Cable-suspended Robot Research Articles

Design of a Cable-Suspended Robot for Early Stage Gait Rehabilitation

Design of a Cable-Suspended Robot for Early Stage Gait Rehabilitation

Beyond-the-static-workspace point-to-point trajectory planning of a 6-DoF cable-suspended mechanism using oscillating SLERP

This paper presents a general framework for the planning of point-to-point motions that extend beyond the static workspace of six-degree-of-freedom cable-suspended parallel mechanisms. The proposed translational trajectories are based on a generalization of the hypocycloidal motion previously introduced for cable-suspended robots. Also, the concept of ideal kinematic state is used to maximize the chances of obtaining feasible trajectories, i.e., trajectories in which tension is maintained in the cables. The rotational component of the trajectories is based on the use of spherical linear interpolation. A novel formulation is proposed to connect two arbitrary orientations through oscillations going through the reference orientation. It is shown that the impact of the translational trajectories on the tension constraints is largely dominant, compared to that of the rotational trajectories. A procedure is presented for the determination of the trajectory parameters in order to ensure the continuity of the trajectories. Trajectory feasibility is verified, including mechanical interferences and singularity detection. Finally, a natural cylindrical coordinate frame is proposed that yields a very intuitive description of the trajectories and simulation results are given to illustrate the effectiveness of the proposed approach.

Workspace analysis and optimal design of dual cable-suspended robots for construction

Given their advantages of large workspaces and high payload-to-weight ratios, cable-driven parallel mechanisms have great potential for use in on-site autonomous construction. This paper proposes a configuration containing two cable-suspended robots driven by eight cable pairs (four cable pairs each), which form parallelograms, to perform construction efficiently in terms of time and space. A core issue of this system is the collision problems that occur in dynamic construction processes. The use of the distance between two spatial line segments is proposed to calculate collision detection, and the wrench-feasible workspace is examined to analyze the collision-free buildable workplace. The operation mode of dual cable-suspended robots for construction is discussed herein. Further, the design variables of the dual cable-suspended robot are optimized using multi-objective particle swarm algorithm to ensure a sufficiently large collision-free buildable workspace with suitable scale and payload of the frame of the cable robots for construction.

Feedback motion control of a spatial double pendulum manipulator relying on swept laser based pose estimation

Spatial pose estimation devices for mobile and cable-suspended robots have been rapidly developed. The HTC Vive sensor, which operates with swept laser beams, has aroused many researchers’ interest. We present experiments with a double pendulum robot equipped with the HTC Vive Tracker. A linear feedback controller ensured the tracking of pre-defined end-effector trajectories of various speeds. The pose feedback of the controller was provided by the HTC Vive. As a reference, the realized trajectory was measured by the OptiTrack motion capture system. We report that the motion control of a spatial double pendulum robot can be achieved by using a linear feedback controller together with cable winch and fan actuators providing six independent inputs. The accuracy of the HTC Vive was proved to be sufficient for the feedback position control of indoor mobile robots. We report that the error strongly correlates with the linear/angular velocity, the acceleration and the jerk.

Motion control of a cable-suspended robot using image recognition with coordinate transformation

This study will concern the implementation of a vision-based controller for cable-suspended robots, and especially for the pick-and-place function. This work will develop a novel algorithm that combines cable-suspended robot coordinate transformation with image recognition to manipulate the suspended gripper to the desired position for material-handling tasks. Two webcams sense the position of the end-effector; one will be used to calculate the horizontal planar coordinate of the target, and the other will be used to determine the vertical height of the target. Accordingly, the two-dimensional spatial image can be converted into three-dimensional image coordinates. Based on the sensed information, the robot can convert the position of the target to required cable lengths and then drive the servomotor to retract (or release) the cables to move the suspended gripper to the desired position. Various experiments will be conducted to verify the proposed methodology. The framework that is developed herein is easily implemented for real-time control and is suitable for inclusion in mechatronic kits in a university control course. The large variety of ideas that are addressed in this work apply to cranes, aerostats, and other large-scale manufacturing equipment that requires cable-driven robots.

Adaptive robust control of a four-cable-driven parallel robot

This present study introduces an adaptive control strategy for four-cable robots. An adaptive sliding mode control to overcome the uncertainties of the system as well as avoidance of estimating an upper bound of the system uncertainties is presented. The proposed controller is designed based on the Lyapunov stability theory. Therefore, it ensures the stability of the closed-loop system and makes the tracking error converge to zero. In this robot, the cables can only pull the end-effector but not push it; therefore, we present a simple mathematical solution to design a positive tension controller for the cable suspended robot with redundant cables. The properties of the proposed method such as high performance tracking, disturbance rejection and insensitivity to parameter variations are demonstrated by simulation.

Adaptive robust control of a four-cable-driven parallel robot

This present study introduces an adaptive control strategy for four-cable robots. An adaptive sliding mode control to overcome the uncertainties of the system as well as avoidance of estimating an upper bound of the system uncertainties is presented. The proposed controller is designed based on the Lyapunov stability theory. Therefore, it ensures the stability of the closed-loop system and makes the tracking error converge to zero. In this robot, the cables can only pull the end-effector but not push it; therefore, we present a simple mathematical solution to design a positive tension controller for the cable suspended robot with redundant cables. The properties of the proposed method such as high performance tracking, disturbance rejection and insensitivity to parameter variations are demonstrated by simulation.

Differential Noncircular Pulleys for Cable Robots and Static Balancing

In this paper, we introduce a mechanism consisting of a pair of noncircular pulleys with a constant-length cable. While a single noncircular pulley is generally limited to continuously winding or unwinding, the differential cable routing proposed here allows to generate nonmonotonic motions at the output of the arrangement, i.e., the location of the idler pulley redirecting the cable. The equations relating its motion to rotation angles of the noncircular pulleys and to the cable length are presented in the first part of this paper. Next, we introduce a graphical method allowing us to obtain the required pulley profiles for a given output function. Our approach is finally demonstrated with two application examples: the guiding of a cable-suspended robot along a complex trajectory using a single actuator, and the static balancing of a pendulum with a 360 deg rotational range of motion.

Design and implementation of a multi-degrees-of-freedom cable-driven parallel robot with gripper

Cable-driven parallel robots comprise driven actuators that allow controlled cables to act in parallel on an end-effector. Such a robotic system has a potentially large reachable workspace, large load capacity, high payload-to-weight ratio, high reconfigurability, and low inertia, relative to rigid link serial and parallel robots. In this work, a multi-degrees-of-freedom cable-suspended robot that can carry out pick-and-place tasks in large workspaces with heavy loads is designed. The proposed cable-driven parallel robot is composed of a rigid frame and an end-effector that is suspended from eight cables—four upper cables and four lower cables. The lengths of the cables are computed from the given positions of the suspended end-effector using a kinematic model. However, most multi-cable-driven robots suffer from interference among the cables, requiring a complex control methodology to find a target goal. Owing to this issue with cable-driven parallel robots, the whole control structure decomposes positioning control missions and allocates them into upper level and lower level. The upper level control is responsible for tracking the suspended end-effector to the target region. The lower level control makes fine positional modifications. Experimental results reveal that the hybrid control mode notably improves positioning performance. The wide variety of issues that are considered in this work apply to aerostats, towing cranes, locomotion interfaces, and large-scale manufacturing that require cable-driven parallel robots.

Algae Harvesting from Large Outdoor Ponds Using a Novel Parallel Robot System

This paper presents a novel method for effective, economical, energy-efficient algae harvesting from large (1-4 acre) outdoor circulating raceway pond systems: a portable 4-cable-suspended robot. Algae, used as an alternative energy crop to produce biofuels (and other consumer products), still remains too expensive. One of the greatest expenses in processing algae is the harvesting process. To replace the typical energy-intensive pumping of the entire pond water through algae filters, we propose using a cable-suspended robot to collect algae, which largely then drains of water while the robot translates the product to a collection point. An additional benefit of our concept, in additional to lower harvesting cost, is that the algae still growing in the pond is not shocked as in the current pumping process, leading to better, healthier yields. Further, the proposed robot system is portable, capable of harvesting multiple ponds while algae continues to grow.

Dynamically Feasible Periodic Trajectories for Generic Spatial Three-Degree-of-Freedom Cable-Suspended Parallel Robots1

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 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 centers.

SDRE controller for motion design of cable-suspended robot with uncertainties and moving obstacles

In this paper an optimal control approach for nonlinear dynamical systems was proposed based on State Dependent Riccati Equation (SDRE) and its robustness against uncertainties is shown by simulation results. The proposed method was applied on a spatial six-cable suspended robot, which was designed to carry loads or perform different tasks in huge workspaces. Motion planning for cable-suspended robots in such a big workspace is subjected to uncertainties and obstacles. First, we emphasized the ability of SDRE to construct a systematic basis and efficient design of controller for wide variety of nonlinear dynamical systems. Then we showed how this systematic design improved the robustness of the system and facilitated the integration of motion planning techniques with the controller. In particular, obstacle avoidance technique based on artificial potential field (APF) can be easily combined with SDRE controller with efficient performance. Due to difficulties of exact solution for SDRE, an approximation method was used based on power series expansion. The efficiency and robustness of the SDRE controller was illustrated on a six-cable suspended robot with proper simulations.

Tracking Control and Vibration Reduction of Flexible Cable-Suspended Parallel Robots using a Robust Input Shaper

The control of flexible cable-driven parallel robots usually requires not only the feedback from the joints, but the feedback from the end-effector pose or cable tension. This paper presents a new approach for reducing the vibration of flexible cable-suspended robots, using only the feedback from the joints. First, the dynamic equations of a 6DOF cable-suspended parallel robot with elastic cables were derived by Gibbs-Appel formulation. Subsequently, three different control approaches were investigated based on the computation load and required sensors. As a result, a feedback linearization method based on the rigid model of the system was selected. In order to reduce the vibration, a robust input shaping method was employed to prevent excitation of natural modes. Simulation results revealed that the proposed approach leads to a noticeable vibration and settling time reduction in cases of low and high cable stiffness, respectively. Moreover, another simulation compares the presented approach with a composite controller, which uses the feedbacks from the end-effector and actuators. Thereafter, the performance of the approach in vibration reduction is quantitatively shown. Finally, experimental validation of the approach was accomplished by frequency analysis of the vibration obtained from the IMU sensor, attached to the end-effector.

Modeling and control of a cable-suspended robot for inspection of vertical structures

In this paper, a cable-driven system is examined for the application of inspection of large, vertical-walled structures such as chemical storage tanks, large ship hulls, and high-rise buildings. Such cable-driven systems are not commonly used for these tasks due to vibration, which decreases inspection accuracy and degrades safety. The flexible nature of the cables make them difficult to control. In this paper, input shaping is implemented on a cable-driven system to reduce vibration. To design the input shapers, a model of the cable-driven system was developed. Analysis of the dominant dynamics and changes in them over the large workspace are also presented. The performance improvements provided by the input shaping controller are quantified through a series of simulations.

A modularized cable-suspended robot: Implementation and oscillation suppression control

Cable-suspended robots are categorized as a style of parallel manipulator that has appealed interest for manipulation jobs. This article presents a design for a cable-suspended robot system with oscillation suppression control. The major benefits of the system design are as follows: modular, transportable, reconfigurable, and easy to install. This robotic system consists of the main object, which is a suspended platform and a cable winch that maneuvers the main object by regulating cable lengths. Furthermore, this study presents a combined control module to serve as an associate controller to stabilize the system. The associate controller positions and oscillates the suppression properties by integration feedback control with the shaping signals. The fuzzy controller is rule based and constructed based on associate controller performance-related knowledge to act as a controller. Accordingly, the proposed control scheme effectively reduces cable oscillation, especially when fuzzy control methodology is applied. The broad variety of problems deliberated in this study can be applied to assembly, automation, and large-scale manufacturing that requires a cable-suspended system.

A mechatronic kit with a control methodology for a modualized cable-suspended robot

Cable-suspended robots are categorized as a type of parallel manipulator that has recently attracted interest in terms of manipulation tasks. The main goal of this paper is to develop a novel mechatronic kit with a control methodology for a modularized cable-suspended robot. The advantages of such system owns modular and reconfigurable over conventional robots. In addition, position and orientation of the end-effector is forced toward the desired values by control of cable lengths. Hence, the new approach for forward and inverse kinematic calculation procedure based on the change of the cable lengths is used to measure the position and orientation of the mobile platform. Furthermore, the input shaping algorithm is implemented for point-to-point control purposes. The modified input shaping uses the s curve command (S-type) to offer superior performance than conventional trapezoidal command (T-type) in point-to-point positioning control. Experimental validation demonstrates the cable oscillation suppression effectiveness of the proposed S-type input shaping control command.

Optimal regulation of a cable suspended robot equipped with cable interfering avoidance controller

Closed-loop regulation of a spatial cable suspended robot is performed in this paper subject to maximizing the Dynamic Load Carrying Capacity (DLCC) of the end-effector while the cable interference is avoided actively. Optimization is performed between two predefined boundaries and considering the cable interference constraint. This constraint is satisfied by designing a controller which prevents the cables’ collision. The overall formulation of the closed-loop optimal control based on Feedback linearization is derived in this paper for planning the optimal path with the highest load capacity. Then a complementary adaptive controller is designed and implemented to the main controller which is responsible for providing cable interfering avoidance. The efficiency of the designed controller for preventing the cables’ collision is shown by performing and analyzing some comparative simulations conducted on an under constrained cable robot with six cables and six DOFs. All results related to regulation, tracking and DLCC are compared between the simple optimal closed-loop system and the system which is equipped with the proposed cable interfering avoidance controller. It is proved that the planned path satisfies cable interference constraint while its DLCCs are optimized.

Large-scale 3D printing with a cable-suspended robot

Although additive manufacturing (AM) is now a well-established industry, very few large-scale AM systems have been developed. Here, a large-scale 3D printer is introduced, which uses a six-degree-of-freedom cable-suspended robot for positioning, with polyurethane foam as the object material and shaving foam as the support material. Cable-positioning systems provide large ranges of motion and cables can be compactly wound on spools, making them less expensive, much lighter, more transportable, and more easily reconfigurable, compared to the gantry-type positioning systems traditionally used in 3D printing. The 3D foam printer performance is demonstrated through the construction of a 2.16-m-high statue of Sir Wilfrid Laurier, the seventh Prime Minister of Canada, at an accuracy of approximately 1cm, which requires 38h of printing time. The system advantages and drawbacks are then discussed, and novel features such as unique support techniques and geometric feedback are highlighted. Finally, a description of the planned system modifications is provided.

Geometry Selection of a Redundantly Actuated Cable-Suspended Parallel Robot

This paper is dedicated to the geometry selection of a redundantly actuated cable-suspended parallel robot intended to manipulate heavy payloads over a wide workspace. Cable-suspended refers here to cable-driven parallel robots in a crane-like setting, where all the cable drawing points are located on top of the base frame, gravity being used to keep the cables taut. Geometry selection consists of determining the relative positions of the cable drawing points on the base frame and of the cable attachment points on the mobile platform together with the cable arrangement between these two sets of points. An original performance index is introduced. It is defined as the maximum acceptable distance between the mobile platform geometric center and the center of mass of the set consisting of the platform and a payload. This performance index is of particular interest in heavy payload handling applications. Used within a two-phase geometry selection strategy, it yields a new cable-suspended robot geometry having a very large workspace to footprint ratio and able to handle heavy payloads. A large-dimension redundantly actuated cable-suspended robot was built in order to demonstrate these capabilities.

2P1-O04 洗浄機能を有したワイヤ移動式橋梁検査ロボットの開発

2P1-O04 洗浄機能を有したワイヤ移動式橋梁検査ロボットの開発