Research

Ph.D. Research

Design and Control of a Hybrid Thrustered Cable-Suspended Parallel Robot (TCSPR) using a Fully-actuated Hexarotor

To investigate hybrid cable–thruster actuation, a small-scale prototype of the TCSPR system was developed, including the mechanical structure, control architecture, and an online force distribution algorithm. The platform consists of a cable-suspended parallel robot integrated with a fully actuated hexarotor mounted on the end-effector (EE). Three cables driven by motorized winches provide the primary translational actuation, enabling efficient positioning over a large workspace. Meanwhile, the hexarotor generates controlled thrust forces and torques to regulate the EE orientation and to assist in maintaining cable tension when the robot operates near the boundaries of the feasible workspace.

A decoupled control framework was implemented to coordinate the cable-driven and thruster-based subsystems. The cable-driven mechanism is responsible for regulating the EE position through winch control, while the hexarotor stabilizes and controls the EE orientation using onboard sensing and attitude control. This separation of responsibilities allows the system to achieve stable 6-DOF motion while reducing control complexity.

To ensure coordinated operation between cables and thrusters, an online force distribution algorithm was developed. The algorithm computes feasible cable tensions and propeller thrusts in real time based on the desired pose of the EE. By allocating forces among the actuators, the method maintains positive cable tensions, avoids actuator saturation, and ensures stable system operation throughout the workspace.

To experimentally validate the system, a spatial trajectory was designed to simulate an inspection task, where the end-effector scans an object while maintaining a desired viewing direction. The trajectory consists of linear motions for repositioning and circular paths around the target at different heights, allowing the robot to observe the object from multiple viewpoints while keeping the sensor oriented toward it. This trajectory simultaneously requires coordinated translation and orientation control, providing a representative benchmark for evaluating the hybrid actuation system.

The experiments demonstrate stable 6-DOF trajectory tracking and confirm that the hybrid cable–thruster architecture can expand the feasible workspace and enable motions that are difficult to achieve with conventional cable-suspended robots.

Master Research

Fig. TCSPR with three cables and six tilt propellers

Fig. Schematic diagram of the fully-actuated hexaroter of the TCSPR

Design of a TCSPR using Hexarotor and Wrench-feasible Workspace Analysis

As a continuation of my earlier conceptual study on Hybrid Thrustered Cable-Suspended Parallel Robots (TCSPRs), this research proposes and analyzes a new configuration that combines three tensioned cables with a fully-actuated hexarotor mounted on the end-effector.

In this design, the three cables are connected to the EE’s center of mass and used exclusively for generating translational forces, while the six thrusters, arranged diagonally in a fully-actuated hexarotor configuration, produce independent forces and torques. Unlike conventional multirotors, this hexarotor is not to generate lift for flight but to generate downside force for maintaining cable tension and enabling attitude control. The separation of responsibilities allows for decoupled control of position and orientation, simplifying control logic and improving performance.

A static wrench model is developed, and the system’s Wrench-Feasible Workspace (WFW) is analyzed. The WFW represents the set of poses at which the robot can generate any desired wrench within actuator limits. Simulation results show that the integration of the hexarotor significantly expands the WFW, particularly when handling lightweight end-effectors, and improves the robot's ability to maintain stable tension throughout a wide range of configurations.

Based on its performance in analysis, I consider this configuration highly promising and proceed with building a prototype to test its feasibility in practice.

Fig. Wrench-feasible workspace of the TCSPR with (right) and without (left) the application of hexarotor

Conceptual Design of a Hybrid Thrustered Cable-Suspended Parallel Robots (TCSPRs)

As part of my master's research, I worked on the conceptual design of a Hybrid Thrustered Cable-Suspended Parallel Robot (TCSPR)—a novel robotic structure that combines cable-driven parallel mechanisms with propeller-based actuation.

Cable-Driven Parallel Robots (CDPRs) are known for their lightweight structures and high payload-to-weight ratios, making them ideal for large workspace applications. Among them, Cable-Suspended Parallel Robots (CSPRs) suspend the end-effector (EE) from above using cables and utilize gravity to keep the cables in tension. However, this reliance on gravity presents a critical trade-off:

A heavier EE improves tension stability but reduces acceleration and safety.
A lighter EE improves dynamics but may result in slack cables, leading to control failure.

To overcome this, I proposed integrating thrusters mounted on the EE to supplement cable forces and provide additional wrench capability. This hybrid design improves controllability, safety, and workspace usability, particularly for lightweight EEs.

A general static model was established to describe the combined wrench effect of both cables and thrusters. As a case study, I designed a configuration consisting of six cables and three contra-rotating propeller (CRP) units, where each CRP provides unidirectional thrust while canceling drag torque. Simulation results showed that the use of thrusters can significantly increase cable tension in critical poses and maintain control where traditional CSPRs would fail.

This work represents a new direction in large-scale mobile parallel robotics, offering improved force controllability and design flexibility for applications such as robotic painting, inspection, and surface processing compared with traditional CSPRs.

Fig. General schematic diagram of TCSPRs

Fig. A TCSPR with 6 cables and 3 CRP thrusters

Undergraduate Research

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