Design Optimization of 3-DOF Redundant Planar Parallel Kinematic Mechanism Based Finishing Cut Stage for Improving Surface Roughness of FDM 3D Printed Sculptures

This paper describes the optimal design of a 3-DOF redundant planar parallel kinematic mechanism (PKM) based finishing cut stage to improve the surface roughness of FDM 3D printed sculptures. First, to obtain task-optimized and singularity minimum workspace of the redundant PKM, a weighted grid map based design optimization was applied for a task-optimized workspace without considering the redundancy. For the singularity minimum workspace, the isotropy and manipulability of the end effector of the PKM were carefully modeled under the previously obtained redundancy for optimality. It was confirmed that the workspace size increased by 81.4%, and the internal singularity significantly decreased. To estimate the maximum rated torque and torsional stiffness of all active joints and prevent an undesired end effector displacement of more than 200 , a kinematic stiffness model composed of active and passive kinematic stiffness was derived from the virtual work theorem, and the displacement characteristic at the end effector was examined by applying the reaction force for the PLA surface finishing as an external force acting at the end effector. It was confirmed that the displacement of the end effector of a 1-DOF redundant PKM was not only less than 200 but also decreased from 40.9% to 67.4% compared to a nonredundant actuation.

Design of an Ankle Rehab Robot With a Compliant Parallel Kinematic Mechanism

In this article, we present the design of a novel ankle rehabilitation robot (ARR), called the Flex-ARR, that employs a compliant parallel kinematic mechanism (PKM) with decoupled degrees-of-freedom. While multiple ARRs have been developed and commercialized, their clinical adoption has been limited primarily because they do not emulate the natural motion of the ankle. Based on a review of existing ARRs and their limitations, this article defines functional requirements and design specifications for an optimal ARR. These are then used to develop a design strategy followed by conceptual and detailed design of a novel ARR. The proposed Flex-ARR is designed to collocate the biological center of rotation of the ankle with that of the robot's center of rotation to allow natural ankle motion. The strategic use of a compliant PKM in the Flex-ARR not only absorbs any residual misalignment between these two centers but also helps inherently accommodate variations in user foot sizes with minimal adjustments. Detailed design includes the ARR structure with adjustable features, compliant PKM optimization, sensor and actuator selection, and an alignment tool.

A Planar Parallel Device for Neurorehabilitation

The patient population needing physical rehabilitation in the upper extremity is constantly increasing. Robotic devices have the potential to address this problem, however most of the rehabilitation robots are technically advanced and mainly designed for clinical use. This paper presents the development of an affordable device for upper-limb neurorehabilitation designed for home use. The device is based on a 2-DOF five-bar parallel kinematic mechanism. The prototype has been designed so that it can be bound on one side of a table with a clamp. A kinematic optimization was performed on the length of the links of the manipulator in order to provide the optimum kinematic behaviour within the desired workspace. The mechanical structure was developed, and a 3D-printed prototype was assembled. The prototype embeds two single-point load cells to measure the force exchanged with the patient. Rehabilitation-specific control algorithms are described and tested. Finally, an experimental procedure is performed in order to validate the accuracy of the position measurements. The assessment confirms an acceptable level of performance with respect to the requirements of the application under analysis.

Calibration of In-Plane Center Alignment Errors in the Installation of a Circular Slide with Machine-Vision Sensor and a Reflective Marker

This paper describes a method for calibrating in-plane center alignment error (IPCA) that occurs when installing the circular motion slide (CMS). In this study, by combini ng the moving carriage of the CMS and the planar PKM (parallel kinematic mechanism) with the machine tool, the small workspace of the PKM is expanded, and the workpiece is placed on the table with the CMS installed is processed through the machine tool. However, to rigidly mount the CMS on the table, the preload between the guide and the support bearings must be adjusted with the eccentric bearing, and in this process, the IPCA occurs. After installing a reflective marker on the PKM, the PKM is slowly rotated along with the ring guide in the way of stop-and-go without the PKM’s own motion. Then, using a machine vision camera installed at the top of the CMS, the IPCA, which is the difference between the actual center position and the nominal center position of the CMS with respect to the camera, can be successfully calibrated through the circular fitting process. Consequently, it was confirmed that the IPCA of 0.37 mm can be successfully identified with the proposed method.

Design of an Ankle Rehab Robot With a Compliant Parallel Kinematic Mechanism

In this paper, we present the design of a novel ankle rehabilitation robot (ARR), called the Flex-ARR, that employs a compliant parallel kinematic mechanism (PKM) with decoupled degrees of freedom. The Flex-ARR is designed to collocate the biological center of rotation of the ankle with that of the robot’s center of rotation to allow natural ankle motion. While multiple ARR designs have been developed in research labs and some are commercially available, their clinical adoption has been limited because they do not emulate the natural motion of the ankle. The Flex-ARR leverages a unique PKM design that uses compliance to absorb minor misalignments between the center of rotation of the ankle and the robot, thereby allowing natural ankle motion. Also, because of its unique design, the PKM inherently accommodates variations in user foot sizes with minimal adjustments. The Flex-ARR is designed to provide multiple training modes that allow for both rehabilitation and assessment modalities. This paper provides a review of the literature to identify the key factors that have limited the clinical adoption of existing ARRs. Based on this, functional requirements and design specifications for an optimal ARR are defined. This is then used to develop a design strategy, followed by conceptual and detailed design.

Soft pneumatic actuator-driven origami-inspired modular robotic “pneumagami”

This article presents a new modular robotic platform for enabling reconfigurable, actively controlled, high-degree-of-freedom (high-DoF) systems with compact form factor. The robotic modules exploit the advantages of origami-inspired construction methods and materials, and soft pneumatic actuators (SPAs) to achieve an actuator embedded, parallel kinematic mechanism with three independently controlled “waterbomb” base legs. The multi-material, layer-fabricated body of the modules features selectively compliant flexure hinge elements between rigid panels that define the module as a kinematic 6R spherical joint. The precision layer-fabrication technique is also used to form embedded distribution channels within the module base to connect actuators to onboard control hardware. A decentralized control architecture is applied by integrating each module with small-scale solenoid valves, communication electronics, and sensors. This design approach enables a single pneumatic supply line to be shared between modules, while still allowing independent control of each leg joint, driven by soft, inflatable pouch actuators. A passive pneumatic relay is also designed and incorporated in each module to leverage the coupled, inverted inflation, and exhaust states between antagonistic actuator pairs allowing both to be controlled by a single solenoid valve. A prototype module is presented as the first demonstration of integrated modular origami and SPA design, or pneumagami, which allows predefined kinematic structural mechanisms to locally prescribe specific motions by active effect, not just through passive compliance, to dictate task space and motion. The design strategy facilitates the composition of lightweight, high-strength robotic structures with many DoFs that will benefit various fields such as wearable robotics.