Hybrid Robot Research Articles

A Human-Guided Vision-Based Measurement System for Multi-Station Robotic Motion Platform Based on V-Rep

SUMMARYIn the manufacturing process of sophisticated and individualized large components, classical solutions to build large machine tools cannot meet the demand. A hybrid robot, which is made up of a 3 degree-of-freedom (3-DOF) parallel manipulator and a 2-DOF serial manipulator, has been developed as a plug-and-play robotized module that can be rapidly located in multi-stations where machining operations can be performed in situ. However, processing towards high absolute accuracy has become a huge challenge due to the movement of robot platform. In this paper, a human-guided vision system is proposed and integrated in the robot system to improve the accuracy of the end-effector of a robot. A handheld manipulator is utilized as a tool for human–robot interaction in the large-scale unstructured circumstances without intelligence. With 6-DOF, humans are able to manipulate the robot (end-effector) so as to guide the camera to see target markers mounted on the machining datum. Simulation is operated on the virtual control platform V-Rep, showing a high robust and real-time performance on mapping human manipulation to the end-effector of robot. And then, a vision-based pose estimation method on a target marker is proposed to define the position and orientation of machining datum, and a compensation method is applied to reduce pose errors on the entire machining trajectory. The algorithms are tested on V-Rep, and the results show that the absolute pose error reduces greatly with the proposed methods, and the system is immune to the motion deviation of the robot platform.

Insect–Computer Hybrid Robot Achieves a Walking Gait Rarely Seen in Nature by Replacing the Anisotropic Natural Leg Spines With Isotropic Artificial Leg Spines

This paper demonstrates that our developed beetle-computer hybrid legged robot achieves backward walk, which is impossible by intact beetles themselves in nature. Judging from the curvature of the natural leg spine, we hypothesized that the natural spine has an anisotropic function: the natural spine would provide foot traction only in forward walk but not in backward. The hypothesis was verified as beetles hardly walk backward due to often slips. We then designed an artificial leg spine, which isotropically functions in walk: the foot traction was increased and slipless walk was achieved in both backward and forward walk with the artificial spines being implanted into the beetle legs. For these investigations, a wireless communication device, or “backpack,” was mounted and wired to a live beetle for electrically stimulating leg muscles to remotely modulate leg motions and to perform the forward and backward walk on demand. Overall, the beetle hybrid robot revealed the anisotropic function of the natural leg spine and also achieved the backward walk, which the intact beetle cannot intrinsically perform.

Evolution and Current Applications of Robot-Assisted Fracture Reduction: A Comprehensive Review.

Robots in orthopedic surgery have been developed rapidly for decades and bring significant benefits to the patients and healthcare providers. However, robotics in fracture reduction remains at the infant stage. As essential components of the current robotic system, external fixators were used in fracture reduction, including the unilateral and Ilizarov-like ring fixators. With emerging of the industrial robots and mechanical arms, their sterilized variants were developed as the serial robots, including the traction device and robotic arm, for fracture reduction. Besides, parallel robots (e.g., Gough-Stewart platform) were devised for lower extremity traction and fracture reduction. After combining the advantages of the serial and parallel mechanisms, hybrid robots can fulfill specific clinical requirements (e.g., the joint fracture, including multiple major fragments). Furthermore, with the aid of intra-operative navigation systems, fracture reduction can be performed under real-time guidance. The paper presents a comprehensive overview of the advancement of the robots in fracture reductionand evaluates research challenges and future perspectives, including ergonomic and economic issues, operation time, artificial realities and intelligence, and telesurgery.

An iterative tuning approach for feedforward control of parallel manipulators by considering joint couplings

Feedforward control is an effective way to improve the joint tracking accuracy of robotic systems. This paper presents an iterative approach for feedforward controller parameter tuning of parallel manipulators that considers joint couplings (cross-talk). Based upon a compound control strategy, increments of the feedforward tuning parameters are iteratively updated by minimizing the sum of squares of joint tracking errors at each step. A plant-free identification Jacobian is formulated using the measured data associated with a number of sequential statuses within each iteration cycle. Experiments on the 3-DOF parallel mechanism within a 5-DOF hybrid robot verify parameter convergence and the extrapolation capability of the proposed approach. Compared to otherwise similar feedforward control not considering joint couplings, the root mean square of joint tracking errors was reduced by up to 22% when the mechanism moved at high speed along a path in the neighborhood of the reference configuration.

Dynamics and control of a 7-DOF hybrid manipulator for capturing a non-cooperative target in space

This paper proposes a 7-DOF hybrid serial-parallel manipulator for capturing a non-cooperative target in space and discusses its dynamics and control. The hybrid manipulator is connected in a series by a 3-DOF parallel part with 1-PU&2-PUS configurations and a 4-DOF serial part with a 4R configuration. First, the UP-RRRR equivalent serial mechanism is presented for the kinematic analysis of the hybrid manipulator. Utilizing the Newton-Euler method, the dynamic model of the equivalent serial mechanism is derived in a recursive form. Then the dynamic equations of the parallel part in recursive form are also developed using the Newton-Euler method. Based on the complete dynamic model, we propose a control scheme for a hybrid robot to capture a non-cooperative target in a zero-gravity environment, including three modules: admittance control, motion estimation of the target satellite, and feedforward of the reaction forces. Finally, experimental results of full physical experiments based on air-bearing testbeds confirm the validity of the proposed control scheme for the hybrid robot to capture a non-cooperative target in space.

A Robotic Deburring Methodology for Tool Path Planning and Process Parameter Control of a Five-Degree-of-Freedom Robot Manipulator

Industrial robotics is a continuously developing domain, as industrial robots have demonstrated to possess benefits with regard to robotic automation solutions in the industrial automation field. In this article, a new robotic deburring methodology for tool path planning and process parameter control is presented for a newly developed five-degree-of-freedom hybrid robot manipulator. A hybrid robot manipulator with dexterous manipulation and two experimental platforms of robot manipulators are presented. A robotic deburring tool path planning method is proposed for the robotic deburring tool position and orientation planning and the robotic layered deburring planning. Also, a robotic deburring process parameter control method is proposed based on fuzzy control. Furthermore, a dexterous manipulation verification experiment is conducted to demonstrate the dexterous manipulation and the orientation reachability of the robot manipulator. Additionally, two robotic deburring experiments are conducted to verify the effectiveness of the two proposed methods and demonstrate the highly efficient and dexterous manipulation and deburring capacity of the robot manipulator.

Control of the Multi-Legged Robots on Planar, Unstable and Vibrating Ground

In this paper, we developed and investigated numerically a general kinematic model of a multi-legged hybrid robot equipped with a crab-like and/or mammal-like legs. To drive the robot’s limbs, a novel generator of gait was employed and tested. The simulation model developed in Mathematica is suitable for virtual study and visualization of the locomotion process. In contrast to our previous studies, in this paper we focused only on precise control the position of the robot during walking in different directions. We are able to simultaneous control all six spatial degrees-of-freedom of the robot’s body (three deviations and three rotations along and around three different axes, respectively), as well as all robot’s legs. As a result, the investigated robot can be considered and used as a fully controlled walking Stewart platform. What is more, the used algorithm can also be successfully employed to coordination and control all limbs of the robot on unstable or vibrating ground. As an example, the control algorithm can be used to stabilize spatial position of the robot when the supporting ground becomes vibrating or unstable, and it will keep the robot stable and prevent it from falling over. Since the recent versions of Mathematica allows to communicate with different microcontrollers such as Arduino Uno or Raspberry Pi, the developed simulation algorithms can be relatively simply adopted to control real constructions of different multi-legged robots.

Terminal Position and Orientation Coupling in Lower Mobility Robots

Abstract The kinematics has attracted continuous interests in the field of robotics. Terminal position and orientation coupling phenomenon is the key problem and the first consideration in the kinematics of lower mobility robots. However, this property was usually neglected or has not been well solved. This paper discusses the terminal position and orientation coupling issues in lower mobility robots, especially for the lower mobility hybrid robots. First, this paper reveals the terminal position and orientation coupling in serial and parallel robots. Then, based on elimination theory, an approach for establishing the terminal position and orientation coupling equations for hybrid robots is proposed, which is illustrated in detail by the (3-RPS) + (RR) and (3-RPS) + (3-RCR) hybrid robots. The results show that the hybrid robots have highly nonlinear terminal position and orientation coupling relations, which are more complicated than serial and parallel robots. The research of this paper is valuable in kinematics modeling of robots.

A Screw Theory-Based Semi-Analytical Approach for Elastodynamics of the Tricept Robot

Taking the well-known Tricept robot as an example, this paper presents a semi-analytical approach for elastodynamic modeling of five or six degrees of freedom (DOF) hybrid robots composed of a 3-DOF parallel mechanism plus a 2- or 3-DOF wrist. Drawing heavily on screw theory combined with structural dynamics, the kinetic and elastic potential energies of the parallel mechanism and of the wrist are formulated using the dual properties of twist/wrench systems and a static condensation technique. This results in a 9-DOF dynamic model that enables the lower-order dynamic behavior over the entire workspace to be estimated in a very efficient and accurate manner. The lower-order natural frequencies and mode shapes estimated by the proposed approach are shown to have very good agreement with those obtained by a full-order finite element (FE) model. It thus provides a very time-effective tool for optimal design within a virtual prototyping framework for hybrid robot-based machine tools.

Transition mechanism design of a hybrid wheel-track-leg based on foldable rims

Hybrid mobile robots with multiple locomotion modes are getting more and more popular in search and rescue (SAR) and explosive object disposal (EOD) missions because of their good terrain adaptability. Present researchers devote themselves to develop efficient and reliable transition method between different locomotion modes to make the hybrid robot more compact and flexible. In this paper, we present a novel transition mechanism for a hybrid wheel-track based on foldable rims. The wheel rim is cut into four segments so that it is foldable. And the transition between wheel and track is achieved by the folding or unfolding of the foldable rim. According to its geometrical property during the transition process, a single-freedom supporting spoke is proposed to drive the foldable rim’s transformation. We analyze the length and angle varying principles of the supporting spoke by utilizing the kinematic mode based on screw theory. According to above results, five different kinds of transition mechanism of the supporting spoke is designed, performance comparison among which is conducted by dynamic simulations. Two of the five candidate transition mechanisms are picked up for their smaller driving force requirements. Their 3D printing prototypes are also fabricated and experiments show that the hybrid wheel-track can switch between wheel and track successfully. Compared to most hybrid robots which have separate wheels, tracks and legs, this transition mechanism makes the robot own both compact structure and multimodal locomotion.

Adaptive robustSMC of hybrid robot for automobile electro‐coating conveying

For a novel hybrid robot for automobile electro-coating conveying, an adaptive robust sliding-mode controller is proposed to improve the control performances and counteract the influences of uncertainties including modelling error, friction, and external disturbance. One remarkable feature of the controller lies in that it does not require the boundary of the uncertainties in the hybrid robot by designing a novel gain adaptation law. The law is capable of dynamically adjusting control gains to avoid selecting excessively bigger values of the control gains, and further attenuating the chattering phenomenon of the super-twisting sliding-mode control (SMC) simultaneously. Moreover, disturbance observer is used to estimate and compensate various uncertainties to further improve the robustness of the control system. The stability of the designed control algorithm is proved by Lyapunov stability theorem. The simulation and experimental results show that the adaptive robust SMC has superior tracking performance and is able to attenuate the chattering phenomenon effectively in the presence of modelling error, frictions, and external disturbances.

Mechanism design and analysis of a proposed wheelchair-exoskeleton hybrid robot for assisting human movement

Abstract. As a conventional mobile assistance device, a wheelchair makes people suffer from skin injuries such as bed sores and ulcer, owing to sitting on a wheelchair for a long period. And the wheelchair is barely able to adapt to complex terrains, such as stairs. With the development of robotic technology, the rise of lower-limb exoskeleton robotics provides a new means of motion assistance, and provides training of motor ability. However, it can't support a user to compete long-distance movement because a user need consume much energy to keep balance. Considering the merits and demerits of wheelchairs and exoskeletons, we propose a novel hybrid motion assistant robot that combines both. The biggest challenge is the design of a mechanism that can transform the robot from a wheelchair into an exoskeleton, as well as the reverse transformation. To achieve this goal, the mechanism must be able to achieve three configurations: the wheelchair configuration, the support configuration, and the exoskeleton configuration. To reduce the weight of the robot and make it more compact, the linkages and actuators in the mechanism are designed to be reusable when the configuration changes. The mechanism is designed based on the analysis of functional requirements, and distributed synthesis of the mechanism is adopted. The kinematics and statics of every configuration are discussed in detail, to obtain the most reasonable dimensions using the particle swarm optimization algorithm. The mechanism performance is simulated and verified using ADAMS software. Finally, an experimental prototype is constructed for preliminary tests.

Deformation analysis and hole diameter error compensation for hybrid robot based helical milling

Deformation analysis and hole diameter error compensation for hybrid robot based helical milling

Design and Kinematic Analysis of a Novel Hybrid Kinematic Mechanism With Seven-Degrees-of-Freedom and Variable Topology for Operation in Space

We propose a novel hybrid robot with seven degrees-of-freedom (DOF) and variable topology for operation in space. Design specifications of the space robot are presented for the type synthesis of hybrid mechanisms. Based on GF set theory, three design rules are given, thus providing the design method of the 7DOF hybrid space robot mechanism. Twenty-four combinations of the hybrid robotic mechanisms are obtained. The final synthesized configuration for the design of the space robot has a 3DOF parallel module and a 4DOF serial module with four revolute (RRRR) joints. The parallel module consists of a limb with universal-prismatic (UP) joints and two limbs with universal-prismatic-spherical (UPS) joints. The topology of the hybrid robot can be changed, and it will become an RPRR four-bar mechanism when it is folded for launch. The closed-form solution for the inverse displacement model is developed, and then the forward displacement equations are also obtained. After that, the Jacobian matrix is derived from the displacement model; the Jacobian matrix will analyze the singularity and workspace. We find that there are four singularities of mechanisms. The dexterous workspace of the hybrid robot is a good match for the grapple operation in space. An experiment with the prototype shows the present hybrid robot can grapple to a satellite-rocket docking ring and therefore validates the kinematic equations.

Locomotion unit for mobile robots

The first part of the paper presents a short introduction into the hybrid robots field and a classification for the wheel-leg hybrid robots. The second part presents the design and functionality of the locomotion unit proposed by the authors and the last part details the development paths proposed by the authors for this locomotion unit.

Kinematic calibration of a 6-DOF hybrid robot by considering multicollinearity in the identification Jacobian

This paper presents a systematic approach for the kinematic calibration of a 6-DOF hybrid polishing robot. It concentrates particularly on dealing with ill-conditioning that arises from multicollinearity in the identification Jacobian as a consequence of limited pose measurements. A linearized error model is formulated, using screw theory, by considering all possible source errors at the joint/link level. Calibration is based upon pose error measurements captured using a laser tracker when the polishing head undergoes pure translation within the task workspace. A two-step procedure for error parameter estimation and pose error compensation is then proposed: (1) coarse estimation and compensation of the encoder offsets using linear least squares; and (2) fine estimation of the whole set of identifiable error parameters using a Liu estimation and subsequent modification of the NC trajectory dataset of the polishing head. Both simulations and experiments on a prototype machine show that the overall standard deviation of the error parameters identified by Liu estimator is much less than that estimated by linear least squares, confirming its greater robustness in the presence of measurement uncertainty. The proposed approach results in satisfactory pose accuracy of the polishing head throughout the entire task workspace.

An engineering-oriented motion accuracy fluctuation suppression method of a hybrid spray-painting robot considering dynamics

Due to the complex dynamic characteristics of a hybrid spray-painting robot, the motion accuracy fluctuates in the workspace. In order to reduce the accuracy fluctuation of the hybrid robot, this paper proposes an engineering-oriented motion accuracy assurance method by considering dynamic characteristics, including workspace optimization and control parameters design. First, the dynamic model of the hybrid spray-painting robot is derived based on the virtual work principle, and a dynamic evaluation index is investigated to describe the possible maximum dynamic load. Then, based on the evaluation index, the relative location of the task workspace for painting an aircraft wing in the whole workspace is optimized. Then, a control parameters design approach is presented to ensure that the robot always has desired accuracy in the optimized task workspace. Finally, some experiments are performed, and the results show that the robot has better performance in the optimized task workspace with the designed control parameters, which proves the effectiveness of the proposed method.

Inverse kinematics of a 5-axis hybrid robot with non-singular tool path generation

Abstract This paper deals with non-singular tool path generation of a 5-axis hybrid robot named TriMule, which is designed for large part machining in situ. It is observed that at a singularity pose sudden changes occur in rotation of the C-axis and lengths of three telescopic legs. It is found that when the tool axis rotates about the axis normal to the plane expanded by the tool axis and the singular axis, the singular axis itself is forced to rotate simultaneously about the same axis in the opposite direction. This exploration enables the minimum rotation angle of the tool axis to be determined accurately for avoiding singularity and reducing machined surface errors caused by tool axis modification, leading to the development of an algorithm for non-singular tool path generation by modifying a partial set of the control points of B-splines. Both simulation and experiment on a prototype machine are carried out to verify the effectiveness of this approach.

Control of Pole-Climbing Robot Orientation using Self-Tuning Method

This paper describes the method to control a hybrid robot whose main task is to climb a pole to place an object on the top of the pole. The hybrid pole-climbing robot considered in this paper uses 2 Planetary PG36 DC-motors as actuators and an external rotary encoder sensor to provide a feedback on the change in robot orientation during the climbing movement. The orientation control of the pole-climbing robot using self-tuning method has been realized by identifying the transfer function of the actuator system under consideration, being followed with the calculation of control parameters using the self-tuning pole-placement method, and furthermore being implemented on the external rotary encoder sensor. Self-tuning pole-placement method has been explored to control the parameters q<sub>0</sub>, q<sub>1</sub>, q<sub>2</sub>, and p<sub>1</sub> of the controller. The experiments were done on a movement path in a form of a cylindrical pole. The first experiment was done based one the change in rotation angle of the rotary sensor with the angle values greater than 50˚ in the positive direction, whereas the second experiment was done with the angle values greater than -50˚ in the negative direction. The experiment results show that the control of the robot under consideration could maintain its original position at the time of angle change disturbance and that the robot could climb in a straight direction within the specified tolerance of orientation angle change.

Screw theory based mathematical modeling and kinematic analysis of a novel ankle rehabilitation robot with a constrained 3-PSP mechanism topology

As a common athletics injury in orthopedics clinic, ankle injury may affect a person’s daily life and ankle injury rehabilitation has gained increasing interests from the medical and robotic societies. A novel hybrid ankle rehabilitation robot is proposed, which composing of a serial and a parallel part. In order to analyze its kinematic performances, the parallel part of the robot is simplified as a constrained 3-PSP parallel mechanism. A mathematical model for the parallel part of the robot is established based on the screw theory. Then the inverse kinematics is obtained, and the reciprocal twists, Jacobian matrices and the singularity of the robot are analyzed. Finally the workspace of the central point on the moving platform is predicted. The kinematic analyses manifest that the proposed hybrid rehabilitation robot not only can realize three kinds of ankle rehabilitation motions, but also can eliminate singularity with enhanced workspace. The workspace of the central point reveals that the hybrid robot can fully meet the demanded rehabilitation space by comparing with the clinic demands. Our results reveals the characteristic structure of the hybrid rehabilitation robot and its superiority, it offers some basis data for the future enhancement of the device.