Journal of Mechanisms and Robotics

Design, Development, and Functional Evaluation of Neck Assistive Cervical Kit: NACK

2026-01-01T00:00:00Z

Design, Development, and Functional Evaluation of Neck Assistive Cervical Kit: NACK Catakli, Ahmet Emre; Sezgin, Omer; Unal, Ramazan; Sendur, Polat Abstract. Neck pain is a common issue caused by prolonged static postures and cumulative fatigue, negatively impacting quality of life. While cervical collars support individuals with chronic neck injuries, there is a need for preventive solutions for healthy individuals, particularly office workers exposed to prolonged sitting and repetitive motions. The study introduces a novel ergonomic assistive device designed to reduce neck strain among office workers. Design objectives are based on the range of motion during daily activities for head motion as reported in the literature. Concept development was supported using a previously validated 20 degrees-of-freedom adams model of the cervical spine. Various design alternatives were evaluated using the model to identify the design that satisfied specific design criteria. The conceptual design was translated into a mechanical design, and a prototype was subsequently manufactured. Performance was evaluated on 20 healthy subjects using an inertial measurement unit and electromyography (EMG) sensors to compare two conditions: without device and with neck assistive cervical kit (NACK). Range of motion analysis revealed that the NACK condition reduced cervical mobility by 35.6%, 59.3%, and 53.4% in sagittal, lateral, and axial rotation directions compared to without device. Statistical analysis of EMG data using paired t-tests revealed significant reductions in muscle activation, with sternocleidomastoid activity decreasing by 23–29% maximum voluntary contraction (MVC) (p < 0.01) and upper trapezius activity decreasing by 10–15% MVC (p < 0.05). The results indicate that NACK provides support that limits excessive head movements while significantly reducing neuromuscular demand on the cervical musculature, thereby enhancing comfort and productivity in workplace environments.

Lie Group Formulation of Recursive Dynamics Algorithms of Higher Order for Floating-Base Robots

2026-01-01T00:00:00Z

Lie Group Formulation of Recursive Dynamics Algorithms of Higher Order for Floating-Base Robots Ali, Ahmed; Gabellieri, Chiara; Franchi, Antonio Abstract. In this article, we describe procedures for computing higher-order time derivatives of the Lie group Newton–Euler, articulated body inertia, and hybrid dynamics algorithms for floating-base trees, where the base configuration evolves on SE(3) and the attached mechanism is an open kinematic tree with configuration on the (n1+n2)-dimensional manifold Tn1×Rn2, using spatial representation of twists. After presenting the algorithms, we collect the resulting recursions into closed-form equations of motion, identifying an admissible Coriolis matrix satisfying the passivity property, and showing that the articulated inertia tensor remains unchanged across all time derivatives. We then apply the developed methods to a 12-degrees-of-freedom (DoF) aerial manipulator to derive analytical expressions for its geometric forward and inverse dynamics along with their first time derivatives, whereas the numerical simulations successfully evaluate these dynamics up to fifth order. Finally, to demonstrate their practical utility, we benchmark the proposed extensions and show that, in the considered tests, their computational cost scales quadratically with the derivative order, whereas the automatic-differentiation baseline exhibits exponential scaling.

Gravity Compensation for Variable Payloads Using Slider-Guided Compression Springs

2026-01-01T00:00:00Z

Gravity Compensation for Variable Payloads Using Slider-Guided Compression Springs Tadese, Addisu Kidanemariam; Nguyen, Vu Linh; Patel, Brijesh; Lin, Po Ting Abstract. Gravity compensation is crucial for improving the energy efficiency of robotic systems, but achieving static balancing with variable payloads remains a design challenge. This article proposes a gravity compensation mechanism for variable payloads (GCVPs), designed for static balancing of variable payloads over a full range of motion. The GCVP integrates a slider, a pair of compression springs, and an adjustable pivot pin. Variable compensation is achieved by modulating the pivot radial position inside the slider to alter the stored energy in the springs without changing their stiffness parameters. The design methodology employs the potential energy conservation and virtual work principles to formulate the spring stiffness independent of the angular position of the payload. Numerical and experimental tests were used to show the performance of the GCVP. Numerical simulations demonstrate a torque reduction of up to 98.4%. Furthermore, experimental validation under variable loading (0.5–2 kg) shows a reduction in the peak torque from 1.29 N m to 0.16 N m (for 0.5 kg load) and from 4.61 N m to 0.51 N m (for 2 kg load). Similar reductions for intermediate loads were also observed, resulting in a maximum balancing efficiency of 90.05%.

Exact Kinematic Synthesis of a Novel Planar Eight-Bar Mechanism for Advanced Motion Generation

2026-01-01T00:00:00Z

Exact Kinematic Synthesis of a Novel Planar Eight-Bar Mechanism for Advanced Motion Generation Cervantes-Sánchez, J. Jesús; Rico-Martínez, José María; García-García, Ricardo; Alberto García-Murillo, Mario Abstract. This article presents a successful design method of a novel planar linkage with a single degree-of-freedom, intended for advanced motion generation, which allows one to visit, in an exact manner, up to nine prescribed poses. The synthesis approach is based on formulating novel and explicit existence conditions, which are easy to understand and have a simple physical meaning, for the legs that make up the entire linkage. These conditions lead to a single closed-form design equation that must be valid for each prescribed pose. A challenging case study proposed in the literature is used to demonstrate the simplicity and potential of the proposed synthesis approach.