Abstract The subject of this paper is about the design, modeling, control and perfor- mance evaluation of a low cost and versatile robotic solution for logistics. The robot under study, named FASTKIT, is obtained from a combination of mobile robots and a Cable-DrivenParallelRobot (CDPR). FASTKIT addresses an industrial need for fast picking and kitting operations in existing storage facilities while being easy to install, keeping existing infrastructures and covering large areas. The FASTKIT prototype consists of two mobile bases that carry the exit points of the CDPR. The system can navigate autonomously to the area of interest. Once the desired position is attained, the system deploys the CDPR in such a way that its workspace corre- sponds to the current task specification. The system calculates the required mobile base position from the desired workspace and ensures the controllability of the plat- form during the deployment. Once the system is successfully deployed, the set of stabilizers are used to ensure the prototype structural stability. Then the prototype gripper is moved accurately by the CDPR at high velocity over a large area by con- trolling the cable tension.
4 CNRS, Laboratoire des Sciences du Num´erique de Nantes, UMR CNRS 6004, 1, rue de la
No¨e, 44321 Nantes, France, email@example.com
Abstract. A MobileCable-DrivenParallelRobot (MCDPR) is a special type of Reconfigurable Cable-DrivenParallelRobot (RCDPR) composed of a classical Cable-DrivenParallelRobot (CDPR) mounted on multiple mobile bases. The additional mobility of the mobile bases allows such systems to autonomously modify their geometric architecture, and thus make them suitable for multiple manipulative tasks in constrained environments. Moreover, these additional mo- bilities make MCDPRs kinematically redundant. Therefore, the subject of this paper is to introduce a two stage path planning algorithm for MCDPRs. The first stage searches for a feasible and collision free path of mobile bases. The second stage deals with generating an optimal path of the moving-platform to displace it from an initial to a desired pose. The proposed algorithm is validated through simulation on a three degree-of-freedom (DoF) point mass moving-platform dis- placed by four cables with each cable carried by an independent mobile base. Keywords: MobileCable-DrivenParallelRobot, Reconfigurability, Kinematic Redundancy, Path Planning, Wrench Analysis
VII. C ONCLUSION
In this paper, the Available Wrench Set required to trace the Wrench Feasible Workspace of a MobileCable-DrivenParallelRobot (MCDPR) has been determined. The proposed workspace considers the cable tension limits and the static equilibrium of the mobile bases. Two different approaches, the convex hull and the hyperplane shifting method, are used to illustrate how the additional constraints can be considered. The additional constraints modified the shape of the AWS, forming new facets and reducing the capability of the cables to apply wrenches on the platform. Future work will focus on extending this approach to spatial MCDPRs consisting of more than two mobile bases and taking into account wheel slipping constraints. Furthermore, the evolution of the MCDPR workspace during their deployment will be studied.
In this paper, we have proposed a methodology to determine the Available Wrench Set of MobileCable-DrivenParallel Robots. The Available Wrench Set is required to trace the Wrench-Feasible Workspace of MobileCable-DrivenParallel Robots. The proposed workspace depends, not only on the Static Equilibrium of the moving-platform, but on the Static Equilibrium of the Mobile Bases. The Available Wrench Set is formed using two different approaches i.e. Convex Hull and the Hyperplane Shifting Method. The equivalence of both approaches were shown. Initially all the conditions associated with the Static Equilibrium of a MobileCable-DrivenParallelRobot are formulated. Compared to the classical Cable-DrivenParallel Robots, the additional Static Equilibrium conditions associated with the Mobile Bases may affect the Available Wrench Set. Multiple case studies are carried out in order to show that the approach is applicable to both planar and spatial MobileCable-DrivenParallel Robots. The proposed approach is experimentally validated on a MobileCable-DrivenParallelRobot with a point-mass end-effector and two Mobile Bases. Future work will focus on exploiting the proposed methodology in order to find the wrench-feasible poses during the trajectory planning of MobileCable-DrivenParallel Robots.
Optimization based Trajectory Planning of MobileCable-DrivenParallel Robots
Tahir Rasheed 1 , Philip Long 2 , Adolfo Suarez Roos 3 and St´ephane Caro 4
Abstract— A MobileCable-DrivenParallelRobot (MCDPR) is composed of a classical Cable-DrivenParallelRobot (CDPR) carried by multiple mobile bases. The additional mobilities due the motion of the mobile bases allow such systems to autonomously modify their geometric architecture, and thus make them suitable for multiple manipulation tasks in con- strained environments. Moreover, these additional mobilities mean MCDPRs are kinematically redundant and may use this redundancy to optimize secondary task criteria. However, the high dimensional state space and closed chain constraints add complexity to the motion planning problem. To overcome this, we propose a method for trajectory planning for MCDPRs per- forming pick and place operations in cluttered environments by using direct transcription optimization. Two different scenarios have been considered and their results are validated using a dynamic simulation software (V-REP) and experimentally.
Some papers deals with the velocity analysis of parallel manipulators . How- ever, few focus on the twist analysis of CDPRs . This paper deals with the kine- matic modeling of MCDPRs that is required to analyze the kinematic performance of the robot. The paper is organized as follows. Section 2 presents the kinematic model of MCDPRs. Section 3 deals with the determination of the Available Twist Set (ATS) for MCDPRs using the kinematic modeling of the latter. The ATS can be used to obtain the twist capacities of the moving-platform. Section 4 presents the twist capacities of the moving-platform for the MCDPRs under study. Finally, conclusions are drawn and future work is presented in Section 5.
Fig. 8 Locations of the geometric center of the CAROCA mobile platform leading to some cable-
tubular structure is replaced with a single cylinder, to simplify the analysis of the in- terference regions. The results are shown in Fig. 8. For the cylinder included into the working area of the CDPR, eight interferences regions, namely one for each cable, are obtained. It is noteworthy that those regions are valid for a constant orientation of the mobile-platform.
Abstract—This paper proposes a Cable-DrivenParallelRobot
(CDPR) with three mobile cranes for search-and-rescue operations. Each mobile crane is composed of a reconfigurable telescopic boom, which can rotate. A cable is mounted from the tip of the telescopic boom to the end-effector. The locations of mobile cranes are fixed, but the configuration of the telescopic boom can be adjusted to enlarge the workspace and to maintain the overall system in equilibrium. The static equilibrium of end-effector and mobile cranes is initially studied to determine the cable tension distribution and wrench-feasible-workspace. To guarantee all mobile cranes to be always in a static equilibrium when executing a given task, the telescopic booms are reconfigured. Three case studies for the reconfigurable CDPR with multiple mobile cranes are presented to compare the tension distribution and workspace size.
allow the interference to be avoid, the latter approach may not be suitable for physical interaction with humans. Usually, the mobile platform’s trajectory is modified in order to avoid contact between two cables, and in some cases, the working space may also be limited. But during physical interaction where the CDPM is used as a collaborative handle, the trajectory depends on human actions and is considered a setpoint. In the literature, there are only a few studies where collisions between cables are permitted. For example,  proposes a method that allows collisions between cables in order to increase the workspace but the cables can still be crossed. This situation can cause unpredictable behavior depending on the mechanism geometry and cable dimensions. Indeed, the control could be disturbed for a brief time, since the cables in contact can generate significant frictions and then vibrations. As a result, the mechanism produces sudden displacements once the friction overcomes. Therefore, this situation may be dangerous to the operator in the case of a physical interaction. In , the authors present an approach based on admittance control where contact between a robot limb and the environment is allowed. The collaboration task is performed within the limits of the robot kinematic possibilities, by eliminating a column in the Jacobian that corresponds to the contact point position. The robot motion is adapted but can still move following an optimal trajectory with the contact as a constraint. This approach is also applied in a parallel mechanism  where an algorithm selects a cable to be released when interference occurs. Results demonstrate that the method is conclusive. However, this method could limit the workspace for our mechanism. In general, two cables are required to pull the mobile platform upwards and allow vertical displacements. If one of these two cables is released, movement may be compromised. In our work, we propose a new way to manage the contact point and prevent cables from crossing during physical interaction.
3 LIRMM, Universit´e de Montpellier, CNRS, Montpellier, France
Fig. 1. Cable-drivenparallelrobot CoGiRo with a 7-DOF robotic arm.
of a 6D workspace. Fast heuristic approaches are proposed in  whereas certified calculations based on interval analysis are introduced in , . Besides, an approximate deter- mination of the volume swept by a cable when the mobile platform of a CDPR moves within a prescribed workspace is discussed in  and the geometric determination of cable- cylinder collision loci within the workspace of a CDPR is dealt with in . In the latter, the cylinder is a fixed object located inside the CDPR workspace. Moreover, in , the collision-free printing workspace is calculated for fully- constrained CDPRs intended to print large-dimension objects in a sequence of horizontal layers. While all these methods determine various types of cable collision loci within a prescribed workspace, other previous works address the issue of checking cable collisions along a prescribed CDPR mobile platform path , , , which is also the purpose of the present paper. In , a classic discretized collision checking applied to CDPRs is presented. More advanced methods based on interval analysis, which can account for parameter uncertainties and round-off errors in numerical calculation, are introduced in , .
A general CDPR has a fixed cable layout, i.e. fixed exit points and cable config- uration. This fixed geometric structure may limit the workspace size of the manip- ulator due to cable collisions and some extrernal wrenches that cannot be accepted due to the robot configuration. As there can be several configurations for the robot to perform the prescribed task, an optimized cable layout is required for each task considering an appropriate criterion. Cable robots with movable exit and/or anchor points are known as Reconfigurable Cable-DrivenParallel Robots (RCDPRs). By appropriately modifying the geometric architecture, the robot performance can be improved e.g. lower cable tensions, larger workspace and higher stiffness. The re- cent work on RCDPR [2, 3, 9, 12, 15] proposed different design strategies and algo- rithms to compute optimized cable layout for the required task, while minimizing appropriate criteria such as the robot energy consumption, the robot workspace size and the robot stiffness. However, for most existing RCDPRs, the reconfigurability is performed either discrete and manually or continuously, but with bulky reconfig- urable systems.
In this paper, a methodology to determine the optimal kine- matic redundancy scheme of Planar MobileCableDriven Par- allel Robots (PMCDPRs) with one degree of kinematic redun- dancy for fast pick-and-place operations is described. First, the Static equilibrium (SE) constraints of PMCDPRs associated with the Mobile Bases (MBs) are formulated that are required to fully characterize the Available Wrench Set (AWS) of the latter. Then, a bi-objective optimization problem that corresponds to mini- mization of the total trajectory time and maximization of the robot average robustness index throughout the trajectory is for- mulated in order to determine the optimum kinematic redun- dancy scheme. A case study of a PMCDPR composed of two MBs, four cables and a three degree-of-freedom (DoF) moving platform is considered. Future work will deal with the experi- mental validation and the extension of the proposed methodol- ogy to spatial MobileCableDrivenParallel Robots (MCDPRs) with higher degrees of kinematic redundancy.
2 Tahir Rasheed, Philip Long, David Marquez-Gamez, and St´ephane Caro
numerous advantages over conventional robots, e.g, high accelerations , large payload capabilities , and large workspace .
However, a major drawback in classical CDPRs having fixed cable layout, i.e, fixed exit points and cable configuration, is the potential collisions between the cables and the surrounding environment which can significantly reduce the robot workspace. Better performances can be achieved with an appropriate CDPR archi- tecture. Cable robots with a possibility of undergoing a change in their geometric structure are known as Reconfigurable Cable-DrivenParallel Robots (RCDPRs). Different strategies have been proposed for maximizing the robot workspace or in- creasing platform stiffness in the recent work on RCDPRs . However, reconfig- urability is typically performed manually for most existing RCDPRs.
Cable loops have been addressed in several papers ,  and it was em- ployed in  for actuation of a hoist mechanism embedded in a MP. In the latter the large rotational amplitudes provided by a cable loop was used to actuate a one Degree of Freedom (DoF) mechanism, while here we employ two cable loops to actuate a tilt-roll wrist having a large rotational workspace. H. Khakpour et al. in , and  introduced differentially drivencableparallel robots using cable differentials. They proved that, by replacing single-actuated cables with differential cables the static and wrench feasible workspaces of CDPRs can be extended.
Abstract The research work presented in this paper introduces a Reconfigurable CableDrivenParallelRobot (RCDPR) to be employed in industrial operations on large structures. Compared to classic Cable-DrivenParallel Robots (CDPR), which have a fixed architecture, RCDPR can modify their geometric parameters to adapt their own characteristics. In this paper, a RCDPR is intended to paint and sandblast a large tubular structure. To reconfigure the CDPR from one side of the structure to another one, one or several cables are disconnected from their current anchor points and moved to new ones. This procedure is repeated until all the sides of the structure are sandblasted and painted. The analysed design procedure aims at defining the positions of the minimum number of anchor points required to complete the task at hand. The robot size is minimized as well.
2 Manipulator Architecture
The end-effector is a sphere supported by actuated omni-wheels as shown in Fig. 1. The wrist contians three passive ball joints at the bottom and three active omni- wheels being driven through drums. Each cable makes several loops around each drum. Both ends are connected to two servo-actuated winches, which are fixed to the base. When two servo-actuated winches connected to the same cable turn in the same direction, the cable circulates and drives the drum and its associated omni- wheel. When both servo-actuated winches turn in opposite directions, the length of the cable loop changes, and the sphere centre moves. To increase the translation workspace of the CDPR, another cable is attached, which has no participation in the omni-wheels rotation. The overall design of the manipulator is shown in Fig. 2.
As the name suggests, a cable-drivenparallelrobot (CDPR) is a parallelrobot that is actuated by flexible cables instead of rigid links. The main advantages of CDPRs are their large workspace (WS), low mass in motion, high veloc- ity and acceleration capacity , and reconfigurability . However, their accuracy should be substantially improved to meet a broader spectrum of industrial applications. In that sense, different approaches can be considered, such as the use of: (i) more precise, but more complex CDPR models ; (ii) force sensors to measure cable tensions ; (iii) angular position sensors to measure cable angle position ; and (iv) exteroceptive sensors, such as cameras, to measure where the robot is with respect to its environment   . Vision-based control is becoming more and more popular with the novel robot tasks, human-robot collaboration, and the need for robustness to different uncertainties. There are two main approaches of visual servoing: it can be either image-based or pose-based . In the latter, using informa- tion from the image and some additional knowledge about the object (usually its model), the pose of the object with respect to (w.r.t.) the camera is retrieved. Then the control scheme is minimizing the difference between this acquired pose and the desired one. In image-based visual servoing, 2D image coordinates of the object or other image data are retrieved instead of a Cartesian pose. Here, the control This work is supported by IRT Jules Verne (French Institute in Research and Technology in Advanced Manufacturing Technologies for Composite, Metallic and Hybrid Structures) in the framework of the PERFORM project.
c CNRS, Laboratoire des Sciences du Num´erique de Nantes, UMR CNRS 6004, 1, rue de la No¨e, 44321 Nantes, France
∗ Corresponding author. Tel.: +33-240-376-925; fax: +33-240-376-925. E-mail address: Saman.Lessanibahri@ls2n.fr
Cable-DrivenParallel Robots (CDPRs) also noted as wire-driven robots are parallel manipulators with ﬂexible cables instead of rigid links. A CDPR consists in a base frame, a Moving-Platform (MP) and a set of cables connecting in parallel the MP to the base frame. CDPRs are well-known for their advantages over the classical parallel robots in terms of large workspace, reconﬁgurability, large payload capacity and high dynamic performance. In spite of all the mentioned advantages, one of the main shortcomings of the CDPRs is their limited orientation workspace. The latter drawback is mainly due to cable interferences and collisions between cables and surrounding environment. Hence, a planar four-Degree-of-Freedom (DoF) under-constrained CDPR with an articulated MP is introduced and studied in this paper. The end-effector is articulated through a cable loop, which enables the robot to obtain a modular pose determination, namely orientation and positioning. As a result, the mechanism under study has an unlimited and singularity-free orientation workspace in addition to a large translational workspace. It should be noted that some unwanted rotational motions of the moving platform, namely, parasitic inclinations, arise due to the cable loop. Finally, those parasitic inclinations are modeled and assessed for the mechanism at hand.
Fig. 1: Architecture of a CDPR developed in the framework of the IRT Jules Verne CAROCA project.
CDPRs have several advantages such as a relatively low mass of moving parts, a potentially very large workspace due to size scalibility, and reconfiguration capa- bilities. Therefore, they can be used in several applications, e.g. heavy payload han- dling and airplane painting , cargo handling , warehouse applications , large-scale assembly and handling operations [28, 33], and fast pick-and-place oper- ations [18, 21, 29]. Other possible applications include the broadcasting of sporting events, haptic devices [8, 10, 31], support structures for giant telescopes [35, 34], and search and rescue deployable platforms [23, 24]. Recent studies have been per- formed within the framework of an ANR Project CoGiRo  where an efficient cable layout has been proposed  and used on a large CDPR prototype called CoGiRo.
In order to avoid such situations, Marionet-Assist was designed, built and integrated in a full-scaled apartment (see. Fig.1). Marionet-Assist is a cable-drivenparallelrobot (CDPR) which provides services such as walking-aid, lifting people, and may also be used to collect information concerning for example the health of the user. The parallel structure allows for an easy lift of elderly people and has less intrusivity and a much more lighter design than any serial one. The limited workspace which is the usual drawback of parallel robots has been overcome by choosing a cable-driven mechanism ,  with motorized drums that are used that can coil or uncoil the wires .