The study of the relationship between the desired system dynamics and the actuation wrench producing those dynamics is important for robotic system analysis. For traditionally actuated robots, the quality indices of dexterity and manipulability quantify this relationship. However, for unilaterally actuated robots (UARs), such as grasping hands and cable-driven parallel robots (CDPRs), these indices cannot be applied due to the unilateral actuation constraint. In this paper, the quality indices of unilateral dexterity ( UD ) and unilateral maximum force amplification (UMFA) are established for UARs with arbitrary number of actuators. It is shown that these quality indices provide task-independent quantifications of the physical properties of robustness and force amplification for UARs, and they can measure the mechanism’s capability both in singular and nonsingular poses. With these indices, manipulability ellipsoid-derived measures can be applied to arbitrary UARs. The significance of the quality indices for robot synthesis and motion generation analysis is illustrated through two case studies: a five-fingered grasp selection problem and the workspace analysis of a spatial CDPR.

This paper presents a singularity study on a special class of spatial Cable-Suspended Parallel Mechanisms (CSPMs) with merely three translational degrees of freedom using redundant actuators. This paper focuses on the CSPMs which have the capability to perform the purely translational movement with pairwise cables as parallelograms. There are two types of singularity to be discussed, which result from dynamic equations of CSPMs and the parallelogram constraint of pairwise cables. To ensure three-translational dofs without rotation of the end-effector, the matrix formed by normals of the planes based on each pairwise cables should maintain in full rank. In the case study, four typical designs of CSPMs with a planar end-effector and a spatial end-effector are discussed to clarify and conclude the singularity features of CSPMs with actuation redundancy. The results show that for some architectures there exist both types of singularity for redundantly actuated CSPMs with pairwise cables but for some other architectures the redundant actuation exerts no effect on the singularity issue.

Binary-state and component independent assumptions will lead to doubtful and misleading redundancy allocation schemes which may not satisfy the reliability requirements for real engineering applications. Most published works proposed methods to remove the first assumption by studying the degradation cases where multiple states of a component are from the best state to the degradation states then to the completely failed state. Fewer works focused on removing the second assumption and they only discussed dependent failures which are only a special case of component dependency. This work uses the Semi-Markov process to describe a two-component system for redundancy allocation. In this work, multiple states of a component are represented by multiple output levels, which are beyond the scope of degradation, and the component dependency is not limited to failure dependency only. The load sharing is also taken care of in the proposed work. The optimal redundancy allocation scheme is obtained by solving the corresponding redundancy allocation optimization problem with the reliability measure, the system availability, obtained through the Semi-Markov process model being constraint. Two case studies are presented, demonstrating the applicability of the propose method.

Wrench-closure is an important property of cable-driven parallel manipulators (CDPMs), representing the ability to generate wrench in any direction by positive cable forces. For single link CDPMs, it is well known that m ≥ n + 1 cables are necessary for an n degrees-of-freedom CDPM to achieve wrench-closure. However, for multilink cable-driven manipulators (MCDMs), this condition is too relaxed and the cable routing should also be considered. In this paper, necessary conditions to achieve wrench-closure for MCDMs are mathematically derived based on the cable routing arrangements. Since the approach is independent on the exact attachment locations, the proposed necessary conditions can be efficiently validated during the design and synthesis of MCDMs. Analysis is performed on a range of different MCDM structures to identify cable arrangements that do not satisfy wrench-closure for an MCDM.

The recently popularized domain of additive manufacturing (AM) has much to offer to medical device development, especially to the growing field of minimally invasive surgery (MIS). With the advancements in AM materials, one could soon envision materializing not only the proofs of concept but also the final clinically approved instruments. DragonFlex—the world's first AM steerable MIS instrument prototype—was recently devised with the aim to follow this vision. Apart from the medical device design restrictions, several limitations of AM materials and processes had to be considered. The aim of this paper is to present these insights to those opting for this means of manufacture, serving as a helpful design and material guide. Over the course of its development, DragonFlex has gone through four design generations so far, each differing in the AM material and process used. Due to being a prototype of a MIS instrument of miniature dimensions, the printing processes were limited to stereolithography (SLA), as to achieve the best possible precision and accuracy. Each SLA process and material brought along specific advantages and disadvantages affecting the final printout quality, which needed to be compensated for either at the design stage, during, or after printing itself. The four DragonFlex generations were printed using the following SLA techniques and materials in this order: polymer jetting from Objet VeroBlue™; SLA Digital Light Processing™ (DLP) method from EnvisionTEC ® NanoCure RCP30 and R5; conventional SLA from 3D Systems Accura ® 60; and DLP based SLA process from a ceramic composite. The material choice and the printing orientation were found to influence the final printout accuracy and integrity of thin features, as well as material's postproduction behavior. The polymeric VeroBlue™ proved structurally sound, although suffering from undermined accuracy and requiring postprocessing, hence recommended for prototyping of upscaled designs of looser manufacturing tolerances or overdimensioned experimental setups. The NanoCure materials are capable of reaching the best accuracy requiring almost no postprocessing, thus ideal for prototyping small intricate features. Yet their mechanical functionality is undermined due to the high brittleness of RCP30 and high flexibility of R5. The transparent Accura ® 60 was found to lose its strength and appeal due to high photosensitivity. Finally, the ceramic composite shows the best potential for medical use due to its biocompatibility and superior mechanical properties, yet one has to compensate for the material shrinkage already at the design stage.

This paper presents the mechanical design of a novel surgical robotic platform, specifically developed for single-port laparoscopy (SPL). The greatest constraint is the small size of the skin incision through which the robot must operate. Several technical and technological challenges have been tackled to meet the stringent requirements imposed by the surgical procedure at hand. In this paper, a detailed mechanical description of the system is provided, fulfilling the necessary design requirements. The main outcome of this work is a compact, light-weight (total weight approximately 6 kg) and highly dexterous bimanual robot capable of overcoming the current drawbacks experienced in SPL when using traditional medical devices. The system has been assessed in terms of tracking accuracy, resulting in satisfactory and promising performance.

This paper deals with the design of a cable-driven manipulator (CDM) with instrumented structure for magnetic resonance imaging (MRI)-guided interventions. The strong magnetic field and the limited space inside the scanner constitute two severe design constraints. To handle them, a new synthesis approach for CDM is proposed in order to optimize the device compactness. This approach is based on the use of the zonotope properties to optimize the robot geometry, and the interval analysis tools for its validation. Remote actuation with Bowden cables is considered for MRI-compatibility. High friction along the line transmissions can then be expected which leads to a new instrumentation for cable tension evaluation. A prototype is manufactured and assessed. The principle of the instrumentation is validated as well as the user requirements in terms of workspace and ability to resist to external forces applied by the physician.

China is now building the world’s largest single dish radio telescope in Guizhou province, which is called Five-hundred meter Aperture Spherical radio Telescope (FAST). The main purpose of this paper is to present an effective dimensional design method on the six-cable driven parallel manipulator of FAST. Sensitivity design method is adopted for the six-cable driven parallel manipulator of FAST. Cable has the capability to bear tension but not compression, so that cable driven parallel manipulator may not be controlled as expected if tension of one cable is small or zero. Therefore, for dimensional design of the six-cable driven parallel manipulator, three functions to evaluate tension performance were proposed. The tension performance functions can reflect the uniformity of cable tension and controllability of the six-cable driven parallel manipulator. According to the sensitivity design method and tension performance evaluating functions, a set of optimized dimensional parameters is calculated for constructing the six-cable driven parallel manipulator of FAST. In order to verify the optimization design result, a similarity model of the six-cable driven parallel manipulator was set up in Beijing. A serial of experiments shows that tension performance of the six-cable driven parallel manipulator satisfies the system’s requirement. More importantly, it provides a theoretical reference for further study on dimensional design of a cable driven parallel manipulator with large span.

In this paper, a technique to generate the wrench-closure workspace for general case completely restrained cable driven parallel mechanisms is proposed. Existing methods can be classified as either numerically or analytically based approaches. Numerical techniques exhaustively sample the task space, which can be inaccurate due to discretisation and is computationally expensive. In comparison, analytical formulations have higher accuracy, but often provides only qualitative workspace information. The proposed hybrid approach combines the high accuracy of the analytical approach and the algorithmic versatility of the numerical approach. Additionally, this is achieved with significantly lower computational costs compared to numerical methods. It is shown that the wrench-closure workspace can be reduced to a set of univariate polynomial inequalities with respect to a single variable of the end-effector motion. In this form, the workspace can then be efficiently determined and quantitatively evaluated. The proposed technique is described for a 3 degrees of freedom (3-DOF) and a 6-DOF cable driven parallel manipulator. A detailed example in workspace determination using the proposed approach and comparison against the conventional numerical approach is presented.

This paper deals with the design of a new class of hybrid mechanism dedicated to humanoid robotics application. Since the designing and control of humanoid robots are still open questions, we propose the use of a new class of mechanisms in order to face several challenges that are mainly the compactness and the high power to mass ratio. Human ankle and wrist joints can be considered more compact with the highest power capacity and the lowest weight. The very important role played by these joints during locomotion or manipulation tasks makes their design and control essential to achieve a robust full size humanoid robot. The analysis of all existing humanoid robots shows that classical solutions (serial or parallel) leading to bulky and heavy structures are usually used. To face these drawbacks and get a slender humanoid robot, a novel three degrees of freedom hybrid mechanism achieved with serial and parallel substructures with a minimal number of moving parts is proposed. This hybrid mechanism that is able to achieve pitch, yaw, and roll movements can be actuated either hydraulically or electrically. For the parallel submechanism, the power transmission is achieved, thanks to cables, which allow the alignment of actuators along the shin or the forearm main axes. Hence, the proposed solution fulfills the requirements induced by both geometrical, power transmission, and biomechanics (range of motion) constraints. All stages including kinematic modeling, mechanical design, and experimentation using the HYDROïD humanoid robot’s ankle mechanism are given in order to demonstrate the novelty and the efficiency of the proposed solution.

A novel hybrid cable-driven mechanism with Cartesian motion is introduced. It consists of a rigid-link Cartesian mechanism and a cable drive system with stationary actuators to provide the motion. The cable drive system is self-stressed meaning that the tension in the cables required to keep them taut is provided internally and hence does not depend on either actuation redundancy or external sources such as gravity. This keeps the number of actuators at minimum and also eliminates the static loading of actuators as well as redundant work. The kinematic analysis of the mechanism is presented. The forward and inverse kinematic solutions are found and shown to be linear and pose independent. Also the stiffness of the mechanism induced by the compliance of the cable is analyzed to find the weakest stiffness. For this purpose, a parameter called “compliance length” is defined and used. Compliance length presents the stiffness of the mechanism by the length of the cable with the same stiffness. It makes the analysis independent from the design and the properties of the cable and can be quite useful in the design process. Finally, two dynamic models are given for the mechanism depending on whether or not the cable is stretchable and the properties of each model are discussed.

This paper addresses the issues of control and workspace determination of planar active tensegrity or tensegritylike structures. The motion of such structures is generally produced by actuated cables, which cannot tolerate compressive forces. Hence, a controller, which not only satisfies the system dynamic equations but also maintains positive tension in cables, is necessary. A null-space controller based on feedback linearization theory is developed for this purpose. This controller utilizes redundant active cables to overactuate the system. The concept of a “dynamic workspace” for these structures is then introduced. This workspace consists of all configurations that are achievable from a given initial configuration while maintaining positive tensions throughout the entire system motion, and it is a powerful tool in analyzing the performance of a variety of tensegrity structures. This idea extends the concept of the static workspace, which consists of statically maintainable configurations, by incorporating system motion and dynamics to guarantee positive tensions during transition between the states. A critical benefit of this procedure is that it may be used to find the dynamic workspace of a system regardless of whether actuator redundancy is utilized, and thus it can be used to objectively illustrate the degree to which overactuation improves mobility of a tensegrity structure. The effectiveness of the developed concepts is demonstrated through computer simulation and actual physical experimentation.

Over the past decade, cable-driven parallel mechanisms have been used for several purposes. In this paper, a novel application is proposed, namely, using two 6DOF cable-driven parallel mechanisms sharing a common workspace to obtain the mechanical base for the design of a locomotion interface. The methodology used to develop the architecture of the mechanisms is presented, and the two main criteria used to optimize the geometry are described. These criteria are based on the wrench-closure workspace and a detection of the mechanical interferences between all the entities of the locomotion interface (cables and moving bodies). Then, the final design is described and its performances are given. Finally, in order to validate the relevance of the mechanism for the locomotion interface’s design, tensile forces in the cables are computed to observe the maximal values reached during a typical human gait trajectory.

Cable transmissions offer several advantages such as high stiffness to weight ratio, high strength, low friction, and absence of backlash, which makes them appropriate for demanding mechanical applications. However, while extensively used as rotational transmissions, there are only a few examples of linear cable transmissions in the literature. The reason is that the up-to-date designs are based on a cable layout that leads to cable length changes during movement. This, in turn, produces negative effects such as transmission nonlinearity and cable fatigue. In this paper, an alternative design for linear cable transmissions is presented. The new design overcomes the aforementioned problems through a proper cable layout. Different applications of the new transmission are reported, validating the proposed design.

This paper illustrates the use of dynamic performance analysis in the design of legged robots, specifically hexapods. This is accomplished by comparing the dynamic performance of a cable-driven hexapod to that of a more conventional design in which the actuators are mounted at the joints. By integrating the actuators into the torso and through the use of cable transmission, the mass and inertias of the legs are reduced in order to attain high accelerations and backdrivability. The dynamic performance described herein is bounded by the actuator torque limits and the no-slip condition at the ground contact points. The result is a description of how well each hexapod can accelerate its torso without causing slippage at the ground contact points.

In this paper we present a study of the dynamics and control of a helicopter carrying a payload through a cable-suspended robot. The helicopter can perform gross motion, while the cable suspended robot underneath the helicopter can modulate a platform in position and orientation. Due to the underactuated nature of the helicopter, the operation of this dual system consisting of the helicopter and the cable robot is challenging. We propose here a two time scale control method, which makes it possible to control the helicopter and the cable robot independently. In addition, this method provides an effective estimation on the bound of the motion of the helicopter. Therefore, even in the case where the helicopter motion is unknown, the cable robot can be stabilized by implementing a robust controller. Simulation results of the dual system show that the proposed control approach is effective for such a helicopter-robot system.

This paper develops analytical techniques to delineate the workspace boundaries for parallel mechanisms with cables. In such mechanisms, it is not only necessary to solve the closure equations but it is also essential to verify that equilibrium can be achieved with non-negative actuator (cable) forces. We use tools from convex analysis and linear algebra to derive closed-form expressions for the workspace boundaries and illustrate the applications using planar and spatial examples.

Modal disparity and a topology optimization problem seeking to maximize this disparity are introduced, with the goal of developing a new methodology for control of vibration in flexible structures. Modal disparity is generated in a structure by the application of external forces that vary the stiffness of the structure. When the forces are switched on and off and, as a result, the structure is switched between two stiffness states, modal disparity results in vibration energy being transferred from a set of not-controlled modes to a set of controlled modes. This allows the vibration of the structure to be completely attenuated by removing energy only from a small set of controlled modes. A topology optimization problem determines the best locations for application of the external forces. Simulation results are presented to demonstrate control of vibration exploiting modal disparity in two three-dimensional (3D) frame structures.

This paper presents a method for characterizing the performance limitations imposed by the yielding of the cables in systems with cable-driven transmissions. The method involves developing a rigid-body model of the system, where the cable tensions are considered as reaction forces. The kinematic coupling between links in the mechanism due to the use of cables is also considered. Here, the limitations on dynamic performance caused by cable yielding are added to the limitations caused by the bounds on actuator torque capacity, in order to give a more comprehensive description of the system’s capabilities. A two degrees-of-freedom planar mechanism is analyzed in order to illustrate the methodology.