A new VSJ mechanism for multi-directional passivity and quick response

Human lower limbs have particular flexibility. Both the efficiency of bipedal walking and the ability to protect actuators with low energy loss are worthy references for the design of bipedal robots. This paper proposes a design for a biped robot with joints of variable stiffness. The robot has three degrees of freedom in the sagittal plane in each leg. The hips and knees are driven directly by the motor, while the ankles are passive joints with adjustable stiffness. After a comprehensive investigation, a variable stiffness mechanism was introduced based on lever principles, and driven by a motor that can realize real-time adjustment. Simulations verified the necessity of variable stiffness joints in the robot. The variable stiffness joint can absorb the ground impact on each joint, reduce the energy loss of the motor, and improve the efficiency of movement.

This paper presents a novel truss-shaped variable-stiffness deployable robotic grasper to grasp large unknown objects, the grasper comprises a series of basic modules and has the advantages of a large workspace, adjustable stiffness, and a high deploy/fold ratio. First, detailed mechanism designs of the grasper and variable-stiffness joint are introduced, and a mobility analysis and variable stiffness analysis are conducted. Second, the structural analysis of the basic module is carried out, by which several major indices, including deploy/fold ratio, grasping angle, deployment angle, grasping torque, and deployment torque, can be calculated. Third, kinematic analysis is presented to provide the workspace and kinematic simulation, and then the joint trajectory planning based on fifth-order polynomial is also conducted. Fourth, the condition of stable grasp is analyzed and a mathematical model of grasping motion is established. Adam optimization algorithm is then applied to optimization of the mathematical model and a grasping simulation is performed with objects of various sizes and for various working states of the variable-stiffness joint. Finally, a simple physical prototype is fabricated, and variable-stiffness experiments and grasping experiments confirm that the proposed grasper shows excellent grasping performance.

Low-cost variable stiffness joint design using translational variable radius pulleys

Humans have the remarkable ability to manage foot-ground interaction seamlessly across terrain changes despite the high dynamic complexity of the task. Understanding how adaptation in the neuromotor system enables this level of robustness in the face of changing interaction dynamics is critical for developing more effective gait retraining interventions. We developed an adjustable surface stiffness treadmill (AdjuSST) to trigger these adaptation mechanisms and enable studies to better understand human adaptation to changing foot-ground dynamics. The AdjuSST system makes use of fundamental beam-bending principles; it controls surface stiffness by controlling the effective length of a cantilever beam. The beam acts as a spring suspension for the transverse endpoint load applied through the treadmill. The system is capable of enforcing a stiffness range of 15-300kN/m within 340 ms, deflecting linearly downwards up to 10 cm, and comfortably accommodating two full steps of travel along the belt. AdjuSST offers significant enhancements in effective walking surface length compared to similar systems, while also maintaining a useful stiffness range and responsive spring suspension. These improvements enhance our ability to study locomotor control and adaptation to changes in surface stiffness, as well as provide new avenues for gait rehabilitation.

Humans have the remarkable ability to manage foot-ground interaction seamlessly across terrain changes despite the high dynamic complexity of the task. Understanding how adaptation in the neuromotor system enables this level of robustness in the face of changing interaction dynamics is critical for developing more effective gait retraining interventions. We developed an adjustable surface stiffness treadmill (AdjuSST) to trigger these adaptation mechanisms and enable studies to better understand human adaptation to changing foot-ground dynamics. The AdjuSST system makes use of fundamental beam-bending principles; it controls surface stiffness by controlling the effective length of a cantilever beam. The beam acts as a spring suspension for the transverse endpoint load applied through the treadmill. The system is capable of enforcing a stiffness range of 15-300kN/m within 340 ms, deflecting linearly downwards up to 10 cm, and comfortably accommodating two full steps of travel along the belt. AdjuSST offers significant enhancements in effective walking surface length compared to similar systems, while also maintaining a useful stiffness range and responsive spring suspension. These improvements enhance our ability to study locomotor control and adaptation to changes in surface stiffness, as well as provide new avenues for gait rehabilitation.

Some research institutions have developed biped-walking robots aimed for prospective cooperative working with humans. Among various research items related to them, waist joint is important because it gives so much influence to the stability of upper body. Many biped-walking robots developed so far use a single rotary joint in waist joint, but it has a crucial drawback in energy consumption to stabilize the upper body. In our research a new mechanism has proposed, which consists of a crossover 4-bar linkage controlled by two motors via springs. The crossover 4-bar linkage is intrinsically more stable than a single rotary joint. Two springs are arranged counteractively to regulate the stiffness of the waist joint. This paper shows a stability index to evaluate stability of the crossover 4-bar linkages. It also proposes a mechanism of the waist joint followed by examinations of allocation of the linkages and springs in terms of stiffness control. We developed a test machine based on the simulation results and achieved some experiments, which clearly showed the experimental results are well coincident with the theoretical one.

Compliant robots with constant joint stiffness (Serial Elastic Actuators - SEA), on the contrary to ones with variable joint stiffness (Variable Stiffness Actuators – VSA), have limited capabilities for modulating robot mechanical impedance in the interaction task. However, in the case of kinematic redundancy in specific tasks, robots can exploit the null space to adjust End-Effector (EE) Cartesian stiffness. Thus, prior knowledge of the task path or the operational workspace can be used to pre-compute joint stiffness that can enable maximal ratio between maximal and minimal stiffness of the robot’s EE during the task execution, and therefore shape achievable EE stiffness to best fit the task execution. In that light, this paper elaborates on the preselection of joint stiffnesses which influences the achievable robot’s Cartesian stiffness in a specific task. Besides optimizing the available operational EE stiffness, by pre-computed joint stiffness values, the robot will be able to adapt better to specific tasks and provide a better framework for safe and efficient physical human-robot interaction. The paper presents an approach to the selection of predefined joint stiffness values of the 7-DOFs KUKA LWR, where joint stiffness is achieved/emulated with torque feedback. In the simulation experiments, the approach is depicted in the preselection of two joint stiffness values within the prescribed range, while other joint stiffness is set constant.

Human hands can not only grasp objects of various shape and size and manipulate them in hands but also exert such a large gripping force that they can support the body in the situations such as dangling a bar and climbing a ladder. On the other hand, it is difficult for most robot hands to manage both. Therefore in this paper we developed the hand which can grasp various objects and exert large gripping force. To develop such hand, we focused on the thumb CM joint with wide range of motion and the MP joints of four fingers with the DOF of abduction and adduction. Based on the hand with large gripping force and flexibility using machined spring, we applied above mentioned joint mechanism to the hand. The thumb CM joint has wide range of motion because of the combination of three machined springs and MP joints of four fingers have variable rigidity mechanism instead of driving each joint independently in order to move joint in limited space and by limited actuators. Using the developed hand, we achieved the grasping of various objects, supporting a large load and several motions with an arm.

Recently, progress has been made in the development of mechanical joints with variable intrinsic stiffness, opening up the search for application areas of such variable-stiffness joints. By varying the stiffness of its joints, the resonant frequency of a system can be tuned to perform cyclical tasks most energy-efficiently, making the variable-stiffness joint a candidate element for an advanced prosthetic device specifically designed for the cyclical task of drumming. A prerequisite for a successful variable-stiffness drumming prosthesis is the ability of human drummers to profitably employ different stiffness levels for playing different beats. In this pilot study, 29 able-bodied subjects (20 drumming novices and 9 experts) wear a cuff on the forearm, to which a drumstick is connected using changeable adapters, consisting of several leaf springs with different stiffness and one maximally stiff connection element. The subjects are asked to play simple regular drum beats at different frequencies, one of which is the resonant frequency of the adapter-drumstick system. The subject's performance of each drumming task is rated in terms of accuracy and precision, and the effort is measured using questionnaires for the perceived stress as well as electromyography (EMG) for the muscular activity. The experiments show that using springs instead of the stiff connection leads to lower muscular activity, indicating that humans are able to use the energy-storing capabilities of the springs, or that muscular activity is reduced due to the lower mass of the springs. However, the perceived stress is increased and the novices' performance lowered, possibly due to a higher cerebral load for controlling the elastic system. The hypothesis that “matching the resonant frequency of the spring-drumstick system to the desired frequency leads to better performance and lower effort” is not confirmed. Possible explanations are discussed. In conclusion, a series-elastic element appears to lower the muscular effort of drumming, while a stiff connection appears to minimize the mental load and has a positive effect on the performance of drumming novices.

PurposeThis paper aims to test the empirical validity of the dynamic trade-off theory in its symmetric and asymmetric versions in explaining the capital structure of a panel of publicly listed US industrial firms over the period from 2013 to 2019. It analyzes the existence of an adjustment of leverage toward its target level and whether the speed of this adjustment is influenced by the debt measure, the model specification or/and the fact that the actual debt ratio is higher or lower than its long-term target level.Design/methodology/approachThis paper uses a quantitative research methodology using panel data analysis under the partial adjustment model and the error correction model using the generalized moment method in first differences and in systems to explore the dynamic nature of firms’ capital structure behavior.FindingsThe results show that the effects of the conventional determinants of leverage are globally consistent with the trade-off theory predictions. The dynamic versions confirm that firms exhibit leverage-targeting behavior. Although this speed of adjustment (SOA) depends on the debt and model specifications, it is around 60% on average. The estimated SOA is higher for the market leverage measure compared to the book leverage. The asymmetric adjustment model reveals that firms are more sensitive to reducing leverage than increasing it when they are away from their target; overleveraged firms exhibit approximately 5% faster adjustment than underleveraged firms when book leverage is used.Originality/valueThe originality of this research paper lies in its development and test of an asymmetric model to allow the leverage adjustment speed to vary depending on whether the firm’s debt ratio is above or below its target level and the methodological approach as well as the different model specifications used and the insights generated through the application of rigorous econometric techniques.

3D-printing is a potential manufacturing process for optimizing the design and manufacture of ankle foot orthosis (AFOs). The feasibility of an AFO with interchangeable strut that is suitable for 3D-printing is created and evaluated. A segmented AFO with 3D-printed custom footplate and calf shell connected by a custom-made strut is studied. The duration of a healthy subject wearing the 3D-printed segmented AFO in daily activities is used to evaluate the feasibility and durability to integrate 3D-printed AFOs into orthotics practice. The 3D-scanning of a patient's leg is first conducted. The scanned 3D surface is modified by creating the clearance around bony prominences and trimlines for the footplate and calf shell. The footplate has a custom-shaped inside to match with the foot and a standard shape outside at the top to match and connect with the strut. For the calf shell, the inside shape is custom fit with the shank and the outside shape is standard to connect with the strut. Material extrusion is the 3D-printing process selected. Tree-like support structures are used to avoid the use of soluble support material and to eliminate the risk of residual chemical solvent in the orthosis. The segmented AFO with material extrusion footplate and calf shell was tested in a healthy subject with an active lifestyle, offering comfort, and stability for over 4 months without breakage. This segmented AFO is durable, requires short 3D-printing time, and enables the quick adjustment of bending stiffness via an interchangeable strut design.

We analyze the impacts of information technology (IT) and e-commerce (EC) investments and time trends of the speeds of adjusting the observed (actual) toward the desired (maximum) pay upon chief executive officer (CEO) compensation in US firms, based on the adjustment model and its associated adjustment valuation (AV) approach, under the assumption of stochastic and dynamic adjustment speed (AS); and, then, we compare the new results to the findings of Lin and Chen (2024) based on the assumption of dynamic and variable AS. A comparative analysis strongly suggests that the new results are more realistic in a world full of uncertainty (Lin et al., 2019, pp. 769 and 777).

In this paper the reoccurring question of whether the life insurance industry's largest insurers possess and benefit from unique mortgage investment opportunities is examined. A portfolio adjustment model is presented which incorporates mortgage commitment behavior. Using this model and data for 15 insurers, speed of adjustment parameters are estimated for each insurer. The speed of adjustment, which is utilized as a measure of mortgage lending efficiency, is found to be invariant with respect to insurer size. This evidence suggests that the likelihood of significant aggregation bias in previous econometric work on life insurer mortgage investment is quite low. Amidst the vast and growing literature on bank and nonbank demand for financial assets, only a few studies have pursued questions concerning individual firm investment behavior. This preoccupation with aggregate analysis is surprising to the extent that the framework for financial modeling, first introduced by Meigs [23], DeLeeuw [12], and Goldfield [14], evolved from the fixed capital investment literature where models of aggregate behavior generally follow from investigations of how individual economic units behave.1 To assume incorrectly that firms behave in much the same way will not, in accordance with the doctrine of positive economics, invalidate the theory underlying the model. To assume incorrectly homogeneous behavior among firms may, however, lead to specifications bias and inconsistent estimates of model parameters. In this paper, the empirical question of homogeneous firm behavior is examined for life insurer mortgage lending activity. The purpose of the investigation is to consider the reoccurring question of whether certain very large [26, p. 559, n. 15] or super large [8, p. 269] life insurers possess and benefit from unique mortgage investment opportunities among firms in the industry. The examination is conducted using a partial adjustment model which specifically incorporates determinants of forward commitment behavior in the adjustment from desired to actual mortgage stocks. The empirical analysis uses annual data from 15 insurers over the period 1951 through

PurposeThis paper aims to investigate the non-homogeneity in the speed of adjustment (SoA) of the capital structure of manufacturing companies. It also attempts to study the key determinants that accelerate the speed of adjustment towards the target leverage level.Design/methodology/approachUsing the dynamic panel fraction (DPF) estimator on the partial adjustment model, the study captures the heterogeneous SoA of 2,866 firms across eight prominent sectors of the Indian manufacturing industry from 2009 to 2020. To ensure robustness, the empirical inferences of DPF are cross-verified with the estimates of panel-corrected standard errors (PCSE).FindingsThe authors find a combination of the capital structure's slow, moderate and rapid adjustment speed along with the relevance of trade-off theory. Interestingly, the lowest and fastest SoA is recorded by the dwindling textile sector and expanding food and agro sector, respectively. Profitability, firm size, asset tangibility and non-debt tax shields are the key firm-specific parameters that impact the SoA towards the target.Originality/valueAvailing the rarely employed estimator ‘DPF’ and the objective of documenting diverse and non-uniform adjustment speeds across the Indian manufacturing sectors marks a novel addition to capital structure literature.

<h3>ABSTRACT</h3> As a shortcut for mobile input, quick response (QR) code is increasingly being integrated in cross-media advertising campaigns in many countries of the world. Questions remain, however, about its actual use in different media, the motivations for consumers to use it and, especially, the perceived risks associated with using QR code. This study represents an initial exploration into these important issues. Findings from three studies in Japan indicate that QR codes are largely used in print media for promoting loyalty programs; convenience, savings, and quality are drivers of QR-code use; and perceived risks vary among different contexts in which consumers scan QR codes. Implications are presented for the effective use of QR code in mobile promotion.