Giuk Lee

High-payload climbing and transitioning by compliant locomotion with magnetic adhesion

This paper presents a new climbing robotic mechanism for high-payload climbing and wall-to-wall transitioning. Payload capacity and transition ability are very important in climbing-robot applications for heavy industries and construction industries. The proposed robotic platform consists of three magnetic tread-wheel modules that are connected by links with two compliant joints. The front compliant joints are passive type with a torsion spring, and the rear compliant joints are active type with torque-controlled motors. A torque-controlled tail is attached at the end of the third module. Various transitions are achieved by the compliant joints, which change shape depending on the external conditions. High payloads are achieved by the large contact area of three magnetic tread-wheel modules. Detailed design issues are presented with analyses of the design parameters. The robot can perform two internal and two external transitions against gravity and every possible transition in the side surface driving direction. The robot can carry 10 kg payloads on vertical surfaces and on a ceiling. The ability to overcome a 30 mm diameter obstacle on vertical surfaces is also verified by experiments. The proposed robotic platform is going to be used in heavy industries.

Minimizing Energy Consumption of Parallel Mechanisms via Redundant Actuation

This paper shows that redundant actuation can reduce the energy consumption of parallel mechanisms, in some cases by a considerable margin. A theoretical analysis for the energy-saving mechanism is elucidated, and an energy consumption model for a servo-motor system is proposed. Our hypothesis is experimentally verified with a widely used two degree of freedom parallel mechanism design driven by three actuators. Experimental results show that redundant actuation can reduce the electrical energy consumption of the actuators by up to 45% compared to the corresponding nonredundantly actuated version of the mechanism.

MultiTrack: A multi-linked track robot with suction adhesion for climbing and transition

Abstract Wall-to-wall transitions, attachment to various materials, and high payload capacity are important requirements for high-rise building cleaning using robots. In this paper, we present a new robotic platform, called the “MultiTrack”, that satisfies these requirements. The MultiTrack employs a multi-linked track mechanism and pneumatic adhesion technology. The MultiTrack can perform wall-to-wall transitions by dexterous motion, can be attached to various materials by suction, and can provide high payload capacity. The robot consists of five driving modules and two connecting links that are connected by six active joints. The center of the robot has a steering suction pad that is used in steering. Each driving module has a caterpillar track with six suction pads. During the rotation of the track, the suction pads are automatically activated or deactivated by mechanical valves and guide rails. The locomotion strategy for wall-to-wall transitions is determined by kinematic analysis. A stability analysis of the worst-case scenario was performed to derive relationships between the required adhesion force and other design parameters. The MultiTrack is 1600 mm × 1000 mm × 300 mm in size, weighs 70 kg, and has a 15-kg payload capacity. It can transit from a floor to a vertical wall and can climb over a thin (130-mm-thick) wall.

Combot: Compliant climbing robotic platform with transitioning capability and payload capacity

Transitioning capability and high payload capacity are problems for climbing robots. To increase the possible applications for climbing robots, these two abilities are required. We present a new climbing robotic platform named “Combot” to achieve both transitioning capability and high payload capacity. The robot is composed of three main modules with flexible magnetic treads, connecting links with torsion springs and torque-controlled motors, and an active tail at the end of the robot. The robot can perform internal and external transitions using compliant torques from the torsion springs and the active tail. The compliant torques are changed according to external structures; thus, a complex feedback controller is not required. The payload capacity of the robot is measured by 10 kg (1.56 times the robot mass) during flat surface vertical climbing. The robot is expected to be used to move heavy materials to high places in the ship building industry.

Compliant track-wheeled climbing robot with transitioning ability and high-payload capacity

We presents a high-payload climbing robot based on a compliant track-wheel mechanism. The compliant track-wheel mechanism changes the configuration of the robot according to the conditions of the external structures without feedback control; and the robot can perform 90-degree wall-to-wall internal and 240-degree wall-to-wall external transitions. Segmented magnets on the track-wheel are used to attach onto steel walls. The large contact area of the magnets achieves a relatively high-payload capacity of 3 kg compared to the robot mass of 4 kg. The parametric design based on kinematics and statics was developed to guarantee stable climbing. Experimental verification of the payloads and the transitions are presented. We expect that the robot can be applied to move heavy materials to high places in shipbuilding and plant industries.

Series of Multilinked Caterpillar Track-type Climbing Robots

Climbing robots have been widely applied in many industries involving hard to access, dangerous, or hazardous environments to replace human workers. Climbing speed, payload capacity, the ability to overcome obstacles, and wall-to-wall transitioning are significant characteristics of climbing robots. Here, multilinked track wheel-type climbing robots are proposed to enhance these characteristics. The robots have been developed for five years in collaboration with three universities: Seoul National University, Carnegie Mellon University, and Yeungnam University. Four types of robots are presented for different applications with different surface attachment methods and mechanisms: MultiTank for indoor sites, Flexible caterpillar robot FCR and Combot for heavy industrial sites, and MultiTrack for high-rise buildings. The method of surface attachment is different for each robot and application, and the characteristics of the joints between links are designed as active or passive according to the requirement of a given robot. Conceptual design, practical design, and control issues of such climbing robot types are reported, and a proper choice of the attachment methods and joint type is essential for the successful multilink track wheel-type climbing robot for different surface materials, robot size, and computational costs.

Energy savings of a 2-DOF manipulator with redundant actuation

This paper covers the energy-saving features of a robotics system by redundant actuation. By installing more actuators than the degrees of freedom, the actuating torques can be distributed This distribution can reduce the overall energy loss, which reduces the overall energy consumption. An experiment was conducted with a 2-DOF general manipulator and redundant actuated manipulator; these were made to follow a typical welding pathway used in an automotive factory. The results showed that the redundant manipulator saved up to 38% electrical energy for actuation compared to the general manipulator.

Optimal dimensioning of redundantly actuated mechanism for maximizing energy efficiency and workspace via Taguchi method

A kinematic optimization of a redundantly actuated parallel mechanism is developed via the Taguchi method to maximize the sum of energy efficiency and workspace. In the optimization process, the energy consumption in a representative pathway of a predefined workspace is used as the performance index of the energy efficiency. The horizontal reach and stroke, and the vertical reach of mechanism, are used for the performance index of the workspace. The kinematic parameters of a chain that was added to the proposed non-redundantly actuated parallel mechanism as an extension to achieve redundant actuation are selected as the controllable factors. The velocity of the end-effector is considered to be a noise factor. Because the Taguchi method was originally used for robust optimization, we can improve the energy efficiency and workspace under various velocities for the end-effector. In the first stage of optimization, the number of controllable factors is reduced, and their correlations are eliminated using a response analysis. Quasi-optimized results are derived after the second stage of optimization. The optimized redundantly actuated parallel mechanism result is validated by comparing the energy efficiencies and workspaces of the original and optimal redundantly actuated parallel mechanisms.

Design of a Transformable Track Mechanism for Wall Climbing Robots

This paper presents a transformable track mechanism for wall climbing robots. The proposed mechanism allows a wall climbing robot to go over obstacles by transforming the track shape, and also increases contact area between track and wall surface for safe attachment. The track mechanism is realized using a timing belt track with one driving actuator. The inner frame of the track consists of serially connected 5R-joints and 1P-joint, and all joints of the inner frame are passively operated by springs, so the mechanism does not require any actuators and complex control algorithms to change its shape. Static analysis is carried out to determine design parameters which enable 90o wall-to-wall transition and driving over projected obstacles on wall surfaces. A Prototype is manufactured using the transformable track on which polymer magnets are installed for adhesion force. The size of the prototype is 628mmⅩ200mmⅩ150mm (LengthⅩWidthⅩHeight) and weight is 4kgf. Experiments are performed to verify its climbing capability focusing on 90o wall to wall transition and driving over projected obstacle.

Calibration of encoder indexing of a redundantly actuated parallel mechanism to eliminate contradicting control forces

ABSTRACT This paper presents the kinematic calibration of a two degree-of-freedom redundantly actuated parallel mechanism (RAPM), with the aim of eliminating contradicting control forces (CCF). The kinematic errors in the RAPM induce CCFs, especially in the case of decentralized individual position control, which is the standard control method used in industrial applications. The encoder indexing errors of the actuated joints are known to be of strong influence on the CCFs. Therefore, it is believed that the CCFs will be eliminated if the encoder indexing errors are corrected. We proved this through experiments. We performed the calibration using a projection technique, wherein we projected tracking error terms onto orthogonal complementary terms of the constraint Jacobian between the independent joints and actuated joints. Using this projection technique, the effect of tracking error terms from the joint stiffness and external force is eliminated. During the calibration process, the tracking errors in the actuated joints are measured. Using these errors, we derived the optimal values of the encoder indexing error by minimizing the objective function. We verified the calibration result by comparing the CCFs measured before calibration with those measured after calibration, for the case of individual PID position control. Our results confirmed that the calibration procedure of encoder indexing errors successfully reduces the average norm value of CCFs from 366 N to 13 N.