support stiffness and driving speed capabilities don't appreciably change as the flexures are deformed over the system's full range. Although the hexblade positioner introduced here is designed to enable rapid high-resolution 3D printing in harsh, high-vibration environments (e.g., on a large vibrating structure orbiting earth or inside a fast-moving vehicle), the positioner is suited for any high-precision application that requires high speeds and large ranges of motion along all 6° of freedom. • We introduce a high-speed large-range 6-axis flexure-based precision motion stage. • A matrix-based analytical approach is introduced to model its dynamic behavior. • The approach is used to determine the design's optimal geometric parameters. • The approach is verified using FEA and validated using experimental measurements. • Frequency-sweep data is measured from a fabricated design version along all 6 axes. [ABSTRACT FROM AUTHOR]

Context: Hexapod circular external fixators allow bone manipulation in all planes to correct complex deformities. However, the patient must perform the strut adjustments consistently and correctly, often multiple times daily for weeks or months, to achieve intended corrections. This presents a potential source of variability, error, and anxiety to the patient. A computer-programmed, robotic automated motorized strut adjustment technology (Maxframe Autostrut™ Multi-Axial Correction System, Orthospin Ltd., Yoqneam, Israel) has been developed which automatically adjusts the struts without patient or clinician involvement. Aims: The aims of this study were as follows: first, to determine whether the motors performed the programmed initial and residual schedules and, second, to identify technology-specific problems and their management. Settings and Design: This was a retrospective observational study of a consecutive series of the first 16 patients who had the motorized hexapod frame applied. Subjects and Methods: A chart review was performed to record demographic information, indications and goals for hexapod frame care, whether the care goals were achieved, and whether unexpected and/or adverse events occurred (such as technical difficulties and medical complications) and the management of those issues. Statistical Analysis Used: Not applicable. Results: All patients achieved the index and residual adjustments as programmed. Conclusions: The Autostrut™ system appears reliable and safe. It executes programmed index and residual adjustments as well as strut change scenarios as directed. The system recognizes unexpected mechanical or programming issues and ensures patient safety by halting progress and alerting the patient. Future versions of the technology may benefit from added features such as remote reprogramming or current strut position monitoring. [ABSTRACT FROM AUTHOR]

Terrain adaptation research can significantly improve the motion performance of hexapod robots. In this paper, we propose a method that combines reinforcement learning with a central pattern generator (CPG) to enhance the terrain adaptation of hexapod robots in terms of gait planning. The hexapod robot’s complex task presents a high-dimensional observation and action space, which makes it challenging to directly apply reinforcement learning to robot control. Therefore, we utilize the CPG algorithm to generate the rhythmic gait while compressing the action space dimension of the agent. Additionally, the proposed method requires less internal sensor information, which exhibits strong applicability. Finally, we conduct experiments and deploy the proposed framework in the simulation environment. The results show that the terrain adaptation policy trained in our framework enables the hexapod robot to move more smoothly and efficiently on rugged terrain compared to the traditional CPG method.

The research is aimed at finding the structure and parameters of the optimal control law for stabilizing the angular position of the Stewart platform (hexapod), designed to ensure takeoff and landing of an unmanned aerial vehicle from the deck of a ship in the high sea. The task of stabilizing the angular position of hexapod is to provide small angles of its deviation in the horizon plane under the action of nondeterministic external disturbances and factors, namely, in the conditions of the sea oscillation, with significant fluctuations in wind force and its direction. The action of these factors causes not only a decrease in the accuracy of stabilization of the platform in the horizon plane in the conditions of random motions, but also the output of control actions at the boundary of limits of the operating zone of the hexapod. To solve this problem, the method of synthesis of the optimal multidimensional system of object stabilization is used. It works under the influence of multidimensional stationary random useful signals, disturbances, and measuring noises. [ABSTRACT FROM AUTHOR]

Purpose: The pre-clinical testing of cardiovascular implants gains increasing attention due to the complexity of novel implants and new medical device regulations. It often relies on large animal experiments that are afflicted with ethical and methodical challenges. Thus, a method for simulating physiological heart motions is desired but lacking so far. Methods: We developed a robotic platform that allows simulating the trajectory of any point of the heart (one at a time) in six degrees of freedom. It uses heart motion trajectories acquired from cardiac magnetic resonance imaging or accelero-meter data. The rotations of the six motors are calculated based on the input trajectory. A closed-loop controller drives the platform and a graphical user interface monitors the functioning and accuracy of the robot using encoder data. Results: The robotic platform can mimic physiological heart motions from large animals and humans. It offers a spherical work envelope with a radius of 29 mm, maximum acceleration of 20 m/s2 and maximum deflection of ±19° along all axes. The absolute mean positioning error in x-, y- and z-direction is 0.21 ±0.06, 0.31 ±0.11 and 0.17 ±0.12 mm, respectively. The absolute mean orientation error around x-, y- and z-axis (roll, pitch and yaw) is 0.24 ±0.18°, 0.23 ±0.13° and 0.18 ±0.18°, respectively. Conclusion: The novel robotic approach allows reproducing heart motions with high accuracy and repeatability. This may benefit the device development process and allows re-using previously acquired heart motion data repeatedly, thus avoiding animal trials. [ABSTRACT FROM AUTHOR]

The article considers the design features of mobile robots-hexapods. It has been established that such a mobile platform is a bionic system that uses six legs to move and mimics the appearance and way of moving a spider. The robot hexapod has six moving parts, and only three workers are enough to ensure its movement. The advantages of the robot are its high passability on uneven surfaces compared to wheeled platforms. A laboratory model of an automated mechatronic robot-hexapod system has been developed. The classic design implementation of the robot was chosen, which provides six limbs with three degrees of mobility, which are placed symmetrically on three moving links on both sides of the robot and are driven by eighteen servomotors. A robot control system has been developed, which consists in planning the movement of the robot taking into account the information coming from the sensors, which, in turn, provide general feedback, providing information about various parameters of the external environment. To perform the movements of the hexapod, an appropriate algorithm is implemented, which provides the division into two groups of limbs of the robot and a system of remote control. Simulation of robot movement was performed using ROS + Gazebo.

Abstract Aim The correction accuracy of the Taylor Spatial Frame (TSF) fixator depends considerably on the precise determination of the mounting parameters (MP). Incorrect parameters result in secondary deformities that require subsequent corrections. Different techniques have been described to improve the precision of MP measurement, although exact calculation is reportedly impossible radiologically. The aim of this study was to investigate the accuracy of intraoperative and postoperative radiographic measurement methods compared to direct MP measurement from TSF bone mounting. Methods A tibial Sawbone® model was established with different origins and reference ring positions. First, reference MPs for each origin were measured directly on the frame and bone using a calibrated, digital vernier calliper. In total 150 MPs measured with three different radiographic measurement techniques were compared to the reference MPs: digital radiographic measurements were performed using soft-copy PACS images without (method A) and with (method B) calibration and calibrated image intensifier images (method C). Results MPs measured from a non-calibrated X-ray image (method A) showed the highest variance compared to the reference MPs. A greater distance between the origin and the reference ring corresponded to less accurate MP measurements with method A. However, the MPs measured from calibrated X-ray images (method B) and calibrated image intensifier images (method C) were intercomparable (p = 0.226) and showed only minor differences compared to the reference values but significant differences to method A (p

This article is a historical perspective on how the study of the neuromechanics of insects and other arthropods has inspired the construction, and especially the control, of hexapod robots. Many hexapod robots’ control systems share common features, including: 1. Direction of motor output of each joint (i.e. to flex or extend) in the leg is gated by an oscillatory or bistable gating mechanism; 2. The relative phasing between each joint is influenced by proprioceptive feedback from the periphery (e.g. joint angles, leg load) or central connections between joint controllers; and 3. Behavior can be directed (e.g. transition from walking along a straight path to walking along a curve) via low-dimensional, broadly-acting descending inputs to the network. These distributed control schemes are inspired by, and in some robots, closely mimic the organization of the nervous systems of insects, the natural hexapods, as well as crustaceans. Nearly a century of research has revealed organizational principles such as central pattern generators, the role of proprioceptive feedback in control, and command neurons. These concepts have inspired the control systems of hexapod robots in the past, in which these structures were applied to robot controllers with neuromorphic (i.e. distributed) organization, but not neuromorphic computational units (i.e. neurons) or computational hardware (i.e. hardware-accelerated neurons). Presently, several hexapod robots are controlled with neuromorphic computational units with or without neuromorphic organization, almost always without neuromorphic hardware. In the near future, we expect to see hexapod robots whose controllers include neuromorphic organization, computational units, and hardware. Such robots may exhibit the full mobility of their insect counterparts thanks to a ‘biology-first’ approach to controller design. This perspective article is not a comprehensive review of the neuroscientific literature but is meant to give those with engineering backgrounds a gentle introduction into the neuroscientific principles that underlie models and inspire neuromorphic robot controllers. A historical summary of hexapod robots whose control systems and behaviors use neuromorphic elements is provided. Robots whose controllers closely model animals and may be used to generate concrete hypotheses for future animal experiments are of particular interest to the authors. The authors hope that by highlighting the decades of experimental research that has led to today’s accepted organization principles of arthropod nervous systems, engineers may better understand these systems and more fully apply biological details in their robots. To assist the interested reader, deeper reviews of particular topics from biology are suggested throughout.

This paper presents some comparative results obtained from a batch of tests in order to determine the optimal software algorithm implementation designed for the command of a multiapplication cobotic platform with remote control function. The application shown is a high precision measurement system for the movement of a high-precision touch probe manipulated with an intelligent cobotic platform (consisting of two robots series-parallel with 11 DOF) in order to obtain accurate measurement values. The movement of the touch probe is done with high precision using a hexapodal system. [ABSTRACT FROM AUTHOR]

The paper presents a design of a six-legged robot (hexapod) that will serve as a flexible platform for practical exercises for electrical engineering students. The aim is to offer students a realistic fairly complex system, enabling to learn about various aspects of a hardware and software integration in the process of the embedded system design. The robot design offers many possibilities for upgrades, with a considerable attention paid to the ease of maintenance and protection against errors in programming and/or operating the robot. These are often unavoidable during the learning process and are at the same time the best source of experience for future engineers. [ABSTRACT FROM AUTHOR]