Justus Laurens Herder

Translational stiffness of the replaced shoulder joint.

Results after a total shoulder arthroplasty in rheumatoid patients are poor, indicated by loosening of especially the glenoid component, bad joint functionality and the possibility of a joint dislocation. The failure mechanisms behind this are multiple, including patient, surgical and design factors. These results must be improved. At present, the optimal geometrical prosthesis component design, focused on joint conformity and constraint, still has to be investigated. Proper understanding of the effect of geometrical design parameters on the theoretical relationship between joint translations and joint forces may contribute to improved designs. The main objective of this study is to theoretically describe this relationship and to investigate the joint translational stiffness, which can be used to investigate the effect of design parameters on joint motion. Joint translational stiffness is the gradient of the subluxation force with respect to the humeral head displacement. For this static analysis a potential field is introduced, as the result of a joint compressive force (muscle forces) and a subluxation force (external forces). The positive and negative stiffness during articulation inside and subluxation outside the glenoid cavity, lead to stable and unstable equilibrium joint positions, respectively. A most lateral position of the humeral head centre coincides with a zero subluxation force; at this position the humerus is dislocated and a restoring force is needed to relocate the humeral head. Joint conformity and compression force influence the joint translational stiffness during articulation inside the glenoid cavity, whereas during articulating outside the glenoid cavity this is influenced by the joint compression force and humeral radius of curvature. The glenoid radius of curvature influences the contact point and, in combination with the glenoid superior-inferior chord length, it also influences the constraintness angle, which influences the maximum allowable subluxation load to prevent a joint dislocation. This constraintness angle together with the joint conformity also influences maximum joint translations before articulation outside the glenoid cavity. Furthermore, the sign of the joint translational stiffness determines the stability of shoulder motion, which is stable and unstable if this stiffness is positive and negative, respectively.

Development of a Mobile Arm Support (Armon): Design Evolution and Preliminary User Experience

This paper regards three design iterations of a mobile arm support (Armon): the initial proof-of-concept version, the intermediate clinical-experimental version, and the present first-product version. This is done by comparing the mechanical architecture, features and specification on the one hand, and some user experiences with these successive devices on the other hand. Furthermore, several users report on their use of the device in activities of daily living.

A review of assistive devices for arm balancing

Due to neuromuscular disorders (e.g., Duchenne Muscular Dystrophy) people often loose muscle strength and become wheelchair bound. It is important to use muscles as much as possible. To allow this, and to increase independency of patients, an arm orthoses can be used to perform activities of daily life. The orthoses compensates for the gravity force of the arm, allowing people to perform movements with smaller muscle forces. For patients, the aesthetics of the orthosis is one of the critical issues. This paper presents the state-of-the-art in passive and wearable active arm orthoses, and investigates how to proceed towards a suitable structure for a wearable passive arm orthosis, that is able to balance the arm within its natural range of motion and is inconspicuous; in the ideal case it fits underneath the clothes. Existing devices were investigated with respect to the body interface, the volume, and the workspace. According to these evaluation metrics it is investigated to what extent the devices are wearable and inconspicuous. Furthermore, the balancing principle of the devices, the architecture, force transmission through the devices, and alignment with the body joints are investigated. It appears that there is only one wearable passive orthosis presented in literature. This orthosis can perform throughout the natural workspace of the arm, but is still too bulky to be inconspicuous. The other passive orthoses were conspicuous and mounted to the wheelchair. Except one, the wearable active orthoses were all conspicuous and heavy due to a large backpack to enclose the actuators. They also could not achieve the entire natural workspace of the human arm. A future design of an inconspicuous, wearable, passive arm orthoses should stay close to the body, be comfortable to wear, and supports pronation and supination.

Energy-Free Adjustment of Gravity Equilibrators Using the Virtual Spring Concept

People with neuromuscular diseases often have limited muscle force, and many rely on mobile arm supports to move their arms. Most of these make use of static balancing, a useful concept to reduce the operating effort of mechanisms, where spring mechanisms are used to achieve a constant total potential energy, thus eliminating any preferred position. Once statically balanced, the mechanism can be moved virtually without operating energy. This allows the patients using an arm support to move their arms freely. In some cases it is desirable to adjust the balancer characteristic, for instance due to a change of payload when picking up an object. In all available arm support mechanisms this adjustment is associated with considerable mechanical effort, while clearly this application would benefit greatly from an energy-free adjustment. Recently several methods have been invented to adjust spring and linkage-based static balancers with no need for external energy, by conserving the total energy in the system. The technique discussed in this paper is based on substituting an initial spring by two substitute springs. The two substitute springs generate a virtual spring with the same spring properties as the initial spring, with one unique difference: the virtual spring can be elongated or shortened while no work is done. Consequently, no external energy is needed for the adjustment. A table-top demonstrator has been developed, showing the feasibility of the concept.

Guidelines for Low Mass and Low Inertia Dynamic Balancing of Mechanisms and Robotics

Dynamic balance of machines is important when, for example, high precision in combination with low cycle times is necessary. One of the major problems with dynamic balancing is that considerable mass and considerable inertia need to be added to the mechanism. So far, only a few studies have been carried out into the comparison of various dynamic balancing principles in order to reduce these additions. Based on the findings of these studies, this paper aims to formulate guidelines for the design of dynamically balanced mechanisms with low mass and low inertia additions. Furthermore, the influence of limited design space on the resulting mass and inertia is investigated

Bistable Compliant Mechanisms: Corrected Finite Element Modeling for Stiffness Tuning and Preloading Incorporation

Bistable straight-guided buckling beams are essential mechanisms for precision engineering, compliant mechanisms, and MEMS. However, a straightforward and accurate numerical modeling have not been available. When preloading effects must be included, numerical modeling becomes an even more challenging problem. This article presents a straightforward numerical model for bistable straight-guided buckling beams, which includes preloading effects as well. Adjusting the bistable force–displacement characteristic by variation of design parameters and preloading is also investigated. Both lumped compliance and distributed compliance are considered in this work. In order to validate the model, measurements have been performed. It was shown that a small precurvature of bistable straight-guided buckling beams is crucial to avoid convergence into higher order buckling modes in nonlinear analysis of ANSYS™ and to obtain reliable results. Transient analysis using ANSYS™ with subsequent preloading and motion displacements can incorporate preloading effects. Moreover, the model correction allows accurate description of the increased symmetry and energy efficiency of the bistable behavior in case of increasing (in order of effectiveness) the initial angle and preloading for the case of distributed compliance. This behavior was observed by increasing the initial angle, thickness, and length of the rigid segment for the case of lumped compliance.

A structured overview of trends and technologies used in dynamic hand orthoses

The development of dynamic hand orthoses is a fast-growing field of research and has resulted in many different devices. A large and diverse solution space is formed by the various mechatronic components which are used in these devices. They are the result of making complex design choices within the constraints imposed by the application, the environment and the patient’s individual needs. Several review studies exist that cover the details of specific disciplines which play a part in the developmental cycle. However, a general collection of all endeavors around the world and a structured overview of the solution space which integrates these disciplines is missing. In this study, a total of 165 individual dynamic hand orthoses were collected and their mechatronic components were categorized into a framework with a signal, energy and mechanical domain. Its hierarchical structure allows it to reach out towards the different disciplines while connecting them with common properties. Additionally, available arguments behind design choices were collected and related to the trends in the solution space. As a result, a comprehensive overview of the used mechatronic components in dynamic hand orthoses is presented.

The Scope for a Compliant Homokinetic Coupling Based on Review of Compliant Joints and Rigid-Body Constant Velocity Universal Joints

Many applications require a compliant mechanism to transmit rotation from one direct to another direct with constant velocity. This paper presents a literature survey towards the design of compliant constant velocity universal joints. The traditional constant velocity universal joints available from the literature were studied, classified and their mechanical efficiencies were compared. Also the graph representation of them was studied. In the same manner, literature review for different kind of compliant joints suitable for the Rigid-Body-Replacement of constant velocity universal joints was also performed. For the first time a comparison with analytical data of compliant joints was performed. All of compliant universal joints are non-constant velocity and designed based on rigid Hooke’s universal joint. Also we show there are no equivalent compliant joints for some rigid-body joints such as cylindrical joint, planar joint, spherical fork joint and spherical parallelogram quadrilateral joint. However, we may achieve them by combining numbers of available compliant joints. The universal joints found are non-compliant non-constant velocity universal joint, non-compliant constant velocity universal joint or compliant non-constant velocity universal joint. A compliant constant velocity universal joint has a great horizon for developments, for instance in medical or rehabilitation devices.Copyright

Dynamic Balancing of Clavel’s Delta Robot

The Delta robot has shown to be a useful device in many applications. Due to large accelerations however, vibrations can decrease the accuracy and performance considerably. Instead of common techniques to reduce vibrations such as damping or including waiting times in the motion cycle, this article shows how the Delta robot can be dynamically balanced in a practical way by which all vibrations are eliminated. Because of its specific architecture, the Delta robot can be force balanced with only three counter-masses and two additional links. Moment balancing can be achieved by active actuation of three additional rotating inertias

Double Pendulum Balanced by Counter-Rotary Counter-Masses as Useful Element for Synthesis of Dynamically Balanced Mechanisms

Complete dynamic balancing principles still cannot avoid a substantial increase of mass and inertia. In addition, the conditions for dynamic balance and the inertia equations can be complicated to derive. This article shows how a double pendulum can be fully dynamically balanced by using counter-rotary counter-masses (CRCMs) for reduced additional mass and inertia. New CRCM-configurations were derived that have a low inertia, a single CRCM or have all CRCMs near the base. This article also shows how a CRCM-balanced double pendulum can be used as building element in the synthesis of balanced mechanisms for which the balancing conditions and inertia equations can be written down quickly. For constrained mechanisms the procedure is to first write down the known balancing conditions and inertia equations for the balanced double pendula and subsequently substitute the kinematic relations.