It is known that in the creation of isotropic magnetic manipulation systems using a set of stationary electromagnets, eight electromagnets are necessary to ensure that there are no singularities in the workspace. A variety of eight-electromagnet configurations have been proposed to date. In the first contribution of this letter, we conduct a critical comparison of these proposed configurations, and find that certain configurations are superior in terms of field and torque generation, whereas others are superior in terms of force generation due to the spatial derivative of the field. All of the prior configurations comprise a high degree of symmetry, yet access to the workspace varies widely between designs. In the second contribution of this letter, we propose a new configuration that does not comprise the symmetry seen in prior systems, and also provides more open access to the manipulation workspace than prior systems, yet still exhibits an isotropic workspace with comparable performance to prior systems. We conclude that designers of isotropic eight-electromagnet manipulation systems should not feel obliged to incorporate symmetry into their design.

In systems comprising stationary electromagnets designed for magnetic manipulation and remote magnetic actuation, the standard method for achieving some desired system output (e.g., magnetic force and torque) is to form a matrix that maps the electromagnets’ electrical currents to the resulting output, and then use the pseudoinverse of that matrix to solve for the currents. However, this method does not account for the nonlinear nature of the saturation limits of the amplifiers and power supply, nor does it account for the temperature in the electromagnets, both of which limit the system's overall performance in practice. In this letter, we propose improved current-solving methods that account for these real-world system limitations. We demonstrate how the performance of systems can be improved by increasing both the achievable output magnitudes and the total operating time to achieve those outputs, and how the risk of overheating can be eliminated.

Background: Although experiences in the operating room can help surgeons to learn simple bone-drilling techniques, outside training may be better suited for complex procedures. We adapted a rotary handpiece to evaluate the bone-drilling skills of orthopaedic resident physicians during the 2017 Southwest Orthopaedic Trauma Association (SWOTA) motor skills course. Methods: Twenty-five postgraduate year (PGY)-1 orthopaedic residents from 7 institutions were asked to perform a bicortical drilling task 3 times both before and after attending a motor skills course. Kinetic and kinematic data were collected using force, acceleration, and visual sensors. Results: Sixteen parameters were measured. The interdependence of these parameters (taken separately for precourse and postcourse performance) is presented. Evidence for motor skill acquisition across a short time scale is elucidated. Noteworthy correlations include overpenetration with force (0.65 mm), palmar-dorsal (P-D) toggle (0.65°), vibration in the P-D direction (0.53 m/s²), time (−0.41 sec), and RPM (revolutions per minute; −0.36); time with both RPM (0.38) and P-D toggle (−0.40°); and force with both RPM (−0.41) and P-D toggle (0.32°). Differences in performance before and after the motor skills course include reduction in overpenetration (28.8 to 18.2 mm), reduction in skiving (22% to 6%), and reduction in preparation time (27.3 to 9.65 sec). Additionally, there were several differences in performance by institution that were significant (overpenetration, toggle in the P-D and radial-ulnar [R-U] directions, and both drilling force and drilling time). Conclusions: Understanding how performance and outcome parameters are correlated provides powerful insight into how surgical procedures can be best performed. In particular, we hope that these findings will inform new training paradigms. Variations in resident training from 1 institution to another are evidenced in surgical performance. Similarly, the methods used here to quantify changes in performance across the 3-day SWOTA training course allow a unique vehicle for optimization of these types of training opportunities outside of the operating room.

Dynamic displacement measurement of objects can be challenging due to the limitations of conventional methods and pricey instrumentation of unconventional methods, such as laser scanners. In this research, Close Range Photogrammetry (CRP) is used as an affordable non-contact method to measure 3D dynamic displacements. It is proposed as a reliable alternative to traditional dynamic deformation measurement methods such as displacement sensors or accelerometers. For this purpose, dynamic displacements of a three-dimensional one-story building frame model on a one-dimensional shake table are determined by using the traditional method of attached accelerometer and CRP. The results of the CRP method are compared with the results of the traditional methods as well as numerical models. The results show a good agreement which evidences the reliability of the CRP with regular cameras.

A perennial challenge when rendering a virtual surface with an impedance-type haptic interface is making the surface feel hard without destroying its realism, since simply increasing its stiffness can lead to instability. One way to increase the perceived hardness without increasing stiffness is to implement a braking pulse or other high-frequency haptic contact event. Traditionally, such events are implemented as a force along the surface normal, which may leave some of the actuators of the haptic device underutilized. We propose a hybrid force-moment braking pulse, which includes a nonrealistic rendered moment to exploit a haptic illusion. We describe how to implement such a hybrid force-moment braking pulse in general, considering the saturation of the haptic device's actuators. In a human-subject study, we find that a virtual surface rendered with these hybrid force-moment braking pulses is perceived as harder than the same virtual surface rendered with a traditional braking pulse, without harming the surface's realism, for the majority of users. The moment-based haptic illusion also has the potential to be superimposed on other types of haptic contact events to improve the perceived hardness.