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A 3-degree-of-freedom (DOF) 3-UPU translational parallel mechanism (TPM) is one of the typical TPMs. Despite comprehensive studies on 3-UPU TPMs in which the joint axes on the base and the moving platform are coplanar, only a few 3-UPU TPMs with skewed base and moving platform have been proposed, and the impact of link parameters on constraint singularity loci of such TPMs has not been systematically investigated. The advances in computing comprehensive Gröbner system (CGS) or Gröbner cover of parametric polynomial systems provide an efficient tool for solving this problem. This paper presents a systematic classification of 3-UPU TPMs with skewed base and moving platform based on constraint singularity loci. First, the constraint singularity equation of a 3-UPU TPM is derived. Using Gröbner cover, the 3-UPU TPMs are classified into 12 types. Finally, a novel 3-UPU TPM is proposed. Reconfiguration analysis shows that unlike most existing 3-UPU TPMs which can transit from a 3-DOF translational mode to two or more 3-DOF operation modes, the proposed 3-UPU TPM can only transit from a 3-DOF translational mode to one general 3-DOF operation mode. The singularity locus divides the workspace of this 3-UPU TPM into two constraint singularity-free regions. As a by-product, a 3-UPU parallel mechanism that the moving platform can undergo 3-DOF translation and 1-DOF infinitesimal rotation is revealed. This work provides a solid foundation for the design of 3-UPU TPMs and a starting point for the classification of 3-UPU parallel mechanisms.

This paper describes the design of a robot platform that can collect and disposing waste in passenger trains. It covers an analysis of the key design considerations for success in operating in a train environment, as well as considerations in manipulating waste in an often-confined space. The design constraints are analyzed for their importance in the successful development of a train cleaning robot. The analysis informs the development of three robot designs. These designs are assessed in their appropriateness for development against a baseline design that uses readily available parts. Among the three designs developed, one uses a vacuum powered arm similar to the type utilized in manufacturing plants, one is based on the dustpan and brush used in domestic cleaning, and one is based on a conveyor belt. These designs are assigned a percentage suitability for implementation in the automated train carriage cleaning system. Using the key values and the requirements the design should fulfil, a systematic investigation is undertaken. This investigation finds the conveyor belt design most appropriate for application due to the sustainable design and effective cleaning that can be undertaken without additional tools.

The design of XY compliant parallel manipulators (CPMs) remains challenging considering the tradeoff between mirror-symmetry for better constrained undesired rotations and a small footprint, although a significant number of XY CPMs have been reported in extensive applications. This paper presents a new XY CPM using mirror-symmetry without increasing its footprint, mainly aiming to reduce the undesired parasitic rotations of input and output motion stages. The concept of mirror-symmetry is deployed to tackle the parasitic rotations, with the help of using a multilayer compact XY CPM design method. A nonlinear and analytical model of the proposed XY CPM is derived using free body diagrams and the beam constraint model (BCM) to accurately analyze its performance characteristics over a large range of motion. The designed XY CPM is then verified by the nonlinear finite element analysis (FEA) method. Finally, the proposed multilayer design is fabricated using two pieces of aluminum plate and it is mounted in a measurement system to experimentally validate several performance characteristics. The analytical, FEA, and/or experimental results show that the proposed design can sufficiently constrain undesired motions including parasitic rotation of input and output stages, cross-axis coupling error, and actuator isolation index. Compared with exiting designs, the proposed design also shows its merits in large motion range and out-of-plane stiffness.

This paper presents a series of deployable mechanisms based on n-UU (universal joint) Wren parallel mechanism (PM) units, which undergo one degree-of-freedom (DOF) Borel–Bricard motion. First, the PM unit is developed into ortho-planar mechanisms by adopting an R–R joint. The link parameters of the mechanism are optimized to maximize the folding ratio while avoiding interference. Then, the optimized PM units are piled up to construct a novel 1DOF multilayer mechanism that has the largest folding ratio among similar structures in the literature. Moreover, polyhedral deployable mechanisms are obtained by connecting the PM unit using U joint or UU joint. Apart from saving space, the polyhedral mechanisms can transform among different shapes of polyhedrons. Finally, variations of the n-UU PM are investigated with different shapes of platforms, and each mechanism has its unique movement characteristics.

This paper deals with the structure synthesis and reconfiguration analysis of variable-DOF (variable-degree-of-freedom) single-loop mechanisms with prismatic joints based on a unified tool—the dual quaternion. According to motion polynomials over dual quaternions, an algebraic method is presented to synthesize variable-DOF single-loop 5R2P mechanisms (R and P denote revolute and prismatic joints, respectively), which are composed of the Bennett and RPRP mechanisms. Using this approach, variable-DOF single-loop RRPRPRR and RRPRRPR mechanisms are constructed by joints obtained from the factorization of motion polynomials. Then reconfiguration analysis of these variable-DOF single-loop mechanisms is performed in light of the kinematic mapping based on dual quaternions as well as the prime decomposition. The results show that the variable-DOF 5R2P mechanisms have a 1DOF spatial 5P2P motion mode and a 2DOF Bennett-RPRP motion mode. Furthermore, the variable-DOF 5R2P mechanisms have two transition configurations, from which the mechanisms can switch among their two motion modes.

This research constitutes a systematic investigation of the effect of image view on Convolutional Neural Networks (CNNs) when trained to detect waste in train carriages. Additionally, this research identifies neural network architecture and training conditions for use in an automated train cleaning robot. Specifically, we investigate the relationship between the size of the CNN training dataset, whether these images are taken from a view sympathetic to the CNN application, and the effectiveness of the trained networks. Three datasets were constructed specifically for this research; a large dataset of 58,300 studio images of waste in a variety of conditions, a smaller dataset of 4,515 images taken of actual waste items on trains, and a dataset of 7,290 images of actual waste on trains used to test the CNNs. The images taken on trains were captured from the perspective of a hypothetical cleaning robot that would use these networks. Additionally, we provide a comparison of MobileNetV2, ShuffleNet, and SqueezeNet CNNs based on their suitability for implementation in an automated train cleaning system, and the optimum conditions to do so. Training with a smaller dataset of images taken from a “robot-eye view” resulted in an average increase in classification accuracy of 10.5%, with the largest increase being 26%, when compared to training with a larger dataset of images of waste items in various poses. ShuffleNet was identified as the optimally performing CNN for waste detection, achieving an accuracy of 88.61% when trained with a small dataset of images sympathetic to the end use. MobileNetV2 was found to perform optimally with a larger dataset of training images, even if these are less specific to the application of the network.

A 3-UPU translational parallel mechanism (TPM) is one of typical TPMs. Several types of 3-UPU TPMs have been proposed in the literature. Despite comprehensive studies on 3-UPU TPMs in which the joint axes on the base and the moving platform are coplanar, only a few 3-UPU TPMs with a skewed base and moving platform have been proposed. However, the impact of link parameters on singularity loci of such TPMs has not been systematically investigated. The advances in computing CGS (comprehensive Gröbner system) or Gröbner cover of parametric polynomial systems provide an efficient tool for solving this problem. This paper presents a systematic classification of 3-UPU TPMs, especially those with a skewed base and moving platform, based on constraint singularity loci. First, the constraint singularity equation of a 3-UPU TPM is derived. To simplify this equation, the coordinate frame on the base (or moving platform) is set up such that the centers of three U joints are located on different coordinate axes. Using Gröbner Cover, the 3-UPU TPMs are classified into 20 types based on the constraint singularity loci. Finally, a novel 3-UPU TPM is proposed. Unlike most of existing 3-UPU TPMs which can transit to two or more 3-DOF operation modes at a constraint singular configuration, the proposed 3-UPU TPM can only transit to one general 3-DOF operation mode in a constraint singular configuration. The singularity locus divides the workspace of this 3-UPU TPM into two constraint singularity-free regions. This work provides a solid foundation for the design of 3-UPU TPMs and a starting point for the classification of a general 3-UPU parallel mechanism.

The design of XY compliant parallel manipulators (CPMs) remains challenging considering the tradeoff between the mirror-symmetry for better constrained undesired rotations and the small footprint, although a significant number of XY CPMs have been reported in extensive applications. This paper presents a new XY CPM using mirror-symmetry without increasing its footprint, mainly aiming to reduce the undesired parasitic rotations of input and output motion stages. The concept of higher degree of stiffness centre symmetry is deployed to tackle the parasitic rotations, leading to a multi-layer compact XY CPM design with each layer being a rotation-symmetrical design. A nonlinear and analytical model of the proposed XY CPM is derived using free body diagrams and the Beam Constrained Model (BCM) to accurately analyse its performance characteristics over a large range of motion. The designed XY CPM is then verified by the nonlinear finite element analysis (FEA) method. Finally, the proposed multi-layer design is comprehensively compared with the well-received single-layer rotation-symmetrical design. It is shown in the new design that the parasitic rotations of input and output stages along with the actuator isolation are significantly reduced and that the out-of-plane-stiffness is also significantly increased.

A geometric method to the static balancing of mechanisms constructed using spherical chain units is presented. A (serial) spherical kinematic chain unit is composed of n moving links, whose masses are considered, connected by revolute (R) joints the axes of which intersect at a fixed point. The mass of each link can be balanced using one spring without any auxiliary parallelogram. The balancing can be achieved readily with almost no calculation. One end of each spring is fixed right above the intersection of the joint axes and the other end is attached to the point that is on the line defined by the intersection and the equivalent center of mass of the corresponding link (combining the masses of the link and the payload). This method is then applied to the mechanisms constructed using spherical kinematic chain units, and the ones constructed using spherical kinematic chain units and other types of kinematic chain units. By distributing the mass of a link onto its adjacent links, the static balancing of the mechanism is reduced to those of several spherical kinematic chain units, which can be balanced using the proposed method. Two examples are given, including a Bennett plano-spherical hybrid linkage and a 3-RRS parallel mechanism to illustrate the proposed method for static balancing.

This paper discusses a novel optimization method to design statically balanced manipulators. Only springs are used to balance the manipulators composed of revolute (R) joints. Since the total potential energy of the system is constant when statically balanced, the sum of squared differences between the two potential energy when giving different random values of joint variables is set as the objective function. Then the optimization tool of MATLAB is used to obtain the spring attachment points. The results show that for a 1-link manipulator mounted on an R joint, in addition to attaching the spring right above the R joint, the attachment point can have offset. It also indicates that an arbitrary spatial manipulator with n link, whose weight cannot be neglected, can be balanced using n springs. Using this method, the static balancing can be readily achieved, with multiple solutions.

The type/number of operation modes of a parallel manipulator (PM) may vary with the link parameters of the PM. This paper presents a systematic classification of a 3-RER PM based on the type/number of operation modes. Here, R and E denote revolute joint and planar joint, respectively. The 3-RER PM was proposed as a 4-degree-of-freedom (DOF) 3T1R PM in the literature. Using the proposed method, classification of a PM based on the type/number of operation modes can be carried out in four steps, including formulation of constraint equations of the PM, preliminary classification of the PM using Gröbner cover, operation mode analysis of all the types of PMs using primary decomposition of ideals, and identification of redundant types of PMs. The classification of the 3-RER PM shows that it has 13 types. Besides the two 4-DOF 3T1R operation modes, different types of 3-RER PMs may have up to two more 3-DOF or other types of 4-DOF operation modes. Motion characteristics of the moving platform of 3-RER PMs are also identified using Euler parameter quaternions. This work is the first systematic study on the impact of link parameters on the operation modes of the 3-RER PM and provides a solid foundation for further research on the design and control of 3-RER PMs and other multi-mode (or reconfigurable) PMs.

Obstacle avoidance is a major hurdle when implementing mobile robots and swarm robots. Swarm robots work in groups and therefore require an efficient and functional obstacle avoidance algorithm to stay collision free between themselves and their surroundings. This paper reviews previous research in obstacle avoidance implementation using the force field method (FFM), also known as potential field method (PFM). Moreover, this paper aims to execute simulations using a modified and simplified force field algorithm. The obtained results are analysed to identify the performance characteristics and the time taken to perform tasks using a singular mobile robot against a swarm robot environment consisting of four and ten robots, respectively. Simulations showed that the algorithm was successful in navigating obstacles for both single and swarm robot environments. A single robot was found to take up to 340% longer to arrive at the required location compared to the first robot in the experiment.

This paper proposes a new kind of modular rolling robot called multi-loop rover (MLR), which is essentially a multi-loop linkage that is able to roll and switch its rolling directions. For ease of rolling, the MLR retains a multi-loop topological structure composed of a number of strut and node modules. First, the modular design and assembling method are introduced to construct an MLR. Then, the mobility is analyzed based on screw theory, and a brief formula is presented to calculate the degree-of-freedoms of the robot. The results show that all node modules only have translational motions, which can significantly reduce the complexity of kinematics. The forward and inverse kinematics are conducted to show the deformation properties. Based on the kinematic rolling principle, the morphing strategies for rolling and turning functions are developed. Finally, a physical prototype is manufactured and a serial of experiments are carried out to verify the proposed method.

This paper deals with the construction and reconfiguration analysis of a spatial mechanism composed of four circular translation (G) joints. Two links connected by a G joint, which can be in different forms such as a planar parallelogram, translate along a circular trajectory with respect to each other. A spatial 4G mechanism, which is composed of four G joints, usually has one degree-of-freedom (DOF). First, a 2-DOF spatial 4G mechanism is constructed. Then, a novel variable-DOF spatial 4G mechanism is constructed starting from the 2-DOF 4G mechanism using the approach based on screw theory. Finally, the reconfiguration analysis is carried out in the configuration space using dual quaternions and tools from algebraic geometry. The analysis shows that the variable-DOF spatial 4G mechanism has one 2-DOF motion mode and one to two 1-DOF motion modes and reveals how the 4G mechanism can switch among these motion modes. By removing one link from two adjacent G joints each and two links from each of the remaining two G joints, we can obtain a queer-rectangle and a queer-parallelogram, which are the generalization of the queer-square or derivative queer-square in the literature. The approach in this paper can be extended to the analysis of other types of coupled mechanisms using cables and gears and multi-mode spatial mechanisms involving G joints.

Planar parallelogram mechanisms (PPMs) have been used in many applications either as standalone pieces or as compositional joints of mechanisms, such as parallel mechanisms, remote center mechanisms and variable-DOF mechanisms. An n -RR PPM is composed of congruent base and moving platform connected with n RR links of equal link lengths. Although it is well known that an n -RR PPM has one 1-DOF circular translation mode, whether an n -RR PPM has structure/motion modes in addition to the 1-DOF motion mode and how the link parameters affect the number of extra motion/structure modes of the n -RR PPMs have not been well investigated. This paper is about the motion/structure mode analysis and classification of n -RR PPMs. Firstly, the motion/structure mode analysis of 3-RR PPMs is carried out. Then conditions for an n ( n > 3 )-RR PPM to have the same motion/structure modes as a 3-RR PPM are revealed. Finally, n ( n ≥ 3 )-RR PPMs are classified into three types. In addition to one 1-DOF motion mode, Types I, II and III PPMs have two, one or zero structure mode respectively. This work provides a foundation for the construction and analysis of several variable-DOF mechanisms composed of PPMs.

SUMMARYA novel reconfigurable tri-prism mobile robot with eight modes is proposed. The robot is composed of two feet connected by three U-R-U (universal-revolute-universal) limbs. The robot incorporates the kinematic properties of sphere robots, squirming robots, tracked robots, wheeled robots and biped robots. In addition, the somersaulting and turning modes are also explored. After the description of the robot, the DOF (degree-of-freedom) is calculated based on screw theory. The 3D model and simulations indicate that the robot can cross several typical obstacles and can also be folded via two approaches. Finally, the prototype experiments are presented to verify the feasibility of the proposed mobile robot in different motion mode.

This paper presents a unified geometric modeling and solution procedure for direct kinematic analysis of a class of parallel mechanisms based on conformal geometric algebra (CGA). After locking the actuated joints, such parallel mechanisms will be turned into a 3-RS structure, which is composed of two triangular platforms connected by three RS serial chains in parallel. Using the proposed approach, the univariate polynomial equation for the direct kinematic analysis of these parallel mechanisms can be derived in three steps. Firstly, the positions of two of the three spherical joints on the moving platform are formulated by the intersection, dissection and dual of the basic geometric entities under the frame of CGA. Secondly, a coordinate-invariant equation expressed in terms of geometric entities is derived via CGA operation. Thirdly, a univariate polynomial equation is obtained directly from the aforementioned coordinate-invariant equation by using tangent-half-angle substitution. Several case studies are then presented to verify the solution procedure. The novelties of this approach lie in that: (1) The formulation is concise and coordinate-invariant and has intrinsic geometric intuition due to the use of CGA; (2) No algebraic elimination procedure is required to derive the univariate polynomial equation; and (3) The proposed approach is applicable to the direct kinematics of this family of parallel mechanisms with any link parameters.