Cable-driven Parallel Mechanism Research Articles

Analysis of Cable-Force Transmission Characteristics and Disturbing Force/Moment of High-Acceleration Cable-Driven Parallel Mechanism

During the landing process of a probe, the backshell separation stage is full of uncertainty and risk. To mitigate this, it is necessary to simulate spacecraft separation prior to launch to verify safety and performance. A high-acceleration cable-driven parallel mechanism is normally used to simulate the force state required for the backshell to separate. Unfortunately, little attention has been paid to research the cable force on the end-effector, especially under high acceleration. In this article, a dynamic model of the cable-force transmission is proposed. The influences of disturbing force/moment on the position and orientation of the end-effector and axial force are analyzed. Indices for evaluating the performance of the cable-force transmissions are proposed. The factors affecting the performance are also explored. Finally, the experimental results are used to verify the correctness of the proposed dynamic model. The deviation caused by the disturbing force/moment is basically consistent with the desired deviation. The increase in the disturbing force/moment correspondingly reduces the resultant force of the end-effector. A series of experiments provide guidance and a theoretical basis for a ground simulation experiment of spacecraft separation.

Haptic User Interface of a Cable-Driven Input Device to Control the End Effector of a Surgical Telemanipulation System

Abstract In robotic telemanipulation for minimally-invasive surgery, lack of haptic sensation and non-congruent movement of input device and manipulator are major drawbacks. Input devices based on cable-driven parallel mechanisms have the potential to be a stiff alternative to input devices based on rigid parallel or serial kinematics by offering low inertia and a scalable workspace. In this paper, the haptic user interface of a cable-driven input device and its technical specifications are presented and assessed. The haptic user interface allows to intuitively control the gripping movement of the manipulator’s end effector by providing a two-finger precision grasp. By design, the interface allows to command input angles between 0° and 45°. Furthermore, interaction forces from the manipulator’s end effector can be displayed to the user’s twofinger grasp in a range from 0 N to 6 N with a frequency bandwidth of 17 Hz.

A New Approach of Soft Joint Based on a Cable-Driven Parallel Mechanism for Robotic Applications

A soft joint has been designed and modeled to perform as a robotic joint with 2 Degrees of Freedom (DOF) (inclination and orientation). The joint actuation is based on a Cable-Driven Parallel Mechanism (CDPM). To study its performance in more detail, a test platform has been developed using components that can be manufactured in a 3D printer using a flexible polymer. The mathematical model of the kinematics of the soft joint is developed, which includes a blocking mechanism and the morphology workspace. The model is validated using Finite Element Analysis (FEA) (CAD software). Experimental tests are performed to validate the inverse kinematic model and to show the potential use of the prototype in robotic platforms such as manipulators and humanoid robots.

Design and experimental validation of a disturbing force application unit for simulating spacecraft separation

The separation of the heatshield and backshell as the spacecraft enters the atmosphere and decelerates is a highly challenging task during the exploration of an exoplanet. Owing to its high complexity, few experimental validations have been performed so far for this separation process. In this paper, a novel disturbing force application unit is designed, which can simulate the disturbing forces and disturbing moments. It is deployed in a cable-driven parallel mechanism which is used to simulate the heatshield and backshell separation. This cable-driven parallel mechanism is presented from the aspects of mechanical design, kinematic analysis, dynamic analysis, numerical simulation, and experimental validation. First, the kinematic and dynamic model of the cable-driven parallel mechanism is established. Then, the definition of disturbing force controllable workspace is proposed. The workspace quality coefficient, which checks whether the end-effector is close to the workspace boundary, is presented. The configuration design is discussed. Third, numerical simulations are implemented to investigate the effects of axial forces, disturbing forces and disturbing moments on the end-effector position and orientation. Finally, an experimental platform is built. Experimental verification of the separation of the heatshield and backshell in different conditions are implemented. A series of experimental results show that both heatshield and backshell are safely separated from the lander. The proposed cable-driven parallel mechanism can accurately simulate the disturbing force during the separation process of the heatshield and the backshell.

Variable stiffness control of redundant cable-driven parallel mechanism for on-orbit assembly

Variable stiffness control of redundant cable-driven parallel mechanism for on-orbit assembly

Development of a new 3T1R type cable-driven haptic device

In this work, structural synthesis of lower-mobility cable-driven parallel mechanisms (CDPMs) is conducted to clearly identify all feasible structures of the lower-mobility CDPMs with n-degrees-of-freedom, which are driven by n +1 cables fixed on the ground. Through the synthesis, geometric information of various and some new promising structures of unconstrained and constrained lower-mobility CDPMs such as actuation cable wrenches, cable position vector, and required constraint wrenches, are successfully extracted. Then a promising 3T1R type CDPM structure is selected to develop as a haptic device. Its position analysis is conducted and its input-to-output force model is derived. Also, its feasible workspace and its input-to-output force transmission characteristics are examined. Then a prototype haptic device is implemented which is controlled by Raspberry Pi microprocessors. Through a virtual wall following operation by the operator, its operational capability as a haptic device is verified.

Design and Performance of an Elbow Assisting Mechanism

An elbow assisting device is presented as based on a cable-driven parallel mechanism with design solutions that are improvements from a previous original design. The new mechanism, ideal for domestic use, both for therapies and exercises, is characterized by low-cost, portable, easy-to-use features that are evaluated through numerical simulations and experimental tests whose results are reported with discussions.

LaryngoTORS: A Novel Cable-Driven Parallel Robotic System for Transoral Laser Phonosurgery

Transoral laser phonosurgery is a commonly used surgical procedure in which a laser beam is used to perform incision, ablation or photocoagulation of laryngeal tissues. Two techniques are commonly practiced: free beam and fiber delivery . For free beam delivery, a laser scanner is integrated into a surgical microscope to provide an accurate laser scanning pattern. This approach can only be used under direct line of sight, which may cause increased postoperative pain to the patient and injury, is uncomfortable for the surgeon during prolonged operations, the manipulability is poor and extensive training is required. In contrast, in the fiber delivery technique, a flexible fiber is used to transmit the laser beam and therefore does not require direct line of sight. However, this can only achieve manual level accuracy, repeatability and velocity, and does not allow for pattern scanning. Robotic systems have been developed to overcome the limitations of both techniques. However, these systems offer limited workspace and degrees-of-freedom (DoF), limiting their clinical applicability. This work presents the LaryngoTORS, a robotic system that aims at overcoming the limitations of the two techniques, by using a cable-driven parallel mechanism (CDPM) attached at the end of a curved laryngeal blade for controlling the end tip of the laser fiber. The system allows autonomous generation of scanning patterns or user-driven free-path scanning. Path scan validation demonstrated errors as low as 0.054 $\pm$ 0.028 mm and high repeatability of 0.027 $\pm$ 0.020 mm (6 × 2 mm arc line). Ex vivo tests on chicken tissue have been carried out. The results show the ability of the system to overcome limitations of current methods with high accuracy and repeatability using the superior fiber delivery approach.

Reconfigurable fully constrained cable driven parallel mechanism for avoiding interference between cables

Cable driven parallel mechanisms (CDPMs) have attracted much attention due to their many advantages over conventional parallel mechanisms, such as the significantly large workspace and the dynamics capacity. One of the main issues involved in designing CDPMs is avoiding cable-cable collision, especially when an operator is sharing the same workspace with the moving parts of the mechanism. This paper aims to model and simulate a reconfigurable fully constrained CDPM and solve the forward and inverse kinematics given that the attachment points on the rails move up and down in real time, unlike conventional CDPMs where the attachment points are firmly fixed on specific positions on the rails. The new idea of reconfiguration is then used to avoid interference between two cables in real time by moving one cable's attachment point on the frame to increase the shortest distance between them while keeping the trajectory of the end effector unchanged. This new approach was tested by creating a simulated intended cable interference trajectory, hence detecting and avoiding cable collision using the proposed real time reconfiguration while maintaining the end effector trajectory.

Stiffness analysis of cable-driven parallel mechanisms with cables having large sustainable strains

A cable-driven parallel mechanism is driven by a group of cables. Cable-driven parallel mechanisms can use various cables (e.g. steel cables, nylon cables, isoprene rubber cables, and extension springs) with different sustainable strains. This paper studies the stiffness of cable-driven parallel mechanisms with cables having large sustainable strains, aiming to achieve significantly adjustable overall stiffness. The overall stiffness of a cable-driven parallel mechanism can be decomposed into the constant base stiffness and the adjustable strain stiffness. This paper proposes and mathematically proves a theorem that guarantees that the overall stiffness of a cable-driven parallel mechanism at an arbitrary stable pose can be dominated by the adjustable strain stiffness when cable strains are larger than 100%. The theorem employs the minimum eigenvalues of stiffness matrices to characterize the stiffness of cable-driven parallel mechanism. The theorem provides a sufficient condition that guarantees that the overall stiffness of a cable-driven parallel mechanism at an arbitrary stable pose can be significantly adjusted (i.e. the adjustable strain stiffness contributes more than the constant base stiffness in determining the overall stiffness). The theorem is verified through the simulation of a cable-driven parallel mechanism with six degrees of freedom and seven cables.

Optimal Design and Force Control of a Nine-Cable-Driven Parallel Mechanism for Lunar Takeoff Simulation

Traditional simulation methods are unable to meet the requirements of lunar takeoff simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have the advantages of high payload to weight ratio, potentially large workspace, and high-speed motion, these mechanisms have the potential to be used for lunar takeoff simulations. Thus, this paper presents a parallel mechanism driven by nine cables. The purpose of this study is to optimize the dimensions of the cable-driven parallel mechanism to meet dynamic workspace requirements under cable tension constraints. The dynamic workspace requirements are derived from the kinematical function requests of the lunar takeoff simulation equipment. Experimental design and response surface methods are adopted for building the surrogate mathematical model linking the optimal variables and the optimization indices. A set of dimensional parameters are determined by analyzing the surrogate mathematical model. The volume of the dynamic workspace increased by 46% after optimization. Besides, a force control method is proposed for calculating output vector and sinusoidal forces. A force control loop is introduced into the traditional position control loop to adjust the cable force precisely, while controlling the cable length. The effectiveness of the proposed control method is verified through experiments. A 5% vector output accuracy and 12 Hz undulation force output can be realized. This paper proposes a cable-driven parallel mechanism which can be used for lunar takeoff simulation.

Efficient optimal force distribution method of the parallel mechanism with actuator redundancy based on geometric interpretation

A numerically efficient force distribution method for actuator saturation avoidance is proposed, which is applicable to two different types of the mechanisms with two degrees of actuator redundancy, parallel mechanism (PM) and cable-driven parallel mechanism (CDPM). The proposed method searches the optimal force solutions based on their geometric interpretation. Each actuator force with two degrees of actuator redundancy is expressed as a plane equation with respect to two intermediate variables. Thus, the optimal forces are found by searching for both the intersections between force planes and the common intersection points among those force planes. The proposed method for each of PM and CDPM is described. Then for two different exemplary mechanisms, the 2T2R -type 4 -DOF CDPM with six actuation cables and for the 2T1R -type planar 3- DOF PM with five active joints, comparative simulations moving along the spiral trajectory are conducted, employing three different methods, the proposed method and the other two typical off-line methods, the interior point method and the linear matrix inequality method. It is confirmed from those simulation results that the computational efficiency of the proposed method in finding their desired optimal force solutions is superior to the ones of the other two typical offline optimal searching methods and also sufficiently fast enough in real time applications.

Cable interference control in physical interaction for cable-driven parallel mechanisms

Cable interferences and collisions can lead to unpredictable behavior when a human physically interacts with a cable-driven parallel mechanism through its mobile platform. This paper presents an interactive control approach to prevent two cables in interference from folding onto one another, and thus preserve the cable-mechanism geometry. In this approach, the controller generates a repulsive force to prevent the cables from crossing. Therefore, the task is executed within the cable-driven parallel mechanism's geometric limits. The repulsive force applied by the controller is derived from the gradient of the minimum distance between any pair of cables of the parallel mechanism. In turn, this minimum distance between cables is computed from the Karush-Kuhn-Tucker conditions of the associated optimization problem. The approach was tested and validated on a parallel mechanism driven by seven cables.

Design of convex variable radius drum mechanisms

Variable radius drum (VRD) mechanisms represent an interesting alternative to more conventional transmission mechanisms whereby highly flexible input-output relationships may be achieved. The design of such mechanisms implies the determination of the VRD’s profile based on performance criteria whose evaluation generally assumes continuous contact between the cable and the VRD. Although it has been previously acknowledged that this assumption is only valid if the VRD is convex, this condition has not yet have been verified. This deficiency is addressed herein by proposing a design approach which takes into account the requirement of VRD convexity. The approach is based on the formulation of a constrained minimization problem where a convexity constraint, evaluated using interval analysis techniques to ensure its satisfaction throughout the VRD’s operating range, is applied. The proposed method is quite general and may be used in the design of VRDs based on various performance requirements. The effectiveness of the proposed approach is validated through its use in the design of VRDs for the static balancing of a one-degree-of-freedom robot arm as well as a one-degree-of-freedom parallel cable-driven mechanism. The method is demonstrated to be successful in producing VRD mechanisms that meet specified design criteria.

A cable-driven parallel manipulator with force sensing capabilities for high-accuracy tissue endomicroscopy

PurposeEndomicroscopy (EM) provides high resolution, non-invasive histological tissue information and can be used for scanning of large areas of tissue to assess cancerous and pre-cancerous lesions and their margins. However, current robotic solutions do not provide the accuracy and force sensitivity required to perform safe and accurate tissue scanning.MethodsA new surgical instrument has been developed that uses a cable-driven parallel mechanism (CPDM) to manipulate an EM probe. End-effector forces are determined by measuring the tensions in each cable. As a result, the instrument allows to accurately apply a contact force on a tissue, while at the same time offering high resolution and highly repeatable probe movement.Results0.2 and 0.6 N force sensitivities were found for 1 and 2 DoF image acquisition methods, respectively. A back-stepping technique can be used when a higher force sensitivity is required for the acquisition of high quality tissue images. This method was successful in acquiring images on ex vivo liver tissue.ConclusionThe proposed approach offers high force sensitivity and precise control, which is essential for robotic EM. The technical benefits of the current system can also be used for other surgical robotic applications, including safe autonomous control, haptic feedback and palpation.

On the real-time calculation of the forward kinematics of a suspended cable–driven parallel mechanism with 6-degree-of-freedom wave compensation

A real-time forward kinematics method was proposed in this article and was used for a suspended cable-driven parallel mechanism with 6 degree-of-freedom wave compensation. The problem of the forwar...

Dynamic modeling and control of a cable-driven parallel mechanism with a spring spine

This paper presents dynamic model and control system designing of a cable-driven flexible mechanism, which is composed of a moving platform, a fixed base, a column compression coil spring and three driving cables. The deformation of lateral dynamic bend for the spring is described by using the coupling theory of the rigid body’s plane rotary movement and the flexible body’s flexible deformation. Based on the description of the deformation of lateral dynamic bend for the flexible spring, the assumed mode method (AMM) and Lagrange’s equation are applied to the formulation of the mechanism’s dynamic model. Then, two system controllers are designed by using the linear quadratic optimal control (LQOC) method. Finally, the analyses of the simulation and the experiment are presented to validate the availability of the theoretical model for control and the proposed control method.

Design and Nonlinear Control of a 2-DOF Flexible Parallel Humanoid Arm Joint Robot

The paper focuses on the design and nonlinear control of the humanoid wrist/shoulder joint based on the cable-driven parallel mechanism which can realize roll and pitch movement. In view of the existence of the flexible parts in the mechanism, it is necessary to solve the vibration control of the flexible wrist/shoulder joint. In this paper, a cable-driven parallel robot platform is developed for the experiment study of the humanoid wrist/shoulder joint. And the dynamic model of the mechanism is formulated by using the coupling theory of the flexible body’s large global motion and small flexible deformation. Based on derived dynamics, antivibration control of the joint robot is studied with a nonlinear control method. Finally, simulations and experiments were performed to validate the feasibility of the developed parallel robot prototype and the proposed control scheme.

Workspace analysis and verification of cable-driven parallel mechanism for wind tunnel test

Cable-driven parallel mechanism is a special kind of parallel robot in which traditional rigid links are replaced by actuated cables. This provides a new suspension method for wind tunnel test, in which an aircraft model is driven by a number of parallel cables to fulfil 6-DOF motion. The workspace of such a cable robot is limited due to the geometrical and unilateral force constraints, the investigation of which is important for applications requiring large flight space. This paper focuses on the workspace analysis and verification of a redundant constraint 6-DOF cable-driven parallel suspension system. Based on the system motion and dynamic equations, the geometrical interference (either intersection between two cables or between a cable and the aircraft) and cable tension restraint conditions are constructed and analyzed. The hyperplane vector projection strategy is used to solve the aircraft’s orientation and position workspace. Moreover, software ADAMS is used to check the workspace, and experiments are done on the prototype, which adopts a camera to monitor the actual motion space. In addition, the system construction is designed by using a built-in six-component balance to measure the aerodynamic force. The results of simulation and tests show a good consistency, which means that the restraint conditions and workspace solution strategy are valid and can be used to provide guidance for the cable-driven parallel suspension system’s application in wind tunnel tests.

The design of a new remote manipulator for space operation using a 4-cable-driven thrusters-embedded configuration

A new remote manipulator based on cable-driven parallel mechanism (CDPM) is designed for space long-distance operations (e.g. space capture/docking and other long-distance space activities) in this paper. By controlling the cables and thrusters which are equipped on the manipulator simultaneously, the new remote manipulator can achieve expected position, linear velocity, and angular velocity. The new manipulator has a larger controllable workspace compared with usual CDPMs. The structure and characteristics of this manipulator are discussed in this paper. The volume and characteristics of the workspace are also discussed. The influence of the distance on the static equilibrium is studied. The simulation results show that the workspace of this new manipulator is larger than usual CDPM's. The results also indicate that the cable forces and thruster vectors can completely constrain the manipulator and meet the requirements of space activities. The results of the simulation also show that the controllable workspace of the manipulator is not continuous at some regions. Hence, trajectory planning is necessary.