Cable-suspended robot

Cable-suspended robots may move beyond their static workspace by keeping all cables under tension, thanks to end-effector inertia forces. This may be used to extend the robot capabilities, by choosing suitable dynamical trajectories. In this paper, we consider three-dimensional (3D) elliptical trajectories of a point-mass end effector suspended by three cables from a base of generic geometry. Elliptical trajectories are the most general type of spatial sinusoidal motions. We find a range of admissible frequencies for which said trajectories are feasible; we also show that there is a special frequency, which allows the robot to have arbitrarily large oscillations. The feasibility of these trajectories is verified via algebraic conditions that can be quickly verified, thus being compatible with real-time applications. By generalizing previous studies, we also study the possibility to change the frequency of oscillation: this allows the velocity at which a given ellipse is tracked to b...

Highlights • A cable-suspended robot is presented with a spatial purely translational motion. • Several special architectures are identified with distinctive and useful features. • The singularity-free/reachable/interference-free workspaces are analytically found. • The theoretical findings are validated by experimental tests. • The robot can perform dynamic trajectories outside the static equilibrium workspace.

Cable-Driven Parallel Robots (CDPRs) displace the end-effector (EE) by means of cables configured in a parallel fashion. When a CDPR employs fewer cables than the degrees of freedom (DoFs) of its EE, it is underactuated and underconstrained. As a result, only a limited subset of the EE DoFs can be controlled assigning specific cable lengths, and determining the EE pose through direct kinematics (DK) is unfeasible, since it also depends on mechanical equilibrium. To estimate the EE pose, then, it may be convenient to acquire and combine redundant measurements. This paper introduces a sensor fusion technique that aims at achieving the optimal estimation of the pose of a generic UACDPR. Sensor fusion is achieved by an iterative nonlinear weighted least-square algorithm, which is solved by a Gauss-Newton-like method. A novel criterion for terminating iterations, which is physically sound and straightforward to implement, is put forward. Different redundant measurements are experimentally compared, so as to show the performance of the method with different sensors involved.

A cable suspended robot can be moved beyond its static workspace while keeping all cables in tension, by relying on end-effector inertia forces. This allows the robot capabilities to be extended by choosing suitable dynamical trajectories. In this paper, we study 3D elliptical motions, which are the most general case of spatial sinusoidal oscillations, for a robot with a point-mass end-effector and an arbitrary base architecture. We find algebraic conditions that define the range of admissible frequencies for feasible trajectories; furthermore, we show that, under certain conditions, a special frequency exists, which allows arbitrarily large oscillations to be reached. We also study transition trajectories that displace the robot from an initial state of rest (within the static workspace) to the elliptical trajectory, and vice versa.

Cable-suspended robots may move beyond their static workspace by keeping all cables under tension, thanks to end-effector inertia forces. This may be used to extend the robot capabilities, by choosing suitable dynamical trajectories. In this paper, we consider three-dimensional (3D) elliptical trajectories of a point-mass end effector suspended by three cables from a base of generic geometry. Elliptical trajectories are the most general type of spatial sinusoidal motions. We find a range of admissible frequencies for which said trajectories are feasible; we also show that there is a special frequency, which allows the robot to have arbitrarily large oscillations. The feasibility of these trajectories is verified via algebraic conditions that can be quickly verified, thus being compatible with real-time applications. By generalizing previous studies, we also study the possibility to change the frequency of oscillation: this allows the velocity at which a given ellipse is tracked to b...

In this paper, we have presented the 3D cables parallel robot in pyramid’s form. The dynamic equation has been established including the dynamic behavior, in this context; we investigated to use the Runge Kutta method of 4th order to solving non-linear partial differential equation of our system. The main contribution of this work is firstly: a graphical user interface (GUI) has been developed and implemented based on the geometric model, in order to visualizing the position of end effect or, taking account model uncertainties and payload variation. Secondly, we have studied and solved our system’s dynamical equation with implementation the PD control. This last, applied for different trajectories so as to test the accurate tracking the desired trajectory simulation using MATLAB software. As a result, the simulation tests on this robot verify the efficiency performance of the proposed controller.

The paper investigates the motion planning of a suspended service robot platform equipped with ducted fan actuators. The platform consists of an RRT robot and a cable suspended swinging actuator with ducted fans that form a subsequent parallel kinematic chain. The system is redundant and, in spite of the complementary ducted fan actuators, it is underactuated. The paper discusses the inverse dynamics problem and proposes trajectory generation methods for the motion planning of the complex hybrid robotic system. The closed form results include the desired actuator forces as well as the nominal swing angle corresponding to the desired motion of the carried payload. Numerical simulation and experiments demonstrate the applicability of the presented concepts.

As the additive manufacturing industry grows, it is compounding the global plastic waste problem. Distributed recycling and additive manufacturing (DRAM) offers an economic solution to this challenge, but it has been relegated to either small-volume 3D printers (limiting waste recycling throughput) or expensive industrial machines (limiting accessibility and lateral scaling). To overcome these challenges, this paper provides proof-of-concept for a novel, open-source hybrid 3D printer that combines a low-cost hanging printer design with a compression-screw-based end-effector that allows for the direct extrusion of recycled plastic waste in large expandable printing volumes. Mechanical testing of the resultant prints from 100% waste plastic, however, showed that combining the challenges of non-uniform feedstocks and a heavy printhead for a hangprinter reduced the strength of the parts compared to fused filament fabrication. The preliminary results are technologically promising, however, and provide opportunities to improve on the open-source design to help process the volumes of waste plastic needed for DRAM to address the negative environmental impacts of global plastic use.

This paper addresses the direct geometrico-static analysis of under-constrained cable-driven parallel robots with 3 cables. The task consists in finding all equilibrium configurations of the end-effector when the cable lengths are assigned. An interval-analysis-based procedure is proposed to numerically find the real solutions of the problem for a robot of generic geometry. Three equation sets obtained by different approaches are implemented in the problem-solving algorithm and a comparison between the main advantages and disadvantages of each one of them is reported.

The systems for observation of the workspace with moving objects have been developed and analyzed worldwide in various research areas and for different purposes. It is important that both kinematic and dynamic modeling of these systems is considered. Relatively new systems that are designed and analyzed are parallel systems. Authors of the paper [1] consider the kinematic design of a planar three-degree-of-freedom parallel manipulator. They have established and analyzed four different optimal design criteria. Cable-driven parallel robot has attracted the interest of researchers since the very beginning of the study of parallel robots presented in [2]. This type of robot has the advantage of having light mobile mass, simple linear actuators with possibly relatively large stroke and less risk of interference between the legs. On the other hand their major drawback is that wire actuator can only pull and not push. In previous researches several prototypes of cable-driven parallel robot...

Variable-Stiffness Actuators are continuously increasing in importance due to their characteristics that can be beneficial in various applications. It is undisputed that several one-degree-of-freedom (DoF) solutions have been developed thus far. The aim of this work is to introduce an original two-DoF planar variable-stiffness mechanism, characterized by an orthogonal arrangement of the actuation units to favor the isotropy. This device combines the concepts forming the basis of a one-DoF agonist-antagonist variable-stiffness mechanism and the rigid planar parallel and orthogonal kinematic one. In this paper, the kinematics and the operation principles are set out in detail, together with the analysis of the mechanism stiffness.

This paper studies the kinematics and statics of cable-driven parallel robots with less than six cables, in crane configuration. A geometrico-static model is provided, together with a general procedure aimed at efficiently solving, in analytical form, the inverse and direct position problems. The stability of equilibrium is assessed within the framework of a constrained optimization problem, for which a purely algebraic formulation is provided. A spatial robot with three cables is studied as an application example.

This paper presents an efficient interval-analysis-based algorithm to solve the direct geometrico-static problem (DGP) of underconstrained cable-driven parallel robots (CDPRs). Solving the DGP for a generic CDPR consists of finding all possible equilibrium poses of the end effector for the given cable lengths. Since cables impose unilateral constraints, configurations with one or more slack cables may occur. When the number of taut cables is smaller than six the robot is underconstrained and the DGP solutions must be found considering loop-closure and mechanical equilibrium equations simultaneously. The presented algorithm can find all DGP solutions of a generic CDPR in a numerically robust and safe way. By using interval analysis the proposed procedure can directly search for real solutions with non-negative cable tensions and it can take advantage of the physical constraints of the robot. The implemented procedure is discussed in detail, and the testing and experimental validation...

We consider dynamic motions of a spatial robot suspended by six cables, arranged so as to form three parallelograms. Each parallelogram is composed by two parallel cables sharing the same length. Due to this arrangement, the end-effector can only translate. The cables in each parallelogram can be actuated by one motor: only three motors are then required, which reduces the robot complexity and cost. This robot may perform pick-and-place operations over large workspaces. We find tight conditions for feasibility of dynamic trajectories for the general architecture, and also special conditions such that the robot is dynamically equivalent to a 3-cable robot with a point-mass end-effector: then, the feasibility conditions previously developed for the dynamic trajectories of 3-cable point-mass robots can be profitably reused for the present case. To practically realize such dynamic trajectories, we also analyze the reachable, singularity-free and interference-free workspace, finding analytical expressions of their loci. Finally, we perform experiments where the robot follows dynamic trajectories outside its static workspace, thus finding confirmation that the orientation remains approximately constant.

Cable suspended robots may move beyond their static workspace by keeping all cables under tension, thanks to end-effector inertia forces. This may be used to extend the robot capabilities, by choosing suitable dynamical trajectories. In this paper, we consider 3D elliptical trajectories of a point-mass end-effector suspended by 3 cables from a base of generic geometry. Elliptical trajectories are the most general type of spatial sinusoidal motions. We find a range of admissible frequencies for which said trajectories are feasible; we also show that there is a special frequency which allows the robot to have arbitrarily large oscillations. The feasibility of these trajectories is verified via algebraic conditions that can be quickly verified, thus being compatible with real-time applications. By generalizing previous studies, we also study the possibility to change the frequency of oscillation: this allows the velocity at which a given ellipse is tracked to be varied, thus providing more latitude in the trajectory definition. We finally study transition trajectories to move the robot from an initial state of rest (within the static workspace) to the elliptical trajectory (and vice versa) or to connect two identical ellipses having different centres.

—In this paper we present a new family of overhead travelling cranes based on variable radius drums, called Cable-Based Robotic Cranes (CBRCs). A Variable Radius Drum (VRD) is characterized by the variation of the spool radius along its profile. This kind of device is used, in this context, for the development of a cable-robot, which can support and move a load through a planar working area with just 2 degrees-of-freedom. Firstly, we present the kinematic analysis and the synthesis of the geometry of VRD profile. Then, the schema of a bi-dimensional horizontal moving mechanism, based on the VRD theory, and an experimental prototype of a three-dimensional CBRC are presented. The features of this wire-based overhead crane and an analysis of cables tensions are discussed. Finally, the performance of this mechanism is evaluated, demonstrating a deviation between the end-effector and the nominal planar surface of less than 1% throughout the whole working area.

In this paper, a new method of recording the position and orientation of the end effector as a feedback of a spatial cable-suspended robot is presented based on coupling the data of image processing and laser sensors. All of the degrees of freedoms (DOFs) of the end effector can be easily fed back through the proposed protocol in an online way and with the highest accuracy. This method has advantages over encoder feedback method since encoder feedback method does not consider the effect of structural uncertainties like vibrations of the cables. Also, the proposed method is preferable to ultrasonic sensor feedback method or accelerometers, because it does not suffer from the effect of reflecting the sound from obstacles and indoor small room syndrome or the accelerometer noise problems. It is possible to use this setup in almost every environmental situation and for any configuration of the end effector. The position and orientation of the end effector recorded in an online way are used to prepare a feedback signal and control the robot in a closed-loop way using feedback linearization approach. A simulation study is carried out on the ICaSbot which is a spatial cable-suspended robot. Finally, experimental tests are conducted on the ICaSbot to validate the proposed algorithm and simulation results performed in the MATLAB environment.

We present in this paper a new mechanical architecture for a parallel manipulator. We address the problem of the determination of the singular configurations of this architecture. Then we show that the direct kinematic problem has at most 16 solutions and exhibit an algorithm to find all the solutions.

There are two main systems that can be used to coil and uncoil the wires of a wire-driven parallel robots: a rotary motor that turns a drum on which the wire is coiled or a linear motor with a pulley system. The rotary category may be divided into two sub-categories: the system with a spiral guide for the coiling, allowing only layer for the wire and the system without guide, that allows for several wire layers with the drawback that the amount of coiled wire for one motor turn depends upon the number of layer. All three systems are ...

This paper presents an efficient interval-analysis-based algorithm to solve the direct geometrico-static problem (DGP) of underconstrained cable-driven parallel robots (CDPRs). Solving the DGP for a generic CDPR consists of finding all possible equilibrium poses of the end effector for the given cable lengths. Since cables impose unilateral constraints, configurations with one or more slack cables may occur. When the number of taut cables is smaller than six the robot is underconstrained and the DGP solutions must be found considering loop-closure and mechanical equilibrium equations simultaneously. The presented algorithm can find all DGP solutions of a generic CDPR in a numerically robust and safe way. By using interval analysis the proposed procedure can directly search for real solutions with non-negative cable tensions and it can take advantage of the physical constraints of the robot. The implemented procedure is discussed in detail, and the testing and experimental validation on working prototypes are presented.

Abstract This paper studies under-constrained cable-driven parallel robots with three cables. A major challenge in the study of these manipulators is the intrinsic coupling between kinematics and statics, which must be tackled simultaneously. In this contribution, a general elimination procedure is provided that solves the direct geometrico-static problem, which consists in determining the platform posture and the cable tensions when the cable lengths are assigned. The problem is proven to have up to 156 complex solutions.

This paper presents the inverse geometrico-static analysis of under-constrained cable-driven parallel robots with 4 cables.
The problem consists in finding all equilibrium configurations of the end-effector when either its orientation or the center-of-mass's position is assigned.
In both cases, a further point of the end-effector is constrained to lie on a given plane.
A major challenge is posed by the intrinsic coupling between kinematics and statics, which must be tackled simultaneously.
The problems at hand are solved by analytical elimination procedures, thus leading to univariate polynomials free of spurious factors.
All potential solutions may be real.