Joint Workspace Research Articles

Research of the Joint Workspaces and Kinematic Efficiency of Man-Machine Systems of Bicycles

Bicycle design largely contradicts human motion, necessitating consideration of both the bicycle structure and the kinematic efficiency in the dimensions of the rider’s limbs, as well as human factor engineering, i.e. comfortability. By focusing on the kinematic model of 5-bar linkage and joints workspace, this study examines the most appropriate bicycle design and the riding posture to ensure that muscles can produce the effective moment and increase driving efficiency of a crank necessary. For upright, racing and recumbent bicycle types, assumptions are made regarding mobility analysis and the system of man-machine systems of bicycles estimated as well. Simulation results can identify the major dimensions of bicycle designing for different riders efficiently by inputting physical measurements of the rider and the angle range of driving force, subsequently increasing the riding efficiency to decrease the load of lower limbs of riders and satisfying ergonomic requirements of bicycle riders.

A Kinematic Model Used to Customize Design of Manual Wheelchair

That wheelchair user’s shoulder joint injuries are directly related to poor wheelchair design and the location of the wheelchair driving mechanism has been proven clinically. This work presents a novel approach to rapidly customize the design of manual wheelchairs, such that each user can easily obtain a custom manual wheelchair, thereby reducing the potential for shoulder joint injury. In this study, a human-chair system composed of a human body and a wheelchair was simulated as a plain single-loop five-bar linkage. Mobility analysis was conducted to identify the corresponding joint workspace. By analyzing linkage movement and the upper-limb muscle strength of a user, the optimal location of the wheel hub and optimal radius of the handwheel were identified as the bases of a customized design for manual wheelchairs.

Joint workspace of parallel kinematic machines

Robot workspace is the set of positions a robot can reach. Workspace is one of the most useful measures for the evaluation of a robot. Workspace is usually defined as the reachable space of the end-effector in Cartesian coordinate system. However, it can be defined in joint coordinate system in terms of joint motions. In this paper, workspace of the end-effector is called task workspace, and workspace of the joint motions is called joint workspace. Joint workspace of a parallel kinematic machine (PKM) is focused, and a tripod machine tool with three degrees of freedom (DOF) is taken as an example. To study the joint workspace of this tripod machine tool, the forward kinematic model is established, and an interpolating approach is proposed to solve this model. The forward kinematic model is used to determine the joint workspace, which occupies a portion of the domain of joint motions. The following contributions have been made in this paper include: (i) a new concept so-called joint workspace has been proposed for design optimization and control of a PKM; (ii) an approach is developed to determine joint workspace based on the structural constraints of a PKM; (iii) it is observed that the trajectory planning in the joint coordinate system is not reliable without taking into considerations of cavities or holes in the joint workspace.

Integrated Design Toolbox for Tripod-Based Parallel Kinematic Machines

This paper presents a concept and implementation of a toolbox for design and application of tripod-based parallel kinematic machines (PKMs). The toolbox is a suite of design tools to support users from conceptual design to actual application of tripod-based PKMs. These design tools have been individually developed in different languages and development environments, and are integrated seamlessly using a JAVA-based platform. Users can access all the design tools through a friendly graphical user interface (GUI). It is the first computer-aided design system specially developed for tripod-based PKMs. The toolbox includes some innovative methodologies, such as a forward kinematics solver, the concept of joint workspace, on-line monitoring based on forward kinematics, and the concept of motion purity. The paper gives an overview on the toolbox architecture and some key technologies.

Forward kinematic solution and its applications for a 3-DOF parallel kinematic machine (PKM) with a passive link

In this paper, a 3-DOF parallel kinematic machine (PKM) with a passive link is introduced. The forward kinemaic model is established, and a new technique is proposed to solve this model. The developed forward kinematic solver (FKS) is employed in two new applications: the determination of joint workspace and sensor-based real-time monitoring. A joint workspace concept is proposed for the optimization of a PKM structure. It is defined as a reachable area in the joint coordinate system under given ranges of active joint motions. The larger a joint workspace is, the higher utilization of joint motion capacity is. Sensor-based monitoring is applied in real-time system operation, by which a remote user can monitor a PKM through Internet based on the feedbacks of the joint encoders or the on-site stereo camera.

Coordinated turn-and-reach movements. II. Planning in an external frame of reference.

The preceding study demonstrated that normal subjects compensate for the additional interaction torques generated when a reaching movement is made during voluntary trunk rotation. The present paper assesses the influence of trunk rotation on finger trajectories and on interjoint coordination and determines whether simultaneous turn-and-reach movements are most simply described relative to a trunk-based or an external reference frame. Subjects reached to targets requiring different extents of arm joint and trunk rotation at a natural pace and quickly in normal lighting and in total darkness. We first examined whether the larger interaction torques generated during rapid turn-and-reach movements perturb finger trajectories and interjoint coordination and whether visual feedback plays a role in compensating for these torques. These issues were addressed using generalized Procrustes analysis (GPA), which attempts to overlap a group of configurations (e.g., joint trajectories) through translations and rotations in multi-dimensional space. We first used GPA to identify the mean intrinsic patterns of finger and joint trajectories (i.e., their average shape irrespective of location and orientation variability in the external and joint workspaces) from turn-and-reach movements performed in each experimental condition and then calculated their curvatures. We then quantified the discrepancy between each finger or joint trajectory and the intrinsic pattern both after GPA was applied individually to trajectories from a pair of experimental conditions and after GPA was applied to the same trajectories pooled together. For several subjects, joint trajectories but not finger trajectories were more curved in fast than slow movements. The curvature of both joint and finger trajectories of turn-and-reach movements was relatively unaffected by the vision conditions. Pooling across speed conditions significantly increased the discrepancy between joint but not finger trajectories for most subjects, indicating that subjects used different patterns of interjoint coordination in slow and fast movements while nevertheless preserving the shape of their finger trajectory. Higher movement speeds did not disrupt the arm joint rotations despite the larger interaction torques generated. Rather, subjects used the redundant degrees of freedom of the arm/trunk system to achieve similar finger trajectories with differing joint configurations. We examined finger movement patterns and velocity profiles to determine the frame of reference in which turn-and-reach movements could be most simply described. Finger trajectories of turn-and-reach movements had much larger curvatures and their velocity profiles were less smooth and less bell-like in trunk-based coordinates than in external coordinates. Taken together, these results support the conclusion that turn-and-reach movements are controlled in an external frame of reference.

On the kinematic design of the 5R planar, symmetric manipulator

A complete kinematic characterization of the 5R planar, symmetric manipulator, intended as a design aid, is proposed in this paper. The characterization scheme relies on the configuration of the Cartesian workspace plots (CWP), the Cartesian workspace singularity plots (CWSP), the joint workspace plots (JWP) and the joint workspace singularity plots (JWSP). These plots are given in terms of two nondimensional geometric parameters, λ and μ, that represent the lengths of the manipulator links; these parameters can be used to investigate the relationships between the link lengths of the manipulator and the underlying workspace and singularity distribution. The plots can be regarded as an atlas of the workspace and singularity distribution that should find applications in analysis and design.

Multilegged walker design—the joint torque versus workspace compromise

A machine's weight is directly related to the strength of the installed joint actuators, and it is reasonable to assume that minimizing the installed joint torques will minimize the machine weight. Unfortunately, the workspace area will also reduce with the installed joint torques; thus there must be a compromise between weight (joint strength) and workspace. Methods are presented to generate the set of static workspaces corresponding to a range of installed joint torques. In this way the relationship between the workspace area and installed joint torque can be established. A numerical example is presented which shows that a small reduction in the workspace area can lead to a substantial reduction in installed joint torque and hence machine weight.