Philosophical arguments about government contracting either categorically oppose it on legitimacy grounds or see it as largely anodyne. I argue for a normatively distinct kind of contracting – the advance market commitment, or AMC – and show that it is justified by the same liberal values that justify the welfare state.

This paper presents a concurrent optimization approach for the design and motion of a quadruped in order to achieve energy-efficient cyclic behaviors. Computational techniques are applied to improve the development of a novel quadruped prototype. The scale of the robot and its actuators are optimized for energy efficiency considering the complete actuator model including friction, torque, and bandwidth limitations. This method and the optimal bounding trajectories are tested on the first (non-optimized) prototype design iteration showing that our formulation produces a trajectory that (i) can be easily replayed on the real robot and (ii) reduces the power consumption w.r.t. hand-tuned motion heuristics. Power consumption is then optimized for several periodic tasks with co-design. Our results include, but are not limited to, a bounding and backflip task. It appears that, for jumping forward, robots with longer thighs perform better, while, for backflips, longer shanks are better suited. To explore the tradeoff between these different designs, a Pareto set is constructed to guide the next iteration of the prototype. On this set, we find a new design, which will be produced in future work, showing an improvement of at least 52% for each separate task.

In this paper, the design and experimental validation of a knee exoskeleton are presented. The exoskeleton can capture the negative work from the wearer’s knee motion while decreasing the muscle activities of the wearer. First, the human knee biomechanics during the normal walking is described. Then, the design of the exoskeleton is presented. The exoskeleton mainly includes a left one-way transmission mechanism, a right one-way transmission mechanism, and a front transmission mechanism. The left and right one-way transmission mechanisms are designed to capture the negative work from the wearer’s knee motion in the stance and swing phases, respectively. The front transmission mechanism is designed to transform the bidirectional rotation of the wearer’s knee joint into the generator unidirectional rotation. Additionally, the modeling and analysis of the energy harvesting of the exoskeleton is described. Finally, walking experiments are performed to validate the effectiveness of the proposed knee exoskeleton. The testing results verify that the developed knee exoskeleton can output a maximum power of 5.68 ± 0.23 W and an average power of 1.45 ± 0.13 W at a speed of 4.5 km/h in a gait cycle. The average rectus femoris and semitendinosus activities of the wearers in a gait cycle are decreased by 3.68% and 3.40%, respectively.

This paper focuses on the design, analysis, and multi-objective optimization of a novel 5-degrees of freedom (DOF) double-driven parallel mechanism. A novel 5-DOF parallel mechanism with two double-driven branch chains is proposed, which can serve as a machine tool. By installing two actuators on one branch chain, the proposed parallel mechanism can achieve 5-DOF of the moving platform with only three branch chains. Afterwards, analytical solution for inverse kinematics is derived. The 5$\times$5 homogeneous Jacobian matrix is obtained by transforming actuator velocities into linear velocities at three points on the moving platform. Meanwhile, the workspace, dexterity, and volume are analyzed based on the kinematic model. Ultimately, a stage-by-stage Pareto optimization method is proposed to solve the multi-objective optimization problem of this parallel mechanism. The optimization results show that the workspace, compactness, and dexterity of this mechanism can be improved efficiently.

This paper presents a study on the effect of design parameters of an underactuated hand on its grasp performance. Three kinds of grasp performance characteristics are considered: grasp range, grasp strength, and immobilizing grasp range. Grasp strength is defined as the stiffness of the grasp. Immobilizing grasps are those in which the object cannot be moved for a force up to a certain threshold. In general, underactuated hands cannot produce immobilizing grasps. However, we show that immobilizing grasps can be created by including joint limits in the hand design. We consider the effect of two design parameters on the grasp performance: torque ratio and finger-base distance. Results show that an optimal finger-base distance and torque ratio exists that maximizes the grasp range and grasp strength. Also, the immobilizing grasp range is increased by decreasing the finger-base distance and increasing the torque ratio and joint limits.

We analyze the design of an international climate agreement. In particular, we consider two goals of such an agreement: overcoming free-rider problems and adjusting for differences in mitigation costs between countries. Previous work suggests that it is difficult to achieve both of these goals at once under asymmetric information because countries free ride by exaggerating their abatement costs. We argue that independent information collection (investigations) by an international organization can alleviate this problem. In fact, though the best implementable climate agreement without investigations fails to adjust for individual differences even with significant enforcement power, a mechanism with investigations allows adjustment and can enable implementation of the socially optimal agreement. Furthermore, when the organization has significant enforcement power, the optimal agreement is achievable even with minimal investigative resources (and vice versa). The results suggest that discussions about institutions for climate cooperation should focus on information collection as well as enforcement.

To overcome the physical limitations of mechanical bone cutting in minimally invasive surgery, we are developing a miniature parallel robot that enables positioning of a pulsed laser with an accuracy below 0.25 mm and minimizes the required manipulation space above the target tissue. This paper presents the design, control, device characteristics, functional testing, and performance evaluation of the robot. The performance of the robot was evaluated within the scope of a path-following experiment. The required accuracy for continuous cuts was achieved and reached 0.176 mm on the test bench.

The paper presents a comprehensive design process for the development of the minimally actuated Closed Loop Articulated Mechanical (CLAM) hand. Each of the fingers is designed as a planar one degree of freedom eight-bar linkage with an anthropomorphic backbone chain. The fingers movement is based on experimentally obtained physiological precision grasping task, with incorporated second-order task specifications, related to maintaining fingertip–body contact with a minimum number of fingers. Instead of actuating individual joints in each finger, the mechanism generates the desired anthropomorphic grasping trajectory using a single actuator in each finger. The paper offers not only details on multi-loop articulated hands design based on anthropometric data and physiological task with second-order effects for maintaining the object–fingertip contact, but also shows how this class of hands that have been considered mostly for adaptive grasping can be successfully utilized for precision grasping. The minimal number of fingers and actuators can simplify the control, resulting in a robust, lightweight, and cost-effective solution for the precision grasping of a variety of objects with different shapes and geometries.

This paper investigates the relationship between economic theory and theories of justice in the design of public policy. In particular, it focuses on the role of mechanism design in policy contexts beset with issues of social, racial and distributive justice. Economists’ involvement in redesigning Boston’s algorithm for allocating K-12 students to public schools serves as an instructive case study. The paper draws on the distinction between ideal theory and non-ideal theory in political philosophy and the concept of performativity in economic sociology to argue that mechanism design can enact elaborate ideal theories of justice. A normative gap thus emerges between the goals of the policymakers and the objectives of economic designs. As a result, mechanism design may obstruct stakeholders’ avenues for normative criticism of public policies, and serve as a technology of depoliticization.

This paper presents the design, analysis and experimentation of a Discrete Modular Serpentine Tail (DMST). The mechanism is envisioned for use as a robotic tail integrated onto mobile legged robots to provide a means, separate from the legs, to aid stabilization and maneuvering for both static and dynamic applications. The DMST is a modular two-degree-of-freedom (DOF) articulated, under-actuated mechanism, inspired by continuum and serpentine robotic structures. It is constructed from rigid links with cylindrical contoured grooves that act as pulleys to route and maintain equal displacements in antagonistic cable pairs that are connected to a multi-diameter pulley. Spatial tail curvatures are produced by adding a roll-DOF to rotate the bending plane of the planar tail curvatures. Kinematic and dynamic models of the cable-driven mechanism are developed to analyze the impact of trajectory and design parameters on the loading profiles transferred through the tail base. Experiments using a prototype are performed to validate the forward kinematic and dynamic models, determine the mechanism's accuracy and repeatability, and measure the mechanism's ability to generate inertial loading.

We adopt mechanism design to study the effects of inflation on output, trade, and capital accumulation. Our theory captures multiple channels for individuals to respond to inflation: search intensity, market participation, and substitution between money and a higher return asset. We characterize constrained efficient allocations and show inflation has nonmonotonic effects on the frequency of trades (extensive margin) and the total quantity traded (intensive margin). The model features monetary superneutrality for low inflation rates, nonlinearities in trading frequencies, and substitution of money for capital for higher inflation rates. While these effects are difficult to capture in previous models, we show how they are intimately related by all being features of an optimal trading mechanism.