Search

Spraying robot is a kind of important industrial equipments. However most of them cannot flexibly change their workspace. In order to obtain a spraying robot with extremely large workspace but a small storage space, we synthesize an innovative mobile robot with a telescopic forearm. First, the structure of a four-side deployable arm to generate straight line motion for the mobile robot is proposed. It adequately enlarges the workspace and reduces the storage space because of the stretchable structure. Based on the new structure, the homogeneous transformation matrix and Jacobian matrix of the forward and inverse kinematics are deduced in details for workspace evaluation. Geometry analysis indicates that the four-side deployable structure effectively extends the arm of the robot, and therefore it has much larger workspace than its existing counterparts do.

In this paper, a spatial mechanism is proposed to achieve higher stiffness, higher strength and higher reliability for a landing gear system. Two non-coplanar spatial six-bar linkages are creatively designed to generate double-lock loading configuration with redundant constraints. For every spatial six-bar linkage, starting from the existing four-bar linkages, two other links are particularly synthesized to obtain double-lock function for the working configuration. Two such linkages are optimized in geometry to get a complete retraction for the sake of both providing overconstraints and saving the storage space. Based on the structure of double-lock landing gear, kinematics is conducted to obtain the complete folding and unfolding. Statics and stiffness analysis are investigated to further confirm the mechanical advantages of the landing gear system.

This paper researches on a stretchable coating robot arm for extremely large parts. It has high enough lateral and vertical stiffnesses within the reachable workspace to keep the required spraying accuracy. According to the functional independence principle, the vertical stiffness is kept by screw driving mechanism working in the vertical direction while the lateral stiffness is safeguarded by an overconstrained stretchable arm. In this paper, the focus is put on the stiffness synthesis of the stretchable arm's strengthened connecting frames by discussing both their lateral stiffness and unit-stiffness under different topologies. The stretchable arm consists of a four-sided scissor-form structure of pivoted links interconnected by strengthened connecting frames at each deployable layer, forming a multi-planar laterally overconstrained structure. Different frames have different stiffnesses and self-weights because of their different topologies. Therefore, the unit-stiffness, which is the ratio between the lateral stiffness and self-weight, is applied as it proved to be a resourceful design index in evaluating the planar stretchable arm. This paper proposes a topological design solution for the strengthened connecting frames, positively influencing the stretchable coating robotic arm's mechanical performance in engineering application.

This paper focuses on the design of a flapping wing robot and proposes a unified design formula for planar four-bar linkages with arbitrary n prescribed positions. The absolute coordinates of a circle point corresponding to every prescribed position are expressed by those of the first one through matrix transformation. Because the distance between any circle point and center point is always equal to the length of the side link jointed with the fixed base, a set of quadratic equations for the distance constraints are obtained. Expanding and rearranging these equations presents a linear system for the coordinates of center point. The condition for existing solution of these equations requires that the rank of the augmented rectangle coefficient matrix, C , should always be less than 3 as there are only two unknown coordinates for the center point. The rectangle augmented coefficient matrix C is ( n − 1) × 3, and therefore it can be transformed to a 3 × 3 square matrix, M , by left multiplying the transpose of C . This provides a unified expression for the design of a planar four-bar linkage with arbitrary n positions for a flapping wing.

This paper investigates the effect of gyroscopic moment on the induction of damage of a tapered roller bearing. High speed and high load are the typical characteristics of nowadays express trains which rely heavily on the tapered roller bearings. However, the phenomena of damage, especially for the side damage, of rollers and ring raceways in tapered roller bearings cannot be neglected with the occurrence of super speed trains in China. It first presents the geometry of a tapered roller bearing and then discusses the angular speed relationship between the rotations around the axis of shaft and self-axes of rollers. Gyroscopic moment is then established with geometry parameters of the bearing and physical parameters of the rollers. Then the effect of gyroscopic moment of rollers is discussed and the criterion that the pose of the tapered rollers should not be affected by the gyroscopic moment is obtained for the first time. This new theoretical result offers a design criterion for high speed tapered roller bearings. Analysis indicates that the gyroscopic moment could not bring any direct damage to the rollers and raceways but it does provide the boundary conditions to induce the side damage of rollers and raceways when the parameters of a bearing are not properly designed.

This paper proposes an independent suspension whose alignment parameters are theoretically invariable during jounce and rebound. Each kinematic chain of the suspension consists of a 3-RRR linkage that could automatically compensate for the axial distance change. The motions of the 3-RRR linkages and the knuckle are investigated from the viewpoints of screw theory and geometry. The equivalent torsional stiffness, bending stiffness and shear stiffness of a 3-RRR linkage are investigated to demonstrate the feasibility of engineering applications. Research results show that this complex linkage has better mechanical properties than those of a prismatic joint when used as a passive connection. As a result, the 3-RRR linkage has accurate alignment ability on the one hand and could keep the compact space in design while having the required strength and compliance on the other hand.

This paper proposes a foldable stair that can be deployed for use and folded for conservation and investigates the geometry and statics of the structure. It not only has the moving flexibility of a mechanism but also has the high stiffness and high strength of statically indeterminate structures. The primary linkage is a deployable scissor-like element which forms the staircase after expanding. This paper starts with the analysis of the geometry of planar four- and six-bar mechanisms and processes to synthesize the foldable stair and then investigates its statics. The paper further investigates redundant inner forces of every link based on the second Castigliano theorem, develops a foldable stair model, assembles and manufactures. Working experiments verify the theoretical results and the outstanding advantages over the general fixed stairs.

Forklift truck is one of the most important tools in logistics. However, the general mast system of a forklift truck not only restrains the driver's vision, but also increases the whole weight of a truck and decreases the fuel economy. Therefore, this paper focuses on the innovative design of a new lifting mechanism for forklift truck. Firstly, a spatial multi-link lift-guidance mechanism is proposed. And then, under the constraints of this mechanism, the mobility of the fork and fork frame is investigated in theory. Lastly, a new lifting mechanism based on it is presented and computer simulation is used to demonstrate the feasibility of motion. This multi-link lifting mechanism takes advantage of flexible cable drive and rigid body guidance, which not only provides the operator with a wider field of vision but also reduces the equilibrate weight of a vehicle and therefore improves the fuel economy.

This paper aims at investigating the mechanism theory and application of deployable structures based on scissor-like element (SLE). The deployable structure has a wide application both in space structures and in general mechanical engineering. However, the mechanism theory of such deployable structures based on SLE is seldom probed systematically. Therefore, this paper starts from the mobility analysis of simple planar linkages, and then explores the mechanism theory of spatial deployable units utilized in flat, cylindrical and spherical deployable structures. The theoretical results obtained in this paper have a general adaptation in conceiving any kinds of deployable structures.

The fact that symmetry of a spatial parallel mechanism can be directly mapped into the workspace of the end-effector is defined as a strengthened theorem and is proved by utilizing the group theory. If the order of the symmetry group of the mechanism structure is n, then the searching range can be reduced to 1 n of the initial one. This can lead to significant reductions of the computation task and time because only a fraction of the workspace may need to be investigated for a symmetric mechanism, the merits of which are especially obvious if discretization algorithms are used. Firstly, the symmetry mapping from the mechanism structure into the workspace is generalized in a much more extension by a group theoretical proof. And then, examples are presented to illustrate the applications of this research result in reducing the searching tasks of the reachable workspace of an end-effector. The strengthened theorem herein will be adapted to all symmetry cases and will be most useful for the conceptual design of spatial parallel mechanisms, particularly for those with complicated symmetries.

In this paper, we propose a programmable algorithm to investigate the configuration degree of freedom (CDOF) of a spatial parallel mechanism in one Cartesian coordinate system with reciprocal screw theory. According to the physical meaning of reciprocal screws, we first obtain the terminal constraints of every kinematic chain which connects the end-effector with the fixed base, and then gain the free motion(s) of the end-effector and its degree of freedom (DOF). Through analyzing the controllability of the end-effector, we investigate the instantaneous screw expressions for the free motions of the end-effector of a spatial parallel mechanism and the CDOF of the mechanism. The whole mathematical analysis process can be directly embedded in a kind of CAD software, in which the imperfect Kutzbach Grubler formulas or its amendments are mostly utilized to analyze the DOF.

In this paper, we propound an analogous symmetric theorem of workspace for spatial parallel manipulators with identical kinematic chains, and then present a strict mathematic proof by splitting the problem into planar symmetry, rotational axis symmetry and point symmetry (centrosymmetry). Examples demonstrate that this theorem can be utilized to investigate the geometry shapes of the workspace and to guide the conceptual design of spatial parallel manipulators, especially for those complicated spatial parallel manipulators with full degrees of freedom (DoF). The theorem offers a concrete safeguard for the workspace analysis of any symmetric spatial parallel manipulators.

In this paper, we make an analysis on the singularity of spatial parallel manipulator. Although many scholars have discussed this topic, their works mainly focused on finding the methods to divide the cases of singularity or searching the solutions with Jacobian matrices. This paper, on the other hand, addresses the singularity problems of the manipulator with its terminal constraints, which are the reciprocal screws of the manipulator’s sub-kinematic chains. Through investigating the kinematic screws and the terminal constraints of the sub-chains, this method not only avoids solving the Jacobian matrices, but also points out the physical meaning of singularity. Application analyses are presented to demonstrate the effectiveness of the method.

Based on the author’s research results on high-speed travelling type of double four-rod spatial parallel mechanism in new type virtual axis machine tools with combined architecture, this paper lays emphasis on the problems of singularity analysis and singularity loci calculation of such mechanism. In theory, it has found out three kinds of singularity loci of the mechanism by utilizing an identification matrix that is constructed on the conception of screw, and revealed the relationship between the structural parameter b and the singularity loci, thus laid a theoretical foundation for optimizing the parameter of the mechanism. In aspect of application, by applying the result in the design of new five-coordinate virtual axis machine tool with combined architecture, it has effectively solved the affection of singularity, greatly increased the working space of the machine tool and achieved good effect.