On the Design of a Portable Force Illusion Device for Navigation Aids

Navigation aids rely mostly on (audio)visual cues when it comes to communication with the user. An alternative and more intuitive communication modality may be provided by means of haptic guidance generated by a portable mechatronic device. Especially visually impaired and blind people may benefit from a device that generates the illusion of an external force; it may possibly eliminate the need for a guide dog. This paper investigates constant-velocity crank-driven mechanisms which are able to generate such a force illusion by means of a reciprocating mass. The focus of this paper is on the generation of the illusion itself rather than manipulating the direction of this force. The force illusion is a result of successive positive and negative reaction forces with unequal amplitude, generated by a reciprocating mass. The acceleration ratio of the mass is selected as the main evaluation criterion for comparing different types of candidate mechanisms. Because the input is a simple motor rotating at a constant velocity, the synthesis of the mechanism is key to generating proper acceleration profiles. A brute-force approach is used for the synthesis procedure, i.e., characteristic distances and link lengths are varied with steps of 1mm for each of the candidate mechanisms, thereby generating very large numbers of variants. Kinematic performance reveal typical acceleration ratios in the range of 1 to 19; where a ratio of one does not result in a force illusion while a ratio of 19 might be demanding on the physical design. An objective evaluation leads to selecting the Square Recti-Linear mechanism as the overall most promising candidate mechanism. A prototype of this mechanism is then presented to demonstrate the working principle. The shape of the prototype’s force profile over time is measured experimentally and is shown to be very similar to the profile obtained by simulation. The reciprocating mass accounts for almost one fifth of the total mass of the prototype, resulting in a strong force illusion in comparison with gravitational forces.

A Task Driven Approach to the Synthesis of Spherical 4R Linkages Using Algebraic Fitting Method

This paper studies the problem of spherical 4R motion approximation from the viewpoint of extraction of circular geometric constraints from a given set of spherical displacements. This paper extends our planar 4R linkage synthesis work to the spherical case. By utilizing kinematic mapping and quaternions, we map spherical displacements into points and the workspace constraints of the coupler into intersection of algebraic quadrics (called constraint manifold), respectively, in the image space of displacements. The problem of synthesizing a spherical 4R linkage is reduced to finding a pencil of quadrics that best fit the given image points in the least squares sense. Additional constraints on the pencil identify the quadrics that represent a spherical circular constraint. The geometric parameters of the quadrics encode information about the linkage parameters which are readily computed to obtain a spherical 4R linkage that best navigates through the given displacements. The result is an efficient and largely linear method for spherical four-bar motion generation problem.

Microsurgical Devices by Pop-Up Book MEMS

The small scale of microsurgery poses significant challenges for developing robust and dexterous tools to grip, cut, and join sub-millimeter structures such as vessels and nerves. The main limitation is that traditional manufacturing techniques are not optimized to create smart, articulating structures in the 0.1–10 mm scale. Pop-up book MEMS is a new fabrication technology that promises to overcome this challenge and enable the monolithic fabrication of complex, articulated structures with an extensive catalog of materials, embedded electrical components, and automated assembly with feature sizes down to 20 microns. In this paper, we demonstrate a proof-of-concept microsurgical gripper and evaluate its performance at the component and device level to characterize its strength and robustness. 1-DOF Flexible hinge joints that constrain motion and allow for out-of-plane actuation were found to resist torsional loads of 22.8±2.15 N·mm per mm of hinge width. Adhesive lap joints that join individual layers in the laminate structure demonstrated a shear strength of 26.8±0.53 N/mm2. The laminate structures were also shown to resist peel loads of 0.72±0.10 N/mm2. Various flexible hinge and adhesive lap components were then designed into an 11-layered structure which ‘pops up’ to realize an articulating microsurgical gripper that includes a cable-driven mechanism for gripping actuation and a flexural return spring to passively open the gripper. The gripper prototype, with final weight of 200 mg, overall footprint of 18 mm by 7.5 mm, and features as small as 200 microns, is able to deftly manipulate objects 100 times is own weight at the required scale, thus demonstrating its potential for use in microsurgery.

Synthesis of Planar Mechanisms for Pick and Place Tasks With Guiding Locations

A novel dimensional synthesis technique for solving the mixed exact and approximate motion synthesis problem for planar RR kinematic chains is presented. The methodology uses an analytic representation of the planar RR dyads rigid body constraint equation in combination with an algebraic geometry formulation of the exact synthesis for three prescribed locations to yield designs that exactly reach the prescribed pick & place locations while approximating an arbitrary number of guiding locations. The result is a dimensional synthesis technique for mixed exact and approximate motion generation for planar RR dyads. A solution dyad may be directly implemented as a 2R open chain or two solution dyads may be combined to form a planar 4R closed chain; also known as a planar four-bar mechanism. The synthesis algorithm utilizes only algebraic geometry and does not require the use of a numerical optimization algorithm or a metric on planar displacements. Two implementations of the synthesis algorithm are presented; computational and graphical construction. Moreover, the kinematic inversion of the algorithm is also included. An example that demonstrates the synthesis technique is included.

Design and Fabrication of an Arm Exoskeleton for Aim Stabilization

Accurately aiming and firing a pistol requires a steady hand. While many devices can steady a shooter’s arm or hand by restricting movement or degrees-of-freedom, few devices actively reduce involuntary tremors while allowing larger voluntary aiming movements. This paper details the design and fabrication of an arm exoskeleton that can actively damp arm tremors while allowing voluntary aiming movements. The device allows five degrees-of-freedom and is very lightweight due to its cable-driven architecture and use of carbon fiber composite materials. Tremorous movement is filtered out from voluntary motion, and an adaptive algorithm provides a tremor-cancelling signal to the cable control motors.

Developing Metrics for Comparison of Mobile Robots Performing Welding Tasks

Developments in mobile robotic systems are leading to new methods and techniques for manufacturing processes in fields that traditionally have not seen much automation. Some of these tasks require process validation prior to use in the manufacturing process. One such example process is welding. However, there is a lack of industry standards for mechanized or robotic welding that can impede the introduction of mobile robotic welding systems in the market place. There is also a lack of generalized fitness measures that gauge the suitability of mobile robot topologies or dimensional designs to a set of tasks and can be used in the design or verification process. This paper will propose such a metric and demonstrate its use in evaluating mobile robot designs for welding tasks. The approach will be based on the representation of a general task as a pair of n-dimensional subsets in the Euclidean n-space. Similarly, the robot capabilities are represented as n-dimensional subsets (manipulability and torque ellipse) in the Euclidean n-space. The motivation is to enable a direct geometric comparison of the capabilities of the robot to the requirements of the task yielding a quantitative measure of fitness. This method is suggested to be well suited to tasks comprised of a relatively short sequence of well-defined motions, called gaits, which are performed repeatedly or in a periodic manner. Some examples are welding, swimming, painting or inspection. The paper will demonstrate the use of this metric in the evaluation and design of mobile robots for welding tasks with a desired set of weld pattern motions. Three mobile welding platforms having different topological kinematic arrangements will be evaluated based on this design verification metric. This metric will further be shown to supplement the weld qualification process through verification of the motion control portions of the weld process based on a specific robot design. The method will contribute to the design and development of mobile robotic welding systems to become viable and accepted manufacturing processes.

Soft Pneumatic Artificial Muscles With Low Threshold Pressures for a Cardiac Compression Device

In this paper, we present the design, fabrication and characterization of fully soft pneumatic artificial muscles (PAMs) with low threshold pressures that are intended for direct cardiac compression (DCC). McKibben type PAMs typically have a threshold pressure of at least 100 kPa and require rigid end fittings which may damage soft tissue and cause local stress concentrations, and thus failure points in the actuator. The actuator design we present is a variant on the McKibben PAM with the following key differences: the nylon mesh is embedded in the elastomeric tube, and closure of the end of the tube is achieved without rigid ends. The actuators were tested to investigate the effects of mesh geometry and elastomer material on force output, contraction, and rise time. Lower initial mean braid angles and softer elastomer materials provided the best force, contraction, and rise times; Up to 50 N of force, 24% contraction, and response times of 0.05 s were achieved at 100 kPa. The actuators exhibited low threshold pressures (<5 kPa) and high rupture pressures (138 kPa – 720 kPa) which suggest safe operation for the DCC application. These results demonstrate that the actuators can achieve forces, displacements, and rise times suitable to assist with cardiac function.

Control and Tension Estimation of a Cable Driven Mechanism Under Different Tensions

This paper proposes a method to estimate and compensate for the changes of cable tension in the control of cable driven mechanisms. Cable tension may depend on various factors, including mechanism design, fabrication and operation. In many systems it is also an adjustable parameter that affects the performance of the control system. An implementation of the unscented Kalman filter is used for the simultaneous estimation of the states and parameters of a cable driven mechanism. Changes in cable tension are captured in the estimated parameters which, along with system states, are used by a model predictive controller to generate appropriate control actions. The method is described and its effectiveness is shown for a single degree of freedom cable driven robot. In addition, the correlation between the cable tension and the estimated robot parameters provides a way of estimating the tension. It is shown that cable tension can be inferred from one of the estimated robot parameters, namely cable stiffness.

Dimensional Synthesis of Planar Eight-Bar Linkages Based on a Parallel Robot With a Prismatic Base Joint

This paper details the dimensional synthesis for the rigid body guidance of planar eight-bar linkages that could be driven by a prismatic joint at its base. We show how two RR cranks can be added to a planar parallel robot formed by a PRR and 3R serial chain to guide its end-effector through a set of five task poses. This procedure is useful for designers who require the choice of ground pivot locations. The results are eight different types of one-degree of freedom planar eight-bar linkages. We demonstrate the design process with the design of a multifunctional wheelchair that could transform its structure between a self-propelled wheelchair and a walking guide.